PREPARATION AND CHARACTERIZATION OF ETHYLENE VINYL ACETATE 
COPOLYMER/POLY(LACTIC ACID)/SUGARCANE BAGASSE COMPOSITES FOR 
WATER PURIFICATION 
by 
THOLLWANA ANDRETTA MAKHETHA (B.Sc. Hons.) 
2009062932 
Submitted in accordance with the requirements for the degree 
MASTER OF SCIENCE (M.Sc.) 
Department of Chemistry 
Faculty of Natural and Agricultural Sciences 
atthe 
UNIVERSITY OF THE FREE STATE (QWAQWA CAMPUS) 
SUPERVISOR: MR K. MPITSO 
CO-SUPERVISOR: PROF A.S. LUYT 
January 2016 
DECLARATION 
I declare that the thesis hereby submitted by me for the Master of Science degree at the 
University of the Free State is my own independent work and has not prev iously been submitted 
by me at another university/ faculty. I furthermore cede copyright of the thesis in favour of the 
University of the Free State. 
<- 1Boulib 
Makhetha T.A. (Ms) 
DEDICATION 
This work is dedicated to the entire fami ly of Makhetha and yilika for their love and support. To 
Maofela Beauty Makhetha (mom), Musuwe Edward Makhetha (father), Nongwenynkomo 
Roselinah Nyilika (grandmother) whose support and perseverance is gently appreciated and 
who instilled in me the importance of education at an early age and to Karabo Makhetha 
(sister). 
"Now I believe and I declare my life will never be the same again" 
II 
ABSTRACT 
Excessive release of heavy metals into the environment due to industrialization and urbanization 
has posed a great problem to the world. Heavy metal ions do not degrade, therefore they can give 
bad effect to human body and the environment itself. The purpose of this study was to prepare 
polymer/natural fibre composites to be used in water purification, specifically to remove lead ions 
from contaminated water. PLA/EVA blends and PLA/EVA /SCB composites were successfully 
prepared by melt mixing. The lower viscosity of PLA, the lower interfacial tension between PLA 
and SCB, and the wetting coefficient of PLA/SCB being larger than I, all suggested that SCB 
would preferably be in contact with PLA, despite PLA's relatively high crystallinity. A fairly good 
dispersion of SCB in the PLA matrix was observed. PLA and EV A were also completely 
immiscible, with the 50/50 w/w PLA/EVA  sample showing a co-continuous morphology and the 
70/30 w/w sample showing EV A dispersed as small spheres in the continuous PLA phase. 
Exposed fibre ends were observed in the composites in some SEM pictures which were believed 
to add to the efficiency of metal adsorption. The two polymers in the blend seemed to have 
protected the SCB from thermal degradation, because the mass loss of SCB degradation 
products was on ly observed at higher temperatures when incorporated in the blends. Although 
this behaviour may imply that the prepared composites can be used at temperatures above 200 
°C, which is the degradation temperature of pure SCB, it is also possible that the release of the 
volati le SCB degradation products was delayed as a result of interaction with one or both 
polymers. The impact properties depended more on the PLA:EVA  ratio than on the presence 
of SCB. The PLA/EV A blends showed two melting peaks at approximately the same 
temperatures as those of the neat polymers, which confirms the complete immiscibility of PLA 
and EV A at all investigated compositions. 
It was further observed that the water absorption increased with an increase in SCB loading in 
the composites. The main parameters that influenced lead ion sorption on SCB and 
PLA/EV A/SCB composites were the initial concentration, contact time, and the pH value. It 
was observed that more lead was adsorbed than one would expect if the partial coverage of the 
fibre by the polymer is taken into account, and therefore it may be assumed that some of the 
lead was trapped inside the cavities in the composites and that the polymers may also have 
played a role in the metal complexation process, since both polymers have functional groups 
that cou ld interact with the lead ions. The metal impurities underwent monolayer adsorption. 
111 
TABLE OF CONTENTS 
Page 
DECLARATION 
.. 
DEDICATION 11 
ABSTRACT lll 
TABLE OF CONTENTS lV 
LIST OF TABLES Vl 
.. 
LIST OF FIGURES Vll 
LIST OF ABBREVIATIONS AND SYMBOLS lX 
CHAPTER 1 (Introduction and literature review) 1 
1.1 General introduction 
1.2 Literature review 4 
1.2. 1 Natural fi bres: Sources and classification 4 
1.2.2 Properties of natural fi bres 5 
1.2.2.1 Structure, physical, and mechanical properties of natural fibres 8 
1.2.3 Sugarcane bagasse (SCB) 9 
1.2.3 .1 Chemical composition of SCB 10 
1.2.3.2 Thermal properties of SCB 10 
1.2.4 Composite properties 1 1 
1.2.4.1 M odification of polym er/natural fibre composites 11 
1.2.4.2 Morphologies of polymer blends/natural fibre composites 12 
1.2.4.3 Mechanical properties of polymer blends/natural fibre composites 13 
1.2.5 Water absorption of polymer/natural fi bre composites 14 
1.2.6 Adsorption 14 
1.2.6. 1 Uses of natural fibres as adsorbents in water treatment 15 
1.2.6.2 Adsorption isotherms 16 
IV 
1.3 Aims and objectives 19 
1.4 Outline of the thesis 19 
1.5 References 19 
CHAPTER 2 (Materials and methods) 34 
2. 1 Materials 34 
2.2 Methods 35 
2.2.1 Pre-treatment of sugarcane bagasse 35 
2.2.2 Sample preparation 35 
2.3 Sample analysis 36 
2.4 References 41 
CHAPTER 3 (Results and discussion) 43 
3. 1 Selective di spersion of the SCB in the polymer blends 43 
3.2 Morphology 45 
3.2. 1 Optical microscopy 45 
3.2.2 Scanning electron microscopy (SEM) 47 
3.2.3 Fourier-transform infrared {FTIR) spectroscopy 49 
3.3 Impact strength 51 
3.4 Thermal analysis 53 
3.4. 1 Thermogravimetric anal ysis (TGA) 53 
3.4.2 Differential scanning calorimetry (DSC) 57 
3.5 Water absorption 63 
3.6 Atomic absorption spectroscopy (AAS) 65 
3.7 References 72 
CHAPTER 4 (Conclusions) 78 
ACKNOWLEDGEMENTS 80 
APPENDIX 81 
v 
I 
I 
LIST OF TABLES 
Page 
Table 2.1 Composition of SCB 34 
Table 2.2 Sample compositions used in this study 36 
Table 3.1 MFI , density and surface properties of PLA, EVA  and SCB 44 
Table 3.2 Interfacial tension and wetting coefficient of the investigated 
materials 45 
Table 3.3 Impact properties of all the investigated samples 53 
Table 3.4 TGA results for investigated samples 54 
Table 3.5 Melting and crystallization temperatures and enthalpies of EVA 
in the blends and composites 61 
Table 3.6 Melting and crystallization temperatures and enthalpies of PLA 
in the blends and composites 62 
Table 3.7 AAS results of all investigated samples at different initial 
concentrations 66 
Table 3.8 AAS results of all investigated samples at different pH level 67 
Table 3.9 AAS results of all investigated samples at different contact time 68 
Table 3.10 Freundlich isotherm constants for the sorption oflead Pb(ll) 
ions by the different composite samples 70 
Table 3.11 Langmuir isotherm constants for the sorption oflead Pb(ll) ions by 
different composite samples 72 
VI 
LIST OF FIGURES 
Page 
Figure 1.1 Chemical structure of cellulose 6 
Figure 1.2 Chemical structure of hemicellulose 7 
Figure 1.3 Chemical structure of lignin 7 
Figure 1.4 Structure of natural fibre cell 9 
Figure 3.1 Optical microscopy pictures of (a) 66.5/28.5/5 w/w 
PLA/EVA/SCB, (b) 59.5/25.5/ 15 w/w PLA/EVA/SCB, 
(c) 56/24/20 w/w PLA/EVA/SCB and (d) 49/21/30 w/w 
PLAIEVA /SCB 46 
Figure 3.2 Optical microscopy images of (a) 80/20 w/w PLA/SCB, 
and (b) 80/20 w/w EVA/SCB 46 
Figure 3.3 SEM images of the fractured surfaces of (a) 50/50 
wlw PLAIEVA, (b) 47.5/47.5/5 w/w PLA/EVA /SCB, 
(c) 42.5/42.5/ 15 w/w PLA/EVA /SCB, (d) 35/35/30 w/w 
PLA/EVA/SCB, (e) 70/30 w/w PLA/EVA, 
(f) 66.5/28.5/5 w/w PLA/EV A/SCB, (g) 59.5/25.5/15 w/w 
PLA/EVA /SCB, and (h) 49/21/30 w/w PLA/EV A/SCB 48 
Figure 3.4 FTIR spectrum of SCB 50 
Figure 3.5 FTTR spectra of the PLA/EVA blend and the PLAIEVA/SCB 
bio-composites 51 
Figure 3.6 Impact strengths of the PLA/EVA blends and PLA/EVA /SCB 
composites at different SCB contents 52 
Figure 3.7 (a) TGA and (b) derivative TGA curves of PLA, EVA and SCB 55 
Figure 3.8 (a) TGA and (b) deri vative TGA curves of70/30 w/w PLA/EVA 
and its bio-composites 56 
Figure 3.9 DSC second heating curves of the neat PLA, neat EVA, the 
50/50 PLA/EVA  blend and composites based on its blend 57 
Figure 3.10 DSC second heating curves of the neat PLA, neat EVA , the 
70/30 PLA/EVA  blend and composites based on its blend 59 
VII 
Figure 3.11 DSC cooling curves of PLA, neat EV A, the 50150 
PLA/EV A blend and composites based on its blend 59 
Figure 3.1 2 DSC cooling curves of PLA, neat EV A, the 70/30 
PLA/EV A blend and composites based on its blend 60 
Figure 3.1 3 Water absorption curves and composites based on (a) 50/50 and 
(b) 70/30 w/w PLA/EVA 64 
Figure 3. 14 Freundlich plots from which the data in Table 3.7 were obtained 70 
Figure 3.15 Langmuir plots from which the data in Table 3.7 were obtained 72 
VIII 
LIST OF ABBREVIATIONS AND SYMBOLS 
yd dispersive component of surface energy 
yP polar component of surface energy 
Wa wetting coefficient 
AAS atomic absorption spectroscopy 
b sorption energy 
BHT butylated hydroxy toluene 
Ca adsorbed concentration 
Ce final concentration 
Co initial concentration 
DCP dicumyl peroxide 
flH e crystallization enthalpy 
fl Hee cold crystallization enthalpy 
fl Hen normalised cold crystallization enthalpy 
L'lHccn normalised crystallization enthalpy 
L'lHm melting enthalpy 
L'lHmn normalised melting enthalpy 
L'lH0m specific enthalpy of melting 
DSC differential scanning calorimetry 
EVA ethylene vinyl acetate 
FTIR Fourier-transform infrared spectroscopy 
y surface energy 
KF adsorption capacity 
MFI melt flow index 
n adsorption intensity 
PBSA polybutylene succinate adepate copolymer 
PCL poly( E-caprolactone) 
phr parts per hundred rubber 
PLA poly(lactic acid) 
PLLA poly(L-lactic acid) 
qe equilibrium adsorption capacity 
qm sorption capacity 
IX 
R2 significant correlation 
RL separation factor 
rpm revolutions per minute 
SCB sugarcane bagasse 
SEM scanning electron microscopy 
Tee cold crystallization temperature 
Tg glass transition 
TGA thermogravimetric analysis 
Tm melting temperature 
TPS thermoplastic starch 
v volume 
VA vinyl acetate 
Wa actual mass 
x 
CHAPTER 1 
Introduction and literature review 
1.1 General introduction 
Water pollution by heavy metals has received a lot of attention across the world. The metals which 
contaminate water are produced from liquid waste di scharged from a number of industries such as 
electroplating, textil es, tanneries, oil refineries, mining, and smelters. The most toxic metals, even 
at lower concentrations, are copper, zinc, lead, chromium, cadmium and nickel. These metals can 
damage nerves, liver, bones and also interfere with the normal functioning of various metallo-
enzymes. They can cause high blood pressure, harmfu l effect on kidneys, electrolyte imbalance, 
stomach cramps and allergic skin reaction. Lead ion is a hazardous material that is commonly 
found in industrial wastewater, thus its removal is of utmost importance. It causes plant and animal 
death as well as anemia, brain damage, mental deficiency, anorexia, vomiting and malaise in 
humans [ 1-5]. Consequently, there is a need to look into new and di fferent methods of removing 
lead from aqueous medium. 
Various methods have been used for the removal of heavy metals from aqueous solution. These 
methods include membrane fi ltration [6,7], coagulation and precipitation [8-1 3], ion-exchange 
[ 14, 15] and adsorption [ 16-20]. Only a few of these methods have been accepted due to low cost, 
effi ciency and applicability to a wide variety of pollutants [14]. Membrane filtration is capable of 
reducing heavy metals at low concentrations. However, the major problem of this method is 
limited life time before membrane fouling occurs [6,7]. Coagulation and precipitation methods 
have been widely used for the removal of heavy metals [8-1 3]. At high pH levels, heavy metals 
can be precipitated as insoluble hydroxide or sometimes as sulphides. The disposal of the 
precipitated waste has been the main problem with these methods. Ion-exchange is metal selecti ve, 
it has a limited p H tolerance, high regeneration and does not present a sludge disposal problem 
like coagulation and precipitation [ 14, 15] . However, ion-exchange has both high initial capital and 
maintenance costs [ 15]. Amongst the mentioned methods, adsorption has been proven to be a 
highly effective technique for the removal of heavy metals from waste streams [ 16-20]. 
Adsorption is the process through which a substance, originally present in one phase, is removed 
from that phase by accumulation at the interface between that phase and a separate (solid) phase. 
With adsorption, there is a wide variety of target pollutants, high capacity, fast kinetics and 
poss ibly selective depending on adsorbent [ 15-16). The adsorption process can take place in 
systems such as liquid-gas, liquid-liquid, solid-liquid and solid-gas. The adsorbing phase is the 
adsorbent, and the material concentrated or adsorbed at the surface of the adsorbing phase is the 
adsorbate [2 1]. 
Various materials have been used as adsorbents for the removal of heavy metals. These adsorbents 
include zeolites [22-25), activated carbon [26-29), modified silica gel [30-32) and natural fi bres 
[33-37). Zeolites, activated carbon (except when natural fibres are used for the production of 
activated carbon) and modified silica gel are expensive and they are not environmentally friendly. 
A number of studies have shown that natural fibres can be used as an alternative for removing 
metals in contaminated water [33-37). This was attributed to the low cost, low density, high 
availability and environmental friendliness of natural fibres. Moreover, natural fibres require little 
processing and are selective adsorbents of heavy metals. 
A number of studies have reported on the removal of heavy metals using sugarcane bagasse (SCB) 
[38-41 ]. SCB is a fibrous material left after the crushing of cane stalk and juice extraction. 
Structurally, sugarcane is composed of an outer rind and inner pith. The majority of sucrose 
together with bundles of small fibres are found in the inner pith. The outer rind contains longer 
and finer fibres, in a random arrangement throughout the stem and bound together by lign in and 
hemicelluloses. Sugarcane bagasse is a lignocellulosic plant waste which is composed of cellulose, 
hemicellulose, lign in, pectin, waxes, water-soluble substances, and moisture [40). It is used as a 
metal adsorbent due to ( i) benign lignocellulosic material , (ii) inexpensive (sugarcane industry 
waste), and (iii) rich in oxygen containing functional groups such as phenols and carbonyls. It has 
pronounced capability for uptake of heavy metals in aqueous solution with no need of chemical 
modification. The main problem regarding the use of natural fibres like SCB as adsorbents is that 
they are easily degraded by microbes when in aqueous medium and they cannot be used for a long 
period of time [42). Therefore there is a need to protect or mask fibres against bacterial contact. 
