Phosphorus Polyester — an Alternative to Low‐Molecular‐Weight Flame Retardants in Poly(Butylene Terephthalate)?

Pyrolysis, fire behaviour and mechanical properties of a blend of poly(butylene terephthalate) (PBT) with a phosphorus polyester (PET‐P‐DOPO) are investigated and compared with PBT/aluminium diethylphosphinate (AlPi‐Et) composites. The PBT/PET‐P‐DOPO is immiscible and exhibits gas‐phase and condensed‐phase activity, whereas AlPi‐Et in PBT results mainly in flame inhibition. Only higher loadings of AlPi‐Et yield significant condensed‐phase activity. Using the same phosphorus content, PBT/PET‐P‐DOPO and PBT/AlPi‐Et exhibit similar reductions in fire load (22%) and flame spread (17% assessed by fire growth rate, FIGRA), compared with PBT. In contrast to AlPi‐Et, the addition of PET‐P‐DOPO does not decrease the tensile strength of PBT. Thus, PET‐P‐DOPO is an interesting alternative to low‐molecular‐weight flame retardants.