This study developed bio-based waterborne polyurethane (BWPU) dispersions containing lignin as a sustainable filler with castor oil (CO), polycaprolactone diol (PCL), or poly(trimethylene ether) glycol (PO3G). The effects of the polyol structure and the presence of lignin on the mechanical performance, thermal stability, water absorption, ethanol resistance, and UV-blocking capabilities of the resulting BWPU samples were evaluated. The results revealed that lignin affects the molecular packing and interchain interactions of CO-based BWPU, thus improving its tensile strength and thermal stability while reducing its water absorption and ethanol permeability. In the PCL-based BWPU, lignin had a minimal impact on water absorption and ethanol resistance but led to greater UV-blocking ability due to interactions between the semi-crystalline matrix of PCL and the aromatic structure of the lignin. In the PO3G-based BWPU, lignin disrupted the polymer network, increasing its water absorption and reducing its ethanol resistance but significantly improving its elongation and UV-shielding behavior. These results highlight the dual role of lignin as a sustainable reinforcing agent and functional additive in enhancing the properties of BWPU. By tailoring the polyol structure and optimizing lignin use, this study demonstrates a framework for the development of eco-friendly PU composites suitable for use as coatings, barriers, UV-shielding films, and packaging

In this study, we introduce a novel approach for synthesizing lignin-incorporated castor-oil-based cationic waterborne polyurethane (CWPU-LX), diverging significantly from conventional waterborne polyurethane dispersion synthesis methods. Our innovative method efficiently reduces the required solvent quantity for CWPU-LX synthesis to approximately 50% of that employed in traditional WBPU experimental procedures. By incorporating lignin into the polyurethane matrix using this efficient and reduced-solvent method, CWPU-LX demonstrates enhanced properties, rendering it a promising material for diverse applications. Dynamic interactions between lignin and polyurethane molecules contribute to improved mechanical properties, enhanced thermal stability, and increased solvent resistance. Dynamic interactions between lignin and polyurethane molecules contribute to improved tensile strength, up to 250% compared to CWPU samples. Furthermore, the inclusion of lignin enhanced thermal stability, showcasing a 4.6% increase in thermal decomposition temperature compared to conventional samples and increased solvent resistance to ethanol. Moreover, CWPU-LX exhibits desirable characteristics such as protection against ultraviolet light and antibacterial properties. These unique properties can be attributed to the presence of the polyphenolic group and the three-dimensional structure of lignin, further highlighting the versatility and potential of this material in various application domains. The integration of lignin, a renewable and abundant resource, into CWPU-LX exemplifies the commitment to environmentally conscious practices and underscores the significance of greener materials in achieving a more sustainable future.