Without a doubt, belly soils, that under-aircraft mess that can stretch the length of the fuselage, represent some of the toughest-to-remove soils on any aircraft made all the more difficult to clean with the added impact of higher velocities and ambient temperature dynamics. For those who must deal with this special challenge on a routine basis, belly soils represent an added occasion for both excessive damage and maintenance infrastructure cost that may be mitigated with the use of biobased “cleaning” surfactants and miscible co-solvents. Yes, there is a very successful and proven alternative to age-old traditional and surface-damaging chemicals such as oxidizers and caustics which do not actually clean but rather they remove soils by actually removing fractions of the underlying surface materials, whether paints, decals or metals. And those same products serve to embrittle elastomerics such as rubberoids nylon and high impact plastics.
Belly soils are comprised of waste soils that are enamelized or polymerized by the laminar flow of hot gases and atmosphere that can quickly make the smear of galley and toilet waste, combustion exhaust, hydraulic and brake fluids; fuels, atmospheric dusts such as pollens and aerosols, insects, waxes, lignens, micro-spoor forms, bacteria and even blood waste from birds. After hours of flight time, these “belly soils” can accumulate in a layered, adhesive-like smeared mess that can only barely be removed with aggressive mechanical brushing or damaging corrosive solutions and hydrocarbon solvents including but not limited to: metasilicates, phosphates, SLES and SLAS, peroxides, sulfoxides, silicones, napthalenes, and hydroxides. In fact the use of such chemistries may actually serve to “fix” these soils more tenaciously to the substrate surfaces.
Of the various chemical options including anionic, cationi,c and non-ionic surfactants; amphoteric detergents and acids, it is biobased, non-ionic surfactants that offer the least invasive and non-damaging results, especially when combined with a miscible co-solvent as demonstrated by TURI in comparative testing performed back to 2009 and 2010. It is generally accepted today that non-ionic surfactants enhanced with biobased fatty alcohols, fatty esters, and terpene based solvents in a standing emulsion or suspension are able to address most any of the common belly soils without measurable degradation to surface bonding, metals, decals, paints, sealants, and tertiary materials, or in the reflectance (shine) of the finished surface.
The next consideration is for a miscible co-solvent component which most typically will form a temporary suspension with the surfactant. Likely candidates will include terpenes such as D-Limonene, Pinene, and Citrusene; Glycerols such as glycerin derived from soy, corn, palm, and other plant oils; fatty alcohols such as furfuryl alcohol often derived from sugars or fatty esters such as soy methyl ester. All of these serve to boost the cleaning release of the aqueous based surfactant and they will typically be non-toxic and readily biodegradable. These types of cleaning suspensions will also easily meet the current Boeing, Airbus, and Mcdonnell Douglas airframe cleaning certifications such as D6-17487, Rev. R.
In all events, these cleaning products should be used before surface sealants are applied for long-term protection against ambient corrosion.
In application, these surfactant and co-solvent solutions are commonly available from the leading manufacturing suppliers and the products are both long-lasting and temperature stable. The use of medium strength synthetic or natural bristle brushes or cleaning cloths should be all that is necessary for soil removal without harmful abrasives (green pads) or scowering rouges. If they meet the current USDA biopreferred certification standard, they will likely contain primarily plant (or animal) sourced chemical constituents and their MSDS disclosure will not contain harsh sodium or detergent chemicals. The cleaning operations manager will want to screen their chemical acquisition program to avoid such materials in order to protect the finish and structural integrity of the airframe. In all events you will want to know that the products are compliant to the current specified manufacturer’s cleaning test protocol and is legally sewerable in your local municipal waste water treatment system without pacivisation or additional chemical treatment apart from routine oil water and solids filtration. A list of current USDA Biopreferred aviation cleaning chemicals is available at: https://www.biopreferred.gov/BioPreferred/faces/catalog/Catalog.xhtml.
Kim C. Kristoff is the president of GEMTEK, Phoenix, AZ, a leading biobased chemical manufacturer specializing in seed oil derived surfactants, solvents, lubricants, and specialty chemicals for industry and transportation applications including aviation. Kristoff has been a biobased industry consultant, member of several state and federal biobased advisory committees, and a contributing author to technical journals in North America. For more information visit www.gemtek.com.
