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This article discusses the effect of UV-C radiation on two types of cured polymer resins, epoxy and polyester, intended for use in disinfection chambers. The exposure of the samples to UV-C rays lasted 168 h. Our evaluation covered two aspects: the effect of UV-C rays on the flammability and flame retardancy of the resins, and the effect of UV-C rays on the adhesion of the resins to the steel substrate. It was found that the applied halogen and halogen-free organophosphate agents can be used for the tested resins under UV-C conditions (e.g. disinfection chambers), and no negative impact of UV-C radiation on the performance of these flame retardants was found. The use of the tested types of resins in the form of thin coatings on a steel substrate is feasible in disinfection chambers under UV-C radiation conditions, as the obtained results indicate that the radiation did not affect the adhesion of the coating. The visible effect of UV-C radiation on both the tested resins was discoloration, giving yellow and brown colors. Our results suggest that further studies, probably involving longer UV-C exposure, would be advisable. [ABSTRACT FROM AUTHOR]

In this study, thiol-functionalized ladder-like polysesquioxanes end-capped with methyl and phenyl groups were synthesized via a simple sol-gel method and characterized through gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA). Additionally, epoxy blends of different formulations were prepared. Their structural, flame-retardant, thermal, and mechanical properties, as well as volatile organic compound (VOC) emissions, were determined using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), TGA, scanning electron microscopy (SEM), limiting oxygen index (LOI), cone calorimetry, and a VOC analyzer. Compared to epoxy blends with flame retardants containing elemental phosphorus alone, those with flame retardants containing elemental phosphorus combined with silicon and sulfur exhibited superior thermal, flame-retardant, and mechanical properties with low VOC emissions. SEM of the residual char revealed a dense and continuous morphology without holes or cracks. In particular, LOI values for the combustion of methyl and phenyl end-capped polysilsesquioxane mixtures were 32.3 and 33.7, respectively, compared to 28.4% of the LOI value for the blends containing only phosphorus compounds. The silicon–sulfur–phosphorus-containing blends displayed reduced flammability concerning the blends using a flame retardant containing only phosphorus. This reflects the cooperative effects of various flame-retardant moieties. [ABSTRACT FROM AUTHOR]

Transparency is an important property for polymer flame retardants, especially epoxy resin (EP) flame retardants, and flame-retardant epoxy resins that maintain a high transparency and low chromatic aberration play important roles in the optical, lighting, and energy industries. Herein, a DOPO-based flame retardant 6,6′-((sulfonylbis(4,1-phenylene))bis(oxy))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) with a high transparency and low chromatic aberration was prepared via the classical Atherton–Todd reaction and named SBPDOPO. Its chemical structure was characterized with Fourier IR spectroscopy and NMR spectroscopy. An EP loaded with 7 wt% SBPDOPO passed the UL-94 V-0 rating with an LOI value of 32.1%, and the peak heat release rate, total heat release, and total smoke production were reduced by 34.1%, 31.6%, and 27.7%, respectively, compared with those of pure EP. In addition, the addition of SBPDOPO improved the thermal stability, residual mass, and glass transition temperature of the EP. On this basis, the EP containing 7 wt% SBPDOPO maintained a high transparency and low color aberration, with a transmittance of 94% relative to that of pure EP and a color aberration ΔE of 1.63. Finally, the flame-retardant mechanism of SBPDOPO was analyzed, which demonstrated that it exerted both gas-phase and condensed-phase flame-retardant effects, and that SBPDOPO/EP had high potential for application scenarios in which both flame retardancy and transparency are needed. SBPDOPO/EP has great potential for applications requiring both flame retardancy and transparency. [ABSTRACT FROM AUTHOR]

Paraffin is a potential thermal energy storage material, but leakage and flammability are the two major problems affecting its storage and safe use. Here, a novel flame retarded paraffin/epoxy resin composite was developed by using paraffin, epoxy resin and hollow metal organic framework (W‐UiO66‐PPA) as thermal energy storage material, supporting material and flame retardant, respectively. The thermal energy storage and flame retardancy performances were examined with differential scanning calorimetry, vertical burning, limiting oxygen index and cone calorimeter tests. The results show that the paraffin/epoxy resin retains intact without leakage when the content of paraffin reaches 40 wt%, and this material exhibits high melting latent heat and remarkable thermal recycling property. In addition, the flame retarded paraffin/epoxy resin shows excellent flame retardancy, which is attributed to the following three aspects: (1) the hollow structure with open vertices of W‐UiO66 is capable of absorbing and collecting the combustible gasses produced by the combustion of epoxy resin; (2) the Zr and W elements of W‐UiO66 can facilitate catalytic charring and form a dense char layer; (3) phosphorous‐containing free radicals are able to capture OH· and O· free radicals during the combustion of paraffin and epoxy resin, thus interrupting the combustion chain reaction. On the whole, the flame retarded paraffin/EP possesses excellent thermal energy storage, thermal recycling, and flame retardancy properties. Our work provides a fantastic inspiration for the rational design of other flame retarded form‐stable phase change materials. [ABSTRACT FROM AUTHOR]

To alleviate the fire hazard of epoxy resin (EP), an efficient flame retardant (ADM) containing phosphophenanthrene and thiazole groups is synthesized and used as co-curing agent for 4,4′-diaminodiphenyl methane to prepare EP/ADM composites. EP/4 mass% ADM composites with phosphorus content of only 0.25 mass% reach UL-94 V-0 rating and the limiting oxygen index value is high to 35.8%. The results reveal that the peak heat release rate, total smoke production, and total heat release of EP/4 mass% ADM composites are reduced by 24%, 14.4% and 16.7%, respectively, in comparison with those of pure EP. The improvement in flame retardancy is mainly attributed to the decomposition of DOPO which produces HPO• and PO• to capture the reactive radicals in the gaseous phase. The thiazole group releases hindered amine groups and inactive gas with a dilution effect in the gaseous phase thus further enhancing the effect of the phosphophenanthrene group. Besides, ADM helps to increase the glass transition temperature (Tg) of EP/ADM composites, which is 176 °C for EP/4 mass% ADM composites, which is higher than the value (172 °C) of EP. [ABSTRACT FROM AUTHOR]

Developing highly efficient and multifunctional epoxy resins (EPs) that overcome the shortcomings of flammability and brittleness is crucial for pursuing sustainable and safe application but remains a huge challenge. In this paper, a novel biomass-containing intumescent flame retardant containing a rigid–flexible and multi-siloxane bridge structure (DPB) was synthesized using siloxane; 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO); and biomass vanillin. DPB could facilitate the formation of a carbon residual with an intumescent structure, which effectively blocked the propagation of heat and oxygen. As a result, the peak heat release rate (pHRR) and total heat release (THR) of DPB/EP-7.5 decreased by 38.8% and 45.0%, respectively. In terms of mechanical properties, the tensile and flexural elongations at break of DPB/EP-7.5 increased by 77.2% and 105.3%, respectively. Impressively, DPB/EP-7.5 had excellent dielectric properties, with a dielectric constant of 2.5–2.9. This was due to the Si-O bonds (multi-siloxane bridges) contained in DPB/EP, which can quench the polarization behavior of the hydroxyl group. This paper provides a facile strategy for the preparation of multifunctional EP, which will pave the way for the promotion and application of EP in the high-end field. [ABSTRACT FROM AUTHOR]

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]

This study presents the preparation and flammability characteristics of polymeric composites based on the epoxy resin Epidian® 601. The triethylenetetramine (TETA) and commercial curing agents based on polyamines (IDA and PAC) were used as crosslinking compounds. Moreover, two flame retardant compounds were added to this composition, the commercial Fire Retardant (FR) and triphenyl phosphate (TP). The chemical structure of the composites and the course of curing processes were confirmed by the ATR/FT-IR (Attenuated Total Reflection–Fourier Transform Infrared) analysis. The influence of different amounts of FR or TP on the flammability and thermal resistance was discussed in detail. After the flammability test the samples were also studied to assess their thermal destruction. In addition, the composites were subjected to the swelling tests, solvent resistance, and microscopic observations. The DSC curves revealed that all materials were characterized by good thermal properties. All materials were temperature resistant up to 300 °C. Furthermore, the measurements of the hardness of the composite demonstrated that the material EP601 + TETA + 10 %FR is the hardest. The addition of FR and RP influenced the flammability of the composites increasing the thermal resistance. The ageing tests in methanol, acetone, hydrochloric acid, and potassium hydroxide were also carried out. [ABSTRACT FROM AUTHOR]

