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1.
Naoki Shinozaki Ryoji Takahashi Satoshi Sato Toshiaki Sodesawa 《Journal of Sol-Gel Science and Technology》2007,43(3):275-282
The bending strength and the Young’s modulus of bimodal porous silica gels having different porosity were evaluated. The porosity
of the gel increased by aging the gel under basic conditions, and decreased with increasing the calcination temperature. The
mesopores disappeared on calcination at 1,050 °C, whereas continuous macropores retained their morphology up to 1,050 °C for
all the samples. Both the bending strength and the Young’s modulus of the bimodal porous silica gels were expressed as power-law
functions of the bulk density, and no effect of bimodal pore structures on mechanical properties was observed. We also found
linear correlation between the bending strength and the elasticity. The bimodal porous silica had higher strength and elastic
modulus compared with other porous materials at the same porosity probably due to the presence of homogeneous micrometer-scale
macropores. 相似文献
2.
The effect of fiber content on the mechanical and thermal expansion properties of biocomposites based on microfibrillated cellulose 总被引:1,自引:1,他引:0
A new method to obtain composites of phenolic resin reinforced with microfibrillated cellulose with a wide fiber content was
established and the mechanical properties were evaluated by tensile test. A linear increase in Young’s modulus was observed
at fiber contents up to 40 wt%, with a stabilizing tendency for higher fiber percentages. These results were ratified by measurements
of the coefficient of thermal expansion (CTE) relative to fiber content, which indicated a strong thermal expansion restriction
rate below 60 wt% fiber content, indicating the effective reinforcement attained by the cellulose microfibrils. The low CTE
achieved of 10 ppm/K is one of the important properties of cellulose composites. 相似文献
3.
Noriyuki Isobe Masahiro Sekine Satoshi Kimura Masahisa Wada Shigenori Kuga 《Cellulose (London, England)》2011,18(2):327-333
Cellulose-synthetic polymer nanocomposite films were prepared by immersion of cellulose gel in polymer solutions followed
by dry casting. The cellulose hydrogel was prepared from aqueous alkali-urea solution. As the synthetic polymer, polystyrene
(PS) and poly(methyl methacrylate) (PMMA) were used. The polymer content could be changed between 10 and 80% by changing polymer
concentration of immersing solution. While the mechanical properties of the cellulose-PMMA composite films showed a nearly
linear dependence on PMMA content, those of cellulose-PS composites showed an anomalous behavior; both tensile strength and
Young’s modulus showed prominent maxima at 15–30 wt% PS contents. This anomaly may have resulted from the specific interaction
between the aromatic ring of PS and the hydrophobic plane of the glucopyranoside. Both PMMA and PS composite films showed
significant improvements in dimensional thermal stability; up to 25 wt% synthetic polymer content, the coefficient of thermal
expansion (CTE) was as low as ca. 30 ppm/K, about 1/3 of the pure polymers. This indicates that the regenerated cellulose
network is effective in suppressing thermal expansion of the synthetic polymers. 相似文献
4.
Polymer nacomposites based on thermosetting (epoxy resins) and thermoplastic (PA-12) polymer matrices with fulleroid and carbon
modifiers are synthesized through in situ polymerization, and the mechanical properties are investigated. The introduction
of fulleroid modifiers has almost no effect on the mechanical properties of thermosetting formulations; however, in the case
of thermoplastic formulations, Young’s modulus and tensile strength increase by 30–40% after introduction of 0.02–0.06 wt
% fulleroid modifiers. 相似文献
5.
Soo-Jin Park George G. Chase Kwang-Un Jeong Hak Yong Kim 《Journal of Sol-Gel Science and Technology》2010,54(2):188-194
Flexible mats of titania fibers are prepared by calcination of electrospun polyvinylpyrrolidone fibers containing titanium
isopropoxide precursor. Structural investigation of the calcinated nanofibers by X-ray diffraction (XRD) and electron diffraction
(ED) combined with the morphologies by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show
the titania fibers, with an average diameter of 180 nm, were comprised of anatase and rutile crystals. The mechanical, chemical
and thermal properties of the titania fiber mats are further investigated by the techniques of Instron mechanical tester,
thermogravimetric analyzer (TGA), and Fourier transform infrared spectroscopy (FT-IR). The titania fiber mat prepared in this
method exhibited a significant flexibility with 461 MPa Young’s modulus. 相似文献
6.
