Cornstarch and tannin in phenol-formaldehyde resins for plywood production

The aim of this work is to demonstrate the performances of cornstarch-quebracho tannin-based resins designed as adhesive in the plywood production. In this way, the cornstarch and quebracho tannin was introduced in the classic adhesive formulation in order to supply a part of phenol-formaldehyde (PF). The physical properties (rheological characterization, thermogravimetric analysis and solid phase C-13 NMR analysis) of the formulated resins were measured. In order to evaluate the mechanical performances of optimal cornstarch-quebracho tannin-based resins. plywood panels were produced and mechanical properties were investigated. These mechanical properties included tensile strength, wood failure and 3-point bending strength. The performance of these panels is comparable to those of plywood panels commercial PF made. The results showed that plywood panels bonded with cornstarch-quebracho tannin-PF resins (15:5:80, w/w/w) exhibited better mechanical properties than plywood panels commercial PF made. The introduction of small proportions of cornstarch and quebracho tannin in PF resins contributes to the improvement of the boiling water performance of these adhesives. The formaldehyde emission levels obtained from panels bonded with cornstarch-duebracho tannin-PF were lower to those obtained from panels bonded with control PF. Solid state CPMAS NMR spectra indicates that no reaction at all between PF resins and cornstarch and quebracho tannin. Even when reaction does evidently not occur, the addition of cornstarch and quebracho tannin improves markedly the water resistance of PF resins. (C) 2009 Elsevier B.V. All rights reserved.