Flame Retardant Epoxy Composites Research Articles

Dual function of carboxymethyl cellulose scaffold: A one-stone-two-birds strategy to prepare double‐layer hollow ZIF-67 derivates for flame retardant epoxy composites

Aluminum hypophosphite (AHP) has been used as a flame retardant for a long time. Previous studies about AHP employed in flame retardant materials mostly focus on coating, modification, and complex system. It is valuable to explore simple experimental steps to prepare nano hybrids with AHP and metal–organic frameworks (MOFs). We found acidic substances could etch zeolitic imidazolate framework-67 (ZIF-67) to obtain MOF derivatives. Unfortunately, AHP and ZIF-67 could not directly form a hybrid. Therefore, carboxymethylcellulose (CMC) is introduced as a dual function layer (buffer and support). The CMC resists the complete conversion of ZIF-67 etched by phosphoric acid to amorphous cobalt phosphate hydrate (ACP). Meanwhile, CMC containing hydroxyl groups combines with AHP through electrostatic interaction and coordination bonds. A double-layer hollow MOF derivative is synthesized through this one-stone-two-birds strategy. Due to multiple flame retardant elements and unique nanostructure, this MOF derivative endows epoxy (EP) resin with excellent flame retardancy. With 2.0 wt% addition, the peak heat release rate (pHRR) and total heat release (THR) of EP/AHP/ACP@CMC are decreased by 47.8 and 21.0 %, respectively. This study proposes a novel scheme that converts AHP into MOF derivatives as high-performance FRs.

Enhancing char formation of flame retardant epoxy composites: Onigiri-like ZIF-67 modification with carboxymethyl β-cyclodextrin crosslinking

To enhance char formation of flame retardant epoxy (EP) composites, carboxymethyl β-cyclodextrin (CM-β-CD) is employed as an etchant for or ZIF-67 derivatives. In the early stage, etching plays a dominant role. The mismatch in size between CM-β-CD opening and ZIF-67 pore leads to the stacking of carboxyl cobalt complexes on the shell. When the reaction time is prolonged, crosslinking occurs between carboxyl and hydroxyl groups. Crosslinked CM-β-CD weakens and eventually stops the etching process. Triethyl phosphate (TEP), an additive to improve flame retardancy, is also absorbed on the shell in this one-pot synthesis. Herin, the synthesis of metal-organic framework (MOF) derivatives can impart multiple functions to MOF. This novel nanohybrid significantly improved flame retardancy of EP composites with only 2.0 wt% loading. The peak heat release rate (pHRR) and total smoke production (TSP) were reduced by 54.8 and 46.9%, respectively. The integrated multi-element system resulted in an expanded and reinforced char layer. This study proposes a simple and precise method for controlling the structure of MOF-carbohydrate hybrids through competition between chemical reactions.

Uniformly-Dispersed Black Phosphorene as Flame-Retardant Epoxy Composites via Iterative Dispersion Strategy

Uniformly-Dispersed Black Phosphorene as Flame-Retardant Epoxy Composites via Iterative Dispersion Strategy

Facile Approach for Preparing Chitosan/Phosphaphenanthrene-Containing Epoxy Resins with Superior Flame Retardancy and Mechanical Properties

