Knowledge of bromobutyl rubber (BIIR)

[Rubber Technology Network - Basics]

Bromobutyl rubber (BIIR) is a modified product of IIR. The purpose of modification is to improve the activity of IIR, improve its compatibility with unsaturated rubber, and improve self-adhesiveness, mutual viscosity and co-crosslinking ability while maintaining The original features of IIR. After IIR bromination, in addition to increasing the cross-linking position, it also enhances the reactivity of the double bond. This is because the bond energy of the C-Br bond is small, and the brominated butyl rubber has a higher vulcanization reaction activity, so it has a faster vulcanization rate and a stronger vulcanization suitability, and is more co-vulcanized than a general-purpose rubber. it is good. Compared with ordinary butyl rubber, bromobutyl rubber adds the following characteristics: (1) fast vulcanization speed; (2) good compatibility with natural rubber and styrene-butadiene rubber; (3) natural rubber, styrene-butadiene The bonding performance of the rubber is improved; (4) it can be vulcanized by zinc oxide alone (BIIR is the only elastomer which can be vulcanized by sulfur alone or vulcanized with zinc oxide), and the vulcanization method is diversified; (5) it has good heat resistance.

With so many advantages, bromobutyl rubber is gradually replacing ordinary butyl rubber in various applications, such as radial tires, bias tires, sidewalls, inner tubes, container liners, pharmaceutical stoppers and machine liners. And other industrial products. Bromobutyl rubber is an irreplaceable raw material for the manufacture of tubeless tires and medical products.

Method for producing 1 bromobutyl rubber

The preparation methods of BIIR include dry-mixing bromination and solution bromination. The dry-mixing bromination method is obtained by thermally kneading N-bromosuccinimide, dibromodimethylhydantoin or activated carbon bromine (mass fraction 0.312) with IIR on an open mill. BIIR; solution bromination is prepared by dissolving IIR in a chlorinated hydrocarbon solvent and then introducing bromine having a mass fraction of about 0.03. The process is continuous and the product quality is uniform and stable. The optimum mass fraction of bromine in BIIR is 0.017-0.022.

Application study of 2 bromobutyl

2.1 Process requirements

The bromobutyl rubber has a double bond on the molecular chain and contains a bromine atom. Therefore, vulcanization can be carried out by various methods, and the vulcanization system should be selected according to the physical properties required for the rubber product. The mixing, calendering and extrusion process of bromobutyl rubber is similar to ordinary butyl rubber with the same Mooney viscosity. However, since bromobutyl rubber has a faster vulcanization speed and is easy to be scorched, the following should be noted:

1. The temperature of the rubber compound. If the mixing temperature of the bromobutyl rubber exceeds 130 ° C, there is a risk of scorching, and if the temperature is too high, the rubber is easily broken, resulting in poor processing of the rubber compound.

2. Bromobutyl rubber is corrosive to the mold, so it should be protected during molding, such as using high quality molds and coating protection, avoiding the use of water-based release agent and maintaining high temperature, avoiding mold temperature fluctuations. Wait.

2.2 Combined use and blending system

2.2.1 IIR/BIIR

The use of BIIR/IIR can improve the processability and physical properties of the IIR, while also shortening the curing time of the IIR, and the adhesiveness of the interface with the glue is large, and the viscosity of the rubber is lowered, and the processing property is improved. In addition, the addition of ordinary butyl rubber to bromobutyl rubber is also an important way to reduce production costs.

The combination of ordinary butyl rubber and bromobutyl rubber can improve the self-adhesiveness of the rubber compound and has good process performance. With the increase of the amount of bromobutyl rubber in the rubber, the vulcanization rate is obviously accelerated, and the ultraviolet absorbance and easy oxide of the rubber are used. The two indicators will gradually improve; and the change of the bromobutyl content in the rubber will not have much influence on the physical and mechanical properties and aging properties of the combined rubber; the vulcanization system of the common butyl rubber and bromobutyl rubber will be used. Sulfur vulcanization or morphine is effective in vulcanization.

2.2.2 NR/BIIR combined system

Bromobutyl rubber can be used in combination with natural rubber in any ratio. The combination of bromobutyl rubber and natural rubber has a fast vulcanization rate, which improves the airtightness of natural rubber and improves its heat resistance, weather resistance and resistance to various chemicals. Natural rubber can improve the adhesion of bromobutyl rubber-based compounds.

