TEMPO-modified Nanocellulose-based Dynamic Polymer Networks for Sustainability

Polymer films and coatings are essential for protecting surfaces, but mechanical damage often leads to premature replacement, increased maintenance, and material waste. Self-healing and reprocessable polymers can address these issues, although many reported systems still require high activation temperatures, show a compromise between healing and strength, or depend on organotin catalysts. In this work, we present a tin-free dynamic polymer network that combines renewable nanocellulose reinforcement with bismuth-mediated bond exchange. The self-healing polymer was prepared from a hydroxyl-functional acrylate copolymer crosslinked with hexamethylene diisocyanate in the presence of bismuth neodecanoate and TEMPO-oxidized cellulose nanocrystals (TCNCs). In this network, bismuth promotes thermally activated transesterification within the urethane-acrylate matrix, while the carboxylate-rich TCNC surface provides hydrogen-bonding and bismuth–carboxylate coordination sites. As a result, TCNCs act not only as reinforcing fillers but also as dynamic interfacial components that assist stress transfer and network reconstruction after damage. The TCNC loading had a clear influence on the balance between stiffness, chain mobility, and healing efficiency. Among the prepared films, the 3 wt% TCNC-containing network showed the most balanced performance, with a tensile strength of approximately 11 MPa, 94% scratch healing after 12 h at 70 °C, and 98% recovery in a macroscopic cut-healing test. The same material also retained more than 90% of its tensile strength after repeated cut-and-press recycling. These results suggest that integrating renewable nanocellulose with organotin-free dynamic chemistry is an effective strategy for designing longer-lasting, repairable, and reprocessable polymers. (Acknowledgement: Ministry of Trade, Industry & Energy of the Republic of Korea (RS-2024-00430401, RS-2025-11162970))