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About Phenol Formaldehyde Resin

Learn more about this material and its uses in manufacturing.

Xomety X
By Team Xometry
March 9, 2023
 8 min read
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Phenol formaldehyde (PF) resin is a chemical compound formed when phenol and formaldehyde react together. It is used in many industries because of its strength, versatility, and stability. In the woodworking industry, it is employed as a bonding agent between wood laminates. Also, because it is a thermal insulator, PF is able to withstand high temperatures. 

Resins from the PF family are referred to by different terms including phenoplast resin and phenolic resin. Based on the molecular structure of the PF resin, the ratio of phenol to formaldehyde, and the catalyst used to control the reaction, they can be classified into two main types: resole and novolac. This article will further discuss and expand on the subject of phenol formaldehyde resin.

What Is Phenol Formaldehyde Resin?

Phenol formaldehyde resin, or PF, is sometimes referred to as phenolic resin. It is a synthetic polymer created by the reaction of phenol (or a phenol substitute) with formaldehyde. The properties of phenolic resins vary depending on the quantity or ratio of phenol and formaldehyde during the reaction as well as the type of catalyst used. Catalysts can be either acids or bases. 

The large networks of molecules that form during the reaction are permanently bonded. PF is quite a useful synthetic polymer. It was the first synthetic resin to be employed commercially, falling under the moniker, Bakelite. Bakelite was an early form of plastic that used to end up in devices such as radios and telephones. Also, PFs come in handy in the manufacturing of laboratory countertops, billiard balls, adhesives, and coatings. For more information, see our guide on 3D Printing Materials.

What Are the Other Terms for Phenol Formaldehyde Resin?

Phenol formaldehyde is not the only name used to describe this synthetic polymer. Other names include: phenolic resin, phenoplast, phenol formaldehyde, and phenolic plastic. In the commercial space, it is sometimes referred to by trade names such as: Novotext, Micarta, and Bakelite. Phenolic resin is popular in the industry thanks to its good dimensional stability, high heat resistance, and good electrical resistance. 

There are, however, some drawbacks. The most notable among them is the fact that these resins are surprisingly brittle despite being known for their durability. As a result, phenoplast is often produced with strengthening filler material. 

Where Is Phenol Formaldehyde Resin Used?

Phenol formaldehyde resin finds relevance in many industries including: automotive, construction, and woodworking industries. Automotive components such: as brake pads, fuel pumps, and transmission parts are all made with phenolic-based resins. In the woodworking space, phenol formaldehyde is sometimes used in the manufacturing of medium-density fiberboard and particleboard. Those materials find application in furniture making, cabinetry, and flooring products. The function of the resin is to create a strong and durable bond between the wood fibers. The resulting bond is impervious to moisture and insects. Based on the increasing number of uses for PF resin, it will clearly continue to be an important material. It is a valuable resin that is essential to many industrial processes. 

What Is the Structure of Phenol Formaldehyde Resin?

The structure of phenol formaldehyde resin is dependent on the ratio of phenol to formaldehyde as well as the type of catalyst present — either an acid or a base. Table 1 below describes two common structures of phenolic resin:

Table 1: Two Common Structures of Phenolic Resin
Structure of Phenolic ResinDescriptionRatio of Phenol to FormaldehydeUses
Structure of Phenolic Resin
Resole
Description
Created when phenol is reacted with excess formaldehyde in the presence of water and a base.
Ratio of Phenol to Formaldehyde
Low
Uses
Used as adhesives between layers of plywood.
Structure of Phenolic Resin
Novolac
Description
Created by reacting excess phenol with formaldehyde in the presence of an acidic catalyst. The resulting synthetic polymer is often ground to powder before being mixed with a filler and heated in a pressurized mold.
Ratio of Phenol to Formaldehyde
High
Uses
Environments where temperatures are high. For example, Novolacs are used in the handles of kitchen pots.

What Is the Color of Phenol Formaldehyde?

Phenol formaldehyde resins are known for their amber color. These materials are usually opaque with colors ranging from yellow, light amber-brown to dark brown, and sometimes even black. Pure phenol is typically a colorless liquid but may appear pink or red. Formaldehyde is a colorless gas with a strong odor. Both chemicals should be handled with care as exposure can lead to adverse health effects. 

What Are the Properties of Phenol Formaldehyde Resin?

