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Membranes Decreased (membrane + decreased)
Selected AbstractsPermeation of urea through various polyurethane membranesPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 11 2009Atsushi Watanabe Abstract BACKGROUND: Controlled-release systems using polymer membranes are very important in agriculture for labour-saving and effective delivery of pesticides and other agents. Polymer-coated granules are one of the most useful formulations, and a study of the factors for polymer design is necessary to achieve various release patterns. A permeation study using plain membranes was carried out in order to clarify parameters, and the results were compared with the release from polymer-coated granules. RESULTS: The permeation coefficient of urea through a plain polyurethane membrane decreased significantly as the urethane and alkyl side chain content increased. The glass transition temperature and crosslink density of the polyurethanes hardly influenced its permeability. The release rate from polyurethane-coated granules was also reduced by alkyl side chains. However, it was faster than that through a plain membrane because of capsule expansion by continuous water penetration and structural changes in the membrane. CONCLUSION: The release rate of urea through a polyurethane plain membrane and from polyurethane-coated granules can be controlled by changing the chemical properties of the membrane. In addition, physical properties such as the glass transition temperature Tg or crosslink density should be considered to assess the release profile from polyurethane-coated granules. Copyright © 2009 Society of Chemical Industry [source] Syntheses of esters through poly(styrene sulfonic acid)/poly(vinyl alcohol) membrane reactorASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010Tadashi Uragami Abstract Cation exchange membranes prepared from poly(styrene sulfonic acid) (PSA) and poly(vinyl alcohol) (PVA) were cross-linked by both glyoxal and gultaraledehyde and cross-linked membranes furthermore were annealed. The ion exchange capacity of the resulting PSA/PVA membranes increased, and the water content and degree of swelling of PSA/PVA membrane decreased with increasing annealing time. The syntheses of esters from alcohol and acetic acid through various PSA/PVA membranes have been carried out in a diaphragm type cell consisting of two detachable parts in which the membrane was set in the middle of the two parts of cell. When an aqueous solution of alcohol and acetic acid on one part of cell and p -chloro benzene (Cl-Bz) on another part were set, esters formed by the catalytic action of PSA/PVA membrane increased on the Cl-Bz phase with time. These results support that the PSA/PVA membrane could perform both the reaction and separation. The formation of esters in this membrane reactor was a secondary reaction as well as general the esterification between alcohols and acids. The catalytic action in the esterification of the PSA/PVA membranes prepared by changing the ratio of PSA/PVA and the amount of casting solution was also investigated. The rate of esterification reaction was significantly dependent on the number of sulfonic acid group in the effective membrane volume. The rate of reaction per mEq SO3H increased with an increase of the degree of swelling of the membrane and decreasing membrane thickness. In the esterifications of methanol, ethanol and n -propanol with acetic acid, the reactivity through the PSA/PVA membrane was higher than that with HCl as catalyst. In that of n -butanol with acetic acid, however, it was vice versa. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Annealing effect of perfluorosulfonated ionomer membranes on proton conductivity and methanol permeabilityJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Yinghao Luan Abstract Perfluorosulfonated ionomer (PFSI) was synthesized and PFSI membranes were prepared via a solution-cast method and annealed at different temperatures from 150 to 230°C. The annealing effect on water content, proton conductivity, and methanol permeability were reported and discussed. X-ray diffraction and small angle X-ray scattering were used to test the structure of the membranes. It was found that annealing increased the proton conductivity of the membranes because heat-treatment helped to free the sulfonic groups that were buried in the polymer segments and form more organized ionic clusters. Water content and methanol permeability of the annealed membranes decreased with increasing annealing temperature. Simultaneously, annealing induced more compact chain packing structure, which eventually affected the transport of the proton and methanol through these ionomer membranes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] A composite polymer/tricalcium phosphate membrane for guided bone regeneration in maxillofacial surgeryJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 5 2001Anita A. Ignatius Abstract The aim of the study was the development of a resorbable membrane for guided bone regeneration (GBR) with improved biocompatibility, which should be stiff enough to avoid membrane collapse during bone healing. Combining a bioactive ceramic with a resorbable polymer may improve the biocompatibility and osteoconductivity of resorbable devices. The present article describes the preparation, the mechanical properties, and the in vitro degradation characteristic of a composite membrane made of poly(L, DL-lactide) and ,-tricalcium phosphate in comparison to a membrane made of pure poly(L, DL-lactide). The tensile strength and the elastic modulus as well as the molecular weight of the membranes were measured after in vitro degradation in buffer at 37 °C up to 28 weeks. The initial tensile strength of the composite and the polymer membrane was 37.3 ± 2.4 MPa and 27.7 ± 2.3 MPa and the elastic modulus 3106 ± 108 MPa and 3101 ± 104 MPa, respectively. The mechanical properties remained constant up to 8 weeks and then decreased slowly until week 28. The molecular weight of both membranes decreased steadily from 170,000 D to 30,000 D. It was concluded that the mechanical requirements for a membrane for GBR were fulfilled by the composite membrane. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 564,569, 2001 [source] Water/Ethanol Selectivity of New Organic-Inorganic Hybrid Membranes Fabricated from Poly(vinyl alcohol) and an OligosilaneMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 7 2007Tadashi Uragami Abstract To control the swelling of PVA membranes, mixtures of PVA and an inorganic oligosilane were prepared using sol-gel reactions to yield new PVA/oligosilane hybrid membranes. In the separation of an ethanol/water azeotropic mixture during pervaporation, the effect of the oligosilane content on the water/ethanol selectivity of PVA/oligosilane hybrid membranes was investigated. The water/ethanol selectivity of PVA/oligosilane hybrid membranes was higher than that of PVA membranes, but the water/ethanol selectivity of hybrid membranes decreased with increasing oligosilane content. In order to increase the water/ethanol selectivity, PVA/oligosilane hybrid membranes were annealed. The water/ethanol selectivity of annealed PVA/oligosilane hybrid membranes was greater than un-annealed hybrid membranes, and significantly governed by the oligosilane content, which could be attributed to both sorption and diffusion selectivities. The relationship between the structure of un-annealed and annealed PVA/oligosilane hybrid membranes along with permeation and separation characteristics of an ethanol/water azeotropic mixture during pervaporation are discussed in detail. [source] | |||||||||||||