Thermal behavior of carboxymethyl cellulose in the presence of polycarboxylic acid crosslinkers

Journal of Thermal Analysis and Calorimetry - In this paper, the thermodynamic (energy and exergy) analysis and water analysis of a modified solar still augmented with copper tube heat exchanger in...     

Interaction of cellulose with amine oxide solvents

Cellulose I, mainly as ramie or as Avicel microcrystalline cellulose, has been monitored by optical microscopy and by ¹³C CPMAS NMR, over the course of its dissolution in hot N-methylmorpholine N-oxide solvent. Its interaction with the near-solvent N-ethylmorpholine N-oxide and related non-solvents has also been investigated. NMR shows that N-methylmorpholine N-oxide partly converts crystalline cellulose I into amorphous solid cellulose. The changes in chemical shift imply increased flexibility at the glycosidic bonds. In contrast, N-ethylmorpholine N-oxide converts cellulose I to cellulose III_I, without dissolution. Microscopy shows that the ramie fibres swell laterally, and at least some also shorten longitudinally, during dissolution. Model studies using methyl--d-glucopyranose show no evidence from ¹³C chemical shifts for different modes of binding with different solvents. However, N-methylmorpholine N-oxide binds more strongly to methyl--d-glucopyranose in DMSO than does N-ethylmorpholine N-oxide, whereas N-ethylmorpholine N-oxide binds better to H₂O. Also, ¹³C T ₁ values for aqueous cellobioside show increasing rotational freedom of the –CH₂OH sidechains as N-methylmorpholine N-oxide is added. Together, these observations imply the initial penetration of solvents and near-solvents between the molecular cellulose sheets. Subsequently, N-methylmorpholine N-oxide breaks H-bonds, particularly to O-6, just sufficiently to loosen individual chains and then dissolve the sheets.     

Determination of thorium in zirconium-hafnium mixtures by aromatic polycarboxylic acids

Summary Results are presented for 1,3,5-benzenetricarboxylic (trimesic), 1,2,4-benzenetricarboxylic (trimellitic) and 1,2,4,5-benzenetetracarboxylic (pyromellitic) acids as precipitants for thorium. Trimesic and pyromellitic acids have been found to be better reagents than trimellitic acid. Thorium and zirconium-hafnium mixtures can be separated by precipitating zirconium-hafnium first in 0.5–0.8 N acid solution and then precipitating thorium in the filtrate at 3–4 pH. The separations are quite reproducible. The precipitates in all cases are ignited to the respective oxides. 5–10 mg samples of thorium can be estimated and separated from 10–50 mg samples of zirconium and/or hafnium. Results of investigations on interferences of cations and anions and pyrolysis curves for the decomposition of precipitates are presented.

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Zusammenfassung Als Fällungsmittel fÜr Thorium wurden 1,3,5-Benzoltricarbonsäure (Trimesinsäure), 1,2,4,5-Benzoltetracarbonsäure (Pyromellitsäure) und 1,2,4-Benzoltricarbonsäure (Trimellitsäure) untersucht, wobei die beiden ersten sich als gÜnstiger erwiesen haben. Gemische von Thorium und Zirkonium/Hafnium kÖnnen getrennt werden, indem man zuerst Zr/Hf in 0,5–0,8 n saurer LÖsung fällt und anschlie\end Thorium aus dem Filtrat bei pH 3–4 niederschlägt. Die Trennung ist gut reproduzierbar. Die Niederschläge werden jeweils zu den entsprechenden Oxiden verglÜht. 5–10 mg Th kÖnnen von 10–50 mg Zr und/oder Hf getrennt werden. StÖrungen durch andere Kationen und Anionen wurden untersucht und Pyrolysekurven fÜr die Zersetzung der Niederschläge aufgestellt.

     

Sorption properties of cellulose filters with covalently immobilized thiosemicarbazide

A novel thin-layer cellulose adsorbent bearing chemically immobilized thiosemicarbaside is synthesized. The adsorbent is used for the preconcentration of cobalt(II), mercury(II), and cadmium(II) followed by their X-ray fluorescence quantification in the concentrate. The physicochemical parameters of metal sorption are determined.     

