PREPARATION AND CHARACTERISATION OF POLYMER COMPOSITES WITH BLOODMEAL by CHERYL-ANN ELIZABETH CLARKE (B.Sc. Hons.) Submitted in accordance with the requirements for the degree MASTER OF SCIENCE (M.Sc.) Department of Chemistry Faculty of Natural and Agricultural Sciences at the UNIVERSITY OF THE FREE STATE (QWAQWA CAMPUS) SUPERVISOR: PROF A.S. LUYT January 2016 Dedication This work is dedicated to my parents, my mother Maryncha Clarke, and my late father, Robert Clarke. Thank you for your eternal and unwavering reassurance and support, through everything that life has thrown at us. I would also like to thank my brothers, Christopher and Richard Clarke for always being there for me. Lastly, I don' t think I would have come thi s far without the motivation and determination inspired by my amazing husband, Quintin Konig. I love you, you are my rock! Thank you for everything! ii Abstract This research focuses on the fabrication of composites produced by the combination of BM (bloodmeal) with HOPE (high-density polyethylene). HOPE was chosen because it is amongst the most widely used synthetic plastic material worldwide, thus a study of improving the degradability of these materials can be regarded as worthwhile. HOPE was combined with dried BM. The BM was blended with the polymers using mechanical mixing at 150 °C and subsequent melt-pressing at the same temperature into films of different thicknesses. The morphology, thermal and mechanical properties, and water absorption were investigated using moisture analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (TOA), optical microscopy, scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, and tensile testing before and after periods of underground ageing. Moisture analysis revealed that the addition of BM to HOPE moderately increased the moisture content of the composites. Morphological investigations showed good dispersion of BM in the polyethylene matrix, but the effects of ageing were not highly evident. DSC results indicated that the presence of BM did not significantly influence the crystallization behaviour of HOPE since the melting temperatures and melting enthalpies varied only slightly for each composition. The mechanical properties for BM composites for all ageing times showed similar trends, such as a large initial increase in modulus for I% BM added. The modulus decreased slightly as the BM content increased. Overall, the mechanical properties remained relatively constant with underground ageing time. In conclusion, it seems as if the presence of BM in HOPE had an influence on the mechanical properties and water absorption behaviour of the composites, but did not observabl y accelerate the underground environmental degradation of this polymer over periods as long as 36 weeks. iii Table of contents Page Declaration Dedication I i Abstract Iii Table of contents Iv List of tables Vi List of figures Vii List of symbols and abbreviations Ix Chapter 1: Introduction and literature review 1 I. I Overview 1.2 Polyethylene 1.3 Literature review 2 1.3. 1 Polymers and (bio)degradability 2 1.3 .2 Degradation of polymer materials 6 1.3.3 Proteins: C lassification and properties 10 1.3.4 Prote ins as materials 11 1.3.5 Blood meal 13 1.3.6 Bloodmeal-based thermoplastics 14 1.3.7 Bloodmeal-filled polymers 14 1.4 Objectives of this study 15 1.5 Thesis outline 15 1.6 References 15 Chapter 2: Materials and methods 22 2.1 Materials 22 2. 1.1 High-density polyethylene 22 2. 1.2 Blood meal 22 2.2 Sample preparation 23 2.3 Characterisation techniques 24 2.3.1 Moisture content 24 iv 2.3.2 Water absorption 24 2.3.3 Underground ageing test 25 2.3.4 Differential scanning calorimetry (DSC) 26 2.3.5 Thermogravimetric analysis (TGA) 26 2.3.6 Fourier-transform infrared (FTIR) spectroscopy 27 2.3.7 Optical microscopy 27 2.3.8 Scanning electron microscopy (SEM) 28 2.3.9 Tensile testing 28 2.4 References 29 Chapter 3: Results and discussion 31 3.1. l Moisture content 31 3.1.2 Water absorption 32 3. 1.3 Differential scanning calorimetry (DSC) 34 3.1.4 Thermogravimetric analysis (TGA) 37 3. 1.5 Fourier-transform infrared (FTIR) spectroscopy 41 3. 1.6 Microscopy 44 3. 1.6.1 Optical microscopy 44 3.1.6.2 Scanning electron microscopy (SEM) 47 3.1.7 Tensi le testing 49 3.2 References 59 Chapter 4: Conclusions 63 Acknowledgements 65 Appendix 66 v List of tables Table 2. 1 Information received with bloodmeal 22 Table 2.2 Table of composite proportions 23 Table 3. 1 Water absorption for pure HOPE, as well as the 90/10 wlw and 80/20 33 wlw HOPE/BM composite films prior to underground ageing Table 3.2 Melting and crystallization temperatures and enthalpies obtained from 36 the cooling and second heating curves for all the composites prior to underground ageing and after underground ageing fo r 36 weeks Table 3.3 Average char values for unaged bloodmeal, HOPE, and bloodmeal 41 composites, as well as HDPE and 80/20 w/w HDPE/BM composite aged underground for 36 weeks Table 3.4 Table of carbonyl index values calculated fo r 0.2 mm thick composite 43 fi lms Table 3.5 Table of carbonyl index values calculated for 0. 7 mm thick composite 43 films Table 3.6 Table of carbonyl index values calculated for 1.0 mm thick composite 44 films Table 3.7 Table of optical microscopy images of 0.2 mm thick composite fi lms 45 Table 3.8 Table of optical microscopy images of 1.0 mm thick composite films 46 Table A. I .I Structures of amino acids 66 Table A. 1.2 Amino acid content of bloodmeal 69 Table A.3. 1 Moisture content for pure bloodmeal powder 70 Table A.3.2 Table of DSC results fo r unaged HDPE fi lms of different thicknesses 70 Table A.3 .3 Table of DSC heating curves for all the composites, unaged and 71 composites aged for 36 weeks Table A.3.4 Table of DSC cooling curves for a ll the composites, unaged and 73 composites aged for 36 weeks Table A.3.5 Table of FTIR spectra for all the composites, unaged and composites 77 aged for 36 weeks vi Table A.3.6 Table of stress-strain curves for pure HDPE and 80/20 w/w HDPE/BM composite films, unaged and composites aged for 36 weeks vii List of figures Figure 1.1 Schematic diagram of polymer degradation under aerobic and anaerobic 9 conditions Figure 1.2 General structure of an amino acid 10 Figure 2. 1 The positioning of composite samples in soil for the underground 25 ageing test before covering with soil Figure 2.2 Dimensions of the dumbbell-shape used for tensile testing 29 Figure 3. I Moisture content of pure bloodmeal powder and of HOPE/BM 31 composites prior to underground ageing Figure 3.2 DSC second heating curves of pure HOPE and 80/20 HOPE/BM 35 composites prior to underground ageing and after underground ageing for 36 weeks Figure 3.3 DSC cooling curves of pure HOPE and 80/20 HOPE/BM composites 35 prior to underground ageing and after underground ageing for 36 weeks Figure 3.4 TGA curves of unaged bloodmeal, pure HOPE and the HOPE/BM 38 composites films prior to underground ageing Figure 3.5 TGA curves of unaged bloodmeal, pure HOPE and 80/20 HOPE/BM 40 composite fi lms prior to underground ageing and after underground ageing for 36 weeks Figure 3.6 SEM images of a) unaged HDPE, b) HOPE aged underground fo r 36 48 weeks, c) unaged 80/20 w/w HOPE/BM, and d) 80/20 w/w HOPE/BM aged underground for 36 weeks Figure 3.7 Young's modulus values for unaged composite fi lms with different 50 thicknesses Figure 3.8 Elongation at break values for unaged composite films with di fferent 51 thicknesses Figure 3.9 Yield stress values fo r unaged composite fi lms with different 52 thicknesses Figure 3.10 Young's modulus for all compositions of the 0.2 mm thick composite 53 fi lms versus ageing time vii i Figure 3. 11 Young's modulus for all compositions of the 0.7 mm thick composite 54 films versus ageing time Figure 3. I 2 Young's modulus for all compositions of the 1.0 mm thick composite 55 films versus ageing time Figure 3. 13 Percent changes of modulus between fourth and thirty-six weeks of 55 ageing Figure 3. 14 Elongation at break values versus ageing time for 0.2 mm thick 56 composites Figure 3. I 5 Elongation at break values versus ageing time for 0.7 mm thick 57 composites Figure 3.16 Elongation at break values versus ageing time for I .0 mm thick 58 composites Figure 3. I 7 Stress at yield values versus ageing time for 0.7 mm thick composites 58 Figure A.3. 1 Comparison of water absorption values for pure HOPE, as well as 90/10 70 w/w and 80/20 w/w HOPE/BM composite fi lms prior to underground ageing Figure A.3.2 Carbonyl index values of 0.2 mm films of all composites with age ing 75 time Figure A.3.3 Carbonyl index values of0.2 mm film s of all composites with ageing 75 time Figure A.3.4 Carbonyl index values of 0.2 mm films of all composites with ageing 76 time ix List of symbols and abbreviations ATR-FTIR attenuated total reflectance Fourier-transform infrared spectroscopy BM blood meal E4 average modulus after four weeks of underground ageing (first ageing time) average modulus after thirty six weeks of underground ageing (final ageing time) enthalpy of crystallization normali sed enthalpy of crystallization enthalpy of melting normalised enthalpy of melting DNA deoxyribonucleic acid OMA dynamic mechanical analysis DSC differential scanning calorimetry ESC environmental stress cracking FTIR Fourier-transform infrared spectroscopy GPC gel permeation chromatography IR infrared HOPE High-density polyethylene LOPE low-density polyethylene LLD PE linear low-density polyethylene Minitial initial mass MS mass spectrometry M wet mass after immersion NMR nuclear magnetic resonance PE Polyethylene PLA poly(lactic acid) POM polarized optical microscopy sos sodium dodecyl sulphate SEM scanning electron microscopy TGA thermogravimetric anal ysis Tc crystallization tern perature x glass transition temperature melting temperature UHMWPE ultra-high molecular weight polyethylene ULMWPE ultra-low molecular weight polyethylene UV ultra violet XRD X-ray diffraction xi Chapter 1 Introduction 1.1. Overview Polymers are applied in a broad variety of products and are utili sed in an extensive range of industries. Synthetic polymers are derived from non-renewable raw materials, and as these oil reserves are consumed, the cost of this resource escalates. These man-made materials are persistent in the environment, so numerous studies of substitutes for synthetic polymer materials have taken place. In addition, a significant amount ofresearch has been applied to the study of degradable polymers to alleviate the adverse impact on the environment [1-3). This chapter consists of an introduction to, and a literature review of protein/polymer composites, and in particular, bloodmeal and bloodmeal/polymer composite classifications and properties. 1.2. Polyethylene: Classification and properties Polyethylene (PE) is currently one of the most widely used synthetic materials due to its low cost, simple processing, good mechanical properties, superior chemical resistance and light weight. Polyethylene has a very simple structure, and is one of the simplest commercial polymers. The polymer consists of ethylene monomers polymerised under specific temperature and pressure conditions through the action of catalysts, resulting in a long chain of carbon atoms with two hydrogen atoms attached to each carbon atom. Polymerisation conditions influence the incidence of secondary chains that branch out from the primary chain. Polyethylene can be arranged into sub-groups such as high-density polyethylene (HOPE), low-density polyethylene (LOPE), linear low-density polyethylene (LLOPE), ultra-high-molecular-weight polyethylene (UHMWPE), and ultra-low-molecular-weight polyethylene (ULMWPE), to name a few. The difference between the polyethylene sub-groups is based on variables such as the extent and type of branching, the crystal structure and the molecular weight, which also directly affects the characteristics of the material [4 ] . 1 LOPE is produced under high pressure conditions and the end product is a polymer with a large degree of branching, consequently the long polymer chains cannot pack tightly together and thus LOPE possesses a lower density than HOPE. The manufacture of HOPE occurs at lower pressures and the polymer consists of very long, straight chains with a low degree of branching. HOPE has higher crystallinity than LOPE since the HOPE polymer chains are more linear than the LOPE chains, which results in more effective packing into crysta l larnellae. Consequently, the properties of HOPE and LOPE will vary slightly [4]. Polyethylene can be utilised in its pure form, or in blends with other natural or synthetic polymers, resulting in a large range of materials. Various fi llers can also be incorporated in the processing of polyethylene to augment or integrate useful properties in the end product. Applications are highl y varied and include products in almost every industry, from the food packaging industry, agriculture, chi ldren's toys, shopping bags and even in the medical industry [5 ,6]. Polyethylene is resilient to degradation given that it is made up of long hydrophobic carbon chains and possesses high molecular weight that makes it resistant to hydro lysis and microbial attack. The PE products wi ll not biodegrade unless it is subjected to spec ifi ed treatment or if biodegradable fillers are included during plastic processing. The fact that it does not biodegrade results in vast accumulation of wastes that can have devastating effects on the ecosystem of an area [5]. Increasing the biodegradable character of polyethylene, without significantly altering the fundamental properties and adversely affecting the functionality, would prove to be usefu l taking into consideration the fact that polyethylene is so extensively utilised . 1.3. Literature review 1.3. 1. Polymers and (bio )degradability A synthetic polymer is a " man-made·' material, deri ved from petroleum oil and is designed by scienti sts and engineers to serve a specific purpose. Properties of synthetic polymers vary greatl y. Thermosetting polymers are material s that soften when heated but become permanently hard and ri gid after cooling as a result of the fo rmation of covalent bonds between mo lecules. Epoxy resins or rubber that has been vulcanised, are examples of thermosetting polymers. 