Phenolharz

Phenolharz, or phenolic resin, is a thermosetting polymer produced by the condensation of phenol (or substituted phenols) with formaldehyde. When cured, these resins form crosslinked networks that are heat resistant, dimensionally stable, and chemically durable. Phenolformaldehyde resins were among the first synthetic polymers and are still widely used in electrical, automotive, and construction applications due to their combination of heat resistance and electrical insulation.

There are two main families of phenol-formaldehyde resins: novolac and resol. Novolac resins are prepared with a phenol-to-formaldehyde ratio that results in linear prepolymers and require a separate curing agent, such as hexamethylenetetramine (HMTA) or melamine, to crosslink during processing. Resol resins are formed with excess formaldehyde under alkaline conditions and cure upon heating without an added hardener, through rapid crosslinking that develops as the resin is heated. In practice, blends and modified formulations are common to tailor curing behavior and properties.

Key properties include high thermal stability, good chemical resistance, and strong mechanical rigidity, but they tend to be brittle and relatively dense. They are also excellent electrical insulators and exhibit low creep at elevated temperatures, making them suitable for electrical laminates, molding compounds, and coatings. Phenol-formaldehyde resins are widely used in plywood and other wood composites as adhesives, in brake linings, foundry sand binders, and in various high-temperature or chemically demanding applications. They can be dark in color and may release formaldehyde during curing, requiring appropriate handling and ventilation.

Historically, phenolharz contributed to the development of Bakelite, one of the first synthetic plastics. Today they remain important for applications where heat resistance, dimensional stability, and electrical insulation are essential.