Effect of Chain Extension on the Properties of PLA/TPS blends and Film Blowing Processing

摘要

In this paper, the effect of a multifunctional epoxy-acrylic-styrene copolymer on the properties of PLA/Thermoplastic Starch (PLA/TPS) blends was investigated and its effect on the processing of blown films was clarified. The PLA/TPS blends were prepared by twin-screw extrusion. The dry-starch and plasticizers were mixed together in the first half of the extruder to complete starch gelatinization. Water was removed by devolatilization at mid-extruder and the PLA matrix was mixed with the water-free TPS in the latter portion of the compounding process. The standard blends comprised 27%TPS in the PLA matrix. The TPS phase comprised 36% plasticizers in the form of glycerol and sorbitol mixtures. Oscillatory-shear rheology was used to monitor changes in blend viscosity. Scanning electron microscopy on microtomed and acid-etched samples was carried out to assess the blend morphology. It was found that the viscosity of the PLA/TPS blends was dramatically increased by adding a small amount of epoxy-based chain extender (CE). This is of great interest for film-blowing since this process requires materials with high melt strength. Film blowing trials on a lab-scale equipment showed that PLA/TPS film could be successfully blown when sufficient levels of chain-extenders were used.