Influences of organic-modified Fe-montmorillonite on structure, morphology and properties of polyacrylonitrile nanocomposite fibers

The Fe-montmorillonite (Fe-MMT) combined catalysis effects of Fe ion with barrier effects of silicate clays, was firstly synthesized by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The organic-modified Fe-montmorillonite (Fe-OMT) was dispersed in the N, N-dimethyl formamide (DMF) and then compounded with polyacrylonitrile (PAN) solution which was dissolved in DMF. The composite solutions were electrospun to form PAN/Fe-OMT nanocomposite fibers. The influences of the Fe-OMT on the structure, morphology, thermal, flammability and mechanical properties of PAN nanocomposite fibers were respectively characterized by X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), Scanning electron microscopy (SEM), Thermogravimetric analyses (TGA), Micro Combustion Calorimeter (MCC) and Electronic Single Yarn Strength Tester. It was found from XRD curves that there was not observable diffraction peak of silicate clay, indicating that the silicate clay layers were well dispersed within the PAN nanofibers. The HRTEM image indicated that the multilayer stacks of nanoclays could be found within the nanofibers and were aligned almost along the axis of the nanofibers. The SEM images showed that the diameters of nanocomposite fibers were decreased with the loading of the Fe-OMT. The TGA analyses revealed that the onset temperature of thermal degradation and charred residue at 700°C of PAN nanocomposite fibers were notably increased compared with the pure PAN nanofibers, contributing to the improved thermal stability properties. It was also observed from MCC analyses that the decreased peak of heat release rate (PHRR) of the PAN nanocomposite fibers reduced the flammability properties. The loadings of Fe-OMT increased the tensile strength of PAN nanocomposite fibers, but the elongation at break of PAN nanocomposite fibers was lower than that of the PAN nanofibers.     

Effect of boron phosphate on the mechanical, thermal and fire retardant properties of polypropylene and polyamide-6 fibers

The effect of boron phosphate (BPO₄) nanoparticles on the mechanical, thermal, and flame retardant properties of polypropylene (PP) and polyamide 6 (PA-6) fibers are investigated by tensile testing, thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), and micro combustion calorimeter (MCC). The addition of BPO₄ reduces the mechanical properties of the both PP and PA-6 fibers. According to the TGA results, the addition of BPO₄ does not change the thermal behavior of PP fiber and slightly reduces the thermal stability of PA-6 fiber by about 30 °C. According to MCC results, the addition of BPO₄ does not change the effective total heat evolution and heat release rate (HRR) peak for PP fibers. Although the inclusion of BPO₄ does not change the total heat evolution of PA-6 fiber, it reduces the HRR peaks due to increase in barrier effect of char.     

Preparation of electrospun LA-PA/PET/Ag form-stable phase change composite fibers with improved thermal energy storage and retrieval rates via electrospinning and followed by UV irradiation photoreduction method

In this paper, novel electrospun LA-PA/PET/Ag phase change composite fibers with different amount of Ag nanoparticles were prepared via the technique of electrospinning followed by UV irradiation method. The morphological structure, thermal energy storage properties, thermal energy storage and release rates of prepared LA-PA/PET/AgNO₃ and LA-PA/PET/Ag composite fibers were investigated by scanning electron microscope (SEM), high-resolution transmission electron microscope (HR-TEM), differential scanning calorimeter (DSC), and the measurement of melting and freezing times, respectively. The SEM images revealed that electrospun LA-PA/PET/AgNO₃ and LA-PA/PET/Ag composite fibers possessed the smooth morphologies with cylindrical shape. The corresponding average fiber diameters gradually decreased with increasing content of the AgNO₃ in the solutions, and slightly smaller than those of the LA-PA/PET composite fibers with oblate morphology and wrinkled surfaces. Yellow-brown coloration of electrospun LA-PA/PET/Ag phase change composite fibers were observed after UV irradiation treatment, which demonstrated that Ag ions were successfully reduced to Ag nanoparticles. The TEM images revealed that these reduced Ag nanoparticles were homogenously dispersed within the composite fibers. The results from DSC measurements indicated that the phase change temperatures and enthalpies of electrospun LA-PA/PET/Ag phase change composite fibers with different Ag content have not be influenced by the UVirradiation treatment. The thermal energy storage and release rates of electrospun LA-PA/PET/Ag phase change composite fibers were also improved due to the combination of reduced Ag nanoparticles. These UV-irradiated electrospun phase change composite fibers with excellent thermal energy storage properties can be acted as a novel form-stable PCMs for the applications related to storage and retrieval of thermal energy.     

