Influence of polymer co-intercalation on guest release from aminopropyl-functionalized magnesium phyllosilicate mesolamellar nanocomposites

Abstract

Protonation of the interlayer aminopropyl groups of a synthesized organo-functionalized 2 : 1 trioctahedral magnesium phyllosilicate was used to prepare exfoliated cationic organoclay dispersions that were subsequently re-assembled in the presence of anionic guest molecules, such as ibuprofen, epigallocatechin gallate (EGCG), poly(styrene sulfonate) (PSS), poly(acrylic acid) (PAA), or polymethyl-acrylamidopropanesulfonic acid (PMAPSA), to produce a range of novel intercalated layered nanocomposites. Re-assembled organoclays containing ibuprofen or epigallocatechin gallate co-intercalated with various types of polymer molecules were also prepared. In each case, X-ray diffraction studies confirmed the formation of intercalated or co-intercalated lamellar nanocomposites with expanded interlayer (d₀₀₁) spacings. We demonstrate that pH dependent oxidation of EGCG is curtailed when intercalated within the organoclay interlayers. Significantly, the ibuprofen release profiles in water or simulated gastric fluid (pH = 2) indicated that extraction of the biomolecule into solution could be delayed or accelerated depending on the type of polymer co-intercalated. Whereas co-intercalation of PSS increased the rate of ibuprofen release, extraction of the drug from nanocomposites containing PMAPSA was significantly reduced. In contrast, PAA-containing ibuprofen/organoclay nanocomposites showed release profiles that were only marginally reduced compared with those for ibuprofen alone. Steric and electrostatic interactions between the entrapped polymer and drug molecules are discussed to account for these observations.