RTI or rubber-technical products have special characteristics, thanks to which they remain in great demand. Especially modern ones. They have improved indicators of elasticity, impermeability to other materials and substances. Also possess high rates electrical insulating and other qualities. It is not surprising that it is rubber goods that are increasingly used not only in the automotive industry, but also in aviation.
When the vehicle is actively operated and has high mileage, technical condition RTI is significantly reduced.
A little about the features of rubber rubber wear
Aging of rubber and some types of polymers occurs under conditions that are influenced by:
- warmly;
- light;
- oxygen;
- ozone;
- stress / compression / extension;
- friction;
- working environment;
- operational period.
A sharp drop in conditions, especially climatic ones, has a direct impact on the state of rubber goods. Their quality is deteriorating. Therefore, polymer alloys are increasingly used, which are not afraid of lowering degrees and increasing them.
With a decrease in the quality of rubber-technical products, they quickly fail. Often it is the spring-summer period, after the winter cold, that is the turning point. When the temperature on the thermometer rises, the aging rate of rubber goods increases by 2 times.
To ensure the loss of elasticity, for rubber-technical products, it is enough to survive a significant and sharp cold snap. But if the linings and bushings change their geometric shapes, small tears and cracks appear, this will lead to a lack of tightness, which, in turn, leads to breakdowns of systems and connections in the car. The minimum that can manifest itself is a leak.
When comparing rubber products, neoprene is better. Rubber rubber goods are more susceptible to changes. If you do not protect both those and others from the sun, fuels and lubricants, acidic or corrosive liquids, mechanical damage, they will not be able to pass even the minimum operational period specified by the manufacturer.
Features of different rubber goods
The properties of polyurethane and rubber rubber products are completely different. Therefore, the storage conditions will differ.
Polyurethane differs in that it:
- plastic;
- elastic;
- not subject to crumbling (unlike rubber products);
- does not freeze like rubber when the temperature drops;
- does not lose geometric shapes;
- with elasticity, firm enough;
- resistant to abrasive substances and aggressive media.
Obtained by liquid mixing, this material is widely used in the automotive industry. Synthetic polymer is stronger than rubber. With a homogeneous composition, polyurethane retains its properties in different conditions, which simplifies the conditions and characteristics of its use.
As can be seen from the above material, polyurethane benefits from rubber products in terms of properties. But it doesn't apply universally. In addition, silicone alloys are emerging. And what is better - not every driver understands.
Polyurethane takes longer to manufacture technologically. It takes 20 minutes to produce rubber rubber goods. And 32 hours for polyurethane. But rubber is a material born by mechanical mixing. This affects its compositional heterogeneity. And also entails a loss of elasticity and homogeneity of the components. It is rubber hoses and sealed linings that solidify and become harder during storage, crack on the surface and become soft inside. Their term is only 2 - 3 years.
Care and storage
Very much depends on the state and quality of rubber goods important process- control over management. To understand the importance of rubber-technical products, you need to know that violations in their structure lead to the following consequences:
- increased tire wear under heavy load due to improper operation of some systems and connections;
- irregularities in the braking path;
- tangible violations in feedback with steering wheel control;
- destruction of parts-neighbors or in nearby nodes.
Rubber goods must be stored:
- Fold freely so that there is no undue stress or compaction;
- Monitor the necessary temperature regime in the range from zero to plus 25 degrees Celsius;
- In conditions where there is no high humidity, above 65%;
- In rooms where there are no fluorescent lamps (it is better to replace them with incandescent lighting devices);
- In conditions where there is no supply of ozone in large quantities or devices that produce it;
- Paying attention to the presence / absence of direct rays of the sun (there can be no direct exposure to UV as well as conditions that create thermal overheating for rubber products).
With temperature fluctuations during the cold period and hot season, it is necessary to understand that the guaranteed storage period of rubber goods is narrowed to a figure equal to 2 months.
There has always been controversy and controversy around the age or "aging" of tires. In some countries, there were even requirements for manufacturers to print the deadline for use on rubber, just like on food. In some states of America, a brochure describing possible problems if the tires are not changed for a long time.
The chemical process that causes rubber to age is called oxidation. With constant contact with oxygen, the rubber begins to dry and becomes more rigid, which is expressed in cracks on the surface. Most interestingly, the tire begins to age from the inner layers of the carcass, and not from the outside. Due to the hardening of the elements of the composition, the delamination process begins when the rubber fragments peel off from the cord layers.
The aging rate is determined by four main factors.
The quality of the insulating layer. A thin layer from the inside of the tire, made of butyl rubber, is designed to prevent the air pumped into the wheels from escaping. But still, some percentage of oxygen will seep through this layer, causing a chemical reaction with the inner layers.
Air pressure. The effect of oxidation increases in proportion to the air pressure, the more the faster. That is, inflated rubber will age much faster than deflated.
Temperature. High temperatures increase the reactivity of the oxygen, making it easier for it to seep through the rubber seal layer and easier to interact with the inner tread layers.
Frequency of use. While driving, under pressure centrifugal force, the lubricant inside the tire circulates through a system of micropores, that is, it starts to move. Thus, "oiling" the rubber. When the wheels are idle, this does not happen and they begin to dry faster.
German ADAC recommends changing tires every 6 years, regardless of the appearance. In 1990 the group BMW manufacturers, Volkswagen, Mercedes-Benz, General motors made a joint statement that tires over 6 years old are not recommended for use. In 2005, Daimler / Chrysler stated that it recommends that tires be inspected closely after 5 years and replaced after 10. Later, the recommendation was supported by Michelin and Continental.
The Americans looked at car insurance claims for wheel problems and came up with an interesting pattern. 77% of all insurance claims were made in the five southernmost states, and in 87% of these cases, tires were over 6 years old. This indirectly confirms the negative effects of high temperatures over time.
The trend was also monitored that tires with high index speeds lose their condition more slowly. It should also be said that older tires are more prone to uneven wear, especially when it comes to summer tires for cars.
