An eleven-layer co-extruded film for aeronautics and a process for its preparation

Abstract

The application relates to the technical field of vacuum bag film for aviation manufacturing, and discloses an eleven-layer co-extrusion film for aviation and a preparation process, specifically: a single alkenyl double epoxy compound is used to perform grafting modification treatment on polyamide acid through a carboxyl-epoxy ring-opening reaction to prepare alkenyl functionalized processable polyimide; 3-mercapto propionic acid is used to modify nylon 6 resin through an amino-carboxyl condensation reaction to prepare a mercapto functionalized nylon; under hot melting conditions, the alkenyl functionalized processable polyimide and the mercapto functionalized nylon are induced to react through a free radical initiator to prepare PA-PI alloy masterbatch; the masterbatch is used as a functional modification component of co-polyamide 6 / 66 resin; and through an eleven-layer co-extrusion blowing process, an eleven-layer co-extrusion film is prepared; the film product has excellent comprehensive performance and can be used as a high-temperature-resistant vacuum bag film for curing of aviation composite materials.

Description

TECHNICAL FIELD

[0001] The application relates to a vacuum bag film for aviation manufacturing, in particular to an eleven-layer co-extrusion film for aviation and a preparation process. BACKGROUND

[0002] In the field of aviation, the proportion of fiber-reinforced thermosetting resin-based composite materials applied on aircraft is increasing, and the autoclave molding process is the most common molding method for fiber-reinforced thermosetting resin-based composite materials, and the molded components are mostly used for the main load-bearing and secondary load-bearing structures of the aircraft.

[0003] In the autoclave molding process, the vacuum bag film, as one of the key auxiliary materials, is mainly used to build a closed vacuum environment during the curing period to ensure that the pre-impregnated layers are fully compacted, volatile substances are removed, and high temperature and high pressure are withstood.

[0004] Market research shows that nylon has become the preferred material for vacuum bag films due to its low air permeability, high strength, toughness, and high temperature resistance. Its production process mainly includes pure nylon extrusion (single-layer casting) and multi-layer co-extrusion. The nylon molecular chain contains a large number of amide bonds, and these polar groups can form hydrogen bonds with water molecules, making nylon have a certain hygroscopicity. In a humid environment, the vacuum bag film made of nylon will absorb water, causing the intermolecular forces to weaken, the material to plasticize, and the mechanical properties to decrease, resulting in size expansion. This change will affect the adhesion and sealing performance of the vacuum bag film.

[0005] Polyimide has excellent high temperature resistance and extremely low hygroscopicity, and can be used as a modified component to improve the dimensional stability and durability of nylon film in high temperature and high humidity environments. However, polyimide has a narrow processing window, high melt viscosity, and difficult melt processing, and its chemical structure is significantly different from that of nylon, which may lead to phase separation when directly mixed. Therefore, techniques such as copolymerization, graft modification, reactive compatibilization, or the introduction of compatibilizers are usually used to improve the compatibility and processing performance of the two materials, achieving performance synergy. SUMMARY

[0006] The application develops a processable polyimide containing alkenyl reactive functional groups and a functionalized nylon resin containing thiol reactive sites. Under hot melt conditions, the two materials undergo thiol-alkenyl click reaction induced by free radical initiators to achieve covalent bonding, and PA-PI alloy masterbatch is prepared. The PA-PI alloy masterbatch is used as a functional modification component of the nylon resin raw material, and an eleven-layer co-extrusion film product is prepared through an eleven-layer co-extrusion blow molding process. The eleven-layer co-extrusion film can be used as a high-temperature-resistant vacuum bag film for curing of aviation composite materials.

