Posted on 15/10/2019 in 2019
Research into bio-based PIN flame retardants

Xin Wang, University of Science and Technology of China, presented proposed PIN FRs derived from bio-based cardanol, tested in epoxies, including by reaction with organic phosphorus chemicals such as phosphaphenanthrene or benzoxazine, with zirconium phosphate, in combination with boron graphene nanosheets and in layered double hydroxides. The chemical properties of cardanol enable functional modification and contribute to improve hardening of epoxies. 6% loading of a zirconium phosphate – cardanol derivative reduced total heat release of the epoxy by nearly 50% and total smoke emission by over 25%.

Gyorgy Marosi, Budapest University of Technology and Economics, claimed that to address public and regulator concerns about “plastics”, the objective should be to develop recycling and use of bio-based polymers. He presented a number of innovative applications of bio-based materials integrating fire safety, including phosphorylation of chemicals extracted from organic materials to produce bio-sourced flame retardants, use of bio-sourced fibres, including production of carbon fibres from cellulose and nano-fibres from bio-sourced cyclodextrin or chitosan. Some of the examples referred to materials approved for pharmaceutical purposes. The health and environmental safety of other synthetic organic molecules and nano-fibres were not addressed, whereas the use of bio-sourced materials gives no indication of safety of derived chemical.

Yun Liu, Qingdao University, China, showed studies of flame retardancy of alginate fibres. Alginates are water-soluble polysaccharides and bio-based fibres can be produced by wet spinning of sodium alginate solution, extracted from marine algae, into solutions of e.g. calcium chloride. These fibres show inherent fire resistance, and tests showed that blending with cotton fibres improved fire performance (lower peak heat release rate, longer time to ignition).

Ravi Mosurkal, US Army Combat Capabilities Development Command Soldier Center, Natick, MA, explained that the Army is working to ensure fire safety of soldiers clothing both in combat and day-to-day. Current solutions (e.g. using FRACU Flame-Resistant Army Combat Uniform and Nomex) are expensive and pose durability issues and the army wishes to find FR solutions for nylon-cotton blends. A combination of bio-based tannic acid and phytic acid has been tested as coating. Both of these are widely available from plants and are recognised to be safe for health and the environment. The tannic acid provides a carbon source and phytic acid provides phosphorus, together generating intumescent char, resulting in effective fire protection, reducing heat release by around 37%. Fabric properties were not significantly reduced. Unfortunately the fire performance is lost after only one wash, apparently not because of loss of the coating, but because of chelation by metal ions in laundering cycle and loss of phosphorus. Work is underway to find a solution for durability.

Laurent Ferry, C2MA Alès, France, presented work looking at use of tannins extracted from regional Cévennes chestnut tree wood by-products. Tannins are polyphenolic compounds. Gallic acid and ellagic acid, can be purified from chestnut tannin. These chemicals (industrially supplied) were reacted with boric acid, because this chemical is widely used in wood preservation. The resulting boron tannin derivatives were tested as flame retardants in DGEBA/IPDA epoxy. Promising results for fire performance were obtained, including a 2/3 reduction in peak heat release rate. Work is underway to improve extraction and purification from chestnut wood by-products and to generate small particles for better dispersion in polymers.

Sheng Zhang, Beijing University of Chemical Technology, China, summarised research into use of different phosphorylated derivatives of bio-sourced chitosan as a flame retardant in TPU (thermoplastic polyurethane). Chitosan is the only naturally occurring alkaline polysaccharose. Chitosan was modified by reaction with organic chemicals (Schiff-base, with the objective of improving thermal stability), with phosphonates and with montmorillonite clay, and these were tested in combination with APP, AlPi, melamine polyphosphate, including layer-by-layer. 19% APP plus 6% modified chitosan, or 9% AlPi plus 1% combined chitosan / phosphorus / montmorillonite, both achieved UL94-V0 (3.2 mm).

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