A highly stable transparent fluororesin and its preparation method and use

Abstract

The present invention discloses a highly stable transparent fluororesin, its preparation method, and its use, belonging to the technical field of solar photovoltaic cell materials. By screening the molecular weights of ionic liquid monomers and polyionic liquids, the present invention ensures that the transparency of PVDF remains above 83% while preventing precipitation. This method can meet the requirements of photovoltaic cell materials with high transparency requirements and harsh application environments, and has promising application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of solar photovoltaic cell materials, and particularly relates to a highly stable transparent fluororesin and a preparation method and application thereof. Background Art

[0002] As the size of photovoltaic cells continues to increase, the weight of the modules also increases, which poses a challenge to some scenarios with limited load-bearing capacity (such as industrial plants). In order to reduce the weight of the modules, developers usually start with thinning the glass and optimizing the aluminum alloy frames. In recent years, with the deepening of research, some high-performance polymer materials have gradually attracted attention. These materials are not only light in weight, have good light transmittance, strong weather resistance, and excellent packaging performance, but also have good flexibility, making non-glass packaging possible, thereby significantly reducing the weight of the modules. Lightweight modules are particularly suitable for projects with insufficient load or impenetrable roofs.

[0003] The core of lightweight flexible components lies in the transparent front panel. This front panel must not only have excellent light transmittance and UV resistance, but also provide sufficient mechanical strength to withstand harsh environmental conditions such as wind and hail. Furthermore, its coefficient of thermal expansion must match that of other packaging materials. Currently, typical transparent front panel materials include ETFE (ethylene tetrafluoroethylene copolymer), fluorocarbon resin, PVF (polyvinyl fluoride), and PVDF (polyvinylidene fluoride).

[0004] PVDF is a crystalline polymer with a glass transition temperature of -39°C, a crystalline melting point of approximately 170°C, and a thermal decomposition temperature above 316°C. It has excellent mechanical properties and good impact resistance, durability, and chemical stability. At room temperature, PVDF is not corroded by acids, alkalis, strong oxidants, and halogens. It is very stable to organic solvents such as aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, and aldehydes. Its performance remains essentially unchanged in hydrochloric acid, nitric acid, sulfuric acid, and dilute and concentrated (40%) alkali solutions, as well as at temperatures up to 100°C. It is also resistant to gamma rays and ultraviolet radiation. However, due to its high crystallinity, its light transmittance is difficult to meet the requirements of a transparent front panel.

[0005] There is an urgent need to develop a material that is both transparent and not prone to precipitation to meet the field of photovoltaic cell materials that have high requirements for transparency and are used in harsh environments. Summary of the Invention

[0006] In order to solve the above problems existing in the prior art, the purpose of the present invention is to provide a highly stable transparent fluororesin and a preparation method and use thereof.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a fluororesin, which is prepared from polyionic liquid and fluorine-containing polymer as raw materials, wherein the mass ratio of the polyionic liquid to the fluorine-containing polymer is 1:(5-50); and the molecular weight of the polyionic liquid is 1657-6794.

[0009] Furthermore, the mass ratio of the polyionic liquid to the fluorine-containing polymer is 1:(10-20), and the molecular weight of the polyionic liquid is 1657-3170.

[0010] Furthermore, the fluorine-containing polymer is an ethylene-tetrafluoroethylene copolymer, a fluorocarbon resin, polyvinyl fluoride or polyvinylidene fluoride; the polyionic liquid is obtained by reacting an ionic liquid monomer, a chain transfer agent and an initiator as raw materials, and the molar ratio of the ionic liquid monomer, the chain transfer agent and the initiator is (200-300):(1-30):(0.5-8); the reaction conditions are inert medium protection, the reaction temperature is 40-120° C., and the reaction time is 10-50 hours;

[0011] The ionic liquid monomer is at least one of 1-vinyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-vinyl-3-methylimidazolium bromide, and 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; the chain transfer agent is at least one of cyanomethyldodecyl trithiocarbonate, 2-cyano-2-propyldodecyl trithiocarbonate, S,S-dibenzyl trithiocarbonate, 2-phenylethylbenzenedithiol ester, and carbazole-9-dithiobenzyl ester; and the initiator is at least one of azobisisobutyronitrile, azobisisoheptonitrile, azobisisovaleronitrile, and dimethyl azobisisobutyrate.

