A method for chemical recycling of PLA-containing blended plastics

Abstract

The present invention discloses a method for chemically recycling PLA-containing blended plastics, belonging to the technical field of plastic degradation and recycling. The present invention solves the problem that the existing chemical recycling methods cannot meet the separation and recycling of PLA-containing blended plastics. The present invention heats and depolymerizes the PLA-containing blended plastics in a polar organic solvent under the catalysis of a zinc-based or magnesium-based catalyst to obtain the depolymerization product lactide monomer of polylactic acid, and directly separates to obtain other blended components. The recycling process provided by the present invention has mild reaction conditions, the catalyst used is environmentally friendly, the purity of the recovered lactide monomer reaches more than 99%, and at the same time, the efficient and high-yield separation and recycling of other components in the mixed plastics are realized, which is of great significance to environmental protection and the research on the utilization of waste plastics.

Description

Technical Field

[0001] The present invention relates to a method for chemical recycling of PLA-containing blended plastics, belonging to the technical field of plastic degradation and recycling. Background Art

[0002] PLA is a biodegradable plastic with biocompatibility and excellent mechanical properties. However, due to its inherent brittleness, low elongation at break, low impact strength, and poor heat resistance, the application fields of PLA are limited. In practical applications, it is often used in blends with other components, such as PBAT, PBS, etc.

[0003] However, at present, the traditional depolymerization methods for single polylactic acid products cannot be used for PLA / PBAT, PLA / PBS and other mixed plastics in actual production applications, and the separation and recycling of such mixed plastics cannot be achieved. Traditional waste plastic treatment methods such as incineration and landfill have caused a large amount of carbon dioxide emissions and environmental pollution. Therefore, providing a method for chemically recycling PLA-containing blended plastics under mild conditions is of great scientific and economic value and is of great significance for environmental protection and sustainable development. Summary of the Invention

[0004] Aiming at the problem that the existing chemical recycling methods cannot meet the separation and recycling of PLA-containing blended plastics, the present invention provides a method for chemical recycling of PLA-containing blended plastics.

[0005] The technical solution of the present invention:

[0006] One of the purposes of the present invention is to provide a method for chemical recycling of PLA-containing blended plastics, the method comprising the following steps:

[0007] S1, mixing the blended plastic particles, a catalyst and an organic solvent, and depolymerizing under normal pressure and heating conditions;

[0008] S2, filtering the depolymerized solution after cooling, and subjecting the filtrate to distillation and drying treatments to obtain the depolymerization product lactide, and drying the filter residue to obtain the blended components.

[0009] Further defined, in S1, the blended plastic is a blend composed of PLA and blended components PBAT, PBS, PE, PP, PVC or PET.

[0010] Even further defined, the blended plastic is one or more of waste, scraps generated during processing, and unqualified products, mixed in any proportion.

[0011] Even further defined, the proportion of PLA in the blended plastic is 0.1 to 50 wt.%.

[0012] Further limitation: In S1, the catalyst is zinc bis(bis(trimethylsilyl)amide) or magnesium bis(bis(trimethylsilyl)amide).

[0013] Further limitation: In S1, the dosage of the catalyst is 0.1 - 50 wt.% of the blended plastic.

[0014] Further limitation: The organic solvent is a polar organic solvent.

[0015] Further limitation: The organic solvent is DMF, DMSO, GVL or MeCN.

[0016] Further limitation: In S1, the reaction temperature is 25 - 250 °C.

[0017] Further limitation: In S1, the reaction time is 2 - 10 h.

[0018] Further limitation: The depolymerization product lactide obtained in S2 is recrystallized twice with toluene and then dried to obtain pure lactide.

[0019] Further limitation: The purity of the pure lactide is above 99%.

[0020] Further limitation: The recovery rate of the blended components is above 90%.