2 Thermoplastics, such as polyethylene, are materials that become soft and flexible on heating and subsequently solidify and harden upon cooling. The softening and hardening process can be repeated as required, thus thermoplastic polymers are fairly easy to process [4 ]. Physical properties of polymers, such as melting temperature (Tm) and glass transition temperature (Tg ), also vary, and these properties are direct! y related to features such as the degree of crystallinity, extent of chain branching or the amount of cross-linking. These features can help to differentiate a material into sub-groups such as high-density polyethylene (HDPE), linear-low density polyethylene (LLDPE) and low-density polyethylene (LDPE). Certain synthetic polymers possess favourable mechanical properties, for example good tensile strength or high elongation. Additives, such as colouring agents, stabilisers or plasticisers, are often added to polymers during manufacture or processing, either to aid processing or to improve performance during use [4]. A shortcoming and significant drawback of synthetic polymers is that these materials are persistent in the environment. All polymers undergo degradation, even synthetic materials; the only variable is the rate of degradation which can lead to an enduring presence in the environment. Recalcitrant behaviour is attributable to properties such as hydrophobicity, high molecular weight, and the chemical and structural composition of the material. These polymers easily accumulate in the environment and can become hazardous to the ecology of the area. This is especially true for materials designed for one-time use such as food packaging, disposable cutlery, plastic bottles, and so on [3 ,7-9]. Changes in polymer properties due to chemical, physical or biological reactions resulting in bond scissions and subsequent chemical transformations are categorised as polymer ageing or degradation. These modifications cause the loss or alteration in material features such as mechanical properties, thermal or optical characteristics demonstrated by crazing, cracking, erosion, discoloration and phase separation. There are several classes of degradations which materials can undergo, for example, photo-oxidati ve, thermal, mechanical, catalytic and bio- degradation. The type of degradation is determined by the conditions to which the substance is exposed, such as elevated temperature, moisture and exposure to sunlight. Biological elements, such as bacteria and fungi , can also attack materials under certain conditions. The constituents of the material also has an effect on the ability of the material to degrade, for example the 3 presence of labile bonds in the polymer chain, or the inclusion of substances such as starch or proteins with higher rates of degradation [7-12]. The degradation of a polyolefin material , like polyethylene, consists of a two-step process, oxidation of the polyolefin followed by attack of micro-organisms to achieve bio-degradation. During oxidation, the alkane chains are oxidised to ketones which are then cleaved by hydrolysis to give the corresponding acid. This improves the hydrophilic nature of the polymer that promotes further hydrolysis of the polymer. The second step is known as biodegradation since the oxidation yields lower molecular weight products that can be degraded by the enzymes of microorganisms. Degradation of synthetic polymers can be influenced by the presence of stabilisers that inhibit deterioration. Recent studies have shown that the incorporation of natural fillers, such as proteins or plant fibres, can improve the degradability of synthetic polymers, especially since the inclusion enhances the hydrophilic properties of the material, which allows for hydrolysis and further oxidative attack [3,7, 13-18]. Environmental conditions cause deterioration of polymeric material by means of hydrolysis, oxidation and photo-degradation. This initial degradation decreases the size of the polymer molecules to allow microbiological attack during biodegradation. Biodegradation or decomposition of the polymer is achieved by microorganisms such as bacteria and fungi that essentially digest and metabolise small molecules of the material to achieve mineralisation. The molecules should be of sufficiently low molecular weight since large polymer molecules cannot pass through the cell membrane of the microorganism [3, 14,17, 19,20] There are polymers, derived from renewable biomass, that can be considered to be biodegradable, but these polymers do not occur without human intervention. Poly(lactic acid) (PLA) is an example of such a polymer. PLA belongs to the family of aliphatic polyesters derived from a-hydroxy acids (mainly starch and sugars). A more accurate description of PLA is a "bio-based plastic" since the monomers are produced through an industrial fermentation process. The thermal and mechanical properties of biodegradable polymers are normally not suited for the applications that synthetic polymers have been designed for, and bio-based polymers can be more expensive to manufacture [3 ,21,22]. 4 Natural polymers are produced by living organisms but must be refined or processed before use. Examples of naturally occurring polymers are natural rubber, silk, wool, DNA, cellulose and proteins. Natural polymers are also known as biological polymers, or biopolymers. Compared to the simple, more random structure of synthetic polymers, biopolymers have complex molecular groupings of structures that adopt specific and well-defined shapes. The precision of the arrangement of the structures is ultimately what makes the molecules able to function in organisms. Natural polymers occur in a large variety of structures and compositions. These polymers are classified according to the nature of the repeating unit they are made of: (i) polysaccharides are made up of simple sugars, such as glucose; (ii) proteins are composed of amino acids; and (iii) DNA molecules consist of nucleotides, covalently bonded into nucleic acids. Biopolymers are capable of biodegradation, meaning that the polymer material is eventually broken down into carbon dioxide (C02), water (H20) and organic residues [11 ,23]. Blending of natural polymers with synthetic polymers can create novel materials and improve selected properties of the material, for example, the mechanical properties of the natural polymer are enhanced and the degradability of the synthetic polymer is augmented. Natural polymers occur in a large variety of structures and compositions, from proteins to polysaccharides and are readily acquired since they are abundant, widely available and a sustainable resource. All these factors combined effectively lowers the cost of acquisition [3 ,9,10,24-26]. Careless littering of plastic materials in particular and ignorance result in the accumulation of waste in the environment, which is not aesthetically pleasing and could become a health hazard for all life forms. As an alternative to the use of completely natural polymers, it has become popular to combine natural and synthetic polymers. These blends possess the functional properties of the synthetic polymers, with the added benefit of improved degradability due to the addition of the natural elements. Biodegradable polymers create the prospect of possible solutions to waste-disposal problems associated with traditional petroleum-based plastics. Biodegradation is dependent on the initial abiotic oxidation of the polymer that results from exposure to the elements, namely sunlight, wind, rain and elevated temperatures before micro- organisms can be effective. As a consequence of contact with the external environment, preliminary degradation produces lower molecular weight molecules that are more susceptible to microbial attack [7,24]. 5 Water sensitivity of natural polymers The hydrophobic or hydrophilic nature of a material will determine the extent to which water will be absorbed by the material. The structure of most natural polymers contains polar chemical groups, which makes these materials hydrophilic. A hydrophilic character promotes degradation, since hydrolysis can be a major feature in the degradation of polymeric materials [27]. Water can be absorbed by a polymer via diffusion during humid conditions or surface water resulting from rainfall or condensation. Absorption of water may result in swelling of the material. The presence of water initiates the hydrolysis of the polymer and rupturing of the polymer backbone that lead to the creation of oligomers and monomers. As degradation progresses, changes in the microstructure of the matrix occur due to the formation of pores. Lower molecular weight products can be released. The sensitivity of natural polymers to water can impede functioning and natural polymers are inclined to exhibit inferior mechanical properties [26,28-30]. Many polymer composites, when exposed to wet or humid environment, can absorb water with detrimental consequences. The absorbed water may affect the material by swelling (dimensional changes), reduction of the glass transition temperature (plasticisation), or reduction in physical or mechanical properties such as stiffness, strength or hardness. Diminished properties can also result from an interaction of any of the composite components with the absorbed water molecules. The amount of water absorbed is directly related to the amount of degradation that occurs due to hydrolysis. Hence, the rate of the degradation of materials such as synthetic polymers is improved [28]. 1.3.2. Degradation of polymer materials Polymer degradation is defined as a Joss or change in the characteristic properties of a material. Degradation results from changes in the physical or chemical structure of the polymer due to 6 various external and internal factors, as described earlier. In some cases, degradation processes result in reduced molecular weight. Degradation can also be associated with the process of ageing. The exposure of a polymeric material to a certain environment over time is known as weathering of that material. Weathering can occur in a natural environment, such as outdoor conditions during use, or in a simulated environment, such as soil burial, UV radiation treatment or water submersion. The process in a simulated environment is termed artificial ageing or weathering. Environmental conditions that polymers are subjected to during the weathering period can result in changes in appearance, modified mechanical properties, and so on [6 ,31- 33]. Ageing According to the Oxford Dictionary, ageing is defined as the process of becoming older, or increasing in age. Ageing is the inevitable deterioration of the material structure and loss of functionality due to modified physical and/or chemical structure. This process is understood to involve changes in the properties of a material, either spontaneously or through deliberate action over a period of time. The adjective used to describe the degradation or ageing process explains the manner in which physical or chemical changes in the polymer can occur. For example, aqueous ageing arises due to the action of water or moisture on the polymer; oxidative degradation is caused by the action of an oxidising agent on a material , and the process that occurs when the polymer is in contact with soil is known as underground ageing. Physical ageing is a thermodynamic process that causes changes in the physical structure of polymers. Over time, short segments of the polymer chain are subjected to small-scale rearrangements that affect physical properties such as density, crystallinity and changes in dimensions. During use, molecular rearrangements resulting from applied stress cause certain polymers to undergo crazing. Crazing is the formation of cavities that look like cracks, but the gap between the surfaces of the cavity is linked by fibrils of the polymer. The size of a cavity is often smaller than a few micrometres. Initiation of crazes is influenced by increased tensile stress and factors in the material environment such as absorbed water that increases molecular mobility. A crack can be defined as the line where a material is broken but not separated. Stress cracking is defined as an external or internal crack in a material caused by tensile stress. This type of cracking usually entails brittle failure, and rarely involves the formation of fibrils that connect the failure surfaces. Stress cracking is often explained as slow crack growth, and the most well-known 7 type is referred to as environmental stress cracking (ESC). Environmental stress cracking is caused by the combined action of mechanical stress with chemical agents and/or radiation. It is believed that ESC is initiated at imperfections or impurities in the polymer structure. The environmental agent responsible for the initiation of the crack is indicated by the name given to the cracking process, for example oxidative cracking, UV cracking, etc. A material , exposed to conditions that facilitate an environmental factor to move down the length of the crack, will experience plasticisation of the high-stress region of the crack tip. Under continued stress, the crack will spread through the material, resulting in failure on (6,31-34]. Environmental degradation In general, most synthetic polymers are inherently resistant to environmental factors, and hence, environmental degradation. For the duration or their use, polymer materials are exposed to environmental factors, which can adversely affect the properties of the polymer. Environmental degradation of polymers is the deterioration of polymer properties due to the action of environmental factors, such as heat, light, moisture, oxygen, or biological organisms. Polymeric materials susceptible to environmental factors are known as environmentally degradable polymers. Under environmental exposure, high thermal energy can cause depolymerisation; solar radiation can result in photo-initiated oxidation; the presence of water, under the right conditions, results in hydrolytic reactions; and exposure to ozone can produce free radicals. Consequently, the formation of smaller polymer fragments ensues, which facilitates the attack of biological organisms. Degradation that results from the action of biological organisms, naturally present in the environment, is known as biodegradation. Biological organisms that attack polymers, and cause depolymerisation, are known as depolymerases (Figure 1.1) (10,26,31 ,32]. 8 IP OLBffR I ~ ~ DEPOLB IERASES ~ OUGO:\'lERS DL\IERS MOi'"O~bIERS Microbial biomasi ~licrobia l biomau ~ CIL/lbS c~ c~ H:O lbO • ROBIC A.~i AEROBIC Figure 1.1 Schematic diagram of polymer degradation under aerobic and anaerobic conditions [7] Additives that are able to improve degradation reactions are known as pro-degradants. These additives are usually added to polymers during the melt stage to increase the rate of oxo- degradation by improving the efficiency of reactions with atmospheric oxygen during functioning. Oxo-degradation proceeds via photo-degradation and oxidation reactions. Pro- degradant additives can be transition metal salt complexes or other transition metal free compounds that possess chromophoric groups. Transition metal ions, in their various forms, are the most extensively used pro-degradant additive. The decomposition of hydro-peroxides into free radicals is catalysed by transition metal complexes and the photo-sensitivity of the material is increased, which promotes UV degradation. Some of the most commonly used transition metals include iron, cobalt and manganese. Bloodmeal contains iron in the heme-complex present in blood. The heme-complex is fundamentally involved in the transport of oxygen and carbon dioxide in the blood of an organism. Proteins are linear polypeptide molecules with a precise length. A polypeptide chain comprises a distinct combination of twenty (20) covalently bonded amino acids. An understanding of the chemical reactivity of the amino acid functional groups is important because they provide many reaction sites for potential cross-linking or chemical grafting. Beef blood meal contains more lysine, threonine, valine, leucine, tyrosine, and phenylalanine while pork blood meal contains more histidine, arginine, proline, glycine, and isoleucine. Of these, cysteine and lysine are the most reactive amino acids [6,26,35]. Different analytical techniques can be used to estimate the extent of degradation in the material. Alterations in morphology such as increased surface roughness, etc., can be observed with 9 microscopic techniques. Changes in rheological properties such as altered crystal structure, etc., can be determined using mechanical testing, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Chemical modifications of the material structure can be distinguished with spectroscopic methods, such as Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) and mass spectrometry (MS), etc. Gel permeation chromatography (GPC) can confirm changes in molecular weight of the material. Gravimetric measures can be employed to determine weight loss, but differences are often negligible and can be attributed to loss of volatile or soluble impurities [2, 17 ,26,34]. Degradation of polymer waste through various means is one alternative to deal with the accumulation of waste material in the environment. Biodegradation of synthetic materials and the assimilation into the environment is the ultimate objective of research into sustainable substances. 1.3.3. Proteins: Classification and properties Essential components in each living cell, proteins function as important structural components of skin, hair, muscle and nervous tissue. Proteins also serve biological functions in living organisms as enzymes and hormones. Proteins are natural polymers that can originate from both plant and animal sources, for example, soy proteins are extracted from plants and bloodmeal is derived from animal blood. The structures of proteins are divided into primary, secondary, tertiary and quaternary structures. The most basic components of proteins are amino acids. The general structure of an amino acid is shown in Figure 1.2. The primary structure is the order in which the amino acids are joined to form the polypeptide chain. The specific amino acid sequence is determined by the genetic code of the organism. An amino acid is made up of an amino group, a carboxyl group and a side chain, or "R group". H I Amino C- Carboxylic group acid group Si•de ch ain Figure 1.2 General structure of an amino acid [36] 10 These "R groups" can impart specific characteristics to the amino acid, for example hydrophilic or hydrophobic behaviour. Amino acids can be considered as the ' building blocks' of proteins, as monomers are the constituent parts of a polymer. There are twenty known structures of amino acids, as shown in Table A. I . I in the Appendix [36]. 