Crimped polymer nanofibres by air-driven electrospinning

Electrospinning is a well-known process for producing sub-micron scale polymer filaments through an electrostatic field. This paper presents a very simple “confined” air-driven electrospinning system, in which polyamide nanofibres are produced in the form of continuous crimped filaments. The reported system consists of a vertical cylinder with a weak tangential air-flow feeding from the top, placed between the capillary source electrode and the grounded target collector. The air-flow drives the polymer jet inside the electrostatic field, curls up the filament and reduces the deposition area on the collector surface. Numerical evaluations of both the electrostatic field and the air-flow path within the chamber are reported. The proposed configuration has been successfully tested electrospinning a solution of polyamide-6 in formic acid, varying the applied voltage and the distance between the electrodes. SEM observations of the electrospun fibres revealed that a large amount of crimped nanofibres was produced free from bead defects.     

Pickering emulsions co-stabilised by cellulose nanofibres and nicotinamide mononucleotide

Cellulose - Emulsified solid particles adsorbed at the oil–water interface can stabilise Pickering emulsions by acting as a physical barrier to the coalescence of oil droplets. Cellulose...     

Spectral studies of SnO2 nanofibres prepared by electrospinning method

Tin oxide nanofibres with 100-150 nm diameter has been prepared, for the first time by calcination of poly(vinyl acetate) (PVAc)/SnO2 composite fibres prepared by electrospinning method as precursor. Scanning electron microscopic images revealed cylindrical morphology of the fibres after calcination at 600 degrees C. Both, X-ray diffraction (XRD) and Raman spectral data confirmed the presence of phase pure tetragonal rutile tin oxide after calcination process. Room temperature photoluminescence (PL) spectra of tin oxide nanofibres under excitation at 325 nm wavelength show a strong green emission at 525 nm with a band gap of 2.41 eV. FT-IR spectra confirmed the formation of pure tin oxide after calcination at 600 degrees C and complete removal of PVAc during calcination. UV-vis spectrum of the fibres showed absorption at 315 nm due to the direct electron transfer in tin oxide.     

Surface oxidation of carbon nanofibres

Carbon nanofibres of the fishbone and parallel types were surface-oxidised by several methods. The untreated and oxidised fibres were studied with infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy (XPS). Oxidation in a mixture of concentrated nitric and sulfuric acids proved to be the most effective method for creating oxygen-containing surface groups. This treatment results not only in the formation of carboxy and carboxyic anhydride groups, but also in the generation of ether-type oxygen groups between graphitic layers that are puckered at their edges. The IR spectroscopic data clearly show that the formation of oxygen-containing surface groups occurs at defect sites on the carbon nanofibres and that oxidation proceeds via carbonyl groups and other oxides to carboxy and carboxyic anhydride groups. Owing to the presence of defects, the two types of fibre have similar surface reactivities. With parallel nanofibres, in contrast to fishbone fibres, the macroscopic structure was severely affected by treatment with HNO(3)/H(2)SO(4). The HNO(3)/H(2)SO(4)-treated fibres are highly wettable by water.     

Cellulose destruction by electron-beam-induced heating

An efficient method for producing furfural and other furan derivatives from cellulose was proposed. Radiolytic destruction of cotton cellulose, sulfate and sulfite pine celluloses, and carboxymethylcellulose was studied under electron-beam-induced distillation conditions. The yield of the liquid distillate from cellulose of various origin was about 60%. Furfural and its derivatives with the molecular weight up to 140 were the predominant products. Grinding and preheating of cellulose increase the fraction of furan derivatives in the condensate. The liquid products are partially transformed into high-molecular-weight compounds that are distilled with difficulty and that are involved in the formation of wood charcoal in the yield of about 20%.     

