Physical/thermal properties and heat seal ability of bilayer films based on fish gelatin and poly(lactic acid)

Abstract

Bilayer films of fish gelatin (FG) and poly(lactic acid) (PLA) with different FG/PLA layer thickness ratios (9:1, 8:2, 7:3, 6:4 and 5:5) were prepared by casting and characterized. Bilayer films exhibited lower tensile strength (TS) but higher elongation at break (EAB) than PLA film (p < 0.05). All bilayer films showed lower water vapor permeability (WVP) and transparency, compared to FG film. Bilayer films had the less barrier property toward UV light transmission, especially with increasing PLA layer thickness ratio. All bilayer films exhibited better oxygen barrier property (oxygen permeability of 5.07–5.88 × 10−18 mol m−1 s−1 Pa−1) than PLA film and FG layer thickness had no impact on oxygen permeability of resulting bilayer films. Based on scanning electron microscopic (SEM) study, all films showed smooth surface and two layers of cross-section were observed for all bilayer films. Bilayer films were heat sealable. The lowest seal strength and seal efficiency were attained for film with FG/PLA layer thickness ratio of 5:5 (p < 0.05). DSC analysis revealed that the FG/PLA (6:4) bilayer film exhibited two distinct endothermic peaks, corresponding to the melting transition of gelatin and PLA. Thus, the mechanical and barrier properties as well as heat seal ability of bilayer films were determined by the thickness ratios of FG and PLA layers.