Volume 68, Issue 3

The hypothesis has been tested that a carboxymethyl hemicellulose improves more effectively the dry strength of papers than a native hemicellulose. To that end, β- d -glucan from oat was treated with an alkaline ethanolic solution of sodium chloroacetate for different times to obtain a range of carboxymethylated β- d -glucan (CM-glucan) samples. The derivatization was confirmed by Fourier transform infrared spectroscopy and elemental analysis. The physical properties of paper concerning burst and tensile strength as well as folding endurance were essentially improved if CM-glucan was added to unbleached kraft fiber suspension from pine before papermaking. The effects could be maximized by a proper selection of carboxymethylation time and the amount of CM-glucan added to the suspension. The effect was also beneficial in the case of recycled fibers.

Hemp fibers were modified with 3-isopropenyl-dimethylbenzyl isocyanate (TMI), in presence of dibutyltin dilaurate (DBT) as a catalyst. Then reinforced hemp-unsaturated polyester (UPE) composites were prepared with modified fibers by means of hand lay-up compression molding. The fiber treatments significantly increased the tensile strength (TS), flexural strength (FS), and water resistance of the resulting composites, while their flexural modulus (FM) was not influenced. The tensile-fractured surfaces of the composites were observed by SEM and the images revealed that fiber treatments significantly improved the interfacial adhesion between hemp fibers and UPE resins. FT-IR spectra and X-ray photoelectron spectroscopy (XPS) analysis indicated that the treated-fibers were partly covalently bound to TMI.

The chemical composition and morphology of pulp fibers have a significant impact on the properties of fiber products. Pulp samples from a novel unique Eucalyptus triple hybrid [ Eucalyptus grandis × ( Eucalyptus urophylla × Eucalyptus globulus )] were obtained by various pulping processes – kraft, soda-anthraquinone (NaOH-AQ), and thermomechanical pulping (TMP). The chemical composition of the fiber surfaces was evaluated by X-ray photoelectron spectroscopy (XPS). The surface lignin content of NaOH-AQ pulp fibers was lower than that of the kraft counterpart. However, kraft pulp handsheets showed better physical and mechanical properties. XPS data strongly suggests that together with the pulp bulk chemical composition the xylan is more abundant on the surface of kraft fibers, which is reflected on their better mechanical properties. Moreover, the relatively low surface lignin content in TMP pulp compared to wood suggests that defibration takes place in the secondary wall, where lignin is less concentrated.

Homogeneous and transparent CNF films, fabricated from the (2,2,6,6- tetramethylpiperidin-1-yl) oxyl (TEMPO)-modified CNF suspension, were laminated onto wood flakes (WF) based on phenol-formaldehyde (PF) resin and the reinforcement potential of the material has been investigated. The focus was on the influence of CNF film lamination, relative humidity (RH), heat treatment, and anisotropic properties of WF on the CNF-WF laminate tensile properties (elastic modulus, ultimate tensile strength, strain to failure). Results demonstrated that CNF-WF laminates had improved mechanical performance as compared to the neat WF. In the WF transverse direction, there were gains of nearly 200% in Young’s modulus and 300% in ultimate tensile strength. However, in the WF axial direction, the reinforcement effect was minor after PF modification of the wood and the presence of the CNF layers. The effective elastic moduli of the CNF-WF laminates were calculated based on the laminated plate theory, and the calculation in both axial and transverse directions were in agreement with the experimental results.

There is a growing need to characterize the mechanical properties of single bamboo fibers with their high potential in commercial applications. In this paper, an improved microtensile technique has been applied to measure the tensile strength of fibers isolated from Ma bamboo ( Dendrocalamus latiflorus Munro) as an important commercial bamboo species in China. The property variation with respect to the age and locations within a culm was in focus. Ma bamboo fibers had superior stiffness and strength data compared with those of softwood fibers. Four-year-old Ma bamboo fibers are stiffer and stronger than 1-year-old fibers. Their in-trunk variation is rather small both in radial and longitudinal directions. This is due to the relatively constant microfibrillar angle in bamboo culms. Accordingly, the large variations in the bulk mechanical properties of bamboo are mainly attributable to fiber distribution density in the culm rather than the fiber itself.

Bending properties have been determined by mechanical testing [modulus of elasticity (MOE) and modulus of rupture (MOR)] and by means of longitudinal (L) and transverse (T) vibration nondestructive methods on 150 sawn timber pieces of Pinus radiata D. Don, with the dimensions of 80×120 mm cross-section and 2500 mm long, from Catalonia, Spain. The fundamental vibration frequency was measured by recording the sound produced by hitting the piece in L and T directions, and this signal was analyzed by fast Fourier transform sound analyzer. The dynamic MOE was obtained for both procedures and compared with static MOE and MOR. The notion of concentrated knot diameter ratio (CKDR) was introduced to improve the prediction of MOR. CKDR gives better results when this parameter is referred to the central portion of piece length. Both methods (L and T frequencies) have similar accuracy in prediction of mechanical properties, but the first one is simpler and has some practical advantages. The timber graded with this nondestructive method offers better results than the visual grading rules for the same output.

