Increase In Char Yield Research Articles

Biomass-derived Schiff base compound enabled fire-safe epoxy thermoset with excellent mechanical properties and high glass transition temperature

Abstract Recently, biomass-derived fire-safe epoxy thermosets have been developed for the substitute of petroleum-derived bisphenol A epoxy thermosets due to the shortage of petroleum resources and the negative health impacts of petroleum-derived products. However, the synthesis of bio-based epoxy thermosets combining excellent mechanical properties and fire-safety performance is still a great challenge. In this paper, a novel Schiff base compound 4,4′-((1E,1′E)-((oxybis(4,1-phenylene))bis(azanylylidene))bis(methanylylidene))bis(benzene-1,2-diol) (PH-ODA) was efficiently synthesized from bio-based protocatechualdehyde. PH-ODA was subsequently reacted with epichlorohydrin to obtain the epoxy monomer (1E,1′E)-N,N′-(oxybis(4,1-phenylene))bis(1-(3,4-bis(oxiran-2-ylmethoxy)phenyl)methanimine) (PH-ODA-EP). After curing PH-ODA-EP with 4,4′-diaminodiphenylmethane (DDM), the cured resin PH-ODA-EP/DDM network possessed a high glass transition temperature (Tg) of 204.9 °C and showed a 181.8%, 105.8% and 87.0% increase in char yield (in N2) (41.7% vs. 14.8%), storage modulus (at 30 °C) (6.01 GPa vs. 2.92 GPa) and tensile modulus (6.21 GPa vs. 3.32 GPa), respectively, compared with the cured bisphenol A epoxy resin (DGEBA)/DDM. Moreover, PH-ODA-EP/DDM possessed excellent fire-safety properties (limited oxygen index (LOI) value = 40.5%) due to the introduction of Schiff base structure, showing a 90.9% and 72.0% reduction (compared with DGEBA/DDM) in peak heat release rate and total heat release value. This work provided a facile and sustainable route for synthesizing Schiff base compounds using biomass-derived resources, exhibiting great potential for the application in high-performance fire-safe epoxy thermosets.

Effects of zirconium carbide content on thermal stability and ablation properties of carbon/phenolic composites

Ceramic particles were utilized to improve thermal stability and ablation properties of carbon/phenolic (C/Ph) composites. In this study, zirconium carbide (ZrC) modified C/Ph composites were fabricated by vacuum impregnation method, and effects of ZrC content on thermal stability and ablation properties were investigated by thermogravimetry analysis and plasma wind tunnel test. Moreover, morphological characterization was carried out using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Experimental results showed that increasing ZrC content could lead to an evident increase in char yield, but an observable reduction in linear ablation rates and back-face temperatures because of the formation of ZrO2 layer on the ablation surface. The work provided an effective way to improve thermal stability and ablation properties of C/Ph composites.

From Cells to Residues: Flame-Retarded Rigid Polyurethane Foams

ABSTRACT Rigid polyurethane foams (RPUFs) exhibit short times to ignition as well as rapid flame spread and are therefore considered to be hazardous materials. This paper focuses on the fire phenomena of RPUFs, which were investigated through a multimethodological approach. Water-blown polyurethane (PUR) foams without flame retardants (FRs) as well as water-blown PUR foams containing triethyl phosphate as a gas phase-active FR were examined. The aim of this study is to clarify the influence of the FR on the fire phenomena during combustion of the foams. Additionally, materials’ densities were varied to range from 30 to 100 kg/m3. Thermophysical properties were studied by means of thermogravimetry; fire behavior and flammability were investigated via cone calorimeter and limiting oxygen index, respectively. During the cone calorimeter test, the temperature development inside the burning specimens was monitored with thermocouples, and cross sections of quenched specimens were examined visually, giving insight into the morphological changes during combustion. The present paper delivers a comprehensive study, illuminating phenomena occurring during foam combustion and the influence of a FR active in the gas phase. The superior fire performance of flame-retarded PUR foams was found to be based on flame inhibition, and on increased char yield leading to a more effective protective layer. It was proven that in-depth absorption of radiation is a significant factor for estimation of time to ignition. Cross sections investigated with the electron scanning microscope exhibited a pyrolysis front with an intact foam structure underneath. The measurement of temperature development inside burning specimens implied a shift of burning behavior towards that of non-cellular materials with rising foam density.

