Reduction In Peak Heat Release Rate Research Articles

Fabrication and Properties of Biobased Layer-by-Layer Coated Ramie Fabric-Reinforced Unsaturated Polyester Resin Composites

Ramie fabrics were modified with biobased electrolytes, i.e. cationic chitosan and anionic phytic acid, and the flame retardant cationic electrolyte melamine by a layer-by-layer (LbL) assembly method. Then, the LbL-modified fabric-reinforced unsaturated polyester resin (UPR) composites were fabricated by a hand lay-up method. The onset thermal degradation temperature of the LbL-modified fabric-reinforced UPR composites was lower than that of the raw fabric-reinforced UPR sample, while char residues of the composites were greatly improved and the release of combustible organic volatiles was suppressed during the combustion. Moreover, the flame retardancy of the composites was enhanced with increasing the LbL assembly number, which was evidenced by the markedly reduced peak heat release rate and the total heat release values obtained from cone calorimetric tests. The limiting oxygen index value of the composites was increased from 26.0% to 34.5%.

Melamine resin/graphite nanoflakes hybrids and its vacuum-assisted prepared epoxy composites with anisotropic thermal conductivity and improved flame retardancy

Melamine resin/graphite nanoflakes hybrids (MGNH) were synthesized by in situ polymerization. The SEM and TEM demonstrate that melamine resin was self-deposited on the surface of the flakes. MGNH is uniform sheeted hybrids which exhibits excellent dispersiveness. MGNH/epoxy composite (MGNH/EP) is prepared via vacuum-assisted method. The special prepared method endows MGNH/EP with interesting anisotropic thermal conductivity. The coefficient of thermal conductivity of the composite in normal direction is 0.4024 W m−1 K−1, while that of MGNH/EP in horizontal direction is 1.5596 W m−1 K−1. The optical microscope image of the composite suggests that the nanoflake is arranged as a parallel conduction medium, it is demonstrated that direct flake-flake conduction can form heat-transfer passages, which contributes to the higher thermal conductivity of the composite in horizontal direction. Also, MGNH/EP shows excellent flame retardant properties, evidenced by the dramatically reduced peak heat release rate and 51% of total heat release values compared with neat EP obtained from a microcombustion calorimeter. The reduced fire hazard can mainly attributed to the synergistic effects of melamine resin and graphite nanoflakes.

Layered double hydroxide-oxidized carbon nanotube hybrids as highly efficient flame retardant nanofillers for polypropylene.

Aqueous miscible organic layered double hydroxides (AMO-LDHs) can act as organophilic inorganic flame retardant nanofillers for unmodified non-polar polymers. In this contribution, AMO [Mg3Al(OH)8](CO3)0.5·yH2O LDH–oxidized carbon nanotube (AMO-LDH–OCNT) hybrids are shown to perform better than the equivalent pure AMO-LDH. A synergistic effect between the AMO-LDH and OCNT was observed; this endows the hybrid material with enhanced flame retardancy, thermal stability, and mechanical properties. The thermal stability of polypropylene (PP) was significantly enhanced by adding AMO-LDH–OCNT hybrids. For PP mixed with AMO-LDH–OCNT hybrids to produce a composite with 10 wt% LDH and 2 wt% OCNT, the 50% weight loss temperature was increased by 43 °C. Further, a system with 10 wt% of AMO-LDH and 1 wt% OCNT showed a peak heat release rate (PHRR) reduction of 40%, greater than the PHRR reduction with PP/20 wt% AMO-LDH (31%). The degree of dispersion (mixability) between AMO-LDH and OCNT has a significant effect on the flame retardant performance of the hybrids. In addition, the incorporation of AMO-LDH–OCNT hybrids led to better mechanical properties, such as higher tensile strength (27.5 MPa) and elongation at break (17.9%), than those composites containing only AMO-LDH (25.6 MPa and 7.5%, respectively).

