Preparation, properties, and structure-property relationships of graphene-polymer nanocomposites
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The overall objective of this work was to develop processing, structure, and property relationships in graphene/polymer nanocomposites. To this end, different types of graphene platelets were produced from graphite oxide, dispersed into various thermoplastics and elastomers, and the morphology and properties of the resulting nanocomposites were evaluated. A range of tests were carried out on the nanocomposites to assess property improvements, including stress-strain testing, dynamic mechanical analysis, and thermal and electrical conductivity testing. Extensive morphological characterization, primarily through transmission electron microscopy (TEM) analysis, was performed to gain insight into the mechanisms behind the observed property improvements. The processing method used to disperse graphene platelets into a given polymer was found to exert significant influence over the nanocomposite morphology and properties. In both thermoplastics and elastomers, liquid-based dispersion methods were typically found to yield a better dispersion of graphene platelets compared with melt processing; the effectiveness of melt processing appeared to depend in part upon the method used to produce the graphene platelets. Latex compounding of graphene platelets and natural rubber generated nanocomposites with a network morphology with properties that were sensitive to further processing. The effect of graphene platelet intrinsic structure on nanocomposite properties was studied and property improvements with other nanofillers were compared to graphene platelets. The impact of platelet oxidation on nanocomposite properties was explored in two different systems and produced varying results depending on the polarity of the polymer matrix. An increased average aspect ratio of graphene platelets was not found to improve mechanical properties or a lower percolation threshold when dispersed in natural rubber. Graphene platelets produced superior reinforcement to multi-walled carbon nanotubes and exfoliated montmorillonite when dispersed in natural rubber; however, the carbon nanotubes produced the largest thermal and electrical conductivity enhancements. Qualitative observation of platelet dispersion by TEM was found to provide excellent correlation with nanocomposite properties when comparing different processing methods or filler materials. The average platelet aspect ratio of three different nanocomposite systems was determined by quantitative TEM analysis and used as a parameter in composite models to generate modulus predictions. Good agreement was found between model predictions and the experimental data.