首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Different shapes of dispersed phase such as sphere, laminar and fibrillar can form in the matrix phase of polymer blends. Production of blend fibers in melt spinning process can result more effective in fibrillar phase morphology formation than in other processes. In this research, the matrix-fibril morphology development during the melt spinning of polypropylene/poly(butylenes terephthalate) was studied. The shapes of blend dispersed phase collected from different zones of the melt spinning line were evaluated by scanning electron micrographs (SEM) and rheological mechanical spectra (RMS). The results showed that fibrillar shape could not be created in the PP/PBT blend fiber samples exited from the spinneret orifice (gravity spun fibers) at low contents (5 percent) of the PBT dispersed phase. However, a complete fibrillar structure was formed in all the as-spun PP/PBT blend fiber samples (melt drawn). The rheological evaluations confirmed a network structure resulting from fibril formation for the samples with high contents (20–40 %) of the PBT dispersed phase and the formation of spherical shape with low contents (5–10 %) of the PBT dispersed phase in matrix of the blend fibers. It was observed that the flow fields of processing zones and blend ratio, in producing the blend fibers, have intensive effects on morphological variations; besides there was a strong relation between the mechanical and morphological properties.  相似文献   

2.
Yarn structure plays an important role in determining the properties of spun yarns. Recently, a modified spinning technique has been developed for producing a low torque and soft handle singles yarn by modifying the fiber arrangement in a yarn. Comparative studies revealed that the finer modified yarns possess significantly higher strength and lower hairiness over the conventional yarns of the same twist level, implying a different structure of finer modified yarn. Thus this paper aims to quantitatively study the structures of the finer conventional and modified cotton yarn (80 Ne) produced at the same twist level. Various measuring techniques, namely the Scanning Electron Microscope (SEM), cross section technique and tracer fiber technique, are adopted to analyze their structural characteristics, including fiber configuration, fiber spatial orientation angle, fiber packing density, yarn surface appearance, and fiber migration behavior. Results showed that finer modified yarns exhibit a smoother surface and much more compact structure with less hairiness. The fibers in the finer modified yarn have a complicated fiber path with relatively lower fiber radial position, larger migration frequency and magnitudes. In addition, it was noted that 73% of fibers in the finer conventional yarn follow concentric conical helix, which is contrary to those in the coarser conventional yarn. The analyses conducted in this paper provide deep insights into the mechanism of modified spinning technique and evidential explanations on the difference of properties between the finer conventional and modified yarns.  相似文献   

3.
In this study, poly (vinylpyrrolidone-acrylonitrile-vinylpyrrolidone) (PVP-AN-VP) was synthesized by three-step solution free radical polymerization. The copolymer could be directly blended with polyethersulfone (PES) using NMP as a solvent, and then PES hollow fiber membrane was prepared by using dry-wet spinning technique based on a liquid-liquid phase separation technique. Adding the copolymer could effectively reduce the BSA adsorption and suppress the platelet adhesions. Meantime, the antifouling property of the membranes increased with the increase of the copolymer amounts. Furthermore, activated partial thromboplastin time (APTT) of the modified PES hollow fiber membrane increased by 50 % compared to that of pure PES membrane. The efficient surface modification by blending PVP-AN-VP copolymer suggested that the modified PES membrane have potential to be used in blood purification fields.  相似文献   

4.
Electrospinning is an efficient method to produce polymer fibers with a diameter range from nanometers to a few microns using an electrically driven jet. Electrospun nanofiber nonwoven fabrics can be applied into different areas with higher air volume fraction, especially applied into textile materials with good warmth retention property. In this article, the air volume fraction in nonwoven mats made of electrospun nanofibers was verified by studying fiber volume fraction in the mats. Then the relationship between fiber volume fraction and fiber diameter was derived, and the fiber volume fraction is in direct ratio to the square of fiber radius. By experimental verification, to get electrospun PAN nanofiber nonwoven mats with high air volume fraction about 99 %, it can fix the polymer concentration on 8 %. The voltage fixed on 20 kV, the tip-to-collector distance on 15 cm. The experiment is in accordance with the theory excellently.  相似文献   

5.
A cone-shape spinneret with air-suction assisted was used for the production of ultrafine fibers by melt electrospinning. The influence of the applied voltages on the number of jets and the effects of the different types of air flow (air blowing and air suction) on the fiber bundle were studied. It was demonstrated that the breadth of the diameter distribution of the fibers decreases markedly and the production rate was also improved when air suction and higher applied voltages were applied. Therefore this new melt electrostatic spinning equipment can meet the need of some special applications and industrial mass production of nanofibers.  相似文献   

