Bio‐based novolac resins from cashew nut processing waste: Alternative resource for the development of high‐value sustainable products

Abstract In the last decades, there is an increasing trend for replacing petro‐based adhesives with sustainable and eco‐friendly alternatives, especially in the wood industry. In this work it was developed and characterized novolac‐type phenolic resins from the full use of the cashew nut shell liquid (CNSL), an agro‐industrial residue and a rich source of phenolic compounds, sustainable alternative to petroleum‐derived chemicals, to develop bio‐based polymers. CNSL and paraformaldehyde were reacted, using oxalic acid as a catalyst, under a solvent‐free methodology. A dark and viscous resin of high molar mass and thermally stable was obtained. The development of highly bio‐based adhesives was proposed by combining CNSL‐based novolac resin (CNSL‐nov) with commercial epoxy resin (DGEBA), as an alternative to conventional hardeners. The use of the epoxy‐novolac system proved to be efficient and promising in obtaining new highly cross‐linked polymers with excellent thermal performance and with potential for wood industry, improving the bio‐based content of high‐performance adhesive.