Method for recycling waste photovoltaic backboard polyester through click-dynamic cross-linking upgrading

Abstract

The invention discloses a method for recycling waste photovoltaic backboard polyester through click-dynamic crosslinking upgrading, and particularly relates to the field of new energy photovoltaic module recycling. The method comprises the following steps: crushing a PET polyester plate separated from a waste photovoltaic backboard, mixing the crushed PET polyester plate with dihydric alcohol and a catalyst, and heating to carry out glycolysis reaction so as to realize partial degradation and hydroxyl end capping of PET. A curing process is carried out by utilizing a reaction of carbon-carbon double bonds introduced in a repolymerization process and a dynamic cross-linking agent, and the prepared regenerated polyester product has excellent mechanical properties and excellent reprocessing properties. According to the method, no waste is generated in the polymerization process, the reaction is green and efficient, the performance of the product is close to that of commercially available PET plastic, the product is easy to reprocess, the product can be quickly healed at the temperature of 80 DEG C for 15 minutes after cracks appear, the product can be reprocessed into sheets at the temperature of 100 DEG C for 2 hours after being ground into powder, the recycling energy consumption is greatly reduced, and the commercial polyester material is expected to be partially replaced.

Description

Technical Field

[0001] The invention belongs to the field of photovoltaic component recycling, and in particular relates to a method for recycling waste photovoltaic backplane polyester by click-dynamic cross-linking. Background Art

[0002] Recycling and resource utilization of waste polymer materials is an important part of developing a green, low-carbon circular economy. With the massive increase in demand for green energy, my country's new energy industry has developed rapidly and has now become the world's largest photovoltaic application market. The service life of photovoltaic modules is generally 20 to 25 years.

[0003] The polymer backsheet is an important component of photovoltaic modules. It is generally a composite structure with PET film as the base film, and fluorine film or other plastic films adhered to both sides of the base film by adhesives. The middle layer of PET polyester material with a high proportion mainly plays the role of electrical insulation, chemical barrier and mechanical support. Fluorine-containing multi-layer co-extruded photovoltaic backsheets are difficult to separate and recycle. The existing recycling methods are mainly thermal, chemical and physical recycling methods. The thermal decomposition method consumes a lot of energy and produces toxic gases to pollute the environment. The chemical depolymerization method usually faces problems such as low recycling rate, high cost, harsh conditions, and poor performance of recycled products.

[0004] Therefore, there is an urgent need to provide a simple, efficient and environmentally friendly method for recycling photovoltaic backplane polyester to fill the last link in the green and low-carbon circular development of the photovoltaic industry chain, and to promote the healthy development of the photovoltaic recycling industry and the efficient use of resources. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for recycling waste photovoltaic backplane polyester by click-dynamic cross-linking, aiming to solve the problems of low resource utilization, environmental pollution and poor performance of recycled products in existing recycling schemes. Its characteristics are:

[0006] The carbon-carbon double bonds are introduced into the polyester main chain by repolymerizing partially degraded and hydroxyl-terminated PET oligomers with bio-based unsaturated dibasic acids, and the material is solidified by a thiol-ene click reaction under the treatment of a borate dynamic crosslinker. No waste is generated during the polymerization process, the reaction is green and efficient, and the prepared recycled polyester has excellent mechanical properties and is easy to reprocess, greatly reducing recycling energy consumption, and is expected to partially replace commercial polyester materials.

[0007] The present invention first discloses a method for recycling waste photovoltaic backplane polyester by click-dynamic cross-linking, comprising the following steps:

[0008] (1) The discarded photovoltaic backsheet is stirred in a renewable and environmentally friendly solvent at a certain stirring rate of 60-80° C. for 0.5-1 h. After the adhesive layer is completely swollen, it is taken out, and the PET layer is peeled off and crushed;

[0009] (2) adding the above materials to a certain amount of glycolysis catalyst and diol solvent, heating to 190-220° C. and stirring at a certain stirring rate for 2-6 h until PET is converted into a white slurry and then stopping the reaction;

[0010] (3) washing the white slurry with excess water to remove the diol, then filtering to obtain a mixture precipitate, drying it at 30° C. for 12-24 hours, and then grinding it into powder;

[0011] (4) mixing the powder with a bio-based unsaturated dibasic acid at a molar ratio of 1:1 and a certain amount of catalyst into a three-necked flask, introducing nitrogen gas and heating to 180° C. for polymerization for 4-6 h to obtain a polyester with a carbon-carbon double bond in the main chain;

[0012] (5) Add a certain amount of dynamic crosslinking agent and photoinitiator to the polyester with carbon-carbon double bonds in the main chain, stir until the mixture is uniform, pour into a mold, and treat under ultraviolet light for 15-30 minutes to fully crosslink to obtain a recycled polyester material.

