Electroactive γ-Phase, Enhanced Thermal and Mechanical Properties and High Ionic Conductivity Response of Poly (Vinylidene Fluoride)/Cellulose Nanocrystal Hybrid Nanocomposites

Abstract

Cellulose nanocrystals (CNCs) were incorporated into poly (vinylidene fluoride) (PVDF) to tailor the mechanical and dielectric properties of this electroactive polymer. PVDF/CNC nanocomposites with concentrations up to 15 wt.% were prepared by solvent-casting followed by quick vacuum drying in order to ensure the formation of the electroactive γ-phase. The changes induced by the presence of CNCs on the morphology of PVDF and its crystalline structure, thermal properties, mechanical performance and dielectric behavior are explored. The results suggest a relevant role of the CNC surface -OH groups, which interact with PVDF fluorine atoms. The real dielectric constant ε' of nanocomposites at 200 Hz was found to increase by 3.6 times up to 47 for the 15 wt.% CNC nanocomposite due to an enhanced ionic conductivity provided by CNCs. The approach reported here in order to boost the formation of the γ-phase of PVDF upon the incorporation of CNCs serves to further develop cellulose-based multifunctional materials.

Keywords: PVDF; cellulose nanocrystals; electrical properties; mechanical properties; nanocomposites.

Figure 1

(a) Representative TEM images, (b) FTIR spectrum, and (c) XRD pattern of cellulose nanocrystals (CNCs).

Figure 2

SEM micrographs of cryogenically fractured poly (vinylidene fluoride) (PVDF) (a and c at higher magnification) and PVDF/CNC 10 wt.% nanocomposite surfaces (b and d at higher magnification).

Figure 3

(a) Wide angle X-ray diffraction (WAXD) patterns; (b) FTIR spectra and (c) enlarged FTIR spectra of the PVDF/CNC nanocomposites and (d) peak deconvolution of the FTIR spectra in the 925–700 cm⁻¹ region for PVDF.

Figure 4

(a) DSC heating curves and (b) TGA traces of the PVDF/CNC nanocomposites.

Figure 5

(a) Stress–strain tensile curves of the PVDF/CNC nanocomposites and (b) experimental data and fitting results according to the modified Halpin–Tsai model.

Figure 6

Dielectric spectroscopy results. (a) Frequency dependence of the real part of the permittivity, (b) tangent loss, (c) real part of the dielectric constant and dielectric loss tangent at 1 KHz as a function of CNC concentration, and (d) concentration dependence of the real part of the permittivity for PVDF/CNC nanocomposites.