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An overview of alginates as flame-retardant materials: Pyrolysis behaviors, flame retardancy, and applications
Abstract
Alginates, a kind of naturally occurring polysaccharides, have been exploited for functional materials owing to their versatility, sustainability, nontoxicity, and relatively low cost. Inherent flame retardancy is one of the most attractive features of alginates, as it enables the high-value-added utilization of alginates for eco-friendly flame-retardant materials. Now, the influence of metal ions on the flame retardancy and pyrolysis behaviors of alginates has been systematically studied; besides, the applications of alginates for flame-retardant materials have been greatly developed, such as for preparing flame-retardant fibers, fabrics, aerogel composites, and foams, as well as serving as a component or modifier of functional coatings, hybrids, and additives. This review will give an overview of the recent progress and the prospects of using alginates in flame-retardant fields, which can guide the design of bio-based flame retardants and benefit the further development of more diverse applications of alginates.
... In the field of textiles, the microencapsulation technology could be used for aromatic, flame retardant, UV resistance, and other functions arrangement of textiles Massella et al. 2019;Shahid ul and Butola 2019;Xu et al. 2021). Nowadays, the aromatic microcapsules with slow-releasing properties have been gradually applied to various textiles such as clothing, bedding, silk stockings, scarves, and so on (Ma et al. 2023;Nelson 2002;Valle et al. 2021;Wei et al. 2014;Xiao et al. 2021). ...
The growing interest in green synthesis and multifunctional application of microcapsules is due to their eco-friendly nature, health benefits, safety advantages, controlled release capabilities, and enhanced protection and stability. In this study, chitosan microcapsules were synthesized using a green double emulsion-simple coacervation method. The shell and core materials are derived from plants and are environmentally friendly, while the preparation process does not require volatile organic solvents. Both water-soluble vitamin C (VC) and oil-soluble lemon essential oil (LEO) were loaded as active substances in the chitosan microcapsules. The prepared microcapsules are about 3 μm in size and exhibit good thermal stability. Further modified microcapsules with UV crosslinked monomers could be coated on the fabric to form a functional fabric coating as well as UV crossing linkers. The obtained functional fabric based on chitosan microcapsules has the slow-release property of VC and LEO. The sustained-release VC exhibits a skincare effect and is beneficial to human health. Furthermore, this coated fabric has durable antibacterial properties due to the synergistic effect of LEO and chitosan. This method offers a sustainable solution for creating innovative microcapsules with diverse applications such as medical textiles, home textiles, cosmetics, and more.
Graphical abstract
... On the one hand, the presence of transition metals in ATH@SA@Fe 3+ could efficiently catalyze the charring process of asphalt binder undergoing dehydrogenation, cyclization and the polyaromatic reaction of the pyrolysis products to high-quality stable char residue. On the other hand, the presence of sodium alginate in ATH@SA@Fe 3+ enabled the carbonization process of decarboxylation, breaking and esterification of the glyosidic bond at lower temperatures [16], which providing a protective shield to leads the decrease in heat and mass transfers between the fire and the asphalt binder material. ...
... They migrated onto the outer surface of chars during combustion; then, their aggregations could improve the mechanical strength and supporting ability of char layer. More importantly, the compact char layer could bring about better barrier effect on the isolation of heat and oxygen, delaying the diffusion of flammable gases, then inhibiting the flame propagation and the fire intensity [43]. As a result, a substantial improvement on flame retardancy with 30.1% on LOI, V0 in UL-94, and 79.6% reduction on PHRR were achieved in PBS composites. ...
Biodegradable poly(butylene succinate) (PBS) is considered as promising material to replace conventional nondegradable polymers in various engineering fields, but the applications are limited by its inherent flammability and low electrical conductivity. In this study, the synergistic effect of carbon nanotube (CNTs) on improving thermal stability, flame retardancy, and electrical conductivity of poly(butylene succinate)/piperazine pyrophosphate (PBS/PAPP) composites was investigated. Thermogravimetric analysis (TGA) demonstrated that the addition of CNTs could improve the thermal stability of PBS/PAPP composites, where the maximum mass loss temperature (Tmax) of PBS/18PAPP-2CNT increased by 9.1 °C in comparison with that of PBS/20PAPP. Meanwhile, PBS/18PAPP-2CNT exhibited the optimal flame retardancy with limited oxygen index (LOI) of 30.1%, V0 rating in UL-94 vertical burning test, and 79.6% reduction on the peak of heat release rate (PHRR) in cone calorimeter test. The synergistic effect of CNTs and PAPP was beneficial to construct high-quality char layer, resulting in the enhanced flame retardancy of PBS. Furthermore, the CNTs could improve the electrical conductivity of PBS/PAPP composites with low percolation threshold of 1.75 wt%, which was ascribed to the “volume excluded effect” of PAPP. Thus, the current work provided an efficient strategy to prepare multifunctional PBS composites to meet various engineering applications.
... The combustion of a polymer is a multistage process, including complex chemical and physical interactions [14]. The supply of heat, fuel, and oxygen are the three necessary factors required to maintain the combustion cycle [15]. Generally, the combustion process of a polymer is divided into four stages: heat, pyrolysis, ignition, and combustion [16]. ...
Due to the enhancement of people’s environmental awareness, flame-retardant epoxy resin (EP) tends to be non-toxic, efficient, and multi-functional, and its development is systematic. At present, many new flame retardants or intrinsic modification methods reported in studies can effectively improve the flame retardability and thermal stability of EP. However, many aspects still need to be further improved. In this review, the flame-retardant mechanism and method of flame-retardant epoxy resins are briefly analyzed. The research progress of the flame-retardant modification of epoxy resin by physical addition and chemical reaction is summarized and discussed. Furthermore, the research trend of flame-retardant epoxy resin in the field of fire-protective coatings is discussed, and future problems in this field are put forward. This work may provide some new insights for the design of multi-functional integrated epoxy resin fireproof coatings.
... These materials have magnetic properties due to the nano ferric oxide nanoparticles (NFO), which possess fantastic properties like excellent adsorption capacity, reactivity, mechanical properties, biocompatibility, and chemical and thermal stability [9][10][11][12][13][14][15]. The NFO has novel properties such as small size, large surface area, magnetic properties, and functionality, allowing them to be successfully applied in pollutant decontaminating [16][17][18][19][20]. Alginates, derived from naturally occurring polysaccharide substances [21], have become popular as functional materials due to their flexibility, cost-effectiveness, nontoxicity and sustainability [22]. Additionally, they exhibit excellent biocompatibility and are able to undergo mild gelation through interactions with metal ions [23]. ...
A mixture of tea waste (TW), alginate (ALG), and nano iron (Fe) was used to prepare environment-friendly smart beads of composites to decontaminate the water from petroleum oil spillage. ALG and TW represented the hydrophilic pattern incorporation, while the addition of iron nanoparticles resulted in the nanocomposites (ALG/TW/Fe and ALG/Magnetite (Fe3O4)) developing magnetic properties. These properties enable the nanocomposites to be suspended at the interface between oil and water, thus enhancing the efficiency of the smart beads, including their derivatives ALG/TW and ALG/Fe, to decontaminate the water from petroleum oil spillage effectively. The prepared nanocomposite characterisations were carried out thermally by Thermogravimetric analysis (TGA), and their crystallinity was analysed through x-ray diffraction (XRD). These nanocomposites were examined for water absorption capacity (water uptake %WR), exchange ions (ion exchange capacity IEC), and electrical conductivity. The scanning electron microscope (SEM) was used to assess their morphological structure. The created nanocomposites' shape and size were measured using transmission electron microscope (TEM), which ensured that the iron nanoparticles were close to 21.2 nm in size and ovular in shape. The nanocomposites' porosity was appraised through positron annihilation lifetime spectroscopy (PALS). These beads were successfully used for water/oil decontamination with a yield of 99.8% and an efficiency percentage of 99.65%. The ALG/TW/Fe was regenerated by exposing them to a potential gamma irradiation dose of 10 kGy. Regeneration enabled durability for up to ten cycles but with a 48% decrease in their efficiency.
... char layer can bring about better barrier effect on the isolation of heat and oxygen, delaying the diffusion of flammable gases, then inhibiting the flame propagation and the fire intensity [40]. As a result, a substantial improvement on flame retardancy with 30.1% on LOI, V0 in UL-94 and 79.6% reduction on PHRR were achieved in PBS composites. ...
