聚烯烃共混物注射制品的形态控制与多层次结构

从注射制品形态控制和结构表征的角度探讨高分子材料加工-形态-性能之间的关系.研究中采用动态保压成型方法来制备注射样品,在注射成型过程中引入剪切应力场的作用,制得的样品表现出明显的多层次结构,从外向里分别为皮层、剪切层、芯层,表现出不同的相形态、结晶形貌以及取向行为.研究发现,剪切应力对聚烯烃的形态发展和结构变化具有重要影响.在剪切应力的作用下,聚烯烃共混物中分散相会发生变形、取向,从而导致共混物的相转变点发生移动;结晶形态从球晶转变为shish-kebab结构;聚烯烃共混物在高剪切应力下相容,低剪切下发生相分离;HDPE/PP共混物的注射制品中出现附生结晶等现象.

SPATIAL HIERARCHY AND INTERFACIAL STRUCTURE IN INJECTION-MOLDED BARS OF POLYOLEFIN BLENDS

Some important results about the injection molding of polyolefin blends were reported in this article.Due to the shear stress and thermal gradients,usually,injection molded parts contain a hierarchy of macromolecular arrangements and a skin-core structure.In this work,the phase morphology and interfacial structure of injection molded bars of polyolefin blends have been investigated in detail from the skin to the core,layer by layer.For preparation of injection-molded bars with high-level orientation dynamic packing injection molding technology was applied to exert oscillatory shear on the molten composite through two pistons that moved reversibly with the same frequency during the solidification stage.It was found that,under the effect of shear stress,(1) the dispersed phase of polymer blends was deformed and oriented,resulting in a change of the phase inversion as well as the mechanical properties of polymer blends;(2) shish-kebab structure instead of spherulite structure was formed;(3) the blends became homogeneous at higher shear stress,while phase separation was induced at lower shear stress;(4) epitaxial growth occurred in injection molded bar of HDPE/iPP blends.Our goal was to study the relationship between processing,morphology and mechanical properties of polymer materials in terms of the morphology controlling and structure characterization of injection-molding samples,and to provide a new way of improving the mechanical properties and service life of polymer materials through injection molding technology.