Conclusions:
If the tires on your car are older than 6 years, this does not mean that they should be changed. Just carefully examine them for cracks on the sidewalls, if any, this is a signal that it is time to look for new or used tires. According to the Shinkomplekt website, recently, sales of used wheels in the world are growing due to the poor economic situation.
Spare wheels for jeeps, which hang on the tailgate when inflated and in direct sunlight in summer, age and dry especially quickly. If tires are stored flat and protected from the sun indoors, they will retain their condition longer.
Aging rubber- the oxidation process during long-term storage or during operation, leading to a change in its physical and mechanical properties (Fig. 8.4).
The main cause of aging is the oxidation of rubber, i.e. the addition of oxygen at the site of double bonds in the rubber, as a result of which its molecules are torn apart and shortened.
This leads to a loss of elasticity, embrittlement and, finally, the appearance of a network of cracks on the surface of the aged rubber.
Exposure to heat, light, radiation, mechanical deformation and the presence of oxidation catalysts (salts of metals of variable valence) activate and accelerate the oxidation of rubbers and rubber.
Due to the fact that the role of the factors activating oxidation varies depending on the nature and composition of the rubber, the following types of aging are distinguished.
Heat aging
Table 8.3.
Physical and mechanical properties of the most important aviation rubbers and their application
| Rubber brand | Rubber | σ z, MPa | ε z | θ z | Shore hardness, MPa | t xp,° C | Relation to organic solvents | Application |
| % | ||||||||
| NK NK | 1.6 | 45…60 0,4…0,6 | -50 -50 | Unstable Same | Sealing parts, oil seals, shock absorbers Sealing parts, shock absorbers | |||
| 15RI10 | Nc | 0,3…0,4 | -55 | » | Aircraft wheel cameras | |||
| 14RI324 | Nc | 0,7…1,4 | -56 | » | Aviation tires | |||
| SKN | 1,0…1,4 | -28 | Persistent | Inner layer and fittings for flexible fuel tanks | ||||
| NO-68-1 | Nairnt * SKN | 0,7…1,2 | -55 | Also | Sealing parts for movable joints | |||
| B-14-1 | SKN | 1,6…1,9 | -50 | » | Sealing parts for fixed connections | |||
| IRP-1354 | SKTFV * | 0,6…1,0 | -70 | Unstable | Gaskets, caps, tubes, | |||
| IRP-1287 | SCF | 1,2…15 | -25 | Persistent | Sealing parts, rubber-metal seals | |||
| TRI-1401 | SKTV | 1,0…1,8 | -50 | Unstable | Sealing hoses | |||
| IRP-1338 | SKTV | 5,0 | 0,7…1,2 | -70 | Persistent | Gaskets, caps, tubes |
* Synthetic heat resistant rubber with phenyl and vinyl radicals
Heat aging(thermal, thermo-oxidative) occurs when elevated temperatures 4 as a result of heat-activated rubber oxidation. The rate of heat aging increases with increasing temperature. When exposed to heat, aging occurs throughout the rubber mass.
Rice. 8.4. Effect of aging duration on temporary resistance ( a) and elongation ( b) rubbers based on natural ( 1 ), styrene-butadiene ( 2 ) and chloroprene ( 3 ) rubbers
Light aging is the result of light-activated rubber oxidation. In practice, during the operation of rubber products (tires, balloons, etc.), the combined action of oxygen and light is always observed. The most effective effect is violet and ultraviolet light radiation. Light aging changes the properties of the rubber, starting from the surface layers. The resistance of rubber to light aging is determined by the properties of rubbers and other rubber ingredients, which can act as light filters, light stabilizers, such as zinc oxide or titanium oxide.
Ozone aging- the destruction of rubber under the influence of ozone is one of the most active types of aging. Unlike oxygen aging, which occurs throughout the mass, ozone acts on the rubber surface. By the nature of the reactions occurring, ozone aging of rubbers differs from aging under the influence of atmospheric oxygen... Ozone interacts with rubber at the site of double bonds to form ozonides:
which, turning into isoozonides
decompose with the formation of rubber oxidation products. In the presence of deformation on the rubber surface under the action of ozone, cracks appear, directed perpendicular to tensile stresses. Growing rapidly, they lead to the destruction of rubber.
Under the action of ozone on unstretched rubber, a brittle film appears on its surface, but cracks do not appear. The presence of many antioxidants, such as wax, reduces ozone aging.
Aging due to mechanical stress and oxidative processes, activated by mechanical action, leads to a loss of strength and ductility of rubber. Certain types of rubber products (tires, sleeves, belts, etc.) are exposed to different types deformations, as a result of which oxidative processes intensify with an increase in the amplitude of mechanical deformations. It is necessary to introduce appropriate additives into the rubber to reduce the effect of dynamic loads on the properties of rubber.
Radiation aging under the influence of ionizing radiation leads to a sharp deterioration in the physical and mechanical properties of rubber. When irradiated, free polymer radicals are formed in rubber, which interact with oxygen. In addition, in an air atmosphere, the effect of ozone generated as a result of air ionization can be superimposed on the aging process of rubber under the influence of radiation. The aging rate depends on the radiation dose rate.
Atmospheric aging rubber proceeds in real atmospheric conditions of operation, when there is a combined effect of oxygen, ozone, light, heat, humidity and mechanical stress. The action of all these factors gives rise to numerous simultaneously occurring chemical reactions that contribute to the aging of rubber.
The fight against aging consists in the introduction of antioxidants into the rubber compound, as well as reflectors of sunlight, such as aluminum powder. During operation, to increase the service life of aircraft wheels, they are charged with nitrogen, which significantly slows down the aging of rubber. Aging can be slowed down by observing the established rules for the use and storage of rubber products.
Performance properties rubbers are determined by the competing effects of destruction and crosslinking. The most stable rubbers are based on polysiloxanes, fluoroelastomers and chlorosulfonated polyethylene. The strength and plasticity of such rubbers after 10 years of open exposure to the external environment change by no more than 10 ... 15% . The weather resistance of rubbers is significantly influenced by the presence of fillers, modifiers, vulcanizing additives.
