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排序方式: 共有152条查询结果,搜索用时 15 毫秒
1.
Expanded polytetrafluoroethylene (ePTFE) membranes were modified by graft copolymerization with methacryloxyethyl phosphate (MOEP) in methanol and 2‐butanone (methyl ethyl ketone (MEK)) at ambient temperature using gamma irradiation. The effect of dose rate (0.46 and 4.6 kGy h?1), monomer concentration (1–40 %) and solvent were studied and the modified membranes were characterized by weight increase, X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). XPS was used to determine the % degree of surface coverage using the C? F (ePTFE membrane) and the C? C (MOEP graft copolymer) peaks. Grafting yield, as well as surface coverage, were found to increase with increasing monomer concentration and were significantly higher for samples grafted in MEK than in methanol solution. SEM images showed distinctly different surface morphologies for the membranes grafted in methanol (smooth) and MEK (globular), hence indicating phase separation of the homopolymer in MEK. We propose that in our system, the non‐solvent properties of MEK for the homopolymer play a more important role than solvent chain transfer reactions in determining grafting outcomes. Copyright © 2005 Society of Chemical Industry 相似文献
2.
Lisbeth M Ottosen Ana T Lima Anne J Pedersen Alexandra B Ribeiro 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2006,81(4):553-559
The possibility of using fly ash from municipal solid waste incineration (MSWI) in, for example, concrete is considered. MSWI fly ash, however, has too high a concentration of heavy metals, which may cause leaching problems during use or problems with waste handling at the end of the lifetime of the concrete. The Cl content in MSWI fly ash is also too high and will cause corrosion problems in reinforced concrete. The possibility of removing some of the unwanted heavy metals (Cu and Pb) together with Cl from an MSWI fly ash suspended in water using an electrodialytic separation method was investigated. The removal of Pb and Cu was found to be highly pH dependent and the highest contents removed were 41 and 90%, respectively. The Cu concentration of the ash decreased from 2200 to 860 mg kg?1 but the Pb concentration increased from 8560 to 16 800 mg kg?1, showing that Pb is mainly found in the ash fraction that is least soluble. Hence electrodialytic treatment of the ash suspended in water is not a solution to improve the ash quality in terms of Pb. The water‐soluble Cl content per unit weight of the original ash was 12.4%. The removal of water‐soluble Cl was efficient and >98% of Cl was removed (calculated on the basis of mean initial and final concentrations). This result indicates that electrodialytic extraction may be a method that can be used for the removal of Cl from ash prior to its utilization in concrete. Copyright © 2006 Society of Chemical Industry 相似文献
3.
Florian Sahling Lisbeth Buschkühl Horst Tempelmeier Stefan Helber 《Computers & Operations Research》2009
This paper presents a new algorithm for the dynamic multi-level capacitated lot sizing problem with setup carry-overs (MLCLSP-L). The MLCLSP-L is a big-bucket model that allows the production of any number of products within a period, but it incorporates partial sequencing of the production orders in the sense that the first and the last products produced in a period are determined by the model. We solve a model which is applicable to general bill-of-material structures and which includes minimum lead times of one period and multi-period setup carry-overs. Our algorithm solves a series of mixed-integer linear programs in an iterative so-called fix-and-optimize approach. In each instance of these mixed-integer linear programs a large number of binary setup variables is fixed whereas only a small subset of these variables is optimized, together with the complete set of the inventory and lot size variables. A numerical study shows that the algorithm provides high-quality results and that the computational effort is moderate. 相似文献
4.
JC Neal S Stolnik E Schacht ER Kenawy MC Garnett SS Davis L Illum 《Canadian Metallurgical Quarterly》1998,87(10):1242-1248
Poloxamer 407 and poloxamine 908 have been used by many research groups to modify the surface of both model latex and biodegradable nanospheres, thereby producing nanospheres that have shown reduced protein adsorption in vitro and extended circulation times in vivo. A potential limitation of such systems is the desorption of the copolymer coating layer. We describe a two-stage process to radiolabel poloxamer 407 and poloxamine 908 that has facilitated an investigation into this potential desorption, in vitro. The first stage of the labeling procedure involved the substitution of the terminal hydroxyl groups in each poly(ethylene oxide) (PEO) chain of poloxamer 407 and poloxamine 908 with an amino group. The aminated copolymers were then radiolabeled with 125Iodine Bolton-Hunter reagent. The efficiency of labeling was calculated to be approximately 20% for the tetramine poloxamine 908 and approximately 33% for the diamine poloxamer 407. Remaining free amino groups were then either acetylated, using acetic anhydride, or left in the free amino form. Covalent linkage of the radiolabel to the copolymer was confirmed by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. The stability of the link between radiolabel and copolymer to hydrolysis was also confirmed; <4% loss of radiolabel occurred from poloxamine 908 after incubation in phosphate-buffered saline (PBS) at 37 degrees C for 8 days. The radiolabeled copolymers (with the free amino groups acetylated) were then used in experiments that have given the first direct evidence that adsorbed copolymers can be displaced by serum proteins in significant amounts from the surface of model and biodegradable nanospheres. The displacement was highly dependent on copolymer-nanosphere compatibility, with up to 78% of 125I tetramine poloxamine 908 being displaced from poly(lactide-co-glycolide) (PLGA) nanospheres in 24 h, compared with 20% displacement of 125I tetramine poloxamine 908 in 24 h from polystyrene nanospheres. These results have direct implication for the future design of drug delivery systems based on coated nanospheres. 相似文献
5.
6.
