Estimation of hydrolysis and biodegradation processes in ethylene terephthalate and lactic acid copolymers

Copolyesters (CPEs) of ethylene terephthalate (ET) and L-lactic acid (LA) c ontaining different amount of LA units, arranged mainly individually in cop olymer (CP) chains, were examined. CPEs in the form of sheet samples were h ydrolytically degraded and composted. Hydrolytic degradation, carried out a t 55 degreesC, showed high hydrolytic susceptibility of CPs having short en ough ET sequences; disintegration of samples and high weight loss was then observed. According to GPC studies, the hydrolytic degradation of CPs had b ulk and statistical character. Weight losses were mainly connected with the formation of low molecular (ET)x oligomers capable of dissolving in a hydr olysing medium. Composting tests, carried out at 50 degreesC, showed relati vely higher degradation changes for the better hydrolyzable CPs. Molecular weight changes of composted samples also had statistical character, but deg radation proceeded slower than in hydrolysis tests at higher proceeding tem perature. Concurrently, much higher changes of sample surface and thickness were observed than in the hydrolysis test alone.