Comparative observation of accelerated degradation of poly( l-lactic acid) fibres in phosphate buffered saline and a dilute alkaline solution

Abstract

Accelerated degradation of poly( l- lactic acid) (PLLA) fibres was carried out in phosphate buffered saline (PBS) (pH 7.4) and a dilute NaOH solution (pH 11.0) at 80 °C for up to 7–8 days. Characterization of the viscosity-average molecular weight, the mass loss, the thermal behaviours, the morphology and the tensile properties of the PLLA fibres was performed. The results suggested that the PLLA fibres degraded in PBS followed a typical bulk degradation mechanism, but the PLLA fibres degraded in the dilute NaOH solution showed both bulk degradation and surface erosion. The melting temperature of the fibres measured by differential scanning calorimetry decreased notably in both media, while the crystallinity increased. Scanning electron microscopy showed many microcracks on the fibre surfaces across the fibre axis after degradation. Apparently because of these morphological defects and the sharp drop of the molecular weight, the fibres lost their tensile strengths almost completely after 5 days of accelerated degradation. By that time, the mass of the fibres had begun to decrease. The results generated in the accelerated degradation of fibres in PBS as well as in dilute NaOH at 80 °C could have useful implications for the in vitro degradation of PLLA fibres at 37 °C.