Synthesis and characterization of compatibilized poly(ϵ-caprolactone)/granular starch composites

To improve the mechanical properties of granular corn starch‐filled poly(ϵ‐caprolactone) (PCL) compositions, three strategies were investigated including the hydrophobic coating of starch granules by reaction with n‐butyl isocyanate, the addition of PCL‐grafted dextran (PGD) as an amphiphilic compatibilizer, and the use of PCL‐grafted granular starch (PGS). Except for the chemical modification of granular starch by reaction with n‐butyl isocyanate, the synthesis of both PGD and PGS relies upon the controlled ring‐opening polymerization (ROP) of ϵ‐caprolactone (CL) initiated by Al‐alkoxides generated onto the polysaccharide, either dextran or starch particles. While the hydrophobic coating of starch only provides higher tensile strength and elongation at break, these properties as well as Young's modulus and strength at yield of the PCL/starch blends were remarkably increased by locating the PCL‐grafted dextran at the filler/matrix interface. It is however worth pointing out that a tougher and stiffer material was obtained by melt blending PGS and pure PCL. These property changes were analyzed and clearly related to parameters such as filler dispersion, interfacial tension, interfacial adhesion and reinforcement by PCL crystallites.