A flame retardant precursor named DTDO, which contains phosphorus, nitrogen and silicon, was synthesized and grafted to graphene oxide (GO) to prepare functional graphene oxide (FGO), which was further applied to prepare a crosslinked organic/inorganic hybrid intumescent flame retardant (FGOS) through in situ sol gel process. 3 wt% loading of FGOS can reduce the combustion parameters of inflammable epoxy resin (EP) obviously, such as the heat release rate (28.1% reduction), smoke production rate (19.6% reduction), and average mass loss rate (61.2% reduction). The EP/FGOS-3 sample shows a LOI value of 29.1% and passes UL-94 and V-0 flammability rating, and the char residue increased from 0.3% to 8.5%. The results indicates a significant enhanced flame retardancy of EP, phosphorus, nitrogen, silicon, and GO in FGOS promoted the forming of a compact and porous char layer, thus to prevent further combustion and improve the flame retardancy of EP. [ABSTRACT FROM AUTHOR]

To overcome the high flammability and brittleness of epoxy resins without sacrificing their glass transition temperature (Tg) and mechanical properties, three epoxy-terminated hyperbranched flame retardants (EHBFRs) with a rigid central core and different branches, named EHBFR-HB, EHBFR-HCM, and EHBFR-HBM, were synthesized. After chemical structure characterization, the synthesized EHBFRs were introduced into the diglycidyl ether of bisphenol A (DGEBA) and cured with 4, 4-diaminodiphenylmethane (DDM). The compatibility, thermal stability, mechanical properties, and flame retardancy of the resultant resins were evaluated. Results showed that all three EHBFRs could significantly improve the fire safety of cured resins, and 30 wt. % of EHBFRs (less than 1.0 wt. % phosphorus content) endowed cured DGEBA with a UL-94 V-0 rating. In addition, the increased rigidity of branches in EHBFRs could increase the flexural strength and modulus of cured resins, and the branches with appropriate rigidity were also beneficial for improving their room temperature impact strength and Tg. [ABSTRACT FROM AUTHOR]

[Display omitted] • An organophosphinic acid salt flame retardant DPM was facilely synthesized. • DPM promoted the curing process of epoxy resins. • The low addition of DPM resulted in excellent flame retardancy. • The addition of DPM increased both strength and toughness. Achieving flame retardancy in epoxy resin (EP) while preserving its essential properties, including strength, toughness, and thermal stability, offers considerable challenges in the application of flame retardant EP modifications. In this study, we were successful in synthesizing a novel ionic-based flame retardant, organophosphinic acid salt (DPM), using a simple ionic reaction. DPM possesses a unique structure consisting of rigid groups and flexible chain segments. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) techniques were used to characterise the structure of DPM. Incorporating DPM into the EP yielded remarkable improvements in mechanical properties, reduced fire hazard, enhanced processability, a lower curing temperature, and good thermal stability. The EP/DPM-7.5 composites demonstrated excellent flame retardancy by effortlessly achieving a V-0 rating in vertical combustion (UL-94) testing, while an impressive limited oxygen index (LOI) value of 36.3% was attained, a substantial 42.4% enhancement compared to the EP. Moreover, cone calorimeter (CC) tests revealed that EP/DPM-7.5 exhibited a 41.7% decrease in peak heat release rate (PHRR), a decreased fire growth rate index (FIGRA), and an increased fire performance index (FPI). Additionally, the tensile strength and flexural strength of EP/DPM-7.5 improved by 26.0% and 23.7%, respectively. Comparatively, EP/DPM-5 maintained the glass transition temperature (T g) and thermal stability of the EP while significantly enhancing the impact strength by 85.4%. The newly developed flame retardant, DPM, exhibited excellent comprehensive performance and fire safety characteristics, thereby demonstrating the significant potential for practical applications in flame retardant EP systems. [ABSTRACT FROM AUTHOR]

A unique mono-component intumescent flame retardant, named PPy-MAPP, of which melamine-coated ammonium polyphosphate (MAPP) was microencapsulated by polypyrrole (PPy), was synthesized and carefully characterized. The obtained PPy-MAPP was applied to epoxy resin (EP) for obtaining flame-retarded EP composites. The results show that PPy-MAPP imparts better flame retardancy and smoke suppression properties to EP compared to the same addition of MAPP. The EP composite with 15 wt% PPy-MAPP easily passes the UL94 V-0 rating and achieves an LOI value of 42.4%, accompanied by a 61.9% reduction in total heat release (THR) and a 73.9% reduction in total smoke production (TSP) when compared with pure EP. The char residue analysis shows that PPy-MAPP can promote a generation of more phosphorus-rich structures in the condensed phase that improve the integrity and intumescence of char against fire. The mechanical test indicates that PPy-MAPP has a less negative effect on the tensile strength and elastic modulus of epoxy resin due to the good compatibility between PPy-MAPP and the EP matrix, as supported by differential scanning calorimetry (DSC) analyses. In this paper, these attractive features of PPy-MAPP provide a new strategy to prepare satisfactory flame retardant and super flame retarding EP composites. [ABSTRACT FROM AUTHOR]

A novel bio-based flame retardant designated AVD has been synthesized in a one-pot process via the reaction of 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO), vanillin (VN), and 2- aminobenzothiazole (ABT). The structure of AVD was confirmed using Fourier transform infrared spectroscopy (FTIR), and 1H and 31P nuclear magnetic resonance spectroscopy (NMR). The curing process, thermal stability, flame retardancy, and mechanical properties of the epoxy resin (EP) modified with AVD have been investigated comprehensively. The extent of curing, the glass transition temperature and the crosslinking density of the blend decreased gradually with increasing AVD content. The thermogravimetric analysis (TGA) was used to demonstrate that the presence of AVD reduced the thermal decomposition rate for EP and enhanced the formation of carbon residue during resin decomposition. A blend of 7.5 wt% AVD (0.52% phosphorus) displays a UL-94V-0 rating and a LOI of 31.1%. Reduction of the peak heat release rate, total heat release rate and total smoke production was 41.26%, 35.70%, and 24.03%, respectively, as compared to the values for pure EP. The improved flame retardancy of the flame retardant epoxy (FREP) may be attributed to the formation of a compact and continuous protective char layer into the condensed phase as well as the release of non-combustible gases and phosphorus-containing radicals from the decomposition of AVD in the gas phase. AVD is a new and efficient biobased flame retardant for epoxy with great prospects for industrial applications. [ABSTRACT FROM AUTHOR]

We successfully prepared a highly effective flame-retardant additive called hsalbenzoguanamine phosphaphenanthrene (HDPD) through salicylaldehyde and nitrogen-rich benzoguanamine. The introduction of HDPD into epoxy resin (EP) sharply enhanced the flame retardancy of EP/HDPD thermosets. The introduction of 6 wt% HDPD into EP succeeded in reaching the V-0 rating. Limited oxygen index results revealed the high flame-retarding performance of HDPD. Cone calorimeter test data revealed that heat and smoke released from EP/6 wt% HDPD thermoset were significantly restrained. In addition, EP/6 wt% HDPD thermoset demonstrated excellent transmittance and mechanical strength. The transmittance of EP/6 wt% HDPD was assessed from 520 to 800 nm. The results showed that transmittance of EP/6 wt% HDPD were nearly 90% of the control group. [ABSTRACT FROM AUTHOR]

• 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]

