Various ones provide ample opportunities to create specific designs and parts. It is no coincidence that such elements are used in a variety of fields: from mechanical engineering and radio engineering to medicine and agriculture. Pipes, components for machines, housings for devices and household products are just a long list of what can be created from plastic.

Main varieties

Types of plastics and their use are based on which polymers are used - natural or synthetic. They are subjected to heat and pressure, after which they are molded into products of varying complexity. The main thing is that during these manipulations the shape of the finished product is preserved. All plastics are thermoplastic, that is, reversible, and thermosetting (irreversible).

Reversibles become plastic under the influence of heat and further pressure, while fundamental changes in composition do not occur. A pressed product that has already become hard can always be softened and given a certain shape. There are known types of plastics (thermoplastics) such as polyethylene and polystyrene. The first is distinguished by its resistance to corrosion and dielectric properties. On its basis, pipes, films, sheets are produced, and it is widely used as an insulating material.

From styrene to polystyrene

As a result of the polymerization of styrene, polystyrene is obtained. Various parts are subsequently created from it using casting or pressing. These types of plastics are widely used for the production of large parts and products, for example, elements for refrigerators or bathrooms. Among thermosetting plastics, press powders and fibers are most often used, which can be further processed to produce various parts.

Plastic is a very easy-to-work material that can be used to create many products. Depending on the thermal properties, the following types of plastic processing are distinguished:

1. Pressing. This is the most popular method of producing products from thermoactive materials. Molding is performed in special molds under high temperatures and pressure.
2. Injection molding. This method makes it possible to create products of different shapes. To do this, special containers are filled with molten plastic. The process itself is highly productive and cost-effective.
3. Extrusion. Through such processing, many types of plastic products are obtained, for example, pipes, threads, cords, films for various purposes.
4. Blowing. This method is an ideal opportunity to create three-dimensional products that will have a seam where the mold closes.
5. Punching. This method creates products from plastic sheets and plates using special molds.

Features of polymerization

Plastic can be produced by polymerization and polycondensation. In the first case, monomer molecules bind, forming polymer chains without releasing water and alcohol; in the second, by-products are formed that are not associated with the polymer. Various methods and types of plastic polymerization make it possible to obtain compositions that differ in their initial properties. The correct temperature and heat of reaction play an important role in this process so that the molding compound polymerizes correctly. When polymerizing, it is important to pay attention to the residual monomer - the less it is, the more reliable and longer the plastic will be in use.

Porosity

If the polymerization conditions have been violated, this can lead to defects in the finished products. Bubbles, stains and increased internal tension will appear in them. There are different types of plastic porosity:

1. Gas. It appears due to the fact that the polymerization regime is disrupted, and benzoyl peroxide boils. If gas pores form in the thickness of the prosthesis, then it needs to be redone.
2. Granular porosity occurs due to an excess of polymer powder, evaporation of the monomer from the surface of the material, or insufficient mixing of the plastic composition.
3. Compression porosity. Occurs due to a decrease in the volume of the polymerizing mass under the influence of insufficient pressure or lack of molding mass.

What to consider?

You should be aware of the types of porosity in plastic and avoid defects in the final product. It is also necessary to pay attention to fine porosity on the surface of the prosthesis. This happens due to too much monomer, and the porosity is not polished. If internal residual stress is generated while working with plastic, the product will crack. This situation occurs due to a violation of the polymerization regime when the object is in boiling water for too long.

In any case, the deterioration of the mechanical properties of polymer materials ultimately leads to their aging, and therefore the production technology must be fully followed.

Basic plastics - what are they?

The material in question is widely used in the manufacture of bases for removable laminar dentures. The most popular types of base plastics have a synthetic base. The mass for bases is usually a combination of powder and liquid. When they are mixed, a molding mass is created, which hardens when heated or spontaneously. Depending on this, a hot-curing or self-hardening material is obtained. Basic hot polymerization plastics include:

• ethacryl (AKR-15);
• acrel;
• fluorax;
• acronyl.

The materials for creating removable dentures are elastic plastics, which are needed as soft shock-absorbing pads for bases. They must be safe for the body, firmly connected to the base of the prosthesis, maintain elasticity and constant volume. Among such plastics, eladent, which is a lining for the bases of removable dentures, and orthoxyl, which is obtained on the basis of siloxane resin, deserve attention.

Construction Materials

The main types of plastics are used in different areas of construction, depending on the composition. The most popular materials include the following:

1. Polymer concrete. This is a composite plastic that is created on the basis of thermosetting polymers. In terms of physical and mechanical properties, polymer concretes based on epoxy resins are considered the best. The fragility of the material is compensated by fibrous fillers - asbestos, fiberglass. Polymer concretes are used to create structures that are resistant to chemicals.
2. Fiberglass plastics are modern types of construction plastics, which are sheet materials made of glass fibers and fabrics bonded with a polymer. Fiberglass is created from oriented or chopped fibers, as well as fabrics or mats.
3. Floor materials. They are represented by different types of roll coatings and liquid viscose compositions based on polymers. Linoleum based on polyvinyl chloride, which has good thermal and sound insulation properties, is widely used in construction. A seamless mastic floor can be created based on a mixture of raw materials with oligomers.

Plastic and its markings

There are 5 types of plastics that have their own designation:

1. Polyethylene terephthalate (lettered PETE or PET). It is economical and has a wide range of applications: used for storing various drinks, oils, and cosmetics.
2. High density polyethylene (labeled as HDPE or PE HD). The material is economical, lightweight, and resistant to temperature changes. It is used for the manufacture of disposable tableware, food storage containers, bags, toys.
3. Polyvinyl chloride (labeled as PVC or V). This material is used to create window profiles, furniture parts, stretch ceiling film, pipes, floor coverings and much more. Due to the content of bisphenol A, vinyl chloride, phthalates, polyvinyl chloride is not used in the production of products (containers, dishes, etc.) for food storage.
4. Polyethylene (labeled LDPE or PEBD). This cheap material is used in the production of bags, garbage bags, linoleum and compact discs.
5. Polypropylene (lettered PP). It is durable, heat-resistant, suitable for the production of food containers, food packaging, toys, syringes.

