Cellulose nanofibers from curaua fibers

Curaua nanofibers extracted under different conditions were investigated. The raw fibers were mercerized with NaOH solutions; they were then submitted to acid hydrolysis using three different types of acids (H₂SO₄, a mixture of H₂SO₄/HCl and HCl). The fibers were analyzed by cellulose, lignin and hemicellulose contents; viscometry, X-ray diffraction (XRD) and thermal stability by thermogravimetric analysis (TG). The nanofibers were morphologically characterized by transmission electron microscopy (TEM) and their surface charges in suspensions were estimated by Zeta-potential. Their degree of polymerization (DP) was characterized by viscometry, crystallinity by XRD and thermal stability by TG. Increasing the NaOH solution concentration in the mercerization, there was a decrease of hemicellulose and lignin contents and consequently an increase of cellulose content. XRD patterns presented changes in the crystal structure from cellulose I to cellulose II when the fibers were mercerized with 17.5% NaOH solution. All curaua nanofibers presented a rod-like shape, an average diameter (D) of 6–10 nm and length (L) of 80–170 nm, with an aspect ratio (L/D) of around 13–17. The mercerization of fibers with NaOH solutions influenced the crystallinity index and thermal stability of the resulting nanofibers. The fibers mercerized with NaOH solution 17.5% resulted in more crystalline nanofibers, but thermally less stable and inferior DP. The aggregation state increases with the amount of HCl introduced into the extraction, due to the decrease of surface charges (as verified by Zeta Potential analysis). However, this release presented nanofibers with better thermal stability than those whose acid hydrolysis was carried out using only H₂SO₄.     

Oxidation and structural changes in NMMO-regenerated cellulose films

Carbonyl and carboxyl groups introduced by oxidative processes during production and purification of celluloses determine intra- and intermolecular interactions and thus application-related bulk and surface properties of cellulosic materials. We report a comprehensive approach to the quantification of carboxyl and carbonyl groups in cellulose films upon reconstitution from NMMO solutions. Measurements of the excess conductivity were combined with the determination of the molecular weight distribution, quantification of the carboxyl and carbonyl group content, crystallinity and film swelling in aqueous solutions. TEMPO-oxidized, NMMO-regenerated cellulose films were additionally analysed as a reference system for extensive cellulose oxidation. Our reported data demonstrate that dissolution of cellulose in NMMO results in the formation of onic acids, chain degradation, increased ionization and film swelling, whereas TEMPO-oxidation introduced carbonyl groups as well as onic and uronic acids causing a significantly increased charging, ion accumulation and swelling even at higher crystallinity.     

The accessibility of cellulose as determined by dye adsorption

The accessibility of cotton cellulose was determined after it had been mercerized both in the slack and tension states. Mercerized samples were either dried or retained in the undried state before dyeing to determine their accessibilities by the adsorption of Direct Blue 1. Samples were characterized also by techniques such as moisture adsorption, water retention value (WRV) and X-ray analysis. It appeared that the crystallinity of cotton mercerized under tension was slightly increased during dyeing. Dye adsorption increased in the order nonmercerized <tension-mercerized <slack-mercerized. Products mercerized and not dried adsorbed more dye than counterparts given the same swelling treatment but dried after mercerization. The presence of dye in a sample mercerized and undried before dyeing did not affect its crystallinity. From both the dye adsorption and WRV data it was concluded that structural collapse of the fibre is greater for the slack-mercerized product than its tension-mercerized counterpart after it is dried. It was also concluded from dye adsorption and water adsorption data that about 34% of the internal surface of cotton and mercerized cotton, available for water adsorption, is inaccessible to Direct Blue 1.     

Mercerized cellulose biocomposites: a study of influence of mercerization on cellulose supramolecular structure, water retention value and tensile properties