Biodegradable poly (butylene succinate) (PBS) is considered as promising material for replacing conventional nondegradable polymers in various engineering fields, but its applications are limited by inherent flammability and low electrical conductivity. In this study, the synergistic effect of carbon nanotube (CNTs) on improving thermal stability, flame retardancy and electrical conductivity of poly(butylene succinate)/piperazine pyrophosphate (PBS/PAPP) composites was investigated. Thermogravimetric analysis (TGA) demonstrated that the addition of CNTs could improve the thermal stability of PBS/PAPP composites, where the maximum mass loss temperature ( T max ) of PBS/18PAPP-2CNT increased by 9.1 o C in comparison with that of PBS/20PAPP. Meanwhile, PBS/18PAPP-2CNT exhibited the optimal flame retardancy with limited oxygen index (LOI) of 30.1%, V0 rating in UL-94 vertical burning test and 79.6% reduction on the peak of heat release rate (PHRR) in cone calorimeter test. The synergistic effect of CNTs and PAPP was beneficial to form high-quality char layer, resulting in the enhanced flame retardancy of PBS. Furthermore, the CNTs could improve the electrical conductivity of PBS/PAPP composites with low percolation threshold of 1.75 wt%, which was ascribed to the “volume excluded effect” of PAPP. Thus, the current work provided an efficient strategy to prepare multifunctional PBS composites to meet various engineering applications.
... Plastic is one of the most utilized materials in children's toys and excersise equipment. Plastic materials are not only not as strong as the new types of nanocomposites but also toxic to nature (Xu et al. 2021b). There has been much effort Corresponding author, Ph.D., E-mail: 30-007@gduf.edu.cn ...
Combating the worldwide environmental threat of plastic waste pollution has become a priority. Plastic pollution has the potential to impact land, rivers, and seas, since many marine and terrestrial organisms have perished as a result of plastic's non-biodegradability and soil dangers. For this consumption, it seems required to manufacture and use new renewable resources. Renewable materials for diverse applications have been created utilizing nanotechnology, which may replace conventional materials for children's activities and sports equipment. This study investigates and suggests that nanotechnology-based materials be replaced with conventional materials to save the environment in manufacturing equipment for children's physical activities. On the basis of the mechanical sciences, a stability study of the bending behavior of small-scale structures will be performed for the various recommended materials.
... In addition, the abundant marine resource has received much attention compared with the scarcity of land resources recently. Especially, the degradable calcium alginate (Alg) bio-based ber has become a hotspot due to the excellent intrinsic ame retardant performance, sustainability and environmental friendliness 22 . But the mechanical performance of Alg ber is too poor to process and use by itself 23 . ...
A depleting fossil reserve and the troublesome recycling corresponding waste is worldwide problem. This work upcycled polyester waste fiber with intrinsic nonflammable bio-based alginate fiber via opening-combing-needle punching technique into a fire-proof building material to reduce waste disposal and carbon footprint. The composite was proved to generate minor amount of smoke and heat, and abundant nonflammable CO 2 and H 2 O in the pyrolysis process.With very limited flammable H 2 , CO and C 2 H 4 , those can be completely diluted by the nonflammable gases. Furthermore, the credible flame-retardant mechanism of fuel-dilution effect was proposed, that was the final formed Ca-C residual chars cooperating with larger number of nonflammable gaseous volatile employed as a natural barrier to impede the heat, O 2 and mass transfer, which can dramatically reduce the fire hazard. Taken together, this research recycled the waste chemical fiber into the outstanding fire-proofing composite applied in the construct field by a cost-effective and eco-friendly method.
... More surprisingly, Wnek et al. found that metal ions can change the thermal degradation process of acid source in EP-based intumescent coatings [27]. Xu et al. demonstrated that the metal ion can induces competitive pattern of dehydration and esterification pathways, thus influence the carbonization and gas release processes [28]. That is to say the transition metal manifested great potential on adjusting the match degree of the carbonization and abundant gas release process, thus improved the intumescent behaviors of IFRs. ...
The intumescence, compactness, and strength of char are the key points to the intumescent flame retardant system. However, the char residues of flame retardant polymers rarely exhibit all three characteristics, especially strength. Herein, a novel Cu2+-doped intumescent flame retardant (Cu–CHP) was prepared without producing any waste. When Cu–CHP was exposed at a high temperature (~1400 ◦C), it can rapidly expand and carbonize to form dense char. Surprisingly, the intumescent char residue of Cu–CHP can hold up more than 2000 times its own weight. Benefitting from the excellent intumescent charring capacity of Cu–CHP, the resultant EP/ Cu–CHP18% composite can withstand around 600 s penetrating of butane flame (~1400 ◦C) because of strong dense char protection, and only 0.9 wt% Cu2+ content resulted in the limiting oxygen index (LOI) of EP/ Cu–CHP18% increases to 31% and the vertical burning (UL-94) reaches V-0 rating. Additionally, its peak heat release rate, total smoke production, and fire growth rate are significantly reduced by 70%, 53%, and 75%, respectively, compared with neat epoxy resin. Especially, the smoke density of EP/Cu–CHP18% was dramatically dropped by more than 68%. Because a Cu2+-doped intumescent, compact, and strong char residue was produced during burning. This work provides a new strategy to impart excellent flame retardancy and smoke suppression to highly flammable polymers by building metal-doped strong intumescent char residues.
... According to statistics, about 165,000 people are killed by fire every year. Due to the wide variety of materials, it is impossible to prepare all materials into flame retardant from the technical level and technical point of view [4,5]. Therefore, applying flame retardant and thermal insulation coatings on the surface of materials has become the object of competitive research [6]. ...
In response to high environmental requirements, an incombustible inorganic intumescent flame retardant coating was prepared from amorphous aluminum phosphate emulsion as the matrix, with boron carbide as the modifier. The influence of boron carbide (B4C )on the fire resistance performance and physic-chemical properties of coatings were studied by means of large panel combustion method, smoke density test, Fourier transformed infra-red analysis (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (BET method) and pore size analysis. With the addition of 0.75 wt.% B4C, the backside temperature of APB3 coating (aluminum phosphate-based coating modified with 0.75 wt.% B4C) after an hour was only 140 ℃, 33.4 % lower than that of blank APB0 coating. And the smoke density (Ds) of APB3 was only 64.73 %, 36.3 % lower than that of blank APB0. The foaming expansion caused by decomposition reactions, the structural improvement caused by boron carbide oxidation, and the formation of ablative resistant ceramics and glass were the main reasons for excellent flame retardant and thermal insulation performance. Remarkably, the melting B2O3 generated from the oxidation of B4C could repair cracks, modify pore structure, improve the integrity of closed pores, increase the specific surface area of porous structure, and promote the formation of borosilicate glass. Due to the structural integrity of the outermost coating surface caused by the oxidation of B4C and the construction of borosilicate glass, much gas was shielded inside the coating, making the coating more eco-friendly. Besides, APB3 coating has good water resistance. After immersion in water for 360 h, the reduction rate of fire resistance performance of the coating was only 17.1 %. This work provides theoretical guidance for broadening the types of intumescent coatings and promotes the development of inorganic green coatings.
Worldwide, more than 140 million tons of petroleum-based plastics are consumed yearly, with rising global demand exacerbating the environmental problems. Recycling of plastics solely does not provide a comprehensive solution. Recently, many countries have been investing in eco-friendly solutions, focusing on renewable energies and biodegradable polymers. In this chapter, the potential of algae to fulfill societal needs and mitigate the global demands with value-added chemicals is investigated. Several algal species can valorize waste biomass and remediate wastewater to remove nitrogen, phosphorus, and heavy metals, all while providing bio-based and biodegradable polymeric material in the form of biomass. The major benefit of algae-derived biopolymers over other platforms lies in their autotrophic nature, ultimately geared toward negative carbon footprint biorefinery process and contributing to a sustainable circular economy. Still, the “uneconomical” production, largely attributed to cultivation systems and product titers, remains the major roadblock for market entry of algae-derived biopolymers. Overall, this chapter aims to present and critically analyze the current status and production technologies for algal-derived biopolymers, including polyhydroxybutyrate (PHB) and its equivalents. This work also summarizes the recent process development approaches and optimization opportunities of different algae-derived biopolymers.
Packaging materials play the role of isolation and protection in product storage, transportation, sales, and other links. However, wood fiber-based and polymer-based packaging materials used for carrying, packaging, bedding, supporting, and reinforcing goods have the drawback of low ignition point, and flame retardant treatment is required for these materials. Aiming at the flame retardant treatment of wood fiber-based packaging materials and polymer-based packaging materials, the application of biobased flame retardants limits or eliminates the detrimental effects on wellbeing and environments which are usually the result of petroleum-based counterparts. In this paper, combined with the development status of biobased flame retardants in the flame retardant treatment of packaging materials, different biobased flame retardants are classified according to the types of functional groups, like bio-based polysaccharide, amino acid flame retardants, phosphate, and phenolic flame retardants. The modification methods, decomposition process, and flame retardant mechanism of different biobased flame retardants have been analyzed. What’s more, the advantages and problems in the development and application have been summarized, and new ideas are provided to develop biobased flame retardants with better performance and more environment-friendliness.
