Morphological Changes of Annealed Poly-ε-caprolactone by Enzymatic Degradation with Lipase

The effects of crystallinity and temperature on enzymatic degradation of poly-epsilon-caprolactone (PCL) films and structural changes after degradation have been studied using weight loss, differential scanning calorimetry, and optical microscopy. The weight loss during the enzymatic degradation of PCL suggested that the extent of biodegradation and the rate of degradation strongly depend on the initial crystallinity. PCL films of lower crystallinity (24%) degraded much faster than films of higher crystallinity (45%). The crystallinity of low-crystalline PCL films increased with increasing degradation time, whereas the crystallinity of high-crystalline PCL films decreased with time. The spherulite size increased with increasing degradation time for low-crystalline samples but decreased with time for high-crystalline samples. These results revealed that degradation occurs first in the amorphous region where the degradation rate is much higher, and the crystalline region of the PCL film started to degrade simultaneously for those PCL with higher crystallinity. The enzymatic degradation of PCL proceeded from the free amorphous to restricted amorphous followed by lamellar edges, where PCL chains have higher mobility irrespective of hydrolysis temperature. Caproic acid was identified as the primary product formed after degradation and confirmed by proton nuclear magnetic resonance spectroscopy, suggesting that degradation occurs through the depolymerization mechanism. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 202-211, 2010