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

The hydrolysis of poly(ethylene terephthalate) (PET) was studied at 10 0-degrees-C in distilled water, using molecular weight, crystallinity ratio, water equilibrium concentration and gravimetric (in the dry sta te) determinations. The crystallinity ratio and water equilibrium conc entration increase noticeably during exposure. The classical second or der kinetic model was applied to the amorphous phase, taking into acco unt the increase in its hydrophilicity. This leads to a relatively goo d representation of the polymer behaviour, the second order rate const ant being k = 1.83 x 10(-8) kg mol-1 s-1. The sample (dry) weight incr eases 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 monoeste r are released. This leads to good predictions at the semi-quantitativ e level. It thus appears that neither autocatalysis nor preferential h ydrolytic attack at chain ends are needed to explain the behaviour of PET during its hydrolysis. A simple second order, random chain scissio n process seems to be sufficient to describe this behaviour.