Green Modification of Maple Leaf-Derived Lignin-Containing Nanocellulose through Mechanochemistry for 3D Printable Pickering Emulsions

Mechanochemistry offers a simple and sustainable approach to chemical modification. In this work, lignin-containing cellulose nanocrystals (LCNCs) and lignin-containing cellulose nanofibrils (LCNFs) derived from fallen maple leaves are modified with isoleucine by ball milling, and their potential as sustainable stabilizers of high internal phase Pickering emulsions (HIPPEs) for extrusion-based 3D printing is investigated. For the first time, it has been observed that LCNCs swell significantly after ball milling, with length and diameter increases of approximately 4.3 times and 30 times, respectively, while LCNFs undergo defibrillation and size reduction by about 61% without noticeable swelling. Isoleucine is selected as a model amino acid to modify LCNCs and LCNFs and successfully improves their wettability, which increases the contact angle from 74.6° to 94.1° for LCNCs and from 63.9° to 82.6° for LCNFs, resulting in improved emulsifying performance. Despite different swelling ratios, HIPPEs stabilized by isoleucine-modified LCNCs exhibit superior rheological properties and 3D printing performance (printing precision of about 96%) compared to isoleucine-modified LCNFs and other biopolymer stabilizers, enabling high shape fidelity and structural integrity of printed items. Therefore, this work demonstrates the feasibility of ball milling-assisted amino acid modification of nanocellulose for the development of sustainable and high-performance all biobased HIPPEs.