Performance Of Epoxy Composites Research Articles

Transforming environmental sustainability: Lime‐treated used coffee grounds for innovative eco‐friendly epoxy composite materials

AbstractThis study proposes an innovative method to recycle used coffee grounds into environmentally friendly epoxy composite materials while emphasizing the sustainability of this process. This approach focuses on using lime‐treated coffee grounds as a reinforcing agent for epoxy composites. Diverse analytical techniques such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and mechanical testing according to international standards have been used to evaluate the properties of materials. Coffee grounds have been treated by soaking in Ca(OH)2 solution with different concentrations (0.1 m, 0.3 m) and processing times (1, 3 and 5 days), then combined with epoxy resin to form composite materials. The results showed that using coffee grounds treated with Ca(OH)2 significantly improved the stability and performance of epoxy composites. The best fire retardant performance was achieved with a Ca(OH)2 solution with a concentration of 0.3 m and a treatment time of 3 days, with a limiting oxidation index (LOI) of 21.6%. Furthermore, the compressive strength increased by about 20.79% compared to pure epoxy resin. This study highlights the potential of optimizing coffee grounds treatment parameters with Ca(OH)2 to improve the properties and performance of epoxy composites, thereby promoting practical application and environmental protection.

High performance epoxy composites modified by a ladder-like polysilsesquioxane

Developing transparent epoxy resins (EPs) with high mechanical properties, thermally stable, and superior dielectric properties is of vital importance for electronics and communication application. Here we synthesized a novel ladder-like polysilsesquioxane containing phenyl and amino groups (N-PPSQ) via a facile co-condensation process for EP modification. The N-PPSQ features a highly regular ladder-like structure with several reactive amino groups anchored, as confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and nuclear magnetic resonance silicon spectroscopy (29Si NMR). Different EP/N-PPSQ composites with optimized additive contents were prepared. Compared to the pure EP, 10 wt% N-PPSQ addition helps to increase the impact strength of EP by a maximal 73 % while simultaneously improving the tensile and flexural properties. With maintained high transparency and enhanced hygrothermal stability, the EP/N-PPSQ composite shows lower dielectric constant and dielectric loss than pure EP. The work demos a fine solution to improving the toughness, dielectric properties and hygrothermal stability without sacrificing the mechanical and optical properties of EP.

Surface functionalization of zirconium phosphate via sol-gel chemistry for optimizing fire safety and mechanical property of epoxy/intumescent flame retardant composites

Even though the incorporation of zirconium phosphate (ZrP) nanosheets can enhance fire safety of epoxy (EP) resin, the sole addition of ZrP nanosheets cannot make EP resin pass the UL94 V0 rating and obtain high limit oxygen index (LOI). Meanwhile, traditional intumescent flame retardants (IFR) also deteriorate the mechanical properties of EP/ZrP composites. Herein, for optimizing fire safety and mechanical property, organically modified ZrP (OZrP) nanosheets are prepared based on simple sol-gel chemistry and further combined with IFR to enhance the overall performance of EP composite. Compared to LOI values of pure EP (25) and EP/IFR composite (38), incorporating 2.0 wt% OZrP nanosheets further increase LOI to 44. Meanwhile, EP/IFR/2.0 wt% OZrP composite successfully pass the UL94 V0 rating at the thickness of 0.8, 1.6, and 3.2 mm. As expected, the deterioration of mechanical performance of epoxy resin caused by the addition of IFR is obviously suppressed by introducing OZrP nanosheets, confirmed by impact strength of up to 12.7 kJ/m2 of EP/IFR/3.0 wt% OZrP composite. In the cone calorimeter test, the combination of 2.0 wt% OZrP and 20.0 wt% IFR significantly decreases the peak value of heat release rate and total heat release of EP resin by 83.9 % and 59.7 %. According to the microstructure and chemical composition of char residue, an intumescent and graphitized char formation mechanism is raised for the significantly enhanced fire safety in EP/OZrP/IFR composites. The optimization effect of OZrP nanosheets in the fire safety and mechanical property of epoxy/intumescent flame retardant composites further promote the practical application of epoxy resin.

