Stretchable, Ultratough, and Intrinsically Self-Extinguishing Elastomers with Desirable Recyclability

Intrinsic Flame-Retardant Solid-Solid Organic Phase Change Materials for High-Security Thermal Management

Organic phase change materials (PCMs) provide great potential for zero-energy thermal management thanks to superior thermal storage cyclability, stable phase change temperature, and low supercooling behavior. However, liquid leakage and flammability are long-standing defects that limit their practical utilization in thermal management. Here, an intrinsic flame-retardant solid-solid organic phase change material synthesis strategy is realized by a facile multicomponent reaction (MCR) from dimethyl phosphite, benzaldehyde, and alcohol under mild conditions. Owing to the presence of phosphine oxygen bond, the dipole moment of the PCMs is enhanced, thereby an elevated intermolecular interaction is attained, which works along with π-π stacking force and hydrogen bonding to restrain the amorphous state to a solid appearance above the melting temperature. In the meantime, the phosphine oxygen bond endows robust flame-retardancy to PCMs by forming phosphates in the condensed phase. A deep insight behind the crystal-to-amorphous transition process is revealed through experimental and density functional theory (DFT) calculations by varying the chain length of alcohol. Notably, the easily accessible raw materials and facile operation technique render the strategy applicable across diverse organic PCMs. High-security thermal management in wooden furniture and lithium-ion batteries (LIBs) is further demonstrated, and it is revealed the safe working time of LIBs can be prolonged almost 100 times compared with blank setups.

Strong, tough, and UV-resistant polylactic acid composites by incorporating doped carbon dots

The application of polylactic acid (PLA) is still restricted due to its suboptimal mechanical and thermal properties, as well as its vulnerability to oxidative degradation under ultraviolet light (UV). To enhance these properties, fluorine, nitrogen, sulfur-doped carbon dots (FNS-CDs) were fabricated in this study and further employed as nano-reinforcing materials for PLA. Here, FNS-CDs were obtained via the solvothermal method, with citric acid and 3-fluoroaniline serving as carbon, fluorine, and nitrogen sources, while dimethylsulfoxide functioned as the solvent and sulfur source. Subsequently, PLA-based composites were produced by the melt blending technique through blending FNS-CDs with PLA. With the optimal loading of FNS-CDs, the resulting PLA-based composites exhibited remarkable strength and toughness, excellent thermal stability, and efficient UV resistance. Compared with pure PLA, the tensile strength and tensile toughness of PLA-based composites containing 1.5 wt% FNS-CDs increased by 81.4 % and 147.6 % respectively, the crystallinity rose by 25.5 %, and the UV-resistance value was also significantly enhanced. This research demonstrates the considerable potential applications of doped carbon dots in the field of high performance and multi-functional polymer composites.

Ultrarobust, Stretchable, and Highly Elastic Supramolecular Elastomer with Hydrogen-Bond Interactions via sp2 Hybridized Boron-Urethane Bonds

Elastomers are omnipresent in everyday life and industry, yet the development of an elastomer with both superb stress and toughness presents a prodigious challenge. In this report, a high-strength, tough, and high-elastic elastomer derived from sp2 hybrid orbitals of phenylboronic acid was designed. The spatial conformation of network becomes significantly more compact due to the sp2 hybridization of boron. This enhances supramolecular hydrogen bonding interactions, resulting in a marked improvement in the material's mechanical properties. Notably, the hydrogen bonding energy in the polyurethane chain segments enhanced by 37%. The robust hydrogen bonding imparts the elastomer with super high true stress (1.30 GPa), superior toughness (442.2 MJ·m-3), and super puncture resistance strength of 167.8·N·mm-1. The material exhibited excellent fatigue resistance during continuous tensile cycles, while the irreversible deformation disappeared after standing at room temperature. Moreover, the elastomer bespeaks extraordinary elastic restorability, swiftly reverting to its primitive length after being extended to 16 times. This work provides a strategy that the mechanical properties of materials can be enhanced and toughened by utilizing spatial conformational changes in intermolecular interactions.

Near Infrared Light-Based Non-Contact Sensing System for Robotics Applications

With the development of artificial intelligence and the Internet of Things, non-contact sensors are expected to realize complex human-computer interaction. However, current non-contact sensors are mainly limited by accuracy and stability. Herein, an intelligent infrared photothermal non-contact sensing system is developed that provides long-distance and high-accuracy non-contact sensing. A black phosphorus (BP)-based composite organogel is designed, which exhibits excellent photothermal properties and environmental stability, as the active material. This material can detect patterns created by near-infrared (NIR) light through various patterned masks monitored by an infrared thermal imager. The constructed non-contact sensing system is capable of accurately recognizing 26 letters with an impressive accuracy rate of 99.4%. Furthermore, even small size non-contact sensors can maintain high sensitivity and stability across a wide temperature range, at long working distances, and under different current intensities and dark conditions, demonstrating exceptional robustness. Combined with machine learning method, it is demonstrated that the non-contact sensing system excels in pattern recognition and human-computer interaction. These features highlight its potential applications in intelligent robotics and remote control systems.