In this study the effect of the mercerization degree on the water retention value (WRV) and tensile properties of compression molded sulphite dissolving pulp was evaluated. The pulp was treated with 9, 10, or 11 % aqueous NaOH solution for 1 h before compression molding. To study the time dependence of mercerization the pulp was treated with 12 wt% aqueous NaOH for 1, 6 or 48 h. The cellulose I and II contents of the biocomposites were determined by solid state cross polarization/magic angle spinning carbon 13 nuclear magnetic resonance (CP/MAS ¹³C NMR) spectroscopy. By spectral fitting of the C6 and C1 region the cellulose I and II content, respectively, could be determined. Mercerization decreased the total crystallinity (sum of cellulose I and cellulose II content) and it was not possible to convert all cellulose I to cellulose II in the NaOH range investigated. Neither increased the conversion significantly with 12 wt% NaOH at longer treatment times. The slowdown of the cellulose I conversion was suggested as being the result from the formation of cellulose II as a consequence of coalescence of anti-parallel surfaces of neighboring fibrils (Blackwell et al. in Tappi 61:71–72, 1978; Revol and Goring in J Appl Polym Sci 26:1275–1282, 1981; Okano and Sarko in J Appl Polym Sci 30:325–332, 1985). Compression molding of the partially mercerized dissolving pulps yielded biocomposites with tensile properties that could be correlated to the decrease in cellulose I content in the pulps. Mercerization introduces cellulose II and disordered cellulose and lowered the total crystallinity reflected as higher water sensitivity (higher WRV values) and poorer stiffness of the mercerized biocomposites.     

Water dispersion of cellulose II nanocrystals prepared by TEMPO-mediated oxidation of mercerized cellulose at pH 4.8

Mercerized wood cellulose was oxidized by 4-acetamide-TEMPO/NaClO/NaClO₂ system at 60 °C and pH 4.8 for 1–5 days. Mostly individual nanocrystals 4–7 nm in width and 100–200 nm in length were obtained by ultrasonication of the oxidized product in water. The nanocrystals had the cellulose II structure, and carboxylate contents of 2.0–2.4 mmol/g, indicating that these carboxylate groups were selectively formed on the cellulose II crystallite surfaces in mercerized cellulose. Moreover, the original wood cellulose and mercerized cellulose were acid-hydrolyzed, and then subjected to the TEMPO-mediated oxidation under the same conditions at pH 4.8 to prepare reference samples. TEM images, light transmittance and rheological properties of water dispersions showed that the nanocrystals prepared from mercerized cellulose by the TEMPO oxidation and sonication in water had the highest dispersibility of individual nanocrystals with less amounts of bundles in water, resulting from the highest carboxylate contents.     

Preparation and characterization of oxidized regenerated cellulose film for hemostasis and the effect of blood on its surface

Hemostatic effects of oxidized regenerated cellulose (ORC) are well-known but its mechanism has never been demonstrated clearly. Since thrombus formation is a kind of surface phenomenon, we changed the morphology of cellulose to form a kind of membrane with ionic liquid as solution, and also we prepared ORC films with nitrogen dioxide(NO₂)/carbon tetrachloride(CCl₄) oxidation system reacting for 16, 40, 64 and 88 h, respectively. FTIR and NMR spectra showed that NO₂/CCl₄ oxidation system had a high selectivity on hydroxyl group at C6 of regenerated cellulose. With the oxidation time prolonging, the carboxyl content was enhanced and the DP was reduced. The XPS results suggested that a new carboxyl bond was formed due to the increasing of oxygen content. From contact angle analysis, the wettability of blood on the ORC film surface was better than that of the regenerated cellulose film, which was beneficial for the blood to spread. SEM photographs showed that the ORC film oxidized for 40 h could adsorb and activate more platelets and erythrocytes. Hemostatic evaluation and enzyme-linked immunosorbent assay indicated that the ORC film had a dramatic hemostatic performance, and the products of platelets release reaction, activated platelets glycoprotein and activated clotting enzymes were increased simultaneously. Moreover, the possible mechanism of the hemostasis for ORC film was discussed.     

Water-Soluble Magnetic Nanocomposites Based on Carboxymethyl Cellulose and Iron(III) Oxide

The one-step synthesis of water-soluble composites from maghemite (γ-Fe₂O₃) nanoparticles with a diameter of 12 ± 4 nm and a biocompatible polysaccharide, namely, sodium salt of carboxymethyl cellulose, is described. The role of the polymer matrix consists in stabilization of the resulting nanoparticles by the electrostatic interaction of polymer carboxyl groups with the surface atoms of iron in the (3+) oxidation state. The dissolution of the composites in water affords aggregatively stable dispersions responding to the external magnetic field. The content of the magnetic phase (iron oxide) in the formulation of the maghemite–carboxymethyl cellulose composite is defined by the ratio of components during the synthesis.     

