An improved method for measuring the thermal coefficient of linear expansion of flexible polymer films

Abstract

A novel method has been developed and tested to determine accurately the linear coefficient of thermal expansion α of flexible films without subjecting a specimen to a tensile load continuously during the measurement of expansion data. Other methods have invariably required the application of a tensile load which commonly leads to creep during the experimental time. The new method involves mounting an Invar jig in the lower grip in a Dynastat. The closed‐loop servo control in the Dynastat enables the length of a specimen to be determined at a series of decreasing or increasing temperatures without subjecting the specimen to a tensile load, except momentarily on occasion while length data are being determined. Otherwise, a specimen is subjected to a small bending force. To demonstrate that the method gives valid results, α for an aluminum foil was determined and found to agree exactly with literature data. Expansion coefficients and values of the glass transition temperature (Tg) were determined on FEP and PFA Teflon films and also on a commercially available polyimide film, Upilex‐SGA. Copyright © 1990 John Wiley & Sons, Inc.