Surface functionalization of rubber latex nanoparticles with sulfidosilane moieties

Abstract

Polybutadiene latex particles were functionalized with bis [3-(triethoxysilyl) propyl] tetrasulfide (TESPT) in the presence of zinc oxide as an activator and ethanol as a co-solvent. The success of this reaction was confirmed both by the peaks attributed to Si-O groups at 1085 and 1110 cm 21 and C-S bond at 630 cm 21 which appeared after reaction in Attenuated Fourier Transform Infrared (ATR-FTIR) Spectra and also by increasing in the particle size diameter of latex particles (from 95 to 127 nm) in Dynamic Light Scattering analysis. X-ray Diffraction results also showed changes in crystalline structure of the modified particles (as a strong decrease in the intensity of peak at 2h519.54). The effect of reactant concentration in a constant amount of TESPT (by varying the water and ethanol content), reaction time, activator size (micro and nanoparticles), and pH (7, 8.5) were investigated on degree of grafting (obtained from thermogravimetric analysis and ATR-FTIR spectra), particle size diameter, cross-link density, and swelling ratio of the samples. The amounts of silane grafting and cross-link density of polymer particles were increased by an increase in the reaction time. The highest grafting degree was observed at low concentration of TESPT. Silane functionalization was also improved in a slight basic condition (pH58.5) rather than neutral pH. The grafting reaction took place such as sulfur pre-vulcanization and the possible mechanism of this reaction was discussed.