Preparation and characterization of ethylene vinyl acetate copolymer/poly(lactic acid)/sugarcane bagasse composites for water purification

[摘要] Excessive release of heavy metals into the environment due to industrialization and urbanizationhas posed a great problem to the world. Heavy metal ions do not degrade, therefore they can givebad effect to human body and the environment itself. The purpose of this study was to preparepolymer/natural fibre composites to be used in water purification, specifically to remove lead ionsfrom contaminated water. PLA/EVA blends and PLA/EV A/SCB composites were successfullyprepared by melt mixing. The lower viscosity of PLA, the lower interfacial tension between PLAand SCB, and the wetting coefficient of PLA/SCB being larger than I, all suggested that SCBwould preferably be in contact with PLA, despite PLA's relatively high crystallinity. A fairly gooddispersion of SCB in the PLA matrix was observed. PLA and EV A were also completelyimmiscible, with the 50/50 w/w PLA/EV A sample showing a co-continuous morphology and the70/30 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 believedto add to the efficiency of metal adsorption. The two polymers in the blend seemed to haveprotected the SCB from thermal degradation, because the mass loss of SCB degradationproducts was only observed at higher temperatures when incorporated in the blends. Althoughthis 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 thevolati le SCB degradation products was delayed as a result of interaction with one or bothpolymers. The impact properties depended more on the PLA:EV A ratio than on the presenceof SCB. The PLA/EV A blends showed two melting peaks at approximately the sametemperatures as those of the neat polymers, which confirms the complete immiscibility of PLAand EV A at all investigated compositions.It was further observed that the water absorption increased with an increase in SCB loading inthe composites. The main parameters that influenced lead ion sorption on SCB andPLA/EV A/SCB composites were the initial concentration, contact time, and the pH value. Itwas observed that more lead was adsorbed than one would expect if the partial coverage of thefibre by the polymer is taken into account, and therefore it may be assumed that some of thelead was trapped inside the cavities in the composites and that the polymers may also haveplayed a role in the metal complexation process, since both polymers have functional groupsthat could interact with the lead ions. The metal impurities underwent monolayer adsorption.

[发布机构] University of the Free State