Addition Of Polysulfide Research Articles

CNFs from softwood pulp fibers containing hemicellulose and lignin

The energy demand to produce cellulose nanofibrils, CNFs, is high and additionally the cost of the starting material, the pulp, is substantial as high purity cellulose dissolving pulp is generally used. Pulps aimed for board and paper are produced at higher yield as they contain hemicelluloses and, in the case of unbleached pulp, lignin, and would be a more economical starting material for CNFs. It is of interest to understand how the presence of hemicellulose and lignin affects the fibrillation process and CNF properties. Kraft cooks of softwood were performed as well as kraft cooks with addition of polysulfide to increase the hemicellulose content. Part of the pulps were bleached to remove residual lignin, thus making it possible to compare pulps with and without lignin. Higher amount of hemicellulose had an obstructive effect on the enzymatic pre-treatment whereas lignin had no adverse effect on enzyme accessibility. Increased amount of charged groups improved the accessibility for enzymes. Both hemicellulose and lignin were carboxymethylated when pre-treatment by carboxymethylation was employed. However, carboxymethylation partly dissolved hemicelluloses. The tensile strength of CNF films was independent of the chemical composition of the pulp and the pre-treatment strategy. However, since the enzymatic pre-treatment decreased the cellulose DP more, CNF films from enzymatically pre-treated pulps had generally lower tensile strength.

Low temperature fracture toughness of polysulfide modified BPA-epoxide primers

A mixture of amidoamine and polysulfide crosslinkers were used to toughen a BPA-epoxide primer. Viscoelastic properties, fracture toughness, impact resistance, adhesion strength, corrosion properties were investigated. Fracture toughness study was conducted at ambient and low temperatures to approximate an aircraft at altitude. At ambient temperature, the amidoamine was sufficiently flexible due to ethylene oxide soft segments. However, at low temperature, the addition of polysulfide showed improved fracture toughness. The SEM of fractured surface revealed that fracture toughness improvement at low temperature is due to the both cavitation and shear yielding of polysulfide domains and epoxide matrix which dissipate energy and increase the toughness.

Polysulfide solution effects on Li[sbnd]S batteries performances

Recently, rechargeable LiS batteries, a next-generation energy storage system, are deeply studied due to their theoretical specific energy density. However, to produce batteries comparable to those already available on the market some drawbacks must be overcome, including essentially self-discharge, high internal resistance and rapid capacity fading upon cycling. In this work the use of polysulfide solutions either as additives or as active material in LiS batteries is proposed. The addition of polysulfides to the electrolytic solution improves the cell performances in terms of specific capacity and coulombic efficiency, passing from a capacity of about 150 mAh/g with a coulombic efficiency of about 0.85 to a capacity of 600 mAh/g with a coulombic efficiency of about 0.99 after 10 cycles. In batteries where polysulfide solutions are used as cathodic material, the obtained performances are even higher, reaching specific capacities of 420–450 mAh/g after about 70 cycles. Moreover, the cells tested with carbon paper as electrode support shows a greater reversibility, with a coulombic efficiency very close to 1. Finally, reducing the potential window from 3 to 1.5 V to 2.8–1.7 V, the cells show high stability and efficiency, reaching specific capacity values of about 600 mAh/g after 200 cycles.

Ion conductive polymer electrolyte membranes based on star-branched poly(ethylene-glycol tri-acrylate) and polysulfide macromonomers

