ATHAS data bank

Although Equation (4) is conceptually correct, the application to experimental data should be undertaken cautiously, especially when an arbitrary baseline is drawn to extract the area under the DSC melting peak. The problems and inaccuracy of the calculated crystallinities associated with arbitrary baselines have been pointed out by Gray [36] and more recently by Mathot et al. [37,64—67]. The most accurate value requires one to obtain experimentally the variation of the heat capacity during melting (Cp(T)) [37]. However, heat flow (d(/) values can yield accurate crystallinities if the primary heat flow data are devoid of instrumental curvature. In addition, the temperature dependence of the heat of fusion of the pure crystalline phase (AHc) and pure amorphous phase (AHa) are required. For many polymers these data can be found via their heat capacity functions (ATHAS data bank [68]). The melt is then linearly extrapolated and its temperature dependence identified with that of AHa. The general expression of the variation of Cp with temperature is... 

ATHAS data bank, http //athas.prz.rzeszow.pl/... 

Figure 2.46 illustrates the completed analysis. A number of other polymers are described in the ATHAS Data Bank, described in the next section. Most data are available for polyethylene. The heat capacity of the crystalline polyethylene is characterized by a T dependence to 10 K. This is followed by a change to a linear temperature dependence up to about 200 K. This second temperature dependence of the heat capacity fits a one-dimensional Debye function. Then, one notices a slowing of the increase of the crystalline heat capacity with temperature at about 200 to 250 K, to show a renewed increase above 300 K, to reach values equal to and higher than the heat capacity of melted polyethylene (close to the melting temperature). The heat capacity of the glassy polyethylene shows large deviations from the heat capacity of the crystal below 50 K (see Fig. 2.45). At these temperatures the absolute value of the heat capacity is, however, so small that it does not show up in Fig. 2.46. After...

The quite complicated temperature dependence of the macroscopic heat capacity in Fig. 2.46 must now be explained by a microscopic model of thermal motion, as developed in Sect. 2.3.4. Neither a single Einstein function nor any of the Debye functions have any resemblance to the experimental data for the solid state, while the heat capacity of the liquid seems to be a simple straight line, not only for polyethylene, but also for many other polymers (but not for all ). Based on the ATHAS Data Bank of experimental heat capacities [21], abbreviated as Appendix 1, the analysis system for solids and liquids was derived. 

General descriptions B Wunderlich and S Z D. Cheng, Gazz Chim TUtIiana,116, 345 (1986) B. Wunderlich, Shin Netsu Sokuteino Shinpo, , 71-100 (1990) B. Wunderlich, Pure Chem., 67, 1919(1995). Experimental data ATHAS data bank, request newest copy from the author. 

The discussion of T, ° must involve four independent variables, namely the enthalpies and entropies of both the melt and the crystal. It, however, will be shown that good estimates of T, ° can be made by using empirical rales for ASf sio , to be derived next. For similar macromolecules AHf sio is usually also similar and derivable from the chemical structure. For aliphatic polyesters, for example, AHfusio 2.3 kJ (mole of backbone atoms) For a summary of extrapolated equilibrium data the ATHAS Data Bank, summarized in Appendix 1, should be consulted. 

The reversing heat capacity and the total heat-flow rate of an initially amorphous poly(3-hydroxybutyrate), PHB, are illustrated in Fig. 6.18 [21]. The quasi-isothermal study of the development of the crystallinity was made at 296 K, within the cold-crystallization range. The reversing specific heat capacity gives a measure of the crystallization kinetics by showing the drop of the heat capacity from the supercooled melt to the value of the solid as a function of time, while the total heat-Uow rate is a direct measure of the evolution of the latent heat of crystallization. From the heat of fusion, one expects a crystallinity of 64%, the total amount of solid material, however, when estimated from the specific heat capacity of PHB using the ATHAS Data Bank of Appendix 1, is 88%, an indication of a rigid-amorphous fraction of 24%. 

The reversing specific heat capacity in the glass transition region is illustrated in Fig. 6.52 [21 ]. The analysis in terms of the ATHAS Data Bank heat capacities shows that there is no low-temperature contribution due to conformational motion below the glass transition. The glass transition of the semicrystalline sample is broadened to higher temperature relative to the amorphous sample, as found in all polymers. Of... 

Table of Thermal Properties of Linear Macromoiecuies and Related Small Molecules—The ATHAS Data Bank°... 

This table includes all data collected, measured, and updated as of November 1994. Please correspond with us about improvements, new data, errors, etc. In the column of the table labeled, (a) represents the amorphous sample, and (c) represents the 100% crystalline sample the mark represents heat capacities for semicrystalline polymers the mark next to the reference numbers, given in italics, indicates that an update is available only in the ATHAS Data Bank. The last line for each entry lists the abbreviation under which data can be retrieved in the computer version of the data bank, available in our web-site, and also listed the reference number to the last update on the given entry. At this reference, information on the source of the experimental data can be found. 

This brief summary reveals a too complex issue to be discussed in all details in a single book chapter. More information is available through the 2879 screens of the computer course Thermal Analysis of Materials, available by downloading from the Internet [1] and the reference work of 2547 pages on Thermal Characterisation of Polymeric Materials [2], or in the treatises on Thermal Analysis of Polymeric Materials [3] and Macromolecular Physics [4-6]. General information and data can be found in Calorimetry [7], the Encyclopaedia of Polymer Science and Engineering [8], the Polymer Handbook [9] and the ATHAS Data Bank [10]. All these sources should give you access to the information needed for interpretation of the instrumental and polymeric materials problems beyond this chapter. 

The description of the theory of heat capacity and the application of heat capacity measurements have been given by Wunderlich and other researchers [2,3-17]. The most comprehensive and updated heat capacity data are collected in the ATHAS data bank (Advanced THermal Analysis) which has been developed over the last 25 years by Wunderlich (Chemistry Department, The University of Tetmessee), and coworkers. 

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