[0021] The present invention has the following beneficial effects compared with the prior art:

[0022] (1) The present invention realizes the selective cleavage of the polylactic acid molecular chains in the blended plastic under mild conditions, achieves the depolymerization of PLA in the blended plastic, selectively depolymerizes to obtain lactide monomers and separates other blended components. The obtained lactide monomers can be directly reused, reducing industrial steps and costs, and conforming to the principle of sustainable development.

[0023] (2) The method provided by the present invention has good substrate generality and has good depolymerization effects on both PLA / PBAT plastic mixtures and PLA / PBS plastic mixtures with different PLA mass fractions, and can efficiently recover the products.

[0024] (3) The present invention selects a catalyst with high catalytic efficiency, which can complete the catalysis with a relatively low catalyst loading, has a high product yield, few side reactions, and good economic benefits. Description of the Drawings

[0025] Figure 1 1H NMR spectrum of the lactide obtained in Example 1; Detailed Embodiments

[0026] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given in conjunction with the embodiments of the specification.

[0027] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways than those specifically described herein, and those skilled in the art can make similar generalizations without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0028] Secondly, as used herein, an "embodiment" or "embodiments" refers to a particular feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it an isolated or alternative embodiment that is mutually exclusive with other embodiments.

[0029] Example 1:

[0030] Depolymerization of PLA / PBAT plastic bags involving zinc bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0031]

[0032] The specific operation process is as follows:

[0033] A. Depolymerization: Take a 100 mL Schlenk flask, evacuate, bake, and replace with argon. Then, in a glove box, add 12 g (57.1 mmol of polymer repeating units) of plastic bag fragments, add 0.6 g of Zn[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to polymer repeating units), add 57 mL of DMF, and stir and react at 160 °C in a fume hood. After reacting for 4 h, take a sample for NMR detection. The results show that the conversion rate of PLA is 100% and the yield of lactide is 100%.

[0034] B. Separation:

[0035] ① After the reaction solvent is cooled, filter and dry to obtain 4.8 g of filter residue PBAT, with a recovery rate of 96.2%.

[0036] ② After a large amount of DMF is removed by distillation from the filtrate obtained in step ①, add n-heptane to the reaction system and perform azeotropic distillation with the remaining DMF. After drying, a yellow viscous solid, lactide, is obtained.

[0037] C. Purification: Add toluene to the lactide solid collected in step B for recrystallization. After drying, a white powdery solid product, lactide, is obtained, 4.7 g, with a yield of 67% and a purity of 99.8%, as Figure 1 shown.

[0038] Example 2:

[0039] Depolymerization of PLA / PBAT plastic bags involving zinc bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0040]

[0041] The specific operation process is as follows:

[0042] A. Depolymerization: Take a 100 mL Schlenk flask, evacuate, bake, and replace with argon. Then, in a glove box, add 12 g (57.1 mmol of polymer repeat units) of plastic bag fragments, add 0.6 g of Zn[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to polymer repeat units), add 57 mL of DMSO, and stir and react at 160 °C in a fume hood. After reacting for 5 h, take a sample for NMR detection. The results show that the conversion rate of PLA is 100% and the yield of lactide is 100%.

[0043] B. Separation:

[0044] ① After the reaction solvent cools down, filter and dry to obtain 4.8 g of PBAT as the filter residue, with a recovery rate of 96.8%.

[0045] ② After the filtrate obtained in step ① is distilled to remove a large amount of DMSO, add n-heptane to the reaction system, and perform azeotropic distillation with the remaining DMSO. After drying, obtain yellow viscous solid lactide.

[0046] C. Purification: Add toluene to the lactide solid collected in step B for recrystallization. After drying, obtain 4.9 g of white powdery solid product lactide, with a yield of 69% and a purity of 99.2%.

[0047] Example 3:

[0048] Depolymerization of PLA / PBAT plastic bags involving zinc bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0049]

[0050] The specific operation process is as follows:

[0051] A. Depolymerization: Take a 100 mL Schlenk flask, evacuate, bake, and replace with argon. Then, in a glove box, add 12 g (57.1 mmol of polymer repeat units) of plastic bag fragments, add 0.6 g of Zn[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to polymer repeat units), add 57 mL of GVL, and stir and react at 160 °C in a fume hood. After reacting for 6 h, take a sample for NMR detection. The results show that the conversion rate of PLA is 100% and the yield of lactide is 100%.

