A novel direct coupling of simultaneous thermal analysis (STA) and Fourier transform-infrared (FT-IR) spectroscopy

Evolved gas analysis (EGA) from thermal analyzers such as thermogravimetry (TG) or simultaneous thermal analysis (STA) which refers to simultaneous TG–DSC is well established since it greatly enhances the value of TG or TG–DSC results. The sensitive and selective FT-IR technique is in particular useful for the analysis of organic molecules but also for infrared active permanent gases evolved during most decomposition processes. The coupling interface between thermal analyzers and FT-IR spectrometers usually consists of heated adapters and a flexible, heated transfer line. In this work, a novel direct coupling of an STA instrument and an FT-IR spectrometer without a transfer line is presented. A very small FT-IR spectrometer is directly mounted on top of the STA furnace leading to a compact and fully integrated STA–FT-IR coupling system. The possibilities and the value of simultaneous STA–FT-IR measurements are demonstrated for organic, biomass, and ceramic samples in the temperature range between room temperature and about 1,500 °C. Various samples from the field of inorganics and organics—especially polymers—were furthermore measured showing the advantages of the direct STA–FT-IR coupling compared to state-of-the-art STA–FT-IR coupling using a heated transfer line: we found that the time delay caused by the volume of the transfer line itself is rather negligible whereas a significantly better correlation between gas detection and TG results was observed in case of some highly condensable decomposition gases. Aspects of quantification of evolved gases are furthermore discussed as well as the known nonlinearity of FT-IR detection at higher gas concentrations.     

Evolved Gas Analysis of Some Solid Fuels by TG-FTIR

FTIR spectrometry combined with TG provides information regarding mass changes in a sample and permits qualitative identification of the gases evolved during thermal degradation. Various fuels were studied: coal, peat, wood chips, bark, reed canary grass and municipal solid waste. The gases evolved in a TG analyser were transferred to the FTIR via a heated teflon line. The spectra and thermoanalytical curves indicated that the major gases evolved were carbon dioxide and water, while there were many minor gases, e.g. carbon monoxide, methane, ethane, methanol, ethanol, formic acid, acetic acid and formaldehyde. Separate evolved gas spectra also revealed the release of ammonia from biomasses and peat. Sulphur dioxide and nitric oxide were found in some cases. The evolution of the minor gases and water parallelled the first step in the TG curve. Solid fuels dried at 100°C mainly lost water and a little ammonia. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermogravimetric Fourier Transform Infrared Spectroscopy of Hydrocarbon Fuel Residues

Although thermogravimetric analysis (TG) has become an indispensable tool for the analysis and characterization of materials, its scope is limited as no information is obtained about the qualitative aspects of the evolved gases during the thermal decomposition. For processes involving mass loss, a powerful technique to provide this missing information is Fourier transform infrared spectroscopy (FT-IR) in combination with TG. It supplies a comprehensive understanding of thermal events in a reliable and meaningful way as data are obtained from a single sample under the same conditions. The coupling TG/FT-IR is used in fuel analysis for the identification of residual volatiles, to determine their sequence of release and to resolve thermogravimetric curves. In this work, the usefulness of TG/FT-IR for characterizing middle distillate fuel residues is illustrated with some typical examples of recent application. A Bio-Rad FTS 25 FT-IR spectrometer coupled with a TA Instruments TGA 2950 thermogravimetric analyzer was used for data aquisition. The results obtained demonstrate the utility of this combined technique in determining the decomposition pathway of tarry materials at various stages of pyrolysis, thereby allowing new insights into the complex thermal behaviour of hydrocarbon residual systems. This revised version was published online in August 2006 with corrections to the Cover Date.     

