Phosphorus-based Flame Retardants Research Articles

Phosphorus-based flame retardant acrylic pressure sensitive adhesives with superior peel strength and transfer characteristics

Acrylic pressure sensitive adhesives (PSAs) are widely utilized in various fields due to their excellent thermal, weather, and oil resistance. However, due to their flammability, they are vulnerable to fire, which brings a critical challenge for their application in various industries. Here, new phosphorus-based acrylic PSAs which show excellent flame retardancy are demonstrated, without sacrificing adhesion properties. By controlling the monomer composition based on five different monomers, we synthesized seven acrylic copolymers for PSAs, and investigated the correlation between monomer composition and adhesion characteristics in terms of peel strength and transfer characteristics. Among seven polymers, A5H5 which exhibits the highest peel strength (1117 gf/in.) and superior transfer characteristics (transfer area 8.30 %) is selected for further investigation. The phosphorous-based acrylic PSAs are prepared through addition of different amounts of dimethyl methylphosphonate in A5H5 polymeric matrix, and thoroughly investigated in terms of flame retardancy and adhesion characteristics in terms of peel strength and transfer characteristics. The phosphorus-based PSA (A5H5-D30) exhibited superior flame retardancy of V-0 rating under the UL-94 characterization method. Furthermore, the A5H5-D30 present excellent film transfer characteristic showing a transfer area of 0 % and residue of 0 wt% in air without massive decrease in peel strength (991 gf/in.).

The effect of phosphorus based flame retardants on the thermal and fire retardant properties of chicken feather/thermoplastic polyurethane composites

The aim of the study was to enhance the flame-retardant properties of chicken feather (CF) reinforced thermoplastic polyurethane (TPU) composites by incorporating three different phosphorus-based flame retardants, namely aluminum hypophosphite (AHP), ammonium polyphosphate (APP), and aluminum diethyl phosphinate (AlPi), at concentrations of 5, 10, and 20 wt%. The effectiveness of the additives was evaluated through various tests, including limiting oxygen index (LOI), vertical burning test (UL 94 V), thermogravimetric analysis (TGA), and mass loss calorimeter test (MLC). The results indicated that all three additives exhibited flame retardant properties in both the condensed and gas phases, but APP and AHP performed better than AlPi due to their enhanced char formation capabilities. The flame retardant effectiveness of the additives decreased in the order of APP > AHP > AlPi.

Synthesis and evaluation of an eco-friendly and durable flame-retardant cotton fabrics based on a high-phosphorous-content

Cotton fabrics are extremely flammable. Therefore, ammonium salt of dipentaerythritol hexaphosphoric acid (ADPHPA), a novel reactive phosphorus flame retardant without halogen and formaldehyde, was synthesized by solvent-free synthesis method. Surface chemical graft modification was chosen to introduce flame retardant, imparting its flame retardancy and washability. SEM indicated that ADPHPA entered the interior of cotton fiber, which was grafted with OH of control cotton fabrics (CCF) by forming POC covalent bonds to obtain treated cotton fabrics (TCF). There were no apparent differences in the fiber morphology and crystal structure after treatment according to SEM and XRD analysis. TG analysis demonstrated that the decomposition process of TCF was changed compared with CCF, while lower heat release rate and total heat release of TCF indicated its combustion efficiency was also reduced based on cone calorimetry test. Meanwhile, in the durability test, TCF had undergone 50 laundering cycles (LCs) in accordance with AATCC-61-2013 3A standard and had a short vertical combustion charcoal length, which were able to be regard as durable flame-retardant fabrics. The mechanical properties of TCF decreased to a degree, but did not affect the actual use of cotton fabrics. Taken as a whole, ADPHPA has research significance and development potential as a durable phosphorus-based flame retardant.

High-Efficient Flame-Retardant Finishing of Cotton Fabrics Based on Phytic Acid.

