Highly-Loaded Thermoplastic Polyurethane/Lead Zirconate Titanate Composite Foams with Low Permittivity Fabricated using Expandable Microspheres.

Gayaneh Petrossian,Cameron Hohimer,Amir Ameli

doi:10.3390/polym11020280

Abstract

The sensitivity enhancement of piezocomposites can realize new applications. Introducing a cellular structure into these materials decreases the permittivity and thus increases their sensitivity. However, foaming of piezocomposites is challenging because of the high piezoceramic loading required. In this work, heat-expandable microspheres were used to fabricate thermoplastic polyurethane (TPU)/lead zirconate titanate (PZT) composite foams with a wide range of PZT content (0 vol % to 40 vol %) and expansion ratio (1–4). The microstructure, thermal behavior, and dielectric properties of the foams were investigated. Composite foams exhibited a fine dispersion of PZT particles in the solid phase and a uniform cellular structure with cell sizes of 50–100 μm; cell size decreased with an increase in the PZT content. The total crystallinity of the composites was also decreased as the foaming degree increased. The results showed that the relative permittivity (εr) can be effectively decreased by an increase in the expansion ratio. A maximum of 7.7 times decrease in εr was obtained. An extended Yamada model to a three-phase system was also established and compared against the experimental results with a relatively good agreement. This work demonstrates a method to foam highly loaded piezocomposites with a potential to enhance the voltage sensitivity.

Highlights

Great attention has been paid to functional polymer composites, such as conductive [1,2], piezoresistive [3], and piezoelectric [4,5] composites, as they combine the advantages of the constituent materials
The conventional piezoelectric sensors are mainly made of piezoceramics, notably lead zirconate titanate (PZT) and barium titanate (BTO)
The cell density was slightly increased with PZT content, which compensated for the decreased cell size at a constant expansion ratio

Summary

Introduction

Great attention has been paid to functional polymer composites, such as conductive [1,2], piezoresistive [3], and piezoelectric [4,5] composites, as they combine the advantages of the constituent materials. The conventional piezoelectric sensors are mainly made of piezoceramics, notably lead zirconate titanate (PZT) and barium titanate (BTO). These materials can have large piezoelectric charge constants (d), they are very brittle and difficult to shape into mechanically compliant structures [13]. Polymers can be ductile, easy to shape, and low in material and processing cost Piezopolymers, such as polyvinylidene fluoride (PVDF) and its copolymers and ferroelectrets ( known as piezoelectrets), were developed mainly to address the limitations of piezoceramics. Their weak piezoelectric response and low thermal stabilities, together with limited flexibility, limits their applications [14]

Methods

Results

Conclusion