Phenol Formaldehyde Resin Structure Preparation and Properties

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:

1. The reaction of phenol with formaldehyde produces a thermosetting network polymer.

2. 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:

1. Temperature 

2. pH

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:

1. Methylene Bridge:  \[HOC_6H_4CH_2OH  + C_6H_5OH  \rightarrow (HOC_6H_4)^2CH_2  +  H_2O\]

2. 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:

• Caps

• Handles

• Buttons

• Radio cabinets

• Furniture

• Knobs

• Vacuum cleaner

• Cameras

• Ashtrays

• 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.