Mechanical Properties Of Epoxy Resin Research Articles

Improving Processability and Mechanical Properties of Epoxy Resins with Bio‐Based Flame Retardants

AbstractIntegrating flame retardant additives into epoxy resins is an essential strategy for improving their fire resistance. However, introducing flame retardant groups often compromises the processability and mechanical integrity of the resins. In this research, we synthesized a novel, bio‐based flame retardant, referred to as DPN, using naringenin and chlorodiphenylphosphine as precursors via a straightforward single‐step process. The addition of DPN dramatically decreased the viscosity of Hydantoin Epoxy Resin, from 7468 mPa·s to 1285 mPa·s. Furthermore, when cured with 4,4‐diaminodiphenylmethane (DDM), the composite containing 5 equivalents of DPN (DPN‐5) exhibited a remarkable improvement in mechanical strength, reaching 190 MPa, significantly outperforming the pure thermoset (DPN‐0: 104 MPa), while preserving high transparency. Combustion tests further confirmed that DPN significantly boosts the flame resistance of the thermoset, with DPN‐5 achieving a Limiting Oxygen Index (LOI) of 37% and securing a UL‐94 V‐0 rating. Cone calorimetry analysis showed that DPN‐5 effectively reduced heat and smoke production during combustion, achieving a 13.4% reduction in Peak Heat Release Rate and a 28.2% decrease in Total Heat Release compared to DPN‐0. This study underscores the potential of multifunctional bio‐based flame retardants derived from renewable resources in advancing the development of high‐performance materials.This article is protected by copyright. All rights reserved.

Mechanical Properties and Failure Behavior of Epoxy Rubber Powder Composites Reinforced with Hollow Beads

In this paper, new epoxy resin/rubber powder/hollow beads three-phase composites were prepared by designing the incorporation of fly ash hollow beads with different mass fractions (5%, 10%, 15%, and 20%) as new reinforcing phases into epoxy resin/rubber powder two-phase composites with 5% mass fraction of carbon black rubber powder. Quasi-static compression tests were conducted at room temperature to test the compressive properties of the oxygen resin/rubber powder/hollow beads composites. Calculate the energy absorption properties and energy absorption efficiency of the composites from the compression curves. Fracture characteristics of compressed material specimens with microscopic morphology were observed by scanning electron microscopy. By systematically analyzing the effect of fly ash hollow beads content on the mechanical properties of epoxy resin/rubber powder/hollow beads three-phase composites, it was found that fly ash hollow beads as reinforcing materials can effectively improve the brittleness and yield strength of epoxy resin/rubber powder as well as the energy-absorbing properties and efficiency of the composites. The energy absorption properties of the epoxy resin/rubber powder/hollow beads composites increased and then decreased with the increase in the mass fraction of fly ash hollow beads. In the epoxy resin/rubber powder/hollow beads composites, the most significant performance was observed when the mass fraction of fly ash was 10%.

Eco-friendly preparation of advanced epoxy composites and their pyrolysis and flame retardant mechanisms

Traditional additive flame retardants pose issues including high dosage, easy precipitation, and poor compatibility with the matrix. Designing efficient organic-inorganic synergistic flame retardants can enhance the flame retardancy and mechanical properties of epoxy (EP) composites while reducing their smoke toxicity. In our study, we initially employed Tetrakis(hydroxymethyl)phosphonium sulfate (THPS) for intercalation modification of montmorillonite (MMT). Subsequently, we achieved a green and efficient exfoliation of MMT by reacting urea with hydroxyl groups, resulting in the simultaneous preparation of efficient organic/inorganic synergistic flame retardants (THPSU-MMT). EP composites containing 5wt% THPSU-MMT can attain UL-94 V0 classification. Furthermore, the peak heat release rate (PHRR), total heat release (THR), and peak release rates of CO can be reduced by up to 78.42 %, 62.26 %, and 72.50 %, respectively. Simultaneously, we systematically investigated the synergistic flame retardant mechanism of the EP composite. The findings reveal that THPSU-MMT exhibits a dual flame retardant effect in both the gaseous and condensed phases. Moreover, the combination of MMT and THPSU substantially enhances the presence of phosphorus-containing pyrolysis products in the condensed phase. The fire performance index (FPI) of the flame retardant EP increased from 0.05 m2/s/W in pure EP to 0.36 m2/s/W, attributed to the enhanced catalytic carbonization and assisted gas-phase free radical capture. Additionally, the flame spread index (FGI) decreased from 11.55 kW/m/s in pure EP to 1.18 kW/m/s, signifying a substantial enhancement in fire safety. Furthermore, the THPSU-MMT synergistic flame retardants improved the tensile strength of EP composites. This study offers an environmentally friendly and efficient approach for the effective exfoliation of MMT, while also presenting novel concepts for the design of efficient organic-inorganic synergistic flame retardants.