[0007] A preparation process of an eleven-layer co-extrusion film for aviation includes the following steps:

[0008] Step one: synthesis of mono-olefin double epoxy compound;

[0009] Based on the carboxyl-epoxy ring opening reaction mechanism, the mono-olefin double epoxy compound is used for grafting modification treatment of polyamide acid to prepare olefin functionalized processable polyimide;

[0010] Step two: based on the amino-carboxyl condensation reaction mechanism, 3-mercaptopropionic acid is used for modification treatment of nylon 6 resin to prepare mercapto functionalized nylon;

[0011] Step three: under the condition of hot melting, the olefin functional group in the olefin functionalized processable polyimide and the mercapto functional group in the mercapto functionalized nylon are induced to occur click reaction by free radical initiator to realize the reactivity of polyimide and nylon, and PA-PI alloy master batch is prepared;

[0012] Step four: the PA-PI alloy master batch is used as the functional modification component of copolymerized polyamide 6 / 66 resin, and eleven-layer co-extrusion film for aviation is prepared by eleven-layer co-extrusion blowing process.

[0013] Preferably, the preparation method of the mono-olefin double epoxy compound is as follows:

[0014] In the presence of photoinitiator, the click reaction occurs between the olefin functional group of 1 mole equivalent of N-methyl diallyl amine and the mercapto functional group of 2.01-2.09 mole equivalents of 2-mercaptoethoxy ethanol under the action of ultraviolet light to generate intermediate a;

[0015] The nucleophilic substitution reaction occurs between the hydroxyl functional group of 1 mole equivalent of intermediate a and the acyl chloride functional group of 2.01-2.09 mole equivalents of 10-undecenoyl chloride to generate intermediate b;

[0016] Under the oxidation of organic peroxy acid, the epoxidation reaction occurs between the olefin functional group of intermediate b to generate intermediate c;

[0017] By using the nucleophilic substitution reaction mechanism, the quaternary ammonium reaction occurs between the tertiary amine group of 1 mole equivalent of intermediate c and the bromine functional group of 1.01-1.09 mole equivalents of 6-bromo-1-hexene to generate the mono-olefin double epoxy compound.

[0018] Preferably, the photoinitiator is one of 2,2-dimethoxy-2-phenylphenylacetone, 2-hydroxy-2-methyl-1-phenylpropanone and 2,2-diethoxyphenylacetone.

[0019] Preferably, the organic peroxy acid is one of peroxoacetic acid, peroxobenzoic acid and m-chloroperbenzoic acid.

[0020] Preferably, the free radical initiator is one of dicumyl peroxide, tert-butyl hydroperoxide, dibenzoyl peroxide, tert-butyl peroxybenzoate.

[0021] Preferably, the preparation method of the alkenyl functional processable polyimide is:

[0022] The polyamic acid is obtained by condensation polymerization reaction in N,N-dimethylacetamide solvent with pyromellitic dianhydride and 4,4-diamino diphenyl ether as monomers;

[0023] The alkenyl functional processable polyimide is obtained by ring-opening reaction of the epoxy functional group in the mono-alkenyl double epoxy compound with the carboxyl functional group in the polyamic acid, and then high-temperature thermal imidization process is carried out by programmed temperature rising.

[0024] Preferably, the formula of the PA-PI alloy master batch is: 20-30wt% alkenyl functional processable polyimide and 70-80wt% thiol functional nylon.

[0025] Preferably, the formula of the alkenyl functional processable polyimide is: 4-6 parts by weight of pyromellitic dianhydride, 3-5 parts by weight of 4,4-diamino diphenyl ether and 0.1-1 parts by weight of mono-alkenyl double epoxy compound.

[0026] Preferably, the formula of the thiol functional nylon is: 8-10 parts by weight of nylon 6 resin and 0.5-2 parts by weight of 3-mercaptopropionic acid.

[0027] The thickness of the eleven-layer co-extrusion film for aviation prepared according to the above process is 40-60μm.