Fabrication and characterization of polyamide6-room temperature ionic liquid (PA6-RTIL) composite nanofibers by electrospinning

In the present work, polyamide6-room temperature ionic liquid (PA6-RTIL) composite nanofibers and membranes were successfully prepared for the first time by an electrospinning technique. The surface morphology, component analysis, mechanical properties, thermal properties and conductivity of the PA6-RTIL composite membranes were investigated by field-emission scanning electron microscope (FE-SEM), fourier transform infrared spectrometer (FT-IR), tensile testing, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and digit multimeter, respectively. The morphology, fiber diameter, mechanical strength of the obtained fibers can be controlled by changing experimental parameters for electrospinning, especially the content of RTIL in original electrospun mixture solution. The composite fibrous membranes showed ideal mechanical properties and significantly enhanced conductivity, which may be attributed to intrinsic high mechanical strength of PA6 and conductivity of RTIL.     

The effect of zinc ion content on flame retardance and thermal degradation of alginate fibers

The study employs limiting oxygen index (LOI) measurements, cone calorimetry (CONE) and thermogravimetric analysis (TGA) to examine the catalytic effect of zinc ion content on the flame retardance and thermal degradation of alginate fibers. LOI results show that all zinc alginate fibers are intrinsically flame retardant, with LOI values of over 27.0, as compared with about 24.5 for alginic acid fiber. The heat release rate (HRR) and total heat release values of zinc alginate fibers (obtained from CONE) are significantly less than those of alginic acid fiber, and decrease with increasing zinc ion content. TGA indicates that char formation increases and maximum thermal weight-loss rate is reduced when zinc content in the fibers is increased. The residues of zinc alginate fibers keep their shapes better than those of the alginic acid fiber. Further discussion of the combustion process and flame retardant mechanism is presented.     

Effects of ferric chloride on structure, surface morphology and combustion property of electrospun polyacrylonitrile composite nanofibers

In this work, the pure polyacrylonitrile (PAN) nanofibers and PAN/FeCl₃ composite nanofibers were prepared by an electrospinning process. Electrospinning solution properties including viscosity, surface tension and conductivity, had been measured and combined with the results of Scanning electron microscopy (SEM), Atomic force microscope (AFM) and Micro Combustion Calorimeter (MCC) to investigate the effects of FeCl₃ on the structure, surface morphology and combustion property of electrospun PAN nanofibers, respectively. It was found from SEM images that the diameters of composite nanofibers were decreased with the addition of FeCl₃, which was attributed predominantly to the increased conductivity of the polymer solutions compared to viscosity and surface tension. The AFM analyses revealed that the surface morphology of electrospun nanofibers changed from smooth and wrinkle-like structure (without FeCl₃) to rough and ridge-like structure (with FeCl₃). The results characterized by MCC showed that the loading of FeCl₃ decreased the heat release rate (HRR) and improved the combustion property of composite nanofibers.     

