The Study Of Crystallization Behavior Of PTT And Its Modified Systems

Poly trimethylene terephthalate (PTT) and poly trimethylene(terephthalate/isophthalate) (PTTI) were prepared by polycondensation, and polytrimrthylene terephthalate (PTT)/multi-walled carbon nanatubes (MWNTs) compositeswith varying composition from PTT and MWNTs were prepared by mixed solution method.The compositions were determined by ¹H NMR. The crystallization behavior of PTTIcopolyesters and PTT/MWNTs composites was studied by DSC, WAXD and PLM. Thepretreated effect of MWNTs was studied by TG, IR and Raman.The total crystallization rates of PTTI became slow with the corporation of IPA,which caused a poor crystallization polyester. PTTI copolyester with 60mol% becomescompletely amorphous. The results of DSC and PLM inform us that the nucleation andglowth mechanism of the PTT homopolyester is not affected by incorporating thenon-crystallizable or poorly crystallizable IPA unit into the polymer backbone. Thecrystallization pattern of PTTI was studied by PLM, indicating that a decrease of spherulitesize was observed, while its number became larger with increasing the crystallizationundercooling degree. Nonisothermal melt-crystallization kinetics for PTTI copolyesterswere studied suggesting that the crystallization rate is accelerated by increasing the coolingrate, but retarded by incorporating the IPA unit into the polymer backbone. And the valueof the modified Avrami exponent is 2.12-3.84, whereas the value of the Ozawa exponent is2.7-4.0. All above indicate that the mechanism ofnonisothermal crystallization is similar toisothermal crystallization's.The MWNTs is oxidized with HNO₃, and then Ti (OC₄H₉) 4 is used as coupling agentto pre-treat the purified product. Through these two steps, the raw material of MWNTs arepurified and functional groups such as carboxyl group and hydroxyl group are introducedwhich greatly improved the stability of MWNTs and the dispersion and compatibility of itin PTT matrix largely. The effect of MWNTs content on nonisothermal crystallizationbehavior of the composites was studied by differential scanning calorimetry. Theundercooling degreesΔT_hS of these composites decline significately and decrease by 10℃at the MWNTs content of 0.05wt% The main reason of being acceleratedcrystallization of PTT by MWNTs is that MWNTs can act as nucleating agents of PTT, andthis is proved by the studies of the crystallization morphology and nonisothermal crystallization kinetics. The nonisothermal crystallization kinetics of PTTI copolyestersand PTT/MWNTs composite were provided satisfactory descriptions by the Avramiequation, while Ozawa equation gave a worse treatement.