Hwanmyeong Yeo

Organosolv pretreatment with various catalysts for enhancing enzymatic hydrolysis of pitch pine (Pinus rigida)

Three different types of catalysts were evaluated for organosolv pretreatment with pitch pine (Pinus rigida). Sulfuric acid, magnesium chloride, and sodium hydroxide for acid, neutral and base catalysts, respectively, were used, and ethanol was the organic solvent. The pretreatment process was conducted at different temperatures and times. The enzymatic hydrolysis process followed to estimate the digestibility of the biomass. The digestibility of pitch pine by pretreatment process with 1% sulfuric acid at the optimal condition was approximately 55-60%, and that by 1% magnesium chloride was nearly 60%. The pretreatment with 1% sodium hydroxide had no effect on digestibility at 10%, but the digestibility improved by more than 80% when the concentration was increased to 2%. Theoretical ethanol yield was the highest at organosolv pretreatment with sulfuric acid at 70% and the lowest with sodium hydroxide at 45%.

Comparison of pyrolytic products produced from inorganic-rich and demineralized rice straw (Oryza sativa L.) by fluidized bed pyrolyzer for future biorefinery approach.

The objectives of this study were to investigate the effects of inorganic constituents on the fast pyrolysis of the biomass and to determine the yields as well as physicochemical properties of pyrolytic products. The pyrolytic products were obtained from raw and demineralized rice straw using a fluidized bed type pyrolyzer at different temperatures. As pyrolysis temperature increased, total biooil yield gradually decreased from 46.6 to 29.6 wt.% for the raw-straw, and from 55.4 to 35.3 wt.% for the demineralized rice straw. For demineralized rice straw, higher pyrolysis temperatures promoted gasification reactions but reduced char formations. However, char yield for the raw-straw was relatively unaffected by temperature due to an increase in carbonization reactions that were catalyzed by some inorganics. Certain inorganic constituents in the biomass were distinctively distributed in the biooil, and ICP-ES and GC/MS analysis indicated that some inorganics may be chemically bound to cell wall components.

Some considerations in heterogeneous nonisothermal transport models for wood: a numerical study

This study compares a number of coupled heat and mass transfer models and presents numerical comparisons of phenomenological coefficients between the four models (Stanish, Perre, Pang, and Avramidis) that are most frequently used in the literature to describe wood-drying processes. The USDA sorption isotherm, the Hailwood-Horrobin model, was adopted to calculate the relations between moisture content in wood and water vapor pressure at any temperature. Due to different assumptions about the driving forces of heat and mass transfer, coefficients in each model represent different values for moisture content and temperature and are closely related to each other. In the case of isothermal mass transfer, the moisture diffusion coefficient in the transverse directions from the Stanish and Pang models increased with decreasing moisture content. This contradicts the Avramidis and Perre models and numerous experimental results. Thermal diffusion effects on the drying process may not be predominant because the nonisothermal state is relatively short. Therefore, the Perre model, which does not consider the thermal diffusion effect, has been used successfully in the drying simulation. However, it may be erroneous in certain cases when the nonisothermal state prevails over the system, such as building physics. The Pang model cannot explain the phenomena of thermal diffusion and moisture thermodiffusion. It might be reasonable to modify the thermal diffusion of the Avramidis model, which is lower than that of the Stanish model. The apparent heat diffusivity was higher than the true heat diffusivity.

The effect of openings on combined bound water and water vapor diffusion in wood

This study was undertaken to estimate the effect of openings between cell walls on combined bound water and water vapor diffusion in wood. Using a newly developed model, the radial and tangential moisture diffusion coefficients can be predicted depending on the opening area. The new model explicitly involves a term for water vapor diffusion through the openings, as well as a term for the combined diffusion of bound water and water vapor. A classical model developed by Stamm and Choong had higher longitudinal moisture diffusion coefficients than that in the parallel model at higher moisture content, which is inconsistent with the Wiener bound rule. The new model suggested in this article is useful for analyzing the experimental results and understanding the variability of the diffusion coefficients.

Shear Performance of PUR Adhesive in Cross Laminating of Red Pine

Cross laminated timber (CLT) has been an rising issue as a promising building material replacing steel-concrete in mid story rise construction. But, there was no specific standard for CLT because it had been developed in industrial section. Recently, new draft for requirements of CLT was proposed by EN which suggested to evaluate the performance of adhesive in CLT by the same method as glulam. But, it has been reported that shear performance of cross laminated timber is governed by rolling shear. There- fore, block shear tests were carried out to compare parallel to grain laminating and cross laminating using commercial one component PUR (Poly urethane resin). The result showed that the current glulam standard for evaluating bonding performance is not appropriate for CLT. Beacause shear strength of cross lami- nating decreased to 1/3 of parallel to grain laminating and this strength was representing shear performance of wood itself not the bond. However, cross laminating showed no significant effect on wood failure. Thus, wood failure can be used as a requirement of CLT bonding. Based on the results, cross laminating effect should be included when evaluating adhesive performance of CLT correctly and should be con- sidered as an important factor.

