Browsing by Author "Rathnayake, R.M.M.D."

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    Degradation of vulcanized natural sesame oils
    (Uva Wellassa University of Sri Lanka, 2015) Rathnayake, R.M.M.D.; Jayasuriya, C.K.
    Vulcanized rubber products used in various applications cause serious environmental issues due to their very slow degradation (Treloar, 2005, Blackley, 1997). The present research focuses on enhancing degradation of vulcanized rubber products which are discarded after their usage. Due to the unsaturated nature, rubber molecules are susceptible to degradation in the presence of peroxide radicals (Adhikari, et al 2000). Therefore, it is expected that the peroxide radicals produced in the oxidation of natural oils can enhance degradation. The oxidation of a natural oil increases with it’s degree of unsaturation which increases the rate of degradation. Therefore, highly unsaturated locally available soybean and sesame oil were used in the study. Materials and Methods Vulcanized rubber samples were prepared according to the tire tread formulation. Technically specified rubber (TSR) (100.00 g) was added into the internal mixer and allowed to crush well. Then stearic acid (2.00 g) and zinc oxide (5.00 g) were added and mixed well. After about 3 minutes carbon black (N 375 black) (73.00 g) and process oil (naphthenic oil) (5.00 g) were collected into the internal mixer. Finally, antidegradent N- isopropyl- N- phenyl-p- phenylenediamine (IPPD) (2.70 g) and wax (1.00g) were added and allowed to mix well. The prepared mixture was taken out from the internal mixer and set aside to cool. After cooling, the mixture was processed in the two roll mill for about 7- 8 minutes at the same time adding the accelerator N- tert- butyl- 2- benzothiazolesulferamide (TBBS) (1.00 g) and sulphur (2.50 g). Finally a thick rubber sheet was obtained. Then the sample was cooled for 16 h and vulcanization of the samples was carried out in the hydraulic hot press at 150 ºC for 28 minutes to produce sheets of thickness approximately 3 mm (White, 1995). The resulting rubber sheets were cut into square pieces (7.5 × 11.0 cm ) and immersed in soybean and sesame oil for different period of times at room temperature. In addition, the effect of these oils on degradation in the presence of sun light and copper catalyst, only for 5-week time period was also studied. At the end of the each time period, samples were taken out from the oil and wiped well before testing and characterization. Tensile properties (ISO 37-1977) and tear strength (ISO 34-1979) were determined with reference to the vulcanized rubber sample which was not immersed in oil (blank). The thermal properties were obtained by exposing the samples to a temperature range of (23-500) °C at an increasing rate of 5 °C min Results and Discussion Stress- Strain curves for natural rubber samples immersed in soybean oil and in sesame oil are given in Figures 1 and 2, respectively. According to the results all the samples immersed in sesame oil and soybean oil, have reduced their tensile strengths compared to the blank. The tensile strength values of the samples immersed in soybean oil for equal time period are lower than those immersed in sesame oil. According to the results, when the exposure time is increased the tensile strength values in both type of oils have decreased significantly. The greater losses of tensile strengths were shown by the samples in the presence of sun light and copper catalyst. Similar pattern of results were obtained for tear strength (Figure 3). TGA results show that the degradation temperatures of all the samples immersed in sesame oil and soybean oil have been reduced compared to the blank sample. The degradation temperatures of the samples, immersed in soybean oil are lower than those immersed in sesame oil for the same time period.