Chemically Recyclable Supramolecular Thermosets toward Strong and Reusable Hot-Melt Adhesives
Chunyang Bao, Yanlong Yin, Yuhan Ding, Jianyu Liu, Yang Xu, Ruoxuan Miao, Zhijie Liu, Baorong Duan, Yusheng Qin, Zhirong Xin
Abstract
Chemically recyclable thermosets are an ideal substitute for traditional thermosets in the development of a circular economy and sustainable environment. However, the development of efficient and easy-to-achieve chemical recycling strategies remains challenging. Herein, a series of supramolecular thermosets that can be chemically recycled under mild acid conditions at room temperature are fabricated by cross-linking the polyimine polymers with dynamic boroxines (PI x -Boroxine). By tailoring the molar content of boroxines, the PI 1.2 -boroxine can exhibit a tensile strength of ∼30.6 MPa, a tensile yield strength of 33.0 MPa, an elongation at break of ∼111.6%, and a Young’s modulus of ∼679.6 MPa. Because of the dynamic nature of boroxines and imine bonds, the PI x -boroxine supramolecular thermoset exhibits fast stress relaxation behavior, which enables them to have good reprocessing ability. These unique features can also guarantee the PI x -boroxine supramolecular thermosets to be a high-performance reusable hot-melt adhesive. The maximum lap shear strength of the PI x -Boroxine-based hot-melt adhesives in stainless steel bonding adhesive can reach ∼18.6 MPa, which is comparable to that of commercial hot-melt adhesives. Meanwhile, the PI x -Boroxine-based hot-melt adhesives can be reused at least 10 times with only a small amount of reduction in lap shear strength. More importantly, the PI x -boroxine supramolecular thermosets can be easily depolymerized in a 0.1 M HCl/H 2 O solution at room temperature. Further, the monomers can be easily and efficiently separated by a simple separation procedure. The recovered monomers can also be reused to fabricate new PI x -boroxine supramolecular thermosets without losing their mechanical properties. This work provides a new design strategy to develop high-performance thermosets with easy-to-achieve chemical recyclability, which will contribute to the sustainable development of modern society.