• P-derived flame retardants were covalently added to EP using diisocyanate as bridge. • Mechanical properties of EP were obviously enhanced due to the formed PU network. • P-derived flame retardants conferred flame retardant properties to EP. The high brittleness and flammability issues of epoxy resins (EPs) seriously limit their high-performance applications in industries. However, most of the current research has been failing to simultaneously enhance both toughness and flame retardancy of EP by a facile method. In this work, three phosphaphenanthrene derivatives (DOPO, ODOPM and DOPA) were applied to prepare intrinsic flame-retardant epoxy resins by using diphenylmethane-4,4′-diisocyanate (MDI) as a bridge. The as-prepared EP/MDI/DOPO, EP/MDI/ODOPM, and EP/MDI/DOPA exhibited obviously enhanced flame retardancy and mechanical performance relative to EP. As the P content reached 1 wt%, the limiting oxygen indexes (LOIs) and vertical combustion (UL-94) levels of EP/MDI/DOPO, EP/MDI/ODOPM and EP/MDI/DOPA reached 28.9 %, 31.2 %, and 33.4 %, and V-1, V-0, and V-0. The impact strengths of EP/MDI/ODOPM and EP/MDI/DOPA containing 0.75 wt % of phosphorus were higher than that of EP by 209.3 % and 212.4 %, respectively, due to the covalent linkage between the phosphaphenanthrene-derived groups, MDI, and polymer network. Thereby, a simple method is revealed in this work to improve both fire retardance and toughness of EP, which facilitates its high-performance development. [ABSTRACT FROM AUTHOR]

Achieving a balance between flame retardancy and overall performance in epoxy resin (EP) continues to be a significant challenge. In this study, a new multi-DOPO-based reactive flame retardant (DZH) was synthesized successfully using a simple one-pot method and employed as a co-curing agent with DDM. The results indicated that the inclusion of DZH decreased the activation energy of the curing reaction system. Furthermore, the presence of DZH, with its remarkable charring ability, enhanced the formation of char residues under high-temperature conditions. Notably, the flame retardancy and mechanical properties of the EP/DZH system were significantly enhanced at certain additions. When added at only 5 wt% (phosphorus content: 0.525 wt%), the LOI value of the EP/DZH-5 increased from 24.4 % to 35.3 % for the EP matrix and achieved a V-0 rating in accordance with UL-94. Meanwhile, EP/DZH-5 exhibited a reduction of 44.1 % in pHRR and 24.3 % in SPR. The superior flame retardancy of the EP/DZH system was attributed to the dual flame-retardant mechanism exhibited in both the gaseous and condensed phases. In addition, the abundant presence of rigid phosphaphenanthrene groups and π-π interactions between benzene rings led to an improvement in the tensile strength and tensile modulus, which rose to 91.0 MPa and 1.76 GPa, respectively, from 79.5 MPa and 1.26 GPa of EP in the case of EP/DZH-3. The utilization of this flame retardant, based on multi-DOPO, offers a promising approach for the development of high-performance epoxy resins. [Display omitted] • A one-pot method successfully synthesized a flame retardant with ample aromatic and reactive functional groups. • DZH accelerated the cross-linking reaction of EP system. • A low addition amount of DZH provided excellent flame retardancy and mechanical properties. • The biphasic flame-retardant mechanism of DZH was revealed in detail. [ABSTRACT FROM AUTHOR]

With the specialization and diversification of the use environment of composite products, composite materials should have good comprehensive properties. Abiding by this target, we successfully prepared a transparent epoxy resin (EP) composite with flame retardancy, low smoke, enhanced toughness, high glass transition temperature by blending the flame-retardant POI synthesized in this work. POI was synthesized from phosphophenanthrene, vanillin and histidine, and the combination of these three raw meticulously selected endowed POI molecule with excellent versatility. EP composite modified with 10 wt% POI (EP/POI-10) obtained a limiting oxygen index (LOI) of 30.5% and received the V-0 grade (UL-94). The reduction of total smoke production by 78.1% via cone calorimeter tests was obtained. The impact strength of EP/POI-7 increased by 48.2% due to the energy dissipation of cracks from POI. The comprehensive analysis of the dual-phase revealed that the improvement of flame retardance was attributed to the joint action of the gaseous phosphorus free radicals quenching and the protecting of condensed coke. Moreover, EP/POI obtained high glass transition temperature as well as good transparency. [Display omitted] • A bio-based flame retardant molecule POI was synthesized. • High-performance composites of EP/POI with high T g , toughened and transparent were prepared. • The EP/POI showed a remarkable smoke suppression effect with a 78.1% reduction in TSP. [ABSTRACT FROM AUTHOR]

An inorganic–organic nanohybrid flame retardant, HNT@CS@Fe3O4, is prepared by Halloysite nanotubes (HNT) as nanotemplate, chitosan (CS) as char-forming agent and ferroferric oxide (Fe3O 4) playing in a catalytic role, aiming to endow enhanced flame-retardant performance of its nanohybrid. Results show that HNT@CS@Fe3O4 nanohybrids have a corn-like structure and can significantly improve the flame retardancy and thermal stability of epoxy resin (EP). Especially, the initial thermal degradation temperature of EP/HNT@CS@Fe3O4 is significantly improved by 2 4 ∘ C relative to pure EP, and the residual carbon yield under air atmosphere is 8.8 wt.%, which is significantly higher than other EP composites, indicating a higher thermal stability is offered by the as-prepared nanohybrid. The limiting oxygen index of EP/10HNT@CS@Fe3O4 is 31.3%, which is 10.2% higher than that of pure EP. Meanwhile, the HNT@CS@Fe3O4 nanofiller reduces the peak heat release rate, CO production and peak smoke production release of EP nanocomposite by 32.0%, 44.0% and 33.0% in a cone calorimeter test, respectively. This is because the HNT-based composite can form a three-dimensional network structure into the EP matrix to inhibit heat release and diffusion of flammable moieties upon burning of EP. In the meantime, the incorporated Fe3O4 nanoparticle can in situ catalyze the charring of CS and EP matrix on the surface of HNT during the combustion process, which also contributes to the significantly increased fire safety of EP. An inorganic–organic nanohybrid flame retardant with corn-like structure, HNT@CS@Fe3O4, is successfully prepared by halloysite nanotubes (HNT) as nano-template, chitosan (CS) as char-forming agent and ferroferric oxide (Fe3O4) playing a catalytic role. HNT@CS@Fe3O4 nanohybrids significantly improve the flame retardancy of epoxy resin (EP). Excellent flame retardancy is attributed to in-situ charring of CS and EP on the surface of HNT which forms dense and continuous protective layers against the fire. [ABSTRACT FROM AUTHOR]

A high-efficiency flame retardant composed of phosphaphenanthrene, benzothiazole and imidazole groups (PBI) was synthesized and served as flame retardant co-curing agent to reduce the fire hazard of epoxy resin (EP). The chemical structure of PBI was characterized by Fourier transform infrared spectroscopy (FTIR), high-resolution mass spectroscopy (HR-MS), 1H and 31P nuclear magnetic resonance (NMR). The curing behavior, thermal stability and flame retardant properties of the prepared EP systems were investigated. The curing behavior study disclosed that PBI accelerated the crosslinking reaction of EP and was chemically bonded with EP matrix to obtain intrinsic flame retardant thermoset. The resulting EP thermosets showed only slight decrease in glass transition temperature (T g). The thermogravimetric analysis (TGA) results indicated both the catalytic decomposition and catalytic charring effects of PBI demonstrated by decreased thermal stability and enhanced charring capability of EP/DDS/PBI thermosets. The combustion test results showed remarkable improvement in the flame retardant properties of EP/DDS/PBI thermosets. When the phosphorus content was only 0.75 wt%, EP/DDS/PBI-0.75 thermoset achieved a limiting oxygen index (LOI) value of 34.6% and passed UL94 V-0 rating. Moreover, the peak of heat release rate (pk-HRR), average of heat release rate (av-HRR) and total heat release (THR) values were decreased by 48.7%, 31.1% and 28.3%, respectively, in comparison with those of the EP/DDS thermoset. The flame retardant effect of PBI on EP was attributed to the catalytic charring effect to form protective char layer in condensed phase and release of free radicals with quenching effect and nonflammable gases with diluting effect in gaseous phase. • A DOPO based reactive flame retardant (PBI) constructed by multiple heteroaromatic groups was successfully synthesized. • PBI accelerated the crosslinking reaction of EP. • Blowing-out effect was observed for EP/DDS/PBI thermosets. • PBI exhibited bi-phase flame retardant effect on EP. [ABSTRACT FROM AUTHOR]

