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Noemi Merayo Ana Balea Elena de la Fuente Ángeles Blanco Carlos Negro 《Cellulose (London, England)》2017,24(2):677-692
Although the positive effect that cellulose nanofibers (CNF) can have on paper strength is known, their effect on flocculation during papermaking is not well understood, and most relevant studies have been carried out in presence of only cationic starch. Flocculation is the key to ensuring retention of fibers, fines, and fillers, and furthermore floc properties have a great influence on paper quality. The aim of this research is to study the interactions between CNF and flocculants by assessing the effect of two types of CNF, from eucalyptus and corn, on the flocculation process induced by three different retention systems [a dual system, polyvinylamine (PVA), and cationic starch as reference]. The results showed that CNF interacted with the flocculants in different ways, affecting flocculation efficiency and floc properties. In general, addition of CNF increased floc stability and minimized overdosing effects. Moreover, presence of CNF increased floc size for given PVA dose; therefore, CNF addition could contribute to improve the wet end in the paper machine if combined with the optimal flocculant and dose. 相似文献
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George Pitsevich Elena Shalamberidze Alex Malevich Valdas Sablinskas Vytautas Balevicius Lars G. M. Pettersson 《Molecular physics》2017,115(20):2605-2613
The frequencies and intensities of vibration–rotational transitions of water molecules in an argon matrix were calculated for temperatures of 6 and 30 K. The rigid asymmetric top approximation was used with available literature values of the effective rotational constants in the ground and excited vibrational states. The calculations were carried out by taking into account the existence of a non-equilibrium population distribution between the rotational levels of ortho- and para-water isomers. It was assumed that the temperature relaxation of the population of rotational levels is independent of the ortho- and para-isomers. Comparison of the results of the theoretical calculations with experimental literature data shows good agreement for the majority of the rotational structure lines for symmetric and antisymmetric stretching vibrations both in the frequency values and in the values of the relative intensities. 相似文献
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Novel semiflexible polyazomethines containing chromophoric units into azomethine mesogenic core have been synthesised by condensation of a flexible dialdehyde with mesogenic diamines containing fluorene, antraquinone, pyrimidine, azobenzene and benzophenone. The thermotropic behaviour of the resulting polyazomethines was assessed by differential scanning calorimetry, polarised light microscopy and investigations of the miscibility relations. While the pure polyazomethines showed a birefringent viscous texture difficult to be ascribed, by mixing with a liquid crystal dimer, clear Schlieren or marbled textures were observed, indicating a nematic mesophase. The polymers exhibited violet, blue or yellow light emission. 相似文献
149.
The New Data for the Reaction of Arylenedioxy Trihalogenophosphoranes with Alkyl- and Arylacetylenes
Vladimir F. Mironov Alfiya A. Shtyrlina Ravil R. Petrov Tamara A. Baronova Fedor F. Alekseev Elena N. Varaksina 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1381-1385
The new data concerning the reaction between substituted arylenedioxy trihalogenophosphoranes and monoalkyl- or arylacetylenes are summarized. The reaction leads to formation of six-membered heterocycles-2-oxo-4-R-benzo[ e ]-1,2-oxaphosphorin-3-enes. The substituent effects in the phosphorane and acetylene molecules on the ipso -substitution and halogenation regiochemistry are discussed. The ipso -substitution of tert -butyl group on chlorine and the exchange of bromine on chlorine and iodine on hydrogen have been observed, along with formation of benzophosphorines. The interaction of tetrachloro- ortho -benzoquinone with phosphorus trichloride and arylacetylenes is proposed as a new modification of the reaction leading to the formation of benzo[ e ]-1,2-oxaphosphorines. The structures of some benzo[ e ]-1,2-oxaphosphorines are determined by the single crystal X-ray diffraction. 相似文献
150.
Vasily S. Minkov Evgeny A. Kapustin Elena V. Boldyreva 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(4):416-420
The title compound, betaine 0.77‐perhydrate 0.23‐hydrate, (CH3)3N+CH2COO−·0.77H2O2·0.23H2O, crystallizes in the orthorhombic noncentrosymmetric space group Pca21. Chiral molecules of hydrogen peroxide are positionally disordered with water molecules in a ratio of 0.77:0.23. Betaine, 2‐(trimethylazaniumyl)acetate, preserves its zwitterionic state, with a positively charged ammonium group and a negatively charged carboxylate group. The molecular conformation of betaine here differs from the conformations of both anhydrous betaine and its hydrate, mainly in the orientation of the carboxylate group with respect to the C—C—N skeleton. Hydrogen peroxide is linked via two hydrogen bonds to carboxylate groups, forming infinite chains along the crystallographic a axis, which are very similar to those in the crystal structure of betaine hydrate. The present work contributes to the understanding of the structure‐forming factors for amino acid perhydrates, which are presently attracting much attention. A correlation is suggested between the ratio of amino acid zwitterions and hydrogen peroxide in the unit cell and the structural motifs present in the crystal structures of all currently known amino acids perhydrates. This can help to classify the crystal structures of amino acid perhydrates and to design new crystal structures. 相似文献