What is Polyurethane?

What is polyurethane? What are its properties. Polyurethane foams or polyurethane-based products; Polyurethane foams or polyurethane-based products are formed by the chemical reaction of two main components called the polyol system (Component A) and isocyanate (Component B). Here are more detailed explanations of these components: Component A: Polyol System The polyol system is a mixture created by blending polyether- or polyester-based polyols in appropriate proportions. Catalysts, silicone, colorants, blowing agents and other chemicals may also be added to this mixture. The polyol system contains free hydroxyl (OH) groups. Component B: Isocyanate Isocyanates are chemicals that contain free NCO (isocyanate) groups and undergo an exothermic reaction when mixed with the polyol system. Isocyanates are defined and named according to their NCO percentage. For example, the NCO percentage of MDI is 31, while that of TDI is 48. When the polyol system (Component A) and isocyanate (Component B) are mixed in specific ratios and at a specific temperature, an exothermic reaction occurs, and as a result of this reaction, polyurethane foam or product is formed. Heat and gases are released during the reaction. The reaction (foaming) proceeds in three dimensions, so polyurethane foam fills all the cavities of the container or mold it is placed in, taking its shape. The spreading ability of polyurethane foams is superior to that of other chemical products. Whether polyurethane foams are rigid, semi-rigid or flexible depends on the OH and NCO percentages in the components. In rigid foams the OH percentage is generally above 300, while in semi-rigid foams it is 100. These ratios determine the mechanical properties of the resulting foam. Polyurethane foams are used in insulation materials, filling materials, packaging materials, furniture production, the automotive sector, the construction sector and many industrial applications. While flexible polyurethanes are used in comfort-providing products such as cushions, upholstery and mattresses, rigid polyurethanes are preferred in applications requiring durability such as insulation panels, core materials and structural parts. Polyurethane properties: 1. Chemical Structure: Polyurethanes are the general name for polyurethane resins formed by the reaction of a polyol and an isocyanate compound. As a result of this reaction, carbonyl groups containing urethane groups, which form the main structural units of polyurethane, are produced. This structure gives polyurethane its elastic, durable and versatile properties. 2. Flexibility and Durability: Because polyurethanes have an elastic structure, they provide flexibility in various applications. This elasticity allows the material to deform and recover its shape. In addition, thanks to their high durability, polyurethanes are resistant to impacts and abrasion. 3. Lightness: Polyurethane materials are generally lightweight and do not cause a weight increase in the area where they are applied. These properties make them preferred for increasing fuel efficiency and optimizing carrying capacity, especially in industries such as automotive, aviation and maritime. 4. Insulation Properties: Polyurethanes provide high thermal and acoustic insulation performance. Because of these properties, they are widely used in the construction sector. Polyurethane foam is used for wall, roof and floor insulation in buildings, while polyurethane spray foam is preferred for filling gaps and providing insulation. 5. Chemical Resistance: Polyurethanes are resistant to most chemicals. These properties enable polyurethanes to be used in industrial coatings, paints and varnishes, sealing materials and chemical storage tanks. 6. Versatility: Polyurethanes can be found in many different forms. They can be produced in rigid, elastic or foam form. This versatility allows polyurethanes to be customized according to different application needs. 7. Application Areas: Polyurethanes have a wide range of uses. In the automotive industry they are used in the production of vehicle parts, in making fillings and for insulation purposes. In the construction sector they are used in building materials, insulation products, adhesives and coatings. They are also used in furniture production, textile coatings, shoe soles, sports equipment, electronic devices and many other areas. The wide range of use and versatility of polyurethane make it a versatile material and ensure that it is preferred in many industrial applications. General Properties of Polyurethane The general properties of polyurethane largely depend on the structure of the polymer backbone. These properties result from the ability to be adapted to characteristics such as high strength, high rigidity or high flexibility. Impact Resistance: The exceptional impact resistance of polyurethane provides resistance to cracking, tearing, breaking and swelling even at low temperatures. Abrasion Resistance: Polyurethane, used especially in the mining, oil and gas industries, offers solutions to significant abrasion problems. It shows a significant abrasion advantage over other materials in laboratory tests and field applications. Ease of Molding: Polyurethane parts are usually produced by casting into cheaper, low-pressure molds. Liquid-form polyurethane can fill complex mold cavities without the need for high-pressure molds and presses. Mechanical Durability: Polyurethane can withstand both tensile and compressive forces. It can deform but return to its original shape when the load is removed. Fast Production: Due to short lead times and economical tooling costs, polyurethane is often preferred for one-off parts, prototypes or high-volume mass production runs. Temperature Properties of Polyurethane Polyurethanes can withstand a wide temperature range, allowing them to retain their original shape and physical properties even in harsh conditions. Standard thermoset polyurethanes can withstand temperatures between -26°C and 93°C. However, some polyurethane products can better tolerate high temperatures up to 148°C. Beyond these temperatures, thermoset polyurethanes may tend to weaken or degrade over time. Thermal Conductivity Value Thermal conductivity refers to the heat transfer of the material. Polyurethane has high thermal conductivity. This value determines the insulation capacity of a product. Water Vapor Diffusion Resistance (Water Vapor Permeability) The water vapor diffusion resistance factor expresses the ratio of the water vapor permeability of air to the water vapor permeability of the sample. Polyurethanes generally show resistance to acid vapor and acids. Dimensional Stability Thanks to its thermoset structure, polyurethane exhibits excellent dimensional stability. This stability allows long-term use in the temperature range of -30°C to +90°C, depending on the density and type of the coatings. Mechanical Properties The mechanical properties of polyurethane foam are affected by the internal and external structure, the shape and size of the cells, the filling volume and the properties of the polymer used. In rapid and dynamic situations, the mechanical properties of compressed polyurethane foams are affected by the friction of the cellular structure and the air in the cells. Fire Resistance Polyurethanes can offer improved fire resistance using special formulations. Their chemical structure has the property of protecting against fire by charring instead of melting when in contact with flame. Resistance to Acid Vapor and Acids The chemical resistance of polyurethane varies depending on its formulations. In general, polyester-type polyurethanes are more resistant to oils, solvents and weak acids/bases. Polyurethanes have more chemical resistance than many metals, rubbers and plastics. Application Areas of Polyurethane Polyurethane is commonly used in flexible foam form in home furnishings such as furniture, bedding and carpet underlay. It is also used in rigid foam form in areas such as the heating and insulation sectors and heating and cooling systems. It is also frequently used as a rubber binder in the footwear sector.