Search Results (67)

Halogenated flame retardants have been amongst the most widely used and effective solutions for enhancing fire resistance. However, their use is currently strictly regulated due to serious health and environmental concerns. In this context, phosphorus-based and mineral flame retardants have emerged as promising alternatives. Despite this, their combined use is neither straightforward nor guaranteed to be effective. This study scrutinizes the interactions between these two classes of flame retardants (FR) through a systematic analysis aimed at elucidating the antagonistic pathways that arise from their coexistence. Specifically, this study focuses on two inorganic fillers, mineral huntite and chemically precipitated magnesium hydroxide, both of which produce basic oxides upon thermal decomposition. These fillers were incorporated into a poly(butylene terephthalate) (PBT) matrix to be utilized as advanced-mattress FR coating fabric and were subjected to a series of flammability tests. The pyrolysis products of the prepared polymeric composite compounds were isolated and thoroughly characterized using a combination of analytical techniques. Thermogravimetric analysis (TGA) and differential thermogravimetric analysis (dTGA) were employed to monitor decomposition behavior, while the char residues collected at different pyrolysis stages were examined spectroscopically, using FTIR-ATR and Raman spectroscopy, to identify their structure and the chemical reactions that led to their formation. X-ray diffraction (XRD) experiments were also conducted to complement the spectroscopic findings in the chemical composition of the resulting char residues and to pinpoint the different species that constitute them. The morphological changes of the char’s structure were monitored by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). Finally, the Limited Oxygen Index (LOI) and UL94 (vertical sample mode) methods were used to assess the relative flammability of the samples, revealing a significant drop in flame retardancy when both types of flame retardants are present. This reduction is attributed to the neutralization of acidic phosphorus species by the basic oxides generated during the decomposition of the basic inorganic fillers, as confirmed by the characterization techniques employed. These findings underscore the challenge of combining organophosphorus with popular flame-retardant classes such as mineral or basic metal flame retardants, offering insight into a key difficulty in formulating next-generation halogen-free flame-retardant composite coatings. Full article

Silica fume-based geopolymer composite coatings, an approach to using metallurgical solid waste, exert flame retardancy with ecological, halogen-free, and environmentally friendly advantages, but their fire resistance needs to be improved further. Herein, a silica fume-based geopolymer composite flame-retardant coating was designed by doping boric acid (BA), zinc phytate (ZnPA), and melamine (MEL). The results of a cone calorimeter demonstrated that appropriate ZnPA and BA significantly enhanced its flame retardancy, evidenced by the peak heat release rate (p-HRR) decreasing from 268.78 to 118.72 kW·m⁻², the fire performance index (FPI) increasing from 0.59 to 2.83 s·m²·kW⁻¹, and the flame retardancy index increasing from 1.00 to 8.48, respectively. Meanwhile, the in situ-formed boron phosphate (BPO₄) facilitated the residual resilience of the fire-barrier layer. Furthermore, the pyrolysis kinetics indicated that the three-level chemical reactions governed the pyrolysis of the coatings. BPO₄ made the pyrolysis E_α climb from 94.28 (P5) to 127.08 (B3) kJ·mol⁻¹ with temperatures of 731–940 °C, corresponding to improved thermal stability. Consequently, this study explored the synergistic flame-retardant mechanism of silica fume-based geopolymer coatings doped with ZnPA, BA, and MEL, providing an efficient strategy for the high-value-added recycling utilization of silica fume. Full article

This study explores the flame retardancy and structural behavior of silicone foam composites filled with halogen-free flame retardants, aiming to evaluate their feasibility for use in mass transportation applications. Silicone foam specimens incorporating magnesium hydroxide and expandable graphite were prepared and compared with unfilled silicone foam under both static and dynamic loading conditions. Uniaxial compression and simple shear tests were conducted to assess mechanical behavior, and a second-order Ogden model was employed to represent hyperelasticity in the finite element analysis. Fire performance was evaluated using cone calorimeter tests in accordance with ISO 5660-1. The results showed a 53.6% reduction in peak heat release rate (PHRR) and a 48.1% decrease in MARHE upon the addition of flame retardants, satisfying relevant fire safety standards. Although the addition of fillers increased the compressive stiffness and reduced rebound resilience, static comfort indices remained within acceptable ranges. These findings confirm that halogen-free filled silicone foams exhibit significantly enhanced fire retardancy while maintaining sufficient mechanical integrity and seating comfort, demonstrating their potential as eco-friendly alternatives to conventional polyurethane foams in large-scale transportation applications. Full article

