The problem of increasing the durability of rubber products is directly related to increasing the resistance to abrasion various types aging. One of the most common and destructive types of aging is atmospheric aging of rubber, which affects almost all products that come into contact with air during operation or storage.
Atmospheric aging is a complex of physical and chemical transformations occurring under the influence of atmospheric ozone and oxygen, solar radiation and heat.
Under atmospheric conditions, as well as during thermal aging, rubbers gradually lose their elastic properties, regardless of whether they are in a stressed or unstressed state.
Rubbers based on NC with light fillers age especially intensively. Quickly (after 1-2 years) there is a noticeable change in the properties of rubbers made from nitrile butadiene rubber, styrene butadiene rubber and nairite. In addition to a relatively rapid change in color, the surface layer first softens and then gradually becomes hard and takes on the appearance of embossed leather. At the same time, the surface is covered with a network of cracks due to the simultaneous influence of ozone and tensile forces on it. Cracking of rubber under atmospheric conditions occurs at a relatively high speed and is therefore the most dangerous type of aging.
To protect rubber from cracking, two types of protective agents are used:
· antiozonants;
An effective reduction in the rate of change in the physical and mechanical properties of rubbers during atmospheric aging, as well as during thermal aging, can be achieved with the help of antioxidants, mainly for NC-based rubbers.
Heat resistance– the ability of rubber to maintain properties when exposed to elevated temperatures. Typically, this term refers to resistance to thermal aging, during which a change in the chemical structure of the elastomer occurs. Changes in the properties of rubber during thermal aging are irreversible.
With the same vulcanizing system, rubbers have minimal resistance to thermal aging based on isoprene rubber. At 80-140°C, the destruction reactions of the spatial network of the vulcanizate usually occur mainly, and at 160°C, the reactions of cross-linking of rubber macromolecules occur. The change in mechanical properties is largely due to the destruction of macromolecules, the intensity of which increases in air.
Rubbers based on styrene butadiene rubber (BSR) are more heat-resistant (and heat resistance increases significantly with increasing vulcanization duration) and are less susceptible to oxidation than rubbers based on isoprene rubber. The degree of cross-linking increases with increasing temperature and duration of aging.
Typically, mineral fillers provide higher thermal aging resistance for SBR-based rubbers compared to carbon black. The degree of influence of fillers depends on the composition of the rubber mixture and aging conditions.
In rubber based on nitrile butadiene rubber (NBR) thermal aging resistance increases with increasing acrylonitrile (AN) content in the rubber. Rubber vulcanized with sulfur has minimal resistance to thermal aging.
During thermal aging of rubber based on chloroprene rubber cross-linking of macromolecules occurs. Carbon black, silicon dioxide, and mineral fillers are used as fillers. Polyesters, sulfoesters, rubrax, coumaron-indene and petroleum polymer resins are used as softeners.
Heat resistance may increase when added to rubber compound paraffin oil, diphenylamine, alkylated diamines and phenolic antioxidants, as well as mixtures of various antioxidants.
Thermal aging under compression is most important for rubbers used as sealing materials. In this case, the aging resistance is assessed by measuring the stress relaxation under compression and residual compression deformation (RCS). The heat resistance of rubber under compression is also characterized by the following indicators: τ (T; 50%) and τ (T; 80%) - duration of aging at temperature T until the ODS value is reached equal to 50 and 80%, respectively; T ( τ , 50%) and T ( τ , 80%) - aging temperature over time τ , at which the ODC value reaches 50 and 80%, respectively.
The ODS value increases sharply, and the contact stress decreases in the first period of aging, then these values change at a much slower rate. An increase in temperature also leads to a significant acceleration of stress relaxation and an increase in ODS. Therefore, small deviations in temperature or aging duration can significantly change these indicators during the initial period of aging.
The resistance of rubber to thermal aging during compression mainly depends on the type of rubber, the structure and density of the spatial mesh, and test conditions.
Increasing the duration of vulcanization always leads to a decrease in ODS, since this usually increases the network density, and in sulfur vulcanizates the degree of sulfidity of cross-links decreases.
The presence of moisture and traces of alkali in the rubber compound reduces the heat resistance during compression. The rate of stress relaxation increases with increasing humidity in an inert environment or in air.
To create rubbers with new properties, it is very promising to use new chemical additives with multifunctional action in rubber mixtures. When rubbers are mixed with such additives, compositions are formed, the use of which allows one to greatly change the properties of both rubber compounds and the rubbers obtained from them.
The possibility of using multifunctional additives is associated with their chemical structure, state of aggregation and influence on the structure of elastomeric compositions. The correct selection and introduction of additives into the rubber mixture can facilitate its processing (plasticization effect), change the adhesiveness, cohesive strength, vulcanization parameters and many other characteristics.
Depending on the chemical structure and amount of multifunctional additives, the properties of rubber obtained from such compositions (elasticity, frost and heat resistance, strength, dynamic and fatigue characteristics, hardness and abrasion resistance, etc.) change significantly.
The advantage of multifunctional additives is their availability. In this regard, a wide variety of products of natural and synthetic origin are currently used or tested in rubber compounds. For example, olioester acrylates are plasticizers during processing and reinforcing fillers in the vulcanization composition; paraffins (oleoethylenes) facilitate the processing of mixtures and protect rubber from ozone cracking; fatty acids (oleoethylene carboxylic acids) not only reduce the viscosity of rubber compounds, but also affect the cross-linking of rubber, increasing the efficiency of using vulcanizing systems.
