An overview of alginates as flame-retardant materials: Pyrolysis behaviors, flame retardancy, and applications

Nanocellulose-based porous lightweight materials with flame retardant properties: A review

This review discusses the development and application of nanocellulose (NC)-aerogels, a sustainable and biodegradable biomaterial, with enhanced flame retardant (FR) properties. NC-aerogels combine the excellent physical and mechanical properties of NC with the low density and thermal conductivity of aerogels, making them promising for thermal insulation and other fields. However, the flammability of NC-aerogels limits their use in some applications, such as electromagnetic interference shielding, oil/water separation, and flame-resistant textiles. The review covers the design, fabrication, modification, and working mechanism of NC porous materials, focusing on how advanced technologies can impart FR properties into them. The review also evaluates the FR performance of NC-aerogels by employing widely recognized tests, such as the limited oxygen index, cone calorimeter, and UL-94. The review also explores the integration of innovative and eco-friendly materials, such as MXene, metal-organic frameworks, dopamine, lignin, and alginate, into NC-aerogels, to improve their FR performance and functionality. The review concludes by outlining the potential, challenges, and limitations of future research on FR NC-aerogels, identifying the obstacles and potential solutions, and understanding the current progress and gaps in the field.

Functional use of carbon dioxide for the sustainable valorization of orange peel in the pyrolysis process

Although biomass is carbon-neutral, its use as a primary feedstock faces challenges arising from inconsistent supply chains. Therefore, it becomes crucial to explore alternatives with reliable availability. This study proposes a strategic approach for the thermochemical valorization of food processing waste, which is abundantly generated at single sites within large-scale processing plants. As a model biomass waste from the food industry, orange peel waste was particularly chosen considering its substantial consumption. To impart sustainability to the pyrolysis system, CO2, a key greenhouse gas, was introduced. As such, this study highlights elucidating the functionality of CO2 as a reactive feedstock. Specifically, CO2 has the potential to react with volatile pyrolysates evolved from orange peel waste, leading to CO formation at ≥490 °C. The formation of chemical constituents, encompassing acids, ketones, furans, phenols, and aromatics, simultaneously decreased by 15.1 area% in the presence of CO2. To activate the efficacy of CO2 at the broader temperature spectrum, supplementary measures, such as an additional heating element (700 °C) and a nickel-based catalyst (Ni/Al2O3), were implemented. These configurations promote thermal cracking of the volatiles and their reaction kinetics with CO2, representing an opportunity for enhanced carbon utilization in the form of CO. Finally, the integrated process of CO2-assisted catalytic pyrolysis and water-gas shift reaction was proposed. A potential revenue when maximizing the productivity of H2 was estimated as 2.62 billion USD, equivalent to 1.11 times higher than the results from the inert (N2) environment. Therefore, utilizing CO2 in the pyrolysis system creates a promising approach for enhancing the sustainability of the thermochemical valorization platform while maximizing carbon utilization in the form of CO.

High thermal buffer and radiative cooling sodium alginate-based Janus aerogel enables multi-scenario thermal management for firefighting clothing

Firefighting clothing is an indispensable protective equipment for firefighters performing rescue activities under extreme heat and fire conditions. However, few bio-based thermal management materials that provide thermal comfort to firefighters in different operational scenarios have been reported. Herein, we present a novel strategy to prepare Janus-type aerogels based on sodium alginate biological macromolecules, consisting of a SiO2 nanoparticle layer and a microencapsulated paraffin@SiO2 phase-change composite layer. A passive radiative cooling and thermal energy storage was integrated into a functional dual-mode material system. Results show that Janus-type aerogel to cool down by 11.5 °C on a hot summer day. Meanwhile, paraffin@SiO2 has a high melting enthalpy of 127.5 J g-1 that effectively buffers temperature rise during the phase-change process. This Janus-type aerogel has ultra-low heat insulation (0.042 W/(m·K)), it can delay approximately 76.6 s to reach second-degree burn time for skin at a radiant heat exposure of 18.4 kW m-2. The work provides an innovative way to develop bio-based thermal management materials, which could enable multi-scenario thermal management for firefighting clothing.

Construction of chitosan/alginate aerogels with three-dimensional hierarchical pore network structure via hydrogen bonding dissolution and covalent crosslinking synergistic strategy for thermal management systems

To replace traditional petrochemical-based thermal insulation materials, in this work, the chitosan (CHI)/alginate (ALG) (CA) aerogels with three-dimensional hierarchical pore network structure were constructed by compositing CHI and ALG using a synergistic strategy of hydrogen bonding dissolution and covalent crosslinking. The structure and properties were further regulated by crosslinking the CA aerogels with epichlorohydrin (ECH). The CA aerogels exhibited various forms of covalent crosslinking, hydrogen bonding and electrostatic interactions, with hydrogen bonding content reaching 79.12 %. The CA aerogels showed an excellent three-dimensional hierarchical pore network structure, with an average pore size minimum of 15.92 nm. The structure regulation of CA aerogels obtained excellent compressive properties, with an increase of stress and strain by 137.61 % and 45.05 %, which can support a heavy object 5000 times its weight. Additionally, CA aerogels demonstrate excellent thermal insulation properties and low thermal conductivity, comparable to commercially available insulation materials. More importantly, CA aerogels have good cyclic insulation stability and thermal properties, and they have a flame retardancy rating of V-0, which shows the stability of insulation properties and excellent safety. CA aerogels provide new ideas for the development of biomass thermal insulation materials and are expected to be candidates for thermal management applications.