In this study, an efficient phosphorus-containing flame retardant, PAPBTCA, was synthesized from phytic acid, pentaerythritol, and 1,2,3,4-butane tetracarboxylic acid, and its structure was characterized. PAPBTCA was finished on cotton fabrics by the pad-dry-curing process, and the flame retardancy, flame-retardant durability, and wrinkle resistance of the obtained flame-retardant fabrics were investigated. It should be noted that the heat release rate value of the flame-retardant cotton fabrics treated with 200 g/L PAPBTCA decreased by 90% and its excellent flame retardancy was maintained after 5 washing cycles. Meanwhile, the wrinkle resistance of flame-retardant cotton fabrics has been significantly improved. In addition, compared with the control, the breaking force loss of PAPBTCA-200 in the warp and weft directions was 24% and 21%, respectively. This study provides a new way to utilize natural phosphorus-based flame retardants to establish multifunctional finishing for cotton fabrics.

Exposure to nitrogenous based flame retardants in Chinese population: Evidence from a national-scale study

Extensive use of nitrogen-based flame retardants (NFRs) has resulted in their widespread environmental occurrence. To investigate human exposure to NFRs on a national scale, the abundance and spatial distribution of NFRs were assessed in urine specimens collected from 13 cities in China. Six out of eight target NFRs were detectable in more than half of the urine samples, and the total concentrations of NFRs ranged from 3.22 to 880 ng/mL with a median of 46.7 ng/mL. Cyanuric acid was the most abundant chemical, accounting for 66.2%, followed by melamine (16.3%), ammelide (10.8%), and ammeline (6.11%). Regional differences in concentrations and composition profiles of NFRs were observed within China as a result of different production and application profiles. In addition, we found that urinary NFRs levels were much higher than but statistically correlated with that of organophosphates (r2 = 0.69, p < 0.05), another class of phosphorus-based flame retardant, implying similar emission sources and/or human exposure pathways. Furthermore, the estimated daily intakes and hazard quotients revealed that the Chinese population's exposure to NFRs is within safe limits. To the best of our knowledge, this is the first study to document the ubiquitous occurrence and region-specific variations of human exposure to NFRs in China.

A Bridge-Linked Phosphorus-Containing Flame Retardant for Endowing Vinyl Ester Resin with Low Fire Hazard

The high flammability of vinyl ester resin (VE) significantly limits its widespread application in the fields of electronics and aerospace. A new phosphorus-based flame retardant 6,6'-(1-phenylethane-1,2 diyl) bis (dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (PBDOO), was synthesized using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and acetophenone. The synthesized PBDOO was further incorporated with VE to form the VE/PBDOO composites, which displayed an improved flame retardancy with higher thermal stability. The structure of PBDOO was investigated using Fourier transformed infrared spectrometry (FTIR) and nuclear magnetic resonances (NMR). The thermal stability and flame retardancy of VE/PBDOO composites were investigated by thermogravimetric analysis (TGA), vertical burn test (UL-94), limiting oxygen index (LOI), and cone calorimetry. The impacts of PBDOO weight percentage (wt%) on the flame-retardant properties of the formed VE/PBDOO composites were also examined. When applying 15 wt% PBDOO, the formed VE composites can meet the UL-94 V-0 rating with a high LOI value of 31.5%. The peak heat release rate (PHRR) and the total heat release (THR) of VE loaded 15 wt% of PBDOO decreased by 76.71% and 40.63%, respectively, compared with that of untreated VE. In addition, the flame-retardant mechanism of PBDOO was proposed by analyzing pyrolysis behavior and residual carbon of VE/PBDOO composites. This work is expected to provide an efficient method to enhance the fire safety of VE.

Synergistic Enhancement of Flame Retardancy Behavior of Glass-Fiber Reinforced Polylactide Composites through Using Phosphorus-Based Flame Retardants and Chain Modifiers.

