The mechanical properties,microstructures and mechanism of carbon nanotube-reinforced oil well cement-based nanocomposites

High performance cement-based nanocomposites were successfully fabricated through the use of oil well cement filled with multiwalled carbon nanotubes (MWCNTs) as reinforcements. The dispersibilities of four dispersing agents for the MWCNTs were investigated and compared. The dispersed morphologies and structural characteristics of the MWCNTs were analyzed via TEM, FTIR and Raman spectroscopy studies. The effects of MWCNT addition on the rheological behavior and fluidity of oil well cement slurry were discussed. The mechanical properties of the cement-based nanocomposites with different MWCNT content values and different curing ages were explored and analyzed. Furthermore, the microstructures of the MWCNT reinforced cementitious nanocomposites were characterized via XRD, SEM, EDS, total porosity and pore size distribution studies. The results demonstrated that the 28 day compressive strength and 28 day flexural strength of the 0.05 wt% MWCNT cementitious nanocomposite increased by 37.50% and 45.79%, respectively, compared with a pure cement matrix. The elastic moduli of a 0.05 wt% MWCNT cementitious sample declined by 19.07% and 35.39% under uniaxial and triaxial stress, respectively. XRD and pore structure analysis indicated that the MWCNTs could accelerate the hydration process, increase the amount of hydration products and optimize the pore size distribution within the matrix. Additionally, crack bridging, pulling out, network filling and a calcium-silicate-hydrate (C–S–H) phase were exhibited by SEM images. Meanwhile, the reinforcing and toughening mechanism of MWCNTs was also discussed; these had a beneficial influence on the mechanical properties.

The reinforcing and toughening mechanism of MWCNTs in cementitious nanocomposites under the external load.     

Continuous and rapid fabrication of photochromic fibers by facilely coating tungsten oxide/polyvinyl alcohol composites

Photochromic fibers have attracted great attention due to their wide use in areas of military camouflage, safety warnings, anti-counterfeiting, entertainment, etc. Compared with photochromic organic materials, inorganic photochromic tungsten trioxide (WO₃) materials have been extensively studied, because of their good stability and cost efficiency. In this work, we report the continuous fabrication of photochromic fibers in a simple and low-cost way by dip-coating WO₃/PVA composites. The prepared photochromic fibers show fast and reversible color switch from light yellow to dark blue upon UV irradiation and infrared heating treatment. The obtained photochromic fibers can be produced on a large scale and be woven into various patterns with good mechanical strength and washability, showing great potential in developing photochromic textiles.

Photochromic fibers have attracted great attention due to their wide use in areas of military camouflage, safety warnings, anti-counterfeiting, entertainment, etc.     

Preparation of Ni/C porous fibers derived from jute fibers for high-performance microwave absorption

Composites obtained by incorporating magnetic nanoparticles into porous carbon materials are promising in serving as microwave absorbing materials. In this study, Ni/C porous fibers were successfully synthesized through a simple in situ template method by using low-cost jute fibers as carbon source and template. The results showed that the Ni nanoparticles were uniformly loaded on the surface and hollow porous structure of the Ni/C porous fibers. Meanwhile, the content and size of the Ni nanoparticles on the Ni/C porous fibers can be controlled. Due to a suitable filling content, the synergistic effect of dielectric loss, interface polarization loss, magnetic loss and porous structure of the Ni/C porous fibers, an excellent microwave absorption performance was achieved. The minimum reflection loss value reached −43.0 dB, and a reflection loss value less than −10 dB was in the frequency range of 11.2–16.1 GHz with 2.0 mm thickness. In particular, under matching thickness (1.5–3.5 mm), the values of all the reflection loss peaks were below −20.0 dB. It is believed that this work can not only provide a new way to design excellent carbon-based microwave absorbing materials, but also offer an effective design strategy to synthesize biomass nanocomposites.

Ni/C porous fibers derived from jute fibers exhibited excellent microwave absorption performance.     

