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PubMed2006

[FTIR and thermal analysis study of GAP and GAP/B].

The thermal decomposition of GAP and GAP/B in air and nitrogen were studied by FTIR and TG-DTG. The analysis by FTIR and TG-DTG shows that the azide group elimination reactions of GAP begin at about 170 degrees C and finish around 250 degrees C, and the depolymerization of GAP delays by 40 degrees C; Boron changes the mechanism of thermal decomposition process of GAP, and the results show that GAP/B starts losing mass between 55 and 70 degrees C, which is much earlier than GAP itself does. Furthermore, the depolymerization of GAP almost takes place at the same temperature with the azide group elimination. Some kinetics parameters of the reactions were calculated based on Kissinger's processing methods. The results show that the activation energies of the thermal decomposition of GAP and GAP/B are lower and the reactions are easier to occur under air. The possible reason is that the oxygen containing thermal decomposition of GAP has happened.

English Abstract↗
PubMed2001

An improved three-dimensional direct numerical modelling and thermal analysis of a female breast with tumour.

It is well known that malignant tumour tissue generally has higher metabolic and blood perfusion rates than most normal tissues. The authors aim to show that the tissue temperature profile within the breast and the surface temperature profile can be quantified to develop an expert system or diagnostic tool for breast cancer detection. The surface temperature and tissue temperature profiles are analysed for a three-dimensional numerical model of a normal breast and a breast with a tumour. Tumours of different sizes are placed at various locations. In the model, the tissue temperature profile is distorted at the tumour location and was found to compare well with in vivo tests. It was also found that as the tumour was moved to deeper locations its effect on surface temperature was lower. It was observed that small tumours in deeper regions do not have a significant isolated impact on the surface. The numerical results could also capture a shift in the position of the tumour. For tumours greater than 10 mm in the superficial regions and of significant size in deeper regions, it could be seen that the surface temperature distribution of the breast is directly related to the position and size of the tumour embedded in it. The feasibility of providing a diagnostic tool in conjunction with numerical modelling and high-resolution thermograms is also discussed.

Analysis of Variance↗
PubMed1988

Thermal analysis.

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Calorimetry↗
PubMed1987

Evaluation of reversible polymorphic phase transitions by thermal analysis.

Crystalline states of 1,2-dihydro-6-neopentyl-2-oxonicotinic acid, an investigational antidiabetic drug, were evaluated by thermal analyses. Two polymorphs were detected for the drug, Form I (m.p. 193 degrees C) and Form II (m.p. 196 degrees C). Interconversion of the polymorphs upon cyclic solid-melt transitions provided confirmation of the crystal forms. Solidification of the melt was observed to occur either at 162 or 182 degrees C with the formation of Form I or Form II crystals, respectively. Form I underwent partial conversion to Form II upon heating at 10 degrees C min-1 when nucleating crystals of Form II were present in the sample. Differential scanning calorimetry (DSC) thermograms were recorded for different lots of the drug, solvent-recrystallized samples, and a series of known mixtures of Form I and II polymorphs. The study illustrates the usefulness of cyclic heat-cool studies to characterize polymorphic crystal forms of drugs.

Crystallization↗
PubMed2006

Thermal analysis.

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Biochemistry↗
PubMed1982

Structural domains of vesicular stomatitis virus. A study by differential scanning calorimetry, thermal gel analysis, and thermal electron microscopy.

Differential scanning calorimetry has been used in combination with thermal gel analysis and electron microscopy to identify and study the structural domains of the membrane-enclosed vesicular stomatitis virus and its isolated internal components. Three major endothermic transitions centered at approximately 52, 76, and 80 degrees C and at least two minor transitions are observed at pH 7.0 for the intact virion. Thermal gel analysis suggests the possibility that specific proteins of vesicular stomatitis virus are involved in two or more of the calorimetric transitions. The effect of heating to defined temperatures on the morphology of the virion was studied by negative stain electron microscopy. The results of these "thermal EM" studies show discrete irreversible morphological changes in the virion which seem to coincide with the three major calorimetric transitions.

Animals↗
PubMed2000

Thermal analysis studies of poly(etheretherketone)/hydroxyapatite biocomposite mixtures.

Biocomposite formulations which have the potential to combine the proven mechanical performance of poly(etheretherketone) (PEEK) with the inherent bioactivity of hydroxyapatite (HA), may have a utility as load-bearing materials in a medical implant context. The effect of thermal processing on the relevant properties of the PEEK and/or HA components in any fabricated composite structure is, however, an important consideration for their effective exploitation. This paper reports the results of a detailed thermal characterization study of a series of PEEK/HA mixtures using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC). The TGA analyses show minimal weight loss for all of the mixtures and for a pure PEEK sample up to approximately 530 degrees C. Above this point there is a sharp on-set of decomposition for the PEEK component in each case. The temperature at which this feature occurs varies for each mixture in the approximate range 539-556 degrees C. This observation is supported by the presence of exotherms in the corresponding DSC scans, in the same temperature region, which are also assigned to PEEK decomposition. The temperature at which the degradation on-set occurs is found to decrease with increasing HA contribution. The use of the modulated DSC technique allows a number of important thermal events, not easily identifiable from the data obtained by the conventional method, to be clearly observed. In particular, the glass transition temperature (Tg) of the polymer can now be accurately determined. Using these thermal analysis data, calculations of the % crystallinity of PEEK in the mixtures have been made and compared with that of a 100% polymer sample. From these studies it is evident that the presence of HA does not adversely affect the degree of crystallinity of the PEEK component in the mixtures of interest over the thermal range studied.

Journal Article↗
PubMed1989

Dynamic mechanical thermal analysis of dental polymers. I. Heat-cured poly(methyl methacrylate)-based materials.

The visco-elastic characteristics of homogeneous, heterogeneous and fibre-reinforced poly(methyl methacrylate) for use as denture base resins were measured by a dynamic mechanical thermal analyser in the frequency range 0.033-90 Hz. Dynamic Young's modulus of both polyethylene woven yarn and the polyaramid plain fabric-reinforced acrylics showed considerable improvement over the conventional denture base, whereas the carbon fibre-reinforced acrylic produced results lower than expected. From the loss tangent curves of the homogeneous and heterogeneous methacrylates their transition temperatures were recorded and the reciprocals of both the alpha and beta absorption temperatures were plotted against frequency to obtain their respective activation energies.

Dental Materials↗