Investigation of the effect of cupric chloride on thermal stabilization of polyamide 6 as carbon fiber precursor

An investigation on the role of cupric (Cu²⁺) ion incorporation during the thermal stabilization of polyamide 6 fibers was carried out using a combination of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) measurements. Cupric chloride pretreated and thermally stabilized polyamide 6 (PA6) fibers was characterized by a reduction in fiber diameter and linear density values together with color changes from light brown to black with increasing stabilization time. PA6 fibers were properly stabilized after 8 h of stabilization time prior to carbonization. The results obtained from DSC and TGA measurements indicated that there was an improvement in the thermal stability when cupric (Cu²⁺) ions were incorporated into the polymer structure. TGA thermograms showed the relative improvement in thermal stability as indicated by increasing char yield with progressing time. Char yield reached a maximum value of 33.6 % at 1000 °C for the cupric chloride pretreated PA6 fibers stabilized for 12 h at 180 °C. Experimental results obtained from DSC and X-ray diffraction methods suggested the loss of crystallinity as a result of perturbation of hydrogen bonds with progressing time. The formation of cupric ion-amide coordination bonds improved the thermal stabilization by encouraging the development of ladder-like structures. The investigation resulted in a new method of evaluation of X-ray stabilization index specifically intended for the thermally stabilized PA6 fiber.     

The role of Na-montmorillonite on thermal characteristics and morphology of electrospun PAN nanofibers

Polymer organic-inorganic hybrid nanofibers constitute a new class of materials in which the polymeric nanofibers are reinforced by uniformly dispersed inorganic particles having at least one dimension in nanometer-scale. In the present study, polyacrylonitrile (PAN) and PAN/Na-montmorillonite (PAN/Na-MMT) nanofibers were conducted via electrospinning process. Electrospun PAN and PAN/Na-MMT fibers with the respective mean fiber diameter of about 220 and 160 nm were prepared. The influence of the clay-montmorillonite on the morphology and diameter of nanofibers was investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The microscopic techniques propose that the PAN/Na-MMT composite nanofibers show lower mean fiber diameter than the neat PAN nanofibers. Besides, the difference in nanoclay-content has a slight effect on the distribution of fibers diameter. Thermogravimetric analysis (TGA) results suggest that introduction of clay-nanomaterials improves the thermal characteristics of fibers.     

Synthesis,structure and thermal protective behavior of silica aerogel/PET nonwoven fiber composite

In recent years, flexible, mechanically strong and environmental friendly thermal insulation materials have attracted considerable attention. In this work, silica aerogel/polyethylene terephthalate (PET) nonwoven fiber composite with desirable characteristics was prepared via a two-step sol-gel process followed by an ambient drying method through immersing the PET nonwoven fiber into silica sol. The silica aerogel particles were characterized by FTIR, FE-SEM, TGA and nitrogen adsorption analysis. The morphology and hydrophobic properties of neat PET nonwoven fiber and its silica aerogel composite were also investigated. For studying thermal protective properties, the thermal diffusivity was calculated from temperature distribution curves. The mean pore size of 11 nm, the surface area of 606 m²/g and the total pore volume of 1.77 cm³/g for the silica aerogel particles in the composite are obtained from nitrogen adsorption analysis, indicating the aerogel can maintain its high porosity in the nonwoven composite structure. Silica aerogel particles were efficiently covered the surface of the PET fibers and completely filled the micron size pores of the nonwoven fiber leading to a stronger hydrophobicity and higher thermal insulation performance in the aerogel composite samples compared to the neat PET nonwoven. In this regard, an almost 64 % decrease in the thermal diffusivity was achieved with 66 wt% silica aerogel.     

Study on the creep and recovery behaviors of UHMWPE/CNTs composite fiber

The creep and recovery behaviors of UHMWPE and UHMWPE/CNTs composite fibers at different temperature were studied using Dynamic Mechanical Analysis (DMA). It was found that the creep strain of the UHMWPE and the UHMWPE/CNTs fibers increased with temperature rising. And creep strain of the composite fibers was always lower than that of the neat UHMWPE fiber. Burger’s model and Weibull distribution are employed to simulate the creep and recovery behaviors of the two fibers. The results show elasticity, stiffness and the recovery property of the composite fiber were improved by adding multi walled carton nanotubes.     

