EP Composites Research Articles

A facile method for synthesis of novel phenyl phosphates flame retardants and their application in epoxy resin

AbstractPiperazinyl phenyl phosphate (PPOP) and 4,4‐diaminodiphenylmethyl phenyl phosphate (DPOA) containing phosphorus and nitrogen elements as flame retardants applied for epoxy resin (EP) were successfully synthesized, and substantiated by Fourier transform infrared spectra (FTIR), 1H and 31P nuclear magnetic resonance (NMR) and elemental analysis (EA). The limiting oxygen index (LOI) of the EP composites with 3 wt% of PPOP and DPOA attained 33.6% and 34.2%, both acquired the UL‐94 V‐0 rating, respectively. The peak of heat release rate (pHRR), the total heat release (THR) and the total smoke production (TSP) of EP/PPOP‐1 decreased by 21.0%, 25.6%, and 18.7%, respectively. For EP/DPOA‐1, the pHRR, THR, and TSP were brought down by 23.5%, 21.8%, and 26.4%, respectively. Flame‐retardant mechanisms were explicitly evaluated by the scanning electron microscope (SEM), Raman spectroscopy and thermogravimetric analysis‐infrared spectrometry (TG‐IR). This proposed method not only could produce efficient flame retardant for EP but provide new ideas for replacing existing halogenated flame retardants.

Organic-Inorganic Modification of Magnesium Borate Rod by Layered Double Hydroxide and 3-Aminopropyltriethoxysilane and Its Effect on the Properties of Epoxy Resin.

To alleviate the safety hazards associated with the use of epoxy resin (EP), a multifunctional filler was designed. This study firstly combines the superior mechanical properties of magnesium borate rods (MBR) with the excellent smoke suppression and flame-retardant characteristics of layered double hydroxide (LDH). H2PO4− intercalated LDH (LDHP) was coated on the MBR surface to obtain inorganic composite particles MBR@LDHP. Subsequently, MBR@LDHP was modified with 3-aminopropyltriethoxysilane (APES) to obtain organic-inorganic composite particles MBR@LDHP-APES. Eventually, the hybrid particles were added to EP to prepare the composite materials. Thereafter, the morphology, composition, and structure of MBR@LDHP-APES were characterized utilizing scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD). The results indicated the successful preparation of MBR@LDHP-APES, after which we investigated the effects of MBR@LDHP-APES on the smoke suppression, flame retardancy, and mechanical characteristics of EP. As observed, the EP composites containing 7.5 wt% MBR@LDHP-APES exhibited superior smoke suppression and flame retardancy abilities. The limiting oxygen index reached 33.5%, which is 36.73% greater than pure EP, and the lowest values of total heat and smoke release were observed for the composite materials. In addition, the mechanical properties test revealed that MBR@LDHP-APES considerably enhanced the tensile strength as well as the flexural strength of the composites. Furthermore, mechanistic studies suggested that the barrier effect of MBR, endothermic decomposition of LDHP, and the synergistic effect of LDHP and APES contributed essentially to the smoke suppression and flame-retardant properties of the material. The findings of this research point to a potential method for enhancing the EP’s ability to suppress smoke and flames while enhancing its mechanical properties.

Effect of a Novel Graphene on the Flame Retardancy and Thermal Degradation Behavior of Epoxy Resin

The effect of graphene modified with a phosphorus and silicon-containing compound (GO-DOPO-V) on the flame retardancy and thermal stability of epoxy resin (EP) was studied by cone calorimetry and thermogravimetric analysis (TGA) in nitrogen. After incorporation of 2 wt% GO-DOPO-V into EP, maximum decreases of 28.8% in peak heat release rate (pHRR) and 15.6% in total heat release (THR) were achieved compared to that of pure EP. It was shown that GO-DOPO-V significantly promoted the formation of an EP tight char layer and the char residue of EP/GO-DOPO-V composite at 600 °C was 13.39 wt%, which was almost twice that of pure EP. Furthermore, the non-isothermal degradation behavior of EP/GO-DOPO-V composites were investigated also in a nitrogen atmosphere. It was found that the addition of GO-DOPO-V changed the degradation behavior of EP composites in the early and middle stages. Both the Kissinger and Flynn–Wall–Ozawa methods revealed that the addition of GO-DOPO-V increased the thermal degradation activation energy of EP, and improved the flame retardancy of the polymer matrix.

