The world of composites covers a range of materials and applications. Flexible composites have long been manufactured to perform specific functions in generally demanding environments. Their tremendous strength-to-weight ratio and design flexibility make them ideal in structural components for the transportation industry. High strength, lightweight premium composite materials, such as carbon fiber and epoxies, are being used for aerospace applications and in high performance sporting goods.
Although the possible material combinations in composites are practically unlimited, the constituent forms that make up the composites are more restricted and consist of fibers, particles, laminates or layers, flakes, fillers and matrixes. In general terms, flexible composites can be constructed of any combination of two or more materials—metallic, organic or inorganic. When combined, these substances offer properties that are not available from any of the ingredients alone.
Composites solve problems, raise performance levels and enable the development of many new products and applications. Because of these advantages, they are being used in a growing number of industries.
Manufacturers, designers and engineers recognize the ability of flexible composite materials to produce high quality, durable, cost-effective products. Saint-Gobain Performance Plastics in Taunton, Mass., manufactures coated and laminated composite fabrics for many applications. Among them are structural applications that require high strength, longevity and other properties best met with the use of PTFE (Polytetrafluoroethylene) coated and/or laminated composites.
Mike Lussier, sales and market manager with Saint-Gobain, says one segment of the company’s business that embraces flexible composites is air-supported radomes used to protect large advanced communications arrays. Typical radomes are structural, weatherproof enclosures that protect microwave antenna. They are constructed in a myriad of shapes and sizes, depending on the specific equipment being housed.
“The most innovative composite material introduced over the last several years is RAYDEL® Q65,” Lussier says. “This quadriaxially reinforced PTFE/ Kevlar® composite fabric provides 200 mph wind speed capability for air-supported fabric structures used in the radome industry.”
RAYDEL is a microwave transmissive composite designed specifically for use in RF applications. The Q Series is made of Kevlar and PTFE. Its quadriaxial, multi-ply, laminated construction provides superior dimensional stability, even in the most extreme environments. The composite offers durable hydrophobicity, enhanced flexural characteristics, high tear strength and excellent high temperature and fire resistance.
As Lussier explains, three-ply laminate fabric with orthogonal (0°, 90°) and two plies of skewed (0°, -45° and 0°, +45°) substrate provide a high shear modulus composite. This fabric construction reduces the deflection of the structures under wind loads by 80 percent.
Another key segment for Saint-Gobain that involves flexible composites is tensioned fabric structures, or the architectural market. “Our SHEERFILL® brand is over 40 years old; the first installation at the University of La Verne in California is over 41 years old and still features the original fabric,” Lussier says.
Several years ago, Saint-Gobain’s EverClean® Photocatalytic Topcoat using photoactive TiO2 in the outer layer was introduced when AT&T Stadium, home of the Dallas Cowboys, was built. “The EverClean topcoat provides enhanced self-cleaning, as the photoactive TiO2 actively breaks down organic matter and other contaminants, making them easier to rinse off when it rains.” The photocatalytic activity also aids in the reduction of NOx pollution in the air. With a cleaner and whiter surface, it maintains high solar reflectivity and helps reduce demand for cooling in the space below.
“This past year, several of the stadiums used for the FIFA World Cup™ in Brazil were covered with SHEERFILL Architectural Membrane with EverClean Photocatalytic Topcoat, including Mineirão Stadium in Belo Horizonte, which achieved a LEED Platinum rating,” Lussier says.
Warwick Mills Inc., New Ipswich, N.H., also offers a range of protective flexible composites that are engineered to combine their woven fabrics of high performance synthetic fibers with their protective coatings and impermeable films, which may also incorporate active chemistries or expandable foams.
“This results in composites that are high strength, lightweight, flexible and durable,” says Leslie Richardson, technical sales representative at Warwick Mills. “These protective composites offer puncture resistance from spikes and bullets to a multitude of other threats.” The company’s protective composites are used in inflatable, military, law enforcement, industrial and medical applications, with crossover use among many of them.
Warwick Mills’ inflatable composites are used for emergency structures for disasters, military tents and other inflatable protective structures. In addition to being high strength, flexible and durable, they must be packable and deployable and have an impermeable barrier film to protect from chemicals.
