Development of Defatted Soy Flour-Based Adhesives by Acid Hydrolysis of Carbohydrates.

Peitao Zheng,Feng Li,Yangting Ou,Qiaojia Lin,Yuqi Li,Nairong Chen

doi:10.3390/polym9050153

Abstract

Soy-based adhesives are attracting increasing attention in recent years because they are a renewable and environmentally friendly raw material. Defatted soy flour (DSF), comprised of 50% protein and 40% carbohydrate, is the most widely used raw material for the preparation of soy-based adhesives that are unfortunately hampered by poor gluability and water resistance. In the present study, we developed a self-crosslinking approach to prepare a formaldehyde-free defatted soy flour-based adhesive (SBA). Carbohydrates in the DSF were hydrolyzed with 0% (controls), 0.5%, 1.0%, 2.0%, 3.0% and 5.0% hydrochloric acid, and cross-linked with proteins to prepare the SBA. The effect of hydrolyzed carbohydrates on the performance of the SBA was investigated, and hydrolyzed carbohydrates significantly increased the amount of reducing sugars, but decreased insoluble substances. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses revealed an enhanced cross-linking structure with fewer hydrophilic groups in cured SBAs. Maillard reactions between hydrolyzed carbohydrates and proteins resulted in SBAs with better gluability, rheological properties and thermal stability than controls. Scanning electron microscopy (SEM) images showed that plywood bonded with SBA had a higher wood failure rate than controls. This approach has potential for preparing bio-adhesives with enhanced properties from other natural resources with a similar polysaccharides and protein composition.

Highlights

Wood adhesives play a dominant role in the wood fabrication industry, such as producing plywood and particleboard
We recently described a Defatted soy flour (DSF)-based adhesive in which polysaccharides are enzymolyzed to reducing sugars, and the addition of Viscozyme L improved the water resistance [25]
The Maillard reaction refers to the interaction initiated between the amino groups of proteins and the aldehyde groups of reducing sugars, and this reaction may lead to a loss of NH2 and the formation of Amadori compounds (C–O), Schiff bases (C–N) and pyrazines (C–N) [35]

Summary

Introduction

Wood adhesives play a dominant role in the wood fabrication industry, such as producing plywood and particleboard. Heat treatment and different denaturation agents including acid, salt, alkali, urea, sodium dodecyl sulfate, hydroxymethyl phenol, neopentyl glycol diglycidyl ether, and 2-octen-1-ylsuccinic anhydride have been employed to modify proteins in order to improve the water resistance of the soy-based bio-adhesives [13,14,15,16,17,18,19]. Such adhesives have good strength, the high price of soy protein isolates makes them a less attractive starting point for a wood adhesive. Many attempts to modify soy protein in DSF have been

Methods

Results

Conclusion