Improved adhesion, heat resistance, anticorrosion properties of epoxy resins/POSS/methyl phenyl silicone coatings

A series of coatings composed of hydroxyl-terminated methyl phenyl silicone rubber (PSi) and silanized epoxy resins (SERs) were prepared in a facile way. Four kinds of SERs with different structures and degree of functionality were synthesized successfully and used to modify the silicone coating. The obtained room temperature vulcanized (RTV) silicone coatings showed excellent adhesion, great heat resistance and anticorrosion properties. Compared with pure PSi, the coatings containing 25 wt% SERs showed better thermal properties, manifested as delayed degradation temperature and greatly increased char yield at 800℃. The adhesion of coatings all reached the highest level (degree 0) which exceeded that of pure PSi coating (degree 2). Furthermore, the anticorrosion property of the coatings in 5 wt% acid, alkaline, and saline environments was all improved. The incorporation of SERs improved the compatibility between the silicone rubber and epoxy resins, in which the epoxy group created more adhesion of cured blended coating and POSS led a significant enhancement in thermal and anticorrosive properties. Their combined effect endowed silicone coatings with more application prospects.

A novel exploration of metal–organic frameworks in flame-retardant epoxy composites

In this work, a series of transition metal–organic frameworks (MOFs) were prepared through self-assembly of organic bridging ligands and transition metal ions. The structure of MOFs samples was analyzed by XRD, FTIR, TG, and TEM. The influences of MOFs on flame resistance, toxicity reduction, and smoke suppression of epoxy were explored in detail. The findings presented that low addition amount of MOFs had a positive effect on decreasing the fire hazards of epoxy. Loading of 2 mass% MOFs into epoxy led to the decrease in thermal degradation rate and increase in char yields. Meanwhile, the values of peak heat release rate, total heat release, and average mass loss rate of epoxy composites were cut down effectively, in comparison with neat epoxy. Moreover, the remarkable decrease in smoke production rate, total smoke production, and CO, CO2 yield could be provided by cone calorimeter test. The char residues after cone calorimeter test were investigated by SEM and Raman spectra, and the flame-retardant mechanism was discussed.

Synthesis of an aromatic N-heterocycle derived from biomass and its use as a polymer feedstock

Aromatic N-heterocyclic compounds are very important chemicals, which are currently produced mostly from petroleum. Here we report that a pyridazine-based compound 6-(4-hydroxy-3-methoxyphenyl)pyridazin-3(2H)-one (GSPZ) can be efficiently synthesized by the Friedel-Crafts reaction of guaiacol and succinic anhydride, both of which can be derived from biomass. GSPZ is then treated with bio-based epichlorohydrin to prepare the epoxy resin precursor GSPZ-EP. With 4,4'-diaminodiphenylmethane as curing agent, GSPZ-EP possesses higher glass transition temperature (187 oC vs. 173 oC) and shows a 140%, 70 and 93% increase in char yield (in N2), storage modulus (30 oC) and Young’s modulus, respectively when compared with a standard petroleum-based bisphenol A epoxy resin. Moreover, the cured GSPZ-EP shows good intrinsic flame retardancy properties and is very close to the V-0 rating of UL-94 test. This work opens the door for production of aromatic N-heterocyclic compounds, which can be derived from biomass and employed to construct high performance polymers.

