Preparing Flexible, Ductile, and Transparent Lignocellulose Composite Films via a Chemical (Betaine) and Mechanical (3D Printing) Combined Approach

Developing highly mechanically resilient and transparent cellulose films is critical for use in next-generation degradable electronics. The use of synthetic plasticizers and additives is a detour that impairs the biocompatibility and biodegradability of the final product. This study utilized betaine, which can be easily obtained from vegetables, in preparing flexible, ductile, and highly transparent lignocellulose nanofibrils (LCNFs) films through direct ink writing (DIW). An optimum 40 wt % betaine content of dry LCNFs endowed the films with outstanding optical transmittance (87%) at 800 nm. The maximum elongation at break of the betaine-containing lignocellulose nanofibril (LCNFsB) film reached 13.9 ± 0.5%, representing a 309% increase compared to the plain LCNFs film. We systematically investigated the shear-induced alignment between the DIW and doctor blade patterning (weak shear force) approaches. The DIW printed films exhibited an overall more uniform arrangement of fibrils and better control during the aligned film preparation. Thus, a higher tensile strength (40 ± 0.7 MPa) of the PLCNFsB-40% film than that of the DBLCNFsB-40% film (29 ± 1.19 MPa) was achieved. Overall, a combination approach of adding a green and inexpensive additive of betaine (chemical) and shear force-induced fibril orientation (mechanical) contributes to LCNFs films for applications in next-generation flexible electronics.