Construction of a hybrid flame retardant based on mesoporous silica for enhancing fire safety, smoke suppression, and mechanical properties of epoxy resins

AbstractIn order to improve the fire safety of epoxy resins (EPs), the SBA‐15 based hybrid flame retardant (SNAZD) was synthesized via an organic–inorganic hybridization strategy of mesoporous silica SBA‐15. Relying on electrostatic interaction, the zinc amino‐tris‐(methylenephosphonate) (Zn‐ATMP) was successfully introduced into the pore channels of SBA‐15. Then, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was successfully loaded into the pores of SBA‐15 under vacuum. The results show that the EP composites with the 5%SNAZD sample (sample EP‐5%SNAZD) showed a LOI value of 30.9% and achieved the vertical burning V‐0 rating. In comparison to EP, the peak heat release rate, peak smoke production rate, and production rate of CO of EP‐3%SNAZD were reduced by 32.2%, 31.9%, and 20.0%, respectively. This is due to the presence of Si, P, N, and Zn elements in the SNAZD, which promoted the generation of a high yield of dense char residue and inhibited the release of toxic gasses. And the impact strength and flexural strength of EP‐1%SNAZD were increased by 19.5% and 15.6%, respectively, and the E' of EP‐5%SNAZD increased by 49.1% when compared with the neat EP. This work provides a general strategy for the design of mesoporous hybrid flame retardant and creates additional opportunities for applications of EP.

Thermally conductive h-BN/EP composites oriented by AC electric field induction

The excellent electrical insulation properties and mechanical properties of epoxy resin (EP) have led to its rapid development in the field of microelectronic packaging. However, the poor thermal conductivity of epoxy resins (thermal conductivity of only 0.14 W/(m·K)) limits the development of components for high power. Adding h-BN to epoxy resin to prepare composites can effectively improve the thermal conductivity of epoxy resin. In this paper, h-BN/EP high thermal conductivity composites were prepared by means of AC electric field induction with the goal of making the composites low loading and high thermal conductivity (loading of 10 wt%). It was shown that the h-BN/EP composite had the highest thermal conductivity of 0.310 W/(m·K) when applied to an AC electric field of 120 V/mm and 50 Hz for 1 h. It was 2.214 times higher than that of EP and 1.325 times higher than that of the same-loaded h-BN/EP composite (0.234 W/(m·K)). A thermal conductivity model that can predict the thermal conductivity of composites prepared using the same type of method is also developed, which extends the applicability of the thermal conductivity model. The prepared composites have good thermal management capability. The method is easy to be engineered and has great potential for use in electronic packaging and even other high thermal conductivity applications.

Evaluation of the curing reaction of epoxy resins by electrochemical measurement and molecular orbital method

