Poly(lactic acid)/thermoplastic starch sheets: effect of adipate esters on the morphological, mechanical and barrier properties

Blends of poly(lactic acid) (PLA) and thermoplastic starch (TPS) plasticized with adipate esters (diisodecyl adipate and diethyl adipate) having different molecular weight were used to produce sheets. The calendering-extrusion process at a pilot scale was used, and the mechanical, barrier, and morphological characterization of the obtained materials were performed. The increase in the TPS content affected the mechanical properties of the sheets by increasing the elongation and decreasing the rigidity. TPS conferred a more hydrophilic character to the sheets, as observed from the water vapor permeability results. The sheets plasticized with diisodecyl adipate (DIA), having a higher molecular weight, had better mechanical and barrier properties than diethyl adipate (DEA) plasticized sheets, indicating that DIA was more effective as plasticizer. Micrographs obtained by confocal laser microscopy and scanning electron microscopy showed different morphologies when different proportions of PLA and TPS were used (dispersed or co-continuous structures), which were strongly associated with the mechanical and barrier properties.