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Composite materials made of bio-based matrices reinforced with natural fibers are a potential solution to meet the environmental constraints of manufacturing industries. Interactions between a partially bio-based epoxy resin and flax fibers were investigated in three different ways. An internally developed experiment named Curing Thermal Monitoring (CTM) revealed that curing of epoxy–amine composite plates is accelerated by a factor 2 when reinforced by flax fibers containing 10% wt water. Deeper insight obtained using differential scanning calorimetry (DSC) revealed that the curing acceleration effect of water increases the variation of entropy and lead to higher activation energy values (Eα ≈ 55 kJ/mol). Dynamic mechanical analysis (DMA) measurements highlight that composite with wet fibers has a higher glass transition temperature (Tg = 60 °C) value after manufacturing, which is a consequence of the higher reactivity induced by water. By contrast, composite reinforced by dried flax fibers showed a lower curing reactivity and thus lower Eα values (≈ 43 kJ/mol) and Tg value (48 °C) after manufacturing. Both composites were stored under relative humidity conditions after manufacturing and evidenced an increase in Tg due to water absorption. A post-curing helped the composite with dried fibers to reach maximum Tg = (92 °C) while this was not the case for composite with wet fibers due to chaotic network geometry caused by the entropic effect (89 °C). Water contained in the flax fibers can act as a plasticizer after the post-curing as the Tg decreases with the absorbed water. This work gives a better understanding of the role of water naturally contained in flax fibers and point out the fact that monitoring the moisture of flax fibers is a key parameter to manufacture bio-based composites. [ABSTRACT FROM AUTHOR]

Acylhydrazone bonds can participate in dynamic exchange reactions under acid-stimulated conditions, and disulfide bonds can participate in dynamic exchange reactions under thermally stimulated conditions. It is of great significance to prepare epoxy vitrimer that can rapidly self-repair under acid and thermal stimulation conditions. In this paper, vanillin was used as raw material, and monomer (VAN-AD) containing acylhydrazone bond was synthesized by reaction with adipic dihydrazide. Then, VAN-AD and 4-aminophenyl disulfide (SS) were cured together with glycerol triglycidyl ether to prepare an epoxy vitrimer with acylhydrazone and disulfide dual dynamic covalent bonds. Where VAN-AD provides some of the flexible chain segments and acylhydrazone bonds and SS provides the aromatic phenyl and disulfide bonds. The material was prepared in a simple process and under mild condition, and the properties of the material were optimized by changing the ratio of VAN-AD to SS. The Tg of the material was 50 °C when the ratio of SS was the highest, the thermal stability was enhanced with the increase of the ratio of SS, and the maximum tensile strength up to 50.9 MPa, and the material can be completely degraded by DMF with 5% HCl. It is worth noting that the material shows rapid self-healing properties under acid-heat conditions, self-healing rates up to 97.37%, and the tensile strength can reach 26 MPa after repair. The material can be successfully remodeled by hot pressing for 1 h at 140 °C and 10 MPa. [ABSTRACT FROM AUTHOR]

This study utilizes mechanical interlocking as a method to improve the adhesion between the 3D carbon felt foam (CFs) and the epoxy matrix (EP). Hydrothermally, Co3O4 nanoarrays in nanostrips, nanowires, nanoprisms, and nanostars were added to CFs surfaces. Pure 3D carbon fiber-epoxy composites had 62.7% higher storage modulus and 7.8% higher glass transition temperature than pure epoxy. The 3D carbon fiber/epoxy composite with Co3O4 nanowires has a storage modulus of 5297 MPa and a Tg of 148.4 °C, which is higher than that of pure 3D CFs and other nanocomposites. Compared to pure 3D CFs/ EP, Co3O4 nanowires boost flexural strength by 75.0%. Nano-strip, nano-prismatic, and nanostar composites improve 53.6%, 21.4%, and 11.43%, respectively. Pure 3D CFs boost epoxy matrix impact strength to 174.6%. The impact strength of the Co3O4 nano-wire@CFs/EP composite is 45.6% higher than that of the 3D CFs/EP composite. Nano-strip, nano-prismatic, and nano-star modifications are 31.2%, 19.5%, and 2.5%. 3D CFs/EP composites have a 69 MPa initial tensile strength. However, Co3O4 nano-wires increase tensile strength by 73% to 130 MPa. Nano-strip, nano-prismatic, and nanostar composites outperform 3D CFs/EP by 68%, 33%, and 7%, respectively. In 3D CFs/EP composites, Co3O4 nanowires reduce wear by 50.0% and friction by 27.9%. [ABSTRACT FROM AUTHOR]

Out-of-oven curing of epoxy resins with economical and energy-efficient techniques is vital for manufacturing advanced composite structures. In this study, the effects of a magnetic particle (MP)-induced in situ heating technique on the heating temperatures and mechanical properties of epoxy resins were investigated. The results showed that the proposed technique quickly increased the epoxy resin temperature and steadily heated the polymer until it was fully cured. With increasing MP concentrations from 6 wt% to 22 wt%, a notable increase in the heating ratio from 3.27 °C/min to 8.96 °C/min and steady increases in the heating temperature from 92.61 °C to 115.03 °C were observed. Surface modification of the MPs improved the homogeneity of the heating field and cross-linking and also increased the heating ratio and steady heating temperature. With merely 2.5 h of induction heating, the flexural moduli and strengths of functionalized MP/epoxy samples with MP loads of 6 wt%, 13 wt% and 22 wt% were 45.1%, 42.8%, 40.5% and 6.3%, 33.5%, 39.4% higher than those of oven-cured control samples. These findings provide essential knowledge for fabricating advanced polymeric composite structures without an oven. [ABSTRACT FROM AUTHOR]

Thermosetting epoxy resins are widely used as bearings, gears, gaskets, and other components. The tribological properties of epoxy resins play an important role in ensuring the life and reliability of the components. A novel self-lubricating microcapsule was synthesized in this study by in situ polymerization using ionic liquid as the core material and polyurea formaldehyde (PUF) as the wall material. The effects of the ionic liquid microcapsule content on the coefficient of friction, wear rate, and surface morphology of the epoxy resin composites were investigated under dry friction conditions. The results showed that the incorporation of self-lubricating microcapsules significantly improved the friction and wear properties of the composites, and the 5 wt.% microcapsule/epoxy composites had the best tribological properties, with the coefficient of friction decreasing from 0.634 to 0.062 and the wear rate decreasing from 6.64 × 10–4 mm3/(N m) to 1.64 × 10–5 mm3/(N m). Compared with the pure epoxy resin, the friction coefficient of the composites was reduced by 90.22% and the wear rate was reduced by 97.53%. The wear mechanism of epoxy resin changes from severe fatigue wear and adhesive wear to slight abrasive wear. This is because after friction destroys the composite, the embedded microcapsules rupture, releasing the lubricant and forming a transfer film that lubricates the friction surface. At the same time, the addition of microcapsules enhances the tensile strength and hardness of the epoxy resin. This study would provide the experimental basis for the design and performance enhancement of epoxy composites with high self-lubricating properties. The prepared epoxy composites are expected to be applied to self-lubricating spherical plain bearings and other mechanical parts. [ABSTRACT FROM AUTHOR]

