## Water-Mediated Melt Compounding to Produce Thermoplastic Polymer-Based Nanocomposites: Structure-Property Relationships

• Nanotechnology is now recognized as one of the most promising areas for technological development in the 21st century. In materials research, the development of polymer nanocomposites is rapidly emerging as a multidisciplinary research activity whose results could widen the applications of polymers to the benefit of many different industries. Nanocomposites are a new class of composites that are particle-filled polymers for which at least one dimension of the dispersed particle is in the nanometer range. In the related area polymer/clay nanocomposites have attracted considerable interest because they often exhibit remarkable property improvements when compared to virgin polymer or conventional micro- and macro- composites. The present work addresses the toughening and reinforcement of thermoplastics via a novel method which allows us to achieve micro- and nanocomposites. In this work two matrices are used: amorphous polystyrene (PS) and semi-crystalline polyoxymethylene (POM). Polyurethane (PU) was selected as the toughening agent for POM and used in its latex form. It is noteworthy that the mean size of rubber latices is closely matched with that of conventional toughening agents, impact modifiers. Boehmite alumina and sodium fluorohectorite (FH) were used as reinforcements. One of the criteria for selecting these fillers was that they are water swellable/ dispersible and thus their nanoscale dispersion can be achieved also in aqueous polymer latex. A systematic study was performed on how to adapt discontinuousand continuous manufacturing techniques for the related nanocomposites. The dispersion of nanofillers was characterized by transmission, scanning electron and atomic force microcopy (TEM, SEM and AFM respectively), X-ray diffraction (XRD) techniques, and discussed. The crystallization of POM was studied by means of differential scanning calorimetry and polarized light optical microscopy (DSC and PLM, respectively). The mechanical and thermomechanical properties of the composites were determined in uniaxial tensile, dynamic-mechanical thermal analysis (DMTA), short-time creep tests, and thermogravimetric analysis (TGA). PS composites were produced first by a discontinuous manufacturing technique, whereby FH or alumina was incorporated in the PS matrix by melt blending with and without latex precompounding of PS latex with the nanofiller. It was found that direct melt mixing (DM) of the nanofillers with PS resulted in micro-, whereas the latex mediated pre-compounding (masterbatch technique, MB) in nanocomposites. FH was not intercalated by PS when prepared by DM. On the other hand, FH was well dispersed (mostly intercalated) in PS via the PS latex-mediated predispersion of FH following the MB route. The nanocomposites produced by MB outperformed the DM compounded microcomposites in respect to properties like stiffness, strength and ductility based on dynamic-mechanical and static tensile tests. It was found that the resistance to creep (summarized in master curves) of the nanocomposites were improved compared to those of the microcomposites. Master curves (creep compliance vs. time), constructed based on isothermal creep tests performed at different temperatures, showed that the nanofiller reinforcement affects mostly the initial creep compliance. Next, ternary composites composed of POM, PU and boehmite alumina were produced by melt blending with and without latex precompounding. Latex precompounding served for the predispersion of the alumina particles. The related MB was produced by mixing the PU latex with water dispersible boehmite alumina. The composites produced by the MB technique outperformed the DM compounded composites in respect to most of the thermal and mechanical characteristics. Toughened and/or reinforced PS- and POM-based composites have been successfully produced by a continuous extrusion technique, too. This technique resulted in good dispersion of both nanofillers (boehmite) and impact modifier (PU). Compared to the microcomposites obtained by conventional DM, the nanofiller dispersion became finer and uniform when using the water-mediated predispersion. The resulting structure markedly affected the mechanical properties (stiffness and creep resistance) of the corresponding composites. The impact resistance of POM was highly enhanced by the addition of PU rubber when manufactured by the continuous extrusion manufacturing technique. This was traced to the dispersed PU particle size being in the range required from conventional, impact modifiers.

$Rev: 13581$