Preparation of VB‐a/POSS hybrid monomer and its polymerization of polybenzoxazine/POSS hybrid nanocomposites

A benzoxazine monomer (VB‐a) containing an allyl groups was synthesized through the Mannich condensation of bisphenol A, formaldehyde, and allylamine (bisphenol‐A and allylamine as VB‐a). This monomer was then reacted with polyhedral oligomeric silsesquioxane (POSS) through hydrosilylation, followed by thermal curing to form poly(VB‐a)/POSS hybrid nanocomposites. The curing behavior of the nanocomposites was monitored using Fourier transform infrared spectroscopy (FTIR), and their thermal and morphological properties were investigated through thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and scanning electron microscopy. DMA revealed that the glass transition temperatures of the poly(VB‐a)/POSS nanocomposites were higher than that of the pristine poly(VB‐a), presumably because the POSS cages effectively hindered the motion of the polymer chains. TGA confirmed that the thermal degradation temperatures and char yields of the polybenzoxazines increased after incorporation of the POSS moieties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrospinning functional nanoscale fibers: a perspective for the future

Over the past decade, electrospinning has grown from a small niche process to a widely used fiber formation technique. Applying a strong electric potential on a polymer solution or melt produces nanoscale fibers. These nanofibers form non‐woven textile mats, oriented fibrous bundles and even three‐dimensional structured scaffolds, all with large surface areas and high porosity. Major applications of electrospun membranes include tissue engineering, controlled drug delivery, sensing, separations, filtration, catalysis and nanowires. This perspective article highlights many recent advances in electrospun fibers for functional applications, with an emphasis on the advantages and proposed technologies for these non‐woven fibrous scaffolds. Copyright © 2007 Society of Chemical Industry     

A facile approach to fabricate porous nylon 6 nanofibers using silica nanotemplate

Porous Nylon 6 nanofibers were prepared using silica nanoparticles as the template. Firstly, Nylon 6/silica composite nanofibers were prepared as precursors by electrospinning Nylon 6 solutions containing different contents of silica nanoparticles. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the surface morphology and the inner structure of composite nanofibers; where it was found that silica nanoparticles were distributed both inside and on the surface of nanofibers. Analytical techniques [Fourier transform infrared (FTIR), differential scanning calorimetry, thermal gravimetric analysis (TGA), and wide‐angle X‐ray diffraction) were used to study the structure and properties of these composite nanofibers. The glass transition, melting, and crystallization processes of the fibers were affected by the addition of silica nanoparticles. Secondly, porous Nylon 6 nanofibers were obtained by removing silica nanoparticles via hydrofluoric acid treatment. The removal of silica nanoparticles was confirmed using FTIR and TGA tests. SEM and TEM observations revealed the formation of the porous structure in these nanofibers. After the formation of the porous structure, Brunauer–Emmett–Teller specific surface areas of nanofibers were increased as compared to solid Nylon 6 and composite nanofibers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Innovative Electrospinning Method of Depositing Functionally Graded and Aligned Multidirectional Polymer Nanofibers

An innovative setup in which multiple electrodes, whose potentials can be switched on or off, was used for producing electrospun fibers. By controlling the activation time and sequence of switching between adjacent electrodes, the electrical field and thus the charge-carrying fibers can be directed to different locations. It has been demonstrated that a variety of functionally graded architectures having preferred alignments can be produced. The simulation results point to possible mechanisms for directional deposition of fibers. The electrospun fibers can be varied in a controlled manner to produce mats containing random, aligned, or multidirectional nanofibrous patterns.     

