Recycling method of high polymer material and fiber product

Abstract

The purpose of the present invention is to provide a recycling method for easily recovering a high-recyclability polymer material from a solid mixture containing a polyester and a polymer material using a process having a low environmental burden. A method for recycling a polymer material, in which a solid mixture of a polyester and a polymer material is heated in the presence of water, the polyester and water are separated from the solid mixture by melting, and the polymer material is recovered as a solid, when the melting point of the polyester in air is Tm, the polymer material has a melting point higher than Tm or does not have a melting point and is a solid at Tm, and the heating is performed at a temperature of (Tm-70) DEG C or more and (Tm-10) DEG C or less.

Description

Technical Field

[0001] The present invention relates to a method for recycling a polymer material and also to a fiber product made of polymer fibers which are the polymer material obtained by the above-mentioned recycling method. Background Art

[0002] In recent years, the recycling of waste has attracted attention from the viewpoint of reducing environmental load. However, the recycling of solid mixtures containing polyester and polymer materials has not progressed because it is difficult to separate the polyester from the polymer materials.

[0003] As a solid mixture containing polyester and a polymer material, for example, a fiber product containing polyester fibers and polymer fibers is known. As a method for recycling the above-mentioned fiber product, a method is known in which a polymer fiber such as cotton fiber is decomposed by heat treatment under a strongly acidic condition of pH 2 or less, and the polyester fiber is recovered as a solid (Patent Documents 1 and 2).

[0004] However, when the recycling method under the aforementioned strong acidic conditions is used, the polymer fibers are recovered as decomposed products without maintaining their shape, so the use of the reuse is limited and the recyclability cannot be said to be high. In addition, when the recycling method under the aforementioned strong acidic conditions is used, the post-treatment of the strong acidic waste liquid is complicated, and there are also concerns about the environmental load.

[0005] On the other hand, as a method for decomposing polyester fibers without decomposing cotton fibers, which are polymer fibers, in a fiber product containing polyester fibers and polymer fibers, heat-treating the fiber product under a strong alkaline condition of pH 10 or higher is known (Patent Document 2).

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-35022

[0009] Patent Document 2: Japanese Patent Application No. 2021-510754 Summary of the invention

[0010] Problem that the invention aims to solve

[0011] However, in the above-mentioned recycling method under strong alkaline conditions, the polymer fibers may be damaged due to the strong alkaline treatment, so it cannot be said that the recyclability is sufficiently high. In addition, in order to set the strong alkaline conditions, chemical reagents such as sodium hydroxide are used, so complicated post-treatment such as waste liquid treatment is required, and there is also concern about environmental load.

[0012] The present invention has been accomplished in view of the foregoing circumstances, and an object thereof is to provide a recycling method for simply recovering a highly recyclable polymer material from a solid mixture containing a polyester and a polymer material by a process with less environmental load.

[0013] Means for Solving the Problems

[0014] The inventors of the present invention conducted intensive studies to solve the foregoing problems, and as a result, found that when a solid mixture of a polyester and a polymer material is heated in the presence of water, even at a temperature lower than the melting point in air, the foregoing polyester melts and separates from the foregoing solid mixture together with water, and the foregoing polymer material can be recovered in the form of a solid, and according to this method, a polymer material with high recyclability can be obtained with less environmental load and simply, thereby completing the present invention.

[0015] That is, the present invention is specified by the following constituent conditions.

[0016] [1] A recycling method, which is a recycling method of a polymer material for heating a solid mixture of a polyester and a polymer material in the presence of water, separating the foregoing polyester and water together from the foregoing solid mixture by melting, and recovering the foregoing polymer material in the form of a solid.

[0017] When the melting point of the foregoing polyester in air is set as Tm,

[0018] the foregoing polymer material has a melting point higher than Tm, or does not have a melting point and is a solid at Tm.

[0019] The foregoing heating is performed at a temperature of (Tm - 70)°C or higher and (Tm - 10)°C or lower.

[0020] [2] The recycling method according to [1], wherein the pressure during heating is the saturated water vapor pressure at the heating temperature.

[0021] [3] The recycling method according to [1] or [2], wherein the foregoing polyester is a polyester fiber, the foregoing polymer material is at least one polymer fiber selected from synthetic fibers, regenerated fibers, semi-synthetic fibers, inorganic fibers, and natural fibers, and the foregoing solid mixture is a fiber product composed of a polyester fiber and a polymer fiber.

