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The effective utilization of the inner part of oil palm trunk (OPT), generally considered a waste product, is desired. In this study, particleboards were manufactured using the inner part of OPT with a bio-based adhesive made of sucrose and ammonium dihydrogen phosphate (ADP). The mixture ratio of sucrose to ADP and the resin content were changed to investigate the optimum condition of the adhesive. The pressing condition was set at 180 °C for 10 min, and the target density was 0.8 g/cm3. The optimum mixture ratio of sucrose to ADP was 80:20, and the optimum resin content was 20 wt%. The manufactured boards had modulus of rupture (MOR) and modulus of elasticity (MOE) in bending values of 16.4 MPa and 4.3 GPa, respectively. The internal bond strength (IB) was 1.85 MPa, and the thickness swelling (TS) was 9.6%. This indicated that the constructed particleboard was comparable to the 13 types of JIS A 5908 standard (2003). In addition, the particleboard had good termite and decay resistance, similar to those of OPT particleboards made with synthetic adhesives. It was clarified that excellent particleboard could be manufactured from the inner part of OPT and a bio-based adhesive made of sucrose and ADP.

Citric acid was utilized as a bonding agent in the production of Sembilang bamboo particleboard. The limitation in using bamboo for particleboard production is that the silica content in bamboo skin can accelerate particleboard processing machines' bluntness and reduce particle adherence in particleboard manufacturing. This research aimed to investigate the influence of bamboo skin and citric acid content on the characteristics of Sembilang bamboo particleboard. Particleboards were prepared using bamboo particles (type A) and unskinned bamboo particles (type B). The citric acid solution (59%) was sprayed over the surface of bamboo particles to obtain three different levels of citric acid, i.e., 15, 20, and 25 % (based on bamboo particles’ dry weight). The Sembilang bamboo particleboards were manufactured using a hot-pressing machine at 200°C, 5 MPa for 10 min. The particleboard targeted density was 0.8 g/cm3. The type B particleboards’ internal bond (IB), modulus of rupture (MOR), water absorption (WA), and thickness swelling (TS) were superior compared to the type A particleboards. This was influenced by the lower concentration of silica in type B particleboards, which tend to allow an intimate contact area among particles and citric acid then produced better quality particleboards compared to type A particleboards. The type B particleboards met the obligation of JIS A 5908 for type 18 particleboard in terms of modulus of rupture, modulus of elasticity, and internal bond, however, only fulfilled the type 8 particleboard in terms of screw holding power. The physical properties of Sembilang bamboo particleboard were also improved when using type B bamboo particles and adhered with citric acid at a level of 25%.

This study investigated the effects of adding ammonium dihydrogen phosphate (ADP) on the physical and chemical changes of a water-soluble extract of the inner part of oil palm trunk (OPT) to clarify the bonding mechanism of the binderless particleboard. The extract’s effect on ADP-added binderless particleboard was also investigated. OPT particles were treated by hot water at 60 °C for 6 h. Water-soluble extract and treated OPT particles were obtained. ADP was added to the water-soluble extract at 0, 10, and 40 wt%, and the mixtures were heated at 180 °C for 10 min. Furthermore, binderless particleboards using the treated particles were manufactured with similar condition. The 10 wt% ADP mixture changed the water-soluble extract to an insoluble substance, which was twice that of with 0 wt.% ADP addition. Infrared spectroscopy revealed peaks of furan and carbonyl in the insoluble substance. This indicated that the free sugar content in the water-soluble extract would change to furan compounds. Thermal analysis revealed that the resulting insoluble substance had good thermal stability, suggesting a high-molecular-weight substance. The insoluble substance would contribute to bonding of the binderless particleboards. In particular, a significant contribution to the water resistance was observed.

Prohydrojasmon (PDJ), a synthetic derivative of the plant hormone jasmonic acid, has been identified as a plant growth regulator used in various fruit and rice seedlings. In this study, we demonstrate the inhibition of transpiration by PDJ in the indica rice cultivar cv. Takanari compared with commercially available microcrystalline and paraffin wax agents in a greenhouse. Microcrystalline and paraffin wax agents inhibited approximately 30%–50% transpiration 3 h after application, and the inhibition lasted for seven days after treatment, depending on the concentration and the agent used. In contrast, PDJ inhibited approximately 40%–80% transpiration compared with control 0.5 h after treatment, and the effect lasted for one day. However, the effect almost disappeared 7 days after treatment. Thus, PDJ affects transpiration differently than commercially available products and could be used to lower excess transpiration in rice, specifically when an early, transient, and reversible inhibition is needed.

