Method for separating composite material, and recycling method

Abstract

The present invention addresses the problem of efficiently separating and recovering a polyamide resin from a composite material containing the polyamide resin. The present invention provides a method for separating a composite material, said method comprising: preparing the composite material, which contains a first material containing a polyamide resin and a second material and a first solvent containing formic acid and a halogenated hydrocarbon; bringing the composite material into contact with the first solvent to selectively dissolve the first material in the first solvent, whereby a first mixture containing the second material and a first solution in which the first material is dissolved in the first solvent is obtained; separating the first solution and the second material from the first mixture; precipitating the first material by adding to the separated first solution a second solvent that is a poor solvent of the first material, whereby a second mixture containing the precipitated first material and a mixed solvent of the first solvent and the second solvent is obtained; and separating the deprecipitated posited first material and the mixed solvent from the second mixture.

Description

Method for separating and recycling composite materials

[0001] The present invention relates to a method for separating and recovering a polyamide resin from a composite material containing the polyamide resin, and a recycling method including the separation method.

[0002] Polyamide resin, one of the major engineering plastics, is easily moldable and has excellent mechanical properties, electrical properties, heat resistance, and other physical and chemical properties. For this reason, it is widely used in vehicle parts, electrical and electronic equipment parts, and other precision instrument parts. Furthermore, when the resin alone is insufficient in terms of mechanical properties, sliding properties, thermal stability, dimensional stability, etc., it is combined with other materials and used as a composite material for a variety of applications. Examples of materials that can be combined with polyamide resin include various inorganic fillers such as clay minerals, mica, glass fiber, and carbon fiber; woven fabrics such as glass fiber and carbon fiber; and other resin materials such as polyolefins, acrylonitrile-butadiene-styrene copolymers (ABS), polyphenylene ether, and polyester.

[0003] On the other hand, it is said that almost half of greenhouse gas emissions from waste comes from waste plastics in general waste and industrial waste. ２ To reduce CO ２ Establishment of manufacturing technology for functional chemicals using this as a raw material and exhaust CO ２ While plastics are increasingly being used for other purposes, the establishment of plastic recycling technology is becoming increasingly important.

[0004] Under these circumstances, various recycling technologies for polyamide composite materials have been proposed. For example, Patent Documents 1 and 2 propose a chemical recycling method in which polyamide 6 or a polyamide 6 / polyester-based resin composition is depolymerized, and the resulting monomer and reaction mixture (filler such as glass fiber) are separated and recovered.

[0005] Furthermore, recycling methods that do not decompose polyamide resins down to monomers have also been proposed (Patent Documents 3 and 4, and Non-Patent Document 1). Patent Document 3 proposes a polyamide composition recycling method that includes a solution heating step in which a polyamide resin composition is heated together with ethylene glycol at a temperature of 180°C or higher to separate the polyamide resin dissolved in ethylene glycol from insoluble components, and a polyamide recovery step in which the resulting polyamide resin is recovered. Non-Patent Document 1 proposes a method in which polyamide 6 (PA6) is dissolved at room temperature in a mixed solvent of hydrochloric acid and benzyl alcohol, followed by removal of carbon fibers. Furthermore, formic acid has long been known to be a good solvent for polyamide resins, and Patent Document 4 proposes a method in which a polyamide resin is dissolved in formic acid, dimethyl ether is used as a poor solvent, and the dissolved polyamide resin is reprecipitated, separated, and recycled.

[0006] Japanese Patent Application Laid-Open No. 2000-034363 Japanese Patent Application Laid-Open No. 2022-529336 Japanese Patent Application Laid-Open No. 2018-172618 WO2010-101579

[0007] Sakamoto, Daisuke, Kumagai, Tomoya, Oguma, Hiroyuki, Harada, Masanori, Sekine, Masahiro, "Recycling of carbon fiber reinforced nylon composites using solvents," Research Report of Saitama Prefectural Industrial Technology Center, Vol. 16, 18-22 (2018).

[0008] However, the chemical recycling method (Patent Documents 1 and 2) requires a repolymerization step to obtain a polymer again from the monomer, which increases the environmental load and the recycling costs, and is an obstacle to practical use.

[0009] On the other hand, the techniques proposed in Patent Documents 3 and 4 and Non-Patent Document 1 do not decompose polyamide resins down to monomers, and therefore do not require a repolymerization step. However, the method of Patent Document 3 requires dissolving polyamide resins in a solvent at high temperatures (180°C or higher), which again increases recycling costs and environmental impact. Furthermore, while the methods proposed in Non-Patent Document 1 and Patent Document 4 enable decomposition treatment of polyamide resins at room temperature, the method of Non-Patent Document 1 may result in a decrease in the molecular weight of the recycled polyamide resin, raising concerns about a decline in quality.

[0010] In the method proposed in Patent Document 4, the dimethyl ether used as the poor solvent has a low boiling point (-23.6°C), raising concerns about the risk of fire or explosion. Furthermore, while formic acid used as the good solvent effectively dissolves polyamides with short alkylene groups (chains), such as polyamide 6 and polyamide 66, it is difficult to dissolve polyamide resins with long alkylene groups, such as polyamide 11 and polyamide 12, in a short time at room temperature. In practical applications, waste materials (polyamide resin composite materials) to be recycled (decomposed) often contain multiple types of polyamide resins, and the types of polyamide resins contained are often unknown. Therefore, recycling methods for waste materials (polyamide resin composite materials) require good solvents that can be used with a wide variety of polyamide resins, including polyamide 11 and polyamide 12. Furthermore, from the perspective of reducing recycling costs, the good solvents used must also be inexpensive. For example, solvents capable of dissolving polyamide 11, polyamide 12, etc. include m-cresol and 1,1,1,3,3,3-hexafluoro-2-propanol, but these are high-cost solvents and are not practical.

[0011] The present invention has been made in view of the above-mentioned problems, and provides a separation method that can efficiently separate and recover a polyamide resin from a composite material containing the polyamide resin.

[0012] As a result of extensive research into achieving the above object, the inventors have found that the above object can be achieved by the following configuration: In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits.

[0013] [1] A method for separating a composite material, the method comprising: preparing a composite material containing a first material including a polyamide resin and a second material, and a first solvent including formic acid and a halogenated hydrocarbon; contacting the composite material with the first solvent to selectively dissolve the first material in the first solvent, thereby obtaining a first mixture including a first solution in which the first material is dissolved in the first solvent, and the second material; separating the first solution and the second material from the first mixture; adding a second solvent that is a poor solvent for the first material to the separated first solution to precipitate the first material, thereby obtaining a second mixture including the precipitated first material and a mixed solvent of the first solvent and the second solvent; and separating the precipitated first material and the mixed solvent from the second mixture. [2] The polyamide resin may be polyamide 4T, polyamide 5T, polyamide 4, polyamide 6, polyamide 10, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 611, polyamide 612, polyamide 6 / 6I, polyamide 66 / 6I, polyamide 6I, polyamide 6T, polyamide 6T / 11, polyamide 6C, polyamide 810, polyamide 812, polyamide M8T, polyamide M8N, polyamide 9T, polyamide The method for separating a composite material according to [1], wherein the polyamide resin is at least one selected from the group consisting of polyamide 9T / M8T, polyamide 9N, polyamide 9N / M8N, polyamide 10T, polyamide 10T / 11, polyamide 1010, polyamide 1012, polyamide 11 / 1010, polyamide 12 / 1010, polyamide 6I / 6T, polyamide 6T / 10T, polyamide 66 / 6I / 6T, polyamide 2M5T, polyamide 2M5C, and polyamide MXD6. [3] The method for separating a composite material according to [1], wherein the polyamide resin is a polyamide resin having an alkylene group having 10 or more carbon atoms. [4] The method for separating a composite material according to any one of [1] to [3], wherein preparing a first solvent includes preparing the first solvent using a raw material having a formic acid content of 80% by mass or more. [5] The method for separating a composite material according to any one of [1] to [4], wherein the halogenated hydrocarbon is an aprotic solvent. [6] The method for separating a composite material according to any one of [1] to [5], wherein the halogenated hydrocarbon is a chlorinated hydrocarbon.[7] The method for separating a composite material according to [6], wherein the chlorinated hydrocarbon is at least one selected from the group consisting of dichloromethane, chloroform, 1,2-dichloroethane, and 1,2-dichloropropane. [8] The method for separating a composite material according to any one of [1] to [7], wherein in the first solvent, a ratio (A / B) of the volume (A) of formic acid to the volume (B) of the halogenated hydrocarbon is 3 / 7 to 7 / 3. [9] The method for separating a composite material according to any one of [1] to [8], wherein a solids concentration in the first mixture is 1% by mass to 40% by mass.

