Enhanced Char Formation Research Articles

Sb‐intercalated layered double hydroxides–poly(vinyl chloride) nanocomposites: Preparation, characterization, and thermal stability

ABSTRACTIn this study, a novel ‐intercalated layered double hydroxide (Sb‐LDH) was prepared by simultaneous recovering of LDH structures and intercalation of into LDH layers. The prepared Sb‐LDH composites remain the hydrotalcite structure with layered geometry and show higher thermal property than that of LDH. When applied to poly(vinyl chloride) (PVC) composites, Sb‐LDH showed limited thermal stability for PVC at the early stage of thermal and thermooxidative degradation processes. However, Sb‐LDH could retard the thermal cracking of the carbonaceous conjugated polyene of PVC which may hinder further degradation, and the moderate amount of Sb‐LDH (1, 2, and 5 wt %) in PVC resin can retard the process of decarbonation and enhance char formation. Sb‐LDH also promoted the transparency of PVC but darkened the color. With the advantages of transparency promotion, high temperature resistance, and long‐term stability, the prepared Sb‐LDH is a potential thermal stabilizer for PVC resins. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42524.

Effect of functionalized magnetite nanoparticles and diaminoxanthone on the curing, thermal degradation kinetic and corrosion property of diglycidyl ether of bisphenol A-based epoxy resin

To prepare a high-performance epoxy resin with excellent thermal, chemical and corrosion stability, diaminoxanthone (DAX) was used to cure diglycidylether of bisphenol-A (DGEBA)-based epoxy resin and blend of DGEBA with functionalized Fe3O4 nanoparticles. Kinetic parameters of curing and thermal degradation of epoxy resin systems were estimated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The 10% weight loss temperature has been increased from 340 °C to 366 °C and there was an increase in the char yield from 32.6% to 45.3% for the above systems. The corrosion performance of epoxy coated carbon steel was examined by potentiodynamic polarization, along with immersion test in 1.0 mol/L HCl solution. The results showed that epoxy resins cured with DAX had low tendency to corrosion. In addition, the cured epoxy resin containing 10% Fe3O4 had higher anticorrosion activity than bare DGEBA system. The results showed that functionalized Fe3O4 nanoparticles enhanced char formation and improved the thermal stability as well as anticorrosion activity of the resin.

Polymer/Layered Compound Nanocomposites: a Way to Improve Fire Safety of Polymeric Materials

The review on the fire safety of polymer/layered compounds nanocomposites are summarized and discussed. Emphasis on flammable performance of polymer nanocomposites containing layered compounds, mainly montmorillonite, layered double hydroxides, layered metal phosphate, layered carbon materials and the compounds combined with conventional flame retardant additives, are also introduced based on the open literatures. Derived from those research, the combination of multiple methods and technologies including the catalyzing effect metal ion and the barrier effect of the layered compounds, are predicted to have a high probability to enhance char formation, restrain the release of combustible gases and improve the flame retardancy of polymeric materials.

Study of the reactions between tetrabromobisphenol A and PbO and Fe2O3 in inert and oxidizing atmospheres by various thermal methods

DSC, TG, and TG–MS techniques were used to investigate the reactivity of PbO and Fe2O3 with HBr from thermal degradation of tetrabromobisphenol A under inert and oxidizing atmospheres. The HBr acted as an excellent brominating agent for PbO and separated Pb as a volatile bromide (79 and 90% in He and He+5vol% O2, respectively) from the solid up to 580°C. For Fe2O3, the amount of vaporized bromide was only 20 and 13% under inert and oxidizing atmospheres, respectively. In inert atmosphere the formed char acted as a reducing agent for converting the remaining oxides into metallic forms. For TBBPA+PbO, about 3% of metallic Pb remained in the residue as most of the oxide vaporized below 970°C. The unreacted Fe2O3 underwent progressive reduction into metallic Fe (75%), which remained in the residue. In oxidizing atmosphere, the unreacted PbO vaporized completely, while the Fe2O3 remained unchanged in the residue. The organic char decomposed and vaporized as carbon mono- and di-oxides. Simultaneous TG–MS measurements indicated that the presence of PbO and Fe2O3 strongly accelerated TBBPA degradation and enhanced char formation.

