For polymer nanocomposites, the small size of the fillers makes it difficult to analyze the degree of mixing quantitatively and often requires direct assessment via transmission electron microscopy (TEM). To date, qualitative comparisons and indirect measurements of the degree of mixing by measurement of certain properties are the most common methods. Better methods to quantitatively characterize the degree of mixing in nanocomposites would aid in studies investigating the effect of process conditions on the mixing behavior. Alumina/PET nanocomposites of identical composition, but with different degrees of mixing were prepared using a batch mixer. For evaluation of the degree of mixing with respect to both dispersion and distribution, three different techniques were applied and compared. TEM particle density was useful for dispersion, but did not adequately characterize distribution, while the Morisita's index gave poor results due to a wide range of effective particle sizes. Both methods ranked the samples differently compared to direct visual observation. In contrast, the skewness calculated by the quadrat method produced results consistent with visual rankings, and was found to be most effective in comparing and quantifying the degree of mixing. Although the quadrat method requires proper selection of quadrat size for a particular particle concentration, the skewness from the quadrat method was found to be most suitable as a standard index for the degree of mixing in nanocomposites. The usefulness of the quadrat method was verified using a second set of nanocomposites prepared by a twin screw extruder showing the potential for application of this technique for process development and quality control in commercial nanomanufacturing processes.

Elastomers show improved properties when reinforced with nanoclay at low filler loadings, but dispersion of the clay is difficult in non‐polar polymers, such as ethylene propylene diene monomer (EPDM). In this work several compatibilization approaches were studied, including the addition of EPDM modified with maleic anhydride (EPDM‐g‐MA) and the use of organoclay modified with maleic anhydride‐grafted liquid vinyl polybutadiene (LVPB‐g‐MA). The use of LVPB‐g‐MA‐modified organoclay increased the degree of dispersion as measured by X‐ray diffraction, giving increased thermal stability and modulus, and decreased swelling. Flame resistance was poorer for the EPDM/LVPB‐g‐MA‐modified organoclay system compared to the unmodified EPDM/organoclay compound. The resistivity of the nanoclay‐filled composites was lower than the reference EPDM compound, but dielectric properties for the LVPB‐g‐MA modified organoclay were similar to the reference.magnified image

Polymer nanocomposites have been studied extensively, but few references mention the importance of processing and how to characterize the degree of mixing. In this work, we report the influence of fill factor on the degree of mixing and thermal properties for a nanocomposite system consisting of alumina nanoparticles in polyethylene terephthalate (PET) prepared in a batch mixer. The degree of mixing for the resultant polymeric nanocomposites was quantified by three different techniques; TEM particle density, Morisita's index, and skewness. All of these methods quantify the degree of mixing based on the number of the particles in selected areas of TEM images using image analysis software. TEM particle density and skewness gave similar results, with a maximum in the degree of mixing around a fill factor of 0.70, while Morisita's index displayed a constant increase in degree of mixing with increasing fill factor. Tg was depressed by the filler and with increasing degree of mixing. The depression of Tg in the composite was maximized at a fill factor of 0.70, confirming that the analysis of TEM particle density and skewness are valid techniques to assess the degree of mixing. POLYM. ENG. SCI., 47:2049–2056, 2007. © 2007 Society of Plastics Engineers

Alumina/poly(ethylene terephthalate) nanocomposites were prepared by melt compounding with a twin-screw extruder. The melt temperature, screw rotation speed, and feed rate were selected as important processing parameters, and their effects on the degree of mixing were studied with full-factorial, two-level experimental design. To quantitatively assess the effects of the processing parameters, the degree of mixing of the nanocomposites was evaluated by the skewness of the quadrat method based on the number of particles in transmission electron microscopy images. The screw speed was found to be the most important processing parameter controlling the degree of mixing under the conditions in this investigation. The specific energy input (SEI), related to the shear intensity, was found to correlate closely to the degree of mixing. The degree of mixing improved with increased SEI up to a limiting value, termed the critical SEI, indicating that there may be a critical value required for the optimum dispersion of a given system. A modeling approach was proposed to determine the critical SEI needed for complete mixing. Initial results showed that the critical SEI predicted by this model was within a factor of 3.5 of that obtained experimentally, demonstrating the utility of this approach for the dispersion of nanofillers.