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• A syringaldehyde derived epoxy resin monomer (SA-TAG-EP) was developed. • The bio-based epoxy system showed a record T g of 224 °C, high strength and modulus. • The bio-based epoxy system showed satisfactory intrinsic flame retardancy. Due to increasing environmental concerns, global warming, and the decline of oil reservoirs, the use of bio-epoxy resins derived from sustainable resources is recommended. The development of bio-based epoxy resins with considerable thermal stability, mechanical strength, and appropriate intrinsic flame retardant potential is highly demanded. In this study, a new Schiff-based epoxy monomer, triglycidyl ether of syringaldehyde (SA-TAG-EP), was synthesized from renewable syringaldehyde. After the 4,4′-diaminodiphenylmethane (DDM)-based curing process, an intrinsically flame-retardant resin (SA-TAG-EP/DDM) with C, H, N, and O elements was achieved. SA-TAG-EP/DDM showed higher glass transition temperature (224.9°C) and greater mechanical strength, including a tensile strength of 66.8 MPa and an elongation at break of 3.91%, compared to petroleum-based bisphenol A epoxy thermoset. It also passed the V-0 flammability rating in the UL-94 test and exhibited a 38.5% limiting oxygen index, 48.9% char yield under N 2 , and a lower peak heat release rate than that of petroleum-based bisphenol A epoxy thermoset. We proposed a simple and sustainable route for the synthesis of Schiff base epoxy compounds from biomass-derived resources, which demonstrates significant mechanical properties and increased flame retardant potential. [ABSTRACT FROM AUTHOR]

• A series of coatings with high transparency and excellent pencil hardness levels were prepared on polycarbonate (PC) substrates via a two-step UV-curing process with TAEP and MAAR. • The coupling effect of the combustion behaviours of the UV-cured coatings and the PC substrates was particularly investigated to give insight into a holistic picture of the combustion of the coated PC composites. • The composite UV-cured coatings successfully suppressed the heat release and improved the flame retardancy of the PC samples thanks to the phosphorus-nitrogen synergistic flame-retardant effect in the condensed phase. • A potential strategy to further enhance the flame-retardant ability of the UV-cured coatings lies in improving the thermal and mechanical stabilities of the intumescent char layers. There is an urgent demand for flame retardant treatment of polycarbonate (PC) with as little adverse impact on the inherent advantages of PC as possible, especially the high transparency. Herein, a flame-retardant coating with high transparency was successfully prepared on PC via a two-step ultraviolet-curing (UV-curing) process with tri(acryloyloxyethyl) phosphate and melamine acrylate resin. All the coated PC composites showed high transparency and excellent pencil hardness levels (6H). The coupling effect of the combustion behaviours of the UV-cured coatings and the PC substrates was particularly investigated to give insight into a holistic picture of the combustion of the coated composite systems. Specifically, all the composite UV-cured coating samples (T2M1, T1M1 and T1M2) formed highly expanded char with honeycomb-like inner structure due to the phosphorus-nitrogen synergistic effects, which could efficiently suppress mass and heat transfer, thereby protecting the PC substrates from the harsh conditions of high temperature and realizing significantly enhanced flame retardancy of the PC samples. Improving the thermal and mechanical stabilities of the intumescent carbon layers may be a practical strategy to achieve further improved flame retardant capabilities of the PC samples. Additionally, the PC-T2M1 composite exhibited the optimal flame retardant effect, realizing significantly suppressed heat release in the cone calorimeter tests, reaching UL94 V-0 rating and showing long fire resistance time thanks to the intumescent char. The UV-cured coating method introduced in this work had great potential in spawning new strategies for designing advanced flame retardant coatings for polymer substrates. [Display omitted] [ABSTRACT FROM AUTHOR]

