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  • 1
    Electronic Resource
    Electronic Resource
    Degradation studies of novel degradable starch-polyethylene plastics containing oxidized polyethylene and prooxidant (1994)
    Springer
    Journal of polymers and the environment 2 (1994), S. 27-38 
    Details
    ISSN: 1572-8900
    Keywords: Degradable plastics ; oxidized polyethylene ; prooxidant ; thermal degradation ; photodegradation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Linear low-density polyethylene films were prepared that contained native corn starch (7, 14, or 28%), low or high molecular weight oxidized polyethylene (15%), and a prooxidant mixture (18% POLYCLEAN II) that contains manganese and vegetable oil. For each mixture all components were first mixed at high temperatures in a twin-screw extruder and pelletized. The pellets were cast into films using a single-screw extruder. Oxidized-polyethylene addition did not impair the transparency and thickness of the films and did not reduce the percentage elongation, whereas significant reductions in film mechanical properties were observed. Thermal and photodegradation properties of each film were evaluated by 70°C forced-air oven treatment (20 days), by high-temperature, high-humidity treatment in a steam chamber (20 days), and by exposure to ultraviolet light (365 nm; 4 weeks). Changes in the mechanical properties of the films were determined by an Instron Universal Test Machine; in the carbonyl index, Fourier transform infrared spectroscopy; and in molecular weight, by high-temperature gel-permeation chromatography (HT-GPC). The addition of oxidized polyethylene, especially high molecular weight oxidized polyethylene, and up to 14% starch to the films significantly increased the rate of thermal and photodegradation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02073484
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  • 2
    Electronic Resource
    Electronic Resource
    Purification and characterization of endo-xylanases from Aspergillus niger. II. An enzyme of pl 4.5 (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 27 (1985), S. 533-538 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A homogeneous endo-xylanase (1,4-β-D-xylan xylanohydrolase, EC 3.2.1.8) was obtained from a crude Aspergillus niger pentosanase by chromatography with Ultrogel AcA 54, SP-Sephadex C-25 at pH 4.5, DEAE-Sephadex A-25 at pH 5.4, Sephadex G-50, and SP-Sephadex C-25 with a gradient from pH 2.8 to pH 4.6. It was much more active on soluble than on insoluble xylan, yielding large amounts of unreacted xylan and a mixture of oligosaccharides with chain lengths from two to six. No xylose or L-arabinose was produced. There was high activity on a xylopentaose through xylononaose mixture, but not on xylobiose, xylotriose, or xylotetraose. The enzyme had slight activity on untreated cellulose, carboxymethylcellulose, and pectin. Molecular weight was ca. 1.4 × 104, with an isoelectric point of 4.5 and an amino acid profile high in acidic but low in sulfur-containing residues. In a 25-min assay at pH 4.7, this endo-xylanase was most active at 45°C, with an activation energy from 5 to 35°C of 33.3 kJ/mol. The optimum pH for activity was 4.9. Decay in buffer was first order, with an activation energy at pH 4.7 from 48 to 53°C of 460 kJ/mol. Optimum pH for stability was about 5.6, where the half-life at 48°C in buffer was ca. 40 h.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260270421
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  • 3
    Electronic Resource
    Electronic Resource
    Thermodynamic and kinetic analysis of the dimerization of aqueous glyoxal (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 18 (1986), S. 775-789 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Equilibria and rates of interconversion between monomeric and dimeric glyoxal were measured in aqueous solution. The equilibrium constant [G2]/[G1]2 was 0.56 M-1 at 25°C, and was hardly affected by changes of ionic strength and pH but increased rapidly with increase of temperature. The rate of depolymerization was first-order in dimer, with the pseudo first-order rate coefficient in the pH range 1.3-7.8being of the form b1[H3O+] + b2 + b3[OH-]/(1 + b4[OH-]) + b5[OH-]. Coefficients b1 and b2 were more strongly affected by changes of temperature, though [OH-] was much the more effective catalyst. This rate form has not previously been observed for monomer-dimer inter-conversion of α-hydroxycarbonyls and α-dicarbonyls or for related reactions such as mutarotations and hydrations. Equivalent rate forms arisefrom reactions where an intermediate at steady state and low concentration is produced.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550180705
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetic analysis of the disproportionation of aqueous glyoxal (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 18 (1986), S. 757-773 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rates of disproportionation of 0.015-0.4 mM aqueous glyoxal toglycolic acid were measured at 0.24-75 mM NaOH and constant ionic strength, leading to the empirical rate expression r = (a1[OH-] + a2[OH-]2) [GT]/(1 + a3[OH-]), where [GT] is the total glyoxal concentration. These results were confirmed in bicarbonate/carbonate buffer and at 2-20 mM [GT]. The rate form is in contradiction to earlier work on glyoxal, which suggested a second-order dependence on [OH-], but agrees with the rate equation for phenylglyoxal disproportionation. The kinetic data can be explained by a mechanism postulating the presence of monohydrated and dihydrated forms of glyoxal in equilibrium, with the rate-limiting steps being intramolecular hydride ion transfers to the unhydrated carbonyl carbon of the mono- and divalent anions of glyoxal monohydrate.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550180704
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    Paper (German National Licenses)
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