Quantitative analysis of nanoscale electrical properties of CNT/PVDF nanocomposites by current sensing AFM

Probing 3D percolation of a CNT/polymer nanocomposite system with CS-AFM, supported by complementary techniques to understand the dispersion matrix.

Influence of Melt-Mixing Process Conditions on Mechanical Performance of Organoclay/Fluoroelastomer Nanocomposites

In this study, Cloisite 20A, an organically modified Montmorillonite (Mnt), has been incorporated into Fluoroelastomer (FKM) through melt intercalation technique. Since the nanocomposite preparation method and conditions, and consequently, the resulting morphology play a critical role in the final properties, the effect of different process conditions such as time, temperature, and shear rate on the vulcanization, thermal and mechanical properties have been investigated. The morphology of nanocomposites, prepared at different melt-mixing conditions, was studied using X-ray diffraction (XRD). Rheological, thermal and mechanical behaviors were investigated by moving die rheometer (MDR), thermal gravimetric analysis (TGA), and tensile strength test respectively. Also, the crosslinking density has been measured for the nanocomposites. The best mechanical performance of clay/FKM nanocomposites was attained by optimization of the melt-mixing conditions. We achieved the following enhancements for FKM by clay incorporation: enhancement of tensile strength up to 70 %; elongation up to 94 %; and modulus up to 405 %. Process temperature was found to have a critical role in the final properties of the nanocomposites, while mixing residual time and shear rate had a moderate effect. The most desirable properties and curing behaviors, including highest maximum torques, cure rates, crosslinking densities, fast crosslinking kinetics, high intercalation and best improved tensile strengths, resulted with specific combination of melt-mixing parameters.

PVDF/Carbonnanotubes/Nanoclay Composites for Piezoelectric Applications

Poly(vinylidene) fluoride (PVDF) nanocomposite samples were prepared by incorporation of carbon nanotubes (CNT) and nanoclay into PVDF using a twin screw extruder. Carbon nanotube was added to improve electrical conductivity and nanoclay was included to enhance β crystal formation for piezoelectric property. X-ray diffraction (XRD) results showed that partial melt intercalation of PVDF in clay was achieved. The XRD results also revealed that CNT and nanocaly addition increased β phase crystal amount in PVDF. FTIR spectroscopy measurements confirmed the XRD results and showed that the effect of nanoclay on β phase crystal formation of PVDF was more prominent than CNT. It was found that shear rate applied during crystallization would improve β phase crystal formation but only for the neat PVDF. Electrical conductivity results showed that addition of CNT improved conductivity as a percolation of 2 wt.% was observed. It was found that dispersion of CNT into PVDF matrix is very crucial for obtaining a higher conductivity. The results showed that clay incorporation into CNT nanocomposite improved electrical conductivity. The TEM micrographs showed bundles of CNT were adhered to clay particles. That was considered an indication of affinity between CNT and organically modified clay. The results of compounding of CNT and nanoclay with PVDF in batch mixer also revealed improvement in electrical conductivity when clay was added into PVDF/CNT composite in melt state. The conductivity improved with mixing time for both systems: PVDF/CNT and PVDF/CNT/nanocaly.

On-line Visualization of PS/PP Melting Mechanisms in a Co-rotating Twin Screw Extruder

The melting and deformation mechanisms of polystyrene (PS) and polypropylene (PP) blends were investigated through on-line visualization of the co-rotating twin-screw extrusion process. Two compositions, PP/PS (80:20) and PS/PP (80: 20) were chosen as the model systems for this study. A sliding barrel technique was used to realize the on-line visualization using a glass window in the barrel. The axial temperature and pressure profiles along the screw channel were measured using the same sliding technique. It was found that in the PP/PS (80:20) blend, in which PP was the major phase, there was a combined melting of PS and PP, whereas in the PS/PP (80:20) blend, in which PS was the major phase, there was initial melting of PS alone and then combined melting of PS and PP. In the partially filled region, heat conduction from the hot barrel was the major source for heating polymer pellets under the conditions studied here; while in the fully filled region, viscous energy dissipation (VED) generated most of the heat for melting of polymer pellets. The pressure profiles along the extrusion channel gave us insight into the melting process for the two blends. It was found that if there was some molten polymer in the fully filled region, the overall melting process was accelerated due to heating from viscous dissipation.

Electrical and rheological percolation of polymer nanocomposites prepared with functionalized copper nanowires

The morphological, electrical and rheological characterization of polystyrene nanocomposites containing copper nanowires (CuNWs) functionalized with 1-octanethiol is presented. Characterization by SEM and TEM shows that surface functionalization of the nanowires resulted in significant dispersion of CuNWs in the PS matrix. The electrical characterization of the nanocomposites indicates that functionalized CuNWs start to form electrically conductive networks at lower concentrations (0.25 vol% Cu) than using unfunctionalized CuNWs (0.5 vol% Cu). The organic coating on the nanowires prevents significant changes in the electrical resistivity in the vicinity of the percolation threshold. Percolated nanocomposites showed electrical resistivity in the range of 10(6)-10(7) Ω cm. The transition from liquid-like to solid-like behavior (rheological percolation) of the nanocomposites was studied using dynamic rheology at 200 °C. Unfunctionalized CuNWs result in electrical and rheological percolation at similar concentrations. Functionalized CuNWs show rheological percolation at higher concentration (1.0-2.0 vol%) than that required for electrical percolation. This is attributed to the decrease in the interfacial tension between nanowires and polymer chains and its effect on the viscoelastic behavior of the combined polymer-nanowire networks.

Microwave sintering process model

In order to simulate and optimize the microwave sintering of a silicon nitride and tungsten carbide/cobalt toolbits process, a microwave sintering process model has been built. A cylindrical sintering furnace was used containing a heat insulating layer, a susceptor layer, and an alumina tube containing the green toolbit parts between parallel, electrically conductive, graphite plates. Dielectric and absorption properties of the silicon nitride green parts, the tungsten carbide/cobalt green parts, and an oxidizable susceptor material were measured using perturbation and waveguide transmission methods. Microwave absorption data were measured over a temperature range from 20 degrees C to 800 degrees C. These data were then used in the microwave process model which assumed plane wave propagation along the radial direction and included the microwave reflection at each interface between the materials and the microwave absorption in the bulk materials. Heat transfer between the components inside the cylindrical sintering furnace was also included in the model. The simulated heating process data for both silicon nitride and tungsten carbide/cobalt samples closely follow the experimental data. By varying the physical parameters of the sintering furnace model, such as the thickness of the susceptor layer, the thickness of the allumina tube wall, the sample load volume and the graphite plate mass, the model data predicts their effects which are helpful in optimizing those parameters in the industrial sintering process.