The advent of plastic Types and types of plastic, classification of plastic. What kind of material is used in the production of plastic containers. Plastic. What is plastic

Disposal of waste from plastic production should be carried out in recycling plants in special acid-resistant installations, but if possible waste-free production it is better to send plastic waste for recycling.

You can learn about environmental problems associated with the release of radioactive substances.

One of the most popular holiday destinations among Russian tourists in the region are discussed in our review.

The impact of environmental disasters on the world's oceans of the planet, read the link.

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Composition and properties

Getting plastics

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

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

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

Depending on the behavior of the polymer during heating, two types of plastics are distinguished - thermoplastics, materials that can be repeatedly heated and pass from a solid to a viscous-fluid state, and thermoplastics that 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 polymers, branched and network-spatial.

According to the composition of macromolecules, polymers are divided into three classes:

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

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

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

Macromolecules are flexible and able to change shape under the influence of thermal motion 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 a segment, i.e., by the number of units in it, which, under the conditions of a given specific effect on the polymer, manifest themselves as kinetically independent units, for example, in the HDTV field as dipoles. According to the reaction to external electric fields, polar (PE, PP) and non-polar (PVC, polyaxylonitrile) polymers are distinguished. Attractive forces act between macromolecules, caused by van der Waals interaction, as well as hydrogen bonds, ionic interaction. Attractive forces are manifested 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

According to the structure, two types of plastics are distinguished - crystalline and amorphous. In crystalline, in contrast to amorphous, not only short-range, but also long-range order is observed. Upon transition from a viscous-fluid state to a solid state, the 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, amorphous regions always remain in crystalline polymers. By changing the cooling rate, it is possible to control the structure and, consequently, the properties of the welded joint.

A 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 location of the axes of chain macromolecules mainly along one direction, which leads to the manifestation of anisotropy in the properties of a plastic product. Obtaining 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 the entropy elasticity due to the motion of the segments.

Reaction of plastics to the thermomechanical cycle

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

Basic plastics for welded structures

The most common engineering plastics are a group of thermoplastics based on polyolefins: high and low pressure polyethylene, polypropylene, polyisobutylene.

Polyethylene [..-CH 2 -CH 2 -...] n high and low pressure - crystalline thermoplastics, differing from each other in strength, rigidity, and pour point. Polypropylene [-CH 2 -CH(CH 3)-] n is more temperature resistant than polyethylene, and has greater strength and rigidity.

Significant volumes are used of chlorine-containing plastics based on polymers and copolymers of vinyl chloride and vinylidene chloride.

PVC(PVC) [-(CH 2 -CHCl-)] n - an amorphous polymer of a linear structure, in the initial state it is a rigid material. When a plasticizer is added to it, a very plastic and well-welded material can be obtained - a plastic compound. From rigid PVC - vinyl plastic - sheets, pipes, rods are made, and from plastic compound - film, hoses and other products. Foamed materials (polystyrenes) 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 well-defined melting point. Domestic industry mainly produces aliphatic polyamides used for the manufacture of fibers, casting of machine parts, and films. Polyamides include, in particular, the well-known polycaprolactam and polamide-66 (nylon).

Polytetrafluoro-ethylene-fluorolone-4 (fluoroplast 4) received the greatest popularity from the group of fluorolones. Unlike other thermoplastics, when heated, it does not turn into a viscous state even at a degradation temperature (about 415 ° C), therefore its welding requires special techniques. At present, the chemical industry has mastered the production of well-welded fusible fluorolones; F-4M, F-40, F-42, etc. Welded structures made of fluorine-containing plastics have exceptionally high resistance to aggressive environments and can withstand workloads in a wide temperature range.

On the basis of acrylic and methacrylic acid are produced acrylic plastics. The most well-known derivative based on them in practice 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, have also found use. All plastics of this group are well welded.

A group of plastics based on polystyrene. This linear thermoplastic is highly heat weldable.

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

In welded structures, plastics based on polycarbonates- polyesters of carbonic acid. They have a 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 3-5 mm granules. 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 to transport aggressive products, including oil and gas containing hydrogen sulfide and carbon dioxide and chemical (non-aromatic) reagents in chemical production. Reservoirs and tanks for the transportation of acids and alkalis, pickling baths and other vessels are lined with plastic sheets, connected by welding. Sealing with plastic compound of rooms contaminated by isotopes, covering floors with linoleum are also carried out by welding. Conservation food products in tubes, boxes and jars, packaging of goods and postal parcels sharply accelerated with the use of welding.