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.
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.
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.
Cotton and calcium alginate (CA) fibers are both polysaccharide-based fibers, but they possess different flame retardancy. The detailed comparisons on flame retardancy and combustion behavior of polysaccharide fabrics are of interest. In this study, the difference between the fabrics made of these two fibers in the combustion process, pyrolysis products and the morphology and chemical structures of char residues were performed by vertical burning, thermal gravimetric analysis, Fourier Transform Infrared Spectrometer (FTIR) and scanning electron microscopy. Compared with cotton fabric, CA fabric had no after-flame when it was burned vertically, and the smoldering time was longer. Especially, the smoke release rate, peak heat release rate and total heat release were much lower versus cotton fabric, indicating that CA fabric had much lower fire hazards than cotton fabric. The results of thermogravimetric analysis coupled with FTIR (TG-FTIR) suggested that CA fabric exhibited a different thermal degradation pathway versus cotton fabric. Under the same quality, CA fabric produced more char residues after combustion, and chrysanthemum-like calcium oxide were generated on the surface of char residues as protective barrier, leading to the enhanced flame retardancy of CA fabric.
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.
Fireproofing the polyvinyl alcohol (PVA) membrane is an essential and urgent reinforcement to ease the restriction in flame‐resistant requirements. The traditional method by the physical and heterogenous introduction of a large number of metal hydroxides, halogenated and organic compounds efficiently enhance the flame‐retardancy but severely weakens the biocompatibility, mechanical strength, and transparency of PVA membranes. In this work, two bio‐extracted compounds, phytic acid (PA) and creatine (CR) are employed to construct a fireproof, tough and transparent PVA membrane. The LOI of the PVA/PACR membrane increases from 18% to 30% and reaches a V–0 grade in UL‐94 testing. Meanwhile, the mechanical strength receives 20% reinforcement due to a chemical crosslinking between PVA, PA, and CR. Intriguingly, unsaturated chemical bonds from PA and CR endow a favorable UV‐absorbing capacity to the PVA membrane, which will benefit the anti‐aging and food freshness retaining demands in advanced packaging applications.
Looking for innovative, more efficient and cost-effective synthesis methods of flame retardants (FRs) polymers is arousing increasing interest in the research community. The main aim is to develop human and environmentally safe flame retardants using renewable resources. Consequently, hazardous halogen flame retardants are being replaced by phosphorus, nitrogen and polymer/inorganic nanocomposite flame retardants. In view of the growing consumption of plastics as well as natural materials, here is an increasing demand for specific flame retardants and innovative and at the same time environmentally friendly methods of their synthesis. Reversible-deactivation radical polymerization (RDRP) techniques might be a breakthrough tool for the precise synthesis of FRs. Such techniques provide an opportunity to synthesize polymers with complex architectures, defined molecular weight and low dispersity (Ð) both in solution and grafted directly from modified materials. Therefore, this review summarizes the use of RDRP techniques of various monomers over the past 10 years for the synthesis of flame retardant additives as well as for direct surface modification towards reducing flammability.
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.
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 facile design for value‐added recycling of metallurgical solid waste is urgent for developing safe and sustainable human settlements. Therefore, novel DOPO/flake graphite (FG) co‐doped silica fume‐based geopolymer coatings for flame‐retarding plywood were prepared to seek a halogen‐free and low‐carbon Si‐C‐P fireproof method. The results show that appropriate DOPO (1 wt%) constitutes an enhanced flame retardancy, evidenced by the reduced peak of heat release rate (decreases from 153.48 to 96.94 kW m−2) and the rising flame retardancy index (climbs from 1.00 to 2.32). Meanwhile, its pyrolysis is identified as the three‐level chemical reaction model (F3), the hydrogen bond crosslinking between the POC and HOSiO results in a rising Eα at 1000–731°C (increases from 163.60 to 198.83 kJ mol−1). Finally, the synergistically flame‐retardant mechanism consists of water volatilization at 100°C, the as‐formed porous carbonaceous layer at about 200°C, transformations of DOPO at 300–500°C, the formed DOPO derivatives at 500–700°C, and the decomposition of DOPO derivatives (condensed phase barrier) above 700°C, respectively. The yielded residues generate a 56% formaldehyde adsorption rate. It proposes a halogen‐free and low‐carbon strategy for designing Si‐C‐P hybrid flame‐retarding coatings, indicating an ecological direction for the value‐added utilization of metallurgical solid waste.
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).
We adopted a straightforward yet efficient method to improve mechanical property of alginate fiber by doping cellulose nanocrystal and Na2CO3 in the spinning solution to fabricate CaCO3-cellulose nanocrystal reinforced alginate fiber. Comparative analysis demonstrated that this composite fiber containing 0.30% cellulose nanocrystal and 0.40% Na2CO3 achieved a maximum breaking strength of 1.42 ± 0.32 cN/dtex, three times more than the pristine alginate fiber. Doped Na2CO3 triggered in situ generating CaCO3 particle during formation of the fiber and deposited extra NaCl particle, which can endow the composite fiber with remarkable fire resistant performance. Also, the composite fiber released limited heat, smoke and toxic gaseous compounds, assisting to reduce fire hazard. Finally, the flame-retardant mechanism of fuel-dilution cooperating with a physical barrier of residue char was proposed. It has a synergistic effect with nonflammable emissions on the inhibition of inflammable emission, generated heat and incoming oxygen transmission, which impeded further combustion. The prepared composite fiber has robust mechanical performance and excellent fire-proofing ability, making it an ideal candidate as flame resistant household textile.
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.
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.
Inorganic-organic hybrid coatings prepared via an impregnation assembly of eco-friendly materials exhibited dramatically flame-retardant properties on flexible polyurethane foam (FPUF). A nickel-complex of tea polyphenols (TP-Ni) was synthesized, and TP-Ni and laponite (LAP) were coated on the surface of FPUF. LAP/TP-Ni can be homogeneously dispersed on the surface of FPUF. Moreover, the melt-dripping phenomenon of 1LAP/4TP-Ni/FPUF was completely inhibited during the vertical flame test (UL-94) with 41.2 wt% weight gain, and it showed self-extinguished behaviors at once and passed the UL-94 V-0 rating. Additionally, the values of peak heat release rate and peak smoke production rate of 1LAP/4TP-Ni/FPUF were reduced by 71.6% and 60.9%, compared with the control. The content of gaseous toxic substances, such as CO and NCO-containing compounds, was also decreased, indicating the effect of TP-Ni/LAP on the toxicity suppression of flame-retardant FPUF. Encouragingly, the coatings deteriorated the tensile property of FPUF inconspicuously. Interestingly, the coatings do not contain traditional flame retardant elements, which offers an innovative approach for designing flame retardants. Thus, these inorganic-organic hybrid coatings show the promising potential to decrease the fire risk of FPUF.
The design and exploitation of highly fire-safe aerogel with ultrasensitive fire-warning response and highly efficient thermal management capabilities are urgently needed to protect firefighters from burn injuries during fire operations and rescue. Herein, an ultralight temperature-triggered fire-warning aerogel composited of polyethylene glycol (PEG)@modified wood powder (MW)/amino-functionalized carbon nanotube (A-CNT)/calcium alginate (CA) (abbreviated as [email protected]) was fabricated. Benefiting the rapid decrease in electrical resistance of A-CNT at high temperatures, [email protected] achieved an ultrafast fire warning response time of ∼2.03 s when exposed to fire. Meanwhile, PEG was encapsulated into MW and acted as microtubule phase-change material ([email protected]) in aerogel to effectively delay the heat penetration into [email protected] The stiff MW served as the backbone endowed the fire-warning aerogel a “stiff-soft” structure that increased the mechanical resilience. [email protected] achieve flyweight density (0.038 g/cm³), low thermal conductivity (0.06233 ± 0.0012 W/m⋅K), and outstanding self-extinguishment (<1.02 s). This work provides an environmental friendliness approach to design an ultralight early fire-warning aerogel in firefighting clothing for enhancing the fire safety of firefighters.
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.
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.