Synergistic effect of modified anhydrous magnesium carbonate and hexaphenoxycyclotriphosphazene on flame retardancy of ethylene-vinyl acetate copolymer

Ethylene-vinyl acetate copolymer (EVA) is widely used in various applications; however, its flammability limits its application in wire and cable industries. In this study, 3-methacryloxypropyltrimethoxysilane (KH570) was successfully grafted onto the surface of anhydrous magnesium carbonate (AMC) by alkali activation treatment. The KH570 modified AMC (AMC@KH570) was then introduced into the EVA matrix along with hexaphenoxycyclotriphosphazene (HPCTP) to assess their effects on the flame retardancy and mechanical properties of EVA composites. The results illustrate a significant synergistic effect in enhancing the flame retardancy of EVA composites by using AMC@KH570 and HPCTP, and the limiting oxygen index (LOI) and vertical burning test (UL-94) of EVA filled with 5 wt% HPCTP and 45 wt% AMC@KH570 (mAMC/H-45-5) reached 27.6% and V-0, respectively. The flame retardant mechanism was investigated by thermogravimetric/infrared (TG-IR) spectroscopy and residual carbon composition analysis. The results show that the thermal decomposition of AMC@KH570 and HPCTP consists of gas dilution, free radical quenching, and catalytic carbonization. Furthermore, KH570 works as a bridge to improve the compatibility of AMC and EVA matrix, which offsets the mechanical loss of EVA to some extent. The present research provides a new path to modify AMC and fabricate EVA composites with excellent flame retardant properties.

Preparation and application of halogen-free and efficient Si/P/N-containing flame retardants on cotton fabrics

Cotton fabric is extensively utilized due to its numerous applications, but the flammability associated with cotton fabric poses potential security risks to individuals. A halogen-free efficient flame retardant named poly [(tetramethylcyclosiloxyl spirocyclic pentaerythritol)-piperazin phosphate] (PCPNTSi) was developed to consolidate the fire retardance of cotton fabrics. After PCPNTSi treatment, the limiting oxygen index (LOI) of cotton fabric with 30 % weight gain (CP3) was raised to 32.8 %. In the vertical flammability test (VFT), CP3 has self-extinguished performance with a char length of 8.7 cm. The heat release rate (HRR) of cotton fabric with 20 % weight gain (CP2) is 78.8 % lower than that of pure cotton fabric (CP0). In addition, the total smoke release (TSP) of CP2 is 41.7 % lower than that of CP0, indicating PCPNTSi gives cotton fabric a good capability to inhibit smoke release. Finally, the possible flame retardant mechanism was discussed by the data of scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), Fourier Transform infrared spectroscopy (FT-IR) and thermogravimetric infrared spectroscopy (TG-IR). The results show that PCPNTSi is an intumescent flame retardant acting in both gas phase and solid phase.

A step towards tuning the jute fiber structure and properties by employing sodium periodate oxidation and coating with alginate

This paper outlines a novel simple protocol for tuning the structure and properties of jute using sodium periodate (NaIO4) oxidation and coating with alginate. When compared to the raw jute, fabrics oxidized with a 0.2 or 0.4 % NaIO4 solution for 30-120 min exhibited an increased aldehyde group content (0.185 vs. 0.239-0.398 mmol/g), a significantly increased negative zeta potential (from -8.57 down to -20.12 mV), a slight disruption of fiber crystallinity, 15.1-37.5 % and 27.9-49.8 % lower fabric maximum force and stiffness, respectively. Owing to the removal of hydrophobic surface barrier, decreased crystallinity index and the presence of micropores on the fabrics' surfaces, oxidized fabrics have a 22.3-29.6 % improved ability for moisture sorption compared to raw fabric. Oxidized fabrics characterized by very long wetting times and excellent antioxidant activities (> 98 %), can find applications as hydrophobic packaging materials. To further extend the utilization of jute in biocarpet engineering such as water-binding geo-prebiotic supports, oxidized fabrics were coated with alginate resulting in 7.9-24.9 % higher moisture sorption and 352-660 times lower wetting times than their oxidized counterparts. This modification protocol has never been applied to lignocellulosic fibers and sheds new light on obtaining jute fabrics with tuned structure and properties intended for various applications.