Application of TG/FTIR to the study of the regeneration process of husy and HZSM5 zeolites

The effect of regeneration conditions on the composition of the gases evolved during the catalytic pyrolysis of low density (LDPE) and high density polyethylene (HDPE) with HUSY and HZSM5 catalysts has been analysed by the TG/FTIR technique. When regenerated HUSY was employed, the evolution of the gases obtained was similar to that with fresh HUSY, indicating that the regeneration treatment did not affect its properties. Nevertheless with HZSM5, as the regeneration temperature was higher, the composition of the gases gradually became more similar to that evolved in the thermal process.     

Thermal Characterization of Materials Using Evolved Gas Analysis

Thermal analysis combined with evolved gas analysis has been used for some time. Thermogravimetry (TG) coupled with Fourier transform infrared (FTIR) spectroscopy(TG/FTIR), Thermogravimetry (TG) coupled with mass spectrometry (TG/MS), and Thermogravimetry (TG) coupled with GC/MS offers structural identification of compounds evolving during thermal processes. These evolved gas analysis (EGA) techniques allow to evaluate the chemical pathway of the degradation reaction by determining the decomposition products. In this paper the TG/FTIR, TG/MS, and Pyrolysis/GC-MS systems will be described and their applications in the study of several materials will be discussed, including the analysis of the degradation mechanisms of organically modified clays, polymers, and coal blends. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal and electrical behavior of hybrid thermosets based on epoxy and maleimide resins cured with p-aminobenzoic acid

Two thermoset systems based on maleimides and diglycidyl ether of bisphenol A (DGEBA) cured with p-aminobenzoic acid were characterized in terms of thermal and electrical behavior. Thermal characterization has been undertaken by means of thermogravimetric analysis in nitrogen atmosphere up to 600°C using simultaneous thermogravimetric/Fourier transform infrared/mass spectrometry (TG/FT-IR/MS) analysis. In the first stage of thermal degradation, the global kinetic parameters [activation energy (E_a) and preexponential factor (log A₁ (s⁻¹))] were calculated using the isoconversional method of Friedman. The energies variation as well as the shape of the differential thermal analysis curves suggests that the thermal decomposition process occurred in multiple stages. The evolved gases analysis was conducted by simultaneous TG/FT-IR/MS coupled techniques. Dielectric relaxation spectroscopy characterization was also made.     

Combined thermogravimetry and fourier transform infrared spectroscopy techniques for gas evolution analysis

The usefulness of thermogravimetry has been amply demonstrated for a wide variety of material analysis applications. In many instances, however, additional information is required for adequate characterization of the sample and its thermal decomposition behaviour. In this respect, the analysis of evolved gases, or condensed liquids, has proven a highly useful approach. Among the various physical methods used for analysis of the thermal degradation products, infrared spectroscopy has often been found very powerful, being versatile, rapid and widely accessible. In this study, we report a simple new approach in which the evolved gases and condensed liquids from the thermal decomposition of various products are recuperated in an infrared gas cell and on a PVC membrane filter, respectively. The gaseous components were analysed by transmission FT-IR, and the condensed liquid products were examined directly on the PVC membrane by FT-IR in the internal reflexion mode. The technique was used, for example, to examine the pyrolysis products (gases and liquid) of Koberit, a proposed substitute for asbestos. The method was also applied to the study of chemically derivatized asbestos materials in an attempt to unravel the surface chemical modifications.     

A quantitative study of carbon monoxide and carbon dioxide evolution during thermal degradation of flame retarded epoxy resins

Thermogravimetric analysis (TGA) combined with infrared analysis of the evolved gases analysis (EGA) has been used to study the thermal degradation behaviour of epoxy resin both in air and nitrogen. The mass loss as a function of temperature has been correlated with the evolution of carbon monoxide (CO) and carbon dioxide (CO₂), and oxygen consumption as measured using an oxygen analyser. An analytical technique has been developed to quantitatively measure the carbon monoxide and dioxide gases evolved. The effect of a range of flame retardants containing phosphorus, nitrogen and halogen elements on CO and CO₂ evolution during thermal degradation of flame retarded epoxy resins has also been observed.     

