Research On Rheological Behaviors And Crystallization Properties Of PE Blends Melting Dominated By Elongational Deformation

The final properties of polymer is gradually formed in the process of extrusion.Researchers always focus on the stationary state of the polymer phase transition, which arethe beginning state and the final state. While the dynamic process which is from thedisordered state(initial state) to the metastable state, then finally get to the ordered state isless studied. Meanwhile the larger evolution of morphology of the polymer blends generallyoccurs in the initial molten state. Therefore, the study of the rheological properties andcrystallization properties of the blends during the melting state has a great significance ofrevealing the melting mechanism and optimizing the the performance of the final product.The processing and plasticating and conveying mechanism of the vane extruder based on theelongational rheology are total different from the screw extruder based on the shear rheology.Through the research on the morphology evolution of the melting process and the heologicalproperties and crystallization properties of the blends in the vane extruder, from thetheoretical and experimental profoundly reveals the mechanism of the melting andplasticizing in the vane extruder which has important scientific and practical significance tothe development and improvement of the polymer processing theory based on elongationalrheology.The assembled vane extruder with visual effects is independently developed which isconstituted of several groups of vane plasticating and conveying units. By this equipment, themelting process was studied in three sections which are initial stage of melting, the stage ofbasic melting and the stage of completely melting, and sampling along the way. After deeplyanalyzing the morphological evolution through the photos of the sampling, and the rules ofthe rheological and crystallization properties of PE blends by the characterization of the thesampling, it is found that:For PE blends, when HDPE content is relatively low or high, meltig mechanism mainlyare VED and thermal conduction, when the ratio of the two phrase is almost the same, meltigmechanism mainly are weak PED, VED and thermal conduction. The evolution of the meltprocess is from rich-melt suspension stage to the stage of melt surrounding by a large numberof small amount of solid to the final process of a large number of melt. For HDPE/LDPE blends, during the melting process, when HDPE content is relativelylow, shear viscosity increases after the first lower; when HDPE content is relatively high,shear viscosity increases with the increase of groups of vane units. For HDPE/PS blends,shear viscosity is basically stable during the initial stage of melting and the stage of basicmelting, after the stage of completely melting, shear viscosity increases after the first lower.For HDPE/LDPE blends, along the direction of extrusion, the melting process enhancedthe crystallization of HDPE. For HDPE/PS blends, the interdiffusion of PS and HDPEaffected the crystallization of HDPE, the melting process gradually decreased thecrystallization of HDPE.