[0028] Preferably, the product structure of the eleven-layer co-extrusion film for aviation is:

[0029] The formula of the first layer, the sixth layer and the eleventh layer is 60-80wt% copolymerized polyamide 6 / 66 resin and 20-40wt% PA-PI alloy master batch, and the amount is 5-25 parts by weight;

[0030] The formula of the second layer and the tenth layer is 70-90wt% copolymerized polyamide 6 / 66 resin and 10-30wt% PA-PI alloy master batch, and the amount is 5-10 parts by weight;

[0031] The formula of the third layer, the fourth layer, the fifth layer, the seventh layer, the eighth layer and the ninth layer is 85-95wt% copolymerized polyamide 6 / 66 resin and 5-15wt% PA-PI alloy master batch, and the amount is 5-10 parts by weight.

[0032] Preferably, the amount of the first layer is 5-15 parts by weight;

[0033] Preferably, the amount of the sixth layer is 5-10 parts by weight;

[0034] Preferably, the amount of the eleventh layer is 15-25 parts by weight. Beneficial effects

[0035] The present application is based on the principle of molecular design, using N-methyl diallylamine as the connecting framework, introducing flexible ether chain by thiol-alkenyl click reaction with 2-mercaptoethoxy ethanol, then introducing epoxy functional group by reacting with undecylenoyl chloride and performing epoxidation treatment, and then introducing terminal alkenyl functional group by quaternization reaction with 6-bromo-1-hexene, to prepare a monoalkenyl bisepoxy composite flexible compound;

[0036] The alkenyl functionalized processable polyimide is obtained by ring-opening reaction of the epoxy functional group in the monoalkenyl bisepoxy composite flexible compound with the carboxyl functional group in the polyimide precursor (polyamide acid), and high temperature thermal imidization process through programmed temperature rising;

[0037] The modification of nylon 6 resin by 3-mercaptopropionic acid is realized by amide condensation reaction of the carboxyl functional group of 3-mercaptopropionic acid with the terminal amino functional group on the molecular backbone of nylon 6 resin, and the mercapto-functionalized nylon is obtained;

[0038] Under the condition of hot melting, the reactive compounding of polyimide and nylon is realized by click reaction of the alkenyl functional group in the alkenyl functionalized processable polyimide with the mercapto functional group in the mercapto-functionalized nylon induced by free radical initiator, and PA-PI alloy master batch is obtained, which is used as the functional modification component of nylon resin, and an eleven-layer co-extrusion blown film for aviation is prepared by adopting eleven-layer co-extrusion film forming process. The tensile strength of the film product is >60MPa after heat treatment at 210℃ for 12h, and the moisture absorption rate is <1.0wt% after 24h at 25℃ / 100%RH, which completely meets the use requirements of high temperature vacuum bag film for aviation composites on temperature resistance and low moisture expansion. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is the chemical structural formula of intermediate a;

[0040] Figure 2 is the chemical structural formula of intermediate b;

[0041] Figure 3 is the chemical structural formula of intermediate c;

[0042] Figure 4 is the chemical structural formula of monoalkenyl bisepoxy composite flexible compound;

[0043] Figure 5Performance test results of an eleven-layer co-extruded film for use in aviation. DETAILED DESCRIPTION

[0044] The present application designs and synthesizes a mono-olefin double epoxy complex flexible compound, which integrates thioether group, oxygen ether group and alkyl flexible structural unit, and regulates the flexibility and reactivity of the molecular chain segment through the synergistic effect of multi-functional groups. On the one hand, the compound is used for grafting modification of polyimide, and by introducing flexible structure into the rigid main chain of polyimide, the free volume between the molecular chains is increased, the moving and twisting space of the molecular chain is expanded, and the movement ability of the molecular chain is improved, so that the melt viscosity is reduced and the processing performance is improved. On the other hand, the compound is used for compounding with nylon resin through covalent bond, and a PA-PI alloy master batch with good compatibility with nylon and melt processability is prepared.