Nattakan Soykeabkaew Chandeep Sian Saharman Gea Takashi Nishino Ton Peijs 《Cellulose (London, England)》2009,16(3):435-444
All-cellulose nanocomposites using bacterial cellulose (BC) as a single raw material were prepared by a surface selective
dissolution method. The effect of the immersion time of BC in the solvent (lithium chloride/N,N-dimethylacetamide) during preparation on the nanocomposite properties was investigated. The structure, morphology and mechanical
properties of the nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, and tensile testing.
The optimum immersion time of 10 min allowed the preparation of nanocomposites with an average tensile strength of 411 MPa
and Young’s modulus of 18 GPa. With the longest immersion time of 60 min, the prepared composite sheet turns to express a
very high toughness characteristic possessing a work-to-fracture as high as 16 MJ/m3. These biobased nanocomposites show high performances thanks to their unique structure and properties. 相似文献
7.
In the present study, a series of iPP/SiO2 nanocomposites, containing 1, 2.5, 5, 7.5, 10 and 15 wt% SiO2 nanoparticles, were prepared by melt mixing in a twin screw co-rotating extruder. Poly(propylene-g-maleic anhydride) copolymer (PP-g-MA) containing 0.6 wt% maleic anhydride content was added to all nanocomposites at three different concentrations, 1, 2.5 and 5 wt%, based on silica content. Mechanical properties such as tensile strength at break and Young’s modulus were found to increase and to be mainly affected by the content of silica nanoparticles as well as by the copolymer content. For the tensile strength at break as well as for yield point, a maximum was observed, corresponding to the samples containing 2.5-5 wt% SiO2. At higher concentrations, large nanosilica agglomerates are formed that have as a result a decrease in tensile strength. Young’s modulus increases almost linearly on the addition of SiO2, and takes values up to 60% higher than that of neat iPP. Higher concentrations of PP-g-MA resulted in a further enhancement of mechanical properties due to silica agglomerate reduction. This finding was verified from SEM and TEM micrographs. Evidently the surface silica hydroxyl groups of SiO2 nanoparticles react with maleic anhydride groups of PP-g-MA and lead to a finer dispersion of individual SiO2 nanoparticles in the iPP matrix. The enhanced adhesion in the interface of the two materials, as a result of the mentioned reaction, has been studied and proved by using several equations. The increased Vicat point of all nanocomposites, by increasing the PP-g-MA content, can also be mentioned as a positive effect. 相似文献
8.
Their mesoscopic dimensions (including a nanometer scale diameter and a micrometer scale length) make nanotubes a unique and
attractive object of study, including the study of their mechanical properties and fracture in particular. The investigation
of the mechanical properties of individual WS2 nanotubes is a challenging task due to their small size. Hence, various microscopy based techniques were used to overcome
this challenge. The Young’s modulus was studied by techniques like atomic force microscope (AFM) and scanning electron microscope
(SEM); it was also calculated by using the density-functional-based tight-binding (DFTB) method. Tensile tests and bending
tests of individual WS2 nanotubes were performed as well. Furthermore, the shock wave resistance of these nanotubes was tested. The Young’s modulus
of WS2 nanotubes was found to be in the range of 150–170 GPa, which is in good agreement with DFTB calculations. WS2 nanotubes also showed tensile strength as high as 16 GPa and fracture strain of 14%. These results indicate the high quality
of these nanotubes which reach their theoretical strength. The interlayer shear (sliding) modulus was found to be ca. 2 GPa,
this value is in good agreement with DFTB calculations. Moreover, the nanotubes were able to withstand shock waves as high
as 21 GPa. 相似文献
9.
Polymer nanocomposites based on polyamide and fulleroid modifiers are synthesized through in situ polymerization, and their
mechanical and electric properties are studied. After introduction of 0.001–0.1 wt % fulleroid modifiers, Young’s modulus
and the strength of thermoplastic composites increases by 15–20%, practically independently of the amount of filler. This
circumstance is due to the fact that the introduction of fulleroid fillers causes selective crystallization of polyamide 6
only in the α form. The introduction of fullerene fillers considerably improves the tribological characteristics of polymer
nanocomposites, thereby decreasing the friction coefficient by a factor of 2. The electric properties of nanocomposites are
studied also. 相似文献
10.
