Manufacturing technology optimization of laminated veneer lumber from intact corn stalk rinds

The utilization of agro-residues as a kind of raw material for making composite board is beneficial to boom rural economy, protect forest and construct ecological agriculture. Corn stalk rind separated by the rind-pith-leaf separation equipment, as the major component of corn stalk, can be used as raw material for producing composite board because of its high mechanical strength. The intact corn stalk rinds after the removal of the epidermis in different heights and the polymeric diphenylmethane isocyanate(pMDI) were used as the material, and the composite boards from the intact corn stalk rinds were produced by a new technology for the laminated veneer lumbers(LVL) in this study. The influences of the sampling height, the mass fraction of adhesive, the hot-pressing temperature, and the hot-pressing time on the physical and mechanical properties of the LVL were investigated. The following physical and mechanical properties were measured according to GB/T17657-2013: modulus of rupture, modulus of elasticity, internal bond strength, thickness swelling in 2 hours, and water absorption in 2 hours. The results showed that the mechanical properties of the LVL at the root and the ear part were better than those at the top part except the IB; with an increase of the mass fraction of adhesive, the mechanical properties of the LVL such as the MOR, the MOE, and the IB increased significantly(P<0.01), while the values of physical properties such as the TS2h and WA2h were decreased; the mechanical properties of the LVL were better when the hot-pressing temperature was 150℃ and the hot-pressing time was 6 min, but the values of physical properties were increased with the hot-pressing time increasing. The optimal parameters for the manufacturing process of LVL from corn stalk rinds were as follows: The sampling height at the root, the adhesive content of 12%, the hot-pressing temperature of 150 ℃, and the hot-pressing time of 6 min. Under the optimized conditions, the MOR, MOE, IB, TS2h and WA2h of the LVL were(74.6±1.45) MPa,(6705.5±116.3) MPa,(1.40±0.02) MPa, 6.6%±0.32% and 31.9%±2.09%, respectively. The mechanical and physical properties of the LVL could meet the Chinese national standard requirements for flooring fiberboard belonging to ordinary type and the LVL with the modulus of elasticity of 6 000 MPa. These findings provide theoretical basis and technological support for the board-making process by intact corn stalk rinds and the improvement of physical and mechanical properties of the board.