What is Polyurethane (PU)? Where is Polyurethane Material Used?
Urethane chemistry began to be discovered in 1849. In those years, Wurtz and Hoffman discovered a reaction involving isocyanate and hydroxyl compound. In 1937, Dr. Otto Bayer has adapted this reaction to a commercial use. And nylon, which was preferred in the industrial world before this process, has slowly begun to be replaced by polyester-based urethane polymers. With the beginning of the Second World War, the decrease in the use of main materials such as rubber due to the limitation of resources allowed the development of polyurethane materials for fibers, foams and coatings.
Polyurethanes, which are used in the production of many products in our living spaces today and constitute one of the most important polymer classes, constitute a polymer group containing diisocyanate and diol groups in various proportions and combinations in their structures. The reason why polyurethane material is the most preferred polymer group; It is obtained from liquid monomers in an easy process with low energy requirement. It also constitutes a widespread product group, from soft, linear elastomers to hard thermosetting foams.
What is Polyurethane (PU)?
Polyurethane material is formed by reacting a polyol with a diisocyanate in the presence of appropriate catalysts and additives.
- Component (Component A): Polyol
- Component (Component B): Isocyanate
Polyol: It is a mixture of polyether or polyester based polyols and catalysts, silicones, colorants, fluffing agents and other chemicals added into them in appropriate proportions. These mixtures carry free hydroxyl (OH) in their structure.
Isocyanate They are chemicals that react exothermically with polyol system when mixed with it and carry free NCO. Isocyanates are recognized and named according to the number of NCOs they carry.
What is Polyurethane (PU) Foam and Why is it Used?
Polyurethane foam is obtained by mixing polyurethane systems in a certain ratio. This material is used to provide high levels of heat, sound or water insulation.
What Are Polyurethane Foam Types?
There are many different types of polyurethane foams depending on their properties such as hardness, flexibility and surface texture. The fact that it can be produced in the desired forms and sizes has enabled it to have a very wide application area. Polyurethane foams are structurally classified asrigid polyurethane foams, flexible polyurethane foams, semi-rigid polyurethane foams, elastomer polyurethane foams, spray polyurethane foams etc. They are separated as .
What is the Difference Between Flexible Polyurethane Foam and Rigid Polyurethane Foam?
Flexible polyurethane (PUR) foams are open-cell, chemically or physically foamed copolymers formed by diisocyanates containing two or more -NCO groups and polyols containing two or more -OH groups linked by urethane groups. They can also be defined as open-cell structured polyurethane foams with limited size stretching and reshaping. Flexible polyurethane foams are light and robust as well as very comfortable. It is used in many different sectors, especially in mattresses, furniture and automotive.
Rigid polyurethane foams have a much lower coefficient of thermal conductivity (lambda) than other insulation materials such as wood, rock wool and polystyrene, thanks to their high closed cell content and the insulating gases they contain. Therefore, the thermal insulation provided by rigid polyurethane foams is much higher than other insulation materials. It is used in many different sectors, from thermal insulation of buildings, heaters and coolers to the production of wood imitation products for decorative purposes.
In Which Sectors is Polyurethane Used?
A wide range of diisocyanates and polyols can be used in the production of polyurethanes. This provides a wide range of products to meet the needs of special applications in many different sectors. In addition, the fact that it is physically easy to process and shape, and that it has both a rigid and flexible structure allows it to be used at a high rate in industrial areas.
Polyurethane foams have a low thermal conductivity coefficient. With this feature, polyurethane foams provide excellent insulation properties. It is preferred more frequently than conventional products as insulation material in many sectors from the protection of food from spoilage in the cooling sector to energy and heat consumption in building insulation.
The main reason why polyurethane material is preferred more than conventional products is that by changing the raw materials and proportions used, products with very different properties, different forms and sizes can be obtained.
- Footwear Industry
Polyurethane is highly preferred in the footwear industry as it meets the main criteria sought in the production of soles, slippers and insole with its properties such as comfort, flexibility, durability and lightness. It is used in a wide range of areas within the sector, from the production of low density slipper soles to the production of worker shoe soles that require high flexibility and durability.