2 
Thermoplastic, thermosets and biodegradable polymers have been widely used as matrices 
(masking agents) for various applications. These applications include structural (automoti ve), 
packaging and other areas of composites [4 3-4 7], but less work has been done on composites for 
water purification. Biodegradable matrices offer many advantages over their counterparts, which 
lately give them wide application in composite technology. Biodegradable polymers are plastics 
obtained from renewable resources synthesized from petroleum-based chemicals and they are 
environmentally friendly, fully degradable and sustainable. Biodegradable polymers such as poly 
(lactic acid) (PLA), poly(~-carprolactone) (PCL), thermoplastic starch (TPS) and polybutylene 
succinate adepate copolymer (PBSA) have been used by numerous researchers (48-50]. PLA 
displays a variety of characteristics which enable its use as a polymer matrix for fibre composites. 
It is a hydrophobic synthetic polymer made from renewable agricultural feedstock (corn starch) 
through fermentation followed by the polymerization of lactic acid. Its characteristics include: 
environmental friendliness, biocompatibility, ease processability and less energy dependence. 
Despite its advantages, PLA cannot be used in certain applications due to its hydrophobic nature, 
brittleness and poor toughness. The disadvantages of PLA can be improved by blending with 
fl exible polymers or addition of filler [48]. 
Production of polymeric material from existing polymers is an important method and is called 
polymer blending. A mixture of at least two polymers or copolymers is known as a polymer blend. 
The advantages of polymer blending include cost effectiveness and less time-consumption than 
the development of new monomers as the basis for new polymeric materials. Additional ly, a wide 
range of material properties is within reach by merely changing the blend composition. Polymer 
blending is performed to improve polymer properties such as mechanical strength, 
biocompatibility and thermal stability that individual polymers do not possess. Many studies have 
been done on the polymer blending of PLA with other polymers such as polypropylene, ethylene 
vinyl acetate and poly(butylenes adepate-co-terephthalate) [41-55]. Ethylene vinyl acetate (EVA) 
is a good candidate to be blended with PLA since it has excellent flexibility, fracture toughness, 
adhesion to other organic/ inorganic materials with long life time. However, due to their 
incompatibility, EV A and PLA cannot be successfull y blended without significant reduction in 
mechanical properties. Hence, dicumyl peroxide (DCP) was used to improve the interaction 
between EV A and PLA, aiming to produce materials with improved properties. 
3 
In this study PLA/ EVA/ SCB compos ites were prepared for the removal of lead metal ions from 
aqueous media. However, SCB is incompatible with non-polar hydrophobic polymers due to their 
polar and hydrophilic nature, the incompatibility of hydrophi lic and hydrophobic po lymers is well 
documented [56-58]. This incompatibility leads to weak interfacial adhe ion and non-uniform 
dispersion of the fi ll er within the matrix during compounding. Due to the weak filler-matrix 
interaction, a decrease in the mechanical properties with its incorporation is one of the inherent 
problems [57] . To overcome this problem, several strategies have been proposed to enhance the 
adhesion between the natural fibre and the polymer matrix. These strategies genera ll y involve 
modifications of the fibre and/or the matrix by physical or chemical methods. Chemical 
modification of the natural fibres includes: acetylation, mercerization, cyanoethylation, peroxide 
treatments, graft copolymerization (methylmethacrylate, acrylamide, and acrylon itri le) as well as 
various coupling agents (silane, isocyanate and titanate based compounds) (58-60]. Among all 
these methods, mercerization has shown a better compatibi lization effect in polymer matrix based 
natural fibres [ 6 1-64]. 
In this study, SCB which is the residue left after crushing sugarcane stalks for the extraction of the 
sucrose-rich juice, has been selected because it is a highly promising metal adsorbent (65]. This is 
so because sugarcane is highly productive, abundant and contains functiona l groups that are 
responsible for metal complexation or ion-exchange (66]. The metal adsorption effic iency of 
PLA/EVA /SCB biocomposites was investigated by flame atomic absorption spectroscopy (AAS). 
This technique is preferred because of its specificity, sensitivity, precision, s implicity and 
relatively low cost per analysis (67]. To our knowledge, there are no reports on PLA/EVA/SCB 
bio-composites and it is important to understand their effect on the removal of heavy metals from 
aqueous media. 
1.2 Literature review 
1.2.J Natural fibres: Sources and classification 
Natural fibres are raw materials directly obtainab le from animal, vegetable, or mineral sources. 
Vegetable fibres are extracted from plants and are classified into three categories, depending on 
4 
the part of the plant they are extracted from. ( I) Fruit fibres are extracted from the fruits of the 
plant, they are light and hairy, and allow the wind to carry the seeds. (2) Bast fibres are found in 
the stems of the plant providing the plant its strength. Usually they run across the entire length of 
the stem and are therefore very long. (3) Fibres extracted from the leaves are rough and sturdy and 
form part of the plant's transportation system, they are called leaf fibres. Natural fibres were and 
still are the basis for producing clothes, papers, tools, and building materials. They are rigid, 
crystalline cellulose microfibril-reinforced amorphous lignin and/or hemicellulose matrices. 
Natural fibres are cheap, non-abrasive, have low density, abundant, low energy consumption, 
biodegradable, recyclable and renewable (57]. 
1.2.2 Properties of natural fibres 
Properties as well as the quality of a fibre depend on factors such as maturity and the processing 
methods adopted for the extraction of the fibres. An increase in diameter of a fibre results in a 
decrease in modulus. Properties such as density, electrical resistivity, ultimate tensile strength and 
initial modulus are related to the internal structure and chemical composition of the fi bres. The 
smaller the angle between the axis and the fi bre fibrils, the better the mechanical properties, i.e. 
the strength and sti ffuess of the fibre. These properti es are also considerably affected by the 
chemical constituents and complex chemical structure of natural fi bres. Cellulose content and 
microfibrillar angle cannot be correlated with fibre strength, because of the very complex structure 
of natural fibres. Filament and individual fibre properties can vary widely depending on various 
factors such as source, age, separat ing technique, moisture content, history of the fi bre and speed 
of testing (57 ,68-96]. 
Plant or lignocellulosic fibres are considered as naturally occurring composites consisting mainly 
of cellulose fi brils embedded in a lignin matrix. The main constituents of the plant fibres are 
cellulose, hemicellulose, and lignin with other constituents like pectins, waxes, water-soluble 
substances, and moisture (42,57,68-72]. The chemical composition of lignocellulosic fibres 
depends on various factors such as species, variety, type of soil used, weather conditions, part from 
which the fibres are extracted, and age of the plants (73]. 
5 
Cellulose is a natural polymer made by linking of sma ller molecules (F igure I . I ) . The links in the 
cellulose chain consist of sugar, /J-D-glucose. The sugar units are linked when water is eliminated 
by combining the H and - OH group. Linking just two of these sugars produces a di saccharide 
called cellobiose. In the cellulose chain, the glucose units are in 6-membered rings, called 
pyranoses. T hey are j oined by single oxygen atoms (acetal li nkages) between the C -1 of one 
pyranose ring and the C-4 of the next ring. Since a molecule of water is lost due to the reaction of 
an alcoho l and a hemiacetal to form an acetal, the glucose units in the cellulose polymer are 
referred to as anhydroglucose units. The cellulose molecular structure is the reason for its 
hydrophilicity, chirality, degradability, and its unique reactivities . Cellulose is easily hydrolyzed 
by acids to water-soluble sugars, but is resistant to strong alkali [42,57,68-72]. 
Figure 1.1 Chemical structure of cellulose [72] 
Hemicellulose consists of linear homo- or copolymers of variable degree of branching (usually 
single monosaccharidic branches) and with occasional (3-1 3 wt. %) replacement of O H groups by 
0 -acetyl groups (Figure 1.2). It contains a group of polysaccharides compiled of fi ve and six 
carbon ring sugars. It di ffers from cellulose in three aspects, firstly, it contains severa l sugar units; 
secondl y they exhibit a considerable degree of chain branching containing pendent side groups 
giving rise to its ion crystalline nature. The third aspect is its degree of polymerization, which is 
30-50, I 0-100 times less than that of cellulose. Hemicellulose is very hydrophilic, soluble in alkali 
and easily hydrolyzed in acids [42,57,68-72]. 
6 
'o~ OH 
Aco-YW 
OH OH OAc 
OH~~~ 
OH~ 
OAc 6i OH 
2 
Figure 1.2 Chemical structure of hemicellulose 1721 
Lignin is a complex hydrocarbon polymer with both aliphatic and aromatic constituents , and it is 
totall y insoluble in most of the solvents and cannot be broken down into monomeri c units (Figure 
1.3). Lign in is considered to be a thermoplastic polymer having a glass transition temperature of 
around 90 °C and a melting temperature of around 170 °C. It is totally amorphous and hydrophobic 
in nature. It can be hydrolyzed by acids, but it is soluble in hot alkali, readily ox idized and easily 
condensable with phenol. The structure, properties and morphology of the fibre is influenced by 
the lignin content [42,57,68-72]. 
H HO 
H_.C:O 
0 11 0 11 0 11 
(• I l•l (< ) 
Figure 1.3 Chemical structure of lignin 1721 
7 
Pectin is a collecti ve name for heteropolysacharides and they provide flexibility to plants. They 
are soluble in water only after a partial neutralization with alkali or ammonium hydroxide 
[42,57,68-72]. 
Wax consists of different types of alcohols, which are insoluble in water as well as several acids 
(palmitic acid, oleaginous acid and stearic acid). The part of the fibres which can be extracted with 
organic solutions is made up of wax. Wax generally influences the wettability as well as the 
adhesion characteristics of the fibres [4 2,68-73]. 
1.2.2.1 Structure, physical, and mechanical properties of natural fibres 
A single fi bre of all plant based natural fi bres consists of several cell s. The structure and the 
properti es of natural fibres are determined and influenced by the dimensions and the arrangements 
of unit cell s in a fi bre. The dimensions of individual cells in natural fibres are dependent on the 
species, maturity and location of the fi bres in the plant and also on the fi bre extraction conditions. 
These cell s are formed out of crystalline microfi brils based on cellulose, which are connected to a 
complete layer by amorphous lignin and hemicellulose. The diameter o f these microfibrils ranges 
from I 0 to 30 nm, and each microfibril is made up of30-100 cellulose molecules in extended chain 
conformation. Every fibril has a complex, layered structure consisting of a thin primary wall that 
is the first layer deposited during cell growth encircling a secondary wall. The secondary wall is 
made up of three layers, and the thick middle layer determines the mechanical properties of the 
fi bre. The middle layer consists of a seri es of helically wound cellular microfibril s formed from 
long chain cellulose molecules as seen in Figure 4 . The angle between the fibre axis and the 
microfibrils is called the microfibrill ar angle. The characteristic value for this parameter varies 
fro m one fibre to another. The spiral angle of the fibril s and the content of cellulose generally 
determine the mechanical properties of the cellulose based natural fi bres. There are several 
physical properti es that are important to know about for each natural fibre, before that fibre can be 
used to reach its highest potential. These properties include fibre dimensions, defects, strength, 
variabil ity, crystall inity, and structure [57,68-69,7 1]. 
8 
Secondary wall S3 Lumen 
Secondary wall S2 
Helically 
arranged 
crystalline 
microfibrils 
Secondary wall S 1 
of cellulose 
Primary wall 
Amcxphous 
region mainly 
Disorderly arranged 
consisting ol ligiin .__.....__ crystalline cellulose 
and hemicellulose 
microfibrils networks 
Figure 1.4 Structure of natural fibre cell 168] 
The properti es of a fibre such as tensile strain, tensile stress, specific tensile modulus, and specific 
tensile strength were evaluated as a fu nction of geometrical variation, extraction method and the 
diameter of the fi bres [74] . It was found that the density of various natural fibres are likely to vary 
depending on the process of fibre extraction, age of the plant, moisture present in the fib re and the 
soil condition in which the plant has grown. It was observed that the fai lure of fi bres in tension is 
due to pull-out of microfibrils accompanied by tearing of cell wall s. The tendency of fi bre pull -
out decreases with increasing speed of testing. Generally it was observed that an increase in 
cellulose content results in an increase in tensile strength and the Young's modulus of the fi bres. 
The sti ffness of the fibres is determined by the microfibrillar angle [75]. 
1.2.3 Sugarcane bagasse (SCB) 
SCB is a fi brous residue which remams after sugarcane (Saccharum officinarum) stalks are 
crushed to extract their juice. SCB which has short renewal times, wide availability, 
biodegradability, ease of cultivation and low cost, associated with excellent physical and 
mechanical characteri stics, is currently the most widely used natural fibre. It is currently used as a 
renewable natural fibre for the manufacture of composites materials [4 4]. The SCB as well as any 
other types of plant biomass is composed by cellulose, hemicellulose, lignin, and small amounts 
9 
of extractives and mineral salts. Sugarcane stalk is made up of shorter segments and joints. Each 
joint consists of two distincti ve parts i.e. node and intemode. The cross-section of the intemode is 
composed of the rind (outer layer) and the pith (inner layer). The majori ty of sucrose along with 
bundles of small fi bres is found in the pith. The rind consists of numerous longer and finer fibre 
bundles composed of elemental fibres in discrete elongated units embedded in a matrix of lignin 
and hemicellulose. These elemental fi bres are bound together by an amorphous matrix of lign in 
and hemicellulose to form fibre bundles [76-78]. 
1.2.3.1 Chemical composition of SCB 
The chemical composition of SCB fi bres have been reported by many researchers [79-83]. These 
researchers fo und varied contents of cellulose (40-50%), hemicellulose (24-35%), lignin (20-30%) 
and small amounts of ash and acetyl groups. This variation in chemical composition of SCB fibres 
was attributed to the fact that the chemical composition of lignocellulosic fibres depends on 
various factors such as species, variety, type of soil used, weather conditions, part from which the 
fi bres are extracted, and age of the plant [76,77]. 
1.2.3.2 Thermal properties of SCB 
The thermal properties of SCB fi bres have been studied by a number of researchers usmg 
thermogravimetric analysis (TGA) (84-87]. The results of the weight loss of SCB fibres as a 
function of temperature for these studies can be summari zed as follows: the first small change in 
weight up to 100 °C was related to water loss associated with moisture present in the SCB. Between 
100 and 200 °C, the SCB was thermally stable. Between 200 and 300 °C, the weight loss was 
about 10%. From 300 to 400 °C, the fibre di splayed considerable mass loss (more than 70%) due 
to decomposition of both cellulose and hemicellulose. Above 400 °C, degradation of fibres can be 
attributed to the breakage of bonds of the lignin. Above 500 °C, only about 1% ash was observed. 
Therefore, 200 °C can be considered as the maximum temperature up to which SCB fibres can be 
used. 
10 
1.2.4 Composite properties 
Composites consist of one or more discontinuous phases embedded in a continuous phase. The 
discontinuous phase is usually harder and stronger than the continuous phase and is called the 
'reinforcement' or 'reinforcing material', whereas the continuous phase is termed as the 'matrix'. 