[0022] [4] The recycling method according to [3], wherein the foregoing polymer material is at least one natural fiber selected from cotton fiber, wool fiber, and silk fiber.

[0023] [5] The recycling method according to [3] or [4], wherein the equivalent circle diameter of the cross section of the polyester fiber is 1 to 100 μm, and the equivalent circle diameter of the cross section of the polymer fiber is 1 to 100 μm.

[0024] [6] The recycling method according to any one of [3] to [5], which is a recycling method for recovering the polymer fiber from the fiber product.

[0025] The aforementioned fiber product is a knitted fabric, a woven fabric or a nonwoven fabric.

[0026] The polymer fiber maintains the form when used as a fiber product.

[0027] [7] A recycled product comprising, in at least a portion of its raw materials, a polymer material obtained by the recycling method described in any one of [3] to [6],

[0028] The aforementioned polymer material is cotton fiber,

[0029] The aforementioned recycled products are recycled cotton products.

[0030] [8] A method for recycling polyester, comprising recovering the polyester separated from the solid mixture in the recycling method according to any one of [1] to [6].

[0031] [9] A recycled polyester product comprising, in at least a part of its raw materials, the polyester obtained by the recycling method according to [8].

[0032]

[10] A fiber product comprising a polymer fiber having a melting point exceeding 255°C or being solid at 255°C and having no melting point, wherein the polymer fiber contains a polyester having a weight average molecular weight of not less than 1,000 and not more than 10,000 in an amount of not more than 5% by mass in the polymer fiber.

[0033] Effects of the Invention

[0034] According to the present invention, a recycling method for recovering a highly recyclable polymer material from a solid mixture containing polyester and a polymer material can be provided by a process with little environmental load. In addition, according to the present invention, a fiber product made of polymer fibers as a recycled product can also be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 These are microscope photographs of the knitted fabric in Example 3 before and after the treatment. DETAILED DESCRIPTION

[0036] <<Recycling Methods for Polymer Materials>>

[0037] The polymer material recycling method of the present invention has the following characteristics: a solid mixture of polyester and polymer material is heated under specific conditions in the presence of water, the polyester is separated from the solid mixture together with water by melting, and the polymer material is recovered as a solid. According to the polymer material recycling method of the present invention, a polymer material with high recyclability can be obtained simply with little environmental load. In addition, the polyester separated in the polymer material recycling method of the present invention is separated from the solid mixture by melting, so it is not completely decomposed and can be recovered and recycled usefully.

[0038] <Polyester>

[0039] The polyester contained in the solid mixture is not particularly limited, as long as it is a polymer compound having an ester bond in the main chain obtained by polycondensation of a dicarboxylic acid component and a diol component. Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, and derivatives thereof. Examples of the diol component include ethylene glycol, 1,3-propylene glycol, butanediol, polyethylene glycol, diethylene glycol, neopentyl glycol, and derivatives thereof.

[0040] As the polyester, a polyester obtained by using an aromatic dicarboxylic acid as a dicarboxylic acid component is preferred. As the polyester, specifically, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene 2,6-naphthalate are preferred, polyethylene terephthalate and polyethylene 2,6-naphthalate are more preferred, and polyethylene terephthalate is further preferred.

[0041] The polyester may be a homopolyester or a copolyester. In addition, the polyester may contain a third component other than the dicarboxylic acid component and the diol component as a copolymer component. As the polyester, specifically, it is preferred to use polyethylene terephthalate as the main component, and the content of polyethylene terephthalate in the polyester is more preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, and may also be 100% by mass. That is, the content of polyethylene terephthalate in the polyester is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, and more preferably 90 to 100% by mass.

[0042] The melting point (hereinafter also referred to as Tm) of the polyester in air (i.e., in an atmospheric atmosphere) is preferably 200 to 280°C, more preferably 210°C or higher, further preferably 220°C or higher, further preferably 240°C or higher, and more preferably 275°C or lower, further preferably 270°C or lower. That is, Tm is more preferably 210 to 275°C, further preferably 220 to 275°C, further preferably 240 to 270°C.

