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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Thermodynamic Parameters Relative to the Melting of Cellulose Tributyrate

Piana, Umberto, Pizzoli, Maria, Buchanan, Charles M. 01 January 1995 (has links)
Wide-angle X-ray scattering (WAXS) and differential scanning calorimetry (d.s.c.) measurements were made on cellulose tributyrate (CTB). In one case, CTB precipitated from solution in powdered form was annealed at different temperatures. In a second case, CTB was isothermally crystallized either from the melt or from the glass. Samples annealed from the powder showed higher crystallinity with respect to samples crystallized from the glassy or molten state. By applying the Hoffman-Weeks method to the melting temperatures of isothermally crystallized samples, a value of 192 °C for the equilibrium melting temperature of CTB was obtained. From calorimetric results on samples with different crystalline/amorphous ratio, a linear dependence between ΔHm and ΔCp was found, whose extrapolation gave 34.5 J g-1 for the equilibrium heat of fusion ΔHm°. A correlation between the experimental melting enthalpy arising from d.s.c. measurements and the percentage crystallinity estimated by WAXS measurements was attempted. In this manner a second, surprisingly high, value (67 J g-1) for ΔHm° was found. The difference between the values obtained from the two methods is believed to be due to the presence of macroscopic order in the amorphous phase, which influences the value of the WAXS crystallinity.

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