Functionalized Carbon Nanotubes with Phosphorus- and Nitrogen-Containing Agents: Effective Reinforcer for Thermal, Mechanical, and Flame-Retardant Properties of Polystyrene Nanocomposites

Aminated multiwalled carbon nanotubes (A-MWCNT) were reacted with diphenylphosphinic chloride (DPP-Cl) to prepare the functionalized MWCNT (DPPA-MWCNT). A-MWCNT and DPPA-MWCNT were respectively mixed with polystyrene (PS) to obtain composites through the melt compounding method. SEM observations demonstrated that the DPPA-MWCNT nanofillers were more uniformly distributed within the PS matrix than A-MWCNT. PS/DPPA-MWCNT showed improved thermal stability, glass transition temperature, and tensile strength in comparison with PS/A-MWCNT, resulting from good dispersion and interfacial interactions between DPPA-MWCNT and PS matrix. The incorporation of DPPA-MWCNT to PS significantly reduced peak heat release rate, smoke production rate, and carbon monoxide and carbon dioxide release in cone calorimeter tests. The enhanced fire-retardant properties should be ascribed to the barrier effect of carbon nanotubes, which could provide enough time for DPPA-MWCNT and its functionalized groups to trap the degrading polymer radicals to catalyze char formation. The char layer served as an efficient insulating barrier to reduce the exposure of polymer matrix to an external heat source as well as retarding the flammable gases from feeding the flame.

Studies on Synthesis of Electrochemically Exfoliated Functionalized Graphene and Polylactic Acid/Ferric Phytate Functionalized Graphene Nanocomposites as New Fire Hazard Suppression Materials.

Practical application of functionalized graphene in polymeric nanocomposites is hampered by the lack of cost-effective and eco-friendly methods for its production. Here, we reported a facile and green electrochemical approach for preparing ferric phytate functionalized graphene (f-GNS) by simultaneously utilizing biobased phytic acid as electrolyte and modifier for the first time. Due to the presence of phytic acid, electrochemical exfoliation leads to low oxidized graphene sheets (a C/O ratio of 14.8) that are tens of micrometers large. Successful functionalization of graphene was confirmed by the appearance of phosphorus and iron peaks in the X-ray photoelectron spectrum. Further, high-performance polylactic acid/f-GNS nanocomposites are readily fabricated by a convenient masterbatch strategy. Notably, inclusion of well-dispersed f-GNS resulted in dramatic suppression on fire hazards of polylactic acid in terms of reduced peak heat-release rate (decreased by 40%), low CO yield, and formation of a high graphitized protective char layer. Moreover, obviously improvements in crystallization rate and thermal conductivities of polylactic acid nanocomposites were observed, highlighting its promising potential in practical application. This novel strategy toward the simultaneous exfoliation and functionalization for graphene demonstrates a simple yet very effective approach for fabricating graphene-based flame retardants.

Construction of β-FeOOH nanorod-filled layer-by-layer coating with effective structure to reduce flammability of flexible polyurethane foam

The β-FeOOH nanorod-filled coatings were deposited onto flexible polyurethane foam by layer-by-layer assembly technique to reduce its flammability. The coatings were constructed by two assembly systems: one was bilayer system, which was comprised of polyethylenimine and β-FeOOH nanorods; other one was trilayer system, which was comprised of polyethylenimine, β-FeOOH nanorods, and sodium alginate. Scanning electron microscopy images indicated that the randomly oriented and entangled network structure can only be observed for the coating that assembled by trilayer system. Cone calorimetry test revealed that the coating assembled by trilayer system can lead to significant reduction in peak heat release rate compared with those of control foam, 61.8% peak heat release rate reduction ever occurred to the eight trilayers coated sample, but the coating assembled by bilayer system has slight reduction (<20%). The result is attributed to trilayer approach being beneficial to fabricate coating with sufficient thickness to protect the underlying foams during burning. Copyright © 2016 John Wiley & Sons, Ltd.