High Performance Epoxy Composites Containing Nanofiller Modified by Plasma Bubbles.

The thermal conductivity of polymer materials is a fundamental parameter in the field of high-voltage electrical insulation. When the operating frequency and power for electrical equipment or electronic devices increase significantly, the internal heat will increase dramatically, and the accumulation of heat will further lead to insulation failure and serious damage of the whole system. The addition of filler with high thermal conductivity into polymer is a common solution. However, the interfacial thermal resistance between filler and bulk materials is the major obstacle to improve thermal conductivity. Herein, in order to reduce the interfacial thermal resistance, nanofillers are modified by plasma technology. The surface modification of nano-Al2O3 is carried out using plasma bubbles with three atmospheres (Ar, Ar+O2, air) as well as coupling agent. The situation of surface grafting before and after the modification is characterized using FTIR, XPS, and SEM. The effect of the mechanism of modification on the thermal conductivity and reaction pathway is investigated. The results showed that the thermal conductivity after plasma modification is increased significantly. Especially, the thermal conductivity is increased by 35% for the sample modified by Ar+O2 atmosphere. This results because more hydroxyl is introduced on the filler surface by the plasma bubbles, which enhance the interface compatibility between filler and epoxy. In addition, surface insulation performance for the modified samples also is enhanced by 14%. This is associated with the change of surface resistance and trap distribution. These results provide potential support for the development of fabrication for high performance epoxy composites.

Flame retardancy and wear resistance of epoxy composites modified by whisker-shaped nickel phyllosilicate and microencapsulated ammonium polyphosphate.

Whisker-shaped nickel phyllosilicate (NiPS) was synthesized using rod-like nickel-based metal-organic frameworks as the hard templates, and highly efficient flame retardant and wear resistant EP composites were prepared by synergizing with microencapsulated ammonium polyphosphate (MFAPP). The research results indicated that at a total addition amount of 8 wt% and a mass ratio of 2 : 5 for NiPS to MFAPP, the limiting oxygen index of the EP composite was 28.2%, which achieved the V-0 rating in the UL-94 standard. Meanwhile, the peak of heat release rate and total heat release was reduced by 33.9% and 22%, respectively, compared with pure EP. The synergistic system of NiPS and MFAPP promoted the formation of high-quality char layer, preventing the diffusion of heat, oxygen, and combustible gases effectively during combustion of the EP composite. Dry friction test showed that the wear rate of the EP composite was 0.847 × 10-5 mm3 N-1 m-1, which was 87.9% lower than pure EP, indicating a significant improvement in wear resistance. This study provided a promising method for the preparation of high performance epoxy composites with excellent flame retardancy and wear resistance.

Carbon nanotube-vertical edge rich graphene hybrid sponge as multifunctional reinforcements for high performance epoxy composites

Thermal management materials with excellent electromagnetic interference (EMI) shielding performance have attracted research interest in the field of modern electronic devices. Herein, vertical edge rich graphene (VG) was in-situ grafted on the carbon nanotube (CNT) sponge to create connective 3D hybridized carbon skeleton with covalent bonding, then CNT-VG/epoxy composites were constructed to meet the needs of multifunctional application. Impressively, mainly owing to the connectivity of 3D CNT sponge, the conduction ability of interfaces and the defect-rich structure of VG, the obtained CNT-VG/epoxy composites possessed an enhanced EMI shielding effectiveness of 46.9 dB with a thickness of 1 mm and an improved thermal conductivity of 2.23 W m−1 K−1 which contributes to superior thermal management capability. In addition, the excellent structural design also increases the flexural strength by 349.39% compared to pure epoxy resin, achieving a flexural strength of 275.32 MPa and a work of fracture of 9956.98 kJ m−3. The novel multifunctional CNT-VG/epoxy composites with enhanced mechanical property show a bright application prospect in next-generation electronic devices.

