Polymer-layered silicate nanocomposites : synthesis, structure and properties

Polymer-layered silicate nanocomposites are a new class of high performance materials, consisting of nanometer scale inorganic particles or fillers dispersed in organic polymer matrices. This new family of composite materials exhibits remarkable improvements of properties when compared with the pure polymers or conventional (micro- or macro-) composite materials, even with only a small weight fraction of the nano-fillers. The general objective of this dissertation is to discover the processing-microstructure-property relationships of polymer-layered silicate nanocomposites. Most efforts were dedicated to the formation of highly exfoliated structures. To achieve the goal, innovative techniques were newly developed in order to facilitate the clay exfoliation. The current work includes two experimental systems which are epoxy-clay nanocomposite and SBS/PP blend-clay nanocomposite, i.e., one is based on thermosets and the other is based on thermoplastics. In addition, this study will contribute values on two different nanocomposite fabrication methods: in situ polymerization method and polymer melt compounding method. The mechanisms of the penetration of monomers (for epoxy system) and polymers (for SBS/PP blend system) into the clay gallery and the delamination of the clay were looked into through the studies on these two systems. A preliminary evaluation of nanocomposite properties was also carried out. For epoxy-clay nanocomposites, different microstructures (intercalation and exfoliation) were synthesized using two commercial types of organically modified montmorillonite (MMT). A highly disorderly exfoliated nanocomposite based on anhydride-cured epoxy system was achieved via a new approach using clay modified with an epoxy-curing accelerator and a slurry method. It was found that the catalytic function of the surfactants inside the clay galleries drives the epoxy curing rate of intragallery to be faster than that of extragallery, leading to a high level of exfoliation. With adding clay fillers, the epoxy-clay nanocomposites showed reduced CTE and moisture absorption. For SBS/PP blend-clay nanocomposites, an intercalated structure of organically modified MMT in matrix was formed through a pre-dispersion in paraffin oil and a melt intercalation with polymer matrix in a Haake Mixer. TEM micrographs showed that the clay prefers to stay in the PP phase and close to the SBS-PP interface. It was proven that this new nanocomposite possesses enhanced tensile properties without the trade-off of its impact resistance.