Thermal degradation of polystyrene composites. Part II. The effect of nanoclay

In this work, thermal degradation behavior polystyrene/organoclay nanocomposites containing tribromophenol end-capped brominated epoxy oligomer, (BE) with or without Sb2O3 were investigated systematically via direct pyrolysis mass spectrometry. Incorporation of organically modified montmorillonite into polystyrene, (PS) matrix not only increased thermal stability but also the probability of radical recombination, disproportionation and carbonization reactions causing increase in the char yield. Exfoliation of organoclay in BE phase of PS-BE matrix affected the extent of radical coupling and disproportionation reactions between the thermal degradation products of PS and organic modifier. In addition, the evolution of BE based products was hindered partly and the attacks of HBr to epoxy units generating H2O became more efficient. During the pyrolysis of polystyrene/organoclay nanocomposite involving both BE and Sb2O3, the relative yields diagnostic products of both oxybromides and bromides of antimony were increased significantly in the temperature region where PS decomposition took place which in turn increased the efficiency of radical scavenging and reduced peak heat release rate while increasing limiting oxygen index.

Preparation of zinc hydroxystannate-decorated graphene oxide nanohybrids and their synergistic reinforcement on reducing fire hazards of flexible poly (vinyl chloride).

A novel flame retardant, zinc hydroxystannate-decorated graphene oxide (ZHS/GO) nanohybrid, was successfully prepared and well characterized. Herein, the ZHS nanoparticles could not only enhance the flame retardancy of GO with the synergistic flame-retardant effect of ZHS but also prevent the restack of GO to improve the mechanical properties of poly (vinyl chloride) (PVC) matrix. The structure characterization showed ZHS nanoparticles were bonded onto the surface of GO nanosheets and the ZHS nanoparticles were well distributed on the surface of GO. Subsequently, resulting ZHS/GO was introduced into flexible PVC and fire hazards and mechanical properties of PVC nanocomposites were investigated. Compared to neat PVC, thermogravimetric analysis exhibited that the addition of ZHS/GO into PVC matrix led to an improvement of the charring amount and thermal stability of char residue. Moreover, the incorporation of 5 wt.% ZHS/GO imparted excellent flame retardancy to flexible PVC, as shown by increased limiting oxygen index, reduced peak heat release rate, and total heat release tested by an oxygen index meter and a cone calorimeter, respectively. In addition, the addition of ZHS/GO nanohybrids decreased the smoke products and increased the tensile strength of PVC. Above-excellent flame-retardant properties are generally attributed to the synergistic effect of GO and ZHS, containing good dispersion of ZHS/GO in PVC matrix, the physical barrier of GO, and the catalytic char function of ZHS.

Evaluating the Effectiveness of Complex Fire-Retardants on the Fire Properties of Ultra-low Density Fiberboard (ULDF)

The preparation conditions of complex fire-retardant (FR) agents containing boron compounds (BF, X1), nitrogen-phosphorus compounds (NPF, X2), silicon compounds (SF, X3), and halogen compounds (HF, X4) for ultra-low density fiberboard (ULDF) were optimized using a response surface methodology. The effects and interactions of X1, X2, X3, and X4 on the fire properties of ULDF were investigated. An optimum char yield of 61.4% was obtained when the complex fire-retardant agents contained 33.9% boron, 27.2% nitrogen-phosphorus, 15.0% silicon, and 28.6% halogen. Compared with control fiberboard (CF), the heat release rate (HRR) profiles of all fiberboards with FRs were reduced. The peak HRR reduction in BF and NPF was more pronounced than for SF and HF at this stage. And the mixed fiberboard (MF) had the lowest pkHRR of 75.02 kW m−2. In total heat release (THR) profiles, all fiberboards with FRs were lower than the CF. Unlike the HRR profiles, HF had the lowest THR profile of 15.33 MJ m−2. Additionally, Si compounds showed greater effectiveness in preventing ULDF mass loss than BF, NPF, and HF. MF showed the highest residual mass (40.94%). Furthermore, the synergistic effect between four FR agents showed more significant results in ULDFs.

