Influence of air content on thermal degradation of poly(ethylene terephthalate)

The aim of these research is to investigate the air content on aging of poly-(ethylene terephthalate) (PET) preforms. Three air pressures were selected and in each pressure 5 samples were aged during 21 days in 80°C. Three samples were selected to be cut for determination of density with the use of hydrostatic method. Sample mass, Young modulus and surface roughness were measured for each sample before and after aging and differences between those parameters were presented as results. The changes of parameters may lead to a conclusion that mechanism of polymeric chain oxidation is dominant during thermal aging of PET. However aging process is not the fastest in atmospheric pressure but in lower air contents. This effect may be caused by greater evaporation of small molecule degradation products and shifting of reaction equilibrium in the direction of further decomposition.