Abstract
Phenol–formaldehyde (PF) resin continues to dominate the resin industry more than 100 years after its first synthesis. Its versatile properties such as thermal stability, chemical resistance, fire resistance, and dimensional stability make it a suitable material for a wide range of applications. PF resins have been used in the wood industry as adhesives, in paints and coatings, and in the aerospace, construction, and building industries as composites and foams. Currently, petroleum is the key source of raw materials used in manufacturing PF resin. However, increasing environmental pollution and fossil fuel depletion have driven industries to seek sustainable alternatives to petroleum based raw materials. Over the past decade, researchers have replaced phenol and formaldehyde with sustainable materials such as lignin, tannin, cardanol, hydroxymethylfurfural, and glyoxal to produce bio-based PF resin. Several synthesis modifications are currently under investigation towards improving the properties of bio-based phenolic resin. This review discusses recent developments in the synthesis of PF resins, particularly those created from sustainable raw material substitutes, and modifications applied to the synthetic route in order to improve the mechanical properties.
Highlights
Phenolic resin synthesized from phenol and formaldehyde continues to adorn the resin industry, over a century after its first development, due to its versatile properties and performance in a wide variety of applications
Phenolic resin is classified into novolac or resol resin based on the pH and phenol to formaldehyde ratio used in the reaction
Compared with tannin-phenol-formaldehyde (TPF) resin, depolymerized tannin-substituted PF resin (DTPF) resin shows a 67.6% decrease in gel time, while the mass loss after hydrolysis decreased by 26.3%, the bonding strength increased by 63.6%, and the formaldehyde emission decreased by 64.4% [21]
Summary
Phenolic resin synthesized from phenol and formaldehyde continues to adorn the resin industry, over a century after its first development, due to its versatile properties and performance in a wide variety of applications. (1) moving towards more sustainable bio-sources of raw materials; (2) improving health and safety during manufacture and end use; and (3) enhancing the performance characteristics of the resin. These motivations are discussed in the following paragraphs. This review focuses on the recent developments in the synthesis and applications of phenolic resin It will discuss the classification of phenolic resin based on the synthesis conditions, biobased substitutes for phenol, and formaldehyde, and the modifications performed on the reagents to enable the production of resin from more sustainable resources for a variety of industrial applications
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