For processes such as RTM and LRTM, ATH at levels up to 40% by weight are successfully used to meet many FR standards. To put this in perspective, an open mold FR resin can be used with ATH at levels greater than 60% by weight. However, ATH cannot be used in the infusion process because the material’s high viscosity. The infusion process is under vacuum, and a filled resin cannot flow through the reinforcement as it is filtered out. Therefore, the one of the biggest challenges for resin suppliers is the development of non-halogen FR resins that don’t require ATH.

Panel Fabrication

During fabrication, FRP panels are typically encapsulated in plastic film to keep the process clean while producing flat, smooth, embossed or corrugated shapes and surfaces. The highest volume throughput process is the high-temperature continuous process. The stationary room temperature, hand lay-up batch process is more suitable for better aesthetics. Resins currently being used successfully are based on ATH-filled systems, but the panel fabrication process faces many of the same challenges as open molding.

In addition, numerous other fabrication methods, including pultrusion and sheet molding compound (SMC), are utilized when manufacturing end-use products with fire retardancy requirements. No matter what fabrication process is used, some of the common challenges with processing FR resins include:

  • Meeting the required FR standards
  • Handling higher processing viscosities
  • The inability to use filled systems
  • Increased weight
  • Translucency
  • Achieving the required mechanical properties

One notable drawback to unfilled FR resins is the increased cost. However, unfilled FR resins can be cost effective overall when you consider advantages such as higher glass reinforcement content, improved mechanical performance, reduced thickness and decreased weight. In addition, unfilled resins can be processed easier, which leads to an increased production rate.

During the past decade, research and development has come a long way on environmentally friendly, non-halogenated alternatives. By working closely with fabricators, resin suppliers have solved many fabrication challenges. Given the exceptional properties of some emerging FR resins, there is a bright future for the next generation of fire-retardant composites produced using fabrication processes that are not suitable or ideal at this time with existing FR technologies.

Michael Siegel is product leader for corrosion and fire-retardant resins at AOC. Email comments to

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