A moisture-proof composite film applied to ocean storage and transportation and a preparation method thereof

Abstract

The application relates to the technical field of container cargo packaging, and particularly discloses a moisture-proof composite film applied to ocean storage and transportation and a preparation method thereof. A kind of double stearyl ester fluorine-containing alkenyl coupling agent based on a tartaric acid skeleton is synthesized through molecular design means, and is recorded as DFUE. DFUE is covalently connected with Fe3O4 nanoparticles modified by a mercapto silane coupling agent through a mercapto-alkene click reaction to obtain DFUE functionalized Fe3O4, which is recorded as DFUE@Fe3O4. Then, DFUE@Fe3O4 is melt blended and granulated with polyethylene resin, and a moisture-proof composite film is prepared through a multi-layer co-extrusion film blowing process, so that the magnetic adsorption performance, the mechanical property and the moisture-proof performance are simultaneously improved.

Description

Technical Field

[0001] This invention relates to the field of container cargo packaging technology, specifically to a moisture-proof composite film for ocean storage and transportation and its preparation method. Background Technology

[0002] Containers, typically made of steel, are the most widely used means of loading ocean cargo as enclosed metal boxes. During ocean voyages, containers experience drastic temperature differences between day and night. During the day, the rising temperature inside the container causes moisture to evaporate, while at night, the sudden drop in temperature causes moisture to condense, forming "container rain," which can easily lead to moisture damage, mold, corrosion, or packaging failure in the cargo. To reduce the adverse effects of moisture condensation on the cargo, a moisture-proof membrane is usually laid on the inner wall of the container or the outer surface of the cargo to form a sealed barrier against condensation and external moisture.

[0003] Polyethylene film has become an important material for moisture-proof packaging of cargo in containerized ocean shipping due to its advantages such as good moisture resistance, low cost, excellent processing performance, and non-toxicity. However, the installation of ordinary polyethylene moisture-proof film inside containers usually requires manual cutting, pasting, or mechanical fixing, which is cumbersome, labor-intensive, and adhesive fixing methods can easily leave residue on the inner wall of the container, which is not conducive to the rapid turnover of containers.

[0004] Magnetic polyethylene film can adhere to the inner wall of steel containers using its own magnetism, offering advantages such as easy installation and disassembly, no adhesive required, no residue, and rapid deployment. Iron(III) oxide (Fe3O4) possesses excellent magnetic properties, making it an ideal functional filler for preparing magnetic polyethylene moisture-proof films. However, the strong polarity of Fe3O4 nanoparticles leads to poor interfacial compatibility with the non-polar polyethylene matrix, causing them to easily agglomerate during melt processing. This results in uneven magnetic distribution, decreased mechanical properties, and unsatisfactory moisture-proof performance.

[0005] In existing technologies, silane coupling agents, such as 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, or 3-mercaptopropyltrimethoxysilane, are commonly used to modify the surface of Fe3O4 to improve its interfacial bonding with the polymer matrix. However, traditional silane coupling agents typically only provide short-chain alkyl groups or a single reactive group, resulting in limited chain entanglement with the long-chain molecules of polyethylene. Furthermore, they lack additional low-surface-energy hydrophobic enhancement functions, making it difficult to simultaneously improve the mechanical and moisture-proof properties of the composite film while maintaining its magnetic properties.

[0006] Furthermore, ethylene-vinyl alcohol copolymer (EVOH) is a commonly used high-barrier layer in multilayer co-extruded moisture-proof films. However, because EVOH contains a large number of hydroxyl groups in its molecular chain, it is easily plasticized by water molecules after absorbing moisture, leading to a significant decrease in its barrier properties under high humidity conditions. This poses a challenge to the moisture-proof stability of containers in tropical seas and long voyages. If the functional layer can provide hydrophobic protection at the molecular level, it will help slow down the moisture absorption and degradation of EVOH, thereby forming a multi-scale synergistic moisture-proof system.

[0007] Therefore, there is an urgent need to develop a moisture-proof composite membrane for ocean storage that combines magnetic adsorption properties, excellent moisture-proof properties, good mechanical properties, and humid heat stability. Summary of the Invention

[0008] This invention synthesizes a fluorinated alkenyl coupling agent based on a tartaric acid backbone, denoted as DFUE, through molecular design. DFUE is covalently linked to Fe3O4 nanoparticles modified with a mercaptosilane coupling agent via a mercapto-alkene click reaction to obtain DFUE-functionalized Fe3O4, denoted as DFUE@Fe3O4. Subsequently, DFUE@Fe3O4 is melt-blended and granulated with polyethylene resin, and a moisture-proof composite film is prepared using a multilayer co-extrusion blown film process, thereby simultaneously improving magnetic adsorption properties, mechanical properties, and moisture-proof properties.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A moisture-proof composite film for ocean storage and transportation, the moisture-proof composite film comprising at least one polyethylene functional layer, at least one barrier layer and at least one adhesive layer; the polyethylene functional layer comprising polyethylene resin and DFUE-functionalized Fe3O4; the DFUE-functionalized Fe3O4 is covalently linked by a thiolized Fe3O4 and a fluorinated alkenyl coupling agent DFUE based on a tartaric acid skeleton through a thiol-alkene click reaction; the molecular structure of the coupling agent DFUE comprises a tartaric acid skeleton, two stearoyl ester segments, a fluorinated alkyl ester segment and a terminal alkenyl ester segment.

[0011] Furthermore, the tartaric acid skeleton is selected from the 2,3-dihydroxysuccinic acid skeleton derived from L-tartaric acid, D-tartaric acid, meso-tartaric acid, or DL-tartaric acid; the fluorinated alkyl group in the fluorinated alkyl ester segment is a C3-C10 polyfluoroalkyl group; and the terminal alkenyl group in the terminal alkenyl ester segment is a C6-C18 terminal alkenyl group.

[0012] Furthermore, the tartaric acid skeleton is L-tartaric acid; the fluorinated alkyl group in the fluorinated alkyl ester segment is 2,2,3,3,4,4,5,5-octafluoropentyl; and the terminal alkenyl group in the terminal alkenyl ester segment is 10-undecen-1-yl.

[0013] Furthermore, in the polyethylene functional layer, the amount of DFUE-functionalized Fe3O4 added is 3-20 parts by weight, based on 100 parts by weight of polyethylene resin.

[0014] Furthermore, the barrier layer is an ethylene-vinyl alcohol copolymer barrier layer; the adhesive layer is a maleic anhydride-grafted polyethylene adhesive layer.

