Structure and Properties of Regenerated Cellulose Films Prepared from Cotton Linters in NaOH/Urea Aqueous Solution

Abstract

Regenerated cellulose (RC) films having various viscosity-average molecular weights ( M η ) ranging from 2.2 × 10 4 to 8.2 × 10 4 g/mol were prepared from cotton linters in 6 wt % NaOH/4 wt % urea aqueous solution by coagulation with 2 M acetic acid and 2% H 2 SO 4 aqueous solution. The dissolution of cellulose and the structure, transparency, and mechanical properties of the RC films were investigated by 13 C NMR, ultraviolet, and infrared spectroscopies; scanning electron microscopy; X-ray diffraction; and a strength test. The RC films exhibited the cellulose II crystalline form and a homogeneous structure with 85% light transmittance at 800 nm. 13 C NMR spectroscopy indicated that the presence of urea in NaOH aqueous solution significantly enhanced the intermolecular hydrogen bonding between cellulose and the solvent, resulting in a higher solubility of cellulose and the complete transition of its crystalline form from I to II. The tensile strength (σ b ) of the RC films in the dry state increased with increasing M η up to 6.0 × 10 4 g/mol and then hardly changed. The values of σ b and the breaking elongation (ε b ) of the RC film having M η = 6.0 × 10 4 g/mol by coagulation with 2% H 2 SO 4 were found to be 106 MPa and 8.0%, respectively, in the dry state and 17.0 MPa and 10.7%, respectively, in the wet state, and the strength was much higher than that of commercially available cellophane. Therefore, a novel and nonpolluting process for the manufacture of cellulose film and fiber from cotton linters in 6 wt % NaOH/4 wt % urea aqueous solution is provided in this work.