[10] The method for separating a composite material according to any one of [1] to [9], wherein the first material of the composite material is selectively dissolved in the first solvent in an environment of 0°C to 40°C.

[11] The method for separating a composite material according to any one of [1] to

[10] , wherein the absolute value of the difference between the boiling point of the second solvent and the boiling point of the formic acid and the absolute value of the difference between the boiling point of the second solvent and the boiling point of the halogenated hydrocarbon are 5°C or more.

[12] The method for separating a composite material according to any one of [1] to

[11] , further comprising separating the second solvent from the mixed solvent by distillation.

[13] The method for separating a composite material according to

[12] , comprising separating the mixed solvent into the first solvent and the second solvent by distillation.

[14] The method for separating a composite material according to

[12] , comprising separating the mixed solvent into the second solvent, the formic acid, and the halogenated hydrocarbon by distillation.

[15] A method for recycling a composite material, comprising the separation method according to any one of [1] to

[14] .

[0014] According to the present invention, polyamide resin can be efficiently separated and recovered from a composite material containing the polyamide resin.

[0015] 1 is a block flow diagram illustrating a method for separating a composite material in a first embodiment.

[0034] Photographs showing the results of Experiment 1 show the solubility of polyamide 11 (PA11) in a formic acid (FA)-dichloromethane (DCM) mixed solvent at 23°C. (Left) Immediately after addition, (Right) After standing for 1 hour. FA / DCM volume ratios: (a) 1:0, (b) 1:1, (b) 0:1. Photographs showing the results of Experiment 1 show the solubility of polyamide 11 (PA11) in formic acid (FA)-dichloromethane (DCM) mixed solvents with different mixing ratios: FA / DCM volume ratios: (b-1) 9:1, (b-2) 7:3, (b-3) 3:7, (b-4) 1:9. Photographs showing the results of Experiment 2 show the solubility of polyamide 11 (PA11) in mixed solvents of formic acid (FA) and different types of halogenated hydrocarbons. Types of halogenated hydrocarbons: (b-5) dichloroethane, (b-6) chloroform, (b-7) carbon tetrachloride. Photographs showing the results of Experiment 3. The solubility of PA11 in an FA / DCM mixed solvent (volume ratio 1:1) at 5°C is shown. (a) Immediately after addition, (b) After standing for 2 hours. Photographs showing the results of Experiment 4. Dissolution of PA11 in an FA / DCM mixed solvent (volume ratio 1:1) at room temperature: (a) Immediately after addition, (b) After standing for 1 hour. (c) Recycled PA11 separated and recovered after the addition of acetone. (d) Recycled solvent separated and recovered (from left: FA, DCM, acetone). FT-IR spectra of PA11 before and after the recycling process in Experiment 4. (a) PA11 film before treatment, (b) PA11 film after treatment, (c) PA11 powder after treatment. XRD patterns of PA11 film before and after the recycling process in Experiment 4. (a) PA11 film before treatment, (b) PA11 film after treatment. Figures showing DSC curves of PA11 before and after the recycling treatment in Experiment 4. (a) Before treatment, (b) After recycling treatment. Insert table: melting point (Tm) and crystallization temperature (Tc) of each sample. Figures showing stress-strain curves of PA11 film (0.2 mm) before and after the recycling treatment in Experiment 4. (a) Before treatment, (b) After recycling treatment. Photographs showing the results of Experiment 6. Figures showing the results of a solubility test of various composite materials in FA / DCM (1:1) solvent (temperature 23°C, treatment time 1 hour).(a) PA11-NaTSM 7 wt%, (b) PA11-CF 20 wt%, (c) PA12-CF 20 wt%, (d) PA66-CF 20 wt%, (e) PA6-GF 20 wt%, (f) PA6I / 6T-Ser 7 wt%. SEM images of the filler before and after recycling in Experiment 6. (a) NaTSM before treatment, (b) recycled TSM after treatment. XRD patterns of the filler before and after recycling in Experiment 6. (a) NaTSM before treatment, (b) recycled TSM after treatment. SEM images of the filler before and after recycling in Experiment 6. (a) Ser before treatment, (b) recycled Ser after treatment. XRD patterns of the filler before and after recycling in Experiment 6. (a) Ser before treatment, (b) recycled Ser after treatment. 1 shows SEM images of filler (recovered filler) after recycling in Experiment 6. (a) Recovered from Sample 2 (PA11 / CF), (b) Recovered from Sample 3 (PA12 / CF), (c) Recovered from Sample 4 (PA66 / CF). 1 shows SEM images of filler recovered from Sample 5 (PA6 / GF) after recycling in Experiment 6. 1 shows a diagram and photographs showing the results of Experiment 7. 1 shows a dissolution test of a three-layer laminate film (PA11 / PP / PA11): (a) structure of the laminate film, (b) laminate film before treatment, and (c) laminate film after treatment. 1 shows a diagram and photographs showing the results of Experiment 8. 1 shows a dissolution test of a three-layer sheet (PA11 / CF fabric / PA11): (a) laminate sheet before treatment, and (b) laminate sheet after treatment.

[0016] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments. Furthermore, among the components in the following embodiments, components that are not recited in the claims that represent the highest concepts are described as optional components.

[0017] [First Embodiment] As the first embodiment, a method for separating a composite material will be described. In this separation method, a polyamide resin is extracted with a solvent and recovered from a composite material containing the polyamide resin. The present inventors discovered that using a mixed solvent of formic acid and a halogenated hydrocarbon as an extraction solvent (first solvent) can efficiently dissolve not only polyamide resins with short alkylene chains, such as polyamide 6 and polyamide 66, but also polyamide resins with long alkylene chains, such as polyamide 11 and polyamide 12 (for example, in a short time at room temperature), and thus arrived at the present invention.

