Eleven-layer co-extruded film for aviation and preparation process

Abstract

The invention relates to the technical field of vacuum bag films for aeronautical manufacturing, and discloses an eleven-layer co-extruded film for aeronautical use and a preparation process thereof, and the preparation process specifically comprises the following steps: carrying out grafting modification treatment on polyamide acid by using a monoalkenyl diepoxy composite flexible compound through a carboxyl-epoxy ring-opening reaction to prepare alkenyl functionalized processable polyimide; the preparation method comprises the following steps: carrying out modification treatment on nylon 6 resin by using 3-mercaptopropionic acid through an amino-carboxyl condensation reaction to prepare mercapto functionalized nylon; under the hot melting condition, alkenyl functionalized processable polyimide and sulfydryl functionalized nylon are induced to be subjected to reactive compounding through a free radical initiator, PA-PI alloy master batch is prepared, the master batch serves as a functional modification component of copolymerized polyamide 6 / 66 resin, an eleven-layer co-extrusion film is prepared through an eleven-layer co-extrusion blow molding process, and the eleven-layer co-extrusion film is used as a functional modification component of the copolymerized polyamide 6 / 66 resin. The film product has excellent comprehensive performance and can be used as a high-temperature-resistant vacuum bag film for curing aviation composite materials.

Description

Technical Field

[0001] This invention relates to the field of vacuum bag film technology for aerospace manufacturing, specifically to an eleven-layer co-extruded film for aerospace applications and its preparation process. Background Technology

[0002] In the aerospace field, fiber-reinforced thermosetting resin matrix composites are being used more and more in aircraft. Autoclave molding is the most widely used and common molding method for fiber-reinforced thermosetting resin matrix composites, and its molded components are mostly used in the main load-bearing and secondary load-bearing structures of aircraft.

[0003] In the autoclave molding process, vacuum bag film is one of the key auxiliary materials. It is mainly used to create a closed vacuum environment during the curing cycle to ensure that the prepreg layers are fully compacted, volatiles are removed, and the prepreg can withstand high temperature and high pressure.

[0004] Market research shows that nylon, due to its low air permeability, high strength, toughness, and high-temperature resistance, has become the preferred material for vacuum bag films. Its production processes are mainly divided into two categories: pure nylon extrusion (single-layer casting) and multi-layer co-extrusion. Nylon molecular chains contain a large number of amide bonds; these polar groups can form hydrogen bonds with water molecules, giving nylon a certain degree of hygroscopicity. In humid environments, vacuum bag films made of nylon will absorb moisture, leading to a weakening of intermolecular forces and plasticization of the material. This manifests as a decrease in mechanical properties and dimensional expansion, which affects the fit and sealing performance of the vacuum bag film.

[0005] Polyimide possesses excellent high-temperature resistance and extremely low moisture absorption, making it suitable as a modifier to improve the dimensional stability and durability of nylon films under high-temperature and high-humidity environments. However, polyimide suffers from a narrow processing window, high melt viscosity, and difficulties in melt processing. Furthermore, its chemical structure differs significantly from that of nylon, and direct mixing may lead to phase separation. Therefore, techniques such as copolymerization, graft modification, reactive compatibilization, or the introduction of compatibilizers are typically employed to improve the compatibility and processing performance of both materials, achieving synergistic performance. Summary of the Invention

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

[0007] A process for preparing an eleven-layer co-extruded film for aerospace applications includes the following steps: Step 1: Synthesize a monoalkenyl diepoxy compound with flexible 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.

[0008] Preferably, 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.

[0009] Preferably, the photoinitiator is one of 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropanone, and 2,2-diethoxyacetophenone.

[0010] Preferably, the organic peroxyacid is one of peracetic acid, peroxybenzoic acid, and m-chloroperoxybenzoic acid.

[0011] Preferably, the free radical initiator is one of dicumyl peroxide, tert-butyl hydroperoxide, benzoyl peroxide, and tert-butyl peroxide.

[0012] Preferably, 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.

[0013] Preferably, the PA-PI alloy masterbatch is formulated as follows: 20-30 wt% alkenyl functionalized processable polyimide and 70-80 wt% mercapto-functionalized nylon.

[0014] Preferably, 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; Preferably, 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.