Preparation and flammability properties of hybrid materials containing phosphorous compounds via sol-gel process

Organic-inorganic hybrid coatings containing phosphoric acid (PA) bonded to the organic-inorganic network were prepared from tetraethoxysilane (TEOS) using a sol-gel process. The effect of sol-gel phosphate-based flame retardant coating on polyacrylonitrile fabric properties (flammability, stiffness, and strength) was investigated. Sample characterization of the coated samples were investigated using differential thermal/thermogravimetric analysis (DTA/TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD), and scanning electron microscopy (SEM). The results showed that hybrid coating on the polyacrylonitrile fabrics influenced fabric stiffness, strength, and flammability. And also, flammability of the coated samples after washing cycles was investigated, and the flame retardancy properties of the samples after 10 repeated washings were not completely lost.     

Hybrid multi-scale basalt fiber-epoxy composite laminate reinforced with Electrospun polyurethane nanofibers containing carbon nanotubes

In this study, we report the fabrication and evaluation of a hybrid multi-scale basalt fiber/epoxy composite laminate reinforced with layers of electrospun carbon nanotube/polyurethane (CNT/PU) nanofibers. Electrospun polyurethane mats containing 1, 3 and 5 wt% carbon nanotubes (CNTs) were interleaved between layers of basalt fibers laminated with epoxy through vacuum-assisted resin transfer molding (VARTM) process. The strength and stiffness of composites for each configuration were tested by tensile and flexural tests, and SEM analysis was conducted to observe the morphology of the composites. The results showed increase in tensile strength (4–13 %) and tensile modulus (6–20 %), and also increase in flexural strength (6.5–17.3 %) and stiffness of the hybrid composites with the increase of CNT content in PU nanofibers. The use of surfactant to disperse CNTs in the electrospun PU reinforcement resulted to the highest increase in both tensile and flexural properties, which is attributed to the homogeneous dispersion of CNTs in the PU nanofibers and the high surface area of the nanofibers themselves. Here, the use of multi-scale reinforcement fillers with good and homogeneous dispersion for epoxy-based laminates showed increased mechanical performance of the hybrid composite laminates.     

Influence of N-, P- and Si-based Flame Retardant Mixtures on Flammability,Thermal Behavior and Mechanical Properties of PA6 Composite Fibers

This research investigated the influence of two flame retardant (FR) mixtures consisting melamine cyanurate (MeCy) and aluminum diethylphosphinate (AlPi), and MeCy and sodium aluminosilicate (SASi) at different weight ratios, on the flammability, thermal behavior and mechanical properties of polyamide 6 (PA6) composite yarns produced by meltspinning. The morphological and chemical properties of PA6/FR filaments were investigated by scanning electron microscopy and Fourier-transform infrared spectroscopy, flame retardancy by vertical burning test UL-94, thermal behavior by thermogravimetric and differential scanning calorimetric analyses, and mechanical properties by tensile tests. The results indicate that within the UL 94 V2 rating, the composite yarns differed significantly from each other in their burning and dripping behavior. The incorporation of both mixtures, MeCy+AlPi and MeCy+SASi, into the PA6/FR yarns significantly decreased the afterflame time relative to pristine PA6, confirming a lower production of flammable volatiles. This phenomenon was attributed mainly to MeCy, which caused an immediate extinguishment of the flame after the withdrawal of the igniting flame. Compared to one component MeCy, the incorporation of the MeCy+SASi mixture enhanced the thermooxidative stability of the PA6/FR yarns because of their additive effect at higher concentrations. In contrast, an antagonistic effect was obtained for the MeCy+AlPi mixture, irrespective of the concentration. Since the incorporation of MeCy+SASi did not drastically reduce the tensile properties of filaments, this mixture enables the production of the PA6/MeCy+SASi composite yarns with the enhanced flame retardancy and thermo-oxidative stability.     