The application of carbon fiber epoxy resin composite (CFRP) in the aerospace industry is limited by the laser treatment, because of the poor oxidation resistance and anti-laser ablation performance of the composites. The application of a coating on components is an effective method to improve their laser ablation resistance. The nitride coatings, consisting of Si3N4, AlN, BN, and an epoxy resin, were applied onto the CFRP using brush painting. When irradiating at 100 W/cm2 for 5 s, the damage has occurred on the coating with Si3N4 and AlN, and the BN coating remains original morphology at 100 W/cm2 for 20 s. With the power density has increased to 200 W/cm2, the serious ablation damage occurs in the BN coating irradiated for 10 s. Due to the heat absorption of resin pyrolysis and the low thermal conductivity of CFRP, the highest back-surface temperature is only 75 °C. The laser protection performance of CFRP should mainly improved by increasing the reflectivity of the coating. [ABSTRACT FROM AUTHOR]

Realizing nano-filler well dispersed in epoxy matrix is essential for the fabrication of high-performance epoxy composites. However, the aggregation of untreated nano-filler in epoxy resin during static curing greatly reduces the material performance. Herein, we report an effective and facile approach to fabricate well-dispersed silica nanoparticle (SiNP)-reinforced epoxy composites through dynamic crosslinking depending on vitrimer chemistry. The epoxy vitrimer synthesized by dynamic crosslinking method was named as EVD, and the epoxy vitrimer synthesized by static curing method was named as EVS. EVD/SiO2 nanocomposites were prepared by dynamic crosslinking technology with unmodified nano-SiO2 as a reinforcement filler, sebacic acid as a curing agent, diglycidyl ether of bisphenol A (DGEBA) as an epoxy monomer, zinc acetylacetonate as a transesterification catalyst, and a torque rheometer (internal mixer) as a dynamic crosslinking equipment, and EVS/SiO2 nanocomposites were prepared by traditional static curing method as counterparts. The structure, properties, and stress relaxation of the EVD/SiO2 and EVS/SiO2 were comparatively investigated in detail. When the loading amount of SiO2 was 5 wt%, EVD/SiO2-5 indicated 2.38 times tensile strength and 2.06 times elongation at break of EVS/SiO2-5. The Young's modulus of EVD/SiO2-5 (6.76 ± 1.07 MPa) was slightly higher than that of EVS/SiO2-5 (5.81 ± 1.06 MPa), which was attributed to more well-dispersed SiNP in EVD/SiO2-5. Moreover, the amount of SiO2 can be filled up to 40 wt% in epoxy vitrimer to obtain high-modulus (1001 times of pure vitrimer) composite. We believe that this study provides a new idea for the preparation of other vitrimer composites with desired properties. [ABSTRACT FROM AUTHOR]

An ultra-fast humidity sensor is a useful sensing node in medical monitoring and industrial processing units. In this paper, epoxy-carbon nanotubes (CNTs) nanocomposites-based humidity sensors at various CNTs concentrations were fabricated by spin coating technique. The structural and morphological properties of the prepared samples were studied by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM), respectively. Fourier transform infrared spectroscopy (FTIR) was employed to characterize the functional groups of the composites. Thin films of the synthesized nanocomposites were deposited onto the surface of interdigitated electrodes (IDEs) and humidity sensing properties were investigated at different working frequencies (0.1–1.5 kHz) in the humidity range 30–90% RH at room temperature. Additionally, response/recovery time and sensitivity of fabricated devices were also measured. The obtained experimental results revealed that CNTs concentration plays a key role in the sensing properties of the current sensors. The optimum CNTs concentration was found to be 1.0 wt % by virtue of its high sensitivity, quick capacitive response/recovery time (14 s/6 s) and resistive response/recovery time (10 s/5 s) as compared to the pristine epoxy and CNTs. [ABSTRACT FROM AUTHOR]

Laminated composites with complex structures, such as L, C, or T-shaped geometries, are used at junction parts in the automotive and aerospace industries. Due to delamination failure in the curved or angled region, these structures are relatively weak in the through-thickness direction when subjected to complex loading. To overcome the issue of weak delamination resistance, this study is aimed at investigating the effect of various reinforcements on the strength properties and delamination resistance of glass/epoxy curved laminates under a four-point bending test. Experimental research was carried out on glass/epoxy curved laminates strengthened by combining three different types and geometries of reinforcement. These included chopped short fibers and glass fiber patches between each ply at the corner region of curvature, and stitching of aramid filament at the corner region of 90-degree bending. A 4 mm pitch interval was observed to enhance curved beam strength, interlaminar tensile strength and delamination resistance. The obtained findings show that glass/epoxy curved laminates reinforced with chopped kenaf short fiber, 45° glass fiber and a single stitch at the corner show greater enhancement in curved beam strength by 52.7, 34.3, and 5.6%, respectively, compared to the baseline sample. Similarly, interlaminar tensile strength improved by 69.3, 40, and 78.5% compared to the baseline sample. On the other hand, curved laminates needled with a single stitch at the corner show higher delamination resistance than other reinforcements. The experimental results correlate well with the damage morphology indicated in SEM fractographic images. [ABSTRACT FROM AUTHOR]

The movement of water molecules at the atomic scale within the calcium silicate hydrate (C–S–H) gel pores serves a dual role: it creates an environment for harmful chemical reactions within the pores and functions as a carrier for the transport of detrimental ions, thereby affects the mechanical properties and durability of cementitious materials. However, direct experimental observation poses substantial challenges. This study offers new insights into how temperature (253 K, 273 K, 293 K, and 313 K) affects the capillary transport of water molecules in epoxy-modified C–S–H. The findings demonstrate that the pore size undergoes continuous changes during immersion due to epoxy clustering or detachment, resulting in three scenarios: narrowing of epoxy/C–S–H channels (253 K, 273 K), channel blockage (293 K), and complete detachment (313 K). Moreover, the interactions between water molecules and epoxy lead to epoxy detachment or cluster formation on the C–S–H surface. As the temperature increases, the interaction between C–S–H and cross-linked epoxy resin weakens. The coordination between C–S–H and epoxy resin decreases, while the coordination with water increases. This paper provides valuable insights into the transport behavior of liquids within the epoxy-modified C–S–H pores of cement-based materials. It contributes to a better understanding of how liquids move and interact within the modified pore structure, which is beneficial for enhancing the performance and properties of cement-based materials. [ABSTRACT FROM AUTHOR]

With the fast growing of oily contaminants, continuous oil/water separation with high flux is in demand. Superhydrophilic/superoleophobic composites are considered as ideal candidates. In this work, the oil–water separation composite is from superhydrophilic copper mesh coated by robust superhydrophilic/superoleophobic paint based on fluorine-containing epoxy resin. Firstly, a superhydrophilic/superoleophobic coating with excellent comprehensive properties was prepared through hydrophilic epoxy and superhydrophilic/superoleophobic TiO2. Then copper mesh was treated into being superhydrophilic, and the superhydrophilic/superoleophobic coating was sprayed on the superhydrophilic copper mesh to obtain oil–water separation material. As a result, the oil–water separation efficiency of the separation material is higher than 99.7%, the water flux is higher than 80,000 L m−2 h−1, and it has excellent mechanical properties. The oil–water separation material is promising for the applications. [ABSTRACT FROM AUTHOR]