Epoxy resin is a thermosetting resin with excellent mechanical properties. It has been pointed out that there are problems on its mechanical properties due to poor polymerization of the epoxy ring caused by water and chlorine impurities during resin production. In this study, we focused on the electrochemical behavior during curing reaction of epoxy resin. To investigate the electrochemical reaction, galvanostat meter was used to measure the voltage behavior during chemical reaction. Molecular Orbital (MO) method was used to understand the mechanisms of voltage behavior during curing reaction. Furthermore, the effect of water existence during curing reaction was investigated by experimentally and analytically. As a result of experimental electrochemical reaction, we successfully measured the voltage behavior associated with the curing reaction. In the case of MO analysis, the epoxy and curing agent models were prepared. Before the reaction, each molecule had zero charge, but after the reaction, it was confirmed that the epoxy had a positive charged and the amine had a negative charged. It is thought that the voltage could be observed due to the movement of this charge during curing reaction. It has been also demonstrated through experimentation and analysis that water accelerates the curing reaction. It was observed that the accelerating effect amplifies as the quantity of water increases. Building upon these results, it was confirmed that the factor leading to the increase in voltage is due to the amount of water. To examine the presence of chlorine impurities during the production of epoxy resin, MO analysis was conducted on the production reaction of epoxy prepolymers. The findings indicated that as the water content increases, the reaction that results in the production of by-products is amplified. This outcome suggested that by-products were already incorporated during the formation of the epoxy. In conclusion, this study provides significant insights into the electrochemical behavior during the curing reaction of epoxy resin, the role of water in accelerating the reaction, and the impact of chlorine impurities during resin production. The findings pave the way for further research to optimize the production process and enhance the mechanical properties of epoxy resin.

Effect of plant short fibers on the mechanical properties of carbon fiber reinforced epoxy matrix by using FEM based numerical homogenization technique

In this study, we utilized the material design library in Ansys Product 2022 R1 to analyze the impact of short plant fibers on the mechanical properties of epoxy resin. We employed the representative volume element (RVE) approach and examined different volume fractions up to 50%. The technique employed in this study was multi-scale modeling based on the finite element method (FEM) for numerical homogenization. Subsequently, we used the same software to develop a five-layer laminated composite. The samples were based on epoxy resin enriched with short plant fibers at fractions of 20% and 30%, as well as pure epoxy resin. The laminated composites were reinforced with carbon fibers. The objective of this study was to analyze the mechanical response of each sample during a tensile test, focusing on multiple parameters. The sought-after results included total deformation, directional deformation, equivalent and elastic stress (Von-mises). The samples containing epoxy resin enriched with 30% of short hemp fibers exhibited remarkable mechanical strength compared to the other samples. These results suggest that the incorporation of short hemp fibers into the matrix led to a significant improvement in the mechanical strength of the composite.

The Flame Retardant and Mechanical Properties of the Epoxy Modified by an Efficient DOPO-Based Flame Retardant.

Currently, the mechanical performance reduction caused by excessive phosphorus content in the halogen-free flame-retardant EP has been an obstacle to its extensive application. This study presents the effective synthesis of a novel flame-retardant BDD with great efficiency, achieving an optimum phosphorus level of merely 0.25 wt %. The structure of BDD was verified by FTIR, 1H NMR, 31P NMR and XPS spectra. To investigate the flame-retardant properties of BDD, several EPs with various phosphorus levels were synthesized. The addition of phosphorus to the EP significantly increases its LOI value from 25.8% to 33.4% at a phosphorus level of 0.25 wt%. Additionally, the resin achieves a V-0 grade in the UL 94 test. The P-HRR and THR of the modified resin measured by the cone calorimeter are also significantly reduced. At the same time, the addition of a modest quantity of BDD has a minimal impact on the mechanical properties of epoxy resin. This study shows that the removal of hydroxyl groups significantly enhances the fire resistance of phosphate-based flame retardants, thereby providing a novel approach to synthesizing efficient flame retardants.

APTES modification of ZIF-67@M(OH)(OCH3) for enhanced flame retardancy and mechanical properties of epoxy resins

APTES modification of ZIF-67@M(OH)(OCH3) for enhanced flame retardancy and mechanical properties of epoxy resins

Preparation and mechanical properties of epoxy resin filled with shaped hybrid nanobrushes

Nanostructure formed through self-assembly of block copolymer has been used to modify epoxy resins and the shape of the nanobrushes has a significant effect on its properties. Through RAFT polymerization and bulk self-assembly of PMMA-b-PTEPM block copolymers, SiO2@PMMA hybrid nanobrushes was prepared with three different shapes, i.e., nanospheres, nanowires and nanosheets. According to the transmission electron microscope results, all three kinds of nanobrushes were well dispersed in the epoxy resins. The differential scanning calorimeter and thermogravimetric analysis tests showed that the addition of these nanobrushes has no significate effect on the curing behaviour and the glass transition temperature of epoxy resins. Their modification effects have been investigated through tensile, bending and impact tests. Compared with the neat epoxy resin, the bending and tensile strengths of 0.5 wt% nanosphere-filled epoxy resins were increased by 11.7% and 27.0%, and the impact strength of 0.5 wt% nanowire-modified epoxy resins was increased by 93.0%. And the nanosphere-modified epoxy resins showed a better comprehensive performance.

