Vulcanization elastomeric compositions

The ZnCFO action as vulcanization active component of elastomeric compositions on the basis of rubbers of general and special assignment with various vulcanization systems is investigated. 

Key words Polymer-inorganic composite Vulcanization active component Elastomeric composition Vulcanization Morphological structure Physical-mechanical properties. 

An estimation of ZnCFO efficiency as vulcanization active component was carried out in modelling unfilled elastomeric compositions on the basis of isoprene, butadiene-nitrile, chloroprene and butyl rubbers of sulphur, thiuram, peroxide, metaloxide and resin vulcanization systems. 

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). 

Figur 5. Rheometer data of sulfur vulcanization process of modeling unfilled elastomeric compositions on the basis of isoprene mbber at 155°C with ZnCFO as the activator ...

Figure 6. Influence of activator type on vulcanization network character of the elastomeric compositions ...

Influence of the ZnCFO contents (3,0 5,0 7,0 phr) on crosslink kinetics of the modelling unfilled rubber mixes from NBR-26 of sulfur, thiuram and peroxide vulcanization of recipe, phr NBR-26 - 100,0 sulfur - 1,5 2-mercaptobenzthiazole - 0,8 stearic acid - 1,5 tetramethylthiuramdisulfide - 3,0 peroximon F-40 - 3,0, is possible to estimate on the data of fig. 7. As it is shown, the increase of ZnCFO concentration results in increase of the maximum torque and, accordingly, crosslink degree of elastomeric compositions, decrease of optimum cure time, that, in turn, causes increase of cure rate, confirmed by counted constants of speed in the main period (k2). The analysis of vulcanizates physical-mechanical properties testifies, that with the increase of ZnCFO contents increase the tensile strength, hardness, resilience elongation at break and residual deformation at compression on 20 %. That is, ZnCFO is effective component of given vulcanization systems, as at equal-mass replacement of known zinc oxide (5,0 phr) the cure rate, the concentration of crosslink bonds are increased and general properties complex of rubber mixes and their vulcanizates is improved. 

The comparative estimation of efficiency of zinc oxide and ZnCFO similar concentrations (3,0 5,0 7,0 phr) as the agents of metaloxide vulcanization system was carried out on example of modelling unfilled elastomeric compositions from chloroprene rubber of recipe, phr chloroprene rubber - 100,0 magnesium oxide - 7,0. Kinetic curves of rubber mixes curing process at 155°C are shown on fig. 8. The analysis of the submitted data testifies, that at increase of zinc oxide contents vulcanization kinetics is changed as follows the scorch time and optimum cure time are decreased, the cure rate is increase. Vulcanization... 

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

It is possible to explain the decrease of ZnCFO efficiency as component of various vulcanization systems for rubbers of general and special assignment in the earlier submitted line (fig. 10) also by character of formed morphology of compositions. So, at use of ZnCFO as the activator of sulfur vulcanization the structure of rubbers with the minimal value of parameter r is formed, and at transition from sulfur to peroxide vulcanization of elastomeric compositions the particles size of heterophase is increased (fig. 11 b). 

ZnCFO is the effective vulcanization active component of the sulfur, thiuram, peroxide and metaloxide vulcanization systems for isoprene, nitrile-butadiene and chloroprene rubbers at the same time it is not effective in resin vulcanization system for butyl rubber. On a degree of positive influence on the properties of elastomeric compositions vulcanization systems with ZnCFO are arranged in a line ... 

Fischer (1973) used the DV process to prepare compositions containing partially vulcanized rubber. It has since been found that improved, very strong elastomeric compositions of EPDM and polypropylene could be prepared by... 

Other Elastomeric Compositions Prepared by Dynamic Vulcanization... 

The discovery of vulcanization by Charles Goodyear in 1839 and the industrialization of Europe and North America enabled the tire to evolve from a rubberized canvas covering a rubber tube to a complex fabric, steel, and elastomeric composite. 

Dynamic vulcanization (DV) is also considered. DV is the crosslinking of one polymer in a blend of polymers during its mixing therein, all polymers of the blend being in the molten state. The process is used in the preparation of thermoplastic elastomeric compositions from rubber-plastic blends. 

Excellent elastomeric NBR-nylon compositions have also been prepared by dynamic vulcanization during the melt-mixing of intimate blends of NBR with various nylons. In this case, the effect of curatives was complicated by the fact that some nitrile rubbers tend to self-cure at temperatures of mixing. Sulfur, phenolic, maleimide, or peroxide curatives can be used. The thermoplastic elastomeric compositions prepared by the dynamic vulcanization of nylon-NBR blends are highly resistant to hot oil. As in the case of the EPDM-polyolefin blends, increases in the amount of rubber in the composition reduce stiffness but increase resistance to permanent set. 

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