Simultaneous thermogravimetry

Cano, G. Simultaneous Thermogravimetry and Gas Analysis. Application to the Study of the Decomposition of Calcium Oxalate. Bull. Soc. Chim. France 2540/2542 (1963). 

Through the use of simultaneous thermogravimetry modulated beam mass spectrometry, optical microscopy, hot-stage time-lapsed microscopy, and scanning electron microscopy measurements, the physical and chemical processes that control the thermal decomposition of RDX 9 below its melting point (160-189 °C) have been identified (Scheme 17) <2005PCA11236>. 

Although water is known as a natural plasticizer for many polar polymers such as nylon, polyester resins, and cellulosic polymers, similar behavior for polyacrylamide and poly(acrylamide-co-acrylic acid) has not been investigated. In this study, the effect of water content (and/or thermal history) on the Tg s of acrylamide-based pol3 TOers was studied by Differential Scanning Calorimetry (DSC), Thermogravimetry (TG), Thermomechanical Analysis (TMA), and Simultaneous Thermogravimetry - Mass Spectrometry (TG/MS). 

Figures 4.179 and 4.180 illustrate two furnaces for TGA for different temperature ranges. The figures are self-explanatory. Several different sample holders are shown in the bottom portions of the figures. The multiple holders can be used for simultaneous thermogravimetry and DTA, the single cmcibles are used for simple thermogravimetry. The major problem for the combined thermogravimetry and DTA technique is to bring the thermocouple wires out of the balance without interference with the weighing process. Even the temperature control of the sample holder may be a major problem in vacuum experiments since the thermocouple does not touch the sample. The cmcibles are made of platinum or sintered aluminum oxide. Typical sample masses may vary from a few to several hundred milUgrams.

Raemaekers KGH and Bart JCJ (1997) Application of simultaneous thermogravimetry - mass spectrometry in polymer analysis. Thermochimica Acta 295 1-58. 

Raemaekers, K.G.H., Bart, J.C.J. (1997) Applications of simultaneous thermogravimetry-mass spectrometry in polymer analysis. Thermochim. Acta, 295,1-58. 

Behrens, Jr., R., (1986), A New Simultaneous Thermogravimetry and Modulated Molecular Beam Mass spectrometry Apparatus for Quantitative Thermal Decomposition Studies , Rev. Sci. Instrum., 58, pp. 451- 461. 

This route was described more or less simultaneously by Karasz et al. 235) and by Murase et al.236). The precursor polymer is typically prepared by reaction of the appropriate bis(chloromethyl)arylene compound with dimethylsulfide in a polar solvent237,238). The product is a water-soluble polymer which can be cast to give thin films. Elimination of hydrochloric acid and dimethyl sulfide takes place on heating the film in the range 200 to 300 °C and can be monitored by thermogravimetry and by the development of colour and conductivity 239. Poly(p-phenylene vinylene), prepared by the precursor route, can be doped to much higher conductivities than the conventionally synthesised polymer. 

Thermal analysis is a group of techniques in which a physical property of a substance is measured as a function of temperature when the sample is subjected to a controlled temperature program. Single techniques, such as thermogravimetry (TG), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric thermal analysis, etc., provide important information on the thermal behaviour of materials. However, for polymer characterisation, for instance in case of degradation, further analysis is required, particularly because all of the techniques listed above mainly describe materials only from a physical point of view. A hyphenated thermal analyser is a powerful tool to yield the much-needed additional chemical information. In this paper we will concentrate on simultaneous thermogravimetric techniques. 

The thermal characterisation of elastomers has recently been reviewed by Sircar [28] from which it appears that DSC followed by TG/DTG are the most popular thermal analysis techniques for elastomer applications. The TG/differential thermal gravimetry (DTG) method remains the method of choice for compositional analysis of uncured and cured elastomer compounds. Sircar s comprehensive review [28] was based on single thermal methods (TG, DSC, differential thermal analysis (DTA), thermomechanical analysis (TMA), DMA) and excluded combined (TG-DSC, TG-DTA) and simultaneous (TG-fourier transform infrared (TG-FTIR), TG-mass spectroscopy (TG-MS)) techniques. In this chapter the emphasis is on those multiple and hyphenated thermogravimetric analysis techniques which have had an impact on the characterisation of elastomers. The review is based mainly on Chemical Abstracts records corresponding to the keywords elastomers, thermogravimetry, differential scanning calorimetry, differential thermal analysis, infrared and mass spectrometry over the period 1979-1999. Table 1.1 contains the references to the various combined techniques. 

Thermogravimetry coupled to infrared spectrometry has been carried out at the anal3dical centre of the CNRS at Lyon-Vemaison. Weight loss of about 100 mg of skeleton powder during heating from ambient to 500 °C was continuously recorded. Simultaneously, emitted water and CO2 were measured by infrared absorption at 1508 cm and 2363 cm respectively (Cuif et al. 2004). 

Three furnaces are available a low-temperature unit with a maximum temperature of KXXFC, a high-temperature unit for use up to 1600°C, and a super high-temperature model with a maximum temperature of 2400°C. These furnaces are illustrated in Chapter 6 (Figure 6.5). The sample holders are also discussed in Chapter 6 because of their simultaneous use for DTA and thermogravimetry. 

Although the principal thermal analysis techniques are thermogravimetry, differential thermal analysis, and differential scanning calorimetry (see Chapter 1), there are a number of other thermal techniques, besides those discussed elsewhere in this book, that are useful for solving chemical and technological problems. Some of these methods are of recent development and hence little used at the present time, but they possess the potential for wider use in the future. Many of these techniques are employed to supplement or complement the three principal techniques of TG. DTA. and DSC, either in the simultaneous (single sample) or concurrent multiple samples) modes. 

It should be noted that, in many cases, the use of only a single thermal analysis technique may not provide sufficient information about a given system. As with many other analytical methods, complementary or supplementary information, as can be furnished by other thermal analysis techniques, may be required. For example, it is fairly common to complement all DTA or DSC data with thermogravimetry. If one or more gaseous products result, evolved gas analysis may prove useful in solving the problem at hand. Simultaneous thermal techniques are helpful in this respect in that several types of data are obtained from the same sample under identical pyrolysis conditions. 

Other techniques may be coupled with thermogravimetry to provide very useful data and to confirm supposihons. One such instrument combines DSC and TG (simultaneous DSC/TG) and may facilitate the elucidahon of unexpected events obtained from a DSC investigation alone. Other examples of valuable coupling of instmments include TG-FT-IR, TG-Raman, and TG-MS, where the gases that may be produced during a TG inveshgahon are analysed by an FT-IR, Raman, or mass spectrometer, respectively, that have been linked in sequence to the TG instmment [72]. 

Very often thermogravimetry alone cannot give enough information about the reactions being studied. Other measurements often add to the knowledge gained. These ancillary techniques may be applied at the same time as the TG measurement is being applied and are then referred to as simultaneous and are discussed in Chapter 6. Alternatively other measurements may take place in separate experiments in separate apparatus. This is referred to as combined measurements. Simultaneous measurements include differential thermal analysis (DTA) and evolved gas analysis (EGA). These are explained in later chapters. 

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