Advancements in traditional and nanosized flame retardants for polymers—A review

National urinary metabolites of organophosphate flame retardants in urban Chinese residents

Organophosphate flame retardants (OPFRs) are extensively added to household products for fire safety. However, little is understood about the national scale of human exposure levels and the factors influencing OPFRs in developing countries. In this study, five metabolites of OPFRs (mOPFRs) were determined for the first time in the urine of 1184 general population in 26 provincial capitals of mainland China. The detection frequency and median concentration of ∑5mOPFRs were 86.0% and 61 μg/L, respectively, with bis(1-chloro-2-propyl) phosphate, bis(2-chloroethyl) phosphate (BCEP), and diphenyl phosphate predominantly accounting for 75.9% of the total. Human exposure to OPFRs is higher in western China than in other Chinese regions. Gender, age, bottled water, and takeout consumption significantly influenced the urinary mOPFRs. Monte Carlo simulations showed that 3.6% of participants had hazard indices values higher than one, indicating that a small proportion of the Chinese population exposed to OPFRs had potential non-carcinogenic risks. Here, BCEP was the primary contributor, making up 81.5% of the total risk. This study indicated that investigating human exposure to OPFRs is imperative, especially the safety of these substances as a substitute for polybrominated diphenyl ethers.

Alginate-based flame-retardant coatings for sustainable fire protection: A review

With a growing global focus on sustainability, bio-based flame retardants like alginates are becoming key alternatives to conventional resource-heavy options. Sourced from renewable seaweed, alginates are esteemed for their film-forming properties, environmental compatibility, and modification versatility. These qualities make them ideal for creating flame-resistant coatings. This review examines recent progress in alginate-based flame-retardant coatings, emphasizing synthesis methods, functionalization strategies, mechanisms, and performance assessments. A comparative analysis of coating techniques is presented, including conventional coatings approaches, sol-gel processes, and layer-by-layer (LbL) assembly. Modified alginates and additive flame retardants, including metal salts and nanoparticles, are discussed in detail. The findings suggest that alginate-based coatings hold significant promise for sustainable fire protection across multiple sectors, including textiles, construction, and electronics. Future research directions are also outlined, emphasizing the optimization of formulations and scalability for industrial applications.

Recent Advancements of Bio-Derived Flame Retardants for Polymeric Materials

The sustainable flame retardancy of polymeric materials is a key focus for the direction of the next generation in the field of fire safety. Bio-derived flame retardants are gaining attention as environmentally friendly additives due to their low ecological impact and decreasing costs. These compounds can enhance char formation in polymeric materials by swelling upon heating, attributed to their functional groups. This review explores various biomolecules used as flame retardants, including phytic acid, chitosan, lignin, tannic acid, and bio-derived phosphorus and nitrogen compounds, emphasizing their flame-retardant properties and compatibility with different polymer matrices. The primary focus is on the structural characteristics, modifications, and flame-retardant behaviors of these bio-derived additives, particularly regarding their mechanisms of action within polymeric materials. Finally, the review explores the opportunities, current challenges, and future directions for the practical application of bio-derived flame retardants in polymer materials.

Chitosan-based biopolyelectrolyte complexes intercalated montmorillonite: A strategy for green flame retardant and mechanical reinforcement of polypropylene composites

Due to dwindling petroleum resources and the need for environmental protection, the development of bio-based flame retardants has received much attention. In order to explore the feasibility of fully biomass polyelectrolyte complexes (PEC) for polyolefin flame retardant applications, chitosan (CS), sodium alginate (SA), and sodium phytate (SP) were used to prepare CS-based fully biomass PEC intercalated montmorillonite (MMT) hybrid biomaterials (SA-CS@MMT and SP-CS@MMT). The effects of two hybrid biomaterials on the fire safety and mechanical properties of intumescent flame-retardant polypropylene (PP) composites were compared. The SP-CS@MMT showed the best flame retardancy and toughening effect at the same addition amount. After adding 5 wt% SP-CS@MMT, the limiting oxygen index (LOI) value of PP5 reached 30.9 %, and the peak heat release rate (pHRR) decreased from 1348 kW/m2 to 163 kW/m2. In addition, the hydrogen bonding between polyelectrolyte complexes significantly improved the mechanical properties of PP composites. Compared with PP2, the tensile strength of PP5 increased by 59 %. This study provided an efficient and eco-friendly strategy for the large-scale production of renewable biomaterials with good thermal stability and expanded the application of macromolecular biomaterials in the field of fire safety.

