The Physicochemical Changes of Cellulose Hydrolyzed with HCl Vapor after Pretreatment with FeCl3

Improving the accessibility of cellulose is essential for the production of derivative products. This can be achieved by modifying its physicochemical properties. This research aimed to investigate the properties of cellulose extracted from the torch ginger stem. The cellulose was pretreated with FeCl₃ and then hydrolyzed using HCl vapor at a 37% concentration. Hydrolysis was conducted in a pressurized HCl vapor system at 27.60 kPa and 30 °C for 0–24 h. Similar treatment was conducted to cellulose without FeCl₃ (unpretreated). The results show that FeCl₃ pretreatment significantly decreased degree of polymerization (DP) from 0 to 24 h compared to unpretreated cellulose. The hydrolysis reaction occurred above the saturation point of HCl. When the cellulose was hydrolyzed with HCl vapor, cellulose morphology, thermal properties, and functional groups remained largely unchanged, respectively, as observed by FESEM, TGA, and FTIR methods. However, the X-ray diffractograms and FTIR spectra revealed that decrystallization of FeCl₃ pretreated cellulose occurred after 10 h of hydrolysis. The 24 h hydrolysis yield for FeCl₃ unpretreated and pretreated cellulose was 90.6% (DP of 118) and 86.8% (DP of 76), respectively. Therefore, this hydrolysis system can be considered an important pretreatment method for preparing cellulose derivatives.