Cellulose-based polymer electrolyte derived from waste coconut husk: residual lignin as a natural plasticizer

Cellulose was isolated from waste coconut husk (Cocos nucifera) via alkali and single bleaching treatment. The isolated cellulose (CH-A-1B) was found to have residual lignin which imparts amorphous character to the polymer matrix as confirmed by X-ray diffraction analysis (XRD). Fourier transform infrared (FTIR) peak at 1507 cm−1 confirmed the presence of lignin and the appearance of three new peaks at 1320, 1416, and 1595 cm−1 showed successful attachment of carboxymethyl group onto the cellulose backbone. Carboxymethylation of cellulose from CH-A-1B produced carboxymethyl cellulose (CMC) with lower crystallinity compared to that of the double bleaching treatment cellulose (CH-A-2B). The CMC film prepared by solvent-casting method from CH-A-1B using 38 wt% NaOH possessed the highest conductivity of σ = 4.82 × 10−4 mS cm−1. The electrochemical properties of the CMC polymer electrolyte and the degree of crystallinity of the polymer matrix were found to be influenced by the amount of lignin content which acts as a natural plasticizer.