[0018] The separation method of this embodiment includes at least the following steps S1 to S5 (see FIG. 1 ): (S1) preparing a composite material including a first material containing a polyamide resin and a second material, and a first solvent containing formic acid and a halogenated hydrocarbon, (S2) contacting the composite material with the first solvent to selectively dissolve the first material in the first solvent, thereby obtaining a first mixture including a first solution in which the first material is dissolved in the first solvent, and the second material, (S3) separating the first solution and the second material from the first mixture, (S4) adding a second solvent that is a poor solvent for the first material to the separated first solution to precipitate the first material, thereby obtaining a second mixture including the precipitated first material and a mixed solvent of the first solvent and the second solvent, and (S5) separating the precipitated first material and the mixed solvent from the second mixture.

[0019] The separation method of this embodiment may further include the following step S6 (see FIG. 1 ): (S6) A step of separating the second solvent by distillation from the mixed solvent separated from the second mixture. Details of each of steps S1 to S6 are described below.

[0020] <Step S1> In this step, a composite material and a first solvent are prepared. The composite material includes a first material containing a polyamide resin and a second material different from the first material.

[0021] The type of polyamide resin contained in the first material is not particularly limited, but it is preferable that at least a portion of it contains an aliphatic skeleton. Polyamide resins containing an aliphatic skeleton have the advantage of being easily soluble in the first solvent. Polyamide resins containing an aliphatic skeleton include aliphatic polyamide resins whose skeleton is formed by a chain of carbon atoms, and semi-aromatic polyamide resins whose skeleton is formed by a chain of carbon atoms and aromatic rings. The polyamide resin containing an aliphatic skeleton may be a polycondensate of a single type of monomer, or a copolycondensate of multiple types of monomers. The polyamide resin may be composed of a polyamide resin containing an aliphatic skeleton, or may also contain an aromatic polyamide resin (aramid).

[0022] Examples of polyamide resins containing an aliphatic skeleton include polyamide 4T, polyamide 5T, polyamide 6, polyamide 10, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 611, polyamide 612, polyamide 6 / 6I, polyamide 66 / 6I, polyamide 6I, polyamide 6T, polyamide 6T / 11, polyamide 6C, polyamide 810, polyamide 812, polyamide M8T, polyamide Examples include polyamide M8N, polyamide 9T, polyamide 9T / M8T, polyamide 9N, polyamide 9N / M8N, polyamide 10T, polyamide 10T / 11, polyamide 1010, polyamide 1012, polyamide 11 / 1010, polyamide 12 / 1010, polyamide 6I / 6T, polyamide 6T / 10T, polyamide 66 / 6I / 6T, polyamide 2M5T, polyamide 2M5C, and polyamide MXD6.

[0023] In the separation method of the present embodiment, by using the first solvent, not only polyamide resins having short alkylene groups in the repeating units but also polyamide resins having long alkylene groups can be dissolved efficiently (for example, at room temperature in a short time). The long alkylene group is, for example, an alkylene group having 8 or more carbon atoms (-C ｎ H ２ｎ -, 8≦n), or an alkylene group having 10 or more carbon atoms (-C ｎ H ２ｎThe upper limit of the number of carbon atoms in the alkylene group is not particularly limited, but examples thereof include alkylene groups having 18 or less carbon atoms (-C ｎ H ２ｎ −, n≦18).

[0024] The polyamide resin contained in the first material may be one type or two or more types. By using the first solvent, the separation method of the present embodiment can be applied to a wide variety of polyamide resins.

[0025] The first material may be composed solely of polyamide resin, or may contain other components in addition to polyamide resin. Furthermore, the main component may be polyamide resin. The proportion of polyamide resin in the first material is, for example, 40% to 100% by mass, 95% to 100% by mass, or 100% by mass. The other components that may be contained in the first material are components that are compatible with polyamide resin in the composite material (i.e., components that are compatible with polyamide resin), such as melamine-based flame retardants and industrial lignin. The other components are dissolved in the first solvent together with the polyamide resin in step S2, which will be described later, and are ultimately recovered together with the polyamide resin.

[0026] The second material contained in the composite material is a material of a different type from the first material described above. In the composite material, the second material, such as various filler materials, textiles, or other resin materials, is compounded to complement the performance of the polyamide resin depending on the application. The second material is insoluble in the polyamide resin and insoluble in the first solvent.

[0027] Examples of the second material include fillers added to improve the performance of polyamide resins or to reduce costs. For example, fillers for improving strength include glass fiber, carbon fiber, aramid fiber, potassium titanate, and cellulose nanofiber. Fillers for adjusting the balance of physical properties include calcium carbonate, talc, mica, and silica. Fillers for imparting electrical conductivity include carbon black, carbon nanotubes, graphite, carbon fiber, metal powder, metal fiber, and metal foil. Fillers for improving thermal conductivity include aluminum oxide, aluminum nitride, boron nitride, and beryllium oxide. Fillers for improving sliding properties include graphite, hexagonal boron nitride, molybdenum sulfide, Teflon® powder, and talc. Fillers for imparting flame retardancy include antimony oxide, aluminum hydroxide, magnesium hydroxide, zinc borate, red phosphorus, ammonium polyphosphate, and melamine polyphosphate. Fillers for scattering and reflecting light include titanium oxide, glass beads, calcium carbonate, aluminum powder, and mica. Examples of fillers for imparting ultraviolet absorption functionality include titanium oxide, zinc oxide, iron oxide, and cerium oxide. Examples of fillers for imparting magnetism include various magnetic materials, various ferrites, and magnetic iron oxide. Examples of fillers for imparting gas barrier properties include mica, smectite, and layered double hydroxides.

[0028] Examples of the second material include woven fabric reinforcement materials such as glass fiber fabric, carbon fiber fabric, and cellulose fiber fabric. For example, carbon fibers include PAN-based, pitch-based, and rayon-based carbon fibers. In this embodiment, any of these may be used, but PAN-based carbon fibers are often used because of their versatility. Carbon fibers are available in various weaves, such as unidirectional, plain weave, twill weave, random weave, triaxial weave, and three-dimensional weave, and are used depending on the application.

[0029] Further, examples of the second material include polyolefin, acrylonitrile-butadiene-styrene copolymer (ABS), polyphenylene ether, polyester, etc. These resins are incompatible with polyamide resin, and can be used as a polymer alloy with polyamide resin, or as a sheet or film laminated with a polyamide resin member.

[0030] The ratio of the first material to the second material in the composite material is not particularly limited and may be determined appropriately depending on the application of the composite material. For example, the mass ratio (first material) / (second material) may be 99 / 1 to 1 / 99, or 95 / 5 to 40 / 60.

[0031] Specific applications and products using the composite material of this embodiment are not particularly limited, and include a variety of products. Examples include automobile parts, electrical and electronic parts, films, sheets, pipes, tubes, daily necessities, containers, toys, building materials, fibers (clothing, carpets, etc.), sports equipment, rigid substrate materials, chopped fiber laminate sheets, continuous fiber laminate sheets, etc. Using the separation method of this embodiment, it is possible to separate and recover polyamide resin (first material) and a second material other than polyamide resin from these products. The recovered polyamide resin and / or second material can also be reused (recycled).

