排序方式: 共有56条查询结果,搜索用时 15 毫秒
31.
Lidia Testova Marc Borrega Lasse K. Tolonen Paavo A. Penttilä Ritva Serimaa Per Tomas Larsson Herbert Sixta 《Cellulose (London, England)》2014,21(3):2007-2021
Aqueous-phase prehydrolysis followed by alkaline pulping is a viable process to produce wood-based dissolving pulps. However, detailed characterisation of the achievable pulp quality, performance and cellulose structure is yet lacking. In this study, the production of hemicellulose-lean birch soda-anthraquinone pulps after prehydrolysis under various intensities was investigated. Increasing prehydrolysis intensity resulted in pulps of higher purity but lower cellulose yield and degree of polymerisation. Higher cellulose yield by using sodium borohydride during pulping was achieved at the expense of reducing pulp purity. Cellulose crystallinity was similar in all pulps indicating simultaneous degradation of both crystalline and amorphous cellulose regions. Reinforced prehydrolysis seemingly increased the cellulose crystal size and the interfibrillar distances. Moderate intensity prehydrolysis (170 °C) resulted in a pulp well suited for viscose application, whereas reinforced prehydrolysis favoured the production of acceptable cellulose triacetate dope. The performance of the pulps in viscose and acetate applications was strongly related to the chemical and structural properties. 相似文献
32.
If the gradient of u(x) is nth power locally integrable on Euclidean n-space, then the integral average over a ball B of the exponential of a constant multiple of |u(x)−uB|n/(n−1), uB=average of u over B, tends to 1 as the radius of B shrinks to zero—for quasi almost all center points. This refines a result of N. Trudinger (1967). We prove here a similar result for the class of gradients in Ln(log(e+L))α, 0?α?n−1. The results depend on a capacitary strong-type inequality for these spaces. 相似文献
33.
Kirsi S. Mikkonen Jasna S. Stevanic Catherine Joly Patrice Dole Kari Pirkkalainen Ritva Serimaa Lennart Salmén Maija Tenkanen 《Cellulose (London, England)》2011,18(3):713-726
Two future wood biorefinery products, spruce galactoglucomannans (GGM) and microfibrillated spruce wood cellulose (MFC), were
mixed to form composite films. The films were plasticized with different amounts of glycerol, and the preparation of films
was successful even with low glycerol contents. The film properties were studied using optical microscopy and scanning electron
microscopy, x-ray diffraction, water sorption, dielectric analysis, moisture scanning dynamic mechanical analysis, and tensile
testing. The addition of MFC clearly affected the properties of the films by decreasing the moisture uptake and increasing
the relative humidity of softening of the films and by increasing the glass transition temperature, tensile strength, and
Young’s modulus of the films. The effect of MFC addition on the tensile properties of films was emphasized at low glycerol
contents. The addition of MFC did not affect the degree of crystallinity of GGM in the films, which was between 20 and 25%.
MFC can be efficiently used as reinforcement of GGM films to form wood-based composite materials and to prepare GGM-based
films and coatings with low plasticizer content. 相似文献
34.
Structure of cellulose and microcrystalline cellulose from various wood species, cotton and flax studied by X-ray scattering 总被引:2,自引:1,他引:1
Kirsi Leppänen Seppo Andersson Mika Torkkeli Matti Knaapila Nina Kotelnikova Ritva Serimaa 《Cellulose (London, England)》2009,16(6):999-1015
The structure of microcrystalline cellulose (MCC) made by mild acid hydrolysis from cotton linter, flax fibres and sulphite
or kraft cooked wood pulp was studied and compared with the structure of the starting materials. Crystallinities and the length
and the width of the cellulose crystallites were determined by wide-angle X-ray scattering and the packing and the cross-sectional
shape of the microfibrils were determined by small-angle X-ray scattering. The morphological differences were studied by scanning
electron microscopy. A model for the changes in microfibrillar structure between native materials, pulp and MCC samples was
proposed. The results indicated that from softwood or hardwood pulp, flax cellulose and cotton linter MCC with very similar
nanostructures were obtained with small changes in reaction conditions. The crystallinity of MCC samples was 54–65%. The width
and the length of the cellulose crystallites increased when MCC was made. For example, between cotton and cotton MCC the width
increased from 7.1 nm to 8.8 nm and the length increased from 17.7 nm to 30.4 nm. However, the longest crystallites were found
in native spruce wood (35–36 nm). 相似文献
35.
