Mussel-Inspired Strong Adhesive for Sand Fixation Based on Tannic Acid with Analysis of Adhesion Mechanisms

The natural polymers in chemical sand fixation for desertification control have been used increasingly utilized. However, natural polymers' limited cohesive and adhesive properties lead to insufficient compressive strength in the stabilized sand mass. To address this issue, a complementary strategy based on multiple cross-linking and multisite hydrogen bond adsorption has been proposed to enhance both cohesive and adhesive forces of natural polymers during sand fixation. This approach involves covalent cross-linking with N,N'-methylenebis-(acrylamide) (MBA) and reinforcement of the cohesive structure through hydrogen bonds provided by tannic acid. The polyphenolic groups introduced by MBA confer strong adhesion to sand particles, thereby simultaneously improving the cohesion and adhesion. In compression tests of sand columns with optimally proportioned sand stabilizers, the modified sand stabilizer increased the compressive strength of the sand columns by 37.7% compared with the pure carboxymethyl cellulose (CMC) sand stabilizer. Spectroscopic, rheological, and thermal analyses of the sand stabilizer revealed the formation of diverse cross-linked structures ranging from covalent cross-linking to composite hydrogen-bonded cross-linking related to the hydrogen-boding adsorption between tannic acid and silica. Correspondingly, the adsorption energies calculated by DFT ranged from -36.962 to -84.39 kcal/mol, which are significantly higher than those of the hydroxyl, amino, and carboxyl groups (with absolute values less than 1 kcal/mol). This study provides new insights into the interfacial adsorption mechanisms between polyphenolic groups and silica and offers theoretical support for improving the sand-stabilizing performance of natural polymers.