Adhesive performance of cottonseed protein modified by catechol-containing compounds

Cottonseed protein has been shown to have promising adhesive properties as an eco-friendly and effective polymeric wood adhesive. In this work, we adopted the biomimetic concept from mussel adhesion, where phenolic residues, particularly catechol-type of structures, have been found to contribute towards the adhesive behavior of the materials secreted by mussels. Thus, we chose catechol, gallic acid and caffeic acid as possible modifiers for cottonseed protein isolate (CPI) adhesives. At concentrations between 50 and 200 mM, the acids improved the dry adhesive performance of CPI by 18–40%. At a 50 mM concentration, gallic and caffeic acids showed 46 and 27% enhancements in hot water adhesive performance relative to CPI alone but only showed slight enhancements for the water soak of 7 and 12%, respectively. For CPI with 200 mM of gallic or caffeic acids, the hot-water resistance and soak tensile strength decreased relative to the CPI control. For all three adhesion tests, 50 mM catechol exhibited no statistical improvement over the CPI control. The corresponding evaluations with soy protein isolate (SPI) showed only marginal improvements in dry adhesive performance for gallic acid, caffeic acid, and catechol, each at 200 mM concentration. Through this work, two new promoters for CPI adhesion (gallic and caffeic acids) have been discovered. In addition, some mechanistic information concerning the adhesion of catechol-like structures has been obtained.