Effect of CO2 Gas on the Swelling and Tribological Behaviors of NBR Rubber in Water

The swelling and tribological behaviors of nitrile-butadience（NBR） rubbers with three acrylonitrile contents（N18,N26 and N41） in water with different CO2 gas flows are investigated by immersion and wear experiments.The results show that the bubbles of CO2 into water severely destroy the cross-linking network of rubber and form defects on the surface,such as cracks,holes and lamellar perks.These defects lead to an increase in the static and dynamic swelling increment.The dynamic swelling increment is almost three or four times larger than the static swelling increment.The hardness and wear resistance of rubbers in water with CO2 gas remarkably decreases in contrast to that in water,and they gradually decrease with an increase in the gas flow in water.The bubbles of CO2 decrease the steady frictional coefficient of rubber in water due to the presence of the gas in water lubricant film.The steady frictional coefficient in water with different CO2 gas flow basically remains 0.1.N41 with high acrylonitrile content shows better swelling and wear resistances than N18 and N26 because of its dense molecular network.