Biobased Flame Retardant Epoxy Resins and Composites
Plastics Engineering
Preparatory and Physical Chemistry of Polymers
Final Report Abstract
The project addressed distinct routes to flame-retardant bio-epoxy thermosets and composites with natural fibres, one of the most important tasks concerning the flame retardancy of highperformance polymeric materials. Unmodified bio-epoxy thermosets and composites with natural fibres are flammable and require flame retardancy for applications such as the transportation sector. In general, natural fibres are characterized by combustibility higher than glass or carbon fibres, which exhibit inert behaviour during pyrolysis. Furthermore, the aliphatic structures of many biobased raw materials crucially enhance the flammability of biopolymers. The various approaches addressed in this work show that there is strong demand for enhancing the intrinsic flame retardancy of bio-epoxy-based thermosets and biocomposites. Hereby the project delivered a systematic scientific description of the challenges, but clearly proposed fewer solutions than pronounced in the original application. However, it is essential to enhance bio-epoxy resins and their biocomposites with efficient biobased charring groups or additives. The comparison of different hardeners demonstrates that rather small changes in the molecular structure of the thermosets yield significant differences in pyrolysis and flammability. Although the intrinsic flame retardancy was lacking, sets of multicomponent materials indicate possible routes to synergistic combinations in order to realize halogen-free flame retardancy, fulfilling the demands for materials applied in railway vehicles or aviation. The current shift towards using renewable sources was addressed. The works in this project clearly demonstrate the huge gap between the many sophisticated systems proposed in literature and the dearth of systems available commercially, neither as products, nor as pilot samples, nor as any material support derived from current developments. Thus, we selected biochar and electro-spun cyclodextrin fibres as two examples of biobased raw materials that are both available and show promise for multifunctional impacts. The search for efficient specific interactions with biobased raw materials to boost fire retardancy is simultaneously a challenge and a solution. For instance, the desired reactivity also demands the development of curing procedures for the thermosets and their biocomposites, as well as protocols for preparing proper test specimens. In terms of performance, the combination of biochar and APP is proposed as a particularly promising route. In general, optimizing the protective properties of the fire residue via synergistic interactions between flame retardant and bio-filler is identified as a possible gamechanger. Combinations with flame retardants that work mainly in the gas phase yielded superposition of the flame-retardant effects. The BAM employee learned a great deal during a guest stay at SCU in China, working in the synthesis laboratories and preparing bio-epoxy-based composites with natural fibres. We also learned a lot about working together with Chinese scientists, especially when the originally planned working program did not function well, and when unforeseen circumstances such as the coronavirus pandemic prevented so much of the personnel exchange. Considerable efforts went into the production of comparable sets of test specimens to compensate for the sorely lacking exchange of materials. Comprehensive investigation of pyrolysis, flammability, and fire behaviour was applied to understand the burning and fire phenomena of the biocomposites and their flame retardancy. We identified and quantified the different flame-retardant modes of action, and we proposed the mechanisms behind flame retardancy and synergy. This work offers a systematically scientific data basis to explain the fire behaviour of bio-epoxy-based composites with kenaf fibres, sketches some promising routes, and can be used as a foundation for evidenced-based assessments and future development. Although the project fell short of the initially planned flame-retardant bio-epoxy systems and was crucially delayed, we addressed nearly all the topics of the project application with alternative approaches.
Publications
- "Flame Retardant Properties of Kenaf Fibrereinforced Bio Epoxy Composites", 18th European Meeting on Fire Retardant Polymeric Materials, FRPM21, Budapest, Hungary, 29 August – 1 September 2021
S. F. Falkenhagen, Y.-Z. Wang, B. Schartel
- "Black as Hell, Strong as Death and Sweet as Love - Pyrolyzed Waste Materials and Cyclodextrins as Effective Filler in Flame Retarded Epoxy Composites", 3rd International Conference on Eco-friendly Flame Retardant Additives and Materials, Alés, France, 17–18 May 2022
S. F. Falkenhagen, K. Bordácsné Bocz, Y.-Z. Wang, B. Schartel
