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  • 1
    Electronic Resource
    Electronic Resource
    Enhanced leaf chlorophyll levels in plants treated with seaweed extract (1996)
    Springer
    Journal of applied phycology 8 (1996), S. 535-543 
    Details
    ISSN: 1573-5176
    Keywords: Ascophyllum nodosum ; betaines ; commercial seaweed extract ; leaf chlorophyll ; soil application
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Application to the soil of an aqueous alkaline extract ofAscophyllum nodosum resulted in higher concentrations of chlorophyll in the leaves of treated plants in comparison to control plants treated with an equivalent volume of water. Positive results were obtained with all species tested (tomato, dwarf French bean, wheat, barley, maize). When the seaweed extract was applied as a foliar spray, similar effects on leaf chlorophyll contents were obtained, except in the case of dwarf French bean plants, for which no significant difference was recorded between test and control plants. When the betaines present in the seaweed extract were applied as a mixture in the same concentrations as those in the diluted seaweed extract (γ-aminobutyric acid betaine 0.96 mg L−1, δ-aminovaleric acid betaine 0.43 mg L−1, glycinebetaine 0.34 mg L−1), very similar leaf chlorophyll levels were recorded for the seaweed extract and betaine treated plants. This suggests strongly that the enhanced leaf chlorophyll content of plants treated with seaweed extract is dependent on the betaines present.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02186333
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  • 2
    Electronic Resource
    Electronic Resource
    Determination of organotin compounds in environmental samples by supercritical fluid extraction and gas chromatography with atomic emission detection (1993)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 106-112 
    Details
    ISSN: 0935-6304
    Keywords: Capillary GC ; Atomic emission detector ; Supercritical fluid extraction ; Organotin compounds ; Complexation ; Grignard derivatization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The extraction of six tetraalkyltin and seven ionic organotin compounds from spiked topsoil samples with supercritical carbon dioxide and carbon dioxide modified with 5 percent methanol was investigated. Analysis of the soil extracts was performed by gas chromatography with atomic emission detection. Retention times, minimum detectable concentrations, and detector linear ranges are included for nine organotin compounds (seven of the nine compounds were derivatized with n-pentylmagnesium bromide prior to gas chromatographic analysis). A 23 factorial experimental design was used to study the effect of three variables (pressure, temperature, and extraction time) on compound recovery. The results indicate that the tetraalkyltin compounds are extracted from topsoil samples with recoveries ranging from 90 to 110 percent. Recoveries for the ionic organotin compounds ranged from 50 to 75 percent for trimethyltin chloride, triethyltin bromide, and tributyltin iodide; they were below 20 percent for dimethyltin dichloride, dibutyltin dichloride, diphenyltin dichloride, and butyltin trichloride. When sodium diethyldithiocarbamate was added to the soil samples prior to extraction, followed by extraction with carbon dioxide modified with 5 percent methanol, recoveries ranged from 70 to 90 percent for trimethyltin chloride, triethyltin bromide, dimethyltin dichloride, tributyltin iodide, and dibutyltin dichloride; recoveries were approximately 40 percent for butyltin trichloride and diphenyltin dichloride.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240160208
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  • 3
    Electronic Resource
    Electronic Resource
    Network parameters and scaling behaviour of chemically crosslinked hydrogels of poly[(N,N-dimethylacrylamide)-co-(methyl methacrylate)] (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 198 (1997), S. 1885-1892 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Copolymerization of N,N-dimethylacrylamide (DMA) with methyl methacrylate in both the presence and absence of ethylene dimethacrylate (EDMA) was effected to very high conversion by γ-irradiation. The resultant xerogels were swollen to equilibrium in water at five specific temperatures within the interval 280.2-338.2 K. The volume fractions of the polymer φ2 in the hydrogels were determined from the measured dimensions, and compression-strain measurements yielded the polymer-water interaction parameter, the effective crosslinking densities, and Young's moduli Y. The observed dependence of these parameters on copolymer composition and content of EDMA is discussed. A scaling law of the form Y ∝ φr2 is obeyed well by hydrogels of xerogels containing 80 wt.-% DMA (r = 2.37 ± 0.10) and moderately well by hydrogels of xerogels with only 50 wt.-% DMA (r = 2.54 ± 0.10).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1997.021980617
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  • 4
    Electronic Resource
    Electronic Resource
    Tensile yielding and microstructures of blends of isotactic polypropylene and linear low-density polyethylene (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 813-822 
    Details
    ISSN: 0887-6266
    Keywords: blends ; tensile yielding ; Eyring's theory ; stress-whitening ; microvoiding ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Thin sheets of isotactic polypropylene (iPP) and linear low-density polyethylene (LLDPE) blends were studied by tensile testing, optical microscopy (OM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Eyring's two-process yielding theory was used to analyze the data of yield stress as a function of strain rate and temperature, and satisfactory curve-fitting results were obtained. Furthermore, stress whitening was found to have occurred in the necked regions of tensile specimens under a certain range of yielding conditions. These conditions corresponded to the activation of Process II yielding of Eyring's theory. The whitening was found to be a result of formation of microvoids that initiated at the interface between iPP and LLDPE. © 1995 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1995.090330510
