Dynamics of Natural Rubber as a Function of Frequency, Temperature, and Pressure. A Dielectric Spectroscopy Investigation

• Published in: Macromolecules Vol. 43; no. 11; pp. 5094 - 5102
• Main Authors: Ortiz-Serna, P, Díaz-Calleja, R, Sanchis, M. J, Floudas, G, Nunes, R. C, Martins, A. F, Visconte, L. L
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 08-06-2010
• Subjects: Applied sciences; Exact sciences and technology; Natural polymers; Natural rubber; Physicochemistry of polymers; Alpha relaxation; Humidity effect; Activation volume; Natural rubber; Experimental study; Activation energy; Dielectric relaxation
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma1004869

Natural rubber (NR) isolated from Hevea Brasiliensis was investigated by differential scanning calorimetry, dielectric spectroscopy, and high-pressure dielectric spectroscopy. In the range of frequencies (5 × 10−2 to 3 × 106 Hz), temperatures (−120 to 120 °C), and pressures (0.1 to 240 MPa) studied, the dielectric spectra exhibit two overlapped α-processes but no subglass relaxations. Thermal measurements revealed the presence of some moisture in NR. To elucidate the influence of water, dielectric measurements were carried out in dry and wet NR samples. The origin of the two dielectrically active processes was discussed in terms of (i) the apparent activation volume, (ii) the pressure coefficient of the respective glass temperatures, and (iii) the values of the ratio of activation energies, at constant volume and pressure. The latter allowed extracting the relative contribution of thermal energy and volume for each dynamic process. On the basis of these results, the faster α-processes is assigned to the rigidified rubber backbone dynamics whereas the slower to fatty acids (such as stearic acid) that are linked to the rubber chain.