Jie Liu

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Name: 刘杰; Liu, Jie

Organization: Beijing University of Chemical Technology , China

Department: Key Laboratory of Carbon Fiber and Functional Polymers

Title: (PhD)

TOPICS

Material Chemistry

Polymer

Stimuli Responsive Polymers PH Responsive Polymers Stimuli Responsive Polymers PH Responsive Polymers

Chemicals
References

Effects of carbonization tension on the structural and tensile properties of continuous bundles of highly aligned electrospun carbon nanofibers

Co-reporter:Sai Ma, Jie Liu, Meimei Qu, Xiaoxu Wang, Ruoyu Huang, Jieying Liang

Materials Letters 2016 Volume 183() pp:369-373

Publication Date(Web):15 November 2016

DOI:10.1016/j.matlet.2016.07.144

•Highly aligned carbon nanofibers were prepared under different carbonization tensions.•Mechanical and structural properties of CNFs were investigated.•Moderate tension during carbonization could increase mechanical and structural properties of CNFs.•The carbonization tension would be an important factor affecting the quality of CNFs.The ultimate goal of this study was to further improve tensile properties of continuous bundles of highly aligned carbon nanofibers. The hypothesis was that adopting moderate tension during carbonization could improve the formation and orientation of graphite crystallites, leading to increased tensile properties of carbon nanofibers. In this study, bundles consisting of highly aligned PAN copolymer nanofibers were first prepared by electrospinning and collected via a flowing water bath, followed by 3-time stretching and oxidative stabilization. The stabilized PAN nanofibers were then carbonized under tensions of 10–50 cN which corresponding to 254.7–1273.5 MPa, respectively. The effects of carbonization tension on structural and tensile properties of carbon nanofibers were investigated by WAXD, Raman spectroscopy and filament specimen methods. The results indicated that the orientation of graphite crystallites in carbon nanofibers could be improved by increasing carbonization tensions from 254.7 MPa to 509.4 MPa; and the highest tensile strength and modulus of carbon nanofibers could reach 1115 MPa and 194.5 GPa, respectively.

Effects of chemical composition and post-spinning stretching process on the morphological, structural, and thermo-chemical properties of electrospun polyacrylonitrile copolymer precursor nanofibers

Co-reporter:Jie Liu, Lizhen He, Sai Ma, Jieying Liang, Yong Zhao, Hao Fong

Polymer 2015 Volume 61() pp:20-28

Publication Date(Web):20 March 2015

DOI:10.1016/j.polymer.2015.01.063

•Three types of unidirectionally aligned PAN precursor nanofibers were prepared.•The nanofibers were prepared via electrospinning and then stretching in hot water.•Morphological, structural, and thermo-chemical properties of nanofibers were studied.•The PI-3 nanofibers would be suitable for making high-performance carbon nanofibers.Electrospun polyacrylonitrile (PAN) copolymer nanofibers (particularly those after the post-spinning stretching process) are expected to be an innovative type of precursors for making continuous carbon nanofibers with superior mechanical properties. In this study, three types of unidirectionally aligned PAN-based nanofibers including homo-PAN, binary-PAN (a PAN copolymer with itaconic acid units), and ternary-PAN (a PAN copolymer with itaconic acid and methyl acrylate units) were prepared by the electrospinning technique; thereafter, the nanofibers (in the form of bundles) were stretched into 3 times of their original lengths in hot water at 97 °C. The effects of chemical composition and post-spinning stretching process on morphological, structural, and thermo-chemical properties of these precursor nanofibers were investigated. The results indicated that, the stretched electrospun binary-PAN nanofibers possessed the most desired thermo-chemical properties, macromolecular regularity, crystal and macromolecule orientations, and dimensional stability; and thus they are suitable for the development of high-performance carbon nanofibers.