Machine building parts. In chemical engineering, bodies and blades of various types of mixers are welded, bodies and rotors of pumps for pumping aggressive media, filters, bearings and gaskets made of fluoroplastic, lighting fixtures are welded from polystyrene, non-conductive gears, rollers, couplings, rods are made of nylon, non-lubricated bearings are made of fluorolon , fuel displacers, etc.

Weldability evaluation of plastics

Main stages of the welding process

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

At close contact of the activated layers, the forces of intermolecular interaction should 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 self-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 - the base material.

The 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 pressure-activated surfaces of the parts to be joined are approached under pressure due to shear deformations, the flow of the polymer melt occurs. As a result, ingredients that prevent the approach and interaction of juvenile macromolecules are removed from the contact zone (gas, oxidized interlayers are evacuated). Due to the difference in melt flow rates, mixing of melt macrovolumes in the contact zone is not excluded. Only after the removal or destruction of defective layers in the contact zone, when the juvenile macromolecules approach at the distance of action of van der Waals forces, interaction (seizure) occurs between the macromolecules of the layers of the surfaces of the parts to be joined. This autohesive process occurs at the micro level. It is accompanied by interdiffusion of macromolecules due to the energy potential and non-uniformity of the temperature gradient in the area of ​​the surfaces to be welded.

So, in order to form a welded joint of 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 actively shear deformations occur in the melt - the destruction and removal of defective layers on the contact surfaces, the less pressure must be applied to connect 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 range of viscosity. Therefore, viscosity can serve as one of the signs that determine the weldability of a plastic: the lower it is in the range of viscous flow, 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 prevent the interaction of macromolecules. However, heating for each polymer is limited by a certain temperature of destruction T d, above which its decomposition - destruction occurs. Thermoplastics differ in the boundary values ​​​​of the temperature range of viscosity, i.e., between their flow temperature T T and destruction T d (Table 37.2).

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

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

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

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

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

In the experimental evaluation of 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 punched out of 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 improving weldability

Schemes of the mechanism of formation of welded joints in thermoplastics. An increase in their weldability can be carried out by expanding the temperature range of viscous flow, 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 an insufficient amount of melt (when welding reinforced films), when welding dissimilar thermoplastics, the additive in composition must have an affinity for both welded materials;

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

forced mixing of the melt in the seam by shifting the parts to be joined not only along the upset line, but also reciprocating across the seam by 1.5-2 mm or by applying ultrasonic vibrations. Activation in the melt mixing contact zone can be carried out after the joined edges are melted with a heating tool having a ribbed surface. The properties of the welded joint can be improved by subsequent heat treatment connections. In this case, not only residual stresses are removed, but it is possible to correct the structure in the seam and the heat-affected zone, especially in crystalline polymers. Many of the measures outlined 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 upon heating to the viscous-flowing 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, the parts of which cannot pass into a viscous state upon reheating. To initiate chemical reactions, various reagents are introduced into the joint zone during such welding, depending on the type of plastic being joined. The process of chemical welding, as a rule, is carried out by heating the place of welding.

Volchenko V.N. Welding and welded materials v.1. -M. 1991

The problems of nicotine addiction, drug addiction, alcoholism, the spread of HIV infection and a sharp increase in mortality from cardiovascular diseases do exist, they are talked about and written a lot. At the same time, two other major problems remain almost unnoticed: the poisoning of us and our children with plastics and medicines. We wrote about medicines for children in the last article, and now it's time to talk about plastics.

Disposable tableware, plastic food containers, bottles, toys, a plastic kettle, plastic bags - we and our children regularly come into contact with all these and many other plastic products. Plastic has become a part of our lives, and every year we think less and less about its harmful effects on health. Well, except that they bought a new kettle, and the water from it smells of something chemical - this is a reason for reflection, if it doesn’t smell, then we won’t even think about anything.

