PET-based carbon dots and preparation method and flame-retardant application thereof

Abstract

The invention discloses a PET (Polyethylene Terephthalate)-based carbon dot which is prepared by taking PET waste as a precursor and adopting a one-step pyrolysis method, and the PET-based carbon dot has remarkably improved fluorescence quantum yield and has a good flame-retardant modification effect on polymers such as PET / PA6 (Polyethylene Terephthalate) / PA6 (Polyamide 6) / PA66 (Polyamide 66) and the like.

Description

Technical Field

[0001] This invention relates to the field of novel fluorescent nanomaterials, specifically to PET-based carbon dots, their preparation methods, and flame-retardant applications. Background Technology

[0002] Carbon dots (CDs) are a general term for various luminescent carbon nanoparticles mainly composed of carbon elements. They are a type of zero-dimensional carbon nanomaterial with a diameter generally between 1 and 10 nm and are usually composed of tens to hundreds of carbon atoms.

[0003] The preparation of CDs includes traditional synthesis methods, such as chemical oxidation, electrochemical methods, hydrothermal methods, microwave-assisted synthesis, and pyrolysis, as well as sustainable synthesis methods, which are classified into alkaline catalytic methods, autothermal synthesis methods, and reduction methods based on differences in synthesis equipment and energy types.

[0004] The inventors have previously reported the preparation of carbon dots using polyester as a precursor, as described in CN2021111591819. By using polyester as a carbon source and supplementing it with dopants, carbon dots with high fluorescence intensity can be obtained. Furthermore, these carbon dots have good salt and acid resistance, and have promising applications in fluorescence imaging. However, the fluorescence quantum yield of the carbon dots in this report is not high, and the preparation process involves many steps and is complex. Summary of the Invention

[0005] The inventors discovered that PET-based carbon dots (rPET-CDs) can be prepared by a one-step pyrolysis method using PET waste as a precursor, which significantly improves the fluorescence quantum yield and the obtained PET-based carbon dots have good flame retardant properties, thus completing this invention.

[0006] The purpose of this invention is to provide PET-based carbon dots, which are prepared by a one-step pyrolysis method using PET products and alkanolamines, and the PET-based carbon dots have a graphite carbon structure.

[0007] In this invention, PET waste is preferably used as the PET product for preparing PET-based carbon dots.

[0008] In a preferred embodiment, the temperature for preparing PET-based carbon dots by pyrolysis of PET and ethanolamine is 240-300°C, preferably about 260°C.

[0009] In a preferred embodiment, the time for preparing PET-based carbon dots by pyrolysis of PET and ethanolamine is 10 hours or more, preferably 12-36 hours, and more preferably about 18 hours.

[0010] In a preferred embodiment, when preparing PET-based carbon dots, the ratio of PET to ethanolamine is preferably 100:(55-75) based on the mass ratio of PET to the volume ratio of ethanolamine, and more preferably 100:65.

[0011] The PET-based carbon dots provided by this invention have a significant absorption peak at 247 nm in the UV-Vis absorption spectrum, indicating the formation of a graphitic carbon structure.

[0012] The PET-based carbon dots provided by this invention exhibit maximum fluorescence intensity at an excitation wavelength of 340 nm, with a fluorescence emission wavelength of approximately 430 nm, displaying strong blue fluorescence and a fluorescence quantum yield as high as 54.68%.

[0013] The PET-based carbon dots provided by this invention have a weight loss of 5 wt% at temperature (T5). wt％ The flame retardant temperature is 372℃, which is much higher than the processing temperature of conventional polymers, making it applicable to the flame retardant modification of conventional polymers. Studies have found that it has good flame retardant modification properties for polyesters, polyamides, polylactic acid, etc., and especially excellent flame retardant modification properties for PET, PA6, and PA66.

[0014] When the PET-based carbon dots provided by the present invention are used for flame retardant modification of polymers, the amount used is preferably 1-10% of the total weight of the PET-based carbon dots and the polymer, more preferably 2-5%, and most preferably about 3%.