Morphological, Thermal, and Mechanical Assessment of Polypropylene and Ammonium Phosphate Composites Enhanced with Lignosulfonate and Zirconium

Polypropylene and ammonium phosphate (AP) composites were synthesized at a 25 wt% concentration. The changes in the morphological, thermal, and physical behavior of the composites were analyzed with the addition of lignosulfonate (LG) and zirconium phosphate (ZrP). Additionally, metallic zirconium was deposited onto lignosulfonate using the magnetron sputtering technique to develop polypropylene and zirconium-modified lignosulfonate (LGMod) composites. Thus, composites of PP/25AP, PP/25AP/8LG/5ZrP, and PP/25AP/8LGMod were synthesized. The synthesis involved mixing the materials in a Hake mixer, followed by compression molding. The composites were characterized by field emission scanning electron microscopy (SEM-EDS), a thermogravimetric analysis (TGA) with combustion parameters, a vertical burn test (UL-94), a thermal camera, and mechanical properties. All composites achieved a V2 rating according to UL-94 standards. The PP/25AP extinguishes flames more quickly compared to other materials, approximately 99.2% faster than PP and showed the lowest temperature variation and mass loss after burning. The PP/25AP/8LG/5ZrP composite exhibited a 7% higher rigidity and 84.5% better flame retardancy compared to pure PP. Additionally, substituting ZrP with LGMod led to a lower environmental impact and improved thermal properties, despite some mechanical disadvantages.

Analysis of the flame retardancy effect of boron-containing compound on polyester-cotton blended fabric

Flame-retardant finishing of textile materials is crucial for ensuring human safety and mitigating fire hazards. Though various textile fibers have inherent flame-resistant properties, cotton fiber has a higher affinity to burn. This research focused on developing non-durable FR treatments for cotton-rich polyester-cotton (T/C) blended products economically, using boron-containing compounds. Because of the high melting point use of borax on T/C fabric reduces the fabric's flammability. Boric acid was also used as an auxiliary substrate and Di-sodium hydrogen phosphate dihydrate was used for its cleaning and softening properties. Borax and boric acid create a layer of char when burned and stop the flame. We used the impregnation method for this finishing process. After the chemical finish on different types of T/C fabric, we completed different types of tests like 45 0 flame retardant, LOI, SEM, breaking strength, drapability, crease recovery, and water vapor transmission tests, and found the desired properties. It increased the flame retardancy and crease recovery properties but the slight reduction of the fabric strength was noticed in case of excessive coating. Water vapor transmission property also reduced gradually with the increase of chemical concentration. Since the chemicals are available in the local market and lower in cost than common FR chemicals, it is more economical.

Recent Developments of Nano Flame Retardants for Unsaturated Polyester Resin

For many years, efforts have been made to reduce the flammability of unsaturated polyester resins (UPRs), which are often used in the rail, shipbuilding, and construction industries. Without modification, they often fail to meet fire safety standards. Despite a rich history of flame retardants (FRs) applied to UPRs, researchers seek new solutions that will provide lower flammability and smoke density, as well as attaining a lower environmental impact from the composites. The objective of the study is to highlight the most important recent research on promising nano FRs in order to promote their further development. Mechanisms of action of several groups of nano FRs, such as clay-based, carbon-based, transition metal compounds, layered double hydroxides, polyhedral oligomeric silsesquioxanes, and others, including bio-based, have been studied. Particular emphasis has been laid on nano FRs applied to UPRs, and their influences on thermal stability, flammability, and mechanical properties. Moreover, the environmental impact and toxicity of nano FRs have been discussed. Results have proved that nano FRs applied at low loadings may significantly improve thermal stability, with a simultaneous increase or only a slight decrease in mechanical properties. However, attention on related environmental issues has highlighted the necessity of carefully selecting novel nano FRs.

Nanoclay-reinforced alginate aerogels: preparation and properties

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

Fire Retardant Phase Change Materials-Recent Developments and Future Perspectives

The accumulation of thermal energy in the form of latent heat of phase transition using phase change materials (PCMs) is one of the most attractive and studied research areas with huge application potential in both passive and active technical systems. The largest and most important group of PCMs for low-temperature applications are organic PCMs, mainly paraffins, fatty acids, fatty alcohols, and polymers. One of the major disadvantages of organic PCMs is their flammability. In many applications such as building, battery thermal management, and protective insulations, the crucial task is to reduce the fire risk of flammable PCMs. In the last decade, numerous research works have been performed to reduce the flammability of organic PCMs, without losing their thermal performance. In this review, the main groups of flame retardants, PCMs flame retardation methods as well as examples of flame-retarded PCMs and their application areas were described.