Popular types of plastics are polystyrene and polycarbonate. They have found wide application in a variety of industries.

Areas of application

Various types of plastics are used in a wide variety of industries. At the same time, the requirements for them are approximately the same - ease of operation and safety. Let's take a closer look at the types of thermoplastic plastics and their areas of application.

Plastic	Scope of application
Polyethylene (high and low pressure)	Production of packaging, unloaded parts of machines and equipment, cases, coatings, foil.
Polystyrene	Production of equipment, insulating films, styropian.
Polypropylene	It has found wide application in car parts and elements for refrigeration equipment.
Polyvinyl chloride (PVC)	Production of chemical equipment, pipes, various parts, packaging, floor coverings.
Polycarbonates	Production of precision machine parts, equipment, radio and electrical equipment.

Thermosetting types of plastics (table)

Material	Scope of application
Phenoplastics	They are used to create haberdashery products (buttons, etc.), ashtrays, forks, sockets, radio and telephone housings.
Aminoplasty	Used for the manufacture of wood glue, electrical parts, haberdashery, thin coatings for decoration, and foam materials.
Fiberglass	They are used in the manufacture of power electrical parts in mechanical engineering, large-sized products of simple shapes (car bodies, boats, instrument housings, etc.).
Polyesters	Rescue boats, car parts, furniture, hulls of gliders and helicopters, corrugated slabs for roofs, lamp shades, antenna masts, skis and poles, fishing rods, safety helmets, and the like are created using polyesters.
Epoxy resin	It is used in electrical machines, transformers (as high-voltage insulation) and other devices, in the production of telephone fittings, in radio engineering (for the production of printed circuits).

Instead of a conclusion

In this article we looked at the types of plastics and their applications. When using such materials, many factors are taken into account, ranging from physical and mechanical properties to operating features. Despite its efficiency, plastic has a sufficient level of safety, which significantly expands the scope of its application.

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Composition and properties

Production of plastics

Plastics are materials made from synthetic or natural polymers (resins). Polymers are synthesized by polymerization or polycondensation of monomers in the presence of catalysts under strictly defined temperature conditions and pressures.

Fillers, stabilizers, and pigments can be introduced into the polymer for various purposes; compositions can be made with the addition of organic and inorganic fibers, meshes and fabrics.

Thus, plastics in most cases are multicomponent mixtures and composite materials, whose technological properties, including weldability, are mainly determined by the properties of the polymer.

Depending on the behavior of the polymer when heated, two types of plastics are distinguished - thermoplastics, materials that can be heated repeatedly and at the same time transition from a solid to a viscous-fluid state, and thermosets, which can undergo this process only once.

Structural features

Plastics (polymers) consist of macromolecules in which a large number of identical or unequal atomic groups alternate more or less regularly, connected by chemical bonds into long chains, the shape of which distinguishes between linear, branched and network-spatial polymers.

Based on the composition of macromolecules, polymers are divided into three classes:

1) carbon-chain, the main chains of which are built only from carbon atoms;

2) heterochain, the main chains of which, in addition to carbon atoms, contain oxygen, nitrogen, and sulfur atoms;

3) organoelement polymers containing atoms of silicon, boron, aluminum, titanium and other elements in the main chains.

Macromolecules are flexible and capable of changing shape under the influence of the thermal movement of their units or an electric field. This property is associated with the internal rotation of individual parts of the molecule relative to each other. Without moving in space, each macromolecule is in continuous motion, which is expressed in a change in its conformations.

The flexibility of macromolecules is characterized by the size of the segment, i.e., the number of units in it, which, under the conditions of a given specific impact on the polymer, manifest themselves as kinetically independent units, for example, in a high-frequency field as dipoles. Based on their response to external electric fields, polar (PE, PP) and non-polar (PVC, polyaxylonitrile) polymers are distinguished. There are attractive forces between macromolecules caused by the van der Waals interaction, as well as hydrogen bonds, and ionic interaction. Attractive forces appear when macromolecules approach each other by 0.3-0.4 nm.

Polar and non-polar polymers (plastics) are incompatible with each other - there is no interaction (attraction) between their macromolecules, i.e. they do not weld together.

Supramolecular structure, orientation

Based on their structure, there are two types of plastics: crystalline and amorphous. In crystalline ones, in contrast to amorphous ones, not only short-range, but also long-range order is observed. During the transition from a viscous-fluid state to a solid, macromolecules of crystalline polymers form ordered associations-crystallites, mainly in the form of spherulites (Fig. 37.1). The lower the cooling rate of the thermoplastic melt, the larger the spherulites grow. However, even in crystalline polymers, amorphous regions always remain. By changing the cooling rate, you can regulate the structure, and therefore the properties of the welded joint.

The sharp difference in the longitudinal and transverse dimensions of macromolecules leads to the possibility of the existence of an oriented state specific to polymers. It is characterized by the arrangement of the axes of chain macromolecules predominantly along one direction, which leads to the manifestation of anisotropy in the properties of a plastic product. The production of oriented plastics is carried out by their uniaxial (5-10-fold) drawing at room or elevated temperature. However, upon heating (including welding), the orientation effect decreases or disappears, since the macromolecules again take on the thermodynamically most probable configurations (conformations) due to entropic elasticity caused by the movement of the segments.

