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AUG 2016

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27 CompositesWorld.com NEWS Smart Fiber Sizing and is moving at speeds approaching 100 mph [160 kph]," explains James C. Watson, associate director, fiberglass science and tech- nology, for PPG Industries, "and we're doing it 24 hours a day, 7 days a week, 365 days a year. We never stop." "It's a little bit of a challenge," he quips, pointing out that after it is applied, the sizing also must remain on the fiber and perform its functions throughout all subsequent phases of the glass manu- facturing process, the customer's part manufacturing process and the finished part's lifecycle. He adds that in terms of the total composite, sizing can make up as little as 0.2-0.3% of the final product, yet it has an "amazing impact on productivity and part performance." What is sizing? Sizing describes, respectively, the coating itself and the coating process. Whittington's Dictionary of Plastics (ird ed., CRC Press, 1993) defines the latter as "applying a material to a surface to fill pores to smooth it and reduce absorption of a subsequently applied adhesive or coating; or to otherwise modify the surface." Today, sizing chemists (see Fig. 2, above) primarily aim first to protect the fiber by reducing friction during processing and to prevent fiber breakage during part manufacturing. Second, they provide a compatible interface between the fiber and the matrix resin in the composite part. Specifically, sizing enables transfer of stress across the fiber/resin interface. "e sizing controls the interface between the glass and the resin and, therefore, optimization of the sizing chemistry gives you the best interfacial performance between the glass and the resin. Good interfacial performance leads to improved mechanical performance and to better processability as well," explains Christopher Skinner, director of products for the strategic marketing group at glass fiber manufacturer Owens Corning (OC, Toledo, OH, US). Glass fiber sizing primarily comprises a film former, typically chemically similar to the intended matrix resin, and a coupling agent, almost always an organic silane base in a complex mixture of chemistries that gives the inorganic glass fiber the ability to bond well with the organic resin matrix. e silane coupling agent acts as a primer that enables the film former to attach to the fiber and also adhere to the polymer matrix. Watson points out that silanes are the glass fiber sizings chemists' workhorses. "But as we move forward to higher temperature, higher durability, longer life term, better fatigue performance and other improved performance, we must ask ourselves if there are better organic silane molecules that can be used to bring those properties to bear — even though they are invariably more expensive." Differentiation + optimization Today, there are no general-purpose sizings — no one-size-fits-all formulae, says Steve Bassetti, global marketing manager, fibers and composites, for fiber sizing supplier Michelman (Cincinnati, Ohio, US). "Several key variables need to be understood in the sizing selec- tion process," he says, expanding on his theme: "Clearly, [one is] the resin that the fiber is going to be put into, be it polyester, epoxy, polypropylene, nylon, PAEK or other." Fausto Pellegrini, key account manager and team leader for Aliancys (formerly DSM Composites, Schaffhausen, Switzerland) Fig. 2 Distinctive and proprietary formulations Chemists mix sizing in a cleanroom environment. Sizing chemistry is among the most highly guarded of trade secrets, in part because it is one of the factors that most distinguishes one fiber product from another. Source | Michelman Fig. 3 Sizings tailored to the task at hand Car interior instrument panel support beams, arm rest frames and center console supports are among the many parts made from fiberglass/polypropylene with sizings tailored, customized and optimized in a way appropriate to the end-use application. Source | Michelman / Photo | Thinkstock (Photographer / Maudib)

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