Improving the exfoliation of layered silicate in a poly(ethylene terephthalate) matrix using supercritical carbon dioxide

Abstract

Supercritical carbon dioxide (scCO2) was used as a processing aid to improve the level of exfoliation achievable in a PET-layered silicate nanocomposite produced from melt compounding. Layered silicate and scCO2 were allowed to mix for a period of time before being released into the second stage of a single screw extruder. The rapid expansion forced silicate particles into a modified hopper containing neat PET pellets.The mixture of layered silicate and PET was immediately melt mixed in a single screw extruder, cooled in a water bath and pelletized. Two sets of samples each containing layered silicate with different surface chemistries were produced with this method at 1, 3 and 5 wt% silicate. For comparison, samples of the same weight fraction and type of silicate were produced from a traditional melt compounding method. Wide angle x-ray diffraction (WAXD), mechanical testing and rheological analysis were used in order to characterize the silicate morphology, the composite mechanical properties and the relative amount of degradation between the various samples. Results show that scCO2 processed samples contain a higher degree of layered silicate exfoliation than samples produced with traditional melt compounding. Mechanical property improvements are shown to be dependent on the type of silicate surface modification employed. Finally, degradation of the PET matrix appears to be far less extensive in the scCO2 processed samples as shown from rheological data.iii Acknowledgements

Clay exfoliation and polymer/clay aerogels by supercritical carbon dioxide

“…Many reports show that different processing techniques based on supercritical carbon dioxide (scCO 2 ) constitute effective ways to increase dispersion and delamination in polymer/clay nanocomposites (Ma et al, 2007; Nguyen and Baird, 2007; Treece and Oberhauser, 2007; Samaniuk et al, 2009; Baker et al, 2011; Feng-hua et al, 2011; Chen et al, 2012). However, X-ray characterization of most samples show the presence of basal 00 l reflections, clearly indicating that treatments with scCO 2 are generally unsui to induce complete organoclay exfoliation (Ma et al, 2007; Nguyen and Baird, 2007; Treece and Oberhauser, 2007; Samaniuk et al, 2009; Thompson et al, 2009; Baker et al, 2011; Feng-hua et al, 2011; Chen et al, 2012).…”

“…However, X-ray characterization of most samples show the presence of basal 00 l reflections, clearly indicating that treatments with scCO 2 are generally unsui to induce complete organoclay exfoliation (Ma et al, 2007; Nguyen and Baird, 2007; Treece and Oberhauser, 2007; Samaniuk et al, 2009; Thompson et al, 2009; Baker et al, 2011; Feng-hua et al, 2011; Chen et al, 2012). …”

Improved mechanical properties of organoclay/nylon 6 nanocomposites prepared via a supercritical carbon dioxide‐aided, melt blending method

“…The use of supercritical carbon dioxide (scCO 2 ) in combination with single‐screw compounding has been considered as an alternative route for the preparation of polymer–clay nanocomposites in order to achieve similar dispersions as twin‐screw compounding . Nguyen and Baird developed a method to combine the benefits of melt compounding with the exfoliating capability of scCO 2 .…”

Enhanced dispersion of nanoclays in poly(ethylene terephthalate)/clay nanocomposites using supercritical carbon dioxide

“…Polyethylene terephthalate (PET), due to its versatile properties, such as low cost, excellent impact resistance, chemical resistance, transparency, and good barrier properties, has become one of the most widely applied semicrystalline polymers in a variety of applications, ranging from food and beverage pack‐aging to textiles to automotive components . However, to pursue higher performance applications, further improvement in mechanical and thermal properties of PET is needed .…”