POLYURETHANE

Polyurethane has a wide range of applications in water-based, solvent-based, and hot melt adhesives. Furthermore, polyurethane can be thermoplastic or reactive, and can be a single-component or two-component system. The chemical properties of urethanes determine the versatility and variability of polyurethanes. Polyurethanes are primarily obtained through the condensation reaction of isocyanates and alcohols, and can also be formed through the polymerization reaction of polyisocyanates and hydroxyl compounds (including polyols), such as polyesters and polyethers.

The most important polyurethane products currently include foam plastics, adhesives, coatings, and elastomers. 

1. Polyurethane Foam Plastics. These are mainly made from diisocyanates and polyether-type or polyester-type polyols, catalysts, blowing agents, foam stabilizers, and other additives to produce soft or rigid polyurethane foam plastics. There are three foaming processes: prepolymerization, semi-prepolymerization, and one-step process. Semi-prepolymerization and prepolymerization are suitable for small-batch production, while one-step process is suitable for large-batch production. Rigid or soft polyether-type or polyester-type polyurethane foam plastics are thermosetting plastics, and their properties vary considerably depending on the raw materials and formulation used. They possess properties such as oil resistance, cold resistance, heat insulation, and sound absorption, and can be used as thermal insulation materials, insulating materials, soundproof structural materials, leak-proof materials, shockproof packaging materials, sound-absorbing materials, padding materials, and dust removal and filtration materials.

2. Polyurethane Adhesives. These are two-component systems composed of polyisocyanates and hydroxyl-containing polyester compounds, which are directly mixed during use. This adhesive exhibits high adhesion to various materials, and the cured product is stable against water, mineral oils, and the atmosphere. It can be used for bonding metal, glass, plastic, and ceramic structures in construction, machinery, and aerospace.

3. Polyurethane Chemicalbook Coatings. Various polyurethane coatings can be prepared by combining different types of isocyanates with different polyesters, polyethers, and polyols. These are mainly divided into two categories: two-component and one-component. Two-component polyurethane coatings are polyether-type, where polyisocyanates and polyethers are directly mixed. One-component polyurethane coatings are unsaturated polyester-type, including blocked, oil-modified, and moisture-curing types. Application methods include impregnation, spraying, and electrodeposition. The coating possesses good insulation, strong adhesion, wear resistance, oil resistance, water resistance, and resistance to inorganic acid vapors. It can be used in concrete building structures, chemical instruments, aircraft parts, furniture, etc.

4. Polyurethane Elastomers. Depending on the formulation, polyurethane can exhibit elasticity within a certain temperature range; this is called a polyurethane elastomer. Bayer AG of Germany was the first company in the world to synthesize polyurethane elastomers. It can be divided into three main types: castable, compounded, and thermoplastic elastomers. This material possesses both the elasticity of rubber and the processability of plastics, hence it is also called a plastic elastomer. It has excellent oil resistance, wear resistance, low-temperature elasticity, and aging resistance, and can be used to manufacture automobile bearings, high-speed transmission belts in the textile industry, and electrical wires and cables used in oil fields and geological exploration teams.