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Phenolic Resins: Properties, Types, Applications and Production
Phenolic resins, also known as phenol formaldehyde resins, are synthetic polymers that are produced from the reaction of phenol or substituted phenol with formaldehyde. They were some of the earliest plastics developed by mankind and have found widespread use due to their good electrical insulation properties, heat resistance and affordable price point.
Raw Materials
The main raw materials used for producing phenol-formaldehyde resins are phenol and formaldehyde. Phenol is obtained by cumene process, which involves alkylation of benzene with propylene to produce cumene, followed by oxidation to obtain phenol. Formaldehyde is produced via metal-catalyzed oxidation of methanol. Sodium hydroxide or hydrochloric acid are used as catalysts for the polymerization reaction. Other additives like fillers, accelerators, hardeners may also be used depending on the end use of the resin.
Types of Phenolic Resins
Phenolic Resins are classified according to their method of production and curing behavior into the following main types:
- Novolac resins - Produced by reacting phenol with less than 1 mole of formaldehyde per mole of phenol. Require a hardener to cure. Have good thermal stability.
- Resoles - Produced by reacting phenol with excess formaldehyde (more than 1 mole per mole of phenol). Can self-cure under acidic or alkaline conditions upon heating.
- Modified resins - Are made by modifying the basic novolac or resole structure to impart special properties like improved flexibility, electrical characteristics, flame retardancy etc.
- Liquid resins - Are low molecular weight versions of resoles, processed as liquids for applications like paints and varnishes.
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