Towards an understanding of the heat distortion temperature of thermoplastics

TLDR

Heat distortion temperature (HDT) correlates with modulus–temperature behavior, being well‑defined for amorphous polymers due to the sharp modulus drop at Tg, while for semi‑crystalline polymers it is harder to predict because of a modulus plateau, sensitivity to thermal history, and possible filler‑induced increases. HDT may not accurately indicate the upper use temperature for semi‑crystalline polymers in load‑bearing situations, as significant stiffness can persist beyond the HDT.

Abstract

Abstract A systematic understanding of the heat distortion temperature (HDT) of amorphous and semi‐crystalline polymers is possible through a direct correlation with the modulustemperature behavior. For amorphous polymers, the precipitous drop in modulus at the glass transition temperature makes the HDT a well‐defined, reproducible and predictable property. Furthermore, the addition of reinforcing fillers has a negligible effect on the HDT of the amorphous polymer. For semi‐crystalline polymers, however, the exact opposite may hold true. The modulus exhibits a “plateau” region between the glass transition and the melting transition. Hence the HDT often is difficult to predict, is sensitive to thermal history and may be greatly increased through the addition of fillers. More importantly, the HDT may not be an accurate measure of the upper use temperature for semi‐crystalline polymers in load bearing situations since considerable stiffness may still be retained even upon exceeding the HDT.