Preparation of high-strength photochromic alginate fibers based on the study of flame-retardant properties

Color-changing fibers have attracted much attention for their wide applications in camouflage, security warnings, and anti-counterfeiting. The inorganic color-changing material tungsten trioxide (WO3) has been widely investigated for its good stability, controllability, and ease of synthesis. In this study, photochromic alginate fibers (WO3@Ca-Alg) were prepared by incorporating UV-responsive hybrid tungsten trioxide nanoparticles in the fiber production process. The prepared photochromic alginate fibers changed from white to dark blue after 30 min of UV irradiation and returned to their original color after 64 h. It can be seen that WO3@Ca-Alg has the advantage of long color duration. The strength of this fiber reached 2.61 cN/dtex and the limiting oxygen index (LOI) was 40.9 %, which indicates that the fiber exhibited mechanical resistance and flame-retardant properties. After the cross-linking of WO3@Ca-Alg by sodium tetraborate, a new core-shell structure was generated, which was able to encapsulate tungsten trioxide in it, thus reducing the amount of tungsten trioxide loss, and its salt and washing resistance was greatly improved. This photochromic alginate fiber can be mass produced and spun into yarn.

Bio-based alginate and Si-, P- and N-containing compounds cooperate toward flame-retardant modification of polyester fabrics

Imparting flame retardancy to polyester fabrics is still a pressing issue for the textile industry. To this end, a composite coating was developed by phosphite, pentamethyldisiloxane, urea and sodium alginate, and then applied together with calcium chloride to prepare flame-retardant polyester fabrics. The optimized polyester fabrics named PF-HUSC exhibited a rough surface with P, Si, N and Ca element distributions, as observed by scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDX). Flame retardancy evaluations showed that the damaged length of PF-HUSC with a limiting oxygen index (LOI) value of 35.3 ± 0.3 % was reduced from the contrastive 17.6 ± 0.4 cm to 4.6 ± 0.2 cm after vertical burning test. Thermogravimetric (TG) test confirmed that PF-HUSC retained a char residue as high as 35.1 % at 700 °C. Cone calorimetry test displayed that the total heat release (THR) and total smoke production (TSP) values of PF-HUSC were reduced to 3.1 MJ/m2 and 1.1 m2, respectively, as compared to those of pure polyester fabrics. More importantly, PF-HUSC still exhibited higher LOI value than that of pure polyester fabrics after 25 washing cycles. Hence, the coating scheme is considered as a new method to expand the preparation of flame-retardant polyester fabrics.

Eco-friendly phosphorus-free flame-retardant coating for microfiber synthetic leather via alginate-based layer-by-layer technology

The excellent comprehensive properties of microfiber synthetic leathers have led to their wide application in various aspects of our lives. However, the issue of flammability remains a significant challenge that needs to be addressed. Nowadays, the bio-based chemicals used in the flame-retardant materials have extremely grabbed our eyes. Herein, we developed an ecologically friendly flame-retardant microfiber synthetic leather using phosphorus-free layer-by-layer assembly technology (LBL) based on natural polysaccharide alginate (SA) coupled with polyethyleneimine (PEI) and 3-aminopropyltriethoxysilane (APTES). The effect of different LBL coating systems on the flame retardancy of microfiber synthetic leather was investigated. The results demonstrated that the introduction of APTES can completely inhibit the melt-dripping by enhancing char formation through silica elements. Furthermore, the trinary coating system consisting of SA/APTES/PEI exhibited excellent flame retardancy by combining gas-phase action from PEI and condensed-phase function from APTES. This modified microfiber synthetic leather showed a significantly higher limiting oxygen index (LOI) value of 33.0 % with no molten droplet. Additionally, the SA-based coating slightly suppressed the heat release, resulting in a 20 % reduction in total heat release during the combustion test. Overall, this work presents a facile and environmentally-friendly approach for achieving flame-retardant and anti-dripping microfiber synthetic leather.

Nanoclay-reinforced alginate aerogels: preparation and properties

Flame-retardant materials that are mechanically robust, low cost and non-toxic from green and renewable resources are highly demanded in many fields. In this work, aerogels of alginate extracted from seaweeds were fabricated and reinforced with nanoclay. The nanoclay particles increase the molecular ordering (crystallinity) of the aerogels through physical interactions with alginate molecules. They also served as cross-linkers and flame-retardant additives to improve the mechanical strength, elasticity, thermal stability and flame-retarding properties of the aerogels. Under exposure to a butane flame (750 °C), the aerogels maintained their structural integrity and did not produce drips. An optimal loading of nanoclay which led to the best flame retardancy (non-flammable) of the aerogel was determined. The results of this work demonstrate that alginate-nanoclay composite aerogels can be promisingly used as flame-retardant thermal insulation materials.

