Preparation of water-resistant adhesives from soy flour with less water-soluble components for wood bonding

Abstract

Purpose The purpose of this paper is to prepare a water-resistant adhesive (SA) from soy flour (SF) with less water-soluble components. Design/methodology/approach Defatted SF was suspended and stirred in water. Then, the pH of dispersion was adjusted to a predetermined value (i.e. 8, 9 or 10) by the addition of 2M sodium hydroxide (NaOH) solution. After stirring at a predetermined temperature (25°C, 35°C, 45°C) for different time (1 h, 2 h, 3 h), the 2M hydrochloric acid (HCl) solution was added in a dropwise manner into the dispersion until the pH value was adjusted to 4.5. Then, the dispersion was centrifuged at 6,000 rpm for 2 min. The obtained precipitate with less water-soluble components was used as an adhesive (SA) directly. Findings SA had a wet strength of 1.02 MPa when used for the fabrication of poplar plywood. Polyvinyl alcohol (PVA) solution was applied to improve the tack of SAs to wood surface and the viscosities of SAs were decreased from 10,200 cP to 4,100 cP at room temperature after the PVA addition. The soy proteins in SAs were not denatured to a large extent according to the differential scanning calorimetry and light microscopy. The remained multilevel structures of soy protein played a positive contribution to the water resistance of SAs, and the bond lines of cured SAs were much more stable than those of the cured SF and soy protein concentrate (SPC). Research limitations/implications The fluidity and solid content of soy adhesives is much lower than formaldehyde adhesives. Further investigations are needed to improve the fluidity of soy adhesives with high solid contents. Originality/value Novel water-resistant soy adhesives were provided.

A Review of Strategies to Enhance the Water Resistance of Green Wood Adhesives Produced from Sustainable Protein Sources

“…Gui et al centered their research on the preparation of water-resistant soy flour adhesives through the reduction in the water-soluble constituents [120]. Previous research has shown that poor water resistance is mainly caused by feedstock water-soluble components [29].…”

“…Previous research has shown that poor water resistance is mainly caused by feedstock water-soluble components [29]. The design approach involved suspending the defatted soy flour in water followed by the adjustment of the dispersion pH at different temperatures and time points to 4.5 by adding NaOH and HCl solution, respectively [120]. Then, the sample with less water-soluble constituents was separated through a centrifugation [120].…”

“…The design approach involved suspending the defatted soy flour in water followed by the adjustment of the dispersion pH at different temperatures and time points to 4.5 by adding NaOH and HCl solution, respectively [120]. Then, the sample with less water-soluble constituents was separated through a centrifugation [120]. The application of the modified soy flour adhesive on poplar plywood shows that it had a wet strength of 1.02 MPa [120].…”

Fully Biobased Adhesive from Chitosan and Tannic Acid with High Water Resistance

“…To enhance the water resistance of adhesives, several aspects have been investigated, including increasing the cross-linking within the adhesive material, − adding modified fillers, , and removing hydrophilic content or introducing hydrophobic components. , However, these methods normally involve synthetic materials and complicated treatment processes and still do not deliver long-term water resistance. Learning from nature, a promising strategy for improving the water resistance of adhesives is to mimic the wet adhesion mechanisms of mussels. − These marine organisms secrete a complex protein-based adhesive, enabling firm attachment to various substrates underwater.…”

A Tough and Mildew-Proof Soybean-Based Adhesive Inspired by Mussel and Algae

“…However, the low bonding strength, poor water and mildew resistance of the protein-based adhesives have limited their applications. Up to date, some modification methods have been effective in improving the performances of soybean protein adhesive, such as denaturing agent- [8], cross-linking agents- [9,10], and biomimetic chemistry modification [11], etc. However, all of these methods involved in using the fossil resources, and the modification process is cumbersome, which have increased the cost and processing time for the adhesive preparation.…”