Mechanical property optimization of wet-spun lignin/polyacrylonitrile carbon fiber precursor by response surface methodology

Lignin, nature’s abundant polymer with a remarkably high carbon content, is an ideal bio-renewable precursor for carbon fiber production. However, the poor mechanical property of lignin-derived fibers has hindered their industrial application as carbon fiber precursor. In this work, process engineering through the application of computational modeling was performed to optimize wet-spinning conditions for the production of lignin precursor fibers with enhanced mechanical properties. Continuous lignin-derived precursor fibers with the maximum possible lignin content were successfully produced in a blend with polyacrylonitrile, as a wet-spinning process facilitator. Response surface methodology was employed to systematically investigate the simultaneous influence of material and process variables on mechanical properties of the precursor fibers. This allowed generating a mathematical model that best predicted the tensile strength of the precursor fibers as a function of the processing variables. The optimal wet-spinning conditions were obtained by maximizing the tensile strength within the domain of the developed mathematical model.     

Carbon nanotubes and pleural damage: perspectives of nanosafety in the light of asbestos experience

Carbon nanotubes are molecular-scale one-dimensional manufactured materials which display several potential applications in engineering and materials science. Burgeoning evidence demonstrates that carbon nanotubes and asbestos share comparable physical properties. Therefore carbon nanotubes might display toxic effects and the extent of the toxicity is more specifically directed to lung and pleura. These effects are related to properties of carbon nanotubes, such as their structure, length, aspects ratio, surface area, degree of aggregation, extent of oxidation, bound functional group, method of manufacturing, concentration and dose. At the present there is no global agreement about the risk of carbon nanotubes on human health and in particular on their transformation capacity. Safety concerns regarding carbon nanotubes can be ameliorated. In this context, it is important to put the known hazards of carbon nanotubes into perspective. Here is presented an overview about toxicity issues in the application of carbon nanotubes to biological systems, taking into consideration the already known asbestos-induced mechanisms of biological damages.     

Processing and Characterisation of Hybrid Aramid Fabrics Reinforced with Cross-linked Electrospun PVB Composite Nanofibres

The aim of this study was to fabricate a new kind of hybrid fabric composites with the cross-linked electrospun poly(vinyl butyral) (PVB) composite nanofibres. The experiments were performed with the 10 wt.% PVB/ethanol solution for electrospinning where the modified silica nanoparticles (mSiO₂), the oxidised single-walled carbon nanotubes (o-SWCNT) and the o-SWCNT/mSiO₂ hybrid nanoparticles were added to the solution. The electrospun fibres were crosslinked with glutaraldehyde (GA) afterwards in order to reinforce the composite structure by bonding to the p-aramid fabrics. The chemical and thermo-mechanical properties of the hybrid fabric composites were evaluated. The greatest improvement in thermo-mechanical properties was achieved by the sample which contained the cross-linked PVB fibres with the o-SWCNT/mSiO₂ hybrid nanoparticles.     

Design of Chitosan-Grafted Carbon Nanotubes: Evaluation of How the –OH Functional Group Affects Cs+ Adsorption

In order to explore the effect of –OH functional groups in Cs⁺ adsorption, we herein used the low temperature plasma-induced grafting method to graft chitosan onto carbon nanotubes (denoted as CTS-g-CNTs), as raw-CNTs have few functional groups and chitosan has a large number of –OH functional groups. The synthesized CTS-g-CNT composites were characterized using different techniques. The effect of –OH functional groups in the Cs⁺ adsorption process was evaluated by comparison of the adsorption properties of raw-CNTs with and without grafting chitosan. The variation of environmental conditions such as pH and contact time was investigated. A comparison of contaminated seawater and simulated groundwater was also evaluated. The results indicated that: (1) the adsorption of Cs⁺ ions was strongly dependent on pH and the competitive cations; (2) for CNT-based material, the –OH functional groups have a positive effect on Cs⁺ removal; (3) simulated contaminated groundwater can be used to model contaminated seawater to evaluate the adsorption property of CNTs-based material. These results showed direct observational evidence on the effect of –OH functional groups for Cs⁺ adsorption. Our findings are important in providing future directions to design and to choose effective material to remedy the removal of radioactive cesium from contaminated groundwater and seawater, crucial for public health and the human social environment.     