Kinetic Analysis of Lignin Hydrothermal Conversion in Sub- and Supercritical Water

Hydrothermal conversion of lignin was conducted in subcritical temperatures of 300–370 °C and residence times of 0.5–10 s at a pressure of 25 MPa. This additional work (subcritical conditions, 300–370 °C) was used as a comparison with our previous study (supercritical conditions, 390–450 °C) to further investigate the temperature effect on lignin decomposition. Subsequently it was our aim to examine its overall reaction kinetics at wider temperature range, and conclusively we determined each of the reaction natures (radical or ionic reaction) as deduced previously in our original proposed lignin conversion pathways. Due to the change in the properties of water under sub- and supercritical conditions, ionic reactions were expected to deviate from Arrhenius behavior. This was caused by the affected stability of the ions in the reaction from the change in the dielectric constant and ionic product. However, radical reactions could not be expected to be affected by the change in the dielectric constant or ionic product, thus Arrhenius behavior could be expected. Lignin conversion under subcritical conditions occurred rapidly although a higher degree of depolymerization was achieved under supercritical temperatures. In addition, supercritical conditions tremendously enhanced char formation compared to subcritical conditions. This was conclusive evidence that radical reaction played a vital role in char formation mechanism. In addition, the rate constant of the overall lignin decomposition under both sub- and supercritical conditions was observed to obey Arrhenius behavior; however, some of the reactions in the proposed network deviated from this behavior in the supercritical region.

Development of HDPE/EPDM‐g‐TMEVS nanocomposites with enhanced electrical and flame properties

AbstractNanoclay reinforced HDPE/silane grafted EPDM composites have been developed using an epoxy functionalized HDPE as compatibilizer.The nanoclay has been varied from 0% to 10% in the composites along with the incorporation of compatibilizer and without compatibilizer in a brabender plasticorder.The dielectric and fire retardant properties of these nanocomposites have been examined. Addition of nanoclay enhanced char formation with increased values of limiting oxygen index. Electrical properties such as volume and surface Resistivity improved with addition of nanoclay and compatibilizer. The values of tan δ increased with increase in grafted EPDM and silanated nanoclay loading. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Synthesis, characterization and curing properties of a novel cyclolinear phosphazene-based epoxy resin for halogen-free flame retardancy and high performance

A novel cyclolinear phosphazene-based epoxy resin has been synthesized through a four-step synthetic route. The curing behaviors of this epoxy resin with methyl tetrahydrophthalic anhydride, 4,4′-diaminodiphenylmethane, and novolak as hardeners were investigated by differential scanning calorimetry (DSC). The thermal behaviors and stabilities were also evaluated with DSC and thermogravimetric analysis. These thermosets achieved high glass transition temperatures over 150 °C and also gained good thermal stabilities with high char yields. The flammability characteristics of the cyclolinear phosphazene-based epoxy thermosets were investigated by limiting oxygen index (LOI) and UL-94 vertical burning experiments. The high LOI values and UL-94 V-0 classification of these epoxy thermosets indicate that the incorporation of phosphazene rings into the molecular backbone imparts non-flammability to the epoxy resin as a result of the unique combination of phosphorus and nitrogen following by a synergistic effect on flame retardancy. The analysis of the residual chars collected from the UL-94 test demonstrates that cyclotriphosphazene moieties of this epoxy resin can enhance char formation during combustion serving as a barrier against heat and oxygen diffusion, and consequently the flame retardancy of the thermosets is improved significantly.

A review on flame retardant technology in China. Part II: flame retardant polymeric nanocomposites and coatings

AbstractThe progress of flame retarded polymer nanocomposites and coatings in China over the past decades are described in this review. Emphasis on flammability performance of polymer nanocomposites containing nanofillers, mainly layered inorganic compounds, nanofibers and nanoparticles, combined with conventional flame retardant additives are addressed based on the open literature. Polymeric coatings with improved flame retardancy prepared using a wide variety of additives and UV‐curing technology are also introduced. Derived from this research, the combination of multiple methods and technologies including catalyst and nanotechnology, is predicted to have a high probability to enhance char formation and improve the flame retardancy of polymeric materials. Copyright © 2011 John Wiley & Sons, Ltd.