1.3.4. Proteins as materials Substantial quantities of animal derivatives from livestock, bred for meat, dairy and eggs, is wasted because these parts of the animal are not fit for human consumption. Unused animal products, such as rawhide, bone, blood and other tissues, are subjected to rendering processes resulting in many useful products. Rendering involves both chemical and physical modification of the substance to generate or convert the protein in a usable form. The rendering industry provides an assortment of useful products of animal origin such as bloodmeal, bone meal, feathermeal, fishmeal , meat meal, and poultry meal. These products were previously used as animal feed, but are currently used mostly as fertilisers. If the animal products are not processed by the rendering industry, an accumulation of animal derivatives could hinder the meat industry, intensify environmental pollution and present a potential hazard to human and animal health [37-39]. Research focused on the development of sustainable materials to replace synthetic plastics has explored protein-based plastics. Proteins originate from renewable resources as derivatives from agricultural practices, and most importantly, proteins are biodegradable or compostable. This is beneficial from an environmental and economic perspective. In general, proteins consist of approximately I 00-500 amino acid residues covalently bonded in a polypeptide chain. Each protein of a particular type has a characteristic amino acid sequence; subsequently there exists a considerable assortment of proteins. In addition, various interactions take place between amino acid residues of a polypeptide chain, between individual polypeptide chains and between whole proteins. Materials produced from proteins accordingly possess a wide range of properties [38,40,41]. Present in all living cells, protein substances are widely varied and can be recovered from many resources as by-products or wastes of the agricultural and horticultural industries. The proteins 11 must often be removed or extracted from plant or animal tissues. Abundant proteins such as soy from plants, and proteins such as gelatine or bloodmeal from animals, have been manufactured into plastics with reasonable properties. Soy protein is extracted as a by-product from soybeans and was one of the first biopolymers from agriculture used for the manufacture of moulded materials. Soy protein plastics are brittle and require plasticisers for improved mechanical properties. Some components of Ford cars were manufactured with a phenol- formaldehyde/soybean flour mixture in the 1930s although, due to the expense of extracting the proteins and progress in the development of synthetic plastics, this practice was stopped (11 ,40,42-44). A protein, m its native form, exists m a folded conformation stabilised by hydrophobic interactions, hydrogen bonding, and electrostatic interactions between amino acid functional groups. These interactions between the components of proteins must be disrupted before the proteins can be efficiently processed into a material. Proteins are sensitive to changes in temperature and pH which can rupture low-energy intermolecular bonds that stabilise the protein; this is known as denaturation of the protein. Denaturation of the protein serves to disentangle and uncoil the protein structures. The disruption of the interactions and bonds between the amino acids of the polypeptide chain allows new interactions to form during processing. Once the protein has been denatured, the polypeptide chains can rearrange into a three-dimensional structure, stabilised by interactions between the protein components. Production of protein-based materials typically makes use of either wet processes, e.g. casting, or dry processes, such as extrusion. Each technological process is dependent on the specific properties of the protein. The complicated nature of proteins thus limits possible processing conditions [12,39,40,45). The most important aspect of materials produced from proteins is that the materials can be composted or can be considered as biodegradable. The proteins are derived from renewable resources, which aid the economical sustainability of the product. These materials could be applied in the packaging industry where the plastic material is usually disposed of after a single use. Plastic materials derived from proteins usually possess inferior mechanical properties such as reduced flexibility and brittle behaviour. For this reason, several researchers have investigated 12 the incorporation of various additives, such as plasticisers, to improve these properties. A balance between improving the performance of the material with the addition of chemicals, and the inherent biodegradable character of the material must be maintained [4 1,46]. An alternative to the addition of chemicals to the material is to produce composites of natural and synthetic polymers, such as polyethylene (PE) with bloodmeal. The polymers are mixed to obtain a trade-off of beneficial properties, such as the functional mechanical properties of polyethylene with improved degradability [24,47]. 1.3.5. Bloodmeal Blood is classified as a specialised kind of connective tissue and serves many vital roles in an organism. The main component of blood is water, better known as blood plasma. The rest of the constituents are suspended in the plasma. Typical elements of blood are red blood cells (erythrocytes), white blood cells (leukocytes), plasma proteins, platelets, hormones, enzymes, nutrients, gases, and wastes. Each component serves a critical function and the blood, in its entirety, serves various regulatory roles in the organism. The erythrocytes comprise the majority of the solid components of blood. Blood possesses a higher concentration of iron than the flesh of an animal. The iron, present in the haemoglobin sub-units of erythrocytes, functions to bind molecular oxygen that enters the vessels of the lungs during inhalation, and conveys it to the body tissues by means of the circulatory system. Iron in the haemoglobin complex is also responsible for the red colour of blood, since the iron oxidises in air, which gives blood its red hue. Bovine blood is composed of approximately 80% water, 15% protein, 5% nutrients, gases and wastes. The amino acid content of bloodmeal is tabulated in Table A.1 .2 in the Appendix [30,48]. In 2010111, roughly 3-million head of cattle were slaughtered in South Africa for commercial markets or for small enterprises. There is considerable consumption of beef and veal in South Africa [49]. Slaughterhouses and rendering plants typically dispose of the blood produced from slaughtering cattle via incineration, to produce blood-char, or through drying, to produce bloodmeal. Essentially, bloodmeal is the components of blood with the plasma, or water, removed. Bloodmeal is a dry, inert powder which is currently used as a high-nitrogen fertilizer. The use of bloodmeal as a high protein addition to animal feed was prohibited due to the 13 outbreak of the Aphtae epizooticae (foot-and-mouth) disease in cattle. It is one of the highest non-synthetic sources of nitrogen. A renewable source of protein is therefore available and recent research has investigated bloodmeal-based thermoplastics and their properties [24,46,4 7, 50]. 1.3.6. Bloodmeal-based thermoplastics At the University of Waikato in New Zealand, researchers have done extensive studies on the production of bloodmeal-based thermoplastics. They have shown that bloodmeal can be extruded and injection moulded for various applications when bloodmeal is treated with denaturants, reducing agents and plasticisers. Each chemical additive has a specific effect on the protein during processing; these additives thus also influence the properties of the resulting thermoplastic. Examples of chemicals that act to denature protein molecules are sodium dodecyl sulphate (SDS) and urea. The protein must undergo denaturation for the protein-protein interactions to be disrupted. The reducing agent, sodium sulphate, serves to cleave covalent cross-links of the bloodmeal proteins, facilitating processing. The action of the reducing and denaturing agents allow new interactions to form between molecules. Water is a low molecular weight molecule with a sufficiently high boiling point, which serves as a plasticiser in bloodmeal-based thermoplastics, improving processability [43,46,50-53]. 1.3. 7. Bloodmeal-filled polymers Blends and composites ofbloodmeal with synthetic polymers, such as UHMWPE, LLDPE, and polybutylene succinate (PBS), have been the topic of various studies in previous years. Early research has shown that the interfacial adhesion between the matrix and filler was inadequate and required the use of chemical additives to enhance compatibility between the phases. Evidence of the poor adhesion was the noteworthy decrease in mechanical properties for materials without additives. The incompatibility of the blend is mainly due to the hydrophobic nature of synthetic polymers and the hydrophilic nature of bloodmeal. Incompatibility of the constituents was also evident in morphological observations since blends without additives displayed phase separation. In studies that exercised contact angle measurements, the materials with increased bloodmeal content presented an increased hydrophilic nature, although this was not true for blends containing compatibiliser. Similarly, water absorption experiments showed 14 improved water absorption for blends containing bloodmeal compared to the neat polymer. Investigations of thermal properties of proteins indicated that the proteins could be processed using traditional processing methods [24,54,55]. 1.4. Objectives of this study The present work aims to produce polyethylene-bloodmeal (BM) composites with HOPE. The thermal behaviour was determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The mechanical properties of the composites were studied using tensile testing. The effect of the addition of bloodmeal on the environmental degradation of HDPE was investigated. Morphology of the aged samples was examined with attenuated total reflectance (ATR)-FTIR spectroscopy, optical microscopy and scanning electron microscopy (SEM). 1.5. Thesis outline The outline of this thesis is as follows: Chapter 1: General introduction and literature review Chapter 2: Materials and methods Chapter 3: Results and discussion Chapter 4: Conclusions 1.6. References 1. G. Scott. "Green" polymers. Polymer Degradation and Stability 2000; 68:1- 7. DOI: 10.10 l 6/SOl 41-3910(99)00182-2 2. D.M. Wiles, G. Scott. Polyolefins with controlled environmental degradability. Polymer Degradation and Stability 2006; 91 :1581-1592. DOI: 10.1016/j.polymdegradstab.2005.09.010 15 3. S. Karlsson, A. -C. Albertsson. Techniques and mechanisms of polymer degradation. In: G. Scott, D. Gilead (eds), Degradable Polymers, Springer: The Netherlands (1995). ISBN: 978-90-48 1-6091 -4, 978-94-017-1217-0 4. J.M.G. Cowie. Polymers: Chemistry and Physics of Modern Materials, 2nd Edition. Blackie Academic & Professional: London (1993). ISBN: 9780748740734 5. B. Singh, N. Sharma. Mechanistic implications of plastic degradation. 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Available from: http://etd.lib.clemson.edu/documents/1285620642/Nzioki_ clemson_ 0050M_ 10666.pdf 25. E.M. Bevilacqua, E.S. English, J.S. Gall. Mechanism of polyethylene oxidation. Journal of Applied Polymer Science 1964; 8: 1691-1698. DOI: 10.1002/app.1964.070080419 26. N. Lucas, C. Bienaime, C. Belloy, M. Queneudec, F. Silvestre, J.-E. Nava-Saucedo. Polymer biodegradation: Mechanisms and estimation techniques - A review. Chemosphere 2008; 73 :429-442. DOI: 10.1016/j .chemosphere.2008.06.064 27. S. Massey. Action of water in the degradation of low-density polyethylene studied by X- ray photoelectron spectroscopy. eXPRESS Polymer Letters 2007; 1: 506-511. DOI: 10.3144/expresspolymlett.2007.72 28. J.R. White, A. Turnbull. Weathering of polymers: Mechanisms of degradation and stabilization, testing strategies and modelling. Journal of Materials Science 1994; 29:584- 613. DOI: 10.1007/BF00445969 29. T. Ojeda, A. Freitas, K. Birck, E. Dalmolin, R. Jacques, F. Bento, F. Camargo. Degradability of linear polyolefins under natural weathering. Polymer Degradation and Stability 2011; 96:703-707. DOI: 10.1016/j.polymdegradstab.2010. 12.004 30. T. Hicks. Environmental Aspects of Proteinous Bioplastic. The University of Waikato; 2010. Available from: http://researchcommons.waikato.ac.nz/handle/l 0289/4297 31. K. Hatada, R.B. Fox, J. Kahovec, E. Marechal, I. Mita, V. Shibaev. Definitions of terms relating to degradation, aging, and related chemical transformations of polymers. Pure and Applied Chemistry 1996; 68:2313-2323. DOI: 10.1351 /pacl 99668122313 18 32. M. Roylance, D. Roylance. Fonns of polymer degradation. In: L.H. Hihara, R.P.I. Adler, R.M. Latanision (eds), Environmental Degradation of Advanced and Traditional Engineering Materials, CRC Press: Florida (2013). ISBN: 978-1-4398-1926-5, 978-1-4398-1927-2 33. S. Grima, V. Bellon-Maurel, P. Feuilloley, F. Silvestre. Aerobic biodegradation of polymers in solid-state conditions: A review of environmental and physicochemical parameter settings in laboratory simulations. Journal of Polymers and the Environment 2000; 8:183-195. DOI: 10.1023/ A: 1015297727244 34. J.R. White. Polymer ageing: Physics, chemistry or engineering? Time to reflect. Comptes Rend us Chimie 2006; 9: 1396-1408. DOI: 10.1Ol6/j.crci.2006.07.008 35. S.L. Kramer, P.E. Waibel, B.R. Behrends, S.M. El Kandelgy. Amino acids in commercially produced blood meals. Journal of Agricultural and Food Chemistry 1978; 26:979-981 . DOI: 10.1021/jf60218a033 36. G.A. Petsko, D. Ringe. Protein Structure and Function. New Science Press: London (2004). ISBN: 9781405119221 37. D.L. Meeker. Essential rendering: All about the animal by-products industry. National Renderers Association: Fats and Proteins Research Foundation - Animal Protein Producers Industry (2006). ISSN: 0965466035 9780965466035 38. S. Shanna, J.N. Hodges, I. Luzinov. Biodegradable plastics from animal protein coproducts: Feathenneal. Journal of Applied Polymer Science 2008; 110:459-467. DOI: 10.l 002/app.28601 39. C.J.R. Verbeek, L.E. van den Berg. Extrusion processing and properties of protein-based thennoplastics. Macromolecular Materials and Engineering 201 O; 295: 10-21 . DOI: 10.1002/mame.200900167 40. P.M. Guerrero Manso. Processing and characterization of soy protein-based materials. University of the Basque Country 2013. Available from: https://addi .ehu.es/handle/1081Oil0153 19 41. 0. Orliac, F. Silvestre. New thermo-moulded biodegradable films based on sunflower protein isolate: Aging and physical properties. Macromolecular Symposia 2003 ; 197: 193- 206. DOI: 10.1002/masy.200350718 42. V.M. Hernandez-Izquierdo, J.M. Krochta. Thermoplastic processing of proteins for film formation - A review. Journal of Food Science 2008; 73 :R30- R39. DOI : 10.11 l l /j .1750-3841.2007.00636.x 43. C.J.R. Verbeek, L.E. van den Berg. Development of proteinous bioplastics usmg bloodmeal. Journal of Polymers and the Environment 2011 ; 19: 1-10. DOI: 10.1007/sl0924-010-0232-x 44. G.H. Brother, L.L. McKinney. Protein plastics from soybean products. Industrial & Engineering Chemistry 1940; 32: 1002-1006. DOI: 10.102 l/ie50367a034 45. J.R. Barone, W.F. Schmidt, N.T. Gregoire. Extrusion of feather keratin. Journal of Applied Polymer Science 2006; 100: 1432-1442. DOI: 10.1002/app.23501 46. C.J .R. Verbeek, L.E. van den Berg. Mechanical properties and water absorption of thermoplastic bloodmeal. Macromolecular Materials and Engineering 2011 ; 296:524- 534. DOI: 10.1002/mame.201000374 47. Sharma S. Fabrication and characterization of polymer blends and composites derived from biopolymers. Clemson University; 2008. Available from: http://etd.lib.clemson.edu/documents/ l 239894269/Sharma_ clemson_ 0050D _ 10001 .pdf 48. Grindley HS. Nitrogenous constituents of feeding stuffs. Journal of Animal Science 1917; 1:133-141. ISSN: 0021-8812, 1525-3163 49. Abstract of Agricultural Statistics 2012. Available from: http://www.nda.agric.za/docs/statsinfo/Ab2012.pdf [Accessed: April 2013] 50. C.J.R. Verbeek, T. Hicks, A. Langdon. Degradation as a result of UV radiation of bloodmeal-based thermoplastics. Polymer Degradation and Stability 2011 ; 96:515- 522. DOI: 10.1016/j.polymdegradstab.2011.01.00 51. C.J .R. Verbeek, E. Klunk.er. Thermoplastic protein nano-composites using bloodmeal and bentonite. Journal of Polymers and the Environment 2013; 21 :963-970. 