Flame retardancy properties of neat PLA can be improved with different phosphorus-based flame retardants (FRs), however, developing flame retardant PLA-based engineering composites with maintained mechanical performance is still a challenge. This study proposes symbiosis approaches to enhance the flame retardancy behavior of polylactide (PLA) composites with 20 wt% short glass fibers (GF). This was first implemented by exploring the effects of various phosphorus-based FRs up to 5 wt% in neat PLA samples. Among the used phosphorus-based FRs, the use of only 3 wt% of diphosphoric acid-based FR (P/N), melamine coated ammonium polyphosphate (APPcoated), and APP with melamine synergist (APP/Mel) resulted in achieving the V0 value in a vertical burning test in the neat PLA samples. In addition to their superior efficiency in improving the flame retardancy of neat PLA, P/N had the least negative effect on the final mechanical performance of PLA samples. When incorporated in PLA composites with 20 wt% GF, however, even with the use of 30 wt% P/N, the V0 value could not be obtained due to the candlewick effect. To resolve this issue, the synergistic effect of P/N and aromatic polycarbodiimide (PCDI) cross-linker or Joncryl epoxy-based chain-extender (CE) on the flame retardancy characteristics of composites was examined. Due to the further chain modification, which also enhances the melt strength of PLA, the dripping of composites in the vertical burning test terminated and the V0 value could be reached when using only 1 wt% PCDI or CE. According to the scanning electron microscopic analysis, the use of noted chain modifiers further homogenized the distribution and refined the particle size of P/N within the PLA matrix. Hence this could synergistically contribute to the enhancements of the fire resistance performance of the PLA composites. Such incorporation of P/N and chain modifiers further leads to the enhancement of the mechanical performance of PLA composites and hence the resultant product can be proposed as a promising durable bioplastic engineering product where fire risk exists.

Influence of phosphorus-based flame retardants on polypropylene insulation for high-voltage power cable applications

For high voltage (HV) power cable applications, various studies have been performed to improve the mechanical and electrical properties of polypropylene (PP)-based insulation materials to replace crosslinked polyethylene. However, studies on the effect of additives to yield additional PP properties are still lacking. Herein, we prepared PP blends by melt-mixing widely used commercial flame retardants for PP with isotactic PP (iPP) and investigated their electrical breakdown, flame retardancy behaviors, and UV stability. Among the five kinds of flame retardants employed, aluminum hypophosphite (AHP), aluminum diethyl phosphinate, melamine pyrophosphate, ammonium polyphosphate (APP), and APP treated with silane, AHP was very effective in minimizing the decrease of the direct current breakdown strength of iPP at both 25 °C and 110 °C in the range of 5–20 phr. Particularly, only AHP afforded V-2 grade flame retardancy to iPP, and the flame retardancy was maintained even when the content was reduced to 3 phr. Furthermore, upon exposure to ultraviolet (UV) rays for 5 d, the tensile strength of pristine iPP decreased by approximately 44%, while that of a blend with 3 phr AHP decreased by only 10%. The study results will contribute to the optimization of power cable products through the use of appropriate flame retardants in the design of high-performance PP-based HV insulation materials.

Synthesis of a phosphorus-based epoxy reactive flame retardant analog to diglycidyl ether of bisphenol A (DGEBA) and its behavior as a matrix in a carbon fiber composite

This paper describes the synthesis of a phosphorus-based flame retardant that is a chemical analog of diglycidyl ether of bisphenol A (DGEBA), as well as its incorporation as a matrix into carbon fiber laminates. Carbon fiber composites, if used for structural applications in mass transport vehicles (aircraft, trains), will require some aspects of improved fire performance to be used safely in those applications. The first phase of work involved the development of two separate synthesis routes to produce the flame retardant monomer, referred to as Phosphorus-DGEBA or simply P-DGEBA. The second step was to determine the viability of the compound's polymerization behavior through various experimental mixing formulations and curing conditions with an aliphatic amine curing agent. Differential scanning calorimetry (DSC) was used to evaluate the curing behavior of P-DGEBA when mixed with DGEBA and an aliphatic amine curing agent and dynamic mechanical analysis (DMA) was used to observe the glass transition temperature (Tg) of the carbon fiber composites. Thermogravimetric analysis (TGA) was also used to investigate the thermal stability and thermal degradation behaviors of the P-DGEBA/DGEBA blends. The final step included the fabrication of composites and their flammability testing using a cone calorimeter. DMA testing for P-DGEBA measured a Tg that was 10 °C higher than a DGEBA based carbon fiber composite, and DSC studies found that the P-DGEBA / DGEBA blend polymerized well with the amine curing agent. The TGA, MCC, and cone calorimeter data yielded mixed results with TGA and MCC suggesting a more condensed phase / char formation flame retardant activity for P-DGEBA, while cone calorimeter suggested a more vapor phase flame retardant activity. Overall, the P-DGEBA shows some promise as a reactive FR for epoxy + carbon fiber composites, but more study is needed.

