Volume 14 Issue 4

As a purified form of cellulosic fiber, dissolving pulp is an important starting material for many value-added cellulose products. Dissolving pulp is mainly produced by either the pre-hydrolysis kraft (PHK) process or the acid sulfite (AS) process. The dissolving pulp market has been booming in many developing countries in recent years. As one of the biggest producers of dissolving pulp in the world, China is also importing a large amount of dissolving pulp from other countries. It is expected that the production capacity of dissolving pulp in China will increase significantly in the near future.

Chitosan has a molecular structure very similar to that of cellulose, except that one of the –OH groups on each repeating unit (at the C2 position) is replaced by an amine group. Since chitosan has abundant water-loving groups and is soluble in weakly acidic aqueous solution, one might expect films prepared from casting of chitosan solutions to be hydrophilic. Experiments have shown wide variability, often indicating a hydrophobic character of the chitosan films. A 2008 article by Cunha et al. presented evidence suggesting that the apparent hydrophobicity was attributable to impurities. However, not all the evidence was consistent. In particular, extraction of chitosan film with methanol failed to increase the polar component of surface free energy. It is proposed in this editorial that the explanation can be found in a differing water-affinity of chitosan polymer segments, depending on their orientation. This explanation, if valid, is consistent with differences in the hydrophilic or hydrophilic character of different crystalline faces of cellulose.

Although wrinkling is not appreciated in some of its manifestations, there are other instances for which it is essential to study and comprehend various physical phenomena related to wrinkling. Cellulose nanocrystals (CNCs) have some excellent intrinsic properties, i.e., high aspect ratio, percolation function, and good mechanical strength that have potential to affect wrinkling. Since the production period of bacterial cellulose is longer, it is efficient to use CNC as a substitute for bacterial cellulose in such applications. The network structure of bacterial cellulose can be mimicked by CNC fabric, which comprises several wrinkled CNC layers.

The effects of ethanol or acetone addition (2.5% to 40% w/w) and high ionic strength (50 mM to 1000 mM NaCl) on the rheology of carboxymethylated (NFC-carb) and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized (NFC-TEMPO) nanofibrillated cellulose (NFC) suspensions were studied. Morphological characterization and centrifugation showed that NFC-TEMPO had a much finer overall morphology than NFC-carb. Rheological measurements were taken at 1.3 wt% using a stress-controlled rheometer equipped with cone and plate measurement tools with rough surfaces. The dynamic moduli were investigated through oscillatory stress sweeps. The results showed that as little as 2.5% (w/w) of either ethanol or acetone decreased the viscosity and the dynamic moduli, while 40% (w/w) increased the viscosity to values higher than those of the aqueous suspensions, doubled the storage modulus, and extended the gel-like behavior. Increasing the NaCl concentration from 50 mM to 100 mM drastically increased viscosity; moreover, the storage modulus in the elastic region linearly increased with increasing NaCl concentrations in the range of 100 mM to 1000 mM, suggesting the increased content of interparticle bonds with NaCl addition. The elastic domain was also extended from 10 Pa to 50 Pa and above 500 Pa with acetone addition (40%) and NaCl addition, respectively.

Effects of moisture content (MC) were investigated for the mechanical properties of oak wood (Quercus petraea Liebl.) using micro-size test specimens. The micro-size specimens for bending, tensile, and compression tests were prepared and divided into five groups. Each group was conditioned at a different relative humidity and temperature to achieve MC values of 8%, 12%, 16%, 20%, and above-fiber-saturation-point MCs. After conditioning, the bending strength, modulus of elasticity (MOE) in bending, tensile strength, and compression strength values were determined. The results showed that MC had statistically significant effects on all the measured mechanical properties in the micro-size oak wood samples. The greatest decrease was observed for the compression strength, while the lowest decrease was observed for the tensile strength, when MC increased. The changing rates induced by 1% MC were calculated as 3% for bending strength, 2.5% for the MOE, 2.0% for the tensile strength, and 3.1% for the compression strength.

Lipases are enzymes commonly used in industry. This study describes the production of lipolytic enzyme via a newly isolated strain of Aspergillus oryzae under a submerged fermentation process. Five strains of A. oryzae were isolated from oil-contaminated soil and water as well as dead decaying organic matter. Qualitative screening revealed that A. oryzae RBM4 strain was a lipase producer, and the process was optimized for enhanced production. Incubation time, incubation temperature, initial pH, use of agricultural by-products, nitrogen sources, and substrates were tested. The results revealed that initial pH 5.5(12.7 U/mL/min) in 72 h (19.39 U/mL/min) at 30 °C (27.40 U/mL/min) sorghum (35.66 U/mL/min), NaNO3 (17% more than blank), yeast extract (47.95 U/mL/min), and Shan ghee (58.12 U/mL/min) were the best conditions. Extracellular lipase production was increased up to 78% by applying all the above conditions.

