Search

Endowing rigid polyurethane foam (PUF) with a good fire-retardancy is essential for improving fire safety. Chemical improvement in fire-retardancy by using reactive-type flame retardants is better because of the disadvantages of traditional additive-type flame retardants. A reactive flame retardant tri-glycidyl phosphate (POG), which was synthesized by using phosphorus oxychloride and glycidol, was bound to the cross-linked network structure of PUF. The effects of POG on the physical-mechanical properties, morphology, thermal stability and fire-retardancy of PUF system were systematically investigated. Research results showed that POG resulted in an improvement in the thermal insulation ability and a slight decrease in the compressive strength of PUF. Furthermore, thermogravimetric analysis certified that the thermal stability and the char yield at 700 °C of PUF were significantly enhanced by incorporating POG. The limiting oxygen index increased to 22.3% with rising loading of POG. Moreover, a 30.2% decline in total heat release was achieved, the time to flameout was significantly shortened. Additionally, the vertical burning test illustrated that POG effectively limited the spread of flame and eliminated melt dripping. Further study confirmed that the fire-retardancy of PUF was significantly improved by inhibiting flame in the gas phase and charring in condensed phase.

To explore the more effective non-halogen flame retardants in epoxy resins, a flame retardant named ABD owning relatively short bridged bonds and a hydroxyl group was synthesized via addition reaction between acrolein and 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO). Then, ABD was applied into flame retardant epoxy resin, diglycidyl ether of bisphenol-A, cured by 4,4′-diamino-diphenylmethane. When the mass fraction of ABD in epoxy resin was only 3 wt%, the thermoset acquired a higher limited oxygen index (LOI) value 36.2% and passed UL94 V-0 rating. ABD also reduced all the values of peak of heat release rate (pk-HRR), total heat release (THR), average effective heat of combustion (av-EHC), total mass loss (TML) and average CO 2 yield, and increased the residue yield. In contrast to DOPO, ABD can impose the higher LOI value, the higher UL94 rating and the lower peak value of HRR to epoxy thermosets. Further, the results from the cone calorimeter test reveal that the better flame retardant performance of ABD was caused by quenching effect from phosphaphenanthrene groups in gas phase and the charring effect from the joint action of phosphaphenanthrene group and hydroxyl group in condensed phase simultaneously. The excellent flame retardant performance of ABD is from its higher phosphorus contents and its special hydroxyl group.

Ammonium polyphosphate modified with β-Cyclodextrin (β-CD) as intumescent flame retardants was prepared and then incorporated in rigid polyurethane foam (RPUF) to improve thermal stability and flame retardancy. Scanning electron microscope (SEM), Transmission electron microscope (TEM), Fourier-transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS) were used to characterize the modified APP (β-APP). The results showed that the surface of β-APP was covered of β-CD and the dispersibility of β-APP in substrate was improved apparently. In addition, the influence of β-APP on the cell structure, crosslink density, thermal stability and flame retardancy of RPUF were investigated. The results showed that β-APP was able to promote cellular distribution of RPUF into smaller and homogeneous. The results of dynamic thermomechanical analysis (DMA) and thermogravimetric analysis (TGA) indicated that the glass transition temperature (T g ) and crosslink density of β-APP/RPUF increased obviously, and the thermal stability of β-APP/RPUF was better than other FR-RPUFs. During combustion, flame spreading speed of 25 wt%β-APP/RPUF reduced by 67.3% relative to pure RPUF and extinguish time decreased to 2.1s with the most complete inner char and the most dense outside char. In addtion, peak heat release rate (PHRR) of the sample decreased by 43.8% compared to pure RPUF. Therefore β-APP exhibited a prominent charring property and flame-retardant effect in condensed phase for RPUF.

The microscale combustion calorimetry study of polymer mixture pyrolysis is presented. Binary mixtures of HDPE with a number of massively produced polymers (LDPE, PET, PS, PP, PC, PVC, PMMA), binary PC-PS and PMMA-PVC mixtures, and the ternary mixture composed of HDPE, PC, and PS are considered. The extent of interaction between the mixture components in pyrolysis is assessed by comparing the shapes of the measured temperature dependencies of the heat release rate in volatile oxidation with those for the curves obtained by the mass-weighted summation of the individual contributions of the pure polymers constituting the mixture. The strongest interaction is observed in HDPE-PET, HDPE-PS, HDPE-PS-PC, and in PMMA-PVC mixtures. A destabilizing interaction occurs in mixtures containing polyethylene and polystyrene, while the presence of polyvinylchloride has a stabilizing effect. In the binary mixtures, no clear correlation of the dependence of the conversion-averaged apparent activation energy (obtained by the iso-conversional method of Friedman) on the component proportion has been observed. In HDPE-PET mixture, in which the temperatures of peak pyrolysis rates are separated, the dependence of the apparent activation energy on conversion is interpreted in terms of the dependencies derived for pyrolysis of the individual components. Except for PMMA-PVC mixtures, in all binary mixtures considered in this work the heat of volatile combustion and the char yield were found to be additive quantities and varied almost linearly with the variation of the component mass fractions. Dissimilar to that, the PMMA-PVC mixtures produced a higher amount of charring residue and a lower heat of combustion of volatiles compared to the component-based predictions assuming additivity.

Carbon/Phenolic Composites (CPCs) are among most important Thermal Protection System (TPS) materials. In addition to the challenges related to the manufacturing issues - partially covered in this paper - the possibility to properly characterize the thermo-physical and thermo-mechanical properties of CPCs is extremely important. These data are not only used to size the TPS of a space vehicle or the nozzle components of a Solid Rocket Motor (SRM) but they are also essential to model the response of a CPC in a given hyperthermal environment. However, most of the papers reporting the thermo-physical and thermo-mechanical properties of CPCs are based on very old testing facilities and, in many cases, special equipments have been developed ad-hoc. As a result, the aim of this paper was to identify a feasible approach able to assess the heat capacity as a function of temperature (up to 550°C) of CPCs through the use of common DSC and TGA analysis, taking into account all the degradation steps of the polymeric matrix undergoing charring. The possibility to evaluate the heat of decomposition of high char yield matrices through the introduced protocols was also discussed.

Aiming at improving fire retardancy of epoxy resin (EP), the thermal-exfoliated boron nitride nanosheets (BN) underwent the bio-inspired polydopamine (PDA) nano-coating and in-situ interfacial growth of iron-derived nanocatalyst (Fe) to prepare nanohybrid (BN@PDA@Fe). The design complied with principles: 1) PDA promoted the dispersion of BN in EP matrix and offered active sites for functionalization 2) bio-stabilized iron-derived nanoparticles catalyzed the polyaromatic reaction towards higher quality. Resultantly, 6 wt% BN@PDA@Fe increased limiting oxygen index (LOI) of EP by 10.0% and suppressed fire spread in UL-94 test. The peak heat release rate (pHRR) was reduced by 38.9% with notably suppressed CO and smoke production. Ignition time, as a key aspect of fire safety, was effectively delayed due to enhanced thermal conductivity of BN-based EP nanocomposites. The optimization of char structure due to the interfacial charring accounted for the improved fire retardancy. In perspective, the bio-inspired engineering of BN offered a viable approach to improving fire safety of polymers.