[0052] B. Separation:

[0053] ① After the reaction solvent was cooled, 4.9 g of filter residue PBAT was obtained by filtration and drying, with a recovery rate of 98.2%.

[0054] ② After a large amount of GVL was removed from the filtrate obtained in step ① by distillation, n - heptane was added to the reaction system, and azeotropic distillation was carried out with the remaining GVL, and yellow viscous solid lactide was obtained after drying.

[0055] C. Purification: The lactide solid collected in step B was recrystallized with toluene, and after drying, 4.0 g of white powdery solid product lactide was obtained, with a yield of 56% and a purity of 99.8%.

[0056] Example 4:

[0057] Depolymerization of PLA / PBAT plastic bags participated by zinc bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0058]

[0059] The specific operation process is as follows:

[0060] A. Depolymerization: Take a 100 mL Schlenk flask, evacuate and replace with argon, then in the glove box, add 12 g (57.1 mmol of polymer repeat units) of plastic bag fragments, add 0.6 g of Zn[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeat units), add 57 mL of MeCN, and stir and react at 160 °C in the fume hood. After reacting for 10 h, a sample was taken for NMR detection, and the results showed that the conversion rate of PLA was 78% and the yield of lactide was 78%.

[0061] B. Separation:

[0062] ① After the reaction solvent was cooled, 4.9 g of filter residue PBAT was obtained by filtration and drying, with a recovery rate of 98.8%.

[0063] ② The filtrate obtained in step ① was removed of MeCN in vacuo, and yellow viscous solid lactide was obtained after drying.

[0064] C. Purification: The lactide solid collected in step B was recrystallized with toluene, and after drying, 6.1 g of white powdery solid product lactide was obtained, with a yield of 86% and a purity of 99.6%.

[0065] Example 5:

[0066] Depolymerization of PLA / PBAT plastic bags participated by magnesium bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0067]

[0068] The specific operation process is as follows:

[0069] A. Depolymerization: Take a 100 mL Schlenk flask, evacuate, bake and replace with argon, then in the glove box, add 12 g (57.1 mmol polymer repeating units) of plastic bag fragments, add 0.6 g of Mg[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeating units), add 57 mL of DMF, and stir and react at 160 °C in the fume hood. After reacting for 2 h, take a sample for NMR detection. The results show that the PLA conversion rate is 100% and the lactide yield is 100%.

[0070] B. Separation:

[0071] ① After the reaction solvent is cooled, filter and dry to obtain 4.8 g of filter residue PBAT, with a recovery rate of 97.3%.

[0072] ② After a large amount of DMF is removed by distillation from the filtrate obtained in step ①, add n-heptane to the reaction system, perform azeotropic distillation with the remaining DMF, and dry to obtain yellow viscous solid lactide.

[0073] C. Purification: Add the lactide solid collected in step B to toluene for recrystallization, and after drying, obtain 3.8 g of white powdery solid product lactide, with a yield of 54% and a purity of 99.2%.

[0074] Example 6:

[0075] Depolymerization of PLA / PBAT plastic bags participated by magnesium bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0076]

[0077] The specific operation process is as follows:

[0078] A. Depolymerization: Take a 100 mL Schlenk flask, evacuate, bake and replace with argon, then in the glove box, add 12 g (57.1 mmol polymer repeating units) of plastic bag fragments, add 0.6 g of Mg[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeating units), add 57 mL of DMSO, and stir and react at 160 °C in the fume hood. After reacting for 3 h, take a sample for NMR detection. The results show that the PLA conversion rate is 100% and the lactide yield is 100%.

[0079] B. Separation:

[0080] ① After the reaction solvent was cooled, 4.8 g of the filter residue PBAT was obtained through filtration and drying, with a recovery rate of 95.8%.