A universal strategy toward flame retardant epoxy resin with ultra-tough and transparent properties

Flame-retardant epoxy composites have important application value in flexible optoelectronic devices, artificial intelligence and 5G fields. The flame retardancy of these composites, however, are often promoted at the expense of mechanical properties and transparency, particularly the toughness. In this work, we propose a simple strategy of introducing proper rigid-flexible groups into phosphorus-based flame retardant which realizes a dual performance improvement simultaneously in epoxy resin. The modified flame retardant epoxy resin has a limiting oxygen index (LOI) value of 32.3%, a high transmittance of approximately 92%, an excellent smoke and heat suppression properties. Remarkably, the addition of phosphorus-based flame retardant containing rigid-flexible groups (TOD) significantly enhances the mechanical properties of epoxy resin, especially the toughness. The impact strength is obviously increased from 6.8 kJ/m2 to 25.2 kJ/m2, with an increase of 271%, which mainly due to the flexible Si-O segment in TOD. This work provides a universal strategy for the design of flame retardant, ultra-tough and transparent epoxy resin, implying its enormous potential to promote the commercial application of epoxy resin.

Mechanical Properties of Polypropylene-Based Flame Retardant Composites by Surface Modification of Flame Retardants.

A flame retardant refers to a substance that can be added to a material having the property of being efficiently combusted to improve the material physically and chemically. It should not affect the physical properties required for the final product. Halogen-based compounds are representative flame retardants with excellent flame retardancy. However, their use is limited due to restrictions on the use of chemicals introduced due to human safety. Magnesium hydroxide, one alternative material of halogen flame retardants, is widely used as an eco-friendly flame retardant. However, the most significant disadvantage is high load. To find a solution to this problem, many studies have been conducted by mixing magnesium hydroxide with other additives to create a synergistic effect. In this study, flame retardancy and mechanical properties of polypropylene-based flame retardant composites as a function of mixing surface-modified magnesium hydroxide with phosphorus-based flame retardants were investigated. All materials including PP, additives, and flame retardants were mixed using an extrusion process. Specimens were prepared by an injection process of the compound made after mixing. As a result of the evaluation of the mechanical properties by the modified flame retardant, the relational expression of the mechanical performance degradation as a function of the amount of addition was obtained, and the tensile (CBATS) and bending strength (CBABS) were performed on the amount of flame retardant added. The relational expression obtained in this study is considered to be a formula for predicting the strength reduction according to the addition amount of the modified flame retardant and can be used in industry. In addition, it was found that the addition amount of the modified flame retardant had a greater effect on the lowering of the bending strength.

Phosphorus-free hyperbranched polyborate flame retardant: Ultra-high strength and toughness, reduced fire hazards and unexpected transparency for epoxy resin

The design of high transparent epoxy resins (EPs) with excellent flame retardancy and mechanical strength is still intractable, while the current use of phosphorus-based flame retardant usually destroys the transparency and color of EPs. This work reports a phosphorus-free hyperbranched polyborate (HBPB) as a multifunctional flame retardant additive for EPs. The HBPB was synthesized via a facile, one-pot, solvent- and catalyst-free polycondensation with branched aliphatic backbone and borate group, which features good compatibility within resin matrix and does not affect its curing processability. Compared to neat EP, the as-constructed EP composite with 9% addition of HBPB displays the high fire resistance (30.2% LOI value and UL-94 V0 rating), and the fire hazards such as smoke, heat and toxic gases release are significantly reduced without introducing phosphorus group. Surprisingly, the EP material can well maintain its high transparency and color with ultra-high toughness (21.38–40.50 kJ m−2) and flexural strength (137.03–197.08 MPa) achieved, especially the glass-transition temperature can be improved from 150 °C to 170 °C, making it superior to previously described counterparts. Highlighting the compelling results, this work provides a promising candidate on seeking the halogen-free solutions to alleviate the high price of phosphorus-based FRs, and paves a useful strategy toward designing high transparent, high-performance polymeric materials.