How long have you been doing repairs in the apartment, even a small one? Surely many of you are happy with the new plastic windows, new laminate, linoleum, carpet, vinyl wallpaper or stretch ceilings. Congratulations, it is quite possible that your apartment is uninhabitable and more like a gas chamber in the near future.

Sellers in grocery stores, home appliance stores or construction stores will assure you of the absolute safety of the products they sell. The vast majority of them do not even know what they are talking about, and those who know will calmly lie to their eyes, realizing that the consequences of their lies will appear in years.

Plastic is a collective term for a wide range of synthetic or semi-synthetic materials used in the manufacture of products. industrial production. The production of plastic products is characterized by simplicity and low cost, while the properties of this material allow it to be widely used.

How do you know how dangerous plastic is?

On each plastic product, the manufacturer must indicate the material from which it is made. The vast majority of manufacturers honestly label. If there is no marking, then the plastic is definitely hazardous to health. There are 7 types of markings:

As you can see, they differ only in numbers, each of which corresponds to a certain polymer from which this plastic is made. Under these triangles may contain additional letter designations. Some manufacturers put additional markings, for example, this:

This marking means that this plastic is safe for food use. However, it is not required and you can do without it. The most important thing is to remember what the numbers mean, but first a little background on some dangerous substances:

1. Phthalates- salts and esters of phthalic (orthophthalic) acid. Toxic, capable of causing serious diseases of the nervous and cardiovascular systems. There is reason to believe that phthalates have a carcinogenic effect and can cause cancer. Banned in Europe and the US for the manufacture of children's toys.
2. Formaldehydes- methanal or formic aldehyde. It is toxic, affects the nervous and respiratory systems, negatively affects the reproductive system and can cause genetic disorders in offspring. Carcinogen.
3. Styrenes- phenylethylene, vinylbenzene. Slightly toxic, affects mucous membranes. It has carcinogenic properties, can act as chemical estrogen, which will adversely affect reproductive functions.
4. Vinyl chloride- an organic substance, which is the simplest chlorine derivative of ethylene. It is toxic, affects the central nervous system, skeletal system, brain, heart, liver, causes systemic lesions of the connective tissue, destroys the immune system. It has a carcinogenic, mutagenic and teratogenic (causes malformations in embryos) effect.
5. Bisphenol A- diphenylpropane. It is similar to estrogens, causes brain diseases, disrupts the reproductive system, causes cancer, leads to male and female infertility, inhibits the functions of the endocrine system, leads to impaired brain development in children, and the development of cardiovascular pathologies.

All these substances are auxiliary, they are contained in one or another type of plastic and thanks to them the desired consumer properties (elasticity, hardness, heat resistance, etc.) are achieved. The plastic itself will calmly pass through the gastrointestinal tract without causing harm (unless it has a mechanical effect), but the excipients are dangerous. You also need to understand that the final product may not be toxic, but it may contain residues of the toxic raw materials from which it was made.

Types of plastics and their marking

Number 1- polyethylene terephthalate. Letter marking PETE or PET.

Cheap, thanks to which it is found almost everywhere. It contains most drinks, vegetable oils, ketchups, spices, cosmetics.

Safety. Suitable for single use ONLY. Repeated use may release phthalates.

Number 2- high density polyethylene. Letter marking HDPE or PE HD.

Cheap, lightweight, resistant to temperature effects (range from -80 to +110 degrees C). Disposable tableware, food containers, bottles for cosmetics, packaging bags, bags, toys are made from it.

Safety. It is considered relatively safe, although formaldehyde may be released from it.

Number 3- polyvinyl chloride. Letter marking PVC or V.

This is the same PVC from which window profiles, furniture elements, films for stretch ceilings, pipes, tablecloths, curtains, floor coverings, containers for technical liquids are made.

Safety. Prohibited for food use. It contains bisphenol A, vinyl chloride, phthalates, and may also contain mercury and/or cadmium. We would like to say that you need to buy expensive window profiles, expensive stretch ceilings, expensive laminate and this will make your life safe, but this will not be true. High price product does not provide any warranty.

Number 4- low density polyethylene. Letter marking LDPE or PEBD.

A cheap and common material from which most bags, trash bags, CDs, linoleums are made.

Safety. Relatively safe for food use, in rare cases it can release formaldehyde. Plastic bags not as dangerous to human health as dangerous to the ecology of the planet.