In the flow forming technique of wood, a wood block is flowed into metal dies to mold the material into a three-dimensional complex shape. The purpose of this study was to investigate the effect of molding load and the mechanical properties of the molded material in the case that wood as a raw material was irradiated with electron beam (EB). The EB-irradiated wood board was impregnated with thermosetting resin and was subsequently molded into the material by adding pressure and heating in a closed metal die. It was found that the molding load of the impregnated wood was decreased with increasing the EB absorbed dose. The mechanical properties of the molded material were evaluated using modulus of elasticity (MOE) and modulus of rupture (MOR) in a three-point bending test. With increasing EB dose, MOR decreased greatly, while MOE decreased slightly. The EB irradiation on raw wood made it possible to mold the material at low load, though higher dose irradiation caused larger decreases in the mechanical properties.

NO2 sorption ability of cedar (Cryptomeria japonica) timbers was evaluated using a new measuring system that was developed in our previous study. Four drying conditions were applied, namely natural drying and three kinds of kiln-drying at 45, 60, and 105 °C. Aeration experiments were conducted using discoid specimens which had a thickness in the longitudinal direction of 1.5 mm, and a diameter of 10 mm. The moisture content was conditioned to 0 or 9 ± 1.0% in each drying condition. As a result, the NO2 sorption ability declined as the drying temperature increased. Based on the analysis of extractives, it was shown that the extractives content had a high correlation with the contribution ratio of extractives in the NO2 sorption volume of the specimens that were dried below 60 °C. Therefore, it was elucidated that the specimen dried naturally has the greatest NO2 sorption ability. Furthermore, the result of the gas chromatography–mass spectrometry (GC/MS) indicated that abietadiene influenced the NO2 sorption ability. Also, the NO2 sorption volume was high especially at the initial stage, which is higher under the condition with moisture.

Prohydrojasmon (PDJ) is a synthetic derivative of the plant hormone jasmonic acid (JA), which is used in apples, grapes, and mandarin oranges as a plant growth regulator. Here, we show that irrigation of PDJ could prevent spindly growth of rice seedlings in both indica and japonica cultivars. PDJ also inhibited root elongation in hydroponically growing seedlings in various cultivars. The higher dry root weight following PDJ application than the controls was observed in two japonica cultivars. Furthermore, its reduction was slight in comparison with the inhibition of root elongation. Starch degradation in the endosperm of seedlings grown in PDJ solution was slower than those grown in the control. The inhibition of root elongation could be mediated by the combined application of PDJ and appropriate concentrations of a synthetic auxin, NAA (1-Naphthaleneacetic acid). Additionally, we generated transgenic rice carrying sGFP driven by the PBZ1 promoter, a marker gene for abiotic and biotic stress responses. The expression of PBZ1p::sGFP was induced by PDJ treatment in the roots and seeds. PDJ could be used as a plant growth regulator to prevent spindly growth and to induce stress responses in rice seedlings.

The effective use of agricultural residues is desirable. In this study, the manufacturing of mouldings using sweet sorghum bagasse powder and citric acid as an adhesive was attempted. The effects of the application method and citric acid content on the bending properties and water resistance of the mouldings were investigated. Powder and liquid applications were used. The citric acid solid content based on the total weight of the mouldings was adjusted to 0, 15, 20, 25, and 30 weight percent. The dumbbell-shaped moulding was manufactured at 200°C and 4 MPa for 10 minutes. The relationship between the bending properties and citric acid content differed depending on the application method; the powder application was effective for obtaining high bending properties with a lower citric acid content. The water resistance of the moulding was greatly affected by the application method when a low citric acid content was used, and it was affected by the citric acid content when a high citric acid content was used. According to the data measured from Fourier-transform infrared spectroscopy, it was easy to contain unreacted citric acid in the moulding with the powder application, and an ester linkage formed easily when the liquid application was used. It was suggested that the citric acid tends to work as an adhesive in the powder application, and it tends to modify the bagasse powder in the liquid application.