The development of polyamide 6.6 nanofibres with a pH-sensitive function by electrospinning

The development of a pH-sensitive nanofibrous sensor could contribute to interesting applications thanks to the combination of the pH-sensitive functionality and the unique characteristics of nanofibres. The effect of the addition of pH-sensitive dyes to the polymer solution is however unknown. Moreover also the halochromic behaviour of the resulting nonwovens can be influenced by this incorporation. Therefore, we studied the production of halochromic nano nonwovens by adding various pH-indicator dyes to a polyamide 6.6 polymer solution prior to electrospinning. Next, the halochromism of two selected dyes (Bromocresol Purple and Brilliant Yellow) was investigated as case studies. Our results show that the pH-indicator addition has no influence on the average fibre diameter. Poorly dissolved dyes cause however instabilities in the process as seen by the droplet formation. The investigated nanofibrous structures showed a clear colour change with a change in pH. This halochromic behaviour was however different from the behaviour of the dye in solution due to dye-fibre interactions. Generally it can be concluded that a nanofibrous pH-sensor can be developed by electrospinning with incorporated pH-indicator dyes.     

Template-free assembly of 2D-electrolytes into nanofibres

The assembly of graphene-based materials into nanofibres is of intense technological interest for numerous applications ranging from tissue engineering and drug delivery to fuel cells and space elevators. We demonstrate a composite nanofibre synthesis process using functionalised graphene structures in liquid medium (two-dimensional [2D] electrolytes) as building blocks. The approach consists in simultaneous scrolling and reacting 2D electrolytes, leading to a dimensional reduction of 2D materials into one-dimensional nanostructures. The spontaneous self-assembly and cross-linking processes allow to produce nanofibres without the need of fibrillation techniques, such as wet-spinning or external templates.     

Carboxymethylation of Cellulose by Microwave irradiation

Cellulose may be readily converted into ethers involving primary and secondary alcohol groups in each monomer unit and the glycosidic bonds. However, these reactions are rather more complicated than with simple substances, because the stereochemistry of the cellulose molecule is such that the vast majority of its hydroxyl groups form intra-chain hydrogen bonds or inter-chain hydrogen bonds with contiguous molecules. Carboxymethylcellulose (CMC) has played an important part in the commercial uses of cellulose derivatives. CMC becomes alkali and water soluble. The polarity can, in fact, be increased by introduction of ionizing groups, ie carboxymethyl group. CMC is generally produced by the reaction of alkali cellulose with chloroacetic acid.     

Cellulose nanocrystal submonolayers by spin coating

Dilute concentrations of cellulose nanocrystal solutions were spin coated onto different substrates to investigate the effect of the substrate on the nanocrystal submonolayers. Three substrates were probed: silica, titania, and amorphous cellulose. According to atomic force microscopy (AFM) images, anionic cellulose nanocrystals formed small aggregates on the anionic silica substrate, whereas a uniform two-dimensional distribution of nanocrystals was achieved on the cationic titania substrate. The uniform distribution of cellulose nanocrystal submonolayers on titania is an important factor when dimensional analysis of the nanocrystals is desired. Furthermore, the amount of nanocrystals deposited on titania was multifold in comparison to the amounts on silica, as revealed by AFM image analysis and X-ray photoelectron spectroscopy. Amorphous cellulose, the third substrate, resulted in a somewhat homogeneous distribution of the nanocrystal submonolayers, but the amounts were as low as those on the silica substrate. These differences in the cellulose nanocrystal deposition were attributed to electrostatic effects: anionic cellulose nanocrystals are adsorbed on cationic titania in addition to the normal spin coating deposition. The anionic silica surface, on the other hand, causes aggregation of the weakly anionic cellulose nanocrystals which are forced on the repulsive substrate by spin coating. The electrostatically driven adsorption also influences the film thickness of continuous ultrathin films of cellulose nanocrystals. The thicker films of charged nanocrystals on a substrate of opposite charge means that the film thickness is not independent of the substrate when spin coating cellulose nanocrystals in the ultrathin regime (<100 nm).     

