Heat-sealable, transparent, and degradable arabinogalactan/polyvinyl alcohol films with UV-shielding, antibacterial, and antioxidant properties.

Petroleum-based packaging materials are nondegradable and unsustainable and thus are harmful to the environment. Renewable packaging films prepared from bio-based raw materials are promising alternatives to petroleum-based packaging materials. In this study, colorless and transparent bio-based films were successfully cast using a solution containing a mixture of arabinogalactan (AG) and poly (vinyl alcohol) (PVA). Vanillin was incorporated into the mixture to endow the films with UV-shielding, antioxidant, and antibacterial properties. The morphological, physical, antioxidant, and antibacterial properties of the blend films were then characterized. At an AG:PVA weight ratio of 1:3, and the vanillin content was 0.15 %, the tensile strength of the AG/PVA/Vanillin (APV) films reached ~28 MPa, while their elongation at break reached ~475 %. The addition of vanillin significantly affected the antioxidant and antibacterial properties of the blend films, which exhibited superb UV barrier capacity. The APV films exhibited extremely low oxygen transmittance, delaying the onset of mold/rot in strawberries and reducing their weight loss. Because of the heat sealability of the blend films, they can be used for encapsulating various substances, such as concentrated laundry liquid. Moreover, the blend films were recyclable and biodegradable. Thus, these films have great potential for applications that require sustainable packaging.

High-Performance Flexible Ionically Conductive Superhydrophobic Papers via Deep Eutectic Polymer-Enhanced Interfacial Interactions.

Endowing paper with highly flexible, conductive, and superhydrophobic properties will effectively expand its applications in fields such as green packaging, smart sensing, and paper-based electronics. Herein, a multifunctional superhydrophobic paper is reported in which a highly flexible transparent conductive substrate is prepared by introducing a hydrophobic deep eutectic polymer into the ethylcellulose network via a matrix swelling-polymerization strategy, and then the substrate is modified using fluorinated silica to impart superhydrophobicity. By introducing soft deep eutectic polymers, (1) the superhydrophobic paper can efficiently dissipate energy during deformation, (2) intrinsically ion-conducting deep eutectic polymers can endow the material with good electrical sensing properties, and (3) meanwhile, enhanced interfacial interactions can anchor inorganic particles, thereby improving the coating stability. The prepared superhydrophobic paper has an ultrahigh water contact angle (contact angle ≈ 162.2°) and exhibits a stable electrical response signal to external deformation/pressure, and the electrical properties are almost unaffected by external water molecules. In addition, the superhydrophobic paper was able to withstand 5000 bending-recovery cycles at a large angle of 150°, exhibiting stable electrical performance. The design concepts demonstrated here will provide insights into the development of superhydrophobic paper-based flexible electronic devices.

Green, recyclable, mechanically robust, wet-adhesive and ionically conductive cellulose-based bioplastics enabled by supramolecular covalent hydrophobic eutectic networks.

The development of novel cellulose-based bioplastics (CBPs) is highly desirable because CBPs are green, rationally use resources, and lead to a reduction in environmental pollution compared to alternative materials. However, incorporating high transparency, water resistance, mechanical robustness, wet-adhesion, ionic conductivity and recyclability into CBP remains a challenge. In this paper, novel CBPs with supramolecular covalent networks are fabricated by introducing polymerizable hydrophobic deep eutectic solvents (HDES) into ethylcellulose (EC) networks through in situ plasticization followed by a rapid photopolymerization process. The excellent molecular interfacial compatibility enables EC to be loaded with a high content of poly(HDES), while allowing high transparency (more than 90 %) of the prepared CBPs. Multiple intermolecular interactions provide CBPs with mechanical robustness, water resistance, and underwater adhesion, and CBPs can be readily recovered by the solvent in a closed loop. Moreover, CBPs possess inherent ionic conductivities, and using them as green substrates, personalized electroluminescent devices can be successfully constructed. The method proposed in this paper provides a new strategy for the preparation of multifunctional CBPs, which will greatly enrich their applications in self-adhesive materials, green flexible electronics and other package materials.

