ELASTIC MODULUS OF VULCANIZATES AS RELATED TO CARBON BLACK STRUCTURE.

The elastic modulus G//f prime of filled SBR vulcanizates has been measured as a function of strain amplitude A. At low loadings of carbon black (20 phr) the value of G//f prime (at 25 degree C, 0. 25 Hz) can be predicted within 5 per cent from the gum modulus G//g prime by the Guth-Gold equation. At normal loadings (50 phr) the value of G//f prime can be predicted fairly well from this treatment if the measurements are made at high amplitude. The dependence of the high-amplitude G//f prime on frequency and temperature is essentially the same for various reinforcing and semi-reinforcing blacks. The dependence of G//f prime on A is primarily a function of surface area. With graphitized blacks the low-amplitude G//f prime is higher than that of the ungraphitized blacks, but the high-amplitude G//f prime is low probably due to molecular slippage. ″New technology″ blacks, including N339 and N351, give a high-amplitude G//f prime comparable to that of conventional blacks, but give a higher G//f prime at low amplitude, indicating a more effective network structure.