This article presents star-branched polymeric co-networks consisting of a three-arm poly(ethylene glycol) acrylate macromonomers (PEG3A) and a three-arm polysulfide (PS) via UV photopolymerization for the development of ion conductive polymer electrolyte membrane (PEM) containing succinonitrile (SCN) plasticizer and lithium bis(trifluoromethane sulfonyl)imide (LITFSI) salt. The hyperbranched co-network (PS-co-PEG3A) exhibits a lower glass transition temperature (Tg = −49 °C at 50:50) relative to that of 3-arm (PEG3A), i.e., Tg of −32 °C, showing systematic variation with polysulfide addition. In the tensile tests, elongation-at-break of PEM – PS-co-PEG3A is higher, but it occurs at the expense of lower tensile strength and modulus. Moreover, PEM – PEG3A exhibits higher strength and modulus relative to those of PEM – PS-co-PEG3A copolymer, but its ionic conductivity is lower (i.e., 3.41 × 10−4 S/cm for PEM – PEG3A versus 1.35 × 10−3 S/cm for PEM – PS-co-PEG3A at 21 °C). This improved ionic conductivity may be attributed to reduced crosslinking density associated with the formation of SC bonds upon addition of polysulfide. The PEM – PS-co-PEG3A co-network is thermally stable up to 130 °C tested and exhibited reasonably good anodic stabilities up to 4.5 V versus Li/Li+. In the CV tests in half-cells configuration with LiFePO4 cathode against Li/Li+, the specific discharge capacity was found to be 120 mAh/g with capacity retention of about 97% for 50 cycles tested.

Nanoscale Morphological Changes at Lithium Interface, Triggered by the Electrolyte Composition and Electrochemical Cycling

Understanding the electrochemical and morphological properties of the Li-electrolyte interface plays a central role in the implementation of metallic Li in safe and efficient electrochemical energy storage. The current study explores the influence of soluble polysulfides (PS) and lithium nitrate (LiNO3) on the characteristics of the solid electrolyte interphase (SEI) layer, formed spontaneously on the Li surface, prior to electrochemical cycling. Special attention is paid to the evolution of the electrochemical impedance and nanoscale morphology of the interface, influenced by the contact time and electrolyte composition. The basic tools applied in this investigation are electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM) performed at the nanoscale, and X-ray photoelectron spectroscopy (XPS). The individual addition of polysulfides and LiNO3 increases the interface resistance, while the simultaneous application of these components is beneficial, reducing the SEI resistive behavior. The electrochemical cycling of Li in nonmodified 1,2-dimethoxy ethane (DME) and tetraethylene glycol dimethyl ether (TEGDME) based electrolytes leads to slight morphological changes, compared to the pristine Li pattern. In contrast, we found that in the presence of PS and LiNO3, the interface displays a rough and inhomogeneous morphology.

Improving the Tribological Properties of Gear Synchronizations by Adjusting the Metalworking Fluid Composition of the Grinding Process

The modification of tribological properties of highly loaded components by selecting a suitable manufacturing process is state-of-the-art. Beyond the generation of microgeometrical structures, the present study investigates the potential of chemical alterations, i.e., metalworking fluid additives engaged in a grinding process to improve the chemical surface properties of machined gear synchronizations. These gearbox components ensure a uniform switching operation by harmonizing the number of revolutions between the power transmitting components by friction. A short running-in phase and a friction coefficient which is constant over the entire duration of use are required. The results show that the addition of polysulfide as well as zincdialkyldithiophosphate in the metalworking fluid could considerably reduce the friction coefficient fluctuations and the running-in phase of the generated synchronizations in later operation tests. The wear distances were lower although the machined parts revealed higher surface roughnesses as the reference workpieces, which indicates the formation of sorption or reaction layers of the additives with the metal surface.

硫化油脂添加油を用いたステンレス鋼のMQL切削

This paper describes effect of combination of MQL and water mist supply on cutting load in stainless steel cutting when adding polysulfide to MQL lubricant. Generally, it is considered that the largest effect of combination use of water-mist on cutting performance is a chilling effect. However, addition of polysulfide to MQL lubricant as additive exhibited excellent lubricity in stainless steel heavy drilling if applying combination use of water-mist. From the friction tests under some lubricating conditions, it is suggested that existence of water in heated cutting zone can alter the oxidation state of stainless steel surface and then enhance forming reaction layers of polysulfide on the surface.

