Studies on ground EPDM vulcanisate as filler in window seal formulation

Abstract

The processability, curing characteristics, and mechanical properties of a window seal compound based on highly filled and oil extended EPDM rubber (R-EPDM) containing ground EPDM vulcanisate of known composition (W-EPDM) simulating the waste window seal product have been studied. A conventional mechanical grinder with a rotating abrasive wheel was used for grinding the aged vulcanisate. The Mooney viscosity of R-EPDM increased linearly with volume fraction of W-EPDM. Rheological behaviour, studied using a Monsanto processability tester in the shear rate range of 306 7 to 1533 s-1, showed that the surface smoothness of the R-EPDM extrudates was slightly impaired by the addition of W-EPDM, although the die swell remained almost constant. Mooney scorch time decreased with progressive addition of W-EPDM, presumably owing to the migration of accelerators from W-EPDM to R-EPDM. While the minimum rheometric torque ML increased, the maximum rheometric torque MH and Deltatorque (i.e. MH-ML) decreased with increasing loading of W-EPDM. The decrease in Δtorque may be due to the migration of sulphur from R-EPDM to W-EPDM. Although the tensile strength and elongation at break remained almost constant, the modulus, hardness, abrasion resistance, and tear strength of the vulcanisates progressively decreased with W-EPDM loading. While hysteresis loss of the vulcanisates decreased, resilience increased slightly and the tension set remained constant as the W-EPDM loading increased. The deterioration in some physical properties on incorporation of the ground vulcanisate up to a loading of 200 phr is marginal compared with previously reported results on utilisation of ground waste rubbers such as cryoground rubber tyres in virgin rubbers.