Differential thermal analysis transition temperatures

The thermal glass-transition temperatures of poly(vinyl acetal)s can be determined by dynamic mechanical analysis, differential scanning calorimetry, and nmr techniques (31). The thermal glass-transition temperature of poly(vinyl acetal) resins prepared from aliphatic aldehydes can be estimated from empirical relationships such as equation 1 where OH and OAc are the weight percent of vinyl alcohol and vinyl acetate units and C is the number of carbons in the chain derived from the aldehyde. The symbols with subscripts are the corresponding values for a standard (s) resin with known parameters (32). The formula accurately predicts that resin T increases as vinyl alcohol content increases, and decreases as vinyl acetate content and aldehyde carbon chain length increases. 

ASTM E 1356-98, ASTM Book of Standards 2002. Standard Test Method for Assignment of the Glass Transition Temperature by Differential Scanning Calorimetry or Differential Thermal Analysis . ASTM International, Conshohocken, PA. 

Experimental Methods In Differential thermal analysis (DTA) the sample and an inert reference substance, undergoing no thermal transition in the temperature range under study are heated at the same rate. The temperature difference between sample and reference is measured and plotted as a function of sample temperature. The temperature difference is finite only when heat is being evolved or absorbed because of exothermic or endothermic activity in the sample, or when the heat capacity of the sample changes abruptly. As the temperature difference is directly proportional to the heat capacity so the curves are similar to specific heat curves, but are inverted because, by convention, heat evolution is registered as an upward peak and heat absorption as a downward peak. 

The measurements of Young s modulus in dependence of the temperature (dynamic-mechanical measurements, see Sect. 2.3.5.2) and the differential thermal analysis (DTA or DSC) are the most frequently used methods for determination of the glass transition temperature. In Table 2.10 are listed and values for several amorphous and crystalline polymers. 

Differential thermal analysis (DTA) has provided a wealth of information regarding the thermal behavior of pure solids as well as solid mixtures [10]. Melting points, boiling points, transitions from one crystalline form to another, and decomposition temperatures can be obtained for pure materials. Reaction temperatures can be determined for mixtures, such as ignition temperatures for pyrotechnic and explosive compositions. 

The glass-transition temperatures for solution-polymerized SBR as well as ESBR are routinely determined by nuclear magnetic resonance (nmr), differential thermal analysis (dta), or differential scanning calonme-... 

Chackrabijrtty, D. M. Transition temperatures in some polymers by differential thermal analysis. J. Chem. Phys. 26, 427 (1957). 

Sheets of Kraton 102 were prepared by casting from solution in benzene, cyclohexane, and tetrahydrofuran. The lower (1,4-polybutadiene) transition temperature was —88°C for all samples by differential thermal analysis (DTA) on a duPont thermal analyzer at a heating rate of 5°C/ minute. The upper transition temperature of the triblock could not be... 

Thermal properties are measured and evaluated by some of the methods also mentioned in Chapter 2. For identification of transition temperatures, measurements of heats of fusion, and so on, differential thermal analysis (DTA) and differential scanning calorimetry (DSC) are much used. Thermal stability is measured by thermogravimetric analysis (TGA), although this technique can give overly optimistic results unless used with great care. 

An other method to study structures during cooling and warming is differential thermal analysis (DTA) (Figure 1.25). It measures the different course of temperature between the sample and a probe, which changes its thermal behavior uniformly but does not have a phase transition in the measured temperature range. Such an instrument is illustrated in Figure 1.26. 

Differential Thermal Analysis (DTA). The differential thermal analysis test serves to examine transitions and reactions which occur on the order between seconds and minutes, and involve a measurable energy differential of less than 0.04 J/g. Usually, the measuring is done dynamically (i.e., with linear temperature variations in time). However, in some cases isothermal measurements are also done. DTA is mainly used to determine the transition temperatures. The principle is shown schematically in Fig. 2.20. Here, the sample, S, and an inert substance, /, are placed in an oven that has the ability to raise its temperature linearly. 

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