PEGylated chitosan derivatives: Synthesis, characterizations and pharmaceutical applications 总被引:1,自引:0,他引:1
Luca CasettariDriton Vllasaliu Enzo CastagninoSnjezana Stolnik Steven Howdle Lisbeth Illum 《Progress in Polymer Science》2012,37(5):659-685
This review sets out to describe and discuss the synthetic approaches and the fields of application of PEGylated chitosan copolymers especially for medical use. The PEGylation of chitosan and chitosan derivatives is able to add new physicochemical properties to the cationic polysaccharide polymers, thereby overcoming some limitations, especially regarding their solubility and their use in drug and gene delivery (DNA and siRNA). All methods of derivatization have been considered and described together with the different methods of characterization of the copolymers. The capacities of PEGylated chitosan to reduce chitosan toxicity, to enhance membrane permeation and to form thermosensitive hydrogels have also been discussed. 相似文献
7.
Morrey M Nisbet A Thome D Savkin M Hoe S Brynildsen L 《Radiation protection dosimetry》2004,109(1-2):89-96
This paper looks at the key issues that need to be addressed during the transition from the emergency phase to the late phase of a radioactive release, and the development of the initial late phase strategy. It discusses the extent to which current national plans and international advice address the needs of decision makers following contamination of inhabited areas and food production systems. Based on this the following recommendations are made: (1) the issues that will arise at the start of the late phase response to a radioactive release require preparation work in advance of any release; (2) this preparation should consider the adequacy of legislation, technical data and modelling, options for waste storage and disposal, resources for monitoring and implementing clean up; (3) late phase preparedness requires regular exercising and (4) the possibility of terrorist releases adds further emphasis to the need for preparedness for the late phase. 相似文献
8.
Grøndahl L Cardona F Chiem K Wentrup-Byrne E Bostrom T 《Journal of materials science. Materials in medicine》2003,14(6):503-510
Highly porous PTFE membranes are currently being used in facial reconstructive surgery. The present study aims at improving this biomaterial through creating a more bioactive surface by introducing ionic groups onto the surface. The unmodified PTFE membrane does not induce inorganic growth after immersion in simulated body fluid (SBF) for up to 4 weeks. Copolymeric grafting with acrylic acid (AAc) by means of gamma irradiation and subsequent in vitro testing in SBF reveals that this copolymer initially acts as an ion-exchange material and subsequently induces growth of a calcium phosphate phase (Ca/P=2.7) when large amounts (15%) of pAAc are introduced onto the membrane surface. This copolymer is not expected to function well from a biomaterials perspective since SEM showed the pores on the surface to be partly blocked. In contrast, the surface of monoacryloxyethyl phosphate (MAEP)-modified samples is altered at a molecular level only. Yet the modified materials are able to induce calcium phosphate nucleation when the external surface coverage is 44% or above. The initial inorganic growth on these membranes in SBF has a (Ca+Mg)/P ratio of 1.1 (presumably Brushite or Monetite). The secondary growth, possibly calcium-deficient apatite or tricalcium phosphate, has a (Ca+Mg)/P ratio of 1.5. This result is a promising indicator of a bioactive biomaterial. 相似文献
9.
Benítez B Archile A Rangel L Bracho M Hernández M Márquez E 《Archivos latinoamericanos de nutrición》2002,52(3):307-312
The purpose of this research was to evaluate the nutritional quality and acceptability of a meat product formulated with mechanically deboned poultry meat (40%), bovine plasma (40%) and bovine red cells (3%) as major ingredients. Proteins, fat, humidity and ash were determined by AOAC procedure, iron and calcium by Atomic Absorption Spectrometry and essential amino acids by HPLC. Biological evaluation was performed using digestibility and PER procedures. To evaluate the acceptability (flavor, color and odor) of the product were used 277 children. Results indicated that 100 g of the formulated meat product contain 10.7 g of proteins, 4.4 g of fat, 68.6 g of humidity, 2.9 g of ash, 4.9 mg of iron, 46.6 mg of calcium. Essential amino acids are above the FAO requirements for a highly nutritional protein digestibility (92.4%) and PER (2.18). Acceptability was 91.3% for flavor, 81.2% for color and 92.4% for odor. The high nutritional quality and acceptability along with the low cost make this meat product suitable for government social programs. 相似文献
10.
Electrokinetic desalination of glazed ceramic tiles 总被引:1,自引:0,他引:1
Lisbeth M. Ottosen Célia M. D. Ferreira Iben V. Christensen 《Journal of Applied Electrochemistry》2010,40(6):1161-1171
Electrokinetic desalination is a method where an applied electric DC field is the driving force for removal of salts from porous building materials. In the present paper, the method is tested in laboratory scale for desalination of single ceramic tiles. In a model system, where a tile was contaminated with NaCl during submersion and subsequently desalinated by the method, the desalination was completed in that the high and problematic initial Cl− concentration was reduced to an unproblematic concentration. Further conductivity measurements showed a very low conductivity in the tile after treatment, indicating that supply of ions from the poultice at the electrodes into the tile was limited. Electroosmotic transport of water was seen when low ionic content was reached. Experiments were also conducted with XVIII-century tiles, which had been removed from Palacio Centeno (Lisbon) during renovation due to damage of the glazing from the presence of salts. These tiles were severely contaminated with both chlorides and nitrates, and one of the tiles also contained sulphates though at a low concentration. The charge transfer was too low in the experiments to obtain full desalination, but promising results were obtained as significant decreases (>81% Cl−, ~59% NO3 − and ~22% SO4 2−) were seen. 相似文献