Alkaline steeping of dissolving pulp. Part II: Soluble compounds in the press lye

This work describes the comprehensive characterization of the degradation products obtained after the alkaline steeping of dissolving pulp. Total chlorine free bleached beech sulfite pulp was treated with 18 % sodium hydroxide at different temperatures (40, 50 and 60 °C) for time periods of up to 80 h. After the removal of the insoluble cellulose, the remaining alkali solution was treated with sulfuric acid to precipitate the β-fraction. With extended treatment times and temperatures, the proportion of xylan in the β-fraction is increased. However, the molar mass distribution and the amount of 4-O-methylglucuronic acid in the β-fraction revealed no clear trend as a function of the treatment conditions. In total 13 hydroxy acids were identified in the acid soluble γ-fraction, of which glucoisosaccharinic, glycolic, lactic and xyloisosaccharininc acids were among the most abundant hydroxy acids representing the degradation products from C6- and C5-sugars.     

On the reaction of chlorodithiophosphoric acid pyridiniumbetaine with polyfunctional nucleophiles: Part II. Reaction with thiosemicarbazide derivatives

Chlorodithiophosphoric acid pyridiniumbetaine, PyPS₂Cl (I), reacts with thiosemicarbazide derivatives (RNH)(H₂NNMe)CS, R= iso-propyl, tert-butyl, in acetonitrile in the absence of any HCl-acceptor to form new compounds with a five-membered heterocycle, i.e. 5-iso-propylamino-4-methyl-2-sulfido-2-thioxo-1,3,4,2λ⁵-thiadiazaphospholan-5-onium (II) or 5-tert-butylamino-4-methyl-2-sulfido-2-thioxo-1,3,4,2λ⁵-thiadiazaphospholan-5-onium (III). The triethylammonium salt of 1,3-bis-(N-methyl-N′-tert-butyl-thioureido)-2,4-disulfido-2,4-dithioxo-1,3-diaza-2λ⁵,4λ⁵-diphosphetidine (IV) is formed when the reaction is carried out in the presence of triethylamine. The prepared compounds were characterized by ³¹P NMR, FT-IR spectroscopies, mass spectrometry and the molecular structures of II, III and IV were determined by X-ray crystallography.     

Molecular emission cavity analysis: Part 15. Determination of sulphite in soft drinks

The sample (10 μl) is injected into concentrated phosphoric acid at 72°C and the sulphur dioxide evolved is determined by S₂ emission measurement.     

Understanding the pyrolysis of CCA-treated wood: Part II. Effect of phosphoric acid

The pyrolysis process of chromated copper arsenate-treated wood impregnated with phosphoric acid (2–6 wt.%) has been investigated using a Kugelrohr short-path distillation apparatus. The presence of phosphoric acid is shown to change the overall pyrolysis kinetics and yields of products resulting in a decrease in the amount of volatile products and an increase in the char formation. The yield of levoglucosan was found to decrease in the presence of relatively higher concentrations of phosphoric acid, while the yield of levoglucosenone increased. The pyrolysis of chromated copper arsenate-treated wood in the presence of phosphoric acid gave rise to 22% (on water-free tar basis) levoglucosenone. Such data demonstrates the potential for a new pathway toward the rational utilization of chromated copper arsenate-treated wood waste.     

Simultaneous determination of sulphide and sulphite by gas-phase molecular absorption spectrometry. Comparative study of different calculation methods

A method for the simultaneous determination of sulphide and sulphite is described, which involves continuous H(2)S and SO(2) generation, preconcentration in a liquid nitrogen trap and measurement of the molecular absorption spectra of volatiles in the gas phase in 190-220 nm range. Under the recommended conditions (sample flow: 50 ml/min and concentrated sulphuric acid flow: 12 ml/min; generation time: 4 min) linear response ranges from 0.05 mug/ml for S(2-) and 0.20 mug/ml SO(2-)(3) are obtained with detection limits of 0.05 and 0.20 mug/ml respectively. Synthetic mixtures of the two components have been solved and a comparative study of different calculation methods has been made. In conclusion, multiwavelength methods offer better precision and accuracy.     

Vibrational studies in aqueous solutions: Part II. The acid oxalate ion and oxalic acid

Assignments for oxalic acid in solution are re-examined. A detailed assignment of the IR and Raman spectra of the acid oxalate ion is presented for the first time. Raman spectroscopy is used to study the first ionization of oxalic acid.     

