A toughened interlayer for laminated composites and method of making same

Abstract

The present application is suitable for the technical field of composite materials, and provides a laminated composite material toughened intermediate layer and a preparation method thereof.The preparation method comprises the following steps: using a wet non-woven material processing method to obtain an aramid short fiber wet-laid non-woven felt; then activating the surface of the aramid fiber by hydrofluoric acid etching; grafting soluble polyether ether ketone resin with active end groups on the surface of the aramid fiber, while realizing the impregnation of the aramid fiber; and making the polyether ether ketone resin grafted on the surface of the aramid fiber crystallize again through an acidification reduction reaction.The present application regulates the interface bonding performance of the aramid toughened intermediate layer in the laminated composite material, while keeping the original crystallinity of the polyether ether ketone resin, can effectively improve the interlaminar toughness of the carbon fiber reinforced polyether ether ketone composite laminated plate, can significantly reduce the possibility of interlaminar cracking, provides a new scheme for the interlaminar toughening of this kind of material, and has potential application prospects in the field of special materials for aerospace, etc.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of composite materials, and particularly relates to a laminated composite material toughened intermediate layer and a preparation method thereof. BACKGROUND

[0002] High-performance fiber-reinforced polyether ether ketone-based composite materials have broad application prospects in the fields of aerospace, medical treatment, automobiles, unmanned aerial vehicles and industrial products, among which continuous carbon fiber-reinforced polyether ether ketone (CF / PEEK) composite materials are the composite materials with the highest strength and the most extensive application. The excellent mechanical properties of carbon fibers endow the laminated composite materials with excellent in-plane mechanical properties, however, the load and energy are only transmitted between the carbon fiber layers by polyether ether ketone (PEEK) resin, resulting in relatively weak mechanical properties of the material in the thickness direction. In the actual application process, when the laminated plate is subjected to external load, damage will first occur in the relatively weak resin area inside the laminated plate, and delamination damage is prone to occur. Delamination damage is one of the main failure modes of composite materials, and once it occurs, the mechanical properties of the fibers cannot be fully utilized, which will affect the overall mechanical properties and service life of the composite materials and limit the application of the composite materials. Therefore, improving the interlaminar properties and delamination resistance of the composite materials is of great significance for the application and development of CF / PEEK composite materials.

[0003] At present, the methods for improving the interlaminar fracture toughness of composite materials mainly include resin toughening, Z-direction toughening and interlaminar toughening. Among them, interlaminar toughening is to add toughening materials (such as films, particles and fibers, etc.) in the middle of the composite material layers to achieve the purpose of toughening. This interlaminar toughening technology does not change the original molding process of the composite material, and the implementation process is relatively easy, and the strengthening effect is relatively obvious. The toughening layer can bridge the micro-cracks in the resin-rich area and deflect the cracks, which can absorb a large amount of energy, thereby increasing the interlaminar fracture toughness of the composite material. The thickness of the interlaminar film will affect the overall thickness of the part, and thus affect the mechanical properties of the composite material; the uniform distribution of the interlaminar particles is difficult to control; and the interlaminar fibers have the advantages of high uniformity, large specific surface area and little influence on the thickness of the composite material, etc., and have become a research hotspot for interlaminar toughening. At the same time, chopped fibers are easy to obtain, have low processing cost, and can solve the problem of resource waste in the production process of long fibers and composite materials, and are an ideal interlaminar toughening material. Therefore, it is of great value to use chopped fibers to carry out research on the interlaminar toughening of composite materials.

[0004] The toughening form of the short aramid fiber not only has the debonding, pulling out and transverse fracture of the fiber, but also has the unique longitudinal tear toughening. It has been found that the toughening effect of the short aramid fiber is obviously better than that of carbon fiber, glass fiber and basalt fiber. However, most of the current researches are focused on the interlaminar toughening of carbon fiber reinforced epoxy resin composite (CF / EP) by the short aramid fiber. As to how to apply this technology to the interlaminar toughening of CF / PEEK composite, there is no relevant report in China at present. Therefore, the present application provides a laminated composite toughening intermediate layer and a preparation method thereof. SUMMARY

[0005] The present application aims to provide a laminated composite toughening intermediate layer and a preparation method thereof, and aims to solve the problems in the background art.

