1,721,008 research outputs found
Formation of nanostructured cellulose stearoyl esters via nanoprecipitation
No full textNanoparticles (NPs) from derivatives of native polysaccharides have not been as intensively studied yet as those from synthetic polymers. In this report, NPs in aqueous suspensions were fabricated using cellulose stearoyl esters (CSEs) with different molecular weights via nanoprecipitation using dropping and dialysis techniques. The average diameters of NPs depended strongly on the concentrations of CSE solutions, molecular weights of CSE and also the nanoprecipitation technique. Both nanoprecipitation techniques are based on different mechanisms and NPs from dialysis are generally larger than NPs from dropping. The mechanism for dropping nanoprecipitation was further analyzed based on the properties of NPs which contain crystallized stearoyl groups in CSE chains. The average diameters of freshly-prepared CSE nanoparticles decreased with rising temperature, which is accompanied by the release of THF from the interior of NPs. The intensity of the size reduction of up to 35% depended on the one hand on the concentration of CSE solutions, and on the other hand on the molecular weights of CSEs. Finally, it was shown that these NPs can be used for the fabrication of temperature-responsive superhydrophobic surfaces
Thermo-responsive superhydrophobic paper using nanostructured cellulose stearoyl ester
No full textHydrophilic paper was rendered with hydrophobic and superhydrophobic property after the treatment with solutions and nanoparticles of cellulose stearoyl ester (CSE), respectively. Cellulose stearoyl ester with a degree of substitution of 2.99 was synthesized from cellulose using stearoyl chloride. By dip-coating paper in CSE solution of at least 3 mg/ml in toluene, paper became hydrophobic with stable water contact angles of more than 120°. After further spray-coating using CSE nanoparticles that were prepared from CSE solution via nanoprecipitation, paper surface became superhydrophobic with water contact angles of larger than 150°. These superhydrophobic surfaces also exhibited self-cleaning character. Furthermore, the superhydrophobic paper surfaces showed a temperature-responsive character and could be turned hydrophobic after a heat-treatment at 70 °C for 5 min
Facile formation of stimuli-responsive, fluorescent and magnetic nanoparticles based on cellulose stearoyl ester via nanoprecipitation
No full textIn comparison to stimuli-responsive, multi-functional nanoparticles (NPs) from synthetic polymers, such NPs based on sustainable, naturally occurring polysaccharides are still scarce. In the present study, stable stimuli-responsive, fluorescent and magnetic NPs were fabricated using cellulose stearoyl esters (CSEs) consisting of cellulose and stearoyl groups. The multifunctional NPs with the average diameters between 80 and 250 nm were obtained after facile nanoprecipitation using CSE solutions containing Fe3O4-NPs. Using the aqueous solution of fluorescent rhodamine B as precipitant, NPs with rhodamine B on NP surface were obtained. Rhodamine B could be released depending on the temperature. In comparison, stearoylaminoethyl rhodamine B can be encapsulated in CSE-NPs, which renders obtained NPs reversible fluorescence in response to UV illumination and heat treatment
Superhydrophobic surfaces fabricated from nano- and microstructured cellulose stearoyl esters
No full textRobust, superhydrophobic and self-cleaning films were fabricated using nano- or microstructured cellulose fatty acid esters, which were prepared via nanoprecipitation. The superhydrophobic films could be coated on diverse surfaces with non-uniform shapes by distinct coating techniques
Solid-State Spectroscopic Characterization of α-Chitins Deacetylated in Homogeneous Solutions
No full textControlling water transportation within hydrogels makes hydrogels attractive for diverse applications, but it is still a very challenging task. Herein, a novel type of dually electrostatically crosslinked nanocomposite hydrogel showing thermoresponsive water absorption, distribution, and dehydration processes are developed. The nanocomposite hydrogels are stabilized via electrostatic interactions between negatively charged poly(acrylic acid) and positively charged layered double hydroxide (LDH) nanosheets as well as poly(3‐acrylamidopropyltrimethylammonium chloride). Both LDH nanosheets as crosslinkers and the surrounding temperatures played pivotal roles in tuning the water transportation within these nanocomposite hydrogels. By changing the surrounding temperature from 60 to 4 °C, these hydrogels showed widely adjustable swelling times between 2 and 45 days, while the dehydration process lasted between 7 and 27 days. A swift temperature decrease, for example, from 60 to 25 °C, generated supersaturation within these nanocomposite hydrogels, which further retarded the water transportation and distribution in hydrogel networks. Benefiting from modified water transportation and rapidly alternating water uptake capability during temperature change, pre‐loaded compounds can be used to track and visualize these processes within nanocomposite hydrogels. At the same time, the discharge of water and loaded compounds from the interior of hydrogels demonstrates a thermoresponsive sustained release process
Synthesis of carboxyl cellulose sulfates with regioselective sulfation and regiospecific oxidation using cellulose trifluoroacetate as intermediates
