Blog viết cho nhân viên Cty cao su Việt.
SBR, một loại cao su tổng hợp được sử dụng phổ biến.
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| SBR, một nguyên liệu cao su dễ dùng |
Các tài liệu cao su trong thư viện vLAB cũng có nhiều, tuy nhiên để góp thêm những tư liệu khác, BP Nhãn hiệu có đường dẫn sau, mời các bạn tìm đọc nguyên gốc.
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4.0 Properties of E-SBR: E-SBR is commercially available in Mooney viscosities ranging from 30 to about 120 (ML1+4@125C). Lower Mooney viscosity E-SBR grades band more easily on the mill, incorporate fillers and oil more readily, show less heat generation during mixing, are calendered more easily, shrink less, give
higher extrusion rates and have superior extrudate appearance than the higher Mooney viscosity grades. On the other hand, the high Mooney viscosity SBR’s have better green strength, less porosity in the vulcanizate, and accept higher filler and oil loadings.
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| Hiểu được cấu trúc SBR, sẽ dễ sử dụng |
As the molecular weight of the SBR increases, the vulcanizate resilience and the mechanical properties, particularly tensile strength and compression set, improve. The processability of SBR improves as its molecular weight distribution broadens. Formation of high molecular weight fractions with the increase in the average molecular weight can however, prevent improvements in the processability. This is due to the fact that the tendency for gel formation also increases at higher molecular weights.
In addition to the polymer viscosity, polymerization temperature also plays an important role in shaping the processability. E-SBRs produced at low polymerization temperatures have less chain branching than those produced at higher temperature. At an equivalent viscosity, cold polymerized E-SBR is normally easier to process than hot polymerized E-SBR, and this applies particularly to a better banding on mills, less shrinkage after calendering, and a superior surface of green tire compounds. Hot rubbers give better green strength because they have more chain branching.
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| Sản phẩm dùng cao su SBR |
The styrene content of most emulsion SBR varies from 0% to 50%. The percent styrene of most commercially available grades of E-SBR is 23.5%. In vulcanizates of SBR, as styrene content increases, dynamic properties and abrasion resistance decrease while traction and hardness increase.
Polymerization temperature also affects the microstructure of E-SBR. In the cold polymerized E-SBRs, the butadiene component has, on average, about 9% cis-1.4, 54.5% trans-1.4, and 13% of vinyl-1.2 structure. At a 23.5% bound styrene level, the glass transition temperature, Tg, of SBR is about –50°C. As the styrene content in the SBR increases, the glass transition temperature also increases. Rubbers with very low Tg values are characterized by a high resilience and good abrasion resistance, but have poor wet traction. By contrast, those rubbers with high Tg, as, for instance, SBR 1721, exhibit a low resilience and poor abrasion resistance with an excellent wet traction.
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| SBR có thể có ứng dụng rộng |
The emulsifier remains in the rubber after coagulation can also have an influence on the processability. Rosin acid emulsifiers impart better knitting, tack and adhesion to the SBR polymer. Generally, polymers emulsified with rosin acid have better extrusion rates, slower cure rates, poorer heat resistance and can cause mold fouling and polymer discoloration. Fatty acid emulsified SBR polymers generally have less tack, faster curing, and high tensile properties. A compromise of the above properties is obtained by using a mixed rosin acid/fatty acid emulsifier system.
4.1 Mechanical Properties. Since SBR lacks the self-reinforcing qualities of natural rubber due to stress induced crystallization, gum vulcanizates of SBR have lower tensile properties. The tensile property of E-SBR vulcanizates depends in great measure on the type and amount of filler in the compound. Cured gum stocks have only 2.8 to 4.2 MPa tensile strength, while fine particle carbon black loadings can produce tensile strength of 27.6 Mpa. Though the compression set of some of the common E-SBR compounds is high, by proper compounding and blending, it is possible to obtain E-SBR vulcanizates with a low compression set.
4.2 Electrical Properties. SBR is a non-polar polymer and its vulcanizates are poor conductors of electricity. The electrical properties of E-SBR depend to a large extent on the amount and type of emulsifier and coagulating agent(s) used.
4.3 Resistance to Fluids. While E-SBR vulcanizates are resistant to many polar solvents such as dilute acids and bases, they will swell considerably when in contact with gasoline, oils, or fats. Due to this limitation, SBR cannot be used in applications that require resistance to swelling in contact with hydrocarbon solvents.
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| vLAB có thể kiểm tra các chỉ tiêu một sản phẩm dùng SBR |
4.3 Cure Properties. SBR can be cured with a variety of cure systems including sulfur (accelerators and sulfur), peroxides and phenolic resins. Processing of SBR compounds can be performed in a mill, internal mixers or mixing extruders. SBR compounds are cured in a variety of ways by compression, injection molding, hot air or steam autoclaves, hot air ovens, microwave ovens and combinations of these techniques.
5.0 Types of SBR: There is a large variety of E-SBR types based on the styrene content, polymerization temperature, staining or non-staining antioxidants, oil and carbon black content. Each of these basic classifications include a variety of SBR polymer variations with respect to Mooney viscosities, coagulation types, emulsifier type, oil levels, and carbon black types and levels. Tabe 1 shows the basic groups of E-SBR.
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