Effects of the nature and combinations of solvents in the intercalation of clay with block copolymers on the properties of polymer nanocomposites

Abstract

Polystyrene (PS) nanocomposites were prepared by the free-radical polymerization of styrene in the presence of organically modified montmorillonite (MMT) clays. MMT clay was modified with a low-molecularweight and quarternized block copolymer of styrene and 4-vinylpyridine [poly(styrene-b-4-vinylpyridine) (SVP)] with 36.4 wt % PS and 63.6 wt % poly(4-vinylpyridine) (P4VP). Special attention was paid to the modification, which was carried out in different compositions of a solvent mixture of tetrahydrofuran (THF) and water. The swelling behavior of the MMT clay was studied by an Xray diffraction technique. The diffraction peak shifted to lower 2y angles for all of the modified clays, which indicated the intercalation of the quarternized SVP copolymer into the MMT layers in different degrees. Higher interlayer distances, which showed a high degree of block copolymer insertion, were obtained for solvent compositions with THF in water. The resultant nanocomposites were characterized by X-ray diffraction, atomic force microscopy, scanning electron microscopy, thermogravimetric analysis, and dynamic mechanical analysis. The desired exfoliated nanocomposite structure was achieved when the MMT modification was conducted in 50 or 66 wt % THF, whereas the other modifications all resulted in intercalated structures. The resulting exfoliated nanocomposite was found to have better thermal stability and dynamic mechanical performance compared to the others, even with 2% clay loading.

Swelling of organoclays in styrene. Effect on flammability in polystyrene nanocomposites

“…The higher the swelling volume the higher the degree of organoclay exfoliation in polymer matrix after polymerization of styrene in the presence of organoclay. The use of other solvent mixtures (tetrahydrofuran and water) resulted in different clay intercalation with styrenevinylpyridine (SVP, 36.40 wt% styrene and 63.60 wt% 4-vinylpyridine) block copolymers in the in situ formation of polystyrene/clay nanocomposite and the most effective exfoliated nanocomposite, showed the highest thermal stability and the best dynamic mechanical responses [11]. The significant enhancement of both tensile and flexural strength in polymer/clay nanocomposites is usually attributed to the delaminated clay formation [12].…”