Polystyrene Nanocomposites Prepared By Water-assisted Mixing Extrusion And Their Foaming Behavior

On the basis of improving the properties for polymer-based nanocomposites, how to reduce the energy consumption gains more and more attentions in their preparation. In this dissertation, polystyrene/graphene oxide(PS/GO) nanocomposite samples containing 3 different GO contents(0.1, 0.3 and 0.5 wt%) and PS/multi-walled carbon nanotubes with carboxyl(MWCNTs-COOH) nanocomposite samples containing 3 different MWCNTs-COOH contents(0.1, 0.3 and 0.5 wt%)were prepared by using water-assisted mixing extrusion equipment. Microstructure, tensile strength, rheological behavior, and thermal properties of the prepared nanocomposite samples were investigated. Then, the PS and its two kinds of nanocomposites were foamed using high-pressure vessel for investigating the effects of foaming conditions on the cellular structure.The GO suspension was prepared by sonication. Then, the prepared suspension was injected into PS melt during water-assisted mixing extrusion to prepare PS/GO samples. The results demonstrate that the GO was well exfoliated and dispersed in network structure in the PS matrix. This is attributed to the fact that aqueous suspension of the GO injected into flowing PS melt was broken into finer drops continuously because of strong mixing of the extruder screws; moreover, PS chains was easy to intercalate and exfoliate the GO layers because of plasticizing and swelling effects of water during melt mixing. The PS/GO samples exhibit higher elastic moduli, complex viscosities, and relaxation times in low frequencies as compared to the PS sample, which is because stronger intermolecular force between well dispersed GO layers in network structure and PS restricts PS chains mobility. The PS/GO samples exhibit higher thermal stability than the PS sample, which is due to the GO network in the PS matrix and the π bond at the GO surface.The MWCNTs-COOH suspension was prepared by sonication. Then, the prepared suspension was injected into PS melt during water-assisted mixing extrusion to prepare PS/ MWCNTs-COOH nanocomposite samples. The results show that the PS/MWCNTs-COOH samples exhibit higher elastic moduli and complex viscosities in low frequencies and higher thermal stability, glass transition temperature and tensile strength compared to the PS sample. Upon adding the same contents of nanofillers, the PS/GO nanocomposite samples exhibit better thermal stability and tensile strength than the PS/MWCNTs-COOH nanocomposite samples due to the difference of the microstructure of the GO and MWCNTs-COOH and of their dispersion in the PS matrix.The PS and its nanocomposites were foamed by using supercritical carbon dioxide as blowing agent. The effects of foaming temperature and pressure on the cellular structure of the foamed samples were analyzed. The order of cell diameters for the foamed samples prepared under the same foaming conditions is PS>PS/MWCNTs-COOH>PS/GO. The addition of the nanofiller to the PS matrix decreases the mean cell diameter and increases the cell density. The foamed PS/GO nanocomposite samples exhibit better cellular structure than the foamed PS/MWCNTs-COOH nanocomposite samples. The foamed PS and its nanocomposite samples using a varying-temperature mode exhibit a bi-modal cell structure. Adding the nanofillers to the PS matrix increases the density of larger cells.