No description available.

Distribution, cytological organization and development of laticifers In some latex bearing plants were studied by the use of optical and electron microscopy. Seven species from five different families were used In a comparative study, which were Meconopsis cambrica & Papaver rhoeas (Papaveraceae), Hevea brasiliensis & Euphorbia wulfenii (Euphorbiaceae), Musa acuminata (Musaceae), Mandevilla splendens (Apocyanaceae) & Taraxacum officinale (Compositae/Asteraceae). Several preparation procedures have been compared and optimised for the structural preservation of the laticifers and for examination of their distribution in these taxa. Methods of fixation have been studied. Fresh unfixed samples showed good structural information and laticifer distribution in the tissue. This technique was also very fast and convenient to use. In practice this protocol can be applied in monitoring and screening bulk samples in a breeding program, where speed and convenience are very important. Samples fixed with aldehyde fixative gave reasonably good results for histology study but not at the electron microscope level. The samples fixed with this fixative however, were highly suited to Immunohistochemical work. This information is invaluable and will be used and adapted for Hevea study in Malaysia. Both osmium and a combination of osmium tetroxide and zinc iodide were superior in term of ultrastructural preservation. Embedding media for laticifers were compared. For histological and immunohistochemical studies, Paraplast wax was used. The preparation procedure was easy and convenient, and overall structural information of laticifers was good. Spurr resin and araldite are both epoxy resins, but samples embedded in araldite gave better, more acceptable results. The carcinogenic nature of Spun- resin means that it must be handled with extreme caution, making it a less convenient embedding medium. The only acrylic resin was LR White, which was initially Intended for an immunocytochemistry study where the priority was to retain antigenic sites. Samples embedded with this resin did not show good structural information. The final set of procedures evaluated was staining methods. The staining procedure has to be fast, must differentially stain laticifers and must be reliable. These stains can be grouped into two categories; standard histological stains such as Toluidine Blue and Safranin O with Astra Blue, and fluorescent stains such as Calcofluor, ANS and Acridine Orange. However almost all stains tested failed to differentially stain latex or laticifers. They however did assist in clarifying for identification the location and distribution of laticifers in the tissues. Using Toluidine Blue was very fast and easy, but all the fluorescent stains are faster and easier to use. Laticifers in all species examined, exhibited a similar pattern of distribution. They were located in the cambial regions of stems, petioles, leaves and roots, or closely located within the vascular bundle.

No description available.

Thesis (Ph. D.)--Lehigh University, 1997. / Includes vita. Includes bibliographical references.

Thèse--Sc. nat.--Montpellier II, 1981. / Bibliogr. p. 229-274.

Thesis (Ph. D.)--Lehigh University, 2004. / Includes bibliographical references and vita.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1946. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [118]-120).

Thesis (doctoral)--Rijksuniversiteit te Utrecht, 1983. / Includes bibliographical references.

Thesis (Ph. D.)--Lehigh University, 2006. / Includes bibliographical references and vita.

Atualmente, nanocompósitos têm sido alvo de grande interesse científico e tecnológico. Além do negro-de-fumo e da sílica, materiais já consagrados como nanopartículas de reforço para uma grande variedade de borrachas, outras nanopartículas funcionalizadas têm sido o centro das atenções. Especialmente, nanopartículas bidimensionais (lâminas) e unidimensionais (tubos ou fibras, com destaque aos nanotubos de carbono) têm surgido como excelentes candidatos a partículas de reforço e apresentando efeito superior, já a frações volumétricas muito pequenas, bem inferiores às aplicadas tradicionalmente. Este trabalho tinha como objetivo investigar a epoxidação de polibutadieno e explorar a potencialidade de sílicas lamelares, especialmente filossilicatos 2:1, como agentes efetivos de reforço e barreira. Para alcançar este objetivo uma nova tecnologia de mistura e dispersão para a argila montmorilonita (MMT) foi desenvolvida. Baseia-se na Coagulação Dinâmica Contínua de Látex (“Continuous Dynamic Latex Coumpounding - CDLC"), na qual MMT é misturada ao látex de borracha e dispersa, adequadamente, em um regime especial de fluxo. O método vale-se do potencial que a água possui de enfraquecer os contatos interlamelares da MMT. Látices de NR, SBR, NBR e XNBR foram investigados. As condições de processo afetam a morfologia dos nanocompósitos, determinada por MET e DRX. A polaridade das borrachas influencia a dispersão da MMT e, consequentemente, as propriedades finais dos nanocompósitos. Comparando-se estes nanocompósitos com compósitos obtidos com negro-de-fumo, sílica precipitada ou mesmo com argila obtidos pelo processo da incorporação no estado fundido, os de CDLC exibem desempenho de reforço e uma resistência à permeação superiores, mesmo aplicando-se frações volumétricas de carga bem inferiores. Paralelamente, mostrou-se que é possível epoxidar polibutadieno comercial, a partir do meio reacional de polimerização, em ciclohexano, limitando-se em 30% em mol, face ao limite de solubilidade da borracha epoxidada no solvente. Nanocompósitos de polibutadieno epoxidado com argila foram preparados obtendose também propriedades melhores do que a borracha epoxidada pura. Com estes resultados, o presente trabalho mostra novas oportunidades para a obtenção de nanocompósitos elastoméricos. / Nowadays, polymer nanocomposites received an increasing scientific and technological interest. Besides carbon black and silica which have been proven reinforcing nanofillers for a large variety of rubber, other types of functional nanoparticles are coming in the center of this attention. Especially two-dimensional nanoparticles (platelets) and one-dimensional tubes or fibers (i.e. carbon nanotubes) are serious candidates to determine large reinforcing effects as for less volume fraction than traditional fillers. This work had as objective to investigate the epoxidation of polybutadiene and to explore the potential of layered silicas, especially 2:1 phylosilicates, as reinforcing agents and effective permeation barriers. In order to achieve this objective a new mixing and dispersion technology for montmorillonite (MMT) was developed in this work. This technology is based on “Continuous Dynamic Latex Compounding” (CDLC), in which MMT is mixed with a rubber latex and well dispersed in particular flow regime. Due to the coagulation of the latex, it was possible to prepare superior types of rubber nanocomposites. One important fact is that the interlayer contacts in the MMT tactoids are weakened by swelling in water. Latices of NR, SBR, NBR and XNBR have been used. It is shown that the process conditions affect the phase morphology of nanocomposites characterized by transmission electron microscopy and x-ray diffraction. The polarity of rubbers influence the dispersion of MMT as well as the properties of the resulting nanocomposites. Compared to nanocomposites filled with carbon black, precipitated silica, or those obtained by melt mixing, nanocomposites by CDLC demonstrate a better reinforcement and permeation resistance at far less volume fractions. The epoxidation of commercial polybutadiene with high cis content, from its commercial solution (cyclohexan), was possible, but due to the solubility of epoxidized polymer, the system coagulated and gelated when a epoxidation degree of 30 mol% was reached, independent of the initial concentrations of reagents. Nanocomposites from polybutadiene, 14 and 19 mol% epoxidation degree, and organoclay were prepared. The mechanical and barrier properties had been superior to those compositions of epoxidized polybutadiene without clay. By this achievements, the present work demonstrate new opportunities for polymeric nanocomposites.