Enhancement of mechanical properties in reactive polyurethane film via in-situ assembly of embedded cellulose nanocrystals

Comparing to the solvent-based and waterborne polyurethanes (PU), the solvent-free reactive PU (RPU) is prepared via in-situ polymerization and film-formation of isocyanate-capped prepolymers and macromolecular polyols in solvent-free system. Thus, the carbon emissions and environmental pollutions are significantly reduced. However, the rapid polymerization also challenges the well control of structure and properties, especially the ordered microstructures. In this work, an efficient approach is applied to enhance the mechanical property of RPU via chemically bonding cellulose nanocrystals (CNCs) with isocyanates in a solvent-free system. The well distributed spot-like structure in the RPU film is realized and significantly improve the mechanical property due to the synergistic effect of hydrogen bonds and urethane bonds. Only adding 1 wt% of CNCs, the tensile strength and elongation at break are profoundly increased to 25.4 ± 1.5 MPa and 748 ± 50.0%, respectively. Both values are 490% and 16% better than that without CNCs. Additionally, the thermal stability is also improved. The initial decomposition temperature is 29 °C higher than that without CNCs. This approach provides a simple method for developing bio-based RPU with well-ordered structures, showing great potential in applications such as environmentally friendly materials and high-performance polymers.

High-Durability Cellulose-Based Composite Paper with Superior Electromagnetic Interference Shielding

Highly efficient electromagnetic interference (EMI) shielding materials are critical for portable hardware and flexible electronics, where mechanical durability often poses challenges. Here, the excellent wear resistance and flexibility of thermoplastic polyurethane are utilized to provide a "protective layer" for EMI equipment. A carbon nanotube/cellulose/thermoplastic polyurethane (CNT/paper/TPU) composite paper with a three-layer structure was prepared using a coating method. Strong hydrogen bonds between CNTs, cellulose, and TPU ensured robust integration. The composite, with a thickness of 0.54 mm and conductivity of 1040 S/m, achieved exceptional EMI shielding effectiveness of 69.0 dB. It demonstrated durability against water, solvents, bending, and friction while maintaining shielding performance. Furthermore, its excellent mechanical properties and fatigue resistance significantly enhance equipment lifespan. Therefore, it is expected that this work will open a simple strategy for developing materials with excellent durable EMI shielding properties.

Low-Cost Intrinsic Flame-Retardant Bio-Based High Performance Polyurethane and its Application in Triboelectric Nanogenerators

Flammability is a significant challenge in polymer-based electronics. In this regard, triboelectric nanogenerators (TENGs) have enabled a safe means for harvesting mechanical energy for conversion into electrical energy. However, most existing polymers used for TENGs are sourced from petroleum-based raw materials and are highly flammable, which can further accelerate the spread of fire and harm the ecological environment. In addition, the existing intrinsic flame-retardant TENGs are not elastic at room temperature, which may potentially damage the flexible equipment and harm firefighters. This study presents an intrinsic flame-retardant bio-based elastic phytic acid polyurethane (PUPA) synthesized using a simple and efficient one-pot polycondensation. The cross-linked structure and polar phosphorus-containing segments of PUPA are fabricated into PUPA-TENG, demonstrating a superior elasticity (elongation up to 660%), flame retardancy (UL94 V-0), impact resistance (34.71 MJ m-3), and dielectric constant (Dk = 9.57). Consequently, this study provides a simple strategy for tailoring TENGs toward environmentally friendly and secure power generators and electronics, which can effectively reduce fire hazards and potentially be applied to other fire-risk fields such as personal protection, firefighting, and new energy.

Complementary Nucleobase-Containing Double-Network Elastomers with High Energy Dissipation and Room-Temperature Fast Recovery

Elastomers have been widely employed in various industrial products such as tires, actuators, dampers, and sealants. While various methods have been developed to strengthen elastomers, achieving continuously high energy dissipation with fast room-temperature recovery remains challenging, prompting the need for further structural optimization. Herein, high energy dissipated and fast recoverable double-network (DN) elastomers are fabricated, in which the supramolecular polymers of complementary adenine and thymine serve as the first network and the covalently cross-linked soft polymer as the second network. Both networks are efficiently prepared via photopolymerization. The resulting DN elastomer displays high energy dissipation and room temperature fast recovery, which can be attributed to the good independence of supramolecular and covalent networks. Furthermore, it is demonstrated that the DN elastomer can be exploited as excellent cushioning materials under continuous impacts. This work presents a feasible avenue for fabricating DN elastomers with high energy dissipation and fast recovery based on the multiple hydrogen bonds of complementary nucleobases.