Summary. Despite the existing variety of plastics, rubbers, sealing and sealing materials, there is a great need for the development of new, promising materials focused on the needs of astronautics. It arose in connection with the tightening requirements to reduce the number of technological processes in the manufacture of products, expansion temperature range, efficiency and duration of active existence of spacecraft and launch vehicles. The tasks are set to create new classes of plastics and rubbers, sealants and compounds (including conductive rubbers and sealants; thermo-, frost-, aggressive-resistant rubbers; thermo-, aggressive-resistant anaerobic sealants; heat-conducting compounds that absorb microwave energy). Such materials will make it possible to create structural elements that will determine the technical progress of the 21st century.
Will they serve you for a very, very long time? Do you think that vehicle mileage is the biggest enemy of tires? But this is not the case. Have you ever wondered what happens to tires on cars that are not actually used? In fact, tires can be completely worn out even if your car just stands still.
To begin with, let us remind you that tires are the only vehicle components that directly interact with the road surface. Therefore, no driver should ever forget about them. Remember that every day the tires of a car on the road receive colossal loads. Naturally, over time, the condition of the tires deteriorates. But of course everyone knows about this. After all, everything is logical. , the more tire wear. After all, all tires are designed for a certain mileage.
But unfortunately, for some reason, many car owners forget that, in addition to mileage, rubber can simply age and wear out over time, even if the car is used very rarely or is stationary.
So even if your car is stationary, over time the new rubber will become unusable.
Pay attention to the old cars in the yards, which have been standing for many years and are gradually rotting. Surely you saw how over time in such cars, rubber cracks, swells, which subsequently bursts.
So why do car tires reach this degradation stage even when the car is not in use?
First, let's take a look at the design of the tire. The main ingredient in a tire is obviously rubber. Also in the structure there is a metal layer that strengthens the walls of the tire.
If you've ever seen it torn or torn car tire, you probably noticed that the ends of the metal layer, as well as other layers of the tire, protrude from the cut torn ends of the damaged rubber.
As for the degradation of automobile rubber, we must remember from school that rubber is rubber.
Rubber is an organic material found in plants and trees. Naturally, rubber must be biodegradable.
True, modern rubber is, of course, no longer pure rubber. However, today car tires still rubber, but not natural. The chemical industry does not stand still. For a long time in the world, in the automotive industry, completely synthetic rubber has been used, which is much better than natural rubber both in properties and in cost.
True, despite the fact that the synthetic rubber used in tires is mixed with various polymers, which make the rubber stronger and more resistant to external aggressive conditions, over time, even the synthetic material is subject to aging and destruction. The thing is that carbon is still present in the rubber, which is a natural chemical element that is part of many substances on the planet. So for carbon, which even if produced by an artificial method, it is quite natural to change its state over time.
You may have noticed that as the performance of older tires deteriorates, they become tougher and therefore more brittle. Don't believe me? Then come up to old car, which has been thrown in the yard for a long time and kick the wheel. And you will understand how much old rubber became solid.
Why does rubber get stiff over time?
Vulcanization of rubber, which shows how the chemical bonds of polymers are strengthened
All of this is related to the vulcanization process. Vulcanization is the industrial process of hardening rubber using sulfur and other "accelerators" that create bonds between the molecules that make up the rubber. As a result of this process, the rubber becomes suitable for use in the required conditions, which are associated with constant stress - the rubber becomes stronger. Also, the vulcanization process gives the tires flexibility.
This is achieved through heat and pressure in the conditions of the plant where the car tires... But even after the tires have left the factory, the vulcanization process does not stop. Once the tires are on open space, then they begin to absorb light energy, heat, and also begin to undergo constant friction during the operation of the car. As a result, the chemical compounds in tire rubber continue to cure over time. That is, in fact, the tires are getting stronger and stronger. However, in this case, the flexibility of the rubber is lost. Ultimately, the vulcanization process does its evil deed. Rubber grows stronger over time to the point where it simply starts to crack and collapse.
But this is not the only process that spoils any even if the car is rarely used.
The list of causes of tire degradation also includes a process that leads to the oxidation of rubber. The combination of oxygen and ozone impairs the strength and elasticity of tires.
In particular, the combination of oxygen and ozone destroys the bond between the metal layer of the tires and the rubber.
In addition, as the rubber is constantly heated, the combination of heat and oxygen changes the polymers contained in the rubber. As a result, the rubber from this process begins to harden until it becomes brittle. As a result, cracks appear on the surface of the tires.
The last natural cause of tire aging is water. Rubber is considered waterproof. But after years of tire use, water can seep into the rubber and bind to the metal components that are inside the tire structure. Accordingly, this leads to a deterioration in the tire bonding properties of the metal carcass and the rubber.
Sooner or later, this will lead to a decrease in heat resistance and strength inside the tire. As a result, the internal connections of the tire structure will begin to collapse, which will inevitably lead to tire damage.
Frequent mistakes car owners make that lead to quick tire damage
One of the common mistakes motorists make when using new tires is wrong parking car. This is especially true for novice drivers who do not pay attention to rubber.
For example, many of us, when parking a car, drive into a curb, bump or hole. As a result, the wheel of the car remains under high blood pressure as a result of a decrease in volume due to rubber creasing. This decrease in tire volume results in an increase in air pressure on the tire walls.
As a result, leaving the car constantly on an uneven surface, you will accelerate the oxidation of rubber, and also cause compressed air have a detrimental effect on the internal structure of the tire structure. As a result, accelerates general process degradation of tires and their wear rate naturally increases.
One more a common mistake car owners, which leads to rapid wear and damage to tires, is the operation of the machine with wheels that do not have correct pressure in tires.
For example, if the tires have insufficient pressure, which is recommended by the manufacturer, then during the operation of the car a large amount of heat is generated due to the increase in friction. This is due to the fact that under-inflated tires have a larger contact patch of the tire with the road surface. Ultimately, this accelerates the process of rubber wear.
