Preparation of PET-based carbon dots by pyrolysis and its application in PET flame retardancy
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.
polyethylene terephthalatecarbon dotspyrolysisflame retardant modificationco-mixingpolyester recycling and utilization
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