Composites Simultaneous Thermal Analysis

Small particle sizes of raw batch materials accelerate melting and homogenization via an increase in the reaction area between raw materials. However, the use of very fine raw materials has an associated dusting problem along with the added cost of particle size reduction. In the following, simultaneous thermal analysis in conjunction with x-ray diffraction were used to determine the fusion path in a typical glass composition as a function of particle size. 

Table 2 Some parameters evaluated from TG/DTG/DTA simultaneous thermal analysis of natural filler/glycerol plasticized starch matrix composites...

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... 

Principles and Characteristics Simultaneous thermal analysis techniques, such as TG-DSC/DTA offer vital information on polymer structure based on heat flow behaviour and mass change [290], but little direct information on the composition of evolved gas products. A more complete thermal profile is provided when a thermal analyser is coupled to an identification tool. Henderson et al. [433] have recently described TG-DSC/DTA with evolved gas analysers (MS and FTIR). The skimmer coupling is the most advanced commercial way of combining a thermobalance or simultaneous TG-DSC/DTA instrument with a quadrupole mass spectrometer [338]. For descriptions of interface techniques in this coupled instrumentation, cfr. ref. [411]. Simultaneous TG-DSC-MS is capable of operation up to 2000°C [434]. 

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. 

The compositions of the products were determined by inductively coupled plasma (ICP) with a Perkin-Elmer plasma 40 emission spectrometer. Simultaneous differential thermal analysis and thermogravimetric (DTA-TG) curves were carried out by using Perkin-Elmer DTA-7000, TGA-7 PC series thermal analysis instrument in air with a heating rate of 10 °C /min. The infrared (IR) spectra were recorded on an Impact 410 IR spectrometer on samples pelletized with KBr powder. Valence states were determined by X-ray photoelectron spectroscopy (XPS). The XPS for powder samples fixed on double sided tapes was measured on an ESCA-LAB MKII X-ray photoelectron spectrometer. The Cis signal was used to correct the charge effects. 

Comparison of several techniques (namely Fourier transform infrared spectroscopy (FTIR), simultaneous thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) and ultrasonic spectroscopy) for assessing the residual physical and mechanical characteristics of polymer matrix composites (PMCs) exposed to excessive thermal loads showed the measured power spectra of ultrasonic energy to correlate with performance of graphite fibre epoxy matrix composites exposed to thermal degradation, and also that analyses with the three techniques all pointed to the same critical temperature at which thermally induced damage increased sharply [58],... 

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. 

Potential compositional analysis. While the strong dependence of retention on the chemical composition of the polymer has only recently been firmly established, this dependence opens the way for the characterization of chemical composition by thermal FFF. It is likely that thermal FFF can be combined with another method sensitive only to molecular size (such as SEC or flow FFF), to provide simultaneous information on molecular mass and compositional distributions, which might be particularly useful for copolymers [28]. 

A differential photocalorimeter can be interfaced with a thermal analysis system to measure the heat absorbed or released by a sample as the sample and an inert reference are simultaneously exposed to UV radiation of known wavelength and intensity during programmed heating or in an isothermal manner. Important applications include UV curing studies of compositions, formulations, and mechanisms of UV-curable materials and coatings. 

While additive analysis of polyamides is usually carried out by dissolution in HFIP and hydrolysis in 6N HC1, polyphthalamides (PPAs) are quite insoluble in many solvents and very resistant to hydrolysis. The highly thermally stable PPAs can be adequately hydrolysed by means of high pressure microwave acid digestion (at 140-180 °C) in 10 mL Teflon vessels. This procedure allows simultaneous analysis of polymer composition and additives [643]. Also the polymer, oligomer and additive composition of polycarbonates can be examined after hydrolysis. However, it is necessary to optimise the reaction conditions in order to avoid degradation of bisphenol A. In the procedures for the analysis of dialkyltin stabilisers in PVC, described by Udris [644], in some instances the methods can be put on a quantitative basis, e.g. the GC determination of alcohols produced by hydrolysis of ester groups. 

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