Polyurethane (PUR)-based artificial leathers are often used as interior materials in public area, making flame retardants (FRs) necessary. The mode of action of different FRs varies depending on the chemical class and the structure of the supplied material. Usually, FRs are designed for bulk materials like foams, e.g., for upholstery, the main application of PUR. However, in thin materials, FRs act differently, thus leaving the PUR without sufficient flame resistance. In this study, PUR films and artificial leathers were equipped with twelve commercially available, halogen-free FRs in various concentrations and combinations. Fire resistance was tested with LOI measurements, cone calorimetry, horizontal burning behavior, and thermogravimetric analyses. An organophosphorus FR proved to be the most suited for flame-resistant artificial leather. The LOI was increased from 20 to 24.2%, the peak heat release rate was reduced by about 30%, and the sample was self-extinguishing in horizontal burning behavior. Phosphinates and aluminum trihydroxide were the least efficient FRs. Combinations of bentonite with phosphorus-based FRs showed synergistic effects in reducing the probability of igniting the material. The results demonstrate that sufficient flame retardancy for PUR-based thin materials can be achieved with commercially available halogen-free FRs, paving the way for more sustainable and greener materials by substituting ecologically harmful and health-damaging FRs. Full article

The foamed structure of recycled polyethylene-terephthalate (rPET) is a promising solution for industrial applications; however, the remedy for its inherent melt-dripping property is still a challenging topic. In our research, we were able to improve the flame retardancy of the endothermic–exothermic hybrid rPET foam by adding a different mixture of flame retardants to the formula. Three different kinds of halogen-free flame retardant agents were used: ammonium polyphosphate-based Exolit AP 422 (AP), organic aluminum phosphate in the form of Exolit OP 1240 (OP), and Budit 342 containing melamine polyphosphate (MPP). The hybrid flame retardant mixture, by combining the swelling and charring mechanism, increased the flame retardancy of the samples. The sample made with 15 phr OP and 5 phr MPP displayed outstanding performance, where five samples were capable of self-extinguishing in 5 s, while only slightly decreasing the tensile and flexural strength properties and simultaneously increasing the Young and flexural modulus compared to the reference sample. The addition of MPP reduced the porosity in many cases, while preventing cell coalescence. Our results prove that the hybrid flame retardant agent frameworks efficiently increase the flame retardancy of rPET foams, facilitating their application in industrial sectors such as the aerospace, packaging, renewable energy, and automotive industries to realize sustainability goals. The utilization of halogen-free flame retardants is beneficial for better air quality, reducing toxic gas and smoke emissions. Full article

In the present work, carbonate minerals are added in non-polar and polar polymer matrices to develop halogen-free flame-retardant composites. The examined fillers of calcium carbonate and magnesium carbonate delivered improved rheological performance in both non-polar (PE) and polar (EVA/PE) polymer compounds compared to the natural magnesium hydroxide and huntite/hydromagnesite mineral fillers. The presence of EVA in the matrix enhanced the mechanical behavior of all compounds in tensile testing. The thermal stability of the composites was particularly improved for the polar systems with the incorporation of the carbonate minerals, as this was evidenced under thermogravimetric analysis. The dielectric behavior of the fabricated systems was examined via broadband dielectric spectroscopy. The HFFR compounds attained higher values of the real part of dielectric permittivity from the unreinforced systems in the whole frequency and temperature range of the conducted tests. This behavior is ascribed to the higher permittivity values of the fillers with respect to the polymer matrices and the occurrence of interfacial polarization. All minerals improved the flame retardancy of the compounds in terms of LOI values, while the addition of EVA yielded further improvements, especially for the magnesium carbonate and the magnesium hydroxide minerals. Full article

