Contribution of lignin in esterified lignocellulose nanofibers (LCNFs) prepared by deep eutectic solvent treatment to the interface compatibility of LCNF/PLA composites

Abstract

It is important to improve the interface compatibility between lignocelluloses (LCs) and biodegradable polylactic acid (PLA) for the preparation of strong composite materials. In the current study, esterified lignocellulose nanofibers (LCNFs) with high yield were prepared from LCs with different lignin contents (0.83–17.45 %) by swelling with a lactic acid/choline chloride deep eutectic solvent (LA/ChCl DES) at 100 ℃ for 3 h followed by mechanical colloid milling. Esterification occurred along with nanofibrillation of the LCs to obtain LCNFs having ester bonds with diameters mostly less than 100 nm. Lignin remained in the LCNFs with various contents. Uniform LCNF/PLA composites were prepared by a direct blending method. Lignin in the esterified LCNFs acted as an interface adhesive and played a key role in increasing the LCNFs interface compatibility with PLA, as well as strengthening the mechanical properties of the composites. The optimized flexural properties of the composites reached a maximum value of 204.5 MPa when 20 % LCNF (containing 10.92 % lignin) was added, which was 120.6 % higher than that of pure PLA. The prepared high-strength biodegradable composites have broad application prospects and great potential to replace non-degradable plastics.