6.
A series of blend nanofiber mats comprising poly(vinyl alcohol) (PVA) and polyurethane (PU) were prepared by dual-jet electrospinning in various parameters. Orthogonal experimental design was used to investigate how those parameters affected on fiber diameters and fiber diameter distribution. Altogether three parameters having three levels each were chosen for this study. The chosen parameters were tip-to-collector distance (TCD), voltage and tip-to-tip distance (TTD). Fiber diameters, thermal properties, mechanical properties and hydrophilicity of the blend nanofiber mats were examined by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), tensile test, contact angle and water absorption test, respectively. The results showed that the optimum conditions for PVA/PU blend nanofiber mats fabricated by dual-jet electrospinning were TCD of 20 cm, voltage of 18 kV and TTD of 4 cm. Besides, the thermal stability of PVA/PU blend nanofiber mats had been improved compared with pure nanofibers. Furthermore, the elongation and tensile strength of the blend nanofiber mats were significantly increased compared with pure PVA and pure PU, respectively. And the blend nanofiber mats exhibited well hydrophilicity.  相似文献   

7.
Aligned fibers in micro-/nano-scale have attracted more attention especially in tissue engineering field because cells can orientation growth along the fiber. However, it is still a huge technological challenge in achieving it as a result of the inherent bending instability of an electrospinning jet. Herein, we report a novel and simple spinning approach, in which low dielectric constant of dioxane was judiciously used as solvent for spinning dope, to obtain electrospinning jet with low induced charge, therefore eliminating electrically and aerodynamically driven bending instability, and forming a stable and low forward-moving velocity jet longer than 100 cm. This consequently allows for readily collecting and fabricating individual fibers, well-aligned ultrafine fiber arrays over large areas. Our approach has proved to be effective in preparing well-aligned ultrafine fibers from biodegradable poly(D, L-lactic acid) with different molecular mass, natural polymer acetyl cellulose and synthesized non-biodegradable polymer polystyrene.  相似文献   

8.
The application of post treatments in preparation of high flux membranes is expanding rapidly. In this work, several hybrid post treatments have been introduced and used for change in the water flux of polysulfone (PSf) hollow fiber membranes. Dry wet spinning method was employed for fabrication of PSf hollow fiber membrane from spinning dope in mass ratio of 15:5:80 of PSf/PVP-K90/NMP. The simultaneous effects of single and hybrid post treatments containing traditional hypochlorite; high pressure injection technique (HPI) of hypochlorite, hot air and hot water treatments on the morphology and water flux of fabricated hollow fibers has been investigated. AFM analysis and image processing of SEM microphotographs of hollow fibers were used for structural studies. The mechanical properties of hollow fibers as well as strain at break and strength also were studied. It was found that the pores size and surface roughness parameter of hollow fiber membranes have been increased after traditional hypochlorite, HPI technique and hot water treatments while decreased when heat treated in air. In general all the employed hybrid post treatments caused to increase in the pores size of hollow fibers although the pores size increase rate in the membranes treated by the hybrid post treatments involving hot air was much lower than the others. The mechanical properties of hollow fibers have been decreased after hybrid and single post treatments containing traditional hypochlorite, HPI technique and hot water treatment while slightly increased after post treatments containing hot air. It was stated that the fabricated PSf hollow fibers were considerably affected by the employed hybrid post treatments. This can be attributed to the combine effects of used post treatments.  相似文献   

9.
As nonwoven mats are randomly oriented fiber assemblies, the tensile strength of nonwoven mats is determined by their microstructural factors, such as fiber orientation, fiber volume fraction, and fiber-fiber contact level. The complex microstructure of nonwoven mats must be reasonably simplified to properly predict their mechanical properties within affordable efforts. In this study, a new parameter, so called contact efficiency, is defined to describe the fiber-fiber contact level of nonwoven mats. Micro X-ray computer tomography (CT) is employed to characterize the microstructure of needlepunched nonwoven mats made of polypropylene short fibers. The fiber orientation and volume fraction are obtained by analyzing 2D sectional CT image of the nonwoven mat, while the contact efficiency is determined from 3D CT image. A statistical model, developed originally for staple yarns, is modified to predict the tensile strength of the nonwoven mat using the microstructural factors obtained from CT analysis. The prediction is then compared with experiments to validate that the current model incorporating the contact efficiency is highly suitable for predicting the tensile strength of nonwoven mats.  相似文献   

