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

A universal eco-friendly flame retardant strategy for polylactic acid fabrics and other polymer substrates

Various polymer substrates have their particular combustion features, therefore, developing an effective universal flame retardant strategy for various polymer substrates is of great practical importance. Meanwhile, as substitutes for petroleum-based products, bio-based flame retardants and biodegradable polylactic acid (PLA) meet the requirements of sustainable development. In this work, a fully bio-based flame retardant coating (PAGS) was prepared using phytic acid (PA) and guanosine (GS). PAGS was used as a universal flame retardant coatings for polylactic acid (PLA) fabrics and other substrates, including cotton fabrics, polyethylene terephthalate (PET) fabrics, polyamide (PA) fabrics, polyurethane (PU) foams, polyethylene terephthalate (PET) films, and woods. The PAGS-treated substrates were able to self-extinguish and eliminate molten droplets. Similarly, the PAGS coating significantly suppressed the heat release of each substrate. The P-containing free radicals in the gas phase were able to interact with highly reactive H, HO and alkyl radicals, blocking the chain reaction during combustion. The flammable gas density was also diluted by nonflammable gases. The formed continuous porous and dense intumescent char layer hindered heat and oxygen. It is suggested that this work provides a simple and efficient flame retardant strategy for improving the fire safety of various polymer substrates.

Chitin and Chitosan as Polymers of the Future-Obtaining, Modification, Life Cycle Assessment and Main Directions of Application

Natural polymers are very widespread in the world, which is why it is so important to know about the possibilities of their use. Chitin is the second most abundant reproducible natural polymer in nature; however, it is insoluble in water and basic solvents. Chitin is an unused waste of the food industry, for which there are possibilities of secondary management. The research led to obtaining a soluble, environmentally friendly form of chitin, which has found potential applications in the many fields, e.g., medicine, cosmetics, food and textile industries, agriculture, etc. The deacetylated form of chitin, which is chitosan, has a number of beneficial properties and wide possibilities of modification. Modification possibilities mean that we can obtain chitosan with the desired functional properties, facilitating, for example, the processing of this polymer and expanding the possibilities of its application, also as biomimetic materials. The review contains a rich description of the possibilities of modifying chitin and chitosan and the main directions of their application, and life cycle assessment (LCA)-from the source of the polymer through production materials to various applications with the reduction of waste.

Fabrication of an Eco-Friendly Clay-Based Coating for Enhancing Flame Retardant and Mechanical Properties of Cotton Fabrics via LbL Assembly

An eco-friendly clay-based synergistic flame-retardant coating was established on cotton fabrics via facile layer-by-layer assembly derived from polyethyleneimine (PEI), attapulgite clay (ATP), and phytic acid (PA). The fabricated flame-retardant (FR) cotton fabrics demonstrated improved thermal stability. Compared to untreated cotton fabrics, the limiting oxygen index of Cotton-8TL was improved to 27.0%. The peak heat release rates of the prepared FR cotton fabrics were lower than that of the pristine cotton fabrics, showing a maximum reduction of 41%. The deposition coating system improved the amount of char residue effectively. The intumescent flame-retardant mechanism was proposed through the analysis of char residue and the suppression properties of volatile gases. Furthermore, compared with those of the untreated cotton fabrics, the tensile strength and elongation at break of the FR cotton fabrics in the warp direction were improved by 20% and 47% remarkably, respectively. A feasible surface modification strategy was provided for the flame-retardant treatment of cotton fabrics with the improvement of mechanical properties.

High-Performance Liquid Crystalline Polymer for Intrinsic Fire-Resistant and Flexible Triboelectric Nanogenerators

Flammability is a great challenge in the fields of electronics. The emergence of triboelectric nanogenerators (TENGs) provides a safe way to harvest environmentalally friendly energy and convert it into more secure power sources. Especially, polymer-based TENGs significantly accelerate the practical application of self-powered flexible electronics. However, most of the existing polymeric materials for TENGs are easily flammable and melt, dripping, in a fire scenario, and cannot be reused after combustion, which greatly limits the application of TENGs under extreme conditions. Herein, a fire-resistant TENG based on all-aromatic liquid crystalline poly(aryl ether ester) (LCP_AEE ) synthesized via simple and efficient one-pot melt polycondensation is reported. The highly rigid main chain of LCP_AEE endows the LCP-TENG with outstanding anti-dripping, temperature- and fire-resistance. The resultant LCP-TENG exhibits excellent electrical output performance, which is attributed to the high dielectric constant (ε' = 4.8) and fibrous-structured morphology of LCP_AEE . The device can maintain over 65% of open-circuit voltage even after 16 s combustion (≈520 °C). Consequently, this work offers a novel strategy for tailoring the TENGs toward a secure power generator and electronics with fire hazard reduction, and potential application in firefighting, personal protection, and other extreme temperature environments.

