Location: Commodity Utilization ResearchTitle: Comparison of the wood bonding performance of water- and alkali-soluble cottonseed protein fractions
Submitted to: Journal of Adhesion Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2020
Publication Date: 7/1/2021
Citation: He, Z., Cheng, H.N., Nam, S. 2021. Comparison of the wood bonding performance of water- and alkali-soluble cottonseed protein fractions. Journal of Adhesion Science and Technology. 35(14):1500-1517. https://doi.org/10.1080/01694243.2020.1850612.
Interpretive Summary: The interest in plant seed protein isolates as wood adhesives has resurrected recently, as these plant materials are considered renewable and environment-friendly. In this work, cottonseed protein was sequentially separated into water-soluble (CSPw) and alkali-soluble (CSPa) fractions to increase the mechanism knowledge of seed protein products functioning as wood adhesives. The dry, wet, and soaked (i.e., wet and then re-dried) strengths at break of the wood pairs bonded by CSPa were always higher than the corresponding values by CSPw. While the fresh adhesive slurries of CSPw showed higher viscosity values than CSPa slurries, the oven-dried adhesive slurries of CSPw possessed higher solubility than CSPa. Thus, the higher solubility of CSPw might have contributed to its poor bonding capability and low water resistance. Infrared spectroscopic data and contact angle analysis evidenced the difference in wettability between CSPw and CSPa and leaching-out of carbohydrates during water soaking. These observations would be helpful for design and tuning of cottonseed protein's functional performance in green applications. Future studies should examine how different isolation methods impact the bonding performance of plant seed protein products.
Technical Abstract: The interests in biobased wood adhesives have been steadily increasing in recent years. Cottonseed protein isolate has shown the potential as one of the renewable biobased adhesives. For a better understanding of the adhesive performance and mechanisms of cottonseed protein, in this work, we sequentially separated the isolated material into water-soluble (CSPw) and alkali-soluble (CSPa) fractions. The adhesive properties of both fractions on bonding maple wood veneers were tested at their natural pH (4.0 for CSPw and 7.0 for CSPa) and a common pH 11.0. The dry, wet, and soaked (i.e., wet and then re-dried) strength at break of the wood pairs bonded by CSPa were always higher than the values found for CSPw under the same conditions. Per the solubility and rheological analysis, the observed differences in bonding performance could be attributed to the fact that CSPw is more hydrophilic and lower in pI. ATR-FTIR analysis was directly applied to the adhesive-coated surface area of maple strips cohesively broken at strength tests. Quantitative FTIR spectral features and quantitative contact angle measurement of the adhesive-coated maple surface evidenced the better wettability of cured CSPa than CSPw adhesives. Leaching-out of carbohydrates during water soaking was reduced from the former relative to the latter. These observations increased the mechanistic knowledge of seed protein products functioning as wood adhesives, and would be helpful for the design and tuning of their future functional performance in green applications.