10.
Solution blowing process is a new nanofiber fabricating method with high productivity. In the present study, nylon 6 nanofiber mats were solution blown and the effects of spinning conditions on nanofibers morphology were investigated. The fiber diameter ranged from 150 to 750 nm which was affected by solution concentration, gas pressure and solution feeding rate. The solution blown fibers were three-dimensional curly which made loose construction in bulk. The filtration performance of solution blown mats was evaluated. The tested solution blown nanofiber mats showed high filtration efficiency of 83.10 % to 93.45 % for 0.3 µm particles filtration and extremely low pressure drop of 15.37 to 30.35 Pa. The results indicate the solution blown nanofiber mats will find potential application of high efficiency and low resistance filter.  相似文献   

11.
We reported the controlled surface morphologies and the cell culture of polyelectrolyte multilayer coated nylon 6 fibrous mats with different number of layers. Polyelectrolyte multilayer coated nylon 6 fibers were successfully prepared by an alternative deposition of alginic acid sodium salt and chitosan via a Layer-by-Layer (LbL) electrostatic self-assembly. The surface morphology, stiffness, and hydrophilicity of polyelectrolyte multilayer coated nylon 6 fibrous mats could be finely tuned by regulating the number of polyelectrolyte nanocoating. It was observed that the morphology of polyelectrolyte multilayer coated nylon 6 fibers was uniform and smooth, indicating a dense and harder nanocoating of polyelectrolytes onto nylon 6 fibers. Compared to pure nylon 6 fibrous mat (tensile strength ～10.6±1 MPa), the tensile strength of polyelectrolyte coated nylon 6 fibrous mats was largely increased to 35.2±2 MPa for 5 bilayers coated fiber mats. In addition, it was found that at an initial stage after 1 day of cell culturing, the electrospun nylon 6 fibrous mats coated with 5 bilayer of alginic acid and chitosan show the highest cell affinity (good adhesion), while the electrospun nylon 6 fibrous mats coated with 10 bilayer show the lowest cell affinity. After cell seeding for 3 days, it was observed that rate of proliferation is enhanced by increasing the number of bilayer up to 3 bilayers (good proliferation), and then drastically decreased with further increasing the number of bilayer.  相似文献   

12.
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.  相似文献   

13.
The effect of the non-solvent spinning performance of nanofibers has not yet been clearly explained. To clarify this, nanofiber membranes were prepared using the roller electrospinning technique from polyvinyl butyral (PVB) solutions containing ethanol as a solvent and water as a non-solvent. A Hansen solubility graph was drawn to evaluate the non-solvent and solvent systems. The relationships among the presence of non-solvent additives, the properties of spinning solutions (viscosity, conductivity, and surface tension), current per one Taylor cone, spinning performance of fiber membranes and fiber morphology were studied. The experimental results of this work showed that the non-solvent system had positive effects on fiber diameter and web surface, resulting in a low diameter and bead-free surface, while also decreasing spinning performance.  相似文献   

14.
Natural fiber reinforced polypropylene (PP) biocomposites were fabricated by blending long-and-discontinuous (LD) natural fibers (NF) with LD PP fibers. Firstly, random fiber mats were prepared by mixing NFs and PP fibers using a carding process. Then, heat and pressure were applied to the mats, such that the PP fibers dispersed in the mats melted and flowed out, resulting in the formation of consolidated sheets upon subsequent cooling. The effect of the fiber volume fraction on the mechanical properties of the bio-composites was scrutinized by carrying out tensile and flexural tests and observing the interface between the fiber and matrix. It was observed that the natural LD fiber content needs to be maintained at less than the nominal fiber fraction of 40 % by weight for the composites fabricated using the current method, which is quite low compared to that of continuous or short fiber reinforced composites. The limited fiber fraction can be explained by the void content in the biocomposites, which may be caused by the non-uniform packing or the deficiency of the matrix PP fibers.  相似文献   

15.
This study is the first step to investigate usability of shape memory polyurethane (SMPU) fibers for smart garment applications. SMPU fibers were spun by wet spinning process and chemical/mechanical characterization was carried out. SMPU solutions were prepared with two different concentrations (20 % and 25 %) and three different coagulation bath concentrations (0 %, 1 % and 3 %) were used for determining optimum spinning parameters. For investigating influences of spinning process on crystal structure, mechanical, thermal and shape memory performances of fibers, X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM) and mechanical tests were conducted. DSC and DMA analysis results show that shape memory polyurethane fibers have a glass transition temperature about 35-40 oC which is suitable for body temperature. Moreover, SMPU fibers showed good tensile performance with an average tenacity of 1.38 cN/dtex and elongation at break of 350 %. Thermo mechanical test results showed that, all shape memory fibers have good shape memory effect with recovery and fixity ratios up to 91 % and 71 % respectively.  相似文献   

