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SEP 2017

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NEWS 71 CompositesWorld.com SMC Renaissance, Part 2 for conventional SMC compounding. However, a multi-year development project aimed at creating a stronger, tougher composite system to meet the railway industry's stringent flame/smoke/ toxicity (FST) requirements provided the opportu- nity to give it a try. Partially funded by the provin- cial government of Ontario, Canada, the project involved research institute Fraunhofer Project Centre for Composites Research (FPC, London, ON, Canada), resin supplier Huntsman Poly- urethanes (Auburn Hills, MI, US), and fiberglass source Johns Manville (Denver, CO, US). ree key elements made the project feasible. e first was Huntsman's prior work to chemi- cally decouple PUR viscosity build from resin "snap cure." is permitted formulators to build in both a long latency/outlife at low viscosity, which ensured thorough infusion and fiber wetout of even large parts, and a rapid cure (see Learn More). e second was FPC's work, along with co-owner Fraunhofer Institute for Chemical Research (F-ICT, Pfinztal, Germany) and machinery OEM Dieffenbacher GmbH (Eppingen, Germany) on the direct-SMC (D-SMC) process, where compounding occurs very close (physi- cally and temporally) to molding without the need for the 48- to 72-hour maturation period that is common with conventional SMC. e chemistry of the VITROX resin system that Huntsman is supplying more or less necessitates making PUR SMC via a direct process. "e great thing about urethanes is they react with everything, but the bad thing about urethanes is that they react with everything, too," quips Dr. Michael Connolly, program manager – urethane composites at Huntsman Polyurethanes. "Still, VITROX chemistry allows us to separate out snap cure at high temps vs. an early maturation stage … and to separate exotherm control from molding," he adds. "at feature has proven useful for a lot of composite processes." SMC is now one of them. e third element to the project's success was Johns Manville's work on sizing chemistry. Since calcium carbonate (the most common SMC filler) and some urethane catalysts can be incompatible, alternative fillers (in this case, glass microspheres and milled glass) had to be used. In fact, specific grades of chopped and milled glass and glass microspheres were selected so as not to inhibit the reaction of the PUR matrix, because some sizing chemistry also can be an issue with the reactive PUR matrix. "Standard SMC fiberglass sizing needs to be styrene-soluble for good wetout, but that doesn't Rapid-cure SMC for rail? An area of important change is work to broaden SMC beyond conventional formulations. This front and back view of a seat frame (top and middle) exemplifies work by a group including Fraunhofer Project Centre for Composites Research (London, ON, Canada), Huntsman Polyurethanes (Auburn Hills, MI, US) and Johns Manville (Denver CO, US) to develop fast-curing polyurethane SMC (PUR SMC) via the direct-SMC process for the railway industry. Early materials (bottom photo) have demonstrated good mechanicals and anti-flame-spread values and are VOC-free, but have not yet met railway industry smoke requirement. Source | Huntsman Polyurethanes

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