Preparation and characterization of ethylene vinyl acetate copolymer/poly(lactic acid)/sugarcane bagasse composites for water purification
Makhetha, Thollwana Andretta
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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/EV A/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/EV A 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 only 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:EV A 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 could interact with the lead ions. The metal impurities underwent monolayer adsorption.