The influences of GO-SHS hybrids on the mechanical and dielectric properties of EP composites

The influences of GO-SHS hybrids on the mechanical and dielectric properties of EP composites

Highly Thermal Conductive and Electrically Insulating Epoxy Composites Based on Zinc-Oxide-Coated Silver Nanowires.

Nano-ZnO particles were deposited on the surface of silver nanowires (AgNWs) by the precipitation method, and the obtained AgNW@ZnO filler with core-shell structure was added to epoxy resin to prepare AgNW@ZnO/EP thermally conductive composites. The ZnO coating on the surface of AgNWs effectively improves the thermal conductivity of the composites. When 8 wt% AgNW@ZnO filler was added to the epoxy resin, the thermal conductivity of the AgNW@ZnO/EP composite increased to 0.77 W/(m·K). The enhancement of the thermal conductivity is attributed to the fact that ZnO effectively improves the interface bonding between AgNWs and the epoxy matrix, thus strengthening the contact between AgNWs. In addition, the electrical insulation of the AgNW@ZnO/EP composites was improved upon the introduction of the ZnO coating over AgNWs. For the filler content of 8 wt%, the volume resistivity of the AgNW@ZnO/EP composites was found to be higher than 1013 Ω·cm. AgNW@ZnO/EP composites have also exhibited low dielectric constant and good thermal stability.

Novel design and synthesis of bio-based polyelectrolyte complexes for enhancing the flame retardancy of epoxy resin

The flame-retardant efficiency of a single flame retardant is often not as expected, but the process of synthesizing new high-efficiency flame retardants is usually complicated and harsh. Here, a bio-based polyelectrolyte complexes (PA-Ni-PEI) was synthesized by reacting biomass phytic acid, nickel ion and polyethylenimine, and then incorporated into EP as a flame-retardant additive for improving the thermal stability and flame retardancy properties. When the adding of PA-Ni-PEI complexes is 2.0 wt%, the peak heat release rate (PHRR), the total heat release (THR), the total smoke release (TSR) and smoke factor (SF) with a reduction of 30.4%, 24.9%, 36.0% and 55.4%, respectively, and the char residue was improved by 53.9%, compared to EP. The improvement in fire safety was ascribed to the early degradation of EP catalyzed by the decomposition products of the composites, resulting in the formation of a dense, robust and stable cross-linked char layer to prevent heat and oxygen from contacting with epoxy resin. Simultaneously, water and nitrogen-containing incombustible gas are released to reduce the concentration of combustible gas. A new idea for the preparation of EP composites with excellent flame retardancy property was provided by this work.

The Improved Antiwear and Anticorrosion Properties of Epoxy Resin with Metal-Organic Framework ZIF-8 Containing Lubrication Oil.

Zeolitic imidazolate framework-8 (ZIF-8) was fabricated as a lubrication container to encapsulate lubrication oil, which was added to epoxy resin (EP) as a filler to get the self-lubricating ZIF-8/EP composites coating. The antiwear and anticorrosion peculiarities of EP can be significantly improved by the encapsulation method. The antiwear peculiarities of EP were evaluated by the macroscopic ball-disk friction tests with the 9Cr18 steel ball as the counterface material. The result demonstrates that the coefficient of friction (COF) and wear rate of the self-lubricating ZIF-8/EP composites were reduced by 82.1% and 93.5% compared with that of the pure EP, respectively. Importantly, the ZIF-8/EP composite shows anticorrosion performance in the artificial seawater (ASW). The constant phase element and effective capacitance of the coating containing ZIF-8 fillers are lower than that of the non-containing coating. In addition, the diameter of the capacitive arc and the impedance modulus of the coating containing ZIF-8 + YR1800 are higher than those of the coating non-containing, which proved that the corrosion resistance of the EP is improved by the ZIF-8 + YR1800.

