Effect of pH on the Formation of Porous Clay Heterostructures (PCHs) and Hybrid PCHs (HPCHs)

A porous clay heterostructure (PCH) and hybrid organic-inorganic PCH (HPCH) were prepared through surfactant-directed assembly of tetraethoxysilane (TEOS) and TEOS/methyltetraethoxysilane (MTS) into the galleries of Na-bentonite clay, respectively. The reaction involves hydrolysis and condensation of TEOS and MTS in the presence of intragallery surfactant templates (cetyltrimethylammonium ion and dedecylamine). Before the synthesis, Na-bentonite clay was adjusted pH into 4 conditions including pH 9, 7, 5 and 3. To investigate the effect of pH on the formation of mesoporous structure and measure pore size, the products were characterized by N₂ adsorption and FTIR techniques. The results showed that the PCHs and HPCHs had surface areas of 501-668 and 469-582 m2/g, pore volume of 0.43 - 0.64 and 0.33-0.49 cc/g, and average pore sizes in the small mesopore to supermicropore range of 3.01-3.85 and 3.19-3.88 nm, respectively. New applications of the PCH and HPCH materials are expected in active packaging for entrapping systems. Each material in 1 wt% was mixed with surlyn ionomer 2 wt%, and polypropylene (PP) for preparation of PP nanocomposites via melt intercalation method. Subsequently, the nanocomposites were fabricated to thin film by blow film extrusion machine. To investigate gas permeability of PP/PCH and PP/HPCH nanocomposites, these films were measured oxygen and ethylene permeability. The results revealed that gas permeability of these nanocomposite films are less than that of PP virgin film. So these materials could be found new application in active packaging.