Fracture Behavior in Nailing Adhesion using Needle-like Polyolefin Crystals

What is it about?

In this study, we report on the fracture behavior observed during the debonding of our previously developed “nailing adhesion” system. In this adhesion method, spontaneously formed nanoscale needle-like polyolefin crystals physically fasten a polyurethane adhesive to a polyolefin substrate in a manner analogous to mechanical nailing. Polyethylene (PE) and polypropylene (PP) were employed as the polyolefin substrates. Because these unique needle-like crystals bridge the two plastics, this method enables adhesion to untreated PE and PP—materials traditionally regarded as extremely difficult to bond. We have previously shown that, even when using the same polyurethane adhesive, the length of the resulting needle-like crystals differs between PE and PP, leading to corresponding differences in peel strength.

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Why is it important?

To elucidate the origin of this intriguing contrast, we conducted a comprehensive analysis combining multiple characterization techniques. Our results reveal that the fracture behavior of the needle-like crystals differs fundamentally between PE and PP, and that these differences govern the overall adhesion performance. The relatively ductile PE needles undergo elongation under applied stress and eventually fail by rupture, a process that consumes significant energy due to deformation of the polymer. In contrast, the stiffer PP needles fracture in a brittle manner without noticeable elongation, completing the failure process with considerably lower energy input.

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