Properties of composites are strongly dependent on the properties of their constituent materials, 
their distribution and the interaction between them. The composite properties may be the volume 
fraction sum of the properties of the constituents or the constituents may interact in a synergistic 
way resulting in improved or better properties. Apart from the nature of the constituent materials, 
the geometry of the reinforcement (shape, size and size distribution) influences the properties of 
the composite to a large extent. The concentration distribution and orientation of the reinforcement 
a lso affect the properties. 
1.2.4. t Modification of polymer/natural fibre composites 
Composites based on natural fibres are an interesting alternative when moderate mechanical 
properties are required. Since the interfacial bonding between the reinforcing fibres and the 
polymer matrix is an important element in real izing the mechanical properties, several authors 
[57,70,71,88-9 1] focused their studies on the treatment of fibres to improve the bonding with the 
polymer matrix. The mechanical properties of the composites are controlled by the properties and 
quantities of the component materials and by the character of the interfacial region between the 
matrix and reinforcement. Lack of good interfacial adhesion makes the use of cellular fibre 
composites less attractive. Natural fibre composites combine good mechanical properties with low 
specific mass, but their high level of moisture absorption, poor wettability and insufficient 
adhesion between the untreated fibre and the polymer matrix leads to debonding with age. To 
improve the properties of the composites, it is necessary to improve the adhesion between the 
hydrophilic fibre and the hydrophobic matrix by modifying the fibre surface. Natural reinforcing 
fibres can be modified by physical and chemical methods. Physical modification changes the 
structural and surface properties of the fibre, thereby influencing the mechanical bonding with the 
matrix. The chemical modification of the fibres alters the surface properties so that better wetting 
of the fibres w ith the matrix is possible. This removes the organic residues from the surfaces of 
11 
the fibres which enhances the adhesion, because natural fibres are coarse in structure, and thus 
enable an interlocking mechanism with the matrix. According to the principles of interface 
coupling, the hydrophilic carboxyl group of an organic acid as a modifier is expected to react with 
the hydroxyl groups on the surface of natural fibre, and the hydrophobic group should react or 
have relatively high compatibility with the polymer matrix. The combined effects of these 
interactions wi ll effectively improve the fibre dispersion and resultant adhesive coupling. There 
are various chemical treatments available for the fibre surface modification. Chemical treatment 
includes alkali, si lane, acetylation, benzoylation, acrylation, isocynates, maleated coupling agents 
and permanganate treatment. 
Alkaline treatment or mercerization is one of the most used chemical treatments of natura l fi bres 
when used to reinforce thermoplastics and thermosets. The important modification done by 
alkaline treatment is the disruption of hydrogen bonding in the network structure, thereby 
increasing surface roughness. This treatment removes a certain amount of lignin, wax and oils 
covering the external surface of the fibre cell wall , depolymerizes cellulose and exposes the short 
length crystallites. Addition of aqueous sodium hydroxide (NaOH) to natural fibre promotes the 
ionization of the hydroxyl group to an alkoxide. 
(I. I) 
Thus, alkaline processing directly influences the ce llulosic fibril, the degree of polymerization and 
the extraction of lignin and hemicellulosic compounds. It was reported that alkaline treatment had 
two effects on the fibre 1) It increased surface roughness resulting in better mechanical 
interlocking, and 2) it increased the amount of cellulose exposed on the fibre surface, therefore 
increasing the number of possible reaction sites [92]. 
J. 2.4.2 Morphologies of polymer blends/natural fibre composites 
Improved interfacial adhesion usually leads to better fibre dispersion and transfer of stress from 
one phase to the other. Several methods have been reported for improving the interfacial 
compatibi lity between hydrophilic cellulosic fibres and hydrophobic polymer matrices 
12 
[57,70, 7 1,88-9 1] . The influence of these modification methods in the morphologies and interfacia l 
properties of polymer blends reinforced natural fibre composites have been investigated by several 
researchers [93-98), and compared with their unmodified counterparts. It was generally observed 
that the interfac ial bonding between the fibre and the polymer blend improved when the fibre 
surfaces were treated with chemical or physical treatments, when only the polymer matrix was 
modified, or when both of them were modified. The untreated composites, on the other hand, 
showed poor interfacial adhesion, as the ex istence of fibre pull-out from the matrix material during 
fracture, and their surfaces remained practically clean. Moreover, the absence of any physical 
contact between the fibre and the matrix was also detected. 
1.2.4.3 Mechanical properties of polymer blends/natural fibre composites 
Mechanical properties of polymer blends/natural fibre composites were reported in a number of 
papers [93-98]. It was generally found that the Young's moduli and tensile strength of the polymer 
blends/natural fibre composites were dependent on the improved dispersion and interfacial 
adhesion. Well dispersed composites resulted in an increase in Young's moduli as well as an 
increase in tensile strength. This was due to the presence of well dispersed additional reinforcement 
structures that make the matrix tougher. Elongation at yield and yield stress did not show similar 
trends, but varied according to the investigated polymer blends/natural fibre composites. The 
decrease in elongation at yield was due to decrease in the flexibility of the composite due to the 
addition of the filler. It was generally seen that the% elongation at break point decreases with the 
addition of fillers, despite the state of the interface between the different phases. Natural fibres are 
generally known to increase stiffuess which in turn enhances modulus of composites when they 
are used as rein forcement. Generally, it was found that the impact strength of polymer blend 
composites decreases as the fibre content increases. The decrease in impact strength as fibre 
content increases was attributed to fibre bundle or agglomerate formation which reduces the 
transfer of the external forces between fibre and the matrix . It was also reported that the mechanical 
properties of natural fibre-polymer blend composites depend on several other factors such as the 
type of cellulosic fibres, fibre length, loading, and orientation, as well as the processing conditions 
during composite preparations [99) . It can be concluded that untreated composites usuall y have 
13 
poor mechanical properties than the blends or treated composites due to poor interfacial bonding 
between the fibre and the polymer blend matri x. 
1.2.5 Water absorption of polymer/natural fibre composites 
Moisture penetration into composite materials is conducted by three different mechanisms as 
reported by many researchers [ 100-103]. The main process consists of diffusion of water 
molecules inside the micro-gaps between polymer chains. The other common mechanisms are 
capillary transport into the gaps and flaws at the interfaces between fibres and polymer, because 
of the incomplete wettabil ity and impregnation; and transport by micro-cracks in the matrix formed 
during the compounding process. In general, diffusion behaviour in polymers can be classified 
according to the relative mobility of the penetrant and of the polymer segments. The capillary 
mechanism involves the fl ow of water molecules into the interface between fibres and matrix. It 
is particularly important when the interfac ial adhesion is weak and when the debonding of the 
fi bres and the matrix has started. On the other hand, transport by micro-cracks includes the flow 
and storage of water in the cracks, pores or small channels in the composite structure. 
Several researchers [ 104- 106] reported that natural fi bre-polymer composites has high water 
uptake compared to neat polymer matri ces, which showed that polymers have little water 
absorption effect. Thermoplastic and bio-degradable polymers are hydrophobic in nature and 
therefore would reduce water uptake in the composites. Water absorption effect on composites 
increased with an increase in fi bre content. This was attributed to the hydrophilic nature of the 
natural fibres resulting into poor interfac ial bonding with hydrophobic thermoplastics thus 
allowing water penetration through the composite materials. An increase in hydrophilic natural 
fi bre content results into a less hydrophobic thermoplastic material to encapsulate fibres and 
therefore increased water uptake. 
1.2.6 Adsorption 
Adsorption is a process of binding molecules or partic les onto the external surface of solid or 
internal surface if the material is porous in a very thin layer. Adsorption process proceeds in three 
14 
steps: i) Transfer of the adsorbate molecules through the film that surrounds the adsorbent. ii) 
Diffusion through the pores if the adsorbent is porous. iii) Uptake of the adsorbate molecules by 
active surface, including formation of the bond between the adsorbate and the adsorbent. 
Adsorption can occur in two ways which are the chemisorption and physisorption. In 
chemisorption the forces involved are valence forces of the same kind as those operating in the 
formation of chemical compounds. Chemisorption is favoured at high temperature because 
chemical reactions proceed more rapidl y at an elevated temperature. With physisorption the forces 
that are involved are intermolecular forces (van der Waals forces) of the same kind as those 
responsible for the imperfection of real gases and the condensation of vapours. These forces do 
not involve a significant change in the e lectronic orbita l patterns of the species involved. ln 
physisorption, adsorbed molecules are not attached to a specific site at the surface of adsorbent but 
are free to undergo translational movement within the interface. It is predominant at low 
temperature and is characterized by relatively low energy of adsorption. The rate of adsorption 
depends on the rate at which the molecules move by diffusion in solution or the rate at which the 
molecules can reach available surface by diffusing through the film and the pores. Adsorption 
capacity depends on the physical and chemical characteristics of both the adsorbent and adsorbate, 
the concentration of the adsorbate in liquid solution, the experimental conditions such as 
temperature and solution pH, and the amount of time the adsorbate is in contact with the adsorbent 
[I 07]. 
1.2.6.1 Uses of natural fibres as adsorbents in water treatment 
There were a fair number of studies on the use of natural fibres as adsorbents of heavy metals [ 108-
114]. The removal of metal ions from aqueous media using natural fibres is based on metal 
biosorption. The process of biosorption involves a solid phase (sorbent) and a liquid phase 
(solvent) containing a dissolved species to be sorbed. Due to a high affinity of the sorbent for the 
metal ion species, the latter is attracted and bound by a complex process affected by several 
mechanisms. These mechanisms involve chemisorption, complexation, adsorption on the surface 
and pores, ion exchange, chelation, adsorption by physical forces, entrapment in inter and 
intrafibrill ar capillaries and spaces of the structural polysaccharides network as a result of the 
concentration gradient and diffusion through the cell wall and membrane. Natural fi bres are 
15 
composed of many constituents; amongst these consti tuents are functional groups that have the 
affini ty for metal complexation. These functional groups present in natural fi bres include 
acetamido, carbonyl, phenolic, structural polysaccharides, amido, amino, sulphydryl carboxyl 
groups, alcohols and esters. 
There are a number of parameters that have been reported when using natural fi bres as adsorbents 
( 104-114]. These parameters include pH level of the solution, contact time between the adsorbent 
and the adsorbate, temperature of the so lution, the amount of the adsorbent and the initial 
concentration of the solution. It was generally found that the adsorption efficiency increased with 
an increase in pH level. However, it was found that at lower pH levels the removal effic iency was 
very low because of the large number of hydronium ions (H30 +) in the solution. Metal ions have 
to compete with these hydronium ions for the adsorbent sites. It was al so fo und that the functional 
groups in natural fi bres were protonated at lower pH levels and hence rendered unavailable for ion 
exchange and complexation with the metal ions. At pH levels of 3 to 7 the adsorption efficiency 
was very high due to less competition, resulting in large numbers of adsorption sites in the 
adsorbate. These investigations also showed that at pH levels higher than 7, meta l ions start to 
precipitate which defeats the very purpose of employing adsorption. Adsorption of heavy metals 
by natural fibres was found to initia lly increase with an increase in contact time until it reaches 
equilibrium i.e. there are no more available sites on the adsorbent. It was generally observed that 
the percentage removal of heavy metals decreased with an increase in initial concentration. At 
lower concentration, most of the metal solution will react with the binding sites due to the larger 
surface area of the adsorbent, and thus facili tate almost complete sorption. At higher 
concentrations, more metal ions were left unabsorbed in the solution due to the saturation of the 
binding sites. However, Putra et al. [ 114] found that the signi ficant amount of metal ions adsorbed 
at high initial metal concentrations can be related to two main factors: i) probability of collision 
between metal ions with the bio-sorbent surface, and ii) high rate of metal ions diffusion onto the 
bio-sorbent surface. It was also seen from these results that the removal efficiency increased 
rapidly with an increase in bio-sorbent, which was attributed to increased surface area of the bio-
sorbent and the avai labil ity of more binding sites due to increased amount of bio-sorbent. 
1.2.6.2 Adsorption isotherms 
16 
Adsorption isotherms represent the relationship between the amount adsorbed by a unit weight of 
solid sorbent and the amount of solute remaining in the solution at equilibrium. The Langmuir and 
Freundlich isotherm models are frequently used for describing short term and mono component 
adsorption of metal ions by di fferent materials. Simplicity and easy interpretability are some of 
the reasons for the extensive use of these models. A number of reports were published on these 
models [ 115-1 21]. To calculate the adsorption capacity of metal ions on the fi bres at equilibrium, 
qc is calculated according to Equation 1.2. 
qe= CC - C 0 m e ) V ( 1.2) 
where Vis the volume of the solution and m is the mass of sorbent used. C,, (mg L-1) and Ce (mg 
L-1) are the ini tial and equilibrium concentrations of the metal ions. 
Langmuir adsorption isotherm 
The Langmuir isotherm, also called the ideal localized monolayer model, was developed to 
represent chemisorption. Langmuir theoretically examined the adsorption of gases on solid 
surfaces, and considered sorption as a chemical phenomenon. The Langmuir equation relates the 
coverage of molecules on a solid surface to concentration of a medium above the solid surface at 
a fixed temperature. This isotherm is based on the assumption that adsorption is limited to mono-
layer coverage, all surface sites are alike and can only accommodate one adsorbed molecule, the 
abil ity of a molecule to be adsorbed on a given site is independent of its neighbouring sites' 
occupancy, adsorption is reversible and the adsorbed molecule cannot migrate across the surface 
or interact with neighbouring molecules. By applying these assumptions and the kinetic principle 
(rate of adsorption and desorption from the surface is equal), the Langmuir equation can be written 
in a hyperbolic form Equation 1.3. 
(1.3) 
17 
where qe is the adsorption capacity at equilibrium (mg g- 1 ) , qmax is the theoretical maximum 
adsorption capacity of the adsorbent (mg g-1) and, as such, can be thought of as the best cri terion 
for comparing adsorptions, K L is the Langmuir affinity constant (L mg-1) and Ce is the supernatant 
equilibrium concentration of the system (mg L-1) . This isotherm equation has been most frequently 
applied in equilibrium studies of adsorption, but it should be realized that the Langmuir isotherm 
offers no insights into aspects of adsorption mechanisms. 
Freundlich adsorption isotherm 
The Freundlich isotherm was originally of an empirical nature, but was later interpreted as sorption 
onto heterogeneous surfaces or surfaces supporting sites of varied affiniti es. It is assumed that the 
stronger binding sites are occupied first and that the binding strength decreases with increasing 
degree of site occupation. The Freundlich isotherm can describe the adsorption of organic and 
inorganic compounds on a wide variety of adsorbents. According to thi s model the adsorbed mass 
per mass of adsorbent can be expressed by a power law function of the solute concentration as in 
Equation 1.4. 
( 1.4) 
where KF is the Freundlich constant related to adsorption capacity (mg g-1) and n is the 
heterogeneity coefficient (dimensionless). For lineari zation of the data, the Freundlich equation is 
written in logari thmic form Equation 1.5. 
1 
logq = logK F+ (-n ) log C ( 1.5) e e 
The plot of log qc versus log Ce has a slope equal to I In and an intercept equal to log K F. On 
average, a favourable adsorption tends to have a Freundlich constant n between I and I 0. Larger 
values of n imply stronger interaction between the adsorbent and the adsorbate, whi le 1/n equal to 
1 indicates linear adsorption leading to identical adsorption energies for all sites. Linear adsorption 
generally occurs at very low solute concentrations and low loading of the adsorbent. 
18 
1.3 Aims and objectives 
~ The main ai m of this study was to formulate effective and environmentall y friendly 
PLA/EV A/SCB biocomposites for the removal of lead (Pb). 
