Light-activated self-healing poly (lactic acid) for durable FDM 3D printing applications

Fused Deposition Modelling (FDM) is an additive manufacturing technique that allows the fabrication of complex and customized parts. However, FDM-based pieces exhibit low mechanical performance due to the inherent limitations of this technology: poor interlayer adhesion and internal voids. As a result, the mechanical durability is reduced contributing to the problem of plastic waste generation. In this sense, the introduction of dynamic crosslinkers into the thermoplastic can be particularly beneficial, since they not only reinforce the polymer matrix but also impart self-healing functionality. As a consequence, the service life of FDM components is further extended. Here, we develop a coumarin-modified poly (lactic acid) formulation capable of intrinsic, light-activated self-healing. Upon ultraviolet irradiation under optimized solid-state conditions of irradiance and temperature, coumarin moieties grafted onto the PLA backbone undergo [2π + 2π] cycloaddition, generating photocrosslinked networks. Evidence of photocrosslinking was confirmed by the formation of a gel fraction (9.6 %) and a 72 % increase in storage modulus. Mechanical scratches on FDM specimens were subsequently irradiated, showing accelerated scratch closure and a smaller reduction in storage modulus (9.5 %) compared to neat PLA (32 %). These results suggest that dimerized coumarin units partially undergo reversible cleavage and re-dimerization during the healing process, enabling repeated recovery of mechanical stability. This represents the first demonstration of light-activated self-healing in FDM-printed PLA. Unlike previously reported extrinsic self-healing approaches in PLA, which rely on single-use microcapsule systems, the present work achieves intrinsic, repeatable self-healing within the PLA matrix. By combining biobased composition with extended functionality and durability, this research advances a sustainable strategy for additive manufacturing, addressing both the mechanical limitations of FDM and the broader challenge of reducing plastic waste. • Coumarin-functionalized PLA was 3D printed via Fused Deposition Modelling (FDM). • UV-induced photocrosslinking improved stiffness by 72 % over neat PLA. • Self-healing reduced storage modulus loss from 32 % to 9.5 %. • Photocrosslinked PLA presents a greater dimensional stability under enzymatic conditions.