Stretchable, self-healable integrated conductor based on mechanical reinforced graphene/polyurethane composites

Recyclable Dynamic Covalent Networks Derived from Isocyanate Chemistry: The Critical Role of Electronic and Steric Effects in Reversibility

The dynamic covalent networks (DCNs), featuring dynamic covalent bonds (DCBs) formed through isocyanate-involved chemistry, potentially contributes to a circular economy in polyurea and polyurethane industries, due to the inherent recyclability of DCNs. Over the past decade, remarkable progress has been made in the development of isocyanate-derived DCBs (IdDCBs) for the synthesis of recyclable DCNs, aiming to substitute conventional, non-recyclable materials. Herein, the fundamental aspect of the IdDCB-related chemistries reported to date is investigated, and it is found that their reversibility is governed by electronic and steric effects. This discovery encourages us to structure the review into three sections. The first section examines the reversibility of various IdDCBs through the lens of electronic and steric influences. The findings show that the reversibility of some IdDCBs is driven by a single chemical effect, with the examples of steric effect contributing to the dynamic behavior of thiourethanes and hindered ureas, while other cases of reversibility arise from a combination of two or more chemical effects. The knowledge thus established allows to categorize and discuss the technologically relevant DCNs, with particular emphasis on how these chemical effects influence their recyclability. Finally, the review concludes by highlighting several potentially impactful research directions that merit further exploration.

Self-Healing Polyurethane Elastomers with Superior Tensile Strength and Elastic Recovery Based on Dynamic Oxime-Carbamate and Hydrogen Bond Interactions

The preparation of self-healing polyurethane elastomers (PUEs) incorporating dynamic bonds is of considerable practical significance. However, developing a PUE with outstanding mechanical properties and high self-healing efficiency poses a significant challenge. Herein, this work has successfully developed a series of self-healing PUEs with various outstanding properties through rational molecular design. These PUEs incorporate m-xylylene diisocyanate and reversible dimethylglyoxime as hard segment, along with polytetramethylene ether glycol as soft segment. A significant amount of dynamic oxime-carbamate and hydrogen bonds are formed in hard segment. The microphase separated structure of the PUEs enables them to be colorless with a transparency of >90%. Owing to the chemical composition and multiple dynamic interactions, the PUEs are endowed with ultra-high tensile strength of 34.5 MPa, satisfactory toughness of 53.9 MJ m-3, and great elastic recovery both at low and high strains. The movement of polymer molecular chains and the dynamic reversible interactions render a self-healing efficiency of 101% at 70 °C. In addition, this self-healing polyurethane could still maintain high mechanical properties after recycling. This study provides a design strategy for the preparation of a comprehensive polyurethane with superior overall performance, which holds wide application prospects in the fields of flexible displays and solar cells.

Room-temperature self-healing polyurethane-cellulose nanocrystal composites with strong strength and toughness based on dynamic bonds

Self-healing materials suffer from a trade-off relationship between their self-healing ability and mechanical strength, which limits their applications. Therefore, we developed a room-temperature self-healing supramolecular composite based on polyurethane (PU) elastomer, cellulose nanocrystals (CNCs), and multiple dynamic bonds. In this system, the abundant hydroxyl groups on the surfaces of the CNCs form multiple hydrogen bonds with the PU elastomer, yielding a dynamic physical cross-linking network. This dynamic network enables self-healing without degrading the mechanical properties. As a result, the obtained supramolecular composites exhibited high tensile strength (24.5 ± 2.3 MPa), good elongation at break (1484.8 ± 74.9 %), favourable toughness (156.4 ± 31.1 MJ m^-3, which is equivalent to that of spider silk and 5.1-times higher than that of aluminium), and excellent self-healing efficiency (95 ± 1.9 %). Notably, the mechanical properties of the supramolecular composites were almost completely retained after reprocessing three times. Further, using these composites, flexible electronic sensors were prepared and tested. In summary, we have reported a method for preparing supramolecular materials having high toughness and room temperature self-healing ability that have applications in flexible electronics.

Injectable chitosan-based self-healing supramolecular hydrogels with temperature and pH dual-responsivenesses

In this study, a supramolecular hydrogel was fabricated with orotic acid (OA) modified chitosan (OACS) and 2,6-diaminopurine (DAP). The obtained OACS-DAP supramolecular hydrogels have dual responsiveness to temperature and pH. Phase transition experiments indicate this is a temperature-dependent thermoreversible supramolecular hydrogel. Rheological experiments proved the formation of the supramolecular hydrogel and its thixotropic properties. FTIR spectra confirmed that hydrogen bonds and π-π interactions are the main driving forces for OACS and DAP to form hydrogels through intermolecular self-assembly. XRD pattern confirmed the amorphous morphology of OACS-DAP hydrogels. The hydrogel has excellent electrical conductivity with a conductivity of 9.48 μ S·cm^-1. And can achieve the precise release of gastrointestinal drugs. OACS-DAP hydrogel is expected to have better applications in the field of gastrointestinal drug release.

A review on room-temperature self-healing polyurethane: synthesis, self-healing mechanism and application

Polyurethanes have been widely used in many fields due to their remarkable features such as excellent mechanical strength, good abrasion resistance, toughness, low temperature flexibility, etc. In recent years, room-temperature self-healing polyurethanes have been attracting broad and growing interest because under mild conditions, room-temperature self-healing polyurethanes can repair damages, thereby extending their lifetimes and reducing maintenance costs. In this paper, the recent advances of room-temperature self-healing polyurethanes based on dynamic covalent bonds, noncovalent bonds and combined dual or triple dynamic bonds are reviewed, focusing on their synthesis methods and self-healing mechanisms, and their mechanical properties, healing efficiency and healing time are also described in detial. In addition, the latest applications of room-temperature self-healing polyurethanes in the fields of leather coatings, photoluminescence materials, flexible electronics and biomaterials are summarized. Finally, the current challenges and future development directions of the room-temprature self-healing polyurethanes are highlighted. Overall, this review is expected to provide a valuable reference for the prosperous development of room-temperature self-healing polyurethanes.

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A Flexible Sandwich Structure Carbon Fiber Cloth with Resin Coating Composite Improves Electromagnetic Wave Absorption Performance at Low Frequency

In order to improve the electromagnetic wave absorbing performance of carbon fiber cloth at low frequency and reduce the secondary pollution caused by the shielding mechanism, a flexible sandwich composite was designed by a physical mixing coating process. This was composed of a graphene layer that absorbed waves, a carbon fiber cloth layer that reflected waves, and a graphite layer that absorbed transmitted waves. The influence of the content of graphene was studied by a control variable method on the electromatic and mechanical properties. The structures of defect polarization relaxation and dipole polarization relaxation of graphene, the interfacial polarization and electron polarization of graphite, the conductive network formed in the carbon fiber cloth, and the interfacial polarization of each part, combined together to improve the impedance matching and wave multiple reflections of the material. The study found that the sample with 40% graphene had the most outstanding absorbing performance. The minimum reflection loss value was -18.62 dB, while the frequency was 2.15 GHz and the minimum reflection loss value compared to the sample with no graphene increased 76%. The composites can be mainly applied in the field of flexible electromagnetic protection, such as the preparation of stealth tent, protective covers of electronic boxes, helmet materials for high-speed train drivers, etc.

Dynamic covalent polymers enabled by reversible isocyanate chemistry

Reversible isocyanate chemistry containing urethane, thiourethane, and urea bonds is valuable for designing dynamic covalent polymers to achieve promising applications in recycling, self-healing, shape morphing, 3D printing, and composites.