Response of plastics to the thermomechanical cycle

All engineering thermoplastics are in a solid state (crystalline or vitrified) at normal temperatures. Above the glass transition temperature (Tst), amorphous plastics transform into an elastic (rubber-like) state. With further heating above the melting temperature (Tm), crystalline polymers transform into an amorphous state. Above the flow temperature T T, both crystalline and amorphous plastics transform into a viscous flow state. All these changes in state are usually described by thermomechanical curves (Fig. 37.2), which are the most important technological characteristics of plastics. The formation of a welded joint occurs in the range of the viscous-flow state of thermoplastics. When heated above T T, thermoset plastics undergo radical processes and, unlike thermoplastics, form spatial polymer networks that are not capable of interaction without their destruction, which requires the use of special chemical additives.

Basic plastics for welded structures

The most common engineering plastics are groups of thermoplastics based on polyolefins: high- and low-density polyethylene, polypropylene, polyisobutylene.

Polyethylene [..-CH 2 -CH 2 -...] n high and low pressure - crystalline thermoplastics that differ in strength, rigidity, and flow point. Polypropylene [-CH 2 -CH(CH 3)-] n is more temperature resistant than polyethylene, and has greater strength and rigidity.

Chlorine-containing plastics based on polymers and copolymers of vinyl chloride and vinylidene chloride are used in significant quantities.

Polyvinyl chloride(PVC) [-(CH 2 -CHCl-)] n is an amorphous polymer of linear structure, in the initial state it is a rigid material. By adding a plasticizer to it, you can obtain a very plastic and well-welded material - a plastic compound. Sheets, pipes, rods are made from rigid PVC - vinyl plastic, and film, hoses and other products are made from plastic compound. Foam materials (foam plastics) are also made from PVC.

A significant group of polymers and plastics based on them are polyamides containing amide groups [-CO-H-] in the chain of macromolecules. These are mostly crystalline thermoplastics with a clearly defined melting point. The domestic industry produces mainly aliphatic polyamides used for the manufacture of fibers, casting machine parts, and producing films. Polyamides include, in particular, the well-known polycaprolactam and polynamide-66 (kapron).

The most famous of the fluorolone group is polytetrafluoroethylene-fluorolone-4 (fluoroplastic 4). Unlike other thermoplastics, when heated, it does not transform into a viscous-flow state even at the destruction temperature (about 415°C), so its welding requires special techniques. Currently, the chemical industry has mastered the production of well-welded fusible fluorolone; F-4M, F-40, F-42, etc. Welded structures made of fluorine-containing plastics have exceptionally high resistance to aggressive environments and can withstand work loads in a wide temperature range.

Produced on the basis of acrylic and methacrylic acid acrylic plastics. The most commonly used derivative based on them is the plastic polymethyl methacrylate (trademark “plexiglass”). These highly transparent plastics are used as light-conducting products (in the form of sheets, rods, etc.). Copolymers of methyl methacrylate and acrylonitrile, which have greater strength and hardness, are also used. All plastics in this group are well welded.

A group of plastics based on polystyrene. This linear thermoplastic is well weldable using heat methods.

For the manufacture of welded structures, mainly in the electrical industry, copolymers of styrene with methyl styrene, acrylonitrile, methyl methacrylate and, in particular, acrylonitrile butadiene styrene (ABS) plastics are used. The latter differ from brittle polystyrene by higher impact strength and heat resistance.

In welded structures, plastics based on polycarbonates- polyesters of carbonic acid. They have higher melt viscosity than other thermoplastics but weld satisfactorily. Films, sheets, pipes and various parts, including decorative ones, are made from them. Characteristic features are high dielectric and polarization properties.

Shaping of plastic parts

Thermoplastics are supplied for processing in granules measuring 3-5 mm. The main technological processes for the manufacture of semi-finished products and parts from them are: extrusion, casting, pressing, calendering, produced in the temperature range of the viscous-flow state.

Pipelines made of polyethylene and polyvinyl chloride pipes are used for transporting aggressive products, including oil and gas containing hydrogen sulfide and carbon dioxide and chemical (non-aromatic) reagents in chemical production. Reservoirs and tanks for transporting acids and alkalis, pickling baths and other vessels are lined with plastic sheets connected by welding. Sealing with plastic in rooms contaminated with isotopes, covering floors with linoleum is also carried out using welding. Preservation of food products in tubes, boxes and jars, packaging of goods and postal parcels is greatly accelerated with the use of welding.

Engineering parts. In chemical engineering, housings and blades of various types of mixers, housings and rotors of pumps for pumping aggressive media, filters, bearings and gaskets made of fluoroplastic are welded; lighting fixtures are welded from polystyrene; non-conductive gears, rollers, couplings, rods are made from nylon; non-lubricating bearings are made from fluorine rubber. , fuel displacers, etc.

Assessing the weldability of plastics

Main stages of the welding process

The process of welding thermoplastics consists of activating the surfaces of parts to be welded, either already in contact (), or brought into contact after (, etc.) or simultaneously with activation (, ultrasonic welding).

With close contact of the activated layers, intermolecular interaction forces must be realized.

During the formation of welded joints (during cooling), the formation of supramolecular structures in the weld occurs, as well as the development of intrinsic stress fields and their relaxation. These competing processes determine the final properties of the welded joint. The technological task of welding is to bring the properties of the seam as close as possible to the original - base material.