Flame-retardant epoxy (EP) composites with excellent mechanical properties that can be produced via facile, cost-effective, and environmentally friendly fabrication are highly desirable. A variety of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivatives are used as flame retardants for EP resin due to their high efficiency, but their synthesis is often complicated. In this work, a biomass chitosan (CS) was chosen as a synergist for DOPO to obtain high-performance, fire-safe EPs through simple blending. The total loading of CS and DOPO was limited to 10 wt % in EP, with mass ratios of CS/DOPO being 1:1, 1:2, 1:3, 2:1, or 3:1. At CS/DOPO ratios of 1:2 and 2:1, the obtained EP/10% CS1/DOPO2 and EP/10% CS2/DOPO1 achieved a UL-94 V-0 rating, and their limiting oxygen index increased to 33.7 and 32.5%, respectively. Compared with virgin EP, the heat release and smoke generation of EP/10% CS1/DOPO2 and EP/10% CS2/DOPO1 decreased, especially the total smoke production decreasing by 61.9 and 71.0%. Furthermore, the flexural strength of EP/10% CS1/DOPO2 and EP/10% CS2/DOPO1 was 36.0 and 38.4% higher than that of EP, respectively. The results indicated the synergistic effects of DOPO and CS in enhancing both flame retardancy and mechanical properties of EPs. This work offers a simple and practical strategy for preparing flame-retardant EPs with satisfactory mechanical properties.

Fabrication of layered double hydroxide@ferric decorated polyphosphazene hybrid architecture towards simultaneously improved fire safety, smoke suppression and mechanical strength of epoxy resin

The requirement of high-efficiency flame retardants for epoxy (EP) resin is urgent due to its high flammability. Herein, a hybrid architecture (LDH@PZE-Fe) was synthesized via intercalation by surfactant and interfacial modification by ferric decorated and amino groups-containing polyphosphazene (PZE) to enhance the fire safety and smoke suppression of EP. With the introduction of 2.5 wt% LDH@PZE-Fe, EP/LDH@PZE-Fe achieved UL-94 V-0 rating with a LOI value of 27.5%. Moreover, EP/LDH@PZE-Fe performed superiorly in inhibiting the release of heat and smoke. Such high-efficiency flame-retardancy was ascribed to the combined action both in condensed and gaseous phases, which was verified by analyzing the morphology and structure of the char layer and the composition of pyrolysis gases. Additionally, EP/LDH@PZE-Fe exhibited satisfactory impact strength and enhanced glass transition temperature due to the good compatibility of LDH@PZE-Fe with EP matrix. Therefore, the flame-retardant EP composites had potential applications as highly flame-retardant materials.

The influence on flame retardant epoxy composites by a bird's nest-like structure of Co-based isomers evolved from zeolitic imidazolate framework-67

The machining of metal-organic frameworks (MOFs) based templates into diverse layered double hydroxides (LDHs) is essential to maximize their advantages in flame retardant polymers. However, improving the thermal stability of LDHs has so far continued to be a great challenge. Herein, a MOFs sacrificial template has been developed to realize the controlled synthesis of two Co-based isomers, namely CoCo-LDH and cobalt basic carbonate (CBC), with the construction of three different nanostructures of carbonate intercalated CoCo-LDH nanocage (LDH), single yolk@shell CBC@CoCo-LDH (s-CBC@LDH), and multi-yolk@shell CBC@CoCo-LDH (m-CBC@LDH). The thermal stability of CoCo-LDH is enhanced by controlling the reaction time. Moreover, CoCo-LDH from m-CBC@LDH decomposes at the right temperature while CBC nanoparticles further enhanced the flame retardancy. To demonstrate the high performance conjecture on the structure-property relationship, the as-synthesized Co-based isomers were individually integrated into the epoxy matrix to evaluate its comprehensive properties. Compared to LDH and s-CBC@LDH, m-CBC@LDH imparts superior thermal stability, flame retardancy, and comparable mechanical properties onto the epoxy composites. With the incorporation of 2 wt.% m-CBC@LDH, the peak of heat release rate and total heat release are decreased by 38.5% and 19.6%, respectively. This work provides a design direction for improving the flame retardant of epoxy resin.