The most relevant properties of polysaccharide aerogels in practical applications are determined by their microstructures. Hydration has a dominant role in altering the microstructures of these hydrophilic porous materials. In order to understand the hydration induced structural changes of monolithic Ca-alginate aerogel, produced by drying fully crosslinked gels with supercritical CO2, the aerogel was gradually hydrated and characterized at different states of hydration by small angle neutron scattering (SANS), liquid-state nuclear magnetic resonance (NMR) spectroscopy and magic angle spinning (MAS) NMR spectroscopy. First, the incorporation of structural water and the formation of an extensive hydration sphere mobilize the Ca-alginate macromolecules and induce the rearrangement of the dry-state tertiary and quaternary structures. The primary fibrils of the original aerogel backbone form hydrated fibers and fascicles resulting in the significant increase of pore size, the smoothing of the nanostructured surface and the increase of the fractal dimension of the matrix. Due to the formation of these new superstructures in the hydrated backbone, the stiffness and the compressive strength of the aerogel significantly increase compared to its dry-state properties. Further elevation of the water content of the aerogel results in a critical hydration state. The Ca-alginate fibers of the backbone disintegrate into well-hydrated chains, that eventually form a quasi-homogeneous hydrogel-like network. Consequently, the porous structure collapses and the well-defined solid backbone ceases to exist. Even in this hydrogel-like state, the macroscopic integrity of the Ca-alginate monolith is intact. The postulated mechanism accounts for the modification of the macroscopic properties of Ca-alginate aerogel in relation to both humid and aqueous environments.
Increasing demands in minimization of fire risks and meeting fire safety requirements by polymers require advances in knowledge of flame-retardant materials suitable for use in fire-retardancy applications. The present work represents the seminal review of alginate/polymer-based materials as flame retardants. Alginates are suitable for this application as they represent alternatives to petroleum-based polymer feedstocks. The content of the present work is structured into four sections: synthesis and structure, including alginate synthesis and modification by polymeric conjugation; properties, including four-stage mechanism of thermal degradation; applications, including commercial information on alginates and polymers; and flame retardancy, including comprehensive summaries of test methods and published data, discussion of key parameters, eight fire retardancy mechanisms, four char generation mechanisms, and extensive quantitative analysis of polymer char formation. The final section culminates in a first-principles approach to the prediction of quantitative polymer char formation. The goal of the review is to provide guidance for the application of alginates and alginates conjugated with fire-retardant polymers as a new generation flame retardant material.
Blending has been applied to combine the advantages of individual fibers, but the flame retardancy of a blended fiber depends on the interaction of the components. In this work, polyamide (PA) fibers were blended with alginate fibers to obtain a blended non-woven fabric and the flame retardancy of the natural/synthetic blended fabric was highlighted. Inspiringly, the two fibers mixed uniformly by the easy-to-handle blending, and the blend’s components did not affect each other’s thermal decomposition. With the addition of 50 wt% alginate fibers, the blended fabrics achieved self-extinguishing without any melt dripping in the vertical flame test, because the melted PA was limited in the area of the charred alginate fibers in the shape of films and bladders; besides, they showed strong decreases in peak heat release rate (56%), total heat release (59%), and total smoke release (66%) compared with PA fibers in the cone calorimeter test. Alginate fibers exhibited both vapor- and condensed-phase flame-retardant activities in the blended system, which was further confirmed by thermogravimetric analysis and thermogravimetry/infrared spectrometry.
To enhance the fire safety of epoxy resins (EP) without affecting other properties, a novel organophosphorus compound named DDPPM has been synthesized and used as co-curing agent to obtain inherent flame-retardant EP. The Fourier transform infrared spectroscopy (FT-IR), ¹H nuclear magnetic resonance (¹H NMR), and ³¹P nuclear magnetic resonance (³¹P NMR) proven the successful synthesis of DDPPM. The mechanical results demonstrated that the mechanical properties of the epoxy resin did not deteriorate after adding DDPPM, and differential scanning calorimetry (DSC) shown that the glass transition temperature (Tg) of EP/DDPPM was maintained. Importantly, the EP/DDPPM presented satisfying flame-retardant efficiency in limiting oxygen index (LOI) and vertical burning tests. Incorporating 2 wt% DDPPM, the EP achieved the UL 94 V-0 rating and the LOI value was 31%. Meanwhile, the cone calorimeter (CC) test verified that DDPPM contributed to the reduction of heat and smoke release accompanied by increasing char yield. The thermogravimetric analysis/infrared spectrometry (TG-FTIR), pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) and char analysis certified the flame inhibition and charring effect of DDPPM in EP.
Ecofriendly bio-based alginate fibres are one of the inherently flame-retardant fibres. Can the incorporation of alginate fibres to viscose fibres enhance the flame retardancy and decrease the smoke release of prepared viscose/alginate blended nonwoven fabrics? Aiming to resolve this question, in the present work, viscose/alginate blended nonwoven fabrics were prepared in a green way without any pollution. Vertical flame test, cone calorimetry test and microscale combustion calorimetry results indicated that the incorporation of alginate fibres enhanced the flame retardancy and fire behaviors; what is more, the incorporation of alginate fibres seriously prolonged time to ignition. The results mentioned above indicate that alginate fibres can enhance the flame retardancy and inhibit the smoke release of viscose fibres. The incorporation of alginate fibres altered the thermal stability of viscose fibres and decreased the flammable gas emissions, thus improving the flame retardancy of viscose/alginate blended nonwoven fabrics. A conclusion can be made that inherently bio-based alginate fibres can be used as a kind of flame retardant to flame-retard viscose fibres.
Graphic abstract
The incorporation of alginate fibres improves the flame retardancy and suppresses the release of smoke for viscose/alginate blended nonwoven fabrics.
Biological molecules can be obtained from natural sources or from commercial waste streams and can serve as effective feedstocks for a wide range of polymer products. From foams to epoxies and composites to bulk plastics, biomolecules show processability, thermal stability, and mechanical adaptations to fulfill current material requirements. This paper summarizes the known bio-sourced (or bio-derived), environmentally safe, thermo-oxidative, and flame retardant (BEST-FR) additives from animal tissues, plant fibers, food waste, and other natural resources. The flammability, flame retardance, and—where available—effects on polymer matrix’s mechanical properties of these materials will be presented. Their method of incorporation into the matrix, and the matrices for which the BEST-FR should be applicable will also be made known if reported. Lastly, a review on terminology and testing methodology is provided with comments on future developments in the field.
The protective clothing of firefighters requires specialised fire-resistant materials to ensure their safety. In this work, a novel fire-resistant material was prepared by laminating an interpenetrating polymer network (IPN) hydrogel on cotton fabric. The hydrogel-fabric laminates can be used as a flame-retardant material to produce firefighter protective clothing. The IPN hydrogel layer comprised poly (N-isopropylacrylamide) (PNIPAAm), sodium alginate (SA) and silver nanoparticles (Ag NPs). The chemical structures, swelling ratio, thermal properties, microstructures and tensile properties of the synthesised IPN hydrogel were investigated using Fourier transform-infrared spectroscopy (FTIR), X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy and tensile testing, respectively. Results revealed that the water content of IPN hydrogel was approximately 2186% at 20 °C, indicating excellent ability to absorb energy as water heats up and evaporate. FTIR results showed that the PNIPAAm and SA were only physical interpenetrated within the IPN hydrogel. Moreover, compared with pure PNIPAAm, IPN hydrogel displayed better elastic and breaking strength. Vertical burning findings indicated that the hydrogel-fabric laminates did not burn when exposed to flame for 12 s, whereas natural cotton fabric was burned out. Finally, the fire-resistant hydrogel displayed excellent antibacterial activity against Staphylococcus aureus and Escherichia coli through the introduction of Ag NPs, and the antibacterial activity for both microorganisms exceeded 96%. Overall, this study provided an easy approach to producing a fire-resistant material by laminating a hydrogel and a fabric that may save lives.
Advanced thermal management materials with low thermal conductivity and robustness have been a research hotspot for energy conservation and sustainable development. However, the brittleness of inorganic materials and the high flammability of polymers remain a challenge for industrial applications. Herein, we demonstrated a novel strategy to fabricate the organic/inorganic composite aerogel based on the combination of hydroxyapatite (HAP) and chitosan (CS). The combination of chemical crosslinking and unidirectional freeze-drying method can significantly improve the mechanical properties and thermal stability, and the obtained anisotropic microstructure have a significant effect on thermal conductivity. Compared with the non-crosslinked HAP-Si/CS composite aerogel, the crosslinked HAP-Si/CSG composite aerogel has high mechanical strength (0.82−2.37 MPa) and high specific modulus (41.22−129.20 kN m kg-1). In addition, the as-prepared HAP-Si/CSG composite aerogel exhibit a lower radial direction thermal conductivity (28.16−37.43 mW m−1 K−1) than that of axial direction. Meanwhile, the composite aerogel constructed by HAP nanostructure embedded in the CS sheets have better limit the heat transfer and block the combustion of organic compounds, showing excellent fire resistance. Thus, biomass-based composite aerogel will be a sustainable and renewable functional material with high mechanical properties and thermal insulation, which further expected to promote the high value utilization of biopolymers.