Comparative evaluation of two substrates for urinary determination of p-aminobenzoic acid by room-temperature phosphorimetry

Filter paper (S & S 903) impregnated with diethylenetriaminopentaacetic acid, and Whatman DE-81 anion-exchange paper are evaluated for quantitation of urinary p-aminobenzoic acid. The two substrates are compared with respect to drying characteristics, pH variations, heavy atom effect, and some other variables. Impregnated S & S 903 paper is superior in terms of drying characteristics and background interferences but DE-81 has several advantages including lower detection limit, wider pH range, and ready availability. Although both substrates seem applicable to clinical application, DE-81 is probably more useful.     

Comparative study between a CMS membrane and a CMS adsorbent: Part II. Water vapor adsorption and surface chemistry

The adsorption/desorption equilibria of water vapor in a carbon molecular sieve (CMS) membrane and a commercial CMS adsorbent were determined, exhibiting S-shaped, type V isotherms. The fits of several models found in the literature to the experimental data were evaluated. The results obtained led to the development of a new model accounting for both adsorption and desorption and essentially based on the work of Lagorsse et al. (2005) [15]. Furthermore, the adsorption kinetics was also assessed for both materials and well described by a linear driving force model. The existence of hydrophilic groups responsible for water vapor adsorption in such carbonaceous materials has been related to the surface chemistry by means of X-ray microanalysis and by thermogravimetry. It was concluded from X-ray microanalyses that the carbon membrane presents a lower C/O ratio and is thus more sensitive towards water vapor exposure, as evidenced by the measured water adsorption at lower relative pressures. It was also observed that the diffusion rates are higher for the CMS membrane than for the CMS adsorbent.     

On the admittance of lipid bilayer membranes: Part II. Uncouplers and ion carriers

Rangarajan's modular formalism has been applied to those cases in which ion transport across an ultra-thin membrane is associated with membrane permeation of a neutral species. A single connectivity diagram can be used to represent the admittance in the presence of an ion carrier or of either a monomeric or a dimeric uncoupler.     

Alkaline steeping of dissolving pulp. Part I: cellulose degradation kinetics

The production of cellulosic man made fibres by the viscose process has been known for more than 120 years now, but still some aspects are not sufficiently understood in detail. The carbohydrates in the pulp are exposed to varying conditions during the manufacturing process. In the first production step of steeping, the strong alkaline treatment leads to undesirable loss reactions of the cellulose. In this study, a comprehensive kinetic model was developed for process simulation of cellulose degradation for the fist time comprising primary and secondary peeling, stopping and alkaline hydrolysis. A total chlorine free bleached beech sulfite pulp was treated with 18 % sodium hydroxide at 40, 50 and 60 °C for time periods up to 80 h. The corresponding reaction rates, activation energies and frequency factors for all reaction steps were calculated. The peeling-off reaction was of great significance for the cellulose yield loss, due to a contribution of the secondary peeling after random chain scission. The moderate decrease of the intrinsic viscosity and the changes in molar mass distribution indicated the validity of the assumption. Further, a reduction of the carbonyl and an increase of the carboxyl groups in the cellulose were observed due to the formation of the stable metasaccharinic acid at the reducing ends of the molecules. The fibre morphology was investigated by SEM measurements. Already short alkaline treatment times favored the dissolution of fibril fragments from the fibre surface leading to a smooth fibre surface.     

Mechanisms of antioxidant action: Transformations involved in the antioxidant function of zinc dithiocarbamate: Part II

The initial transformation products from reactions of zinc dialkyl dithiocarbamates with hydroperoxides have been identified by spectrophotometric and kinetic methods. It is shown that reactions of the zinc complex with tertiary butyl hydroperoxide, unlike those of the corresponding nickel complexes, do not give rise to disulphide as the first transformation product. The initial product in the case of the zinc complex was found to be the zinc dialkyl dithiopercarbamate, ZnDMSO. The evidence presented rules out the involvement of the further oxygenated product, the zinc dialkyl dithiocarbomylsulphinate, ZnDMSO₂.     

Structural analogues of aporphines. Part II: Synthesis of some isomers of lysergic acid derivatives

Isomers of lysergic acid derivatives ( 3 , 22 , 23 and 24 ). analogous to aporphine, have been synthesized from the key intermediate ketone 12 .     

