Research Articles

The objective of this study was to improve the properties of Korean white pine (Pinus koraiensis Sieb. & Zucc.) and royal paulownia (Paulownia tomentosa (Thunb.) Siebold & Zucc. ex Steud.) via heat treatment. The woods were treated at 160 °C, 180 °C, 200 °C, and 220 °C for 2 h. The effect of mechanical restraint through clamping during heat treatment on the dimensional stability, physical, and mechanical properties was evaluated. The results showed that increased temperature increased the weight loss and volume shrinkage, while equilibrium moisture content and wettability decreased. Royal paulownia showed higher weight loss, but lower shrinkage and equilibrium moisture content, when compared to Korean white pine. The samples with clamps in both woods had lower weight loss and volume shrinkage after heat treatment. The modulus of elasticity and modulus of rupture decreased with increased temperature followed by a noticeable decrease obtained after heat treatment at 200 °C and 220 °C. Clamping minimized strength reduction in both woods. Consequently, it was suggested that mechanical restraint was a useful method to maintain the wood properties during heat treatment.

The demand for and the consequent production of porous materials, such as wood, increase with industrial development and income. If a smoldering fire occurs in a porous material such as wood flour, it is difficult to find the fire location because of the development of a downward deep-seated fire. In this study, a down-scaled downward deep-seated fire model was adopted for wood flour to experimentally and theoretically elucidate the propagation phenomena of the downward velocity of deep-seated fires and subsequently predict their location. The experiment was performed on radiata pine wood flour with the density range of 0.2038 to 0.2343 g/cm3. Different tendencies were observed quantitatively in the downward temperature profiles with the changes in the volumetric mass density of the wood flour. Based on these results, it can be concluded that the deep-seated fire propagation speed is in the range of 0.0014 to 0.0018 cm/s. The practical applications of this result would be in effective extinguishing of fires in wood flour factories and silos by predicting the fire site based on the determination of the speed of propagation of the downward deep-seated fire.

Torrefaction can increase the energy yield of biomass for better utilization in bioenergy, but chemical changes occur during the pretreatment process. Wood residues of Cupressus lusitanica, Dipteryx panamensis, Gmelina arborea, Tectona grandis, and Vochysia ferruginea were torrefied for three different time periods (8, 10, and 12 min) and three different temperatures (200, 225, and 250 °C). The mass loss, net calorific value, ash, volatiles, lignin, cellulose, extractives, and infrared spectra were evaluated. The results showed that the mass loss in torrefied biomass varied between 10% and 70%, ash content varied between 0.19 and 7.00%, and volatiles content varied between 63 and 85%. Net calorific value values varied between 17 and 23 MJ/kg, increasing with the increased torrefaction temperature. Cellulose varied between 49.85 and 67.57%. Lignin varied between 27.33 and 41.09%. The extractives varied between 3.70 and 16.86%. The change in the ratio of intensity (RI) for the bands identified using FTIR analyses showed that large changes occurred in hemicellulose components. The multivariate analysis showed that lignin, ash, extractives in hot water, volatiles, and mass loss were the variables that contributed most. The analysis of all these variables showed that torrefaction at 250 °C for 12 min presented the greatest biomass degradation. Torrefaction at 200 °C and 225 °C for 8, 10, and 12 min was optimal for thermal treatment of the biomass of these woody species.

Urea-formaldehyde (UF) resins based on different formaldehyde/urea (F/U) mole ratio were synthesized with oxidized cassava starch added at the final stage of the resin synthesis process. The basic characteristics of resins including solid content, viscosity, and curing time were studied, and the dry and wet bond strengths were evaluated by producing a three layer plywood. Additionally, the curing characteristics of different resins were investigated via differential scanning calorimetry (DSC). Structural distributions between UF and oxidized cassava starch were examined via FT-IR and 13C NMR analysis. The results indicated that the addition of oxidized starch not only improved resin bond strength but also notably reduced the curing start temperature of modified resins. Furthermore, a negative relationship between F/U mole ratio and the extent of reduction was identified. The structural distribution of UF resins changed dramatically because of oxidation cassava starch addition, but the changes varied due to different F/U mole ratios.

Antibacterial properties of wood structural components and extractives were investigated against methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli O157:H7 by placing bacterial inoculum on the model surfaces and incubating them for 2, 4, and 24 h. After incubation, the amount of viable bacteria on the surfaces was studied. The film coverage and thickness were evaluated with atomic-force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The extracts were analyzed with gas chromatography–mass spectrometry (GC-MS). The results showed that films fully covered the glass surfaces. The XPS results confirmed the analysis of GC-MS, which revealed more similarities between the extractives of pine heartwood and spruce heartwood than between pine heartwood and pine sapwood. Only the pine heartwood extract showed an antibacterial effect against E. coli O157:H7. In contrast, MRSA was susceptible to all of the extracts and milled wood lignin (MWL).