20 DOI: 10.1007/s l0924-013-0610-2 52. C.J.R. Yerbeek, N.J. Koppel. Moisture sorption and plasticization of bloodmeal-based thermoplastics. Journal of Materials Science 2012; 47:1187-1195. DOI : 10.1007/sl0853-011-5770-7 53. C.J.R. Yerbeek, L.E. van den Berg. Structural changes as a result of processing in thermoplastic bloodmeal. Journal of Applied Polymer Science 2012; 125:E347- E355. DOI: 10.1002/app.36964 54. K.I.K. Marsilla, C.J.R. Verbeek. Properties of blends of Novatein thermoplastic protein from bloodmeal and polybutylene succinate using two compatibilizers. International Journal of Chemical Engineering and Applications 2013; 4:106-110. DOI: 10.7763/IJCEA.2013.Y4.273 55. K.I.K. Marsilla, C.J.R. Verbeek. Properties of bloodmeal/linear low-density polyethylene blends compatibilized with maleic anhydride grafted polyethylene. Journal of Applied Polymer Science 2013;130:1890-1897. DOI: 10.1002/app.39323 21 Chapter 2 Materials and Methods 2.1 Materials 2.1.1 High-density polyethylene (HDPE) HOPE was supplied in pellet form by Safripol Pty. Ltd. from Sasolburg, South Africa. It has a density of 0.956 g cm·3 and a crystalline melting range of 130-133 °C. It shows a tensile yield strength of 27 MPa, an ultimate tensile strength of 38 MPa, and ultimate elongation values can be greater than 600%. 2.1.2 Bloodmeal (BM) Bloodmeal was received from Comchem Trading subsidiary, TALCHEM. The following specifications were supplied: Table 2.1 Information received with bloodmeal Content Proportion I g kg-1 Protein 750 (min) Phosphorous 2 (min) Fat 60 (min) Fat 80 (max) Calcium 5 (max) Moisture 100 (max) During bloodmeal production, the proteins are treated at elevated temperatures for the elimination of pathogens and the removal of water. Increased temperature conditions also result in cross-linking between reactive proteins, which hinders further processing without the addition of chemicals [1]. We did not use chemical additives, and we did not process the bloodmeal before use. 22 Thermogravimetric analysis (TGA) analysis ofbloodmeal showed the initial mass loss to occur around I 00 °C, and this was attributed to the removal of water. Further mass loss from approximately 200 °C is believed to result from the rupture of peptide bonds of the protein molecule [2]. Our tests showed similar results. 2.2 Sample preparation The bloodmeal powder was sieved using a stainless steel King Test Laboratory Test Sieve with an aperture size of 600 µm . Before mixing, the bloodmeal was placed in an oven at 80 °C overnight to remove any absorbed water and kept at 40 °C until all composites of polyethylene and bloodmeal had been prepared. A colour change from brown to dark brown was observed after the bloodmeal was placed in the oven. Samples were prepared according to the weight percentages in Table 2.2. Table 2.2 Table of composite proportions Weight% HDPE Weight % bloodmeal 100 0 99 1 95 5 90 IO 80 20 The HDPE pellets were used directly from the bag without drying. The HDPE-bloodmeal composites were prepared by a melt mixing process using a Brabender PLASTICORDER PL 2100 at 150 °C. The mixing was done at a speed of 30 rpm, and the dried bloodmeal was added after a minute and allowed to blend for a total of I 0 minutes. Thin fi lms with thicknesses of approximately 0.2, 0. 7 and 1.0 mm were prepared for each composition. The material was placed on the melt press at 180 °C, allowing the material to melt whi le gradually increasing the applied pressure. After 5 minutes, the pressure was increased to 50 bar for an additional 5 minutes. 23 2.3 Characterisation techniques 2.3.1 Moisture content The moisture content of the composites had to be determined to verify the effect of the addition of blood meal to polyethylene in terms of moisture content. The presence of bloodmeal in HOPE was expected to increase the moisture content of the composites to some extent. Moisture content of the samples was determined gravimetrically by weighing bloodmeal powder and pieces of composite material (average weight of approximately 1 g, Mini1ia1), followed by drying (Mdry) in an air-circulating oven at 80 °C over-night (± 24 hours). Moisture content of the 0.2 mm composite films were tested for each composition. An average of three specimens were tested. The percentage moisture content was calculated with Equation 2. 1 [3]. . = M(initial) -M(dry) ] [ % Moisture content C .. I) x 100% (2. 1) M tnitia 2.3.2 Water absorption The purpose of the water absorption testing was to show whether the presence of blood meal in polyethylene improved the water absorption of the composites. Improved absorption of water enhances the prospect of hydrolytic degradation in the material. The ability of the material to absorb water was investigated by cutting 15 x 15 mm samples (average weight of 0.42 g). The samples were weighed (Mini1ia1) and then immersed in 100 ml deionised water at room temperature. Surface water was removed from the blends using a paper towel before re-weighing (Mwe1) after 48 hours submersion in deionised water. For testing the water absorbance of pure bloodmeal, approximately 1 g (Mini1 ia1) was weighed and placed in an oven at 80 °C overnight. The dried bloodmeal was then placed in a desiccator to cool for an hour. Once cooled, the bloodmeal powder was mixed with I 00 ml deionised water and left at ambient temperature for 48 hours. The bloodmeal was filtered under vacuum using a Buchner funne l before re-weighing (Mwe1) at ambient temperature. 24 The difference between the initial mass (Mini1ia1) and the mass after immersion (Mwe1) was used to calculate the percentage water absorption using Equation 2.2. . M(wet) - M(initial) Percentage water absorption = C . . I) x I 00 (2.2) M m1lla An average of three specimens were tested. 2.3.3 Underground ageing test The aim of the underground ageing test was to simulate natural weathering conditions to test whether the addition of bloodmeal influenced the degradation of HDPE, and therefore the temperature and humidity were not controlled in these tests. Samples of varying thickness (~0.2 , 0.7, and 1.0 mm) were buried vertically in soil for 36 weeks. Approximately 500 ml of water was added to the soil every week and the humidity of the soil was monitored using a Major Tech MT662 Thermo-hygro humidity meter. Figure 2.1 The positioning of composite samples in soil for the underground ageing test before covering with soil A set of composite films were removed from the soil after four weeks, and then every eight weeks after that for a total of 36 weeks. Excess soil was wiped from the surface of the films, which were then rinsed with deionised water and dried with a paper towel. The films were left at ambient temperature for 24 hours before the films were characterised. Observations of the characterisations were correlated with ageing processes. 25 2.3.4 Differential scanning calorimetry (DSC) The thermal transitions that a material undergoes during heating or cooling processes can be studied using a DSC. These thermal transitions, such as melting during heating, or crystallization during cooling, can provide valuable information about the material being tested. Clearly modified thermal transitions evident in thermal traces could lead a researcher to expect changes in other characteristic properties of the materia l in question. For example, changes in the crystal structure that can result from the incorporation of filler substances can alter the mechanical properties of a material [ 4]. DSC analyses were performed in a Perkin-Elmer DSC 6000 differential scanning calorimeter in flowing nitrogen atmosphere (20 ml min-1). The samples having masses of 6-7 mg each were sealed in aluminium pans and heated from 0 to 200 °C, cooled from 200 to 0 °C and reheated from 0 to 200 °C at a rate of 10 °C min-1• Three samples from each composition were analysed. Only the second heating scan was used to determine the melting enthalpies and temperatures. The crystallization enthalpies and temperatures were determined from the cooling scan. 2.3.5 Thermogravimetric analysis (TGA) TGA is a technique which follows the mass of the sample as a function of temperature or time, under controlled conditions. The thermal trace, recorded as mass percentage versus temperature or time, supplies information regarding the thermal stability, decomposition and degradation temperatures, and the moisture or volatile content of the material under the specified conditions. A Perkin Elmer STA 6000 simultaneous thermal analyser was used to study the influence of the addition of bloodmeal on the thermal stability of polyethylene. Samples with masses of22 mg were heated from 25 to 600 °C at a heating rate of 10 °C min·' and a nitrogen flow rate of 20 ml min-1• TGA was done on all the compositions of the unaged composite samples, bloodmeal , HDPE, and 20% BM containing samples aged underground for 36 weeks. The analyses were performed in triplicate for each composition and ageing time, and the average values and standard deviations are reported. 26 2.3.6 Fourier-transform infrared (FTIR) spectroscopy FTI R spectroscopy is a simple characterisation technique that provides useful information about the sample being examined. Chemical bonding and molecular structure can be investigated using the principle that molecules in a sample vibrate at a distincti ve frequency when irradiated with infrared (IR) light. Particular bonds in certain molecules provide a characteristic spectrum, allowing specific chemical groups to be identified in a materi al. The technique is non- destructive, and only very small amounts of the materia l are required for analysis, which is ideal when working with a limited amount of sample. A PIKE MiracleTM ATR, with a diamond crystal, connected to a Perkin-Elmer Spectrum 100 FTIR spectrometer, was used for the examination of the composites. A clean, empty diamond crystal was used for the collection of the background spectrum. The ATR-FTIR spectra were recorded between 4000 and 650 cm·1 at a resolution of 8 cm·1• The carbonyl index can be used as a measure of the extent ofo xidation of a material. Calculation oft he carbonyl index is achieved by tak ing the ratio of the carbonyl absorbance to the distinctive C-H stretching absorbance at 1465 cm·1• In an FTIR spectrum, carbonyl groups are observed in the 1680-1850 cm·1 range. A broad peak in thi s range can indicate the presence of different oxidised groups due to the overlapping bands of the carbonyl groups. The carbonyl index of the composites was fo llowed to verify whether ox idation processes had occurred during the underground ageing study [5,6]. 2.3. 7 Optical microscopy Microscopy techniques, such as optical microscopy and scanning electron microscopy (SEM), are often used to observe and investigate the morphology of samples. Optical microscopy was implemented to distinguish the overall di spersion of bloodmeal in HOPE; therefore the films were not exan1ined at high magnifications. Optical microscopy was performed using a Zeiss microscope at 20x magnification. The 0.2 mm films and the 1.0 mm fi lms of all the compositions were examined fo r unaged films and films 27 aged underground for 36 weeks. An AxioCam ERc5s camera, connected to the microscope, captured the pictures using Zeiss software. 2.3.8 Scanning electron microscopy (SEM) SEM is a technique used to investigate the morphology of a sample. An electron beam is generated in the microscope, which is then guided down the microscope column to the sample situated on the stage, under vacuum. Once the primary electrons of the electron beam collide with the particles of the sample, the electrons are scattered and travel on a new trajectory. An incident electron can be scattered in different ways, depending on the interaction with the sample, and specific detectors are used to detect and interpret these signals to provide information about the sample surface. The SEM can record images at very high magnifications. SEM images are useful for observing the topography of a sample, for determining the dispersion of filler particles in a polymer matrix, identifying phase separation in a polymer blend and visualisation of the interaction between composite components [7]. A Tescan VEGA 3 SEM with a secondary electron detector was used to acquire the images of the composites. The surfaces of the samples were coated with carbon before examination to provide a conductive surface for the imaging to occur. Images were taken at 51 , I 00, and 200 times magnification and a voltage of 20 kV. 2.3.9 Tensile testing Depending on the interactions between the filler and the polymer matrix, the mechanical properties of a composite can vary from that of the pure substance. Variations in the mechanical properties can give some insight into the anticipated effect of a specific treatment on a material. Reported outcomes of underground ageing on polymer materials include increased modulus and yield stress, as well as decreased elongation at break values. Ageing processes involve abiotic and biotic reactions. Abiotic reactions, such as oxidation, typically precede biotic processes, such as biodegradation. Synthetic polymers, with high molecular weight components, usually require extended periods of time before biodegradation will occur. 28 The tensile testing was performed on a Hounsfield H5KS universal tensi le testing machine. A minimum of six dumbbell-shaped samples were tested fo r each composition, for each film thickness, for every ageing time, and the average results are presented. The dimensions of the dumbbell-shape are indicated in Figure 2.2. 45nvn Figure 2.2 Dimensions of the dumbbell-shape used for tensile testing Young's modulus was calculated from the initial part of the stress-strain curve (within 1.8% strain) for all the films, at each ageing time. The stress at yield and elongation at break values were determined by reading the values off the stress-strain curves for all the composites. The changes in the above properties were fo llowed to detect the influence of so il buria l on the materials over time. 2.4 References 1. C. J. R. Verbeek, L. E. van den Berg. Development of proteinous bioplastics using bloodmeal. Journal of Polymers and the Environment 20 11 ; 19: 1- 10. DOI: 10.1 007/s 10924-010-0232-x 2. B. M. Nzioki. Biodegradable Polymer Blends and Composites from Proteins Produced by Animal Co-Product Industry. Clemson University 2010. Available from: http://etd.lib.clemson.edu/documents/1285620642/Nzioki_ clemson_ 0050M_ l 0666. pdf 3. J.E. Reeb, M.R. Milota. Moisture content by the oven-dry method for industrial testing. Available from: http://ir.library.oregonstate.edu/xmlui/handle/l 957/5 I 90 4. J.M.G. Cowie. Polymers: Chemistry and Physics of Modem Materials, 2nd Edi tion. Blackie Academic & Professional: London (1 993). ISBN: 9780748740734 5. A. Ammala, S. Bateman, K. Dean, E. Petinakis, P. Sangwan, S. Wong, Q. Yuan, L. Yu, C. Patrick, K. H. Leong. An overview of degradable and biodegradable polyolefins. Progress in Polymer Science 20 11 ; 36:1 015-1049. 29 DOI: 10.1016/j.progpolymsci.2010.12.002 6. E. Chiellini, A. Corti, S. D' Antone R. Baciu. Oxo-biodegradable carbon backbone polymers - Oxidative degradation of polyethylene under accelerated test conditions. Polymer Degradation and Stability 2006; 91 :2739-2747. DOI: 10.1016/j.polymdegradstab.2006.03.022 7. M. Dunlap, J.E. Adaskaveg. Introduction to the scanning electron microscope - theory, practice, & procedures. Available: https://imf. ucmerced.edu/downloads/semmanual .p df. [Accessed: 08-0ct-2015]. 