[0012] Furthermore, the molar ratio of the ionic liquid monomer, the chain transfer agent, and the initiator is 250:(5-20):(1-4); the inert medium is nitrogen, the reaction temperature is 70° C., and the reaction time is 24 hours;

[0013] The fluorine-containing polymer is polyvinylidene fluoride, the ionic liquid monomer is 1-vinyl-3-methylimidazolium bis(fluorosulfonyl)imide salt, the chain transfer agent is cyanomethyl dodecyl trithiocarbonate, and the initiator is azobisisobutyronitrile.

[0014] Furthermore, the molar ratio of the ionic liquid monomer, the chain transfer agent and the initiator is 250:

[0015] (12~20):(3~4).

[0016] Furthermore, the molar ratio of the ionic liquid monomer, the chain transfer agent and the initiator is 250:12:3.

[0017] The present invention also provides a method for preparing the fluororesin. The method comprises heating the fluoropolymer to a molten state, adding the polyionic liquid, and mixing to obtain the fluororesin.

[0018] Furthermore, the mixing temperature is 100-300°C.

[0019] Furthermore, the mixing temperature is 180-200°C.

[0020] The present invention also provides uses of the fluororesin in the fields of photovoltaics, biomedicine, microelectronics and environmental monitoring.

[0021] Furthermore, the use is in the preparation of solar photovoltaic cells.

[0022] The present invention has achieved the following beneficial effects:

[0023] The present invention screens the molecular weights of ionic liquid monomers and polyionic liquids to ensure that the transparency of PVDF remains above 83% while making it less likely to precipitate. This can meet the field of photovoltaic cell materials with high transparency requirements and harsh application environments, and has good application prospects.

[0024] Obviously, based on the above contents of the present invention, according to common technical knowledge and customary means in this field, without departing from the above basic technical ideas of the present invention, other various forms of modifications, replacements or changes can be made.

[0025] The following further describes the above content of the present invention in detail through specific embodiments in the form of examples. However, this should not be construed as limiting the scope of the above subject matter of the present invention to the following examples. All technologies implemented based on the above content of the present invention fall within the scope of the present invention. DETAILED DESCRIPTION

[0026] The raw materials and equipment used in the present invention are all known products and are obtained by purchasing commercially available products.

[0027] The following experiments, where no temperature is specified, are reactions conducted at room temperature, which is 25±5°C.

[0028] The PVDF used in the specific embodiment of the present invention was purchased from Zhejiang Funolin Chemical New Materials Co., Ltd., model FL2006.

[0029] In a specific embodiment of the present invention, the molecular weight is a number average molecular weight.

[0030] Example 1: Preparation of modified PVDF 1

[0031] 1. Preparation method of polyionic liquid 1:

[0032] 1-Vinyl-3-methylimidazolium bis(fluorosulfonyl)imide salt (molecular weight 289.28, 72.32 g, 250 mmol), cyanomethyldodecyl trithiocarbonate (CTA, molecular weight 317.58, 6.35 g, 20 mmol) and initiator azobisisobutyronitrile (AIBN, molecular weight 164.21, 0.657 g, 4 mmol) were weighed on an electronic balance, mixed evenly and poured into a 250 mL clean, dry round-bottom flask. The mixture was placed in a pre-set 70°C oil bath, vacuumed and circulated with N2 for three times under an anhydrous and oxygen-free apparatus, and reacted under N2 protection for 24 h to obtain polyionic liquid 1.

[0033] 2. Preparation method of modified PVDF 1:

[0034] 100 g of PVDF was put into an internal mixer at 190° C., and after it melted, 5 g of the polyionic liquid 1 prepared in step 1 was added and mixed for 5 minutes. After taking out, the mixture was compression molded in a 0.3 mm thick mold at 190° C. for 5 minutes to obtain modified PVDF 1.

[0035] Example 2: Preparation of modified PVDF 2

[0036] 1. Preparation method of polyionic liquid 2:

[0037] 1-Vinyl-3-methylimidazolium bis(fluorosulfonyl)imide salt (molecular weight 289.28, 72.32 g, 250 mmol), cyanomethyldodecyl trithiocarbonate (CTA, molecular weight 317.58, 3.81 g, 12 mmol) and azobisisobutyronitrile (AIBN, molecular weight 164.21, 0.493 g, 3 mmol) were weighed on an electronic balance, mixed evenly and poured into a 250 mL clean, dry round-bottom flask. The mixture was placed in a pre-set 70°C oil bath, vacuumed and circulated with N2 for three times under an anhydrous and oxygen-free apparatus, and reacted under N2 protection for 24 h to obtain polyionic liquid 2.

