Lignocellulose nanofiber/polylactic acid (LCNF/PLA) composite with internal lignin for enhanced performance as 3D printable filament

Abstract

The use of lignocellulose materials to prepare reinforced composites for 3D printing is promising. In this study, lignocellulose nanofibers (LCNFs) with different lignin contents (0.2–8.5%) were prepared and compounded with polylactic acid (PLA) for fabricating a 3D printable filament. The internal lignin of LCNFs served as an adhesive for improving the interfacial compatibility of LCNF/PLA composites. Alkali lignin (AL), as an external lignin, was used as a control sample. LCNFs, with a high yield of 85%, a diameter of less than 100 nm, and a length of several microns, were prepared by the swelling of glycerol and 0.64% (w/w) sulfuric acid and colloid mill grinding. Complexation of cellulose nanofiber (CNF) and LCNF with PLA can enhance the mechanical strength of PLA composites. Specifically, the flexural strength of the CNF/PLA composite was increased from 92.7 MPa to 151.2 MPa by combining 10% CNF (without lignin) with PLA. The flexural strength of LCNF/PLA composite with internal lignin content of 3.7% (0.37% of the total mass) was increased from 151.2 MPa to 234.5 MPa, which is 153.0% higher than that of pure PLA. However, external AL had an adverse influence on the mechanical strength of the AL/CNF/PLA composites. In addition, the 3D printable filament prepared using the LCNF/PLA composite exhibited good thermal stability, which was suitable for common fused deposition modeling (FDM) 3D printers. Various 3D printing materials, such as cake, egg, ball, bowl, dumbbell and strip shaped products, were designed and prepared by LCNF/PLA composites.