Electronic structures of aromatic amine N-oxides

The electronic structures of heterocyclic amine N-oxides, nitrones, and nitrile N-oxides were systematically studied by the Pariser-Parr-Pople method. In addition, the intensity of n- ^* transition pertinent to conjugated N-oxide systems has been calculated. The results of these calculations were compared with the experimental ones reported hitherto and also carried out in the present work. The electronic structure and spectra of aromatic amine N-oxides were thus discussed in detail.

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Zusammenfassung Die elektronische Struktur heterozyklischer Amin-N-Oxide, Nitrone und Nitril-N-Oxide wird systematisch mit Hilfe der Pariser-Parr-Pople-Methode untersucht. Au\erdem wurde die IntensitÄt von n- ^*-übergÄngen konjugierter N-Oxide berechnet. Die Resultate wurden mit bekannten sowie eigenen experimentellen Ergebnissen verglichen. Die Elektronenstruktur und die Spektren aromatischer Amin-N-Oxide wurden so im Detail diskutiert.

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Résumé La structure électronique d'amine N-oxydes, de nitrones, et de nitrile N-oxydes ont été étudiés systématiquement par la méthode de Pariser-Parr-Pople. De plus, l'intensité de la transition n- ^* des systémes N-oxydes conjugués a été calculée. Les résultats de ces calculs ont été comparés aux résultats expérimentaux rapportés précédemment et également à ceux du présent travail. La structure électronique et le spectre des N-oxydes d'amines aromatiques ont ainsi été discutés en détail.

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Presented at the 21st (Osaka, April 1968) Annual Meeting of the Chemical Society of Japan, and the Symposium of Structure Chemistry and the Electronic State of Molecules (Tokyo, October 1968).     

Water redispersible cellulose nanofibrils adsorbed with carboxymethyl cellulose

Cellulose nanofibrils (CNFs) are difficult to redisperse in water after they have been completely dried due to the irreversible agglomeration of cellulose during drying. Here, we have developed a simple process to prepare water-redispersible dried CNFs by the adsorption of small amounts of carboxymethyl cellulose (CMC) and oven drying. The adsorption of CMC onto CNFs in water suspensions at 22 and 121 °C was studied, and the adsorbed amount of CMC was measured via conductimetric titration. The water-redispersibility of dried CNFs adsorbed with different amounts of CMC was characterized by sedimentation test. Above a critical threshold of CMC adsorption, i.e. 2.3 wt%, the oven dried CNF–CMC sample was fully redispersible in water. The morphology, rheological, and mechanical properties of water-redispersed CNF–CMC samples were investigated by field emission scanning electron microscopy, viscosity measurement, and tensile test, respectively. The water-redispersed CNFs preserved the original properties of never dried CNFs. This new method will facilitate the production, transportation and storage, and large-scale industrial applications of CNFs.     

Biogas upgrading with novel cellulose nano-crystals and polyvinyl amine nanocomposite membranes

A novel crystalline nano cellulose (CNC) and polyvinyl amine (PVAm) based nanocomposite membranes were synthesized and evaluated for biogas upgrading. Different concentrations of CNC was incorporated in 3 wt % PVAm solution on commercial polysulfone (PSf) sheet using dip coating method. The effect of feed pressure (5, 10 and 15 bar) was investigated for the CO₂/CH₄ separation. The incorporation of CNC increased the crystallinity of membranes. The thickness of selective layer enhanced to 2.16 μm from 1.5 μm with increasing concentration of CNC. However, degree of swelling reduced from 75.88% to 68.93 with CNC concentration at 1.5 wt%. The best results were shown by PVAm membrane with 1 wt % CNC concentration i.e. CO₂ permeance of 0.0216 m³(STP)/m².bar.hr and selectivity (CO₂/CH₄) of 41.The permeance decreased approximately 1.8 folds for PVAm/1CNC membrane with the increase in pressure from 5 to 15 bar. However, selectivity dropped from 41 to 39 for formulated membranes.     

