Phenol Formaldehyde Resin Meaning
Phenol formaldehyde resin (plastic) was the first commercial polymers used in the 20th century. We abbreviate the Phenol formaldehyde resin as PF. It is also known as the phenolic resin, one of the first synthetic polymers that we can obtain by the reaction of phenol or substituted phenol with formaldehyde.
What are Phenol and Formaldehyde?
Here, phenol is an aromatic alcohol that we can obtain from benzene. Bakelite is a phenolic plastic. Further, formaldehyde is reactive and can be derived from methane (CH4).
Phenol formaldehyde resin chemical formula is C8H6O2. It has various properties that we will discuss on this page.
Also, we will understand the phenol formaldehyde resin structure, phenol formaldehyde resin preparation, and phenol formaldehyde reaction.
What is Phenol Formaldehyde Resin?
Phenol formaldehyde Resin or PF are synthetic high polymers.
We can produce PF by the reaction with phenol and substituted phenol with formaldehyde.
Besides polyurethanes and polyesters, phenolic and epoxy resins are the widely known applications for technical lignins in thermosetting materials.
We produce phenolic resins by a step-growth polymerization reaction that can be either in the presence of acid or base (used as catalysts).
PFs are normally in liquid state and their specific gravity ranges from 1.12 to 1.16.
Now, let’s have a look at the Phenol Formaldehyde Resin Structure.
Phenol Formaldehyde Resin Structure
The Phenol formaldehyde resin structure looks like the following:
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Along with the structure, every chemical compound has several properties that we will understand below.
Phenol Formaldehyde Resin Properties
In Phenol formaldehyde, an exclusive range of molding powders is available in which the composition of the resin, fillers, etc, varies to provide moldings suitable for many purposes.
Here, the commonly used techniques for its preparation are compression and transfer processes.
The below table shows the illustration of the chemical and physical properties of Phenol Formaldehyde Resin or PF:
How Phenol Formaldehyde Resins are Produced?
The two following main production methods are:
The reaction of phenol with formaldehyde produces a thermosetting network polymer.
Another approach restricts the formaldehyde to produce a prepolymer known as a volcano.
A volcano can be molded, and therefore, cured with the addition of formaldehyde and heat.
There are many variations in both production and input materials that we use to produce a wide variety of resins for particular purposes.
Now, let’s understand the Phenol Formaldehyde Resin Preparation.
Phenol Formaldehyde Resin Preparation
A step-growth polymerization reaction that can be either acid - or base-catalysed method is used for Phenol-formaldehyde resins (as a group) preparation.
Since formaldehyde (a reactive derivative of methane) exists as a dynamic equilibrium of methylene glycol oligomers for the most part in the solution.
Further, the concentration of the reactive form of formaldehyde depends on the following two factors:
First Preparation Process
Phenol on reacting with formaldehyde at the ortho and para-sites, namely - 2, 4, and 6 sites permit up to 3 units of formaldehyde to associate with the ring.
The involvement of involves the formation of a hydroxymethyl phenol is crucial in all the cases of the initial reaction:
\[C_6H_5OH + CH_20 \rightarrow HOC_6H_4CH_2OH\]
Phenol Formaldehyde 4 - Hydroxybenzyl alcohol
The hydroxymethyl group is capable of reacting with either of the following:
A free ortho or para-site or
With another hydroxymethyl group.
The first reaction produces a methylene bridge, and the second gives an ether bridge in the following reactions:
Methylene Bridge: \[HOC_6H_4CH_2OH + C_6H_5OH \rightarrow (HOC_6H_4)^2CH_2 + H_2O\]
Ether Bridge: \[2 HOC_6H_4CH_2OH \rightarrow (HOC_6H_4)2O + H_2O\] PF Resin
Here, the diphenol a.k.a \[(HOC_6H_4)2CH_2\] is also known as "dimer". Also, we call it the bisphenol F.
The bisphenol F is a crucial monomer in epoxy resin production. Further, Bisphenol-F links generate tri- and tetra-and higher phenolic oligomers.
Phenol Formaldehyde Resin Applications
Phenol formaldehyde Resin has several uses in industry. Besides this, it possesses the following applications:
1. In-Circuit Board Preparation
Phenolic resins are primarily used for making circuit boards like PCB.
Further, we find the applications of phenolic resins in Electrical equipment.
2. Day-to-Day Applications
Also, it is needed in the following areas:
Engine ignition equipment
We also find its use in Laminated Materials like Laminated sheets, rods, and tubes, made in great variety from fabric, paper, wood veneers, etc impregnated with phenolic resins providing a variety of materials of widely differing properties.
Industrial Applications of Phenol Formaldehyde Resin
In industrial practice, the two basic methods are used for transforming the polymer into useful resins:
1. First Method
An excess of formaldehyde is made to react with phenol in the presence of a base catalyst in water solution to produce a low-molecular-weight prepolymer called a resole.
