Vulcanization comparison

This is another example of what has variously been called a pseudo-Diels-Alder, ene, or no-mechanism reaction (Hoffmann, 1969). It is similar to the reaction written for the attack of rubber molecules by phenolic curatives or the in situ formed nitroso derivative of the quinoid (e.g., benzoquinonedioxime) vulcanization system. It is also closely related to the sulfurization scheme written for accelerated-sulfur vulcanization. Comparisons between accelerated sulfur, phenolic, quinoid, and maleimide vulcanization can then be visualized as follows ... 

PA-12/ENR Mechanical properties/morphology/temperature scanning stress relaxation measurement/ optionally with dynamic vulcanization/ comparison to blends with unfimctionalized NR Narathichat et al. 2011... 

Po[yamine disulphides do not inhibit peroxide vulcanization of polyethylene, are stable in air up to 300-350°C, exhibit good compatibility and show no sweating out from the polyethylene mass. Table 8 gives the comparison between the efficiency of polyamine disulphides as thermostabilizers of cured polyethylene. 

Modified PAN fibres have been obtained from copolymers containing up to 15% or ISP units using the wet spinning process30. Some properties of modified fibres are presented in Table 1. For comparison are also given the properties of fibres obtained from copolymers additionally crosslinked with conventional crosslinking agents used in the vulcanization of nitrile rubbers. 

Puskas, J.E., Kumar, B., Ebied, A., and Lamperd, B. Novel Butyl Composites for Less-Lethal Ammunition. Papei 126, ACS Rubber Division, 164th Technical Meeting, October 14—17, Cleveland, OH, 2003. Puskas, J.E., Kumar, B., Ebied, A., and Lamperd, B. Comparison of the Performance of Vulcanized Rubbers and Elastomer/TPE Composites for Specialty Applications. Proceedings of the Polymer Processing Society, 2004. 

Table 14.2 provides comparisons of the different classes of accelerators based on their rates of vulcanization. The secondary accelerators are seldom used alone, but are generally found in combination with primary accelerators to gain faster cures. 

Peroxides vulcanization of EPDM is growing in popularity because of enhanced aging resistance. A comparison of sulfur- and peroxide-cure system is shown in Table 14.31 [53]. 

Fig. 97.—Comparison between theoretical and experimental stress-strain curves for vulcanized rubber for elongations =0.40 to 2.0. Points are experimental data those for a <1 were obtained by inflating a rubber sheet. (Treloar. )...

Thermodynamic Analysis. As reported previously, the storage modulus G of PDMS networks with tetrafunctional crosslinks is independent of frequency between 10 3 and 1 Hz (21). This behaviour which is entirely different from that of vulcanized natural rubber or synthetic polyisoprene networks, was attributed to the lack of entanglements, both trapped and untrapped, in these PDMS networks. Figure 4 shows that G of a network with comb-like crosslinks is also frequency independent within an error of 0.5%. For comparison, two curves for PDMS having tetrafunctional crosslinks are also shown. The flat curves imply that slower relaxations are highly unlikely. Hence a thermodynamic analysis of the G data below 1 Hz can be made as they equal equilibrium moduli. 

The pigments are also required to have a specific heat resistance. This is tested on five colorations with different pigment concentrations in the range 0.01 to 1% together with 10 times the amount of chalk. The colorations placed side by side are vulcanized hot for 15 minutes at 140°C and evaluated coloristically against the corresponding untreated comparison coloration. 

The influence of ZnCFO concentration (3,0 5,0 7,0 phr) on formation of properties complex of the unfilled rubber mixes and their vulcanizates on the basis of isoprene rubber of the following recipe, phr isoprene rubber - 100,0 sulfur - 1,0 di - (2-benzothiazolyl) -disulfide - 0,6 N, N -diphenylguanidine - 3,0 stearic acid - 1,0, was carried out in comparison with the known activator - zinc oxide (5,0 phr). The analysis of Rheometer data of sulfur vulcanization process of elastomeric compositions at 155°C (fig. 5) shows, that on crosslink density and cure rate, about what the constants of speed in the main period (k2) testify, they surpass the control composition with 5,0 phr of zinc oxide. Improvement of the complex of elastic - strong parameters of rubbers with ZnCFO as at normal test conditions, and after thermal air aging (tab. 1), probably, is caused by influence of the new activator on vulcanization network character. So, the percent part of polysulfide bonds (C-Sx-C) and amount of sulfur atoms appropriating to one crosslink (S atoms/crosslink) in vulcanizates with ZnCFO are decreased, the percent part of disulfide bonds (C-S2-C) is increased (fig. 62). 

