We developed sustainable, recyclable carbon fibre-reinforced polyimine vitrimer composites
with enhanced flame retardancy via a combination of resorcinol bis(diphenyl phosphate)
(RDP) in the matrix and a 10 %P ammonium polyphosphate (APP) intumescent coating,
offering a promising alternative to conventional epoxy systems for advanced applications.
Fire performance was evaluated using Limiting Oxygen Index (LOI), UL94, and mass loss
calorimetry (MLC) tests. The APP coating acted via a condensed‐phase mechanism, forming
a dense, phosphorus oxide‐rich char that reduced the peak heat release rate (pHRR)
from 289 kW/m2 to 126 kW/m2—the lowest observed among the tested formulations. Scanning
electron microscopy and energy-dispersive X-ray spectroscopy (SEM‑EDS) analysis revealed
significant phosphorus enrichment in the outer char layer and, notably, an increased
phosphorus content in the inner char when RDP was incorporated into the matrix. This
synergistic effect indicates that RDP’s gas‐phase action effectively complemented
APP’s condensed‐phase mechanism, further enhancing LOI, extending time to ignition
(TTI), and reducing total heat release (THR), significantly improving overall fire
resistance. Although benchmark epoxy composites exhibited higher tensile strengths,
the vitrimer systems maintained competitive mechanical properties alongside superior
recyclability, the ability to apply the intumescent coating via hot pressing, and
intrinsic repairability. Overall, the dual-action flame retardant strategy achieved
by combining RDP and APP significantly improved fire performance, demonstrating the
potential of these advanced composites for multifunctional material applications.