Interfacially-engineered PBA based hierarchical structure with Ni(OH)2 nanocatalyst towards fire retardation of epoxy resin

The extended usage of epoxy resin (EP) has suffered from the notorious issue of high fire hazard, including the release of considerable heat and emission of abundant toxicants (smoke and toxic gasses). Hence, a prussian blue analogue (PBA) based hierarchical structure (Co@Ni(OH)2-A) with Ni(OH)2 nanocatalyst, is proposed via interfacial-engineering strategy, towards reducing the fire hazard of EP. As revealed, Co@Ni(OH)2-A shows strong interfacial catalytic strengths both in charring of decomposed volatiles and oxidizing of toxic gasses. By using 4.0 wt% Co@Ni(OH)2-A, the peak heat release rate, peak smoke production rate, total smoke production and peak CO production rate are reduced by 45.5%, 55.0%, 44.3% and 65.3%, respectively. Fire resistance comparison with previous works confirms the advantage of Co@Ni(OH)2-A in toxicants elimination. Owing to the well-generated hierarchical structure-polymer interfaces, the greatly enhanced mechanical property is obtained. Generally speaking, Co@Ni(OH)2-A holds exceptional efficacy in promoting the polymer fire safety and mechanical performance. This investigation may offer useful enlightenments for acquiring high-performance EP composites via designing PBA based flame retardants with hierarchically tailored structure.

Transparent, flame retardant, mechanically strengthened and low dielectric EP composites enabled by a reactive bio-based P/N flame retardant

• A reactive bio-based P/N flame retardant (named VTP) as a multifunctional additive was prepared successfully. • VTP simultaneously improved the flame retardancy, glass-transition temperature and dielectric properties of EP. • EP/VTP composites exhibited the excellent smoke suppression and improved mechanical properties. With the application of epoxy resin (EP) in high-end fields such as electronics and appliances, 5 G communication, rail transit interior decoration and so on, the requirements of flame retardant, lightweight and high performance are also put forward for EP products. Thus, it is of great significance to prepare EP composites with excellent comprehensive properties. For the sake of achieving this target, we synthesized a reactive bio-based P/N flame retardant (named VTP) as a multifunctional additive to develop high-performance EP composites with excellent flame retardance, mechanical properties, transparency and thermal oxidation stability. As expected, VTP possessed excellent flame-retardant efficiency thanks to the synergism of tetrazoles, phosphaphenanthrene and vanillin, only 5 wt% of which made EP/VTP-5% sample achieve UL-94 V-0 rating, increased limiting oxygen index (LOI) value to 30.5%, and reduced the peak of heat release (PHRR) and total smoke production (TSP) by 36.1% and 37.9% respectively. Besides, the tensile strength and glass transmission temperature (T g ) of EP/VTP composites were increased as compared to unmodified EP, as well as high transparency was retained. This work provided a very good idea and experimental basis for the preparation of high-performance EP resin.

Effect of functionalized oyster shell powder with ammonium polyphosphate on fire safety performance of epoxy resin

In recent years, bio-based flame retardants have attracted extensive interest on account of their environmental-friendly character compared with traditional flame retardants. It is reported that oyster shell powder (OSP), composed of 95% calcium carbonate and 5 % organic matter, displays excellent flame retardant potential. In this paper, a novel bio-based flame retardant named functionalized oyster shell powder (FOSP) was prepared by mechanochemistry strategy based on OSP and ammonium polyphosphate (APP) and applied to enhance the fire safety of epoxy resin (EP) composites. The results showed that FOSP emerged with notable effects in improving the fire safety performance for EP composites. Compared with pure EP, the peak value of smoke production rate (pSPR) and peak value of heat release rate (pHRR) reduced by 69.4 % and 78.2 %, respectively. In addition, the char yields of EP composites were higher than EP. Conspicuously, the total CO production for EP composites with the addition of FOSP decreased by 44.9 % compared with EP composites with the addition of APP. Therefore, OSP, a typical marine solid waste, will become a promising candidate for high fire safety polymers.

A phosphaphenanthrene-based derivative as multifunctional flame retardant for epoxy resins

In this work, the transparent, mechanically strengthened, flame retardant and smoke suppression epoxy resin (EP) composites was prepared by the addition of an indole/phosphaphenanthrene-based compound (IDT). The results presented that limiting oxygen index (LOI) of EP composite containing 5 wt% IDT raised to 32% and it passed a UL-94 V-0 rating. In the meantime, compared with EP, total smoke production (TSP) and the peak of heat release (PHRR) of EP/IDT5 were decreased by 51.9% and 32.1%, respectively. The flame-retardant mechanism of EP/IDT was also explored by pyrolysis/gas chromatography–mass spectrometry (Py-GC/MS), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Besides, the bending and tensile strengths were improved thanks to the presence of π-π conjugation and hydrogen bonds between IDT and EP. This work provided a promising way to meet the increasing multifunctional requirements of EP composites.