Analysis of the solid electrolyte interphase formed with an ionic liquid electrolyte for lithium-sulfur batteries

We have investigated the formation of the solid electrolyte interphase (SEI) on lithium electrodes in the presence of an ionic liquid electrolyte with a particular focus on the influence of polysulfides present in the electrolyte on the SEI. The electrochemical performance of symmetric cells with lithium electrodes and electrolytes composed of N-Methyl-(n-butyl)pyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14-TFSI) and LiTFSI, with and without the addition of polysulfides, were analyzed as well as the chemical composition of the SEI, before and after cycling. The cycling behavior of the symmetrical cells shows that the SEI films are relatively stable in the ionic liquid electrolyte, also in the presence of polysulfides. However, the presence of polysulfides results in a higher SEI layer resistance (RSEI) and a higher activation energy. From X-ray photoelectron spectroscopy spectra (XPS), with argon-ion sputtering for depth profiling, we find that the SEI is formed by decomposition products from both cations and anions of the electrolyte. The XPS spectra show that the presence of polysulfides alters the decomposition process of the electrolyte, resulting in a SEI film with different chemical composition and structure, in line with the results from the electrochemical performance.

Effect of Additives on Polysaccharide Retention in Green Liquor Pretreatment of Loblolly Pine for Enzymatic Hydrolysis

In order to improve polysaccharide retention during pretreatment and increase enzymatic hydrolysis efficiency, green liquor (GL) pretreatment was performed at: (1) higher GL sulfidity; (2) higher sulfidity with the addition of sodium polysulfide; (3) higher sulfidity with the addition of sodium borohydride; or (4) higher sulfudity with the addition of sodium tetraborate. The results indicate that green liquor pretreatment with the higher sulfidity, with the addition of polysulfide and with the addition of sodium borohydride, is effective in increasing enzymatic conversion of the pretreated pulps. The addition of sodium tetraborate, on the other hand, is not effective. These measures can be combined with oxygen delignification and/or mechanical refining to further improve the enzymatic hydrolysis efficiency. Up to 80% of the polysaccharides in softwood can be converted to fermentable sugars, but only with the addition of 40 FPU enzyme dose.

A larch biorefinery: Influence of washing and PS charge on pre-extraction PSAQ pulping

This study deals with a biorefinery concept based on larch wood. Wood chips of Siberian larch (Larix sibirica Lebed.) were treated with water before pulping at the optimal pre-extraction (PE) condition of 150 °C and 90 minutes. Through PE, about 12.4% of the wood mass is dissolved, mainly from the arabinogalactan hemicellulose component. Fermentation of the hemicellulose-rich larch extract with Bacillus coagulans resulted in consumption of all C6 and C5 sugars and produced lactic acid in high yield. PE before pulping resulted in lower (4 to 5%) pulp yield than for control kraft pulps. However, the pulp yield loss may be reduced by addition of polysulfide (PS) and anthraquinone (AQ). The present study focuses on the effect of the degree of washing of the extracted chips and that of the PS charge in PSAQ pulping on the final properties of the pulp. Three different levels of washing and three different PS charges were tested. The characteristics of the extract, wash water, pulp, and black liquor samples were determined. The amount of sugars in the combined stream of collected extract and wash water obtained by mild washing was 10.2% on o.d. wood.

The nickel enzyme methyl-coenzyme M reductase from methanogenic archaea: In vitro induction of the nickel-based MCR-ox EPR signals from MCR-red2.