Number 5- polypropylene. Letter marking PP.

Durable and heat-resistant plastic from which food containers, food packaging, syringes, toys are made.

Safety. Pretty safe, but certain conditions may release formaldehyde.

Number 6- polystyrene. Letter marking PS.

Cheap and easy to manufacture plastic, from which almost all disposable tableware is made, yogurt cups, trays for meat, fruits and vegetables (they are made from foamed polystyrene, i.e. expanded polystyrene), food containers, toys, sandwich panels, heat-insulating plates.

Safety. It can release styrene, which is why disposable tableware is called disposable.

Number 7- polycarbonate, polyamide and other types of plastics. Letter marking O or OTHER.

AT this group includes plastics that have not received a separate number. They are used to make baby bottles, toys, water bottles, packaging.

Safety. They contain Bisphenol A, more precisely, some of them contain, and some plastics from this group, on the contrary, are distinguished by increased environmental friendliness.

Conclusion

Mankind has become so dependent on plastics that to abandon their use, at least in Food Industry turns out to be impossible. Read the Bisphenol A specification again, and then think about it: almost 100% of all bottles with nipples for artificial feeding of children are made of plastics containing BPA. confidently expect them to flood our market and lower their prices. So this will be another weighty argument in favor of breastfeeding.

Do your best to minimize contact with plastics. This does not mean that you need to shy away from plastic now, just that you need to use it wisely now that you know much more about it. Inspect plastic containers and get rid of everything except polypropylene products (number 5 or PP marking), and even better - give preference to products made of glass, wood, metal. It is quite possible that economical housewives kept plastic containers from ice cream or jam, what plastic are they made of?

Be careful with plastic toys, especially for small children. Make sure that the products have certificates of conformity with hygiene standards.

If you have made repairs using plastic products, then for several weeks it is better not to live in this apartment and come only to thoroughly ventilate the room.

When buying another plastic product, make it a rule to smell it. It is simple and takes literally a second, which will be enough to capture the unpleasant smell. Its absence does not mean safety, but if it is, then even a simple hair comb should be abandoned.

Everyone can protect their own health and the health of their children, after all, it is not so difficult.

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


However, the average person is unlikely to have a good idea of ​​what plastic is and what it is made of.

What is plastic?

Currently, plastics, or plastics, are called a whole group of materials of artificial (synthetic) origin. They are produced by a chain of chemical reactions from organic raw materials, mainly from natural gas and heavy oil fractions. Plastics are organic substances with long polymer molecules, which 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 spheres of life, from manufacturing computer technology to caring for young children.

How were plastics invented?

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

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

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

Varieties of plastics

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

According to their composition, plastics are divided into:

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


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

- Fibre-reinforced plastics - reinforced with fiberglass, asbestos fiber, cotton, etc.;

- casting masses - plastics that do not contain other components, except for polymer compounds;

- press powders - plastics with powder additives.

According to the type of polymer binder, plastics are divided into:

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

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

- epoxy resins using epoxy resins as a binder.

According to the internal structure and properties, plastics are divided into two large groups:

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

— thermoplastics, with initial structure linear type, upon curing, acquiring a network structure, but upon reheating, completely losing their properties.

Thermoplastics can be reused many times by simply crushing and melting them. Thermosetting plastics are, as a rule, somewhat better than thermoplastics in terms of working qualities, but with strong heating, their molecular structure is destroyed and is not restored in the future.

What are plastics made from?

The raw materials for the vast majority of plastics are coal, natural gas and oil. Simple (low molecular weight) gaseous substances - ethylene, benzene, phenol, acetylene, etc., are isolated from them by chemical reactions, which are then converted into synthetic polymers in the course of polymerization, polycondensation, and polyaddition reactions. The excellent properties of polymers are explained by the presence of high-molecular 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 available 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.

Plastic occupies an important place among the most commonly used materials today. The variety of its types and properties allows it to be used in various fields of production. What are the types of plastics? What are their properties? How exactly are they used? We will consider the details in this article.

Types of plastics

So, the types of material under consideration are divided into a number of different categories, taking into account the following features:

• rigidity;
• fat content;
• chemical composition.