[0015] Furthermore, the moisture-proof composite film is a nine-layer co-extruded film, comprising, in sequence:

[0016] First layer: 100wt% LLDPE functional layer containing DFUE-functionalized Fe3O4; dosage is 20-30 parts by weight;

[0017] Second layer: 100wt% HDPE layer; dosage is 8-12 parts by weight;

[0018] Third layer: 100wt% PE-g-MAH adhesive layer; dosage is 3-5 parts by weight;

[0019] Fourth layer: 100wt% EVOH barrier layer; dosage is 3-6 parts by weight;

[0020] Fifth layer: 100wt% PE-g-MAH adhesive layer; dosage is 3-5 parts by weight;

[0021] Sixth layer: 100wt% LLDPE functional layer containing DFUE-functionalized Fe3O4; dosage: 20-30 parts by weight;

[0022] Seventh layer: 100wt% PE-g-MAH adhesive layer; dosage is 3-5 parts by weight;

[0023] Eighth layer: 100wt% HDPE layer; dosage is 8-12 parts by weight;

[0024] Ninth layer: 100wt% m-LLDPE layer; dosage: 10-18 parts by weight;

[0025] The total thickness of the moisture-proof composite film is 80-120μm.

[0026] Furthermore, the thiolized Fe3O4 is prepared by surface modification of Fe3O4 nanoparticles with a thiol silane coupling agent; the average particle size of the Fe3O4 nanoparticles is 10-200 nm; the thiol silane coupling agent is selected from at least one of 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane; and the thiol content of the thiolized Fe3O4 is 0.2-0.8 mmol / g.

[0027] A method for preparing a moisture-proof composite film includes the following steps:

[0028] S1. Synthesis of coupling agent DFUE: DFUE is prepared by sequentially passing dibenzyl tartrate as the starting material through hydroxystearylation, catalytic hydrogenolysis of benzyl tartrate, diacid cyclic anhydride formation, selective ring opening of fluorinated alcohol and esterification of terminal alkenyl alcohol.

[0029] S2. Preparation of mercapto-modified Fe3O4: Fe3O4 nanoparticles were reacted with a mercaptosilane coupling agent in an ethanol / water mixed solvent to obtain SH@Fe3O4;

[0030] S3. Preparation of DFUE-functionalized Fe3O4: SH@Fe3O4 and DFUE were subjected to a mercapto-alkene click reaction in the presence of a photoinitiator and under ultraviolet light to prepare DFUE@Fe3O4;

[0031] S4. Preparation of LLDPE composite functional masterbatch: DFUE@Fe3O4 and LLDPE resin are melt-blended and extruded in the presence of antioxidants and granulated. Nitrogen gas is used for protection during the granulation process.

[0032] S5. Multilayer co-extrusion blown film: The LLDPE composite functional masterbatch is melt-plasticized with HDPE resin, PE-g-MAH resin, EVOH resin and m-LLDPE resin respectively through multiple extruders, and then combined through a multilayer co-extrusion die, blow-molded, cooled, drawn and wound to obtain the moisture-proof composite film.

[0033] Furthermore, the specific steps for synthesizing DFUE in step S1 are as follows:

[0034] (1) Dibenzyl tartrate was reacted with stearoyl chloride under the catalysis of 4-dimethylaminopyridine (DMAP) and organic base to prepare dibenzyl-2,3-di-O-stearoyl tartrate.

[0035] (2) Under Pd / C catalysis, the dibenzyl-2,3-di-O-stearoyl tartaric acid ester was debenzylated by atmospheric pressure hydrogenation to obtain 2,3-di-O-stearoyl tartaric acid;

[0036] (3) The 2,3-di-O-stearoyl tartaric acid was dehydrated and cyclically formed in the presence of acetic anhydride and a catalytic amount of sodium acetate to obtain 2,3-di-O-stearoyl tartaric acid cyclic anhydride.

[0037] (4) The cyclic anhydride and the fluorinated alcohol undergo a selective ring-opening reaction under the catalysis of DMAP and organic base to obtain a monofluorinated ester intermediate.

[0038] (5) The monofluorinated ester intermediate and the terminal alkenyl alcohol are esterified in the presence of EDCI·HCl and DMAP catalyst and BHT inhibitor to obtain DFUE.

[0039] Furthermore, in step S3, the mass ratio of SH@Fe3O4 to DFUE is 1:0.5-1:2;

[0040] The photoinitiator is selected from at least one of benzoin dimethyl ether, 2-hydroxy-2-methylphenylacetone, or 2,2-diethoxyacetophenone, and the amount added is 1-5 wt% of the total mass of SH@Fe3O4 and DFUE.

[0041] The ultraviolet light wavelength is 320-400 nm, and the reaction time is 2-10 h;

[0042] In step S4, the melt blending temperature is 150-200℃, the screw speed is 100-300 r / min, and the antioxidant is selected from at least one of antioxidant 1010 and antioxidant 168, with an addition amount of 0.1-0.5 wt% of the LLDPE resin mass.

[0043] The process parameters for each extruder in step S5 are as follows:

[0044] Extruder for LLDPE functional layer containing DFUE@Fe3O4: Temperature 170-210℃, screw speed 40-80r / min;

[0045] HDPE layer extruder: Temperature 170-210℃, screw speed 20-50r / min;

[0046] PE-g-MAH adhesive layer extruder: temperature 150-195℃, screw speed 10-30r / min;

[0047] EVOH barrier layer extruder: temperature 185-220℃, screw speed 10-30r / min;

[0048] m-LLDPE layer extruder: temperature 175-215℃, screw speed 20-50r / min;

[0049] Co-extrusion die temperature: 195-220℃; cooling air ring temperature: 15-25℃; blow-up ratio: 1.8-3.0; draw ratio: 3-10.

[0050] The beneficial effects of this invention are as follows:

[0051] (1) This invention uses molecular design methods, with tartaric acid as the core skeleton, and adopts a synthesis strategy of carboxyl protection, hydroxy stearyl acylation, catalytic hydrogen deprotection, diacid cyclic anhydride formation, selective ring opening of fluorinated alcohols and esterification of terminal alkenyl alcohols to prepare DFUE, a bis-stearyl ester fluorinated alkenyl coupling agent based on tartaric acid skeleton.

[0052] The bisC18 stearyl ester segment in the DFUE molecule can form effective chain entanglement and a certain degree of co-crystallization with the polyethylene molecular chain, thereby improving the interfacial compatibility between Fe3O4 and the polyethylene matrix; the fluorinated alkyl ester segment has low surface energy characteristics, which can improve the hydrophobic and moisture-proof performance of the composite film at the molecular level; the terminal alkenyl group can form a stable thioether covalent bond with mercapto-alkene click reaction with mercapto-modified Fe3O4, so that DFUE is stably anchored on the Fe3O4 surface.

[0053] (2) The DFUE synthesis route of this invention adopts a strategy of carboxybenzyl ester protection → hydroxystearyl acylation → catalytic hydrogenolysis to debenzylate → diacid cyclic anhydride formation → selective ring-opening of fluorinated alcohols → esterification of terminal alkenyl alcohols. Compared with the direct stepwise esterification route, this route has the following advantages:

[0054] The carboxyl group is protected first to prevent side reactions between stearoyl chloride and the carboxyl group;

[0055] Symmetrical cyclic anhydrides are ring-opened by fluorinated alcohols to form half-ester half-acid intermediates, which solves the problem of selective esterification of two carboxyl groups.