Guar-based aerogels with oriented lamellar structure and lightweight properties for flame-retardant and thermal insulation

In this study, a multi-functional guar gum aerogel with the oriented lamellar structure, which introduced sodium silicate (Na2O·nSiO2) and phytic acid (PA) as thermal insulation additives and flame-retardant agents, respectively, was fabricated via freeze drying. Our aerogel's chemical structure, morphology, and thermal and mechanical properties were analyzed. The oriented lamellar structure was attributed to the orientated growth of ice crystals, which was induced by the "silicate-guar, guar-phytate, and phytate-silicate" multiple hydrogen bonds formed between Na2O·nSiO2, PA, and guar gum. The density of the sample with 2 wt% PA could reach 0.0335 g·cm-3, and the porosity was 5 %, along with a specific pore volume of 0.8144 cm3·g-1. The mechanical properties and thermal insulation performed significant differences in the radial and axial direction of the oriented lamella (nearly 100 % resilience while 50 % deformation quantity and 0.0235 W/(m*K) of thermal conductivity in the radial direction, up to 0.079 MPa of compressive strength in the axial direction). The presence of PA attached a good flame-retardant ability to our aerogel (The Limiting Oxygen Index (LOI) was 30.77 %). This work provides a novel and promising method for developing anisotropic aerogel with excellent potential in building energy efficiency and flame-retardant.

Enhanced safety and strength of cotton fabrics through a novel 'H-shaped' multiple flame retardant elements agent

In response to the new concept of green sustainability, it is necessary to expand the functionality of bio-based natural fibers (such as cotton fabrics) to replace fabrics made from fossil fuels. One potential way of achieving this is through the use of phosphorus, boron and nitrogen based organic flame retardants. This article designs a special flame retardant system with high efficiency, high durability, and enhanced fabric strength. An "H" shaped flame retardant (TBSA) is synthesized using hydroxyethyl methylene phosphate, pentaerythritol diborate, and cyanuric chloride. After simple treatment, flame retardant fabric (TBSA/Cotton) is obtained, with a LOI value of 48.8 %. Self extinguishing is completing in the vertical flame test. The high FR efficiency reflects the progressiveness of multi flame retardant elements. It is worth noting that TBSA/Cotton exhibits excellent durability and improves the strength of the fabric. This is attributed to the covalent bonding between the "H" type flame retardant and multiple cellulose molecules, which compensates for the cracks and holes at the submicroscopic scale of natural cellulose and weakens the molecular slip effect. The research results of this article provide a good opportunity for the development of biomass cellulose flame retardant materials.

3D Printed All-Natural Hydrogels: Flame-Retardant Materials Toward Attaining Green Sustainability

Biomass-based hydrogel is a promising flame-retardant material and has a high potential for applications in transportation, aerospace, building and electrical engineering, and electronics. However, rapid vat photopolymerization (VP) 3D printing of biomass-based hydrogels, especially that of all-natural ones, is still rare. Herein, a new class of VP 3D-printed hydrogels with strong covalent networks, fabricating using fully biomass materials and a commercial liquid crystal display (LCD) printer assembled with low-intensity visible light is presented. Encouragingly, the highly ordered layer-by-layer packing structures provided by VP 3D printing technology endow these hydrogels with remarkable flame retardancy, exceptional temperature resistance, advantageous combustion behaviors, and favorable mechanical strength, in particular, giving them a better limit oxygen index (83.5%) than various biomass-based hydrogels. The proposed approach enables the green design as well as the precise and efficient preparation for flame-retardant materials, paving the way for the future flame-retardant materials toward attaining green sustainability.

PVA/sodium alginate multi-network aerogel fibers, incorporated with PEG and ZnO, exhibit enhanced temperature regulation, antibacterial, thermal conductivity, and thermal stability

This paper presents a novel approach for the fabrication of polyvinyl alcohol (PVA)/sodium alginate (SA) aerogel fibers with a multilayered network structure using wet spinning and freeze-thaw cycling techniques. The multiple cross-linking networks regulate the pore structure, leading to the formation of stable and tunable multilevel pore architectures. PEG and nano-ZnO were successfully loaded onto the PVA/SA modified aerogel fibers (MAFs) using vacuum impregnation. MAFs exhibited excellent thermal stability at 70 °C without leakage after 24 h of heating. Furthermore, MAFs demonstrated excellent temperature regulation performance, with a latent heat of 121.4 J/g, which accounts for approximately 83 % of PEG. After modification, the thermal conductivity of MAFs was significantly improved, and they exhibited excellent antibacterial properties. Therefore, MAFs are expected to be widely used in intelligent temperature-regulating textiles.