Perspective on Carbon Fiber Woven Fabric Electrodes for Structural Batteries

The purpose of this work is to explore effective means of fabricating nanostructure-deposited continuous woven carbon fabric and to investigate the feasibility of using this material in structural battery applications. In order to prove this concept, two types of nanostructured carbon fabric electrodes – one with vertically-aligned carbon nanotubes (VACNTs) formed directly on carbon fabric utilizing iron (Fe) nanoparticles and Al buffer layers, the other with the same VACNTs on a chemical vapor-deposited graphene surface utilizing Ni seed layers on the carbon fabric – were fabricated to investigate material electrical performances as battery electrodes. The reversible specific capacity of 250 mAh/g on average at C/20 with good cyclic retention in these three all-carbon electrodes, including pristine carbon fabric, suggests a promising structural battery electrode for low-current battery applications. Even though the capacity of VACNT-grafted carbon fabrics was limited due to poor wetting of the VACNT forest with electrolyte caused by the lack of functionalization of the VACNT, their excellent cyclic performances and galvanostatic curves support the idea that the carbon nanotube and carbon fabric combination can be utilized in battery applications. However, pristine-carbon fabric is still a good candidate for battery applications because of its simplicity of mass production.     

Preparation and properties of alkaline functionalized carbon nanotubes reinforced polyurethane composites

Composites consisting of polyurethane (PU)/carbon nanotubes (CNTs) have been successfully prepared by solution mixing method. CNTs were modified through mechano-chemical reaction to increase the compatibility with PU via hydrogen bondings. SEM microphotographs proved that modified CNTs (M-CNTs) became shorter and FTIR spectra showed that hydroxyl groups had been introduced to the surface of M-CNTs. SEM images of PU/M-CNTs composites also proved that M-CNTs were effectively dispersed in PU matrix. Mechanical property tests showed that addition of M-CNTs could significantly improve the tensile properties of PU/M-CNTs composite (breaking strength enhancement ratio for composite with 5.0 wt% M-CNTs was 103.81 %). The thermal stability of composites with M-CNTs was also improved. The initial degradation temperature enhancement was 19.9 oC for the composite with 0.5 wt% M-CNTs. Electrical property tests showed that the electrical properties were improved by adding M-CNTs. The volume conductivities increased 3 and 5 orders of magnitude for the composites with 5.0 wt% and 10 wt% M-CNTs, respectively. The addition of M-CNTs had little effect on the elastic properties of the composites.     

Morphology of highly porous conducting polyaniline nanofibres synthesized in a multi-phase system

Polyaniline nanofibres are typically synthesized in a two-phase system with aniline placed in one liquid phase and the initiator in the other. The authors modified this method by introducing the monomer as a salt, thus creating a third, solid phase. This salt is in the organic phase as acetonitrile. Salts of aniline+DBSA and aniline+CSA were examined. As both these salts have limited solubility in acetonitrile, they do not dissolve during polymerization. To further reduce their solubility, acid was also added to both liquid phases. DBSA and CSA were used in the organic phase while in the aqueous phase, hydrochloric acid, sulfuric acid, DBSA and CSA were used along with the initiator (APS). Numerous polymerizations were carried out to examine various phase compositions. SEM, FTIR and UV-Vis observations revealed interesting properties of the polyaniline obtained in this way. Its morphology and spectroscopic properties strongly depend on the combination of the components used in each phase. Amorphous polyaniline was obtained as were well-developed spatial forms such as blades, spheres or nanofibres.     

重庆马铃薯产业经济调研情况分析与建议

在调研重庆马铃薯概况、加工情况、批发市场、产地价及均价、销售量、农户信息(包括总耕地面积、马铃薯栽培面积、生产类型、栽培品种、家庭年消费量、技术需求)等指标的基础上,对种植马铃薯的收益、物质与服务费用、人工成本等情况进行了分析,认为重庆马铃薯产业呈现面积单产齐增加的局面,但加工业发展水平滞后,商品薯产地价和批发价较低,农户种植马铃薯纯收益较低,应从5个方面进行建设,促进重庆马铃薯产业的健康发展。     

Low Molecular Weight Polypyrmidine for Release and Size Controlled Process of Single-Walled Carbon Nanotubes

A process for controlling the size of Single-walled carbon nanotubes (SWCNTs) sorting was achieved by combining various centrifugation speeds with polypyrimidine’s properties of dispersion and release SWCNTs upon acid treatment. At first, the SWCNTs wrapped by polypyrimidine were sperated into different size by centrifugating at various speeds. Then, these size-selected hybrids were treated with H₂SO₄ (98 %) to release free SWCNTs from hybrids, meanwhile the copolymer was collected for reuse. The purity of the released size-controlled SWCNTs was found to be higher than the commercial SWCNTs. The simple synthetic procedure of the copolymer, the low cost of H₂SO₄ and low centrifugation speed allow the process of size-controlled SWCNTs sorting to more practical applications and industrial scaling up.     