Novel elastomer‐dumbbell functionalized POSS composites: Thermomechanical and Morphological Properties

Nanocomposites consisting of poly(styrene‐b‐butadiene‐b‐styrene) (SBS) and polyhedral oligomeric silsesquioxanes (POSS) were prepared using a solvent dispersion method. Dumbbell‐shaped POSS fillers were prepared using diacyl chlorides to bridge the POSS molecules. Infrared spectroscopy confirmed functionalization. Scanning electron microscopy revealed an increase in filler aggregation with concentration, with preferential phase selectivity. Polydispersity increased with filler concentration while d spacing was influenced by phase selectivity and domain‐filler compatibility. Functionalized POSS improved thermal stability by imparting restrictions of SBS chain motions. Tensile stress–strain analysis revealed an increase in modulus, yield strength, and strain hardening with filler concentration, while creep deformation decreased and permanent strain increased with POSS content. Storage modulus, loss modulus, and glass transition temperature increased with filler content due to effective SBS–POSS interaction. Nanocomposite properties were influenced by filler concentration, the phase of the filler was dispersed throughout and the length of the alkyl “barbell” on the dumbbell‐shaped POSS. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrospinning of cellulose nanofibers from ionic liquids: The effect of different cosolvents

Cellulose was electrospun with various concentrations of ionic liquid and cosolvent. Three different cosolvents were used in this study; dimethylacetamide (DMAc), dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO). The cosolvents were added to modify the viscosity, electrical conductivity, and surface tension of the solutions. The solubility of cellulose in ionic liquids is highly affected by changes in solvent properties on the molecular level in the binary solvent systems. The difference in molecular structure of the cosolvents and the interactions between cosolvent and ionic liquid can explain the difference in dissolution power of the cosolvents. Scanning electron microscope (SEM) was used to characterize electrospun cellulose fibers. For the systems tested the importance of having a rather high viscosity and high surface tension, and some degree of shear thinning to produce fibers is shown. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

电纺PAN纳米纤维的碳化工艺研究

研究了电纺方法制备的聚丙烯腈(PAN)纳米纤维的碳化工艺。利用热重/差热(TG/DTA)分析仪对其升温过程中的物理化学反应过程进行了分析,讨论了在空气和氮气两种氛围内原纤维的热氧化、分解过程,发现在290℃附近PAN纤维发生强烈的氧化反应,温度达到930℃时,原纤维几乎完全转化为碳纤维。利用扫描电镜(SEM)和Raman光谱仪对不同温度下稳定化和碳化处理得到PAN基碳纤维进行了深入的研究,得到了电纺PAN原纤维碳化的工艺规律。     

Electrospinning of PLA and PLA/POSS nanofibers: Use of Taguchi optimization for process parameters

It is known that electrospinning is the most practical technique to obtain unique nanofibrous structures, such as neat PLA (polylactide) and PLA filled with POSS (Polyhedral Oligomeric Silsesquioxane) particles. On the other hand, due to the so many different process parameters to consider, production of these fibers are extremely difficult and time consuming. That is, use of a certain statistical optimization technique in the design of experiments would be necessary. Therefore, the main purpose of this study was to determine the optimum electrospinning parameters by applying the Taguchi technique first to neat PLA and then to reveal the applicability of these parameters for the electrospinning of PLA/POSS nanofibers. It was observed that instead of conducting 81 experiments to determine the most significant four optimum process parameters for PLA, use of Taguchi L₉ orthogonal array experiment matrix, that is, conducting only nine experiments, reduced time, labor and material consumption considerably. For the smallest electrospun PLA fiber diameter, the optimum parameters determined were; “PLA solution concentration” of 8% w/v, “solution feeding rate” of 1.8 mL/h, “needle-to-collector distance” of 18 cm, and “applied voltage” of 15 kV. Moreover, it was generally concluded that these same parameters could be also used for the electrospinning of PLA/POSS nanofibers after addition of only 3 wt% KCl salt into the polymer solution.     