Influence of alkaline metal ions on flame retardancy and thermal degradation of cellulose fibers

Cellulose-Na and cellulose-K fibers are obtained by alkalization and etherification of viscose fiber. Flame retardancy and thermal degradation of cellulose-Na and cellulose-K fibers are investigated using limiting oxygen index (LOI), cone calorimetry (CONE), thermal gravimetry (TG), and differential TG (DTG). The LOI values of cellulose-Na and cellulose-K fibers are 33 and 30, compared with about 20 for viscose fiber. In CONE studies, cellulose-Na and cellulose-K fibers show much lower heat release rates, total heat release and effective heats of combustion than viscose fiber does. In addition, TG and DTG studies reveal that the second initial degradation temperature, the temperature of maximum degradation rate and the maximum degradation rate for cellulose-Na and cellulose-K fibers are much lower than those of viscose fiber. Cellulose-Na and cellulose-K fibers generate much more residue or carbonaceous char than viscose fiber does. Scanning electron microscopy studies of combustion residues after LOI testing indicate that cellulose-Na and cellulose-K fibers produce massive, thick residue crusts.     

Evaluation of procedures to quantify solvent retention in electrospun fibers and facilitate solvent removal

Electrospun fiber scaffolds crafted from polyesters are studied extensively for potential tissue engineering applications. For translation of electrospun fibers into the clinic, the FDA requires analysis and quantification of any organic solvent that may be retained in the fibers since many organic solvents can negatively affect cells and tissues. If a significant amount of solvent is retained, then developing procedures for efficient solvent removal may enhance the clinical potential of these materials. In this study we use fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and nuclear magnetic resonance spectroscopy (NMR) to analyze solvent retention. A correlative analysis shows that both FTIR and TGA accurately predicted retention of two different solvents (HFP and chloroform) in our electrospun PLLA scaffolds, thus validating these procedures. We also assess the efficacy of various fiber treatment methods to facilitate organic solvent removal and conclude that submersion in 70 % ethanol and heat treatment at 100 °C were the most efficient methods of removing solvent from electrospun PLLA fibers.     

Nanocellulose reinforced PVA composite films: Effects of acid treatment and filler loading

Nanocellulose was prepared by acid hydrolysis of microcrystalline cellulose (MCC) at different hydrobromic acid (HBr) concentrations. Polyvinyl alcohol (PVA) composite films were prepared by the reinforcement of nanocellulose into a PVA matrix at different filler loading levels and subsequent film casting. Chemical characterization of nanocelluloses was performed for the analysis of crystallinity (X_c), degree of polymerization (DP), and molecular weight (M_w). The mechanical and thermal properties of the nanocellulose reinforced PVA films were also measured for tensile strength and thermogravimetric analysis (TGA). The acid hydrolysis decreased steadily the DP and M_w of MCC. The crystallinity of MCC with 1.5 M and 2.5 M HBr showed a significant increase due to the degradation of amorphous domains in cellulose. Higher crystalline cellulose showed the higher thermal stability than MCC. From X-ray diffraction (XRD) analysis, nanocellulose samples showed the higher peak intensity than MCC cases. Reduction of MCC particle by acid hydrolysis was clearly observed from scanning electron microscope (SEM) images. The tensile and thermal properties of PVA composite films were significantly improved with the increase of the nanocellulose loading.     

Synthesis,analysis and simulation of carbonized electrospun nanofibers infused carbon prepreg composites for improved mechanical and thermal properties

