12 research outputs found

    2‑Bromopropionyl Esterified Cellulose Nanofibrils as Chain Extenders or Polyols in Stoichiometrically Optimized Syntheses of High-Strength Polyurethanes

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    2-Bromopropionyl bromide esterified cellulose nanofibrils (Br-CNFs) facilely synthesized from one-pot esterification of cellulose and in situ ultrasonication exhibited excellent N,N-dimethylformamide (DMF) dispersibility and reactivity to partially replace either chain extender or soft segment diol in the stoichiometrically optimized syntheses of polyurethanes (PUs). PUs polymerized with Br-CNF to replace either 11 mol% 1,4-butadiol chain extender OHs or 1.8 mol% polytetramethylene ether glycol OHs, i.e., 1.5 or 0.3 wt% Br-CNF in PUs, exhibited an over 3 times increased modulus, nearly 4 times higher strength, and a 50% increase in strain. In either role, the experimental modulus exceeding those predicted by the Halpin–Tsai model gave evidence of the stoichiometrically optimized covalent bonding with Br-CNF, while the improved strain was attributed to increased hydrogen-bonding interactions between Br-CNF and the soft segment. These new Br-CNFs not only offer novel synthetic strategies to incorporate nanocelluloses in polyurethanes but also maximize their reinforcing effects via their versatile polyol reactant and cross-linking roles, demonstrating promising applications in the synthesis of other polymers

    Dual Wet and Dry Resilient Cellulose II Fibrous Aerogel for Hydrocarbon–Water Separation and Energy Storage Applications

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    Cellulose fibrous aerogels have been fabricated by a facile and aqueous process that disintegrated electrospun cellulose fibers (ECFs) and reassembled via freezing/freeze-drying with significantly improved dry resiliency and spontaneous 89% shape recovery from ca. 70% compressive strain. Owing to the resilient and 200–300 nm wide ECFs, the cellulose fibrous aerogels exhibited excellent dual dry and wet resiliency as well as improved pore accessibility. The fibrous cellular walls interconnect the aerogel pore structure to allow extraordinary liquid absorption capacity up to 373 g/g, accounting for 95% of the theoretical absorption capacity. Both highly dry resilient and absorbent properties of the ECF aerogel are highly advantageous for hydrocarbon/oil contamination removal and for hydrocarbon/water separation applications. In addition, the ECF aerogel could be carbonized into carbon aerogel in supercapacitors for energy storage

    Self-assembling of TEMPO Oxidized Cellulose Nanofibrils As Affected by Protonation of Surface Carboxyls and Drying Methods

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    Self-assembling of cellulose nanofibrils (CNFs) as affected by varying extent of protonation on C6 surface carboxyls was investigated under freeze-drying and air-drying processes. Surface carboxyls were protonated from 10.3 to 100%, all on the same TEMPO oxidized and mechanically blended CNFs with identical geometries and level of oxidation. Upon freeze-drying, all CNFs assembled into amphiphilic mass. The mostly charged CNFs assembled into the finest and most uniform fibers (ϕ = 137 nm) that absorbed significantly more nonpolar toluene than water; whereas the fully protonated CNFs assembled extensively into porous and more thermally stable ultrathin filmlike structures that absorbed water and toluene similarly. Ultrafiltration and air-drying induced cyrstallization led to more thermally stable, semitransparent, and hydrophilic films that showed no affinity toward nonpolar toluene. In essence, CNFs could be tuned by varying the degree of surface carboxyl protonation, along with drying processes, to create fibrous to film morphologies, amphiphic to hydrophilic properties, and higher thermal stability

    Preparation of Activated Carbon and Silica Particles from Rice Straw

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    An efficient three-step process using toluene/ethanol, NaClO<sub>2</sub>, and KOH has been successfully devised to isolate pure cellulose from rice straw while generating two filtrates as activated carbon and silica precursors. The NaClO<sub>2</sub> dissolution filtrate contains oxidized lignin and hemicellulose as carbon precursors as well as sodium carbonates as activating agents for direct carbonization (800 °C) into highly porous (0.90 cm<sup>3</sup>/g), high specific surface area (997 m<sup>2</sup>/g), activated carbon particles (100–500 nm). The KOH dissolution filtrate contains mainly potassium silicate that could be precipitated by dilute acidified poly­(ethylene oxide) and calcinated (500 °C) to pure, uniformly sized (100–120 nm), nonporous silica nanospheres. Deriving these additional activated carbon and silica particles along with nanocellulose creates advance materials while fully utilizing all major components in rice straw, the highest quantity agricultural crop byproduct in the world

    Synthesis of Cellulose Nanofibril Bound Silver Nanoprism for Surface Enhanced Raman Scattering

