Semitransparent films from low-substituted carboxymethylated cellulose fibers

Cellulose-derived films have received attention for possible use in the packaging industry. However, the poor mechanical properties of the biofilm are the main concern. This study aims to mildly carboxymethylate cellulose fibers and esterify the generated carboxymethylated cellulose fibers (CMF) for film production. The physicochemical alteration of cellulose fibers via carboxymethylation and esterification was confirmed by means of solid-state carbon NMR, FTIR, and XPS analyses. The carboxymethylation of cellulose fibers impacted their surface morphology and fiber length dramatically. The results confirmed that the carboxymethylated cellulose fibers (CMF) with a 1.2 mmol/g carboxylate group generated films with the highest mechanical properties. The higher degree of carboxymethylation tended to reduce the mechanical properties but improved the optical properties of the CMF film as smaller CMF could scatter light more effectively. The use of acetic acid (3 wt%) was crucial in the esterification of CMF to generate CMF film with the highest tensile strength (60.8 MPa), but a higher concentration of acetic acid would impair the mechanical properties of the film. The great tensile strength of the CMF derived film (60.8 MPa) and the relatively uncomplicated fabrication procedure of CMF films are promising for some applications, such as bags and agriculture uses. However, the water uptake of the CMF films was relatively high (3–4 g/g), and further research needs to address this challenge.