Fly Ash Epoxy Composites with Superior Fire Retardant Properties

Epoxy was loaded with varying concentrations of fly ash and was characterized for its structural properties using XRD and SEM. The XRD results revealed reduction of crystallinity with increase in filler content indicating that the composites are semi crystalline in nature. The SEM images showed that at lower concentration of filler content, fly ash is uniformly distributed within the epoxy and at higher concentrations of fly ash, agglomerates were observed. Mechanical properties such as tensile and compressive properties were estimated and the results showed that, the composites exhibit enhanced tensile strength and compressive strength for epoxy with 20 wt% fly ash. Flammable properties such as heat release rate, peak heat release rate, time to ignition, CO and CO2 yields are estimated and reported. Decrease in combustion time, peak heat release rate, time to ignition, CO and CO2 yields with increase in filler content clearly indicates the superior flammability performance of epoxy composites loaded with fly ash.

Thermal stability and gamma ray shielding properties of tungsten borides/epoxy micro-composites

Particle reinforced epoxy matrix composites have recently been intensively prepared and investigated in numerous publications as a promising alternative gamma ray shielding materials. In this work, a DDM (4,4′-diaminodiphenylmethene) hardener modified by AA (acrylic acid) was used to cure the epoxy resin (E51) at room temperature. To obtain high performance epoxy composites, 30% by weight of tungsten borides WB and WB2 microparticles treated with a KH-560 silane coupling agent were incorporated into the epoxy matrix (EP0) and the composites were coded as EP30WB and EP30WB2, respectively. SEM (scanning electron microscopy) analysis confirmed the good dispersion of these fillers within the polymeric matrix. The structure of the synthesized epoxy matrix and its related composites were characterized using the FTIR (Fourier transform infrared) analysis. According to the FTIR spectra, the epoxy matrix as well as the micro-composites were effectively cured in less than 4 h. This rapid curing process can be justified by the reaction of the epoxy and acrylamide groups as well as the strong reactivity of DDM with AA. The thermal stability of the samples was evaluated by DSC (differential scanning calorimetry) and TGA (thermal gravimetric analysis). DSC analysis revealed that EP30WB2 has a high exothermic peak (166.68 °C) compared to EP30WB (154.48 °C). In addition, the TGA analysis showed that T5% (temperature of 5% weight loss) increased from 207.01 °C for EP0 to 339.65 °C for EP30WB and 346.92 °C for EP30WB2. Meanwhile, the char yield (Yc) at 800 °C has increased from 23.85% for EP0 to 40.36% for EP30WB and 45.99% for EP30WB2, respectively. Moreover, using a Cs-137 radioactive source, the linear and mass attenuation coefficients (μ, μm), half-value layer (HVL), ten-value layer (TVL) and radiation protection efficiency (RPE) for the epoxy matrix EP0, EP30WB and EP30WB2 micro-composites were experimentally determined. The shielding efficiency for EP0 was 17% and it was improved to 32% and 35% by filling EP0 matrix with WB and WB2, respectively.

Effect of carbazole coating on TiO2 nanoparticles as a photosensitizer and MWCNTs on the performance of epoxy composites

