Synergistic effects of processing and nanofiber reinforcement on the mechanical and ferroelectric performance of geopolymer matrix composites

This study involved the evaluation of mechanical and ferroelectric properties of a new class of nanofiller infused inorganic polymer (geopolymer, GP). To evaluate the mechanical performance, compressive strength and fracture resistance of neat and nanofillers infused GP were studied at various treatment temperatures. It was found that, addition of 5 vol% alumina nanofiber (ANF), increased compressive strength and modulus by over 30% and 60%, respectively, while it increased fracture toughness (KIC) by over 60% compared to the baseline specimens. Simultaneously, ferroelectric properties were investigated at various treatment temperatures (250 °C, 650 °C and 870 °C). Remarkably, higher ferroelectric hysteresis was observed with the GP treated at 870 °C and remnant polarization increased with the addition of alumina nanofiber. Scanning Electron Microscopy confirmed that neat materials are composed of particles embedded into the poly-condensed matrix, where particle nature existed until the treatment temperature reached above 870 °C. X-ray diffraction analysis suggests that, baseline geopolymer started becoming crystalline while the particle nature gradually disappeared with heating at or beyond 870 °C. The bonding between the polymer and alumina nanofiber tends to be stronger with increasing treatment temperature. The increase in KIC with the addition of 2 vol% and 5 vol% alumina nanofibers (ANF) is due to homogeneous dispersion of high interfacial strength nanofillers, which essentially create strong crack bridging and crack deflection effect. The increase in ferroelectric hysteresis is potentially due to the formation of hierarchical order and domain reorientation of the materials.