Metal compound-enhanced flame retardancy of intumescent epoxy resins containing ammonium polyphosphate

Controllable Self-Assembly of Carbon Nanotubes on Ammonium Polyphosphate as a Game-Changer for Flame Retardancy and Thermal Conductivity in Epoxy Resin

The optimization of flame retardancy and thermal conductivity in epoxy resin (EP), utilized in critical applications such as mechanical components and electronics packaging, is a significant challenge. This study introduces a novel, ultrasound-assisted self-assembly technique to create a dual-functional filler consisting of carbon nanotubes and ammonium polyphosphate (CNTs@APP). This method, leveraging dynamic ligand interactions and strategic solvent selection, allows for precise control over the assembly and distribution of CNTs on APP surfaces, distinguishing it from conventional blending approaches. The integration of 7.5 wt.% CNTs@APP10 into EP nanocomposites results in substantial improvements in flame retardancy, as evidenced by a limiting oxygen index (LOI) value of 31.8% and achievement of the UL-94 V-0 rating. Additionally, critical fire hazard indicators, including total heat release (THR), total smoke release (TSR), and the peak intensity of CO yield (PCOY), are significantly reduced by 45.9% to 77.5%. This method also leads to a remarkable 3.6-fold increase in char yield, demonstrating its game-changing potential over traditional blending techniques. Moreover, despite minimal CNTs addition, thermal conductivity is notably enhanced, showing a 53% increase. This study introduces a novel approach in the development of multifunctional EP nanocomposites, offering potential for wide range of applications.

Highly efficient metal-organic framework based intumescent poly(L-lactic acid) towards fire safety, ignition delay and UV resistance

Developing multifunctional biodegradable PLA with ignition delay, high efficient fire retardancy, and UV resistance properties is a challenging task owing to its high flammability, and mutually exclusive phenomenon between the latter two properties. In this work, we report a superior efficient synergistic action combining piperazine pyrophosphate (PAPP) and a Co based metal-organic framework (ZIF-67). Results illustrated that with merely 0.06 wt% ZIF-67, intumescent PLA containing 4.96 wt% PAPP reached UL-94 V0 rating. The PLA/4.9PAPP/0.1MOF sample possessed a limiting oxygen index (LOI) value at 33 %, exhibited a 28 % reduction in peak heat release rate (pHRR) and a 67 % increase in fire propagation index (FPI). Moreover, the presence MOF delayed the ignition time of PLA by 12 s due to the highly porous structure of MOF and its chemical heat-sink performance. Insightful reaction to fire mechanism in the condensed phase via TG-FTIR and Raman revealed that a crack free protective intumescent char layer with higher graphitization degree was formed, which effectively enhanced the barrier effect and minimize the heat and fuel transfer. In addition, the UV resistance of PLA composites is enhanced, remaining at and below 5 % transmittance in the UVA and UVB areas. This work provides a green production way of multifunctional degradable materials and broadens their application fields.

Evaluation of Mono and Bimetallic Ferrocene-Based 1,2,3-Triazolyl Compounds as Burning Rate Catalysts for Solid Rocket Motor

We reported mono and bimetallic ferrocene-based 1,2,3-triazolyl compounds as potential burning rate catalysts in their neutral and ionic forms. All complexes reported here were characterized using 1H and 13C NMR, elemental analysis, and Mössbauer spectroscopy, which was performed for neutral and oxide compounds. The complexes present quasireversible redox potentials with higher oxidative ability than ferrocene and catocene under the same conditions. The complexes were tested as catalysts on the thermal decomposition of ammonium perchlorate (AP) and examined by a differential scanning calorimetry technique to gain further knowledge about their catalytic behavior. Compound 1 causes a decrease of the high-temperature decomposition (HTD) of AP positively, decreasing the decomposition temperature of AP to 345 °C and consequently increasing the energy release to 1939 J·g-1. We took the residues from the pans after testing from the DSC to elucidate the underlying reaction pathways. We obtained the size of the nanostructures formed after thermal decomposition of AP determined by the TEM technique. The diameter and size distribution of iron oxide nanoparticles formed depend on the alkyl sidechain of the triazolium ring, which induces the formation of nanoparticles with a double diameter and size distribution compared to their neutral analogues, suggesting that the possible intermediate for the mechanism degradation of AP by ferrocene derivatives is nanoscale Fe2O3 or similar oxides.