Cocklebur-Inspired Robust Non-flammable Polymer Thermo Conductor for CPU Cooling

Efficient computer central processing units (CPUs) heat dissipation demands polymer-based thermal interface materials that combine high thermal conductivity with strong mechanical properties, eliminating the need for additional fasteners. However, polymers with high thermal conductivity often suffer from insufficient mechanical strength and other challenges, including high production costs, elevated interfacial thermal resistance, and flammability. Inspired by the 3D "spininess-seeds-bark" structure of cocklebur, cast polyurethane (PUC) composites are developed using copper ethylenediamine methylene-phosphonate as the "spininess" and functionalized alumina microspheres as the "seeds" filler. This spininess configuration prevents organophosphate self-polymerization, imparting self-extinguishing properties to the polymer, while also enhancing the mechanical strength and thermal conductivity by connecting the "seeds" to the matrix. The bark-like structure enables effective interlocking of functional particles, optimizing the synergy within the composite. The elevated surface reduces interfacial thermal resistance, leading to enhanced thermal conductivity. The resulting PUC composites demonstrate impressive performance, with a tensile strength of 15.9 MPa and thermal conductivity of 2.51 W m⁻¹ K⁻¹, providing effective continuous cooling for high-power CPUs. These composites offer low density, broad availability, and environmental sustainability, making them promising candidates for sustainable electronics and new energy applications, aligned with global development strategies.

Significantly suppressing CO release achieved by the catalysis effect of nanostructured rare earth/manganese oxides: Application in flame retardant thermoplastic polyurethane

There is significant smoke and toxic volatiles generated from the combustion of thermoplastic polyurethane (TPU), which has compromised its application and posed a significant threat to human life. Here, the hydrothermal-citrate complexation method synthesised the rare earth Mn-based composite catalyst and blended with TPU to mitigate smoke release and toxic gas generation during TPU combustion. The results demonstrate that the inclusion of 3 wt% Mn-La and Mn-Ce catalysts into TPU leads to a 41.3% and 33.6% decrease in maximum smoke density (Ds max), respectively, along with a 52.4% and 50.5% reduction in peak CO production rate (pCOPR). The mechanism of rare earth Mn-based catalyst-based smoke suppression and toxicity reduction in TPU is explained at a microscopic scale based on density functional theory (DFT) research: the introduction of catalyst bolsters the adsorption of O2 and CO on the surface of TPU nanocomposites and facilitates the oxidation of CO. Additionally, it can expedite the formation of dense carbon layers and impede heat and mass transfer. The TPU nanocomposites exhibit excellent flame retardancy and effective smoke suppression. A feasible strategy for manufacturing fire-safety TPU nanocomposites with favorable comprehensive properties is proposed.

In Situ Anchoring Functional Molecules to Polymer Chains Through Supramolecular Interactions for a Robust and Self-Healing Multifunctional Waterborne Polyurethane

Nowadays, much attention is paid to the development of high-performance and multifunctional materials, but it is still a great challenge to obtain polymer materials with high mechanical properties, high self-healing properties, and multifunctionality in one. Herein, an innovative strategy is proposed to obtain a satisfactory waterborne polyurethane (PMWPU-Bx) by in situ anchoring 3-aminophenylboronic acid (3-APBA) in a pyrene-capped waterborne polyurethane (PMWPU) via supramolecular interactions. The multiple functional sites inherent in 3-APBA can produce supramolecular interactions with groups on PMWPU, promoting the aggregation of hard domains in the polymer network, which confers the PMWPU-Bx strength (7.9 MPa) and high modulus (243.2 MPa). Meanwhile, the dynamic natures of boronic ester bonds formed by the condensation of 3-APBA endow PMWPU-Bx with a high self-healing efficiency. Additionally, PMWPU-Bx exhibits fluorescence tunability due to the controlled π-π stacking. In this research, the strategy of anchoring functional molecules onto polymers through supramolecular interactions synchronously achieves the high performance and the multi-functionality of waterborne polyurethanes, but also broadens their potential applications in the fields of optical anticounterfeiting and encrypted information transmission.