The largest amount of bromobutyl rubber used in tire production is in the hermetic layer formulation for tubeless tires. Some studies have compared the bromobutyl rubber inner liner with bromobutyl rubber/natural rubber and the innerliner. The results show that the combination of BIIR and NR is to improve the adhesion of the rubber itself and improve it. Its physical properties shorten its vulcanization time. It has also been pointed out in the literature that BIIR and NR do not use 100% instead of 100% for the inner liner formulation because of the production cost and production process control. However, it should be noted that since the blending of BIIR and NR is difficult to achieve homogeneous in actual use, it will adversely affect the performance of the rubber compound. In recent years, the development trend has been obtained by the combination of BIIR rubber and NR. Oil-free low Mooney viscosity, easy to process 100% BIIR to ensure minimum air and water permeability. The current use of BIIR in air-tight formulations varies with tire products. Companies with well-known brands use 100% BIIR or CIIR; all-steel-loaded tubeless radial tires and high-speed passenger tires (such as V Level, Z) will use 100% BIIR or CIIR. BIIR rubber and NR are used for all-steel tires with inner tube radial tires and lower speed passenger tires (such as S-class and T-class).

2.2.3 EPDM/BIIR combined system

The combination of bromobutyl rubber and EPDM rubber can change the vulcanization rate (as the content of bromobutyl rubber in the co-adhesive rubber increases, the vulcanization rate drops sharply until the content of bromobutyl rubber reaches 50%. , followed by the opposite trend), improving the bonding, airtightness and damping properties of the rubber based on this. Conversely, EPDM can improve the low temperature brittleness of the rubber based on bromobutyl rubber. , ozone and heat resistance.

2.2.4 BIIR/CR combined system

The purpose of the combination of bromobutyl rubber and neoprene is mainly to reduce the cost of the rubber based on bromobutyl rubber. The bromobutyl rubber, like the G and W type chloroprene rubbers, can be vulcanized with zinc oxide or sulfur. The combination of bromobutyl rubber and chloroprene rubber has good heat resistance and ozone resistance, and is resistant to compression set and weathering resistance as the chloroprene rubber.

2.2.5 BIIR/NBR combined system

The use of nitrile rubber in bromobutyl rubber can improve the oil and chemical resistance of the rubber compound and improve the compression set property of the product, but the physical and mechanical properties are poor. In combination with nitrile rubber, bromobutyl rubber can also improve the low temperature flexibility, ozone resistance, ester and ketone resistance of nitrile rubber, but the oil resistance and tensile strength are reduced.

2.2.6 BR/BIIR combined system

The purpose of the combination of butadiene rubber and bromobutyl rubber is to use the good wet traction of bromobutyl rubber and the better wear resistance of the butadiene rubber and the low rolling resistance to complement each other. BR/BIIR blending compound is used in tread rubber and reinforced with silica, because the tread rubber containing bromobutyl rubber has good wet traction, but the abrasion resistance is very poor. First, the interaction between butyl rubber and carbon black is poor, and the coupling of rubber and silica through silane can greatly improve the interaction between butyl rubber and filler, and obtain a good reinforcing effect. The addition of silica-reinforced bromobutyl rubber to the butadiene rubber tread compound has significantly improved the three properties of the tread rubber, such as wear resistance, traction and rolling resistance.

2.3 Recycling of bromobutyl rubber

Bromobutyl rubber has a good recycling function, which is also a big advantage of bromobutyl rubber unlike other rubbers. The regeneration process of bromobutyl rubber is very simple, does not require complicated processes such as high-temperature desulfurization, can be used after a certain mastication, and is well mixed with the original rubber of bromobutyl rubber. With the increase of the amount of reclaimed rubber, the tensile strength of the bromobutyl compound added with reclaimed rubber will gradually decrease and the elongation will gradually increase, but this change is not obvious, especially the amount of reclaimed rubber. Within 15%, the performance of the bromobutyl rubber is kept very good, and the reclaimed rubber does not have much influence on the aging properties of the bromobutyl group. In addition, the use of recycled rubber and raw rubber does not substantially affect the chemical properties of the product.

2.4 BIIR cross-linking process and mechanism

Scott PJ et al. studied the thermal stability of BIIR and small molecule model (BPMN), and found that the generalized analysis of BPMN small molecule model is very close to the actual behavior of BIIR, which can be applied to the study of BIIR vulcanization mechanism. When BIIR is at the vulcanization temperature, isomerization will occur. The production of isomerization depends to a large extent on the concentration of hydrogen bromide in the system. When hydrogen bromide is detached from BIIR, a conjugated diene will form in the BIIR molecular chain. Structure, and is accompanied by isomerization.