Preparation of Polyuronic Acid from Cellulose by TEMPO-mediated Oxidation

Various cellulose samples were oxidized by 2,2,6,6,-tetramethylpipelidine-1-oxyl radical (TEMPO)-NaBr-NaClO systems, and the effects of oxidation conditions on chemical structures and degrees of polymerization of the products obtained were studied. In the case of regenerated and mercerized celluloses, almost all C6 primary alcohol groups were selectively oxidized to carboxyl groups, and water-soluble polyglucuronic acid (cellouronic acid) sodium salts were obtained almost quantitatively; the degrees of polymerization were influenced greatly by the amount of TEMPO added, and the oxidation time and temperatures. Cellouronic acids prepared from mercerized linter and kraft pulps had size exclusion chromatograms with two separate peaks due to higher and lower molecular weight fractions. On the other hand, only small amounts of carboxyl groups were introduced into native cellulose samples. Since polyglucuronic acids prepared from cellulose by the TEMPO–NaBr– NaClO systems regularly consist of the glucuronic acid repeating unit, differing from the conventional water-soluble cellulose derivatives, they may open new fields of cellulose utilization.     

Identification of the Active Sites for Low Temperature CO Oxidation over Nanocrystalline Co3O4 Catalysts

The microstructural properties of dry‐grinding derived Co₃O₄ catalysts pretreated under different atmospheres, in relation to the activities on CO oxidation were investigated. The Co₃O₄ synthesized by soft reactive grinding and pretreated with O₂ resulted in the best activity, with 100% conversion of CO at ?52 °C, superior to that of Co₃O₄ pretreated with He. To find out the active sites on Co₃O₄ for low temperature CO oxidation, the characterizations of the cobalt oxides had been investigated by means of N₂ physisorption, XRD, TEM, H₂‐TPR, CO‐titration, XPS and O₂‐TPD technologies. XPS of Co2p results show that it is difficult to ascribe the difference in catalytic performance to the surface concentration of active Co³⁺ sites. A correlation between the activity and the CO‐titration and O₂‐TPD results for Co₃O₄ reveals that a high abundance of readily accessible superficial electrophilic oxygen (O^?) species is important for achieving a high activity. Therefore, CO oxidation takes place on the surface active oxygen sites in Co₃O₄ crystallites via the suprafacial mechanism.     

Formation of <Emphasis Type="Italic">N</Emphasis>-acylureas on the surface of TEMPO-oxidized cellulose nanofibril with carbodiimide in DMF

A method for conversion of carboxyl groups present on the surface of TEMPO-oxidized cellulose nanofibrils to N-acylureas using carbodiimide was developed. A TEMPO-oxidized cellulose nanofibril with free carboxyl groups (TOCN–COOH) dispersed in N,N-dimethylformamide (DMF) is prepared from a bleached kraft pulp, and then the TOCN–COOH is reacted with either N,N′-diisopropylcarbodiimide (DIC) or N,N′-dicyclohexylcarbodiimide (DCC) under apparently homogeneous conditions. FT-IR and solid-state ¹³C NMR analyses showed that the reaction products contained N-acylurea groups, and yields were >80%. Conversion ratios of carboxyl groups to N-acylureas are approximately 80 and 60%, when DIC and DCC, respectively, of 5 mol per mole of carboxyl groups are used as the reagents. X-ray diffraction analysis demonstrated that neither crystallinity nor crystal width of the original wood cellulose I structure was changed by the N-acylurea formation. The isolated and never-dried TOCN-N-acylureas are nano-dispersed in DMF but not in i-PrOH or dioxane. Pellets of the TOCN-N-acylureas had water-contact angles of >70°.     

Study on valence adjustment of Pu in 1?bp solution of CIAE-APOR process with N2O4

Oxidation of Pu(III) in 1 bp solution to Pu(IV) was studied using the salt-free oxidant N₂O₄. It was proved that the reductants N,N-dimethylhydroxylamine (DMHAN) and monomethyl-hydrazine (MMH) present in 1 bp solution of CIAE-APOR process can be oxidized and removed from the solutions also by N₂O₄ before the oxidation of Pu(III). The effects of the acidity, the temperature and the amount of N₂O₄ added on the oxidation of DMHAN and MMH were studied.     