'Rigid-flexible' strategy for high-strength, near-room-temperature self-healing, photo-thermally functionalised lignin-reinforced polyurethane elastomers

Lignin is the most abundant and only renewable aromatic polymer in nature. Herein, a flexible matrix and the rigid lignin were rationally integrated to prepare high-strength, near-room-temperature self-healing, processable lignin-reinforced polyurethane elastomers (LZPUs). Reversible hydrogen and oxime-amino ester bonds were introduced into the matrix to provide excellent dynamic properties and abundant ligands for lignin-matrix coordination bonds. Abundant metal coordination bonds were constructed between the matrix and lignin via the introduction of Zn2+, which not only effectively enhances the dispersibility and compatibility, but also provides an excellent energy dissipation mechanism for the LZPUs. One of the prepared elastomers, LZPUs, exhibited a high strength of 40.5 MPa, which is twice that of the blank sample and 1.6 times that of the sample without Zn2+. It maintained kinetic stability at mild temperature, but it exhibited a self-healing efficiency of 91.3 % in strength and 99.8 % in elongation at break after decoupling with trace ethanol (≈ 50 μL) at 35 °C. It exhibited a self-healing efficiency of 93.6 % in strength under 1 sun irradiation (0.1 W cm-2) for 4 h. We believe this elastomer offering high mechanical properties with multi-functionality can be applied in flexible drives and photo-thermal power generation.

High-performance epoxy resin with flame-retardant, transparent, and ultraviolet shielding properties based on a vanillin-based multifunctional macromolecule

Flame-retardant epoxy resins with tough, transparent, ultraviolet shielding, and low dielectric properties have fascinating prospects in electronic and electrical applications, but it is still challenging at present. In this work, a bio-based macromolecule was synthesized from vanillin (a lignin derivative), phenyl dichlorophosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO), and poly(propylene glycol) bis(2-aminopropyl ether). The bio-based macromolecule, namely, MFR, was designed and added to the epoxy resin (EP). The cured EP containing 15 wt% MFR (i.e., EP/MFR15) exhibits excellent flame retardancy with an Underwriter Laboratory 94 (UL-94) V-0 rating and a limiting oxygen index (LOI) of 29.2 %. Furthermore, the peak heat release rate (PHRR) and total heat release rate (THR) are drastically reduced by 59.5 % and 40.7 %, respectively. Meanwhile, EP/MFR15 shows 20.3 % and 43.8 % improvements in tensile strength and toughness, respectively. Moreover, MFR simultaneously endows EP with accessional ultraviolet shielding performance and low dielectric constant without sacrificing transparency. This work provides a promising strategy for fabricating a bio-based macromolecular flame retardant and preparing a high-performance EP composite with versatile properties.

Super-Durable, Tough Shape-Memory Polymeric Materials Woven from Interlocking Rigid-Flexible Chains

Developing advanced engineering polymers that combine high strength and toughness represents not only a necessary path to excellence but also a major technical challenge. Here for the first time a rigid-flexible interlocking polymer (RFIP) is reported featuring remarkable mechanical properties, consisting of flexible polyurethane (PU) and rigid polyimide (PI) chains cleverly woven together around the copper(I) ions center. By rationally weaving PI, PU chains, and copper(I) ions, RFIP exhibits ultra-high strength (twice that of unwoven polymers, 91.4 ± 3.3 MPa), toughness (448.0 ± 14.2 MJ m-3), fatigue resistance (recoverable after 10 000 cyclic stretches), and shape memory properties. Simulation results and characterization analysis together support the correlation between microstructure and macroscopic features, confirming the greater cohesive energy of the interwoven network and providing insights into strengthening toughening mechanisms. The essence of weaving on the atomic and molecular levels is fused to obtain brilliant and valuable mechanical properties, opening new perspectives in designing robust and stable polymers.

Microstructure Evolution of Reactive Polyurethane Films During In Situ Polyaddition and Film-Formation Processes

Due to the advantages of low energy consumption, no air and water pollutions, the reactive polyurethane films (RPUFs) are replacing the solvated and waterborne PUFs nowadays, which significantly promotes the green and low-carbon production of PU films. However, the microstructure evolution and in situ film-formation mechanism of RPUFs in solvent-free media are still unclear. Herein, according to time-temperature equivalence principle, the in situ polyaddition and film-formation processes of RPUFs generated by the typical polyaddition of diisocyanate terminated prepolymer (component B) and polyether glycol (component A) are thoroughly investigated at 25 °C. According to the temporal change of viscosity, the RPUFs gradually transfer from liquid to gel and finally to solid state. Further characterizing the molecular weight, hydrogen bonds, crystallinity, gel content, and phase images, the polyaddition and film-formation processes can be divided into three stages as 1) chain extension and microcrystallization; 2) gelation and demicrocrystallization; 3) microphase separation and film-formation. This work promotes the understanding of the microstructure evolution and film-formation mechanism of RPUFs, which can be used as the theoretical guidance for the controllable preparation of high-performance products based on RPUFs.

