Effect of hydrolytic degradation on the microstructure of quenched, amorphous poly(glycolic acid): an X-ray scattering study of hydrated samples

The effect of hydrolytic degradation on the microstructure of unoriented, q uenched poly(glycolic acid) (PGA) was investigated using simultaneous small - and wide-angle X-ray scattering (SAXS/WAXS). Samples were analysed immedi ately after removal from the degradation media in order to prevent dehydrat ion. Analysis showed that the material initially contained a small degree o f crystallinity. On degradation, the material rapidly crystallized, develop ing a broadly similar morphology to samples crystallized from the melt. The behaviour of these new structures on degradation was similar to that obser ved in the precrystallized samples previously reported. The crystal density remained constant and little change was seen in the lateral extent of the crystal lamellae. Both the crystallinity and SAXS scattering power (or inva riant) increased during the first 30 days which may be due to the preferent ial removal of amorphous material and further crystallization of amorphous chains. The crystallization of amorphous material was facilitated by plasti cization due to the ingress of water and the cleavage of amorphous chains. In both quenched and precrystallized material, the average lamellar spacing fell and then rose during degradation. It is not possible to interpret thi s unambiguously from the SAXS data alone. It may be partially the consequen ce of a two-stage removal of amorphous material. Alternatively, the behavio ur may be explained by changes in the osmotic potential of the amorphous la yer on degradation, together with insertion crystallization. (C) 1999 Socie ty of Chemical Industry.