Technological additives – targeted additives that, when added to rubber compounds in small quantities, improve their technological properties.
Ingredients that improve the processability of rubber compounds and have long been used in the rubber industry include mainly liquid and thermoplastic plasticizers. However, while having a positive effect on the technological properties of mixtures, they negatively affect performance characteristics rubber
Based on their chemical nature, technological additives are classified into:
1. Fatty acids and their derivatives (salts and esters).
2. Emulsion plasticizers.
3.High boiling polyglycols.
4. Resins (resin acids and their derivatives).
11.Properties and types of glass
Glass is a solid amorphous thermoplastic material obtained by supercooling a melt of various oxides. The composition of glass includes glass-forming acid oxides (SiO 2, A 12 O 3, B 2 O 3, etc.), as well as basic oxides (K 2 O, CaO, Na 2 O, etc.), which give it special properties and color . Silicon oxide SiO 2 is the basis of almost all glasses and is included in their composition in an amount of 50 ... 100%. According to their purpose, glass is divided into construction (window, showcase, etc.), household (glass containers, dishes, mirrors, etc.) and technical (optical, lighting and electrical, chemical laboratory, instrument, etc.).
Important properties of glass are optical. Ordinary glass transmits about 90%, reflects 8% and absorbs 1% of visible light. The mechanical properties of glass are characterized by high compressive strength and low tensile strength.
The heat resistance of glass is determined by the temperature difference that it can withstand without breaking when suddenly cooled in water. For most glasses, heat resistance ranges from 90 to 170°C, and for quartz glass consisting of pure SiO 2 - 1000°C. The main disadvantage of glass is its high fragility.
Ozone aging, ozone cracking (ozone cracking, Ozonriβbildung, vieillissement al, ozone) is rubber stretched under the influence of ozone. Ozone aging is one of the types of so-called corrosion cracking which is observed when chemically or physically active media act on stressed materials (for example, ammonia on brass, detergents on, acids or alkalis on rubber from polysulfide rubbers, HF for rubbers made from silicone rubbers). Tensile stresses arise in rubbers during static or dynamic one- or two-dimensional stretching or shear deformation.
For ozone aging to occur, the presence of even traces of ozone, which is always contained in the atmosphere, is sufficient (2-6)·10 -6%; (hereinafter the volumetric concentration of ozone is indicated) and, in addition, can be formed under certain conditions in enclosed spaces. The main reason for the presence of ozone in the atmosphere is the effect of short-wave solar radiation on air oxygen.
Ozone is also formed as a result of photochemical oxidation of organic impurities contained in the air with the participation of nitrogen dioxide. This process is especially intense in large cities, where air pollution from engine exhaust gases causes high concentrations of ozone. [up to (50-100)·10 -6% ].
In enclosed spaces, ozone can be formed under the influence of UV-Sveta, γ -rays, X-rays, during electrical discharges, as well as during the oxidation of organic compounds.
Mechanism ozone aging
The mechanism of ozone aging is a sharp acceleration of the destruction of stressed rubber, caused by the addition of ozone along the multiple bonds of rubber macromolecules: The stress that arises in rubber at small deformations, promoting the destruction of the macromolecule and preventing the recombination of macroradicals, accelerates the appearance and growth of microcracks, initially directed along the tensile axis. The rupture of weak bridges between these microcracks leads to the appearance of transverse cracks visible to the eye. At large deformations (hundreds of percent), cracks remain longitudinal as they grow, since due to orientation effect the bridges between the cracks acquire greater strength.
Kinetics of ozone aging of polymer materials
With static voltage σ (or deformation ε ) in the process of ozone aging can be distinguished 2 main stages of ozone aging:
- induction period τ and, the end of which practically coincides with the moment of crack appearance;
- period of development of visible cracks τ tu, which occurs mainly at the stage of stationary growth rate τ st(picture 1).
As the stress increases, its destructive effect increases, but the simultaneously developing orientation of macromolecules leads to strengthening of the polymer, which makes its further destruction more difficult. Because the in the first stage of ozone aging occurring on the rubber surface, the destructive role of stress increases due to the increasing proportion of fresh, newly formed surface, then τ and usually decreases monotonically with increasing ε
(picture 1). The state of its surface does not play a role in the development of cracks deep in the sample; at this stage of ozone aging is more pronounced orientation hardening, in connection with which crack growth rate passes through a maximum in the region of the so-called critical strain ε cr (figure 2).
Time before breakup τ р =τ and +τ tu depends on σ
(or ε
) as well as τ and(picture 1), or passes through a minimum in the region ε cr(for large deformations - through a maximum due to exhaustion orientation hardening effect (figure 2). The first dependence, characteristic of ozone-resistant rubbers, is observed when t r determined by duration τ and (τ and /τ р ≈1), the second - if t r determined by the length of the period τ tu (τ and /t r<<1).
Meaning ε cr determined by two factors: degree of reduction τ р with growth σ And degree of increase τ p with the development of the orientation effect.
Factors influencing the rate of ozone aging
Intermolecular interaction
An increase in , making it difficult to orient macromolecules during deformation and helping to increase the durability of rubber, can lead to shear ε cr towards its higher values. This dependence is observed, in particular, in the series of unfilled vulcanizates of the following polymers:
natural rubber< гуттаперча < хлоропреновый каучук.
Meaning ε cr also increases with the introduction of active fillers into rubbers with relatively weakly expressed intermolecular interactions. Thus, with an increase in the amount of gas channel black in natural rubber from 0 to 90 parts by mass ε cr increases from 15 before 50% . In the case of a significant decrease in intermolecular interactions (for example, when dibutyl phthalate is introduced into chloroprene rubber), the value ε cr decreases sharply. The change in intermolecular interaction also explains the effect on the value ε cr temperature, and other factors.
