Wet-skid resistance

The overall traction performance will be determined both by the relative size of the three zones, and the level of friction in each zone. Thus, to improve wet-skid resistance, the goals should be to increase the traction zone relative to the squeeze-hlm and transition zones, and to increase the level of frichon in the transition and traction zones. 

FIGURE 33.17 Effect of silica surface area on wet-skid resistance of vulcanizates filled with different fillers. 

FIGURE 33.18 Wet-skid resistance measured by GAFT as a function of load for compounds with a variety of fillers. 

The major use for polybutadiene is in tires, with over 70 percent of the polymer produced used by the tire industry. Cured polybutadiene has excellent low-temperature properties, high resiliency, and good abrasion resistance due to its low glass transition temperature. However, this same fundamental property also leads to very poor wet skid resistance. For this reason, polybutadiene is blended with other polymers such as natural rubber and... 

A present day challenge to carbon black technologists is to optimize the balance between tire wear, tire hysteresis that determines the rolling resistance, and wet skid resistance. It is now recognized that besides the morphology, while the wear resistance is closely related to the polymer-filler interaction and dispersion... 

We have made tire treads with some of the rubber compositions that were used for the study of tan 5 and Tg, shown in Figure 19, The test results on coefficient of wet skid resistance of tread rubbers and rolling... 

Fig. 20. Plot of coefficient of wet skid resistance versus rolling resistance for the rubbers in Fig. 19.

Retrospective View of Vinyl-BR Properties In the 1950s, the Phillips Petroleum Company and the Firestone Tire and Rubber Company started commercial production of polybutadienes by organolithium polymerization for use in tyres. These solution BRs, having low vinyl contents (8-10%), were used in blends with emulsion SBR in tyre treads for balancing traction and wear performance properties. In the early 1970s when styrene monomer was in short supply, developments from Phillips Petroleum Company and EniChem (formerly the International Synthetic Rubber Company) showed that vinyl-BRs with 50-55% vinyl content behaved like emulsion polymerized SBR in tyre tread formulations and exhibited very similar tread wear and wet skid resistance. Tread compounds containing 45%-vinyl polybutadiene showed lower heat build-up and better blow-out resistance than E-SBR and blends of E-SBR with cw-BR. EniChem introduced trial quantities of a medium-vinyl butadiene rubber (MVBR) under the name Intolene 50 in 1973. 

Gu et al. prepared Octadecyl ammonium montmorillonite/natural rubber/cfs-1,4-polybutadiene (OMMT/NR7BR) nanocomposites by direct mechanical blending. Two tan 5 peaks corresponded to the small glass transition peak of BR at lower and that of NR at higher temperature (Fig. 32). Both of the NR and BR phase of OMMT/ NR/BR (4 mass %) showed lower tan 8 peak values than the NR/BR hybrids and tan 8 of NR phase shifted to higher temperature. These observations can be related to the decreased mobility of the rubber molecules due to the strong interaction between the rubber matrix and OMMT [111-113]. The tan 8 value of OMMT/ NR/BR (4 mass %) at 0 °C was slightly lower than that of the pure NR/BR, which indicated that the nanocomposite had better wet skid resistance properties [110]. 

The primary application for halobutyl rubber is in tires. The combination of low gas and moisture permeability, high heat and flex resistance, and ability to covulcanize with highly chemically unsaturated rubber has secured the use of these rubbers in the innerliners of tubeless tires. Passenger tires use chlorobutyl alone or in a blend with 20 to 40% natural rubber. High-service steel-belted truck tires use 100% bromobutyl innerliner compoimds. Chlorobutyl is also used for truck inner tubes for its superior heat resistance compared to butyl rubber. Halobutyl rubbers are added to sidewall compounds for improved ozone and flex resistance, and to certain tread compounds for improved wet skid resistance and traction. 

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