Warfighters benefit from specially functionalized textiles that will protect from hazardous chemicals without sacrificing comfort or durability that restrict human factors or performance. Previously, superomniphobic repellent coatings used polymers derived from per- polyfluoroalkyl substances (PFAS) chemistry. The performance requirements may still be met by using other physiochemical functionalization strategies for textile treatments.

This project will leverage the team’s experience and patented processes for chemically functionalizing and coating textiles with selected nanomaterials. The resulting, controlled surface topography can yield omniphobic characteristics that suspend liquid droplets above the otherwise absorbent fibers and fabrics. The aqueous-based functionalization chemistry and PFAS-free reagents meet the environmentally-friendly objectives of the statement of need (SON). The resulting textiles will be evaluated at the team’s advanced test facilities to determine whether performance objectives of the SON are met by the approach.

Textiles will be treated using aqueous-based siloxane chemistry to deposit a functionalized, porous, conformal interpenetrating siloxane network around the fibrils and fibers of the target textile. Nanomaterials will be entrained and chemically bound in and to the network to yield an engineered, structured surface that will repel liquids [1] [2]. The microwave-catalyzed silane condensation yields a conformal coating on each individual fibril of the fabric. Previous work showed the approach treats woven, non-woven, knit, cotton, wool, rayon, polyester, polyamide, and polyaramid– fibers and fabrics. The siloxane coating is deposited as an open porous network that encapsulates the particles on the surface without obscuring the surface roughness. The microwave promoted siloxane crosslinking creates a conformal coating that encases each fiber and fibril versus a non-uniform coating that is established using traditional heat driven siloxane condensation techniques (Figure 1). Two classes of nanomaterials will be used to functionalize in and to the siloxane network layer, polyhedral oligomeric silsesquioxane (POSS) and chitosan. The POSS materials are a cage-structured, organic-inorganic hybrid nanoparticle wherein the structure provides a versatile backbone that can be modified with additional functional groups. Chitosan has an inherent low surface energy and is amenable to chemical functionalization as well as structural changes that can improve repellant characteristics. A series of laboratory-scale syntheses and textile coatings will be completed, and the material screened for needed performance characteristics. Through an iterative refinement and down-selection process, the best candidate combinations will be selected. Standard-scale fabric swatches will be coated and provided to the U.S. Army Combat Capabilities Development Command test facility for evaluation in formal tests (Military Specification, American Association of Textile Chemists and Colorists, ASTMD).

Figure 1: SEM micrographs of coated omniphobic fibers (left) plasma-polymerized PFAC8- treated, (center) microwave- assisted FS-treated, and (right) wet processing [images from 1]

High-performance consumer fabrics are typically water-repellent to provide a wearer additional protection from elements and greater comfort. Specialty materials for gear such as military battle dress uniforms aim for additional performance factors (e.g., protection from chemical agents, flame retardancy, oil- and fuel-repellency, and compatibility with other operational materiel and requirements). Previous generations of PFAS based coatings provided the desired characteristics for the applications, but this PFAS-free option should achieve similar performance. The described topic provides an environmentally conscious alternative. Chitosan is a waste product of the shellfish industry. Its sustainable nature, along with its non-toxic, biocompatible, biodegradable, and antimicrobial aspects provide attractive features for a potential material to meet the SON specified objectives.

References:

[1] R. Saraf, H. J. Lee, S. Michielson, J. Owens , C. Willis, C. Stone and E. Wilusz, "Comparison of three methods for generatingsuperhydrophobic, superoleophobic nylon nonwoven surfaces," Journal of Materials Science, vol. 46, pp. 5751-5760, 2011.

[2] A. B. Cassie and S. Baxter, "Wettability of Porous Surfaces," Transactions of the Faraday Society, vol. 40, pp. 546-551, 1944.