DeterminaÃÃo de um novo valor para a entalpia de fusÃo do cristal perfeito de acetato de celulose

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The enthalpy of fusion of a perfect crystal of cellulose acetate was calculated in this thesis. In order to do so, cellulose samples from different sources were acetylated through the heterogenous acetilation methodology. The cellulose acetate samples were characterized by differencial scanning calorimetry (DSC) and by wide angle X-ray diffraction (WAXD). The X-ray diffractograms were deconvoluted into halos and peaks using the Pseudo-Voigt peak function of program Origin 7.0. Two hypotheses were proposed in order to fit the deconvolution patterns into the two-phase model. In the first, the amorphous regions of the material was considered to be represented by the area of the halo located at 21 and the crystalline area by the maxima at 8Â, 11Â, 13 and 16Â. In the second hypothesis, the amorphous region was considered to be represented by the areas of the maxima at 11 and 21Â, and the crystalline region by the maxima at 8Â, 13 and 16Â. The WAXD crystallinities of the samples were then calculated from these values. The first hypothesis was ignored for presenting a very high crystallinity value for a sample that did not present an enthalpy of fusion. The second hypothesis was used, but the linear regression that defined the relationship between the enthalpy of fusion and the crystallinity of the materials was forced through zero. Through this relationship, the enthalpy of fusion of a perfect crystal of cellulose acetate was calculated to be 58.8 J/g.

ASSUNTO(S)

dsc cellulose acetate crystallinity cristais quimica acetato de celulose entalpia de fusÃo waxd deconvolution waxd cristalinidade enthalpy of fusion,

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