Rubber zinc complexes

The Auger depth profile obtained from a plasma polymerized acetylene film that was reacted with the same model rubber compound referred to earlier for 65 min is shown in Fig. 39 [45]. The sulfur profile is especially interesting, demonstrating a peak very near the surface, another peak just below the surface, and a third peak near the interface between the primer film and the substrate. Interestingly, the peak at the surface seems to be related to a peak in the zinc concentration while the peak just below the surface seems to be related to a peak in the cobalt concentration. These observations probably indicate the formation of zinc and cobalt complexes that are responsible for the insertion of polysulfidic pendant groups into the model rubber compound and the plasma polymer. Since zinc is located on the surface while cobalt is somewhat below the surface, it is likely that the cobalt complexes were formed first and zinc complexes were mostly formed in the later stages of the reaction, after the cobalt had been consumed. 

Other flame retardants and/or smoke suppressants can also be used such as magnesium hydroxide, magnesium carbonate, magnesium-zinc complexes and some tin-zinc compositions. Zinc oxide is a common ingredient in many rubber base formulations used as part of the curing system. At the same time, the action of zinc oxide is similar to that of antimony trioxide, but less effective. 

Roseocobalt — see Cobalt, aquapentaammine-Roseopentaammine —see Aquapentaammine Roussin s black, 4, 1191 Roussin s red, 4, 1191 Roussin s salts, 4,240, 1243 Rubber vulcanization zinc complexes in, 5, 998 Rubeanic acid — see Dithiooxamid Rubidium complexes... 

Zinc dithiocarbamates have been used for many years as antioxidants/antiabrasives in motor oils and as vulcanization accelerators in rubber. The crystal structure of bis[A, A-di- -propyldithio-carbamato]zinc shows identical coordination of the two zinc atoms by five sulfur donors in a trigonal-bipyramidal environment with a zinc-zinc distance of 3.786 A.5 5 The electrochemistry of a range of dialkylthiocarbamate zinc complexes was studied at platinum and mercury electrodes. An exchange reaction was observed with mercury of the electrode.556 Different structural types have been identified by variation of the nitrogen donor in the pyridine and N,N,N, N -tetra-methylenediamine adducts of bis[7V,7V-di- .vo-propyldithiocarbamato]zinc. The pyridine shows a 1 1 complex and the TMEDA gives an unusual bridging coordination mode.557 The anionic complexes of zinc tris( V, V-dialkyldithiocarbamates) can be synthesized and have been spectroscopically characterized.558... 

Zinc complexes are important as additives for rubber polymers. Dithiocarbamate complexes are most commonly used here, but bis(8-hydroxyquinolinato)zinc inhibits the thermal decomposition of poly[(trifluoroethoxy)(octafluoropentoxy)phosphazene]. The zinc is thought to complex residual P—OH groups in the polymer chain, which would otherwise lead to rearrangement and chain scission.126... 

Activators which increase the vulcanization rate by reacting with the accelerators yielding rubber-soluble complexes. Zinc oxide and stearic acid are widely used as activators. 

Zinc complexes of dithiocarbamates and of other sulfur compounds are important accelerators in the vulcanization of rubber by sulfur. The iso-structural Zn and Cd compounds, [M(S2CNEt2)2]2, achieve 5-coordination... 

Rheumatoid arthritis gold drugs, 875 Riboflavin 5 -phosphate zinc complexes, 958 RNA polymerases zinc, 1007 Rubber vulcanization zinc complexes in, 998... 

Activators. Activators are chemicals that increase the rate of vulcanization hy reacting first with the accelerators to form rubber-soluhle complexes. These complexes then react with the sulfur to form sulfurating agents (eqs. 14,15). The most common activators are combinations of zinc oxide and stearic acid. Other fatty acids used include lauric, and oleic, acids. Soluble zinc salts of fatty acid such as zinc 2-ethylhexanoate are also used, and these rubber-soluble activators are effective in natural rubber to produce low set, low creep compoimds used in load-bearing applications. Weak amines and amino alcohols have also been used as activators in combination with the metal oxides. Natural rubber usually contains sufficient levels of naturally occurring fatty acids to solubihze the zinc salt. However, if these fatty acids are first extracted by acetone, the resultant clean natural rubber exhibits a much lower state of cime. Therefore, to ensme consistent cure rate, fatty acids are usually added. Synthetic rubbers, especially the solution polymerized elastomers, do not contain fatty acids and require their addition to the cure system. 

Perthiomercaptides are also believed to be formed when certain sulphur-donors such as tetramethyl thiuram disulphide reacts with the zinc complex. It is thus possible to vulcanize a rubber by a mechanism broadly similar to that of an accelerated sulphur system without the use of elemental sulphur. 

