Non-isothermal crystallization behavior of poly (trimethylene terephthalate), synthesized with different catalysts

Non-isothermal crystallization behavior of PTT resins synthesized with different catalysts was studied by using differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The results showed that with the increase of the cooling rate, the crystallization temperature for poly(trimethylene terephthalate) (PTT) resin decreased, which indicated that the crystallization process was controlled by the nucleation. Catalyst had no effect on the crystallization development process, but had somewhat effect on the non-isothermal crystallization mechanism. The average values of Avrami exponent, for PTT with different catalysts were between 3 and 4. It was assumed that the non-isothermal crystallization mechanism for PTT with or without catalyst was the combination of homogenous and heterogeneous nucleation and spherulite growth, but it mainly depended on the latter. For sample 4, the non-isothermal crystallization underwent secondary crystallization process when cooling rate was over 20 degreesC/min. At the same cooling rate, the crystallization temperature, the crystallization ability and the crystallization late of PTT resins followed the sequence as: sample 2 > sample 1 approximate to sample 3 approximate to sample 4, which proved that catalysts could significantly prompt crystallization. The cooling rate had significant effect on the crystallization ability parameters of PTT, i.e., with the increase of cooling rate, the crystallization ability declined. Although catalyst could increase the crystallization ability of PTT, the effect was very limited because the effect of the molecular weight on the crystallization ability would be superior to the catalyst when the molecular weight of PTT was significantly high. The specific surface area of catalyst had also a great influence on the spherulitic morphology of PTT formed in the cooling process. The spherulite dimensions decrease with increasing the specific surface area of catalyst because of an increase in the nucleation rate, which produces more and smaller spherulites that can not grow larger before impinging on each other.