Experimental and theoretical studies of agglomeration effects in multi-walled carbon nanotube-polycarbonate melts

Abstract

Abstract. In this study we report on morphological and rheological characterization of multi-walled carbon nanotube (MWNT)-polycarbonate composites produced by injection molding. The main focus is to carry out nonlinear viscoelastic experiments that allow following the structural rearrangements of carbon nanotubes in the polycarbonate melt. Small angle X-ray scattering reveals only a slight orientation of MWNTs in the as-received samples, i.e. after application of extremely high shear rates. Thus, the main structural effect observed during the stress growth experiment is the breakage of MWNT agglomerates. To study this effect in detail a flocculation experiment, in which the sample undergoes oscillatory deformation first at a small strain amplitude in the linear regime succeeded by higher amplitudes in the nonlinear regime, has been carried out. The agglomeration process manifests itself in an increase of the storage and loss moduli in the linear regime, whereas the deagglomeration process does vice versa. The corresponding effects can be described in the frame of a superposition approach that takes into account the stress contribution of the polycarbonate matrix, the hydrodynamic reinforcement due to embedded nanotubes and the viscoelastic stress due to the presence of a MWNT-network.

Viscoelastic melt rheology and time–temperature superposition of polycarbonate–multi-walled carbon nanotube nanocomposites

“…A region where moduli are independent of strain amplitude then appears with increasing amplitude, extending to strains beyond 10 % strain for the unfilled PC, but only to 0.5 % strain for the filled PC. The earlier onset of nonlinearity has been previously attributed to the effect of strain amplification: the matrix experiences a higher local strain than the macroscopic strain due to the presence of the stiff nanotubes (Richter et al 2009;Costa et al 2008). This effect is generally enhanced by confinement of polymer chains located near the surface of a nanotube (Stöckelhuber et al 2011;Vilgis 2005).…”

Superposition approach for description of electrical conductivity in sheared MWNT/polycarbonate melts

“…In the case of random orientation distribution of rod-like inclusions one obtains the isotropic conductivity of composite which is proportional to the isotropic matrix conductivity with the coefficient of proportionality given by Equation (2). Fitting the viscoelastic data for the same MWNTpolycarbonate composite, we found that the average aspect ratio of the multi-wall carbon nanotubes is about 40 [42]. This value roughly corresponds to the ratio of the Kuhn segment length, reported for the carbon nanotubes to be about 1 !m [45], to the nanotube diameter (13-16 nm).…”

“…to the conditions relevant for nanocomposite processing. Theoretical predictions at the temperature of 340°C, which was found to be optimal for the injection moulding of MWNT/polycarbonate melts [42], are shown on the same Figures 5a and 5b as a black solid line. Additionally, on Figure 5d we present the model predictions for the system with 5 wt% MWNTs at three melt temperatures (265, 295 and 340°C).…”

“…To describe shear-induced changes in the electrical conductivity of a polymer melt filled with attractively interacting conductive particles, we propose to use a superposition approach similar to that applied by us recently for description of viscoelastic properties of the same nanocomposite system [42]. In the framework of superposition approach we assume that the filler particles can be divided into the percolating and non-percolating phases (see Figure 1).…”

Nanocomposites of Multiphase Polymer Blend Reinforced with Carbon Nanotubes: Processing and Characterization

“…Carbon nanotubes orientation in the final nanocomposite and agglomeration effect appearing during injection molding has been investigated with rheology tests showing the indication of nanofiller alignment sensitivity to the high shear conditions. [103] Visco-elastic properties of matrix in presence of nanofiller network is strongly related to CNT re-agglomeration process. Various methods are used to carry out such functionalization, with the use of main types polymerizations including ionic, [110][111][112] redox [113] and metallocene catalysis [114][115] as well as electrochemical grafting [116] used widely e.g.…”