Chemically Recyclable Supramolecular Thermosets toward Strong and Reusable Hot-Melt Adhesives

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 highperformance 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.

Dual Dynamic Cross-Linked Epoxy Vitrimers Used for Strong, Detachable, and Reworkable Adhesives

“…The tensile strength of DA30–DTSA70 was higher than others; at the same time, the order of magnitude of τ was the same as that of the reported high-strength vitrimer (reference S7 in Figure S9). …”

“…In order to further explore methods on enhancing adhesive strength of RTAs, dynamic covalent networks containing both rigid and flexible segments have attracted attention. The contradiction between strength and self-healing efficiency can be overcome by adjusting two types of polymer segments. ,, Zhao et al prepared a dynamic imine cross-linked polyimide adhesive film that included rigid and flexible segments. Adhesive strength to steel and carbon fiber-reinforced epoxy resin composite materials (CFRC) was 9.96 and 7.19 MPa, respectively.…”

“…Up until now, researchers have successfully synthesized new adhesives based on DCBs, realizing the integration of advantages of TA and HMA. − Furthermore, a notable advantage of some DCB-based novel adhesives is that they can be precured into films and placed at the joints. This feature significantly improves the uniformity, reliability, and stable storage time of adhesives. − ,, Zhang et al synthesized cross-linked polyurethane adhesive films containing dynamic polyurea bonds using diisocyanate and piperazine. The lap shear tests showed that maximum adhesive strength to aluminum plates was 1.9 MPa, and the minimum strength loss rate after 10 cycles was 21.1% .…”

“…Bao et al prepared a polyimide adhesive film with dynamic imine bonds and dynamic boron cross-links. Adhesive strength to stainless steel reached 18.6 MPa, and the recovery rate of strength reached 83.3% after 6 cycles . Although the combination of rigid and flexible chain segments was beneficial for improving strength while maintaining self-healing, research on this kind of adhesives is still insufficient, especially in terms of the impact of segment composition on the performance of vitrimers.…”

Mechanically Strong and Tough Plant Oil-Based Poly(ester amide) Vitrimers with Closed-Loop Recyclability

“…Plastics are integral to our daily lives, with hundreds of millions of tons of plastic being industrially produced annually. − Among them, chemically cross-linked thermoset plastics with prominent mechanical performance are usually characterized by structural stability and solvent resistance . As a result, the permanently cross-linked covalent networks make the plastics difficult to degrade or recycle, which has raised serious concerns on environmental issues including waste of resources and environmental pollution. − To solve this issue, a strategy of introducing dynamic covalent bonds into thermosetting plastics to construct covalent adaptive networks has been proposed .…”