Over a short period of time, electronic assemblies have been dramatically developed with smaller size and lighter weight and 3D printing plays a crucial role in their future production. However, it is difficult to develop epoxy resins and other thermoset resins for this process because of the polymer's liquid state during processing. This work uses a UV curing technique for making flexible epoxy/multi-walled carbon nanotubes (MWCNTs) composites that are suitable for future 3D printing applications. The synthesized carbazole-coated TiO 2 nanoparticles, used as a photosensitizer, were characterized by their photoabsorbance, morphology, and surface property before use. The results indicated that the TiO 2 nanoparticles coated with 75 wt% carbazole were appropriate for UV-cured flexible epoxy/MWCNT composites because of its fast cure kinetics after irradiation by a UV light source. The epoxy/MWCNT composites displayed low tensile properties because of the agglomeration of MWCNTs inside the epoxy matrix. In addition, the epoxy/MWCNT composites showed slightly lower thermal expansion with high electrical properties with a large amount of MWCNTs in the epoxy composites. • The synthesis and characterization of carbazole coating on TiO 2 nanoparticle as a new photosensitizer for fast curing epoxy composite with MWCNTs • The morphological, mechanical, thermal, and electrical properties of flexible epoxy composites after complete cure by UV technique.

Phosphoric acid derived efficient reclaimation of carbon fibre for re-manufacturing high performance epoxy composites reinforced by highly-aligned mat with optimized layup

This study presented an economic and closed-loop recycling approach of carbon fibre reinforced polymers (CFRP) comprising phosphoric acid derived efficient reclaimation of recycled CF (rCF) and re-manufacture of high performance epoxy (EP) composites reinforced by highly-aligned rCF mat. The integral rCF with clean surface and intact graphitization structure showed the high retention ratios of 97.1 and 99.5% in tensile strength and modulus, respectively, as well as highly-aligned arrangement of rCF mat with preferential alignment degree (PAD) of 83.5% much contributed to increasing its maximum volume fraction up to ~ 40% in composites. Thus, through fully utilizing the property anisotropy and structural designability of aligned rCF, mechanical and EMI shielding performance of rCF/EP composites were significantly enhanced via optimizing mat layup configurations.

A cast-in-place fabrication of high performance epoxy composites cured in an in-situ synthesized 3D foam of nanofibers

A cast-in-place process is usually adopted to prepare bicontinuous composites which display good mechanical properties and excellent comprehensive performance. But the construction of an intercommunicating porous skeleton seems to be cumbersome and low efficient. Here we report a three-dimensional nanofibers foam (3D NFF), which has been fabricated and applied to enhance epoxy resin composite. The 3D NFF skeletons with densities from 0.028 to 0.218 g/cm3 were fabricated by regulating the conditions for the nanofiber growth. The 3D NFFs were conveniently modified with a silane coupling agent to improve the interface interaction with the epoxy matrix. Compared to the pure epoxy, the compressive strength of the cast-in-place processed 3D NFFs/epoxy composite was improved by 436.8% at loading of 3.9 wt%, and the flexural strength was increased by 133.5% at loading of 5.3 wt%. While the compressive and flexural strength of the NFPs/epoxy composite prepared through traditional mixing method was increased by 173.6% at loading of 3.9 wt%, and 63.1% at loading of 5.3 wt%, respectively.

Evaluation of mechanical and thermal properties of epoxy composites reinforced with CaSiO3 particulate fillers

In the present numerical and experimental work, performance of epoxy composites with Wollastonite (CaSiO3) micro-particles that are systematically introduced into an epoxy matrix for reinforcement purposes is evaluated and presented. Magnetic stirrer is used to achieve homogeneous dispersion of the micro-particles into epoxy resin. The influence of CaSiO3 particles on hardness, flexural strength and impact strength was investigated. It is found that incorporation of CaSiO3 particles yield an effective improvement of the epoxy resin with a micro-particle content of 1–2 wt%. Composites reinforced with these particles showed increase in mechanical properties when compared to neat epoxy resin. Further, thermal behavior of both, neat and filler reinforced composites has been studied by Thermogravimetric analysis (TGA), to reveal the thermal stability of composites. In addition, mathematical models for hardness, flexural strength and impact strength are developed using Minitab 17 software. The developed models revealed high degree of correlation between experimental and predicted values.

