Fabrics go multifunctional

Textiles have evolved from being commodity materials to providing an array of benefits, including additional comfort and protection, improved hygiene and support for health care. The innate nature of fibers can provide certain special characteristics—cotton adds breathability and a smooth hand, and wool offers thermal comfort, for example.

But due to the growing need for multiple functionalities and sophisticated applications, a combination of approaches is needed in meeting expectations for today’s high-performance functional fabrics. These involve the use of different combinations of fibers (natural and synthetic) as well as different mechanical and chemical processing approaches to develop textiles with enhanced characteristics and additional applications.

Functionality, in a simple sense, means having characteristics that are different from basic properties, such as those required in commodity textiles. The basic characteristics of commodity textiles are generally qualities such as mechanical strength, durability, drapability and so forth. But functional fabrics should have properties and applications beyond these, such as flame resistance, water repellency, stain repellency, ballistic protection and medical or hygiene benefits.

Functionality can be provided to fabrics using many different approaches, but the major criterion should be that while imparting the additional capabilities, the basic nature of the textile should not be affected. In addition, depending on the nature of the application and whether it’s for consumer or industrial use, one must also be aware of cost.

Functional fabrics have to be designed based on need, application and market adoptability; however, in the case of common consumer applications, there needs to be a balance between added characteristics and cost.

Phase I

Three phases in the development of functional fabrics can be identified. First, incremental approaches have been successful utilizing different blends of fibers and conventional textile manufacturing techniques to develop fabrics for defense and industrial applications. The advent of high-performance fibers, such as Kevlar® and Nomex® made by DuPont™ and FR-regenerated cellulosics, has helped with improving military combat uniforms that are a blend of nylon and cotton (NYCO) fibers.

These high-performance fibers can be blended intimately or used to develop core/sheath yarns and blended fabrics on highly productive weaving machines such as rapier, air-jet and water-jet looms. Cotton spinning systems were fine-tuned to develop high-performance blended yarns with reduced hairiness that can be used to develop blended fabrics for military uniforms using a compact spinning concept.

Such processing procedures can be conveniently grouped as Phase I development: procedures that can be easily followed by the conventional textile sector by using diversification approaches.

The cotton industry has practiced this concept and done well in transforming cotton from a commodity fiber to a high-performance fiber. Cary, N.C.-based Cotton Inc. has developed TransDRY® moisture management technology that makes cotton to wick away moisture quickly and STORM COTTON™, which provides water repellency to cotton without compromising its innate comfort. These technologies clearly adhere to the definition of functional fabrics.

Phase II

Currently, Phase II of functional textile development is getting rather focused attention. Relatively modern manufacturing methods—such as a variety of improved nonwoven technologies, nanofiber and nano-coating methods, soft and hard composite production techniques and improved finishing chemistries—are aiding commercially viable technologies. An early commercial success in this regard is nano technology-based fluid-repellent clothing from Nanotex®.

In a similar vein, filtration companies such as Minneapolis, Minn.-based Donaldson Co. Inc. have been using nanofiber-based substrates to improve intended applications. In this case, adding nanofiber substrates to base filter substrates, like wet-laid cellulosics, increases its filtration capability without affecting pressure drop very much. This, too, meets the basic definition of functionality.

In addition to the filtration sector, the defense clothing sector has also been an early adopter of nanotechnologies to enhance protection and filtration capabilities. The U.S. Army Natick Research Center has done significant work with nanofiber substrates as a way to reduce the use of activated carbon for lighter weight chemical countermeasure fabrics and, at the same time, enhance the adsorption capability of chemical-biological protective clothing.

The U.S. Department of Defense (DoD) has made enormous investments in research on nanoparticles, such as nano-metaloxide particles and nanofibers. Such research investments have resulted in functional textiles that not only trap toxic chemical warfare agents, but also catalytically degrade those chemical agents. Functional fabrics that have multiple capabilities are commonly known as self-cleaning textiles. Early research pioneered with the support of the DoD has resulted in spin-off technologies, such as UV-protective clothing and superhydrophobic textiles. Many particle-embedded textiles have fluid repellency and flame retardancy while maintaining breathability, textile feel and drapability.

Phase III

Emerging functional textiles belong in Phase III development. This phase is slowly growing and considers those textile technologies and products that are currently in pilot manufacturing and/or at the laboratory R & D stage. Predominantly, this development phase involves importing technologies and principles from basic scientific disciplines and allied technological fields, such as bioengineering, mechanical engineering and chemical engineering.

One good example is the use of atmospheric plasma to impart hydrophilicity and hydrophobicity to cotton textiles. Plasma is high-energy physics, and plasma treatment changes the surface qualities of materials without affecting the bulk characteristics. Food packaging and semiconductor wafer industries are effectively using plasma-processing techniques.

This technique has now moved away from a vacuum-based batch process to high-speed atmospheric plasma, and can be easily adapted to the textile industry. Hartland, Wis.-based ITW Pillar Technologies is active in this field and has production machinery that will benefit the textiles sector.

North Carolina State University (NCSU) was one of the early users of plasma technologies for developing functional materials. The Nonwovens and Advanced Materials Laboratory at Lubbock-based Texas Tech University is also exploiting atmospheric plasma for developing functional cotton materials for industrial applications. Superhydrophobic chemistries are being explored to develop chemical- and water-repellent textiles for medical and defense applications.

There are opportunities to borrow nascent and emerging technologies, such as superfluid extraction and laser processing methods, to develop nanopore-based high-performance textiles. Coated textiles, after being treated with superfluid extraction, can result in nanopores, which provides and/or preserves the comfort of textiles. Mumbai-based The Synthetic & Art Silk Mills’ Research Association (SASMIRA) is working on super-critical fluid techniques to impart waterless finishes to textiles.

The next phase of functional textiles development should focus on cost-effective and highly productive methods in order to gain consumer acceptance. Sustainable methods, biomimetic approaches and natural products-based chemistries have to be seriously pursued, so the textile industry can develop eco-friendly products that are also cost-effective. A concerted effort among research organizations and the industry is needed and should include a careful look at new developments in basic scientific fields that can be adopted by the textile industry.

Seshadri Ramkumar, Ph.D., is a professor in the Nonwovens & Advanced Materials Laboratory, Texas Tech University.