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Fabulous Fabrics

August 12, 2010

Microscopic view of a nonwoven textile

By Jay Mayfield

If you’ve never thought much about nonwoven textiles before, don’t be surprised; you’re not alone. Very few of us realize the importance of these materials in our daily lives. In fact, every breath each of us takes indoors is likely filtered through some kind of nonwoven fabric.

In recent decades, nonwoven textiles have found their way into a myriad of applications, from air and water filters to clothing and medical supplies; and with each passing year, Gajanan Bhat, a faculty member of UT Knoxville for the past 20 years, has been helping advance the technology that lies behind their creation.

Bhat, a professor of materials science and engineering, oversees the UT Nonwovens Research Laboratory, a research and development facility on campus that serves as a proving ground for new nonwoven technologies. By working with partners in industry, Bhat and his team have helped spur new waves of innovation, making these materials more useful and effective.

Blowing and Going

There are two major avenues to the creation of nanofiber nonwovens: electrospinning and melt blowing. Bhat’s team focuses on melt blowing, which requires fewer hazardous chemicals and less energy overall.

The fabric begins as small plastic pellets, roughly the texture of sand, but more slippery to the touch. Those pellets are melted at a high temperature and then blown through a specially manufactured die having hundreds of tiny holes. When the plastic is forced through the holes, it becomes a series of tiny fibers, which solidify as they move through the air.

Meltblown fabrics are created with a highly specialized manufacturing process  that is continually refined

Meltblown fabrics are created with a highly specialized manufacturing process that is continually refined

Once they pass through the die, the fibers land on a fast-moving conveyor belt, layering on top of one another and creating a fabric. The key to making the process effective is the ability to control the width of the fibers and the size of the spaces among the fibers.

Recently, the diameter of the fibers used in the process has shrunk dramatically, from 2-5 to 0.2-0.4 microns. (By way of comparison, the average diameter of a human hair is 75 microns.) Just looking at the fabrics, it’s hard to tell the difference between the larger and smaller fibers. The difference becomes clear in the feel.

The fabrics feel cottony between the fingers, but as the fibers reduce in size, the material becomes noticeably lighter and airier, something along the consistency of cotton candy, if a little less granular. It’s that airy consistency that makes the fabric such a good filter.

Filtration Fundamentals

“We know how large a bacterium or virus is,” says Bhat, “so we can engineer a fabric designed to filter a specific type of organism or pollutant based on how large the average pore is between fibers.”

Indeed, it’s what is not in the fabrics that makes them so useful, and why manufacturers line up to spend time working with Bhat and his team to improve the fabrics they create. By controlling the size of spaces among the fibers, the fabrics’ properties as filters and barriers can be tailored to very specific functions.

Gajanan Bhat tests the filtering properties of a new nonwoven textile

Gajanan Bhat tests the filtering properties of a new nonwoven textile

In medical applications, you’ll find the nonwoven fabrics in expected places, such as blood filters used in transfusions and dialysis. You’ll also find them, however, in the garments worn by surgical team members. Since air passes through them, nonwoven fabrics for attire in operating rooms are more comfortable and functionally useful than impenetrable plastic coveralls.

The companies that work with Bhat, however, go far beyond the medical field in how they put nonwoven fabrics to use. The materials are likely to be in your car’s oil filter, your home’s air filter, and, of course, the coffee machine. Nonwoven fabrics are also finding applications in personal protection clothing and alternative energy storage systems. In fact, it’s that wide variety of applications that brings companies to UT Knoxville to work with Bhat to refine their processes.

Scaling Up

One of Bhat’s major goals is finding ways to increase the production speed and efficiency for melt-blown nanofiber nonwoven materials, helping new developments scale up from the laboratory to the production line.

In recent months, Bhat and his team have added new capabilities to create fibers at the nanoscale level, a development that has already attracted the interest of numerous industrial partners.

It’s those partners who drive Bhat’s research. As an engineer, Bhat is seeking applied solutions to current issues, and working relationships with companies that use nonwoven materials ensures that his work remains current and relevant.

The UT Knoxville nanofiber manufacturing facility—the only one of its kind in the world—is a small-scale version of what might be seen in a modern factory, and it allows researchers to effectively model the process to prepare it for commercial production.

“We offer a service to the textile industry through our research,” says Bhat. “We have a facility for testing new ways of improving processes, and we help advance fabric innovations.  It’s a two-way street that puts UT Knoxville at the forefront of research and innovation.”