Posted on 08/07/2022 in Fire Safety 2022
PIN flame retardants for wood and fibres

Adèle Lamandé, CSTB France (national construction technical centre), presented studies of gas emissions from timber laminates under different oxygen concentrations, intended to simulate different fire conditions. She underlined that three quarters of deaths in building fires are from smoke. Cone calorimeter tests with spruce cross-laminates (polyurethane adhesive) showed increasing emissions of carbon monoxide, formaldehyde and methane, with decreasing oxygen concentrations (18%, 15% compared to 21% in air) and emissions of ethene and propane at 15% oxygen.

Henri Vahabi, University of Lorraine France, presented trials of electrically conductive, PIN flame retardant coating of flax textiles by hydrochloric acid treatment, then polyethylenimine (PEI), ammonium polyphosphate (APP), and poly(aniline-co-melamine) – montmorillonite (MMT) composite. This resulted in conductive (1-8×10-7 S/cm), non-ignitable fibres, peak heat release rate < 10% that of untreated fibres, which maintained conductivity after 30 seconds flame application. In further tests, the flax textile was treated with sodium hydroxide, polyethyleneimine, then phytic acid, resulting in a 3.4% phosphorus loading. This resulted in high charring, peak heat release rate reduced to 25% that of untreated fibres, increased abrasion resistance and increased fibre elongation before break.

Baljinder Kandola, Bolton University UK, summarised studies over past decades on using plant fibres to reinforce polymers. The most widely studied fibres are hemp and jute, in polypropylene and also with some in poly lactic acid (PLA). The plant fibres show generally inferior mechanical properties than glass or carbon fibre, and also challenges with water uptake, fibre-polymer interface compatibility and flammability. Interfacing can be improved in polypropylene by surface treatment with silanes, but this is less effective in PLA. Atmospheric plasma treatment enhances interfacial adhesion in both PP and PLA composites. Different PIN flame retardants have been tested including ammonium sulfamate, guanidine dihydrogen phosphate, guanylurea methyl phosphate. While all of these flame retardants have been effective in flax/PLA composites in obtaining UL94 V0 rating, in flax/PP only guanylurea methyl phosphate has been effective. Flame retardants cause a reduction in the mechanical properties of the composites but silanisation and plasma pre-treatment of fabrics either alone or in sequence had significant effects in partly restoring mechanical properties of FR-Flax/PP composites.

Sandra Falkenhagen, BAM Germany, summarised fire testing of partly bio-based epoxy resin reinforced with natural kenaf fibres, using various different PIN flame retardants. Alumina trihydrate, aluminium diethyl phosphinate (AlPi), a DOPO-based phosphonamidate and ammonium polyphosphate all successfully showed to be effective PIN flame retardants, showing that PIN FRs can effectively enhance fire safety of sustainable materials. Fire performance was further improved by addition of organic bio-sourced materials, including biochars (pyrolyzed cocoa shells, pyrolyzed roadside grass cuts), hydroxypropyl-ß-cyclodextrin, sulfobutylether-ß-cyclodextrin. Further work is needed to demonstrate the mechanical performance and weathering durability (e.g. resistance to water uptake) of the natural fibre in the presence of the organic additives and the PIN FRs.

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