[0043] The shape of the polyester in the solid mixture is not particularly limited as long as it is a solid, and examples thereof include granular, fibrous, film-like, sheet-like, and irregular shapes. The polyester is preferably polyester fiber.

[0044] The polyester fiber may be a short fiber or a long fiber, and may or may not have a curl. In addition, the polyester fiber may be a solid fiber, a hollow fiber, or a core-sheath type, eccentric type, or other composite fiber. In the case of a composite fiber with a polymer compound other than polyester, the content of the polymer compound other than polyester in the fiber is preferably 40% by mass or less, more preferably 30% by mass or less, further preferably 20% by mass or less, and further preferably 10% by mass or less, and as a lower limit, it can be as long as it exceeds 0% by mass, and it can also be 0.01% by mass. That is, when the polyester fiber is a composite fiber with a polymer compound other than polyester, the content of the aforementioned polymer compound in the fiber is preferably 0.01 to 40% by mass, more preferably 0.01 to 30% by mass, further preferably 0.01 to 20% by mass, and further preferably 0.01 to 10% by mass.

[0045] The cross-sectional shape of the polyester fiber is not particularly limited, and may be circular, polygonal, or irregular. The equivalent circular diameter of the cross section of the polyester fiber is preferably 1 to 100 μm, more preferably 5 μm or more, and further preferably 10 μm or more. In addition, it is more preferably 90 μm or less, further preferably 80 μm or less, and further preferably 70 μm or less. That is, the equivalent circular diameter of the cross section of the polyester fiber is more preferably 5 to 90 μm, further preferably 5 to 80 μm, and further preferably 10 to 70 μm. By setting the above range, it is easy to melt and separate the polyester from the solid mixture. It should be noted that the equivalent circular diameter of the cross section of the fiber can be obtained, for example, by visual measurement using an electron microscope, or by calculation based on the fineness and density of the raw materials constituting the fiber.

[0046] <Polymer Materials>

[0047] The polymer material is not particularly limited as long as it has a melting point in air higher than the aforementioned Tm, or has no melting point and is solid at Tm, and the polymer or polymer material having such characteristics will be referred to as polymer A or polymer material A, respectively, hereinafter. By making the polymer material A have such a characteristic related to the melting point, the polymer material A will not melt even if the polyester is melted, and the polymer material A can be recovered as a solid from the solid mixture.

[0048] When the polymer material A has a melting point, as the melting point, it is preferably (Tm + 5) °C or higher, more preferably (Tm + 10) °C or higher. In addition, the upper limit is not particularly limited and can be (Tm + 20) °C or lower. That is, when the polymer material A has a melting point, the melting point is preferably (Tm + 5) to (Tm + 20) °C, more preferably (Tm + 10) to (Tm + 20) °C. According to the recycling method of the polymer material of the present invention, even if the melting point difference between the polyester and the polymer material A is small, since the polyester melts at a temperature lower than the melting point, the polymer material A can be recovered in the form of a solid.

[0049] Examples of the polymer material A include materials composed of a polymer A compound having a molecular weight exceeding 10,000, and it can be any one of a synthetic material, a recycled material, a semi-synthetic material, and a natural material. As the synthetic material, specifically, resins other than the aforementioned polyesters such as polyolefins, polystyrenes, polyamides, polyimides, polyamide-imides, polyvinyl alcohols, polyurethanes, polyvinyl acetates, polyvinyl chlorides, polyvinylidene chlorides, polycarbonates, acrylic resins, and phenolic resins can be cited; rubbers such as silicone rubbers and fluororubbers; and their derivatives, modified products, copolymers, and mixtures. As the recycled material, rayon, cuprammonium fiber, etc. can be cited. As the semi-synthetic material, acetate, Promix, etc. can be cited. As the natural material, plant fibers such as cotton and hemp can be cited; silk; animal hairs such as wool, cashmere, angora, mohair, alpaca, and camel hair; polysaccharides such as cellulose, chitin, and chitosan; and proteins such as sericin, fibroin, keratin, and casein can be cited. As the polymer material A, a natural material is preferred. Synthetic materials, recycled materials, and semi-synthetic materials are easily reconstituted by polymerization or the like after decomposition. In contrast, if natural materials such as cotton and animal hair decompose, it is difficult to regenerate them into their original composition. However, according to the method of the present invention, the decomposition of the polymer material A can be suppressed, which is beneficial to the recycling of the polymer material A.

