Improved dispersion of grafted starch granules leads to lower water resistance for starch-g-PLA/PLA composites

Polylactide (PLA) was grafted on the surface of starch (St) granules to improve the interfacial adhesion between starch granules and PLA matrix in starch/PLA blends. The grafting significantly improved strain at failure values of St-g-PLA/PLA 25:75 blends as compared to starch/PLA 25:75 blends. However, unexpectedly the water resistance of the films significantly deteriorated after the surface grafting. SEM and FTIR analysis showed that St-g-PLA was evenly distributed at the film surface and in the bulk, while unmodified starch was encapsulated inside the PLA matrix. This resulted in rapid leaching of St-g-PLA from the films during aging in water, while the unmodified starch granules were protected by PLA matrix.