Flame-Resistant Poly(vinyl alcohol) Composites with Improved Ionic Conductivity

Abstract

Flame-resistant polymer composites were prepared based on polyvinyl alcohol (PVA) as a polymer matrix and a polyphosphonate as flame retardant. Oxalic acid was used as crosslinking agent. LiClO₄, BaTiO₃, and graphene oxide were also incorporated into PVA matrix to increase the ionic conductivity. The obtained film composites were investigated by infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry and microscale combustion tests. Incorporating fire retardant (PFRV), BaTiO₃, and graphene oxide (GO) into a material results in increased resistance to fire when compared to the control sample. A thermogravimetric analysis revealed that, as a general trend, the presence of PFRV and BaTiO₃ nanoparticles enhances the residue quantity at a temperature of 700 °C from 7.9 wt% to 23.6 wt%. Their dielectric properties were evaluated with Broad Band Dielectric Spectroscopy. The electrical conductivity of the samples was determined and discussed in relation to the LiClO₄ content. The electrical properties, including permittivity and conductivity, are being enhanced by the use of LiClO₄. Additionally, a relaxation peak has been observed in the dielectric losses at frequencies exceeding 103 Hz. The electrical properties, including permittivity and conductivity, are being enhanced by the use of LiClO₄. Additionally, a relaxation peak has been observed in the dielectric losses at frequencies exceeding 103 Hz. Out of the various composites tested, the composite containing 35 wt% of LiClO₄ exhibits the highest alternating current (AC) conductivity, with a measured value of 2.46 × 10^-3 S/m. Taking into consideration all the aspects discussed, these improved composites are intended for utilization in the manufacturing of Li-Ion batteries.

Keywords: dielectric spectroscopy; flame resistance; ionic conductivity; polyphosphonate; polyvinyl alcohol.

Scheme 1

Synthetic pathway to prepare phosphorus-containing polyphosphonate PFRV.

Figure 1

FTIR spectrum (a), TG, DTG (b), and DSC ((b) inset) curves of PFRV.

Figure 2

FTIR spectra of PVA composites.

Figure 3

Polarized light microscopy micrographs of the as synthesized PVA composites: PVA-0 (a), PVA-1 (b), PVA-2 (c), PVA-3 (d), PVA-4 (e), PVA-5 (f), PVA-6 (g); the insets of the SEM micrographs are given for PVA composites PVA-0 (a), PVA-1 (b), PVA-2 (c), PVA-3 (d).

Figure 4

EDX diagram and EDX mapping of PVA-2 (a) and EDX diagram and EDX mapping of PVA-3 (b).

Figure 5

TG (a), DTG of the PVA composites (b) and DSC curves of PVA composites (c).

Figure 6

SEM micrographs of PVA-composites heated up to 700 °C PVA-0 (a), PVA-1 (b), PVA-2 (c), PVA-3 (d), with the heating rate of 10 °C/min, under nitrogen atmosphere and EDX mapping of PVA-2 (e) and PVA-3 chars (f) heated up to 700 °C.

Figure 7

Heat release rates versus temperature for PVA composite samples (a) and heat release rates versus time for PVA composite samples (b).

Figure 8

Frequency dependence of the: real part of permittivity (a), dielectric loss (b), and conductivity at room temperature for PVA-composites (c). The electrical conductivity of PVA-composites measured at frequency of 10 MHz (d).

Figure 9

Frequency-dependent variation of the AC conductivity of PVA-composites measured at different temperatures (a–f). Arrhenius plots and the extracted activation energy values (g).