Validation of Hazardous Air Pollutant (HAP)-Free Torque Seal Inspection Lacquer

Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio

Tuesday, December 01 2009

Testing determined that a HAP-free version of the sealant produced results similar to the original version.

The Army uses numerous adhesives and sealants, among other coating materials, that contain significant amounts of hazardous air pollutants (HAPs). This work examines laboratory and field demonstration/validation of one sealant, Torque Seal. A HAP-free alternative to Torque Seal containing ethanol as the carrier solvent has been identified. Laboratory testing including adhesion, resistance to fluids, resistance to humidity, and drying time validated that the HAP-free sealant performs very similarly to the baseline Torque Seal containing methanol (HAP). Furthermore, a demonstration study at Fort Rucker, AL, using a UH-1 helicopter rotor, shows that the HAP-free sealant performed as well as the Torque Seal.

Torque Seal is used primarily to detect tampering or loosening of mechanical fasteners on military aircraft. Applied after bolts or fittings are in proper torque or position, the product gives inspectors visual evidence of any movement or tampering. Torque Seal dries to form a very brittle film that will crack, flake, or crumble when minimal force is applied. Other key product attributes include excellent adhesion to most surfaces and fast drying. The manufacturer refers to this product as an inspection seal lacquer or anti-sabotage lacquer. The fast-drying characteristic of Torque Seal is achieved by using low-boiling- point solvents as carriers, specifically ethanol and methanol. While both solvents are volatile organic compounds (VOCs), only methanol is classified by the EPA as a HAP. The reported HAP content of this material is 20% by weight. This report summarizes laboratory and field trial results for the HAP-free formulation of Torque Seal containing only ethanol, versus the current product containing ethanol and methanol.

The viscosities of the wet sealants were measured using a TA Instruments AR2000 rheometer in steady shear flow experiments using a 40-mm, cross-hatched parallel plate geometry with a peltier and a solvent trap containing ethanol, at 20 °C. Thermogravimetric analysis (TGA) was run on the samples of dried formulation solids using a TA Instruments TGA 2950. Wet formulation samples were dried in an oven until the sample weight remained constant. This dried material was pulverized in a coffee bean grinder to allow the release of any trapped solvent. Oven drying of the pulverized sample continued until the sample weight was again constant. The TGA instrument measures the sample mass as a function of temperature throughout the experiment. The percent mass remaining at the end of the run is the residual inorganic ash content. Three samples of each formulation were run to get a good measure of percent error.