Mechanical, thermal, tribological and flammability properties of hybrid synthetic wollastonite nanofiber/graphene oxide reinforced polybutylene terephthalate nanocomposites

Abstract

The demand of lightweight materials and fuel economy enhancement has driven the development of polymer nanocomposites. In this study, novel nanocomposites based on polybutylene terephthalate (PBT) and synthetic wollastonite nanofibers (SWN) were developed. SWN were synthesized via hydrothermal reaction under different reaction mediums and temperatures, followed by calcination. The products were confirmed as high-purity wollastonite in nanosize, with either granular or fiber form. SWN with highest aspect ratio of 16.3 produced under reaction medium mixture of 20 v/v% ethanol, 80 v/v% water and reaction temperature of 200 °C, was used in PBT nanocomposites. The effect of SWN contents on the mechanical, thermal, tribological and flammability properties of the PBT/SWN nanocomposites were studied. Test samples were fabricated via melt compounding method. The addition of SWN into PBT resulted in the maximum increment of tensile strength (6%) and Young’s modulus (13%) due to its reinforcing effect and good interactions with PBT matrix via hydrogen bonding. However, elongation at break and impact strength demonstrated decreasing trends with increasing SWN contents. PBT reinforced with 1.0 phr SWN exhibited the best combination of stiffness and toughness. A significant increase in wear resistance (73%) was observed at the same SWN content, whereas friction coefficient decreased with increasing SWN contents. The incorporation of SWN had increased the thermal properties and the thermal stabilities of the nanocomposites, and simultaneously suppressed the peak rate of heat release and the rate of production of smoke and toxic gases. PBT/SWN 1.0 nanocomposite with the most balanced properties was used to compare with the natural wollastonite (NW)- and graphene oxide (GO)-reinforced PBT composites at the same content. Similar to SWN, hydrogen bonds were formed between the NW filler-PBT matrix interface. However, due to the larger surface area possessed by SWN, its nanocomposite exhibited higher tensile strength, Young’s modulus and wear resistance than that of NW. GO demonstrated poor interfacial adhesion with PBT matrix, thus had inferior mechanical properties and wear resistance. Nonetheless, PBT/GO 1.0 nanocomposite had the best anti-friction performance among the PBT composites due to the lubricating ability of GO. All fillers were able to improve the thermal and the flammability properties of PBT, where the degradation temperatures were significantly increased for PBT/SWN 1.0 and PBT/GO 1.0 nanocomposites by 9 - 14 °C. PBT/SWN 1.0 nanocomposite was also used as the base material to fabricate PBT/SWN/GO hybrid nanocomposites with 0.5 - 2.0 phr GO contents. By increasing the GO contents in hybrid nanocomposites displayed further improvement in Young’s modulus (16%) due to the better dispersion of GO nanosheets. However, due to the lacking of interfacial adhesion between GO and PBT matrix, the tensile strength, elongation at break, impact strength and wear resistance of hybrid nanocomposites were inferior than PBT/SWN 1.0 nanocomposite. The addition of 1.5 phr GO had attained the lowest friction coefficient with 34% reduction from that of neat PBT. Hybridization of SWN and GO further promoted crystallization, delayed the thermal degradation and improved the flame retardancy of hybrid nanocomposites. Overall study showed that the multifunctional PBT nanocomposites based on SWN and GO have great potential for lightweight structural components, thereby expanding the applications of PBT in automotive industry.