Effect of reactive time on flame retardancy and thermal degradation behavior of bio-based zinc alginate film

A bio-based zinc alginate film was prepared via a facile ionic exchange and casting approach. Effects of reactive time on the flame retardancy and thermal stabilities of zinc alginate film were studied systemically; and the pyrolysis mechanism of zinc alginate was investigated. According to the results in vertical burning (UL-94) and thermogravimetric analysis (TGA) tests, the optimized reactive time was 2 h. Microscale combustion calorimetry (MCC) results indicated that the addition of zinc ion significantly increased the flame retardancy of alginate, showing in the reduction of peak heat release rate (PHRR), from 105 to 12.0 W/g; and the reactive time had no obvious effect on the reduction of PHRR for zinc alginate. Thermogravimetric analysis coupled with Fourier transform infrared analysis (TG-FTIR) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) results showed that zinc alginate produced much less flammable products than sodium alginate did in whole thermal degradation process. The results implied that zinc ion had the catalysis effect during the pyrolysis process. Finally, the possible thermal degradation mechanism of zinc alginate was proposed.

Comparative study on synergistic effect of LDH and zirconium phosphate with aluminum trihydroxide on flame retardancy of EVA composites

Flame-retardant ethylene vinyl acetate (EVA) composite based on aluminum trihydroxide (ATH), layered double hydroxide (LDH) and organo-modified zirconium phosphate (mZrP) were prepared by melt-compounding method. The synergistic effect of LDH and mZrP with ATH on the fire behavior and thermal stability of EVA composites was studied by limiting oxygen index, UL-94 test, cone calorimeter and thermogravimetric analysis. EVA composite with ATH and LDH passed the V-0 rating while EVA composite with ATH and mZrP exhibited relatively low peak heat release rate. EVA/ATH composite with 10 mass% LDH exhibited a char yield of 34 % at 700 °C, while its counterpart with 10 mass% mZrP showed 29 %, indicating LDH possessed superior flame-retardant synergistic efficiency with ATH over mZrP in terms of promoting char formation. Regarding the heat release rate (HRR), EVA/ATH composite with 10 mass% mZrP displayed a 73 % reduction in PHRR, whereas its counterpart with the equivalent loading of LDH showed a lower flame-retardant synergistic efficiency (a 58 % reduction in peak HRR). The results above demonstrated that LDH mainly functioned as catalyst in char formation, while mZrP was beneficial to restraining heat release.

One-pot, bioinspired coatings to reduce the flammability of flexible polyurethane foams.

In this manuscript, natural materials were combined into a single "pot" to produce flexible, highly fire resistant, and bioinspired coatings on flexible polyurethane foam (PUF). In one step, PUF was coated with a fire protective layer constructed of a polysaccharide binder (starch or agar), a boron fire retardant (boric acid or derivative), and a dirt char former (montmorillonite clay). Nearly all coatings produced a 63% reduction in a critical flammability value, the peak heat release rate (PHRR). One formulation produced a 75% reduction in PHRR. This technology was validated in full-scale furniture fire tests, where a 75% reduction in PHRR was measured. At these PHRR values, this technology could reduce the fire threat of furniture from significant fire damage in and beyond the room of fire origin to being contained to the burning furniture. This flammability reduction was caused by three mechanisms-the gas-phase and condensed-phase processes of the boron fire retardant and the condensed-phase process of the clay. We describe the one-pot coating process and the impact of the coating composition on flammability.

MoS2 nanolayers grown on carbon nanotubes: an advanced reinforcement for epoxy composites.