[0050] The shape of the polymer material A in the solid mixture is not particularly limited as long as it is a solid, and examples thereof include granular, fibrous, film-like, sheet-like, and irregular shapes, and a fibrous shape is preferred. As the fibrous polymer material A (polymer A fiber), natural fibers such as plant fibers and animal fibers are preferred; synthetic fibers such as acrylic fibers, polyurethane fibers, fluorine fibers, phenolic fibers, polyamide fibers, polyimide fibers, and polyamide-imide fibers are preferred; recycled fibers such as rayon fibers, lyocell fibers, and cuprammonium fibers are preferred; semi-synthetic fibers such as acetate fibers, triacetate fibers, and Promix fibers are preferred; and inorganic fibers such as glass fibers are preferred. More preferably, natural fibers are preferred, and further preferably, cotton fibers, silk fibers, and wool fibers are preferred. Even more preferably, cotton fibers are preferred.

[0051] The polymer A fiber can be a staple fiber or a filament fiber, and can have crimp or no crimp. In addition, the polymer A fiber can be a solid fiber, a hollow fiber, or a composite fiber such as a core-sheath type or an eccentric type.

[0052] The cross-sectional shape of the polymer A fiber is not particularly limited and can be circular, polygonal, or irregular. As the equivalent circle diameter of the cross-section of the polymer A fiber, it is preferably 1 to 100 μm, more preferably 5 μm or more, further preferably 10 μm or more. In addition, it is more preferably 90 μm or less, further preferably 80 μm or less, and even more preferably 70 μm or less. That is, the equivalent circle diameter of the cross-section of the polymer A fiber is more preferably 5 to 90 μm, further preferably 5 to 80 μm, and even more preferably 10 to 70 μm. By setting it within the aforementioned range, it is easy to recover the polymer A fiber in the form of a solid from the solid mixture.

[0053] <Solid mixture>

[0054] As the solid mixture, there is no particular limitation as long as it is a solid containing the aforementioned polyester and the aforementioned polymer material A. It is preferably a substance highly combined with polyester and polymer material A, such as a fiber-reinforced material formed by combining polymer A fibers and a polyester resin, a composite material such as a fiber product formed by combining polyester fibers and polymer A fibers, and more preferably a fiber product. In the present invention, since the polyester can be melted and removed at a temperature lower than the melting point in air, even for a composite material, the polymer material A can be simply recovered with less environmental load.

[0055] In the aforementioned fiber product, a yarn containing polyester fibers and no polymer A fibers (hereinafter also simply referred to as polyester yarn), a yarn containing polymer A fibers and no polyester fibers (hereinafter also simply referred to as polymer yarn), a yarn containing polyester fibers and polymer A fibers (hereinafter also referred to as composite yarn), etc. can be used. The polyester yarn can be either a staple fiber yarn or a filament yarn. The polymer yarn can be either a staple fiber yarn or a filament yarn, but when the polymer yarn is composed of natural fibers other than silk fibers, a staple fiber yarn is preferred.

[0056] The polyester yarn can be a single yarn or a ply yarn with a yarn other than the polymer yarn. In addition, the polymer yarn can be a single yarn or a ply yarn with a yarn other than the polyester yarn.

[0057] The aforementioned composite yarn can, for example, be a blended yarn composed of polyester staple fibers and polymer A staple fibers, or a multifilament or blended woven yarn composed of polyester filament fibers and polymer A filament fibers, or a core-spun yarn composed of polyester staple fibers and polymer A elastic filament fibers (such as polyurethane elastic fibers). Further, the composite yarn can be a ply yarn composed of a polyester yarn (which can be either a staple fiber yarn or a filament yarn) and a polymer yarn (which can be either a staple fiber yarn or a filament yarn, preferably a staple fiber yarn). As the ply yarn, examples include twist yarns (such as two-ply yarns, three-ply yarns, four-ply yarns, etc.), covering yarns, and combined yarns. From the viewpoint of effectively utilizing polymer A staple fibers, blended yarns and ply yarns are preferred, and blended yarns and twist yarns are more preferred.

[0058] The fineness of the composite yarn is, for example, 0.1 to 5000 tex, preferably 1 to 3000 tex, and more preferably 3 to 1500 tex. Regardless of the fineness of the composite yarn, polyester fibers can be removed with excellent removal rates.

