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  • 1
    Electronic Resource
    Electronic Resource
    Ageing effects and internal stresses in quenched unfilled and clay-filled high density polyethylene (1988)
    Springer
    Colloid & polymer science 266 (1988), S. 509-517 
    Details
    ISSN: 1435-1536
    Keywords: Polyethylene ; unfilled ; polyethylene ; clay-filled ; ageing effects ; internal stresses ; stress relaxation ; creep behaviour ; effects of clay filling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The stress relaxation and creep behaviour of high density polyethylene (HDPE), unfilled or filled with clay particles, were measured after different ageing times after quenching from 120 °C. The measurements were performed at room temperature in the uniaxial extension mode. Ageing time had a pronounced influence on the viscoelastic properties, e.g. the creep curves shifted to longer times with increasing ageing time. The internal stresses, as evaluated from stress relaxation data, were found to increase markedly when the ageing period was extended, and it was suggested that this behaviour may be associated with relaxation of thermal residual stresses. It was furthermore suggested that the change in residual stresses, in addition to the physical ageing process, could also affect the ageing behaviour of HDPE, i.e. the change in viscoelastic properties with ageing time. Clay addition changes the ageing behaviour of HDPE, which could be attributed to a change in the internal stress dependence of the ageing time and/or to a difference in the physical ageing process. The effects of a surface treatment on the ageing of HDPE-clay composites are also evaluated and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01420761
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  • 2
    Electronic Resource
    Electronic Resource
    Interfacial effects on the ageing behavior of high density polyethylene filled with glass spheres (1988)
    Springer
    Colloid & polymer science 266 (1988), S. 990-998 
    Details
    ISSN: 1435-1536
    Keywords: Ageing ; fillers ; polyethylene ; surface-treatment ; silane layers ; viscoelastic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The stress relaxation and creep behavior of unfilled high density polyethylene (HDPE) and HDPE filled with untreated and surface-treated glass spheres were measured at room temperature. A silane-based coupling agent capable of providing a covalent bond between HDPE and the glass spheres was used for the surface-treatment. Two different amounts of the coupling agent were employed giving silane layers on the fillers with different thicknesses. The effect of ageing time at room temperature on the viscoelastic properties after quenching from 100 °C to room temperature in ice water was also investigated. The effects of the surface treatment of the fillers and the ageing time was characterized by means of the internal stress (σ i ) concept. Theσ i -value increased with the degree of interaction of the filler/matrix interface and the ageing time. It was here not possible to superimpose the different flow curves with regard to the ageing time with sufficient accuracy. This is due to the variation ofσ i with ageing time. The surface-treatment of the filler had a marked effect on the creep behavior at high applied stress levels and on the ageing behavior of the composites, presumably due to the formation of an interphase region close to the filler surface with different properties and different ageing characteristics than that of the bulk of the matrix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01428807
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    A model for the effect of physical ageing on the stress relaxation behavior of high density polyethylene (1989)
    Springer
    Rheologica acta 28 (1989), S. 147-153 
    Details
    ISSN: 1435-1528
    Keywords: Internalstress ; physicalageing ; amorphous phase ; stressrelaxation ; polyethylene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The stress relaxation behavior of high density polyethylene (HDPE) can be affected by ageing processes; e.g., with increasing storage time at a low temperature following a quench from a high temperature (close to the melting point) the relaxation curves change shape. More specifically, the stress level approached after very long loading times in a stress relaxation experiment increases with the ageing time. Here this stress level is denoted “the internal stress”σ i. Struik has pointed out that physical ageing may also occur in semicrystalline polymers like HDPE. The physical ageing should then be associated with that part of the amorphous phase which is closest to the surfaces of the crystallites. This part of the amorphous phase of HDPE can be assumed to have a restricted mobility at room temperature and may have a partially “glassy” character. In this paper a model for explaining the increase inσ i for HDPE with increasing ageing time is proposed and discussed. It is based on the separation of the amorphous phase into two parts as suggested by Struik. The glassy part of the amorphous phase ages in a way similar to that of an entirely amorphous polymer quenched to a temperature below its glass transition, while the more rubbery phase is assumed not to undergo any physical ageing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01356975
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  • 4
    Electronic Resource
    Electronic Resource
    In vitro propagation of Populus x wilsocarpa — a hybrid of ornamental value (1989)
    Springer
    Plant cell, tissue and organ culture 18 (1989), S. 209-219 
    Details
    ISSN: 1573-5044
    Keywords: BAP ; elongation phase ; NAA ; micropropagation ; physiological state ; rooting, shoot multiplication ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Populus x wilsocarpa, a hybrid of important ornamental value, cannot be seed-propagated, nor grafted, since a compatible rootstock has not been identified. A micropropagation protocol consisting of a series of steps was therefore developed to facilitate the commercial production of this species. The technique involved the transfer of swelling buds to a growth initiation medium with the following composition: N6 macronutrients, MS micronutrients and vitamins supplemented with 0.5 mg l-1 BAP. The best buds were from dormant twigs, stored at 0–2°C and then forced to burst prior to culture initiation. Shoot multiplication was on a basal WPM medium including 0.1 mg l-1 BAP and 0.001 mg l-1 NAA. Shoot elongation and rooting was also on a basal WPM medium supplemented with 1.0 mg l-1 GA3 followed by a transfer to a peat-perlite mix in the greenhouse.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00047747
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    Paper (German National Licenses)
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