共查询到20条相似文献,搜索用时 511 毫秒
1.
Anna Olszewska Paula Eronen Leena-Sisko Johansson Jani-Markus Malho Mikael Ankerfors Tom Lindström Janne Ruokolainen Janne Laine Monika Österberg 《Cellulose (London, England)》2011,18(5):1213-1226
This paper deals, with cationically modified NanoFibrillar Cellulose (cat NFC), obtained by reacting a dissolving pulp with
2,3-epoxypropyl trimethylammonium chloride (EPTMAC). The cat NFC was thoroughly characterized in terms of morphology and physical
properties. The dimensions of individual cellulose nanofibrils were determined by atomic force microscopy (AFM) imaging in
water and in air. Fibrils as thin as 0.8–1.2 nm were observed in water. The fibril diameter changed upon drying and the average
size was further quantified by image analysis. The experiments showed the importance of characterizing nanocellulosic materials
in situ before drying. The fibril size in air was confirmed by cryogenic transmission electron microscopy (cryo-TEM), and
it was found to be 2.6–3.0 nm. Smooth ultrathin films of cationic NFC were prepared by spincoating on silica substrates. The
effect of electrolyte concentration and pH on swelling of the cationic NFC film was studied using a quartz crystal microbalance
with dissipation. The results showed that at pH = 8 the cat NFC film was insensitive to electrolyte changes while at pH = 4.5,
the water content of the film decreased with increasing ionic strength. The electrophoretic mobility measurements showed a
cationic zeta potential for the cat NFC that decreased at increasing pH, verifying the swelling behaviour. 相似文献
2.
Sinke H. Osong Sven Norgren Per Engstrand Mathias Lundberg Mehedi Reza Vuorinen Tapani 《Cellulose (London, England)》2016,23(6):3611-3624
It has been a challenge to develop rapid online characterisation techniques for nanocellulose given the fibrillar structure of the nanoparticles. The crill optical analyser uses optical response signals in the infrared (IR) and ultraviolet (UV) wavelength ranges to evaluate the particle size properties of micro/nanofibrillar cellulosic materials. In this work, the crill analyser was used to measure the projected areas of UV and IR light sources by measuring the light blocked by nanocellulosic particles. This work uses the crill methodology as a new, simplified technique to characterise the particle size distribution of nanocellulosic material based on chemi-thermomechanical pulp (CTMP), thermomechanical pulp (TMP), and sulphite pulp (SP). In the first part, hydrogen peroxide pretreatment of CTMP and TMP in a wing mill refiner followed by high-pressure homogenisation to produce microfibrillated cellulose (MFC) was evaluated using the crill method. In the second part, TEMPO oxidation of CTMP and SP combined with high-shear homogenisation to produce MFC was studied using the crill method. With 4 % hydrogen peroxide pretreatment, the crill values of the unhomogenised samples were 218 and 214 for the TMP and CTMP, respectively, improving to 234 and 229 after 18 homogenisation passes. The results of the TEMPO method indicated that, for the 5 mmol NaClO SP-MFC, the crill value was 108 units at 0 min and 355 units after 90 min of treatment, a 228 % improvement. The CTMP and TMP fibres and the MFC were freeze dried and fibrillar structure of the fibres and microfibrils was visualised using scanning electron and transmission electron microscopy. 相似文献
3.
Masayuki Hirota Naoyuki Tamura Tsuguyuki Saito Akira Isogai 《Cellulose (London, England)》2010,17(2):279-288
Mercerized wood cellulose was oxidized by 4-acetamide-TEMPO/NaClO/NaClO2 system at 60 °C and pH 4.8 for 1–5 days. Mostly individual nanocrystals 4–7 nm in width and 100–200 nm in length were obtained
by ultrasonication of the oxidized product in water. The nanocrystals had the cellulose II structure, and carboxylate contents
of 2.0–2.4 mmol/g, indicating that these carboxylate groups were selectively formed on the cellulose II crystallite surfaces
in mercerized cellulose. Moreover, the original wood cellulose and mercerized cellulose were acid-hydrolyzed, and then subjected
to the TEMPO-mediated oxidation under the same conditions at pH 4.8 to prepare reference samples. TEM images, light transmittance
and rheological properties of water dispersions showed that the nanocrystals prepared from mercerized cellulose by the TEMPO
oxidation and sonication in water had the highest dispersibility of individual nanocrystals with less amounts of bundles in
water, resulting from the highest carboxylate contents. 相似文献
4.
