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  • 1990-1994  (20)
  • 1980-1984  (7)
  • Chemistry  (27)
  • 1
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 196 (1992), S. 49-61 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Hydrogele wurden aus methylmethacrylat (MMA) and N-Vinyl-2-pyrrolidon (NVP) mit 1,2,2-Trimethylolpropantrimethacrylat (TPTA) als Vernetzungsmittel hergestellt. Die Terplymerisation wurden mittels UV-strahlung (365 nm) initiiert, wobei kleine Mengen an Diethoxycetophenon (DEAP) als Photosensibilisator sowie Triethanolamin(TEA)als Beschleuniger und Verdünner verwendet wurden. Die Hydrogele wurden durch Messung des Wasserrückhaltevermögens, der Sauerstodiffusions- und permitionskoeffizienten, der mechanischen Eigenschaften und der Lichtdurchlässigkeit charakterisiert. Dabei zeigte sich, daß die Hydrogele bis zu 80 Gew.-% Wasser aufnehmen können, wobei mit steigendem Wassergtehalt deren mechanische Festigkeit drastisch sinkt. Der Ssuerstoffdiffusionskoeffizient der gequollenen Hydrogele beträgt 10-6 cm2s-1, der Sauerstoffpermeationskoeffizient 1013 cm2s-1Pa-1, und die Lichtdurchlässigkeit liegt im Bereich von 500 bis 700 nm bei über 90%.
    Notizen: Hydrogels are synthesized from methyl methacrylate (MMA) and N-vinyl-2-pyrrolidone (NVP) with 1,1,1-trimethylol propane trimethacrylate (TPTA) as a crosslinking agent. It was polymerized under UV radiation (365nm) with a small amount of photosensitizer, diethoxy acetophenone (DEAP), acclerator and diluent, triethanol amine (TEA). The hydrogels were characterized by measuring the water retention, dissolved oxygen diffusivity and permeability, mechanical strength, and light transparency. The hydrogels can retain water up to 80 wt.-% and the mechanical strenght is weakened as the water content is increased in the gel. The dissolved oxygen diffusivity and permeability in the swelling hydrogels are determined to be 10-6 cm2/sec and 1013 cm2s-1 Pa-1, respectively. The light transparency is over 90% in the wave lenght ranging from 500 to 700 nm.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 27 (1982), S. 1177-1190 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A polymer with high aromaticity and/or cyclic ring structures chain backbone usually has high heat, thermal, and flame resistance. Two diglycidyl ethers of bisphenols were prepared from 4,4′ isopropylidenediphenol (DGEBA) and 9,9-bis(4-hydroxyphenyl) fluorene (DGEBF) for evaluation. Four boroxines - trimethoxyboroxine (TMB), triethoxyboroxine (TEB), triisopropoxyboroxine (TIPB) and triphenoxyboroxine (TPB) - were used as the curing agents. DGEBA and DGEBF cured with various boroxines indicate that the trend for their respective glass transition temperature (Tg's), degradation temperatures (Td's), and gel fractions are TMB-cured epoxy ≈ TEB-cured epoxy 〈 TIPB cured epoxy 〈 TPB cured epoxy. The DGEBF system usually has a higher Tg, Td, gel fraction, oxygen index (OI), and char yield than the related DGEBA system. DGEBF/DGEBA (80/20 mol ratio) shows a synergistic effect in regard to char formation. This effect exists not only in the copolymer system but also in blended homopolymers of the separately cured resins. A modified mechanism for the polymerization of phenyl glycidyl ether (PGE) with TMB has been proposed.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 1539-1547 
    ISSN: 0887-624X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The photochemical polymerization rates of isoprene, ethyl methacrylate, and of styrene in various aromatic solvents were measured. The average lifetimes of propagating radicals were measured by the rotating sector method. The polymerization rate constants, Kp, were determined and compared with dipole moments (μ) and Hammett σ constants for the aromatic solvents. Linear correlations of log(kp/kp, benzene) vs. μ and σ were obtained.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 36 (1990), S. 983-992 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The viable fraction of immobilized cells in a bioreactor may be critical in predicting long-term or steady-state reactor performance. The assumption of near 100% viable cells in a bioreactor may not be valid for portions of immobilized cell reactors (ICRs) characterized by conditions resulting in appreciable death rates. A mathematical model of an adsorbed cell type ICR is presented in which a steady-state viable cell fraction is predicted, based on the assumptions of no cell accumulation in the reactor and a random loss of cells from the reactor. Data on cell death rates, cell growth rates, and productivity rates as functions of temperature, substrate, and ethanol concentration for the lactose utilizing yeast K. fragillis were incorporated into this model. The steady-state reactor viable cell fraction as predicted by this model is a strong function of both temperature and ethanol concentration. For example, a stable 20% viable fraction of the immobilized cells is predicted in ICR locations experiencing continuous conditions of either 30 g/L ethanol at 40°C, or 95 g/L ethanol at 25°C. Steady-state ICR “plug flow” concentration profiles and column productivities are predicted at three operating temperatures, 20, 30, and 40°C using two different models for ethanol inhibition of productivity. These profiles suggest that the reactor operating temperature should be low if higher outlet ethanol concentrations are desired. Three reactor design strategies are presented to maximize the viable cell fraction and improve long-term ethanol productivity in ICR's: (1) reducing outlet ethanol concentrations, (2) rotating segments of an ICR between high and low ethanol environments, and (3) simultaneous removal of the ethanol produced from the reactor as it is formed.