In the present study, carbon nanotubes (CNTs) wrapped with MoS2 nanolayers (MoS2-CNTs) were facilely synthesized to obtain advanced hybrids. The structure of the MoS2-CNT hybrids was characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy measurements. Subsequently, the MoS2-CNT hybrids were incorporated into EP for reducing fire hazards. Compared with pristine CNTs, MoS2-CNT hybrids showed good dispersion in EP matrix and no obvious aggregation of CNTs was observed. The obtained nanocomposites exhibited significant improvements in thermal properties, flame retardancy and mechanical properties, compared with those of neat EP and composites with a single CNT or MoS2. With the incorporation of 2.0 wt % of MoS2-CNT hybrids, the char residues and glass transition temperature (Tg) of the EP composite was significantly increased. Also, the addition of MoS2-CNT hybrids awarded excellent fire resistance to the EP matrix, which was evidenced by the significantly reduced peak heat release rate and total heat release. Moreover, the amount of organic volatiles from EP decomposition was obviously decreased, and the formation of toxic CO was effectively suppressed, implying the toxicity of the volatiles was reduced and smoke production was obviously suppressed. The dramatically reduced fire hazards were generally ascribed to the synergistic effect of MoS2 and CNTs, containing good dispersion of MoS2-CNT hybrids, catalytic char function of MoS2 nanolayers, and physical barrier effects of MoS2 nanolayers and CNT network structure.

Water-soluble polyelectrolyte complexes that extinguish fire on cotton fabric when deposited as pH-cured nanocoating

In an effort to quickly impart flame retardant behavior to cotton fabric, and in ambient conditions, a water-soluble polyelectrolyte complex (WPEC) was evaluated. A OnePot mixture consisting of polyethylenimine and poly(sodium phosphate) imparts self-extinguishing behavior in a single step. This nanocoating maintains the fabric's weave structure by conformally coating individual fibers. Appreciable weight gain (23%) is achieved with just a single 30 s immersion in the WPEC suspension. Treatment of this coating with acidic buffer further renders it insoluble in water and durable to rinsing. Uncoated cotton is readily consumed during vertical flame tests, while OnePot-coated fabric, followed by buffer treatment of pH 5 or lower (16.5% weight gain or less), self-extinguishes through an intumescent mechanism. Microscale combustion calorimetry reveals a total heat release reduction of 88% and peak heat release rate reduction of 81%. This work demonstrates the ability of a WPEC nanocoating to prevent ignition of cotton fabric with few processing steps and relatively low weight gain.

Thermal and flammability study of polystyrene composites containing magnesium–aluminum layered double hydroxide (MgAl–C16 LDH), and an organophosphate

The flame retardancy and thermal stability of polystyrene compounded with Bis(2,4-dicumylphenyl)pentaerythritol diphosphate (DPP) and or a palmitate containing magnesium aluminum LDH (MgAl–C16 LDH) were investigated via thermogravimetric analysis, cone calorimetry, and pyrolysis combustion flow calorimetry. Cone calorimetry and thermogravimetry measurements revealed that the addition of 5 and 10 mass% of MgAl–C16 LDH to PS resulted in substantial reduction in peak heat release rate (PHRR) (47 and 61 %, respectively) of the polymer and minimal improvements in thermal stability (5 and 2 °C, respectively, for the temperature at which 50 % mass loss occurs, ΔT50). On the other hand, there was insignificant reduction in PHRR for composites containing DPP at loadings of 5 mass%, while loadings of 10 mass% resulted in a relatively low reduction of 22 %. This difference was attributed to the more compact residue formed by the LDH systems during cone calorimetry analysis. There was substantial improvements in the thermal stability of PS compounded with 10 mass% of DPP with ΔT50 being 21 °C. The combination of DPP and LDH resulted in a negative effect on the flammability performance of the LDH; thus, we did not observe any synergism between the LDH and DPP. Results from micro-scale combustion calorimetry did not correlate with results from cone calorimetry.

