In a fiber-polymer composite, the matrix polymer is usually the limiting factor when it comes to meeting high fire protection requirements. Especially the frequently used epoxy or polyester systems, but also widely used thermoplastics such as polypropylene or polyamide, quickly reach their limits here. This is a major hindrance, especially for use in transport and mobility applications and in the construction industry. Since the end of 2018, the “Institut für Verbundwerkstoffe” (Institute of Composite Materials, IVW), together with the “Sächsisches Textilforschungsinstitut” (Saxon Textile Research Institute, STFI) and Centexbel, has been conducting research within the framework of the Cornet project "SusComTrab" (Flame retardant sustainable composites for transport and building applications), and is therefore working on a wide variety of solutions for these applications.
A promising approach in this context is the use of benzoxazine resin as matrix material. The resin system "Curabox 24-111" from Bitrez Ltd. is used for the tests at IVW. In addition to its high temperature resistance and flame retardant properties, benzoxazine resin does not contain any solvents which outgas during processing and is therefore also interesting concerning occupational safety. However, the processing is challenging and therefore a focus of the research project. As a cross-linking resin, a liquid impregnation process, such as resin transfer molding (RTM), is an obvious processing route. Hereby, a fiber reinforcement is placed in a closed mold and impregnated with the resin system by overpressure. In contrast to the resin systems typically used in RTM, benzoxazine is a resin system with only one component and is present as a brittle solid in the non-cross-linked state at room temperature. For the impregnation of the fiber reinforcement, it must therefore first be melted at about 60°C. Even at further increased injection temperature, the viscosity does not drop below 500 mPas and is thus significantly higher than that of classic RTM resin systems. This results in comparatively long cycle times and difficulties in ensuring complete impregnation of the reinforcing textile. As a result, economical feasibility is often not achieved. In this project, the IVW is therefore investigating the possibilities of processing benzoxazine as a powder resin. The resin is milled to a powder and spread on the reinforcement textile. It is then pressed in a temperature-controlled tool, where the benzoxazine is melted, the fiber reinforcement impregnated and the system cross-linked. In an autoclave reference process good laminate
qualities could be achieved. Initial tests using hot pressing proved the feasability. Further research is currently being carried out to optimise the particle size distribution in the powder, the powder distribution in the process, the processing parameters and the resin formulation.
The project SusComTrab" (Flame retardant sustainable composites for transport and building applications) is funded by the Federal Ministry of Economics and Energy, based on a resolution of the German Bundestag. Funding reference number: 226 EBG
Jan Eric Semar, M.Sc.
Imprägnier- und Preformtechnologien
Telefon: +49 631 31607 35