Analysis, thermogravimetric

Thermogravimetric analysis (TGA) is a suitable technique for the study of explosive reactions. In TGA the sample is placed on a balance inside an oven and heated at a desired rate and the loss in the weight of the sample is recorded. Such changes in weight can be due to evaporation of moisture, evolution of gases, and chemical decomposition reactions, i.e. oxidation. 

The endotherm at 192 °C is due to the fi-d crystalline phase change, and the exotherm at 276 °C is due to the violent decomposition of HMX. Thermal pre-ignition and ignition temperatures of explosive substances can be obtained from DTA and TGA thermograms. 

Thermogravimetric analysis (TGA) is the most widely used thermal analysis technique, although other techniques such as differential scanning calorimetry (DSC) and differential thermal analysis (DTA) have also been used for polymer blends (see Table 8.1). In this section, we will limit our discussion to TGA, as its results (such as onset degradation temperature, degradation rate, and kinetic parameters) are most indicative of the fire performance of materials in fires. 

Flame retardant nanocomposites with polymer blends 

Thermogravimetric analysis measures variations in the weight of a sample under consideration as a function of time or temperature. The technique is 

Thermogravimetric (TGA) analysis was run to investigate the thermal behavior of resulted nanocomposite. The derivative traces were analyzed for each constituent in order to determine the decomposition temperatxire, while weight traces were used to determine the weight loss associated with the decomposition of this constituent (ASTM E 1131). In addition, the ash content was computed from the final weight. Table 13.3 shows TGA traces for neat CAB, whiskers-filled CAB nanocomposite and kenaf whiskers from previous study. 

In the present study, TG-FTIR analysis was conducted to investigate the thermal degradation behavior as well as the weight loss rate of KL and LGC. Apart from that, this analysis was carried out using Thermal Analyzer, model TGA/SDTA 851 fitted with Fourier Transform Infrared (Mettler Toledo) in order to analyze the evolved gases that result from the thermal decomposition of samples. The samples were heated from 30-900°C at the heating flow rate of 2 0° C/min in nitrogen gas at the flow rate of 30 mL/min. 

The thermal decomposition behavior of the ungrafted KL and LGC was distinguished by the TGA thermal analysis. The TGA 

Isothermal methods have generally been used for the study of thermal degradation mechanisms and the determination of kinetic parameters. In recent years, however, dynamic thermogravimetric analysis (TGA) has been developed. In this case, polymer samples are weighed in a 

In favourable cases, determination of reaction order, global activation energy and frequency factor is rapid and easy. Thus, for reactions of the type 

Some of the various methods developed to analyse the weight loss curve will now be outlined. 

This technique was used by Coulson and co-workers [36] to determine chlorine in chlorinated rubbers. 

These data confirm that degradation processes do not appear to play a role in the thermal studies described here. 

The results described here indicate that differences in the degree and type of tacticity of PPBA samples fail to influence the structure of these polymers as revealed by x-ray diffraction. 

This is a very important finding since it implies that the structure of the polymer is, in this case, independent of the polymerization procedure. Several authors have implicitly granted the possibility to obtain polymers with mesomorphic structure lies in the availability of mesogenic monomers, and on the possibility to polymerize them in the mesomorphic phase. Our results contradict the suggestions. The only difference one can reasonably expect between polymers prepared in the mesomorphic and isotropic phase 

Our results also indicate that thermal history and sample preparation conditions can alter the morphology and texture of the polymer and also influence the melting point. The preferred orientation of the smectic layered structure of the cast films on the glass substrate is not altogether unexpected since such observations are commonly found among mesogenic compounds. 

The different thermal behavior of PPBA samples with different tacticities is intriguing and perhaps associated with small differences in the mode of packing of aromatic side groups within the layers, not observable by x-ray diffraction. 

1 Bubbling the exit gas through a fluid has the added benefit of a continuous check for specimen chamber gas leaks. If a gas leak exists, the fluid will not bubble, even though a positive pressure is applied at the inlet. 

TG with a horizontal gas flow to minimize these problems by having the specimen basket show minimal profile with respect to the gas flow direction. Still another interesting design to minimize gas flow and buoyancy effects is described in section 5.2. 