A Novel Approach to Prepare Uniaxially Aligned Nanofibers and Longitudinally Aligned Seamless Tubes Through Electrospinning

A novel method to produce uniaxially aligned nanofibers is described, in which a pair of parallel auxiliary electrodes at a positive potential is placed between the needle and the collector electrodes. Charged nanofibers ejecting from the polymer solution are pre‐aligned by the electrostatic repulsion originating from the auxiliary electrodes and deposited on the collector electrodes, forming a narrow mat with the fiber segments strongly curved. By adjusting the conductivity and shape profile of the collector, the curved segments can be straightened longitudinally. A seamless tube composed of longitudinally aligned nanofibers can be obtained. Such seamless tubes may be useful as biomaterials in tissue engineering.

     

Kinetics analysis and physical properties of photocured silicate-based thiol-ene nanocomposites: The effects of vinyl POSS ene on the polymerization kinetics and physical properties of thiol-triallyl ether networks

The kinetics and thermal/physical properties of the trithiol-TAE (triallyl ether) system were measured with respect to increasing polyoligomeric silsesquioxane (POSS) concentrations in order to understand how the presence of POSS nanoparticles affects network formation at low loadings. Vinyl POSS monomer (vPOSS-Bu₄) with both vinyl and carboxylate pendant groups was synthesized via a thermally initiated, free-radical reaction to improve the compatibility of the inorganic particles with the trithiol and triallyl ether comomoners. Chemically modified vPOSS-Bu₄ particles were incorporated into the trithiol-TAE polymer networks by a thiol-ene free-radical photopolymerization at molar concentrations of 0, 1, and 5 ene mol%. The polymerization rates were analyzed using real-time FTIR and photo-DSC. The polymerization rates showed no significant changes with increasing vPOSS-Bu₄ concentration. Thermal analyses of the films by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) demonstrated that thermal stability improves without affecting T _g as the POSS concentration increased. Additionally, scratch resistance increased and flame spread decreased markedly with increasing POSS concentration for concentrations up to 5 mol% vPOSS-Bu₄.     

On the electrospinning of poly(vinyl alcohol) nanofiber mats: A revisit

Electrospinning was used to fabricate mats of poly(vinyl alcohol) (PVA; M_w = 72,000 Da, degree of hydrolysis ≈ 97.5–99.5) nanofibers from PVA solutions in reverse osmotic water. The effects of solution concentration, applied electrical potential, sonication, and collection distance on morphological appearance and diameters of the as‐spun fiber mats as well as those of the individual fibers were carefully investigated mainly by scanning electron microscopy. The effect of the distance from the center of the as‐spun fiber mat on morphological appearance and diameters of the as‐spun fibers was also investigated. The mechanical integrity of some as‐spun PVA fiber mats was also investigated. At all concentrations and applied electrical potentials investigated, the average diameters of the as‐spun PVA fibers ranged between 85 and 647 nm. The use of sonication to prepare a PVA solution caused the viscosity of the solution to decrease; hence, the observed decrease in the average diameters of the as‐spun fibers and the average diameters of the as‐spun fibers were practically the same throughout the as‐spun fiber mat. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Solution blow spinning: A new method to produce micro‐ and nanofibers from polymer solutions

A solution blow spinning technique was developed using elements of both electrospinning and melt blowing technologies as an alternative method for making non‐woven webs of micro‐ and nanofibers with diameters comparable with those made by the electrospinning process with the advantage of having a fiber production rate (measured by the polymer injection rate) several times higher. The diameters of fibers produced ranged from 40 nm for poly(lactic acid) to several micrometers for poly(methyl methacrylate). This solution blow spinning method uses a syringe pump to deliver a polymer solution to an apparatus consisting of concentric nozzles whereby the polymer solution is pumped through the inner nozzle while a constant, high velocity gas flow is sustained through the outer nozzle. Analysis of the process showed that pressure difference and shearing at the gas/solution interface jettisoned multiple strands of polymer solution towards a collector. During flight, the solvent component of the strands rapidly evaporates forming a web of micro and nanofibers. The effect of injection rate, gas flow pressure, polymer concentration, working distance, and protrusion distance of the inner nozzle was investigated. Polymer type and concentration had a greater effect on fiber diameter than the other parameters tested. Injection rate, gas flow pressure, and working distance affected fiber production rate and/or fiber morphology. Fibers were easily formed into yarns of micro‐ and nanofibers or non‐woven films that could be applied directly onto biological tissue or collected in sheets on a rotating drum. Indeed, virtually any type of target could be used for fiber collection. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A novel strategy to achieve NaGdF4:Eu3+ nanofibers with color‐tailorable luminescence and paramagnetic performance