[0059] When the fiber product is composed of a polyester yarn and a polymer yarn, it may not contain a composite yarn of polyester fiber and polymer A fiber. However, the fiber product is preferably composed of a composite yarn of polyester fiber and polymer A fiber, and more preferably, 50% by mass or more of all the yarns constituting the fiber product is the composite yarn. Even when polyester fibers and polymer A fibers are combined as complexly as in the composite yarn, in the present invention, polyester can be simply separated with a small environmental load, and thus polymer material A can be simply recovered. In addition, since the aforementioned polyester is separated by melting, it is not completely decomposed. Therefore, the separated polyester can also be recovered and usefully recycled.

[0060] Examples of the fiber product include knitted fabrics, woven fabrics (woven cloth), non-woven fabrics, etc., and knitted fabrics and woven fabrics are preferred. In addition, the fiber product can also have a laminated structure having two or more layers selected from knitted fabrics, woven fabrics, and non-woven fabrics in the layer direction or the surface direction.

[0061] The knitted fabric can be composed of one yarn or two or more yarns. In the case of being composed of one yarn, it is preferably composed of a composite yarn containing polyester fiber and polymer A fiber. When composed of two or more yarns, polyester yarns, polymer yarns, and composite yarns can be appropriately used.

[0062] The knitting structure is not particularly limited and can be either weft knitting or warp knitting. Weft knitting includes plain stitch (knitting stitch, plain stitch (Japanese: tenjikuami)), rib stitch (rib stitch (Japanese: azamiami)), purl stitch, double rib stitch, etc. Warp knitting includes single-bar tricot, single-bar raschel, double-bar raschel-tricot, tricot, and warp raschel stitch.

[0063] The woven fabric may be a blended woven fabric (especially a woven fabric using a blended yarn containing polyester fiber and polymer A fiber), an interwoven woven fabric (especially an interwoven woven fabric using a twisted yarn composed of polyester yarn and polymer yarn; an interwoven woven fabric using one of the polyester yarn and the polymer yarn as the warp or weft yarn and the other as the weft or warp yarn; an interwoven woven fabric using one of the polyester yarn and the polymer yarn as the warp and weft yarn and partially blending the other), etc.

[0064] There is no particular restriction on the structure of woven fabrics, and examples include plain weave, twill weave, satin weave, and modified weaves formed by appropriately changing or combining these three basic weaves (single special weaves such as honeycomb weave, yin-yang lattice weave, jacquard weave, etc.; multi-layer weaves such as warp and weft double weave, concave-convex weave, etc.), pile fabric, weft knitted pile fabric, warp knitted pile fabric, towel fabric, gauze fabric, etc.

[0065] Examples of the nonwoven fabric include air-through nonwoven fabric, spunbond nonwoven fabric, spunlace nonwoven fabric, meltblown nonwoven fabric, resin-bonded nonwoven fabric, and needle-punched nonwoven fabric.

[0066] In the solid mixture, the content of the polyester is preferably 1 to 100 parts by mass, more preferably 1.5 parts by mass or more, further preferably 3.0 parts by mass or more, more preferably 80 parts by mass or less, further preferably 70 parts by mass or less, and further preferably 60 parts by mass or less, relative to 100 parts by mass of the polymer material A. That is, the content of the polyester is more preferably 1.5 to 80 parts by mass, further preferably 1.5 to 70 parts by mass, and further preferably 3.0 to 60 parts by mass relative to 100 parts by mass of the polymer material A. By setting the above range, the polyester is melted and separated from the solid mixture, and the polymer material A is easily recovered in the form of a solid.

[0067] In the solid mixture, the content of the polymer material A is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 40% by mass or more, further preferably 50% by mass or more, further preferably 60% by mass or more, and less than 100% by mass, preferably 98% by mass or less, and more preferably 95% by mass or less. That is, the content of the polymer material A is preferably 20 to 98% by mass, more preferably 30 to 98% by mass, further preferably 40 to 98% by mass, further preferably 50 to 98% by mass, and further preferably 60 to 95% by mass, relative to the total amount of the solid mixture. By setting the above range, the polyester is melted and separated from the solid mixture, and the polymer material A is easily recovered in the form of a solid.

