Date

2015

Author

Balık, Erdem

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In recent years, boron nitride nanotubes (BNNTs) have been added to polystyrene (PS) which is a widely used thermoplastic polymer in order to improve its thermal and mechanical properties. Solution mixing and melt blending techniques are commonly used methods to prepare polymer-boron nitride nanotube (BNNT) composites. However, these two composite preparation methods have a common problem about the dispersion of fillers in the polymer matrix. In this study, PS-BNNT composites were prepared using masterbatch with extrusion method at 0.5, 1, and 3 wt % BNNT loadings in order to disperse the nanotubes in the polymer matrix homogeneously. The composites with 0.5 wt% BNNTs were also obtained from in-situ polymerization and extrusion method, separately. Neat PS and all the composites were characterized in terms of their morphology, mechanical and thermal properties. PS was synthesized using solution and bulk polymerization techniques. The effect of polymerization time and initiator concentration in bulk polymerization on the vi molecular weight of PS was studied in order to find the best synthesis conditions for PS production. The best synthesis conditions were determined as a polymerization reaction time of 3 hrs, an initiator concentration of 0.01 mol/L and a reaction temperature of 95 oC. Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), viscosity average molecular weight (Mv), Melt Flow Index (MFI) and Gel Permeation Chromatography (GPC) characterization methods were used to compare the properties of synthesized PS with commercial PS. The results of all the characterization methods revealed that PS was successfully synthesized and its molecular weight was close to that of commercial PS. BNNTs used in the polymer composite were successfully synthesized from the reaction of ammonia gas with a powder mixture of elemental boron and iron oxide. The formation of hexagonal boron nitride was proved by XRD analysis. Results of SEM analyses indicated that the nanotubes were dispersed homogeneously for the composites with 0.5 wt% BNNTs prepared by masterbatch with extrusion method. The tensile and impact strengths of these composites were improved remarkably with respect to neat polymer and the composites prepared using the other methods. The agglomeration of BNNTs in the polymer matrix increased with an increase in BNNT addition. Differential Scanning Calorimetry analysis showed that the glass transition temperature of the composites prepared by masterbatch with extrusion method was decreased with respect to the synthesized PS. Also, no significant change in terms of glass transition temperature of the composites was observed with the addition of BNNTs. Thermal gravimetric analysis (TGA) of the composites prepared by masterbatch with extrusion method showed that the thermal stability of composites remained unchanged with the addition of BNNTs.

Subject Keywords

Polymerization., Polystyrene., Boron nitride., Nanotubes., Composite materials.

URI

http://etd.lib.metu.edu.tr/upload/12618452/index.pdf
https://hdl.handle.net/11511/24434

Collections

Graduate School of Natural and Applied Sciences, Thesis