Luminescent‐magnetic bifunctional NaGdF₄:Eu³⁺ nanofibers were fabricated through the bond of electrospinning followed by calcination with fluorination technology for the first time. The structure, morphologies, luminescence, and magnetism of nanofibers have been characterized using various techniques. X‐ray diffraction measurement indicates that NaGdF₄:Eu³⁺ nanofibers are hexagonal phase. Scanning electron microscope measurement shows that the mean diameters of electrospinning‐made polyvinyl pyrrolidone/[NaNO₃+Gd(NO₃)₃+Eu(NO₃)₃] composite nanofibers and NaGdF₄:Eu³⁺ nanofibers are, respectively, 428±4 and 231±4 nm under the confidence level of 95%. Under 274‐nm ultraviolet light excitation, NaGdF₄:Eu³⁺ nanofibers exhibit characteristic ⁵D_3,2,1,0→⁷F_J emissions of Eu³⁺ and the tendency of color tones of samples varies from blue, cold white, warm white to red via varying Eu³⁺ content. In addition, samples exhibit paramagnetic features and the magnetic properties of NaGdF₄:Eu³⁺ nanofibers are tailorable by modulating the doping concentration of Eu³⁺. More importantly, the color‐tailorable luminescence and paramagnetic properties are simultaneously realized in single‐phase NaGdF₄:Eu³⁺ nanofibers, which ideally suit to apply in many fields such as lighting and color displays, bioimaging, and magnetic resonance imaging. This design conception and construction strategy may provide some new guidance for synthesizing other rare‐earth fluorides nanomaterials of multifarious morphologies.     

Global View and Trends in Electrospun Nanofiber Membranes for Particulate Matter Filtration: A Review

Numerous experimental works for particulate matter (PM) filtration by electrospun nanofiber membranes (ESNFMs) are published in the last 10 years (2010–2021). Organizing and comparing the large amount of the available information to identify the best trends constitutes a big challenge. This review classifies all kinds of ESNFMs considering their physical, chemical, or electrical characteristics. All of them are obtained by modifying several parameters during a specific stage associated to the electrospinning process (ES). In this review, each of these stages is considered a "moment” as a particular instant in time. According to that, three modifications are made: Moment 1—before ES, which refers to changes in polymeric solution composition; moment 2—during ES, which refers to modifying parameters while ES is performed; and moment 3—after ES, which involves applying post-treatments directly on the membrane. After classifying all kinds of filters by moments, a detailed comparison of ESNFMs with the highest quality factors for PM_0.3 is presented, finding out the best trends and comparing their main filtration parameters as well, where the most promising ones correspond to charged and nanofiber/nets membranes, due to their high capture efficiencies (>95%) while maintaining low pressure drops (<100 Pa).     

One-Pot Process: Microwave-Assisted Keratin Extraction and Direct Electrospinning to Obtain Keratin-Based Bioplastic