[0056] Introducing the terminal alkenyl group in the final step avoids the risk of alkenyl group reduction during the catalytic hydrogenolysis step.

[0057] (3) In this invention, an EVOH high-barrier layer is introduced as the core barrier layer in the membrane structure design, forming a multi-scale moisture-proof system with the DFUE@Fe3O4 functional layer. The fluorinated segments in the DFUE molecule provide hydrophobicity at the molecular level, while the EVOH layer provides high barrier at the macroscopic level. The two work together to reduce water vapor and oxygen permeation. At the same time, the fluorinated hydrophobic segments in the DFUE can slow down the migration of water molecules to the EVOH layer in the functional layer, thereby effectively inhibiting the plasticization degradation of EVOH in high humidity environments. This allows the composite membrane to maintain excellent barrier performance under humid and hot conditions, making it particularly suitable for tropical seas and long-haul container storage and transportation.

[0058] (4) Since Fe3O4 imparts magnetic adsorption function to the composite film, DFUE modification improves the interfacial bonding between Fe3O4 and polyethylene matrix, and the EVOH layer provides high barrier properties, the moisture-proof composite film prepared by this invention can simultaneously achieve magnetic adsorption, mechanical property improvement and moisture-proof performance enhancement, and is particularly suitable for moisture-proof packaging of steel containers for ocean storage and transportation. Detailed Implementation

[0059] The present invention will be further described below with reference to embodiments. It should be understood that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of protection of the present invention. Without departing from the concept of the present invention, those skilled in the art can make appropriate adjustments to the types of raw materials, dosage ranges, process conditions, or membrane structures, and these equivalent or alternative methods should all fall within the scope of protection of the present invention.

[0060] It should be particularly noted that the following embodiments are illustrated using L-tartaric acid as the starting material, but the tartaric acid skeleton described in this invention is not limited to the L configuration. It can also be derived from D-tartaric acid, meso-tartaric acid, or DL-tartaric acid via a similar route, and all fall within the scope of protection of this invention. The two chiral carbon atoms of the tartaric acid skeleton shown in the structural formula of this invention do not explicitly indicate their stereoconfiguration and should be understood to encompass various isomers.

[0061] Example 1:

[0062] Synthesis of DFUE compounds

[0063] This embodiment prepares a bis-stearyl fluorinated alkenyl coupling agent DFUE based on a tartaric acid backbone.

[0064] Sub-step (1): Synthesis of dibenzyl-2,3-di-O-stearoyl tartrate

[0065] In a 500 mL four-necked flask equipped with a mechanical stirrer, a constant pressure dropping funnel, a reflux condenser, and a nitrogen delivery tube, 16.52 g of dibenzyl tartrate (CAS No. 2918-14-9, 0.05 mol) and 0.31 g of 4-dimethylaminopyridine (DMAP, 2.5 mmol) were added to 150 mL of anhydrous dichloromethane and stirred under nitrogen protection until completely dissolved.

[0066] The mixture was cooled to 0°C in an ice-water bath, and 14.85 g of diisopropylethylamine (DIPEA, 0.115 mol) was added. 33.32 g of stearoyl chloride (0.11 mol, 2.2 equivalents) was dissolved in 50 mL of anhydrous dichloromethane and slowly added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel, keeping the system temperature below 5°C. After the addition was complete, the reaction was maintained at 0°C for 1 hour. The ice bath was then removed, and the temperature was slowly raised to room temperature (25°C), with stirring continuing for 12 hours.

[0067] After the reaction was complete, the organic phase was washed successively with 0.5 mol / L dilute hydrochloric acid (100 mL × 2 times), saturated sodium bicarbonate aqueous solution (100 mL × 2 times), and saturated sodium chloride aqueous solution (100 mL × 1 time). The organic phase was collected, dried overnight with anhydrous sodium sulfate, filtered, and dichloromethane was removed by rotary evaporation. The crude product was purified by silica gel column chromatography with petroleum ether / ethyl acetate = 15:1 (V / V) as the eluent. It was then dried under vacuum at 45 °C for 12 h to give a white waxy solid dibenzyl-2,3-di-O-stearoyl tartrate in 88% yield.

[0068] The structural formula of dibenzyl-2,3-di-O-stearoyl tartrate is:

[0069] .

[0070] FT-IR, KBr, ν / cm -1 :

[0071] 3062, 3028, 2916, 2849, 1742, 1602, 1455, 1378, 1265, 1170, 1105, 1028, 736, 721, 697.

[0072] Among them, 3062 and 3028cm -1 Absorption due to the stretching vibration of the =CH ring of benzene; 2916 and 2849 cm⁻¹ -1 Absorbed by the stretching vibration of long-chain alkyl CH; 1742 cm⁻¹ -1 Absorbed by the C=O stretching vibration of the ester group; 1602 cm⁻¹ -1 Absorption due to C=C skeletal vibration of the benzene ring; 1455 and 1378 cm⁻¹ -1 Absorption for CH bending vibrations; 1265, 1170, 1105 and 1028 cm -1 Absorption due to COC / CO stretching vibration of the ester bond; 736 and 697 cm⁻¹ -1 Absorption due to out-of-plane bending vibration of the monosubstituted benzene ring CH; 721 cm⁻¹ -1 Absorption is achieved by the rocking vibration of long-chain methylene groups.

[0073] Sub-step (2): Catalytic hydrogen desorption of benzyl group to prepare 2,3-di-O-stearoyl tartaric acid

[0074] In a 250 mL round-bottom flask, 8.61 g of dibenzyl-2,3-di-O-stearoyl tartrate (0.01 mol) was dissolved in 80 mL of a tetrahydrofuran / methanol mixed solvent, wherein the volume ratio of tetrahydrofuran to methanol was 4:1. 0.86 g of a 10 wt% Pd / C catalyst was then added to the system.

[0075] After purging the atmosphere inside the bottle three times with hydrogen balloons, the reaction was stirred for 12 hours under normal pressure hydrogen (1 atm) and room temperature (25°C). The reaction process was monitored by thin-layer chromatography (TLC), with petroleum ether / ethyl acetate as the developing solvent, Rf≈0.75 for the starting material and Rf≈0.20 for the product.

[0076] After the reaction was complete, the Pd / C catalyst was removed by diatomaceous earth filtration, and the diatomaceous earth filter cake was washed with 50 mL of tetrahydrofuran. The filtrates were combined, the solvent was removed by rotary evaporation, and the solution was dried under vacuum at 50 °C for 10 h to obtain a white waxy solid, 2,3-di-O-stearoyl tartaric acid, in 95% yield.