However, even these points do not reflect the main criterion that most clearly demonstrates the nature of a particular polymer. It's about how plastic behaves when heated. Given this point, the following types of plastics are distinguished:

• thermoplastics;
• thermoplastics;
• elastomers.

To determine which category a material belongs to, it is necessary to evaluate its size, shape, chemical composition, as well as the arrangement of molecules.

Thermoplastics

The type of plastics under consideration is characterized by the following behavior when heated: after they have been heated once (for example, during production), they acquire an absolutely solid state and become insoluble. They can no longer be softened by any subsequent heating. This process experts call irreversible curing.

The macromolecular structure of thermosets is initially linear. However, during the heating process, the properties of the plastic change. So, its molecules, figuratively speaking, are sewn together. In this case, a special spatial structure (network) is formed. This is what allows the material in question to become completely inelastic and exceptionally hard. Moreover, it is not able to re-transition into a viscous state.

Due to these features, thermoplastics cannot be recycled, they cannot be welded or formed into a product upon reheating (since the material will simply collapse due to the breakdown of molecular chains).

In what areas is it appropriate to use plastics of this kind? As a rule, it is their heat resistance that is used. Therefore, from such materials are made:

• crankcase details in the engine compartment;
• body parts (external, large-sized).

Thermoplastics

The classification of plastics distinguishes another type of them - thermoplastics. Their peculiarity lies in the fact that these materials melt under the influence of high temperatures, but when cooled, they quickly return to their original state. The molecular chains of this type of plastic are either slightly branched or linear. When the product is exposed to low temperatures, it is brittle and hard. This is due to the fact that the molecules are placed extremely close to each other, which almost completely limits their movement. As soon as the temperature rises a little, the molecules get the opportunity to move, which significantly weakens the bond between them. During the described process, the material becomes more ductile. If the temperature continues to rise, then the intermolecular bonds finally weaken, and now they slide relative to each other. At this time, the plastic becomes viscous and incredibly elastic. If the temperature is lowered, then all these processes will reverse.

If the temperature is controlled in such a way as to prevent overheating, which provokes the breakdown of the molecular chain, then the processes described above can be repeated an infinite number of times. Using these properties of plastics of this category, they are repeatedly processed into a variety of products. This allows less pollution of the environment, because plastic waste in the soil decomposes from one to four hundred years.

Moreover, due to the features described above, thermoplastics can be easily soldered or welded. Any mechanical damage can be corrected by proper temperature exposure.

The use of plastics of this type is widespread in the automotive industry (manufacturing of wheel covers, bumpers, panels, lamp housings, frames, exterior mirrors, bumper grilles, and so on).

Basic thermoplastics:

• polyvinyl chloride;
• polyvinyl acetate;
• polyoxymethylene;
• polypropylene;
• polyamide;
• copolymers of butadiene, styrene and acrylonitrile;
• polycarbonate;
• polystyrene;
• polyethylene;
• polyvinyl acetate.

Elastomers

The main characteristic of plastics in this category is elasticity. In practice, this is manifested by the fact that in the case of a force impact, such a material exhibits incredible flexibility, and after its termination, it takes its former shape in a short time. Moreover, this property is retained by elastomers in an extremely wide temperature range. Experts call it the limits of -60 and +250 degrees. The macromolecules of elastomers are similar to those of thermosets - they are spatially reticulated. However, the distance between them is much larger, due to which these plastics are able to exhibit such properties.

Among other things, such a network structure makes the plastics of the group in question soluble and completely infusible, but they tend to swell.

Materials that fall into this category:

• silicone;
• polyurethane;
• rubber.

These materials have found practical application in the automotive industry, where all three of their types are successfully used. Such plastic is used for the manufacture of seals, tires, spoilers and so on. Mixtures of the above three types of materials are also formed. They are called blends. Their properties differ depending on what ratio of components is used in this case.

PET

Polyethylene terephthalate is a material from which disposable bottles are made. It is disposable, because when reused, the material in question is capable of releasing extremely toxic substances for the human body into the water, which negatively affect the hormonal balance. Therefore, if you pour liquid into a bottle that is no longer new, remember that such hazardous elements, how different kind alkalis and many bacteria for which PET is an ideal breeding ground.