Nature and frequency of deformities
Compared to ozone rate under static deformations, at repeated deformations with a constant frequency can be observed as acceleration ozone aging (in rubbers made from nitrile butadiene rubbers), and its slowdown(in rubbers made from natural rubber).
In some rubbers with increase strain frequencies manifests itself relaxation hardening, leading to reduction of ozone aging. In the region of low frequencies (up to 100 vibrations per minute), the highest rate of ozone aging of most rubbers is observed at frequency of 10 vibrations per minute. Rubbers containing waxy substances, the layer of which on the surface of the rubber is easily destroyed by repeated deformations, significantly are more susceptible to ozone aging under these conditions than under static deformations.
Ozone concentration
Reducing ozone concentration WITH sharply slows down ozone aging, and the dependence remains up to its atmospheric concentrations τ = kС -n, Where k And n- constant, and τ maybe like τ and, so t r. In case of large τ (years) the application of this dependence is complicated by changes in rubber exposure conditions (stress relaxation, migration to the rubber surface antiozonants etc.), influencing the values k And n.
Ozone concentration does not affect position ε cr and the value of the activation energy of ozone aging. The latter is very small (tens of kJ/mol, or several kcal/mol) and, therefore, change in the rate of ozone aging with temperature caused mainly by changes in the mobility of macromolecules. This is confirmed by the fact that the rate of crack growth obeys the equation Williams - Landell - Ferry(see Viscous flow state), which describes relaxation processes.
The influence of temperature, moisture and solar radiation on the rate of ozone aging
A decrease in temperature leads to a sharp slowdown in ozone aging; under test conditions at a constant value ε ozone aging practically stops at temperatures 15-20 °C higher than the glass transition temperature of the polymer.
Solar radiation greatly accelerates ozone aging due to photo-oxidation of rubber, accompanied by the destruction of macromolecules, an increase in the mobility of macroradicals, and also as a result of a general increase in the temperature of the rubber. Moisture, being sorbed by relatively hydrophilic rubbers (for example, from natural or chloroprene rubber) and promoting a more uniform distribution of stress on their surface, somewhat slows down the ozone aging of these rubbers.
Ozone resistance of rubber (classification of rubber by ozone resistance)
The ability of rubber to resist ozone aging depends significantly on the type of rubber.
Resistance to ozone aging(under conditions of static deformation up to 50%) rubbers based on various rubbers can be divided into into four groups:
- Particularly resistant rubber do not collapse for a long time (years) at atmospheric ozone concentrations and are stable for more than 1 hour at concentrations O 3 order 0,1 - 1%. These properties have rubber based on saturated rubbers- fluorine-containing, ethylene-propylene, polyisobutylene, chlorosulfonated polyethylene and, to a lesser extent, silicone rubber; the latter are destroyed by acidic substances, which are easily formed in the presence of ozone.
- Durable rubber do not collapse for several years in atmospheric conditions and are stable for more than 1 hour at concentrations O 3 near 0,01% . This group includes rubbers based on rubbers that weakly interact with ozone due to low content of multiple bonds in them(for example, rubber from butyl rubber) or due to the presence of bonds that are not very active towards ozone (for example, rubber from urethane and polysulfide rubbers), as well as rubber from chloroprene rubbers, stabilized antiozonants.
- Moderately resistant rubber stable in atmospheric conditions from several months to 1-2 years, and at concentrations O 3 near 0,001% - more than 1 hour. This group includes rubber from unstabilized chloroprene rubber and from others unsaturated rubbers(natural, synthetic isoprene, butadiene-styrene, butadiene-nitrile), containing antiozonants. Big durability of chloroprene rubber to ozone is explained by the peculiarities of its physical structure (easy crystallization, strong intermolecular polar interactions), causing the formation of obtuse-angled, rounded, slowly growing cracks.
- Unstable rubber stable in atmospheric conditions from several days to 1 month, and at concentrations O 3 - 0,0001% - more than 1 hour. Rubbers made from unstabilized rubbers of the previous group are classified as unstable, with the exception of rubbers made from chloroprene rubber. Increasing the resistance of rubbers of this group to ozone aging is achieved by introducing into them antiozonants And waxes, applied to rubber ozone-resistant coatings from chloroprene rubber, chlorosulfonated polyethylene, etc., chemical treatment(for example, hydrogenation) of the rubber surface to reduce the content of unsaturated bonds in macromolecules, as well as changing the design of products in order to reduce tensile stresses under operating conditions.
For methods of protecting rubber from ozone aging, see also Antiozonants.
In addition to the type of rubber, the resistance of rubber to ozone aging is influenced by the composition of rubber compounds. Thus, under test conditions at the same deformation ε values τ and And t r for rubbers containing fillers And plasticizers, will be less than for unfilled ones.
The deterioration of ozone resistance is due to the following reasons:
- increase in stress associated with the introduction of fillers,
- reduction in the strength properties of rubber due to the introduction of plasticizers.
Resistance of rubber to ozone aging assessed by changes in the following characteristics of stretched samples:
1)degree of cracking (for this, a conditional 4-, 6- or 10-point scale is drawn up based on photographs of samples);
2)time before cracks appearτ and;
3)time before breakup t r.
It is convenient to monitor the kinetics of crack development by the decrease in force R in a stretched ozonized sample. Wherein t r corresponds to the moment when P = 0.
