Dual melting endotherms in the thermal analysis of poly(ethylene terephthalate)

Abstract

A modified mathematical model based on the melting and recrystallization of an initial distribution of melting temperatures satisfactorily predicts the melting behavior of PET in differential scanning calorimetry. The simulated DSC curves produced in this work agreed fairly well not only with experimental DSC curves performed by Holdsworth et al., but also with the DSC traces provided by SSP PET pellets. The model, taking into account the initial distribution of melting points and the distribution of melting points for the recrystallized material, succeeded in analyzing the origin of dual endotherms of PET with various thermal histories, thereby elucidating the effect of changing crystallization temperature and time, the heating rate in the DSC heating scan, as well as the SSP process on the melting behavior of PET completely. Furthermore, it has been analytically proven that the crystallinity measured on a DSC diagram could not be equal to the weight percentage of crystalline state in the initial specimen. The deviation of the measured crystallinity, as observed relevant to the melting and recrystallization processes, is caused by the changes of the heat of fusion with the melting temperature as well as the difference of heat capacities of liquid and solidstate polymer.

Nonisothermal crystallization kinetics of poly(ethylene terephthalate)/antimony‐doped tin oxide nanocomposites

“…Moreover, the degree of crystallinity ( X c ) can be calculated from the heat that evolves during crystallization (Δ H c ) with the following relation: where Δ H m is the heat of fusion for 100% crystalline PET and b is the weight fraction of the filler in the composite. Here, we adopted 140 J/g as the value of Δ H m 20. The values of X c of PET and its nanocomposites, obtained with eq.…”

Sequence distribution, crystallization and melting behavior of poly(ethylene terephthalate-co-trimethylene terephthalate) copolyesters

“…DSC heating scans, after isothermal or non-isothermal crystallization, showed multiple melting endotherms for aromatic polyesters and copolyesters [13,16,[33][34][35][39][40][41][42][43][44][45][46][47][48][49][50][51]. Traditional DSC measurements result from the summation of endothermic and exothermic processes.…”

Surlyn�/silicate hybrid materials. I. Polymerin situ sol-gel process and structure characterization

“…10 In the revised view of Eisenberg et al the idea of an ionic domain glass transition was replaced by a concept of the onset of chain segmental mobility in these restricted mobility regions. 13 These investigators also call attention to a similar secondary crystal formation that takes place in nonionic ethylene copolymers [e.g., poly(ethylene terephthalate) 14 ] and mention that this low temperature endotherm is, in fact, not unique to ionomers. 11,12 These secondary crystallites are said to be prevented from thickening because carboxylic acid and salt groups act as defects that cannot be incorporated into thick crystal lamellae.…”