Mechanical and physical properties of wheat straw boards bonded with a tannin modified phenol–formaldehyde adhesive

The objective of this work is to evaluate the mechanical and physical properties of three-layer boards made with wheat straw and bonded with a tannin-based adhesive. The mechanical properties of panels were evaluated by the static bending (modulus of rupture – MOR and modulus of elasticity – MOE) and the internal bond (IB) tests. Physical properties such as water absorption (WA) and thickness swelling (TS) in water were determined. In general, all types of straw panels made produced in this work met the MOR, MOE, IB and TS requirements for general uses according to European standards. Although, wheat straw boards made with tannin-modified PF resins had slightly poorer mechanical properties compared to the boards made with pure PF, the T10% PF resin showed higher bond ability than other modified PF resins. The highest MOR, MOE, IB and the lowest WA and TS were achieved at a 12 min press time and by using T10% PF resin. An increase in the press time positively affected the physical and mechanical properties of the panels produced. With respect to the findings of this study, it may be stated that wheat straw can be used as a promising raw material for panel production with the use of a tannin-modified PF adhesive.