Polyurethane is a polymer with urethane bonds obtained by reacting isocyanate groups with hydroxyl groups.
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By changing the type and composition of the primary raw materials and the molding method, polyurethane can be made spongy, flexible like rubber, or hard like rubber tires.
Figure 1. Polyurethane synthesis reaction formula
Polyurethane can be divided into two broad categories in terms of appearance: foam-based, which is porous, and non-foam-based, which is rubber-like. Since the uses for each are quite different, they are described separately below.
Foam-based polyurethane comes in two types: soft foam and hard foam. Soft foam, in particular, is used in various applications, from everyday items to industrial uses. Soft foam applications include sponges used in kitchens, cushions for headphones and other devices, rollers for industrial equipment, and soundproofing materials.
Rigid polyurethane foam applications are often used in construction sites as heat insulators.
Non-foamed polyurethane has high elasticity and toughness and is used as elastic structural materials such as rubber and elastomers, as well as fibers, paints, and adhesives.
As elastomers, they are used in tires, belts, gaskets, rollers, machine parts, and automobile bumpers. Polyurethane fibers, called spandex, are also widely used in clothing such as jackets, pants, swimwear, sportswear, etc., due to their high elasticity.
Figure 2. Typical examples of raw materials that make up polyurethane
The raw materials used to make polyurethane include diisocyanates, which have bifunctional isocyanate groups in their molecules, polyols, which have hydroxyl groups in their molecules, and low molecular weight diols.
While there are only a few types of diisocyanates used in polyurethane, there is a very wide range of polyols, which are the raw materials for the hydroxyl group component. This is because polyols themselves are polymers with molecular weights ranging from several hundred to several thousand, and they are composed of a wide range of monomer combinations.
The low molecular weight diols are typical examples of hydroxyl group components, and their dimers are also used as low molecular weight diols. Triols with three hydroxyl groups and alcohols with a single hydroxyl group are also used to adjust the molecular weight.
The characteristics of polyurethane vary greatly depending on the type of raw material used in the mixture. In general, polyurethanes have excellent mechanical strength (elasticity and toughness) and the following characteristics:
These characteristics vary greatly depending on the combination of raw materials used. For example, hardness and strength differ greatly depending on the ratio of polyol and low molecular weight diol used. In addition, the polyol component contributes significantly to weather resistance and hydrolysis resistance. Therefore, it is important to design molecules that match the required performance.
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Figure 3. Reaction Formula for Urethane Foam Foaming
Polyurethane foam is a sponge-like molded product produced by foaming polyurethane during the molding process. There are multiple methods of manufacturing polyurethane foam, including slab molding, in which a mixture of raw materials is foamed without being placed in a mold and then cut into the shape of the product. Other methods are mold molding, where a mold is used to form the product into the required shape, and laminate molding, which is useful for producing large insulation boards.
1. Soft Foam-Based Polyurethane
In soft foam polyurethane, water is added as a foaming agent to the raw material polyol, and the isocyanate groups react with the water to produce carbon dioxide gas. At the same time, resinification by the reaction of polyol, low molecular weight diol, and isocyanate proceeds, so that each bubble of carbon dioxide gas cures in a continuous state to form a porous foam.
During the reaction with water, the isocyanate becomes an amine. However, due to the extremely high reactivity of amines, it immediately reacts with another isocyanate group to form a urea bond. For this reason, the composition of soft foam-based polyurethane contains not only urethane bonds but also many urea bonds.
Huntsman’s MDI-based rigid polyurethane foam plays a critical role in reducing food waste and extending the life of perishable goods. Our rigid foam provides outstanding thermal insulation properties, leading to its widespread application throughout the supply chain of perishable goods – from the refrigerated processing plants to the insulated storage warehouses and walk-in freezers, to refrigerated transport vehicles, storage pods and grocery store freezers.
From grocery stores to consumers’ dining tables, our foams are used in cool boxes and domestic refrigerators to keep food fresh and tasty.
Learn MoreHunstman offers a wide range of MDI-based polyurethanes products that are used in building, construction and infrastructure applications. MDI-based polyurethane is the most effective insulant available in the market and so is widely used to provide energy saving solutions in residential and commercial buildings. Polyurethane insulation is used in roofs, interior and exterior walls, floors, doors and ceiling cavities, pipes, as well as building exterior applications, in both new and retrofit construction projects. Our insulation products also increase a building’s air quality, reduce moisture infiltration, and make buildings stronger and quieter.
The outstanding thermal insulation qualities of MDI-based polyurethane foam have seen its use in district heating systems – where it insulates the huge pipes that are used to transport energy – increase significantly in recent years.
Huntsman is a pioneer in composite wood products, including medium-density fiberboard, particleboard and oriented strand board, which are produced using MDI resins. Composite wood products are used in building and construction to replace steel joists and beams.
Our MDI-based coatings are used to seal floors, decks and driveways, providing protection and extending the life of the surface. And our thermoplastic polyurethanes (TPUs) are used to protect cables and wires in residential, commercial and industrial buildings.
Learn MoreHuntsman’s thermoplastic polyurethanes (TPUs) are widely used in a variety of consumer electronics, due to their excellent durability, flexibility, pleasant haptics, soft touch and grip – from the household wiring that runs low-amp domestic appliances to the molded parts found in your TV, computers and hand-held devices. Additionally, TPUs can be found in cable power systems, protective cases, printed circuit boards and other technical parts used in medical, technology, smart fabrics, wearables, IoT (Internet of Things) and other consumer electronic devices, including plasma screens, mobile phones, smart watches, tablets and laptops. Other TPU characteristics include scratch, abrasion and impact resistance, good vibration absorption and chemical resistance. TPUs can also be formulated for specific functionality such as flame retardancy, anti-static or conductive, transparency and matte finish.
Learn MoreHuntsman’s MDI and polyols are the key ingredients in the production of flexible polyurethane foam, a highly versatile cushioning material used in furniture, mattresses and pillows. Huntsman works in close partnership with customers to ensure that consumer needs for comfort are constantly improved. Within the polyurethane formulated systems, our pioneering JEFFCAT® catalysts provide emissions reduction, performance and power for polyester, polyether and viscoelastic applications.
Our innovative formaldehyde-free MDI resins deliver significant improvements in the production and performance of furniture-grade Medium Density Fiberboard (MDF), High Density Fiberboard (HDF) and Particleboard (PB), that are widely used in furniture production for the home and the office.
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