30 Chapter 3 Results and Discussion 3.1.1 Moisture content The moisture content of pure bloodmeal and the HOPE/BM composites was determined using the method described in Section 2.3.1. The difference in the mass measured before and after exposure to heat in the oven can be thought of as the amount of moisture released from the sample. '::le. 5.0 --0 -~ 4.5 1 c 0 (.) -. Q..). :l (/) ·5 E ~ 0.25 cro Q) e Q) .-a. c .iOi)l s 0.00 BM HOPE 99/1 95/5 90/10 80/20 Weight percentage bloodmeal I% Figure 3.1 Moisture content of pure bloodmeal powder and of HDPE/BM composites prior to underground ageing stored at room temperature Pure HOPE is inherently hydrophobic and does not absorb water, neither does it release any moisture. Given that pure bloodmeal powder released approximately 5% moisture (Figure 3. 1) , it was expected that the bloodmeal contained in the polymer would emulate this behaviour. It can be seen that the moisture content increases with the amount of bloodmeal in the composite. 31 Experimental results showed that 99/ 1 HOPE/BM composite released slightly more moisture than predicted. A possible explanation for thi s observation is that mixing the hydrophi lic bloodmeal with the hydrophobic HDPE could have forced the minor phase, with very low content, to the surface of the polymer film, thereby maintaining a mostly hydrophobic core. The bloodmeal particles that would be exposed at the surface of the polymer and could release any moisture bound to the bloodmeal particle. Conversely, for the 5, I 0 and 20% bloodmeal containing composites, the moisture released was less than expected. As the bloodmeal content increased, the hydrophilic particles could cluster together in the bulk of the film. Since the HOPE enveloped the bloodmeal particles, a barrier was formed, preventing the escape of moisture. It was shown that bloodmeal powder naturally contained some moisture (as seen in Table A.3.1 in the Appendix). When mixing bloodmeal powder with HOPE, the expected amount of moisture was not released, so the moisture present in the bloodmeal had been retained in the polyethylene/bloodmeal composite. These results indicate that the addition of bloodmeal to HOPE can increase the moisture content of the resulting composite to some extent. The increased moisture contained in the composite could promote hydrolytic degradation of the material. 3.1.2 Water absorption The water absorption of pure bloodmeal and the HOPE/BM composites was determined as described in Section 2.3.2. It was confirmed that the films that did not contain bloodmeal did not absorb any water since polyethylene does not possess any hydrophilic groups. Water can only be absorbed by the composite ifthe bloodmeal particles are localised on the surface of the film, thus an approximation of the amount of bloodmeal particles exposed on the surface of the films was made. An estimation of water absorption per composite was based on the amount of bloodmeal present in the composite, assuming that all the bloodmeal particles in the sample could absorb water. A comparison of these estimated values with the experimentally determined values indicated that the bloodmeal was not uniformly distributed in the HOPE films. The values varied with thickness and with bloodmeal content, as shown in Table 3. 1. 32 Water absorption of the composites was expected to decrease as the film thickness increased. This trend was observed for the HD PE/BM 90/10 composite fi lms. It was also expected that films containing a higher weight percentage of bloodmeal would absorb more water. T ill s was only part ia lly observed. For the 0.2 mm thick fi lms, the bloodmeal partic les were most likely situated completely on the surface of the polymer, especially at high content. Considering that the adhesion between the filler and matri x was probably not optimal (because the polymer is hydrophobic and bloodmeal is hydrophilic), a surface particle could easily become dislodged from the po lymer matrix, thus negatively affecting the ability of the composite to absorb water. Table 3.1 Water absorption for pure HOPE, as well as the 90/10 and 80/20 w/w HOPE/BM composite films prior to underground ageing Estimated % of Film Water Expected water Sample BM exposed on thickness absorption I % absorption I % film surface Bloodmeal - 78 ± 0 - - HOPE 0.2 mm 0 0 - HOPE l.Omm 0 0 - 90/10 w/w 0.2mm 1.7 ± 0.0 7.8 22 HD PE/BM 90/10 w/w 1.0 mm 0.7 ± 0.0 7.8 9 HOPE/BM 80/20 w/w 0.2 mm 1.2 ± 0.0 15.6 8 HD PE/BM 80/20 w/w 1.0 mm 1.9 ± 0.0 15.6 12 HD PE/BM Bloodmeal has demonstrated an affinity for water, and is able to absorb large amounts of water, even under ambient conditions. This could be beneficial in a humid composting environment to a id the degradation of the bloodmeal proteins [ 1,2]. Although bloodmeal has a highl y hydrophilic nature, it appears as if the incorporation of bloodmeal powder in HOPE does not significantly enhance the ability o f the material to absorb water. The opposing characteristics of the matrix and filler, regarding the hydrophobicity of 33 HOPE and the hydrophilicity of bloodmeal, give n se to the varying distribution of the components within the composite. As the major phase of the composite, HOPE surrounds and covers the bloodmeal particles, especially in thicker films. This isolates the particles and prevents interaction with water or the environment. The composites can absorb only small amounts of water since some of the bloodmeal particles could be positioned exposed, on the surface of the film. The fact that only limited amounts of water are absorbed could be beneficial during the life cycle of the material. Initially, the service life of the material is not drastically shortened since the material properties are largely preserved. When the time comes to discard the material , under the right conditions, hydrolytic degradation initiated by absorbed water can potentially contribute to the degradation processes [3- 5). 3.1.3 Differential scanning calorimetry (DSC) The DSC was used to study the influence of the addition of bloodmeal and environmental ageing on the melting and crystallization of HDPE. It was important to establish whether the bloodmeal particles would disrupt the crystal structure of HDPE, since this would ultimately affect the mechanical properties of the material. As can be seen in Figure 3.2 and 3.3 , the melting and crystallization peaks did not shift with increasing bloodmeal content. It can be inferred that the inclusion of bloodmeal in HOPE does not have an observable effect on the crystal structure of the polymer. Table 3.2 shows the results obtained from the DSC analyses of the different composites. The melting temperatures did not change significantly with an increase in bloodmeal content or with extended ageing time. Similarly, during cooling, the crystallization temperatures also displayed very little variation with either composition or ageing time. 34 - --HOPE - unaged a. 4 - - HOPE - aged for 36 weeks ::J - --- - 80/20 w/w HOPE/BM - unaged I 0 "C .......... 80/20 w/w HOPE/BM - aged for 36 weeks V· c ~ 3 J' I 1 -3- 2 -0 i:;:::: ro Q.l ..c "C Q.l CJ) ro \\' ............... -........ ...... '..~_ :-_: -: _-: _-: _-:- E..... z0 80 100 120 140 Temperature I °C Figure 3.2 DSC second heating curves of HDPE and 80/20 w/w HDPE\BM composites prior to underground ageing and after underground ageing for 36 weeks -···-····-······-·····-·····-·-··-······-····-······· -- -~ -3 i:;:::: ro Q.l ..c -4 "C Q.l CJ) ro -5 --HOPE - unaged E - - HOPE - aged for 36 weeks ..... - - - - 80/20 w/w HOPE/BM - unaged z0 -6 ········· 80/20 w/w HOPE/BM - aged for 36 weeks 80 100 120 140 Temperature I °C Figure 3.3 DSC cooling curves of HDPE and 80/20 w/w HOPE/BM composites prior to underground ageing and after underground ageing for 36 weeks 35 Table 3.2 Melting and crystallization temperatures and enthalpies obtained from the cooling and second heating curves for all the composites prior to underground ageing and after underground ageing for 36 weeks (1 mm thick samples) HEATING Sample Tm/°C AHm I J 1r1 AHmnorm I J !f1 Pure HDPE 133.2 ± 0.2 198.3 ± 5.5 198.3 ± 5.5 9911 w/w 133.2 ± 0.2 199.4 ± 4.6 20 1.4 ± 4.6 HD PE/BM 9515 wlw 133.5 ± 0.4 200.0 ± 7.2 2 10.5 ± 7.6 Unaged HD PE/BM 9011 0 w/w 133.0 ± 0.4 177.7 ± 11.6 197.4 ± 12.9 HD PE/BM 80/20 w/w 132.7 ± 0.2 159.8 ± 8.5 199.8 ± 10.7 HD PE/BM Pure HDPE 133.4 ± 0.1 198.1 ± 5.4 198. I ± 5.4 9911 w/w 133.2 ± 0.2 194.6 ± 6.0 196.5 ± 6.1 HD PE/BM 9515 wlw Aged underground 133 .5 ± 0.3 187.6 ± 3.9 197.5 ± 4.1 HD PE/BM for 36 weeks 90/10 w/w 133.5 ± 0.7 181.0 ± 20.5 20 1.1 ± 22.8 HD PE/BM 80/20 w/w 133.3 ± 0.3 183. 1 ± 10.0 228.9 ± 12.4 HOPE/BM COOLING Sample Tc/°C Alic I J !t1 AHcnorm I J !t1 Pure HOPE 1I7.6 ± 0.4 -191.7 ± 9.2 -191.7 ± 9.2 9911 w/w 118.0 ± 0.2 -168.I ±25.7 -169.8 ± 26.0 HOPE/BM 9515 wlw I 17.6 ± 0.2 -1 64.2 ± 5.7 -I 72.8 ± 6.0 Unaged HOPE/BM 9011 0 w/w 11 7.8 ± 0.4 -1 55.2 ± 3.9 -172.4 ± 4.3 HOPE/BM 80/20 w/w 117.7 ± 0.2 - 148.3 ± 5.2 -185.4 ± 6.5 HOPE/BM Pure HOPE I I 7.6 ± 0.3 -192.6 ± 14.8 -192.6 ± 14.8 99/ 1 w/w 118.0 ± 0.2 -1 68.0 ±3 1.1 - I 69. 7 ± 3 1 .4 HOPE/BM 9515 wlw Aged underground 117.7 ± 0.3 -1 69.3 ± 7.8 -I 78.2 ± 8.2 HOPE/BM for 36 weeks 9011 0 w/w 117.5 ± 0.8 -171.7 ± 14.4 -190.8 ± 16.0 HOPE/BM 80/20 w/w 11 7.3 ± 0.2 -181.6 ± 13.6 -299.9 ± 16.9 HOPE/BM Tm = peak temperature of melting; llHm = melting enthalpy; Tc = peak temperature of crystallization; L'lHc = crystallization enthalpy; llHmnorm and llHc110rm = enthalpies normalised with respect to the amount of HOPE in the sample. 36 The calculated enthalpy values were nonnalised with respect to the amount of HOPE in the samples. Comparison of the nonnalised enthalpy values for pure HOPE, unaged and aged underground fo r 36 weeks, shows that ageing processes did not have any effect on the crystal structure of the pure polymer. For the composites containing I and 5% bloodmeal , the enthalpy decreased slightly for the aged sample, but it increased slightly for the 90110 HOPE/BM composite, and significantly for the 80/20 HOPE/BM composite. This indicates an increase in total crystallinity of the HOPE in the san1ples [6]. It has been shown by a number of authors that the degradation of polymeric substances is initiated in the amorphous parts of the material [7,8]. It can therefore be concluded that the observed increase in crystallinity resulted from recrystalli zation of the amorphous phase induced by ageing and the presence of BM particles. The crystallization enthalpy values of all the composites correspond well with the melting enthalpy values, which is what one would expect. The heating and cooling curves of all of the composites can be found in the Appendix. 3.1.4 Thermogravimetric analysis (TGA) The TGA curves of the unaged HOPE, bloodmeal, and HOPE/BM composites are shown in Figure 3.4. HOPE degrades in a single degradation step from approximately 455 °C. The two- step degradation of pure BM can be attributed to the loss of water between 100 and 200 °C, and the degradation of the protein structure of BM between 275 and 320 °C [9, 1O ]. The average BM residue at 600 °C was 29.4%. Essentially, char is sample content that cannot be dissociated into smaller volatile fragments at the highest temperature of the specific thermogravimetric analysis test. The discussion that fo llows is an explanation of the possible constituents of the BM char. 37 - --·- \ 80 \ \ \ \ I \ \ 'cF. 60 \ \ (/) ' \ (/) ro ::? 40 -._ -·- ·- --HOPE ·- -·-· 20 - - 99/1 w/w HOPE/BM - · - 95/5 w/w HOPE/BM - · · - 90/10 w/w HOPE/BM - -- -- 80120 w/w HOPE/BM 0 - ·- ·- Bloodmeal 100 200 300 400 500 600 Temperature I °C Figure 3.4 TGA curves of unaged bloodmeal, pure HDPE and the HDPE/BM composite films prior to underground ageing Blood is made up of two main components, namely the blood plasma (- 80%) and the cellular fraction which contains fat, carbohydrates and minerals (- 20%). Blood plasma consists mostly of water (- 90%), while plasma proteins make up the remainder. Most of the water is removed from the plasma during the spray drying process of bloodmeal production. Since the plasma component also contains proteins, when plasma is dehydrated, the residua l proteins, minerals and fat can contribute to the cellular fraction of the bloodmeal. It has been reported that once dehydrated, the remaining plasma components can retain about 7% moisture, which works out to approximately 5.6% of the total mass of blood (11 ,12]. This value correlates well with the value determined for pure BM in the moisture content experiment in this study. From the TOA curve for BM, the mass lost at 200 °C was approximately 6%. This is attributed to loss of moisture from the sample, which a lso correlates with the reported moisture content values. The combined fat and carbohydrate content of blood constitutes 0.3%, while the mineral content amounts to just more than 0.6% of the cellular fraction of the blood. The remaining constituent of the cellular fraction are proteins (- 17%) that are made up of amino acids [I I] . The e lements present in amino acids are mainly carbon, hydrogen, nitrogen and oxygen. The nitrogen present 38 in amino acids could contribute to the char content if the atoms recombine under the high heat conditions to form inorganic compounds, such as ammonium nitri tes or nitrates. Similarly. recombi nation of carbon atoms to form carbides, carbonates, and cyanides (CN), all of which are considered to be inorganic, could marginally contribute to some char fo rmation [ 13- 15] . Certain amino acids, such as cysteine and methionine, are known to conta in sulphur (amino acid structures are available in the Appendix). Using values from literature, the sulphur- conta ining amino acids of a protein sample could be equivalent to approximately 1.7% [16]. The amount of sulphur in a protein san1ple containing cysteine and methionine is considerably lower than about 0.06%. Thus, it is improbable that the presence of sulphur will affect the inorganic content of the protein sample to a noteworthy extent. Considering all of the above information, the maxi mum possible char content for pure BM could be equivalent to approximately 20%, which is lower than the observed char content. A feasible explanation for this result is the addition of additives to the blood before or during processing. An example is sodium citrate which acts as an anti-coagulant during the spray- drying process, acids and sequestering agents may also be used to aid processing [ 12, 17]. Added chemicals were not specified by the supplier of the bloodmeal, and attempts to find relevant information were not successful. In conclusion, the observed high char residue could have resulted fro m the presence of inorganic compounds added to the BM during processing, or compounds that formed during the analysis. It is also possible that the residue was sample matter that was not burnt off under the analysis conditions and temperature. The TGA analysis of unaged HOPE shows the expected curve with a single degradation step (Figure 3.5). The degradation curve o f HOPE aged underground for 36 weeks is virtuall y identical to that of the unaged HOPE. This shows that the period of underground ageing had no discernible effect on the pure HOPE films. The HDPE/BM composites di splayed three degradation steps (Figures 3.4 and 3.5). The initial degradation was between I 00 and 250 °C. The mass loss at 250 °C is approximately 1.9 and 2.7% of the unaged and aged 80/20 w/w HOPE/BM composite samples, respectively. These results support the results for the water absorption tests and show that it is possible that more BM is exposed on the film surface of the aged samples, thus more moisture was absorbed by the aged composite. It is conceivable that if BM partic les were situated very close to the film surface, with only a thin coating of HDPE, 39 the abrasive soil environment of the underground ageing test could have, at least partially, exposed some of the BM particles. 100 ,._~_ __-_ ._.~. ~.~..~.,--~-~--~.-~---------~- ------------. . ·- - ~ ---:·.-~' .-;:: :::-; :::-.: ::-:.~.' ·. .. :, 80 \\ ·,. ' ' 60 \ ' (/) (/) ' ' ro ~ ........ I --. \ 40 ••. .. I - \--·--------- 20 --HOPE - unaged - - HOPE - aged 36 weeks ''1 - · - 80120 w/w HOPE/BM - unaged - - - - 80/20 w/w HOPE/BM - aged 36 weeks ~-. =.·. - -.