Modified oligoether-diamine synthesis for the preparation of crystallizable polymers based on epoxyurethane oligomers

A modified synthetic method for amino-terminated oligo tetramethylene oxides is presented. Diamines were synthesized via a three-step route from oligo tetramethylene oxide diol with an average molecular weight of 2000. The final step – oligoether-diphthalimide hydrazinolysis – has been improved. The yield of the target product has been shown to be more than 1.5 times higher when the molar ratio of the reacting components was changed. The oligoether-diamine and the reaction intermediates have been identified by 1H and 13C NMR spectroscopy. It has been demonstrated that the synthesized amine can be used as a curing agent for epoxy urethane oligomers. It is shown that the glass transition temperature of the cured elastomers is lower than −70 °C. These elastomers can be recommended for the use in the conditions of the Arctic and the Far North or Far South of the globe.

Synergistic Effects of Diatoms on Intumescent Flame Retardant High Impact Polystyrene System

In this work, aiming to improve the flame retardancy performance of high impact polystyrene (HIPS), HIPS compounds were synthesized with the addition of intumescent flame retardant (IFR: mass ratio of APP and PER was 3:1) and diatoms into HIPS matrix by melt blending method. It was found the IFR/diatoms system exhibited high flame retardant efficiency and catalytic carbonization effect to HIPS matrix in the burning process. The LOI value of HIPS-2 compound with the addition of 28 wt% IFR and 2 wt% diatoms was increased to 29.0% and passed V-0 rating. The value of PHRR for HIPS-2 compound is about 460.58 kW/m² compared with 937.22 kW/m² of pure HIPS and the value of THR for HIPS-2 compound is about 32.9 MJ/m² compared with 62.7 MJ/m² of pure HIPS, suggesting that the addition of IFR/diatoms system can decrease the values of PHRR and THR, which shows the synergistic effect between IFR and diatoms on reducing heat release. The 21.9% reduction in Av-EHC and 41.4% reduction in TSP seen on introducing an IFR/diatoms system indicates effective smoke suppression, which potentially would significantly reduce the death rate in real fire accidents. The TG-IR results indicated that the IFR/diatoms flame retardant system functioned in the gas phase to suppress the flame. The SEM images showed the char residue produced was more compact and continuous, which suggests that the IFR/diatoms flame retardant system exhibits barrier and catalytic effects to block heat transferring and promote char forming. The tensile strength and impact strength of HIPS-2 compound were 22.95 MPa and 2.63 KJ/m², respectively. The tensile strength and impact strength were increased by 34.13% and 19.55% compared with that of pure HIPS.

Synthesis and Study of Physical and Mechanical Properties of Urethane-Containing Elastomers Based on Epoxyurethane Oligomers with Controlled Crystallinity

The influence of the molecular weight of oligoamine, oligoether, and the type of diisocyanate on the physical and mechanical properties of elastomers with urethane hydroxyl hard segments was studied. For this purpose, oligoetherdiamines with molecular weights ~1008 and ~1400 g mol⁻¹ were synthesized by a three-stage method. Epoxyurethane oligomers were synthesized according to a two-step route with an oligodiisocyanate as an intermediate product. A series of 12 elastomers with controlled crystallinity were synthesized from these elastomers and amines. The deformation and strength properties of the elastomers were studied.

Preparation, Structure and Properties of Urethane-Containing Elastomers Based on Epoxy Terminal Oligomers

The effect of polyester oligoethylene adipate molecular weight, diisocyanate structure, and chain extender on the properties of epoxyurethane-based oligomer elastomers was studied in this research. Oligoethylene adipates were obtained via polycondensation of adipic acid and ethylene glycol. Epoxyurethane oligomers were synthesized according to a two-step route with an oligodiisocyanate as an intermediate product. The elastomers with hard urethane hydroxyl blocks were synthesized from oligodiisocyanates. The deformation and strength properties of the elastomers were studied.