Controlled polymerization of 3,4-dihydro-2H-1,3-benzoxazine and its properties tailored by Lewis acids

Polymerization reaction of a typical thermosetting benzoxazine monomer, BA-a, is tailored intentionally by particular Lewis acids including aluminium trichloride (AlCl3), phosphorus pentachloride (PCl5) and zinc chloride (ZnCl2), and polybenzoxazines with different crosslinking structures are obtained. Their rheological behaviors, polymerization mechanisms, chemical crosslinking structures and thermal properties are systematically studied. The results suggest that AlCl3 and PCl5 are much more efficient than ZnCl2 to affect the polymerization reaction of BA-a. PCl5 and AlCl3 can promote the generation of more carbocations, thus the polymerization of benzoxazine follows cationic chain polymerization mechanism. However, in the presence of less effective ZnCl2 or in the case of neat benzoxazine, the polymerization follows step polymerization mechanism. It is learned that the Lewis acids can promote crosslinking reaction of dangling arylamine benzene rings and form arylamine Mannich linkages that vary with the catalytic efficiency of the Lewis acids. As a result, the increase of impact strength by 36.4%, the increase of flexural strength by 243.4%, the increase of flexural modulus by 42% and the increase of char yield by 18.6% (absolute value) can be achieved by using different Lewis acids.

Synthesis of a novel DOPO‐based polyphosphoramide with high char yield and its application in flame‐retardant epoxy resins

AbstractA novel and highly effective flame retardant (FR), DOPO‐TPMP oligomer, was synthesized by a simple condensation of 4‐(hydroxymethyl)‐2,6,7‐trioxa‐1‐phosphabicyclo[2.2.2]octane‐1‐oxide and phosphorus oxychloride followed by a polycondensation reaction with 6‐(2,5‐dihydroxyphenyl)‐6H‐dibenzo[c,e][1,2]oxaphosphinine‐6‐oxide. The chemical structure of DOPO‐TPMP was well characterized using Fourier transform infrared and NMR spectra. DOPO‐TPMP was used as an additive‐type FR for epoxy resin (EP). The FR properties of the resultant EP composites were investigated by limiting oxygen index (LOI) test, UL‐94 vertical burning test and cone calorimeter measurements. Specifically, the EP composite containing 10.0% DOPO‐TPMP achieved a LOI value of 36.1%, V‐0 rating in the UL‐94 test and a 58% reduction in peak heat release rate. Further mechanism analysis attributed the enhanced flame retardancy to the increased char yield on the addition of DOPO‐TPMP. © 2019 Society of Chemical Industry

Flame retardant effect and mechanism of a novel DOPO based tetrazole derivative on epoxy resin

A novel highly efficient flame retardant with phosphaphenanthrene group and tetrazole ring, 6-(((1H-tetrazol-5-yl)amino)(4-hydroxyphenyl)methyl)dibenzo[c,e][1,2]oxaphosphinine 6-oxide (ATZ), was synthesized and incorporated into epoxy matrix as co-curing agent to remarkably improve the flame retardancy of epoxy resin. The curing behaviors of epoxy systems were investigated by non-isothermal differential scanning calorimetry (DSC) tests. The thermal and flame retardant properties of epoxy thermosets were studied by thermogravimetric analysis (TGA), DSC analysis, limiting oxygen index (LOI), UL-94 and cone calorimeter test. Moreover, the flame retardant mechanism was comprehensively investigated by analyzing the thermo-oxidative degradation and pyrolysis behaviors, along with the morphology and structure of residual char of epoxy thermosets. It showed that ATZ could accelerate the crosslinking reaction of epoxy system. The incorporation of ATZ resulted in the decrease of glass transition temperature (Tg) and initial degradation temperature, while the increase of char yield at high temperature of epoxy thermoset. With the incorporation of 6 wt% ATZ, the thermoset achieved an LOI value of 33.7% and V-0 rating in UL-94 test. Moreover, the peak heat release rate (PHRR) in cone calorimetry test decreased by 26% in comparison with that of neat EP, accompanied with lower total heat release (THR) and total smoke production (TSP). The flame retardant mechanism was ascribed to the barrier effect of intumescent and compact phosphorus-rich char layers with honeycombed cavity structure inside in the condensed phase, and quenching effect of phosphorous radicals and diluting effect of nonflammable gases in the gas phase. The interesting blowing out effect observed during UL-94 test arose from the intensive release of pyrolytic gases with considerable phosphorous radicals and nonflammable gases from the surface of sealed char layers.

