Dynamic crosslinked rubbers for a green future:A material perspective

Conventional rubber products, such as tires, seals, tubing, and damping systems are manufactured via a vulcanization process, which forms covalently crosslinked network structures and ensures mechanical robustness, thermal stability and chemical resistance. However, the covalent networks are permanent and these products cannot be reprocessed or reshaped, which makes vulcanised rubbers one of the major challenges facing waste management and the circular economy. To reduce waste pollution for products such as tires, conventional vulcanised rubbers must be replaced with reversibly crosslinked structures which are able to achieve mechanical robustness and chemical stability, whilst also being able to be reprocessed, reshaped, reused and recycled. State-of-the-art developments in supramolecular chemistry have shed light on a new generation of reprocessable elastomers and rubbers, which have the potential to tackle the long-standing issue of waste tire pollution. The introduction of dynamic covalent bonds or supramolecular interactions in traditional elastomers can produce reversibly crosslinked structures, where the synergy between the dynamic bonds in the network are carefully optimised to balance the ease of processing, mechanical properties, and structural stability. Furthermore, dynamic covalent bonds and supramolecular interactions can provide ‘living’ functions to elastomers, such as self-healing and stimuli-responsiveness. These properties can be further enhanced by the addition of nanofillers with tailored surface chemistry to provide a dual role as a dynamic crosslinker and reinforcing element. To create reprocessable and recyclable elastomers, the coupling of multiple dynamic interactions provides unlimited possibilities to optimise the structure and properties of recyclable rubbers. Here we critically overview the applications of dynamic chemistry in rubbers, with a focus on macromolecular design and strategies to balance the mechanical, functional (e.g. self-healing) and reprocessing properties.</p

Photopolymerizable Ionogel with Healable Properties Based on Dioxaborolane Vitrimer Chemistry

Ionogels are solid polymer gel networks loaded with ionic liquid (IL) percolating throughout each other, giving rise to ionically conducting solid electrolytes. They combine the mechanical properties of polymer networks with the ionic conductivity, non-volatility, and non-flammability of ILs. In the frame of their applications in electrochemical-based flexible electronics, ionogels are usually subjected to repeated deformation, making them susceptible to damage. It appears critical to devise a simple and effective strategy to improve their durability and lifespan by imparting them with healing ability through vitrimer chemistry. In this work, we report the original in situ synthesis of polythioether (PTE)-based vitrimer ionogels using fast photopolymerization through thiol-acrylate Michael addition. PTE-based vitrimer was prepared with a constant amount of the trithiol crosslinker and varied proportions of static dithiol spacers and dynamic chain extender BDB containing dynamic exchangeable boronic ester groups. The dynamic ionogels were prepared using 50 wt% of either 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide or 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate, both of which were selected for their high ionic conductivity. They are completely amorphous (Tg below &minus;30 &deg;C), suggesting they can be used at low temperatures. They are stretchable with an elongation at break around 60%, soft with Young&rsquo;s modulus between 0.4 and 0.6 MPa, and they have high ionic conductivities for solid state electrolytes in the order of 10&minus;4 S&middot;cm&minus;1 at room temperature. They display dynamic properties typical of the vitrimer network, such as stress relaxation and healing, retained despite the large quantity of IL. The design concept illustrated in this work further enlarges the library of vitrimer ionogels and could potentially open a new path for the development of more sustainable, flexible electrochemical-based electronics with extended service life through repair or reprocessing

Dynamic crosslinked rubbers for a green future:A material perspective

Conventional rubber products, such as tires, seals, tubing, and damping systems are manufactured via a vulcanization process, which forms covalently crosslinked network structures and ensures mechanical robustness, thermal stability and chemical resistance. However, the covalent networks are permanent and these products cannot be reprocessed or reshaped, which makes vulcanised rubbers one of the major challenges facing waste management and the circular economy. To reduce waste pollution for products such as tires, conventional vulcanised rubbers must be replaced with reversibly crosslinked structures which are able to achieve mechanical robustness and chemical stability, whilst also being able to be reprocessed, reshaped, reused and recycled. State-of-the-art developments in supramolecular chemistry have shed light on a new generation of reprocessable elastomers and rubbers, which have the potential to tackle the long-standing issue of waste tire pollution. The introduction of dynamic covalent bonds or supramolecular interactions in traditional elastomers can produce reversibly crosslinked structures, where the synergy between the dynamic bonds in the network are carefully optimised to balance the ease of processing, mechanical properties, and structural stability. Furthermore, dynamic covalent bonds and supramolecular interactions can provide ‘living’ functions to elastomers, such as self-healing and stimuli-responsiveness. These properties can be further enhanced by the addition of nanofillers with tailored surface chemistry to provide a dual role as a dynamic crosslinker and reinforcing element. To create reprocessable and recyclable elastomers, the coupling of multiple dynamic interactions provides unlimited possibilities to optimise the structure and properties of recyclable rubbers. Here we critically overview the applications of dynamic chemistry in rubbers, with a focus on macromolecular design and strategies to balance the mechanical, functional (e.g. self-healing) and reprocessing properties.</p

Interpenetrating Liquid Crystal Elastomer and Ionogel as Tunable Electroactive Actuators and Sensors

International audienceElectroactive liquid crystal elastomers (eLCEs) are used to make actuators and soft robotics. However, most eLCEs are monofunctional with one type of deformation (bending or contraction). Recently, a trilayer eLCE are reported by combining ion-conducting LCE and ionic electroactive polymer device (i-EAD). This i-EAD-LCE is bifunctional and performs either bending or contractile deformation by controlling low-voltage stimulation. Nevertheless, it has a Young's modulus of only 1.63 MPa. To improve the mechanical performance, the i-EAD-IPN-LCE is prepared here, whose central membrane is composed of interpenetrating LCE and ionogel (i-IPN-LCE) instead of a single ion-conducting LCE. This i-EAD-IPN-LCE with a typical thickness of 0.5 mm can function not only as linear and bending actuators, but also as a sensor. As a linear actuator, its Young's modulus, actuation stress, and strain are 51.6 MPa, 0.14 MPa and 9%, respectively, reaching skeletal muscles’ values. As a bending actuator, its bending strain difference Δε is 1.18% with 3 mN output force. It can also operate as a sensor producing 0.4 mV Open-Circuit-Voltage to respond to bending deformation (Δε = 9%). Therefore, this i-EAD-IPN-LCE is a promising system for the fabrication of robust electroactive devices and sensors with multiple degrees of freedom

Ionofibers: Ionically Conductive Textile Fibers for Conformal i-Textiles

With the rise of ion-based devices using soft ionic conductors, ionotronics show the importance of matching electronic and biological interfaces. Since textiles are conformal, an essential property for matching interfaces, light-weight and comfortable, they present as an ideal candidate for a new generation of ionotronics, i-textiles. As fibers are the building blocks of textiles, ionically conductive fibers, named ionofibers, are needed. However, ionofibers are not yet demonstrated to fulfill the fabric manufacturing requirements such as mechanical robustness and upscaled production. Considering that ionogels are known to be conformal films with high ionic conductivity, ionofibers are produced from commercial core yarns with specifically designed ionogel precursor solution via a continuous dip-coating process. These ionofibers are to be regarded as composites, which keep the morphology and improve the mechanical properties from the core yarns while adding the (ionic) conductive function. They keep their conductivity also after their integration into conformal fabrics; thus, an upscaled production is a likely outlook. The findings offer promising perspectives for i-textiles with enhanced textile properties and in-air electrochemical applications.WEAFIN