[0015] The thickness of an eleven-layer co-extruded film for aviation prepared according to the above process is 40-60 μm.

[0016] Preferably, the product structure of the eleven-layer co-extruded film for 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.

[0017] Preferably, the amount of the first layer is 5-15 parts by weight; Preferably, the sixth layer is used in an amount of 5-10 parts by weight; Preferably, the amount of the eleventh layer is 15-25 parts by weight. Beneficial effects

[0018] Based on molecular design principles, this invention uses N-methyldiallylamine as a linking framework. First, it introduces a flexible ether chain by reacting with 2-mercaptoethoxyethanol via a mercapto-alkenyl click reaction. Then, it reacts with undecenoyl chloride and undergoes epoxidation to introduce epoxy functional groups. Finally, it introduces terminal alkenyl functional groups by reacting with 6-bromo-1-hexene via a quaternization reaction to obtain a monoalkenyl diepoxy composite flexible compound. Alkenyl functionalized processable polyimide is obtained by ring-opening reaction between the epoxy functional group in the monoalkenyl diepoxy composite flexible compound and the carboxyl functional group in the polyimide precursor (polyamic acid), followed by a high-temperature thermal imidization process through programmed temperature rise. The modification of nylon 6 resin by 3-mercaptopropionic acid is achieved by the amidation condensation reaction between the carboxyl functional group of 3-mercaptopropionic acid and the terminal amino functional group on the molecular backbone of nylon 6 resin, thus obtaining mercapto-functionalized nylon. Under hot-melt conditions, a click reaction is induced between the alkenyl functional groups in alkenyl-functionalized processable polyimide and the thiol functional groups in thiol-functionalized nylon by a free radical initiator, achieving reactive composite of polyimide and nylon to obtain PA-PI alloy masterbatch. Using this masterbatch as a functional modifying component of nylon resin, an eleven-layer co-extrusion blow molding process is adopted to produce an eleven-layer co-extruded film for aerospace applications. The film product has a tensile strength >60MPa after heat treatment at 210℃ for 12h, and maintains a moisture absorption rate of <1.0wt% at 25℃ / 100%RH for 24h, which fully meets the requirements of high-temperature vacuum bag film for aerospace composite materials for temperature resistance and low moisture expansion. Attached Figure Description

[0019] Figure 1 Here is the chemical structural formula of intermediate a; Figure 2 Here is the chemical structural formula of intermediate b; Figure 3 Here is the chemical structural formula of intermediate C; Figure 4 The chemical structural formula of a monoalkenyl diepoxy compound is shown. Figure 5 These are the performance test results for an eleven-layer co-extruded film used in aviation. Detailed Implementation

[0020] This invention designs and synthesizes a monoalkenyl diepoxy composite flexible compound that integrates thioether, oxyether, and alkyl flexible structural units. Through the synergistic effect of multiple functional groups, the flexibility and reactivity of the molecular chain segments are regulated. On the one hand, it is used to graft and modify polyimide, introducing a flexible structure into the rigid main chain of polyimide, increasing the free volume between its molecular chains, expanding the space for movement and torsion of the molecular chains, and improving the mobility of the molecular chains, thereby reducing its melt viscosity and improving its processing performance. On the other hand, it is covalently bonded to nylon resin to prepare a PA-PI alloy masterbatch with good compatibility with nylon and capable of melt processing.