Tomáš Nedelčev Igor Krupa Pavol Hrdlovič Jozef Kollár Dušan ChorvátJr. Igor Lacík 《Journal of Sol-Gel Science and Technology》2010,55(2):143-150
Fluorescent probes pyrene (Py), di(1-pyrenylmethyl)ether (DiPyM) and newly synthesized 2,3-bis-[4-(1-pyrenemethoxy)methylphenyl]butane
(DiPyS) were used to monitor the formation and aging of silica hydrogel prepared from poly(glyceryl silicate) (PGS) sol. The
fluorescence emission spectra of these probes are sensitive to their environment and this feature is utilized for monitoring
the evolution of silica hydrogels prepared in this work. The polarity of hydrogel matrix during sol–gel transition assessed
by all three pyrene probes decreases in the first stage of hydrogel formation, for about 2 h, followed by a gradual increase
in polarity and reaching the constant level after 24 h for at least 2 weeks. The process of crosslinking was assessed by DiPyM
and DiPyS. These fluorescent probes possess two pyrene structures, which ability to form a dynamic intramolecular excimer
can be used to monitor the degree of hydrogel crosslinking with time. These data support the polarity measurements that the
hydrogel network is predominatly formed within the first 2 h, stabilized within the 24 h, and that there is a minor increase
in the network density for about 10 days until reaching the constant level. In addition, utilizing the second-order diffraction
of scattered excitation light may also be used to obtain an adequate information about the silica hydrogel evolution. In summary,
this paper demonstrates that pyrene-type fluorescent probes represent simple and precise tool for characterization of formation
and aging of the silica hydrogels. 相似文献
11.
Mussel-inspired chemistry in producing mechanically robust and bioactive hydrogels as skin dressings
The development of hydrogels as skin dressings demonstrates a great potential in real life applications. To achieve this, the hydrogel has to conquer its natural poor mechanical strength, and to prolong its lifetime, antifatigue and self-healing properties originating from dynamic interactions are also required. As skin dressings, the hydrogel needs to maintain its ductility while pursuing the above mentioned properties. In this work, poly(ethylene glycol) diacrylate is used to produce skin dressings by reinforcing poly(ethylene glycol) diacrylate/alginate double network hydrogels with a crosslinker from mussel-inspired chemistry, which is 3,4-dihydroxy-l-phenylalanine. This crosslinking methodology significantly improved mechanical strength of the hydrogel, with 11,200% increase in compressive failure strength; it endowed the hydrogel with outstanding antifatigue and training strengthening properties that makes its mechanical strength increasing in a 50 cycles compressive test; the hydrogel showed excellent self-healing properties that in rheological characterization; it also displayed enhanced storage modulus after withstanding a shear strain up to 1100%; meanwhile, the hydrogel exhibited extreme ductility with an elastic modulus of only 10.90–16.53 kPa. 3,4-dihydroxy-l-phenylalanine also renders the hydrogel its inherent antioxidant activity, conductivity, and bioadhesiveness. Together with the highly transparent appearance, the hydrogels possess a great potential and practibility in the fields of skin dressings. 相似文献
12.
Ru Chen Yuezhen Bin Yumiko Nakano Naoko Kurata Masaru Matsuo 《Colloid and polymer science》2010,288(3):307-316
In an attempt to improve the mechanical property of polyethylene composite at high temperature, crosslinking of ultrahigh-molecular-weight
polyethylene (UHMWPE) and carbon fiber (CF) blends was carried out by using dicumyl peroxide (DCP). The specimens were prepared
by gelation/crystallization from solutions. The effect of chemical crosslinking on mechanical and electrical properties of
UHMWPE/CF blends with composition of 1/0, 1/0.25, and 1/1 (w/w) were investigated in detail. Electrical conductivity and thermal mechanical properties of the blends with the 1/1 composition
were greatly improved by incorporation of enough content of CF and adequate crosslinking network formation. Surprisingly,
the Young’s modulus of the 1/1 blend reached 20 GPa at room temperature (20 °C). On the other hand, heat treatment at 135 °C
played an important role for obtaining a high PTC effect for the UHMWPE-CF blend in which the PTC intensity reached 107. 相似文献
13.
Z. Osman 《Journal of Thermal Analysis and Calorimetry》2012,107(2):709-716
In this article, autocondensation reactions of Acacia nilotica spp. nilotica (Ann) tannin extracts solutions have been studied at several pH values by thermomechanical analyzer (TMA). TMA has been chosen
for this study as it has been shown to give results more rapidly and more precisely than panels. It also tends to exaggerate
the differences in results which render it an excellent tool for comparison. Therefore, autocondensation reactions were studied
and compared with its polycondensation reactions upon addition of different hardeners such as paraformaldehyde, urea, and
PMDI at same pH values. The aim was to evaluate the tannin’s reactivity and therefore its suitability for the production of
commercially and technically viable tannin adhesives for wood products. The results of autocondensation showed that the maximum
Young’s modulus values (3300 and 3600 MPa) were obtained at pH 4. However, these values have been achieved at high temperature
(160 and 208 °C). Results of copolymerization reaction of the tannins with different hardeners revealed that some of these
co-reactants were found to depress tannins autocondensations, while others appear to enhance the formation of the final networking.