[0015] When PET-based carbon dots are blended with PET, PA6, or PA66, the resulting modified PET, PA6, or PA66 exhibits good flame retardancy, such as limiting oxygen index.

[0016] The present invention has the following beneficial effects:

[0017] (1) The PET-based carbon dots provided by the present invention have good dispersibility and thermal properties, and can be used for polymer flame retardant modification;

[0018] (2) The PET-based carbon dots provided by this invention have extremely high fluorescence quantum yield;

[0019] (3) The flame-retardant PET / PA1 / PA66 obtained by PET-based carbon dot blending modification provided by the present invention all exhibit excellent flame-retardant properties. Attached Figure Description

[0020] Figure 1 The fluorescence spectra of the PET-based carbon dots obtained in Examples 1 and 2 are shown;

[0021] Figure 2 The fluorescence spectrum of the PET-based carbon dots obtained in Comparative Example 1 is shown.

[0022] Figure 3 The fluorescence spectrum of the PET-based carbon dots obtained in Comparative Example 2 is shown;

[0023] Figure 4The fluorescence emission spectra of the PET-based carbon dots obtained in Example 1 under excitation light of different wavelengths are shown.

[0024] Figure 5 The absolute fluorescence quantum yield of the PET-based carbon dots obtained in Example 1 is shown; Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present invention will become clearer and more apparent.

[0026] Example 1: Preparation of PET-based carbon dots

[0027] 2g of PET and 0.5, 0.7, 0.9, 1.1, 1.3, and 1.5mL of ethanolamine were added to 50mL reaction vessels and reacted at 260℃ for 18h. The crude product was dissolved in 20mL of anhydrous ethanol and transferred to a glass bottle. Coarse filtration was performed using a Buchner funnel, and fine filtration was performed using a sand core filter. Then, rotary evaporation was performed. The rPET-CDs solution after rotary evaporation was placed in a beaker and dried in an electric thermostatic drying oven and a vacuum freeze dryer to obtain PET-based carbon dots (rPET-CDs) solid.

[0028] Example 2: Preparation of PET-based carbon dots

[0029] 2g of PET and 0.5, 0.7, 0.9, 1.1, and 1.5mL of ethanolamine were added to 50mL reaction vessels and reacted at 260℃ for 18h. The crude product was dissolved in 20mL of anhydrous ethanol and transferred to a glass bottle. Coarse filtration was performed using a Buchner funnel, and fine filtration was performed using a sand core filter. Then, rotary evaporation was performed. The rPET-CDs solution after rotary evaporation was placed in a beaker and dried in an electric thermostatic drying oven and a vacuum freeze dryer to obtain PET-based carbon dots (rPET-CDs) solid.

[0030] Fluorescence spectra of the products in Examples 1 and 2 are as follows Figure 1 As shown, by Figure 1 It can be seen that the fluorescence intensity is highest, reaching 1.3 × 10⁻⁶, when the amount of ethanolamine used is 1.3 mL. 6 au.

[0031] Comparative Example 1: Preparation of PET-based carbon dots

[0032] 2g of PET and 1.3mL of ethanolamine were added to a 50mL reactor and reacted at 200℃, 220℃, 240℃, and 260℃ for 18h, respectively. The crude product was dissolved in 20mL of anhydrous ethanol and transferred to a glass bottle. Coarse filtration was performed using a Buchner funnel, and fine filtration was performed using a sand core filter. Then, rotary evaporation was performed. The rPET-CDs solution after rotary evaporation was placed in a beaker and dried in an electric thermostatic drying oven and a vacuum freeze dryer to obtain PET-based carbon dots (rPET-CDs) solid.

[0033] Product fluorescence spectrum as follows Figure 2 As shown, by Figure 2 It can be seen that the fluorescence intensity is highest when the reaction temperature is 260℃.

