ABSTRACT
The value of crosslink density is calculated through macroscopic measurements in swell or in modulus, although microscopic studies revealed that crosslinks are distributed in-homogeneously by Small Angle Neutron Scattering (SANS). Since sulfur vulcanization is accompanied with zinc oxide, stearic acid and accelerators, zinc oxide (which is crystal and makes cluster) attracts sulfur and accelerator, then creates higher crosslink density area around zinc oxide. The molecular weight of polymer chains between crosslink points may have a broad distribution due to the in-homogeneous distribution of crosslink points, although we calculate one averaged value of crosslink density in a macroscopic sample. According to the theory of rubber elasticity of non-Gaussian chain, the extensibility of vulcanized rubber is limited by the molecular weight of polymer chains between crosslinks. In the case of poly sulfide, a crosslink bridge itself can be deformed like a chain since sulfur atoms can make long chains and networks which are called as amorphous sulfur or plastic sulfur or rubber sulfur at certain conditions.
