Preparation and properties of three layer sheets based on gelatin and poly(lactic acid)

Abstract

Glycerol plasticized-gelatin (Ge-30Gly) and poly(lactic acid) (PLA) films were prepared by heat-compression molded and then piled together to produce a biodegradable three-layer sheet with PLA as outer layers and Ge-30Gly as inner layer. Multilayer sheets displayed a compact and uniform microstructure due to the highly compatible individual layers which could interact by strong hydrogen bonding. Lamination reduced total soluble matter compared to the single layers while keeping transparency. Tensile strength of the multilayer sheet (36.24±4.27 MPa) increased 16-folds compared with that of Ge-30Gly. Lamination also had beneficial effect on the barrier properties. The WVP of the multilayer sheet (1.2±0.1 10-14 kg∙m·Pa-1·s-1∙m-2) decreased compared with that of Ge-30Gly while the oxygen permeability (17.1±2.3 cm3(O2)·mm·m-2·day-1) was reduced with respect to that of neat PLA and was comparable to the value of Ge-30Gly layer. The individual layers and multilayer sheet were submitted to degradation under indoor soil burial conditions. Biodegradation of multilayer as well as individual components was evaluated by monitoring water absorption and weight loss. During the time of the experiment, weight loss of multilayer sheet show two stages. During the first stage, the weight loss of the film increased rapidly due to the lost of Ge-30Gly inner layer. From 25th day until 120th day no further changes were observed suggesting that the inner layer was completely biodegraded. Visually, multilayer sheet turned from transparent to opaque after 120 days due to an increment of the crystallinity of the PLA polymer matrix. It was confirmed by DRX. SEM analysis shows that after 25th days a significant change in the overall morphology of multilayer sheet can be observed. This suggested that Ge inner layer promote the PLA outer layer degradation, probably because the Ge hydrophilicity allows the water molecules to penetrate more easily within the PLA and to trigger the hydrolytic degradation process faster.