Synthesis of a novel type of high‐efficiency boron‐containing Schiff base flame retardant for epoxy resin

AbstractBoron‐containing Schiff base flame retardant ((E)‐2‐([2,4‐dihydroxybenzylidene]amino)ethyl dihydrogen borate (B‐HIBD) was prepared easily and successfully. Thermogravimetric analysis (TGA) showed that when the additive amount was only 3 wt%, the introduction of B‐HIBD significantly improved the thermal stability of epoxy resin (EP) composites. The cone calorimeter test showed that compared with pure EP, the peak of heat release rate (PHRR), total heat release (THR), smoke production rate (SPR)，total smoke production (TSP) ，and the releasing of CO for 3 wt% B‐HIBD/EP reduced by 58.2, 18.3, 65.9, 51.2, and 28.4%, respectively, showing that B‐HIBD could significantly enhance the fire safety of EP composites. This promotion has been embodied not only in the catalysis function of the Schiff base group containing benzene ring but also in borate participating in the carbon‐forming process, promoting the dehydration and carbonization of the EP surface and delaying the transfer of mass and heat in the combustion process, which enhance performance for flame retardant. So it is an efficient strategy to develop a novel type of high‐efficiency boron‐containing Schiff base flame retardant to improve the fire safety for EP.

Improvement of mechanical properties and flame retardancy of epoxy resin by phosphorylated cyclotriphosphazene hyperbranched polymeric flame retardants

A new phosphorylated cyclotriphosphazene hyperbranched polymer (HBPDP) was prepared by a nucleophilic substitution reaction of diphenyl chlorophosphate (DPCP) with a cyclotriphosphazene hyperbranched polyester (HBP) and introduced into epoxy resin (EP) materials. The introduction of HBPDP can improve the tensile strength and toughness of EP materials. Among them, the strength and toughness of 1% HBPDP/EP composites reached the best with 82.74 MPa and 408.50 J/m3, respectively. As the loading of HBPDP increased, the strength and toughness of HBPDP/EP composites decreased. Furthermore, the inclusion of HBPDP accelerated EP material degradation and increased the residue. More crucially, introducing HBPDP to EP materials can lower the amount of heat, smoke, and harmful gases released during burning, as well as enhance the flame retardancy and smoke suppression properties of the materials. The results showed that when 5 wt% HBPDP was added, the LOI value of EP composites reached 29.7%, which passed the UL-94 V-0 rating test. Meanwhile, compared with pure EP, the THR, TSP and smoke CO content of 5% HBPDP/EP composites were reduced by 27.3%, 20.3% and 60.7%, respectively, generating more and denser residual carbon layers.

Achieving High Thermal Conductivity in Epoxy Resin Composites by Synergistically Utilizing Al2O3 Framework and BN Sheet as Fillers

AbstractThe application of high thermal conductive Epoxy resin (EP) is an efficient way to improve the heat dissipation in electronic device. In this work, the thermal conductivity of EP is significantly improved by synergistically utilizing Al2O3 framework (AF) and boron nitride sheet (BN) as fillers. The polyurethane foams with different pore sizes are used to prepare AF for the first time. The microstructure characterization demonstrates the successful preparation of AF/EP and AF‐BN/EP with different AF pore size. The thermal conductivity of AF/EP is superior to that of Al2O3/EP composites with randomly distributed Al2O3 nanoparticles. The smaller pore of AF is beneficial to achieving a greater thermal conductivity in AF/EP composites. Especially, by combing BN with AF can further improve the thermal conductivity of AF‐BN/EP composites. The optimal value of 1.18 W m−1 K−1 (5.42 times high than pure EP) is obtained for 60 ppi‐AF‐20 wt% BN/EP composite. Besides, the dielectric property shows that by combining of AF and BN increases the permittivity, as well as low dielectric loss. The high thermal conductivity and excellent dielectric property are simultaneously achieved by synergistically utilizing AF and BN fillers, the resultant EP composites have great potential to be used in electronic devices.

