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A novel in situ method to determine volume shrinkage of curing adhesives

ABSTRACT This publication presents a novel in-situ method, which combines a rotational rheometer and optical measurement of the sample geometry for accurate determination of volume shrinkage. The presented method includes shrinkage measurements in the rotational rheometer with simultaneous observation of the specimen’s meniscus by a laser distance sensor. The combination enables detection of time-dependent dimensional changes in axial and lateral direction. Therefore, volumetric shrinkage can be detected accurately in a rheometer for the first time. To establish the methodology, measurements were carried out on two non-curing resin components. For validation, experiments with constant volume at different gap sizes were carried out. Results indicate that the accuracy of the method enables the measurement of shrinkage of reactive adhesives. For a translucent adhesive or resin, it was also shown that the penetration behaviour of the light can be taken into account when evaluating the results. Subsequently, the extension of a rotational rheometer by an optical distance measurement allowed evaluation of volume shrinkage for a 2-component epoxy by tracking changes in the axial gap and of the meniscus (lateral shrinkage) for two testing scenarios. This approach extends and improves previous methods that only determine the volume shrinkage by tracking the plates of a rheometer. Furthermore, trim gaps and other edge effects may be taken into account as well, focussing on their deviation from the otherwise assumed cylindrical shape.