Journal of Textile Research ›› 2025, Vol. 46 ›› Issue (10): 19-29.doi: 10.13475/j.fzxb.20250201001

• Fiber Materials • Previous Articles     Next Articles

Preparation and properties of Lyocell fiber with silicon-containing modified phosphorus-nitrogen flame retardant

GAO Min1, CHENG Chunzu1,2(), XU Zhongkai1, ZHAO Qingbo1, ZHANG Dong1, DAI Xinxin1   

  1. 1. State Key Laboratory of Bio-Based Fiber Materials, China Textile Academy, Beijing 100025, China
    2. Tianjin Key Laboratory of Pulp and Paper, Tianjin University of Science & Technology, Tianjin 300457, China
  • Received:2025-02-06 Revised:2025-06-04 Online:2025-10-15 Published:2025-10-15
  • Contact: CHENG Chunzu E-mail:chengchunzu@cta.gt.cn

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Abstract:

Objective Lyocell fiber is a green and environmentally regenerable cellulose fiber, but has high flammability and high flame propagation. With wide application of Lyocell fibers in the fields of textile materials, nonwoven materials and high-performance filler materials, the potential danger of fire is increasing, which is a serious threat to the safety of people's lives and properties. Therefore, it is necessary to prepare flame retardant Lyocell fibers to slow down their thermal decomposition process and reduce their flammability.

Method Silicon-containing modified phosphorus-nitrogen flame retardant Si-DDPON was prepared by modifying 1,2-bis(2-oxo-5,5-dimethyl-1,3,2-dioxyphosphacyclohexy-2-imino)ethane(DDPON)with tetraethylorthosilicate (TEOS), and then Si-DDPON was used to prepare flame retardant Lyocell fibers by physical blending process. The effects of Si-DDPON on the micro morphology, thermal properties, flame retardant properties and mechanical properties of Lyocell fibers were characterized and analyzed by using scanning electron microscope, thermogravimetric analyzer, limiting oxygen index and mechanical properties tests. The pyrolysis gas and the char morphology of the Lyocell fibers were analyzed by the thermogravimetric-infrared spectroscopy and Raman spectroscopy, and the retardant mechanism was explored.

Results After modified by TEOS, the water contact angle of DDPON was increased from (44.5°±0.9°) to (128°±2.7°), and the water solubility was reduced from 0.86 g/(100 gH2O) to 0.001 9 g/(100 gH2O) at 98 ℃, showing excellent hydrophobicity and water resistance. Scanning electron microscopy and X-ray photoelectron spectroscopy results showed that a small amount of flame retardant particles were attached to the surface of Lyocell fibers after the addition of Si-DDPON. Scanning electron microscopy and energy dispersive spectrometer results showed that the fiber cross-section was uniformly distributed by Si-DDPON. Thermogravimetric experiments demonstrated that the maximum thermal degradation temperature of Lyocell fiber was reduced from 357.4 ℃ to 316.0 ℃, and the amount of residual carbon was increased from 6.1% to 19.6% at 800 ℃ when Si-DDPON with a mass fraction of 35% was added, indicating that the thermal stability of the Lyocell fibers had been greatly improved. Limiting oxygen index(LOI) results indicated that the LOI value of Lyocell fibers increased from 18.0% to 28.5% when the mass fraction of Si-DDPON was 35%, and the LOI value of the fibers remained at 28% after 20 washing cycles, which showed a good performance of water washing resistance. The results of mechanical property tests showed that the mechanical properties of Lyocell fibers were reduced by the addition of Si-DDPON. However, the dry breaking strengths and wet breaking strengths of 35%Si-DDPON-Lyocell fibers were 2.87 cN/dtex and 2.46 cN/dtex, respectively, which retained 75.5% and 75.7% of the pure Lyocell fibers. The analysis of flame retardant mechanism demonstrated that Si-DDPON can improve the flame retardancy of Lyocell fibers by acting on both gas phase and condensed phase. In the gas phase, Si-DDPON inhibited the generation of flammable gas products and promoted the release of non-flammable gas during the combustion process of Lyocell fibers, whereas in the condensed phase, Si-DDPON promoted the formation of a stable expanded char layer and increased the degree of graphitization of the carbon layer, which improved the flame retardant performance of Lyocell fibers.

