Thermal properties and enzymatic degradation of blends of poly(ε-caprolactone) with starches

Waste disposal is an increasing problem as the availability of landfill areas diminishes. Growing environmental concerns have led to the development of alternative biodegradable materials with properties comparable to conventional polymeric materials such as polyethylene and polypropylene. Poly(ε-caprolactone) (PCL) is a biodegradable, aliphatic polyester that is attractive because of its availability, variable biodegradation, and good mechanical properties. However, the use of PCL is limited by its high cost. This problem can be overcome by blending PCL with starch, an inexpensive, biodegradable polysaccharide. In this work, we studied the properties of PCL with the cornstarches Amidex 3001 (A1), Amidex 4001(A2) and Penetrose 80 (A3), using PCL/starch proportions of 25/75, 50/50 and 75/25. Thermal analysis of the blends was done by differential scanning calorimetry (DSC) and the susceptibility to enzymatic degradation was assessed in samples of films incubated with 1.0 mg/ml of proteinase K in 0.05 M Tris buffer, pH 8.6, at 37 °C for 72 h. The addition of starch reduced the crystallinity of PCL proportionally to the amount of starch added to the blend (from 0.9 to 39.6%, except for the A350/PCL50 blend for which there was an 8.7% increase in crystallinity). This reduction in crystallinity favored enzymatic degradation by proteinase K, which increased with increasing starch content. However, there was no difference among the starches studied. Light microscopy confirmed that enzymatic digestion affected mainly the starch.