Effect of thermally stable oligomerically modified clay on the properties of aramid-based nanocomposite materials
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Muhammad Ilyas Sarwara) Department of Chemistry, Quaid-i-Azam University, Islamabad-45320, Pakistan; and Department of Materials Science and Engineering, University of Delaware, Newark, Delaware 19716 (Received 18 February 2008; accepted 21 August 2008)
Oligomerically modified reactive montmorillonite clay was used in the preparation of aramid-layered silicate nanocomposites. The dispersion behavior of organoclay was monitored in the aramid matrix synthesized from 4-aminophenylsulfone and isophthaloyl chloride in dimethylacetamide. These polyamide chains were end-capped with carbonyl chloride groups to interact chemically with oligomerically modified layered silicate. Thin composite films containing 2 to 20 wt% of organoclay were probed for x-ray diffraction (XRD), transmission electron microscopy (TEM), mechanical testing, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and water absorption measurements. XRD and TEM results described the distribution level of clay platelets and morphology of hybrid materials. Mechanical measurements revealed that modulus and strength improved up to 6 wt% clay loading, while toughness of nanocomposites increased with the addition of 2 wt% clay content in the matrix. The elongation showed a decreasing trend with increasing clay content in the hybrids. Thermal-decomposition temperatures of the nanocomposites were in the range 225 to 450 °C. The glass-transition temperature increased up to 12 wt% addition of organoclay in the matrix relative to pristine aramid depicting interfacial interactions among the phases. Water absorption of the nanocomposites reduced with augmenting organoclay loading, indicating decreased permeability.
I. INTRODUCTION
The uniform distribution of organoclays into the host polymer matrices can lead to enhancement in the mechanical, thermal, and flammability properties of the resulting nanocomposites. Many studies have been documented with improved properties including aliphatic polyamides,1–4 polystyrene,5,6 PMMA,6,7 polypropylene,8,9 epoxies,10,11 polyester,12 poly(etherimide),13 polyimides,14–16 elastomers,17,18 PVC, and PVC-coPVA-PVAc.19 Montmorillonite (MMT) clay exists as stacks of platelets due to strong electrostatic forces between the layers and usually disperses poorly in hydrophobic polymers. The replacement of interlayer sodium ions with organic cations usually increases d-spacing between the layers facilitating delamination of clay platelets in the matrix. The common choices for organic a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0406 3330
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 12, Dec 2008 Downloaded: 25 Mar 2015
modifiers are ammonium ions of long-chain aliphatic molecules. The organoclays preferred for dispersion in the heat-resistant polymers stipulated enough thermal stability to withstand severe conditions, particularly in polymer matrices used to prepare nanocomposites either through melt intercalation or cured at high temperature to
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