Polymeric materials: technology, types, production and application

Polymeric materials are chemical macromolecular compounds, which consist of numerous low molecular weight monomers (links) of the same structure. Often the following monomeric components are used for the manufacture of polymers: ethylene, vinyl chloride, vinylidene chloride, vinyl acetate, propylene, methyl methacrylate, tetrafluoroethylene, styrene, urea, melamine, formaldehyde, phenol. In this article, we will consider in detail what polymeric materials are, what are their chemical and physical properties, classification and species.

Types of polymers

A feature of the molecules of this material is a large molecular mass, which corresponds to the following value: M> 5 * 103. Compounds with a lower level of this parameter (M = 500-5000) are commonly called oligomers. In low-molecular compounds, the mass is less than 500. The following types of polymeric materials are distinguished: synthetic and natural. The latter include natural rubber, mica, wool, asbestos, cellulose, etc. However, the main place is occupied by synthetic polymers, which are obtained as a result of the process of chemical synthesis from compounds of low molecular weight. Depending on the method of manufacturing high-molecular materials, polymers are distinguished, which are created either by polycondensation or by the addition reaction.

Polymerization

This process is a combination of low molecular weight components in high molecular weight to produce long chains. The magnitude of the polymerization level is the number of "measures" in molecules of a given composition. Most often, polymeric materials contain from one thousand to ten thousand of their units. The following commonly used compounds are obtained by polymerization: polyethylene, polypropylene, polyvinyl chloride, polytetrafluoroethylene, polystyrene, polybutadiene, etc.

Polycondensation

This process is a step-by-step reaction that consists in combining either a large number of monomers of the same type or a pair of different groups (A and B) into polycondensors (macromolecules) with the simultaneous formation of the following by-products: methyl alcohol, carbon dioxide, hydrogen chloride, ammonia, water and Etc. Polycondensation produces silicones, polysulfones, polycarbonates, aminoplasts, phenolic, polyesters, polyamides and other polymeric materials.

Polyaddition

This process is understood to mean the formation of polymers as a result of the multiple-attachment reactions of monomeric components that contain limiting reaction pools to monomers of unsaturated groups (active rings or double bonds). Unlike polycondensation, the polyaddition reaction proceeds without isolation of by-products. The most important process of this technology is the curing of epoxy resins and the production of polyurethanes.

Classification of polymers

In composition, all polymer materials are divided into inorganic, organic and elementoorganic. The first of them (silicate glass, mica, asbestos, ceramics, etc.) do not contain atomic carbon. Their basis is the oxides of aluminum, magnesium, silicon, etc. Organic polymers form the most extensive class, they contain atoms of carbon, hydrogen, nitrogen, sulfur, halogen and oxygen. Organoelemental polymer materials are compounds that, in addition to the listed chains, contain silicon, aluminum, titanium, and other elements capable of combining with organic radicals. In nature, such combinations do not arise. These are exclusively synthetic polymers. Typical representatives of this group are compounds on a silicone-based basis, the main chain of which is constructed from oxygen and silicon atoms.

To produce polymers with the necessary properties in technology, not often "pure" substances are used, but their combinations with organic or inorganic components. A good example is the polymeric building materials: metal plastics, plastics, fiberglass, polymer concrete.

Structure of polymers

The peculiarity of the properties of these materials is due to their structure, which, in turn, is divided into the following types: linear-branched, linear, spatial with large molecular groups and very specific geometric structures, and also a ladder. Let us consider briefly each of them.

Polymeric materials with a linear-branched structure, besides the main chain of molecules, have lateral branches. Such polymers include polypropylene and polyisobutylene.

Materials with a linear structure have long zigzag-like or spiral-twisted chains. Their macromolecules are primarily characterized by repetitions of sites in one structural group of the link or chemical unit of the chain. Polymers with a linear structure are distinguished by the presence of very long macromolecules with a significant difference in the character of bonds along the chain and between them. There are intermolecular and chemical bonds. The macromolecules of such materials are very flexible. And this property is the basis of polymer chains, which leads to qualitatively new characteristics: high elasticity, as well as the absence of brittleness in the hardened state.

And now we learn what polymer materials with spatial structure are. These substances form strong chemical bonds in the transverse direction when the macromolecules join together. As a result, a network structure is obtained, in which the heterogeneous or spatial basis of the grid. Polymers of this type have greater heat resistance and rigidity than linear polymers. These materials are the basis of many non-metallic structural materials.

Molecules of polymeric materials with a ladder structure consist of a pair of chains that are connected by a chemical bond. These include organosilicon polymers, which are characterized by increased rigidity, heat resistance, in addition, they do not interact with organic solvents.

