Effect of Post-spinning Modification on the PAN Precursors and Resulting Carbon Fibers

The impregnation of a special grade PAN precursor,fibers wus carried out in a 8 wt% KMnO4 aqueous solution to obtain modified PAN precursor fibers. The effects of modification on the chemical stncture and the mechanical properties of precursor fibers thermally stabilized and their resulting carbon fibers u＇ere characterized by the combiination use of densities, wide-angle X-ray diffraction （WAXD）, X-ray photoelectron speetroscopy （XPS）, elemental analysis （ EA ）, Fourier traasform infrared spectroscopy （FT-IR） and scanning electron microscope （SEM）, etc.KMnO4 as a strong oxidizer can swell, oxidize and corrode the skin of a precursor.fiber, and transform C≡N groups to C≡N ones, meamchile , it can decreuse the crystal .size increuse the orientation index and the costallinity index, furthermore it can increuse the densities of modified PAN precursors and resuhing thermally stabilized fibers. As a result, the carbon fibers developed from modified PAN fibers show an improvement in tensile strength of 31.25 % and an improvement in elongation of 77.78 % , but a decrease of 16. 52% in Young＇s modulus.

Comparative Study on Preparing Carbon Fibers Based on PAN Precursors with Different Comonomers

Two different PAN precursors with various comonomers were wet-spun. The properties and structurul changes of PAN precursors and their evolution during preoxidation and carbonization process were characterized by the use of DSC , FTIR and traditional parameters, e g, tensile strength. It is demonstrated that acrylamide（ AAM ） is very effective to make the DSC peak be separated compared to methyl acrylate （ MA ）. As a result, carbon fibers developed from AAM-contained precursors have a better tenacity compared to those developed from MAcontained ones.

Comparison of Structure and Properties among Various PAN Fibers for Carbon Fibers

To find out the high-quality polyacrylonitrile (PAN) fibers, some differences are sought by comparing domestic PAN fibers with the foreign ones. X-ray diffractometer (XRD), transmission electron microscope (TEM), Fourier transform infrared (FT-IR) spectrometer, elemental analyzer, tensile-testing machine and high-temperature differential scanning calorimeter (DSC) are used to characterize the individual microstructure, chemical structure, elemental content, mechanical properties and thermal properties. It is found that high-quality PAN fibers have high density, lower titre, higher or adequate tensile strength, and they also have better conglomeration structure, smaller crystal dimension with dispersive distribution, less microvoids and flaws.

DSC Study on the Polyacrylonitrile Precursors for Carbon Fibers

Different polyacrylonitrile （PAN） precursor fibers that displayed various thermal properties were studied by using differential scanning calorimetry （DSC）. Results showed that some commercial PAN precursor fibers displayed double separated peaks and these fibers were of high quality because of their process stability during their conversion to carbon fibers of high performance. Some fabrication processes, such as spinning, drawing, could not apparently change the DSC features of a PAN precursor fiber. It was concluded that the thermal properties of a PAN precursor fiber was mainly determined from its comonomer content type and compositions.

Effect of UV Irradiation on PAN Precursor Fibers and Stabilization Process

A low-cost rout for modification the polyacrylontrile（PAN） precursor fibers was developed.The approach involved pretreatment PAN precursor fibers with UV irradiation for various periods of time before the fibers were stabilized.The effect of UV irradiation on the chemical structure,orientation factor,density,crystallite size and morphology of the fibers in the process of stabilization was characterized by use of fourier transform infrared spectroscopy（FTIR）,float-sink procedure,X-ray diffraction（XRD）,scanning electron microscope（SEM）,respectively.The results showed that UV irradiation could increase the density of the fibers in stabilization process.FTIR analysis indicated that the cyclization of nitrile groups was initiated at room temperature by UV irradiation.The transformation of C≡N groups to C=N ones was accelerated in the process of stabilization.The orientation factor of irradiated fibers was also increased.The crystallite size was decreased at first and increased later,and the better irradiation time of UV was 3 min according to the XRD test.SEM analysis indicated that irradiation could decrease the internal and surface defects of the stabilized fibers treated at 300 ℃.

Deformation Resistance Effect of PAN-based Carbon Fibers

The deformation resistance effect of polyacrylonitrile （PAN）-based carbon fibers was investigated, and the variatipn law of electrical resistivity under tensile stress was analyzed. The results show that the gauge factor （fractional change in resistance per unit strain） of PAN-based carbon fibers is 1.38, which is lower than that of the commonly-used resistance strain gauge. These may due to that the electrical resistivity of carbon fibers decreases under tensile stress. In addition when the carbon fibers are stretched, the change of its resistance is caused by fiber physical dimension and the change of electric resistivity, and mainly caused by the change of physical dimension. The mechanical properties of carbon fiber monofilament were also measured.