Mechanism of formation of welded joints

Rheological concept. According to the rheological concept, the mechanism of formation of a welded joint includes two stages - at the macroscopic and microscopic levels. When the surfaces of the parts being connected, activated in one way or another, come together under pressure due to shear deformations, a flow of the polymer melt occurs. As a result of this, ingredients that prevent the approach and interaction of juvenile macromolecules are removed from the contact zone (gas, oxidized layers are evacuated). Due to the difference in melt flow rates, mixing of macrovolumes of the melt in the contact zone cannot be ruled out. Only after the removal or destruction of defective layers in the contact zone, when the juvenile macromolecules come close to the distance of action of Van der Waals forces, does interaction (grasping) occur between the macromolecules of the layers of the joined surfaces of the parts. This autohesive process occurs at the micro level. It is accompanied by the interdiffusion of macromolecules, caused by the energy potential and the unevenness of the temperature gradient in the zone of the surfaces being welded.

So, in order to form a welded joint between two surfaces, it is necessary first of all to ensure the flow of the melt in this zone.

The flow of the melt in the welding zone depends on its viscosity: the lower the viscosity, the more active shear deformations occur in the melt - destruction and removal of defective layers on contacting surfaces, the less pressure must be applied to join the parts.

The viscosity of the melt, in turn, depends on the nature of the plastic (molecular weight, branching of polymer macromolecules) and the heating temperature in the viscosity range. Consequently, viscosity can serve as one of the signs that determines the weldability of plastic: the lower it is in the viscosity range, the better the weldability and, conversely, the higher the viscosity, the more difficult it is to destroy and remove from the contact zone the ingredients that interfere with the interaction of macromolecules. However, heating for each polymer is limited by a certain destruction temperature Td, above which its decomposition—destruction—occurs. Thermoplastics differ in the boundary values ​​of the temperature range of viscosity, that is, between the temperature of their fluidity T T and destruction T d (Table 37.2).

Classification of thermoplastics according to their weldability. The wider the range of viscosity of a thermoplastic (Fig. 37.3), the practically easier it is to obtain a high-quality welded joint, because temperature deviations in the weld zone are reflected less in the viscosity value. Along with the viscosity range and the minimum level of viscosity values ​​within it, the gradient of viscosity change in this range plays a significant role in the rheological processes during weld formation. The following quantitative indicators of weldability are taken: temperature range of viscosity flow ΔT, minimum viscosity value η min and gradient of viscosity change in this range.

According to weldability, all thermoplastic plastics can be divided according to these indicators into four groups (Table 37.3).

Welding of thermoplastic plastics is possible if the material goes into the state of a viscous melt, if its temperature range of viscosity is wide enough, and the gradient of change in viscosity in this range is minimal, since the interaction of macromolecules in the contact zone occurs along a boundary with the same viscosity.

In general, the welding temperature is set based on the analysis of the thermomechanical curve for the plastic being welded, we take it 10-15° below Tg. The pressure is taken such as to evacuate the melt of the surface layer into the flash or destroy it, based on the specific depth of penetration and thermophysical indicators welded material. The holding time t CB is determined based on the achievement of a quasi-stationary state of melting and penetration or by the formula

where t 0 is a constant that has the dimension of time and depends on the thickness of the material being joined and the heating method; Q - activation energy; R - gas constant; T - welding temperature.

When experimentally assessing the weldability of plastics, the fundamental indicator is the long-term strength of the welded joint operating under specific conditions in comparison with the base material.

Samples cut from a welded joint are tested for uniaxial tension. In this case, the time factor is modeled by temperature, i.e., the principle of temperature-time superposition is used, based on the assumption that at a given stress the relationship between long-term strength and temperature is unambiguous (Larson-Miller method).

Methods for increasing weldability

Schemes of the formation mechanism of welded joints of thermoplastics. Their weldability can be increased by expanding the temperature range of viscosity, intensifying the removal of ingredients, or destroying defective layers in the contact zone that prevent the approach and interaction of juvenile macromolecules.

Several ways are possible:

introduction of an additive into the contact zone in case of insufficient amount of melt (when welding reinforced films); when welding dissimilar thermoplastics, the composition of the additive must have an affinity for both materials being welded;

introducing a solvent or a more plasticized additive into the welding zone;

forced mixing of the melt in the seam by displacing the parts to be joined not only along the upset line, but also back and forth across the seam by 1.5-2 mm or by applying ultrasonic vibrations. Activation of melt mixing in the contact zone can be carried out after melting of the joining edges with a heating tool having a ribbed surface. The properties of the welded joint can be improved by subsequent heat treatment of the joint. In this case, not only residual stresses are removed, but it is also possible to correct the structure in the weld and heat-affected zone, especially in crystalline polymers. Many of the above measures bring the properties of welded joints closer to the properties of the base material.

When welding oriented plastics, in order to avoid loss of their strength due to reorientation when heated to a viscous-fluid state of the polymer, chemical welding is used, i.e., a process in which radical (chemical) bonds between macromolecules are realized in the contact zone. Chemical welding is also used when joining thermosets, parts of which cannot transform into a viscous-flow state when reheated. To initiate chemical reactions, various reagents are introduced into the joint zone during such welding, depending on the type of plastic being joined. The chemical welding process is usually carried out by heating the welding site.

Volchenko V.N. Welding and materials to be welded, volume 1. -M. 1991

Polymers are an important part of the chemical industry. Therefore, everyone who works in the chemical industry or is interested in it knows main types of plastics.

The chemical industry specializes in the production of products by chemically processing raw materials. The industry is quite complexly structured and includes more than 20 segments. One of them is the production of polymers. This directly applies to the production of plastics, which relates to organic chemistry.

The production of polymer materials is developing dynamically and gaining momentum. To some extent, it determines the development of scientific and technological progress.

The plastics industry occupies a special place in the chemical industry. They are used in many sectors of the national economy.

Types of plastics

Plastics are organic materials created from synthetic or natural polymers. Polymers are high molecular weight natural or synthetic compounds.

