Showing papers on "Epoxy published in 2018"

A review of extending performance of epoxy resins using carbon nanomaterials

Abstract: Carbon nanomaterials are receiving worldwide attention because of their multi-faceted superiority in thermal conductivity, flame retardancy, mechanical stability, electrical conductivity, and biocompatibility. In this review, a survey of the literature on extending performance of epoxy resins based on carbon nanomaterials is presented. The structure-performance relationships for different carbon nanomaterials modified epoxy are closely analyzed. The performance extension in mechanical, electrical, thermal conductivity, flame retardancy, antidegradation, and tribological properties of epoxy are reviewed in detail. Other application areas including biocompatibility, biodegradability, gas barrier properties, shape memory, and electromagnetic interference shielding are touched. The challenges and opportunities in carbon nanomaterials functionalized epoxy composites are also discussed.

Construction of 3D Skeleton for Polymer Composites Achieving a High Thermal Conductivity

Abstract: Owing to the growing heat removal issue in modern electronic devices, electrically insulating polymer composites with high thermal conductivity have drawn much attention during the past decade. However, the conventional method to improve through-plane thermal conductivity of these polymer composites usually yields an undesired value (below 3.0 Wm-1 K-1 ). Here, construction of a 3D phonon skeleton is reported composed of stacked boron nitride (BN) platelets reinforced with reduced graphene oxide (rGO) for epoxy composites by the combination of ice-templated and infiltrating methods. At a low filler loading of 13.16 vol%, the resulting 3D BN-rGO/epoxy composites exhibit an ultrahigh through-plane thermal conductivity of 5.05 Wm-1 K-1 as the best thermal-conduction performance reported so far for BN sheet-based composites. Theoretical models qualitatively demonstrate that this enhancement results from the formation of phonon-matching 3D BN-rGO networks, leading to high rates of phonon transport. The strong potential application for thermal management has been demonstrated by the surface temperature variations of the composites with time during heating and cooling.

Comparison of carbon nanotubes and graphene oxide coated carbon fiber for improving the interfacial properties of carbon fiber/epoxy composites

Abstract: By designing the fiber/matrix interface, the properties of the carbon fiber-reinforced composite can be changed significantly. In this work, carboxylic-functionalized carbon nanotubes (CNTs) and graphene oxide (GO) were separately deposited on the carbon fiber (CF) surface to increase the interfacial properties of composites. The properties of fibers such as the surface topography, surface chemical composition and surface energy were examined, and the interfacial shear strength between the fibers and the matrix was examined using a microdroplet test. In addition, CNT-coated, GO-coated and pristine unidirectional carbon fiber fabrics were used to manufacture CF/epoxy composites via the vacuum-assisted resin transfer molding method, and their moisture absorption and interlaminar shear strength were measured. The results reveal that both CNTs and GO can significantly improve the interfacial properties of composites. The CNT/CF-reinforced composites have higher shear strength, and the GO/CF-reinforced composites have better humidity resistance. The interfacial reinforcing mechanisms of the composites with CNTs and GO were compared.

A Catalyst-Free Epoxy Vitrimer System Based on Multifunctional Hyperbranched Polymer

Abstract: To date, all epoxy vitrimer systems reported in the literature rely on addition of significant amounts of catalysts to achieve the dynamic transesterification reaction (TER). However, the catalysts used in vitrimers are often toxic and have poor miscibility with organic compounds, and they may further comprise the application performance like corrosion resistance. Moreover, the reprocessing and recycling properties are highly dependent on the loading amount and the type of catalyst. In this study, two hyperbranched epoxy (HBE) prepolymers are synthesized and then reacted with succinic anhydride to prepare a catalyst-free epoxy vitrimer system. It is demonstrated that both the curing during the preparation of the cross-linked materials and the TER in the resulting cross-linked materials proceed properly without addition of external catalyst. We attributed this phenomenon to the abundant free hydroxyl groups in HBE which serve as both reacting moiety and catalyst in both curing and the TER processes. At ele...

