Examples of polymers. Special mechanical properties. Physical properties of polymers

Polymer

Polymer- a high-molecular compound, a substance with a large molecular weight (from several thousand to several million), consists of a large number of repeating atomic groups of the same or different structure - constituent units, interconnected by chemical or coordination bonds into long linear ones (for example, cellulose) or branched (for example, amylopectin) chains, as well as spatial three-dimensional structures.

Often in its structure one can distinguish a monomer - a repeating structural fragment that includes several atoms. Polymers consist of a large number of repeating groups (units) of the same structure, such as polyvinyl chloride (-CH2-CHCl-) n, natural rubber, etc. High molecular weight compounds, the molecules of which contain several types of repeating groups, are called copolymers.

A polymer is formed from monomers as a result of polymerization or polycondensation reactions. Polymers include numerous natural compounds: proteins, nucleic acids, polysaccharides, rubber and other organic substances. In most cases, the concept refers to organic compounds, but there are also many inorganic polymers. A large number of polymers are obtained synthetically based on the simplest compounds of elements of natural origin through polymerization reactions, polycondensation and chemical transformations. The names of polymers are formed from the name of the monomer with the prefix poly-: poly ethylene, poly propylene, poly vinyl acetate...

Due to their valuable properties, polymers are used in mechanical engineering, the textile industry, agriculture and medicine, automobile and shipbuilding, and in everyday life (textiles and leather goods, dishes, glue and varnishes, jewelry and other items). Rubbers, fibers, plastics, films and paint coatings are made from high-molecular compounds. All tissues of living organisms are high-molecular compounds.

Polymer Science

Synthetic polymers. Artificial polymer materials

Man has been using natural polymer materials in his life for a long time. These are leather, fur, wool, silk, cotton, etc., used for the manufacture of clothing, various binders (cement, lime, clay), which, with appropriate processing, form three-dimensional polymer bodies, widely used as building materials. However industrial production The development of chain polymers began at the beginning of the 20th century, although the prerequisites for this were created earlier.

Almost immediately, the industrial production of polymers developed in two directions - by processing natural organic polymers into artificial polymer materials and by producing synthetic polymers from organic low-molecular compounds.

In the first case, large-scale production is based on cellulose. The first polymer material from physically modified cellulose – celluloid – was obtained at the beginning of the 20th century. Large-scale production of cellulose ethers and esters was established before and after World War II and continues to this day. Films, fibers, paints and varnishes and thickeners are produced on their basis. It should be noted that the development of cinema and photography was possible only thanks to the advent of transparent nitrocellulose film.

The production of synthetic polymers began in 1906, when L. Baekeland patented the so-called bakelite resin - a condensation product of phenol and formaldehyde, which turns into a three-dimensional polymer when heated. For decades it has been used to make housings for electrical appliances, batteries, televisions, sockets, etc., and is now more often used as a binder and adhesive.

Classification of polymers

Based on their chemical composition, all polymers are divided into organic, organoelement, and inorganic.

• Organic polymers. Formed with the participation of organic radicals (CH3, C6H5, CH2). These are resins and rubbers.
• Organoelement polymers. They contain organic radicals in the main chain inorganic atoms(Si, Ti, Al), combined with organic radicals. They don't exist in nature. An artificially obtained representative is organosilicon compounds.
• Inorganic polymers. They are based on oxides of Si, Al, Mg, Ca, etc. There is no hydrocarbon skeleton. These include ceramics, mica, asbestos.

It should be noted that technical materials often use combinations of individual groups of polymers. These are composite materials (for example, fiberglass).

Based on the shape of macromolecules, polymers are divided into linear, branched, ribbon, spatial, and flat.

Based on their phase composition, polymers are divided into amorphous and crystalline.

Amorphous polymers are single-phase and built from chain molecules collected in packs. Packs can move relative to other elements.

Crystalline polymers are formed when their macromolecules are sufficiently flexible and form a structure.

Based on polarity, polymers are divided into polar and nonpolar. Polarity is determined by the presence in their composition of dipoles - molecules with an isolated distribution of positive and negative charges. In nonpolar polymers, the dipole moments of atomic bonds are mutually compensated.

With respect to heat, polymers are divided into thermoplastic and thermosetting.

Natural organic polymers

Natural organic polymers are formed in plant and animal organisms. The most important of them are polysaccharides, proteins and nucleic acids, of which the bodies of plants and animals largely consist and which ensure the very functioning of life on Earth. It is believed that the decisive stage in the emergence of life on Earth was the formation of more complex - high-molecular - molecules from simple organic molecules.

Features of polymers

Special mechanical properties:

• elasticity - the ability to undergo high reversible deformations under a relatively small load (rubbers);
• low fragility of glassy and crystalline polymers (plastics, organic glass);
• the ability of macromolecules to orient under the influence of a directed mechanical field (used in the manufacture of fibers and films).

Features of polymer solutions:

• high solution viscosity at low polymer concentration;
• The dissolution of the polymer occurs through the swelling stage.