[0077] The structural formula of 2,3-di-O-stearoyl tartaric acid is:

[0078] .

[0079] FT-IR, KBr, ν / cm -1 :

[0080] 3100 (broad peak), 2955, 2920, 2850, 1743, 1710, 1465, 1378, 1285, 1160, 935, 720.

[0081] Among them, 3100cm -1 A broad absorption of carboxylic acid OH is observed nearby (typically at 2500-3300 cm⁻¹). -1 (broad peak); 1743cm -1 Absorbed by the C=O stretching vibration of the stearoyl ester group; 1710 cm⁻¹ -1 The absorption is due to the stretching vibration of the carboxyl group (C=O). Compared with the precursor, the benzene ring-related absorption peaks (3062, 3028, 1602, 736, 697 cm⁻¹) are different. -1 The obvious disappearance of the benzyl protecting group indicates that it has been effectively removed.

[0082] Sub-step (3): Dehydration of diacid to form cyclic anhydride, preparation of 2,3-di-O-stearoyl tartaric acid cyclic anhydride.

[0083] In a 100 mL round-bottom flask, 6.55 g of 2,3-di-O-stearoyl tartaric acid (0.01 mol) was added to 30 mL of acetic anhydride (0.32 mol, approximately 32 equivalents), and a catalytic amount of sodium acetate (0.08 g, 1 mmol) was added. The mixture was stirred and heated to 70 °C under nitrogen protection and reacted for 4 h.

[0084] After the reaction was complete, most of the acetic anhydride and the byproduct acetic acid were removed by vacuum distillation at 60 °C and -0.095 MPa. 30 mL of anhydrous toluene was added to the residue, and the mixture was rotary evaporated twice at 60 °C and -0.095 MPa to remove residual acetic anhydride and acetic acid, yielding a pale yellow waxy solid, 2,3-di-O-stearoyl tartaric acid cyclic anhydride. This intermediate was used directly in the next reaction without further purification.

[0085] The structural formula of 2,3-di-O-stearoyl tartaric acid cyclic anhydride is:

[0086] .

[0087] FT-IR, KBr, ν / cm -1 :

[0088] 2955, 2921, 2851, 1868, 1790, 1746, 1465, 1375, 1255, 1095, 918, 722.

[0089] Among them, 1868 and 1790cm -1 The cyclic anhydride exhibits a characteristic double peak at C=O, which can be attributed to the asymmetric and symmetric stretching vibrations of the carbonyl group, respectively. Simultaneously, the carboxylic acid shows a broad OH peak and a peak at 1710 cm⁻¹. -1 The disappearance of the C=O absorption peak of the carboxylic acid indicates that the diacid has been dehydrated to form a cyclic anhydride structure.

[0090] Sub-step (4): Ring-opening of fluorinated alcohol to prepare monofluorinated ester intermediate.

[0091] In a 100 mL Schlenk flask under nitrogen protection, the freshly prepared 2,3-di-O-stearoyl tartrate cyclic anhydride (approximately 0.01 mol) was dissolved in 50 mL of anhydrous dichloromethane, and 0.12 g DMAP (1.0 mmol) and 1.01 g triethylamine (0.01 mol) were added.

[0092] The mixture was cooled to 0°C in an ice bath. 2.32 g of 2,2,3,3,4,4,5,5-octafluoropentanol (0.01 mol) was dissolved in 10 mL of anhydrous dichloromethane and slowly added dropwise to the reaction mixture over 20 min. After the addition was complete, the mixture was reacted at 0°C for 1 h, then heated to room temperature (25°C) and reacted for another 8 h.

[0093] After the reaction was complete, the organic phase was washed successively with 0.5 mol / L dilute hydrochloric acid (50 mL × 2 times) to remove triethylamine and DMAP, followed by washing with saturated sodium chloride aqueous solution (50 mL × 1 time). The organic phase was collected, dried over anhydrous sodium sulfate, and then dichloromethane was removed by rotary evaporation. The crude product was purified by silica gel column chromatography with petroleum ether / ethyl acetate / glacial acetic acid = 6:1:0.05 (V / V / V). The target fraction was collected, rotary evaporated, and then dried under vacuum at 45 °C for 8 h to obtain a pale yellow waxy solid monofluorinated ester intermediate. The combined yield of the cyclic anhydride reaction and ring-opening steps was 82%.

[0094] The structural formula of the monofluorinated ester intermediate is:

[0095] .

[0096] FT-IR, KBr, ν / cm -1 :

[0097] 3150 (broad peak), 2955, 2919, 2850, 1744, 1715, 1240, 1188, 1138, 1060, 719.

[0098] Among them, 3150cm -1 A broad absorption of carboxylic acid OH is observed nearby; 1715 cm⁻¹ -1 Absorbed by the stretching vibration of the carboxyl group C=O; 1744 cm⁻¹ -1Absorption is due to the C=O stretching vibration of the ester group. Compared with the anhydride precursor, 1868 and 1790 cm⁻¹... -1 The disappearance of the characteristic bimodal peaks of cyclic anhydrides indicates that the anhydride has been ring-opened by fluorinated alcohols; 1240, 1188 and 1138 cm⁻¹ -1 The presence of multiple characteristic absorption peaks of CF indicates that fluorine-containing groups have been successfully introduced.

[0099] Sub-step (5): Esterification of terminal alkenyl alcohols to prepare DFUE compounds

[0100] In a 100 mL round-bottom flask, 4.48 g of a monofluorinated ester intermediate (0.005 mol) and 0.06 g of DMAP (0.5 mmol) were dissolved in 40 mL of anhydrous dichloromethane, and 5 mg of 2,6-di-tert-butyl-4-methylphenol (BHT) was added as a polymerization inhibitor. Under nitrogen protection, the system was cooled to 0 °C in an ice bath, and 0.94 g of 10-undecen-1-ol (CAS No. 112-43-6, 0.0055 mol, 1.1 equivalents) was added and stirred until homogeneous.

[0101] Subsequently, 1.15 g of EDCI·HCl, i.e., 0.006 mol (1.2 equivalents) of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, was directly added to the reaction system. After reacting at 0 °C for 1 h, the temperature was raised to room temperature (25 °C) and the reaction was continued for 14 h in the dark.

[0102] After the reaction was complete, the organic phase was washed successively with 0.5 mol / L dilute hydrochloric acid (40 mL × 2 times), saturated sodium bicarbonate aqueous solution (40 mL × 1 time), and saturated sodium chloride aqueous solution (40 mL × 1 time). The organic phase was collected, dried over anhydrous sodium sulfate, and then dichloromethane was removed by rotary evaporation (rotary evaporation water bath temperature not exceeding 35℃). The crude product was purified by silica gel column chromatography with petroleum ether / ethyl acetate = 10:1 as the eluent. The target fraction was collected, rotary evaporated, and then dried under vacuum at 35℃ for 6 h to obtain a pale yellow waxy solid DFUE compound in 82% yield.