There is controversy concerning the presence of xyloglucans in gelatinous (G) layers of Populus spp. tension wood, particularly in mature G-fibers. Transmission electron microscopy (TEM) immunogold localization combined with LM15 antibody (recognizes XXXG-motif of xyloglucans, heptasaccharide) was used to investigate the distribution of xyloglucan epitopes in both transverse and radial sections of P. tremula tension wood. Results provided clear evidence for the presence of xyloglucans in both mature and developing G-layers. Developmental decrease of LM15 epitope localization in G-layers was also detected during G-fiber maturation. High magnification TEM observations showed specific localization of LM15 epitopes on newly synthesized cellulose macrofibrils present in the innermost layer of developing G-layers adjacent to the cell lumen, suggesting linkage between xyloglucans and cellulose macrofibrils. Possible mechanisms were discussed for developmental changes of xyloglucan with respect to the different results reported in the literature.

The application of chitosan biopolymer with and without nanoparticles in the papermaking process was investigated. The effect of the chitosan’s molecular weight on its interaction with silica nanoparticles in recycled old corrugated container pulp was studied. Initially, the nanosilica particles were analyzed via atomic force microscopy and scanning electron microscopy, which confirmed the spherical shape of the silica nanoparticles with diameter less than 5 nm. Dynamic light scattering method was used to determine the zeta potential and the hydrodynamic radius of the chitosan with different molecular weights. Infrared spectroscopy was used to show the possibility of hydrogen bonding between the chitosan and the nanosilica. The results showed that the chitosan with low and medium molecular weights in alkaline and in some neutral suspensions had better process performances. Increasing the molecular weights of the chitosan improved the mechanical properties. The influence of chitosan on the process parameters was dependent on different factors such as its configuration in the aqueous media before and after adsorption, its ability to penetrate the fiber pores, and its charge density. In contrast, the effect of chitosan on the strength of paper was influenced by its performance following adsorption and retention within the fibrous mat.

Thermogravimetric combustion characteristics of ginkgo leaves (GK), pine needles (PN), corn straw (CS), aspen leaves (AS), and white poplar leaves (WP) were studied. Results showed that the combustion of selected samples consisted of at least two weight loss stages. Besides, characteristic temperatures lagged towards high temperature zones under high heating rate, which was considered as the effect of insufficient transfer of heat. The combustion of volatile compounds and char from PN and CS was isolated under high heating rate and consequently the exothermic rate around 300 °C was intensified and the exothermic rate over 400 °C was decreased, while the maximum heat release rates of GK, AS, and WP were transferred into high temperature zones with the increasing of heating rate. The average activation energy of PN and CS was high though their combustion completed at a lower temperature, which was possibly due to the low average energy of molecules in samples in low temperature environment. The aromaticity, degree of condensation, CH2/CH3, and structure parameters of oxygen-containing functional groups were calculated according to the peak areas derived from the convolution of FTIR spectra. These parameters explained the discrepancy in both reactivity and exothermic behaviors of biomass samples during combustion.

The strength performance of edge connections between the cross-laminated timber (CLT) panels, as currently applied to CLT construction, was compared to that of connections reinforced with glass fiber-reinforced plastic (GFRP) by means of a tensile-type shearing test. In this study, the reinforced half-lapped connection is intended to prevent CLT from coming apart due to failure of self-tapping screws (STS) by bonding GFRP sheets to connections between CLT panels. The end-distance and edge-distance of this reinforced half-lapped connection were designed to equal 5D (where D is the fastener diameter) and 4D, respectively, which is shorter than the 6D recommended by European Technical Approval (ETA). Nevertheless, the yield strength was increased by 7%, and the stiffness by 92%, compared to the non-reinforced half-lapped connection. In addition, the internal spline connections using GFRP-reinforced plywood were 57 and 36% higher than the connection made up of LVB or plywood, respectively, and the energy dissipation percentages were 400 and 76%, respectively. These results indicate that the reinforcement effect of the connection by the GFRP was very significant. On the other hand, the half-lapped connection of the larch CLT improved the strength performance as the end-distance increased, and the end-distance had a greater effect on the strength performance than the edge-distance.