--- O - - - - - Bloodmeal 100 200 300 400 500 600 Temperature I °C Figure 3.5 TGA curves of unaged bloodmeal, HDPE and the 80/20 w/w HOPE/BM composite films prior to underground ageing and after underground ageing for 36 weeks Further increase in temperature shows two more degradation steps for the composites. The first degradation step is the degradation of the BM proteins present in the composite, which occurs because the biological BM particles are less thermally stable than the synthetic polyethylene molecules. The second degradation step between 450 and 500 °C is the degradation of polyethylene. It was observed that the addition of BM to HOPE did not affect the thermal stability of HOPE in the composites. If it is taken into account that HOPE represents the largest part of all the composites, it can be seen from Figures 3.4 and 3.5 that there are no major shifts in the curves from approximately 450 °C. This shows that the degradation of HOPE is unaffected by the addition of BM. Based on the char residue of pure BM, the expected char content of the composites was estimated and is shown in Table 3.3, along with the observed char content values. The unaged composites exhibited char residues of approx imately 0.6, 0.6, 2.1 , and 3. 7%. The composite containing 10% BM content showed an average char residue of 2. 1% which is very close to the estimated char value for that composition. This result confirms 40 the BM content of the 10% samples and illustrates that BM was well dispersed in the composite. For the other compositions, the observed char residue varied to some extent from the expected char values. This is probably the result of inefficient distribution of the BM particles in HOPE (evident from the higher standard deviation values). The hydrophilic BM particles probably formed agglomerates in the hydrophobic polyethylene in certain parts of the composite film. Table 3.3 Average char values for unaged bloodmeal, HDPE, and bloodmeal composites, as well as HDPE and 80/20 w/w HDPE/BM composite aged underground for 36 weeks Expected char Char content Sample content I% from TGA curves I% Bloodmeal 20 29.4 ± 0.5 HDPE unaged 0 0.2 ± 0.1 HOPE aged 36 weeks 0 0.2 ± 0.0 9911 wlw HOPE/BM unaged 0.3 0.6 ± 0.8 9515 w/w HOPE/BM unaged 1.5 0.6 ± 0.1 90110 w/w HOPE/BM unaged 2.9 2. 1 ± 0.4 80/20 w/w HDPE/BM unaged 5.9 3.7 ± 0.6 80/20 w/w HOPE/BM aged 36 weeks 5.9 3.5 ± 0.7 The unaged and aged composite samples fo llowed very similar traces, illustrating that the period of underground ageing had no perceivable effect on the thermal stability of the composite films. 3.1.5 Fourier-transform infrared (FTIR) spectroscopy FTIR spectra were acquired to verify the presence of certain chemical groups. The existence of certain chemical groups, such as carbonyl compounds, could confirm the occurrence of degradation processes, such as oxidation. Calculation of the carbonyl index is useful to determine the extent of oxidation that has occurred by measuring the intensiti es of the carbonyl peaks relative to that of the characteristic C-H stretch of the observed spectra [18] . 41 The results of the carbonyl index calculations did not show any observable trends. When amino acids link together to form proteins, a covalent peptide bond fo rms between the carboxyl group and amine group of two neighbouring amino acids. Thus. there are carbonyl groups present in the peptide bonds of proteins, and in certain side chains of the integral amino acids. The structures of the 20 known amino acids are available in the Appendix. The ex istence of these carbonyl groups in bloodmeal protein complicated the measurement of the carbonyl index. Additionall y, proteins and their secondary structures possess characteristic infrared bands, such as the amide I and amide II bands, respectively observed within the frequency ranges 1600- 1690 and 1480-1 575 cm·1• The amide I band is designated to C=O stretching, while the amide II band is assigned to CN stretching and NH bendi ng of the peptide bond [1 9]. Peaks detected in these ranges could also be associated with various carbonyl groups and with the characteristic C-H stretching absorbance which are used for carbonyl index measurements. It can be seen in the tables below that the calculated values for the carbonyl index did not change signi ficantl y. It can therefore not be said with certainty that the detem1ined carbonyl index values were an indication of oxidation of the polymer due to ageing, or as a result of chemical groups present in bloodmeal. When comparing carbonyl index values with ageing time, the following observations were noted. For the thinnest composite fi lms (-0.2 mm), the carbonyl index of the pure HOPE and the I% composite remained fai rly constant as the ageing time increased. The carbonyl index of the 5% composi te initially increased slightly, but evened out with ageing time. The I 0 and 20% composite carbonyl indices varied marginall y to a more significant degree as ageing time increased. Values of the carbonyl index of the - 0.7 mm composite films for all compositions, including pure HOPE, remained within a simi lar range over the ageing period. The 5, 10 and 20% composites all showed a higher carbonyl index value for the longest ageing time. The thickest composite fi lms (- 1.0 mm) displayed similar results, with the exception that the carbonyl index of only the 20% composite increased significantly after 36 weeks of underground ageing. The FTIR spectra of the composites, and graphs of carbonyl index versus ageing time, are available in the Appendix. It could not be defi nitively concluded whether the measured carbonyl index was the result of the oxidation of the polymer, due to ageing, or as a consequence of the presence of the bloodmeal proteins in the composites. 42 Table 3.4 Carbonyl index values calculated for 0.2 mm thick composite films Ageing time 99/1 w/w 95/5 w/w 90/10 w/w 80/20 w/w HDPE (weeks) HD PE/BM HOPE/BM HOPE/BM HOPE/BM 0 0.83 0.82 0.82 0.82 0.82 4 0.83 0.82 0.85 0.82 0.86 12 0.83 0.82 0.83 0.86 0.83 20 0.83 0.82 0.83 0.85 0.83 28 0.82 0.83 0.83 0.85 0.82 36 0.82 0.82 0.83 0.83 0.86 Table 3.5 Carbonyl index values calculated for 0. 7 mm thick composite films Ageing time 99/1 w/w 95/5 w/w 90/10 w/w 80/20 w/w HDPE (weeks) HOPE/BM HDP E/BM HD PE/BM HD PE/BM 0 0.82 0.82 0.82 0.83 0.83 4 0.82 0.82 0.82 0.82 0.83 12 0.82 0.82 0.83 0.83 0.83 20 0.83 0.82 0.82 0.83 0.83 28 0.82 0.82 0.83 0.83 0.82 36 0.82 0.82 0.85 0.84 0.86 43 Table 3.6 Carbonyl index values calculated for 1.0 mm thick composite films Ageing time 99/1 w/w 95/5 w/w 90/10 w/w 80/20 w/w HDPE (weeks) HD PE/BM HD PE/BM HD PE/BM HD PE/BM 0 0.82 0.81 0.82 0.82 0.83 4 0.82 0.82 0.82 0.83 0.85 12 0.83 0.82 0.83 0.83 0.85 20 0.84 0.82 0.82 0.84 0.83 28 0.82 0.82 0.83 0.83 0.82 36 0.82 0.84 0.85 0.83 0.93 3.1 .6 Microscopy 3.1.6. 1 Optical microscopy Optical microscopy was used to investigate the morphology of the composites. A 20x magni fication was utilized on the 0.2 mm and 1.0 mm composite films to characteri se the overall dispersion of bloodmeal in HDPE. Environmental degradation or deterioration of a polymeric material is defined as any chemical or physical change in a polymer caused by environmental factors such as light, heat, moisture, biological activity or altered chemical condition. Degradation is evident in property changes of the polymer that most often result from modified structural characteri stics, such as changes in crystallinity. Changes in the exterior surface, colour or texture can be a simple indication that material properties have been altered. These macroscopic observations can be a useful method to discern possible variations in material properties before more complicated and time- consuming characterisation techniques can be performed (20]. 44 Table 3. 7 Optical microscopy images of 0.2 mm thick composite films Unaged samples Samples aged 36 weeks • •• .. .. , • • ,,. A 9911 w/w ' 'f HD PE/BM • • ' ' • • . . ... .• !!!!!! ' !!!!!! • .. .. ~ ... . .. ; . • • • •. • ' .. : :'" # " . " . • •. . ' .. .. .. ... . .,, ,• ... ~. · . . 95/5 w/w . ~ . . ,, HD PE/BM .. • - ~ ' - • • . • . • .. .. . • ... .. ·. " . · ~ . . ~ . " ... ... .•. • ' 90/10 w/w HD PE/BM 80/20 w/w HD PE/BM 45 Table 3.8 Optical microscopy pictures of 1.0 mm thick composite films Unaged samples Samples aged 36 weeks • • 1 • • 99/1 w/w .. • . . ... HOPE/BM •• 9515 w/w HOPE/BM 90/10 w/w HD PE/BM 80/20 w/w HD PE/BM 46 The BM partic les appeared to be fairly evenl y dispersed throughout the HOPE matrix (Tables 3 .6 and 3. 7). The expected noticeable effects of ageing and degradation. for example, discolouration, or the development of cracks in the polymer surface. were not observed in the aged films. Bubbles were seen in some of the films of both thicknesses, and for both the unaged and aged samples. This could have resulted due to air trapped in the polymer, or around the BM particles, during mixing or melt pressing. The presence of bubbles are also an indication that the adhesion between the HDPE and the BM parti cles was imperfect. The presence of bubbles in the composite films can compromise the structural integrity of the materia l and can negatively impact mechanical properties. In genera l, it was observed that the presence of BM did not improve the mechanical properties of the composites due to imperfect adhesion between the HOPE matrix and the BM particles. The occurrence of bubbles very possibly contributed to the negative effects of BM on the mechanical properties. Addition of compatibi lising agents could aid the mixing process, making sure the components have better adhesion [2 1,22]. Ho les were seen in the 0.2 mm thick aged films, but not in the 1.0 mm films. Since the adhesion between the BM particles and the HOPE was not ideal, it is possible that a BM particle could have become dislodged from the thin HOPE matri x in the abrasive soil environment, during underground ageing, or during handling. In the thicker films, the BM particles had greater coverage by the polymer and would not have been as easily removed. 3.1.6.2 Scanning electron microscopy (SEM) Images o f the unaged and aged samples of HOPE and the 80/20 w/w HOPE/BM composites were obtained using SEM. It was observed that the surface of the HOPE samples looked very similar before and after underground ageing (Figure 3.6a and 3.6b). Since it is well known that polyethylene is resistant to degradation, it was expected that the material would not exhibit any changes due to underground ageing. 47 Figure 3.6 SEM images of a) unaged HDPE, b) HDPE aged underground for 36 weeks, c) unaged 80/20 w/w HOPE/BM, and d) 80/20 w/w HOPE/BM aged underground for 36 weeks. In Figure 3.6, the images of the unaged and aged 80/20 w/w HD PE/BM composites are shown as (c) and (d), respectively. The surface of the particles of the unaged samples appeared smooth, it seems that the particles are covered by a thin layer of HDPE. It was clearly seen that the particle surface in the aged samples was coarse and irregular, as if the surrounding HDPE had been 'eaten away' or degraded. This irregular surface was observed for the whole sample of 80/20 w/w HOPE/BM composites that was investi gated after ageing for thirty-six weeks. A possible explanation for this observation is that the presence of BM in the HOPE film, in the underground soil conditions, caused some degradation of the HDPE. 48 3.1.8 Tensile testing Tensile tests of unaged samples were performed to show the initial effects of the addition of bloodmeal on the mechanical properties of HOPE. The mechan ical properties of the aged samples were investigated to evaluate the influence of the bloodmeal in HOPE over time. The yield stress and elongation at break values were read off the stress-strain curves for a ll the composites. Young's modulus, or elastic modulus, was calculated from the initial part o f the stress-strain curve (within 1.8% strain) for all film thicknesses of each ageing time. The structure of the crystalline regions in a polymeric material, e.g. amount of crystallites, crysta llite sizes, etc. , play an important role in the mechanical properties of a material. The degree of crysta ll inity directly affects the strength of a material, and its ductility. In this study, three films of differing thicknesses where prepared for each composition, 0.2, 0.7, and 1.0 mm. During the preparation of the composite films, the degree of crystallinity slightly increased as the thickness of the films increased since the thicker films could cool from the melt somewhat slower than the thinner films. The influence of pre-cooling is evident in the comparison of the properties exhibited by the films of diffe rent thicknesses. This effect is also supported by the melting enthalpy results obtained by the DSC analyses in this study, i.e. ~Hmnorm(HDPE) = 182.4 J.g-1 for the 0.2 mm film, and ~Hm"0rm(HDPE) = 198.3 J. g-1• The results table can be found in Table A.3.2 in the Appendix. The samples were prepared using a cooling rate that corresponds with that used during industrial production conditions. HOPE prepared in this way tends to crystallize over time, a process known as physical ageing, or structural recovery [23,24]. This crystallization can be accelerated by using additional thermal treatment before ageing, such as heat treatment in an oven or radiation with UV light. In many similar experiments, authors performed thermal treatments of the samples before performing an ageing experiment to stabilise the samples and produce a uniform thermal history [25-27]. This strategy was not implemented in this study, because the intention of this work was to investigate the effect of fi lm thickness and also the ageing behaviour of samples prepared in ' real' industrial conditions. Young's modulus versus weight percentage BM of the unaged samples for all the compositions are presented in Figure 3.7. The composite sample containing 1% BM showed higher modulus 49 values than HOPE. This could be the result of the higher crystallinity of the sample, as can be seen from the DSC results (Table 3.2). After the initia l increase. the modulus of the samples decreased with increasing concentration of BM, fo r all the film thicknesses. Considering that the norma lised melting enthalpies, i.e. the degree of crystallinity. of the 10 and 20% samples are similar to that of HOPE, it can be concluded that the decrease in modulus with an increasing concentration of BM is probably due to a softening effect of the organic filler in the composite . The results also show that the effect of thickness is not very pronounced. Samples with a thickness of0.2 mm show somewhat lower values of modulus, which can be explained by lower crystallinity values compared to the thicker film samples. - - 0.2 mm 7 - .-. 0.7 mm - -•- -1.0mm 6 3 0 5 10 15 20 Wt.% bloodmeal Figure 3.7 Young's modulus values for unaged composite films with different thicknesses Figure 3.8 shows the average elongation at break values for the unaged composites for all three thicknesses. As the BM content of the composite was increased, the elongation at break values decreased, with the larges decrease observed for the lowest BM content. The elongation at break for HDPE was significantly higher than that of the composites, which was expected since polyethylene in generally known for its good mechanical properties. The elongation at break values of the composites decreased with BM loading due to the imperfect adhesion between HOPE and BM, and the BM particles acting as stress concentration points, because of their respecti ve hydrophobic and hydrophilic natures. For HDPE, the elongation at break increased so as the film thickness increased because the thicker film contained a slightly higher degree of crystallinity due to the effect of pre-cooling. This was also observed for the I and 5% composites, but not fo r the I 0 and 20% composites, possibly because the likelihood of agglomeration of BM particles increased as the BM content increased. The changes in elongation at break with increasing BM concentration are conspicuous, which leads to the inference that the inclusion of BM in HOPE considerably affects the amorphous phase of HOPE. Since the elongation at break is mostly dependent on the viscosity of the amorphous phase at the temperature of testing, decreased elongation at break values indicate an influence of the addition of BM to the amorphous phase of the polymer [28- 30] . These changes in the amorphous phase of HOPE had no effect on the crysta lline phase, since the melting temperature of the composites containing BM were relatively similar to the melting temperature of HOPE, as seen in Table 3.2. 