Tunable production strategy for lignin-containing cellulose nanofibers from aspen biochemical mechanical pulp

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Lignin retention during nanocellulose production critically influences the ultraviolet (UV) barrier, antioxidant, mechanical, and hydrophobic properties of bio-based films, but conventional single-step treatments offer limited compositional tunability. Here, we integrate beating pretreatment with tartaric acid (TA) hydrolysis to produce lignin-containing cellulose nanofibers (LCNFs) from aspen biochemical mechanical pulp. By varying beating degree (20–60 °SR) and TA dosage (TA:pulp = 2:1–4:1), the lignin content, fibril morphology (predominantly 20–40 nm), and surface chemistry of LCNFs were systematically regulated. The resulting films exhibited tunable tensile strength (19.15–42.44 MPa), water contact angle (54.30–73.05 °), and DPPH radical scavenging activity (up to 57.76%), with all samples completely blocking UVB radiation. Rather than a single optimum, the beating–TA combination defines a two-dimensional control space for tailoring LCNF properties to specific performance requirements.