Stoichiometrically and sequentially optimized periodate–chlorite oxidations generate tunable C2,C3 dialdehyde–dicarboxylate CNFs/CNCs for tough amphiphilic and wet shape recoverable aerogels.

With downward pressure on the value of almond hulls (AHs), the major byproduct from the largest tree nut crop globally, the streamlined production of several grades of cellulose nanofibrils (CNFs) toward novel aerogels with concurrent sugar extraction was introduced to synergistically drive these products toward commercial adoption. Hot water extraction produced 50% lignocellulose (LC) with equal water-soluble sugars from AH of a soft-shell variety. Aqueous NaOH and NaClO 2 /KOH treatments isolated ca. 15% alkali cellulose and 12% cellulose, respectively. Coupled 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation and blending yielded 88, 91, and 95% LC micro-/nanofibrils (LCMNFs), alkali cellulose nanofibrils (ACNFs), and cellulose nanofibrils (CNFs) with, respectively, 0.76, 1.02, and 0.84 mmol/g surface carboxyls in a similar 4:1 width-to-thickness aspect ratio and ultrahigh length-to-thickness aspect ratios (800−1900). The LCMNF aerogel was mostly wet-resilient, wet-stable, and dry/wet shape-recoverable, whereas the most charged ACNFs gave the stiffest aerogel [31.6 kPa/(mg/cm 3 )].

Municipal solid waste (MSW) is a major source of greenhouse gas emissions unless its carbons are sequestered into highervalue products. This study focuses on isolating organic solids and cellulose-rich fibers from MSW via high-pressure steam treatment and converting the fibrous, prepulped materials from wastepaper, packaging materials, cardboard, etc., into value-added cellulose nanofibrils. Chemical−mechanical defibrillation of steam-treated municipal solid waste was optimized using heterogeneous and nonregioselective carboxymethyl etherification coupled with shearing by blender, thus transforming a heterogeneous mix of MSW into homogeneous carboxymethyl holocellulose nanofibrils without the use of conventional pretreatments of crude cellulosic feedstock. These carboxymethylated, hemicellulose-coated, cellulose nanofibrils were isolated quantitatively at >95% yield with widths 3−8 nm, thicknesses 1−3 nm, and lengths up to 1000 nm. We posit that this advancement of combining an inexhaustible, global supply of waste cellulose, large-scale steam autoclaving pretreatment, and an industrially relevant carboxymethylation process could unlock the higher potential of sustainable cellulosic nanomaterials for a circular economy.

Rice straw cellulose nanofibrils from the optimal 2,2,6,6-tetramethylpiperidine-1-oxyl oxidation/blending process carrying 1.17 mmol/g surface carboxyls were protonated to varying charged (COO − Na + ) and uncharged (COOH) surfaces. Reducing the electrostatic repulsion of surface charges by protonation with hydrochloric acid from 11 to 45 and 100% surface carboxylic acid most prominently reduced the aerogel densities from 8.0 to 6.6 and 5.2 mg/cm 3 while increasing the mostly open cell pore volumes from 125 to 152 and 196 mL/g. Irrespective of charge levels, all aerogels were amphiphilic, super-absorptive, stable at pH 2 for up to 30 days, and resilient for up to 10 repetitive squeezing-absorption cycles. While these aerogels exhibited densitydependent dry [11.3 to 1.5 kPa/(mg/cm 3 )] and reduced wet [3.3 to 1.4 kPa/(mg/cm 3 )] moduli, the absorption of organic liquids stiffened the saturated aerogels. These data support protonation as a critical yet simple approach toward precise control of aerogels' dry and wet properties.