• An organic-inorganic hybrid flame retardant (THPSU-MMT) was synthesized. • EP-MMT composites have good flame retardancy and comprehensive properties. • The thermal decomposition of EP-MMT composites was studied. • It provides a green and efficient method for exfoliation of montmorillonite. Traditional additive flame retardants pose issues including high dosage, easy precipitation, and poor compatibility with the matrix. Designing efficient organic-inorganic synergistic flame retardants can enhance the flame retardancy and mechanical properties of epoxy (EP) composites while reducing their smoke toxicity. In our study, we initially employed Tetrakis(hydroxymethyl)phosphonium sulfate (THPS) for intercalation modification of montmorillonite (MMT). Subsequently, we achieved a green and efficient exfoliation of MMT by reacting urea with hydroxyl groups, resulting in the simultaneous preparation of efficient organic/inorganic synergistic flame retardants (THPSU-MMT). EP composites containing 5wt% THPSU-MMT can attain UL-94 V0 classification. Furthermore, the peak heat release rate (PHRR), total heat release (THR), and peak release rates of CO can be reduced by up to 78.42 %, 62.26 %, and 72.50 %, respectively. Simultaneously, we systematically investigated the synergistic flame retardant mechanism of the EP composite. The findings reveal that THPSU-MMT exhibits a dual flame retardant effect in both the gaseous and condensed phases. Moreover, the combination of MMT and THPSU substantially enhances the presence of phosphorus-containing pyrolysis products in the condensed phase. The fire performance index (FPI) of the flame retardant EP increased from 0.05 m2/s/W in pure EP to 0.36 m2/s/W, attributed to the enhanced catalytic carbonization and assisted gas-phase free radical capture. Additionally, the flame spread index (FGI) decreased from 11.55 kW/m/s in pure EP to 1.18 kW/m/s, signifying a substantial enhancement in fire safety. Furthermore, the THPSU-MMT synergistic flame retardants improved the tensile strength of EP composites. This study offers an environmentally friendly and efficient approach for the effective exfoliation of MMT, while also presenting novel concepts for the design of efficient organic-inorganic synergistic flame retardants. [Display omitted] [ABSTRACT FROM AUTHOR]

Due to the inherent flammability of polypropylene (PP), it is limited in the application of flame retardant materials. In this work, a novel char forming agent, hyperbranched phosphorus-containing polyurethane (HPPU), was synthesized and used as efficient char forming agent. When ammonium polyphosphate (APP) was combined with HPPU, APP/HPPU endow PP significantly improved flame retardancy than single APP. Although the total carbon monoxide production (TCOP) of some PP/APP/HPPU composites is higher than that of PP/APP composite, it is still lower than that of neat PP. LOI (limited oxygen index) and UL-94 tests reveal that PP composites with 25 wt% HPPU/APP with ratio of 4:1 are able to reach 27 vol% and V-0 rating, respectively. The addition of 25 wt% APP/HPPU with ratio of 2:1 into PP can result in decrease in peak heat release rate of about 72%, decrease in total heat release of about 38% and decrease in TCOP of about 93%. APP/HPPU promotes PP to form more stable, compact, and continuous char layer which effectively hinder heat and oxygen transfer and protect the inner matrix from decomposition. Thermogravimetric-infrared results reveal that the gas phase flame retardant mechanism of APP/HPPU is the dilution effect of ammonia from APP and the flame inhibition effect of phosphorus-containing species from HPPU. Image 1 • A novel hyperbranched phosphorus-containing polyurethane (HPPU) is firstly synthesized. • LOI and UL-94 tests revealed that the addition of 25 wt % HPPU/APP into neat PP was able to reach 27 % and V-0 rating. • APP/HPPU exhibit remarkable flame retardant and carbon monoxide (CO) suppression to PP composites. [ABSTRACT FROM AUTHOR]

• A vanillin-derived bisDOPO co-curing agent (DVD) was successfully synthesized from vanillin and DOPO. • The introduction of DVD improved the mechanical properties of epoxy thermosets. • Epoxy with an ultra-low P content of 0.42 wt% exhibited an LOI of 30.5% and reached a UL-94 V-0 rating. To prepare transparent and flame-retardant epoxy thermosets, a vanillin-derived bisDOPO co-curing agent (DVD) was synthesized from vanillin and DOPO. The influence of DVD on the curing kinetics of the epoxy systems was investigated by non-isothermal differential scanning calorimetry (DSC). The introduction of DVD increased the activation energy of the curing process. Compared with pure epoxy, the storage modulus at 30 °C and tensile strength of EP/DVD-5% increased by 35.7% and 145%, respectively. Additionally, the epoxy thermosets still maintained excellent transparency. The addition of DVD improved the flame-retardant performance of epoxy thermosets by promoting the formation of char and reducing the thermal decomposition rate. Most importantly, DVD showed high flame retardant efficiency for the resulting epoxy thermosets. Specifically, with the incorporation of 5 wt% DVD (only 0.42 wt% phosphorus loading), the resulting epoxy thermoset exhibited a limiting oxygen index (LOI) value of 30.5% and reached a UL-94 V-0 rating. The cone calorimetry results showed that the total heat release (THR), peak value of heat release rate (PHRR), and total smoke production (TSP) of EP/DVD-5% decreased by 32%, 42%, and 21%, respectively, compared with the unmodified EP. The modes of action of flame retardant analysis indicated that DVD exhibited high flame retardant efficiency by serving as a charring promotor in the condensed phase and acting as a radical scavenger in the gaseous phase. The above results demonstrate that DVD is a promising flame retardant agent to render epoxy thermosets simultaneously improved flame retardancy, mechanical strength and transparency. [ABSTRACT FROM AUTHOR]