[0068] The solid mixture may contain other components besides polyester and polymer material A. Examples of other components include polymer materials (low melting point polymer materials) having a melting point in air equal to or lower than that of polyester, pigments, dyes, stabilizers, tackifiers, plasticizers, anti-degradation agents, fillers, ultraviolet absorbers, antioxidants, antibacterial agents, antistatic agents, lubricants, etc. Other components may be only one kind or may contain two or more kinds.

[0069] The aforementioned low melting point polymer material is melted and removed together with the polyester, so it does not hinder the recycling of the polymer material A. On the other hand, it is preferably less because it contaminates the recycled polyester. The content of the low melting point polymer material is, for example, 80 parts by mass or less, preferably 50 parts by mass or less, more preferably 20 parts by mass or less, and most preferably 0 parts by mass relative to 100 parts by mass of the polyester. That is, the content of the low melting point polymer material is preferably 0 to 80 parts by mass, more preferably 0 to 50 parts by mass, further preferably 0 to 20 parts by mass, and most preferably 0 parts by mass relative to 100 parts by mass of the polyester.

[0070] The total content of other components other than the low melting point polymer material in the solid mixture is preferably 10% by mass or less, more preferably 8% by mass or less, further preferably 5% by mass or less, and further preferably 2% by mass or less. That is, the total content of other components other than the low melting point polymer material is preferably 0 to 10% by mass in the solid mixture, more preferably 0 to 8% by mass, further preferably 0 to 5% by mass, and further preferably 0 to 2% by mass.

[0071] <Handling of Solid Mixture>

[0072] The solid mixture is heated at a temperature of (Tm-70)°C or higher and (Tm-10)°C or lower in the presence of water, the polyester is separated from the solid mixture together with water by melting, and the polymer material A is recovered as a solid. It should be noted that the solid refers to a state in which the shape before heating is maintained, unlike the decomposition product.

[0073] The polymer material recycling method of the present invention can be processed by placing the solid mixture into a treatment tank together with water, or by adding steam using a boiler such as a high-pressure boiler after placing the solid mixture into the treatment tank. Regardless of which method is used, it is sufficient to adjust the temperature to a predetermined value in the presence of water.

[0074] The polymer material recycling method of the present invention may include a washing step of washing the solid mixture before the heat treatment. By washing, the aforementioned other components other than the polyester and polymer material A contained in the solid mixture can be reduced. As the washing liquid, water, an organic solvent, etc. can be used. As the aforementioned organic solvent, there is no particular limitation and it can be appropriately selected according to the component to be reduced. It is preferably a non-polar solvent, and hydrocarbon solvents, etc. can be listed. Only one type of washing liquid can be used, or two or more types can be used in combination.

[0075] As a cleaning method, the solid mixture may be immersed in a cleaning liquid, or the cleaning liquid may be sprayed onto the solid mixture. When the solid mixture is immersed in a cleaning liquid, it may be stirred during the immersion. As the temperature of the cleaning process, for example, 5 to 60° C. is preferred, and 5 to 40° C. is more preferred. When cleaning is performed by immersion, the solid mixture and the cleaning liquid may be separated by a known solid-liquid separation method.

[0076] The washed solid mixture may be directly subjected to the aforementioned heat treatment, or may be subjected to the aforementioned heat treatment after being dried using a known drying apparatus such as a hot air dryer, for example, at 40 to 80° C. for 1 to 60 minutes.

[0077] The water used in the heat treatment is not particularly limited, and for example, industrial water, tap water, etc. can be used. If necessary, distilled water, ion exchange water, etc. can be used. The amount of water used in the heat treatment is not particularly limited, and for example, it is preferably 30% or more of the volume of water relative to the volume of the reaction vessel (treatment tank), more preferably 45% or more, and further preferably 60% or more. The preferred amount of water varies depending on the volume of the reaction vessel used, but it is particularly preferably an amount that reaches the saturated water vapor pressure during the heat treatment.

[0078] The heat treatment is preferably carried out under the condition of pH 5.8 to 8.6, more preferably pH 6.0 to 8.4. The polymer material recycling method of the present invention is not carried out under strongly acidic or strongly alkaline conditions, but is treated within the aforementioned pH range, so there is no need for post-treatment such as neutralization of the waste liquid, and it is a simple method with low environmental load.