Special Chemical properties:

• the ability to dramatically change its physical and mechanical properties under the influence of small quantities of a reagent (vulcanization of rubber, tanning of leather, etc.).

The special properties of polymers are explained not only by their high molecular weight, but also by the fact that macromolecules have a chain structure and have a unique inanimate nature property - flexibility.

Polymers, or macromolecules, are very large molecules formed by the bonds of many small molecules, called constituent units, or monomers. The molecules are so large that their properties do not change significantly when several of these building blocks are added or removed. The term "polymer materials" is a general one. It combines three broad groups of synthetic plastics, namely: polymers; plastics and their morphological variety - polymer composite materials (PCMs) or, as they are also called, reinforced plastics. What is common to the listed groups is that their obligatory part is the polymer component, which determines the basic thermal deformation and technological properties of the material. The polymer component is an organic high-molecular substance obtained as a result of a chemical reaction between the molecules of the original low-molecular substances - monomers.

Polymers are usually called high-molecular substances (homopolymers) with additives introduced into them, namely stabilizers, inhibitors, plasticizers, lubricants, antiradicals, etc. Physically, polymers are homophasic materials; they retain all the physicochemical features inherent in homopolymers.

Plastics are polymer-based composite materials containing dispersed or short-fiber fillers, pigments and other bulk components. Fillers do not form a continuous phase. They (dispersed medium) are located in a polymer matrix (dispersed medium). Physically, plastics are heterophasic materials with isotropic (identical in all directions) physical macroproperties.

Plastics can be divided into two main groups - thermoplastic and thermoset. Thermoplastics are those that, once formed, can be melted and remolded; thermosetting, once formed, no longer melts and cannot take another shape under the influence of temperature and pressure. Almost all plastics used in packaging are thermoplastics, such as polyethylene and polypropylene (members of the polyolefin family), polystyrene, polyvinyl chloride, polyethylene terephthalate, nylon (nylon), polycarbonate, polyvinyl acetate, polyvinyl alcohol, and others.

Plastics can also be categorized based on the method used to polymerize them into polymers produced by addition to polycondensation. Addition polymers are produced by a mechanism that involves either free radicals or ions, in which small molecules quickly add to the growing chain without forming companion molecules. Polycondensation polymers are produced by reacting functional groups in molecules with each other so that a long chain of polymer is formed in stages, and typically produces a low molecular weight co-product, such as water, during each reaction step. Most packaging polymers, including polyolefins, polyvinyl chloride and polystyrene, are addition polymers.

The chemical and physical properties of plastics are determined by their chemical composition, average molecular weight and molecular weight distribution, processing (and use) history, and the presence of additives.

Polymer reinforced materials are a type of plastic. They differ in that they use not dispersed, but reinforcing, that is, reinforcing fillers (fibers, fabrics, tapes, felt, single crystals), which form an independent continuous phase in the PCM. Certain varieties of such PCMs are called laminated plastics. This morphology makes it possible to obtain plastics with very high deformation-strength, fatigue, electrical, acoustic and other target characteristics that meet the highest modern requirements.

The polymerization reaction is the sequential addition of molecules of unsaturated compounds to each other to form a high-molecular product - a polymer. Alkene molecules that undergo polymerization are called monomers. The number of elementary units repeated in a macromolecule is called the degree of polymerization (denoted n). Depending on the degree of polymerization, substances with different properties can be obtained from the same monomers. Thus, short chain polyethylene (n = 20) is a liquid with lubricating properties. Polyethylene with a chain length of 1500-2000 links is a hard but flexible plastic material from which films can be made, bottles and other glassware, elastic pipes, etc. Finally, polyethylene with a chain length of 5-6 thousand links is a solid substance from which cast products, rigid pipes, and strong threads can be prepared.

If a small number of molecules take part in the polymerization reaction, then low molecular weight substances are formed, for example dimers, trimers, etc. The conditions for polymerization reactions are very different. In some cases, catalysts and high pressure are required. But the main factor is the structure of the monomer molecule. Unsaturated (unsaturated) compounds enter into the polymerization reaction due to the cleavage of multiple bonds. The structural formulas of polymers are briefly written as follows: the formula of the elementary unit is enclosed in brackets and the letter p is placed at the bottom right. For example, the structural formula of polyethylene is (-CH2-CH2-)n. It is easy to conclude that the name of the polymer is composed of the name of the monomer and the prefix poly-, for example polyethylene, polyvinyl chloride, polystyrene, etc.

Polymerization is a chain reaction, and in order for it to begin, it is necessary to activate the monomer molecules with the help of so-called initiators. Such reaction initiators can be free radicals or ions (cations, anions). Depending on the nature of the initiator, radical, cationic or anionic polymerization mechanisms are distinguished.

The most common hydrocarbon polymers are polyethylene and polypropylene.

Polyethylene is produced by the polymerization of ethylene: Polypropylene is produced by the stereospecific polymerization of propylene (propene). Stereospecific polymerization is the process of obtaining a polymer with a strictly ordered spatial structure. Many other compounds are capable of polymerization - ethylene derivatives having the general formula CH2 = CH-X, where X are various atoms or groups of atoms.

