Fabrication of lignin-containing nanocellulose and films based on wheat straw pretreated by deep eutectic solvent

Objective In order to efficiently utilize wheat straw raw materials, a new type of deep eutectic solvent (DES) was developed to achieve the preparation of lignin containing nanocellulose and the subsequent construction of functional materials.

Method Wheat straw was used as the raw material. Lignin-containing nanocellulose was prepared by different DES pretreatments (benzyltrimethylammonium chloride-oxalic acid DES and benzyltriethylammonium chloride-oxalic acid DES) combined with high-pressure homogenization. Polyvinyl alcohol (PVA)/lignin-containing nanocellulose composite films were prepared using the solution casting method. The study comparatively examined the microstructure, chemical groups, thermal stability, dispersibility of the lignin-containing nanocellulose, as well as the optical properties, microstructure, and mechanical properties of the composite films.

Result The residues of wheat straw pretreated by benzyltrimethylammonium chloride-oxalic acid DES showed smaller residue sizes and enhanced thermal stability. The obtained lignin-containing nanocellulose exhibited stronger negative charge (−8.62 mV) and the composite films demonstrated higher haze (36.82%). In contrast, lignin-containing nanocellulose prepared with benzyltriethylammonium chloride-oxalic acid DES maintained higher transparency of the composite films (> 67%) and achieved a maximum film tensile strength of 57.16 MPa.

Conclusion Benzyltrimethylammonium chloride-oxalic acid DES is more advantageous in enhancing the negative charge of lignin-containing nanocellulose and increasing the haze of the composite films. Benzyltriethylammonium chloride-oxalic acid DES is more effective in improving the transparency and mechanical strength of the composite films, meeting the needs of different light management applications.