Adhesive

An adhesive is a substance capable of bonding two surfaces by attaching to one or both surfaces. Adhesives differ from mechanical fasteners in that they create a bond through wetting, interfacial interactions, and often chemical reaction, rather than relying solely on fit. The resulting joint depends on adhesive and cohesive strengths, surface preparation, curing conditions, and environmental exposure.

Adhesives are categorized by origin (natural and synthetic) and by curing mechanism (solvent-based, water-based, hot-melt, reactive curing, or UV/light-curing). Natural examples include starch pastes, animal glues, and casein. Synthetic families include epoxies, polyurethanes, vinyl acetates, cyanoacrylates, silicones, and acrylics. Common curing methods are solvent evaporation, moisture cure, heat cure, UV cure, and two-part chemical cure.

Common adhesive types and typical uses include epoxies for high-strength structural bonds; polyurethanes for flexible joints and impact resistance; cyanoacrylates for rapid bonding; silicone for high temperature and weather resistance; acrylics for bonding dissimilar materials; hot-melt adhesives for fast setting; pressure-sensitive adhesives for tapes and labels; contact adhesives for laminates.

Applications span automotive, aerospace, construction, electronics, woodworking, packaging, and biomedical devices. Performance depends on bond strength (peel, shear), gap filling, elasticity, temperature and chemical resistance, cure time, and shelf life.

Substrates include metals, wood, plastics, ceramics, and composites. Failures may be adhesive (at the interface), cohesive (within the adhesive), or substrate-related.

Safety and environmental considerations include potential toxicity of monomers, volatile organic compounds, and worker exposure during curing. Proper ventilation, handling, disposal, and compliance with regulations are essential.