Shigehisa Ishihara

Analysis of chemical structure of wood charcoal by X-ray photoelectron spectroscopy

Wood charcoal carbonized at various temperatures was analyzed by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffractometry to investigate the changes of chemical structures during the carbonization process. From the infrared spectra, the carbon double bonds and aromatic rings were seen to form at a carbonization temperature of about 600°C. From the XPS spectra, the ratio of aromatic carbons increased in the temperature range 800–1000°C and over 1800°C. The condensation of aromatic rings proceeded as carbonization progressed. The drastic reduction of electrical resistivity of charcoals was observed in almost the same temperature range. It was found that the condensation of aromatic rings had some relation to the decline in electrical resistivity. Wood charcoal carbonized at 1800°C was partly graphitized, a finding supported by the results of X-ray diffraction and XPS. The functional groups containing oxygen diminished with the increase in carbonization temperature.

Adsorption capacities and related characteristics of wood charcoals carbonized using a one-step or two-step process

Sugi (Cryptomeria japonlca D. Don) wood powder was carbonized at varying temperatures by a onestep process up to 1000‡C and a two-step process using wood charcoal as the raw material up to 1600‡C. This study was conducted to evaluate the adsorptive properties of wood charcoal and discuss the mechanism of its adsorptive function in relation to the physical and anatomical characteristics of wood after carbonization. Anatomical characteristics of carbonized wood materials were directly observed under heating using an environmental scanning electron microscope (ESEM); the cell wall structures were analyzed by high-resolution transmission electron microscope (HRTEM). The largest weight losses were observed at the highest temperatures, in both the one-step and twostep processes but leveled off above 800‡C. Shrinkages in the tangential, radial, and longitudinal directions increased with carbonization temperature, peaking at 1000‡C. Direct observations by ESEM showed distinct shrinkage at around 400‡C. The first trial observations by HRTEM on the changes in the ultrastructure of cell walls of wood charcoals were done, and it was assumed to affect the formation of micropores. Adsorption was found to follow the Langmuir isotherm model. With the one-step carbonization process, the iodine adsorption capacities of the carbonized wood powders increased with increasing carbonization temperature, peaking at 800‡C, but decreased at higher temperatures. The wood powder carbonized at 1000‡C with the two-step process showed the highest capacity, but further heating up to 1400‡C drastically decreased the adsorption. The shrinkage of cells was related to the increases and decreases in its specific surface area. Specific surface area and total pore volume were evidently related to the adsorptive properties.

Thermal constants of wood during the heating process measured with the laser flash method

The thermal diffusivity, specific heat, and thermal conductivity of 13 species of wood were measured by means of the laser flash method to investigate the thermal properties of wood during the heating process. The temperature ranged from room temperature to 270°C in air or under vacuum. The thermal diffusivity varied little during the heating process up to 240°C. The values in air were larger than those under vacuum. There was a linear relation between the specific heat and the ambient temperature, and the specific heat under vacuum was larger than that in air at high temperature. The thermal conductivity increased with density and the ambient temperature. To discuss the effects of the atmospheric conditions on the thermal constants of wood, a theoretical model of thermal conductivity was proposed and its validity examined, where the wood was assumed to be a uniformly distributed material composed of cell walls and air.

Removal of mercury and other metals by carbonized wood powder from aqueous solutions of their salts

Sugi (Cryptomeria japonica D. Don) wood powder was carbonized at varying temperatures and used as a material to remove heavy metals from their aqueous solutions. Single solutions of mercuric chloride and mixed aqueous solutions containing lead nitrate, arsenic chloride, and cadmium chloride as well as mercuric chloride (1, 5, and 10 ppm) were prepared to determine the efficiency of removing heavy metals by these materials. Wood powder and carbonized wood at 200°, 600°, and 1000°C removed mercury within the concentration range 1–10ppm; mercury was preferentially removed even when mixed with other heavy metals. Wood powder carbonized at 1000°C achieved the best removal of heavy metals among the wood-based materials and even commercial activated carbon in both single and mixed solutions.

Functionally graded wood in fire endurance with basic nitrogen compounds and phosphoric acid

Fire-retardant wood treatment with fire-retardant chemicals consisting of basic nitrogen compounds and phosphoric acid have been thoroughly examined. The fire retardance and endurance of wood were influenced by the treatment method. Here two treatment methods were compared, heat-pressed treatment method improved these qualities more than heat-dried treatment method. Furthermore, to gain lasting fire retardance, it was considered necessary to react basic nitrogen compounds and phosphoric acid with formaldehyde as in the dicyandiamide-formaldehyde-phosphoric acid or melamine-dicyandiamide-formaldehyde-phosphoric acid system. In the treated wood, the concentration of chemicals gradually decreased as it approached the center. The functional fire retardance could be graded in accordance with the chemical content.

