Phenolic Resin Introduction
Phenolic resins or phenol formaldehyde resins are synthetic polymers that are obtained by the reaction of phenol or their derivatives with formaldehyde in the presence of a catalyst and are classified into two categories of Resole and Novolac based on the type of catalyst.
Phenolic resins are used in the manufacture of composites, electronics, as well as thermal shields. Phenolic resins based on alkaline catalysts are called Resoles and are mostly used in the production of abrasives, refractory products, carbon-magnesite bricks, adhesives in the production of various wood parts and electrical insulation, all kinds of non-dry industrial adhesives and production of can varnish. Phenolic resins based on acid catalysts are called Novalac and are used in the production of abrasion resistant materials (cutting and sub-stone), brake pads, shoe adhesives, various types of industrial felt, casting industry and production of coating sands.
Resole resins are inherently thermoset and will be cured and networked due to heat but, Novalac resins thermoplastic and will be networked by adding the curing agent.
Phenolic resins brittle without fillers and the use of fillers and other additives to create the desired properties in them is normal.
Phenolic Resins Synthesis
Polymerization of phenol formaldehyde to Novalac resin is performed in the presence of an acidic catalyst. Oxalic acid, hydrochloric acid and sulfuric acid are common catalysts in this reaction. Novalac resin is soft and can be molded. Hexa Methylene Tetra Amine (HMTA) is used as the hardener of this polymer.
Resolve resins are produced in the presence of an alkaline catalyst such as ammonia, sodium carbonate, or sodium hydroxide. The curing reaction of the product can be done by heating in a mold with a temperature above the gel point.
Resolve resins have active groups of methylol and hydroxyl. In higher temperatures, Resoles form larger molecules with methylene networks without adding curing agent. In this case, the phenol-aldehyde reaction is a condensation reaction because of water as a by-product.
Phenolic Resin application
Phenolic resins are usually opaque and change color from pale amber to dark brown to black. The dark color of phenolic resins limits their application. Phenolic resins are available in the form of flakes, liquid films and powders.
Phenolic resins are among the most widely used resins, but they can be synthesized for engineering structures. phenolic are the second most widely used thermosetting resins.
Phenolic resins are used in the thermal insulation and fire retardant industry. This resin has a very high heat resistance despite its low strength compared to epoxy resin.
Production of brake pads, clutch discs, adhesives, variety of industrial felts, abrasives, can varnish, billiard balls, fiberglass and laboratory plates are other applications of phenolic resins.