TG-DTA/DSC

HPLC-PDA-MS) are already being used. Although HPLC-NMR-MS provides a very powerful approach for compositional and structural analysis, it by no means represents the limit of what is possible in terms of hyphenation. On-line extraction and the attachment of multiple detectors (e.g. IR, F) make the technique even more powerful. Other analytical laboratories such as TG-DTA-DSC-FTIR, TD-CT/Py/GC-MS/FTIR and HPLC-UV/NMR/IR/MS have been put to work, but do not represent practical solutions for routine polymer/additive analysis. 

The evaluation of combustion performance and safety of Mg/polytetrafluroethylene (PTFE) pyrotechnic compositions by means of TG-DTA has been reported by Miyake and co-workers [83]. Similar work on different pyrotechnic systems containing a chlorinated rubber binder has made use of TG-DSC and TG-DTA-MS [59-62], The hyphenated technique TG-DTA (DSC) has recently been reviewed [56]. 

The principal role of EGD and EGA is mainly as complementary techniques for other thermal analysis data. Samples are studied by TG, DTA, DSC and other thermal analysis techniques first and if the decomposition reactions are unknown, EGA is usually called on to determine the composition of the reaction products. With these known, as well as the other physicochemical data, the chemical pathway of the reaction can usually be elucidated. As mentioned earlier, the EGD-EGA data can often be obtained simultaneously with the other thermal data using multiple techniques with a substantial saving of time and effort. 

The main changes in this edition are as follows (1) Numerous new applications of thermal analysis techniques have been added to the chapters on TG, DTA, DSC, EGD/EGA, and others. (2) Other techniques, not used as often, are described in greater detail, such as EGD/EGA, TMA, DMA. thermoptometry, thermoelectrometry, thermosonimetry, and others. (3) The chapter on EGD/EGA has been rewritten, as has the chapter on miscellaneous techniques. (4) The determination of purity by DSC has been rewritten. (5) Commercially available instruments have been briefly described for each technique, including the application of microcomputers to many of these instruments. 

Maciejewski et al. [74] convincingly demonstrated the complexity of the ostensibly simple decomposition of CoC204 2H2O, by applying a combination of experimental techniques including TG, DTA, DSC, X, TG-MS, and pulse thermal analysis. The process was demonstrated to involve numerotis reactions that occur in both the solid and gas phases. 

Nikolova and Popova [137] reported a new cobalt(II) trihydrogen hexaoxoperiodate tetrahydrate, C0H3IO64H2O, synthesized and characterized by quantitative analysis, TG, DTA, DSC and IR spectroscopy. Based on DTA and DSC data, die following diermal decomposition scheme has been proposed ... 

Srinivasan and Sawant investigated, by thermal and spectroscopic methods, the Mg(II) complexes of nitro-substituted benzoic acids. TG, DTA, DSC and spectroscopic methods were used to investigate the thermal behaviour and structure of the compounds [Mg(H20)6](4-nba)2 2H20, [Mg(H20)6](3-... 

The ICTAC definition of EGA a technique in which the nature and/or amount of a volatile products released by a substance are measured as a function of temperature as the substance is subjected to a controlled temperature programme is unsatisfactory in describing the current practice of EGA as a TA technique. In many ways it is too broad, since it includes other techniques such as pyrolysis-GC, and in other ways too narrow, as it would exclude studying the changing nature of the gas stream as it is passed over the sample, as in catalytic studies. The definition does not require an evolved gas analyser to be coupled to another technique, but in practice this is nearly always the case. This section will deal with EGA as it is usually carried out, which is simultaneously, combined with another technique. The commonest combinations are those with TG and TG-DTA/DSC, where EGA assists in interpreting the chemistry of the events leading to weight losses. 

There has been a multitude of approaches to EGA, ranging from simple methods for answering a particular need to sophisticated research tools. Nearly all TA instruments use a flowing purge gas, which contains the chemical information that is sought. At the simplest level, holding a piece of wet litmus paper, or other indicator in the effluent stream from the instrument, may answer the question at hand. Beyond this, almost every type of gas detector/analyser has been linked to every type of TA equipment, and most manufacturers offer one or more methods for EGA, usually in combination with TG or TG-DTA/DSC. The approach taken in any instance depends on the information required, and there is no truly universal solution. 

Copper-based catalysts are of considerable importance for industrial reactions, e. g. partial oxidation reactions. This contribution reports on a broad study of the catalytic activity of copper in model redox reactions, e. g. methanol oxidation and oxidative coupling of methane. In addition the interaction of Cu with these reactive gases was investigated by thermoanalytic techniques (TG/DTA, DSC), temperature programmed oxidation and reduction (TPO/tpR) and thermal desorption spectroscopy (TDS). Scanning electron microscopy (SEM) and electron backscattering diffraction (EBSD) was additionally used to characterise the copper catalyst before and after catalytic action. 

Basic configuration— TMA commonly consists of a stress generator, displacement detector, furnace, furnace temperature controller, temperature programmer and temperature detector. In a modern TA system, the sample holder part is connected to the workstation which is used in TG DTA, DSC, etc., as shown in Figure 2.1. A typical arrangement of TMA is shown in Figure 2.18. 