A flame retardant named ODOPB-Borate constructed by phosphaphenanthrene (DOPO) and borate groups was synthesized via esterification reaction between boric acid and 10-(2,5-dihydroxyphenyl)-10-H-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB). The molecular structure of ODOPB-Borate was characterized and verified. To research the group synergistic effect of phosphaphenanthrene and borate groups, ODOPB-Borate was incorporated into epoxy resin, diglycidyl ether of bisphenol-A (DGEBA), cured by 4,4-diamino-diphenyl sulfone (DDS). ODOPB-Borate increased the LOI and particularly improved the UL94 classification of epoxy resin thermosets, and also reduced the heat release of epoxy thermosets. Further, the decrease of total mass loss value of thermoset containing ODOPB-Borate revealed that ODOPB-Borate facilitated the EP composites to form more residue. The analyzed pyrolysis route of ODOPB-Borate revealed that ODOPB part mainly exerted quenching effect in gas phase and the borate part mostly remained in condensed phase and promoted charring effect and smoke suppressing effect. The synergistic effect from phosphaphenanthrene and borate groups endowed epoxy resins with flame retardancy. Moreover, ODOPB-Borate also increased the glass transition temperature and impact strength of epoxy resin.

The introduction of traditional flame retardants into epoxy resins (EP) usually generated a number of harmful smoke during burning. A novel flame retardant (dZIF-8) was synthesized via functionalization of zeolitic imidazolate frameworks-8 by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivatives (DMZ). The flame retardancy and smoke suppression of the dZIF-8 modified EP were studied. The combustion results showed that dZIF-8 can effectively reduce the fire risk of EP. Compared with the neat EP, the value of peak heat release rate (PHRR), the total smoke release rate (TSRR) and the maximum smoke density of the EP containing 2% dZIF-8 were decreased by 51%, 47% and 36%, respectively. The TG-FTIR results showed that the production of the pyrolysis gaseous products was inhibited by dZIF-8 during the decomposition of EP. In addition, the synergistic effect between the DMZ and the zeolitic imidazolate frameworks-8 improved the flame retardancy of the EP. Meanwhile, the increase in the flame-retardant performance of the dZIF-8 modified EP was caused by the quenching effect of the free radical containing phosphorus in gas phase and the charring effect of pyrophosphoric acid and zinc oxide in condensed phase. The morphology of dZIF-8 crystal changed from granular to laminar, indicating that the introduction of DMZ affected the crystal growth of dZIF-8. The laminar structure of the dZIF-8 provided a layered barrier effect during the burning process of EP.

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

A bi-DOPO type of prepolymer for flame retardancy epoxy resins with intrinsically flame-retardant was successfully synthesized by reacting of 6,6′-((6,6′-dihydroxy-[1,1′-biphenyl]-3,3′-diyl) bis (propane-3,1-diyl)) bis(dibenzo[c,e][1,2] oxaphosphinine 6-oxide) (DOBP) with bisphenol A. The characterization of the cured epoxy resins, such as cone calorimeter, TGA/infrared, Raman and SEM indicated that DOBP with double 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) structure endowed the epoxy resins with excellent flame retardancy, including limiting oxygen index of 40.0%, V-0 rating in UL-94, remarkable smoke suppression and flame inhibition. The quenching effect of gaseous phase and charring effect of condensed phase of phosphaphenanthrene groups in prepolymer together contributed to the improvement on the flame retardant performance of the epoxy resins. In addition, due to the rigid structure of DOBP molecules, the cured d-FREP possessed high glass transition temperature of up to 192.9°C, and the tensile modulus of which was increased about 55% compared with the neat epoxy resins.

Highlights Poly(BHDB-Bz) exhibited a relatively high glass transition temperature (285 oC) Poly(BHDB-Bz) displayed a high LOI value (40.0%) and a UL-94 V-0 rating owing to its superior charring ability Poly(BHDB-Bz) showed an extremely low HRC (35.5 J/(g•K)) which is lower than most synthetic polymers Despite many superior advantages including high heat resistance, low dielectric constant, low water absorption, and low curing shrinkage, the flammability of polybenzoxazines restricts their widespread applications in electronic realms. It is thereby essential to synthesize flame retardant polybenzoxazines for broadening their applications. In this work, we synthesized an anti-flammable bio-based benzoxazine monomer (BHDB-Bz) derived from furfurylamine. As a control sample, another bio-based benzoxazine monomer (BPA-Bz) was also synthesized from furfurylamine and bisphenol A. The molecular structure of BHDB-Bz and BPA-Bz was confirmed by FTIR, and 1H- and 13C-NMR spectra. Two kinds of bio-based polybenzoxazines, poly(BHDB-Bz) and poly(BPA-Bz), were obtained through thermally-induced ring-opening polymerization. Poly(BHDB-Bz) exhibited a relatively high glass transition temperature (285 °C), a high initial decomposition temperature (379 °C under nitrogen and 388 °C under air), and an extremely high char yield under nitrogen (65.9%), all of which were better than poly(BPA-Bz). Benefitting from the superior charring ability of desoxyanisoin structure, poly(BHDB-Bz) exhibited outstanding anti-flammability, whereas poly(BPA-Bz) was flammable. Specifically, poly(BHDB-Bz) displayed a high LOI value (40.0%), a UL-94 V-0 rating, and an extremely low heat release capacity (35.5 J/(g•K)). This work provides a facile and sustainable strategy for developing an anti-flammable benzoxazine thermoset without introducing flame retardant additives.

The flame-retardant thermoplastic polyurethane (TPU) with remarkable smoke suppression, anti-dripping and mechanical properties has been still a big conundrum in the field of fire safety science. In this article, an urethane-based phosphonate ester (UPE) flame retardant additive was successfully synthesized and incorporated into TPU. The fire safety, mechanical performance and flame-retardant mechanisms of TPU/UPE composites were lucubrated. With the incorporation of only 10 wt% UPE, TPU/10 wt% UPE composites passed UL-94 V-0 rating without dripping and the limited oxygen index (LOI) value reached 28.8%. Cone calorimetry tests indicated that the peak value of heat release and smoke production of TPU/10 wt% UPE composites were significantly diminished with the reduction of 70.6 and 54.1% in comparison with that of pure TPU. The analysis of flame-retarded mechanism for TPU/UPE indicated that UPE efficiently exerted free radical capture effect in gaseous phase, and stimulated the decomposition and charring of TPU composites in advance and the formation of high-quality char layer exerted isolation role in condensed phase. Therefore, the fire safety of TPU composites was enhanced by the incorporation of UPE. Meanwhile, the mechanical performance of TPU/UPE composite was well remained due to the good compatibility between UPE and TPU matrix. This work supplied a promising way for fabricating fire-safety TPU composites with preferable comprehensive properties.

A novel charring agent (PEPAPC) containing pentaerythritol and triazine structure, was successfully prepared via the nucleophilic substitution reaction of cyanuric chloride, 2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-4-methanol (PEPA), and piperazine. Then, different proportions of PEPAPC and ammonium polyphosphate (APP) were added into polypropylene (PP) at a 20% total loading via melt blending. The results of limiting oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis (TGA) and cone calorimeter test revealed that PEPAPC/APP system could effectively enhance the thermal stability and flame retardance of PP. When the weight ratio of APP to PEPAPC was 3:1 with a 20% loading (PP6), the PP composite achieved the highest LOI value of 28% and passed the vertical burning test (UL-94) V-0 rating. Meanwhile, PP6 showed the highest amount of char residues via TGA test and the lowest PHRR (253 kW/m2) via cone calorimeter test. Moreover, Scanning electron microscopy (SEM) also indicated that PEPAPC/APP system benefited to the formation of more compact char layer which hindered the transfer of volatiles and heat during burning. The investigation of their water resistance demonstrated that the PP6 still obtained a UL-94 V-0 rating after 72 h dipping in hot water.