Mechanistic Insights into the Thermal Decomposition of Ammonium Perchlorate: The Role of Amino-Functionalized Magnetic Nanoparticles

This work reports the characterization and application of two promising nanocatalysts for the thermal decomposition of ammonium perchlorate (AP). To obtain these composite materials, magnetite nanoparticles (Fe₃O₄ NP_s) were functionalized with two different amine derivative groups, tertiary amine (Fe₃O₄ NP_s-A1) and quaternary amine. X-ray photoelectron spectroscopy and differential scanning calorimetry provided mechanistic insights into the thermal decomposition of AP. Furthermore, tertiary and quaternary amine groups play a critical role, where the presence of an extra proton could favor an electron-proton transfer as the rate-determining step. Moreover, Fe₃O₄ NP_s-A1 causes a diminution of the high-temperature decomposition of AP positively to 335 °C, increasing the energy release by 278 J g^-1 and consequently affording the lowest activation energy (102 kJ mol^-1), indicating a low degree of thermal stability, and accelerating the thermal decomposition of AP.

Heterobimetallic Catalysts for the Thermal Decomposition of Ammonium Perchlorate: Efficient Burning Rate Catalysts for Solid Rocket Motors and Missiles

We show the synthesis and characterization of four heterobimetallic compounds derived from s-indacene of general formula [{(CO)₃Mn}-s-Ic-{MCp*}]^q with M = Fe, Co, Ni, and Ru; q = 0, 1+. The complexes reported here were characterized by ¹H and ¹³C NMR, elemental analysis and FT-IR. Additionally, the X-ray crystal structure of [(CO)₃Mn-s-Ic-FeCp*] (1) and Mössbauer spectra are reported. The heterobimetallic compounds exhibit higher quasireversible redox potentials compared with ferrocene and catocene under the same reaction conditions. The complexes were tested as catalysts on the thermal decomposition of ammonium perchlorate examined by a differential scanning calorimetry technique to study their catalytic behavior. Compound (1) causes a decrease of ammonium perchlorate's decomposition temperature to 315 °C, consequently increasing the heat release by 138 J·g^-1. Conversely, [{(CO)₃Mn}-s-Ic'-{CoCp*}] (2) presents a higher heat release (2462 J·g^-1), comparable to catocene.

Reactive and Additive Modifications of Styrenic Polymers with Phosphorus-Containing Compounds and Their Effects on Fire Retardance

Polystyrene, despite its high flammability, is widely used as a thermal insulation material for buildings, for food packaging, in electrical and automotive industries, etc. A number of modification routes have been explored to improve the fire retardance and boost the thermal stability of commercially important styrene-based polymeric products. The earlier strategies mostly involved the use of halogenated fire retardants. Nowadays, these compounds are considered to be persistent pollutants that are hazardous to public and environmental health. Many well-known halogen-based fire retardants, regardless of their chemical structures and modes of action, have been withdrawn from built environments in the European Union, USA, and Canada. This had triggered a growing research interest in, and an industrial demand for, halogen-free alternatives, which not only will reduce the flammability but also address toxicity and bioaccumulation issues. Among the possible options, phosphorus-containing compounds have received greater attention due to their excellent fire-retarding efficiencies and environmentally friendly attributes. Numerous reports were also published on reactive and additive modifications of polystyrene in different forms, particularly in the last decade; hence, the current article aims to provide a critical review of these publications. The authors mainly intend to focus on the chemistries of phosphorous compounds, with the P atom being in different chemical environments, used either as reactive, or additive, fire retardants in styrene-based materials. The chemical pathways and possible mechanisms behind the fire retardance are discussed in this review.

Recent Developments in the Flame-Retardant System of Epoxy Resin

With the increasing emphasis on environmental protection, the development of flame retardants for epoxy resin (EP) has tended to be non-toxic, efficient, multifunctional and systematic. Currently reported flame retardants have been capable of providing flame retardancy, heat resistance and thermal stability to EP. However, many aspects still need to be further improved. This paper reviews the development of EPs in halogen-free flame retardants, focusing on phosphorus flame retardants, carbon-based materials, silicon flame retardants, inorganic nanofillers, and metal-containing compounds. These flame retardants can be used on their own or in combination to achieve the desired results. The effects of these flame retardants on the thermal stability and flame retardancy of EPs were discussed. Despite the great progress on flame retardants for EP in recent years, further improvement of EP is needed to obtain numerous eco-friendly high-performance materials.

