Particleboard is widely used for making bookshelf, furniture, cabinets and many other interior products. At present, particleboard is mainly produced with wood particles and urea-formaldehyde (UF) resins. The emission of carcinogenic formaldehyde in the production and use of particleboard has generated an urgent need for development of a formaldehyde-free wood adhesive for making particleboard. Formaldehyde is derived
from natural gas whose reserve is finite. It is also desirable to develop a wood adhesive from renewable material for making particleboard. Soy flour is inexpensive, abundant, renewable and readily available. A formaldehyde-free wood adhesive consisting of soy flour (SF) and a curing agent (CA) CA1000 has been used for
commercial production of interior plywood since 2004. However, this CA-soy adhesive has high viscosity and is difficult to be sprayed onto wood particles with a conventional spraying nozzle. This study developed a new method of using this CA-soy adhesive for making particleboard. This new method involved the coating of
wood particles with a dilute soy slurry in water, the drying of the soy-coated wood particles, the spraying of the CA onto the dried soy-coated wood particles, the formation of a particleboard mat with the CA-soy-coated wood particles and the hotpressing
of the mat into particleboard. The high viscosity of the adhesive was no longer an issue with this new method. For investigation of the effectiveness of this new method, effects of particleboard density, adhesive usages for both core and face particles, the solids content of the soy slurry, hot-press time, hot-press temperature, the storage time of the soy-coated wood particles, and the soy/CA ratio on the internal bond strength (IB), the modulus of rupture (MOR), and the modulus of elasticity
(MOE) of the resulting particleboard were investigated in detail.
Results demonstrated that this new method had wide operational windows for making particleboard and allowed the strengths of particleboard bonded with this CA-soy adhesive to exceed the industry requirements of M-2 particleboard. The optimal conditions of using this method for making particleboard in terms of enhancing the IB, MOR, and MOE were: 760 kg/m³ of the particleboard density, 11 wt% resin usage for the core particles, 12 wt% resin usage for the face particles, 20 wt% solids content of the soy slurry, 180 °C of the hot-press temperature, 224 s of the hot-press time, 1:7 CA/SF weight ratio, and 36 h of the storage time for the wet soy-coated wood particles
