Large-scale, thick, self-assembled, nacre-mimetic brick-walls as fire barrier coatings on textiles

Organized mineralized cellulose nanostructures for biomedical applications

Cellulose is the most abundant naturally-occurring polymer, and possesses a one-dimensional (1D) anisotropic crystalline nanostructure with outstanding mechanical robustness, biocompatibility, renewability and rich surface chemistry in the form of nanocellulose in nature. Such features make cellulose an ideal bio-template for directing the bio-inspired mineralization of inorganic components into hierarchical nanostructures that are promising in biomedical applications. In this review, we will summarize the chemistry and nanostructure characteristics of cellulose and discuss how these favorable characteristics regulate the bio-inspired mineralization process for manufacturing the desired nanostructured bio-composites. We will focus on uncovering the design and manipulation principles of local chemical compositions/constituents and structural arrangement, distribution, dimensions, nanoconfinement and alignment of bio-inspired mineralization over multiple length-scales. In the end, we will underline how these cellulose biomineralized composites benefit biomedical applications. It is expected that this deep understanding of design and fabrication principles will enable construction of outstanding structural and functional cellulose/inorganic composites for more challenging biomedical applications.

LLAM-MDCNet for Detecting Remote Sensing Images of Dead Tree Clusters

Clusters of dead trees are forest fires-prone. To maintain ecological balance and realize its protection, timely detection of dead trees in forest remote sensing images using existing computer vision methods is of great significance. Remote sensing images captured by Unmanned aerial vehicles (UAVs) typically have several issues, e.g., mixed distribution of adjacent but different tree classes, interference of redundant information, and high differences in scales of dead tree clusters, making the detection of dead tree clusters much more challenging. Therefore, based on the Multipath dense composite network (MDCN), an object detection method called LLAM-MDCNet is proposed in this paper. First, a feature extraction network called Multipath dense composite network is designed. The network’s multipath structure can substantially increase the extraction of underlying and semantic features to enhance its extraction capability for rich-information regions. Following that, in the row, column, and diagonal directions, the Longitude Latitude Attention Mechanism (LLAM) is presented and incorporated into the feature extraction network. The multi-directional LLAM facilitates the suppression of irrelevant and redundant information and improves the representation of high-level semantic feature information. Lastly, an AugFPN is employed for down-sampling, yielding a more comprehensive representation of image features with the combination of low-level texture features and high-level semantic information. Consequently, the network’s detection effect for dead tree cluster targets with high-scale differences is improved. Furthermore, we make the collected high-quality aerial dead tree cluster dataset containing 19,517 images shot by drones publicly available for other researchers to improve the work in this paper. Our proposed method achieved 87.25% mAP with an FPS of 66 on our dataset, demonstrating the effectiveness of the LLAM-MDCNet for detecting dead tree cluster targets in forest remote sensing images.

Barrier Effects of Cellulosic Fibers with Hybrid Coating Based on Zirconium Metal-Organic Framework

Metal-organic frameworks (MOFs) have great potential for the development of fire barriers for flammable materials. Accordingly, zirconium-based metal-organic framework (Zr-MOF), branched polyethyleneimine (BPEI), and vinyltriethoxysilane (VTES) were deposited to produce composites assembled on cellulosic fibers to investigate their barrier effects. The structure, morphology, and thermal properties of the cellulosic fibers were characterized using FTIR spectroscopy, SEM, and TGA. Compared with the untreated cotton sample, the temperature of the maximum rate of weight loss (T_max) of C-Zr-MOF/BPEI/VTES increased from 479 to 523.3 °C and the maximum weight loss rate (R_max) at T_max decreased from 37.6 to 17.2 wt%/min. At 800 °C, the pristine cotton was burned out without residues whereas the residual char content of the C-Zr-MOF/BPEI/VTES sample was 7.2355 wt%. From the vertical burning tests, the results suggested that the C-Zr-MOF/BPEI/VTES sample had better barrier effects by reducing the flame-spread speed and generating more protective char layers.

