Investigation of extrusion defects

In the case of the second fault, in which DSC indicated a contaminant, no significant difference in TMA response was found between matrix and fault position, and this led to the conclusion that this fault was not a consequence of pre-cross-linking. 

The cross-linking of materials such as polyethylene, ethylene propylene rubber and some other rubbers used for cable insulation and sheathing is conventionally measured for quality purposes by means of a test of elongation imder a specified load at elevated temperature of the permanent set measured when the load is removed and the sample allowed to cool. This hot-set test is very good when it is possible to cut appropriately sized tensile test dumb-bells for the measurement. Where samples are irregular and small, as may be the case in work of a more investigative nature, it is much more difficult to apply, and TMA has been applied, albeit in a fairly qualitative way, to the problem of finding out if a specimen is cross-linked. 

It would be possible to obtain more quantitative data by measurement of gel fraction by solvent extraction of the material in order to effect calibration but this is a time-consuming process and for a single measurement it would render the TMA measurement redundant. If the TMA data are considered hkely to prove fit for purpose, they can be obtained easily and quickly, an advantage in an environment where information maybe required on an urgent basis. 

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