Discussion on the physical properties of rubber compounds

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1. Tensile strength Tensile strength represents the ultimate ability of a product to resist tensile damage (1) Tensile strength of rubber: Unfilled vulcanized rubber: polyurethane rubber PUR>natural rubber NR/isoamyl IR>chloroprene rubber CR>butyl rubber IIR>chlorosulfonated polyethylene CSM>butadiene rubber NBR/fluorine rubber FKM>butadiene rubber BR>ethylene propylene diene monomer rubber EPDM>styrene-butadiene rubber SBR>acrylate rubber ACM>chlorohydrin rubber CO>silicone rubber Q Filled vulcanized rubber: polyurethane rubber PUR>polyester thermoplastic elastomer>natural rubber NR/isoamyl IR>SBS thermoplastic elastomer>butadiene rubber NBR/chloroprene CR>styrene-butadiene rubber SBR/ethylene propylene diene monomer rubber EPDM/fluorine rubber FKM>chlorosulfonated polyethylene CSM>butyl rubber IIR>butadiene rubber BR/chlorohydrin rubber CO>acrylate rubber ACM>silicone rubber Q Under rapid deformation, the tensile strength of rubber is higher than that under slow deformation; the tensile strength tested at high temperature is much lower than the tensile strength at room temperature. (2) The influence of the vulcanization system For commonly used soft vulcanized rubber, when wanting to increase the tensile strength through the vulcanization system, the traditional vulcanization system of sulfur-accelerator should be used, and the dosage of sulfur should be appropriately increased. At the same time, the accelerator should be thiazoles such as M, DM and guanidine, and the dosage should be increased appropriately. (3) Influence of the filling system. The smaller the particle size of the filler, the larger the specific surface area, and the greater the surface activity, the better the reinforcing effect. For vulcanized rubber based on crystalline type (such as natural rubber), the tensile strength may decrease monotonically as the amount of filler increases. For vulcanized rubber based on amorphous type (such as styrene-butadiene rubber), the tensile strength increases with the amount of filler, reaches a maximum value, and then decreases. For vulcanized rubber based on low-unsaturation rubber (such as EPDM rubber, butyl rubber), the tensile strength increases with the increase in the amount of filler, and can remain unchanged after reaching the maximum value. For thermoplastic elastomers, fillers reduce the tensile strength. In general, when the amount of carbon black in soft rubber is 40-60 parts, the tensile properties of the vulcanized rubber are better. (4) Effect of softening system In general, adding softener will reduce the tensile strength of vulcanized rubber. However, when the amount of softener does not exceed 5 parts, the tensile strength of vulcanized rubber may increase. Because it contains a small amount of softener, the dispersion effect of carbon black can be better. Aromatic hydrogen oil has little effect on the tensile strength of non-polar unsaturated rubber (isoprene rubber, butadiene rubber, styrene-butadiene rubber) vulcanized rubber. A dosage of 5-15 parts of paraffin oil has a great influence on the tensile strength of non-polar unsaturated rubber (isoprene rubber, butadiene rubber, styrene-butadiene rubber) vulcanized rubber. For polar unsaturated rubber (such as butadiene rubber, chloroprene rubber), it is best to use aromatic hydrogen oil and ester softeners (such as DBP, DOP, etc.) (5) Other methods to improve the tensile strength of vulcanized rubber: blending rubber with certain resins; such as natural rubber, styrene-butadiene rubber and high styrene resin blending. Natural rubber and polyethylene blending. Butadiene rubber and polyvinyl chloride blending, ethylene propylene rubber and polypropylene blending. Chemical modification of rubber. Modification of fillers ==> using surfactants or coupling agents. 2. Tear strength Tear strength is a phenomenon in which cracks or cracks in materials rapidly expand and crack when stressed, causing damage. (1) Tear strength of various rubbers (vulcanized rubber): natural rubber NR> polyester thermoplastic elastomer> isoprene rubber IR> polyurethane rubber PUR> chlorohydrin rubber CO> nitrile rubber NBR> butyl rubber IIR> neoprene CR> chlorosulfonated polyethylene CSM> SBS thermoplastic elastomer> butadiene rubber BR> styrene-butadiene rubber SBR> ethylene propylene diene monomer rubber EPDM> fluorine rubber FKM> silicone rubber Q> acrylate rubber ACM (2) The relationship between tear strength and vulcanization system: The relationship between tear strength and cross-link density has a maximum value. Generally, as the cross-link density increases, the tear strength increases and reaches a maximum value; then as the cross-link density increases, the tear strength decreases sharply. It is similar to tensile strength, but the cross-link density for optimal tear strength is lower than the cross-link density for optimal tensile strength. The traditional vulcanization system of sulfur-accelerator should be used, and the sulfur dosage is 2.0-3.0 parts. The accelerator should be of moderate activity and good flatness, such as DM, CZ, etc.; over-sulfur has a large impact. In natural rubber, if an effective vulcanization system is used instead of the ordinary vulcanization system, the tear strength will be significantly reduced. However, the effect of over-sulfur is not significant. (3) The relationship between tear strength and filling system: As the carbon black particle size decreases, the tear strength increases. Carbon black with low structure is beneficial to improving tear strength. Increasing the amount of highly wear-resistant carbon black in natural rubber can increase the tear