Three phosphazene-triazine bi-group flame retardant additives (A1, A2, A3) with different terminal groups were synthesized from hexachlorocyclotriphosphazene (HCCP), cyanuric chloride and amine compounds (ethylenediamine, aniline, or p-phenylenediamine). Then they were applied with ammonium polyphosphate (APP) to prepare flame-retardant polylactic acid (PLA), separately. The molecule structures and thermal stabilities of these three flame retardant additives were characterized by Fourier transformed infrared spectrometry (FTIR), 1H and 13C Solid-State NMR spectrometer and thermogravimetric analysis (TGA). The flame-retardant properties and mechanism of the flame-retardant PLA composites were investigated by the limited oxygen index (LOI) test, vertical burning test, cone calorimeter test (CCT), scanning electron microscopy (SEM), and thermogravi-metric analyzer coupled to a Fourier-transform infrared spectrometer (TGA-FTIR). Results showed that the combination of phosphazene-triazine bi-group flame retardant additive with amino-terminated groups (A1 or A3) and APP brought better flame retardant properties to PLA resin than that of A2 without amino-terminated groups. PLA/A1/APP system got the best flame retardant properties, which exhibited the highest LOI value of 34.3% and preferably achieved UL-94 V-0 rating without dripping. Meanwhile, it not only obtained the lowest pk-HRR, THR, and TSR, but also reserved the largest amount of residual char, compared with other flame-retardant PLA composites. Such a significant improvement in flame retardancy was attributed to the PO2· radical quenching effect and inert gas dilution effect in gas phase, as well as barrier and protective effect and charring effect in condense phase. Besides, the poor performance on flame retardancy of PLA/A2/APP system was due to the lack of barrier and protective effect and charring effect in condense phase. All these revealed that the adjustment on terminal groups of flame-retardant additives not only affects their flame-retardant work mode, but also helps to explore the more efficient flame-retardant structures or systems.

Two kinds of polyamide charring agents, poly(piperazinyl malonamide) (PPMA) and poly(piperazinyl succinamide) (PPSA), were synthesized, and their only difference is that PPSA increases one methylene in the main chain compared with PPMA, which were confirmed via Fourier transform infrared spectroscopy (FTIR), Elemental analysis (EA), 1 H nuclear magnetic resonance ( 1 H-NMR) spectrum and 13 C solid NMR spectrum. Thermogravimetric (TG) analysis showed that the residue of PPMA was remarkably higher than that of PPSA during the thermal decomposition process. When they were used to flame retard EVA, PPMA showed higher efficiency than PPSA for passing the UL-94 V-0 rating, increasing the oxygen index (OI), and decreasing the total heat release (THR) and total smoke production (TSP); while the PPSA was more efficient in decreasing the peak of heat release rate (PHRR) and the peak of smoke production rate (peak SPR). The investigation for the pyrolysis products of PPMA and PPSA demonstrated that various aromatic structures were produced due to the dehydrogenation of piperazine ring during the decomposition of PPMA and PPSA, which endowed them with excellent charring capability, and the charring efficiency of PPMA was higher than that of PPSA. However, the PPSA with lower charring capability tended to decompose and cyclize to the imides and volatilize into the gas phase, which resulted in the more ideal microstructure of PPSA system than that of PPMA system, finally led to the lower PHRR and peak SPR of PPSA system in cone calorimeter test.

International audience; Various amounts of a phosphonium ionic liquid (IL169) were used as curing agents as well as flame retardants of epoxy prepolymer in order to prepare epoxy networks with improved fire properties. The flame retardancy of these resins was investigated using thermogravimetric analysis (TGA), pyrolysis combustion flow calorimetry (PCFC) and cone calorimetry. Phosphonium ionic liquid significantly reduced flammability without further addition of flame retardants due to the high amount of phosphorus (up to 3.69 wt%). The Peak of heat release rate decreases from 1099 kW/m(2) to 300 kW/m(2) in cone calorimeter at 35 kW/m(2) when incorporating 30 phr of IL169. Phosphorus modifies pyrolysis pathway, promotes charring and may act as flame inhibitor. The char layer protects the underlying polymer, leading to a high unburnt polymeric fraction. Char properties were studied using PCFC, Raman spectroscopy and X-ray tomography. Phosphorus improved the graphitization of the char and its thermooxidative stability.

An efficient zinc borate/silica composite flame retardant (CFR), with accumulating nano-silica (SiO2) on the surface of grown zinc borate (ZnB) flakes to form a core/shell structure, was synthesized via a facile precipitation route. When mixed with methyl vinyl silicone rubber (VMQ), this combined structure of CFR brought advantages in both flame retardancy and mechanical properties. During a process of combustion, these CFR particles migrated and assembled on the surface of combustion zone, increasing the local concentration and generating a tight and intumescent surface char layer even at a lower loading amount. In comparison with the VMQ/physical mixture (PM, with the same proportion of SiO2 and ZnB), the EVA/CFR formulation passed a UL94 V–0 rating and got a LOI value of 29.5, when used as an alternative of SiO2 filler. Meanwhile, CFR played an effective role in inhibiting the spread of fire; VMQ/CFR showed a fire growth index (FGI) of 0.56 much lower than 0.92 of VMQ/PM. In this case, the heat release rate (HRR), total heat released (THR) and smoke production rate (SPR) were considerably reduced. Moreover, the mechanical properties of VMQ/CFR blends, including both tensile strength (TS) and elongation at break (EAB), were significantly enhanced.

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

A novel halogen-free flame retardant (DTB) containing phosphorus, nitrogen and boron was successfully synthesized. The chemical structure of DTB was characterized by Fourier transform infrared spectroscopy (FTIR), 1 H and 31 P nuclear magnetic resonance (NMR). DTB was then blended with diglycidyl ether of bisphenol-A (DGEBA) to prepare flame-retardant epoxy resins. Thermal properties, flame retardancy and combustion behavior of the cured EP thermosets were investigated by thermogravimetric analysis (TGA), limited oxygen index (LOI) measurement, UL94 vertical burning test and cone calorimeter test. The results indicated that DTB significantly improved the flame retardancy as well as smoke inhibition performance of EP/DTB thermosets. Compared with the neat EP thermoset, the LOI of EP/DTB-3 thermoset was increased to 35.6% and the sample reached UL94 V-0 rating; the average of heat release rate (av-HRR), total heat release (THR) and total smoke production (TSP) of EP/DTB-3 thermoset were decreased by 33.3%, 33.0% and 35.5%, respectively. TGA results indicated that the char yields of EP/DTB thermosets were increased by 45.1–72.8% compared with that of the neat EP thermoset. The FTIR, SEM-EDX and Py-GC/MS results indicated that DTB contributed to form intumescent and glassy char layers and decomposed to generate free radicals with quenching effect. DTB was effective radical trapper as well as efficient charring agent for epoxy resin and exerted flame-retardant effect in gaseous and condensed phases simultaneously.

In this paper, a novel phosphorus/nitrogen-containing compound (DMT) constructed by maleimide, phosphaphenanthrene and triazine-trione was successfully synthesized. The chemical structure of DMT was characterized by Fourier transform infrared spectroscopy (FTIR), 1 H and 31 P nuclear magnetic resonance (NMR). DMT was then blended with diglycidyl ether of bisphenol-A (DGEBA) to prepare a series of flame-retardant epoxy resins. The flame retardancy and combustion behavior were evaluated using limited oxygen index (LOI), vertical burning (UL94) and cone calorimeter test. The results indicated that DMT dramatically enhanced the flame retardancy of epoxy resin. When the phosphorus content was only 1.0%, the EP/DMT-1.0 sample had a LOI value of 35.8%, and achieved UL94 V-0 rating. The combustion parameters disclosed that DMT obviously weakened the heat release intensity. Compared with the neat EP sample, the peak of heat release rate (pk-HRR), average of heat release rate (av-HRR) and total heat release (THR) of EP/DMT-1.25 sample were decreased by 59.4%, 28.2% and 27.4%, respectively. The decreased av-EHC of EP/DMT thermosets indicated that DMT inhibited the gaseous phase combustion due to the gaseous phase quenching effect of phosphorus-containing free radicals derived from the decomposed DOPO group. The condensed phase studies indicated that DMT promoted the charring of EP matrix and formation of phosphorus-containing char layer with compact and intumescent structure. DMT exerted bi-phase flame retardant effect.