[0045] Example one:

[0046] The mono-olefin double epoxy complex flexible compound is prepared by the following process:

[0047] Process one: in the presence of a photoinitiator, a click reaction occurs between the alkyl functional group of 1 mole equivalent of N-methyl diallylamine and the thiol functional group of 2.02 mole equivalents of 2-mercaptoethoxy ethanol under the action of ultraviolet light, to generate intermediate a, whose chemical structural formula is as shown in Figure 1 ;

[0048] Among them, the photoinitiator can be selected from one of 2,2-dimethoxy-2-phenyl phenylacetone, 2-hydroxy-2-methyl-1-phenylpropanone and 2,2-diethoxy phenylacetone; 2,2-dimethoxy-2-phenyl phenylacetone is selected in this embodiment;

[0049] Process two: a nucleophilic substitution reaction occurs between the hydroxyl functional group of 1 mole equivalent of intermediate a and the acyl chloride functional group of 2.03 mole equivalents of 10-undecenoyl chloride, to generate intermediate b, whose chemical structural formula is as shown in Figure 2 ;

[0050] Process three: under the oxidation of an organic peroxy acid, an epoxidation reaction occurs to the alkyl functional group of intermediate b, to generate intermediate c, whose chemical structural formula is as shown in Figure 3 ;

[0051] Among them, the organic peroxy acid can be selected from one of peroxoacetic acid, peroxybenzoic acid and m-chloroperbenzoic acid; m-chloroperbenzoic acid is selected in this embodiment;

[0052] Process four: using the mechanism of nucleophilic substitution reaction, through the quaternary ammonium reaction of 1 mole equivalent of the tertiary amine group of intermediate c and 1.02 mole equivalents of the bromine functional group of 6-bromo-1-hexene, a mono-olefin double epoxy compound with complex flexible type is generated, and its chemical structural formula is as shown in Figure 4

[0053] The specific experimental steps for preparing the mono-olefin double epoxy compound with complex flexible type are as follows:

[0054] Under the protection of nitrogen, 2.2 g of N-methyl diallylamine, 0.1 g of 2,2-dimethoxy-2-phenylacetophenone and 20 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask, stirred at room temperature until completely dissolved, then 40 mL of anhydrous N,N-dimethylformamide solution dissolving 4.9 g of 2-mercaptoethoxy ethanol was added dropwise to the three-necked flask under ultraviolet lamp irradiation (360 nm, 10 cm), and the reaction was continued to be stirred under ultraviolet lamp irradiation for 60 min after the dropwise addition was completed. After rotary evaporation under reduced pressure, washing with deionized water and drying, intermediate a was obtained;

[0055] 3.5 g of intermediate a and 30 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask, stirred at room temperature until completely dissolved, then 30 mL of anhydrous N,N-dimethylformamide solution dissolving 4.0 g of 10-undecenoyl chloride was added dropwise to the three-necked flask under the protection of nitrogen, and the reaction was stirred at 60°C for 5 h. After cooling to room temperature, 1.5 mL of 5 wt% sodium carbonate aqueous solution was added dropwise, rotary evaporation was performed under reduced pressure, washing was performed with deionized water, and drying was performed to obtain intermediate b;

[0056] 3.4 g of intermediate b and 30 mL of chloroform were added to a three-necked flask, stirred at room temperature for 30 min, then 20 mL of chloroform solution dissolving 1.5 g of m-chloroperbenzoic acid was added to the three-necked flask, and the reaction was stirred at 55°C for 16 h. After cooling to room temperature, rotary evaporation was performed under reduced pressure, washing was performed with saturated sodium bicarbonate aqueous solution and deionized water in sequence, and drying was performed to obtain intermediate c;

[0057] 2.4 g of intermediate c and 20 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask, stirred at room temperature until completely dissolved, then 10 mL of anhydrous N,N-dimethylformamide solution dissolving 0.6 g of 6-bromo-1-hexene was added to the three-necked flask, and the reaction was stirred at 40°C for 5 h. After cooling to room temperature, rotary evaporation was performed under reduced pressure, and drying was performed to obtain a mono-olefin double epoxy compound with complex flexible type;