Performance of palm fibers as stationary phase for capillary gas chromatographic separations

Herein we report the first example of exploring bio-based materials, palm fibers (PFs), as a stationary phase for capillary gas chromatographic separations. The PFs capillary column was fabricated by the sol–gel coating method and showed a weak polar nature and high column efficiency over 4699 plates per m for n-dodecane, naphthalene and n-octanol. Importantly, the column exhibited high selectivity and resolving capability for more than a dozen mixtures covering a wide-ranging variety of analytes and isomers. In addition, it was applied for the determination of isomer impurities in real samples, proving its good potential for practical gas chromatographic analysis.

Herein we report the first example of exploring bio-based materials, palm fibers (PFs), as a stationary phase for capillary gas chromatographic separations.     

Preparation of environment-friendly solid epoxy resin with high-toughness via one-step banburying

Solid epoxy resin is highly desired in adhesives, electronic materials and coatings due to the attractive characteristics of solvent-free, highly efficient utilization and convenient storage and transportation. However, the challenges remain in fabricating high-toughness solid epoxy resin through a facile and efficient way. Here, a high-performance environment-friendly solid epoxy resin was fabricated by employing maleic anhydride grafted ethylene-vinyl acetate copolymer (EVA-g-MAH) as the flexibilizer via one-step banburying method. The results showed that the modified epoxy resin maintained a high glass transition temperature (T_g) and thermal stability, while its impact strength, tensile toughness and flexural toughness were significantly increased compared with the neat epoxy resin. The impact strength, tensile toughness and flexural toughness of R-EM10 are improved 138%, 195% and 149%, respectively. The EVA-g-MAH was introduced in the epoxy matrix as a separate phase to increase toughness via transfer stress and dissipated energy. The attractive properties of this facile fabrication process and the high-toughness, as well as the environment-friendly performance make this solid epoxy highly promising for large-scale industrial application.

High-toughness and environment-friendly solvent free solid epoxy resin through a low-cost, facile and large-scale fabrication process.     

Multiwall-carbon-nanotube/cellulose composite fibers with enhanced mechanical and electrical properties by cellulose grafting

Multiwall-carbon-nanotube (MWCNT)-cellulose/cellulose composite fibers with promoted mechanical and electronic activities were synthesized. Remarkably, the dispersion of MWCNTs in the composite fibers was facilitated through cellulose grafting, resulting in the tensile strength of the obtained MWCNT-cellulose/cellulose composite fibers being increased to 304.6 MPa with 10 wt% MWCNTs involved, which was almost 106.8% higher than that of pristine MWCNT/cellulose fibers with the same amount of MWCNTs. In addition, the electrical conductivity of the MWCNT-cellulose/cellulose composite fibers was enhanced to 1.3 × 10⁻¹ S cm⁻¹ with the dispersion of 10 wt% MWCNTs, which was almost 108 times higher than that of pristine MWCNT/cellulose fibers with the same amount of MWCNTs.

MWCNT-cellulose/cellulose composite fibers with enhanced mechanical and conducting properties were prepared via facilitating the dispersion of MWCNTs in fibers.     

A state-of-the-art review on coir fiber-reinforced biocomposites

The coconut (Cocos nucifera) fruits are extensively grown in tropical countries. The use of coconut husk-derived coir fiber-reinforced biocomposites is on the rise nowadays due to the constantly increasing demand for sustainable, renewable, biodegradable, and recyclable materials. Generally, the coconut husk and shells are disposed of as waste materials; however, they can be utilized as prominent raw materials for environment-friendly biocomposite production. Coir fibers are strong and stiff, which are prerequisites for coir fiber-reinforced biocomposite materials. However, as a bio-based material, the produced biocomposites have various performance characteristics because of the inhomogeneous coir material characteristics. Coir materials are reinforced with different thermoplastic, thermosetting, and cement-based materials to produce biocomposites. Coir fiber-reinforced composites provide superior mechanical, thermal, and physical properties, which make them outstanding materials as compared to synthetic fiber-reinforced composites. However, the mechanical performances of coconut fiber-reinforced composites could be enhanced by pretreating the surfaces of coir fiber. This review provides an overview of coir fiber and the associated composites along with their feasible fabrication methods and surface treatments in terms of their morphological, thermal, mechanical, and physical properties. Furthermore, this study facilitates the industrial production of coir fiber-reinforced biocomposites through the efficient utilization of coir husk-generated fibers.

The coir fibers could be used as prominent biocomposite materials.     