[0006] The object of the present application is achieved by the following technical solutions:

[0007] A preparation method of a laminated composite toughening intermediate layer, comprising the following steps:

[0008] Step 1: cut the aramid fiber to 5-6 mm, put it into deionized water, add a compounded dispersant, control the dispersant ratio, beating speed (500 r / min) and pulp content (representing "put 0.5-2.3 g of short aramid fiber cut to 5-6 mm into a beaker containing 5 L of deionized water") and other parameters to ensure that the aramid fiber is fully dispersed in the dispersant solution; then perform sedimentation and solid-liquid separation by vacuum suction technology (use a 18 mm diameter large sand core funnel to filter) to obtain an aramid short fiber wet-laid nonwoven felt;

[0009] Step 2: etch the aramid short fiber wet-laid nonwoven felt by hydrofluoric acid to bring a large number of -F groups on the surface of the aramid fiber as subsequent reaction grafting sites; and the etched aramid fiber surface produces obvious etching and peeling traces, so that it changes from a smooth surface to a relatively rough surface, increasing the physical anchoring effect of the resin and the aramid fiber;

[0010] Step 3: synthesize a high-toughness ketone imine biphenyl polyether ether ketone (PEEK) resin soluble in organic solvents as an interface modification macromolecule and impregnating liquid of the aramid short fiber wet-laid nonwoven felt, which specifically includes: first, synthesize a polyether ether ketone polymer monomer containing a ketone imine structure by Schiff base reaction, then prepare an end-capped monomer with an amino group by Friedel-crafts acylation reaction and reduction reaction; then, polymerize the polymer monomer with biphenol, and add the end-capped monomer with an amino group in the late stage of polymerization to cap the polymer, so as to ensure the successful performance of the subsequent grafting reaction, and obtain a soluble polyether ether ketone resin;

[0011] Step 4: One-step interfacial modification of aramid short fiber wet-laid nonwoven felt to obtain aramid short fiber toughened interlayer after surface modification;

[0012] Step 5: The polyether ether ketone resin in the aramid short fiber felt is reduced to crystalline polyether ether ketone by acidification and reduction, and the target crystalline polyether ether ketone grafted and impregnated aramid short fiber toughened interlayer is obtained, which provides an interlayer toughening effect for the subsequent high-temperature hot-pressed carbon fiber reinforced polyether ether ketone composite material.

[0013] Further, it specifically includes the following steps:

[0014] Step 1: Put 0.5-2.3 g of aramid fiber cut to 5-6 mm into a beaker containing 5 L of deionized water, add a compounded dispersant: 0.03% (wt%) sodium dodecyl benzene sulfonate (SDS), 0.01% (wt%) anionic polyacrylamide (APAM), and 0.06% (wt%) polyethylene oxide (PEO), use a mechanical stirrer to stir at a speed of 500 r / min for 120 min, use a large sand core funnel with a diameter of 18 mm for suction filtration, and obtain a uniformly dispersed aramid short fiber wet-laid nonwoven felt with a surface density of 25-100 g / m 2 , 100°C drying for 12h;

[0015] Step 2: Use a 10% (wt%) hydrofluoric acid solution to treat the aramid short fiber wet-laid nonwoven felt after drying, continuously soak for 30 min, then wash with deionized water for 3 times, each time for 1 h, to ensure that the residual hydrofluoric acid is removed, and then vacuum dry at 100°C for 12h, to obtain a fluorinated aramid short fiber wet-laid nonwoven felt;

[0016] Step 3: The 1,1-bis(4-fluorophenyl)-N-phenylmethanimine with ketimine structure generated by the reaction of aniline and 4,4'-difluorobenzophenone is used as a polymer monomer to prevent the formation of a crystalline structure and make the polymer have good solubility. Through step-by-step polymerization reaction and amino end-capping in the later stage of the reaction, a soluble polyether ether ketone resin is prepared;

[0017] Step 4: Weigh 0.5-2.3 g of soluble polyether ether ketone resin, dissolve it in 50 ml of tetrahydrofuran solution, and use it all to impregnate and graft the fluorinated aramid short fiber wet-laid nonwoven felt. Seal the system for 12h and shake appropriately. After grafting is complete, open the system and wait for the solvent to completely evaporate at room temperature. Then, high-temperature hot-pressing is performed at 140°C and 10MPa for 20min to obtain an aramid short fiber toughened interlayer after surface modification (i.e., a smooth aramid short fiber toughened interlayer grafted and impregnated with amorphous polyether ether ketone), with a surface density of 50-200 g / m 2 ;

[0018] Step 5: Using a 1L capacity hydrothermal synthesis reactor liner, load 500mL of 1M hydrochloric acid solution for acidification of the reduction reaction, trim the surface modified aramid short fiber toughened intermediate layer prepared in step 4 to the appropriate size so that it can be completely immersed in the hydrochloric acid solution in the reactor, place the liner in the hydrothermal synthesis reactor, tighten the lid, heat at 150°C for 12h, remove the reduced aramid short fiber toughened intermediate layer, wash thoroughly with water, and vacuum dry to obtain the target crystalline polyether ether ketone grafted and impregnated aramid short fiber toughened intermediate layer.