Many components are used within the manufacturing process of flexible composites. While some companies manufacture the entire composite product, others rely on industry players to provide the individual constituents that comprise the end product.
Texonic, based in St-Jean-sur-Richelieu, Quebec, Canada, is a producer of technical fabrics used in medium- to high-end composite products as well as personal and ballistic protection. They do not manufacture composite material, but as a raw material manufacturer, Texonic manufactures and supplies a portion of the ultimate composite material, which is the reinforcement. The other portion (more or less 50 percent), which Texonic does not supply, is a resin.
From conventional to unique 3-D architectures, Texonic has been recognized for its product MartinFuse™, a noncrimp fabric specially designed to be used in closed molding processes without a flow media and providing higher mechanical properties.
“Currently, composite parts made out of carbon fiber reinforcement, glass fiber and hybrids are quite common and growing fast,” says Nicolas Juillard, president and CEO of Texonic. “Hybrids (namely blends of different fibers) are being understood and used more and more.”
Most of what Texonic produces in the area of composites is based on Fiberglass® carbon, aramid and basalt fiber and is being used in applications that are rather rigid.
Juillard adds that special weaves of composites for better performances and processing in architectural applications are making their way very fast because they bring more value, better performance and are easier to process. Texonic’s products are available in North America, Europe and Southeast Asia through their distributors’ partners.
Connecting with performance
Structural and geometrical characteristics of the constituents within flexible composites make important contributions to the composite’s properties. The shape and size of the individual constituents, their structural arrangement and distribution, and the relative amount of each are important factors contributing to the overall performance of the composite. These are what give composite materials much of their versatility.
The technology that goes into the material that Warwick produces starts with the selection of the fiber for the woven based on specific properties and the weave pattern. “Each component of a composite must contribute to the overall system performance and also be durable for years of service in the environment it will be used in,” Richardson says.
Warwick Mills’ protective flexible composites made for body armor applications protect from spikes, knives and bullets. “Fiber selection and weave type are critical to the performance to not only stop specific threats but, with ballistic applications, must protect from the energy of back-face signature,” Richardson says.
For Saint-Gobain, the technology that goes into the material and its performance for its intended use are closely evaluated. “Critical to the material performance is achieving the right balance of strength, flexibility, interlayer adhesion and overall coating composition,” Lussier says. “Because the components, and their design, are so important to the performance of the composite, we perform all design, weaving, coating and lamination ourselves, under one roof.”
Juillard stresses that today’s flexible composite technology needs to produce composites that are lightweight, more durable, easier to process, energy saving, while incorporating recycled components. “The market is looking for faster cycles, price competitiveness, better performance and automated processing,” Juillard says.
What the future holds
Where is the flexible composite market headed? Are there specific materials that will be more commonly used? Juillard is seeing strong growth of flexible composites within the civil engineering arena.
“This segment is growing very fast and can represent huge quantities in the sector of composites,” Juillard says. “Transportation is growing fast as well, including aerospace, trains, buses and trucks. But the biggest growing sector for flexible composites is—and will be—automotive, while marine, sports and leisure remain strong traditional sectors.”
For the structural markets, Lussier says the desire is always for stronger and lighter flexible composite materials. For Saint-Gobain’s architectural markets, Lussier sees a broader use of different materials on the same project. “Where we might supply one product for the roof of a sports stadium, we now may supply two or three different products, with different characteristics to meet specific needs,” Lussier says.
In addition to the above trends, Saint-Gobain is seeing the market looking for new materials—higher strength for sure, but perhaps different colors or variations in light transmission for their membranes. “Mostly, we see the need to enhance the sustainability of our products,” Lussier says. “Helping building owners achieve LEED Platinum is rewarding, and very much a big step in that direction. We expect to see continued research and development in the area of energy and sustainability that will yield even more benefits in the future.”
Richardson of Warwick Mills also believes there will be an increasing demand for higher strength, lighter and more durable materials to replace heavier and more rigid materials, as energy demands and sustainability become increasingly important. “The market is seeking lighter, stronger, more flexible and durable composites,” Richardson says. “The next generation flexible composites will include more active chemistries, ‘smart’ technologies and nanomaterials.”