Kaolin-embedded cellulose hydrogel with tunable properties as a green fire retardant

This study reports the synthesis of methylene bisacrylamide (MBA) crosslinked cellulose-kaolin (CMK) composite hydrogels. The internal structures of hydrogels were deduced using network parameters, viz. elastic modulus, average molecular weight, mesh size, and effective crosslink. Meanwhile, combustion behavior was investigated using the cone calorimeter test (CCT), limiting oxygen index (LOI) test, vertical flammability test (VFT), and open fire test (OFT). Our results revealed that kaolin addition improves the fire retardancy of hydrogels but reduces their swelling ability. Hydrogel having cellulose to MBA ratio of 1:2 and 2 % w/v kaolin (CM2K2) produced 63 % wt. char residue and the hydrogel-coated cotton fabric exhibited the lowest heat release rate (HRR) of 26.60 kJ/m² and total heat release (THR) of 0.9 MJ/m². The LOI of the cotton fabric surged from 20 % to 34.37 % after hydrogel coating. Kinetic analysis using the isoconversional model yielded the highest activation energy (216 kJ/mol) for the CM2K2 hydrogel, corroborating the increased LOI after kaolin addition. VFT and OFT validated the delay in the burning process and the formation of a char layer, which protected the underlying layer of cotton from burning. Overall, cellulose-kaolin hydrogels developed in this study are effective green fire retardant coatings for flammable materials.

Development of a New Type of Flame Retarded Biocomposite Reinforced with a Biocarbon/Basalt Fiber System: A Comparative Study between Poly(lactic Acid) and Polypropylene

A new type of partially biobased reinforcing filler system was developed in order to be used as a flame retardant for polylactic acid (PLA) and polypropylene (PP)-based composites. The prepared materials intended for injection technique processing were melt blended using the novel system containing ammonium polyphosphate (EX), biocarbon (BC), and basalt fibers (BF). All of the prepared samples were subjected to a detailed analysis. The main criterion was the flammability of composites. For PLA-based composites, the flammability was significantly reduced, up to V-0 class. The properties of PLA/EX/BC and PLA/EX/(BC-BF) composites were characterized by their improved mechanical properties. The conducted analysis indicates that the key factor supporting the effectiveness of EX flame retardants is the addition of BC, while the use of BF alone increases the flammability of the samples to the reference level. The results indicate that the developed materials can be easily applied in industrial practice as effective and sustainable flame retardants.

Flame Retardant Coatings: Additives, Binders, and Fillers

This review provides an intensive overview of flame retardant coating systems. The occurrence of flame due to thermal degradation of the polymer substrate as a result of overheating is one of the major concerns. Hence, coating is the best solution to this problem as it prevents the substrate from igniting the flame. In this review, the descriptions of several classifications of coating and their relation to thermal degradation and flammability were discussed. The details of flame retardants and flame retardant coatings in terms of principles, types, mechanisms, and properties were explained as well. This overview imparted the importance of intumescent flame retardant coatings in preventing the spread of flame via the formation of a multicellular charred layer. Thus, the intended intumescence can reduce the risk of flame from inherently flammable materials used to maintain a high standard of living.

Recent Advances in Halogen-Free Flame Retardants for Polyolefin Cable Sheath Materials

With the continuous advancements of urbanization, the demand for power cables is increasing to replace overhead lines for energy transmission and distribution. Due to undesirable scenarios, e.g., the short circuit or poor contact, the cables can cause fire. The cable sheath has a significant effect on fire expansion. Thus, it is of great significance to carry out research on flame-retardant modification for cable sheath material to prevent fire accidents. With the continuous environmental concern, polyolefin (PO) is expected to gradually replace polyvinyl chloride (PVC) for cable sheath material. Moreover, the halogen-free flame retardants (FRs), which are the focus of this paper, will replace the ones with halogen gradually. The halogen-free FRs used in PO cable sheath material can be divided into inorganic flame retardant, organic flame retardant, and intumescent flame retardant (IFR). However, most FRs will cause severe damage to the mechanical properties of the PO cable sheath material, mainly reflected in the elongation at break and tensile strength. Therefore, the cooperative modification of PO materials for flame retardancy and mechanical properties has become a research hotspot. For this review, about 240 works from the literature related to FRs used in PO materials were investigated. It is shown that the simultaneous improvement for flame retardancy and mechanical properties mainly focuses on surface treatment technology, nanotechnology, and the cooperative effect of multiple FRs. The principle is mainly to improve the compatibility of FRs with PO polymers and/or increase the efficiency of FRs.