[0019] Further, the synthesis process of the soluble polyether ether ketone resin in step 3 includes the following steps:

[0020] Step 31: Synthesis of polymeric monomer 1,1-bis(4-fluorophenyl)-N-phenylmethanimine containing ketimine structure by Schiff base reaction; the specific operation is as follows: put toluene (80mL), aniline (14mL, 150mmol), 4,4'-difluorobenzophenone (22.0g, 100mmol), molecular sieve (4Å, 50g, activated for 4h at 400℃) into a 250mL three-necked flask, heat the reaction system to reflux under nitrogen environment and react for 24h, then filter out the molecular sieve, evaporate the toluene in the filtrate to obtain a red-brown crude product; since the polymeric monomer has a higher purity requirement, the crude product is recrystallized in methanol for three times to obtain light yellow block-shaped crystals, and the yield is 62%;

[0021] Step 32: Synthesis of 4-fluoro-4'-nitrobenzophenone by Friedel-crafts acylation reaction of fluorobenzene and 4-nitrobenzoyl chloride; the specific operation is as follows: first, add fluorobenzene (80mL) to a 250mL three-necked flask, then add 4-nitrobenzoyl chloride (18.5g, 100mmol) to the flask and stir until completely dissolved; then place the three-necked flask in an ice bath at 0°C, slowly add the pre-ground anhydrous AlCl3 (17g, 128mmol) (pay attention to keep the temperature low during the addition), after stirring at 0°C for 2h, heat the mixture to reflux temperature and maintain for 6h, after the reaction is completed, cool to room temperature; then slowly add 100mL of deionized water to the three-necked flask, then heat to reflux temperature, and remove the excess fluorobenzene through a Dean-Stark water trap; after the fluorobenzene is completely removed, cool the reaction system to room temperature, pour the product into cold water, and the blocky beige crude product precipitates at the bottom, filter the blocky beige crude product and wash it with sodium hydroxide solution (0.5M) and deionized water three times; recrystallize the crude product in ethanol twice to obtain light yellow crystals of 4-fluoro-4'-nitrobenzophenone, with a yield of about 85%;

[0022] 4-fluoro-4'-nitrobenzophenone was reduced to 4-fluoro-4'-aminobenzophenone using tin(II) chloride dihydrate; the procedure was as follows: methanol (150 mL), 4-fluoro-4'-nitrobenzophenone (0.012 mol, 2.94 g) were first added to a 250 mL three-necked flask, then tin(II) chloride dihydrate (0.06 mol, 13.48 g) was added to the flask; after 6 h of reaction at reflux temperature, the insoluble material was filtered off; the pH of the filtrate was adjusted to 9 with a saturated aqueous solution of Na2CO3 to remove the excess tin salt; after filtration, the mixture was extracted twice with ethyl acetate, the organic phases were combined and dried over anhydrous sodium sulfate, then the sodium sulfate was filtered off, the solvent was removed from the organic phase by rotary evaporation, and the orange product was dried in vacuo, with a yield of about 68%;

[0023] Step 33: polymerization was performed using 1,1-bis(4-fluorophenyl)-N- phenylmethanimine and biphenol in a 1:1.03 ketone:phenol ratio; the procedure was as follows: 1,1-bis(4-fluorophenyl)-N-phenylmethanimine (5.866 g, 20 mmol), biphenol (4.008 g, 22 mmol), sulfolane (23.51 mL), anhydrous potassium carbonate (3.648 g, 26.4 mmol) and toluene (11.755 mL) were sequentially added to a 250 mL three-necked flask; the system was first heated to 120°C for 3 h, and toluene was used to remove the water produced during the reaction, and turbidity was observed in the water trap; then the temperature was increased to 190°C to start the polymerization reaction, and the viscosity of the polymer increased continuously as the reaction proceeded, and a viscous dark yellow polymer solution was formed after 12 h; after the polymerization was complete, the heating power was reduced, and the system was cooled to 130°C, and 4-fluoro-4'-aminobenzophenone end-capping agent (0.901 g, 3 mmol) was added, and the reaction was continued at 120°C for 4 h; the product was discharged into methanol to obtain an amino-terminated strip-shaped polymer, which was crushed and washed with ethanol, water and ethanol three times at reflux temperature; finally, the product was dried in a vacuum oven for 12 h to obtain an orange-yellow powder of soluble polyether ether ketone resin.