Over-inflated tires become stiffer and less elastic. As a result, excess pressure appears inside the tires, which is exerted on the metal layer of the tires. As a result, in the event of impacts, the inner layer of tires can become short term get out. Simply put, a "hernia" of the wheel will appear. As a result, you will have to replace the tire with a new one. Especially inflated tires do not like pits and other irregularities.
What is the shelf life of car rubber?
As we have already said, even if you do not operate the car with new tires, sooner or later the tires will become unusable. And the aggressive natural environment that surrounds us will spoil them.
What is the lifespan of tires in terms of time, regardless of the mileage? According to experts and tire manufacturers, this period ranges from 6 to 9 years from the date of their production.
Also, many tire manufacturers advise drivers to change tires for a new one as soon as signs of degradation, wear, etc. were found. For example, when cracks are found in the side walls of tires, when the tread is damaged, when even small hernias are formed, etc.
Therefore, every driver should not rely only on the mileage of the car when deciding whether to change tires for new ones.
Content1. LITERARY REVIEW.
1.1. INTRODUCTION
1.2. AGING OF RUBBERS.
1.2.1. Types of aging.
1.2.2. Heat aging.
1.2.3. Ozone aging.
1.3. ANTI-AGING AGENTS AND ANTI-ZONANTS.
1.4. POLYVINYL CHLORIDE.
1.4.1. PVC plastisols.
2. CHOICE OF THE DIRECTION OF RESEARCH.
3. TECHNICAL CONDITIONS FOR THE PRODUCT.
3.1. TECHNICAL REQUIREMENTS.
3.2. SAFETY REQUIREMENTS.
3.3. TEST METHODS.
3.4. MANUFACTURER'S WARRANTY.
4. EXPERIMENTAL.
5. OBTAINED RESULTS AND THEIR DISCUSSION.
CONCLUSIONS.
LIST OF USED LITERATURE:
Annotation.
In the domestic and foreign industry for the production of tires and rubber goods, antioxidants are widely used, used in the form of high-molecular-weight pastes.
In this work, we investigate the possibility of obtaining an antiaging paste based on combinations of two antioxidants diafen FP and diafen FF with polyvinyl chloride as a dispersion medium.
Changes in the content of PVC and antioxidants, it is possible to obtain pastes suitable for protecting rubbers from thermal oxidative and ozone aging.
Work done in pages.
20 literary sources were used.
The work has 6 tables and.
Introduction.
The most widespread in the homeland of industry were two antioxidants diafen FP and acetanyl R.
The small assortment represented by two antioxidants is due to a number of reasons. The production of some antioxidants has ceased to exist, for example, neozone D, while others do not respond modern requirements applied to them, for example, diafen FF, it fades on the surface of rubber compounds.
Due to the lack of domestic antioxidants and the high cost of foreign analogues In this work, we investigate the possibility of using the composition of antioxidants diafen FP and diafen FF in the form of a highly concentrated paste, a dispersion medium in which PVC is.
1. Literary review.
1.1. Introduction.
Protecting rubbers from heat and ozone aging is the main goal of this work. The composition of diafen FP with diafen FF and polyvinyliporide (dispersed medium) is used as ingredients that protect rubber from aging. The process for making anti-aging paste is described in the experimental section.
Anti-aging paste is used in rubbers based on SKI-3 isoprene rubber. Rubbers based on this rubber are resistant to the action of water, acetone, ethyl alcohol and are not resistant to the action of gasoline, mineral and animal oils, etc.
During the storage of rubbers and the operation of rubber products, an inevitable aging process occurs, leading to a deterioration in their properties. To improve the properties of rubbers, diafen FF is used in a composition with diafen FP and polyvinyl chloride, which also make it possible to some extent solve the problem of rubbers fading.
1.2. Aging of rubbers.
During the storage of rubbers, as well as during the storage and operation of rubber products, an inevitable aging process occurs, leading to a deterioration in their properties. As a result of aging, tensile strength, elasticity and elongation are reduced, hysteresis losses and hardness increase, abrasion resistance decreases, plasticity, viscosity and solubility of unvulcanized rubber change. In addition, as a result of aging, the service life of rubber products is significantly reduced. Therefore, increasing the resistance of rubber to aging is of great importance for increasing the reliability and performance of rubber products.
Aging is the result of exposure of rubber to oxygen, heat, light and especially ozone.
In addition, the aging of rubbers and rubbers is accelerated in the presence of polyvalent metal compounds and with multiple deformations.
The aging resistance of vulcanizates depends on a number of factors, the most important of which are:
- the nature of rubber;
- properties of antioxidants, fillers and plasticizers (oils) contained in rubber;
- the nature of vulcanizing substances and vulcanization accelerators (the structure and stability of sulfide bonds arising during vulcanization depend on them);
- degree of vulcanization;
- solubility and diffusion rate of oxygen in rubber;
- the ratio between the volume and the surface of a rubber product (with an increase in the surface, the amount of oxygen that penetrates into the rubber increases).
The greatest resistance to aging and oxidation is characteristic of polar rubbers - butadiene-nitrile, chloroprene, etc. Non-polar rubbers are less resistant to aging. Their resistance to aging is mainly determined by the peculiarities of the molecular structure, the position of the double bonds and their number in the main chain. To increase the resistance of rubbers and rubbers to aging, antioxidants are introduced into them, which slow down oxidation and aging.
1.2.1. Types of aging.
Due to the fact that the role of the factors activating oxidation varies depending on the nature and composition of the polymer material, the following types of aging are distinguished in accordance with the predominant influence of one of the factors:
1) thermal (thermal, thermooxidative) aging as a result of heat-activated oxidation;
2) fatigue - aging as a result of fatigue caused by the action of mechanical stress and oxidative processes, activated by mechanical action;
3) oxidation activated by metals of variable valence;
4) light aging - as a result of oxidation activated by ultraviolet radiation;
5) ozone aging;
6) radiation aging under the influence of ionizing radiation.