[0079] The water used in the heat treatment may contain components other than water, such as solvents, surfactants, organic components, inorganic components, acids, etc., as long as the pH is within the aforementioned range, but preferably does not contain these components other than water. The content of components other than water in the treatment liquid is preferably 10% by mass or less, more preferably 5% by mass or less, and further preferably 3% by mass or less. That is, the content of components other than water in the treatment liquid is preferably 0 to 10% by mass, more preferably 0 to 5% by mass, and further preferably 0 to 3% by mass.

[0080] The temperature of the heat treatment is (Tm-70)°C or higher and (Tm-10)°C or lower, preferably (Tm-60)°C or higher, more preferably (Tm-50)°C or higher, and further preferably (Tm-30)°C or higher, and further preferably (Tm-15)°C or lower, and further preferably (Tm-20)°C or lower. That is, the temperature of the heat treatment is preferably (Tm-60) to (Tm-15)°C, more preferably (Tm-50) to (Tm-15)°C, and further preferably (Tm-30) to (Tm-20)°C. In the above temperature range, the melting of the polyester proceeds faster than the decomposition of the polymer material A, so the polymer material A can be recovered from the solid mixture as a solid material having a shape before the treatment.

[0081] It should be noted that, since the present invention performs the heat treatment in the presence of water, the polyester can be effectively melted even within the aforementioned temperature range of the heat treatment. When the heat treatment is performed in an air atmosphere, the polyester does not melt within the aforementioned heating temperature range, and therefore the polyester cannot be removed from the solid mixture. In addition, when the polymer material A is a natural fiber, if the heat treatment is performed in an air atmosphere, the natural fiber may change color, but if the heat treatment is performed in the presence of water, the change of color of the natural fiber can be suppressed, and the natural fiber with better recyclability can be recovered.

[0082] As the heating means, known means can be used, and examples thereof include a method of obtaining high-pressure steam from a boiler or the like, a method of using a heater, etc.

[0083] The heat treatment is preferably carried out under pressure, and more preferably under pressure at the saturated water vapor pressure at the heating temperature. For example, when the polyester contained in the solid mixture is polyethylene terephthalate (PET) having a melting point of 255°C, the temperature for the heat treatment is 185°C or higher and 245°C or lower, and the saturated water vapor pressure calculated by the Wagner formula is 1.124561 MPa at 185°C and 3.65425 MPa at 245°C. Therefore, when the polyester contained in the solid mixture is PET, the pressure during the heat treatment is preferably 1.124561 MPa or higher and 3.65425 MPa or lower.

[0084] The time of the heat treatment may be appropriately selected according to the combination of the polyester and the polymer material A, and is preferably 3 to 400 minutes, more preferably 5 to 350 minutes, and further preferably 5 to 100 minutes. By setting the heat treatment time within the above range, the decomposition of the polymer material A can be suppressed, and the polyester can be fully melted, so that the polyester can be separated from the solid mixture and the polymer material A can be recovered as a solid.

[0085] It should be noted that the heating time from (Tm-100)°C to the heat treatment temperature is preferably 60 minutes or less, more preferably 30 minutes or less. In addition, the time until (Tm-100)°C is reached after the heat treatment is preferably 60 minutes or less, more preferably 30 minutes or less. After the heat treatment, the cooling can be carried out by natural cooling or by using a known cooling device.

[0086] For example, the heating temperature and heating time in the heat treatment of a solid mixture containing polyester fibers as polyester and natural fibers as polymer material A are preferably any one of the following (1) to (6), more preferably any one of the following (2) to (5), and even more preferably the following (4).

[0087] (1) The heating temperature is 190°C to 200°C, and the heating time is 10 minutes to 350 minutes.

[0088] (2) The heating temperature is more than 200°C and less than 210°C, and the heating time is more than 10 minutes and less than 180 minutes.

[0089] (3) The heating temperature is higher than 210°C and lower than 220°C, and the heating time is higher than 5 minutes and lower than 100 minutes.

[0090] (4) The heating temperature is higher than 220°C and lower than 230°C, and the heating time is higher than 5 minutes and lower than 50 minutes.

[0091] (5) The heating temperature is higher than 230°C and lower than 240°C, and the heating time is higher than 5 minutes and lower than 30 minutes.

[0092] (6) The heating temperature is higher than 240° C. and lower than 245° C., and the heating time is higher than 5 minutes and lower than 20 minutes.

