Investigation of the effect of exposure time at room temperature in a structural epoxy resin adhesive film

Abstract

The exposure of epoxy based adhesive films to room temperature provides conditions that directly affects their physical properties. For structural adhesive AF191, application in the aerospace industry, this can be confirmed by the sudden loss of tack. Therefore, the behavior of the chosen resin system was experimentally studied, by means of the exposure to laboratory environment at pre determinated time interval and different storage periods (–18°C).The effect of the exposure was evaluated by means of physicochemical tests based on international standards, being complimented by not normalized empirical tests that aimed to observe some specific behavior of the resin, like flow and solubility. From the results, it was possible to observe changes in the physicochemical behavior that affects the adhesive processability conditions such as adhesive flow capacity, self adhesiveness reduction and solubility to organic solvent. These changes suggest that there was a possible increase in the number of crosslinking of the polymer matrix at room temperature. This fact however was not proven by the used thermal analysis method (differential scanning calorimetry – DSC), where since there was no significant change in cure enthalpy was observed during the exposure period. This can be attributed to a very low curing rate of the matrix or just low sensitivity of the method. The change in behavior can be related to the lamination process the polymer matrix caused by moisture absorption due to the hygroscopic nature of the epoxy matrix, which can be found in the progressive increase in the volatile content test. The storage period was efficient indicating no significant change in the characteristics evaluated the adhesive.

Keywords:
adhesive; epoxy resin; cure; flow; solubility