Posted on 08/07/2022 in Fire Safety 2022
New applications for PIN flame retardants

Sabyasachi Gaan, EMPA Switzerland, presented testing of PIN FRs in reactive extrusion of polyamide. An oligomeric phosphorus PIN flame retardant was embedded in polyamide, by reaction of a phosphorylated vinyl monomer (DVPPO) with the cyclic amine (piperazine) in extrusion of polyamide polymer to fibres, so embedding the resulting phosphorus-nitrogen macromolecules in the polyamide matrix. The resulting fibres with 0.7% phosphorus loading showed good fire performance and acceptable mechanical performance. The oligomeric P-N PIN FR showed a chain length of 500 – 10 000 and showed negligible leaching from the extruded fibres (in chloroform and water even at 100°C). Tests on DVPPO showed no cytotoxicity (genotoxicity, cell ROS). Piperazine is also known to have a positive health and environment profile.

Maël Kervran, University of Lorraine, France, presented tests of PIN flame retardants in PLA/PHB (75:25) biopolymer blends (polylactic acid / polyhydroxybutyrate). The nitrogen PIN FR melamine diethenalomine formaldehyde (MDF), the phosphorus-nitrogen PIN FR ammonium polyphosphate (APP) and the mineral clay sepiolite were tested, concluding that optimum fire performance was achieved with a combination of the three additives.

Jonathan Salle, CREPIM France, presented testing of lithium ion batteries. The fire risk caused by batteries, in particular in electric vehicles, is resulting in development of a number of new test methods for batteries or battery casings, adapted to specific battery uses: UL 2580, NF EN 62619, R100, UL 2596, GMW 18435 etc.

Louis Meunier, UMET Lille, France, explained the potential interest of “vitrimers” as recyclable alternatives to high-performance thermoset polymers. Vitrimers are polymers with thermally-activated covalent interlinking bonding, resulting in behaviour like a thermally-reversible thermoset, so enabling melting for mechanical recycling. Flame retardants for vitrimers are to date little developed and pose challenges regarding impact on the vitrimer cross-linking process. A vitrimer consisting of epoxy, PBT (butylene terephthalate) and a transesterification catalyst was tested with three different PIN flame retardants: polyphosphonate, zinc phosphinate and aluminium phosphinate (AlPi). The first two interfered with the vitrimer cross-linking, whereas AlPi caused cross-linking without using the catalyst. 15% AlPi enabled UL 94 V-0. Stress relaxation tests confirmed that the material with PIN FR behaved as a classical vitrimer, and the material was easily reinjected to prepare samples for further analysis proving the thermally triggered ability of the network to be reprocessed and thus recycled.
José-Marie Lopez Cuesta, Mines Alès France, presented tests of PIN FR combinations for Fused Fibre Filament 3D printing of PLA (poly lactic acid). The main PIN FRs used were ammonium polyphosphate (APP), or encapsulated APP, at 17% loading. Additions were tested of lignin, sepiolite, halloysite nanotubes and LDH (layered double hydroxide) of aluminium – zinc – phosphorus – hydrotalcite. 3D printed samples showed slightly (APP) or significantly (encapsulated APP) lower fire performance than molded samples, probably because of porosities in 3D printed materials. Except for lignin, the various additives showed no significant improvement in fire performance when encapsulated APP is used, and in some cases deteriorated fire performance (e.g. LDH), showing that different additives can show either synergies or antagonism.

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