[0032] Next, the first solvent will be described. The first solvent is a good solvent for the first material and includes formic acid and a halogenated hydrocarbon. Formic acid has long been known as a good solvent for polyamide resins, selectively dissolving polyamide resins while not dissolving other resins (e.g., olefin resins such as polypropylene resins). However, when the proportion of non-amide groups in the polyamide resin is high (e.g., when the alkylene groups in the repeating units are long), it has been difficult to dissolve such polyamide resins using formic acid alone. Although formic acid is classified as a lower aliphatic carboxylic acid, using other lower aliphatic carboxylic acids (e.g., acetic acid, propiolic acid, acrylic acid, propionic acid, isocrotonic acid, butyric acid, etc.) instead of or in addition to (mixed with) formic acid has not been able to efficiently dissolve such polyamide resins. The present inventors conducted extensive research to solve this problem and discovered that by using a mixed solvent of formic acid and a halogenated hydrocarbon as the extraction solvent (first solvent), it is possible to dissolve not only polyamide resins with short alkylene chains but also polyamide resins with long alkylene chains in a short time in an unheated environment while maintaining the property of selectively dissolving polyamide resins (i.e., the property of not dissolving the second material), thereby completing the present invention. Although the mechanism behind this is unclear, it is presumed that the formic acid acts on the amide groups of the polyamide resin, and the halogenated hydrocarbon acts on the portions of the polyamide resin other than the amide groups (e.g., alkylene groups), efficiently widening the gap between the polymer chains of the polyamide resin (i.e., dissolving).

[0033] The first solvent selectively dissolves the polyamide resin, but is unlikely to cause damage to the polyamide resin itself, such as decomposition, etc. Therefore, the polyamide resin recovered by the separation method of this embodiment can maintain the same physical properties (chemical structure, mechanical strength, molecular weight, etc.) as before decomposition.

[0034] The halogenated hydrocarbon is not particularly limited, but is preferably an aprotic solvent from the viewpoint of promoting dissolution of the polyamide resin. Furthermore, if the boiling point of the halogenated hydrocarbon is too low, there is a risk of fire or explosion. Furthermore, the halogenated hydrocarbon is preferably liquid at room temperature and normal pressure (room temperature, atmospheric pressure) so that it functions as a solvent. From these viewpoints, the boiling point of the halogenated hydrocarbon is preferably 30°C to 120°C or 60°C to 100°C. Furthermore, when performing step S6 (separation of the mixed solvent) described below, the boiling point of the halogenated hydrocarbon preferably differs from the boiling point of the second solvent by 5°C or more. Furthermore, when separating formic acid and the halogenated hydrocarbon, their boiling points preferably differ by 5°C or more. In this specification, when the term "boiling point" is used simply without specifying the external pressure, it refers to the boiling point at 1 atmosphere (0.1 MPa).

[0035] As the halogenated hydrocarbon, chlorinated hydrocarbons are preferred because they are inexpensive. Examples of chlorinated hydrocarbons include dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, and 1,2-dichloropropane, with dichloromethane, chloroform, 1,2-dichloroethane, and 1,2-dichloropropane being preferred. One type of halogenated hydrocarbon may be used alone, or two types may be used in combination.

[0036] In the first solvent, the ratio (A / B) of the volume (A) of formic acid to the volume (B) of the halogenated hydrocarbon is not particularly limited and may be adjusted appropriately taking into consideration the type of polyamide resin to be dissolved, the ambient temperature, etc. From the viewpoint of promoting dissolution of the polyamide resin, for example, the ratio (A / B) may be 1 / 9 to 9 / 1, preferably 3 / 7 to 7 / 3, and more preferably 4 / 6 to 6 / 4.

[0037] The first solvent may be composed only of formic acid and halogenated hydrocarbon, or may contain other components as long as the effects of this embodiment are achieved. The total amount of formic acid and halogenated hydrocarbon in the first solvent is, for example, 80% by mass to 100% by mass, 90% by mass to 100% by mass, or 100% by mass.

[0038] Furthermore, if the proportion of water contained in the first solvent is high, formic acid may be acidic and corrosive, potentially reducing the molecular weight of the polyamide resin. Furthermore, if the proportion of water is high, the water may separate from the halogenated hydrocarbon, potentially preventing the formation of a homogeneous first solvent. Therefore, it is preferable that the proportion of water contained in the first solvent is low, for example, 15% by mass or less, 5% by mass or less, or 0% by mass.

[0039] The first solvent can be prepared by mixing formic acid and a halogenated hydrocarbon in a predetermined ratio by a conventionally known method. Since the first solvent preferably contains less water, the formic acid concentration (formic acid content) of the formic acid raw material (product, reagent) used to prepare the first solvent is preferably 80% by mass or more (water content: less than 20% by mass), 88% by mass or more (reagent grade, water content: less than 12% by mass), or 100% by mass (anhydrous formic acid).

[0040] <Step S2> Next, the composite material is brought into contact with a first solvent to selectively dissolve the first material in the first solvent, thereby obtaining a first mixture containing a first solution in which the first material is dissolved in the first solvent and the second material that is not dissolved.

[0041] The method for contacting the composite material with the first solvent and dissolving it is not particularly limited, and conventionally known methods can be used. For example, the composite material is immersed in the first solvent either as is or after being cut into pieces of appropriate size. Mechanical stirring, ultrasound, a shaking device, or the like may be used to promote dissolution of the first material. From the viewpoint of dissolving the first material in a short time, it is preferable to use ultrasound. On the other hand, in the separation method of this embodiment, the second material can also be recovered, but from the viewpoint of suppressing damage to the second material, it is preferable not to use ultrasound, and it is more preferable to leave the material standing. By using the first solvent, various types of polyamide resins can be selectively dissolved without using ultrasound, etc.

[0042] In step S2, the ratio of the composite material to the first solvent to be brought into contact with it is not particularly limited and may be determined appropriately depending on the type of composite material, etc., so as to promote dissolution of the first material. For example, the amounts of the composite material and the first solvent used may be adjusted so that the solids concentration (i.e., the proportion of the composite material) in the first mixture obtained in step S2 is 1% by mass to 40% by mass, or 5% by mass to 25% by mass. Furthermore, the amounts of the composite material and the first solvent used may be adjusted so that the concentration of the first material in the obtained first solution is 0.1% by mass to 35% by mass, or 0.4% by mass to 24% by mass.

[0043] The environmental temperature at which step S2 is carried out is not particularly limited and may be, for example, 0°C to 40°C. By using the first solvent, dissolution and extraction of the polyamide resin is possible even in an uncontrolled temperature environment, from winter (e.g., 0°C) to summer (e.g., 40°C). Temperature control of the first solvent and the first solution is also unnecessary, and these temperatures may be set to 0°C to 40°C, similar to the environmental temperature. Note that when the dissolution treatment temperature (temperature of the environment, first solvent, first solution, etc.) exceeds 40°C, the solubility of the polyamide resin is improved, enabling a reduction in the time required. When this point is important, step S2 may be carried out at a treatment temperature exceeding 40°C.

[0044] The treatment time (dissolution time) of step S2 is not particularly limited and may be adjusted appropriately depending on the type of composite material, ambient temperature, stirring means, etc., and may be, for example, 10 minutes to 6 hours, or 30 minutes to 3 hours. In this embodiment, by using the first solvent, it is possible to dissolve the polyamide resin in a relatively short time even in a room temperature environment. For example, in the examples described below, the polyamide resin was able to dissolve in about 1 hour to 2 hours.

[0045] <Step S3> Next, the first solution and the second material are separated from the obtained first mixture. The method for separating the first solution and the second material is not particularly limited, and conventional methods such as centrifugation and filtration can be used. The separated second material can be washed, dried, and recovered as needed. The first solvent of this embodiment selectively dissolves the first material (polyamide resin) and is less likely to damage the second material. Therefore, the second material recovered by the separation method of this embodiment can maintain the same physical properties as before decomposition.

