Journal of Textile Research ›› 2024, Vol. 45 ›› Issue (10): 1-8.doi: 10.13475/j.fzxb.20230708301

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Preparation of PET-based carbon dots by pyrolysis and its application in PET flame retardancy

BING Linhan1, WANG Rui1,2, WU Yuhang1, LIU Botong1, HUANG Hanjiang1, WEI Jianfei1,2()   

  1. 1. School of Materials Design and Engineering, Beijing Institute of Fashion Technology, Beijing 100029, China
    2. Beijing Key Laboratory of Clothing Materials R&D and Assessment, Beijing Institute of Fashion Technology, Beijing 100029, China
  • Received:2023-10-19 Revised:2024-07-13 Online:2024-10-15 Published:2024-10-22
  • Contact: WEI Jianfei E-mail:weijianfei@bift.edu.cn

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Abstract:

Objective In order to improve the flame retardant properties of polyethylene terephthalate (PET), PET-based carbon dots (PET-CDs) were prepared by pyrolysis using PET waste as a precursor, and PET com-plexes (PET-CDs-PET) were prepared by mixing them with PET using physical blending method. The transformation from PET waste to flame-retardant PET was achieved. PET oligomers were prepared by microwave method, and then PET-CDs were prepared by pyrolysis reaction of PET oligomers with ethylenediaminetetraacetic acid. PET-CDs of different qualities were crushed in a pulveriser together with PET slices to obtain four kinds of PET-CDs-PETs with different contents of PET-CDs.

Method Transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier infrared spectroscopy were used to analyse the structure of PET-CDs, and the optical properties of PET-CDs were investigated with the help of fluorescence spectrometer and UV analyser. The effects of different additive amounts of PET-CDs on the flame retardancy of PET were investigated by the limiting oxygen index (LOI), vertical combustion (UL-94), and cone calorimetry. The effect of PET-CDs on the flame retardancy of PET with different additions was also investigated by using a material. The mechanical properties of PET-CDs-PET were investigated by a material strength tester.

Results As far as the structure is concerned, the prepared PET-CDs are quasi-spherical, with uniform particle distribution and no agglomeration. The particle size ranged from 0.44 nm to 4.39 nm, the average particle size was 1.85 nm, the lattice spacing was 0.25 nm, and the surface contained hydroxyl, carboxyl, and amine functional groups. In terms of optical properties, the prepared PET-CDs ethanol solutions showed dark brown colour under indoor natural light and blue fluorescence in UV analyser when irradiated by UV lamp with wavelength of 365 nm. The fluorescence of PET-CDs ethanol solutions was typical excitation wavelength-dependent, with the optimal excitation wavelengths and emission wavelengths of 320 nm and 420 nm, respectively. The absolute fluorescence quantum yield reached 25.73% under the light excitation at 320 nm, and the UV-visible absorption spectrum had an obvious absorption peak at 293 nm. In terms of flame retardant properties, the thermal stability of PET-CDs met the requirements of blending with PET, and the residual carbon of PET was increased by adding PET-CDs into PET. The LOI values of PET-CDs was increased and then decreased after the addition of PET-CDs with different contents, but all of them were higher than that of pure PET. The UL-94 fire ratings were all V-2 with different additions of PET-CDs. The LOI value of PET-CDs 1%-PET was 30%, and there was no significant decrease in the mechanical properties of PET at this additive amount, so the optimal additive amount of PET-CDs was 1%. The total heat release of PET-CDs 1%-PET was decreased by 1.5%, the total smoke release by 8.1%, the peak value of CO by 42%, the peak value of CO2 by 35.9%.

Conclusion The preparation of CDs from PET waste as raw material can provide a new method for the reuse of waste, and the PET waste can be used in the flame retardant modification of PET materials after the preparation of CDs, forming a green and benign cycle. At the same time, the application of CDs in the flame retardant field not only broadens the scope of its application, but also provides a new flame retardant in this field.

