Adhesive performance of cottonseed protein modified by catechol-containing compounds

Authors: Cheng, Huai; Kilgore, Kaylin; Ford, Catrina; Smith, Jade; Dowd, Michael; He, Zhongqi

Submitted to: Journal of Adhesion Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2021
Publication Date: 8/1/2022
Citation: Cheng, H.N., Kilgore, K., Ford, C., Smith, J., Dowd, M.K., He, Z. 2022. Adhesive performance of cottonseed protein modified by catechol-containing compounds. Journal of Adhesion Science and Technology. 36:1781-1793. https://doi.org/10.1080/01694243.2021.1984713.
DOI: https://doi.org/10.1080/01694243.2021.1984713

Interpretive Summary: Soy protein is now commercially used as a green alternative to formaldehyde resins and polyurethanes in wood adhesives. A problem with protein adhesives is its relatively poor water resistance. We are aware of the current research interest in using mussel-inspired adhesion to design new polymeric adhesive systems, where the consensus is that mussel adhesion is caused by catechol-type of structures. In this work, we combined the protein adhesives with the biomimetic concept from mussel adhesion. Thus, we tested three catechol-containing compounds (catechol, gallic and caffeic acids) for their adhesive modifying properties on soy and cottonseed proteins. The gallic and caffeic acids were effective modifiers for cottonseed protein at 50 mM concentration with good dry adhesive strength and water resistance, but catechol showed no significant improvement over cottonseed protein by itself. For soy protein, only marginal improvements were observed for gallic and caffeic acids. This study has given us two new promoters for cottonseed protein adhesion, and this information is useful as we continue to develop cottonseed protein as a promising wood adhesive material.

Technical Abstract: 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, useful mechanistic information concerning the adhesion of catechol-like structures has been obtained.