EP Resin Research Articles

High strength, low flammability, and smoke suppression for epoxy thermoset enabled by a low-loading phosphorus-nitrogen-silicon compound

In order to develop high-performance epoxy resins (EP), a novel phosphorus/nitrogen-containing phenylsiloxane macromolecule (DP-PPD) has been synthesized as a multi-functional additive. The DP-PPD macromolecules can simultaneously enhance the mechanical strength, flame retardancy, and smoke suppression performance for EP at low loading. Compared with unmodified EP, only by introducing 2 wt% DP-PPD, the impact strength, flexural strength and flexural modulus are greatly increased by 100%, 12.9% and 38.7%, respectively, due to flexible phenylsiloxane units and covalent interaction with EP matrix. Meanwhile, the resultant EP containing barely 3 wt% DP-PPD reaches V-0 rating in UL-94 test and shows a high limiting oxygen index of 30.1%. The cone calorimeter test results reveal that the peak of heat release rate, total heat release, and total smoke release of 9%DP-PPD/EP are decreased by 31.4%, 35.4%, and 20.0%, respectively, compared to those of unmodified EP. The mechanism analysis confirms that abundant aromatic rings, siloxane, and DOPO units in DP-PPD can synergistically promote the formation of P–Si-containing hybrid char layer for EP resins during combustion, thus leading to satisfied flame retardancy and smoke suppression. Meanwhile, the reduction of volatilized organic products and the emergence of phosphorous fragments indicates the flame inhibition effect of DP-PPD. Moreover, DP-PPD has little negative effect on the heat resistance of EP. This efficient single-component multi-functional additive provides a new strategy for the construction of high-performance macromolecular materials.

Physico-Mechanical Properties of Nano Silica-Filled Epoxy-Based Mono and Hybrid Composites for Structural Applications

This research article describes the results of nano-silica (nSiO2) filled epoxy (Ep) mono composites with different contents (0.5, 1.0, 1.5, 3, and 5 wt.%) and carbon fabric-reinforced epoxy (CFE) with 1.5 and 3 wt.% of nSiO2 hybrid composites and their physical and mechanical properties characterized by different techniques as per ASTM standards. Mechanical mixing and sonication techniques were followed to disperse nSiO2 into Ep resin. Furthermore, the same nSiO2/Ep is reinforced with carbon fabric by hand lay-up followed by vacuum-bagging technique. The morphological features were studied by scanning electron microscopy. The properties of the Ep based mono and hybrid composites showed that the hardness, tensile strength/modulus, and flexural strength/modulus, as well as impact strength of the composites enhanced with nSiO2 wt.% up to 3 wt.% for mono and hybrid composites and decreased thereafter; suggesting that the beneficial properties ensued up to 3 wt.% nSiO2 content.

A special filler for epoxy resin to enhance the T peel strength of adhesive

AbstractThe filler that could enhance the T peel strength of adhesive was prepared using graphene oxide (GO) grafted with toluene diisocyanate (TDI) and amino terminated poly(butadiene‐acrylonitrile) (ATBN). As a result of structure characterization, the ATBN‐TDI‐GO structure with dissociated ‐NCO groups was built. The T peel strength of the adhesive containing 25 wt% ATBN, 17 wt% TDI, and 0.5 wt% GO increased to 18.47 N/mm, which increased by 4.75 times compared with pure epoxy resin (EP), and other mechanical properties of the adhesive were enhanced. The reason for the increasing of bonding properties was chemical bonding built between the adherent and the adhesive by the surplus ‐NCO groups provided by the ATBN‐TDI‐GO filler. The effect of physical adsorption provided by ATBN and the chemical bonding between the matrix resin and ATBN‐TDI‐GO filler also could toughen the EP resin. The design of the EP filler could provide a new method for adhesive manufacture.

Highly Oriented Graphite Aerogel Fabricated by Confined Liquid-Phase Expansion for Anisotropically Thermally Conductive Epoxy Composites.

