Preparation and characterization of epoxy-crosslinked soy protein adhesive

Abstract

In this study, the soy protein was degraded and cross-linked with trimethylolpropane triglycidyl ether (THPTG) at 80 °C to prepare wood adhesive for interior plywood. Namely, by adding sodium hydroxide (NaOH), functional groups (-NH₂, -COOH, and -OH) in soy protein were exposed and then reacted with epoxy groups to form a crosslinked water-resistance soy-protein adhesive under alkali condition. The optimum formulation of this adhesive was investigated. The molecular weights, chemical structure, bonding properties and water-resistance were characterized by gel permeation chromatography-multi-angle laser light scattering (GPC-MALLS), Fourier transform infrared spectroscopy (FTIR), plywood bonding test and three-cycle soak test. Results showed that at 2% NaOH, the molecular weight of soy protein isolate degradation (DSP) presented as 3.473e + 04 g·mol⁻¹ was homogeneous and resulted in greater increase of amide II and amide III. The cross-linking reaction between THPTG and DSP resulted in the increase of both viscosity and sensitivity of infrared absorption peaks of –O–H (3100 cm⁻¹) and C-N (1190 cm⁻¹). Also, the adhesives synthesized from the SPI denatured with 2% NaOH and 9% THPTG did meet the wet strength for interior-use plywood panels (≥0.7 MPa) according to the China Industry Standard GB/T 9846.3-2004 and water resistance according to American National Standard for Hardwood and Decorative Plywood/Hardwood Plywood and Veneer Association.

Keywords:

• Soy protein isolate
• cross-linking
• wet shear strength
• water resistance

Additional information

Funding

The authors are grateful for the financial support of the National Key Research and Development Program of China [2016YFD060070502].