Polyurethane: what is this material, characteristics, composition, application

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Information about polyurethane first appeared in 1937. The work on its synthesis was carried out by Otto Bayer. He used polyesters and diisocyanates in liquid form as the main components. The resulting polyurethane had higher qualities in comparison with plastic, which was found in all industries at that time.

Polyurethane is a unique type of material characterized by a wide range of applications. It contains 2 types of raw materials: isocyanates and polyols. They are formed on the basis of petroleum products. The properties of polyurethane and products made from it largely depend on the ingredients from which this material is made. Its production involves the use of catalysts, stabilizers and other elements in a certain ratio.

What it represents and why it’s good

A synthetic substance with a polymer structure, due to the mixing of components, is capable of acquiring various qualities. It can be plastic and rigid, and also have different coefficients of friction. Withstands stretching up to 500% and temperature changes from -60 to +80 degrees.

Plastic is an elastomer that can return to shape after deformation loads are removed. The basis is made up of long chains of macromolecules of the urethane group. Specific features are acquired by adding additional elements.

Polyurethane technical characteristics: chemical and physical properties

The main advantage of this type of raw material is the ability to give it a variety of qualities. As an elastomer, it retains its geometry perfectly and is able to return to its original state many times. According to this indicator, this material is ahead of its main competitor - rubber. Thanks to this, it shows high wear resistance.

What is polyurethane, the chemical composition of the material and properties

Main components:

• • polyols – long chains;
• • diols – short;
• • diisocyanates.

Due to the combination of components, the necessary elasticity qualities are imparted. The results are stable compounds that retain their parameters at different temperatures and are not inclined to react with the environment. Plastic retains its structure in the presence of: oils, acids, alkalis and fats. Does not undergo hydrolysis, resistant to microorganisms (fungi, bacteria, archaea). The substance easily tolerates moderate exposure to ultraviolet radiation. It is not oxidized by ozone like rubber. This increases the service life of products.

Physical qualities

The main advantage is the ability to temporarily change the geometry and the ability to add a variety of additional properties. Products based on this material are used in various industries because it:

• • capable of returning to its original shape after removing the force;
• • shows high wear resistance;
• • maintains quality factor during heating and cooling;
• • does not allow electricity to pass through;
• • has a thermal conductivity coefficient from 0.19 to 0.25 depending on hardness;
• • creates an airtight film;
• • has a relatively low specific gravity;
• • it is possible to create parts with different transparency coefficients.

Advanced Guide to Polymers. Properties of thermoplastics. Polyurethanes. TPU

The value of polyurethanes to piping system manufacturers is great because these materials are used to produce a large number of seals for pipes, fittings and pipeline fittings. Let's start looking at this group of materials with the most typical member of this family - thermoplastic polyurethane elastomer, which is variously abbreviated as TPU, PUR or PU, although the last two abbreviations can also be applied to polyurethane thermosets, so we will use the abbreviation TPU here.

Thermoplastic polyurethane is a melt-processable thermoplastic elastomer with high strength and flexibility. TPU provides a large number of combinations of physical and chemical properties for the most demanding applications such as automotive, wire and cable, breathable leisure films, sports and textile weatherproof coatings, non-yellowing films and of course seals for piping components. TPU has properties between those of plastic and rubber. Due to its thermoplastic nature, it has a number of advantages over other elastomers that cannot match it, such as tensile strength, elongation at break and load-bearing capacity. Thermoplastic polyurethane (TPU) was discovered in 1937 by Otto Bayer and his collaborators in the laboratories of I.G. Farben in Leverkusen, Germany. Manufacturers of thermoplastic polyurethanes produce material under brands such as Elastollan (BASF), Desmopan (Covestro), Diprane and Hyperplast (DuPont) and many others.

Types of polyurethane

The chemical industry produces three main classes.

