Chemical functionalization of polyamide 6.6 fabrics

Polyamide 6.6 (PA 6.6) fibers, produced from adipic acid and hexamethylenediamine, are among the most consumed synthetic textile fibers used for garments. Fibers are hydrophobic, which makes dyeing difficult and affects wearing comfort. In the present work, chemical treatments of PA 6.6 fibers were carried out and compared with respect to their effect on fiber properties and obtained surface modifications. Scoured knitted PA 6.6 fabrics (opaque) were treated with hydrochloric acid (0–3 M) and sodium hydroxide (3 M) for up to 3 h at 60 °C. The fibers were characterized with respect to bulk and surface modifications such as amino and carboxyl end groups, superficial dyeing below the T_G of the fiber, surface structure with SEM and AFM analysis. Furthermore a new analytic procedure for the determination of surface amino groups was tested. Both chemical treatments resulted in a significant increase in the amount of amino groups on the fiber, but especially the treatment with HCl 3 M caused a more drastic surface modification of the fibers, however, not only restricted to the fiber surface. AFM and SEM analysis have shown a significant change in surface roughness on the nanoscale, which in addition to the creation of surface functional groups increases the fiber’s hydrophilicity and reactivity.     

Effect of Au in V2O5/SiO2 and MoO3/SiO2 catalysts on physicochemical and catalytic properties in oxidation of C3 hydrocarbons and of CO

Silica supported vanadia and molybdena catalysts with, and without Au, were prepared, characterized with XRD, TEM, XPS, H₂-TPR and probe reaction of isopropanol decomposition, and tested in the oxidation of propene, propane and CO. The presence of Au: (a) does not affect markedly structural and textural properties, such as specific surface area, size of V₂O₅ or MoO₃ crystallites, or the electronic state of V and Mo ions, (b) increases the reducibility of vanadia and molybdena phase, (c) enhances the dehydrogenation properties in isopropanol decomposition, and (d) modifies catalytic activity in oxidation reactions. The Au particles increase the total activity in CO oxidation. For propane oxidation at high temperatures the increase in total activity is observed, with the decrease in the selectivity to oxidative dehydrogenation product (propene) and increase in the selectivity to CO₂. The catalytic performance in propene oxidation at 200–300 °C depends on the Au presence and the composition of the reaction mixture. The gold-containing catalysts favour allylic oxidation of propene to acrolein and oxyhydration to acetone, and suppress the C₂ products (ethanal, acetic acid) of partial degradation of a propene molecule. In the presence of hydrogen in the reaction mixture, higher selectivities of acetone (product of oxyhydration) were observed for all the catalysts.     

The production of polycarbosilane-derived porous carbon fibers

When a C-rich polycarbosilane (PCS) fiber is pyrolyzed in the presence of KOH, a porous carbon fiber was obtained after acid washing. During the process, silicon was almost completely eliminated and a large microporosity was formed. The porous carbon fibers have a surface area of 1100 m²/g and an average pore size of 2.80 nm. These materials are called “organic-carbide-derived carbons”.     

Preparation of carbon fibers from linear low density polyethylene

Carbon fibers were produced from linear low density polyethylene (LLDPE) instead of commonly used precursors, such as viscose rayon, mesophase pitch and polyacrylonitrile (PAN). Cross-linked fibers were produced at various temperatures, times and stress conditions during a sulfuric acid treatment using LLDPE fibers obtained from dry-wet spinning. The effects of cross-linking were analyzed using a range of characterization techniques, such as differential scanning calorimetry, color change, fourier transform infrared spectroscopy, elemental analysis, density, scanning electron microscopy, and single filament mechanical properties. The carbonization process of cross-linked fibers was carried out at 950 °C for 5 min in a nitrogen atmosphere. The carbon fibers with the best mechanical properties were obtained from the cross-linked fiber with the highest tensile modulus. In particular, the carbon fibers with the best mechanical properties (tensile strength and tensile modulus of 1.65 GPa and 110 GPa, respectively), similar to commercial-grade carbon fiber, were obtained from the cross-linked fiber that had undergone a carbonization process with a stress of 0.25 MPa after an acid treatment for 150 min at 140 °C and a stress of 0.26 MPa.     