In this study, we present an alternative fabrication technique to obtain functionally graded polymer–metal composites. The aim is to obtain a composite material with a graded damping factor, which is provided by the presence of pseudoelastic nickel–titanium (NiTi) fibres within an epoxy resin matrix. A preliminary dynamic mechanical characterisation of the NiTi wire revealed a pre-strain dependency of its damping factor. By fabricating wires with curved geometries in the free state, we were able to obtain fibres with a graded level of pre-strain when straightened. This feature in turn imparts a graded damping response. When encapsulating the straightened fibres in an epoxy resin, the graded damping response is transferred to the composite. [ABSTRACT FROM AUTHOR]

The mechanisms of reinforcement of an epoxy resin by the addition of graphene nanoplatelets (GNPs) has been studied in detail. It is found that the addition of GNPs increases both the stiffness and fracture toughness of the epoxy resin. The dependence of the flexural modulus upon the volume fraction of the GNPs has been modelled using a combination of the rule of mixtures and shear lag analysis and it is shown that the reinforcement is controlled principally by the aspect ratio (length/thickness) of the GNPs. The dependence of the fracture energy upon the GNP volume fraction has been modelled assuming failure takes place through the debonding of the GNP particles followed by their pull-out and it is again shown that the aspect ratio of the GNPs is a vital parameter in controlling the level of toughening. It is found that the behaviour can be modelled using a similar value of GNP aspect ratio to model both the flexural stiffness and fracture behaviour, demonstrating the importance of this parameter in controlling the mechanical properties of GNP/epoxy resin nanocomposites. [ABSTRACT FROM AUTHOR]

Polyoxymethylene (POM) has poor impact resistance, and it is a notch sensitive material. In this study, castor oil-based glycidyl carbamate polyurethane elastomer (GCE) was synthesized and used as an impact modifier in POM. Three impact modifiers were made containing 0.8, 1, 1.2 mol (13, 17, 20%) glycidol. Polyblends of POM/GCE were melt blended using twin screw extruder having high dispersion mixing screw configuration. In each blend composition, GCE was varied from 5, 10, 20 and 30%. Blends were studied for their mechanical, thermal, rheological and morphological properties. Reaction of epoxy group of GCE with hydroxyl group of POM was expected during the melt blending to improve the sufficient compatibility between them, with glycidol being used as a compatibalizing agent in synthesis of GCE. [ABSTRACT FROM AUTHOR]

Epoxy resins are widely used in a variety of application fields, thanks to their good mechanical strength, chemical resistance and adhesion to several substrates. Nowadays, the quite majority of epoxy resins are based on derivatives of bisphenol A (BPA), which poses serious health concerns. This issue is pushing the research towards suitable bio-based alternatives to this product, being furan-based epoxies very promising in this respect. In a previous work, 2,5-bis[(oxiran-2-ylmethoxy)methyl]furan (BOMF) was cured with methyl nadic anhydride (MNA), and successfully used as tinplate coating. Herein, in a view of increasing the sustainability of these epoxy resins, we have replaced MNA with maleic anhydride (MA), which can be derived from vegetable feedstocks, thus obtaining a fully bio-based epoxy resin. This latter has then been used as adhesive for carbon fiber-reinforced thermosetting plastics (CFRP). The curing process of the resin was monitored by differential scanning calorimetry (DSC) and chemo-rheological analysis. The results highlighted the significantly higher reactivity of BOMF towards MA compared to the diglycidyl ether of BPA (DGEBA). The crosslinked samples were characterized in their thermal, mechanical and adhesive properties. In comparison to DGEBA/MA and BOMF/MNA, BOMF/MA showed higher ultimate strain and slightly lower glass transition temperature, tensile modulus and ultimate strength. Interestingly, BOMF/MA displayed outstanding adhesive strength on CFRP joints, outperforming the DGEBA-based counterpart by three times. Indeed, by properly selecting the anhydride curing agent, a highly ductile fully bio-based material was developed for high performance adhesive applications. The overall results demonstrate that the properties of BOMF-based epoxy resins can be tailored to meet technical and safety requirements of downstream applications, representing a sustainable alternative to traditional systems containing DGEBA. [ABSTRACT FROM AUTHOR]

The effect of ion implantation on interfacial properties of carbon fiber composites was studied by means of a combination of experiments and molecular simulations. In this study, copper ions were implanted into carbon fibers according to the designed technical parameters. Molecular simulation was involved to verify the bidirectional diffusion of copper ions at the interphase during the curing process, accompanied by reverse penetration of epoxy and amino groups into the ion layer. Meanwhile, the treated fiber monofilament can maintain mechanical strength similar to that of commercial fibers. The implanted copper ions were also beneficial to the ring-open reaction of epoxy groups. After ion implantation, the interfacial modulus transition layer of the resulting composites was broadened, leading to a 73.6% increment in the interfacial shear strength compared to that of commercial fibers, which can be ascribed to the modified interfacial interaction between carbon fibers and resin matrix. Therefore, the ion implantation has been proven to be an effective and potential approach in improving the interfacial properties of fiber-reinforced composites. [ABSTRACT FROM AUTHOR]

Metals with anti-icing and anti-corrosion properties are necessary in marine fields. Here, a robust decoupling superhydrophobic coating with anti-icing and anti-corrosion performance was fabricated by sequential spraying unmodified micron-sized SiO2 particles and modified nano-sized TiO2 particles. The unmodified micron-sized SiO2 particles with sturdiness act as a protective framework for the modified nano-sized TiO2 particles with superhydrophobicity, which effectively enhance the robustness of coatings. Consequently, the decoupling coating reveals the excellent superhydrophobicity (contact angle > 157°, roll off angle < 5°) and promising robustness (the friction coefficient of ~ 0.25). In addition, the superhydrophobic property endows the coating with admirable anti-icing performance, in which the icing time of decoupling coating is about 10 times of the substrate. The synergistic effect of epoxy resin adhesive layer and superhydrophobicity enables the decoupling coating exhibit excellent anti-corrosion property in electrochemical measurements and immersion tests. Therefore, the decoupling superhydrophobic coating with significant performance advantages could expand the application fields of other various solids. [ABSTRACT FROM AUTHOR]

Vessels inevitably suffer from hull corrosion and encounter contaminated seawater during their service, which is imperative to find a way to both resist corrosion and effectively purify the water. Herein, N-deficient g-C3N4 was prepared by alkali-assisted thermal polymerization and combined with an epoxy resin to successfully synthesize a CNx/EP composite coating with excellent corrosion resistance and effective degradation of organic pollutants in simulated marine environment. Furthermore, corresponding characterization verified that the synthesized N-deficient carbon nitride exhibited high specific surface area and better water dispersibility. In addition, the corrosion resistance of the coatings was investigated by open-circuit potential (OCP), electric polarization curves, and electrochemical impedance spectroscopy (EIS), and the results showed that the CNx-1/EP coating presented the optimal corrosion resistance with a maximum impedance radius of 2.84 × 107 Ω cm2, which was two orders of magnitude higher than that of pure EP coating. The degradation experiments demonstrated that the degradation rate of methyl blue (MB, 30 mg L−1) reached 68% over CNx/EP coating within 4 days' sunlight irradiation. Finally, the photocatalytic corrosion protection and degradation mechanism of the CNx/EP coating was discussed. This work provides new design ideas for the construction of multifunctional anti-corrosion coatings. [ABSTRACT FROM AUTHOR]

