Research Articles

This study aimed to investigate the changes in the fiber characteristics, relative crystallinity, and impact toughness of heat-treated Eucalyptus urophylla × E. camaldulensis. Samples were treated in a superheated steam kiln at 160, 180, 200, and 220 °C for 3 h. The crystallinity, length-width ratio of fibers, and impact toughness of the heat-treated and untreated wood were determined. The cellulose crystalline regions experienced no obvious change. However, the length-width ratio and the relative crystallinity of the fibers increased as the temperature increased. Results indicated a clear inverse trend in the impact toughness and relative crystallinity. Finally, the results could provide a new method for non-destructive testing of wood.

In the present study, polypropylene, recycled natural rubber gloves, and oil palm ash composites (PP/rNRg/OPA) were prepared using an internal mixer. The effects that OPA loading had on the processability, tensile properties, morphology, and thermal stability of the PP/rNRg/OPA composites were investigated. The stabilization torque, tensile modulus, and thermal stability all increased; however, the elongation at break decreased as the OPA loading increased. The tensile strength increased to a maximum of 4 parts per hundred rubber (phr) OPA loading, and subsequently decreased. At 4 phr OPA, the filler was well-dispersed and had a good interaction with the matrix, whereas the agglomeration and detachment of OPA was observed at high loading rates of OPA in the PP/rNRg/OPA composite. Thermogravimetric analysis (TGA) indicated that the thermal stability of the composite increased as the OPA loading increased. Further evidence for the increased thermal stability can be found when analyzing the decomposition temperatures at different stages and maximum weight loss, where higher decomposition temperatures corresponded to composites with higher OPA loadings.

This paper reports the influence of densification and cyclic loading on the bending strength of laminated beech (Fagus sylvatica L.). There have been many studies dealing with the bending strength of solid or laminated wood; however, densification is much less explored with respect to its use in the production of laminated wood. Laminated beech wood was loaded using three different numbers of cycles (1000, 2000, and 3000 cycles). Bending strength values of the cyclically loaded laminated wood ​​were compared with that of laminated wood that was not cyclically loaded. The laminated wood was formed by a combination of densified and non-densified veneers, as well as polyvinyl cholride (PVC) fabric. The results show that the laminated wood consisting of densified and non-densified veneers, eventually with PVC film included, reached higher values of bending strength in comparison with the traditional composition consisting of non-densified veneers. Densification had a strong impact on the bending strength. Laminated wood composed solely with densified veneers achieved by 17.4% higher bending strength compared to the reference. On the other hand, the number of cycles did not influence the bending strength to a meaningful extent.

The thermostability and mechanical properties of ultra-low density fiberboard (ULDF) were improved with the different content of silica sol. Microstructure and properties of ULDF were tested using scanning electron microscope (SEM), thermogravimetric analyzer (TGA), and microcomputer control electronic universal testing machine. The microstructures and the relative density of ULDFs were different with changes in Si sol content. The TGA results showed that the residual weight of ULDF was increased with the increasing content of silica sol and that the thermostability of ULDFs was improved. The modulus of rupture (MOR), modulus of elasticity (MOE), and the internal bond strength (IB) of ULDF were significantly improved from 0.12, 10.86, and 0.020 MPa to their maximum values of 0.23, 23.36, and 0.031 MPa while 4% silica sol was added.

To enhance the properties of sodium silicate wood adhesive modified by PVOH (polyvinyl alcohol), different organic additives (compound A) and inorganic fillers (compound B) were added into the system. Their effects on the thermal stability and molecular structure of the composite adhesive were investigated by scanning electron microscopy (SEM), spectroscopic analysis (FT-IR), differential scanning calorimetry (DSC), and thermo- gravimetric analysis (TGA). The results showed that when the compound A consisting of amino acid, TEOS (Tetraethyl orthosilicate), sodium dodecyl sulfate with the mass ratio of 5:3:3 and B consisting of 50% active magnesium oxide and 50% nano-silica were added into the cross-linked sodium silicate adhesive system with the ratio of 90:3, the bonding and water resistance properties were improved by 97.6% and 46.7%, or 13.7% and 36% relative to pure and cross-linked sodium silicate, respectively. The addition of organic additives and inorganic fillers had a good effect on both the bonding strength and thermal stability of sodium silicate wood adhesive modified by PVOH.

