Enzymatic degradation of blends of poly (epsilon-caprolactone) and poly(styrene-co-acrylonitrile) by Pseudomonas lipase

In polymer blends, the composition and microcrystalline structure of the bl end near surfaces can be markedly different from the bulk properties. In th is study, the enzymatic degradation of poly(epsilon -caprolactone) (PCL) an d its blends with poly(styrene-co-acrylonitrile) (SAN) was conducted in a p hosphate buffer solution containing Pseudomonas lipase, and the degradation behavior was correlated with the surface properties and crystalline micros tructure of the blends. The enzymatic degradation preferentially took place at the amorphous part of PCL film. The melt-quenched PCL film with low cry stallinity and small lamellar thickness showed a higher degradation rate co mpared with isothermally crystallized (at 36, 40, and 44 degreesC) PCL film s. Also, there was a vast difference in the enzymatic degradation behavior of pure PCL and PCL/SAN blends. The pure PCL showed 100% weight loss in a v ery short time (i.e., 72 h), whereas the PCL/SAN blend containing just 1% S AN showed similar to 50% weight loss and the degradation ceased, and the bl end containing 40% SAN showed almost no weight loss. These results suggest that as degradation proceeds, the nondegradable SAN content increases at th e surface of PCL/SAN films and prevents the lipase from attacking the biode gradable PCL chains. This phenomenon was observed even for a very high PCL content in the blend samples. In the blend with low PCL content, the inacce ssibility of the amorphous interphase with high SAN content prevented the a ttack of lipase on the lamellae of PCL. (C) 2002 John Wiley & Sons, Inc, J Appl Polym Sci 83: 868-879, 2002.