In order to obtain compact epoxy-based organic coatings with superior corrosion resistance and self-healing performance, a novel Ti3C2Tx/LDH-epoxy hybrid coating was prepared on AZ31 magnesium alloy in this work. The layered double hydroxide (LDH) adopted here is MgAl-LDH intercalated by the cysteine acid (Cys), an environmentally friendly organic acid anions, as corrosion inhibitors, and the MXene (Ti3C2Tx)/MgAl-LDH (TML) heterostructure nanosheets were grown by a facile in situ assembled method. The morphology, composition, structure and the corrosion protection of the Ti3C2Tx/MgAl-LDH-epoxy (EP-TML) composite coatings were systematically investigated and compared with the other three epoxy-based coatings: bare waterborne epoxy resin (EP), Ti3C2Tx pigmented in EP (EP-T), MgAl-LDH in EP (EP-ML). It is found that the TML heterostructure has good dispersion and compatibility with the epoxy resin. The corrosion current density and the impedance value at low frequency (|Z|0.01 Hz) of the EP-TML composite coating are 1.4 × 10–9 A/cm2 and 1.66 × 107 Ω cm2, which is 4 orders of magnitude lower than that of the uncoated Mg substrate and 1–2 orders of magnitude higher than that of EP (8.7 × 105 Ω cm2), respectively, indicating its excellent corrosion resistance. And the self-healing efficiency of EP-TML composite coating is found to be higher as 56.17% after 6 days immersion in a corrosive environment. The significant improvement of the anti-corrosion and self-healing performance of the EP-TML composite coating are mainly ascribed to the synergistic effect of "barrier effect" of TML and the corrosion inhibition effect of the cysteine acid encapsulated in MgAl-LDH. This work provides some valuable insights to widen the functional application of Ti3C2Tx and the design of highly corrosion-resistant and self-healing organic coatings for Mg alloys. [ABSTRACT FROM AUTHOR]

In this research, a reversibly thermochromic wood (RTW) was fabricated by using epoxy resin and reversibly thermochromic microcapsule (RTM) impregnating delignified wood. RTM showed sphere morphology with an average diameter of 33.6 µm. Delignification and bleaching of wood enrich its pore structure apparently, and the cumulative pore volume increased by 127% compared to natural wood. The color of RTW varies with temperature within the range of 12–28 °C. We suggest that RTW can be applied in decoration, smart window or thermosensitive element due to its reversible thermochromic character and transmittance. [ABSTRACT FROM AUTHOR]

Interfacial characteristics are critical to the insulation performance of dielectric nanocomposites (NCs). However, the impact of physicochemical properties on interfacial characteristics and resultant dielectric properties is still unclear. In this study, the interfacial characteristics of epoxy resin/polyhedral-oligomeric-silsesquioxane (EP/POSS) are tailored by POSS functional groups, including octa-glycidyl (OG) and epoxycyclohexyl (ECH), to improve the dielectric performance. The characterization and experimental results show that the EP/OG-POSS exhibits better interfacial compatibility and dielectric performance than the EP/ECH-POSS. The molecular dynamic simulation results show that compared with the EP/ECH-POSS, the better interfacial compatibility of the EP/OG-POSS is derived from the intrinsically stronger interfacial interaction between the OG-POSS and EP, which results in a higher interfacial crosslinking degree and a more compact interfacial structure. It further reduces the free volume and mean square displacement of molecular chains. Thus, besides the self-crosslinking of EP matrix, the incorporation of the OG-POSS introduces more interfacial crosslinking sites, which can also act as deep traps for charges. The more the interfacial crosslinking sites, the deeper the traps. These deep traps hinder the charge transport, ultimately improve the volume resistivity and maintain uniform space charge distribution. Therefore, an effective approach is proposed to improve the charge-trapping behavior and dielectric properties of NCs by tailoring interfacial crosslinking sites. [ABSTRACT FROM AUTHOR]

Here we contrast the molecular dynamics of epoxy nanocomposites filled with three different types of silica-based nanoparticles with different architectures, namely solid core, core–shell and hollow and with varying degree of crystallinity. The samples are characterised by Fourier transform infrared spectroscopy, differential scanning calorimetry, broadband dielectric spectroscopy and dynamic mechanical analysis (DMA). Widely known relaxations such as α, β, γ, normal mode and interfacial polarisation are observed and discussed. An additional relaxation named omega (ω) is also observed, whose dielectric strength is inversely correlated to the crystallinity of the nanoparticles. We suggest that this may be attributed to the polarizing interaction of the hydroxyl groups of silanols with the hydroxy ether groups of the polymer chain. The ω is absent in DMA confirming it as a polarisation phenomenon. At lower concentration of silanols, the ω largely overlaps with β, effectively becoming an integral part of it. Finally, two interfacial polarisation relaxations are observed in the case of core–shell structures, originating from the core–shell and shell–polymer interface but, due to the similar real permittivity values of the core, shell and the polymer, their dielectric strength is weak. [ABSTRACT FROM AUTHOR]

In this work, oxidized carbon nitride (O-C3N4) nanoparticles were obtained by oxidizing the graphitized carbon nitride (C3N4) nanoparticles, which were used to improve the mechanical properties and thermal stability of epoxy resin. The crystal structure, morphology and chemical structure of C3N4 and O-C3N4 were characterized by X-ray diffraction, scanning electron microscopy and Fourier infrared spectroscopy, respectively. Which ensures that they were prepared successfully. In order to compare the reinforcing effect of C3N4 and O-C3N4, they were dispersed in epoxy resin as fillers, respectively. The results show that the optimum content of C3N4 and O-C3N4 was 0.3 Phr and 0.5 Phr, respectively. The tensile strength of the composites was increased by 17% and 24% compare to the pure epoxy, respectively. Meanwhile, the impact toughness was increased by 63% and 180%, respectively. [ABSTRACT FROM AUTHOR]

Modifying epoxy resin with carbon nanomaterials is one of the promising methods to improve the fiber-reinforced polymer (FRP)/concrete interfacial properties, and such manipulation first requires comprehensive understanding of the bonding mechanism between the modified epoxy resin and the concrete matrix. In this paper, the interfacial bonding properties between epoxy resins modified by graphene oxide (GO) nanosheets and calcium silicate hydrate (C–S–H), the main bulk phase of concrete, are investigated using molecular dynamics simulation. At the molecular level, the GO-epoxy/C–S–H interface is constructed, and the mechanical behaviors of the interfacial system are simulated at elevated temperatures (from 298.15 to 433.15 K). Results show that the GO modification significantly enhances the mechanical resistance of the epoxy/C–S–H interface, as evidenced by the increase in the pulling force threshold of ~ 20%. Analysis reveals that the polar groups on the GO surface strengthen the interfacial ionic and structural hydrogen bonds, thus improving the bonding integrity of the epoxy/C–S–H interface. At elevated temperature levels, the high thermal stability of the GO-epoxy molecule, as well as its low energy loss with the C–S–H matrix, is the main driver for the enhanced thermal and mechanical properties of the epoxy/C–S–H interface. [ABSTRACT FROM AUTHOR]