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 36 (1990), S. 975-982 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The effects of ethanol on reactor performance were studied in a small, 5-cm packed height, “differential” type immobilized cell reactor. Lactose utilizing yeast cells, Kluyveromyces fragilis, were absorbed to a porous adsorbant sponge matrix in a gas continuous reactor. Step changes in the feed ethanol concentration to the column (10-130 g/L) were used to test the reactor response over extended periods of time (about 30-50 h per dosage level) followed by a return to basal zero inlet ethanol feed. Effluent cell density and effluent cell viability were measured at intervals. An inhibitory response in ethanol productivity to feed dosage ethanol levels above 20 g/L was detected almost immediately, with a near steady state response noted within 2.5 h of initiating the dosage. Feed ethanol levels above 50 g/L resulted in a subsequent gradual decrease in reactor productivity over time, which was associated with a decrease in the fraction of viable shed cells in the reactor effluent. The reactor response to a step removal of the ethanol inhibition was also monitored. Quick and complete rebounding of the fermentation rate to the original basal rate was noted following dosage concentrations of under 50 g/L ethanol. Recovery rates slowed following ethanol dosage levels above 50 g/L. Viable shed cell density improved overtime during the slow recovery periods. Growth rates (as determined by shed cell density) were more strongly inhibited than productivity. Growth responded more slowly to changes in ethanol environment as growth rates at 30 h fell to about 40% of the rates measured 7.5 h after initiation of a dosage level. It is concluded that ethanol contributions to cell injury and death (and consequent ICR performance degradation) may be more important than ethanol inhibition of productivity rates in the long-term operation of immobilized cell reactors at ethanol concentrations over 50 g/L.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 36 (1990), S. 993-1001 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The effect of reduced nutritional levels (particularly nitrogen source) for immobilized K. fragilis type yeast were studied using a trickle flow, “differential” plug flow type reactor with cells immobilized by adsorption onto an absorbant packing matrix. Minimizing nutrient levels in a feed stream to an immobilized cell reactor (ICR) might have the benefits of reducing cell growth and clogging problems in the ICR, reducing feed preparation costs, as well as reducing effluent disposal costs. In this study step changes in test feed medium nutrient compositions were introduced to the ICR, followed by a return to a basal medium. Gas evolution rates were monitored and logged on a continuous basis, and effluent cell density was used as an indicator of cell growth rate of the immobilized cell mass. Startup of the reactor using a YEP medium showed a rapid buildup of cells in the reactor during the initial 110 h operation. The population density then stabilized at 1.6 × 1011 cells/g sponge. A defined medium containing a complex mix of essential nutrients with an inorganic nitrogen source (ammonium sulfate) was able to maintain 90% of the productivity in the ICR as compared to the YEP medium, but proved unable to promote growth of the immobilized cell mass during startup. Experiments on reduced ammonium sulfate in the defined medium, and reduced yeast extract and peptone in YEP medium indicated that stable productivity could be maintained for extended periods (80 h) in the complete absence of any nutrients besides a few salts (potassium phosphate and magnesium sulfate). It was found that productivity rates dropped by 35-65% from maximal values as nitrogenous nutrients were eliminated from the test mediums, while growth rates (as determined by shed cell density from the reactor) dropped by 75-95%. Thus, nutritional deficiencies largely decoupled growth and productivity of the immobilized yeast which suggests productivity is both growth- and non-growth-associated for the immobilized cells. A yeast extract concentration of 0.375 g/L with or without 1 g/L ammonium sulfate was determined to be the minimum level which gave a sustained increase in productivity rates as compared to the nutritionally deficient salt medium. This represents a 94% reduction in complex nitrogenous nutrient levels compared to standard YEP batch medium (3 g/L YE and 3.5 g/L peptone).
