Research and Innovation

Jaime Grunlan, Texas A&M University, USA, presented polyelectrolytes as a solution for application of PIN flame retardant solutions to different materials. Two different chemicals are dissolved in water and a pH change causes the two to react together, to bind to the substrate and to generate a stable PIN flame retardant treatment (see pinfa Newsletter n°139, Ecofram 2022). Polyelectrolytes can be used for fire protective coatings, in foams, in fused-filament 3D-printing elements. Polyelectrolyte coatings can be applied ‘layer-by-layer’ by repeated alternating baths of positively and negatively charged compounds, or in one-pot processes using a mixture of two compounds where the reaction between the two is initiated by a pH change. Coatings are typically <500 nm thick, so conserving substrate mechanical performance. Examples presented included PIN FR coating of polystyrene, heat protective coating of carbon fibre composites (combining nitrogen intumescence and clay ceramic charring), cotton, wood composite construction panels, polyurethane foam, PLA-based 3D-printer filament.

Thomas Mayer-Gall, Deutsches Textilforschungszentrum Nord-West (DTNW), presented development of innovative PIN flame retardant solutions for wood, polymers and textiles. Nitrogen, phosphorus and sulphur containing silanes, with three reactive groups, can be added to classical polyurethane or acrylate coatings for wood products to provide a PIN intumescent fire-protective coating. They can also be used to encapsulate flame retardant additive or polymer additives to ensure polymer compatibility. Trials of reactive phosphonates in different polymers showed no flame retardancy effect at 10-20% loading, except in PMMA (polymethyl methacrylate), showing that reactive FRs have to be specifically tailored to different polymers to be effective.

De-Yi Wang, IMDEA Materials Institute (Madrid Institute for Advanced Studies), presented research into flame retardants and fire safety. He underlined the need for research to increase understanding of complex FR – polymer systems: interactions between FRs and synergists, different FR mechanisms, modification of thermal degradation of polymers, different aspects of fire performance (heat release rate, fire spread, resistance to ignition, smoke …). A promising route is the use of machine learning for molecular design of PIN flame retardants. Also, new test methods are needed for new applications, in particularly batteries.

Interview: Inovia

Jeff Xu, presented the company’s ionic liquid additive PIN flame retardant technology. Ionic liquids are based on salts, containing phosphorus, nitrogen and sulphur, in which one ion has delocalised charge and one component is organic biodegradable (see pinfa Newsletter n°135). They can be liquid or low melting temperature solids and offer structural design flexibility, enabling compatibility with different polymers and inclusion of different active PIN groups (phosphorus, nitrogen, mineral ions) and can improve polymer processing (melt-flow). The ionic group generates electrostatic bonds between polymer chains, so preventing leaching of the ionic liquid FR and reducing leaching of other additives (UV, colour …). Ionic liquids prevent flaming dripping, enabling UL 94 V-0 without using PFAS, by ensuring that the molten dripping polymer does not burn. Inovia today has a 6000 t/y pilot plant in China to produce phosphonium ionic liquids (e.g. n-alkylphosphonium). The products are REACH registered, non-volatile and are not Classified for health or environment impacts. Inovia ionic liquids developed to date are adapted for polycarbonate (can achieve UL 94 V-0 @ 0.5 mm and low smoke with < 3% loading), TPUs (UL 94 V-0 @ 1.6 mm with <2% loading）, PMMA (UL 94 V-0 @ 1.6 mm with <10% loading), polyamide PA66, PBT (UL 94 V-0 @ 1.6 mm with 14% loading). Because of the low loadings needed, Inovia consider that costs are comparable to other flame retardant solutions.