[0024] A laminated composite material toughened interlayer prepared according to the preparation method described above.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] 1. The application creatively proposes to introduce a wet-laid nonwoven felt of aramid short fibers modified by "homologous" resin interface as a toughening interlayer in the CF / PEEK composite material layer. This design first combines the toughness advantage of aramid fibers with the high toughness and good compatibility of polyether ether ketone resin from the molecular and material structure level, creatively solves the interface bonding problem between aramid interlayer and CF / PEEK resin matrix, and further realizes the synergistic and efficient toughening of the composite material interlayer.

[0027] 2. The key innovation of the toughening intermediate layer of the application lies in that the aramid fiber surface grafted resin and the whole layer impregnated resin used are polyether ether ketone which is completely homologous to the pre-impregnated tape matrix resin of the CF / PEEK composite material. This "homologous" resin design fundamentally realizes the grafting and impregnation of soluble polyether ether ketone on aramid fibers, and after subsequent reduction treatment, the crystallinity of polyether ether ketone can be restored, which is convenient for hot pressing. This design can ensure that the toughening layer and the main composite material resin matrix have excellent compatibility, and avoid the generation of heterogeneous interface or phase separation, which is the basis for realizing high-strength interface.

[0028] 3. In view of the challenge that the inert surface of aramid fibers is difficult to combine well with the resin, the application creatively adopts hydrofluoric acid treatment to fluorinate the surface of aramid fibers. This treatment not only significantly changes the physical appearance of the fiber surface, but more importantly, it can generate active groups in situ on the surface, providing necessary reaction sites for subsequent precise interface chemical regulation, which is a key step to realize strong interface bonding.

[0029] 4. The application successfully restores the inherent crystallization characteristics of soluble polyether ether ketone by implementing a specific reduction reaction treatment on the soluble polyether ether ketone resin layer grafted on the surface of aramid fibers, and converts the amorphous structure introduced due to the pursuit of solubility into high-crystallinity PEEK. This "interface crystallization" technology maximizes the elimination of weak interface bonding risks caused by differences in resin state, thereby realizing high-strength interface fusion with the matrix resin. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The figure is a schematic diagram of the preparation method of the application.

[0031] Figure 2 The figure is a scanning electron microscope photo of the fluorinated aramid short fiber wet-laid nonwoven felt in Example 1.

[0032] Figure 3 The figure is a physical photo of the aramid short fiber toughening intermediate layer grafted and impregnated with crystalline polyether ether ketone in Example 1.

[0033] Figure 4A scanning electron microscope photograph of the crystalline polyether ether ketone grafted and impregnated aramid short fiber toughened interlayer surface in Example 1.

[0034] Figure 5 A tensile stress-strain curve of the crystalline polyether ether ketone grafted and impregnated aramid short fiber toughened interlayer in Example 1.

[0035] Figure 6 A differential scanning calorimeter (DSC) curve of the crystalline polyether ether ketone grafted and impregnated aramid short fiber toughened interlayer in Example 1. DETAILED DESCRIPTION

[0036] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present application, the technical solutions of the present application are described in detail below, but cannot be understood as limiting the scope of implementation of the present application.

[0037] The specific implementation of the present application is described in detail below in combination with specific examples. EXAMPLE

[0038] This example provides a preparation method of an aramid short fiber interlayer with interlaminar toughening effect of laminated composite material, and the specific steps are as follows:

[0039] (1) Put 1.13 g of aramid fiber cut to 6 mm into a beaker containing 5 L of deionized water, add a compound dispersant: 0.03% (wt%) sodium dodecyl benzene sulfonate (SDS), 0.01% (wt%) anionic polyacrylamide (APAM) and 0.06% (wt%) polyethylene oxide (PEO), use a mechanical stirrer (Jianbo Technology, JB80-SH) to stir at a speed of 500 r / min for 120 min, use a large sand core funnel with a diameter of 18 mm for suction filtration, and obtain a uniformly dispersed aramid short fiber wet-laid nonwoven felt with a surface density of 50 g / m 2 , 100°C drying for 12 h.

[0040] (2) Use a 10% (wt%) hydrofluoric acid solution to treat the aramid short fiber wet-laid nonwoven felt after drying, continuously soak for 30 min, then wash with deionized water for 3 times, 1 h each time, to ensure that the residual hydrofluoric acid is removed, and vacuum dry at 100°C for 12 h to obtain a fluorinated aramid short fiber wet-laid nonwoven felt. Figure 2 A scanning electron microscope of the fluorinated aramid short fiber wet-laid nonwoven felt, and it can be seen from the figure that there are obvious etching and peeling marks on the surface of the aramid fiber, proving that the active -F group has been successfully carried on the surface of the aramid fiber.