A novel flame retardant poly (piperazine phosphaphenanthrene) (DOPMPA) was successfully synthesized via two step reactions using DOPO and piperazine as reactants and characterized by infrared spectrometry (FT-IR), nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The DOPMPA was used to enhance flame retardancy of epoxy resin (EP). When the addition content of DOPMPA in EP was 13 wt%, the EP/DOPMPA sample passed a UL-94 V-0 rating and possessed a high limited oxygen index (LOI) value of 34%. Cone calorimeter tests showed that the release of heat and smoke for EP/DOPMPA samples decreased significantly compared with neat EP. Moreover, the reduction of average effective heat of combustion (av-EHC) value with the increased addition of DOPMPA confirmed that DOPMPA had a flame-inhibition activity in gashouse phase. The analysis of the char residues after cone calorimeter test exhibited that DOPMPA promoted the swell of the sample and compacted char layer. Furthermore, the pyrolysis analysis of DOPMPA was investigated by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), which illustrated that DOPMPA decomposed into many fragments with quenching effect toward combustion. • A novel flame retardant (DOPMPA) containing DOPO and piperazine structure was synthesized. • DOPMPA endowed EP with excellent fire safety. • DOPMPA played a flame-retardant role in both condensed and gaseous phases. [ABSTRACT FROM AUTHOR]

It is well known that the high loading of flame retardants is needed to improve the flame-retardant property of epoxy resins accompanied with the serious deterioration of their thermal and mechanical properties. A novel flame retardant with the high flame-retardant effect, namely 1-(4-hydroxyphenyl)-3-(10-oxido-5H-phenophosphazine-10-yl) pyrrolidine-2,5-dione (DPPA-HPM), was synthesized to solve the problem. The nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry verified the successful synthesis of DPPA-HPM. DPPA-HPM was an efficient flame retardant for epoxy resin. Only 1.5 wt% loading of DPPA-HPM was found to endow the epoxy resin with UL-94 V-0 rating and the high limited oxygen index value of 29.5%. Moreover, the flame-retarded epoxy resin possessed the good comprehensive properties with the maintained glass transition temperature and the improved flexural strength as compared with the control epoxy resin, which exhibits good potential application prospects. • A novel environment-friendly halogen-free flame retardant for epoxy resins, namely DPPA-HPM, was successfully synthesized. • Only 1.5 wt% loading of DPPA-HPM was found to endow epoxy resin with UL-94 V-0 rating and the high LOI value of 29.5%. • Compared with the control epoxy resin, the flame-retarded epoxy resin possessed the good comprehensive properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel phosphorus-containing tertiary amine hardener (DCM) is synthesized. • DCM endows epoxy resin with desired heat resistance and char-forming capacity. • DCM improves the mechanical stiffness, robustness and toughness of epoxy resin. • DCM imparts superior flame retardancy and smoke suppression to epoxy resin. Although current phosphorus (P)-based hardeners endowed epoxy resins (EPs) with intrinsic flame retardancy, their addition usually reduced thermal and mechanical properties. In this work, a novel phosphorus-containing tertiary amine hardener (DCM) was synthesized using diphenylphosphinic chloride and 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), and applied to fabricate high-performance EP/DCM. Introducing P-containing group reduced the reactivity of tertiary amine of DCM, but EP/DCM gelled at 100 °C within 11.3 min, showing modest-temperature curing character. EP/DCM exhibited higher glass-transition temperature (T g) and char yield than virgin EP/DMP-30. Moreover, EP/DCM featured superior mechanical properties, of which the tensile strength, elongation at break and impact strength increased by 61.2%, 72.0% and 198.5%, respectively, relative to those of EP/DMP-30. DCM endowed EP thermosets with remarkable flame retardancy and smoke suppression. The limiting oxygen index (LOI) and UL-94 rating of EP/DCM reached 35.7% and V-0, respectively, with 36.2% and 22.6% reductions in peak heat release rate (PHRR) and peak smoke production rate (PSPR) compared with those of EP/DMP-30. This work pioneers an innovative strategy for creating high-performance EPs with satisfactory heat resistance, fire safety, and mechanical properties by curing with P-containing tertiary amine hardeners. [ABSTRACT FROM AUTHOR]

• Single component phosphamide-based intumescent flame retardant with reactivity to epoxy group was synthesized. • Fire safety of epoxy resin with phosphamide-based intumescent flame retardant was greatly enhanced. • The release of smoke and toxic gases such as CO/CO 2 was remarkably inhibited. • The mechanical property of flame-retardant epoxy resin was maintained to some extent. • The mechanism of phosphamide-based intumescent flame retardant was well investigated. To develop a low flammability and smoke epoxy resin, benzothiazole-based phosphamide (DOP-ABZ) was prepared through the reaction of 2-chloro-5,5-dimethyl-1,3,2-dioxaphosphinane-2-oxide (DOP) and 2-aminobenzothiazole (ABZ). Intumescent flame-retardant (IFR) epoxy thermosets (EP) with different loadings of DOP-ABZ were prepared according to the assigned curing procedure. The thermal stability of IFR-EP decreased as compared to that of EP, but the flame retardancy of IFR-EP were greatly improved. EP/20 wt% DOP-ABZ passed UL-94 V-0 rating and got a high LOI value of 28.3%. Meanwhile, cone calorimeter tests showed that the heat release rate greatly decreased from 1139.7 kW/m2 of EP to 238.9 kW/m2, and the productions of smoke/toxic gases including CO and CO 2 were also remarkably reduced. Furthermore, the mechanical strength of EP/17.5 wt% DOP-ABZ was enhanced to some extent, i.e. tensile strength increased from 71 MPa of EP to 81 MPa, flexural strength from 98 to 119 MPa, and impact strength from 22 to 32 kJ/m2. Finally, the flame-retardant mechanism was disclosed that DOP-ABZ produced phosphorus-containing acids so as to dehydrate and carbonize epoxy macromolecules leading to the formation of graphitized chars. Meanwhile, the nitrogen/sulfur-containing intermediates simultaneously released noncombustible gases to expand the as-formed char, and then interrupt the combustion reaction. [ABSTRACT FROM AUTHOR]

A phosphorus-nitrogen reactive flame retardant curing agent poly-(isophorondiamine spirocyclic pentaerythritol bisphosphonate) (PIPSPB) was synthesized. The chemical structure of the obtained compound was identified by FTIR, 1HNMR, and mass spectroscopies. Different proportions of DDS and PIPSPB were compounded as the curing agents to prepare a series of flame retardant epoxy resins with different phosphorus contents. The curing behavior of E-44/PIPSPB + DDS system was studied by DSC. A series of tests were conducted to characterize E-44/PIPSPB + DDS thermosetting system's performance. The result demonstrates that the residual carbon content of EP/PIPSPB + DDS system is obviously higher than that of EP/DDS system after 500 °C with the increase of phosphorus content in the system, and the heat release rate of the system during combustion is significantly reduced. The generated phosphorus-containing carbon layer is obviously foamed, which shows that the flame retardancy of the system is the result of the combined action of condensed phase and gas phase. When the phosphorus content is 1.77wt%, EP-3 successfully passed UL94 V-0 flammability rating, the LOI value was as high as 29%, the impact strength and tensile strength of it were 6.08KJ/m2 and 49.10MPa respectively, the adhesive strength could reach 13.89 MPa, the system presents a good overall performance. [ABSTRACT FROM AUTHOR]

Abstract: A novel mono-component intumescent flame retardant named pentaerythritol phosphate melamine salt (PPMS)-functionalized expandable graphite (PPMS-EG) was synthesized and carefully characterized by Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance spectroscopy, scanning electron microscopy (SEM)-energy-dispersive X-ray spectrometry, and thermo-gravimetric (TG) analyses. Then, PPMS-EG was incorporated into epoxy resin (EP) to enhance fire safety. The flammability properties of EP composites were investigated by limiting oxygen index (LOI), UL94 vertical burning test, and cone calorimeter test. As expected, PPMS-EG imparts good flame retardancy to epoxy resin, and EP matrix with 20 mass% PPMS-EG passes the UL94 V-0 rating and the LOI value reaches 27.3%. Cone calorimeter test shows that the incorporation of PPMS-EG dramatically reduces the heat release and smoke production of EP, and the peak heat release rate and peak smoke production rate of EP composite with 15 mass% PPMS-EG are reduced by 68.7% and 46.3%, respectively, compared to those of EP. By comparison with either PPMS or expandable graphite, the same addition of PPMS-EG produces higher flame-retardant and smoke suppression efficiencies in EP matrix due to the formation of a more compact and intumescent char layer, as determined from digital photographs and SEM images. TG results show that PPMS-EG significantly enhances the thermal stability and char-forming ability of EP composites. Char residue analysis reveals that PPMS-EG positively contributes to the formation of more phosphorus-rich cross-linking char and aromatic char in the condensed phase, thus exhibiting a more thermally stable char against the release of heat and smoke. Overall, PPMS-EG can be used as a highly efficient mono-component intumescent flame retardant for preparing super flame-retarded EP composites.Graphical abstract: [ABSTRACT FROM AUTHOR]

