Study of the modification of montmorillonite with monofunctional and trifunctional vinyl chlorosilane

• Silylation of montmorillonite was performed with two kind of vinylchlorosilane.
• Grafted amount increased and grafting yield decreased with increase of initial silane concentration.
• The most grafting yield and basal spacing was obtained by monochlorosilane.
• According to the results, the silylation mechanism was proposed.

Montmorillonite (Cloisite®Na+) was modified with dimethylchlorovinylsilane (DMCVS) and trichlorovinylsilane (TCVS), in order to replace the silanol groups of clay mineral with silane vinyl groups (silylation reaction). The grafting reaction was studied using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Variation of the grafted amount and the grafting yield was evaluated as a function of the initial silane concentration. The grafted amount was increased with both mono- and trichlorosilane concentrations; where, the reaction yield decreased. Since the reaction will liberate HCl, the effect of the presence of NaHCO3 in the reaction media, was studied. Silylation with monofunctional silane leads to higher grafting amount compared to silylation with trifunctional one. The mechanism of silylation reaction was determined and the effect of the number of silane functional groups on the reaction mechanism was studied. The highest grafted amount and grafting yield were achieved with the initial silane concentration of ~ 4 mmol/g of DMCVS. The basal spacing of the silylated montmorillonites (Mt) was observed to be more than the basal spacing of pristine Mt.