HYDROLYSIS ETCHING OF CRYSTALLINE AND AMORPHOUS POLY(ETHYLENE-TEREPHTHALATE) - INFLUENCE OF MOLECULAR-WEIGHT AND MICROSTRUCTURE

The degradation of samples of amorphous and semicrystalline PET with different molecular weights by means of hydrolysis at 180-degrees-C has been investigated by measuring the weight loss and the x-ray crystallinity as a function of etching timne. It is shown that during the first hours of etching, a concurrent crystallization of the amorphous samples takes place. It is found that weight loss values of amorphous samples after long etching times are higher than the weight loss of the crystallized materials. Results also indicate that weight loss depends to some extent on the initial degree of crystallinity of the material. It is emphasized that the lateral size of the crystallites is a major parameter in determining the total amount of etched material. Analysis of results further confirms that mainly the amorphous regions lying outside of the lamellar stacks are removed by hydrolysis. However, the crystals formed during annealing of the amorphous samples at 180-degrees-C are less perfect and the lamellar stacks in these samples are more affected by the hydrolysis attack than in the previously crystallized PET samples.