Comparative evolved gas analyses on thermal degradation of thiourea by coupled TG-FTIR and TG/DTA-MS instruments

Identification and monitoring of gaseous species released during thermal decomposition of pure thiourea, (NH₂)₂C=S in argon, helium and air atmosphere have been carried out by both online coupled TG-FTIR and simultaneous TG/DTA-MS apparatuses manufactured by TA Instruments (USA). In both inert atmospheres and air between 182 and 240°C the main gaseous products of thiourea are ammonia (NH₃) and carbon disulfide (CS₂), whilst in flowing air sulphur dioxide (SO₂) and carbonyl sulphide (COS) as gas phase oxidation products of CS₂, and in addition hydrogen cyanide (HCN) also occur, which are detected by both FTIR spectroscopic and mass spectrometric EGA methods. Some evolution of isothiocyanic acid (HNCS) and cyanamide (NH₂CN) vapours have also observed mainly by EGA-FTIR, and largely depending on the experimental conditions. HNCS is hardly identified by mass spectrometry. Any evolution of H₂S has not been detected at any stage of thiourea degradation by either of the two methods. The exothermic heat effect of gas phase oxidation process of CS₂ partially compensates the endothermicity of the corresponding degradation step producing CS₂.     

Zum Einfluss des Schwefels bei der Sauerstoffbestimmung nach dem Heissextraktionsverfahren

The results of the determination of oxygen in materials with a high content of sulphur by the method of inert gas fusion may be erroneous because of the production of CS₂. Contrary to earlier investigations, the effect is found not to occur in the case of high sulphur steel (0.22% S) if an impulse-furnace instrument is used. However, when sulphide materials are analysed the interference appears even with very small samples.     

Effect of wet spinning parameters on the properties of novel cellulosic fibres

Novel cellulose fibres (Biocelsol) were spun by traditional wet spinning technique from the alkaline solution prepared by dissolving enzyme treated pulp directly into aqueous sodium zincate (ZnO/NaOH). The spinning dope contained 6 wt.% of cellulose, 7.8 wt.% of sodium hydroxide (NaOH) and 0.84 wt.% of zinc oxide (ZnO). The fibres were spun into 5% and 15% sulphuric acid (H₂SO₄) baths containing 10% sodium sulphate (Na₂SO₄). The highest fibre tenacity obtained was 1.8 cNdtex⁻¹ with elongation of 15% and titre of 1.4 dtex. Average molecular weights and shape of molecular weight distribution curves of the celluloses from the novel wet spun cellulosic fibre and from the commercial viscose fibre were close to each other.     

Influence of finishing oil on structure and properties of multi-filament fibers from cellulose dope in NaOH/urea aqueous solution

Cellulose multi-filament fibers have been spun successfully on a pilot plant scale, from a cellulose dope in 7 wt% NaOH/12 wt% urea aqueous solution pre-cooled to −12 °C. Coagulation was accomplished in a bath with 10 wt% H₂SO₄/12 wt% Na₂SO₄ and then 5 wt% H₂SO₄ aqueous solution. By using different finishing oil, including H₂O, 4% glycerol aqueous solution, 2% polyvinyl alcohol (PVA) aqueous solution, 2% polyethylene glycol octyl phenylether (OP) aqueous solution, mobol and 2%glycerol/1%PVA/1%OP aqueous solution (PGO), we prepared six kinds of the cellulose multi-filaments, with tensile strength of 1.7–2.1 cN/dtex. Their structure and properties were investigated with scanning electron microscope (SEM), ¹³C NMR solid state, wide-angle X-ray diffraction (WAXD) and tensile testing. The cellulose fibers treated with PGO possessed higher mechanical properties and better surface structure than others. Interestingly, although the orientation of the cellulose multi-filaments is relatively low, the tensile strength of the single-fiber was similar to that of Lyocell. It was worth noting that the dyeability of the multi-filament fibers was superior to viscose rayon.     

Dissolving-grade birch pulps produced under various prehydrolysis intensities: quality,structure and applications

Aqueous-phase prehydrolysis followed by alkaline pulping is a viable process to produce wood-based dissolving pulps. However, detailed characterisation of the achievable pulp quality, performance and cellulose structure is yet lacking. In this study, the production of hemicellulose-lean birch soda-anthraquinone pulps after prehydrolysis under various intensities was investigated. Increasing prehydrolysis intensity resulted in pulps of higher purity but lower cellulose yield and degree of polymerisation. Higher cellulose yield by using sodium borohydride during pulping was achieved at the expense of reducing pulp purity. Cellulose crystallinity was similar in all pulps indicating simultaneous degradation of both crystalline and amorphous cellulose regions. Reinforced prehydrolysis seemingly increased the cellulose crystal size and the interfibrillar distances. Moderate intensity prehydrolysis (170 °C) resulted in a pulp well suited for viscose application, whereas reinforced prehydrolysis favoured the production of acceptable cellulose triacetate dope. The performance of the pulps in viscose and acetate applications was strongly related to the chemical and structural properties.     

