High lignin-containing nanocelluloses prepared via TEMPO-mediated oxidation and polyethylenimine functionalization for antioxidant and antibacterial applications

Abstract

Lignin-containing nanocelluloses (LNCs) have attracted tremendous research interest in recent years due to less complex extraction processes and more abundant functionality compared to lignin-free nanocelluloses. On the other hand, traditional defibrillation primarily based on bleached pulp would not be readily applied to lignin-containing pulps due to their complex compositions. This study was focused on LNC extraction from lignin-containing pulp via 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation. Three types of switchgrass pulp with varying composition were prepared using different acid-catalyzed pretreatments. The pulps contained as high as 45.76% lignin but minor/no hemicellulose, corresponding to up to 23.72% lignin removal and 63.75–100% hemicellulose removal. TEMPO-mediated oxidation yielded 52.9–81.9% LNCs from respective pulps. The as-produced LNCs possessed aspect ratios as high as 416.5, and carboxyl contents of 0.442–0.743 mmol g⁻¹ along with ζ-potential of −50.4 to −38.3 mV. The TEMPO-oxidized LNCs were further modified by polyethylenimine (PEI), which endowed the LNCs with positive charges plus antioxidant and antibacterial activities. Specifically, the PEI-modified LNCs almost fully scavenged 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) radicals at 50 mg L⁻¹ and suppressed the growth of Gram-positive Staphylococcus aureus at 250 μg mL⁻¹.