What Is Phenolic Resin?

Phenolic resin is a heat-cured plastic formed from a reaction of a carbon-based alcohol and a chemical called aldehyde. Formaldehyde is a common raw material for this type of resin, but others related chemicals can be used. The resin is hard, heat resistant, and can be mixed with a wide range of materials for industrial and residential uses.

A phenol is an aromatic hydrocarbon, which means it contains a group of six carbons linked in a circular arrangement. This molecular shape permits the molecule to link to other molecules at selected sites around the ring. An aldehyde provides a linking molecule that creates a regular pattern or grid of phenol groups. The reaction occurs with heat and creates a very strong, stable polymer called a thermoset plastic. Hydroxybenzene, or C₆H₆O, is often called phenol and is a common raw material. Other phenol chemicals can be used, including material separated from cashew nut shells.

There is a range of uses for phenolic resin in commercial and home applications. It can be cured around a canvas or fiber core to create rigid parts used for pump impellers, gears or other heat-resistant applications. If paper is saturated with this resin, a popular laminate for kitchens and bathrooms can be created. In the early 20th century, the resin was mixed with wood fibers to create Bakelite®, a popular material for oven handles, cooking tools and decorative door and cabinet parts.

Phenolic resin board is widely used for electronic circuit boards into the 21st century. The cured resin is often mixed with small amounts of natural or synthetic fibers to prevent breakage, because the resin can be brittle when cured. The boards do not conduct electricity, and will resist heat generated by electronic equipment.

Compressors and pumps can use phenolic parts due to their chemical and heat resistance. The uncured resin is a liquid, so custom part shapes can be molded to meet specific requirements. Parts are lightweight and can replace metal in aviation or marine applications where weight savings are needed.

Fire resistance is a key benefit to phenolic resin, because the material chars rather than burns. Char is a reaction where the molecules are changed to a carbon structure rather than burning away as ash. Resins that are exposed to extreme heat give off very few toxic fumes, making them useful in aircraft and automotive parts. In spacecraft, heat shields and rocket nozzles can be made from phenolic resins, providing a material that will wear away and resist burning.

The circular carbon shape of phenols makes the resins useful as adhesives. They form good chemical bonds with a wide range of materials, and will create a very stable adhesive bond when cured. These adhesives are widely used for laminated, or layered, construction boards, decorative wallboard, and interior surfaces in transportation equipment.