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Chemistry and Industry of Forest Products ›› 2014, Vol. 34 ›› Issue (2): 33-39.doi: 10.3969/j.issn.0253-2417.2014.02.006

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Thermal Decomposition Mechanism and Kinetics of Ursolic Acid and Caffeic Acid

XIAO Zhuo-bing, GUO Man-man, GUO Rui-ke   

  1. Key Laboratory for Forest Products and Chemical Industry Engineering, Jishou University, Zhangjiajie 427000, China
  • Received:2013-04-09 Online:2014-04-25 Published:2014-04-26

Abstract: Two kinds of natural organic acid, ursolic acid and caffeic acid were analyzed under the nitrogen atmosphere by thermogravimetry combined fourier transform infrared spectroscopy (TG-FT-IR). Experimental data of TG were computationally processed by three kinds of thermal analysis kinetics methods (Coats-Redfern, Achar and Malek methods), through which the most probable mechanisms and functions of each stage were inferred and the values of apparent activation energy Ea and pre-exponential factor A were also obtained. The results showed that according to percentage of weight loss, molecular simulation and infrared spectrum of evolved gases, the cracking of chemical bonds was confirmed. Thermal decomposition of ursolic acid began at 236.8 ℃ and ended at 431.2 ℃ with a complete mass loss while after 153.0 ℃ caffeic acid underwent the two-stage thermal decomposition. The most probable mechanisms of ursolic acid and caffeic acid at the first stage and the second stage were two-dimension diffusion, two-dimension diffusion and three-dimension diffusion, corresponding with Valensi equation, Jander equation and Z.-L.-T. equation, respectively. Ea of ursolic acid and caffeic acid at first stage and second stage were 228.26, 111.28 and 231.75 kJ/mol while their lnA were 39.56, 25.78 and 43.50, respectively. According to kinetic parameters, shelflives of ursolic acid and caffeic acid at 25 ℃ were 4-5 years and 3 years, respectively.

Key words: ursolic acid, caffeic acid, TG-FT-IR, thermal decomposition mechanism, decomposition kinetics

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