Types of polymers:

Polyolefins are a class of polymers of the same chemical nature (chemical formula -(CH2)-n) with a diverse spatial structure of molecular chains, including polyethylene and polypropylene. By the way, all carbohydrates, for example, natural gas, sugar, paraffin and wood have a similar chemical structure. In total, 150 million tons of polymers are produced annually in the world, and polyolefins make up approximately 60% of this amount. In the future, polyolefins will surround us in much to a greater extent than today, so it’s useful to take a closer look at them.

The complex of properties of polyolefins, including such as resistance to ultraviolet radiation, oxidizing agents, tearing, puncturing, shrinkage during heating and tearing, varies within very wide limits depending on the degree of orientational stretching of molecules during the production process polymer materials and products.

It should be especially emphasized that polyolefins are environmentally cleaner than most materials used by humans. The production, transportation and processing of glass, wood and paper, concrete and metal uses a lot of energy, the production of which inevitably pollutes the environment. When disposing of traditional materials, harmful substances are also released and energy is consumed. Polyolefins are produced and disposed of without separating harmful substances and with minimal energy consumption, and when burning polyolefins, a large amount of clean heat is released with by-products in the form of water vapor and carbon dioxide. Polyethylene

About 60% of all plastics used for packaging are polyethylene, mainly due to its low cost, but also due to its excellent properties for many applications. High density polyethylene (HDPE - low pressure) has the simplest structure of all plastics, consisting of repeating ethylene units. -(CH2CH2)n- high density polyethylene. Low density polyethylene (LDPE - high pressure) have the same chemical formula, but differs in that its structure is branched. -(CH2CHR) n- low density polyethylene Where R can be -H, -(CH2)nCH3, or a more complex structure with secondary branching.

Polyethylene, due to its simple chemical structure, is easily folded into crystal lattice, and therefore tends to high degree crystallinity. Chain branching interferes with this ability to crystallize, resulting in fewer molecules per unit volume, and therefore lower density.

LDPE - high-density polyethylene. Plastic, slightly matte, waxy to the touch, processed by extrusion into blown film or flat film through a flat die and chilled roller. LDPE film is strong in tension and compression, resistant to impact and tear, and durable at low temperatures. It has a peculiarity - a rather low softening temperature (about 100 degrees Celsius).

HDPE - low-density polyethylene. HDPE film is rigid, durable, and less waxy to the touch compared to LDPE films. It is obtained by extruding a blown hose or extruding a flat hose. The softening temperature of 121°C allows for steam sterilization. The frost resistance of these films is the same as that of LDPE films. Resistance to tension and compression is high, and resistance to impact and tear is less than that of LDPE films. HDPE films are an excellent barrier to moisture. Resistant to fats and oils. The “rustling” T-shirt bag (“rustling”) in which you pack your purchases is made of HDPE.

There are two main types of HDPE. The "older" type, produced first in the 1930s, polymerizes at high temperatures and pressures, conditions that are energetic enough to allow a significant occurrence of chain reactions that lead to the formation of branches, both long and short. chains. This type of HDPE is sometimes called high-density polyethylene (HDPE, HDPE, due to the high pressure), if there is a need to distinguish it from linear low-density polyethylene, a “younger” type of LDPE. At room temperature, polyethylene is a fairly soft and flexible material. It retains this flexibility well in cold conditions, making it suitable for frozen food packaging. However, when elevated temperatures ah, such as 100 °C, it becomes too soft for a number of applications. HDPE has a higher brittleness and softening point than LDPE, but is still not suitable for hot fill containers.

About 30% of all plastics used for packaging are HDPE. It is the most widely used plastic for bottles due to its low cost, ease of molding, and excellent performance for many applications. In its natural form, HDPE has a milky white, translucent appearance, and is thus not suitable for applications where exceptional transparency is required. One disadvantage of using HDPE in some of its applications is its tendency to undergo stress cracking when exposed to the environment, defined as failure plastic container under conditions of simultaneous stress and contact with the product, which individually does not lead to destruction. External stress cracking in polyethylene is related to the crystallinity of the polymer.

LDPE is the most widely used packaging polymer, accounting for approximately one third of all packaging plastics. Due to its low crystallinity, it is a softer, more flexible material than HDPE. It is the preferred material for films and bags due to its low cost. LDPE offers better clarity than HDPE, but still lacks the crystal clarity desired for some packaging applications.

PP - polypropylene. Excellent transparency (with rapid cooling during the shaping process), high melting point, chemical and water resistance. PP allows water vapor to pass through, which makes it indispensable for “anti-fog” packaging of food products (bread, herbs, groceries), as well as in construction for hydro-windproofing. PP is sensitive to oxygen and oxidizing agents. It is processed by extrusion blowing or through a flat die with pouring onto a drum or cooling in a water bath. Has good transparency and gloss, high chemical resistance, especially to oils and fats, does not crack when exposed to environment.

