| Ethylene propylene rubber (EPR) was blended with low molecular weight high vinyl polybutadiene (1,2-PBd), in a novel approach to rubber reinforcement. The blends were crosslinked with various levels of dicumyl peroxide. Cure behavior, crosslink density and mechanical properties were determined. Electron microscopy was used to study morphology. Neat EPR and 1,2-PBd were also characterized.; Neat EPR cured with low peroxide level strain-crystallized. Crosslinking efficiency was low because of chain scission. Modulus and crosslink density increased with peroxide level. Tensile strength passed through a maximum, and ultimate elongation and tear strength decreased. Glass transition temperature and vulcanizate density were affected little by curative concentration.; Vinyl polybutadiene reacts with dicumyl peroxide in a free radical chain reaction. Crosslinking efficiencies were much higher than unity. Properties of 1,2-PBd changed markedly upon curing with different levels of peroxide. Crosslink densities, crosslinking efficiencies, glass transition temperatures, and densities, were much higher than those for EPR. PBd flexural modulus and tensile strength increased (with peroxide) then reached a plateau when glassy.; In the blends, 1,2-PBd initially plasticizes EPR, then increases crosslinking rate. Transmission Electron Microscopy investigations of both uncured and cured blends indicate phase separation. Domains were interpreted as 1,2-PBd. The matrix was interpreted as EPR and regions of miscible EPR/1,2-PBd. Densities, crosslinking efficiencies, crosslink densities, and moduli of blends were higher than those for EPR. Tensile properties for blends were intermediate to those for the raw materials. 1,2-PBd reinforced EPR. Tear energies of blends decreased with increasing peroxide level and tearing was stick-slip. At the same peroxide level, blends had lower tear energies than the pure EPR, however, blends had much higher moduli. At the same stiffness, the tear strengths of blends were 1--7 times greater than those for EPR. |