• Microwave assisted grafting of AA onto the PA6.6 fabric surfaces was done. • Layer by layer deposition and HP cross-linking were followed. • A maximum reduction in pHRR by ca. 50% was achieved. • Super-hydrophilic surfaces were obtained. • Such coating could retain anti-dripping properties even after 10 launderings. Microwave-assisted surface modification of polyamide 6.6 (PA6.6) fabrics was carried out in a grafting polymerization technique in the presence of acrylic acid (AA) monomer with an aim to enhance the extent of surface functional groups onto the PA6.6 fabric surfaces. In the next step, the surface modified fabric substrate was gone through a layer by layer (LbL) deposition process in the presence of some hybrid (organic/inorganic) polyelectrolytes in imparting hydrophylic and flame retardant properties and finally, the as prepared coating was subjected to a cross-linking treatment aided by hypo-phosphorus acid (HP) in enhancing the stability of the same. From the obtained results, it was revealed that the simultaneous microwave assisted grafting, LbL deposition and HP cross-linking left positive impacts in improving the flame retardant performance and hydrophilicity of PA6.6 fabrics along with the enhancement of coating stability in laundering. For example, acrylic acid grafted PA6.6 fabric sample with a 5-BL deposition and cross-linked with HP (i.e., PA6.6-g-AA-5BL-HP) attained a limiting oxygen index (LOI) value up to 23.5%, while exhibiting a significant level of reduction in the peak heat release rate (pHRR) by ca. 50 %. In line, a super-hydrophilic surface was obtained for this fabric sample as the water contact angle value declined to 0º. Furthermore, such kind of surface modification displayed a considerable level of coating stability during laundering as the anti-dripping properties still exist even after 10 home launderings. [Display omitted] [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 novel cactus-like structure of BP@MoS 2 hybrids was designed and synthesized. • The tensile strength and fracture strength of WPU/BP@MoS 2 -2.0 increase by 57.7% and 36.5%. • The PHRR and TSP of WPU/BP@MoS 2 -2.0 reduce by 50.3% and 52.0%. • BP and MoS 2 have a cooperative effect in suppressing the heat release behavior of WPU/BP@MoS 2. Design novel flame retardant and mechanical enhancing agents of waterborne polyurethane (WPU) is a crucial issue for expanding its application. Herein, BP@MoS 2 hybrids was designed and prepared to enhance the fire safety and mechanical properties of WPU and BP@MoS 2 possessed a novel cactus-like structure. BP@MoS 2 was prepared in a two-step method including preparation of black phosphorus (BP) sheets by chemical vapor transfer method and preparation of BP@MoS 2 by in situ growth of molybdenum disulfide (MoS 2). with adding 2.0wt% BP@MoS 2 , the tensile strength and fracture strength of WPU/BP@MoS 2 -2.0 increase by 57.7% and 36.5%, respectively. The peak value of heat release rate (PHRR) and total smoke production (TSP) of WPU/BP@MoS 2 -2.0 also reduce by 50.3% and 52.0%, which indicates that fire safety and mechanical performance of WPU/BP@MoS 2 -2.0 is effectively enhanced. Meanwhile, BP@MoS 2 has both condensed phase and gas phase flame retardant effect on WPU. In condensed phase, the residue char of WPU/BP@MoS 2 is with excellent physical barrier effect. In gas phase, BP@MoS 2 can inhibit the generation of flammable volatiles such as aromatic and aliphatic compounds during burning of WPU/BP@MoS 2 , thereby inhibiting the heat release and smoke release behavior of WPU/BP@MoS 2. [Display omitted] [ABSTRACT FROM AUTHOR]

