Flame retardancy and smoke suppression properties of flexible polyurethane foams containing an aluminum phosphate microcapsule

A novel aluminum phosphate (ALP) microcapsule was synthesized with the aim of enhancing the flame retardancy and smoke suppression properties of flexible polyurethane (PU) foams. Meanwhile, the ALP microcapsule was analyzed by SEM, XRD, and EDX. The ALP microcapsule was added into PU foams to prepare flame retardant PU composites which show good flame retardancy, thermal stability, synergy effect and anti-dripping performance. Meanwhile, the LOI of the PU composites was about 28.5% and a V-0 rating in UL-94 was attained in the case of 15 wt% of the flame retardant compared to 21.0% and no rating for pure PU. An SDR of the PU composites of about 16.0% was attained in the case of 20 wt% of the flame retardant compared to 29.0% for pure PU. The gaseous phase mechanism of PU composites was investigated with thermogravimetry and Py-GC-MS. SEM, EDX and FTIR were employed to investigate the chemical structure and composition of the residual char of the flame retardant PU composites after TG tests. The results indicated that the ALP microcapsule could serve as an outstanding flame retardant that operates by both chemical (condensation) and physical (cooling and blocking) mechanisms. This suggests that the ALP microcapsule may provide a promising option for a new, cost-effective, eco-friendly, yet efficient flame retardant.