Improvement of water resistance of wheat flour‐based adhesives by thermal–chemical treatment and chemical crosslinking

Abstract

A water‐resistant adhesive for plywood panels for engineered wood floors was developed using thermal–chemically treated wheat flour (WF), polyvinyl alcohol (PVA), and polymeric diphenylmethane diisocyanate (p‐MDI) as the cross‐linker. The thermal–chemical treatment was performed at 100°C in the presence of sulfuric acid or sodium dodecyl sulfate (SDS). Fourier transform infrared spectroscopy, X‐ray diffraction spectroscopy, and scanning electron microscopy were used to investigate the chemical structure, crystalline degree, and morphology change, respectively, of the thermal–chemically treated WF. The boiling water‐insoluble content and acetaldehyde values of the thermal–chemically treated WF were also evaluated and compared with those of the controls—native WF and thermally treated WF alone. The bond property evaluation showed that the water resistance of the thermal‐SDS‐treated WF (T‐SDS‐WF)‐based adhesive was significantly improved, which is mainly attributed to the formation of a three‐dimensional crosslinking network resulting from self‐crosslinking of the wheat protein, the Maillard reaction between the wheat starch and wheat protein, and the increased crosslinking between T‐SDS‐WF and p‐MDI. Overall, the developed WF‐based adhesive is a promising bio‐based candidate in the production of plywood for engineered wood floors.

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

“…Thus, Bai et al worked on investigating the possibility of preparing water-resistant wheat-flour-based adhesives for wood applications by subjecting wheat flour to thermal-sodium dodecyl sulfate (SDS) or thermal-acid treatment, followed by cross-linking with a reactive polymeric diphenylmethane disocyanate (p MDI) resin coupled with the addition of a polyvinyl alcohol solution as an aqueous polymer [55].…”

“…Improved cross-linking density from self-aggregation and inter-change reaction between wheat proteins, the Maillard reaction between wheat starch and wheat protein, and the cross-linking reaction between thermal-SDS-treated wheat flour and cross-linker p-MDI all contributed to the adhesive's increased water resistance, which increased the wet strength from 0.29 MPa to 1.22 MPa [55]. Nevertheless, the thermal-chemical treatment should be performed in the presence of non-toxic chemical substances.…”

Ethanol as an alternative to water vapor for saving energy and fossil fuels in thermoelectric plants

“…However, water has a high boiling point (at sea level of 100°C) and a high heat of vaporization value (the amount of energy required to transform a fixed amount of a liquid substance into vapor at a constant temperature). (Bai et al, 2021;Yang et al, 2021;Yin et al, 2021). The heat of vaporization of water is about 540 cal/g at 100°C.…”