Effects of hydrochloric acid vapor on the water uptake of cellulose

Cotton linter derived cellulose fibers (Whatman filter papers) were exposed to HCl vapor from a 35% solution for varied periods and the accessibility within the fibers was characterized, mainly via their water vapor uptake. Through dynamic vapor sorption (DVS) and Fourier transform infrared spectroscopy coupled with deuterium exchange, we observed that the water vapor uptake decreased after the HCl exposure and that the most significant changes took place already after 120 min of hydrolysis. Water retention values (WRV), on the other hand, nearly halved as the extent of hydrolysis proceeded all the way down to the leveling off degree of polymerization.

However, under these conditions, the crystallinity of cellulose increased only moderately, the crystal size did not change, and the sample morphology remained unaltered. Analysis of the pore size distribution and specific surface area by calorimetric thermoporometry, and N2 adsorption measurements revealed that both the average pore size and the specific surface area decreased even after short hydrolysis treatments. These results were further complemented by inverse gas chromatography analysis to monitor the changes in surface energy due to the progressing hydrolysis.