Graphene-based thermally conductive polymer composites are of great importance for the removal of the excess heat generated by electronic devices. However, due to the orientation of graphene sheets in the polymer matrix, the through-plane thermal conductivity of polymer/graphene composites remains far from satisfactory. We here demonstrate a confined liquid-phase expansion strategy to fabricate highly oriented confined expanded graphite (CEG) aerogels. After being incorporated into epoxy resin (EP), the resulting EP/CEG composites exhibit a high through-plane thermal conductivity (4.14 ± 0.21 W m-1 K-1) at a quite low filler loading of 1.75 wt % (0.91 vol %), nearly 10 times higher than that of neat EP resin and 7.5 times higher than the in-plane thermal conductivity of the composite, indicating that the CEG aerogel has a high through-plane thermal conductivity enhancement efficiency that outperforms those of many graphite/graphene-based fillers. The facile preparation method holds great industrial application potential in fabricating anisotropic thermally conductive polymer composites.

Development of cashew nut shell carbon reinforced thiourea based biophenolic benzoxazine‐epoxy composites: High performance biobased coating materials

AbstractThe research work focused on the preparation of biobased eugenol benzoxazine (EUBz) using thiourea as amine resource and their conversion into EUBz‐epoxy (EUBz‐EP) blend matrix and EUBz‐EP blend composites. In the present work, thiourea‐based eugenol‐benzoxazine monomer was synthesized using eugenol as phenolic compound, thiourea as amine resource and paraformaldehyde. The molecular structure of monomer was confirmed by FTIR, NMR, and Maldi mass studies. The thiourea‐based EUBz properties were enhanced by the blending of EP resin and reinforced with varying weight percentages of amine functionalized cashew nut shell carbon (f‐CSC). The thermally cured f‐CSC/EUBz‐EP composites possesses a higher glass transition temperature of 202.9°C when compared to that of the EUBz matrix (104.2°C), which might arise due to the higher crosslinking density resulted from the reinforcement of EP resin with f‐CSC. In addition, the hydrophobic behavior of the prepared composite materials is improved by blending the EUBz with EP resin and reinforcing with f‐CSC. The enhancement of the value of contact angle from 80.3° to 105.9° infers the improvement of hydrophobic behavior of f‐CSC reinforced EUBz‐EP blend composites. The corrosion rate and protection efficiency of 5 wt% f‐CSC/EUBz‐EP composites exhibits 0.814 (mm/year) and 99.97%, respectively. Data obtained from different studies suggested that the f‐CSC reinforced EUBz‐EP blended composites can be used in the form of sealants, encapsulants, adhesives, and coatings for different industrial and engineering applications.

Anticorrosion and electromagnetic interference shielding behavior of candle soot‐based epoxy coating

ABSTRACTThis article presents candle soot (CS) as anticorrosion coating material for mild steel (MS) in 3.5 wt % of NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy. CS is easily available, low‐cost material, and characterized by using X‐Ray diffraction (XRD), Raman spectroscopy, UV–vis spectroscopy, Fourier‐transform infrared (FTIR), and scanning electron microscopy (SEM). CS is superhydrobhobic in nature that helps to prevent corrosion by repelling water molecules from MS surface. The electrochemical results confirmed the prevention in corrosion process for MS using candle soot‐epoxy (CS‐EP) based anticorrosion coatings. The CS‐based coatings displayed outstanding barrier properties in 3.5 wt % of NaCl solution in comparison to the neat EP coating. Different candle CS‐EP coating combinations were tested that exhibited excellent corrosion inhibition performance with highest protection increased up to 98.45% at 0.2 wt % of CS. The surface morphological studies were used to analyze the MS surface conditions in absence and presence of CS‐EP coating in 3.5 wt % of NaCl solution. CS‐EP admixtures were also tested for their shielding effectiveness in the frequency range of 8.2–12.4 GHz and it has been found that on incorporation of 0.2 wt % of CS in EP resin total shielding effectiveness (SET) increased to −5.3 dB as compared to −0.33 dB for neat EP. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48675.

Ultrasonic-assisted rapid preparation of three-phase nanocomposites: The effects of zinc manganite nanoparticles and polyurethane on the thermomechanical, physicochemical, and antibacterial properties of polymer matrix composites