Cellulose–silica composite aerogels from “one-pot” synthesis

Cellulose–silica composite aerogels were prepared via “one-pot” process: aqueous solutions of cellulose–8 wt% NaOH and sodium silicate were mixed, coagulated and dried with supercritical CO₂. The system was studied both in the fluid and solid (dry) states. Cellulose and sodium silicate solutions were mixed at different temperatures and concentrations; mixture properties were monitored using dynamic rheology. The gelation time of the mixture was strongly reduced as compared to that of cellulose–NaOH solutions; we interpret this phenomenon as cellulose self-aggregation inducing partial coagulation due to competition for the solvent with sodium silicate. The gelled cellulose/sodium silicate samples were placed in aqueous acid solution which completed cellulose coagulation and led to in situ formation of sub-micronic silica particles trapped in a porous cellulose matrix. After drying with supercritical CO₂, an organic–inorganic aerogel composite was formed. The densities obtained were in the range of 0.10–0.25 g/cm³ and the specific surface area was between 100 and 200 m²/g. The silica phase was shown to have a reinforcing effect on the cellulose aerogel, increasing its Young’s modulus.     

Metal sulfide: An efficient promoter for the synthesis of 2-mercaptobenzothiazoles from 2-haloanilines and carbon disulfide

A convenient method has been developed for the preparation of a variety of 2-mercaptobenzothiazoles from 2-haloanilines and CS₂ mediated by metal sulfide. In this reaction, 2-haloanilines reacted with CS₂ in the presence of Na₂S?·?9H₂O to form 2-mercaptobenzothiazoles. Na₂S?·?9H₂O functioned both as an activator of CS₂ and as a base. Furthermore, NMR analysis was used to identify the different reaction mechanisms of 2-haloanilines and CS₂ mediated by Na₂S or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), which demonstrated that Na₂S interacted only with CS₂, while DBU reacted with both 2-iodoaniline and CS₂.     

Synthesis of cellulose carbamate by supercritical CO2-assisted impregnation: Structure and rheological properties

Cellulose carbamate, an environmentally friendly material presents an interesting alternative to petroleum-based polymers because of its renewable, biodegradable, biocompatible nature and its solubility in conventional solvents. In synthesis process of cellulose carbamate, urea was firstly impregnated into the cellulose pulp by supercritical CO₂(scCO₂), followed by the esterification of cellulose. The structure of cellulose carbamate was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The rheological properties of these cellulose carbamates in 9% sodium hydroxide solution were investigated, using a range of the nitrogen content, concentrations and shear rates.     

Thermal behavior of cellulose fibers with enzymatic or Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> treatment

Summary New regenerated cellulose fibers were developed during the last decades as environmentally friendly systems. In this work, three fibers: lyocell, modal and viscose were subjected to an enzymatic treatment. Likewise, different lyocell fibers were washed in a Na₂CO₃ solution under severe conditions. Analysis was performed by means of differential scanning calorimetry, thermogravimetry and scanning electron microscopy. In all samples, at low temperature, water desorption was detected. Furthermore, thermal analysis shows wide exothermic processes that began between 250 and 300°C corresponding to the main thermal degradation and it is associated to a depolymerization and decomposition of the regenerated cellulose. It is accompanied with mass more than 60% mass loss. Kinetic analysis was performed and activation energy values 152-202 kJ mol^-1 of the main degradation process are in agreement with literature values of cellulose samples.     

Réduction du soufre par un sulfure et oxydation électrochimique d'un sulfure dans le diméthylsulfoxyde

Progressive addition of sodium sulphide to a sulphur solution in dimethylsulphoxide results in the formation of polysulphide ions, identical to those obtained by electrochemical reduction of sulphur in the same solvent. Conversely, electrochemical oxidation of sulphide leads to the formation of sulphur-sulphur bonds, and cyclooctasulphur S₈ is finally obtained.     

An investigation of the sulphur(−II)/sulphur(0) system on bold electrodes

Sulphur deposited on gold by the anodic oxidation of sulphur(−II) species in solution has been studied by X-ray photoelectron spectroscopy. The initial layer behaved as gold sulphide. Multilayers of sulphur had a lower volatility and a smaller electron binding energy than bulk elemental sulphur, indicating that there is interaction with the underlying gold or gold sulphide.The anodic oxidation of sulphur(−II) to sulphur, and the reverse process, has been investigated on gold using the rotating ring disc electrode technique. Polysulphide ions were formed as intermediates in both processes. Polysulphides were also produced by chemical reaction of deposited sulphur with sulphur(−II) species in solution. The polysulphide intermediates were identified as S²⁻₅ at pH 13, a mixture of species with average stoichiometry S²⁻_3.3 at pH 9.2 and S²⁻₂, possibly HS⁻₂, at pH 6.8.     

