The Preparation Of The PET/PBT Alloy And The Study Of Its Crystallization Behavior

Both PET and PBT have excellent thermostability, corrosionstability, weatherability, electrical insulating property and low frictioncoefficient. The big difference of properties between them was that PEThas a slow crystallization rate, but PBT could crystallize at a fast rate.Blend PBT with PET will make up the absence of the application of PETin the area of engineering plastics because of its bad crystallinity andincrease performance-price ratio, in terms of the processing craft, blendPBT with PET will raise the crystallization rate of PET, which will solvethe problem that PET would easily warped in the process of molding andhas a long moulding period. However, trans-esterification would easilytake place between PET and PBT in the melts at high temperature, whichwill affect the crystallization behavior and decrease the strength ofPET/PBT alloy. Therefore, this study is a basic research forcrystallization behavior which have big influence in the melting thermalbehavior of PET/PBT blending system and the mechanical properties ofPET/PBT alloy. The main research contents are as follow:(1)Compared the properties of PET/PBT with PET and PBT. Thepellet of PET/PBT alloy and the testing spline was prepared through meltextrusion and injection molding respectively. The results showed that, thestrength of PET/PBT improved compared with PET and PBT, thecrystallization rate relation of them was VPBT>VPET/PBT>VPET, all of theircrystal particle size were very small and the crystal structure was compact,so the PLM testing didn’t show the cross extinction feature. In addition,the two melting peaks in the DSC curves of second heating of PET/PBTmoved to lower temperature and closer to each other because oftrans-esterification.(2)The influence of trans-esterification inhibitor on thecrystallization behavior of PET/PBT melting blends. Compared the effectof several kinds of trans-esterification inhibitor through two times ofcirculated heating scan, it showed that TPPi with an amount of0.5%could improve the mechanical properties of PET/PBT alloy and make the blending system holding two separated melting peaks at the same time,which indicated that the trans-esterification in the blends have beeninhibited effectively, the presentention in the influence on thecrystallization was that the crystallization temperature of the systemincreased by12.8℃, the crystallization process accelerated andcrystallized more sufficient. After all, chose TPPi with an amount of0.5%as the trans-esterification inhibitor in the follow-up study.(3)The influence of different nucleating agents’s on PET/PBT/TPPi melting blends. The DSC test indicated that,1%of talc, nano-SiO2,nano-TiO2and Surlyn can raise the melting point and crystallizationtemperature of PET/PBT,1%of nano-SiO2, nano-TiO2and CaCO3couldeffectively accelerated the crystallization process. Some of the systemsshowed double crystallization peaks which was rare in others’ study, andit was mainly because of the different nucleating effect of the nucleatingagents on PET and PBT and the synergistic effect between them. Theisothermal crystallization behavior was analyzed through the Avramiequation modified by means of Jeziorny, the main process of isothermalcrystallization of the systems that added nucleating agents except formodified nano-SiO2and nano-TiO2kept good linearity. However, all ofthe nucleating agents didn’t raise the main mechanical properties of themelt blending system, only the hardness of each system increased afteradded each of the nucleating agents.