Mold Pressure and Filler Concentration Effect on Both – the Percolation Threshold and Piezo-Resistive Effect of the Polyisoprene-Nanostructured Carbon Black Composites

Industry demands on cheap, full scale tactile sensors, capable to be embedded into material or structure being monitored. Previous research reported polyisoprene-nanostructured carbon black composite (PNCBC) as a promising material for this use. PNCBC is made when certain concentration of high-structure nano-size extra conductive carbon, close to that of a percolation threshold, is well dispersed into a rubber matrix before vulcanizing. In such case reversible tenso-resistance effect as well as piezo-resistance effect with up to 4 orders of magnitude is observed. During previous research, it was concluded that technological parameters like mold pressure, vulcanizing time and filler distribution have a critical effect on final properties of PNCBC. In this work we have ascertained, how the mold pressure during vulcanizing have an effect on electric properties of PNCBC. Extra conductive carbon black was mixed into polyisoprene matrix by means of cold rolls for 20 minutes at room temperature. Afterwards the raw material was vulcanized using different mold pressures. Specific electric resistance and piezo-resistance effect were determined depending on filler concentration and mold pressure. By evaluating results, conclusions were made, that not always the best conductivity and piezo-resistance effect of PNCBC are gained using typical mold pressures, used in classic rubber industry. The mechanism of the effect of mold pressure on the final sensor properties and the percolative behavior of PNCBC is discussed