Mechanical properties butyl rubber

Rubber consumption is dominated by tyre production. In these, conveyor belts, and pressure hoses, thin layers of either steel wire or polymeric fibre reinforcement take the main mechanical loads. These layers, with rubber interlayers, allow flexibility in bending, whereas the reinforcement limits the in-plane stretching of the product. The applications are dominated by natural rubber and styrene butadiene copolymer rubber (SBR). Other rubbers have specialised properties butyl rubbers have low air permeability, nitrile rubbers have good oil resistance, while silicone rubbers have high and low temperature resistance. Rubbers play a relatively small role in this book, but the rubbery behaviour of the amorphous phase in semi-crystalline thermoplastics is important. 

Rubber. The mbber industry consumes finely ground metallic selenium and Selenac (selenium diethyl dithiocarbamate, R. T. Vanderbilt). Both are used with natural mbber and styrene—butadiene mbber (SBR) to increase the rate of vulcanization and improve the aging and mechanical properties of sulfudess and low sulfur stocks. Selenac is also used as an accelerator in butyl mbber and as an activator for other types of accelerators, eg, thiazoles (see Rubber chemicals). Selenium compounds are useflil as antioxidants (qv), uv stabilizers, (qv), bonding agents, carbon black activators, and polymerization additives. Selenac improves the adhesion of polyester fibers to mbber. 

Forms of BR and polyisobutylene. The properties of butyl rubber and polyisobutylene depend on their moleeular weight, degree of unsaturation, nature of the stabilizer incorporated during manufacture and, in some cases, chemical modification. It is common to produce halogenated forms of butyl rubber to increase polarity and to provide a reactive site for alternate cure mechanisms [6],... 

Butyl latices are prepared by emulsification of butyl rubber. Butyl latex has excellent mechanical, chemical and freeze-thaw stability, and when dried it shows the typical properties of butyl rubber [7]. 

The reactive extrusion of polypropylene-natural rubber blends in the presence of a peroxide (1,3-bis(/-butyl per-oxy benzene) and a coagent (trimethylol propane triacrylate) was reported by Yoon et al. [64]. The effect of the concentration of the peroxide and the coagent was evaiuated in terms of thermal, morphological, melt, and mechanical properties. The low shear viscosity of the blends increased with the increase in peroxide content initially, and beyond 0.02 phr the viscosity decreased with peroxide content (Fig. 9). The melt viscosity increased with coagent concentration at a fixed peroxide content. The morphology of the samples indicated a decrease in domain size of the dispersed NR phase with a lower content of the peroxide, while at a higher content the domain size increases. The reduction in domain size... 

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. 

Chemical pretreatments with amines, silanes, or addition of dispersants improve physical disaggregation of CNTs and help in better dispersion of the same in rubber matrices. Natural rubber (NR), ethylene-propylene-diene-methylene rubber, butyl rubber, EVA, etc. have been used as the rubber matrices so far. The resultant nanocomposites exhibit superiority in mechanical, thermal, flame retardancy, and processibility. George et al. [26] studied the effect of functionalized and unfunctionalized MWNT on various properties of high vinyl acetate (50 wt%) containing EVA-MWNT composites. Figure 4.5 displays the TEM image of functionalized nanombe-reinforced EVA nanocomposite. 

The vulcanization of polychloroprene (Neoprene) is carried out in different ways. Vulcanization by sulfur, even with an accelerator, is not practiced to a large extent. Vulcanizations by metal oxides (without diamine), either alone or in combination with sulfur (sometimes together with an accelerator), give the best physical properties for the crosslinked product. Halogenated butyl rubber is crosslinked in a similar manner. The mechanism for crosslinking by metal oxide alone is not established [Stewart et al., 1985 Vukov, 1984]. 

Berlin and coworkers (5,56) desired to obtain a material with an increased mechanical strength. They carried out a plasticization of bulk ami emulsion polystyrene molecular weight 80000 and 200000 respectively at 150-160° C, with polyisobutylene, butyl rubber, polychloroprene, polybutadiene, styrene rubber (SKS-30) and nitrile rubber (SKN 18 and SKN 40). The best results were obtained with the blends polystyrene-styrene rubber and polystyrene-nitrile rubber. An increase of rubber content above 20-25% was not useful, as the strength properties were lowered. An increase in the content of the polar comonomer, acrylonitrile, prevents the reaction with polystyrene and decreases the probability of macroradical combination. This feature lowers the strength, see Fig. 14. It was also observed that certain dyes acts as macroradical acceptors, due to the mobile atoms of hydrogen of halogens in the dye, AX ... 