Aurélie Rattaz Shree Prakash Mishra Bruno Chabot Claude Daneault 《Cellulose (London, England)》2011,18(3):585-593
The purpose of this work was to study the influence of acoustic cavitation on the oxidation of a mill bleached machine dried
hardwood Kraft pulp. The oxidation of the pulp was carried out using 4-acetamido-TEMPO coupled with NaOCl/NaBr as co-oxidizer.
The carboxylate content was increased by about 30% without any adverse impact on the degree of polymerization in the case
of oxidations under acoustic cavitation compared to the reference without acoustic cavitation. A close correlation between
the yield of nanocellulose and the carboxylate content of the oxidized pulps was observed. The individualized cellulose nanofibres
were 3–4 nm in width and a few microns in length. 相似文献
5.
A softwood bleached kraft pulp (SBKP) was subjected to electro-mediated oxidation in water with TEMPO or 4-acetamido-TEMPO
without any chlorine-containing oxidant. Solid recovery ratios of water-insoluble fractions of the oxidized SBKPs were more
than 80%, and C6-carboxylate contents increased up to approximately 1 mmol g−1 after oxidation for 48 h. Significant amounts of C6-aldehyde groups (0.17–0.38 mmol g−1) were also formed in the oxidized SBKPs. The degree of polymerization decreased from 2,200 to 520 and 1,400 by the oxidation
for 48 h with TEMPO at pH 10 and 4-acetamido-TEMPO at pH 6.8, respectively. The original cellulose I crystal structure and
crystallinity of SBKP were maintained after the oxidation, indicating that all C6-oxidized groups were selectively formed
on crystalline cellulose microfibril surfaces. The oxidized SBKPs with carboxylate contents of more than 0.9 mmol g−1 were convertible to individual cellulose nanofibrils in yields of more than 80% by disintegration in water. 相似文献
6.
Enhancing the effectiveness of a laccase–TEMPO treatment on sisal pulp by increasing pulp consistency was for the first time
found to increase the biorefining potential of this enzyme–mediator system. The operating conditions used were those previously
found to maximize oxidative functionalization and paper strength. Prior to the enzyme treatment, the pulp was refined at a
variable intensity (0, 3,000 and 4,500 revolutions) in order to ascertain whether the increased surface area would lead to
enhanced functionalization and boost the refining effect as a result. Increasing pulp consistency increased the contents in
aldehyde and carboxyl groups by 130% and 94%, respectively. Also, it resulted in more marked reduction of pulp viscosity during
the enzyme treatment, especially at a high refining intensity; this had a detrimental effect on fibre strength and significantly
reduced tear strength in the refined pulp. Oxidized pulp exhibited a considerably increased water retention value with respect
to the initial pulp, particularly after refining. Dry tensile index was increased by 21, 18 and 12%, and burst index by 23,
16 and 13% at 0, 3,000 and 4,500 rev, respectively, by the laccase–TEMPO treatment as a result of increased inter-fibre hydrogen
bonding offsetting the loss of fibre strength, an effect that can provide substantial savings in refining energy. Based on
the results, a laccase–TEMPO treatment is an enzymatic booster of mechanical refining with the added advantages of providing
unaltered drainability and increased air permeability. The most salient effect of the laccase–TEMPO treatment was an increase
in wet tensile strength (by 160, 553 and 588% at 0, 3,000 and 4,500 rev, respectively) that can be ascribed to inter-fibre
covalent bonding through hemiacetal linkages promoted by aldehyde groups. The improvement was much greater than that obtained
at a lower consistency under identical conditions. 相似文献
7.