Reactive cyclic phosphonamide flame retardant for epoxy resins

ABSTRACTTo take the advantage of reactivity of five‐membered cyclic phosphorus compounds, 1,2,3‐tri‐phenyl‐1,3,2‐diazaphospholidine‐2‐oxide (TPDPO) was explored as a reactive flame retardant for epoxy resins (EPs). Through model compounds, it has been established that TPDPO selectively reacts with the secondary hydroxyl group and is inert toward both aryl amino groups and epoxide groups. The result of Soxhlet extraction supports that TPDPO is permanently bonded to the cured EPs. At a loading of only 8 wt % (0.74 wt % phosphorus), TPDPO enables the cured epoxy to achieve a UL‐94 V0 rating. The thermogravimetric analysis–Fourier transform infrared analyses of the gaseous products suggest that the excellent flame retardancy of EP–TPDPO is partly due to the enhanced dehydration process of the epoxy. Also an increased char yield and the formation of a coherent char layer contribute to the good fire performance of EP–TPDPO. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 47411.

Phosphorus-Based α-Amino Acid Mimetic for Enhanced Flame-Retardant Properties in an Epoxy Resin

This work demonstrates the introduction of a phosphonate moiety into a commonly used curing agent, 4,4′-diaminodiphenylmethane (DDM), via an α-aminophosphonate. This compound (DDMP) can be prepared and isolated in analytical purity in under 1 h and in good yield (71 %). Thermoset polymer (epoxy-derived) samples were prepared using a room-temperature standard cure (SC) and a post-cured (PC) protocol to encourage incorporation of the α-aminophosphonate into the polymer network, with improved flammability properties observed for the latter. Thermogravimetric analysis under a nitrogen atmosphere showed increased char yield at 600°C, and similar observations were made when analysis was conducted in air. Significant reductions in flammability are observed at very low phosphorus content (P% = 0.16–0.49 %), demonstrated by higher char yields (25.5 from 14.0 % in air), decreased burn time from ignition (60 to 24 s), and decreased mass loss after ignition (87.6 to 58.5 %). Limiting Oxygen Index for the neat polymer (P% = 0 %, 20.3 ± 0.8 %) increased with increasing α-aminophosphonate additive (P% = 0.16 %, 20.8 ± 0.6 %; P% = 0.32 %, 21.4 ± 0.4 %; P% = 0.49 %, 22.6 ± 0.8 %).

Stepwise pyrolysis of mixed plastics and paper for separation of oxygenated and hydrocarbon condensates

Mixed plastics and papers are two of the main fractions in municipal solid waste which is a critical environmental issue today. Recovering energy and chemicals from this waste stream by pyrolysis is one of the favorable options to achieve a circular economy. While pyrolysis products from plastics are mainly hydrocarbons, pyrolysis products from paper/biomass are highly oxygenated. The different nature of the two pyrolysis products results in different treatments and applications as well as economic values. Therefore, separation of these two products by multi-step pyrolysis based on their different decomposition temperatures could be beneficial for downstream processes to recover materials, chemicals and/or energy. In this work, stepwise pyrolysis of mixed plastics and paper waste was performed in a batch type fixed bed reactor using two different pyrolysis temperatures. Neat plastic materials (polystyrene, polyethylene) and cellulose mixtures were used as starting materials. Then, the same conditions were applied to a mixed plastics and paper residue stream derived from paper recycling process. The condensable products were analyzed by GC/MS. It was found that pyrolysis temperatures during the first and second step of 350 and 500 °C resulted in a better separation of the oxygenated and hydrocarbon condensates than when a lower pyrolysis temperature (300 °C) was used in the first step. The products from the first step were derived from cellulose with some heavy fraction of styrene oligomers, while the products from the second step were mainly hydrocarbons derived from polystyrene and polyethylene. This thus shows that stepwise pyrolysis can separate the products from these materials, although with some degree of overlapping products. Indications of interaction between PS and cellulose during stepwise pyrolysis were observed including an increase in char yield, a decrease in liquid yield from the first temperature step and changes in liquid composition, compared to stepwise pyrolysis of the two materials separately. A longer vapor residence time in the second step was found to help reducing the amount of wax derived from polyethylene. Results from stepwise pyrolysis of a real waste showed that oxygenated and acidic products were concentrated in the liquid from the first step, while the product from the second step contained a high portion of hydrocarbons and had a low acid number.

