Fully recyclable and regeneratable plant-based adhesives

Abstract

Recyclable adhesives promise lower cost and environmental impact, but combining full reversibility, high strength, and facile regeneration using only benign, natural components is still difficult. Building on highly tunable and dynamic supramolecular interactions, we present a fully recyclable and regenerable plant-based supramolecular adhesive (RRPA) composed of tannic acid (TA), β-cyclodextrin (β-CD), and water. Extensive hydrogen bonding among TA and β-CD, with water acting as a dynamic bridging component, forms a reversible network that enables strong cohesion and interfacial adhesion while preserving the water-triggered debonding feature. Spectroscopic and spectrometric analyses, including FT-IR, variable-temperature ¹H-NMR, and 2D-NOESY, evidence temperature-sensitive, reversible hydrogen bonds. Guided by molecular simulation and DFT-level thermodynamic analysis, we identify an optimal β-CD : TA molar ratio of 1 : 3 and a residual water content of 15 wt%, which together balance cohesive strength and interfacial hydrogen bonding. The optimized RRPA achieves lap-shear strengths exceeding 3.1 MPa on alumina and >2.7 MPa on stainless steel, with strong adhesion to hydrophilic substrates (e.g., wood, glass) and lower strength on hydrophobic polymers (PET, PI, PTFE). The adhesive is fully water-dissolvable, enabling closed-loop recycling by simple dissolution and redrying; after 100 cycles, it retains ∼70–80% of its initial adhesion strength (∼1.7 MPa), with thermal stability up to ∼250 °C prior to TA decomposition. The water-triggered debonding of the RRPA enables temporary bonding under dry conditions and complete recycling in water, making it attractive for reversible assembly, recyclable composites, and conservation of sensitive artifacts.