Testing in an ozone environment is an effective method for studying the durability of rubber at small deformations (tens of percent), characteristic of the operating conditions of most rubber products. Test results at elevated ozone concentrations also make it possible to predict rubbers that are not resistant to ozone, since in this case the durability is determined by the resistance of rubber to ozone aging.
Bibliography: Zuev Yu. S., Destruction of polymers under the influence of aggressive media, 2nd ed., M., 1972. Yu. S. Zuev,
Content1. LITERATURE REVIEW.
1.1. INTRODUCTION
1.2. AGING OF RUBBERS.
1.2.1. Types of aging.
1.2.2. Thermal aging.
1.2.3. Ozone aging.
1.3. ANTI-AGINGANTS AND ANTI-ZONANTS.
1.4. POLYVINYL CHLORIDE.
1.4.1. PVC plastisols.
2. CHOOSING A 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 PART.
5. RESULTS OBTAINED AND THEIR DISCUSSION.
CONCLUSIONS.
LIST OF REFERENCES USED:
Annotation.
Antioxidants used in the form of high-molecular pastes have become widespread in the domestic and foreign industry for the production of tires and rubber goods.
This work explores the possibility of obtaining an antiaging paste based on combinations of two antioxidants diaphene FP and diaphene FF with polyvinyl chloride as a dispersion medium.
By changing the content of PVC and antioxidants, it is possible to obtain pastes suitable for protecting rubber from thermal-oxidative and ozone aging.
The work is done on pages.
20 literary sources were used.
The work contains 6 tables and.
Introduction.
The two antioxidants most widely used in the domestic industry are diafen FP and acetanil R.
The small range represented by two antioxidants is explained by a number of reasons. The production of some antioxidants has ceased to exist, for example, neozone D, and others do not meet modern requirements for them, for example, diaphen FF, it fades on the surface of rubber compounds.
Due to the lack of domestic antioxidants and the high cost of foreign analogues, this work examines the possibility of using the composition of the antioxidants diaphene FP and diaphene FF in the form of a highly concentrated paste, a dispersion medium in which PVC is used.
1. Literature review.
1.1. Introduction.
Protecting rubber from thermal and ozone aging is the main goal of this work. As ingredients that protect rubber from aging, a composition of diaphene FP with diaphene FF and polyvinyl poride (dispersed medium) is used. The process of making anti-aging paste is described in the experimental part.
Anti-aging paste is used in rubbers based on SKI-3 isoprene rubber. Rubbers based on this rubber are resistant to water, acetone, ethyl alcohol and not resistant to gasoline, mineral and animal oils, etc.
When storing rubber and using rubber products, an inevitable aging process occurs, leading to a deterioration in their properties. To improve the properties of rubber, diaphene FF is used in composition with diaphene FP and polyvinyl chloride, which also help to some extent solve the issue of rubber fading.
1.2. Aging of rubber.
When storing rubber, 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 decrease, hysteresis losses and hardness increase, abrasion resistance decreases, and the ductility, viscosity and solubility of unvulcanized rubber changes. 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 rubber's exposure to oxygen, heat, light and especially ozone.
In addition, the aging of rubbers is accelerated in the presence of polyvalent metal compounds and with repeated deformation.
The resistance of vulcanizates to aging 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 that arise during vulcanization depend on them);
- degree of vulcanization;
- solubility and diffusion rate of oxygen in rubber;
- the relationship between the volume and surface of a rubber product (as the surface increases, the amount of oxygen penetrating into the rubber increases).
Polar rubbers – nitrile butadiene, chloroprene, etc. – are characterized by the greatest resistance to aging and oxidation. Non-polar rubbers are less resistant to aging. Their resistance to aging is determined mainly by the characteristics of the molecular structure, the position of double bonds and their number in the main chain. To increase the resistance of 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 factors activating oxidation varies depending on the nature and composition of the polymer material, the following types of aging are distinguished according to the predominant influence of one of the factors:
1) thermal (thermal, thermo-oxidative) aging as a result of oxidation activated by heat;
2) fatigue - aging as a result of fatigue caused by mechanical stress and oxidative processes activated by mechanical stress;
3) oxidation activated by metals of variable valency;
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 work examines the effect of anti-aging PVC dispersion on the thermal-oxidative and ozone resistance of rubbers based on non-polar rubbers. Therefore, thermal-oxidative and ozone aging are discussed in more detail below.
1.2.2. Thermal aging.
Thermal aging is the result of simultaneous exposure to heat and oxygen. Oxidative processes are the main cause of thermal aging in the air.
Most 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. Heavily oxidized soot can be a catalyst for rubber oxidation. Low-oxidized (furnace, thermal) carbon blacks, as a rule, slow down the oxidation of rubbers.
During thermal aging of rubber, which occurs at elevated temperatures, almost all basic physical properties change irreversibly. mechanical properties. The change in these properties depends on the relationship between the processes of structuring and destruction. During thermal 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 thermal 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 conditional stresses at given elongations and an increase in residual deformations.
The relationship of a filler to oxidation will depend on its nature, the type of inhibitors incorporated into the rubber, and 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 the decomposition of hydroperoxides by a molecular mechanism and thus contribute to the protection of rubbers from aging.
The nature of the vulcanization network has a significant influence on thermal aging. At moderate temperatures (up to 70°), free sulfur and polysulfide cross-links slow down oxidation. However, with increasing temperature, the rearrangement of polysulfide bonds, which may also involve free sulfur, leads to accelerated oxidation of vulcanizates, which turn out to be unstable under these conditions. Therefore, it is necessary to select a vulcanization group that ensures the formation of cross-links that are resistant to rearrangement and oxidation.
