Eutectic Open Times of APO Mixtures, 1993 Hot Melt Symposium Proceedings

L. W. Hilscher

Typical users of APO’s expect that the open time of a mixture of two APO’s can be safely interpolated from the open times of the neat materials. Surprisingly this is not always the case. In some instances the open time of the mixture is significantly shorter than the open time of the neat polymers. The description ‘eutectic open time’ has been conferred to this phenomenon due to its similarity to the eutectic fusion/melting points well known in metallurgy/chemistry.

Examples of eutectic open times which demonstrate dramatic deviations from expected values are known, but more subtle differences can also be important. To reliably detect these requires a test with improved reproducibility over those we have used in the past. We have developed such a test for measuring polymers/formulations with relatively long open times (twenty seconds or more). It incorporates mechanical operations as much as possible to minimize the variation associated with human execution and judgment. It also makes use of a bond strength vs open time curve instead of a single open time value.