Wet traction

Snow and wet traction are highly dependent on the tread pattern. Although the tread pattern overwhelms the compound properties in significance, the latter can play a role in optimizing snow traction. Compounds using polymers with low glass-transition temperature, T (—40 to —OS " C), remain more flexible at low temperatures. Tread compounds with low complex modulus at 0—20°C have better snow traction. 

The operational-factor tests performed with A1 filled compounds in comparison with A2 filled compounds revealed higher predicted wear resistance and wet traction with the same level of rolling resistance. At the same time the graph of tan 8 versus temperature in Figure 17.6 shows that tan 8 is higher than that of the A2 compound at low temperatures (-20°C). 

Use of highly dispersible silica together with silanes and high vinyl S-SBR has met all critical magic triangle requirements like good dry and wet traction, reduction in tread wear, and low RR. 

Three-Zone Concept of Wet Traction or Wet Skidding of Tires.948... 

Generally, the Mooney viscosity of S-SBR is higher than E-SBR. Thus, it accepts higher filler and oil loadings. The effect of composition on the property of S-SBR is similar to that of E-SBR. As the styrene content increases, the rolling resistance, traction, and hardness increase, while the wear resistance decreases. With the increase of vinyl content, the wet traction increases. 

S-SBR grades have excellent balance between wet traction and rolling resistance therefore, they can be used for low fuel consumption tire treads in all-season tires and high-quality rubber goods. In applications of S-SBR, carbon black and silica will often be added to enhance the property. 

For the loss tangent properties, the magnitudes of tan 5 for both CB and SSF composites are similar. The magnitude of tan 5 has practical importance in rubber applications such as tires. A rubber composite that has a smaller tan 5 value tends to have a reduced rolling resistance and save energy, while a larger tan 6 tends to have an improved skid resistance and wet grip. The ability of SSF to absorb some moisture in a wet state tends to reduce G , increase tan 5, and lead to better wet traction. 

The relative levels of each of the three isomers in a polymer such as BR can have a dramatic effect on the material s performance. For example, lithium-catalyzed solution polymers, with approximately 36% cfj content, tend to process easily, whereas high-cw Ti and Ni polymers (92% cis) are more difficult to process at factory processing temperatures but show better abrasion resistance. Y igh-trans BR (93% trans) tends to be a tough, crystalline material at room temperature. High vinyl-butadiene BR polymers in tire treads tend to show good wet skid and wet traction performance (Mezynski and Rodgers, 1993 Simpson, 1978 Nordsiek, 1985 Rodgers et al., 2004). 

Addition of a catalyst modifier during the preparation of solution-polymerized, lithium-catalyzed BR results in an increase in the vinyl-1,2-butadiene level in the polymer and causes an increase in Fg. There is a corresponding drop in abrasion resistance and an increase in wet traction. 

The ratio of net contact to gross tread surface area decreases as wet traction becomes more important. Tables 14.3 and 14.4 illustrate the net-to-gross percentage for various tire tread patterns. 

PROPERTIES OF SPECIAL INTEREST Standard emulsion SBR is a general purpose rubber. Most widely used synthetic rubber in the world. Better tire tread-wear and aging properties than natural rubber. Good abrasion resistance and crack initiation resistance. Poor in tack and heat build-up. Physical properties are poor without reinforcing fillers. Solution SBR is a speciality rubber and more expensive than emulsion SBR. Solution SBR with high vinyl and styrene levels is used in high performance tire treads to improve wet traction. Also used as impact modifier in plastics and as thermoplastic elastomers. 

Brantley and Day then conducted a study to compare the tire performance of emulsion- and solution-polymerized SBR [12]. The authors noted that solution-polymerized polymers, which tend to have a narrower molecular weight distribution and lower Tg than equivalent emulsion-polymerized polymers, have lower hysteretic properties. Tliey then showed that a solution SBR with the same bound styrene as an emulsion SBR will give lower rolling resistance, improved dry traction, and better tread wear. Emulsion SBR, however, tends to show better wet skid, wet traction, and wet handling performance. Kern and Futamura later elaborated on this work by evaluating the impact of... 

The rolling resistance of tires made from NR or SBR is reduced by the presence of increasing amounts of BR. This reduces the fuel consumption of vehicles on the road. However, the presence of BR gives rise to poor wet traction, but the presence of about 40 percent (of the polymer) BR gives improvements in ice traction. In addition, BR has a great tolerance for high levels of extender oil and carhon black. 

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. 

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