Experimental study on the properties of modern blue clay brick for Kaifeng People's Conference Hall

This article presents building assessment research comprising on-site inspections, indoor scientific tests, and material performance studies on the wall blue clay bricks in the Kaifeng People's Conference Hall, objectively developing an enhanced scientific understanding to renovate modern buildings. Using X-ray diffraction (XRD), scanning electron microscopy (SEM), alongside a parametric study of density, moisture content, water absorption, void ratio, frosting, compressive strength, and softening coefficient in assessing the material health of the blue clay bricks and it's non-key parts, in developing "appropriate and compatible renovation" to repair contemporaneous buildings. The composition, pore characteristics, weathering degree, and mechanical properties of the blue clay brick samples were analyzed. These parameters showed that blue clay brick fired at less than 1000 °C; the main mineral composition as quartz, followed by albite, mica, and anorthite. Its density was 1.573 g/cm³, less than the 1.70 g/cm³ of ordinary clay brick. According to the standards, the water absorption was greater than that of regular sintered bricks by more than 18% and was slightly frosted. Compressive strength being less than MU10 did not meet the current design specifications for masonry. Its softening coefficient was between 0.70 and 0.85, but its water resistance was relatively good. The research results provide an essential reference for judging the health and longevity of modern buildings to achieve scientific guidelines for practical protection.

Osmotic Delamination: A Forceless Alternative for the Production of Nanosheets Now in Highly Polar and Aprotic Solvents

Repulsive osmotic delamination is thermodynamically allowed "dissolution" of two-dimensional (2D) materials and therefore represents an attractive alternative to liquid-phase exfoliation to obtain strictly monolayered nanosheets with an appreciable aspect ratio with quantitative yield. However, osmotic delamination was so far restricted to aqueous media, severely limiting the range of accessible 2D materials. Alkali-metal intercalation compounds of MoS₂ or graphite are excluded because they cannot tolerate even traces of water. We now succeeded in extending osmotic delamination to polar and aprotic organic solvents. Upon complexation of interlayer cations of synthetic hectorite clay by crown ethers, either 15-crown-5 or 18-crown-6, steric pressure is exerted, which helps in reaching the threshold separation required to trigger osmotic delamination based on translational entropy. This way, complete delamination in water-free solvents like aprotic ethylene and propylene carbonate, N-methylformamide, N-methylacetamide, and glycerol carbonate was achieved.

Coordination-driven interfacial cross-linked graphene oxide-alginate nacre mesh with underwater superoleophobicity for oil-water separation

Inspired by the seashell nacre and seaweed, a novel GO-Ca²⁺-SA nacre-inspired hybrid mesh was prepared via an interfacial layer-by-layer self-assembly and cross-linking, using graphene oxide (GO) and sodium alginate (SA) as the building blocks and calcium chloride as the coordination agent, respectively. Hybrid mesh was characterized by FTIR, XPS, XRD, SEM and contact angel instrument, showing superhydrophilic and underwater superoleophobic property and low oil adhesion, due to its wrinkle and rough surface, and high hydration ability of GO-Ca-alginate nanohydrogels. The separation efficiencies of various oil-water mixtures were above 99 %, with a highest flux of 119,426 L m^-2 h^-1. Hybrid mesh showed an orderly layered "brick and mortar" microstructure with many ultrasmall nanoscaled protuberances. Ca²⁺ ions could chelate with SA to form the "egg-box" structure, and interact with GO nanosheets. Hybrid mesh possessed high salt/acid/alkaline tolerance, abrasion resistance, mechanical property with Young's modulus of 35.8 ± 4.9 GPa, and excellent cycling stability.

Self-Assembled Bioinspired Nanocomposites

Bioinspired materials engineering impacts the design of advanced functional materials across many domains of sciences from wetting behavior to optical and mechanical materials. In all cases, the advances in understanding how biology uses hierarchical design to create failure and defect-tolerant materials with emergent properties lays the groundwork for engaging into these topics. Biological mechanical materials are particularly inspiring for their unique combinations of stiffness, strength, and toughness together with lightweightness, as assembled and grown in water from a limited set of building blocks at room temperature. Wood, nacre, crustacean cuticles, and spider silk serve as some examples, where the correct arrangement of constituents and balanced molecular energy dissipation mechanisms allows overcoming the shortcomings of the individual components and leads to synergistic materials performance beyond additive behavior. They constitute a paradigm for future structural materials engineering-in the formation process, the use of sustainable building blocks and energy-efficient pathways, as well as in the property profiles-that will in the long term allow for new classes of high-performance and lightweight structural materials needed to promote energy efficiency in mobile technologies.This Account summarizes our efforts of the past decade with respect to designing self-assembling bioinspired materials aiming for both mechanical high-performance structures and new types of multifunctional property profiles. The Account is set out to first give a definition of bioinspired nanocomposite materials and self-assembly therein, followed by an in-depth discussion on the understanding of mechanical performance and rational design to increase the mechanical performance. We place a particular emphasis on materials formed at high fractions of reinforcements and with tailor-made functional polymers using self-assembly to create highly ordered structures and elucidate in detail how the soft polymer phase needs to be designed in terms of thermomechanical properties and sacrificial supramolecular bonds. We focus on nanoscale reinforcements such as nanoclay and nanocellulose that lead to high contents of internal interfaces and intercalated polymer layers that experience nanoconfinement. Both aspects add fundamental challenges for macromolecular design of soft phases using precision polymer synthesis. We build upon those design criteria and further develop the concepts of adaptive bioinspired nanocomposites, whose properties are switchable from the outside using molecularly defined triggers with light. In a last section, we discuss how new types of functional properties, in particular flexible and transparent gas barrier materials or fire barrier materials, can be reached on the basis of the bioinspired nanocomposite design strategies. Additionally, we show new types of self-assembled photonic materials that can even be evolved into self-assembling lasers, hence moving the concept of mechanical nanocomposite design to other functionalities.The comparative discussion of different bioinspired nanocomposite architectures with nematic, fibrillar, and cholesteric structures, as based on different reinforcing nanoparticles, aims for a unified understanding of the design principles and shall aid researchers in the field in the more elaborate design of future bioinspired nanocomposite materials based on molecular control principles. We conclude by addressing challenges, in particular also the need for a transfer from fundamental molecular materials science into scalable engineering materials of technological and societal relevance.