Adiprenes

These are elastic substances with good shape retention characteristics. They are used to make protective boots, tire treads for automobile transport, gaskets and seals, rollers for carts and conveyors, coatings for gratings and components in the manufacturing industry. The parts are used in cyclones, screens and separators (to protect products from wear). Frames for casting are made from plaster and concrete.

Vulkollans

Due to its increased hardness and temperature range from -60 to +120 degrees, at which the parameters do not change, this material is necessary for creating supports, bushings, and silent blocks.

Vulcoprenes

These are the types that are used for subsequent vulcanization in combination with other polymers (rubber). Allows you to achieve high abrasion rates.

Specifications

The group has quite diverse properties depending on the molecular composition and manufacturing technology. This determines the prevalence of this raw material in different areas of life.

Peculiarities:

• • Density ranges from 30 to 300 kg/m3, and is achieved using additives and production method.
• • Has a hardness of 40 to 98 units on the Shore scale. This allows you to expand the range of use.
• • Polyurethane has a wide operating temperature range from -60 to +80 degrees. There are species that can not lose their qualities at 140℃.
• • Elastic. Deformation up to 650% is possible.
• • Has high resistance, can act as an insulator.
• • The specific gravity is low, which makes the structure lighter.
• • Not subject to destruction by nitrogen, like rubber.
• • Resistant to hydrocarbon solvents (lubricating fats, kerosene, oil, diesel fuel, isooctane, petroleum ether).
• • Reacts poorly to the presence of benzene and toluene. It swells with an increase in volume up to 60% and loses its technical characteristics.
• • Has different coefficient of friction. Programming is possible depending on need.
• • Not susceptible to damage from microorganisms and fungi.
• • It is possible to give different light absorption coefficients from transparent to black.
• • Has good water resistance properties at room temperature.

Advantages and disadvantages

Depending on what polyurethane is made of, it has both positive and negative features.

The advantages include:

• • Elasticity. According to this indicator, it confidently outperforms rubber.
• • Wear resistance. Thanks to this quality, it is widely used in the shoe industry and in the manufacture of various wheels and rollers for warehouse equipment. On the MPlast website you can select the necessary products at an affordable price.
• • The surface has a smooth structure, which allows it to maintain its presentation during use.
• • Over time, the technical characteristics remain the same (not subject to aging).
• • Resistant to most organic solvents.
• • Insensitive to ultraviolet light.
• • This plastic can be given different coefficients of friction. Depending on the needs, it is possible to create a slippery surface or good grip.
• • Easy to process. Allows casting, thermal molding, foaming and other methods.
• • Does not allow air to pass through. Thin coating makes it airtight.
• • Is a dielectric. 2 mm does not allow breakdown when 20 kilovolts are applied.

Disadvantages include:

• • Instability to media containing aromatic hydrocarbons (benzene, toluene), as well as to some acids, turpentine and chlorine-containing compounds.
• • Limited use in clothing and footwear due to breathability.
• • Becomes brittle when exposed to low temperatures for a long time.
• • Has complex recycling technology.
• • Difficult to recycle.

Let's sum it up

Polyurethane is a popular material from which thousands of items are made. It is resistant to mechanical stress, high and low temperatures, and aggressive substances. But despite all the advantages, the material has an important drawback - difficult disposal.

Nowadays there is an increasing demand for environmentally friendly products that are easy to recycle. The global trend is the desire to reduce the amount of waste on the planet. Polyurethanes will be in demand until they have analogues that can be completely recycled.

Where is polyurethane used?

Chemical plants produce this material in three forms: solid (sheet, rod, granular), fluid and foam. The first is used for the production of gaskets, protective cuffs, bushings, silent blocks and press seals. This substance has gained great popularity in the production of tubeless tires for sporting goods (roller skates, skateboards), for baby strollers, and technological equipment (trucks, electric cars, warehouse carts, guides for conveyors). These products are presented in a wide range in.

Liquid is used for sealed anti-corrosion coating of a wide variety of structures: concrete floors, roofs, screen surfaces, conveyor belts. It is used as a component in sealants, glue, varnish, and paint. During subsequent processing by vulcanization, complex protective elements are made from it: moldings and cuffs.