Tensile behaviors of ECR-glass and high strength glass fibers after NaOH treatment

ECR-glass and high strength glass (S-glass) fibers were treated in 2 mol/l NaOH solution up to 5 h. The strength maintenance ratio and mass loss ratio of the fibers after treatment were investigated. The surface morphologies were characterized using scanning electron microscopy, and changes of chemical composition were analyzed by energy dispersive X-ray spectroscopy and Fourier transform infrared spectrometry. The alkali resistance and tensile strength of the S-glass fibers are higher compared to those of the ECR-glass fibers as they received less alkaline attack because of the more compact SiO₂ network and the formation of a protective layer on the S-glass fiber surface. The S-glass fibers have a higher mass loss due to the smaller diameter and thinner corrosion layer.     

Surface defect healing effect of silica coatings on silicon nitride fibers

In this study, silica coatings with different thickness were prepared on silicon nitride fibers by a continuous dip-coating method. The effects of the coatings on the mechanical properties of the silicon nitride fibers were investigated. The SiO₂ coatings with uniform thickness were prepared from a sol solution with a concentration of 0.75 wt% and then heat-treated at 400 °C, and the strength of the fibers was improved by the treated coating. The tensile strength of a coated fiber was approximately 26% higher than that of an uncoated fiber because the thin coating healed the surface defects. Our study also confirmed that the size of sol particles must match that of the flaws on the fiber surface before these flaws could be effectively repaired. Finally, a probable mechanism will be proposed here to explain this effect. The present results demonstrate that the strength of silicon nitride fibers can be enhanced by coating them through the sol–gel process, and the findings are expected to provide guidelines for repairing strength-limiting flaws in other fibers.     

The structure and properties of ribbon-shaped carbon fibers with high orientation

Using a naphthalene-derived mesophase pitch as a starting material, highly oriented ribbon-shaped carbon fibers with a smooth and flat surface were prepared by melt-spinning, oxidative stabilization, carbonization, and graphitization. The preferred orientation, morphology, and microstructure, as well as physical properties, of the ribbon-shaped carbon fibers were characterized. The results show that, the ribbon-shaped fibers possessed uniform shrinkage upon heat treatment, thereby avoiding shrinkage cracking commonly observed in round-shaped fibers. As heat treatment progressed, the ribbon-shaped graphite fibers displayed larger crystallite sizes and higher orientation of graphene layers along the main surface of the ribbon-shaped fiber in comparison with corresponding round-shaped fibers. The stability of the ribbon-shaped graphite fibers towards thermal oxidation was significantly higher than that of K-1100 graphite fibers. The longitudinal thermal conductivity of the ribbon fibers increased, and electrical resistivity decreased, with increasing the heat treatment temperatures. The longitudinal electrical resistivity and the calculated thermal conductivity of the ribbon-shaped fibers graphitized at 3000 °C are about 1.1 μΩ m and above 1100 W/m K at room temperature, respectively. The tensile strength and Young’s modulus of these fibers approach 2.53 and 842 GPa, respectively.     

ZrB2-based composites toughened by as-received and heat-treated short carbon fibers

In order to improve the fracture toughness of ZrB₂ ceramics, as-received and heat treated short carbon fiber reinforced ZrB₂-based composites were fabricated by hot pressing. The toughening effects of the fibers were studied by investigating the relative density, phase composition, microstructure and mechanical properties of the composites. It was found that the densification behavior, microstructure and mechanical properties of the composites were influenced by the fibers’ surface condition. The heat treated fiber was more appropriate to toughen the ZrB₂-based composites, due to the high graphitization degree, low surface activity and weak interfacial bonding. As a result, the fracture toughness of the composites with heat-treated fiber is 7.62 ± 0.12 MPa m^1/2, which increased by 10% as compared to the composites with as-received fiber (6.89 ± 0.16 MPa m^1/2).     