2D Hexagonal Boron Nitride-Coated Cotton Fabric with Self-Extinguishing Property

Here, we report on the fabrication of flame retardant hydrophobic cotton fabrics based on the coating with two-dimensional hexagonal boron nitride (2D hBN) nanosheets. A simple one-step solution dipping process was used to coat the fabrics by taking advantage of the strong bonding between diethylenetriamine and hBN on the cotton surface. Exposure to direct flame confirmed the improvement of the flame retardant properties of the coated cotton fabrics. In turn, removal of the flame source revealed self-extinguishing properties. Molecular dynamics simulations indicate that hBN hinders combustion by reducing the rate at which oxygen molecules reach the cotton surface. This time-saving and one-step approach for the fabrication of flame-retardant cotton fabrics offers significant advantages over other, less efficient production methods.

Mild and Versatile Functionalization of Nacre-Mimetic Cellulose Nanofibrils/Clay Nanocomposites by Organocatalytic Surface Engineering

Development of surface-engineering strategies, which are facile, versatile, and mild, are highly desirable in tailor-made functionalization of high-performance bioinspired nanocomposites. We herein disclose for the first time a general organocatalytic strategy for the functionalization and hydrophobization of nacre-mimetic nanocomposites, which includes vide supra key aspects of surface engineering. The merging of metal-free catalysis and the design of nacre-mimetic nanocomposite materials were demonstrated by the organocatalytic surface engineering of cellulose nanofibrils/clay nanocomposites providing the corresponding bioinspired nanocomposites with good mechanical properties, hydrophobicity, and useful thia-, amino, and olefinic functionalities.

Waterborne Methacrylate-Based Vitrimers

We demonstrate waterborne, unimolecularly dissolved vitrimer prepolymer systems that can be transferred into a vitrimer material using catalytic transesterification. The one-component prepolymer system can be processed via film casting and subsequent heat-induced cross-linking. A variation of the density of side chain hydroxy groups over ester and amide groups in the methacrylate/methacrylamide backbone, as well as of the Lewis acid catalyst loading, allow control of the extent of cross-linking and exchange rates. The increase of the amount of both catalyst and hydroxy groups leads to an acceleration of the relaxation times and a decrease of the activation energy of the transesterification reactions. The system features elastomeric properties, and the tensile properties are maintained after two recycling steps. Thus far, vitrimers have been limited largely to hydrophobic polymers; this system is a step forward toward waterborne, one-component materials, and we demonstrate its use in waterborne bioinspired nanocomposites.

Investigation on the Preparation and Properties of CMC/magadiite Nacre-Like Nanocomposite Films

The layered hydrated sodium salt-magadiite (MAG), which has special interpenetrating petals structure, was used as a functional filler to slowly self-assemble with sodium carboxy-methylcellulose (CMC), in order to prepare nacre-like nanocomposite film by solvent evaporation method. The structure of prepared nacre-like nanocomposite film was characterized by Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) analysis; whereas, it was indicated that CMC macromolecules were inserted between the layers of MAG to increase the layer spacing of MAG by forming an interpenetrating petals structure; in the meantime, the addition of MAG improved the thermal stability of CMC. The tensile strength of CMC/MAG was significantly improved compared with pure CMC. The tensile strength of CMC/MAG reached the maximum value at 1.71 MPa when the MAG content was 20%, to maintaining high transparency. Due to the high content of inorganic filler, the flame retarding performance and the thermal stability were also brilliant; hence, the great biocompatibility and excellent mechanical properties of the bionic nanocomposite films with the unique interpenetrating petals structure provided a great probability for these original composites to be widely applied in material research, such as tissue engineering in biomedical research.

