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Nanocomposites based on blends of polystyrene

Dike, Ali Sinan
Due to brittleness of polystyrene, PS, its usage area is restricted. To solve this problem and expand the usage area of PS, it can be blended and impact modified with an elastomeric material. In this study, the decrease in the modulus and tensile strength imparted by impact modification was overcome by reinforcing this mixture by incorporating organoclays and producing nanocomposites. This study consists of two parts. In the first part of this study three different types of aliphatic elastomeric materials and three different types of organoclays were used and their effects on the morphology, mechanical, thermal, and rheological properties of PS were investigated. Lotader AX8900, Lotader AX8840 and Lotader 2210 were chosen as the aliphatic elastomeric compatibilizers; and Cloisite® 15A, Cloisite® 25A and Cloisite® 30B were chosen as the organoclays. Organoclay content was kept at 2% and elastomer content was kept at 5% throughout the first part of the study. In the second part of this study, an aromatic elastomer; Styrene-Butadiene- Styrene rubber, SBS, was chosen as the elastomeric compatibilizer and maleic anhydride was grafted onto SBS rubber at different ratios. Grafting was made by means of a co-rotating twin screw extruder. Cloisite® 30B was used as the organoclay. In order to investigate the effects of organoclay addition on the v properties of the PS and PS / Elastomer blends, PS / Elastomer blends were also prepared and their properties were also investigated. Clay content was varied between 0% and 4%, and the elastomer content was varied between 0% and 40% throughout the second part of the study. All samples were prepared by a corotating twin screw extruder, followed by injection molding at appropriate conditions. In order to investigate the state of dispersion and the basal spacings of the organoclays in the PS matrix, XRD analyses were carried out. No significant improvement was observed on the basal spacing of the nanocomposites prepared in the first part of the study, but nanocomposites prepared in the second part of the study exhibited intercalated or exfoliated structures. In order to investigate the average domain sizes of the elastomeric phases, SEM analyses were carried out. To remove the elastomeric phase from the PS matrix, etching was done with n-Heptane in an ultrasonic bath at room temperature. Average domain sizes increased as the elastomer content increased in the binary blends and ternary nanocomposites. In order to investigate the flow behaviour of the raw materials and the samples prepared throughout this study, MFI tests were carried out. In the first part of the study, addition of elastomer and organoclay decreased the MFI values, as expected. Although both PS and elastomeric materials used in the second part of the study have similar MFI values, samples prepared with these materials exhibited higher MFI values than both of the polymers. In order to investigate the effects of the compatibilizer type, organoclay type, and concentration of materials on the mechanical properties of the prepared samples, tensile and unnotched Charpy impact tests were performed. Due to incompatibility of the elastomeric phase with the PS matrix, no significant improvement was observed in tensile properties of the nanocomposites prepared in the first part of this study. In the second part of the study, the aromatic elastomers enhanced the intercalation / exfoliation of clay layers resulting in higher tensile strength, modulus, elongation at break and impact strength with respect to neat PS. vi In order to observe the effects of organoclay and elastomer addition on the thermal properties of blends and nanocomposites prepared in this study, Differential Scanning Calorimetry analyses were done. By this analysis, glass transition temperature, Tg was measured. Elastomer addition increased the Tg of the samples, whereas organoclay addition did not affect the Tg significantly.