Investigation of Polymer Integrated Smart Piezoelectric Fillers

This study investigates the influence of fillers on the piezoelectric response and material properties of PVDF and epoxy-based polymer composites, focusing on fracture behaviour, mechanical performance, thermal behaviour, and structural integrity. PVDF films were produced using solvent casting and hot pressing followed by various processing techniques aimed at increasing the β phase content of PVDF. A contact poling unit was designed, and the poling process was optimised. The optimal processing sequence - solvent casting, hot pressing, quenching, and cold rolling - yielded 81% β phase content. PVDF based piezoelectric composites were prepared using this sequence with 0.2 wt.% multiwalled carbon nanotubes (MWCNT), 20 wt.% barium titanate (BT), and 20 wt.% silane-modified BT. A maximum d33 value of 13.2 pC/N was achieved through solvent casting, hot pressing, quenching, and stretching. The PVDF composites were produced using cold rolling, as tearing occurred during the stretching step. However, cold rolling negatively affected the morphology. The maximum d33 value achieved was 4.7 pC/N, observed in the MWCNT-added PVDF composites. Epoxy-based piezoelectric composites were prepared by integrating 20 wt.% PVDF (P) with 5 wt.% or 20 wt.% BT and 5 wt.% silver (S), using two curing agents of different flexibilities. The highest piezoelectric response (1.35 V) was achieved in P0BT20S0 samples cured with the more flexible agent. The lowest response (0.21 V) occurred in P20BT5S5 samples due to the agglomeration of BT and S particles. Reference P0BT0S0 samples cured with the less flexible agent showed higher glass transition temperature (81.2 °C), tensile strength (44.3 MPa), modulus (2206 MPa), and lower fracture toughness (2.0 MPa.m1/2) and fracture energy (1652 J/m2) compared to those cured with the more flexible agent. The study further examined the effect of core-shell rubber (CSR) and BT on epoxy. In the first set, 30 wt.% CSR was added with varying nano-sized BT into epoxy resin. Increasing BT content led to higher tensile modulus and crosslink density; but tensile strength, lap shear strength, and glass transition temperatures did not change significantly. Agglomerations occurred at 10 wt.% BT, slightly reducing mechanical properties. The highest fracture toughness and fracture energy were obtained with 5 wt.% BT (2.28 MPa·m1/2, 2006 J/m2), while the maximum voltage output response (0.50 V) was recorded at 20 wt.% BT. In the second set, with 20 wt.% BT and varying CSR, the compositions exhibited brittle failure. Tensile strength and modulus decreased as CSR content increased. Optimal fracture toughness and energy were achieved with 5 wt.% CSR (2.15 MPa·m1/2, 1921 J/m2), and the highest voltage response (1.85 V) was observed with 15 wt.% CSR. To extend the scope of this study, a PVDF based piezoelectric film was integrated into CFRP as a mid-layer. The PVDF+MWCNT solution was poured onto a PPS layer, dried, hot-pressed, and perforated. CFRP laminates were produced via vacuum infusion. The effects of the piezoelectric layer and perforation on performance were investigated. Flexural modulus dropped from 87.7 GPa to 72.5 GPa and 76.6 GPa with non-perforated and perforated PVDF, respectively. Despite this, the composite generated 100 mV at 0.4 Hz under a compression force of 10 N. The results showed that incorporating a PVDF-PPS layer into CFRP is promising for potential sensing applications.