Significant temperature gradients in the furnace chamber will cause gaseous flow from hot to cold, which may apply a spurious force to the specimen pan. This is a more severe effect for chambers under moderate vacuum ( thermomolecular flow [3]). Purge gas flow direction may be an important consideration, in order to avoid condensation of gaseous products on the hangdown wire, or along the balance beam, as the gas flows out of the hot zone of the furnace. 

Temperature calibration of a thermogravimetric analyzer is more complicated than with other thermoanalytical devices, since in most designs, the thermocouple junction cannot be in contact with the specimen or its container. Beyond gas flow shielding problems, temperature differences between the specimen and thermocouple junction can be exacerbated by a vacuum atmosphere in which there is no conductive medium for heat transfer and thus temperature equilibration. Even if both the specimen and thermocouple junction are exposed to the same heat flow at a given time, the specimen has a much higher total heat capacity hence, the specimen will lag the thermocouple junction in temperature. 

Calibration techniques may be used to correlate specimen temperature to that measured by the thermocouple. A series of high purity wires may be suspended in the region where the specimen crucible would normally be located. If the furnace temperature is slowly raised through the melting point of a particular wire, a significant weight loss will be recorded when the wire melts. Care must be taken that the wires do not extend into a zone of the furnace at a higher temperature than that seen by the specimen. A series of fuseable wires, such as Indium (156.63), lead (327.50), zinc (419.58), aluminum 

X-ray diffraction experiments enable the structures of unknown crystals, as well as the orientation and perfection of large single crystals and their lattice parameters, to be determined. Many solids from small molecules to large proteins can be profiled using this analytical technique. 

Analytical Instrumentation A Guide to Laboratory, Portable and Miniaturized Instruments G. McMahon 

The source is the furnace temperature (and environment) controller. The required temperature programs, heating and/or cooling, come from here. 

A sample is placed into a tared TGA sample pan attached to a sensitive microbalance assembly. The sample holder portion of the TGA balance assembly is subsequently placed into the high temperature furnace. There are a number of different set-ups for how the sample is placed in the balance, each having its own advantages and disadvantages. The first is where the sample is placed horizontally relative to the balance and furnace, the second is where the sample is placed in the pan by top-loading and the third is where the sample is suspended in the furnace. 

The balance assembly measures the initial sample weight at room temperature and then continuously monitors changes in sample weight (losses or gains) as heat is applied to the sample. The balance and furnace data are collected during the experiment and sent to the PC for manipulation. 

Weight changes in a material as it is heated, cooled, or held at a constant temperature in an inert atmosphere are measured to determine composition and thermal stability (weight versus temperature plots). The technique is used primarily to determine the composition of polymers and to predict their thermal stability at temperatures up to 1000 C. The technique can characterise materials that exhibit weight loss or gain due to decomposition, oxidation, or dehydration. It is especially useful for studying polymers 

Temperature versus weight plots provide information on  

A combination of TGA analysis with Fourier transform IR (FT-IR) spectroscopy with periodic analysis of the evolved gases is a very useful means of studying polymer decomposition. 

Goals of TGA separation are accuracy, reliability, completeness of separation and minimum turnaround time. Mass changes as small as 50-100 fj,g can nowadays be detected. In developing an efficient test one needs to balance the needs for resolution, accuracy and test time. 

It should be noted that TGA will not always be accurate because various components in polymeric formulations are not observed as independent weight loss in TG curves (e.g. sulfur, accelerators, antioxidants and antidegradants in elastomers) and may undergo weight loss over a large temperature range. Low-MW volatile products (e.g. oils, waxes, plasticisers and resins) tend to overlap with polymer decomposition for most choices of method parameters. In the presence of multiple decomposition 

In controlled transformation rate thermal analysis (CRTA), instead of controlling the temperature (as in conventional thermal analysis (Fig. 2.8a)), some other physical or chemical property X is modified, which is made to follow a pre-determined programme X = f(t) under the appropriate action of temperature (Fig. 2.8b) [7]. Heating of the sample may be controlled by any parameter finked to the rate of thermally activated transformations, such as total gas flow (EGD control constant decomposition rate thermal analysis [199]), partial gas flow (EGA 

