Moisture-sensitive smart hot-melt adhesive from polyamide 6

The bonding strength of a hot-melt adhesive composed of polyamide 6 (PA6) and lithium bromide (LiBr) with a metal plate was evaluated. PA6 containing LiBr showed strong lap shear strength with a metal plate immediately after hot-melt adhesion above the melting point of PA6, e.g., 1.0 MPa between PA6/LiBr (90/10) and aluminum plates. Owing to the high adhesive strength, the cohesive failure and/or plastic deformation of PA6 was detected during lap shear strength measurements. In contrast, separation was achieved without any difficulty after moisture absorption with a low strength, e.g., 0.1 MPa between PA6/LiBr (90/10) and aluminum plates. Furthermore, there was no trace of the adhesive on the metal plate after peeling. Therefore, this smart hot-melt adhesive provides an easy-peeling nature only through exposure to humid conditions as a trigger, which can be employed for various applications such as high-performance masking films.