A simple one-pot method to prepare UV-absorbent lignin/silica hybrids based on alkali lignin from pulping black liquor and sodium metasilicate

A novel coprecipitation process was developed to prepare lignin/silica hybrids using sodium metasilicate and alkali lignin (AL) from pulping black liquor. AL was first modified by quaternization to synthesize quaternized alkali lignin (QAL). The QAL/SiO 2 hybrids with different contents of lignin, which were prepared via the coprecipitation of QAL and sodium metasilicate in aqueous solution, were microspheres having a diameter of 300–400   nm and that were analyzed by SEM, TEM, FT-IR, XPS, XRD, and TG analysis. Interestingly, these novel QAL/SiO 2 hybrids showed excellent UV-absorption performance and could effectively protect the polyurethane (PU) film from UV radiation when they were blended with PU. The UV transmittance of the PU film was reduced from 13.4% to 0.1% below 315   nm and from 74.8% to 9.7% below 400   nm when the content of the QAL/SiO 2 hybrids increased from 0 to 1.0 wt%. Furthermore, the mechanical properties were also improved owing to the good compatibility between the QAL/SiO 2 hybrids and PU. The results of this study are of significant and practical importance to the value-added utilization of lignin.