[0103] The structural formula of the DFUE compound is:

[0104] .

[0105] FT-IR, KBr, ν / cm -1 :

[0106] 3076, 2955, 2917, 2849, 1746, 1641, 1465, 1375, 1238, 1132, 1060, 993, 910, 721.

[0107] Among them, 3076cm -1Absorption due to the terminal alkenyl =CH stretching vibration; 1641 cm⁻¹ -1 Absorption for C=C stretching vibrations; 993 and 910 cm -1 The absorption by the out-of-plane bending vibration of the terminal =CH2 indicates that the undecenyl group was successfully introduced; 1715cm -1 The disappearance of the C=O absorption peak of carboxylic acid and the broad OH peak of carboxylic acid near 3150 cm⁻¹ indicates that the remaining carboxyl group has been esterified; 1238 and 1132 cm⁻¹ -1 The characteristic absorption of CF indicates that the fluorine-containing groups are retained after the reaction.

[0108] 1 HNMR, CDCl3, 400MHz, δ / ppm:

[0109] 0.87-0.90 (t, 6H);

[0110] 1.20-1.38 (m, approx. 68H);

[0111] 1.53-1.58 (m, 4H);

[0112] 1.63-1.69 (m, 2H);

[0113] 2.01-2.05 (q, 2H);

[0114] 2.29–2.39 (m, 4H);

[0115] 4.10-4.18 (m, 2H);

[0116] 4.54-4.58 (m, 2H);

[0117] 4.77-4.81 (m, 2H);

[0118] 4.95-5.12 (dd, 2H);

[0119] 5.76-5.84 (m, 1H);

[0120] 6.03-6.28 (tt, 1H).

[0121] Among them, 0.87-0.91 ppm corresponds to the terminal methyl hydrogen of the stearoyl long chain; 1.20-1.38 ppm mainly corresponds to the long chain methylene hydrogen; 2.29-2.39 ppm corresponds to the methylene hydrogen adjacent to the carbonyl group in the stearoyl group; the signal in the range of 4.10-4.18 ppm mainly corresponds to the methylene hydrogen adjacent to the ester bond; 4.95-5.12 ppm and 5.76-5.84 ppm correspond to the characteristic hydrogen of the terminal alkenyl group; and 6.03-6.28 ppm corresponds to the -CF2H hydrogen signal in the fluorinated segment.

[0122] The overall yield of the six-step synthesis is approximately 56% (88% × 95% × 82% × 82%).

[0123] Example 2:

[0124] Preparation of DFUE-functionalized Fe3O4

[0125] Sub-step (a): 3-Mercaptopropyltrimethoxysilane (silane coupling agent KH-590) was used to modify Fe3O4 to prepare thiolized Fe3O4.

[0126] Under a nitrogen atmosphere, 5 g of Fe3O4 nanoparticles (approximately 50 nm in diameter) were added to 100 mL of a 95% (v / v) ethanol / water mixed solution, wherein the volume ratio of ethanol to water was 9:1. The system was ultrasonically dispersed for 30 min.

[0127] Subsequently, 2.0 g of silane coupling agent KH-590 was added, the system temperature was raised to 70 °C, and the reaction was stirred for 3 h. After the reaction was completed, the solid particles were collected by magnetic separation and washed three times with anhydrous ethanol and twice with deionized water, and then vacuum dried at 60 °C for 12 h to obtain mercaptolated Fe3O4, denoted as SH@Fe3O4.

[0128] The thiol content in SH@Fe3O4 was determined using the Ellman reagent method, and the result was 0.42 mmol SH / g.

[0129] Sub-step (b): Preparation of DFUE-functionalized Fe3O4 by thiol-alkene click reaction

[0130] 2g of SH@Fe3O4 and 2g of DFUE compound were added to 40mL of anhydrous toluene and ultrasonically dispersed for 20min. Then, 0.1g of benzoin dimethyl ether was added as a photoinitiator and stirred until homogeneous.

[0131] Under 365nm ultraviolet light irradiation, the system was continuously stirred for 6 hours, causing the thiol groups on the surface of SH@Fe3O4 to undergo a thiol-alkene click reaction with the terminal alkenyl groups in the DFUE molecule, forming a stable thioether bond.

[0132] After the reaction, the solid particles were collected by magnetic separation and washed three times with anhydrous toluene and twice with anhydrous ethanol to remove unreacted DFUE and free initiator. The residual photoinitiator content should be less than 50 ppm as determined by HPLC. Subsequently, the particles were vacuum dried at 60 °C for 8 h to obtain DFUE-functionalized Fe3O4, denoted as DFUE@Fe3O4.

[0133] Thermogravimetric analysis (TGA) showed that the grafting rate of DFUE on the Fe3O4 surface was approximately 12 wt%, corresponding to an organic layer thickness of approximately 2-3 nm. Vibrating sample magnetometer (VSM) measurements revealed that the saturation magnetization of DFUE@Fe3O4 was 58.2 emu / g (compared to 68.5 emu / g for the original Fe3O4), with a magnetic retention rate of approximately 85%, which meets the requirements for magnetic adsorption applications.

[0134] Example 3:

[0135] Preparation of LLDPE composite functional masterbatch

[0136] (1) Preparation of LLDPE composite functional masterbatch a

[0137] Table 1 Raw material formulation of LLDPE composite functional masterbatch a

[0138] raw material Dosage (by weight) LLDPE resin, grade DFDA7047 100 <![CDATA[DFUE@ Fe3O4]]> 5 Antioxidant 1010 0.2 Antioxidant 168 0.2

[0139] After the raw materials are mixed evenly, they are placed in a twin-screw extruder for melt blending, extrusion, and granulation. The feed section temperature is 150℃, the plasticizing section temperature is 180℃, the metering section temperature is 195℃, and the die head temperature is 190℃; the screw speed is 250 r / min; the extruder barrel is protected with nitrogen gas to prevent Fe3O4 from oxidizing to γ-Fe2O3 during processing, thus producing LLDPE composite functional masterbatch a.

[0140] (2) Preparation of LLDPE composite functional masterbatch b: The only difference between it and LLDPE composite functional masterbatch a is that the amount of DFUE@Fe3O4 is adjusted from 5 parts by weight to 10 parts by weight.

[0141] (3) Preparation of LLDPE composite functional masterbatch c: The only difference between it and LLDPE composite functional masterbatch a is that the amount of DFUE@Fe3O4 is adjusted from 5 parts by weight to 15 parts by weight.

[0142] Example 4:

[0143] Preparation of moisture-proof composite film

[0144] (1) Preparation of moisture-proof composite film A

[0145] Step 1: Nine-layer membrane structure design

[0146] The moisture-proof composite membrane A is configured as a nine-layer co-extruded membrane structure, and the formulation and dosage of each membrane layer are shown in Table 2 below.

