synopslsThe solubility of cellulose triacetate in a range of solvents was measured, and the results for tetrachloroethane, chloroform, and acetic acid were compared with those from initial phase separation in solvent-nonsolvent mixtures and viscosity-concentration studies. The correlation found between solubilities, precipitation values, and values of the Huggins viscosity constant is discussed with reference to the type of polymer-solvent interaction proposed previously to explain fractionation behavior. A qualitative comparison of solubility-swelling behavior was also made for a very low molecular weight cellulose triacetate sample in a wide range of solvents. Results are compared with those for higher molecular weight samples and discussed with regard to the cohesiveenergy densities of solvent and polymer. Some attempt has been made to predict suitable solvents for cellulose triacetate, based on consideration of their molecular structures.
SynopsisUsing petroleum ether as a precipitant and chloroform-acetone mixture as solvent, six fractions of cellulose triacetate were obtained by fractional precipitation. The molecular weight of each fraction was obtained from osmotic pressure measurements carried out on chloroform solutions. It was shown that virtual nonfractionability of cellulose triacetate with regard to molecular weight occurred in this system. This behavior was also observed in attempts to fractionate it from tetrachloroethane or acetic acid solutions. These results are explained by the hypothesis that specific polymer-solvent interaction takes place due to hydrogen bonding.
Moisture sorption data of Form C samples have been obtained using a McBain-Bakr sorption balance and these were used to calculate effective area of molecular contact of the cross-linked samples with the Brunauer-Emmet-Teller (BET) equation. A probable explanation is advanced for the maxima and minima in moisture regains of cross-linked in the swollen state samples and the effective area/HCHO relationship. Attempts have been made to infer the distribution of cross-links trom the moisture sorption data of the cross-linked samples. Iodine accessibility values of formaldehyde-crosslinked fibre and dye pickup studies of formaldehyde-crosslinked fabric support an earlier assumption that the primary wall is ruptured under Form W conditions.
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