Synergetic Effect of α-ZrP Nanosheets and Nitrogen-Based Flame Retardants on Thermoplastic Polyurethane

3D Large Space Warp-Knitted Composite Fabric with Heating and Insulation for Extremely Cold Environments

The extremely cold environment restricts certain activities, making the preparation of a material with both heating and insulation functions a significant challenge. This study presents the large space warp-knitted composite fabric (LSWCF) as an electric heating inflatable material with a three-dimensional structure. It is designed and developed from three modes to mitigate heat loss. The top layer of LSWCF is combined with the electric heating film as the heating layer, showing high electric heating efficiency (577.33 °C/(W·cm-2)), high electrothermal conversion efficiency (95%), and excellent conductivity (12.5 S/cm). The bottom layer of LSWCF is coated with TiO2/WPU coatings as a thermal radiation layer. The inflated LSWCF retains a substantial volume of still air within its middle layer and exhibits low thermal conductivity (0.037 W·m-1·K-1), with resulting minimization of heat loss due to convection and conduction. LSWCF's radiant coating, on the other hand, reduces heat loss through directed radiation. Contributed to the structural design, the LSWCF demonstrates an enhanced ability to generate heat at low temperatures (up to 35 °C at -20 °C, 980 W·m-2) compared to the existing literature. This study offers a novel strategy for the development of materials for use in extremely cold environments.

Triggering the Interplay of sp2-sp3 Carbon-Assisted Sustained Tribofilm via Two-Dimensional Surface Modulation for Exceptional Wear Resistance of Steel Surfaces

The relentless wear and friction of steel-based moving machinery have created ongoing challenges that hinder their industrial applications. One promising solution is the use of reduced graphene oxide (rGO) as a lubricant due to its excellent mechanical strength and promising tribological properties. However, its tendency to self-agglomerate presents a major hurdle for its practical use. This study aims to combat the restacking of rGO nanosheets by strategically intercalating self-assembled α-ZrP between the rGO layers, unlocking exceptional wear resistance in mild steel through hot-dip galvanization. The multilayer architecture of the developed coatings ensures lubrication through layer slippage during friction, while the coexistence of sp2-sp3 hybridized carbons further extends wear life, with the Zn-0.22/ZP_5@G coating exhibiting the highest wear resistance (0.277 × 10-7 mm3 N-1 m-1). The as-tailored composite coating, featuring a tribolayer composed of graphitic sp2 carbons, ZrO2, Zr(PO4)2, and Fe2O3, serves as an effective dissipative medium for contact stress. The formation of diamond-like sp3 carbons induced by the tribological process further contributes to the increased hardness of the resulting tribofilm. The reduced generation of the π-conjugated system in the composite prevents the movement of electrons toward the cathodic site, while the passivation effect induced by the composite effectively inhibits electrolyte permeation, resulting in substantial corrosion resistance. The exemplary wear resistance with remarkable anticorrosion performance achieved in this study offers significant improvement in the realm of hard coatings for mechanical applications, including moving machinery and manufacturing. Hence, the system can find effective use in such industries following the completion of relevant case studies.

Synthesis of nitrogen and phosphorus-doped chitosan derivatives for enhanced flame retardancy, smoke suppression, and mechanical properties in epoxy resin composites

Biomass-based flame retardants have attracted significant academic interest due to their environmental benefits and sustainability. Nevertheless, devising straightforward, eco-friendly, and mild methodologies to synthesize flame retardants of epoxy resins (EP) remains a formidable challenge. This paper reports the successful synthesis of a novel nitrogen and phosphorus-doped chitosan derivatives flame retardant (MMCA) utilizing phytic acid, chitosan, and melamine cyanurate via electrostatic self-assembly and physical encapsulation in an acidic aqueous solution. The incorporation of 5 wt% MMCA into the EP readily achieved a UL-94 V-0 rating. This improvement can be primarily attributed to the early formation of a continuous, dense, robust, and expanded char layer during combustion, coupled with the synergistic flame retardant mechanisms of radical scavenging and the dilution of non-combustible gases. Compared to pristine EP, EP/5MMCA exhibited significant reductions of 23.7 %, 29.2 %, and 24 % in total smoke production rate, peak heat release rate, and peak smoke production rate, respectively. Moreover, the strategic introduction of MMCA also enhanced the glass transition temperature, storage modulus, and crosslinking density of EP, improving its tensile, compressive and impact properties. This study proposes a simple, viable, and environmentally sustainable strategy for the fabrication of biomass-based flame retardants, resulting in notable improvements the flame retardancy, smoke suppression, fire safety, and mechanical robustness of EP.

