Tailoring Renewable Photopolymers with Lignin: Printability, Surface and Antioxidant Properties

This study explores the incorporation of organosolv (LGO) and deep eutectic solvent-derived (LGD) lignin, both native and acrylated, into a 50:50 wt % mixture of two biobased monomers, polyethylene glycol dimethacrylate (PEG200DMA) and 1,10-decanediol diacrylate (C10DA), for digital light processing (DLP). Lignin physicochemical properties, dispersion stability, and UV absorptivity were characterized to predict effects on printability. Native lignin strongly reduced light penetration, requiring higher photoinitiator content and longer exposure times to ensure interlayer adhesion, whereas acrylation partially mitigated this effect via lower absorptivity and reactive acrylate groups. Dynamic mechanical and thermal analyses revealed reduced cross-link density and lower glass transition temperatures for composites containing native lignin, whereas composites with acrylated lignin exhibited higher cross-link density and enhanced thermal stability. All lignin composites exhibited decreases in tensile strength and elongation at break, but native lignin composites showed partial recovery of tensile toughness at moderate loadings along with increased hardness, whereas acrylated lignin composites became more brittle due to increased network stiffness and lignin aggregation. Surface analyses demonstrated smoother finishes, improved resolution, and more homogeneous wettability with native lignin. Antioxidant activity was preserved after printing in both types of native lignin but suppressed after acrylation. Above all, unmodified LGO at 2–4 wt % provided the best balance between smaller particle size, compatibility with the resin used and printing parameters offering the best approach for high-resolution, mechanically robust, and multifunctional biobased DLP resins. The choice of lignin type in sustainable additive manufacturing is critical, depending on the careful selection of lignin-matrix pair, desired final properties and cost-effectiveness.