This paper investigates the effect of anti-aging PVC dispersion on the thermal-oxidative and ozone resistance of rubbers based on non-polar rubbers. Therefore, below, thermal-oxidative and ozone aging is considered in more detail.
1.2.2. Heat aging.
Heat aging is the result of simultaneous exposure to heat and oxygen. Oxidative processes are the main cause of heat aging in air.
Most of the ingredients affect these processes to one degree or another. Carbon black and other fillers adsorb antioxidants on their surface, reduce their concentration in the rubber and therefore accelerate aging. Strongly oxidized soots can catalyze the oxidation of rubbers. Low-oxidized (furnace, thermal) soots, as a rule, slow down the oxidation of rubbers.
With heat aging of rubbers, which occurs at elevated temperatures, almost all basic physical and mechanical properties are irreversibly changed. The change in these properties depends on the ratio of the processes of structuring and destruction. During heat aging of most rubbers based on synthetic rubbers, structuring predominantly occurs, which is accompanied by a decrease in elasticity and an increase in rigidity. During heat aging of rubbers made from natural and synthetic isopropene rubber and butyl rubber, destructive processes develop to a greater extent, leading to a decrease in conventional stresses at a given elongation and an increase in residual deformations.
The ratio of filler to oxidation will depend on its nature, on the type of inhibitors introduced into the rubber, and on the nature of the vulcanization bonds.
Vulcanization accelerators, like products and their transformations remaining in rubbers (mercaptans, carbonates, etc.), can participate in oxidative processes. They can cause molecular decomposition of hydroperoxides and thus help to protect rubbers from aging.
The nature of the cure network has a significant influence on thermal aging. At moderate temperatures (up to 70 °), free sulfur and polysulfide cross-links slow down oxidation. However, as the temperature rises, the rearrangement of polysulfide bonds, in which free sulfur can also be involved, leads to accelerated oxidation of vulcanizates, which are unstable under these conditions. Therefore, it is necessary to select a vulcanization group that ensures the formation of crosslinks resistant to rearrangement and oxidation.
To protect rubbers from heat aging, antioxidants are used to increase the resistance of rubbers and rubbers to oxygen, i.e. substances with antioxidant properties - primarily secondary aromatic amines, phenols, bisphinols, etc.
1.2.3. Ozone aging.
Ozone has a strong effect on the aging of rubbers, even in low concentrations. This is sometimes revealed already in the process of storage and transportation of rubber products. If at the same time the rubber is in a stretched state, then cracks appear on its surface, the growth of which can lead to rupture of the material.
Ozone, apparently, is attached to rubber through double bonds with the formation of ozonides, the decomposition of which leads to the rupture of macromolecules and is accompanied by the formation of cracks on the surface of stretched rubbers. In addition, during ozonation, oxidative processes develop simultaneously, contributing to the growth of cracks. The rate of ozone aging increases with an increase in the concentration of ozone, the magnitude of deformation, an increase in temperature, and upon exposure to light.
A decrease in temperature leads to a sharp slowdown in this aging. Under test conditions at a constant value of deformations; at temperatures 15-20 degrees Celsius higher than the glass transition temperature of the polymer, aging almost completely stops.
The ozone resistance of rubbers depends mainly on the chemical nature of the rubber.
Rubbers based on various rubbers can be divided into 4 groups according to their ozone resistance:
1) especially resistant rubbers (fluoroelastomers, EPDM, KhSPE);
2) resistant rubbers (butyl rubber, perite);
3) moderately resistant rubbers, not cracking under the influence of atmospheric ozone concentrations for several months and resistant for more than 1 hour to ozone concentrations of about 0.001%, based on chloroprene rubber without protective additives and rubbers based on unsaturated rubbers (NK, SKS, SKN, SKI -3) with protective additives;
4) unstable rubber.
The most effective in protecting against ozone aging is the combined use of antiozonts and waxy substances.
Chemical antiozonants include N-substituted aromatic amines and dihydroquinoline derivatives. Antiozonants react on rubber surfaces with ozone with high speed significantly exceeding the rate of interaction of ozone with rubber. As a result of this process, ozone aging is slowed down.
Secondary aromatic diamines are the most effective anti-aging and anti-ozones for protecting rubbers from heat and ozone aging.
1.3. Antioxidants and antiozonants.
The most effective antioxidants and antiozonants are secondary aromatic amines.
They are not oxidized by molecular oxygen either in dry form or in solutions, but are oxidized by rubber peroxides during heat aging and dynamic work causing the chain to come off. So diphenylamine; N, N ^ -diphenyl-nphenylenediamine during dynamic fatigue or heat aging of rubbers is consumed by almost 90%. In this case, only the content of NH groups changes, while the nitrogen content in rubber remains unchanged, which indicates the addition of an antioxidant to the rubber hydrocarbon.
Antioxidants of this class have a very high protective effect against heat and ozone aging.
One of the widespread representatives of this group of antioxidants is N, N ^ -diphenyl-n-phenylenedialine (diafen FF).
It is an effective antioxidant that increases the resistance of rubbers based on SDK, SKI-3 and natural rubber to the action of multiple deformations. Diafen FF paints rubber.
Diafen FP is the best antioxidant to protect rubbers from heat and ozone aging, as well as from fatigue; however, it is distinguished by a relatively high volatility and is easily extracted from rubbers with water.
N-Phenyl-N ^ -isopropyl-n-phenylenediamine (Diafen FP, 4010 NA, Santoflex IP) has the following formula:
With an increase in the value of the alkyl group of the substituent, the solubility of secondary aromatic diamines in polymers increases; increased resistance to water washout, reduced volatility and toxicity.
Comparative characteristics diafen FF and diafen FP are given because in this work studies are carried out, which are caused by the fact that the use of diafen FF as an individual product leads to its "fading" on the surface of rubber compounds and vulcanizates. In addition, in terms of protective action, it is somewhat inferior to diafen FP; has, in comparison with the latter, a higher melting point, which adversely affects its distribution in rubbers.
