The Influence Of Vibration To Crystallization Of Isotactic-Polypropylene

Vibration injection molding (VIM) is a technology that pulls vibration in the traditional injection, which induces the vibration shear-flow of polymer melt, furthermore, by the orientation and induction of vibration shear-flow, improved the orientation and crystallinity of polymer, decreased the size of spherulites, changed the crystal morphology, then coming to improve the properties and quality of injection plastics.However, the VIM process is very complex, so it's hard to go deeply into the crystal morphology of polymer in vibration.This paper researched the effects of small amplitude vibration field (supported by DMA) in iPP crystallizing, under different temperatures, time, amplitudes and frequencies.The work and main results are summarized as follows:1.Connect the variations of dynamic mechanical performance parameters with the crystallization process, by studying the variations of storage modulus-time in vibration which observed in DMA experiments.By calculating, the dates of storage modulus-time changed into the dates of relative crystallinity-time, the induction time and crystalline rate are described by relative crystallinity. The results indicated that, induction time shortened and crystalline rate fastened under low temperature, which isn't much influenced by different amplitudes and frequencies.2.Crystallization induction time and completed time in DMA are much longer than that in DSC;this may be caused by the way of vibration. Here the vibration is periodically offered by the DMA up and down, which brings about oriented and disorientation of the molecular chain in melt polymer, then lengthen the induction time and shorten the crystalline rate.3.Crystallinity of iPP under vibration or nonvibration was investigated through differential scanning calorimeter (DSC).The results reveal that, crystallinity of vibration sample increases with time, while it is larger than that of nonvibration samples under the same amplitude and frequency.4.Crystal morphology of iPP under vibration or nonvibration was investigated through polarizing microscope (PLM).The observation reveals that, the sizes of iPP spherulites decrease under vibration.