The Research Of Modifying Of Biodegradable Polylactide Film

Polylactide(PLA) is a kind of ideal green environmentally friendly polymer materials, which has many advantages, such as renewable, competitive, good transparency, high tensile strength, bending strength and modulus, can be instead of traditional petroleum base commodity polymers and has attracted more and more interest in many areas. Unfortunately, pure PLA is very brittle and has poor toughness, which is difficult to meet the requirements of many applications and greatly limits its extensive application, therefore the toughening modification of PLA has become the focus of the academic and industrial research.1. Glycidyl methacrylate-functionalized methyl methacrylate–butyl acrylate copolymer(GACR) was synthesized by core-shell emulsion polymerization, the GACR with core-shell ratio of 80/20 was used to modify PLA. PLA/PDEGA GACR film was prepared by melt blending method and extrusion blown film process. The influence of the content of GACR on modification of PLA was investigated. DSC analysis result showed that crystallinity degrees of the PLA/PDEGA/GACR films were slightly decreased with increasing GACR content. Rheological result showed GACR increased the strength of the melt, which was beneficial to the blown film processing of PLA. DMA analysis showed that rigid of blend decreased and soft of blend increased, the more content of GACR was added, the softer the blends were. SEM of film tearing fracture morphology suggested the occurrence of shear yielding induced by cavitation of GACR particles was the major tearing mechanism. The elongation at break as well as the tear strength of PLA/PDEGA/GACR films was improved significantly compared with neat PLA. The tear strengths of the 77/7/16 PLA/PDEGA/GACR film in the machine direction and transverse direction were about 1.85 and 1.73 times that of neat PLA film, respectively. It was proved that the PLA/PDEGA/GACR blown films were high tearing resistance films. The spherulite size and biodegradability of the PLA/PDEGA/GACR films decreased.2. Another biodegradable poly(butylene succinate)(PBS) was used to toughen PLA. PLA/PPA/PBS film with different PBS content was prepared by melt blending method and extrusion blown film process. In the case of fixed PPA content, the influence of the content of PBS on modification of PLA was investigated. DSC analysis indicated that PBS decreased the cold crystallization ability of PLA, made crystallinity increase, PLA and PBS was incompatible system. The result of rheological characterization suggested that modulus and viscosity of PLA/PPA/PBS reduced with the PBS content increasing, which may result from that the compatibility is poor between PLA and PBS. DMA result showed that the increase of PBS content decreased the rigidity of blend and the PLA/PPA/PBS blends became more flexible. The change of the PBS content had no significant effect on the glass transition temperature of PLA. Mechanical test results showed that the addition of PBS improved the elongation at break and tear strength, but the extent of the improvemnet was not very big. The blend films had good light transmittance. Tearing fracture scanning micrographs suggested that the PLA/PPA/PBS films had occurred shear yield, which is a typical ductile fracture. The thin film tearing mechanism of PLA/PBS system is mainly shear yield.