Phase composition of polymers

These materials are systems that consist of amorphous and crystalline regions. The first of them helps to reduce stiffness, makes the polymer elastic, that is capable of large deformations of a reversible nature. The crystalline phase contributes to an increase in their strength, hardness, modulus of elasticity, as well as other parameters, while reducing the molecular flexibility of the substance. The ratio of the volume of all such regions to the total volume is called the degree of crystallization, where the maximum level (up to 80%) are polypropylenes, fluoroplasts, high-density polyethylenes. The lower level of crystallization is possessed by polyvinyl chlorides, low-density polyethylenes.

Depending on how the polymer materials behave when heated, they are usually divided into thermosetting and thermoplastic.

Thermoset polymers

These materials primarily have a linear structure. When heated, they soften, but as a result of the chemical reactions in them, the structure changes to a spatial one, and the substance turns into a solid one. In the future, this quality is preserved. On this principle, polymeric composite materials are constructed. Subsequent heating does not soften the substance, but only leads to its decomposition. The finished thermosetting mixture does not dissolve and does not melt, therefore its recycling is unacceptable. This type of material includes epoxy silicone, phenol-formaldehyde and other resins.

Thermoplastic polymers

These materials, when heated, first soften and then melt, and upon subsequent cooling they solidify. Thermoplastic polymers under such treatment do not undergo chemical changes. This makes this process completely reversible. Substances of this type have a linear-branched or linear structure of macromolecules, between which small forces act and there are absolutely no chemical bonds. These include polyethylenes, polyamides, polystyrenes, etc. The technology of polymeric materials of thermoplastic type provides for their manufacture by injection molding in water-cooled forms, pressing, extrusion, blowing and other methods.

Chemical properties

Polymers can be present in the following states: solid, liquid, amorphous, crystalline phase, as well as highly elastic, viscous and glassy deformation. The wide application of polymeric materials is due to their high resistance to various aggressive media, such as concentrated acids and alkalis. They are not subject to electrochemical corrosion. In addition, as the molecular weight increases, the solubility of the material in organic solvents decreases. And polymers that have a spatial structure are not affected at all by the mentioned liquids.

Physical properties

Most polymers are dielectrics, in addition, they belong to non-magnetic materials. Of all the structural substances used, only they have the least thermal conductivity and the greatest heat capacity, and also the thermal shrinkage (about twenty times greater than that of the metal). The cause of leakage losses by various sealing units under low temperature conditions is the so-called glass transition of rubber, as well as a sharp difference between the expansion coefficients of metals and rubbers in a vitrified state.

Mechanical properties

Polymeric materials have a wide range of mechanical characteristics, which strongly depend on their structure. In addition to this parameter, various external factors can exert a great influence on the mechanical properties of the substance. These include: temperature, frequency, duration or loading rate, type of stress state, pressure, nature of the environment, heat treatment, etc. A particular feature of the mechanical properties of polymeric materials is their relatively high strength with very low stiffness (compared to metals).

Polymers are usually divided into solid, the modulus of elasticity of which corresponds to E = 1-10 GPa (fibers, films, plastics), and soft highly elastic substances, the modulus of elasticity is E = 1-10 MPa (rubber). The patterns and mechanism of destruction of both are different.

Polymer materials are characterized by pronounced anisotropy of properties, as well as a decrease in strength, the development of creep under the condition of prolonged loading. Together with this they have quite a high resistance to fatigue. Compared with metals, they are characterized by a more pronounced dependence of mechanical properties on temperature. One of the main characteristics of polymeric materials is deformability (compliance). In this broad parameter, it is common to assess their main operational and technological properties over a wide temperature range.

Polymeric materials for flooring

Now consider one of the options for the practical use of polymers, revealing the full range of these materials. These substances have found wide application in construction and repair and finishing works, in particular in the flooring. Huge popularity is explained by the characteristics of the substances under consideration: they are resistant to abrasion, low heat conductivity, have little water absorption, are sufficiently strong and hard, have high paint and varnish qualities. The production of polymeric materials can be divided into three groups: linoleums (rolls), plate products and mixtures for the device of seamless floors. Now let us briefly examine each of them.

Linoleum is made on the basis of different types of fillers and polymers. They can also include plasticizers, processing aids and pigments. Depending on the type of polymer material, there are polyester (glyptal), polyvinyl chloride, rubber, colloxylin and other coatings. In addition, in structure, they are divided into non-basic and sound-insulated base, single-layered and multilayered, with a smooth, fleecy and corrugated surface, as well as single and multi-color.

Tile materials made on the basis of polymer components have very low abrasion, chemical resistance and durability. Depending on the type of raw materials, this type of polymer products are divided into kumaronopolivinyl chloride, coumarone, polyvinylchloride, rubber, phenolite, bituminous tiles, as well as chipboard and wood fiber boards.

Materials for seamless floors are the most convenient and hygienic in operation, they have high strength. These mixtures are usually divided into polymer cement, polymer concrete and polyvinyl acetate.