An oil–water microemulsion system, having been successfully used for synthesizing polypyrrole (PPy) nanoparticles, is introduced
for preparing PPy–multi-walled carbon nanotube (MWCNT) nanocomposites via in situ chemical oxidative polymerization. The structures
and the physical properties of the PPy–MWCNT nanocomposites are also investigated. The studies show that PPy can coat MWCNTs
to form core–shell structure. The backbone structure of PPy is not damaged by the introduction of MWCNTs, and the PPy in the
PPy–MWCNT nanocomposites is still amorphous as pure PPy. The conductivities of PPy–MWCNT nanocomposites are higher than that
of pure PPy and are enhanced with the increase in the MWCNT–monomer mass ratio. Furthermore, a model is supposed to be used
for illustrating the mechanism for PPy–MWCNT nanocomposite formation via in situ microemulsion synthesis. 相似文献
8.
Cellulose dissolution in water-based solvents is essential for processing of regenerated cellulose products such as fibres,
films and particles. Cellulose dissolution in NaOH–urea aqueous solution has emerged as a simple and attractive alternative
for processing cellulose solutions. However, this solvent requires energy intensive pretreatments such as milling or refining.
In this paper we investigate a one step chemical pretreatment method using ethanol–hydrochloric acid prior to the dissolution
of cellulose in NaOH–urea–water. The dissolution mechanism of the pretreated sample was initially examined in diluted cupri-ethylenediamine
and 7% NaOH–12% urea–water solvent using optical microscopy methods and field emission scanning electron microscopy. The apparent
energy of activation for the viscous flow of ethanol–acid pretreated pulp in NaOH–urea–water was calculated using rheological
methods. Our results showed that the dissolution of pretreated pulp was achieved up to 4% cellulose concentration. We suggest
that the enhancement of dissolution was due to a combination of degradation of remnant primary fibre wall layer and reduction
of degree of polymerization of cellulose. 相似文献
9.
Stefan Veigel Ulrich Müller Jozef Keckes Michael Obersriebnig Wolfgang Gindl-Altmutter 《Cellulose (London, England)》2011,18(5):1227-1237
Cellulose nanofibrils were prepared by mechanical fibrillation of never-dried beech pulp and bacterial cellulose. To facilitate
the separation of individual fibrils, one part of the wood pulp was surface-carboxylated by a catalytic oxidation using (2,2,6,6-tetramethylpiperidin-1-yl)oxyl
(TEMPO) as a catalyst. After fibrillation by a high pressure homogenizer, the obtained aqueous fibril dispersions were directly
mixed with different urea–formaldehyde-(UF)-adhesives. To investigate the effect of added cellulose filler on the fracture
mechanical properties of wood adhesive bonds, double cantilever beam specimens were prepared from spruce wood. While the highest
fracture energy values were observed for UF-bonds filled with untreated nanofibrils prepared from wood pulp, bonds filled
with TEMPO-oxidized fibrils showed less satisfying performance. It is proposed that UF-adhesive bonds can be significantly
toughened by the addition of only small amounts of cellulose nanofibrils. Thereby, the optimum filler content is largely depending
on the adhesive and type of cellulose filler used. 相似文献
10.