Polycondensation of the Ann tannins with 8% paraformaldehyde and 10% PMDI gave the maximum Young’s modulus values at lower
temperature (91–101 °C) and acidic pH5. However, the addition of 20 and 30% PMDI achieved the best Young’s modulus values
2300 and 3300 MPa, respectively, at pH 4. Furthermore, the obtained values were comparable to those obtained by the addition
of urea and the self condensation reactions. This is very important for particleboard production from economical and technical
point of view. It has been noticed that the addition of hardeners lowered the temperature of hardening, and the obtained values
were more consistent with the pH acidity. The study concluded that the tannins of Ann were very reactive, and therefore, it
could be a potential precursor for particleboard adhesives. The results also indicated that the tannins can be used alone,
and it would possibly produce zero emission environmentally friendly particleboard. 相似文献
14.
Ke Chen Zhihao Bao Ai Du Xiurong Zhu Jun Shen Guangming Wu Zhihua Zhang Bin Zhou 《Journal of Sol-Gel Science and Technology》2012,62(3):294-303
A rapid and facile synthesis of resorcinol/formaldehyde cross-linked silica (RF/SiO2) aerogels was carried out in one pot based on an acid-catalyzed route, instead of the previously reported base-catalyzed
ones. The gelation time was reduced to several hours at room temperature while it took several days even under heating conditions
in the base-catalyzed ones. The interpenetrating network of RF/SiO2 aerogels showed similar porous structures with those of silica aerogels or RF aerogels. Their thermal conductivity was as
low as that of the typical glass wool materials. The mechanical properties are characterized by dynamic mechanical analysis
and compression testing. At room temperature, the results of compression testing show that the compressive Young’s modulus
or ultimate failure strength of RF/SiO2 aerogel specimen is higher than that of native SiO2 aerogels with a similar density. The one-pot method improves the efficiency and reduces the cost of RF/SiO2 aerogels. The hierarchical porous carbon monoliths are also converted from carbonized RF/SiO2 aerogels by an additional HF treatment. Hence, they could be further explored as multifunctional candidate materials for
thermal, mechanical, and electrochemical applications. 相似文献
15.
Effect of annealing temperature on the quality of Al-doped ZnO thin films prepared by sol–gel method
Lai Chi-ming Lin Keh-moh Rosmaidah Stella 《Journal of Sol-Gel Science and Technology》2012,61(1):249-257
The different thermal expansion coefficients and lattice mismatch between ZnO and Al may produce residual stress in Al-ZnO
(AZO) thin films. Annealing processes can be applied to modulate this residual stress. In this study, three different rapid
thermal annealing (RTA) temperatures (350, 450, and 600 °C) were applied to an AZO thin film, prepared using sol–gel method.
The mechanical properties, optical properties, and structure of the AZO thin film were investigated experimentally. The results
show that increasing the RTA temperature increased the Young’s modulus and hardness of the films. The grain size of the films
also increased with increasing RTA temperature. However, the film thickness and shear stress component decreased with increasing
RTA temperature. Both compressive and tensile stress decreased gradually with increasing film thickness after RTA treatment.
It was demonstrated that the use of a relatively high RTA temperature can effectively relax the residual stress in AZO thin
films. 相似文献
16.
L.Y. Lee S.C. Wu S.S. Fu S.Y. Zeng W.S. Leong L.P. Tan 《European Polymer Journal》2009,45(11):3249-3256
In this work we present the synthesis of a biodegradable, elastomeric material with a wide range of mechanical properties. The synthesis of the material was done by condensation polymerization of malic acid and 1,12–dodecandiol. The synthesized materials have low Young’s modulus ranging from about 1 to 4 MPa and a high elongation at break of 25–737% depending on the crosslinking density of the system. The cell growth observed under microscope showed good proliferation at 3 days of culture indicating good biocompatibility and support of L929 cells growth. The fabrication of 3D scaffold from these materials using the super critical CO2 foaming method was also attempted. This method of scaffold fabrication is appropriate for materials that are easily hydrolysable and it also has the advantage of being a solvent free process. These materials are generally soft, biocompatible and biodegradable making them suitable for tissue engineering of soft tissues that are elastic in nature like muscles and blood vessels. 相似文献
17.