A novel charring foaming agent N -methyl triazine-ethylenediamine copolymer defined as MTEC was synthesized from cyanuric chloride, methylamine and ethylenediamine through nucleophilic reaction. Its chemical structure was well characterized by Fourier transform infrared spectroscopy, elemental analysis and 13 C solid-state nuclear magnetic resonance. The wettability of flame retardant was evaluated by water contact angle (CA) tests, and the synthesized MTEC present excellent hydrophobic property with the water CA of 117°. Meanwhile, the water CA of the prepared intumescent flame retardant (IFR) system containing MTEC, ammonium polyphosphate and silica reached 104° and also presented hydrophobic property. The obtained IFR was incorporated into polypropylene (PP) resin to prepare flame retardant PP composites, and the flame retardancy, thermal degradation behavior, water resistance and flammability behavior for IFR-PP were investigated by limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimeter and thermogravimetric analysis (TGA) tests. Water resistant properties of IFR-PP composites were evaluated by soaking the samples into distilled water at 70 °C for 168 h. The results demonstrated that IFR-PP samples both passed UL-94 V-0 flammability rating before water treated and after hot water soaking and drying when the loading amount of IFR was 22 wt %, the LOI value of IFR-PP only decreased from 29.6 to 29.3% and the mass loss percent was only 0.17 and 0.69% for 3.2 and 1.6 mm samples after water soaking and drying. The TGA results indicated that the incorporation of IFR promoted PP matrix decomposition and charring at a relative low temperature, and then enhanced the char yield and thermal stability for IFR-PP composites at high temperature. The cone calorimeter tests revealed that the introduction of IFR greatly decreased the combustion parameters, such as heat release rate (HRR), smoke production rate (SPR) and so on. After water resistance test, the combustion parameter for IFR-PP was slightly increased. The scanning electron microscopy (SEM) tests indicated the introduction of IFR benefited to the formation of a sufficient, intumescent and homogeneous char layer on the materials surface during burning, which effectively prevented the underlying materials from further degradation and combustion. The structure and morphology of char layer for IFR-PP remained very well after water treated, consequently the water-treated IFR-PP presented excellent flame retardancy.

Fabricating an effective synergism between the condensed phase (char-forming) and the gas phase (free-radical quenching) is recently considered to be a very promising way to prepare high-efficient intumescent flame retardants. In this work, a novel hindered amine phosphorous-nitrogen macromolecular charring agent (HAPN) with free-radical quenching capability was synthesized and characterized. Then it was combined with ammonium polyphosphate (APP) to flame-retard polypropylene (PP). The flame retardancy and thermal stability of PP/HAPN/APP mixtures were investigated by limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimetric test (CCT) and thermogravimetric analysis (TGA). When the content of HAPN/APP was 25 wt%, PP/HAPN/APP could self-extinguish at 36 s after igniting in the oxygen concentration of 29.5% and achieve a UL-94 V-0 rating. Meanwhile, the peak heat release rate (PHRR), total heat release rate (THR), average heat release rate (AV-HRR) and average mass loss rate (AV-MLR) were significantly decreased. The flame retardant mechanism of HAPN/APP was explored and the results revealed that there was an effective synergism between the condensed phase and the gas phase during the combustion. In the condensed phase, HAPN could make PP involve into the char-forming reaction to promote the formation of compact and firm intumescent char layer. Simultaneously, the nitroxyl radical generated by HAPN could effectively restrain and even extinguish the flame in the gas phase by quenching the active free-radicals.

The flame retardants aluminum poly-hexamethylenephosphinate (APHP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide(DOPO) were incorporated into diglycidyl ether of bisphenol A (EP) thermoset, and then the synergistic flame-retardant behavior and mechanism of APHP/DOPO were investigated. Comparing with the thermosets with 6%APHP and 6%DOPO alone, 2%APHP/4%DOPO/EP thermosets obtained the higher limited oxygen index, higher UL94 rating, decreased peak of heat release rate and less total heat release from cone calorimeter test. The results reveal a synergistic effect between APHP and DOPO. The synergistic effect of APHP/DOPO in gaseous phase obviously reduced effective heat of combustion, which implies the better flame inhibition effect through quenching free radical chain reaction of combustion. The synergistic charring effect in condensed phase led to the higher char yield, which locked more carbonaceous contents in residue and form more barrier to heat spreading. All the results were caused by the early decomposed DOPO that interacted with the later decomposed APHP to produce more char and decease release of the inflammable gas. Therefore, the burning intensity of APHP/DOPO thermosets obviously was weakened by the synergistic effect of APHP/DOPO.

The preparation of halogen-free flame retardant thin-wall polycarbonate (PC) sheet with high performance is a global challenge. In our research, a composite flame retardants system composed of polysiloxane and perfluorinated sulfonate combined with a macromolecular charring agent, linear phenolic resin (LPR) could endow PC sheets (thickness: 0.4 mm) with UL94-V0 rating, showing high flame resistance efficiency. Regrettably, this efficient flame retardant system made the aging properties of PC seriously deteriorated due to the transesterification reaction between the phenolic hydroxyls and PC macromolecular chains, thus losing practical applied value. Introducing a small amount of boron acid (HB) could solve the fatal shortcoming through a quick coordination reaction between the boron atom and phenolic hydroxyl to effectively protect the PC backbone chains, and meanwhile further improve the flame retardance by increasing the charring stability of LPR due to the formed B–O bond with higher energy.

Blends of cotton with synthetic fibers are widely used for various military and industrial applications. Nylon-cotton (NYCO) blends offer high durability and strength from nylon and the softness of cotton, but both fiber types are highly flammable. Previously reported flame retardant coatings for cotton fabric, comprised of a complex of polyethylenimine and a polyphosphate, are not able to protect NYCO textiles, so a new generation of water-soluble polyelectrolyte complex coating is needed. The basis of this new treatment is an aqueous complex of polyethylenimine and ammonium polyphosphate that forms melamine polyphosphate in-situ during exposure to a melamine-containing solution. NYCO fabric was rendered self-extinguishing in a vertical flame test and pyrolysis combustion flow calorimetry showed a 28% reduction in total heat release, and a 65% reduction of cotton's peak heat release, with less than 20 wt% coating. The effectiveness of this halogen-free, flame retardant coating is due to condensed phase activity that includes cooling effects and charring. The ease of this coating procedure and the use of more environmentally benign chemicals deposited from aqueous solutions make this an industrially feasible alternative to current treatments.

The influence of a hypophosphite/cyclotetrasiloxane bi-group compound (MVC-AlPi) on the efficiency of intumescent flame retardant polypropylene (PP/IFR) consisting of ammonium polyphosphate (APP) and hyperbranched triazine-based charring agent (HTCFA) was investigated through evaluating the fire behavior and thermal stability by limiting oxygen index (LOI), the vertical burning tests (UL94), cone calorimeter and thermogravimetric analysis (TGA). The scanning electron microscopy (SEM), fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the final residues. The thermal decomposition and char-forming behavior between MVC-AlPi and each IFR formulation was studied by TGA and thermogravimetry-fourier transform infrared spectroscopy (TG-IR) test. Results revealed that a little amount substitution of IFR by MVC-AlPi imparted overall improvement in flame retardancy with reduced heat/smoke release and UL 94 V-0 rating for composites with a total loading of only 18 wt% instead of 25 wt%. The thermal decomposition behavior analysis exhibited a synergistic char-forming effect after the combination of MVC-AlPi, improving high-temperature thermal stability and yield of residual char with phosphorus- and silicon-containing crosslinked structures due to the interactions between MVC-AlPi and IFR, especially APP. The introduction of silicon into the cross-linked structures generated a fishnet-like protective device covering on the char surface inhibiting bursting the foamed carbonaceous structures and buttressed cell walls not to be fractured, leading to the formation of an integrated and thick intumescent char layer, plus the factor of the early and gentle release of non-flammable gases. This lifted flame retardant efficiency mainly contributed to the condense-phase mechanism with not ignored flame inhibition of phosphorus-containing free radicals generated from MVC-AlPi pyrolysis in gas phase. This work provided a potential way to enhance the flame retardant efficiency of IFR system.

