High-density polyethylene (HDPE)/hydrotalcite nanocomposites were prepared and characterized with a partially neutralized sodium ionomer of poly(ethylene-co-methacrylic acid) (EMAA) as a compatibilizer. Moreover, nanocomposites based on this ionomer were characterized as patterns to analyze the interactions between the hydrotalcite sheets and the methacrylic groups on the ionomer. Hydrotalcite particles were organically modified with sodium dodecyl Sulfate ions. Their presence in the interlayer space was confirmed by means of Fourier transform infrared spectroscopy (FTIR) and Xray diffraction (XRD). Morphological analysis carried out with XRD and transmission electron microscopy (TEM) revealed the partially exfoliated/intercalated structure achieved in the nanocomposites. The mechanical properties of the HDPE nanocomposites mainly depended on the nature of the polymer matrix. Higher values of the tensile strength and Young's modulus were found in the EMAA nanocomposites. Thermogravimetric analysis (TGA) showed that hydrotalcite particles improved the thermal stability and delayed the onset decomposition temperature of both HDPE and EMAA nanocomposites. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 950-958, 2009