Waterborne polyurethane preparation methods can be divided into external emulsification method, internal emulsification method, acetone, pre polymers.
A, external emulsification method external emulsification method require additional emulsifier, force the polyurethane dispersion in water.
The legal system of emulsion particle coarse causes the emulsion stability, emulsifier dosage big lead to film the result is bad, film-forming poor water resistance, mechanical performance is not good, the resulting polyurethane product performance affected, it has basically not adopt the method of polyurethane products.
Within the second, the internal emulsification method emulsification method is also called the emulsification method, polyurethane chain segment contained hydrophilic ingredients without additional emulsifier dispersed into stable emulsion.
This method is simple and the application range is extensive, therefore has become the main method used in waterborne polyurethane
production and research.
Can be divided into internal emulsification method and acetone, pre polymers and molten dispersion method, etc.
Since the preparation of waterborne polyurethane emulsion is the most commonly used method of acetone and pre polymers.
Three, acetone method first isocyanate and generate - polymer polyols
NCO terminal base polyurethane pre polymers, in the presence of acetone, pre polymers and small molecular chain extender and hydrophilic chain extender chain extension reaction, generate high molecular weight polyurethane pre polymers, and then make its dispersed in water to form emulsion, and waterborne polyurethane emulsion is obtained by vacuum distillation from acetone namely.
Acetone method is: the advantages of easy operation, good repeatability;
Acetone low boiling point, miscibility with water and is easy to be recycled;
In addition to produce high molecular weight polymers, emulsion film-forming performance is good.
The disadvantage of acetone method is: acetone has a low boiling point and volatile, easy to cause environmental pollution;
Complex process, high cost, low safety, is not conducive to industrial production.
This method is the main method of production of waterborne polyurethane.
Four, firstly the dimer method (synthetic pre polymers containing hydrophilic group, make its dispersed in water under high speed stirring, chain growth of emulsion in water at the same time, generate - waterborne polyurethane
Advantage is the dimer method avoids using a large number of organic solvents, and the process is simple, convenient for industrialized continuous production.
The disadvantage is that the dimer method (extender chain reaction in the multiphase system, reaction can't control by the quantitative way.
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