In this paper, an organic/inorganic phosphorus–nitrogen–silicon flame retardant (DPHK) was synthesized by Kabachnik-Fields reaction and the sol-gel method, then it was used as a reactive flame retardant to prepare flame-retardant and smoke-suppressant epoxy resins (EP). The influence of DPHK on the flame retardancy of EP was investigated by limiting oxygen index (LOI), vertical burning test (UL-94 V) and cone calorimeter (CC) test. The results revealed that the EP containing only 3 wt% DPHK achieved UL-94 V-0 rating, and the corresponding LOI value reached 29%. Furthermore, the cone calorimeter results demonstrated that the DPHK effectively reduced the heat release rate (HRR) and total release rate (THR) of the EP. Compared with EP, the peak of heat release rate (PHRR) and THR of 4%DPHK-EP reduced by 36% and 30%, respectively. More importantly, the incorporation of DPHK suppressed the release of toxic fuel (CO) and smoke of EP, meanwhile, the increased char residue and CO/CO2 ratio of the DPHK-EP samples proved that DPHK presented not only the condensed-phase activity but also gas-phase activity. Furthermore, the involved gases and char residues were studied by using thermogravimetric analysis coupled with coupled with Fourier transform infrared spectrometry (TG-FTIR), pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), scanning electronic microscope together with the energy dispersive X-ray spectrometer (SEM-EDX) and X-ray photoelectron spectroscopy (XPS). The results certified the charring effect of the phosphaphenanthrene group and the enhancing effect of the silicon group. Subsequently, the flame inhibition effect and lesser combustible gases release enhanced the flame-retardant properties of EP.

It is always a big challenge for fabricating flame-retarded and smoke-suppressed polymers with excellent mechanical properties in fire-safety material field. In this work, novel organic-inorganic hybrid nanoparticles named phosphoryl polyethyleneimine amide-layered double hydroxide (PPEIA-LDH) were prepared via a simple reaction process. When the PPEIA-LDH nanoparticles were used to prepare flame-retardant thermoplastic polyurethane (TPU), it was found that a small amount of PPEIA-LDH remarkably reduced the fire hazard of TPU via a typical intumescent flame-retardant mode. Only 6.0 wt% PPEIA-LDH endowed TPU with a limiting oxygen index of 29.0% and a UL-94 V-0 rating, and also reduced total smoke production and total heat release of TPU by 31.6 and 49.9%, respectively, moreover, mechanical properties of TPU did not show any decrease in this case. The analysis for flame-retardant and smoke-suppression mechanisms demonstrated that synergistic charring between the organic component and the inorganic component in PPEIA- LDH played a crucial role in reducing the fire hazard of TPU. Excellent mechanical properties of TPU/PPEIA-LDH is ascribed to the uniform dispersion of PPEIA-LDH and good interfacial interaction with TPU. This work demonstrates that organic-inorganic hybrid nanoparticle may provide a promising solution for fabricating fire-safety polymers with excellent overall performance.

A DOPO-based phosphorus compound (DOPA) was synthesized and applied onto the pure and chitosan (CS) modified polyamide 66 (PA66) fabric surfaces via a simple pad-dry-cure method to improve the flame retardant properties of the same. The pure and chitosan modified fabric samples treated with DOPA at different content % degraded in a different way as the char residue formation and releasing of volatile and non-volatile gas species were dissimilar which were evident from the thermogravimatric and thermogravimetric-gas chromatography-mass spectroscopy (TG-GC-MS) test analysis. Obtained results also showed that no dripping occurred in the vertical burning test and a sharp increase in limiting oxygen index (LOI) values was noticed for all the treated fabric samples. CS modified PA66 fabric sample treated with a 10 wt % of DOPA exhibited a greater reduction in pHRR by 40% and showed superior flame retardant performance compared to the only DOPA treated pure fabric sample. The superb flame retardant properties of CS modified fabrics were due to the co-presence of DOPA and CS; where a synchronized gas phase and a condensed phase flame retardant mechanism was realized as DOPA showed a quenching effect in a gas phase mechanism and simultaneously, catalyzed the charring of CS in a condensed phase activity which was also justified from the TG-GC-MS analysis, TGA and FTIR analysis of char residues. However, this kind of facile application showed poor wash durability and deteriorated the physical properties of the fabric materials specifically treated with a higher DOPA content.

A novel polyhydroxy triazine-based charring agent, N-tris(hydroxymethyl)-amino triazine-piperazine copolymer (TTPC), was synthesized from piperazine, cyanuric chloride and tris(hydroxymethyl) aminomethane. The chemical structure of TTPC was characterized by Fourier transform infrared spectroscopy and 13C solid-state nuclear magnetic resonance. TTPC, ammonium polyphosphate (APP) and zinc borate (ZB) were then introduced into polypropylene (PP) by melt compounding to improve the fire performance of the composites. The test results showed that the presence of 21% APP-TTPC-ZB with mass ratio of 16:4:1 could significantly reduce the peak heat release rate from 1547 to 230 kW/m2, increase the limiting oxygen index value from 18.0 to 29.6% and upgrade the UL-94 rating from no rating to V-0, accompanied by the elimination of melt dripping. The thermal stability and charring behaviors of the composite samples were investigated by thermogravimetric analysis. The results showed that TTPC was a highly efficient charring agent, and ZB could act as synergist in the intumescent system. Based on the comprehensive study of fire performance, char morphology and mechanical properties, it can be concluded that TTPC is a superior charring agent, especially compared with the generally used pentaerythritol.

An inherent flame-retardant PA6 (FR-PA6) containing polydiphenylsiloxane (PDPS) was synthesized under the action of ethylene glycol (EG) via a facile “2-step” bulk polymerization. Inspiringly, EG acted not only as a ‘chain-linker’ to connect PA6 oligomer with PDPS moiety but also as a charring agent to increase the charring capacity of FR-PA6 after combustion. The prepared FR-PA6 reached 28.3% of limiting oxygen index (LOI), and passed the V-0 level of UL94 test with suppressed melt-dripping. After investigating the char residues and pyrolysis volatiles of FR-PA6 after combustion, the formation of silicon-rich protective layer was proved to be the essential factor to increase the flame retardancy of FR-PA6 via reducing the diffusion of pyrolysis volatiles, restricting the heat transfer and mass loss as well as preventing polymer melts from dripping. This work thus makes a worthwhile contribution to the development of FR-PA6 by offering a novel route that is easily accessible to industrial fabrication.

A phosphaphenanthrene flame retardant, DCAD, was synthesized by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), p-phenylenediamine and bio-based material cinnamaldehyde. After being incorporated into epoxy thermosets, DCAD can impose better flame retardancy and physical-mechanical properties to epoxy thermosets. 4%DCAD/EP achieved a LOI value of 35.6% and passed the UL94 V-0 rating, obviously decreased peak value of heat release rate, and generated the compact, stable and foam-like char layer during combustion. Through tracking by the gas-phase real-time infrared spectrum and observing the microscopic structures of residue, the higher flame retardancy of DCAD was attributed to the effectively quenching effect in gas phase and the high-quality charring effect in condensed phase. In addition, the N–H structures in reactive-type DCAD molecule can react with the epoxy groups of epoxy resin and two C C bonds in DCAD can form elastomer-like crosslink, resulting in that 4%DCAD/EP owned a raised impact strength of 25.74 kJ/m2 and did not decrease the glass transition temperature obviously in contrast to neat epoxy resin.