Strong and Healable Elastomers with Photothermal-Stimulus Dynamic Nanonetworks Enabled by Subnano Ultrafine MoO3-x Nanowires

One-dimensional nanomaterials have become one of the most available nanoreinforcing agents for developing next-generation high-performance functional self-healing composites owing to their unique structural characteristics and surface electron structure. However, nanoscale control, structural regulation, and crystal growth are still enormous challenges in the synthesis of specific one-dimensional nanomaterials. Here, oxygen-defective MoO3-x nanowires with abundant surface dynamic bonding were successfully synthesized as novel nanofillers and photothermal response agents combined with a polyurethane matrix to construct composite elastomers, thus achieving mechanically enhanced and self-healing properties. Benefiting from the surface plasmon resonance of the MoO3-x nanowires and interfacial multiple dynamic bonding interactions, the composite elastomers demonstrated strong mechanical performance (with a strength of 31.45 MPa and elongation of 1167.73%) and ultrafast photothermal toughness self-healing performance (20 s and an efficiency of 94.34%). The introduction of MoO3-x nanowires allows the construction of unique three-dimensional cross-linked nanonetworks that can move and regulate interfacial dynamic interactions under 808 nm infrared laser stimulation, resulting in controlled mechanical and healing performance. Therefore, such special elastomers with strong photothermal responses and mechanical properties are expected to be useful in next-generation biological antibacterial materials, wearable devices, and artificial muscles.

Ultrarobust, Self-Healing Poly(urethane-urea) Elastomer with Superior Tensile Strength and Intrinsic Flame Retardancy Enabled by Coordination Cross-Linking

Poly(urethane-urea) elastomers (PUUEs) have gained significant attention recently due to their growing demand in electronic skin, wearable electronic devices, and aerospace applications. The practical implementation of these elastomers necessitates many exceptional properties to ensure robust and safe utilization. However, achieving an optimal balance between high mechanical strength, good self-healing at moderate temperatures, and efficient flame retardancy for poly(urethane-urea) elastomers remains a formidable challenge. In this study, we incorporated metal coordination bonds and flame-retarding phosphinate groups into the design of poly(urethane-urea) simultaneously, resulting in a high-strength, self-healing, and flame-retardant elastomer, termed PNPU-2%Zn. Additional supramolecular cross-links and plasticizing effects of phosphinate-endowed PUUEs with relatively remarkable tensile strength (20.9 MPa), high elastic modulus (10.8 MPa), and exceptional self-healing efficiency (above 97%). Besides, PNPU-2%Zn possessed self-extinguishing characteristics with a limiting oxygen index (LOI) of 26.5%. Such an elastomer with superior properties can resist both mechanical fracture and fire hazards, providing insights into the development of robust and high-performance components for applications in wearable electronic devices.

Malleable, Ultrastrong Antibacterial Thermosets Enabled by Guanidine Urea Structure

Dynamic covalent polymers (DCPs) that strike a balance between high performance and rapid reconfiguration have been a challenging task. For this purpose, a solution is proposed in the form of a new dynamic covalent supramolecular motif-guanidine urea structure (GUAs). GUAs contain complex and diverse chemical structures as well as unique bonding characteristics, allowing guanidine urea supramolecular polymers to demonstrate advanced physical properties. Noncovalent interaction aggregates (NIAs) have been confirmed to form in GUA-DCPs through multistage H-bonding and π-π stacking, resulting in an extremely high Young's modulus of 14 GPa, suggesting remarkable mechanical strength. Additionally, guanamine urea linkages in GUAs, a new type of dynamic covalent bond, provide resins with excellent malleability and reprocessability. Guanamine urea metathesis is validated using small molecule model compounds, and the temperature dependent infrared and rheological behavior of GUA-DCPs following the dissociative exchange mechanism. Moreover, the inherent photodynamic antibacterial properties are extensively verified by antibacterial experiments. Even after undergoing three reprocessing cycles, the antibacterial rate of GUA-DCPs remains above 99% after 24 h, highlighting their long-lasting antibacterial effectiveness. GUA-DCPs with dynamic nature, tuneable composition, and unique combination of properties make them promising candidates for various technological advancements.

