Vulcanizate tensile properties, effect

Among the main molecular structural variables in EPDMs that are stipulated by catalyst systems and that affect the vulcanizate tensile properties we may mention molecular weight (MW) and MWD, degree of unsaturation (LG=C 1) and its distribution in the polymer, composition (C S) and monomer sequence length distribution along molecular chains, and long-chain branching if present. Effect of... 

The various properties of the silica filled compounds were improved compared to the unfilled compounds. The torque values of the filled compounds were increased due to the increase in viscosity. The scorch time and optimum cure time significantly decreased due to the heat conduction of filler particles. Tear and tensile properties of the silica filled compounds were considerably higher because of the effects of strain amplification and hysteresis of the silica filled vulcanizates. ... 

Figure 2.8 (a) Influence of carbon black particle size on tensile properties of rubber vulcanizates [95] (b) Stress-strain softening behavior (Mullins effect) of carbon blackfilled natural rubber compound... 

Tensile properties are normally measmed at room temperature (about 23°C). Equipment is available for doing this at lower or higher temperatures, which have a pronounced efFect on the hardness and stiffiiess of a vulcanizate. 

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. 

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. 

Graphitized carbon blacks, thus undoubtly display reinforcing abilities which become obvious when considering the tensile strength of the unfilled vulcanizate. It follows that the formation of a filler-elastomer chemical bond is not a requirement for reinforcement to occur. It strongly participates, however, in its effectiveness, and determines the good mechanical properties connected with rubber reinforce-... 

Figure 7. Effect of the pyrolysis temperature on physical properties (a) — (g) of rubber vulcanizates (MP test) (a) tensile strength (b) elongation (c) 300% modulus (d) tear strength (e) hardness (f) cut growth (g) abrasion. Test recipe of rubber compounds is the same as in Table III (Q) 15 (A) 20 ( 3>) 30 (ffz) 4 ...

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