Investigations of cement early hydration in the presence of chemically activated fly ash

The paper describes an attempt of chemical activation of fly ash and claims the usefulness of combination of such investigation methods as calorimetry and infrared absorption for investigations of early periods of cement hydration. The research samples were cement pastes made with an addition of fly ash and admixtures of chemical activators, CaCl₂, Na₂SO₄ and NaOH, whereas a cement paste without fly ash addition and a cement-fly ash paste (both without admixtures) were used as reference samples. In order to investigate early periods of cement pastes hydration, the amount and rate of heat release were registered, and IR spectrums were checked at appointed hydration moments. As a result, it was shown that the combination of calorimetric and IR absorption methods in the investigations of early periods of cement hydration was useful. It was confirmed that the use of chemical activators CaCl₂, Na₂SO₄ and NaOH accelerated the hydration of cement pastes containing fly ash additive in early hours after adding water. The action of activators on hydrating cement system is different for each of investigated compounds.     

Synergistic effects and mechanism of ZnCl2 on intumescent flame-retardant polypropylene

The synergistic effects of ZnCl₂ on polypropylene (PP)/ammonium polyphosphate/pentaerythritol have been studied. The cone calorimeter test, limiting oxygen index, and UL-94 data show that suitable amount of ZnCl₂ can greatly increase the flame-retardant property of PP/intumescent flame retardant (IFR)/ZnCl₂ blends, however, the corresponding smoke release increased for PP/IFR/ZnCl₂ blends when compared with PP/IFR without ZnCl₂. The dynamic Fourier transfer infrared spectra reveal that the ZnCl₂ accelerated the formation of charred layers with P–O–P and P–O–C complexes which formed from burning of polymer materials. The morphological structures of charred residues observed by scanning electron microscopy give the positive evidence that ZnCl₂ can promote the formation of compact intumescent charred layers and prevent the charred from cracking, which effectively protects the underlying polymer from burning. The thermogravimetric analysis data show that the PP/IFR/ZnCl₂ sample has higher thermal stability than that of PP/IFR and PP/IFR/ZnO samples. However, the corresponding charred residues are much lower than that of PP/IFR/ZnO sample. All the above data indicated that the synergistic mechanism of ZnCl₂ with IFR in PP system can be ascribed to catalyze effects in condense phase and serve as a radical scavenger in vapor phase.     

Inorganic Salts Induce Thermally Reversible and Anti‐Freezing Cellulose Hydrogels

Inspired by the anti‐freezing mechanisms found in nature, ionic compounds (ZnCl₂/CaCl₂) are integrated into cellulose hydrogel networks to enhance the freezing resistance. In this work, cotton cellulose is dissolved by a specially designed ZnCl₂/CaCl₂ system, which endows the cellulose hydrogels specific properties such as excellent freeze‐tolerance, good ion conductivity, and superior thermal reversibility. Interestingly, the rate of cellulose coagulation could be promoted by the addition of extra water or glycerol. This new type of cellulose‐based hydrogel may be suitable for the construction of flexible devices used at temperature as low as ?70 °C.     

Fire reaction properties of polystyrene-based nanocomposites using nanosilica and nanoclay as additives in cone calorimeter test

Using nanofiller additives in the polymer matrix to form nanocomposites is a potential way of reducing the flame spread and enhancing flame retardancy of polymeric materials during fire. To understand the fire reaction properties and the relative performance of flame-retardant additives in polymer during well-developed fire, neat polystyrene, polystyrene–silica and polystyrene–nanoclay (MMT) have been tested in a cone calorimeter. The neat polystyrene and the polystyrene nanocomposites have been prepared via an in situ polymerization method. An external heat flux of 50 kW m^?2 was applied in the test, and parameters such as heat release rate, peak heat release rate, time to ignition, smoke toxicity, CO and CO₂ yield have been investigated. Both neat polystyrene and polystyrene nanocomposites have shown the trend of a thermally thick charring polymer in the heat release rate over time data. The nanocomposites had an overall better flame retardancy than the neat polystyrene in terms of lower peak heat release rate, lower average mass loss rate and enhanced char formation. The nanocomposites had also reduced smoke emission with lower CO and CO₂ yield compared to the neat polystyrene. The overall flame retardancy was enhanced as the nanofiller loading was increased for both the nanosilica and MMT nanocomposites.

