Tunable dialdehyde/dicarboxylate nanocelluloses by stoichiometrically optimized sequential periodate–chlorite oxidation for tough and wet shape recoverable aerogels

Abstract

Sequential periodate–chlorite (PC) oxidation has been optimized stoichiometrically according to the non-crystalline content in cellulose to generate a variety of versatile C2,C3 dialdehyde/dicarboxylate nanocelluloses (NCs) while economizing chemical and shear force inputs. The robust primary sodium periodate (NaIO₄) oxidation not only regioselectively cleaved the C2–C3 carbon bond to oxidize the vicinal hydroxyls to aldehydes, but also governed the lengths of NCs, i.e., cellulose nanofibrils (PC-CNFs) at near-equal NaIO₄ to non-crystalline anhydroglucose unit (AGU) stoichiometry and cellulose nanocrystals (PC-CNCs) at a doubled ratio. Secondary sodium chlorite (NaClO₂) oxidation facilely converted C2,C3 dialdehydes to dicarboxylates and, upon deprotonation, facilitated defibrillation to NCs, irrespective of extents of carboxylation or charges. The optimal 0.5 : 1 NaIO₄/AGU and 1 : 1 NaClO₂/AGU oxidation produced highly uniform 1.26 nm thick, 3.28 nm wide, and ca. 1 μm long PC-CNFs with tunable surface aldehyde (0.71–0.0 mmol g⁻¹) and carboxylate (0.64–1.35 mmol g⁻¹) content at 94–98% yields. The C2–C3 glucosidic ring opening and oxidation along the 110 or 10 crystalline surfaces increased the heterogeneity of the hydrophilic surfaces and flexibility of PC-CNFs to influence their self-assembling into fibrils and amphiphilic superabsorbent aerogels. The ultra-light (ρ = 10.3 mg cm⁻³) aerogels showed an ultra-high dry specific compression modulus (50.2 kPa mg⁻¹ cm⁻³) and specific stress (8.2 kPa mg⁻¹ cm⁻³ at 0.8 strain), cyclic wet compressive behavior, and excellent water-activated shape recovery following 0.8 strain dry compression.