Ordered mesoporous Ga2O3 and Ga2O3–Al2O3 prepared by nanocasting as effective catalysts for propane dehydrogenation in the presence of CO2

Thermally stable mesoporous gallium and gallium–aluminum (atomic ratio of Ga/Al = 4/1 and 1/4) oxides with controlled textural and structural properties were prepared by means of the nanocasting approach. All materials have uniform micron-sized particles, with a quite narrow pore-size distribution centered in the range of 6.2–6.5 nm and specific surface areas as high as 231–322 m²·g^− 1. Pure mesoporous gallium and gallium–aluminum (Ga/Al = 4:1) oxides exhibit a promising catalytic performance in the dehydrogenation of propane to propene in the presence of CO₂ (DHP-CO₂). Over the most active materials, during 4 h on stream at 823 K, propene was produced with the yield of 10–18% and high selectivity of 91–95%. Moreover, pure mesoporous gallium oxide exerted a higher resistance on deactivation during the DHP-CO₂ process in comparison with gallium oxide prepared without a hard template.     

Carbon fibers from dry-spinning of acetylated softwood kraft lignin

An acetylated softwood kraft lignin was dry-spun into precursor fibers and successfully processed into carbon fibers with a tensile strength exceeding most values reported in prior studies on lignin-based carbon fibers. Limited acetylation of lignin hydroxyl groups enabled dry-spinning of the precursor using acetone (solvent) followed by thermo-oxidative stabilization. Resulting carbon fibers (∼7 μm diameter) displayed a tensile modulus, strength, and strain-to-failure values of 52 ± 2 GPa, 1.04 ± 0.10 GPa, and 2.0 ± 0.2%, respectively. Because of solvent diffusion during dry-spinning, fibers displayed a crenulated surface that can provide a larger specific interfacial area for enhanced fiber/matrix bonding in composite applications.     

Urease-carrying electrospun polyacrylonitrile mat for urea hydrolysis

Electrospinning was used to fabricate beadless microfibrous polyacrylonitrile (ePAN) mats with an average fiber diameter of 1448 ± 380 nm from a 10 wt.% PAN in dimethylformamide (DMF) dope solution at applied voltage of 18 kV and 20 cm fiber collection distance. Urease (EC 3.5.1.5) was then covalently immobilized on dispersed microfibrous ePAN mats following the chemical treatment of fibers with ethylenediamine (EDA) and glutaraldehyde (GA). The optimal concentration of GA for immobilization was 5%. The amount of loaded urease reached 157 μg/mg mat, exhibiting 54% of the free urease activity. The surface chemistry of as-spun and chemically treated fibers was examined with Fourier transform infrared (FTIR) spectroscopy. Field emission scanning electron microscopy (FESEM) was used to study the morphology and diameter of the pristine, chemically treated, and urease-immobilized microfibrous mats. Immobilized urease showed increased temperature for maximum activity (from 37 to 50 °C for free and immobilized urease, respectively) and improved storage stability (20 days). The immobilized urease was also less sensitive to the changes in pH, especially in acid conditions. In addition, nearly 70% of initial activity of the immobilized urease was retained after 15 cycles of reuse, which proved the applicability of the electrospun fibers as successful enzyme carriers.     

Highly efficient oxidation of diphenylmethane to benzophenone employing a novel ruthenium catalyst with tert-butylhydroperoxide under mild conditions

The ruthenium complex Ru(bpbp)(pydic) (bpbp = 2,6-bis(1-phenylbenzimidazol-2-yl), pydic = pyridine-2,6-dicarboxy acid) has been synthesized and tested in the selective oxidation of diphenylmethane to benzophenone utilizing tert-butylhydroperoxide as the terminal oxidant. The influence of various reaction parameters such as temperature, catalyst amount and nature of solvent on the activity and selectivity was evaluated. Diphenylmethane was converted with 94% conversion and 100% selectivity to benzophenone under the optimized reaction conditions, in which the turnover number (TON) of catalyst reached 94,000. Moreover, a plausible reaction mechanism through redox ruthenium species was proposed.     

