Rheologicaland Mechanical Properties Of PP Modified With In-situ Fibrillation Composite Of PA6

This work was supported by the National Natural Science Foundation (projectnumber:50973050). In-situ fibrillation composite method was chosen to improve thecomplex flow instabilities and helix distortion happened in polypropylene randomcopolymer (PP-R) extrusion process, as well as mechanical properties ofhomo-polypropylene (PP-H). Nylon6as the modified material was chosen to preparePP-R/PA6and PP-H/PA6in-situ fibrillation composites. Nylon6was used, because itwas easy to form fibers. The main results are as followed.The results suggested that melts of polypropylene exhibited a peculiar extrudatedistortion at high pressure. The extrudate from short die appeared regular helicaldistortion. Correspondingly, a regular twist occurred at the long die extrudate. Thewavelength and channel of helix are shorter and shallower, respectively, as the extrusionrate became higher, regular distortion would grow into irregular, and even melt fracture.The emergence of helix distortion depended on the viscoelasticity, molecularstructures and process conditions of PP melts. The results suggested that PP-R with highmolecular weight and high viscoelasticity would cause their severe helical distortion.Comparatively, PP-H and PP-B with lower molecular weight were difficult to get helicaldistortion. With increasing temperature and reducing extrusion rate, the helical distortionwas eased. Experiments showed that the headstream of distortion of PP-R was located atthe die entrance. The factures which was perpendicular to sprue such as strong tensileflowing, high stress concentration and annular secondary flow at the die entrance were themain reasons for helical distortion. The degree of annular secondary flow was related to the molecular structures of polymer.The method of in-situ fibrillation was taken to prepare PP-R/PA6composites, PA6fibers were found in PP-R matrix, and the diameter of fibers was about200~500nm.Compatibility of PA6and PP-R was improved by a small amount of PP-g-MAH, whichwas the key factor in the in-situ fibrillation process. Rheological experiments manifestedthat the flow stability of composite materials was improved, helical distortion waspostponed, and the appearance of extrudate became better. The critical shearing rate ofhelix distortion was from353s-1up to1027s-1.By PA6fibers viscoelasticity of PP-R melt was changed, and shear viscosity andmelt elasticity of composites were made lower than pure resin. Meanwhile, shear thinnedwas made more obvious. PP-R chains were hindered to stack by PA6fibers. Also, this hadan effect on the heterogeneous nucleation, increasing quantity of crystal but reducingdimension of crystal.The method of in-situ fibrillation was taken to prepare PP-H/PA6composites. Theirtensile and flexural strength along the orientation of fibers, and their impact strengthperpendicular to the orientation of fibers were all improved significantly.Keeping the morphology of PA6micro fibers had an obvious effect on themechanical properties of composites. Experiments showed that injection temperature washigher than the PA6melting point, and PA6micro fibers returned into sphericalmorphology. PP-R could not be reinforced by PA6micro fibers, making the mechanicalproperties of composites decreased.