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Biting the bullet: new nonwoven finding application in ballistic protection.

Biting The Bullet: New Nonwoven Finding Application In Ballistic Protection

Although it may not have known it at the time, the ballistic protection business took a significant step forward in 1985 when Allied-Signal introduced "Spectra," a high strength, extended chain polyethylene fiber that is, ounce for ounce, 10 times stronger than steel. Its unique properties suggested that Spectra could become a strong competitor within a number of markets for high strength, lightweight applications, including ropes, cordage, sails, cut-resistant gloves and, perhaps most significantly, bullet resistant armor.

Powerful automatic and semi-automatic weapons have been changing the nature of "life on the street" for police, so to bring Spectra to the armor market Allied-Signal's product development team targeted civilian law enforcement agencies, traditionally a receptive area for new technologies. The timing was right because new federal standards were being drafted by The National Institute of Justice (NIJ), which was looking at performance characteristics that stretched the limits of any woven fabric.

"We had the strongest fiber in the world, but the weaving process itself was a problem," Steven Young, manager of business development at Allied-Signal's High Performance Fibers Technical Center, Petersburg, VA, recently told Nonwovens Industry. "The open, interlaced construction of wovens in certain conditions allow projectiles to move the fibers aside during the ballistic event.

"Woven fabrics could (and still do) meet the new NIJ requirements being considered, but we knew a nonwoven material could eliminate much of the bulk and perhaps even improve the impact resistance," he said. "This, combined with the fact that we were new to the market, took us down the path that led to the development of |Spectra Shield.'"

Enter Spectra Shield

Three years later, in February, 1988, the company introduced Spectra Shield, described as "both a material and a process." Spectra Shield - the material - is a thin, flexible unidirectional (0-90 degree) composite structure. The use of a low modulus, low specific gravity matrix in combination with high strength fibers produces a soft and flexible nonwoven composite. The result is incredibly lightweight impact performance. The fiber's high modulus and low density produces a high strain-wave velocity (12,300 m/sec) upon ballistic impact, roughly twice that of aramid fibers. The net gain is extremely rapid dissipation of energy from the point of ballistic impact.

Spectra Shield's cross ply composite structure (Figure 1) allows the projectile to engage many more fibers at ballistic impact because of the wide dispersion of filaments in the untwisted yarn. The unidirectional processing maximizes both strength retention and uniformity in the final product design.

"Probably most important of all is the tremendous results we're getting in the field," Mr. Young said. "The toughened structure composed of unidirectional fibers in a flexible resin produces a composite that can withstand angle shots and multiple bullet impacts. It's better than anything we've seen previously."

The Spectra Shield product has also been able to minimize the effects of what is referred to as blunt trauma. Even though body armor stops a projectile, the wearer still has to deal with blunt trauma, the energy transition to the body upon impact. The high energy produced is similar to a blow from a sledgehammer.

Among its other advantages: Spectra Shield has moisture and chemical resistance unmatched by competitive fibers. It is chemically resistant against a variety of strong acids, bases and cleaning agents, such as bleach. And, with a .97 g/cc specific gravity, Spectra Shield floats.

Spectra Shield in combination with other materials has demonstrated exceptional resistance to heat and flame in vest applications. Measured against criteria from the University of San Francisco, the polyethylene molecule has demonstrated a reluctance to give off flammable gases needed for combustion. Laboratory tests have shown the Spectra Shield vest provides protection far beyond temperatures the human body can withstand.

A Desert Storm Veteran

Soft body armor or bullet resistant vests (nothing is 100% bullet proof) are only part of the story. The same technology used for nonwoven sheets can be used for rigid armor. Flexible sheets of Spectra Shield can be stacked and molded into rigid panels for hard armor application. Because it is already pre-pregged, the rigid panels can be fabricated at less cost than competitive fabrics. The end product is also much lighter.

"Hard armor is used for police barricades and SWAT team ballistic shields, but the real potential has been in the military," Mr. Young said. Spectra Shield is being used as protective panels on the C-130 aircraft, helicopters and protective radar domes. "Rigid Spectra Shield along with our vests were in action throughout Desert Storm," he added.

