Dispersion of flame‐retardant powdered phosphorylated kraft pulp fibers in polyester resin and their effect on the flammability of glass‐reinforced composites

Materials used in many sectors like building or transportation must respect flame resistance standards. In this work, a dispersion of flame retardant phosphorylated kraft fibers (PKF), used in replacement of aluminum trihydroxide (ATH) in a polyester resin of a glass-reinforced composite laminate, and their impact on the flame retardancy of the material was investigated. SEM and EDS images showed a regular and homogeneous distribution of PKF in the resin matrix. The addition of PKF in the resin has a significant impact on the flammability parameters of the composite. For the tested experimental conditions, powdered PKF can be dispersed into the resin at a maximum powder/resin ratio of 20 wt% to maintain a low enough viscosity of resin for molding and procure a significant weight reduction of the laminate. However, there seems to be several unprotected areas in the material, by either PKF or ATH, that could promote flame propagation and smoke emission. Complete coverage of laminate with PKF will need to be achieved for a complete substitution of ATH.