Tire innerliners

Wire cords are particularly subject to degradation of their adhesion values by moisture. To combat this, halogenated butyl (HIIR) is used in tire innerliners because of its property of low air and water vapor diffusion rates. Moisture is present in most air pumps and many tires are mounted with water left in the tire on mounting. For these reasons tires and tire compounds are tested extensively at simulated aging conditions in the laboratory and on test vehicles before they are sold to the customer. 

Halogenation of the isoprenyl unit provides enhanced cure reactivity to the rubber molecule, increases the covulcanizability and adhesion to unsaturated tire elastomers, and opens the field of tubeless tire innerliners. 

Halobutyl rubber (HIIR) is used primarily in tire innerliner and white sidewalls. These elastomers are best for tire air retention owing to lower air permeability as well as aging and fatigue resistance. The chlorinated (CIIR)... 

Critical to a tire s life cycle performance is the ability to maintain air pressure. Tire innerliners composed of halobutyl-based compounds exhibit very low air and moisture permeability. Therefore, tires built with the proper selection of compounds can reduce the rate of premature failure, again delaying entry into the scrap tire and solid waste streams. 

Table 9.36 illustrates how the incorrect selection of a tire innerliner polymer will lead to more rapid deterioration in tire performance properties. Replacement of chlorobutyl with natural mbber or reclaimed butyl will lead to a more rapid loss in tire air pressure and loss in overall tire performance (Niziolek, 2000). 

Bromobutyl rabber is relatively impermeable to air and moisture and it is often a major portion of the tire innerliner composition. The addition of the starch/plasticizer dispersion composite further reduces the already low air permeability of the butyl rubber-based com-positioa Starches with high softening points are difficult to incorporate it into rabber composition without plasticizer. ... 

Table 4.11 Model formulations for an automobile tire innerliner and summary of properties. . ...

N650 High modulus, high hardness, low die swell, smooth extrusion Tire innerliners, carcass, belt, sidewall compounds, seals, friction compounds, sheeting... 

Talc is used in tires in white sidewall compounds to provide a smooth appearance to the buffed sidewall. The large platelets of talc provide a barrier to gas and moisture permeability in compounds, which allows talc to be used in applications such as hydraulic and automotive hoses, barrier films, and tire innerliners. 

Applications conveyor belts, curing bladders, hoses, membranes, pharmaceutical stoppers, seals, tank liners, tire innerlines, tire non-staining sidewalls ... 

The major reason that butyl rubber is used in the tire industry is its superior resistance to air permeability, as weii as other gases. Butyi has approximately 13 times greater resistance to air permeability than natural rubber. This makes it ideal for use in making tire innerliners and inner tubes. While some polar specialty elastomers can also provide good air permeability resistance, they are far more expensive and generally do not possess the right combination of other needed properties. 

Halobutyl rubber is used mostly to make the innerliner compound for today s modern tubeless tires. This is because halobutyl rubber is compatible with general-purpose rubbers, can be covulcanized with them, and can impart good adhesion to them. Virtually all tubeless tire innerliners use halobutyl rubber. 

The technical alternatives to halobutyl rubber in tire innerliner applications are very poor, in the short term. However, with the development of new innerliner compounds based on DIMS (see below), a substitution could be achieved long term with much development work. 

A new BIMS/nylon thermoplastic vulcanizate innerliner is being investigated for possible use as a tire innerliner. 

Of course, before BIMSM was invented, XIIR (halobutyl rubber) was (and still is) extensively used for tire innerliners. If there were a shortage of BIMSM, the tire industry should be able to return to XIIR-based innerliners. 

Bromine is used to haiogenate butyi rubber (HR) into bromobutyl rubber (BUR), which is iargeiy used in tire innerliners. 

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