In sucrose/citric acid based wood adhesive, the detailed bonding mechanism has still been unknown. Here, we investigated the detailed chemical structures of this adhesive wood (Japanese cedar)-based molding by using heteronuclear single quantum coherence–nuclear magnetic resonance (HSQC-NMR). NMR peaks associated with the furan-type structure appeared, suggesting that the furan compound was formed from sucrose and converted to a furan polymer during the adhesive process and that some of the furan structures in the polymers were ester-bonded with citric acid. The secondary forces between the furan polymers and wood components were thought to contribute to the adhesive effect. In our analysis of the interphase structure, primary hydroxyl groups of both polysaccharides and of lignin substructures were found to be esterified with citric acid. Additionally, some of the glycosidic bonds in polysaccharides were cleaved during the acidic condition produced by citric acid. The above results provided evidence of the polymerization of sucrose-derived 5-HMF, the esterification of wood components, and the degradation of polysaccharides during the molding process. Citric acid functioned as a clamp between the obtained furan polymer and the wood components. The sucrose/citric acid based wood adhesive can be defined as a hybrid-type wood adhesive, involving both secondary forces and chemical bonding interactions.

In sucrose/citric acid based wood adhesive, the detailed bonding mechanism has still been unknown. Here, we investigated the detailed chemical structures of this adhesive wood (Japanese cedar)-based molding by using heteronuclear single quantum coherence–nuclear magnetic resonance (HSQC-NMR). NMR peaks associated with the furan-type structure appeared, suggesting that the furan compound was formed from sucrose and converted to a furan polymer during the adhesive process and that some of the furan structures in the polymers were ester-bonded with citric acid. The secondary forces between the furan polymers and wood components were thought to contribute to the adhesive effect. In our analysis of the interphase structure, primary hydroxyl groups of both polysaccharides and of lignin substructures were found to be esterified with citric acid. Additionally, some of the glycosidic bonds in polysaccharides were cleaved during the acidic condition produced by citric acid. The above results provided evidence of the polymerization of sucrose-derived 5-HMF, the esterification of wood components, and the degradation of polysaccharides during the molding process. Citric acid functioned as a clamp between the obtained furan polymer and the wood components. The sucrose/citric acid based wood adhesive can be defined as a hybrid-type wood adhesive, involving both secondary forces and chemical bonding interactions.

Wood-based materials are used for construction and furniture etc. The demand is expected to increase due to population growth and economic development. Wood-based materials are considered as sustainable material because wood is the main raw material. However, adhesives are indispensable when manufacturing those, and almost wood adhesives are made from chemicals derived from fossil resources. In recent years, breaking away from dependence on fossil resources has become an important global issue. One of the purposes of this work is to develop bio-based adhesives with simple preparation, low dependence of fossil resources and high adhesiveness. Novel bio-based adhesives using citric acid and/or sucrose are being researched. On the other hand, considering significant decrease of global forest area, alternative raw components for wood-based materials is desperately needed in the future. Un-utilized lignocellulosic biomass such as agricultural wastes would be promising for these. The utilization of agricultural wastes also contributes to carbon fixation of lignocellulosic biomass. Now, researchers at the Laboratory of Sustainable Materials are interested in developing new wood-based materials that combine agricultural wastes with bio-based adhesives. These efforts will make wood-based materials more sustainable and environmentally friendly.

Thermal flow molding of wood powder was carried out with a natural binder consisting of sucrose and citric acid (SC binder) for fabricating wood products without synthetic resins. The testing of thermal flow and molding of the wood powder with SC binder was done to analyze the effect of added SC binder, as well as to optimize the molding conditions, such as temperature, binder content, and mixture ratio of the sucrose and citric acid. The wood powder with SC binder flowed successfully at an optimum temperature of 180 °C in the thermal flow test. In addition, it was possible to form a composite wood plate by molding with thermal flow, and the moldability was improved by increasing the sucrose ratio in the SC binder. Density, bending strength, and thickness swelling after water immersion of the plate molded under the optimum molding conditions were 1.4 g/cm3 to 1.5 g/cm3, 28 MPa to 37 MPa, and 7% to 10%, respectively. These results indicated a possibility