A typical halogen-free flame-retardant (HFFR) formulation for electric cables may contain polymers, various additives, and fire-retardant fillers. In this study, composites are prepared by mixing natural magnesium hydroxide (n-MDH) with linear low-density polyethylene (LLDPE) and a few types of ethylene–octene copolymers (C₈-POE). Depending on the content of LLDPE and C₈-POE, we obtained composites with different crystallinities that affected the final mechanical properties. The nucleation effect of the n-MDH and the variations in crystallinity caused by the blending of C₈-POE/LLDPE/n-MDH were investigated. Notably, in the C₈-POE/LLDPE blend, we found a decrease in the crystallization temperature of LLPDE compared to pure LLDPE and an increase in the crystallization temperature of C₈-POE compared to pure C₈-POE. On the contrary, the addition of n-MDH led to an increase in the crystallization temperature of LLDPE. As expected, the increase in the crystallinity of the polyolefin matrix of composites led to higher elastic modulus, higher tensile strength, and lower elongation at break. It has been observed that crystallinity also influences fire performance. Overall, these results show how to obtain the required mechanical features for halogen-free flame-retardant compounds for electric cable applications, depending on the quantities of the two miscible components in the final blend. Full article

Despite the mechanical and physical properties of polyurethane foams (PUF), their application is still hindered by high inflammability. The elaboration of effective, low-cost, and environmentally friendly fire retardants remains a pressing issue that must be addressed. This work aims to show the feasibility of the successful application of natural nanomaterials, such as halloysite nanotubes and nanocellulose, as promising additives to the commercial halogen-free, fire-retardant triphenyl phosphate (TPP) to enhance the flame retardance of open-cell polyurethane foams. The nanocomposite foams were synthesized by in situ polymerization. Investigation of the mechanical properties of the nanocomposite PUF revealed that the nanoscale additives led to a notable decrease in the foam’s compressibility. The obtained results of the flammability tests clearly indicate that there is a prominent synergetic effect between the fire-retardant and the natural nanoscale additives. The nanocomposite foams containing a mixture of TPP (10 and 20 parts per hundred polyol by weight) and either 10 wt.% of nanocellulose or 20 wt.% of halloysite demonstrated the lowest burning rate without dripping and were rated as HB materials according to UL 94 classification. Full article

With the rapid development of electronic information technology, higher requirements have been put forward for the dielectric properties and load-bearing capacity of materials. In continuous glass fiber-reinforced thermoplastic composites, polypropylene matrix is a non-polar polymer with a very low dielectric constant and dielectric loss, but polypropylene is extremely flammable which greatly limits its application. Aiming at the better application of flame retardant-modified continuous glass fiber-reinforced polypropylene composites (FR/GF/PP) in the field of electronic communication, the effects of four different kinds of flame retardants (Decabromodiphenyl ethane (DBDPE), halogen-free one-component flame retardant (MONO), halogen-free compound flame retardant (MULTI), and intumescent flame retardant (IFR)) on the properties of FR/GF/PP were compared, including the mechanical properties, dielectric properties and flame-retardant properties. The results showed that among the FR/GF/PP, IFR has the highest performance in mechanical properties, MULTI has better performance in LOI, DBDPE and IFR have better performance in flame retardant rating, and DBDPE and IFR have lower dielectric properties. Finally, gray relational analysis is applied to propose an approach for selecting the optimal combination (flame retardant type and flame-retardant content) of comprehensive performance. In the application exemplified in this paper, the performance of IFR-3-modified GF/PP is optimized. Full article