Electrical properties of graphene/waterborne polyurethane composite films

Graphene is classified as a carbon-based material. Structurally, graphene is made up of carbon-based two-dimensional atomic crystals and a one atom thick planar sheet of sp²-bonded carbon atoms. This sort of arrangement in graphene makes it a unique material with exceptional mechanical, physicochemical, thermal, electrical, optical, and biomedical properties. Methods for graphene-based fabric production mainly use graphene-based materials such as graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO) coated on fabric or yarn. Waterborne polyurethane (WPU) is one of the most rapidly developing and active branches of polyurethane chemistry. More and more attention is being paid to graphene-coated fabrics owing to their low temperature flexibility, the presence of zero or very few VOCs (volatile organic compounds), water resistance, pH stability, superior solvent resistance, excellent weathering resistance, and desirable chemical and mechanical properties. It is used as a coating agent or adhesive for fibers, textiles, and leather. Also, graphene-containing materials have been used to enhance the properties of WPU. In this study, graphene/WPU composite solution and film was prepared to conduct basic research for developing electrical heating textiles which is not harmful to the human body, flexible and excellent in electrical properties. Graphene/WPU composite solutions were prepared with a graphene content of 0, 2, 4, 8, and 16 wt%, and graphene/WPU film was prepared with solution casting method. The graphene contents were analyzed for their surface morphology, electrical properties, and electrical heating properties.     

Gallium arsenide (GaAs) nanofibers by electrospinning technique as future energy server materials

Gallium arsenide (GaAs) does have superior electronic properties compared with silicon. For instant, it has a higher saturated electron velocity and higher electron mobility. Weak mechanical properties and high production cost are the main drawbacks of this interesting semiconductor. In this study, we are introducing production of GaAs nanofibers by electrospinning methodology as a very low cost and yielding distinct product technique. In general, nano-fibrous shape is strongly improving the physical properties due to the high surface area to volume ratio of this nanostructure. The mechanical and environmental properties of the GaAs compound have been modified since GaAs nanofibers have been produced as a core inside a poly(vinyl alcohol) (PVA) shell. GaAs/PVA nanofibers were prepared by electrospinning of gallium nitrate/PVA solution in presence of arsenic vapor. The whole process was carried out in a closed hood equipped with nitrogen environment. FT-IR, XPS, TGA and UV-Vis spectroscopy analyses were utilized to confirm formation of GaAs compound. Transmission electron microscope (TEM) analysis has revealed that the synthesized GaAs compound is crystalline and does have nano-fibrous shape as a core inside PVA nanofibers. To precisely recommend the prepared GaAs nanofiber mats to be utilized in different applications, we have measured the electric conductivity and the band gap energies of the prepared nanofiber mats. Overall, the obtained results affirmed that the proposed strategy successfully remedied the drawbacks of the reported GaAs structures and did not affect the main physical properties of this important semiconductor.     

糯小麦的开发和应用研究进展

旨在总结糯小麦的应用现状,分析制约糯小麦推广应用的关键问题,为糯小麦规模化推广应用提供参考。在糯小麦理化特性方面,重点简述糯小麦的淀粉构成及糊化特性;在糯小麦应用方面,主要对其在食品加工及其他工业生产领域的应用研究进行概述。其中,在食品改良方面,添加少量糯小麦可提升食品的口感和货架期,尤其在冷冻食品中具有独特优势;在酒精工业中,添加糯小麦可明显提升酒精转化率和白酒口感;此外,糯小麦可作为一种新材料,在新型食品开发、造纸、医药等众多工业生产领域有良好的应用潜力。糯小麦淀粉特性优异,在众多领域拥有广阔的应用前景,但目前有关糯小麦在食品加工中的应用价值研究尚未达成一致结果,且尚未见其大面积推广和成功用于商业应用的报道,这些均有待进一步研究。     

