Dingguo Zhou

Preparation and Properties of Electrospun Poly (Vinyl Pyrrolidone)/Cellulose Nanocrystal/Silver Nanoparticle Composite Fibers

Poly (vinyl pyrrolidone) (PVP)/cellulose nanocrystal (CNC)/silver nanoparticle composite fibers were prepared via electrospinning using N,N′-dimethylformamide (DMF) as a solvent. Rheology, morphology, thermal properties, mechanical properties, and antimicrobial activity of nanocomposites were characterized as a function of material composition. The PVP/CNC/Ag electrospun suspensions exhibited higher conductivity and better rheological properties compared with those of the pure PVP solution. The average diameter of the PVP electrospun fibers decreased with the increase in the amount of CNCs and Ag nanoparticles. Thermal stability of electrospun composite fibers was decreased with the addition of CNCs. The CNCs help increase the composite tensile strength, while the elongation at break decreased. The composite fibers included Ag nanoparticles showed improved antimicrobial activity against both the Gram-negative bacterium Escherichia coli (E. coli) and the Gram-positive bacterium Staphylococcus aureus (S. aureus). The enhanced strength and antimicrobial performances of PVP/CNC/Ag electrospun composite fibers make the mat material an attractive candidate for application in the biomedical field.

Microporous activated carbon from pinewood and wheat straw by microwave-assisted KOH treatment for the adsorption of toluene and acetone vapors

Pinewood and wheat straw activated carbons were prepared by KOH and microwave heating, and their adsorption properties were determined. The pinewood and wheat straw activated carbons achieved total pore volumes of 0.93 and 0.60 cm3 g−1, surface areas of 2044 and 1250 m2 g−1, as well as a high contribution of micropores of 75% and 76%, respectively, at a KOH/char ratio of 3.0, in less than 30 min at 600 W and in the presence of humidity. The adsorption properties of the activated carbons were quantified using toluene and acetone adsorption at 200 ppm and adsorption isotherms. Equilibrium isotherm data were fitted using the Dubinin–Radushkevich model.

Effects of thermomechanical refining conditions on the morphology and thermal properties of wheat straw fibre

Abstract Wheat straw fibre is prepared by a thermomechanical (TM) refining system. This study investigated the effects of refining steam pressure (4, 6, 8 and 10 bar) and refiner speed (2500 and 3000 rpm) on the morphology and thermal properties of the resulting fibres. After TM refining, the fibres exhibited more surface irregularities and heterogeneities as well as decreased fibre length. The fine content decreased with increasing steam pressure, but the aspect ratio increased. The findings show that higher steam pressure (8 bar) results in more effective wheat straw refining. Refining lowers the pH. Thermogravimetric analysis showed that TM refining does not influence the thermal properties of wheat straw fibres. Weight loss has to be taken into account upon exposure to temperatures around 170°C. The silica content of the fibres was significantly reduced through refining.

Effect of conditioning history on the characterization of hardness of thermo-mechanical densified and heat treated poplar wood

Abstract Poplar wood was modified by a combination of thermo-mechanical densification (TMD) and heat treatment (HT) process at five temperatures ranging from 170 to 210°C. A new two-step conditioning method (CM) is suggested, in the course of which the modified wood is submitted to 50°C/99% RH→25°C/65% RH, where RH means relative humidity in the climate chamber. The traditional one-step CM (25°C/65% RH) served as reference. The effects of conditioning history on hardness were observed and analyzed along with the change of dimensional stability. The hardness of the modified wood was lower in the case of the proposed CM due to more set-recovery release, but the extent of that decreased with the HT temperature. For a good hardness, HT200°C should be selected with the proposed CM, which is different from the optimization output of 180°C obtained from the traditional CM. In conclusion, a specific assessment method for the performance characterization of this type of modified wood would be beneficial for the combined TMD and HT processes.

Creep behavior of borate-treated strandboard: Effect of zinc borate retention, wood species, and load level

Creep performance of zinc borate-treated strandboard from southern pine (Pinus taeda L.) and red oak (Quercus falcata) was investigated at 25°C temperature and 65% relative humidity. It was shown that the borate treatment had some signifi cant effect on creep defl ection of the test panels, and the effect varied with wood species. There was no signifi cant effect of creep loading on residual bending properties of treated strandboard under the stress levels used. The four element spring-dashpot creep model fi tted the creep data well. The predicted creep defl ection for a 10-year loading duration under both 15% and 40% stress levels met the National Design Specifi cation for Wood Construction despite of the noticeable borate treatment effect on creep. Future work is needed to study the creep behavior under combined mechanical and moisture loadings for treated structural panels.

Cellulose Nanocrystals (CNCs) from Corn Stalk: Activation Energy Analysis

Cellulose nanocrystals (CNCs) were isolated from corn stalk using sulfuric acid hydrolysis, and their morphology, chemical structure, and thermal stability properties were characterized. The CNCs had an average length of 120.2 ± 61.3 nm and diameter of 6.4 ± 3.1 nm (L/D = 18.7). The degree of crystallinity of the CNCs increased to 69.20% from the 33.20% crystallinity of raw corn stalk fiber, while the chemical structure was well kept after sulfuric acid hydrolysis. Thermal stability analysis showed that the degradation temperature of the CNCs reached 239.5 °C, which was higher than that of the raw fiber but lower than that of the extracted cellulose. The average activation energy values for the CNCs, evaluated using the Friedman, Flynn-Wall-Ozawa (F-W-O) and Coats-Redfern methods, were 312.6, 302.8, and 309 kJ·mol−1 in the conversion range of 0.1 to 0.8. The isolated CNCs had higher values of activation energy than did the purified cellulose, which was attributed to the stronger hydrogen bonds present in the crystalline domains of CNCs than in those of cellulose. These findings can help better understand the thermal properties of polymer/CNC composites.