Adsorption of mercury by sugi wood carbonized at 1000°C

The ability of sugi wood carbonized at 1000°C to adsorb mercury was examined using aqueous solutions of mercuric chloride. Parameters studied include contact time, pH, adsorption temperature, and initial concentration of mercury in solution. Results showed that sugi wood carbonized at 1000°C could effectively remove mercury from aqueous solutions. The carbonized wood showed high adsorption ability for mercury at a wide pH range (pH 3–9), but its ability drastically decreased at pH 11. Adsorption decreased with increases in adsorption temperatures, indicating that the processes were exothermic in nature. Adsorption was found to follow the Freundlich isotherm model. The adsorption capacity of carbonized sugi wood was comparable to that of commercial activated carbon.

Improving fire retardancy of fast growing wood by coating with fire retardant and surface densification

Fire retardant fast-growing wood product was developed by coating with fire retardant and densifying the surface of wood. Trimethylol melamineformaldehyde resin mixed with phosphoric acid was coated on the wood surface, preheated and followed by hot pressing. Effects of the amount of coating, preheating temperature, and densifying ratio on the fire retardancy of sugi (Cryptomeria japonica D. Don) wood, and pressing temperature and pressing time on that of albizia (Paraserianthes falcataria Becker) wood were discussed. Bending strength, creep performance under fire and fire retardancy were evaluated. The results showed that the treatments improved the fire retardancy of woods without reduction in the bending strength.

Improvement of fire retardancy of plywood by incorporating boron or phosphate compounds in the glue

A practical approach to enhancing the fire retardancy of wood-based materials by adding fire-retardant chemicals to the glue was developed. Plywoods were manufactured using urea melamine formaldehyde resin mixed with ammonium pentaborate or dihydrogen phosphate. Treated plywoods had better incombustibility than untreated ones. X-ray photoelectron spectroscopy (XPS) analysis clearly demonstrated the distribution of boron and phosphorus, which had migrated from the glue to the wood, contributing to better fire retardant properties. The cross-sectional micrographs from scanning electron microscopy showed that untreated specimens exhibited a foamy structure near the interface in the glue layer and the deformed structure of wood cells. The cell structure and cell wall thickness retained intact in the specimens treated with urea melamine formaldehyde resin mixed with ammonium pentaborate or dihydrogen phosphate. When observing the effect of the thickness of overlay veneers on incombustibility, a shorter glowing time was obtained from the specimens with a thicker surface layer when the fire retardant chemical was added at 2%, but the differences were smaller at the higher chemical retention of 4%. A similar tendency was observed for the char length.

The functionally graded wood observed from chemical and thermal perspectives

The fire retardance of wood treated with basic nitrogen compounds and phosphoric acid is improved. It was investigated which chemicals were suitable for the fire retardant treatment of wood and how chemicals influenced fire retardance and endurance from the perspective of chemical reaction and also it was investigated how chemicals and treatment methods influenced fire retardance and endurance from a thermal perspective. Although the fire endurance was improved by a heat-pressed treatment method, the chemical reaction was carried out by heat irrespective of the pressing or drying method. The wood structure would become complex as the cross-linked structure occurred by chemicals and pressure. Its structure would be maintained at combustion. Fire endurance of wood is shown to be related to a cross-linked structure created by a chemical and/or physical reaction rather than thermal factors related to the carbonized product.

The functional gradient of fire resistance laminated board

Although the fire resistance of wood depends on its dimensions, it needs a lot of time and energy to fire retard thick wood On the other hand, it is easier and takes less time and energy to treat thin materials. The fire resistance of wood was improved by compressed treatment, even untreated wood, and moreover compressed wood loaded with chemicals was improved more. Fire resistance of a laminated board was the same as a solid compressed board, and also fire resistance of a laminated board which was arranged with compressed thin wood on two sides of untreated wood showed similar fire endurance. A laminated lathe veneer board showed better fire resistance than solid untreated wood and a laminated board with treated veneers arranged concentratively showed better fire resistance than it did when arranged dispersively. So it was judged that it was important to retard fire ignition and to form a carbonized layer effectively in a fire by physical and chemical treatment, especially on the surface of a material.