Preparation of a strong, high prepressing intensity, and multifunction soybean protein adhesive by using hyperbranched functional polymer
Zheng Liu, Tao Liu, Jieyu Zhang, Yue Li, Jing Luo, Jianzhang Li, Sheldon Q. Shi, Qiang Gao, An Mao
Abstract
The preparation of a soybean protein adhesive with good prepressing intensity, mildew proof, flame retardant, and high bond strength are conducive to the wide application of a soybean protein adhesive, which is important but challenging for the wood-based panel industry. In this study, two hyperbranched functional polymers were designed. Hyperbranched polyamide (HP) was grafted by 3-hydroxyphenylphosphinyl-propanoic acid (PPA) to obtain [email protected] and then combined with self-synthesized epoxidized tannin (ETA) to modify the soybean protein adhesive. The hyperbranched functional polymer [email protected] and ETA reacted with soybean protein to form a hyperbranched cross-linking structure and a hydrogen bond network, which noticeably improved the toughness and bond strength of the adhesive. The wet shear strength of the resultant plywood was improved by 110.9% to 1.35 MPa. The formed hyperbranched hydrogen bond network also significantly improved the prepressing intensity (by 129.0% to 0.71 MPa). In addition, the anti-mildew time increased from 24 h to 120 h. The time to block combustibles increased from 5 s to 80 s, and the limiting oxygen index improved from 23.5% to 38.5%. The use of hyperbranched functional polymers created covalent and non-covalent hybrid networks provides an effective and convenient strategy for developing high-strength and multifunctional composites, such as bio-adhesives, hydrogels, and films.