Katrin Schwikal Thomas Heinze Bodo Saake Jürgen Puls Abdulaziz Kaya Alan R. Esker 《Cellulose (London, England)》2011,18(3):727-737
In this study, correlations between the charge density of adsorbed cationic xylans and the mechanical properties of selected
pulps are discussed. Hand-sheet experiments were carried out using birch sulfate pulp and spruce sulfite pulp after the adsorption
of 2-hydroxypropyl-trimethylammonium-4-O-methylglucuronoxylans (HPMAGXs) with different molar degrees of substitution (MS) in the range of 0.06–0.19. The charge density
of the HPMAGX in water was determined by polyelectrolyte titration. Properties such as the tensile and burst index increased
after HPMAGX addition and showed an optimum depending on the MS, which was 0.1 for both pulps. Other properties like the tear-index
or the specific volume changed depending on the pulp. Beating experiments were also performed and showed an increasing tensile
index of birch kraft pulp in the range of 53.7 to 85.7 N m g−1 for a beating time of 10 min. The adsorption of HPMAGXs with different MS onto thiol-based self-assembled monolayers (SAMs)
on gold and regenerated cellulose surfaces were studied using surface plasmon resonance (SPR). Electrostatic interactions
were found to be the most important factors affecting HPMAGX adsorption, and a strong correlation between HPMAGX adsorption
onto carboxyl-terminated SAMs (SAM-COOH) and paper strength when HPMAGX was used as a papermaking additive was observed. 相似文献
11.
G. Bannach R. Arcaro D. C. Ferroni A. B. Siqueira O. Treu-Filho M. Ionashiro E. Schnitzler 《Journal of Thermal Analysis and Calorimetry》2010,102(1):163-170
Thermogravimetry (TG), differential thermal analysis (DTA), differential scanning calorimetry (DSC) as well as X-ray diffraction
powder (DRX) patterns and Fourier transformed infrared spectroscopy (FTIR) were used to study ketoprofen, ibuprofen, and naproxen.
The chemical or physical properties of the studied compounds were established and when possible by X-ray powder diffractometry
and/or infrared spectroscopy were used. In this investigation, quantum chemical approach was used to determine the molecular
structures using Becke three-parameter hybrid method and the Lee–Yang–Par (LYP) correlation functional. The performed molecular
calculations in this work were done using the Gaussian 03 routine. Theoretical calculations help in interpretations of FTIR
spectra supplying structural and physicochemical parameters. 相似文献
12.
Chen Shifu Zhao Wei Liu Wei Zhang Sujuan 《Journal of Sol-Gel Science and Technology》2009,50(3):387-396
In this paper, p–n junction photocatalyst NiO/ZnO was prepared by the sol–gel method using Ni (NO3)2 and zinc acetate as the raw materials. The structural and optical properties of the p–n junction photocatalyst NiO/ZnO were
characterized by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM),
Brunauer–Emmett–Teller (BET) analysis, UV–Vis diffuse reflection spectrum (DRS) and the fluorescence emission spectra. The
photocatalytic activity of the photocatalyst was evaluated by photocatalytic reduction of Cr2O7
2− and photocatalytic oxidation of methyl orange (MO). The results showed that the photocatalytic activity of the p–n junction
photocatalyst NiO/ZnO is much higher than that of ZnO on the photocatalytic reduction of Cr2O7
2−. However, the photocatalytic activity of the photocatalyst is much lower than that of ZnO on the photocatalytic oxidation
of methyl orange. Namely, the p–n junction photocatalyst NiO/ZnO has higher photocatalytic reduction activity, but lower photocatalytic
oxidation activity. The heat treatment condition also influences the photocatalytic activity strongly, and the best preparation
condition is about 400 °C for 2 h. Effect of the heat treatment condition on the photocatalytic activity of the photocatalyst
was also investigated. The mechanisms of influence on the photocatalytic activity were discussed by the p–n junction principle. 相似文献
13.
Poonam M. Shewale A. Venkateswara Rao A. Parvathy Rao S. D. Bhagat 《Journal of Sol-Gel Science and Technology》2009,49(3):285-292
In the present paper, attempts have been made to produce transparent silica aerogels with low density and better hydrophobicity
by controlled sol–gel route and subsequent atmospheric pressure drying. The hydrogels were prepared by hydrolysis and polycondensation
of sodium silicate (Na2SiO3) in the presence of acetic acid catalyzed water followed by several washing steps with water, methanol and hexane, respectively.
