共查询到20条相似文献,搜索用时 15 毫秒
1.
Daniela A. Bocchini Valquiria B. Damiano Eleni Gomes Roberto Da Silva 《Applied biochemistry and biotechnology》2003,106(1-3):393-401
The alkalophilic Bacillus circulans D1 was isolated from decayed wood. It produced high levels of extracellular cellulase-free xylanase. The enzyme was thermally
stable up to 60°C, with an optimal hydrolysis temperature of 70°C. It was stable over a wide pH range (5.5—10.5), with an
optimum pH at 5.5 and 80% of its activity at pH 9.0. This cellulase-free xylanase preparation was used to biobleach kraft
pulp. Enzymatic treatment of kraft pulp decreased chlorine dioxide use by 23 and 37% to obtain the same kappa number (κ number)
and brightness, respectively. Separation on Sephadex G-50 isolated three fractions with xylanase activity with distinct molecular
weights. 相似文献
2.
The effect of Trichoderma reesei cellulases and hemicellulases on the paper technical properties of never-dried bleached kraft pulp 总被引:1,自引:0,他引:1
Four purified cellulases, a xylanase and mannanase from Trichoderma reesei were used to treat never-dried bleached pine kraft pulp prior to refining, and the effects on pulp properties were evaluated.
The enzymatic treatments hydrolysed up to 0.8% of pulp dry weight. The results demonstrated that the individual cellulases
have profoundly different modes of action in modifying pulp carbohydrates. This is especially clear when comparing their effects
at the same level of hydrolysis. Pretreatment with cellobiohydrolases I (CBH I) and II (CBH II) had virtually no effect on
the development of pulp properties during refining, except for a slight decrease in strength properties. On the contrary,
endoglucanase I (EG I) and endoglucanase II (EG II) improved the beatability of the pulp as measured by Schopper--Riegler
value, sheet density and Gurley air resistance. Of the endoglucanases, EG II was most effective in improving the beating response.
The combinations of CBH I with EG I and EG II had similar effects on the pulp properties as the endoglucanases alone, although
the amount of hydrolysed cellulose was increased. Pretreatments with xylanase or mannanase did not appear to modify the pulp
properties. The same enzyme treatments which improved the beatability, however, slightly impaired the pulp strength, especially
tear index at the enzyme dosages used. When compared at a given level of cellulose hydrolysis, the negative effect of EG II
on strength properties was more pronounced compared with EG I. Thus, the exploitation of cellulases for fibre treatments requires
careful optimization of both enzyme composition and dosage. Since the endoglucanases had no positive effect on the development
of tensile strength, it is suggested that the explanation for the increased beating response is increased fibre breakage and
formation of fines, rather than improved flexibilization.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Oguzhan Oguz Nicolas Candau Stphane H. F. Bernhard Cagla Kosak Soz Ozge Heinz Grgory Stochlet Christopher J. G. Plummer Emel Yilgor Iskender Yilgor Yusuf Z. Menceloglu 《Journal of polymer science. Part A, Polymer chemistry》2019,57(24):2543-2556
Colloidal silica nanoparticles (NPs) modified with eight different silane coupling agents were incorporated into an amorphous poly(tetramethylene oxide)‐based polyurethane–urea copolymer matrix at a concentration of 10 wt % (4.4 vol %) in order to investigate the effect of their surface chemistry on the structure–property behavior of the resulting nanocomposites. The rigid amorphous fraction (RAF) of the nanocomposite matrix as determined by differential scanning calorimetry and dynamic mechanical analysis was confirmed to vary significantly with the surface chemistry of the NPs and to be strongly correlated with the bulk mechanical properties in simple tension. Hence, nanocomposites with an RAF of about 30 wt % showed a 120% increase in Young's modulus, a 25% increase in tensile strength, a 15% decrease in elongation at break with respect to the neat matrix, which had no detectable RAF, whereas nanocomposites with an RAF of less than 5% showed a 60% increase in Young's modulus, a 10% increase in tensile strength and a 5% decrease in the elongation at break. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2543–2556 相似文献
4.