Here, the resole frequently found in liquid form or solution, is cured to a solid thermosetting network polymer.
For instance, compressing it between layers of wood veneer, and therefore, heating this assembly under pressure to form plywood.
2. Second Method
This method involves the reaction of formaldehyde with an excess of phenol, in the presence of an acid catalyst.
The second process produces a solid prepolymer known as novolac (or novolak).
Here, novolak resembles the final polymer; however, it has a much lower molecular weight and is still thermoplastic. It means that we can soften it by reheating without undergoing chemical decomposition.
The curing process can be accomplished by grinding the novolac to a powder, therefore, mixing it with fillers such as wood flour, minerals, or glass fibres. Further, heating the mixture in a pressurized mold.
To obtain a thermosetting resin, novolacs need additional formaldehyde or, more commonly, compounds that decompose into formaldehyde upon heating.
FAQs on Phenol Formaldehyde Resin
1. What is Phenol Formaldehyde Resin?
Phenol formaldehyde resins are often known as phenolic resins or phenoplasts. They are synthetic polymers made out of phenol or substituted phenol reacting with formaldehyde. They were the first commercial synthetic resins. They were used to make Bakelite. They have been used to make moulded objects like billiard balls and laboratory surfaces, as well as coatings and adhesives. They were once the principal material used to make circuit boards, but epoxy resins and fibreglass fabric, as well as fire-resistant FR-4 circuit board materials, have essentially supplanted them. To learn more, head over to Vedantu.
2. What are novolaks?
Novolaks are phenol-formaldehyde resins with a molar ratio of fewer than one formaldehyde to phenol. They are frequently made using cresols rather than phenol. Acid-catalysis, such as sulfuric acid, oxalic acid, hydrochloric acid, and, in rare cases, sulfonic acids, are used to complete the polymerization. Methylene and/or ether groups bind the phenolic units together. The molecular weights range from the thousands to tens of thousands of phenol units. The obtained polymer is thermoplastic, and a curing agent or hardener is required to convert it to a thermoset.
3. What are some of the applications of Phenol Formaldehyde Resin?
Phenolic resins are used in a wide range of industrial applications. Phenolic laminates are made by impregnating one or multiple layers of a foundational material with phenolic resin. Then it is laminated with the resin-saturated base material under pressure and heat. During this phase, the resin fully polymerizes, generating the thermoset polymer matrix. The base material picked is chosen according to the final product's intended use. Electrical components like punch-through boards, household laminates, and paper composite panels are created using paper phenolics. In the high-speed bearing industry, glass phenolics are particularly well suited. For density control, phenolic microballoons are used. Phenolic resin is the binding agent in standard brake pads, brake shoes, and clutch discs.
4. What is meant by resoles?
The formaldehyde to phenol ratio in base-catalyzed phenol-formaldehyde resins is more than one. Resoles are the name for these resins. Depending on the resin to be made, phenol, formaldehyde, water, and catalyst are mixed in the appropriate amounts and heated. At roughly 70 °C, the first stage of the reaction produces a thick reddish-brown sticky material with a lot of hydroxymethyl and benzylic ether groups.
The rate of the base-catalyzed reaction increases with pH at first, then plateaus at pH = 10. The phenoxide anion produced by deprotonation of phenol is the reactive species. The negative charge moves around the aromatic ring, activating sites 2, 4, and 6, which then react with formaldehyde.
5. What is hexamethylenetetramine?
The hardener hexamethylenetetramine is used to crosslink novolac. It generates methylene and methylamino bridges at temperatures above 90 °C. Novolac resins can also benefit from the use of resoles as a curing agent (hardener). In each case, the curing agent is a source of formaldehyde. It acts as a connecting factor between the novolac chains and eventually crosses linking the system completely.
Novolacs can be made use of as a high-temperature resin, a tyre tackifier, carbon brakes, photoresists, a binder for carbon bonded refractories, and an epoxy resin curing agent. The Vedantu app and website contain free study materials.
6. State the use of phenolic resins.
We find the applications of phenolic resin in the following domains:
In building panels gears and bearings
Clutch and brake linings
Jigs and dies
In the case of cast resins, casting and the potting process are used for producing several types of phenolic resins.
7. State the use of Phenol Formaldehyde Resin in electrical equipment production.
The most significant application of phenol-formaldehyde resins is the production of composite boards, like plastic laminate.
Further, the boards are constituted of a relatively inconsistent material, attached by a phenol resin acting as a glue.
We can also use several materials, like wood chips, paper, cloth, sand, fiberglass.
The phenol resin makes up just a small part of the total, down to 10%. Workbench tops make the most use of composite boards; however, we also find its higher prized usages in floors, doors, machinery parts, and printed circuit boards.
8. State the properties of yellow Phenol Formaldehyde.
Tires, and tubes
Maximum Acidic Value: Phenolic Acidity