~ To study the thermal properties of the composites using thermogravimetric anal ysis to 
understand the influence of the presence and amount of filler on the thermal stabi lity of the 
biocomposites. 
~ To study the morphologies and the interfac ial adhesion between the polymers and the filler 
by us ing scanning electron and optical microscopy. 
~ To determine the impact properties of the composites in order to establish their durability 
during use. 
~ To test the effectiveness of the biocomposites for heavy metal removal through atomic 
absorption spectroscopy (AAS). 
~ To investigate the effect of contact time, pH level, and initial concentration on 
biocomposites. 
~ To use the Langmuir and Freundlich adsorption isotherms to interpret the adsorption 
behav iour of lead ions onto the bio-composites. 
1.4 Thesis outline 
The outline of this thesis is as follows: 
~ Chapter I: General introduction and literature rev iew 
~ Chapter 2: Material s and methods 
~ Chapter 3: Results and discussion 
~ Chapter 4: Conclusions 
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19 
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33 
CHAPTER2 
Materials and methods 
2.1 Materials 
Poly(L-lactic acid) (PLLA) was supplied by Toyota Motor Co., Japan. It has a molecular weight 
of 557 000 g mo1·1, viscosity of 5340 Pas at 180 °C, Tmo f 170- 180 °C , Tg of 50-60 °C , and a density 
of 1.248 g cm·3. 
The ethylene vinyl acetate copolymer (EVA-460) was manufactured and supplied in granule form 
by DuPont Packaging & Industrial Polymers. EVA -460 contains 18% by weight of vinyl acetate 
(VA) with a butylated hydroxy toluene (BHT) antioxidant therma l stabi lizer. It has a melt flow 
index (MFI) of 2.5 g/ I 0 min ( 190 °C/2. 16 kg, ASTM D 1238/ ISO I 1330), Tm of 88 °C, Vi cat 
softening point of 64 °C, and a density of 0.941 g cm·3. 
Sugarcane bagasse (SCB) was supplied by a farm in Craddock near Port El izabeth, South Africa. 
Table 2.1 Composition of SCB 
Sample Lignin I % Cellulose I % Hemicellulose I % 
Sugarcane bagasse (SCB) 2.8 ± 1.3 48.8 ± 0.1 47.2± 0.8 
Dicumyl peroxide was suppl ied by Sigma-Aldrich, Krugersdorp, South Afi-ica as a white 
crystalline powder with an assay of 99%. It was used as a free radical initiator and has a melting 
point of 39 °C and a molar mass of 270 g mo1·1• 
34 
2.2 Methods 
2.2.1 Pre-treatment of SCB 
SCB was washed extensive ly w ith boi ling distilled water to remove any excess sugar conta ined 
with in and to prevent fu ngal growth. SCB was air dried for 24 hours fo llowed by oven drying for 
another 24 hours at 80 °C to remove moisture. It was then soaked in I 0% NaOH for I hour and 
washed several times with distilled water to remove the remaining alka li from the fi bre. SCB was 
then immersed in 0.25 M acetic acid to neutra lize it, and litmus paper was used to check the 
neutrality of the SCB. D istil led water was used to wash the remaining acetic acid. A vacuu m fi lter 
was used to fi lter SCB, and it was air dried for 24 hours followed by oven drying for 24 hours at 
80 °C. After drying, it was crushed with an analytica l mill to obtain a fine powder which was sieved 
w ith a 425 µm sieve. The reasons for applying alkaline treatment on the fi bre surface were: ( i) to 
distribute the hydrogen bonds in the network structure, thereby increasing the surface roughness, 
( ii) to remove a certain amount of lignin, wax and natural oi ls covering the external surface of the 
fibre wall , and (ii i) to depolymerise and expose the short length crysta lli tes [I] . 
2.2.2 Sample preparation 
The sample ratios (quantities) of the biocomposites are shown in Table 2. 1. PLA and EVA were 
oven dried at 60 °C for 24 hours to remove any moisture trapped with in the granules. All the 
samples were prepared by melt mix ing using a Brabender Plastograph with a 50 ml interna l mixer. 
The samples were prepared at 180 °C, at a speed of 60 rpm for 15 min. A temperature of 180 °C 
was chosen to fu ll y melt the crysta ls, and at the same time avoiding sample degradation and high 
torque levels in the Brabender [2]. PLA and EV A were physically premixed and fed into the heated 
mixer. They were allowed to mix for 2 min , after which SCB was introduced and the mixing 
continued for another 13 min. 0.1 phr DC P was added to the mi xture (PLA/EV A/SCB) one minute 
before the end of the mixing time. DCP was used to improve adhes ion between PLA and EV A. 
PLA/EV A/SCB samples were then me lt pressed at 180 °C for I 0 min under 50 kPa using a 
hydraulic melt press. They were cooled for 5 min between steel bars and cut for different 
characterizations. 
35 
·Table 2.2 Sample compositions used in this study 
PLA/EV A/SCB(w/w) PLA/EV A/SCB(w/w) PLA/ EV A/SCB(w/w) 
5015010 70/30/0 90/ 1010 
47.5/47.5/5 66.5/28.5/5 85.5/9.5/5 
45/45/ 10 63/27/1 0 81/9/ 10 
42.5/42.5/ 15 59.5/25.5/15 76.5/8.5/ 15 
40140120 56/24/20 72/8/20 
35/35/30 49/2 1/30 6317/30 
2.3 Sample analys is 
To determine the viscosity of the polymers, a melt flow index of the two polymers in the blend 
was determined using a CEAST Melt Flow Junior. Ten samples each of both polymers were 
analysed at 190 °C. The amount of samples which flowed through the die over a period of I 0 
minute under 2.1 6 Kg weight was determined in each case. 
Contact angle tests were performed at room temperature on surface energy evaluation system. 
Contact ang les o f two test liquids (di still ed water H10 and diiodomethane C H2'2) were measured 
by depositing a drop on the sample and the values were estimated as the tangent normal to the drop 
at the intersecti on between the sessile drop and the surface. Images were taken w ithin 30 seconds 
of the drop deposition to avoid solvent evaporation. The reported contact angle values are the 
average of at least fi ve measurements at di fferent spots of the surface of the sample. Surface 
energies of SCB were obtained from the literature [3]. Distilled water (H20) and diiodomethane 
(CH2b ) were used as po lar and non-polar so lvents, respectively. The li terature values o f their 
surface energies are: (H20; yP = 34.2 mJ m·2; C H2'2; y d = 17.8 mJ m·2. The contact ang le, total 
surface energy, as well as their dispersive and polar surface components, were calculated using 
Owens-Wendt h method (Equations 2.1 and 2.2) [ 4-7]. 
(2. 1) 
(2.2) 
36 
where() is the contact angle, y is the surface energy, the subscripts 's ' and ' I' indicate solid and 
liquid respectively, while the superscripts ' d ' and 'p' indicate the di spersive and polar components, 
respectively. The interfacial tensions between the components in a blend were calculated from 
contact angle measurement results using the geometric mean equation (Equation 2.3) [ 4-7]. 
(2.3) 
where y12 = interfacial tension between components I and 2 in the blend, y1 and y2 are the total 
surface energies of components I and 2, yf and yf are the di spersive surface energies of 
components 1 and 2, and yf and yf are the polar surface energies of the components 1 and 2 in 
the composites. The wetting coefficient was calculated using the interfacial tensions of the 
PLA/EVA, PLA/SCB and EVA/SCB from Young's equation (Equation 2.4) [4-8]. 
OJa = rP LA/SCB - rE VAI SCB (2.4) 
r PLAI El'A 
where YPLA/SCB is the interfacial tension between PLA and SCB, YEVA/ SCB is the interfacial tension 
between EVA and PLA, and YPLA / EVA is the interfacial tension between PLA and EVA. If Wa < 
-1, the particles are predicted to be located in polymer B in this case (EVA). If Wa > 1 they are 
dispersed in polymer A (PLA), and ifthe value of Wais between -I and 1, the particles are likely 
to di sperse on the interface of the two polymers in the blend. 
An optical microscope (CETl-Topic B, Be lgium) was used to examine the dispersion of the fibres 
in the polymer matrices, as well as the morphologies of the composite samples. The micrographs 
of the biocomposites were taken at 4x (SP 4x/O. l 0/ 160/-) magnification. 
The morphologies of the blends and the PLA/EV A/SCB biocomposites were investigated by a 
TESCAN VEGA 3 scanning electron microscope (SEM). All the blends and biocomposite samples 
were fractured under liquid nitrogen to avoid any disturbance to the molecular structure. They 
37 
were coated with gold to ensure that the charge deposited on the sample surface by the electron 
beam was able to leak away to the earth [9, IO] , and examined at an acceleration voltage of I 5 kV. 
Attenuated total re fl ectance Fourier-transform infrared spectroscopy (A T R-FTIR) spectra of the 
neat materia ls and the PLNEV NSCB samples were obtained using a Perkin Elmer Spectrum I 00 
FTIR spectrometer. The samples were analysed over a range of 650-4000 cm·1 with a resolution 
of 4 cm·1• All the spectra were averaged over 16 scans. 
A Ceast Impactor II was used to investigate the impact properties of the blends and composites, in 
order to establish whether SCB gave rise to improved im pact properties. The samples were 
rectangular with a width of I 0 mm, a thickness of 3 mm and length of 83 mm, and they were V-
notched (3 mm deep) edgewise. The pendulum hammer was situated at an angle of 50° from the 
release spot and the samples were tested at an ambient temperature of 24 °C. Five samples of each 
composition were tested and the average and standard deviation values are presented. 
Samples (2 mm x I 0 mm x 40 mm) o f 50/50 and 70/30 w/w PLNEVA, as well as thei r composites 
containing respectively 15, 20 and 30% SCB, were first dried at 30 °C in an oven for 24 hours to 
ensure that they were complete ly dry. The weights of the samples were recorded before they were 
immersed in di stilled water at various time intervals. At each interval, the samples were removed 
from the di stilled water and blot dri ed with a paper towel before recordi ng their masses after 
inserti on in water. This procedure was repeated until there was no further increase in the weight 
of the samples. All the measurements were done in triplicate, and the mean and standard deviation 
values were calculated. The percentage water absorption was calculated using Equation 2.5. 
%W = Wi- W; x lOO (2.5) 
W ; 
where Wi s the total water absorbed, W1i s the final we ight of the sample after a certa in time t of 
water immersion, and 1¥i is the initial sample mass. 
38 
A fl ame atomic absorption spectrometer (G BC 909AA) was used for the adsorption analysis of 
the samples. The adsorption experiments were done by measuring 50 mL of the metal solutions 
into a I 00 mL beaker and adding 2 g of the prev iously prepared compos ites (cut into small str ips 
of about 2 mm x 40 mm x I Omm) into the metal solution. The beaker containing the adsorbent and 
the metal solution was placed on a magnetic stirrer and stirred at 150 rpm at a room temperature 
of 25.6 °C for a peri od of 5 hours to ensure equilibrium. The suspension was filtered us ing 
Whatman filter paper. The first 5 mL of each filtrate was thrown away because fi lter paper is 
cellulose and can absorb some metal ions. The atomic absorption spectrophotometer was used to 
ana lyse the concentrations of metal ions present in the filtrate. The amount of concentration of the 
metal ions adsorbed Ca by the adsorbent was eva luated using Equation 2.6. 
(2.6) 
where C0 and Ce are the initia l and final concentrations (mg L-
1) of the heavy metals present in the 
metal solution before and after adsorption for a ti me t. Ce represents the concentrations (mg L-1) of 
heavy metal ions in the metal solution when equilibrium was attained. The percentage of metal 
ions removed was obtained from Equation 2.7. 
(2.7) 
where R is the removal efficiency of the adsorbent. 
Effect of contact time: The effect of contact time on the removal of the metal ions was studied 
for a period of 5 hours. 2 g of the adsorbents (PLA/EV A/SCB biocomposites) were added to 
di fferent beakers contai ning 50 mL of metal so lutions at a pH of 5. The beaker was closed with a 
sapphire, p laced in a magnetic stirrer, and agitated at 150 rpm for each of the d ifferent contact 
times chosen (30 min, I hr, 3 hr, and 5 hr). The content of each beaker was fi ltered and analysed 
a fter each agitation time. 
39 
Effect of pH: The effect of pH on the adsorption of the metal ions was studied over a pH range of 
3 to 9. For this particular study, 50 mL of metal solution was measured into di fferent I 00 mL 
beakers and 2 g of the adsorbent, being the optimum adsorbent from the previous experiment, was 
added and agitated at 150 rpm for 5 hours. The pH was adjusted using I M HC I and I M NaOH 
for each of the chosen pH values (3, 5, 7 and 9). Whatman filter paper was used to filter the mixture 
and the filtrate analysed to determine the concentrations of metal ions. 
Effect of initial concentration: The initial concentration of the metal solution was varied from 
I 00 to 400 ppm. 2 g of the adsorbents was added to different beakers containing 50 mL of metal 
solution, closed and agitated in a magnetic stirrer for a peri od of 5 hours at room temperature. The 
content of each fl ask was then filtered and analysed after the agitation time. 
Thermogravimetric analysis in a Perkin- Elmer STA6000 thermogravimetric analyser was used to 
study the thermal stabilities of the neat PLA, EVA, and SCB, and the biocomposite samples. 20-
25 mg samples were heated under a flowing nitrogen atmosphere (20 mL min-1) from 30 °C to 550 
°C at a heating rate of I 0 °C min-1, and the corresponding mass loss was recorded. 
Differential scanning calorimetry (DSC) analyses were performed in a Perkin-Elmer Pyris-1 
differential scanning ca lorimeter DSC. Samples of 5-10 mg were sealed in a luminium pans and 
heated under nitrogen flow (20 mL min-1) from -I 0 to 195 °C at a heating rate of 10 °C min-1, and 
kept at this temperature for I min to erase the thermal history. The samples were then cooled and 
re-heated under the same conditions. At least three separate measurements were made to ensure 
reproducibility. The glass transiti on, cold crystallization, and melting temperatures, as well as the 
melting and cold crystall ization entha lpies, of the samples were determined from the second 
heating runs as the average of three measurements . The degree of crystallinity was calculated using 
the total enthalpy method, according to Equation 2.8. 
X = /). H mX J 00 (2.8) c D. fl o 
Ill 
40 
where Xe is the degree of crystallinity, ~Hm is the specific entha lpy of melting of a polymer, and 
~H0m is the spec ific enthalpy of melting for 100% crysta ll ine PLA and EVA. Values of93 .0 J g·1 
and 272 J g·1 for PLA and EVA were used respective ly in the calculations. 
2.4 References 
[ I] E. Jayamani , S. Hamdan, S.K. Heng, Md. R. Rahman, M.K. Bakri , A. Kakar. The effect 
of natural fibres mercerization on natural fibres/polypropylene composites: A study of 
thermal stabi lity, morphology and infrared spectrum. Austra lian Journal of Basic and 
Applied Sciences 2014; 8:332-340. 
[2] S.M.A. Andrabi. Sawdust of lam tree (Cordia africana) as a low-cost, sustainable and 
easi ly avai lable adsorbent for the removal of tox ic metals like Pb(ll) and N i(ll) from 
aqueous solution. European Journal of Wood and Wood Products 20 11 ; 69:75-83. 
DOI: I0. 1007/s00107-009-0398-x 
[3] D. Pasquini , M.N. Belgacem, A. Gandini, Antonio A.S. Curvelo. Surface esterification of 
cellulose fibers: Characterization by DRIFT and contact angle measurements. Journal of 
Colloid and interface Science 2006; 295:79-83. 