High impact polystyrene (HIPS) flame retarded by expandable graphite (EG) alone or in combination with microencapsulated red phosphorus (MRP) was prepared by melt compounding and investigated in terms of its fire property and charring behavior by limiting oxygen index, UL-94, cone calorimeter test, thermal analysis and scanning electron microscopy. It has been shown that EG itself has some flame-retarding and good smoke-suppressing effect on HIPS, but the flame retardant efficiency is rather low. The addition of a small amount of MRP can improve the flame retardancy and smoke suppression of the HIPS/EG composite and decrease the loading of flame retardant considerably. The HIPS/EG/MRP composite with a mass ratio of 80/15/5 produces more char yield and exhibits good flame retardancy and smoke suppression simultaneously. The thick and thermally stable intumescent char residue covered on the surface of the HIPS/EG/MRP composite can serve as an effective barrier against heat transfer and mass exchange between flame area in the gas phase and the polymer in the condensed phase. The temperature inside the HIPS/EG/MRP (80/15/5) composite is decreased more than that inside the HIPS/EG (80/20) composite upon burning. Due to a lower effective heat flux, the pyrolysis rate of the polymer is decreased. Moreover, fuel release rate is reduced because of the increasing thermal insulation property and char yield. As a result, the flame retardancy of the HIPS/EG/MRP composite is increased noticeably. The burnt residue of the HIPS/EG/MRP composite in cone calorimeter test is not homogeneous and contains much undecomposed polymer beneath the expanded char layer.

International audience; This study presents a two-steps synthesis of novel additive or reactive phosphorus-and-sulfur-containing flame retardants (P-FR) for epoxy thermosets. The first step consists in totally epoxydizing the phloroglucinol. Then, the epoxy functions grafted are partially or totally open by a thiol bearing a phosphonate group to obtain a reactive P-FR and an additive P-FR respectively. The two synthesized P-FR are then incorporated into a DGEBA-IPDA matrix according to an appropriate approach. The impact of these P-FR on glass transition temperature (Tg) is assessed by DSC. Tg values exhibit the plasticizing effect of the additive P-FR and the loss of epoxy functionality due to the incorporation of the reactive P-FR. The thermal properties of the prepared thermosets are characterized by TGA, showing the more efficient action of the reactive P-FR in condensed phase (charring). TGA-FTIR coupling show the presence of phosphorus-containing gases released during the thermal degradation but these P-containing gases have no radical scavenging action in the gas phase. PCFC analyses prove the similar flame retardant properties of the two P-FR by reducing significantly the pHRR, the THR and the EHC. The cone calorimeter tests exhibit a strong intumescent effect of the residue brought by the two P-FR, leading to insulating expanded residue.

The aim of this study was to investigate the acid catalysis of boron phosphate (BP) to model compound dipentaerythritol (DPER) which acted as char source during the thermal degradation and combustion. Various amounts of BP were added in DPER and then the thermal degradation and combustion behaviors were studied by means of thermogravimetric analysis (TGA) and microscale combustion calorimeter (MCC). Evolved Gases were evaluated using TGA-FTIR; solid residues were fully characterized by FTIR, X-ray photoelectron spectroscopy (XPS), Raman analysis and scanning electron microscopy (SEM). The results of TGA and MCC showed that the addition of BP leaded to the earlier thermal degradation of DPER and increased the amount of char residues, significantly decreased the peak heat release rate of DPER; the results of TGA-FTIR, XPS, Raman analysis and SEM revealed that the presence of BP accelerated the dehydration of DPER, kept more carbon and oxygen elements in condensed phases, promoted the formation of compact and stable char layer. This study indicated that Lewis acidic and Bronsted acidic sites in BP altered the single degradation pathway and catalyzed the crosslinking and char forming of DPER. BP maybe as a potential acid source applied in intumescent flame retardant polymers in future.

In spite of inherent low flammability, wool fibres have not been thoroughly investigated in fire retardant performance of natural fibre polymer composites. In the present work, polypropylene (PP)-short wool fibre composites were produced by compounding in a twin screw extruder and compression moulding. The enhancement of fire retardancy of the composites by adding wool and ammonium polyphosphate (APP) was confirmed by flammability tests. The cone calorimeter and vertical burn tests showed a significant decrease in heat release rate and a direct flame self-extinguishment of composites, respectively. Furthermore, the cone calorimeter experiments and char morphology have revealed that different polymer viscosities in the composites can influence the APP dispersion, leading to different flammability characteristics. The charring tendency of wool contributed to the formation of a rigid char layer and an increase in the amount of residues in the compact micro-structure of PP-wool-APP composites. The effects of wool and APP on mechanical properties have also been reported with improved tensile moduli of PP-wool-APP composites over those of neat PPs.

Controlled atmosphere, radiation-driven gasification experiments were conducted on a series of synthetic polymers including poly(acrylonitrile butadiene styrene), poly(ethylene terephthalate), poly(methyl methacrylate)-poly(vinyl chloride) alloy (Kydex) and polyetherimide. Mass loss rate and non-radiated surface temperature of coupon-sized material samples were measured simultaneously and recorded as a function of time. These temperature data were combined with the results of broadband radiation absorption measurements and previously conducted thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) to characterize the transport of thermal energy inside the gasifying materials through inverse modeling. Subsequently, complete pyrolysis models, based on the kinetics and thermodynamics of the thermal decomposition derived from the TGA and DSC experiments, were formulated and employed to predict the mass loss rate histories obtained at 30–90 kW m −2 of external radiant heat flux simulating fire exposure. Satisfactory predictions were obtained for all materials with the exception of polyetherimide, which highly intumescent behavior introduced large uncertainties in the gasification conditions.

Rigid steric hindering spiro-bisphosphates (PDMPDP and PDBPDP) were synthesized from spiro-pentaerythritol chlorophosphate and 2,6-dimethylphenol and o-tert-butylphenol respectively in order to investigate the effect of steric hindering groups on the flame retardant mechanism of bisphosphates and the effect of rigid spiro-pentaerythritol structure on the heat distortion temperature (HDT) of polycarbonate. A comparison of the steric hindering spiro-bisphosphates with the simplest phenyl spiro-bisphosphate (PDPDP) and commercial resorcinol bis(diphenyl phosphate) (RDP) on the flame retardancy of polycarbonate reveals that the presence of a thermally stable steric hindering group not only changes the efficiency but also shifts the mode of flame retardancy. In spite of low phosphorus content, PDMPDP and RDP show the highest efficiency of flame retardancy toward polycarbonate as evidenced by UL-94 combustion results with RDP exhibiting the strongest vapor phase action, PDMPDP the second, and PDPDP the least as judged from the phosphorus distribution in the vapor and the condensed phase. This is parallel to the tendency of chemical interactions between polycarbonate and flame retardants with PDPDP demonstrating the greatest interaction as proven by TGA study in air. It is suggested that the charring process of PDPDP interferes with that of polycarbonate and leads to microporous char that is seen in SEM and partially responsible for the poor flame retardancy of PDPDP. Compared to PC/RDP, PC/PDMPDP has a high HDT value.

A novel hyperbranched charring foaming agent (HCFA), successfully prepared via an A2B3 approach with about 97% yield, was combined with ammonium polyphosphate (APP) to flame-retard polypropylene (PP) at a 30 wt% loading. The results of thermogravimetric analyses of various PP samples in air and nitrogen showed that the HCFA/APP system could effectively improve the thermal and thermal-oxidative stabilities of the char residues. And PP3 with a 3/1 mass ratio of APP to HCFA left the highest amount of char residue at 800 °C. The studies of their flammability revealed that the addition of HCFA can make great contribution to the increase of the limiting oxygen index and the UL-94 V0 rating, and the decrease of the heat release rate (HRR) and fire growth index (FGI) of PP/APP/HCFA composites relative to PP with 30 wt% APP. The investigation of their water resistance demonstrated that the PP composites with a mass ratio of APP to HCFA being between 3:1 and 1:1 still obtained a UL-94 V-0 rating after 168 h soaking in hot water, due to the delayed migration of intumescent flame retardant from the complexation between hydrophilic APP and hydrophobic HCFA. Besides, their mechanical properties were also investigated.

