Physical and mechanical properties of a reversible adhesive for automotive applications

In this work, a hot-melt adhesive used by automotive industries for bonding plastic components has been modified with three different percentages of nanofiller (iron oxide) in order to make the adhesive electromagnetically sensitive and to perform adhesive joint separations. Fe3O4 particles with a weight concentration of 3%, 5% and 10% were embedded in the adhesive matrix. Single Lap Joint (SLJ) tests showed that a slight increase of the maximum load and a more ductile behaviour are obtained. The sensitivity of these modified adhesive performance to the induction heating process was studied with respect to some relevant parameters: the current (or power), the frequency of the electromagnetic induction field and the shape of the coil. Furthermore, the diameter of the hollow copper coil was modified in order to understand whether the coil temperature has an effect on the separation time. The separation time, that is an index of the time needed to reach the melt of the adhesive and the consequent SLJ separation, together with the temperature profile of the adhesives have been used to evaluate the sensitivity of these adhesives to the process parameters. The analysis on the temperature and separation time showed that the most influencing parameter is the frequency of the electromagnetic induction field. As expected, also the shape of the coil influences the separation time, in particular, the adhesive joint separated with the pancake coil showed lower values of the separation time compared to the solenoidal coils. Scanning Electron Microscope (SEM) showed that iron oxide particles tend to form small agglomerate that resulted well dispersed in the adhesive matrix. Thermogravimetric analysis (TGA) was used to verify that the separation procedure do not degrades these modified adhesives.