Strong, bacteriostatic and transparent polylactic acid-based composites by incorporating quaternary ammonium cellulose nanocrystals

Renewable natural fibers (e.g., cellulose nanocrystals (CNCs)) are being applied for reinforcing bio-based polylactic acid (PLA). For improvement in the interfacial compatibility between CNCs and PLA and the dispersibility of CNCs, a quaternary ammonium salt-coated CNCs (Q-CNCs) hybrid was prepared in this study based on an esterification self-polymerization method, and such hybrid was further utilized as a new strengthening/toughening nanofiller for producing the Q-CNCs-reinforced PLA composite. The results confirmed that quaternary ammonium salt coatings could efficiently enhance CNCs/PLA interfacial compatibility via mechanical interlocking and semi-interpenetrating networks. Attributing to the synergistic effect of quaternary ammonium salts and CNCs, a considerable enhancement in processing, mechanical, and thermal properties was gained in the obtained Q-CNCs-reinforced PLA composite. With the addition of 0.5 wt% Q-CNCs, the tensile strength, Young's modulus, and elongation at break of the Q-CNCs-reinforced PLA composite was raised by approximately 23 %, 37 % and 18 %, respectively; compared with pure PLA, the obtained composite had excellent bacteriostatic properties and good transparency. This work discusses the development of high-performance, low-cost and sustainable PLA-based composites on a potential application in packaging materials.

Synchronous modification of ZIF-67 with cyclomatrix polyphosphazene coating for efficient flame retardancy and mechanical reinforcement of epoxy resin

Cyclomatrix polyphosphazenes have attracted widespread attention in the field of polymer flame retardancy. Nevertheless, the optimal manifestation of their distinctive structural attributes and flame-retardant properties necessitates a judicious selection of condensation monomers and synergistic templates during the fabrication of polyphosphazene flame retardants. In our previous studies, it was discovered that when ZIF-67 is functionalized with polyphosphazene, the by-product HCl from phosphazene polycondensation causes etching on ZIF-67. Based on this "synchronous etching" effect, a series of hybrid materials comprising cyclomatrix polyphosphazene and ZIF-67, denoted as ZIF-67@PDS (PDS, poly-(cyclotriphosphazene-co-4,4'-diaminodiphenyl sulfone)), ZIF-67@PBS (PBS, poly-(cyclotriphosphazene-co-Bisphenol A)), and ZIF-67@PZS (PZS, poly-(cyclotriphosphazene-co-4,4'-sulfonyldiphenol)), was synthesized utilizing DDS (4,4'-diaminodiphenyl sulfone), BPA (Bisphenol A), and BPS (4,4'-sulfonyldiphenol) monomers as precursors, respectively. Upon the incorporation of 2.0 wt.% of ZIF-67@PDS, ZIF-67@PBS, and ZIF-67@PZS, the flame retardant and mechanical characteristics of EP composites exhibited marked enhancement. The unique structural characteristics of hybrid and the synergistic effects of Co-P-N contribute to the improvement of comprehensive properties. Compared with pure EP, EP/ZIF-67@PZS has the best enhancement effect, and its pHRR, THR, and TSP decreased by 34.0%, 30.0%, and 40.5%, respectively. In terms of mechanical strength, ZIF-67@PZS also increases the flexural strength of EP by 37.42%. Relying on the "synchronous etching" effect, this study explores and verifies the effective combination of ZIF-67 and different types of polyphosphazenes, and obtains a series of ZIF-67-derived cyclomatrix polyphosphazene hybrids with different morphologies and properties in one step. It provides a new idea and strategy for the simultaneous modification of polyphosphazene materials and the preparation of multifunctional flame retardants in the future.

Controlled Structural Relaxation of Aramid Nanofibers for Superstretchable Polymer Fibers with High Toughness and Heat Resistance

Polymer fibers that combine high toughness and heat resistance are hard to achieve, which, however, hold tremendous promise in demanding applications such as aerospace and military. This prohibitive design task exists due to the opposing property dependencies on chain dynamics because traditional heat-resistant materials with rigid molecular structures typically lack the mechanism of energy dissipation. Aramid nanofibers have received great attention as high-performance nanoscale building units due to their intriguing mechanical and thermal properties, but their distinct structural features are yet to be fully captured. We show that aramid nanofibers form nanoscale crimps during the removal of water, which primarily resides at the defect planes of pleated sheets, where the folding can occur. The precise control of such a structural relaxation can be realized by exerting axial loadings on hydrogel fibers, which allows the emergence of aramid fibers with varying angles of crimps. These crimped fibers integrate high toughness with heat resistance, thanks to the extensible nature of nanoscale crimps with rigid molecular structures of poly(p-phenylene terephthalamide), promising as a template for stable stretchable electronics. The tensile strength/modulus (392-944 MPa/11-29 GPa), stretchability (25-163%), and toughness (154-445 MJ/cm3) are achieved according to the degree of crimping. Intriguingly, a toughness of around 430 MJ/m3 can be maintained after calcination below the relaxation temperature (259 °C) for 50 h. Even after calcination at 300 °C for 10 h, a toughness of 310 MJ/m3 is kept, outperforming existing polymer materials. Our multiscale design strategy based on water-bearing aramid nanofibers provides a potent pathway for tackling the challenge for achieving conflicting property combinations.