ZIF-8@APP was prepared by in situ growth of ZIF-8 on the surface of ammonium polyphosphate (APP) through co-precipitation method. The ZIF-8@APP/EP composites were prepared by adding ZIF-8@APP into epoxy resin (EP). The composites with loading of ZIF-8@APP showed good flame retardancy, smoke suppression and mechanical properties simultaneously. The limiting oxygen index (LOI) of the flame retarded composites containing 10 wt% of ZIF-8@APP was 32.6% and the UL-94 test reached V-0. Meanwhile, the peak heat release rate and total heat release of the composites with 5 wt% of ZIF-8@APP were reduced by 60.8 and 35.5% compared with pristine epoxy resin. The ZIF-8 particles on APP improved interface actions between APP and EP matrix, which led to the enhancement in mechanical properties of the flame-retardant composites. [ABSTRACT FROM AUTHOR]

High-performance epoxy–SBA-15 nanocomposites were prepared by ultrasonic dual-mode mixing (UDMM) technique. The dynamic and static mechanical properties of the epoxy nanocomposites were assessed. The addition of 0.5 wt% of SBA-15 improves the storage modulus (13%) and marginally varies the glass transition temperature (~ 2%) of the respective epoxy nanocomposites. However, the failure strength (~ 77%) and strain (~ 180%) increased significantly without affecting its modulus. The FESEM images of the fracture surface of epoxy nanocomposite reveal a much rougher surface compared to neat epoxy. The addition of SBA-15 into epoxy resin restricts the movement of the cracks and deflects them to follow a meandering way and hence, creating relatively rougher surfaces. The addition of higher wt% of SBA-15 is found unable to improve the dynamic and static mechanical properties of the epoxy nanocomposites. The homogeneous dispersion of SBA-15 via UDMM results in the conversion of hydrophilic epoxy into a highly hydrophobic one. This work has the potential to open up a new avenue for SBA-15 to fabricate cost-effective epoxy nanocomposites with better thermo-mechanical and tuned wetting properties. [ABSTRACT FROM AUTHOR]

Non-covalently functionalized boron nitride nanoplatelets (BNNPs) were mixed with the epoxy resin and fabricated into nanocomposites. The BNNPs were non-covalently functionalized with melamine to enhance dispersion and matrix interfacial bond strength with the matrix. Melamine-functionalized BNNPs (M-BNNPs) were simultaneously synthesized and functionalized via modified mechanical exfoliation process. The mechanical properties of M-BNNP-reinforced epoxy (M-BNNP/epoxy) nanocomposites included marked strengthening effects (84.3% in terms of Young's modulus, 29.1% in terms of universal test strength, and 134% in terms of fracture toughness) after adding only 2 wt% M-BNNPs to the epoxy matrix. The experimental Young's modulus were compared to those of the Halpin–Tsai model. Our materials exhibited much great fracture toughness than commercial dental resins, suggesting that the M-BNN/epoxy resins may find dental applications. [ABSTRACT FROM AUTHOR]

An efficient and economical strategy for rapid microencapsulation of 1-butylimidazole (1-BMI) was developed. The strategy is based on the thiol-yne click reaction of trimethylolpropane tris(3-mercaptopropionate) and 1,7-octadiyne in oil-in-water emulsion. The thiol-yne click reaction is not only green and efficient, but also improves the cross-linking density of shell. Thus, the obtained shell prevents the leakage of curing agent and prolongs the storage period of EP/MCs system. The whole process of preparing 1BMI-MCs only took 40 min. Moreover, the effects of stirring speed and the ratio of 1BMI on the size and core content of microcapsules (MCs) were investigated. Results demonstrated that the optimal particle size was about 10.8 μm, and the maximum content of 1BMI in MCs was 33% corresponding to 60% 1BMI in oil phase. Afterward, the 1BMI MCs were used as latent curing agent (LCA) for epoxy resin (EP). In the curing reaction of the epoxy resin, the 1BMI-MCs exhibited a delayed kinetic behavior compared to pure 1BMI. Furthermore, the E-51/MCs system had a storage term of 16 weeks. The shell material not only had no effect on curing effect of E-51, but also toughen the cured EP systems. This paper provided a promising method for long-term storage of LCA. [ABSTRACT FROM AUTHOR]

Simply filling the metal foam as a thermally conductive filler into the polymer matrix can improve the thermal conductivity of the polymer matrix, but it still cannot greatly improve the thermal conductivity of the composites. In this paper, the epoxy resin/copper foam-nickel (EP/CF-Ni) composite thermal conductive material was prepared by a combination of electroplating and vacuum liquid impregnation. The deposition of nickel increases the heat dissipation area of the copper foam and at the same time widens the heat conduction path of the materials. By comparing EP/CF with different pores and EP/CF-Ni with different deposition times, it was found that the thermal conductivity of EP/CF-Ni composites could reach 5.215 W/(mK) at 7.3 wt% nickel deposition, which enhanced 2507% and 75% compared to pure epoxy and copper foam matrix composites, respectively. The deposition of nickel further improves the wear resistance of the composite. This experiment reveals the synergistic effect of thermal conductivity of metallic Ni and 3D copper foam, and provides some reference opinions for the field of thermal conductivity of metallic foam. [ABSTRACT FROM AUTHOR]

The epoxy-based nanocomposites are widely used in the aerospace field, which experience harsh conditions with extremely low and high temperatures. The temperature dependence of the properties of epoxy-based nanocomposites in a wide range of temperatures is of great importance for their application. In this work, we used the molecular dynamics (MD) simulation and experimental methods to comprehensively study the temperature dependence of epoxy-based nanocomposites. Three kinds of nanofillers, prepared by grafting three epoxy monomers with different functionality degrees to graphene oxide (GO), were used. The dynamic behavior, interfacial properties and mechanical properties of the nanocomposites in a wide range of temperatures were investigated by MD simulation. Simulation results showed that as temperature decreased from 600 to 4 K, all the nanocomposites exhibited decreased molecular mobility, increased interfacial interaction energy and increased Young's modulus. The tensile properties of the nanocomposites at room temperature (RT), liquid nitrogen temperature (LNT) and liquid helium temperature (LHeT) were also experimentally measured, which agreed well with the simulation results. The tensile strength of nanocomposites increased at LNT compared to that at RT, and then decreased at LHeT. Furthermore, the toughening mechanisms of EFGO to epoxy resin at different temperatures were discussed. The results are expected to provide a new insight into the design and preparation of nanocomposites applied at various temperatures. [ABSTRACT FROM AUTHOR]