Foam is used for insulation of buildings and technological devices. It produces light and elastic soles for sports shoes and light-duty tires. It is not possible to list what is made from polyurethane. This material is widely in demand:

• • In heavy industry, where vibration stands are used, and where the use of conditionally movable units is necessary.
• • In the construction industry. They insulate the surfaces of buildings and create a film that protects against atmospheric influences.
• • In the automotive industry. It is used to make tires, silent blocks, cuffs and gaskets, and protective covers.
• • In medicine. It became widespread because of its neutrality. The products do not emit harmful substances and do not react with medications. Flexibility and high wear resistance allow it to be used in the preparation of prostheses, condoms, implants and coatings for equipment (crutches, beds, handrails, wheelchairs).
• • In the furniture industry. Used in the production of mattresses, garden furniture, fasteners, chairs and tables, elements for decorative finishing.
• • In the manufacture of sports accessories: treadmills, rollers, restraints in exercise machines, sneakers and sneakers, anti-slip coatings, impregnation of covers.
• • In light industry. The material is used to make shoe soles, rivets, bathroom rugs, and orthopedic insoles. Fabric imitating genuine leather is produced.

What and how is polyurethane made from?

The initial raw material for production is oil. It produces two main components - isocyanate and polyol. Their percentage composition, as well as the presence of additives, determine the physical properties of the final product. The result can be a solid, liquid or viscous substance suitable for further processing, like a regular polymer.

The fiber leaves the plant for processing in the form of granules, rods, sheets or in a liquid state. Initially, the appropriate color and degree of transparency are given. These types of supplies allow us to use simple technological solutions to produce certain products needed by the consumer.

Production

Polyurethane is a derivative of polyol and isocyanate, products of the petrochemical industry. To achieve certain technical properties, various additives are added to them, that is, when producing polyurethane as a raw material, it is necessary to take into account its further scope. Today it is the most sought after polymer in the world across all major industry segments. Both foreign and domestic materials are represented on the synthetic polymer market.

In the production of products, technological methods such as casting, extrusion, pressing, and pouring are used.

Forming methods

The buyer requires a functional product that has certain properties. To achieve this, processing methods are used that are similar to those used with all plastics.

Extrusion

Polyurethane polymer is excellent for injection molding. Under pressure, the heated and softened material is fed into the outlet of the extruder. Hardening occurs in this same zone. As a result, the output is a rod with a given cross-section or a flat sheet. The resulting rolled product is cut or rolled into rolls.

Casting

This method is the most common. It is used to manufacture products with complex geometries: bushings, supports, cuffs, seals, hydraulic elements and bearings. The advantage is easy automation of the process and the ability to produce large batches. For the manufacture of piece parts, the dimensions of which can be up to several tons, casting is used on a bench. The softened mass is poured into the frame, followed by hardening and acquiring a stable shape.

To speed up the process, increased pressure is used in automatic lines. The method differs little from the technology of products made from any plastic. It is often necessary to coat a metal workpiece with polymer. Then softened polyurethane is applied manually or under computer control to the item. As it cools, the layer becomes elastic and creates a protective film.

Pressing

The prepared material (sheet, rod or granular) is fed to the apparatus, where it is shaped using extreme pressure in a limited space. The process may be accompanied by preheating or softening of the substance due to compression. This produces a part with changed properties and a clearly defined geometry. In production, this action is controlled using software.

Fill

To produce artistic or piece goods, the natural casting method is used. Liquid material is placed manually into the prepared mandrel. Under the influence of high temperature or reagents, the device freezes, maintaining the required configuration. In this way you can make a small series of any blanks. More often used for the manufacture of large forms and decorative elements.

Casting products

The most common method of producing polyurethane products is casting. It is used to manufacture products such as bushings, cuffs, rings, bearings, self-lubricating parts, suspension parts, sealing elements for hydraulic and pneumatic mechanisms. A big advantage of producing polymer products by pouring is the low cost of molds, which makes the finished product attractive in price.