[0058] The nuclear magnetic resonance hydrogen spectrum of the mono-olefin double epoxy compound with complex flexible type is characterized as follows: 1 ​H NMR (CDC13, 400 MHz) δ: 1.17-1.61 (m, 32H), 1.86-1.94 (m, 4H), 2.09-2.14 (m, 2H), 2.29-2.32 (t, 4H), 2.69-2.73 (t, 4H), 2.83-2.87 (t, 4H), 3.29 (s, 3H), 3.49-3.73 (m, 20H), 4.33-4.36 (t, 4H), 4.96-5.14 (dd, 2H), 5.71-5.81 (m, 1H).

[0059] Example Two:

[0060] The preparation steps of the alkenyl functionalized processable polyimide are as follows:

[0061] Step one, preparation of polyamide acid (polyimide precursor): using pyromellitic dianhydride and 4,4-diamino diphenyl ether as monomers, polyamide acid is obtained by polycondensation reaction in N,N-dimethylacetamide solvent, the preparation steps are as follows: 4.0 g of 4,4-diamino diphenyl ether and 40 mL of N,N-dimethylacetamide are added to a three-necked flask, stirred at room temperature until completely dissolved, placed in an ice bath, 40 mL of N,N-dimethylacetamide solution dissolved with 4.4 g of pyromellitic dianhydride is slowly added to the three-necked flask in three times at 5°C, the interval between each addition is 10 min, after the addition is completed, the stirring reaction is maintained at 5°C for 16 h, and polyamide acid is obtained;

[0062] Step two, preparation of alkenyl functionalized processable polyimide: first, the ring opening reaction of the epoxy functional group in the mono-alkenyl double epoxy compound and the carboxyl functional group in the polyamide acid occurs, then the high temperature thermal imidization process is carried out by programmed temperature rising, and the alkenyl functionalized processable polyimide is obtained, the preparation steps are as follows: 0.5 g of mono-alkenyl double epoxy compound is added to the polyamide acid prepared in step one, the temperature is raised to 80°C and stirred for 30 min, after cooling to room temperature, vacuum degassing is carried out, poured into a polytetrafluoroethylene mold, naturally leveled off, and the excess part is scraped off with a scraper, placed in an intelligent high temperature test box for 12 h of solvent removal at 100°C, 1 h of temperature maintenance at 120°C, cooled to room temperature, and programmed temperature rising is carried out at 60°C / 1 h, 80°C / 1 h, 120°C / 1 h, 150°C / 1 h, 200°C / 1 h, 201°C / 1 h (here, 1 h of programmed temperature rising means the time required for slowly rising from the previous temperature to the temperature, and not the residence time at the temperature, and rising from 200°C to 201°C is to maintain the temperature at 200°C), and the alkenyl functionalized processable polyimide is obtained.

[0063] Example Three:

[0064] Preparation of thiol-functionalized nylon: through the amidation condensation reaction of the carboxyl functional group of 3-mercaptopropionic acid with the terminal amino functional group on the molecular backbone of nylon 6 resin, the modification of nylon 6 resin by 3-mercaptopropionic acid is realized, and thiol-functionalized nylon is obtained;

[0065] The specific experimental steps for preparing thiol-functionalized nylon are as follows: 9 g of nylon 6 resin (type F136, amino content 150 meq / kg) and 100 mL of N,N-dimethylformamide are added to a three-necked flask with a water separator, and the temperature is raised to 80°C and stirred until completely dissolved, and then cooled to room temperature. Under the condition of nitrogen protection, 10 mL of N,N-dimethylformamide solution dissolving 1 g of 3-mercaptopropionic acid is added to the three-necked flask, the temperature is raised to 90°C and stirred for 6 h, and then the solvent is removed by rotary evaporation under reduced pressure, and thiol-functionalized nylon is obtained after drying.