By itself, this type of plastic is light, rigid and very durable. Perhaps this is the reason for its unconditional popularity all over the world. It is also particularly heat-resistant (does not deform and does not collapse if it is exposed to temperatures in the range from -40 to +200 degrees). Neither mineral salts, nor oils, nor dilute acids, nor alcohols, nor even the vast majority of organic compounds can cause any harm to the material. At the same time, it is not resistant to certain types of solvents and strong alkalis. When the material burns, a highly sooty flame is produced. Extinguishes spontaneously when removed from fire.

HDPE

Low pressure high density polyethylene is a plastic good quality, which neither initially nor subsequently releases dangerous compounds into the contents of the container. This is the most preferred option for storing water, as the liquid will be safe to drink for a certain time. The abbreviation HDPE is nothing but the designation of food grade plastic.

It is used for the manufacture of various products: some plastic bags, milk packaging, children's toys, reusable sports and tourist bottles, detergent packaging.

Quite dense and rigid, but relatively fragile material.

PVC

Plastic parts in this category are highly toxic. They are able to release at least two dangerous substances that, by their effect on the body, adversely affect the human hormonal balance. The plastic is quite flexible and soft. Typically, it is used to make packaging for children's toys and vegetable oil, as well as blister packs that can store a variety of types of goods. Also, with the help of this plastic, computer cables are sheathed, plumbing parts and plastic pipes are produced.

Recycling on site Russian Federation is not exposed, which means that its use causes significant harm to the environment.

The material in question is incredibly elastic, and also does not burn very well (this is characterized by the fact that at the moment the plastic is removed from the flame it spontaneously dies out). The combustion process is also very interesting: the flame is distinguished by a greenish-blue glow, and the plastic itself is very smokey, a very sharp and pungent smell of emitted smoke is emitted. Burnt plastic looks like a black substance, very similar to coal (with light pressure it quickly turns into soot).

LDPE

This abbreviation stands for "high pressure low density polyethylene". The scope of the considered plastic is large. It is used to make disposable bags and liquid bottles. In the second case, it is absolutely safe, since it does not emit any toxic or harmful chemical compounds into the water that is stored in it. However, the packages that are made from it are better not to use in principle. In any products that are in them, they release substances that can cause serious damage to the functioning of the cardiovascular system.

PP

You also often meet polypropylene in everyday life. This type of plastic is usually either white or translucent. You have often seen packages made from it. Often they sell yogurts or syrups. When heated, polypropylene does not deform or collapse. Since it does not melt when heated, this type of plastic is classified as heat-resistant. It is relatively safe for food storage.

PS

Polystyrene is the material most commonly used to make disposable tableware and, paradoxically, it is the worst suited for these purposes. Why? This is due to the fact that polystyrene under the influence of high temperatures actively releases toxic chemical compounds. Although it is cheap, very light (it is comfortable to hold and easy to transport), and strong enough to withstand a certain amount of liquid and other substances, it should never be used as a container for storing hot foods. . If it is impossible to avoid the use of disposable tableware, it is still preferable to choose paper products.

Other types

The classification of plastics includes all other types of plastics in this group. That is, those that, for certain reasons, cannot be included in the categories described above.

Sometimes one of the types of PVC is mistakenly attributed to them, since, without knowing all its features, they cannot the right way evaluate it and refer to desired group materials. This type of plastic can be distinguished by paying attention to the following features:

• the seam located at the bottom of the product is distinguished by two symmetrical influxes that are noticeable to the eye;
• products, in particular bottles, made of PVC, as a rule, are blue or bluish;
• if such plastic is bent, then a white stripe can be clearly seen along the fold line.

Use after processing

Plastic molding is a complex process. However, their processing is not so simple. So, recycled plastics are used in dentistry, for the manufacture of food packaging, in construction, bottles for various liquids, clothes and shoes are produced.

Conclusion

Different types of plastic have different properties and can be used in a variety of industries. Undoubtedly, its use greatly simplifies our lives. However, it is important to use it wisely so as not to harm your own body. To do this, it is important to navigate the types of plastics, know their inherent characteristics and be able to distinguish them from each other.

Be careful. Whenever possible, use only those types of plastic that are safe for your health and the health of your loved ones. And the information contained in this article will help you in this matter.