Influences of processing on the phase transition and crystallization of polypropylene cast films

Co-reporter:Meng Xu;Shijun Zhang;Jieying Liang;Hui Quan;Jianye Liu;Hongwei Shi;Dali Gao

Journal of Applied Polymer Science 2014 Volume 131( Issue 22) pp:

Publication Date(Web):

DOI:10.1002/app.41100

ABSTRACT

Phase transition and changes of properties of isotactic polypropylene (i-PP) cast films with the processing conditions have been investigated by wide-angle X-ray diffraction, two-dimensional small-angle X-ray scattering, and atomic force microscopy. It was found that chill roll temperature was a major factor, which influenced the formation of mesomorphic phase and its transition to spherulitic structure. Only mesomorphic phase was observed in the films produced under a chill roll temperature of below 40°C. When the roll temperature was increased to 60°C, mesomorphic phase coexisted with spherulitic crystal structure, and totally transformed to monoclinic structure at the roll temperature of 80°C. Differential scanning calorimetry, tensile, and optical tests were also performed on the films. The results showed that the observed structure changes were closely related to the thermal behavior, tensile, and optical properties of the PP films. The influence of die temperature on the films was also discussed, but the effect was much less than chill roll temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41100.

Effect of the oxygen-induced modification of polyacrylonitrile fibers during thermal-oxidative stabilization on the radial microcrystalline structure of the resulting carbon fibers

Co-reporter:Yan Xue, Jie Liu, Feng Lian, Jieying Liang

Polymer Degradation and Stability 2013 Volume 98(Issue 11) pp:2259-2267

Publication Date(Web):November 2013

DOI:10.1016/j.polymdegradstab.2013.08.016

The oxygen-induced modification of polyacrylonitrile (PAN) fibers during the final stage of thermal-oxidative stabilization is used to control the degree of chemical reactions and the radial structural homogeneity of fibers. A radial structure model for oxidized PAN fibers (OFs) and carbon fibers (CFs) has been established by Raman spectroscopy and wide angle X-ray diffraction. According to the model, the cross-section of OFs is divided into the internal and external regions; the oxygen-induced modification has a greater effect on the structural evolution of internal regions than that of external regions. When the oxygen volume content for the modification is 22.2%, the OFs possess the highest level value for degree of disorder (DD) in internal regions. This is inherited by the corresponding CFs with the best radial structure homogeneity and optimum mechanical properties; meanwhile, the coefficient of variation for DD is defined to characterize the radial homogeneity of CFs. The mechanism of the oxygen-induced modification demonstrates that the mechanical properties of the resulting CFs depend on the degrees of the intermolecular cyclization and oxidation which are beneficial to the decrease in CF crystallite size.

Correlative study of critical reactions in polyacrylonitrile based carbon fiber precursors during thermal-oxidative stabilization

Co-reporter:Yan Xue, Jie Liu, Jieying Liang

Polymer Degradation and Stability 2013 Volume 98(Issue 1) pp:219-229

Publication Date(Web):January 2013

DOI:10.1016/j.polymdegradstab.2012.10.018

The correlations and differences among the processes of critical reactions in polyacrylonitrile (PAN) copolymer [containing itaconic acid (IA)] [P(AN–IA)] and terpolymer [containing itaconic acid (IA) and methyl acrylate (MA)] [P(AN–IA–MA)] fibers during thermal-oxidative stabilization have been studied by the comparative method. Fourier transform infrared spectroscopy (FTIR) analyzed the chemical kinetics and structural evolution in two types of PAN precursor fibers; the results indicates that P(AN–IA) possesses lower reaction rates and higher activation energies for critical reactions compared with P(AN–IA–MA). Differential scanning calorimetry (DSC) analyses show that the thermal stability of P(AN–IA) is superior to that of P(AN–IA–MA). FTIR and DSC results demonstrate that the stabilization process of P(AN–IA) is easier to control. By solid state 13C nuclear magnetic resonance, the mechanism of critical reactions verifies that the isomerization among quasi-pyridone, hydroxyl pyridine and pyridone structures in oxidized PAN leads to the amount of resultant groups first increasing and then decreasing.