Acacia saligna wood was impregnated with 5% and 10% concentrations of Paraloid B-72/TiO2 nanocomposites using a soaking technique and evaluated for their antifungal activity against the growth of three molds in vitro, namely, Alternaria tenuissima, Trichoderma harzianum, and Fusarium culmorum. The Titanium (Ti) element peak of 0.14% and 0.23%, was found in the A. saligna wood treated with Paraloid B-72/TiO2 nanocomposites at 5% and 10%, respectively. Consolidant polymer Paraloid B-72 mixed with TiO2 nanocomposites at 5% and 10% showed antifungal activity against the three studied molds, while the linear growth of the studied molds reached the maximum in the control and Paraloid B-72 treatments. The results concluded that using synthesized Paraloid B-72/TiO2 nanocomposite could be considered as a new agent in the wood preservation field by prevention of mold fungal growth over the wood surfaces.

Cellulose nanofiber (CNF) was produced from Japanese cedar using a new environmentally friendly pulping process, i.e. a steam explosion treatment followed by water and acetone extractions. The effect of the steam explosion treatment on the morphological, chemical, and mechanical properties of steam-exploded CNF were clarified. The increase of steam explosion severity markedly decreased the molecular weight of α-cellulose in the steam-exploded cedar pulp. The maximum tensile strength value of 88.9 MPa and Young’s modulus value of 12.9 GPa were obtained for the films made from steam-exploded CNF at a steam pressure of 35 atm for a steaming time of 5 min. The results obtained in this work were useful for developing a new production method of CNF from various steam-exploded woody biomass.

To enhance the yield of alkyl levulinates, a mixed-acid catalyst system consisting of CrCl3 and H3PO4 was investigated for the transformation of furfuryl alcohol (FA). The CrCl3−H3PO4 system exhibited a positive synergistic catalytic activity for the synthesis of alkyl levulinates, which was especially obvious for n-butyl levulinate (BL) synthesis. The strongest synergic effect of mixed-acid system for BL production was achieved at the CrCl3 molar ratio of 0.3 (based on total moles of CrCl3 and H3PO4). Furthermore, the mixed-acid systems consisting of Cr-salts combined with H3PO4 and its salts in catalyzing FA conversion to BL were evaluated, and the evolution process of FA to produce BL was explored in the presence of CrCl3−H3PO4, sole CrCl3, and sole H3PO4. A possible synergistic catalytic pathway of CrCl3 combined with H3PO4 was proposed. Finally, the key process variables were examined. Under optimal conditions, a high BL yield of 95% was achieved from 99% FA conversion catalyzed by the synergy of CrCl3 and H3PO4.

Cellulose nanofibril (CNF) suspensions are not easily coatable because of their excessively high viscosity and yield stress, even at low solids concentrations. In addition, CNF suspensions vary widely in their properties depending on the production process used, which can affect their processability. This work reports roll-to-roll coating of three different types of CNF suspensions with a slot-die, and the influence of rheology and water retention on coatability is addressed. The impact of CMC addition on the high and low shear rate rheology, water retention, coatability, and final coating quality of these suspensions is reported. All three CNF suspensions were coated successfully using the slot-die coating process. CMC addition further improved the coatability by positively influencing both the low and high shear rate viscosity and water retention of the CNF suspensions. All CNF coatings significantly improved the air, heptane vapor, grease and oil barrier, while reducing the water vapor transmission rate to some extent.

Corn straw was used to improve the productivity of a red pigment during the biomembrane surface liquid cultivation of Penicillium novae-zelandiae. Both the dosage and particle size of corn straw powder had a significant effect on the fermentation period and pigment yield. After the optimization, the maximum yield of synthesised red pigment reached 0.43 g/L per day on day 9, which was 2.3 times higher than the initial productivity obtained by biomembrane surface cultivation without corn straw. An analysis on the mechanism suggested that corn straw shortened the fermentation period by providing the support for the growth of P. novae-zelandiae spores and biomembrane formation. Amino acids, including phenylalanine and tyrosine, released by corn straw, were the key reason for the improvement in the pigment yield. In addition, the increase of reducing sugars in the fermentation broth, due to the hydrolysis of cellulose and hemicellulose by the hydrolytic enzymes secreted by P. novae-zelandiae, provided a carbon source for fungal growth that might also be beneficial to pigment production.