Thus, from the analysis of results of experimental researches on estimation of ZnCFO vulcanization activity in comparison with zinc oxide in structure of various vulcanization systems (VS) follows, that its efficiency decreases in line (fig. 10) ... 

Figure 10. Change of elastomeric compositions properties (%) with various vulcanization systems at ZnCFO presence (in comparison with ZnO) ...

The diffusion coefficient D is inversely related to the cross-link density of vulcanized rubbers. When D is extrapolated to zero concentration of the diffusing small molecules, it is related to the distance between the cross-links. Thus, as the cross-link density increases D becomes smaller, as expected. Further, the diffusion coefficient is less for crystalline polymers in comparison with the same polymer except in the amorphous state. In fact, this can be roughly stated as follows. 

By comparison, temperatures as high as 150°C are often required for mold-enclosed hard natural mbber compounds, where mold plattens are direcdy heated by steam or electricity. Synthetic latex mbber compounds, however, can be vulcanized at temperatures higher than those for natural mbber neoprene and acrylonitrile—butadiene can be vulcanized at as high as 135°C. 

This structure has superior water-resistant properties in comparison to conventional polyols used for PU synthesis. Room temperature cures are easily obtained with typical urethane catalysts. Short chain diols, fillers and plasticizers may also be used in their formulations in order to vary physical properties. Formulations usually with NCO/OH ratio of 1.05 are used for this purpose. Such urethanes are reported to be flexible down to about -70 °C. HTPB is regarded as a work horse binder for composite propellants and PBXs. HTPB also successfully competes with widely used room temperature vulcanizing (RTV) silicones and special epoxy resins for the encapsulation of electronic components. HTPB-based PUs are superior in this respect as epoxy resins change their mechanical properties widely with temperature. 

The results demonstrate the versatility of plasma polymerization of various monomers onto rubber fillers and vulcanization ingredients. The largest effects are seen in blends of different rubbers with unequal polarities. Substantial improvements in mechanical properties are seen in comparison with the use of unmodified fillers and curatives. 

Fig. 13.19. Comparison of the activity of Pt for oxygen reduction on high-surface-area titanium carbide and on Pt on Vulcan XC-72R carbon black (see the TEM photographs of the TiC support). (Reprinted from Assessment of Research Needs for Advanced Fuel Cells, S. S. Penner, ed., Pergamon Press, 1986, pp. 14, 87.)...

Fig. 33. Vulcanization kinetics and tensile properties of chlorinated HTI (CHTI, ) and comparison with chlorobutyl rubber (CIIR, ). Recipe as in Fig. 23 except, MBT = 1 T = 160 °C...

Figure 3.78 Exs/tu57Fe MES of isotopically enriched 57FeTPPCl dispersed on Vulcan XC-72 for specimens pyrolyzed at 700°C (lower curve) and 800 °C (middle curve) following washing with an acidic solution. Also shown for comparison is the corresponding spectrum of the specimen pyrolyzed at 800°C before washing.

The catalytic activity of carbon supported electrodes was further improved by replacing the conventional carbon supports like Vulcan XC-72R with carbon nanotubes (CNTs) and carbon nanofibers (CNFs). Carbon nanostructures including CNT and CNF have extremely higher electronic conductivity and specific surface area in comparison with the carbon black.4 The traditional Vulcan XC-72R exhibits an electronic conductivity of 4.0 S cm-1, while the electronic conductivity of CNT and CNF are in the range of 103-104 S cm-1. The high electronic conductivity of CNT and CNF ensures a reliable conductive path connecting Pt particles to supporting electrodes and increases the Pt utilization 27... 

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