Conduits are plastic tubes extensively used to safeguard electrical cables, traditionally made from PVC. Recent safety guidelines seek alternatives due to PVC’s emission of thick smoke and toxic gases upon fire incidents. Polypropylene (PP) is emerging as a viable alternative but requires modification with suitable halogen-free additives to attain flame retardancy (FR) while maintaining high mechanical strength and weathering resistance, especially for outdoor applications. The objective of this study was to develop two FR systems for PP: one comprising a cyclic phosphonate ester and a monomeric N-alkoxy hindered amine adjuvant achieving V0, and another with hypophosphite and bromine moieties, along with a NOR-HAS adjuvant achieving V2. FR performance along with mechanical properties, physicochemical characterization, and dielectric behavior were evaluated prior to and after 2000 h of UV weathering or heat ageing. The developed FR systems set the basis for the production of industrial-scale masterbatches, from which further optimization to minimize FR content was performed via melt mixing with PP towards industrialization of a low-cost FR formulation. Accordingly, two types of corrugated conduits (ø20 mm) were manufactured. Their performance in terms of flame propagation, impact resistance, smoke density, and accelerated UV weathering stability classified them as Halogen Free Low Smoke (HFLS) conduits; meanwhile, they meet EU conduit standards without significantly impacting conduit properties or industrial processing efficiency. Full article

Halogen-free organophosphorus flame retardants have promising application prospects due to their excellent safety and environmental protection properties. A cobalt-coordinated cyclic phosphonitrile flame retardant (Co@CPA) was synthesized via a hydrothermal method using hexachlorocyclotriphosphonitrile (HCCP), 5-amino-tetrazolium (5-AT), and cobalt nitrate hexahydrate (Co(NO₃)2∙6H₂O) as starting materials. The structure was characterized using Fourier transform infrared (FTIR), nuclear magnetic resonance spectroscopy (1H-NMR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Thermoplastic polyurethane (TPU) composites were prepared by incorporating 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphame-10-oxide (ODOPB), Co@CPA, and silicon dioxide (SiO₂) via melt blending. The flame-retardant performance and thermal stability of the TPU composites were evaluated through limiting oxygen index (LOI), vertical combustion (UL-94), TG, and cone calorimetric (CCT) tests. SEM and Raman spectroscopy were used to analyze the surface morphology and structure of the residual carbon. A synergistic flame-retardant effect of ODOPB and Co@CPA was observed, with the most effective flame retardancy achieved at a TPU:ODOPB:Co@CPA:SiO₂ ratio of 75:16:8:1. This composition exhibited an LOI value of 26.5% and achieved a V-0 rating in the UL-94 test. Furthermore, compared to pure TPU, the composite showed reductions in total heat release, CO production, and CO₂ production by 6.6%, 39.4%, and 48.9%, respectively. Our research findings suggest that Co@CPA demonstrates outstanding performance, with potential for further expansion in application areas. Different metal-based cyclic phosphonitrile compounds are significant in enriching phosphorus-based fine chemicals. Full article

Polymeric materials, renowned for their lightweight attributes and design adaptability, play a pivotal role in augmenting fuel efficiency and cost-effectiveness in railway vehicle development. The tailored formulation of compounds, specifically designed for additive manufacturing, holds significant promise in expanding the use of these materials. This study centers on poly(lactic acid) (PLA), a natural-based biodegradable polymeric material incorporating diverse halogen-free flame retardants (FRs). Our investigation scrutinizes the printability and fire performance of these formulations, aligning with the European railway standard EN 45545-2. The findings underscore that FR in the condensed phase, including ammonium polyphosphate (APP), expandable graphite (EG), and intumescent systems, exhibit superior fire performance. Notably, FR-inducing hydrolytic degradation, such as aluminum hydroxide (ATH) or EG, reduces polymer molecular weight, significantly impacting PLA’s mechanical performance. Achieving a delicate balance between fire resistance and mechanical properties, formulations with APP as the flame retardant emerge as optimal. This research contributes to understanding the fire performance and printability of 3D-printed PLA compounds, offering vital insights for the rail industry’s adoption of polymeric materials. Full article

