How to Improve Polyurethane With Molecular Sieve Water Remover
Many polyurethane components and raw materials contain water, and pigments and fillers adsorb a single molecular layer of water on their surfaces. In addition, pigments can adsorb water during storage. Usually, solvents, polyols and other components used in polyurethane reactions require a dry environment.
If the solvent in a solvent-based two-component polyurethane is not de-watered, carbon dioxide will be generated. This can cause the polyurethane to foam during curing. The water-laden polyols and pigments eventually lead to the formation of carbon dioxide bubbles in the cured film. Not only does this cause bubbles and pores, but it can also reduce the gloss of the coating.
Moisture in the construction environment can get into the polyurethane being applied. This problem is quite prominent when spraying polyurethane elastomers. Often the substrate itself may be wet, which will cause additional problems. For example, polyurethane maintenance coatings are typically applied right over a damp surface. Humid conditions and poor removal of moisture from the hydroxyl component of the coating can lead to the production of carbon dioxide gas. This causes bubble holes to form in the coating.
Therefore, moisture needs to be removed from the raw polyurethane material. The physical method of dehydration is the commonly used process. Generally, the oligomeric polyol is dehydrated under high vacuum at 100-120°C for 1 to 2 h. Most of the water can be removed. To meet the requirements of use. The solvent can be added molecular sieve drying, and distillation, to remove the moisture. The filler needs to be dried before use.
In some cases there is no condition to use the above methods for dehydration, then the water can be removed by adding a water removal agent. Physical water removal agent has molecular sieve. Molecular sieve products are available both at home and abroad. Usually obtained by dispersion of molecular sieve microfine powder in plasticizer.
Molecular sieves are used to remove water from the structure of crystallized synthetic zeolite (a special sodium/potassium salt of aluminum silicate), i.e. "activation". The result is a microporous powder solid with specific pore size. Molecular sieves can be selected to adsorb small molecular mixtures, including water molecules. Some molecular sieves are therefore physical water removers (i.e. desiccants).
IRO Chemicals sells industrial molecular sieves in a variety of sizes. They can be used as water-removing (water-absorbing, drying) agents for one-component and two-component polyurethane systems. Available in powder and paste form, details can be found here.
In two-component polychlorinated ester systems, molecular sieves can be added to polyol/color filler mixtures. However, the effect of molecular sieves on the service life should be considered.