[0034] Comparative Example 2: Preparation of PET-based carbon dots

[0035] 2g of PET and 1.3mL of ethanolamine were added to a 50mL reactor and reacted at 260℃ for 6h, 12h, 18h, 24h, and 30h, respectively. The crude product was dissolved in 20mL of anhydrous ethanol and transferred to a glass bottle. Coarse filtration was performed using a Buchner funnel, and fine filtration was performed using a sand core filter. Then, rotary evaporation was performed. The rPET-CDs solution after rotary evaporation was placed in a beaker and dried in an electric thermostatic drying oven and a vacuum freeze dryer to obtain PET-based carbon dots (rPET-CDs) solid.

[0036] Product fluorescence spectrum as follows Figure 3 As shown, by Figure 3 It can be seen that the fluorescence intensity is highest when the reaction time is 18 hours.

[0037] Experimental Example 1: Carbon Dot Performance Test of PET-based Materials

[0038] The PET-based carbon dots prepared in Example 1 using 2g PET and 1.3mL ethanolamine were subjected to fluorescence performance testing, fluorescence quantum yield testing, UV-Vis testing, transmission electron microscopy testing, FTIR testing, XPS testing, and thermal stability analysis. The results are as follows.

[0039] like Figure 4 As shown, by Figure 4 It can be seen that, within the 300-380 nm range, the maximum emission peak position of PET-based carbon dots shifts from the initial 420 nm to 470 nm, exhibiting excitation wavelength dependence. With increasing excitation wavelength, the fluorescence intensity of PET-based carbon dots reaches its maximum at an excitation wavelength of 340 nm.

[0040] Depend on Figure 5 It can be seen that the absolute fluorescence quantum yield (QY) of PET-based carbon dots is 54.68%.

[0041] In the UV-Vis absorption spectrum of PET-based carbon dots, there is a significant absorption peak at 247 nm, indicating the formation of a graphitic carbon structure.

[0042] Transmission electron microscopy images show that the PET-based carbon dots are spherical, exhibiting good dispersibility and no obvious agglomeration. The particle size distribution of rPET-CDs is relatively uniform, with a particle size distribution range of 0.66 nm to 5.01 nm and an average particle size of 2.32 nm.

[0043] The FTIR spectra show that the PET-based carbon dots exhibit the following absorption peaks at 3310 cm⁻¹, 2970 cm⁻¹, and 1630 cm⁻¹, corresponding to the stretching vibrations of NH / OH, CH, and C=O, respectively; the absorption peaks at 1440 cm⁻¹ and 1360 cm⁻¹ are related to C=C; the absorption peak at 1280 cm⁻¹ corresponds to the stretching vibrations of COC or CN; and the absorption peak at 1045 cm⁻¹... -1 The absorption peak at 877 cm⁻¹ reflects the bending vibration of ROR. -1 and 720cm -1 The absorption peak at this point corresponds to the out-of-plane bending vibration peak of NH. This indicates that the surface of rPET-CDs has nitrogen- and oxygen-containing functional groups, such as hydroxyl, carboxyl, and amino groups.

[0044] XPS testing results show that the PET-based carbon dots contain carbon, oxygen, and nitrogen elements. At 284.2 eV, there are absorption peaks for sp2 carbon C=C and CC; at 287.6 eV, there are absorption peaks for carbonyl carbon C=O / C=N; at 285.4 eV, there are characteristic peaks for sp3 carbon CO and CN; at 530.7 eV and 532.1 eV, there are absorption peaks for C=O and CO, respectively; and at 399.2 eV and 401.1 eV, there are absorption peaks for CN and C=N, respectively. This further confirms the presence of amino and carboxyl groups on the surface of rPET-CDs.

[0045] Thermal stability tests show that the PET-based carbon dot rPET-CDs lose 5 wt% of weight at temperature (T5). wt％ The temperature at which the maximum rate of thermal weight loss is 372℃ is the highest. max The temperature was 458℃ and the residual amount was 0.68%, indicating that rPET-CDs have high thermal stability.