     

Synergistic flame‐retardant effect and mechanisms of boron/phosphorus compounds on epoxy resins

To explore the component synergistic effect of boron/phosphorus compounds in epoxy resin (EP), 3 typical boron compounds, zinc borate (ZB), boron phosphate (BPO₄), and boron oxide (B₂O₃), blended with phosphaphenanthrene compound TAD were incorporated into EP, respectively. All 3 boron/phosphorus compound systems inhibited heat release and increased residue yields and exerted smoke suppression effect. Among 3 boron/phosphorus compound systems, B₂O₃/TAD system brought best flame‐retardant effect to epoxy thermosets in improving the UL94 classification of EP composites and also reducing heat release most efficiently during combustion. B₂O₃ can interact with epoxy matrix and enhance the charring quantity and quality, resulting in obvious condensed‐phase flame‐retardant effect. The combination of condensed‐phase flame‐retardant effect from B₂O₃ and the gaseous‐phase flame‐retardant effect from TAD effectively optimized the action distribution between gaseous and condensed phases. Therefore, B₂O₃/TAD system generated component synergistic flame‐retardant effect in epoxy thermosets.     

Study on intumescent flame retarded polystyrene composites with improved flame retardancy

The flame retardancy and thermal stability of ammonium polyphosphate/tripentaerythritol (APP/TPE) intumescent flame retarded polystyrene composites (PS/IFR) combined with organically-modified layered inorganic materials (montmorillonite clay and zirconium phosphate), nanofiber (multiwall carbon nanotubs), nanoparticle (Fe₂O₃) and nickel catalyst were evaluated by cone calorimetry, microscale combustion calorimetry (MCC) and thermogravimetric analysis (TGA). Cone calorimetry revealed that a small substitution of IFR by most of these fillers (≤2%) imparted substantial improvement in flammability performance. The montmorillonite clay exhibited the highest efficiency in reducing the peak heat release rate of PS/IFR composite, while zirconium phosphate modified with C₂₁H₂₆NClO₃S exhibited a negative effect. The yield and thermal stability of the char obtained from TGA correlated well with the reduction in the peak heat release rate in the cone calorimeter. Since intumesence is a condensed-phase flame process, the MCC results showed features different from those obtained from the cone calorimeter.     

Identification of dielectric effects in nanofiltration of metallic salts

Transport of four metallic salts (CuCl₂, ZnCl₂, NiCl₂ and CaCl₂) through a polyamide nanofiltration (NF) membrane has been investigated experimentally from rejection rate and tangential streaming potential measurements. Rejection rates have been further analyzed by means of the steric, electric and dielectric exclusion (SEDE) homogeneous model with the effective dielectric constant of the solution inside pores as the single adjustable parameter.     

Novel tetrapotassium azo diphosphonate (INAZO) as flame retardant for polyurethane adhesives

An inorganic azo diphosphonate (INAZO), (KO)₂(O)P-NN-P(O)(OK)₂·4H₂O, was synthesized and tested as a novel type of flame retardant additive for castor oil and oligomeric methylene diphenyl diisocyanate (PMDI) based two component polyurethane adhesive with or without using dolomite ((CaMg(CO₃)₂) as filler. Flammability according to UL 94 test and performance under forced-flaming conditions (cone calorimeter) were investigated at the additive loadings of 5, 10 and 20 wt %. It was shown that INAZO improves flame retardancy by significantly reducing heat release rate (HRR), maximum average rate of heat emission (MARHE) and total smoke release (TSR) values in comparison to CaMg(CO₃)₂ filled polyurethane adhesives. The macroscopic structure of the sample residues after cone calorimeter measurement was also analysed. The action mechanism of the developed INAZO flame retardant is suggested to be mainly in the condensed phase. UL 94 V-0 rating was achieved in the vertical burning test when 10 wt % loading of INAZO was used, whereas the reference flame retardant ammonium polyphosphate (APP) required a loading of 20 wt % to reach the V-0 classification.     

