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 (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.