The development of a natural adhesive composed of materials derived from non-fossil resources is a very important issue. In this study, only citric acid and sucrose were used as adhesive materials for particleboard. A water solution in which citric acid and sucrose were dissolved was used as an adhesive, and the manufacture of particleboard with a target density of 0.8g/cm 3 was attempted under a press condition of 200˚C for 10 min. The optimum mixture ratio of citric acid and sucrose and the optimum resin content were 25 to 75 and 30wt%, respectively. The modulus of rupture (MOR) and the modulus of elasticity (MOE) in bending were 20.6MPa and 4.6GPa, respectively. The internal bond strength (IB) was 1.6MPa, indicating that the adhesive had excellent bond strength. The thickness swelling (TS) after water immersion for 24h at 20˚C was 11.9%. The board did not decompose even under more severe accelerated treatments. This meant that the adhesion had good water resistance. The MOR, IB and TS of the board were comparable to or higher than the requirement of the 18 type of JIS A 5908 (2003). Consequently, there is a possibility that a mixture of citric acid and sucrose can be used as a natural adhesive for particleboard.

A natural adhesive composed of only citric acid and sucrose was recently proposed, and its detailed bonding performance has been researched in some wood-based materials. In this study, the effects of board density and press temperature on the physical properties of particleboard were investigated. As physical properties, the bending properties, internal bond strength and thickness swelling of the boards were evaluated. When the density was changed from 0.4 to 1.0 g/cm 3 under a press temperature of 200 °C and a press time of 10 min, the board with a density of 0.8 g/cm 3 had the best physical properties. When the board was manufactured at press temperatures ranging from 140 to 240 °C for a press time of 10 min and a target density of 0.8 g/cm 3 , the board manufactured at 200 °C had the best physical properties. The physical properties of the board with a density of 0.8 g/cm 3 manufactured at 200 °C met the type 18 requirements of the Japanese industrial standard for particleboard (JIS A 5908). The results obtained from Fourier transform infrared spectra suggested that the ester linkages resulting from the reaction between citric acid and wood and/or sucrose were the main adhesion mechanism and resulted in particleboard with excellent physical properties.

To design functional materials based on composite materials, it is imperative for us to understand the mechanism of adhesion between different materials such as metal and polymer. In this study, we investigated the adhesion between NiCr alloy film with three different compositions Ni100, Ni90Cr10, Ni60Cr40 and polyimide film using surface forces apparatus combined with optical microscope, which enable the observation of contact area during the measurement of the adhesion. This composite is widely used in the electronic devices as substrates, wiring, etc. The adhesion force measured in air for Ni90Cr10 and Ni60Cr40 decreased by time while that for Ni100 remained constant. In the measurement under nitrogen gas atmosphere, the order of strength became Ni60Cr40 Ni90Cr10 Ni100, and the decrement in adhesion for Ni90Cr10 and Ni60Cr40 was reduced. These results indicated that the Cr has stronger interaction with polyimide compared to Ni, and enhance the adhesion with polyimide. This was also supported by the larger hysteresis in the contact area vs normal load for Ni60Cr40 and Ni90Cr10 surfaces. However, Cr can be oxidized easily by exposure to air, which resulted in the decrease in the adhesion.