Surface degradation of poly(l-lactic acid) fibres in a concentrated alkaline solution

Surface degradation of poly( l -lactic acid) (PLLA) fibres was studied by incubating them in a concentrated NaOH solution at 37 °C for several hours. Characterization of the viscosity-average molecular weight, the mass, the morphology, the thermal behaviours and the tensile properties of the PLLA fibres were investigated. After surface degradation, the viscosity-average molecular weight of PLLA did not drop but apparently showed a slight increase. The diameter and the mass of the PLLA fibres dropped significantly. The fibres lost their surface smoothness and a regular rough topology was generated after 2.5 h of degradation. Thermal studies by differential scanning calorimetry showed that the melting temperatures of the PLLA fibres increased notably but the crystallinity did not change. The tensile properties of the PLLA fibres did not show significant changes in 1 h of degradation. After 2.5 h of degradation, the values of the tensile modulus apparently increased slightly, but the ultimate strength and the maximum elongation showed substantial decreases. The 3% offset strength did not exhibit significant changes during all the degradation. Results suggested that the degradation of PLLA fibres in the concentrated alkaline solution followed a surface erosion mechanism. The effects of degradation may be advantageous in applications where cell attachment is important.