[0147] Table 2 Formulation and dosage of each layer of moisture-proof composite membrane A

[0148] membrane formula Dosage (by weight) First layer 100wt% LLDPE composite functional masterbatch a 25 Second floor 100wt% HDPE resin 10 Third layer 100wt% PE-g-MAH resin 4 Fourth floor 100wt% EVOH resin 5 Fifth floor 100wt% PE-g-MAH resin 4 Sixth floor 100wt% LLDPE composite functional masterbatch a 25 Seventh floor 100wt% PE-g-MAH resin 4 Eighth floor 100wt% HDPE resin 10 Ninth floor 100wt% m-LLDPE resin 13

[0149] Among them, the HDPE resin is grade 5000S (blown film special material, MI about 0.9g / 10min (190℃ / 2.16kg), density about 0.954g / cm³, melting point about 132℃); the LLDPE resin is grade DFDA7047 (MI about 2.0g / 10min); the PE-g-MAH resin is grade NF528; the EVOH resin is grade DC3203RB (ethylene content about 32mol%, processing temperature 190-220℃); and the m-LLDPE resin is grade SP1520 (MI about 1.0g / 10min).

[0150] Step 2: Nine-layer co-extrusion blown film

[0151] The raw materials for each film layer in Table 2 are fed into the hoppers of the nine screw extruders corresponding to the nine-layer co-extrusion film blow molding unit. After melting and plasticizing, the molten resin of each layer is combined at the die head through the distributor, extruded through the die head and blow molded. Then, it is cooled, drawn and wound up to obtain a moisture-proof composite film A with a total thickness of 100μm.

[0152] The process parameters for each layer of the corresponding screw extruder are as follows.

[0153] Screw extruder process parameters for the first and sixth layers (including the LLDPE functional layer with DFUE@Fe3O4):

[0154] Zone 1 temperature 170℃; Zone 2 temperature 190℃; Zone 3 temperature 200℃; Flow channel temperature 195℃; Screw speed 60r / min.

[0155] Screw extruder process parameters for the second and eighth layers (HDPE5000S layers):

[0156] Zone 1 temperature 170℃; Zone 2 temperature 190℃; Zone 3 temperature 200℃; Flow channel temperature 200℃; Screw speed 30r / min.

[0157] Screw extruder process parameters for the third, fifth, and seventh layers (PE-g-MAH bonding layer):

[0158] Zone 1 temperature 150℃; Zone 2 temperature 170℃; Zone 3 temperature 185℃; Flow channel temperature 180℃; Screw speed 20r / min.

[0159] The screw extruder process parameters corresponding to the fourth layer (EVOH barrier layer):

[0160] Zone 1 temperature 185℃; Zone 2 temperature 200℃; Zone 3 temperature 215℃; Flow channel temperature 210℃; Screw speed 20r / min.

[0161] The screw extruder process parameters corresponding to the ninth layer (m-LLDPE layer) are as follows:

[0162] Zone 1 temperature 175℃; Zone 2 temperature 195℃; Zone 3 temperature 205℃; Flow channel temperature 200℃; Screw speed 30r / min.

[0163] Co-extrusion die temperature: 210℃; Cooling air ring temperature: 20℃; Blow-up ratio: 2.5; Traction ratio: 6.

[0164] (2) Preparation of moisture-proof composite film B

[0165] The only difference between moisture-proof composite film B and moisture-proof composite film A is that the LLDPE composite functional masterbatch a used in the first and sixth layers of moisture-proof composite film A is replaced with LLDPE composite functional masterbatch b.

[0166] The other membrane structure, resin grade, amount of each layer, and co-extrusion blown film process parameters are the same as those of moisture-proof composite film A.

[0167] (3) Preparation of moisture-proof composite film C

[0168] The only difference between moisture-proof composite film C and moisture-proof composite film A is that the LLDPE composite functional masterbatch a used in the first and sixth layers of moisture-proof composite film A is replaced with LLDPE composite functional masterbatch c.

[0169] The other membrane structure, resin grade, amount of each layer, and co-extrusion blown film process parameters are the same as those of moisture-proof composite film A.

[0170] Comparative Example

[0171] Comparative Example 1:

[0172] The only difference between Comparative Example 1 (denoted as Composite Membrane D1) and Moisture-proof Composite Membrane A is that the first and sixth layers use pure LLDPE resin to replace the LLDPE composite functional masterbatch a, that is, the membrane does not contain Fe3O4 component, nor does it contain DFUE@Fe3O4 component.

[0173] The other membrane structures, the amount of each layer used, and the co-extrusion blown film process parameters are the same as those of moisture-proof composite membrane A.

[0174] Comparative Example 2:

[0175] The only difference between Comparative Example 2 (denoted as Composite Membrane D2) and Moisture-proof Composite Membrane B is that DFUE@Fe3O4 was prepared using thiolized Fe3O4 (SH@Fe3O4) modified only by the silane coupling agent KH-590 instead of DFUE@Fe3O4. In other words, the Fe3O4 in Comparative Example 2 was only modified with mercaptosilane and did not undergo a further thiol-alkene click reaction with the DFUE compound.

[0176] The other membrane structure, the amount of each layer, and the co-extrusion blown film process parameters are the same as those of the moisture-proof composite membrane B.

[0177] Performance testing

[0178] I. Mechanical property testing

[0179] The tests were conducted according to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets". A universal testing machine was used to test the longitudinal (MD) and transverse (TD) tensile strength and elongation at break of the moisture-proof composite film. The specimen size was 150 mm × 20 mm, the clamping distance was 50 mm, and the testing speed was 150 mm / min.

[0180] II. Barrier Performance Test

[0181] Water vapor transmission rate (WVTR): Refer to GB / T 1037-2021 "Determination of water vapor transmission performance of plastic films and sheets - Cup method for weight gain and weight loss". Test conditions: temperature 23℃, relative humidity 90%.

[0182] Oxygen permeability (OTR): Refer to GB / T 19789-2021 "Test method for oxygen permeability of plastic films and sheets for packaging materials - coulometric test". Test conditions: temperature 23℃, dry (0%RH) and wet (50%RH) conditions, used to evaluate the oxygen barrier performance of EVOH barrier layer in dry and humid environments respectively.

[0183] III. Magnetic Adsorption Performance Test

[0184] Qualitative test: After cleaning the surface of the steel plate with alcohol and letting it dry naturally, each moisture-proof composite film sample (100mm×100mm) was attached to the vertical steel plate surface to observe whether the composite film could adhere to the steel plate surface by its own magnetic adsorption.

[0185] Quantitative testing: Each diaphragm sample was vertically attached to a steel plate, and weights were suspended from the lower end using clamps. The load was gradually increased until the diaphragm detached from the steel plate, and the maximum suspension load per unit area (g / cm²) was recorded. 2 ), to characterize magnetic adsorption force.

