ENHANCED PROPELLANT PERFORMANCE VIA ENVIRONMENTALLY FRIENDLY CURABLE SURFACE COATING

摘要

(Full Manuscript submitted to the Defence Technology Journal) Surface coating of granularpropellants is widely used in a multiplicity of propellants for small, medium and large caliberammunition. All small caliber ball propellants exhibit burning progressivity due to application ofeffective deterrent coatings. Large perforated propellant grains have also begun utilizing plasticizingand impregnated deterrent coatings with the purpose of increasing charge weights for greater energyand velocity for the projectile. The deterrent coating and impregnation process utilizes volatileorganic compounds (VOCs) and hazardous air pollutants (HAPs) which results in propellants thatneed to be forced air dried which impacts air quality. Propellants undergo temperature fluctuationsduring their life. Diffusion coefficients vary exponentially with variations in temperature. A smalltemperature increase can induce a faster migration, even over a short period of time, which can leadto large deviations in the concentration. This large concentration change in the ammunition becomesa safety or performance liability. The presence of both polymeric deterrents and nitroglycerin (NG)in the nitrocellulose matrix and organic solvents leads to higher diffusion rates. This results incontinued emissions of VOCs and HAPs. Conventional polymers tend to partition within thepropellant matrix. In other words, localized mixing can occur between the polymer and underlyingpropellant. This is due to solvent induced softening of the polymer vehicle over the propellant grain.In effect this creates a path where migration can occur. Since nitrate esters, like NG, are relativelysmall, it can exude to the surface and create a highly unstable and dangerous situation for thewarfighter. Curable polymers do not suffer from this partitioning due to “melting” because no VOCsolvents are present. They remain surface coated. The objective of the research effort is to replacethe current solvent based wet deterrent and impregnation coating technology, currently used inpropellant production, with the environmentally friendly novel Light Emitting Diode Ultra-Violet(LED-UV) cured solvent-less advanced surface coating technology. This research effort work is toexplore the use of LED UV curable polymers as deterrent coating materials, which do not sufferfrom this partitioning due to “melting” because of the highly adjustable and attainable networkstructure. The additional objectives are to increase performance without increasing maximumbreech pressure by the slowed and inhibited burning and obtain progressivity at the grain and chargelevels. The surface coating objective is also to achieve a flat temperature coefficient. The low Tgcan prevent the initiation, disrobing, cracking, ablation, penetration, and coating separation at coldtemperatures. The improved mechanical properties across the ballistic temperature range areexpected to improve Insensitive Munitions (IM) characteristics against thermal and spall threats. Thecrosslink LED UV coating polymer structure can inhibit/reduce migration which can preventplasticizer migration and degradation of performance resulting from migration. This migrationresults in large concentration changes in ammunition which becomes a safety or performanceliability].The small scale characterization testing, such as closed bomb testing, small scalesensitivity, thermal stability, and chemical compatibility, will be presented. The 30mm gundemonstration firing data at hot, cold, and ambient temperatures will also be presented.