Thermal stability of polyethylene terephthalate (PET): Oligomer distribution and formation of volatiles

Two ovenable PET (polyethylene terephthalate) samples were investigated under severe heating conditions and oligomers and volatile substances were analysed as potential migrants into foods. The samples were tested for migration into water, 3% acetic acid and 15% ethanol solution for 1 hour at 95 degrees C. Overall migration and the specific migration of terephthalic acid ethylene glycol and diethylene glycol were all very low. The plastics were heated at 150 degrees C, 260 degrees C and 270 degrees C, for 5 minutes 30 minutes and 60 minutes. Oligomer analysis by LC/MS (liquid chromatography-MS) showed that the concentration of the second series alicyclic oligomers increased up to 15-fold oil heating whereas the major oligomer fraction, the cyclic trimer, tetramer, pentamer and hexamer showed only minor concentration changes with heating. Volatiles evolved by the samples were trapped on a Tenax trap and identified by GC/MS (gas chromatography-MS). They were few in number and low in concentration and none merited migration tests. If is concluded that evert when tested tcp to melting point, PET plastics of this type have goon temperature stability and are well suited for high-temperature food contact applications; Copyright (C) 1999 John Wiley & Sons, Ltd.