Water-based polyurethane resins
The first polyurethane was discovered in 1937 by Autobayer in Germany, and after that, these materials made great progress in various industries in the world due to their special properties.
Polyurethane (PU) is the general name of resins that have urethane bonds. The urethane bond is formed through an addition reaction between an isocyanate group and a compound with an active hydrogen such as a hydroxyl group. Isocyanate groups are highly reactive, and for this reason, the progress of their reaction does not require an increase in temperature. (The reaction takes place at room temperature).
Polyurethane can be produced in different forms such as: foam, film, elastomers, powders, liquids and emulsions. Compounds that have an isocyanate group are:
1- 2.4 or 2.6 toluene diisocyanate
2- 4.4 or 2.4 diphenylmethane diisocyanate
3- 1.6 hexamethylene diisocyanate
In addition to the ones mentioned, there are other isocyanate compounds
Compounds that have more than two hydroxyl groups (OH) are called polyols, and the following species are usually used in polyurethane synthesis:
1- Polyether polyol
2- Polyester polyal
3- Polycarbonate Polyol
4- Polycaprolactone Polyl
In addition, instead of hydroxyl groups, compounds such as carboxylic acids and amines, which have active hydrogen, can also be used in combination with isocyanates. If, instead of di-alcohol, a diamine reacts with isocyanate, the resulting resin is placed in the polyurea family. Spandex is a composite with a complex structure that includes both urea and urethane functional groups. Therefore, the variety of reagents that are used against isocyanates leads to the production of polyurethanes in various types with different characteristics. For this reason, when it comes to polyurethanes, it can be said that there are countless types of them.
Applications
Production cost is one of the points that should be considered in the applications of a material. Aliphatic polyurethanes are more expensive than aromatic types. Therefore, the more expensive polyurethanes are mostly used as the outer coating of the devices, while the aromatic and cheaper types are used in the production of base colors and primary coatings.
In total, providing soft seats, non-conductive molds, caps and microstructure washers, durable tires for cars. Sealants, adhesives and polishes are among the applications of polyurethanes.