Preparation and properties of LDHs/polyimide nanocomposites

Layered double hydroxides/polyimide (LDHs/PI) nanocomposites were prepared from solution of polyamic acid (polyimide precursor) and LDH–amino benzoate using N,N-dimethylacetamide as a solvent. LDH–amino benzoate (LDH–AB) was obtained by coprecipitation method. The amino benzoate, grafted on the surface of the Mg/Al nanolayers, as a connector improved the compatibility between the inorganic Mg/Al nanolayers and the organic polyimide molecules. The dispersion behavior of Mg/Al nanolayers was investigated by transmission electron microscopy and X-ray diffraction, indicating that the Mg/Al nanolayers were exfoliated in PI matrix to form LDH–AB/PI nanocomposites. The maximum tensile strength and elongation of the LDH–AB/PI nanocomposites were found with the LDH–AB content of 5 and 4 wt%, respectively. The initial tensile modulus of these nanocomposites was increased with the LDH–AB content. These nanocomposites exhibited higher storage and loss moduli compared to those of pure PI. Tg of these nanocomposites increased with the LDH–AB content. Coefficients of thermal expansion (CTE, below and above Tg) of these nanocomposites deceased with the LDH–AB content. The thermal properties of these nanocomposites were enhanced by the incorporation of Mg/Al nanolayers in PI matrix.