Preparation and Characterisation of Cellulose by Delignification of Eteng (Ceiba pentandra) Wood in Formic Acid-Acetic Acid-Water Solvent Mixtures

Cellulose is a natural polymer obtained from plants with applications in various industrial sectors such as pulp and paper, textiles, coatings, fibre composites, and nanomaterials. This work studied the extraction of cellulose from a tropical agricultural plant residue Ceiba pentandra (C. pentandra) using the organosolv method formic acid (FA)-acetic acid (AA)-water (Wa) mixtures as a function of temperature, time, and composition the cooking solvent mixture. Three different volume ratios FA:AA:Wa of 50:30:20, 40:40:20 and 20:30:50 were investigated. Reaction temperature was varied between 80 and 107 °C and the duration between 40 and 200 min. The efficacy of the cooking reaction was determined by the fibre percent yield and Kappa number of the cooking residue. Cooking residues with relatively higher yields (50–70%) were compared with the conventional Kraft method. The residues with yields between 50 and 60% were bleachable as revealed by their Kappa numbers of around 10–12. Some residues were bleached and the products were characterised by Fourier Transform Infrared (FTIR) spectroscopy, thermogravimetric analyses (TG-DTG) and x-ray diffraction (XRD). The results showed that the bleached products had properties close to those of commercial cellulose exhibiting almost similar FTIR spectra and TG-DTG curves. The optimum formic acid-acetic acid-water mixture 50:30:20 at a mild temperature of 107 °C for 3 h, exhibited an activation energy E_a = 141.12 kJ mol^-1 K^-1 and a high crystallinity rate of 72.95% compared to Kraft and Alcell celluloses. This method can be used as a relatively soft route (at mild temperatures, atmospheric pressure) to produce cellulose from the lignocellulosic residues of tropical eteng, C. pentandra.