Production of boron nitride nanotubes and their uses in polymer composites

Demir, Can
Boron nitride nanotubes (BNNTs), firstly synthesized in 1995, are structural analogues of carbon nanotubes (CNTs) with alternating boron and nitrogen atoms instead of carbon atoms. Besides their structure, mechanical and thermal properties of BNNTs are very similar to the remarkable properties of CNTs. However, BNNTs have higher resistance to oxidation than CNTs. Also, BNNTs are electrically isolating. Therefore, they are envisioned as suitable fillers for the fabrication of mechanically and thermally enhanced polymeric composites, while preserving the electrical isolation of the polymer matrix. In this study, polypropylene (PP) – boron nitride nanotube (BNNT) composites were prepared using a twin-screw extruder. Mechanical and thermal properties of PP–BNNT composites were investigated as a function of nanotube loading. The nanotubes used in the composites were synthesized from the reaction of ammonia gas with a powder mixture of elemental boron and iron oxide. X-ray diffraction (XRD) analysis revealed the predominant hexagonal boron nitride in the synthesized product. Multi-wall nanotubes with outer diameters ranging from 40 to 130 nm were observed with SEM and TEM analyses. Tensile testing of PP–BNNT composites revealed slight increases in the Young’s modulus and yield strength of neat PP with 0.5 and 1 wt% of the as-synthesized BNNT additions. On the other hand, due to the agglomeration of BNNTs, elongation at break and tensile strength values of composites decreased with increasing nanotube content. In the case of using 0.5 wt% loading of purified and then surface modified BNNTs, slight improvement in all mechanical properties of neat PP was achieved. Differential scanning calorimetry (DSC) analysis revealed a noticeable increase in the crystallization temperature of BNNT–added composites. Coefficient of linear thermal expansion (CLTE) of polymeric composites were studied and no significant change in the CLTE of neat PP was observed with the addition of BNNTs. Results of thermal gravimetric analysis (TGA) indicated improvements in the thermal stability of neat PP with BNNT additions.
Citation Formats
C. Demir, “Production of boron nitride nanotubes and their uses in polymer composites,” M.S. - Master of Science, Middle East Technical University, 2010.