Natural rubber (NR)
Non polar crystalline rubber, high elasticity at room temperature, can induce crystallization when stretched, has good self reinforcement, and pure rubber strength can reach 16.7~28.4MPa， Higher after carbon black reinforcement. The elongation rate can reach 1000%, and the elastic modulus is about 3~6MPa。 Excellent flexural fatigue resistance and low heat generation. But the main chain contains a large number of unsaturated double bonds, which have poor resistance to oxygen, ozone, and UV aging, and are prone to cracking. Not resistant to non-polar hydrocarbon solvents (gasoline, benzene, etc.), relatively stable in polar solvents. Good alkali resistance, not resistant to strong acids. The glass transition temperature is about -70 ℃, with a significant decrease in elasticity below 0 ℃ and decomposition starting above 200 ℃. Good processing performance and excellent dispersibility with additives. Commonly used in tires, shock absorbers, rubber hoses, etc.
Styrene butadiene rubber (SBR)
Non polar non crystalline rubber has a lower double bond content than NR, and the benzene ring passivates the double bond activity, so the vulcanization rate is slow, it is not easy to burn, and its heat resistance, oxygen resistance, and sunlight resistance are better than NR. The strength of pure rubber is low (about 2MPa), and after carbon black reinforcement, it can reach 17-24MPa. Elasticity, strength, cold resistance, and flexural flexibility are not as good as NR, with high heat generation, large shrinkage during rolling and extrusion, and poor adhesion. Wear resistance and breathability are better than NR. Oil resistance is poor, but slightly better than NR. Low cost, mainly used for tire tread, rubber shoes, conveyor belts, etc.
Butadiene rubber (BR)
Non polar crystalline rubber, with a high cis structure and a glass transition temperature as low as -105 ℃, is the most cold resistant and elastic rubber in general use. It has excellent wear resistance, low heat generation, and good flexural flexibility. But pure rubber has low strength and needs to be reinforced with carbon black. Its tensile strength and tear strength are not as good as NR. It is not oil resistant and can be filled with a large amount of oil and carbon black to reduce costs. Poor processing performance, poor viscosity, poor resistance to wet and slippery road surfaces, high cold flow, often used in combination with NR. Mainly used for tire sidewall and wear-resistant products.
Isoprene rubber (IR)
Synthetic NR is similar to NR in structure, but with less gel and impurities and uniform texture. Good processability, can eliminate the need for plastic molding, and has minimal shrinkage during extrusion. Elasticity, heat generation, and crack resistance are slightly better than NR, but the tensile stress, tensile strength, and tear strength are slightly lower, and it is easy to stick to the rollers during mixing. The water resistance, electrical insulation, and aging resistance are slightly better than NR. Can be used in conjunction with CR to improve ozone resistance. Suitable for tires, medical products, rubber shoes, etc., it can basically replace NR.
Butyl rubber (IIR)
Co polymerized with isobutene and a small amount of isoprene, with low unsaturation (1.6%)~2.0%). The airtightness is the best among all rubbers, about 8 times higher than NR. Excellent heat resistance, weather resistance, ozone resistance, and acid alkali corrosion resistance, with ozone resistance more than ten times better than NR. Excellent electrical insulation, with a volume resistance of up to 10¹ ⁶Ω · Cm. Low elasticity, good shock absorption, -30~+Excellent damping performance within the temperature range of 50 ℃. Disadvantages: slow vulcanization, poor self adhesion and mutual adhesion, poor oil resistance, and low room temperature elasticity. The vulcanization speed and adhesion can be improved by halogenation modification. Mainly used for inner tubes, airtight layers, sealing products, and shock absorbers.
Ethylene propylene rubber (EPM/EPDM)
Saturated main chain rubber, binary EPM without double bonds, requiring peroxide vulcanization; A small amount of third monomer is introduced into ternary EPDM, which can be sulfurized with sulfur. The aging resistance is extremely excellent, with ozone resistance far superior to IIR and CR. It does not crack after three years of exposure to sunlight and can be used for a long time at 150 ℃, making it the most aging resistant rubber among general rubbers. Resistant to polar chemicals and acids and bases, but not to hydrocarbon oils. The electrical insulation exceeds IIR, with good resilience (50%~60%) and good low-temperature performance (hardening at -57 ℃ and brittleness at -77 ℃). Disadvantages: Slow vulcanization speed, poor compatibility with unsaturated rubber, and poor self-adhesive properties. Cheap price, widely used in rubber hoses, adhesive tapes, automotive sealing strips, wires and cables.