• A liquid flame retardant, phosphorus-containing triacrylate, was synthesized. • Flexible polyurethane/phosphorus-containing polyacrylate IPN foams were prepared by simultaneous strategy. • Flame retardancy, thermal stability and mechanical properties of IPN foams were improved concurrently. Even though organophosphorus additives can improve flame retardancy and compress strength of flexible polyurethane foam (FPUF), but thermal stability and resilience are deteriorated. In this work, phosphorus-containing monoacrylate and triacrylate, (dimethoxyphosphoryl)methyl acrylate (DMPMA) and tris(acryloyloxymethyl)phosphine oxide (TAMPO), were synthesized. The liquid DMPMA and/or TAMPO were added into FPUF ingredients with radical initiator and polymerized in the heating process after foaming to form FPUF/polyacrylate composites. The neat and modified foams were controlled to have similar densities. Gel content of more than 96% was obtained for FPUF incorporated with TAMPO. And structure of interpenetrating polymer network (IPN) of FPUF3-5 loaded 20 wt% DMPMA and TAMPO of polyol (ratio of 3:1, 1:1 and 1:3 respectively) was further confirmed by their bicontinuous phase morphology with nanoscale domain uniformly distributed. All modified foams attain improved flame retardancy. Simultaneously increased thermal stability, compression force deflection (CFD) value and resilience were achieved by FPUF4-5. Especially, FPUF4 exhibits satisfied flame retardancy (limited oxygen index of 22.1%, pass of TB117-2000 vertical burning test, prolonged time to ignition, 49% decrement of peak heat release rate and 33% reduction of total heat release), elevated thermal stability and improved compressive (15% improvement of CFD) and resilient (5.2% raise of resilience) properties, concurrently. Therefore, DMPMA and TAMPO have great potential as liquid additive-type flame retardants for manufacturing flame retardant, supportive and comfort FPUF in seating and cushioning applications. [ABSTRACT FROM AUTHOR]

• A bio-based epoxy monomer (HECarCP) was synthesized from cardanol and cyclophosphazene. • HECarCP/DDM thermoset showed a high LOI value of 33.0% and UL-94 V-0 classification. • Peak heat release rate of HECarCP/DDM was 63% lower than that of DGEBA/DDM. • Total smoke production of HECarCP/DDM was 72% lower than that of DGEBA/DDM. • HECarCP/DDM displayed much better toughness than the DGEBA/DDM. Petroleum-based diglycidyl ether bisphenol A (DGEBA)-type epoxy is one of the most popular thermosetting materials currently, but it suffers from brittleness, flammability and non-renewability. In this study, an intrinsically flame retardant bio-based epoxy monomer (HECarCP) was synthesized from cardanol and cyclophosphazene. Subsequently, HECarCP was cured by 4,4'-diaminodiphenyl methane (DDM) to obtain a thermosetting material. Compared to the cured DGEBA/DDM thermoset, the cured HECarCP/DDM thermoset showed lower initial decomposition temperature; however, the earlier thermal decomposition caused by cyclophosphazene core contributed to char formation in return. As well, the HECarCP/DDM exhibited slightly lower tensile strength but much higher elongation at break than the DGEBA/DDM, overcoming the drawback of brittleness of the DGEBA/DDM. More importantly, the cyclophosphazene core provided intrinsic flame retardancy to the HECarCP/DDM thermoset, which displayed a relatively high LOI value of 33.0% and UL-94 V-0 classification. In cone calorimeter measurement, the peak heat release rate, total heat release and total smoke production of the HECarCP/DDM thermoset was declined by 63%, 24% and 72%, respectively, compared to those of the DGEBA/DDM, owing to the formation of a thermally stable and insulating char layer during combustion. This study paves the way for broadening applications of cardanol in fabrication of high-performance bio-based thermosetting polymers with excellent comprehensive properties. [ABSTRACT FROM AUTHOR]

