DSC and TG analysis

Another reported study involved the preparation of four niclosamide solvates and the determination of the stability of the crystal forms in different suspension vehicles by DSC and TG analysis. Thermal analysis showed that the niclosamide solvates were extremely unstable in a PVP-vehicle and rapidly changed to monohydrated crystals. A suspension in propylene glycol was more stable and TG analysis showed that crystal transformation was less rapid [18]. 

Ti- and Fe-catalyzed solid state transformation of LiAlH4 in Li3AlH6, A1 and H2 upon baU-milling has been reported by Balema et al. [139, 193, 194]. Reversible hydrogen storage via Ti-catalyzed Li3AlH6 (max. 1.8 wt.% H2) has been reported by Chen et al. [195]. The result is based on DSC and TG analysis and has not yet been confirmed. 

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. 

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to measure the glass transition temperatures (Tgs) of the uncured and cured AT-resins respectively (Figure 6). 

Early devices fbr thermogravimetric analysis were limited in precision and convenience when compared with DTA or DSC equipment. Now devices for simultaneous DSC and TG are on the market which can operate at high temps in reactive atms permitting the simulation of high temp reactions on a micro scale. The use of TG for the study of reaction kinetics was described in Sect 5.3.3. An exptl study of the sublimation of ammonium perchlorate was published by Jacobs and Jones (Ref 25). Similar techniques should find application in the study of other propint systems. The product gases have been collected for further analysis using gas chromatography and mass spectrometry... 

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). 

Thermal analysis is capable of providing accurate information on the phase transition temperatures, degradation temperatures, heat capacity, and enthalpy of transition of polymers using comparatively simple DTA, DSC, and TG instruments. The measurement time is short compared with other techniques, such as viscoelastic measurement and nuclear magnetic resonance spectroscopy. Moreover, any kind of material, e.g., powders, flakes, films, fibers, and liquids, may be used. The required amount of sample is small, normally in the range of several milligrams. 

Figure 21. Differential scanning calorimetry and thermogravimetry of oxygen chemisorption on cellulose char at 118 C. The analysis was carried out on 2.5-mg samples in aluminum pans using a Cohn R-lOO electrobalance and a DuPont calorimeter cell attached to a DuPont model 990 thermal analyzer, and nitrogen and oxygen gas flows (60 mL/min, dried by passing through H2SO4) were rapidly interchangeable for DSC and TG.

The objective of this work was to analyze the fl iuoisture content-Tg-mechanical properties relationship for pear in the range of low-intermediate moisture levels. To this end, water adsorption and desorption experiments, DSC, and mechanical analysis were carried out. 

DSC and TG were used for quality control of the materials and the technological processes during battery manufacture, Matrakova and Pavlov presented the results of an investigation on lead-acid battery pastes and active materials, aimed to estimate the efficiency of the two thermal methods for the analysis and the control of the processes taking place during battery production and operation [190]. 

Differential Scanning Calorimetiy (DSC) and Thermogravimetric Analysis (TGA) evaluations were performed using Perkin Elmer DSC-2C to obtain the Tg, T, and MI. A Du Pont Model 2950 TGA was used to evaluate the total amount of carbon dioxide uptake in polymers. A constant heating rate of 20°C/min was used in both the DSC and TGA evaluations. 

Table 2.5 summarises the main applications of thermal analysis and combined techniques for polymeric materials. Of these, thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) provide only physical properties of a very specific nature and yield very little chemical information. DMA was used to study the interaction of fillers with rubber host systems [40]. Thermomechanical analysis (TMA) measures the dimensional changes of a sample as a function of temperature. Relevant applications are reported for on-line TMA-MS cfr. Chp. 2.1.5) uTMA offers opportunities cfr. Chp. 2.1.6.1). The primary TA techniques for certifying product quality are DSC and TG (Table 2.6). Specific tests for which these techniques are used in quality testing vary depending upon the type of material and industry. Applications of modulated temperature programme are (i) study of kinetics (ii) AC calorimetry (Hi) separation of sample responses (in conjunction with deconvolution algorithms) and (iv) microthermal analysis.

Quantitative DTA methods for untreated cotton and fabric treated with P- and N-containing flame retardants were suitable for determining the efficiency of FRs and provided data that correlated with oxygen index values [184], Childress etal. [185] described DTA, DSC and TG studies on brominated phosphite and phosphate flame refardants. Nara et al. [186] have studied pyrolysis of tetrabrominated epoxy resin and its Are retardant mechanism. Pyrolysis of DER 542 (brominated epoxy resin) and Epikote 1001 (non-brominated epoxy resin) was investigated by DTA en TG. Bhatnagar et al. [187] have reviewed DTA and DSC studies on flame retardant polymers. Carroll-Porczynski [188] described the applications of simultaneous TG and DTA and DTA/MS analysis for predicting the flame retar-dancy of composite textile fabrics and polymers. The use of DTA to identify mineral flllers in rubber formulations is as old as the technique itself [189],... 

With TG it is also possible to determine glass fibres in polymer systems. Fava [261] recorded TG/DTG curves of PP filled with carbonate and fibreglass. TG is an ideal analytical tool for the control of the glass fibre content in composite materials. Since the glass fibre is thermally inert, there is no problem resolving the weight from the resin (by simple subtraction from 100%). Gibbons [151] has analysed additives such as plasticisers, antioxidants, fillers, and reinforcements for PAll, PE, PP and epoxy resins both qualitatively and quantitatively by DSC and thermomechanical analysis. Fig-... 

