Phytates as renewable flame retardants for unsaturated polyester resins

In modern materials research, reduction of fossil fuel consumption has triggered massive research on bio-based alternatives, especially for polymer composites. While resins in research are frequently replaced by bio-based alternatives, bio-based flame retardants are rarely investigated. This work covers the introduction of nitrogen-based phytates and magnesium phytate into an unsaturated polyester (UP) resin and their influence on mechanical characteristics and flame retardancies. The UP resin is based on 1,3-butanediol and fumaric acid with isobornyl acrylate as the reactive dilutant. The ammonium, piperazinium, melaminium, or magnesium phytates are characterised by FT-IR spectroscopy and 31P NMR spectroscopy for phosphorus quantification. Resin plates were cured without phytates, including 10 parts per hundred parts of resin (phr) of phytate, or 20, 40, and 60 phr for magnesium phytate. The resin plates were characterized by Dynamic Mechanical Analysis (DMA) and Cone Calorimetry. The DMA results remain similar for all plates (glass transition around 125 °C). Upon combustion, nitrogen-based phytates exceed magnesium phytate in reductions of the Maximum Average Rate of Heat Emission (-44% for ammonium vs. up to -35% for magnesium), Total Heat Release (-37% for ammonium vs. up to -25% for magnesium), and Total Smoke Release (-22% for ammonium vs. up to -25% for magnesium). However, they suffer from carcinogenic or teratogenic characteristics, and/or show disadvantageous solubility in water. Additionally, magnesium phytate has 100% biobased carbon content. Still, industrial criteria as formulated in, e.g., DIN EN 45545-2 for railway applications are not met with the presented formulations requiring further optimization before application in composites.