A study of microstructural changes during dehydration of hydrolytically degraded poly(glycolic acid)

The effect of dehydration on the microstructure of hydrolytically degraded, unoriented semi-crystalline poly(glycolic acid), PGA, was examined using environmental scanning electron microscopy (ESEM), thermogravimetric analysis (TGA) and simultaneous small and wide angle x-ray scattering (SAXS/WAXS). Samples were degraded in phosphate-buffered saline solution at 37 degrees C and monitored during dehydration. Few microstructural changes were observed on drying PGA after 1 hour degradation. However, on drying the hydrolytically damaged PGA, the lamellar repeat distance decreased as crystal lamellae collapsed together. The SAXS intensity profile showed voids simultaneously opening. Cracks became visible at the surface and the crystallites became more strained. The changes in surface microstructure on dehydration were found to be dependent on both the extent of hydrolytic attack and on the rate of removal of water. Significant differences in microstructure and degree of hydration were observed between degraded PGA analysed wet, after freeze-drying and after vacuum-drying. These findings indicate the importance of sample preparation in the study of degradable materials.