[0046] Example 4: Preparation of Flame-Retardant PET / PA6 / PA66

[0047] Weigh out 0.00 g, 5.00 g, 10.00 g, 15.00 g, 20.00 g, and 25.00 g of rPET-CDs powder prepared according to Example 1, respectively, and add 500.00 g, 495.00 g, 490.00 g, 485.00 g, 480.00 g, and 485.00 g of PET powder (50 mesh) respectively to prepare rPET-CDs-PET blends of 0 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, and 5 wt%. Place the rPET-CDs-PET blends of different mass fractions into a vacuum oven at 120°C for 12 hours. When the oven temperature drops below 40°C, remove the dried rPET-CDs-PET blends and quickly transfer them to well-sealed sample bottles, seal them with sealing film, and store them. Four types of samples were injection molded using an injection molding machine to obtain rPET-CDs-PET composite materials, namely a 100mm×10mm×3mm rectangular strip, a 100mm×13mm×3mm rectangular strip, a 100mm×100mm×3mm square template, and a 20.00mm×4.00mm×1.50mm dumbbell-shaped strip.

[0048] The differential scanning calorimetry results are shown in the table below.

[0049] sample [CAT g / ℃]]> [CAT cc / ℃]]> <![CDATA[T m / ℃]]> <![CDATA[T mc / ℃]]> <![CDATA[△T mc / ℃ <!-- 3 -->]]> PET 71.62 112.77 246.84 207.09 134.07 1% rPET-CDs-PET 71.81 117.96 247.04 200.36 129.08 2% rPET-CDs-PET 71.20 118.37 246.13 207.93 127.76 3% rPET-CDs-PET 70.33 117.49 244.30 204.19 126.81 4% rPET-CDs-PET 70.55 117.59 243.97 203.54 126.38 5% rPET-CDs-PET 70.88 117.79 243.16 196.91 125.37

[0050] As shown in Table 1, compared with pure PET, rPET-CDs-PET has a higher T... g and T m Not much has changed, T cc Improve, T mc The ΔT decreases as the amount of rPET-CDs added increases. mc As the value decreases, crystallization of rPET-CDs-PET composites becomes easier.

[0051] The results of the TG-DTG analysis are shown in the table below.

[0052]

[0053] It is evident that, compared to pure PET, rPET-CDs-PET has a higher T... 5wt % and T max The decrease indicates that the addition of rPET-CDs accelerated the degradation of PET. The increase in residual mass may be due to the presence of rPET-CDs promoting the carbonization reaction of the polymer at high temperatures, generating more carbonaceous residues.

[0054] The LOI and UL-94 test results are shown in the table below.

[0055]

[0056] The results of the cone calorimetry test are shown in the table below.

[0057]

[0058]

[0059] It can be seen that, compared with pure PET, as the amount of rPET-CDs increases, the PHRR and PSPR of rPET-CDs-PET show a trend of first decreasing and then increasing.

[0060] When the addition amount of rPET-CDs is 3wt%, the PHRR and PSPR of rPET-CDs-PET are 476.91 KW / m³. 2 and 0.174m 2 / s, which is reduced by 39.45% and 25.86% compared with pure PET. The overall results show that when the addition amount of rPET-CDs is 3wt%, it has the best flame retardant effect as a blended flame retardant for PET.

[0061] When the addition amount of rPET-CDs is 3wt%, the FGI of rPET-CDs-PET is 5.30 kW / (m³). 2 ·s), FPI is 0.13 (m 2 Compared to pure PET, the FGI (flame retardancy index) is reduced by 25.35% and the FPI (flame retardancy index) is increased by 85.71% (·s) / kW, indicating a slower fire spread rate, reduced fire intensity growth in the initial stage, and lower fire hazard. The FRI (flame retardancy index) of 1.79 > 1 indicates good flame retardant properties of the rPET-CDs-PET composite material.