TG-DTA/FT-IR method for analyzing thermal decomposition mechanism of polyesters

An attempt to estimate the thermal decomposition mechanism of polymers using the simultaneous TG-DTA/FT-IR system was summarized. The library search of FT-IR spectra at various temperatures and of the subtraction spectrum obtained by subtracting the spectra at different temperatures were used to determine the types of evolved gases from poly(ethylene terephthalate) and poly(butylene terephthalate) at given stages of decomposition. The quantitative analysis of evolved gases was carried out using the specific gas profiles at the specific absorption band. The kinetic parameters were estimated from both TG and spectroscopic curves measured at various heating rates.     

Determining the melting behaviour of ashes from incineration plants via thermal analysis

The ash behaviour comprises one major obstacle towards the efficient utilization of municipal solid wastes, (MSW), in incineration plants. The presence of large amounts of inorganic constituents such as alkali and alkali earth metals, chlorine, sulfur and zinc increase significantly the ash reactivity and lead to severe ash-related problems such as fouling, slagging, corrosion and erosion during their thermal treatment. In this paper, the melting behaviour of various ash fractions originating from the incineration of MSW is studied using simultaneous, (DSC/TG), thermal analysis methods. The produced results provide the basis for improved modelling of the ash behaviour during the incineration of MSW. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterisation of Porous Solids : Edited by S.J. Gregg,K.S.W. Sing and H.F. Stoeckli,Society of Chemical Industry,London, 1979, 392 pp., £ 21.

Techniques combining thermogravimetry (TG) and mass spectrometry (MS) are described whereby TG provides precise heating conditions and weight loss information and MS identifies volatiles evolved during the weight losss process. In the present work the DuPont 990 thermal analysis system, a DuPont 21-104 mass spectrometer, and a Hewlett-Packard 21-MX/Digital Equipment PDP-10 computer system are combined through simple, unique interfaces. The instrumentation features flexibility in thermal treatment of the sample and good atmospheric control. Tests with model substances and practical industrial problems have shown good enrichment and recovery of eluted components and no significant delay in TG operations.     

Investigation of polymers by a novel analytical approach for evolved gas analysis in thermogravimetry

A newly developed measurement technique for evolved gas analysis in thermogravimetry, viz. a thermo balance coupled to comprehensive gas chromatography/single photon ionization mass spectrometry (TG–GC × SPIMS), has been applied to investigate the thermal degradation of two polymers (polycarbonate (PC) blended with ABS and PVC). This detection method provides a two-dimensional analysis of the evolved gaseous products. TG relevant data is obtained as well as an improved resolution power to separate isobaric molecular structures without losing any fraction of the samples. In addition, this solution is not associated with any extension of the measurement time. The assignment of the substance pattern to distinct species is improved compared to solely using MS without a preceding separation step. Furthermore, hitherto undetected compounds when compared to applying TG–SPIMS without GC such as benzonitrile and its methylated derivatives have been found in the evolved gases from the thermal degradation of PC/ABS blend. Finally, a first estimation of the limit of detection has been carried out, yielding 400 ppt for styrene and 500 ppt for toluene from the thermal decomposition of PC/ABS blend.     

Thermal degradation of polyesters by simultaneous TG-DTA/FT-IR analysis

A combination system of thermogravimetric/differential thermal analysis (TG-DTA) and Fourier-transform infrared absorption spectroscopy (FT-IR) was described. This simultaneous TG-DTA/FT-IR technique gave spectroscopic and weight loss information about the thermal degradation process of engineering polyesters; poly(ethylene terephthalate)(PET) and poly(butylene terephthalate)(PBT). The evolved gases from PET were benzoic acid, carbon dioxide and carbon monoxide, while those from PBT were terephthalic acid esters and benzoic acid esters.