Preparation and mechanical properties of Ni/RGO reinforced epoxy resin composites

The graphene/nanonickel composites(Ni/RGO) were prepared by liquid phase reduction method, and the graphene/nanonickel epoxy composites(Ni/RGO/EP) were prepared by in-situ polymerization method. The glass transition temperature (Tg) of the modified epoxy resin was increased by 19°C compared to EP with 2.1 wt% Ni/RGO loading. The tensile strength and hardness increased by 65% and 18%, the impact strength is increased by 10.053 KJ·m−2 compared to EP, and the shear strength reaches 34.78 MPa for the Ni/RGO/EP with 1.7 wt% Ni/RGO loading. It can be seen, that the addition of Ni/RGO greatly improves the heat resistance and mechanical properties of epoxy resin when the Ni/RGO are evenly dispersed into the epoxy resin by emulsion dispersion method.

Enhancement of smoke and toxic gas suppression during combustion and improvement of the mechanical properties of epoxy resin by incorporation of a modified MOF material containing the phosphoheterophene group

A modified MOF material simultaneously improves the flame retardancy and mechanical properties of epoxy resin at low addition amounts.

FLAME RETARDANCE AND MECHANICAL PROPERTIES OF EPOXY RESIN: EFFECTS OF ADDED INORGANIC FLAME RETARDANTS

Effects of ammonium polyphosphate (APP) in combination with zinc borate (ZnB), zirconium oxide (ZrO2), and nanoclay on flame retardance and mechanical properties of epoxy resin have been explored. Data listed from UL-94, limiting oxygen index, and cone calorimeter tests convey that the addition of flame retardants improved the fire behavior of epoxy composites significantly. The EP/APP/ZnB/ZrO2 composite having 10% APP, 5% ZnB and 2% ZrO2 by weight attained the best V-0 rating in the UL-94 test, 29.1% limiting oxygen index value and 42.8% decrease in peak heat release rate in cone calorimeter test. A significant decrease of 48.1% in the total smoke release is observed owing to the smoke suppressant action of ZnB/ZrO2. TGA data of epoxy composite reported 25.8 and 36.7% char yield at 600℃ in air and nitrogen atmospheres, respectively. Also, a significant increase in storage modulus is observed for the EP/APP/ZnB/ZrO2 composite loaded with 2 wt% ZrO2 in dynamic mechanical analysis.

Dynamic reversible mechanism of phenol-carbamate bonds and their potential for the development of thermo-healing, recyclable and high-performance epoxy thermosets

In this paper, a series of small monomers were synthesized to explore the dynamic reversible properties of phenol-carbamate bonds (PCBs), and the bimolecular exchange mechanism of PCBs was verified. Based on this mechanism, a novel thermo-healing recyclable epoxy resin with high mechanical performance and shape memory function was successfully developed. Meanwhile, the number of reversible phenol-carbamate bonds in this system was increased by molecular structure design, which increased the chance of reversible cleavage and recombination of the dynamic covalent bonds. Compared with our previous work, the thermo-healing efficiency of the epoxy thermosets was greatly increased, and the target polymer achieved an excellent balance between high thermo-healing efficiency and good mechanical performance. Further post-treatment experiments show that the cured epoxy resin can also be well recycled by solvent degradation or hot-pressing process. What's more, a novel carbon fiber (CF) reinforced polymer composite material was synthesized by taking that prepared epoxy thermoset as a matrix, which greatly improve the mechanical properties of epoxy resin, and the CF cloths can be recycled when the epoxy resin is removed by chemical degradation. In addition, due to the existence of reversible crystallizable switching segments in the epoxy resin system, when the temperature is above its Tg, it can be triggered by thermal energy, so that the film can rapidly recover from the temporary shape to the permanent shape. This study also provides a new direction for the development of novel multifunctional intelligent polymers.