Effect of Outer Surface Sealing Treatment on the Reduction of Surface Check Occurrence During the Drying of Center-Bored Round Timber

A significant amount of time and energy is required to dry green timber with a large cross-section. Due to long-lasting internal moisture gradients, internal stress is high during the drying of large cross-sectional timber, and the potential for check occurrence is significant. Although many researchers have aimed to develop a method for drying large pieces of wood without the occurrence of drying defects, a procedure for rapidly drying wood without cracks has not yet been developed. In the present study, an outer surface sealing method and center-boring process (i.e., drilling a hole along the central longitudinal axis) was developed to dry timber with a large cross-section without the occurrence of checks. The proposed center-boring procedure reduces the movement of heat and moisture inside the wood and expedites the drying process by sustaining a small MC gradient. Moreover, the outer surface sealing treatment changes the drying stress direction and controls check occurrence. By kiln drying center-bored (80-mm diameter) and outer-surface-sealed round timber pitch pine (Pinus rigida) with an initial MC of 30% and an outer diameter of 140 mm, a final MC of 6% was obtained within 40 hours without the occurrence of any drying defects.

The shrinkage properties of red pine wood assessed by image analysis and near-infrared spectroscopy

ABSTRACT This work focused on the shrinkage and drying stress of red pine (Pinus densiflora) wood during kiln drying and investigated transverse shrinkage and moisture changes in thin specimens using digital image analysis and near-infrared spectroscopy, respectively. The effect of specimen thickness, which ranged from 1 to 10u2009mm on shrinkage, was analyzed under drying conditions with restrained stresses. The shrinkage due to moisture content was presented in the form of an exponential function and a linear function above and below the fiber saturation point, respectively. A shorter existence of the moisture gradient increased the transverse shrinkage. The tangential and radial shrinkage at the tissue level in 30-µm (longitudinal) thick slices was measured and compared with the shrinkage of above specimens with difference thicknesses. The transverse shrinkage of 1-mm-thick specimen is similar to the shrinkage measured using 30-µm-thick slice.

Classification of the conductance of moisture through wood cell components

This study aimed to clarify the conductance of moisture through wood cell components. Moisture diffusion coefficients were determined from three models (Stamm, Siau, and Kang et al.) and cell wall, pit, and ray dimensions were experimentally observed in a wood specimen. Fractions of moisture diffusing along each path in each of the models were analyzed. As moisture content decreased, the fraction of water diffusing as bound water through cell walls in tangential and longitudinal directions decreased while water vapor diffusion through lumens and pits became more dominant. Diffusion coefficients predicted by each model were compared with experimental values. Although predicted values differed from experimental values, predicted trends for diffusion rate dependence on moisture content were similar to the experimental results. In particular, the models of Stamm and Kang et al., which consider moisture transport through rays and pits, show a very consistent trend for transverse diffusion, which is always faster radially than tangentially. Input of more accurate dimensions of cell walls and cavities into the models should result in more reliable values, closer to the experimentally determined diffusion coefficients.

Effect of heat treatment temperature and time on sound absorption coefficient of Larix kaempferi wood

Heat treatment improves the dimensional stability and hydrophobicity of wood, and heat-treated wood is currently attracting attention as a new interior material. However, there are few evaluations where the acoustic properties of heat-treated wood are reported when such wood is used as an interior material. In this study, Larix kaempferi wood, typically used as a building material, was heat-treated at 200, 220, and 240xa0°C for 9, 12, 15, and 18xa0h. The sound absorption coefficients of the treated wood samples were measured at 250, 500, 1000, 2000, and 4000xa0Hz in a reverberation room. The sound absorption coefficient increased with the treatment temperature and the treatment time. The results of this study showed that the high-frequency band range sound absorption coefficient of wood can be increased dramatically by heat treatment.

The effect of controlling the drying distortion of laminas on the production yield of cross-laminated timber (CLT) using Larix kaempferi wood

AbstractThe objective of this study was to evaluate the effect of lamina distortion control on the production yield of cross-laminated timber (CLT) using domestic larch (Larix kaempferi) wood. The measured production yield of CLT was 27xa0%. The yields based on log volume of sawing, planing, cross-cutting, and finish planing of CLT were 49, 66, 96, and 86xa0%, respectively. The yield of sawing and planing can be improved by controlling distortion during drying. Using an experimental enforced-loading apparatus, the cup and twist of laminas were reduced by 50 and 90xa0%, respectively. To analyze the effect of a reduction in sawing dimensions on the final production yield of CLT, an analysis of a geometrically applied sawing pattern of logs was used to predict the sawing yield and the number nof laminas after sawing. The geometrical analysis showed that a change in the sawing dimensions affected the production yield of CLT. If the width and thickness of the sawing dimensions can be reduced by 5xa0mm by decreasing the distortion of lamina during drying, the sawing yield was unchanged (49xa0%), but it was expected that the number of laminas after sawing would increase from 278 to 303. It was also predicted that the production yield of CLT would increase from 27 to 32xa0%.