Highly flame-retardant materials of different divalent metal ions alginate/silver phosphate: Synthesis, characterizations, and synergistic phosphorus-polymetallic effects

Three kinds of divalent metal ions (Ca2+, Cu2+, Zn2+) alginate/silver phosphate (MAlg/Ag3PO4) hybrid materials were prepared via an in-situ method, and the composites were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Fourier transform infrared spectrum (FTIR). To investigate their flame-retardant properties and phosphorus-polymetallic flame-retardant effects, the combustion behavior and flammability of the composites were assessed by using the thermogravimetric analysis (TGA), limiting oxygen index (LOI) and micro-calorimeter tests (MCC). The results show that the three composites were thermally stable, among which the LOI of CaAlg/Ag3PO4, CuAlg/Ag3PO4 and ZnAlg/Ag3PO4 were 62.6 %, 46.5 % and 79.8 %, respectively, which were much higher than the prescribed flame retardants which was 27 %. According to the TGA, the thermal stability was ZnAlg/Ag3PO4 > CaAlg/Ag3PO4 > CuAlg/Ag3PO4. The heat release capacity (HRC) of the above three materials was 49 J/(g·K), 69 J/(g·K), 41 J/(g·K), respectively, and the fire safety performance was also in the same order as the thermal stability. By using the thermogravimetric analysis coupled with Fourier transform infrared analysis (TG-FTIR) and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS), the flame retarding mechanism of MAlg/Ag3PO4 and the synergistic effect of Ag3PO4 and divalent metal ions were proposed based on the experimental data.

Mussel- and nacre-inspired dual-bionic alginate-based hydrogel coating with multi-matrix applicability, high separation stability and antifouling performance for oil/water separation

Natural hydrogel-modified porous matrices with superwetting interfaces are ideal for oil/water separation. In this study, inspired by two marine organisms, a novel hydrogel coating with multi-matrix suitability, high oil/water separation capability and antifouling properties was developed. Specifically, inspired by mussel byssus, hydrogel coating was successfully deposited on porous matrix surface based on the introduction of tannic acid (TA). Moreover, inspired by the "brick and mortar" microstructure of Pinctada nacre, silica particles were in-situ synthesized in the sodium alginate (SA)/Ca2+ hydrogel to provide the filling effect and to increase strength. Furthermore, Sodium alginate-tannic acid-tetraethyl orthosilicate (SA-TA-TEOS) hydrogel coating-modified membrane exhibited super-hydrophilic and underwater super-oleophobic performance (underwater oil contact angle >150°), and achieved efficient oil/water separation for four oil/water emulsions (flux = 493-584 L·m-2·h-1 and rejection = 97.3-99.5 %). The modified membrane also demonstrated good anti-fouling performance and flux recovery. Notably, hydrogel coating-modified non-woven fabric also had high oil/water separation capacity (rejection >98 %) and cyclic stability, which proved the universal applicability of this hydrogel coating. In short, this work provides new insights into the fabrication of hydrogel coating-modified porous materials based upon a marine organism biomimetic strategy, which has potential applications in separating oil/water emulsions in industrial scenarios.

Fabrication of photoluminescent electrically conductive and flame-retardant cellulose fabric incorporating polyaniline/strontium aluminate nanocomposite for a plethora of useful applications

The pad dry cure method was used to coat linen fibers with a smart nanocomposite that has photoluminescence, electrical conductivity, flame resistance, and hydrophobic properties. Environmentally benign silicone rubber (RTV) was utilized to encapsulate nanoparticles of rare-earth activated strontium aluminate nanoparticles (RESAN; 10-18 nm), polyaniline (PANi) and ammonium polyphosphate (APP) into linen surface. The flame resistance of the treated linen fabrics was evaluated for their self-extinguishing capabilities. The flame-retardant qualities of linen were retained for 24 washings. Additionally, the superhydrophobicity of the treated linen has marked improved upon increasing the concentration of RESAN. The colorless luminous film deposited onto linen surface was excited at 365 nm and emitted a wavelength of 518 nm. In accordance with the results of CIE (Commission internationale de l'éclairage) Lab and luminescence analysis, the photoluminescent linen gave rise to diverse colors, including off-white in daylight, green beneath UV radiation and greenish-yellow in a darkened room. The treated linen displayed sustained phosphorescence, as evidenced by decay time spectroscopy. The bending length and air permeability of linen were evaluated for their mechanical and comfort assessment. Finally, the coated linens exhibited remarkable antibacterial activity along with strong UV protection.

Development of a New Clay-Based Aerogel Composite from Ball Clay from Piauí, Brazil and Polysaccharides

The incorporation of polymeric components into aerogels based on clay produces a significant improvement in the physical and thermal properties of the aerogels. In this study, clay-based aerogels were produced from a ball clay by incorporation of angico gum and sodium alginate using a simple, ecologically acceptable mixing method and freeze-drying. The compression test showed a low density of spongy material. In addition, both the compressive strength and the Young's modulus of elasticity of the aerogels showed a progression associated to the decrease in pH. The microstructural characteristics of the aerogels were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The chemical structure was studied by infrared spectroscopy with Fourier transform (FTIR). The TGA curves from a non-oxidizing atmosphere indicated that the clay had a mass loss of 9% above 500 °C and that due to the presence of polysaccharides, the aerogels presented a decomposition of 20% at temperatures above 260 °C. The DSC curves of the aerogels demonstrated a displacement in higher temperatures. In conclusion, the results showed that aerogels of ball clay with the incorporation of polysaccharides, which are still minimally studied, have potential application as thermal insulation considering the mechanical and thermal results obtained.

