Castor oil graphted lignin-based polyurethane film with excellent barrier properties

Bio-based polyurethane materials with good barrier properties are gaining increasing attention for their potential in alleviating energy shortages. In this work, natural lignin first underwent a two-step esterification modification using succinic acid (SA) and 6-mercapto-1-hexanol (6-MCH) modified castor oil. The resulting modified lignin exhibited both flexibility and high reactivity. It was further reacted with hexamethylene diisocyanate (HDI) to synthesize a high-bio-based-content polyurethane material (>70 %) with excellent UV resistance and barrier properties. The incorporation of modified castor oil significantly enhanced the mechanical properties of the lignin-based polyurethane and improved its water vapor barrier performance due to its intrinsic hydrophobicity. When the molar ratio of hydroxyl groups in the modified castor oil to carboxyl groups in the modified lignin was 5:1, the resulting polyurethane (5:1-PU) DEMONSTRATED a tensile strength of 10.0 ± 0.1 MPa, toughness of 468.3 ± 3.3 MJ·m −3 , a water contact angle of 98.3°, and a water vapor transmission rate (WVTR) of 2.10 ± 0.39 g/m 2 ·24h. This approach, which grafts lignin with castor oil, enables the high-value utilization of lignin and offers a sustainable pathway for developing bio-based barrier materials as alternatives to petroleum-based films.