Synergistic flame-retardant effect of expandable graphite and phosphorus-containing compounds for epoxy resin: Strong bonding of different carbon residues

Establishment of a highly efficient flame-retardant system for rigid polyurethane foams based on bi-phase flame-retardant actions

Rigid polyurethane foam (PU), one of the most promising wall insulation materials, exhibits high flammability and fire risk. In this work, PU/EG/HQ composites with highly effective flame retardancy were fabricated by adding two kinds of flame retardants, expandable graphite (EG) and 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphorylphenanthrene-10-oxide (DOPO-HQ), during the synthesis of polyurethane. Thermal stability and flammability were evaluated using the limiting oxygen index (LOI), thermogravimetric analysis (TGA), UL-94 vertical flame results, and cone colorimeter tests. The as-synthesized PU/EG/HQ composites showed a high LOI value, a maximum peak heat release rate (PHRR) value which was decreased by 58.5% and an increased char yield at 800 °C. They also achieved UL-94 V-0 classification. SEM and Raman spectra indicated that the "worm-like" intumescent char layer with a graphitized structure and the formed viscous liquid film were vital factors in the enhancement of the flame retardancy of polyurethane foam in the condensed phase. TG-IR results show that the release of toxic volatiles and flammable gases from the PU/EG/HQ samples was remarkably decreased compared with the release from pure PU. This work associates a gas-solid biphase flame retardancy mechanism with the incorporation of two types of flame retardant and presents an effective method for the synthesis of bi-phase flame-retardant polymers.

Synergistic Effect of Hexaphenoxycyclotriphosphazene and Aluminium Tri-Hydroxide on Flame Retardancy and Smoke Suppression of Epoxy Resin

Flame retardancy and smoke suppression of polymer materials are key problems to be considered for applications that have a potential fire hazard. This study selected hexaphenoxycyclotriphosphazene (HPCTP) and aluminium tri-hydroxide (ATH) powder as an integrated flame retardant treatment in epoxy resin (EP) which is usually used as the matrix of a composite. The characteristics of flame retardancy and smoke suppression were investigated. The results showed that when treated with HPCTP and ATH, the resin exhibits superior properties, resisting flame development and smoke release. Based on analysis of the surface structure of the burned materials by scanning electron microscopy–energy dispersive spectroscopy and X-ray photoelectron spectroscopy, it was confirmed that HPCTP and ATH can attract a lot of heat to slow down decomposition of the resin and produce a comprehensive protection system consisting of a non-flammable gas and solid phases during burning. Non-flammable gas can reduce the concentration of flammable gas to inhibit combustion. In addition, H2O vapour can also reduce the concentration of flammable gas to inhibit combustion. Meanwhile, solid phase films can insulate air to slow down combustion and smoke release.

Novel flame retardancy effect of phenethyl-bridged DOPO derivative on epoxy resin

A series of flame-retardant epoxy resins (EPs) containing either phenethyl-bridged 9 or 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivative (bisDOPO) were prepared. The flame-retardant properties of bisDOPO on EP composites were characterized by the limiting oxygen index (LOI), the UL-94 vertical burning, and the cone calorimeter test (CCT).The LOI of the EP/bisDOPO composites increased from 21.8% to 38.0%, and the hybrids with the 10 wt% bisDOPO obtained a V-0 rating in the UL94 vertical burning test. The char residue following the CCT showed intumescent structures with continuous and compact surfaces that can effectively suppress the spread of the flame and extinguish the fire. This was confirmed through both visual observation and scanning electron microscopy (SEM) measurements. The flame-retardant mechanism was studied by Fourier transform infrared spectroscope (FTIR), thermogravimetric analysis/infrared spectrometry, SEM/energy-dispersive X-ray, and pyrolysis-gas chromatography/mass spectrometry. Overall, bisDOPO was an effective flame retardant with potential applications within EP.

The flame retardancy and smoke suppression effect of a hybrid containing dihydrogen phosphate anion modified reduced graphene oxide/layered double hydroxide on epoxy resin

The structure of RGO–LDH/P and its effect on flame retardancy of epoxy resin.

Flame-retardant effect of a phenethyl-bridged DOPO derivative and layered double hydroxides for epoxy resin

Flame-retardant epoxy resin (EP) composites were prepared by the incorporation of a phenethyl-bridged DOPO derivative (DiDOPO) and modified layered double hydroxide (OLDH).