PVC is used as a binder (dispersed medium) to obtain a paste based on combinations of antioxidants diafen FF and diafen FP.
1.4. Polyvinyl chloride.
Polyvinyl chloride is a polymerization product of vinyl chloride (CH2 = CHCl).
PVC is available in the form of a powder with a particle size of 100-200 microns. PVC is an amorphous polymer with a density of 1380-1400 kg / m3 and a glass transition temperature of 70-80 ° C. It is one of the most polar polymers with high intermolecular interactions. It works well with most commercial plasticizers.
The high chlorine content of PVC makes it a self-extinguishing material. PVC is a polymer for general technical purposes. In practice, we are dealing with plastisols.
1.4.1. PVC plastisols.
Plastisols are dispersions of PVC in liquid plasticizers. The amount of plasticizers (dibutyl phthalates, dialkyl phthalates, etc.) ranges from 30 to 80%.
At ordinary temperatures, PVC particles practically do not swell in these plasticizers, which makes the plastisols stable. When heated to 35-40 ° C, as a result of accelerating the swelling process (gelatinization), plastisols turn into highly bonded masses, which, after cooling, turn into elastic materials.
1.4.2. The mechanism of gelatinization of plastisols.
The mechanism of gelation is as follows. As the temperature rises, the plasticizer slowly penetrates the polymer particles, which grow in size. Agglomerates break down into primary particles. Depending on the strength of the agglomerates, decomposition can begin at room temperature. As the temperature rises to 80-100 ° C, the viscosity of plastosol grows strongly, the free plasticizer disappears, and the swollen polymer grains come into contact. At this stage, called pregelatinization, the material looks completely homogeneous, but the products made from it do not have sufficient physical and mechanical characteristics. Gelatinization is completed only when the plasticizers are evenly distributed in the polyvinyl chloride, and the plastisol turns into a homogeneous body. In this case, the surface of the swollen primary polymer particles melts and plasticized polyvinyl chloride is formed.
2. Choosing a direction of research.
Currently, in the domestic industry, the main ingredients that protect rubber from aging are diafen FP and acetyl R.
The too small assortment represented by two antioxidants is explained by the fact that, firstly, some production of antioxidants ceased to exist (neozone D), and secondly, other antioxidants do not meet modern requirements (diafen FF).
Most antioxidants will fade on rubber surfaces. In order to reduce the discoloration of antioxidants, mixtures of antioxidants with either synergistic or additive properties can be used. This, in turn, allows for the savings of a scarce antioxidant. The use of a combination of antioxidants is proposed to be carried out by individual dosage of each antioxidant, but it is most expedient to use antioxidants in the form of a mixture or in the form of paste-forming compositions.
The dispersion medium in pastes is low-molecular substances, such as oils of petroleum origin, as well as polymers - rubbers, resins, thermoplastics.
In this work, we investigate the possibility of using polyvinyl chloride as a binder (dispersion medium) to obtain a paste based on combinations of antioxidants diafen FF and diafen FP.
The research is due to the fact that the use of diafen FF as an individual product leads to its "fading" on the surface of rubber compounds and vulcanizates. In addition, in terms of the protective effect, Diafen FF is somewhat inferior to Diafen FP; has, in comparison with the latter, a higher melting point, which negatively affects the distribution of diaphene FF in rubbers.
3. Specifications for the product.
This technical condition applies to dispersion PD-9, which is a composition of polyvinyl chloride with an amine type antioxidant.
Dispersion PD-9 is intended for use as an ingredient in rubber compounds to increase the ozone resistance of vulcanizates.
3.1. Technical requirements.
3.1.1. Dispersion PD-9 must be made in accordance with the requirements of these technical conditions according to the technological regulations in the prescribed manner.
3.1.2. In terms of physical indicators, the dispersion of PD-9 must comply with the standards specified in the table.
Table.
Indicator name Norm * Test method
1. Appearance... Crumb dispersion from gray to dark gray According to clause 3.3.2.
2. Linear size of crumb, mm, no more. 40 According to clause 3.3.3.
3. Dispersion mass in a polyethylene bag, kg, no more. 20 According to clause 3.3.4.
4. Mooney viscosity, unit. Mooney 9-25 According to clause 3.3.5.
*) the norms are specified after the release of the pilot batch and statistical processing of the results.
3.2. Safety requirements.
3.2.1. Dispersion PD-9 is a combustible substance. Flash point is not lower than 150 ° C. Autoignition temperature 500 ° C.
The extinguishing agent for a fire is water mist and chemical foam.
Means of individual protection - a poppy "M" gas mask.
3.2.2. Dispersion PD-9 is a low-toxic substance. In case of contact with eyes, rinse with water. The product that has got on the skin is removed by washing off with soap and water.
3.2.3. All working rooms in which work is carried out with dispersion PD-9 must be equipped with supply and exhaust ventilation.
The dispersion of PD-9 does not require the establishment of hygienic regulations for it (MPC and OBUV).
3.3. Test methods.
3.3.1. Take at least three point samples, then combine, mix thoroughly and take an average sample by quartering.
3.3.2. Determination of appearance. The appearance is determined visually during sampling.
3.3.3. Determination of the crumb size. To determine the size of the crumb dispersion PD-9 use a metric ruler.
3.3.4. Determination of the mass of dispersion PD-9 in a polyethylene bag. To determine the mass of the PD-9 dispersion in a polyethylene bag, a scale of the RN-10Ts 13M type is used.
3.3.5. Determination of Mooney viscosity. Determination of Mooney viscosity is based on the presence of a certain amount of a polymer component in a PD-9 dispersion.
3.4. Manufacturer's warranty.
3.4.1. The manufacturer guarantees the compliance of the PD-9 dispersion with the requirements of these specifications.
3.4.2. The guaranteed shelf life of the PD-9 dispersion is 6 months from the date of manufacture.
4. Experimental part.
In this paper, we investigate the possibility of using polyvinyl chloride (PVC) as a binder (dispersion medium) to obtain a paste based on combinations of antioxidants diafen FF and diafen FP. The effect of this anti-aging dispersion on the thermal-oxidative and ozone resistance of rubbers based on SKI-3 rubber is also investigated.
