Research Articles

The cel12B gene was cloned, optimized through directed evolution using error-prone polymerase chain reaction, and then expressed in the Escherichia coli BL21 (DE3) host strain. Five mutants promoting the enzyme activities were selected. The specific activity of the best-evolved Cel16 (L20R, D37V, I108T) was improved approximately 3-fold compared to the parental enzyme. The residual enzyme activity of Cel16 retained 90% of the original when incubated at 90 °C for 2 h, which was similar to the thermostability of the wild type. In addition, the best mutant Cel16, which had two prominent mutant sites, L20R and I108T, was able to increase the cavity polarity because the side chains of arginine and threonine could form hydrogen bonds with the substrate, shrinking the enzyme cavity to some extent and therefore enhancing the enzyme activity.

This study evaluates the impact of the number of cycles of the V313 test (EN 321 2002) on the mechanical properties of 15-mm-thick OSB/3 and OSB/4. The obtained results were compared with the properties of the boards exposed to external environmental conditions. The results of the study indicate that the tested boards were characterized with a 50% decrease in static bending strength and a 70% decrease in tensile strength perpendicular to the plane. However, both types of boards met the requirements of the standard (EN 300 2006) with respect to their modulus of rupture. The method of exposing boards to outdoor conditions has a substantial influence on the change of the physico-mechanical properties of OSBs. In the boards used in this study, however, those changes occurred slower than those evoked by the V313 test, especially after an upright exposure. For these reasons, for that type of board storage, an equation was determined that can bring the property changes following the V313 test into an acceptable range to allow for the evaluation of the board properties. In the case of vertical exposure, from the second year forward, changes in the properties of the OSB/3 were similar to those presented by the boards demonstrated from the second cycle of the V313 test.

Pulp fibers have a strong tendency to form flocs in water suspensions, which may cause their undesirable distribution in the paper sheets. This flocculation can be controlled by adding, e.g., an anionic high molecular weight polyelectrolyte in the fiber suspension. The objective of this study was to investigate the effect of anionic polyelectrolytes on deflocculation kinetics, dewatering, and rheology of cellulosic suspensions. The results showed that both microfibrillated cellulose (MFC) and macroscopic pulp fibers can be dispersed using anionic polyacrylamides (APAM). The higher the molecular weight of APAM, the higher is its effect. Adsorption experiments illustrate that anionic polyelectrolytes do not strongly attach to cellulose surfaces but they can be partly entrapped or can disperse nanocellulose fibrils (increase the swelling). Based on rheological experiments, the MFC network became weaker with APAM addition. Similar to the flocculation mechanism of cellulosic materials with polymers, deflocculation is also time dependent. Deflocculation occurs very rapidly, and the maximum deflocculation level is achieved within a few seconds. When mixing is continued, the floc size starts to increase again. Also dewatering was found to be strongly dependent on the contact time with the APAMs. These results indicate that the positive effects of anionic deflocculants are quickly diminished due to shear forces, and therefore, the best deflocculating effect is achieved using as short a contact time as possible.

The influence of temperature on the compression strength (fc0) in the range of -196 ºC to +220 ºC, and compression modulus of elasticity (Ec0) parallel to the grain of oak (Quercus mongolica Fisch et Turcz.) wood in the range of -196 ºC to +23 ºC were studied. Five specimens were prepared for each temperature level. The specimens were kept at each temperature level for 30 min before a mechanical test was performed in an adjustable-temperature chamber. The results indicated that there were four different failure patterns, depending on the temperature range. When the temperature was decreased from +23 ºC to -196 ºC, the fc0 and Ec0 of wood increased by 283.91% and 146.30%, respectively. The relationships between fc0 and temperature and between Ec0 and temperature could be described by a linear and a polynomial model, respectively. Moreover, the Ec0 could be used to predict fc0 using a polynomial model. However, when the temperature was increased from +23 ºC to +220 ºC, the fc0 decreased by 67%, indicating a non-linear relationship.

Two kinds of macromolecules applied in papermaking were modified with β-cyclodextrin (β-CD) and loaded with ciprofloxacin hydrochloride (CipHCl) in an attempt to compare their potential applications in antimicrobial paper. β-CD grafted cellulose (β-CD-Cel) and β-CD grafted cationic starch (β-CD-CS) were prepared by grafting β-CD onto cellulose fiber and cationic starch using citric acid (CA) and epichlorohydrin (ECH) as crosslinking agents, respectively. β-CD-Cel and β-CD-CS were both loaded with an antimicrobial agent (CipHCl) to form inclusion complexes, namely β-CD-Cel-CipHCl and β-CD-CS-CipHCl. Furthermore, the inclusion complexes were added to the pulp to prepare antibacterial paper. The antimicrobial activity and physical properties of the paper were investigated. The results showed that the paper with both inclusion complexes exhibited excellent antibacterial activity, and the antibacterial activity with β-CD-CS-CipHCl was higher than that with β-CD-Cel-CipHCl. Moreover, the addition of both β-CD-Cel-CipHCl and β-CD-CS-CipHCl affected the tensile and tear strengths of the paper. The paper with β-CD-CS-CipHCl had better physical properties than that with β-CD-Cel-CipHCl because the CS acts as a reinforcing agent in papermaking. These prepared antibacterial paper sheets may be useful for preventing wound and nosocomial infections in the medical and packaging fields.