The surface modification of the wet gel was carried out using a mixture of hexamethyldisilazane (HMDS) in hexane. Since, the
sol–gel chemistry provides a straightforward method to control the physical and optical properties of the aerogels, the influence
of various sol–gel parameters viz. gel washing time, molar ratios of CH3COOH/Na2SiO3 and HMDS/Na2SiO3 and silylation period on the physical and optical properties of the aerogels have been investigated. The aerogels have been
characterized by bulk density, Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric and Differential Thermal
Analysis (TG-DTA), Atomic Absorption Spectroscopy (AAS), Scanning Electron Microscopy (SEM) studies and Contact angle measurements. 相似文献
14.
Modified chitosan 4. Superabsorbent hydrogels from poly(acrylic acid-co-acrylamide) grafted chitosan with salt- and pH-responsiveness properties 总被引:1,自引:0,他引:1
Graft copolymerization of mixtures of acrylic acid (AA) and acrylamide (AAm) onto chitosan was carried out by using potassium persulfate (KPS) as a free radical initiator in the presence of methylenebisacrylamide (MBA) as a crosslinker. The effect of reaction variables, such as MBA concentration and AA/AAm ratio on the water absorbency capacity have been investigated. The polymer structures were confirmed by FTIR spectroscopy. Water absorbencies were compared for the hydrogels before and after alkaline hydrolysis. In the non-hydrolyzed hydrogel, enhanced water absorbency was obtained with increasing AA in monomer feed. However, after saponification, the sample with high AAm ratio exhibited more water absorbency. These behaviors were discussed according to structural parameters. The swelling kinetics of the superabsorbing hydrogels was studied as well. The hydrogels exhibited ampholytic and reversible pH-responsiveness characteristics. The swelling variations were explained according to swelling theory based on the hydrogel chemical structure. The hydrogels exhibited salt-sensitivity and cation exchange properties. The pH-reversibility and on-off switching properties of the hydrogels make the intelligent polymers as good candidates for considering as potential carriers for bioactive agents, e.g. drugs. 相似文献
15.
Drago’s acid–base approach was used to quantify the hydrogen bonding interactions in solvent swelling of cellulose fibers.
The fiber swelling was correlated with acid–base, dispersive interactions and solvent molar volume. The acid–base interaction
potentials of solvents were expressed in terms of their electron pair donor and acceptor numbers. The acid–base interaction
terms of cellulosic materials were determined by using: (1) Flory–Huggins; (2) multiple regression models. We have used the
swelling data of Mantanis and coworkers, which were based on the equilibrium liquid holding capacities of various compressed
fibers in water and series of organic solvents. According to our interpretations, acid–base interactions and molar volume
parameters were the major contributors to the overall solubility parameter. Acid–base interaction terms were balanced in alpha-cellulose
sample. However spruce wood and sulfite pulp samples were more acidic than basic and therefore swollen better in organic basic
solvents. For a good swelling behavior solvent must have high electron pair donor number/acceptor number ratio and high electron
pair donor number–acceptor number difference. 相似文献
16.
Molecularly thin nanoparticles from cellulose: isolation of sub-microfibrillar structures 总被引:1,自引:0,他引:1
We have succeeded in isolating nanostructures from never-dried cellulose wood pulp, in sheet-form that have sub-microfibril
dimensions (single to double digit Å thickness with 100’s of nm in length). A recently developed oxidation procedure by Saito
and co-workers (Biomacromolecules 2006, 7:1687–1691) combined with extensive ultrasonication was used to liberate nanoscale
cellulose fibrils. We show structures, as determined with atomic force microscopy, that compose the well-known cellulose microfibril,
which are tenfold thinner than previous reports on nanoscale celluloses. This work provides indirect evidence in support of,
and is consistent with, the hypothesis that the intersheet van der Waals bonding of the cellulose fibril is significantly
weaker than the intrasheet hydrogen bonding of the cellulose microfibril. The structures are facile to isolate, contain enormous
specific surface area with rich chemical functionality providing potential for numerous novel applications. 相似文献
17.