Preparation of anti-aging paste.
In fig. 1. Shown is the installation for the preparation of anti-aging paste.
The preparation was carried out in glass flask(6) with a volume of 500 cm3. The flask with the ingredients was heated on an electric stove (1). The flask is placed in a bath (2). The temperature in the flask was controlled using a contact thermometer (13). Stirring is carried out at a temperature of 70 ± 5 ° C and using a paddle mixer (5).
Fig. 1. Installation for the preparation of anti-aging paste.
1 - electric stove with a closed spiral (220 V);
2 - bath;
3 - contact thermometer;
4 - contact thermometer relay;
5 - blade mixer;
6 - glass flask.
Ingredient loading order.
The flask was loaded with the calculated amount of diafen FF, diafen FP, stearin and a part (10% wt.) Of dibutyl phthalan (DBP). After that, stirring was carried out for 10-15 minutes until a homogeneous mass was obtained.
Then the mixture was cooled to room temperature.
Then the mixture was loaded with polyvinyl chloride and the rest of the DBP (9% wt.). The resulting product was discharged into a porcelain beaker. Then the product was thermostated at temperatures of 100, 110, 120, 130, 140 ° C.
The composition of the resulting composition is shown in table 1.
Table 1
Composition of P-9 anti-aging paste.
Ingredients% wt. Loading into the reactor, g
PVC 50.00 500.00
Diafen FF 15.00 150.00
Diafen FP (4010 NA) 15.00 150.00
DBF 19.00 190.00
Stearin 1.00 10.00
Total 100.00 1000.00
To study the effect of anti-aging paste on the properties of vulcanizates, a rubber compound based on SKI-3 was used.
The resulting anti-aging paste was introduced into a rubber compound based on SKI-3.
Compositions of rubber compounds with anti-aging paste are shown in Table 2.
The physical and mechanical properties of vulcanizates were determined in accordance with GOST and TU, given in table 3.
table 2
Compositions rubber compound.
Ingredients Bookmark numbers
I II
Mixture codes
1-9 2-9 3-9 4-9 1-25 2-25 3-25 4-25
Rubber SKI-3 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00
Sulfur 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
Altax 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60
Guanide F 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00
White zinc 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00
Stearin 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
Carbon black P-324 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00
Diafen FP 1.00 - - - 1.00 - - -
Anti-aging paste (P-9) - 2.3 3.3 4.3 - - - -
Anti-aging paste P-9 (100оС *) - - - - - 2.00 - -
P-9 (120оС *) - - - - - - 2.00 -
P-9 (140оС *) - - - - - - - 2.00
Note: (оС *) - the temperature of preliminary gelatinization of the paste is indicated in brackets (P-9).
Table 3
Item No. Indicator name GOST
1 Conditional strength at break,% GOST 270-75
2 Conditional voltage at 300%,% GOST 270-75
3 Elongation at break,% GOST 270-75
4 Residual elongation,% GOST 270-75
5 Change of the above indicators after aging, air, 100оС * 72 h,% GOST 9.024-75
6 Dynamic tensile endurance, thousand cycles, E? = 100% GOST 10952-64
7 Shore hardness, standard GOST 263-75
Determination of the rheological properties of anti-aging paste.
1. Determination of Mooney viscosity.
Mooney viscosity was determined using a Mooney viscometer (GDR).
The production of samples for testing and testing itself are carried out according to the methodology set forth in the technical specifications.
2. Determination of the cohesive strength of pasty compositions.
After gelatinization and cooling to room temperature, the paste samples were passed through a gap of 2.5 mm rollers. Then, from these sheets in a vulcanizing press, plates with a size of 13.6 * 11.6 mm and a thickness of 2 ± 0.3 mm were made.
After the plates were cured for 24 hours with a punching knife, the spatulas were cut out in accordance with GOST 265-72 and further, on a tensile testing machine RMI-60 at a speed of 500 mm / min, the breaking load was determined.
The specific load was taken as the cohesive strength.
5. Obtained results and their discussion.
When studying the possibility of using PVC, as well as the composition of polar plasticizers as binders (dispersion medium) to obtain pastes based on combinations of antioxidants diaphene FF and diaphene FP, it was found that the alloy of diaphene FF with diaphene FP in a mass ratio of 1: 1 is characterized by a low rate crystallization and a melting point of about 90 ° C.
Low speed crystallization plays a positive role in the production of PVC plastisol filled with a mixture of antioxidants. In this case, the energy consumption for obtaining a homogeneous composition that does not exfoliate in time is significantly reduced.
The melt viscosity of diafen FF and diafen FP is close to the viscosity of PVC plastisol. This allows mixing the melt and plastisol in reactors with anchor-type stirrers. In fig. 1 shows a diagram of an installation for the production of pastes. The pastes, before their preliminary gelatinization, are satisfactorily drained from the reactor.
It is known that the gelatinization process takes place at 150 ° C and higher. However, under these conditions, the elimination of hydrogen chloride is possible, which, in turn, is capable of blocking the mobile hydrogen atom in the molecules of secondary amines, which in this case are antioxidants. This process proceeds according to the following scheme.
1. Formation of polymeric hydroperoxide during the oxidation of isoprene rubber.
RH + O2 ROOH,
2. One of the directions of decomposition of polymeric hydroperoxide.
ROOH RO ° + O ° H
3. Having removed the oxidation stage due to the antioxidant molecule.
AnH + RO ° ROH + An °,
Where An is an antioxidant radical, for example,
4.
5. The properties of amines, including secondary ones (diafen FF), form alkyl-substituted amines with mineral acids according to the following scheme:
H
R- ° N ° -R + HCl + Cl-
H
This reduces the reactivity of the hydrogen atom.
