Facile synthesis of carboxymethyl cellulose from Indonesia's coconut fiber cellulose for bioplastics applications

Abstract

Coconut fibers contain many lignocellulosic components; therefore, they have the potential to be used as cellulose‐based materials. This study aims to synthesize carboxymethyl cellulose (CMC) for bioplastic applications from coconut fiber cellulose obtained from South Tangerang, Indonesia. The isolation of cellulose was conducted in two key stages: alkaline treatment using a delignification reactor and bleaching with hydrogen peroxide (H2O2). The facile synthesis of CMC involved two important steps: alkaline treatment and carboxymethylation of isolated cellulose. The yield of cellulose isolated from coconut fiber was 16.39% for biomass and 64.84% for delignification products. The cellulose produced exhibited a crystallinity index (C.I.) of 89%. The yield of CMC was 14.67%, with a C.I. was 56.66%. The CMC obtained was categorized as having a medium molecular weight of 249,048 Da with a polymerization degree of 1046. Cellulose starts to decompose at a temperature interval of 292.05–381.45°C, whereas CMC decomposes at a lower temperature interval of 245.42–299.73°C. Thermochemical calculations were conducted by using the density functional theory (DFT), confirming a spontaneous reaction with a Gibbs free energy of −5.25 kJ mol−1. Bioplastics were fabricated in two stages: blending with carboxymethyl chitosan (CMChi) and plasticizing with glycerol. The addition of CMCh increased the C.I. and tensile strength, while the addition of glycerol to CMC/CMChi (80/20) blend‐based bioplastic reduced the C.I. and tensile strength, but enhanced the relative contact angle.Highlights Cellulose was isolated from coconut fibers through a two‐stage process involving delignification and bleaching; Carboxymethyl cellulose was synthesized by monochloroacetic acid in isopropanol with NaOH as the catalyst; The optimum condition for achieving the highest elongation at break among the blending compositions was found in the CMC/CMChi (80/20) blend bioplastic; Adding up to 30 wt% glycerol decreased the tensile strength and increased the elongation at break; The addition of glycerol enhanced the hydrophobic properties of CMC/CMCh blend‐based bioplastics.