用锥形量热仪研究聚乙烯膨胀阻燃体系的燃烧性

利用锥形量热仪在50kW·m^-2热辐照条件下,研究了含淀粉膨胀阻燃线性低密度聚乙烯(LLDPE)体系的燃烧性,获得了最大热释放速率、总热释放、有效燃烧热、最大烟产生速率、总烟释放量及质量损失速度等参数.实验结果表明:含淀粉膨胀阻燃剂能明显降低LLDPE的热释放速率、总热释放和有效燃烧热,淀粉作为膨胀型阻燃剂中的成炭剂,可以部分代替季戊四醇,而对热释放速率影响不大,达到了阻燃和降低成本的目的.该膨胀体系使烟释放变得缓慢,但总烟释放量明显增大.在燃烧时使LLDPE更早地发生热降解,但热降解速度变得缓慢.     

Effects of graphene nanosheets decorated by cerium stannate on the enhancement of flame retardancy and mechanical performances of flexible polyurethane foam composites

As one of the most used polyurethane, flexible polyurethane foam (FPUF) still confronted highly flammable problems. However, current flame retardant employed in FPUF deteriorated the other utilization performances, such as mechanical properties. In this work, cerium stannate decorated graphene nanosheets (GNS@Ce₂Sn₂O₇, GCSO) was prepared to fabricate flame retardant FPUF composites. Compared to pure FPUF, the tensile strength and average compression strength of FPUF composites accomplished 100 and 412% increase, respectively, while the average rebound was basically maintained. In contrast to pure FPUF, total heat release and total smoke production of FPUF composites displayed a 42.2 and 75.1% reduction, respectively. Furthermore, the released toxic gases (such as, CO₂, CO and NO_x) during combustion were greatly decreased. These results were due to the catalytic and barrier effect of GCSO promoting the formation a high-quality char residue with a compact, intact and dense morphology. Therefore, it provides a facile method to fabricate FPUF composites with advanced comprehensive performance for the furniture field.     

Phosphorus‐free boron nitride/cerium oxide hybrid: A synergistic flame retardant and smoke suppressant for thermally resistant cyanate ester resin

Establishing a phosphorus‐free strategy to fabricate high‐performance thermosetting resins owning outstanding thermal resistance, good flame retardancy, and smoke suppression is important for sustainable development. Herein, a unique phosphorus‐free hybrid (BN@CeO₂) was synthesized through chemically grafting cerium oxide (CeO₂) on surface of exfoliated boron nitride (BN) nanosheet with the aids of γ‐aminopropyltriethoxysilane and polydopamine coating, which was then embedded into bisphenol A cyanate ester (BCy) resin to fabricate new BN@CeO₂/BCy composites with high thermal resistance. Compared with BCy resin, the BN@CeO₂/BCy composite with 4 wt% BN@CeO₂ not only has delayed initial ignition time by 23 seconds but also severally shows 58.1%, 23.1%, and 44.4% lower smoke produce rate, total heat release, and peak heat release rate. The study on mechanism behind outstanding flame retardancy reveals that the improved heat resistance and flame retardancy of BN@CeO₂/BCy composite are attributed to multiply effects induced by BN@CeO₂ and its interaction with BCy resin; specifically, these effects come from BN (physical barrier) and CeO₂ (free radical trapping effect and catalytic char layer formation) as well as those from the synergistic effect of BN and CeO₂. These excellent comprehensive properties of BN@CeO₂/BCy composites demonstrate that BN@CeO₂ is an environment‐friendly and synergistic modifier for developing heat‐resisting thermosetting resins with outstanding flame retardancy and smoke suppression.     

Cinetique de polymerisation de monomeres complexes par des acides de Lewis. Etude du systeme methacrylate de methyl-chlorure de zinc-azobisisobutyronitrile

The polymerisation of methyl methacrylate (MMA) initiated by azo-bis-isobutyronitrile (AIBN) in the presence of ZnCl₂ as complexing agent has been investigated. Increase of the polymerisation rate and a minimum in the average polymerisation degree were observed by increasing the ZnCl₂ concentration. By assuming the existence of complexes {AIBN · ZnCl₂} and {MMA · ZnCl₂}, a kinetic scheme is proposed; it is in good agreement with the experimental results and allows calculation of the characteristics of the system.     