Phenol removal from aqueous solution by carbon xerogel

Carbon xerogel (CX) was used for phenol adsorption from aqueous solution. CX was synthesized by sol?Cgel polycondensation of resorcinol with formaldehyde using sodium carbonate (Na₂CO₃) as catalyst. Then, it was dried by convective drying technique and pyrolyzed under inert atmosphere. Phenol adsorption kinetics was very fast, what was attributed to the presence of open pore structure. The kinetic studies showed that the adsorption process could be fitted to a pseudo-second-order model and the particle diffusion process is the rate-limiting step of the adsorption. The phenol removal was maximum and unaffected by pH changes when the initial pH of the phenol solution was in the range of 3?C8. The optimum adsorbent dose obtained for phenol adsorption onto CX was 0.075?g/50?cm³ solution. The Langmuir model described the adsorption process better than the Freundlich isotherm model and the monolayer adsorption capacity is 32?mg?g^?1. Among the desorbing solutions used in this study, the most efficient desorbent was EtOH (100?%) which released about 87?% of phenol bound with the CX.     

Hochdruckversuche: Umsetzungen von kohlenstoffdisulfid mit aminen,amiden und olefinen—V

Suitable tertiary amines react with CS₂, 100°C, 10⁴ atm to give N,N-disubstituted thioformamides. Salts of dialkyldithiocarbamic acids decompose at the same conditions into dialkylthioformamide and sulphur. After addition of cyclohexene, mainly N,N-dialkyldithiocarbamic acid cyclohexyl ester has been obtained. Carbon disulfide and sulphur add to olefins yielding trithiocarbonates. Dimethyl formamide reacts with CS₂ giving dimethyl thioformamide. Mechanisms are discussed with help of¹⁴CS₂ and¹⁴C-dimethyl formamide.     

Extraction and determination of elemental selenium in sediments--a comparative study

This paper proposes a new technique to extract elemental Se from soil and sediment samples. In this study, we have identified that the purchased red elemental selenium standard (PF-Se) was impure and rather consisted of a mixture of CS₂ soluble amorphous elemental Se (ca. 10%, w/w), water soluble oxidized Se (ca. 15-17%, w/w) and, CS₂ insoluble red monoclinic elemental Se. In more recent studies, a slow oxidation and a mineral phase transition of this sample was also observed. The solubility of the amorphous elemental Se in CS₂ was at least 0.64 mg L⁻¹. The black elemental Se purchased from Sigma-Aldrich had a much lower solubility in CS₂ (7.2 μg mL⁻¹) compared to that given in the literature. Any selenium compounds with electrical charge and polar nature is insoluble in CS₂. In a sodium sulphite solution, PF-Se was completely dissolved thus giving a clear indication of the lack of selectivity in that extraction system. Other comparative studies also demonstrated that over extraction did occur with the Na₂SO₃ method. Compared to Na₂SO₃, CS₂ extraction of elemental Se is not only much simpler, straightforward and with higher analytical precision, but also much more selective and accurate. With HG-AFS, the detection limit can reach as low as 1.0 ng g⁻¹ in sediment sample owing to a low reagent blank of CS₂ solvent.     

Reactivity of Dissolving Pulp for Processing Viscose

Summary : Pulp reactivity is a kinetic term and is always connected with a certain derivatization process. The quality and hence the market value of the pulp is determined by such characteristics as α- cellulose content, solubility, brightness, ash content, as well as the amount of soluble material in dichloromethane. However, solubility data, especially S₁₈ and S₁₀ values do not characterise dissolving pulp reactivity. These are indicative of pulp solubility and provide some information regarding losses of material during pulp processing. One way by which the pulp reactivity for viscose making can be characterised is the investigation of the mercerisation step. Following the mercerisation kinetics by help of the molecular weight distribution of cellulose II the behaviour especially of the high molecular weight cellulose gives information regarding the accessibility and therefore, about the reactivity of the pulp aside from losses in low molecular weight cellulose. This behaviour will be shown on different pulps and the physicochemical background will be discussed in relation to results obtained from wide angle X-ray scattering and Raman investigations. The influence of the behaviour of the pulp during mercerising on the viscose process, and the molecular weight distribution of the viscose including the distribution of the xanthogenate groups along the chain was investigated and will also be discussed.     

The Synthesis of Sodium Sulfide Pentahydrate,Na2S·5H2O,Through a Solid-Gas Reaction of Sulfidizing Gas Mixture with Sodium Carbonate,Na2CO3

In this study, the sulfidization of Na₂CO₃ was investigated by using a solid-gas reaction under a sulfidizing gas mixture, which consisted of COS, CS₂, and S₂ gases.