[0046] <Step S4> A second solvent, which is a poor solvent for the first material, is added to the separated first solution to precipitate the first material, thereby obtaining a second mixture containing the precipitated first material and a mixed solvent of the first solvent and the second solvent.

[0047] The poor solvent is not particularly limited as long as it is a solvent that can precipitate a polyamide resin when mixed with the first solution, but a solvent in which the solubility of the polyamide resin is less than 1% by mass at room temperature (20°C to 30°C) is preferred. Examples of poor solvents include aliphatic hydrocarbons such as pentane, hexane, heptane, octane, nonane, n-decane, n-dodecane, n-tridecane, cyclohexane, and cyclopentane; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene, toluene, and xylene; alcohols such as methanol, ethanol, 1-propanol, and 2-propanol; and water. The poor solvent may be composed of only one type of solvent, or may be a mixed solvent of two or more types of solvents.

[0048] If the boiling point of the second solvent is too low, there is a risk of fire or explosion. Furthermore, it is preferable that the second solvent is a liquid at room temperature and normal pressure (room temperature, atmospheric pressure) so that it functions as a solvent at room temperature and normal pressure. From these viewpoints, the boiling point of the second solvent is preferably 30°C to 150°C or 40°C to 100°C. Furthermore, when performing step S6 (separation of the mixed solvent) described below, it is preferable that the boiling point of the second solvent is different from the boiling point of formic acid by 5°C or more, and is also different from the boiling point of the halogenated hydrocarbon by 5°C or more.

[0049] The ratio of the first solvent to the second solvent in the second mixture is not particularly limited, but from the viewpoint of promoting precipitation of the first material (polyamide resin), the mass ratio (first solvent) / (second solvent) may be, for example, 1 / 50 to 1 / 2 (=0.02 to 0.5), or 1 / 20 to 1 / 5 (=0.05 to 0.2).

[0050] The temperature and duration of step S4 are not particularly limited and may be adjusted as appropriate. For example, the temperature may be 20° C. to 40° C., and the duration may be 20 minutes to 60 minutes.

[0051] <Step S5> Next, the precipitated first material and the mixed solvent of the first solvent and the second solvent are separated from the obtained second mixture. The method for separating the first material from the mixed solvent is not particularly limited, and conventionally known methods such as centrifugation and filtration can be used. The separated first material can be washed, dried, and recovered as needed. The drying temperature for the first material is preferably 10°C to 100°C or 30°C to 80°C in order to evaporate the solvent without damaging or decomposing the polyamide resin.

[0052] <Step S6> The separation method of this embodiment may further include a step of separating the second solvent by distillation from the mixed solvent separated from the second mixture. The distillation method is not particularly limited, and a conventionally known method may be used, and the distillation may be performed under normal pressure (atmospheric pressure) or under reduced pressure (vacuum distillation).

[0053] For example, in step S6, the mixed solvent may be separated into two components, a first solvent and a second solvent, by distillation. The separated first solvent (mixed solvent of formic acid and halogenated hydrocarbon) can be reused in the separation method of this embodiment as the first solvent prepared in step S1 (see FIG. 1). The separated second solvent (poor solvent) can be reused as the second solvent used in step S4 (see FIG. 1). By reusing the first solvent and the second solvent, the separation method of this embodiment can further reduce implementation costs and environmental impact.

[0054] When separating a mixed solvent into two components, a first solvent and a second solvent, the boiling point of the second solvent (BP2) does not lie between the boiling point of formic acid (BP11) and the boiling point of the halogenated hydrocarbon (BP12). That is, these boiling points have the relationship BP2<BP11 and BP2<BP12, or the relationship BP2>BP11 and BP2>BP12. Furthermore, from the viewpoint of increasing separation efficiency, it is preferable that the difference in boiling points between the first solvent and the second solvent be somewhat large. For example, under atmospheric pressure (0.1 MPa), when considering the absolute value (d1) of the difference between the boiling point of the second solvent (BP2) and the boiling point of formic acid (BP11 = 100.8°C), and the absolute value (d2) of the difference between the boiling point of the second solvent (BP2) and the boiling point of the halogenated hydrocarbon (BP12), the absolute values ​​of these differences are preferably at least 5°C or more (5°C < d1, d2), more preferably 10°C or more (10°C < d1, d2), and even more preferably 20°C or more (20°C < d1, d2). Furthermore, although not particularly limited, from a practical viewpoint, the absolute values ​​of these differences may be at most 50°C or less (d1, d2 < 50°C). When the first solvent (a mixed solvent of formic acid and a halogenated hydrocarbon) is reused as is, there is no need to separate the formic acid from the halogenated hydrocarbon, and in this case, the absolute value of the difference between BP11 and BP12 (d3) may be less than 5°C.

[0055] In addition, for example, in step S6, the mixed solvent may be separated into three components, i.e., the second solvent, formic acid, and halogenated hydrocarbon, by distillation. By separating the mixed solvent into three individual components, reuse is not limited to the separation method of this embodiment, and reuse in a wide variety of fields is possible.

[0056] When separating a mixed solvent into three components, the hierarchical relationship between the boiling points BP11, BP12, and BP2 is not particularly limited, but from the viewpoint of improving separation efficiency, it is preferable that the difference between the respective boiling points is somewhat large. For example, under atmospheric pressure (0.1 MPa), when considering the absolute value (d1) of the difference between the boiling point of the second solvent (BP2) and the boiling point of formic acid (BP11), the absolute value (d2) of the difference between the boiling point of the second solvent (BP2) and the boiling point of the halogenated hydrocarbon (BP12), and the absolute value (d3) of the difference between the boiling point of formic acid (BP11) and the boiling point of the halogenated hydrocarbon (BP12), the absolute values ​​of these differences are preferably at least 5°C or more (5°C < d1, d2, d3), more preferably 10°C or more (10°C < d1, d2, d3), and even more preferably 20°C or more (20°C < d1, d2, d3). Furthermore, although not particularly limited, from a practical point of view, the absolute value of these differences may be a maximum of 30° C. or less (d1, d2, d3≦30° C.).

[0057] In the separation method of the present embodiment described above, a mixed solvent of formic acid and a halogenated hydrocarbon is used as the first solvent (extraction solvent), thereby enabling efficient solvent extraction and recovery of the first material (polyamide resin) from the composite material. The separation method of the present embodiment is capable of separating various types of polyamide resins, and the dissolution step (step S2) can be performed in a short time under a room temperature environment. The separation method of the present embodiment is less likely to damage the recovered first material (polyamide resin) and second material, allowing them to be reused (recycled).

[0058] Second Embodiment As a second embodiment, a method for recycling a composite material including the separation method of the first embodiment will be described.

[0059] The composite material to be recycled is the same as the composite material described in the first embodiment, and the composite material is used in the various applications and products listed in the first embodiment. By using the recycling method of this embodiment, it becomes possible to disassemble and reuse such applications and products.

[0060] By decomposing the composite material, both the first material and the second material can be recovered. In this embodiment, only the recovered first material (polyamide resin) may be reused (recycled), only the second material may be reused (recycled), or both the first material and the second material may be reused (recycled). As described above, the separation method used in this embodiment (i.e., the separation method of the first embodiment) is unlikely to damage the recovered first material and second material. Therefore, the recycling method of this embodiment enables material recycling in which the first material and / or the second material are reused as raw materials for new products.