Polyurethane (PUR), as an engineering polymer, is widely used in many sectors of industries. However, the high fire risks associated with PUR, including the smoke density, a high heat release rate, and the toxicity of combustion products limit its applications in many fields. This paper presents the influence of silsesquioxane fillers, alone and in a synergistic system with halogen-free flame-retardant compounds, on reducing the fire hazard of polyurethane foams. The flammability of PUR composites was determined with the use of a pyrolysis combustion flow calorimeter (PCFC) and a cone calorimeter. The flammability results were supplemented with smoke emission values obtained with the use of a smoke density chamber (SDC) and toxicometric indexes. Toxicometric indexes were determined with the use of an innovative method consisting of a thermo-balance connected to a gas analyzer with the use of a heated transfer line. The obtained test results clearly indicate that the used silsesquioxane compounds, especially in combination with organic phosphorus compounds, reduced the fire risk, as expressed by parameters such as the maximum heat release rate (HRRmax), the total heat release rate (THR), and the maximum smoke density (SDmax). The flame-retardant non-halogen system also reduced the amounts of toxic gases emitted during the decomposition of PUR, especially NOx, HCN, NH₃, CO and CO₂. According to the literature review, complex studies on the fire hazard of a system of POSS–phosphorus compounds in the PUR matrix have not been published yet. This article presents the complex results of studies, indicating that the POSS–phosphorous compound system can be treated as an alternative to toxic halogen flame-retardant compounds in order to decrease the fire hazard of PUR foam. Full article

Currently, the mechanical performance reduction caused by excessive phosphorus content in the halogen-free flame-retardant EP has been an obstacle to its extensive application. This study presents the effective synthesis of a novel flame-retardant BDD with great efficiency, achieving an optimum phosphorus level of merely 0.25 wt %. The structure of BDD was verified by FTIR, ¹H NMR, ³¹P NMR and XPS spectra. To investigate the flame-retardant properties of BDD, several EPs with various phosphorus levels were synthesized. The addition of phosphorus to the EP significantly increases its LOI value from 25.8% to 33.4% at a phosphorus level of 0.25 wt%. Additionally, the resin achieves a V-0 grade in the UL 94 test. The P-HRR and THR of the modified resin measured by the cone calorimeter are also significantly reduced. At the same time, the addition of a modest quantity of BDD has a minimal impact on the mechanical properties of epoxy resin. This study shows that the removal of hydroxyl groups significantly enhances the fire resistance of phosphate-based flame retardants, thereby providing a novel approach to synthesizing efficient flame retardants. Full article

Wildfires are becoming more intense and more frequent, ravaging the habitations and ecosystems in their path. One solution to reducing the risk of damage to buildings and other structures during a fire event is the use of fire-retardant coatings that can stop or slow down the spread of flames, especially for textile materials. The present study focuses on the preparation and application of halogen-free boron/bentonite-based polymeric fire-retardant (FR) hybrid coating formulations for fabrics such as cotton (CO) and polyester (PE) fibers. For the preparation of FR composites, two types of boron derivatives, disodium octaborate and zinc borate, were used in combination with sodium bentonite. A styrene-acrylic copolymer was specifically synthesized and used as a coating binder for FR components to apply on fabrics. The properties of the synthesized copolymer and FR composites were characterized with a particle size analysis, FTIR spectroscopy, a dynamic mechanical thermal analysis (DMTA), and rheological measurements. The obtained hybrid composites based on styrene-acrylic copolymers and two different inorganic fillers were applied on cotton (CO) and polyester (PE) fabrics with a screen-printing technique, and the flame retardancy performance of the finished textile samples was investigated by means of flame spread and limit oxygen index (LOI) tests. The findings showed that the FR-composite-coated fabrics had higher LOI values and much decreased flame spread rates in comparison with uncoated ones. Among the boron derivatives, the composites prepared with disodium octaborate (FR-A) had much more pronounced LOI values and decreased flame spread behavior in comparison with the composite with zinc borate (FR-B). When compared to a commercial product, the FR-A composite, in conjunction with the specially synthesized polymer, demonstrated commendable fire retardancy performance and emerged as a promising candidate for a halogen-free waterborne fire-retardant coating for fabrics. Full article