l Three different P-compounds were used to prepare the flame retardant coatings for PA66 textiles. l Chitosan, alginate and MMT as additives were also incorporated with the P-compounds. l Graphene phosphonic acid based coating offered a maximum LOI by 27.5% and reduction in pHRR by 45%. l Phytic acid based coating brought a substantial reduction in pHRR and increase in char yield%. l P-compound active in the condensed phase and well-supported with a physical barrier effect seemed to be well-suited for PA66. Three different phosphorus (P) compounds, namely phytic acid (PA), graphene phosphonic acid (GPA) and a DOPO derivative [3-H-P-DOPO HQ (DOH)] having a diverse origin, structure and chemical activity were used along with some naturally derived polyelectrolytes like chitosan (CS), sodium alginate (SA) and montmorillonite (MMT) in a layer-by-layer (LbL) fashion to enhance the flame retardant performance of polyamide 66 (PA66) textiles. Obtained results showed that these P-compounds, irrespective of their varied action surely played a positive role in improving the flame retardancy; though a typical P-compound was effective in modifying a specific type of flame retardant parameter. The formulation containing phytic acid particularly brought a considerable reduction in the peak heat release rate (pHRR) and a handsome increase in residue% due to its dominant activity in the condensed phase flame retardant mechanism. Meanwhile, the application of GPA further modified this condensed phase activity via providing added thermal stability to these residues and thus, a sharp increase in limiting oxygen index (LOI) value up to 27.5% and a maximum reduction in pHRR by 45% was handed. In contrast, the DOPO derivative (DOH) was quite effective in the gas phase mechanism through its radical quenching effect and offered a moderate increase in LOI values (i.e., 24.5%). Finally, it was realized that the formulation containing an engineered structure of a P-compound with graphene, basically worked in the condensed phase mechanism and well supported by thermal insulation effect available from graphene nanosheets and MMT platelets seemed to be an effective solution in escalating the fire performance of PA66 textiles. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The black phosphorus (BP) nanosheets were firstly obtained by the modified lithium ion intercalation method and then functionalized by cetyl-trimethyl ammonium bromide (CTAB). Owing to the electrostatic interactions, the positively charged CTAB was successfully loaded onto the surface of negatively charged exfoliated BP and the BP-CTAB hybrids were finally obtained. It is found that BP-CTAB hybrids exhibits superior promotion effect on fire safety of Polylactic acid (PLA), which can be attributed to its typical layered structure, abundant phosphorus and good dispersion in matrix. Compared with neat PLA, the peak heat release rate (PHRR) of PLA composite with 2 wt% BP-CTAB decreases by 38.8%. Under the same loading of 2 wt%, the PLA/BP-CTAB2.0 shows better flame retardancy than PLA composites with BP or red phosphorus (RP). Moreover, the time to peak heat release rate (T PHRR) of PLA/BP-CTAB2.0 is postponed from 157 to 200 s. Derived from the uniform dispersion of BP-CTAB, the tensile strength of PLA composites are also improved. Meanwhile, the air stability of BP-CTAB in polymer is investigated. It is observed that the A g 1/A g 2 value of BP-CTAB only decreases from 0.57 to 0.54 even after immersion in water for one month, which can be ascribed to the double coating of polymer matrix and CTAB. This work enriches the method of exfoliating BP, and first explores the influence of BP on the flame retardant and mechanical properties of PLA. • Modified lithium ion intercalation method enriches the way of exfoliating BP. • BP-CTAB nanohybrids exhibit significant effect on decrease in PHRR and postponing in T PHRR. • BP-CTAB nanohybrids significantly improve thermal stability of PLA composites. • The air stability of BP-Li nanosheets is enhanced by the double coating of polymer matrix and CTAB. [ABSTRACT FROM AUTHOR]

In this work, a series of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative salts containing phosphorus and nitrogen were synthesized, and their effects on mechanical properties, thermal stability and flame retardancy of flexible polyurethane foam (FPUF) were investigated. Studies have shown that the addition of DOPO derivatives will increase the tensile strength, compression set, and compression hardness of FPUF, but it will lead to a decrease in elongation at break. Thermogravimetric analysis showed that the initial decomposition temperature of FPUF containing DOPO derivatives was reduecd, but the char reside was significantly improved. A series of combustion tests indicated that the addition of DOPO derivative salts can improve the flame retardancy of FPUF, of which 10-hydroxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide dicyandiamide salt (D-DICY) exhibited the best flame retardancy. When the load of D-DICY was 20 phr, the limiting oxygen index (LOI) of foam reached 24.5%, and the peak heat release rate and total heat release were decreased by 55.7% and 52.9%, respectively. Furthermore, based on the analysis of the gas phase combustion products and the char residue of the condensed phase, the possible flame retardant mechanism was proposed. • Novel phosphorus-nitrogen-containing DOPO derivatives were synthesized. • Tensile strength and compression hardness of FPUF are enhanced with the addition of DOPO derivatives. • When the load of D-DICY is 20 phr, the LOI of FPUF reaches 24.5%. • The synthesis steps are simple, low cost and environmental-friendly. [ABSTRACT FROM AUTHOR]