TABLE OF CONTENTS Solvent cementing is a process in which thermoplastics, usually amorphous or low crystallinity, are softened by the application of a suitable solvent, or mixture of solvents, and then pressed together to affect a bond. The resin itself, after evaporation of the solvent, acts as the adhesive. Many thermoplastic resins are easier to join effectively by solvent cementing than by conventional adhesive bonding. Often mixtures of solvents give better results than individual solvents. Frequently, small amounts of the plastic to be cemented are dissolved in the solvents to form "bodied" cements. These additions of polymer aid in gap filling and accelerate setting. They also reduce shrinkage and internal stresses. If the evaporative rates of the solvents used are too high due to excessive volatility of the solvent, crazing or blushing often results.
Welding of polymers occurs when the polymer chains at the surface of one component are mobile enough to entangle with chains in the other component. Usually, thermal energy is applied to raise the temperature of the polymer above the appropriate transition temperature, i.e., the glass transition temperature, T g, for amorphous thermoplastic polymers, or the melting temperature, T m, for semi-crystalline polymers. Above these transition temperatures, polymer chains are more mobile. If two components are brought into intimate contact under these conditions, polymer chain entanglement will occur resulting in a weld.
In solvent welding, a solvent is applied which can temporarily dissolve/swell the polymer at room temperature. When this occurs, the polymer chains...
