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• Mn 3 CoO x was prepared to enhance the fire safety of epoxy resins (EP). • Mn 3 CoO x impressively reduced pHRR and pSPR by 47.5 % and 34.6 %, respectively. • Mn 3 CoO x can effectively catalyze the transformation of hazardous gases. • Recovery of Mn 3 CoO x to 90.0 % in EP composite. The development of metal oxide flame retardants that are easy to synthesize, efficient, and recyclable would be more beneficial to circular economy. In this work, a porous core-shell Mn 3 CoO x was developed to efficiently reduce heat, smoke as well as hazardous gas during the combustion of epoxy resin (EP). Compared with pure EP, the peak heat release rate (pHRR), total heat release (THR), peak smoke production rate (pSPR), total smoke production (TSP), peak CO production rate (pCOPR), and peak CO 2 production rate (pCO 2 PR) of EP/Mn 3 CoO x are reduced by 47.5 %, 21.5 %, 34.6 %, 17.6 %, 58.6 %, and 55.4 %, respectively. It has been shown that Mn 3 CoO x not only catalyzes the formation of high-quality char layer but also effectively catalyzes the conversion of hazardous gas products into CO 2. Recovery experiments of Mn 3 CoO x filler in EP composites show that the recovery of Mn 3 CoO x can reach 90.0 %. This work provides insights into the design of efficient metal oxide flame retardants and ideas for the development of recycled flame retardants. [Display omitted] [ABSTRACT FROM AUTHOR]

• The strength of chars was heightened significantly by the bi-component flame retardant (PODSE/APP). • 20 wt% PODSE/APP led to an 88.1 % and 87.0 % reduction in pSPR and TSP. • The char residue was substantially increased by 89.2 % with 20 wt% PODSE/APP. • PODSE/APP changed the internal structure of chars into honeycomb with higher expanded ratio. The intrinsic flammability and high smoke production are two major defects that epoxy resin (EP) must overcome during the practical application. However, few current studies have acknowledged in both fire resistance and smoke suppression performance, which is vitally interrelated with quality of char layers. Herein, a P/S-containing compounds (PODSE) was prepared via esterification and then supplemented with ammonium polyphosphate (APP) to develop an intumescent flame retardant for heightening the strength of char. With 20 wt% PODSE/APP, the peak of smoke produce rate (pSPR) and total smoke production (TSP) of EP3 reduced by 88.1 % and 87.0 %, respectively, indicative of superior smoke suppression performance. It attained a limited oxygen index (LOI) value of 40.0 % with V-0 rating during vertical burning test (UL-94) and the char residues at 700 °C increased from 15.8 % to 29.9 % compared with pure EP. More importantly, in order to figure out the reason for such highly-improved performance, the residual chars after cone calorimeter (CC) test were comprehensively investigated. The result showed that the internal chars of the samples modified by PODSE/APP exhibited honeycomb-like structure instead of irregular network structure of the one modified with single PODSE, endowing the char layers with higher expanded ratio and strength, which responded to excellent insulation effect. This finding provided theoretical and experimental basis for further exploration of P/S synergistic intumescent flame retardant. [ABSTRACT FROM AUTHOR]

• Two organometallic (Zn and Fe) coordination compounds, modified by phosphonitrile, were prepared. • Zinc-containing coordination compounds exhibited higher efficiency in flame retardant EP. • Combined effect of the catalysis charring effect of metal ions and flame-retardant effect of phosphonitrile. • P- and N-containing cross-linking structures promoted high-temperature stable carbon layer forming. Two organometallic (Zn and Fe) coordination compounds, modified by phosphonitrile, were prepared by solvothermal method. The introduction of the two organometallic coordination compounds significantly improved the flame retardancy, smoke suppression and thermal stability of epoxy resins (EP). Especially, zinc-containing coordination compounds exhibited higher efficiency than iron-containing ones in flame-retardant EP. LOI values of Zn-PDH/EP and Fe-PDH/EP were further enhanced and reached up to 29.8% and 28.9%, respectively. Organometallic coordination compounds modified by phosphonitrile mainly exerted the flame-retardant action in condense phase by the combined effect of the catalysis charring effect of metal ions and flame-retardant effect of phosphonitrile, and thus a high-temperature stable graphitized carbon layer with P- and N-containing cross-linking structures formed. This high-quality carbon layer was a vital factor in improving the heat/smoke suppression properties of EP thermosets. Further, due to the weaker catalytic char-forming effect of iron ions and the formation of fewer cross-linked structures, the strength and barrier properties of the Fe-PDH/EP char layer were relatively lower than those of Zn-PDH/EP. Consequently, Zn coordination compounds presented higher efficiency in suppressing heat/smoke release of EP matrix than Fe hybrids. Finally, the gas-phase function of organometallic coordination compounds should not be overlooked due to releasing phosphorus-oxygen free radicals and N-containing fragments during pyrolysis, exhibiting flame inhibition and dilution effect in gas phase, especially for 6%Zn-PDH/EP. [ABSTRACT FROM AUTHOR]