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Zusammenfassung Es wird ein kombiniertes System aus TG-DTA und FT-IR beschrieben. Mit dieser simultanen TG-DTA/FT-IR-Technik wurden spektroskopische und Massenverlustangaben über die thermische Zersetzung technisch wichtiger Polyester, namentlich von Poly(ethylenterephthalat) (PET) und Poly(Butylenterephthalat) (PBT) ermittelt. Die aus PET freigesetzten Gase waren Benzoesäure, Kohlendioxid und Kohlenmonoxid, die aus PBT freigesetzten Gase hingegen Terephthalsäureester und Benzoesäureester.

     

Pyrolysis of flame retardants and fire protected polymers

The simultaneously working combination of thermal analysis and mass spectrometry (TA/MS) is a very useful method for studying the degradation process of polymeric materials during thermal treatment [1–7]. Beside the thermal effects, as recorded from thermogravimetry (TG) or differential thermal analysis (DTA) the evolved degradation products can be determined and identified by the on - line coupled mass spectrometer. Additional their temperature depending abundance can be registrated. Combustion of polymers in horizontal (BIS) or vertical (VCI) furnaces and subsequent off line high resolution GC/MS analysis of pyrolysis products is suitable for the simulation of burning processes     

TG-FTIR studies on lignin-based polycaprolactones

Thermal degradation behaviour of alcoholysis lignin-based polycaprolactones (ALPCL's) with various molar ratios of β-caprolactone monomer to each hydroxyl group of lignin (CL/OH ratios) was studied by TG-FTIR. The temperature was varied from 20 to 800°C. Thermal degradation temperatures (T_d's) of alcoholysis lignin (AL) and ALPCL's were determined using TG curves. T_d increased with increasing CL/OH ratio, suggesting that AL becomes thermally stable after the derivatization with PCL chains. Mass residue (MR) at 500°C was also determined using TG curves. MR values decreased with increasing CL/OH ratios. The evolved gases formed by thermal degradation of ALPCL's at various temperatures were simultaneously analyzed by FTIR. The main peaks observed for the samples are as follows: wavenumber (assignment): 1160 cm^-1 (vC-O-), 1260 cm^-1(-C(=O)-O-C-), 1517 and 1617 cm^-1 (vC=C), 1770 cm^-1 (vC=O), 2345 cm^-1 (vCO2), 2945 cm^-1 (vC-H) and 3700 cm^-1 (vOH). It was found that the peak intensities for C=O, CH, C-O-C, OH peaks, which were observed for evolved gases at 430°C, increased with increasing CL/OH ratios, suggesting that the evolved gases at 430°C are mainly formed by thermal degradation of PCL chains in ALPCL's. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal behavior of tetradentate Schiff base chromium(III) complexes

Thermal analytical behavior of eight chromium(III) complexes with N,N′-bis(salicylidene)ethylenediamine (salen) Schiff bases, Cr(salen), has been investigated regarding their thermal stability and thermal decomposition pathways. Thus, the ligands and the respective chromium(III) complexes of salen-type Schiff bases derived from salicylaldehyde and its 5-chloro, 5-bromo, 5-methoxy, 5-nitro, 3,5-dicloro, 3,5-dibromo, and 3,5-diiodosalicylaldehyde were synthesized, characterized, and submitted to TG/DTG, DTA, and TG–FTIR evolved gas analysis. The number of steps and, in particular, the starting temperature of decomposition of these complexes was dependent of the ligand nature. The gaseous products evolved during the thermal decomposition of these compounds were identified by TG–FTIR.     

