The rheological properties of binary rubber-carbon black compounds at compositions 5, 20, 30, 40 and 50 volume percent carbon black have been investigated as well as ternary compounds with rubber/carbon black/oil compositions of 70/20/10, 60/20/20 and 50/20/30, respectively. The compounds were investigated using (1) a constant stress creep instrument at very low rates of deformation, (2) a rotational rheometer at intermediate shear rates and (3) a capillary extrusion instrument at higher shear rates. In experiment (1), it was found that below a critical yield stress, the strain becomes saturated and finite. Above this stress the strain becomes unbounded and the compound maintained a steady shear flow. This observation was made for all compounds investigated. The values of the yield stresses obtained using the creep instrument were found to be significantly lower than those obtained from common extrapolations from rotational and capillary rheometers. In the ternary compounds it was also observed that as the oil content increases, not only the viscosity but the yield stress is reduced significantly. This observation is important because it can throw light on the type of interactions between carbon black and the rubber matrix.

No abstract

No abstract

SYNOPSISThe effects of carbon black loadings cp, temperature T, and shear frequency w on dynamic mechanical properties of EPDM gum elastomer and its carbon black compounds were investigated under sinusoidal shear flows. The region of shear flows where the gum elastomer and its carbon black compounds exhibited characteristic plateau in viscoelastic properties were established and found to directly depend on temperature but were inversely proportional to carbon black loading. The gum rubber and its 20% carbon black compound showed rather unusual similar dynamic flow behaviors a t 50 and 100°C attributed to the possible presence of crystallinity from the fractional ethylene components in the gum. This fraction could act as nucleation sites for macrogels that required higher temperatures than 50 and 100°C for melting, particularly in the presence of carbon black particles. Dynamic properties were amplified due to carbon black filler. This effect was more pronounced at low frequencies and at 50 and 15OoC, respectively. At 100°C, amplifications appeared to have been attenuated by the hydrodynamics of the continuum elastomer matrix. This observation helps the further understanding of the filler-elastomer interactions and the critical role played by temperature, particularly as it affects rubber processors. 0

SynopsisThe mechanism and growth of limited swelling of linear high-density polyethylene (LHDPE) in some selected commonly used industrial solvents have been studied. The equilibrium solvent uptake has been used to determine its cohesive energy density. The data obtained during the course of these investigations fits a mechanistic growth model that predicts solvent uptake. This method offers a suitable and alternative way of determining the structural strength and resistance of polymers in contact with common solvents.