Chloroprene rubber (CR)
Polar crystalline rubber, due to its chlorine containing molecular chain, has excellent weather resistance and ozone resistance, and its heat resistance is comparable to NBR. Outstanding flame resistance, releases HCl upon contact with fire, self extinguishes without prolonging combustion, making it the most flame retardant among all general-purpose rubbers. Oil resistance is better than NR and SBR, but not as good as NBR. It is resistant to general acidity and alkalinity, but not to concentrated sulfuric acid and concentrated nitric acid. Good adhesion, commonly used in adhesives. The airtightness is second only to IIR and NBR. Metal oxides (MgO/ZnO) can be used for sulfurization. Disadvantages: Poor storage stability, should not be stored at room temperature for more than one year; Easy to crystallize and harden at low temperatures; Processing temperature sensitivity, easy to stick to rollers, and prone to burning. Mainly used for heat-resistant conveyor belts, oil resistant rubber hoses, wire and cable sheaths, and door and window sealing strips.
Nitrile rubber (NBR)
Polar amorphous rubber, co polymerized with butadiene and acrylonitrile, has enhanced oil resistance with increasing acrylonitrile content (commonly used grades NBR-40, -26, -18). Pure adhesive strength is only 3~4MPa， After carbon black reinforcement, it can reach 25~30MPa。 Good air tightness, second only to IIR. Heat resistance, wear resistance, and aging resistance are better than NR. Disadvantages: poor elasticity, poor cold resistance, and the higher the acrylonitrile content, the more obvious; Extremely poor electrical insulation (but suitable for making anti-static products); Poor ozone resistance, often requiring the addition of anti-aging agents or combined with PVC; Not resistant to concentrated and oxidizing acids. Widely used in oil seals, oil pipelines, oil resistant gaskets, rubber rollers, etc.
Hydrogenated Nitrile Rubber (HNBR)
NBR undergoes hydrogenation treatment, resulting in a highly saturated main chain. While retaining good oil resistance, the heat resistance is greatly improved (up to 150 ℃), with excellent resistance to ozone and chemical media (acid, alkali, H ₂ S, etc.), small compression permanent deformation, and excellent strength and wear resistance. The comprehensive performance is between NBR and fluororubber, with a price lower than fluororubber but much higher than NBR. Slightly poor cold resistance (-55~-38 ℃). Mainly used for harsh working conditions such as oilfield drilling seals, automotive synchronous belts, heat-resistant oil pipes, high-pressure seals, etc.
Introduction to Special Rubber
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Silicone rubber (VMQ)Main chain Si-O bond, with a wide temperature range (-100~+300 ℃), excellent resistance to ozone and electrical insulation. But it has low strength, poor acid and alkali resistance, and is expensive. Used for high/low temperature seals, insulation products, and medical supplies.
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Fluorosilicone rubber (FVMQ)The introduction of trifluoropropyl groups into the silicone rubber side chains not only preserves temperature resistance but also significantly improves oil and solvent resistance. It can be used for a long time at -50~+200 ℃ and can reach up to 250 ℃ in the short term. Used for aviation and automotive oil resistant seals.
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Fluororubber (FKM)Highly resistant to heat oxidation and chemical corrosion, comparable to silicone, with outstanding resistance to strong acids, strong oxidants, and organic solvents. But the cold resistance is poor, the strength decreases rapidly at high temperatures, the price is expensive, and the processing is difficult. Used for sealing aviation engines and corrosion-resistant chemical components.
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Polyurethane rubber (PU)The mechanical strength is extremely high, and the wear resistance ranks first among all rubbers, several times higher than NR. Good air tightness and excellent oil resistance. Disadvantages: Not resistant to high temperatures and water (easily hydrolyzed). It is used for wear-resistant rollers, seals, shock absorption products, and can also be foamed into foam materials.
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Polysulfide rubberThe main chain contains sulfur, with excellent oil resistance, ozone resistance, and good airtightness. It has excellent low-temperature flexibility, but poor strength, heat resistance, and high price.
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Acrylic Rubber (ACM)High polarity saturated rubber, excellent heat and oil resistance, good weather and ozone resistance, but poor water and steam resistance.
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Chlorohydrin rubberIt has both saturation and polarity, comprehensive cold resistance, heat resistance, oil resistance, ozone resistance, flame retardancy, acid and alkali resistance, and is relatively low in price. Used for oil pipes, seals, etc.
