DTA for control of stability in polyolefin wire and cable compounds

Abstract

Differential thermal analysis offers a convenient and rapid way of determining stabilization levels in polyolefin compositions. Since it is normally used at temperatures in the fabrication range, it provides a direct readout of processing stability. At the same time, because the chemistry of the polymer system at these temperatures may be quite different from that at normal use temperatures, judgment must be exercised in attempting to extrapolate high temperature data. New factors can come in at either end of the temperature range which are inoperative at the other extreme.The experimental procedures used are described, and the special precautions necessary for operation down to the 140-150°C range indicated. Problems arising from sample inhomogeneities are discussed, and the critical importance of stabilizer migration in the solid state pointed out, including invalidation of extrapolation down to normal temperatures of data taken above the melting range.

Towards a Non Empirical Kinetic Model for the Lifetime Prediction of Polyethylene Pipes Transporting Drinking Water

“…-Antioxidants concentration (determined by differential calorimetry, assuming that the oxidation induction time (OIT) is directly proportional to the remaining antioxidants concentration [17,18] );…”

Measurement of the oxidative stability of polyethylene by differential thermal analysis

“…There is evidence to show that, for a variety of reasons [3], the induction time for polyethylene materials decreases with age [1 ]. Table 2 gives some results for induction times measured at various time intervals for a sample previously aged Each result is the average of at least four determinations for twelve weeks, and the noted trend is evident.…”

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An evaluation has been made of the experimental features critical to the evaluation of the oxidative stability of polyethylene using constant temperature DTA, with particular reference to the control and measurement of the sample temperature.The use of the DTA technique at constant temperature to measure the oxidative stability of polyethylene and other polyolefines as an alternative to the oxygen adsorption method is well established [1,2]. However, the DTA method relies heavily on the rigorous control of experimental factors in order to produce reliable and accurate results.

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“…However, the DTA method relies heavily on the rigorous control of experimental factors in order to produce reliable and accurate results. One main method for the measurement of oxidative stability involves heating the test sample at a constant temperature of 200 +_ 1 ~ [1 ]. Hence the three essential requirements of any DTA instrument used in this test are the maintenance of the DTA cell within 1 ~ of the required constant temperature for at least the duration of the test; the accurate measurement of the sample temperature; and the capability to display this temperature with high resolution.…”

“…Hence the three essential requirements of any DTA instrument used in this test are the maintenance of the DTA cell within 1 ~ of the required constant temperature for at least the duration of the test; the accurate measurement of the sample temperature; and the capability to display this temperature with high resolution. The present investigation has been concerned with an evaluation of the parameters which are critical to the determination of the oxidative induction time (sometimes abbreviated to OIT [1]) of polyethylene.…”