[0021] Example 1: The preparation process for a monoalkenyl diepoxy composite flexible compound is as follows: Process 1: In the presence of a photoinitiator, a click reaction occurs between the alkenyl functional group of 1 molar equivalent of N-methyldiallylamine and the thiol functional group of 2.02 molar equivalents of 2-mercaptoethoxyethanol under ultraviolet light, generating intermediate a, whose chemical structure is shown below. Figure 1 As shown; The photoinitiator can be selected from one of 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropanone, and 2,2-diethoxyacetophenone; in this embodiment, 2,2-dimethoxy-2-phenylacetophenone is selected. Process 2: A nucleophilic substitution reaction occurs between the hydroxyl functional group of 1 molar equivalent intermediate a and the acyl chloride functional group of 2.03 molar equivalent 10-undecenoyl chloride to generate intermediate b, whose chemical structure is shown below. Figure 2 As shown; Process 3: Under the oxidation of organic peroxyacids, an epoxidation reaction occurs through the alkenyl functional group of intermediate b to generate intermediate c, whose chemical structural formula is as follows: Figure 3 As shown; The organic peroxy acid can be selected from peracetic acid, peroxybenzoic acid, or m-chloroperoxybenzoic acid; in this embodiment, m-chloroperoxybenzoic acid is selected. Step 4: Utilizing a nucleophilic substitution mechanism, a quaternization reaction occurs between the tertiary amine group of 1 molar equivalent intermediate C and the bromine functional group of 1.02 molar equivalent 6-bromo-1-hexene, generating a monoalkenyl diepoxy complex flexible compound, the chemical structure of which is shown below. Figure 4 As shown; The specific experimental steps for preparing monoalkenyl diepoxy composite flexible compounds are as follows: Under nitrogen protection, 2.2 g of N-methyldiallylamine, 0.1 g of 2,2-dimethoxy-2-phenylacetophenone, and 20 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, under UV irradiation (360 nm, 10 cm), 40 mL of anhydrous N,N-dimethylformamide solution containing 4.9 g of 2-mercaptoethoxyethanol was added dropwise to the three-necked flask. After the addition was complete, the reaction was stirred under UV irradiation for 60 min. The mixture was then rotary evaporated under reduced pressure, washed with deionized water, and dried to obtain intermediate a. 3.5 g of intermediate a and 30 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature until completely dissolved. Under nitrogen protection, 30 mL of anhydrous N,N-dimethylformamide solution containing 4.0 g of 10-undecenoyl chloride was added dropwise to the three-necked flask. The mixture was heated to 60 °C and stirred for 5 h. After cooling to room temperature, 1.5 mL of 5 wt% sodium carbonate aqueous solution was added dropwise. The mixture was then rotary evaporated under reduced pressure, washed with deionized water, and dried to obtain intermediate b. 3.4 g of intermediate b and 30 mL of chloroform were added to a three-necked flask and stirred at room temperature for 30 min to dissolve. Then, 20 mL of chloroform solution containing 1.5 g of m-chloroperoxybenzoic acid was added to the three-necked flask, the temperature was raised to 55 °C and stirred for 16 h, cooled to room temperature, and rotary evaporated under reduced pressure. The mixture was washed successively with saturated sodium bicarbonate aqueous solution and deionized water, and dried to obtain intermediate c. 2.4 g of intermediate c and 20 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 10 mL of anhydrous N,N-dimethylformamide solution containing 0.6 g of 6-bromo-1-hexene was added to the three-necked flask. The mixture was heated to 40 °C and stirred for 5 h. After cooling to room temperature, the mixture was evaporated under reduced pressure and dried to obtain a monoalkenyl diepoxy composite flexible compound. The 1H NMR characterization of the monoalkenyl diepoxy complex flexible compound is as follows: 1 H NMR (CDCl3, 400MHz) 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).

[0022] Example 2: The preparation steps for alkenyl-functionalized processable polyimides are as follows: Step 1, Preparation of polyamic acid (polyimide precursor): Using pyromellitic dianhydride and 4,4-diaminodiphenyl ether as monomers, polyamic acid is obtained through polycondensation reaction in N,N-dimethylacetamide solvent. The preparation steps are as follows: Under nitrogen protection, 4.0 g of 4,4-diaminodiphenyl ether and 40 mL of N,N-dimethylacetamide are added to a three-necked flask and stirred at room temperature until completely dissolved. The flask is then placed in an ice bath, and 40 mL of N,N-dimethylacetamide solution containing 4.4 g of pyromellitic dianhydride is slowly added dropwise three times at 5 °C, with each addition occurring 10 min apart. After the addition is complete, the mixture is stirred at 5 °C for 16 h to obtain polyamic acid. Step 2, Preparation of alkenyl-functionalized processable polyimide: First, the epoxy functional group in the monoalkenyl diepoxy composite flexible compound undergoes a ring-opening reaction with the carboxyl functional group in the polyamic acid. Then, a high-temperature thermal imidization process is carried out through programmed temperature rise to obtain the alkenyl-functionalized processable polyimide. The preparation steps are as follows: 0.5g of the monoalkenyl diepoxy composite flexible compound is added to the polyamic acid prepared in Step 1, the temperature is raised to 80℃ and stirred for 30min, after cooling to room temperature, vacuum degassing is performed, and the mixture is poured onto a polytetrafluoroethylene mold and allowed to level naturally. The excess was scraped off with a scraper, and the mixture was placed in an intelligent high-temperature test chamber to desolvent at 100℃ for 12 hours and hold at 120℃ for 1 hour. After cooling to room temperature, the mixture was subjected to programmed temperature increases at 60℃ / 1 hour, 80℃ / 1 hour, 120℃ / 1 hour, 150℃ / 1 hour, 200℃ / 1 hour, and 201℃ / 1 hour (the 1 hour of the programmed temperature increase refers to the time required to slowly rise from the previous temperature to the current temperature, not the time spent at that temperature, and the temperature increase from 200℃ to 201℃ is for holding at 200℃) to obtain alkenyl functionalized processable polyimide.