Conclusion Compared with pure Lyocell fibers, the thermal stability and flame retardant effects of Si-DDPON-Lyocell fibers were significantly improved. When the total amount of Si-DDPON was 35%, the maximum thermal degradation temperature of Lyocell fibers decreased from 357.4 ℃ to 316.0 ℃, the char residue increased by 2.2 times at 800 ℃, and the LOI value of Lyocell fibers rose from 18.0% to 28.5%. Moreover, the LOI value of Si-DDPON-Lyocell fibers remaind at 28.0% after 20 washing cycles, demonstrating excellent wash durability. During the combustion process of Si-DDPON-Lyocell fibers, Si-DDPON acts as a gas-phase flame retardant by reducing the amount of combustible gases and releasing non-combustible gases. Meanwhile, Si-DDPON promots the formation of dense, continuous silicon-containing expanded carbon layer in the condensed phase, both of which work together to enhance the flame retardancy of Lyocell fibers.

Key words: Lyocell fiber, phosphorus nitrogen flame retardant, flame retardant property, mechanical property, flame retardant mechanism

CLC Number: 

  • TS102.5

Fig.1

Hydrolysis (a) and condensation (b) reaction of sol-gel"

Fig.2

FT-IR spectra of flame retardants"

Fig.3

SEM images of flame retardants(×5 000)"

Fig.4

Water solubilities of flame retardants"

Fig.5

Thermal degradation curves of flame retardants in N2 atmosphere. (a) TG curves; (b) DTG curves"

Fig.6

FT-IR spectra of pure Lyocell fiber and Si-DDPON-Lyocell fibe"

Fig.7

SEM images of fibers(×3 000). (a) Pure Lyocell fibers; (b) Si-DDPON-Lyocell fibers"

Fig.8

XPS total scan spectra of fibers"

Fig.9

EDS mapping images of Si-DDPON-Lyocell fibers"

Fig.10

Thermal degradation curves of Lyocell fibers with different Si-DDPON contents in N2 atmosphere. (a) TG curves; (b) DTG curves"

Tab.1

Thermogravimetric data of Lyocell fibers with different Si-DDPON contents in N2 atmosphere"

样品名称 T5%/
℃		 Tmax/
℃		 800 ℃时的
残炭量/%
纯Lyocell纤维 289.5 357.4 6.1
25%Si-DDPPON-Lyocell纤维 288.6 341.3 11.4
35%Si-DDPPON-Lyocell纤维 286.2 316.0 19.6
45%Si-DDPPON-Lyocell纤维 284.4 304.2 27.3

Tab.2

LOI values and washing durability data of Lyocell fibers with different Si-DDPON contents"

样品名称 不同水洗次数下纤维的LOI值/%
0次 5次 12次 20次
纯Lyocell纤维 18.0 - - -
25%Si-DDPPON-Lyocell纤维 26.6 26.3 26.0 25.7
35%Si-DDPPON-Lyocell纤维 28.5 28.2 28.2 28.0
45%Si-DDPPON-Lyocell纤维 28.9 28.5 28.5 28.2

Fig.11

Results of cone calorimetric test of pure Lyocell nonwoven fabric and Si-DDPON-Lyocell nonwoven fabric. (a) HRR; (b) THR"

Tab.3

Data of cone calorimetric test of pure Lyocell nonwoven fabric and Si-DDPON-Lyocell nonwoven fabric"

样品名称 PHRR值/
(kW·m-2)		 THR值/
(MJ·m-2)		 TPHRR/
s		 残炭量/
%
纯Lyocell非织造布 166.7±0.3 1.98±0.01 18±1 0.6±0.1
Si-DDPON-Lyocell非织造布 117.5±0.5 1.51±0.01 20±1 4.8±0.1

Tab.4

Mechanical and hydroscopic properties of Lyocell fibers with different Si-DDPON contents"

样品名称 断裂强度/(cN·dtex-1) 回潮
率/%
干态 湿态
纯Lyocell纤维 3.80±0.12 3.25±0.15 10.80
25%Si-DDPPON-Lyocell纤维 3.24±0.15 2.71±0.17 7.30
35%Si-DDPPON-Lyocell纤维 2.87±0.18 2.46±0.21 7.30
45%Si-DDPPON-Lyocell纤维 2.42±0.23 2.15±0.28 7.08

Fig.12

FT-IR spectra of Lyocell fibers at different temperatures. (a) Pure Lyocell fibers; (b) Si-DDPON-Lyocell fibers"

Fig.13

Raman spectra of carbon residual of Lyocell fibers. (a) Pure Lyocell fiber; (b) Si-DDPON-Lyocell fiber"

Fig.14

SEM images of carbon residual of Lyocell fibers. (a) Pure Lyocell fibers(×2 000); (b) Si-DDPON-Lyocell fibers(×1 000); (c) Si-DDPON-Lyocell fibers(×2 000)"

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