Soy-based adhesive’s sensitivity to microbial attack is an aspect that restricts its future application. In an attempt to combat microbial attacks, several preservatives have been evaluated to determine their effects on mold resistance. In this paper, the inhibitory effect of p-cumylphenol was investigated by observing mold growth on modified soybean-flour adhesives and by evaluating the bonding strength and surface mold growth of bonded poplar plywood. Visual images, scanning electron microscopy, and tensile testing were used. The results showed that the initial microbial attack was delayed and the degree of attack was alleviated because of the preservatives. The bonding strength decreased in samples that contained p-cumylphenol after the samples were exposed to high humidity. Additionally, no correlation was observed between the degree of microbial growth on the surface of the plywood and amount of the preservatives. These results revealed that it was feasible to incorporate p-cumylphenol into soy-based adhesives as glue line treatment to improve the mold resistance. Finally, surface treatment of the veneer should be taken into consideration during the plywood manufacturing.

The mycelial growth ability of 13 white rot fungi were separately evaluated in kraft, organosolv, and soda black liquor agar-plates. The fungus able to best grow and decolorize black liquor agar-plates was grown in organosolv black liquor to investigate whether it reduced organosolv lignin molar mass. The fungus Bjerkandera adusta showed fair mycelial growth and decolorization ability in 10% black liquor-agar plates. To obtain low-molecular weight (MW) lignin, B. adusta was cultivated in 150-mL Erlenmeyer flasks containing 10% black liquor and maintained in a shaking culture for 15 days. Lignin was recovered from each Erlenmeyer flask by acid precipitation and was analysed by size exclusion chromatography (SEC) and Fourier transform infrared (FTIR) spectroscopy. The lowest MW of lignin from black liquor was observed on the 11th and 12th days, at 1461 and 1790 kDa, respectively, with the polydispersity close to 1.0, indicating that the molecules were similar in size. Fourier transform infrared spectra bands showed modification of the lignin structure during 9 days, with new bands appearing after five days of lignin biodegradation.

The aims of this study were to use beeswax impregnation as a wood preservative method and to evaluate its suitability to protect wood species with low resistance to decay. Poplar (Populus × euramericana cv. Pannonia) and beech (Fagus sylvatica) samples were impregnated with beeswax and exposed to soil contact for 18 months. Impregnated samples were separated into three groups, on the basis of their degrees of pore saturation (DPS). With progressing decay, the load-bearing capacity and modulus of elasticity (MOE) of the woods decreased. After one month of soil contact, there was a marked decrease in MOE, which is explained by the increase in the moisture content of the wood. After 18 months, control samples were completely decayed. Nevertheless, impregnated samples showed less decay and a noticeable remaining load-bearing capacity. Impregnation efficiency had a pronounced effect on decay resistance. In both investigated species, samples with higher DPS resulted in less of a decrease in MOE than in samples with lower DPS. Although beeswax is a bio-based material, it showed noticeable decay resistance effects against soft rot. Scanning electron microscopy investigations showed that the impregnation has a barrier effect, mostly in the longitudinal direction, against the spread of the fungi.

Cellulose paper specimens with and without surface modification were compared in order to study their physicochemical compatibility with quantum dots (QDs) for biochemical sensing applications. Silane and chitosan modification methods were applied. The distribution of QDs deposited on untreated paper and papers modified with silane and chitosan were investigated in order to understand the interaction between QDs and fibre. Modified papers were shown to significantly reduce the undesirable redistribution of QDs during paper drying. The retention ability and thermal resistance of QDs to the loss of fluorescence on modified papers were also studied for the purpose of determining the most suitable paper surface modification for developing QD-Paper-based analytical devices (QD-PADs). Furthermore, chitosan-modified paper was used to design QD-PADs to quantify glucose concentration in aqueous samples; the quenching effect of the enzymatic product on the fluorescent emission of QDs was used as the indicator system. The change of fluorescence of QDs was measured by a simple in-house constructed fluorescence imaging system. The detection limit of glucose was 5 mg/dL, which is comparable with other reported paper sensors for detection of glucose.

The SuperBatch™(SB), CompactCooking™(CC), and Lo-Solids™ (LS) modified cooking methods were evaluated relative to the cell wall surface and paper technical properties of bleached Eucalyptus globulus and Eucalyptus nitens. E. globulus pulps presented higher screened yield and brightness than E. nitens, which needed higher H-factor to reach a kappa number target. Independently of the cooking method or species, all the samples consumed similar amounts of ClO2 to reach a brightness of 90% ISO. E. nitens pulps showed lower carbohydrates and higher extractives content on the fiber surface, regardless of the cooking method. E. nitens presented slightly higher surface charge of the bleached pulps. Surface charges of CC and LS pulps were higher independently of cooked Eucalyptus species. Water retention value (WRV) for E. nitens pulps were higher than for E. globulus. No differences were observed in refinability of different cooking methods, however E. nitens pulps showed higher tensile and lower bulk compared to E. globulus. E nitens presented a thinner fiber cell wall than E. globulus. This seems to be more relevant for paper technical properties and WRV than fiber charge or surface composition. No correlation between surface composition, fiber surface properties, and paper technical properties among the cooking methods could be determined.