The efficacy of particleboards manufactured with sodium fluoride against mold fungi and Hylotrupes bajulus (L.) larvae was tested. Laboratory-size particleboards were manufactured from untreated wood particles with inclusion of fine sodium fluoride (NaF) at the 1, 1.5, and 3% levels relative to total particle weight. Sodium fluoride was introduced as powder during the manufacturing process just before blending resin with wood particles. The laboratory mold test indicated that even the lowest level of retention of NaF with or without leaching significantly reduced mold growth on particleboard surfaces when compared to the untreated control specimens. The increased retention of NaF from 1% to 3% further suppressed mold growth towards lowest levels even on leached specimens. The laboratory Hylotrupes bajulus larvae tests revealed that the particleboard environment with or without NaF is not appropriate for larvacidial activity. While the tested biocide, NaF, tested positive against mold growth on particleboard surfaces, no effect was determined relative to larval deaths. RISH, Kyoto University The first author extends his appreciation to RISH, Kyoto University for supporting his stay under the Visiting Professor program between 1 April and 29 September 2016. WOS:000511129100004 2-s2.0-85088274650

This study focused on the effect of an extractive treatment and the application of citric acid on the properties of particleboard made from Salacca frond. In general, extractives have a negative effect on the bondability of synthetic resin. However, the effect of extractives on the bonding mechanism of citric acid as the biobased adhesive is unclear. Unextracted and extracted Salacca frond were used as the raw materials. A hot water extractive treatment was conducted by boiling the particles for 2 h. The boards were manufactured under the following conditions: citric acid content of 0%; 10%; 20% weight percent (wt%), pressing temperature of 180 °C, and pressing time of 10 min. The target density was set at 0.8 g cm-3. The results showed that the addition of citric acid resulted in an increase in the physical and mechanical properties of the particleboard. Interestingly, when a 20% citric acid content was applied, there were no siginificant differences in the physical or mechanical properties of the particleboards made from unextracted and extracted particles. Based on these results, it was concluded that when citric acid is used as adhesive, the hot-water extractive treatment of Salacca frond is not needed.

WOS: 000428487200012 Several formulations of wood-plastic composites and a particleboard were fabricated with combining zinc borate biocide at different retention levels during the manufacturing process. The treated specimens were exposed to a field test under protected above ground conditions for 7 years in southern Japan. During biannual inspections, the specimens were visually inspected and graded for decay and Formosan subterranean termite damage. While zinc borate retention levels tested were able to protect the particleboards from decay activity for 7 years, their efficacy was lower against termite attack. The retention levels tested up to 2% (w/w) helped to reduce termite damage noticeably but failed from full protection (e.g. rating 10) indicating higher zinc borate loadings are required in particleboards if they will be utilized in southern Japan climatic conditions. Wood-plastic composites were also more durable against fungal damage during the 7 years exposure period but this condition seems changed last 18 months since some lower decay ratings were recorded even for zinc borate embedded formulations. While termite destruction diminished significantly with zinc borate integrated formulations, higher retentions might be recommended as threshold for full protection in wood-polypropylene composites.

We developed a new system for measuring the NO2 sorption ability of Japanese cedar (Cryptomeria japonica) wood by referring to Japanese Industrial Standard for JIS R 1701-1 (Test method for air purification performance of photocatalytic materials, Japanese Standard Association, Tokyo, 2004). Aeration experiments were conducted using plated specimen, particle specimen, discoid specimen and wood powder with consideration of aeration condition and surface area which can contact with NO2 gas. In the plated specimen, the NO2 sorption ability was greatly affected by the thickness of longitudinal direction, and high NO2 sorption ability of the transverse section was observed within a thickness range from the surface to ca. 3 mm. The average NO2 sorption volume for discoid specimen for 5 h was approx. five times larger than that those for the plated and particle specimens, which the thickness of longitudinal direction was 1.5 mm. This means that the NO2 sorption effect was especially high under the condition where the NO2 gas passed through tracheid. Also, it was suggested that the interface area between NO2 gas and specimen influenced to the NO2 sorption ability. Furthermore, it was confirmed that the NO2 sorption volume in discoid specimen and the grain size below 0.25–0.50 mm of wood powder reached the greatest.

