Comparative Investigation of NaOH and KOH Treatments for Cellulose Purity and Polymorph Control in Pineapple Leaf Fibers: Crystallinity Changes and Electrochemical Impedance Signatures

Abstract A large percentage of pineapple leaves is now being disposed of as agricultural waste, but this biomass holds a lot of conversion potential to value-added products. This study systematically compares NaOH and KOH treatments for the selective extraction of cellulose microcrystals from pineapple leaves. It investigates how the concentration of alkali varies and affects the cellulose content, crystallinity, and extraction yield. Alkali treatment can be used to remove the noncellulosic constituents efficiently and thus improve cellulose purity. As a result, it enhances the crystallinity of the extracted cellulose by effectively dissolving the amorphous regions. The results from Fourier transform infrared (FTIR) and X-ray diffraction (XRD) confirm structural changes in the cellulose matrix due to alkaline treatment, with XRD analysis indicating the onset of the Cellulose I-to-Cellulose II transformation between 2 and 3 M NaOH and between 3 and 4 M KOH under the investigated treatment conditions. Electrochemical impedance spectroscopy (EIS) revealed that the structural transitions of cellulose significantly modulate the electrochemical properties. Resistance and relaxation behaviors are determined by crystallinity and polymorphic transitions between Cellulose I, amorphous phases, and Cellulose II, with Cellulose I having a greater resistive response, amorphous domains having better conductivity and capacitance, and Cellulose II having dense resistive behavior when dry and capacitive capacities after rehydration. Overall, this study demonstrates that agricultural waste can be converted into highly pure cellulose with tunable crystallinity and electrochemical characteristics, providing mechanistic insights that may inform the future design of cellulose-based electroactive materials. These findings suggest potential relevance to areas such as energy storage, biosensing, and environmentally friendly electronic materials, which warrants further investigation.