Simultaneously achieving strength and toughness in soft materials remains a challenge, especially for physically crosslinked hydrogels with many inactive interaction sites. In this work, inspired by the cooking of thick soup in China, a facile method that includes free water evaporation of the diluted pregel solution followed by crosslinking (WEC) is proposed to fabricate polysaccharide hydrogels. Herein, without the constraints of viscosity and crosslinking, polymer chains can homogenously approach as much as possible, thereby enabling the transformation of inactive supramolecular interaction (H‐bonding and ionic coordination) sites into active sites until reaching the maximum level. Through facilely tuning the concentrating degree, programmed supramolecular interactions, serving as energy‐dissipating sacrificial bonds, impart the hydrogels with strength and toughness over a very wide range, where a “ductile‐to‐tough” transition is discovered to occur first. Using WEC in alginate, the concentration can be as high as 25 wt% without sacrificing processing ability, a result that is significantly beyond common value (3–7 wt%), and the extremely stiff and tough hydrogels are obtained, superior to isotropic alginate hydrogels ever reported. This research offers a facile and versatile strategy to fabricate isotropic polysaccharide hydrogels, which become ideal matrix materials for further fabrication of hybrid or anisotropic hydrogels. Extremely stiff and tough polysaccharide hydrogels are successfully fabricated through free approach of polymer chains, enabling the transformation of inactive dual supramolecular interaction sites into active sites to maximum level. This facile strategy is versatile to water‐soluble polysaccharides in fabricating isotropic hydrogels, which are ideal matrix materials for further fabrication of hybrid or anisotropic hydrogels.
A dual interaction-based (i.e., ionic/covalent) deposition of carbohydrate polymers, namely chitosan (CS) and oxidized sodium alginate (OSA) along with a plant-derived phosphorus-rich compound like phytic acid (PA) and a nitrogen rich compound like melamine (ME) was considered onto the phosphorylated chitosan (PCS) modified polyamide 6.6 (PA6.6) fabric surfaces in order to impart durable flame retardancy along with super-hydrophilicity of the same. Firstly, the pure PA6.6 textile surfaces were modified by PCS via UV-induced grafting and subsequently, the above-mentioned polyelectrolytes were assembled onto the fabric surfaces in a quadralayer fashion [i.e., (CS/ME-OSA-CS/ME-PA) n; “n” represents the number of quadralayers (QLs)]. Here, the amino groups of CS/ME and the aldehyde groups of the OSA were stabilized via covalent interaction and the deposition of positively charged CS/ME and negatively charged phytic acid (PA) formed ionic interaction. In the vertical burning (UL-94) test, both the only PCS grafted and the simultaneously PCS-grafted along with LbL assembled fabrics could completely stop the melt dripping tendency and attained a V-1 rating. In the meantime, the limiting oxygen index (LOI) value received a moderate increase from 18.5 % of pure PA6.6 to 23.5% for the PCS grafted and 8-QLs deposited fabric sample (i.e., PA6.6-g-PCS-8QL). Moreover, the PA6.6-g-PCS-8QL fabric sample exhibited a dramatic decrease in the peak heat release rate (pHRR) and total heat release (THR) by about 45 % and 24.7% respectively alongside enhanced thermal stability. Apart from the appreciable flame retardancy, this fabric sample (i.e., PA6.6-g-PCS-8QL) could boost up the hydrophilicity to attain a water contact angle of 0o. Finally, this dual interaction-based deposition of bio-inspired polyelectrolytes posed a positive impact in enhancing the coating stability in laundering and imparting durable flame retardancy to sustain even up to 20 laundering cycles.
Inspired by the classic dye-fixing process, a novel eco-friendly biomass-based coating that neither uses traditional elements such as Cl, Br, P nor toxic organic solvents was first developed to endow cotton fabrics with durable flame retardancy from biomass tannin (TA), tartar emetic (TE), and Fe²⁺. In this coating system, TA used as a charring agent was fixed onto the fiber surface of cotton fabric by TE in water via the action like dyestuff fixing, while Fe²⁺ coordinated with the hydroxyl of TATE can catalyze TA and cotton fibers to form graphited stable carbon residues for achieving high flame retardance. Consequently, the resultant fabrics showed great flame retardance with excellent durability. Even after 100 laundering or friction cycles, their Limiting Oxygen Index values of ∼27.0 % hardly changed. And the washed flame-retardant cotton fabrics still easily passed the horizontal flammability test with an extremely low destroy spread speed. Moreover, scanning electron microscopy, confocal laser scanning microscope, and cone calorimeter test results all confirmed the durability of the coating. The flame-retardant mechanism analysis demonstrated that the coating could promote the cotton fibers to form dense and regular graphitized carbon layers and effectively protect the matrix from decomposing to flammable gases under high temperatures. In addition to durable flame retardancy, the mechanical properties and hydrophilicity of cotton were slightly influenced by the flame-retardant coating. This eco-friendly biomass-based flame-retardant coating provides a new strategy for fabricating green flame-retardant systems without using hazardous compounds.
Polyester fibers are often applied as filling materials; however, they are flammable and exhibit melt-dripping. In this work, to prepare fibers with high flame retardancy, inherently flame-retardant alginate fibers were blended with polyester fibers, without using any toxic chemicals. The blended fibers with 20 wt.% alginate fibers achieved quick self-extinguishing without any melt-dripping in the vertical flame test and a test according to Pennsylvania Stuffed Toy Regulations. During the cone calorimetry test, the blended materials with 50 wt.% alginate fibers showed a remarkable decrease in heat and smoke release, compared with the blend with 20 wt.% alginate fiber and polyester fibers. Moreover, the alginate fibers could decompose prematurely and then delay the weight loss of polyester components when the natural/synthetic blends were subjected to heating. Also, they exhibited flame-retardant activities both in the vapor phase by the fuel dilution of non-flammable gases and in the condensed phase by forming calcium-enriched residues that were incompatible with polyester melts. Given their ease of preparation and high flame retardancy, the blended fibers have the potential for applications as filling materials of children's toys, furniture, and clothing.
A novel fire-preventing triple-network (TN) hydrogel was prepared and laminated on cotton fabric to improve fire-resistant performance of cellulose fabric. The TN hydrogel composed of Poly (N-isopropylacrylamide) (PNIPAAm)/sodium alginate (SA)/ Poly (vinyl alcohol) (PVA) exhibited excellent swelling ratio, swelling-deswelling behavior and antibacterial property. Results indicated that introduction of SA could improve water retention capabilities of TN hydrogels. Thermogravimetric experiments showed that the thermal stability of hydrogels was best at a SA: PVA ratio of 2:1. Furthermore, the obtained hydrogel-cotton fabric laminates displayed efficient flame retardancy. Compared to original fabric, hydrogel-fabric laminates were nearly undamaged when exposed to fire for 12 s. This result is attributed to energy absorption as water is heated and evaporates in the hydrogel. The present work provides a new concept to prepare fire-resistant polymer fabric, which may be used in fire-protective clothing to protect the skin from burn injuries.
Nanocellulose has been widely concerned and applied in recent years. Because of its high aspect ratio, large specific surface area, good modifiability, high mechanical strength, renewability and biodegradability, nanocellulose is particularly suitable as a base for constructing lightweight porous materials. This review summarizes the preparation methods and applications of nanocellulose-based lightweight porous materials including aerogels, cryogels, xerogels, foams and sponges. The preparation of nanocellulose-based lightweight porous materials usually involves gelation and drying processes. The characteristics and influencing factors of three main drying methods including freeze, supercritical and evaporation drying are reviewed. In addition, the mechanism of physical and chemical crosslinking during gelation and the effect on the structure and properties of the porous materials in different drying methods are especially focused on. This contribution also introduces the application of nanocellulose-based lightweight porous materials in the fields of adsorption, biomedicine, energy storage, thermal insulation and sound absorption, flame retardancy and catalysis.
Bio-composite alginate fibers with binary and ternary blends were prepared by using cellulose nanocrystal (CNC) and hydroxypropyl methylcellulose (HPMC) as composite fillers through wet-spinning method. Structural, thermal, mechanical properties and surface morphology of fibers were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Thermogravimetric Analysis (TGA), Mechanical strength testing, Scanning Electron Microscopy (SEM). The thermal stability and mechanical performance of SA/HPMC and SA/HPMC/CNC composite fibers improved as the increasing of crystallinity and intermolecular H-bonding interaction of the fibers. HPMC is helpful to improve the extensibility and stiffness of alginate fibers, and CNC can further enhance the stiffness of SA/HPMC composite fibers. The tensile strength, elongation at break, the initial modulus and work at break of SA/HPMC/CNC composite fibers were superior to those of alginate fibers. Roughness of surface and tensile section of SA/HPMC and SA/HPMC/CNC composite fibers got increased. Water absorbency and salt resistance were significantly improved.
