Application of superomniphobic finishes on fabrics for chemical protection

Military personnel on patrol and industrial staff are likely to face various hazards from chemicals that can either kill them outright or cause them serious damage. Chemical substances known as chemical warfare agents (CWA) have been used in war zones since the end of the First World War. These chemical warfare agents are particularly dangerous to human life. They cause skin disease, disability and death of soldiers. These chemicals are also widely used for pharmaceutical purposes, for preparation in industrial plants, in laboratories, in nuclear plants and in food items. However, these chemicals cause toxic effects not only to human life but also to the environment as they have polluted widely including buildings, filtration systems, vehicles and equipment. The chemicals spread easily in the environment and remain for a long time. Finally, CWA was banned from use in 1996, but some of them are still being used in the warzone. Protection of people from exposure to hazardous chemicals, such as chemical warfare agents and toxic or corrosive chemicals is essential in today’s battlefield and industries.

Chemical, biological, radiation and nuclear (CBRN) suits are designed for emergency circumstances and are likely to cause a thermal burden when worn over prolonged periods. Special protective clothing is available for use to protect from these chemicals but it is very heavy in weight, uncomfortable and expensive. Exploration of the superomniphobic surface for versatile protection against water, oil, liquids and chemicals has been the key to the development of protective clothing for chemical protection. However, simple, cost-effective methods to develop functional surface on textiles with durability and without compromising comfort much are still of great challenge.

This research aims at developing protective fabrics with a functional coating that is capable of preventing the penetration of water, liquids, oil and certain chemical warfare agents without compromising the fabric weight and comfort properties. The intention of this research is not to develop a replacement for CBRN suits but to develop low-level threat fabrics that can either be used as combat uniforms and selective parts of the uniform or be applied in industrial protection. A widely used coating method of padding-knife coating-padding-curing was employed in this research to perform functional coating on fabrics towards high-performance protective clothing. Polymeric coating of polyurethane or silicone rubber membrane in combination with repellents including polydimethylsiloxane (PDMS), trimethylated silica (TMS) and fluoro-polymers was developed to form superomniphobic surface on cotton and

polycotton fabrics, and a comparison with coated fabrics with plasma treated fabrics and industrial fabrics was performed to justify the developed technology from this research. The coated fabrics were characterised by thickness, morphology and chemical components to understand the structure and mechanism of the coating. Measurements of protection against water, oil, aqueous liquids and chemicals and hydrostatic pressure were performed to test the versatile protection of the coated fabrics. Besides, the air permeability, water vapour permeability, thermal resistance, handle, stiffness and moisture management properties were tested to study of the comfort of the coated fabrics.

It was found that the combination of polyurethane membrane and PDMS-TMS acted as repellents to give better results in terms of protection against water, liquids, oil, chemical, hydrostatic pressure on the fabric surface. The developed surface presented hydrophobicity with a water contact angle of around 150o, and the droplets of water, oil, aqueous liquids and chemicals were repelled for long periods. A cross-linked network was formed between the membrane and the PDMS-TMS, resulted in the excellent durability of the coating against different cycles of laundering and crocking together with rubbing. The comfort of the coated fabrics was compromised due to the blocking of the porous structure of the fabrics, but the selection of the coated membrane such as the thermoplastic polyurethane would improve the comfort to some extent. The coated fabrics were comparable to the plasma treated fabrics for defence and industrial fabrics in terms of protection and the coated fabrics can withstand much higher hydrostatic pressure than the other two. The advent of high-performance coating was suitable for long time protection for chemical as well as comfortable properties for the protective clothing for military and industry.