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    Silver nanoprisms (AgNPs) were robustly synthesized using TEMPO-oxidized cellulose nanofibrils (CNFs) as a dual capping and shape-regulating agent for the first time. Reducing AgNO<sub>3</sub> with NaBH<sub>4</sub> in CNF suspensions produced smaller but more uniform Ag nanospheres (AgNSs) with increasing Ag<sup>+</sup>/CNF ratios. CNF bound AgNSs were facilely transformed to AgNPs by etching with H<sub>2</sub>O<sub>2</sub>, supporting the capping and shape-regulating capability of CNFs. AgNPs could also be synthesized directly in a one-shot reduction reaction with NaBH<sub>4</sub> in the presence of both CNFs and H<sub>2</sub>O<sub>2</sub>. The AgNPs transformed from CNF bound AgNSs are similar to those synthesized directly, but more stable against H<sub>2</sub>O<sub>2</sub>. Successful synthesis of AgNPs with 80–320 nm truncated edges was confirmed by light blue solution color, sharp out-of-plane quadruple resonance peak at 334 nm and prominent in-plane dipole resonance peaks at 762–900 nm. The [111] lattice plane of AgNP was clearly evident by its predominant XRD peak at 38°, confirming the unique shape-regulating ability of the nearly fully surface carboxylated CNFs. The CNF surface bound AgNPs were easily fabricated into freestanding CNF/AgNPs films that showed excellent surface enhanced Raman scattering of Rhodamine 6G with analytical enhancement factor of 5 × 10<sup>3</sup> in contrast to none from the CNF/AgNSs film

    Dual Wet and Dry Resilient Cellulose II Fibrous Aerogel for Hydrocarbon–Water Separation and Energy Storage Applications

    No full text
    Cellulose fibrous aerogels have been fabricated by a facile and aqueous process that disintegrated electrospun cellulose fibers (ECFs) and reassembled via freezing/freeze-drying with significantly improved dry resiliency and spontaneous 89% shape recovery from ca. 70% compressive strain. Owing to the resilient and 200–300 nm wide ECFs, the cellulose fibrous aerogels exhibited excellent dual dry and wet resiliency as well as improved pore accessibility. The fibrous cellular walls interconnect the aerogel pore structure to allow extraordinary liquid absorption capacity up to 373 g/g, accounting for 95% of the theoretical absorption capacity. Both highly dry resilient and absorbent properties of the ECF aerogel are highly advantageous for hydrocarbon/oil contamination removal and for hydrocarbon/water separation applications. In addition, the ECF aerogel could be carbonized into carbon aerogel in supercapacitors for energy storage

    Surface and Structure Characteristics, Self-Assembling, and Solvent Compatibility of Holocellulose Nanofibrils

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    Rice straw holocellulose was TEMPO-oxidized and mechanically defibrillated to produce holocellulose nanofibrils (HCNFs) at 33.7% yield (based on original rice straw mass), 4.6% higher yield than cellulose nanofibril (CNF) generated by the same process from pure rice straw cellulose. HCNFs were similar in lateral dimensions (2.92 nm wide, 1.36 nm thick) as CNF, but longer, less surface oxidized (69 vs 85%), and negatively charged (0.80 vs 1.23 mmol/g). HCNFs also showed higher affinity to hydrophobic surfaces than CNFs while still attracted to hydrophilic surfaces. By omitting hemicellulose/silica dissolution step, the two-step 2:1 toluene/ethanol extraction and acidified NaClO<sub>2</sub> (1.4%, pH 3–4, 70 °C, 6 h) delignification process for holocellulose was more streamlined than that of pure cellulose, while the resulting amphiphilic HCNFs were more hydrophobic and self-assembled into much finer nanofibers, presenting unique characteristics for new potential applications

    Dual Wet and Dry Resilient Cellulose II Fibrous Aerogel for Hydrocarbon–Water Separation and Energy Storage Applications

    No full text
    Cellulose fibrous aerogels have been fabricated by a facile and aqueous process that disintegrated electrospun cellulose fibers (ECFs) and reassembled via freezing/freeze-drying with significantly improved dry resiliency and spontaneous 89% shape recovery from ca. 70% compressive strain. Owing to the resilient and 200–300 nm wide ECFs, the cellulose fibrous aerogels exhibited excellent dual dry and wet resiliency as well as improved pore accessibility. The fibrous cellular walls interconnect the aerogel pore structure to allow extraordinary liquid absorption capacity up to 373 g/g, accounting for 95% of the theoretical absorption capacity. Both highly dry resilient and absorbent properties of the ECF aerogel are highly advantageous for hydrocarbon/oil contamination removal and for hydrocarbon/water separation applications. In addition, the ECF aerogel could be carbonized into carbon aerogel in supercapacitors for energy storage

    Assembling and Redispersibility of Rice Straw Nanocellulose: Effect of <i>tert</i>-Butanol

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    Self-assembling of sulfuric-acid-hydrolyzed cellulose nanocrystals (CNCs, 6.4 nm wide) and TEMPO oxidized cellulose nanofibrils (CNFs, 2.1 nm wide) from aqueous suspensions was induced by rapid freezing (−196 °C, 10 min) and slow lyophilization (−50 °C, 0.05 mbar, 2 days). The assembled structures contain submicron (200–700 nm) wide and tens of micrometer long fibers at up to 0.1–0.5% and 0.01–0.05%, the critical fiber-to-film transformation concentrations for CNCs and CNFs, respectively. The assembled fiber widths were significantly reduced to ∼40 nm, that is, by 1 order of magnitude, when 10% of the aqueous media was replaced with <i>tert</i>-butanol. Further increasing <i>tert</i>-butanol contents in the media to 93/7 (CNCs) and 50/50 (CNFs) <i>tert</i>-butanol/water, both at 0.1% nanocellulose concentration, reduced longitudinal assembling for CNCs and lateral assembling for CNFs as well as increased critical fiber-to-film transformation concentration for CNFs. While all assembled structure could be redispersed in water, those from <i>tert</i>-butanol/water could also be easily redispersed in DMF aided with brief 2 min ultrasonication. None of the assembled structures could be redispersed in the lower dielectric constant ethanol, acetone or chloroform
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