Facile construction of agar-based fire-resistant aerogels: A synergistic strategy via in situ generations of magnesium hydroxide and cross-linked Ca-alginate

Biomass-based aerogel materials have many advantages, such as low thermal conductivity and non-toxicity. These materials are environmentally friendly and have broad development potential in the fields of packaging, cushioning and green building insulation. However, defects, such as low mechanical strength and poor fire safety, greatly limit the application of these materials. In this work, the agar/polyvinyl alcohol composite aerogel modified by the magnesium hydroxide (MH)/sodium alginate (SA) composite flame retardant system was developed by using a freeze-dried technology and the strategy of in-situ generation of MH and crosslinking of SA. The results showed that the MH/SA dramatically enhanced the mechanical and thermal stability of the composites. The compression modulus of AP-M35S15 was 2.37 MPa, which was 152.13 % higher than that of AP-M50. The limiting oxygen index value of AP-M35S15 was 34.1 % and reached V-0 level in the vertical burning test, which was better than those of the samples with a single MH effect. The cone calorimetric test showed that the MH/SA composite flame retardant system performed better in extending the ignition time, slowing down the heat release rate and reducing the total heat release and had a more complete dense carbon structure after burning.

A biomimetic structured bio-based flame retardant coating on flexible polyurethane foam with low smoke release and antibacterial ability

Flexible polyurethane foam (FPUF) is widely used in our life, but it is inherent flammable. The demand for environmental-friendly multi-functional FPUF has been increasing rapidly in the last decade. In this work, a novel bio-based flame retardant coating was constructed by chemically reacting sodium alginate (OSA) and polydopamine (PDA) on the FPUF, followed by depositing nanorod-like β-FeOOH molecules through complexation reaction to form a biomimetic structure. The limiting oxygen index of the coated FPUF samples reached 25.5%. The peak heat release rate was reduced by 45.0%, and the smoke density of the coated sample was decreased by 69.1% compared to that of the control FPUF sample. It was proposed that the OSA-PDA-β-FeOOH decomposed during combustion to promote the formation of compact crosslinked char and released inert gases to dilute the combustible gases, and the β-FeOOH transferred to Fe₂O₃ to settled the smoke particles reducing the smoke release. Furthermore, the coating with shark skin like structure endowed FPUF antibacterial ability because of its good superoleophobicity underwater. This work provided a novel strategy to construct a biomimetic multifunctional coating on the FPUF.

Amphiphilic sodium alginate-polylysine hydrogel with high antibacterial efficiency in a wide pH range

Bacterial infection is a major pathological factor leading to persistent wounds. With the aging of population, wound infection has gradually become a global health-issue. The wound site environment is complicated, and the pH changes dynamically during healing. Therefore, there is an urgent need for new antibacterial materials that can adapt to a wide pH range. To achieve this goal, we developed a thymol-oligomeric tannic acid/amphiphilic sodium alginate-polylysine hydrogel film, which exhibited excellent antibacterial efficacy in the pH range from 4 to 9, achieving the highest achievable 99.993 % (4.2 log units) and 99.62 % (2.4 log units) against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, respectively. The hydrogel films exhibited excellent cytocompatibility, suggesting that the materials are promising as a novel wound healing material without the concern of biosafety.

Growth of copper organophosphate nanosheets on graphene oxide to improve fire safety and mechanical strength of epoxy resins

With the high integration of electronic products in our daily life, high-performance epoxy resins (EP) with excellent flame retardancy, smoke suppression, and mechanical strength are highly desired for applications. In this study, copper organophosphate nanosheets were evenly grown on the surface of graphene oxide (GO) via a self-assembly process based on coordination bonding and electrostatic interactions. The resultant nanohybrid endowed EP with satisfactory flame retardant effect and improved mechanical properties. Incorporating functionalized nanosheets of merely 1 wt% loading, the impact strength of the EP nanocomposites improved by 147% when compared to 1% EP-GO. Additionally, the nanosheets inhibited the smoke and heat release of EP, and the limiting oxygen value of EP-EGOPC reached ∼29%. The mechanism analysis verified that the existence of organophosphate and copper-containing components associated with the physical barrier of GO promoted the hybrid aromatization of the char layer, thereby improving the fire safety of epoxy matrix. This research offers a new interfacial method for designing functional nanosheets with good interface compatibility and high flame-retardant efficiency in polymers.

