Tread stocks

Standardisation of EPDM characterisation tests (molecular composition, stabiliser and oil content) for QC and specification purposes was reported [64,65]. Infrared spectroscopy (rather than HPLC or photometry) is recommended for the determination of the stabiliser content (hindered phenol type) of EP(D)M [65]. Determination of the oil content of oil-extended EPDM is best carried out by Soxhlet extraction using MEK as a solvent [66], A round robin test was reported that evaluated the various techniques currently used in the investigation of unknown rubber compounds (passenger tyre tread stock formulations) [67]. 

Naphthas are used in the rubber industry for dampening the play and tread stocks of automobile tires during manufacture to obtain better adhesion between the units of the tire. They are also consumed extensively in making rubber cements (adhesives) or are employed in the fabrication of rubberized cloth, hot-water bottles, bathing caps, gloves, overshoes, and toys. These cements are solutions of rubber and were formerly made with benzene, but petroleum naphtha is now preferred because of its less toxic character. 

Wear Resistance in Tire Tread Stocks and The Effects of Compound Loading Variants on Wear Resistance," Preprint of Paper A-19 Presented to Inti. Rubber Conf., Prague, Czechoslovakia, Sept. 17-20, 1973. 

Figure 32 Uncured RPA ian<5 response vs. Banbury kilouaii hour at dump for NR truck tread stocks. RP.A test conditions l4"o strtiin. 10 cpm. and 100 ( test temperature. 

The RPA can also do a stress relaxation test, Figure 37 shows RPA stress relaxation decay curves from three truck tread stocks of the same formulation. Each curve indicates different qualities of mix caused by variations in mixing work history (variations in total energy at Banbury dump). As the energy at dump for these tread mixes increases, the peak torque decreases, the slope of the log-log plot of the stress relaxation curve becomes steeper, the regression line intercept decreases, the integrated area under the curve decreases, and the time to a given % drop decreases [133]. Therefore a simple stress relaxation test is a fast and effective w ay to measure variations in viscoelastic properties for both raw rubber and mixed stocks. 

Figure 37 Comparison of RPA stress relaxation decay curves for three truck tread stocks with different qualities of mix caused by indicated variations in mixing work history (energy at Banbury dump).

At the same time, Peddini et al. described the preparation of nanocomposites from styrene-butadiene mbber (SBR) and multiwall carbon nanotubes (MWCNT). MWCNT are important nanostructures due to the exceptionally high modulus and aspect ratios there has been much interest in using them as reinforcing agents for polymer composites. Styrene-butadiene rubber (SBR), commonly used as a tread stock for tires, is employed here as the matrix for creation of a masterbatch with oxidized MWCNT (12.3-15 wt%). These materials do not show a high level of electrical conductivity as might be expected from a percolation concept, signifying excellent tube dispersion and formation of a bound rubber layer on the discrete MWCNT [126]. 

Fig. 4.7. Tensile strength-brittle point relationships of tread stock vulcanizates of natural (Hevea) rubber compared with those of synthetic rubbers of less regular structure. (Reprinted with permission from Ind. Eng. Chem., 38, 1061 (1946). Copyright by the American Chemical Society.)...

Wet skid and rolling resistance measurements on tyres retreaded with ENR-25 compounds (Table 12) show that these tread stocks have both superior wet grip to an oil extended styrene butadiene rubber (OESBR 1712), and lower rolling resistance than NR. " These results are sununarized in a Morton-Krol-type plot in Fig. 18. The tyre wear properties of ENR-25 black and black/silica (35 15) filled compounds are comparable with an NR tread stock. Improvements in wear can be obtained by blending with BR. 

Crowt ier, B. G., Effects of process oils on the vulcanizate properties of a natural rubber tread stock, Nat. Rubber TechnoL, 14(2), 1983, 79. 

DPG is the most commonly used member of the guanidine class of rubber accelerators. DPG is commonly used as a secondary accelerator (or kicker ) with primary sulfenamide accelerators and sometimes with thiazole accelerators as well. DPG is also a silanization accelerator. It can interact with the silica surface, which then reacts with organosilanes in tread stocks to help reduce rolling resistance. DPG is not as chemically active as the thiuram or dithiocarbamate accelerators. 

DPG is mainly used as a secondary accelerator or kicker with sulfenamide or thia-zole primary accelerators. It is not as chemically active as the thiuram or dithiocar-bamate secondary accelerators. DPG Is sometimes used as a secondary accelerator in tire tread stocks loaded with silica to help promote silanization. 

Following World War II the focus on SBR turned to development of specific products demonstrating improvement in selected properties over natural rubber as well as the original SBR. The first such development was the emulsion polymerization of styrene and butadiene at low temperature in the presence of a redox catalyst system. The product from this type of process represented a marked improvement over natural rubber in tread stocks for passenger car tires. Subsequently, application of or-ganolithium catalysis permitted development of solution-polymerized SBRs that offered improvements over emulsion SBR in curing rate... 

The first silane applications in mbber tires used mercaptosilane to modify siliea and clay fillers. Commercial applications were limited to specialty areas, such as white sidewall components, some tread stocks, and some off-road tires, but processing and physical property deficiencies limited commercial applications. However, Degussa Corporation, which... 

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