Chlorosulfonated polyethylene: A versatile polymer for damping acoustic waves
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I.
INTRODUCTION
VISCOELASTIC polymers are the most frequently used means for damping or absorbing acoustic waves. Structural vibrations are damped by adhering free or constrained layers ~ of viscoelastic polymer to the structure to dissipate flexural wave energy or by using dynamic vibration absorbers, t2] which use stiffness elements consisting of viscoelastic polymers. Fluidborne waves are dissipated by lining the boundary with viscoelastic layers containing perforations or voids sealed to prevent entry of the liquid, t3j In each of these applications, the dissipation of energy is associated with either the shear or the extensional modulus. These moduli are inherently strong functions of frequency and temperature, t4J Herein lies one of the most difficult challenges facing the acoustical design engineer. Viscoelastic materials must be available which can provide the necessary degree of damping over perhaps several decades of acoustic frequencies while exposed to the conditions dictated by the environment. T h e a d v e r s e environmental conditions may include exposure to ultraviolet radiation, ozone, high humidity, liquid or vaporized solvents, and variation in temperature of several decades, to name a few. The purpose of this paper is to describe a family of materials, chlorosulfonated polyethylenes, which offers the versatility needed to provide the necessary acoustic properties in many adverse environments.
WAYNE T. READER, Principal Research Scientist, is with Vector Research Company, Inc., Bethesda, MA 20817. ROBERT W. MEGILL, Senior Technical Consultant, is with E.I. DuPont de Nemours & Company, Inc., Newark, DE 19711. This paper is based on a presentation made in the symposium "Acoustic/Vibration Damping Materials" presented during the TMS Fall Meeting, Indianapolis, IN, October 1-5, 1989, under the auspices of the TMS Physical Metallurgy Committee. METALLURGICAL TRANSACTIONS A
II. PHYSICAL PROPERTIES OF C H L O R O S U L F O N A T E D POLYETHYLENES
Chlorosulfonated polyethylenes have been available since the early 1950s in a number of types primarily characterized by their chlorine content. The chlorine content of the commercially available HYPALON* fam*HYPALON is a trademark of E.I. DuPont de Nemours, Inc., Wilmington, DE.
ily, for example, varies between approximately 23 and 43 wt pct. A primary consequence of the chlorine content is to control the glass transition temperature, Tg, and hence, the physical properties and applications for which they are used. tS] Figure 1 illustrates the dependence of Tg upon the chlorine content, showing that Tg varies from about - 30 ~ to 2 ~ as the chlorine content of the polymers varies from about 23 to 43 pct. Dividing the materials into three categories according to chlorine content, some of their major physical properties and applications are summarized in the following, tSj (1) Low chlorine content, 20 to 28 pct: (a) ' significant crystallinity (hence, properties lie between those of thermoplastics and elastomers); (b) good strength with or without vulcani
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