Citric acid has been investigated as a good adhesive for particleboard. This research studied the effect of starch addition on the properties of citric acid-bonded particleboard. Starch provides hydroxyl groups that can react with the carboxyl group in citric acid. Three kinds of starches were used in this research, i.e. corn, ganyong (Canna edulis Ker-Gawl), and garut (Maranta arundinacea L.) starches. Petung (Dendrocalamus sp.) bamboo particles were used as raw material. The mixture ratios of citric acid/starch were set at 100/0, 87.5/12.5, and 75/25 (w/w), while the resin content was set at 30 wt.% based on air-dried particles. The boards were then manufactured under pressing conditions of 180 °C for 10 min. Based on the physical and mechanical properties of the particleboards, it was concluded that the addition of starch tended to enhance the mechanical properties, while decreasing the physical properties of the boards. An addition of 12.5 wt.% starch in citric acid was the optimum resin ratio for manufacturing bamboo particleboard. Maranta and canna starches provided higher mechanical properties compared to corn starch. A FTIR analysis clearly showed that the intensity of carbonyl groups increased with increasing of starch content, which indicated that crosslinking between starch and citric acid occurred.

WOS: 000416255500012 The feasibility of sodium fluoride (NaF) incorporation as a biocide in the manufacture of particleboard was examined. Laboratory-scale particleboards prepared from untreated wood particles were incorporated with NaF powder at target retentions of 1, 1.5 and 3% of the total particle weight. An in-line treatment method was used to introduce the biocide during the blending stage just before adhesive application. Standard static bending and water resistance (water absorption and thickness swelling) tests indicated that embedding of the powder biocide up to the 3% level did not cause any detrimental effects on mechanical and physical properties. The laboratory decay and termite resistance tests showed that even the lower retention levels of 1 and 1.5% NaF were enough to suppress fungal and termite activity and significantly reduce the mass loss and consumption rate values of the specimens when compared to the untreated controls. Spectrophotometric analysis of leachate waters and the mass losses of the leached specimens revealed the tendency of the NaF to be depleted from the composite specimens. Therefore, the tested biocide was found to be appropriate for interior or protected above-ground outdoor exposure conditions. RISH, Kyoto University The first author extends his appreciation to RISH, Kyoto University, for support under the Visiting Professor program between April 1 and September 29, 2016, and to Mr. Akio Adachi for specimen preparations and Ms. Nuriye Peaci for English proofreading of the manuscript.

This study has focused on solute diffusing into cell walls in solution-impregnated wood under conditioning, process of evaporating solvent. The amount of the diffusion is known to be determined by the solute diffusivity and the solute-concentration difference between cell walls and cell cavities. Purpose of this paper was to clarify the effect of temperature only on the solute diffusivity that is directionally related to the thermal vibration of the solute molecule. The cross-cut block of hinoki (Chamaecyparis obtusa), polyethylene glycol (PEG1540), and water was employed as wood sample, solute, and solvent, respectively. The sample impregnated with a 20 mass% solution was conditioned at 20, 35, or 50 °C to finish the solute diffusion evaluated using the dimension of the sample that was conditioned followed by drying in a vacuum. To unify the solute-concentration difference, for all temperatures, the equilibrium moisture content was unified and the solvent-evaporation rate was controlled in three ways during conditioning. The solute diffusivity was higher in order of 35, 50, and 20 °C, which was evaluated by the solute diffusion at the same evaporation rate. It is clarified that the diffusivity increases with increasing the dimension of cell walls rather than with increasing the thermal vibration of solute molecule.

Converting biomass waste to high value-added product, such as biocomposite, tends to attract the interest of researcher and industry. Reducing the utilization of synthetic resin adhesives becomes one of the important points, considering the safe global environment. Binderlessboard is a product whose bonding depends mainly on the chemical composition of the raw materials. The aim of this research was to develop bio-based composites made from bamboo biomass waste materials. This report focused on the physical and mechanical properties of the particleboards. To improve the properties of the boards, the possibility of using citric acid was investigated and discussed. Petung bamboo particles (Dendrocalamus asper Backer) were used in this research. The contents of citric acid were ranged in 0% (binderlessboard), 10%, and 20% based on dried particles. The dimension of the boards was 25 x 25 x 0.7 cm, with the target density was 0.9 g/cm3. The particleboards were hot pressed at 200ºC and 220ºC for 10 and 15 min. The physical and mechanical properties of those particleboards were then evaluated based on Japanese Industrial Standard A 5908 for particleboard. The results showed that the physical and mechanical properties of the boards improved significantly by adding the citric acid. The bamboo particleboards obtained had good properties, with the spesific IB, specific MOR and specific MOE values under the optimum condition of 20 wt % citric acid content and 200ºC hot press were 0.44 MPa, 15.1 MPa and 4.6 GPa, respectively. It stated that bamboo particleboards bonded using citric acid had high performance on mechanical properties and good dimensional stability.

