Embrittlement of polybutylene terephthalate induced by injection molding

Abstract

Embrittlement caused by injection molding was investigated on a commercial grade of Polybutylene terephthalate (PBT). The effect of temperature and residence time in the barrel on mechanical properties was studied. Results were discussed from macromolecular analysis by Gel Permeation Chromatography and crystallinity measurements by differential scanning calorimetry. It was shown that embrittlement exclusively occurs by a chain scission process in those conditions. Oxygen is shown to play a negligible role in degradation while thermolysis seems to be the main source of degradation. It was here described by a first simple kinetic model based on the beta abstraction of hydrogen at the vicinity of ester groups. A processing window was thus determined using this model and might help practitioners for processing PBT parts.