As a commercial product, Spectra Shield material has been an "enormous" success. The NIJ formally announced its newest standard for bullet resistant vest in 1987. The first Spectra Shield vest was qualified by the NIJ in April, 1988 and introduced commercially that summer. Since then, Allied has expanded its production facilities three times and a fourth was scheduled to go on-line last month."

The Manufacturing Process

Central to the success of Spectra Shield was the development of a suitable manufacturing process. It took two years to develop Spectra Shield as a commercial product, but what eventually emerged was a new approach to making nonwovens that can eventually be used with other synthetic fibers (Figure 2).

"It was a real push," recalled James Dunbar, director-Spectra High Performance Fibers. "The strategy was to move quickly into the commercial market in order to establish a competitive position against other technologies."

"To develop the unidirectional/cross ply processing equipment we needed to manufacture the material. We enlisted an eight member team from Tech Center, Allied-Signal's R&D labs (which had developed the original Spectra fiber) and then drew in people from four other companies," Mr. Dunbar added. "We knew where we wanted to go. We had a good idea of how we'd get there. But we needed to find the people and organizations willing to invest the time and effort it would take. Our main objective was to translate research into commercial volume production of Spectra Shield."

Repeated experimentation with various resins finally resulted in the creation of the matrix formulation for Spectra Shield. Shell Chemical's "Kraton" resin was found to promote the necessary adhesion of the Spectra fiber.

The Allied-Signal corporate research team, based in Morristown, NJ, offered the conceptual ideas on how the fiber orientation should be manipulated. Cape Composites, San Diego, CA, a group of individuals with 200 years of combined experience in aerospace composites, also joined the development team.

"They brought knowledge of unidirectional materials and equipment to the project," Mr. Young said. At this point the unidirectional manipulation of the fiber had to go beyond methods used in aerospace technology. The idea was, in effect, to pack as much of the Spectra fiber material as possible into the smallest space, "like choosing cappellini instead of lasagna."

Allied had wanted to use very thin fibers, but the Spectra laminates were just too thin to process on conventional equipment. Early on in the process the expanded development group worked with a 12 inch unidirectional prepreg machine (which was originally used to make 12 inch wide carbon fiber tapes) and began production of Spectra Shield panels for testing. At the same time, commercial scale manufacturing equipment was in development.

Adhesion and high speed cutting requirements mandated new technology. Fiber bundles were spread and coated with the highly flexible Kraton resin to hold fibers in place during manufacturing. The cross ply process was utilized to seal the layers into place. Multiple trials were completed to achieve selection of the proper fiber/resin volume fractions for ballistic response.

Throughout the development, municipal government and federal agencies conducted independent ballistic tests using experimental batches of Spectra Shield. The responses from these tests were recycled into each successive trial. Their feedback provided end user verification on performance. All through this stage, results from testing and customer response were put back into research, bringing the development process full circle.

"We were successful," Mr. Young said. "A flexible nonwoven composite was developed that could meet and in some circumstances even exceed the new NIJ standards. We knew we had a winner." Using the test equipment, Allied made its first commercial sales in 1988. Production was limited to low volume custom orders for body armor manufacturers who wanted state-of-the-art products for high profile customers. In October, 1989, large scale commercial scale manufacturing began.

Patents were filed late in 1990 for the unidirectional cross ply processing machinery. Commercial production and sales volumes have reportedly tripled each year since 1988. This is projected to continue through 1991.

"Future applications for the Spectra Shield material are exciting," Kevin McCarter, market development engineer, told Nonwovens Industry. "Currently we are developing technology to lower the weight and increase the performance of this nonwoven material. There are other potential applications for the processing technology we are just beginning to explore. Through modification of resin and fiber properties, applications can be used to manufacture a multiplicity of fabrics."

PHOTO : Figure 1: Comparison of woven fabrics and Spectra Shield

PHOTO : Figure 2: Conceptual view of Spectra Shield manufacturing
COPYRIGHT 1991 Rodman Publications, Inc.
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Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Technical Nonwovens; Allied-Signal Inc.'s Spectra, nonwoven fabric
Publication:Nonwovens Industry
Date:Apr 1, 1991
Previous Article:Opportunities for nonwoven fabrics in the industrial protective apparel market.
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