Fully Bio-Based, Flexible, Non-isocyanate Polyurethane Foams With High Lignin Content for Protective Packaging Applications

Polyurethane foam is a valuable material with applications across the automotive, packaging, construction, appliance, and furniture industries. However, traditional polyurethane foams are made from petroleum-based precursors including harmful isocyanates. Isocyanates are the leading cause of workplace asthma and are made from toxic phosgene gas, representing a challenge to green chemistry principles such reducing risk and environmental footprint. To address these concerns, non-isocyanate polyurethane (NIPU) foams have been the focus of research for the past decade, but they still face significant challenges in achieving commercial viability. NIPUs replace the traditional polyurethane reaction with a safer, non-isocyanate process most often employing cyclic carbonates and diamines. Current approaches to NIPU foams struggle to meet the low-density and flexibility of commercial foams and also employ many petroleum-derived and toxic agents. This work demonstrates the use of kraft lignin, a crosslinked aromatic polymer produced by the dominant chemical pulping process today, as an effective raw material for flexible NIPU foams, reaching densities below 70 kg/m3 while displaying flexibility. A biobased, aliphatic agent was added in various amounts to introduce flexibility to the polymer structure while modifying the viscosity of the reaction mixture to enable increased rise height for products containing over 30% lignin. The thermal, mechanical, cushion testing, and burn testing results of a series of NIPU foams are compared to a conventional PU reference foam and the structure-property relationships of the novel materials are explored based on the lignin-to-aliphatic content. The results show a fully biobased, flexible, NIPU foam from lignin that can approach commercial properties, helping to demonstrate the relevance of NIPU foams for many applications focusing on protective packaging applications.