Effect of pH and pH-Shifting on Adhesion Performance and Properties of Lignin-Protein Adhesives

HighlightsLignin improved the wet adhesion strength of soy protein adhesives when pH shifted from 8.5 to 4.5.Lignin increased the water resistance of soy protein adhesives from 5% to 40% at pH 12.Lignin improved the thermal resistance of soy protein adhesives.pH and pH-shifting treatments led to property changes of lignin, soy protein, and lignin-soy protein.Abstract. Concerns about public health and the environment have created strong interest in developing alternative green products. The focus of this research was to study the effect of lignin on soy protein (SP) adhesives under different pH and pH-shifting treatments. Additionally, this research was designed to understand the consequence of pH and pH-shifting treatments on the adhesion performance of SP and lignin-SP (LSP) adhesives as well as the characteristics, solubility, glue line patterns, and physiochemical properties. To study the aggregation, soluble, and denatured stages of protein, the protein solutions were adjusted to pH 4.5, 8.5, and 12, respectively. In addition, the study of pH-shifting treatments was performed at pH 8.5 and 12 to unfold and denature the protein, respectively. The protein structure was then refolded by adjusting the pH to 4.5 in adhesive slurries. The adhesives presented good adhesion performance under dry conditions with wood failure in most treatments, while satisfactory wet adhesion performance was obtained at pH 4.5, 8.5 to 4.5, and 12. Shifting the pH from 8.5 to 4.5 increased the lignin-protein interaction and provided the best improvement in adhesion performance. Lignin strengthened the protein structure, increased the water resistance, and improved the thermal stability of SP adhesives. At an extremely high pH, the water resistance of SP increased from 5% to 40% with the addition of lignin. Lignin showed great potential for increasing the wet strength of SP adhesives. The SP and LSP properties and adhesion performance could be adjusted and improved by pH and pH-shifting processes. Lignin-SP interactions, water resistance, and glue line pattern proved to be significant factors contributing to adhesion performance. Keywords: Adhesive, Lignin, Lignin-protein interactions, pH, pH-Shifting, Protein.

Bio-adhesives from unfolded soy protein reinforced by nano-chitosan for sustainable textile industry

Biodegradable adhesives from nano-chitosan-reinforced unfolded soy protein have been fabricated to potentially reduce environmental pollution and drive a sustainable textile industry. The weak adhesion strength and poor water stability of soy protein films limit their use in the textile industry. In this work, the influence of sodium-dodecyl-sulfonate on unfolding of soy protein, and the reinforcement effects of nano-chitosan on the tensile properties of unfolded soy protein adhesives were investigated. The results demonstrate that the bio-adhesives developed had 157% and 85% increments on tensile strength and water stability compared with unmodified soy protein. Also, dry and wet strength of the pulp/viscose wet-laid nonwovens were increased 43% and over 100% after adhesion, indicating that modified soy protein shows promise for use as a textile bio-adhesive for sustainable industry.