• A bio-based flame retardant (FDI) was synthesized for epoxy resin. • FDI endows EP with excellent flame retardancy and low dielectric properties. • The introduction of FDI significantly improved the toughness of epoxy resin. The development of high-performance EP composites with high glass transition temperature (T g), excellent flame retardancy, and UV resistance is a challenging topic in the flame retardancy community. In this work, a bio-based phosphorus/nitrogen/sulfur (P/N/S) containing flame retardant (FDI) was prepared from furfural, 2-amino-5-nitrothiazole, and DOPO. It was applied to improve the flame retardant, dielectric, and UV-resistant properties of EP. Thanks to the combination of phosphorus, nitrogen, and sulfur in FDI, the EP/FDI composites showed superior flame retardancy. Only adding 5 wt% FDI made EP achieve UL-94 V-0 flammability rating with a limiting oxygen index (LOI) of 27%. Meanwhile, EP/FDI-5% composite showed significant reduction of 65.1% and 33.6% in total smoke production (TSP) and the peak heat release rate (pHRR), respectively. The flame-retardant mechanisms of EP/FDI thermosets were investigated by residual char photographs, SEM, XPS, and Py/GC-MS. Moreover, compared to pure EP, EP/FDI composites showed excellent UV resistance, low dielectric properties, and high glass transition temperature, which was expected to be extensively used in multiple areas of production. [ABSTRACT FROM AUTHOR]

• Two nitrogen-containing polyhedral oligomeric silsesquioxanes (N-POSSs) are synthesized via one-pot method. • N-POSSs endow with ultra-high thermal stability and are suitable for industrialized production. • Adding 4 wt% of AP-POSS reduces the peak heat release rate of epoxy resin by 60.6%. • N-POSSs apparently reduce fire hazards of the formed EP composites. • The flame retardant mechanism of N-POSSs for EP is fully illustrated. Despite remarkable advances in developing flame retardants and smoke suppressants for epoxy resin (EP), engineering nitrogen-containing polyhedral oligomeric silsesquioxane (N-POSS) to impart superior fire safety properties to EP has remained an intractable challenge. In this work, two nitrogen-containing polyhedral oligomeric silsesquioxanes (N-POSSs), namely, aminoethyl-aminopropyl-hepta-phenyl polyhedral oligomeric silsesquioxane (AEAP-POSS) and aminopropyl-hepta-phenyl polyhedral oligomeric silsesquioxane (AP-POSS), were synthesized through the "corner-capping" reaction. The molecular structures of N-POSSs were fully characterized by FTIR, 1H NMR, 29Si NMR and MALDI-TOF MS, and the synthesized AEAP-POSS and AP-POSS were introduced into EP to solve the shortcomings of flammability. TGA results showed that the incorporation of 4 wt% N-POSS nanoparticles distinctly improved the char residue at 800 °C, which significantly enhanced the thermal stability of the EP composites. When 4 wt% of AP-POSS was introduced into EP, reductions in the peak of heat release rate (p-HRR), fire growth index (FGI), peak of smoke production rate (p-SPR), and the peak of CO production rate (p-COP) reached to 60.6%, 70.2%, 52.3% and 60.4%, respectively. Subsequently, TG-FTIR and XPS were utilized to investigate the flame retardancy and smoke suppression mechanism. Our work presented a considerable advancement for the facile fabrication of flame retardants based on nitrogen-containing polyhedral oligomeric silsesquioxane compounds. [Display omitted] [ABSTRACT FROM AUTHOR]