In this work attention has been focused on the effects of papermaking beating, web forming and sizing operations on the physical/chemical
surface properties of bleached Eucalyptus globulus kraft fibres. Inverse gas chromatography (IGC) was used to determine the dispersive component of surface tension (γsd) as well as the acidic/basic character (according to the Lewis concept) of the solid surfaces (pulp fibres and pulp handsheets).
The results have shown that the main effect of beating is to increase the fibre's Lewis acidic character. Web forming caused
a strong decrease in γsd and significant increments in the adhesion works of both acidic and basic probes, lowering the ratio between the two. Nevertheless,
the surface of handsheets still exhibited a dominant acidic character. The sizing operation did not change the dispersive
component of the surface tension significantly but decreased the difference between the adhesion works of the acidic and basic
probes, rendering the handsheet surface less Lewis acidic and more Lewis basic. Thus, although internal sizing is expected
to strongly influence liquid spreading at the paper surface and liquid penetration of the fibre's network, it is concluded
that beating and web forming lead to important changes in the surface energetic properties of the Eucalyptus globulus kraft fibres. 相似文献
5.
Krista Koljonen Monika Österberg Marjatta Kleen Agneta Fuhrmann Per Stenius 《Cellulose (London, England)》2004,11(2):209-224
The effect of pH on the formation of precipitates (lignin, extractives and metals) on kraft pulp surfaces was examined by electron spectroscopy for chemical analysis, time-of-flight secondary ion mass spectrometry and atomic force microscopy (AFM). A softwood kraft pulp slurry from an oxygen delignification stage was diluted to 3% consistency with water or an acidic Z filtrate. After heating to 70 °C the pH was lowered from 11 to 2–5, using sulphuric acid. Lignin and extractives precipitated at pH values below 6, and their amounts increased with decreasing pH. Most of the precipitated lignin was found on the pulp surface after sheet forming, whereas the main part of the precipitated extractives could be easily washed away with water. The layer of precipitated lignin was apparently thicker than the layer of extractives. AFM showed the precipitated material as a granular phase. Neither surface morphology nor surface coverage depended on the addition of Z filtrate. The amount of metals ID the pulp and on the pulp surface decreased when pH was lowered to 2. More metals, such as Ca and Mg, were detected ID the pulps as well as on the sheet surfaces when the pulp was diluted with Z filtrate. Strength and bonding properties of the pulp sheets were slightly impaired by the precipitated material. Acidification appears to be the main reason for the precipitation of both lignin and extractives on the pulp surfaces. This should be taken into account when filtrates are recycled ID the bleaching or washing of pulps. 相似文献
6.
7.
Using the simultaneoussaccharification and fermentation (SSF) technique, pulp mill solid waste cellulose was converted into
glucose using cellulase enzyme and glucose into lacticacid using NRRL B445. SSF experiments were conducted at various pH levels,
temperatures, and nutrient concentrations, and the lactic acid yield ranged from 86 to 97%. The depletion of xylose in SSF
was further investigated by inoculating NRRL B445 into a xylose-only medium. On prolonged incubation, depletion of xylose
with lactic acid production was observed. An experimental procedure with a nonglucose medium was developed to eliminate the
lag phase. From xylose fermentation, Lactobacillus delbrueckii yielded 88–92% lactic acid and 2–12% acetic acid. 相似文献
8.
水热改性对氧化铝载体织构和表面性质的影响 总被引:2,自引:0,他引:2
The alumina support was treated in the moderate aqueous hydrothermal condition to avoid from the excess growth of boehmite (AlOOH) crystals which usually results in the obvious decrease of the specific surface area (BET). The experimental results indicated that the hydrothermal treatment of the alumina support at 140 ℃ for 2 hours promoted the formation of the plate-like AlOOH crystallites on the surface of the support via dissolution-precipitation route. The occurrence of the nano plate-like structure led to the improvement in the structural and surface properties, such as the increase of the specific surface area, the surface hydroxyl concentration and the surface acidity. 相似文献
9.