[0066] Example Four:

[0067] Preparation of PA-PI alloy masterbatch I, the formula is: 25wt% alkenyl functionalized processable polyimide and 75wt% thiol-functionalized nylon, the preparation method is: under the condition of hot melting, the click reaction of alkenyl functional group in alkenyl functionalized processable polyimide and thiol functional group in thiol-functionalized nylon is induced by free radical initiator, the effective compounding of polyimide and nylon is realized, and PA-PI alloy masterbatch I is obtained;

[0068] Among them, the free radical initiator can be selected from one of dicumyl peroxide, tert-butyl hydroperoxide, dibenzoyl peroxide and tert-butyl peroxybenzoate; in this experimental example, dicumyl peroxide is selected;

[0069] The specific experimental steps for preparing PA-PI alloy masterbatch I are as follows: 2.5 g of alkenyl functionalized processable polyimide, 7.5 g of thiol-functionalized nylon and 0.1 g of dicumyl peroxide initiator are added to a high-speed mixer and mixed uniformly, and then added to a twin-screw extruder for extrusion granulation to obtain PA-PI alloy masterbatch I;

[0070] Among them, the process parameters of the twin-screw extruder are set as follows: preheating temperature 250°C, temperatures of zones 1-6 are 250°C, 270°C, 280°C, 290°C, 295°C and 290°C respectively, and the rotating speed is 400 r / min.

[0071] Example Five:

[0072] Preparation of PA-PI alloy masterbatch II, the formula is: 20wt% alkenyl functionalized processable polyimide and 80wt% thiol-functionalized nylon, the preparation method is the same as that of PA-PI alloy masterbatch I in example four.

[0073] Example Six:

[0074] Preparation of PA-PI alloy masterbatch III, the formula is: 30wt% alkenyl functionalized processable polyimide and 70wt% thiol functionalized nylon, the preparation method is the same as that of PA-PI alloy masterbatch I in example four.

[0075] Example seven:

[0076] An eleven-layer co-extrusion film for aviation, the film structure and the raw material formula and amount of each film layer are shown in Table 1;

[0077] Table 1 Experimental formula of eleven-layer co-extrusion film for aviation

[0078] Among them, the model of copolymerized polyamide 6 / 66 resin is C40LN 09;

[0079] The PA-PI alloy masterbatch is one of PA-PI alloy masterbatch I, PA-PI alloy masterbatch II, and PA-PI alloy masterbatch III.

[0080] Example eight:

[0081] A preparation process of an eleven-layer co-extrusion film for aviation, specifically: according to the formula of the eleven-layer co-extrusion film for aviation, the ingredients are prepared, and each layer of raw material is respectively put into the hopper of the eleven-layer co-extrusion film blowing machine set eleven screw extruders, the molten resin is converged at the die head through the flow divider, extruded, blown and pulled (the blow-up ratio is controlled at 3.1), cooled and wound, to prepare the eleven-layer co-extrusion film for aviation;

[0082] Among them, the process parameters of the screw extruders corresponding to the first layer to the eleventh layer are set as follows: the temperatures of 1-3 zones are 250℃, 280℃, and 295℃ respectively, the flow channel temperature is 290℃, and the rotation speed is 80r / min;

[0083] Among them, when the PA-PI alloy masterbatch is PA-PI alloy masterbatch I, the prepared film product is recorded as eleven-layer co-extrusion film for aviation I;

[0084] When the PA-PI alloy masterbatch is PA-PI alloy masterbatch II, the prepared film product is recorded as eleven-layer co-extrusion film for aviation II;

[0085] When the PA-PI alloy masterbatch is PA-PI alloy masterbatch III, the prepared film product is recorded as eleven-layer co-extrusion film for aviation III.

[0086] Comparative example:

[0087] A conventional eleven-layer co-extruded film was prepared, which differed from the eleven-layer co-extruded film for aviation I only in that the raw material formula of the first layer to the eleventh layer was all 100 wt% copolymerized polyamide 6 / 66 resin (i.e. no PA-PI alloy masterbatch I was used).