• Nitrogen-rich tetrazole was phosphorylated to chemically modify epoxy resin (EP). • The modified EP exhibited remarkable smoke suppression and flame retardancy. • The modified EP presented strengthened mechanical properties. In this work, aiming to obtain multifunctional epoxy resin (EP) possessing flame retardancy and light smoke without compromising the mechanical properties, a novel nitrogen-rich phosphinic amide named D -5-AT was synthesized and then incorporated to EP. The results showed that UL-94 V-0 rating of EP with 7.5 wt% D -5-AT was available and limiting oxygen index (LOI) was up to 35.1%. Meanwhile, in the presence of D -5-AT, the heat release and smoke production of EP/D-5-AT materials were effectively suppressed during combustion as compared with EP. The improvement mentioned above was found related to the condensed and gaseous flame retardant effect of D -5-AT through the investigation on char residues of EP/D-5-AT materials and volatiles of D -5-AT. Besides, because of the existence of more hydrogen bonds and bulky group by virtue of the introduction of D -5-AT, the mechanical properties of modified EP were strengthened as well. This work offered a promising method to meet the ever-increasing requirement of multi-functionality of epoxy resins. [ABSTRACT FROM AUTHOR]

• Co-based metal-organic framework with phosphonate and triazole structures (PN-MOF) was synthesized. • PN-MOF significantly improved the flame retardancy and smoke suppression of epoxy resin. • PN-MOF functioned both in condensed and gaseous phases. • PN-MOF exhibited positive effects on the glass transition temperature and mechanical properties. A phosphonate and triazole containing binary carboxylic acid ligand was synthesized via azide-alkyne "click" reaction, which was further coordinated with cobalt nodes to form metal-organic framework (MOF) containing two important fire retardant elements, phosphorus and nitrogen (PN-MOF). With the loading of 6 wt% PN-MOF in epoxy resin (EP), the peak heat release rate, average heat release rate, total heat release, and total smoke production of EP/PN-MOF composites dramatically decreased by 44.6%, 52.9%, 44.0% and 36.2%, respectively. Meanwhile, the limiting oxygen index increased from 24.3% to 29.8%. Thanks to the excellent catalytic activity of PN-MOF in carbonation and oxidation, the release of toxic gasses from the composites was significantly reduced, particularly, the production of CO was decreased by 48% in comparison with neat EP. In addition, the glass transition temperature and modulus of EP/PN-MOF composites were increased, suggesting a strong interfacial interaction between PN-MOF and EP matrix. Overall, this research provides an efficient strategy for the preparation of MOF-type flame retardant to simultaneously enhance the flame retardancy and physical properties of polymeric materials. [ABSTRACT FROM AUTHOR]

• A novel flame retardant with strawberry-like architecture was synthesized. • The charring catalytic effect of Ni(OH) 2 remarkably improved the fire safety of EP. • PZS@PDA@Ni(OH) 2 promoted completely combustion of EP and reduced the release of CO. • PZS@PDA@Ni(OH) 2 -EP showed higher glass transition temperature. Organic-inorganic hybrid materials have received widespread attention because they combine the excellent characteristics of organic polymers and inorganic materials. In this work, a nanohybrid flame retardant PZS@PDA@Ni(OH) 2 with strawberry-like architecture is prepared via the coating of biomimetic polydopamine (PDA) on polyphosphazene microspheres (PZS), followed by the self-assembly of Ni(OH) 2. The effects of PZS@PDA@Ni(OH) 2 on combustion behavior and smoke release of epoxy resin (EP) are characterized by cone calorimetry test (CCT), Thermogravimetric analysis-infrared spectrometry (TG-IR) and Raman tests. The results show that EP composites with 5 wt% PZS@PDA@Ni(OH) 2 give rise to 69.8% reduction in peak heat release rate (pk-HRR) and possess the limiting oxygen index (LOI) of 31.8%, achieving UL-94 V-0 rating. Besides, owing to the synergistic effect of phosphorus-nitrogen and catalytic charring effect of Ni(OH) 2 nanoparticles, the char residual of EP composites exhibits compact and dense structure, which is responsible for the remarkable flame retardancy. Meanwhile, Ni(OH) 2 nanoparticles play a catalytic role in conversion of flammable gases, and the carbon monoxide production (COP) of EP composites with 5 wt% PZS@PDA@Ni(OH) 2 is reduced by 58.3%. As a highly efficient flame retardant, PZS@PDA@Ni(OH) 2 has promising potential in reducing the fire hazards of EP composites. [ABSTRACT FROM AUTHOR]