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  • 5
    Electronic Resource
    Electronic Resource
    A study of tensile yielding of isotactic polypropylene (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 2037-2047 
    Details
    ISSN: 0887-6266
    Keywords: iPP ; yielding ; Eyring processes ; crazing ; stress-whitening ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The yielding behavior of isotactic polypropylene (iPP) sheets prepared by hot pressing was studied by tensile testing. The corresponding microstructural changes in the specimens after testing were investigated by image analysis, optical microscopy (OM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The yielding of iPP was found to follow a two-process Eyring yielding model. In the necked regions, stress-whitening occurred only in specimens tested over a certain range of strain rates and temperatures. The occurrence of the stress-whitening was correlated well with the activation of Process II in the two-process Eyring model. SEM revealed that the stress-whitening in the necked regions was associated with the formation of craze-like structures that were parallel to the loading direction. Furthermore, DSC analysis showed that the necked regions of the unwhitened tensile specimens had an additional low-temperature melting peak. However, no additional melting peaks were found in the stress-whitened specimens. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090321210
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of pH on the swelling behaviour of hydrogels based on N-isopropylacrylamide with acidic comonomers (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 1127-1134 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Hydrogels have been prepared by free radical polymerization in aqueous solution of N-isopropylacrylamide (NIPA) and of NIPA with acrylic acid (AA), methacrylic acid (MAA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). For each copolymerization three comonomer feeds were used and for all systems three concentrations of a crosslinker were employed. For all of the 30 polymers previously obtained, swelling data in deionised water were extended here by corresponding data measured in aqueous media of pH = 1 and pH = 12. Starting at ca. 15°C phase diagrams of swelling ratio r( = mass hydrogel/mass xerogel) were determined at several temperatures (T) up to ca. 70°C and reversibility in swelling/deswelling behaviour was verified on cooling back to 15°C. In some instances a lower critical swelling temperature (Tc) was located, whereas in others there was merely a continuous decrease in r with T. Swellability at pH = 1 is lower than that in pure water, the reduction in r increasing with content of acidic comonomer. At pH = 12 a similar reduction in r was observed in gels containing AA and AMPS, whereas with MAA as comonomer r is equal to or greater than the value in pure water. The findings are discussed on the basis of the influence of pH on the ionisation of carboxyl groups, hydrogen bonding, and chelation.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Observations by DSC on bound water structure in some physically crosslinked hydrogelsDedicated to Professor Ron Koningsveld on the occasion of his 70th birthday. (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 37 (1995), S. 63-67 
    Details
    ISSN: 0959-8103
    Keywords: poly(N-vinyl-2-pyrrolidone-co-methyl methacrylate) ; hydrogel ; physical crosslinking ; DSC ; non-freezing water ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Linear, compositionally homogeneous copolymers containing 23-62 wt% N-vinyl-2-pyrrolidone (VP) were prepared by a semi-continuous copolymerisation with methyl methacrylate (MMA) in the absence of chemical crosslinker. Films cast from solution in chloroform were swollen in water at various temperatures (T) within the range 283-343 K. The total water content (11-80 wt%) of the resultant hydrogels at swelling equilibrium, as well as its subdivision into freezing and non-freezing water components, were measured and found to be dependent on copolymer composition and T. The network structure of these hydrogels is considered to arise from a combination of normal VP-water interactions with physical crosslinking due to hydrophobic MMA sequences, and the novel, albeit only semi-quantitative, findings are discussed on this basis.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pi.1995.210370108
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  • 8
    Electronic Resource
    Electronic Resource
    Study of dispersion morphologies of isotactic polypropylene and linear low density polyethylene blends by scanning electron microscopy (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 60 (1996), S. 1461-1473 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Isotactic polypropylene (iPP) and linear low-density polyethylene (LLDPE) blends with five different component ratios were prepared by melt mixing. The blends were subsequently remelted at 200°C for 1, 2, 3, 5, 8, 12, 20 min, and 2 h. The morphologies of the heat-treated and as-blended materials were studied on the cryogenically fractured surfaces of these blends by scanning electron microscopy (SEM). It was found that the morphologies of the blends with equal component ratio were highly unstable in remelting, while those blends with the lowest minor component ratios were the most stable ones, showing a growth in the size of the dispersed particles. © 1996 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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