What Does Phenolic Resin (PF) Mean?
Phenolic resin, also known as phenolic formaldehyde resin (PF), is a synthetic resin produced from the polymerization of a phenol (C6H5OH) and a formaldehyde (CH2C=O). The polymer consists of repeating units of –[(C6H3OH)-CH2]- with methylene (-CH2-) linkages bridging carbon positions to the phenolic hydroxide group (-OH).
There are two types of phenolic resins, phenolic novolac resins and phenolic resol resins, depending on the conditions used to create the polymer. Phenolic novolac resins are further modified with a cross-linker for them to harden. Both types are known for high chemical and water stability and temperature stability above 300°C (572°F). Some phenolics can withstand temperatures that are as high as 550°F. Many have proved to be impervious to condensation.
Phenolic resins can accurately be seen as the first polymeric products that were produced commercially from simple compounds that had low molecular weight, as they were the first synthetic resins at that time to be exploited.
Phenolic resins are used in a myriad of industrial products as well as being widely used in the manufacture of circuit boards. Due to its great hardness, PF resins are often used to produce products such as billiard balls, chemically resistant countertops, circuit boards and other panels. In other cases, PF resins are useful for laminations and as a binding agent for parts such as brake pads. They often find applications as coatings and adhesives.
Corrosionpedia Explains Phenolic Resin (PF)
Phenolic resins contain many desirable characteristics, such as high mechanical strength, extent stability and heat resistance, as well as being highly resistant to various acids, beverages and several solvents.
The major use of phenolic resin is as a bonding agent. Phenolic resin easily penetrates and adheres to the structure of many organic and inorganic fillers and reinforcements, which makes it a suitable candidate for various end uses. A brief thermal exposure to complete the cross-linking or "thermoset" process results in achieving final properties. The unique ability of phenolic resin to "wet out" and to cross-link throughout the fillers and reinforcements helps in engineering the desired mechanical, thermal and chemically resistant properties.
How Phenolic Resins Are Prepared
Phenolic resol resins are prepared in conditions with the formaldehyde to phenol ratio being greater than 1 (typically 1.5). The reaction is catalyzed by a base to create a reactive phenoxide (C6H5O-) group, which reacts with the formaldehyde to create hydroxylmethyl phenol units. Thermosetting at 120°C (248°F) initiates crosslinking, which creates a highly networked polymeric structure with good thermal stability, hardness and chemical resistance.
Phenolic novolac resins are prepared when the formaldehyde to phenol ratio is less than 1 under acidic catalytic conditions. The molecular weights of the produced intermediate polymers are in the low thousands, with only 10-20 repeating units. In order to gain the strong properties of PF resins, the material is thermoset with a cross-linker such as hexamethylenetetramine. Phenolic resins typically range from yellow to dark-red.
Although it has proven very useful, phenolic resin's drawback is the highly toxic nature of formaldehyde when it comes in contact with the eye and when ingested, as well as its moderately toxic nature when in contact with the skin.