Particles filled vulcanizates, in case that they have strong interface activities, make a higher structure system and give a great effect to the dynamic properties.
In these rubber vulcanizate systems that make heterogeneous structures, it is a most important problem that we should study the relationship between dynamic or physical values of microstructual element and macroscopic dynamic values of composite systems.
In this paper we presented equations that lead the relations of approximation about spin-spin relaxation time, volume ratios of the particles filled vulcanizates, Young's modulus, bulk modulus and Poisson's ratio of the composite system.
And we confirmed that we could use these eqations with good accuracy under static conditions to pure gum vulcanizates that had various crosslinking densities and CaCO₃ or HAF filled vulcanizates.

View full abstract

Direct adhesions of pre-cured rubber vulcanizates (EPDM or SBR) with uncured rubber compounds (SBR or EPDM) through vulcanization were carried out and their adhesive strength of the obtained samples were measured. The effect of the process oils on the adhesive strength between pre-cured EPDM and uncured SBR has been investigated in regard to several kind of process oils and their loadings in both rubbers. The adhesive strength among the two rubber components compounded with the aromatic process oil in all oils used here showed the highest strength of the adhesion. It was also shown that the strength of the adhesion increased with increasing the aromatic oil loading in the pre-cured EPDM and with decreasing that in the uncured SBR compound before the adhesion through vulcanization.
On the other hand, the adhesion of the pre-cured SBR with the uncured EPDM compound through vulcanization was not improved by compounding the various oils and by varying the oil loading. To improve the adhesion strength in such a case, the compounding of an adhesion promotor such as the system of the resorcinols and hexamethylene tetramine which are commercially available was found to be useful. Especially, an excellent adhesive strength is obtainable by compounding the adhesive promotor with specified accelerators to uncured EPDM compound.

View full abstract

Natural rubber (NR) and isoprene rubber (IR) were cured by sulfur and accelerator to give rubber vulcanizates. Both vulcanizates were subject to solvent extraction to purify them, followed by the γ-ray irradiation in air at room temperature. The deterioration by γ-ray (0-20Mrad) was investigated by the changes of tensile properties, hardness, swelling, and ATR-IR spectra. The tensile strength decreased much by a few Mrad irradiation, which is elucidated due to the difficulty of stretch-induced crystallization of polyisoprene after the irradiation. Modulus at 50-% elongation, network-chain density, and hardness did not show significant variation with the γ-ray dose. These irradiation results suggest both degradation and crosslinking occur comparably in the rubber vulcanizates and the regularity of polyisoprene chains may be somewhat randomized to prevent them from crystallizing on stretching.

View full abstract