Flame Retardant Epoxy Composites on the Road of Innovation: An Analysis with Flame Retardancy Index for Future Development

Nowadays, epoxy composites are elements of engineering materials and systems. Although they are known as versatile materials, epoxy resins suffer from high flammability. In this sense, flame retardancy analysis has been recognized as an undeniable requirement for developing future generations of epoxy-based systems. A considerable proportion of the literature on epoxy composites has been devoted to the use of phosphorus-based additives. Nevertheless, innovative flame retardants have coincidentally been under investigation to meet market requirements. This review paper attempts to give an overview of the research on flame retardant epoxy composites by classification of literature in terms of phosphorus (P), non-phosphorus (NP), and combinations of P/NP additives. A comprehensive set of data on cone calorimetry measurements applied on P-, NP-, and P/NP-incorporated epoxy systems was collected and treated. The performance of epoxy composites was qualitatively discussed as Poor, Good, and Excellent cases identified and distinguished by the use of the universal Flame Retardancy Index (FRI). Moreover, evaluations were rechecked by considering the UL-94 test data in four groups as V0, V1, V2, and nonrated (NR). The dimensionless FRI allowed for comparison between flame retardancy performances of epoxy composites. The results of this survey can pave the way for future innovations in developing flame-retardant additives for epoxy.

Facile synthesis of a flame retardant melamine phenylphosphate and its epoxy resin composites with simultaneously improved flame retardancy, smoke suppression and water resistance

A flame retardant melamine phenylphosphate (MPhP) was facilely synthesized by the reaction of phenylphosphoric acid (PPA) and melamine (MEL), and was characterized by FTIR and NMR. Epoxy resin (EP) composites containing MPhP were prepared, and the effect of MPhP content on flame retardancy, smoke suppression, mechanical properties and thermal stability of the composites was investigated. It is observed that the LOI of the EP composite with 20 wt% MPhP (EP/MPhP20) is 26.5%, and the composite EP/MPhP20 reaches a UL 94 V-0 rating. Cone calorimeter test results show that the peak heat release rate, total heat release and total smoke release of EP/MPhP20 decrease by 51%, 34%, and 24%, respectively compared with those of pure EP. The flame retardancy of the EP/MPhP composites after the water treatment at 80 °C for 72 h is basically maintained, indicating that the composites have good water resistance. The mechanical strengths of the EP/MPhP composites decrease gradually with an increase in the MPhP content. Moreover, the thermal stability of the EP/MPhP composites was studied.

Salen Complexes as Fire Protective Agents for Thermoplastic Polyurethane: Deep Electron Paramagnetic Resonance Spectroscopy Investigation

The contribution of copper complexes of salen-based Schiff bases N, N'-bis(salicylidene)ethylenediamine (C1), N, N'-bis(4-hydroxysalicylidene)ethylenediamine (C2), and N, N'-bis(5-hydroxysalicylidene)ethylenediamine (C3) to the flame retardancy of thermoplastic polyurethane (TPU) is investigated in the context of minimizing the inherent flammability of TPU. Thermal and fire properties of TPU are evaluated. It is observed that fire performances vary depending upon the substitution of the salen framework. Cone calorimetry [mass loss calorimetry (MLC)] results show that, in TPU at 10 wt % loading, C2 and C3 reduce the peak of heat release rate by 46 and 50%, respectively. At high temperature, these copper complexes undergo polycondensation leading to resorcinol-type resin in the condensed phase and thus acting as intumescence reinforcing agents. C3 in TPU is particularly interesting because it delays significantly the time to ignition (MLC experiment). In addition, pyrolysis combustion flow calorimetry shows reduction in the heat release rate curve, suggesting its involvement in gas-phase action. Structural changes of copper complexes and radical formation during thermal treatment as well as their influence on fire retardancy of TPU in the condensed phase are investigated by spectroscopic studies supported by microscopic and powder diffraction studies. Electron paramagnetic resonance (EPR) spectroscopy was fully used to follow the redox changes of Cu(II) ions as well as radical formation of copper complexes/TPU formulations in their degradation pathways. Pulsed EPR technique of hyperfine sublevel correlation spectroscopy reveals evolution of the local surrounding of copper and radicals with a strong contribution of nitrogen fragments in the degradation products. Further, the spin state of radicals was investigated by the two-dimensional technique of phase-inverted echo-amplitude detected nutation experiment. Two different radicals were detected, that is, one monocarbon radical and an oxygen biradical. Thus, the EPR study permits to deeply investigate the mode of action of copper salen complexes in TPU.