Migration of Quaternary Ammonium Cations from Exfoliated Clay/Low-Density Polyethylene Nanocomposites into Food Simulants

Clay/polymer nanocomposites (CPNs) are polymers incorporating refined clay particles that are frequently functionalized with quaternary ammonium cations (QACs) as dispersion aids. There is interest in commercializing CPNs for food contact applications because they have improved strength and barrier properties, but there are few studies on the potential for QACs in CPNs to transfer to foods under conditions of intended use. In this study, we manufactured low-density poly(ethylene) (LDPE)-based CPNs and assessed whether QACs can migrate into several food simulants under accelerated storage conditions. QACs were found to migrate to a fatty food simulant (ethanol) at levels of ∼1.1 μg mg^-1 CPN mass after 10 days at 40 °C, constituting about 4% total migration (proportion of the initial QAC content in the CPN that migrated to the simulant). QAC migration into ethanol was ∼16× higher from LDPE containing approximately the same concentration of QACs but no clay, suggesting that most QACs in the CPN are tightly bound to clay particles and are immobile. Negligible QACs were found to migrate into aqueous, alcoholic, or acidic simulants from CPNs, and the amount of migrated QACs was also found to scale with the temperature and the initial clay concentration. The migration data were compared to a theoretical diffusion model, and it was found that the diffusion constant for QACs in the CPN was several orders of magnitude slower than predicted, which we attributed to the potential for QACs to migrate as dimers or other aggregates rather than as individual ions. Nevertheless, the use of the migration model resulted in a conservative estimate of the mass transfer of QAC from the CPN test specimens.

Polymer nanocomposites having a high filler content: synthesis, structures, properties, and applications

The recent development of nanoscale fillers, such as carbon nanotubes, graphene, and nanocellulose, allows the functionality of polymer nanocomposites to be controlled and enhanced. However, conventional synthesis methods of polymer nanocomposites cannot maximise the reinforcement of these nanofillers at high filler content. Approaches for the synthesis of high content filler polymer nanocomposites are suggested to facilitate future applications. The fabrication methods address the design of the polymer nanocomposite architecture, which encompasses one, two, and three dimensional morphologies. Factors that hamper the reinforcement of nanostructures, such as alignment, dispersion of the filler and interfacial bonding between the filler and polymer, are outlined. Using suitable approaches, maximum potential reinforcement of nanoscale fillers can be anticipated without limitations in orientation, dispersion, and the integrity of the filler particle-matrix interface. High filler content polymer composites containing emerging materials such as 2D transition metal carbides, nitrides, and carbonitrides (MXenes) are expected in the future.

A green approach to fabricating nacre-inspired nanocoating for super-efficiently fire-safe polymers via one-step self-assembly

Developing a high efficient, environmental-friendly and universal fire-safe strategy for combustible polymers is crucial but challengeable. Inspired by nacre, we developed a super-efficiently fire-safe nanocoating based on carboxymethyl chitosan (CCS) and modified montmorillonite (MMT) via one-step self-assembly. The nanocoating possessed well-arranged nacre-like hierarchical microstructure, exhibiting high transparency and specific nacre-like iridescence. More importantly, the nanocoating endowed many large-scale polymer substrates, such as polyester film, cotton fabric and polyurethane foam, with super-efficient fire-safety by dip-coating or spray-coating. All the coated substrates were self-extinguished in the burning tests. Meanwhile, their heat release and smoke production were decreased remarkably. Most notably, the peak heat release rate, total heat release, peak smoke production rate and total smoke production of polyurethane foam were decreased by 84.1%, 89.4%, 84.4% and 95.2%, respectively. Additionally, no organic solvent, halogen and phosphorus element were involved, which was environmental-friendly. Our findings provide a super-efficient, economical, universal and green fabrication strategy for fire-safe polymers.

Fabrication of Water-Resistant Nacre-like Polymer/Clay Nanocomposites via in Situ Polymerization

Fabrication and characterization of water-resistant nacre-like polymer/clay nanocomposites, in which clay platelets and hydrophobic polymer chains are alternately stacked in parallel, are reported. Hydrophilic clay was converted by an ion-exchange reaction with a methacrylate monomer having a long alkyl chain and a quaternary ammonium salt group at the end. The subsequent in situ polymerization bound the neighboring clay surfaces, leading to the preferential orientation of the clay platelets owing to their high aspect ratio. The composites maintained excellent mechanical properties even after being immersed in water for more than a day. Strong shape stability was observed in water as well as in various organic solvents.