Influence of a hydrocarbon side chain on the performance of Physaria fendleri-Castor oil polyurethane packaging adhesives

Polyurethanes (PU) are an important class of materials used in various applications across industries. With increased global interest in sustainable and environmentally benign packaging, there is high demand to replace traditional petroleum-based materials with renewable, bio-derived sources. This research developed PU adhesives for multilayer flexible food packaging using Physaria fendleri oil (formerly Lesquerella fendleri) and Ricinus communis (Castor oil), each possessing naturally occurring hydroxyl functional groups. Physaria oil has, on average, hydroxyl functionality on two of the three fatty acids compared to all three for Castor oil; therefore systematically varying the concentration of each oil and maintaining a constant crosslink density for each adhesive facilitates an understanding of the effect of Physaria oil's unreacted hydrocarbon sidechain on physical properties in biobased adhesives. The results of this study determined that the peel resistance of polyethylene and polyethylene terephthalate substrates adhered with adhesives containing varying amounts of Physaria and castor oils possessed average peel strengths of 6–8 N relatively independent of composition. Furthermore, the glass transition temperatures were measured to be within the range of −25 to −44 °C with higher concentrations of the hydrocarbon sidechain resulting in lower Tgs. These physical properties indicate their use in multilayer food packaging adhesive applications where isocyanate PU adhesives are still commonplace. Understanding the PU adhesive network structure-property relationships will help develop the next generation of bio-derived PU adhesives with additional sources of renewable feedstocks for food packaging applications