Posted on 15/10/2019 in 2019
Researching new FR coating technologies

Bartosz Weclawski, University of Bolton, UK, presented research into use of plasma technology based on an atmospheric pressure plasma and high power UV laser. Multiplexed Laser Surface Enhancement (MLSE from MTIX Ltd., UK) can bond fire retardant precursors physico-chemically and even covalently into a fabric, followed by plasma/UV, so avoiding the conventional wet processing cycles. Using this technology, the nylon 6.6 (PA66) component of the nylon 6.6/cotton blends (type Nyco, commonly used for US Army personnel uniforms) was flame retardant functionalised. Results of tests of formation of covalent bonds with reactive flame retardants like DOPO were presented. Thermal degradation and flammability studies on functionalised nylon 6.6 fabrics were discussed.

Jaime Grunlan Texas A&M University, presented research into layer-by-layer coating application of PIN flame retardants to textiles, to wood and to flexible polyurethane foam. Application uses aqueous solutions of combinations of clay minerals, ammonium polyphosphate, melamine compounds, poly(allyl amine) and sodium hexametaphosphate. Such coatings showed to provide effective fire performance at around 20% w/w (textiles, self-extinguishing) or 6% w/w (wood). Some applications have been licenced and patents are pending. Work is currently underway to improve durability of treatments (to date, textiles only washed five times).

Federico Carosio, Politecnico di Torino, also presented water-based layer-by-layer and one step application of PIN flame retardants to flexible polyurethane foam to cover the foam 3D structure. Application of a combination of graphene nanoplatelets, phosphorus-based compounds, alginate and nanoclays (e.g. montmorillonite, sepiolite) at a total loading of 30 to 70 % w/w achieved self-extinguishing, no melt-dripping and also smoke emission reduction of up to 75%. The foams could resist penetration of an 800°C flame, retaining thermal insulation properties. Mechanical performance of the treated foam was acceptable after 50 compression cycles and testing with 2 000 cycles is underway.

Sophie Duquesne, University of Lille, France, presented a one-step process being researched for surface application of PIN flame retardant coatings to polycarbonate. A combination of two polymers (epoxy and silicone) with PIN FRs is applied and is optimised to self-stratify, because of incompatibility of the polymers. This self-stratyfying process enables in one pass to obtain a good adhesion (epoxy) to the substrate (polycarbonate) whereas the top layer (silicone) containing the FRs brings both weather resistance and fire retardant performance. A 200 µm layer containing minerals (e.g. iron oxide or calcium carbonate) enabled to achieve UL94-V0 (3 mm) and to increase the LOI from 27 (neat PC) to 35.

Anne-Lise Davesne, University of Lille, France, presented studies of thin metal coatings on polymers, as radiant heat reflectors contributing to fire resistance. 500 nm metal/dielectric coatings were deposited on polypropylene and polyamide 6, using physical vapour deposition (pulsed DC magnetron sputtering of pure metal targets). This metal layer alone increased ignition time, reduced heat transmission, but did not reduce heat release. Combination with a PIN FR intumescent, expandable graphite (for PP), and Exolit Clariant OP1311 (for PA6), showed extended ignition time (8 minutes vs. 40 seconds in neat PP, and 15 minutes vs. 1 minute in neat PA6) and peak heat release rate (PHRR) reduced by around half.

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