High‐Performance, Light‐Stimulation Healable, and Closed‐Loop Recyclable Lignin‐Based Covalent Adaptable Networks

Abstract

In this work, high‐performance, light‐stimulation healable, and closed‐loop recyclable covalent adaptable networks are successfully synthesized from natural lignin‐based polyurethane (LPU) Zn2+ coordination structures (LPUxZy). Using an optimized LPU (LPU‐20 with a tensile strength of 28.4 ± 3.5 MPa) as the matrix for Zn2+ coordination, LPUs with covalent adaptable coordination networks are obtained that have different amounts of Zn. When the feed amount of ZnCl2 is 9 wt%, the strength of LPU‐20Z9 reaches 37.3 ± 3.1 MPa with a toughness of 175.4 ± 4.6 MJ m−3, which is 1.7 times of that of LPU‐20. In addition, Zn2+ has a crucial catalytic effect on “dissociation mechanism” in the exchange reaction of LPU. Moreover, the Zn2+‐based coordination bonds significantly enhance the photothermal conversion capability of lignin. The maximum surface temperature of LPU‐20Z9 reaches 118 °C under the near‐infrared illumination of 0.8 W m−2. This allows the LPU‐20Z9 to self‐heal within 10 min. Due to the catalytic effect of Zn2+, LPU‐20Z9 can be degraded and recovered in ethanol completely. Through the investigation of the mechanisms for exchange reaction and the design of the closed‐loop recycling method, this work is expected to provide insight into the development of novel LPUs with high‐performance, light‐stimulated heal ability, and closed‐loop recyclability; which can be applied toward the expanded development of intelligent elastomers.

Degradable and Biobased Covalent Adaptable Networks for Light Controllable Switch

“…Preparation of LPU and LPU-G. According to our previous research, 21,22 lignin-based polyurethane CANs were synthesized with NCO/OH = 0.8. In the first step, the hydroxyl values of lignin-graphite composite particles and lignin were characterized using 31 P NMR.…”

“…These nanocomposites demonstrated repeatable PTC behavior and allowed for reprocessing and closed-loop chemical recycling . Leveraging the polyhydroxyl groups on the surface of lignin, our previous studies have shown the successful preparation of lignin-based adaptable polyurethane networks (LPU) capable of exchange reactions without the use of a catalyst. , In this study, by incorporating lignin-graphite nanosheet composite particles, we obtained lignin-based stimulus-responsive polyurethane (LPU-G) with the LPTC effect. Furthermore, the utilization of biobased PDI and a significant amount of lignin endowed LPU and LPU-G with degradability.…”

Lignin Modification for Enhanced Performance of Polymer Composites

“…249 Polyurethanes possess unique qualities that make them valuable, including low density, high strength-to-weight ratio, low thermal conductivity, low moisture permeability, and good dimensional stability. 250 The mechanical performance of polyurethane foams is classified based on their core densities and the use of stiff or semirigid polymers. In the study conducted by Wang et al 251 petrochemical polyols were partially substituted with alkali lignin during the develop PU.…”

“…However, lignin can now be utilized to create a three-dimensional cross-linking structure that improves the material’s tensile strength and durability. , Polyurethanes made from biomass sources are more easily broken down by natural processes compared to those made from polyols derived from petroleum . Polyurethanes possess unique qualities that make them valuable, including low density, high strength-to-weight ratio, low thermal conductivity, low moisture permeability, and good dimensional stability . The mechanical performance of polyurethane foams is classified based on their core densities and the use of stiff or semirigid polymers.…”

Room-Temperature Dynamic and Creep-Resistant Covalent Adaptive Networks via Phase-Locked Benzimidazole Urea Bonds: Toward Recyclable Elastomers for Wearable Electronic Devices

“…Elastomers are widely used as substrates for fabricating flexible electronic devices − as they possess excellent resilience performance and allow for excellent conformal contact with the body or internal organ surfaces to enable strain sensing with high sensitivity for potential applications in soft robotics, human–machine interfaces5, − and healthcare. − Electronic waste generated after service failure from wearable flexible devices causes serious pollution and has attracted widespread attention and deserves to be disposed of. Thermoplastic elastomer − with physical cross-linking via supramolecular interaction such as hydrogen bonding, − metal coordination, − and ionic interaction or microphase separation structures combined − by these interactions have been widely employed to fabricate healable and recyclable wearable electronic devices, but at the expense of sacrificing the resilience performance and creep resistance which has a big influence on the sensitivity and service stability of the fabricated devices. Chemical cross-linking of the elastomer via covalent bonds is capable of improving the resilience and dimension stability, but the challenge remains in achieving the recycling of the devices after service failure.…”