[0081] ② After a large amount of DMSO was removed by distillation from the filtrate obtained in step ①, n-heptane was added to the reaction system and azeotropically distilled with the remaining DMSO, and a yellow viscous solid lactide was obtained after drying.

[0082] C. Purification: The lactide solid collected in step B was added with toluene for recrystallization, and after drying, 4.4 g of white powdery solid product lactide was obtained, with a yield of 63% and a purity of 99.5%.

[0083] Example 7:

[0084] Depolymerization of PLA / PBAT plastic bags participated by magnesium bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0085]

[0086] The specific operation process is as follows:

[0087] A. Depolymerization: Take a 100 mL Schlenk flask, evacuate, bake and displace with argon, then in the glove box, add 12 g (57.1 mmol of polymer repeating units) of plastic bag fragments, add 0.6 g of Mg[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to polymer repeating units), add 57 mL of GVL, and stir and react at 160 °C in the fume hood. After reacting for 5 h, a sample was taken for NMR detection, and the results showed that the conversion rate of PLA was 100% and the yield of lactide was 100%.

[0088] B. Separation:

[0089] ① After the reaction solvent was cooled, 4.8 g of the filter residue PBAT was obtained through filtration and drying, with a recovery rate of 96.6%.

[0090] ② After a large amount of GVL was removed by distillation from the filtrate obtained in step ①, n-heptane was added to the reaction system and azeotropically distilled with the remaining GVL, and a yellow viscous solid lactide was obtained after drying.

[0091] C. Purification: The lactide solid collected in step B was added with toluene for recrystallization, and after drying, 4.3 g of white powdery solid product lactide was obtained, with a yield of 61% and a purity of 99.4%.

[0092] Example 8:

[0093] Depolymerization of PLA / PBAT plastic bags participated by magnesium bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0094]

[0095] The specific operation process is as follows:

[0096] A. Depolymerization: Take a 100 mL Schlenk flask, evacuate, bake and replace with argon. Then, in the glove box, add 12 g (57.1 mmol of polymer repeating units) of plastic bag fragments, add 0.6 g of Mg[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeating units), add 57 mL of MeCN, and stir and react at 160 °C in the fume hood. After reacting for 1 h, take a sample for NMR detection. The results show that the conversion rate of PLA is 100% and the yield of lactide is 100%.

[0097] B. Separation:

[0098] ① After the reaction solvent cools down, filter and dry to obtain 4.8 g of filter residue PBAT, with a recovery rate of 96.8%.

[0099] ② Evaporate MeCN from the filtrate obtained in step ① in vacuo and dry to obtain yellow viscous solid lactide.

[0100] C. Purification: Add the lactide solid collected in step B to toluene for recrystallization, and after drying, obtain 2.4 g of white powdery solid product lactide, with a yield of 34% and a purity of 99.7%.

[0101] Example 9:

[0102] Depolymerization of PLA / PBS straws participated by zinc bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0103]

[0104] The specific operation process is as follows:

[0105] (1) Take a 100 mL Schlenk flask, evacuate, bake and replace with argon. Then, in the glove box, add 12 g (57.1 mmol of polymer repeating units) of straw fragments, add 0.6 g of Zn[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeating units), add 57 mL of DMF, and stir and react at 160 °C in the fume hood.

[0106] (2) After reacting for 6 h, take a sample for NMR detection. The results show that the conversion rate of PLA is 100% and the yield of lactide is 100%.

[0107] (3) Separation of the reaction product:

[0108] ① After the reaction solvent was cooled, 7.0 g of filter residue PBS was obtained through filtration and drying, with a recovery rate of 92.7%.

[0109] ② After a large amount of DMF was removed from the filtrate obtained in step ① by distillation, n-heptane was added to the reaction system, and azeotropic distillation was carried out with the remaining DMF. After drying, a yellow viscous solid, lactide, was obtained.

