Abstract:
The lignin-based film was obtained by addition polymerization of lignin and polycaprolactone (PCL) by using hexamethylene diisocyanate (HDI) as the linking agent and stannous isooctylate as the catalyst. The structure and properties of the materials were characterized by infrared spectroscopy (FT-IR), NMR, XRD, thermogravimetry (TG), mechanical properties, contact angle, UV test and scanning electron microscopy (SEM). The effects of lignin content, isocyanate fraction and molecular weight of PCL on the properties of the films were also investigated. The results showed that the biodegradable soft polycaprolactone was successfully introduced into the lignin. The initial degradation temperature reached at 338.10 ℃ with the mass fraction of lignin of 36.36%, indicating that the modification enhanced the thermal stability of lignin. The obtained film was flexible without breaking and exhibited prominent mechanical strength. The elongation at break and tensile strength of the film could reach at 1 114.84% and 17.66 MPa at the mass fraction of lignin of 9.09%, respectively .With the increase of mass fraction of lignin, the mechanical properties of the film were decreased, but when the mass fraction of lignin was 27.27%, the elongation at break, tensile strength and elastic modulus of the film could still reach about 235.09%, 24.70 MPa and 262.49 MPa, respectively. Furthermore, the hydrophilic properties of the film was tunable with respect to the composition which could be adjusted as on-demand during practical applications. Exceptionally, UV absorption test manifested that the films had extraordinary UV-shielding property and could block against 100% UV light in the UV region (290—400 nm). Thus, these lignin-based films have great prospect for diverse promising applications, such as agricultural fields, packaging areas and UV-shielding biomaterial fields.