[0013] Furthermore, the renewable environmentally friendly solvent in step (1) is (R)-(+)-limonene; the stirring conditions are: stirring temperature 60-80° C., stirring time 0.5-1 h, stirring rate 400 r / min;

[0014] Furthermore, in step (2), the glycolysis catalyst is selected from tetrabutyl titanate, zinc acetate or cobalt acetate; and the diol is selected from ethylene glycol or propylene glycol.

[0015] Furthermore, in step (2), the amount of the glycolysis catalyst added is 0.5-1% of the total mass of the first intermediate material and the diol solvent; and the certain stirring rate is 400 r / min.

[0016] Furthermore, in step (2), the mass ratio of the first intermediate material to the diol is 1:1-2.

[0017] Furthermore, in step (4), the bio-based unsaturated dibasic acid is selected from any one of fumaric acid, maleic acid or muconic acid; the catalyst is selected from any one of tetrabutyl titanate, zinc acetate or cobalt acetate, and the added amount is 0.5-1% of the total mass of the powder and the dibasic acid.

[0018] Furthermore, in step (5), the dynamic crosslinking agent is 2,2′-(1,4-phenylene)bis[1,3,2-dioxaborolane-4-methylthiol]; and the photoinitiator is selected from 2,2-diethoxyacetophenone or benzoin dimethyl ether.

[0019] Furthermore, the molar equivalent ratio of the dynamic crosslinking agent and the photoinitiator in step (5) to the unsaturated dibasic acid in step (4) is 0.5-1:0.1-0.2:1.

[0020] The present invention also discloses a recycled polyester material obtained by any of the above-mentioned click-dynamic cross-linking methods for upgrading and recycling waste photovoltaic backplane polyester.

[0021] Compared with the prior art, the click-dynamic cross-linking upcycling method for waste photovoltaic backplane polyester of the present invention has the following effects:

[0022] (1) The present invention is the first to apply a simple, green and efficient click chemistry reaction to the recycling of waste polyester. The dynamic borate bonds introduced between PET molecular chains give it excellent mechanical properties and reprocessability.

[0023] (2) By controlling the degradation reaction time and temperature, the molecular weight of some degraded waste can be adjusted. By controlling the cooling rate during solidification, the crystallinity of the recycled polyester product can be regulated to achieve adjustable performance. The final product has a low reprocessing energy barrier, which greatly reduces recycling energy consumption and is expected to partially replace commercial polyester materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the chemical change process in the material preparation method described in the embodiment of the present invention.

[0025] Figure 2 This is a diagram of separating the photovoltaic back panel described in Example 1 of the present invention.

[0026] Figure 3 This is a GPC chart of the molecular weight of the waste PET polyester after degradation described in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] The present invention is specifically described below through examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make some non-essential improvements and adjustments to the present invention based on the above content.

[0028] Embodiment 1:

[0029] 30g of waste photovoltaic backsheet was stirred in limonene at a stirring rate of 400r / min at 60℃ for 0.5h until the adhesive layer was completely swollen, and then the PET layer was removed and crushed. 10g of the above materials were mixed with 0.15g of tetrabutyl titanate and 20g of ethylene glycol, heated to 200℃, and stirred at 400r / min for 2h until PET was converted into a white slurry and the reaction was stopped. The white slurry was washed with excess water to remove ethylene glycol, and then filtered to obtain a mixture precipitate, dried at 30℃ for 24h, and ground into powder. The powder was mixed with maleic acid at a molar ratio of 1:1 and 0.5wt% tetrabutyl titanate and placed in a three-necked flask, nitrogen was introduced and heated to 180℃ for polymerization for 6h to obtain a polyester with a carbon-carbon double bond in the main chain. The maleic acid content was set to 1 molar equivalent, 0.5 molar equivalent of dynamic crosslinker and 0.2 molar equivalent of benzoin dimethyl ether were added to a three-necked flask, stirred until well mixed and poured into a mold, and treated under ultraviolet light for 30 minutes to fully crosslink to obtain a recycled polyester material. Based on the low energy barrier reversible reconstruction characteristics of the dynamic borate ester bond, the recycled polyester can be quickly healed at 80°C for 15 minutes after being cut, and the powdered product can be processed into a sheet at 100°C for 2 hours.

[0030] according to Figure 2 The results show that the photovoltaic backsheet treated with the renewable and environmentally friendly solvent limonene can be easily separated, laying the foundation for the preparation of the first intermediate material.

[0031] according to Figure 3 From the results, it can be seen that after degradation for 4 hours in the case of the first intermediate material: ethylene glycol solvent = 1:2, the obtained product has a uniform molecular weight distribution, Mw = 753, PDI = 1.056336, and is preliminarily determined to be a trimer of BHET, providing a basis for subsequent repolymerization with bio-based unsaturated dibasic acid.