[0041] (3) Synthesis of polyether ether ketone monomer 1,1-bis(4-fluorophenyl)-N- phenylmethanimine with ketimine structure through Schiff base reaction. Toluene (80 mL), aniline (14 mL, 150 mmol), 4,4'-difluorobenzophenone (22.0 g, 100 mmol), and molecular sieves (4 A, 50 g, activated for 4 h at 400 °C) were added to a 250 mL three-necked flask. The reaction system was heated to reflux under nitrogen and reacted for 24 h, and then the molecular sieves were removed by filtration. The toluene in the filtrate was evaporated to dryness to obtain a red-brown crude product. Since the polymer monomer has a high requirement for purity, the crude product was recrystallized three times in methanol to obtain light yellow block crystals with a yield of 62%.

[0042] (4) Synthesis of 4-fluoro-4'-nitrobenzophenone through Friedel-crafts acylation reaction of fluorobenzene and 4-nitrobenzoyl chloride. First, fluorobenzene (80 mL) was added to a 250 mL three-necked flask, and then 4-nitrobenzoyl chloride (18.5 g, 100 mmol) was added and stirred until completely dissolved. Then the three-necked flask was placed in an ice bath at 0 °C, and anhydrous AlCl3 (17 g, 128 mmol) that was previously ground was slowly added (the temperature was kept low during the addition). After stirring at 0 °C for 2 h, the mixture was heated to reflux temperature and maintained for 6 h. After the reaction was completed, the reaction system was cooled to room temperature. Then 100 mL of deionized water was slowly added to the three-necked flask. Subsequently, the temperature was raised to reflux temperature, and excess fluorobenzene was removed by a Dean-Stark water trap. After the fluorobenzene was completely removed, the reaction system was cooled to room temperature, and the product was poured into cold water. The blocky beige crude product precipitated at the bottom. The blocky beige crude product was filtered and washed three times with sodium hydroxide solution (0.5 M) and deionized water, respectively. The crude product was dissolved in ethanol and recrystallized twice to obtain light yellow crystals of 4-fluoro-4'-nitrobenzophenone with a yield of about 85%.

[0043] 4-Fluoro-4'-nitrobenzophenone was reduced to 4-fluoro-4'-aminobenzophenone using tin(II) chloride dihydrate. First, methanol (150 mL) and 4-fluoro-4'-nitrobenzophenone (0.012 mol, 2.94 g) were added to a 250 mL three-necked flask, and then tin(II) chloride dihydrate (0.06 mol, 13.48 g) was added to the flask. After reacting at reflux temperature for 6 h, the insoluble material was filtered off. The filtrate was evaporated and concentrated, and then the pH of the filtrate was adjusted to 9 with a saturated aqueous Na2CO3 solution to remove excess tin salt. After filtration, the mixture was extracted twice with ethyl acetate, and the combined organic phase was dried with anhydrous sodium sulfate. After filtering off the sodium sulfate, the organic phase was subjected to solvent removal by a rotary evaporator to obtain an orange product, which was dried in vacuum with a yield of about 68%.

[0044] (5) Polymerization was carried out using 1,1-bis(4-fluorophenyl)-N- phenylmethanimine and diphenylolpropane in a ratio of ketone: phenol = 1: 1.03. In a 250 mL three-necked flask, 1,1-bis(4-fluorophenyl)-N- phenylmethanimine (5.866 g, 20 mmol), diphenylolpropane (4.008 g, 22 mmol), sulfolane (23.51 mL), anhydrous potassium carbonate (3.648 g, 26.4 mmol), and toluene (11.755 mL) were sequentially added. The system was first heated to 120 °C for 3 h, and toluene was used to carry out the water generated in the reaction. A turbidity was observed in the Dean-Stark trap. Then the system was heated to 190 °C to start the polymerization reaction. The viscosity of the polymer increased continuously, and a viscous dark yellow polymer solution was formed after 12 h. After the polymerization was completed, the heating power was reduced, and the system was cooled to 130 °C. 4-fluoro-4'-aminobenzophenone end-capping agent (0.901 g, 3 mmol) was added, and the reaction was continued at 120 °C for 4 h. The product was discharged in methanol to obtain an amino-terminated strip-shaped polymer, which was crushed and washed with ethanol, water, and ethanol three times at reflux temperature. Finally, the product was dried in a vacuum oven for 12 h to obtain an orange-yellow powder of soluble polyether ether ketone resin.