Recyclable High Performance Epoxy Composites Based on Double Dynamic Carbon–Nitrogen and Disulfide Bonds

Recycling of the thermosetting resin is a big challenge due to the formation of cross-linked, three-dimensional network structures after curing. In this study, a simple mild and effective method wa...

High performance epoxy composites prepared using recycled short carbon fiber with enhanced dispersibility and interfacial bonding through polydopamine surface-modification

The critical issue and challenge in reusing recycled carbon fiber (rCF) was to fully exerting its outstanding properties via an efficient and environmental-friendly way. In this study, the strengthening effects of polydopamine surface-modified recycled short CF (pDop-rSCF) on mechanical, thermo-mechanical, electrical and electromagnetic properties of epoxy (EP)-based composites were systematically evaluated. The dispersibility of pDop-rSCF in suspension used for fabricating nonwoven mat was quantitatively characterized with crowding factor N, dispersion coefficient β and fractal dimension D. Significant enhancements were achieved in tensile and flexural properties, interlaminar shear strength, storage modulus and electromagnetic interference shielding capability of EP composites reinforced with pDop-rSCF nonwoven mat, which was primarily ascribed to chemically strengthened interfacial bonding between pDop-rSCF and EP matrix and the increased connectivity among pDop-rSCFs with excellent dispersion.

Enhanced visco-elastic and rheological behavior of epoxy composites reinforced with polyimide nanofiber

High performance epoxy composites are now a days a must in several industrial applications. In the present work electrospun polyimide (PI) nanofibers with excellent thermal and mechanical properties was used as a reinforcement in epoxy matrix via a simple mechanical mixing followed by thermal curing method. Well defined electrospun nanofibers of aromatic polyimide (PI) were successfully prepared from electrospinning Poly (amic acid) (PAA) and subsequent thermal treatment. The fiber morphology was analyzed using Transmission electron microscopy (TEM) and Atomic force microscopy (AFM). PI/epoxy nanocomposites with different PI loadings were prepared using chopped PI mats. The dynamic mechanical performance of these PI/epoxy composites was investigated to determine the influence of PI fibers in reinforcing the epoxy matrix. The fracture toughness of these composites displayed a note worthy improvement of 20 % at 1 w% loaded samples and the surface of the fractured samples was investigated by Scanning electron microscope. The rheological properties of these systems show a tremendous increase in the storage and loss modulus when compared to neat systems. In addition flow models were employed to model the rheological data and the comparison was made with the experimental data.

3D-structured assembly of RGO and Ag nanowires for enhanced microwave absorption performance epoxy composites

A 3D structured RGO–AgNWs/EP composite was prepared which composed of 1D silver nanowires and 2D reduced graphene oxide (RGO) sheets. It was found that the electromagnetic wave absorption ability of pure RGO in the matrix was constrained by the agglomeration and defective conductive network. The results show that the addition of silver nanowires significantly enhanced the complex effective permittivity of the composites. Importantly, the absorbing properties can be controlled by the amount of silver nanowires interspersed between the layers of RGO. Besides, a representative sample with only 1% graphene sheets and 15% silver nanowires exhibited a prominent performance whose minimum peak value was up to − 33.2 dB at 11.5 GHz and the corresponding bandwidth was 3.3 GHz with a layer of 1.8 mm. Therefore, the 3D structured RGO–AgNWs assembly has a bright prospect in lightweight and high-performance microwave absorbers.

Superior mechanical enhancement of epoxy composites reinforced by polyimide nanofibers via a vacuum-assisted hot-pressing

High performance epoxy composites are highly required in many applications. In this work, polyimide electrospun nanofibers (PIENFs) with excellent thermal and mechanical properties were used to reinforce the epoxy matrix by a vacuum-assisted hot-pressing procedure. The morphologies of PIENFs and PI/epoxy composites were investigated by scanning electron microscopy (SEM). Thermogravimetric analyses (TGA) was used to characterize the thermal properties of PI/epoxy composites and calculated the actual weight amount of PIENFs in the composites. The effects of nanofiber amount and the degree of fiber alignment on the mechanical properties of PI/epoxy composites have been studied. Owing to the superior mechanical performance of PIENFs and the strong interfacial adhesion, the PI/epoxy composites presented significantly mechanical improvement as compared to the pure epoxy.