In this study, we demonstrate the in-situ synthesis of a functional hybrid material of calcium alginate (CaAlg)/nano-silver phosphate (nano-Ag3PO4). The morphology of nano Ag3PO4 was in spherical shape with a diameter of 10–60 nm, and uniformly distributed in the continuous phase of CaAlg. The limiting oxygen index (LOI) of the hybrid material reached 61.4%, which was about 53.0% higher than that of CaAlg. In addition, its heat release rate, total heat release and smoke emission were much lower than those of CaAlg. The thermogravimetric analysis coupled with Fourier transform infrared analysis and pyrolysis-gas chromatography–mass spectrometry results indicate that the synthesized material released less flammable gas, compared to CaAlg, and the thermal mechanism of CaAlg/Ag3PO4 was proposed based on the data. Furthermore, the antibacterial rate of the hybrid material against common pathogens was >97%. This study prefigures the promising application of the marine polysaccharide functional materials in the field of the fire protection and epidemic prevention.
A new biosourced composite foam (AF, associating foamed alginate matrix and orange peel filler) is successfully tested for fire-retardant properties. This material having similar thermal insulating properties and density than fire-retardant polyurethane foam (FR-PUF, a commercial product) shows promising enhanced properties for flame retardancy, as assessed by different methods such as thermogravimetric analysis (TGA), pyrolysis combustion flow calorimetry (PCFC) and a newly designed apparatus called RAPACES for investigating large-scale samples. All these methods confirm the promising properties of this alternative material in terms of fire protection (pHRR, THR, EHC, time-to-ignition, flame duration or production of residue), especially for heat flux not exceeding 50 kW m⁻². At higher heat flux (i.e., 75 kW m⁻²), flame retardant properties tend to decrease but maintains at a higher level than FR-PUF. The investigation of the effect of AF thickness showed that the critical thickness (CT) is close to 1.5–1.7 cm: heat diffusion and material combustion are limited to the CT layer that protects the underlying layers from combustion. A multiplicity of factors can explain this behavior, such as: (a) negligible heat conduction, (b) low heat of combustion, (c) charring formation, and (d) water release. Water being released from underlying layers, dilutes the gases emitted during the combustion of superficial layers and promotes the flame extinction.
The membrane is one of the key inner parts of lithium-ion batteries, which determines the interfacial structure and internal resistance, ultimately affecting the capacity, cycling, and safety performance of the cell. In this article, an alginate-based fiber composite membrane was successfully fabricated from cellulose and calcium alginate with flame retardant properties via a traditional papermaking process. In the membrane, the calcium alginate plays a bridging role and the cellulose acts as a filler. After 100 cycles, lithium-ion batteries by the alginate-based fiber separator exhibited better capacity retention ratios (approximately 90%) compared with those of commercial PP separators. Furthermore, the alginate-based fiber separator demonstrated fine thermal stability and electrochemical properties, showing a stable charge-discharge capability and no hot melt shrinkage at higher temperatures, which is a breakthrough in improving the safety of the cell. This research affords a new way for the large-scale fabrication of safe lithium-ion battery separators.
Bio-based materials have been noticed for the continuous environmental pollution and resource shortage. In this paper, lignosulfonate (LS) and chitosan (CS) were selected to be flame-retardants. In the vertical flame test (VFT), LS/cotton-17.1 wt%, CS/LS/cotton-17.0 wt%, and CS/LS/cotton-25.2 wt% obtained lower afterflame times than that of uncoated cotton fabrics, while LS/cotton-17.1 wt% had serious afterglow time of 70 s. However, the afterglow time of CS/LS/cotton-25.2 wt% was 11 s, which decreased owing to the increased amount of CS. LS/cotton-17.1 wt%, CS/LS/cotton-17.0 wt%, and CS/LS/cotton-25.2 wt% presented limiting oxygen index values of 24.7%, 25.0%, and 26.0%, respectively. The scanning electron microscope images of char residues after the VFT showed that CS and LS formed an intumescent flame-retardant system, and cotton fibers remained intact structure. Meanwhile, the results of thermogravimetric analysis suggested that flame-retardant cotton fabrics can generate stable char residues. In N2 atmosphere, CS/LS/cotton-25.2 wt% generated 27.1% stable char residues. Moreover, the addition of CS/LS decreased the heat release rate and total heat release values and this system perform well in smoke suppression. The flame mechanism of the system might belong to gas-phased because more non-combustible products are generated in the thermal degradation process.
To improve the high-temperature resistance and inhibit the secondary disasters (such as explosion/radiation leakage attributing to power failure or short circuit) after fire, polymer-based ceramifiable composites (PCCs) have grown significantly in fire protection field caused by strong self-supporting and water spraying ceramic layer at 600–1000 °C. Generally, PCCs are fabricated through incorporating fluxing agent, silicate fillers, synergist, flame retardant and so on into polymer matrix. The polymer matrix could provide the composites with good processability, the ability to ease shaping and high elasticity. In this review, the different PCCs are compared and the effects of polymer matrix on the ceramization mechanism of composites are discussed. The factors influencing the self-supporting strength and water-resistant spraying time of ceramifiable polymer-based composites such as the type and incorporation amount of silicate fillers, ceramization temperature and fluxing agent are discussed. Meanwhile, the influence of flame retardant on the flame retardancy and ceramization property of PCCs is analyzed. Some perspectives and future directions on how to highly generate flame-retarding and strong self-supporting ceramifiable composites are proposed.
The present study reports the successful synthesis of the flame-retardant and smoke-suppressant flexible polyurethane foam (FPUF) through the use of a fully bio-based coating. Hydroxyapatite (HAP) is added to the solutions containing sodium alginate (SA) and chitosan (CH), respectively, to create negative and positive charges for Layer-by-Layer (LbL) assembly. The influence of the solution concentrations and bilayers numbers deposited on the flame-retardant and mechanical properties of FPUF samples is investigated systematically. Benefitting from the presence of such a fully bio-based coating, the resultant FPUF can afford excellent smoke-suppressant and flame-retardant features. In particular, the FPUF coated by 9 bilayers of HAP-SA/HAP-CH exhibits significantly declined peak heat release rate, total release rate and smoke production release by 77.7%, 56.5% and 53.8%, respectively. The compression test verifies the coated FPUFs exhibit lower recovery properties compared with the uncoated one. These results demonstrate that a green and cost-effective strategy is provided for producing flame-retardant, anti-dripping and smoke-suppressant FPUFs.
In this paper, an organic/inorganic phosphorus–nitrogen–silicon flame retardant (DPHK) was synthesized by Kabachnik-Fields reaction and the sol-gel method, then it was used as a reactive flame retardant to prepare flame-retardant and smoke-suppressant epoxy resins (EP). The influence of DPHK on the flame retardancy of EP was investigated by limiting oxygen index (LOI), vertical burning test (UL-94 V) and cone calorimeter (CC) test. The results revealed that the EP containing only 3 wt% DPHK achieved UL-94 V-0 rating, and the corresponding LOI value reached 29%. Furthermore, the cone calorimeter results demonstrated that the DPHK effectively reduced the heat release rate (HRR) and total release rate (THR) of the EP. Compared with EP, the peak of heat release rate (PHRR) and THR of 4%DPHK-EP reduced by 36% and 30%, respectively. More importantly, the incorporation of DPHK suppressed the release of toxic fuel (CO) and smoke of EP, meanwhile, the increased char residue and CO/CO2 ratio of the DPHK-EP samples proved that DPHK presented not only the condensed-phase activity but also gas-phase activity. Furthermore, the involved gases and char residues were studied by using thermogravimetric analysis coupled with coupled with Fourier transform infrared spectrometry (TG-FTIR), pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), scanning electronic microscope together with the energy dispersive X-ray spectrometer (SEM-EDX) and X-ray photoelectron spectroscopy (XPS). The results certified the charring effect of the phosphaphenanthrene group and the enhancing effect of the silicon group. Subsequently, the flame inhibition effect and lesser combustible gases release enhanced the flame-retardant properties of EP.
The effect of the blending amount of alginate fibres to cotton fibres on thermal stabilities, surface micromorphologies, flame-retardant and combustion properties of prepared cotton/alginate blended fibres were explored. The alginate fibres improved the thermal degradation properties at a higher temperature zone, showing in the increase of the residual chars. The alginate fibres enhanced flame-retardant properties and fire behaviors of prepared cotton/alginate blended fibres. The alginate fibres obviously decreased total heat release, peak heat release rate, total smoke production, CO2 production, and the released amount of inflammable volatiles. And the flame-retardant properties of cotton/alginate blended fibres can meet the requirements of filling materials for indoor furniture.