• A phosphaphenanthrene/benzimidazolone-containing flame retardant (POBDBI) was synthesized successfully. • POBDBI imparted excellent flame retardancy and smoke suppression to EP. • POBDBI exerted flame-retardant effect both in condensed phase and gaseous phase. A novel flame retardant POBDBI was generated by the reaction of p-dibenzaldehyde, 5-amino-2-benzimidazolinone and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and employed to epoxy resin. The structure of POBDBI was measured by FT-IR and NMR tests. Then flame-retardant EP was fabricated by using POBDBI as a flame-retardant. The thermal stability, flame-retardant performance and fire behavior were investigated by a serious of comprehensive instruments. Combustion tests show the flame-retardant performance of composite materials has been significantly improved. For example, the EP/POBDBI-1.0 with the phosphorus content of 1.0% accorded a V-0 rating and its limiting oxygen index (LOI) value increased to 36.5%. Besides, total smoke production (TSP), peak heat release rate (PHRR) and total heat release (THR) of EP/POBDBI-1.0 dropped significantly, and the corresponding values were decreased by 48.4%, 48.9% and 8.7%, respectively. At the same time, the composition, morphology of chars and gaseous products of POBDBI were studied by X-ray photoelectron spectroscopy (XPS), FT-IR, scanning electron microscope (SEM) and Py-GC/MS. These results presented that POBDBI could not only exerted free radical capture effect, but also enhanced the density of char residue. [ABSTRACT FROM AUTHOR]

A novel phosphorus-nitrogen flame retardant named as melamine phenyl phosphate (MAPPO) was synthesized successfully via the neutralization reaction between phenylphosphonic acid (PPOA) and melamine (MA). The chemical structure of MAPPO was characterized by Fourier transform infrared spectra (FT-IR), nuclear magnetic resonance (NMR) and element analysis (EA). MAPPO was introduced into epoxy resin by blending to improve the flame retardancy. Flame retardancy and combustion behavior of EP/MAPPO were investigated by limiting oxygen index (LOI) test, vertical burning (UL-94) test and cone calorimeter test. UL-94 and LOI tests results showed EP containing 18 wt% MAPPO passed the UL-94 V-0 rating and got a high LOI value of 33%. In the cone calorimeter test, compared with that of EP, the values of peak of heat release rate (HRR), total heat release (THR), peak of smoke production rate (PSPR) and total smoke production (TSP) of modified EP were reduced by 58.7%, 40%, 49% and 61.6%, respectively. By analyzing the volatile pyrolysis products of MAPPO, it was known that MAPPO mainly produced CO 2 , NH 3 , H 2 O and other nitrogen-containing compounds, which diluted the concentration of fuel gases and oxygen during combustion. Meanwhile, the char residue of EP/MAPPO system after combustion was also analyzed by scanning electron microscope (SEM), FT-IR and Raman tests, and the results showed MAPPO was able to promote the crosslinking of EP leading to the formation of compact char layer containing P–O–C, P O and C C, etc. In a word, the enhancement in flame retardancy was attributed to both dilution effect of non-combustible gases and barrier effect of compact char. • A novel organic intumescent flame retardant (MAPPO) was synthesized successfully. • MAPPO greatly enhanced the flame retardancy and smoke suppression of EP. • MAPPO mainly played a flame-retardant role in condense phase. [ABSTRACT FROM AUTHOR]