| This work was supported by the National Natural Science Foundation (project number: 50973050). In order to improve the complex flow instabilities and helix distortion happened in polypropylene random copolymer (PP-R) extrusion process, as well as mechanical properties of homo-polypropylene (PP-H), in-situ fibrillation composite method were chosen in this work. Fiber-forming materials, including polyethylene terephthalate (PET) and polyamide (PA), were chosen to prepare PP-R/PET and PP-H/PET composites by in-situ fibrillation composite method. The main results as followed.The results suggested that melts of PP-R exhibited a peculiar extrudate distortion at moderate extrusion rate(300～1000s-1). The extrudate from short die appeared regular helical distortion. Correspondingly, a regular twist occured at the long die extrudate. Analysis showed that the headstream of distortion was located at the die entrance. Degree of helical distortion was enhanced with increasing extrusion rate. As the extrusion rate became higher, regular distortion would grew into irregular, and even melt frature.The emergence and feature of helix distortion could be influenced by temperature, die diameter and the structure of materials. With the increasing of temperature and die diameter, the flow disturbance at the die entrance relieved, thereby the helical distortion eased. High molecular weight, high viscoelasticity and significant stress concentration of two kinds of PP-R caused their severe helical distortion. Comparatively, PP-H and PP-B with low molecular weight were difficult to helical distortion. The molecular structure of PP-R maybe had some branched-chain, which was one reason for helical distortion.The manifestation of stress concentration of PP-R melts at die entrance was intense secondary flow. Annular secondary flow at die entrance, which was perpendicular to sprue, was proved in the experiment. Velocity contrast, caused by annual flow at die entrance and inertial flow out of the die, was the main reason for helical distortion. The degree of secondary flow was not only related to the molecular weight and viscoelasticity of material melts, but also relevant to the molecular structure of materials.The method of in-situ fibrillation was taken to prepare PP-R/PET and PP-R/PA6 composites, and in-situ formed PET fibers were found in PP-R matrix. Rheological experiments manifested that: to the composites with a few in-situ formed PET or PA fibers, the flow stability was improved, helical distortion was postponed, and the appearance of extrudate became better. Besides, adding a few glass fibers or kaolin could also improve the helical distortion of PP-R. Analysis of mechanism showed that adding a few anisotropic additives could reduce the viscosity and elasticity of melt, and inhibit annular secondary flow happened at the die entrance, all of which were reasons for the improvement of rheological properties of PP-R melt.The in-situ fibrillation of PET gave rise to the anisotropic mechnical properties of T30S. Tensile and flexural strength along the orientation of fibers were improved, but impact strength perpendicular to the orientation of fibers was reduced. Factors, including: composites ratio, compatibilizer, draw ratio and injection temperature, could influence the effect the in-situ fibrillation of PET, thus influence the mechnical properties of T30S/ PET in-situ fibrillation composites.The compatibility of T30S phase and PET phase was low. After being composited, the melt temperature and glass transition temperature of two phases changed little. But in the process of crystallization, two phase could disturbed each other, which reduced the size of spherulites. There exited activation to the heterogeneous nucleation effect of PET disperse phase. Phase separation could happen with the increase of PET. Adding little compatibilizer could improve the compatibility of two phases obviously.
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