Effect of concentration and surface modification of single walled carbon nanotubes on mechanical properties of epoxy composites

Single walled carbon nanotubes (SWNTs) are considered as a highly potential reinforcement material for the epoxy composites. Dispersion of SWNTs in epoxy and poor interfacial strain transfer are two major challenges. Surface functionalization is one efficient way to change the dispersion and interfacial properties of SWNTs. In this study, five different modification methods of SWNTs were used, and the functional groups on the SWNTs were tested by X-ray photoelectron spectroscopy and Raman spectroscopy. The SWNTs/epoxy composite were prepared using dimethylformamide (DMF) as the solvent. SWNTs at two concentration levels of 0.05 wt% and 0.5 wt% and with five different surface modifications were filled in to epoxy resins. The dispersion of the nanotubes in epoxy resin was evaluated by light optical microscope (LOM), with high content of SWNTs more aggregates appear. The interfacial strain transfer was tested by Raman shift of the 2D band when applying a strain on the epoxy composite sample. With equal strain levels in the composite more strain was transferred from epoxy matrix to SWNTs with 0.05 wt% of SWNTs than the 0.5 wt% of SWNTs filled epoxy resin. Mechanical properties were influenced by the strain transfer efficiency and the curing degree of the samples.     

A novel multi-wall carbon nanotubes/poly(n-butylacrylate-co-butyl methacrylate) hybrid resin: synthesis and oil/organic solvents absorption

A novel multi-wall carbon nanotubes/poly(n-butylacrylate-co-butyl methacrylate) hybrid resin (MWCNTs- PBABMA), which was further applied to absorb oils and organic solvents, was synthesized by using a combination of surface modification and suspension polymerization. Firstly, the surfaces of MWCNTs-COOH were modified and functionalized by silane coupling agent (KH 570) to enhance the surface reactivity. Then, the MWCNTs-PBABMA hybrid resin was synthesized by suspension polymerization. The oil absorption properties of the hybrid resin are investigated by varying the amount of surface modified carbon nanotubes, and the results indicated that the oil absorption properties of prepared MWCNTs-PBABMA hybrid resin could be improved by the addition of MWCNTs. Besides, the absorption properties of the MWCNTs-PBABMA hybrid resin for oils and organic solvents are 2.01-37.87 g/g, partly depending on the density and viscosity of the absorbate. The MWCNTs-PBABMA hybrid resins could be reused for oils absorption, at least four times, with a slight decline in their absorption properties. These results indicate that hybrid resins may potentially serve as oils absorbents for treatment of oily wastewater.     

Optimum manufacturing conditions of activated carbon fiber absorbents. I. Effect of flame retardant reagent concentration

In this paper, viscose rayon-based knitted fabrics were utilized as the precursor to produce activated carbon fiber absorbents (ACFA). To obtain better pore characteristics and higher weight yield of ACFA, the effect of flame retardant reagent concentration was studied. Experimental results revealed that both BET surface area and micropore volume increased with increasing flame retardant reagent concentration. On the other hand, both weight yield and micropore volume ratio (V_mic/V_tot) decreased as the flame retardant reagent concentration increased. It was therefore concluded that controlling the flame retardant reagent concentration at 30% not only could obtain better absorption property of ACFA but also helped maintain its production efficiency.     

Control of Shear Thickening Onsets by Nanoparticles

With various applicability of shear thickening fluids (STFs), control of rheological properties of STFs has been a major interest to industry. While carbon nanotubues and graphene have often been employed as fillers of STFs, little has been examined for their individual and combined effects on shear thickening behavior. In this study, the onset of viscosity increase of STFs was examined for the addition of: 1D functionalized multi-walled carbon nanotubes (fMWCNTs); 2D reduced graphene oxides (rGO); 3D network of MWCNTs-rGO hybrids (H); and spherical iron oxides (Fe₃O₄). To overcome the poor dispersibility of carbon particles, carbon nanotubes were functionalized to attach carboxylic groups (fMWCNTs), and graphene oxides (GOs) were reduced using TiO₂ particles. Large hydrodynamic diameters of fMWCNT, rGO, and their hybrids of percolated network facilitated the interactions with silica particles in STF, decreasing the onset of shear thickening. Among the tested particles, STF with hybrids (H-STF) exhibited the lowest critical shear rate and the highest viscosity, due to the hybrid’s 3D network structure in which long and tortuous fMWCNTs bridged adjacent rGOs. The addition of Fe₃O₄ to HSTF shifted the shear thickening onset to a higher shear rate. The results demonstrate that the shear thickening onsets can be controlled by the selective additions of nanoparticles.     