500_,----,I,,.....-~~ ~~~~~~~~~~~~~~---. -11--0.2 mm - e- 0.7 mm 400 J - ·&- · 1.0mm -ro 300 c 0 ',+::; ro g> 200 0 w *- 100 0 5 10 15 20 wt.% bloodm eal Figure 3.8 Elongation at break values for unaged composite films with different thicknesses Before the yie ld point of a material, if a force exerted, the material will deform elastically and can return to its ori ginal shape when the applied force is removed. A fter the yield point, the materia l is irreversibly deformed. The stress at yield can be explained as the stress at which a material begins to deform plastically and will not return to its original shape if the applied force 51 is removed [3 1) . Similar to the results for Young·s modulus (Figure 3.7), the initial addition of BM showed an increase in the yield stress, compared to HOPE. Further increase in BM content exhibited lower yield stresses. This was due to the poor adhesion that was observed between the BM particles and the PE matrix, as was also evident in the other mechanical properties. It was expected that the stress at yield would increase with the thickness of the films. This result was observed to some extent for all the composite compositions. -.-0.2 mm 25 - ~- - ..- 0 .7 mm ,~ ......., , ,., - ·• - · 1.0 mm .... .~.... · ..... . .... .... ..... . ',..... . ....., VJ .... . .... ' ·, VJ Q) ........ ' .;:; 15 VJ .... .... ' ·, "'C ..... , ~ , . Q) >= .... ...'. .·..., ..... . 10 ... ..... ....... .... ! 0 5 10 15 20 Wt.% blood meal Figure 3.9 Yield stress values for unaged composite films with different thicknesses Figures 3.9 to 3. 11 illustrate the effect of underground ageing on Young 's modulus of the composite films of different thicknesses. During the first four weeks' ageing time, fo r all the film thicknesses, Young's modulus increased by about 200% for all the composi tions of the composite films. This observation is a consequence of the process of natural stabili sation or crystallization of the material with time, also known as physical ageing, or str uctural recovery [23,24). For all the film thicknesses, Young's modulus only slightly fluctuated with an increase in underground ageing time. The changes in modulus were more pronounced in the 0.2 mm composite fi lms and became less pronounced as the film thickness increased. It was also noted that the modulus generally decreased with increasing BM load. The modulus values remained fairly constant after the first ageing time for neat HOPE (Figure 3.9). This was a predictable outcome since it was not anticipated that the underground ageing 52 treatment would have a significant effect on synthetic polymer films. Young's modulus showed a moderate increase fo r the 1% BM composite from fou r to twenty weeks of ageing in soil. Although, after 20 weeks, the modulus decreased. As the ageing time increased for the 5, 10, and 20% BM samples, the modulus decreased to varying extents. It can be seen in Figure 3.9 that the decrease in modulus corresponds with the BM content of the films. Composites with higher BM content contained more BM particles, and therefore there is a higher possibly of the occurrence of agglomeration. The DSC results showed a decrease in crystallinity, and the BM particles probably do not have a high enough inherent stiffness to compensate for the loss of stiffness brought about by the lower crystallinity. Since the adhesion between the BM and HOPE was not ideal, it is plausible that some of the BM partic les could have become dislodged from the HOPE matrix with time, leaving small "holes" in the film . The consequence would be most pronounced for the 0.2 mm thick composite films. This "perforated area" in the film would compromise the structural integrity of the film, reducing the strength of the material. 18 -II-HOPE -y- 90/10 w/w HOPE/BM -+-99/1 w/w HOPE/BM -+-80/20 w/w HOPE/BM -&-95/5 w/w HOPE/BM 16 ro a.. 14 -~- -------..-._._ ___ ·~ . en ::::i 12 >- ----- ::::i - -1~ '"=:::::::: ~ "O 0 E 10 ~ --~· en -Cl c: 8 ::::i 0 >- ----~ 6 • 4 -4 0 4 8 12 16 20 24 28 32 36 40 Ageing time I weeks Figure 3.10 Young's modulus for all the 0.2 mm thick composite films as function of ageing time Figure 3.10 and 3. 11 show that, for the 0.7 and 1.0 mm HOPE films, the values for Young's modulus show only minor fluctuations with increasing underground ageing time. In contrast to the results for the 0.2 mm thick fi lm of 1% BM, the modulus values for the 0.7 and 1.0 mm films followed a simi lar trend to that of HDPE for the same film thicknesses. As explained 53 earlier, the effect of pre-cooling could have occurred in the thicker fi lms with low BM content, resulting in slightly more crystalline material that possesses a higher modulus. Higher contents of BM also only displayed minor fluctuations as the ageing time increased for both 0.7 and I .0 mm fi lm thicknesses. The influence of ageing was marginally more prominent for the 0.7 mm thick films than fo r the 1.0 mm thick films, also as a consequence of the effect of pre-cooling of the thicker composite films. 22 - HOPE --.- 90/10 w/w HOPE/BM ---99/1 w/w HOPE/BM -+- 80/20 w/w HOPE/BM 20 - • - 95/5 w/w HOPE/BM ro 18 0.... ~ 16 -.. CJ) :::J 14 :::J -0 12 0 E 10 CJ) -C) c: 8 :::J 0 >- 6 4 2 -4 0 4 8 12 16 20 24 28 32 36 40 Ageing time I weeks Figure 3.11 Young's modulus for all the 0. 7 mm thick composite films as function of ageing time A summary of the behaviour of Young' s modulus as a function of underground ageing time is presented in Figure 3. I 2 for all the film thicknesses. It presents a comparison of the modulus values between 4 and 36 weeks of underground ageing. In order to exclude from the ageing behaviour of the composites the effects of crystallization that occur due to physical ageing, the modulus of the unaged samples during the first four weeks were omitted. 54 22 - HOPE -T- 90/10 w/w HOPE/BM __._ 99/1 w/w HOPE/BM -+- 80120 w/w HOPE/BM 20 -A- 95/5 w/w HOPE/BM ro 18 0... 16 -1:::::==-- -~(- /) 14 :::::J ·~~=---.·.. :::::J "'C 12 0 E • • 10 (/) -0> c 8 :::::J 0 >- 6 4 2 • -4 0 4 8 12 16 20 24 28 32 36 40 Ageing time I weeks Figure 3.12 Young's modulus for all the 1.0 mm thick composite films as function of ageing time ~o.2mm 20 - • - 0.7 mm ¥' ' _...._ _ 1.0 mm .. ' { ' ' -0 ~ - 0 ' .t.- ·- ·- · - ·-·-·-·- ·-· J. '' 0 '_;j ' .r.o... ' ' (/) .- - - - .. - - - - - - - - - -· :::::J -20 :::::J "'C 0 ~ -40 0 5 10 15 20 Wt..% bloodmeal Figure 3.13 Percent change in modulus between the fourth and thirty-sixth week of ageing The changes presented are calculated according to Equation 3. 1. 55 (3 .1 ) where £ 36 is the average modulus after thirty six weeks of underground ageing (final ageing time) and £4 is the average modulus after four weeks of underground ageing (first ageing time). The representation indicates that the effect of underground ageing is more pronounced in the 0.2 mm thick composite films. This is a reasonable conclusion since the thinner films, having a reduced cross-sectional area, possess a higher sensitivity to the progress of ageing effects from the film surface to the sub-surface of the film. - HOPE - _..,._ - 90/10 w/w HOPE/BM - e- 99/1 w/w HOPE/BM ........ 80/20 w/w HOPE/BM 1000 -•- 95/5 w/w HOPE/BM -f ~ c '/ t"· ·- ·- · - ·- ·- ·- - · - ·- ·-!- · - · - · - t 0 iii •. ? / ---~., -.~. .: .~. ~·------------------- 'T' x- .'.-·l ....................... f ...... ..............-..y -------- T 0~ .... --r .. ............. .. ... 10 0 8 16 24 32 40 Ageing time I weeks Figure 3.14 Elongation at break values versus ageing time for 0.2 mm thick composites 56 - HOPE --•-- 90/10 w/w HOPE/BM - e- 99/1 w/w HOPE/BM ........ 80/20 w/w HOPE/BM - .&- 95/5 w/w HOPE/BM ~ 1000 .Q...). •1 I ~ ·- - ! ...0... ro c --·-- 0 / ,_ - - - -·- - - - --·-- - - -· :;::; ~ 100 .L / ·- - - • - • - · - . - • - - - · - · - ·- • - -& - • - • - • - -• c 0 .}~ ~> ~~ :.:.~~ .:.~.~ .:.~.:.-..~ .~·~·~ ·~·~·~·~·-:- .~.~.~ ------·----------y w ~ ., 'CF. •.'., / .· •·······.. .• 10 0 8 16 24 32 40 Ageing time I weeks Figure 3.15 Elongation at break values versus ageing time for 0. 7 mm thick composites Figures 3. 13, 3.14, and 3.1 5 present the effect of ageing on the elongation at break for the samples with different thicknesses. For all the film thicknesses, the HOPE again showed significantly higher values than the composites. Generally, the elongation at break values decreased with an increase in BM content, which is a consequence of the poor adhesion between the hydrophobic HOPE matrix and the hydrophi lic BM particles. The elongation at break of all the samples, for each composition and all film thicknesses exhibited a noteworthy increase during the first fo ur weeks of ageing, again due to the pre-cooling effect of the samples. The values remained relative ly constant, for all the fi lm thicknesses, but the 20% BM composite films displayed the most observable deviations with prolonged ageing time. 57 -HOPE - -"Y·- 90/10 w/w HOPE/BM - .- 99/1 w/w HOPE/BM ··+ .. 80/20 w/w HOPE/BM - .&- 95/5 w/w HOPE/BM ~ .~_ 1000 ..0 ) . r--·-· ..., ro c ·-----·---- -.--- - _,_ - - - -· 0 :;:; ro Ol r g I - ·- ·-A-·- ·- ·-· - · - · -·-.A 100 w .I '!':..-'--~ ·. ------·T - - - - - -- ···T- - - -- - - -- ·"Y ,I • 'CF- //_/~ ............... ····· · ····················• ····················• ··················· · / / .... ...... 10 -5 0 5 10 15 20 25 30 35 40 Ageing time I weeks Figure 3.16 Elongation at break values versus ageing time for l.O mm thick composites 28 - HOPE - •. ,... • 90/10 w/w HOPE/BM _.,_ 99/1 w/w HOPE/BM ....... 80/20 w/w HOPE/BM 26 - A- 95/5 w/w HOPE/BM 24 ar.o. 22 ~I ~ ~ 20 - - - - -~- . - _;.-. --------·· . . -- I ·· - ·- ·- ·-•- ·--=- -:----ct== ·.::-- - - · ..... ...... ...... . ~ 18 <1> ... ~ 16 ...... ----. ---.. ,._- "'O 14 ·--Q) --..... ~ 12 ...... ------..... 10 8 ............................................................. ....................... ... ........... . 6-+-~~~~~~~~~--,.--...-~~~~--,.--...-~~ -5 0 5 10 15 20 25 30 35 40 Ageing time I weeks Figure 3.17 Stress at yield values versus ageing time for 0.7 mm thick composites The effects o f underground ageing on the stress at yield were observed to be similar for the samples with different thicknesses. For this reason, only the effects of ageing on the yield stress of the 0. 7 mm thick samples is presented in Figure 3.1 6. The influence of pre-cooling on the 58 yield stress was not as clearly observed for all compositions of the 0.7 mm thick films. The HOPE values were onl y slightly higher than those of the composites, with the yield stress for the I and 5% samples being comparatively similar to those of HOPE over time. The I 0% BM samples presented a well-defined decrease in yield stress with increasing ageing time. For the 20% BM samples, the yield stress was considerably lower than those of the other composites, but consistent with HDPE, and the I and 5% composites, the values remained relatively constant over time. The yield point of a material is the point at which elastic deformation can no longer occur. Thus, the stress at yield can be thought of as the minimum stress at which permanent strain materialises [32]. Since the observed values for the stress at yield did not display any significant changes with ageing time, it can be said that the stress at yield characteri stics of the material were not noticeably altered due to underground ageing. The yield stress clearly decreased as the weight percentage of bloodmeal increased due to poor adhesion between the HOPE matrix and the BM particles. 3.2 References I . S. Massey. Action of water in the degradation of low-density polyethylene studied by X- ray photoelectron spectroscopy. eXPRESS Polymer Letters 2007; 1: 506-5 11. DOI: 10.3 l 44/expresspolymlett.2007.72 2. M. Elanmugilan, P.A. Sreekumar, N. K. Singha, A.-H. Mamdouh A. , S. K. De. Aging of low-density polyethylene in natural weather, underground soil aging and sea water: Effect of a starch-based prodegradant additive. Polymer Engineering & Science 20 13; 53 :2389- 2397. DOI: 10.1002/pen.23494 3. A. Ammala, S. Bateman, K. Dean, E. Petinakis, P. Sangwan, S. Wong, Q. Yuan, L. Yu, C. 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ISBN: 9780748740734 32. J.M. Ward, J. Sweeney. An Introduction to the Mechanical Properties of Solid Polymers, 2nd Ed. John Wiley & Sons (2005). ISBN: 978-0-470-02037-1 62 Chapter 4 Conclusions This work aimed to prepare HDPE composites with bloodmeal, in an endeavour to create a degradable material with similar properties to neat HDPE. The main objective was to alleviate the increasing amount of environmental pollution caused by non-degradable synthetic wastes. Both unaged and aged composites were characterised with thermal methods, the mechan ical properties were studied, and the morphology was investigated with ATR-FTIR spectroscopy, optical microscopy and SEM. The two microscopy techniques were used to assess the distribution of BM in the HDPE matrix, and attempt to identify any ageing effects on the film surfaces resulting from underground ageing. The optical microscopy pictures showed that the BM was relatively well dispersed in HDPE. No obvious signs of ageing such as cracking, di scolouration or yellowing, was observed with optical microscopy. The SEM images of the surface of the 80/20 w/w HD PE/BM sample, subjected to underground ageing for thirty-six weeks, appeared as if the HDPE around the BM particles had been "eaten away" or degraded. From the images it could be concluded that degradation of the HDPE film surface could have occurred due to underground ageing processes. It was seen that the period of underground ageing exhibited a more pronounced effect on the mechanical properties of the thinnest composite films (0.2 mm), compared to those of the thicker composite films. This was expected since the BM particles were situated on or near the surface of the films and the thinnest films possessed a smaller cross-sectional area, making the films more susceptible or receptive to the effects of ageing. It was established that the addition of BM to HOPE does increase the moisture content of the composite to a certain degree. The moisture content of the composites was expected to increase with the addition of BM, and this was only partia lly observed because of the encapsulating influence of HDPE. The ability of the material to absorb water was marginally improved with the addition of BM, as seen in the results of the water absorption experiments. Increased 63 moisture retained within the composite could promote hydrolytic degradation of the material, but thi s aspect was not investigated in thi s study. Thus, the addition of bloodmeal could affect the accepted mechanism of the degradation of polyethylene to include hydrolytic degradation. The inclusion of BM increased the modulus of the unaged composites due to the reinforcing effect of the filler, but this improvement was only observed for the I% BM composite. Generally, there was a decrease in the modulus, stress at yield, and elongation at break of the unaged composites. The adhesion between the BM particles and the HOPE matrix appeared to be fai rly poor. which negatively affected the mechanical properties. The duration of underground ageing did not significantly affect the mechanical properties of the composites since the average values did not fluctuate to a large extent. As a general conclusion, it was found that the inclusion of bloodmeal in HOPE did not have an obviously positive or negative influence on the properties or environmental degradation of the resulting composites. Underground ageing of up to 36 weeks had little effect on the properties of the material, compared to the unaged material. No unambiguous claims can therefore be made about the effect of the addition of BM on the degradation characteristics of HOPE derived from the characterisations performed in this study. It is suggested that the underground ageing period be extended to at least 52 weeks, and that UV-initiated degradation in the open air also be investigated . This can be complemented by artificial ageing in a weatherometer. Another possibility is the improvement of the interaction between the BM particles and the HOPE matrix in order to reduce the negative influence of BM on the mechanical properties of HOPE, and to possibly contribute to more effective environmental degradation. 