A traditional intumescent flame retardant (IFR) has very poor water resistance due to the existence of ammonium polyphosphate (APP). How to improve the water resistance of APP or IFR without sacrificing its flame retardancy is an important issue for the wide application of IFR. In this study, the coated APP with polysiloxane shell (Si-APP) was prepared by in situ polymerization, and was used to flame retard polypropylene (PP) together with charring agent (CA). The resulting Si-APP was characterized by Fourier transform infrared spectra (FTIR), transmission electron micrographs (TEM) and thermogravimetric (TG) analysis. The water solubility of Si-APP was also investigated. The thermal stability and combustion behaviors of PP/Si-APP/CA and PP/APP/CA composites were also investigated through TG, limiting oxygen index (LOI), vertical burning test (UL-94), and cone calorimeter (CC) test. The results showed that the coated APP with polysiloxane shell could significantly improve the flame retardancy of IFR PP systems. At a total flame retardant loading of 25 wt%, the LOI value of PP/Si-APP/CA was 34.0%, which was higher than 30.6% of PP/APP/CA, and the UL-94 rating of the former was V-0 in the case of the specimen thickness of 1.6 mm, while the later was V-2 rating. CC test results showed that the average value of heat release rate (HRR), the total heat release (THR), and the peak of smoke production rate (SPR) of PP/Si-APP/CA decreased in comparison with PP/APP/CA system, especially, THR decreased by 50.0%. Further, the char residue of the former increased significantly compared with the latter, greatly increased by 238.9%. In addition, the thermal stability and water resistance of IFR PP composites were also improved due to the modification of APP. The mechanism for the improvement of flame retardancy was also discussed based on the experimental results. All these results illustrate that the coating of APP with polysiloxane shell is an efficient method to improve the flame retardancy and water resistance of APP-containing IFR PP systems.

Bismuth subcarbonate ((BiO)2CO3·xH2O) nanoplate, a bismuth-containing layered nanomaterial, is successfully applied in improving fire safety properties of polymers for the first time. The introduction of (BiO)2CO3·xH2O (≤6.2 wt%) into poly(methyl methacrylate) (PMMA) matrix by in situ polymerization method enhances the thermal stability, flame retardancy and smoke suppression properties remarkably including increased onset degradation temperature (T0.1, by 58 °C) and mid-point degradation temperature (T0.5, by 24 °C), and decreased peak heat release rate, total heat release, toxic volatile organic products (VOP) and smoke density. Morphological studies of PMMA/(BiO)2CO3·xH2O nanoplate composites by Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) suggest that (BiO)2CO3·xH2O nanoplates are well dispersed in the PMMA matrix. Thermal decomposition behaviors investigated by Thermogravimetric analysis (TGA) and char analysis studied by Fourier transform infrared spectra (FTIR) demonstrate the catalytic charring effect of (BiO)2CO3·xH2O to PMMA matrix. Due to the char formation during degradation, the toxic VOP amount and smoke evolution from PMMA combustion are reduced. Meanwhile, thermal decomposition of (BiO)2CO3·xH2O can release carbon dioxide (CO2) and water, which was evidenced by thermogravimetric analysis/infrared spectrometry (TGA-IR) results. The (BiO)2CO3·xH2O nanoplates combines several flame-retardant strategies including the char formation, dilution effect of CO2 and water, and physical barrier effect, and thus enhance the thermal stability, flame retardancy and smoke suppression of PMMA/(BiO)2CO3·xH2O composites simultaneously.

Ammonium polyphosphate (form I APP) was modified via ion exchange reaction with ethylenediamine, and the resulting modified ammonium polyphosphate (MAPP) was used alone to prepare intumescent flame-retardant (IFR) polypropylene (PP) via melt blending. The flame retardancy of PP containing MAPP was investigated by limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter (CC). The LOI value of PP containing 40 wt% of MAPP reached 32.5%, which increased by 56.9% compared with that of PP with the same content of APP, and the UL-94 rating was V-0 in the case of specimen thickness of 1.6 mm, while the latter had no rating. CC test results showed that the heat release rate (HRR), the mass loss rate (MLR) and the smoke production rate (SPR）of PP/MAPP system decreased significantly compared with neat PP and PP/APP systems. Especially the fire growth rate (FGR) and SPR peak of PP containing 35 wt% MAPP decreased by 89.1% and 63.2% respectively compared with those of PP containing 35 wt% APP. These results demonstrated that only by incorporating the MAPP without additional charring agents, could PP be successfully flame retarded. Fourier transform infrared spectroscopy (FTIR) etc. were used to investigate the flame retardant mechanism of MAPP, and it was found that both the generation of carbon–carbon double bonds after the scission of C–N bonds and the residue consisting of some stable structures such as P–N–C and C–N etc. caused the charring ability to increase dramatically, which must be the principal reason for the much better flame retardancy of PP/MAPP system without any additional charring agent compared with APP.

A novel oligomeric charring agent (PTCA) containing triazine and diphenyl group was synthesized by cyanuric trichloride, diphenylamine and ethylenediamine through nucleophilic reaction. The structure and thermal stability of PTCA were characterized by Fourier transform infrared spectrometry (FT-IR), element analysis testing and thermogravimetric analysis (TGA). The effectiveness of the novel intumescent flame retardant system (ammonium polyphosphate and PTCA, abbrev. IFRs) on fire retardancy and thermal stability of polypropylene (PP) was investigated through UL-94, limiting oxygen index (LOI) tests, cone calorimeter tests and thermogravimetric analysis (TGA). UL-94 vertical burning test revealed that the addition of 20 wt% IFRs into neat PP was enough to reach V-0 rating. LOI value of PP by addition of 20 wt% IFRs rose from 17.5 to 31 vol%. Moreover, a remarkable decrease in peak heat release rate (PHRR: −90%), total heat release (THR: −54%) and total smoke release (TSR: −51%) was revealed when the loading of IFRs was 20 wt%. TGA results showed that PTCA presented good char formation ability, and it would greatly increase the thermal stability of PP when combined with APP. The Fourier transformed infrared spectra (FTIR) revealed that the flame retardant mechanism might be ascribed to aromatic and phosphoric char formed during combustion. Additionally, the structure and morphology of char residues were further studied by SEM and Raman spectra.

The effects of aluminium phosphinate (AlPi) on the flame retardancy of three different polymers, namely, poly(2, 6-dimethyl-1, 4-phenylene oxide) (PPO), thermoplastic polyurethane (TPU) and polypropylene (PP), were investigated through cone calorimeter tests (CONE), vertical burning tests (UL-94), limiting oxygen index (LOI), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) observation. The results showed that the amounts of AlPi needed to reach V-0 UL-94 rating in the PPO, TPU and PP matrices were 0 wt%, 30 wt% and 50 wt%, respectively. Moreover, the addition of AlPi significantly increased the LOI values of PPO and PP, but had almost no effect on that of TPU. With the addition of AlPi, the peak of heat release rate (PHRR) of PPO and TPU decreased whereas that of PP increased. The total heat evolved (THE) of all polymers decreased by adding AlPi into the polymers. With the addition of AlPi, PPO composite formed a dense char layer and showed the best flame retardancy, TPU composite formed a thinner char layer and PP composite did not form char layer during combustion. Based on the thermal degradation behaviour and the char residue of these composites, the flame retardancy mechanisms of the three systems were discussed. For AlPi/PPO composites, the flame retardancy mechanism was condensed phase charring mechanism because of the formation of continuous char layer during combustion. For AlPi/TPU composites, AlPi acted mainly in gas phase, and a synergistic reaction of phosphorus and nitrogen compounds occurred and diethylphosphic acid providing flame inhibition was released during the burning process. As a result, the addition of AlPi successfully reduced the melt-dripping and enhanced flame retardancy of TPU matrix. For AlPi/PP composites, AlPi acted as a flame inhibitor in gas phase, decreasing the effective heat of combustion of the volatiles (THE/TML) and increasing the amount of CO.