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 an epoxy-based coating reinforced with silica aerogel and ammonium polyphosphate additives

Flame retardant (FR) additives may degrade polymers’ mechanical performance. In this work, FR epoxy composites fabricated based on two popular FR agents of ammonium polyphosphate (APP) and silica aerogel (SAG) are investigated. Several mechanical properties of these composites, including compressive, micro-hardness, and Izod impact, were investigated for different filler loadings. Although the addition of 10 vol.% APP improved compressive modulus, yield strength, and micro-hardness, it degraded the impact strength. The incorporation of SAG made the composites more ductile, improved the impact strength, but deteriorated their compressive properties. Samples containing both SAG and APP demonstrated synergetic effects evident by their enhanced compressive properties and hardness. The findings of this study can guide the design of epoxies with both exceptional FR and mechanical performance.

Synthesis of novel calixarene‐based intumescent flame retardant and application of flame retardant epoxy resin

AbstractA new intumescent flame retardant containing APP, MEL and p‐tert‐Butylcalix[4]arene was synthesized and added to epoxy (EP) resin in different proportions with aluminum hydroxide (ATH). The flame retardancy, thermal stability and smoke suppression of flame retardant EP composites were studied. When adding 20% APP to EP matrix, the limiting oxygen index can reach 30.5%. After adding synergist ATH, the amount of char residue in air at 700°C increased significantly from 0.83% to 15.80%, indicating that its heat resistance and oxidation resistance were improved. In terms of peak heat release rate (pHRR), the pHRR of ATH synergistic flame‐retardant EP composites can be reduced to 128.53 kW/m2 (EP3), which is much lower than pure EP and FR/EP composites, indicating that FR and ATH has a good synergistic flame retardant effect. For the stable carbon layer produced, on the one hand, it can block the release of combustible gas, and on the other hand, it can function as heat insulation and oxygen barrier inside the matrix.

Growing metal–organic framework nanoparticles on short carbon fibers to improve flame retardancy, smoke suppression and mechanical properties of the flame retardant epoxy composites

Growing metal–organic framework nanoparticles on short carbon fibers to improve flame retardancy, smoke suppression and mechanical properties of the flame retardant epoxy composites

Recyclable flame-retardant epoxy composites based on disulfide bonds: Flammability and recyclability

A series of recyclable epoxy resin (REP) composites are successfully prepared in this study, aiming to improve flame retardancy while keep good recyclability and mechanical properties. The commercial 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-Oxide (DOPO) with high reactive P–H bond is used as highly-efficient flame retardant in this work. Compared with pure epoxy resin with a limited oxygen index of 21.7% and no rating in vertical burning test, recyclable epoxy resin only with 3 wt% DOPO acquires a limited oxygen index value of 27.8% and V-0 rating. In addition, REP composites containing 4 wt% DOPO displays quick self-extinguishing behavior, which shows the 43.5% drop of the peak heat release rate. The main reason might be that traditional phosphorous-containing flame retardant existing in REP composites can play a positive role in both condensed phase and gas phase when burning. On the other hand, both scanning electron microscopy and Raman results also further affirm the improved flame retardancy. Moreover, flame-retardant REP composites can also maintain good transparency and mechanical properties. As well as the favorable recyclability originated from the special exchangeable disulfide crosslinks. High-Performance REP composites possessing expected flame retardancy, recyclability and good mechanical properties pave the way to broaden applications of thermoset epoxy materials.

Basalt Fiber-Based Flame Retardant Epoxy Composites: Preparation, Thermal Properties, and Flame Retardancy.

We aimed to study the impact of surface modification of basalt fiber (BF) on the mechanical properties of basalt fiber-based epoxy composites. Four different types of pretreatment approaches to BF were used; then a silane coupling agent (KH550) was applied to further modify the pretreated BF, prior to the preparation of epoxy resin (EP)/BF composites. The combination of acetone (pre-treatment) and KH550 (formal surface treatment) for basalt fiber (BT-AT) imparted the EP/BF composite with the best performance in both tensile and impact strengths. Subsequently, such modified BF was introduced into the flame-retardant epoxy composites (EP/AP750) to prepare basalt fiber reinforced flame-retardant epoxy composite (EP/AP750/BF-AT). The fire behaviors of the composites were evaluated by vertical burning test (UL-94), limiting oxygen index (LOI) test and cone calorimetry. In comparison to the flame-retardant properties of EP/AP750, the incorporation of BF-AT slightly reduced LOI value from 26.3% to 25.1%, maintained the good performance in vertical burning test, but increased the peak of the heat release rate. Besides, the thermal properties and mechanical properties of the composites were investigated by thermogravimetric analysis (TGA), universal tensile test, impact test and dynamic mechanical analysis (DMA).

