adhesives

Adhesives are substances used to bond two surfaces together. They work by forming a bond at the interface (adhesion) and by maintaining internal cohesion within the adhesive; the overall strength depends on the interaction with the substrate, the adhesive formulation, and the curing conditions.

Adhesives are categorized as natural or synthetic. Natural adhesives include animal glues, starch- or casein-based glues used in bookbinding and woodworking. Synthetic adhesives comprise thermosetting resins such as epoxies and phenolics, thermoplastic polymers such as polyvinyl acetate and hot-melt formulations, and reactive systems like cyanoacrylates, silicones, and acrylics.

Curing mechanisms vary: some adhesives cure by chemical reaction, some set through solvent evaporation, moisture curing, or heat and UV activation. Substrates and surface preparation (cleanliness, roughness, compatibility) strongly influence bond performance.

Applications span woodworking, metal fabrication, plastics, electronics, packaging, construction, and medical or dental uses. Performance factors include bond strength under load, temperature and chemical resistance, aging, and environmental considerations such as VOC emissions.

The development of synthetic adhesives in the 20th century expanded capabilities and enabled modern manufacturing.