Waterborne polyurethane (WPU) is a new type of polyurethane system, which uses water instead of organic solvent as the dispersing medium. It is also called WPU, waterborne polyurethane or waterborne polyurethane. Waterborne polyurethane (WPU) has the advantages of water as solvent, pollution-free, safe and reliable, excellent mechanical properties, good compatibility and easy modification.
The use of toxic solvents in the synthesis of polymer materials can ensure their recycling and reduce their residues in products, which is also the research content of green synthesis of polymers. The synthesis of waterborne polyurethane resin is a typical example in this respect.
Waterborne polyurethane resin is a uniform emulsion formed by dispersing polyurethane in water. It has the advantages of non combustible, small odor, no pollution to environment, energy saving, convenient operation and processing. It is widely used as adhesive and coating.
Compared with solvent-based polyurethane binder, waterborne polyurethane has the following characteristics:
(1) Most waterborne polyurethane resins do not contain reactive NCO groups, so the resins are cured mainly by the cohesion and adhesion of the polar groups within the molecule. The carboxyl group and hydroxyl group in waterborne polyurethane can participate in the reaction under suitable conditions, and make the binder cross-linking.
(2) Viscosity is an important parameter for the performance of adhesives. The viscosity of waterborne polyurethane resin is generally adjusted by water soluble thickener and water.
(3) Because the volatility of water is worse than that of organic solvents, the drying of waterborne polyurethane binder is slower and the water resistance of the material is worse.
(4) Waterborne polyurethane resin can be mixed with a variety of waterborne resins to improve performance or reduce costs. At this time, attention should be paid to the electrical properties and acidity and alkalinity of waterborne polyurethane resin, otherwise it may cause condensation of waterborne polyurethane resin.
(5) Waterborne polyurethane resin has small odor, easy operation and easy cleaning of residue.