Alginate Fiber-Grafted Polyetheramine-Driven High Ion-Conductive and Flame-Retardant Separator and Solid Polymer Electrolyte for Lithium Metal Batteries

Traditional polymer-based separators and solid polymer electrolytes (SPEs) often suffer from inherent poor flame retardancy and unsatisfied ionic conductivity, which seriously affect the safety and energy storage performance of lithium metal batteries (LMBs). Inspired by the mechanism of Li⁺ conductivity, an alginate fiber (AF)-grafted polyetheramine (AF-PEA) separator with efficient Li⁺ transport and excellent flame retardancy is dedicatedly designed, which also can act as the backbone for PEO-based SPEs (PEO@AF-PEA). Based on the intrinsic flame retardancy of the AF, the AF-PEA shows self-extinguishing ability, and its Li⁺ transport ability (1.8 mS cm^-1 at 25 °C) is enhanced by grafting the ion-conductive PEA chain segment. By simulating the transport and distribution of Li⁺ in the AF-PEA, the PEA with 7-segment chain lengths can uniformly fill the Li⁺ transport space between the alginate backbone to promote the Li⁺ adsorption and the utilization of Li⁺ anchoring points in PEA side chains, increasing the Li⁺ transport rate and migration capacity. The LiFePO₄/Li solid-state battery assembled using PEO@AF-PEA SPEs exhibits high safety and excellent cycling performance (exceeding 100 mAh g^-1 after 1500 cycles at 2 C current density and 80 °C with less than 0.016% capacity decay for each cycle).

In Situ Generating CaCO3 Nanoparticles Reinforced Nonflammable Calcium Alginate Biocomposite Fiber

Petroleum-based synthetic flame-proof fiber releases toxic volatile organic compounds in thermal decomposition process and has other problems, like tickling feeling and high density. A natural polysaccharide, calcium alginate, is an intrinsic fire-resistant biodegradable material, but its limited mechanical performance prevents it from being a practical flame-retardant fabric. To address this problem, Na₂CO₃ was doped into alginate spinning solution to obtain in situ generating CaCO₃ nanoparticle-reinforced alginate fiber by microfluidic spinning technique. Comparative analysis illustrated that incorporation of 0.50% Na₂CO₃ into the fiber greatly improved its mechanical performance; meanwhile, in situ generated CaCO₃ nanoparticles also throttled oxygen and heat flow in burning, endowing the fiber with excellent flame retardancy. The prepared composite fiber released less heat, smoke, and toxic volatile organic compounds in burning, which reduced the fire hazard. The formed residue char and pyrolysis products functioned as the physical barrier and displayed a synergistic effect to inhibit oxygen and heat transmission and impede the further combustion. All of the results demonstrate that the obtained fiber exhibits a good mechanical and flame-retardant performance, making it an ideal candidate as a fire-protection textile.

Fabrication, Property and Application of Calcium Alginate Fiber: A Review

As a natural linear polysaccharide, alginate can be gelled into calcium alginate fiber and exploited for functional material applications. Owing to its high hygroscopicity, biocompatibility, nontoxicity and non-flammability, calcium alginate fiber has found a variety of potential applications. This article gives a comprehensive overview of research on calcium alginate fiber, starting from the fabrication technique of wet spinning and microfluidic spinning, followed by a detailed description of the moisture absorption ability, biocompatibility and intrinsic fire-resistant performance of calcium alginate fiber, and briefly introduces its corresponding applications in biomaterials, fire-retardant and other advanced materials that have been extensively studied over the past decade. This review assists in better design and preparation of the alginate bio-based fiber and puts forward new perspectives for further study on alginate fiber, which can benefit the future development of the booming eco-friendly marine biomass polysaccharide fiber.

Development of functional glow-in-the-dark photoluminescence linen fabrics with ultraviolet sensing and shielding

Linen fibres were coated with a glow-in-the-dark photoluminescence, flame-retarding, and hydrophobic smart nanocomposite using the pad-dry-curing process. Ecologically friendly ammonium polyphosphate and lanthanide-activated strontium aluminium oxide (LSAO) nanoparticles were immobilized into linen fabric using eco-friendly room-temperature-vulcanizing silicone rubber. Different analytical techniques were used to examine the morphological characteristics and elemental compositions of LSAO nanoparticles and treated linen textiles. The self-extinguishing properties of the treated linen textiles were tested for their fire resistance. After 24 washing cycles, the coated linen samples retained their flame-retarding properties. The treated linen's superhydrophobicity rose in direct proportion to the LSAO concentration. After being excited at 365 nm, the colourless luminescent film that was coated on linen surface gave out an emission wavelength of 519 nm. The photoluminescent linen was monitored to create a range of different colours, including off-white in daytime light and green under ultraviolet (UV) light radiation, according to the Commission Internationale de l'éclairage laboratory colorimetric coordinates and photoluminescence spectra. Emission, excitation, and lifetime spectral analysis of the treated linen revealed persistent phosphorescence. For mechanical and comfort evaluation, the coated linen textiles' bending length and air permeability were assessed. Good UV light shielding and enhanced antibacterial activity were detected in the treated linens.