A generalizable reactive blending strategy to construct flame-retardant, mechanically-strong and toughened poly(L-lactic acid) bioplastics

Poly(L-lactic acid) (PLA) is an environmentally-friendly bioplastic with high mechanical strength, but suffers from inherent flammability and poor toughness. Many tougheners have been reported for PLA, but their synthesis usually involves organic solvents, and they tend to dramatically reduce the mechanical strength and cannot settle the flammability matter. Herein, we develop strong, tough, and flame-retardant PLA composites by reactive blending PLA, 6-((double (2-hydroxyethyl) amino) methyl) dibenzo [c, e] [1,2] oxyphosphate acid 6-oxide (DHDP) and diphenylmethane diisocyanate (MDI) and define it PLA/xGH, where x indicates that the molar ratio of -NCO group in MDI to -OH group in PLA and DHDP is 1.0x: 1. This fabrication requires no solvents. PLA/2GH with a -NCO/-OH molar ratio of 1.02: 1 maintains high tensile strength of 63.0 MPa and achieves a 23.4 % increase in impact strength compared to PLA due to the incorporation of rigid polyurethane chain segment. The vertical combustion (UL-94) classification and limiting oxygen index (LOI) of PLA/2GH reaches V-0 and 29.8 %, respectively, because DHDP and MDI function in gas and condensed phases. This study displays a generalizable strategy to create flame-retardant bioplastics with great mechanical performances by the in-situ formation of P/N-containing polyurethane segment within PLA.

How the chemical structure of phosphoramides affect the fire retardancy and mechanical properties of polylactide?

Phosphoramides, as a kind of high-efficient fire retardants, have been designed in many structures and endowed exceptional fire retardancy to polylactide (PLA). However, due to ignorance of the structure-property correlation, the effect of phosphoramides' structure on the fire retardancy and mechanical properties of PLA is still unclear. Herein, a series of biobased phosphoramides (phosphoramide (V1), linear polyphosphoramide (V2) and hyperbranched polyphosphamide (V3)) were designed and incorporated into PLA, and the structural effect of phosphoramides on the fire-retardant and mechanical properties of PLA was deeply researched. Among three kinds of phosphoramides, the hyperbranched polyphosphoramide is more effective than the corresponding linear polyphosphoramide and phosphoramide in improving the fire-retardant and anti-dripping properties of PLA, and only linear polyphosphoramide shows a positive effect in the mechanical strength of PLA. This work provides a feasible strategy for creating mechanically robust and fire-retardant polymer composites by molecularly tailoring the structure of fire retardants and uncovering their structure-property relationship.

Structure of Metal-Organic Frameworks Eco-Modulated by Acid-Base Balance toward Biobased Flame Retardant in Polyurea Composites

Biobased-functionalized metal-organic frameworks (Bio-FUN-MOFs) stand out from the crowd of candidates in the flame-retardant field due to their multipathway flame-retardant mechanisms and green synthesis processes. However, exploring and designing Bio-FUN-MOFs tend to counteract the problem of compromising the flame-retardant advantages of MOFs themselves, which inevitably results in a waste of resources. Herein, a strategy in which MOFs are ecologically regulated through acid-base balance is presented for controllable preparation of Bio-FUN-MOFs by two birds with one stone, i.e., higher flame-retardant element loading and retention of more MOF structures. Specifically, the buffer layer is created on the periphery of ZIF-67 by weak etching of biobased alkali arginine to resist the excessive etching of ZIF-67 by phytic acid when loading phosphorus source and to preserve the integrity of internal crystals as much as possible. As a proof of concept, ZIF-67 was almost completely etched out by phytic acid in the absence of arginine. The arginine and phytic acid-functionalized ZIF-67 with yolk@shell structure (ZIF@Arg-Co-PA) obtained by this strategy, as a biobased flame retardant, reduces fire hazards for polyurea composites. At only 5 wt % loading, ZIF@Arg-Co-PA imparted polyurea composites with a limiting oxygen index of 23.2%, and the peaks of heat release rate, total heat release, and total smoke production were reduced by 43.8, 32.3, and 34.3%, respectively, compared to neat polyurea. Additionally, the prepared polyurea composites have acceptable mechanical properties. This work will shed light on the advanced structural design of polymer composites with excellent fire safety, especially environmentally friendly and efficient biobased MOF flame retardants.