[0038] 2. Preparation method of modified PVDF 2:

[0039] 100 g of PVDF was put into an internal mixer at 190° C., and after it melted, 5 g of the polyionic liquid 2 prepared in step 1 was added and mixed for 5 minutes. After taking out, the mixture was compression molded in a 0.3 mm thick mold at 190° C. for 5 minutes to obtain modified PVDF 2.

[0040] Example 3: Preparation of modified PVDF 3

[0041] The preparation method of Example 2 is referred to, except that 10 g of the polyionic liquid 2 prepared in step 1 is added instead of 5 g of the polyionic liquid 2 prepared in step 1 in step 2, to obtain modified PVDF 3.

[0042] Example 4: Preparation of modified PVDF 4

[0043] The preparation method was similar to that in Example 2, except that 1-vinyl-3-methylimidazolium bis(fluorosulfonyl)imide (molecular weight 289.28, 72.32 g, 250 mmol) in step 1 was replaced with 1-vinyl-3-methylimidazolium bromide (molecular weight 203.08, 50.77 g, 250 mmol) to obtain modified PVDF 4.

[0044] Example 5: Preparation of modified PVDF 5

[0045] The preparation method of Example 2 was followed, except that 1-vinyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide (molecular weight 289.28, 72.32 g, 250 mmol), cyanomethyl dodecyl trithiocarbonate (CTA, molecular weight 317.58, 3.81 g, 12 mmol) and azobisisobutyronitrile (AIBN, molecular weight 164.21, 0.493 g, 3 mmol) in step 1 were replaced with 1-allyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide (100.83 g, 250 mmol), cyanomethyl dodecyl trithiocarbonate (CTA, molecular weight 317.58, 1.91 g, 6 mmol) and azobisisobutyronitrile (AIBN, molecular weight 164.21, 0.197 g, 1.2 mmol) to obtain modified PVDF 5.

[0046] Example 6: Preparation of modified PVDF 6

[0047] The preparation method was carried out according to Example 2, except that cyanomethyl dodecyl trithiocarbonate (CTA, molecular weight 317.58, 3.81 g, 12 mmol) and azobisisobutyronitrile (AIBN, molecular weight 164.21, 0.493 g, 3 mmol) in step 1 were replaced with cyanomethyl dodecyl trithiocarbonate (CTA, molecular weight 317.58, 1.59 g, 5 mmol) and azobisisobutyronitrile (AIBN, molecular weight 164.21, 0.164 g, 1 mmol) to obtain modified PVDF 6.

[0048] Comparative Example: Preparation of Modified PVDF 7

[0049] The preparation method was carried out according to Example 2, except that cyanomethyldodecyl trithiocarbonate (CTA, molecular weight 317.58, 3.81 g, 12 mmol) and azobisisobutyronitrile (AIBN, molecular weight 164.21, 0.493 g, 3 mmol) in step 1 were replaced with cyanomethyldodecyl trithiocarbonate (CTA, molecular weight 317.58, 7.9 g, 25 mmol) and azobisisobutyronitrile (AIBN, molecular weight 164.21, 0.821 g, 5 mmol) to obtain modified PVDF 7.

[0050] The beneficial effects of the present invention are demonstrated by experimental examples below.

[0051] Experimental Example 1: Performance of the modified PVDF of the present invention

[0052] The molecular weight Mn and molecular weight distribution index PDI of the polyionic liquids prepared in Examples 1-6 and the comparative example were measured by gel permeation chromatography (GPC), and the transmittance of the modified fluororesin material (i.e., modified PVDF) was tested by UV-visible photometer. The stability of the polyionic liquid was evaluated by placing the sample film in an oven at 60°C and observing whether oily substances were precipitated on its surface after 30 days.

