| Polymer nanocomposites offer potential for a wide variety of applications due to the large improvements in properties at low filler loadings. These new materials can potentially be used for unlimited commercial applications and have received considerable attention in recent years. Developments in this field have been primarily carried out with nanoclays. Although structure-property relationships have been investigated thoroughly, commercialization is inhibited by difficulties related to obtaining homogeneous materials via standard mixing processes. Consequently, understanding of the proper mixing process for these particles, as well as the development of characterization methods to assure the quality of mixing is critical. Due to the small size of the particles, it is difficult to measure the degree of mixing in terms of both dispersion and distribution. The high magnifications required to observe dispersion of small particles limits the viewing window, such that observation of distribution is challenging. Quantification approaches for the degree of mixing are required for properly assessing the relationship between the degree of mixing and properties.; The objectives of this research are to select the proper direct method to measure the degree of mixing quantitatively for nanocomposites, to evaluate the effects of melt processing parameters on the mixing and properties, and to explain and predict theoretically the characteristics of melt compounding process for polymer nanocomposites.; In this work, part I is a general introduction on nanocomposites. This part summarizes the prior art for preparation and properties of nanocomposites, primarily for clays. In addition recent work on melt processing is included.; Part II of this dissertation describes a characterization method for the degree of mixing in nanocomposites and demonstrates the validity of the method. In order to avoid complexities from orientation effects of the filler, spherical nanoalumina was used in this research. Three techniques: TEM density, Morisita's index, and skewness of the quadrat method were compared for evaluation of samples, which were prepared by a batch mixer and have well-defined levels of mixing. All three techniques are based on analysis of the numbers of the particles in the selected area. The images of the nanocomposites were taken by TEM and the numbers of the particles were counted by image analysis software. This study demonstrated skewness of the quadrat method ranked the samples most effectively and could quantify the degree of mixing for nanocomposites.; The third part of this dissertation evaluated the influence of fill factor on the degree of mixing and thermal properties for a batch mixer. The degree of mixing for the resulting polymeric nanocomposites was quantified by three different techniques as described in Part II. Non-isothermal behavior studied by DSC showed that Tg was decreased for nanocomposites; the trend of the variation in thermal properties was consistent with the analysis of the degree of mixing, again confirming the validity of skewness to measure mixing. In this study, the optimized fill factor to prepare nanocomposites was obtained and the effect of fill factor on the mixing and properties was determined.; In Part IV, the effect of processing parameters on the degree of mixing was reported for a continuous melt compounding process using a twin-screw extruder. Melt temperature, screw rotation speed, and feeder rate were selected as important processing parameters, and their effects on the degree of mixing were studied by full factorial 2-level designed experiments. TEM images and mechanical properties were used to characterize the composites of the degree of mixing. The nanocomposites were analyzed quantitatively by skewness of the quadrat method. Degree of mixing was interpreted in terms of the processing parameters, and favorable conditions were found for each parameter. Enhancements in mechanical properties were o... |
