Simultaneous measurement of rheological and conductive properties of carbon black filled ethylene–tetrafluorothylene copolymer

Abstract

Composites composed of carbon black (CB) filled polymers have been widely applied in many areas such as electromagnetic/radio-frequency interference shielding, electrostatic discharge, conductive adhesives for die attachment in electronic packaging applications, and electroactive polymeric sensors in hand prostheses [1, 2]. It is well known that the morphology and properties of filled polymer composites are greatly influenced by the state of filler dispersion [3]. Due to the small size and high specific surface, the filler particles are favorable to form a three-dimensional flocculation structure [4]. Even though scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations can give us a lot of information on structure and morphology involving fillers, they only reflect the dispersion localized within a two-dimensional microscopic site and thereby are easily misinterpreted with respect on the correlation of the information to the real dispersion space and its contribution to the target properties [5, 6]. It is accepted that dynamic rheological measurements are effective for dealing with the structure and morphology of filled polymers as well as the filler dispersion because the structure of samples tested is indestructible under small strain (c) amplitudes [7]. The rheological properties of highly filled polymer composites may provide essential information about the flocculation structure of the filler that contributes to the physical properties such as mechanical strength, electrical resistivity, and heat conductivity [8]. Much work has been performed on the rheological behavior of various filled polymers. Krishnamoorti and Giannelis [9] observed nonterminal low-frequency rheological behavior in nanocomposites containing layered silicates. Zhang and Archer [10] reported a transition to solid-like response at low oscillation frequencies due to the presence of a filler network in poly(ethyl oxide)/silica nanocomposites. Simultaneous measurement of rheological and conductive behaviors under c has been made on CB-filled natural rubbers [11] or vulcanizates [12] to study the carbon black structure inside these materials. It was found that shear moduli and electrical conductivity vary in an approximately similar way as the amplitude of dynamic oscillation increases. In the aforementioned literatures, small strain oscillation was achieved by using spring while the large one is controlled using machine driving or hand wheel. Recently, Pan and Mckinley [13] studied viscoelasticity and conduction behaviors of an electrorheological fluid suspension using simultaneous measurement technique. To our knowledge, few work has been reported to study filled semicrystalline polymers at temperatures above melting point (Tm) using simultaneous measurement of rheological and conductive behaviors. In a previous paper [14], we examined the conductive behavior of ethylene–tetrafluorothylene (ETFE) copolymer/CB composites and found that the switching characteristic show a reproducible stability at the upper limit of the percolation transition. Here we present some unique results from simultaneous measurements of the dynamic storage modulus (G0) and electrical resistance (R) for ETFE/CB melt. It is noted that the modified rheometer allows us to obtain the data of measuring G0 and R for ETFE/CB composites in a relative wide strain range in one mode. The composites were prepared by mixing ETFE (ETFE750 from DuPont, density 0.942 g cm , melting point Z. Liu Y. Song J. Zhou Q. Zheng (&) Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, 310027, P.R. China e-mail: zhengqiang@cmsce.zju.edu.cn