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Polyurethane is widely used in water-based, solvent-based and hot melt adhesives. In addition, the polyurethane may be thermoplastic or reactive, or it may be a one-component or two-component system.
The chemistry of the carbamate determines the versatility and variability of the polyurethane. Polyurethanes are mainly obtained by polycondensation of isocyanates and alcohols, and it is possible that polyisocyanates and hydroxy compounds (including polyols) are formed by polymerization, such as polyesters and polyethers.
At present, the most important polyurethane products are foams, adhesives, coatings and elastomers.
1. Polyurethane foam. Soft or rigid polyurethane foams are mainly made from diisocyanates and polyether or polyester polyols, catalysts, blowing agents, foam stabilizers and other auxiliaries. The foaming process has three kinds of pre-polymerization method, semi-prepolymerization method and one-step method. The semi-prepolymerization and prepolymerization methods are suitable for small batch production, and the one-step method is suitable for mass production. Rigid or soft polyether or polyester polyurethane foams are all thermoset plastics, and their properties vary greatly depending on the materials and formulations used. They are resistant to oil, cold, heat, sound absorption, etc. They can be used as insulation materials, insulation materials, sound-insulating structural materials, anti-leakage materials, shock-proof packaging materials, sound-absorbing materials, gasket materials, dust-removing filter materials, etc.
2. Polyurethane adhesive. A two-component system consisting of a polyisocyanate and a hydroxyl-containing polyester compound, the two components being mixed directly when used. The glue has high adhesion to various materials, and the cured product is stable to water, mineral grease, atmosphere, etc., and can be used for metal, glass, plastic, ceramic structure connection of construction, machinery, aviation, and the like.
3. Polyurethane coatings. A variety of polyurethane coatings can be prepared by using different kinds of isocyanates in combination with different polyesters, polyethers and polyols, mainly in two-component and one-component. The two-component polyurethane coating is a polyether type, which is a direct mixing of a polyisocyanate and a polyether; a one-component polyurethane coating is an unsaturated polyester type, including a closed type, an oil-modified type, and a moisture-cured type. The construction methods include dipping, spraying, electrodeposition, and the like. The coating has good insulation, strong adhesion, abrasion resistance, oil resistance, water resistance and inorganic acid vapor resistance. Can be used in concrete building structures, chemical instruments, aircraft parts, furniture, etc.
4. Polyurethane elastomer. According to different formulations, polyurethane can be made elastic in a certain temperature range, which is called polyurethane elastomer. The world's first synthetic polyurethane elastomer is the Bayer company in Germany. It can be divided into three major types: cast, mixed, and thermoplastic elastomers. This material is not only a rubber elastic but also a plastics, so it is also called a plastic elastomer. It has excellent oil resistance, wear resistance, low temperature elasticity and aging resistance. It can be used to manufacture automotive bushings, bearings, high-speed transmission belts in the textile industry, oilfields, electric surveys and wires for geological exploration teams.
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