Thermogravimetric analysis sample requirements

The method known as thermogravimetric analysis (TGA) requires little more than accurate and sensitive weighing equipment since the resulting information consists of the sample weight as a function of time with increasing temperature. The ideal but seldom realized goal is to achieve a uniform temperature increase of the test material. 

Powdering, or grinding, of samples is a simple preparation method required in a number of spectrometric and spectroscopic techniques, such as x-ray diffraction (XRD), nuclear magnetic resonance (NMR), differential thermal analysis (DTA), thermogravimetric analysis (TG), or ATR-FTIR spectroscopy. Control of the particle size during grinding must be taken into account in attempting to obtain reliable results. 

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. 

Perhaps the be.st known method of endpoint determination is thermogravimetric analysis or loss on drying analysis. This method requires an operator to stop the process and gather a representative sample for analysis. The drying process resumes while the sample is analyzed po.sing the po.ssibility that the material may exceed the acceptable endpoint while the analysis is made. Loss on drying is not specific to a particular component as all volatile components are driven off in the analysis. 

A combination of GC/MS with thermogravimetric analysis simplifies analysis because the sample is ran directly from TGA which does not require sample preparation. TGA is interfaced with GC/MS through evolved gas collector which contains primary and secondary desorption elements which supply GC with samples. ... 

Though methods for identification of man-made fibers utilizing differential scanning calorimetry, differential thermal analysis, and thermogravimetric analysis have been reported, the sample amounts required are too large for actual case studies, so these methods are rarely used in forensic identification and are only adopted in very specific cases. 

In the thermogravimetric analysis, the use of samples with similar masses is a requirement in order to obtain comparable results [23]. Sampling should be done with instruments that do not induce stress or produce heat (even locally). Analyzed samples should have the same thermal and mechanical history, as previous heat-treatments and mechanical processing significantly influence the thermal events that occur in the sample and can result in different outcomes for the same chemical species. This is owned to the fact that the sample internal energy affects the thermal analysis, and the internal energy can be modified by the aforementioned thermal or mechanical processes [21]. 

In thermogravimetric analysis (TG), the weight changes are determined as the sample is heated at a uniform rate. It differs from the semistatic or static method in which the sample is held at a constant temperature for a required period of time. In concrete investigations, TG is commonly used with DTA to follow the hydration reactions. The first derivative of change of mass (DTG) can also be used for identification purposes as it yields sharper peaks. TG cannot detect crystalline transitions as they do not involve weight losses. 

As remarked earlier, greater loadings are required for cross-linked samples than for the corresponding uncross-linked material in order to achieve sufficient penetration to adequately detect the crystalline melting point with confidence. TMA data would typically be used in conjunction with some or all of FTIR spectra, DSC responses and also data from thermogravimetric analysis (TGA) as appropriate, in order to more fully characterise an unknown. 

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