Temperature retraction test

A particular form of recovery test developed as a measure of low temperature behaviour is the so-called temperature-retraction test (TR test) which is standardised internationally as ISO 292113. The test consists of stretching a dumb-bell test piece, placing it in the stretched condition in a... 

In principle, any of the low temperature tests can be used to study crystallisation effects by conditioning the test pieces at the low temperature for much longer times than is usual. In fact, most of the standard methods include a clause to the effect that the method can be used in this way. In the temperature retraction test, it is suggested that the greater degrees of applied elongation are used when the effects of crystallisation are to be considered, because crystallisation is more rapid in the strained state. 

The obvious ways to measure the temperature at which the ability to recover from a deformation is lost are by the loss tangent from dynamic tests or by compression or tension set measurements. Dynamic analyzers arc an excellent way of characterizing low-temperature characteristics, stiffness as well as viscous loss, but they are a relatively modern invention and expensive. It is, how ever. a little. surprising that rebound resilience tests have not been commonly used. Set is quite often used, with compression set being favored over tension set. A particular form of recovery test developed and standardized for measurement of low-temperature behavior is the so-called temperature retraction test. This consists of stretching a dumbbell test piece, placing it in a bath at -70 C. and allowing it to retract as the temperature is raised- in a sense a variation on tension set. 

In the temperature retraction test (ASTM D 1329), the test specimen is stretched to a specified elongation and then frozen at -70°C. Then it is gradually warmed until it begins to retract toward its original unstretched dimensions. The temperature at which the specimen retracts by 10 percent correlates with the brittleness temperature. 

ISO 2921 1997 Rubber, vulcanized - Determination of low-temperature characteristics -Temperature-retraction procedure (TR test)... 

ASTM D1329, 2002. Retraction at lower temperatures (TR Test). 

In Scandinavia the temperature retraction (or TR) test is reported to be especially popular and to give the best overall level of reproducibility [59]. The test described in ISO 2921. BS903, Part A29, and ASTM DI329 involves first cooling an extended test piece to a temperature at which it does not recover and then measuring the temperature at which a specified retraction occurs. 

Low-temperature properties D1329 Evaluating rubber property— retraction at lower temperatures (TR test) 9.01... 

ASTM D1329-08, Standard Test Method for Evaluating Rubber Property — Retraction at Lower Temperatures (TR Test) (Philadelphia, 2008)... 

Low Temperature Properties. The property of solvent resistance makes fluorosihcone elastomers usefiil where alternative fluorocarbon elastomers cannot function. The abiHty to retract to 10% of their original extension after a 100% elongation at low temperature is an important test result. Eluorosihcones can typically pass this test down to —59°C. The brittle point is approximately —68°C. 

It has been shown [56] that if we measure the areas under the approach and retract curves of the force-distance plot we can get quantitative values of the resilience. Resilience is closely related to the ability of the polymer chain to rotate freely, and thus will be affected by rate and extent of deformation, as well as temperature. Different materials will respond differently to changes in these variables [46] hence, changing the conditions of testing will result in a change in absolute values of resilience and may even result in a change in ranking of the materials. Compared to more traditional methods of resilience measurement such as the rebound resiliometer or a tensUe/compression tester. 

One method for determining the state of cure of a mbber compound. A sample of the rubber is stretched, cooled to a temperature of around -70 °C while stretched and then released. As the temperature rises the mbber retracts and the T-50 value is the temperature at which it has lost 50% of its original elongation. The T-50 test is now obsolescent. 

Correlations have been established between TIO (the temperature at which 10% retraction occurs) and brittleness temperature for broadly similar rubbers and between T70 and low-temperature compression set. The test can also be adapted to give a measure of crystallization. 

R.F. Boyer (Michigan Molecular Institute, Midland, Michigan) I have a comment in response to Prof. Maxwell s point. I have seen some Japanese data [T. Kato and N. Yanagihara, J. Appl. Polym. ScL, 26, 2139-2145 (1981)] on oriented poly(methyl methacrylate) in which the loss of orientation occurs largely at Tg but partly at Tn, however, T/ seems to be lower than what you would observe in a static DSC test without orientation. So, the retraction force is actually lowering the Til temperature. 

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