Poultry feathers are among the most abundant and polluting keratin-rich waste biomasses. In this work, we developed a one-pot microwave-assisted process for eco-friendly keratin extraction from poultry feathers followed by a direct electrospinning (ES) of the raw extract, without further purification, to obtain keratin-based bioplastics. This microwave-assisted keratin extraction (MAE) was conducted in acetic acid 70% v/v. The effects of extraction time, solvent/feathers ratio, and heating mode (MAE vs. conventional heating) on the extraction yield were investigated. The highest keratin yield (26 ± 1% w/w with respect to initial feathers) was obtained after 5 h of MAE. Waste-derived keratin were blended with gelatin to fabricate keratin-based biodegradable and biocompatible bioplastics via ES, using 3-(Glycidyloxypropyl)trimethoxysilane (GPTMS) as a cross-linking agent. A full characterization of their thermal, mechanical, and barrier properties was performed by differential scanning calorimetry, thermogravimetric analysis, uniaxial tensile tests, and water permeability measurements. Their morphology and protein structure were investigated using scanning electron microscopy and attenuated total reflection-infrared spectroscopy. All these characterizations highlighted that the properties of the keratin-based bioplastics can be modulated by changing keratin and GPTMS concentrations. These bioplastics could be applied in areas such as bio-packaging and filtration/purification membranes.     

Polymer nanotube nanocomposites: Correlating intermolecular interaction to ultimate properties

Polymer nanocomposite films containing 5 wt% single-walled carbon nanotubes (SWNT) or 5 wt% multi-walled carbon nanotubes (MWNT) with random copolymers of styrene and vinyl phenol were processed from dimethyl formamide solutions. Vinyl phenol mole ratio in the copolymer was 0, 10, 20, 30, and 40%. FTIR analysis indicates that the composites containing the copolymer with 20% vinyl phenol exhibit the maximum intermolecular interactions (hydrogen bonding) between the hydroxyl group of the vinyl phenol and the carbon nanotube functional groups. Tensile properties and electrical conductivity also are the highest in the samples containing the copolymer with 20% vinyl phenol. Thus, these results show that the optimization of the extent of intermolecular interactions between a polymer chain and a carbon nanotube results in an optimal increase in macroscopic properties. Moreover, the extent of intermolecular hydrogen bonding can be improved by optimizing the accessibility of the functional groups to participate in the non-covalent interaction. In this system, this optimization is realized by control of the amount of vinyl phenol in the copolymer, i.e. the copolymer composition.     

A Novel Fabrication Method for Poly(propylene)/Clay Nanocomposites by Continuous Processing

Summary: It is well known that poly(propylene)/clay (PP/clay) nanocomposite forms an exfoliated structure when mixed with maleic anhydride‐functionalized polypropylene (MAPP). This can be easily achieved by melt processing, however, the use of functionalized chemicals like MAPP costs a lot preventing its commercial application. Recently, it was reported that the exfoliated structure of PP/clay nanocomposite could be obtained without using any compatibilizer such as MAPP when exposed to the electric field. They could regulate the degree of dispersion and exfoliation by controlling the amount of clay loading, the strength of electric field, the time exposed to the electric field, etc. However, this was accomplished by applying the electric field on a rheometer for a long time. It will be practically attractive if we produce PP/clay nanocomposites via continuous processing like extrusion. A new design concept is required for this purpose. In this study, we present a novel method to continuously produce PP/clay nanocomposites using the electric melt pipe equipped with a twin‐screw extruder. Rheology, XRD, and SEM measurements confirm the formation of nanocomposites. Thermal‐ and dynamic‐mechanical analysis also shows the enhancement of the properties. Though, in this study, only a partial intercalation was achieved through continuous processing, it shows a possibility to produce nanocomposites by this approach. As this is a physical process that can be adapted to the conventional extrusion, the approach suggested in this study may be extended to other polymer/clay nanocomposite systems as well.

Schematic diagram of electric melt pipe equipped with a twin‐screw extruder.     

小分子在高分子载体中平衡溶解度的测定方法

提出了一种获得任意温度下小分子在高分子载体中平衡溶解度的方法,结合使用热分析实验得到的熔点数据和Flory-Huggins高分子溶液理论来取得完整的溶解度-温度曲线.选用小分子药物芬布芬/聚乙烯基吡咯烷酮(Fen/PVP)作为模型体系进行研究来说明了该方法的应用.这种方法可以推广应用于一般的小分子/高分子体系中.