Research Article. Role of ascorbic acid and iron in mechanical and oxygen absorption properties of starch and polycaprolactone multilayer film

Abstract A trilayer film based on thermoplastic starch (TPS) for the core layer and poly(ε-caprolactone) (PCL) for the skin layers was obtained by coextrusion. Ascorbic acid and iron powder were added at respectively 15% and 1.5% w/w in the TPS layer for their capacity to act as oxygen scavenger, making the film usable as active food packaging. This study demonstrates that these compounds also play a role in the interactions between the different layers. FTIR measurements show that ascorbic acid migrates at the interface between TPS and PCL, where it acts as a compatibiliser between both polymers, probably by creating new interactions between polar functions of both polymers. This leads to a better adhesion of the different layers, demonstrated by the increase of the adhesion energy from 4.10−3 N·mm−1 for the multilayer film TPS-PCL to 12.10−3 N·mm−1 for the multilayer film containing the active components. Thanks to this compatibilising effect, the mechanical properties of the multilayer film containing ascorbic acid and iron are widely improved with an average maximal tensile strength of 7 MPa, against 3.7 MPa for the multilayer film without the active components and with an elongation at break of respectively 1450% against 290%. However, despite the hydrophobicity of PCL, the water sorption of the TPS-based layer is only slightly reduced. The multilayer film shows active oxygen scavenging properties but the rate of this reaction is divided by two compared to the active film without PCL layers (15 days to reach less than 1% oxygen for the active film without PCL layers and approximately 30 days to reach the same oxygen level with the multilayer active film).