Influence Of α Nucleating Agent And Process Conditions On The Crystallization And Mechanical Properties Of Polypropylene Injection Molded Parts

Due to low rigidity, low heat distortion temperature, large molding shrinkage,poor transparency disadvantages of polypropylene(PP), these disadvantages limit itswide applications. By adding nucleating agent into PP matrix can improve thecrystallization properties of PP, refine the grain size, increase the degree ofcrystallinity, thus can improve the rigidity and transparency of polypropylene.This paper studied the influence of nucleating agent DMDBS on the crystalmorphology and mechanical properties of polypropylene.Blends of PP and nucleatingagent having different mass percents (0.1wt%,0.2wt%,0.3wt%,0.4wt%) wereprepared; Polarizing microscope (PLM) and differential scanning calorimetry (DSC)were used to analyze the effect of nucleating agent content on PP crystallization,withthe increasing of DMDBS content from0.1%to0.4%, the PP spherulite size wasdecreased, but the crystallinity was obviously improved;The DSC results showed thatthe melting peak was moved to higher temperature slightly and melting peak widthwas narrowed with the elevating of DMDBS content,these results could explain thatthe crystalline perfect degree of PP was enhanced, grain size became more uniform.Finally, mechanical properties of the modified PP were measured. The results showedthat when0.3%DMDBS was added into PP, tensile strength and bending strength ofPP reached to the maximum values,37.7MPa and62.73MPa, respectively, increasedby10.6%and47.28%individually compared to that of pure PP;However, with theincreasing of DMDBS content from0.1%to0.4%, the impact strength was obviouslydecreased, when the content of nucleating agent was0.4%, the impact strengthdecreased by about26.6%compared to the pure PP counterpart.Secondly,the effects of processing parameters (melt temperature, hold pressure,injection pressure) on the crystallinity and mechanical properties of PP were studiedin this paper. With different processing conditions, the PP samples were molded to bestudied the influence of different injection processing parameters on the crystallinityof the production by DSC testing. The crystallinity of the sample reduced gradually with an increase in melt temperature, The crystallinity of the sample appeared a trendof increasing first and decreasing with an increase in holding pressure and injectionpressure.The results of the mechanical properties experimental showed that lowermelt temperature should be adopted to improve tensile strength, bending strength andimpact strength of the samples,With an increase in holding pressure and injectionpressure, tensile strength, bending strength and impact strength appeared a trend ofincreasing first and decreasing,Clearly,the holding pressure and injection pressureexisted an optimal value.Finally,the effect sequence of the process parameter was obtained by orthogonaldesign method in this paper.