Polystyrene adhesive joining

Complex assemblies of polystyrene, usually molded in section, may be joined by means of solvents and adhesives. Polystyrene is soluble in a wide variety of solvents. According to their relative volatilities they may be divided into three groups—fast drying, medium drying, and slow drying. 

Solvents, or solvents containing small amounts of hodying resin, are used for bonding thermoplastic resins and film adhesives. An example is toluol, which can he used to soften and dissolve polystyrene molded articles to allow joining the softened pieces. Ketones can be used to bond PVC films in a similar manner. A small amount of resin can be used to thicken the solvent so that a sufficient amount would stay in place to dissolve the substrate. It should be noted, however, that solvent welding of molded plastics can cause stress cracking and weakening of the structure as the parts age. ... 

The most common means of joining some plastics is to employ what has been called a plastic dope or plastic cement. The type will vary depending on the plastic adherend to be joined, since the best choice of plastic dope for that adherend will be a solvent blend of that adherend. PVC, ABS, polystyrene, and polycarbonate, for example, form durable bonded joints through the use of solvent adhesives made by blending suitable solvents with solid plastic of the same composition as the adherend to be joined. After the solvent dissipates from the bondline, the joint is virtually continuous plastic across the interface. This is often referred to as a welded plastic joint. 

Plastics that are readily bonded with induction methods include aU grades of ABS, nylon, polyester, polyethylene, polypropylene, and polystyrene, as well as those materials often considered more difficult to bond such as acetals, modified polyphenylene oxide, and polycarbonate. Reinforced thermoplastics with filler levels up to 65 percent have been joined successfully. Many combinations of dissimilar materials can be bonded with induction welding processes. Table 8.5 shows compatible plastic combinations for electromagnetic adhesives. Thermoset and other nonmetallic substrates can also be elec-tromagnetically bonded. In these applications the bonding agent acts as a hot-melt adhesive. 

Polystyrene is a transparent hard plastic with a tendency to brittleness which can lead to cracking under stress. Coloured versions are also available as with other types of polymer. Toughened or high impact grades have been developed to overcome the cracking problem - more will be said about these later. Polystyrene is an easy material to join using suitable solvent-based adhesives capable of softening the surface. 

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