[0186] IV. Contact Angle Test

[0187] The water contact angle of the functional layer surface of each membrane sample was measured using a contact angle meter. Five points were measured for each sample and the average value was taken to characterize the contribution of the fluorinated segments of DFUE to the surface hydrophobicity.

[0188] V. Interlayer peel strength test

[0189] Referring to GB / T 8808-1988 "Peel Test Method for Flexible Composite Plastic Materials", the T-type peel method was used to determine the interlayer peel strength between the PE-g-MAH adhesive layer and the adjacent EVOH layer and LLDPE layer. The peel speed was 200 mm / min and the sample width was 15 mm.

[0190] VI. Damp heat aging test

[0191] Each membrane sample was aged for 30 days in a constant temperature and humidity chamber at 50℃ and 95% relative humidity to simulate the working conditions of a container in "tropical sea area + long voyage". The water vapor transmission retention rate (i.e., the ratio of WVTR before aging to WVTR after aging) was tested to evaluate the damp heat stability.

[0192] The test results are shown in Table 3.

[0193] Table 3. Comprehensive Performance Test Results of Moisture-proof Composite Film

[0194]

[0195] As shown in Table 3, the moisture-proof composite films A, B, and C prepared by this invention can all be magnetically adsorbed onto the surface of the steel plate and can adhere well to the surface of the steel plate. The magnetic adsorption force increases from 0.8 g / cm² with the increase of DFUE@Fe3O4 dosage. 2 Increased to 2.4 g / cm³ 2 Comparative Example 1 does not contain Fe3O4, and therefore does not possess magnetic adsorption properties. This demonstrates that the introduction of Fe3O4 can endow the moisture-proof composite film with magnetic adsorption function, making it suitable for rapid installation and removal of the inner walls of steel containers.

[0196] In terms of mechanical properties: Compared with Comparative Example 1, the longitudinal tensile strength of the moisture-proof composite membrane B increased from 30.2 MPa to 46.8 MPa (an increase of approximately 55.0%), and the transverse tensile strength increased from 27.8 MPa to 42.5 MPa (an increase of approximately 52.9%). Although the elongation at break decreased slightly due to the introduction of rigid nanofillers, it still remained above 480%, meeting the flexibility requirements of container moisture-proof membranes. This indicates a significant synergistic effect between DFUE@Fe3O4 and the EVOH barrier layer, which can simultaneously improve the bidirectional mechanical properties and moisture-proof performance of the composite membrane.

[0197] Compared with Comparative Example 2: the longitudinal tensile strength of the moisture-proof composite membrane B increased from 35.6 MPa to 46.8 MPa (an increase of approximately 31.5%); the water vapor transmission rate increased from 2.10 g / (m²) to 46.8 MPa. 2 The concentration of 24h decreased to 0.40 g / (m 2(24h) (reduced by approximately 81.0%); the water contact angle increased from 96° to 112°, indicating that when Fe3O4 is modified with KH-590 alone, the mercaptosilane segments are relatively short, resulting in limited compatibility and hydrophobic enhancement with the polyethylene matrix. In contrast, the bis(C18) stearyl ester segments in the DFUE molecule significantly improve the interfacial compatibility between Fe3O4 and the polyethylene matrix, while the fluorinated segments further reduce the surface energy of the material, thereby significantly improving the mechanical properties, hydrophobic properties, and moisture-proof properties of the composite film.

[0198] Dosage effect: As the amount of DFUE@Fe3O4 increased from 5 parts by weight to 15 parts by weight, the water vapor permeability of the moisture-proof composite membrane increased from 0.55 g / (m²) to 15 parts by weight. 2 The concentration of 24h decreased to 0.35 g / (m 2 Over 24 hours, the water contact angle increased from 108° to 115°, indicating a significant dose-dependent effect of the hydrophobic contribution of the fluorinated segments in the DFUE molecule. The longitudinal tensile strength of the moisture-proof composite film reached its highest value of 46.8 MPa when the DFUE@Fe3O4 content was 10 parts by weight; when the content increased to 15 parts by weight, the tensile strength slightly decreased to 44.5 MPa, possibly due to localized agglomeration of Fe3O4 nanoparticles at high filler content, leading to stress concentration. Therefore, considering moisture-proof performance, mechanical properties, and processing stability, the preferred content of DFUE@Fe3O4 is 8-12 parts by weight per 100 parts by weight of LLDPE resin.

[0199] Oxygen barrier performance: Under dry conditions, the oxygen permeation of all membrane samples from this invention was less than 0.85 cm⁻¹. 3 / (m 2 The pressure drop (0.1 MPa over 24 hours) is mainly due to the contribution of the high-barrier EVOH layer. Under humid conditions (50% RH), the OTR of all samples in this invention remained at 1.38-1.62 cm⁻¹. 3 / (m 2 (24h·0.1MPa); while in Comparative Examples 1 and 2, the OTR increased to 4.20 and 2.85 cm, respectively, under wet conditions. 3 / (m 2 (24h, 0.1MPa). This indicates that the hydrophobic protective effect of the fluorinated segments of DFUE can effectively inhibit the degradation of the barrier properties of EVOH caused by moisture plasticization.

[0200] Interlayer peel strength: The interlayer peel strength of all samples in this invention is between 4.2-4.7 N / 15 mm, which is comparable to that of Comparative Example 1 and Comparative Example 2, indicating that the introduction of DFUE@Fe3O4 did not adversely affect the adhesion performance between the PE-g-MAH adhesive layer and the adjacent layers.

[0201] Moisture and heat aging stability: After aging at 50℃ and 95%RH for 30 days, the WVTR retention rate of each sample of the present invention was higher than 92%, which was significantly better than that of Comparative Example 1 (68%) and Comparative Example 2 (78%), indicating that the present invention has excellent moisture resistance stability under long ocean voyage conditions.

[0202] in conclusion

[0203] This invention synthesizes a fluorinated alkenyl coupling agent DFUE based on a tartaric acid backbone, and covalently links it with thiolized Fe3O4 via a thiol-alkene click reaction to prepare a DFUE@Fe3O4 functional filler. This functional filler possesses magnetic properties, polyethylene compatibility, and low surface energy hydrophobicity.

[0204] Introducing DFUE@Fe3O4 into the LLDPE functional layer and combining it with an EVOH high-barrier layer to construct a multi-layer co-extruded moisture-proof composite film can significantly improve the composite film's magnetic adsorption properties, biaxial tensile strength, moisture and water resistance, oxygen barrier properties, and hygrothermal aging stability. This moisture-proof composite film can adhere to the inner wall of steel containers through its own magnetic adsorption, and features convenient installation, no adhesive required, no residue, strong water and oxygen barrier properties, good mechanical properties, and excellent hygrothermal stability. It is particularly suitable for moisture-proof packaging of goods during ocean container storage and transportation.

