From Properties of Thermoset Plastics
Types of Thermoset Plastics
Thermoset plastics are derived from amorphous polymers. They possess the functional group of polymers through which polymerization and condensation reaction occurs to give a new type of thermoset product.
Thermoset plastics are categorized into phenolic resins, amino resins, polyester resins, silicon resins, epoxy resins, and polyurethanes.
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...
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