Methyl-coenzyme M reductase (MCR) is a nickel enzyme catalyzing the formation of methane from methyl-coenzyme M and coenzyme B in all methanogenic archaea. The active purified enzyme exhibits the axial EPR signal MCR-red1 and in the presence of coenzyme M and coenzyme B the rhombic signal MCR-red2, both derived from Ni(I). Two other EPR-detectable states of the enzyme have been observed in vivo and in vitro designated MCR-ox1 and MCR-ox2 which have quite different nickel EPR signals and which are inactive. Until now the MCR-ox1 and MCR-ox2 states could only be induced in vivo. We report here that in vitro the MCR-red2 state is converted into the MCR-ox1 state by the addition of polysulfide and into a light-sensitive MCR-ox2 state by the addition of sulfite. In the presence of O(2) the MCR-red2 state was converted into a novel third state designated MCR-ox3 and exhibiting two EPR signals similar but not identical to MCR-ox1 and MCR-ox2. The formation of the MCR-ox states was dependent on the presence of coenzyme B. Investigations with the coenzyme B analogues S-methyl-coenzyme B and desulfa-methyl-coenzyme B indicate that for the induction of the MCR-ox states the thiol group of coenzyme B is probably not of importance. The results were obtained with purified active methyl-coenzyme M reductase isoenzyme I from Methanothermobacter marburgensis. They are discussed with respect to the nickel oxidation states in MCR-ox1, MCR-ox2 and MCR-ox3 and to a possible presence of a second redox active group in the active site. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00775-001-0325-z.

Hydrogen production by methanogens under low-hydrogen conditions.

Hydrogen production was studied in four species of methanogens (Methanothermobacter marburgensis, Methanosaeta thermophila, Methanosarcina barkeri, and Methanosaeta concilii) under conditions of low (sub-nanomolar) ambient hydrogen concentration using a specially designed culture apparatus. Transient hydrogen production was observed and quantified for each species studied. Methane was excluded as the electron source, as was all organic material added during growth of the cultures (acetate, yeast extract, peptone). Hydrogen production showed a strong temperature dependence, and production ceased at temperatures below the growth range of the organisms. Addition of polysulfides to the cultures greatly decreased hydrogen production. The addition of bromoethanesulfonic acid had little influence on hydrogen production. These experiments demonstrate that some methanogens produce excess reducing equivalents during growth and convert them to hydrogen when the ambient hydrogen concentration becomes low. The lack of sustained hydrogen production by the cultures in the presence of methane provides evidence against "reverse methanogenesis" as the mechanism for anaerobic methane oxidation.

The Early Diagenetic Formation of Organic Sulfur in the Sediments of Mangrove Lake, Bermuda

Due to a low mineral content, the sapropelic sediments depositing in Mangrove Lake, Bermuda, provide an excellent opportunity to explore for possible additions of sulfur to organic matter during the early stages of diagenesis. We evaluated early diagenetic organic sulfur transformations by monitoring the concentrations and stable isotopic compositions of a number of inorganic and organic sulfur pools, thereby accounting for all of the sulfur in the sediments. We have identified and quantified the following sulfur pools: porewater sulfate, porewater sulfide, elemental sulfur, pyrite sulfur, hydrolyzable organic sulfur (HYOS), chromium-reducible organic sulfur (CROS), and nonchromium-reducible organic sulfur (Non-CROS). Of the organic sulfur pools, the Non-CROS pool is by far the largest, followed by CROS, and finally HYOS. By 60 cm depth these pools contribute, respectively, to 85, 7.9, and 3.6% of the total solid phase sulfur. The HYOS pool is probably of biological origin and shows no interaction with the sulfur compounds produced during diagenesis. By contrast, CROS is produced, most likely, from the diagenetic addition of polysulfides to functionalized lipids in the upper, H 2S-poor, elemental sulfur-rich, region of the sediment. A portion of this sulfur pool is unstable and decomposes on contact with the H 2S-rich porewaters. The portion of CROS that remains in the sulfidic waters appears to readily exchange sulfur isotopes with H 2S. While some of the Non-CROS pool is of biological origin, some is also formed by the diagenetic addition of sulfur to organic compounds in the upper H 2S-poor region of the sediment. By contrast with CROS, Non-CROS is not diagenetically active in the H 2S-rich porewaters. Overall, somewhere between 27 and 53 % of the organic sulfur buried in Mangrove Lake sediments is of diagenetic origin, with the remaining organic sulfur derived from biosynthesis. We extrapolate our Mangrove Lake results and calculate that in typical coastal marine sediments between 11 and 29 μmol g −1 of organic sulfur will form during early diagenesis, of which 2–5 μmol g −1 will be chromium reducible.

