Production and properties of flexible sodium silicate films from rice hull ash silica

Flexible self-supported films were produced from rice hull ash silica extract. Silica was extracted from rice hull ash using 1 N NaOH. This extract was concentrated by volume reduction and adjusted to 3 N NaOH. Concentrated silica extracts in 3 N NaOH solution were used to produce flexible silicate films. XRD analysis showed that silicate existed in an amorphous form in the film. The effect of methyl oleate (MO) as a plastisizer in the presence and absence of the emulsifier lecithin on the film properties was also investigated. FTIR data indicated that the interaction of silicate and MO in the films was mainly due to siloxane groups. This interaction resulted in significant changes in film network and film flexibility. Percent elongations as measured by a texture analyzer for silicate film, silicate film with MO and silicate film with MO and lecithin were 12, 15 and 17, respectively. Mechanical strength of silicate films was not significantly affected by addition of MO and lecithin. All the silica based films were permeable to water vapor. However. they were excellent barriers for hexane and iso-octane. (C) 1999 Elsevier Science Ltd. All rights reserved.