Kinetic study of the dehydrogenation reaction in polyacrylonitrile-based carbon fiber precursors during thermal stabilization

Co-reporter:Yan Xue;Jieying Liang

Journal of Applied Polymer Science 2013 Volume 127( Issue 1) pp:237-245

Publication Date(Web):

DOI:10.1002/app.37878

Abstract

The kinetics of dehydrogenation reaction and the structural evolution in polyacrylonitrile precursor fibers during thermal stabilization in air have been studied by Fourier transform infrared spectroscopy. The results indicate that, with the progress of dehydrogenation, the absorbance of methylene groups (CH₂) gradually decreases, whereas that of methine groups (CH) gradually increases. The dehydrogenation reaction in the fibers is basically completed after 20-min stabilization above 255°C. According to the Beer–Lambert law, the values of the absorbance for both CH₂ groups and the resulting CH groups have been calculated and converted into the concentration fractions of CH₂ groups via the Lorentzian multipeak fitting. According to the principles of chemical kinetics, the dehydrogenation reaction has been determined as a pseudo-second-order reaction with an activation energy of 107.6 kJ mol⁻¹. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Continuous bundles of aligned electrospun polyacrylonitrile copolymer nanofibers prepared via the flowing water bath and their morphological, structural, and componential variations during the opposite-directional diffusion process

Co-reporter:Jie Liu, Qiong Liu, Sai Ma, Jieying Liang, Xiaojing Ma, Hao Fong

Polymer 2013 Volume 54(Issue 18) pp:4987-4996

Publication Date(Web):16 August 2013

DOI:10.1016/j.polymer.2013.07.017

Continuous bundles of aligned electrospun polyacrylonitrile (PAN) copolymer nanofibers were prepared via collection with flowing water at varied temperatures. The morphological and structural properties, as well as the density and residual solvent amount, of electrospun nanofibers in different bundles were investigated. The results indicated that with the increase of water temperature, both diffusion coefficients of solvent (i.e., N,N-dimethylformamide) and non-solvent (i.e., H2O) increased; the surface roughness of nanofibers also increased, and the cross-section of electrospun nanofibers changed in shape from circular to irregular. With the decrease of water temperature from 25 to 2 °C, the average radius of gyration value (related to the average size of micro-voids in the nanofibers) decreased from 10.9 to 6.8 nm, the crystallinity value increased from 54.6% to 57.9%, and the nanofiber density increased from 1.191 to 1.202 g/cm3. It is envisioned that the continuous bundles of aligned electrospun PAN copolymer nanofibers collected with the flowing water bath at a low temperature (e.g., 2 °C) might be an innovative type of precursor for making the carbon nanofibers with superior mechanical strength.

The demonstration of a dense and stable circumferential layer in the subsurface of polyacrylonitrile fibers for carbon fibers

Co-reporter:Feng Lian;Yan Xue;Zhaokun Ma;Jieying Liang

Fibers and Polymers 2013 Volume 14( Issue 2) pp:243-249

Publication Date(Web):2013 February

DOI:10.1007/s12221-013-0243-z

The radial structure of polyacrylonitrile (PAN) copolymer fibers was investigated quantitatively by etching layer by layer in an improved permanganic etchant; meanwhile the effect of the etchant on the fiber surface was taken into consideration. The aggregated structure (crystal size, crystallinity, orientation and density) and thermal stability of each circumferential layer of PAN fibers were determined in detail according to a model proposed in the study. A denser layer with a thickness of about 1 µm was observed in the subsurface (2 µm from the PAN fiber surface), possessing a greater crystal size and crystallinity as well as a relatively higher thermal stability than other layers. This layer was considered to be a barrier for the diffusion of oxygen into PAN fibers during the stabilization and accelerated the formation of a core-shell structure in the resulting carbon fibers.

