The Study On Dependence Of Macromolecular Structure Of Polypropylene Crystallization With Nucleating Agents

In this paper,crystallization behaviors of isotactic polypropylene(iPP) with different macromolecular structures,such as isotactic homopolymer polypropylene (iPP),random copolymer PP with 3 mol%polyethylene(PPR3260),random copolymer PP with 10 mol%polyethylene(PPR7726),and 8 mol%polyethylene (EPS30R) were studied through addition of commercialα-form nucleating agent (NA) 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol(DMDBS) andβ-form NA aryl amides compound(TMB-5),respectively.The results show that the nucleation efficiency of NA during the PP crystallization process depends on the PP macromolecular structure.DMDBS or TMB-5 has an apparent nucleation effect in iPP and PPR3260,the crystallization temperature is enhanced greatly and the spherulites size is decreased dramatically.However,the crystallization behavior of PPR7726 is not influenced by the addition of DMDBS.Furthermore,compared with the crystallization behavior of iPP with DMDBS,a more interesting phenomenon during the crystallization of PPR3260 with the same DMDBS content is observed.The crystallization and melting behaviors of NAs nucleated iPP, polypropylene grafted by maleic anhydride(PP-MA) and their blend iPP/PP-MA(50/50) were also comparatively studied.DMDBS and TMB-5 were used.It is interesting to observe that,although DMDBS shows excellent nucleation effect for virgin iPP,the crystallization behaviors of PP-MA and blend of iPP/PP-MA are completely independent on the addition of DMDBS.However, whether in iPP,PP-MA or in iPP/PP-MA blend,TMB-5 presents good nucleation effect and theβ-PP is the main crystalline structure.Further results based on the master batch suggest that DMDBS is well dispersed in iPP but aggregated in PP-MA,however TMB-5 shows good dispersion in both iPP and PP-MA.Our results show that the dispersability of NA is one of the key factors determining the nucleation effect of NA.This paper also studys the crystallization behavior of PP-MA with TMB-5. The isothermal and nonisothermal crystallization kinetics of PP-MA and nucleated PP-MA are comparatively researched based on the concentration ofβ-NA of 0.2wt%.Subsequent melting behaviors after isothermal and nonisothermal crystallization processes are also investigated to explore the crystalline structures formed during the crystallization.The results indicate that TMB-5 is still very efficient in influencing the crystallization of PP-MA through increasing the nucleation density and accelerating the spherulites growth rate,leading to large amounts ofβ-phase formation during the crystallization process.