Creep Behavior of Polystyrene/Fluorohectorite Micro‐ and Nanocomposites

Summary: Pristine FH is incorporated into a PS matrix by melt blending with and without latex precompounding of PS and FH. Direct melt blending results in microcomposites, whereas the latex‐mediated (masterbatch) technique results in PS/FH nanocomposites. The tensile creep response of the micro‐ and nanocomposites are determined in short‐term creep tests. The resistance to creep is improved with increasing dispersion of FH in the PS matrix. Master curves (creep compliance vs. time), constructed based on isothermal creep tests performed in the temperature range between 5 and 45 °C, show that the FH reinforcement affects mostly the initial creep compliance (interphase effect). On the other hand, the stable creep is matrix (bulk) dominated. It is established that the Williams‐Landel‐Ferry equation is fairly applicable to the creep results.

Scheme of the change of creep compliance as a function of time for micro‐ and nanocomposites with an amorphous matrix.     

Effect of nanofiller aspect ratio on the stress relaxation and creep response of toughened pom composites

Ternary composites composed of polyoxymethylene (POM), polyurethane (PU), and sodium fluorohectorite (FH) or sodium bentonite (BN) were produced by the melt compounding masterbatch (MB) technique. The related MB was produced by mixing the PU latex with water-swellable FH or BN. The dispersion of the nanofillers in the composites was studied by X-ray diffraction techniques. The crystallization of the POM-based systems was inspected by polarized optical microscopy (PLM). The stress relaxation and creep properties of the composites were determined in short-time stress relaxation and creep tests (creep at various temperatures), respectively. The POM/PU/FH composites produced by the MB technique outperformed the POM/PU blend and the POM/PU/BN system in respect to most of the stress relaxation and creep characteristics. This fact was attributed to the higher aspect ratio of FH compared with that of BN. The master curves (creep compliance vs. time) constructed by employing the time-temperature superposition principle showed that the Findley power law was fully applicable to the experimental results obtained.     

Processing,structure, and mechanical properties of alumina-nanofilled polystyrene composites

Binary composites composed of polystyrene (PS) and a synthetic boehmite alumina were produced by using the water-mediated melt compounding (WMC) and direct melt compounding (DMC) techniques. The alumina particles were dispersed in water at ambient temperature. The aqueous alumina suspension was injected into molten PS in a twin-screw extruder to prepare reinforced polymer composites. The dispersion of the alumina was studied by transmission and scanning electron microcopy techniques (TEM and SEM, respectively). The mechanical and thermomechanical properties of the composites were determined by employing a dynamic-mechanical thermal analysis (DMTA) and short-time creep and uniaxial static tensile tests. It was found that the direct melt compounding of the alumina with PS resulted in microcomposites, whereas the water-mediated melt compounding technique gave rise to nanocomposites. The incorporation of alumina into the PS nanocomposites increased their stiffness, tensile strength, and creep resistance. However, the elongation of the PS nanocomposites at break was smaller than that of the PS microcomposites.     

Novel method for dispersion of multiwall carbon nanotubes in poly(ethylene oxide) matrix using dicarboxylic acid salts

A simple and novel aqueous method was elaborated to disperse multiwall carbon nanotubes (MWCNT) in a poly(ethylene oxide) (PEO) matrix using the sodium salts of suberic acid (half and fully neutralized versions, HNSA and FNSA, respectively) as the modifiers. The incorporation of HNSA significantly improved the dispersion of MWCNT in PEO as reflected in a significant increase in melt viscosity and storage modulus in rheological measurements and dynamic mechanical thermal analysis, respectively. FNSA was proved to be the less efficient in this respect. This was explained in terms of cation‐Π (between FNSA, HNSA, and electron cloud of the CNT) and H‐bonding interactions (between HNSA and PEO) in accordance with Fourier transform infrared spectroscopic results. The dielectric and crystallization behaviors of the PEO/MWCNT/salt systems were studied and discussed, as well. The advantage of this method, applicable for water soluble polymers, is that it does not fully destroy the Π electron cloud of CNT opposed to chemical functionalization techniques. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1156–1165, 2009     

Structure-stress relaxation relationship in polystyrene/fluorohectorite micro-and nanocomposites

Sodium fluorohectorite (FH) was incorporated into polystyrene (PS) in amounts of 4.5 and 7 wt.% by melt mixing, with and without latex precompounding. The latex precompounding was used for the latex-mediated predispersion of FH particles. The related masterbatch was produced by mixing PS latex with the water-swellable FH, followed by drying. The dispersion of FH in PS was studied by transmission-, scanning electron-, and atomic force microscopy techniques (TEM, SEM, and AFM, respectively). The stress relaxation in the PS composites was determined in short-term isothermal tests. The latter were performed at various temperatures between 25 and 75°C. The direct melt mixing of FH with PS resulted in microcomposites, whereas the masterbatch technique gave rise to nanocomposites. The master curves (relaxation modulus vs. time), constructed by applying the time-temperature superposition principle (TTSP), showed that the Williams-Landel-Ferry (WLF) equation, the Maxwell model, and the Findley power law were fairly applicable to the experimental results obtained. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 5, pp. 709–722, September–October, 2008.     

Experimental comparison of manufacturing techniques of toughened and nanoreinforced polyamides

Composites consisting of polyamide-6 (PA-6), nitrile rubber (NBR), and sodium fluorohectorite (FH) or alumina silicate (Sungloss; SG) were produced by different techniques with latex precompounding. Their tensile and thermomechanical properties were determined by using tensile tests and a dynamic-mechanical analysis, performed at various temperatures. The PA-6/NBR composite systems produced by the direct melt compounding outperformed those obtained by using the masterbatch technique with respect to the strength and ductility, but the latter ones had a higher storage modulus.     

Investigation of the rheological properties and die swell of polylactic acid/nanoclay composites in a capillary rheometer

The purpose of this research was to investigate the rheological behavior and extrudate swell of polylactic acid (PLA) filled with a nanoclay. The effects of the amount of nanoclay and surface treatment were studied by a capillary rheometer. The dispersion of the nanoclay was inspected by using the scanning electron microscopy. Generally, PLA/nanoclay composites exhibited a pseudoplastic rheological behavior as the shear stress and die swell increased with increasing shear rate. However, the shear viscosity decreased. The die swell also increased with increasing shear stress. The elongation viscosity decreased with increasing elongation rate. The incorporation of nanoclay decreased the shear stress and shear viscosity to a lesser degree than the elongation viscosity.