Phenol formaldehyde resin

Lore & Background

Phenol formaldehyde resins are formed by a step-growth polymerization reaction that can be either acid- or base-catalysed. The initial reaction involves the formation of a hydroxymethyl phenol, which can further react to form methylene or ether bridges. There are two main production methods: the acid-catalyzed reaction with excess phenol yields novolac, a thermoplastic prepolymer that requires a curing agent such as hexamethylenetetramine to crosslink into a thermoset. The base-catalyzed reaction with excess formaldehyde yields resole, a thermoset that cures upon heating without additional crosslinkers.

Reader's Guide

Phenol formaldehyde resins were the first commercial synthetic resins and remain important in many industrial applications. They are used in molded products like billiard balls and laboratory countertops, as well as in coatings, adhesives, and laminates. Novolacs serve as tire tackifiers, high temperature resins, binders for carbon bonded refractories, and curing agents for epoxy resins. Resoles are widely used for gluing building materials such as exterior plywood and oriented strand boards. Phenolic laminates, made by impregnating paper, fiberglass, or cotton with resin, are used in electrical components, bearings, and countertops. The resin is also a key component in ablative heat shields for spacecraft, where it pyrolizes to absorb thermal energy. Despite being largely replaced by epoxy resins in circuit boards, phenolic resins persist in many specialized roles due to their hardness, thermal stability, and chemical resistance.

Did You Know?

• Phenol formaldehyde resins were the first commercial synthetic resins, used as the basis for Bakelite.
• Novolac resins require a hardener such as hexamethylenetetramine to form a thermoset, while resoles cure without a crosslinker.
• The white rot fungus Phanerochaete chrysosporium and Rhodococcus phenolicus can degrade phenol formaldehyde.