Polyurethane adhesives include polyisocyanate solution adhesives, thermoplastic polyurethane solution adhesives, reactive single-component and two-component polyurethane solution adhesives, solvent-free polyurethane liquid adhesives, water-dispersed, hot-melt and reactive hot-melt polyurethane adhesives, etc. At present, the main applications of polyurethane adhesives are thermoplastic polyurethane solution adhesives and reactive single - and two-component polyurethane solution adhesives.The non-organic solvation of polyurethane adhesives can be done in three ways: water-based, heat-melted and 100% liquid. In these three approaches, water as a solvent instead of organic solvent in water because of the application process and conditions and the original solvent adhesive is not different, has a unique advantage, has been rapidly developed.According to the more mature application forms, waterborne polyurethane adhesives can be divided into three categories:(1) water-dispersible polyisocyanate adhesive, whose main component is polyisocyanate containing hydrophilic group, which can be automatically dispersed in water; It is mainly used in the manufacture of wood-based panels and as a curing agent for other types of waterborne polyurethane adhesives.(2) vinyl polyurethane water-based adhesive, which is a vinyl water-based polymer emulsion - polyisocyanate two-component adhesive, mainly used for wood bonding;(3) water-dispersible polyurethane (PUD) adhesive.According to the appearance, waterborne polyurethane can be divided into emulsion polyurethane, polyurethane water dispersion and water soluble polyurethane. According to the isocyanate raw material of polyurethane, it can be divided into aromatic isocyanate type, aliphatic isocyanate type and aliphatic isocyanate type.Waterborne polyurethane is divided into anionic polyurethane emulsion, cationic polyurethane emulsion and non-ionic polyurethane emulsion according to whether its main chain or side chain contains ionic groups.