- Building and Insulation Sector
Polyurethane is mostly used for thermal insulation in buildings and structures. Thanks to its thermal insulation and airtightness, it traps heat in the environment. For this purpose, it is produced as plates, sandwich panels and pipe sections or used as spray polyurethane foam by spraying method in the construction area. Polyurethane foam provides energy savings by adding high insulation performance to buildings with its low conductivity feature.
Polyurethane has fire prevention feature. According to the new European norms, it is a product in fire class E (difficult flammable material). This feature increases the fire resistance in buildings. In addition, polyurethane is used for waterproofing purposes as coating, protection, adhesive and filling materials in buildings and structures. Therefore, it is possible to use polyurethane-based materials in almost every part of a building from the foundation to the roof.
- Furniture Sector
Polyurethane is frequently preferred in the furniture industry thanks to its long life, easy shaping, paintability, lightness and ease of application.
Esnek poliüretan köpük ailesinden HR (High Resilience) poliüretan köpükler ofis koltuğu üretiminde, visko (hafızalı) poliüretan köpükler yatak ve yastık üretiminde kullanılırken sert poliüretan köpükler ise mobilya sektöründe ahşap taklidi dekorasyon ürünlerinin üretiminde kullanılır.
- Automotive Sector
The most important reasons for the increasing use of polyurethane in the automotive sector are low-cost parts production and assembly, light weight, impact resistance, the ability to produce different properties according to the application area, flexibility and corrosion resistance. In particular, integral polyurethane foams from the polyurethane foam family are used in the production of automobile accents such as steering wheels, armrests, consoles, bumpers, etc. In addition, flexible polyurethane foams are used in automotive sound insulation thanks to their sound insulation properties, and HR foam systems from the same group are frequently used in automotive seat production. The impermeability feature of polyurethane allows it to be used as a sealing material in the production of automotive cable sheaths.
- Heating and Cooling Sector
Polyurethane is used in boilers and solar energy panels in the heating sector and in industrial and domestic refrigerators (ice cabinets), cold rooms and refrigerated cases in the cooling sector to provide thermal insulation. Rigid polyurethane foams from the polyurethane foam family reduce the energy consumed and provide high efficiency by maintaining the desired temperature in these products with the insulation feature it offers thanks to its low thermal conductivity.
- Aircraft Industry
Polyurethane is used in many areas in airplanes. Flexible polyurethane foams are used in the production of airplane seats, providing passengers with a comfortable travel experience. Since polyurethane coatings have high abrasion resistance, they are used in cabin walls, ceilings, upper partitions and toilets. In addition, polyurethane foams are also preferred as sealing materials in airplanes.
- Defense Industry
Military equipment is expected to be able to withstand harsh conditions for long periods of time. Durability, comfort and high performance are very important for these materials.
Polyurethane foams are frequently used in the production of products such as impact pads, tactical helmets, soles of combat boots, etc. in the defense industry thanks to their lightness, high abrasion resistance and flexibility.
- Medical and Medical Products
Polyurethane is frequently preferred in the production of medical parts thanks to its many advantages such as high flexibility, high comfort coefficient (SAG), adjustable hardness range, long service life. Polyurethane provides ergonomic features to many medical products with its ability to return to its original shape (resilient).
- Packaging Technology
Polyurethane foam is also used in packaging production thanks to its flexibility, lightness and easy shaping. Companies that produce small, lightweight or impact-sensitive products often prefer to use polyurethane foam in the packaging of their products. Polyurethane foam is also used in the packaging of many fragile parts in the electronics and automotive sectors. One of the reasons why polyurethane foam is frequently preferred in the packaging sector is that it can be produced in the sizes and hardnesses required according to the size and type of the product to be packaged.
- Maritime
Polyurethane foam is used to provide thermal insulation in ship, boat and yacht engines. For this purpose, polyurethane coatings, rubber binders, rigid polyurethane foams are used. Thanks to the high mechanical and external resistance properties of polyurethane, the hull of the boat is protected from water, weather conditions, corrosion and other factors that affect hydrodynamics and reduce the life of the boat. Polyurethane is also used for sound insulation in boats, minimizing noise.
