Rubbers, fatigue tensile strength

Molar mass, chain orientation, reinforcement, rubber additions Tensile strength, toughness, impact resistance, fatigue resistance... 

As can be seen in Table 30 Co-, Ni-, Ti- and Nd-based catalyst systems yield BR with cis- 1,4-contents >90%. A direct consequence of high cis-1,4-contents is strain-induced crystallization of raw rubbers as well as of the respective vulcanizates. As the cis- 1,4-content is extraordinary high in Nd-BR, strain-induced crystallization is particularly pronounced for this BR-grade. As strain-induced crystallization beneficially influences the tack of raw rubbers as well as tensile strength and resistance of vulcanizates to abrasion and fatigue the high cis- 1,4-content makes Nd-BR particularly useful for tire applications. 

However, the difference in olefin concentration of EPDM and natural rubber results in a cure-rate misbatch leading to an incompatible blend. This has been recognized to cause both inferior static and dynamic mechanical properties such as poor tensile strength, fatigue resistance, and high hysteresis in the rubber blend (17). 

Filler dispersion is a property that determines how well the filler partciles in a given rubber compound are dispersed as a result of the mixing process. This relates to carbon black dispersion as well as the dispersion of nonblack fillers such as silica, clay, calcium carbonate, titanium dioxide, etc. Also rubber curatives such as sulfur and accelerators can be poorly dispersed (commonly these ingredients are added late in the mixing cycle). Poor dispersion makes a mixed stock less uniform, and commonly the cured ultimate tensile strength will have more variability. Poor dispersion can affect other important cured physical properties such as abrasion, tear, and fatigue resistance, flexometer heat buildup, and other dynamic properties. 

A tire is a textile-steel-rubber composite the steel and textile cords reinforce the rubber and are the primary load-carrying structures within the tire. Because of the performance demands of fatigue resistance, tensile strength, durability, and resilience, seven principal materials have been found suitable for tire application cotton, rayon, nylon, polyester, steel, fiberglass, and aramid the latter three materials find primary usage in the tire crown or belt region. 

Fig. 13. Aging properties of cured natural rubber. A conventional cure system, B semi-EV, C EV system, tensile strength loss (%), fatigue life, andhardness change.

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