Qingwen Wang

Comparative properties of cellulose nano-crystals from native and mercerized cotton fibers

Stable aqueous suspensions of cellulose nano-crystals (CNCs) were fabricated from both native and mercerized cotton fibers by sulfuric acid hydrolysis, followed by high-pressure homogenization. Fourier transform infrared spectrometry and wide-angle X-ray diffraction data showed that the fibers had been transformed from cellulose I (native) to cellulose II (mercerized) crystal structure, and these polymorphs were retained in the nanocrystals, giving CNC-I and CNC-II. Transmission electron microscopy showed rod-like crystal morphology for both types of crystals under the given processing conditions with CNC-II having similar width but reduced length. Freeze-dried agglomerates of CNC-II had a much higher bulk density than that of CNC-I. Thermo-gravimetric analysis showed that CNC-II had better thermal stability. The storage moduli of CNC-II suspensions at all temperatures were substantially larger than those of CNC-I suspensions at the same concentration level. CNC-II suspensions and gels were more stable in response to temperature increases. Films of CNC and Poly(ethylene oxide) were tested. Both CNC-I/PEO and CNC-II/PEO composites showed increased tensile strength and elongation at break compared to pure PEO. However, composites with CNC-II had higher strength and elongation than composites with CNC-I.

Chemical mechanism of fire retardance of boric acid on wood

It is commonly accepted that the fire retardant mechanism of boric acid is a physical mechanism achieved by the formation of a coating or protective layer on the wood surface at high temperature. Although a char-forming catalytic mechanism has been proposed by some researchers, little direct experimental support has been provided for such a chemical mechanism. In this paper, new experimental results using thermal analysis, cone calorimetry (CONE), and gas chromatography–Fourier transform infrared spectroscopy (GC–FTIR) analysis are presented and the fire retardant mechanism of boric acid on wood is discussed. Basswood was treated with boric acid, guanylurea phosphate (GUP), and GUP–boric acid. Treated wood was then analyzed by thermogravimetry (TG/DTG), differential thermal analysis (DTA), CONE, and GC–FTIR analysis. Thermogravimetry showed that the weight loss of basswood treated with boric acid was about three times that of untreated or GUP-treated wood at 165°C, a temperature at which GUP is stable. The DTA curve showed that boric acid treated basswood has an exothermal peak at 420°C, indicating the exothermal polymerization reaction of charring. CONE results showed that boric acid and GUP had a considerable synergistic fire retardant effect on wood. The GC–FTIR spectra indicated that compounds generated by boric acid treated wood are different than those generated by untreated wood. We conclude that boric acid catalyzes the dehydration and other oxygen-eliminating reactions of wood at a relatively low temperature (approximately 100–300°C) and may catalyze the isomerization of the newly formed polymeric materials by forming aromatic structures. This contributes partly to the effects of boric acid on promoting the charring and fire retardation of wood. The mechanism of the strong fire retardant synergism between boric acid and GUP is due to the different fire retardant mechanisms of boric acid and GUP and the different activation temperatures of these two chemicals.

Recent progress of catalytic pyrolysis of biomass by HZSM-5

Biomass can be converted into a variety of fuels and chemicals using different technologies. One such process is fast pyrolysis, which is convenient for the conversion of biomass primarily into liquid products known as bio-oils. These bio-oils, however, must be upgraded if they are to be used as a replacement for diesel and gasoline fuels. At present, when improving the quality of bio-oils, catalytic vapor cracking is generally considered superior to other catalytic upgrading technologies, such as hydrotreating and esterification. This review summarizes the current status of research concerning both the catalytic pyrolysis of biomass and the catalytic cracking of bio-oil using the zeolite HZSM-5, focusing on the specific catalysts employed, as well as the upgrading methods and reaction mechanisms.

Effect of Experimental Parameters on Morphological, Mechanical and Hydrophobic Properties of Electrospun Polystyrene Fibers

Polystyrene (PS) dissolved in a mixture of N, N-dimethylformamide (DMF) and/or tetrahydrofuran (THF) was electrospun to prepare fibers with sub-micron diameters. The effects of electrospinning parameters, including solvent combinations, polymer concentrations, applied voltage on fiber morphology, as well as tensile and hydrophobic properties of the fiber mats were investigated. Scanning electron microscope (SEM) images of electrospun fibers (23% w/v PS solution with applied voltage of 15 kV) showed that a new type of fiber with double-strand morphology was formed when the mass ratio of DMF and THF was 50/50 and 25/75. The tensile strength of the PS fiber film was 1.5 MPa, indicating strong reinforcement from double-strand fibers. Bead-free fibers were obtained by electrospinning 40% (w/v) PS/DMF solution at an applied voltage of 15 kV. Notably, when the ratio of DMF and THF was 100/0, the maximum contact angle (CA) value of the electrospun PS films produced at 15 kV was 148°.

