Thermoplastic starch and poly(ε-caprolactone) blends: morphology and mechanical properties as a function of relative humidity

This paper describes the elaboration and characterization of biodegradable films from thermoplastic starch (TPS) and poly(ε-caprolactone) (PCL) blends. The films were obtained by a single screw extrusion process. Two PCLs of different molecular weights (37,000 and 50,000 g.mol−1, referred as PCL37 and PCL50) have been tested. Phase distribution of PCL and thermoplastic starch (TPS) has been characterized by FTIR, DSC and SEM. For the blend with PCL37, material surface is enriched with PCL, whereas in the blend with PCL50, TPS and PCL phases are more homogeneously distributed. Evolution of crystalline structure of the different formulations has been studied by X-ray diffraction, and mechanical properties by tensile tests. Maximal deformation of TPS/PCL blends is smaller than that of TPS, attesting the lack of compatibility between both polymers. Blending with PCL modifies the crystalline structure of TPS. Water resistance of the blends has been characterized by water sorption and water contact angle measurements. The decrease in water absorption for the blends was attributed to the decrease of starch content. At the surface of the material, water resistance of TPS/PCL50 blends is improved.