Structure and thermo-chemical properties of continuous bundles of aligned and stretched electrospun polyacrylonitrile precursor nanofibers collected in a flowing water bath

Co-reporter:Jie Liu, Gui Chen, Hui Gao, Lifeng Zhang, Sai Ma, Jieying Liang, Hao Fong

Carbon 2012 Volume 50(Issue 3) pp:1262-1270

Publication Date(Web):March 2012

DOI:10.1016/j.carbon.2011.10.046

Continuous bundles of aligned and stretched electrospun polyacrylonitrile (PAN) precursor nanofibers were prepared in an attempt to develop carbon nanofibers with superior strength. The bundles were prepared through collection of electrospun nanofibers with a flowing water bath followed by stretching in water at 97 °C. Their morphologies, structures, and thermo-chemical properties were characterized by SEM, XRD, and DSC. The shrinkages in boiling water and the amounts of residual solvent were also measured. The results indicated that, the nanofibers in the bundles were uniform with smooth surfaces and small variations in diameters; after stretching the bundles by 4 times, the average fiber diameter was reduced to 56%, while the crystallinity of PAN was improved by 72%. The post-spinning stretching process facilitated the stabilization of PAN, as evidenced by the shift of the cyclization reaction to a lower temperature with smaller activation energy and larger enthalpy change. In comparison with the commonly adopted nanofiber collection method of a rotating drum, the flowing water bath method results in higher degree of uni-axial alignment and more desired structures of nanofibers.

Stretching-induced deformation of polyacrylonitrile chains both in quasicrystals and in amorphous regions during the in situ thermal modification of fibers prior to oxidative stabilization

Co-reporter:Feng Lian, Jie Liu, Zhaokun Ma, Jieying Liang

Carbon 2012 Volume 50(Issue 2) pp:488-499

Publication Date(Web):February 2012

DOI:10.1016/j.carbon.2011.09.003

In situ thermal stretching to modify the conformation of polyacrylonitrile (PAN) chains in quasicrystals and amorphous regions is carried out on PAN copolymer fibers prior to oxidative stabilization. Meanwhile, a model to evaluate the deformation of PAN quasicrystals and amorphous regions is proposed, in which deformation behavior (orientation or extension) and type (elastic or plastic) in the two regions are analyzed. PAN chains exhibit various deformations as a consequence of combined thermal treatment and mechanical stretching. The orientation of PAN chains occurs prior to their extension when the stretching ratio is under 1.06, however, no significant orientation but extension is observed when the deformation ratio ranges from 1.08 to 1.16. As the stretching ratio increases, elastic-dominated orientation of PAN chains is stronger in quasicrystals before 1.03 and is prominent in amorphous regions between 1.04 and 1.08. The mechanical properties of the resulting carbon fibers strongly depend on the orientation degree of PAN chains in amorphous regions.

Effects of deformation-induced orientation on cyclization and oxidation of polyacrylonitrile fibers during stabilization process

Co-reporter:Jie Liu 刘杰;Feng Lian;Zhao-kun Ma;Jie-ying Liang

Chinese Journal of Polymer Science 2012 Volume 30( Issue 6) pp:786-795

Publication Date(Web):2012 November

DOI:10.1007/s10118-012-1165-8

Orientation of copolymer polyacrylonitrile (PAN) chains during their deformation prior to stabilization and the further effect on the stabilization were investigated in detail. Results reveal that the orientation of PAN chains presents a saturation point of 69.51% when the deformation ratio reaches approximately 1.07, meanwhile the cyclization rather than the oxidation has a stronger dependence on the orientation of PAN chains during stabilization. The cyclization is facilitated that the cyclization degree is increasing while the activation energy is decreasing obviously as a consequence of the developing orientation of PAN fibers before the saturation point; however, it is restrained during the further deformation of PAN fibers after the point. The resulting carbon fibers obtained from the PAN fibers prepared at the saturation point possess the highest mechanical properties of 4.07 GPa in tensile strength and 249.0 GPa in tensile modulus.