Eliane Trovatti Susana C. M. Fernandes Laurent Rubatat Carmen S. R. Freire Armando J. D. Silvestre Carlos Pascoal Neto 《Cellulose (London, England)》2012,19(3):729-737
Bionanocomposites with improved properties based on two microbial polysaccharides, pullulan and bacterial cellulose, were
prepared and characterized. The novel materials were obtained through a simple green approach by casting water-based suspensions
of pullulan and bacterial cellulose and characterized by TGA, RDX, tensile assays, SEM and AFM. The effect of the addition
of glycerol, as a plasticizer, on the properties of the materials was also evaluated. All bionanocomposites showed considerable
improvement in thermal stability and mechanical properties, compared to the unfilled pullulan films, evidenced by the significant
increase in the degradation temperature (up to 40 °C) and on both Young’s modulus and tensile strength (increments of up to
100 and 50%, for films without glycerol and up to 8,000 and 7,000% for those plasticized with glycerol). Moreover, these bionanocomposite
films are highly translucent and could be labelled as sustainable materials since they were prepared entirely from renewable
resources and could find applications in areas as organic electronics, dry food packaging and in the biomedical field. 相似文献
18.
Effects of chemical modification on the structure and mechanical properties of starch-based biofilms
《Monatshefte für Chemie / Chemical Monthly》2012,16(5):335-343
Abstract
In this work, chemically modified corn starch and plasticized corn starch biofilms were obtained and characterized in four steps: (1) preparation of corn starch microparticles, (2) preparation of malic acid-modified corn starch microparticles (MA–SM), (3) preparation of corn starch biofilms and MA–SM-plasticized corn starch biofilms, and (4) characterization of the biofilms. The effects of MA–SM concentration (4, 8, and 12% based on the amount of corn starch) on the structural characteristics and mechanical properties of the biofilms were investigated. Changes in the starch granules after chemical modification were studied by X-ray diffraction, FT-IR spectroscopy, and scanning electron microscopy. The presence of ester carbonyl group stretching vibration at 1,720 cm−1 in FT-IR spectra was evidence of reaction of the starch microparticles with malic acid. The tensile yield strength and Young’s modulus of the films increased with increasing MA–SM content. Water uptake decreased from 69.8% for biofilm without MA–SM to 52.7% for biofilm with MA–SM. The improvement of these properties in the plasticized product could be attributed to the good interaction between the MA–SM filler and the corn starch. 相似文献19.
Effect of different additives on bacterial cellulose production by Acetobacter xylinum and analysis of material property 总被引:1,自引:0,他引:1
Bacterial cellulose (BC) demonstrates unique properties including high mechanical strength, high crystallinity, and high water
retention ability, which make it an useful material in many industries, such as food, paper manufacturing, and pharmaceutical
application. In this study, different additives including agar, carboxymethylcellulose (CMC), microcrystalline cellulose,
and sodium alginate were added into fermentation medium in agitated culture to enhance BC production by Acetobacter xylinum. The optimal additive was chosen based on the amount of BC produced. The produced BC was analyzed by using X-ray diffraction
(XRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and dynamic mechanical analysis
(DMA). Among the evaluated additives, CMC yielded highest BC production (8.2 g/L) compared to the control (1.3 g/L). The results
also indicated that CMC-altered BC production increased with CMC addition and reached saturation around 1%. The variation
between replicates for all analysis was <5%. From XRD analysis, however, the crystallinity and crystal size decreased as CMC
addition increased. FESEM results showed CMC-altered BC produced from agitated culture retained its interweaving property.
TGA results demonstrated that CMC-altered BC had about 98% water retention ability, which is higher than BC pellicle produced
with static culture. CMC-altered BC also exhibited higher T
max compared to control. Finally, DMA results showed that BC from agitated culture loses its mechanical strength in both stress
at break and Young’s modulus when compared to BC pellicle. This study clearly demonstrated that addition of CMC enhanced BC
production and slightly changed its structure. 相似文献
20.
Water-in-Oil high internal phase emulsions (HIPEs) whose continuous phase is polymerizable gave access to highly porous polymeric
materials (polyHIPEs). These emulsions were prepared with a laboratory-made homogenizer whose shear frequency and time could
be varied to study the influence of the emulsification conditions on the polyHIPEs morphology. Intensive and/or long shear
induced a reduction of the cell and connection diameters without any modification of the material global porosity. The mechanical
properties were evaluated by estimating the Young’s modulus from compression tests. The mechanical behavior was analogous
for all materials possessing a characteristic polyHIPE structure, even if cell sizes were different between samples. 相似文献