The first reaction is desulfuration (reaction 1), giving rise to crosslink shortening and leading eventually to monosulfide crosslinks. This reaction was shown to be effected by zinc complexes derived from the accelerator (or sulfur donor) and the zinc compounds present in the rubber mix. Examples of such complexes are (1) and (2). (1 and 2 are formalized structures and represent the stoichiometry but not necessarily the actual structures of the complexes.) The sulfur removed from the polysulfides is able to sulfurate more alkene to form additional crosslinks. 

The balance between these two reactions was found to determine, in large measure, the type of vulcanizate network formed. If the concentration in the rubber of zinc accelerator-thiolate complexes such as (1) and (2) is high, the polysulfide crosslinks are desulfurated rapidly to stable monosulfides and a heat-resistant network with a high degree of crosslinking is formed — the so-called efficient vulcanization system. If the zinc complexes are present in low concentration or are insufficiently soluble, desulfuration is slow and, unless the vulcanization temperature is low, the polysulfide crosslinks suffer thermal decomposition with consequent modulus reversion and extensive modification of the main chains (conventional or inefficient vulcanization). 

The pieces of cloth are then plied up and moulded at about 170°C for 30-60 minutes. Whilst flat sheets are moulded in a press at about lOOOlbf/in (7 MPa) pressure, complex shapes may be moulded by rubber bag or similar techniques at much lower pressures ( 15 Ibf/in ) (0.1 MPa) if the correct choice of resin is made. A number of curing catalysts have been used, including triethanolamine, zinc octoate and dibutyl tin diacetate. The laminates are then given a further prolonged curing period in order to develop the most desirable properties. 

Tsai et al. have also used RAIR to investigate reactions occurring between rubber compounds and plasma polymerized acetylene primers deposited onto steel substrates [12J. Because of the complexities involved in using actual rubber formulations, RAIR was used to examine primed steel substrates after reaction with a model rubber compound consisting of squalene (100 parts per hundred or phr), zinc oxide (10 phr), carbon black (10 phr), sulfur (5 phr), stearic acid (2 phr). 

Paints are complex formulations of polymeric binders with additives including anti-corrosion pigments, colors, plasticizers, ultraviolet absorbers, flame-retardant chemicals, etc. Almost all binders are organic materials such as resins based on epoxy, polyurethanes, alkyds, esters, chlorinated rubber and acrylics. The common inorganic binder is the silicate used in inorganic zinc silicate primer for steel. Specific formulations are available for application to aluminum and for galvanized steel substrates. 

Phenolic antioxidants in rubber extracts were determined indirectly photometrically after reaction with Fe(III) salts which form a red Fe(II)-dipyridyl compound. The method was applicable to Vulkanox BKF and Vulkanox KB [52]. Similarly, aromatic amines (Vulkanox PBN, 4020, DDA, 4010 NA) were determined photometrically after coupling with Echtrotsalz GG (4-nitrobenzdiazonium fluoroborate). For qualitative analysis of vulcanisation accelerators in extracts of rubbers and elastomers colour reactions with dithio-carbamates (for Vulkacit P, ZP, L, LDA, LDB, WL), thiuram derivatives (for Vulkacit I), zinc 2-mercaptobenzthiazol (for Vulkacit ZM, DM, F, AZ, CZ, MOZ, DZ) and hexamethylene tetramine (for Vulkacit H30), were mentioned as well as PC and TLC analyses (according to DIN 53622) followed by IR identification [52]. 8-Hydroquinoline extraction of interference ions and alizarin-La3+ complexation were utilised for the spectrophotometric determination of fluorine in silica used as an antistatic agent in PE [74], Also Polygard (trisnonylphenylphosphite) in styrene-butadienes has been determined by colorimetric methods [75,76], Most procedures are fairly dated for more detailed descriptions see references [25,42,44],... 

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). 

That is, the analysis of the received results, has shown an opportunity of equal-mass replacement of the traditional activator - zinc oxide on the new polymer - inorganic composite (5,0 phr) at maintenance of a high activation level of sulfur vulcanization process of rubber mixes on the basis of diene isoprene rubber and improvement of the physical-mechanical properties complex of their vulcanizates. 

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 role of activators in the mechanism of vulcanization is as follows. The soluble zinc salt forms a complex with the accelerator and sulfur. This complex then reacts with a diene elastomer to form a rubber—sulfur—accelerator cross-link cursor while also liberating the zinc ion. The final step involves completion of the sulfur cross-link to another mbber diene segment (18). 

Zinc oxide, as an amphoteric material, reacts with acids to form zinc salts and with strong alkali to form zincates. In the vulcanization of rubber, the chemical role of zinc oxide is complex and the free oxide is required, probably as an activator. 

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