Studies On The Dynamic Rheological Properties And Crystallization Of GF/PP Composites

The rheological behavior of filled polymer melt is not only determined by the physical and chemical properties of the filler but also determined by morphology, interaction between filler and matrix. Meanwhile, the rheological behavior of filled polymer melt have important influence on processing performance and final performance of the filler polymer. The relationship between morphological structure and rheological behavior of the composites have drawn increasing attention because of the need of academic research and industrial applications. But so far, the study of the rheological behavior of filled polymer most focused on the particle filled system. The study for the rheological behavior of fiber filled polymer system was still scant, especially for the evolution of morphological structure of fiber filled polymer system under shear field. We constructed a single shear field through steady shear test method. The dynamic rheological behavior, morphological structure and crystallization behaviors of GF/PP composites were investigated.Firstly, the melt of PP/GF composites were sheared at 200℃. The crystallization behaviors and crystallization morphology of GF/PP composites were investigated. The results of DSC and XRD showed that the crystallization behaviors and crystalliz-ation morphology of composite PP/GF(treated)/PP-g-MA were influenced by the shear rate. There formed oriented crystals such asβcrystal, rod-like crystals and needle-like crystal at low shear rate, but only a crystal at high shear rate in composite PP/GF(treated)/PP-g-MA. However, the influence of shear field on composite PP/GF(untreated)/PP-g-MA, PP/GF(treated), PP/GF(untreated)was not obvious. There were only a spherulites in these three composites.In order to investigate the morphology structure of composite melt, we constructed the same shear field. The dynamic rheological behavior of the oriented melt was studied by ARES. The results showed that the modulus and viscosity of composite PP/GF(treated)/PP-g-MA increased at low shear rate, the decreased at high shear rate. The modulus and viscosity of composite PP/GF(untreated)/PP-g-MA PP/GF(treated), PP/GF(untreated) decreased with the increase of shear rate. In additional, relaxation time of chains at appropriate shear rate could be extended. Furthermore, relaxation time of chains was also extended when GF was treated.According to the results of rheological behavior and crystallization behavior, we proposed a model and described the evolution mechanism of composites' morphological structure under shear field. In the composite whose interfacial adhesion was strong, glass fiber and PP molecules chains were all oriented along the flow direction at low shear (<3s-1), leading the random network to be stretched and oriented. The order degree of the whole network was enhanced largely, so modulus and viscosity increased. PP chains did not relax rapidly because of the traction of GF. So the relax time was long. The oriented structure did not relax in short period of time. They could induce the formation of oriented crystals. However, in the composite whose interfacial adhesion was weak, even weak shearing strength can separate PP chains from glass fiber, leading the relaxation of the PP chains. The order degree of the whole network decreased. So the modulus and viscosity decreased with the increase of shear rate. Moreover, the relax time of PP chains was short. The oriented structure could not maintain, so couldn't induce the formation of the oriented crystals.