Preparation and characterisation of hydrotalcite/carboxyadamantane intercalation compounds as fillers of polymeric nanocomposites

Abstract

Mono- and di-carboxyadamantane derivatives were intercalated via ion-exchange procedure onto hydrotalcites with formula [Zn_0.65Al_0.35(OH)₂](A)_0.35·nH₂O where A is Cl^– or ClO₄^–. Furthermore, an intercalation compound of [Mg_0.65Al_0.35(OH)₂](CO₃)_0.175·0.5H₂O containing the mono-carboxyadamantane has been obtained by using the “memory effect” of the hydrotalcite. The obtained materials were characterised for their composition, thermal behaviour, X-ray diffraction patterns, FT-IR absorption spectra and BET specific surface areas. Structural and chemical considerations indicated that mono-carboxylic guests are accommodated in the interlayer region as an ordered bifilm of anions while the di-carboxylic guests give rise to a bifilm of partially interdigitated anions. The presence of hydrophobic anions makes the interlayer region of the hydrotalcites compatible with hydrophobic polymers, such as medium density polyethylene. As an example, the preparation and characterisation of a nanocomposite of polyethylene filled with MgAl hydrotalcite/carboxyadamantane are reported. The nanocomposite, containing 5% w/w of inorganic residue, was prepared by melt compounding and was characterised with X-ray powder diffraction and thermogravimetric techniques. The obtained results showed that the presence of the organically modified hydrotalcite lamellae shields in part the polymer from thermal oxidation, increasing the degradation temperature by about 160 °C and producing a char residue greater than pure polyethylene.