Effects of chemical modification on the mechanical properties of wood

Chemical modification has been recognized as an efficient strategy for dimensionally stabilizing wood and protecting it from environmental damage, such as deterioration due to weathering and fungal decay during the service period. Studies reported in the literature mainly concern the establishment of workable modification techniques, testing methodologies, and assessment of the durability of modified wood. The development of wood modification techniques has recently been reviewed; limited information is however given on the effects of chemical modification on the mechanical properties of wood that are of importance to it as an engineering material. This paper reviews the effects of wood modification, typically by heat treatments and impregnation with low molecular weight resins, reactive monomers, or hot melting paraffins on the mechanical properties of wood. The modifying variables associated with mechanical properties of wood such as wood species, treating temperature and time, catalyst, type of solvent, weight percent gain, and molecular structures of the modifying agent were analysed and the results interpreted. The reasons for changes in the mechanical properties of wood are discussed.ZusammenfassungChemische Modifikation wird als ein wirksames Verfahren zur Verbesserung der Dimensionsstabilität und zum Schutz gegen umweltbedingte Schäden wie zum Beispiel Holzabbau aufgrund von Bewitterung oder Pilzbefall während der Gebrauchsdauer angesehen. In der Literatur vorhandene Studien befassen sich hauptsächlich mit geeigneten Behandlungsverfahren, Prüfmethoden und der Beurteilung der Dauerhaftigkeit von modifiziertem Holz. Die Entwicklung von Holzbehandlungsmethoden wurde kürzlich beschrieben, jedoch gibt es nur wenig Informationen hinsichtlich der Einflüsse einer chemischen Modifikation auf die mechanischen Eigenschaften von Holz im Hinblick auf seine Nutzung als Bau- und Werkstoff. In diesem Artikel werden die Einflüsse einer chemischen Modifikation, üblicherweise durch Hitzebehandlung oder Imprägnierung mit niedermolekularem Harz, reaktiven Monomeren oder heiß schmelzenden Paraffinen, auf die mechanischen Eigenschaften von Holz untersucht. Einflussgrößen auf die mechanischen Eigenschaften von Holz wie Holzart, Behandlungstemperatur und –dauer, Katalysator, Art des Lösungsmittels, prozentuale Gewichtszunahme und molekulare Struktur des Modifiziermittels wurden untersucht und die Ergebnisse diskutiert. Gründe für die Änderungen der mechanischen Eigenschaften wurden erörtert.

Thermal and burning properties of wood flour- poly(vinyl chloride) composite

The present study deals with the effects of wood flour on thermal and burning properties of wood flour-poly(vinyl chloride) composites (WF-PVC) using thermogravimetric (TG), cone calorimetry (CONE), and pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS). TG tests show that an interaction occurred between wood flour and PVC during the thermal degradation of WF-PVC. Wood flour decreased the temperature of onset of decomposition of PVC. However, the char formation could be increased by adding wood flour to PVC. CONE test indicates that wood flour had positive effects on heat release and smoke emission of PVC. Comparing with PVC, WF-PVC reduced average heat release rate and the peak HRR by about 14 and 28%, respectively; smoke production rate was also decreased. The degradation mechanism was studied by Py–GC/MS. The results show that the volatile pyrolysis products of WF-PVC are very different from PVC. The yields of HCl and aromatic compounds decreased dramatically, and the aliphatic compounds increased by the incorporation of WF.

Facile extraction of cellulose nanocrystals from wood using ethanol and peroxide solvothermal pretreatment followed by ultrasonic nanofibrillation

Cellulose nanocrystals (CNCs) were successfully extracted from wood flour by a two-step process that comprised ethanol and peroxide solvothermal pretreatment and an ultrasonic disintegration process. Characterization results showed that 97% of the total lignin and 70% of the hemicellulose could be fractionated in a single ethanosolv pretreatment step. Additional treatment with alkaline hydrogen peroxide removed the residual lignin and hemicellulose and resulted in high purity cellulose. The CNCs obtained after ultrasonication displayed a similar yield, size, morphology, and crystallinity but had better thermal stability and film forming properties than those produced by concentrated acid hydrolysis. Overall, the solvothermal treatment using ethanol and its combination with peroxide is an ideal substitute method for pretreatment of lignocellulose. Further integration of such pretreatments with ultrasonication provides a promising efficient process with low environmental impact for production of CNCs.