Rubber-toughened polystyrene composites were obtained similarly by polymerising the dispersed phase of a styrene/SBS solution o/w HIPE [171], or a styrene/MMA/(SBS or butyl methacrylate) o/w HIPE [172], The latter materials were found to be tougher, however, all polymer composites had mechanical properties comparable to bulk materials. Other rubber composite materials have been prepared from PVC and poly(butyl methacrylate) (PBMA) [173], via three routes a) blending partially polymerised o/w HIPEs of vi-nylidene chloride (VDC) and BMA, followed by complete polymerisation b) employing a solution of PBMA in VDC as the dispersed phase, with subsequent polymerisation and c) blending partially polymerised VDC HIPE with BMA monomer, then polymerisation. All materials obtained possessed mixtures of both homopolymers plus some copolymer, and had better mechanical properties than the linear copolymers. The third method was found to produce the best material. 

Known as EPR. this material is of limited use hecausc it cannot be vulcanized in readily available systems. However, (he rubbers arc made from low -cost monomers, have good mechanical and elastic properties, and outstanding resistance to ozone, heal, and chemical attack. They remain flexible to very low temperatures (brittle point about -95 C), They are superior to butyl rubber in dynamic resilience. 

By analogy with the works which dealt with cellulose micro crystal-reinforced nanocomposite materials, microcrystals of starch [95] or chitin [96, 97] were used as a reinforcing phase in a polymer matrix. Poly(styrene-co-butyl acrylate) [95,96], poly(e-caprolactone) [96], and natural rubber [97] were reinforced, and again the formation of aggregates or clustering of the fillers within the matrices was considered to account for the improvement in the mechanical properties and thermal stability of the respective composites processed from suspensions in water or suitable organic solvents. 

The most important characteristics of butyl rubber are its low permeability to air and its thermal stability. These properties account for its major uses in inner tubes, tire inner liners, and tire curing bladders. Because of the poor compatibility of butyl with other rubbers (with respect to both solubility and cure), the halobutyls are preferred. The brominated p-methylstyrene-containing butyl rubbers are used in a number of grafting reactions for tire applications and adhesives. Other uses for butyl rubber are automotive mechanical parts (due to the high damping characteristics of butyl), mastics, and sealants.55... 

If a rubber-like polymer is used as the vinyl polymer, this IPN will show good damping properties at elevated temperatures. So, butyl acrylate, ethylene glycol dimethacrylate, phenolic novolac, and bisphenol A type epoxies were used as IPN components. The dynamic mechanical properties of these IPNs were examined first, because the loss tangent is very important to damping properties. Then the damping properties of IPN and commercial chloroprene rubber were measured at various temperatures. 

Figure 19.13 shows the dynamic mechanical properties of such a blend of sPS with a mixture of Kraton G 1651 (15 %) and microsuspension rubber particles (20%) consisting of 60% butyl acrylate (BA) core grafted with 40% styrene shell (S//BA). The glass transition temperatures of the Kraton (-60 °C) and the butyl acrylate (-45 °C) phases can be easily distinguished from one another. The TEM image of such a product after deformation is shown in Figure 19.14. The annealed specimen is shown since the two rubber types are better discernible than in the nonannealed sample. As expected, crazing and voiding in the rubber particles dominate. The product had the following notched impact strengths (ISO 179/eA) injection moulded (80 °C mould temperature) 6.3, injection moulded (140 °C) 4.0 and annealed 3.7kJ/m2.

It is also possible to manipulate the structure by introducing other monomers into the polymer chain, changing the mechanical properties of the final material by copolymerization. It is also common, for economic reasons or to increase mechanical properties, to add particulate solids to the polymer, such as wood flour or other additives, that will affect the final mechanical properties. Another common approach is the preparation of blends of two different polymers, which are commonly nonsoluble in each other, as a strategy to increase some mechanical properties such as impact strength, as in the well-studied case of nylon toughening by butyl rubber [8, 9],... 

Other systems investigated by this group are butyl rubber, - natural rubber sensitized with acrylates,chloroprene, chlorobutyl rubber and nitrile rubber.More recently, Perera has examined the relationship between chemical changes in radiation-grafted natural rubber, determined using MAS NMR, and mechanical properties measured using dynamic mechanical analysis. 

---