64 Acknowledgements " I can do a ll things through Christ who strengthens me" Philippians 4: 13 Firstly, I would like to thank my supervisor, Prof. A.S. Luyt for his support and guidance throughout my research project. Prof. Luyt always led by example, and I learnt a great deal from him. I would also like to express my gratitude to Dr. D. Dudic who was a constant source of assistance with hi s famous "step by step" statements of encouragement. Thank you gentlemen, without the benefit of your assistance, I would not have achieved this milestone. 1 would like to thank the University of the Free State (UFS) for fi nancial support and allowing this opportunity to further my studies and pursue my goals. I am also grateful to all my friends and colleagues in the Polymer Research Group of UFS (Qwaqwa Campus), always ready with words of encouragement and advice. Special thanks to Dr. Puseletso Mofokeng and Ms. Motshabi Sibeko, whose friendship and inspiration is a reliable constant. To Mrs. Marlize Jackson, the Faculty secretary, thank you fo r all the help and friendship you provided throughout the duration of my studies. Your contribution to our Faculty is invaluable. Many thanks to the Konig and De Wet families for the constant love and support. Finally, I would like to thank everyone who has supported me academically and emotionally during this time, especially my friends and family, may God bless you all! 65 Appendix Table A.1.1 Structures of amino acids [ 1] AMINO PROPERTIES OF SIDE STRUCTURE ACID CHAIN Non-polar I hydrophobic NH2 I Alanine HJC- y - COOH Uncharged H Aliphatic NH2 Hydrophilic H1N I Arginine ' C- N CH2 CH1 CH2 ? COOH HN~ H H Alkaline, positively charged NH2 Polar I hydrophilic I Asparagine H2N - CO- CH2 ? COOH H Uncharged Aspartate I NH2 Hydrophilic I HOOC CH2 ? COOH Aspartic acid H Acidic, negatively charged Polar I hydrophilic NH2 I Cysteine HS- CH2 c COOH Uncharged I H Sulphur-containing NH2 Polar I hydroph il ic I Glutamine HlN- CO CH1- CH2 c COOH I H Uncharged Glutamate I NHz Hydrophilic I HOOC CH2 CH2 c COOH I Glutarnic acid H Acidic, negatively charged 66 Non-polar NH2 I Glycine H c COOH Uncharged I H Aliphatic NH2 I Hydrophilic Histidine c COOH HV CH2 I H Alkaline, positively charged Non-po lar I hydrophobic CHl NH2 I lsoleucine H.,C- CH2- CH - C - COOH Uncharged H Aliphatic Non-polar I hydrophobic HlC NH2 I Leuc ine \ CH - CH2 ? COOH Uncharged ~ H Aliphatic NHz Amphipathic I Lycine H,N CHz CHz CH2 CH2 c COOH I H Alkaline, positively charged Polar I amphipathic NH2 I Methionine HJC - S - CH2 - CH2 c COOH Uncharged I H Sulphur-containing Non-polar I hydrophobic NH2 I Phenylalanine Q cHz? COOH Uncharged H Aromatic cHz- cH"z < Non-polar I hydrophobic Pro line H,/ ~ Uncharged OOH 67 Aliphatic NH2 Polar I hydrophilic Serine HOHzC c COCH H Uncharged NH2 Polar I Threonine HlC - CHOH- y - COOH H Uncharged Non-polar I arnphipathic NH1 I CHJ c COOH Tryptophan C\;J I Uncharged H H Aromatic Polar I arnphipathic NH1 I Tyrosine HO 0 CHz ? COOH Uncharged H Aromatic Non-polar I hydrophobic HiC NHz I Valine \ CH c COOH Uncharged / I HsC H A liphatic 68 Table A.1.2 Amino acid content of bloodmeal 12) AMINO ACID CONTENT /% Alanine 7.73 ± 0.09 Apartic acid 10.51 ± 0.09 Arginine 4.14 ± 0.06 Cystine 0.99 ± 0.002 Glutamic acid 8.74 ± 0. 10 Glycine 4.29 ± 0.08 Histidine 6.05 ± 0.30 lsoleucine 0.93 ± 0.03 Leucine 12.55 ± 0. 10 Lysine 9.46 ± 0. 19 Methionine 0.70 ± 0.03 Phenylalanine 6.78 ± 0.10 Pro line 3.72 ± 0.09 Serine 3.97 ± 0.10 Threonine 3.89 ± 0.1 4 Tyrosine 2.49 ± 0.06 Valine 8.84 ± 0. 11 69 T a ble A .3 .1 M 01. sture content or pure bl oo d mea powd er Average I Initial BM mass I g After d rying I g Difference I g Moisture I% O/o 1.0188 0.961 9 0.0569 5.6 1.0122 0.96 0.0522 5.2 5.0 ± 0.7 1.0100 0.9668 0.0432 4.3 3.0 -.- ------------- -----, • Pure HOPE • 90/10 HOPE/BM 2.5 - 4 80/20 HOPE/BM ~ ~ 2.0 c: .Q • ~1 .5 rn .0 aco; 1.0 iii ~ • 0.5 0.0 • • I I I I I 0.2 OA o~ o~ 1.0 Film thickness I mm Figure A.3.1 Comparison of water absorption values for pure HOPE, as well as 90/10 w/w and 80/20 w/w HDPE/BM composite films prior to underground ageing Table A.3.2 Table of DSC results for unaged HDPE films of different thicknesses HEATING Sample Tm/°C AHm I J g-1 AHmnorm / J g-1 0.2 mm 130.1 ± 0.4 182.4 ± 3.6 182.4 ± 3.6 Unaged 0.7mm 133.1 ± 0.3 196.2 ± 2.8 196.2 ± 2.8 Pure HDPE l.Omm 133.2 ± 0.3 198.3 ± 4.1 198.3 ± 4. 1 COOLING Sample Tc/°C AHc I J g-1 AHcnorm / J g-1 0.2 mm 114.9 ± 0.5 -176.3 ± 10.4 -176.3 ± 10.4 Unaged 0.7mm 117.5 ± 0.2 -189.7 ± 8.3 -189.7 ± 8.3 Pure HDPE 1.0mm 117.6 ± 0.4 -191.7 ± 9.2 -191.7 ± 9.2 70 Table A.3.3 Table of DSC heating curves for all composites, unaged and composites aged for 36 weeks SECOND HEATING HOPE - unaged HOPE- aged 36 weeks 4 - Pure HOPE 1 4 - Pure HOPE 1 - - Pure HOPE 2 - - Pure HOPE 2 - - Pure HOPE 3 - - Pure HOPE 3 50 75 100 125 150 50 75 100 125 150 Temperature / ' C Temperature I •c 9911 w/w HOPE/BM - unaged 99/ l w/w HOPE/BM - aged 36 weeks - 9911 HOPEIBM 1 4 - 9911 HOPEIBM 1 Ci: 4 - - 9911 HOPEIBM 2 - - 99/1 HOPEIBM 2 :> - - 9911 HOPEIBM 3 - - 99/1 HOPEIBM 3 0 ~ ~ 3 'e> -3: ~ m"" .c; 50 75 100 125 150 50 75 100 125 150 Temperature I ·c Temperature / ' C 7 1 9515 w/w HDPE/BM - unaged 9515 w/w HDPE/BM - aged 36 weeks 9515 HDPEIBM 1 - 9515 HDPEIBM 1 - 9515 HDPEIBM 2 - - 95/5 HDPEIBM 2 • - 95/5 HDPEIBM 3 - · - 95/5 HDPEIBM 3 50 75 100 125 150 50 75 100 125 150 Temperature / •c Temperature I ·c 90/10 w/w HDPE/BM - unaged 9011 0 w/w HD PE/BM - aged 36 weeks - 90110 HDPEIBM 1 - 90/10 HDPEIBM 1 a: - - 90110 HDPEIBM 2 - 90/10 HDPEIBM 2 :> - - 90110 HDPEIBM 3 - 90/10 HDPEIBM 3 .0., , c ~ ~Ol ~ ~ 0:: '.,..s.":,:,: -~ ~ 0 0 z 50 75 100 125 150 50 75 100 125 150 Temperature I ' C Temperature I •c 80/20 w/w HDPE/BM - unaged 80/20 w/w HDPE/BM - aged 36 weeks - 80/20 HDPEIBM 1 - 80120 HDPEIBM 1 g: 3 =::~g:~~~~ a: - 80120 HDPEIBM 2 :> - 80120 HDPEIBM 3 .0., , .0., , c c ~ ~ ·oi 2 ·oi ~ ~ ~ ~ c;:: 0:: ~ '("I) .s::: .s::: al al .!!1 .!!1 0 § c;; e 0 z0 z 50 75 100 125 150 50 75 100 125 150 Temperature / •c Temperature / ' C 72 Table A.3.3 Table of DSC cooling curves fo r all composites, unaged and composites aged for 36 weeks COOLING HOPE - unaged HOPE - aged 36 weeks a: 0 a: " " 0 0 0 "'cO -g -.!!. .!!. "' ' <» ~ ~ ·2 -~ ·2 ~ ~ "(.i",j "(.i",j .J:: .. .J:: .. "'O .~ ~ ~ -Pure HOPE 1 ~ ..--Pure HOPE 1 0 - PureHDPE2 - PureHDPE2 z - PureHDPE3 0 -6 - Pure HOPE 3 -6 z 50 75 100 125 150 50 75 100 125 150 Temperature / ' C Temperature I ' C 99/1 w/w HOPE/BM - unaged 99/1 w/w HOPE/BM - aged 36 weeks a: " 0 a: 0 "0 0 "'cO "'cO .!!. .!!. ."' \ -"' \ ~ ~ ·2 ~ ;: ~ (.i,j (.i,j .J:: .J:: .. ~ ~ ~ .5 ==:~=:~ ~ - 9911 HOPE/BM 1 - 9911 HOPE/BM 2 z0 - 9911 HOPE/BM 3 ~ -6 - 9911 HOPE/BM 3 50 75 100 125 150 50 75 100 125 150 Temperature I ·c Temperature / ' C 73 9515 wlw HDPE/BM - unaged 9515 w/w HOPE/BM - aged 36 weeks Ci Ci ::> 0 ::> 0 0 0 -0 -c0 c ~ ~ ~ \ '0> '0> ii: ·2 ii: ·2 ~ ~ n""; "n"; ."t:': ·• ."t:': . 4 -0 ~ .~ ~ - 9 515 HOPE/BM 1 I ~ ~ 9515 HOPE/BM 1 \, 0 - - 9515 HOPE/BM 2 0 - - 9515 HOPE/BM 2 z -6 - - 9 515 HOPE/BM 3 z -6 - - 9515 HOPE/BM 3 50 75 100 125 150 50 75 100 125 150 Temperature / ·c Temperature I ·c 90110 w/w HOPE/BM - unaged 90110 w/w HOPE/BM - aged 36 weeks 0 - - 0 Ci Ci - - ::> ::> 0 ' 0 -0 -0 c -1 ' -1 ~ ' c I ~ ' I O> · 2 ' 0> ·2 ~ I ii: I ~ . 3 I ~ .3 "n"; I n""; I ."' I t:: -4 .t":': -4 I -0 ,, -0 ."!!!' .~ .5 .5 - 90/10 HOPE/BM 1 ~ -90l10 HOPEIBM 1 ~ ~ - 90/10 HOPE/BM 2 - - 90/10 HOPE/BM 2 z0 ~ - 90/10 HOPE/BM 3 - - 90/10 HOPE/BM 3 z0 -6 -6 50 75 100 125 150 50 75 100 125 150 Temperature / •c Temperature / •c 80/20 w/w HOPE/BM - unaged 80/20 w/w HOPE/BM - aged 36 weeks Ci 0 - - -- - ~--- Ci 0 ::> " ::> - 0 't. 0 -0 I -0 c ~ -1 I c · 1 ! ~ '0> '0> ~ ·2 ·2 ~ ~ ~ "" .3 n; ·3 "n"; ."t:': .! ~ -4 i -4 ~ - 80/20 HOPE/BM 1 n; - 80l20 HOPE/BM 1 ~ - - 80/20 HOPE/BM 2 E .5 - - 80120 HOPE/BM 2 z0 ~· - - 80/20 HOPE/BM 3 ~ - - 80l20 HOPE/BM 3 I' · 5 50 75 100 125 150 50 75 100 125 150 Temperature / •c Temperature I •c 74 -4 0 4 8 12 16 20 24 28 32 36 40 Ageing time I weeks Figure A.3.2 Carbonyl index values of 0.2 mm films of all composites with ageing time 0.88 - • - HOPE - ..-- 90/10 w/w HOPE/BM ---+--- 99/1 w/w HOPE/BM --+-- 80/20 w/w HOPE/BM - & - 95/5 w/w HOPE/BM 0.86 x Q) 0.84 "O c >c . 0 .r0o o.a2 () 1 -4 0 4 8 12 16 20 24 28 32 36 40 Ageing time I weeks Figure A.3.3 Carbonyl index values of 0. 7 mm films of all composites with ageing time 75 0.94 - • - HOPE -~- 90/10 w/w HOPE/BM -+- 99/1 w/w HOPE/BM --+- 80/20 w/w HOPE/BM • N' 0.92 - • - 9515 w/w HOPE/BM ..- .!'.--- ~ 0.90 N . c • • 0 0.84 ..0 '- k/.~ ' ~··~ ro u 0.82 7~.~. ! ! • 0.80 -4 0 4 8 12 16 20 24 28 32 36 40 Ageing time I weeks Figure A.3.4 Carbonyl index values of 1.0 mm film s of all composites with ageing time 76 Table A.3.5 Table of FTIR graphs for all the composites, unaged and composites aged for 36 weeks - - - Composite film thickness 0.2mm 0.7 mm 1.0 mm 100 r , 100 ,- 100 ~ 90 ' ,--- ,- 90 r ,-- 90 r r 80 ,-80 80 "O ~ ~ *- 70 *- 70 * 70 e1l .-§ ~ 8 c 60 8 -8 c c 60 60 c -~ ~ ~ e1l E 50 .E E 50 c '=-' ., ., 50 ., c 40 c c ·~ ~ E E E 40 I- e1l -HOPE I- 40 -HOPE I- - HOPE ~ < ~ 30 - 9911 wlw HOPE/BM - 99/1 wlw HOPE/BM 30 - 99/1 wlw HOPE/BM ~ 9515 wlw HOPE/BM 30 - 9515 wlw HOPE/BM - 95/5 wlw HOPE/BM = 20 - 90/10 Ylw HOPE/BM - 90/10 Ylw HOPE/BM 20 - 90/10 w/w HOPE/BM - 80/20 Ylw HOPE/BM 20 - 80/20 Ylw HOPE/BM - 80/20 w/w HOPE/BM 10 10 4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000 Wavenumber I cnf' Wavenumber I cm·' Wavenumber I cm·' 77 100 100 ,-- 100 I r - 90 r 90 r '-.r--' ,--90 ,-r, v ~ r r I 80 r 0- 1, 80 r I r -'if. 70 YV- lr r 80 r----... -'if. v 70 'if. - ~ry , 70 8 Q) -Q) () () ~ c 60 c 80 c 60 ~ .~E ~ ~ E 50 ~ 50 E 50 ~ "c ' c e e"' "c' 40 e f- 40 --HOPE f- --HOPE f- 40 - -HOPE "' --9911 w/w HOPE/BM 30 -- 9911 wlw HOPE/BM --9911 w /w HOPE/BM 30 -- 9515 wlw HOPE/BM -- 9515 w/w HOPE/BM 30 --9515 w/w HOPE/BM -- 90110 wlw HOPE/BM 20 - - 90/10 v.lw HOPE/BM --90110 wlw HOPE/BM 20 -- 80120 wlw HOPE/BM -- 80120 w1w HOPE/BM 20 --80l20 v.lw HOPE/BM 10 4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000 Wavenumber I cm·' Wavenumber I cm·' Wavenumber I cm·' Composite film thickness 0.2 mm 0.7mm 1.0mm 100 100 100 ~, r ~ ,-- .......... ~ 90 r ~, 90 -~ 'r ~~I r 90 r ~; ·r '---' ,--80 r v-- o r; , ~ ~'( - 80 - r _\\ - 80 r----.. r 'if. 0~ - 70 -~ , 'if. -70 \!!] - ~~; ..5.. ~ 8c 8 -8 70 c c ~ *"' 60 "' 60 "' 60 bJ) ~ ' .=... E .=E = 50 50 E ~ e"c' "c ' "c' 50 ~ N 40 e 40 e bJ) f- --HOPE f- --HOPE f- 40 --HOPE ~ < --9911 w/w HOPE/BM --9911 w/w HOPE/BM --9911 w/w HOPE/BM 30 --9515 w/w HOPE/BM 30 -- 9515 w/w HOPE/BM --9515 w/w HOPE/BM --90/10 w1w HOPE/BM --90110 wlw HOPE/BM 30 --90110 v.lw HOPE/BM 20 --80l20 wlw HOPE/BM 20 -- 80120 v.lw HOPE/BM --80120 wlw HOPE/BM 20 4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000 Wavenumber I cm·• Wavenumber I cm·' Wavenumber I cm·' 78 100 100 ~ 100 ~ r -- ~~ -~r-90 90 r --, "--- --, 90 ~ ,_ '<; ,..-- - -,-,...... 80 l"'Y"\ r 'l ~- ' 80 -- - r ---'-- 80 "V *- 70 " *- 70 ~' * 70 8 60 60 60 ~ c: 8 8 c: c: ~ 50 50 50 ~ . ~E ~., ..E , . ~E 40 40 ., 40 ~ c: c: = e c: 30 e e I- 30 --HOPE 30 I- --HOPE I- --HOPE M 20 -- 9911 wlw HOPE/BM 20 --9911 wlw HOPE/BM 20 --9911 wlw HOPE/BM -- 9515 wlw HOPE/BM -- 9515 wlw HOPE/BM 9515 wlw HOPE/BM 10 -- 90110 w/w HOPE/BM 10 --90/10 wlw HOPE/BM 10 -- 90/ 10 wlw HOPE/BM --80/20 wlw HOPE/BM - - 80/20 wlw HOPE/BM 80/20 wlw HOPE/BM 0 0 0 4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000 Wavenumber I cm·' Wavenumber I cm·• Wavenumber I cm 1 Composite film thickness 0.2 mm 0.7mm 1.0 mm 79 100 100 100 .__ , ~ r 90 '---- 90 90 ~ , r ,_ ~ .____ r 'r , __ ~I r--... - r 80 '\.,.- r--'~\ -80 ---- ,---._ /-, 80 r *- r r \A' 0~ \} \} 70 70 * 70 ~ 8 -8 -8 c 60 60 c 60 c Q,j J'!! J'!! J'!! Q,j ..E. .E 50 50 50 ~ .. .E. c c c 40 40 00 ~ ~ ~ t- 40 --HOPE t- --HOPE t- --HOPE M --99/1 wlw HOPE/BM 30 -- 99/ 1 w/w HOPE/BM 30 --99/1 w/w HOPE/BM 30 -- 9515 wlw HOPE/BM -- 9515 wlw HOPE/BM --9515 wlw HOPE/BM - - 90/10 wlw HOPE/BM 20 -- 90/10 IM'w HOPE/BM 20 --90/10 IM'w HOPE/BM 20 --80/20 wlw HOPE/BM --80/20 wlw HOPE/BM - - 80/20 IM'w HOPE/BM 10 10 4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000 Q,j Wavenumber I cm·' Wavenumber I cm·' Wavenumber I cm·' .-§ ~ 'Q=j ~ < 100 100 - - 100 - ' ~ 90 90 - r '\.../""1 ...........,, 90 ~ v,r - 80 ,__..__ r ~ ~ ,,- 80 ~I - ~ 80 r- '-- b~ ~ 70 0 ~ryl *- - ~ v *- - - \.... ., 60 70 70 ~I ~ u c 8 8 c c Q,j Q,j ="' 50 J'!! 60 E .E .= "' 60 E 40 ~ .. .. 50 .. c c c 50 \C ~ 30 ~ ~ t- --HOPE t- - - HOPE t- --HOPE M 40 40 20 -- 99/1 wlw HOPE/BM --9911 w /w HOPE/BM --9911 wlw HOPE/BM 9515 w/w HOPE/BM -- 9515 w /w HOPE/BM 9515 wlw HOPE/BM 10 - - 90110 wlw HOPE/BM 30 --90/10 wlw HOPE/BM 30 --90/10 wlw HOPE/BM -- 80/20 wlw HOPE/BM --80/20 wlw HOPE/BM --80/20 wlw HOPE/BM 0 20 20 4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000 4000 3500 3000 2500 2000 1500 1000 Wavenumber I cm·• Wavenumber I cm·' Wavenumber I cm·' Table A.3.6 Table of stress-strain curves for pure HOPE and 80/20 w/w HDP E/BM composite films, unaged and composites aged for 36 weeks 80 Composite film thickness 0.2mm 0.7mm l.Omm 20 -· . 20 ~ ~ tIi ~/~ , , 20 ;-"-'- ~ .. l I\ y.:::-:.:~~---~= ,----·_,. ·.·"' ..., ,,: ·-· -·-:.:-:,:; '"'-· ··- -- .. '~ .. _, ~ s~ :t: 15 15 \i-: . I ·-- a. a. Q ~ \\ ...' a. ~ r -·- I \ ~ ~ ~ "' 10 "' ~- i:l 10 = Q.. !: ' -------. i:l 10 \~!: 1\ ....... - -........ ·, ·~ Q (/) -\ (/) ~ ~ - < =~ --Test 1 -·-- Test 4 - -Test 1 - - - -Test 4 --Test 1 - -- Test 4 "=" - - -Test 2 Test 5 - - - Test 2 Test 5 - - - Test 2 Test 5 0 Q.. Test 3 - - - Test 6 Test 3 - - - Test 6 Test 3 - - - Test 6 0 200 400 600 800 0 200 400 600 8() 200 400 600 800 104 Strain(%) Strain(%) Strain(%) 81 Composite film thickness 0.2 mm 0.7mm 1.0 mm 3~-------------------~ ~ '~a ~ ~ ~ ~ .-5 .. .. ,., ~ a.. '~~-~:==:.>:;.:. : .. : .: ·::.:;.::::. .o , .:····-,., a.. L::r. ~ :.::. ::: .7-.:- ;::-r.,_, --, '"'·~--~~:\ - ~->- .. b~: ~=::~,~::-:-_;._-== "-.:.: - -· - - - - - - - - - .. • a.. M ~ ~ ~ I ~ ~ ::! \ ::! -·-·- - .. _ - ::! = Q.. ~ ·~ Cf) Q ~ ~ ~ < ::i:: --Test 1 - - Test 4 --Test 1 - - Test 4 --Test 1 ~ t. - - · Test 2 Test 5 - - · Test 2 - - Test 4 0 - - · Test 2 Test 5 = Test 3 ····· Test 6 0 Test 3 · ·•·· Test 6 o i 1 Test 3 Test 5 I Q.. '-..--~-,--~--r--~--,--~--r-~--i I I I I I i I 0 200 '°° 600 aoo 1000 1200 0 1000 2000 3000 • OOO 50C 0 500 1000 1500 2000 2500 3000 Strain(%) Strain(%) Strain(%) ~ --Test 1 - ·-· Test4 Test 7 --Test1 - Test 4 10 --Test 1 - - Test• Test 7 ~ : ' - - · Test 2 - - Test 5 Test 8 - - · Test 2 Test 5 Test 2 Test 5 ~ ' Test 3 · ··· · Test 6 Test 3 ····· Test 6 ~ Test3 ·· Test 6 = 10 .. 10 ~e ::; ~ .. .. ,. . ' r ,,.,. ,·r -- .. .. .. '_ ; :,.., - -\ .. 'i.... a.. a.. 1/ ,'' : -... I ' ~ a.. :r-~·,-,--;< ·.: ' ~ ;. ,•- • , ~ ,,,, I \1".\ ~ ' ' I ~ ~ Q.. ::! ,r - .... ~ ,I,i , -. ::! I ' \ , = ~ \ \ ,' ' ~. ·~ Q Cf) ::c: I~ I ...... ~ \. ~ ~ \ \. Cf) • I ' Cf) ·., \ I \ i ' < I ' "' ' ' ' -! I, ·~ i ·-.... 1 \ ' ·' ' ··. ' ..... ' ~ 0 l ' =~ 10 20 0 10 20 0 10 20 = Strain(%) Strain (%) Strain (%) QO 82 Composite film thickness 0.2mm 0.7mm 1.0 mm 12 .... - .. -- --Test 1 - - Test 4 16 - Test1 - - Test411 --Test 1 - - Test 4 ,- ·- - - · Test2 Test 5 - - · Test2 Test 5 1 4i - - · Test 2 Test 5 ::; 1 0 .. Test 3 - - - Test 6 1 . Test3 Test3 ·· Tesl6 ---~ -- 1 2 .i.:.:_c 1 2 I 08 ' ~ ~ -- I 1 0 __ , ' 1 0 \ .'. -s f . ~-. Q. 0'".. . ' - .,, '0".. - ----. -- ' 0'".. 08 ,_'~/. .. -- - - - -":.:., , '.;: Q ~ 06 08 I ~ =~ :c I ~ :l . ' :l 'I I ( ", ' :l 06 l '\ , E ' - E 06 I ,, 0.4 I ·- 'I E ·~ ~ (f) (f) I o• , .. ......... ' (f) \ • ' I ' 0 4 I }!, i' ~ ~ I ' I < = 02 ' I I- ~! ·, I 02 '· .... 02 '!•• .N =.._ 00 00 00 " 00 20 40 60 80 100 120 140 160 0 20 40 60 80 1 0 20 40 60 80 Strain (%) Strain(%) Strain (%) 83 References: I . M.-P. Lefranc, V. Giudicell i, C. Ginestoux, J. Jabado-Michaloud, G. Folch, F. Bellahcene. Y. Wu, E. Gemrot, X. Brochet, J. Lane, L. Regnier, F. Ehrenmann, G. Lefranc, and P. Duroux. IMGT(R), the international lmMunoGeneTics information system(R). Nucleic Acids Research 2009; 3 7: DI 006-D I 012. DOI: 10.1093/nar/gkn838 2. S.L. Kramer, P.E. Waibel , B.R. Behrends, S.M. El Kandelgy, Amino acids in commercially produced blood meals. Journa l of Agricultural and Food Chemistry I 978; 26:979- 98 I . DOI: I0.102 1/jf60218a033 84