In this work, five additives were used, namely: (5,6-diphenyl-6H-1,3,4-thiadiazin-2-amine)(Additive I). (5,6-diphenyl-2-[(Z)-(2,4,6-trimethyl-2H-1,3-thiazin-5-yl)diazenyl]-6H-1,3,4-thiadiazine)(Additive II). (5-(1,4-phenylene)bis (1,3,4-thiadiazinol-2-amine)(Additive III). (2,2-(1,4-phenylene)bis(4,5-dihydro-1, thiazole-4-carboxylicacid)(Additive IV). (5,5'-[1,4-phenylene bis(4,5-dihydro-1.3-thiazole-2,4-diyl) bis (1,3,4-thiadiazol-2-amine))(Additive V). The effects of these additives on flammability of some of the thermosetting polymers (unsaturated polyester and epoxy resins), have been studied. Sheets of the specimens (resins with different weight percentages of additives), in dimensions (150X150X3) mm were prepared. Two standard test methods used to measured the flame retardation which are: (ASTM: D-2863) and (ASTM: D-635). Results are obtained from these tests indicated that, additive IV has high efficiency as flame retardant, self-extinguishing (S.E.) at the percentage (0.2 %) for unsaturated polyester resin and the percentage (0.4 %) for epoxy resin. Also self-extinguishing (S.E.) at the percentage (0.4%) for additives II in unsaturated polyester resin and the (0.6%) for additives II in epoxy resin; Additive V show low effect on flammability in both resins. [ABSTRACT FROM AUTHOR]

To simultaneously improve the storage stability of epoxy/imidazole systems and flame retardancy without sacrificing the thermal, mechanical and dielectric properties of thermosets, a novel multifunctional polyetherimide containing benzimidazole and phosphorus (mPI) was synthesized and used as a hardener for diglycidyl ether of bisphenol A (DGEBA). In addition to retaining the effective curing behavior of imidazole, mPI, a macromolecular hardener and flame retardant, could endow the mixture of DGEBA and mPI (EP/mPI) with the long latent period and thermosets with the high performance. The results showed that mPI was unreactive at ambient temperature and underwent the rapid curing reaction at 170 °C that is a little higher than its glass transition temperature (T g) of 164.7 °C, and EP/mPI showed the long thermal latent period of 70 days or more. Meanwhile, the cured EP/mPI attained the UL-94 V-0 rating with the LOI value of 31.2%. Besides, EP/mPI thermoset showed a 42.9 °C, 47.6 °C, 18.2 °C, 135.4% and 60.6% increase in the T g , heat deflection temperature, temperature at 5% mass loss, storage modulus and Young's modulus, respectively, as well as a 3.6% decrease in the dielectric constant at 100 MHz, in comparison with those of the traditional cured DGEBA/benzimidazole (EP/BIM). This work provides a facile strategy to prepare one-pot epoxy/imidazole formulations and flame-retarded epoxy thermosets with high performance by using the well-designed multifunctional polyetherimides as a hardener and flame retardant, which has good application prospects in electronics. [Display omitted] [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]

A novel P/N/S-containing flame retardant DHBAZ was synthesized with 9, 10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, p -hydroxybenzaldehyde and 2-aminothiazole, and used as a co-curing agent for epoxy resin (EP). With the aid of DHBAZ, EP/7.5% DHBAZ passed UL-94 V-0 rating, and owned a LOI value of 31.4%. Besides, DHBAZ also played a positive role in inhibiting the release of heat and the production of smoke. Through non-isothermal DSC tests it revealed that in the presence of DHBAZ, epoxy resin was cured at a lower temperature and showed lower curing-reaction activity energy. DMA analyses indicated that EP/7.5% DHBAZ showed an increased storage modulus, and it had a close glass transition temperature with EP. While, DHBAZ presented a decreased effect on the thermal stability of epoxy resin acquired from TG analyses. Finally, the flame-retardant mechanism studied by TG-FTIR and py-GC/MS deduced that DHBAZ worked in the gaseous phase by producing P , PO and incombustible gases. [ABSTRACT FROM AUTHOR]

[Display omitted] • A cubic metal organic flame retardant with single crystal structure and rich in nitrogen was synthesized by hydrothermal method. • The peak heat release rate of EP composite loaded with 9 phr R1-MOF decreased by 51.3%. • Flame retardant shows high flame retardancy and smoke suppression performance, and significantly reduces the toxicity of EP. • Synergistic flame retardancy between N element and metal ions in metal organic framework ligands. Toxic substances released during the combustion of epoxy resin (EP) not only cause casualties, but also pollute the environment. Hence, aiming at the flammability of EP, a new triazine based metal organic framework (R1-MOF) was successfully synthesized by solvothermal method to reduce the fire resistance of EP. The single crystal structure of MOF was determined by X-ray single crystal diffraction, and the regular hexahedral structure of the crystal was determined by scanning electron microscope. The peak heat release rate, smoke generation rate, CO generation and CO 2 generation of EP composite loaded with 9 per 100 parts of matrix resin (phr) of R1-MOFs were decreased by 51.3, 41.5, 45.3, and 39.1%, respectively, showing high flame retardancy and smoke suppression performance, and significantly reducing the toxicity of EP. It mainly benefited from the flame retardant N element in MOF ligand and the synergistic effect between ligand and metal ions. In this study, a new type of MOF flame retardant was proposed, which provided a new way to design efficient flame retardants, smoke suppressants and detoxification flame retardants. [ABSTRACT FROM AUTHOR]

Fire-safety epoxy resin with excellent comprehensive performance becomes the requirement for further application in the industry. As a commercially available compound, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) exhibits strong potential to develop effective flame retardants for epoxy resin due to its reactive group of P H and dominant function in gas phase. In order to overcome the adverse effect on mechanical properties and improve flame-retardant effectiveness, DOPO has been used as an initial reactant to synthesize various compounds for epoxy resin. In terms of the different substituents at phosphorus atom in DOPO including P C, P O/P N, and P-ring structure, this work reviews the research progress of these derivatives with the phosphorus element only from DOPO structure in the last decade. Around the relationship between chemical structure and properties, the effect of DOPO-containing compounds on the properties of epoxy resin is discussed, mainly involving flame-retarded performance, heat resistance, and mechanical properties. Although a large number of DOPO derivatives has been designed and used for epoxy resin, some issues still need to be improved, such as migration of flame retardants, deterioration of mechanical properties, processibility, economic competitiveness, and so on. Therefore, an efficient flame retardant can not only improve the flame retardation at low loading but also maintain original outstanding properties of epoxy resin. Through tailoring the chemical structure, to endow epoxy resin with outstanding comprehensive performance in an eco-friendly and economic manner is the further development tendency for DOPO-based flame retardants. • Flame-retardant epoxy resins with excellent comprehensive performance were reviewed. • DOPO-based flame retardants with different substituents were discussed. • Contribution of different chemical structures to flame retardancy were assessed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A phosphorus/silicon-containing polyethylenimine curing agent (PES) was synthesized. • PES endowed EP with high visible light transmittance and improved UV protection. • PES imparted superior and durable fire safety to EP. • PES displayed strengthening and toughening effects towards EP. Epoxy resin (EP) features superior comprehensive performances, but inherent flammability seriously limits its industrial applications. Current flame-retardant strategies often bring about enhanced flame retardancy but deteriorated mechanical, thermal and optical properties and neglect flame retardant durability. Herein, a phosphorus/silicon-containing polyethylenimine (PES) is designed as a multifunctional curing agent for EP. Replacing polyethylenimine (PEI) with PES maintains high visible light transmittance of EPs and improves the UV-blocking properties. The EP cured by 30 wt% PES (EP/30PES) exhibits enhanced mechanical properties compared with the EP cured by 15 wt% PEI (EP/15PEI). EP/30PES achieves a limiting oxygen index (LOI) of 35.0% and a UL-94 V-0 rating, and its peak smoke release rate (PSPR) reduces by 63.8% relative to that of EP/15PEI. Hence, the great flame retardancy, smoke suppression and mechanical performances of EP/30PES enable it to outperform previous flame-retardant EP/aliphatic amine counterparts. Meanwhile, EP/30PES shows durable flame retardancy, which still achieves a UL-94 V-0 classification after acid/alkali/aging resistance tests. This work provides an advanced design of multifunctional curing agents to create durable fire-safe EPs with great UV-shielding and mechanical performances. [ABSTRACT FROM AUTHOR]