[0110] ③ The solid obtained in step ② was collected, recrystallized with toluene, and after drying, the product lactide, a white powdery solid, 3.5 g, with a yield of 79% and a purity of 99.3%, was obtained.

[0111] Example 10:

[0112] Depolymerization of PLA / PBS straws participated by zinc bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0113]

[0114] The specific operation process is as follows:

[0115] (1) Take a 100 mL Schlenk flask, evacuate, bake and replace with argon, then in the glove box, add 12 g (57.1 mmol of polymer repeating units) of straw fragments, add 0.6 g of Zn[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeating units), add 57 mL of DMSO, and stir and react at 160 °C in the fume hood.

[0116] (2) After reacting for 7 h, a sample was taken for NMR detection. The results showed that the conversion rate of PLA was 100% and the yield of lactide was 100%.

[0117] (3) Separation of the reaction product:

[0118] ① After the reaction solvent was cooled, 7.2 g of filter residue PBS was obtained through filtration and drying, with a recovery rate of 95.6%.

[0119] ② After a large amount of DMSO was removed from the filtrate obtained in step ① by distillation, n-heptane was added to the reaction system, and azeotropic distillation was carried out with the remaining DMSO. After drying, a yellow viscous solid, lactide, was obtained.

[0120] ③ The solid obtained in step ② was collected, recrystallized with toluene, and after drying, the product lactide, a white powdery solid, 3.3 g, with a yield of 75% and a purity of 99.4%, was obtained.

[0121] Example 11:

[0122] Depolymerization of PLA / PBS straws participated by zinc bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0123]

[0124] The specific operation process is as follows:

[0125] (1) Take a 100 mL Schlenk flask, evacuate, bake and replace with argon. Then, in the glove box, add 12 g (57.1 mmol of polymer repeating units) of straw fragments, add 0.6 g of Zn[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeating units), add 57 mL of GVL, and stir and react at 160 °C in the fume hood.

[0126] (2) After reacting for 8 h, take a sample for NMR detection. The results show that the conversion rate of PLA is 100% and the yield of lactide is 100%.

[0127] (3) Separation of the reaction product:

[0128] ① After the reaction solvent is cooled, filter and dry to obtain 7.1 g of filter residue PBS, with a recovery rate of 93.9%.

[0129] ② After a large amount of GVL is removed by distillation from the filtrate obtained in step ①, add n-heptane to the reaction system and perform azeotropic distillation with the remaining GVL. After drying, a yellow viscous solid, lactide, is obtained.

[0130] ③ Collect the solid obtained in step ②, add toluene for recrystallization, and after drying, obtain the product lactide, 2.9 g of white powdery solid, with a yield of 65% and a purity of 99.3%.

[0131] Example 12:

[0132] Depolymerization of PLA / PBS straws participated by zinc bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0133]

[0134] The specific operation process is as follows:

[0135] (1) Take a 100 mL Schlenk flask, evacuate, bake and replace with argon. Then, in the glove box, add 12 g (57.1 mmol of polymer repeating units) of straw fragments, add 0.6 g of Zn[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeating units), add 57 mL of MeCN, and stir and react at 160 °C in the fume hood.

[0136] (2) After reacting for 10 h, take a sample for NMR detection. The results show that the conversion rate of PLA is 83% and the yield of lactide is 83%.

[0137] (3) Separation of the reaction product:

[0138] ① After the reaction solvent was cooled, 7.2 g of filter residue PBS was obtained by filtration and drying, with a recovery rate of 95.3%.

[0139] ② The filtrate obtained in step ① was removed of MeCN under vacuum and dried to obtain yellow viscous solid lactide.

[0140] ③ The solid obtained in step ② was collected, recrystallized with toluene, and dried to obtain the product lactide, 3.7 g of white powdery solid, with a yield of 83% and a purity of 99.2%.

