Microstructure transformation due to hydrolytic degradation of ethylene terephthalate/lactic acid copolyesters
Polimery 2002, No 7/8, 528
Wide-angle (WAXS) and small-angle (SAXS) X-ray scattering methods have been used to study the supermolecular structure of ethylene terephthalate and lactic acid copolyesters having different chemical structure of macromolecules. The effect of copolymers chemical structure on their microstructure was investigated using crystallized (annealed) polymer samples. It has been found that the crystalline phase in the copolyesters contains mainly PET segments (ET sequences). The degree of crystallinity decreases with lowering the length of (ET)x sequences (X values). The crystallized copolymers of sufficiently long ET sequences showed lamellar structure (long period reflex) in SAXS studies. Copolyester specimens in form of monofilaments („as spun” as well as annealed) were subjected to hydrolytic degradation at pH 7.35 and temp. 60 °C over a time period of up to 9 weeks. Intensity of degradation changes (ηred and weight of the specimens) as well as intensity and nature of microstructure changes (WAXS and SAXS data) were highly dependent on chemical structure of the copolymers. Microstructure changes, especially SAXS characteristics, were also highly dependent on the initial morphology of the specimens, i.e. on whether they were crystallized or not before degradation.
Keywords: ethylene terephthalate/lactic acid copolyesters, hydrolytic degradation, microstructure investigation, microstructure changes, SAXS, WAXSperties