Polymeric mixing and ultrasonic dispersion method as a green, fast, effective, and inexpensive technique was utilized to prepare epoxy/polyurethane/zinc manganite nanoparticles (EP/PU/ZnMn2O4 NPs) nanocomposites. The ZnMn2O4 NPs and PU were used for the optimization of mechanical properties of EP resin. Response surface methodology (RSM) coupled with central composite design (CCD) was employed to obtain suitable mathematical models as function of physico- and thermomechanical factors. The weight fractions of PU and ZnMn2O4 NPs were chosen as the independent variables, and the effect of these variables on the mechanical properties of the EP resin was investigated. The tensile test showed that the addition of the PU and ZnMn2O4 NPs in the polymer matrix improved the mechanical properties. The dynamic mechanical analysis results showed that the storage modulus and the glass transition temperatures of the nanocomposites increased and decreased, respectively. The optimum values of PU and ZnMn2O4 NPs contents for good mechanical properties were determined as 0.73 weight percentage (wt%) and 0.15 wt% ratio to EP resin, respectively. The antibacterial properties of the optimum sample were also investigated, and the results showed that, with the addition of the NPs, the antibacterial performance of EP/PU increased. The X-ray diffraction, Fourier-transform infrared, scanning electron microscopy/energy-dispersive X-ray analysis, diffuse reflectance spectroscopy (DRS), and vibrating sampler magnetmeter analyses were also applied to study the chemical and magnetic properties of the optimized nanocomposite samples.

Facile strategy and mechanism of greatly toughening epoxy resin using polyethersulfone through controlling phase separation with microwave‐assisted thermal curing technique

ABSTRACTToughening has been the essential issue for developing high‐performance thermosetting resins. Herein, starting from polyethersulfone (PES) and bisphenol A epoxy resin (EP), a facile strategy is developed to prepare tough resins through controlling phase structure with microwave‐assisted thermal curing. PES/EP resins cured with the assistance of microwave curing (m‐PES/EP) have two major differences compared with those using traditional heat curing (t‐PES/EP), one is high degree of phase separation, and the other is phase separation mechanism. Initial phase separation of all t‐PES/EP resins follows spinodal decomposition mechanism, while those of m‐PES/EP systems with 8 wt% and 18 wt% of PES follow nucleation and growth mechanism. These differences are derived from the fact that microwave curing has much faster phase separation rate and curing reaction rate than thermal curing owing to the higher thermal effect. Differences in phase structure bring different macro performances, and m‐PES/EP systems have higher impact strengths, fracture toughnesses, and flexural strengths than t‐PES/EP resins. This investigation provides a facial and effective way of developing higher performance thermoplastic/thermosetting resin system through controlling phase structure. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2020,137, 48394.

Effect of modified bentonites on the crosslinking process of epoxy resin with alifphatic amine as curing agent

In this work the influence of modified bentonites on the process of epoxy crosslinking with triethylenetetramine (TETA) was investigated. Bentonites (BS) modified with quaternary phosphonium (QPS) and ammonium (QAS) salts were used as a nanofiller in the epoxy matrix (EP) in the amounts of 1 and 3 wt %. Gel time of the compositions was investigated using rotational rheometer at 30, 45 and 60 °C and activation energies of the compositions were determined. The storage G’ and loss G” moduli crossover criterion was used to determine the nanocomposites gel time variation. On the basis of the obtained results, it was found that the addition of modified aluminosilicates decreased the gel time of epoxy compositions at 30 and 45 °C, while at 60 °C it increased compared to unmodified epoxy resin. The obtained results indicate that the amount of modified aluminosilicate and the type of salt influence the reactivity of epoxy compositions. Among the tested systems, the most reactive was the composition of EP+3%BSQPS1, because the gel time at 30 °C and activation energy decreased by 1500 s and 8 J/mol, respectively, in relation to the unfilled EP resin. A more catalytic effect was observed in the case of bentonites modified with quaternary phosphonium salts, which may be associated with lower phosphorus electronegativity in relation to nitrogen and a lower viscosity of these systems.

Preparation and mechanical performances of carbon fiber reinforced epoxy composites by Mxene nanosheets coating

Known as a new kind of two dimensional materials, Mxene has attracted much attention in applications in polymer based composites because of their unique mechanical, thermal, and electrical properties. In this work, we report on the synergistic enhancement of Ti3C2Tx Mxene nanosheets coated on carbon fiber (CF/Mxene) to epoxy resin. Ti3C2Tx Mxene nanosheets were synthesized by HF etching and sonicating and used as surface sizing agent to modify NH2-CF by electrostatic self-assembly. NH2-CF/Mxene reinforced epoxy resin (NH2-CF/Mxene/EP) composites were prepared using a solution blending method. Their structure, morphology and performance were investigated. It is observed that Mxene possesses nanosheet structure and functional groups which are responsible for improving interfacial adhesion between NH2-CF and EP resin. The structural characterization showed that Mxene nanosheets are successfully attached to the NH2-CF surfaces. Importantly, the tensile strength, flexural strength, shear strength, and impact strength of NH2-CF/Mxene/EP composites have respectively increased by 40.8, 45.9, 38.5, and 74.4% compared to those of pristine CF/EP composites, suggesting that Ti3C2Tx Mxene nanosheets use is a promising approach for improving the mechanical properties of EP-based composites.

