Abstract
Purified cotton linters presoaked in AcOH, were acetylated at 70° and 90°C with a minimized amount of Ac2O and H2SO4.
(1) The average degrees of polymerization of the triesters obtained were between 115 and 180 at 70°, and between 105 and 120 at 90°C. The acetylation was carried out using either 250% or 300% of Ac2O, based on the weight of cellulose. The rate of the reaction is more strongly dependent on the amount of H2SO4 than on the amount of Ac2O. The minimized amount of Ac2O is 4 moles per glucose anhydride, and the value is almost the theoretical one, as a little more of Ac2O than the theoretical value (3 moles per glucose anhydride) is usually required to acetylate the low molecular compounds which are decomposition product of cellulose by acetylation at higher temperatures.
(2) The more the amount of H2SO4 and the higher the temperature of the reaction, the faster the rate of reaction increases. The triesters were obtained by 0.7% and 0.5 of H2SO4 based on the weight of the cellulose at 70°C for 90 and 120 minutes, respectively.
(3) The minimized amounts of H2SO4 to obtain the triesters are 0.5% at 70°C and 0.2% at 90°C. The difference in these minimized amounts may be caused by the fact the rate of acetylation is determined by the cyclic reaction of H2SO4 which is affected by temperature.
