Study On Crystallization Behavior,Mechanical Properties And Foaming Properties Of Modified Polypropylene

Due tothe excellent comprehensive properties,foamed polypropylene has received extensive attention and can be used in many fields.However,the foaming property of PP is poor,in order to improve its foaming property,this paper used homopolypropylene（HPP）as the basic material,HPP/graphene oxide（GO）,HPP/amination multi-walled carbon nanotubes（NH₂-MWCNTs）nanocomposite and HPP/polypropylene block copolymer（PP-B）/8%GO blend were obtained separately,which were foamed with supercritical carbon dioxide as blowing agent by low-temperature impregnation and rapid pressure reduction process.The crystallization behavior,mechanical propertyand foaming property of nanocomposite systems andblend were studied,the influences of type and content of nucleating agent,foaming temperature and saturation pressureand mechanical property on cell morphology were analyzed.Experimental results showed that the crystallization type of pure HPP was homogeneous nucleation.Therefore,its initial crystallization temperature and the crystallization peak temperature were low,the crystallization nucleation rate was slow,spherulites were large in size and structurally regular.However,for HPP/GO nanocomposite,HPP/NH₂-MWCNTs nanocomposite and HPP/PP-B/8%GO blends,homodisperse GO,NH₂-MWCNTs and PP-B all can be as nucleator to induce heterogeneous nucleation,so the initial crystallization temperature and the crystallization peak temperature of the system were increased,the crystallization nucleation rate was increased,the size of spherulites was decreased and the density was increased.In HPP/GO and HPP/NH₂-MWCNTs nanocomposite,GO and NH₂-MWCNTs can play important roles to improve the mechanical properties of system,in HPP/PP-B/8%GO blend,PP-B can also improve the melt strength of system.The crystallization behavior and mechanical property of HPP were improved by nanocomposite modification and blend modification.The improvement of these two aspects can improve the bubble nucleation efficiency and inhibit the cell growth during the foaming process,so the average cell size of the foams was smaller,the average cell density was increased,and the foaming performance was improved.When the content of GO was 8%,the content of NH₂-MWCNTs was 1%,and the HPP/PP-B was 70/30,the foaming performance of the system was improved most significantly.In HPP,HPP/GO,HPP/NH₂-MWCNTs and HPP/PP-B/8%GO foams,there were a large number of nano-scale cells.