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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.
... Alginate has a broad range of applications; it is used in the food and packaging industry [4], biomedical sciences and engineering [8,9], the pharmaceutical industry [10], dentistry [11], wastewater treatment [12], and textile printing [13]. Apart from this, it is also used as a flame retardant and insulation material [14][15][16]. Alginate materials are used in the form of film, beads, capsules, fibers, sponges, foams, hydrogels, and 3D-printed matrices [17,18]. The disadvantages of using alginate without other components lie in its low stability and poor mechanical properties [4]. ...
... Naturally occurring gum arabic, which is a non-toxic and biodegradable anionic polysaccharide [30,31] obtained from the acacia tree, is known for its role as a stabilizer, Alginate has a broad range of applications; it is used in the food and packaging industry [4], biomedical sciences and engineering [8,9], the pharmaceutical industry [10], dentistry [11], wastewater treatment [12], and textile printing [13]. Apart from this, it is also used as a flame retardant and insulation material [14][15][16]. Alginate materials are used in the form of film, beads, capsules, fibers, sponges, foams, hydrogels, and 3D-printed matrices [17,18]. The disadvantages of using alginate without other components lie in its low stability and poor mechanical properties [4]. ...
Citation: Damjanović, R.; Vuksanović, M.M.; Petrović, M.; Radovanović, Ž.; Stavrić, M.; Jančić Heinemann, R.; Živković, I. Expanded Perlite-Abstract: In sustainable construction and packaging, the development of novel bio-based materials is crucial, driving a re-evaluation of traditional components. Lightweight, biodegradable materials, including xerogels, have great potential in architectural and packaging applications. However, reinforcing these materials to improve their mechanical strength remains a challenge. Alginate is a promising matrix material that may be compatible with inorganic fibrous or particulate materials. In this study, biocomposite xerogel-structured foam materials based on an alginate matrix with expanded perlite reinforcement are improved using certain additives in different weight ratios. The plasticizers used include glycerol and gum arabic, while chitosan was added as an additional reinforcement, and iota carrageenan was added as a stabilizer. The tested specimens, with varying weight ratios of the added components, showed good mechanical behavior that highlights their potential use as packaging and/or architectural materials. The influence of the presence of different components in the composite material specimens on the modulus of elasticity was investigated using SEM images and FTIR analyses of the specimens. The results show that the specimen with the largest improvement in the elastic modulus contained a combination of chitosan and glycerol at a lower percentage (1.96 MPa), and the specimen with the largest improvement in tensile strength was the specimen containing chitosan with no plasticizers (120 kPa), compared to cases where combinations of other materials are present.
... J Mater Sci films have been investigated in detail, and the blend films of alginate and other polysaccharides have been reported [26]. If the alginate and HPMC mixed can be prepared the environmental protection packaging films, it is a problem worth exploring [36]. ...
... Alginate [25,26] is a natural growth polysaccharide material extracted from brown algae, which has the higher biocompatibility, sustainability, low toxicity and relatively low cost [27,28]. It is a linear copolymer containing of β-d-mannuronic acid (M) and α-lguluronic acid (G) distributed in diverse M/G ratios [29,30], is a spontaneously existing nontoxic reproducible raw found in all species of brown algae [31]. ...
The crosslinked of hydroxypropyl methylcellulose (HPMC) and sodium alginate (SA) with a range of weight ratios formed blend films. Antibacterial packaging films (HPMC/ZA blend film) were prepared by simple ion exchange method with HPMC/SA blend film. The mixture of Zn²⁺ gave a plenty effect of the prepared films. The microstructure, physical properties, structure, and antibacterial properties of crosslinked films were investigated in detail. It was found that the infrared shifted peaks of O–H stretching and O–H bending in crosslinked HPMC/ZA film, which was caused by the formation of hydrogen bond between HPMC and ZA. SEM images of HPMC5/ZA5 blend film exhibited rougher structure. In addition, the light transmission, thermal properties, water vapor permeability, and antibacterial activity of HPMC5/ZA5 blend film are obviously enhanced, compared with HPMC/SA blend film. Furthermore, HPMC5/ZA5 blend film exhibited better antibacterial activity against S. aureus and E. coli, revealing the possible application on food packaging.
