Research Articles

In this study the effect of different levels of dissolved oxygen tension (d.o.t) on the production of three main components of extracellular cellulases (FPase, CMCase and β-glucosidase) at a fixed agitation speed by Aspergillus terreus was investigated. Growth of A. terreus and cellulase production were modeled based on logistic and Luedeking-Piret equations. The results from the model fit well with the experimental data, confirming that the models were appropriate for describing and representing growth and cellulase production at various d.o.t levels. The models showed that the production of FPase and CMCase were growth-associated processes. Cell growth and cellulase production were approximately two-fold higher in a stirred tank bioreactor compared with a shake-flask culture. At a d.o.t of 55% air saturation, cell growth and cellulase production were higher than at low d.o.t (40% air saturation) or high d.o.t (80% air saturation). The highest activities of FPase (2.33 U ml-1), CMCase (51.10 U ml-1), and β-glucosidase (16.18 U ml-1) were obtained at a d.o.t of 55% air saturation, yielding overall productivities of 19.40, 425.00, and 67.40 U l.h-1, respectively.

This study evaluates the use of steam explosion (SE) as a pre-treatment of Eucalyptus globulus chips, aimed at making this wood suitable as feedstock in biorefineries or alternative processes such as biopulping. Several SE treatments were applied, modifying the following variables: previous hydration of the chips, number of SE cycles, and duration of the first cycle. Chemical composition and structural properties were analyzed after all treatments. Our results show that acetone and hot water extractives contents increased between 1.0% and 6.2% and between 3.6% and 7.1%, respectively, depending on SE operational conditions. Holocellulose content was also observed to decrease (9.4 to 15.6%), while the Klason lignin underwent a slight solubilization. Furthermore, greater water retention capacity and new bigger sized pores were found in the exploded samples. It is reasonable to expect that these changes would facilitate the subsequent implementation of chemical or biological treatments of the cellulose fraction in the biorefinery design.

In previous studies we found significant differences in the suberin content with respect to the bark layer of Quercus suber samples. In this study the monomer composition of suberin from the two bark layers (i.e., back and cork) of three provenances (Extremadura, Castile-la Mancha, and Portugal) was investigated using pyrolysis in the presence of tetramethylammonium hydroxide (TMAH) with gas chromatography-mass spectrometry (GC/MS). The major compounds released were octadec-9-enedioic acid, docosanedioic acid, and 9,10-epoxyocta-decanedioic acid with mean values of 17%, 14.5%, and 11%, respectively. The former is more abundant in back than in cork, and the latter in cork than in back with mean differences, in terms of percentages, between the back and cork of 4.3 ± 0.81 and 2.2 ± 0.52, respectively.

A novel class of hydrogel was prepared by graft copolymerization of acetic acid lignin (AAL) and N-isopropylacrylamide (NIPAAm) in the presence of N,N'-Methylenebisacrylamide (MBAAm) as the crosslinker and H2O2 as the initiator. The impact of AAL content on the hydrogel properties were investigated in terms of their swelling behavior, thermal behavior, and interior morphology. The data showed that these newly synthesized hydrogels were temperature-sensitive. Differential scanning calorimetry (DSC) curves demonstrated that the lower critical solution temperature (LCST) of the lignin-based hydrogels was approximately 31°C. The thermogravimetric analysis (TGA) data revealed that the temperature of rapid decomposition of all the hydrogel samples was within a narrow range of 400 to 410°C. Furthermore, the scanning electron microscopy (SEM) images showed that the pore size of the hydrogel increased with increasing the AAL content.