P/N/S flame retardant based on DOPS-triazine groups for improving the flame retardancy, char formation properties and mechanical properties of epoxy resin

As epoxy resins (EPs) are widely used in adhesives, electronic packaging materials and aerospace, it is essential to construct new and efficient flame-retardant EP systems to reduce the risk of fire caused by their flammability. In this study, the condensation reaction of melamine (MEL) and 4-hydroxybenzaldehyde (PHBA) produced the intermediate melamine Schiff base (MSB), which was then successfully synthesized with 9,10-dihydro-9-oxa-10-phospha- phenanthrene-10-sulfide (DOPS) by addition reaction to produce a DOPS-triazine intumescent flame retardant MPD containing a novel structure of P/N/S, and applied to fabricate high-performance EP/MPD. As expected, the MPD has good flame-retardant properties due to the synergistic effect of DOPS groups and triazine groups. The thermoset resin EP/MPD passes the UL-94 V-0 test with the addition of only 7.5 % MPD and has a high LOI value of 32.7 %, which is 47.3 % higher than that of pure EP. In addition, the peak heat release rate (PHRR), total heat release (THR) and fire growth rate (FIGRA) of EP/MPD-12.5 % decreased by 33.9 %, 67.7 %, and 65.8 %, respectively, compared with that of pure EP. From the viewpoint of the char formation performance, the expansion height of the char residue of EP/MPD after combustion increased significantly up to 5.6 cm, which was over three times greater than the pure EP value. Moreover, the appropriate amount of MPD can effectively improve the flexural and impact strengths of EP thermosets. This study provides a new idea for the preparation of high-performance flame retardant MPD without affecting the mechanical properties of EP.

Electrical characteristics of different concentration of silica nanoparticles embedded in epoxy resin

In this study, modified epoxy nanocomposite was produced by incorporating SiO2 nanoparticles of 15–30 nm in size, with different concentrations ranging from 1 to 20 wt%. The electrical properties of the epoxy nanocomposite were measured at room temperature in the frequency range of 10−2–107 Hz. To determine the impact of nanoparticles on the epoxy composition, scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDS), Fourier transform infrared spectra (FTIR) spectroscopy, and Raman spectroscopy were conducted. With an increase in filler (SiO2 nanoparticles) content, the electrical characteristics of the epoxy nanocomposite exhibited multiple changes. At low concentrations, all electrical properties experienced a notable increase. The epoxy with 15 wt% of SiO2 nanoparticles samples had a lower permittivity, loss number, conductivity, and capacitance than the unfilled epoxy. At medium concentrations (5 to 15 wt%), the formation of immobilized nanolayers has an impact on permittivity, loss number, conductivity, and capacitance, which have decreased; impedance and modulus increased. The initiation of contact between the nanofillers at a concentration of 20 wt% leads to the formation of continuous interfacial conductive pathways, resulting in a dramatic increase in the permittivity, conductivity, and capacitance of the composites, while concurrently reducing impedance.

An experimental study for using nano-alumina to improving mechanical properties of epoxy resin for assembling glass artifacts

Purpose This study aims to assess the efficacy of nano-alumina (nano-Al2O3) in improving the performance of epoxy adhesives used to assemble archaeological glass. The conservators face a significant problem in assembling this type of artifact. Therefore, the assembling process is considered one of the important stages that must be taken care of to preserve these artifacts from damage and loss. Design/methodology/approach To evaluate the stability of adhesives, the samples were subjected to artificial aging under varying environmental conditions. Some investigative techniques and mechanical testing were used in this study to evaluate the selected materials. It includes a transmission electron microscope, X-ray diffraction, visual assessment, digital microscope, scanning electron microscopy (SEM), color change and tensile strength test. Findings The visual evaluation and the digital microscope results showed that the epoxy/nano-Al2O3 greatly resisted artificial aging. Although slight yellowing was present, it did not significantly affect the general appearance of the samples. On the other hand, the pure epoxy sample showed cracks of different sizes on its surface due to aging, as evidenced by SEM examination. Furthermore, epoxy/nano-Al2O3 has a better tensile strength (11.27 MPa) and slight color change (ΔE = 2.06). Originality/value The main objective of the experimental study was to identify appropriate adhesive materials that possess key properties such as non-yellowing and improved tensile strength by conducting various tests and evaluations. Ultimately, the goal was to identify materials that could serve as effective adhesives for assembling the archaeological glass.

