High-stability transparent fluororesin as well as preparation method and application thereof

Abstract

The invention discloses high-stability transparent fluororesin as well as a preparation method and application thereof, and belongs to the technical field of solar photovoltaic cell materials. By screening the molecular weight of the monomer of the ionic liquid and the molecular weight of the polyionic liquid, the transparency of PVDF is kept at 83% or above, meanwhile, the PVDF is not prone to precipitation, the requirement for the field of photovoltaic cell materials with the high requirement for transparency and the severe application environment can be met, and good application prospects are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of solar photovoltaic cell materials, and in particular 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 components also increases, which brings challenges to some scenes with limited load-bearing capacity (such as industrial plants). In order to reduce the weight of components, developers usually start with thinning glass and optimizing 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 components. Lightweight components are particularly suitable for projects with insufficient load or impenetrable roofs.

[0003] The core of lightweight flexible components lies in the transparent front panel. The transparent front panel must not only have good light transmittance and UV resistance, but also provide sufficient mechanical strength to withstand the impact of harsh environments such as wind and hail. In addition, its thermal expansion coefficient must match other packaging materials. At present, 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 about 170°C, a thermal decomposition temperature of more than 316°C, excellent mechanical properties, and good impact resistance, toughness, 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 basically 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 plate.

[0005] There is an urgent need to develop a material that is both transparent and not prone to precipitation, so as 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 object 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 solution:

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

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

[0010] Further, the fluoropolymer is ethylene - tetrafluoroethylene copolymer, 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, 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 under the protection of an inert medium, the reaction temperature is 40 - 120 °C, and the reaction time is 10 - 50 h;

[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 cyanomethyl dodecyl trithiocarbonate, 2 - cyano - 2 - propyl dodecyl trithiocarbonate, S,S - dibenzyl trithiocarbonate, 2 - phenylethyl phenyl disulfide ester and carbazole - 9 - dithiobenzyl ester, and the initiator is at least one of azobisisobutyronitrile, azobisisoheptonitrile, azobisisovaleronitrile and dimethyl azobisisobutyrate.

[0012] Further, 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 h;

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

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

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

[0016] Further, 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 preparation method of the above-mentioned fluororesin. The preparation method is to heat a fluoropolymer to a molten state and then add the above-mentioned polyionic liquid and mix them to obtain the fluororesin.

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

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

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

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

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

[0023] By screening the monomers of the ionic liquid and the molecular weight of the polyionic liquid, the present invention can ensure that the transparency of PVDF remains above 83%, and at the same time, it is not easy to precipitate, which can meet the requirements of the photovoltaic cell material field with high requirements for transparency and harsh application environments, and has good application prospects.

[0024] Obviously, based on the above content of the present invention, according to the common general technical knowledge and customary means in the art, without departing from the above basic technical idea of the present invention, various other forms of modifications, substitutions or changes can be made.

[0025] The following is a further detailed description of the above content of the present invention through specific embodiments in the form of examples. However, this should not be understood 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 belong to the scope of the present invention. Specific Embodiments

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

[0027] In the following experiments, if the temperature is not specified, the reaction is carried out under normal temperature conditions. Normal temperature means room temperature, which is 25±5°C.

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

[0029] The molecular weight mentioned in the specific embodiments of the present invention is the number average molecular weight.

[0030] Example 1: Preparation of Modified PVDF 1

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

[0032] Weigh 1-vinyl-3-methylimidazolium bis(fluorosulfonyl)imide (molecular weight 289.28, 72.32 g, 250 mmol), cyanomethyl dodecyl trithiocarbonate (CTA, molecular weight 317.58, 6.35 g, 20 mmol) and initiator azobisisobutyronitrile (AIBN, molecular weight 164.21, 0.657 g, 4 mmol) on an electronic balance. After mixing evenly, pour them into a 250 mL clean and dry round-bottom flask. Place the mixture in a pre-set oil bath at 70 °C, evacuate and purge with N2 three times under an anhydrous and anaerobic device, and react for 24 h under N2 protection to obtain poly(ionic liquid) 1.

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

[0034] Put 100 g of PVDF into a kneader at 190 °C. After it melts, add 5 g of poly(ionic liquid) 1 prepared in step 1 and mix for 5 min. After taking it out, press it into a mold with a thickness of 0.3 mm at 190 °C for 5 min to obtain modified PVDF 1.

[0035] Example 2: Preparation of modified PVDF 2

[0036] 1. Preparation method of poly(ionic liquid) 2:

[0037] Weigh 1-vinyl-3-methylimidazolium bis(fluorosulfonyl)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) on an electronic balance. After mixing evenly, pour them into a 250 mL clean and dry round-bottom flask. Place the mixture in a pre-set oil bath at 70 °C, evacuate and purge with N2 three times under an anhydrous and anaerobic device, and react for 24 h under N2 protection to obtain poly(ionic liquid) 2.

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

[0039] Put 100 g of PVDF into a kneader at 190 °C. After it melts, add 5 g of poly(ionic liquid) 2 prepared in step 1 and mix for 5 min. After taking it out, press it into a mold with a thickness of 0.3 mm at 190 °C for 5 min to obtain modified PVDF 2.

[0040] Example 3: Preparation of modified PVDF 3

[0041] Referring to the preparation method of Example 2, the difference is only that: adding 5 g of the poly(ionic liquid) 2 prepared in Step 1 in Step 2 is replaced by adding 10 g of the poly(ionic liquid) 2 prepared in Step 1, thus obtaining modified PVDF 3.