... Third, by eliminating free radicals or sabotaging chemical chain processes, some flame retardants can interfere with combustion reactions in the gas phase. This may lessen the amount of fuel available for burning, which would limit the rate of combustion as a whole [50]. ...
The increasing use of hydrogen as a clean energy carrier has underscored the necessity for advanced materials that can provide safe storage under extreme conditions. Carbon fiber-reinforced epoxy (CFRP) composites are increasingly utilized in various high-performance applications, including automotive, aerospace, and particularly hydrogen storage tanks, due to their exceptional strength-to-weight ratio, durability, excellent corrosion resistance, and low thermal conductivity. However, the inherent flammability of epoxy matrices poses significant safety concerns, particularly in hydrogen storage, where safety is paramount. This review paper provides a comprehensive overview of the recent progress in enhancing the fire safety of CFRP. The focus is on innovative strategies such as developing novel flame-retardant (FR) additives, intumescent coatings, and nanomaterial reinforcements. It analyzes the effectiveness of these strategies in improving the fire performance of CFRP composites, including their flame retardancy, smoke suppression, and heat release rate reduction. The review paper also explores the application of fire modeling tools to predict the fire behavior of CFRP composite hydrogen storage tanks under various fire scenarios. Additionally, the review discusses the implications of these advancements on the performance and safety of hydrogen storage tanks, highlighting both the progress made and the challenges that remain.
... The combustion process is a complex chemical reaction that involves mass and heat transmission [37]. Heating, thermal breakdown, ignition, and combustion are the four main steps the combustion process generally goes through [38,39]. The epoxy resin's temperature rises initially as it draws in heat from a foreign source. ...
Additive flame retardant offers several advantages in terms of formulation, improved performance and reduced environmental impact. These additives result in superior thermal management and the delay of thermal runaway events which ensures safety as well as durability. This review underlines the importance of appropriate additive flame retardant selection such as zinc borate, alumina and other inorganic flame retardants within the epoxy matrix. This study sets itself apart by introducing modeling and simulation techniques and comparing various additive flame retardants in terms of enhancing flame retardant properties, tensile strength and toughness of the composite. It also includes a more in-depth examination of manufacturing processes, burning mechanism and stabilization of polymer composite. The importance of conducting characterization such as cone calorimetry, UL-94 test is summarized for validating the desired flame retardant properties. Furthermore, it addresses the principal challenges and offers strategies to overcome these challenges based on the current research landscape.
... In order to create highperformance materials, blending has been employed to combine the benefits of individual materials. 180 As shown in Table 3, alginate can be blended with a variety of different materials to generate fibers and create new applications. The electrospinning process is hindered by the high electrical conductivity of alginate due to its polyelectrolytic nature, which poses challenges in achieving electrospinnability. ...
Alginate has gained extensive attention due to its versatile properties and numerous applications in different fields. Due to the abundant availability of raw alginate in nature and its advantage of being easily recycled, alginate-based materials are conducive to advancing the shift away from an economy dependent on fossil fuels to a more environmentally friendly and sustainable one. In addition, its inherent biocompatibility makes alginate a fascinating biomedical material. This comprehensive review presents a detailed analysis of alginate, focusing on its structural characteristics, physicochemical and biological properties, current processing technologies, and modification strategies. This review explores the diverse applications of alginate-based materials in biomedicine and healthcare, considering drug delivery systems, tissue engineering, and wound dressings. Additionally, this review looks into the environmental applications of alginate in biosensors and waste-water treatment. The challenges associated with alginate utilization and future perspectives for research and development are also presented. This review provides a comprehensive overview of alginate, offering valuable insights into its properties, applications, and potential for future applications across various industries.
... The condensed phase products of IAE/IAB hydrogel were characterized by FTIR. The C=O of carboxyl groups (1727 cm -1 ) is completely consumed at 450 °C for IAE/IAB hydrogel via decarboxylation pattern (Figure 4d) [28]. The characteristic C-O-C band at 1186 cm -1 cannot be detected for IAE/IAB hydrogel after 300 °C [29], meaning that water is not generated after this temperature region. ...
