Observation and Control\nof Single-Component Adhesion\nInterphase of Polyamide 66 through Confocal Raman Microspectroscopy

Manufacturing using adhesion technology has attracted\nmuch attention.\nExamples of adhesion include the lay-up of carbon fiber reinforced\nthermoplastic prepregs and the lamination of food packaging. In single-component\nadhesion systems, the analysis of the boundary region poses challenges\nbecause of the absence of chemical and physical discrimination at\nthe adhesion interphase. Polyamide 66, one of the typical engineering\nplastics, is widely accepted as a structural material in automobiles\nand packaging films. Therefore, finer control of adhesion with polyamide\n66 is crucial for advancing adhesion manufacturing. In this work,\nwe focused and investigated the interphase of a single-component\nadhesion system with polyamide 66. For the analyses of single-component\npolyamide 66 laminates, an adhesion system with nondeuterated and\ndeuterated polyamides was utilized, and their interphase structures\nwere evaluated by confocal Raman microspectroscopy. The interphase\nregion of the adhesion specimens was able to be characterized and\nevaluated, revealing an expansion to a thickness of several micrometers.\nThe interphase thickness was increased with thermal annealing postlamination,\nwhereas no thickness increase was observed in adhered specimens using\nthe polyamide 66 substrates through thermal crystallization before\nlamination. The formation of the interphase region can be attributed\nto the crystal growing and lamella interlocking in the boundary region.\nMoreover, the larger interphase thickness was strongly associated\nwith an increase in adhesion fracture toughness. These results suggested\nthat the adhesion properties of crystalline substrates were decided\nby crystallization behavior and the thermal annealing process, even\nwhen using the same component adhesion systems.