Aliphatic polyester-grafted starch composites by in situ ring opening polymerization

Catalyzed Ring-Opening Polymerization (ROP) of lactones, such as ε-caprolactone and δ-valerolactone, has been investigated for preparing aliphatic polyester-grafted corn starch compositions. The polymerization has been carried out either in bulk (without solvent) or in 10 wt% granular starch in toluene suspension, after adequate activation of the starch surface amylose/amylopectin hydroxyl groups into aluminum alkoxides. This activation has been done by in situ reaction with triethylaluminum and has proved to be very effective in promoting fast ROP and also covalent grafting of the polyester chains onto the starch surface. Drying of the starch granules constitutes a key-step of the proposed process. The actual fixation of the initiator onto the starch surface has been checked by XPS analysis whereas good adhesion between the two components has been evidenced by SEM observations. Growth of the polyester chains on the starch granules has been followed by the increase of the mean diameter of the 'encapsulated' granules as attested by laser scattering granulometry.