共查询到13条相似文献,搜索用时 15 毫秒
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The work reported demonstrates an simple method of extracting cellulose nanofibers (CNF) from cellulose microfibers (CMF) obtained from the plant Stipatenacissima. Here, a method for the production of CNF from CMF extracted from Alfa grass by exfoliation in polyvinyl alcohol (PVA) solution, is demonstrated. The CMF were produced in powder form and exfoliated in PVA aqueous solution to produce composites with 2, 4, 5 and 10?wt-% of CNF. Scanning Electron Microscopy demonstrated exfoliation of CMF, dispersion of the CNF and wetting by the polymer. The composites were characterised by thermogravimetry, differential scanning calorimetry, X-ray diffraction and tensile testing. The addition of CNF to PVA reduced the crystallinity degree of PVA. The large increase of the Young’s modulus from 38 to 113% (relative to pure PVA) for composites with 2 to 10?wt-% of CNF incorporation is consistent with the extensive exfoliation of CMF into CNF and its excellent interface with PVA. 相似文献
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The main objective of this work is to evaluate the inclusion of nanoparticles to partially hydrolyzed polyacrylamide/resorcinol/formaldehyde gel systems to improve the stability under static and dynamic conditions. Oxide nanoparticles (<100 mg·L−1) of SiO2, Al2O3, MgO, and Cr2O3 were employed and characterized by their physicochemical properties. Gels were prepared and subsequently placed at 70 °C for evaluating the nanoparticles influence in gel strength through rheological properties and syneresis measurements. Al2O3 nanoparticles showed the highest potential for the reduction of the syneresis phenomena, followed by MgO and Cr2O3. The SiO2 nanoparticles lead to a higher degradation of the gel. As the zeta potential increases, the syneresis of the gel system decreases. The nanoparticles did not significantly affect the storage modulus, describing similar gel strength than the original gel. Also, displacement tests showed an incremental of 64% of oil recovery regarding the system in the absence of Al2O3 nanoparticles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47568. 相似文献
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Poly vinyl alcohol (PVA) with pendent carboxyl group was synthesized and verified. The collagen was chemical crosslinked with the produced PVA under the help of crosslinker. Then, the PVA–collagen hydrogels were prepared through the repeated freezing–thawing. Since the water states in hydrogels play an important role in the performance of the product, thermogravimetric (TG) analysis and differential scanning calorimeter (DSC) were conducted to study the different states of water. The results indicated that the weight ratio of nonfreezable water to dry gel in PVA–collagen hydrogels was about 25%. Meanwhile, the swelling behaviors in distilled water and 0.9% saline were studied. The one‐phase exponential associate equation can fit the process very well. Calculated from the simulation equation, the swelling ratios at equilibrium in distilled water and saline were 14.353 g/g dry gel and 14.205 g/g dry gel, respectively. The results illustrated that the ions in solution would decrease the swelling ratio of the hydrogel. At the same time, the lyophilization might have slighter influence to the microstructure of hydrogels and should be more suitable for the swelling research than heat drying. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
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The water binding properties of crosslinked copolymers of acrylamide with tetraethyleneglycol diacrylate triethyleneglycol dimethacrylate, N,N′-methylene bisacrylamide and divinylbenzene were investigated. It was observed that the freezing water contents of these copolymers depend on nature of the monomers and crosslinkers, as well as on the extent of crosslinking. 相似文献
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The rheological properties of some newly developed polymer compositions have been investigated with and without crosslinking. These polymer compositions were developed as a water shutoff and sand consolidation treatment agents for producing oil and gas wells. The effects of several variables on the rheology of the compositions were evaluated over a wide range of temperatures (25–110°C), shear rates (0–500 s?1), brine percentages (0–15%), crosslinker types and concentrations (0–3%), and polymer concentrations (6–50%). It was found that increasing the shear rate from 0 s?1 to 100 s?1 caused shear thinning and reduction of the viscosity of the dilute solutions (6–13%) from 25 cP to ~ 3 cP at 80°C. In contrast, for the concentrated solutions (20–50%), the viscosity dropped slightly in the shear rate range 0–10 s?1, and subsequently decreased more slowly up to shear rates of 500 s?1. The viscosities of all polymer solutions dropped by a factor of 2 as the brine concentration increased from 0% to 15%. Finally, aging time coupled with shear rates and higher percentages of crosslinkers accelerate the buildup of viscosity and gelation time of the polymer compositions. For concentrated solutions, shear rates ranging within 0–200 s?1 accelerated gelation time from 9.75 h to 2–3 h, when they were sheared at 80°C. The polymeric solutions exhibited Newtonian, shear‐thinning (pseudo‐plastic), and shear‐thickening (dilatant) behavior, depending on the concentration, shear rate, and other constituents. In most cases, the rheological behavior could be described by the power law. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
