Thermal analysis, polysaccharides

Morita, H. (1956a). Characterization of starch and related polysaccharides by differential thermal analysis. Anal. Chem. 28, 64-67. 

In the case of differential thermal analysis (DTA), most of the graft copolymers exhibit exothermic peaks at higher temperatures. These exothermic peaks can be related to different decomposition phases of TGA. Exothermic peaks at a lower temperature correspond to the release of energy during the volatilization process, whereas, higher temperature exothermic peaks correspond to the decompositions of other polysaccharide contents [67]. 

Differential thermal analysis (DTG) deals with the rate of decomposition of mass with respect to time. In the case of most of the graft copolymers, rate of weight loss as a function of time (mg/min) is lower than that of backbones [68]. However, in some other cases it has been found to be higher due to the disturbance in the crystalline lattice of the natural polysaccharides upon the incorporation of polyvinyl chains through graft copolymerization (Figure 2.7). 

Thermal stability is a crucial factor when polysaccharides are used as reinforcing agents because they suffer from inferior thermal properties compared to inorganic fillers. However, thermogravimetric analysis (TGA) of biocomposites suggested that the degradation temperatures of biocomposites are in close proximity with those of carbon black composites (Table-1). 

A technique for the controlled thermal degradation of polysaccharides by Curie-point pyrolysis with analysis of the pyrolysis products by field ionization m.s. has been developed. Integrated ion recording by photographic detection gives reproducible fingerprints in a method which appears to be a useful tool for the characterization and identification of microgram quantities of polysaccharides. 

In brief, a DSC instrument comprises two cells fixed in an adiabatic chamber. One cell contains the sample to be tested, the second cell contains a reference solution or an empty DSC pan. The adiabatic chamber is maintained under pressure to avoid the evaporation of the sample (Plum, 2009). A DSC-thermogram represents the plot of heat capacity difference ACp (between the sample and the reference) as a function of temperature. Thermodynamic parameters, such as T, AH and AS, could be determined by the DSC curve analysis. T is the temperature at which the concentration of denatured and native forms of the protein are equal. This specific temperature is also called the midpoint of the thermal transition. AH represents the enthalpy of thermal transition determined from the integration of the DSC curve. The entropy (AS) of the thermodynamic transition of the protein may be calculated from the integrated area under the curve of AC /T vs. T. The free energy (AG), which gives an indication of the protein stability, can also be determined at any temperature from the values of AH and AS (O Brien and Haq, 2004 Plum, 2009). Thermal and thermodynamic properties of proteins analyzed by DSC are greatly affected by the experimental conditions used, such as pH, salts, alcohols, and the presence of other food components (e.g., lipids, polysaccharides) (Grinberg et al, 2009). 

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