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SEP 2017

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NEWS 75 CompositesWorld.com SMC Renaissance, Part 2 LLC (Dublin, OH, US). Depending on application performance and cost requirements, Magna also uses hybrid-UP and modified- VE chemistry from several suppliers. New compounding changes: The move to low- and no-VOCs Traditionally there have been two methods for compounding SMC — more common and lower tempera- ture solvent-based compounding or higher temperature hot-melt compounding, which requires specialized equipment and is similar to that used by prepreg- gers. Compounding of SMC is changing and is doing so in direct reaction to recent European Union and North American VOC reduction mandates, specifically, those aimed at styrene emissions. Unfortunately, styrene — the low-cost but highly effective diluent that formula- tors and compounders favor for solvent-based compounding to reduce resin viscosity for good fiber and filler wetout, improve handling, drive crosslink density, increase shelf life, reduce auto- polymerization issues and enhance UV stability — isn't easily replaced. Resin suppliers and compounders now face a difficult choice: Either find non-styrene diluents that work well enough for them to continue using solvent-based compounding methods, or switch to hot-melt processing methods that will require significant capital expenditures. ere are pros and cons associ- ated with each approach. In the pursuit of low- or no-VOC resin systems for both SMC and true prepreg compounding, Polynt-Reichhold LLC (Durham, NC, US) has led the charge. "Five years ago, 90% of the resins we made for SMC and prepreg were styrenated," says John Ilkka, Polynt- Reichhold's business development manager – advanced materials. "Our leadership at the time chal- lenged our R&D; team to look at alter- native ways to create polymers without styrene. While we considered other reactive diluents, like vinyl toluene or vinyl benzene — which also are currently under scrutiny — our management was concerned that if we went down that path and regula- tory authorities expanded the list of prohibited solvents, then we'd be back to square one again. Because of that, we've opted to take the harder route and create a less expensive system without reactive diluents." "Our strategy has been focused on the structural side, on deliv- ering snap-cure, room-temp storage composite solutions with zero VOCs that work with either glass or carbon and that empha- size molding productivity for SMC and prepreg applications," adds Steven Hardebeck, Polynt-Reichhold technology director North America – composites. "Fortunately, the initiator and cure mecha- nism is the same between our older styrenated SMCs and the Compounding of SMC is changing in reaction to EU and North American VOC reduction mandates.

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