Thermodynamic pathway of lignocellulosic acetylation process

Abstract

The use of natural cellulosic fibers as materials in the reinforcements of polymer composites and sorption of oil from water, has directed more focus on acetylation than other known chemical modification methods. Cellulose can be modified by acetylation to provide a suitable and cost effective cellulose acetate which have high hydrophobic characteristics and are biodegradable. In this study, lignocellulosic samples—oil palm empty fruit bunch (OPEFB), pride of Barbados pods (POBP) and cocoa pods (CP)—with different compositions of lignin and hemicellulose, were acetylated using solvent free method. Effect of temperature on the acetylation of these samples at different reaction times were studied and used for the thermodynamic studies. Analysis of variance (ANOVA) was used to test the significance of temperature variation with weight percent gain (WPG) due to acetylation of the lignocellulosics at different reaction times. FTIR studies showed evidence of successful acetylation reaction. ANOVA test showed no statistical difference in the observed variation of WPG due to acetylation of all the lignocellulosic samples, with temperature at different reaction times. The best acetylating period for OPEFB, POBP and CP were 60, 30 and 90 min respectively. Acetylation of the lignocellulosic samples were found to occur by absorbing heat from the environment. Values of entropy changes were positive while Gibb’s free energy change values were negative except at operating temperature of 303 K. Thus, acetylation of these lignocellulosic samples were spontaneous except at 303 K. Acetylated POBP has the lowest heat capacity (0.82 kJ mol−1 K−1) compared to acetylated OPEFB (1.47 kJ mol−1 K−1) and CP (1.15 kJ mol−1 K−1). Low critical WPG showed that the mechanism of acetylating these materials were diffusion controlled. The critical temperatures of OPEFB, POBP and CP acetylation were found to be 282.6 K, 223.2 K and 260.5 K respectively. Thus, acetylation of these lignocellulosic samples were successful and found to be energy efficient.