Have you heard of phenolic resins? Here are the properties and uses.
According to Thomas Net:
“Phenolic (PF) resins are thermoset polymers – meaning they cure in an altered form from their uncured state and cannot be re-melted in the manner of thermoplastics. Thermoplastics are generally recyclable for this reason, while thermosets generally are not (though phenolic is something of an exception). Phenolic resins are some of the oldest of the thermosetting resins. Other thermosets include polyester, urethane, melamine, and epoxy.
Properties
“Phenolic resins, called by the tradename Bakelite®1 after inventor Leo Baekeland, are known for their heat resistance, hardness, dimensional stability, and chemical and electrical resistance. They can be brittle. The resins are classified as novolac and resole: the former being catalyzed in acid and requiring a curing agent (two-stage); the latter being catalyzed in alkali with no curing agent needed (single-stage).
“Some phenolics can be made to withstand temperatures as high as 550°F. Most are resistant to steam. PMCs, or phenolic molding compounds, are manufactured in a variety of formulations for increased fire resistance, plating application, etc. in the molded products.
“Glass fiber and specialty molding compounds are employed in molding parts that will see high mechanical and thermal stresses such as pump impellers. Carbide is added to compounds that are used to mold elements for sleeve bearings to increase slip.
Applications
“Phenolic resins were first combined with paper and fabrics by Westinghouse to produce Micarta®2 for use as insulation in electrical equipment. It is still used today for circuit boards and other electrical applications due to its excellent electrical characteristics. It has become a popular material for knife handles as it machines readily, polishes well, and has an intrinsic grip when wet. The original material was green or black but is now manufactured in an array of colors to meet the aesthetic requirements of knifemakers.
“Phenolic resins are used in other applications both alone and as additives. Their high heat resistance makes them useful as binders in the friction materials of clutch discs and brake pads, as well as in abrasive cut-off wheels and the like.
“The resins are used as tack enhancers to improve the manufacture of vulcanized products such as tires. They are combined with sand to create metal casting molds. They serve as binding agents in the manufacture of refractory brick.
“A large consumer of phenolic resins is the lumber industry especially in North America where it is used in the manufacturing of OSB, or oriented strand board.
“Products manufactured from phenolic usually incorporate fillers and are commonly compression-molded but they may be injection molded or resin transfer molded as well. Fillers such as cotton improve impact strength, while glass and mineral fillers improve heat resistance and stiffness. Processing times are usually longer than for thermoplastics because of the exothermic chemical reaction that must take place rather than simple hardening through cooling. In addition, molded parts are often put through separate heat treatment, adding to overall processing times. Products manufactured in this way include cookware and stove handles, automotive ashtrays, motor brush holders, bottle caps, etc. Phenolic molding compounds are typically powders rather than the pellets used in thermoplastics molding. Molding produces very little shrinkage and parts are dimensionally stable even at elevated temperatures.
“Various phenolic laminates are readily available in sheet form and sometimes as rods and tubes. Such sheets are used extensively for circuit board substrates.
Physical attributes
“Phenolic materials are available in only a limited range of colors, notably black and brown, and sometimes red and green. Molding compounds are available as both single- and two-stage forms, with single-stage compounds useful for in-mold metal placement where corrosion is a concern. The material bonds well and also accepts mechanical assembly. Metal components may be pressed or screwed into place.
“The properties tabulated below are for a particular phenolic material. Specifiers should inquire with manufacturers regarding the characteristics of other formulations.
“As with most thermosets, recycling of phenolic is not possible in the manner of thermoplastic as the material takes on a permanent change in form once it is heated. Some success with reusing ground phenolic as a filler has been reported, with as much as 10% being added without detriment to the characteristics of the finished products.
Costs
“Phenolic resins are especially economical compared with many other thermosets and thermoplastics. Economies are somewhat offset by the longer processing times and post-processing work required by the material as compared with high-temperature thermoplastics.
Chemical resistance
“Phenolic resins are compatible with organic and halogenated solvents such as carbon tetrachloride but generally do poorly in contact with inorganic bases and oxidizers. Blends are available which meet UL fire ratings. Phenolic resins are popular in some transit and architectural applications due to their low smoke emissions.
Physical Properties of Micarta® Sheet
“Table 1 below provides a summary of some of the physical properties of Micarta® sheet phenolic resin.
Table 1 – Physical Properties of Micarta® Sheet Phenolic Resin
| Property | Metric units | Imperial units |
| Maximum Operating Temperature | 140°C | 285°F |
| Tensile Strength | 90 MPa | 13,000 psi |
| Flexural Strength | 152 MPa | 22,000 psi |
| Water Absorption 24 hrs | 1.8% | |
| Density | 1.34 g/cm3 | 0.048 lb/in.3 |
Summary
“This article presented a brief discussion on phenolic (PF) resins including the physical properties and uses of the material. For more information on other resins, consult our other guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view details on specific products. Additional information about thermoset resins may also be found at the site of the Thermoset Resin Formulators Association.”