Plastics are divided into several groups. Main types: simple and complex. Simple ones consist of pure polymers, while complex ones contain, in addition to polymers, various binding liquids, plasticizers, stabilizers, dyes, hardeners, lubricants, antistatic agents, etc.

Plastic masses have low thermal conductivity and high thermal expansion. Unlike steel, they expand 10-30 times more. They tend to be non-magnetic, chemically resistant and have low density. Other types of materials can be made from them, that is, they are technologically advanced.

As for the disadvantages, plastics are prone to aging and have low viscosity compared to other substances. They are characterized by low elasticity and low heat resistance.

The main types of plastics include thermoplastics and thermosets. Thermoplastics have the ability to melt when heated and to harden back at low temperatures. This property depends on the structure of the polymers: it can be linear, branched or amorphous.

Thermosets do not have the ability to soften. They first melt and then harden without being reprocessed.

Plastics are divided into:

• fabrics and films;


• fiberglass;


• plexiglass;


• foam plastics;


• vinyl plastic;


• wood plastics.

All these types of plastics are created in production and are actively used in everyday life. Synthetic plastics are created by isolating from coal, oil or natural gas through polymerization, polycondensation and polyaddition reactions of starting materials.

Depending on the purpose, there are the following methods for processing the main types of plastics:

• casting;


• extrusion;


• pressing;


• vibration shaping;


• foaming;


• casting;


• welding;


• vacuum forming.

Production of main types of plastics in the chemical industry

The production of plastic masses has found wide application in everyday life. However, in the modern world their production is on a huge scale, which negatively affects the environment.

For example, a plastic bag or plastic bottle takes fifty years to decompose, polluting the environment.

Given these circumstances, the issue of recycling and disposal of plastics arises. Their maximum use gives rise to new types of materials, which contributes to the development of not only the plastics industry, but also the chemical industry as a whole.

The main types of plastics are an important component of the chemical industry. The achievements and problems of the industry are most widely and fully revealed to producers and consumers at the annual Chemistry exhibition. And for many years now it has been organized by one of the world’s largest exhibition complexes, Expocentre Fairgrounds.

The colossal experience and vast knowledge of its specialists allows it to hold the event at the highest level. This contributes to a significant influence on the development of the chemical industry, and opens up wide research opportunities for its representatives.

Khimiya also facilitates the conclusion of new contracts with foreign companies, which significantly increases the competitiveness of goods.

Plastics

This article was written in the early 70s by a prominent Soviet chemist, prof. Elena Borisovna Trostyanskaya, author of many works, textbooks and books on the chemistry of polymers and plastics. However, over the past more than 30 years, the article has not lost any of its relevance. Of course, some of the plastic production data given here is out of date. It should also be noted that polypropylene has now become one of the leaders among plastics, along with polyethylene and polystyrene.

Plastic masses, plastics, plastics - materials containing a polymer, which during the formation of products is in a viscous or highly elastic state, and during operation - in a glassy or crystalline state. Depending on the nature of the processes accompanying the molding of products, plastics are divided into thermosets and thermoplastics. Thermal plastics include materials whose processing into products is accompanied by a chemical reaction of the formation of a network polymer - hardening; in this case, the plastic irreversibly loses its ability to transform into a viscous-flow state (solution or melt). When molding products from thermoplastics, no curing occurs, and the material in the product retains the ability to return to a viscous-flow state.

Plastics usually consist of several mutually compatible and non-compatible components. Moreover, in addition to the polymer, the composition of the plastic may include fillers of polymeric materials, plasticizers that lower the flow point and viscosity of the polymer, stabilizers of polymeric materials that slow down its aging, dyes, etc. Plastics can be single-phase (homogeneous) or multiphase (heterogeneous, composite) materials. In homogeneous plastics, the polymer is the main component that determines the properties of the material. The remaining components are dissolved in the polymer and are capable of improving certain of its properties. In heterogeneous plastics, the polymer acts as a dispersion medium (binder) in relation to the components dispersed in it, which make up independent phases. To distribute external influences on the components of heterogeneous plastic, it is necessary to ensure strong adhesion at the interface of contact between the binder and filler particles, achieved by adsorption or chemical reaction of the binder with the surface of the filler.

Filled plastics

The filler in plastic can be in gas or condensed phases. In the latter case, its elastic modulus may be lower (low modulus fillers) or higher (high modulus fillers) than the elastic modulus of the binder.

Gas-filled plastics include foam plastics - the lightest materials of all plastics; their apparent density is usually from 0.02 to 0.8 g/cm 3 .

Low-modulus fillers (they are sometimes called elasticizers), for which elastomers are used, without reducing the heat resistance and hardness of the polymer, give the material increased resistance to alternating and impact loads (see Table 1), and prevent the growth of microcracks in the binder. However, the coefficient of thermal expansion of elasticized plastics is higher, and the deformation resistance is lower than that of monolithic binders. The elasticizer is dispersed in the binder in the form of particles 0.2-10 microns in size. This is achieved by polymerization of the monomer on the surface of synthetic latex particles, hardening of the oligomer in which the elastomer is dispersed, and mechanical grinding of a mixture of rigid polymer and elastomer. Filling should be accompanied by the formation of a copolymer at the interface between the elasticizer particles and the binder. This ensures a cooperative response of the binder and elasticizer to external influences under operating conditions of the material. The higher the elastic modulus of the filler and the degree of filling of the material with it, the higher the deformation resistance of the filled plastic. However, the introduction of high-modulus fillers in most cases contributes to the occurrence of residual stresses in the binder, and, consequently, to a decrease in the strength and solidity of the polymer phase.