Intumescing multilayer thin film deposited on clay-based nanobrick wall to produce self-extinguishing flame retardant polyurethane

Significant loss of life and property results each year from fires fueled by polyurethane found in household furnishings. Established layer-by-layer flame retardant systems were combined to produce a stacked nanocoating for flame retarding polyurethane foam. A bilayer system of chitosan (CH) and vermiculite provides a nanobrick wall exoskeleton, protecting the polyurethane long enough for an intumescing system of CH and ammonium polyphosphate to activate and form a bubbled char layer. Stacking these two recipes allows the foam to self-extinguish when exposed to a butane torch without any flame spread or shrinking of the foam, two things commonly observed with either coating alone. Cone calorimetry revealed a significant peak heat release rate reduction of 66 % relative to the uncoated foam. This study demonstrates the ability to combine flame retardant mechanisms sequentially. This nanocoating acts as an environmentally benign template for flame retarding various complex substrates, especially those found in household furnishings.

TiO2 loaded on graphene nanosheet as reinforcer and its effect on the thermal behaviors of poly(vinyl chloride) composites

• Titanium dioxide/graphene hybrid was synthesized by a one-pot solvothermal route. • The graphene/TiO 2 hybrid was employed to enhance the properties of PVC materials. • The composite exhibited the increased glass transition temperature and storage modulus. • The HCl release rate was reduced by the addition of graphene/TiO 2 hybrid into PVC. Titanium dioxide/graphene hybrids were synthesized by a facile in situ solvothermal route and introduced to enhance the properties of the poly(vinyl chloride) (PVC) materials. X-ray diffraction and transmission electron microscopy results indicated that TiO 2 nanoparticles were homogeneously anchored on the graphene oxide nanosheets and the reduction of graphene oxide occurred simultaneously during the one-pot solvothermal process. With the incorporation of 2.0 wt% graphene/TiO 2 hybrids, a 3.5 °C increment in the glass transition temperature and a 50% increase in the storage modulus were observed compared to neat PVC. The improvement of the temperature of maximum mass loss rate and reduction of maximum mass loss rate were also observed from thermogravimetric analysis, indicating the enhanced thermal stability of PVC composites. Moreover, the reduced peak heat release rate and HCl release rate obtained from microscale combustion calorimeter and thermogravimetric analysis-infrared spectrometry indicated the superior fire safety of PVC composites. The changes of the fire behavior were primarily attributed to the synergistic effects of graphene/TiO 2 hybrids: the adsorption and barrier effect of fillers slow down the thermal degradation of polymer, and restrain the heat transfer and the flammable or toxic gaseous products release.

Influence of exfoliated graphite nanoplatelets on the flammability and thermal properties of polyethylene terephthalate/polypropylene nanocomposites

Nanocomposites based polyethylene terephthalate (PET)/polypropylene (PP) (70/30 wt%) blends and exfoliated graphite nanoplatelets (GNP) as reinforcing fillers were developed using melt extrusion process. The filler concentration was varied between 0 -5.98 wt percent (%) (0–7 phr). The resulting nanocomposites were characterized in terms of flame retardancy, thermal conductivity, thermal behavior, morphology and structure. Cone calorimeter analysis, limiting oxygen index (LOI) and UL94 flame rating tests revealed that addition of GNPs to PET/PP improved the flame retardancy of PET/PP/GNP nanocomposites significantly. Cone calorimeter data show a significant reduction of peak heat release rate (PHRR), mass loss rate and delayed time to ignition (TTI) due to addition of GNPs to PET/PP blend. As much as 37% reduction in PHRR and 32% increase in TTI were observed for the maximum GNP loading. Enhancements of flammability properties were attributed to the development of compact, dense, uniform char layers on the surface of nanocomposites. The effective thermal conductivity was found to vary linearly with GNP loading which was attributed to the formation of effective interconnected heat conduction bridges formed by the GNPs. It was found that the effective thermal conductivity of the nanocomposites was increased by about 80%, i.e. from 1.2 W/m.K for the unreinforced PET/PP blend to 1.9 W/m K for the 5.98 wt% (7 phr) reinforced PET/PP/GNP nanocomposites. Differential scanning calorimetry results indicated that the addition of GNPs increased crystallization temperatures but decreased degree of crystallinity of PET/PP/GNP nanocomposites. However; the melting points remained essentially unaffected. Transmission electron microscopy and field emission scanning electron microscopy showed uniform dispersion of GNPs in the matrix with the formation of interconnected GNP sheets at 3 phr. Isolated instances of exfoliation of GNPs was also observed.