Mechanical behaviour of MWCNTs reinforced electrospun nanofibres

Abstract

The nanoscale dimension of electrospun polymeric nanofibres produced by electrospinning are highly captivating, yet facing limitation of resisting external forces due to the weak tensile properties. Carbon nanotubes providing tremendous toughness due to extraordinary strong sp² bonding network of carbon atoms in honeycomb lattice structure, augmented the physical resistant strength and is easily recover to its original state after load is removed. This study reports the performance of multi-walled carbon nanotubes (MWCNTs) as filler in the electrospinning of poly (_L-lactide)-co-ε-caprolactone) (PLCL) composite nanofibres. Voltage of 10?kV is applied to the spinning solution mixture of 11?wt% (w/v) PLCL and MWCNTs, yielded nanofibres having diameters less than 400?nm. Results obtained showed the formation of composite nanofibres with tailored tensile behavior by modifying the content of MWCNTs. The addition of MWCNTs improved the tensile properties of resultant composite nanofibres, signified by tensile strength of 5.82 to 15.95?MPa, which were obtained using 0.1 to 1.0?wt% of MWCNTs. The structural integrity of nanofibres mats were retained in phosphate buffer saline (PBS) medium. Scanning Electron Microscopy (SEM) micrographs revealed the minimal of fiber deformation over 30?days of incubation and are closely identical to the initial diameter of as-spun fiber.     

Cellulose Esters Prepared by Wood Esterification

Trends in the yields and properties of cellulose esters are studied as a function of wood esterification conditions. The yield, total extent of cellulose ester substitution, and degree of conversion depend on the duration and acylation temperature     

双螺杆挤出机纺制的纤维素纤维

以离子液体氯化1-烯丙基-3-甲基咪唑([AMIM]Cl)为溶剂,采用双螺杆挤出机溶解并纺制了较高质量分数的纤维素纤维,测定了纤维素纤维的结构与性能以及纤维中[AMIMCl]残余质量分数,观察了纤维的微观形貌。结果表明:双螺杆挤出机能溶解并纺制较高质量分数的纤维素纤维,可达30%,纤维素纤维晶型由浆粕的Ⅰ型转变为Ⅱ型,纤维结晶度小于纤维素浆粕。成形过程中,纤维中的离子液体难于完全除去,导致纤维素纤维分解温度下降。实验范围内,纤维素质量分数为20%时,纤维断裂强度最高,为0.51cN/dtex。     

纤维素酶降解纤维素机理的研究

纤维素是自然界中含量最多的一类碳水化合物,同时它也是地球上数量最大的可再生资源。纤维素酶是一种高活性生物催化剂,在纤维素类资源的利用方面发挥重要的作用。本文综述了纤维素、纤维素酶的分子结构和纤维素酶对纤维素的降解机理,影响酶解的主要因素以及提高酶解效率的主要措施,并对纤维素酶研究存在的问题以及今后的发展作了进一步展望。     

The Structure of Cellulose by Conformational Analysis. Part 4. Crystalline Cellulose II

The Kolpack, Weih, and Blackwell antiparallel central chain model was found to be the most energetically stable for the crystalline structure of cellulose II. Computational results indicated that the two most probable Sarko models are considerably less stable and less probable. The conformations of the monomers terminating the crystalline zone have been described. The predominance of van der Waals and H-bond interactions in the crystalline zone have been confirmed, and the H-bond values, locations, and distribution in the crystalline zone have been accurately mapped. The cellulose II crystallite has been confirmed to be considerably more stable than the cellulose I crystallite. Positions of atomic groups from the ab initio conformational analysis are consistent with the x-ray data for the Kolpack, Weih, and Blackwell model.     

