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

Regenerated cellulose (RC) films having various viscosity-average molecular weights (M η) ranging from 2.2 × 104 to 8.2 × 104 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% H2SO4 aqueous solution. The dissolution of cellulose and the structure, transparency, and mechanical properties of the RC films were investigated by 13C 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. 13C 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 (σb) of the RC films in the dry state increased with increasing M η up to 6.0 × 104 g/mol and then hardly changed. The values of σb and the breaking elongation (εb) of the RC film having M η = 6.0 × 104 g/mol by coagulation with 2% H2SO4 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.