Characterisation of Poly (vinylidene flouride) Nanofibrillar Materials -Electrical and Mechanical Properties

Abstract

Poly(vinylidene fluoride) (PVDF) has been recognized as a crucial electroactive polymer. Therefore, a lot of research has been conducted in terms of morphology, polymorphism behaviour and molecular orientation of the polymer. β-phase polymorphic modification, which shows strong ferro- and piezoelectric property, can be obtained by subjecting highly oriented PVDF fibres to high electric fields. This research aims at producing PVDF nanofibrillar materials: PVDF nanofibrillar single polymer composite (NF-SPC) and electrospun PVDF, including the β-phase, by using two different manufacturing techniques: microfibrillar reinforcement composite (MFC) concept and electrospinning. Furthermore, the electrical and mechanical properties of the final products from the two techniques are characterized. The two different manufacturing techniques needed different experimental materials and set up. PVDF NF-SPC was prepared by the hot compaction of PVDF fibrils extracted from a linear low density polyethylene (LLDPE) and PVDF composite. A high electric field was used to drive out electrospun PVDF fibrils from the solution mixed with PVDF powder and solvent of dimethyl formamide (DMF) and acetone. These two final products were characterized by differential scanning calorimetry (DSC) for thermal analysis, Fourier transform infrared (FTIR) for polymorphic change, and scanning electron microscopy (SEM) for morphology of constituents. Measurement of ferro- and piezoelectric behaviour of poled specimens were performed and mechanical properties were measured by tensile testing. Highly oriented nanofibrils were observed from the two specimens with high aspect ratios. The formation of the β-phase was clearly detected by FTIR spectra compared to undrawn isotropic PVDF. Higher remnant polarisation values were obtained from the specimens, which demonstrated the β-phase polymorphic modification. Furthermore, piezoelectric resonance behaviour was revealed from the two products by an impedance analyzer. In the tensile testing, the PVDF NF-SPC and the electrospun PVDF showed 304 and 89.9 % increase in ultimate tensile strength over isotropic PVDF, respectively.