High-resolution thermogravimetric analysis of poly(trimethylene terephthalate) with different molecular weights

Poly(trimethylene terephthalate) samples with different molecular weights and poly(ethylene terephthalate) were investigated by high-resolution thermogravimetry in nitrogen at an auto-stepwise heating rate, The auto-stepwise heating-rate approach consists of two steps. The sample is heated at an initial rate until a weight change begins, and then is heated further at a step rate until the end of this weight change. The two-step sequence of heating is repeated for each weight change encountered. Both the beginning and the end of the weight change are defined as the step on and the step off criteria, of which the corresponding weight-loss rates are decided by the operator, Experiments were performed from ambient temperature to 600 degreesC at an initial heating rare of 50 K/min and three step-heating rates of 0.5 K/min, 1.0 K/min, and 7.0 K/min, The step on (off) criterion used was 2%/min (1%/min). The thermogravimetry and derivative thermogravimetry curves of poly(trimethylene terephthalate) samples obtained from auto-stepwise heating-rate mode indicated a degradation of multiple weight-loss stages. The first small weight-loss stage (weight loss 2 similar to4%) was highly sensitive to molecular weight. The temperature at the maximum weight-loss rate of this stage increased significantly with molecular weight. The weight loss during this step decreased steadily with increasing molecular weight, and was in good agreement with the value predicted on the basis of complete volatilization of the 1,3-propanediol unit and carbon dioxide devaluated from chain ends and the residual catalysts. For the poly(trimethylene terephthalate) samples with high molecular weight the first small weight-loss stage diminished. Molecular weight also affected the major decomposition process (weight loss 83 similar to 90%). The temperature at the maximum weight-loss rate of the major stage increased slightly with increasing molecular weight, The influence of step-heating rate on the thermal decomposition characteristics was preliminarily investigated. Additionally, the difference among various themogravimetric analysis algorithms was discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.