Improving the Thermal Stability of Textile Fibers By Natural Fiber Welding

Natural Fiber Welding (NFW) is an Ionic Liquids (IL) based engineering process that can manipulate biopolymer matrices without destroying their underlying structure. It can be used to incorporate functional materials into the biopolymer matrix. In this study, we evaluate how NFW can be used to improve the thermal stability of natural textile fibers. First, a variety of synthesized and/or commercially available flame-retardant micro/nanomaterials are welded onto the surface of the fibers. Then, using thermogravimetric (TG) analysis, we demonstrate how each coating can enhance the thermal stability of the textile yarn. In some cases, thermal stability improves by as much as 25 °C, primarily through delays in the onset of thermal decomposition and increased char yield. Our data reveal strong potential for NFW to be used to deliver fiber-welded textile yarns with improved thermal stability.

Catalytic mechanism of sulfuric acid in cellulose pyrolysis: A combined experimental and computational investigation

Sulfuric acid (H2SO4) is widely used as a strong acid catalyst in biomass pyrolysis process, and exhibits prominent catalytic effects on the pyrolytic reactions and product distribution. In this study, the fundamental catalytic mechanism of H2SO4 on cellulose pyrolysis process was investigated via combined experimental and computational methods. Both thermographic analysis (TGA) and pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) experiments were performed to reveal the pyrolytic characteristics and product distribution in the H2SO4-catalyzed pyrolysis of cellulose. In addition, quantum chemistry methods were employed to build the reaction models and investigate the major H2SO4-assisted reactions in initial cellulose pyrolysis process, i.e., depolymerization of the cellulose chain, bridged dehydration, ring-opening, ring-contraction and dehydration of the free hydroxyl groups. The results indicate that the H2SO4-assisted depolymerization via C1-O1 bond scission and bridged dehydration reactions take place in a two-step mechanism involving a sulfate ester intermediate. While other reactions occur via a one-step mechanism involving only hydroxyl group or both hydroxyl and sulfonic groups of H2SO4. The activation energies of above reactions are all decreased by adding H2SO4, and thus lowering the degradation temperature of cellulose. Among all initial pyrolytic reactions, dehydration reactions which are inconspicuous in the non-catalytic process, become very important in the catalytic process, because their activation energies are decreased dramatically by adding H2SO4 (from 322.7 to 372.1 to 152.2–237.7 kJ/mol). The promoting effect on the dehydration reactions plays a vital role in the increased char yield and significant change of organic volatile product distribution. Through the promoted dehydration reactions, unsaturated structures of cellulose are formed, which is favorable for the formation of certain dehydrated products at the expense of depolymerized and ring scission products.

Flame-retardant thermoplastic polyester based on multiarm aluminum phosphinate for improving anti-dripping

A novel multiarm aluminum salt of pentaerythrityl ester of tetra(carboxyethylmethylphosphinic acid) (Alcpp) was synthesized and added into thermoplastic polyester elastomer (TPEE). Thermal analysis, evolved gas analysis (TGA-FTIR), flammability tests (LOI, UL94), microcombustion calorimeter (MCC) and chemical analyses of residues (SEM-EDX) were used. Alcpp provides TPEE with desired flame retardancy and anti-dripping property and shows a good compatibility with TPEE. TGA-FTIR and SEM-EDX analysis show that Alcpp can depress the heating release and promote the char forming and acts mainly in condensed phase. In addition, Alcpp combining with MPP achieves better fire-resistant performance than Alcpp alone. When total additives is kept 28 wt%, 25 wt% Alcpp combining 3 wt% MPP exhibits the optimum synergy by increasing char yield and depressing heat release and flammability. The reason for the synergy is due to a strong compact carbonaceous char resulting from reaction between Alcpp and MPP, which effectively prevent the dripping of the TPEE during combustion.

