Novel aromatic phosphonates as flame retardants for polybutylene succinate

• Thermally stable aromatic phosphonates as efficient flame retardants. • Lower proportion of flame retardants required due to synergism. • Improved flame retardancy by incorporation of aldehyde groups. Novel potential phosphonate flame retardants were synthesized from renewable building blocks. The additives were characterized using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and nuclear magnetic resonance spectroscopy (NMR). Polybutylene succinate was compounded and injection molded with phosphonate concentrations of 2–10 wt. % and tested via UL-94 resulting in a shortening of burning time and reduction of burning droplets. Furthermore, synergistic combinations of the novel phosphonates with 2,5-dioxopyrrolidin-1-yl 2,4,6-trimethylbenzenesulfonate were investigated. Best results were achieved with phosphonates where the aromatic ring is substituted with aldehyde groups and the additional use of the sulfonate. TGA and NMR analysis provided indications of the involved flame retardant mechanism.