The high flammability of cellulosic materials somewhat limits their practical application. The introduction of an environmentally benign flame retardant coating for cotton fabric was achieved by hydrolyzing tetraethoxysilane and doping the silica sol with phytic acid in the presence of sodium alginate. The hybrid silica sol had high condensation degree and the modified silica particles had a spherical structure. The coated cotton fabrics with the hybrid PA/silica sol systems showed enhanced thermal stability at high temperatures, and displayed significantly suppressed heat and smoke generation ability, compared with the uncoated one. The hybrid silica sol coatings influenced the combustion performance of cotton via a charring action, and endowed the cotton fabrics with self-extinguishing ability during the vertical flammability test, demonstrating the improvement in fire resistance. The coated cotton fabrics displayed enhanced char yields, whilst maintained their texture structures after burning. Besides, the silicon- and phosphorus-containing components were also found to have a synergistic flame retardant action on cotton.
Bioderived flame retardants represent one class of most promising sustainable additives for creating flame retardant polylactic acid (PLA) because of their marginal impact on the biodegradability of PLA. Ammonium polyphosphate (APP) has demonstrated high flame-retardant effectiveness in PLA but its flame-retardant efficiency remains unsatisfactory even if after modifications. Herein, we report the facile fabrication of core-shell bioderived flame retardants by using APP as the core, and the chitosan (CS)/alginate (AA) bilayer as the shell through self-assembly in aqueous solution. The resultant core-shell flame retardant, [email protected]@AA-nBL (where "BL" is referred to a CS&AA bilayer; "n" denotes 1-3 BL), can endow PLA with improved flame retardancy without negatively affecting the thermal properties. The PLA containing 10wt% [email protected]@AA-3BL shows the highest LOI value (30.6%) and achieves a UL94 V-0 rating in the vertical burning test. Meanwhile, the cone calorimetry results demonstrate that the peak of heat release rate and total heat release are respectively decreased by 23% and 11% relative to the PLA bulk. Such enhanced flame retardancy is mainly due to the excellent char-forming capability of [email protected]@AA. Moreover, the inclusion of 10wt% [email protected]@AA-3BL gives rise to ~ 23% increase in the impact strength of PLA possibly because of their interfacial hydrogen-bonding interactions. This work provides a facile and green strategy for preparing highly effective bioderived flame retardants for PLA, and thus expects to expand the practical applications in industry.
The small molecular volatilized during the leather fogging process will pollute the air environment inside the car and make leather products flammable. In this paper, layered double hydroxide (LDH) was modified by different dosage of oxidized sodium alginate (OSA) via exfoliation-reassembly, and its structure were investigated by XRD and TEM. Then modified Zanthoxylum Bungeanum Maxim Seed Oil/ OSA modified LDH (MZBMSO/OSA-LDH) were obtained by introducing OSA modified LDH (OSA-LDH) into modified Zanthoxylum Bungeanum Maxim Seed Oil (MZBMSO), and used MZBMSO/OSA-LDH in leather fatliquoring process. The effect of the introduction of OSA-LDH on the anti-fogging and flame retardancy of leather was investigated. Compared to the MZBMSO treated leather, MZBMSO/OSA-LDH-0.2 treated leather exhibited remarkable improvement on fogging value of the leather, which was decreased by 45%. Furthermore, the leather treated by MZBMSO/OSA-LDH-0.4 has reduction of length of charring and smoke density around 36.1% and 37.5%, respectively. A potential interaction mechanism demonstrates that under the influence of OSA-LDH, an organic-inorganic interpenetrating network structure formed by leather collagen fibers-fatliquor molecule-LDH layer, which utilized to the steric hindrance and adsorption effect to hinder small molecule migration inside the leather fibers, thereby suppressing the fogging of the leather.
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.
Flexible polyurethane (FPU) foam as a primary softening material is utilized in soft furnishings of upholstered mattresses and furniture. High flammability of this soft furnishing material usually leads to residential fires, causing severe fatalities. In the present study, we proposed a bio-based and environmentally-friendly flame retardant multilayered coating consisted of laponite (LAP), branched polyethyleneimine (BPEI), sodium alginate (SA) and chitosan (CH) that was deposited onto FPU foams to enhance their fire safety property. Based on the thermogravimetric analysis results, it was indicated that after the deposition of LAP, the thermal stability of the coated FPU foams increased sharply. Foam treated with 9 quad layers (QL) of BPEI/SA/CH/LAP multilayered coating showed self-extinguishing behavior in an open flame burning test. Furthermore, the values of peak heat release rate (PHRR), total heat release (THR) and smoke release rate (SPR) of the coated FPU foams reduced considerably in comparison to those of the pure FPU foam. Specifically, 9 QLs of BPEI/SA/CH/LAP declined the PHRR and the THR by 74% and 42.6%, respectively. The coated FPU foam also showed self-extinguishing and anti-dripping features in an open flame testing. Therefore, it can be stated that LAP-based coating has incredible benefits in decreasing fire risk of FPU foams. Moreover, the flame retardant mechanism of this LAP-based multilayered coating was proposed. The LAP-based coating functioned as a physical insulating barrier that successfully retarded the permeation of the flammable volatiles, heat and oxygen. Hence, the significant decrease in PHRR with the self-extinguishing behavior was achieved, implying promising potential of this LAP-based multilayered coating to enhance the fire safety of FPU foams.
Bio-based flame retardants represent one of the most promising directions of next-generation flame retardants due to their sustainability, environmental benefits and comparable efficiency to current flame retardant systems. The aromatic structure and high charring capability have enabled lignin to demonstrate promising flame retardant applications in polymeric materials. Recent years have clearly witnessed the flame retardancy potential of the pristine lignin and its derivatives in a wide range of polymeric materials. Unfortunately, to date there remains a lack of a critical review on the preparation, modifications and application of lignin-derived flame retardants for polymeric materials. This review focuses on the flame retardancy effects of pristine lignin and chemically modified lignin by introducing elements phosphorus (P) and/or nitrogen (N), as well as their synergistic effects with current flame retardants additives. This review also comprehensively compares the flame retardancy performances of different lignin-derived flame retardants in various polymeric matrices such as polylactic acid, polypropylene and polyamide 11. Following some conclusions, some future perspectives are also presented along with new opportunities for the development of more efficient and effective lignin-based flame retardants for polymeric materials.
Clay-based aerogel is a promising material in the field of thermal insulation and flame retardant, but obtaining clay-based aerogel with high fire resistance, low thermal conductivity, hydrophobicity and mechanical robustness remains a challenge. In this work, palygorskite-based aerogel was successfully fabricated via combining with a very small proportion of alginate to form a distinctive hierarchically meso–microporous structure. By employing ethanol solution (EA) replacement method and freeze-drying process, the resultant aerogel exhibited ultra-low density (0.035-0.052 g/cm3), practical mechanical strengths (0.7-2.1 MPa), and low thermal conductivity of 0.0332-0.165 W/mK (25-1000°C). The hydrophobicity of aerogel was achieved by simple chemical vapor deposition of methyltrimethoxysilane (MTMS). The Pal-based aerogel showed good performance in both fire resistance with high limiting oxygen index up to 90%, and heat resistance with tolerance of flame up to 1000 ℃ for 10 min. This renewable Pal-based aerogel with a 3D framework is a promising material to be applied in fields of construction and aerospace for thermal insulation and high fire resistance.
A bio-based Mg(OH)2@tin [email protected] tannate ([email protected]@TAZn) composite was synthesised via layer-by-layer assembly method. Chemical bonds formed by chelating metal ions with phytic acid and tannic acid were involved in this synthesis. [email protected]@TAZn was then incorporated into PVC and its effects on flame retardancy, smoke suppression and mechanical properties were investigated. The core-shell structure and binding states between each layer (Mg–O–P, P–O–C) of the composite were examined. The limiting oxygen index (LOI) and cone calorimeter test results showed that the addition of 10 ph [email protected]@TAZn effectively enhanced the flame retardancy and smoke suppression of PVC. The LOI value of the 10 ph [email protected]@TAZn-incorporated PVC sample increased to 30.3% because of the combination of the gas dilution effect of vapor generated by the degradation of MH and synergistic catalytic carbonisation of PASn and TAZn. The second peak heat release rate, second peak smoke production rate and total smoke production of PVC/[email protected]@TAZn composite decreased by 40.8%, 72.2% and 35.2%, respectively. The increase in the interfacial contact area of PASn and the enhancement of interfacial interaction of TAZn significantly improved the tensile strength, elongation at break, and impact strength of PVC. This study presents a promising approach to synthesise flame-retardant PVC with excellent smoke suppression and mechanical properties.