Catalytic graphitization of Mo-B-doped polyacrylonitrile(PAN)-based carbon fibers

A novel carbon fiber pretreatment was proposed.Polyacrylonitrile(PAN)-based carbon fibers were first anodized in H3PO4 electrolyte to achieve an active surface,and then coated with Mo-B catalysts by immersed the carbon fibers in a uniformly dispersed Mo-B sol.The as-treated carbon fibers were then graphitized at 2 400 ℃ for 2 h.The structural changes were characterized by X-ray diffractometry(XRD),Raman spectroscopy,scanning electron microscopy(SEM) and high-resolution transmission electronic microscopy(HRTEM).The results show that much better graphitization can be achieved in the presence of Mo-B,with an interlayer spacing(d002) of 0.335 8 nm and a crystalline size(Lc) of 28 nm.

Effect of Electrochemical Treatment in Aqueous Ammonium Bicarbonate on Surface Properties of PAN-based Carbon Fibers

The surface properties of PAN-based carbon fibers electrochemically treated in aqueous ammonium bicarbonate before and after treatment were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Dynamic Contact Angle Analysis (DCAA). The results of characterization indicated that the oxygen and nitrogen contents in carbon fiber surface were significantly increased by electrochemical treatment, and amide groups was introduced onto it, which was related with the electrolyte. The AFM photographs illustrated that the roughness of the fiber surface was also increased. The wettibality of the fibers was improved after treatment because the surface energy especially the polar part of it was increased.

THE CONVERSION OF PAN-BASED STABILIZED FIBER TO CARBON FIBER

When the PAN-based stabilized fiber(PAN-SF) was converted to the carbon fiber, the effect of some of the carbonizing parameters on the structure and properties of the resulting carbon fibers, such as the molecular structure development, element contents, morphology and mechanical properties, was discussed. The results show that the carbonizing temperature, the purity of the inert gas and the de-oil pretreatment of the tiber have a great influence on them.

New Evaluation on the Preoxidation Extent of Different PAN Precursors

Structural changes in carbon fibers at each stage of, especially, preoxidation process are well known to play a great role in achieving the ultimate product quality. Differential scanning calorimetry (DSC), scanning electron microscope (SEM), density method and optical microscope were used to characterize the preoxidation extent. A conventional approach, e.g., density aim, to evaluate the extent of preoxidation is not very exact. A DSC curve of a PAN precursor only can provide general information, major in the temperature regime of preoxidation reaction. However, the evaluation of a preoxidation extent, especially from conventional preoxidation temperature with a great span regime of 200~400癈, is put forward in this paper, in which the evolution of core/shell morphological structure is a kind of straightforward evidence.

Surface State of Carbon Fibers Modified by Electrochemical Oxidation

Surface of polyacrylonitrile (PAN)-based carbon fibers was modified by electrochemical oxidation. The modification effect on carbon fibers surface was explored using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Results showed that on the modified surface of carbon fibers, the carbon contents decreased by 9.7% and the oxygen and nitrogen contents increased by 53.8% and 7.5 times, respectively. The surface roughness and the hydroxyl and carbonyl contents also increased. The surface orientation index was reduced by 1.5% which decreased tensile strength of carbon fibers by 8.1%, and the microcrystalline dimension also decreased which increased the active sites of carbon fiber surface by 78%. The physical and chemical properties of carbon fibers surface were modified through the electrochemical oxidative method, which improved the cohesiveness between the fibers and resin matrix and increased the interlaminar shear strength (ILSS) of carbon fibers reinforced epoxy composite (CFRP) over 20%.

Effects of Pre-oxidation Conditions on Adsorption Performance of Activated Carbon Fibers

In order to investigate the effects of pre-oxidation conditions on adsorption performance of activated carbon fibers ( ACFs) ,electrospun polyacrylonitrile ( PAN) fiber webs were adopted as precursors for preparing ACFs. Firstly,the webs were stabilized under different pre-oxidation conditions; secondly,the pre-oxidative fibers were chemically activated by high temperature treatment in nitrogen. Pre-oxidation temperature,heating rate,and treatment time are the main factors on affecting the adsorption performance of the ACFs. Scanning electron microscope ( SEM) , differential scanning calorimeter ( DSC ) ,and Fourier transform infrared spectroscopy ( FTIR ) were used to characterize the structure and property of the pre-oxidative fibers,and the dynamic benzene adsorption capacity of benzene of ACFs was measured. The results indicate that the moderate pre-oxidation condition is necessary to prepare the ACFs with better adsorption capacity,and the optimal oxidation conditions are to increase from room temperature to 230 ℃ with a heating rate of 0. 75 ℃·min - 1 ,held at the peak temperature for 30 min.