Revealing and modeling of fire products in gas-phase for epoxy/black phosphorus-based nanocomposites

This work aims at revealing and optimizing the mechanism, to promote the design of phosphorus-based flame retardants (PFRs) for controlling the spread of fire risk caused by the continuous spread of polymers. Herein, we synthesized about 10 nm TiO2 grown in situ on the surface of BP through a simple hydrothermal procedure to introduce it into epoxy (EP/BP-TiO2). In the first place, EP/BP-TiO22.0 nanocomposite achieves a reduction of 58.96% and 50.35% in PHRR and THR, respectively. Secondly, the pyrolysis of BP from Pn to P4, P3 and P2 is revealed. As a guide, P4 is established as a characteristic product of the analytical model for evaluating the effects in the gas phase for BP-based hybrids. Finally, this work clarifies the enhancement path for BP-TiO2 is optimized for the capturing of OH· and H· radicals by P4(POx). Crucially, this study reveals and controls the mechanism of the BP-based hybrids at the molecular level, which is expected to provide a promising analytical model for broad market PFRs design to address the risks and challenges of casualties and ecology caused by composites fire.

Preparation of Ni-Fe layered double hydroxides and its application in thermoplastic polyurethane with flame retardancy and smoke suppression

Aluminum hypophosphite (AHP), as an effective phosphorus-based flame retardant used in thermoplastic polyurethane (TPU), released a large amount of smoke and toxic gasses during combustion. In this work, a flame retardant filler, Ni-Fe layered double hydroxides (NiFe-LDHs), was synthesized and applied in TPU together with AHP. The limiting oxygen index (LOI) of the TPU/6AHP/1NiFe-LDH composite reached 30.7% with a V-0 rating in the UL-94 test. Compared with neat TPU, the peak heat release rate (pHRR) and total heat release (THR) values of TPU/6AHP/1NiFe-LDH sample were reduced by 67.9% and 40.8%, respectively. Moreover, both the smoke production and CO/CO2 yield were also decreased sharply. It was proposed that NiFe-LDH provided the effect of catalyzing char formation, and the obtained dense char layer was able to block both heat and smoke release. In addition, the addition of NiFe-LDH had little effect on the mechanical properties of TPU, and the tensile strength and elongation at break only decreased by 6.0% and 6.9%, respectively. This work provides a new strategy for fillers and flame retardants to improve the flame retardant properties and smoke suppression of TPU.

It Takes Two to Tango: Synergistic Expandable Graphite-Phosphorus Flame Retardant Combinations in Polyurethane Foams.

Due to the high flammability and smoke toxicity of polyurethane foams (PUFs) during burning, distinct efficient combinations of flame retardants are demanded to improve the fire safety of PUFs in practical applications. This feature article focuses on one of the most impressive halogen-free combinations in PUFs: expandable graphite (EG) and phosphorus-based flame retardants (P-FRs). The synergistic effect of EG and P-FRs mainly superimposes the two modes of action, charring and maintaining a thermally insulating residue morphology, to bring effective flame retardancy to PUFs. Specific interactions between EG and P-FRs, including the agglutination of the fire residue consisting of expanded-graphite worms, yields an outstanding synergistic effect, making this approach the latest champion to fulfill the demanding requirements for flame-retarded PUFs. Current and future topics such as the increasing use of renewable feedstock are also discussed in this article.

Synthesis of reactive phosphorus-based carbonate for flame retardant polyhydroxyurethane foams

Polyurethane (PU) foams are widely used for many applications, however the use of toxic isocyanate monomers for their synthesis has recently led researchers to non-isocyanate PU foams. The most promising alternative is the aminolysis of cyclic carbonate which yields polyhydroxyurethanes (PHU). Nevertheless, the obtained foams suffer from significant flammability and require the introduction of flame retardants to improve their flame retardant properties. Hence, this article demonstrates the first synthesis of PHUs foams containing phosphorus-based flame retardants. The flame retardant were allowed to react with the monomers to prevent any leaching from the foams. Moreover, several structures of cyclic carbonates were analyzed in order to determine the influence of aromatic rings on both thermal stability and mechanical properties of foams by thermogravimetric analyses, differential scanning calorimetry and dynamic mechanical analyses. The flame retardant properties were studied with a cone calorimeter and pyrolysis combustion flow calorimeter. The best results were obtained by the foam containing 2 wt% of phosphorus and two aromatic rings in the cyclic carbonate structure. Cone calorimeter analysis showed a total heat release of 13.1 KJ.g−1 versus 19.1 KJ.g−1 for the DOPO-free foam.