[0141] Example 13:

[0142] Depolymerization of PLA / PBS straws participated by magnesium bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0143]

[0144] The specific operation process is as follows:

[0145] (1) Take a 100 mL Schlenk flask, evacuate and bake it and replace it with argon, then in the glove box, add 12 g (57.1 mmol polymer repeating units) of straw fragments, add 0.6 g of Mg[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeating units), add 57 mL of DMF, and stir and react at 160 °C in the fume hood.

[0146] (2) After reacting for 3 h, take a sample for NMR detection. The results show that the conversion rate of PLA is 100% and the yield of lactide is 100%.

[0147] (3) Separation of the reaction product:

[0148] ① After the reaction solvent was cooled, 7.3 g of filter residue PBS was obtained by filtration and drying, with a recovery rate of 96.2%.

[0149] ② After a large amount of DMF was removed from the filtrate obtained in step ① by distillation, n-heptane was added to the reaction system, and it was co-distilled with the remaining DMF and dried to obtain yellow viscous solid lactide.

[0150] ③ The solid obtained in step ② was collected, recrystallized with toluene, and dried to obtain the product lactide, 3.2 g of white powdery solid, with a yield of 72% and a purity of 99.5%.

[0151] Example 14:

[0152] Depolymerization of PLA / PBS straws participated by magnesium bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0153]

[0154] The specific operation process is as follows:

[0155] (1) Take a 100 mL Schlenk flask, evacuate, bake and replace with argon. Then, in the glove box, add 12 g (57.1 mmol of polymer repeating units) of straw fragments, add 0.6 g of Mg[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeating units), add 57 mL of DMSO, and stir and react at 160 °C in the fume hood.

[0156] (2) After reacting for 5 h, take a sample for NMR detection. The results show that the conversion rate of PLA is 100% and the yield of lactide is 100%.

[0157] (3) Separation of the reaction product:

[0158] ① After the reaction solvent cools down, filter and dry to obtain 7.3 g of filter residue PBS, with a recovery rate of 96.7%.

[0159] ② After distilling off a large amount of DMSO from the filtrate obtained in step ①, add n-heptane to the reaction system and perform azeotropic distillation with the remaining DMSO. After drying, obtain yellow viscous solid lactide.

[0160] ③ Collect the solid obtained in step ②, add toluene for recrystallization, and after drying, obtain the product lactide, 3.0 g of white powdery solid, with a yield of 68% and a purity of 99.4%.

[0161] Example 15:

[0162] Depolymerization of PLA / PBS straws participated by magnesium bis(bis(trimethylsilyl))amide. The depolymerization process is as follows:

[0163]

[0164] The specific operation process is as follows:

[0165] (1) Take a 100 mL Schlenk flask, evacuate, bake and replace with argon. Then, in the glove box, add 12 g (57.1 mmol of polymer repeating units) of straw fragments, add 0.6 g of Mg[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeating units), add 57 mL of GVL, and stir and react at 160 °C in the fume hood.

[0166] (2) After reacting for 4 h, take a sample for NMR detection. The results show that the conversion rate of PLA is 100% and the yield of lactide is 100%.

[0167] (3) Separation of the reaction product:

[0168] ① After the reaction solvent was cooled, 7.2 g of filter residue PBS was obtained by filtration and drying, and the recovery rate was 94.8%.

[0169] ② After a large amount of GVL was removed from the filtrate obtained in step ① by distillation, n - heptane was added to the reaction system, and azeotropic distillation was carried out with the remaining GVL, and yellow viscous solid lactide was obtained after drying.

[0170] ③ The solid obtained in step ② was collected, recrystallized with toluene, and after drying, 2.6 g of product lactide, a white powdery solid, was obtained, with a yield of 59% and a purity of 99.7%.

[0171] Example 16:

[0172] Depolymerization of PLA / PBS straws participated by magnesium bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0173]

[0174] The specific operation process is as follows:

[0175] (1) Take a 100 mL Schlenk flask, evacuate, bake and replace with argon, then in the glove box, add 12 g (57.1 mmol of polymer repeating units) of straw fragments, add 0.6 g of Mg[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeating units), add 57 mL of MeCN, and stir and react at 160 °C in the fume hood.