[0053] Table 1 Properties of modified PVDF of the present invention

[0054]

[0055] The results, as shown in Table 1, show that the low-molecular-weight polyionic liquid obtained in the comparative example readily migrates and precipitates from PVDF at high temperatures, while the relatively high-molecular-weight polyionic liquids obtained in Examples 1-6 do not readily migrate and precipitate from PVDF at high temperatures. A further comparison of Examples 1-3 and 6 reveals that, given the same monomers, the polyionic liquid obtained in Example 6 has the highest molecular weight, but the resulting modified PVDF has the lowest light transmittance. This demonstrates that controlling the molecular weight of the polyionic liquid is crucial to achieving both high light transmittance and high stability in a modified PVDF.

[0056] In addition, further comparison of Examples 3, 4, and 5 shows that the light transmittance of the modified PVDF obtained in Example 3 is significantly better than that of Examples 4 and 5, indicating that selecting 1-vinyl-3-methylimidazolium bis(fluorosulfonyl)imide salt as the monomer of the ionic liquid is more conducive to improving the light transmittance of the modified PVDF.

[0057] Therefore, in order to obtain a modified PVDF material with good stability and high transmittance, it is necessary to select a suitable ionic liquid monomer and a polyionic liquid with a suitable molecular weight.

[0058] In summary, the present invention screens the molecular weights of ionic liquid monomers and polyionic liquids to ensure that the transparency of PVDF remains above 83% while making it less likely to precipitate. This can meet the field of photovoltaic cell materials with high transparency requirements and harsh application environments, and has good application prospects.

Claims

1. A fluororesin, characterized in that: The fluororesin is prepared from polyionic liquid and fluoropolymer as raw materials, wherein the mass ratio of the polyionic liquid to the fluoropolymer is 1: (5-50); the molecular weight of the polyionic liquid is 1657-6794; The fluorine-containing polymer is an ethylene-tetrafluoroethylene copolymer, a fluorocarbon resin, polyvinyl fluoride or polyvinylidene fluoride; the polyionic liquid is obtained by reacting an ionic liquid monomer, a chain transfer agent and an initiator as raw materials, and the molar ratio of the ionic liquid monomer, the chain transfer agent and the initiator is (200-300): (1-30): (0.5-8); the reaction conditions are inert medium protection, the reaction temperature is 40-120° C., and the reaction time is 10-50 hours; The ionic liquid monomer is at least one of 1-vinyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-vinyl-3-methylimidazolium bromide, and 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; the chain transfer agent is at least one of cyanomethyldodecyl trithiocarbonate, 2-cyano-2-propyldodecyl trithiocarbonate, S,S-dibenzyl trithiocarbonate, 2-phenylethylbenzenedithiol ester, and carbazole-9-dithiobenzyl ester; and the initiator is at least one of azobisisobutyronitrile, azobisisoheptonitrile, azobisisovaleronitrile, and dimethyl azobisisobutyrate.

2. The fluororesin according to claim 1, characterized in that: The mass ratio of the polyionic liquid to the fluorine-containing polymer is 1: (10-20), and the molecular weight of the polyionic liquid is 1657-3170.

3. The fluororesin according to claim 1 or 2, characterized in that: The molar ratio of the ionic liquid monomer, chain transfer agent, and initiator is 250: (5-20): (1-4); the inert medium is nitrogen, the reaction temperature is 70° C., and the reaction time is 24 h; The fluorine-containing polymer is polyvinylidene fluoride, the ionic liquid monomer is 1-vinyl-3-methylimidazolium bis(fluorosulfonyl)imide salt, the chain transfer agent is cyanomethyl dodecyl trithiocarbonate, and the initiator is azobisisobutyronitrile.

4. The fluororesin according to claim 3, characterized in that: The molar ratio of the ionic liquid monomer, the chain transfer agent and the initiator is 250: (12-20): (3-4).

5. The fluororesin according to claim 4, characterized in that: The molar ratio of the ionic liquid monomer, chain transfer agent and initiator is 250:12:

3.

6. The method for preparing the fluororesin according to any one of claims 1 to 5, characterized in that: The preparation method comprises heating the fluorine-containing polymer to a molten state, adding the polyionic liquid according to any one of claims 1 to 5, and mixing to obtain the product.

7. The preparation method according to claim 6, characterized in that: The mixing temperature is 100-300°C.

8. The preparation method according to claim 7, characterized in that: The mixing temperature is 180-200°C.

9. Use of the fluororesin according to any one of claims 1 to 5 in the fields of photovoltaics, biomedicine, microelectronics and environmental monitoring.

10. The use according to claim 9, characterized in that: The application is in the preparation of solar photovoltaic cells.

Images