Browsing by Author "Meincken, M."

Now showing 1 - 6 of 6
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    Advantages of scanning probe microscopy in polymer science
    (Academy of Science for South Africa, 2004) Meincken, M.; Sanderson, R. D.
    We introduce the atomic force microscope (AFM) and its capabilities with special regard to its use in polymer science. It shows several advantages over other analytical techniques, such as scanning electron microscopy, differential scanning calorimetry, and dynamic mechanical analysis. Its main advantage is that the samples need not be prepared specially and can therefore be studied in their native environment. Further-more, the AFM can be used to detect physical properties locally on a molecular scale, which may be of interest for characterizing polymer blends or structured polymers.
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    Analysis of gamma-ray and neutron-induced chromosome aberrations in CHO-K1 cells using the atomic force microscope
    (Academy of Science for South Africa, 2004) Meincken, M.; Smit, B. S.; Sanderson, R. D.; Slabbert J. P.
    THE ENUMERATION OF CHROMOSOME aberrations remains a popular method to relate DNA damage to radiation dose delivered, and is the basis of efforts to improve aberration assays. In the work reported here, atomic force microscopy was used to study the induction of chromosome aberrations in CHO-K1 cells, after irradiation with 1-3 Gy p(66)/Be neutrons and 2-7 Gy 60Co γ-rays. The investigation showed that small structures, not normally well defined using conventional microscopy, can be resolved and identified with the atomic force microscope. Furthermore, the height information gathered by atomic force microscopy is useful for eliminating counting mistakes, which might be caused by chromatid or chromosome overlaps. The superior resolution of atomic force microscopy over conventional optical microscopy renders the scoring of as few as 20 cells per dose point as sufficient to draw accurate dose curves that correctly express the biological damage induced by different radiation sources.
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    Atomic force microscopy to determine the surface roughness and surface polarity of cell types of hardwoods commonly used for pulping
    (Academy of Science for South Africa, 2007) Meincken, M.
    ATOMIC FORCE MICROSCOPY CAN BE USED to determine the surface roughness and surface polarity of different cell types originating from hardwood species. This analytical method allows images representing the topography and polarity of a surface to be captured simultaneously at a molecular (nanometre) resolution. The distribution of hydrophilic (polar) groups on these cell surfaces influences the subsequent processing of woodpulp in paper manufacture. These surface properties of fibres, vessel elements and parenchyma cells were investigated for Acacia mearnsii, Eucalyptus grandis, E. dunnii and E. macarthurii. A clear distinction was observed between the cell types and the species in terms of polarity and surface roughness. All four species are currently being used for paper manufacture in South Africa, but not with equal success. This study may help to explain the differences in pulp quality obtained for the various species.
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    Evaluation of Irvingia kernels extract as biobased wood adhesive
    (SpringerOpen, 2020-02-22) Alawode, A. O; Eselem-Bungu, P. S; Amiandamhen, S. O; Meincken, M.; Tyhoda, L.
    Irvingia tree species have been earmarked for domestication in many countries due to their potential as raw materials for various applications, which include biodiesel, cosmetics, perfume, soap, etc. Presently, there is no information on the utilization of kernel seed extract as a potential source of green wood adhesive. This study is focused on investigating the properties of adhesives produced from kernel seeds of two Irvingia wood species i.e. Irvingia gabonensis (IG) and Irvingia wombolu (IW), as well as investigating the improved properties derived from the effect of modification using a few selected modifying agents including glutaraldehyde, glyoxal, epichlorohydrin (EPI) and an acid/base type process modification. Polyethylene (PE) was used along with the glutaraldehyde, glyoxal and epichlorohydrin modifiers in the modification process. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were conducted to study the effect of modification on adhesive properties. The glycosidic carbon of the unmodified extracts and that of the EPI modified sample were not sensitive to chain conformations. Principal components (PC) 1 and 2 explained 85.19 and 9.54%, respectively, of the total variability in FTIR spectra among the modified and unmodified adhesives. The unmodified samples for IG and IW exhibited one peak with crystallization temperatures of 18.7 and 14.4 °C, respectively, indicating only one component exhibits some low degree crystallinity. The adhesive properties of the modified extracts were tested on wood veneers according to ASTM standard. The shear strength of the modified adhesives ranged from 1.5 to 3.93 MPa and 1.7 to 4.05 MPa for IG and IW, respectively. The modified samples containing PE showed marked improvement in the shear strength. The highest values were about 63% higher than the shear strength of unmodified samples with least shear strength. The results indicated that the modification of Irvingia-based adhesives had a great contribution to their performance as natural wood adhesives.
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    Physiological and growth responses to pollutant-induced biochemical changes in plants : a review
    (University of Tehran, 2020) Mulenga, C.; Clarke, C.; Meincken, M.
    ENGLISH ABSTRACT: Industrial activities compromise the ambient air quality at a local, regional and global level through gaseous and dust emissions. This study reviews uptake mechanisms and the associated phytotoxicity of pollutants in plants, focusing on heavy metals and SO2. It further describes detoxification mechanisms and the resultant biochemical and physiological changes in plants. Finally, the morpho-physiological and growth responses to stress-induced biochemical changes are discussed. Heavy metals and SO2 enter the plant tissue through the stomata, cuticular layers, lenticels and root hairs. In the plant cells, SO2 converts to SO32- or SO42- ions upon reacting with water molecules, which in excess are toxic to plants. However, the detoxification process of SO32- increases the production of reactive oxygen species (ROS). ROS are toxic to plants and damages biomolecules such as lipids, proteins, carbohydrates and DNA. On the other hand, heavy metals, such as Cu and Fe catalyse the Fenton/Haber-Weiss reactions, breaking down H2O2 into OH•. Additionally, Pb and Zn inhibit the activities of ROS-detoxifying enzymes, while other heavy metals bind to cellular layers making them rigid, thereby reducing cell division. Therefore, pollutant toxicity in plants affects biochemical parameters damaging organic molecules and limiting cambial activity. Damaged biomolecules inhibit the plant's capacity to carry out physiological functions, such as photosynthesis, stomatal functions, transpiration and respiration while impaired cambial activity reduces cell division and elongation resulting in reduced plant growth and productivity.
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    Surface polarity determination of wood fibres after different pre-treatments and bisulphite pulping
    (Academy of Science for South Africa, 2008) Meincken, M.; Matyumza, N. C.
    THE SURFACE POLARITY OF PULP FIBRES originating from four different wood species commonly used for pulping in South Africa has been determined after various pre-treatments, and after magnesium bisulphite pulping. The presence as well as the distribution of polar groups on the fibre surface strongly affects inter-fibre bonding in paper. Bonding consists mostly of hydrogen bonds between free hydroxyl groups on the fibre surface. Surface polarity was examined by atomic force microscopy in pulsed-force mode. This technique allows the imaging of the polarity of a surface with a nanometre-scale molecular resolution. It is thus sensitive to individual functional groups, mostly hydrophilic hydroxyl groups. Polarity differences between the various wood species have been observed. We compare these observations with the varying pulp quality that arises from the pulp composition. Improvement in pulp quality may be possible if fibre surface properties are used as guidance criteria for the choice of a specific pre-treatment method.