[0045] (6) 1.13 g of soluble polyether ether ketone resin was weighed and dissolved in 50 mL of tetrahydrofuran solution, which was used to impregnate and graft fluorinated aramid short fiber wet-laid nonwoven felt. The system was sealed for 12 h and shaken appropriately. After the grafting was completed, the system was opened, and the solvent was allowed to evaporate at room temperature. Then, high-temperature hot pressing was performed at 140 °C and 10 MPa for 20 min to obtain an aramid short fiber toughened intermediate layer after surface modification.

[0046] (7) A 1 L capacity hydrothermal synthesis reactor liner was used to load 500 mL of 1 M hydrochloric acid solution for acidification and reduction reaction. The aramid short fiber toughened intermediate layer after surface modification prepared above was trimmed to an appropriate size so that it could be completely immersed in the hydrochloric acid solution in the reactor. The liner was placed in the hydrothermal synthesis reactor, the lid was tightly screwed, and heating was performed at 150 °C for 12 h. The reduction completed composite material toughened intermediate layer was taken out, washed with water thoroughly, and vacuum dried to obtain the target crystalline polyether ether ketone grafted and impregnated aramid short fiber toughened intermediate layer (i.e., interface modified aramid short fiber toughened intermediate layer), with a final areal density of about 100 g / m 2 . Figure 3 It is a real photo of the surface, which is uniform and consistent, and no obvious cloud spots and holes exist. Figure 4 It is a scanning electron microscope photo of the surface, which shows that the aramid fibers are randomly distributed, and the resin is uniformly coated. Figure 5The stress-strain curve read after the tensile property test of the same shows that the stress linearly increases at the initial stage of the tension, and the maximum breaking stress is close to 15 MPa, proving that the intermediate layer has good mechanical properties. Figure 6 The DSC test result of the same shows that in the heating process, the exothermic peak in the medium temperature zone (about 250-350℃) corresponds to the crystallization exothermic of the regular arrangement of the molecular chain of the polyether ether ketone, and the endothermic peak in the high temperature zone (about 350-450℃) represents the melting of the crystalline polyether ether ketone, which is opposite to the EXO (exothermic) direction. This shows that after acidification and reduction, the soluble polyether ether ketone on the surface of the aramid short fiber toughened intermediate layer is modified, the ketone imine structure is removed, the crystallization exothermic peak and the melting endothermic peak reappear, proving that the crystallization ability is restored, and the soluble polyether ether ketone on the surface of the aramid short fiber toughened intermediate layer can restore the crystallization characteristics. Example

[0047] This example provides a preparation method of an aramid short fiber intermediate layer with interlaminar toughening effect of laminated composites, which is different from example 1 in that the weight of aramid fiber in step (1) is changed to 0.56g, and the areal density of the uniformly dispersed aramid short cut fiber web is 25g / m 2 . The weight of polyether ether ketone resin in step (6) is also changed to 0.56g, and the aramid short fiber toughened intermediate layer of the target crystalline polyether ether ketone grafting and impregnation is obtained, and the final areal density is about 50g / m 2 . Example

[0048] This example provides a preparation method of an aramid short fiber intermediate layer with interlaminar toughening effect of laminated composites, which is different from example 1 in that the weight of aramid fiber in step (1) is changed to 2.26g, and the areal density of the uniformly dispersed aramid short cut fiber web is 100g / m 2 . The weight of polyether ether ketone resin in step (6) is also changed to 2.26g, and the aramid short fiber toughened intermediate layer of the target crystalline polyether ether ketone grafting and impregnation is obtained, and the final areal density is about 200g / m 2 . Example

[0049] The resin fiber ratio of the intermediate layer provided in examples 1-3 is 1:1. In order to prepare an intermediate layer with different resin fiber ratio, this example provides a preparation method of an aramid short fiber intermediate layer with interlaminar toughening effect of laminated composites, which is different from example 1 in that the weight of aramid fiber in step (1) is changed to 1.13g, and the areal density of the uniformly dispersed aramid short cut fiber web is 50g / m 2The weight of the polyether ether ketone resin in step (6) is changed to 2.26 g, and a target crystalline polyether ether ketone grafted and impregnated aramid short fiber toughened interlayer is obtained, and the final areal density is about 150 g / m 2 The soluble polyether ether ketone resin: aramid fiber (wt%) = 2:1. Embodiment

[0050] The embodiment provides a preparation method of an aramid short fiber interlayer with a laminated composite interlayer toughening effect, which is different from that of embodiment 1 in that the weight of the aramid fiber in step (1) is changed to 0.56 g, and the areal density of the uniformly dispersed aramid short fiber web is 25 g / m 2 The weight of the polyether ether ketone resin in step (6) is changed to 1.12 g, and a target crystalline polyether ether ketone grafted and impregnated aramid short fiber toughened interlayer is obtained, and the final areal density is about 75 g / m 2 The soluble polyether ether ketone resin: aramid fiber (wt%) = 2:1.

