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One of the current challenges in the development of flame retardants is the preparation of an environmentally friendly multi-element synergistic flame retardant to improve the flame retardancy, mechanical performance, and thermal performance of composites. This study synthesized an organic flame retardant (APH) using (3-aminopropyl) triethoxysilane (KH-550), 1,4-phthalaadehyde, 1,5-diaminonaphthalene, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as raw materials, through the Kabachnik-Fields reaction. Adding APH to epoxy resin (EP) composites could greatly improve their flame retardancy. For instance, UL-94 with 4 wt% APH/EP reached the V-0 rating and had an LOI as high as 31.2%. Additionally, the peak heat release rate (PHRR), average heat release rate (AvHRR), total heat release (THR), and total smoke produced (TSP) of 4% APH/EP were 34.1%, 31.8%, 15.2%, and 38.4% lower than EP, respectively. The addition of APH improved the mechanical performance and thermal performance of the composites. After adding 1% APH, the impact strength increased by 15.0%, which was attributed to the good compatibility between APH and EP. The TG and DSC analyses revealed that the APH/EP composites that incorporated rigid naphthalene ring groups had higher glass transition temperatures (Tg) and a higher amount of char residue (C700). The pyrolysis products of APH/EP were systematically investigated, and the results revealed that flame retardancy of APH was realized by the condensed-phase mechanism. APH has good compatibility with EP, excellent thermal performance, enhanced mechanical performance and rational flame retardancy, and the combustion products of the as-prepared composites complied with the green and environmental protection standards which are also broadly applied in industry. [ABSTRACT FROM AUTHOR]

[Display omitted] • A phosphorus-containing benzotriazole flame retardant PDI was successfully synthesized. • EP/PDI had demonstrated excellent smoke and heat suppression performance. • PDI had enhanced and toughened EP. The preparation of flame retardant, strong yet tough, and transparent epoxy resin (EP) composites faces significant challenge. In this study, a phosphorus-containing benzotriazole flame retardant PDI was successfully synthesized. It was important to highlight that the EP/PDI-11 % achieved a limiting oxygen index (LOI) of 32 % and was classified as UL-94V-0 rating. Furthermore, it exhibited a significant reduction in both total smoke production (TSP) and peak heat release rate (pHRR), which decreased by 64.1 % and 46.9 % respectively when compared to EP. Meanwhile, PDI simultaneously enhanced the mechanical strength and toughness of EP, and adding 5 wt% PDI resulted in a 27.2 % improvement in tensile strength, a 53.3 % increase in elongation at break and a 91.4 % increase in impact strength for EP-5 %. Notably, PDI had the ability to promote curing, and the curing peak temperature of EP was advanced by about 20 ℃. In addition, PDI enhanced the insulation and UV resistance properties of EP/PDI, and the high transparency of EP/PDI composites also maintained. [ABSTRACT FROM AUTHOR]

The intumescence, compactness, and strength of char are the key points to the intumescent flame retardant system. However, the char residues of flame retardant polymers rarely exhibit all three characteristics, especially strength. Herein, a novel Cu2+-doped intumescent flame retardant (Cu–CHP) was prepared without producing any waste. When Cu–CHP was exposed at a high temperature (∼1400 °C), it can rapidly expand and carbonize to form dense char. Surprisingly, the intumescent char residue of Cu–CHP can hold up more than 2000 times its own weight. Benefitting from the excellent intumescent charring capacity of Cu–CHP, the resultant EP/Cu–CHP 18% composite can withstand around 600 s penetrating of butane flame (∼1400 °C) because of strong dense char protection, and only 0.9 wt% Cu2+ content resulted in the limiting oxygen index (LOI) of EP/Cu–CHP 18% increases to 31% and the vertical burning (UL-94) reaches V-0 rating. Additionally, its peak heat release rate, total smoke production, and fire growth rate are significantly reduced by 70%, 53%, and 75%, respectively, compared with neat epoxy resin. Especially, the smoke density of EP/Cu–CHP 18% was dramatically dropped by more than 68%. Because a Cu2+-doped intumescent, compact, and strong char residue was produced during burning. This work provides a new strategy to impart excellent flame retardancy and smoke suppression to highly flammable polymers by building metal-doped strong intumescent char residues. [Display omitted] • Cu2+-doped flame retardant was prepared without producing any wastes. • Cu2+-doped intumescent, compact, and strong char residue was produced. • Excellent flame retardancy and smoke suppression were imparted to epoxy resin. • The intumescent flame retardant mechanism was proposed. [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]

• 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]

Epoxy resin (EP) suffers from inherent flammability, many efforts had been made to address this issue. In this work, melamine hydroxy ethylidene diphosphonate wrapped montmorillonite (Mt@MHEDP) was successfully prepared through in situ fabrication to endow EP with lower fire hazards. The prepared Mt@MHEDP was well characterized by XRD, FTIR and SEM-EDS, a series of EP/Mt@MHEDP composites were prepared. The fire performance and thermal stability of EP composites were evaluated by LOI, cone calorimeter test and TGA. The flame-retardant mechanism was investigated by SEM and TG-IR. Due to the presence of MHEDP particles on Mt, the prepared Mt@MHEDP was dispersed uniformly in the EP matrix. From cone test, peak heat release rate (p-HRR) and flame growth index (FGI) of EP composites were reduced by 31.7% and 38.6%, respectively, with the addition of 8 wt% Mt@MHEDP. Moreover, the peak smoke production rate (p-SPR) and peak CO production rate were decreased by 30.9% and 40.4%, respectively. From TG-IR, the release of toxic CO and organic volatiles during the decomposition was decreased significantly, implying the lower toxicity and higher fire safety. The enhanced flame retardancy, suppressed smoke production and lower toxicity can be attributed to the synergetic effect of Mt and MHEDP. Unlabelled Image • Mt was successfully wrapped by melamine salt through in situ fabrication. • The release of toxic gases during the combustion was significantly suppressed. • The compatibility between modified Mt and EP was improved. • Synergetic effect between Mt and melamine salt contribute to the high fire safety. [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]