The properties of plastic with a solid filler are determined by the degree of filling, the type of filler and binder, the adhesion strength at the contact boundary, the thickness of the boundary layer, the shape, size and relative position of the filler particles. Plastics with small filler particles evenly distributed throughout the material are characterized by isotropic properties, the optimum of which is achieved at a degree of filling that ensures the adsorption of the entire volume of the binder by the surface of the filler particles. With increasing temperature and pressure, part of the binder is desorbed from the surface of the filler, due to which the material can be molded into products of complex shapes with fragile reinforcing elements. Small filler particles, depending on their nature, increase the elastic modulus of the product, its hardness, strength to varying degrees, and give it frictional, antifriction, thermal insulation, heat-conducting or electrically conductive properties.

To obtain low-density plastics, fillers in the form of hollow particles are used. Such materials (sometimes called syntactic foams) also have good sound and heat insulation properties.

The use of natural and synthetic organic fibers, as well as inorganic fibers (glass, quartz, carbon, boron, asbestos) as fillers, although it limits the choice of molding methods and makes it difficult to manufacture products of complex configurations, but sharply increases the strength of the material. The strengthening role of fibers in fiberglass, materials filled with chemical fibers (so-called organofibers), carbon fibers (see Carbon plastics) and glass fibers manifests itself already at a fiber length of 2-4 mm. As the length of the fibers increases, the strength increases due to their mutual interweaving and a decrease in stresses in the binder (with a high-modulus filler), localized at the ends of the fibers. In cases where this is allowed by the shape of the product, the fibers are fastened together in threads and in fabrics of various weaves.

Plastics filled with fabric (textolites) are layered plastics characterized by anisotropy of properties, in particular, high strength along the filler layers and low strength in the perpendicular direction. This disadvantage of laminated plastics is partly eliminated by the use of so-called. bulky fabrics in which individual fabrics (layers) are intertwined. The binder fills the gaps in the weaves and, when cured, fixes the shape given to the workpiece from the filler.

In products of simple shapes, and especially in hollow bodies of rotation, filler fibers are located in the direction of action of external forces. The strength of such plastics in a given direction is determined mainly by the strength of the fibers; the binder only fixes the shape of the product and evenly distributes the load across the fibers. The elastic modulus and tensile strength of the product along the fiber arrangement reach very high values ​​(see Table 1). These indicators depend on the degree of filling of the plastic.

For panel structures, it is convenient to use laminated plastics filled with wood veneer or paper, including synthetic fiber paper (see Wood plastics, Getinaks). A significant reduction in the weight of the panels while maintaining rigidity is achieved by using materials of a three-layer, or sandwich, structure with an intermediate layer of polystyrene foam or honeycomb.

Main types of thermoplastics

Among thermoplastics, the most diverse uses are polyethylene, polyvinyl chloride and polystyrene, mainly in the form of homogeneous or elasticized materials, less often gas-filled and filled with mineral powders or synthetic organic fibers.

Polyethylene-based plastics are easily molded and welded into products of complex shapes, they are resistant to shock and vibration loads, chemically resistant, and have high electrical insulating properties (dielectric constant 2.1-2.3) and low density. Products with increased strength and heat resistance are made from polyethylene filled with short (up to 3 mm) fiberglass. With a filling degree of 20%, tensile strength increases by 2.5 times, bending strength by 2 times, impact strength by 4 times and heat resistance by 2.2 times.

Rigid plastic based on polyvinyl chloride - vinyl plastic, including elasticized (impact-resistant), is much more difficult to mold than polyethylene plastics, but its strength to static loads is much higher, creep is lower and hardness is higher. Plasticized polyvinyl chloride plastic is more widely used. It is easily formed and reliably welded, and the required combination of strength, deformation stability and heat resistance is achieved by selecting the ratio of plasticizer and solid filler.

Plastics based on polystyrene are molded much easier than those made from vinyl plastic, their dielectric properties are close to the properties of polyethylene plastics, they are optically transparent and in terms of strength to static loads they are not much inferior to vinyl plastic, but they are more fragile, less resistant to solvents and are flammable. Low impact strength and fracture due to the rapid growth of microcracks - properties especially characteristic of polystyrene plastics - are eliminated by filling them with elastomers, i.e. polymers or copolymers with a glass transition temperature below - 40 ° C. Elasticated (impact-resistant) polystyrene of the highest quality is produced by polymerization of styrene on particles of styrene-butadiene or nitrile-butadiene latex.

The material, called ABS, contains about 15% gel fraction (block and graft copolymers of polystyrene and these butadiene copolymers), which makes up the boundary layer and connects the elastomer particles to the polystyrene matrix. The frost resistance of the material is limited by the glass transition temperature of the elastomer, the heat resistance is limited by the glass transition temperature of polystyrene.

The heat resistance of the listed thermoplastics is in the range of 60-80 ° C, the coefficient of thermal expansion is high and amounts to 1 x 10 -4 , their properties change sharply with a slight change in temperature, deformation resistance under load is low. Thermoplastics belonging to the group of ionomers, for example, copolymers of ethylene, propylene or styrene with monomers containing ionogenic groups (usually unsaturated carboxylic acids or their salts), are partly free of these disadvantages. Below the flow temperature, due to the interaction of ionogenic groups between macromolecules, strong physical bonds are created, which are destroyed when the polymer softens. Ionomers successfully combine the properties of thermoplastics, favorable for molding products, with the properties characteristic of network polymers, i.e., with increased deformation resistance and rigidity. However, the presence of ionic groups in the polymer reduces its dielectric properties and moisture resistance.

Plastics with higher heat resistance (100-130 °C) and less sharp changes in properties with increasing temperature are produced on the basis of polypropylene, polyformaldehyde, polycarbonates, polyacrylates, polyamides, especially aromatic polyamides. The range of products made from polycarbonates, including those filled with fiberglass, is rapidly expanding.