Norway spruce specimens 50x30x30mm with initially determined ultrasonic characteristics in the longitudinal, radial, and tangential directions were subjected to bio-attacks with the brown-rot fungi Serpula lacrymans, Coniophora puteana,or Gloeophyllum trabeum, and the white-rot fungus Trametes versicolor, respectively. Bio-attacks lasted 4, 8, 12, or 16 weeks. Decreases of the ultrasonic wave velocities (Dc) and the dynamic modulus of elasticity (DMOEd) depended more or less closely on the enlarged degrees of rot in the spruce wood, and as the dynamic modulus of elasticity decreased approx. 1.7 to 2.3 times more than corresponding weights (Dm from 2.01 to 42.35%) or 2.1-3.4 times more than corresponding densities (Dr from 2.42 to 26.63%). Two sample t-test analyses of slopes “a” in the linear regressions Dc or DMOEd = a.(Dm) or a.(Dr) showed that drops of the ultrasonic and elastic characteristics of wood having the brown rot were not influenced by the fungus species. On the other hand, the velocity of ultrasonic waves in the longitudinal direction and the dynamic modulus of elasticity appeared to be suitable for distinguishing the brown rot from the white rot at known decreases of wood density. The anatomical direction of wood was a significant factor only for the white rot, when approx. 2-times higher decrease of the ultrasonic wave velocities was determined in the radial and tangential directions compared to the longitudinal one.

The chemical composition of Astragalus armatus contains quite a high amount of extractives in organic solvents (close to 13%), but a low percentage of lignin (around 17%) and an acceptable content of holocellulose (54%). The α-cellulose content is around 35%, and the ash content is around 3%. Using the insight of such data, the soda-anthraquinone cooking of Astragalus armatus produced lignocellulosic fibres. Different cooking temperatures (100, 120, 140, and 160°C) were tested and the delignification duration was 2 h. A yield of about 30% w/w was obtained, and the obtained pulps had a kappa number of 25. Finally, the isolated fibres were used to produce paper samples with a basis weight of 60 g/m2. The structural and mechanical properties of the prepared samples were close to those of other common annual plant-based fibre mats.

When increasing the wood fiber (WF) content in extruded wood fiber/plastic composites (WPC) foams, a good balance between reducing the cost and obtaining good cell morphology should be maintained. This study examines the relationship between WF content and the foam morphology in WPC foams. The role of WF as cell nucleating agent at low concentrations (10 wt.%) was observed, as WPC foam with 10 wt.% WF had lower average cell size and higher cell density than neat HDPE foams. Increasing the WF content further, decreased the average cell size and cell density, and increased the foam density of WPC foams. These results were linked to the rheological properties and crystallization behavior of HDPE and WPC with different WF content.

This article describes a facile method for the preparation of cellulosic catalyst paper: the in situ synthesis of gold nanoparticles (AuNPs) on zinc oxide (ZnO) whiskers, the preferential support for AuNPs, preloaded into a paper matrix. The ZnO paper composites were fabricated using a high-speed and low-cost paper-making technique, and immersed in an aqueous solution of HAuCl4. After drying, fine 5 nm AuNPs were successfully formed on the ZnO whiskers inside the paper matrix. As-prepared AuNPs@ZnO whisker-containing paper (AuNPs@ZnO paper) is similar to ordinary paper products, being flexible, lightweight, and easy to handle. The AuNPs@ZnO paper exhibited a high catalytic efficiency towards the reduction of 4-nitrophenol to 4-aminophenol in aqueous media. Furthermore, the addition of a polyamideamine epichlorohydrin resin provided a wet strength to the AuNPs@ZnO paper, which enables several catalyst recycles with no significant losses in catalytic activity.

Paper sludge and extraction liquor from water prehydrolysis of Eucalyptus chips before pulping are potential raw materials for ethanol production in an integrated forest biorefinery concept. Ethanol production from paper sludge, extraction liquor from water prehydrolysis of Eucalyptus chips, and a mixture of both using separate hydrolysis and fermentation were investigated. The hydrolysate composed of 51.01±0.72 g/L glucose, 30.11±0.09 g/L xylose, and 13.65±0.94 g/L cellobiose, which was obtained by enzymatic saccharification of the mixture at an initial consistency of 6% (w/v, expressed in terms of total carbohydrate mass), was used for ethanol production by yeast SHY07-1 without prior detoxification and nutrient supplementation. A final ethanol concentration of 36.82±0.35 g/L was achieved, corresponding to an ethanol yield of 0.45±0.04 g/g with a fermentation efficiency of 80.71±0.03% and an ethanol productivity of 0.31±0.01 g/(L h). This confirmed the feasibility of co-fermentation of these two materials for bioconversion to ethanol.