[0023] Example 3: Preparation of thiol-functionalized nylon: The modification of nylon 6 resin by 3-mercaptopropionic acid is achieved by the amidation condensation reaction between the carboxyl functional group of 3-mercaptopropionic acid and the terminal amino functional group on the molecular backbone of nylon 6 resin, thus obtaining thiol-functionalized nylon. The specific experimental steps for preparing mercapto-functionalized nylon are as follows: 9g of nylon 6 resin (model F136, amino content 150meq / kg) and 100mL of N,N-dimethylformamide are added to a three-necked flask equipped with a water separator. The mixture is heated to 80℃ and stirred until completely dissolved. After cooling to room temperature, under nitrogen protection, 10mL of N,N-dimethylformamide solution containing 1g of 3-mercaptopropionic acid is added to the three-necked flask. The mixture is heated to 90℃ and stirred for 6h. The solvent is removed by rotary evaporation under reduced pressure. After drying, mercapto-functionalized nylon is obtained.

[0024] Example 4: PA-PI alloy masterbatch I was prepared with the following formulation: 25 wt% alkenyl-functionalized processable polyimide and 75 wt% thiol-functionalized nylon. The preparation method was as follows: under hot melting conditions, a free radical initiator was used to induce a click reaction between the alkenyl functional groups in the alkenyl-functionalized processable polyimide and the thiol functional groups in the thiol-functionalized nylon, thereby achieving effective composite of polyimide and nylon and obtaining PA-PI alloy masterbatch I. The free radical initiator can be selected from one of dicumyl peroxide, tert-butyl hydroperoxide, benzoyl peroxide, and tert-butyl peroxide; in this experimental example, dicumyl peroxide was selected. The specific experimental steps for preparing PA-PI alloy masterbatch I are as follows: 2.5g of alkenyl functionalized processable polyimide, 7.5g of mercapto-functionalized nylon and 0.1g of dicumyl peroxide initiator are added to a high-speed mixer and mixed evenly, and then added to a twin-screw extruder for extrusion granulation to obtain PA-PI alloy masterbatch I. The process parameters of the twin-screw extruder are set as follows: preheating temperature 250℃, temperatures of zones 1-6 are 250℃, 270℃, 280℃, 290℃, 295℃, and 290℃ respectively, and rotation speed is 400r / min.

[0025] Example 5: PA-PI alloy masterbatch II was prepared with the following formula: 20 wt% alkenyl functionalized processable polyimide and 80 wt% mercapto-functionalized nylon. The preparation method was the same as that for PA-PI alloy masterbatch I in Example 4.

[0026] Example 6: PA-PI alloy masterbatch III was prepared with the following formula: 30 wt% alkenyl functionalized processable polyimide and 70 wt% mercapto-functionalized nylon. The preparation method was the same as that for PA-PI alloy masterbatch I in Example 4.

[0027] Example 7: An eleven-layer co-extruded membrane for aviation is shown in Table 1, with its membrane structure and the raw material formulation and dosage of each membrane layer. Table 1 Experimental formulation of eleven-layer co-extruded film for aerospace applications ; Among them, the model of the copolyamide 6 / 66 resin is C40LN 09; PA-PI alloy masterbatch is one of PA-PI alloy masterbatch I, PA-PI alloy masterbatch II, and PA-PI alloy masterbatch III.