Biomass-based hydrogels have received extensive attention due to their flame retardant properties and environmental friendliness. The dilemma that non-renewable energy resources are increasingly depleted, leads us to place high expectations on renewable natural clean energy, as well as to conduct in-depth research on the efficient utilization and green preparation processes for the clean energy. In this study, we introduce a green and sustainable method for the design and preparation of flame-retardant materials by integrating two new class of itaconic acid-based hydrogels in conjunction with the rapid vat photopolymerization (VP) 3D printing technology. The hydrogels prepared by this method exhibit exceptional flame retardancy, mechanical robustness and superior high-temperature resistance. This research provides novel strategies and essential guidance for the green synthesis and sustainable development of next-generation flame retardant materials.
... At the same time, the addition of metal ions also enables the aerogel to produce metal oxides or metal carbonates that cover its surface during combustion, insulating it from air and flame. 35 To improve the mechanical properties and flame-retardant properties of PVA, inorganic nanofillers such as magnesium hydroxide, 36 carbon nanoparticles, 37 and graphene 38 can be added optionally. HNTs are natural nanomaterials with a hollow tubular structure. ...
... Tỷ lệ các monome này (tỷ lệ M/G) thể hiện cấu trúc chuỗi phẳng giống như dải ruy băng và cấu trúc linh hoạt (chuỗi giàu M), cấu trúc phân tử cứng (chuỗi giàu G). Các khối M-G bao gồm các liên kết glycosid trục-vành (axial-equatorial) và liên kết glycosid vành-trục (equatorial-axial) xen kẽ khâu các phần còn lại (Xu et al., 2021). Tóm lại, chuỗi GG > MM > MG mô tả độ cứng của gel natri alginate trong môi trường nước theo tỷ lệ M/G. ...
Gel của Ca-alginate trong nước được ứng dụng nhiều trong vật liệu màng composite với nhiều ứng dụng linh hoạt đã được nhiều nhà khoa học phát hiện ra. Bên cạnh đó, xu hướng sử dụng vật liệu da thân thiện môi trường đã phát triển rất nhiều ở các nước trên thế giới. Bài báo này nhằm cung cấp những thông tin về vật liệu màng composite và vật liệu giả da Bioleather dựa trên liên kết ion gel của Ca- Alginate trong môi trường nước.
... The impact of different metal ions on the thermal decomposition of alginate varies (Cao et al. 2020). Ca 2+ is capable of significantly improving the flame retardancy of alginates due to its good affinity to alginate chains and high thermal stability of char residues (Xu et al. 2021). Huang et al. synthesized calcium alginate (CaAlg)/hydroxyapatite (HAP) hybrid material by a sol-gel method, the results show that the thermal stability and flame retardancy of the hybrid material are significantly improved (Huang et al. 2022). ...
In modern society, with the rapid increase in energy consumption, there is a growing interest in the effective utilization of bio-resources. Biomass aerogels have considerable academic research value due to their eco-friendly attributes and renewable nature. In this work, sodium alginate (SA) and sodium lignosulfonate (SLS) are employed as the matrix, which are dually cross-linked with Ca²⁺ and bis[tetrakis(hydroxymethyl)phosphonium] sulfate (THPS). Subsequently, a well-formed aerogel (CA-SP) is obtained through the lyophilization process. The formed dual crosslinking network and the “egg-box” structure endow the CA-SP aerogel with superior flame retardancy and thermal insulation properties, as evidenced by a limiting oxygen index value of 40.8%, achievement of the UL94 V-0 rating and low total heat release (1.35 MJ·m⁻²). Moreover, the THPS simultaneously endows the SA-SP aerogel with excellent flame retardancy and antimicrobial effect. The exceptional flame retardancy, smoke suppression capabilities, and antimicrobial effects of the CA-SP aerogel expand its prospects for application.
... Besides, the modified fibers are dyeable and demonstrated excellent dyeing rates and color fastness after dyeing. These properties would offer new possibilities for the usage of alginate fibers as materials for daily clothing, medical dressings, and fireproof fabrics (Sharma et al. 2020;Ma et al. 2017;Hu and Lin 2022;Xu et al. 2021). ...
