Noncrystallizing rubbers

Figure 18.17 shows that the characteristics of the stress-strain curve depend mainly on the value of n the smaller the n value, the more rapid the upturn. Anyway, this non-Gaussian treatment indicates that if the rubber has the idealized molecular network strucmre in the system, the stress-strain relation will show the inverse S shape. However, the real mbber vulcanizate (SBR) that does not crystallize under extension at room temperature and other mbbers (NR, IR, and BR at high temperature) do not show the stress upturn at all, and as a result, their tensile strength and strain at break are all 2-3 MPa and 400%-500%. It means that the stress-strain relation of the real (noncrystallizing) rubber vulcanizate obeys the Gaussian rather than the non-Gaussian theory. 

FIGURE 26.56 Log Abrasion loss by a blade (solid lines) and log cut growth rate (dashed hnes) of noncrystallizing rubber compounds as function of log frictional and log tearing energy, respectively isomerized natural rubber (NR), 2 styrene-butadiene rubber (SBR), and 3 acrylate-butadiene rubber (ABR). (From Champ, D.H., Southern, E., and Thomas, A.G., Advances in Polymer Friction and Wear, Lieng Huang Lee (ed.), Plenum, New York/London, 1974, p. 134.)... 

With the outbreak of war in 1939 and the consequent shortage of natural rubber in the industrial West, the introduction of the copolymer of butadiene and styrene, then known as Buna or GR-S, as an almost total replacement for natural rubber, would not have been possible without carbon black. It may be stated, with little likelihood of contradiction, that no other product exists which contributes as much strength and abrasion resistance to noncrystallizing rubbers, while maintaining to a large extent their desirable elastic properties, as does carbon black. 

Failure envelopes for real polymers have been most successful for nonfilled, noncrystallizing rubbers. Efforts to find ways of generalizing the principles of superposition to a wider range of commercial rubber compounds continue [8]. 

Chem. Deserp. Partially polymerized (dimerized) rosin CAS 8050-09-7 EINECS/ELINCS 232-475-7 Uses Prep, of varnishes, driers, syn. resins, ink vehicles, floor tile, rubber compds., solder fluxes, elec, insulation oils, optical lens pilches, adhesives and protective coatings for food pkg./processing Features Noncrystallizing, high soften, pi., acidic resin Properties Gardner 8 (60% solids in min. spirits) solid, flakes sol. in aliphatic, aromatic, and chlorinated hydrocarbons, in ketones, esters, natural oils, terpenes, and varnish oils dens. 1.07 kg/l G-H vise. C (60% solids in min. spirits) Hercules drop soften, pt. 102 C flash pt. (COC) 218 C acid no. 144 sapon. no. 160 Polyplate 90 [Huber Engineered Materials]... 

Statement, surprising but true for noncrystallizing elastomers, follows from the equation of state for rubber elasticity and the strength of the carbon-carbon bond. The failure envelope is indeed a powerful tool in dealing with ultimate properties. 

A more striking difference is found between strain-crystallizing and noncrystallizing elastomers when the stress is not relaxed to zero during each cycle. As shown in Fig. 33, the fatigue life of a natural rubber vulcanizate is greatly increased when the minimum strain is raised from zero to, say, 100% because the crystalline barrier to tearing at the tip of a crack does not then... 

Vulcanization Methods for producing a material with good elastomeric properties (rubber) involves the formation of chemical crosslinks between high-molecular-weight linear molecules. The starting polymer (such as raw rubber) must be of the noncrystallizing type (NR is crystallizable), and its glass transition temperature Tg must be well below room temperature to ensure a rubbery behavior. A -axis The axis in the plane of a material used as 0° reference thus the y-axes is the axes in the plane of the material perpendicular to the x-axis thus the z-axes is the reference axis normal to the x-y plane. The term plane or direction is also used in place of axis. 

Butyl Rubbers are noncrystallizing materials used in pressure-sensitive applications, such as bonding polyethylene tapes to steel pipes. 

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