Preparation of Chitosan Nanocompositeswith a Macroporous Structure by Unidirectional Freezing and Subsequent Freeze-Drying

Chitosan is the N-deacetylated derivative of chitin, a naturally abundant mucopolysaccharide that consists of 2-acetamido-2-deoxy-β-d-glucose through a β (1→4) linkage and is found in nature as the supporting material of crustaceans, insects, etc. Chitosan has been strongly recommended as a suitable functional material because of its excellent biocompatibility, biodegradability, non-toxicity, and adsorption properties. Boosting all these excellent properties to obtain unprecedented performances requires the core competences of materials chemists to design and develop novel processing strategies that ultimately allow tailoring the structure and/or the composition of the resulting chitosan-based materials. For instance, the preparation of macroporous materials is challenging in catalysis, biocatalysis and biomedicine, because the resulting materials will offer a desirable combination of high internal reactive surface area and straightforward molecular transport through broad “highways” leading to such a surface. Moreover, chitosan-based composites made of two or more distinct components will produce structural or functional properties not present in materials composed of one single component. Our group has been working lately on cryogenic processes based on the unidirectional freezing of water slurries and/or hydrogels, the subsequent freeze-drying of which produce macroporous materials with a well-patterned structure. We have applied this process to different gels and colloidal suspensions of inorganic, organic, and hybrid materials. In this review, we will describe the application of the process to chitosan solutions and gels typically containing a second component (e.g., metal and ceramic nanoparticles, or carbon nanotubes) for the formation of chitosan nanocomposites with a macroporous structure. We will also discuss the role played by this tailored composition and structure in the ultimate performance of these materials.     

Crystallization behaviour of PP and carbon nanofibre blends

Crystallization behaviour of blends of different MFI isotactic polypropylenes (PP), and blends of PP with carbon nanofibre have been investigated by DSC and polarizing optical microscope. Both higher MFI PP component and the carbon nanofibre in the blend influence the nucleation activity of the melt during non-isothermal crystallization. In presence of carbon nanofibre, the sherulitic growth rate is highly disturbed. The calculation of nucleation activity indicates that carbon nanofibres act as active substrate for heterogeneous nucleation.     

Core-sheath polyurethane-carbon nanotube nanofibers prepared by electrospinning

The core-sheath nanofibers consisting of polyurethane (PU) core and PU composites sheath with multi-walled carbon nanotubes (MWNTs) were prepared by electrospinning. At low MWNT concentration, MWNTs appeared highly aligned along the fiber axis with some curving in nanotubes, whereas in case of high concentration, some aggregation of MWNTs appeared due to difficulty in full dispersion of nanotubes. In comparison of the single component nanofiber webs, the core-sheath nanofiber webs showed much better mechanical properties of modulus and breaking stress, including an exceptional elongation-at-break. It indicates that the CNT-incorporated core-sheath structure is very effective for enhancing the mechanical properties of nanofiber webs. In addition, the core-sheath nanofibers demonstrated the fast shape recovery, compared with one component fibers of pure shape memory PU and PU/MWNTs, which provides the possibility of fabricating more sensitive intelligent materials.     

Effects and Interactions of Medium Components on Laccase from a Marine-Derived Fungus Using Response Surface Methodology

The effects of various synthetic medium components and their interactions with each other ultimately impact laccase production in fungi. This was studied using a laccase-hyper-producing marine-derived basidiomycete, Cerrena unicolor MTCC 5159. Inducible laccases were produced in the idiophase only after addition of an inducer such as CuSO₄. Concentration of carbon and nitrogen acted antagonistically with respect to laccase production. A combination of low nitrogen and high carbon concentration favored both biomass and laccase production. The most favorable combination resulted in 917 U L⁻¹ of laccase. After sufficient growth had occurred, addition of a surfactant such as Tween 80 positively impacted biomass and increased the laccase activity to around 1,300 U L⁻¹. Increasing the surface to volume ratio of the culture vessel further increased its activity to almost 2,000 U L⁻¹.