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.

A novel exploration of metal–organic frameworks in flame-retardant epoxy composites

In this work, a series of transition metal–organic frameworks (MOFs) were prepared through self-assembly of organic bridging ligands and transition metal ions. The structure of MOFs samples was analyzed by XRD, FTIR, TG, and TEM. The influences of MOFs on flame resistance, toxicity reduction, and smoke suppression of epoxy were explored in detail. The findings presented that low addition amount of MOFs had a positive effect on decreasing the fire hazards of epoxy. Loading of 2 mass% MOFs into epoxy led to the decrease in thermal degradation rate and increase in char yields. Meanwhile, the values of peak heat release rate, total heat release, and average mass loss rate of epoxy composites were cut down effectively, in comparison with neat epoxy. Moreover, the remarkable decrease in smoke production rate, total smoke production, and CO, CO2 yield could be provided by cone calorimeter test. The char residues after cone calorimeter test were investigated by SEM and Raman spectra, and the flame-retardant mechanism was discussed.

Cardanol derived benzoxazine in combination with boron-doped graphene toward simultaneously improved toughening and flame retardant epoxy composites

A bio-based phosphorus-containing benzoxazine monomer (CBz) was successfully synthesized through the reaction between cardanol and DOPO-based diamine. In order to simultaneously improve the toughness and flame retardancy of epoxy resin (EP), various contents of CBz in combination with boron-doped graphene (BG) nanosheets were incorporated into EP to obtain boron-doped graphene/cardanol derived benzoxazine-epoxy composites (EP/CBz/BG). By comparison, cardanol derived benzoxazine-epoxy co-polymers (EP/CBz) were also fabricated. Results show that the addition of the as-prepared CBz into EP not only endowed EP with excellent flame retardancy, but also improved the glass transition temperature and impact strength. Specifically, the peak heat release rate of EP composite with 13 wt% CBz and 2 wt% BG decreased by 48% compared to that of neat EP, accompanying with an increase of impact strength by 22%. These favorable features of EP/CBz/BG composites are attributed to the unique structure of CBz and high resistance to thermal decomposition of BG.

Highly transparent and flame-retardant epoxy composites based on a hybrid multi-element containing POSS derivative

Epoxy resin modified with ODMAS comprising a POSS core and sixteen DOPO groups possess high transparency, excellent flame retardant property and enhanced mechanical strength.

Development of cyclophosphazene and rice husk ash incorporated epoxy composites for high performance applications

An amine-terminated cyclophosphazene and 3-aminopropyltrimethoxysilane-functionalized rice husk ash incorporated halogen-free flame-retardant epoxy composites (ATCP/FRHA/Ep) were developed and their thermal, dielectric, hydrophobic and flame-retardant properties were analysed. The cone calorimeter and contact angle results confirm that the ATCP and FRHA materials impart good flame-retardant and water resistance properties to the resultant epoxy composites. A significant improvement in the flame-retardant, glass transition temperature, char yield and dielectric properties was noticed, due to the synergetic effects imparted from the unique combination of phosphorous and nitrogen in the phosphazene ring as well as silica present in the rice husk ash. Obviously, this ATCP/FRHA/Ep flame-retardant system paves a new possibility for high performance non-halogen flame-retardant polymeric materials. Hence, they have become potential candidates for fire-resistant applications in electronic and microelectronics as a sustainable non-flammable polymeric material.