Key words: polyethylene terephthalate, carbon dots, pyrolysis, flame retardant modification, co-mixing, polyester recycling and utilization

CLC Number: 

  • TQ317.9

Tab.1

PET-CDs-PET raw material ratio g"

样品 PET-CDs质量 PET切片质量
纯PET 0 500
PET-CDs 1%-PET 5 495
PET-CDs 3%-PET 15 485
PET-CDs 5%-PET 25 475

Fig.1

TEM image of PET-CDs"

Fig.2

XPS spectra of PET-CDs"

Fig.3

FT-IR spectrum of PET-CDs"

Fig.4

UV-vis absorption spectra of PET-CDs"

Fig.5

Fluorescence emission spectra obtained by excitation of PET-CDs with different wavelengths of light"

Fig.6

PET-CDs fluorescence quantum yield"

Fig.7

Thermogravimetric curves of PET-CDs"

Fig.8

DSC curves of PET and PET-CDs-PET. (a) DSC warming curves; (b) DSC cooling curves"

Tab.2

DSC analysis data for PET-CDs-PET℃"

样品 Tg Tcc Tm Tmc ΔTmc
纯PET 72 134 245 208 37
PET-CDs 1%-PET 71 121 247 202 45
PET-CDs 3%-PET 70 118 245 201 44
PET-CDs 5%-PET 69 116 243 200 43

Tab.3

Thermogravimetric analysis data of PET-CDs-PET"

样品 T5%/℃ Tmax/℃ 残炭量(700 ℃)/%
纯PET 403.33 445.39 8.48
PET-CDs 1%-PET 401.51 445.97 11.52
PET-CDs 3%-PET 398.65 445.07 11.72
PET-CDs 5%-PET 391.99 440.67 8.64

Tab.4

PET-CDs-PET limiting oxygen indices"

样品 LOI值/%
纯PET 23
PET-CDs 1%-PET 30
PET-CDs 3%-PET 26
PET-CDs 5%-PET 25

Tab.5

PET-CDs-PET vertical combustion analysis"

样品 t1/s t2/s 是否
熔滴		 是否
引燃脱
脂棉		 UL-94
等级
纯PET 42.0±10.7 8.7±6.9 是 是 —
PET-CDs 1%-PET 7.7± 1.8 2.8±2.0 是 是 V-2
PET-CDs 3%-PET 2.5± 0.3 1.3±0.3 是 是 V-2
PET-CDs 5%-PET 1.9± 0.5 2.5±0.7 是 是 V-2

Tab.6

PET-CDs-PET cone calorimetric data"

样品 TTI/s PHRR/(kW·m-2) THR/(MJ·m2) CO峰值/(kg·kg-1) CO2峰值/(kg·kg-1) TSR/m2
纯PET 48 892.87 80.1 21.7 196.3 1 995
PET-CDs 1%-PET 60 702.98 78.9 12.6 125.8 1 834
PET-CDs 3%-PET 59 691.34 72.3 6.7 60.1 1 834
PET-CDs 5%-PET 67 677.78 65.7 4.6 58.6 1 710

Fig.9

Photographs of carbon layers after PET-CDs-PET cone calorimetry. (a) Pure PET; (b) PET-CDs 1%-PET; (c) PET-CDs 3%-PET; (d) PET-CDs 5%-PET;(e) SEM image of pure PET; (f) SEM image of PET-CDs 1%-PET"

Tab.7

PET-CDs-PET tensile test data"

样品 拉伸
强度/MPa		 弹性
模量/MPa		 断裂
伸长率/%
纯PET 60.0±1.4 1 079.4±21.4 507.6±27.7
PET-CDs 1%-PET 49.7±1.0 1 045.2±20.3 480.0±11.2
PET-CDs 3%-PET 45.8±1.3 965.7±36.7 41.3±13.8
PET-CDs 5%-PET 8.8±1.0 921.1±63.2 2.8± 0.1
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