By carrying out the process of gelatinization (preliminary gelatinization) at relatively low temperatures (100-140 ° C), the phenomena mentioned above can be avoided, i.e. reduce the likelihood of hydrogen chloride splitting off.
The final gelation process results in pastes with a Mooney viscosity lower than the filled rubber compound and low cohesive strength (see Figure 2.3).
Pastes with low Mooney viscosity, firstly, are well distributed in the mixture, and secondly, minor parts of the components that make up the paste are able to easily migrate into the surface layers of vulcanizates, thereby protecting rubber from aging.
In particular, in the issue of "crushing" of paste-forming compositions, great importance is attached to explaining the reasons for the deterioration of the properties of some compositions under the action of ozone.
In this case, the initial low viscosity of pastes and, moreover, does not change during storage (table 4), allows for a more uniform distribution of the paste, and makes it possible to migrate its components to the surface of the vulcanizate.
Table 4
Indicators of viscosity according to Mooney paste (P-9)
Initial indicators Indicators after storage of the paste for 2 months
10 8
13 14
14 18
14 15
17 25
By varying the content of PVC and antioxidants, it is possible to obtain pastes suitable for protecting rubbers from thermo-absorbing and ozone aging based on both non-polar and polar rubbers. In the first case, the PVC content is 40-50 wt%. (paste P-9), in the second - 80-90% wt.
In this work, vulcanizates based on SKI-3 isoprene rubber are investigated. Physical and mechanical properties of vulcanizates using paste (P-9) are presented in tables 5 and 6.
The resistance of the investigated vulcanizates to thermal-oxidative aging increases with an increase in the content of the anti-aging paste in the mixture, as can be seen from Table 5.
Indicators of changes in the relative strength, standard composition (1-9) is (-22%), while for the composition (4-9) - (-18%).
It should also be noted that with the introduction of a paste that increases the resistance of vulcanizates to thermal oxidative aging, a greater dynamic endurance is imparted. Moreover, explaining the increase in dynamic endurance, it is impossible, apparently, to limit ourselves only to the factor of increasing the dose of the antioxidant in the rubber matrix. PVC is likely to play an important role in this. In this case, it can be assumed that the presence of PVC can cause the effect of the formation of continuous chain structures by it, which are evenly distributed in the rubber and prevent the growth of microcracks arising from cracking.
By reducing the content of anti-aging paste and thereby the proportion of PVC (table 6), the effect of increasing the dynamic endurance is practically canceled. In this case positive influence paste manifests itself only under conditions of thermo-oxidative and ozone aging.
It should be noted that the best physical and mechanical properties are observed when using an anti-aging paste obtained under milder conditions (pregelatinization temperature 100 ° C).
Such conditions for obtaining a paste provide a higher level of stability in comparison with a paste obtained by thermostating for an hour at 140 ° C.
An increase in the viscosity of PVC in a paste obtained at a given temperature also does not contribute to the preservation of the dynamic endurance of vulcanizates. And as follows from Table 6, dynamic endurance is greatly reduced in pastes thermostated at 140 ° C.
The use of diafen FF in a composition with diafen FP and PVC allows to some extent solve the problem of fading.
Table 5
1-9 2-9 3-9 4-9
1 2 3 4 5
Conditional strength at break, MPa 19.8 19.7 18.7 19.6
Conditional stress at 300%, MPa 2.8 2.8 2.3 2.7
1 2 3 4 5
Elongation at break,% 660 670 680 650
Permanent elongation,% 12 12 16 16
Hardness, Shore A, conventional units 40 43 40 40
Conditional strength at break, MPa -22 -26 -41 -18
Conditional stress at 300%, MPa 6 -5 8 28
Elongation at break,% -2 -4 -8 -4
Permanent elongation,% 13 33 -15 25
Dynamic endurance, Eg = 100%, thousand cycles. 121 132 137 145
Table 6
Physical and mechanical properties of vulcanizates containing anti-aging paste (P-9).
Indicator name Mix code
1-25 2-25 3-25 4-25
1 2 3 4 5
Conditional strength at break, MPa 22 23 23 23
Conditional stress at 300%, MPa 3.5 3.5 3.3 3.5
1 2 3 4 5
Elongation at break,% 650 654 640 670
Permanent elongation,% 12 16 18 17
Hardness, Shore A, conventional units 37 36 37 38
Change in indicator after aging, air, 100оС * 72 h
Conditional strength at break, MPa -10.5 -7 -13 -23
Conditional stress at 300%, MPa 30 -2 21 14
Elongation at break,% -8 -5 -7 -8
Residual elongation,% -25 -6 -22 -4
Ozone resistance, E = 10%, hour 8 8 8 8
Dynamic endurance, Eg = 100%, thousand cycles. 140 116 130 110
List of symbols.
PVC - polyvinyl chloride
Diafen FF - N, N ^ - Diphenyl - n - phenylenediamine
Diafen FP - N - Phenyl - N ^ - isopropyl - n - phenylenediamine
DBP - dibutyl phthalate
SKI-3 - isoprene rubber
P-9 - anti-aging paste
1. Research for the composition of diafen FP and diafen FF plastisol based on PVC allows to obtain pastes that do not exfoliate in time, with stable rheological properties and Mooney viscosity, higher than the viscosity of the rubber mixture used.
2. When the content of the combination of diafen FP and diafen FF in the paste is equal to 30% and PVC plastisol 50%, the optimal dosage to protect rubbers from thermooxidative and ozone aging may be a dosage of 2.00 parts by weight, 100 parts by weight of rubber rubber mixtures.
3. An increase in the dosage of antioxidants in excess of 100 parts by weight of rubber leads to an increase in the dynamic endurance of rubbers.
4. For rubbers based on isoprene rubber operating in a static mode, diaphene FP can be replaced with anti-aging paste P-9 in the amount of 2.00 wt h per 100 wt h of rubber.
5. For rubbers operating under dynamic conditions, replacement of the FP diaphene is possible when the antioxidant content is 8-9 wt h per 100 wt h of rubber.
6.
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