Epoxy resins (ERs) are one of the main types of resins used as structural adhesives; however, they present some weakness, which are mostly related to their highly cross-linked network after the curing process. Low electrical and thermal conductivity and low fracture toughness are the major drawbacks of these type of materials, and several efforts have been made over the past few years to overcome them. A critical survey regarding the use of different fillers in ERs systems and the outcome is highlighted and discussed in the present review. The incorporation of fillers into ERs matrix is one of the most successfully explored alternatives to improve the properties of ERs. It is worth to mention that even though ER composites are a widely explored topic, few reports have been focused on a compilation of the most relevant fillers and the main changes on ERs composites performance. Therefore, the present review gives an overview of a vast selection of fillers—natural, metallic, carbon fillers—incorporated in ER matrices to enhance or to meet the requirements for a desired application, such as the increase in the final adhesive toughness. The combination of the top characteristics of fillers and polymers is accomplished, leading to high-performance composites. Among the most promising fillers, carbon nanomaterials, fiber-reinforced polymers, carbon fiber-reinforced polymers, biofillers and metallic and ceramic fillers are described which have the ones having higher application potential. The influence of the addition of these different types of fillers in ERs system properties such as flame retardancy, mechanical and thermal and electrical performance is discussed and reviewed in detail. [ABSTRACT FROM AUTHOR]

Short hemp fibers, an agricultural waste, were used for producing biochar by pyrolysis at 1000 °C. The so-obtained hemp-derived carbon fibers (HFB) were used as filler for improving the properties of an epoxy resin using a simple casting and curing process. The addition of HFB in the epoxy matrix increases the storage modulus while damping factor is lowered. Also, the incorporation of HFB induces a remarkable increment of electrical conductivity reaching up to 6 mS/m with 10 wt% of loading. A similar trend is also observed during high-frequency measurements. Furthermore, for the first time wear of these composites has been studied. The use of HFB is an efficient method for reducing the wear rate resistance and the friction coefficient (COF) of the epoxy resin. Excellent results are obtained for the composite containing 2.5 wt% of HFB, for which COF and wear rate decrease by 21% and 80%, respectively, as compared with those of the unfilled epoxy resin. The overall results prove how a common waste carbon source can significantly wide epoxy resin applications by a proper modulation of its electrical and wear properties. [ABSTRACT FROM AUTHOR]

The use of machine learning (ML) models to screen new materials is becoming increasingly common as they accelerate material discovery and increase sustainability. In this work, the chemical structures of 16 epoxy resins and 19 curing agents were used to build an ML ensemble model to predict the glass transition ( T g ) of 94 experimentally known thermosets. More than 1400 molecular descriptors were calculated for each molecule, of which 119 were chosen based on feature selection performed by principal component analysis. The quality of the trained model was evaluated using leave-one-out cross-validation, which yielded a mean absolute error of 16.15 ∘ C and an R 2 value of 0.86. The trained model was also used to predict T g for 4 randomly selected resin/hardener combinations for which no experimental data were available. The same combinations were then prepared and measured in the laboratory to further validate the ML model. Excellent agreement was found between experimental and predicted T g values. The current ML model was created using only theoretical features, but could be further improved by adding experimental or quantum mechanical properties of the individual molecules as well as experimental processing parameters. The results presented here contribute to improving sustainability and accelerating the discovery of novel materials with desired target properties. [ABSTRACT FROM AUTHOR]

Epoxy-based polymer nanocomposite is an advanced and high-performance material with numerous applications in automobiles, railways, aerospace, and construction industries. High crosslinking density and inherent brittleness limit its applications. Incorporating the oxide nanoparticles (ONPs) or carbon nanotubes (CNT) or their hybrid structures improves the mechanical properties of the epoxy nanocomposite due to the exceptional properties of nanoscale materials. This review article analyzes and summarizes the effects of ONP, CNT, and their hybrid form on the mechanical properties and toughening mechanisms of epoxy nanocomposite based on the recent experimental findings. The possible challenges of the fabrication of hybrid epoxy nanocomposites have also been covered in this work. This article concludes with the possible solutions for the fabrication of hybrid epoxy nanocomposites for improved mechanical performance and their crucial role in future research. [ABSTRACT FROM AUTHOR]

The preparation of bio-based epoxy resin with excellent thermal properties and flame retardant properties from green renewable resources had attracted extensive attention in recent years. Starting from the driving structural properties, the purpose of this study is to prepare multifunctional triglycidylester- diphenolic acid- bio-based epoxy (TDBE) with diphenolic acid (DPA), triglycidyl isocyanurate (TGIC), and 9,10-dihydro-9-oxa-10-phosphophenanthrene 10 oxide (DOPO) as raw materials. TDBE/DDM and bisphenol A epoxy resin curing agent (DGEBA/DDM) was prepared with 4,4 '- diaminodiphenylmethane (DDM) as curing agent. TDBE/DDM has excellent fire safety. LOI value rose from 24.5 to 42.0%, and the UL-94 test level passes V-0 level. In the cone calorimeter test, the peak heat release rate (pHRR) is decreased by 69.3%. Besides, the lap shear TDBE adhesive strength was 42.9 MPa, which increased by 62.5%. This new multifunctional bio-based flame retardant epoxy resin provides a broader application prospect for high-performance materials. [ABSTRACT FROM AUTHOR]

Since electrostatic self-assembly carbon nanotubes–carbon black (CNTs–CB) composite fillers have good electrical conductivity and an easy dispersion process, they were incorporated into epoxy matrix to fabricate the CNTs–CB/epoxy nanocomposites. The mechanical properties, electrical conductivity, piezoresistivity, as well as microstructure characterization of the CNTs–CB/epoxy nanocomposites were experimentally investigated. The piezoresistive mechanisms of the CNTs–CB/epoxy nanocomposites were also established based on tunneling conduction and contacting conduction. The significant improvements in compressive yielding strength and elastic modulus of the nanocomposites could be attributed to the stable interfacial interaction. A moderate percolation threshold was obtained at 0.41 vol% for the CNTs–CB/epoxy nanocomposites in comparison with that of the nanocomposites filled with only CNTs or CB particles. In monotonic compressive loading, the CNTs-CB/epoxy nanocomposites exhibited highly sensitive and remarkably non-monotonic piezoresistive responses, which could be divided into three stages and showed dependence on the distinct evolution of hybrid conductive networks under compression. Moreover, the experimental results of cyclic loadings confirmed the stability, repeatability, and recoverability in piezoresistive responses of the nanocomposites. Overall, the highly sensitive and steadily piezoresistive responses demonstrate that the CNTs–CB/epoxy nanocomposites are attractive to be used as compressive strain sensors for structural health monitoring in civil infrastructures. [ABSTRACT FROM AUTHOR]

A facile and effective method has been developed to prepare highly thermal conductive composites with three-dimensional boron nitride (BN) network based on epoxy spheres (ESs). ESs synthesized and coated with fBN (ESs@fBN) were added into epoxy matrix to construct networks. The formation mechanism of ESs morphology and properties of composites with different content of ESs@fBN were investigated. The thermal conductivity of the composites was enhanced from 0.18 W m−1 K−1 of neat epoxy to 0.67 W m−1 K−1 of composite with only 7.4 wt% fBN. A 272% increment is attributed to the occupation of ESs, which can facilitate to form effective heat dissipating paths at low content of filler and improve the thermal conductivity of the composites. Moreover, the addition of reactive ESs and fBN could lead to an increase in storage modulus and Tg of epoxy resin. This method will give a new consideration for the preparation of thermally conductive composites. [ABSTRACT FROM AUTHOR]

