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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 47 (1993), S. 1905-1914 
    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: The aim of this paper was to study the plasticizing effect of subjecting native/commercial gutta-percha samples to controlled levels of different humidities. It was expected that this study would provide the practicing endodontist with invaluable insight into the mechanical properties of commercial gutta-percha cones (i.e., retrievability, malleability, flexibility, and torsional and bending ability). The “conditioning” of the gutta-percha samples depended greatly on the percentage of compatible/incompatible substances. The mixtures of native gutta-percha with compatible (i.e., wax) showed greater elongation, tensile strength, and number of rotations, but lower deformation angle than the mixtures of native gutta-percha with incompatible substances (i.e., salts, metal oxides). The observed lower values for tensile strength and torsional strain, relative energy to break, and the Young's modulus and the higher values for elongation and number of rotations for wet samples compared to the dry ones were attributed to the plasticizing effect of gutta-percha due to the insertion of water molecules in the polymer chains. © 1993 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 2
    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: The transitions occurring in gutta-percha (transpolyisoprene) below the melting point were determined with DMTA and DSC. A comparison of the results obtained with these two methods showed satisfactory agreement. The thermal properties of native and commercial gutta-percha samples (Tg = 38 ± 2°C and Tm = 69 ± 3°C) were investigated, both before and after annealing (at different times and temperatures), and at environments of different relative humidities. An increase in the draw ratio also proved to enhance the percentage crystallinity (% K) and improve the thermal stability (higher Tgs and Tms) of gutta-percha. Finally, the activation energies ΔE (33.9-40.2 kj/mol × K) at glass transition temperature were determined and correlated to the percentage content (%) of the commercial gutta-percha samples in native gutta-percha. © 1993 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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