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Deconvoluting Nanofiller Reinforcement and Polymer Morphology Via Model Polymer Nanocomposites

Gowri Dorairaju1, Saurabh Toshniwal1, Kunal Tulsyan1, Daniel F. Schmidt1, and Emmanuelle Reynaud2. (1) Plastics Engineering, University of Massachusetts Lowell, 1 University Avenue, Lowell, MA 01854, (2) Mechanical Engineering, University of Massachusetts Lowell, 1 University Avenue, Lowell, MA 01854

In spite of substantial work in the field of polymer nanocomposites, generalized predictions of their mechanical behavior have not yet been achieved. In thermoplastic systems based on nanoclays in particular, substantial mechanical properties enhancements have been observed primarily in polar, semi-crystalline systems such as polyamide-6 [1,2] and poly(vinylidene fluoride) [3,4] – but always accompanied by substantial changes in the morphology of the semi-crystalline polymer. The convolution of these effects – the presence of stiff clay layers and the remodeling of the microstructure of the polymer – represents a significant obstacle in the path to understanding the mechanical properties of these materials.

In order to address this issue, we have chosen a fully amorphous polyamide as a matrix for the production of model nanoclay-based polymer nanocomposites that lack the morphological complexities associated with their semi-crystalline analogs. In particular, we report on the successful twin-screw extrusion and injection molding of systems based on Grilamid TR 90 in combination with Cloisite 30B using realistic, industrial-scale processes and equipment.

Structural analysis of these systems (SAXS, WAXS, TEM) confirms high levels of clay dispersion, consistent with the known compatibility of this nanoclay with polyamides in general. Thermal analyses (TGA, DSC) are used to confirm the clay content and the amorphous character of these materials. Finally, we present DMA data, simultaneous tensile testing / thermal imaging results, and SEM-EDS analyses of the rupture faces in order to shed light on the reinforcement mechanisms active in these systems, and draw comparisons with their semi-crystalline counterparts.

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2. ‘The chemistry of polymer-clay hybrids', A. Okada, A. Usuki, Materials Science and Engineering C, 3, 2, 1995, 109-115.

3. ‘Dramatic Enhancements in Toughness of Polyvinylidene Fluoride Nanocomposites via Nanoclay-Directed Crystal Structure and Morphology', D. Shah, P. Maiti, E. Gunn, D. F. Schmidt, D. D. Jiang, C. A. Batt, E. P. Giannelis, Advanced Materials, 16, 14, 2004, 1173-1177.

4. ‘Effect of Nanoparticle Mobility on Toughness of Polymer Nanocomposites', D. Shah, P. Maiti, D. D. Jiang, C. A. Batt, E. P. Giannelis, Advanced Materials, 17, 5, 2005, 525-528.