DOI: 10. 10 I 6/j.jcis.2005.07.074 
[4] D. Wu, D. Lin, J . Zhang, W. Zhou, Ming Zhang, Y. Zhang, D. Wang, B. Lin. Selective 
localization of nanofillers: Effect on morphology and crystalli zati on of PLA/PCL blends. 
Macromolecular Chemistry and Physics 20 11; 2 12:6 13-626. 
DOI: I0. 1002/macp.201000579 
[5] X. Wang, K. Xu, X. Xu, S. Park, S. Kim. Selective particle distribution and mechanical 
properties of nano-CaC03/ethylene-propylene-diene terpolymer/polypropylene 
composites with high content of nano-CaC03. Journal of Applied Polymer Science 2009; 
11 3: 2485-249 1. 
DOI : I 0. 1002/app 
[6] H. Xiu, H.W. Bai, C.M. Huang, C. L. Xu, X.Y. Li , Q. Fu. Selective localization of titanium 
diox ide nanoparticles at the interface and its effect on the impact toughness of poly(L-
lactide)/poly(ether)urethane blends. Express Polymer Letters 2013; 7:261-271. 
DOI: I 0.3 144/expresspolyrn lett.20 13 .24 
4 1 
[7] F. Fenouillot, P. Cassagnau, J.C. Majeste. Uneven distribution of nanoparticles in 
immiscible fluids: Morphology development in polymer blends. Polymer 2009; 50: 1333-
1350 
DOI: I 0.101 6/j .polymer.2008.12.092 
[8] B. Zhao, R.W. Fu, M.Q. Zhang, H. Yang, M.Z. Rong, Q. Zheng. Effect of soft segments 
of waterborne polyurethane on organic vapour sensitivity of carbon black filled waterborne 
polyurethane composites. Polymer Journal 2006; 38:799-806. 
DOI: IO. I 295/polmj.PJ2005202 
[9] C. E. Carraher Jr. Carraher's Polymer Chemistry 81h Edition. CRC Press Taylor & Francis 
Group: Boca Raton (2011 ). 
[I OJ B.J. Hunt, M.I. James. Polymer Characterisation. Blackie Academic & Professional : 
London ( 1993). 
42 
CHAPTER3 
Results and discussion 
3.1 Selective dispersion of the SCB in the polymer blend 
The selective localization of a filler is important to the morphology design and property control of 
an immiscible polymer blend system. This selective localization behaviour mainly results from 
large differences in the affin ity between the fi ller and the two matrix components. Thermodynamic 
(surface propertie ) and kinetic (viscosity) effects are two factors involved in determining the 
selective localization of tiller in a two-phase polymer blend system. The ti ller will selectively 
locate itself in order to balance viscoelastic properties of the polymer, reduce interfacial tension 
and also reduce the surface energy of the polymer in the system. This may improve the interfacia l 
interaction between the two polymers in the system if the filler is allocated at the interface of the 
two polymers. 
Table 3.1 presents a summary of the melt-flow index (MFI), density and surface properties of PLA, 
EVA  and SCB. The results obtained help to deduce in which polymer will have the closest contact 
with the tiller. Polymers with low viscosities are said to have the ability to accommodate high tiller 
contents [ I] during melt mixing, and this should contribute to SCB diffusing into the PLA phase, 
because PLA has a higher MFI than EVA, which means that it has a lower viscosity. Mofokeng 
and Luyt [2] observed that the filler was dispersed in the polymer with the higher viscosity, which 
they explained in terms of the crystallinity of the polymer, where the filler will tend to locate itself 
on the polymer with lower crystallinity as the tiller will locate itself in the amorphous phase of the 
polymer. As shown further on in this chapter, PLA (47% crystallinity) is more crystall ine than 
EVA  ( 10% crystallinity), and therefore the high crystallinity of PLA should discourage the 
location of SCB in EV A. 
The surface energy values in Table 3. 1 were used to calculate the interfacial tension values and 
wetting coefficient in Table 3.2 according to the geometric mean equation (Equation 3.1 ) [4 -7]. 
43 
(3. 1) 
where y12 = inter fac ial tension between components I and 2 in the blend, y1 and y2 are the total 
surface energies of components I and 2, yf and yf are the di spersive surface energies of 
components I and 2, and Yi and yf are the polar surface energies of the components I and 2 in 
the composites. The calculated interfacial energy results indicate that the interfacial tens ion 
between EV A and SCB is higher than that between PLA and SCB. Although the interfacial tension 
is quite high in both cases (Table 3.2), it is lower fo r the PLA-SCB pair and therefore there is a 
slightly higher probability for SCB to have a greater affi nity fo r PLA. The wetting coeffi cient Wa 
was calculated from the Young's equation (Equation 3.2) [4 -8). 
OJa = rP LAI SCB - rE VA / SCB (3.2) 
r PLA / EVA 
where YPLA/SCB is the interfacial tension between PLA and SCB, YEVA/ SCB is the interfacial tension 
between EVA and PLA, and YPLA/EVA is the interfacia l tension between PLA and EVA. If Wa < 
- 1, the particles are predicted to be located in polymer B, in this case EVA. If Wa > 1, they are 
likely to be dispersed in polymer A, in this case PLA. If the value of Wais between - I and I, the 
particles are likely to disperse on the interface between the two polymers in the blend. In this case, 
Wa = 15.7 w hich indicates that SCB wi ll most likely be dispersed in the PLA phase. 
Table 3.1 MFI, density and surface properties of PLA, EVA  and SCB (values of SCB were 
obtained from literature 131) 
Sample Contact angle I deg Surface energy I mN m-1 MFI I Density I 
H20 CH2h y yd yP (g/10 min) g cm-3 
PLA 63. 1 ± 1.0 32.7 ± 0.4 52.8 43. 1 9.7 8.3 1.25 
EVA 69.7 ± 1.2 27.4 ± 0.4 5 1.3 45.3 6.1 1.2 0.94 
SCB 38 39 51.9 17.8 34.2 - -
y = surface energy, y d = di spersive component of surface energy, yP = polar component of 
surface energy, MFI = melt flow index 
44 
Table 3.2 Jnterfacial tension and wetting coefficient of the investigated materials 
Component couple lnterfacial tension I mN m-1 and wetting coefficient 
PLAIEVA 0.3 
PLA/SCB 12.9 
EVA/SC B 17.6 
Wa 15.7 
Wa = wetting coefficient 
To summarise, the lower viscosity of PLA, the lower interfacial tens ion between PLA and SCB, 
and the wetting coeffic ient of PLA/SCB being larger than I, all suggest that SCB would pre ferabl y 
be in contact with PLA, despite PLA ' s relati vely high crystallinity. 
3.2 Morphology 
3.2.1 Optical microscopy 
Optical microscopy was used to examine both the morphologies as well as the dispersion of the 
fibres in the polymer matrices. Figure 3. 1 shows the optical microscopy images of the 
PLA/EV A/SCB composites, Figure 3.2(a) shows that o f the PLA/SCB composite, and Figure 
3.2(b) that of the EV A/SCB composite. ln general, the images in Figure 3.1 show a good dispersion 
of SCB fibres in the polymer blend matrices for all the composite samples. Even at high contents 
of SCB, good di spers ion is observed w ith little agglomeration. The fibre lengths did not change 
during processing, indicating a low level o f fibre damage during the compos ites preparation. A 
fa irly good di spersion of SCB in the PLA matrix is observed in Figure 3.2(a), while Figure 3.2(b) 
shows that the fibre is strongly ori ented and concentrated at the edge of the EVA sheet. Both these 
observations indicate that SCB has a stronger affin ity for PLA. 
45 
Figure 3.1 Optical microscopy pictures of (a) 66.5/28.5/5 w/w PLA/EVA/SCB, (b) 
59.5/25.5/15 w/w PLA/EVA /SCB, (c) 56/24/20 w/w PLA/EVA /SCB and (d) 49/21/30 w/w 
PLA/ EV A/SCB 
Figure 3.2 Optical microscopy images of (a) 80/20 w/w PLA/SCB, and (b) 80/20 w/w 
EVA/SCB 
46 
3.2.2 Scanning electron microscopy (SEM) 
SEM was used to investigate the morphology and the possible interfacial adhesion between the 
polymers in the blends and the SCB fibre in the composites. The 50150 wlw PLA/EVA  blend in 
Figure 3.3(a) shows phase separation and a clear co-continuous morphology, though it is not 
possible to identify which phase is which directl y from the SEM images. The image shows areas 
of brittle fracture (arrow A), that are probably PLA, and areas where plastic deformation is visible 
(arrow B), that are probably EVA. The samples were fractured under cryogenic conditions for I 0 
seconds. The time used was not long enough to bring the EV A suffic iently below its T g to freeze 
all the mo lecular chain segments of the polymer, well PLA was already well below its Tg at room 
temperature. Under these conditions one could expect that EVA underwent ductile fracture, which 
showed up in the SEM images. The layer covering the fi bre (arrow C in Figure 3.3(d)) is probably 
PLA because of the stronger affi nity SCB has for PLA, as discussed in section 3. 1. No fibre pul l-
outs were observed in the images, probably because of the good wetting o f the fibre by PLA in the 
composites. However, some of the fibre ends were not covered by PLA (arrow D in Figures 3.3(c) 
and 3.3(h)) and therefore adsorption of the metal ions in contaminated water wil l probably take 
place at these fibre ends that are not smoothly covered by PLA. However, Figure 3.3(d) shows 
fibre ends covered by PLA, which may be detrimental for the effective removal of metal impuriti es 
from contaminated water. Large cavities are observed between the PLA and the EVA (Figures 
3.3(a), 3.3(c) and 3.3(d)). These cavities are important for the contaminated water to diffuse 
through the composite and come into contact with the SCB fibre, where the metal impurities can 
be adsorbed. 
47 
Figure 3.3 SEM images of the fractured surfaces of (a) 50/50 w/w PLA/EVA, (b) 47.5/47.5/5 
w/w PLA/EV A/SCB, (c) 42.5/42.5/15 w/w PLA/EVA /SCB, (d) 35/35/30 w/w 
PLA/EV A/SCB,(e) 70/30 w/w PLA/EVA, (f) 66.5/28.5/5 w/w PLA/EV A/SCB, (g) 59.5/25.5/15 
w/w PLA/EV A/SCB, and (h) 49/21/30 w/w PLA/EVA/SCB 
48 
3.2.3 Fourier-transform infrared (FTIR) spectroscopy 
FTIR analyses were carried out to examine the possible interactions between the di fferent 
components in the composites. Figure 3.4 represents the FTIR spectrum of the neat SCB, and this 
spectrum presents a typical cellulose spectrum [9-1 1]. The broad peak between 34 12 and 3444 
cm 1 is indicative of the existence of bound hydroxyl groups of macromolecular association 
(cellulose, pectin, and hemicellulose). The peaks observed at 2920 and 3930 cm- 1 can be assigned 
to the C- H stretching for both cellulose and hemicellulose. The peaks around 1650 and 1750 cm- 1 
are indicative of the free and esterified carboxyl groups in hemicellulose. The peaks at 1457 cm-1, 
1370 cm-' and 1030 cm-1 are for - CH3 asymmetric, -CH symmetric stretching, and - CH aromatic 
stretching in Iignin, respectively. The peak at 1315 cm-1 is for -CH and C- 0 stretching of the 
acetyl group in hemicellulose. The peak at 896 cm-1 is for the glucosidic li nkage [12-14]. 
The spectrum of pure E V A in Figure 3.5 shows absorption peaks around 2850 and 2920 cm-1 that 
correspond to the C- H asymmetric stretching vibrations in the polymer. The characteristic 
absorption peaks of the VA groups are as fo llows: 1736 cm-1 attributed to the stretching vibration 
of the -C=O band; 1240 cm-1 attri buted to the asymmetrical stretching vibration of the C- 0 band; 
1030 cm-1 attributed to the symmetric stretching vibration of the COC band; 7 18 cm-1 attributed to 
the inner rocking vibration of meth ylene. The absorption peaks observed around 1439 cm-1 are 
largely attributed to the contributions fro m both VA and ethylene (-CH2) units [ 15]. For neat PLA 
the absorption peaks at 2997 cm-1 and 2946 cm· ' are the -CH3 asymmetric and symmetric 
stretching vibrations. The peak at 1749 cm-1 is for-C=O, those at 1452, 1382 and 1360 cm-1 the -
C H3 and -CH bending vibrations, at 1266 cm-1 the stretching vibration of COC, those at 1 18 1, 
11 27, and 1044 cm-1 the asym metric and symmetric bending vibrations ofCOC as well as that of 
-CH3 rocking, at 956 cm· ' the C-C stretching vibration, and at 867 cm·' that of C-COO [ 16]. 
There does not seem to be any interaction between the functional groups of PLA and EV A, since 
there are no new peaks or significant peak shifts in the spectrum of the 50/50 w/w PLA/ EVA 
blend (Figure 3.5). This was to be ex pected since PLA and EVA have the same functional groups, 
except the ester group (C-COO) at 867 cm-1 that can on ly be seen for PLA. ln the case of the 
PLA/SCB and EV N SCB composites, if there was strong hydrogen bonding between PLA and 
SCB or EV A and SCB, confirmation of such hydrogen bonding may have been observed as a shift 
49 
in the carbonyl peak at 1750 cm·1• However, no shift in thi s peak was observed, and therefore the 
FTIR analyses did not provide conclusive evidence of such hydrogen bonding between the -C=O 
group on PLA and EV A and the -OH group on SCB. Contrary to our own observations, Penjumras 
and co-workers [1 7] reported shifts of the C=O peak at 1753 cm- 1and the C-0 peak at 1086 
cm- 1 for neat PLA to respectively 1770 cm- 1and I 090 cm- 1 for PLA in biocomposites, which they 
attributed to the formation of hydrogen bonding between - O H in cellulose and C=O and C-0 in 
PLA. Hydrogen bonding between the - C=O groups on PLA and EV A and the -OH group on SCB 
could also not be confi rmed for 40/40/20 w/w PLA/EV A/SCB, s ince there was also no shift in the 
carbonyl peak at 1750 cm·1 for thi s composite. 
88 
86 
~ 
c 
ro 84 
.:E::  
IJ) 
c 
.ro 
82 
........  
0~  80 
78 
76 
4000 3500 3000 2500 2000 1500 1000 
Wavenumber I cm·1 
Figure 3.4 FTIR spectrum of SCB 
50 
40/40/20 w/w PLA/EVA/SCB 
4000 3500 3000 2500 2000 1500 1000 
Wavenumber I cm·1 
Figure 3.5 FTIR spectra of the PLA/EVA  blend and the PLA/EV A/SCB bio-composites 
3.3 Impact strength 
Impact strength testing was used to analyse the mechanical properties of the PLA, EV A, PLA/EV A 
blends and the PLA/EVA/SCB composites. Figure 3.6 and Table 3.3 present the impact strength 
results of the investigated samples. The impact strength of EV A is larger than that of PLA. The 
reason is that EV A is a ductile polymer and PLA is a brittle polymer, and it is well known that 
brittle materials cannot impede crack propagation [ 18]. The 50150 wlw PLNEVA  blend is 
expected to have good impact strength properties because it contains a high EV A content, but in 
this case the 70/30 w/w PLNEV A blend has better impact strength properties. This is probably 
due to the fact that EVA  formed small inclusions in the PLA matrix in the 70/30 w/w PLNEV A 
blend, so that crazes initiated inside the polymer got terminated at the EVA inclusions, and cracks 
did not initially propagate through the polymer. The 50/50 w/w PLNEVA  had a co-continuous 
morphology with phase separation of the two polymers as seen in the previously discussed SEM 
images (section 3.2.2). The cracks between the two polymers will then develop and propagate 
along the interface between the two polymers. 
