This second part of a two-part article will discuss how the nature of thermoplastic polymeric substrates affects adhesion. Characteristics of the bulk properties and surfaces of common thermoplastics will be discussed with regard to their bonding performance. Part I, published on December 12, 2003, dealt with thermosetting plastics and the properties of surfaces in general.
Thermoplastic materials can be joined via solvent cementing or thermal welding as well as adhesive bonding. In these cases, the resin from the plastic part being joined acts as the adhesive. Thus, these other methods of joining will also be considered in this article. The goal is to provide important information that should be considered prior to the bonding of plastics.
Unlike thermosetting resins, the thermoplastic resins will soften on heating or on contact with solvents. They will then harden on cooling or on evaporation of the solvent from the material. This is a result of the non-crosslinked chemical structure of thermoplastic molecules.