Development of a dilatometer and measurement of the shrinkage behaviour of adhesives during cure

The rheological properties of thermosetting adhesives change from liquid to solid via a gelation phase during cure. Accompanying these changes, shrinkage occurs in the adhesives. A dilatometer, designed in-house and developed specifically for this investigation, enables the volume change of the adhesives to be monitored and measured automatically and continuously during the cure in the heating and cooling phases. Furthermore, the different contributions to the volume changes due to thermal expansion, polymerisation shrinkage, and cooling contraction can be separated. During the cure process, the adhesive not only contracts, but this is also coupled with heat generation due to the exothermic nature of the reaction. By recording the variation of temperature within the adhesives being tested, an indication of the shrinkage rate, and the uniformity of contraction within the adhesive during cure was obtained. It has been shown that among the different volume change stages, the largest change generally takes place in the middle stage of the cure process, due to polymerisation shrinkage.