In polyurethane systems, the problem of trace moisture is more or less related to the raw materials. And trace moisture is one of the primary challenges in the manufacture of polyurethane products, which needs molecular sieve as a powerful moisture scavenger to solve it.
Polyurethane Raw Materials
The core materials of polyurethane are isocyanates and polyols, to form carbamate groups through their chemical reaction. Here we list some common materials in the market, to provide some basic understandings.
- Isocyanates: diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), polyaryl polymethylene isocyanate (PADI) etc.
- Polyols: polypropylene glycol (PPG), polytetramethylene ether glycol (PTMEG), adipic acid (AA), butanediol (BDO) etc.
- Chain extenders: propylene glycol (PG), ethylene glycol (EG), polyether triols etc., to adjust the molecular weight and hardness of polyurethane.
- Catalysts: organic tin compounds (such as diethyl stannate) and organic lead compounds, to promote the reaction of isocyanate and polyol.
- Flame retardants: silicon-based and phosphorus-based flame retardants, to improve the flame retardant properties of polyurethane.
- Plasticizers: low molecular weight polyols and polymer processing aids, to adjust the flexibility and ductility of polyurethane.
- Fillers: cellulose, mineral fillers and glass fibers etc., to increase the volume of polyurethane and improve its physical properties.
Trace Moisture Sources
Moisture in raw materials: As is known, polyols are a type of alcohol containing two or more hydroxyl groups in the molecule. Due to the hydrophilic nature of the hydroxyl groups, polyols often carry trace amounts of water. And other materials mostly are solvents, additives or auxiliaries, also contain trace water.
Moisture in the environment: Moisture in the environment is inevitable, whether in the equipment or in the production process.
Moisture Scavenger for Polyurethanes
In the production of polyurethane, the most important chemical reaction is between isocyanates and polyols. However, isocyanates are extremely sensitive to moisture, and even trace amounts of moisture will react with isocyanates to produce carbon dioxide, resulting in bubbles and related problems.
Molecular sieve (activated powder) has excellent chemical stability, and itself will not react with the polyurethane system. When added, the molecular sieve can effectively and selectively absorb trace amounts of moisture in typical polyurethane formulas, and inhibit the occurrence of secondary chemical reactions. As a moisture scavenger for polyurethanes, molecular sieve is truly powerful and incomparable.
