Study On Increasing-viscosity Modification Of Polylactide (pla), Preparation And Properties Pla's Foaming Material

Polylactide (PLA) is a kind of biodegradable polymer prepared by chemical synthesis through renewable plant as raw materials, which can be processed into a variety of film, sheet, fibers and other products widely used in garment, textile, non-woven fabrics, packaging, agriculture, forestry, medical and health supplies, daily necessities and other fields. PLA has excellent biocompatibility, biodegradability, and the ultimate degradated products are carbon dioxide and water, which have no pollution to the environment. However, due to the molecular chain of PLA lacks of long-branched, the melt viscosity is very small, leading to particularly low melt strength, lacking of strain hardening makes it difficult for foaming, and it's difficult to get high magnification of the foaming material. Branching polymer chains, copolymerizing with another monomer, and blending branched or cross-linked polymers are the basic methods to increase its viscosity so that it can be suitable for foaming.In this paper, first through the in situ cross-linking reaction of terminal carboxyl polyester (CP) and epoxy (SE), using melt extrusion and molding method to prepare PLA/SE and PLA/CP/SE composites materials. The effect of the various factors on their rheological properties, thermal properties, morphological structure and mechanical properties has been studied in detail. The results show that the viscosity of the PLA/SE composite materials firstly increases and reaches a level with the increase of SE concentration; DSC and polarized optical microscopy show that the crystallinity firstly reduced and then increasd; SEM and DSC indicate that the PLA/SE system is immiscible; their elongation at break increase, while tensile strength decreased slightly compare to pure PLA. As for the PLA/CP/SE composite materials, with the CP/SE content increasing, their viscosity has a significant increase; DSC and polarized optical microscopy show that the crystallinity obviously decreased; SEM indicates that there exists reaction-induced phase separation in binary polymer; tensile tests show a marked increase in tensile strength, elongation at break did not change significantly. We have successfully prepared high viscosity PLA/CP/SE composite.Secondly, PLA foam can be successfully prepared through traditional compression molding chemical foaming method. The effect of the different factors such as foaming agent content, CP/SE content and process conditions on the properties of PLA foam material has been discussed. Optimal process conditions and appropriate formulas have been found. The density of PLA foam can be controlled from 0.546-0.155g/cm3.