The designing of low-cost, high-performance, bio-based epoxy thermosets that can cope with the global oil crisis and climate change is a challenge. A bio-based epoxy resin was synthesized from gallic acid using epichlorohydrin, and a carboxylic acid-modified tannic acid (CATA) was obtained using simple esterification in which the gallic acid-based epoxy resin (GA-EP)/methyl nadic anhydride (MNA)/2-ethyl-4-methylimidazole (2,4-EMI) curing system was used as a toughener. Moreover, the structural characterization, mechanical performance, curing behavior, and thermal properties of epoxy thermosets were investigated. Consequently, the addition of only 1.0 wt% CATA increased the toughness from 9.9 to 17.3 kJ/m2 by ~ 74.7% relative to the GA-EP/MNA/2,4-EMI system. Furthermore, the 1.0 wt% CATA-toughened GA-EP/MNA/2,4-EMI showed considerable tensile strength of 52.1 MPa. Such toughness and tensile property of the epoxy thermoset was primarily attributed to CATA participating in the cross-linking network and forming a homogenous system after curing. Our study provides a novel strategy for developing cost-effective high-performance bio-based epoxy thermosets. [ABSTRACT FROM AUTHOR]

In this work, the electromagnetic interference (EMI) shielding performance of epoxy composites containing barium hexaferrite (BaM) nanoparticles and graphene nanoplatelets (GNP) over the X-band frequency range of 8–12.4 GHz is presented. The BaM nanoparticles having a platelike morphology were synthesized using a co-precipitation technique and characterized using XRD and SEM. A set of epoxy nanocomposites with varying content of GNP and/or BaM nanoparticles were prepared and characterized for their electrical, magnetic, dielectric, and EMI shielding properties. An electrical percolation threshold value of 4.21 wt% GNP was determined for composites containing 8 wt% BaM, suggesting efficient network formation of GNP in the presence of BaM nanoparticles. The permeability and permittivity results suggest higher dielectric and magnetic loss capability in the composites containing both nanoparticles. Furthermore, the composites containing both BaM and GNP exhibited significantly greater EMI shielding effectiveness (SE) values as compared to those containing equivalent loading of either GNP or BaM, which suggests synergy between these nanoparticles. The one-millimeter thick composite sample containing 8 wt% BaM and 10 wt% GNP exhibited an EMI SE value of 17.2 dB in the X-band frequency range, which equates to attenuation of 98.17% of incident wave power. Schematic representation of attenuation of electromagnetic waves in the epoxy composite containing GNP and BaM. [ABSTRACT FROM AUTHOR]

Magnetostrictive properties of CoMnSi are generally confined by their intrinsic brittleness and difficulty in growing into anisotropic bulk materials. In this study, we present a new type of 〈100〉-oriented CoMnSi microspheres/epoxy resin composite that exhibits a giant and reversible magnetostriction of 6700 ppm. 〈100〉-textured CoMnSi microspheres were synthesized through the non-wettability between CoMnSi liquid and solid dispersions. The microspheres/epoxy composites with a uniform 〈100〉 orientation were produced by applying a simulating rotating magnetic field. The improved magnetostriction in the composite was associated with microspheres' texture as well as their orientation. This work may shed light on the synthesis of textured metal spheres and the development of magnetic composite materials. [ABSTRACT FROM AUTHOR]

This experiment aims to optimize the interface compatibility between the wood template and the resin through silane coupling agent KH550, so as to improve the optical and mechanical properties of transparent wood with solid wood color and texture, and provide a theoretical basis for the application of new materials in the fields of home design and manufacturing. In this study, silane coupling agent was used to directly modify the wood templates from which partial lignin was removed, and then, epoxy resin E57 matched with the refractive index of the wood templates was introduced, and samples were obtained after impregnation and curing. Then, the orthogonal experiment method was used to explore the process conditions used when the optical performance of the samples reached the optimal (the transmittance was 87.5%, and the haze was 35.39% at 800 nm wavelength): KH550 concentration 5 wt%, 20 min, 25 °C. And the order of the influence of various factors on the light transmittance of the samples was: reaction temperature > reaction time > KH550 concentration. Then, through infrared test, X-ray diffraction patterns and electron microscopy, it was concluded that KH550 made more chemical bonds between the wood template and the resin, so the overall interface compatibility of the sample became better. Therefore, the light transmittance, tensile strength and elongation at break of the samples modified by KH550 were significantly improved, and the haze was significantly reduced. In addition, transparent wood still retains part texture of solid wood, which is also the feature of this new material. [ABSTRACT FROM AUTHOR]

In order to improve the interfacial adhesion of epoxy composites, a hierarchical structure including carbon nanotubes (CNTs) grown on carbon fiber (CF) was prepared by a novel vacuum-assisted chemical vapor deposition (CVD) method at relatively low temperature of 400 °C under a pressure of 0.01 MPa. The short beam method and microbond test were used to measure the interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) of epoxy composites reinforced by different CFs. The results showed that the CNTs-grown CF prepared at the H2 flow rate of 9 L/min had the best reinforcement effect. The ILSS and IFSS of its composites were 19.50% and 62.32% higher than that of the CF/epoxy composites without CNTs grown, respectively. The improvement of interfacial adhesion can be attributed to the fact that CNTs inserted into the matrix enhanced the mechanical interlocking between the fiber and the resin and induced the formation of interphase. Also, two failure modes of CNTs have also been observed, which can absorb extra energy and increased the difficulty of the separation of fiber and resin. The increase in the glass transition temperature (Tg) indicated the movement of the polymer molecular chains at the interphase was restricted by CNTs, which also contributed to the improvement of the interfacial adhesion of composites. [ABSTRACT FROM AUTHOR]

One of the major challenges in off-shore tidal and wave energy devices is the ageing of these structures in the hostile marine environment, which limits their operating life. In this research, mechanical properties of aged glass/epoxy and carbon/epoxy composite specimens including tensile strength, Young's modulus, flexural strength, and shear strength, following immersion in a representative accelerated marine degradation environment (artificial seawater, with 3.5% salinity at room temperature and 60 °C) have been investigated. The microstructure and physicochemical characterization of the aged samples were assessed via microscopic imaging, micro-CT scanning and differential scanning calorimetry. The degradation phenomenon was apparent in the change of mechanical properties and microstructure of composite laminates (micro-cracks and debonding between matrix and fibre). Generally, the ageing process had a more severe effect on tensile and shear strengths of glass/epoxy samples than those of carbon/epoxy specimens. Reversely, the results of bending tests of carbon/epoxy composites showed more drop-in flexural properties than glass/epoxy samples. The results revealed that degradation mechanisms continue even after reaching the saturation point in composite materials. The achievements of this research present a good understanding of the effect of degradation of composite materials in salt water to deal with their application in real service environment. [ABSTRACT FROM AUTHOR]

Syntactic foams with high strength and light weight are essential for aerospace and deep sea explorations. In this study, high-performance carbon fiber/hollow glass microspheres/epoxy syntactic foams were prepared, and the reinforcing mechanism of carbon fiber is discussed. The syntactic foam with 3 wt% short carbon fiber achieves a uniaxial compressive strength of 141.7 MPa, which is among the highest values reported in the literature. The thermal conductivity of syntactic foam increased by 66.7% with the addition of 3 wt% short carbon fibers, which helped to control the cracking issue caused by the inner temperature surge during the curing process. Further stress characterizations using fiber Bragg gratings (FBGs) confirmed that carbon fiber can relieve the evolution of thermal stress and reduce the residual thermal stress. [ABSTRACT FROM AUTHOR]