PVC - polyvinyl chloride. It is rarely used in its pure form due to its fragility and inelasticity. Inexpensive. Can be processed into film by blown extrusion or flat-slot extrusion. The melt is highly viscous. PVC is thermally unstable and corrosive. When overheated and burned, it releases a highly toxic chlorine compound - dioxin. Widespread in the 60s and 70s. Being replaced by more environmentally friendly polypropylene.

Polymer Identification

Consumers of polymer films often face the practical task of recognizing the nature of the polymer materials from which they are made. The basic properties of polymer materials, as is well known, are determined by the composition and structure of their macromolecular chains. Hence it is clear that to identify polymer films to a first approximation, an assessment of the functional groups included in the macromolecules may be sufficient. Some polymers, due to the presence of hydroxyl groups (-OH), gravitate toward water molecules. This explains the high hygroscopicity of, for example, cellulose films and a noticeable change in their performance characteristics when moistened. In other polymers (polyethylene terephthalate, polyethylenes, polypropylene, etc.) such groups are absent altogether, which explains their fairly good water resistance.

The presence of certain functional groups in a polymer can be determined on the basis of existing and scientifically based instrumental research methods. However, the practical implementation of these methods is always associated with relatively large time costs and is due to the availability of appropriate types of rather expensive test equipment that requires appropriate qualifications for its use. At the same time, there are quite simple and “fast” practical methods for recognizing the nature of polymer films. These methods are based on the fact that polymer films made from various polymer materials differ from each other in their external signs, physical and mechanical properties, as well as in relation to heating, the nature of their combustion and solubility in organic and inorganic solvents.

In many cases, the nature of the polymer materials from which polymer films are made can be determined by external characteristics, when studying which special attention should be paid to the following features: surface condition, color, gloss, transparency, rigidity and elasticity, tear resistance, etc. For example , non-oriented films made of polyethylene, polypropylene and polyvinyl chloride are easily stretched. Films made of polyamide, cellulose acetate, polystyrene, oriented polyethylene, polypropylene, and polyvinyl chloride do not stretch well. Cellulose acetate films are not tear-resistant, easily split in a direction perpendicular to their orientation, and also rustle when crushed. Polyamide and lavsan (polyethylene terephthalate) films are more tear-resistant and also rustle when crumpled. At the same time, films made of low-density polyethylene and plasticized polyvinyl chloride do not rustle when crushed and have high tear resistance. The results of studying the external characteristics of the polymer film under study should be compared with the characteristic characteristics given in Table. 1, after which some preliminary conclusions can be drawn.

Table 1. External signs

Table 2. Physical and mechanical characteristics at 20°C

Table 3. Combustion characteristics. Chemical resistance

Thus, the results of a comprehensive assessment of individual properties of polymer films in accordance with the methods outlined above make it possible, in most cases, to fairly reliably establish the type of polymer material from which the studied samples are made. If difficulties arise in determining the nature of the polymer materials from which the films are made, it is necessary to conduct additional studies of their properties using chemical methods. To do this, samples can be subjected to thermal decomposition (pyrolysis), and the presence of characteristic atoms (nitrogen, chlorine, silicon, etc.) or groups of atoms (phenol, nitro groups, etc.) prone to specific reactions that result in a very definite indicator effect. The practical methods outlined above for determining the type of polymer materials from which polymer films are made are to a certain extent subjective in nature, and, therefore, cannot guarantee their one hundred percent identification. If such a need nevertheless arises, then you should use the services of special testing laboratories, whose competence is confirmed by relevant certification documents.

Melt flow rate

The melt flow rate of a polymer material is the mass of polymer in grams extruded through a capillary at a certain temperature and a certain pressure drop in 10 minutes. The melt flow rate is determined using special instruments called capillary viscometers. At the same time, the dimensions of the capillary are standardized: length 8.000±0.025 mm; diameter 2.095±0.005 mm; the internal diameter of the viscometer cylinder is 9.54±0.016 mm. Non-integer values ​​of capillary sizes are due to the fact that for the first time the method of determining the melt flow index appeared in countries with the English system of measures. The conditions recommended for determining the melt flow rate are regulated by relevant standards. GOST 11645-65 recommends loads of 2.16 kg, 5 kg and 10 kg and temperatures that are multiples of 10°C. ASTM 1238-62T (USA) recommends temperatures from 125°C to 275°C and loads from 0.325 kg to 21.6 kg. Most often, the melt flow rate is determined at a temperature of 190°C and a load of 2.16 kg.

The value of the fluidity index for various polymer materials is determined at various loads and temperatures. Therefore, it must be borne in mind that the absolute values ​​of the flow rate are comparable only for the same material. For example, you can compare the melt flow index of low-density polyethylene of different brands. Comparing the values ​​of the fluidity indicators of high- and low-density polyethylene does not make it possible to directly compare the fluidity of both materials. Since the first is determined with a load of 5 kg, and the second with a load of 2.16 kg.

