P. GAO, A. Duhduh, A. Kundu, J. Coulter
Keywords: injection molding, VAIM, PLA, crystallinity
Summary:This research was focused on the effect of processing parameters on physical characteristics of poly-lactic acid (PLA) during vibration assisted injection molding (VAIM). PLA is a plant derived biodegradable thermoplastic polymer that has garnered significant attention in recent years. In vibration assisted injection molding process, the travel of the injecting screw is moved back and forth to create an oscillatory motion, the frequency, duration, compression/decompression ratio and the initiation point of which can be individually controlled. In particular, the frequency and duration of vibration during injection molding were controlled for fabricating PLA dog bones. The vibration frequency was varied from 1Hz to 30Hz and the vibration duration was varied between 5 seconds and 10 seconds during injection. A set of parts were fabricated without any vibration for comparison. The effect of the processing conditions on the crystallinity of the PLA parts were systematically studied utilizing a differential scanning electron technique. It was observed that VAIM PLA products have higher total crystallinity than conventionally molded PLA products under identical conditions sans the vibration. Based on these results it was hypothesized that the vibration primarily affects the molecular arrangement of the polymer chains which in turn affects the nucleation density and thus the crystallinity. In addition, it was observed that the cycle time can be reduced by at least 25% when vibration was applied. The presentation will discuss these results in detail and the advantages of vibration assisted injection molding for efficient production of parts with enhanced properties.