The chemical resistance, impact strength and dielectric properties of plastics based on polytetrafluoroethylene and tetrafluoroethylene copolymers are especially high (see Fluoroplastics). Polyurethane-based materials successfully combine wear resistance with frost resistance and long-term strength under conditions of alternating loads. Polymethyl methacrylate is used to make optically transparent weather-resistant materials.

The absence of curing reactions during the molding of thermoplastics makes it possible to extremely intensify the processing process. The main methods of molding thermoplastic products are injection molding, extrusion, vacuum forming and blow molding. Since the melt viscosity of high molecular weight polymers is high, the molding of thermoplastics on injection molding machines or extruders requires specific pressures of 30-130 Mn/m = (300-1300 kgf/cm 2 ).

Further development of the production of thermoplastics is aimed at creating materials from the same polymers, but with new combinations of properties, using elasticizers, powder and short-fiber fillers.

Main types of thermosets

After the molding of thermoset products is completed, the polymer phase acquires a network (three-dimensional) structure. Due to this, cured thermosets have higher hardness, elastic modulus, heat resistance, fatigue strength, and a lower coefficient of thermal expansion than thermoplastics; Moreover, the properties of cured thermosets do not depend so sharply on temperature. However, the inability of cured thermosets to transform into a viscous-flow state forces the synthesis of the polymer to be carried out in several stages.

The first stage ends with the production of oligomers (resins) - polymers with a molecular weight of 500-1000. Due to the low viscosity of the solution or melt, the resin is easy to distribute over the surface of the filler particles, even when the degree of filling reaches 80-85% (by weight). After introducing all the components, the fluidity of the thermoset remains so high that products from it can be molded by pouring (casting), contact molding, or winding. Such thermosets are called premixes when they contain filler in the form of small particles, and prepregs when the filler is continuous fibers, fabric, or paper. The technological equipment for molding products from premixes and prepregs is simple and energy costs are low, but the processes involve holding the material in individual molds to cure the binder. If the resin is cured by a polycondensation reaction, then the molding of products is accompanied by severe shrinkage of the material and significant residual stresses arise in it, and solidity, density and strength do not reach the maximum values ​​(with the exception of products obtained by winding with tension).

To avoid these shortcomings, the technology for manufacturing products from resins cured by a polycondensation reaction provides an additional stage (after mixing the components) - pre-curing of the binder, carried out during rolling or drying. At the same time, the duration of the subsequent holding of the material in the molds is reduced and the quality of the products is improved, however, filling the molds due to a decrease in the fluidity of the binder becomes possible only at pressures of 25-60 MN/m 2 (250-600 kgf/cm2).

The resin in thermosets can cure spontaneously (the higher the temperature, the greater the speed) or with the help of a polyfunctional low-molecular substance - a hardener.

Thermosets with any filler are made using phenolic resins as a binder, often elasticized with polyvinyl butyral, nitrile butadiene rubber, polyamides, polyvinyl chloride (such materials are called phenolics), and epoxy resins, sometimes modified with phenol or aniline formaldehyde resins or curing oligos. ethers .

High-strength plastics with heat resistance up to 200 °C are produced by combining glass fibers or fabrics with curing oligoesters, phenol-formaldehyde or epoxy resins. In the production of products that operate for a long time at 300 °C, fiberglass or asbestos plastics with an organosilicon binder are used; at 300-340 °C - polyimides in combination with silica, asbestos or carbon fibers; at 250-500 °C in air and at 2000-2500 °C in inert environments - phenolics or polyamide-based plastics filled with carbon fiber and subjected to carbonization (graphitization) after molding the products.

High modulus plastics [elastic modulus 250-350 Gn/m 2 (25,000—35,000 kgf/mm 2 )) are produced by combining epoxy resins with carbon, boron or monocrystalline fibers (see also Composite materials). Monolithic and lightweight plastics, resistant to vibration and shock loads, waterproof and maintaining dielectric properties and tightness under complex loading conditions, are made by combining epoxy, polyester or melamine-formaldehyde resins with synthetic fibers or fabrics, paper from these fibers.

The highest dielectric properties (dielectric constant 3.5-4.0) are characteristic of materials based on quartz fibers and polyester or organosilicon binders.

Wood-laminated plastics are widely used in the building materials industry and shipbuilding.

Volume of production and structure of consumption of plastics

Plastic materials based on natural resins (rosin, shellac, bitumen, etc.) have been known since ancient times. The oldest plastic made from an artificial polymer—cellulose nitrate—is celluloid, the production of which began in the USA in 1872. In 1906–10, the production of the first thermosets—materials based on phenol-formaldehyde resin—was launched in pilot production in Russia and Germany. In the 30s In the USSR, USA, Germany and other industrialized countries, the production of thermoplastics - polyvinyl chloride, polymethyl methacrylate, polyamides, polystyrene - is being organized. However, the rapid development of the plastics industry began only after World War II (1939–45). In the 50s In many countries, production of the largest-tonnage plastic—polyethylene—begins.

In 1973, world production of polymers for plastics reached ~ 43 million tons. Of this, about 75% were thermoplastics (25% polyethylene, 20% polyvinyl chloride, 14% polystyrene and its derivatives, 16% other plastics). There is a trend towards a further increase in the share of thermoplastics (mainly polyethylene) in total plastics production.

Although the share of thermoset resins in the total production of polymers for plastics is only about 25%, in fact the production volume of thermosets is higher than thermoplastics due to the high degree of filling (60-80%) of the resin.

The production of plastics is developing much more intensively than traditional construction materials such as cast iron and aluminum.

The consumption of plastics in construction is continuously increasing. P This is due not only to the unique physical and mechanical properties of polymers, but also to their valuable architectural and construction characteristics. The main advantages of plastics over other building materials are lightness and relatively high specific strength. Thanks to this, the weight of building structures can be significantly reduced, which is the most important problem of modern industrial construction.