Highly thermo-stable resveratrol-based flame retardant for enhancing mechanical and fire safety properties of epoxy resins

The integration of flame-retardant additive with both excellent thermal stability and remarkable fire-retarded efficiency into epoxy resins (EP) is highly demanded while challenging. Herein, a novel bio-based flame retardant (referred to DPOR) was synthesized via one-step reaction of resveratrol and diphenylphosphonyl chloride. The as-prepared DPOR exhibited outstanding thermal stability, with an initial thermal decomposition temperature of 438.4 °C, contributing from the reduced intermolecular π–π interaction and incremental oligomerization during the heating process. It was further utilized as additive for the manufacture of high-performance EP composites (EP-DPOR). Notably, DPOR can also act as mechanical reinforcer that enhanced the strength and toughness of EP. The EP-DPOR3 (3 wt% DPOR) showed a superior stretchability (15.9 %) and high tensile strength (59.3 MPa) compared to neat EP (12.4 %, 46.7 MPa). Additionally, the burning test results indicated that DPOR endowed the EP with greatly enhanced flame resistance, achieving a UL-94 V-0 rating with an increase of LOI values to 34.5 % at a low loading of 5 wt%. In cone calorimeter tests, it showed that heat and smoke release was effectively inhibited during combustion in comparison with EP, wherein the PHRR value of EP-DPOR was 27.5 % lower than EP. Thus, it is highly anticipated that DPOR, as a new type of bio-based flame retardant with superior thermal stability and efficient flame- retardant properties, holds a great potential for the development of next-generation flame retardant.

Novel exploration of the flame retardant potential of 1-oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-functionalized metallophthalocyanines in epoxy composites

A series of novel 1-oxo-4-hydroxymethyl-2,6,7-trioxy-1-phosphabicyclo[2,2,2]octane (PEPA)-functionalized metallophthalocyanines (PEPA-MPcs, M = Al, Co, Ni, Zn, and Ce) have been successfully synthesized and characterized. The obtained PEPA-MPcs were added to epoxy resin (EP) to prepare a variety of flame retardant composites (EPP-MPcs) and their thermal behavior and flame retardancy were investigated using thermogravimetric analysis (TGA), the limiting oxygen index (LOI), and cone calorimetry. The flame-retardant mechanism was systematically analyzed in the gas and condensed phases, respectively. The highest LOI value of EP containing 2 wt.% PEPA-MPcs was increased by 19% to 27.6% when compared to pure EP. The peak of heat release rate (pHRR) and the total heat release (THR) values observed for EPP-AlPc were reduced by 64.3% and 48.6%, respectively. The main flame retardant mechanism of the PEPA-MPcs is the synergistic effect of the P and N atoms, including the dilution of highly non-flammable gases in the gas phase and the formation of an intumescent char layer from the condensed phase. Furthermore, the char residues of the EPP-MPcs were significantly increased via the catalysis and surface enrichment of the metal atoms, which reduced the fire hazards of the EP composites. In addition, the EPP-MPcs exhibit excellent mechanical properties and uniform dispersions. This work provides a new approach to the preparation of metal containing/non–halogen/phosphorus-containing flame retardants.

Polyhydric SiO2 coating assistant to graft organophosphorus onto glass fabric for simultaneously improving flame retardancy and mechanical properties of epoxy resin composites

It is still a great challenge to develop epoxy resin/glass fabric (EP/GF) composites with well-balanced enhancements on flame retardancy and mechanical properties. Herein, a novel strategy that polyhydric SiO2 coating assistant to graft organophosphorus (DOPO) onto GF was developed for simultaneously improving flame retardancy and mechanical properties of EP composites. The grafting amount of DOPO could reach to 43.64 wt% via the helpful bridging of polyhydric SiO2, so that EP composites displayed excellent flame retardancy with the LOI of 37.2%, the V0 rating on UL-94 and a 63.3% decrease on PHRR in cone calorimeter test. According to the analysis of char morphology and structure, the flame retarded mechanism was mainly ascribed to the enhanced barrier effect of a continuous and intergrow char layer, which was composed of GF@SiO2 as framework and P-containing condensed carbon as stuffing. Meanwhile, EP composites exhibited outstanding mechanical performances with 35% and 60% increases on tensile strength and impact strength respectively, which resulted from the special molecular structure of GF@SiO2-g-DOPO with strong interfacial adhesion with EP chains via hydrogen bond and chemical bond. In summary, this work will be favorable to design multifunctional polymer composites with well-balanced comprehensive performances, and expand their widespread applications in high-end fields.

