Characterisation of the mechanical performance of a novel thermoplastic film adhesive

This study presents a comprehensive mechanical characterisation of a novel, transparent, amorphous thermoplastic hot-melt adhesive (HMA) film, based on a cyclo olefin polymer, engineered for applications in the automotive, electronics and semi-structural bonding sectors. Quasi-static tensile tests reveal typical thermoplastic behaviour, cold drawing followed by strain hardening, with a Young's modulus of 230 MPa, a tensile strength of 11 MPa and an exceptional elongation at break of 1000%. Thick adherend shear tests (TAST) yield a shear strength of 5 MPa. Fracture behaviour was investigated under Mode I and Mode II loading. Double cantilever beam (DCB) tests on CFRP substrates provide an apparent Mode I fracture energy of 0.43 N/mm. Despite minor substrate rotation and stretching effects, the results indicate a predominantly ductile response of the adhesive layer. End-notched flexure (ENF) tests reveal more complex Mode II behaviour: an initial peak fracture energy of 2.6 N/mm is obtained after a sustained plateau near 0.5 N/mm, interpreted as the onset of permanent plastic damage. This plateau, uncommon in comparable thermoplastic adhesives, suggests a progressive transition from brittle to ductile failure and consistently coincides with adhesive failure at the interface. Dynamic mechanical analysis (DMA) identifies a glass transition temperature of 88°C. Collectively, these results demonstrate that the material offers strong potential for applications requiring thermal resistance and pressure-tolerant bonding, though enhancements in interfacial adhesion are needed to fully optimize performance.