Plastics occupy one of the leading positions among structural materials in mechanical engineering. Their consumption in this industry becomes comparable (in volume units) with the consumption of steel. The feasibility of using plastic in mechanical engineering is determined primarily by the possibility of reducing the cost of products. At the same time, the most important technical and economic parameters of the machines are also improved - weight is reduced, durability, reliability, etc. are increased. Gears and worm wheels, pulleys, bearings, rollers, machine guides, pipes, bolts, nuts, a wide range of technological equipment, etc. are made from plastics. .

The main advantages of plastics, which determine their widespread use in aircraft construction, are lightness and the ability to change technical properties over a wide range. Thermoplastics are used in the production of glazing elements, antenna radomes, for decorative finishing of aircraft interiors, etc., foam and honeycomb plastics are used as fillers for highly loaded three-layer structures.

The areas of application of plastics in shipbuilding are very diverse, and the prospects for use are almost unlimited. They are used for the manufacture of ship hulls and hull structures (mainly fiberglass), in the production of parts for ship mechanisms, instruments, for finishing premises, their heat, sound and waterproofing.

In the automotive industry, the use of plastics for the manufacture of cabins, bodies and their large parts has especially great prospects, because The body accounts for about half the weight of the car and ~40% of its cost. Plastic bodies are more reliable and durable than metal ones, and their repair is cheaper and easier. However, plastics have not yet become widespread in the production of large-sized car parts, mainly due to insufficient rigidity and relatively low weather resistance. Plastics are most widely used for interior decoration of automobiles. Engine, transmission, and chassis parts are also made from them. The enormous importance that plastics play in electrical engineering is determined by the fact that they are the basis or essential component of all insulation elements of electrical machines, devices and cable products. Plastics are often used to protect insulation from mechanical stress and aggressive environments, for the manufacture of structural materials, etc.

Lit.: Encyclopedia of Polymers, t. 1-2, M., 1972-74; Technology of plastics, ed. V. V. Korshaka, M., 1972; Losev I.P., Trostyanskaya E.B., Chemistry of synthetic polymers, 3rd ed., M., 1971; Plastics for structural purposes, ed. E. B. Trostyanskoy, M., 1974.

Our civilization can be called a plastic civilization: various types of plastics and polymer materials can be found literally everywhere.


However, the average person hardly has a good idea of ​​what plastic is and what it is made of.

What is plastic?

Currently, plastics, or plastics, refer to a whole group of materials of artificial (synthetic) origin. They are produced through a chain of chemical reactions from organic raw materials, mainly from natural gas and heavy fractions of oil. Plastics are organic substances with long polymer molecules that consist of molecules of simpler substances connected to each other.

By changing the polymerization conditions, chemists obtain plastics with the desired properties: soft or hard, transparent or opaque, etc. Plastics today are used in literally all areas of life, from the production of computer equipment to the care of small children.

How were plastics invented?

The world's first plastic was made in the English city of Birmingham by metallurgist A. Parks. This happened in 1855: while studying the properties of cellulose, the inventor treated it with nitric acid, thanks to which he launched the polymerization process, obtaining nitrocellulose. The inventor named the substance he created by his own name - parkesin. Parks opened his own company to produce parkesin, which soon became known as artificial ivory. However, the quality of the plastic was poor, and the company soon went bankrupt.

Subsequently, the technology was improved, and the production of plastic was continued by J.W. Hite, who called his material celluloid. A variety of products were made from it, from collars that did not need to be washed to billiard balls.

In 1899, polyethylene was invented, and interest in the possibilities of organic chemistry grew exponentially. But until the mid-twentieth century, plastics occupied a rather narrow market niche, and only the creation of PVC production technology made it possible to produce a wide range of household and industrial products from them.

Types of plastics

Currently, the industry produces and uses many types of plastics.

Based on their composition, plastics are divided into:

- sheet thermoplastic masses - plexiglass, vinyl plastics, consisting of resins, plasticizer and stabilizer;


- laminated plastics reinforced with one or more layers of paper, fiberglass, etc.;

— fiberglass – plastics reinforced with glass fiber, asbestos fiber, cotton fiber, etc.;

- injection molding masses - plastics that do not contain other components other than polymer compounds;

— press powders – plastics with powder additives.

Based on the type of polymer binder, plastics are divided into:

- phenol plastics, which are made from phenol-formaldehyde resins;

— aminoplasts made from melamine-formaldehyde and urea-formaldehyde resins;

- epoxy plastics using epoxy resins as a binder.

Based on their internal structure and properties, plastics are divided into two large groups:

- thermoplastics that melt when heated, but after cooling retain their original structure;

— thermosets with an initial structure of a linear type, which acquire a network structure during curing, but when reheated, completely lose their properties.

Thermoplastics can be used repeatedly; to do this, they just need to be crushed and melted. In terms of working properties, thermosets are, as a rule, somewhat better than thermoplastics, but when subjected to strong heating, their molecular structure is destroyed and is not subsequently restored.

What are plastics made of?

The raw materials for the vast majority of plastics are coal, natural gas and oil. From them, simple (low molecular weight) gaseous substances are isolated through chemical reactions - ethylene, benzene, phenol, acetylene, etc., which are then transformed into synthetic polymers during polymerization, polycondensation and polyaddition reactions. The excellent properties of polymers are explained by the presence of high molecular weight bonds with a large number of initial (primary) molecules.


Some stages of polymer production are complex and extremely environmentally hazardous processes, so the production of plastics becomes accessible only at a high technological level. At the same time, the final products, i.e. Plastics are generally completely neutral and do not have any negative impact on human health.