Saker Saloum Samer Abou Shaker M.Nidal Alkafri Asmhan Obaid Rokayya Hussin 《Surface and interface analysis : SIA》2019,51(7):754-762
Plasma-polymerized hexamethyldisiloxane (pp-HMDSO) thin films have been deposited in a radiofrequency (RF) remote plasma-enhanced chemical vapor deposition (PECVD) system, on different types of substrates: silicon wafers, glass, quartz crystals, and chemiresistor structure. The as-grown thin films have been post treated in two types of reactive plasmas produced in SF6 and O2 gases. The effect of this surface modification on different properties of the as-grown pp-HMDSO thin film (chemical structure, elemental composition, surface morphology, film density and thickness, optical bandgap, and electrical resistivity) has been investigated. It is found that SF6 plasma and O2 plasma surface modifications of the as-grown pp-HMDSO thin film induce property changes different from each other. SF6 plasma converted the as-grown pp-HMDSO film to a more porous material and caused a narrowing of its optical band gap of about 33%, while O2 plasma induced a lowering of film electrical resistivity of about two orders of magnitude. 相似文献
10.
Seyed Rasoul Mousavi Sara Estaji Elham Rostami Hossein Ali Khonakdar Mohammad Arjmand 《先进技术聚合物》2022,33(1):49-65
A novel green surface modification was successfully implemented on alumina nanoparticles using chitosan (CS) to prevent nanoparticles' aggregation. To evaluate the surface changes of nanoparticles, FTIR, TGA, TEM, and SEM analyses were used. The cure kinetics of the uncured samples was analyzed by DSC. Different methods such as KAS, Friedman, Starink, and FWO were applied to measure the activation energy. The activation energy of epoxy reinforced with chitosan-functionalized alumina (epoxy/[CS-EPO-alumina]) was less than that of epoxy reinforced with alumina (epoxy/alumina), which was a confirmation of the positive effect of CS on curing reaction kinetics. Using the Malek method, the Sestak-Berggren autocatalytic equation was chosen to investigate the cure kinetics of the epoxy. It was found that the Sestak-Berggren equation is well matched with the experimental data and the model was suitable to predict the epoxy curing reaction reliably. Moreover, the glass transition temperatures of all samples were approximately the same. The effect of surface modification of alumina on the electrical insulating behavior of epoxy was also studied. It was found that CS functionalized alumina (CS-EPO-alumina) increased volume resistivity of epoxy at a temperature range of 30 to 80°C more than that of alumina. Electric stability and breakdown strength of epoxy/alumina and epoxy/(CS-EPO-alumina) also enhanced, where epoxy/(CS-EPO-alumina) experienced a further increase compared to epoxy. 相似文献
11.
Effect of cold atmospheric plasma treatment on hydrophilic properties of fluorosilicone rubber 下载免费PDF全文
Jiang‐yan Meng Yun‐ying Wang Yun‐ping Wang Zu‐Qun Ding 《Surface and interface analysis : SIA》2016,48(13):1429-1435
Vulcanized fluorosilicone rubber for aviation was treated by argon and oxygen cold atmospheric plasma (CAP) in order to modify its hydrophilic properties. The sample's chemical composition was analyzed by X‐ray photoelectron spectroscopy (XPS). The static contact angle, surface free energy, and adhesion strength were used to indicate the hydrophilic properties. Additionally, the surface morphologies of the specimens were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that the contact angle declined from 101.5° to 22°, and the surface energy rose from 21.3 to 71.2 mJ/m2 after they were treated by argon plasma. Alternatively, the water contact angle decreased to 25.5°, and the surface energy increased to 70.6 mJ/m2 after they were treated by oxygen plasma. In addition, the SEM and AFM images of the samples illustrate that the treated surface of fluorosilicone rubber becomes rougher than the non‐treated surface. The concentrations of carbon (C) and fluorine (F) elements of the material' surface decreased and the contents of O element greatly enriched after plasma treatment. Additionally, chemical group C―O and C―OH appeared after the treatment. However, the hydrophilic effect of the plasma treatment is aged after the specimens were stored for 8–12 h. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
12.
