Research Articles

Effects of temperature and press pressure on the anatomical structure of solid-wood panels produced by using Pinus sylvestris L. (Scotch pine) wood were evaluated. Solid wood panels with dimensions of 250 by 500 by 18 mm were hot-pressed using a laboratory hot press at a temperature of either 120°C or 150°C and pressure of either 5 or 7 MPa for 1 h. Microscopic investigations conducted by Light Microscopy (LM) and Scanning Electron Microscopy (SEM) showed that the highest deformation occurred in earlywood regions of all growth rings for each process condition and the distribution of deformation was not uniform in growth rings. Cell-wall thickness was observed to be an important factor in wood behavior during thermal compressing processes. The results showed clearly that the impact of pressure in wood structure is promoted by increased temperature. Significant densification was observed at the maximum temperature and maximum pressure condition employed in the study, and almost all earlywood layers showed cell collapse. The study revealed that a homogenous structure of growth rings with the uniform earlywood and latewood widths throughout the wood samples plays a major role in prevention of cell collapse. The results indicated that both process conditions and anatomical structure of the wood have an interaction.

Feasibility of electrochemically generated biocides in papermaking was evaluated in pilot scale trials. The trials indicated that electrochemically generated biocides prevent microbial growth and proliferation in broke systems, as well as in water circulations. The spoilage of broke can be delayed, and already spoiled broke can be recovered using these biocides. The improved broke quality increases the stability of the paper machine and, consequently, less broke is produced. The biocides can be added to water or pulp, and they have hardly any negative effect on the process or the end product. The presence of reducing compounds may cause limitations in the use of these oxidative biocides. It was observed that electrochemically generated biocide was also efficient against heat-resistant spores. However, the biocide was less efficient against spores as compared to vegetative cells, both aerobic and anaerobic, especially when the spore numbers were higher than 104 cfu/ml. Onsite oxidant production eliminates the transportation and storage of biocides. Moreover, due to the short time between the production and use, the degradation of the active compounds can be minimized.

This paper describes the development of a simple UV spectroscopic method for determination of silicon content in black liquor. The method is based on the fact that Si (IV) can react with ammonium molybdate to form Si-Mo heterophony acid in an acidic condition (pH=4). The absorption peak of α-Si-Mo heterophony acid is 340 nm. To avoid the compensation of the instrument, 360 nm is used for spectroscopic quantification. A certain time (20 min) for the reaction is necessary. Moreover, it was discovered that 480 nm could be used to develop a dual-wavelength method to account for the spectral interference from dissolved lignin in black liquor. This method is simple, rapid, sensitive, accurate, and has the potential for on-line applications.

It was aimed in this study to determine the effect of the number of joints in frames produced from Oriented Strand Board (OSB) and of the type of adhesive on the diagonal tensile strength (DTS) of the frame. With this objective, a total of 152 specimens were prepared from OSB in accordance with the principles in the EN 2470 test standard. The diagonal tensile test was applied to the specimens in the universal test equipment in accordance with ASTM-D 1037. According to the statistical analysis of the data obtained from the tests, the number of dovetail joints and the type of adhesive had significant effects on the DTS. The highest DTS (0.117 N/mm2) was obtained in the specimens with a single dovetail joint and bonded with the PVAc adhesive. This alternative was followed by the specimens with a double dovetail joint bonded with the PVAc adhesive (0.078 N/mm2) and the specimens with a single dovetail joint bonded with the PU adhesive (0.073 N/mm2). The lowest DTS occurred in the specimens with single and double joints without adhesive. According to these results, adhesive should definitely be used in the corner joining of the dovetail joints, and the single dovetail joint joining type bonded with PVAc adhesive is preferred.

A laboratory flotation column equipped with Venturi aerators and an adjustable froth removal system was used to study the effect of calcium soap and a mixture of calcium soap/alkyl phenol ethoxylate surfactant on ink and fibres transfer during flotation de-inking of a 50% old newprint (ONP) / 50% old magazines (OMG) recovered papers mixture. Mass transport phenomena determining the yield of the flotation process were interpreted using model equations describing particle removal in terms of flotation, entrainment, and drainage in the froth. A decrease in the ink and mineral fillers flotation rate constant, drainage through the froth, and in fibre entrainment was observed when increasing the surfactant concentration. These trends were consistent with the typical dispersing action of the studied nonionic surfactant. An opposite effect on ink and fillers was observed when using calcium soap alone, and the increase in the flotation rate constant and drainage through the froth were consistent with the collecting and defoaming action of the calcium soap. Moreover, fibre entrainment decreased when increasing the soap concentration. The study of the surfactant/soap mixture highlighted the absence of synergy between the calcium soap and the surfactant.

