Quebracho Tannin Bio-Based Adhesives for Plywood.

Area of Science:

• Materials Science
• Wood Science
• Green Chemistry

Background:

• Traditional wood adhesives rely on synthetic polymers, raising environmental concerns.
• Tannin-based adhesives have limitations in solid wood applications due to rigidity and low performance.
• There is a growing demand for sustainable, bio-based alternatives in the wood industry.

Purpose of the Study:

• To characterize a completely bio-based adhesive formulation derived from Quebracho tannin extract and furfural.
• To evaluate the adhesive's performance in bonding beech plywood under varying press conditions.
• To assess the influence of processing parameters on the physical and mechanical properties of the resulting plywood.

Main Methods:

• Characterization of the tannin-furfural adhesive using viscosity, gel time, and Fourier-transform infrared (FT-IR) spectroscopy.
• Plywood fabrication using beech (Fagus sylvatica) and the bio-based adhesive, optimizing press time and temperature.
• Evaluation of physical properties (density, thickness) and mechanical properties (modulus of elasticity, modulus of rupture, tensile shear strength).

Main Results:

• The polyphenolic adhesive exhibited non-Newtonian behavior and good spreadability at room temperature.
• Crosslinking was observed at 100 °C, with optimal mechanical properties achieved between 125 °C and 140 °C press temperature.
• Beech plywood achieved modulus of elasticity between 9600-11,600 N/mm², modulus of rupture of 66-100 N/mm², and dry tensile shear strength of ~2.2 N/mm², but showed delamination after water exposure.

Conclusions:

• The Quebracho tannin-furfural formulation is a viable bio-based adhesive for specific industrial applications, particularly for plywood used in dry environments.
• The adhesive demonstrates potential for recyclability, offering an environmentally friendly alternative to conventional wood glues.
• Further research is needed to enhance the water resistance of tannin-based adhesives for broader applications.