Preparation,molding And Properties Of Elastomer/high Density Polyethylene And Microporous Structure Synergistic Toughening Polypropylene

Polypropylene（PP）is widely used in various fields due to its advantages of heat resistance,corrosion resistance and good mechanical properties.However,the poor impact toughness and low temperature brittleness of PP also restrict its application range.Therefore,in order to improve the impact toughness and low temperature brittleness of PP,in this thesis,EPDM/PP TPV particles were prepared by dynamic vulcanization process,and PP,high density polyethylene（HDPE）and elastomer（EPDM or TPV）were blended by extrusion melt blending to prepare ternary composites.Then,injection molded parts were prepared by injection molding process,and their impact toughness,mechanical properties and low temperature properties were tested by various characterization methods to explore their toughening mechanism.Finally,the injection foamed parts and autoclave foamed parts with different cell structures were prepared by injection foaming molding and supercritical CO₂kettle pressure foaming molding respectively,and the effects of different cell structures on material properties were investigated.The main research results are as follows:（1）By observing the microstructure of the ternary composites,it was found that the compatibility of EPDM/PP TPV particles prepared by dynamic vulcanization process with PP was better than that of EPDM,and the microstructure of PP/HDPE/TPV composites was smoother than that of PP/HDPE/EPDM;（2）The notched impact strength of PP/HDPE/EPDM and PP/HDPE/TPV composites increased with the increase of elastomer（EPDM or TPV）content.When the content of elastomer（EPDM or TPV）was 20%,the notched impact strength of PP/HDPE/EPDM and PP/HDPE/TPV composites were 967.9%and 189.5%higher than that of pure PP,respectively.The composites were tested at low temperature by self-designed liquid nitrogen cooling method and self-made falling ball impact device.The results showed that the addition of HDPE/EPDM or HDPE/TPV significantly improved the low temperature properties of PP;（3）The foaming properties of ternary composites were significantly better than those of pure PP materials,and increased with the increase of elastomer（EPDM or TPV）content.The notched impact strength of PP/HDPE/EPDM and PP/HDPE/TPV composites is generally lower than that of injection molded parts,while the low temperature performance is better than that of injection molded parts when the elastomer content is low;（4）The foaming properties of PP/HDPE/TPV composites were better than PP/HDPE/EPDM.The cell structure of PP/HDPE/TPV composite foams prepared by autoclave foaming showed that the cell size was uniform and the distribution was uniform.The average diameter of the cell could reach 5.49μm and the cell density was 2.41×10⁹cells/cm³.The cell structure of injection molded foams showed that the cell size was different and the distribution was not uniform,and the average diameter of the cell and the cell density could only reach 121.99μm and 1.48×10⁵cells/cm³,respectively.The difference in cell structure is an important reason why the low temperature performance of autoclaved foamed parts is better than that of injection molded foamed parts.The cell structure of autoclaved foamed parts forms a honeycomb-like structure inside the material,which improves the low temperature performance of the material.Through the research of this thesis,the effects of HDPE and elastomers with different characteristics on the impact toughness,low temperature performance and cell structure of PP were preliminarily mastered,and the influence mechanism was understood.Through various molding processes such as injection molding,injection foaming and supercritical CO₂kettle pressure foaming,the idea of molding process angle for PP toughening modification is provided,and it is preliminarily proved that the influence of small and dense cell structure on the low temperature performance of the material is positive.