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Xinqiu Hong Yongjing Xu Liming Zou Yan Vivian Li Junwei He Jiongxin Zhao 《应用聚合物科学杂志》2021,138(10):49971
Polyvinyl alcohol (PVA) fibers were prepared using PVA with different degree of polymerization (DP) under the same wet spinning process. The effect of the DP of PVA on the structures and properties of PVA and PVA fibers were studied by using nuclear magnetic resonance hydrogen spectroscopy (1H-NMR), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimeter (DSC), thermo gravimetric analysis (TGA), and environmental scanning electron microscope (ESEM). The results showed that DP had little effect on the crystallinity and tacticity of PVA, but had a positive effect on melting temperature, and initial decomposition temperature of PVAs. The hot drawing ratio determined by the spinning process where the PVA fibers could be continuously collected without breaking. The drawing ratio was decreased with an increase of DP, resulting in an increase of the final fiber diameter. The PVA fibers with medium DP and medium size demonstrated high strength and high modulus, but relatively low breaking elongation. It suggested that high DP of PVA was not a guarantee of high strength and high modulus PVA fibers, but rather a primary structure factor. The fiber performance was determined by a comprehensive effect combining a variety of factors including polymer properties and spinning conditions. It provided a guideline for PVA fiber manufacture that the PVAs with different DP require different spinning processes to obtain optimal fiber performance. 相似文献
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This article deals with the drug release behavior of theophylline (Th) from poly(vinyl alcohol) (PVA) hydrogels, prepared with magnetic nanoparticles at different particle loadings. These biocompatible matrices were obtained by incorporating different amounts of an aqueous ferrofluid into PVA hydrogels, loaded with Th as a marker for drug‐delivery studies. PVA films with magnetic particles proved to be magnetic field‐responsive materials as the drug release decreased through the application of a relative low and uniform magnetic field for particle concentrations of 0.9% w/w or higher. Moreover, the percentage of restriction of drug release is found to be correlated with particle loading. The in vitro release profiles were analyzed by applying a semiempirical power law to obtain the kinetic parameters. The value of the release exponent was found to be in the range 0.54–0.56 in all experiments, which thus indicates a predominant diffusional mechanism for drug release from these smart magnetic hydrogels. This effect suggests the possibility of modulating the release behavior by controlling the particle content in the preparation of the composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
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In the copper-chlorine (Cu-Cl) thermochemical cycle water is decomposed into its constituents (oxygen and hydrogen) by a series of chemical reactions. The cycle involves five steps in which three thermally driven chemical reactions and one electrochemical reaction take place. Oxygen is produced during one of the main chemical reactions. In the present study, the O2 production step is described with its operational and environmental conditions, and energy and exergy analyses are performed. The cycle is assumed driven using nuclear energy. Various parametric studies are carried out on energetic and exergetic aspects of the step, considering variable reaction and reference-environment temperatures. At a constant reference-environment temperature of 25 °C, the exergy destruction of the O2 production step varies between 4500 and 23,000 kJ/kmol H2 when the reaction temperature increases from 450 to 1000 °C. At a 500 °C reaction temperature and a 25 °C reference-environment temperature, the exergy destruction for this step is found to be 5300 kJ/kmol H2. At a reaction temperature of 500 °C and a reference-environment temperature of 25 °C, the exergy efficiency of the step is determined to be 96% and to decrease with increasing reaction temperature and/or reference-environment temperature. 相似文献