A comparative analysis of photostabilizing effects of hindered amine light stabilizers (HALSs), an ultraviolet absorber (UVA), and zinc borate (ZnB) on wood plastic composites (WPCs) was made in this study to show the influence of the accelerated weathering on the surface degradation and loss of mechanical properties of treated WPCs. The results showed that the UVA was the most effective in preventing composite from being bleached, especially when the aging time was longer than 1000 hours. With the addition of the ultraviolet stabilizers, the contact angles increased, indicating increased water wettability. The contact angle of UVA-containing samples was greater than that of the control and the other samples treated with HALSs and ZnB. Flexural properties of all materials decreased after being weathered under xenon-arc light. Materials treated with UVA had higher retention rates in flexural strength and modulus. The results show that, among the agents used, UVA was the most effective additive in preventing WPCs from ultraviolet degradation.

Alkali extracted lignin (AEL), isolated from corn stalks with dilute alkali solution under mild condition, was used as a low-cost adsorbent for the removal of methylene blue (MB) from aqueous solutions. Batch adsorption studies were conducted to evaluate various experimental parameters such as pH, contact time, and initial dye concentration for the removal of MB. The kinetic data were analyzed using pseudo-first-order and pseudo-second-order kinetic models, and the adsorption kinetics were found to be well represented by the pseudo-second-order kinetic model. The equilibrium data were perfectly fitted to the Langmuir isotherm equation when compared with Freundlich isotherm equation. Based on the Langmuir adsorption isotherm model, the predicted maximum monolayer adsorption capacity was found to be 121.20 mg g-1 (at 30 ºC). The results showed that this adsorbent had a high adsorption capacity, making it a promising alternative for dye removal.

The kinetics and equilibrium binding of Cd(II) ions onto raw water hyacinth (Eichhornia crassipes) biomass (RBH) were investigated with the view to utilize it as a low-cost biosorbent for removal of toxic metal ions from water. The biosorption was analyzed through batch experiments with respect to the effect of contact time, agitation speed, biosorbent dosage, solution pH, Cd(II) concentration, and the presence of other metal ions. Cadmium adsorption onto Eichhornia crassipes biomass was pH- and temperature-dependent, and complete Cd(II) removal from solution was achieved at all Cd(II) concentrations up to 10 mg/L. The biosorption equilibrium was described by Langmuir and Freundlich isotherms, and the RBH Cd(II) uptake capacity was 104 mg/g. The biosorption process followed the pseudo-second-order model (R2 > 0.99). The root biomass of water hyacinth had one of the highest Cd(II) sequestration efficiencies when compared to other biosorbents that have been used to remove Cd(II) from water.

In this work, paper was rendered antimicrobial via applying antimicrobial-modified starch as a coating material onto the paper’s surface. The antimicrobial starch was prepared by covalently bonding guanidine polymers using a coupling reaction. Two different coating layers were applied onto the paper’s surface. The first coating layer contained clay mixed with a latex binder (clay 100 g/latex 20 g). The antimicrobial starches, which possessed different grafting ratios of the antimicrobial agent (30 wt.% and 50 wt.%), were applied as the second coating layer on the paper. The results showed that the coating thickness was approximately constant at 4 μm. In the presence of 0.5 to 1.0 wt.% antimicrobial starch on cellulose fibers, the growth inhibition of bacteria was almost 100%. Additionally, the resulting coated paper exhibited high antimicrobial activities against E. coli. Furthermore, the results showed that the coated papers prevented fungal growth.

In 2008, the European Union Commission put forward a proposal for a new directive on renewable forms of energy. Each of the member states should increase its share of renewable energies in an effort to boost the total share of the EU from the current 8.5% to 20% by 2020. The level of renewable energy in Finland was 28.5% in 2005, and the national target share of renewable energy by 2020 is 38%. To assist in reaching this goal, one solution is to further develop drying techniques of biomasses and utilization of untapped biomasses, because in Finland, up to 20 million tons of waste wood biomass per year are left unused during forestry operations. In this study the drying of biomasses and the condensate, including biodegradation of organic pollutants, is examined. The cost-efficiency and energy-efficiency of wood chips combustion can be increased by drying the wood to optimize moisture content before being utilized in different applications. However, the removal of moisture is the most expensive unit process in combustion. Studied wood species were pine (Pinus sylvestris), spruce (Picea abies), aspen (Populus tremula) and two birch species (Betula pendula and Betula pubescens). The biodegradation degrees of studied organic pollutants in condensing waters were between 25% and 61%. Furthermore, the biodegradation of organic compounds in condensing waters showed that at least the studied condensates can be safely disposed via municipal wastewater treatment plant (WWTP).