Controlled Transformation Rate Thermal Analysis (CRTA) [7,199,200] 

Reaction (Event) Controlled Heating Rate Adaption 

Method 2.1 Determination of Chlorine in Polymers Containing Chloride and Sulfur and/or Phosphorus and/or Fluorine. Oxygen Flask Combustion - Mercurimetric Titration 

This oxygen flask combustion - titration method is capable of determining down to 5 ppm chlorine in polymers without interference from any fluorine, phosphorus, or 

Bromophenol blue indicator solution, dissolve 50 mg of bromophenol blue in 500 ml of ethanol. 

Diphenylcarbazone indicator solution dissolve 20 mg of diphenylcarbazone in 20 ml of etbanol. Keep tbe solution in tbe dark and renew it after 2 weeks. 

The TGA is in principle a microbalance tracking the mass of the sample during time. It is a cheap, simple, fast, and flexible method. The experiments are characterized by heating rate ( 100K/min), temperature level ( 1600 °C), reactive gas supply (e.g., O2, CO2, H2O, H2), pressure level ( 100 bar), and sample chosen ( 100 mg) and more than one run can be accomplished per day. It can be operated in several modes such as isothermal or nonisothermal, constant or changing gas composition, atmospheric, and pressurized. Another advantage is that the investment and operation costs are comparatively low because many suppliers are available to offer such a system and usually only small amounts of coal and gas are required. 

The main points of controversy using TGA for kinetic data extraction is that the conditions in the specific equipment are not fully ideal regarding geometry of the setup (temperature difference between sample and detection point because of the heat of reaction), heat and mass transfer effects (uneven gas penetration into the sample), particle size (internal temperature gradients), and limited heating rate (difference to industrial systems) [59]. 

An important step is to select the appropriate temperature, particle size, and mass for the TGA experiment. The background is to isolate the surface reaction as the rate-limiting step to really measure kinetics of the char-gas reaction, which are not influenced by mass transfer. 

an appropriate particle size must be selected. It is suggested to be 100 pm to 1 mm and sample masses vary between 40 and 1000 mg under pressurized conditions (10-100 bar). 

The second parameter is an appropriate temperature range, which depends on the gas to be tested. For exothermic reactions, such as char and oxygen, 350-400 °C are suitable. For endothermic reactions, such as char contacted with CO2 or steam, a temperature range of 700-950 °C may be appropriate also depending on the reactivity of the feedstock [59,60]. 

Dyakonov and co-workers [25] used programmed TGA and IR spectroscopy in their stndies of the thermal and oxidative stability of some amine-cured epoxy resin systems based on the glycidyl ether of bisphenol-A and aromatic primary amines. They stndied changes in network epoxy resin model systems brought about by exposure to elevated temperatures in the presence and absence of oxygen. 

TCA performed on numerous PN showed that many polymers filled with mont-morillonite and CNTs exhibited improved thermal stabUity, such as in the case of poly (methyl methacrylate) (PMMA) [44], poly(dimethylsiloxane) (PDMS) [45], PA 

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In a thermogravimetric analysis, the sample is placed in a small weighing boat attached to one arm of a specially designed electromagnetic balance and placed inside an electric furnace. The temperature of the electric furnace is slowly increased at a fixed rate of a few degrees per minute, and the sample s weight is monitored. 

The process known as transimidization has been employed to functionalize polyimide oligomers, which were subsequentiy used to produce polyimide—titania hybrids (59). This technique resulted in the successhil synthesis of transparent hybrids composed of 18, 37, and 54% titania. The effect of metal alkoxide quantity, as well as the oligomer molecular weight and cure temperature, were evaluated using differential scanning calorimetry (dsc), thermogravimetric analysis (tga) and saxs. 