Three technologies are used to create products from this polymer by casting: rotational casting, free-form casting and injection molding.

Rotational casting is used to cover large areas and cylindrical parts with polyurethane. The polymer is applied with special equipment onto a rotating shaft, and the entire procedure is controlled by a computer. Rotational casting is carried out without heating, is a low-waste production and allows you to completely adapt to the client’s tasks.

Free casting is used to create complex shapes, in some cases the finished product can weigh half a ton. Thanks to computer control, casting into a mold takes place under precise control of the dosage of the polymer, its temperature and the pressure under which it enters. This allows us to produce high quality products.

Silicone molds are used for free casting, and this method is used to create products in limited editions. The advantage of casting is the short time required and the low cost of the finished product.

Injection molding allows for faster production and is necessary for large batches. This method is suitable not only for polyurethane, but also for other polymers.

Features and interesting facts

Polyurethane was first produced in the 40s in Europe. In the course of long laboratory research, the famous chemist, scientist and technologist Bayer Otto Georg Wilhelm obtained a previously unknown material with stunning technical properties.

In the same year, the first plant was created and the new polymer was released onto the market. But it found widespread use only 20 years later, when it began to be widely used in various industries. The American companies Union Carbide and Mobay Chemical Corporation were the first to produce polyurethane and products made from it.

Recycling

Resistance to weathering and aggressive environments is a challenge when recycling urethane elastomers. Under natural conditions, they do not decompose for decades. The ability to resist ultraviolet radiation and ozone makes this type of plastic a perpetual polluter of the environment. Therefore, the issue of recycling has become acute.

There are several methods to solve the problem:

• • Incineration. Like all hydrocarbons, the polymer is highly susceptible to high-temperature oxidation. But technological additives contain substances that are hazardous to the environment. During combustion, decay products enter the atmosphere.
• • Physical method. Crushed products have found application in construction, as an additive to concrete and asphalt. Due to this, they acquire a second life.
• • Melting. When heated, the waste is given the required shape and put back into circulation. The disadvantage of this method is that it is difficult to obtain a product with clearly defined characteristics from dissimilar components.
• • Glycolysis is the process of breaking down long molecules at high temperatures in the presence of catalysts. The output is short molecular compounds, which subsequently find service in industry (production of paints, varnishes, additives in asphalt concrete).
• • Chemical method. This is the splitting of chains using reagents. The goal is to obtain a substance suitable for further use.

Uniqueness and interesting facts about the use of polyurethane

The ability to give a material a variety of characteristics has allowed it to appear in many industries. When playing sports, we use products made from this polymer. Clothes, shoes, and medical equipment are made from it. Modern transport (cars, airplanes, railway cars) have long used the unique properties of this substance. Its invulnerability has become an environmental problem. A few years ago, a species of fungus was discovered that requires the presence of this plastic to survive. Pestalotiopsis microspora successfully decomposes polyurethane and can be eaten. Gourmets claim that it tastes like bread. Maybe in the future this will be a solution to the recycling problem.

Polyurethane foam

Polyurethane foam stands apart among all polyurethanes. PPU is included in the class of gas-filled plastics, also known as foam plastics. Such plastics consist of about 90 percent air or other gas by volume. Polyurethane foam is divided into two large groups: hard or integral plastic and soft (elastic) polyurethane foam or foam rubber.

Fig.2. The use of elastic polyurethane foam in furniture

PUF is interesting because its synthesis usually occurs at the site of use, and not in a factory (at the same time, furniture foam rubber or pipes in PU foam insulation are still produced in factories). Polyurethane foam is synthesized by mixing a polyol and a polyisocyanate to obtain a polymer matrix highly filled with carbon dioxide.

PUF is biologically neutral; its component, the highly toxic substance isocyanate, can be dangerous if taken in excess. When fire retardants are used in polyurethane components, the material does not support combustion and goes out when the flame is removed.