Ductile adhesive elastomers with force-triggered ultra-high adhesion strength

Elastomers play a vital role in many forthcoming advanced technologies in which their adhesive properties determine materials' interface performance. Despite great success in improving the adhesive properties of elastomers, permanent adhesives tend to stick to the surfaces prematurely or result in poor contact depending on the installation method. Thus, elastomers with on-demand adhesion that is not limited to being triggered by UV light or heat, which may not be practical for scenarios that do not allow an additional external source, provide a solution to various challenges in conventional adhesive elastomers. Herein, we report a novel, ready-to-use, ultra high-strength, ductile adhesive elastomer with an on-demand adhesion feature that can be easily triggered by a compression force. The precursor is mainly composed of a capsule-separated, two-component curing system. After a force-trigger and curing process, the ductile adhesive elastomer exhibits a peel strength and a lap shear strength of 1.2 × 104 N m-1 and 7.8 × 103 kPa, respectively, which exceed the reported values for advanced ductile adhesive elastomers. The ultra-high adhesion force is attributed to the excellent surface contact of the liquid-like precursor and to the high elastic modulus of the cured elastomer that is reinforced by a two-phase design. Incorporation of such on-demand adhesion into an elastomer enables a controlled delay between installation and curing so that these can take place under their individual ideal conditions, effectively reducing the energy cost, preventing failures, and improving installation processes.

Realizing balanced flame retardancy and electromagnetic interference shielding in hierarchical elastomer nanocomposites

The combination of electromagnetic interference (EMI) shielding performance and flame-retardant property is essential for applications in the field of electronics and electrics. To date, there have been few successful cases in achieving such portfolios, due to the different mechanisms and even mutual exclusivity of these two attributes. Herein, an ammonium polyphosphate@chitosan@carbon nanotube (APP@CS@MWCNT) core-multishell hybrid was synthesized by microencapsulation technology. Then, the hybrid was introduced into TPU matrix to fabricate TPU composites, acting as surface layer. Meanwhile, MXene film was used as intermediate layer to construct hierarchical TPU composites. The obtained results showed that after introduction of 1 wt% APP@CS@MWCNT hybrid, the peak of heat release rate (PHRR) and the peak of smoke produce rate (PSPR) of TPU composites decreased by 67.4% and 35.6%, respectively, compared with those of pure TPU. Owing to multiple reflection losses, interface polarization losses, and charge carrier movement-induced thermal dissipation, TPU/15AC@4M-SW exhibited the highest EMI shielding performance, and obtained shielding effectiveness values of 35.7 dB and 38.9 dB in X band and K band, respectively.

Negative Enthalpy Variation Drives Rapid Recovery in Thermoplastic Elastomer

The mechanism behind the resilience of polymeric materials, typically attributed to the well-established entropy elasticity, often ignores the contribution of enthalpy variation (ΔH), because it is based on the assumption of an ideal chain. However, this model does not fully account for the reduced resilience of thermoplastic polyurethane (TPU) during long-range deformation, which is mainly caused by the dynamics of physical crosslink networks. Such reduction is undesirable for long-range stretchable TPU considering its wide application range. Therefore, a negative ΔH effect is established in this work to facilitate instant recovery in long-range stretchable TPU, achieved by constructing a reversible interim interface via strain-induced phase separation. Consequently, the newly constructed dual soft segmental TPU shows resilience efficiency exceeding 95%, surpassing many synthetic high-performance TPUs with typical efficiencies below 80%, and comparable to biomaterials. Moreover, a remarkable hysteresis loop with a ratio exceeding 50%, makes it a viable candidate for applications such as artificial ligaments or buffer belts. The research also clarifies structural factors influencing resilience, including the symmetry of the dual soft segments and the content of hard segments, offering valuable insights for the design of highly resilient long-range stretchable elastomers.

Strategy for Constructing Phosphorus-Based Flame-Retarded Polyurethane Elastomers for Advanced Performance in Long-Term

Polyurethane elastomer (PUE), which is widely used in coatings for construction, transportation, electronics, aerospace, and other fields, has excellent physical properties. However, polyurethane elastomers are flammable, which limits their daily use, so the flame retardancy of polyurethane elastomers is very important. Reactive flame retardants have the advantages of little influence on the physical properties of polymers and low tendency to migrate out. Due to the remarkable needs of non-halogenated flame retardants, phosphorus flame retardant has gradually stood out as the main alternative. In this review, we focus on the fire safety of PUE and provide a detailed overview of the current molecular design and mechanisms of reactive phosphorus-containing, as well as P-N synergistic, flame retardants in PUE. From the structural characteristics, several basic aspects of PUE are overviewed, including thermal performance, combustion performance, and mechanical properties. In addition, the perspectives on the future advancement of phosphorus-containing flame-retarded polyurethane elastomers (PUE) are also discussed. Based on the past research, this study provides prospects for the application of flame-retarded PUE in the fields of self-healing materials, bio-based materials, wearable electronic devices, and solid-state electrolytes.