[0061] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0062] [Experiment 1] <Dissolution Test at Room Temperature> Three types of solvents (a) to (c) were prepared: formic acid (FA) solvent alone (a); FA / DCM mixed solvent (b) prepared by mixing formic acid (FA) and dichloromethane (DCM) at a volume ratio of 1:1; and DCM solvent alone (c). Additionally, mixed solvents (b-1), (b-2), (b-3), and (b-4) were prepared with FA / DCM mixing ratios of 9:1, 7:3, 3:7, and 1:9. FA was a special-grade reagent manufactured by Nacalai Tesque, Inc., and DCM was an anhydrous reagent manufactured by Tokyo Chemical Industry Co., Ltd. Polyamide 11 (PA11) pellets (RILSAN® BML O TLD, manufactured by Arkema Inc.) were used as the polyamide resin.

[0063] To each of the solvents (a) to (c) (16 g each), PA11 pellets (4 g) were added (solid content concentration: 20% by mass) and allowed to stand at 23°C for 1 hour. Figure 2A shows a photograph (Start) taken immediately after adding PA11 to the solvent, and a photograph (1 Hr) taken after allowing to stand for 1 hour. Figure 2B shows a photograph of the pellet sample after adding PA11 pellets (4 g) to each of the mixed solvents (b-1) to (b-4) (16 g each) (solid content concentration: 20% by mass) and allowing to stand at 23°C for 1 hour.

[0064] As shown in Figure 2A, after standing for 1 hour, the FA / DCM mixed solvent (b) completely dissolved the PA11 pellets, resulting in a pale yellow, homogeneous PA11 solution. On the other hand, in the FA-only solvent (a) and the DCM-only solvent (c), swollen PA11 pellets were observed floating in the solvent, and PA11 could not be dissolved at room temperature. As shown in Figure 2B, the PA11 pellets were completely dissolved in the FA / DCM mixed solvent (b-3), and a small amount of solid matter (arrow) remained in (b-2), but dissolved within the time frame by heating at 40°C. Furthermore, in the (b-1) and (b-4) solutions, insoluble components in the form of pellets (arrow) were observed, but the insoluble components dissolved by heating at 80°C and stirring with a magnetic stirrer for 4 hours.

[0065] [Experiment 2] <Solubility test using different halogenated hydrocarbon species> A solubility test was carried out under the same conditions as in [Experiment 1] in a mixed solvent (b) of formic acid (FA) and a halogenated hydrocarbon at a volume ratio of 1:1, except that the halogenated hydrocarbon was changed to dichloroethane (solvent b-5), chloroform (solvent b-6), or carbon tetrachloride (solvent b-7).

[0066] As shown in FIG. 3, although the mixed solvent (b-7) became cloudy, no pellet-like solid matter was observed, and it was confirmed that the compound was dissolved in all of the solvents (b-5), (b-6), and (b-7) without any problems.

[0067] [Experiment 3] <Dissolution test in a low-temperature environment> An FA / DCM mixed solvent (volume ratio 1:1) and PA11 pellets were prepared, similar to those used in Experiment 1. Furthermore, polyamide 66 (PA66) pellets (Amilan (registered trademark) CM3001-N, manufactured by Toray Industries, Inc.) were prepared as a polyamide resin.

[0068] PA66 pellets and PA11 pellets (4 g each) were added to 16 g of a 1:1 volumetric FA / DCM mixed solvent (solids concentration: 20% by mass) and allowed to stand in a refrigerator at 5°C. 20 minutes after the start of standing, the PA66 pellets were uniformly dissolved in the FA / DCM mixed solvent, and after 2 hours, the PA11 pellets were also uniformly dissolved. Figure 4(a) shows a photograph of the pellets immediately after adding them to the solvent, and Figure 4(b) shows a photograph after standing for 2 hours.

[0069] [Experiment 4] (1) Recycling Treatment In this example, hereinafter, treating a sample (polyamide resin or composite material) with a solvent (first solvent) and then recovering the polyamide resin and / or the second material again may be referred to as a “recycling treatment.” In Experiment 4, the recycling treatment involved dissolving the polyamide resin in a solvent and recovering it from the solution, as described below.

[0070] An FA / DCM mixed solvent (volume ratio 1:1) similar to that used in Experiment 1 and PA11 pellets were prepared. First, PA11 pellets (25 g) were added to the FA / DCM mixed solvent (175 g) and allowed to stand at 23°C for 2 hours. This resulted in uniform dissolution of PA11, yielding a PA11 solution (solid content: 12.5% ​​by mass). Figure 5(a) shows a photograph immediately after adding the PA11 pellets to the solvent, and Figure 5(b) shows a photograph after allowing to stand for 2 hours. Next, the PA11 solution was added to 400 mL of acetone, a poor solvent, to precipitate PA11. This resulted in a mixture of precipitated PA11 and the mixed solvent (FA, DCM, acetone). The mixture was filtered, washed, and dried, and separated into precipitated PA11 (Figure 5(c), Recycle PA11) as a white powder and the mixed solvent. The recovery rate of PA11 was approximately 99% by mass.

[0071] The separated mixed solvent was distilled under reduced pressure using an evaporator, and DCM (boiling point: 39.6°C) and acetone (boiling point: 56°C) were recovered in that order. This separated the mixed solvent into three components: acetone, DCM, and FA (boiling point: 100.8°C). The recovered solvents are shown in Figure 5(d). The recovery rate of each solvent was approximately 95% by mass.

[0072] (2) Evaluation of polyamide resin after recycling treatment Using a hot press, a film of approximately 0.2 mm was molded from untreated PA11 pellets (i.e., PA pellets before recycling treatment) (sample (a)). Similarly, a film was also molded from the polyamide resin after recycling treatment (recovered polyamide resin, Recycle PA11) (sample (b)). In addition, to examine the mechanical properties of both polyamide resins, dumbbell test specimens (ISO527-2) were injection molded using a small injection molding machine (MiniJET PRO, manufactured by Thermo Fisher Scientific) at a cylinder temperature of 200°C and a mold temperature of 80°C.

[0073] Samples (a) and (b) were subjected to Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), and tensile testing. FT-IR measurements were also performed on the recovered polyamide resin (powder, sample (c)) before molding. The evaluation results are shown in Figures 6 to 9. The equipment and measurement methods used for each evaluation are described below.

[0074] <Equipment, measurement method, etc. used in each evaluation> FT-IR spectrum measurement: Measurement was performed using a Fourier transform infrared absorption measurement device (IRAffinity, manufactured by Shimadzu Corporation) using the ATR method. XRD measurement: Measurement was performed using an X-ray diffractometer (Cu-Kα radiation) (Ultima-IV, manufactured by Rigaku Corporation) at 40 kV and 30 mA. DSC measurement: Measurement was performed using a differential calorimeter (DSC7020, manufactured by Hitachi High-Tech Corporation) in a nitrogen atmosphere over a range of -50°C to 200°C at a heating rate of 10°C / min. From the measurement results, the melting point (Tm) and crystallization temperature (Tc) of the polyamide resin before and after recycling treatment were determined. The melting curve shows a second heating curve to eliminate the thermal history of the sample. Tensile test: According to ASTM D638, a tensile test was performed using an electromechanical testing machine (Model: EZ-LX, Shimadzu Corporation) at a crosshead speed of 5 mm / min to evaluate the tensile strength and tensile modulus. The strain required to determine the tensile modulus was measured using a video extensometer. The tensile test was performed on each dumbbell test piece with N=3, and the tensile strength and tensile modulus were calculated as the average values.

