Handbook of Thermosetting Foams, Aerogels, and Hydrogels: From Fundamentals to Advanced Applications

Abstract

The development of phenolic resins that invigorated the polymer industry is considered to be the first synthetic resin developed and thus leaves an indelible mark in the field of polymer science. These thermoset resins are synthesized by the condensation polymerization of phenol or a mixture of phenols along with aldehyde. The chemical stability and the properties of the phenolic resins helms hope on the precursors used, i.e., an aldehyde along with the phenolic monomer and the reaction condition. Among the various phenolic resins, phenol-formaldehyde (PF) resin obtained the most attention of researchers, and it is synthesized by taking formaldehyde as the aldehyde monomer along with phenol. In the case of PF resin, depending on the ratio of formaldehyde to phenol and the pH of the reaction, PF resins are classified as Novolac and Resol resins, respectively, and both have their characteristic properties and stability. Looking into the trajectories of research done on phenolic resin, a myriad of researches have been conducted on the synthesis of PF resin from natural sources, an astonishing green approach toward resin synthesis, which can be taken as a substitute for the petroleum-derived monomers. Natural sources like hard and softwood, bark, residual lignin and cashew nut shell liquid (CNSL) have al emerged as potential sources of phenolics, out of which CNSL has gained the most attention because of its low cost and ease of use in synthesizing when compared to other sources. The current chapter gives insight into the synthesis of PF resins (Novolac and Resol resins) along with their characteristic properties and stability and also debates the synthesis of PF-resin from CNSL along with structure-property relations, properties, and applications. © 2024 Elsevier Inc. All rights reserved.