Distributive mixing of carbon nanotubes in poly(caprolactone) via solution and melt processing: Viscoelasticity and crystallization behavior versus mixing indices

Abstract

Different mixing processes give rise to significant differences in the agglomeration and deagglomeration of nanoparticles and how they are mixed and distributed within a polymeric matrix. Here poly(caprolactone), PCL, was compounded with carbon nanotubes, CNTs, at a weight fraction of 0.5% (volume fraction, U 5 0.0027), using both solution and melt processing methods. Microscopy, image analysis, and thermogravimetric analysis, TGA, were used to define and characterize the distributions of the CNT-rich domain sizes and to obtain quantitative mixing indices at different scales of examination. The presence of the CNTs led to the shearinduced crystallization of PCL under conditions at which pure PCL would not crystallize and the microstructures obtained upon shear-induced crystallization were documented via X-ray diffraction, differential scanning calorimetry, and rheological characterization. Shear-induced crystallization occurred at a faster rate (smaller induction times) when the nanocomposites exhibited greater mixing index values. The shear-induced crystallization behavior was found to be a more sensitive indicator of the distributive mixing states of the CNTs in comparison with the widely used linear viscoelastic rheological material functions. The demonstrated methodologies can be used as complementary tools for processing and development of nanocomposites to achieve consistent and reproducible microstructures at various scales of examination and functional properties.

Effect of multistage sonication on dispersive mixing of polymer nanocomposites characterized via shear‐induced crystallization behavior

“…The data in Figure can also be analyzed in terms of a Mixing Index as defined in the literature, which is a value between zero and one which indicates the mixedness of the samples (with values closer to one being better mixed). Mixing Index values of 0.961, 0.977, and 0.997 for a constant Stage 2 sonication time of 10 min and 0.974, 0.988, and 0.991 for a constant Stage 2 sonication time of 60 min, respectively, were calculated for these samples as highlighted in Figure .…”

“…The data in Figure 4 can also be analyzed in terms of a Mixing Index as defined in the literature, 39,40 Our earlier DSC studies 39 highlight the effect of shearing in comparison with quiescent conditions on the crystallinity of the PCL/ CNT nanocomposite samples. Thus to complement the TGA analysis, differential scanning calorimetry (DSC) can be used to examine the crystallization behavior of the samples as a function of Stage 1 and Stage 2 sonication time.…”

Shear viscosity and wall slip behavior of dense suspensions of polydisperse particles

“…Mixing indices can be based on the measurement of concentration variations within the mixture, via various methods including wide-angle x-ray diffraction and/or thermo-gravimetric analysis [92][93][94]. Mixing indices can provide a quantitative understanding of the effects of mixing dynamics and document the effects of the geometries and operating conditions that are used during batch and continuous mixing of concentrated suspensions on the homogeneity of ingredient distributions [12,95].…”

“…The thermo-mechanical history that the suspension is exposed to during processing dictates the homogeneity of the spatial distribution of the particles and consequently the resulting rheological and wall slip behavior [1][2][3][4][5][6]. Ultimate properties including electrical properties [4,7,8], fire retardance [9], crosslink density and swelling [10], energetic properties [11] and the development of crystalline morphologies following shearing [12] are dependent on the dynamics of the mixing processes.…”

Non‐isothermal crystallization of poly(ε‐caprolactone) nanocomposites with soy lecithin‐modified bentonite

“…Particularly, in recent years, PCL has been widely used in the preparation of blends with other biodegradable polymers such as polylactic acid and thermoplastic starch, or as matrix for nanocomposites preparation using natural fillers such as starch nanoparticles, carbon nanotubes, nanoclays, or cellulose nanocrystals . Among them, the use of nanoclay as reinforcement is highlighted thanks to the proven improvements in relevant application properties.…”