Morphology transformation between nanofibres and vesicles controlled by ultrasound and heat in tryptamine-based assembly

A novel low-molecular-mass organic gelator T1 containing tryptamine and sugar segments was designed and synthesised which can gelate alcohols accelerated by heat and sonication. Interestingly, morphology exchange between vesicles as precipitate and a three-dimensional gel network tuned by heating and ultrasound was observed. The mechanism was studied by IR, FL, X-ray diffraction. It was presented that the effect of ultrasound was to disturb the spontaneous self-assembly of T1 molecule, and promote the long arrangement and disordered assembly of T1 molecules into fibrous networks, thus resulting in the gelation in methanol.     

纤维素酶降解纤维素机理的研究进展

纤维素是自然界中含量最多的一类碳水化合物,同时它也是数量最大的可再生资源。纤维素酶是一种高活性生物催化剂,在纤维素类资源的利用方面发挥重要的作用。本文综述了纤维素、纤维素酶的分子结构和纤维素酶对纤维素的降解机理、影响酶解的主要因素以及提高酶解效率的主要措施,并对纤维素酶研究存在的问题以及今后的发展作了进一步展望。     

纤维素及其衍生物的高压静电纺丝

高压静电纺丝作为一种制备纳米纤维的先进技术,近年来受到普遍关注。而纤维素和纤维素衍生物由于其优越的性质已应用于各个领域。运用高压静电纺丝技术对纤维素及其衍生物进行研究,开拓了新的研究领域和发展方向。本文介绍了高压静电纺丝技术的研究背景和原理,总结了近几年研究者们在纤维素以及纤维素衍生物高压静电纺丝方面的工作进展,尤其对不同溶剂体系溶解纤维素用于静电纺丝的优缺点进行了比较,评述了这方面的前沿性探索研究,并对未来的发展进行了展望。     

Adsorption of copper(II) ions by keratin/PA6 blend nanofibres

Mats of randomly oriented nanosized filaments, prepared by electrospinning wool keratin/polyamide 6 blends in formic acid, were evaluated as adsorbents of Cu²⁺ ions. The adsorption capacity was evaluated as a function of the nanofibre composition, specific surface area, initial metal ion concentration, contact time and pH of the solution. The adsorption tests revealed that keratin-based nanofibres highly adsorb Cu²⁺ ions and the adsorption capacity increases with increasing the specific surface area of the nanofibre mats. The maximum adsorption capacities for nanofibre mats containing 50%, 70% and 90% (wt.%) of keratin were found to be 61.7 (mg/g), 90 (mg/g) and 103.5 (mg/g), respectively. The Cu²⁺adsorption onto the keratin rich nanofibres is highly pH-dependent and the optimum pH was found above the isoelectric point of keratin. The experimental data fit the pseudo second-order kinetic model. Infrared analysis demonstrated the formation of complexes between Cu²⁺ ions and keratin that involve terminal free carboxyl groups of the protein.     

NiMoO4 nanofibres designed by electrospining technique for glucose electrocatalytic oxidation

Electrochemical oxidation of glucose is the guarantee to realize nonenzymatic sensing of glucose, but greatly hindered by the slow kinetics of its oxidation process. Herein, various nanomaterials were designed as catalysts to accelerate glucose oxidation reaction. However, how to effectively build an excellent platform for promoting the glucose oxidation is still a great challenge. In our work, 1D CaMoO₄ and NiMoO₄ nanofibres with same morphologies and sub-microstructures were fabricated by electrospinning technique in the first time, and explored to modify the detection electrodes of nonenzymatic glucose sensors. The electrochemical results indicated that the NiMoO₄ based sensor exhibited a good catalytic activity toward glucose including the low response potential (0.5 V), high sensitivity(193.8 μA mM⁻¹ cm⁻²) with a linear response region of 0.01–8 mM, low detection limit (4.6 μM) and fast response time (2 s), all of which are superior to the corresponding values of CaMoO₄ nanofibres and even higher than those of most reported NiO and Co₃O₄ catalysts, which is due to the NiMoO₄ nanofibres are not only advantageous to electron transfer, but can mediated the electrocatalytic reaction of glucose. This work should provide a new pathway for the design of advanced glucose catalysts for nonenzymatic sensor.