Solvent bonding

Solvent bonding is one of several methods of adhesive bonding for joining plastics. Application of a solvent to a thermoplastic material softens the polymer, and with applied pressure this results in polymer chain interdiffusion at the bonding junction. When the solvent evaporates this leaves a fully consolidated bond-line. An advantage to solvent bonding versus other polymer joining methods is that bonding generally occurs below the glass transition temperature of the polymer (approximately 30°C below Tg).
Solvent bonding differs from adhesive bonding since the solvent does not becoming a permanent addition to the joined substrate. Solvent bonding differs from other plastic welding processes in that heating energy is generated by the chemical reaction between the solvent and thermoplastic, and cooling occurs during evaporation of the solvent. 
Solvent bonding can be performed using a liquid or gas solvent. Liquid solvents are simpler and generally have lower manufacturing costs but are sensitive to surface imperfections that may cause inconsistent or unpredictable bonding. Some solvents available may not react with the thermoplastic at room temperature but will react at an elevated temperature resulting in a bond. A curing times are highly variable.
Applying solvent methods.
Four common application methods are:
Thermoplastic and solvent compatibility.
The proper solvent choice for bonding is dependent on the solubility of the chosen thermoplastic in the solvent and the processing temperature. The table below provides a selection of solvents commonly used for bonding specific thermoplastics. Mutual solubility between a polymer and a solvent may be determined using the Hildebrand solubility parameter. Polymers will generally be more soluble in solvents with similar solubility parameters to their own in a given state (liquid or solid). The solubility parameters of polymers are not greatly affected by changes in temperature, however the solubility parameters for liquids is affected by temperature. Increasing the temperature lowers the free energy of mixing, promoting dissolution at the interface and interdiffusion bonding.
Testing solvent-bonded joints.
There are three main mechanical testing methods for plastic bonding joints: tensile testing, tensile shear test and peel test. Tensile testing using a butt joint configuration is not very conducive to polymers, particularly thin sheets due to the challenges of mounting to the load frame. An epoxy may be used for mounting and can lead to failure in the epoxy / polymer interface instead of in the bonded joint. The most common method for testing solvent bonds is the tensile shear test using a lap joint configuration. Specimens are tested in shear to failure at a given overlap cross section via tensile loading. This testing method is particularly conducive to thin specimens due to distortion mitigation distortion in the test specimens due to the loading mechanism. Guidance for tensile shear testing may be found in ASTM D1002-05.
Industrial applications.
There are several industries that utilize solvent bonding for their applications. A few of these include microchip manufacturing, medical, and potable and sanitary plumbing systems.