A new strategy for synthesizing silver doped mesoporous bioactive glass fibers and their bioactivity,antibacterial activity and drug loading performance

A new strategy for preparing mesoporous metal-doped bioactive glass fibers (MBGFs) was designed, which included electrospinning and sulfonating mesoporous PS fibers, precipitating metal ions and bioactive glass sol–gel precursor into the mesoporous polystyrene (PS) fibers and calcinations. Silver-doped mesoporous BGFs (Ag-MBGFs) with a uniform diameter of 1–2 μm and a specific surface area of 40.22 m² g⁻¹ were prepared as an example and characterized by SEM, XRD, TG, ICP and FTIR. These Ag-MBGFs showed excellent bioactivity, antibacterial properties and drug loading and release performance due to their special mesoporous and fibrous structure. The concentration of Staphylococcus aureus decreased from 1 × 10⁸ colony-forming units per mL (CFU mL⁻¹) to 2.5 × 10⁶ CFU mL⁻¹ in 2 h and then to 2 × 10² CFU mL⁻¹ in 12 h when the concentration of the Ag-MBGFs reached 16 mg mL⁻¹. BGFs of different compositions and functions could be prepared by the same strategy in a mesoporous PS fiber template, which could enrich materials for constructing orthopedic implants.

A new strategy for preparing mesoporous metal-doped bioactive glass fibers.     

Fabrication of polyimide/graphene nanosheet composite fibers via microwave-assisted imidization strategy

Here, a rapid and efficient strategy was introduced to prepare polyimide/graphene nanosheet (PI/GN) composite fibers by microwave-assisted imidization. The mechanical properties of the PI/GNs (1 wt%) fibers treated by microwave-assisted imidization were apparently improved with the tensile strength of 1.12 GPa at 350 °C, which was approximately 1.7 times as much as those treated with traditional thermal imidization. The PI/GNs (1 wt%) fibers heated by the microwave-assisted imidization method exhibited excellent thermal stabilities of up to 570.3 °C in nitrogen for a 5% weight loss, and a glass transition temperature above 339 °C. The results of the infrared spectrum and thermal properties indicated that the microwave-assisted treatment could promote the imidization degree of the PI/GN fibers prominently. Meanwhile, as a microwave absorber, graphene nanosheets (GNs) could also promote the imidization process by converting microwave energy into thermal energy. The microwave-polyimide/graphene nanosheet (MW-PI/GN) fibers possessed an optimum tensile strength of 1.38 GPa and modulus of 56.82 GPa at the GN content of 0.25 wt%. The 5% weight loss temperature in nitrogen ranged from 520.9 °C to 570.3 °C, and the glass transition temperature was increased from 305.7 °C to 339.1 °C with increasing the GN content.

Here, a rapid and efficient strategy was introduced to prepare polyimide/graphene nanosheet (PI/GN) composite fibers by microwave-assisted imidization.     

Synergistic effects of CNTs/SiO2 composite fillers on mechanical properties of cement composites

This paper investigated the hybridization use of carbon nanotubes (CNTs) with nano-SiO₂ in cement composites. The (CNTs)/SiO₂ composite fillers were designed and prepared by electrostatic self-assembly technology to reinforce cement composites. The mechanical properties, microstructure and hydration characteristics of cement composites incorporating CNTs/SiO₂ fillers were systematically researched. The morphology and optical microscopy results show that the CNTs inside CNTs/SiO₂ fillers tended to unwind due to the mechanical separation and steric hindrance of nano-SiO₂ particles with certain size, and its agglomeration degree in the suspension greatly alleviated over time. With the appropriate incorporation of CNTs/SiO₂ fillers (containing 0.10 wt% CNTs and 0.50 wt% nano-SiO₂), the flexural strength, compressive strength and flexural toughness of the cement mortar matrix were sharply increased by 33.5%, 36.5% and 56.0% after curing for 28 days compared to the plain sample, respectively. Microscopic observations show that appropriate nano-additives can densify and refine the hydrated microstructure, and the crack-bridging, debonding and pull-out behaviors of CNTs were all observed. Hydration analysis quantitatively reveals that CNTs/SiO₂ fillers significantly accelerated the cement hydration process by virtue of the nano-nucleating action. The reinforcing mechanisms of CNTs/SiO₂ fillers can be attributed to the proposed synergistic effects of CNTs/SiO₂ fillers, which mainly include the better dispersion stability of CNTs, the nucleating effect of nano-additives and the pozzolanic reaction by nano-SiO₂, thus positively leading to increased mechanical properties.

