The Influence Of Shear History On Crystallization Behavior Of Ipp Melt

Polypropylene is one of the most widely used crystalline polymers materials in the industry.Shear and tensile has influence on crystal form of polymer crystalline in the process of manufacturing and lead to the variety in structure performance of products.Isotatic polypropylene(iPP) as one of PP is a polymorphic material with several known crystal modifications,such as monoclinic(α),hexagonal(β) and triclinic(γ),of these polymorphs,βform has excellent mechanical properties because of its special hexagonites structure,for example,excellent toughening property,high elongation at break,excellent tension toughness,high ductility and so on.Hence,the study ofβ-phase formation mechanisms has provided a way by adjusting the parameters to improve the structure and properties of products during machining.In this paper,we first use the melt rate instrument to simulate the process of extrusion and study on the effect of shear history on crystallization behavior of iPP melt.Using characterization means,such as PLM,WAXD,DSC to study on the effect of extrusion conditions and heat treatment process on crystalline morphology, crystalline structure and distribution,crystallinity andβ-phase content,which provides theoretical guidance and experimental evidence for controlling morphology and structure of the polymer in the process of manufacturing.The specific work as following:1.Studied on the effect of extrusion conditions on rheological behavior of iPP melt,and obtained the relationship of temperature and load versus sampling time, shear time and shear rate.2.Studied on the effect of load on crystalline morphology,crystalline structure and distribution by means of PLM and WAXD,found thatαandβform coexistence,βform along theαrow-nuclei generates columnar crystal,and distribution ofβform tends to surface of extrudate with load increase;Quantitative study on the influence of extruding conditions to crystallinity andβ-phase content by means of DSC,It was found thatβ-phase content is more sensitive than crystallinity to load and temperature, and on this basis the processing window that is apt to formβ-phase was proposed.3.Using different heat treatment process endows different heat engine history to sample,studied on the influence of different heat treatment process on the formation ofβ-phase,the results show that the holding time of raw material in the barrel before extrusion,the not eliminative heat engine history of raw material,shear history of melt and the tempering process of sample have significant influence on theβ-phase content;meanwhile,the load and holding time of post extrusion also have influence on the content ofβ-phase that was formed in the process of isothermal crystallization after extrusion.4.Studied on the effect of homopolymerization and copolymerization of PP and different molecular weight on the formation ofβ-phase,and found that single monomer structure of homopolymerization PP is easy to form theβ-phase,and theβ-phase content increases with its molecular weight increase.