Chengrong Qin

Removal of hexenuronic acid by xylanase to reduce adsorbable organic halides formation in chlorine dioxide bleaching of bagasse pulp.

Xylanase-aided chlorine dioxide bleaching of bagasse pulp was investigated. The pulp was pretreated with xylanase and followed a chlorine dioxide bleaching stage. The ATR-FTIR and XPS were employed to determine the surface chemistry of the control pulp, xylanase treated and chlorine dioxide treated pulps. The hexenuronic acid (HexA) could obviously be reduced after xylanase pretreatment, and the adsorbable organic halides (AOX) were reduced after chlorine dioxide bleaching. Compared to the control pulp, AOX could be reduced by 21.4-26.6% with xylanase treatment. Chlorine dioxide demand could be reduced by 12.5-22% to achieve the same brightness. The ATR-FTIR and XPS results showed that lignin and hemicellulose (mainly HexA) were the main source for AOX formation. Xylanase pretreatment could remove HexA and expose more lignin, which decreased the chlorine dioxide demand and thus reduced formation of AOX.

Efficient extraction of bagasse hemicelluloses and characterization of solid remainder

To reduce the degradation of cellulose and obtain high molecular weight of hemicellulose from the extracts, pH pre-corrected hot water pretreatment was developed by employing sodium hydroxide (3.9mol/L). The response surface model was established to optimize the extraction process. The species composition and purity of hemicellulose extract was analyzed by High Performance Liquid Chromatography (HPLC). The obtained solid remainder was analyzed by FTIR and SEM. The results showed that the component of xylose in hemicellulose extract was similar with commercial xylan. FTIR and SEM were shown to be able to evaluate solid remainder composition and surface characterization of the bagasse. The biggest balance between solid remainder and dissolved solid was obtained. Not only the yield of dissolved solid was improved, but the structure of solid remainder was also proved, which was beneficial to pulping and papermaking.

Mechanism and kinetics studies of carboxyl group formation on the surface of cellulose fiber in a TEMPO-mediated system

Abstract2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO) can selectively oxidize primary hydroxyl groups of cellulose to carboxyl groups. However, the depolymerization also occurs during the process. The kinetics and mechanism of carboxyl group formation on the surface of cellulose fiber oxidized by TEMPO/NaClO2/NaClO were discussed. The oxidization and depolymerization of cellulose occurred simultaneously, according to analysis of FTIR and 13C CP/MAS NMR. The glucuronic acid and some small molecular fragments, formed by hydrolysis or β-elimination during the oxidation, are also discussed. The crystallization index increased and crystal size decreased, as shown by X-ray analysis. The degradation steps in the TEMPO/NaClO2/NaClO system was discussed, according to carbon conversion analyzed by 13C CP/MAS NMR. The oxidation of cellulose can be described well by the kinetics model established based on the degradation of cellulose. It was found that temperature is one of the key parameters for controlling the oxdation and degradation level. The possible mechanism for oxidation of cellulose was composed.

The influence of mechanical refining treatments on the rheosedimentation properties of bleached softwood pulp suspensions

To study the effect of mechanical treatments on the rheosedimentation behaviour of pulp fiber suspensions, the settling behaviour, gel point, compressive yield stress and hindered settling function of bleached softwood pulp with different beating degrees at low concentrations were investigated. Over the range of test concentrations, it was found that the settling rates for refined softwood pulps were slower than that without mechanical treatments, and the values of gel points increased approximately linearly with freeness; Both the compressive yield stresses and hindered settling functions of all pulp suspensions increased non-linearly with increasing crowding number, and the hindered settling function was found to be dependent on the crowding number through a power law relationship. Moreover, the compressive yield stresses for softwood pulp suspensions with mechanical treatment were higher than that without refining. However, the same tendency for hindered settling functions was observed only for suspension at crowding number more than 16. The rheosedimentation studies on softwood pulp suspensions revealed that fiber morphology has a great influence on the settling and compressive behaviour.

Effect of hot chlorine dioxide delignification on AOX in bagasse pulp wastewater

This work describes the effect of the hot chlorine dioxide delignification (DHT) on the properties of bagasse fiber and the formation of AOX. The bagasse pulp was subjected to both DHT and normal temperature chlorine dioxide delignification (D0), and the AOX contents in the effluent were determined respectively. The GC–MS results showed that the main components of the D0 stage wastewater were chlorinated hydrocarbons and chlorinated diphenyls. In contrast, those AOXs in the DHT stage wastewater were very few. The GC–MS, ATR-FTIR, and XPS results showed the DHT process is more effective in the removal of the residual phenolic lignin and the hemicellulose-linked HexA compared with D0. Furthermore, in comparison, the AOX content could be reduced by 50% with DHT. The fully bleached pulp obtained via DHTEpD process has a higher brightness than that obtained by D0EpD, which provides a reliable theoretical basis for industrial application.

Superhydrophobic surfaces generated by one-pot spray-coating of chitosan-based nanoparticles

Superhydrophobic surfaces have attracted great attention due to their attractive properties. Biopolymer-based low-cost and environmentally-friendly superhydrophobic coatings with easy-to-perform fabrication methods are always desirable. Herein, we report superhydrophobic surfaces using a one-step spray-coating of chitosan-based nanoparticles. The particles were easily prepared by a nanoprecipitation strategy using synthesized organosoluble chitosan stearoyl ester (CSSE). The resulting particles had an average size of 165 ∼ 235 nm depending on the applied concentration. Subsequently, spray-coating of such particles onto silicon wafer generated a surface with a water contact angle of 155 ± 1°. SEM and AFM images exhibited a nano/microscaled roughness appeared on the coated surface. The superhydrophobic surfaces showed a stable superhydrophobic performance even after storage for 15 days, pH stability between pH 1 to pH 11 and thermal stability until a temperature no more than 50 °C. These properties would broaden the application fields of superhydrophobic surfaces as well as the chitosan itself.