Effect of Cu-doped graphene on the flammability and thermal properties of epoxy composites

Cu-doped graphene (graphenit-Cu) was successfully prepared through chemical reduction method, and its surface morphology, crystalline structure and Cu content in graphenit-Cu were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), inductive couple plasma (ICP) and electrochemical cyclic voltammetry, respectively. Graphenit-ox/epoxy systems and graphenit-Cu/epoxy systems were prepared, and the contents of graphenit-ox and graphenit-Cu were kept as 1 and 3 wt%, respectively. The effect of graphenit-ox or graphenit-Cu on the flame retardancy, combustion properties, thermal degradation and thermomechanical properties of epoxy resin was investigated systematically by limiting oxygen index (LOI), cone calorimeter (Cone), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Compared to graphenit-ox, the addition of graphenit-Cu reduced the heat release rate (HRR), total smoke production (TSP) and smoke production rate (SPR), and improved LOI values of epoxy composites. Moreover, the addition of graphenit-ox also had little flame retardant effect on epoxy composite. The possible synergistic effect between graphene and Cu was confirmed in the flame retardant epoxy composites. TGA and DMA results also indicated the considerable effect on the thermal degradation and thermomechanical properties of epoxy composites with the addition of graphenit-Cu. The results supplied an effective solution for developing excellent flame retardant epoxy composites.

Influence of ferric phosphate on smoke suppression properties and combustion behavior of intumescent flame retardant epoxy composites

This article mainly studies the smoke suppression properties and synergistic flame retardant effect of ferric phosphate (FeP) on flame retardant epoxy resin (EP) using ammonium polyphosphate and pentaerythritol as intumescent flame retardants (IFRs). Then, the smoke suppression and synergistic flame retardant properties of FeP on IFREP composites were evaluated using cone calorimeter test (CCT) and scanning electron microscopy (SEM). The influence of FeP on thermal degradation of IFREP was studied by thermogravimetric analysis/infrared spectrometry in nitrogen atmosphere. Remarkably, the CCT results show that FeP can effectively decrease heat release rate, total heat release, smoke production rate, total smoke production, and smoke factor of flame retardant samples. The SEM results show that FeP can greatly improve the structure of char residue. The TGA results indicate that the material with FeP undergoes degradation in three characteristic temperature stages, which can be attributed to the catalyzing deamination by FeP, the reaction between polyphosphoric acid and FeP, and the rupture of the polyphosphoric acid chain, respectively. The volatilized products formed on thermal degradation of IFREP indicate that the volatilized products are H2O, CO2, CO, carboxylic acid, and aliphatic hydrocarbons according to the temperature of onset formation. Here, FeP is considered to be an effective smoke suppression agent and a good synergism in IFREP composites, which can greatly improve the structure of char residue.

Combustion behavior and thermal pyrolysis kinetics of flame-retardant epoxy composites based on organic–inorganic intumescent flame retardant

A novel organic–inorganic intumescent flame retardant, expandable graphite modified with charring agent (EGM), was synthesized using expandable graphite (EG), phosphorus oxychloride, and pentaerythritol. Then, EGM was used as flame retardant for epoxy resin. And the flame-retardant properties of epoxy composites were investigated by cone calorimeter test (CCT). The thermal degradation behaviors of epoxy composites were studied by thermogravimetric analysis (TG) in nitrogen atmosphere. And the pyrolysis kinetics of the composites was investigated using Kissinger and Flynn–Wall–Ozawa methods. The CCT result indicated that EGM can reduce the heat release rate and smoke production rate more than EG in flame-retardant epoxy composites: a more compact char residue formed on the surface of the sample with EGM than that of the sample with EG during the combustion process. The TG result showed that the sample with EGM has higher thermal stability than the sample with EG. And the data calculated from Kissinger and Flynn–Wall–Ozawa methods showed that both EP-0 and EP-3 had two thermal degradation stages; EGM can improve the E a value of epoxy resins.