Rheological and mechanical properties of epoxy/clay nanocomposites with enhanced tensile and fracture toughnesses

Bamboo-Inspired Crack-Face Bridging Fiber Reinforced Composites Simultaneously Attain High Strength and Toughness

Biological strong and tough materials have been providing original structural designs for developing bioinspired high-performance composites. However, new synergistic strengthening and toughening mechanisms from bioinspired structures remain yet to be explored and employed to upgrade current carbon material reinforced polymer composites, which are keystone to various modern industries. In this work, from bamboo, the featured cell face-bridging fibers, are abstracted and embedded in a cellular network structure, and develop an epoxy resin/carbon composite featuring biomimetic architecture through a fabrication approach integrating freeze casting, carbonization, and resin infusion with carbon fibers (CFs) and carbon nanotubes (CNTs). Results show that this bamboo-inspired crack-face bridging fiber reinforced composite simultaneously possesses a high strength (430.8 MPa) and an impressive toughness (8.3 MPa m1/2 ), which surpass those of most resin-based nanocomposites reported in the literature. Experiments and multiscale simulation models reveal novel synergistic strengthening and toughening mechanisms arising from the 2D faces that bridge the CFs: sustaining and transferring loads to enhance the overall load-bearing ability and furthermore, incorporating CNTs pullout that resembles the intrinsic toughening at the molecular to nanoscale and strain delocalization, crack branching, and crack deflection as the extrinsic toughening at the microscale. These constitute a new effective and efficient strategy to develop simultaneously strong and tough composites through abstracting and implenting novel bioinspired structures, which contributes to addressing the long-standingly challenging attainment of both high strength and toughness for advanced structural materials.

Effects of Block Copolymer Terminal Groups on Toughening Epoxy-Based Composites: Microstructures and Toughening Mechanisms

Despite the considerable research attention paid to block copolymer (BCP)-toughened epoxy resins, the effects of their terminal groups on their phase structure are not thoroughly understood. This study fills this gap by closely examining the effects of amino and carboxyl groups on the fracture toughness of epoxy resins at different temperatures. Through the combination of scanning electron microscopy and digital image correlation (DIC), it was found that the amino-terminated BCP was capable of forming a stress-distributing network in pure epoxy resin, resulting in better toughening effects at room temperature. In a 60 wt.% silica-filled epoxy composite system, the addition of a carboxyl-terminated BCP showed little toughening effect due to the weaker filler/matrix interface caused by the random dispersion of the microphase of BCPs and distributed silica. The fracture toughness of the epoxy system at high temperatures was not affected by the terminal groups, regardless of the addition of silica. Their dynamic mechanical properties and thermal expansion coefficients are also reported in this article.

Comparative Study of Different Methods of Synthesis and Their Effect on the Thermomechanical Properties of a Halogenated Epoxy-Based Flame-Retardant Resin

The work presented in this paper deals with the comparative synthesis of diglycidyl ether-based tetrabromobisphenol-A(TBBPA) using both conventional and nonconventional methods in order to explore materials for better industrial applications with respect to effective yield, cost, and time consideration. The conventional method involved the polycondensation of TBBPA and epichlorohydrin in the presence of an alkali catalyst. The nonconventional routes adopted for the synthesis of the material involved ultrasonication, microwave irradiation, and UV light exposure. The Fourier transform infrared spectroscopy spectra of all the synthesized materials of the resin were found to be identical, and the X-ray diffraction analysis showed the material as amorphous. The mechanical studies of the resins revealed that all these resins synthesized by different methods are strong and possess high viscosity. Based on the overall thermal, rheological, and excellent hydrophobic properties, it can serve as an excellent flame retardant.

Simplified Testing of the Bond Strength of Adhesives Used for Bonded Anchors

The analysis presented in this paper is focused on problems of bond strength as an overall bond quality parameter of industrial adhesives for structural anchoring. In the first part, the problem of bond strength as the most important parameter influencing the final anchor resistance to tension load is described. Further in the text, a new methodology of simplified testing of the strength parameters of adhesives is described. Special test specimens made from steel are repeatedly used in this methodology. Additionally, results of these tests on some new recipes for adhesive are presented. Especially, epoxy resins with special fillers, such as carbon fibres, carbon nanotubes or graphene, were tested. The use of these adhesives in temperatures close to zero degrees Celsius was also tested.

Improving the toughness of thermosetting epoxy resins via blending triblock copolymers

In this study, the triblock copolymer poly(methyl methacrylate)-b-poly(butyl acrylate)-b-poly(methyl methacrylate) (MAM) was used to modify bisphenol A epoxy resin to improve its toughness. The effects of MAM on the curing behaviors, mechanical properties, fracture morphology and thermal properties of epoxy were carefully studied. The results of dissolution experiments show that MAM has good compatibility with epoxy resin under certain conditions. FT-IR and DSC analyses show that adding MAM to epoxy hinders the curing reaction of epoxy resin, without participating in the curing reaction and changing the curing mechanism. The mechanical properties indicated by K_IC and impact strength with an MAM content of 10 phr for the toughened system increase by 91.5% and 83.5%, respectively, compared to the situation without MAM, which may ascribed to the nanoparticles formed during the process of MAM/epoxy blending. In the curing process of an epoxy resin, the typical phase structure that occurs through the self-assembly process can be clearly observed in the MAM/epoxy blends. As the MAM content increases, the amount of nanoparticles gradually increases. This work further confirms that the toughness of the composite material was enhanced to a large extent without significantly decreasing the glass transition temperature of the blends.

In this study, the triblock copolymer poly(methyl methacrylate)-b-poly(butyl acrylate)-b-poly(methyl methacrylate) (MAM) was used to modify bisphenol A epoxy resin to improve its toughness.

