Abdessalem Derdouri

Carbon Nanotube Conductive Networks through the Double Percolation Concept in Polymer Systems

Abstract We investigated the electrical conductivity and percolation behavior of binary and ternary nanocomposites based on multiwalled carbon nanotubes (MWCNs) using polypropylene (PP) and a blend of PP with cyclic butylene terephthalate (CBT). The nanocomposites were prepared by diluting a commercial 20 %wtMWCNT PP masterbatch using optimized melt-mixing conditions. The concentration of carbon nanotubes in the diluted PP samples was as low as 0.5 % and as high as 15 % in weight. For the PP/CBT blend CBT concentration was varied up to 40 %wt while the loading of CNT was from 0 to 5 %wt. SEM and TEM techniques were used to examine the quality of the dispersion and the formation of nanotube networks within the polymer matrix. TEM and Raman spectroscopy results showed that for the diluted PP/MWCNT composites the nanotubes are well aligned in samples obtained the microinjection molding process, although the level of alignment is less with crystalline PP than in an amorphous matrix such as polycarbonate (PC). FTIR and XRD results revealed that the orientation of both polymer chains and crystals decreased with the incorporation of nanotubes into PP. The electrical conductivity was also significantly altered by the nanotube alignment in a PP matrix, as was previously observed for PC/MWCNT composites; the conductivity decreased and the percolation threshold rose in highly sheared samples; however, the presence of a crystalline phase improved the conductivity even for high shear conditions through the phenomenon of double percolation threshold. This last concept refers to the requirement that the filler-rich phase be continuous and conductive and not to the existence of two percolation thresholds at two different CNT concentrations. The electrical conductivity of PP/CBT blends was also improved through a double percolation that is the basic requirement for the conductivity of the ternary nanocomposites.

Design Sensitivity Analysis Applied to Injection Molding for Optimization of Gate Location and Injection Pressure

Abstract In this work, we develop a numerical simulation method to optimize the injection molding process using the design sensitivity analysis (DSA). The optimization concerns the filling stage and focuses on the location of gates in the mold cavity as well as the injection pressure profile, in order to minimize the fill time. Since the problem to be solved involves transient flow with free surface (flow front), the direct differentiation method is used to evaluate the sensitivities of the Hele-Shaw, filling fraction and energy equations with respect to the design variables used in the analysis. The search domain parameterization is coped with using B-spline functions. Sensitivity and state equations are solved by means of finite element method. The proposed numerical approach is combined with the sequential linear and quadratic programming method of the design optimization tools (DOT) to find new design variables at the end of each complete filling simulation. Starting from any initial gate locations and injection pressure profile, the iterative optimization procedure enables us to find the optimal gate locations together with the optimal injection pressure profile. Finally, numerical results involving complex mold geometries are presented and discussed to assess the validity and robustness of the proposed method.

Rheology, Morphology and Temperature Dependency of Nanotube Networks in Polycarbonate/Multiwalled Carbon Nanotube Composites

We present several issues related to the state of dispersion and rheological behavior of polycarbonate/multiwalled carbon nanotube (MWCNT) composites. The composites were prepared by diluting a commercial masterbatch containing 15 wt% nanotubes using optimized melt‐mixing conditions. The state of dispersion was then analyzed by scanning and transmission electron microscopy (SEM, TEM). Rheological characterization was also used to assess the final morphology. Further, it was found that the rheological percolation threshold decreased significantly with increasing temperature and finally reached a constant value. This is described in terms of the Brownian motion, which increases with temperature. However, by increasing the nanotube content, the temperature effects on the complex viscosity at low frequency decreased significantly. Finally, the percolation thresholds were found to be approximately equal to 0.3 and 2 wt% for rheological and electrical conductivity measurements, respectively.

Rheological and Ultrasonic Monitoring of the In‐situ Polymerization of Cyclic Butylene Terephthalate

Dynamic rheological measurements were used to monitor the in‐situ polymerization of cyclic butylene terephthalate (CBT) oligomers. The material is a two‐component system where the catalyst was pre‐blended within the CBT oligomers. The in‐situ polymerization of CBT was also investigated under various conditions of temperature using a device that combines ultrasonic and volumetric measurements. From the measurements of sample volume, ultrasonic velocity and attenuation, a dynamic viscosity can be calculated and used to characterize the polymerization process. The results from both the rheological and ultrasonic approaches will be compared and discussed.

Experimental And Numerical Study Of The Melt Behavior During The Injection Molding Process

In this paper the non‐isothermal flow of a melt polymer during the filling of a rectangular plate is investigated both experimentally and numerically. Two pressure sensors were mounted flush on the slightly tapered rectangular sprue of a center gated plate mold to monitor the time evolution of the wall shear stress prior to entering the cavity. For large injection speeds the pressure drop in the sprue presents a maximum shortly after the beginning of the injection. After this point, the wall shear stress in the sprue drops remaining relatively constant during the late stage of the filling. At low injection speed, the wall shear stress in the sprue increases in time continuously because of the cooling. The filling of the plate is computed using a 3D finite element code and the predicted pressure drop in the sprue is compared with the measurements. Solutions obtained with and without considering the flow in the nozzle illustrate that the nozzle induces important thermal effects and thus need to be taken int...

Experimental and Numerical Investigation of the Flow Behavior in a Tapered Rectangular Sprue

The present study is part of a continuing effort to obtain a better understanding of the rheological behavior during the injection molding of unfilled and reinforced polymers and help improve the prediction by numerical three dimensional simulation of the process. The slightly tapered rectangular sprue of a centrally gated plaque mold was equipped with flush mounted pressure sensors to monitor the time evolution of the wall shear stress prior to entering the cavity. Two Polycarbonate with different zero-shear rate viscosities were tested at various injection speeds. Atter an initial rise, the wall shear stress in the sprue remains constant during the filling stage of the mold. The transient shear viscosity was determined from the known volumetric rate using a simplified one-dimensional flow approach and compared to the viscosity measured by traditional off-line rheometers. A finite element three-dimensional code is used to simulate the flow in the sprue with small and large width over thickness ratios. The pressures predicted are used in combination with the simplified theory to calculate the viscosity and compare the results from the experiments.Copyright