The thermal degradation behavior and fire performance of a series of halogen-free flame-retardant high impact polystyrene (HIPS) composites containing magnesium hydroxide (MH) and microencapsulated red phosphorus (MRP) were studied by various means. It is shown that the oxidation of MRP has much influence on the thermal degradation behavior of the composite. This oxidative reaction releases heat and causes mass gain when the composite is degraded in air. No exothermic peak and mass gain peak appear in nitrogen under identical conditions. The HIPS composite containing both MH and MRP generate a smooth, compact, continuous and stable charred residue layer upon degradation in air and in flame. The residue is mainly composed of amorphous magnesium phosphate and black carbon. At the same loading level of 50 wt%, the composite filled by either MH or MRP individually burns out, drips vigorously and fails to pass the UL-94 test. However, the HIPS/MH/MRP composite self-extinguishes quickly and reaches the V-0 rating with ease. There is appreciable synergism between MH and MRP on the flame retardancy of HIPS. The combination of both flame retardants enhances the charring capacity and fire retardancy of the composite and decreases the loading of flame retardants remarkably. The flame retardant effect occurs mainly in the condensed phase.

Liquid polysiloxane (PSI) and zinc borate (ZB) were combined for the flame retardance of polycarbonate (PC). During polymer combustion, for the PC flame-retarded with PSI only, PSI can form char residue containing silica on the material surface. But the liquid silicone tends to drip with melting polymer and volatilize in high temperature, thus decreasing the charring performance. In the case of only ZB flame retardant involved, this inorganic flame retardant and possible some of its decomposition products (B2O3) more difficultly move to the surface and it appears that they do not effectively contribute to the char formation. Present study suggests that the existing synergism between PSI and ZB is the result of chemical reaction via forming cross-linking B–O–Si structure. As results, the loss of Si/silicone is reduced by eliminating the melt dripping. Meanwhile, boron species can be “dragged” by PSI (in the form of borosiloxane) to the surface of the char residue. Consequently, Si and B elements together contribute to the integrity of char residue layer with better quality, achieving obviously improved flame retardance compared with only PSI and only ZB flame retardant systems.

This paper presents a study of polyethersulfone (PES)/halloysite nanotube (HNTs) nanocomposites prepared by melt compounding either through a simple extrusion process or via a water-assisted extrusion procedure. Scanning and transmission electron microscopy techniques are combined with rheological measurements to assess the influence of polymer end groups (eCl or eOH) and water injection on the HNTs dispersion state. A morphological transition form microcomposite to nanocomposite is achieved when replacing eCl chain ends of PES by eOH groups, especially when water is injected during processing. By a combination of Soxhlet extraction and thermogravimetric analysis, we show that some PES(OH) chains are covalently bonded onto the aluminosilicate surface during extrusion. A mechanism describing the physico-chemical action of water is presented. The best system in terms of clay dispersion has been retained to characterize PES-HNTs nanocomposites with respect to their thermo-mechanical, thermal and fire (mass loss calorimetry and UL-94) properties. Dynamic mechanical analysis shows a significant enhancement in the storage modulus of halloysite-based nanocomposites when compared to the unfilled matrix. The improved thermal and thermo-oxidative stability of PES in presence of HNTs is mainly attributed to the labyrinth effect provided by individually dispersed nanotubes, which is reinforced during the decomposition process by the formation of a protective charred ceramic surface layer. The mechanism of action of HNTs for fire retardancy of PES presumably arises from a synergistic effect between physical (i.e. ceramic-like structure formation and mechanical reinforcement of the intumescent char) and chemical (i.e. charring promotion) processes taking place in the condensed phase. According to this study, the straightforward and cost-effective melt compounding route could pave the way for future development of high-performance nanoscale polymeric materials combining enhanced thermal properties and excellent flame retardant behaviour.

Polyamide 6,6 (PA6,6) is usually fire retarded in bulk, using aluminum diethylphosphinate (AlPi). In one of our recent papers, it was shown that good fire-retardant properties (e.g. V0 at the UL94 test) could also be achieved by applying an intumescent varnish on the PA6,6 surface. Excellent fire-retardant properties were even obtained combining 5% of AlPi in the bulk with an intumescent coating applied on the polymer surface. The Glow Wire Flammability Index (GWFI) test was validated at 960 °C whereas it was only validated at 750 °C without the AlPi. This paper first aims to describe the mechanism of action of an intumescent coating to protect a polymer, as it was never previously studied in the literature. It was evidenced, analyzing with 13 C, 31 P and 27 Al solid state NMR spectra of the materials at different combustion times that during burning one part of the virgin polymer begins to degrade and is mixed with the semi-viscous charring intumescent layer. In some way, due to this mixture of both phases, it is as if the polymer was fire retarded in bulk during burning. The second objective was to investigate the potential synergy between the gas phase fire-retardant mechanism of AlPi and the condensed phase fire protective mechanism of the intumescent coating to explain the enhanced fire-retardant properties. Similarly, using NMR technique, the interest to combine the bulk treatment in low amount and the intumescent coating was evidenced: the AlPi cannot completely sublimate because of the protective coating, and is probably condensed inside the intumescent structure pores. As it is trapped in the condensed phase, it then degrades into aluminophosphates, increasing the heat barrier efficiency of the expanded char layer.

The fire performance of curable-silicone based coatings containing expandable graphite (EG) is evaluated in hydrocarbon fire scenario (standard UL1709) using a lab-scale furnace test. From 5% to 25% of expandable graphite is incorporated in the silicone matrix to make the coating swell during the fire experiment. Fire performance of 25%EG/silicone-based coating is better than that of commercial intumescent paint used as reference. This is explained by a high swelling velocity (18%/s), a high expansion (3400%), an impressive cohesion of the char and a low heat conductivity at high temperature (0.35 W/K m at 500 °C). To elucidate this way of charring, the residue after fire testing was analyzed by scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, X-ray photoelectron spectroscopy and X-ray diffraction. It is shown that the char is composed of two main parts: the top is composed of quartz and amorphous silica which coat graphite flakes and the heart of the char is composed of graphite flakes embedded in degraded silicone forming a complex structure. It is shown that, the good cohesion of the char is due to: (i) the presence of the undegraded silicone matrix; and (ii) the coating of graphite pellets by silicone.

One stage halogen-free flame retardant was prepared by poly(p-ethylene terephthalamide) (PETA) or poly(para-phenylene terephthanlamide) (PPTA) and ammonium polyphosphate (APP), the system had a good flame retardancy on acrylonitrile-butadiene-styrene (ABS) resin when loading was 30% or more, but once mass fraction decreased, the system did not maintain previous flame retardancy. To improve the efficiency of this kind of flame retardant, we mixed PETA with PPTA and introduced red phosphorus to play as the second acid source. This system had two charring process—swell and shrink. The flammability and thermal stability of IFR-ABS composites were investigated by limiting oxygen index (LOI), UL-94 vertical burning and thermo gravimetric analysis (TGA) test. Results showed that this IFR system had both good flame retardant and anti-dripping abilities for ABS, when the mass fractions of APP, PETA, PPTA and red phosphorus were only 12%, 4%, 1.33% and 2.66% respectively, the LOI of flame retardant ABS was 27 and UL-94 vertical burning test reached V-0. The TGA curves suggested that there was a distinct cooperation. Additionally, the structure and the mechanism of charring were studied by FTIR and SEM.