INTERNATIONAL STANDARDS FOR THERMAL PROPERTIES OF POLYMER MELTS.

NIST scientists recently participated in an international round-robin study of the thermal properties of polymer melts, organized by the National Physical Laboratory (NPL) in the United Kingdom. The polydimethylsiloxane (PDMS) sample was studied at seven laboratories around the world, with the results summarized in NPL Report CBTLM S35 published in December 2000. The NIST measurements of the thermal conductivity of liquid PDMS cover the temperature range of reference data used to calibrate thermal conductivity apparatus at temperatures up to 700 K. The NIST data were measured with an absolute transient hot-wire instrument and are the only data available on the PDMS sample at temperatures above 420 K. The agreement between five participating laboratories and the ASTM (D5930-97) recommended value at 298 K is within [+ or -]2% for the thermal conductivity of this sample of PDMS. The NIST measurements supplement existing reference data for the thermal conductivity of liquids, such as water (273 K to 370 K, IUPAC- 1993), toluene (300 K to 550 K, IUPAC-2000), and dimethylphthalate (273 K to 473 K, ASTM D2717-95). These new data improve instrument calibrtions following the ASTM Standard Test Methods D27170-95 for the thermal conductivity of plastics.