To protect rubbers from thermal aging, antioxidants are used that increase the resistance of rubbers and caoutchoucs to oxygen, i.e. substances with antioxidant properties - primarily secondary aromatic amines, phenols, bisfinols, etc.
1.2.3. Ozone aging.
Ozone has a strong effect on the aging of rubber even in low concentrations. This is sometimes discovered during the storage and transportation of rubber products. If 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, attaches to the 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 rubber. In addition, during ozonation, oxidative processes simultaneously develop, promoting the growth of cracks. The rate of ozone aging increases with increasing ozone concentration, amount of deformation, increasing temperature and 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 exceeding the glass transition temperature of the polymer by 15-20 degrees Celsius, aging almost completely stops.
The resistance of rubber to ozone depends mainly on the chemical nature of the rubber.
Rubbers based on various rubbers can be divided into 4 groups based on ozone resistance:
1) especially resistant rubbers (fluororubbers, SKEP, KhSPE);
2) resistant rubber (butyl rubber, pearite);
3) moderately resistant rubbers that do not crack when exposed to atmospheric ozone concentrations for several months and are resistant to ozone concentrations of about 0.001% for more than 1 hour, 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 way to protect against ozone aging is the combined use of anti-ozones and waxy substances.
Chemical antiozonants include N-substituted aromatic amines and dihydroquinoline derivatives. Antiozonants react on rubber surfaces with ozone at a high speed, significantly exceeding the rate of interaction of ozone with rubber. As a result of this ozone aging process is slowed down.
The most effective anti-aging and anti-ozone agents for protecting rubber from thermal and ozone aging are secondary aromatic diamines.
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 thermal aging and during dynamic operation, causing chain separation. So diphenylamine; N,N^-diphenyl-nphenylenediamine is consumed by almost 90% during dynamic fatigue or thermal aging of rubber. 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 thermal and ozone aging.
One of the widespread representatives of this group of antioxidants is N,N^-diphenyl-n-phenylenedialine (diaphen FF).
This is an effective antioxidant that increases the resistance of rubbers based on SDK, SKI-3 and natural rubber to repeated deformations. Diafen FF colors rubber.
The best antioxidant for protecting rubber from thermal and ozone aging, as well as from fatigue, is diaphene FP, but it is characterized by relatively high volatility and is easily extracted from rubber with water.
N-Phenyl-N^-isopropyl-n-phenylenediamine (Diaphen FP, 4010 NA, Santoflex IP) has the following formula:
With an increase in the size of the alkyl group of the substituent, the solubility of secondary aromatic diamines in polymers increases; resistance to water washout increases, volatility and toxicity decreases.
A comparative description of diaphene FF and diaphene FP is given because in this work research is carried out, which is caused by the fact that the use of diaphene FF as an individual product leads to its “fading” on the surface of rubber compounds and vulcanizates. In addition, its protective effect is somewhat inferior to diaphene FP; has a higher melting point in comparison with the latter, which negatively affects its distribution in rubber.
PVC is used as a binder (dispersed medium) to produce a paste based on combinations of the antioxidants diaphene FF and diaphene FP.
1.4. Polyvinyl chloride.
Polyvinyl chloride is a polymerization product of vinyl chloride (CH2=CHCl).
PVC is available in powder form with particle sizes 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 combines well with most commercially produced plasticizers.
The high chlorine content in PVC makes it a self-extinguishing material. PVC is a polymer for general technical purposes. In practice, they deal 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 normal temperatures, PVC particles practically do not swell in these plasticizers, which makes plastisols stable. When heated to 35-40°C, as a result of accelerating the swelling process (gelatinization), plastisols turn into highly cohesive masses, which, after cooling, turn into elastic materials.
1.4.2. The mechanism of gelatinization of plastisols.
The gelatinization mechanism is as follows. As the temperature rises, the plasticizer slowly penetrates the polymer particles, which increase in size. Agglomerates disintegrate into primary particles. Depending on the strength of the agglomerates, decomposition may begin at room temperature. As the temperature increases to 80-100°C, the viscosity of the plastosol increases greatly, the free plasticizer disappears, and the swollen polymer grains come into contact. At this stage, called pre-gelatinization, the material looks completely homogeneous, but 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 particles of the polymer fuses and the formation of plasticized polyvinyl chloride occurs.
2. Choosing the 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 range represented by two antioxidants is explained by the fact that, firstly, some production of antioxidants has ceased to exist (neozone D), and secondly, other antioxidants do not meet modern requirements (diafen FF).
Most antioxidants discolor the rubber surface. In order to reduce the fading of antioxidants, mixtures of antioxidants having either synergistic or additive properties can be used. This in turn makes it possible to save the scarce antioxidant. The use of a combination of antioxidants is proposed to be carried out by individual dosing of each antioxidant, but it is most advisable 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 weight substances, such as oils of petroleum origin, as well as polymers - rubbers, resins, thermoplastics.
This work explores the possibility of using polyvinyl chloride as a binder (dispersion medium) to obtain a paste based on combinations of the antioxidants diaphene FF and diaphene FP.
The research was carried out due to the fact that the use of diaphene FF as an individual product leads to its “fading” on the surface of rubber compounds and vulcanizates. In addition, in terms of protective effect, Diaphene FF is somewhat inferior to Diaphene FP; has a higher melting point in comparison with the latter, which negatively affects the distribution of diaphene FF in rubbers.