It should be noted that the viscosity of polymer melts significantly depends on the applied load. Since the yield index of a particular polymer material is measured only at one load value, this indicator characterizes only one point on the entire flow curve in the region of relatively low shear stresses. Therefore, polymers that differ slightly in the branching of macromolecules or in molecular weight, but with the same melt flow rate, can behave differently depending on processing conditions. However, despite this, the melt flow indicator for many polymers sets the boundaries of the recommended technological parameters of the processing process. The significant spread of this method is due to its speed and accessibility. Extrusion film production processes require high melt viscosities; therefore, grades of raw materials with low rate melt fluidity.

Based on materials from the company "NPL Plastic"

Polymer materials (plastics, plastics) are, as a rule, hardened composite compositions in which polymers and oligomers serve as binders. They received the widespread name “plastics” (which is not entirely correct) because when processed into products they are in a plastic (fluid) state. Therefore, scientifically based names are “polymer materials”, “polymer-based composite materials”.

Polymers (from the Greek poly - many, meres - parts) are high-molecular chemical compounds, the molecules of which consist of a huge number of repeatedly repeating elementary units of the same structure. Such molecules are called macromolecules. Depending on the arrangement of atoms and atomic groups (elementary units) in them, they can have a linear (chain-like), branched, network and spatial (three-dimensional) structure, which determines their physical, mechanical and chemical properties. The formation of these molecules is possible due to the fact that carbon atoms easily and firmly combine with each other and with many other atoms.

There are also formopolymers (prepolymers, prepolymers), which are compounds containing functional groups and capable of participating in reactions of growth or cross-linking of a polymer chain with the formation of high-molecular linear and network polymers. First of all, these are also liquid polyol products with excess polyisocyanates or other compounds in the production of polyurethane products.

By origin, polymers can be natural, artificial and synthetic.

Natural polymers are mainly biopolymers - proteins, starch, natural resins (pine rosin), cellulose, natural rubber, bitumen, etc. Many of them are formed during the process of biosynthesis in the cells of living and plant organisms. However, in most cases, artificial and synthetic polymers are used in industry.

The main raw materials for the production of polymers are by-products of the coal and oil industries, fertilizer production, natural gas, cellulose and other substances. The process of formation of such macromolecules and the polymer as a whole is caused by exposure of the original substance (monomer) to a stream of light rays, electrical discharges of high-frequency currents, heat, pressure, etc.

Depending on the method of producing polymers, they can be divided into polymerization, polycondensation and modified natural polymers. The process of producing polymers by sequentially attaching monomer units to each other as a result of the opening of multiple (unsaturated) bonds is called a polymerization reaction. During this reaction, a substance can change from a gaseous or liquid state to a very thick liquid or solid state. In this case, the reaction is not accompanied by the separation of any low molecular weight by-products. Both monomer and polymer are characterized by the same elemental composition. The polymerization reaction produces polyethylene from ethylene, polypropylene from propylene, polyisobutylene from isobutylene and many other polymers.

During the polycondensation reaction, the atoms of two or more monomers are rearranged and low molecular weight by-products (for example, water, alcohols or other low molecular weight substances) are released from the reaction sphere. The polycondensation reaction produces polyamides, polyesters, epoxy, phenol-formaldehyde, organosilicon and other synthetic polymers, also called resins.

Depending on their relationship to heat and solvents, polymers, as well as materials based on them, are divided into thermoplastic and thermosetting.

Thermoplastic polymers (thermoplastics), when processed into products, can repeatedly transition from a solid state of aggregation to a viscous-fluid state (melt), and when cooled, harden again. They, as a rule, do not have a high temperature of transition to a viscous-fluid state, and are well processed by injection molding, extrusion and pressing. The shaping of products from them is a physical process, which consists in the hardening of a liquid or softened material when it is cooled and no chemical changes occur. Most thermoplastics are also soluble in suitable solvents. Thermoplastic polymers have a linear or slightly branched structure of macromolecules. These include certain types of polyethylene, polyvinyl chloride, fluoroplastic, polyurethanes, bitumen, etc.

Thermosets (thermosets) include polymers whose processing into products is accompanied by a chemical reaction of the formation of a network or three-dimensional polymer (hardening, cross-linking of chains) and the transition from a liquid to a solid state occurs irreversibly. Their cured state is thermostable, and they lose the ability to re-transition into a viscous-fluid state (for example, phenolic, polyester, epoxy polymers, etc.).

Classification and properties of polymer materials

Depending on the composition or number of components, polymeric materials are divided into unfilled, represented by only one binder (polymer) - organic glass, in most cases polyethylene film; filled, which to obtain the required set of properties may include fillers, plasticizers, stabilizers, hardeners, pigments - fiberglass, textolite, linoleum and gas-filled (foam and foam plastics) - polystyrene foam, polyurethane foam, etc.

Depending on the physical condition at normal temperature and viscoelastic properties, polymer materials are hard, semi-rigid, soft and elastic.

Hard materials are hard, elastic materials of an amorphous structure with an elastic modulus of more than 1000 MPa. They break brittlely with negligible elongation at break. These include phenoplasts, aminoplasts, plastics based on glyphthalic and other polymers.

