The thermal oxidation of guayule and hevea rubbers by dynamic differential scanning calorimetry

Abstract

SynopsisThe thermal oxidation of natural rubbers from Hevea brasiliensis (pale crepe and smoked sheet) and Partheniurn argentaturn (Guayule) were studied with differential scanning calorimetry (DSC) using the dynamic method. The atmosphere was oxygen a t 110 ml/min and the temperature range was 393"-473"K. The decomposition reactions showed a pronounced exothermic emission with shoulders on the high-temperature side. The kinetic parameters were computed by using three different mathematical approaches: the heat evolution treatment of Borchardt and Daniels, the diffusion-controlled method by Jander, and the heating rate method developed by Kissinger and Ozawa. The best agreement between these methods was achieved assuming first order in the Borchardt and Daniels method and three-dimensional diffusion with the Jander model. The mass influence was analyzed observing that good agreement is obtained working with sample weight in the order of 3-4 mg. Under such conditions the activation energies (E,) were 16-17,18-19, and 23-24 kcal/mole for the Borchardt-Daniels, Kissinger-Ozawa, and Jander models, respectively.

Characterization of isomeric elastomers using thermal analysis

“…The heats of oxidation are: NR, 2680 1 g-~; IR, 1535 J g-i; guttapercha, 1585 J g-l; and Transpip 100, 1510 J g-l. These values are much higher than those reported previously [23], showing the importance of thermal contact.…”

Compatibility of tire elastomers using derivative heat flow traces in the glass transition region

“…Thus, the larger (AW/AT) area may be ascribed to more intimate contact as well as large surface area of these samples, which could be pressed to a thin film. The importance of thermal contact with the pan to obtain quantitative data was also demonstrated by Goh [5] who used solvent-cast samples and obtained much higher enthalpy values for degradation of NR and gutta-percha in oxygen than those reported earlier [6].…”

Insights into the kinetics of thermally induced crystallization of amorphous calcium phosphate

“…The Borchardt-Daniels method 22 involved the measurement of the integrated intensities of this peak at different time points between its low temperature trough and the maximum and calculating the rate constants at different temperatures and for different reaction orders, n , using the following expressions 23 in which S 0 is the total integrated peak intensity and S T is the peak intensity at temperature T, and ΔH is the heat generated from the beginning of the reaction to the temperature T: k0=ΔH/S0 for n=0 k1/2=ΔH/(2S0[1−(ST/S0)]1/2 for n=1/2 k2/3=ΔH/(3S0[1−(ST/S0)]2/3 for n=2/3 k1=ΔH/(S0−ST) for n=1…”