Alginate fibers made from seaweed have some desirable properties as textile materials, but they also have two shortcomings that limit their usages: they are intolerant to salt, alkali, and detergent, and they are difficult to dye due to the electrostatic repulsion with anionic dyes. To solve the two problems in this project, a process of successive modification of alginate fibers using sodium pyrophosphate, alum, and sodium hydroxide was developed. SEM images and ion content of the modified alginate fibers showed that the fibers did not dissolve in high concentrations of sodium chloride, sodium hydroxide, or standard detergent solution and still maintained their original morphology. Also, the results of FTIR, XPS, XRD, and single-fiber strength tests indicated that the modification process enabled the alginate fibers to form a new tetrahydroxy cross-linking structure and thus improved their mechanical properties. The tetrahydroxy cross-linking structure prevented the dissolution of alginate fibers by blocking the exchange of ions between the fibers and the solution. Besides, the presence of Al³⁺ in the tetrahydroxy cross-linking structure modified the electrostatic repulsion between the alginate fiber and the anionic dye, resulting in high dyeing and dye fixation rates. Thus, the modified alginate fiber can be dyed directly with common dyes without dissolution, solving the above-mentioned two problems. This can enormously expand the potential usages of alginate fibers and therefore has significant academic and practical implications.
Graphical abstract
... The neat AA aerogel ignited after just 11 s and showed a sharp flame at 33 s, with a low PHRR of 84.4 kW/m 2 , indicating low fire intensity (Figure 9a). This initial flame resulted from the heat released during alginate dehydration (the loss of physically adsorbed and chemically bound water), following the decarboxylation and esterification of alginate chains, while releasing NH 4 + ions and H 2 O, CO 2 , and CO [44]. A wide shoulder appeared between 50 and 100 s as a result of char generation through the combustion of these gases. ...
Lightweight materials that combine high mechanical strength, insulation, and fire resistance are of great interest to many industries. This work explores the properties of environmentally friendly alginate aerogel composites as potential sustainable alternatives to petroleum-based materials. This study analyzes the effects of two additives (tannic acid and montmorillonite clay), the orientation that results during casting, and the crosslinking of the biopolymer with glutaraldehyde on the properties of the aerogel composites. The prepared aerogels exhibited high porosities between 90% and 97% and densities in the range of 0.059–0.191 g/cm3. Crosslinking increased the density and resulted in excellent performance under loading conditions. In combination with axial orientation, Young’s modulus and yield strength reached values as high as 305 MPa·cm3/g and 7 MPa·cm3/g, respectively. Moreover, the alginate-based aerogels exhibited very low thermal conductivities, ranging from 0.038 W/m·K to 0.053 W/m·K. Compared to pristine alginate, the aerogel composites’ thermal degradation rate decreased substantially, enhancing thermal stability. Although glutaraldehyde promoted combustion, the non-crosslinked aerogel composites demonstrated high fire resistance. No flame was observed in these samples under cone calorimeter radiation, and a minuscule peak of heat release of 21 kW/m2 was emitted as a result of their highly efficient graphitization and fire suppression. The combination of properties of these bio-based aerogels demonstrates their potential as substituents for their fossil-based counterparts.
... However, their effectiveness varies from one type of fibre to another and according to the composite formulation, leading to inconsistency and trade-offs to keep the product use valid. The combustion behaviour of KFRCs can be affected by the fibre type, fibre weight/volume fraction, thermal conductivity, fibre orientation, aspect ratio, fibre-matrix interface, and agent size, which makes understanding the fibre important [45][46][47]. Out of them, a few aspects have been discussed below to draw out the important factors and their influence on fire-reaction properties. ...
Natural fibres have been used as fibre reinforcements in composites as they offer eco-friendly and economic advantages, but their susceptibility to deterioration when exposed to heat and flames has limited their practical application in fibre-reinforced polymeric composites. Fire-reaction properties have been explored in reasonable detail for plant fibres, but a gap exists in the understanding of animal fibre-reinforced composites. Understanding the thermal and fire reactions of these keratin-rich animal fibres is crucial for material selection and advancing composite product development. The current paper critically discusses the existing research landscape and suggests future research directions. The use of keratinous fibres in composites can definitely improve their thermal stability and fire performance, but it also appears to adversely affect the composite’s mechanical performance. The main part of this paper focuses on the flame-retardant treatment of keratinous fibres and polymer composites, and their behaviour under fire conditions. The final part of this paper includes a brief look at the environmental impact of the treatment methods; the overall processing of keratinous fibre-reinforced composites is also presented to gain further insight.
