TYRE TREAD

Perhaps the main reason for the widespread acceptance of polybutadiene rubbers arose when it was found that they gave a vastly reduced tendency for the circumferential cracking at the base of tyre tread grooves with crossply tyres when used in blends with SBR. With crossply tyres now replaced by radial tyres, this factor is no longer of great importance but the rubbers continue to be used because of the improved tread wear and good low-temperatue behaviour imparted by their use. 

S. Agrawal, S. Mandot, N. Mandal, S. Bandyopadhyay, R. Mukhopadhyay, A.S. Deuri, R. Mallik, and A.K. Bhowmick, Effect of Com Powder as filler in radial passenger tyre tread compound, Journal of Material Science, 41, 5657, 2006. 

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]. 

Following this scheme, Coz and Baranwal [80] have reported the reverse engineering of four unknown cured rubber compounds, representing a radial passenger tyre tread, a radiator hose, an oil pan seal and an engine gasket. 

The symbol for micron (pan), for refractive index and for coefficient of friction. A high mu rubber (fomerly termed high hysteresis, high energy-loss or cling rubber) is one specially developed for the wearing surface of pneumatic tyre treads to improve road holding. 

Polymerised butadiene, made by the use of stereospecific catalysts, cis-1,4-Polybutadiene is widely used in tyre tread compounds. An inherently low temperature and low loss polymer. Polycarbonates... 

Polybutadiene is produced by solution polymerisation, and one important feature governing the performance of the resultant polymer is the cis 1,4, and 1, 2 vinyl contents. High cis 1,4 polymers (>90%) have a Tg around -90 °C, and hence exhibit excellent low temperature flexibility only exceeded by the phenyl silicones. They also exhibit excellent resilience and abrasion resistance unfortunately the high resilience gives poor wet grip in tyre treads, and hence this rubber finds limited use as the sole base for such compounds. 

In all tyres there are three types of components, the reinforcement layer(s), the rubber parts and the steel bead wires which locate a tyre to the wheel, or rim of a vehicle. Rubber is used in packing strips, inner lining, sidewalls and the abrasion-resistant tyre tread. 

The carcinogenicity of polycyclic aromatic compound-rich tyre extender oils has lead to the proposal of a legislative ban on their use in Europe. The suitability of naphthenic oils as non-toxic plasticisers in tyre treads is discussed and results are presented of experimental studies of the use of these plasticisers in SBR, EPDM, sulphur-cured EPDM and peroxide-cured EPDM. Despite their low aromatic content, the naphthenic plasticisers are shown to give good results in SBR, probably as a result of the contribution to solvent characteristics of the naphthenic molecular structure. The use of naphthenic oils is expected to increase worldwide as they are said to be one of the best alternatives to aromatic extracts with regard to solvent properties, compatibility, performance and availability. 

Typical car tyre tread Typical car tyre wall Typical truck tyre tread Typical truck lyre wall Bulk car tyre TDF TDF (de-wired) TDF (de-wired) Car lyre TDF (not de-wired) ... 

Rubber lining Rubber roll covering Tyre carcass Tyre tread Moulded tubes Footwear Soles and heels Mechanical goods Ebonites or hard rubber... 

Tyres are normally cured in a modification of the compression mould where a bladder or an inflated airbag forces and holds the green rubber stock of the tyre against the mould surface during vulcanization. This force reproduces the design of the tyre tread and the heat from the steam is introduced into the bladder to effect the vulcanization. Small size rubber expansion joints used in piping systems are moulded by compression moulding... 

Standard rubbers are given in several of the test method standards. Some are purely for normalizing the abrasive and have no particular service relevance. Others, such as those based on a tyre tread compound or a shoe sole type material, have the advantage of a practical significance as well as a normalizing role. There is no reason at all why, for a particular investigation, an in-house standard representative of the type of material being evaluated should not be used. 

The chemical cross-link density is a central quantity of interest in the elastomer industry, which, in a car tyre for instance, may vary in a well-defined fashion across the tyre tread. Both types of cross-links together determine the moduli of shear and elasticity, G and E, respectively. At small elongations A = L/Lq the tensile stress [Pg.440]

The effect of the different components present in used tyres on the generation of free radicals on coal has been studied by Ibrahim and Seehra22 through ESR experiments. Figure 6.10 shows that the addition of carbon black or SBR to coal at 420 °C leads to a significant increase in the free radical intensity. Likewise, it was observed that the tyre tread and its components lower the temperature of coal thermal cracking, favouring the formation of free radicals on the coal. 

The resins in the friction dust area tend to be rigid and the flexibility and plasticity associated with the long alkyl chain of phenolic lipids have been used in natural rubber vulcanisation by for example incorporating crosslinking with phosphorylated cardanol (ref. 252). Unpolymerised CNSL phenols have been used in natural or diene rubber compositions for tyre treads to give an improved dynamic elastic modulus but with the same hardness as formulations without the phenolic addition (ref. 253). 

As compared to natural rubber, epoxidized grades of natural rubber show improved reinforcement with silica without any coupling agent. Radial tyre tread prepared using formulations based on natural rubber with epoxide... 

Figure 9 Extrudate swell versus residence time within extrusion dies for a tyre tread compound...

Bandyopadhyay S., S. Dasgupta, N. Mandal et al. 2005. Use of recycled tyre material in natural rubber based tyre tread cap compound Part 1 (with ground crumb mbber). Progress in Rubber, Plastics and Recycling Technology. 21(4) 299-317. 

The movement of charge in a blast furnace and the abrasivity of toothpastes can be measured by techniques using P. The isotope has also been utilised to measure tyre tread wear and the thickness of paint films. Radioactive P is used in autoradiography (Chapter 14.2). 

Most of the rubbers, including NR, are available in the form of an aqueous dispersion of rubber particles, known as latex. Natural and synthetic rubbers in vulcanized form are used to prepare various rubber products such as mechanical goods, hoses, soles, V-belts, seals, gaskets, tyre treads, etc. NR in its... 

The first two of these, PI and SBR, are elastomers. SBR is one of the components used in car tyre treads. The last two are solids at ordinary temperatures. In expanded form, PS is used for thermal insulation panels and food containers, whereas in solid form, it is used for transparent cups and yoghurt pots. PMMA, better known by its commercial name Plexiglas, is used for windows, but also for wash basins, baths and street lights. 

For metal adhesion, polyisocyanates are best mixed into a solution of a synthetic or chlorinated rubber. Table 8.3 compares the adhesion of natural rubber tyre tread to mild steel using a polyisocyanate priming cement with that obtained using a chlorinated rubber cement. PVC also adheres well to most substrates treated with diisocyanate adhesion primers. 

One indication of variability can be obtained from tests carried out on reference compounds which had been mixed, vulcanised and tested at Rapra once per week during the period 1959 to 1963. Certain of the compounds selected for the long term ageing programme were identical or similar to these standard reference compounds. As a typical example, the coefficient of variation of the mean results obtained on an SBR tyre tread compound averaged 10% for tensile properties before and after ageing, 20% for compression set and 2.5% for hardness. 

Sandstrom and co-workers utilized the cyclized polyisoprene polymers incorporated into tyre tread compounds to improve traction, tread wear and tear resistance. Cyclized polyisoprene is further based upon the discovery that blends of cyclized polyisoprene polymers with halobutyl rubber and/or NR can be employed as tyre inner liner formulations. 

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