• A bio-based, phosphorus-phosphorus, hyperbranched oligomer (DIT) was synthesized. • DIT enabled EP to achieve durable fire safety. • DIT significantly improved mechanical robustness and toughness of EP. • DIT well maintained high transparency and thermal resistance of EP. The manufacture of transparent, durable fire-safe, strong yet tough epoxy resins (EPs) remains a great challenge. Herein, a novel hyperbranched, P-P synergetic, bio-based flame retardant (DIT) was synthesized, which was composed by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), bio-derived itaconic anhydride (ITA) and trihydroxymethylphosphine oxide (THPO) moieties. Adding 2 wt% DIT enabled the EP/2DIT sample to achieve a UL-94 V-0 rating and a limiting oxygen index (LOI) of 36.6%. The peak heat release rate and total smoke production of EP/4DIT sample with 4 wt% DIT were 23.8% and 19.9% lower than those of virgin EP sample. Notably, the EP/DIT sample featured durable flame retardancy because of the oligomeric structure of DIT. The high flame-retardant efficiency of DIT was mainly due to the synergism between DOPO and THPO. DIT simultaneously strengthened and toughened EP thermoset at a low addition (≤2 wt%), and 2 wt% of DIT increased the elongation at break, tensile strength, flexural strength and impact strength of EP/2DIT sample by 35.8%, 40.5%, 24.2% and 21.2%. Moreover, the glass transition temperature (T g) of EP/2DIT sample was equal to that of EP sample, and the high transparent was maintained. Hence, this work offers an all-rounded design for the creation of durable flame-retardant EPs with superior mechanical properties, thermal resistance and transparency by introducing hyperbranched, P-P, bio-based flame retardants, which shows huge potential and broad prospect. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A new flame retardant DOPONH 2 -S was synthesized. • It solved the problems of epoxy resin (EP) including flammability and brittleness. • DOPONH 2 -S achieved high efficiency in reducing THR, P -HRR and EHC of EP. • DOPONH 2 -S increased the impact strength and thermal stability of EP. Epoxy resin (EP) has two shortcomings: flammability and brittleness. Previous studies have improved brittleness or flame retardancy but they will compromise the glass transition temperature (T g) and thermal stability. Herein, a novel DOPO based phosphorus-, nitrogen- and sulfur-co-contained macromolecular flame retardant (DOPONH 2 -S) was synthesized and incorporated into EP to improve its flame retardancy and toughness with not damaging T g and thermal stability. After curing, both T g and the tensile strength of EP-2 improved at the addition of DOPONH 2 -S is 6.75 wt%. Simultaneously, the thermogravimetric analysis (TGA) results showed DOPONH 2 -S is helpful increasing the thermal stability of EP composites and protecting the polymer from further decomposition. In the fire safety test, EP-2 achieved V-0 rating in the vertical burning test and obtained a limiting oxygen index value of 30.5%. In comparison with pure EP, the peak heat release rate, total heat release and effective heat of combustion of EP-4 incorporated with 10.0 wt% DOPONH 2 -S were reduced by 59.1%, 58.5% and 46.3%, respectively. A two-phase mechanism was discussed to explain the combination effect in DOPONH 2 -S. In condensed-phase, rich char residue prevents the exchange of mass and heat during combustion. It also obstructs the release of combustible gases into the combustion zone. In gas-phase, the produced phosphorus- and sulfur-containing free radicals can capture active free radicals (H· and OH·), thus ending the chain reaction of combustion. Moreover, the addition of DOPONH 2 -S apparently improved the impact strength (62.5%). This work provided ideas for the development of multifunctional EP. [ABSTRACT FROM AUTHOR]

• Multifunctional-efficient flame retardant EAD was designed for epoxy resin. • 0.186 wt% P-loading endowed EP with UL-94 V-0 rating and good thermal stability. • Thermosets exhibited improvement in tensile strength and impact resistance. • DOPO-conjugated structure gave EP transparency and UV-shielding performance. A novel multifunctional flame retardant EAD with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and conjugated structure was successfully synthesized via addition reaction of P H bond and alkynyl group. The structure was characterized by Fourier transform infrared (FTIR) spectra and nuclear magnetic resonance (NMR) spectra. Thermogravimetric analysis (TGA) showed that EAD possessed high thermal stability with 290 ℃ T onset and 20.4% char yield at 700 ℃ due to the presence of rigid structure and crosslinking reaction. When incorporating 2 wt% EAD into epoxy resin, the results from TGA indicated that the modified sample had good thermal stability with a T onset value of 354 ℃ and char-forming performance with 22.9% char yield at 700 ℃, as well as glass transition temperature without any deterioration was obtained. Compared with pure epoxy, the same EAD content with only 0.186 wt% phosphorus loading improved effectively the flame retardancy, reflected by the increased limiting oxygen index (LOI) value of 31.0% and V-0 rating in UL-94 vertical burning test. Results from cone calorimeter test (CCT) further confirmed the positive effect on the fire retardancy, which was expressed as the heat release reduction and smoke suppression. The high-efficient flame retardancy was investigated by analyzing the pyrolysis behavior and char residue, which demonstrated the multiple actions of EAD in gas and condensed phases. The low addition of EAD also brought out the reinforcing and toughening effect for epoxy resin. Moreover, the modified epoxy samples with no more than 2 wt% EAD presented good transparency and UV-shielding performance. [ABSTRACT FROM AUTHOR]

In this work, a P/N-derived flame retardant (DOPO-BNM) was synthesized using 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), 2-aminobenzimidazole, and 3-nitrobenzaldehyde as raw materials. The effects of DOPO-BNM on the flame retardancy, and thermal and mechanical performances of epoxy resin (EP) were comprehensively investigated. With the introduction of 8 wt% DOPO-BNM, the EP/8% DOPO-BNM sample passed a V-0 classification in vertical burning (UL-94) test, and its limiting oxygen index (LOI) increased to 32.5%. In comparison to the EP sample, the EP/8% DOPO-BNM sample exhibited 13.0%, 28.8%, 17.5%, 47.9% and 34.5% reductions in the peak heat release rate (PHRR), total heat release (THR), maximum average rate of heat emission (MARHE), total smoke production (TSP) and average effective heat of combustion (AEHC), demonstrating its enhanced fire safety. Furthermore, the char residue of EP/8% DOPO-BNM sample was increased by 41.2% relative to that of EP sample in the cone calorimetry test. During burning, DOPO-BNM mainly reduced the burning degree of volatiles, and also promoted the char formation. Additionally, DOPO-BNM slightly decreased the glass-transition temperature (T g) of EP thermoset, while it remained the mechanical performances. In summary, the addition of DOPO-BNM not only effectively enhanced the fire safety of epoxy thermoset, but also maintained the thermal and mechanical properties. [Display omitted] • A P/N-containing flame retardant (DOPO-BNM) was synthesized by a one-pot method. • DOPO-BNM enhanced the flame retardancy and smoke suppression of epoxy thermoset. • DOPO-BNM maintained the thermal and mechanical properties of epoxy thermoset. [ABSTRACT FROM AUTHOR]