The definition of polymer thermal stabiUty is not simple owing to the number of measurement techniques, desired properties, and factors that affect each (time, heating rate, atmosphere, etc). The easiest evaluation of thermal stabiUty is by the temperature at which a certain weight loss occurs as observed by thermogravimetric analysis (tga). Early work assigned a 7% loss as the point of stabiUty more recentiy a 10% value or the extrapolated break in the tga curve has been used. A more reaUstic view is to compare weight loss vs time at constant temperature, and better yet is to evaluate property retention time at temperature one set of criteria has been 177°C for 30,000 h, or 240°C for 1000 h, or 538°C for 1 h, or 816°C for 5 min (1). 

T and by dsc, (onset of decomposition) Thermogravimetric analysis ia argon at 10°C heating rate. 

Mixtures can be identified with the help of computer software that subtracts the spectra of pure compounds from that of the sample. For complex mixtures, fractionation may be needed as part of the analysis. Commercial instmments are available that combine ftir, as a detector, with a separation technique such as gas chromatography (gc), high performance Hquid chromatography (hplc), or supercritical fluid chromatography (96,97). Instmments such as gc/ftir are often termed hyphenated instmments (98). Pyrolyzer (99) and thermogravimetric analysis (tga) instmmentation can also be combined with ftir for monitoring pyrolysis and oxidation processes (100) (see Analytical methods, hyphenated instruments). 

Fig. 8. Thermogravimetric analysis of polymers and copolymers of styrene in nitrogen at 10°C/min A represents PS B, poly(vinyltoluene) C, poly(a-methylstyrene) D, poly(styrene-i (9-acrylonitrile), with 71.5% styrene E, poly(styrene-i (9-butadiene), with 80% styrene and F,...

Fig. 11. Thermogravimetric analysis of cellulose triacetate. Method 20°C/min to 700°C, in (N2) at 40 mL/rnin purging rate.

Thermal analysis using differential scanning calorimetry (dsc), thermogravimetric analysis (tga), and differential thermal analysis (dta) can provide useful information about organic burnout, dehydration, and decomposition. 

Thermogravimetric analysis (TGA) Onset temperature of weight loss... 

Homma, H., Kuroyagi, T., Izumi, K., Mirley, C.L., Ronzello, J. and Boggs, S.A., Evaluation of surface degradation of silicone rubber using thermogravimetric analysis, Proc. Int. Symp. Electr. Insul. Mater., 2nd. 1998, 1, pp. 631-634. 

This phenomenon can be demonstrated by both measuring the changes of the thermal properties of the ECA homopolymer and in adhesion tests. The addition of only 1 wt.% of 9 to a sample of the ECA homopolymer significantly increases the onset of decomposition in the thermogravimetric analysis (TGA) of the polymer, as seen in Fig. 9 [29]. 

Thermogravimetric analysis and other studies made on low-molecular weight model compounds such as 1,3, 5,-trichlorohexane [7,8] corresponding to the idealized head-to-tail structure of PVC show these structures to be considerably more stable than the polymer. This abnormal instability of the polymer is attributed to structural irregularities or defects in the polymer chain, which serve as initiation sites for degradation. 

The modified NBR samples were characterized by differential scanning calorimetry [11,78-80,98]. The glass-transition temperature (T ) decreased with the level of hydrogenation. In the case of HFNBR, Tg increased with an increase in the addition of aldehyde groups to the polymer chain. Thermogravimetric analysis of the modified polymers have also been carried out [15]. 

C Duval Inorganic Thermogravimetric Analysis, Elsevier, Amsterdam, 1963... 

Thermogravimetric analysis has also been used in conjunction with other techniques, such as differential thermal analysis (DTA), gas chromatography, and mass spectrometry, for the study and characterisation of complex materials such as clays, soils and polymers.35... 

Thermogravimetric analysis (TGA) 97 Three-phase fluidization studies. . 156... 

It is of interest that thermogravimetric analysis has been used as a means of determining end group purity of PM VIA macromonomers formed by catalytic chain transfer. 

David, The Application of Differential Thermal And Thermogravimetric Analysis to Military High Explosives , NAVORD 5802, AD 232625 (i960) 108) P. Aubertein H. Pascal, Chemical Determination of Some Explosives and Explosive Mixtures , MP 40,113-25 (1958) CA 54, 25825 (1960) 109) E.M. Bens et al, Rapid... 

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