Using grafted poly(ε-caprolactone) for the compatibilization of thermoplastic starch-polylactic acid blends

Abstract

Thermoplastic starch (S) and polylactic acid (PLA) blend films were obtained by melt blending and compression moulding using grafted polycaprolactone with maleic anhydride and/or glycidyl methacrylate (PCLMG or PCLG) as compatibilizers. The effect of both the PLA ratio in the blend (20 and 40% with respect to starch) and the amount of both compatibilizers (2.5 and 5%) on the film properties was analysed. Compatibilized blends presented a better dispersion of the PLA in the continuous starch phase, but the use of PCLG provoked a phase inversion in the matrix when 40% of the starch was substituted by PLA. The compatibilized blend films exhibited higher values of elastic modulus than pure starch films, but were less extensible. The use of compatibilizers did not affect the film's water vapour permeability, which was reduced by up to 33 or 50% for 20 and 40% PLA, respectively, although inverted films with 40% PLA and 5% PCLG, exhibited marked reduction (67%). Compatibilizers decreased the oxygen permeability of the films by about 50%, regardless of the ratio of PLA and the kind and amount of compatibilizer. Therefore, substituting 20% of the starch by PLA and incorporating 5% of PCLG would be a good strategy to obtain films useful for food packaging.