Development And Application Of The Mixer Dominated By Normal Stress In Synergy With In-situ Bubble Stretching

High density polyethylene(HDPE)is a kind of important general plastic,high output,low cost,wide application,but the low strength of the HDPE cannot be compared with engineering plastics.At present,due to the inherent low strength and poor thermal conductivity of the plastics,melt blending is often used in industrial production to prepare polymer composites.The key of this method is to solve the dispersion of reinforcer in composites.In this thesis,we have developed a novel mixer dominated by normal stress.The melt blending process of the new mixer was analyzed in detail,the physical mathematical model of vane plasticizing unit was established and solved,the results showed that the tensile strain rate is much higher than that of shear strain rate in plasticized unit.It is shown that the extruder is controlled by the positive stress.In this paper,the in-situ bubble drawing method was successfully introduced into the melt blending of the mixer dominated by normal stress,which realized the synergistic effect of the positive stress field and the in-situ bubble drawing method in the process of polymer melt blending.By means of the novel mixer,CFs and UHMWPE were well dispersed in HDPE matrix.The structure and properties of HDPE/CFs,HDPE/UHMWPE/CFs composites prepared under normal stress field were studied in this paper.The experimental results showed that CFs,UHMWPE is uniformly dispersed in the matrix when the CFs,UHMWPE content were relatively low.However,when the content of dispersed phase was relatively high,CFs will aggregate in the matrix,and UHMWPE is also distributed unevenly in the matrix.The introduce of CFs and UHMWPE was helpful to improve the mechanical properties,thermal stability,crystallization of composite materials,but reduce the processing fluidity of composite materials.The tensile strength increased from 29 Mpa to 37.4 Mpa,an increase of 29%.In this paper,the structure and properties of HDPE/CFs,HDPE/UHMWPE/CFs composites prepared by positive stress and in-situ bubble drawing were studied.The experimental results showed that the dispersion of CFs and UHMWPE in HDPE matrix is improved under the synergistic effects of normal stress and in-situ bubble stretching.Therefore,the mechanical properties,thermal stability crystallization of composite materials are improved.The tensile strength increased from 28.1 Mpa to 39.1 Mpa,an increase of 39%.At the same time,the dispersion of filler in the matrix increased with the increase of AC content.However,high-speed tension and high-frequency vibration in the expansion process of AC could also cause polymer degrade.The tensile strength of HDPE decreased from 29 Mpa to 28.1 Mpa.Research results showed that the normal stress and the in situ bubble stretching in the polymer melt blending played a synergy,help the dispersed phase well dispersed in polymer matrix.The research enrich the theory of polymer melt blending.There are important academic significance and value in industrial application.