No abstract

Lignin hollow nanospheres with a single hole were prepared through a straightforward self-assembly method, which included dissolving enzymatic hydrolysis lignin, a byproduct derived from biorefinery, in tetrahydrofuran and afterward dropping deionized water to the lignin/tetrahydrofuran solution. The formation mechanism and structural characteristics of the lignin hollow nanospheres were explored. The results indicated that the nanospheres exhibited hollow structure due to the effect of tetrahydrofuran on the self-assembly behavior. Hydrophobic outside surface and hydrophilic internal surface were formed via layer-by-layer self-assembly method from outside to inside based on π–π interactions. The chemical structure of lignin did not produce a significant change in the preparation process of lignin hollow nanospheres. With increasing of initial lignin concentration, the diameter of the nanospheres and the thickness of shell wall increased, while the diameter of the single hole, the surface area, and the pore volume of the nanospheres decreased. The surface area reached the maximum value (25.4 m2 g–1) at an initial lignin concentration of 0.5 mg/mL in setting concentration range. Increasing the stirring speed or dropping speed of water resulted in a decrease of the diameter of the hollow nanospheres. Moreover, an apparent change of the average diameter of the nanospheres was not observed after 15 days, and the nanosphere dispersions were stable at pH values between 3.5 and 12. The lignin hollow nanospheres with a single hole offer a novel route for a value-added utilization of lignin and would improve the biorefinery viability.

Lignin nanospheres/poly(vinyl alcohol) (LNS/PVA) nanocomposite films were prepared through solvent casting approach. Compared with lignin/PVA blend film, LNS could be evenly dispersed in PVA matrix, and the nanocomposite films did not generate macroscopic phase separation. Maximum decomposition temperature (T max ) and glass transition temperature (T g ) of pure PVA film were 264.7 and 104.2 °C, while the T max and T g of the nanocomposite film containing 1 wt % LNS increased to 272.1 and 116.8 °C, respectively. Moreover, with increasing of LNS content in PVA matrix, the T max and T g of the nanocomposite films gradually increased. Adding a certain amount of LNS in PVA could improve mechanical strength of the films under the condition of elongation at break in a small amount of loss. The nanocomposite films outperformed the lignin/PVA blend film in UV-absorbing and transparency, which are a promising candidate for medicine bottles and food packaging.