• A vanillin-derived cyclotriphosphazene-cored triazole compound (HHCTP) was synthesized. • The HHCTP-modified epoxy achieved a UL-94 V-0 classification and an LOI of 31.5%. • The addition of HHCTP preserved the thermo-mechanical properties of epoxy resins. A vanillin-derived cyclotriphosphazene-cored triazole compound (HHCTP) was successfully synthesized as a flame retardant for epoxy thermosets with high efficiency while preserving their thermomechanical properties. 1H- and 31P nuclear magnetic resonance (NMR), as well as Fourier Transform infrared (FT-IR), were applied to confirm the molecular structure of HHCTP. The dynamic mechanical analysis (DMA) measurements demonstrated that the introduction of HHCTP improved the storage modulus of the epoxy composites but decreased the glass transition temperature. The epoxy thermoset containing 7.5 wt% HHCTP (EP/HHCTP-7.5) achieved a UL-94 V-0 classification and an LOI of 31.5%, manifesting its outstanding flame-retardant efficiency. In addition, the cone calorimeter results showed that the total heat release (THR) and the peak value of the heat release rate (PHRR) of EP/HHCTP-7.5 were decreased by 35.6% and 50.0%, respectively, in comparison with those of the unmodified epoxy. To further study the flame retardant mechanism of HHCTP, pyrolytic gas species were detected utilizing thermogravimetric-infrared spectroscopy (TG-FTIR). In addition, the microstructure of the char residues was analyzed via X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) techniques. The phosphazene groups in HHTCP clearly stimulated the production of an intumescent, compact, and strong char layer, which improved the flame retardancy of the DGEBA matrix during burning, according to the SEM data. As a result, the underlying components were protected from further degradation and combustion, resulting in effective flame retardancy of the DGEBA thermoset. [ABSTRACT FROM AUTHOR]

• A versatile phosphorothioate bearing benzimidazole ring (DP-MBI) was synthesized. • EP with 3 wt% DP-MBI passed a V-0 rating and achieved the LOI value of 32.6%. • DP-MBI modified EP presented strengthened mechanical properties. • DP-MBI offered the modified EP high transparency. Integrating excellent flame retardancy, robust mechanical properties and high transparency into epoxy resin (EP) still remains challenging using available flame retardants at a super-low loading. S-benzimidazolyl diphenylphosphorothioate (DP-MBI) has been synthesized in an attempt to address this deficiency. The flammability of EP may be greatly diminished through incorporation of only 3 wt% DP-MBI. The resultant EP blend is self-extinguishing, displaying a V-0 rating and a LOI value of 32.6%. The release of heat and smoke during combustion is lower than those observed for combustion of pure EP. The improvement in flame retardancy is ascribed to the cooperation of phosphorus, nitrogen and sulfur moieties mainly in the gaseous phase. Moreover, by virtue of the incorporation of DP-MBI into the mainchain of epoxy macromolecules, the flexural and impact strength for an EP blend containing 3 wt% DP-MBI increased from 104.7 MPa and 31.1 kJ/m2 for pure EP to 111.2 MPa and 37.1 kJ/m2, respectively. Additionally, besides a good ultraviolet shielding effect, the transparency of the modified EP is 100% of that for pure EP. Generally, a versatile flame retardant for epoxy resins, effective at a super-low loading, with promising potential industrial promising application has been prepared. [ABSTRACT FROM AUTHOR]

A structurally novel halogen-free oligomer poly (benzoguanamine phospholipamide) (BQDP) with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) group and triazine ring was constructed as an effective flame retardant suitable for epoxy resins. BQDP was synthesized successfully via nucleophilic addition reaction between DOPO and intermediate schiff base which was prepared by the condensation reaction of benzoguanamine and terephthalaldehyde. Then, the chemical structure of BQDP was characterized by FTIR and NMR. To determine flame retardant properties and thermal stabilities of the epoxy resin, multiple instruments were performed. BQDP visibly increased the limited oxygen index (LOI) values and UL-94 rating of EP/BQDP samples. Specifically, When EP was incorporated with 5 wt % BQDP (EP-5), the limited oxygen index (LOI) rises from 25.2% to 31.5% and the V-0 rating was reached in UL-94 vertical burning test. BQDP also demonstrated excellent smoke suppression performance, which was inferred from the decreased values of PHRR, THR, TSP and av-EHC, while av-COY and residual mass yields increased by comparing EP and EP/BQDP samples. Furthermore, according to the analyses of SEM, FT-Raman and Py-GC/MS, the results revealed that phosphaphenanthrene combined with triazine exerted the group synergistic effect, then both them played outstanding flame-retardant roles in gaseous and condensed phases. [Display omitted] • A DOPO-based oligomer (BQDP) containing triazine ring and DOPO structures was prepared for EP. • EP/ BQDP composites possessed a LOI of 34% with the loading of 5 wt% BQDP. • BQDP presented self-extinguishing effect on EP. • BQDP significantly decreased heat and smoke release of EP. • BQDP exhibited flame retardant effect both in gaseous and condensed phases. [ABSTRACT FROM AUTHOR]

• MTA-MA was synthesized and used as a novel P-containing anhydride curing agent for EP. • The introduction of MTA-MA hardly affected the mechanical properties of the EP thermoset. • MTA-MA had high flame retardant efficiency in both gas phase and condense phase. Two P-containing anhydrides, ethyl (2,5-dioxotetrahydrofuran-3-yl) (methyl) phosphinate (MTA-MA) and 3-(5-oxido-6H-phosphanthridin-5-yl) dihydrofuran-2,5‑dione (DOPO-MA), were synthesized and used along with methyl tetrahydrophthalic anhydride as co-curing agents for curing epoxy resin (EP, mark E51). Via the cross-linking reaction during the solidifying process, P element was introduced into EP matrix via coherent bond. The results showed that both flame-retarding curing agents improved the flame retardancy of EP and MTA-MA exhibited a better performance than DOPO-MA. When the P content in the EP matrix reached 1.0 wt%, the EP/MTA-MA-1.0 thermoset passed UL-94 V0 rating and the limiting oxygen index (LOI) was 32.6%. In addition, EP/DOPO-MA-1.0 achieved UL-94 V1 rating and the LOI value was 30.2%. Cone calorimeter tests, scanning electron microscopy-energy dispersive x-ray spectroscopy, and pyrolysis gas/mass spectrometry results indicated that EP/MTA-MA exhibited better flame-retardancy performance in both the gas and condense phases. In addition, the thermal stability, mechanical properties, and glass transition temperature of EP/MTA-MA and EP/DOPO-MA were studied. [ABSTRACT FROM AUTHOR]

• A nitrogen heterocyclic/phosphaphenanthrene derivative as reactive flame retardant named as TBO was prepared successfully. • TBO simultaneously improved the flame retardancy, Tg and dielectric properties of EP. • TBO/EP composites exhibited excellent potential in application of high performance polymer. Various approaches have been successfully applied to solve the flammability of epoxy resin (EP) materials, but enhanced flame retardance of EP is often along with deteriorated glass transition temperature (T g) and mechanical property. In order to prepare EP composites with good comprehensive performance, we synthesized a phosphorus-containing triazole derivative named TBO from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 3,5-diamino-triazolz and salicylaldehyde, and attached it into epoxy framework. With 0.75 wt% phosphorus loading, the 0.75-TBO/EP composite had a V-0 rating and a limiting oxygen index of 33%. 1.0-TBO/EP composite also had a V-0 rating and acquired a decrease of 37.6% in peak heat release rate. In addition, the tensile strength and flexural strength of 0.75-TBO/EP increased to 63.9 MPa and 146 MPa from 59 MPa and 134 MPa of EP respectively. Meanwhile, the T g values of TBO/EP elevated to some certain compared to EP. In a word, EP modified with TBO composites owned strong mechanical property, higher T g and excellent flame retardance, indicating great potential for application. [ABSTRACT FROM AUTHOR]