A preliminary experimental study was carried out to examine the ability of a chemically modified Acacia spp. to resist biodegradation. The modifications of Acacia mangium and Acacia hybridwere carried out by propionic anhydride and succinic anhydride in the presence of sodium formate as a catalyst. The treated samples were found resistant to microbial attack, while the untreated ones were damaged on 12 months exposure to a soil burial. The appearance grading, mass loss, mechanical properties, and scanning electron microscopy results revealed that chemical modification enhances the resistance of Acacia mangium and Acacia hybrid wood species to biodegradation.

Modified fillers consisting of kaolin particles encapsulated by starch have recently been demonstrated in mill trials to achieve significant filler loading levels without accompanying strength losses. In this work, laboratory experiments were conducted to explore the potential advantages of using starch-treated pigment for strength increases by application of surface coating. It is found that a platy clay coating will produce a higher increase in strength per unit weight of application compared to a fine clay, and more-so if the clay is encapsulated in starch. Starch encapsulation of clay produces a greater increase in strength than an equivalent weight proportion addition of starch to a kaolin formulation blend. The observations and measurements of changes in various physical properties of the coated samples are explained by a proportionate loss of void volume in the coating from the encapsulation process and the increase of stress transfer through introduction of higher platelet aspect ratio.

Refining of bleached hardwood pulps and bleached softwood pulps having different counter-ions to the charged groups within the fibres was studied. The results show that an energy reduction of 50% for the hardwood pulps and 20% for the softwood pulp can be achieved if the fibres are converted into the Na+-form prior to refining. The results also show that the amount of charged groups in the fibres is important for the refinability, which explains why the refining efficiency is much lower for bleached softwood fibres, which have a much smaller amount of charged groups than the bleached hardwood pulp.

Hesperaloe funifera was characterizedin terms of its contents of holocellulose, α-cellulose, and lignin (74.1, 52.3, and 7.9%, respectively). Also, an experimental factor design was used to examine the influence of operational variables in the diethanolamine pulping of this material (viz. diethanolamine concentration (50-80%), cooking temperature (155-185 ºC), and time (30-90 minutes)) on the contents of holocellulose, α-cellulose, and lignin, as well as the yield, kappa number, and viscosity of the resulting pulps, and also on the brightness, tensile index, stretch, burst index, and tear index of paper sheets made from it. The predictions for these dependent variables departed by less than 1, 7, 6, 2, 2, 4, 15, 11, 12, 10, and 37% from their respective experimental values. Black liquors obtained from the pulping runs were characterized by determining pH, density, TDS, (total dissolved solids), MI (inorganic matter), MO (organic matter), and lignin content; lignin samples were characterized by different techniques (FTIR and TGA). Finally, the black liquors were acidified to separate solid fractions that were subjected to pyrolysis and gasification in order to obtain synthesis and fuel gases.

Cr(III) ions were adsorbed onto polyacrylamide-grafted rubberwood fibre, and effects of aqueous conditions were evaluated. The adsorbent was prepared via graft copolymerization of acrylamide (Am) onto rubberwood fibre (RWF), using ceric ammonium nitrate as an initiator. Fourier transform infrared spectroscopy was used to confirm the formation of PAm-g-RWF. Various variables affecting the adsorption capacity such as the pH of the solution, adsorption time, initial metal ion concentration, and temperature were investigated. The Cr(III) was up to 92% removed by PAm-g-RWF from an initial concentration of 10 mg/L at pH 5.0. Kinetic data fitted very well to a pseudo-second-order rate expression and less well to a pseudo-first-order equation. The equilibrium parameters for adsorption isotherms of the metal ions on the grafted fibre were obtained using Langmuir and Freundlich models, and the Langmuir model was found to be in better correlation with the experimental data with a maximum adsorption capacity of 18.24 mg/g. Thermodynamic parameters such as enthalpy change (ΔH°), free energy change (ΔG°), and entropy change (ΔS°) were calculated; the adsorption process was spontaneous and endothermic.