3. Product specifications.
This technical specification applies to the PD-9 dispersion, which is a composition of polyvinyl chloride with an amine-type antioxidant.
PD-9 dispersion is intended for use as an ingredient in rubber compounds to increase the ozone resistance of vulcanizates.
3.1. Technical requirements.
3.1.1. The PD-9 dispersion must be manufactured in accordance with the requirements of these technical specifications according to the technological regulations in the prescribed manner.
3.1.2. According to physical indicators, the PD-9 dispersion must comply with the standards specified in the table.
Table.
Name of indicator Standard* Test method
1. Appearance. Crumb dispersion from gray to dark gray color According to clause 3.3.2.
2. Linear size of the crumb, mm, no more. 40 According to clause 3.3.3.
3. Weight of dispersion in a plastic bag, kg, no more. 20 According to clause 3.3.4.
4. Mooney viscosity, units. Muni 9-25 According to clause 3.3.5.
*) standards are clarified after the release of a pilot batch and statistical processing of the results.
3.2. Safety requirements.
3.2.1. PD-9 dispersion is a flammable substance. Flash point not lower than 150°C. Self-ignition temperature 500oC.
Fire extinguishing agents for fires include finely sprayed water and chemical foam.
Personal protective equipment – Maki “M” gas mask.
3.2.2. PD-9 dispersion is a low-toxic substance. In case of contact with eyes, rinse them with water. The product that gets on the skin is removed by washing with soap and water.
3.2.3. All work areas in which work is carried out with PD-9 dispersion must be equipped with supply and exhaust ventilation.
The PD-9 dispersion does not require the establishment of hygienic regulations for it (MPC and OBUV).
3.3. Test methods.
3.3.1. At least three point samples are taken, then combined, mixed thoroughly and an average sample is taken using the quartering method.
3.3.2. Determination of appearance. Appearance is determined visually during sampling.
3.3.3. Determination of crumb size. To determine the size of the PD-9 dispersion crumbs, use a metric ruler.
3.3.4. Determination of the mass of PD-9 dispersion in a plastic bag. To determine the mass of the PD-9 dispersion in a plastic bag, scales of the RN-10Ts 13M type are used.
3.3.5. Determination of Mooney viscosity. Determination of Mooney viscosity is based on the presence of a certain amount of polymer component in the PD-9 dispersion.
3.4. Manufacturer's warranty.
3.4.1. The manufacturer guarantees that the PD-9 dispersion meets the requirements of these technical specifications.
3.4.2. The guaranteed shelf life of the PD-9 dispersion is 6 months from the date of manufacture.
4. Experimental part.
This work explores the possibility of using polyvinyl chloride (PVC) as a binder (dispersion medium) to produce a paste based on combinations of the antioxidants diaphene FF and diaphene FP. The influence of this anti-aging dispersion on the thermal-oxidative and ozone resistance of rubbers based on SKI-3 rubber is also being studied.
Preparation of anti-aging paste.
In Fig. 1. The installation for preparing anti-aging paste is shown.
The preparation was carried out in a 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 the bath (2). The temperature in the flask was regulated using a contact thermometer (13). Mixing is carried out at a temperature of 70±5°C and using a paddle mixer (5).
Fig.1. Installation for preparing anti-aging paste.
1 – electric stove with a closed spiral (220 V);
2 – bathhouse;
3 – contact thermometer;
4 – contact thermometer relay;
5 – paddle mixer;
6 – glass flask.
Ingredient loading order.
The calculated amount of diaphene FF, diaphene FP, stearin and part (10 wt.%) of dibutylphthalan (DBP) was loaded into the flask. Then stirring was carried out for 10-15 minutes until a homogeneous mass was obtained.
Next, the mixture was cooled to room temperature.
Then polyvinyl chloride and the remaining part of DBP (9% wt.) were loaded into the mixture. The resulting product was unloaded into a porcelain glass. Next, the product was thermostatically controlled at temperatures of 100, 110, 120, 130, 140°C.
The composition of the resulting composition is given in Table 1.
Table 1
Composition of anti-aging paste P-9.
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
DBP 19.00 190.00
Stearin 1.00 10.00
Total 100.00 1000.00
To study the effect of antiaging paste on the properties of vulcanizates, a rubber mixture based on SKI-3 was used.
The resulting anti-aging paste was introduced into a rubber mixture based on SKI-3.
The compositions of rubber mixtures with anti-aging paste are given in Table 2.
The physical and mechanical properties of vulcanizates were determined in accordance with GOST and TU, given in Table 3.
table 2
Rubber compound compositions.
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
Zinc white 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 (P-9) is indicated in brackets.
Table 3
Item no. Name of GOST indicator
1 Conditional tensile strength, % GOST 270-75
2 Conditional voltage at 300%, % GOST 270-75
3 Elongation at break, % GOST 270-75
4 Permanent elongation, % GOST 270-75
5 Change in the above indicators after aging, air, 100°C * 72 h, % GOST 9.024-75
6 Dynamic tensile endurance, thousand cycles, E?=100% GOST 10952-64
7 Shore hardness, standard unit GOST 263-75
Determination of the rheological properties of antiaging paste.
1. Determination of Mooney viscosity.
Determination of Mooney viscosity was carried out using a Mooney viscometer (GDR).
The production of samples for testing and testing itself is carried out according to the methodology set out in the technical specifications.
2. Determination of the cohesive strength of paste compositions.
Paste samples, after gelatinization and cooling to room temperature, were passed through a 2.5 mm thick roller gap. Then, from these sheets, plates measuring 13.6 * 11.6 mm with a thickness of 2 ± 0.3 mm were produced in a vulcanizing press.
