Evaluation of Low Hazardous Air Pollutant Thermoset Adhesives for the Application of Rubber-to-Metal Bonding on Army Tank Pads and Road Wheels

摘要

The Environmental Protection Agency is in the process of mandating Defense Land Systems and Miscellaneous Equipment and National Emission Standards for Hazardous Air Pollutants that will affect Army surface coating operations. Bonding unvulcanized rubber to a metal substrate in the production and replacement of tank treads, track pad, track shoes, and road wheels uses thermoset adhesives and primers with a high hazardous air pollutant (HAP) content. This research focused on two alternative options to reduce HAP emissions while maintaining performance properties: the replacement of HAP- containing thinners used with rubber-to-metal thermoset adhesives or the use of an entirely new low-HAP adhesive system. Thinner miscibility in the baseline adhesives was conducted to identify acetone, methyl ethyl ketone, and naphtholite 66/3 as compatible non-HAP thinners. Peel adhesion testing was conducted to compare the adhesion strength of each adhesive, both neat and diluted in the test series on each of the rubber compounds used in tank pads, track shoes, and road wheels. The results indicated that a number of the low- HAP adhesives and primer combinations outperformed the baseline HAP-containing materials, including Thixon 532-EF adhesive with naphtholite 66/3 thinning solvent and Megum 3911 primer. This could result in HAP reductions of 10 tons/yr for the rubber-to-metal bonding operation at Red River Army Depot alone.