This paper reports the fabrication, characterization and simulation of electrospun polyacrylonitrile (PAN) nanofibers into pre-impregnated (prepreg) carbon fiber composites for different industrial applications. The electrospun PAN nanofibers were stabilized in air at 270 °C for one hour and then carbonized at 950 °C in an inert atmosphere (argon) for another hour before placing on the prepreg composites as top layers. The prepreg carbon fibers and carbonized PAN nanofibers were cured together following the prepreg composite curing cycles. Energy dispersive X-ray spectroscopy (EDX) was carried out to investigate the chemical compositions and elemental distribution of the carbonized PAN nanofibers. The EDX results revealed that the carbon weight % of approximately 66 (atomic % 72) was achieved in the PAN-derived carbon nanofibers along with nitrogen and lower amounts of nickel, oxygen and other impurities. Thermomechanical analysis (TMA) exhibited the glass transition regions in the prepreg nanocomposites and the significant dependence of coefficient of thermal expansion on the fiber directions. The highest value of coefficient of thermal expansion was observed in the temperature range of 118-139 °C (7.5×10^-8 1/°C) for 0 degree nanocomposite scheme. The highest value of coefficient of thermal expansion was observed in the temperature range of 50-80 °C (37.5×10^-6 1/°C) for 90 degree nanocomposite scheme. The test results were simulated using ANSYS software. The test results may be useful for the development of structural health monitoring of various composite materials for aircraft and wind turbine applications.     

Studies of electrospinning process of zirconia nanofibers

Eletriospinning process was used to fabricate Zirconia nanofibers and polyvinyl pyrrolidone (PVP) was employed in this procedure. SEM, TGA, FT-IR and XRD were used to investigate the electrospinning process. Pure PVP was electrospun at the same conditions as comparisons. The results indicated that the fibers had an average diameter about 80 nm with smooth surface. FT-IR spectrum and TGA curve proved that PVP was removed from the fibers after a thermal treatment. It was found that the crystal structure of Zirconia changed at different calcination temperature. The use of PVP, bicomponent solvent of water and ethanol and inorganic salt had positive effects on the morphology of the fibers.     

Effects of Chemical Functionalization of MWCNTs on the Structural and Physical Properties of Elastomeric Copolyetherester-based Composite Fibers

Elastomeric copolyetherester (CPEE)-based composite fibers incorporating various neat and functionalized multiwalled carbon nanotubes (MWCNTs) were prepared through a conventional wet-spinning and coagulation process. The influence of functionalized MWCNTs on the morphological features, and the thermal, mechanical properties and electrical conductivity of CPEE/MWCNT (80/20, w/w) composite fibers were investigated. FE-SEM images show that a composite fiber containing poly(ethylene glycol)-functionalized MWCNTs (MWCNT-PEG) has a relatively smooth surface owing to the good dispersion of MWCNT-PEGs within the fiber, whereas composite fibers including pristine MWCNTs (p-MWCNT), acid-functionalized MWCNTs (a-MWCNT), and ethylene glycol-modified MWCNTs (MWCNT-EG) have quite a rough surface morphology owing to the presence of MWCNT aggregates. As a result, the CPEE/MWCNT-PEG composite fiber exhibits noticeably increased thermal and tensile mechanical properties as well as a faster crystallization behavior, which stems from an enhanced interfacial interaction between the CPEE matrix and MWCNT-PEGs.     

Effect of inorganic fillers and ammonium polyphosphate on the flammability,thermal stability,and mechanical properties of abaca-fabric/vinyl ester composites

In order to comply with the safety environment requirements, this research is being carried out for reinforcing inorganic additives to improve fire retardancy of composite. In the present study, abaca fabric/vinyl ester (AF/VE) composites were prepared by vacuum assisted resin transfer (VARTM) molding process. For improving flame retardant property of the composites, three different types of halogen free inorganic fillers, i.e. nano-clay (NC), halloysite nanotubes (HNT) and ammonium polyphosphate (APP) were used. The flammability, thermal stability and mechanical properties of composites have been investigated by Horizontal burning test, Thermogravimetric analysis (TGA), tensile, and flexural test respectively. FESEM was used to observe the morphology of the fractured surface of the tensile specimens. Taguchi method was used to optimize the process and minimize the number of experiments for fillers addition. The results showed that the flame retardancy and thermal stability increased with increasing percentage of fillers, but mechanical properties slightly decreased simultaneously.