Construction of Poly(hydrophobic deep eutectic solvent)/Ethylcellulose Composite Films for Green Recyclable Tapes.

Constructing green recyclable cellulose-based tapes with high transparency, mechanical robustness, and strong wet adhesion using natural components is highly desirable but challenging. Herein, novel cellulose-based self-adhesive tapes were reported by coating a polymerizable hydrophobic deep eutectic solvent (DES) on ethylcellulose followed by photopolymerization. The prepared ethylcellulose-based self-adhesive tape (ECSAT) exhibited an optical transmittance of up to ∼88% and could provide strong adhesion by interfacial intermolecular interactions without obstructing information. Due to the hydrophobic nature of the overall structure, ECSAT does not exhibit significant adhesive strength and mechanical degradation under water, acid, and alkali environments. Notably, ECSAT can be completely dissolved in the resultant DES and furthermore reused as a self-adhesive coating. The recycled ECSAT still maintained good optical transparency, mechanical strength, and wet adhesion. We believe that ECSATs with all-around performances have a wide range of applications in packaging and other engineering fields.

Self-adhesive, ionic-conductive, mechanically robust cellulose-based organogels with anti-freezing and rapid recovery properties for flexible sensors.

Cellulose-based functional gels have received considerable attention because of their good mechanical properties, biocompatibility, and low cost. However, the preparation of cellulose gels with self-adhesion, mechanical robustness, ionic conductivity, anti-freezing ability, and environmental stability remains a challenge. Here, gallic acid esterified microcrystalline cellulose (MCC-GA) was obtained by grafting gallic acid (GA) onto the macromolecular chains of microcrystalline cellulose (MCC) through a one-step esterification method. Then the prepared MCC-GA was dissolved in Lithium chloride/dimethyl sulfoxide (LiCl/DMSO) system and polymerized with acrylic acid (AA) to prepare a multi-functional cellulose-based organogel. The prepared MCC-GA/polyacrylic acid (PAA) organogels exhibited enhanced interfacial adhesion through hydrogen bonding, π-π interactions, and electrostatic interactions. Additionally, the MCC-GA/PAA organogels could withstand 95 % of the compressive deformation and rapidly self-recover owing to chemical cross-linking and dynamic non-covalent interactions. The organogels also exhibited excellent anti-freezing properties (up to -80 °C), solvent retention, and ionic conductivity. Considering its excellent overall performance, the MCC-GA/PAA organogel was used as an effective flexible sensor for human motion detection and is expected to play an important role in the future development of flexible bioelectronics.

Water-insensitive self-adhesive elastomers derived from hydrophobic deep eutectic polymers.

Water-insensitive self-adhesive elastomers derived from hydrophobic deep eutectic polymers (HDEPs) are reported. With the help of hydrophobic π-π interactions and dynamic hydrogen bonding networks, the HDEPs performed excellent self-adhesive properties on various materials, even in aqueous environments.

A Repeatable Self-Adhesive Liquid-Free Double-Network Ionic Conductor with Tunable Multifunctionality.

Liquid-free ionic conductors (LFICs) have promising applications in flexible electronics because most ionic conductors currently suffer from ionic liquid leakage or water evaporation issues. However, it has been a formidable challenge for LFICs to achieve long-term repeated self-adhesion on different substrates, especially on soft biological tissues. Based on the double-network design concept, we first fabricate a series of repeatable self-adhesive liquid-free double-network ionic conductors (SALFDNICs), consisting of stretchable first poly(AA-ChCl)-type supramolecular deep eutectic polymer networks and stiff second polydopamine (PDA) networks, which can maintain sufficient dynamic hydrogen bonds and catechol groups in the ionic conductors by preventing the overoxidation of dopamine, thus balancing the contradiction between adhesion and cohesion in liquid-free ionic conductors. Therefore, SALFDNICs can instantly form various interface interaction forces with multiple substrates (adhesion strength up to 757 N/m) and firmly adhere to various substrates for 20 detachment-reattachment cycles with a reduction in adhesion strength of less than 15%. Furthermore, SALFDNICs also have other comprehensive properties, such as optimum self-healing properties (self-healing efficiency of 90%), good stretchability (strain at break of 1200%), and promising conductivity (2.31 × 10-2 S m-1). Therefore, we believe that the extraordinary performance of SALFDNICs is important for improving device integration and the further development of flexible electronics.