Zhou Y Han L Cheng J Guo F Zhi X Hu H Chen G 《Analytical and bioanalytical chemistry》2011,399(5):1901-1906
A method for analysis of diethofencarb and pyrimethanil in apple pulp and peel was developed by using dispersive liquid–liquid
microextraction based on solidification of a floating organic droplet (DLLME-SFO) and high-performance liquid chromatography
with diode-array detection (HPLC–DAD). Acetonitrile was used as the solvent to extract the two fungicides from apple pulp
and peel, assisted by microwave irradiation. When the extraction process was finished, the target analytes in the extraction
solvent were rapidly transferred from the acetonitrile extract to another extraction solvent (1-undecanol) by using DLLME-SFO.
Because of the lower density of 1-undecanol than that of water, the finely dispersed droplets of 1-undecanol collected on
the top of aqueous sample and solidified at low temperature. Meanwhile, the tiny particles of apple cooled and precipitated.
Recovery was tested for a concentration of 8 μg kg−1. Recovery of diethofencarb and pyrimethanil from apple pulp and peel was in the range 83.5–101.3%. The repeatability of the
method, expressed as relative standard deviation, varied between 4.8 and 8.3% (n = 6). Detection limits of the method for apple pulp and peel varied from 1.2–1.6 μg kg−1 for the two fungicides. Compared with conventional sample preparation, the method has the advantage of rapid speed and simple
operation, and has high enrichment factors and low consumption of organic solvent. 相似文献
18.
M. S. Vasil’eva V. S. Rudnev O. E. Sklyarenko L. M. Tyrina N. B. Kondrikov 《Russian Journal of General Chemistry》2010,80(8):1557-1562
Nickel-copper compositions for catalytic oxidation of carbon(II) oxide to carbon(IV) oxide were prepared by impregnation of
oxide films on titanium surface, obtained by plasma electrolytic oxidation followed by annealing. Plasma electrolysis oxide
coatings with a layer thickness of 5 to 50 μm were generated using different electrolytes. The compositions were studied by
X-ray powder diffraction, X-ray spectral analysis, and electron microscopy, and moisture absorption of the initial plasma
electrolytic structures was estimated. A linear correlation was found between the overall concentration of nickel and copper
(4 to 25 mol %) in the surface layer of ∼2–5-μm compositions and their catalytic activity. The overall concentration of nickel
and copper was found to increase in parallel with the moisture absorption of plasma electrolytic oxidation coatings. Nickel-copper
compositions based on plasma electrolytic oxidation coatings generated in a silicate electrolyte displayed the best catalytic,
mechanical, and adhesion properties. 相似文献
19.
Mariusz Trytek Jan Fiedurek Agnieszka Lipke Stanisław Radzki 《Journal of Sol-Gel Science and Technology》2009,51(3):272-286
Two types of porphyrins (water-soluble and water-insoluble) were encapsulated in transparent monolithic silica gels. Their
properties in solutions and at various steps of the sol–gel process were studied by absorption and emission electron spectroscopy.
A photocatalytic system containing porphyrins immobilized in powdered silica gel for α-pinene biomimetic oxidation to pinocarveol,
pinocarvone and myrtenol is reported. The impact of several parameters (visible light irradiation time, organic solvent, the
presence of an electron acceptor/donor, and substrate concentration) on this biotransformation process was investigated and
optimized. It was established that photochemical excitation of sol–gel immobilized metal-free porphyrins is crucial for catalyzed
oxidation of monoterpenes. 相似文献
20.
The growing structural patterns of water clusters with 30–48 water molecules were investigated by means of a combined Monte
Carlo search algorithm and density functional theory computations. The (H2O)30–48 clusters with amorphous core–shell structures are lower in energy than the previously reported fused cage and the tubular
configurations. The significant differences in infrared spectra of these three different structural patterns provide some
clues to identify the structural properties of these medium-sized water clusters in experiments. 相似文献