Studies on thermal and mechanical properties of polyimide–clay nanocomposites

Abstract

Nanocomposites from polyimide and clay were prepared aiming at finding a promising method for enhancing particularly the tensile modulus of polyimide films. Polyimide–clay hybrids were prepared by blending of poly(amide acid) and organically modified-montmorillonite (OMMT) as a type of layered clays. Poly(amide acid) was prepared from the reaction of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA). Also, poly(amide acid) from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) was prepared for comparison. OMMT was prepared by surface treatment of montmorillonite (MMT) with ammonium chloride salt of 12-aminolauric acid. XRD indicated that the OMMT layers were exfoliated and dispersed into the poly(amide acid) and polyimide film. Tensile properties measurements of polyimide–clay hybrids indicated that the addition of 2 wt.% of OMMT increased the tensile modulus of BPDA/PDA polyimide up to 12.1 GPa, which is ca. 42% higher than the pristine BPDA/PDA polyimide. Tensile modulus of PMDA/ODA also increased up to 6.2 GPa, which is ca. 110% higher than that of the original PMDA/ODA polyimide. The glass transition temperatures of the BPDA/PDA nanocomposites were higher than that of the original polyimide. The thermal expansion coefficient of the BPDA/PDA polyimide film decreased by the inclusion of clay. Isothermal and dynamic TGA showed that the both types of polyimide nanocomposites have higher decomposition temperatures in comparison with the original polyimides.