Stress and Strain During the Process of Thermal Stabilization of Modified Pan Precursors

Thermal mechanical analysis,FT-IR,WAXD and some conventional measurements,such as densities and mechanical properties,were used to characterize the effect of the modification using KMnO4 and SnCl4 on the thermal mechanical behaviors and structural changes during the process of thermal stabilization of modified PAN precursors.Compared to the unmodified original PAN precursors,some conclusions were drawn that the thermal stabilization starts at a lower temperature for modified PAN fibers,for example,the peak of thermal stress changes for modified PAN precursors using KMnO4 displays a decrease of 20℃ and a increase of 30% in the ultimate thermal stress,that chemical modification makes structural transformation perfect and increases by 25% of the thermal stress at the temperature range of 230℃-300℃,that the modified PAN fibers display an increase of 100% in the thermal strain,once after pre-oxidized,show an increase of 7.8% in orientation index,and a decrease of 9.9% in crystal size for identical preload in the region of 13.1-14.5MPa.It was also concluded that the modification using SnCl4 would alleviate the changes in physical and chemical stress regimes and result in improvement in structure and decrease in defects.

Characterization of the nanopore structures of PAN-based carbon fiber precursors by small angle X-ray scattering

The nanopore structures in precursors Four carbon-fiber precursors are prepared. They are crucial to the performance of PAN-based carbon fibers are bath-fed filaments （A）, water-washing filaments （B） hot-stretching filaments （C） and drying-densification filaments （D）. Synchrotron radiation small angle X-ray scattering is used to probe and compare the nanopore structures of the four fibers. The nanopore size, discrete volume distribution, nanopore orientation degree along the fiber axis and the porosity are obtained. The results demonstrate that the nanopores are mainly formed in the water-washing stage. During the processes of the subsequent production technologies, the slenderness ratio of nanopores and their orientation degree along the fiber axis increase further and simultaneously, the porosity decreases. These results are helpful for improving the performance of the final carbon fibers.

Activated Carbon Precursors Derived from Jute Fiber:Social,Eco­nomic and Environmental Development

Activated carbon fiber(ACF)is undoubtedly one of the most significant carbon nanocomposite materials to consider from the perspective of application in adsorption.Compared to other commercial porous storage materials,it offers many benefits.With a fiber-like shape and a clearly defined porosity structure,activated carbon fiber(ACF)is a potential microporous material.In general,synthetic carbon fiber(CF)can be used to commercially make ACF with the inclusion of an activation procedure.High packing density,outstanding volumetric capacity,rapid adsorption/desorption,and ease of handling are some of the unique properties of ACF.The production expenses of ACF are made up of fiber processing costs and activation costs,both of which are comparatively more expensive than those of other activated carbons.Recently,researchers have indicated that the manufacturing of ACF from less expensive precursors might be accomplished by preparing activated carbon(AC)from agricultural wastes.In comparison to synthetic ACF,there were fewer details and publicly accessible sources of information about these natural fiber derived ACF.The cost of processing fiber is higher and shaping fiber into the correct shape is challenging.In this study,social and environmental compliance,economic development,advantages of carbon fiber,and applications of carbon fiber are discussed.

凝固浴牵伸对微纳层叠带状PAN原丝性能的影响

采用新型微纳层叠挤出技术制备了层叠带状聚丙烯腈(PAN)碳纤维原丝,利用扫描电子显微镜、X射线衍射仪、万能材料试验机和差示扫描量热仪对原丝的性能进行表征,研究了不同凝固浴牵伸倍数对微纳层叠带状PAN原丝截面形态、结晶性能、力学性能以及热行为的影响。研究结果表明,随着凝固浴牵伸倍数的提高,层叠带状PAN原丝的厚度显著减小,线密度显著降低;层叠带状PAN原丝的结晶度和拉伸强度随着牵伸倍数的提高呈现先增加后减小的趋势,凝固浴牵伸倍数为5.5倍时,获得的层叠带状PAN原丝的性能较好。当凝固浴牵伸倍数从5.5倍增加至6.5倍时,原丝的拉伸强度由26.08 MPa降低至23.36 MPa。实验结果表明,凝固浴牵伸倍数为5.5倍下制备的层叠带状PAN原丝具有较好的综合性能,其结晶度为39.1%,拉伸强度和拉伸模量分别为26.08及661 MPa。

Evolution of the composition and structure of PAN carbon fiber during preoxidation