Advancing interfacial properties of carbon cloth via anodic-induced self-assembly of MOFs film integrated with α-MnO2: A sustainable electrocatalyst sensing acetylcholine

The metal organic frameworks (MOFs) with tunable composition, modified structure, and morphologically controlled nanoarchitectures are quite imperative to improve the electrochemical (EC) performances of sensing platforms. Herein, EC control over the fabrication of HKUST-1 (Cu-MOFs) nanocrystals is achieved via anodic-induced electrodeposition approach following the mixing of Cu²⁺ salt precursor in the vicinity of benzene-1,3,5-tricarboxylate (BTC^3-) ligands. The problem of controlled mass transfer and slow dispersal of MOFs is resolved by EC deposition of pyramidal-octagonal MOFs on a highly conductive and flexible carbon substrate (activated carbon cloth, ACC) wrapped with rGO layers (ACC-rGO@Cu(BTC). Further, α-MnO₂ is integrated on ACC-rGO@Cu(BTC) to achieve the synergistic effect of ternary structure interfaces. The novel ACC-rGO@Cu(BTC)@MnO₂ based flexible electrode exhibits striking EC performance toward non-enzymatic sensing of acetylcholine (ACh) including wide linear range (0.1 µM - 3 mM), lowest detection limit (5 nM, S/N = 3), high selectivity, and long-term stability. Moreover, the developed sensing system has been applied for real-time detection of ACh efflux released from three different cell lines and biological matrices. Our work unlocks a new prospect of precisely structured MOFs with extensive functionalities and scaled-up fabrication methods via selection of nanoscale reaction centers to develop flexible sensing devices.

The improvement of fire safety performance of flexible polyurethane foam by Highly-efficient P-N-S elemental hybrid synergistic flame retardant

Herein, three different phosphorus-containing compounds (methyl phosphoryl dichloride, phenyl phosphoryl dichloride and phenyl dichlorophosphate) were reacted with 2-aminobenzothiazole respectively, and a series of synergistic flame retardants with phosphorus, nitrogen and sulfur elements were synthesized, named MPBT, PPBT and POBT respectively. Then, they were added to prepare flame-retardant flexible polyurethane foam (FPUF). Through the analysis of thermal stability, pyrolysis, heat release and smoke release behavior, the influence of different phosphorus-containing structures on the flame-retardant performance of FPUF was studied, and their flame-retardant mechanism was explored in detail. Among them, MPBT had the highest flame retardant efficiency with the same addition amount (10 wt%). The limiting oxygen index (LOI) value of PU/10.0% MPBT reached 22.5 %, and it successfully passed the vertical burning test. Subsequently, the addition amount of MPBT was increased and the best comprehensive performance of flame-retardant FPUF was explored. The results showed that the LOI value of PU/15.0% MPBT was increased to 23.5%. As for PU/15.0% MPBT, the peak heat release rate (PHRR) was 453 KW/m², which was reduced by 46.64 %; and the flame retardancy index (FRI) value was also increased to 6.88. At the same time, the mechanical properties of flame-retardant FPUF were studied. The tensile strength of PU/15.0% MPBT reached 170 KPa, and the permanent deformation of FPUF/10% MPBT was only 4 %, showing its excellent resilience. The above results show that this phosphorus-containing element hybrid synergistic flame retardant (MPBT) has a very good application prospect in the field of flame-retardant polymer materials.