Preparation of carbon nanotube/epoxy composite films with high tensile strength and electrical conductivity by impregnation under pressure

Based on the production of a carbon nanotube (CNT) assembly, a new technique is developed for preparing CNT/epoxy (EP) composite films with high tensile strength and electrical conductivity. CNTs are synthesized by floating catalyst spray pyrolysis. After self-assembling into a hollow cylindrical assembly, CNTs are drawn and wound on a rotating drum to form a uniform CNT film. EP resin solutions of different concentrations are used to fill into the pores within the film under different pressures and form composite films after hot-press curing. The permeability of the EP resin and thus the interfacial bonding between the CNT and the EP resin are studied by varying the concentration of the EP resin solution and the pressure used for impregnation. Under optimal preparation conditions, the composite film contains CNTs of a high content of 59 wt.%, and shows a high tensile strength of 1.4 GPa and a high electrical conductivity of 1.4×105 S·m−1, 159% and 309% higher than those of the neat CNT film, respectively.

Development of a nanostructured Ce(III)-Pr(III) film for excellently corrosion resistance improvement of epoxy/polyamide coating on carbon steel

Chemical treatment of carbon steel (CS) specimens was done by an eco-friendly Ce (III)-Pr(III) composite nanofilm. The impact of composite film deposition on CS on the epoxy coating (EP) capability for reduction of CS corrosion and delamination rates was examined. The Ce (III)-Pr (III) thin film morphology was studied by field emission-scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS) methods. The EP anti-corrosion capacity promotion on CS by deposition of Ce(III)-Pr(III) composite film was investigated by electrochemical impedance spectroscopy (EIS) and salt spray test. Cathodic delamination (CD) rate of EP/Ce (III)-Pr (III) system was also examined. Furthermore, molecular dynamics (MD) simulations were applied to get microscopic-level insights into the aminoamide hardener/epoxy coating interaction mechanism with Ce (III)-Pr (III) film. It was shown that the film uniformly deposited is mainly composed of oxide/hydroxide of cerium (III) and praseodymium (III) and without crack and defect. Results revealed that the Ce (III)-Pr (III) composite thin film significantly promoted the EP anti-corrosion capability and decreased the CD rate. The computational results proved that the curing agent and crosslinked EP resin adsorbed to praseodymium and cerium oxide surfaces mostly through electrostatic interactions of N and O heteroatoms with surface metal atoms.

Wettability and dynamics of water droplet on a snail shell

HypothesisThere are many natural surfaces with special wettabilities. Snail shells have unique rough structures, which indicates a specific wettability. In this study, the surface of a snail shell was simulated using epoxy resins, and water droplet dynamics on original and simulated snail shells were investigated to understand its special wettability. ExperimentsThe shell of the Euhadra sandai species of snails was used. The surface structure of the snail shell was simulated using epoxy resins. The surface of this EP resin was treated with UV-O3 for different periods of time. Wettabilities and dynamics of water droplet on the samples were characterized. FindingsThe surface of the snail shell with a water contact angle of approximately 85° caused the droplet to spread, which is the first report of water droplet dynamics on the shell surface. The behavior of a water droplet on the shell transformed from the Cassie state into the Wenzel state. Changes in the contact angle and diameter of the droplet base on the snail shell were larger than those on the epoxy resins. The surface roughness and chemical heterogeneity of the snail shell led to distortion of the three-phase contact line and enhancement of the spreading of the water droplet.