The effect of the addition of the nonionic surfactant tributylphenyl-tetraethoxylate to culture media on pH and extracellular
protein content, and on production of β-glucosidase, xylanase, laccase, and manganese-dependent and-independent peroxidases
by the edible fungus Pleurotus ostreatus was determined. The relationship between fermentation parameters and concentration of surfactant was assessed by multiple
linear regression analysis, and the similarities and differences among the fermentation parameters were elucidated by principal
component analysis. Calculations proved that except for xylanase all other cultivation parameters were significantly influenced
by the surfactant, with the effect higher at higher surfactant concentrations. Surfactant increased the production of β-glucosidase
and inhibited laccase and manganese-dependent and-independent peroxidase activities. 相似文献
13.
Functional expression of a β-d-1,4 glucanase-encoding gene (egl1) from a filamentous fungus was achieved in both Escherichia coli and Saccharomyces cerevisiae using a modified version of pRS413. Optimal activity of the E. coli-expressed enzyme was found at incubation temperatures of 60°C, whereas the enzyme activity was optimal at 40°C when expressed
by S. cerevisiae. Enzyme activity at different pH levels was similar for both bacteria and yeast, being highest at 5.0. Yeast expression resulted
in a highly glycosylated protein of approx 60 kDa, compared to bacterial expression, which resulted in a protein of 30 kDa.
The hyperglycosylated protein had reduced enzyme activity, indicating that E. coli is a preferred vehicle for production scale-up. 相似文献
14.
Mohamed A. Abdel-Naby Mona Y. Osman Ahmed F. Abdel-Fattah 《Applied biochemistry and biotechnology》1999,76(1):33-44
Three cellobiases, here called cellobiase A, B, and C, from the culture filtrate of Aspergillus niger A20, were purified by precipitation with ammonium sulphate, gel filtration through Sephadex G-75, and column chromatography
of DEAE-cellulose. The purified enzymes were homogeneous on polyacrylamide disk electrophoresis. The mol wt of the purified
enzymes were estimated by SDS-gelelectrophoresis to be 88,000, 80,000, and 71,000 for cellobiases A, B, and C, respectively.
The enzymes were active at pH 4.5 and 55–60°C. The pattern of their aminoacid compositions showed high contents of aspartic
acid, glutamic acid, threonine, serine, and glycine. The apparent Km values for cellobiose were 0.9, 1.63, and 1.0 mM for cellobiases A, B, and C, respectively. Calcium ions stimulated cellobiases B and C, and Co2+ and Mg2+ ions stimulated cell obiase A. The purified enzymes hydrolyzed cellobiose and aryl-β-d-glucosides, but they had no action on sucrose, maltose, and cellulose. The three cellobiases catalyzed transglycosylate reaction,
and the major product formed from cellobiose was tetramer of glucose. 相似文献
15.
The relationships between the composition, structure, chemistry of the surface, and sensor properties of nanocomposites SnO2-M
n
O
m
(M
n
O
m
= Fe2O3, MoO3, V2O5) obtained by chemical precipitation from solutions were analyzed. The relationships between the elemental and phase composition
of the nanocomposites and the effect of the composition on the nanostructure and the acidic and oxidation properties of the
nanocomposite surface were considered. The modification of the SnO2 surface by other oxides makes it possible to control the type and density of the acid sites and the oxidation properties
of the surface and to enhance the selectivity of the materials in the detection of various gases.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1086–1105, June, 2008. 相似文献
16.
Srivastava P Rai SB Rai DK 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(14):3303-3311
The effects of PbO on optical properties of dysprosium doped calibo glass have been studied. The content of PbO in the glass has been varied from 0 to 60 mol%. The absorption and fluorescence spectra are analyzed in terms of the Judd-Ofelt theory. It is observed that the fluorescence yield is maximum for the glass containing 40 mol% PbO. The I-R absorption spectra of these glasses have also been recorded and interpreted in terms of changes in the structure of the glasses. 相似文献
17.
