Toward Greener and Sustainable Alternatives to Formaldehyde-Based Resins: A Literature Review of Their Types, Synthesis Methods, and Applications

Formaldehyde-based resins, such as urea-formaldehyde (UF), phenol-formaldehyde (PF), and melamine-formaldehyde (MF), are thermosetting polymers widely used in various industrial applications. However, environmental and health concerns associated with formaldehyde emissions and polyol residues have led to an increased interest in developing bio-based alternatives. This overview review focuses on the cashew nut shell liquid (CNSL)-derived resins, particularly cardanol-formaldehyde resins, as a sustainable and low-toxicity choice. This review comprehensively discusses the chemistry and reactivity of CNSL, the types of CNSL-formaldehyde resins, synthesis methods, performance characteristics, and applications. CNSL-formaldehyde resins exhibit adhesive properties comparable to those of conventional PF resins with enhanced flexibility and improved sustainability. They demonstrated varied thermal and mechanical performances based on formulation type, cardanol content, and curing conditions. Its applications include wood adhesives, coatings, corrosion-resistant paints, biocomposites, electrical insulation, and foam products. Finally, this review highlights the potential of CNSL-formaldehyde resins as viable alternatives to formaldehyde-based adhesives, which offers valuable insights for researchers and industry stakeholders pursuing greener and more sustainable resin technologies. Future research should focus on optimizing the catalyst systems, polymerization pathways, and integrating lifecycle analysis to fully realize the potential of these bio-based resins across various sectors.