In previous research, sucrose and citric acid were used to synthesize an eco-friendlyplywood adhesive. Herein, further research was performed to determine the optimal hot-pressingconditions and curing behavior of a sucrose-citric acid (SC) adhesive. The results of dry and wetshear strength measurements showed that the optimal hot-pressing temperature, hot-pressing time,and spread rate of plywood samples bonded by the SC adhesive were 190 &deg, C, 7 min, and 140 g/m2,respectively. When plywood was bonded at the optimal hot-pressing conditions, the wet shearstrength met the requirements of the China National Standard GB/T 9846-2015. Thermal analysisshowed that the thermal degradation and endothermic reaction temperatures of the SC 25/75adhesive were lower than either sucrose or citric acid individually. In addition, the insoluble massproportion increased with the heating temperature and time. The Pyrolysis Gas Chromatographyand Mass Spectrometr (Py-GC/MS) analysis confirmed that the SC adhesive was cured by thereaction between furan compounds, saccharide, and citric acid, and the resulting polymer appearedto be joined by ether linkages.

The development of eco-friendly adhesives is a major research direction in the wood-based material industry. Previous research has already demonstrated the mixture of sucrose and citric acid could be utilized as an adhesive for the manufacture of particleboard. Herein, based on the chemical characteristics of sucrose, a synthesized sucrose-citric acid (SC) adhesive was prepared, featuring suitable viscosity and high solid content. The investigation of synthesis conditions on the bond performance showed that the optimal mass proportion between sucrose and citric acid was 25/75, the synthesis temperature was 100 &deg, C, and the synthesis time was 2 h. The wet shear strength of the plywood bonded with SC adhesive, which was synthesized at optimal conditions and satisfied the China National Standard GB/T 9846-2015. The synthesis mechanism was studied by both 13C NMR analysis and HPLC, and the chemical composition manifesting caramelization reaction occurred during the synthesis process. The results of ATR FT-IR indicated the formation of a furan ring, carbonyl, and ether groups in the cured insoluble matter of the SC adhesive, which indicated dehydration condensation as the reaction mechanism between sucrose and citric acid.

The development of eco-friendly adhesives for wood composite products has been a major topic in the field of wood science and product engineering. Although the research on tannin-based and soybean protein-based adhesives has already reached, or at least nears, industrial implementation, we also face a variety of remaining challenges with regards to the push for sustainable adhesives. First, petroleum-derived substances remain a pre-requisite for utilization of said adhesive systems, and also the viscosity of these novel adhesives continues to limit its ability to serve as a drop-in substitute. Within this study, we focus upon the development of an eco-friendly plywood adhesive that does not require any addition of petroleum derived reagents, and the resultant liquid adhesive has both high solid contents as well as a manageably low viscosity at processing temperatures. Specifically, a system based on sucrose and ammonium dihydrogen phosphate (ADP) was synthesized into an adhesive with ~80% solid content and with viscosities ranging from 480&ndash, 1270 mPa&middot, s. The bonding performance of all adhesive-bound veneer specimens satisfied GB/T 9846-2015 standard at 170 &deg, C hot pressing temperature. To better explain the system&rsquo, s efficiency, in-depth chemical analysis was performed in an effort to understand the chemical makeup of the cured adhesives as well as the components over the time course of curing. Several new structures involving the fixation of nitrogen speak to a novel adhesive molecular network. This research provides a possibility of synthesizing an eco-friendly wood adhesive with a high solid content and a low viscosity by renewable materials, and this novel adhesive system has the potential to be widely utilized in the wood industry.