CNTs/SiO₂ composite fillers are prepared by assembling CNTs with nano-SiO₂ paticles. The synergistic reinforcing effects of the prepared CNTs/SiO₂ fillers on cement composites were researched.     

Expanded graphene oxide fibers with high strength and increased elongation

We report the role of chemically expanded graphite in the fabrication of high-performance graphene oxide fibers by wet spinning. X-ray diffraction peak showed that the interplanar distance of the expanded graphene oxide (EGO) fiber was more than that of graphene oxide (GO) fiber due to the expanded graphite. X-ray photon spectroscopy analysis revealed that EGO was more oxidized than GO. The hydrogen bonding network and secondary intermolecular interaction made the EGO aqueous solution more stable and crystalline, and it was able to be stretched in the coagulation bath. Morphological analysis showed the excellent alignment and compactness of EGO sheets in the fibers. The increased interplanar distance between the EGO sheets favored the edge-to-edge interaction more than the basal plane interaction within the fiber, thus resulting in high mechanical strength (492 MPa) and increased elongation (6.1%).

The increased interplanar distance between the EGO sheets favored the edge-to-edge than basal plane interaction within the fiber, resulting in high mechanical strength (492 MPa) and increased elongation (6.1%).     

A study of bioactive glass–ceramic's mechanical properties,apatite formation,and medical applications

Apparently, bioactive glass–ceramics are made by doing a number of steps, such as creating a microstructure from dispersed crystals within the residual glass, which provides high bending strength, and apatite crystallizes on surfaces of glass–ceramics when calcium ions are present in the blood. Apatite crystals grow on the glass and ceramic surfaces due to the hydrated silica. These materials are biocompatible with living bone in a matter of weeks, don''t weaken mechanically or histologically, and exhibit good osteointegration as well as mechanical properties that are therapeutically relevant, such as fracture toughness and flexural strength. As part of this study, we examined mechanical properties, process mechanisms involved in apatite formation, and potential applications for bioactive glass–ceramic in orthopedic surgery, including load-bearing devices.

Bioactive glass–ceramics are made by several steps, such as creating a microstructure from dispersed crystals within the residual glass, which provides high bending strength, and apatite crystallizes on surfaces of glass–ceramics with calcium ions.     

Preparation and properties of CA/ATP-g-CDs gel fibers for simultaneous detection and adsorption of methylene blue

To detect and adsorb methylene blue (MB) from wastewater simultaneously, a solid fluorescent and absorbent material was designed by immobilizing attapulgite (ATP) on calcium alginate (CA) and reacting with carbon dots (CDs) which were modified by the activation of γ-(2,3-epoxypropoxy) propyltrimethoxysilane (KH-560), then the CA/ATP-g-CDs gel fibers were prepared. The problem of CDs easily falling out of materials was solved. The structures of the gel fibers were characterized by field emission scanning electron microscopy (FE-SEM), specific surface area (BET) and X-ray photoelectron spectroscopy (XPS). The thermal properties were analyzed by thermogravimetry (TG). The adsorption capacity was measured and the effect of initial pH was investigated. The results showed that ATP was successfully reacted with CA and the adsorption capacity was enhanced with the increase of the pH value. CA/ATP-g-CDs gel fibers were favorable materials to detect and adsorb MB simultaneously, and MB could be adsorbed by gel fibers and also the fluorescence of CA/ATP-g-CDs was weakened. At low concentrations of MB (1 μg L⁻¹), the removal efficiency could even be as high as 100%.

To detect and adsorb methylene blue (MB) from wastewater simultaneously, a solid fluorescent and absorbent material was designed by immobilizing attapulgite (ATP) on calcium alginate (CA) and reacting with carbon dots (CDs), then the CA/ATP-g-CDs gel fibers were prepared.     