Ammonium hydroxide detoxification of spruce acid hydrolysates

When dilute-acid hydrolysates from spruce are fermented to produce ethanol, detoxification is required to make the hydrolysates fermentable at reasonable rates. Treatment with alkali, usually by overliming, is one of the most efficient approaches. Several nutrients, such as ammonium and phosphate, are added to the hydrolysates prior to fermentation. We investigated the use of NH₄OH for simultaneous detoxification and addition of nitrogen source. Treatment with NH₄OH compared favorably with Ca(OH)₂, Mg(OH)₂, Ba(OH)₂, and NaOH to improve fermentability using Saccharomyces cerevisiae. Analysis of monosaccharides, furan aldehydes, phenols, and aliphatic acids was performed after the different treatments. The NH₄OH treatments, performed at pH 10.0, resulted in a substantial decrease in the concentrations of furfural and hydroxymethylfurfural. Under the conditions studied, NH₄OH treatments gave better results than Ca(OH)₂ treatments. The addition of an extra nitrogen source in the form of NH₄Cl at pH 5.5 did not result in any improvement in fermentability that was comparable to NH₄OH treatments at alkaline conditions. The addition of CaCl₂ or NH₄Cl at pH 5.5 after treatment with NH₄OH or Ca(OH)₂ resulted in poorer fermentability, and the negative effects were attributed to salt stress. The results strongly suggest that the highly positive effects of NH₄OH treatments are owing to chemical conversions rather than stimulation of the yeast cells by ammonium ions during the fermentation.     

Water structure and electron trapping in aqueous ionic solutions

The optical absorption spectra observed by pulse radiolysis of alkaline (NaOH, KOH, RbOH), chloride (LiCl, MgCl₂, CaCl₂, NaCl, KCl) and perchloride (NaClO₄) solutions at temperature 298 K are reported. Some measurements were performed at low temperature with aqueous ionic glasses. With increasing concentration of the above solutes a uniform blue-shift of the maximum of the solvated electron (e¯_sol) absorption band is observed. Near infrared (NIR) spectroscopy was so used to examine the properties of water in several concentrated electrolyte solutions. It is shown that some inorganic electrolytes (e.g. NaOH, NaClO₄) substantially change the water structure whereas some others (e.g. LiCl, CaCl₂) influence water structure insignificantly. The correlation between the ability of excess electron trapping in electrolyte solutions and water structure deduced from NIR spectroscopy is discussed.     

Synthesis of CeO2‐loaded titania nanotubes and its effect on the flame retardant property of epoxy resin

A series of CeO₂‐loaded titania nanotubes (CeO₂‐TNTs) hybrid materials with different CeO₂ loadings were synthesized by co‐precipitation method and then incorporated into epoxy resin (EP) to prepare CeO₂‐TNTs flame‐retardant epoxy nanocomposites. Structure and morphology characterization indicated the successful synthesis of CeO₂‐TNTs. The effect of CeO₂‐TNTs with different CeO₂ loading capacity on the flame retardance of EP was compared and analyzed by the thermogravimetric analysis, Cone and Raman. The results showed that CeO₂ loading could increase the carbon residue of nanocomposites, reduce the peak heat release rate (PHRR) and total heat release (THR), and improve the fire safety of EP. The residual carbon content of EP/0.1CeO₂‐TNTs sample at 700°C reached 19.8% with the lowest degradation rate, and the PHRR and THR were reduced to 680 kW/m² and 32.9 MJ/m², respectively. Such a significant improvement in flame‐retardant properties for EP could be attributed to the protective effect of CeO₂‐TNTs.     

Fire retardancy effects in single and double layered sol–gel derived TiO2 and SiO2-wood composites

Sol–gel derived TiO₂ and SiO₂-wood inorganic composites are prepared by direct vacuum infiltration of silicon and titanium alkoxide based precursors in pine sapwood in one or two cycles followed by a controlled thermal curing process. The resulting flame retardancy effect is investigated under two different fire scenarios using cone calorimetry and oxygen index (LOI). Heat release rates (HRR) especially the values for the second peak, are reduced moderately for all single layered composites. This effect is more pronounced for double layered composites where HRR was reduced up to 40 % showing flame retardancy potential in developing fires. Beside this, smoke release was lowered up to 72 % indicating that these systems had less fire hazards compared to untreated wood, whereas no meaningful improvement is realized in terms of fire load (total heat evolved) and initial HRR increase. However impressively, the LOI of the composites were increased up to 41 vol% in comparison to 23 vol% for untreated wood displaying a remarkable flame retardancy against reaction to a small flame. An approximate linear interdependence among the fire properties and the material loading as well as fire residue was observed. A residual protection layer mechanism is proposed improving the residue properties for the investigated composites.     

