The effects of filler loading on the tensile and tear properties of SMR L/ENR 25 and SMR L/SBR blends using a semi-efficient vulcanization system was studied. Carbon black (N330), silica (Vulcasil C) and calcium carbonate were used as the fillers and the loading range was from 0 to 40 phr. Tensile strength, M300 (tensile stress at 300% elongation) and tear strength were determined using a Monsanto Tensometer (Model T10) operating at 50 cm/min. Results show that for the carbon black and silica-filled blends, elongation at break decreases, but tensile strength, M300 and tear strength increase with filler loading. The reverse behavior is obtained for the calcium carbonate-filled blends. This observation is attributed to the better rubber-filler interphase, interaction of carbon black and silica compared to the non-reinforcing nature of calcium carbonate, the dilution effect of which becomes more significant as the filler loading is increased. For a fixed filler loading, SMR L/ENR 25 blend consistently exhibits higher tensile strength, M300 and tear strength but lower elongation at break compared to SMR L/SBR blend. This finding is associated with the mutual rubber reinforcement between the two strain-induced crystallizable rubbers (i.e. SMR L and ENR 25), coupled with good rubber-filler interaction, particularly between silica and ENR 25 in the former blend. (C) 2002 Elsevier Science Ltd. All rights reserved.
