- Formaldehyde-based adhesives such as urea-formaldehyde (UF), phenol-formaldehyde (PF) are widely applied in wood-based composite industry. However, these adhesives are all petrochemical-based and could not sustain in a long term due to a limited reserve of oil and natural gas. Moreover, these adhesives emit carcinogenic formaldehyde in the production or use of wood composite panels, thus reducing indoor air quality and posing a health risk to human beings. Soy flour (SF) is an abundant, readily available, renewable, and inexpensive material and is mainly used for food application at present. Its potential for industrial applications has not been fully realized. In this study, we evaluated two SF-based formaldehyde-free wood adhesives for making M-2 Grade particleboard panels.
The first adhesive was composed of SF, polyethylenimine (PEI), maleic anhydride (MA) and sodium hydroxide (NaOH). The weight ratio of SF/PEI/MA/NaOH was 7/1.0/0.32/0.1. The hot-press temperature, hot-press time, panel density and adhesive usages were optimized in terms of enhancing the modulus of rupture (MOR), modulus of elasticity (MOE) and internal bond (IB) of the particleboard panels. It was found that the MOR, MOE and IB exceeded the minimum industrial requirements of M-2 particleboards under the following variables and conditions: hot-press temperature, 170 °C; hot-press time, 270 s; the adhesive usage of surface particles, 10 wt%; the adhesive usage of the core particles, 8 wt%; and the targeted particleboard density, 0.80 g/cm³.
The second adhesive consisted of SF, a new curing agent (CA) and NaOH. Effects of the weight ratio of adhesive components on strengths of the particleboard panels were investigated. It was found that this adhesive resulted in the highest strengths at the SF/NaOH/CA weight ratio of 9/0.3/1. Effects of hot-press temperature and hot-press time on strengths of the panels were also investigated. The MOR, MOE and IB met the minimum industrial requirements of M-2 particleboard panels under the following variables and conditions: hot-press temperature, 190 °C; hot-press time, 270 s; the adhesive usage of surface particles, 12 wt%; the adhesive usage of the core particles, 10 wt%; and the targeted particleboard density, 0.80 g/cm³.