Comparison of the physical properties of different polyimide nanocomposite films containing organoclays varying in alkyl chain lengths

Abstract

Poly(amic acid) (PAA), a precursor of polyimide (PI), is synthesized by reacting dianhydride 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride with diamine 3,3′-dihydroxybenzidine in N,N′-dimethylacetamide. Organoclays with different alkyl chain lengths were dispersed in PAA, and the weight percentages (wt%) of the organoclays varied. The PI hybrid films were prepared over multiple steps under heat treatment conditions. Bentonite (BTN) was used as the pristine clay, and octylamine (C8) and hexadecylamine (C16) were used to chemically modify the surface of BTN to obtain the desired organoclay samples. Organoclays C8-BTN and C16-BTN were dispersed in a PI matrix, and the organoclay content varied in the range of 1–9 wt%. The thermal, morphological, and optical properties of the PI hybrid films were investigated based on the organoclay content. Although the thermal stability of the PI hybrid film improved when a small amount of organoclay was added, it decreased when the nano-filler content exceeded a certain critical content. Specifically, in the hybrid containing C8-BTN, the critical content is 5 wt%, while in the hybrid with C16-BTN, the critical content is 7 wt%. In addition, the morphology of the clay dispersed in the matrix at the critical content showed the best dispersed phase. The physical properties (thermal characteristics, dispersibility, and optical transparency) of the PI hybrid film containing C16-BTN were better than those of the hybrid film containing C8-BTN. However, the thermal expansion of the C8-BTN hybrid was lower than that of the C16-BTN film at the same content.

Keywords

• polyimide
• nanocomposite film
• organoclay