Influences of aging on thermal decomposition mechanism of high performance oxidizer ammonium dinitramide

Ammonium dinitramide (ADN) is one of the several promising new solid propellant oxidizers. ADN is of interest because its oxygen balance and energy content are high, and it also halogen-free. One of the most important characteristics of a propellant oxidizer, however, is stability and ADN is known to degrade to ammonium nitrate (AN) during storage, which will affect its performance. This study focused on the effects of aging on the thermal decomposition mechanism of ADN. The thermal behaviors of ADN and ADN/AN mixtures were studied, as were the gases evolved during their decomposition, using differential scanning calorimetry (DSC), thermogravimetry–differential thermal analysis-infrared spectrometry (TG–DTA-IR), and thermogravimetry–differential thermal analysis-mass spectrometry (TG–DTA-MS). The results of these analyses demonstrated that the decomposition of ADN occurs via a series of distinct stages in the condensed phase. The gases evolved from ADN decomposition were N₂O, NO₂, N₂, and H₂O. In contrast, ADN mixed with AN (to simulate aging) did not exhibit the same initial reaction. We conclude that aging inhibits early stage, low temperature decomposition reactions of ADN. Two possible reasons were proposed, these being either a decrease in the acidity of the material due to the presence of AN, or inhibition of the acidic dissociation of dinitramic acid by NO ₃ ^? .     

Analysis of a Complex Gaseous Mixture by TG-MS and TG-FTIR

The thermal decomposition of sodium ethyl xanthate (SEX) was used to compare the techniques of pyrolysis-gas chromatography-mass spectrometry (py-GC-MS), thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR), and TG-MS. In the py-GC-MS analysis, SEX was pyrolysed at 400°C in an inert atmosphere. Major gases evolved were carbon disulfide, diethyl sulfide, ethanol, and carbonyl sulfide. The TG of SEX exhibited a sharp mass loss at 201°C (42.3%) and a gradual mass loss at 217-325°C (20.8 %). The MS spectra of the evolved gases were complex due to overlapping of molecular, isotope, and fragment ion signals. Using the MS in selected ion monitoring mode, the major gases evolved were found to be carbon disulfide and carbonyl sulfide. The FTIR spectra of the evolved gases displayed vibrational frequencies due to alkanes, carbonyls, carbonyl sulfide, and carbon disulfide. From the analyses it was concluded that py-GC-MS provided unambiguous gas identification. Interpretation of the MS results was reliant on the py-GC-MS results, and the FTIR data was limited to identifying gases with very characteristic vibration frequencies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal analysis and EPR study of copper species in mordenites prepared by conventional and microwave-assisted methods

The main work of this thesis is to study and discuss flame-retardant properties of the flexible polyurethane foam (FPUF) added with borax, expanded graphite (EG), and EG/Borax as flame retardant, respectively. The thermal behavior of samples has been using thermogravimetry (TG) and differential thermogravimetry in air. The activation energies for different stages of thermal degradation are obtained following the equation of Kissinger. The flammability parameters, including limiting oxygen index, rate of heat release, total heat release, yield of CO, yield of CO₂, and smoke production rate, were recorded simultaneously. The char structure was studied by SEM, and their thermal stability and evolved gaseous products were examined by TG analysis–Fourier transform infrared spectroscopy. By analyzing these data, it was concluded that most combustion parameters of FPUF were decreased by the treatment, especially for EG/Borax treatment, which indicated a synergistic effect of flame retardancy. Meanwhile, the probable flame retardation mechanism was proposed.     

The determination of the gases released during heating of a flame retardant for polymers

The oxidative degradation of HET-acid (1,4,5,6,7,7-hexachlorobicyclo [2.2.1] hept-5-en-2, 3-dicarboxylic acid) is studied by the combination of TG, FTIR, MS and GC-MS. The gases evolved during the decomposition of this flame retardant are investigated on-line by FTIR and by MS. Simultaneously the evolved gases are collected by an adsorbent and, after the thermal experiment, desorbed to release the volatile products for identification using GC-MS. The combination of these techniques offers the unambiguous identification of the evolved products as a function of temperature. The main identified products are CO₂, H₂O, Cl₂, HCl, C₂Cl₄, maleic acid anhydride, HET-acid anhydride, chlorinated cyclic hydrocarbons and chlorinated unsaturated linear hydrocarbons.