PSI - Issue 52

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Miray Yasar et al. / Procedia Structural Integrity 52 (2024) 165–175 Miray Yasar et. al. / Structural Integrity Procedia 00 (2019) 000 – 000

( ) = + ⍺ = ( ⍺ )

⍺ +

(2) Previous research studies reported that the ⍺ phase is the dominant phase in solvent-cast PVDF, which requires further thermal annealing or the addition of nanoparticles (Sathiyanathan et al., 2016). Once the PVDF was melted at 180 o C, it included a high amount of ⍺ phase and a low amount of β phase content. Cooling down to room temperature under pressure helps to increase the polar phases in the structure. The composite mostly included polar phases, which were calculated to be 77 േ 3%. The characteristic peaks of the β and phases are in the range of 833-840 cm -1 , which is difficult to distinguish and needs to be confirmed by XRD analyses. Peaks at 1233 cm -1 , 1283 cm -1 , 811 cm -1 and 833 cm -1 exclusively represent the phase and the large peak at 873 cm -1 represents the combination of all three phases (Kaspar et al., 2020). Thus, the material includes both β and phases between 833-840 cm -1 .

Fig. 2. FTIR Analysis of PVDF-MWCNTs Impregnated PPS Veil (PVDF Layer)

3.2. XRD Analyses XRD analyses of the PVDF layer is shown in Figure 3. The ⍺ phase of PVDF showed peaks at 18.4 (020) while the phase showed peaks at 19.1 (002). The β phase of PVDF layer was identified by a peak at 20.6 (110/200) reflection of the orthorhombic β phase (Cai et al., 2017) and 30 (201) reflection of β phase. MWCNTs increases total crystallinity by acting as a nucleating agent (Liu et al., 2013). This observation suggests that the material consists of all three phases, which aligns with the FTIR results. However, the structure was primarily characterized by the dominant 20.6 and 30 degree reflections of the β phase. The FTIR and XRD results confirmed the presence of polar β and phases in the PVDF layer. For the aim of this study, the combination of both polar β and phases was considered to be preferential as both phases result in sufficient piezoelectric coupling for detecting damage.