Biomorphic silicon/silicon carbide ceramics from birch powder

Co-reporter:Zili Yan, Jie Liu, Jianchun Zhang, Tian Ma, Zhengcao Li

Ceramics International 2011 Volume 37(Issue 3) pp:725-730

Publication Date(Web):April 2011

DOI:10.1016/j.ceramint.2010.09.045

Abstract

A novel process has been developed for the fabrication of biomorphic silicon/silicon carbide (Si/SiC) ceramics from birch powder. Fine birch powder was hot-pressed to obtain pre-templates, which were subsequently carbonized to acquire carbon templates, and these were then converted into biomorphic Si/SiC ceramics by liquid silicon infiltration at 1550 °C. The prepared ceramics are characterized by homogeneous microstructure, high density, and superior mechanical properties compared to biomorphic Si/SiC ceramics from birch blocks. Their maximum density has been measured as 3.01 g/cm³. The microstructure is similar to that of conventional reaction-bonded silicon carbide. The Vicker's hardness, flexural strength, elastic modulus, and fracture toughness of the biomorphic Si/SiC were 19.6 ± 2.2 GPa, 388 ± 36 MPa, 364 ± 22 GPa, and 3.5 ± 0.3 MPa m^1/2, respectively. The outstanding mechanical properties of the biomorphic Si/SiC ceramics are assessed to derive from the improved uniform microstructure of the pre-templates made from birch powder.

Investigation of post-spinning stretching process on morphological, structural, and mechanical properties of electrospun polyacrylonitrile copolymer nanofibers

Co-reporter:Chuilin Lai, Ganji Zhong, Zhongren Yue, Gui Chen, Lifeng Zhang, Ahmad Vakili, Ying Wang, Lei Zhu, Jie Liu, Hao Fong

Polymer 2011 Volume 52(Issue 2) pp:519-528

Publication Date(Web):21 January 2011

DOI:10.1016/j.polymer.2010.11.044

Electrospun polyacrylonitrile (PAN) copolymer nanofibers with diameters of ∼0.3 μm were prepared as highly aligned bundles. The as-electrospun nanofiber bundles were then stretched in steam at ∼100 °C into 2, 3, and 4 times of the original lengths. Subsequently, characterizations and evaluations were carried out to understand morphological, structural, and mechanical properties using SEM, 2D WAXD, polarized FT−IR, DSC, and mechanical tester; and the results were compared to those of conventional PAN copolymer microfibers. The study revealed that: (1) the macromolecules in as-electrospun nanofibers were loosely oriented along fiber axes; although such an orientation was not high, a small extent of stretching could effectively improve the orientation and increase the crystallinity; (2) most of macromolecules in the crystalline phase of as-electrospun and stretched nanofibers possessed the zig-zag conformation instead of the helical conformation; and (3) the post-spinning stretching process could substantially improve mechanical properties of the nanofiber bundles. To the best of our knowledge, this study represented the first successful attempt to stretch electrospun nanofibers; and we envisioned that the highly aligned and stretched electrospun PAN copolymer nanofibers could be an innovative type of precursor for the development of continuous nano-scale carbon fibers with superior mechanical strength.

Interfacial and mechanical properties of carbon fibers modified by electrochemical oxidation in (NH4HCO3)/(NH4)2C2O4·H2O aqueous compound solution

