Adhesion to Untreated Polyethylene and Polypropylene by Needle-like Polyolefin Crystals

Polyolefins, such as polyethylene and polypropylene, are globally the most widely used plastics and are considered to be essential materials. Because they lack polar groups, polyolefins are poorly adhesive, which poses serious recycling challenges. Here, we describe a novel adhesion system involving a polyurethane adhesive and an untreated polyolefin, in which the interface is tightly bound by needle-like polyolefin crystals in the same way that nails adhere to wood. The polyurethane and polyolefin inter-diffuse at high temperatures to form a mixed interfacial layer, after which the polyolefin recrystallizes in the layer upon cooling. Polyurethanes with optimally balanced non-polar and polar blocks exhibit superior adhesion due to their larger miscibility windows, polyolefin compatibilities, and the resulting long needle-like polyolefin crystals.

Automated summary

Polyolefins, the most widely used plastics globally, have poor adhesion due to the lack of polar groups, which poses challenges for recycling. In this study, a novel adhesion system using a polyurethane adhesive and an untreated polyolefin was described, where the interface is tightly bound by needle-like polyolefin crystals similar to nails adhering to wood. The polyurethane and polyolefin inter-diffuse at high temperatures, forming a mixed interfacial layer that recrystallizes upon cooling. Polyurethanes with optimally balanced non-polar and polar blocks exhibit superior adhesion due to their larger miscibility windows, polyolefin compatibilities, and the resulting long needle-like polyolefin crystals.