Skin-inspired thermoelectric nanocoating for temperature sensing and fire safety

Temperature sensing enables flammable materials to respond intelligently at high temperature, which is conducive to further improving their fire safety. However, it is still challenging to develop a smart nanocoating with sensitive temperature-sensing and efficient flame retardancy. Inspired by human skin, a thermoelectric flame retardant (TE-FR) nanocoating was fabricated by combining a dermis-mimicking thermoelectric (TE) layer and an epidermis-mimicking flame retardant (FR) layer. The TE-FR nanocoating exhibited accurate temperature sensing at 100-300 ℃ and repeatable fire-warning capability. When being burned, the fire-warning response time of the TE-FR nanocoating was only 2.0 s, and it retriggered the fire-warning device within 2.8 s when it was reburned. Meanwhile, the TE-FR nanocoating exhibited outstanding flame retardancy. The coated polypropylene self-extinguished in the horizontal and vertical burning tests. Besides, its peak heat release rate, total heat release, and peak smoke production rate were significantly reduced. This work proposed an ingenious strategy to fabricate smart nanocoating for temperature sensing and fire safety, which revealed an enticing prospect in the fields of fire protection, electronic skin, and temperature monitor.

Research Progress of Chitosan-Based Biomimetic Materials

Chitosan is a linear polysaccharide produced by deacetylation of natural biopolymer chitin. Owing to its good biocompatibility and biodegradability, non-toxicity, and easy processing, it has been widely used in many fields. After billions of years of survival of the fittest, many organisms have already evolved a nearly perfect structure. This paper reviews the research status of biomimetic functional materials that use chitosan as a matrix material to mimic the biological characteristics of bivalves, biological cell matrices, desert beetles, and honeycomb structure of bees. In addition, the application of biomimetic materials in wound healing, hemostasis, drug delivery, and smart materials is briefly overviewed according to their characteristics of adhesion, hemostasis, release, and adsorption. It also discusses prospects for their application and provides a reference for further research and development.

A Durable, Flexible, Large-Area, Flame-Retardant, Early Fire Warning Sensor with Built-In Patterned Electrodes

Fire has been giving rise to enormous loss of life and property worldwide annually. Early fire warning represents an active and effective means to avoid potential fire hazards before huge losses occur. Despite encouraging advances in early fire warning systems, to date there remains an urgent lack of the design of a durable, flexible, and universal early fire warning sensor for large-area practical applications. Herein, facile fabrication of a durable, flexible, large-scale early fire-warning sensor is demonstrated through constructing a hierarchical flame retardant nanocoating, composed of graphene oxide, poly(dimethylaminoethyl methacrylate), and hexagonal boron nitride, on cotton fabric in combination with the parallelly patterned conductive ink as built-in electrodes. As-designed large-scale sensor (>33 cm and extendable) exhibits a short alarming time of <3 s in response to external abnormal high temperature, heat, or fire. In addition to high washability, flexibility, resistance to abrasion and wear, this hierarchical nanocoating can self-extinguish, thus enabling the sensor to continue warning during fire. This work offers an inventive concept to develop a universal and large-scale very early fire-monitoring platform, which opens up new opportunities for their practical applications in effectively reducing fire-related casualties and economic losses.

Flame-Retardant Systems Based on Chitosan and Its Derivatives: State of the Art and Perspectives

During the last decade, the utilization of chitin, and in par0ticular its deacetylated form, i.e., chitosan, for flame retardant purposes, has represented quite a novel and interesting application, very far from the established uses of this bio-sourced material. In this context, chitosan is a carbon source that can be successfully exploited, often in combination with intumescent products, in order to provide different polymer systems (namely, bulky materials, fabrics and foams) with high flame retardant (FR) features. Besides, this specific use of chitosan in flame retardance is well suited to a green and sustainable approach. This review aims to summarize the recent advances concerning the utilization of chitosan as a key component in the design of efficient flame retardant systems for different polymeric materials.

Fully bio-based coating from chitosan and phytate for fire-safety and antibacterial cotton fabrics

In this study, a fully bio-based coating was constructed by layer-by-layer deposition of chitosan (CS) and ammonium phytate (AP), to obtain fire-safety and antibacterial cotton fabrics. With about 8% weight gains of CS/AP coatings, the treated cotton fabrics self-extinguished in the vertical burning test. The data obtained from cone calorimetry showed CS/AP/cotton had much lower smoke and heat production, which indicated the fire safety of the fabrics was significantly improved for the presence of CS/AP coatings. The flame-retardant mechanism of this system was finally proposed according to the analysis of gaseous products and char residues. What is more, CS/AP coatings had higher antibacterial activity in Gram-negative bacteria and did improve the tensile strength of cotton fabrics compared with AP coating. With its ease of operation and use of non-toxic chemicals, this fully bio-based coating can further offer a feasible flame-retardant and antibacterial solution of the inflammable natural fabrics.