... Due to the versatility of uses of alginate, several new technologies have been developed in order to create sustainable solutions with lower environmental impact, including self-healing asphalt [19], bio-ink for 3D printers [20], flame-retardant materials [21], and alginate-based bio-composite materials for wastewater treatment [22]. By way of exemplification, microorganisms, such as microalgae and cyanobacteria, can be immobilized in sodium or calcium alginate beads, forming small spheres, and used several times without significant loss of cell activity, ensuring the stability of the processes in which they are applied. ...
Alginate is a natural biopolymer synthesized mainly by brown seaweed but also by microorganisms, also called bacterial alginate [1]. Alginate, also known as alginic acid, has a linear structure constituted by unbranched chains of polysaccharides, consisting of blocks of two monomeric uronic acids, β-(1–4)-D-mannuromic acid (D or M), and in its epimere, the α-L-guluronic acid(G) [2, 3]. Due to its composition, the chemical structure of alginate can be considered by combining three types of blocks: GG, MM, and MG, where in the GG blocks there are only α-L-guluronic acid units, in the MM blocks there are only β-(1–4)-D-mannuromic acid units, and in the MG blocks there are alternating units of both acids [3].
The origin of the alginate as well as the age of the seaweed and the harvesting season influence the ratio and the arrangement of the MG blocks, resulting in differ- ent biological and physicochemical properties [4, 5]. In an overview, alginate gels with a low ratio of MG blocks have the characteristics of being stiff and brittle, but if the ratio of MG blocks is high, there is the formation of flexible and elastics gels [5, 6]. For the formation of alginate gels by the addition of calcium ions, a high concentra- tion of the GG blocks guarantees an improvement in gel strength [3]. However, for the formation of polymeric nanoparticles, the more significant presence of MM blocks contributes to the stability of the aggregation of nanoparticles [7].
Alginate is a polysaccharide that has similar characteristics to pectin present in plants; however, it is present in the cell walls of brown algae, of the Phaeophyceae class, in a similar format to cellulose microfibrils, arranged in a crystalline arrange- ment, in addition to being derived from the intercellular matrix of these seaweed
[8]. The most common and easy-to-find species commercially are Ascophyllum, Durvillaea, Ecklonia, Laminaria, Lessonia, Macrocystis, Sargassum, and Turbinaria [9]. Furthermore, alginate can be extracted from bacteria such as Azetobacter Vineland and Pseudomonas species [10].
The most commonly used in industry is sodium alginate, which is extracted through steps involving physicochemical procedures, starting with a treatment of the dry material using formaldehyde, followed by an acid process, after collecting the algae in its marine habitat. After these steps, an alkaline extraction is performed, followed by bleaching, precipitation, and drying [11].
1
Alginate – Applications and Future Perspectives
The applications of alginate currently depend on its characteristics such as low toxicity, anti-inflammation, high absorption, and thickener in food mixtures, in addi- tion to having the ability to accelerate healing in pharmaceutical processes [12]. For these reasons, the polysaccharide is exploited in industries involving food, beverages, fabrics, printing, and pharmaceuticals [13]. An example of its use is in materials from the pharmaceutical and cosmetics industries, which guarantee improved stability and damage control due to external conditions such as temperature and UV light, or even protection in gastric environments, if they are for oral use [14]. In the food industry, alginate applications are based on three properties: thickening, gelling, and film forming [15].
Alginate can also be seen as an additive in packaging, in order to improve the quality and prevent damage to the coated product and promote good conservation because of the added attributes such as antimicrobial and antioxidant action [16]. These packages are edible coatings used as a biopolymer that sits on the surface of the food and is included by methods of molding, coating, extrusion, and dipping, among others [17]. Another area where alginate is highly used is in agriculture where it functions in improving productivity, treating water, and improving the quality of the crop through uses in seed coatings, fruits, and vegetables that help with growth, in addition to being used in formulations that control the use of agrochemicals [18].