Low content Ag-coated poly(acrylonitrile) microspheres and graphene for enhanced microwave absorption performance epoxy composites

Silver nanoparticles was uniformly anchored on the surface of hollow poly(acrylonitrile) microspheres with a facile chemical method using hydrazine hydrate as reductant. Integrating these conducting hollow spheres (PANS@Ag) with chemical reduced graphene oxide (RGO) dispersed in epoxy resin, a lightweight microwave absorber was successfully prepared with enhanced microwave absorption performance. The chemical constitution and surface morphology of as-synthesized RGO and PANS@Ag powders were characterized by XRD, XPS, FE-SEM and SAED, while the electromagnetic properties of these different proportion PANS@Ag-RGO/EP samples were analyzed through vector network analyzer (VNA). The minimum reflection loss (RL) could reach up to −28.1 dB at 8.8 GHz with a layer thickness of 2 mm, and the corresponding effective absorption bandwidth (RL values less than −10 dB) was from 7.9 GHz to 9.8 GHz. However, the dosage of PANS@Ag and RGO was merely 3 wt% and 1 wt%, respectively. As the content of PANS@Ag powders decreased to 1 wt%, the PANS@Ag-RGO/EP samples still retained effective microwave absorption performance and the optimal RL was −14.7 dB. The density of as-prepared absorbers was in the range of 0.49 ∼ 0.87 g cm−3. The low content, low density and enhanced microwave absorption performance endow the hybrid composites with competitive application prospect in stealth technology field.

Nanocellulose composites with enhanced interfacial compatibility and mechanical properties using a hybrid-toughened epoxy matrix

Although there is a growing interest in utilizing nanocellulose fibres (NCFs) based composites for achieving a higher sustainability, mechanical performance of these composites is limited due to the poor compatibility between fibre reinforcement and polymer matrices. Here we developed a bio-nanocomposite with an enhanced fibre/resin interface using a hybrid-toughened epoxy. A strong reinforcing effect of NCFs was achieved, demonstrating an increase up to 88% in tensile strength and 298% in tensile modulus as compared to neat petro-based P-epoxy. The toughness of neat P-epoxy was improved by 84% with the addition of 10wt% bio-based E-epoxy monomers, which also mitigated the amount of usage of bisphenol A (BPA). The morphological analyses showed that the hybrid epoxy improved the resin penetration and fibre distribution significantly in the resulting composites. Thus, our findings demonstrated the promise of developing sustainable and high performance epoxy composites combing NCFs with a hybrid petro-based and bio-based epoxy resin system.

Dielectric and thermal properties of epoxy resins with TiO2 nanowires

Epoxy based composites with reinforced dielectric properties were successfully synthesized by using TiO2 nanowires as inorganic filler. TiO2 nanoparticle/epoxy composites were also prepared as a contrast. TiO2 nanowires were synthesized by a hydrothermal method, with an average diameter of 50 nm and a length of 5 µm. TiO2 nanoparticles were purchased with average diameter of ~60 nm. Scanning electron microscopy images show that two types of fillers are both homogeneously dispersed in the matrix. Although the specific surface area of TiO2 nanoparticles is about twice of that of TiO2 nanowires, remarkable improved dielectric constant, enhanced electrical and thermal conductivity, higher space charge accumulation and stronger charge carrier mobility were observed in nanowire filled epoxy resin at the same filler content. Meanwhile, nanowires composites exhibit excellent glass transition temperature and thermal stability. These results indicated that the geometry of filler had a profound impact on the performance of epoxy composites, and nanowire filling is more effective than nanoparticle filling to enhance the properties of epoxy resin.