DABCO-Intercalated α-Zirconium Phosphate as a Latent Thermal Catalyst in the Reaction of Urethane Synthesis

The mixture of hexamethylene diisocyanate (HDI) and butanol (BuOH) with the intercalation compound of 1,4-diazabicyclo[2.2.2]octane (DABCO) with α-zirconium phosphate (α-ZrP) has been evaluated as a latent thermal catalyst at varying temperatures. α-ZrP·DABCO did not show activity at 25 °C, but showed a high level of activity at a higher temperature of 80 °C. To clarify the reaction behavior of HDI-BuOH with α-ZrP·DABCO, a viscosity value of 1200 mPa·s·g/cm2 was reached at 80 °C for 30 min. To investigate the deintercalation behavior of DABCO from the α-ZrP interlayer, it was investigated in BuOH and in HDI, respectively, under heated conditions. Interestingly, XRD patterns showed a reduction in α-ZrP·DABCO for the interlayer distance due to the deintercalation of DABCO in BuOH, while no changes associated with the deintercalation of DABCO were observed in HDI. Butanol was found to be important for the deintercalation of DABCO. To examine the reactivity of bifunctional monomers, the reaction of 1,4-butanediol (1,4-BDO) and HDI with α-ZrP·DABCO were investigated to show good reactivity at 80 °C and stability at 40 °C.

A high-performance, sensitive, low-cost LIG/PDMS strain sensor for impact damage monitoring and localization in composite structures

Health monitoring of composite structures in aircraft is critical, as these structures are commonly utilized in weight-sensitive areas and innovative designs that directly impact flight safety and reliability. Traditional monitoring methods have limitations in monitoring area, strain limit, and signal processing. In this paper, a multifunctional sensor has been developed using acid-treated laser-induced graphene (A-LIG) with a multi-layer three-dimensional conductive network. Compared to untreated laser-induced graphene, the sensitivity of A-LIG sensor is increased by 100%. Furthermore, PDMS is used to fill the pores, which improves the fatigue performance of the A-LIG sensor. To obtain clear monitoring results, a data conversion algorithm is provided to convert the electrical signal obtained by the sensor into a strain field contour cloud map. The impact test of the A-LIG/PDMS sensor on the carbon fiber panel of the aircraft wing box segment verifies the effectiveness of its strain sensing. This work introduces a novel approach to fabricating flexible sensors with improved sensitivity, extended strain range, and cost-effectiveness. The sensor exhibits high sensitivity (gauge factor,GF≈ 387), is low hysteresis (∼53 ms), and has a wide working range (up to 47%), and a highly stable and reproducible response over multiple test cycles (>18 000) with good switching response. It presents a promising and innovative direction for utilizing flexible sensors in the field of aircraft structural health monitoring.

A Gas-Steamed Route to Mesoporous Open Metal-Organic Framework Cages Enhancing Flame Retardancy and Smoke Suppression of Polyurea

Up to now, metal-organic frameworks (MOFs) with open nanostructures have shown outstanding capabilities in trapping smoke particles compared to the original MOFs. However, only a few MOF-based strategies have been reported to synthesize hierarchical porous cages thus far, which are mainly restricted to environmentally unfriendly wet-chemical liquid methods. Herein, as a proof-of-concept, a gas-steamed metal-organic framework approach was designed to fabricate a series of cheeselike open cages with hierarchical porosity. Briefly, zeolitic imidazolate framework-67 (ZIF-67) and phytic acid were employed as precursor and etchant, respectively. Abandoning the conventional wet-chemical method, the coordination bond of ZIF-67 was cleaved by acidic steam, forming an open framework with a high specific surface area and a hierarchical porous structure. The universality of this method was also confirmed by the selection of different etchants. Impressively, they also show outstanding fume-toxic adsorption capability and labyrinth effects based on abundant and complex porous channels. At only 5 wt % loading, Co3O4@open ZIF-67 cage-2 (Co3O4@OZC-2) imparted polyurea (PUA) composites with a 21.2% limiting oxygen index, and the peak of heat release rate, total heat release, and total smoke production were reduced by around 37.5, 25.5, and 40.4%, respectively, compared to neat PUA. This work will shed light on the advanced structural design of polymer composites with high fire safety, especially smoke suppression performance, so as to obtain more feasible applications.