The density of polymer materials is most often in the range of 900-1800 kg/m3, i.e. they are 2 times lighter than aluminum and 5.6 times lighter than steel. At the same time, the density of porous polymer materials (foams) can be 30..15 kg/m3, and dense ones - exceed 2,000 kg/m3.

The compressive strength of polymer materials in most cases exceeds many traditional building materials (concrete, brick, wood) and is about 70 MPa for unfilled polymers, more than 200 MPa for reinforced plastics, 100.150 MPa for tensile materials for materials with powder filler, and 100.150 MPa for fiberglass materials. 276.414 MPa and more.

The thermal conductivity of such materials depends on their porosity and production technology. For foam and foam plastics it is 0.03.0.04 W/m-K, for the rest it is 0.2.0.7 W/mK or 500.600 times lower than for metals.

The disadvantage of many polymer materials is low heat resistance. For example, most of them (based on polystyrene, polyvinyl chloride, polyethylene and other polymers) have a heat resistance of 60.80 °C. Based on phenol-formaldehyde resins, heat resistance can reach 200 °C, and only on silicone polymers - 350 °C.

Being hydrocarbon compounds, many polymeric materials are combustible or have low fire resistance. Products based on polyethylene, polystyrene, and cellulose derivatives are classified as highly flammable and combustible with abundant soot release. Products based on polyvinyl chloride, polyester fiberglass, and phenolic plastics, which only become charred at elevated temperatures, are difficult to burn. Polymer materials with a high content of chlorine, fluorine or silicon are non-flammable.

Many polymer materials, during processing, combustion and even heating, emit substances hazardous to health, such as carbon monoxide, phenol, formaldehyde, phosgene, hydrochloric acid, etc. Their significant disadvantages are also their high coefficient of thermal expansion - from 2 to 10 times higher than at steel.

Polymer materials are characterized by shrinkage during hardening, reaching 5.8%. Most of them have a low modulus of elasticity, much lower than that of metals. Under prolonged loads they exhibit high creep. With increasing temperature, creep increases even more, which leads to unwanted deformations.

Preface

All types of polymeric materials are substances in which each molecule is a chain of tens or hundreds of thousands of identical groups of atoms connected in series, and the same group of atoms is rhythmically repeated many times.

Contents

The main polymeric materials include resins and plastics. Depending on whether it is a thermoplastic polymer or a thermoset, the material can either soften and harden many times, or, with a single heating, turn into a solid state and permanently lose its ability to melt. The most commonly used modern polymer materials are dispersions, latexes and adhesives.

What are building polymer materials

What are polymer materials and how are they used in construction? All types of polymeric materials are substances in which each molecule is a chain of tens or hundreds of thousands of identical groups of atoms connected in series, and the same group of atoms is rhythmically repeated many times.

The main types of polymer materials are divided into thermoplastic and thermosetting. Thermoplastic polymers are capable of repeatedly softening and hardening with changes in temperature, and also easily swell and dissolve in organic solvents. These include polystyrene, polyethylene and polyvinyl chloride (polyvinyl chloride) resins and plastics.

The main property of thermosetting polymer materials is the transition when heated to an insoluble solid state and the irreversible loss of the ability to melt. Such polymers include phenol-formaldehyde and urea-formaldehyde, polyester and epoxy resins.

Certain types of polymer materials in construction, under the influence of heat, light and atmospheric oxygen, change their properties over time: they lose flexibility, elasticity, in other words, they age.

To prevent aging of modern polymer building materials, special stabilizers (anti-aging agents) are used, which are various organometallic compounds of lead, barium, cadmium, etc. For example, Tinuvin P is used as a stabilizer.

What polymer materials are there and what their main characteristics are, you will learn on this page.

Polymer plastic materials and their properties

One of the main types of polymeric materials is plastics. They are a group of organic materials based on synthetic or natural resin-like high-molecular substances that can be molded under heat and pressure, stably maintaining their given shape.

Polymer plastic materials have good thermal insulation and electrical insulation qualities, corrosion resistance and durability. The average density of plastics is 15-2200 kg/m3; compressive strength - 120-160 MPa. Plastics are endowed with good electrical and thermal insulation properties, corrosion resistance and durability. Some of them are transparent and have high adhesive properties, and also tend to form thin films and protective coatings. Due to their properties, these polymeric materials are widely used in construction, mainly in combination with binders, metals and stone materials.

Plastics consist of a binder - a polymer, a filler, a plasticizer and a curing accelerator. Mineral dyes are also used in the production of colored plastics.

Organic and mineral powders, asbestos, wood and glass fibers, paper, glass and cotton fabrics, wood veneer, asbestos cardboard, etc. are used as fillers in the manufacture of this type of polymer materials. Fillers not only reduce the cost of the material, but also improve certain properties of plastics : Increases hardness, strength, acid resistance and heat resistance. They must be chemically inert, low volatile and non-toxic. Plasticizers in the manufacture of plastics are zinc acid, aluminum stearate and others, which give the material greater plasticity. Catalysts (accelerators) are used in plastics to speed up curing. An example of a catalyst is lime or methenamine, which are used to cure phenol-formaldehyde polymer.

