HYDROLYSIS OF POLY(ETHYLENE-TEREPHTHALATE) - A KINETIC-STUDY

The hydrolysis of poly(ethylene terephthalate) (PET) was studied at 100-degrees-C in distilled water, using molecular weight, crystallinity ratio, water equilibrium concentration and gravimetric (in the dry state) determinations. The crystallinity ratio and water equilibrium concentration increase noticeably during exposure. The classical second order kinetic model was applied to the amorphous phase, taking into account the increase in its hydrophilicity. This leads to a relatively good representation of the polymer behaviour, the second order rate constant being k = 1.83 x 10(-8) kg mol-1 s-1. The sample (dry) weight increases slowly at first for about 20 days of exposure and then decreases rapidly. A kinetic study of the weight balance was made assuming that only monomers (ethylene glycol and terephthalic acid) or the monoester are released. This leads to good predictions at the semi-quantitative level. It thus appears that neither autocatalysis nor preferential hydrolytic attack at chain ends are needed to explain the behaviour of PET during its hydrolysis. A simple second order, random chain scission process seems to be sufficient to describe this behaviour.