Views: 1000 Author: Site Editor Publish Time: 2021-08-13 Origin: Site
Polyurethane is a kind of polymer containing repeated carbamate group. It has excellent mechanical and chemical properties.In the past, most polyurethanes are oil soluble. In recent years, the water-based trend of polyurethane has been formed, and the water-based polyurethanes have become increasingly mature.
★ Waterborne polyurethane classification ★
There are many categories of waterborne polyurethanes, generally there are the following classification methods.
Classification by appearance: waterborne polyurethane can be divided into polyurethane emulsion, polyurethane dispersion, polyurethane aqueous solution.The most commonly used are polyurethane emulsions and dispersions.
Classified by curing mode.Waterborne polyurethane can be divided into two components, one component self - drying, radiation curing three.
Radiation-cured waterborne polyurethane generally contains double bonds and can be initiated by photoinitiator under uv light.
The water-based two-component system is the same as the traditional solvent two-component system, that is, two components A and B need to be mixed to produce cross-linking curing, generally using water-based isocyanate curing agent.
One component waterborne polyurethane can cure at room temperature or at heating.
Classification by properties of hydrophilic groups.According to whether the side chain or main chain of the polyurethane molecule contains ionic groups, that is, whether it is an ionic bond polymer, waterborne polyurethane can be divided into anionic, cationic and non-ionic types.Containing anion, cationic waterborne polyurethane also known as ionomer type waterborne polyurethane.Those that do not contain ionic groups are called non-ionic waterborne polyurethanes.
Polyurethane raw material classification.According to the main types of oligomers polyols can be divided into polyether type, polyester type and polyolefin type, respectively refers to the use of polyether polyols, polyester polyols, polybutadienediol as oligomers and made of waterborne polyurethane.There are polyether - polyester, polyether - polybutadiene and other mixed types.Polyurethane isocyanate raw materials can be divided into aromatic isocyanate type, aliphatic isocyanate type, alicyclic isocyanate type.
According to the waterborne method of polyurethane, it is divided into self - emulsification method and external emulsification method.
Self-emulsifying method, also known as internal emulsifying method, refers to the method of forming stable emulsion without emulsifier because the polyurethane segments contain hydrophilic components.
External emulsification method is also called forced emulsification method. If the molecular chain contains only a small amount of hydrophilic chain segments or groups that are not sufficient for self-emulsification, or does not contain hydrophilic components at all, emulsifier must be added to obtain emulsion.
In contrast, the residual hydrophilic small molecule emulsifier in the emulsion prepared by external emulsification affects the properties of the cured polyurethane film, but the self-emulsification method eliminates this defect.At present, ionic self - emulsification is the main method for preparing waterborne polyurethane.