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

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 (NaIO 4 ) 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 NaIO 4 to non-crystalline anhydroglucose unit (AGU) stoichiometry and cellulose nanocrystals (PC-CNCs) at a doubled ratio. Secondary sodium chlorite (NaClO 2 ) 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 NaIO 4 /AGU and 1 : 1 NaClO 2 /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 11̄0 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.