Flame‐retardant properties of soybean fabric modified with N‐methylol diakyl phosphonopropionamide

AbstractSoybean is a competitive production material for fibers as it is abundant and cost effective. However, an inherent deficiency of soybean fiber is its poor flame‐retardant performance. In this study, the effect of N‐methylol diakyl phosphonopropionamide (Pyrovatex CP) on the flame retardancy of soybean was investigated by the Limiting Oxygen Index (L.O.I.) and the vertical flammability test. Little benefit with regard to flame retardancy was found when soybean was treated with Pyrovatex CP in the absence of additives. However, the incorporation of Lyofix MLF in the finishing treatment (3% w/v) increased the L.O.I. values of soybean fiber and enhanced char formation as indicated by Thermogravimetric Analysis (TGA). Improved fastness to washing was observed at higher application levels of Lyofix MLF (6% w/v). X‐ray Photoelectron Spectroscopy (XPS) indicated that surface phosphorus (% atomic) was reduced following washing for all fabrics examined. In addition, the substantivity of Lyofix MLF to soybean surface was exhibited. The flame‐retardant treatment presented in this article is cost effective and results in wash‐durable flame‐retardant fabrics. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Enhancement of char formation of polymer nanocomposites using a catalyst

Clay-based SAN nanocomposites with zinc chloride as a catalyst were prepared by the solvent casting method to explore possible synergistic flame retardant effects involving enhanced char formation using a catalyst and the formation of a surface-protective layer having a clay network structure. Although the heat release rate and total heat release were significantly reduced by the use of this combination, each additive contributed independently without the desired synergism. This is due to the early formation of many small cracks in the surface layer for SAN-clay nanocomposites (vigorous bubbling associated with evolving thermal degradation byproducts were observed in the cracks) while the rapid char formation by zinc chloride occurred only at the late stage of the fire test. Char formation at long times does not prevent the crack formation or crack growth, so that an effective protective surface layer without openings was not obtained.

Preparation and properties of new flame retardant unsaturated polyester nanocomposites based on layered double hydroxides

The preparation of new layered double hydroxides/unsaturated polyester (LDH/UP) nanocomposites was performed and the effect of LDH on the resin properties was studied. Two different organo-LDHs have been prepared, adipate-LDH (A-LDH) and 2-methyl-2-propene-1-sulfonate-LDH (S-LDH); in order to evaluate the influence of these nanofillers, samples with two different concentrations were dispersed in the matrix. The physical, thermal, mechanical and fire reaction properties of nanocomposites were studied. Intercalated layered structures were observed for the different organo-LDH loadings (1 and 5 wt%). Mechanical properties studied under flexural tests show that incorporation of organo-LDH in the resin reduces the flexural strength of polyester resin while the flexural modulus is unchanged for the S-LDH/UP composites and increased with 1 wt% of A-LDH. Adding 1 wt% of A-LDH to the resin produces an important reduction on the flexural strength, but an increase of the flexural modulus. The study of fire reaction properties, using cone calorimeter, suggested a significant reduction in the UP flammability, by 46 and 32%, by incorporating 1 wt% of A-LDH and 5 wt% S-LDH, respectively. Mass loss curves show enhanced char formation with the different loads tested while the amount of evolved smoke remains quite unchanged.

Thermal and catalytic decomposition of wood impregnated with sulfur- and phosphorus-containing ammonium salts

The decomposition of fir wood, impregnated with diammonium sulfate and diammonium phosphate, has been investigated with a laboratory scale reactor together with gas-chromatographic analysis of gas and condensable organics. The dependence of products and other process variables on the salt concentration in the wood (from 0 to about 20% on a dry wood basis) and the heating temperature (650–900 K) is qualitatively similar for the two cases. Given heating temperatures of about 650–750 K and using as a reference water-extracted wood, diammonium sulfate and diammonium phosphate concentrations of about 1% are apt to cause a small increase (factors of 1.2–2) in the yields of levoglucosan, 5-methyl-2-furaldehyde and 2-acetylfuran, whereas values in the range 2–5% highly augment the yields of levoglucosenone and 2-furaldehyde (factors of 14–16 and 3–2, respectively). Salt concentrations above 10% confer excellent fire retardance properties of wood with total yields of water and char up to about 70 and 85% and ratio values of non-combustible to combustible volatile products up to 3.5 and 6.5, respectively. The displacement of the reaction process at lower temperatures, the higher exothermicity associated with the enhanced char formation, the reduced convective cooling and the endothermicity of salt decomposition also highly affect the conversion times and the overall rates of volatile species release.