Design of reduced graphene oxide decorated with DOPO-phosphanomidate for enhanced fire safety of epoxy resin

A facile approach was developed to simultaneously functionalize and reduce graphene oxide (GO) with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-phosphonamidate. To achieve stable dispersion and effective stress transfer, graphene was functionalized by polyethyleneimine (PEI). To improve the fire resistance of bare graphene, DOPO was grafted on the surface of PEI-reduced graphene oxide (PEI-rGO) to obtain the grafting of DOPO-phosphonamidate on the graphene. A morphological study indicated that, due to the good interfacial interaction between the functionalized graphene and epoxy (EP), functionalized reduced graphene oxide (f-rGO) was well-dispersed in the host polymer. Incorporation of 3.0 wt% f-rGO led to the increased char yields of the EP. Moreover, the storage modulus and glass transition temperature were improved, respectively. The evaluation of combustion behavior demonstrated that the peak heat release rate and total heat release of f-rGO/EP were reduced by 31% and 34.3%, respectively, compared to those of neat EP. This dramatically reduced fire hazards were mainly attributed to the synergistic effect of f-RGO. On one hand, DOPO-phosphonamidate on the surface of GO promoted flame inhibition in the gas phase while protecting the rGO against fire. On the other hand, the adsorption and barrier effect of rGO inhibited the heat and gas release, respectively, promoting the formation of graphitized carbons.

Structure-property relationships in epoxy hybrid networks based on high mass fraction pendant POSS incorporated at molecular level

Epoxy hybrid networks containing up to 50 wt.% pendant polyhedral oligomeric silsesquioxane (POSS) dispersed at molecular level are prepared by polymerizing DGEBA-POSS precursors with 4,4′-diaminodiphenylmethane (DDM). A high molecular weight control precursor was prepared without pendant POSS cage to quantify the effect of pendant POSS cage on network free volume, number of crosslinks per unit volume and glass transition temperature. Differential scanning calorimetry (DSC) shows drastic decrease in Tg with increasing pendant POSS content. The Tg value of hybrid network containing 50wt.% POSS is 100 °C lower than the DGEBA-DDM network compare to 77 °C for epoxy network prepared by high molecular weight control precursor (without POSS cage). In order to establish structure-property correlations, these variations have been correlated with free volume, crosslinking density, and chain packing in the network. For the epoxy hybrid networks containing up to 50wt% pendant POSS, the storage modulus of the glassy state (−50 °C) are lower than that of the DGEBA-DDM network, indicating that incorporation of pendant POSS at molecular level increases the spacing and free volume between the chains, and provides them freedom to promote motions. Also, lower storage modulus values in the rubbery state suggest there is no nano-reinforcement effect of POSS cages even at a very high loading (50wt%). Thermogravimetric analysis (TGA) and cone calorimetry show the POSS containing epoxy nanocomposites display high ceramic yields, suggesting the flame retardant behavior of the materials is improved by the molecular level dispersion of pendant POSS. A total of 62% increase in char yield and 53% decrease in peak heat release rate (PHRR) during combustion were observed in hybrid network containing 50wt% POSS compared to DGEBA-DDM network. This study gives new insights into the effects of structural changes in POSS containing thermosets on their performance properties.

Covalent assembly of MCM-41 nanospheres on graphene oxide for improving fire retardancy and mechanical property of epoxy resin

