Kinetics of natural rubber (NR) vulcanization by lanthanum O, O'-diisopropyldithiophosphate [ La(DiPDP)3 ] was studied. La(DiPDP)3 had remarkable accelerating effect on the vulcanization of NR. The rate constan...Kinetics of natural rubber (NR) vulcanization by lanthanum O, O'-diisopropyldithiophosphate [ La(DiPDP)3 ] was studied. La(DiPDP)3 had remarkable accelerating effect on the vulcanization of NR. The rate constant k6 of the reaction that turned polysulphidic cross-links into the modified main chain was higher than that of desulfuration reaction of polysulfidic cross-links (k3 ). The activation energies (Ea2, Ea3, and Ea6) of the formation, desulfuration, and decomposition of polysulfidic cross-links were 87.57,102.34, and 95.01 kJ · mol^-1, respectively. Activation energy (Eas) of the reaction that turned the cross-link precursors into the modified main chain was 82.67 kJ · mol^-1. It could be concluded that the proportion of polysulphidic cross-links was higher than mono- and di- sulphidic cross-links during induction and curing periods, mono- and di- sulphidic cross-links increased as curing temperature rose. In the temperature range of 140 - 160 ℃, the amounts of polysulphidic cross-links were similar. However, over 160℃, mono- and di- sulphidic cross-links increased rapidly. Moreover, cross-link density of the vulcanizates was determined from the equilibrium-swelling data. A chemical probe detected the concentration of polysulphidic cross-links of vulcanizates. The change trend of the results predicated from equation corresponded to that of the experimental results.展开更多
A lanthanum glutamic dithiocarbamate(La-GDTC) was synthesized. The vulcanization kinetic and crosslinking structure of styrene butadiene rubber (SBR)/La-GDTC/silica(SiO2) composites were studied via vulcanizatio...A lanthanum glutamic dithiocarbamate(La-GDTC) was synthesized. The vulcanization kinetic and crosslinking structure of styrene butadiene rubber (SBR)/La-GDTC/silica(SiO2) composites were studied via vulcanization kinetic simulation,swelling equilibrium and differential scanning calorimeter. Simulated curing parameters showed that the curing rate k2 of the SBR/La-GDTC/SiO2 composite was significantly higher than that of the SBR/La-GDTC composite. Also,swelling equilibrium test turned out that crosslinking density of SBR/LaGDTC/SiO2 composite evolved to higher level,compared to that of the SBR/La-GDTC composite. Ammonia modified swelling equilibrium interpreted both lanthanum ions and carboxyl groups could react with silanol groups of silica particles. Finally,vulcanization activation energies of SBR/La-GDTC/SiO2 composite were lower than that of SBR/La-GDTC composite,without respect to different approaches of the DSC measurement or Oscillated Disc Rheometer test. All the results showed that the lanthanum ions of La-GDTC could act as the metal ion catalyzer of sulfur vulcanization during the crosslinking process,which could be attributed to the unoccupied orbital of lanthanum ions. Therefore,a La-GDTC bridged structure between SBR and silica particles for the SBR/La-GDTC/SiO2 composite was suggested according to the experimental results.展开更多
基金Project supported by the Guangdong Natural Science Foundation (05006563)
文摘Kinetics of natural rubber (NR) vulcanization by lanthanum O, O'-diisopropyldithiophosphate [ La(DiPDP)3 ] was studied. La(DiPDP)3 had remarkable accelerating effect on the vulcanization of NR. The rate constant k6 of the reaction that turned polysulphidic cross-links into the modified main chain was higher than that of desulfuration reaction of polysulfidic cross-links (k3 ). The activation energies (Ea2, Ea3, and Ea6) of the formation, desulfuration, and decomposition of polysulfidic cross-links were 87.57,102.34, and 95.01 kJ · mol^-1, respectively. Activation energy (Eas) of the reaction that turned the cross-link precursors into the modified main chain was 82.67 kJ · mol^-1. It could be concluded that the proportion of polysulphidic cross-links was higher than mono- and di- sulphidic cross-links during induction and curing periods, mono- and di- sulphidic cross-links increased as curing temperature rose. In the temperature range of 140 - 160 ℃, the amounts of polysulphidic cross-links were similar. However, over 160℃, mono- and di- sulphidic cross-links increased rapidly. Moreover, cross-link density of the vulcanizates was determined from the equilibrium-swelling data. A chemical probe detected the concentration of polysulphidic cross-links of vulcanizates. The change trend of the results predicated from equation corresponded to that of the experimental results.
基金Project supported by the National Natural Science Foundation of China (50873036 and 50773021)the Fundamental Research Funds for the Central Universities, SCUT (2009ZM0306)
文摘A lanthanum glutamic dithiocarbamate(La-GDTC) was synthesized. The vulcanization kinetic and crosslinking structure of styrene butadiene rubber (SBR)/La-GDTC/silica(SiO2) composites were studied via vulcanization kinetic simulation,swelling equilibrium and differential scanning calorimeter. Simulated curing parameters showed that the curing rate k2 of the SBR/La-GDTC/SiO2 composite was significantly higher than that of the SBR/La-GDTC composite. Also,swelling equilibrium test turned out that crosslinking density of SBR/LaGDTC/SiO2 composite evolved to higher level,compared to that of the SBR/La-GDTC composite. Ammonia modified swelling equilibrium interpreted both lanthanum ions and carboxyl groups could react with silanol groups of silica particles. Finally,vulcanization activation energies of SBR/La-GDTC/SiO2 composite were lower than that of SBR/La-GDTC composite,without respect to different approaches of the DSC measurement or Oscillated Disc Rheometer test. All the results showed that the lanthanum ions of La-GDTC could act as the metal ion catalyzer of sulfur vulcanization during the crosslinking process,which could be attributed to the unoccupied orbital of lanthanum ions. Therefore,a La-GDTC bridged structure between SBR and silica particles for the SBR/La-GDTC/SiO2 composite was suggested according to the experimental results.