Recent Advances in Bio-Based Additive Flame Retardants for Thermosetting Resins

Thermosetting resins are used in many applications due to their great mechanical properties, chemical resistance, and dimensional stability. However, the flammability of thermosets needs to be improved to minimize fire risk and meet fire safety regulations. Some commercially available flame retardants have an adverse effect on people’s health and the environment. Thus, the development of novel, more sustainable flame retardants obtained or derived from biomass has become an objective of contemporary research. The objective of this study is to summarize recent progress on bio-based flame retardants for thermosetting resins so as to promote their prompt development. Groups of biomass compounds with a potential for flame retardant industrial applications were introduced, and their thermal degradation was investigated. The authors focused mostly on the thermal degradation of composites containing bio-based flame retardants determined by thermogravimetric analysis, their tendency to sustain a flame determined by a limiting oxygen index, and fire behavior determined by a cone calorimeter test. The results showed that the mode of action is mostly based on the forming of the char layer. However, in many cases, there is still a necessity to input a high amount of additive to achieve significant flame retardancy effects, which may adversely impact mechanical properties.

The Influence of Nanoparticles on Fire Retardancy of Pedunculate Oak Wood

Traditional flame retardants often contain halogens and produce toxic gases when burned. Hence, in this study, low-cost, environmentally friendly compounds that act as fire retardants are investigated. These materials often contain nanoparticles, from which TiO2 and SiO2 are the most promising. In this work, pedunculate oak wood specimens were modified with sodium silicate (Na2SiO3, i.e., water glass) and TiO2, SiO2, and ZnO nanoparticles using the vacuum-pressure technique. Changes in the samples and fire characteristics of modified wood were studied via thermal analysis (TA), infrared spectroscopy (FTIR), and scanning electron microscopy, coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). The results of TA showed the most significant wood decomposition at a temperature of 350 °C, with a non-significant influence of the nanoparticles. A dominant effect of sodium silicate was observed in the main weight-loss step, resulting in a drop in decomposition temperature within the temperature range of 36-44 °C. More intensive decomposition of wood treated with water glass and nanoparticles led to a faster release of non-combustible gases, which slowed down the combustion process. The results demonstrated that wood modifications using sodium silicate and nanoparticle systems have potentially enhanced flame retardant properties.

Fire Behavior of Wood-Based Composite Materials

Wood-based composites such as wood plastic composites (WPC) are emerging as a sustainable and excellent performance materials consisting of wood reinforced with polymer matrix with a variety of applications in construction industries. In this context, wood-based composite materials used in construction industries have witnessed a vigorous growth, leading to a great production activity. However, the main setbacks are their high flammability during fires. To address this issue, flame retardants are utilized to improve the performance of fire properties as well as the flame retardancy of WPC material. In this review, flame retardants employed during manufacturing process with their mechanical properties designed to achieve an enhanced flame retardancy were examined. The addition of flame retardants and manufacturing techniques applied were found to be an optimum condition to improve fire resistance and mechanical properties. The review focuses on the manufacturing techniques, applications, mechanical properties and flammability studies of wood fiber/flour polymer/plastics composites materials. Various flame retardant of WPCs and summary of future prospects were also highlighted.

Environmentally Friendly, High-Performance Fire Retardant Made from Cellulose and Graphite

Many materials and additives perform well as fire retardants and suppressants, but there is an ever-growing list of unfulfilled demands requiring new developments. This work explores the outstanding dispersant and adhesive performances of cellulose to create a new effective fire-retardant: exfoliated and reassembled graphite (ERG). This is a new 2D polyfunctional material formed by drying aqueous dispersions of graphite and cellulose on wood, canvas, and other lignocellulosic materials, thus producing adherent layers that reduce the damage caused by a flame to the substrates. Visual observation, thermal images and surface temperature measurements reveal fast heat transfer away from the flamed spots, suppressing flare formation. Pinewood coated with ERG underwent standard flame resistance tests in an accredited laboratory, reaching the highest possible class for combustible substrates. The fire-retardant performance of ERG derives from its thermal stability in air and from its ability to transfer heat to the environment, by conduction and radiation. This new material may thus lead a new class of flame-retardant coatings based on a hitherto unexplored mechanism for fire retardation and showing several technical advantages: the precursor dispersions are water-based, the raw materials used are commodities, and the production process can be performed on commonly used equipment with minimal waste.