Polymer materials: technology, types, production and application

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Polymeric materials are chemical high-molecular compounds that consist of numerous small-molecular monomers (units) of the same structure. Often, the following monomeric components are used for the manufacture of polymers: ethylene, vinyl chloride, vinyl dechloride, 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 types.

Types of polymers

A feature of the molecules of this material is a large molecular weight, which corresponds to the following value: М>5103. Compounds with a lower level of this parameter (M=500-5000) are called oligomers. In low molecular weight 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 a chemical synthesis process from low-molecular-weight compounds. dependingfrom the method of manufacturing high-molecular materials, polymers are distinguished, which are created either by polycondensation or by an addition reaction.

Polymerization

This process is a combination of low molecular weight components into high molecular weight to obtain long chains. The level of polymerization is the number of "mers" in the molecules of a given composition. Most often, polymeric materials contain from a 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 stepwise reaction, which consists in combining either a large number of monomers of the same type, or a pair of different groups (A and B) into polycapacitors (macromolecules) with the simultaneous formation of the following by-products: methyl alcohol, carbon dioxide, hydrogen chloride, ammonia, water, etc. Polycondensation produces silicones, polysulfones, polycarbonates, amino plastics, phenolic plastics, polyesters, polyamides and other polymeric materials.

Polyaddition

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

Classification of polymers

The composition of all polymeric materials are divided into inorganic, organic and organoelement. The first of them (silicate glass, mica, asbestos, ceramics, etc.) do not contain atomic carbon. They are based on oxides of aluminum, magnesium, silicon, etc. Organic polymers constitute the most extensive class, they contain carbon, hydrogen, nitrogen, sulfur, halogen and oxygen atoms. Organoelement polymeric materials are compounds that in the main chains have, in addition to those listed, atoms of silicon, aluminum, titanium and other elements that can combine with organic radicals. Such combinations do not occur in nature. These are exclusively synthetic polymers. Characteristic representatives of this group are organosilicon-based compounds, the main chain of which is built from oxygen and silicon atoms.

To obtain polymers with the required properties, technology often uses not “pure” substances, but their combinations with organic or inorganic components. A good example is polymer 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, spatialwith large molecular groups and very specific geometric structures, as well as stair. Let's briefly consider each of them.

Polymeric materials with a linearly branched structure, in addition to the main chain of molecules, have side branches. These polymers include polypropylene and polyisobutylene.

Materials with a linear structure have long zigzag or spiral chains. Their macromolecules are primarily characterized by repetitions of sites in one structural group of a 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 nature of bonds along the chain and between them. This refers to 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 cured state.

And now let's find out what are polymeric materials with a spatial structure. These substances form, when macromolecules are combined with each other, strong chemical bonds in the transverse direction. As a result, a mesh structure is obtained, which has a non-uniform or spatial basis of the mesh. Polymers of this type have greater heat resistance and rigidity than linear ones. These materials are the basis of many structural non-metallic substances.

Molecules of polymer materials with a ladder structure consist of a pair of chains that are connected by a chemical bond. These includeorganosilicon 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 reversible deformations. The crystalline phase helps to increase their strength, hardness, elastic modulus, and other parameters, while reducing the molecular flexibility of the substance. The ratio of the volume of all such areas to the total volume is called the degree of crystallization, where the maximum level (up to 80%) has polypropylenes, fluoroplasts, high-density polyethylenes. Polyvinyl chlorides, low density polyethylenes have a lower degree of crystallization.

Depending on how 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 chemical reactions occurring in them, the structure changes to a spatial one, and the substance turns into a solid. In the future, this quality is maintained. Polymer composite materials are built on this principle. Their subsequent heating does not soften the substance, but only leads to its decomposition. The finished thermoset mixture does not dissolve or melt, thereforeit is not allowed to recycle it. This type of material includes epoxy silicone, phenol-formaldehyde and other resins.

Thermoplastic polymers

These materials, when heated, first soften and then melt, and then harden when cooled. Thermoplastic polymers do not undergo chemical changes during this treatment. This makes the 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 thermoplastic-type polymeric materials provides for their production by injection molding in water-cooled molds, pressing, extrusion, blowing, and other methods.

Chemical properties

Polymers can be in the following states: solid, liquid, amorphous, crystalline phase, as well as highly elastic, viscous and glassy deformation. The widespread use 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, with an increase in their molecular weight, the solubility of the material in organic solvents decreases. And polymers, which have a three-dimensional structure, are generally not affected by the liquids mentioned.

Physical properties

Most polymers are dielectrics, in addition, they are non-magnetic materials. Of all the structural materials used, only they have the lowest thermal conductivity and the highest heat capacity, as well as thermal shrinkage (about twenty times more than that of metal). The reason for the loss of tightness of various sealing assemblies under low temperature conditions is the so-called glass transition of rubber, as well as the sharp difference between the coefficients of expansion of metals and rubbers in the vitrified state.

Mechanical properties

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

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

Polymeric materials are characterized by a pronounced anisotropy of properties, as well as a decrease in strength, the development of creep under long-term loading. Together with this theyhave relatively high fatigue resistance. Compared with metals, they differ in a sharper dependence of mechanical properties on temperature. One of the main characteristics of polymeric materials is deformability (pliability). According to this parameter, in a wide temperature range, it is customary to evaluate their main operational and technological properties.

Polymer floor materials

Now let's consider one of the options for the practical application of polymers, revealing the full range of these materials. These substances are widely used in construction and repair and finishing works, in particular in flooring. The huge popularity is explained by the characteristics of the substances in question: they are resistant to abrasion, have low thermal conductivity, have little water absorption, are quite strong and hard, and have high paint and varnish qualities. The production of polymeric materials can be conditionally divided into three groups: linoleums (rolled), tile products and mixtures for the installation of seamless floors. Let's take a quick look at each one now.

Linoleums are made on the basis of different types of fillers and polymers. They may also include plasticizers, processing aids and pigments. Depending on the type of polymer material, polyester (glyphthalic), polyvinyl chloride, rubber, colloxylin and other coatings are distinguished. In addition, according to the structure, they are divided into baseless and with a sound and heat insulating base, single-layer and multi-layer, with a smooth, fleecyand corrugated surface, as well as single and multi-color.

Tiled materials made on the basis of polymer components have very low abrasion, chemical resistance and durability. Depending on the type of raw material, this type of polymer products is divided into coumarone-polyvinyl chloride, coumarone, polyvinyl chloride, rubber, phenolite, bituminous tiles, as well as chipboard and fiberboard.

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