Improving adhesion performance of cottonseed protein by the synergy of phosphoric acid and water soluble calcium salts

Authors: LI, JUN - Kansas State University; PRADYAWONG, SAROCHA - Kansas State University; SUN, XIUZHI - Kansas State University; WANG, DONGHAI - Kansas State University; He, Zhongqi; ZHONG, JUNYAN - Intertek Analytical Services; Cheng, Huai

Submitted to: International Journal of Adhesion and Adhesives
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2021
Publication Date: 3/29/2021
Citation: Li, J., Pradyawong, S., Sun, X.S., Wang, D., He, Z., Zhong, J., Cheng, H.N. 2021. Improving adhesion performance of cottonseed protein by the synergy of phosphoric acid and water soluble calcium salts. International Journal of Adhesion and Adhesives. 108. Article 102867. https://doi.org/10.1016/j.ijadhadh.2021.102867.
DOI: https://doi.org/10.1016/j.ijadhadh.2021.102867

Interpretive Summary: Protein has great potential to be bio-adhesives due to the nature of non-toxicity, harmlessness, and non-pollution. One of such protein-based bio-adhesives is that derived from defatted cottonseed meal. Cottonseed protein adhesives have shown a relatively higher water resistance than soy protein isolate due to different amino acid composition and sequence, but is still not as good as synthetic resin. In the work, the combination of cottonseed protein isolate (CSPI) with water soluble calcium salts, such as calcium nitrate and calcium chloride, and phosphoric acid to improve the adhesion performance of cottonseed protein was investigated. Combination of H3PO4 and water soluble CaCl2 further improved the adhesion performance of CSPI in comparison with other modifiers, indicating that free Ca can present a synergy in increasing the crosslinking of CSPI. Comparison of CSPIs with H3PO4/CaCl2 and H3PO4/Ca(NO3)2 indicates that the anions of water soluble calcium salts (CaCl2 and Ca(NO3)2) had insignificant effects on adhesion performance of CSPI. Those findings indicated that mixing of phosphoric acid and some water soluble calcium salts could synergistic ally enhanced the adhesion performance of cottonseed protein, thus improving the industrial acceptability of CSPI-based adhesives.

Technical Abstract: Cottonseed protein has great potential to replace formaldehyde-based adhesives due to the nature of non-toxicity, harmlessness, and non-pollution. Like soy protein-based adhesives, cottonseed protein-based adhesives also face a huge challenge in water resistance. In this work, adhesion performance of cottonseed protein isolate (CSPI) modified by combination of H3PO4 and CaCl2 with different mole ratios was investigated in comparison with those modified by 40 mM H3PO4, CaCO3, CaO, or CaHPO4. Results showed that CSPI with 40 mM CaHPO4 didn’t show a better adhesion performance than those with 40 mM H3PO4, CaCO3, or CaO, indicating the little/no synergy between Ca and P due to the spatial structure restriction of water insoluble CaHPO4. However, combination of H3PO4 and CaCl2 enhanced the adhesion performance of CSPI in comparison with other modifiers, due to free Ca2+ released from water soluble CaCl2 presenting a better synergy with PO3-4. At the optimal loadings of 40 mM H3PO4 and 20 mM CaCl2,71, 86, and 56% increase in dry, wet, and soaked strengths was achieved. In addition, comparison of CSPIs with H3PO4/CaCl2 and H3PO4/Ca(NO3)2 indicates that the anions of water soluble calcium salts [CaCl2 and Ca(NO3)2] had insignificant effects on adhesion performance of CSPI. Those findings indicated that mixing of phosphoric acid and some water soluble calcium salts could synergistically enhanced the adhesion performance of cottonseed protein, thus improving the industrial acceptability of CSPI-based adhesives.