Biobased flame retardants with facile preparation, high performance in smoke suppression, and mechanical reinforcement toward epoxy resins are worth exploring for feasible sustainability. Although some chitosan-containing flame retardants have been successfully developed so far, the synthesis processes for most of them require the use of large volumes of organic solvents and give low synthetic yields. Herein, we report a facile, green, and high-yielding strategy for the synthesis of chitosan−metal complex flame retardants (CS−Fe) by coordination of chitosan with Fe(III) in water. The results show that incorporating 9 wt % CS−Fe enables the EP composites to pass the UL-94 V-1 rating with a limiting oxygen index (LOI) of 29.5%. At the same time, the peak heat release rate, peak smoke production, total smoke production, peak CO production, and fire growth rate of EP/9CS−Fe are significantly reduced, indicating good flame retardancy. Remarkably, the prepared CS−Fe enhanced both the strength and toughness of EP due to the homogeneous dispersion of CS−Fe and the presence of a reaction between CS−Fe and the EP matrix. This work provides a simple and economic strategy for the green preparation of chitosan-based flame retardants with high efficiency.
An environmentally friendly flame retardant named PO‐PA was designed to enhance the flame retardancy of epoxy resin (EP). Following the principles of efficiency and simplicity, PO‐PA was synthesized through a one‐pot reaction between phenyl phosphonic acid and p‐phenylenediamine. The chemical structure of PO‐PA was characterized by Fourier‐transform infrared (FTIR) spectroscopy, X‐ray photoelectron spectroscopy (XPS), elemental analysis (EA) and thermogravimetric analysis (TGA). EP containing 10 wt% PO‐PA (EP/10%PO‐PA) passed the UL94 V‐0 rating without dripping. In the cone calorimeter test, the total heat release and total smoke production of EP/10%PO‐PA decreased by 44% and 65%, respectively. TG‐FTIR and Py‐GC/MS were used to investigate the pyrolysis gases of the EP composites and PO‐PA, respectively. Scanning electron microscopy (SEM), FTIR, EA and XPS were utilized to study the char residues. It was proved that PO‐PA notably promoted the formation of smooth protective char layer in the condensed phase and effectively inhibited the oxidation chain reactions through releasing the phosphorus‐containing radicals in gas phase, which was not mentioned in the similar research based on phenyl phosphonic acid.
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