A nano-micro dual-scale particulate-reinforced copper matrix composite with high strength,high electrical conductivity and superior wear resistance

Due to the contradiction between mechanical properties and electrical conductivity, it is not easy to fabricate materials with both high strength and good wear resistance with favourable electrical conductivity for the application of electrical materials. In addition, strength and wear resistance do not always present a uniform growth trend at the same time. Herein, a novel copper matrix composite reinforced by in situ synthesized ZrB₂ microparticles and nano Cu₅Zr precipitates is successfully prepared by a casting method and sequential heat treatments. The Cu/dual-scale particulate composite possesses a desired trade-off of strength, electrical conductivity and wear resistance. ZrB₂ microparticles form from Zr and B elements in copper melts, and nanoscale Cu₅Zr precipitates form in the matrix after solid solution and aging treatments. The ZrB₂ microparticles, nano Cu₅Zr precipitates, and well-bonded interfaces contribute to a high tensile strength of 591 MPa and superior wear resistance, with a relative electrical conductivity of 83.7% International Annealed Copper Standard.

A nano Cu₅Zr and micro ZrB₂ dual-scale particulate-reinforced copper matrix composite is prepared by in situ synthesis and heat treatment, which has high strength, high electrical conductivity and superior wear resistance.     

The thermo-optic relevance of Ho3+ in fluoride microcrystals embedded in electrospun fibers

Na(Y_1−x−yHo_xYb_y)F₄/PAN (NYF-HY/PAN) composite fibers were synthesized using an electrospinning method, and the sub-micron crystals embedded in the fibers had complete hexagonal crystal structures. Under 977 nm laser excitation, strong green and red up-conversion (UC) emission that originated from flexible fibers were due to the radiative transitions (⁵F₄, ⁵S₂) → ⁵I₈ and ⁵F₅ → ⁵I₈ of Ho³⁺, respectively. The effective green fluorescence emission (539 and 548 nm) can be applied to micro-domain non-contact temperature measurements, realizing rapid and dynamic temperature acquisition in a complex environment without destroying the temperature field. In the temperature range of 313–393 K, the absolute and relative sensitivity of the fibers are 0.00373 K⁻¹ and 0.723% K⁻¹, respectively, which indicates that the NYF-HY/PAN composite fibers have good thermal sensitivity. Composite fibers in which crystallites are embedded have superior properties, with great stability, high sensitivity, and excellent flexibility, providing a reliable reference for developing temperature-sensing materials for the biomedical field.

The morphology of electrospun fibers embedded with microcrystals and the relationship between sensitivity and temperature based on green up-conversion emission are studied.     

Aligned carbon nanotube fibers for fiber-shaped solar cells,supercapacitors and batteries

Aligned carbon nanotube (CNT) fibers have been considered as one of the ideal candidate electrodes for fiber-shaped energy harvesting and storage devices, due to their merits of flexibility, lightweight, desirable mechanical property, outstanding electrical conductivity as well as high specific surface area. Herein, the recent advancements on the aligned CNT fibers for energy harvesting and storage devices are reviewed. The synthesis, structure, and properties of aligned carbon nanotube fibers are briefly summarized. Then, their applications in fiber-shaped energy harvesting and storage devices (i.e., solar cells, supercapacitors, and batteries) are demonstrated. The remaining challenges are finally discussed to highlight the future research direction in the development of aligned CNT fibers for fiber-shaped energy devices.

Aligned CNT fibers emerge as the promising electrodes for fiber energy harvesting/storage devices due to their lightweight, high specific surface areas, outstanding mechanical and electrical property.     

Adsorption of tetracycline antibiotics from an aqueous solution onto graphene oxide/calcium alginate composite fibers

In this study, we report the preparation of a novel environmentally friendly and highly efficient adsorbent, graphene oxide/calcium alginate (GO/CA) composite fibers, via a freeze-drying method using calcium chloride as a cross-linking reagent between graphene oxide and sodium alginate. The maximum tetracycline adsorption capacity of the GO/CA composite fibers predicted by the Langmuir model reached 131.6 mg g⁻¹. The adsorption properties of tetracycline onto the fibers were investigated through several parameters including the solution pH, the adsorbent dose, the initial concentration of tetracycline, and the agitation time. The Langmuir and Freundlich adsorption isotherms were used to investigate the adsorption equilibrium. The kinetics of the adsorption process was predicted using the pseudo-first-order and pseudo-second-order kinetic equations. Furthermore, the mechanism of adsorption was investigated, and it was found that the hydrogen bonding and π–π interaction should serve as predominant contributions to the significantly enhanced adsorption capability.