[0051] Embodiments 2-5 prepare crystalline polyether ether ketone grafted and impregnated aramid short fiber toughened interlayers with different areal densities by adjusting the ratio of aramid fiber to soluble polyether ether ketone resin. The obtained toughened interlayer has stable performance and uniform fiber dispersion. The results show that the toughened interlayer prepared by the application has good designability, and the areal density can be accurately controlled by adjusting the resin / fiber ratio. This provides a basis for studying the influence of different structural parameters on the interlayer toughening effect of laminated composites, and provides a basis for selecting the best ratio in practical applications.

[0052] The above is only a preferred embodiment of the application, and it should be noted that for those skilled in the art, without departing from the concept of the application, several modifications and improvements can be made, which should be considered as the protection scope of the application, and these will not affect the effect and practicality of the application.

Claims

1. A method for the production of a toughened interlayer for a laminated composite material, characterized in that, Comprising the following steps: Step 1: Cut aramid fibers to 5-6mm, put into deionized water, add compound dispersant, control dispersant ratio, beating speed and pulp solid content parameters to ensure that aramid fibers are fully dispersed in the dispersant solution; then collect and separate solid-liquid by vacuum suction technology to obtain aramid short fiber wet-laid nonwoven felt; Step 2: Etch the aramid short fiber wet-laid nonwoven felt with hydrofluoric acid to bring rich -F groups on the surface of aramid fibers as subsequent reaction grafting sites; and the etched aramid fiber surface produces obvious etching and peeling traces, making it change from smooth surface to relatively rough, increasing the physical anchoring effect of resin and aramid fiber; Step 3: Synthesize ketone imine biphenyl polyether ether ketone resin soluble in organic solvent as interface modification macromolecule and impregnating liquid of aramid short fiber wet-laid nonwoven felt, which specifically includes: first, synthesize polyether ether ketone polymer monomer containing ketone imine structure through Schiff base reaction; then, prepare end amino capped monomer through Friedel-crafts acylation reaction and reduction reaction; then, polymerize the polymer monomer with biphenyl diphenol, and add the end amino capped monomer to the polymer at the late stage of polymerization to cap the polymer, to obtain soluble polyether ether ketone resin; Step 4: One-step interface modification of aramid short fiber wet-laid nonwoven felt to obtain aramid short fiber toughening interlayer after surface modification; Step 5: Reduce the polyether ether ketone resin in the aramid short fiber felt to crystalline polyether ether ketone through acidification and reduction to obtain the target crystalline polyether ether ketone grafted and impregnated aramid short fiber toughening interlayer.

2. The production method according to claim 1, characterized by, Specifically comprising the following steps: Step 1: 0.5-2.3 g aramid fiber chopped to 5-6 mm was put into a beaker with 5 L deionized water, and a compound dispersant was added: 0.03 wt% sodium dodecyl benzene sulfonate, 0.01 wt% anionic polyacrylamide, and 0.06 wt% polyethylene oxide, and a mechanical stirrer was used to stir at a speed of 500 r / min for 120 min, and a large sand core funnel with a diameter of 18 mm was used for suction filtration, to obtain a uniformly dispersed aramid short fiber wet-laid nonwoven felt, with a surface density of 25-100 g / m 2 , 100°C drying for 12 h; Step 2: Use 10wt% hydrofluoric acid solution to treat the dried aramid short fiber wet-laid nonwoven felt, continuously soak for 30min, then wash with deionized water for 3 times, each for 1h, 100°C vacuum drying for 12h to obtain fluorinated aramid short fiber wet-laid nonwoven felt; Step 3: Use 1L capacity of water heat synthesis reaction kettle lining, load 1M hydrochloric acid solution 500mL for acidification and reduction reaction, trim the aramid short fiber toughening interlayer after surface modification so that it is completely immersed in the hydrochloric acid solution in the reaction kettle, put the lining into the water heat synthesis reaction kettle, tighten the lid, heat at 150°C for 12h, take out the reduced aramid short fiber toughening interlayer, wash with water and vacuum dry to obtain the target crystalline polyether ether ketone grafted and impregnated aramid short fiber toughening interlayer. Step 4: 0.5-2.3 g of soluble polyether ether ketone resin is weighed and dissolved in 50 ml of tetrahydrofuran solution, and the fluorinated aramid short fiber wet-laid nonwoven felt is immersed and grafted, the system is sealed for 12 h and shaken appropriately, after the grafting is completed, the system is opened, and after waiting for the solvent to completely volatilize at room temperature, high-temperature hot pressing at 140 °C and 10 MPa is carried out for 20 min, and the aramid short fiber toughened middle layer after surface modification is prepared, with a surface density of 50-200 g / m 2 ; The synthesis process of the soluble polyether ether ketone resin in step 3 includes the following steps:

3. The preparation method according to claim 2, characterized in that, ​ Step 31: Synthesis of polymeric monomer 1,1-bis(4-fluorophenyl)-N-phenylmethanimine with ketimine structure by Schiff base reaction; the specific operation is as follows: 80 mL of toluene, 14 mL of aniline, 22.0 g of 4,4'-difluorobenzophenone, and 50 g of 4A molecular sieve are placed in a 250 mL three-necked flask; the reaction system is heated to reflux under nitrogen atmosphere and reacted for 24 h, and then the molecular sieve is removed by filtration; the toluene in the filtrate is evaporated to obtain a red-brown crude product; the crude product is recrystallized in methanol for three times to obtain light yellow block-shaped crystals; Step 32: Synthesis of 4-fluoro-4'-nitrobenzophenone by Friedel-crafts acylation reaction of fluorobenzene and 4-nitrobenzoyl chloride; the specific operation is as follows: first, 80 mL of fluorobenzene is added to a 250 mL three-necked flask, and then 18.5 g of 4-nitrobenzoyl chloride is added and stirred until completely dissolved; the three-necked flask is placed in an ice bath at 0°C, and 17 g of anhydrous AlCl3 is slowly added; after stirring at 0°C for 2 h, the mixture is heated to reflux temperature and kept for 6 h; after the reaction is completed, the reaction system is cooled to room temperature; then 100 mL of deionized water is slowly added to the three-necked flask, and then heated to reflux temperature; the excess fluorobenzene is removed by a Dean-Stark water trap; after the fluorobenzene is completely removed, the reaction system is cooled to room temperature, and the product is poured into cold water to precipitate a blocky beige crude product; after filtration, the crude product is washed with 0.5 M sodium hydroxide solution and deionized water for three times; the crude product is dissolved in ethanol and recrystallized twice to obtain light yellow crystals of 4-fluoro-4'-nitrobenzophenone; 4-fluoro-4'-nitrobenzophenone is reduced to 4-fluoro-4'-aminobenzophenone using tin(II) chloride dihydrate; the specific operation is as follows: first, 150 mL of methanol and 2.94 g of 4-fluoro-4'-nitrobenzophenone are added to a 250 mL three-necked flask, and then 13.48 g of tin(II) chloride dihydrate is added to the three-necked flask; after reaction at reflux temperature for 6 h, the insoluble material is filtered off; the pH value of the filtrate is adjusted to 9 with a saturated aqueous Na2CO3 solution to remove excess tin salt; after filtration, the mixture is extracted twice with ethyl acetate, and the combined organic phase is dried with anhydrous sodium sulfate; after filtering off the sodium sulfate, the organic phase is subjected to solvent removal by a rotary evaporator to obtain an orange product, which is dried in vacuum; Step 33: polymerization was carried out using 1,1-bis(4-fluorophenyl)-N- phenylmethanimine and diphenylolpropane with a ratio of ketone: phenol = 1: 1.03; the specific operation was as follows: 5.866 g of 1,1-bis(4-fluorophenyl)-N- phenylmethanimine, 4.008 g of diphenylolpropane, 23.51 mL of sulfolane, 3.648 g of anhydrous potassium carbonate and 11.755 mL of toluene were sequentially added into a 250 mL three-necked flask; the system was first heated to 120°C and kept for 3 h, and toluene was used to carry out the water generated in the reaction, and turbidity was observed in the water trap; then the temperature was increased to 190°C to start the polymerization reaction, and the viscosity of the polymer continuously increased as the reaction proceeded, and a viscous dark yellow polymer solution was formed after 12 h; after the polymerization was completed, the heating power was reduced, and the system was cooled to 130°C, and 0.901 g of 4-fluoro-4'- aminobenzophenone end-capping agent was added, and the reaction was continued at 120°C for 4 h; the product was discharged into methanol to obtain an amino-terminated strip-shaped polymer, which was crushed and washed with ethanol, water and ethanol for three times at reflux temperature; finally, it was placed in a vacuum oven for drying for 12 h to obtain an orange-yellow powder of soluble poly (ether ether ketone) resin.

4. A toughened interlayer of a laminate composite material produced according to the production process of any one of claims 1-3.

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