Sodium sulfide pentahydrate, Na₂S·5H₂O, was prepared from sodium carbonate, Na₂CO₃, via a sulfidizing gas mixture by a solid-gas reaction under the cooling of a nitrogen atmosphere. The observed phase was found to be the pentahydrated form of sodium sulfide. This crystalline form was determined by X-ray powder diffraction (XRD) technique. Since sodium sulfide is strongly hygroscopic, the pentahydrated crystalline form was observed in XRD measurements for all repeated experiments. The crystal unit cell parameters of the synthesized product were in excellent agreement with values given in the JCPDS card number 18-1249. The sodium sulfide pentahydrate has an orthorhombic crystal structure with the unit cell parameters of a = 6.475, b = 12.55, C = 8.655 Å, space group, Cmcm and Z = 4.     

Photochemical preparation of CdS hollow microspheres at room temperature and their use in visible-light photocatalysis

CdS hollow microspheres have been successfully prepared by a photochemical preparation technology at room temperature, using polystyrene latex particles as templates, CdSO₄ as cadmium source and Na₂S₂O₃ as both sulphur source and photo-initiator. The process involved the deposition of CdS nanoparticles on the surface of polystyrene latex particles under the irradiation of an 8 W UV lamp and the subsequent removal of the latex particles by dispersing in dichloromethane. Photochemical reactions at the sphere/solution interface should be responsible for the formation of hollow spheres. The as-prepared products were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. Such hollow spheres could be used in photocatalysis and showed high photocatalytic activities in photodegradation of methyl blue (MB) in the presence of H₂O₂. The method is green, simple, universal and can be extended to prepare other sulphide and oxide hollow spheres.     

Synthesis of nanosized silicon particles by a rapid metathesis reaction

A solid-state rapid metathesis reaction was performed in a bed of sodium silicofluoride (Na₂SiF₆) and sodium azide (NaN₃) powders diluted with sodium fluoride (NaF), to produce silicon nanoparticles. After a local ignition of Na₂SiF₆+4NaN₃+kNaF mixture (here k is mole number of NaF), the reaction proceeded in a self-sustaining combustion mode developing high temperatures (950–1000 °C) on very short time scales (a few seconds). Silicon nanoparticles prepared by the combustion process was easily separated from the salt byproducts by simple washing with distilled water. The structural and morphological studies on the nanoparticles were carried out using X-ray diffractometer (XRD) and field emission scanning electron microscope (FESEM). The mean size of silicon particles calculated from the FESEM image was about 37.75 nm. FESEM analysis also shows that the final purified product contains a noticeable amount of silicon fibers, dendrites and blocks, along with nanoparticles. The mechanism of Si nanostructures formation is discussed and a simple model for interpretation of experimental results is proposed.     

Radiation effects on polymers—XIII. The application of cellulose acetate-g-polyacrylamide membranes in the process of water desalination by reverse osmosis

Using computerized programs, the water flux and salt rejection properties in reverse osmosis of cellulose acetate-g-acrylamide membranes are determined. Comparisons are made with ungrafted commercial cellulose acetate membranes, using 0.1 and 1.0 M sodium chloride, sodium sulphate and ammonium sulphate solutions. The grafted cellulose acetates show improved water flux but reduced NaCl rejection. However, they show promising prospects in bigger ion separation as for Na₂SO₄ and (NH₄)₂SO₄ solutions.     

Evolved gas analysis of dichlorobis(thiourea)zinc(II) by coupled TG-FTIR and TG/DTA-MS techniques

Identification and monitoring of gaseous species released during thermal decomposition of the title compound 1, Zn(tu)₂Cl₂, (tu=thiourea, (NH₂)₂C=S) have been carried out in flowing air atmosphere up to 800°C by both online coupled TG-EGA-FTIR and simultaneous TG/DTA-EGA-MS. The first gaseous products of 1, between 200 and 240°C, are carbon disulfide (CS2) and ammonia (NH₃). At 240°C, an exothermic oxidation of CS₂ vapors occurs resulting in a sudden release of sulphur dioxide (SO₂) and carbonyl sulphide (COS). An intense evolution of hydrogen cyanide (HCN) and beginning of the evolution of cyanamide (H₂NCN) and isothiocyanic acid (HNCS) are also observed just above 240°C. Probably because of condensation and/or polymerization of cyanamide vapors on the windows and mirrors of the FTIR gas cell optics, some strange baseline shape changes are also occurring above 330°C. Above 500°C the oxidation process of organic residues appears to accelerate which is indicated by the increasing concentration of CO₂, while above 600°C zinc sulfide starts to oxidize resulting in the evolution of SO₂. All species identified by FTIR gas cell were also confirmed by mass spectrometry, except for HNCS. This revised version was published online in July 2006 with corrections to the Cover Date.