Application of nitrile butadiene rubber for flexible,chemically protective coating

Rheological properties of toluene solutions of nitrile butadiene rubber, of different molecular weights (M_w, 290,000,320,000, and 450,000) and acrylonitrile contents (30 and 40 percent), were investigated at low (0.1 S^?1) to medium (20,0 S^?1) shear rates, in order to determine their feasibility for dip-coating applications. The effect of a surface-active additive, bentonite, and the solid content (15 and 20 wt percent) on solution viscosity was of main interest. At low zero-shear viscosity (<50 Pa·S) an excessive sagging of the wet film was experienced; at high zeroshear viscosity (>100 Pa-·S) the coating showed poor leveling. Zeroshear viscosity was found to be less affected by bentonite than oligomer-based solutions, at the same time, the solid content and the molecular weight of the polymer had more pronounced effects. With a proper balance of the parameters, seamless coating films were achieved, with excellent tensile and tear properties, and good permeation resistance against benzene.