In the study, the hierarchical nanohybrid ([email protected]) with mesoporous MCM-41 nanospheres covalent assembling on graphene oxide (GO) nanosheets was successfully prepared, aiming to improve fire retardancy of epoxy resin (EP). Fourier transformation infrared spectra (FTIR), Raman spectra, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) verified [email protected] The nano-dispersion of [email protected] in EP was certified via TEM and XRD. Fire-retardant investigation (cone calorimeter test) revealed that EP nanocomposite with 2 wt% [email protected] possessed a 40.0% drop of peak heat release rate (pHRR) and suppressed smoke production relative to EP/GO. Intriguingly, EP/[email protected] demonstrated lower pHRR than EP/GO-MCM-41 (direct addition of GO and MCM-41). TG analysis indicated [email protected] imparted EP with significantly reduced degradation rate and increased char yield, accompanied by reduced volatile in thermogravimetric analysis couple with Fourier transformation infrared spectra (TG-FTIR) and improved aromatization in variable-temperature FTIR. The impact strength of EP/[email protected] was enhanced by 38.8% compared with EP. Contrastive analysis proposed the mechanism of neighboring synergy of GO and MCM-41, which involved in GO nanosheets wrapped by enormous carbonaceous stuffs due to MCM-41 neighboring catalysis. In perspective, hierarchical nano-assembly with neighboring synergy offered a viable approach for fire-safe polymers.

Enhanced flame retardancy of epoxy resin containing a phenethyl-bridged DOPO derivative/montmorillonite compound

A phenethyl-bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative (DiDOPO) was combined with organically modified montmorillonite and incorporated into an epoxy resin to improve its flame retardancy. When only 3.5 wt% DiDOPO/3.5 wt% organically modified montmorillonite was introduced into epoxy resin, the limited oxygen index rose from 21.8% to 32.2% and achieved a V-0 rating in the UL 94 test. The decomposition and pyrolysis products in the gaseous phase were characterized by thermogravimetry–Fourier transform infrared spectroscopy. The increase in char yield was restricted due to the incorporation of organically modified montmorillonite. Moreover, a large amount of phosphorus was released into the gaseous phase. The evaluation of flame retardancy, based on cone calorimeter data, testified that organically modified montmorillonite improved the protective-barrier effect of the fire due to the epoxy resin/DiDOPO/organically modified montmorillonite residue, which was also proved from the digital photographs and scanning electron microscopy results. Combination of the protective-barrier effect of organically modified montmorillonite and the flame-inhibition effect of DiDOPO exerted a superior flame-retardancy effect, resulting in good performance of epoxy resin/DiDOPO/organically modified montmorillonite flame-retardant. Overall, organically modified montmorillonite was an efficient adjuvant for the flame-retardant epoxy resin/DiDOPO system.

Functional Mechanism of Inorganic Sodium on the Structure and Reactivity of Zhundong Chars during Pyrolysis

The reactivity of Zhundong chars is remarkably affected by the high sodium content of their parent Zhundong coal. The functional mechanism of inorganic sodium (NaCl) on the structure and reactivity of Zhundong chars was investigated in this study. Chars were prepared in a single-bed reactor under different pyrolysis temperatures and durations. Preliminary experimental results showed that inorganic sodium has a dual effect on the char yield of pyrolyzed Zhundong coal: inorganic sodium can decrease char yield at high pyrolysis temperatures of ≥600 °C but increase char yield at the low pyrolysis temperature of 400 °C. Nitrogen adsorption technique and scanning electron microscopy were utilized to identify the effects of inorganic sodium on the physical structure of Zhundong chars. The results showed that inorganic sodium affects pore structure detrimentally, inhibits the growth of char vesicles, and enables the formation of smooth char surfaces. Fourier transform infrared spectroscopy and Raman spectroscopy were used to identify the effect of inorganic sodium on the chemical structure of Zhundong chars and to investigate the homogeneous and heterogeneous NaCl–char interactions that occur during pyrolysis. The results showed that homogeneous and heterogeneous NaCl–char interactions both can affect the char’s chemical structure. Homogeneous NaCl(s)–char interactions accelerate the decomposition of O-containing functional groups and the formation of new Na-containing carboxylic groups. Heterogeneous NaCl(g)–char interactions accelerate the decomposition of functional groups and increase the ratio of small aromatic ring systems to large aromatic ring systems in the char. Thermogravimetric analysis revealed that inorganic sodium has a catalytic effect on the combustion reactivity of Zhundong chars. Finally, the catalytic mechanism of inorganic sodium on the reactivity of Zhundong chars was proposed.