Types of Thermoset Plastics

Phenolic Resins or Phenoplasts

Phenolic resins or phenoplasts are products of phenolic derivatives, such as phenol resorcinol, with aldehydes, such as formaldehyde furfural. Example of a phenolic resin is phenol-formaldehyde, also known as bakelite. This resin is prepared by condensing phenol with formaldehyde in the presence of acidic or alkaline catalyst. The initial reaction results in the formation of mono-, di-, and trimethyl 1 phenol, depending on the ratio of phenol to formaldehyde or P/F, type of catalyst, temperature, and time of reaction.

The reaction between methylol phenols and phenols may occur in the following ways:

• Between the methylol's hydroxyl group and hydrogen in the benzene ring of phenol producing a methylene group.

• Between the two methylol s hydroxyl groups, forming an ether linkage.

In both the above ways, single water molecule is split off. Further heating produces a linear polymer of varying length, resulting in the following resins:

• A-stage resin, also called-resol, contains ether linkages composed of a relatively short, low molecular-weight, linear polymer, which is completely soluble in alkaline solution.

• The B-stage resin, also called resitol, is a rather long, linear-polymer, with a slight amount of cross-linking between chains and is insoluble in the alkaline medium but readily soluble...