After curing the plates for 24 hours, the blades were cut out with a punching knife in accordance with GOST 265-72 and then, using an RMI-60 tensile testing machine at a speed of 500 mm/min, the breaking load was determined.
The specific load was taken as the cohesive strength.
5. The results obtained and their discussion.
When studying the possibility of using PVC, as well as a composition of polar plasticizers as binders (dispersion medium) to obtain pastes based on combinations of antioxidants diaphene FF and diaphene FP, it was revealed that the alloy of diaphene FF with diaphene FP in a mass ratio of 1:1 is characterized by a low speed crystallization and melting point about 90°C.
The low crystallization rate plays a positive role in the manufacturing process of PVC plastisol filled with a mixture of antioxidants. In this case, the energy costs for obtaining a homogeneous composition that does not separate over time are significantly reduced.
The melt viscosity of diaphene FF and diaphene FP is close to the viscosity of PVC plastisol. This makes it possible to mix the melt and plastisol in reactors with anchor-type stirrers. In Fig. Figure 1 shows a diagram of the installation for making pastes. The pastes are drained satisfactorily from the reactor before they are pre-gelatinized.
It is known that the gelatinization process occurs at 150°C and above. 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 polymer hydroperoxide during the oxidation of isoprene rubber.
RH+O2ROOH,
2. One of the directions of decomposition of polymer hydroperoxide.
ROOH RO°+O°H
3. Having completed the oxidation stage due to the antioxidant molecule.
AnH+RO° ROH+An°,
Where An is an antioxidant radical, for example,
4.
5. Properties of amines, including secondary ones (diaphene FF), to 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 gelatinization process (pre-gelatinization) at relatively low temperatures (100-140°C), the phenomena mentioned above can be avoided, i.e. reduce the likelihood of hydrogen chloride liberation.
The final gelatinization process results in pastes with a Mooney viscosity lower than the viscosity of the filled rubber compound and low cohesive strength (see Fig. 2.3).
Pastes with low Mooney viscosity, firstly, are well distributed in the mixture, and secondly, small parts of the components that make up the paste can easily migrate into the surface layers of vulcanizates, thereby protecting the rubber from aging.
In particular, in the issue of “crushing” paste-forming compositions, great importance is attached to explaining the reasons for the deterioration of the properties of some compositions under the influence of ozone.
In this case, the initial low viscosity of the pastes and, in addition, does not change during storage (Table 4), allows for a more uniform distribution of the paste, and allows the migration of its components to the surface of the vulcanizate.
Table 4
Viscosity indicators according to Mooney paste (P-9)
Initial indicators Indicators after storing the paste for 2 months
10 8
13 14
14 18
14 15
17 25
By changing the content of PVC and antioxidants, it is possible to obtain pastes suitable for protecting rubber from thermal oxidation 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 studied. The physical and mechanical properties of vulcanizates using paste (P-9) are presented in Tables 5 and 6.
The resistance of the studied vulcanizates to thermal-oxidative aging increases with increasing content of anti-aging paste in the mixture, as can be seen from Table 5.
Indicators of change in conditional strength, standard composition (1-9) is (-22%), while for composition (4-9) - (-18%).
It should also be noted that with the introduction of a paste that helps increase the resistance of vulcanizates to thermal-oxidative aging, more significant dynamic endurance is imparted. Moreover, in explaining the increase in dynamic endurance, it is apparently impossible to limit ourselves only to the factor of increasing the dose of antioxidant in the rubber matrix. PVC probably plays an important role in this. In this case, it can be assumed that the presence of PVC can cause the formation of continuous chain structures that are evenly distributed in the rubber and prevent the growth of microcracks that occur during cracking.
By reducing the content of anti-aging paste and thereby the proportion of PVC (Table 6), the effect of increasing dynamic endurance is practically canceled. In this case, the positive effect of the paste appears only under conditions of thermal-oxidative and ozone aging.
It should be noted that the best physical and mechanical properties are observed when using antiaging paste obtained under milder conditions (pre-gelatinization temperature 100°C).
Such conditions for obtaining the paste provide a higher level of stability compared to the paste obtained by thermostatting 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 maintaining 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 diaphene FF in composition with diaphene 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 tensile strength, 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 unit. 40 43 40 40
Conditional tensile strength, 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
Physico-mechanical properties of vulcanizates containing anti-aging paste (P-9).
Indicator name Mixture code
1-25 2-25 3-25 4-25
1 2 3 4 5
Conditional tensile strength, 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 unit. 37 36 37 38
Change in indicator after aging, air, 100°C*72 h
Conditional tensile strength, MPa -10.5 -7 -13 -23
Conditional stress at 300%, MPa 30 -2 21 14
Elongation at break, % -8 -5 -7 -8
Permanent 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 diaphene FP and diaphene FF plastisol based on PVC makes it possible to obtain pastes that do not delaminate over time, with stable rheological properties and a Mooney viscosity higher than the viscosity of the rubber mixture used.
2. When containing a combination of diaphene FP and diaphene FF in the paste equal to 30% and PVC plastisol 50%, the optimal dosage for protecting rubber from thermal-oxidative and ozone aging may be a dosage equal to 2.00 parts by weight per 100 parts by weight of rubber mixtures.
3. Increasing the dosage of antioxidants over 100 parts by weight of rubber leads to an increase in the dynamic endurance of rubber.
