Butyl rubber, tensile strength

Butyl ruhher vulcanizates have tensile strengths up to 2,000 psi, and are characterized hy low permeahility to air and a high resistance to many chemicals and to oxidation. These properties make it a suitable rubber for the production of tire inner tubes and inner liners of tubeless tires. The major use of butyl rubber is for inner tubes. Other uses include wire and cable insulation, steam hoses, mechanical goods, and adhesives. Chlorinated butyl is a low molecular weight polymer used as an adhesive and a sealant. 

Fig. 105.—Tensile strengths of butyl rubber fractions each vulcanized to the same cross-linking density p, corresponding to Me = 37,000, plotted against the primary molecular weight M. ...

Fig. 106.—Tensile strengths of the vulcanized butyl rubber fractions (Fig. 105) plotted against (M This quantity is propor-...

When the butyl rubber was compounded with up to 30 percent of polyisobutylene, which, lacking the unsaturated isoprene units, did not enter into the cross-linking reaction, the tensile strengths were, of course, considerably reduced. They were found nevertheless to be accurately represented by the same equation, (53), provided merely that Sa is taken as the fraction of the composite specimen consisting of network chains subject to orientation. Thus, in this case... 

The name given to certain nitroso-secondary aromatic amines which, added in small quantities to butyl rubber, result in improved resilience and higher tensile strength. 

The prevulcanization of natural rubber in latex form has also been a subject of much investigation. The cross-linking mechanism is not yet fully understood, but the water apparently plays a major role in it. Irradiation results in the cross-linking of the rubber molecules and in coarsening of the latex particles. A process of cross-linking of natural rubber latex has been developed to the point that it can be used for an industrial-scale application. The irradiation is performed in aqueous media by electron beam without a prorad (sensitizer) at a dose of 200 kGy (20 Mrad) or in the presence of n-butyl acrylate at considerably lower doses, typically 15 kGy. The cross-linked film exhibits physical properties comparable to those obtained from sulfur cured (vulcanized) film. As an alternative, the addition of a variety of chloroal-kanes makes it possible to achieve a maximum tensile strength with radiation doses of less than 5 Mrad (50 kGy). ... 

Butyl rubber is produced by a process in which isobutylene is copolymerized with a small amount of isoprene using aluminum chloride catalyst at temperatures around — 150° F. (20). The isoprene is used to provide some unsaturation, yielding a product that can be vulcanized (43). Vulcanized Butyl rubber is characterized by high tensile strength and excellent flex resistance furthermore, as a result of its low residual unsaturation (only 1 to 2% of that of natural rubber) it has outstanding resistance to oxidative aging and low air permeability. These properties combine to make it an ideal material for automobile inner tubes (3), and Butyl rubber has continued to be preferred over natural rubber for this application, even when the latter has been available in adequate supply. 

Butyl Rubber. A synthetic rubber produced by copolymerization of isobutene(98%) with a small proportion(ca 2%) of isoprene or butadiene. Polymerization is conducted at-50 to 100° in a liquid hydrocarbon, with A1C13 as catalyst. Its outstanding property compared with other rubbers is impermeability to gases. The uncured rubber is tacky, but it may be compounded like natural rubber and vulcanized. Butyl rubber has good resistance to chemical attack and to aging even at high temps. It has superior vibration insulation characteristics and abrasion resistance, but relatively low tensile strength and poor flame resistance... 

Neoprene is readily crosslinked. Using a nuclear reactor, a high modulus is obtained for doses of 0.04 x 1018 nvt ( 100 Mrad) [439]. Data on other synthetic rubbers have been reviewed by Charlesby [424]. Butyl rubber (polyisobutene) reinforced with carbon black shows a loss in tensile strength and elongation at break and a decrease in modulus. 

High molecular weight polyisobutylene has fair tensile strength, but suffers from the disadvantage of considerable cold flow. A copolymer of butylene with some isoprene for crosslinking is therefore used as a commercial elastomer and called butyl rubber. The isoprene is present in the copolymer in only minor proportions (1.4-4.5%). The uncrosslinked material is very similar to polyisobutylene. Copolymers of isobutylene with other dienes are also called butyl rubbers. They can also be terpolymers, where the third component may be cyclopentadiene for improved ozone resistance. 

PP was blended with 5-50 parts of chlorinated butyl rubber, CBR, in the presence of a non-peroxide curative (e.g., oxides or sulfides of Zn, Cd, Mn, Fe, or Pb) on a roll mill at 138-157 °C. The dynamic vulcanization resulted in materials useful for high tensile strength applications... 

In bromobutyl/chlorobutyl rubber blends, both elastomers have the polyisobutylene backbone and halogen reactive functionality. These polymers, being molecularly miscible, constitute an ideal system for co-vulcanization. Bromobutyl and chloro-butyl can be used interchangeably without significant effect on state of cure as measured by extension modulus, tensile strength, and cure rheometer torque development. Bromobutyl will increase the cure rate of a blend with chlorobutyl. However, where bromobutyl is the major part of the blends, chlorobutyl does not reduce scorch tendencies because the more reactive halogen unit can dominate. 

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