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AUG 2016

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31 CompositesWorld.com NEWS that toughness and fatigue performance of a glass or carbon fiber composite could be significantly improved by adding "small levels of an aqueous emulsion of an epoxy resin containing nanosilica to the sizing," Sprenger says. A 30-40% increase in fatigue performance was achieved in tests with continuous glass fibers and continuous carbon fibers in unidirectional fiber-reinforced epoxy. Sprenger points out that this would be a significant increase in performance of rotor blades for wind energy conversion, for example (see Fig. 5, p. 28). (For more on carbon fiber sizing, see Learn More.) Called Nanopox, the aqueous emulsion as a sizing ingredient has been tested with epoxy resin matrices, and Sprenger and his team are researching its use with unsaturated polyester and vinyl ester resin matrices. Sprenger considers Nanopox a real break- through for sizing manufacturers, at a small additional cost. Further, it is considered viable with any thermoset but, Sprenger says, perhaps not thermoplastic resins. e same nanosilica particles also can be used to modify the matrix resin, which could achieve even bigger improvements in parts such as automotive composite leaf springs. But he adds the caveat that "modifying the matrix comes with a price, and it might correspondingly affect speed of the manufacturing process." Sprenger emphasizes that adding it to the fiber sizing is a very cost- efficient way to improve composite performance in cost-critical applications such as wind turbine rotor blades or mass-produced automotive parts. Smart Fiber Sizing Right sizing for success For many years, as composites fought for a foothold in automo- tive, aircraft, construction, piping and other markets that were quite comfortable at the time with concrete, wood or metal, sizing played a key if often unheralded role in the successful substitution of fiber-reinforced polymers for legacy materials. But even in the most successful cases, designers, manufacturers and end-users want far more than a substitute. ey want fiber-reinforced polymers with ever greater strength, toughness and endurance than legacy mate- rials. And they want faster productivity. All at a lower cost. Can fiber manufacturers, sizing chemists and formulators really achieve the upgrades in performance and productivity that their customers demand? ey are well aware of the need, and they are certainly suiting up for the challenge. Sizing and fiber manufacturers are coordinating with their customers to hear what they want. And they are taking that information back to their scientists, who are focusing their chemistry on fine-tuning sizing formulations to make specialization a reality, developing the specifically tailored, custom- ized and optimized sizings to satisfy industry demands. Donna Dawson is CW's (previously) retired senior writer emertius, now residing and writing in Lindsay, CA, US, in the foothills of the Sierras. donna@compositesworld.com

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