4. For rubbers based on isoprene rubber operating in static mode, you can replace diaphene FP with anti-aging paste P-9 in an amount of 2.00 wt h per 100 wt h of rubber.
5. For rubbers operating under dynamic conditions, replacing diaphene with FP is possible with an antioxidant content of 8-9 parts by weight per 100 parts by weight of rubber.
6.
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– Garmonov I.V. Synthetic rubber. – L.: Chemistry, 1976. – 450 p.
– Aging and stabilization of polymers. /Ed. Kozminsky A.S. – M.: Chemistry, 1966. – 212 p.
– Sobolev V.M., Borodina I.V. Industrial synthetic rubbers. – M.: Chemistry, 1977. – 520 p.
– Belozerov N.V. Rubber technology: 3rd edition, revised. and additional – M.: Chemistry, 1979. – 472 p.
– Koshelev F.F., Kornev A.E., Klimov N.S. General rubber technology: 3rd edition, revised. and additional – M.: Chemistry, 1968. – 560 p.
– Technology of plastics. /Ed. Korshak V.V. Ed. 2nd, revised and additional – M.: Chemistry, 1976. – 608 p.
– Kirpichnikov P.A., Averko-Antonovich L.A. Chemistry and technology of synthetic rubber. – L.: Chemistry, 1970. – 527 p.
– Dogadkin B.A., Dontsov A.A., Shertnov V.A. Chemistry of elastomers. – M.: Chemistry, 1981. – 372 p.
– Zuev Yu.S. Destruction of polymers under the influence of aggressive environments: 2nd edition, revised. and additional – M.: Chemistry, 1972. – 232 p.
– Zuev Yu.S., Degtyareva T.G. Resistance of elastomers under operating conditions. – M.: Chemistry, 1980. – 264 p.
– Ognevskaya T.E., Boguslavskaya K.V. Increasing the weather resistance of rubber due to the introduction of ozone-resistant polymers. – M.: Chemistry, 1969. – 72 p.
– Kudinova G.D., Prokopchuk N.R., Prokopovich V.P., Klimovtsova I.A. // Raw materials for the rubber industry: present and future: Abstracts of the fifth anniversary Russian scientific and practical conference of rubber workers. – M.: Chemistry, 1998. – 482 p.
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– Encyclopedia of Polymers / Ed. Kabanova V.A. and others: In 3 volumes, T. 2. – M.: Soviet Encyclopedia, 1972. – 1032 p.
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How long car tires last depends on the use, technical condition of the car and your driving style. Professional maintenance and constant inspections will ensure safe driving.
Tires are in direct contact with the road, so it is very important to maintain the quality of tires in good condition, because safety, fuel efficiency and comfort depend on their quality. It is necessary not only to select the right tires, but also to monitor their condition to prevent their premature aging and wear.
The main causes of damage and wear of car tires
There are always plenty of unpleasant surprises on the road, which ultimately lead to damage and wear of tires: stones, holes, glass. We can neither predict nor prevent them. But the problems that arise due to high speed, air pressure and overload completely depend on the car owner and are completely solvable.
1. Moving at high speed
Watch the speed limit carefully! When driving at high speeds, the risk of tire damage and wear is most likely, because the tires heat up more and lose pressure faster.
2. Tire pressure
Excessive and insufficient tire pressure reduces the service life of tires and leads to premature wear (overheating of the tire, decreased level of adhesion to the road surface), so it is necessary to monitor sufficient tire pressure.
3. Overload
Follow manufacturers' recommendations regarding load! To avoid overloading your tires, carefully read the load index on the tire sidewall. This is the maximum value and should not be exceeded. When overloaded, severe overheating of the tire also occurs, and, accordingly, its premature aging and wear.
How to protect tires from premature aging and wear
Even the highest quality and most expensive tires do not last long. Wear and aging of a tire is only a matter of time, but we have the power to increase the service life of tires to the maximum. What can you do to extend the life of your tires and protect them from wear? Here are some simple tips:
When should you change your tires?
A weekly tire check (inspecting the tread depth, air pressure in the tires, any damage on the sidewalls of the tires, the appearance of signs of uneven wear) allows you to really assess the degree of wear and aging of the tires. If doubts about the safety of using tires have crept into your head, then contact an experienced specialist for advice on further operation.
The tire must be replaced if:
Tire life
The service life of tires varies greatly, so it is almost impossible to predict how long a particular tire will last. A tire contains various ingredients and rubber compound materials that affect its service life. Weather, usage and storage conditions can also extend or shorten the life of tires. Therefore, in order to increase the service life of tires, protect them from wear and aging, monitor their appearance, maintain tire pressure, the appearance of the following effects: noise, vibration or pull to the side of the car when driving, and of course, store them correctly.
Rules for storing car tires
Even if tires sit unused or rarely used, they age. It is advisable not to store uninflated or dismantled tires in piles for a long time. Also, do not store any foreign objects, especially heavy objects, on the tires. Avoid being near the tires with hot objects, flames, sparking sources and generators. When interacting with tires, it is recommended to use protective gloves.
Tires are stored in a dry, well-ventilated room at a constant temperature, protected from precipitation and direct sunlight. To avoid changing the rubber structure, do not store chemicals or solvents near tires. Avoid storing sharp metal, wood or other objects near tires that could damage them. Black rubber is afraid of excess heat and frost, and excessive humidity leads to its aging. Tires should not be washed under a strong stream of water; soap or a special product is sufficient.
From all that has been said, the conclusion suggests itself that proper storage, operation and a comprehensive check of their condition will help protect tires from wear and aging.