[0088] Performance test:

[0089] I. Thickness test: According to the GB / T 6672-2001 "Plastics - Determination of thickness - Mechanical method" standard, a thickness tester was used to test the thickness of the film sample;

[0090] II. Appearance test: The appearance of the film sample was determined by visual observation;

[0091] III. Mechanical property test:

[0092] (1) 25℃ normal temperature mechanical property test: According to the GB / T 1040.3-2006 "Plastics - Determination of tensile properties - Part 3: test conditions for films and sheets" standard, a sample of 150mm x 20mm (length x width, the length direction is the blown film direction (machine direction)) was stretched at a stretching rate of 50mm / min (stretching test was carried out in the blown film direction) at 25℃, and the machine direction tensile strength of the sample was recorded;

[0093] (2) 210℃ high temperature mechanical property test: According to the GB / T 1040.3-2006 "Plastics - Determination of tensile properties - Part 3: test conditions for films and sheets" standard, a sample of 150mm x 20mm (length x width, the length direction is the blown film direction (machine direction)) was treated in a 210℃ oven for 12h, and then stretched at a stretching rate of 50mm / min (stretching test was carried out in the blown film direction), and the machine direction tensile strength of the sample was recorded;

[0094] IV. Moisture absorption rate test: According to the GB / T 1034-2008 "Plastics - Determination of water absorption" standard, a sample of 60mm x 60mm (length x width) was dried in a 50℃ oven for 24h, then taken out and cooled to room temperature, weighed, and recorded as the initial weight. The dried sample was completely immersed in distilled water (water temperature was controlled at 25℃) for 24h, then taken out with tweezers and the water on the surface of the sample was absorbed with water absorption filter paper, weighed, and recorded as the weight after moisture absorption. The moisture absorption rate of the sample was calculated, and the specific method was as follows:

[0095] Moisture absorption rate (%) = (weight of sample after moisture absorption - initial weight of sample) / initial weight of sample x 100%;

[0096] The test results are shown in Table 2 and Figure 5 .

[0097] Table 2 Performance test results of the eleven-layer co-extruded film for aviation

[0098] By comprehensive analysis of the performance test results, the following conclusions can be drawn:

[0099] Conclusion 1: The moisture absorption and expansion characteristics of the eleven-layer co-extrusion film product prepared from the PA-PI alloy masterbatch are significantly improved;

[0100] Conclusion 2: The longitudinal tensile strength of the eleven-layer co-extrusion film product prepared from the PA-PI alloy masterbatch remains > 60 MPa at 210°C for 12h, showing excellent high temperature resistance.

Claims

1. A process for preparing an eleven-layer co-extruded film for aerospace applications, characterized in that, Includes the following steps: Step 1: Synthesize a monoalkenyl diepoxy compound with flexible chemical structure: ； Based on the carboxyl-epoxy ring-opening reaction mechanism, polyamic acid was grafted with a monoalkenyl diepoxy composite flexible compound to obtain an alkenyl functionalized processable polyimide. Step 2: Based on the amino-carboxyl condensation reaction mechanism, nylon 6 resin was modified with 3-mercaptopropionic acid to obtain mercapto-functionalized nylon. Step 3: Under hot melting conditions, the alkenyl functional groups in alkenyl functionalized processable polyimide and the thiol functional groups in thiol functionalized nylon are induced to undergo a click reaction by a free radical initiator to achieve reactive composite of polyimide and nylon, thus obtaining PA-PI alloy masterbatch; Step 4: Using PA-PI alloy masterbatch as a functional modification component for copolymer polyamide 6 / 66 resin, an eleven-layer co-extruded film for aerospace applications is produced through an eleven-layer co-extrusion blow molding process.

