Response surface methodology for optimization of cellulose extraction from banana stem using NaOH-EDTA for pulp and papermaking

Alkaline pulping using sodium hydroxide (NaOH), also known as soda pulping, is predominantly used to extract cellulose for pulp and papermaking. The NaOH was responsible for the dissolution and removal of lignin but unfortunately, simultaneous hydrolysis of cellulose could not be avoided. Modification for improved lignin removal and cellulose stabilization are always a technical challenge for the pulp and paper industry. Therefore, ethylenediaminetetraacetic acid (EDTA) was considered as an additive to minimize cellulose hydrolysis and thus improve the total yield of cellulose pulp. Response surface methodology (RSM) with central composite design (CCD) was employed for statistical modeling and optimization of NaOH and EDTA charges for maximum pulp yield, lignin removal, and cellulose content. Analysis of variance (ANOVA) revealed a significant interaction effect of NaOH and EDTA charges on pulp yield and its cellulose content. Using the predicted optimum condition of 17.7% NaOH and 10% EDTA, pulping of banana stem at 100 ± 5 °C for 30 min resulted in increasing pulp yield, lignin removal, and cellulose content by approximately 18.5%, 1.1%, and 0.6%, respectively, as compared to pulping without EDTA. Changes in the functional groups monitored using Fourier transform infrared (FTIR) revealed the presence of ester and C–N stretching bands from cellulose extracted with NaOH/EDTA due to successful esterification of EDTA on the cellulose pulp. Further analysis on the viscosity average degree of polymerization found that the cellulose pulp extracted with NaOH/EDTA also has a higher degree of polymerization compared to the pulp extracted without EDTA. Based on these findings, it was concluded that esterification with EDTA has successfully protected the cellulose against alkaline hydrolysis by NaOH. Therefore, the addition of EDTA is a promising approach to improve the pulp yield with high degree of polymerization.