[0176] (2) After reacting for 7 h, a sample was taken for NMR detection. The results showed that the conversion rate of PLA was 100% and the yield of lactide was 100%.

[0177] (3) Separation of the reaction product:

[0178] ① After the reaction solvent was cooled, 7.4 g of filter residue PBS was obtained by filtration and drying, and the recovery rate was 97.9%.

[0179] ② The filtrate obtained in step ① was removed of MeCN in vacuo and yellow viscous solid lactide was obtained after drying.

[0180] ③ The solid obtained in step ② was collected, recrystallized with toluene, and after drying, 2.0 g of product lactide, a white powdery solid, was obtained, with a yield of 46% and a purity of 99.1%.

[0181] Example 17:

[0182] Depolymerization of PLA / PBAT plastic bags with zinc bis(bis(trimethylsilyl)amide). The depolymerization process is as follows:

[0183]

[0184] The specific operation process is as follows:

[0185] A. Depolymerization: Take a 100 mL Schlenk flask, evacuate, bake and replace with argon. Then, in the glove box, add 12 g (57.1 mmol of polymer repeating units) of plastic bag fragments, add 0.6 g of Zn[N(SiMe3)2]2 catalyst (5 wt.%, 1.6 mmol, 2.8 mol% relative to the polymer repeating units), add 57 mL of toluene, and stir and react at 160 °C in the fume hood. After reacting for 24 h, take a sample for NMR detection. The results show that the conversion rate of PLA < 5%, and it is difficult to achieve the depolymerization process of PLA.

[0186] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A method for chemical recycling of PLA-containing blended plastics, characterized in that, Including: S1. Mix the blended plastic particles, catalyst and organic solvent, and depolymerize under normal pressure and heating conditions; The organic solvent in S1 is a polar organic solvent, specifically DMF, DMSO, GVL or MeCN; The blended plastic in S1 is a blend composed of PLA and blending components PBAT, PBS, PE, PP, PVC or PET; The proportion of PLA in the blended plastic is 0.1 - 50 wt.%; The catalyst in S1 is zinc bis(bis(trimethylsilyl))amide or magnesium bis(bis(trimethylsilyl))amide; S2. After the depolymerization solution is cooled, filter it. The filtrate is subjected to distillation and drying treatments to obtain the depolymerization product lactide, and the filter residue is dried to obtain the blending components.

2. The method for chemically recycling the PLA-containing blend plastic according to claim 1, wherein The dosage of the catalyst in S1 is 0.1 - 50 wt.% of the blended plastic.

3. The method for chemically recycling the PLA-containing blend plastic according to claim 1, characterized in that, The reaction temperature in S1 is 25 - 250 °C.

4. The method for chemically recycling PLA-containing blended plastics according to claim 1, characterized in that, The reaction time in S1 is 2 - 10 h.

5. A method for chemically recycling PLA-containing blended plastics, characterized in that, Including: S1. Mix the blended plastic particles, catalyst and organic solvent, and depolymerize under normal pressure and heating conditions; The organic solvent in S1 is a polar organic solvent, specifically DMF, DMSO, GVL or MeCN; The blended plastic in S1 is a blend composed of PLA and blending components PBAT, PBS, PE, PP, PVC or PET; The proportion of PLA in the blended plastic is 0.1 - 50 wt.%; The catalyst in S1 is zinc bis(bis(trimethylsilyl))amide or magnesium bis(bis(trimethylsilyl))amide; S2. After the depolymerization solution is cooled, filter it. The filtrate is subjected to distillation and drying treatments to obtain the depolymerization product lactide, and the filter residue is dried to obtain the blending components; S3. Add the depolymerization product lactide obtained in S2 to toluene and recrystallize it twice, and then obtain pure lactide after drying.

6. The method for chemically recycling PLA-containing blend plastics according to claim 5, characterized in that, The recovery rate of the blending components is more than 90%; the purity of the pure lactide is more than 99%.

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