Peelable Microwave Absorption Coating with Reusable and Anticorrosion Merits

The peelable microwave absorption (MA) coating with reversible adhesion for stable presence on substrates and easy release without any residuals is highly desired in temporary electromagnetic protection, which can quickly enter and disengage the electromagnetic protection state according to the real-time changeable harsh surroundings. On the contrary, with the incorporation of abundant absorbent to achieve excellent MA ability, the tunable adhesion and sufficient cohesion are extremely challenging to fulfill the above requirement. The reported peelable coatings still have problems in controlling adhesion/cohesion strength and coating release, facing substantial residuals after peeling even using complex chemical modification or abundant additives. Herein, a peelable MA coating based on the block characteristics of polar and nonpolar segments of poly(styrene-(ethylene-co-butylene)-styrene) (SEBS) is successfully developed. The polyaniline-decorated carbon nanotube as a microwave absorber plays a positive influence on the adhesion/cohesion of the coating due to bonding interaction. The competitive effective absorption bandwidth (EAB) of 8.8 GHz and controllable yet reversible adhesion release on various substrates and complex surfaces have been achieved. The reusability endows peelable MA coating with 93% retention of EAB even after ten coating-peeling cycles. The coating with excellent chemical and adhesion stability can effectively protect substrates from salt/acid/alkali corrosion, showing over 98% retention of EAB even after 8 h of accelerated corrosion. Our peelable MA coating via a general yet reliable approach provides a prospect for temporary electromagnetic protection.

Covalently surface-grafting α‑zirconium phosphate nanoplatelets enables collagen fiber matrix with ultraviolet barrier, antibacterial, and flame-retardant properties

Manipulating the dispersibility and reactivity of two-dimensional nanomaterials in collagen fibers (CFs) matrix has aroused attention in the fabrication of multifunctional collagen-based nanocomposites. Here, α‑zirconium phosphate nanoplatelets (ZrP NPs) were surface-functionalized with gallic acid (GA) to afford ZrP-GA NPs for engineering CFs matrix. The influence of ZrP-GA NPs on the ultraviolet barrier, antibacterial, and flame-retardant properties of resultant CFs matrix were investigated. Microstructural analysis revealed that ZrP-GA NPs were dispersed and bound within the collagen fibrils and onto the collagen strands in the CFs matrix. The resultant CFs matrix also maintained typical D-periodic structures of collagen fibrils and native branching and interwoven structures of CFs networks with increased porosity and enhanced ultraviolet barrier properties. Inhibition zone testing presented excellent antibacterial activities of the CFs matrix owing to surface grafting of antibacterial GA. Thanks to enhanced dispersion and binding of ZrP NPs with the CFs matrix by surface-functionalization with GA, the resultant CFs matrix reduced the peak heat release rate and the total heat release by 42.9 % and 39.0 %, respectively, highlighting improved flame-retardant properties. We envision that two-dimensional nanomaterials possess great potential in developing reasonable collagen-based nanocomposites towards the manufacture of emergent multifunctional collagen fibers-based wearable electronics.

Synthesis and Applications of Supramolecular Flame Retardants: A Review

The development of different efficient flame retardants (FRs) to improve the fire safety of polymers has been a hot research topic. As the concept of green sustainability has gradually been raised to the attention of the whole world, it has even dominated the research direction of all walks of life. Therefore, there is an urgent calling to explore the green and simple preparation methods of FRs. The development of supramolecular chemistry in the field of flame retardancy is expanding gradually. It is worth noting that the synthesis of supramolecular flame retardants (SFRs) based on non-covalent bonds is in line with the current concepts of environmental protection and multi-functionality. This paper introduces the types of SFRs with different dimensions. SFRs were applied to typical polymers to improve their flame retardancy. The influence on mechanical properties and other material properties under the premise of flame retardancy was also summarized.