Blends of aliphatic polyesters.: III.: Biodegradation of solution-cast blends from poly(L-lactide) and poly(ε-caprolactone)

Phase-separated blend films were prepared with the solution casting method from poly(L-lactide) (PLLA) and poly(epsilon-caprolactone) (PCL) with different PLLA contents [X- PLLA (w/w) = PLLA/(PCL + PLLA)] and their biodegradation was investigated in soil up to 20 months by gravimetry, gel permeation chromatography, tensile testing, differential scanning calorimetry, and scanning electron microscopy. The nonblended PCL film and the blend film with X-PLLA = 0.25 disappeared in 4 and 12 months, respectively, while most of the initial mass remained for the blend film of X- PLLA = 0.75 and the nonblended PLLA film. The decrease in weight remaining, molecular weight, tensile strength, and elongation-at-break was higher for blend films of low X-PLLA. The melting temperature of PLLA in blend films of X-PLLA = 0.5 and 0.75, and of nonblended him, remained around 179 degrees C upon biodegradation in soil for 20 months. The preferred biodegradation of PCL in blend films resulted in formation of microspheres of a PLLA-rich phase at the surface for the blend film of X- PLLA = 0.25 and the porous structure for blend films of X- PLLA = 0.5 and 0.75. Comparison of the weight loss of blend films in biodegradation in soil with that of the nonenzymatic hydrolysis in phosphate-buffered solution revealed preferred enzymatic degradation of PCL and insignificant attack. to PLLA in the blends. (C) 1998 John Wiley & Sons, Inc.