A small amount of compatible solvent is applied at the joint interface. The solvent diffuses into the polymer, softening the surfaces and allowing interdiffusion of the polymer chains across the interface. The weld is formed through the application of pressure. Since the solvent reduces the glass transition temperature (Tg) of the polymer, welds can be formed without the applied heat necessary in other welding processes.
Weld strengths approaching that of the parent material can be achieved, although the presence of residual solvent tends to result in some loss of strength in the joint region. Care has to be taken over selection of the solvent as it can induce stress cracking or crazing in some polymers.
The process of solvent cementing works on the same principle as solvent welding, the difference being that a polymer dissolved in solvent is used instead of a pure solvent. The polystyrene cement used in the construction of 'Airfix' models is an example of a solvent cement.
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