The natural basalt fiber (BF) was incorporated into EVA composites with environmental‐friendly nickel alginate‐brucite based flame retardant (NiFR), to further improve the flame‐retardant effect and mechanical properties. The flame retardancy of EVA composites were characterized by LOI, UL 94, and cone test. With 55 wt% loading, 3BF/52NiFR had the highest LOI value of 31.9 vol.% in all fiber reinforced composites and pass UL 94V‐0 ratting. And comparing to 55B composite with untreated brucite, 3BF/52NiFR decreased peak of heat release rate by 47.8%, total heat release by 21.9%, and total smoke production by 35.5% and kept more residue 54.0% during cone test. Moreover, 3BF/52NiFR also enhanced the mechanical properties of composites by better compatibility with EVA matrix. BF/NiFR exert synergistic flame‐retardant effect major in promoting charring effect in condensed phase during combustion. The fire‐resisted and rigid BF into the char layer reinforced the intensity of protective barrier which prolonged the residence time of pyrolysis carbonaceous groups degraded from EVA matrix, resulting in less heat and smoke release.
Flame retardants mitigate the threat of fire from inherently flammable materials responsible for sustaining a high standard of living. Although bulk flame retardants have proven effective for many years, there is now increased interest in the use of surface treatments to localize flame-retardant chemistry at the exterior of a material, where combustion occurs, in an effort to preserve desirable bulk properties and minimize the amount of additive needed. This Review provides a historical overview that leads to the most promising surface treatments that will help pave the way for developing more effective and non-intrusive flame retardants in the future. The way in which a fire transpires, and the various chemistries and mechanisms used to counteract fire propagation, are discussed. Challenges that remain to improve current flame-retardant surface treatments are also addressed, as the success of these treatments depends on the scalability, durability and ability to impart desired functionality without conferring environmental problems.
An efficient and bio-based alginate pillared hydrotalcite (SA@LDHs) was fabricated via calcination-reconstruction manner with sodium alginate (SA) and hydrotalcite (LDHs-C), and used as novel flame retardant for polypropylene (PP). The morphologies and combustion properties of SA@LDHs and its hybrid with PP composites (PP/SA@LDHs) had been characterized by SEM, TGA, cone calorimetry, LOI and UL-94 measurements. With 30 wt% loading, the SA@LDHs achieved a LOI value of 30.9 % and a UL-94 V-0 rating, whereas the LDHs-C exhibited only LOI value of 27.6 % and a UL-94 V-1 rating. The peak heat release rate, total heat release and total smoke production of PP/SA@LDHs were 260.8 kW m-2, 61.3 MJ m-2 and 8.2 m2, respectively, which presented declines of 69.2 %, 42.8 % and 32.2 % compared with those of Neat PP. These improvements could be attributed to the presence of the radical-trapping effect of SA, which leading to promote PP chains to participate in the carbonization process.
Polyester/cotton (T/C) blends are widely used in the textile industry owed to the combination of both advantages of cotton and polyester. However, T/C blends are highly flammable due to the well-known scaffolding effect of the melting polyester and non-melting cotton fibers. Herein, to reduce the flammability of T/C blends, a nano-coating containing phosphorus, nitrogen and silicon was designed and constructed by layer-by-layer assembly of colloidal silica and polyphosphates. It was confirmed that the homogeneous nano-coating was successfully deposited on the surface of T/C blends, regardless of different surface morphologies and chemical nature of the synthetic and inartificial fibers. Encouragingly, with 15 bilayer nano-coatings (15.5% weight increased), the coated T/C blends achieved self-extinguishing and got away from scaffolding effect in vertical flame test, and showed a little delay of ignition and a strong decrease of heat release during cone calorimetry test, indicating excellent flame retardance of the treated fabrics. The nano-coating had both gaseous- and condensed-phase flame-retardant activity, which was further confirmed by the results of char analysis and thermogravimetric analysis/infrared spectrometry.
Clay aerogels have many attractive properties, such as low thermal conductivities, good thermal stabilities and low flammability. But the generally weak mechanical property severely restrains their practical applications. Incorporation of polymers into clay aerogel could achieve desirable strength, unfortunately, the fire resistance or insulating properties were sacrificed to some extent. In this work, fire-resistant palygorskite/wood fiber composite aerogels with low densities were prepared by an eco-friend freeze-drying method. In the aerogels, palygorskite contents were up to 80 wt% while only a small amount of wood fiber were used as reinforced filler. The composite aerogel had an array of porous structure with intertwined palygorskite fibers as pore walls, which resulted in a low thermal conductivity of 0.033 W/mK. In addition, the composite aerogel exhibited good mechanical strength with the Young's modulus up to 4.7 MPa while the density was lower than 0.08 g/cm³. Overall, an outstanding combination of excellent machinability, thermal stability, high limiting oxygen index, and prominent flame-retardant properties has been achieved in the composite aerogels. This work represents a significant progress of porous materials development and makes the practical applications of clay-based aerogel insulators realistic.
A highly efficient flame-retardant and ultra-low-smoke-toxicity biodegradable material, poly(vinyl alcohol) (PVA)/alginate/montmorillonite (MMT) composite aerogel, was fabricated by a new environment-friendly two-step crosslinking strategy using borate and calcium ions. Compressive and specific moduli of the crosslinked PVA/alginate/MMT (P4A4M4/BA/Ca) aerogel increased to 7.2- and 1.9-folds those of the non-crosslinked aerogel, respectively, and the limited oxygen index value increased to 40.0%. Cone calorimeter tests revealed that the total heat release and peak heat release rate values of the P4A4M4/BA/Ca composite aerogel distinctly decreased. Remarkably, the total smoke release value of the P4A4M4/BA/Ca aerogel was considerably lower than those of non-crosslinked PVA composite aerogels, indicating its superior smoke suppression ability and high fire hazardous safety. The flame-retardancy mechanism of the crosslinked P4A4M4/BA/Ca composite aerogels involved a combination of the gaseous phase and condensed phase flame retardancy. The high-performance PVA/alginate/MMT biodegradable composite aerogels with good sustainability is a promising alternative to conventional flame-retardant foams.
In order to improve the mechanical properties of alginate fiber and enrich its application properties, the metal-alginate fibers were produced with wet spinning in the coagulation bath of Zn2+, Ba2+, Cu2+, Al3+ ions blended with Ca2+ ions. FT-IR and 13C NMR were used to characterize the binding mode of alginic acid with metal ions and the arrangement of G and M groups in the molecular chain. The flame retardancy, mechanical and antibacterial properties of metal-alginate fiber were improved, while its water absorption was decreased. The results of Thermogravimetric (TG) and Limiting oxygen index (LOI) showed that the flame retardancy of metal-alginate fibers was better than that of calcium alginate fibers. The combination of metal ions and alginic acid has different improvement effect of mechanical strength and antimicrobial activity against Escherichia coli and Staphylococcus aureus. The multi-functional fiber is expected to be used in medical textiles and new textile fibers.
Organically modified ammonium polyphosphate (APP) flame retardant is prepared by supramolecular assembly method using melamine formaldehyde (MF) resin and phytic acid (PA) as building blocks. Surface characteristics of APP are modified, resulting in the enhancements in water resistance, dispersion in the polymer matrix and their compatibility. This supramolecular assembly modified APP ([email protected]) matches well with charring-foaming agent (CFA) to achieve excellent fire safety for polypropylene (PP), and the superiority over conventional APP is observed. Heat, CO and CO2 releases of PP are greatly decreased by the intumescent flame retardant (IFR) formulation containing [email protected] and CFA. The modification of APP with MF-PA supramolecules are beneficial to improve the yield, insulation properties, graphitization degree and compactness of char. Flame-retardant mechanisms are demonstrated according to the investigations on gaseous and condensed phase products. This novel and facile modification method provides a new strategy for improving the flame-retardant efficiency of IFR.
In this study, we fabricated a soft, transparent UV-shielding film (Alg-Fe³⁺-EDTA) by crosslinking sodium alginate with a ferric ion solution containing EDTA. The obtained films were characterized via SEM, ATR-FTIR, XRD, TG and DTG; the results indicated that the synergistic gelation of ferric alginate and alginic acid existed in Alg-Fe³⁺-EDTA film. The Alg-Fe³⁺-EDTA film performance to be optimized under the following conditions: 1.6% Fe³⁺, 0.8% EDTA, and crosslinking duration of 12 min. The Alg-Fe³⁺-EDTA film had high visible light transmittance, the UV-C (200–280 nm) and UV-B (280–315 nm) shielding rates were 100%, and the UV-A (315–400 nm) shielding rate was 98.37%; the UPF reached 50+; additionally, the tensile strength and elongation-at-break were 56.85 MPa and 10.45%, respectively, and still have ultraviolet shielding effect under water environments or after strong light irradiation. This work provides an efficient method to improve the optical and mechanical ability of ferric alginate films.