Synthetic polymer materials and their applications

According to the production method, synthetic polymer materials are divided into two classes: class A - polymers obtained by chain polymerization; class B - polymers obtained by polycondensation and stepwise polymerization.

The polymerization process is a combination of identical and different molecules. No by-products are formed during polymerization.

The polycondensation process is a combination large quantity identical and different polyreactive molecules of low molecular weight substances, resulting in the formation of a high molecular weight substance. During the polycondensation process, water, hydrogen chloride, ammonia and other substances are released.

Silicone resins- This is a special group of high-molecular compounds. The peculiarity of these polymer building materials is that they have the properties of both organic and inorganic substances.

The physical and mechanical characteristics of these polymeric materials are virtually unaffected by temperature fluctuations compared to conventional resins, and they are also highly hydrophobic and heat resistant. Organosilicon resins are used to produce various products that are resistant to elevated temperatures (400-500°C).

The main area of ​​application of these synthetic polymeric materials is the production of concrete and mortars to increase their durability. They are also used in the form of protective coatings on natural and artificial stone materials (concrete, limestone, travertine, marble, etc.). Impregnation has a protective effect for 6-10 years, after which it should be renewed.

For impregnation surfaces of products made of natural stone and other building structures, water-repellent organosilicon liquids (GKZh) are used, which are dissolved before use. organic solvents, as well as an aqueous 50% emulsion (milk- white), which is mixed with water in a ratio of 1:10 before use.

Polyvinyl acetate dispersion (PVA) is a product of the polymerization of vinyl acetate into aquatic environment in the presence of an initiator and a protective colloid. It is a viscous, white, homogeneous liquid, without screams or foreign inclusions.

Depending on the viscosity, PVA is produced in three grades: N - low-viscosity, C - medium-viscosity, B - high-viscosity. It is used in the production of polymer-cement mortars, mastics, and pastes, which are used in facing work.

Synthetic latex SKS-65GP- a product of co-polymerization of butadiene with styrene in a ratio of 35:65 (by weight) in an aqueous emulsion using nekal and sodium soap of synthetic fatty acids as an emulsifier. Latex SKS-65GP is used in the production of polymer concrete, emulsion paints, mastics and pastes used in facing work. Latex is also used in various coatings.

Physico-chemical properties of this polymer building material latex SKS-65GP:

• dry matter content,%, not less than 47;
• content of unpolymerized styrene, %, not more than 0.08;
• hydrogen ion concentration (pH), not less than 11;
• surface tension, dynes/cm2, no more than 40;
• viscosity, s - 11-15;
• Ash content,%, no more than 1.5.

Synthetic latex SKS-ZOSHR is a product of joint polymerization of butadiene with styrene in an aqueous emulsion, used as a binder or adhesive material for facing work.

Physico-chemical properties of SKS-ZOSHR latex:

• dry matter content,%, not less than 33;
• gelatinization temperature, °C, not higher than 14;
• free alkali content, %, not more than 0.15.

Characteristics of polymer adhesive materials

Polymer adhesive materials are produced in the form of liquids, powders and films.

There are two types of liquid adhesives. The first type of adhesive compositions are rubbers, resins or cellulose derivatives dissolved in an organic volatile solvent (alcohol or acetone). After the solvent evaporates, a solid adhesive joint is formed. The second type of adhesive composition is aqueous solutions resins specially prepared for adhesives. When properly stored, such solutions do not thicken for several months. Liquid adhesives contain 40-70% solid adhesive.

The most common liquid adhesives are melamine-formaldehyde, phenol-formaldehyde, urea-formaldehyde, rubber, epoxy, polyvinyl acetate, as well as adhesives with the addition of silicones.

CMC glue (sodium salt of carboxymethylcellulose) is used in the manufacture of mastics and solutions used in.

Carbinol glue (vinylacetylene carbolene) is a viscous transparent liquid of light orange color with high adhesive ability. That's why it is called universal. It is capable of gluing various materials, even such as concrete, stone, metal, wood. Hardened carbinol glue is resistant to oils, acids, alkalis, gasoline, acetone and water.

Concentrated nitric acid or benzoyl peroxide are used as catalysts to accelerate the hardening of carbinol glue. The latter is an explosive powder, so it should be stored away from fire.

Carbinol glue is produced on the basis of carbinol syrup (100 parts by weight) in two compositions: in the 1st one, benzoyl peroxide (1-3 parts by weight) is added as a hardener, in the 2nd - concentrated nitric acid (1-2 parts by weight). h.).

Carbinol glue is stored at a temperature of 20°C and in the dark, since under the influence of light it loses its adhesive ability.

Epoxy adhesive is a transparent viscous liquid of light brown color with high adhesive ability. It is used for gluing stone, concrete, ceramic tiles. The hardened seam of epoxy adhesive is resistant to acids, alkalis, solvents, water, as well as to high mechanical loads. The hardeners for epoxy resin are polyethylene polyamine or hexamethylenediamine, and the plasticizer is dibutyl phtholate.

