klej

Klej is the Polish term for glue or adhesive, a substance designed to join two surfaces by forming a bond through adhesion and cohesion. Glues vary widely in composition, performance, and use, and are categorized by their base material and curing mechanism. Common families include water-based glues such as polyvinyl acetate (PVA) and starch-based pastes; solvent- or water-based natural glues; synthetic resins such as cyanoacrylates (super glue), epoxy resins, and polyurethane adhesives; hot melts that solidify on cooling; and specialty adhesives such as silicone and acrylic types used for sealing and flexibility. Each type has typical properties in terms of strength, water resistance, flexibility, open time, and cure time, and many require clamping or pressure during setting.

Glues are employed across many sectors, including woodworking, paper and bookbinding, textiles, ceramics, construction, and packaging. PVA is common in woodworking and crafts, cyanoacrylates provide rapid bonds for small parts, epoxies offer high strength and gap filling, hot melts enable quick assembly, and polyurethane formulations are valued for durability and moisture resistance.

Adhesion and curing depend on the chemical nature of the adhesive. Some set by solvent evaporation, others by moisture-driven polymerization, chemical crosslinking, or two-component mixing. Performance is also affected by surface preparation, substrate compatibility, and environmental conditions such as temperature and humidity.

Safety and handling vary by product. Many glues can irritate skin or eyes, some emit fumes or are flammable, and some require ventilation. Storage typically involves sealed containers protected from heat and moisture. Historically, glues originated from natural materials such as animal collagen, starch, and casein, with modern synthetic adhesives expanding capabilities across industries.