A novel multifunctional organic-inorganic hybrid was designed and prepared based on ammonium polyphosphate (APP) by cation exchange with diethylenetriamine (DETA), abbreviated as DETA-APP. Then DETA-APP was used as flame-retardant curing agent for epoxy resin (EP). Curing behavior, including the curing kinetic parameters, was investigated by differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). The flame retardance and burning behavior of DETA-APP cured EP were also evaluated. The limiting oxygen index (LOI) value of DETA-APP/EP was enhanced to 30.5% with only 15 wt % of DETA-APP incorporated; and the UL-94 V-0 rating could be easily passed through with only 10 wt % of the hybrid. Compared with DETA/EP, the peak-heat release rate (PHRR), total heat release (THR), total smoke production (TSP), and peak-smoke production release (SPR) of DETA-APP/EP (15 wt % addition), obtained from cone calorimetry, were dropped by 68.3, 79.3, 79.0, and 30.0%, respectively, suggesting excellent flame-retardant and smoke suppression efficiency. The flame-retardant mechanism of DETA-APP/EP has been investigated comprehensively. The results of all the aforementioned studies distinctly confirmed that DETA-APP was an effective flame-retardant curing agent for EP.

Aluminum hypophosphite (AP) and aluminum isobutylphosphinate (APBu) were used to flame retard polyamide 6 (PA6). Addition of either AP or APBu resulted in an increased LOI value, UL-94 V-0 rating, and decreased heat release in cone calorimetric tests. However, different chemical structures of two flame retardants caused different flame-retardant effects: APBu endowed PA6 a higher LOI value and better UL-94 result than did AP. Decomposition pathways of AP, APBu, and the corresponding composites were investigated using TGA, TG-IR, Py-GC/MS, and FTIR characterization of the residues. The introduction of AP changed the thermal stability and decomposition behavior of the composites due to the cross-linking reactions occurred, which were proved by rheological analysis and TG-DSC. APBu could not essentially affect the composition of pyrolysis products and decomposition behaviors, but mainly produced phosphorus-containing free radical scavengers in the gaseous phase, which were positive to flame retardation. Finally, the proposed flame-retardant mechanisms of such systems were summarized.

PAz-APP (as a monocomponent hardener) can bring excellent flame retardance and smoke suppression efficiency to the EP system without sacrificing the mechanical properties and glass transition temperature.

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