Cellulose dissolution in lithium chloride/N,N-dimethylacetamide solvent system: Relevance of kinetics of decrystallization to cellulose derivatization under homogeneous solution conditions

Rate constants and activation parameters for decrystallization of Avicel PH-101 cellulose, and bagasse-based cellulose in presence of LiCl/N,N-dimethylacetamide solvent system have been determined from dependence of the index of crystallinity of cellulose, Ic, on time, under nonisothermal conditions. Calculated rate constants and activation parameters are negligibly dependent on the degree of polymerization of the natural polymer. Under experimental conditions used, derivatization of cellulose can be started after 3 h of cellulose–solvent contact. The relevance of our results to the industrial application of derivatization under homogeneous solution conditions is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3738–3744, 1999     

One‐pot synthesis of composite microspheres with core‐shell structure

One‐pot synthesis of thermoresponsive magnetic composite microspheres with a poly(N‐isopropylacrylamide) (PNIPAM) shell and a Fe₃O₄ core is demonstrated. Temperature sensitivity of PNIPAM was adopted to design the novel synthesis pathway. The as‐prepared composite microspheres have an obvious core‐shell structure with a mean size of approximately 250 nm. The Fe₃O₄ core is approximately 5 nm and the thickness of the PNIPAM shell is approximately 10 nm. The content of Fe₃O₄ in the composite microspheres can be controlled by this method. The composite microspheres experience a swelling and shrinking process in water by adjusting the temperature below and above the lower critical solution temperature (LCST) around 32 °C. These microspheres also show fine response to an external magnetic field. This work presents a platform to synthesize organic/inorganic composite microspheres in a facile and efficient approach. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2702–2708     

Catalytic activity of Cu-containing oxide systems with K2CO3 additives in the oxidation of diesel soot by oxygen

It is shown by XRD that mixed oxide phases Cu_0.92Co_2.08O₄ and Cu₄MgO₅ are formed along with the oxides CuO, Co₃O₄, MgO, and CaO under certain conditions. The positive catalytic effect of individual oxides (CuO and Co₃O₄) and mixed oxide systems (CuO-Cu_0.92Co_2.08O₄, CuO-CaO, and Cu-MgO-Cu₄MgO₅) on the oxidation of diesel soot at 280–580°C is established, and a series of catalytic activities CuO-Cu_0.92Co_2.08O₄ > CuO-MgO-Cu₄MgO₅ > CuO-CaO = CuO > Co₃O₄ is revealed. Using TEM, the surface micromorphology of crystallites that form oxide systems is characterized. It is found that a catalytic system’s activity increases as the size and surface smoothness of crystallites diminishes. According to data from X-ray photoelectron spectroscopy, a considerable increase in the concentration of O₂ in soot with CuO and Co₃O₄ additives after its oxidation by oxygen is observed without changing the oxidation state of Cu and Co oxidation. The promoting effect of potassium additives in the form of K₂CO₃ on the investigated catalytic systems during soot oxidation is revealed.     

Size,shape, orientation and crystallinity of cellulose I<Subscript>β</Subscript> by X-ray powder diffraction using a free spreadsheet program

X-ray powder diffraction is one of the most commonly used methods in cellulose science. This technique is used to identify the cellulose allomorphs, their crystallinity, and the size of their crystallites. In this paper, a novel model is introduced that implicitly takes into account the shape and size of cellulose I_β crystallites in the interpretation of powder diffractograms. Because of the limited amount of data in cellulose powder patterns, this model focuses on a small number of adjustable parameters. The method hypothesizes that cellulose I_β crystallites are straight crystalline rods with superelliptical cross-sections. This superellipse is a parametric curve that can, for example, describe various crystallite shapes as rectangles or ellipses. Additionally, preferred orientation along the (0 0 1) crystallographic planes can be modelled using the March–Dollase approach. The simulated background has a semi-empirical form. An initial model comprised cellulose I_β crystallites and the amorphous background. A second model comprised a biphasic distribution of crystallites and the same amorphous background. In this second model, large cellulose I_β crystallites coexisted with more slender crystallites, usually less than 20 Å in lateral size. Cellulose IV_I nanocrystals were selected as a modeling construct to represent these small and distorted forms of native cellulose. Both models produced simulations in excellent agreement with the experimental measurements.     

Effect of surface chemistry on the adsorption of basic dyes on carbon aerogels

This paper focuses on how the surface chemical groups of carbon aerogels (CAs) affect their adsorption properties of basic dyes. First of all, the surface structures of CAs were tailored by controlling carbonization temperatures and oxidation treatments including HNO₃ oxidation, H₂O₂ oxidation and hot air oxidation. The pore structures of samples were investigated by N₂ adsorption–desorption analysis. In addition, their surface chemistries were characterized by Boehm titration, elemental analysis and XPS analysis. Subsequently, the adsorption capacities of the typical basic dyes on them were determined by UV Spectroscopy. The results show that the surface chemistry of CAs plays a key role in dye adsorption performance. HNO₃ oxidation can produce much acidic groups on the surface of sample, such as carboxyl, lactone and phenolic groups, resulting in an increase in the adsorption amounts of basic dyes.     