氢、碳氢燃料对向扩散火焰

A comprehensive analysis of hydrogen/oxygen and hydrocarbon/oxygen counterflow diffu-sion flames has been conducted using corresponding detailed reaction mechanisms. The hydrocarbon fuels contain n-alkanes from CH₄ to C₁₆H₃₄. The basic diffusion flame struc-tures are demonstrated, analyzed, and compared. The effects of pressure, and strain rate on the flame behavior and energy-release rate for each fuel are examined systematically. The de-tailed chemical kinetic reaction mechanisms from Lawrence Livermore National Laboratory(LLNL) are employed, and the largest one of them contains 2115 species and 8157 reversible reactions. The results indicate for all of the fuels the flame thickness and heat release rate correlate well with the square root of the pressure multiplied by the strain rate. Under the condition of any strain rate and pressure, H₂ has thicker flame than hydrocarbons, while the hydrocarbons have the similar temperature and main products distributions and almost have the same flame thickness and heat release rate. The result indicates that the fuels composed with these hydrocarbons will still have the same flame properties as any pure n-alkane fuel.     

The Effects of CO2 Additional on Flame Characteristics in the CH4/N2/O2 Counterflow Diffusion Flame

The effects (chemical, thermal, transport, and radiative) of CO₂ added to the fuel side and oxidizer side on the flame temperature and the position of the flame front in a one-dimensional laminar counterflow diffusion flame of methane/N₂/O₂ were studied. Overall CO₂ resulted in a decrease in flame temperature whether on the fuel side or on the oxidizer side, with the negative effect being more obvious on the latter side. The prominent effects of CO₂ on the flame temperature were derived from its thermal properties on the fuel side and its radiative properties on the oxidizer side. The results also highlighted the differences in the four effects of CO₂ on the position of the flame front on different sides. In addition, an analysis of OH and H radicals and the heat release rate of the main reactions illustrated how CO₂ affects the flame temperature.     

Mechanical and fire retardant properties of EVA/clay/ATH nanocomposites - Effect of particle size and surface treatment of ATH filler

Mechanical and flame retardant properties of ethylene vinyl acetate (EVA) copolymer/organoclay/alumina trihydrate (ATH) nanocomposites have been studied. ATH with different particle sizes, ATH1 (2.2-5.2 μm) and ATH2 (1.5-3.5 μm), and three different surface treatments, uncoated, fatty acid coated and silane coated, have been used. A synergistic effect was observed in EVA/organoclay/ATH nanocomposites with the total heat evolved (THE) and the heat release rate (HRR) lower than that of EVA/ATH composite. It was also found that mechanical and flame retardant properties are affected in different ways by the particle size and the surface treatment of ATH fillers. Improvements in tensile and flame retardant properties were observed in nanocomposites when uncoated ATH fillers and fatty acid coated ATH2 filler were used. On the other hand, silane coating on ATH1 and ATH2 improves limiting oxygen index (LOI) and leads to higher t_ignition and the best char stability after cone calorimeter test.     

The influence of melamine phosphate modified MoS2 on the thermal and flammability of poly(butylene succinate) composites

This work reported a facile fabrication method to modify molybdenum disulfide (MoS₂) nanosheets with common flame retardant melamine phosphate (MAP) and then were incorporated into poly(butylene succinate) by melt blending method with the purpose of improving the thermal and flame retardancy properties. MAP modified MoS₂ nanosheets dispersed well in poly(butylene succinate) composites with intercalated structure. The incorporation of MAP modified MoS₂ nanosheets led to an increase of thermal degradation temperature and char formation as well as reduction of the peak heat release rate. Copyright © 2016 John Wiley & Sons, Ltd.