What property of the rubber does the elongation at fixed strain in the performance indicators of synthetic rubber reflect, and what is its relationship with subsequent processing?
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I’m a bit confused; it’s not entirely clear. I’d appreciate advice from those who are experts, thank you!
Set stress: The load per unit cross-sectional area that must be applied to stretch the specimen to a given length; it is an important indicator of rubber stiffness.
Stress at a fixed strain refers to the force under a specific degree of elongation, and it is an indication of modulus. Set elongation is closely related to both the vulcanization system and the reinforcement system; it is a property of the rubber compound after vulcanization, and it has no direct connection with its processability before vulcanization. The main factors affecting reaction processing performance are plasticity and Mooney viscosity.
But doesn’t the cross-sectional area of the gel change before and after testing? The cross-sectional area after stretching is smaller than that before stretching; which cross-sectional area should be used in the calculations?
Set elongation is calculated based on the cross-section before stretching.
There are standards for tensile strain testing, which involve tension, elongation, and cross-section. For the test specimens used, there are requirements regarding length, thickness, and dimensional specifications. It’s not a random test; otherwise, there would be no comparability.