Photooxidation of cellulose treated with amino compounds

The effect of short wavelength UV radiation on celluloses treated with different amino compounds was studied. Samples of cotton cellulose were treated in aqueous solutions of different pH with polyethylenimine (PEI), hexamethylenetetramine (HMTA) and ethylenediamine (EDA), and irradiated in air with a low pressure mercury vapour lamp for different times. The photoyellowing was measured using standard colorimetry and the degradation processes and products were characterized using diffuse reflectance (FTIR and UV-visible) spectroscopy. The degradation processes were compared with those observed in the same materials during thermal treatments. Celluloses treated with EDA and PEI show an intense photoyellowing which depends on the pH of the treating solution. Colour changes in these materials correlate well with the appearance of imine groups and the disappearance of amino groups, determined by FTIR measurements. However, HMTA-treated cellulose, which suffers an intense thermal yellowing, shows only insignificant photoyellowing. These results were explained considering that the photoyellowing is due to the coloured Schiff bases produced in the condensation between amino and carbonyl groups.     

Reactive interaction of aromatic amines with dialdehyde cellulose gel

A new chromatographic method was developed for separation of amines based on their interaction with aldehyde groups in stationary phase. Expecting specific interaction with aldehyde groups through imine formation (Schiff base), we introduced dialdehyde groups to a commercial cellulose packing by periodate oxidation and examined eluting behavior of various aromatic amines. Primary amines with acid dissociation constants (pKa) greater than 6 showed no delay at pHs of 4.0–5.5, indicating the lack of interaction because of complete protonation. Primary amines with pKa less than 6 showed remarkable delays according to the amount of aldehyde groups on cellulose. The delay was dependent on the pH of eluent. The amines with pKa of 4–5.3 eluted faster at lower pH, apparently because of the change in proportion of free and protonated species. Amines with pKa less than 3.4 also showed delays but they eluted slower at lower pH. The latter behavior can be ascribed to the change in the ratio of free/protonated species of imines formed. Certain degree of steric effect was also noted, that is, compounds with a primary amino group adjacent to bulky substituents (ortho compounds) showed weaker interaction with aldehyde groups than meta- and para-isomers.     

Capillary liquid chromatography with diode array and mass spectrometry detection for heterocyclic aromatic amine determination in ready-to-eat food treated with electron-beam irradiation

In the present paper, we have developed a capillary liquid chromatography with MS detection for the determination at ng g⁻¹ levels of four heterocyclic aromatic amines (MeIQx, norharman, harman and harmine), a group of mutagenic and carcinogenic compounds that can potentially be produced in protein-rich food during processing operations. They have been determined in commercial ready-to-eat (RTE) smoked salmon and soft cheese treated with E-beam irradiation. On the basis of experimental design studies and operating conditions of MS detector, best chromatographic conditions were obtained using a Luna^® C₁₈ capillary column (150 mm × 0.3 mm I.D.) with a mixture of acetonitrile–ammonium formate 5 mM pH 3.6 buffer (13:87, v/v) as mobile phase. To improve sensitivity, large injection volumes (20 μL) and injection solutions of low elution strength were employed. Sample preparation procedure included a previous treatment with 1 M NaOH, followed by two solid-phase extraction steps; firstly on diatomaceous earth and then on mixed-mode cartridges. Heterocyclic amines were detected neither in irradiated and in non-irradiated samples, indicating that they were not formed by the radiation effect even at doses higher than those indicated in the Food Safety Objective established by regulatory agencies. RTE food samples were spiked at concentration levels in the range 10–30 ng g⁻¹. Recoveries higher than 85% (n = 3 for each spiked level) were obtained, showing the effectiveness of the proposed methodology.     

Photoreduction of aromatic compounds via amine exciplexes

Many cata and peri condensed polynuclear aromatic compounds were reduced smoothly by sodium borohydride in absolute ethanol in the presence of a tertiary amine to give products in good yields.     