Using scanning electronic microscope, X-ray diffraction analysis, PYR-GCMS and IR etc., we studied the evolving process of the composition and structure of PAN carbon fiber during preoxidation. In the initial stage of preoxidation, PAN filament tows disappear and become semi-thaw. At first, reactions happen between the copolymers and esters disappear. The molecules annularly crosslink and the index of cyclation slowly increases. It is easy to fix the structure and form defects during the initial and the medium stages, which are most reactive. More traction is advised in these stages to minimize the structural deficiencies. In the medium stage of preoxidation, the fiber was reshaped into new sheet stacks and gradually changed to sheet sectors, and this structure tends to be stable in the final stage. Induced by acid and ester copolymer, PAN fiber forms a very stable cycle structure in the final stage. Besides, monomer, dimmer and trimer obviously decrease. In the final stage of the preoxidation, there exists only the fragment of -CN, and it also disappears at last. The index of cyclation rises with the process of preoxidation and the structural shape stabilizes.

KH-560处理时间对PAN基碳纤维沥青复合材料性能的影响

以硅烷偶联剂KH-560改性的PAN基碳纤维为添加材料,制备了不同KH-560处理时间的PAN基碳纤维沥青复合材料。通过车辙试验、冻融劈裂试验和间接拉伸疲劳试验等研究了KH-560处理时间对沥青复合材料高温稳定性、低温抗裂性、水稳定性、疲劳性能和吸声性能的影响。结果表明,经过KH-560处理后的PAN基碳纤维表面的粗糙度增加,当KH-560处理时间为2 h时,纤维凹槽较深,与沥青的作用面积增大,纤维在复合材料中形成了致密网状结构,增强了PAN基碳纤维复合材料的稳定性。当KH-560处理时间为2 h时,PAN基碳纤维沥青复合材料的高温性能、低温抗裂性能、水稳定性和疲劳性能均最佳,此时其45和60 min的变形量、破坏劲度模量达到最小值,分别为1.851和2.117 mm、2 201 MPa;动稳定度、劈裂抗拉强度和破坏拉伸应变达到最大值,分别为3 077次/mm、4.6 MPa和3479με。在250~1 000 Hz和1 000~1 600 Hz范围内,当KH-560处理时间为2 h时,沥青复合材料的平均吸声系数均达到最大值,分别为0.116和0.127,较未处理的沥青复合材料分别提高了39.76%和45.98%,吸声降噪性能提升显著。综上可知,KH-560的最佳处理时间为2 h。

PAN基碳纤维复合混凝土的制备及氯离子渗透性的影响

以聚丙烯腈(PAN)基碳纤维为无机填料,制备了PAN基碳纤维复合混凝土,研究了PAN基碳纤维掺量对混凝土力学性能、耐磨性能、抗冻性能等的影响。结果表明,PAN基碳纤维的添加加速了水化反应的进行,减少了混凝土结构中的孔隙数量,提高了混凝土的密实度。复合混凝土的抗压强度和抗折强度随PAN基碳纤维掺杂量的增大而先增大后减小,养护28 d,当PAN基碳纤维的掺杂量为0.8%(质量分数)时,抗压强度和抗折强度达到最大值,分别为50.73和5.58 MPa,这是由于PAN基碳纤维的添加使砂浆与集料之间的结合强度增加所致。养护28 d,当PAN基碳纤维的掺杂量为0.8%(质量分数)时,复合混凝土的单位面积磨损量最小为0.95 kg/m^(2),单位面积磨损量降低率最大为55.81%,冻融循环100次时质量损失率最低为1.14%,相对动弹性模量最高达95.03%,复合混凝土的氯离子扩散系数最低为8.1×10^(-8)cm/s,具有优异的抗冻性能和抗氯离子侵蚀能力。

采用夹压法预氧化工艺提高PAN碳纤维超电性能的研究

通过静电纺丝技术得到的聚丙烯腈(PAN)碳纤维作为超级电容器电极材料时,其比容量较低.为提高其性能,开发了一种陶瓷板夹压法预氧化工艺,使得PAN碳纤维的比容量迅速提升.首先采用静电纺丝技术制成PAN纤维膜,将粗细均匀的纤维膜在不同温度下采用陶瓷板夹压法进行预氧化,后经800℃碳化制得碳纤维.探究预氧化温度对碳纤维的形貌、微观结构、电化学性能的影响.实验结果表明,经260℃预氧化得到的碳纤维的电化学性能优异,在1 A/g的电流密度下的比电容可高达286.5 F/g,比传统的直接煅烧方法得到的PAN碳纤维的比容量高2倍.且在2 A/g的电流密度下循环800次,其比电容依旧保持100%.