Flame‐retardant and thermal degradation mechanisms of melamine polyphosphate in combination with aluminum phosphinate in glass fabric‐reinforced epoxy resin

A system based on a nitrogen–phosphorous flame retardant, melamine polyphosphate (MPP), and aluminum phosphinate (OP), was employed to flame‐retard glass fabric‐reinforced epoxy resin composites (GFEP). Surface modification was adopted to effectively solve the aggregation of MPP and OP particles in EP matrix during the curing process. The flammability characteristics and synergistic effect have been studied by using limiting oxygen index (LOI), vertical burning (UL94) tests, thermogravimetric analysis, and pyrolysis‐gas chromatography/mass spectrometry. The flame resistance tests indicated that the synergism system with an optimized ratio achieved UL94 V‐0 (1.6 mm) rating and the LOI value of 33.5%. The chemical composition and structure of residue were characterized by X‐ray photoelectron spectroscopy, Fourier transform infrared, and scanning electron microscopy. It is concluded that the synergistic system having a balance of nitrogen element and phosphorous element accelerate the carbonation of EP resin, which was in favor of the construction of compact and continuous charring structure, thus obtaining satisfactory flame retardance. POLYM. COMPOS., 40:3199–3208, 2019. © 2018 Society of Plastics Engineers

Long-term creep behavior of resin-based polymers in the construction industry

For lifetime assessment of resin-based injection mortar systems in structural applications, a fundamental knowledge of the long-term deformation and failure behavior of such materials is required. This research work addresses the long-term deformation behavior by experimental determination of creep modulus curves for two commercially available epoxy resin (EP) and vinyl ester (VE) resin applied in the construction industry, e.g. for post-installed fastenings, retrofitting and strengthening (FRPCs). The experimental approach involves an accelerated procedure for providing creep modulus data for these complex material systems, considering various material states of practical engineering relevance. Three reference material states were defined as upper and lower bound states, respectively, for the expected creep behavior. They were experimentally accomplished by appropriate temperature and moisture preconditioning. The upper bound reference state I represents and is referred to as the “(fully) cured & dry” state. Conversely, two lower bound reference states representing (a) reference state II “standard-cure – as received” and (b) reference state III “(fully) cured & wet” were defined. For reference state I (upper bound), a stress level of 10 MPa was chosen for the creep experiments at different temperatures, and creep modulus master curves for a temperature of 23 °C and up to 50 years were deduced making use of the time-temperature equivalency principle. The creep modulus curves for the lower bound material reference states II and III were assessed based on modulus reduction factor deduced from short-term tensile experiments together with the functional creep characteristics of the upper bound reference state I. In addition, a hypothetical quasi-worst-case material state as a third “conservative” lower bound state was defined by simply superimposing and hence multiplying the reduction factors for reference states II and III. In this manner, a creep modulus function scatter band for the defined upper and lower bound conditions was achieved, which can be used for deformation modeling and simulation of injection mortar systems. While for the EP resin based resin the effect of curing state was found to be negligible (at least over the range investigated) with the effect of moisture content being more apparent, for the VE resin based resin, both material conditions profoundly affect the creep modulus properties.

Physicochemical and Mechanical Properties of Epoxy/Polyurethane/Nickel Manganite Nanocomposite: A Response Surface Methodology/Central Composite Designs Study

In this study, NiMn2O4 nanoparticles (NPs) were synthesized as a nanofiller via the sol–gel auto-combustion method. Then, epoxy/polyurethane/Nickel Manganite (EP/PU/NiMn2O4) nanocomposites were prepared via the ultrasonic method. Effects of the polyurethane weight percentage and the amount of NiMn2O4 NPs on the mechanical properties of EP resin were investigated using response surface methodology/central composite design (RSM/CCD) method. Tensile test, DMTA, XRD, FT-IR, SEM/EDAX, TGA and DRS analysis were performed to study the mechanical and chemical properties of these nanocomposites. FT-IR spectra of the nanocomposites show strong interactions between hydroxyl groups of NiMn2O4 and EP. SEM and XRD results showed the presence and distribution of NiMn2O4 NPs in polymer matrix and thermogravimetric analysis (TGA) depicts that the nanocomposite has the best thermal stability in relation with EP and EP/PU. DMTA illustrated that the incorporation of NiMn2O4 NPs into EP/PU matrix increased storage module because of good interaction between NiMn2O4 nanoparticle and epoxy group. Tensile test showed the presence of NiMn2O4 NPs in polymer matrix improved the mechanical properties such as ultimate tensile strength, toughness and elongation at break. The optimal values of the PU and NiMn2O4 NPs factors were predicted to be (2.92 wt%) and (0.73 wt%) respectively.