Effect of gamma-irradiation on the mechanical properties of polyacrylonitrile-based carbon fiber

The influence of gamma-irradiation on the structure and mechanical properties of polyacrylonitrile-based carbon fibers was studied. It was observed that the Young’s modulus of the fibers irradiated increased with irradiation dose, increasing to 267 GPa at 300 kGy, a 16.1% improvement compared to that of as-received carbon fiber. However, the tensile strength increased to 5.4 GPa at 30 kGy, i.e., a 17.4% increase, and then dropped to 4.65 GPa at 300 kGy, which is almost the same as for the untreated fiber. Uniform stress model analysis and Raman spectroscopy show that the degree of covalent cross-linking between the graphene planes increased to a maximum at 30 kGy and then remained almost constant with further irradiation. The SEM images show that the degree of surface roughness increased with the increasing irradiation dose. It is believed that when the dose is less than 30 kGy, the increased cross-linking is the dominant effect, and thus improves the tensile strength. On the other hand, further irradiation generates surface flaws, which neutralizes the increase and results in a decrease of tensile strength.     

The effective interfacial shear strength of carbon nanotube fibers in an epoxy matrix characterized by a microdroplet test

The tensile properties of continuous carbon nanotube (CNT) fibers spun from a CNT carpet consisting of mainly double- and triple-walled tubes, and their interfacial properties in an epoxy matrix, are investigated by single fiber tensile tests and microdroplet tests, respectively. The average CNT fiber strength, modulus and strain to failure are 1.2 ± 0.3 GPa, 43.3 ± 7.4 GPa and 2.7 ± 0.5%, respectively. A detailed study of strength distribution of CNT fiber has been carried out. Statistical analysis shows that the CNT fiber strength is less scattered than those of MWCNTs as well as commercial carbon and glass fibers without surface treatment. The effective CNT fiber/epoxy interfacial shear strength is 14.4 MPa. Unlike traditional fiber-reinforced composites, the interfacial shear sliding occurs along the interface between regions with and without resin infiltration in the CNT fiber. Guidelines for microdroplet experiments are established through probability analysis of variables basic to specimen design.     

Synthesis,characterization and enhanced acetone sensing performance of Pd loaded Sm doped SnO2 nanoparticles

In the present communication, we have presented a high performance acetone sensor based on Pd loaded Sm doped SnO₂ nanomaterial. The (0.5, 1, 2 and 3) wt% Pd loaded 6 mol% Sm doped SnO₂ nanoparticles were prepared using a co-precipitation method. The characterization of samples was done by using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FEG-SEM), Energy Dispersive Analysis by X-rays (EDAX), High Resolution-Transmission Electron Microscopy (HR-TEM) and Selective Area Electron Diffraction (SAED) techniques. The gas response studies such as sensitivity, selectivity and stability towards liquid petroleum gas, ammonia, ethanol and acetone were measured at 100 ppm concentrations. The results show that optimum Pd loading (2 wt%) results in smaller crystallite size (~3.1 nm), lower operating temperature (200 °C), higher gas response (94%),better selectivity, faster response (~3 s) and quicker recovery (~12 s) towards acetone.     

Shell–core structured carbon fibers via melt spinning of petroleum- and wood-processing waste blends

In the last decades, carbon fibers with light weight and high strength have experienced the largely increased uses in various industrial applications. However, their expected uses in the automotive industry and building are largely limited because of their high production cost. Herein, we have demonstrated an effective method of making low cost carbon fibers via the melt spinning of petroleum-processing residue (pyrolyzed fuel oil, PFO)/lignin blends. Careful selection of tetrahydrofuran as the solvent to dissolve both PFO and lignin was made to optimize the miscible blend. The melt spinnable blend with a softening point of 260–280 °C exhibited good spinning ability at 280 °C. The plasticizing function of PFO allowed the highly cross linked lignin-based pitch to have high fluidity in the melt spinning process. Based on detailed TEM observations, the thermally treated fiber prepared at 2800 °C exhibited a shell–core structure, consisting of a highly crystalline surface from PFO and an amorphous disordered core from lignin. Such a crystalline surface structure gave rise to a high modulus value (up to 100 GPa) to the prepared carbon fibers.     