Fabrication of Ce-doped MnO2decorated graphene sheets for fire safety applications of epoxy composites: flame retardancy, smoke suppression and mechanism

Ce-doped MnO2–graphene hybrid sheets were fabricated by utilizing an electrostatic interaction between Ce-doped MnO2 and graphene sheets. The hybrid material was analyzed by a series of characterization methods. Subsequently, the Ce-doped MnO2–graphene hybrid sheet was introduced into an epoxy resin, and the fire hazard behaviors of the epoxy nanocomposite were investigated. The results from thermogravimetric analysis exhibited that the incorporation of 2.0 wt% of Ce-doped MnO2–graphene sheets clearly improved the thermal stability and char residue of the epoxy matrix. In addition, the addition of Ce–MnO2–graphene hybrid sheets imparted excellent flame retardant properties to an epoxy matrix, as shown by the dramatically reduced peak heat release rate and total heat release value obtained from a cone calorimeter. The results of thermogravimetric analysis/infrared spectrometry, cone calorimetry and steady state tube furnace tests showed that the amount of organic volatiles and toxic CO from epoxy decomposition were significantly suppressed after incorporating Ce–MnO2–graphene sheets, implying that this hybrid material has reduced fire hazards. A plausible flame-retardant mechanism was hypothesized on the basis of the characterization of char residues and direct pyrolysis-mass spectrometry analysis: during the combustion, Ce–MnO2, as a solid acid, results in the formation of pyrolysis products with lower carbon numbers. Graphene sheets play the role of a physical barrier that can absorb the degraded products, thereby extend their contact time with the metal oxides catalyst, and then promote their propagate on the graphene sheets; meanwhile pyrolysis fragments with lower carbon numbers can be easily catalyzed in the presence of Ce–MnO2. The notable reduction in the fire hazards was mainly attributed to the synergistic action between the physical barrier effect of graphene and the catalytic effect of Ce–MnO2.

Functionalized graphene oxide/phosphoramide oligomer hybrids flame retardant prepared via in situ polymerization for improving the fire safety of polypropylene

A novel strategy based on functionalized graphene oxide (FGO)/phosphoramide oligomer flame retardant was developed to overcome the challenges of the dispersion of graphene sheets in polymer matrix and the ease of the burn-out of graphene under air atmosphere. Graphene oxide (GO) was modified by 4,4-diaminodiphenyl methane (DDM) and then in situ incorporated into phosphoramide oligomer, resulting in a nanocomposite flame retardant (FRs-FGO) containing exfoliated graphene. Subsequently, the flame retardant (FRs-FGO) was incorporated into polypropylene (PP) and simultaneously compatilized with PP-grafted maleic anhydride. TEM results showed that the FGO was dispersed more uniformly in PP than the bare GO because of the strong interfacial interaction and previous exfoliation of FGO in FRs before blending. The thermal properties investigated by thermogravimetric analysis (TGA) indicated that the addition of FRs-FGO into PP resulted in a significant improvement of thermal stability at elevated temperature with higher char yields. Moreover, the crystallization and fire safety properties of PP composites were also improved by the incorporation of FRs-FGO, including increased crystallization temperature (11.4 °C increase), reduced peak heat release rate (66.9% reduction) and decreased total heat release (24.4% decrease), and decreased fire growth rate index (73.0% decrease). The cone results indicated the simple blending of GO with FRs and exhibited less improvement in fire safety properties than FRs-FGO, which resulted from the improved dispersion and thermal stability of FGO sheets. The flame retardant mechanism was because of the shielding effect of FGO and char layers, which could reduce the release of combustible gases and inhibit the mass and heat transfer between the gas phase and condensed phase.