Preparation and origin of thermally resistant biobased epoxy resin with low internal stress and good UV resistance based on SiO2 hybridized cellulose for light emitting diode encapsulation

Big internal stress and poor UV resistance are two bottlenecks of epoxy resins for light emitting diode (LED) encapsulation, and how to solve them with a green method is still a great challenge. Herein, a unique hybrid was synthesized by forming SiO2 particles on surface of cellulose, the hybridized cellulose (mCNC@SiO2) was then used to develop new high performance epoxy resin (mCNC@SiO2/EP) for LED encapsulation. The effect of the content of mCNC@SiO2 on the comprehensive performances of mCNC@SiO2/EP resins was studied. Results show that the presence of mCNC@SiO2 not only greatly reduces the internal stress and improves UV resistance, but also increases moisture resistance while maintaining high heat resistance. When the content of mCNC@SiO2 is only 2.0 wt%, the internal stress is reduced by 62%, thanking to the significant decrease in thermal expansion coefficient, and curing stress derived from the flexibility of Si-O-Si segment in mCNC@SiO2. In addition, mCNC@SiO2/EP resin has good transmittance, proving that the presence of mCNC@SiO2 can effectively alleviate yellowing and improve UV resistance. These excellent comprehensive properties of mCNC@SiO2/EP resin demonstrate that mCNC@SiO2 is a green and multifunctional modifier of epoxy resin for high performance LED encapsulation.

Durability under freeze–thaw cycles of concrete beams retrofitted with externally bonded FRPs using bio-based resins

This study examined the effects of freeze–thaw (FT) cycles on the flexural performance of reinforced concrete beams strengthened with externally bonded fibre-reinforced polymer (FRP) laminates fabricated using bio resins. Six large-scale beams including three retrofitted with bio resin-FRP, two with epoxy-FRP, and one control beam, were tested. A fully bio furfuryl alcohol (FA) resin derived from corn cobs and sugar cane, and a partially bio epoxidized pine oil (EP) resin, were investigated. Additionally, 40 FRP tension coupons fabricated with the bio resins and the epoxy resin were tested to assess the effect of FT cycles on their tensile properties. Specimens were exposed to 300 FT cycles over a period of seven months at a temperature range of +6 to −27 °C. The study showed that this aggressive FT regime did not have a negative effect on the ultimate capacities of the beams or the coupons. In fact, all the conditioned beams had peak loads between 7 and 17% higher than their unconditioned counterparts, which may be attributed to the additional curing of concrete during the thawing phase of the FT cycles by submersion in water. The FT conditioned beams with the FA and the EP resin FRPs had 22 and 25% higher yield loads and 25 and 31% higher ultimate loads, respectively, compared to the FT conditioned unstrengthened beam.

The influence of mesoporous SiO2‐graphene hybrid improved the flame retardancy of epoxy resins

A novel mesoporous SiO2‐graphene nanohybrid was successfully synthesized by a 1‐pot hydrothermal synthesis method using tetraethylortho silicate and graphene oxide as initial materials to improve the dispersion of graphene in epoxy matrix. Subsequently, the SiO2‐graphene nanohybrids were added into epoxy resin to investigate their fire behaviors. It was found that the incorporation of the as‐prepared SiO2‐graphene nanohybrids into epoxy resin obviously increased the flame retardancy, compared with those of neat epoxy. This attractive feature of SiO2‐graphene epoxy nanocomposites was attributed to the barrier effect as well as the labyrinth effect contributed by SiO2‐graphene in EP resin.

Comparative investigation on combustion property and smoke toxicity of epoxy resin filled with α- and δ-MnO2 nanosheets

Manganese dioxide (MnO2) as a promising green material has attracted widely attention in virtue of its outstanding chemical and physical properties. Herein, MnO2 nanosheets with α- and δ- crystal structures were used to comparatively study the influence of crystal structures on the fire resistance of EP resin. Cone calorimeter results confirmed that δ-MnO2 nanosheets achieved better improvements than α-MnO2 nanosheets in reducing the PHRR and THR values as well as suppressing smoke release during combustion process. Moreover, Raman data and SEM tests showed that δ-MnO2 nanosheets could effectively promote the char dense of char residues of EP composites. TG-IR results also indicated that the pyrolysis toxic products were significantly decreased after the incorporation of δ-MnO2 nanosheets. By the way, the mechanical property of EP/δ-MnO2 2% composites had no obvious reduction compared with pristine EP resin, which would not restrict the application of EP resin in fields requiring high mechanical properties.