Solvents play a significant role in adhesives. Some act as mediators in polymerization reactions, slowing down the reaction and facilitating temperature control; others purify monomers and additives; some dissolve the base material to become a component of the adhesive; some dilute the adhesive to a specific viscosity, promoting wetting and facilitating application; some regulate the evaporation rate; some prevent gelation and increase storage stability; some serve as surface cleaning agents before bonding; some are used for direct bonding of certain thermoplastic products; and some can reduce costs and improve efficiency.
Choosing the right solvent is crucial, requiring consideration of multiple factors such as solubility, evaporation rate, safety, economy, availability, and storage stability. A good solvent must possess excellent solubility properties, which can be determined by solubility parameters and hydrogen bonding index. The drying rate of adhesives is directly related to the solvent's evaporation rate. Solvent-based adhesives should ideally have all the solvent evaporate. Generally, faster drying is desired, which necessitates choosing solvents with lower boiling points. Most organic solvents are flammable, and when solvent vapors reach a certain concentration in the air, they can explode. Therefore, solvent safety must be carefully considered. Most organic solvents are also toxic, posing a threat to human health and polluting the environment, and should be given sufficient attention. Solvents constitute a large proportion of solvent-based adhesives, so cost must be considered; inexpensive and readily available solvents should be used whenever possible.
