Phenolic Resins

Abstract

Phenolic resins are a family of polymers and oligomers composed of a wide range of structures based on the various reaction products of phenols with formaldehyde. Applications vary from commodity construction materials to high technology applications in electronics and aerospace. Phenolic resins are prepared using acidic or basic catalysts. Weak Lewis acids, such as zinc acetate, are used for specialty resins. Phenolic novolaks are thermoplastic resins prepared from acid catalysts and a molar excess of phenol. They have a molecular weight of 500–5000 and a glass‐transition temperature T g of 45–70°C. Novolak resins are typically cured with 5–15% hexamethylenetetramine as the cross‐linking agent. Resole‐type phenolic resins are produced with a molar ratio of formaldehyde to phenol of 1.2:1 to 3.0:1 and alkaline catalysts such as NaOH, Ca(OH) 2 , and Ba(OH) 2 . A typical resin has an initial molecular weight of 150 to perhaps 1500. For systems of unsubstituted phenols, the final cross‐link density is 150–300 atomic mass units per cross‐link. In 2001, worldwide consumption of phenolic resins exceeded 4 × 10 6 t; slightly less than half of the total volume was produced in the United States, where the largest volume application is in plywood adhesives and accounts for ca 49% of U.S. consumption. As a mature industry, U.S. production of phenolic resins has paralleled the growth in the GNP. Applications for phenolic resins include coatings, adhesives, carbonless copy paper, molding compounds, bonded and coated abrasives, friction materials, foundry resins, laminates, air and oil filters, wood bonding, fiber bonding, composites, spherical fillers, and fibers. Factors contributing to the health and safety concerns of phenolic resins are related primarily to the presence of unreacted phenol and formaldehyde. Unreacted phenol in a resin can range from >10% for liquid resoles used in impregnation processes to <1% for novolaks intended for use as epoxy hardeners. Free formaldehyde can be 2–4% in liquid adhesives.

The current and emerging sources of technical lignins and their applications

“…In the final stage, the plywood is hot pressed at 140-150 °C to cure the glue by finalizing the crosslinking in PF polymer. 143 Replacing phenol with lignin caused changes both in adhesive synthesis and in the curing. 147 When a portion of phenol was replaced with lignin, the polymerization was faster to form the adhesive, but a higher temperature was needed for curing.…”

“…14). 143 The largest application of PF resins is wood adhesive in the fabrication of plywood, particle board, waferboard, and fiberboard. It is also used in molding compounds, abrasives, coatings, etc.…”

Thermal behavior of elastomer–resin mixtures used as friction materials

“…This article examines the phenolic resin and synthetic rubber binders that form the organic component of the material. Rubbers [mainly nitrile‐butadiene (NBR) and styrene‐butadiene (SBR)3, 4] make the material elastic, while resins confer compactness and wear resistance 5, 6. When the raw materials are mixed, the resin dissolves and is uniformly distributed.…”

Synthesis, Characterization and Thermal Degradation Oligomer and Monomer/Oligomer Metal Complex Compounds of 2‐Methylquinolin‐8‐ol

“…Besides possessing good thermal properties, these polymers or oligomers can be doped to make them electrically conductive (3). The molecular weight distributions of polyphenols significantly influence functional properties (4).…”