Isolation of Cellulose from Poplar Wood by Nitric Acid-Ethanol Treatment and Its Effect on the Quality of Films Cast from Ionic Liquid

Cellulose was successfully isolated from poplar wood chips using a two-step treatment for controlled times. The treatment included nitric acid-ethanol pretreatment and mechanical dispersion. The cellulose specimens were then dissolved in an ionic liquid and cast to prepare cellulose films. The prepared samples and films were examined using scanning electron microscopy (SEM), High Performance Liquid Chromatography (HPLC), Fourier-transform spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and ultraviolet-visible spectroscopy (UV-Vis). The results showed that lignin and hemicellulose reacted and dissolved in the nitric acid-ethanol mixture solution, which broke the biomass recalcitrance and promoted cellulose dispersion in the solvent for preparing uniform films. However, a large amount of cellulose was hydrolyzed within the fourth treatment, resulting in a remarkable decrease in the tensile strength of the films. After three repetitions of treatments, the cellulose had a better average degree of polymerization, crystallinity, and thermal stability. The films had the highest tensile strength of 32.8 MPa, elongation at break of 47.5%, and transmittance that exceeded 80% at the wavelength range of 600 nm to 800 nm, which indicated that the samples were more suitable for film fabrication.