Abstract
Lignocellulosic materials offer a sustainable alternative to fossil-based plastics, but challenges such as inferior mechanical properties and unclear biodegradability hinder their broader application. In this work, we developed biodegradable lignin-based polyurethane (LPU) thermoplastics using kraft lignin and polycaprolactone (PCL) diols with molecular weights of 530 and 2000 g mol⁻¹ (PCL530 and PCL2k, respectively). The LPUs were synthesized via step-growth polymerization and characterized to evaluate its chemical, thermal and mechanical properties. The developed LPU films incorporating PCL2k exhibited superior mechanical properties, with a tensile strength of up to 13.7 MPa and an elongation exceeding 884 %. The LPU inks were formulated at 60 wt% and demonstrated excellent rheological properties for 3D printing via direct ink writing (DIW). Structures were successfully printed both in air and within an ethanol gel-based support medium, achieving a resolution of 410 µm and enabling the fabrication of complex and overhanging geometries. Moreover, Ultraviolet (UV) degradation studies revealed that LPUs prepared with PCL2k (L-PCL2k) demonstrated enhanced UV stability, with only a 4 % reduction in molecular weight, compared to a 15 % loss for LPUs prepared with PCL530 (L-PCL530). The aerobic biodegradation performance of the LPUs in the presence of seawater and sewage sludge demonstrated a 17.4 % biodegradation degree over 90 days. This work demonstrates the potential of lignin-based LPU thermoplastics as biodegradable, mechanically robust, and processable materials for sustainable additive manufacturing.
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•Lignin and polycaprolactone were used to synthesize biodegradable polyurethanes.•LPUs showed tunable mechanical strength and enhanced UV degradation resistance.•LPUs enabled up to 17.4 % biodegradation in seawater-sludge over 90 days.•LPUs were successfully fabricated into complex structures via DIW 3D printing.•This work offers a sustainable route for high-value use of lignin in bioplastics.