Netzsch Geratebau GmbH, Application Note TG-DTA/DSC, MS, FTIR Coupling Systems, Selb (n.d). 

STA 449C TG-DTA/DSC Rapid Visco-Analyzer, RVA TU-1800PC UV-Vis Spectrophotometer... 

Most workers in the pharmaceutical field identify thermal analysis with the melting point, DTA, DSC, and TG methods just described. Growing in interest are other techniques available for the characterization of solid materials, each of which can be particularly useful to deduce certain types of information. Although it is beyond the scope of this chapter to delve into each type of methodology in great detail, it is worth providing short summaries of these. As in all thermal analysis techniques, the observed parameter of interest is obtained as a function of temperature, while the sample is heated at an accurately controlled rate. 

Many different test methods can be used to study polymers and their physical changes with temperature. These studies are called thermal analysis. Two important types of thermal analysis are called differential scanning calorimetry (DSC) and differential thermal analysis (DTA). DSC is a technique in which heat flow away from a polymer is measured as a function of temperature or time. In DTA the temperature difference between a reference and a sample is measured as a function of temperature or time. A typical DTA curve easily shows both Tg and T . 

Major instrumentation involved with the generation of thermal property behavior of materials includes thermogravimetric analysis (TG, TGA), DSC, differential thermal analysis (DTA), torsional braid analysis (TBA), thermomechanical analysis (TMA), thermogravimetric-mass spectrometry (TG-MS) analysis, and pyrolysis gas chromatography (PGQ. Most of these analysis techniques measure the polymer response as a function of time, atmosphere, and temperature. 

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. 

Redfern [94] summarises the advantages of single sample simultaneous TG-DSC (or TG-DTA) as follows ... 

A disadvantage of TG-DSC (or TG-DTA) is that the data obtained give no direct information on the nature of the chemical species involved. A typical modern assembly for simultaneous TG-DSC (or STA ) is shown in Figure 1.2. 

Table 1.4 shows that the most numerous applications of hyphenated thermogravimetric techniques for the study of elastomeric material make use of TG-DTA, followed by TG-FTIR, TG-DSC, TG-MS and TG-DTA-MS, with only occasional recourse to TG-DSC-MS and TG-GC-MS. Table 1.5 indicates the general performance characteristics of the thermogravimetric techniques in use for the study of elastomeric materials. 

The applications of simultaneous TG-FTIR to elastomeric materials have been reviewed in the past. Manley [32] has described thermal methods of analysis of rubbers and plastics, including TGA, DTA, DSC, TMA, Thermal volatilisation analysis (TVA), TG-FTIR and TG-MS and has indicated vulcanisation as an important application. Carangelo and coworkers [31] have reviewed the applications of the combination of TG and evolved gas analysis by FTIR. The authors report TG-FTIR analysis of evolved products (C02, NH3, CHjCOOH and olefins) from a polyethylene with rubber additive. The TG-FTIR system performs quantitative measurements, and preserves and monitors very high molecular weight condensibles. The technique has proven useful for many applications (Table 1.6). Mittleman and co-workers [30] have addressed the role of TG-FTIR in the determination of polymer degradation pathways. 

The TG-DSC technique has recently been reviewed [56]. Redfern [57] has reviewed single sample simultaneous thermal analysis, i.e., TG-DSC and TG-DTA studies of polymers. 

Whereas Redfern [57] has pointed out the advantages of simultaneous thermal analysis techniques (particularly TG-DSC and TG-DTA) over techniques conducted singly, an even more complete thermal profile is provided when a thermal analyser is coupled to some form of gas analyser (MS or FTIR). Mohler and co-workers [51] have reported TG-DSC-MS of the thermal decomposition of the vulcanisation accelerator tetramethyl thiuram disulphide (TMTD) in rubber degradation of TMTD starts at about 155 °C, as evidenced by m/z 76 (CS2) and 44 (radical of the secondary dimethylamine). 

TG-DTA and DSC are suitable for product quality control as exemplified by OIT measurements for polyethylene (PE) and quantitative analysis of the rubber phase in ABS and of a polymer/ softener/soot/mineral filler mixture [77]. 

DTA, DSC, and TG have become routine for monitoring polysaccharide solid-state transformations. Examples of important applications are hydra-... 

Figure 3.21 Effect of total heat capacity differences between sample and reference on baseline position in a DTA/DSC trace. See text for discussion. In addition, this sketch of glass crystallization shows the baseline shifted in the exothermic direction after crystallization In the same region of temperature, the heat capacity of a crystal is less than the corresponding glass above Tg (see sections 3.7.2 and 7.6).

Previously shown was how the activation energy of crystallization may be determined using DTA/DSC (section 3.6). A technique for determining the activation energy of a decomposition reaction using TG will now be developed. 

Figure 7.11 Glass transition of B2O3 glass as determined by heat-flux DSC. Silicate glasses, because of their three dimensional network tend to have smaller volume changes at Tg and hence DTA/DSC traces of this transformation in those glasses are less distinct (13].

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