CompositesWorld
Issue link: https://cw.epubxp.com/i/866813
SEPTEMBER 2017 72 CompositesWorld FEATURE / Advances in SMC work with PUR resin systems," explains Dr. Klaus Gleich, senior research associate-Corporate R&D;, Johns Manville. "We had to watch the film former and other sizing components, because depending on chemistry of the glass sizing system, it can inhibit or kill a catalyst or cause foaming. You always have to adjust glass chemistry for new resins systems, so we had to modify sizing chem- istry to optimize fiber wetout and coupling and to avoid inhibiting the PUR reaction. Fortunately, we'd already done development work with urethanes in LFI [long-fiber injection], so it wasn't too difficult. You want the composite very light and structural, but you also want it affordable." Of 15 initial formulations of fire-retardant PUR SMC that were produced and tested, four were found to have comparable or superior performance to VE SMC, but with much faster cure times. Daniel Park, FPC research engineer, also reported tensile strength increases of 23% (118 MPa), tensile strain-at-break increases of 25% (an elongation at break of 1.7%), and 40% higher energy absorp- tion as measured by Dynatup impact vs. UP SMC formulations. e composite also showed 25% higher Dynatup impact vs. VE SMC formulations with similar fiber content and filler levels, which were used as controls. Grades with a Class A surface are said to be encouraging but still need work to improve finish. ey work well in the D-SMC process where the material is compounded and then molded within a short time, with no maturation step. Although they are in an early stage of development, PUR SMC systems have demonstrated good mechanical performance and flame-spread values and are VOC-free. ey do not, however, yet meet the railway industry's smoke requirement. More work is Prepreg-compatible epoxy SMC Another interesting area of research is being done in the area of epoxy SMC. Hexion Inc. has recently commercialized a B-stageable, 100% epoxy grade specifi- cally designed for automotive SMC, with high mechanical properties, no styrene, and low VOCs. Inherently compatible with epoxy prepreg, epoxy SMCs can be co-molded with them to achieve "tailored" parts. The new system is said to be a low-viscosity formulation with good flow and excellent fiber wetout for high fiber volume fraction with either glass or carbon fiber and has been specifically modified to match the conventional maturation step of VE and UPSMC. It recently was molded into an automotive seat frame and parts reportedly filled completely, including ribs and bosses. Source | Hexion Inc. Recent changes in and variations on sheet molding compound (SMC) formulations have taken it some distance from its historical beginnings and conventional recipes. Do we then need a new definition for this product? Or will the old one still work with minor modifications? Nomenclature can be a tricky thing in industries where product and process complexity guarantees the use of abbreviations — something certainly true in both the automotive and plastics/composites markets. Add to that the creative marketing of those who wish to uniquely brand their companies' newest material or process variant, and the industry's communications are soon awash in interesting terminology that might or might not be meaningful, consistently applied or correctly understood. Toward a consistent definition, Dr. Klaus Gleich, senior research associate – corporate R&D;, Johns Manville (Denver, CO, US), points out, "If you go back to the origins of the term 'prepreg,' then all these materials are prepregs. Any preimpregnated fiber-reinforced, semi-finished material is a prepreg. If you take a composite pipe and overmold it, then the pipe is a prepreg. Even GMT [glass-mat thermoplastic composite] is a prepreg." He adds that practically speaking, and regardless of the type of resin and reinforcement used, the biggest difference between SMC and "true" prepreg is that prepreg is typi- cally stored in a freezer, but SMC is stored and used at ambient temperature. Steven Hardebeck, technology director North America – composites and John Ilkka, business development manager – advanced materials at Polynt- Reichhold LLC (Durham, NC, US ), however, both contend that products that contain continuous reinforcement (unidirectional or weaves, glass or carbon fiber) are not SMC. "Regardless of the process you use to make it, if it's continuous fiber, it's not SMC," argues Hardebeck. Ilkka adds, "I believe the SAMPE [Society for the Advancement of Materials & Process Engineering] guys would probably agree with us." "I don't know who should take responsibility for this in our industry, but I think there would be great value in coming together around a common language," comments Terrence O'Donovan, VP – marketing and sales, Core Molding Technologies Inc. (Columbus, OH, US) and current chair of the Auto- motive Composites Alliance (ACA) of the American Composites Manufacturers Assn. (ACMA, Arlington, VA, US). "As an industry, composites is still immature and evolving, it's still more experimental and novel than commercial and uniform. That's both good and bad," he adds. O'Donovan, who spent the first 20 years of his career in the steel industry, has a unique perspective on the topic. "In the early days, we faced the same thing in the steel industry," he recalls. "Everyone had their own chemistry, their own unique mix of steels, and they were out promoting them as some- thing unique and different." Eventually, the industry came together around the need for standardization through the American Iron & Steel Institute (Washington, DC, US). "We definitely don't want to take away the tailorability of fiber, resin and processing," he notes, "but if we want to be accepted and we want our customers to have confidence we're all talking about the same thing, we're going to have to come together as an industry." SIDE STORY Do we need a new definition for SMC?