Block copolymer additives for toughening 3D printable epoxy resin

We explore the potential for using a brush-coil triblock copolymer to enhance the mechanical properties of epoxy resin for 3D printing applications. Epoxy resins are widely used in structural material and adhesive and have great potential for 3D printing. However, the highly brittle nature of epoxy resins requires the use of large concentrations of toughening agents that pose significant challenges in meeting rheological requirements of 3D printing. We report a reactive brush-coil block copolymer with three distinct blocks that can phase separate and chemically crosslink with the base epoxy resin to form spherical aggregates. Detailed scanning electron microscopy imaging shows that these aggregates can arrest and deflect cracks during propagation and can synergistically strengthen (∼ 1.5×) and toughen (∼ 2×) the epoxy resin with even 1 wt% of the BCP additive to the base resin. Importantly, both the modulus and the glass transition temperatures are preserved. Direct ink writing (DIW) and digital light processing (DLP) 3D printing of the modified resins also shows the same strengthening and toughening effects seen in mold-cast samples, demonstrating its compatibility with 3D printing processes. These findings suggest that brush-coil triblock copolymers additives at very low concentrations can synergistically improve the mechanical properties of epoxy resin for 3D printed parts.

Rapid and scalable synthesis of novel carboxylated aramid nanofibers for simultaneously improving the strength and toughness of carbon fiber/epoxy laminates

Carbon fiber reinforced composites (CFRCs) are widely used in the aviation, aerospace and automotive industries. The modification of CFRCs with nanomaterials has attracted extensive research interests in recent years. Herein, we report the preparation of novel carboxylated aramid nanofibers (cANFs) by polymerization induced self-assembly, i.e. polycondensation of para-phenylenediamine with terephthaloyl chloride in the presence of a polyamide acid as both a dispersant and surface modifier, for the modification of epoxy resin and CFRCs. cANFs effectively improve the mechanical properties of epoxy resin, and after being sprayed onto CF fabrics, greatly improve the mechanical properties of CFRCs. With the addition of only 0.42 mg/cm2 of cANFs on each CF sheets, storage modulus, flexural strength, flexural modulus and total energy dissipation are enhanced by 27 %, 51 %, 29 % and 67 %, respectively; interlaminar shear strength (ILSS) and Mode II interlayer fracture toughness (GIIC) are improved by 24 % and 74 %, respectively. cANFs can be comparable or even superior to most previously reported carbon nanomaterials in improving flexural strength and ILSS; and exceed most previously reported electrospun nanofibrous mats in increasing GIIC. This study provides a new method for the rapid synthesis of functionalized ANFs to simultaneously increase the flexural properties and interlayer properties of CFRCs.

Tensile Stress Reduction and Strain Concentration of Epoxy Resin Caused by Heterogeneity: A Multiscale Approach Combining Molecular Dynamics Simulation and Finite Element Method.

In this study, we investigated the effect of heterogeneity on the mechanical properties of epoxy resin by combining coarse-grained molecular dynamics (CG-MD) and finite element method (FEM) simulations. To evaluate the heterogeneity effect in the uniaxial elongation, heterogeneous and homogeneous FEM models of micrometer-scale cubic epoxy resin were constructed. For the heterogeneous FEM model, parameters of nanometer-scale elements were determined by CG-MD simulations, where nanometer-scale blocks have different cross-linked structures. For the homogeneous FEM model, the averaged parameters were used for all elements. The calculated stress-strain (S-S) curves of the heterogeneous model exhibit similar tensile stress values when compared to the experimental data, whereas the homogeneous model yields notably higher values. Moreover, a clear strain concentration associated with the formation of the shear band-like structure was observed in the heterogeneous model and not in the homogeneous model.