|Why do some glues dry faster than others?
Some glues literally "dry," since they contain a plasticizer chemical that evaporates to leave a firmer plastic. Other glues polymerize directly during the gluing process. For the glues that dry by evaporating plasticizer, the choice of plasticizer is critical. Water leaves relatively slowly compared to volatile organic solvents such as toluene or acetone. That is why water-based white glue dries more slowly than organic-based plastic cement. But the glues that polymerize during the gluing process (they "cure" rather than "dry") have a broad range of speeds. Some of those glues polymerize very rapidly (e.g. superglues and 3-minute epoxies) and some go much slower (normal epoxies). In general, slower glues produce stronger materials because they contain long polymer molecules. The fast curing glues form too many short polymer molecules and are not as tough.