Influence of the type of buffer solution on thermal and structural properties of polylactide-based composites

Hydrolytic degradation depends on internal and external factors. One of the external factors is pH of the degraded medium. In the case of buffer solutions changes in pH are strongly dependant on the capacity. For this reason the aim of this work was to determine the effect of the type of buffer solution on hydrolytic degradation of polylactide and its composites consisting of polylactide (L) as polymer matrix and Montmorillonite K10 (S). Hydrolysis was carried out within a period from 7 to 30 days at 60 °C in two buffers: phosphate buffer solution (pH 7.40) and phosphate-citric buffer solution (pH 7.40). In order to investigate the influence the type of buffer solution has got on hydrolysis, materials were analysed by means of differential scanning calorimetry, thermogravimetric analysis and 1H NMR spectroscopy. Also changes in pH of buffers during degradation process were observed. The results indicated that the type of buffer solution, especially its capacity, strongly influences hydrolytic degradation of polylactide and PLA-based composites. In the buffer solution where pH of the degraded medium is similar to the pKa value, the degradation occurs at a lower rate.