Natural rubber carcass

The carcass requires better flexing properties than the tread and is a blend of natural rubber and SBR, but at least 60% of natural rubber. The sidewalls have a lower percentage of natural rubber, from 0-50%. The liner is made of butyl rubber because of its extreme impermeability to air. 

Vulcanization also allows the casting of complicated shapes such as rubber tires. Natural rubber is putty-like, and it is easily mixed with sulfur, formed around the tire cord, and placed into a mold. The mold is closed and heated, and the gooey mass of string and rubber is vulcanized into a strong, elastic tire carcass. 

A balanced combination of properties is the criterion of performance. In tread-wear resistance, cold butadienerstyrene tires are approximately 20-30 per cent superior to natural-rubber or hot rubber treads. However, in tire carcass or sidewalls, natural rubber exhibits superior performance, especially in truck tires, because of lowfeV heat build-up. 

The most common textile bonding compositions are, of course, the RFL (resorcinol-formaldehyde-latex) dips used to adhere tire carcass rubber to cord reinforcing members. A typical RFL composition calls for a latex terpolymer of styrene-butadiene-vinyl pyridine as well as the resorcinol and hexamethylene tetramine. Some natural rubber latex or regular SBR latex may also be added. The R F resin which forms in situ is able to react chemically with rayon by methylol etherification of the cellulose s hydroxyls. Similar reaction is likely with the amide groups of nylon fibers as shown in Figure 7. 

Volumewise, natural rubber represents about half of all the rubber used in producing tires today. Typically, natural rubber is used as a blend with either SBR or BR in tire rubber compounds. NR/SBR compound blends are used in the tire carcass coat, cushion gum, earth-mover retreads, light truck treads, bead filler, chaffer rim flange, and motorcycle treads. NR/BR compound blends are commonly used to make passenger tire treads, sidewalls, high-performance treads, camelback, and heavy-duty truck treads. 

The most important commercial use of elastomer blends is in the huge tire market. These blends are generally phase separated and represent one of the largest single applications for immiscible or miscible blends. Ckjmpatibilization is achieved via crosslinking reactions across the interface. The use of SBR/PB (polybutadiene) and NR(natural rubber)/PB for tread, NR/SBR/PB and NR/PB for carcass, NR/PB and NR/SBR for sidewall and NR/SBR/PIB... 

Table 1 demonstrates the degree of adhesion obtained on the platen press curing of rubberized 10 oz cotton duck to square woven fabric samples made from rayon, cotton, and nylon. The duck had been skim-coated 90 mils with some typical tire carcass stocks made from neoprene GR-M, SBR, and natural rubber. The other fabrics were precoated with 20% by weight of the MDI-50 adhesive primers. ... 

In sub.sequent work [20-22] van Ooij developed the use of model compounds (in the case of natural rubber,. squalene) to simulate the physical and chemical interactions at the interface of the brass/natural rubber. system. Cuts in a tire carcass may lead to exposure of the steel/brass interface and the galvanic effects that give rise to dezincification may then become important [23]. The use of duplex Zn-Ni on Zn-Co alloys as replacements for brass has been propo.sed in order to... 

The properties required of a liner to perform this function include the ability to adhere permanently to the tyre carcass, heat resistance, flexibility and flex crack resistance over the full operating temperature range and a low level of permeability to air and moisture. Regular butyl rubber cannot be used in this application except, in the form of butyl reclaim, as a flexible, highly impermeable filler for other elastomers, because it cannot be made to adhere strongly enough to the tyre carcass. Bromobutyl rubber possesses all the properties, in ample measure, required for premium quality inner liners, but a few parts of natural rubber are normally included in chlorobutyl liner stocks to ensure that they have adequate cured bond strength (see Tables 16 and 17). 

Heat ageing in the presence of air is often used to categorise rubber compounds. Natural rubber and high c/5-polyisoprenes are not particularly resistant to ageing temperatures above 70 ""C. For some applications, however, polyisoprene compounds may well exceed this temperature during their normal service life and often under dynamic conditions. This would be the case for compounds used in tyre carcass and for wire coat compounds where ingress of air or oxygen is limited. 

Protects against thermo-oxidative degradation in natural and synthetic rubbers as well as plastics. It is commonly used in applications such as tire carcasses, wire breaker retreads, apex, belts, hoses, seals, mechanical goods, footwear and wire. 

Delac . [Uniroyal] Benzothiazole sulfonamides delayed-action accelerator for natural and synthetic rubbers used in tire treads, carcass, mechanicals, and wire jackets. 

---