Fast Determination of Degree of Cross-Linking
When extruding PE, cross-linking can significantly improve the material's properties. In this regard, determining the degree of cross-linking is an important method for monitoring quality. To date, the fraction of cross-linked chains has been established by determining the gel content by means of solvent extraction at an elevated temperature. This test method, however, requires quite a bit of effort.
New investigations show that rheological measurements offer an alternative and reliable approach to determining the degree of cross-linking. This approach exploits the fact that above the melt temperature of the crystals the cross-linked material acts like an elastomer. Using a rheometer, the dynamic modulus can be measured in a dynamic-mechanical experiment. The result is directly proportional to the number of cross-linking locations.
Investigations of silane-cross-linked PE-X have shown that testing for the degree of cross-linking by means of a rheometer exhibits a convincing correlation to methods used to date. Initial investigations of peroxide- and radiation-cross-linked PE pipe confirm that the measurement method can also be applied to these cross-linking agents.
The decisive benefit of the new method is that the test results are available very quickly. The rheological test takes about 7 minutes, while the previously used test method requires approximately 24 hours. Additional benefits include the qualitative and quantitative evaluation of the quality of cross-linking as well as economic and ecological potentials. The new test method thus offers the best prerequisites for in-process monitoring of production in industrial production.
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