Co-reporter:Jie Liu, Yuli Tian, Yujia Chen, Jieying Liang

Applied Surface Science 2010 Volume 256(Issue 21) pp:6199-6204

Publication Date(Web):15 August 2010

DOI:10.1016/j.apsusc.2010.03.141

Abstract

Polyacrylonitrile-based carbon fibers were electrochemical oxidized in (NH₄HCO₃)/(NH₄)₂C₂O₄·H₂O aqueous compound solution to improve its tensile strength and interfacial bounding strength with resin matrix simultaneously. AFM, XPS, XRD and Raman spectra were employed to characterize morphology, chemical states, crystallites size and ordered degree of CFs surface. The results indicated that the optimal modified condition in this paper could increase the tensile strength of CFs by 17.1%, meantime improve the interlaminar shear strength (ILSS) by 14.5%. The improvement of interlaminar shear strength not only causes by increase of surface roughness, but also causes by interaction effects of oxygen-containing and nitrogen-containing functional groups on carbon fibers. Among oxygen-containing functional groups, –COOH functional group plays an important role in enhancing the ILSS. Furthermore, after electrochemical oxidation the crystallites size decreased by 23–27%; ordered degree on CFs surface has an increase with suitable etching which did not peel off the ordered region on CFs surface and create new cracks; both above increase the tensile strength of CFs.

A surface treatment technique of electrochemical oxidation to simultaneously improve the interfacial bonding strength and the tensile strength of PAN-based carbon fibers

Co-reporter:Jie Liu, Yuli Tian, Yujia Chen, Jieying Liang, Lifeng Zhang, Hao Fong

Materials Chemistry and Physics 2010 Volume 122(2–3) pp:548-555

Publication Date(Web):1 August 2010

DOI:10.1016/j.matchemphys.2010.03.045

Electrochemical oxidation surface treatment of polyacrylonitrile-based carbon fibers (CFs) in 0.5 M ammonium oxalate aqueous solution for 94 s with the electric current density being 0.6 mA cm−2 resulted in simultaneous improvements of interfacial bonding strength and tensile strength by ∼8.6% and ∼16.6%, respectively. The improvements were due to the following reasons: (1) besides creating active surface functional groups, the electrochemical oxidation treatment with optimal processing conditions also generated a suitable electrolytic etching capability, which was powerful enough to remove mechanically weak carbonaceous components deposited on the surface of CFs, while was gentle enough not to distinguishably remove structurally ordered sheath region of CFs; (2) the treatment also refined the graphitic crystallites in the sheath region and created additional crystalline impingements/boundaries that could resist to crack growth; and (3) the electrochemical oxidation that preferably started from sharp edges including the tips of micro-cracks mitigated the stress development and propagation. XRD, SEM, Raman, FT-IR, XPS, and an electronic single-filament tensile tester were used to study the structural, morphological, chemical, and mechanical properties of the CFs before and after the treatment. A theoretical model, namely “physical and chemical dual effects through layer-by-layer electrolytic etching”, was proposed to explain the improvements.

Thermo-chemical reactions occurring during the oxidative stabilization of electrospun polyacrylonitrile precursor nanofibers and the resulting structural conversions

Co-reporter:Jie Liu, Peixun Zhou, Lifeng Zhang, Zhaokun Ma, Jieying Liang, Hao Fong

Carbon 2009 Volume 47(Issue 4) pp:1087-1095

Publication Date(Web):April 2009

DOI:10.1016/j.carbon.2008.12.033

Thermo-chemical reactions occurring during the oxidative stabilization of electrospun polyacrylonitrile (PAN) precursor nanofibers with diameters of approximately 300 nm were investigated as well as the resulting structural conversions, and the results were compared to those of conventional SAF 3K (Courtaulds) precursor fibers. The study revealed that: (1) the nitrile groups in the electrospun nanofibers possessed a higher reactivity than those in the SAF 3K fibers; (2) the macromolecules in the electrospun nanofibers predominantly underwent inter-molecular cyclization/crosslinking while those in the SAF 3K fibers underwent intra-molecular cyclization during the early stages of stabilization; and (3) under the same stabilization conditions, the structural conversion from linear macromolecules to aromatic ring/ladder structures in the electrospun nanofibers occurred faster and more thoroughly than in the SAF 3K fibers. These characteristics combined with other properties, including small diameter and high degree of structural perfection, suggest that electrospun PAN precursor nanofibers may be used to develop continuous nano-scale carbon fibers with superior mechanical strength, especially if the electrospun nanofibers could be further aligned and stretched.