Due to the versatility of uses of alginate, several new technologies have been developed in order to create sustainable solutions with lower environmental impact, including self-healing asphalt [19], bio-ink for 3D printers [20], flame-retardant materials [21], and alginate-based bio-composite materials for wastewater treat- ment [22]. By way of exemplification, microorganisms, such as microalgae and cyanobacteria, can be immobilized in sodium or calcium alginate beads, forming small spheres, and used several times without significant loss of cell activity, ensuring the stability of the processes in which they are applied. This technological route has received increasing interest from researchers and scientists in the area of microalgae-based processes for industrial effluent treatment. The microalgae cell immobilization in polymeric alginate matrices can be performed by several methods and can be exploited for the bioremediation of different types of wastewater and contaminants [23].
In short, alginates can be modified into multiple products, such as hydrogels, fibers, films, sponges, capsules, and light foams [22, 24]. These characteristics make this biomaterial interesting to be studied and applied in a vast number of different situations.
In this sense, the chapters presented in this book are intended to provide an in- depth understanding of the applications and future perspectives of alginate, con- tributing to the consolidation of information about its characterization, properties, synthesis, current uses, and trends.
Alginate serves as a structural component of brown algae and assist with the shape of the plant. Alginate is a hydrophilic anionic polysaccharide derived from brown algae, bacteria and has been attracting attention as a promising flame-retardant material in recent years. Alginate is an unbranched polysaccharide composed of two linear copolymer blocks, l-guluronic acid (G) and d-mannuronic acid (M), which provides better thermal stability and flame retardancy to polymer matrices. These properties enhance alginate's high temperature resistance, making it a strong choice for use in flame retardant applications. Alginate is a biodegradable material that acts as a flame retardant by releasing water vapor when exposed to heat or flame, helping the material cool and preventing the spread of fire. Alginate flame retardants typically produce very little smoke when exposed to fire, thus contributing to improved fire safety. The versatility of alginate is also demonstrated by its compatibility with a wide variety of materials, allowing easy integration into fibres, coatings, composites, and foams. Incorporation of alginates into these matrices significantly improves the fire performance of the resulting materials, making them an attractive solution for improving fire safety across a wide range of applications. As research continues to advance, the incorporation of alginate into matrix materials is expected to increase and advance fire safety progress and promote sustainable practices in all industries. This chapter discusses the flame retardancy of alginate incorporated in various polymer matrices, and the structure of alginate that makes it an excellent flame-retardant filler.
Flame-retardants (FR) are essential for improving the combustibility of different materials. However, conventional flame retardants commonly contain toxic and environmentally hazardous substances environment making the development of sustainable and renewable alternatives critical. Lignin, chitosan, and starch are natural polymers derived from plant and seafood sources with significant potential in the development of green flame-retardants. Various mechanisms which includes char formation, gas-phase inhibition, and heat absorption, enable these materials to be used as flame retardants. This chapter focuses on the chemical structures, sources and modification of these bio-based materials, as well as the impact on flame retardancy. The modification of these polymers are being investigated, which demonstrate how incorporating with additives can improve their flame retardancy while eliminating fire dangers, in addition to overcome environmental concerns showed by conventional flame retardants. When modified, they exhibit promising flame-retardant properties, making them ideal candidates for green flame retardant formulations. They are promising candidates for green flame retardant compounds as their composition can be modified to exhibit promising flame-retardant qualities. The chapter further addresses current developments, problems, and future prospective future, underlining the significance of bio-based materials in promoting green flame retardant technology.
This chapter focuses on the synthesis and characterization of nanomaterials derived from biomaterials, which signifies a viable path for improving flame retardancy for various applications. This chapter begins outline the major issues in conventional flame retardant materials, as well as the requirement for sustainable alternatives; and investigates the methods used to produce nanomaterials from biomaterials in order to improve flame retardant properties. Furthermore, chapter discusses the preparation procedures as well as the review of data released on the various mechanical, structural, morphological, and thermal properties of the synthesized nanomaterials. Future perspectives are highlighted to identify new research avenues in terms of tuning properties of bio-based nanomaterials and improve their efficiency for flame retardancy application.