The aggregation and plasticizing of most 9,10-dihydro-9-oxa-10-phosphaphenanthrene −10-oxide (DOPO) derived additives often result in deteriorating the glass transition temperature and mechanical properties of epoxy resins (EP). To address this issue, an imide-DOPO derivative (BMP) with bulky aromatic structure was successfully synthesized. Benefitting from the space hindering and intermolecular interaction (π-π stacking) of BMP, it does not lead to the loss of glass transition temperature, and only a minor damage of tensile and impact strengths is caused. Additionally, with only 0.78 wt% loading of phosphorus (10 wt% BMP), the EP/BMP 10% achieves UL-94 V-0 and high LOI value of 35%. Simultaneously, both the heat release rate and total smoke production are markedly reduced. More excitingly, BMP exhibits aggregation-induced emission enhancement of fluorescence in the N, N -dimethylformamide/water mixed solution as well as epoxy resin. This work provides a new insight in simultaneously imparting flame retardancy and fluorescence to epoxy resins without losing glass transition temperature. [Display omitted] • Imide-DOPO derivative exhibits aggregation-induced emission enhancement. • Imide-DOPO derivative endows epoxy resin with excellent flame retardancy. • No loss of T g while the improvement of flame retardancy. • Fluorescence is imparted to the flame retardant epoxy resin. [ABSTRACT FROM AUTHOR]

A multi-functional kaolinite-based compound (AST@Kaol) was prepared by successive loading of TiO 2 and SiO 2 to the surface of metakaolinite (Kaol), followed by reaction with γ-aminopropyl triethoxysilane (APTES). The hybrid was then introduced to epoxy resin (EP) to enhance flame retardancy, smoke suppression and anti-aging properties. The results demonstrated the presence of only 3 wt% AST@Kaol can increase the value of limit oxygen index (LOI) of EP composite to 27.3% from 25.3% of neat EP, as well as decrease the value of heat release rate, total smoke release and the smoke density by 36.9, 14.3 and 19.9%, respectively, compared to neat EP. Besides, the thermal stability and thermal oxidative resistance of EP composites was enhanced. The mechanism of fire retardancy, anti-ageing and mechanical of the EP composite containing AST@Kaol was also speculated. [Display omitted] •A kaolinite-based compound (AST@Kaol) was prepared by co-precipitation. • The properties of fire retardant and ageing resistance for EP/3% AST@Kaol were improved. • Fire retardancy and ageing resistance mechanism of EP/3% AST@Kaol was analyzed. [ABSTRACT FROM AUTHOR]

Molecules containing different elements and moieties like P-N and P-O-Si have high impact on flame retardant properties. In this study, a novel group of flame retardants based on phosphasilazanes containing a P-N-Si structure is established. Due to introduction of the silazane moiety to various phosphorus environments, further properties, like mechanical or thermal, besides flame retardancy can be altered. The influence of phosphorus or silicon moieties and their mode of action on flame retardant properties is examined. In formulations with a high-performance epoxy resin, thermal properties (glass transition temperature and moisture absorption) and flame retardant performance (UL94 vertical burning test, cone calorimetry) are investigated. Alteration of chemical environment at the phosphorus atom determines various implications on burning behavior. For example, phosphorus-containing moieties promoting char generation and intumescence enhance char yields and other parameters describing flame retardant properties of phosphasilazanes in thermo-analysis as well as in cone calorimetry. On the other hand, higher concentration of silazane groups in the structure leads to higher flammability. Phosphorus moieties acting in gaseous phase cause poor flame retardant properties because they antagonize the char generation of silazanes. [Display omitted] • Phosphasilazanes increase residue in TGA, both in nitrogen and air. • Chemical environment of phosphorus atom determines results in UL94 burner tests ranging from no classification to V-0. • Phosphorus moieties acting in condensed phase enhance flame retardancy of silazane moiety. • Phosphorus moieties acting in gaseous phase or a high content of silicon antagonize the charring effect of the silazane moiety. [ABSTRACT FROM AUTHOR]

• A novel crosslinkable additive flame retardant was prepared by a facial routine. • A better performance was showed comparing with traditional flame retardant. • A leap in flame-retardant properties was presented after crosslinking. With great chemical and physical properties, epoxy resins (EPs) are used almost everywhere in life and engineering, but poor flame-retardant performance hinders them for a wider use. Traditional flame retardants (the most commonly used and researched) usually have dispersion and migration problems (additive ones) or are difficult to synthesize (reactive ones). Herein, a facile crosslinking strategy is used to make traditional additive flame retardants exhibit much better properties. Firstly, a nitrogen/phosphorus containing additive flame retardant with nitrile groups is designed, successfully synthesized, and directly mixed with EP matrix, the secondary crosslinking reaction of nitrile groups inner the flame retardants will occur in cured EP thermosets which was driven by a facile thermal treatment procedure. Then the properties of the flame retardant mixed and crosslinked EP composites are measured by limiting oxygen index (LOI) test, thermogravimetric analyses (TG), UL-94 vertical burning tests, dynamic mechanical analysis and cone calorimeter test, the results show that the crosslink of the additive flame retardant greatly improved the flame-retardant properties, and with 20 wt% loading content of the crosslinked flame retardant, the LOI value reach 46.2% and the peak heat release rate decreases for 77.4% compared with neat EP, furthermore the heat resistance and dynamic mechanical property of the crosslinked samples also get promoted compared with the physical mixed ones. [ABSTRACT FROM AUTHOR]

Epoxy resins (EPs) are a kind of widely used engineering materials, because of their excellent mechanical, chemical and physical properties, but a severe problem they faced is their poor flame retardancy. Single molecule flame retardants have met the bottleneck after the massive researches of the past decade, so, with the development of the polymer technology, hyperbranched flame retardants have been researched and applied, owing to their better and more efficient flame retardancy. Herein, a facile thermal treating procedure was applied to the cured EP thermosets which contained a crosslinkable additive flame retardant to in-situ form a hyperbranched flame retardant. The single molecule flame retardants with N/P elements and crosslinkable nitrile groups were synthesized through an easy method, and physically mixed with EP matrix. After the curing reaction of EP matrix, the thermosets were further treated with a thermal treating procedure, while transferring the single molecule flame retardant into hyperbranched flame retardant, the semi-interpenetrating network was formed at the same time. The flame-retardant properties have been measured by limiting oxygen index (LOI) tests, UL-94 vertical burning tests and cone calorimeter tests, the results showed the flame retardants were extremely efficient and greatly elevated the flame retardancy of EPs, since the 0.5 wt% content could make modified EP samples pass the UL-94 V-0 rate, and with 20 wt% content the LOI value reached 49.5 % and the peak heat release rate reduced for 71.6 % compared with pure EPs. [ABSTRACT FROM AUTHOR]

A novel diaminodiphenylmethane (DDM) modified ammonium polyphosphate (APP) flame retardant, DDP, was successfully synthesized via ion-exchange reaction. DDP was introduced into epoxy resins (EPs) to reduce flammability. A comparable level of DDP exerts better flame-retardant and smoke suppression efficiencies in EP than APP. An EP blend containing 15 wt% DDP displays a limiting oxygen index (LOI) value of 37.1% and a UL 94 V-0 rating, and further exhibits a 32.3% reduction in total heat release and a 48.0% reduction in total smoke production compared with pure EP. The presence of DDP greatly facilitates char formation during combustion, and the char mass from thermal decomposition of an EP blend is 37.8% smaller than that of an EP blend containing 15 wt% DDP at 800 °C. The incorporation of DDP into EP blends has a smaller impact on the glass transition temperature and tensile strength than those of a comparable level of APP. This reflects the better compatibility of DDP with the EP matrix compared with that for APP. [ABSTRACT FROM AUTHOR]

Abstract: The influence of microencapsulated ammonium polyphosphate (MFAPP) on flame retardancy, thermal properties and water resistance of epoxy (EP) composite were investigated by LOI, UL-94, DSC, TG, microscale combustion calorimeter (MCC) and TG-FTIR. The results of DSC show that the shell outside MFAPP can increase its compatibility in EP. EP/MFAPP containing only 9wt% MFAPP can pass V-0 in the UL-94 test, while neat EP cannot pass any rating. Due to the presence of shell, water treatment show few effects on the flame retardancy of EP/MFAPP, while LIO values of EP/APP decrease remarkably after treatment. The presence of MFAPP can reduce the heat release rate and total heat release of EP significantly in MCC test. The reason is that MFAPP can stimulate the dehydration of EP at low temperature and retard the release of pyrolysis gas at high temperature. Moreover, a char formed via the reaction of EP and MFAPP has excellent thermal stability and can prevent underlying materials from further combustion during a fire. [Copyright &y& Elsevier]