Xylose-based transparent UV-curable coatings integrating flame retardancy, UV-triggered self-healing, and closed-loop recyclability without photoinitiator

Abstract

Developing multifunctional, closed-loop recyclable UV-curable coatings that integrate flame retardancy, light-induced self-healing, and degradability remains a significant challenge. Herein, it was reported transparent UV-curable coatings derived from xylose and thioctic acid (TA), which are cured without the use of solvents or photoinitiators. A phosphorus-containing xylose derivative (XDT) was synthesized and copolymerized with TA via UV-induced ring-opening polymerization of cyclic disulfides, forming dynamic covalent networks (XDTN-x). The resulting coatings exhibit outstanding UV-curing characteristics, high optical transparency (>95% transmittance in the visible range), and tunable mechanical properties (tensile strength up to 25.2 MPa, elongation at break up to 72.1%). Remarkably, the presence of dynamic disulfide bonds enables efficient UV-triggered self-healing, achieving up to 90% recovery of tensile strength upon UV irradiation. The incorporation of phosphorus moieties imparts excellent flame retardancy, with a limiting oxygen index (LOI) up to 30.2% and a UL-94 V-0 rating. Furthermore, the network can be selectively degraded under mild acidic conditions, allowing closed-loop recycling: the recovered XDT derivative can be re-cured by UV light to regenerate films and coatings, with properties slightly lower than those of the virgin coating. This work presents a xylose-based, initiator-free UV-curable coating that uniquely combines flame retardancy, UV-triggered self-healing, and closed-loop recyclability, offering a high-performance platform for smart coating applications.