Glucomannan composite films with cellulose nanowhiskers 总被引:1,自引:1,他引:0
Kirsi S. Mikkonen Aji P. Mathew Kari Pirkkalainen Ritva Serimaa Chunlin Xu Stefan Willför Kristiina Oksman Maija Tenkanen 《Cellulose (London, England)》2010,17(1):69-81
Spruce galactoglucomannans (GGM) and konjac glucomannan (KGM) were mixed with cellulose nanowhiskers (CNW) to form composite
films. Remarkable effects of CNW on the appearance of the films were detected when viewed with regular and polarizing optical
microscopes and with a scanning electron microscope. Addition of CNW to KGM-based films induced the formation of fiberlike
structures with lengths of several millimeters. In GGM-based films, rodlike structures with lengths of several tens of micrometers
were formed. The degree of crystallinity of mannan in the plasticized KGM-based films increased slightly when CNW were added,
from 25 to 30%. The tensile strength of the KGM-based films not containing glycerol increased with increasing CNW content
from 57 to 74 MPa, but that of glycerol-plasticized KGM and GGM films was not affected. Interestingly, the notable differences
in the film structure did not appear to be related to the thermal properties of the films. 相似文献
36.
Sami Valkama Juha Hartikainen Mika Torkkeli Ritva Serimaa Janne Ruokolainen Kari Rissanen Gerrit ten Brinke Olli Ikkala 《Macromolecular Symposia》2002,186(1):87-92
Comb-shaped supramolecules are constructed using flexible polymers and semi-rigid conjugated undoped or doped conjugated polymers upon complexing Zinc dodecyl benzene sulphonate, Zn(DBS)2. Selforganized nanostructures are formed in the bulk due to competing attractive interactions (coordination or water mediated hydrogen bonding) and repulsive polar/nonpolar interactions, showing characteristic long periods of ca. 30 Å. 相似文献
37.
N. E. Kotelnikova T. Paakkari R. Serimaa G. Wegener E. Windeisen V. P. Kotelnikov V. N. Demidov A. V. Schukarev 《Macromolecular Symposia》1999,138(1):175-180
The WAXS, SAXS, SEM, TEM, XPS were used to study methods of platinum and palladium aggregates intercalation into the cellulose matrix and changes of cellulose structure after this intercalation. As a result new microcrystalline cellulose - metal compounds containing aggregates of platinum, and palladium were synthesised for the first time using the redox interaction reaction. 相似文献
38.
Summary: Copper and nickel nanoparticles were synthesized in the insoluble microcrystalline cellulose support by reduction of metal ions with several reducers in various media resulting in cellulose-metal nanocomposites. Wide-angle X-ray scattering results showed that supramolecular structure of cellulose did not change. Crystalline Cu2O and Cu0 nanoparticles were prepared with reducers NaBH4 and N2H4 · H2SO4, CuO nanoparticles – with cellulose itself as a reducer. Crystalline Ni0 nanoparticles were synthesized with N2H4 · 2HCl and NaBH4; Ni0 nanoparticles in amorphous form were prepared with KH2PO2 · H2O. SEM revealed large agglomerates of metal particles on the fibre surface. ASAXS and TEM have shown the nanoparticles to be in the range 5–55 nm. 相似文献
39.
40.
K. Jokela A. Vnnen M. Torkkeli P. Starck R. Serimaa B. Lfgren J. Seppl 《Journal of Polymer Science.Polymer Physics》2001,39(16):1860-1875
The objective of this work was to use both X‐ray and differential scanning calorimetry techniques in a comparative study of the lamellar and crystalline structures of heterogeneous and homogeneous ethylene‐α‐copolymers. The samples differed in the comonomer type (1‐butene, 1‐hexene, 1‐octene, and hexadecene), comonomer content, and catalyst used in the polymerizations. Step crystallizations were performed with differential scanning calorimetry, and the crystallinity and lamellar thicknesses of the different crystal populations were determined. Wide‐angle X‐ray scattering was used to determine crystallinities, average sizes of the crystallites, and dimensions of the orthorhombic unit cell. The average thickness, separation of the lamellae, and volume fractions of the crystalline phase were determined by small‐angle X‐ray scattering (SAXS). The results revealed that at densities below 900 kg/m3, polymers were organized as poorly organized crystal bundles. The lamellar distances were smaller and the lamellar thickness distributions were narrower for the homogeneous ethylene copolymers than for the heterogeneous ones. Step‐crystallization experiments by SAXS demonstrated that the long period increased after annealing. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1860–1875, 2001 相似文献