In order to improve the aging resistance of epoxy resin insulation materials and the cost-effectiveness and reliability of power apparatuses, a novel silicone-modified aging-resistant epoxy resin insulation material was developed. The modification was achieved via chemical grating, using dihydroxydiphenylsilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane and dicyclohexylamine. Accelerated thermal aging test, accelerated hydrothermal aging test and electrical tree test were carried out to compare the aging resistance of the novel, existing silicone-modified epoxy resin and unmodified epoxy resin under high temperature, humid environment and strong electric fields. The results show that compared with the unmodified resin, the novel material has advantages in thermal, hydrothermal aging resistance and electrical tree resistance. More specifically, after modification, the dielectric strength of the novel material after thermal aging test was improved by 12%; its partial discharge inception voltage (PDIV) after hydrothermal aging test was increased by 19.4% and the growth rate of electrical trees was 12.68% of that in unmodified resin. Compared with the existing silicone-modified epoxy resin, the novel silicone-modified epoxy resin sacrifices part of the hydrothermal properties, but showed better thermal stability, and the growth rate of electrical trees in the novel silicone-modified epoxy resin was 44.26% of that in the existing resin. [ABSTRACT FROM AUTHOR]

Functional wood is a promising building material. Due to its high mechanical properties, multi-function and low thermal conductivity, modified wood has potential possibility to replace silicate glass. Laterly, many photo-responsive, thermal-responsive and electrical-responsive smart woods have been researched to reduce building energy consumption. However, some smart woods' responsiveness is achieved by adding toxic and expensive functional agent, which may cause problems. Additionally, some smart woods' weatherability is not good enough, which may influence their practical applications. Herein, a reversible photochromic smart wood with high mechanical properties and good weatherability is prepared and studied. To realize photochromism, AG-80/DDM epoxy resin is dipped into the delignified wood. The reversible photochromism of this smart wood is achieved by changing the network structure of AG-80/DDM epoxy resin. Meanwhile, the dipping of AG-80/DDM epoxy resin also provides smart wood with fluorescence, pH-response and excellent weather resistance. This work offers a new perspective and basic data for preparing low-cost reversible photo-responsive smart wood with extreme weather resistance and high mechanical properties, which lays the foundation of potential applications for smart window and building materials. [ABSTRACT FROM AUTHOR]

A balance of sustainability and high fire resistance and smoke suppression is important for the preparation of epoxy resins (EPs). Herein, bio-based iron alginate was used to ameliorate the fire safety of EP matrix. The addition of iron alginate reduced the initial decomposition temperature and temperature at maximum weight-loss rate of EP matrix, whereas obviously improved the char residues at the higher temperature zones. The peak heat release rate, smoke production rate and total smoke production were dramatically decreased by 61.3%, 60.4% and 42.2%, respectively, compared with those of EP matrix. And the presence of iron alginate obtained obviously smoke-suppressant effect on EP/iron alginate composites. Furthermore, the incorporation of iron alginate had no seriously destructive effect on the mechanical properties of EP matrix, while EP/iron alginate-3 exhibited a 13.5% improvement in the impact strength, compared with that of EP matrix. Such desirable features including higher fire resistance and proper smoke suppression make iron alginate a significant strategy for producing fire-safety EP compositions. [ABSTRACT FROM AUTHOR]

This work investigated the impact that the processing of hemp (C. sativa L.) fibre has on the mechanical properties of unidirectional fibre-reinforced epoxy resin composites loaded in axial tension, and particleboard reinforced with aligned fibre bundles applied to one surface of the panel. For this purpose, mechanically processed (decorticated) and un-processed hemp fibre bundles, obtained from retted and un-retted hemp stems, were utilised. The results clearly show the impact of fibre reinforcement in both materials. Epoxy composites reinforced with processed hemp exhibited 3.3 times greater tensile strength when compared to the un-reinforced polymer, while for the particleboards, the bending strength obtained in those reinforced with processed hemp was 1.7 times greater than the un-reinforced particleboards. Moreover, whether the fibre bundles were processed or un-processed also affected the mechanical performance, especially in the epoxy composites. For example, the un-processed fibre-reinforced epoxy composites exhibited 49% greater work of fracture than the composites reinforced with processed hemp. In the wood-based particleboards, however, the difference was not significant. Additionally, observations of the fracture zone of the specimens showed different failure characteristics depending on whether the composites were reinforced with processed or un-processed hemp. Both epoxy composites and wood-based particleboards reinforced with un-processed hemp exhibited fibre reinforcement apparently able to retain structural integrity after the composite's failure. On the other hand, when processed hemp was used as reinforcement, fibre bundles showed a clear cut across the specimen, with the fibre-reinforcement mainly failing at the composite's fracture zone. [ABSTRACT FROM AUTHOR]

The molecular structure of curing agents significantly influences the properties of epoxy resins. In this article, the effect of the molecular structure of curing agents on the thermomechanical (TM) properties of an epoxy resin was investigated by a molecular dynamics method. First, the influence of the sizes of 3D systems on the performance of cured systems was preliminarily analyzed. From the results, four kinds of fully atomistic models were constructed and simulated. The effects of curing agents' molecular chain lengths, polar groups, side-chain groups on the TM properties of epoxy resin systems were analyzed from various perspectives. The results showed that the longer the molecular chain and the smaller the group polarity, the inferior the TM properties of the cured system, and vice versa; further, the side-chain group significantly weakened the movement ability of the chain, which has a primary effect on cured system TM properties. Molecular structures of curing agents have little effect on thermal expansion coefficient and thermal conductivity of epoxy curing systems. [ABSTRACT FROM AUTHOR]

The field of microelectronic devices and 5G communication has an increasing demand for polymer composites with low dielectric constant, low dielectric loss, and good hydrophobicity. However, traditional polymer composites cannot simultaneously satisfy them, which severely hinders their application. In this work, a liquid crystal epoxy resin (LCE4) consisted of a flexible chain and rigid mesogenic unit was prepared and cured with methylhexahydrophthalic anhydride (MHHPA). And the mechanism of the curing reaction and the phase structure of the liquid crystal epoxy resins were investigated. In addition, dielectric hydrophobic liquid crystal epoxy nanometer composite materials were successfully prepared with functionalized mesoporous silica (SBA-15) as a filler. The results showed that pure LCE4 exhibited excellent dielectric properties and thermal stability. Compared with pure LCE4, the composite material for SBA-15 modified with KH560 displayed lower dielectric constant, lower dielectric loss, higher glass transition temperature, and better hydrophobicity. For example, with a 0.5 wt% SBA-15, the dielectric constant and dielectric loss of the composite material were as low as (2.35, 0.025) compared with pure LCE4 (3.25, 0.036) that was reduced by 24.7% and 31%. In addition, the glass transition temperature and water contact angle are increased by 16 °C and 14°, respectively. Composites also showed good thermal stability and mechanical properties. The reasons may mainly be derived from the internal structure of LCE4, the effective modification of mesoporous SBA-15 by KH560, and the excellent dispersion of organic and inorganic phases. [ABSTRACT FROM AUTHOR]