Effects of Chain Extension and Branching on the Properties of Poly (Ethylene-Terephthalate)-Organoclay Nanocomposites
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Effects of Chain Extension and Branching on the Properties of Poly (Ethylene-Terephthalate)-Organoclay Nanocomposites Ali Emrah Keyfoglu and Ulku Yilmazer Department of Chemical Engineering Middle East Technical University Ankara,Turkey, 06531 ABSTRACT The effects of chain extension and branching on the properties of nanocomposites produced from recycled poly (ethylene-terephthalate) and organically modified clay were investigated. As the potential chain extension/branching agent, maleic anhydride (MA) and pyromellitic dianhydride (PMDA) were used. The nanocomposites were prepared by twinscrew extrusion, followed by injection molding. Recycled poly (ethylene-terephthalate) was mixed with 2, 3 or 4 weight % of organically modified montmorillonite. During the second extrusion step, 0.5, 0.75 or 1 weight % of MA or PMDA was added to the products of the first extrusion. The effects of the sequence of addition of the ingredients on the final properties of the nanocomposites were also investigated. X-Ray Diffraction analysis showed that, the interlayer spacing of Cloisite 25A expanded from 19.21 Ǻ to about 28-34 Ǻ after processing with polymer indicating an intercalated structure. PMDA content, MA content and screw speed did not have a significant effect on the expanded interlayer distance. In the first extrusion step, nanocomposites containing 3% organoclay content gave significant increase in Young’s modulus and decrease in elongation at break values indicating good interfacial adhesion. After the addition of anhydrides, it was observed that, in general PMDA improved the mechanical properties of the nanocomposite owing to the branching and chain extension effects that increase the molecular weight. However, MA did not significantly improve the properties, since in this case the chain scission seemed to be more dominant. INTRODUCTION During reprocessing, PET undergoes three different degradation phenomena namely: thermal, mechanical and hydrolytic chain scission. It is known that chain extenders are low molecular weight compounds that can be used to increase the MW of polymers [1]. These are polyfunctional compounds, capable of fast reactions with the hydroxyl or carboxyl end groups of PET. In this study, maleic anhydride (MA) and pyromellitic dianhydride (PMDA) were used as potential chain extenders to overcome the problem of low molecular weight. In the scope of this study, the selected parameters were the organoclay content, sequence of addition of the organoclay and the chain extender type and content. The effects of the selected process parameters on the morphology and mechanical properties of the materials were examined by X-Ray Diffraction (XRD), Melt Flow Index (MFI) and tensile and impact tests.
EXPERIMENTAL Experiments were carried out with PET soft drink bottle regrind ([η] = 0.75 dL/g) purchased from Sasa Company of Adana, Turkey in the form of flakes. The clay used in this study was organically modified montmorillonite (Cloisite® 25A), produced by Southern Clay
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