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Poly(l-lactide)-b-polyethylene glycol-b-poly(l-lactide) (PLLA-PEG-PLLA) is found to be more flexible than PLLA due to the flexibility of PEG middle blocks. Melt flow and mechanical properties of PLLA-PEG-PLLA were improved through post melt blending with a chain extender (CE). In this work, in situ chain-extended PLLA-PEG-PLLAs were synthesized by ring-opening polymerization in the presence of Joncryl® CE. The influence of CE content (1.0, 2.0, and 4.0 phr) on the gel content, melt flow index (MFI), thermal properties, and mechanical properties of the obtained in situ chain-extended PLLA-PEG-PLLAs was investigated. The gel content of in situ chain-extended PLLA-PEG-PLLA increased while the MFI and degree of crystallinity significantly decreased with increasing CE content. The in situ chain-extended PLLA-PEG-PLLA with 1.0 phr CE showed the best tensile properties. The extensibility of in situ chain-extended PLLA-PEG-PLLA films decreased when the CE contents were higher than 1.0 phr. These in situ chain-extended PLLA-PEG-PLLA films can be used as highly flexible bioplastics.

Currently, use of poly(lactic acid) (PLA) is limited for commercial applications because it has a low heat resistance. In this research, an increase of over 40°C heat distortion temperature (HDT) of PLA alloy was obtained by blending PLA with polycarbonate (PC) and a chain extender (CE). Molecular weight, thermal, mechanical and morphological properties of PLA and PC blend with different CE contents were investigated. Gel permeation chromatography (GPC) results showed that some PLA-PC copolymers were produced and the compatibility of the PLA phase and in the PC phase was improved via the chain extension reaction. In addition, the reaction induced by CE also affected the crystallization behaviors of PLA, as observed from differential scanning calorimetry (DSC) results and the enthalpy of melting of PLA decreased with increasing CE content. The combined effects of the CE increasing molecular weight, improving compatibility and limiting the crystallization behavior of PLA/PC alloy greatly improved the HDT.

Water-assisted injection molding (WAIM) has been widely used for tubular plastic parts due to its advantages of relatively low cost and fast cycling time. However, the non-uniform distribution of the wall thickness, especially at the sharp corner, is still a basic problem in the WAIM process. This work presents the effects of sharp corner angles on wall thickness distribution in sections near corners for various processing conditions of the WAIM process, including melt temperature, mold temperature, water delay time, water holding time, and holding pressure. Three grades of polypropylene (PP) resins with different melt flow indices were studied using seven mold geometries that varied the angle of the sharp corner section. The wall thickness distribution at the corner sections were characterized in terms of inner and outer residual wall thicknesses, hollow core ratio, and the percentage of difference between the inner and outer wall thicknesses. In addition, computational fluid dynamic simulations with Moldflow Plastics Insight version 4.1 were performed for each sharp corner angle. It was found that the wall thickness distribution of the straight tube was more uniform than those of the curve tubes. Water injection delay time and water pressure were the major parameters that had a significant impact on the hollowed core ratios, while the percent difference between inner and outer wall thicknesses was mainly influenced by melt temperature.