PFAS free, food-grade, water and grease-resistant coating based on crosslinked shellac for molded pulp products

In this study, insect-based resin, i.e., shellac, was spray-coated onto molded pulp product (MPP) as a water and grease-resistant food-grade barrier coating for packaging applications. The shellac was first crosslinked by curing at 125 °C for 210 min, and DSC confirmed the formation of a thermoset material. Moreover, the Tg of shellac increased after crosslinking, showing a decrease in free volume and a reduction in molecular mobility. The shellac-coated MPP was further crosslinked and then tested for different barrier properties. FE-SEM confirmed the uniform coating of shellac over the MPP, and the crosslinking showed the removal of micro holes from the coating and increased the interfacial bonding with the MPP. The crosslinked shellac coating showed a high water barrier, as Cobb and water vapor transmission rate (WVTR) showed while providing excellent grease resistance through KIT test, mustard oil penetration, and heptane transmission rate (HTR). Further, the crosslinked shellac was also under the migration limit with all the food simulants at room and elevated temperatures, showing the safe usage of different food products at different temperatures. The coating also improved the coated MPP's tensile index and bending stiffness.