In this study, we report the preparation of a novel environmentally friendly and highly efficient adsorbent, graphene oxide/calcium alginate (GO/CA) composite fibers, via a freeze-drying method using calcium chloride as a cross-linking reagent between graphene oxide and sodium alginate.     

Effects of boron nitride nanotube content on waterborne polyurethane–acrylate composite coating materials

Waterborne polyurethane–acrylate (WPUA) is a promising eco-friendly material for adhesives and coatings such as paints and inks on substrates including fibers, leather, paper, rubber, and wood. Recently, WPUA and its composites have been studied to overcome severe problems such as poor water resistance, mechanical properties, chemical resistance, and thermal stability. In this study, composite films consisting of WPUA and rod-type boron nitride nanotubes (BNNTs), which have excellent intrinsic properties including high mechanical strength and chemical stability, were investigated. Specifically, BNNT/WPUA composite films were synthesized by mixing aqueous solutions of BNNT and WPUA via facile mechanical agitation without any organic solvents or additives, and the optimal content of BNNTs was determined. For the 2.5 wt% BNNT/WPUA composite, the BNNTs were found to be well distributed in the WPUA matrix and this material showed the overall best performance in terms of water resistance, thermal conductivity, and corrosion resistance. Owing to these advantageous properties and their environmentally friendly nature, BNNT/WPUA composite coating materials are expected to be applicable in a wide variety of industries.

Composite coating materials consisting of waterborne polyurethane–acrylate (WPUA) and boron nitride nanotubes (BNNTs) showed enhanced mechanical properties, thermal properties and chemical resistance.     

Crack resistance of a noble green hydrophobic antimicrobial sealing coating film against environmental corrosion applied on the steel–cement interface for power insulators

Due to their great load-bearing capabilities, steel–cement interface structures are commonly employed in construction projects, and power utilities including electric insulators. The service life of the steel–cement interface is always decreasing owing to fracture propagation in the cement helped by steel corrosion. In this paper, a noble crack-resistant solution for steel–cement interfaces utilized in hostile outdoor environments is proposed. A Ce-rich, homogeneous, and thick hydrophobic sealing coating (HSC) is developed on the steel–cement interface after 60 minutes of immersion in a 60 000 ppm CeCl₃·7H₂O sealing coating solution. The specimens treated with optimized HSC film demonstrate fissure filling, lowest corrosion current (I_corr) 2.3 × 10⁻⁷ A cm⁻², maximum hardness (109 Hv), oxide-jacking resistance (40 years), hydrophobic characteristics, carbonation resistance, and bacterial corrosion resistance, resulting in a crack-free steel–cement interface. This work will pave the way for a new branch of environmentally acceptable coatings for the construction and power industries.

Due to their great load-bearing capabilities, steel–cement interface structures are commonly employed in construction projects, and power utilities including electric insulators.     

Investigating the reinforcing mechanism and optimized dosage of pristine graphene for enhancing mechanical strengths of cementitious composites

The proposed reinforcing mechanism and optimized dosage of pristine graphene (PRG) for enhancing mechanical, physicochemical and microstructural properties of cementitious mortar composites are presented. Five concentrations of PRG and two particle sizes are explored in this study. The results confirmed that the strength of the mortars depends on the dosage of PRG. The PRG sizes have a significant influence on the enhancement rate of mechanical strengths of the mortars, whereas they do not have a significant influence on the optimized PRG dosage for mechanical strengths. The PRG dosage of 0.07% is identified as the optimized content of PRG for enhancing mechanical strengths. The reinforcing mechanism of PRG for cement-based composites is mostly attributed to adhesion friction forces between PRG sheets and cementitious gels, which highly depends on the surface area of PRG sheets. The larger surface area of PRG sheets has a larger friction area associated with cementitious gels suggested to be one of favorable parameters for enhancing mechanical strengths with graphene additives.

The proposed reinforcing mechanism and optimized dosage of pristine graphene (PRG) for enhancing mechanical, physicochemical and microstructural properties of cementitious mortar composites are presented.