Claims

1. A moisture-proof composite film for ocean storage and transportation, characterized in that, The moisture-proof composite film comprises at least one polyethylene functional layer, at least one barrier layer, and at least one adhesive layer; the polyethylene functional layer comprises polyethylene resin and DFUE-functionalized Fe3O4; the DFUE-functionalized Fe3O4 is covalently linked by a thiolized Fe3O4 and a fluorinated alkenyl coupling agent DFUE based on a tartaric acid backbone via a thiol-alkene click reaction; the molecular structure of the coupling agent DFUE comprises a tartaric acid backbone, two stearoyl ester segments, one fluorinated alkyl ester segment, and one terminal alkenyl ester segment, and its specific structural formula is as follows: 。 2. The moisture-proof composite film according to claim 1, characterized in that, In the polyethylene functional layer, the amount of DFUE-functionalized Fe3O4 added is 3-20 parts by weight, based on 100 parts by weight of polyethylene resin.

3. The moisture-proof composite film according to claim 1, characterized in that, The barrier layer is an ethylene-vinyl alcohol copolymer barrier layer; the adhesive layer is a maleic anhydride-grafted polyethylene adhesive layer.

4. The moisture-proof composite film according to claim 1, characterized in that, The moisture-proof composite film is a nine-layer co-extruded film, comprising, in sequence: First layer: 100wt% LLDPE functional layer containing DFUE-functionalized Fe3O4; dosage is 20-30 parts by weight; Second layer: 100wt% HDPE layer; dosage is 8-12 parts by weight; Third layer: 100wt% PE-g-MAH adhesive layer; dosage is 3-5 parts by weight; Fourth layer: 100wt% EVOH barrier layer; dosage is 3-6 parts by weight; Fifth layer: 100wt% PE-g-MAH adhesive layer; dosage is 3-5 parts by weight; Sixth layer: 100wt% LLDPE functional layer containing DFUE-functionalized Fe3O4; dosage: 20-30 parts by weight; Seventh layer: 100wt% PE-g-MAH adhesive layer; dosage is 3-5 parts by weight; Eighth layer: 100wt% HDPE layer; dosage is 8-12 parts by weight; Ninth layer: 100wt% m-LLDPE layer; dosage: 10-18 parts by weight; The total thickness of the moisture-proof composite film is 80-120μm.

5. The moisture-proof composite film according to claim 1, characterized in that, The thiolized Fe3O4 is prepared by surface modification of Fe3O4 nanoparticles with a thiol silane coupling agent; the average particle size of the Fe3O4 nanoparticles is 10-200 nm; the thiol silane coupling agent is selected from at least one of 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane; the thiol content of the thiolized Fe3O4 is 0.2-0.8 mmol / g.

6. A method for preparing the moisture-proof composite film according to claim 4, characterized in that, Includes the following steps: S1. Synthesis of coupling agent DFUE: DFUE is prepared by sequentially passing dibenzyl tartrate as the starting material through hydroxystearylation, catalytic hydrogenolysis of benzyl tartrate, diacid cyclic anhydride formation, selective ring opening of fluorinated alcohol and esterification of terminal alkenyl alcohol. S2. Preparation of mercapto-modified Fe3O4: Fe3O4 nanoparticles were reacted with a mercaptosilane coupling agent in an ethanol / water mixed solvent to obtain SH@Fe3O4; S3. Preparation of DFUE-functionalized Fe3O4: SH@Fe3O4 and DFUE were subjected to a mercapto-alkene click reaction in the presence of a photoinitiator and under ultraviolet light to prepare DFUE@Fe3O4; S4. Preparation of LLDPE composite functional masterbatch: DFUE@Fe3O4 and LLDPE resin are melt-blended and extruded in the presence of antioxidants and granulated. Nitrogen gas is used for protection during the granulation process. S5. Multilayer co-extrusion blown film: The LLDPE composite functional masterbatch is melt-plasticized with HDPE resin, PE-g-MAH resin, EVOH resin and m-LLDPE resin respectively through multiple extruders, and then combined through a multilayer co-extrusion die, blow-molded, cooled, drawn and wound to obtain the moisture-proof composite film.

7. The preparation method according to claim 6, characterized in that, The specific steps for synthesizing DFUE in step S1 are as follows: (1) Dibenzyl tartrate was reacted with stearoyl chloride under the catalysis of 4-dimethylaminopyridine DMAP and organic base to prepare dibenzyl-2,3-di-O-stearoyl tartrate. (2) Under Pd / C catalysis, the dibenzyl-2,3-di-O-stearoyl tartaric acid ester was debenzylated by atmospheric pressure hydrogenation to obtain 2,3-di-O-stearoyl tartaric acid; (3) The 2,3-di-O-stearoyl tartaric acid was dehydrated and cyclically formed in the presence of acetic anhydride and a catalytic amount of sodium acetate to obtain 2,3-di-O-stearoyl tartaric acid cyclic anhydride. (4) The cyclic anhydride and the fluorinated alcohol undergo a selective ring-opening reaction under the catalysis of DMAP and organic base to obtain a monofluorinated ester intermediate. (5) The monofluorinated ester intermediate and the terminal alkenyl alcohol are esterified in the presence of EDCI·HCl and DMAP catalyst and BHT inhibitor to obtain DFUE.

8. The preparation method according to claim 6, characterized in that, In step S3, the mass ratio of SH@Fe3O4 to DFUE is 1:0.5-1:2; The photoinitiator is selected from at least one of benzoin dimethyl ether, 2-hydroxy-2-methylphenylacetone, or 2,2-diethoxyacetophenone, and the amount added is 1-5 wt% of the total mass of SH@Fe3O4 and DFUE. The ultraviolet light wavelength is 320-400 nm, and the reaction time is 2-10 h; In step S4, the melt blending temperature is 150-200℃, the screw speed is 100-300 r / min, and the antioxidant is selected from at least one of antioxidant 1010 and antioxidant 168, with an addition amount of 0.1-0.5 wt% of the LLDPE resin mass. The process parameters for each extruder in step S5 are as follows: Extruder for LLDPE functional layer containing DFUE@Fe3O4: Temperature 170-210℃, screw speed 40-80r / min; HDPE layer extruder: Temperature 170-210℃, screw speed 20-50r / min; PE-g-MAH adhesive layer extruder: temperature 150-195℃, screw speed 10-30r / min; EVOH barrier layer extruder: temperature 185-220℃, screw speed 10-30r / min; m-LLDPE layer extruder: temperature 175-215℃, screw speed 20-50r / min; Co-extrusion die temperature: 195-220℃; cooling air ring temperature: 15-25℃; blow-up ratio: 1.8-3.0; draw ratio: 3-10.

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