Development and evaluation of oriented strandboard bonded with soy-based formaldehyde-free adhesives

Abstract

Synthetic adhesives like phenol formaldehyde (PF) and isocyanates dominate the wood based structural panel market. The raw materials that makeup these adhesives are based on petroleum and natural gas. The sustainability and the continued success of the wood based structural panel industry will benefit from the development of alternative adhesives from renewable materials. In this study, we developed two soybased formaldehyde free adhesives.

The first adhesive is a formaldehyde-free soy flour (SF)-curing agent (CA) adhesive and was investigated for making randomly oriented strandboard (R-OSB) and oriented strandboard (OSB). Two methods (the wet method and the dry method) were investigated for applying the SF-CA adhesive onto wood flakes. The wet methodincluded the thorough mixing of SF and CA to form an adhesive mixture and then spraying the adhesive mixture onto wood flakes. The SF:CA weight ratio, the adhesive add-on rate, hot-press conditions were optimized in terms of enhancing internal bond strength (IB), modulus of rupture (MOR), and modulus of elasticity (MOE) of the resulting R-OSB panels. The highest IB, MOR and MOE were obtained at the 1:1 SF:CA weight ratio. The IB, MOR and MOE of the R-OSB panels that were made at the adhesive add-on rate of ≥ 7%, a hot-press temperature between 170 °C and 220 °C, and a hot-press time of ≥ 4 min exceeded the minimum industry requirements. The dry method included spraying aqueous CA solution onto a mixture of SF and wood flakes. The dry method was able to increase the SF:CA ratio up to 7:1 where the strengths of the resulting R-OSB panels still exceeded the minimum industry requirements. OSB panels made with the SF-CA adhesive had their strengths higher than or comparable to those commercial OSB panels purchased at a local Home Depot.

The second adhesive investigated was a formaldehyde-free adhesive using soy flour (SF) and was investigated for use in randomly oriented strandboard (R-OSB) and oriented strandboard (OSB). The main ingredients of this adhesive included SF, polyethylenimine (PEI), maleic anhydride (MA), and sodium hydroxide. The application included spraying an aqueous solution of PEI, MA, and sodium hydroxide onto a mixture of wood flakes and SF. The adhesive hot-press conditions and add-on rate were optimized in terms of enhancing internal bond strength (IB), modulus of rupture (MOR), and modulus of elasticity (MOE) of the resulting R-OSB and OSB panels. The highest IB, MOR and MOE of the R-OSB and OSB panels was achieved at a hot-press temperature of 170 °C, a hot-press time of 4-5 min, and an adhesive addon rate of 7% which exceeded the minimum industry requirements. Wax was added to PEI bonded OSB panels. Comparisons of IB, MOR, and MOE with PEI and commercial OSB panels were made. An addition of 1% wax (dry basis wood flakes) showed comparable results to the PEI panels with no wax.