[0032] Embodiment 2:

[0033] 30g of waste photovoltaic backsheet was stirred in limonene at a stirring rate of 400r / min at 60℃ for 0.5h until the adhesive layer was completely swollen, and then the PET layer was removed and crushed. 10g of the above materials were mixed with 0.3g zinc acetate and 20g ethylene glycol, heated to 220℃, and stirred at 400r / min for 2h until PET was converted into a white slurry and the reaction was stopped. The white slurry was washed with excess water to remove ethylene glycol, and then filtered to obtain a mixture precipitate, dried at 30℃ for 24h, and ground into powder. The powder was mixed with fumaric acid at a molar ratio of 1:1 and 0.5wt% tetrabutyl titanate and placed in a three-necked flask, nitrogen was introduced and heated to 180℃ for polymerization for 4h to obtain a polyester with a carbon-carbon double bond in the main chain. The fumaric acid content was set to 1 molar equivalent, 0.7 molar equivalent of dynamic crosslinker and 0.15 molar equivalent of benzoin dimethyl ether were added to a three-necked flask, stirred until well mixed and poured into a mold, and treated under ultraviolet light for 20 minutes to fully crosslink to obtain a recycled polyester material. Based on the low energy barrier reversible reconstruction characteristics of the dynamic borate ester bond, the recycled polyester can be quickly healed at 90°C for 20 minutes after being cut, and the powdered product can be processed into a sheet at 120°C for 2 hours.

[0034] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for recycling waste photovoltaic backsheet polyester by click-dynamic cross-linking, comprising: (1) stirring the discarded photovoltaic backsheet in a renewable and environmentally friendly solvent until the adhesive layer is completely swollen, then taking it out, peeling off and crushing the PET layer, and obtaining a first intermediate material for standby use; (2) adding the first intermediate material to the glycolysis catalyst and the diol solvent, then heating to 190-220° C. and stirring at a certain stirring rate for 2-6 hours until the first intermediate material is converted into a white slurry and the reaction is stopped; (3) washing the white slurry with excess water to remove the diol, then filtering, and drying the resulting mixture precipitate at 30° C. for 12-24 h and then grinding it into powder; (4) mixing the powder with a bio-based unsaturated dibasic acid at a molar ratio of 1:1 and a certain amount of catalyst into a three-necked flask, introducing nitrogen and heating to 180° C. for polymerization for 4-6 hours to obtain a polyester with a carbon-carbon double bond in the main chain; (5) Add a certain amount of dynamic crosslinking agent and photoinitiator to the polyester with carbon-carbon double bonds in the main chain, stir until the mixture is uniform, pour into a mold, treat under ultraviolet light for 15-30 minutes, and fully crosslink to obtain a recycled polyester material.

2. The method for recycling waste photovoltaic backsheet polyester by click-dynamic cross-linking as claimed in claim 1, wherein: The renewable environmentally friendly solvent in step (1) is (R)-(+)-limonene; The stirring conditions are: stirring temperature 60-80° C., stirring time 0.5-1 h, stirring speed 400 r / min.

3. The method for recycling waste photovoltaic backsheet polyester by click-dynamic cross-linking as claimed in claim 1, wherein: The glycolysis catalyst in step (2) is selected from tetrabutyl titanate, zinc acetate or cobalt acetate; The diol is selected from ethylene glycol or propylene glycol.

4. The method for recycling waste photovoltaic backsheet polyester by click-dynamic cross-linking as claimed in claim 1, wherein: The amount of the glycolysis catalyst added in step (2) is 0.5-1% of the total mass of the first intermediate material and the diol solvent; The certain stirring rate is 400r / min.

5. The method for recycling waste photovoltaic backsheet polyester by click-dynamic cross-linking as claimed in claim 1, wherein: Step (2) The mass ratio of the first intermediate material to the diol is 1:1-2.

6. The method for recycling waste photovoltaic backsheet polyester by click-dynamic cross-linking as claimed in claim 1, wherein: The bio-based unsaturated dibasic acid in step (4) is selected from any one of fumaric acid, maleic acid or muconic acid; The catalyst is selected from any one of tetrabutyl titanate, zinc acetate or cobalt acetate, and the added amount is 0.5-1% of the total mass of the powder and the dibasic acid.

7. The method for recycling waste photovoltaic backsheet polyester by click-dynamic cross-linking as claimed in claim 1, wherein: The dynamic crosslinking agent in step (5) is 2,2′-(1,4-phenylene)bis[1,3,2-dioxaborane-4-methylthiol]; The photoinitiator is selected from 2,2-diethoxyacetophenone or benzoin dimethyl ether.

8. The method for recycling waste photovoltaic backsheet polyester by click-dynamic cross-linking as claimed in claim 1, wherein: The molar equivalent ratio of the dynamic crosslinking agent and the photoinitiator in step (5) to the unsaturated dibasic acid in step (4) is 0.5-1:0.1-0.2:

1.

9. A recycled polyester material obtained by the method for upgrading and recycling waste photovoltaic backplane polyester by click-dynamic cross-linking as described in any one of claims 1 to 8.

Images