Thermal decomposition of bisphenol A-based polyetherurethanes blown with pentane: Part II—Influence of the novel NaH 2PO 4/NaHSO 4 flame retardant system

The thermal degradation process of ethoxylated bisphenol A (BPA) and oxyalkylenated 2,6-toluylenediamine-based polyurethane (PU) foams blown with pentane and flame retarded by novel NaH 2PO 4 and NaHSO 4 intumescent system (5:3, w/w) was studied by thermogravimetry coupled with mass spectrometry (TG–MS), thermogravimetry coupled with Fourier transform infrared spectroscopy (TG–FTIR), pyrolysis–gas chromatography coupled with mass spectrometry (Py/GC–MS) and diffuse reflectance Fourier transform spectroscopy (DRIFTS) methods. It has been found that NaH 2PO 4/NaHSO 4 system is active both at the initiation stage of PU decomposition as well as it catalyses cross-linking reactions that lead to enhanced char formation during degradation; both effects contribute to the overall flame retardation effect.

Influence of nano-LDHs on char formation and fire-resistant properties of flame-retardant coating

Flame-retardant nano-coatings were prepared by adding flame-retardant nano-concentrates to APP/PER/EN coating. Dispersion morphology and stability principle of nano-size magnesium aluminum-layered double hydroxides (nano-LDHs) have been studied by using transmission electron microscopy (TEM). Relation of added amount of nano-concentrates in flame-retardant coating to flame-retardant properties for APP/PER/EN system has been studied by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), differential thermal analysis (DTA), thermogravimetry (TG) and fire protection test. It was indicated that nano-LDHs could catalyze the esterification reaction between ammonium polyphosphate and pentaerythritol, and IPN network formed by nano-size thermal-decomposed products of LDH could efficiently enhance char formation and structure of char layer. Only specific content (1.5%) of nano-LDHs in flame-retardant coating could efficiently improve its char layer structure and fire-resistant properties. Nano-LDHs (1.5%) greatly improve mechanical properties (bonding strength, bending resistance and resistance to freeze–thaw cycle) of flame-retardant coating.

Cone calorimetry studies of polymer systems flame retarded by chemically bonded phosphorus

The combustion behaviour of polystyrene flame retarded by the incorporation of phosphorus-containing compounds has been studied by LOI and cone calorimetry. Both ‘reactive’ and ‘additive’ approaches to the incorporation of the phosphorus have been applied and assessed. The data obtained show that the reactive approach results in enhanced char formation during combustion due to a condensed phase mechanism. Flame retardation by the additive systems occurred exclusively in the vapour phase via both chemical and physical interactions. The main advantage of the reactive approach was the maintenance of the physical and chemical properties similar to those of the homopolymer. The phosphorus environment was also a significant factor in terms of the level of flame retardance achieved. Phosphonate species were more effective than were phosphate species.

Evaluation of polar ethylene copolymers as fire retardant nanocomposite matrices

A range of nanocomposite materials was prepared under high shear based on polar polyethylene (PE) copolymer matrices. An organically modified bentonite was used as the smectite clay, with intercalation shown to occur in the presence of poly(ethylene- co-methyl acrylate) (EMA), poly(ethylene- co-vinyl acetate) (EVA), poly(ethylene- co-methyl acrylate- co-acrylic acid) (EMAAA) and poly(ethylene- g-maleic anhydride) as evidenced by small angle X-ray scattering measurements. The thermal stability and flame retardant properties of the polymer–clay composites were measured by thermogravimetry and cone calorimetry, with significant improvements in the heat-release rates and thermal stability of all systems. Enhanced char formation was shown to be responsible for reducing degradation under oxidative conditions.

