Stoichiometry is the chemical relationship of the amount of reactive elastomer polymer to the amount and choice of curing agent used. Selection of proper stoichiometry is our responsibility but it plays an all important part in compression set resistance, cut and tear resistance and flex fatigue resistance. Higher stoichiometry leads to high heat build-up and flex fatigue resistance. While these two characteristics seem to be diametrically opposed, they can be modified to work to our advantage in problem solving. It is important to try to establish whether heat build-up or flex fatigue resistance is the more important property needed for best application performance.
These graphs show the broad effect of stoichiometry on the physical properties of 90A durometer elastomer (GC 1090).