Tunable thermosetting epoxies based on fractionated and well-characterized lignins

Abstract: Here we report the synthesis of thermosetting resins from low molar mass Kraft lignin fractions of high functionality, refined by solvent extraction. Such fractions were fully characterized by 31P NMR, 2D-HSQC NMR, SEC, and DSC in order to obtain a detailed description of the structures. Reactive oxirane moieties were introduced on the lignin backbone under mild reaction conditions and quantified by simple 1H NMR analysis. The modified fractions were chemically cross-linked with a flexible polyether diamine ( Mn ≈ 2000), in order to obtain epoxy thermosets. Epoxies from different lignin fractions, studied by DSC, DMA, tensile tests, and SEM, demonstrated substantial differences in terms of thermo-mechanical properties. For the first time, strong relationships between lignin structures and epoxy properties could be demonstrated. The suggested approach provides unprecedented possibilities to tune network structure and properties of thermosets based on real lignin fractions, rather than model compounds.

A Self-Healable High Glass Transition Temperature Bioepoxy Material Based on Vitrimer Chemistry

Abstract: The design of high glass transition temperature (Tg) thermoset materials with considerable reparability is a challenge. In this study, a novel biobased triepoxy (TEP) is synthesized and cured with an anhydride monomer in the presence of zinc catalyst. The cured TEP exhibits a high Tg (187 °C) and comparable strength and modulus to the cured bisphenol A epoxy. By adopting the vitrimer chemistry, the cross-linked polymer materials are imparted significant stress relaxation and reparability via dynamic transesterification. It is noted that the reparability is closely related to the repairing temperature, external force, catalyst content, and the magnitude of rubbery modulus of the sample. The width of the crack from the cured TEP can be efficiently repaired within 10 min. This work introduces the first high-Tg biobased epoxy material with excellent reparability and provides a valuable method for the design of high-Tg self-healing materials suitable for high service temperature.

Recyclable and Malleable Epoxy Thermoset Bearing Aromatic Imine Bonds

Abstract: A method for preparing reprocessable epoxy thermoset is presented. The process is composed of synthesis of a bisphenol monomer bridged by an imine bond, glycidylation of the bisphenol, and cross-linking with a hardener to form thermoset. The resulting epoxy thermoset possesses comparable properties to conventional high-performance thermosets made from bisphenol A. However, when treated by a stimulus like acid, temperature, and/or water, the described thermoset exhibits reprocessability. Degradation and recycling involve hydrolysis and re-formation of imine bonds; reshaping and repairing of the thermoset are realized through imine exchange reactions. All the described processes require no metal catalyst, press heating, or additional monomer, which significantly widens thermoset reprocessing.

Multistimuli-Responsive Intrinsic Self-Healing Epoxy Resin Constructed by Host-Guest Interactions

Abstract: The self-healing abilities inside polymeric materials are desirable functions in materials science. Host–guest chemistry, combined with excellent properties of graphene, was used for the construction of multistimuli-responsive intrinsic self-healing epoxy materials. By ultraviolet (UV) curing, the unsaturated epoxy resin was connected with β-cyclodextrin/graphene complex through free radical copolymerization. The introduced complex, acting as macro-cross-linker and photothermal agent, can reconnect the damage-induced broken bonds through dynamic host–guest interaction. In this work, the epoxy composites exhibited a high healing efficiency of up to 79.2% and tensile strength of up to 20.8 MPa under heating or near-infrared stimulation, which represent relatively excellent values among all the reported intrinsic self-healing epoxy resin and host–guest self-healing systems.

Vertically Aligned and Interconnected SiC Nanowire Networks Leading to Significantly Enhanced Thermal Conductivity of Polymer Composites

Abstract: Efficient heat removal via thermal management materials has become one of the most critical challenges in the development of modern microelectronic devices. However, previously reported polymer composites exhibit limited enhancement of thermal conductivity, even when highly loaded with thermally conductive fillers, because of the lack of efficient heat transfer pathways. Herein, we report vertically aligned and interconnected SiC nanowire (SiCNW) networks as efficient fillers for polymer composites, achieving significantly enhanced thermal conductivity. The SiCNW networks are produced by freeze-casting nanowire aqueous suspensions followed by thermal sintering to consolidate the nanowire junctions, exhibiting a hierarchical architecture in which honeycomb-like SiCNW layers are aligned. The composite obtained by infiltrating SiCNW networks with epoxy resin, at a relatively low SiCNW loading of 2.17 vol %, represents a high through-plane thermal conductivity (1.67 W m–1 K–1) compared to the pure matrix, whi...

