Journal of Textile Research ›› 2025, Vol. 46 ›› Issue (07): 1-9.doi: 10.13475/j.fzxb.20241004601

• Fiber Materials •     Next Articles

Nanofibrils exfoliated from silk fibroin by deep eutectic solvent and its film-forming properties

JIANG Shuning1, YANG Haiwei1,2(), LI Changlong1, ZHENG Tianliang1, WANG Zongqian1   

  1. 1 School of Textile and Garment, Anhui Polytechnic University, Wuhu, Anhui 241000, China
    2 School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230026, China
  • Received:2024-10-22 Revised:2025-03-27 Online:2025-07-15 Published:2025-08-14
  • Contact: YANG Haiwei E-mail:yanghaiwei@ahpu.edu.cn

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Abstract:

Objective The conventional dissolution-regeneration process destroys the multiscale hierarchical structure of silk fibroin (SF) fibers, resulting in inferior mechanical properties and limited applications of the regenerated SF films. This study aims to extract silk fibroin nanofibrils (SNF) retaining the pristine meso-structure by the green deep eutectic solvent (DES) exfoliation of SF fibers for the preparation of high-strength SNF films.

Method The DESs with different acidities and alkalinities were prepared by mixing choline chloride (ChCl) with urea (Ur), lactic acid (LA), and glycerol (Gly) under heating. The SF fibers were exfoliated using each of the three types of DES, and an optimal DES system was selected based on the exfoliation effect. On this basis, the temperature and time of DES exfoliation of SF fibers were optimized according to the yield of SNF. The recyclability and reusability of DES were also evaluated. Furthermore, the micro-morphology, molecular conformation, and crystal structure of SF fibers were investigated before and after exfoliation. Then, an evolution model of SF fibers to SNF during the exfoliation was constructed to elucidate the molecular mechanism of SF fibers exfoliated by DES. Meanwhile, SNF films were prepared by vacuum filtration. The microstructure, mechanical properties, and optical properties of the SNF films were characterized by scanning electron microscopy, universal testing machine, and UV-Vis spectrophotometer.

Results Compared to ChCl/LA and ChCl/Gly DES, ChCl/Ur DES exhibited a stronger exfoliation capacity for SF fibers. After treatment with ChCl/Ur DES at 110 ℃ for 24 h, a higher yield (49.79%) of SNF was obtained by ultrasonic treatment and centrifugation. The diameters of the extracted SNF were in the range of 20-107 nm (average diameter of 57 nm), showing excellent dispersion stability. Additionally, the DES exhibited superior recyclability and reusability. After 5 cycles, the recovery rate of DES and the yield of SNF remained above 90% and 45%, respectively. The FT-IR spectrum analysis showed that DES mainly disrrupted the SF molecular network in the amorphous region, leading to a higher relative content of β-sheet structures in the SNF. The XRD results confirmed that DES weakened the interfacial interactions among the SF fibers and did not destroy their internal meso-structures. Consequently, the DES-treated SF fibers swelled and loosened, and were gradually exfoliated into micro-nano fibrils. Furthermore, more micro-nano fibrils were promoted to be converted into SNF by ultrasonic treatment. The SNF films prepared by the vacuum filtration assembly were optically transparent (above 87% transmittance) in the visible region (400-800 nm). SEM images showed that the SNF films had tightly arranged nanofibril networks and porous structures. Compared with the regenerated SF films, the SNF films demonstrated superior thermal stability and an increase in breaking strength and toughness of 68.19% and 410%, respectively.

Conclusion The ChCl/Ur DES displayed a strong exfoliation ability to SF fibers. Under the optimal exfoliation process (110 ℃, 24 h) conditions, SNF with high yield and dispersion stability could be extracted after sonication and centrifugation. In addition, DES had satisfactory recyclability and reusability, demonstrating green and sustainable advantages. During the DES exfoliation, DES mainly destroyed the SF molecular network in the amorphous region, leading to the swelling and loosening of the SF fibers, which were then exfoliated into nanofibrils and retained the original β-sheet crystal structures. As a result, the prepared SNFs featured high light transmittance, tightly arranged nanofibril networks, and porous structures. More importantly, SNF films exhibited superior mechanical properties compared to regenerated SF films. This study provides an experimental basis for the green and efficient extraction of SNF and the construction of high-performance silk-based film materials.

Key words: silk fibroin nanofibril, deep eutectic solvent, process optimization, exfoliation mechanism, nanofibril film

CLC Number: 

  • TS141

Fig.1

Schematic diagram of process flow for DES exfoliation of SF fibers"

Fig.2

Influence of different DES on exfoliation effect of SF fibers. (a) Optical photos of pulp-like mixtures formed from different DES-exfoliated SF fibers; (b) SEM images of SF fibers exfoliated by different DESs"

Fig.3

Influences of temperature (a) and time (b) of DES exfoliation on optical transparency of SNF dispersion"

Fig.4

Influences of DES recovery on exfoliation process. (a) Recovery rates of DES at different cycles; (b) Yield of SNF at different cycles; (c) Optical photos of recovered DES at different cycles"

Fig.5

Characterization of micromorphology and dispersion stability of SNF. (a) Tyndall effect photo of SNF dispersions; (b) SEM images of SNF; (c) Diameter distribution of SNF; (d) Zeta potential of SNF dispersions; (e) Optical photos of SNF dispersions before and after storage"

Fig.6

Characterization of molecular conformation of SF fibers and SNF. (a) FT-IR spectra of SF fibers and SNF; (b) Deconvolution results of amide I band in SF fibers; (c) Deconvolution results of amide I band in SNF; (d) XRD spectra of SF fibers and SNF"

Fig.7

Micro-morphology changes of SF fibers during DES exfoliation"

Fig.8

Evolution of SF fibers to SNF during DES exfoliation. (a) Schematic diagram of process of evolution of SF fiber to SNF; (b) Micro-morphology of process of evolution of SF fiber to SNF"

Fig.9

Preparation and morphology characterization of SNF film. (a) Schematic diagram of preparation of SNF film; (b) Optical photos of SNF film; (c) UV-Vis transmittance of SNF film; (d) SEM image of surface of SNF film; (e) SEM images of cross-section of SNF film"

Fig.10

Mechanical properties and thermal stability of SNF film and regenerated SF film. (a) Stress-strain curves; (b) Thermogravimetric curves"

Tab.1

Fracture strength and toughness of SNF film and regenerated SF film"

膜类型 断裂强度/MPa 拉伸韧性/(MJ·m-3)
再生SF膜 21.16±2.09 0.10±0.03
SNF膜 35.59±1.24 0.51±0.01
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