[0028] Example 8: A process for preparing an eleven-layer co-extruded film for aviation is as follows: the raw materials are prepared according to the formula of the eleven-layer co-extruded film for aviation, and the raw materials of each layer are respectively fed into the hoppers of eleven screw extruders of the eleven-layer co-extruded film blow molding unit. The molten resin is combined at the die head through the distributor, and then extruded and blown through the die head (the blow-up ratio is controlled at 3.1). After cooling and winding, the eleven-layer co-extruded film for aviation is prepared. The process parameters for the screw extruders corresponding to the first to eleventh layers are set as follows: the temperatures of zones 1-3 are 250℃, 280℃, and 295℃, respectively; the runner temperature is 290℃; and the rotation speed is 80r / min. Among them, when the PA-PI alloy masterbatch is PA-PI alloy masterbatch I, the prepared membrane product is denoted as eleven-layer co-extruded membrane I for aviation. When the PA-PI alloy masterbatch is PA-PI alloy masterbatch II, the prepared membrane product is denoted as eleven-layer co-extruded membrane II for aviation. When the PA-PI alloy masterbatch is PA-PI alloy masterbatch III, the resulting membrane product is designated as eleven-layer co-extruded membrane III for aerospace applications.

[0029] Comparative example: The conventional eleven-layer co-extruded film is prepared, and its only difference from the eleven-layer co-extruded film I used in aviation is that the raw material formulation of the first to eleventh layers is 100wt% copolyamide 6 / 66 resin (i.e., PA-PI alloy masterbatch I is not used).

[0030] Performance testing: I. Thickness Test: The thickness of the film sample was tested using a thickness gauge in accordance with GB / T 6672-2001 "Mechanical Measurement Method for Determination of Thickness of Plastic Films and Sheets". II. Appearance Test: The appearance of the membrane sample is judged by visual inspection; III. Mechanical property testing: (1) Mechanical property test at room temperature of 25℃: According to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", a 150mm×20mm sample (length×width, with the length direction being the blown film direction (longitudinal)) was subjected to tensile test at a stretching rate of 50mm / min under the condition of 25℃ (tensile test along the blown film direction), and the longitudinal tensile strength of the sample was recorded. (2) 210℃ high temperature mechanical property test: According to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", a 150mm×20mm sample (length×width, with the length direction being the blown film direction (longitudinal)) was treated in a 210℃ oven for 12h and then subjected to a tensile test at a tensile rate of 50mm / min (the tensile test was carried out along the blown film direction). The longitudinal tensile strength of the sample was recorded. IV. Moisture Absorption Rate Test: Following the GB / T 1034-2008 standard "Determination of Water Absorption of Plastics", a 60mm × 60mm (length × width) sample was dried in an oven at 50℃ for 24 hours. After cooling to room temperature, the sample was weighed and recorded as the initial weight. The dried sample was then completely immersed in distilled water (water temperature controlled at 25℃) for 24 hours. It was then removed with tweezers, and the surface moisture was absorbed using absorbent filter paper. The sample was weighed and recorded as the weight after moisture absorption. The moisture absorption rate of the sample was calculated. The specific method is as follows: Moisture absorption rate (%) = (weight of sample after moisture absorption - initial weight of sample) / initial weight of sample × 100%; The test results are shown in Table 2 below. Figure 5 .

[0031] Table 2 Performance test results of eleven-layer co-extruded film for aviation applications ; The following conclusions can be drawn from a comprehensive analysis of the performance test results: Conclusion 1: The hygroscopic expansion characteristics of the eleven-layer co-extruded film product prepared from PA-PI alloy masterbatch are significantly improved; Conclusion 2: The eleven-layer co-extruded film product made from PA-PI alloy masterbatch still has a longitudinal tensile strength of >60MPa after 12 hours at 210℃, showing excellent high-temperature resistance.