[0075] <Evaluation Results> As shown in Figures 6 to 9, almost identical measurement results were obtained for sample (a) and sample (b) in all of the FT-IR (ATR) measurement, XRD measurement, DSC measurement, and tensile test. In the FT-IR (ATR) measurement, the measurement result of sample (c) was also almost identical to that of sample (a) and sample (b). From these results, it was confirmed that the structure, physical properties, mechanical strength, etc. of the polyamide resin (PA11) were almost unchanged before and after the recycling process.

[0076] [Experiment 5] Three types of polyamide resin (PA11, PA6, PA6T / 6I) pellets shown in Table 1 were subjected to the same recycling process as in Experiment 4. The number average molecular weight (Mn) and weight average molecular weight (Mw) of the polyamide resin before and after the recycling process were measured by the methods described below. The results are shown in Table 1.

[0077] <Molecular Weight Measurement Method> The number average molecular weight (Mn) and weight average molecular weight (Mw) of polyamide were calculated by gel permeation chromatography (GPC) in terms of polymethyl methacrylate (PMMA). The molecular weight distribution (Mw / Mn) was calculated by dividing the weight average molecular weight by the number average molecular weight.

[0078] <Measurement conditions> GPC model: Shoko Scientific GPC-104, RI (differential refractive index) detector, Column: Shodex GPC LF-404 x 2 (Showa Denko), Pretreatment: The sample solution was filtered through a membrane filter (0.2 μm). Eluent: A mixture of hexafluoroisopropanol (HFIP) and 10 mmol / L sodium trifluoroacetate was used as the eluent. Flow rate: 0.3 mL / min, Sample solution injection amount: 10 μL, Column temperature: 40°C.

[0079] <Evaluation Results> As shown in Table 1, for all three types of polyamide resins (PA11, PA6, PA6T / 6I), there was no significant change in the number average molecular weight (Mn) and weight average molecular weight (Mw) before and after the recycling treatment, and it was confirmed that the molecular weights (Mn, Mw) were almost maintained.

[0080]

[0081] [Experiment 6] (1) Preparation of Composite Materials Six types of composite materials (pellets made of polyamide resin containing filler, samples 1 to 6) were prepared as shown in Table 2. The notation of the composite materials shown in Table 2 indicates "type of polyamide resin - type of filler (filler content)".

[0082] A predetermined amount of each filler was blended with each polyamide resin shown in Table 2, and the mixture was melt-kneaded in a twin-screw kneader (Kurimoto Iron Works, Ltd., S1KRC) at a cylinder temperature of 230°C to 250°C, and then extruded (molded), cut, dried, etc. to obtain pellets (samples 1 to 6).

[0083]

[0084] <Polyamide resins in Table 2> PA11: Polyamide 11 (RILSAN (registered trademark) BML O TLD, manufactured by Arkema K.K.) PA12: Polyamide 12 (UBE Nylon (registered trademark) 3024U, manufactured by Ube Industries, Ltd.) PA66: Polyamide 66 (Amilan (registered trademark) CM3001-N, manufactured by Toray Industries, Inc.) PA6: Polyamide 6 (Amilan (registered trademark) CM1007, manufactured by Toray Industries, Inc.) PA6I / 6T: Polyamide 6I / 6T (content of isophthalic acid in total dicarboxylic acid units: 70 mol%) (Grivory (registered trademark) G21, manufactured by M-Chemie Japan K.K.)

[0085] <Fillers in Table 2> NaTSM: Na-type tetrasilicon mica (ME100, manufactured by Co-op Chemical Co., Ltd.) CF: carbon fiber, fiber diameter 7 μm, fiber length 6 mm (Pyrofil (registered trademark) TR06NL, manufactured by Mitsubishi Chemical Corporation) GF: glass fiber, fiber diameter 13 μm, fiber length 3 mm (CS3PE944, manufactured by Nitto Boseki Co., Ltd.) Ser: sericite (Sericite FSE, manufactured by Sanshin Mining Co., Ltd.)

[0086] (2) Recycling Treatment An FA / DCM mixed solvent (volume ratio 1:1) similar to that used in Experiment 1 was prepared. 5.7 g of the FA / DCM mixed solvent (solid content: 10% by mass) was added to each of the prepared Samples 1 to 6 (0.63 g), and the mixture was subjected to ultrasonic irradiation for 5 minutes and then allowed to stand for 15 minutes. As a result, the polyamide resin components in each sample were selectively dissolved in the solvent, yielding a polyamide solution (mixture) in which the filler was dispersed. Figures 10(a) to 10(f) show photographs of Samples 1 to 6 immediately after adding them to the solvent ("Before") and after allowing them to stand ("After").

[0087] Next, the filler was separated from each of the six mixtures obtained by filtration, washed, and then dried and recovered. After the filler was separated and recovered, the remaining polyamide solution was poured into acetone, a poor solvent, to precipitate PA11, as in Experiment 4, and the polyamide resin was recovered after filtration, washing, and drying. The recovery rates of the polyamide resin and the filler were both 99% by mass.

[0088] (3) Evaluation of Fillers after Recycling Treatment (3-1) Samples 1 and 6 The fillers used in Samples 1 and 6, NaTSM and Ser, are both plate-like fillers. These fillers that had not been subjected to any treatment (i.e., fillers before recycling treatment) and the fillers recovered from Samples 1 and 6 (i.e., fillers after recycling treatment) were subjected to SEM observation (using a scanning electron microscope (FEI QUANTA 600)) and XRD measurement (conducted in the same manner as in Experiment 3) and compared. The results are shown in FIGS. 11 to 14.

[0089] As shown in Figure 11, the particle shape of NaTSM for Sample 1 was almost the same before the recycling process (Figure 11(a)) and after the recycling process (Figure 11(b)). Also, as shown in Figure 12, the diffraction patterns obtained by XRD measurement were almost the same before the recycling process (Figure 12(a)) and after the recycling process (Figure 12(b)). These results confirmed that the filler (NaTSM) could be recovered from Sample 1 by the recycling process without causing damage (without changing its properties).

[0090] 13 and 14, similar results to those of Sample 1 were obtained for Sample 6. For Sample 6, the particle shape of Ser was almost the same before the recycling process ( FIG. 13(a)) and after the recycling process ( FIG. 13(b)). Furthermore, as shown in FIG. 14, the diffraction patterns obtained by XRD measurement were almost the same before the recycling process ( FIG. 14(a)) and after the recycling process ( FIG. 14(b)). These results confirmed that the filler (Ser, sericite) could be recovered from Sample 6, which uses a semi-aromatic polyamide resin (PA6I / 6T), by recycling without causing damage (without changing its properties).

[0091] (3-2) Samples 2 to 5 The fillers used in Samples 2 to 5 were reinforcing fibers (Samples 2 to 4: carbon fiber (CF), Sample 5: glass fiber). The fillers recovered from Samples 2 to 5 (i.e., the fillers after recycling) were observed under SEM. The results are shown in Figures 15 and 16. As shown in Figures 15 to 16, undamaged reinforcing fibers were recovered from all of Samples 2 to 5.

