What is polyurethane?

What is polyurethane?
Polyurethane foams or polyurethane based products;
Polyurethane foams or polyurethane-based products are formed by the chemical reaction of two main components called polyol system (Component A) and isocyanate (Component B). Here are more detailed descriptions of these components:

I. Component (Component A): Polyol System
Polyol system is a mixture created by mixing polyether or polyester-based polyols in appropriate proportions. Catalyst, silicone, colorant, blowing agent and other chemicals can also be added to this mixture. The polyol system contains free hydroxyl (OH) groups.

II. Component (Component B): Isocyanate
Isocyanates are chemicals containing free NCO (isocyanate) groups that react exothermically when mixed with the polyol system. Isocyanates are identified and named based on the percentage of NCO. For example, MDI has an NCO percentage of 31, while TDI has an NCO percentage of 48.

When the polyol system (Component A) and isocyanate (Component B) are mixed in certain proportions and temperatures, 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, therefore the polyurethane foam takes the shape of the container or mold in which it is placed by filling all the gaps. The spreading properties of polyurethane foams are superior to other chemical products.

Whether polyurethane foams are rigid, semi-rigid or flexible depends on the percentages of OH and NCO in the components. The OH percentage in rigid foams is usually more than 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, automotive industry, construction industry and many industrial applications. While flexible polyurethanes are used in comfort products such as pillows, upholstery and cushions, rigid polyurethanes are used in insulation panels, core goods.

It is preferred in applications that require durability such as floors and structural parts.

Polyurethane properties:

1. Chemical Structure: Polyurethanes is the general name of polyurethane resins formed by the reaction of a polyol and an isocyanate compound. As a result of this reaction, carbonyl groups containing uretone and urethane groups, which form the main structural units of polyurethane, are formed. This structure provides the elastic, durable and versatile properties of polyurethane.

2. Flexibility and Durability: Polyurethanes provide flexibility in various applications because they have an elastic structure. This elasticity makes it possible for the material to change shape and bounce back. In addition, polyurethanes are resistant to impacts and abrasion thanks to their high durability.

3. Lightness: Polyurethane materials are generally light and do not cause weight gain in the area where they are applied. These features are preferred to increase fuel efficiency and optimize carrying capacity, especially in industries such as automotive, aviation and maritime.

4. Insulation Properties: Polyurethanes provide high heat and sound insulation performance. Due to these features, they are widely used in the construction industry. While polyurethane foam is used for wall, roof and floor insulation in buildings, polyurethane spray foam is preferred to fill gaps and provide insulation.

5. Chemical Resistance: Polyurethanes are resistant to most chemicals. These properties enable polyurethanes to be used in industrial coatings, paints and varnishes, sealants and chemical storage tanks.

6. Diversity: Polyurethanes can be found in many different forms. They can be produced in hard, elastic or foam form. This diversity allows polyurethanes to be customized to different application needs.

7. Application Areas: Polyurethanes have a wide range of uses. In the automotive industry,

  It is used in the production of vehicle parts, fillings and insulation purposes. It is used in the construction industry, in building materials, insulation products, adhesives and coatings. They also find use in furniture production, textile coatings, shoe soles, sports equipment, electronic devices and many other areas.

The wide range of uses and diversity of polyurethane make it a versatile material and make it 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 properties such as high strength, high rigidity or high flexibility.

Impact Resistance: Polyurethane's exceptional impact resistance provides resistance to cracking, tearing, breaking and swelling even at low temperatures.

Wear Resistance: Used especially in the mining, oil and gas industries, polyurethane offers solutions to important wear problems. It shows a significant wear advantage over other materials in laboratory tests and field applications.

Ease of Molding: Polyurethane parts are generally produced by casting into cheaper and low-pressure molds. Polyurethane in liquid form can fill complex mold cavities without the need for high-pressure molds and presses.

Mechanical Strength: Polyurethane can withstand both tensile and compressive forces. It can change shape 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, thus retaining their original shape and physical properties even in harsh conditions. Standard thermoset polyurethanes can withstand temperatures from -26°C to 93°C. However, some polyurethane products can better tolerate high temperatures up to 148°C. Outside of these temperatures, thermoset polyurethanes may tend to weaken or deteriorate 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 the air to the water vapor permeability of the sample. Polyurethanes are generally resistant to acid vapor and acids.

Dimensional Stability

Polyurethane exhibits excellent dimensional stability thanks to its thermoset structure. This stability allows long-term use in the temperature range of -30°C to +90°C, depending on the density and type of 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. The mechanical properties of polyurethane foams compressed in fast and dynamic situations are affected by the friction of the cellular structure and the air contained in the cells.

Fire Resistance

Polyurethanes can offer improved fire resistance using special formulations. Its chemical structure has the feature of protecting fire by charring instead of melting when it comes into contact with flame.

Resistance to Acid Vapor and Acid

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 greater chemical resistance than many metals, rubbers and plastics.

Usage Areas of Polyurethane

Polyurethane is widely used in home furnishings such as furniture, bedding and carpet underlay, usually in the form of flexible foam. It is also used in the form of rigid foam in areas such as heat and insulation sectors, heating and cooling systems. It is also frequently used as a rubber binder in the shoe industry.