Simultaneous thermal analysis (STA) refers to the simultaneous application of two or more thermoan-alytical methods on one sample at the same time, such as DTA and thermoconductivity. In practice, however, this term is mostly used for simultaneous measurement of the mass changes and caloric effects on a sample under thermal treatment. The benefits are (i) information on transformation energetics and mass change in one run, under identical conditions (ii) time saving and (Hi) no differences in sample composition for the various thermal measurements - important for non-homogeneous sample materials. Although TG-DSC and TG-DTA are the most widely used of the simultaneous techniques due to... 

Typical applications that are ideal for TG-DSC are temperature stability, decomposition behaviour, drying and firing processes, transition and reaction temperatures, melting and crystallisation processes. Redfern [290] has reviewed single sample simultaneous thermal analysis, i.e. TG-DSC and TG-DTA smdies of polymers, and has reported TG-DSC of an uncured polyimide resin in which a more accurate determination of the quantitative measurement... 

Kodama et al. [291] have reported TG-DSC curves for the analysis of the interaction between vulcanisation accelerators (tetramethylthiuram disulfide, dibenzothiazolyl disulfide, diphenyl-guanidine and Af-cyclohexyl-2-benzothiazolylsul-fenamide) and fillers (CB, hard clay and CaCOs). The initial m.p. of the accelerators was largely influenced by the fillers. Emmott et al. [292] have investigated the complex reaction between Sr(N03)2 and the binder Alloprene (a pyrotechnic system) at about 300°C by simultaneous TG-DSC and TG-DTA-MS. The same techniques were used to examine the Ti-NaNOs-Alloprene and Mg-NaNOs-Alloprene systems [293-295]. 

Apart from the simultaneous coupled thermoana-lytical techniques (TG-DSC and TG-DTA), residue analysis appears to have attracted fewer experimentalists than evolved gas analysis. Nevertheless, the ability to observe a sample by thermooptical methods, such as DSC-thermomicroscopy (or optical DSC), DTA-photometry or video microscopy imaging-TG (VMI-TG), as it is heated under conditions of controlled atmosphere and heating rate, provides a valuable supplement to thermal analysis techniques. In fact, DSC is non-specific and cannot distinguish between a phase change and a fusion reaction. Using thermomicroscopic methods... 

The DSC/DTA TG analysis of a binary pyrolant (CaSi2/PTFE 50/50) reveals onset of a first exothermic reaction at 450 °C with peak at 490°C and a consecutive... 

Thermal analysis techniques have been applied to determine the decomposition of RHA and also to investigate the hydration characteristics of RHA-cement pastes exposed to different conditions. The reported results ofDTA, DSC, and TG of RHA-cement pastes show variations. The thermal curves of RHA from different sources are not comparable because of variation in their physico-chemical characteristics, the conditions under which the husk is heated, and other factors.Thermograms generally show endothermal and exothermal peaks. Those ashes formed at lower temperatures show an exothermal effect for the oxidation of the unbumed carbon. Endothermal effects at about lOO C denote the expulsion of water from the adsorbed surface. The oxidation reactions correspond to the loss of weight in TG. Some DSC results have been obtained for the ash obtained at 1200°C.[ The peaks in DSC (Fig. 22) were interpreted from XRD studies. An exothermic peak at 135°C is attributed to the transformation of the try dimite phase (T toT ) and four endothermal effects at 190,220,235, and 250°C represent the transformation of the low form of disordered cristabolite. The endothermic peak at 250°C is caused by a transformation of the well-crystallized form. 

Thermal analysis techniques, in particular differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), are valuable tools to study the thermal behavior of PEs. DSC allows us to calculate the proportion of crystallinity, to detect the formation of new crystalhne phases, free guest salt or uncomplexed polymer chains, to monitor the loss of solvent(s) (e.g. occluded water, alcohol), to determine the Tg value and to distinguish between endo- and exothermic events. TGA provides rich information... 

In some cases the difference in crystal lattice energy between two polymorphs is relatively small reflecting only a small difference between the unit structure. Hakanen and Laine [15] illustrated the use of thermal analysis to the determination of polymorphs. Using terfenadine, two polymorphs and a solvate were identified using x-ray diffraction (XRD), DSC and TG to determine kinetic parameters for the structural change of the methanol solvate by desolvation on heating. Laine et al [16] examined the polymorphic structures within ibopamin which exists in two monotropic forms. The melting points of Form I and II were 134.8 0.4° and 130.2 0.5° respectively. 

Thermal analysis iavolves techniques ia which a physical property of a material is measured agaiast temperature at the same time the material is exposed to a coatroUed temperature program. A wide range of thermal analysis techniques have been developed siace the commercial development of automated thermal equipment as Hsted ia Table 1. Of these the best known and most often used for polymers are thermogravimetry (tg), differential thermal analysis (dta), differential scanning calorimetry (dsc), and dynamic mechanical analysis (dma). 

The glass transition temperatures (Tg) of both modified and unmodified PSs were determined by DSC analysis, and thermomechanic analysis was controlled by TMK. The results are given in Table 8. It is seen from Table 8 that the highest glass transition temperature (410 K) was obtained with chlorohydrinated PS and that of the lowest (370 K) with olefinic PS. The lowest glass transition temperature in the alkenylated PS caused to elasticity properties on polybutadien and polyisopren fragments. 

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