Studies on lanthanoid sulphites: Part IV. Thermal decomposition of erbium sulphite trihydrate under various experimental conditions

Thermal behaviour of Er₂(SO₃)₃· 3H₃O has been studied by means of TG, DTG, DTA, DSC and EGA techniques. Experimental conditions were also varied, $\text{viz.}$ sample size, heating rate and the atmosphere.The dehydration starts slowly above 150°C but the release of water is rapid around 250°C. SO₂ gas is evolved slowly and simultaneously with H₂O. The anhydrous sulphite is formed below 300°C after which it decomposes through several reactions accompanied by a release of mainly SO₂, but also a small amount of SO₃ near 650°C. In air, there is a clear plateau in the TG curve between 600 and 800°C; the weight loss involved depends strongly on the sample size and heating rate, however. A plausible explanation for the plateau is the formation of a mixture of Er₂(SO₄)₃, Er₂O(SO₄)₂ and Er₂O₂SO₄. The next plateau around 900 – 1000°C corresponds to Er₂O(SO₄)₂ and Er₂O₂SO₄. In nitrogen atmosphere, the first plateau after the anhydrous sulphite appears later in the weight scale as compared to air. Although the position of the plateau corresponds to the sesquisulphide, it is according to X-ray diffraction results a mixture of Er₂O₂(SO₄) and Er₂O₃. In both air and nitrogen, the final reaction step above 1000°C is the formation of Er₂O₃.     

Effect of physico-chemical heterogeneity of natural complexants : Part II. Buffering action and role of their background sites

The peculiar buffering behaviour of the “background sites” of natural heterogeneous complexants is described. Background sites include most of the minor sites, i.e., a group of sites typically comprising not more than ca. 10% of the total sites. Despite this low proportion, they play an important role in controlling free metal ion concentrations in natural systems, because their complexation energy is higher than that of the major sites and their log K values span a broad range of order of magnitudes, owing to the cooperative effect of the large number of site types that they include, together with such continuous secondary effects as those due to a polyelectrolytic interactions and conformational changes. The main characteristics of these sites are summarized and a mathematical and chemical explanation for their cooperative action in controlling the overall free energy of metal ion complexation and the overall buffering intensity of the system is presented. Comparison is made with a classical system made up of a few simple ligands and devoid of secondary effects. The important parameters useful for describing the properties of background sites as a whole are deduced for complexation data obeying the Freundlich isotherm, which has been shown to fit most of the properties of background sites of natural systems.     

A study of freezing-melting hysteresis of water in different porous materials. Part II: surfactant-templated silicas

The freezing-melting hysteresis of water in mesoporous silicas MCM-48, MCM-41 and SBA-16 has been studied by NMR cryoporometry. The hysteresis in MCM-48 was found to exhibit nearly parallel branches, matching type H1 hysteresis that had been observed earlier in controlled pore glass. The same type of hysteresis is observed in two of three different-sized MCM-41 under study (a pore diameter of 3.6 and 3 nm), superimposed with a secondary, extremely broad, type H3 hysteresis. No hysteresis was found in the smallest MCM-41 with a pore diameter < 3 nm. Finally, water in SBA-16 exhibits type H2 hysteresis with the freezing branch being essentially steeper than the melting one, which is attributed to a pore blockage upon freezing, similar to what we observed earlier in Vycor porous glass. The data were analyzed using the model of curvature-dependent metastability of a solid phase upon melting; the validity of this model has been discussed.     

Polarised vibrational spectra of betaine ortho-phosphoric acid complex. Part II. Phase transitions studies

Polarised infrared transmission and Raman spectra of betaine ortho-phosphoric acid crystal in temperature ranges 13-393 and 13-300 K, respectively are reported and discussed in relation to phase transitions: antiferrodistortive at T(c1) = 365 K and antiferroelectric at T(c3) = 81 K. The spectra are consistent with unit cell doubling below T(c3). The participation of all hydrogen bonds apparent in the crystal in the antiferroelectric phase transition was shown. Quite large freedom of -N(CH(3))(3) groups reorientation in the antiferroelectric phase was detected. No changes were found in the transmission spectra taken in the vicinity of the antiferrodistortive phase transition temperature.     

On the nonlinear evolution of the Poisson's ratio under quasi-static loading for a carbon fabric-reinforced thermoplastic. Part II: Analytical explanation

When observing or describing the damage state in a composite material, often only Young's modulus or residual deformation are considered. Generally, however, the Poisson's ratio is more sensitive to damage than those properties. Rather than observing the Poisson's ratio as function of crack density, the evolution of the Poisson's ratio as function of the longitudinal strain was studied in part I of this research, where a peculiar shape of the evolution was observed and proven to be entirely due to the material itself, rather than the sensors used for the strain measurement.In this article, a theoretical explanation for the peculiar evolution of the Poisson's ratio as function of the longitudinal strain is presented. Based on this explanation, extra experiments were conducted for validation purposes.The material used for this study is a carbon fabric-reinforced PPS.