Melt-processed biodegradable polyester blends of poly(L-lactic acid) and poly(ε-caprolactone):: Effects of processing conditions on biodegradation

Biodegradable polyester blends were prepared from poly(L-lactic acid) (PLLA) and poly(F-caprolactone) (PCL) (50/50) by melt-blending, and the effects of processing conditions (shear rate, time, and strain) of melt-blending on proteinase-K- and lipase-catalyzed enzymatic degradability were investigated using gravimetry, differential scanning calorimetry, and scanning electron microscopy. The proteinase-K-catalyzed degradation rate of the blend films increased and leveled off with increasing the shear rate, time, or strain for melt-blending, except for the shortest shear time of 60 s. The optimal processing conditions of melt-blending giving the maximum rate of lipase-catalyzed degradation were 9.6 x 10(2) s(-1) and 180 s, whereas a deviation from these conditions caused a reduction in lipase-catalyzed enzymatic degradation rate. At the highest shear rate of 2.2 x 10(3) s(-1), PCL-rich phase was continuous in the blend films, irrespective of the shear time (or shear strain), whereas PLLA-rich phase changed from dispersed to continuous by increasing the shear time (or shear strain). This study revealed that the biodegradability of PLLA/PCL blend materials can be manipulated by altering the processing conditions of melt-blending (shear rate, time, or strain) or the sizes and morphology of PLLA-rich and PCL-rich domains. The method reported in the present study can be utilized for controlling the biodegradability of other biodegradable polyester blends. (c) 2007 Wiley Periodicals, Inc.