No full textSynthesis of cellulose sulfates (CSs) and carboxyl cellulose sulfates (COCSs) with regioselectively or regiospecifically distributed functional groups within anhydroglucose units was reported. CS with regioselectively distributed sulfate groups at 2,3-O- or 2,6-O-position were homogeneously synthesized and cellulose trifluoroacetate (CTFA) was used as intermediates. The trifluoroacetyl groups were detected primarily at 6-O-position and their distributions could be altered by changing the amount of trifluoroacetyl anhydride (TFAA). Various sulfating agents were used for further homogeneous sulfation of CTFA. The total degree of sulfation (DSS) and the distribution of sulfate groups within the repeating units were affected by the amount of TFAA, the type and amount of sulfating agents. Subsequent homogenous 4-acetamide-TEMPO or TEMPO-mediated oxidation of CS led to COCS with carboxyl groups regiospecifically distributed at C6 position, which may be interesting structural mimics for natural occurring heparin
Reversibly Crystalline Nanoparticles from Cellulose Alkyl Esters via Nanoprecipitation
No full textNanoparticles (NPs) from biopolymers, in particular polysaccharides, attract much attention but they are rarely systematically investigated in comparison to NPs from synthetic polymers. In this report, stable aqueous suspensions of NPs from cellulose alkyl esters with different alkyl chain lengths (cellulose stearoyl, lauroyl, and caproyl ester) and degrees of substitution (DS) are fabricated via nanoprecipitation. Their properties are investigated in terms of the average size, surface charge and polarity, temperature‐responsive crystalline structure, and dry‐state morphology, in relationship with the chemical compositions of cellulose esters. Generally, the average diameters of NPs increase with higher DS and longer alkyl chains length, but the surface hydrophobicity decreases with longer alkyl chain length. The presence of the crystallizable stearoyl groups along polymeric backbones renders polymeric NPs with reversibly temperature‐responsive property. The NPs from cellulose stearoyl esters (CSE) with stearoyl groups of high contents (DS of 1.3 and 3) and poly(vinyl stearate) can be altered between more crystalline, solid nanospheres, and amorphous, liquid nanodroplets without the loss of their stability by changing the temperature. In comparison, NPs from CSE with a low DS of 0.3, cellulose lauroyl and caproyl ester contain only slightly ordered structure
Analysis of carboxylate groups in oxidized never-dried cellulose II catalyzed by TEMPO and 4-acetamide-TEMPO
No full textIn this report, never-dried regenerated celluloses, i.e. cellulose II, from their NaOH/urea/H2O solutions were subjected to TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) or 4-acetamide-TEMPO-mediated oxidation. Water-soluble and -insoluble fractions of carboxyl cellulose (COC) were obtained and their DO were determined to be between 0.08 and 0.85. Apart from conductometric titration, complexometric titration with EDTA was used to analyze the DO of COC. The conductometric titration can be used for lowly or highly oxidized celluloses, while the complexometric titration with EDTA is only adequate for COC with DO lower than 0.6. FT Raman spectroscopy represents characteristic bands of carboxyl and carboxylate groups. It demonstrates the feasibility of establishing novel analyzing methods for DO of COC with high correlation coefficients of up to 0.9867. Moreover, long oxidation duration, high temperature and high amounts of oxidizing agents are important for the synthesis of COC with high DO and yields
Synthesis and spectroscopic analysis of cellulose sulfates with regulable total degrees of substitution and sulfation patterns via 13C NMR and FT Raman spectroscopy
No full textSynthesis and spectroscopic characterisation of cellulose sulfate (CS) were reported. Various CS exhibiting diverse degrees of sulfation (DSS) were prepared through acetosulfation or direct sulfation of cellulose. During the acetosulfation, intermediate product – cellulose acetate sulfate (CAS) – was formed after the comparative esterification and subsequent deacetylation of CAS led to CS. The direct sulfation proceeded quasi-homogeneously and heterogeneously in N,N-dimethylformamide (DMF) or homogeneously in N,N-dimethylacetamide (DMAc)/LiCl mixture. The total DSS between 0.21–2.59 and partial DSS6 as well as DSS2 of up to 1 were determined via elemental analysis and 13C NMR spectroscopy. Besides, solid-state CP/MAS 13C NMR could characterise CS regarding the sulfation. Subsequently, FT Raman investigation of obtained CS was conducted with the aim to establish analysis methods quantifying the total DSS. The intensities of Raman bands ascribed to the vibrations of OSO and C–O–S groups were used as analysis parameters, yielding calibration curves with high correlation coefficients of more than 0.96
Transparent Slippery Surfaces Made with Sustainable Porous Cellulose Lauroyl Ester Films
No full textIn recent years, liquid repellent surfaces have attracted considerable attention because of their wide array of potential applications. In the present study, slippery surfaces were fabricated using novel sustainable, nanoporous cellulose lauroyl ester (CLE) films and slippery lubrication fluid. The nanoporous CLE films were obtained after spray-coating target surfaces using a nanoparticle suspension of CLE that was prepared via nanoprecipitation. After the deposition of the slippery liquid within the porous network, the obtained slippery surfaces exhibit both excellent liquid repellency upon liquid impact and anti-icing properties (by significantly retarding the icing time). Three-dimensional droplet manipulation was also achieved on these surfaces by taking advantage of the materials’ low contact angle hysteresis and low adhesion property
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