Smoke suppression and phosphorus-free condensed phase flame-retardant epoxy resin composites based on Salen-Ni

To avoid potential ecological and health problems caused by phosphorus-based flame retardants, a novel phosphorus-free PBA-Salen-Ni flame retardant is successfully synthesized in this work. In a nutshell, boron-containing metal complexes are prepared by nickel salts and chelating PBA-Salen molecule (PBA: p-phenylenediboronic acid). While the obtained material inherently has good compatibility and can endow polymers with good flame retardant properties at low addition levels. Besides, the char shielding layer and the “labyrinth effect” of the special porous char layer structure formed after the combustion of EP/PBA-Salen-Ni retard the transfer of volatile products, giving EP excellent smoke suppression properties. The results show that the limiting oxygen index value of the EP/PBA-Salen-Ni composites is increased from 25.6% (pure EP) to 30.5%, and it can pass the UL-94 V-0 rating when the addition amount is only 5wt%. Particularly, compared with pure EP, the total smoke production (19.9 m2) and peak heat release rate (859.6 kW m−2) of EP/PBA-Salen-Ni composites are reduced by 36% and 33%, respectively. Therefore, this work provides a new idea for the rational design of phosphorus-free flame retardants that are mainly on condensed phase flame retardancy and have a good smoke suppression effect.

Comparable Investigation of Phosphorus-Based Flame Retardant Electrolytes on LiFePO4 Cathodes

Improving the flame retardant and electrochemical properties of electrolytes is of great significance to enhance the safety of lithium-ion batteries (LIBs). In this work, the effect of cresyl diphenyl phosphate (CDP), dimethyl methyl phosphonate (DMMP), trimethyl phosphate (TMP) and triphenyl phosphate (TPP) as flame retardant additives in the standard electrolyte on the performance of LiFePO4/Li cell are comprehensively studied. The results show that when the mass fraction of flame retardant is less than 20%, the purpose of flame retardant can be achieved in the electrolyte. When the cells without and with 20 wt% of CDP, DMMP, TMP, and TPP additives are, respectively, their capacity retentions are 80, 46, 82, 84, and 57% after 100 cycles at 0.5C. According to characterization analysis, DMMP and TMP can facilitate the formation of stable interface films on cathode and subsequently improve the battery performance. Compared with expensive or complicated synthetic flame retardants, conventional flame retardants like CDP, DMMP, TMP, and TPP have great potential for application in electrolytes to improve the safety of LIBs. This work can provide useful scientific research and industry in the study of phosphorus-based flame retardant electrolytes.

FRX Polymers’ Nofia® flame retardants earn GreenScreen accreditation

FRX Polymers’ polymeric phosphorus-based flame retardants Nofia® CO3000, CO4000 and Nofia CO6000 have been granted a GreenScreen Benchmark™ 3 score, a green non-toxic indicator of ESG compliance. GreenScreen is a method of comparative benchmarking chemical toxicity in the chemical industry.

Chemically Accelerated Stabilization of a Cellulose-Lignin Precursor as a Route to High Yield Carbon Fiber Production.

The production of carbon fiber from bio-based or renewable resources has gained considerable attention in recent years with much of the focus upon cellulose, lignin, and cellulose-lignin composite precursor fibers. A critical step in optimizing the manufacture of carbon fiber is the stabilization process, through which the chemical and physical structure of the precursor fiber is transformed, allowing it to withstand very high temperatures. In this work, thermogravimetric analysis (TGA) is used to explore and optimize stabilization by simulating different stabilization profiles. Using this approach, we explore the influence of atmosphere (nitrogen or air), cellulose-lignin composition, and alternative catalysts on the carbon yield, efficiency, and rate of stabilization. Carbon dioxide and water vapor released during stabilization are analyzed by Fourier transform infrared (FTIR) spectroscopy, providing further information about the stabilization mechanism and the accelerating effect of oxygen and increased char yield (carbon content), especially for lignin. A range of different catalysts are evaluated for their ability to enhance the char yield, and a phosphorus-based flame retardant (H3PO4) proved to be the most effective; in fact, a doubling of the char yield was observed.