Organic-inorganic hybrid engineering MXene derivatives for fire resistant epoxy resins with superior smoke suppression

It is a challenge to integrate organic and inorganic materials to build organic–inorganic hybrid, high-efficiency flame retardants with synergistic effects of both to diminish the fire risks of polymer composites. In this work, an organic–inorganic hybrid strategy was used to prepare leaf-like MXene-based flame retardants (MXene@Bi-MOF) by in situ growth of bimetallic metal–organic frameworks (Bi-MOF) on the surface of MXene and the hybrids were incorporated into epoxy resins to explore their flame retardancy and smoke suppression effects. Specifically, the introduction of MXene@Bi-MOF hybrids not only achieved homogeneous dispersion in EP matrix, but also improved the thermal properties of EP composites, with a 27.7% lower maximum mass loss rate (Rmax) than that of pure EP. In addition, EP composites containing 2 wt% MXene@Bi-MOF exhibited improved fire safety, reduced heat release and inhibited smoke production, as evidenced by a 28.8%, 45.3%, 36.5%, 30.7% and 55.3% drop in peak heat release rate (PHRR), peak smoke production rate (PSPR), total heat release (THR), peak CO production rate (PCO) and smoke factor (SF) value, respectively, as well as growing char yields and lower fire growth index (FGI) value, compared to those of pristine EP. The synergistic action of MXene and Bi-MOF, mainly including the blocking effect of MXene lamellar structure, catalytic carbonization effects as well as catalytic attenuation of the transition metal oxides and gas phase dilution from Bi-MOF, was primarily responsible for the improved fire safety of EP composites.

Adenine as an efficient adsorbent for zinc ions removal from wastewater to in situ form bio-based metal–organic frameworks: A novel approach to preparing fire-safe polymers

In this study, adenine was used as an efficient adsorbent for in situ removal of zinc ions, resulting in the formation of a bio-based metal–organic framework (bioMOF). The as-prepared bioMOF was further used as flame retardant additives to prepare fire-safe polymers. TGA results indicated that the bioMOF can improve the char yield in the EP composites. The EP composite with 8.0 wt% bioMOF displayed a high limiting oxygen index (LOI) of 31.0% as well as a UL-94 V-0 rating. Additionally, the peak heat release rate, total heat release, and smoke production rate of the EP composite with 8.0 wt% bioMOF declined by 56.3%, 50.5%, and 72.0%, respectively. Furthermore, the EP composite with 8.0 wt% bioMOF also displayed higher glass transition temperature and better tensile strength than the pristine EP. This work provides a novel approach to preparing fire-safe polymers through recycling waste from adsorbent materials of water decontamination.

A phosphaphenanthrene‐based derivative for simultaneously improving flame retardant and smoke suppression of epoxy resin composites

AbstractEpoxy resin (EP) have the disadvantage of high flammability and large amount of smoke, which greatly restricts its wide application in basic material. In order to obtain EP with excellent smoke inhibition and flame retardance, the flame retardant called as PBO, which with both condensed phase and gas phase flame‐retardant effects, was synthesized by the reaction among p‐phenylenediamine, DOPO, and indole‐3‐carboxaldehyde. From combustion results, EP containing PBO obtained V‐0 grade with a significantly improvement from 22.5% to 30.2% in limiting oxygen index. In comparison with EP, total smoke production, total heat release and the peak of heat release of EP/PBO‐1.0 were declined by 32%, 41.5%, and 37.4%, respectively. Besides,Tgof EP composites also had a certain degree of improvement, which due to the increase of rigidity and crosslinking density of EP caused by the addition of PBO. Meanwhile, the analysis of chars and pyrolysis products of PBO presented that the improvement was assigned to two phase synergy through barrier effect of chars in condensed phase and interrupt chain reaction in gaseous phase.