Insight into stabilization behaviors of Lignin/PAN-derived electrospun precursor fibers

https://doi.org/10.1016/j.polymdegradstab.2021.109680Get rights and content

Highlights

  • The improvement of thermal properties of Lignin/PAN-derived PFs was ascribed to the transformation from the free-radical reaction to the ionic reaction because of the oxygen structural units in Lignin.

  • The oxygen groups in Lignin acted as a free-radical scavenger to slow down the free radical cyclization of fibers in the low stabilization temperature stage.

  • The carboxyl group in Lignin served as an initiating agent to accelerate the ionic cyclization of fibers in the high stabilization temperature stage.

  • The fibers shrinkage and the rapid heat release were significantly ameliorated, and the activated energy and cyclization temperature decreased as the concentration of Lignin increased.

Abstract

The stabilization behaviors of Lignin/PAN-derived electrospun precursor fibers under the different temperatures and different heating rates were investigated to reveal the effects of oxygen structural unit of Lignin on the oxidation and cyclization reaction of fibers. The results indicated that the introduced Lignin could helpfully reduce the cyclization degree of fibers, accomplishing the stabilization process at a lower temperature. Meanwhile, the introduced Lignin could efficiently attenuate the exothermal rate of fibers, accomplishing the stabilization process with a higher heating rate. Moreover, the abundant oxygen-containing groups in Lignin acted as a free-radical scavenger to slow down the free radical cyclization rate of fibers in the low stabilization temperature stage (<240 °C), while the carboxyl group in Lignin served as an initiating agent to accelerate the ionic cyclization of fibers in the high stabilization stage (>280 °C). It has been established that the oxygen structural unit of Lignin could be a promising candidate to facilitate the stabilization behaviors of PAN-derived fibers.

Introduction

Carbon fibers (CFs) have attracted considerable attention throughout the world as a kind of high strength lightweight material in the composites industry for applications such as aerospace, automotive, and renewable energy resources [1,2]. CFs can be manufactured from pitch [3,4] , rayon [5,6] and polyacrylonitrile (PAN) precursors [7,8], and more than 90% of commercial CFs were produced from PAN-derived precursors [9]. To fabricate the high-performance PAN-based CFs, the precursor fibers (PFs) need undergo a sequence of heating treatment processes (e.g., stabilization in oxidative environment and carbonization in protective atmosphere) [10,11]. Among them, stabilization is of great importance to convert into infusible structure, which preventing the stabilized fibers (SFs) from fusing at the following carbonization process. Meanwhile, stabilization is the most complicated and time-consuming step in the manufacture of CFs [8,12]. Therefore, the optimization of stabilization process is not only beneficial to improve the performance of CFs, but also contribute to minimize their production cost. Thus, many researchers focused on improving the thermal behavior of PAN-derived PFs according to their stabilization conditions, including temperature, time and tension [[13], [14]–15] . Bajaj et al. [16] pointed out that the exothermic reaction of homopolymer PAN-derived PFs such as cyclization was initiated and transferred by free radicals, which would cause the sudden and rapid heat evolution during stabilization. The results showed that their corresponding stabilization processes were difficult to control and the resultant CFs with superior mechanical properties could not be produced because of the chain scission caused by the intense heat release. Generally, acrylonitrile (AN) was copolymerized with other polar comonomers, such as methyl acrylate, acrylic acid, or itaconic acid (IA) to achieve controllable adjustment of PFs during stabilization process, and this design could improve the property of PAN-derived PFs [[17], [18]–19]. Thermal behaviors of copolymer PAN-derived PFs was investigated by Preta et al. [20] . They found that the corporation of certain comonomers (acrylic acid (AA), methacrylic acid (MAA) and IA) could trigger the cyclization reaction and reduce the cyclization temperature. Jin et al. [9] prepared the PAN-derived nanofibers with functional groups through the alkaline hydrolysis modification, and found the cyclization temperature of the hydrolyzed PAN-derived nanofibers was also shifted to a lower temperature owing to the fact that the nitrile (C = N) groups of PAN were converted into the amide (CONH2) and carboxylic (-COOH) groups. Besides, our previous work also clarified the effect of oxygen that was introduced in pitch precursor on the properties and structure evolution of fibers during stabilization, carbonization and graphitization, and found that the introduced oxygen of pitch precursor was beneficial to fabricate the pitch-based CFs with high tensile strength [21]. Therefore, these previous findings implied that the oxygen-containing groups units in PFs would promote the stabilization and carbonization behaviors.

Actually, Lignin is an aromatic biopolymer and has been investigated as a precursor for the production of CFs because of its low-cost and bio-renewable feedstock [22,23]. The molecular structure of Lignin consists of the phenylpropane units with a large number of hydroxyl (–OH), carboxyl (–COOH) and carbonyl (–C = O) oxygen functional groups [24,25] resulting to low spinnability of Lignin and obvious pore structures of Lignin-based CFs with low mechanical properties. However, the blended Lignin/PAN has been used as a low-cost precursor for CFs production to combine the advantages of PAN and Lignin [26,27]. In our previous reports [28], the influence of Lignin units on the properties of Lignin/PAN-derived CFs was demonstrated and the Lignin units exhibited positive effects on the fabrication of Lignin/PAN-derived fibers, especially their stabilization process. Notably, the stabilization behaviors and precise mechanism Lignin/PAN-derived fibers were not clear, though Lignin could attenuate the exothermal reaction to avoid excessive heat eruptions during the stabilization.

