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

Abstract

The effect of hydrolytic degradation on the microstructure of unoriented, quenched poly(glycolic acid) (PGA) was investigated using simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS). Samples were analysed immediately after removal from the degradation media in order to prevent dehydration. Analysis showed that the material initially contained a small degree of crystallinity. On degradation, the material rapidly crystallized, developing a broadly similar morphology to samples crystallized from the melt. The behaviour of these new structures on degradation was similar to that observed 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 invariant) increased during the first 30 days which may be due to the preferential removal of amorphous material and further crystallization of amorphous chains. The crystallization of amorphous material was facilitated by plasticization 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 this unambiguously from the SAXS data alone. It may be partially the consequence of a two-stage removal of amorphous material. Alternatively, the behaviour may be explained by changes in the osmotic potential of the amorphous layer on degradation, together with insertion crystallization. © 1999 Society of Chemical Industry