16.
A two step process was used for the modification of a cellulose/chitin mixed fibers: the first step was an alkali treatment with a NaOH solution (20 %), which was followed by the reaction with one of the reagents such as Nisopropylacrylamide, p-hydroxybenzoic acid, gallic acid, or eugenol. Both the samples activated with the alkali treatment and modified with chemicals were characterized by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and thermal analysis. Results revealed the morphological and structural changes of the fiber surface after the surface grafting, which significantly altered the cellulose/chitin mixed fiber properties. Thermal analysis results showed an increase in the thermal stability of the treated samples. Antioxidant activity of cellulose/chitin mixed fibers modified with phenolic compounds showed that the efficiency depends on the chemical nature of phenolic compound.  相似文献   

17.
Melt blowing is a one-step approach for manufacturing microfibrous nonwovens. In slot-die melt blowing, a pair of air jets with high velocity and temperature is applied on the polymer and attenuates the polymer in to fibers. The fiber motion which was called vibration or whipping plays a crucial role in expressing the drag mechanism. In this study, an improved Lagrangian numerical approach was utilized to simulate the fiber whipping in melt blowing. The fiber whipping simulated in this study was significantly improved compared to other previous works. Meanwhile, the fiber diameter, fiber velocity and fiber temperature below the spinneret were simulated. The numerical simulation indicated that the most attenuation of fiber diameter occurred within 0.07 m below the spinneret; the fiber velocity increased gradually while the air velocity decreased rapidly along the spinning line, and the fiber velocity exceeded the air velocity where below a critical z-position; In addition, the fiber temperature decreased tardier than the decreasing of air temperature. This study illustrated that it was important to optimal design the air flow field which was supposed to fully utilize the air velocity and temperature together. In addition, the energy saving of melt blowing deserved to be taken into consideration.  相似文献   

18.
The spinnability in pre-gelled gel spinning of polyacrylonitrile (PAN) precursor fibers was investigated. The spinning solutions were aged at 25 °C for different times prior to fiber spinning. The pre-gelled spinning solution aged for 2.5 h was much more strain hardening than the ungelled one, which can increase the spinnability of the solution. The maximum take-up velocity of the first winding roller V 1m, which reflects the spinnability of the spinning solutions, was found to be largest when the aging time was 1.5 h. The spinnability increased with the increase of the air gap length and the lengthdiameter ratio L/D of the spinnerette. Once the L/D increased beyond 15, the spinnability hardly changed. The fibers spun from the spinning solution aged for 1.5 h had the best mechanical properties and favorable structure, showing that good spinnability favors the performance increase of resultant PAN precursor fibers.  相似文献   

19.
Carbon fibers and precursor polyacrylonitrile (PAN) fibres that contain either silica or hydroxyapatite particles, imbedded during the spinning process, were studied in this paper. The modified PAN fibers were thermally stabilized using a multi-stage process in the temperature range between 150 to 280 °C in an oxidative environment. Subsequent carbonization leading to obtain carbon fibers was carried on at 1000 °C in an argon atmosphere. The changes of properties of composite precursor fibers taking place during stabilization and carbonization processes were investigated by the combination of Differential Scanning Calorimetry, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy equipped with energy dispersive X-ray spectrometer and ultrasonic methods. Mechanical properties, such as tensile strength, static Young’s modulus, elongation at fracture were analyzed at each stage of thermal stabilization process. Additionally some traditional measurements like fiber diameter and mass were studied. Ceramic powders added to the spinning solution were present also in composites fibers after stabilization and carbonization process. Such modification allows to avoid the post-treatment operations, for example by coating or covering with films, which were usually necessary in order to obtain bioactive character of implants. Modification of carbon fibers using calcium phosphate or silica can lead to the development of a new materials for the manufacturing of implants which can establish direct chemical bonds with bone tissue after implantation.  相似文献   

20.
Graft modification of collagen with acrylonitrile in concentrated aqueous solution of sodium thiocyanate (NaSCN) is developed in this paper. This modification can largely change it’s solubility in water and can be applied in fiber production. Grafting modified collagen is characterized by infrared spectrum and wide angle X-ray diffraction. Wet spinning of PAN fibers containing several content of modified collagen is performed. The tests about these fibers show that breaking strength and sonic orientation decrease as the amount of collagen is raised. The addition of collagen can largely improve the moisture regain of PAN fiber. Micro-appearance of fibers observed under scanning electron microscope (SEM) presents circular cross section and longitudinal grooves on surface, the depth of grooves increases with the increasing draw ratio.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号