Nanoreinforcements of Two-Dimensional Nanomaterials for Flame Retardant Polymeric Composites: An Overview

Polymer materials are ubiquitous in daily life. While polymers are often convenient and helpful, their properties often obscure the fire hazards they may pose. Therefore, it is of great significance in terms of safety to study the flame retardant properties of polymers while still maintaining their optimal performance. Current literature shows that although traditional flame retardants can satisfy the requirements of polymer flame retardancy, due to increases in product requirements in industry, including requirements for durability, mechanical properties, and environmental friendliness, it is imperative to develop a new generation of flame retardants. In recent years, the preparation of modified two-dimensional nanomaterials as flame retardants has attracted wide attention in the field. Due to their unique layered structures, two-dimensional nanomaterials can generally improve the mechanical properties of polymers via uniform dispersion, and they can form effective physical barriers in a matrix to improve the thermal stability of polymers. For polymer applications in specialized fields, different two-dimensional nanomaterials have potential conductivity, high thermal conductivity, catalytic activity, and antiultraviolet abilities, which can meet the flame retardant requirements of polymers and allow their use in specific applications. In this review, the current research status of two-dimensional nanomaterials as flame retardants is discussed, as well as a mechanism of how they can be applied for reducing the flammability of polymers.

Well-controlled foam-based solid coatings

Foam-based solid coatings appear to be a simple solution for giving new properties to solid surfaces. An efficient method is presented for producing open-cell foam coatings having a tunable pore radius distribution (i.e. monodisperse within the range 100-1000 μm, bidisperse or fully polydisperse), tunable thickness, and tunable bulk and surface porosities. This is achieved by mixing a precursor aqueous foam and particle suspension (here a micrometer-sized polyurethane dispersion), and by spreading with a nozzle the resulting particle-loaded foam on the solid surface to be coated. It is shown that the bubble size distribution of the precursor foam can be preserved in the final solid coating. This is highlighted by using a monodisperse aqueous foam, for which coatings showed a polycrystalline structure, as well as bidisperse or fully polydisperse foams. As a major advantage of our method, the bubble size and solid volume fraction are shown to be independent parameters, allowing the size of the microstructural elements to be tuned easily, and so the expected functional properties of the coating. Results obtained with the studied polyurethane dispersion are expected to be reproduced with other dispersions.

Cyclodextrins and Cyclodextrin Derivatives as Green Char Promoters in Flame Retardants Formulations for Polymeric Materials. A Review

Polymers are intrinsically flammable materials; hence, fire retardance (FR) is required in their most common applications (i.e., electronic and construction, to mention some). Recently, it has been reported that cyclodextrin (CD) and cyclodextrin derivatives are beginning to be introduced into Intumescent Fire Retardant (IFR) formulations in place of pentaerythritol, which is used in IFRs that are currently on the market. Since IFRs are of less environmental concern than their hazardous halogen containing counterparts, the use of natural origin compounds in IFRs provides a way to comply with green chemistry issues. BCD and BCD derivatives presence in IFR mixtures promotes a higher yield of blowing gases and char when polymeric materials undergo combustion. Both processes play important roles in intumescence. The key rule to obtain in insulating compact char is the good dispersion of the nanoparticles in the matrix, which can be achieved by functionalizing nanoparticles with BCD derivatives. Moreover, CD derivatives are attractive because of their nanosized structure and their ability to form inclusion complexes with many compounds used as FR components, reducing their release to the environment during their shelf life of FR items. Often, fire retardance performed by BCD and BCD derivatives accompanies other relevant properties, such as improved mechanical resistance, washability resistance, self healing ability, thermal conductivity, etc. The application of CD fire retardant additives in many polymers, such as poly(lactic acid), poly(propylene), poly(vinyl acetate), poly(methyl methacrylate), linear low density poly(ethylene), polyamides, and polyesters are comprehensively reviewed here.

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.