Study on the curing properties of SBR/La-GDTC/SiO2 composites

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/La- GDTC/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.