Selective recovery of gold(III) using cotton cellulose treated with concentrated sulfuric acid

Novel utilization of cotton cellulose was developed by chemically modifying with concentrated sulfuric acid to prepare a novel kind of adsorption gel for gold. The adsorption behaviors of the gel were investigated for various metals from acidic chloride media. The gel was found to be highly selective for Au(III) over other precious and base metals tested over the whole concentration range of hydrochloric acid. The maximum adsorption capacity for Au(III) was evaluated as 6.21 mmol/g at 303 K. The amount of adsorbed Au(III) was increased with increasing temperature. A kinetic study for the adsorption of Au(III) at various temperatures confirmed the endothermic adsorption process following pseudo-first order kinetics. The activation energy was evaluated as 78.8 kJ/mol. Interestingly, it was found that the adsorbed Au(III) was reduced to elemental form which was evidenced by the clearly visible elemental gold particles which was further confirmed by means of the X-ray diffraction spectrum and optical microscope image of the gel after the adsorption of Au(III). The mechanism of Au(III) adsorption on the cotton gel and its reduction to elemental gold was proved from the results of IR-spectra. The main mechanism could be explained in terms of the coordination of Au(III) to oxygen atom of C–O–C linkage of cross linked cotton gel and to the oxygen atoms of the hydroxyl groups at C₂ and C₃ atoms of pyranose ring of cotton cellulose followed by the reduction to metallic gold. The adsorbed gold in the cotton gel can easily be recovered by incineration.     

Photoinduced oxygenation of tryptamines by aromatic amine N-oxides

Irradiation (1) (253-7 nm) of N_a,N_b-dimethyltryptaimne with pyridine N-oxide or benzo[c]cinnoline N-oxide in CH₂Cl₂ yielded 1,8-dimethyl-3a-hydroxy-1,2,3,3a,8-8a,- hexahydropyrrolo[2,3-b]indole (19), while with visible light N_b-(4-cyanobutadienyl)-N_a,N_b,- dimethyltryptamine (21) was obtained. This method was applied to trimethyltryptamine and the corresponding oxindole (34) and the N-formyl derivative (20) were obtained.     

Isothermal pyrolysis of cellulose untreated and treated with some flame-retardants

Linter cellulose, untreated and treated with boric acid, ammonium sulfamate, and guanidine sulfamate, was heated iosthermally in an imaging furnace thermal balance under a flow of helium gas to obtain kinetic parameters of the weight loss and changes in the elemental content and infrared (IR) spectra during pyrolysis. The weight, carbon, hydrogen, and oxygen losses of the untreated cellulose obey a zeroth-order reaction at an early stage and a first-order reaction at a later stage. The Arrhenius parameters for the weight and elemental losses are in agreement for both reactions. The activation energy and preexponential factor of the first-order weight loss are 185 kJ/mol and 2.0 × 10¹³ s^?1, respectively. The carbon, hydrogen, and oxygen losses of the samples treated with boric acid and guanidine sulfamate also obey a first-order reaction at a later stage of pyrolysis. The results of the elemental and IR spectral analyses suggest that the zeroth- and first-order reactions are caused mainly by the production of levoglucosan and that an initial rapid step, especially for the treated samples, is contributed by dehydration.     

Synthesis and dyeing performance of a novel polycarboxylic acid azo dye

A novel reactive polycarboxylic acid dye was synthesized by the reaction of polymaleic anhydride（PMA） with 3-methyl-1-（4- sulfonylphenyl）-4-（4-aminophenylazo）-2-pyrazoline-5-one.The structure of the novel dye was characterized by FTIR,UV-vis and ¹³C NMR spectra.The dyeing properties of dye on cotton were tested,and the novel dye possessed high fixation and good fastness.     

Growth and reactivity of silver clusters in amino polycarboxylic acid solutions

Reduction and subsequent aggregation of silver ions in the presence of various chelating agents such as trans-1,2-diaminocyclohexanetetraacetic acid (DCTA) 1,2-propylenediaminetetraacetic acid (PDTA), diethylenetriaminepentaacetic acid (DTPA), and triethylenetetraaminehexaacetic acid (TTHA) have been studied by pulse radiolysis. Rate constants of formation and transient absorption spectra for the ligand-complexed Ag(0) and Ag(2)(+) have been determined. The redox potential of Ag(+)(L)/Ag(0)(L) becomes more negative than that of Ag(+)/Ag(0). Growth and reactivity of silver clusters were also studied in the presence of methyl viologen (MV(2+)). The kinetics of formation of the MV(+*) radical, produced by the same pulse as in the case of silver atoms, confirms the catalytic electron transfer toward super critical silver clusters in the presence of ligands. The results suggest that catalytic electron transfer activity of silver clusters depends on the ligand.