[0042] Example 4: Preparation of modified PVDF 4

[0043] Referring to the preparation method of Example 2, the difference is only that: 1-vinyl-3-methylimidazolium bis(fluorosulfonyl)imide (molecular weight 289.28, 72.32 g, 250 mmol) in Step 1 is replaced by 1-vinyl-3-methylimidazolium bromide (molecular weight 203.08, 50.77 g, 250 mmol), thus obtaining modified PVDF 4.

[0044] Example 5: Preparation of modified PVDF 5

[0045] Referring to the preparation method of Example 2, the difference is only that 1-vinyl-3-methylimidazolium bis(fluorosulfonyl)imide (molecular weight 289.28, 72.32 g, 250 mmol), cyanomethyl dodecyl trithiocarbonate (CTA, molecular weight 317.58, 3.81 g, 12 mmol) and 2,2'-azobis(2-methylpropionitrile) (AIBN, molecular weight 164.21, 0.493 g, 3 mmol) in Step 1 are replaced by 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (100.83 g, 250 mmol), cyanomethyl dodecyl trithiocarbonate (CTA, molecular weight 317.58, 1.91 g, 6 mmol) and 2,2'-azobis(2-methylpropionitrile) (AIBN, molecular weight 164.21, 0.197 g, 1.2 mmol), thus obtaining modified PVDF 5.

[0046] Example 6: Preparation of modified PVDF 6

[0047] Referring to the preparation method of Example 2, the difference is only that cyanomethyl dodecyl trithiocarbonate (CTA, molecular weight 317.58, 3.81 g, 12 mmol) and 2,2'-azobis(2-methylpropionitrile) (AIBN, molecular weight 164.21, 0.493 g, 3 mmol) in Step 1 are replaced by cyanomethyl dodecyl trithiocarbonate (CTA, molecular weight 317.58, 1.59 g, 5 mmol) and 2,2'-azobis(2-methylpropionitrile) (AIBN, molecular weight 164.21, 0.164 g, 1 mmol), thus obtaining modified PVDF 6.

[0048] Comparative Example: Preparation of modified PVDF 7

[0049] Referring to the preparation method of Example 2, the difference is only that the 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 are replaced with cyanomethyl dodecyl trithiocarbonate (CTA, molecular weight 317.58, 7.9 g, 25 mmol) and azobisisobutyronitrile (AIBN, molecular weight 164.21, 0.821 g, 5 mmol), and modified PVDF 7 is obtained.

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

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

[0052] The number average molecular weight Mn and the polydispersity index PDI of the polyionic liquids prepared in the above Examples 1-6 and Comparative Examples were measured by gel permeation chromatography (GPC), and then the light transmittance of the modified fluororesin material (i.e., modified PVDF) was measured by an ultraviolet-visible spectrophotometer. 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 the surface after 30 days.

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

[0054]

[0055] As shown in Table 1, the low-molecular-weight polyionic liquid obtained in the Comparative Example was prone to migrate and precipitate from PVDF at high temperature, while the polyionic liquids with relatively higher molecular weights obtained in Examples 1-6 were not prone to migrate and precipitate from PVDF at high temperature. Further comparing Examples 1-3 and 6, it can be seen that when the monomers of the ionic liquid are the same, the polyionic liquid obtained in Example 6 has the largest molecular weight, but the light transmittance of the obtained modified PVDF is the lowest, indicating that a specific molecular weight of the polyionic liquid needs to be controlled to obtain a modified PVDF with both high light transmittance performance and high stability.

[0056] In addition, further comparing Examples 3, 4, and 5, it can be seen 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 as the monomer of the ionic liquid is more conducive to improving the light transmittance performance of the modified PVDF.

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

[0058] In summary, through the screening of the monomers of ionic liquids and the molecular weight of polyionic liquids, the present invention ensures that the transparency of PVDF remains above 83%, while making it not easy to precipitate, and can meet the requirements of the photovoltaic cell material field with high transparency requirements and harsh application environments, and has good application prospects.

Claims

1. A fluororesin, characterized in that: The fluororesin is prepared by taking 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.

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 fluorine-containing polymer is ethylene-tetrafluoroethylene copolymer, 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 condition is 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 cyanomethyl dodecyl trithiocarbonate, 2-cyano-2-propyl dodecyl trithiocarbonate, S,S-dibenzyl trithiocarbonate, 2-phenylethylbenzenedithiol ester and carbazole-9-dithiobenzyl ester; and the initiator is at least one of azobisisobutyronitrile, azobisisoheptylnitrile, azobisisovaleronitrile and dimethyl azobisisobutyrate.

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:(5-20):(1-4); the inert medium is nitrogen, the reaction temperature is 70° C., and the reaction time is 24 hours; The fluorine-containing polymer is polyvinylidene fluoride, the ionic liquid monomer is 1-vinyl-3-methylimidazole bis(fluorosulfonyl)imide salt, the chain transfer agent is cyanomethyl dodecyl trithiocarbonate, and the initiator is azobisisobutyronitrile.

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

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

3.

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

8. The preparation method according to claim 7, characterized in that: The mixing temperature is 100-300°C, preferably 180-200°C.

9. Use of the fluororesin according to any one of claims 1 to 6 in the fields of photovoltaics, biomedicine, microelectronics and environmental monitoring.

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

Images