Endowing polyurethane foam with high fire resistance and smoke suppression is a persistent challenge in the combustion industry. This study introduces a graphite‐tailings and calcium‐alginate (GT@CA) gelatum coating that terminates the heat and mass transfer process in a flexible polyurethane foam (PUF) matrix with fire resistance and smoke suppression. The PUF/GT@CA‐3 composite exhibits high flame retardancy with a V‐0 rating in the vertical combustion test. Furthermore, GT@CA forms protective and char layers that terminate the heat and mass transfer during thermal degradation, the thermal stability and fire behavior of the PUF/GT@CA composites are markedly optimized. Meanwhile, the smoke production rate and total smoke production of PUF/GT@CA‐3 composite are dramatically reduced to 1.17 × 10⁻² m²/s and 2.73 × 10⁻¹ m², respectively (81.19% and 83.26% lower than those of pure PUF, respectively). Finally, the flame retardant and smoke suppression mechanism of GT@CA in PUF is deduced. The GT@CA competently promotes the char forming process of the PUF matrix while fabricating an impervious protective layer. The char and protective layers on the PUF surface restrain oxygen diffusion, heat diffusion, and micromolecule volatilization processes. Hence, GT@CA is expected to expand the application range of PUF matrixes in the advanced materials field.
The significant volume of existing buildings and ongoing annual construction of infrastructure underscore the vast potential for integrating large-scale energy storage solutions into these structures. Herein, we propose an innovative approach for developing structural and scalable energy storage systems by integrating safe and cost-effective zinc-ion hybrid supercapacitors into cement mortar, which is the predominant material used for structural purposes. By performing air entrainment and leveraging the adverse reaction of the ZnSO4 electrolyte, we can engineer an aerated cement mortar with a multiscale pore structure that exhibits dual functionality: effective ion conductivity in the form of a cell separator and a robust load-bearing capacity that contributes to structural integrity. Consequently, a hybrid supercapacitor building block consisting of a tailored cement mortar, zinc metal anode, and active carbon cathode demonstrates exceptional specific energy density (71.4 Wh kg−1 at 68.7 W kg−1), high areal energy density (2.0 Wh m−2 at 1.9 W m−2), favorable cycling stability (∼92% capacity retention after 1000 cycles), and exceptional safety (endurance in a 1-hour combustion test). By demonstrating the scalability of the structural energy storage system coupled with solar energy generation, this new device exhibits great potential to revolutionize energy storage systems.
Alginate, a naturally sourced bio-polymer derived mainly from brown seaweed, has gained incredible attention due to its versatile properties and wide range of applications. This review outlines alginate regarding sources, extraction methods, classifications, and critical characteristics. The critical development of alginate, focusing on its application in 3D bioprinting in fields such as vascular tissue formation, bone printing, and cartilage printing, has been discussed. Recent trends regarding the application of alginate in different sectors, from cosmetic textiles to wastewater treatment, wound dressing, and preparation of intelligent materials, have also been probed. The techniques used, benefits, and limitations form the discussion of each application. In addition, future alginate perspectives are discussed by considering current research with potential innovations that can expand its utility. Particular attention is devoted to the promising role of alginate in these emerging technologies that hold promise for radical changes in many industries due to its biocompatibility, biodegradability, and unique physicochemical properties. This review seeks to lay down basic knowledge on alginate by synthesizing the state of the art and, in this way, brings out the gaps that might inspire further studies and development in this dynamic field.
A series of hybrid particles consisting of graphene oxide and magnesium–aluminium-layered double hydroxides (GO/Mg–Al-LDHs) were prepared by the co-precipitation method and then modified by allyltrimethoxysilane (ATMS). X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, Raman spectra and field emission scanning electron microscope (FESEM) micrograph results showed the modified GO/Mg–Al-LDHs were synthesised with a smaller particle size and better dispersion. The polypropylene (PP) composites were prepared via the reactive extrusion method, and the effects of GO content in hybrids on the mechanical properties, processability, thermal stability, flame retardation, melting and crystallisation behaviour of composites were investigated in detail. The comprehensive properties of composites containing GO/Mg–Al-LDHs were excellent compared to those of Mg–Al-LDHs under the same filler concentration. Compared with pure PP, 20 wt-% of GO/Mg–Al-LDHs-2.5 increased the limiting oxygen index (LOI) value of composites from 16.4% to 28.8% with a V-0 level of U-94 testing and decreased the heat release rate (HRR) and total heat release (THR) values from 1206.4 kW/m ² and 133.9 MJ/m ² to 146.9 kW/m ² and 69.6 MJ/m ² . Meanwhile, the tensile, impact strength and elongation at break were 36.2 MPa, 3.0 kJ/m ² and 68.6%, respectively. This work provided an effective strategy for enhancing the dispersion and comprehensive properties of GO/LDHs-based composites.
