Characterization of the UV Oxidation of Raw Natural Rubber Thin Film Using Image and FT-IR Analysis Kim, Ik-Sik; Lee, Bok-Won; Sohn, Kyung-Suk; Yoon, Joohoe; Lee, Jung-Hun;
Characterization of the UV oxidation for raw natural rubber (NR) was investigated in controlled conditions through image and FT-IR analysis. The UV oxidation was performed on a thin film of natural rubber coated on a KBr window at 254 nm and room temperature to exclude the thermal oxidation. Before or after exposure to UV light, image of the NR thin film was observed at a right or tilted angle. FT-IR absorption spectra were measured in transmission mode with the UV irradiation time. The UV oxidation of NR was examined by the changes of absorption peaks at 3425, 1717, 1084, 1477, 1377, and which were assigned to hydroxyl group (-OH), carbonyl group (-C=O), carbon-oxygen bond (-C-O), methylene group , methyl group , and cis-methine group , respectively. During the initial exposure period, the results indicated that the appearance of carbonyl group was directly related to the reduction of cis-methine group containing carbon-carbon double bond (-C=C-). Most of aldehydes or ketones from carbon-carbon double bonds were formed very fast by chain scission. A lot of long wide cracks with one orientation at regular intervals which resulted in consecutive chain scission were observed by image analysis. During all exposure periods, on the other hand, it was considered that the continuous increment of hydroxyl and carbonyl group was closely related to the decrement of methylene and methyl group in the allylic position. Therefore, two possible mechanisms for the UV oxidation of NR were suggested.
G. Van Santvoort, "Geotextiles and Geomembranes in Civil Engineering", p. 517, Roterdam, Netherlands, 1994.
J. L. Morand, "Chain Scission in the Oxidation of Polyisoprene", Rubber Chem. Technol., 50, 373 (1977).
K. A. M. dos Santos, P. A. Z. Suarez, and J. C. Rubim, "Photo-degradation of Synthetic and Natural polyisoprene at Specific UV radiations", Polym. Degrad. Stab., 90, 34 (2005).
M. A. Rodrigues and M. A. Paoli, "The Chemical effects of Photo-oxidation on Isoprene Rubber", Eur. Polym. J., 21, 15 (1985).
J. L. Morand, "Photodegradation of Rubber", Rubber Chem. Technol., 39, 537 (1966).
M. A. Golub and L. C. Stephens, "Photoinduced Microstructural Changes in 1,4-Polyisoprene", Journal of Polymer Science: Part A-1, 6, 763 (1968).
C. Adam, J. Lacoste, and J. Lemaire, "Photo-oxidation of Polyisoprene", Polym. Degrad. Stab., 32, 51 (1991).
S. Yano, "Photo-oxidation of an IR Vulcanizate", Rubber Chem. Technol., 54, 1 (1981).
J. I. Cunneen, "Oxidative Aging of Natural Rubber", Rubber Chem. Technol., 41, 182 (1968).
J. R. Purdon, "The Vanderbilt Rubber Handbook", ed. by Robert F. Ohm, 13th Ed. p. 176, R. T. Vanderbilt Company, Inc., Norwalk 1990.
D. L. Pavia, G. M. Lampman, and G. S. Kriz, "Introduction to Spectroscopy: A Guide for students of Organic chemistry", W.B. Saunders Co., Philadelphia, 1979.
P. O. Bussiere, J. C. Gardette, J. Lacoste, and M. Baba, "Characterization of Photodegradation of Polybutadiene and Polyisoprene: Chronology of Crosslinking and Chain Scission", Polym. Degrad. Stab., 88, 182 (2005).
J. R. Shelton, "Aging and Oxidation of Elastomers", Rubber Chem. Technol., 30, 1252 (1957).
R. L. Pecsok, P. C. Painter, J. R. Shelton, and J. L. Koeing, "Fourier Transform Infrared Studies of the Mechanism of Oxidation of cis-1,4-Polybutadiene", Rubber Chem. Technol., 49, 1010 (1976).
J. R. Shelton, "Review of Basic Oxidation Processes in Elastomers", Rubber Chem. Technol., 45, 359 (1972).
T. Yasuyuki, S. Toshaki, H. Masaharu, K. Eiji, and S. Kazuhiko, European Patent, 0,702,029 B1 (1999).
J. F. Rabek, "Polymer Photodegradation: Mechanisms and Experimental Methods", London, Chapman & Hall, 1995.
P. Carstensen, "Free Radicals in Diene Polymers Induced by Ultraviolet Irradiation I. An ESR Study of cis-1,4-polyisoprene", Rubber Chem. Technol., 45, 918 (1972).