Plastics are usually more difficult to bond than other substrates. The outcome of the bonding process may be as dependent on the plastic substrate as it is on the adhesive being used. This dependence is due to the plastic's unique surface properties as well as its bulk properties.
Plastic surfaces are different from metal, glass, or most other surfaces because they are often unstable and thermodynamically incompatible with the adhesive. Furthermore, the processing aids used in formulating plastic raw materials and in fabricating plastic parts are often not favorable to adhesive bonding. Often the surface that we are bonding is not the surface that we think it is.
This two-part article will discuss how the nature of a polymeric substrate affects adhesion. Bulk properties and surface characteristics of common plastics will be defined and discussed with regard to their bonding behavior. Part I deals with the properties of surfaces and the bulk polymer in general and with specific thermosetting plastics.