Stearate intercalated layered double hydroxides : methods and applications

Abstract

Stearate anions were successfully intercalated into the layered double hydroxide Mg4Al2(OH)12CO3.3H2O (LDH-CO3) by several methods to form LDH-SA. The intercalation method which involved the acid-base reaction between emulsified stearic acid (SA) and the carbonate anions in aqueous media was studied for the first time. This method led to the formation of more LDH-SA than well known methods such as melting the carboxylic acid in the presence of the LDH, allowing the interlayer region to swell in the presence of glycerol and reconstructing the calcined LDH in the presence of aqueous sodium stearate. Other literature methods involve ion-exchange of Cl- in LDH-Cl with stearate in aqueous sodium stearate, usually under N2 atmosphere. The methods developed in this study are more industrially viable because the more easily produced LDH-CO3 is used and no N2 atmosphere is necessary. The LDH-SA was successfully used to intercalate sodium polyvinyl sulphonate by an ion exchange with the intercalated stearate, without the need for a N2 atmosphere. This method of production could be useful for the production of nanocomposites in general, for example anionic polymer chains (such as DNA) and anionic clays. The same intercalation reaction was allowed to take place in situ during the formation of dextrin-alginate-glycerol film solutions in water-ethanol media. The stearate intercalated as a bilayer in the interlayer region of the LDH. The SA to LDH ratio was varied from 100% SA to 100% LDH. Around the middle of the series a minimum water vapour permeability (WVP) was obtained, which corresponded to an 80% reduction in WVP in comparison to the reference (blank) film. Around the middle of the series a maximum increase in Young’s modulus, corresponding to a 213% increase in comparison to the blank film, was obtained. Around the middle of the series a reduction in the intensity of the basal reflection and interlayer distance showed that some exfoliation (delamination) took place.