Preparation And Characterization Of Cellulose From Corncob By Pretreatment Combined With Oxidation Induced By Hydrogen Peroxide

Cellulose is the most abundant renewable biological polymer in the world. At present, cellulose is often used for production of papers,cardboard, fiberboard and other similar products of raw materials. Its excellent features including hydrophilic, chiral, biodegradable, broad chemical modification capacity, the ability of forming crystal fiber, has attracted great attention of scholars. Cellulose with high purity and low polymerization degree can be used for production of chemicals and biological macromolecule material.The paper is divided into four parts, the first part compares the popular dilute acid steam explosion and emerging ultrasonic Fenton pretreatment. Chemical composition and 13C CP/MAS solid-state NMR spectra showed that the dilute acid steam explosion pretreatment mainly removed hemicellulose (removal rate 96.03%), and ultrasonic Fenton pretreatment mainly removed lignin (removal rate 46.60%). Simons’ stain and WRV results show that ultrasonic Fenton pretreatment created more accessible surface area on the surface of the corncob. SEM image showed that dilute acid steam explosion pretreatment mainly fractured corncob structure into small pieces, however ultrasonic Fenton pretreatment mainly made concob surface structure porous, which could make cellulase more into cellulose. The digestion rate of corncob with dilute acid catalytic steam explosion pretreatment (86.8%) is slightly lower than that of ultrasonic Fenton pretreatment (90.34%).The second part, is about optimizing ultrasonic- fenton reaction parameters of degradating lignin sulfonate. With the condition of 5M H2O2, 0.025M FeS04, pH 4.0 and 120 min, the degradation rate of lignin sulfonate was 74.27%, and the molecular weight was 5026 g/mol.Ultraviolet graph indicated that the benzene ring structure of lignin sulfonate fractured. Infrared spectra further showed that benzene ring skeleton of lignin sulfonate broke. This work provides the reference data for the third research.The third part, firstly dilute acid steam explosion pretreatment (0.5%sulfuric acid, 1.0 MPa, 8 min) remove the hemicellulose in the corncob,then the optimized ultrasound fenton reaction (5.37 M H2O2, 0.03 M FeS04, 125 min) and hot ethanol, 80% ethanol, 160 ℃, 90 min) remove the lignin in the residue of steam explosion, the purity of the cellulose was 91.81%. XRD spectra showed that cellulose was no changes in crystal shape and the crystallinity increased, which showed the structure of cellulose was mainly not damaged, and amorphous hemicellulose and lignin had been removed. 13C solid-state nuclear magnetic spectra further showed that almost completely removed lignin and hemicellulose.The last part, firstly dilute acid catalytic steam explosion pretreatment(0.5% sulfuric acid, 1.0 MPa, 8 min) removed the hemicelluloses in the corncob, then hot ethanol (0.02% sodium hydroxide, 80% ethanol,160 ℃, 90 min) and acid peroxide produced in situ (5% concentration,H2O2 0.3 mol/g sample) took off the lignin, also complete bleaching at the same time. The purity of cellulose was 92.97%, which was slightly higher than that of cellulose in the second part. XRD spectrogram results showed that the crystal structure of cellulose was not changed and the crystallinity was increased. FTIR spectrogram further showed that lignin benzene ring skeleton fractured, and beta glycosidic bond links of cellulose was intact,which indicated that the structure of cellulose was not damaged.TGA and DTG curves further showed that the cellulose prepared in the part had better thermal stability than alkali cellulose fiber. The results of polymerization showed that the cellulose prepared by the steam explosion coupling peroxyacetic acid method had low polymerization degree.