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 40 (1992), S. 446-449 
    ISSN: 0006-3592
    Schlagwort(e): urea sensor ; plasma reaction ; poly(propylene) membrane ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Urease was immobilized on the plasma-aminated surface of a hyfrophobic poly(propylene) (PP) membrane. This membrane, with urease matrix on one side while maintaining its original hydrophobic property on the other, was used to construct the urea sensor. The new urea sensors had response sensitivities ranged from 19 mV/decade to 30 mV/decade depending on the conditions of the plasma reaction. The enzyme electrode using single membrane gave a shorter response time as compared to the corresponding conventional electrode employing two seperate PP membranes. The sensitivity of the enzyme electrode increased with increasing buffer pH and reached a maximal level (40 mV/decade) at pH 7.6. The response sensitivity of the electrode was not affected by the change of buffer strength. Deamination of the plasma-modified hydrophobic PP membrane did not occur in aqueous environment judging from the stability of the urea electrode up to 12 days of operation. © 1992 John Wiley & Sons. Inc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 27 (1992), S. 1389-1392 
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 472-476 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Because of differences in chemical structure and rheological characteristics, high density polyethylene (HDPE) and poly(ethylene terephthalate) (PET) are incompatible when blended during recycling of PET soft drink bottles. To improve the properties of the blends, ethylene vinyl acetate copolymer (EVA) was used as a compatibilizer. Based on torque rheometer tests, the higher the concentration of PET in the blends, the higher the initial loading torque. Blends of 50% HDPE and 50% PET had the lowest equilibrium torque. Equilibrium torque was highest at 5% EVA. The presence of EVA made only a slight difference in the glass transition temperatures of HDPE/PET blends. Higher EVA content in the blend resulted in a lower melting endotherm. Thermogravimetric analysis showed that thermal stability was independent of EVA content; but the more PET in the blend, the lower the final weight loss.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 40 (1990), S. 503-521 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The deformation and fracture characteristics of ABS have been investigated under tension, compression, and tension-compression fatigue cycling. The behavior of the rubber-modified polymer is compared with that of unmodified styrene-acrylonitrile, copolymer. The dispersed rubber particles in ABC cause extensive plastic deformation of the matrix material, markedly reduce the compressive yield stress, and, under tensile loading, cause yielding rather than early fracture. Under alternating stress conditions crazes occur sooner and lead to earlier craze breakdown, crack development, and reduced lifetime to fracture. The influence of rate of loading has been studied under applied tension and under fatigue cycling. The tensile yield stress varies linearly with the log of the strain rate in accord with the Eyring rate equation and, from the measured slope, the activation volume is estimated to be 2.2 nm3. The time to fatigue fracture reduces significantly with increasing frequency while cycles to fracture increase at a modest rate. Fatigue failure in ABS is not a cycle-dependent process, nor is it in accord with a damage accumulation model, but it more nearly resembles the former. The influence of a dispersed rubber phase, and of loading rate, on fracture surface morphology is discussed.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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