Claims

1. A process for the preparation of an eleven-layer co-extruded film for aeronautics, characterized in that, The method comprises the following steps: Step 1: synthesis of a single-olefin double epoxy compound with a chemical structure as follows: ； Based on the carboxyl-epoxy ring-opening reaction mechanism, the single-olefin double epoxy compound is used for grafting modification treatment of polyamide acid to prepare olefin functionalized processable polyimide; Step 2: 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; Step 3: 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 a free radical initiator, so that the reactivity of the polyimide and the nylon is compounded, and PA-PI alloy master batch is prepared; Step 4: the PA-PI alloy master batch is used as a functional modification component of copolymerized polyamide 6 / 66 resin, and an eleven-layer co-extrusion film for aviation is prepared through an eleven-layer co-extrusion blowing process.

2. A process for the preparation of an eleven layer co-extruded film for aerospace applications as claimed in claim 1, wherein, The preparation method of the single-olefin double epoxy compound is as follows: In the presence of a photoinitiator, the click reaction of the olefin functional group of 1 mole equivalent of N-methyl diallylamine and the mercapto functional group of 2.01-2.09 mole equivalents of 2-mercaptoethoxy ethanol occurs under the action of ultraviolet light to generate intermediate a; The nucleophilic substitution reaction of 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 occurs to generate intermediate b; Under the oxidation of an organic peroxy acid, the epoxidation reaction of the olefin functional group of intermediate b occurs to generate intermediate c; Based on the nucleophilic substitution reaction mechanism, the quaternary ammonium reaction of 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 occurs to generate the single-olefin double epoxy compound.

3. A process for the preparation of an eleven layer co-extruded film for aerospace applications as claimed in claim 2, wherein, The photoinitiator is one of 2,2-dimethoxy-2-phenylphenylacetone, 2-hydroxy-2-methyl-1-phenylpropanone and 2,2-diethoxyphenylacetone.

4. A process for the preparation of eleven layer co-extruded film for aerospace application as claimed in claim 2 wherein, The organic peroxy acid is one of peroxoacetic acid, peroxobenzoic acid and m-chloroperbenzoic acid.

5. A process for the preparation of eleven layer co-extruded film for aerospace application as claimed in claim 1 wherein, The free radical initiator is one of dicumyl peroxide, tert-butyl hydroperoxide, dibenzoyl peroxide and tert-butyl peroxybenzoate.

6. A process for the preparation of eleven layer co-extruded film for aerospace applications as claimed in claim 1 wherein, The preparation method of the olefin functionalized processable polyimide is as follows: Polyamide acid is obtained by condensation reaction in N,N-dimethylacetamide solvent with pyromellitic dianhydride and 4,4-diaminodiphenyl ether as monomers; The ring-opening reaction of the epoxy functional group of the single-olefin double epoxy compound and the carboxyl functional group of the polyamide acid is carried out, and then the high-temperature thermal imidization process is carried out through programmed temperature rise to obtain the olefin functionalized processable polyimide.

7. A process for the preparation of eleven layer co-extruded film for aerospace applications as claimed in claim 1 wherein, The formula of the PA-PI alloy master batch is as follows: 20-30 wt% of the olefin functionalized processable polyimide and 70-80 wt% of the mercapto functionalized nylon.

8. A process for the preparation of an eleven layer co-extruded film for aerospace applications as claimed in claim 7, wherein, The formula of the alkenyl functionalized 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 part by weight of mono-alkenyl bis-epoxy complex flexible compound; The formula of the thiol 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 according to the process of any one of claims 1-8, characterized by, The thickness of the eleven-layer co-extruded film is 40-60 μm.

10. The eleven layer co-extruded film for aerospace applications according to claim 9, wherein, The product structure of the eleven-layer co-extruded film for aviation is: The formula of the first layer, the sixth layer and the eleventh layer is 60-80 wt% of copolymerized polyamide 6 / 66 resin and 20-40 wt% of PA-PI alloy master batch, and the amount is 5-25 parts by weight; The formula of the second layer and the tenth layer is 70-90 wt% of copolymerized polyamide 6 / 66 resin and 10-30 wt% of PA-PI alloy master batch, and the amount is 5-10 parts by weight; The formula of the third layer, the fourth layer, the fifth layer, the seventh layer, the eighth layer and the ninth layer is 85-95 wt% of copolymerized polyamide 6 / 66 resin and 5-15 wt% of PA-PI alloy master batch, and the amount is 5-10 parts by weight.

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