Cellulose II nanoelements prepared from fully mercerized, partially mercerized and regenerated celluloses by 4-acetamido-TEMPO/NaClO/NaClO2 oxidation

A softwood bleached kraft pulp (SBKP) and cotton lint cellulose were fully or partially mercerized, and these along with celluloses and commercially available regenerated cellulose fiber and beads were oxidized by 4-acetamido-TEMPO/NaClO/NaClO₂ at 60 °C and pH 4.8. Weight recovery ratios and carboxylate contents of the oxidized celluloses were 65–80% and 1.8–2.2 mmol g⁻¹, respectively. Transparent and viscous dispersions were obtained by mechanical disintegration of the TEMPO-oxidized celluloses in water. These aqueous dispersions showed birefringence between cross-polarizers, indicating that mostly individualized cellulose nanoelements dispersed in water were obtained by these procedures. Transmission electron microscopy observation showed that the cellulose nanoelements prepared from mercerized SBKP, repeatedly mercerized SBKP, mercerized cotton lint cellulose, regenerated cellulose beads and 18% NaOH-treated SBKP, i.e. partially mercerized SBKP, had similar morphologies and sizes, 4–12 nm in width and 100–200 nm in length. The 18% NaOH-treated SBKP was converted to cellulose nanoelements consisting of both celluloses I and II.     

Hydrophilic dual‐responsive magnetite/PMAA core/shell microspheres with high magnetic susceptibility and ph sensitivity via distillation‐precipitation polymerization

A facile and effective approach to preparation of dual‐responsive magnetic core/shell composite microspheres is reported. The magnetite(Fe₃O₄)/poly(methacrylic acid) (PMAA) composite microspheres were synthesized through encapsulating γ‐methacryloxypropyltrimethoxysilane (MPS)‐modified magnetite colloid nanocrystal clusters (MCNCs) with crosslinked PMAA shell. First, the 200‐nm‐sized MCNCs were fabricated through solvothermal reaction, and then the MCNCs were modified with MPS to form active vinyl groups on the surface of MCNCs, and finally, a pH‐responsive shell of PMAA was coated onto the surface of MCNCs by distillation‐precipitation polymerization. The transmission electron microscopy (TEM) and vibrating sample magnetometer characterization showed that the obtained composite microspheres had well‐defined core/shell structure and high saturation magnetization value (35 emu/g). The experimental results indicated that the thickness and degree of crosslinking of PMAA shell could be well‐controlled. The pH‐induced change in size exhibited by the core/shell microspheres reflected the PMAA shell contained large amount of carboxyl groups. The carboxyl groups and high saturation magnetization make these microspheres have a great potential in biomolecule separation and drug carriers. Moreover, we also demonstrated that other magnetic polymeric microspheres, such as Fe₃O₄/PAA, Fe₃O₄/PAM, and Fe₃O₄/PNIPAM, could be synthesized by this approach. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Dissolution and regeneration of cellulose in NaOH/thiourea aqueous solution

A novel cellulose solvent, 1.5 M NaOH/0.65 M thiourea aqueous solution, was used to dissolve cotton linters having a molecular weight of 10.1 × 10⁴ to prepare cellulose solution. Regenerated cellulose (RC) films were obtained from the cellulose solution by coagulating with sulfuric acid (H₂SO₄) aqueous solution with a concentration from 2 to 30 wt %. Solubility of cellulose, structure, and mechanical properties of the RC films were examined by infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, ¹³C NMR, and tensile tests. ¹³C NMR analysis indicated that the novel solvent of cellulose is a nonderivative aqueous solution system. The presence of thiourea enhanced significantly the solubility of cellulose in NaOH aqueous solution and reduced the formation of cellulose gel; as a result, thiourea prevented the association between cellulose molecules, leading to the solvation of cellulose. The RC film obtained by coagulating with 5 wt % H₂SO₄ aqueous solution for 5 min exhibited higher mechanical properties than that with other H₂SO₄ concentrations and a homogenous porous structure with a mean pore size of 186 nm for free surface in the wet state. The RC film plasticized with 10% glycerin for 5 min had a tensile strength of 107 MPa and breaking elongation of 10%, and about 1% glycerin in the RC film plays an important role in the enhancement of the mechanical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1521–1529, 2002