Viscoelastic and Mechanical Properties of Polyimide-Clay Nanocomposites
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Viscoelastic and Mechanical Properties of Polyimide-Clay Nanocomposites Mohamed O. Abdalla, Derrick Dean*, Sandi Campbell1 Tuskegee-Center for Advanced Materials, 101 Chappie James Center, Tuskegee University, Tuskegee, Alabama 36088, 1NASA Glenn Research Center, Cleveland, Ohio, 44135. Abstract Polyimide-clay nanocomposites were prepared by blending 2.5 and 5 wt.% of PGV (Na+montmorillonite) and two organically modified PGV (PGVC10COOH, PGVC12) with a methanol solution of PMR-15 precursor. DMA results showed a significant increase in the thermomechanical properties (E′ and E′′) of 2.5 wt.% clay loaded nanocomposites in comparison with the neat polyimide. Increasing the clay loading to 5 wt.% degraded these properties. Higher Tgs were observed for 2.5 wt.% nanocomposites compared to the neat polyimide. A lower CTE was observed only for the PGV/PMR-15 nanocomposite. Flexural properties measurements for the 2.5 wt.% nanocomposites showed an improvement in the modulus, strength and elongation. This trend in the tensile properties was not observed for the 5 wt.% nanocomposites. 1. Introduction Only a few studies [1,2,3] have addressed the high performance thermosets nanocomposites such as PMR-15 (Fig 1.). Polymerizable reactive mixtures (PMR), polyimides are a group of a variety of thermosetting polymers used in high temperature environments (Tg ~ 300-430ºC). PMR-15 is a state of the art thermoset polyimide mainly used as a matrix resin for carbon fiber-reinforced composites for aerospace applications. It was perfected by Serafini et. al. [4] at NASA Lewis Research Center in 1972. The general advantages of PMR-15 composites are their thermal stability up to 300°C, good mechanical properties, relatively easy processing and low cost. In this study, we will report the synthesis and morphological characterization of layered silicates (LS) and organically-modified layered silicates (OLS)/PMR-15 nanocomposites. We will also report the viscoelastic and mechanical properties of the consolidated nanocomposites versus those of the neat polymer. 2. Experimental 2.1. Preparation of organically- modified layered silicates The OLS were synthesized by a cation-exchange reaction between the PGV (Na+montmorillonite, Nanocor, Inc.) and the ammonium salt of modifiers´ (dodecylamine and 11-aminoundecanoic acid). PGV was dispersed in water at 70-80ºC. Excess modifier (twice the cation exchange capacity of the clay) was dissolved in water at 70-80ºC and an equivalent amount of concentrated HCl acid was added to the solution. The dispersion of PGV was added to the solution of the modifier and this mixture was stirred vigorously for 1 h. A white precipitate was isolated by suction-filtration, placed in a 600 ml beaker with 400 ml of hot water, and stirred for 1 h. This process was repeated two times to ensure Q6.30.1 Downloaded from https://www.cambridge.org/core. University of Arizona, on 27 Jul 2018 at 06:48:46, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-726-Q6.
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