Chain Extension And High Performance Of Engineering Plastics

Engineering plastics request high strength which mainly depend on the molecular weight.The molecular weight of PET and PA6are generally not large in order to processconveniently,also the degradation leads to lower molecular weight when processing. Blendsof PET and PA6have both advantages of them, but they are thermodynamically miscible, andthe mechanical properties are poor when simply blending, Therefore compatibilizing isimportant when preparing the blends of PET and PA6Chain extension reaction of PET using styrene-glycidyl methacrylate copolymer(ADR)、4,4’-diphenyl methane diisocyanate(MDI)、 triphenyl phosphite（TPP）in melt process wasstudied. The effect of processing technic、chain-extender content on intrinsic viscosity andcrystallizing behavior were studied.It was showed that ADR got better effect than MDI andTPP in both PET and PA6on chain extension. Also ADR improved the tensile strength ofPET and PA6, and it was not significantly to improve the impact strength of them.Thecrystallizing behavior of PET and PA6became worse after chain extension.Also PET and PA6blends were prepared, The effect of ADR on properties of the blendswas studied.It was showed that there were not only chain extension between ADR with bothPET and PA6,but also the PET-co-PA6copolymer was generated which improved thecompatibility of the PET and PA6blends.The arrangement of reaction order was:chainextension reaction of PET> compatibilizing reaction>chain extension reaction of PA6. MorePET-co-PA6block copolymer was generated with more PA6in the blends,thus thecompatibilization effect was better.The Izod impact strength of PA6/PET(70/30) blends wasimproved from47.8J/m to123.9J/m when1.5phr ADR added in,increased by159%.and thetensile strength decreased from56.5Mpa to54.7MPa,only decreased by3%. Compared to thepure PA6of which tensile strength is54.9MPa,Izod impact strength is101.3J/m,the Izodimpact strength of PA6/PETADR(70/30/1.5) blends increased by22%,and the tensile strengthwas not changing. Scanning electron microscopy (SEM) and dynamic mechanical properties(DMA) analysis showed that, the compatibility of PET and PA6was improved with the ADR; thermal analysis (DSC) showed that, the crystallization PET and PA6were both blocked bythe ADR.