It's amazing how diverse the objects around us and the materials from which they are made are. Previously, around the 15th-16th centuries, the main materials were metals and wood, a little later glass, and almost always porcelain and earthenware. But today’s century is the time of polymers, which will be discussed further.

Concept of polymers

Polymer. What it is? You can answer from different points of view. On the one hand, it is a modern material used to make many household and technical items.

On the other hand, we can say that it is a specially synthesized synthetic substance obtained with predetermined properties for use in a wide specialization.

Each of these definitions is correct, only the first from a household point of view, and the second from a chemical point of view. Another chemical definition is the following. Polymers are compounds based on short sections of a molecular chain - monomers. They are repeated many times, forming a polymer macrochain. Monomers can be both organic and inorganic compounds.

Therefore, the question: “polymer - what is it?” - requires a detailed answer and consideration of all properties and areas of application of these substances.

Types of polymers

There are many classifications of polymers according to various criteria (chemical nature, heat resistance, chain structure, and so on). In the table below we briefly consider the main types of polymers.

There are also polymers of linear, network and branched structure. The basis of polymers allows them to be thermoplastic or thermosetting. They also differ in their ability to deform under normal conditions.

Physical properties of polymer materials

The main two states of aggregation characteristic of polymers are:

• amorphous;
• crystalline.

Each is characterized by its own set of properties and has important practical significance. For example, if a polymer exists in an amorphous state, it means that it can be a viscous flowing liquid, a glass-like substance, or a highly elastic compound (rubbers). It is widely used in the chemical industries, construction, engineering, and the production of industrial goods.

The crystalline state of polymers is rather conditional. In fact, this state alternates with amorphous sections of the chain, and in general the entire molecule turns out to be very convenient for producing elastic, but at the same time high-strength and hard fibers.

Melting points for polymers are different. Many amorphous ones melt at room temperature, and some synthetic crystalline ones can withstand fairly high temperatures (plexiglass, fiberglass, polyurethane, polypropylene).

Polymers can be colored in the most different colors, no limits. Thanks to their structure, they are able to absorb paint and acquire the brightest and most unusual shades.

Chemical properties of polymers

The chemical properties of polymers differ from those of low molecular weight substances. This is explained by the size of the molecule, the presence of various functional groups in its composition, and the total reserve of activation energy.

In general, several main types of reactions characteristic of polymers can be distinguished:

1. Reactions that will be determined by the functional group. That is, if the polymer contains an OH group, characteristic of alcohols, then the reactions in which they will enter will be identical to those of oxidation, reduction, dehydrogenation, and so on).
2. Interaction with NMCs (low molecular compounds).
3. Reactions of polymers with each other to form cross-linked networks of macromolecules (network polymers, branched).
4. Reactions between functional groups within one polymer macromolecule.
5. Disintegration of a macromolecule into monomers (chain destruction).

All of the above reactions occur in practice great importance to obtain polymers with predetermined and convenient properties for humans. Polymer chemistry makes it possible to create heat-resistant, acid- and alkali-resistant materials that at the same time have sufficient elasticity and stability.

Use of polymers in everyday life

The use of these compounds is widespread. Few areas of industry can be recalled National economy, science and technology, which would not require polymer. What is it - polymer farming and widespread use, and what does it end with?

1. Chemical industry (production of plastics, tannins, synthesis of essential organic compounds).
2. Mechanical engineering, aircraft manufacturing, oil refineries.
3. Medicine and pharmacology.
4. Obtaining dyes and pesticides and herbicides, agricultural insecticides.
5. Construction industry (steel alloying, sound and thermal insulation structures, building materials).
6. Manufacturing of toys, dishes, pipes, windows, household items and household utensils.

The chemistry of polymers makes it possible to obtain more and more new materials, completely universal in properties, which have no equal among metals, wood or glass.

Examples of products made from polymer materials

Before naming specific products made from polymers (it is impossible to list them all, there is too much variety), first you need to understand what the polymer provides. The material that is obtained from the Navy will be the basis for future products.

The main materials made from polymers are:

• plastics;
• polypropylenes;
• polyurethanes;
• polystyrenes;
• polyacrylates;
• phenol-formaldehyde resins;
• epoxy resins;
• nylons;
• viscose;
• nylons;
• adhesives;
• films;
• tannins and others.

This is just a small list of the diversity that modern chemistry offers. Well, here it already becomes clear what objects and products are made from polymers - almost any household items, medicine and other areas (plastic windows, pipes, dishes, tools, furniture, toys, films, etc.).

Polymers in various branches of science and technology

We have already touched upon the question of in what areas polymers are used. Examples showing their importance in science and technology include the following:

• antistatic coatings;
• electromagnetic screens;
• housings of almost all household appliances;
• transistors;
• LEDs and so on.

There are no limits to imagination regarding the use of polymer materials in the modern world.

Polymer production

Polymer. What it is? This is practically everything that surrounds us. Where are they made?

1. Petrochemical (oil refining) industry.
2. Special plants for the production of polymer materials and products made from them.

These are the main bases on the basis of which polymer materials are obtained (synthesized).