Char Formation in Polyamides (Nylons 6 and 6.6) and Wool Keratin Phosphorylated by Polyol Phosphoryl Chlorides

Polyamides (nylon 6 and 6.6) phosphorylated by spirocyclic pentaerythritol phosphoryl chloride (SPDPC), cyclic 1,3-propanediol phosphoryl chloride (CPPC), and cyclic 2,2- diethyl-1,3-propanediol phosphoryl chloride (CDPPC) can yield phosphorus levels up to 0.7% (w/w). Calculations suggest that only primary amine groups at the end of the molecular chain are the possible phosphorylation sites. The presence of substituted 1,3-propanediol phosphonate moieties significantly increases polyamide char formation above 500°C, and scanning electron microscopy indicates that the residual char has an intumescent structure. SPDPC-phosphorylated wool keratin yields higher phosphorus levels up to 2.06%. For nylons 6 and 6.6, the presence of a methylolated triazine (as the commercial agent Lyofix MLF NEW, Ciba) in the pad-cured treatment can increase the phosphorus level further to significantly enhance char formation. SEM images suggest that the reacted substrates yield char volume expansions in wool of up to 336% compared to the control sample chars.

An XPS investigation of thermal degradation and charring on poly(vinyl chloride)–clay nanocomposites

More information concerning the thermal degradation and charring of nanocomposites of poly(vinyl chloride), dioctyl phthalate and clay has been obtained by the use of X-ray photoelectron spectroscopy and the acquisition of the carbon (C1s), chlorine (Cl2p), and oxygen (O1s) spectra. In the cases of polystyrene–clay and poly(methyl methacrylate)–clay nanocomposites, it has been shown that the clay migrates to the surface as the temperature is raised and the polymer degrades, thereby confirming the barrier properties as a mechanism by which these materials function. For PVC–clay nanocomposites the surface at high temperatures is dominated by carbon, and not the oxygen of the clay. The presence of the clay does retard the chain-stripping degradation of the PVC and the enhanced char formation accounts for the observation of enrichment of carbon.

A study of the global kinetics of thermal degradation of a fibre-intumescent mixture

A mathematical model is being developed to predict the behaviour of an intumescent flame retardant within a rigid, resin-impregnated, textile-reinforced composite during exposure to heat. As part of a larger programme of research into flame retardant composites, there exist considerable empirical data showing the enhancement of char formation, at temperatures greater than 400 °C, when an intumescent based on melamine phosphate is dispersed on the surface of a flame-retardant, cellulosic fibre. Visil (Sateri, Finland), is a flame-retardant viscose fibre containing polysilicic acid which interacts with phosphate or polyphosphate components of the intumescent to form a resistant char-bonded structure. When introduced into a composite either as a pulverised additive, or as additional layers with glass fabric in the composite structure, it has been shown to promote enhanced char formation. In order to model the thermal decomposition of a cellulosic fibre and intumescent mixture, a number of different decomposition schemes, involving competitive and successive reactions, have been considered. The thermogravimetric mass loss curve displays at least three waves of overlapping reactions, so that the kinetics cannot be estimated by the usual differential or integral methods. A simple, reduced kinetic scheme has been compared with a temperature dependent scheme to determine the effect of increased heating rates on the yield of solid residue. The results will be used in later work for the interpretation of Arrhenius parameters estimated from thermogravimetric data by the method of minimisation of least squares.

Enhancing polymer char formation by reaction with phosphorylated polyols. 1. Cellulose

The use of polyol phosphonyl chlorides or phosphochloridates as phosphorylating agents for cellulose is considered as means of introducing a char-forming centre in association with an acid-generating moiety into a functional polymer which itself is potentially char-forming. The specific polyol phosphonyl chloride used, spirocyclic pentaerythritol di(phosphonyl chloride) or diphosphochloridate (SPDPC) is shown to be able to substitute into cellulose (as cotton) in the presence of a suitable solvent (DMF) and base (pyridine and sodium hydroxide) at levels commensurate with phosphorus concentrations up to 2.5% (w/w). This is equivalent to phosphorylation yields of up to 22.7%. The efficiency of phosphorylation is dependent upon reaction temperature and SPDPC: cotton mass ratios. Highest yields occur when reactions are carried out at respective mass ratios of 4:1 (almost equivalent to a molar ratio of an anhydroglucopyranose repeat: 1/2 SPDPC molecule) at 160°C for 2 h. Thermogravimetric analysis of SPDPC-phosphorylated cellulose shows enhanced char formation over the range 400–740°C with respect to untreated cotton cellulose. Scanning electron microscopy shows chars to be well-defined and quite resistant to oxidation as the temperature rises above 600°C in air.