Improvement of Interfacial Interaction between Hydrophilic Starch Film and Hydrophobic Biodegradable Coating

Starch based materials are a promising biobased polymer with potential applications in packaging; however the use of these materials has been hampered due to high water absorption. The development of water-resistant coatings for starch-based materials has been an ongoing challenge for starch materials due to poor compatibility between hydrophilic starch and hydrophobic coating. In this work polyethylenimine (PEI) was used to improve the bonding between hydrophilic starch and hydrophobic coatings of biobased acrylated epoxidized soybean oil (AESO). Analysis including NMR, FTIR, XPS revealed that PEI interacted effectively with starch films via hydrogen bonding and bonded chemically with AESO through the Michael addition reaction. Shear adhesion testing demonstrated that the interfacial adhesion between the starch and AESO coating was significantly improved following surface treatment with PEI. The best interfacial adhesion strength was achieved when 0.8 wt % PEI with molecular weight of 25K was applied resulting in cohesive failure primarily within starch bulk rather than the interface, whereas poor bonding was observed between AESO and untreated starch. Starch films with PEI treatment and AESO coating maintained original mechanical strength after water soaking for more than 3 h. These results demonstrated the potential of developing new waterproof materials based on renewable and environmental friendly starch and AESO using PEI as a coupling agent.