To gain further insight into the energy dissipation during the wood sawing process, a theoretical model has been developed. The model is based on the assumption that there are two basic causes for energy dissipation during sawing: the creation of a new surface and the compression of material below a saw tooth. It is assumed that both contributions can be dependent on the cutting angle (the angle between the fiber direction and the tangent to the path followed by a saw tooth) because a saw tooth changes its angle of attack during its way through a log. To determine this dependence of the dissipation on the cutting angle, a series of experiments with pine plank sawing were performed by means of different feeding rates and cutting angles while the electrical power supplied to the saw was measured. The parameters in the theoretical model were derived from the experimental findings. Finally, two tests were carried out under different conditions with respect to thickness and cutting angles and the validity of the model was confirmed concerning the prediction of the electrical power consumption.

A mathematical model is discussed in terms of moisture transfer during the drying process of Masson pine ( Pinus massoniana ) lumber in industrial practice. The model was validated by comparing the simulated result of moisture distribution with experimental data. In the model, the wood drying process was divided into two phases. The first one dealt with processes above fiber saturation point (FSP), that was driven by capillary flux of free water and conductive flux of vapor, and the second one dealt with those of below FSP, which was driven by diffusive flux of bound water and vapor. Moisture content distribution (MC D ) inside wood is simulated by solving a parabolic partial differential equation under Dirichlet boundary conditions. The moisture content profile (MC P ) was asymmetrical in experiments, and the simulation result agreed well with the experiments. An easy empirical formulation was also proposed to calculate real wood permeability, as it showed general characteristics of liquid and vapor permeability. This permeability model is verified as the cause of asymmetrical MC P in this paper.

Pitch pine ( P. rigida ) wood was treated with superheated steam (SHS) and the subsequent effects due to drying and heat treatment (HT) were observed. The following treatment parameters were tested: 180°C air HT, 220°C air HT, 0.1 MPa–180°C SHS HT, 0.1 MPa–220°C SHS HT, 0.5 MPa–180°C SHS HT, and 0.5 MPa–220°C SHS HT. No drying checks were observed in the specimens (500×150×50 mm 3 ) treated at 0.5 MPa–220°C SHS and with these treatment parameters, equilibrium moisture content (EMC) was the lowest. Low EMC has an effect on physical properties such as shrinkage, compressive strength parallel to the grain, bending strength, hardness, and decay resistance. Based on the results, it is expected that the green wood in a large scale is possible to be simultaneously dried and heat-treated without occurrence of checks by the SHS HT process.

The effects of mild torrefaction on the pulverization of Norway spruce sawdust have been studied. To this end, sawdust was dried and torrefied below 230°C for different periods of time to obtain samples with mass losses (ML) of 0.2%, 1.4%, and 2.8%, milled in an oscillatory ball mill, and the particle morphology and cellulose crystallinity of the powders were studied. The pretreatment leading to 0.2% ML had no effect on grindability, but that resulting in 1.4% ML improved grindability and a median particle size below 17.4±0.2 μm was attained. Torrefaction involving 2.8% ML reduced the specific energy consumption more than 21% when the targeted median particle size of the torrefied wood was between 18.7±0.5 and 79±3 μm. The mild torrefaction had a negligible influence on the aspect ratio distribution and cellulose crystallinity in the ball-milled wood.

Wood in outdoor exposure undergoes photochemical degradation mainly caused by the combination of UV radiation and moisture, thus appropriate coatings are desirable. In this paper, the wood surface was first treated with CeO 2 sol and then treated with a layer of octadecyltrichlorosilane (OTS) and the created coating was characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDXA), X-ray diffraction (XRD), and FTIR spectroscopy (FTIR). The surface became superhydrophobic as the contact angle (CA) for water of the modified wood was 152°. Accelerated aging tests revealed that the modified wood has an excellent weathering resistance.

The performance of the passive impregnation method of CO 2 -laser incised lumber has been investigated concerning wood preservation against different wood-destroying agents. Copper azole type B (CuAz-B) preservative and polyphosphatic carbamate (PPC) fire retardant were impregnated into Douglas fir and Japanese cedar lumber under both green and kiln-dried conditions. Final drying of the lumber was performed by steam injection or kiln drying. The temperature and pressure change in the lumber, as well as the total chemical retention, penetration, decay resistance, fire retardancy and total treatment time were calculated according to different standards. The preservative retention was higher in the Japanese cedar for both green and kiln-dried conditions (5.32 and 5.58 kg m -3 , respectively) compared to Douglas fir (5.01 and 4.81 kg m -3 ). Fire retardant retentions were more than 100 kg m -3 in all cases. The penetration was approximately 100% throughout the lumber. There were no significant differences in the decay resistance test between the different categories of lumber. Moreover, it was possible to treat the green lumber in less than 48 h starting from the green conditon to the final drying. Hence, the presented passive impregnation technique could be useful for industrial application.

The effects of initial moisture content (MC) on anti-swelling efficiency (ASE), mass loss (ML), and equilibrium MC (EMC) at 65% relative humidity of thermally modified Scots pine sapwood under saturated steam (TM SA ) has been investigated. ML during the TM SA process was higher with the specimens containing moisture before modification compared with initially dry specimens. Surprisingly, the EMC of the modified specimens with initial moisture was higher than that observed with the modified wood that was initially dry before the modification process. Higher initial MC before thermal modification results in a lower ASE.

The antitermite effects of several thione analogues of naturally occurring coumarins have been tested against Coptotermes formosanus by the no-choice test. 2-Thioxogrevillone exhibited the strongest antitermite potential. The thione analogues proved to be more effective as termite pesticide than their natural counterparts.