Preparation, Structure And Mechanical Properties Of Poly (Lactide)/Elastomer/Montmorillonite Composites

Poly(lactic acid) (PLA) is one of the aliphatic polyesters synthesized by lactic acid or lactides. PLA is a biocompatible and biodegradable polymer, which has a wide application in medical and care, apparel, home decoration and various industry areas. Thus, PLA has been defined as one of the most promising polymeric biodegradable materials. However, because of its inherent brittleness, low impact strength and high processing cost, the application of PLA has been greatly limited. In this thesis, the technologies of Polymer/layered silicate clay nanocompoiste and polymer blending are used to prepare PLA/EVA/Montmorillonite composite to improve the mechanical properties of PLA.Firstly, the properties of the raw materials for the composite preparation were tested. Then, PLA/MMT and EVA/MMT composite were prepared on subminiature blending machine and HAAKE Torque Rheometer. WAXD, TEM, DSC, DMA and tensile tests of the composites were conducted and the structure and mechanical properties of the composites were thus studied. Finally, PLA/EVA/MMT composites were prepared and impact tests were carried out. The toughening mechanism of the composites was also preliminarily discussed.According to the results of the experiments, we conclude that:(1) For the PLA/MMT composite, the optimum MMT content is less than 10wt% and in dry state. The optimized preparation conditions for PLA/MMT composite are 145℃, 80r/min, 8min. For EVA/MMT composite, wet MMT is favor to the dispersion of MMT. The optimized preparation conditions for EVA/MMT composite are 145℃, 80r/min, 8min.(2) WAXD,TEM,DSC and tensile tests show that MMT was dispersed in PLA in a form of nano-scaled aggregates. The ordered inter-layer structure of MMT was destroyed partly, that is, a partly exfoliated nanocomposite was prepared. The young's modulus of PLA/EVA composite is obviously improved. The degree of crystallinity of the composite increased, while melting point decreased.(3) In the EVA/MMT composite, samller MMT aggregates are dispersed in EVA than those in PLA/EVA composite, indicating EVA/MMT is also a partly exfoliated nanocomposite. MMT has little influence on the crystallization behavior of the composite. The young's modulus of EVA/MMT composite was greatly increased.(4) For EVA/MMT blends, the content of EVA should be less than 20wt%. After adding EVA-MAH in the blends as a compatibilizer, the mechanical properties of EVA/MMT blends was not improved substantially.(5) The impact test of PLA/EVA/MMT composite show that the impacting strength and tougness of the samples of P/E/M-1,P/E/M-2,P/E/M-5 were improved.