Polyurethane General Properties
The overall properties of polyurethanes largely depend on the structure of the polymer backbone. They can be tailored to have high strength, high rigidity or high flexibility.
- Polyurethane's impact resistance is exceptional, even at low temperatures, so it offers resistance to cracking, tearing, breaking and swelling.
- Polyurethane's abrasion resistance offers a solution to many important applications where severe abrasion is a problem, particularly in the mining and oil and gas industries. In both field application and laboratory testing, polyurethanes show a significant abrasion advantage over many materials.
- Polyurethane parts are usually poured into cheaper, low-pressure molds. As a liquid, polyurethane can fill even complex mold cavities without high-pressure molds and presses.
- Polyurethane can withstand both tension and compression. While it can change shape under heavy load, it can return to its original shape when the load is removed.
- Due to short lead times and more economical tooling costs, polyurethane is often used for one-off parts and prototypes or high-volume reproduction runs.
Polyurethane Temperature
Polyurethanes can withstand a wide range of temperatures, allowing them to retain their original shape and physical properties even under the most extreme conditions. Standard thermoset polyurethanes can withstand temperatures from -26°C to 93°C. However, some polyurethane products can have a higher tolerance to temperatures as high as 148°C. Outside of these temperatures, thermoset polyurethanes tend to weaken or degrade over time.
Thermal Conductivity Value
Thermal conductivity refers to the ability of a material to transfer or conduct heat. Thermal conductivity occurs through molecular agitation and contact. Heat moves along a temperature gradient from an area of high temperature and high molecular energy to an area of lower temperature and lower molecular energy. Thermal conductivity, also known as lambda value, describes the insulating capacity of a product based on the level of thermal conductivity of the material and is usually denoted by k, λ or κ.
Water Vapor Diffusion Resistance (Water Vapor Permeability)
The water vapor diffusion resistance factor is the ratio of the water vapor permeability of the air to the water vapor permeability of the sample. If the temperature is known, the water vapor permeability of the air can be considered constant. Water vapor permeability diffuses from the side with high absolute air humidity to the side with low absolute air humidity.
Dimensional Stability
Polyurethane exhibits excellent dimensional stability due to its thermoset structure. The dimensional stability of polyurethane varies according to the temperature environment. Depending on the density and type of coatings, rigid polyurethane insulation for building applications can be used for long periods of time in the -30°C to +90°C temperature range.
Mechanical Properties
The mechanical properties of polyurethane foam are influenced by the internal and external structure, the shape and size of the cells, the filling volume and the properties of the polymer used. The mechanical properties of polyurethane are affected by contact pressures, stress distribution and strain rate of the stress. The mechanical properties of polyurethane foams compressed in fast and dynamic states are affected by the friction of the cellular structure and the air contained in the cells.
Mechanical Properties of Polyurethane:
Fire Resistance
Polyurethanes have the ability to offer product designers improved fire resistance through customized formulations. Due to their unique chemical structure, polyurethanes are able to meet the most demanding flame resistance requirements. Polyurethane has the ability to retain the core of the fire by charring rather than melting on contact with the flame. This causes the structure to remain stable for some time. The design of the building is very important when it comes to fire safety.
It is important to take into account that most fires are not caused by the materials used to insulate industrial units or houses, but by poor management of the waste accumulated in them or by the human factor.
Resistance to Acid Vapor and Acids
The chemical resistance of polyurethane varies between polyurethane formulations. In general: Polyester type polyurethane is more resistant to oils, solvents and weak acids/bases. And polyether type polyurethane is more resistant to exposure to water.
Polyurethanes have greater chemical resistance than many metals, rubbers and plastics. In general, polyurethanes are resistant to acid vapors and acids as well as other corrosive chemicals.
Where is Polyurethane Used?
Polyurethane, mostly in the form of flexible foam, is one of the most popular materials used in home furnishings such as furniture, bedding and carpet underlay. As a cushioning material for upholstered furniture, flexible polyurethane foam makes furniture more durable, comfortable and supportive. Polyurethane in the form of rigid foam is used in sectors such as the heat and insulation sector, heating and cooling sector. In addition, it is used extensively in the shoe industry, rubber binder and polyurea systems.
