Compounding abrasion resistance

The microstructure of an elastomer similarly can affect the mechanical properties of the compounded elastomer. For solution SBR used in a tire tread compound, an increase in the vinyl butadiene (Figure 4.1) level will increase the Tg, improve tire wet traction performance, and result in a decrease in resistance to abrasion [4]. An increase in the cis-and trans-isomer of butadiene in SBR (styrene butadiene rubber), with a corresponding decrease in vinyl-butadiene isomer, will improve compound abrasion resistance. The amount of styrene in S B R will affect tire traction. Higher levels of styrene tend to give improvements in tire traction and tire/vehicle handling properties. The ratios of styrene, cis-butadiene, trans-butadiene, and vinyl-butadiene determine the ultimate Tg of the polymer. The higher the cis- or trans-butadiene level, the lower the Tg of either SBR or BR. 

The property of polybutadiene of most interest to the mbber compounder is excellent abrasion resistance coupled with excellent resilience. The polymer has very high rebound and low heat generation. With a few exceptions, such as the core of soHd golf balls, the polymer is blended with other polymers to take advantage of its excellent abrasion and rebound. Uses in North America are as follows tires, 500,000 t (74%) plastic modification,... 

Nittile mbber is much like SBR in its physical properties. It can be compounded for physical strength and abrasion resistance using traditional fillers such as carbon black, siUca, and reinforcing clays. The primary benefit of the polymer is its oil and solvent resistance. At a medium ACN content of 34% the swell in IRM 903 oil at 70°C is typically 25—30%. Nitrile mbber processes on conventional mbber equipment and can be compression, transfer, or injection molded. It can also be extmded easily. 

SiHcone elastomers possess outstanding resistance to heat aging. The Si—O—Si backbone imparts resistance to oxygen, o2one, uv, and to some polar fluids. However, the strength of these elastomers is usually just adequate. They have low abrasion resistance and tear strength (see Silicon compounds, silicones). 

The tread is desigaed and compounded for abrasion resistance, traction, low rolling resistance, and protection of the carcass. It often is divided iato two subcomponents to maximize performance the outer tread for surface contact, and the undertread for tying iato the carcass while reduciag tire rolling resistance through decreased hysteresis. 

Fillers, eg, clays and whiting, are used to reduce cost or provide special properties. Fillers do not reinforce mbber deposited from latex, excepting to improve abrasion resistance. They are also used to increase viscosity for latex compound spreading suitabiUty. 

COATED FABRICS abrasion resistance, and flexibiHty at low temperatures. A typical SBR-based formulation is shown in Table 2. Table 2. SBR Compounding Vol6... 

Processings and Properties. Polybutadiene is compounded similarly to SBR and vulcanised with sulfur. The high cis-1,4 type crystallizes poorly on stretching so it is not suitable as a "gum" stock but requires carbon black reinforcement. It is generally used for automotive tires in mixtures with SBR and natural mbber. Its low T (—OS " C) makes it an excellent choice for low temperature tire traction, and also leads to a high resilience (better than natural mbber) which ia turn results ia a lower heat build-up. Furthermore, the high i j -polybutadiene also has a high abrasion resistance, a plus for better tire tread wear. 

Phenol (Cf HjOH) reacts readily with aldehydes to form oil. soluble compounds called phenolic resins that dry rapidly, are hard, chemical and abrasion resistant, but they tend to yellow with age. 

Polychloroprene and acrylonitrile-butadiene rubber compounds have satisfactory chemical resistance but, except for phosphoric acid, are not suitable for mineral acids at higher concentrations. However, they have good resistance to oils, acrylonitrile-butadiene rubber being the better, and so are often used in oil-contaminated aqueous environments. Generally, abrasion resistance is only fair. Normal maximum working temperature is about 100°C. Acrylonitrile-butadiene rubber ebonites are sometimes used especially where solvent contamination occurs, but are normally very brittle and so should be used with care. 

Chlorosulphonated polyethylene rubber (Hypalon) has excellent chemical resistance even to oxidative acids at elevated temperatures. When specially compounded it can have excellent abrasion resistance in some operating conditions. 

The key performance properties of conveyor belts, particularly belt cover compounds, are flex resistance, abrasion resistance, and low heat buildup. The effect of l,3-bis(citraconimidomethyl) benzene on these key properties, in addition to cure characteristics and tensile properties, has been evaluated in a typical, NR-based belt cover formulation listed in Table 14.49. 

Consistent with historical results, the loss modulus at high strain correlates well with laboratory abrasion results. The best correlations occur at high strains, i.e., on the order of 50%-125%. Abrasion losses are considered to be predominantly high-strain events. Thus, the ability of a compound to dissipate energy at high strain will improve the toughness or abrasion resistance of the compound. However, it is important in the tire industry that this increase in hysteresis at high... 

The tensile strength of NR compounds in the presence of cross-link promoters such as dichlorobenzene is increased as compared to the sulfur-accelerator and peroxide-curing systems. The retention of the maximum tensile strength at elevated temperamres is greater for radiation cured than for chemically vulcanized NR [326,327]. Also reported are a higher abrasion resistance [328] and a lower flex life in the case of radiation-cured system. Effect of phenoxy ethyl acrylate (PEA)... 

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