S. Smith P. Wiseman L. Boudreau G. Marangoni R. Palepu 《Journal of solution chemistry》1994,23(2):207-222
Solution properties of aqueous mixtures of the homologous series of polyoxyethene glycol mono-n-butyl ethers C4H9O(CH2CH2O)
m
H (where m=1 to 3) have been investigated using surface tension, density, viscosity and13C NMR techniques. From the experimental data, excess volume and deviation of viscosity and free energy of activation of flow were evaluated and discussed in terms of the molecular interactions between the components. Surface activity of polyoxyethene glycol mono ethers in aqueous dilute solutions was evident from surface tension measurements. Thermodynamic properties of adsorption and apparent micellization or critical aggregation concentration (CAC) in these systems were evaluated and discussed. The CAC values and the aggregation numbers obtained from13C NMR chemical shift data indicate an increase in hydrophobicity with an increase in the value of m, in the polyoxyethene glycol mono-n-butyl ethers, and also agrees with the results obtained from surface tension measurements.Presented at the Symposium, 76th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65th birthday. 相似文献
18.
The Effects of Wheat Bran Composition on the Production of Biomass-Hydrolyzing Enzymes by Penicillium decumbens 总被引:1,自引:0,他引:1
The effects of the starch, protein, and soluble oligosaccharides contents in wheat bran on the extracellular biomass-hydrolyzing
enzymes activities released by Penicillium decumbens mycelia grown in batch fermentations have been examined. The results showed increased starch content correlated directly
with an increase in released amylase activity but inversely with the levels of secreted cellulase and xylanase. High amounts
of protein in wheat bran also reduced the activities of cellulase, xylanase and protease in the culture medium. The effects
of the soluble and insoluble components of wheat bran and cello-oligosaccharides supplements on production of extracellular
cellulase and xylanase were compared. The soluble cello-oligosaccharides compositions in wheat bran were proved to be one
of the most significant factors for cellulase production. According to the results of this research, determining and regulating
the composition of wheat bran used as a fermentation supplement may allow for improved induction of cellulase and xylanase
production. 相似文献
19.
Lithium tungsten borate glass (0.56−x)B2O3–0.4Li2O–xZnO–0.04WO3 (0≤x≤0.1 mol%) is prepared by the melt quenching technique for photonic applications. Small relative values of ZnO are used to improve the glass optical dispersion and to probe as well the role of oxygen electronic polarizability on its optical characteristics. The spectroscopic properties of the glass are determined in a wide spectrum range (200–2500 nm) using a Fresnel-based spectrophotometric technique. Based on the Lorentz–Lorenz theory, as ZnO content increases on the expense of B2O3 the glass molar polarizability increased due to an enhanced unshared oxide ion 2p electron density, which increases ionicity of the chemical bonds of glass. The role of oxide ion polarizability is explained in accordance with advanced measures and theories such as optical basicity, O 1s binding energy, the outer most cation binding energy in Yamashita–Kurosawa's interionic interaction parameter and Sun's average single bond strength. FT-IR measurements confirm an increase in bridging oxygen bonds, as a result of replacement of ZnO by B2O3, which increase the UV glass transmission window and transmittance. 相似文献
20.
Ana B. Pereiro Helena I.M. Veiga José M.S.S. Esperança Ana Rodríguez 《The Journal of chemical thermodynamics》2009,41(12):1419-1423
Density, speed of sound, refractive index, and dynamic viscosity of the ionic liquids (ILs) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, BMpyr NTf2, and trihexyl(tetradecyl) phosphonium dicyanamide, P66614 dca, were studied as a function of temperature at atmospheric pressure. Thermal expansion coefficient, αp, molecular volumes, and standard entropies of these ILs were calculated from the experimental density values. The solubility of three aromatic components (benzene, toluene, and ethylbenzene) in the selected ILs was carried out at T = 298.15 K and atmospheric pressure and compared with literature values for sulfolane. 相似文献