Due to their unique and interesting properties, phenolic resins are used in lots of applications. Here is a list of some of the properties:

  1. Good Thermal Insulation: Phenol formaldehyde resin is very resistant to heat. This is why it is used in tools or implements that must withstand high temperatures. This insulating property makes PF valuable in many applications where heat is involved. 
  2. Low Density: Unlike epoxy resin, which offers similar benefits, phenol formaldehyde is lighter and easy to work with. 
  3. Excellent Durability: Phenoplast products are durable. They have good resistance to wear and tear. This quality makes them useful in situations where strength is important.
  4. Good Chemical Resistance: Phenolic resin is resistant to many chemicals and solvents intended for volatile environments. However, this resin is unsuitable for use in environments containing chromic acid, strong alkalies, or nitric acid. It is known to be resistant to most other common industrial chemicals up to temperatures of about 190°C.

How Is Phenol Formaldehyde Resin Produced?

Phenolic resins can be made in a variety of ways, including by adding modifiers, crosslinkers, and fillers to achieve desired properties. The addition of a hexamethylenetetramine (HMTA) crosslinking agent to the phenolic resin is one of the most widely used techniques for industrial and commercial applications. The "resol" process involves the reaction of phenol and formaldehyde with an alkaline catalyst, followed by the addition of HMTA to crosslink the chains of the polymer. The end product is a thermoset resin that is suitable for a variety of applications due to its high strength, rigidity, and chemical resistance. The "novolac" process, which entails the reaction of phenol with formaldehyde in the presence of an acidic catalyst, is one of the additional techniques for phenolic formulation. 

Listed below are the steps involved in the production of phenol formaldehyde:

  1. Fill 60-80% of a reaction vessel or reactor’s volume with a phenolic compound.
  2. Heat the phenolic compound to a temperature of 60-100°C. Ensure that this temperature is maintained.
  3. Feed an aqueous solution that contains 35-60% by weight of formaldehyde into the heated phenolic compound. The reaction should take place in the presence of an alkaline or acidic catalyst. It is important to note that the rate at which the formaldehyde compound is fed into the phenolic compound should be such that its water gets distilled out at roughly the same rate as it is fed in. If this condition is maintained, the volume of the reaction mass should be about 60-90% of the reaction vessel’s volume.
  4. Remove from heat.
  5. Leave the mixture to cool to room temperature. Afterward, process the resin as desired.

What Is the Preparation Process of Phenol Formaldehyde Resin?

The preparation process of phenol formaldehyde resin is listed below:

  1. Weigh the appropriate quantity of the raw materials (phenol and formaldehyde) before mixing them in a reaction vessel.
  2. Acid or base catalyzation comes next. The catalyst can be hydrochloric acid, sulphuric acid, or ammonia (a weak base). 
  3. Sustain the reaction mass at a temperature of 60-100°C. The ideal temperature is 70-80°C along with a reduced pressure of 37-88 kPa (11-26 inches of mercury).
  4. Leave the resin to cool down to room temperature.

Is Phenol-Formaldehyde Resin Safe?

Yes, phenol formaldehyde resin is safe to use if handled properly. It is not a chemical to be toyed with, however; the chemical reaction should be conducted by someone who is trained to handle the various stages in the process. PF contains formaldehyde which is toxic to the eyes, sinuses, and to a lesser extent, the skin. Phenol, on the other hand, can cause damage to the skin and should not be inhaled due to its toxicity. Additionally, phenolic resins should be properly cured. Trace amounts of unused formaldehyde compounds can cause allergic reactions in people who are especially sensitive to them. 

Another way people come into contact with formaldehyde is during excessive heating, sanding, or machining of cured resins. These operations may cause the decomposition of cured phenolic resins, releasing formaldehyde and other harmful chemicals such as hydrogen cyanide. Take precautions; work in a well-ventilated environment and wear suitable gloves when handling phenolic resins. People who are sensitive to formaldehyde should stay away from the resin, and all necessary steps that will ensure proper curing should be followed closely.

Is Phenol Formaldehyde Heat Resistant?

Yes, phenol formaldehyde is heat resistant. It can be used for applications where heat may be applied. PF is known for its excellent thermosetting property and thermal insulating capability.

Summary

This article presented phenolic resin, explained what is, and discussed the various ways to use this material. To learn more about phenolic resin, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

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Xomety X
Team Xometry
This article was written by various Xometry contributors. Xometry is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding, urethane casting, and more.