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Keywords:

  • degradation;
  • rubber;
  • stabilization;
  • thermogravimetric analysis (TGA);
  • vulcanization

Abstract

This article deals with our study of the thermooxidative degradation of medical natural rubber latex tubes prepared with sulfur-prevulcanized latex (sample I) and peroxide-prevulcanized latex (sample II) in a dynamic air atmosphere by the use of the thermogravimetry/differential thermogravimetry method as well as the evaluation of the thermooxidative stability of these two samples. The test results showed that an oxygen-absorption mass-gain process occurred after a slight mass loss; the mass-gain rate decreased with an increase in the temperature rising rate (β), and this was more prominent in sample II than in sample I. The maximum mass-gain rate of sample II was 1.43% when β was 5°C/min, which was 5.02 times that of sample I; the thermooxidative stability of sample II was also lower than that of sample I. Because the oxygen absorption of sample II clearly caused serious oxidation, the balanced initial temperature, the temperature of the balanced degradation peak, and the balanced final temperature of sample II in the first reaction stage were obviously lower than those of sample I. The apparent activation energy (Eo = 143.6 kJ/mol) of sample I was significantly higher than that of sample II, and the stability of sample I was also higher than that of sample II. The temperature of the balanced degradation peak of sample II in the second reaction stage was higher than that of sample I, and Eo (154.0 kJ/mol) of sample II was significantly higher than that of sample I; the stability of sample II was also higher. Thermogravimetry curves of the two samples at various β values intercrossed each other, and the temperature at the crosspoint and the degradation rate increased linearly as β increased. On the temperature segment from the initial temperature to the crosspoint, the degradation rate of sample II was higher than that of sample I when the temperature of the two samples was the same, but on the segment from the crosspoint to the final temperature, the degradation rate of sample II was lower than that of sample I when the temperature of the two samples was the same. The degradation rate of the samples at 600°C was 99.2–99.5%. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 591–597, 2005