Biodegradable blends and composites of polycaprolactone and starch derivatives

Abstract

High-molecular-weight (40 000 and 80 000 g mol −1) polycaprolactone (PCL) has been blended with high-amylose corn starch (HA-CS, 70% amylose) and waxy corn starch granules, as well as with the non-granular starch acetate derivatives. The properties of films of these blends were evaluated using differential scanning calorimetry, dynamic mechanical thermal analysis and Instron tensile testing, and compared with similar blend films made with poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV, 11.6% HV content). All of the PCL blends and the PHBV blends with granular starch were found to be mechanically compatible but phase-separated. The PHBV/starch acetate blends were also phase-separated, but were too brittle for mechanical testing. The PCL/HA-CS blends were the strongest, with ≈15% lower tensile strength and a 50% higher modulus than PCL, up to 25 wt% HA-CS. Optical microscopy showed that the small size of the HA-CS granules (10 μm) and good dispersion of the granules in the PCL matrix were the reasons for the good mechanical properties compared with the other blends. Crosslinking was found to improve the thermal properties of the blends.