51 
------ 50/50 w/w PLA/EVA 
15 
--+- 70/30 w/w PLA/EVA 
..r:::. 
Ci 
-c 10 .Q...)  -en (.) ro 
a. 
E 
1 
5 
0 5 10 15 20 25 30 
SCB content I % 
Figure 3.6 Impact strengths of the PLA/EVA blends and PLA/EVA/SCB composites at 
different SCB contents 
The impact strength of the PLA/EVA/SCB composites decreased with an increase in SCB content 
for both blend compositions, which is not unexpected since the SCB particles probably acted as 
stress concentrators for the development of cracks. Different factors such as the fi bre selection, 
matrix selection, interfacial strength, fibre dispersion, the interaction between the fi ll er and the 
matrix, the fibre orientation, compos ite manufacturing, and porosity may contri bute to the decrease 
in the mechanical properties of the compos ites [1 9,20] . In our case, the good interaction between 
the SCB and PLA in the blend matrix (section 3.1 ), combined with the weak interaction between 
PLA and EVA (section 3.2.2), probably played the biggest role in influencing the impact stress of 
the composites. As the SCB content increased, more interfacia l voids/cavities were formed as a 
result of the separation between the PLA covered SCB and the EVA. Another reason might have 
been the fi bre o rientation within the matrix, since the best impact strength resul ts are generally 
obtained for compos ites when the fi bre is oriented perpendicu lar to the direction of impact [2 1) . 
In our case the fib res did not have a parti cular orienta tion (secti on 3 .2.1 ), and therefore there was 
little resistance against crack propagation through the sample. Hatta and Akmar [22) a lso observed 
52 
a decrease in the impact strength of the composites and they concluded that their observations were 
the resu lt of the fi bre pul l-out due to the low interfacia l strength between the fi bre and matri x. 
Table 3.3 Impact properties of all the investigated samples 
Sample Impact strength I kJ m·2 
PLA 7.0 ± 1.0 
EVA * 
50150 w/w PLA/EV A 9.2 ± 0.5 
47.5/47.5/5 w/w PLA/ EVNSCB 7. 1 ± 1.0 
45145110 w/w PLA/EVA/SCB 6.7 ± 1.2 
42.5142.5115 wlw PLA/EV N SCB 8.5 ± 0.6 
40140120 wlw PLNEV A/SCB 7.4 ± 0.6 
35135130 wlw PLNEVA /SCB 8.4 ± 0.7 
70/30 w/w PLA/ EV A 12 .8 ± 1.9 
66.5/28.5/5 w/w PLA/ EV NSCB 11.2 ± 0.8 
63/27/10 w/w PLA/ EVA/SCB 9. 1 ± 0.9 
59.5125.5115 w/w PLA/EVA/SCB 9.8 ± I. I 
56124120 wlw PLA/EV A/SCB 8.9 ± 1.3 
49/2 1/30 w/w PLA/ EVA/SCB 9.5 ± 0.4 
* Under the analysis conditions, EV A did not break 
3.4 Thermal analysis 
3.4.1 Thermogravimetric analysis (TGA) 
The TGA was used to determine the therma l stabili ty of all the investigated samples. ln the case 
of the PLA, the TGA curve shows one degradation step at 35 I °C that is the main cha in 
decomposition (Figu re 3. 7). EV A shows two degradation steps at 356 and 460 °C related to the 
removal of acetyl groups and the main chain decomposition, respectively [23,24]. The SCB fi bre 
shows three degradation steps. The fi rst step below I 00 °C corresponds to the evaporization of 
moisture fro m the sample, while the step around 337 °C corresponds to the therma l decomposition 
of hemicellulose and the glycosidic links of cellulose. The step around 455 °C is the result of the 
thermal decomposition of non-cellulosic substances such as lignin [25-27]. SCB normall y forms a 
char that is the result of the exothermic reaction between the glycoladehyde and levoglucosan 
formed by the decomposition of cellulose [28]. In our case, however, there was no thermally stable 
residue up to the max imum temperature o f the ana lysis. 
53 
The PLNEV A blends and PLNEV NSCB composites show two decomposition steps (Figure 
3.8). The first step is a combination of PLA degradation, EVA deacetylation , and the first main 
step of the SCB degradation. The second step is a combination of the degradation of the EV A 
backbone and the lignin from the SCB. The presence of SCB generall y decreases the thermal 
stabi lity of the composite samples (Table 3.4) because of the lower thermal stability of the fibre. 
However, the thermal stability of the composites is higher than that of the SCB, because the higher 
thermal stabil ity polymer matrix protects the SCB from decomposing at its usual decomposition 
temperature. 
It is known that after the deacetylation of EV A, polyene is formed, the degradation of which g ives 
rise to the formation of aromatic and aliphatic volatiles, C02 and H10. The aromatic volati les 
originate from the deacetylated VAc entities, while the aliphatic volatiles are formed by the chain 
scission reactions in polyene (29]. The SCB char probably delays the degradation of polyene in 
the composites, or the diffusion of the volatile (aromatic and aliphatic) degradation products out 
of the degrad ing sample, which is een as an increase in the temperature of the mass loss step 
between 400 and 500 °C with an increase in SCB content. 
Table 3.4 TGA results for investigated samples 
Sample T1/ °C Ti/°C 
PLA 350.7 
EVA 355.7 460.2 
SCB 336.9 455.0 
50150 wlw PLA/EV A 366.3 472.2 
47.5/47.5/5w/w PLA/EVA/SCB 350.6 467.8 
45/45/ I Ow/w PLA/EV A/SCB 352. 1 466.2 
42.5/42.5/ l 5w/w PLA/ EV NSCB 345 .5 476.7 
40/40/20w/w PLNEV A/SCB 335 .0 480.34 
35/35/30w/w PLNEV NSCB 326.I 482.6 
70/30 w/w PLNEV A 362.6 475 .9 
66.5/28.5/5w/w PLNEV NSCB 349.9 474.4 
63/27/ IOw/w PLA/EVNSCB 347.7 480.3 
59.5/25.5/ 15w/w PLNEVA/ SCB 335 .0 481.1 
56/24/20w/w PLNEV NSCB 332.0 479.6 
49/2 l/30w/w PLNEV NSC B 320.0 475.2 
T 1andT2 are the temperatures of the peak maxima of the first and second peak in the derivative TGA curves 
54 
100 (a) 
80 
60 
0~  
(/) 
(/) 
C'O 
::? 40 
20 
-PLA 
- EVA 
0 - SCB 
100 200 300 400 500 600 
Temperature I °C 
0 
-5 
0~  
Cf) -10 
Cf) 
C'O 
-E -15 0 
Q) 
> 
+:; -20 
C'O 
·>c  
Q) 
0 -25 
-30 - PLA 
- EVA 
- SCB (b) 
-35 
100 200 300 400 500 600 
Temperature I °C 
Figure 3.7 (a) TGA and (b) derivative TGA curves of PLA, EVA and SCB 
55 
100 (a) 
80 
60 
0~  
(J) 
(J) 
co 
~ 40 
- - 70/30 w/w PLA/EVA 
-- 66.5/28.5/5 w/w PLA/EVA/SCB 
20 --63127/10 w/w PLA/EVA/SCB 
-- 59.5/25.5/15 w/w PLA/EVA/SCB 
--56/24/20 w/w PLA/EVA/SCB 
0 --49/21/30 w/w PLA/EVA/SCB 
100 200 300 400 500 600 
Temperature I °C 
0~  
(J) 
(J) 
co 
-E -10 0 
(I) 
.~ 
-ro 
·;>;:  -- 70130 w/w PLA/EVA 
(I) -15 -- 66.5128.5/5 w/w PLA/EVA/SCB 
0 
--63/27/10 w/w PLA/EVA/SCB 
-- 59.5125.5/15 w/w PLA/EVA/SCB 
-- 56124/20 w/w PLA/EVA/SCB 
--49/21/30 w/w PLA/EVA/SCB (b) 
100 200 300 400 500 600 
Temperature I °C 
Figure 3.8 (a) TGA and (b) derivative TGA curves of 70/30 w/w PLA/EVA and its bio-
composites 
56 
3.4.2 Differential scanning calorimetry 
DSC analysis was performed to characteri ze the thermal behaviour of the samples used in thi s 
investigation. All the reported DSC heating results were obtained from the second scan to eliminate 
the effect of thermal history. The normalised melting and crystallization enthalpy values shown in 
Tables 3.5 and 3.6 were determined according to Equations 3.3 and 3.4. 
(3.3) 
L\Hcn  = L\HJ w (3 .4) 
where Hm" and He" are the melting and crystallization entha lpies normalised with respect to the 
amount of the respecti ve polymer in the sample, L\Hm and L\Hc are the melting and crystallization 
enthalpies o f the respecti ve polymers, and w is the mass fraction of that po lymer in the blend or 
composite. 
1.2 ~-------------------
- PLA 
a. - EVA 
::> 1.0 - 50/50 w/w PLA/EVA 
.g - 42.5/42.5/15 w/w PLA/EVA/SCB 
c - 35/35/30 w/w PLA/EVA/SCB 
~ 
0.8 
Cl 
~ 0.6 
0 
;: 
iii 
al 0.4 
~ 
"O 
al 
~C1l  0.2 
.E...  
0 
z 0.0 +------- --------
20 40 60 80 100 1W 1~ 1W 1W 
Temperature I °C 
Figure 3.9 DSC second heating curves of the neat PLA, neat EVA, the 50/50 PLA/EVA 
blend and composites based on this blend 
57 
The PLA shows a melting temperature of 176 °C and a crystallization temperature of 13 1 °C, and 
it does not show any cold crystallization exotherms (Figure 3.9). There is also a good correlation 
between its crystallization and melting enthalpies (Table 3.6), which indicates that the polymer 
crystalli zed completely on coo ling. The same is true for EVA that melts around 87 °C and 
crysta lli zes around 70 °C (Table 3.5). The PLA/EVA blends show two melting peaks at 
approximately the same temperatures as those of the neat polymers, which confirms the complete 
immiscibility of PLA and EVA at all the investigated compositions. 
In the 50/50 w/w PLA/ EVA blend (figure 3.9) the heating curve shows two crystallization 
exotherms, one j ust after the melting of EVA and the other one just before the melting of PLA. 
These may be related to the re-crystallization of a fraction of the molten EVA, co ld crystallization 
of the PLA amorphous fractions because of more free volume created by the mo lten EVA , or co-
crystallization o f certain EVA and PLA fractions. Inspection of the di fferent melting and 
crystallization enthalpies shows that there are significant differences between the me lting and 
crystallization enthalpies of EVA in the blend . The sum of the cold crysta llization entha lpies and 
the PLA crystallization entha lpy is also not equal to the melting enthal py of PLA in the blend. 
These di screpancies indicate that the crystallization and melting of respective ly EV A and PLA in 
the 50/50 w/w PLA/EV A blend are influenced in a complex way by the presence of the other 
polymer. 
In the case of the 70/30 w/w PLA/EVA blend (Figure 3.10) the first cold crysta lli zation exothenn 
is absent. This is probably related to the morphology of this blend compared to that of the 50/50 
w/w PLA/EVA blend. The 50150 w/w PLA/EVA blend has a co-continuous morphology, while in 
the 70/30 w/w PLA/EVA blend the EVA is di spersed as spheres in the PLA continuous phase as 
observed in the SEM photos (section 3.2.2). 
The presence of the fibre in the composites also has an influence on the appearance of the co ld 
crystallization peaks, although this influence cannot be directl y related to the polym er ratio or the 
amount of fibre in the respective composites. S ince PLA is expected to be more attracted to the 
fibres, the crystallization of the PLA on the fibre surfaces, and changes in the morphology as a 
result of thi s, may influence the crystallization during heating in a complex way. 
58 
1.2 --- --------------------, 
- PLA 
- EVA 
§" 1.0 - 70/30 w/w PLA/EVA 
o - 59.5/25.5/15 w/w PLA/EVNSCB 
-g - 41 /21/30 w/w PLA/EVNSCB 
~ 0.8 
Ol 
~ 
0.6 
3: 
0 
<;:::: 
-m 0.4 
£ .L-~~----:::::="::?"~ 
.~~  0.2 ~==========::::::=---
.E 
0 
z 0.0 +----------------
20 40 60 80 100 120 140 160 180 
Temperature I °C 
Figure 3.10 DSC second heating curves of the neat PLA, neat EVA, the 70/30 PLA/EVA 
blend and composites based on this blend 
0.0 
~ 
Cl. 
::I 
0 -02 
"O 
c 
~ 
'7 
Ol -0.4 
~ 
3: -0.6 
0 
c;:: 
-ro 
<l> 
£ -0.8 
"O 
<l> - PLA 
-~ 
.E - EVA -1.0 - 50/50 w/w PLA/EVA 
z0  - 42.5/42.5/15 w/w PLA/EVNSCB 
- 35/35/30 w/w PLA/EVNSCB 
-1.2 
20 40 60 80 100 120 140 160 
Temperature I °C 
Figure 3.11 DSC cooling curves of the neat PLA, neat EV A, the 50/50 PLA/EV A blend and 
composites based on this blend 
59 
In comparing the normalised melting enthalpies of PLA in the different samples, there are 
differences but no trend, and one can therefore conclude that neither blending, nor the ratio of the 
polymers in the blends, nor the presence and amount of fi bre in the composites, had a significant 
influence on the crystallinity of PLA. The same can be said for the EVA crystallinity. 
The crystallization temperature of PLA is around 13 1 °C and that of EVA around 70 °C (Tables 
3.5 and 3.6). The PLA/EVA blend shows two crysta llization peaks, which confirms the 
immiscibility of the two polymers. Inspection of the cooling curves shows little change in the 
crystallization temperatures of EVA (Figures 3. 11 and 3.12), which means that neither the 
presence of crysta ll ized PLA nor the presence of fibre had an influence on the crysta llization 
behaviour of EV A. PLA, on the other hand, crystall ized at significantly lower temperatures, 
probably because the molten EV A acts like a plasticizer and creates more free volume for the 
movement of the PLA chains. 