An Ultralight Self-Powered Fire Alarm e-Textile Based on Conductive Aerogel Fiber with Repeatable Temperature Monitoring Performance Used in Firefighting Clothing

Firefighting protective clothing is an essential equipment that can protect firefighters from burn injuries during the firefighting process. However, it is still a challenge to detect the damage of firefighting protective clothing at an early stage when firefighters are exposed to excessively high temperature in fire cases. Herein, an ultralight self-powered fire alarm electronic textile (SFA e-textile) based on conductive aerogel fiber that comprises calcium alginate (CA), Fe₃O₄ nanoparticles (Fe₃O₄ NPs), and silver nanowires (Ag NWs) was developed, which achieved ultrasensitive temperature monitoring and energy harvesting in firefighting clothing. The resulting SFA e-textile was integrated into firefighting protective clothing to realize wide-range temperature sensing at 100-400 °C and repeatable fire warning capability, which could timely transmit an alarm signal to the wearer before the firefighting protective clothing malfunctioned in extreme fire environments. In addition, a self-powered fire self-rescue location system was further established based on the SFA e-textile that can help rescuers search and rescue trapped firefighters in fire cases. The power in the self-powered fire location system was offered by an SFA e-textile-based triboelectric nanogenerator (TENG). This work provided a useful design strategy for the preparation of ultralight wearable temperature-monitoring SFA e-textile used in firefighting protective clothing.

Poly (vinyl alcohol)-alginate as potential matrix for various applications: A focused review

Advances in polymers have made significant contribution in diverse application oriented fields. Multidisciplinary applicability of polymers generates a range of strategies, which is pertinent in a wide range of fields. Blends of natural and synthetic polymers have spawned a different class of materials with synergistic effects. Specifically, poly (vinyl alcohol) (PVA) and alginate (AG) blends (PVAG) have demonstrated some promising results in almost every segment, ranging from biomedical to industrial sector. Combination of PVAG with other materials, immobilization with specific moieties and physical and chemical crosslinking could result in amendments in the structure and properties of the PVAG matrices. Here, we provide an overview of the recent developments in designing PVAG based matrix and complexes with their structural and functional properties. The article also provides a comprehensive outline on the applicability of PVAG matrix in wastewater treatment, biomedical, photocatalysis, food packaging, and fuel cells and sheds light on the challenges that need to be addressed. Finally, the review elaborates the future prospective of PVAG matrices in other unexplored fields like aircraft industry, nuclear science and space exploration.

Preparation of High-Efficiency Flame-Retardant and Superhydrophobic Cotton Fabric by a Multi-Step Dipping

Cotton fabric, as an important material, is suffering from some defects such as flammability, easy pollution and so on; therefore, it is important to make a flame-retardant and superhydrophobic modification on cotton fabric. In this study, we demonstrated a preparation of high-efficiency flame-retardant and superhydrophobic cotton fabric with double coated construction by a simple multi-step dipping. First, the fabric was immersed in branched poly(ethylenimine) (BPEI) and ammonium polyphosphate (APP) water dispersions successively, and then immersed in polydimethylsiloxane (PDMS)/cellulose nanocrystals (CNC)-SiO2 toluene dispersion to form a BPEI/APP/PDMS/CNC-SiO2 (BAPC) composite coating on the surface of the cotton fabric. Here, the hydrophobic modified CNC-SiO2 rods were used to construct the superhydrophobic layer and the BPEI/APP mixture was used as the flame-retardant layer, as well as SiO2 particles which could further improve the flame-retardant effect. PDMS was mainly used as an adhesive between the BPEI/APP layer and the CNC-SiO2 layer. The resulting cotton fabric shows outstanding flame-retardant properties, in that the value of oxygen index meter (LOI) reaches 69.8, as well as excellent superhydrophobicity, in that the water contact angle (WCA) is up to 156.6°. Meanwhile, there is a good abrasion resistance, the superhydrophobicity is not lost until the 16th abrasion cycles and the flame retardant retains well, even after 100 abrasion cycles in an automatic vertical flammability cabinet under a pressure of 8.8 kPa.

Ecofriendly flame-retardant composite aerogel derived from polysaccharide: Preparation, flammability, thermal kinetics, and mechanism

Bio-based aerogel (polysaccharide cryogel) have led to a growing interest because of eco-friendliness, sustainability and excellent thermal insulation properties. Herein, we report an eco-friendly strategy to construct lightweight and porous sodium alginate/carboxymethyl cellulose/chitosan polysaccharide-based composite aerogels (SCC-B) by freeze-drying and post-cross-linking technology. The ester cross-linking of polysaccharide component achieved strong web-like entangled structure when using 1,2,3,4-butanetetracarboxylic acid and sodium hypophosphite as eco-friendly co-additives, meanwhile significantly improved flame retardancy of SCC-B due to phosphorylation. The thermal kinetic behavior of SCC-B was investigated by Flynn-Wall-Ozawa and Kissinger models. Results indicated that peak heat release rate and total heat release of SCC-B decreased from 30 W/g to 20 W/g and 15 kJ/g to 10 kJ/g, respectively. Furthermore, the second-degree burn time of SCC-B reached up to 87.1 s under heat exposure of 11.3 kW/m². These characteristics combine to suggest hopeful prospects for use of SCC-B in the fields of fire-protection clothing as a renewable flame-retardant material.