Double networking cured rubber

Infrared spectroscopy of peroxide cured rubbers has revealed only minimal spectroscopic information on the new cross-linked structure. What has been observed is the decrease in the intensities of the C-H out-of-plane bending modes of the olefin double bond which absorb at 837 cm l for the natural rubber and at 740 cm for cis-1,4-polybutadiene. While these bands reflect losses in the amount of unsaturation in the final material, when compared to the starting material, no evidence of the network carbon-carbon single bond absorption bands has been reported. 

Dry RubbGr. Because of its enhanced crystallizability, guayule rubber can exhibit superior failure properties in unfilled rubber compositions. As a double network, an elastomer cured a second time while in a deformed state guayule rubber exhibits substantially better fatigue resistance than deproteinized Hevea rubber (118). When compounded with carbon black, guayule rubber and Hevea rubber behave similarly (119). In tread and wire skim stocks, the compoimding and performance behavior of guayule rubber was comparable to that of Hevea rubber (Tables 7, 8) (120). 

Abstract The nonlinear viscoelastic behavior of cured rubber is quite different from that of uncured compound, since the presence of crosslink networks. The factors for the influence of the crosslink networks on the nonlinear viscoelastic behaviors of cured rubbers are very complex and obscure. One of the reasons is that the crosslink networks may be consisted of several different types of networks. However, there are few literatures reporting the nonlinear viscoelastic behaviors of cured mbbers with mutle-networks. We reviewed the literatures dedicated to the topic of the non-linear viscoelasticity of simplest mutle-networks—double-network and summarized the useful information as much as possible in the present paper. Song s transient double-network model, double-network formed by twice curing and the specific crosslink network formed in metal salts of unsaturated carboxylic acids reinforced rubbers are introduced in detail. 

The nonlinear viscoelastic behavior of filled vulcanizates is somewhat different from that of filled compounds, since the chemical crosslink network of the rubber matrix is formed and, the physical rubber-filler networks and filler-filler networks are enhanced during curing at a relatively high temperature [7]. Speaking from a broad sense, filled vulcanizates can be viewed as a double network structure in which the nanoparticles supplement the inherent viscoelasticity of crosslink rubbers with additional physical network junctions. 

The presence of filler in the rubber as well as the increase of the surface ability of the Aerosil surface causes an increase in the modulus. The temperature dependence of the modulus is often used to analyze the network density in cured elastomers. According to the simple statistical theory of rubber elasticity, the modulus should increase twice for the double increase of the absolute temperature [35]. This behavior is observed for a cured xmfilled sample as shown in Fig. 15. However, for rubber filled with hydrophilic and hydrophobic Aerosil, the modulus increases by a factor of 1.3 and 1.6, respectively, as a function of temperature in the range of 225-450 K. It appears that less mobile chain units in the adsorption layer do not contribute directly to the rubber modulus, since the fraction of this layer is only a few percent [7, 8, 12, 21]. Since the influence of the secondary structure of fillers and filler-filler interaction is of importance only at moderate strain [43, 47], it is assumed that the change of the modulus with temperature is mainly caused by the properties of the elastomer matrix and the adsorption layer which cause the filler particles to share deformation. Therefore, the moderate decrease of the rubber modulus with increasing temperature, as compared to the value expected from the statistical theory, can be explained by the following reasons a decrease of the density of adsorption junctions as well as their strength, and a decrease of the ability of filler particles to share deformation due to a decrease of elastomer-filler interactions. 

Curing reactions. In each case otherwise linear polymer molecules are joined together by reaction with other molecules to form a crosslinked network. A common example is the use of sulfur to vulcanize rubber in this case sulfur molecules react with double bonds in adjacent polymer chains, and thus bridge them. 

The value ofVjA is determined by the concentration of network knots. These knots usually have a functionality of 3 or 4. This functionality depends on the type of curing agent. Crosslinked polyurethanes cured by polyols with three OH-groups are examples of the three-functional network. Rubbers cured through double bond addition are examples of four-functional networks. 

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