Weavable Transparent Conductive Fibers with Harsh Environment Tolerance.

Fiber and textile electronics provide a focus for a new generation of wearable electronics due to their unique lightness and flexibility. However, fabricating knittable fibers from conductive materials with high tensile and transparent properties remains a challenge, especially for applicability in harsh environments. Here, we report a simple photopolymerization approach for the rapid preparation of a new type of a transparent conductive polymer fiber, poly(polymerizable deep eutectic solvent (PDES)) fiber, which exhibits excellent stability at high/low temperature, in organic solvents, especially in dry environments, and overcomes the volatility and freezability of traditional gel materials. A poly(PDES) fiber possesses outstanding mechanical and sensing properties, including negligible hysteresis and creep, fast resilience after a long stretch (10 min), and signal stability during high-frequency cyclic stretching (1 Hz, 10 000 cycles). In addition, the poly(PDES) fibers are knitted into a plain-structured sensor on textile with breathability and high tolerance to damage, enabling stable and accurate monitoring of human stretching, bending, and rotation motions. Furthermore, its dry-cleaning resistance guarantees the feasibility of long-term monitoring, with the electrical signal remaining stable after five dry-cleaning cycles. These promising features of poly(PDES) fibers will promote potential applications in the fields of human movement monitoring, intelligent fibers, and soft robotics.

Highly Stretchable and Compressible Cellulose Ionic Hydrogels for Flexible Strain Sensors.

Stretchable and compressible hydrogels based on natural polymers have received immense considerations for electronics. The feasibility of using pure natural polymer-based hydrogels could be improved if their mechanical behaviors satisfy the requirements of practical applications. Herein, we report highly stretchable (tensile strain ∼126%) and compressible (compression strain ∼80%) cellulose ionic hydrogels (CIHs) among pure natural polymer-based hydrogels including cellulose, chitin, and chitosan via chemical cross-linking based on free radical polymerization of allyl cellulose in NaOH/urea aqueous solution. In addition, the hydrogels have good transparency (transmittance of ∼89% at 550 nm) and ionic conductivity (∼0.16 mS cm-1) and can be worked at -20 °C without freezing and visual loss of transparency. Moreover, the CIHs can serve as reliable and stable strain sensors and have been successfully used to monitor human activities. Significantly, the various properties of hydrogel can be controlled through rationally adjusting the chemically cross-linked density. Our methodology will prove useful in developing the satisfied mechanical and transparent CIHs for a myriad of applications in flexible electronics.

Highly Transparent, Flexible and Conductive CNF/AgNW Paper for Paper Electronics.

Conductive paper has the advantages of being low-cost, lightweight, disposable, flexible, and foldable, giving it promising potential in future electronics. However, mainstream conductive papers are opaque and rigid, which seriously affect the wide application of conductive paper. In this paper, we demonstrate a highly transparent, flexible, and conductive paper, fabricated by mixing cellulose nanofibers (CNFs) with silver nanowires (AgNWs) and then plasticizing with choline chloride/urea solvent. The as-prepared CNF/AgNW paper showed high transparency (~90% transmittance) and flexibility (~27% strain), and low sheet resistance (56 Ω/sq). Moreover, the resistance change of CNF/AgNW paper increased only ~1.1% after 3000 bending-unbending cycles under a 150° large angle, implying a long working life and stability. In view of this, our methodology has the potential to open a new powerful route for fabrication of paper-based green electronics.