Vulcanizate properties, comparison

BR is used in nearly all parts of the tire with the exception of the inner liner it is always blended with natural rubber (NR) or styrene-butadiene rubber (SBR). Apart from the extrudability, in NR blends the Nd-BR polymers exhibit advantages in all important compound and vulcanizate properties. Also, in SBR blends Nd-BR leads to the best vulcanizate properties in comparison with all other types of BR. 

COMPARISON OF TREAD VULCANIZATE PROPERTIES OF HTSBR WITH... 

Types of Latex Compounds. For comparison with dry-mbber compounds, some examples of various latex compounds and the physical properties of their vulcanizates are given in Table 23. Recipes of natural mbber latex compounds, including one without antioxidant, and data on tensile strength and elongation of sheets made from those, both before and after accelerated aging, are also Hsted. The effects of curing ingredients, accelerator, and antioxidant are also Hsted. Table 24 also includes similar data for an SBR latex compound. A phenoHc antioxidant was used in all cases. 

General Vuleanizate Properties. Table 4 smmnaiizes the properties of CR vulcanizates that ate impoitant to the designers of rubber parts, and compares these properties to those of two competitive materials. The comparison is general and varies depending on compound design (90). The... 

Comparison of vulcanizate tensile properties of the six sets of comparable samples (Figures 7A-F) gave results (Table I, last column) pointing to the ability of the systems in giving decreasing tensile strength in the following orders... 

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). 

The lower reactivity of OTI with respect to HTI (Table 19) is parallel to its be-hanor in radical grafting (Sect. B.l.c)), but in comparison with butyl rubber, OTI is more reactive, as far as the amount of piled rubber indicates. However, levels of triene higher than 4 mol % are necessary to reach fair properties of the vulcanizate. 

Oxygen Aging of Vulcanizates. Examination of Table II (NBR) and Table III (NR) demonstrates clearly that vulcanizates treated with the sulfonyl azide antioxidants retain physical properties to a marked degree after solvent extraction, followed by aging in oxygen. The conventional antioxidants used for comparison, such as PBNA in the NR or Irganox 1076 in the NBR, are removed by the extraction process and therefore afford no protection, resulting in samples too brittle to test. 

PA-6-66 copolymer (35)-NBR (65) vulcanizate) (50) / (PP(50)-EPDM(50) vulcanizate) (50) / PP-MA (10) internal mixer at 220°C / PA + rubber vulcanization and PP + rubber performed in separate steps before blending / mechanical properties vs. use of unfunctionalized PP / comparison to use of functionalized PP in initial vulcanizate / PP-f-carboxymethyl maleamic acid Coran et al., 1985... 

A devulcanization process that utilizes supercritical CO2 as a devulcanization reaction medium in the presence of diphenyl disulfide as a devulcanizing reagent has been reported [45]. The process devulcanizes unfilled NR vulcanizates effectively. Further, a comparison of measured sol/gel components as well as dynamic mechanical properties of the devulcanized rubber products of filled and unfilled NR vulcanizates has indicated that the presence of carbon black in the vulcamizate does not disturb the devulcanization in supercritical CO2. 

Some properties of sodium and zinc vulcanizates are compared with those of the acid precursor in Table 5.16. High tensile strength is a characteristic of ionic vulcanizates. As a comparison, a standard polybutadiene elastomer vulcanized with sulfur gives a strength of 1.9-5.8 MPa (275-841 Ibf/in. ), whereas an equivalent copolymer containing 1.5 mole% methacrylic acid, and vulcanized with... 

Table 37-6. Comparison of the Physical Properties of Vulcanizates from Unfilled Regular and Liquid Rubbers...

The mechanical properties of the control NR composite, untreated HNT-filled NR nanocomposite, treated HNT-filled NR nanocomposite, and silica-filled NR composite are tabulated in Table 19.6. The addition of 10 phr HNT loading increased the tensile modulus and tensile strength compared to the neat NR vulcanizate. However, the values of elongation at break of the HNT filled rubber nanocomposite were decreased in comparison to the unfilled NR vulcanizate. The silica filled NR vulcanizate showed inferior properties as comparison to HNT filled nanocomposites. It is well known that the modulus of rubber vulcanizates is proportional to the degree of crosslink density. Therefore, modulus of rubber vulcanizates increased with the increased of crosslink density. In contrast, the elongation at break decreased with increasing crosslink density. 

Non-linear mechanical properties were observed for rubber eomposites and referred to as the Payne effect. The Payne effeet was interpreted as due to filler agglomeration where the filler clusters formed eontained adsorbed rubber. The occluded rubber molecules within filler elusters eould not eontribute to overall elastic properties. The composites behaved similarly to rubber composites with higher filler loading. Uniform and stable filler dispersion is required for rubber composites to exhibit linear viscoelastic behaviour. Payne performed dielectric measurements on SBR vulcanizates containing silica or carbon black. The dielectric data were used to construct time-temperature superposition master curves. The reference temperature increased with crosslinking but not significantly with filler. Comparison of dynamic mechanical and dielectric results for the SBR blended with NR was made and interpreted. ... 

Properties of Silicone Rubbers. Gum vulcanizates have essentially no tensile strength. Fillers are therefore essential. Reinforcing silicas are frequently used. Even then, the tensile properties and abrasion resistance of silicone rubber vulcanizates are poor in comparison with of other types of elastomer. However, the properties change very little with increasing temperatures. These polymers excel in high-temperature applications. 

Although tread vulcanizates containing only a solution rubber have superior dynamic properties, their main deficiency is their poor ultimate properties, such as tear strength and tensile strength, which relate to wear. The need for improved abrasion resistance in solution rubber is indicated by a comparison of laboratory data (Table 11) for black filled vulcanizates of E-SBR, solution SBR (S-SBR) and MVBR at nearly equivalent 7. For E-SBR, it is possible that a higher tram Icis ratio of the polybutadiene portion and a broader MWD may relate to its better abrasion resistance (Pico Index). The relative values... 

We have discussed above the uncured properties of a synthetic rubber which are similar to those of NR. A major difference between the rubbers is that the synthetic SBR has better thermal oxidative resistance than NR. Under oxidative ageing conditions, 1,4-polybutadiene structure tends to crosslink to a greater extent relative to undergoing chain scission. The reverse is the case for NR (cw-l,4-polyisoprene structure). The greater resistance to oxidative degradation of HTSBR vulcanizates is indicated by a comparison of plots of flex life (cycles to failure) of HTSBR and NR versus strain amplitude, shown in Fig. 34. 

Vieweg S, Unger R, Heinrich G, Donth E (1999) Comparison of dynamic shear properties of styrene-butadiene vulcanizates filled with carbon black or polymeric fillers. J Appl Polym Sci 73(4) 495-503... 

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