Interfacial Architecture Constructed Using Functionalized MWNT Resulting in Enhanced EMI Shielding in Epoxy/Carbon Fiber Composites

In this work, we have attempted to improve electromagnetic interference (EMI) shielding and mechanical behavior of epoxy/carbon fiber (CF) composite, simultaneously, in the presence of functionalized carbon nanotubes. It is well understood that properties of composite depend on the interface between the filler and matrix. Considering this basic understanding, functionalized carbon nanotubes/epoxy nanocomposites were impregnated into a bidirectional carbon fiber (CF) mat and, further, various mechanical and EMI shielding behaviors were studied. Multiwalled carbon nanotubes were functionalized with branched poly(ethyleneimine) (b-MWNT) to tailor the interface of epoxy/CF composites. Laminates with two layers of CF were fabricated with functional MWNT modified epoxy. Scanning electron microscopy was used to analyze the microstructure of epoxy/CF laminates. Lap shear test was performed to analyze adhesion between the modified epoxy and carbon fiber. Further dynamic mechanical analysis in the temperature range of 30-160 °C was performed. Thermal degradation of composites was studied using a thermogravimetric analyzer. Electrical conductivity of laminates was measured using a four-point method on an Agilent probe station. EMI shielding effectiveness (SE) was measured for 0.5 mm-thin laminates in the Ku band. The b-MWNT modified epoxy/CF composites showed excellent SE_T of ca. -60 dB and SE_A of ca. -50 dB, which are of commercial importance. Compared to unmodified epoxy/CF, b-MWNTs/epoxy/CF exhibited 200% increment in EMI SE_T and 35% enhancement in storage modulus due to the improved interface between the epoxy matrix and carbon fiber.

Antibacterial Capability, Physicochemical Properties, and Biocompatibility of nTiO₂ Incorporated Polymeric Scaffolds

Postoperative infection is a common risk which brings about failure in bone transplantation. In this study, nano titanium dioxide (nTiO₂) was incorporated into Polyetheretherketone/polyglycolicacid (PEEK/PGA) blends to construct antibacterial scaffolds via selective laser sintering. Antibacterial capability was assessed using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The results demonstrated that the scaffolds with nTiO₂ presented an effective antibacterial activity, which might be attributed to that nTiO₂ would do the mechanical and oxidative damage to bacteria by occurring contact actions and generating reactive oxygen species (ROS), and thus killed bacteria from structure and function. Moreover, nTiO₂ could enhance the tensile strength and modulus of scaffolds due to the reinforcing effect and its uniform disperse. And the cell culture experiments showed that nTiO₂ stimulated cellular attachment and proliferation. Besides, it also elevated the hydrophily and thermal stability of scaffolds. These results suggested that the polymeric scaffolds incorporated nTiO₂ had potential application in bone tissue engineering.

Increase of tensile strength and toughness of bio-based diglycidyl ether of bisphenol A with chitin nanowhiskers

It is challenging to reinforce and toughen thermoset epoxy resins. We describe a slurry-compounding technique to transfer a uniform dispersion of chitin nanowhiskers (CW) in ethanol into an epoxy matrix. The incorporation of the hydrophilic CW reinforces the oil-soluble diglycidyl ether of bisphenol A (DGEBA). The resultant CW/epoxy bionanocomposites were transparent and showed considerably enhanced thermal and mechanical properties with tensile strength, modulus, toughness, and elongation at break being increased by 49%, 16%, 457%, and 250%, with only 2.5 wt.% CW. This improvement in strength and toughness is rare for thermoset epoxy/rigid nanofiller systems. We hypothesize that CW with many free amine groups could function not only as a nanofiller but also as a macromolecular polyamine hardener that participates in epoxy curing. The strong covalent interaction between the filler and the matrix allowed for efficient load transfer across the interfaces, which accounted for the greater strength and toughness.

Fish DNA-modified clays: Towards highly flame retardant polymer nanocomposite with improved interfacial and mechanical performance

Deoxyribonucleic Acid (DNA) has been recently found to be an efficient renewable and environmentally-friendly flame retardant. In this work, for the first time, we have used waste DNA from fishing industry to modify clay structure in order to increase the clay interactions with epoxy resin and take benefit of its additional thermal property effect on thermo-physical properties of epoxy-clay nanocomposites. Intercalation of DNA within the clay layers was accomplished in a one-step approach confirmed by FT-IR, XPS, TGA, and XRD analyses, indicating that d-space of clay layers was expanded from ~1.2 nm for pristine clay to ~1.9 nm for clay modified with DNA (d-clay). Compared to epoxy nanocomposite containing 2.5%wt of Nanomer I.28E organoclay (m-clay), it was found that at 2.5%wt d-clay loading, significant enhancements of ~14%, ~6% and ~26% in tensile strength, tensile modulus, and fracture toughness of epoxy nanocomposite can be achieved, respectively. Effect of DNA as clay modifier on thermal performance of epoxy nanocomposite containing 2.5%wt d-clay was evaluated using TGA and cone calorimetry analysis, revealing significant decreases of ~4000 kJ/m² and ~78 kW/m² in total heat release and peak of heat release rate, respectively, in comparison to that containing 2.5%wt of m-clay.

The improvement in cryogenic mechanical properties of nano-ZrO2/epoxy composites via surface modification of nano-ZrO2

This study investigated the cryogenic mechanical properties of modified nano-ZrO₂ reinforced epoxy composites.

Effects of 2-D transition metal carbide Ti2CTxon properties of epoxy composites

By means ofin situintercalation polymerization Ti₂CT_x/EP nanocomposites were prepared, which possessed excellent mechanical and tribological properties.