0.0 
a: 
::J -0.2 
0 
'O 
c: 
~ -0.4 
'7 
C> 
~ 
-0.6 
~ 
0 
c;:: 
(ii 
Q) -0.8 
.c 
'O - PLA 
Q) - EVA 
.~E  -1.0 - 70/30 w/w PLA/EVA 
0 - 59.5/25.5/15 w/w PLA/EVA/SCB 
z - 49/21/30 w/w PLA/EVA/SCB -1.2 
20 40 60 80 100 120 140 160 
Temperature I •c 
Figure 3.12 DSC cooling curves of the neat PLA, neat EV A, the 70/30 PLA/EVA blend and 
composites based on this blend 
60 
Table 3.5 Melting and crystallization temperatures and enthalpies of EVA  in the blends 
and composites 
Sample Tc/°C AHc/ J g·1 AHc" I J g·1 Tm/°C ~Hm I J g·1 ~Hm" I J g·1 
EVA 70.2 ± 0.1 28.2 ± 0.4 28.2 87.4 ± 0.3 27.2 ± 1.3 27.2 
50150 w/w 67.7± 0.2 18.6 ± 2.8 37.2 84.7 ± 0.7 12.6 ± 1.4 25.2 
PLA/EVA 
42.5/42.5/15 w/w 68.4 ± 0.2 13.3±0.7 31.3 85.5 ± 0.0 10.9 ± 1.2 25.6 
PLA/EV A/SCB 
35/35/30 w/w 68.3 ± 0.4 I 0.4 ± 0.8 29.7 85.5 ± 0.0 IO.I ± 0.6 28.9 
PLAIEV A/SCB 
70/30 w/w 66.9 ± 0.2 8.6 ± 0.4 28.7 85.4 ± 0.4 7.8 ± 0.2 26.0 
PLA/EVA 
59.5/25.5/ 15 w/w 67. 7 ± 0.3 7.5 ± 0. 1 29.4 84.7 ± 0 .9 8.5 ± 0.5 33.3 
PLA/EV A/SCB 
49/21/ 30 w/w 69.3± 0.1 6.0 ± 0.3 28.6 86.5 ± 0.9 5.6 ± 1.2 26.7 
PLA/EV A/SCB 
Tm - melting peak temperature; t:Ulm - melting enthalpy;~Hm"- melting enthalpy normalised with respect to amount 
of EV A; Tc - crystallization peak temperature, t:Ulc- crystall ization enthalpy, ~l lc"- crystallization enthalpy 
normalised with respect to amount of EV A 
61 
Table 3.6 Melting and crystallization temperatures and enthalpies of PLA in the blends and composites 
Sample .1.H<'' I Tce lPLAI ~Hcc1 I ~Hee l" / Tcci/ °C ~Hcc2 I ~Hcc2" ~Hm" I 
Tc/°C .1.Hc/ J g·1 oc Tm/°C ~Hm I J g·
1 
Jg·• J g·I Jg·• J g·• I Jg·• J g·• 
PLA 13 1.1 ± 0 .7  43.6 ± 3.6 43.6 - - - - - - 176.4 ± 0.1 46.9 ± 0.2 46.9 
50150 wlw 
102.7± 1.1 6.7 ± 0.3 13 .4 I 02.4 ± 0.3 5.2± 1.4 10.4 159.6 ± 0.2 2.1 ± 0.6 4.2 174.8 ± 0.4 24 .5 ± 0.6 49.0 
PLNEVA 
42.5/42.5/ 15 w/w 
104.8 ± 0.4 8.6 ± 0.7 20.2 10 1. 1 ± 0.8 1.7 ± 0.3 4.0 160.9 ± 0.4 1.6 ± 0 .3 3.8 175.7 ± 0.4 21.3 ± l.l 50.1 
PLA/ EVNSCB 
35135130 w/w 
107.0 ± 0.2 10.3 ± 0.5 29.4 - - - 162.5 ± 0. 1 0.7 ± 0. l 2.0 174.9 ± 0.2 16.0 ± 0.6 45.7 
PLA/EVNSCB 
70/30 w/w 
106.6 ± 0.3 24.4 ± 1.2 34.9 - - - 163.3 ± 0.8 2.3 ± 0.4 3.3 177.7±0.8 32. 1 ± 0.7 45.9 
PLNEVA 
59.5/25. 5/1 5 w/w 
105.7 ± 1.0 21.9 ± 0.9 36.8 - - - - - - 172.6 ± 0.2 33.9 ± 0.6 57.0 
PLA/EYNSCB 
49/2 1/ 30 w/w 
107.6 ± 0.1 18.3 ± 0.7 37.3 - - - 165.0 ± 0.5 0.9 ± 0.3 1.8 176.8 ± 0.4 24.6 ± 0.8 50.2 
PLA/EVNSCB 
T.n- melting peak temperature; Tee - cold crystallization temperature; ~Hm- melting enthalpy; ~Hee cold crystal lization enthalpy; ~l lm"- melt ing enthalpy normalised with 
respect to amount o f PLA; ~Hcc"-cold crystallization enthalpy normalised wi th respect to amount of PLA; Tc crystallization peak temperature; W e- crystallization enthalpy; 
~Hc"-crystallization enthalpy normalised with respect to PLA; 1 and 2 after cc indicate first and second cold crystallization peak 
62 
3.5 Water absorption 
Water absorption analysis was used to assess the absorption efficiency of the PLNEVN SCB 
composites. The amount of water absorbed in the composites was calculated from the weight 
di fference between the samples exposed to water and the initially weighed samples (Equation 
3.5) [30-33]. 
%W= w , -W; x 100 (3.5) 
W ; 
where % W is the percentage water absorbed, Wt is the fi nal weight of the sample after a certain 
time t of water immersion, and Wi is the initial sample mass. It was found by other researchers 
[30-34] that there are three ways in which water molecules can enter polymer composites, i.e. 
diffusion, capillary transport and transport due to micro-cracks/micro-voids. In our case, micro-
cracks/micro-voids was the most probable mode of water absorption by the composites, 
because of the obvious voids observed in the SEM photos of the investigated samples (section 
3.2.2). 
Both graphs in Figure 3 . 13 depict an increase in water absorption with an increase in SCB 
loading. This is due to more hydrophilic fibre introduced in the composites, since the absorbed 
water will be retained in the inter-fi brillar space of the cellulosic structure of the fi ller, as well 
as in the interface and micro-voids present in the composites. Another observation is that the 
composites prepared from the 50/50 w/w PLA/EV A blend absorbed more water than those 
prepared from the 70/30 w/w PLA/EV A blend. This is due to the weak interaction between the 
two polymers (section 3.2.2) resulting in more voids/cavities in the 50150 w/w PLA/EVA  blend 
that will more easi ly transport the water to the fibres, and in which more water wi ll be trapped. 
63 
- 50150 w/w PLA/EVA (a) 
14 - 42.5/42.5115 wfw PLA/EVNSCB 
__..,__ 40/40/20 wfw PLA/EVNSCB 
12 ~ 37/35/30 w/w PLA/EVNSCB 
c 
a0 ..... 10 
0 
.2 8 
(I) 
..... 
Q) 
-ro 6 
~ 
~ 4 
2 
0 ...... • • 
10 20 30 40 50 60 70 80 90 100 110 120 130 
Time I hours 
- 70/30 w/w PLN EVA 
- 59.5/25.5/15 w/w PLNEVNSCB (b) 
10 __..,__ 56/24/20 w/w PLA/EVNSCB 
~ 49/21 /30 wfw PLA/EVNSCB 
§ 8 
a.....  
0 
.2 6 
(I) 
..... 
Q) 
-ro 4 
~ 
;:,l2 
0 
2 
0 
20 40 60 80 100 120 
Time I hours 
Figure 3.13 Water absorption curves of the blends and composites based on (a) 50/50 and 
(b) 70/30 w/w PLA/EVA 
64 
3.6 Atomic absorption spectroscopy (AAS) 
AAS analys is was used to determine the adsorption capacity of SCB fibre and the 
PLA/EVA/SCB composites on aqueous media. Natural fibres were used for metal adsorption 
because of their functional groups seen in FTIR (section 3.2.3) that have an affin ity for metal 
complexation. In our case, metal complexation and micro cracks in the composites (observed 
in the SEM photos (section 3.2.2)) will both contribute to the effective removal of lead from 
water. Different parameters have been evaluated in the adsorption capacity of SCB and the 
PLNEV A/SCB composites i.e. initial concentration, pH level and the contact time. The 
normalised adsorption values shown in Tables 3. 7 to 3.9 were determined according to 
Equation 3.6. 
Ca" = Cal(wpvs) (3.6) 
where Ca" is the concentration adsorbed normalised to the amount of the pure SCB in the 
sample, and to the mass of sample used in the test, Ca is the concentration adsorbed, Wf is the 
mass fraction of SCB in the composite, and Ws is the sample mass used in the test. 
Normally one would not expect the PLNEV NSCB composites to adsorb more lead than the 
pure SCB fibre, because the fibre in the composites is covered by polymer, and the only access 
to the fibre is through the micro cracks in the composites. However, inspection of the values in 
Tables 3.7 to 3.9 shows that in some cases more metal was removed by the composites than by 
the neat fibre. Possible reasons for thi s observation are that (i) it was di fficult to completely 
immerse the fibre , which formed the control samples, in the metal ion solution and they could 
therefore not optimally adsorb the metal ions from the solution, and (ii) metal ions could have 
been adsorbed onto the polymer surfaces through their interaction with the functional groups 
on the polymer chains. The 50/50 w/w PLA/ EV A samples have a more co-continuous 
morphology than the 70/30 w/w PLNEV A samples. They should therefore have more 
continuous pathways between the two incompatible polymers that should allow more effective 
penetration of the solution to reach the fibres in the composite. However, inspection of the 
values in Table 3.7 shows that this is not necessari ly true, and there is no direct correlation 
between the amounts of metal removed from the solutions and the respective composite 
morphologies. 
65 
The concentration adsorbed by neat SCB increased with an increase in initial metal 
concentration in the so lution , but approaches saturation at the higher initial concentrations 
(Table 3.7). This may be due to a limited number of adsorption s ites on the fibre that are 
saturated at a certain metal ion concentration. Above this concentration the fibre does not 
adsorb more metal ions if mono-layer adsorption takes place. Based on the results for neat 
SCB, one would expect an increase in the adsorption of the metal impurities with an increase 
in the initial concentration in the composites as well. However, thi s was not generally observed 
(see values marked with an asterisk in Table 3. 7), and it was not possible to repeat the analyses . 
However, a higher adsorption values was observe for the 400 ppm sol ution, which was 
expected due to the larger amount of metal impurities avai lable for adsorption. In the case of 
the composites the efficiency of water diffusion through the sample (which is determined by 
the sample morphology and presence of micro-cracks), and the extent to which the SCB is 
exposed to these micro-cracks, play a much more dominant role. 
Table 3. 7 AAS results of all investigated samples at different initia l concentrations 
Samples (w/w Initial Pb Adsorbent Concentra tion Concentration Pb adsorbed, 
PLA/EVA /SCB) concentration sample Pb adsorbed normalised to amount of fibre in 
/ ppm mass (w) I g (Ca) I ppm sample and amount of sample 
used in test (Can) I oom i:?" 1 
01011 00 100 0.5 80.4 160.8 
0/0/ 100 200 0.5 177.5 355 .0 
0/0/ 100 300 0.5 233.2 466.4 
0/0/ 100 400 0.5 242.0 484.0 
42.5/42.5/ 15 100 2.011 5 52.8 175.0 
42.5/42 .5/ 15 200 2.0625 49.9• 161.3* 
42.5/42 .5/ 15 300 2.0 195 52.0* 17 1. 7* 
42.5/42.5/ 15 400 2.0890 2 15.3 7 12.6 
35135130 100 2.0040 80.9 134.6 
35135130 200 2.0729 52.8• 84.9* 
35135130 300 2.0642 63.9• 103.2* 
35/35/30 400 2.0494 2 12.9 340.4 
59.5125.5115 100 2.0452 82.8 269.9 
59.5/25.511 5 200 2.0806 77. 5* 248.3* 
59.5125.5115 300 2.0676 75.2• 242.5* 
59.5/25.5/ 15 400 2 .0188 272.5 899.9 
49/21 /30 100 2.0607 90.5 146.4 
49/2 1/30 200 2.0958 75.9* 120.7* 
49/2 1/30 300 2.0545 4 7. 1*  76.4* 
4912 1130 400 2.0665 288.7 475.3 
. . . 
At d1f ferent mtt1al concentrations, pH 5 and 5 hour of contact time were used . 
66 
It is observed (Table 3.8) that the Can values are of the same order of magnitude for the same 
sample composition, with no trend in the extent of adsorption . At least one value (marked with 
an asterisk) was too high to make sense in this system . With this system as well, the efficiency 
of water di ffusion through the sample (which is determined by the sample morphology and the 
presence of micro-cracks), the extent to wh ich the SCB is exposed to these micro-cracks, and 
poss ible adsorption on the surfaces of the matrix polymers, probably played a much more 
dominant role, although the hydronium ions (H30 +) in the lower pH so lutions may have 
influenced the adsorption efficiency. The metal ions will have to compete with these 
hydronium ions for the adsorbent sites, or the functional groups in SCB may be protonated at 
these pH levels, and hence rendered unavailable for ion exchange and complexation with the 
metal ions. At the higher pH levels the metal ions may start to prec ipitate, which wi ll reduce 
the efficiency of using SCB as an adsorbent. 
Table 3.8 AAS results of a ll investigated samples at different pH level 
Samples (w/w pH Ad sorbent Concentration C oncentration Pb ad sorbed, 
PLA/EV A/SCB) sample mass Pb adsorbed normalised to amount of fibre in 
(w)/g (Ca) I ppm sample a nd a mou nt of sample used 
in test (Con) I nnm 2 · 1 
01011 00 3 0.5 232.8 465.6 
01011 00 5 0.5 242.0 484.0 
01011 00 7 0.5 2 11 .5 423 .0 
01011 00 9 0.5 195.2 390.4 
42.5/42.5/15 .")'  2.0792 200.0 641.3 
42.5/42.5/ 15 5 2.0 142 215 .3 7 12.6 
42.5/42.5115 7 2.0966 189.4 602.2 
42.5/42.5/15 9 2.0535 173 .7 563.9 
35/35/30 3 2.001 8 174.8 291 . 1 
35/35/30 5 2.0872 2 12.9 340.0 
35/35/30 7 2.0428 174 .8 285.2 
35/35/30 9 2.06 14 160.5 259.5 
59.5/25 .5/ 15 3 2. 10 18 111 .6 354.0 
59.5/25.5/15 5 2.0 188 2 72 .5 899.9* 
59.5/25 .5/ 15 7 2.0451 66.9 21 8. 1 
59.5/25 .5/ 15 9 2.01 88 53.9 17 1.4 
49/2 1/30 3 2 .0473 97.9 159.4 
49/21/30 5 2 .0665 288.7 475 .3 
49/2 1/30 7 2.0837 67.8 108.5 
49/2 1/30 9 2 .0335 39. 1 64. 1 
At d ifferent pl I leve ls , 400 ppm initial concentration was used and 5 hours contact time. 
An increase in the contact time generally resulted in an increase in the concentration per gram 
adsorbed (Table 3.9) for the composites, although the increase is fa irly slow between 60 and 
300 minutes. The diffusion of water is obviously relatively s low through the micro-cracks in 
the blend composite samples, with the optimum adsorption being reached at times longer than 
67 
60 minutes of insertion in the metal ion solution. Contact time had little influence on the 
adsorption effi ciency o f the neat fibre, although a slight increase was observed. This is probably 
due to some penetration of the water in between the fibre fibri ls that allowed access to some 
hidden adsorption s ites. 