Among the various fire‐retardants (FRs) known, phosphorus is vital to the development of effective FRs due to its flexibility. Additionally, the additives and combinations of phosphorus with various multicomponent moieties (e. g. P−Si, P−P, P−B, etc.) can serve the purpose in different phases to improve flame retardance properties. With an increased cognizance of recyclable, eco‐friendly, and bio‐based materials, phosphine oxide‐based materials/coatings can fulfill the criteria for flawless and future FRs. In this regard, the present review highlights the most promising organophosphorus‐based compositions as non‐intrusive FRs. The classification, synthetic methods, related mechanisms, and high‐end FR applications of various recently developed organophosphorus‐based molecules and materials are demonstrated. Among various organophosphorus compounds, the phosphorus‐based polyurethane materials display remarkable FR properties and non‐toxic behavior. Notably, the flame retardance of the epoxy resins is enhanced significantly with the presence of more P=O bonds and amino groups. The limitations and advantages of organophosphorus‐based materials are compared with the traditional FRs. Also, the challenges persisting in improving current flame‐retardant materials need to be addressed. However, the success of these materials and treatment methods strongly depends on the ability to impart desired functionality, durability, and scalability without compromising environmental problems.
This review discusses the development and application of nanocellulose (NC)-aerogels, a sustainable and biodegradable biomaterial, with enhanced flame retardant (FR) properties. NC-aerogels combine the excellent physical and mechanical properties of NC with the low density and thermal conductivity of aerogels, making them promising for thermal insulation and other fields. However, the flammability of NC-aerogels limits their use in some applications, such as electromagnetic interference shielding, oil/water separation, and flame-resistant textiles. The review covers the design, fabrication, modification, and working mechanism of NC porous materials, focusing on how advanced technologies can impart FR properties into them. The review also evaluates the FR performance of NC-aerogels by employing widely recognized tests, such as the limited oxygen index, cone calorimeter, and UL-94. The review also explores the integration of innovative and eco-friendly materials, such as MXene, metal-organic frameworks, dopamine, lignin, and alginate, into NC-aerogels, to improve their FR performance and functionality. The review concludes by outlining the potential, challenges, and limitations of future research on FR NC-aerogels, identifying the obstacles and potential solutions, and understanding the current progress and gaps in the field.
Ethylene-vinyl acetate copolymer (EVA) is widely used in various applications; however, its flammability limits its application in wire and cable industries. In this study, 3-methacryloxypropyltrimethoxysilane (KH570) was successfully grafted onto the surface of anhydrous magnesium carbonate (AMC) by alkali activation treatment. The KH570 modified AMC (AMC@KH570) was then introduced into the EVA matrix along with hexaphenoxycyclotriphosphazene (HPCTP) to assess their effects on the flame retardancy and mechanical properties of EVA composites. The results illustrate a significant synergistic effect in enhancing the flame retardancy of EVA composites by using AMC@KH570 and HPCTP, and the limiting oxygen index (LOI) and vertical burning test (UL-94) of EVA filled with 5 wt% HPCTP and 45 wt% AMC@KH570 (mAMC/H-45-5) reached 27.6% and V-0, respectively. The flame retardant mechanism was investigated by thermogravimetric/infrared (TG-IR) spectroscopy and residual carbon composition analysis. The results show that the thermal decomposition of AMC@KH570 and HPCTP consists of gas dilution, free radical quenching, and catalytic carbonization. Furthermore, KH570 works as a bridge to improve the compatibility of AMC and EVA matrix, which offsets the mechanical loss of EVA to some extent. The present research provides a new path to modify AMC and fabricate EVA composites with excellent flame retardant properties.
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.
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.
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.
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.