strength. When the amount of high wear-resistant carbon black is increased (60-70 parts) in styrene-butadiene rubber, the maximum value appears, and then gradually decreases. Generally, synthetic rubber, especially butyl rubber, can significantly improve the tear strength when reinforced with carbon black. Higher tear strength can be obtained by using isotropic reinforcing fillers, such as carbon black, white carbon black, white yanhua, lithopone and zinc oxide. However, the use of anisotropic reinforcing fillers, such as clay, magnesium carbonate, etc., cannot achieve higher tear strength. Certain coupling agent-modified inorganic fillers, such as calcium carbonate modified with carboxylated polybutadiene CPB, aluminum hydroxide, can also improve the tear strength of styrene-butadiene rubber. (4) The effect of softening system on tear strength. Usually, adding softener will reduce the tear strength of vulcanized rubber. In particular, paraffin oil is extremely detrimental to the tear strength of styrene-butadiene rubber vulcanized rubber. Aromatic hydrogen oil can ensure the tear strength of styrene-butadiene rubber vulcanized rubber. When using petroleum-based softeners as softeners for nitrile rubber and chloroprene rubber, high aromatic hydrogen oil with an aromatic hydrogen content higher than 50-60% should be used instead of paraffin oil. 3. High modulus stress and hardness rubber: chloroprene rubber, nitrile rubber, polyurethane rubber, crystalline rubber such as natural rubber, etc. Whether it is pure rubber vulcanization or filled vulcanized rubber, as the cross-linking density increases, the modulus stress and hardness also rise linearly. The size of the cross-linking density is usually achieved by adjusting the type and amount of vulcanizing agents, accelerators, co-vulcanizing agents, activators and other compounding agents in the vulcanization system. Some accelerators have only one function, and some accelerators have multiple functions; such as thiuram, guanidine and sulfenamide accelerators are very active. The elongation stress of the vulcanized rubber is also relatively high. TMTD has multiple functions, including activation, promotion and vulcanization, so TMTD can effectively increase the elongation stress. In the formula design, in order to keep the tensile stress of the vulcanized rubber constant, when it is necessary to reduce the polysulfide bond content and reduce the sulfur dosage, the accelerator dosage should be increased. The product of the sulfur dosage and the accelerator dosage (sulfur quantity * The amount of accelerator) remains constant. The relationship between filling system and modulus stress: Different types of fillers have different effects on the modulus stress and hardness of vulcanized rubber: fillers with small particle size and high activity will increase the modulus stress and hardness of vulcanized rubber to a greater extent. As the amount of filler increases, the modulus stress and hardness also increase. Carbon black with high structure also has high modulus stress. Generally speaking, the hardness of vulcanized rubber increases with the increase in filler dosage. 4. Abrasion Wear resistance represents the ability of vulcanized rubber to resist material loss due to surface damage under friction. There are three main forms of rubber abrasion: wear, abrasion, fatigue abrasion, curling abrasion, and the wear resistance of vulcanized rubber is related to tensile strength, elongation stress, tear strength, fatigue performance, and viscoelastic properties. The modulus stress has different effects on different types of wear. When the modulus stress is high, the protrusions on the friction surface press into the rubber to a small depth, have strong resistance to deformation, and have a small friction coefficient. The rubber surface is rigid and not easy to wrinkle and cause curling, which is beneficial to wear and curling. Improving the elasticity of the vulcanized rubber will also increase the wear resistance. Influence of rubber type: In general diene rubber, the wear resistance of the vulcanized rubber is as follows: Butadiene rubber > Solution-polymerized styrene-butadiene rubber > Latex-polymerized styrene-butadiene rubber > Natural rubber > Isoprene rubber The wear resistance of butadiene rubber vulcanized rubber increases with the increase in the content of cis chain links (1,4 structure). The elasticity, tensile strength, and tear strength of styrene-butadiene rubber are not as good as natural rubber, but they are better than natural rubber. The wear resistance of styrene-butadiene rubber increases with the increase in molecular weight. The abrasion resistance of ethylene-propylene rubber vulcanizate is better than that of isoprene rubber, and its abrasion resistance increases with the increase of acrylonitrile content. Carboxylic nitrile rubber has good abrasion resistance. The abrasion resistance of ethylene-propylene rubber vulcanizate is equivalent to that of styrene-butadiene rubber. As the Mooney viscosity of raw rubber increases, its abrasion resistance also increases. The abrasion resistance of butyl rubber vulcanized rubber is similar to that of isoprene rubber at 20 degrees; but when the temperature rises to 100 degrees, the abrasion resistance decreases sharply. When butyl rubber is mixed at high temperature, the abrasion resistance of the vulcanized rubber is significantly improved. Vulcanized rubber based on chlorosulfonated polyethylene has high abrasion resistance, and the wear resistance at high temperatures is also good. Acrylic rubber-based vulcanized rubber is slightly worse than nitrile rubber vulcanized rubber. Polyurethane rubber is the most wear-resistant among all rubbers at room temperature.