Herein, the stabilization behaviors of Lignin/PAN-derived PFs were deeply investigated by various characterization techniques. Based on the evolutions of chemical composition, thermodynamics and kinetics process of fibers, this work insighted into the stabilization behaviors of Lignin/PAN-derived PFs according to the effects of oxygen structural units in Lignin, and deeply explored the influence of oxygen containing groups of Lignin on the stabilization of Lignin/PAN-derived PFs. More importantly, the results further demonstrated that introducing the oxygen-rich structural unit in Lignin was a facile and effective strategy to improve the stabilization behavior of the PAN-based fibers.

Section snippets

Materials

The Lignin/PAN-derived electrospun precursor fibers (PFs) were prepared by the electrospinning technology using the PAN (Mw=150,000 g/mol, Sigma-Aldrich, USA) and Lignin (Mw=528 g/mol, Shanghai Macklin Biochemical Co., Ltd., China) as raw materials. Specific experimental parameters were presented in our previous published paper [28]. The obtained Lignin/PAN-derived PFs were named as LPx-PF, where x (0, 10, 20) represented the added Lignin content.

Stabilization of precursor fibers

The PFs were stabilized from room temperature to

General properties of Lignin/PAN-derived precursor fibers

The elemental composition of Lignin/PAN-derived PFs by elemental analysis and XPS analysis are summarized in Table 1. The carbon, hydrogen and nitrogen contents of LP0-PF, LP10-PF and LP20-PF were from 70.05 to 64.63%, 5.75 to 4.01% and 23.17 to 12.21%, respectively. Notably, the oxygen contents of Lignin/PAN-derived PFs increased from 2.79 to 16.52% with the introduction content of Lignin from 0 to 20%, it mean oxygen containing functional groups of PFs could adjust by promoting the content of

Conclusions

In this work, the introduction of Lignin provided abundant oxygen-containing functional groups for the Lignin/PAN-derived PFs, especially carboxyl functional groups. The Lignin was involved into the stabilization process, which improved the fibers shrinkage and significantly improved the rapid heat release. The decreasing of cyclization activation energy was ascribed to the transformation from the free-radical reaction to the ionic reaction. During the stabilization process, the Lignin acted as

CRediT authorship contribution statement

Xiaxiang Zhang: Conceptualization, Methodology, Data curation, Writing – review & editing. Yong Qi: Investigation, Data curation, Formal analysis. Jianxiao Yang: Conceptualization, Supervision, Writing – review & editing, Funding acquisition. Silin Dong: Writing – review & editing. Jiahao Liu: Writing – review & editing. Jun Li: Funding acquisition, Writing – review & editing. Kui Shi: Data curation, Formal analysis, Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no conflict of interest.

Acknowledgments

This research was funded by the National Natural Science Foundation for Young Scientists of China (Grant No.51702094) and the Natural Science Foundation of Hunan Province, China (Grant No. 2020JJ4203 and 2019JJ50651).

References (44)

  • K. Shi et al.

    Effect of oxygen-introduced pitch precursor on the properties and structure evolution of isotropic pitch-based fibers during carbonization and graphitization

    Fuel Process Technol

    (2020)
  • H. Mainka et al.

    Lignin - an alternative precursor for sustainable and cost-effective automotive carbon fiber

    J. Mater. Res. Technol.

    (2015)
  • M. Foston et al.

    NMR a critical tool to study the production of carbon fiber from lignin

    Carbon

    (2013)
  • H.C. Liu et al.

    Rheological behavior of polyacrylonitrile and polyacrylonitrile/lignin blends

    Polymer

    (2017)
  • F.Y. Liu et al.

    Nitrogen, oxygen and sulfur co-doped hierarchical porous carbons toward high-performance supercapacitors by direct pyrolysis of Kraft lignin

    Carbon

    (2019)
  • P. Xu et al.

    A high surface area N-doped holey graphene aerogel with low charge transfer resistance as high performance electrode of non-flammable thermostable supercapacitors

    Carbon

    (2019)
  • L.M. Li et al.

    A doped activated carbon prepared from polyaniline for high performance supercapacitors

    J. Power Sources

    (2010)
  • H.C. Liu et al.

    Stabilization kinetics of gel spun polyacrylonitrile/lignin blend fiber

    Carbon

    (2016)
  • Y.D. Liu et al.

    Gel-spun carbon nanotubes/polyacrylonitrile composite fibers. Part II: stabilization reaction kinetics and effect of gas environment

    Carbon

    (2011)
  • R.V. Ghorpade et al.

    Effect of controlled tacticity of polyacrylonitrile (co) polymers on their thermal oxidative stabilization behaviors and the properties of resulting carbon films

    Carbon

    (2017)
  • W.H. Liu et al.

    The free radical species in polyacrylonitrile fibers induced by gamma-radiation and their decay behaviors

    Radiat. Phys. Chem.

    (2012)
  • W.L. Zhang et al.

    Significantly reduced pre-oxidation period of PAN fibers by continuous electron beam irradiation: optimization by monitoring radical variation

    Polym. Degrad. Stabil.

    (2018)
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