Surface characterization of sulfided precipitated-iron Fischer-Tropsch catalysts by X-ray photoelectron spectroscopy

A series of novel sulfur-containing precipitated-iron catalysts were prepared by the addition of 2000–20000 ppm sulfur (Na2S, (NH4)2S, (NH4)2S5) to iron, during the precipitation reaction. XPS characterization of the highly sulfided catalyst (20000 ppm) after calcination at 200°C and 400°C did not reveal the presence of surface sulfur (160–170 eV region). However, low temperature calcination (200°C) followed by reduction (300°C) revealed surface S2− (162.3 eV), while high temperature calcination (400°C) gave rise to SO42− (169.4 eV) species. Use of a higher reduction temperature (400°C) increased the surface sulfide concentration to 15.6 at% S2− as compared to 1.3 at% after reduction at 300°C. At lower S loadings (2000, 5000 ppm) only sulfate species were observed under analogous conditions. The addition of polysulfide ((NH4)2S5) instead of S2−, resulted in the formation of a surface polysulfide and SO42− surface species. A mechanism for the surface segregation of sulfur after reduction in terms of site competition with oxygen is consistent with the data.

Kinetics of the Reduction of Nitroso Compounds by Hydrosulfide

The reduction of aromatic nitroso compounds (Ar-NO) by hydrosulfide to N-hydroxylamines (Ar-NHOH) has been studied kinetically in aqueous media.In this reaction hydrosulfide is oxydized to sulfur by Ar-NO, and Ar-NO is Ar-NO +H2S→Ar-NHOH+S converted into unstable products (Ar-NHOH) which regenerated the original nitroso compounds by bubbling oxygen through the solution.This process has been successfully utilized for the desulfurization of fuel gas containing hydrogen sulfide.The reduction rate of Ar-NO was accerated by the addition of polysulfide, and that polysulfide is responsible for autocatalytic nature of the reduction.The rate was found to be proportional to the concentration of Ar-NO, hydrosulfide and hydronium ion.The effect of temperature obeyed the Arrhenius equation.

The High Yield Chemical Pulping Process by the Use of Polysulfides Part 2.

To obtain as high an yield as possible in the manufacture of chemical pulp by the use of polysulfides (Na2Sx) the presence of caustic soda (hydroxyl-ions) seems to be undesirable because the carbohydrates in woods will be hydrolyzed partly during they are stabilized by the action of Na2Sx.In order to improve the effectiveness of Na2Sx, therefore, the digestion should be carried out into two stages. In the first stage, Japanese red pine (Pinus densiflora) wood chips are treated with Na2Sx solution, and in the second stage, the pretreated chips are cooked by the use of alkaline aqueous solutions such as caustic soda or kraft white liquor. We call this process P.S.A.The following results were obtained from the cooking experiments.(1) Upon the type of Na2Sx used in the first stage cook, Na2S4 was more profitable than others in the increase of pulp yield.(2) The optimum pretreatment conditions were found to be 5.0% Na2S4 (as Na2O) based on wood chip, 130°C cooking temperature and 60 min. treatment time.(3) The second stage cook with alkaline liquor was carried out under the cooking condition of conventional kraft process. And no difference could be observed essentially between the two different alkaline cooking liquors (caustic soda and kraft white liquor) employed.Compared with the kraft process an increase in yield of pulp 56% on wood resulted from this process. (P.S.A.) This is also approximately twice as much as if the addition of polysulfides was made directly to the cooking liquor.