Table3.9 AAS results of all investigated samples at different contact time 
Samples (w/w Contact Adsorbent C oncentration Concentration Pb adsorbed, 
PLAlEV AlSCB) time (min) sample Pb adsorbed (Ca) norma lised to amount of fibre in 
mass (w) I g I ppm sample a nd amount of sa mple 
used in test (Can) I nnm it ' 
01011 00 30 0.5 206.5 4 13.0 
0101100 60 0 .5 2 11.4 422.8 
0/0/ 100 180 0 .5 2 17.3 434 .6 
0/0/ 100 300 0.5 242 .0 484 .0 
42 .5/42 .5/ 15 30 2.0258 40.4 133.0 
42.5/42.5/ 15 60 2.0427 183.3 598.2 
42.5/42.5/15 180 2.054 1 207.2 672.5 
42.5/42.5/ 15 300 2.0334 2 15.3 712 .6 
35/35/30 30 2.08 58.5 93.8 
35/35/30 60 2.0228 189 .8 3 12.8 
35/35/30 180 2.0532 195.2 3 16 .9 
35/35/30 300 2.0523 2 12 .9 340.0 
59.5/25.5/15 30 2. 1144 30.6 96.5 
59.5/25.5/15 60 2. 1096 163.3 516. l 
59.5/25.5/ 15 180 2.006 19 1.9 637.8 
59.5/25.5/ 15 300 2.0 188 272. 5 899.9* 
49/2 1/30 30 2.03 14 15 1.2 248. 1 
49/2 1/30 60 2.0372 256.6 4 19.9 
49/2 1/30 180 2.0456 274.1 446.6 
49/2 1/30 300 2.0665 288. 7 475.3 
At different contact times, initial concentration used was 400 ppm and 5 pH level 
It is observed from the results above that not only the SCB within the composites is responsible 
for the adsorption of the metal impurities, since the results on the composites show values 
comparable to or even higher than that o f pure SCB. Some of the metal impurities probably 
remain trapped inside the cavities/voids and one or both of the polymers could have played a 
role in the meta l complexation process, since both polymers do have functional groups that 
could interact w ith and adsorb the metal impurities . 
Adsorption isotherms 
An adsorption isotherm equation is an expression of the relation between the amount of solute 
adsorbed and the concentration of the solute in the fluid phase, and it is important in describing 
how adsorbates wi ll interact with adsorbents, and so is crit ical fo r design purposes. Two 
68 
isotherm equations were adopted in th is study, the Freundl ich and Langmuir isotherms. The 
equ ilibrium adsorption capacity qe (mg g-1) was calculated according to Equation 3.8 [35-42]: 
(3.8) 
w here C0 and Ce (ppm or mg L-
1
) were the initial and final concentrations of lead, respecti vely. 
V (L) is the volume of the solution, and W a (g) is the actual mass of SCB used . 
Freundlich 
The Freundlich sorption isotherm, one of the most widely used mathematical descriptions, 
gives an expression encompassing the surface heterogeneity and the exponenti al di stribution 
of active sites and their energies. 
The Freundli ch isotherm is de fined as [35-42]: 
(3.9) 
and the linearized form is: 
I 
logq = logK F+ (- (3.10) 
e n ) logC e 
where Ce is the equilibrium concentration in mg L-1 (AAS reading after removing immersed 
sample), qc is the amount of adsorbate adsorbed per unit weight of adsorbent mg g- 1, KF is a 
parameter related to the temperature, and n is a characteri stic constant for the adsorption system 
studied . The va lue of n indicates a favo urable adsorption when I < n < I 0, and it is more 
favourable if Jin < 1. The plots of log Qc against log Cc are shown in Figure 3. 14. The 
Freundl ich isotherm constants and their correlation coeffi cients R2 are listed in Table 3. 10. It 
is not possible to put a straight line th rough the values of pure SCB in the graph, so the 
Freundli ch isotherm cannot describe these points, probably because adsorption did not take 
place heterogeneously on the fibre surface. This was confirmed when apply ing the Langmuir 
isotherm, which assumes monolayer adsorption and which fitted the data much better. 
69 
2.0 
1.9 • SCB • 42.5142.5115 w/w PLAIEVAISCB 
1.8 ,",' 35135/30 w/w PLA/EVAISCB 59.5/25.5115 w/w PLAIEVAISCB 
1.7 • 49121/30 wlw PLAIEVA/SCB • • 
1.6 
• 
1.5 
~ 
O" 1.4 
Ol 
..Q 
1.3 
1.2 • • • 
1.1 
1.0 
0.9 • 
0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 
log c. 
Figure 3.14 Freundlich plots from which the data in Table 3.7 were obtained 
Table 3.10 Freundlich isotherm constants for the sorption of lead Pb(ll) ions by the 
different composite samples 
Freundlich constants 
Samples (w/w 
n Ri 
PLA/EV A/SCB) Kr 
0/0/ 100 - - -
42.5/42.5/ 15 18.6209 -50.5051 0.2310 
35/35/30 17.330 1 -9.9899 0.4906 
59.5/25.5/15 3 1.2536 -20.0803 0.9442 
49/2 1/30 20.8593 -6.8446 0.7 173 
Langmuir 
The Langmuir equation is based on the assumptions that maximum adsorption corresponds to 
a saturated mono- layer of adsorbate molecules on the adsorbent surface , that the energy of 
adsorption is constant, and that there is no transmigration of adsorbate in the plane of the 
surface. 
The Langmuir isotherm is defined as [35-42) : 
70 
(3 .11 ) 
and the linearized form is : 
(3 .1 2) 
where qm and b are Langmuir constants related to the sorption capac ity and sorption energy, 
respectively, Cc is the equilibrium concentration in mg L-1, and qc is the amount of adsorbate 
adsorbed per unit weight of adsorbent mg g-1• RL in Table 3. 11 is a dimensionless separation 
factor wh ich indicates the favourabil ity and the capacity of the adsorption system, and it is 
obtained from Equation 3. 13 [35-42]. 
(3. 13) 
The RL value indicates the adsorption nature to be either unfavourable (RL> I), linear (RL = I), 
favourab le (0 <RL<  I) or irreversible (RL = 0). 
The plot of Celqc against Cc is shown in Figure 3. 15. The adsorpti on of lead Pb( l I) ions on the 
different adsorbents gives a straight line. lt is clear that the linear fit is fai rl y good and enables 
the applicability o f the Langmuir model. The Langmuir isotherm constants and their corre lation 
coefficients R2 are listed in Table 3. 11 . As can be observed, experimental data were better fitted 
to the Langmuir equation than to the Freundlich equation. The sorption process of metal ions 
on composites fo llows the Langmuir isotherm model, w here the metal ions are taken up 
independently on a single type of binding site in such a way that the uptake of the first metal 
ion does not affect the sorption of the next ion. For the two studied systems, the Langmuir 
isotherm shows more significant correlation (R2> 0.99) than in the case of Freundlich isotherm. 
The sorption capacity qm is high for neat SCB and decreases for the composites, wh ich is to be 
expected because the neat SCB was complete ly exposed to the metal ion solution. It was 
ex pected that the sorption capacity of the composites containing 30% of SCB w ill be higher 
71 
than that of the composites containing 15% of SCB, but the opposite was observed (Table 
3.11 ). The sorption energy b was used to calculate the dimensionless separation factor RL. T he 
separation factor RL indicates that the adsorption nature is favourable for the pure SCB as well 
as the composites since for all the samples 0 <RL<  1. The pure SCB shows a sign ificantl y 
higher value than the composites, which means that the pure SCB more effective ly adsorbs the 
metal ions, which is according to expectation. 
100 
• SCB 
• 42.5/42.5/15 w/w PLNEVNSCB 
4 35/35/30 w/w PLNEV NSCB 
80 T 59.5/25.5/15 w/w PLNEVNSC 
+ 49/21 /30 w/w PLNEVNSCB 
60 
'...J 
-Cl .. 40 
.!;!..  
() • 
20 
0 
0 50 100 150 200 250 
C I mg L·1 
e 
Figure 3.15 Langmuir plots from which the data in Table 3. 7 were obtained 
Table 3.11 Langmuir isotherm constants for the sorption of lead Pb(ll) ions by different 
composite samples 
Langmuir constants 
Sample (w/w 
Qm b RL Ri 
PLA/EVA/SCB) 
0/0/ 100 29.4 0.0 11 4 0.4673 0.9982 
42.5/42.5/ 15 16.7 2.8113 0.0035 0.9984 
35/35/30 10.6 0.0964 0.0940 0.9823 
59.5/25.5/ 15 22.8 0. 149 1 0.0629 0.9983 
49/2 1/30 8.6 0. 1080 0.0847 0.9553 
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77 
CHAPTER4 
Conclusions 
The purpose of thi s project was to prepare polymer/natural fi bre compos ites to be used in water 
pu rificati on applications, specifically to remove lead ions from contaminated water. PLA/EVA 
blends (as control samples) and PLA/EV A/SCB composites were successfull y prepared by 
melt mixing. The results show that SCB had a stronger affinity for PLA than for EV A. PLA 
and EV A were also completely immiscible, with the 50150 w/w PLAIEV A sample showing a 
co-continuous morphology and the 70/30 w/w PLA/ EV A sample showing EV A dispersed as 
small spheres in the continuous PLA phase. Good wetting of the SCB fibre by the PLA was 
observed in the composites, but exposed fi bre ends were observed in some SEM pictures which 
would add to the effi ciency of metal adsorption. 
The two polymers in the blend seemed to have protected the SCB from thermal degradation, 
because the mass loss of SCB degradation products was only observed at higher temperatures 
when incorporated in the blends. Although this behaviour may imply that the prepared 
compos ites can be used at temperatures above 200 °C, which is the degradation temperature of 
pure SCB, it is also possible that the release of the volatil e SCB degradation products was 
delayed as a result of interaction w ith one or both polymers. The impact properties depended 
more on the PLA:EVA ratio than on the presence of SCB. 
The mam aim of thi s research was to formulate effective and environmentally fri endl y 
biocomposites for the removal of lead from contam inated water. The goal was successfull y 
achieved, since a ll the investi gated amples adsorbed the lead. It was observed that more lead 
was adsorbed than one would expect if the partial coverage of the fibre by polymer is taken 
into account, and therefore it may be assumed that some of the lead was trapped inside the 
cavities in the composites and that the polymers may also have played a role in the metal 
complexation process, since both polymers have the functional groups that could interact wi th 
the lead ions. It was found that monolayer adsorption was predominant, since the data best 
fi tted the Langmuir adsorption isotherm. 
78 
In conclusion, the 50/50/15 w/w PLA/ EVA/SCB sample gave the best adsorpt ion values, 
because this sample has a more co-conti nuous morphology that provides continuous pathways 
between the two incompatible polymers that allowed more effective penetration of the solution 
into the composite. While it was found that the 70/30 w/w PLA/EVA based samples have better 
impact strengths than the 50/50 w/w PLA/EV A based samples, the differences are not 
s ignifi cant and therefore the 50/50115 w/w PLA/EVA /SCB composite has an acceptable 
balance of properties to be used for the purpose of water purification. 
Recommendation or future work: 
• Use of the blowing agent in the composites to form a porous membrane that w il l help 
the metal impurities to more easil y come into contact with the fibre. 
• Do a desorption study to check if the composites can be reused after the removal of 
metal impuri ties from water. 
79 
ACKNOWLEDGEMENTS 
First of all I wou ld like to thank God who gave me strength, blessing, and courage during this 
study and during a ll o f my li fe. 
I would like to express my deepest and profound gratitude to my supervisors Prof. Adriaan 
Stephanus Luyt and Mr. Khotso Mpitso for their guidance, encouragement, and endless 
support during my masters study. I learned a lot throughout their supervision. I really feel that 
words wi ll not express my appreciation to whatever they have done for me. 
During my time in postgraduate level, our group has seen many different faces. I am lucky to 
have interacted wi th so many people with vastly different backgrounds. Some people directl y 
helped with my research, while others simply set a good example of hard work and fortitude. 
My genuine gratitude goes to all the colleagues in the Polymer Research Group of UFS 
(Qwaqwa campus), Ms. Thandi Gumede, Ms. Cheryll -Ann Clarke, Ms. Motshabi Sibeko, Dr. 
Puseletso Mofokeng, Mr. Tsietsi Tsotetsi, Mr. Tyson Mosoabisane, Dr. Sha le Sefadi, Mr. 
Benison Mot loung, Mrs. Mothepana Radebe, Mrs. Moipone Malimabe, Dr. Nomampondomise 
Molefe, Mr. Rantoa Moji , Mrs. Marlize Jackson, Dr. Dusko Dudic and Dr. Lebohang Hlalele. 
Special thanks to Mr. Mfiso Mngomezulu for the fruitfu l di scussions we had on my project and 
for always w illing to help me. 
I acknowledge Mr. Patrick Komane from the University of Johannesburg for AAS analysis of 
my samples, and Dr Tshwafo Motaung from the University of Zululand for providing me with 
SCB, I reall y appreciate the good work you did. 
The support I have received from my family is immeasurable. They have been supportive of 
all aspects of my li fe, especially education. I cannot thank them enough. 
Special thanks to Mr. Edwin Lecheko for the constant support, encouragement and patience 
throughout my stud ies. 
Lastl y, I am very grate ful for the financia l support I received from the National Research 
Foundation (NRF) and Sasol Inzalo Foundation (SaIF), South Africa. 
80 
Appendix 
(a) 
80 
60 
40 
-- 50/50 w/w PLNEVA 
20 --47.5/47.515 w/w PLNEVNSCB 
--45/45110 w/w PLNEVNSCB 
--42.5/42.5115 w/w PLNEVNSCB 
0 --40/40/20 w/w PLNEVA/SCB 
--35135130 w/w PLNEVNS CB 
100 200 300 400 500 600 
Temperature I °C 
0 
-2 
0~  
(/) -4 
(/) 
co 
-E -6 0 
Q) 
> -8 
~ 
·>c  
Q) -10 --50/50 w/w PLA/EVA 
0 
--47.5/47. 75/5 w/w PLA/EVA/SC 
-12 --45/45/10 w/w PLA/EVA/SCB 
--42.5/42.5/15 w/w PLA/EVA/SCB 
-14 --40/40/20 w/w PLA/EVA/SCB 
--35/35/30 w/w PLA/EVA/SCB (b) 
-16 
100 200 300 400 500 600 
Temperature I •c 
Figure A.5 (a) TGA and (b) derivative TGA curves of 50/50 w/w PLA/EVA and its bio-
composites 
81 
(a) 
80 
60 
-- 90/10 w/w PLNEVA 
20 --85.5/9.5/5 w/w PLNEVA/SCB 
--81/9/ 10 w/w PLA/EVA/SCB 
--76.5/8.5/15 w/w PLA/EVA/SCB 
-- 7216120 w/w PLNEVA/SCB 
0 --63/7/30 w/w PLNEVA/SCB 
100 200 300 400 500 600 
Temperature I °C 
0 
-5 
0~  
eenn  
ro -10 
-E 0 
Cl> 
:;> 
-15 
:; 
ro 
·>;::  
Cl> 
0 -20 --90/10 w/w PL.NEVA 
--85 519 5/5 w/w PL.NEVA/SCB 
--811910 w/w PL.NEVA/SCB 
-25 --76.5/8.5/15 w/w PL.NEVA/SCB 
--7218120 w/w PL.NEVA/SCB 
--63nt30 w/w PLA/EVA/SCB (b) 
-30 
100 200 300 400 500 600 
Temperature I °C 
Figure A.6 (a) TGA and (b) derivative TGA curves of 90/10 w/w PLA/EVA and its bio-
composites 
82 
a: 
::J 
.g -0.2 
c 
~ 
"';-oi-0.4 
~ 
~ -0.6 
c;::: 
ro 
Q) 
~ -0.8 
-0 
Q) --PLA 
.!::! 
.E -- EVA -1.0 
..... -- 50/50 w/w PLA/EVA 
0 
z -- 70130 w/w PLA/EVA 
--90/10 w/w PLA/EVA 
-1.2 .+--..--~-...,.----,.---~-.....----.-~-.,..----.--~-..-----.------l 
20 40 60 80 100 120 140 160 
Temperature I °C 
Figure B.1 DSC cooling curves of the neat PLA, EVA and the PLA/EVA blends 
83