Highly Flexible and Conductive Cellulose-Mediated PEDOT:PSS/MWCNT Composite Films for Supercapacitor Electrodes

Recent improvements in flexible electronics have increased the need to develop flexible and lightweight power sources. However, current flexible electrodes are limited by low capacitance, poor mechanical properties, and lack of cycling stability. In this article, we describe an ionic liquid-processed supramolecular assembly of cellulose and 3,4-ethylenedioxythiophene for the formation of a flexible and conductive cellulose/poly(3,4-ethylenedioxythiophene) PEDOT:poly(styrene sulfonate) (PSS) composite matrix. On this base, multiwalled carbon nanotubes (MWCNTs) were incorporated into the matrix to fabricate an MWCNT-reinforced cellulose/PEDOT:PSS film (MCPP), which exhibited favorable flexibility and conductivity. The MCPP-based electrode displayed comprehensively excellent electrochemical properties, such as a low resistance of 0.45 Ω, a high specific capacitance of 485 F g-1 at 1 A g-1, and good cycling stability, with a capacity retention of 95% after 2000 cycles at 2 A g-1. An MCPP-based symmetric solid-state supercapacitor with Ni foam as the current collector and PVA/KOH gel as the electrolyte exhibited a specific capacitance of 380 F g-1 at 0.25 A g-1 and achieved a maximum energy density of 13.2 Wh kg-1 (0.25 A g-1) with a power density of 0.126 kW kg-1 or an energy density of 4.86 Wh kg-1 at 10 A g-1, corresponding to a high power density of 4.99 kW kg-1. Another kind of MCPP-based solid-state supercapacitor without the Ni foam showed excellent flexibility and a high volumetric capacitance of 50.4 F cm-3 at 0.05 A cm-3. Both the electrodes and the supercapacitors were environmentally stable and could be operated under remarkable deformation or high temperature without damage to their structural integrity or a significant decrease in capacitive performance. Overall, this work provides a strategy for the fabrication of flexible and conductive energy-storage films with ionic liquid-processed cellulose as a medium.

Rheological and mechanical properties of wood fiber-PP/PE blend composites

For evaluation of the rheological and mechanical properties of highly filled wood plastic composites (WPCs), polypropylene/polyethylene (PP/PE) blends were grafted with maleic anhydride (MAH) to enhance the interfacial adhesion between wood fiber and matrix. WPCs were prepared from wood fiber up to 60 wt.% and modified PP/PE was blended by extrusion. The rheological properties were studied by using dynamic measurement. According to the strain sweep test, the linear viscoelastic region of composites in the melt was determined. The result showed that the storage modulus was independent of the strain at low strain region (<0.1%). The frequency sweep results indicated that all composites exhibited shear thinning behavior, and both the storage modulus and complex viscosity of MAH modified composites were decreased comparing to those unmodified. Flexural properties and impact strength of the prepared WPCs were measured according to the relevant standard specifications. The flexural and impact strength of the manufactured composites significantly increased and reached a maximum when MAH dosage was 1.0 wt.%, whereas the flexural modulus after an initial decreased, also increased with MAH dosage. The increase in mechanical properties indicated that the presence of anhydride groups enhanced the interfacial adhesion between wood fiber and PP/PE blends.

Efficient Flame-Retardant and Smoke-Suppression Properties of Mg–Al-Layered Double-Hydroxide Nanostructures on Wood Substrate

Improving the flame retardancy of wood is an imperative yet highly challenging step in the application of wood in densely populated spaces. In this study, Mg-Al-layered double-hydroxide (LDH) coating was successfully fabricated on a wood substrate to confer flame-retardant and smoke-suppression properties. The chemical compositions and bonding states characterized by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy confirmed the coating constituents of Mg-Al LDH. The coating evenly covered the sample wood surfaces and provided both mechanical enhancement and flame-retardancy effects. The limiting oxygen index of the Mg-Al LDH-coated wood increased to 39.1% from 18.9% in the untreated wood. CONE calorimetry testing revealed a 58% reduction in total smoke production and a 41% reduction in maximum smoke production ratio in the Mg-Al LDH-coated wood compared to the untreated wood; the peak heat release rate and total heat release were also reduced by 49% and 40%, respectively. The Mg-Al LDH coating is essentially hydrophilic, but simple surface modification by fluoroalkyl silane could make it superhydrophobic, with a water contact angle of 152° and a sliding angle of 8.6°. The results of this study altogether suggest that Mg-Al LDH coating is a feasible and highly effective approach to nanoconstructing wood materials with favorable flame-retardant and smoke-suppression properties.