[0062] Example 5: Preparation of Flame-Retardant PA6

[0063] Flame-retardant PA6 was prepared in the same manner as in Example 4, except that 500.00g, 495.00g, 490.00g, 485.00g, 480.00g, and 485.00g of PA6 powder were used respectively.

[0064] The differential scanning calorimetry results are shown in the table below.

[0065]

[0066]

[0067] The results of the TG-DTG analysis are shown in the table below.

[0068]

[0069] It is evident that, after adding rPET-CDs, the T5 of rPET-CDs-PA6 is higher than that of pure PA6.wt％ and T max The residual mass decreased, but increased at 700℃. This increase in residual mass may be due to the presence of rPET-CDs promoting the carbonization reaction of PA6 at high temperatures, generating more carbonaceous residues.

[0070] The LOI and UL-94 test results are shown in the table below.

[0071]

[0072] The results of the cone calorimetry test are shown in the table below.

[0073]

[0074]

[0075] It can be seen that as the amount of rPET-CDs used increases, the PHRR and THR of rPET-CDs-PA6 show a trend of first decreasing and then increasing.

[0076] When the addition amount of rPET-CDs is 3wt%, the THR and PHRR of rPET-CDs-PA6 are 115.8 MJ / m³. 2 and 462.41KW / m 2 Compared with pure PA6, the flame retardancy was reduced by 4.38% and 19.22%; the t-PHRR was 138s, which was extended by 4.17% compared with pure PA6. The overall results show that the flame retardant effect is best when the amount of rPET-CDs added is 3wt%.

[0077] When the addition amount of rPET-CDs is 3wt%, the FGI of rPET-CDs-PA6 is 3.35 kW / (m³). 2 ·s), FPI is 0.14 (m 2 Compared to pure PA6, the FGI (flame retardancy index) is reduced by 15.83% and the FPI (flame retardancy index) is increased by 16.67%, indicating a slower fire spread rate, reduced fire intensity growth in the initial stage, and lower fire hazard. The FRI of 1.20 > 1 indicates good flame retardant properties of the rPET-CDs-PA6 composite material.

[0078] The mechanical property test results are shown in the table below.

[0079] sample Elongation at break (%) PA6 387.20±17.31 1% rPET-CDs-PA6 485.22±5.44 2% rPET-CDs-PA6 486.90±6.07 3% rPET-CDs-PA6 475.78±22.64 4% rPET-CDs-PA6 463.03±18.78 5% rPET-CDs-PA6 451.90±5.12

[0080] It is evident that the elongation at break of PA6 increases significantly after the addition of rPET-CDs-.

[0081] Example 6: Preparation of Flame-Retardant PA66

[0082] Flame-retardant PA66 was prepared in the same manner as in Example 4, except that 500.00g, 495.00g, 490.00g, 485.00g, 480.00g, and 485.00g of PA66 powder were used respectively.

[0083] The differential scanning calorimetry results are shown in the table below.

[0084] sample <![CDATA[T m / ℃]]> <![CDATA[T mc / ℃]]> PA66 261.88 231.08 1% rPET-CDs-PA66 260.69 233.80 2% rPET-CDs-PA66 259.66 233.71 3% rPET-CDs-PA66 259.1 232.61 4% rPET-CDs-PA66 259.57 232.17 5% rPET-CDs-PA66 258.6 230.97

[0085] The results of the TG-DTG analysis are shown in the table below.

[0086]

[0087] After adding rPET-CDs, the T of rPET-CDs-PA66 5wt％ Lower T max The increase in temperature is likely due to the promoting effect of rPET-CDs on the degradation of PA66, causing PA66 to begin decomposition at lower temperatures. Although rPET-CDs catalyze the initial decomposition process, as the temperature continues to rise, the decomposition products of PA66 may form new stable phases with rPET-CDs, delaying further decomposition and thus increasing the temperature of maximum decomposition rate. The increase in residual mass may be due to the presence of rPET-CDs promoting the carbonization reaction of PA66 at high temperatures, generating more carbonaceous residues.