Improved thermal properties of epoxy resin modified with polymethyl methacrylate-microencapsulated phosphorus-nitrogen-containing flame retardant

Epoxy resin (EP) composites with improved thermal resistance were fabricated. To solve the problem of low thermal resistance derived from phosphazene flame-retardant additives, we designed a system based on flame-retardant microcapsules P(H), with hexaphenoxycyclotriphosphazene as the core and polymethyl methacrylate as the shell. The core–shell structure was characterized and confirmed. The thermal resistance of the cured EP composites containing 1 wt% P(H) microcapsules was improved because of the increased glass transition temperatures. The P(2.75H)/EP composites can reach a limited oxygen index of 30.5% and V-1 rating in UL-94 tests. Heat and gas release rates were reduced during combustion tests. Residual images implied that the P(H) microcapsules may promote the formation of a flame-retardant char layer. Pyrolysis analysis demonstrated that the P(H) microcapsules can decompose in two procedures to produce flame-retardant gas components. Therefore, the flame-retardant mechanism involved the flame inhibition effect in the gas phase, and the charring effect in the condensed phase.

Epoxy resin composites with improved thermal resistance and flame retardancy were fabricated based on P(H) microcapsules.

Synthesis of a novel polyphosphate and its application with APP in flame retardant PLA

A phosphorus-containing flame retardant was synthesized via an A₂ + B₃ type reaction of bisphenolic acid-based monomer and phosphorus oxychloride. Then, intumescent flame retardant systems were prepared by combining PFRS with ammonium polyphosphate.

Functionalized allylamine polyphosphate as a novel multifunctional highly efficient fire retardant for polypropylene

In this study, an efficient novel allylamine polyphosphate (AAPP) as a flame retardant (FR) crosslinker is used to improve the thermal stability of flame retarded polypropylene (PP) composites under electron beam treatment.

Flame Retardancy of Sorbitol Based Bioepoxy via Combined Solid and Gas Phase Action

Flame-retarded bioepoxy resins were prepared with the application of commercially available sorbitol polyglycidyl ether (SPE). The additive-type flame retardancy of the cycloaliphatic amine-cured SPE was investigated. Three-percent phosphorus (P)-containing samples were prepared with the application of the liquid resorcinol bis(diphenyl phosphate) (RDP), the solid ammonium polyphosphate (APP), and by combining them. Synergistic effect was found between the inorganic APP and the organophosphorus RDP, when applied in combination: formulations applying RDP or APP alone showed increased limiting oxygen index (LOI) values, however, their UL-94 standard ratings remained HB. When the same amount of P originated from the two additives, V-0, self-extinguishing rating and LOI value of 34% (v/v) was reached. By the combined approach the heat release rate of SPE could be lowered by approximately 60%. The assumed balanced solid and gas phase mechanism was confirmed by thermogravimetric analysis, Fourier transform infrared spectrometry (FTIR) analysis (of the gases formed during laser pyrolysis), attenuated total reflection-infrared spectrometry (ATR-IR) analysis (of the charred residues), as well as by mechanical testing (of the char obtained after combustion).

Synthesis of ferrocene-based saccharides and their anti-migration and burning rate catalytic properties

In the search for ferrocene-based burning rate catalysts (BRCs) with good burning rate catalytic properties and low migration, we synthesized four ferrocene-based saccharides (S-Fcs).

Ferrocene and [3]ferrocenophane-based β-diketonato copper(ii) and zinc(ii) complexes: synthesis, crystal structure, electrochemistry and catalytic effect on thermal decomposition of ammonium perchlorate

Ferrocene and [3]ferrocenophane-based β-diketonato Cu(ii) complexes exhibit enhanced electrochemical behaviors and burning rate catalytic effects compared with the Zn(ii) complexes.