Development of a tannic acid-modified cellulose nanofibril reinforced waterborne polyurethane elastomer for flexible...

Cellulose nanofibrils (CNF) are widely used as nanofillers in waterborne polyurethane (WPU); however, their effectiveness as enhancers is limited by issues such as agglomeration and stress concentration. To address these issues, this study introduces tannic acid (TA) and synthesized a composite material (TA@CNF) by surface-functionalizing CNF with TA. This composite was then incorporated into the WPU system. Nanocomposite films (T_xC₆WPU) with varying TA: CNF mass ratios were prepared via solution casting. Subsequently, MXene conductive coatings were deposited onto these films to fabricate flexible sensing platforms (MXene/T_xC₆WPU). Systematic characterization revealed that adding TA@CNF alters the microstructure, creates a reversible hydrogen-bonding network, and significantly enhances performance. In single tensile tests, a TA:CNF ratio of 4:6 gives the material outstanding mechanical properties. Its tensile strength (4.92 MPa), elastic modulus (2.39 MPa), and toughness (10.73 MJ·m^-3) rise by 500 %, 850 %, and 220 % compared to WPU. Follow-up cyclic tensile tests prove the composite films have good resilience and energy dissipation. TA addition also gives the composite films great adhesion, reaching 380 kPa on wood surfaces. Overall, MXene-integrated films reliably monitor human motion, highlighting their potential for wearable electronics. In summary, this work provides an effective approach to designing high-strength polymer elastomers.