[0088] The LOI and UL-94 test results are shown in the table below.

[0089]

[0090] The results of the cone calorimetry test are shown in the table below.

[0091]

[0092] It can be seen that as the amount of rPET-CDs used increases, the PHRR of rPET-CDs-PA66 shows a trend of first decreasing and then increasing.

[0093] When the addition amount of rPET-CDs was 3wt%, the TTI of rPET-CDs-PA66 was 96s, which was 23.08% longer than that of pure PA66; the PHRR was 621.23KW / m 2 Compared to pure PA66, the concentration was reduced by 2.41%. When the addition amount of rPET-CDs was 2wt%, the TTI of rPET-CDs-PA66 was 85s and 142s, which was reduced by 8.97% compared to pure PA66; the PHRR was 490.67KW / m 2Compared with pure PA66, the flame retardancy was reduced by 22.97%. Overall results indicate that the flame retardant effect was optimal when the amount of rPET-CDs added was 3 wt%.

[0094] When the addition amount of rPET-CDs is 3wt%, the FGI of rPET-CDs-PA66 is 4.53kW / (m³). 2 ·s), FPI is 0.15 (m 2 Compared to pure PA66, the flame retardant ratio (FGI) decreased by 10.47% and the flame intensity index (FPI) increased by 25%, indicating a slower fire spread rate, reduced fire intensity growth in the initial stage, and lower fire hazard. The FRI of 1.26 > 1 indicates good flame retardant properties of the rPET-CDs-PA66 composite material.

[0095] The mechanical property test results are shown in the table below.

[0096] sample Tensile strength (MPa) Elastic modulus (MPa) PA66 79.61±0.47 1299.54±4.94 1% rPET-CDs-PA66 80.29±2.00 1329.38±20.77 2% rPET-CDs-PA66 82.31±0.80 1342.36±16.17 3% rPET-CDs-PA66 83.18±2.83 1345.79±23.35 4% rPET-CDs-PA66 88.45±1.45 1415.17±17.70 5% rPET-CDs-PA66 89.18±5.42 1455.41±80.78

[0097] The present invention has been described in detail above with reference to specific embodiments and / or exemplary examples, as well as the accompanying drawings. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. PET-based carbon dots are prepared by one-step pyrolysis of PET products and ethanolamine. These PET-based carbon dots have a graphite carbon structure.

2. The PET-based carbon dots as described in claim 1, wherein the fluorescence intensity of the PET-based carbon dots reaches its maximum at an excitation wavelength of 340 nm, at which time the fluorescence emission wavelength is approximately 430 nm, and the fluorescence quantum yield reaches 54.68%.

3. A method for preparing PET-based carbon dots, characterized in that, PET products are pyrolyzed with alcoholamines at high temperatures to obtain PET-based carbon dots.

4. The method of claim 3, wherein, The high temperature is 240-300℃, preferably about 260℃.

5. The method of claim 3, wherein, The pyrolysis reaction takes more than 10 hours, preferably 12-36 hours, and more preferably 18 hours.

6. The method of claim 3, wherein, The ratio of PET to ethanolamine is 100g:(55-75)mL, preferably 100g:65mL, based on the mass ratio of PET to the volume ratio of ethanolamine.

7. The method of claim 3, wherein, The PET products are preferably made from PET waste.

8. The use of the PET-based carbon dots of claim 1 for polymer flame retardant modification.

9. Flame-retardant modified PET, obtained by blending the PET-based carbon dots described in claim 1 with PET, wherein, The amount of PET-based carbon dots is 1-10% of their total weight with the polymer, more preferably 2-5%, and most preferably about 3%.

10. A flame-retardant modified polyamide, obtained by blending the PET-based carbon dots of claim 1 with polyamide, wherein, The amount of PET-based carbon dots is 1-10% of their total weight with the polymer, more preferably 2-5%, and most preferably about 3%.

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