Glues

Glues, or adhesives, are substances used to join two surfaces by forming a bond that resists separation. They work by wetting the surfaces, penetrating micro-porosities, and then hardening through chemical reaction, solvent evaporation, or cooling, creating a combination of adhesive and cohesive strength.

Natural glues include animal-based glues, such as collagen derived from bones or hides and fish glue, as well as plant-based glues like starch pastes, dextrin, gum arabic, and casein. These materials have been used for centuries in woodworking, bookbinding, and papermaking, though they generally offer lower water and heat resistance than many synthetic alternatives.

Synthetic polymer-based glues are widely used and include polyvinyl acetate (wood glues), epoxy resins, cyanoacrylates (super glues), polyurethanes, acrylics, and silicone adhesives. Hot-melt adhesives, applied as a molten polymer and set on cooling, provide fast bonding for many packaging and manufacturing tasks. Some glues are pressure-sensitive and bond with light pressure on contact.

Curing mechanisms vary: some adhesives air-dry as the solvent or water evaporates; others cure through chemical reactions (epoxies, polyurethanes), moisture curing (silicones, some polyurethanes), heat, or ultraviolet light. The bond quality depends on surface preparation, material compatibility, temperature, humidity, and load conditions.

Applications span woodworking, paper and packaging, textiles, construction, electronics, and medicine (biocompatible glues and tissue adhesives). Selection depends on substrate, required strength and durability, flexibility, temperature resistance, and permanence. Safety considerations include solvent emissions, skin and respiratory irritation, and proper disposal.