Electromagnetic characteristics and microstructure stability of Nextel 610 fiber after heat treatment

The thermal and microstructure stability of Nextel 610 fibers has great influence on high-temperature application of Nextel 610 fiber-reinforced ceramic matrix composites. In this work, Nextel 610 fibers were heat treated at 500–700 °C in vacuum and 800–1100 °C in Ar atmosphere, respectively. The sizing agent on Nextel 610 fiber surface could be decomposed into pyrolytic carbon, SiC and gaseous little molecules at lower temperatures, otherwise it was decomposed mainly in the form of gaseous little molecules at higher temperatures, so that the complex permittivity firstly increased and then decreased with the increasing of temperatures. The results showed that the annealed Nextel 610 fiber (T>900 °C) could be regarded as electromagnetic wave transparent fibers, while the tensile strength had declined by half when the temperature increased to 1100 °C. Therefore, Nextel 610 fibers after being annealed at higher temperatures could be further used as reinforcement to prepare high temperature ceramic matrix composites for electromagnetic wave absorption and transparent applications.     

Highly selective low-temperature hydrogenation of furfuryl alcohol to tetrahydrofurfuryl alcohol catalysed by hectorite-supported ruthenium nanoparticles

Metallic ruthenium nanoparticles intercalated in hectorite (particle size ~ 4 nm) were found to catalyse the hydrogenation of furfuryl acohol to give tetrahydrofurfuryl alcohol in methanolic solution under mild conditions. The best results were obtained at 40 °C under a hydrogen pressure of 20 bar (conversion 100%, selectivity > 99%). After a total turnover number of 1423, the hectorite supported ruthenium nanoparticles are deactivated but can be recycled and regenerated.     

Thermal behaviour of a series of poly[B-(methylamino)borazine] for the preparation of boron nitride fibers

The thermal behaviour of a series of poly[B-(methylamino)borazine] prepared at various temperatures ranging from 140 to 200 °C is studied in the present paper as potential BN fiber precursors. It was shown that the softening capability of poly[B-(methylamino)borazine] can be tailored by controlling the temperature at which polymers were prepared to achieve melt-spinning and produce high quality green fibers. Thus as-spun fibers could be next converted into boron nitride fibers using ammonia (25–1000 °C) and nitrogen (25–1800 °C) atmospheres. The quality of boron nitride fibers was shown to depend on the first part of the pyrolysis step (25 and 1000 °C; ammonia atmosphere) in which the great majority of the weight loss necessary for boron nitride production occurs. Ideal poly[B-(methylamino)borazine] as BN fiber precursors are those prepared between 170 and 180 °C. They display appropriate melt-spinnability and ceramic conversion capability.     

Influence of oxygen plasma treatment parameters on poly(vinylidene fluoride) electrospun fiber mats wettability

Electrospun poly(vinylidene fluoride) (PVDF) fiber mats find applications in an increasing number of areas, such as battery separators, filtration and detection membranes, due to their excellent properties. However, there are limitations due to the hydrophobic nature and low surface energy of PVDF. In this work, oxygen plasma treatment has been applied in order to modify the surface wettability of PVDF fiber mats and superhydrophilic PVDF electrospun membranes have been obtained. Further, plasma treatment does not significantly influences fiber average size (∼400 ± 200 nm), morphology, electroactive β-phase content (∼80–85%) or the degree of crystallinity (X_c of 42 ± 2%), allowing to maintain the excellent physical–chemical characteristics of PVDF. Plasma treatment mainly induces surface chemistry modifications, such as the introduction of oxygen and release of fluorine atoms that significantly changes polymer membrane wettability by a reduction of the contact angle of the polymer fibers and an overall decrease of the surface tension of the membranes.