Studies on Mechanical and Morphological Characterization of Developed Jute/Hemp/Flax Reinforced Hybrid Composites for Structural Applications

Abstract: In the present study, an attempt has been made to develop and characterize natural fiber-based composites (jute/epoxy, hemp/epoxy, flax/epoxy) and their hybrid composites (jute/hemp/epoxy, hemp/fla...

Excellent corrosion protection performance of epoxy composite coatings filled with silane functionalized silicon nitride

Abstract: Silicon nitride was firstly used as anticorrosive pigment in organic coatings. An effective strategy by combining inorganic fillers and organosilanes was used to enhance the dispersibility of silicon nitride in epoxy resin. The formed nanocomposites were applied to protect Q235 carbon steel from corrosion. The anticorrosive performance of modified silicon nitride with silane (KH-570) was investigated by electrochemical impedance spectroscopy (EIS), water absorption and pull-off adhesion methods. With the increase of immersion time, the corrosion resistance as well as adhesion strength of epoxy resin coating and unmodified silicon nitride coating decreased significantly. However, for the modified silicon nitride coating, the corrosion resistance and adhesion strength still maintained 5.7×1010 Ω cm2 and 7.6 MPa after 2400-h and 1200-h immersion, respectively. The excellent corrosion resistance performance could be attributed to the chemical interactions between KH-570 functional groups and silicon nitride powders, which mainly came from the easy formation of Si-O-Si bonds. Furthermore, the modified silicon nitride coating formed a strong barrier to corrosive electrolyte due to the hydrophobic of modified silicon nitride powder and increased bonds.

Thermal and Mechanical Properties of Bamboo Fiber Reinforced Epoxy Composites.

Abstract: Bamboo fibers demonstrate enormous potential as the reinforcement phase in composite materials. In this study, in order to find suitable NaOH concentration for bamboo fiber treatment, bamboo fibers were treated with 2 wt.%, 6 wt.% and 10 wt.% NaOH solutions for 12 h, respectively. We determined that 6 wt.% NaOH treated bamboo fibers were optimal for the fabrication of bamboo fiber composites by single fiber tensile test, single fiber pull-out test, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The short length bamboo fibers treated with 6 wt.% NaOH solutions were well dispersed in the epoxy matrix by a new preparation method. The effect of fiber content and fiber length on the mechanical behavior of bamboo fiber reinforced epoxy composites was investigated. The results confirmed that fracture toughness and flexural modulus of the composites monotonically increased with fiber length and content. However, for all samples, composites showed negligible difference on the flexural strength. The fracture surfaces of the composites were observed by SEM, revealing that fiber breakage, matrix cracking, debonding, and fiber pull out were major failure types. In addition, thermogravimetric analysis (TGA) was carried out to investigate the thermal behavior of both bamboo fibers and composites.

Micro-crack behavior of carbon fiber reinforced Fe3O4/graphene oxide modified epoxy composites for cryogenic application

Abstract: The epoxy nanocomposites with Fe3O4 modified graphene oxide (Fe3O4/GO) were used to influence the micro-cracks resistance of carbon fiber reinforced epoxy (CF/EP) laminate at 77 K. Fe3O4/GO with good paramagnetic properties were prepared by co-precipitation method and used to modify epoxy for cryogenic applications. Fe3O4/GO modified CF/EP laminates were also prepared through vacuum-assisted resin transfer molding (VARTM). The results show that the Fe3O4/GO can effectively improve the mechanical properties of epoxy (EP) matrix at 77 K and reduce the coefficient of thermal expansion (CTE) of EP matrix. It also can obviously improve the micro-cracks resistance of CF/EP composites at 77 K. Compared to neat EP, the CTE of Fe3O4/GO modified EP composite is decreased 51.6%. Compared to CF/EP composite, the micro-cracks density of Fe3O4/GO modified CF/EP composite at 77 K is decreased 60.0%.