2. The preparation process of an eleven-layer co-extruded film for aerospace applications according to claim 1, characterized in that, The preparation method of the monoalkenyl diepoxy composite flexible compound is as follows: In the presence of a photoinitiator, intermediate a is generated by a click reaction between the alkenyl functional group of 1 molar equivalent of N-methyldiallylamine and the mercapto functional group of 2.01-2.09 molar equivalents of 2-mercaptoethoxyethanol under ultraviolet light. Intermediate b is generated by a nucleophilic substitution reaction between the hydroxyl functional group of 1 molar equivalent intermediate a and the acyl chloride functional group of 2.01-2.09 molar equivalent 10-undecenoyl chloride. Under the oxidative action of organic peroxyacids, an epoxidation reaction occurs through the alkenyl functional group of intermediate b to generate intermediate c; By utilizing a nucleophilic substitution reaction mechanism, a monoalkenyl diepoxy complex flexible compound is generated by quaternization of the tertiary amine group of 1 molar equivalent intermediate c with the bromine functional group of 1.01-1.09 molar equivalent 6-bromo-1-hexene.

3. The preparation process of an eleven-layer co-extruded film for aerospace applications according to claim 2, characterized in that, The photoinitiator is one of 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropanone, and 2,2-diethoxyacetophenone.

4. The preparation process of an eleven-layer co-extruded film for aerospace applications according to claim 2, characterized in that, The organic peroxyacid is one of peracetic acid, peroxybenzoic acid, and m-chloroperoxybenzoic acid.

5. The preparation process of an eleven-layer co-extruded film for aerospace applications according to claim 1, characterized in that, The free radical initiator is one of dicumyl peroxide, tert-butyl hydroperoxide, benzoyl peroxide, and tert-butyl peroxide.

6. The preparation process of an eleven-layer co-extruded film for aerospace applications according to claim 1, characterized in that, The preparation method of the alkenyl-functionalized processable polyimide is as follows: Polyamic acid was obtained by polycondensation reaction of pyromellitic dianhydride and 4,4-diaminodiphenyl ether as monomers in N,N-dimethylacetamide solvent. First, the epoxy functional group in the monoalkenyl diepoxy composite flexible compound undergoes a ring-opening reaction with the carboxyl functional group in polyamic acid. Then, a high-temperature thermal imidization process is carried out through programmed temperature rise to obtain an alkenyl functionalized processable polyimide.

7. The preparation process of an eleven-layer co-extruded film for aerospace applications according to claim 1, characterized in that, The formulation of the PA-PI alloy masterbatch is: 20-30 wt% alkenyl functionalized processable polyimide and 70-80 wt% mercapto-functionalized nylon.

8. The preparation process of an eleven-layer co-extruded film for aerospace applications according to claim 7, characterized in that, The formulation of the alkenyl functionalized processable polyimide is: 4-6 parts by weight of pyromellitic dianhydride, 3-5 parts by weight of 4,4-diaminodiphenyl ether and 0.1-1 parts by weight of monoalkenyl diepoxy composite flexible compound. The formulation of the mercapto-functionalized nylon is: 8-10 parts by weight of nylon 6 resin and 0.5-2 parts by weight of 3-mercaptopropionic acid.

9. An eleven-layer co-extruded film for aerospace applications prepared by the process according to any one of claims 1-8, characterized in that, The thickness of the eleven-layer co-extruded film is 40-60 μm.

10. An eleven-layer co-extruded film for aviation according to claim 9, characterized in that, The product structure of the eleven-layer co-extruded film used in aviation is as follows: The formulations for the first, sixth, and eleventh layers consist of 60-80 wt% copolyamide 6 / 66 resin and 20-40 wt% PA-PI alloy masterbatch, with a dosage of 5-25 parts by weight. The formulations for the second and tenth layers consist of 70-90 wt% copolyamide 6 / 66 resin and 10-30 wt% PA-PI alloy masterbatch, with a dosage of 5-10 parts by weight. The formulations for the third, fourth, fifth, seventh, eighth, and ninth layers consist of 85-95 wt% copolyamide 6 / 66 resin and 5-15 wt% PA-PI alloy masterbatch, with a dosage of 5-10 parts by weight.

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