Jelena Vasiljević, University of Ljubljana, presented tests of three DOPO derivatives as additive PIN FRs in polyamide 6 fibres. The FRs were added in the caprolactam melt before polyamide polymerisation. Only PHED proved compatible with the melt extrusion process (0.35 mm) and with dying (transparent) and at 15% loading achieved self-extinguishing and no flaming drip with ASTM D6143 (filament and textile) and UL94-V0 (1.2 mm woven textile). However, tensile strength was reduced by around 50%. The objective is to avoid compounding, by a one-step polymerisation – FR addition – melt-extrusion.
See also Vasiljević et al. Polymer Degradation and Stability, vol. 166, August 2019, pp 50-59 https://doi.org/10.1016/j.polymdegradstab.2019.05.011
PHED = bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide
Comments from conference participants also referred to developments of one-step polyamide processing using additive PIN FRs. pinfa NOTE: for example, see the EMPA – Litrax process now commercialised by Aquafil.
A prizewinning poster by Marija Čolović, National Institute of Chemistry, Slovenia, presented similar work, but where the DOPO was reacted into the caprolactam monomer of polyamide 6 (not additive) – see summary below.
Yu-Zhong Wang, Sichuan University, Chengdu, China, summarised different approaches to improve fire safety of fibre-reinforced composites where fibres are used to reinforce plastics. Such composites can be problematic in fire because of the “candle wick effect” of the fibres. Two approaches can be combined: treatment of the fibres, and flame retardancy of the plastic matrix. For epoxy resin matrix, studies of a polymeric phosphorus compound (PBHDDP) were presented. For carbon fibres, improvement of the fibre – epoxy resin interface was achieved by phosphorus-containing electrolyte soaking of the fibres before composite molding, resulting in a reduction in peak heat release rate of nearly 50%. For composites of polypropylene reinforced with natural ramie fibre (Chinese nettle), a novel polymeric PIN FR (EPA-APP) was added, showing effectiveness both via bulk flame retardation and by interfacial effects achieved by selective dispersion onto the surface of ramie fibres during processing of the composites.
PBHDDP = poly [4,4-bis(6-hydroxyhexyloxy)biphenyl 9,10-dihydro-10-[2,3-di(hydroxylcarbonyl) propyl]-phosphaphenanthrene-10-oxide