[0092] Next, the change in molecular weight of the polyamide resin before and after the recycling treatment was estimated by flow rate measurement (MVR). As measurement samples, PA11 that had not been subjected to any treatment (i.e., PA11 before the recycling treatment) and PA11 recovered from sample 2 (PA11-CF (20 mass%)) (i.e., PA11 after the recycling treatment) were prepared. The melt volume rate (MVR) was measured using a measuring device (Melt Indexer G-02 (manufactured by Toyo Seiki Seisakusho)) in accordance with JIS K 7210-1. ３ / 10 min) was measured at 200 °C and a load of 2.16 kg. As a result, the PA11 before the recycling treatment was 26.9 cm ３ / 10 min, while the recycled PA11 is 28.0 cm ３ Since there was no significant change in the flow rate, it was found that the molecular weight of the polyamide resin (PA11) was almost the same before and after the recycling treatment.

[0093] (4) Evaluation of Polyamide Resins after Recycling. Table 3 shows the change in molecular weight before and after recycling for three representative samples of the polyamide resin composite materials prepared in [Experiment 6]: Sample 1: PA11-NaTSM (7% by mass), Sample 2: PA11-CF (20% by mass), and Sample 4: PA66-CF (20% by mass). There were no significant changes in the number-average molecular weight (Mn) or weight-average molecular weight (Mw) for each composite material, confirming that the molecular weights (Mn, Mw) were largely maintained. The molecular weights shown in Table 3 were measured using the same method as in Experiment 5 above.

[0094]

[0095] [Experiment 7] (1) Preparation of Composite Material A three-layer film (PA11 / PP / PA11) was prepared as a composite material, as shown in Figure 17(a). PA11 pellets (similar to those used in Experiment 1) and PP pellets (maleic anhydride-modified propylene homopolymer, Admer (registered trademark) QE800, manufactured by Mitsui Chemicals, Inc.) were prepared. Using each pellet, one PP film (0.2 mm) and two PA11 films (0.2 mm) were molded using a heat press (220 °C, 10 MPa). Next, a PP film was sandwiched between two PA11 films and heat pressed at 190 °C and 10 MPa to produce a pale yellow-white three-layer film.

[0096] (2) Dissolution Test An FA / DCM mixed solvent (volume ratio 1:1) (50 mL) similar to that used in Experiment 1 was prepared. The prepared three-layer film was immersed in the mixed solvent at 23°C for 1 hour and then recovered. This immersion caused the PA11 film to selectively dissolve in the solvent, and the solvent after immersion turned pale yellow. The recovered film consisted of only the transparent PP film. Figure 17(b) shows a photograph of the three-layer film before solvent immersion, and Figure 17(c) shows a photograph of the recovered film after solvent immersion.

[0097] [Experiment 8] (1) Preparation of Composite Material A three-layer sheet (PA11 sheet / CF fabric / PA11 sheet) was prepared as a composite material, as shown in Figure 18(a). First, two PA11 films (0.2 mm) were molded using the same method as in Experiment 6, and one CF fabric (PAN-based carbon fiber fabric, Besfight Prepreg, manufactured by Toho Tenax Co., Ltd.) was prepared. Next, the CF fabric was sandwiched between the two PA11 films and hot-pressed at 220 °C and 10 MPa. Furthermore, the sheet edges were reinforced with a flexible adhesive to obtain a three-layer sheet.

[0098] (2) Dissolution Test An FA / DCM mixed solvent (volume ratio 1:1) (100 mL) similar to that used in Experiment 1 was prepared. The prepared three-layer sheet was immersed in the mixed solvent at 23°C for 1 hour and then recovered. This immersion selectively dissolved the PA11 film into the solvent, and the solvent after immersion turned pale yellow. The recovered sheet consisted of only the CF fabric. Figure 18(a) shows a photograph of the three-layer sheet before solvent immersion, and Figure 18(b) shows a photograph of the recovered sheet after solvent immersion.

[0099] Products using composite materials containing polyamide resins include a variety of products, such as automobile parts, electric and electronic parts, etc. The separation method of the present invention can efficiently separate and recover polyamide resins from these products, thereby promoting the recycling of these products.

Claims

1. A method for separating a composite material, comprising: preparing a composite material containing a first material including a polyamide resin and a second material, and a first solvent including formic acid and a halogenated hydrocarbon; contacting the composite material with the first solvent to selectively dissolve the first material in the first solvent, thereby obtaining a first mixture including a first solution in which the first material is dissolved in the first solvent, and the second material; separating the first solution and the second material from the first mixture; adding a second solvent that is a poor solvent for the first material to the separated first solution to precipitate the first material, thereby obtaining a second mixture including the precipitated first material and a mixed solvent of the first solvent and the second solvent; and separating the precipitated first material and the mixed solvent from the second mixture.

2. The polyamide resin is polyamide 4T, polyamide 5T, polyamide 4, polyamide 6, polyamide 10, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 611, polyamide 612, polyamide 6 / 6I, polyamide 66 / 6I, polyamide 6I, polyamide 6T, polyamide 6T / 11, polyamide 6C, polyamide 810, polyamide 812, polyamide M8T, polyamide M8N, polyamide 9T, polyamide 2. The method for separating a composite material according to claim 1, wherein the composite material is at least one selected from the group consisting of polyamide 9T / M8T, polyamide 9N, polyamide 9N / M8N, polyamide 10T, polyamide 10T / 11, polyamide 1010, polyamide 1012, polyamide 11 / 1010, polyamide 12 / 1010, polyamide 6I / 6T, polyamide 6T / 10T, polyamide 66 / 6I / 6T, polyamide 2M5T, polyamide 2M5C, and polyamide MXD6.

3. The method for separating a composite material according to claim 1, wherein the polyamide resin is a polyamide resin having an alkylene group having 10 or more carbon atoms.

4. The method for separating a composite material according to any one of claims 1 to 3, wherein preparing the first solvent includes preparing the first solvent using a raw material having a formic acid content of 80 mass% or more.

5. The method for separating a composite material according to any one of claims 1 to 4, wherein the halogenated hydrocarbon is an aprotic solvent.

6. The method for separating a composite material according to any one of claims 1 to 5, wherein the halogenated hydrocarbon is a chlorinated hydrocarbon.

7. The method for separating a composite material according to claim 6, wherein the chlorinated hydrocarbon is at least one selected from the group consisting of dichloromethane, chloroform, 1,2-dichloroethane, and 1,2-dichloropropane.

8. The method for separating a composite material according to any one of claims 1 to 7, wherein in the first solvent, the ratio (A / B) of the volume (A) of formic acid to the volume (B) of halogenated hydrocarbon is 3 / 7 to 7 / 3.

9. The method for separating a composite material according to any one of claims 1 to 8, wherein the solids concentration in the first mixture is 1% by mass to 40% by mass.

10. A method for separating a composite material according to any one of claims 1 to 9, wherein the first material of the composite material is selectively dissolved in a first solvent in an environment of 0°C to 40°C.

11. A method for separating a composite material according to any one of claims 1 to 10, wherein the absolute value of the difference between the boiling point of the second solvent and the boiling point of the formic acid, and the absolute value of the difference between the boiling point of the second solvent and the boiling point of the halogenated hydrocarbon, are 5°C or more.

12. The method for separating a composite material according to any one of claims 1 to 11, further comprising separating the second solvent from the mixed solvent by distillation.

13. The method for separating a composite material according to claim 12, comprising separating the mixed solvent into a first solvent and a second solvent by distillation.

14. The method for separating a composite material according to claim 12, comprising separating the mixed solvent into the second solvent, the formic acid, and the halogenated hydrocarbon by distillation.

15. A method for recycling composite materials, comprising the separation method according to any one of claims 1 to 14.

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