[0093] The polyester melted by the heat treatment is separated from the solid mixture by the convection of water caused by the heat. In addition, the separation of the molten polyester from the solid mixture can be promoted by applying an external force such as stirring during the heat treatment.

[0094] After the heat treatment, the solids of polymer material A are recovered. As a recovery method, there is no particular limitation, for example, since polymer material A maintains a form, it can be a method of taking it out only from a treatment solution containing polyester, or known solid-liquid separation treatments such as filtration can be performed. It should be noted that during the period when the treatment solution is cooled to ambient temperature after the heat treatment, the molten polyester solidifies. Therefore, in the case of recovering polymer material A from the treatment solution by filtration, the pore size of the filter material is preferably a size that polymer material A cannot pass through and the solidified polyester can pass through. As the pore size of the filter material, for example, it is preferably less than 50 mm, more preferably less than 30 mm, and in addition, it is preferably more than 1 mm, more preferably more than 5 mm. That is, as the pore size of the filter material, it is preferably 1 to 50 mm, more preferably 5 to 30 mm.

[0095] The recovered polymer material A can be subjected to post-treatment such as washing with a washing liquid such as water or an organic solvent, and drying. By having a washing step, the amount of coagulated polyester remaining in the polymer material A can be reduced. As the aforementioned organic solvent, there is no particular limitation, and a non-polar solvent is preferred, and examples thereof include hydrocarbon solvents. The washing liquid can be used alone or in combination with two or more. As a washing method, the polymer material A can be immersed in the washing liquid, or the washing liquid can be sprayed onto the polymer material A. When the polymer material A is immersed in the washing liquid, stirring can be performed during the immersion. As the temperature of the washing step, for example, 5 to 60°C is preferred, and 5 to 40°C is more preferred. When washing by immersion, the polymer material A can be separated from the washing liquid by a known solid-liquid separation method. As drying treatment conditions, there are no particular limitations, and it is preferred to use a known drying device such as an infrared heater, an oven, and a hot air dryer, for example, drying at 40 to 80°C for 1 to 60 minutes.

[0096] The polymer material A obtained by the polymer material recycling method of the present invention suppresses degradation such as decomposition. Moreover, the polymer material A suppresses degradation such as decomposition, so it maintains the shape before treatment and has excellent recyclability. In particular, when the solid mixture is a fiber product, it is preferred that the polymer material A maintains the shape as a fiber or a fiber product. It should be noted that whether the shape is maintained can be confirmed by observation using an electron microscope, etc.

[0097] The polymer material A obtained by the polymer material recycling method of the present invention preferably does not contain polyester, but may contain polyester, and the content of polyester in the polymer material A is preferably 35% by mass or less, more preferably 20% by mass or less, further preferably 10% by mass or less, further preferably 5% by mass or less, further preferably 3% by mass or less. That is, the content of polyester in the polymer material A obtained by the recycling method is preferably 0 to 35% by mass, more preferably 0 to 20% by mass, further preferably 0 to 10% by mass, further preferably 0 to 5% by mass, further preferably 0 to 3% by mass. The content of polyester can be measured, for example, by the method described in the Examples described below.

[0098] The residual rate of polyester in the polymer material A obtained by the polymer material recycling method of the present invention is calculated by the following formula.

[0099] Residual rate (mass %) = (polyester content in the polymer material after treatment / polyester content in the solid mixture before treatment) × 100

[0100] The aforementioned residual rate is preferably 99% by mass or less, more preferably 50% by mass or less, further preferably 25% by mass or less, further preferably 10% by mass or less, further preferably 5% by mass or less, further preferably 3% by mass or less, and particularly preferably 1% by mass or less. That is, the aforementioned residual rate is preferably 0 to 99% by mass, more preferably 0 to 50% by mass, further preferably 0 to 25% by mass, further preferably 0 to 10% by mass, further preferably 0 to 5% by mass, further preferably 0 to 3% by mass, and particularly preferably 0 to 1% by mass.

[0101] The recovered polymer material A can be reused without further treatment such as polymerization, so it has high recyclability. The use of the recovered polymer material A is not particularly limited, for example, it can be used for material recycling by utilizing its shape retention, or it can be depolymerized and used as a monomer for chemical recycling.

[0102] The polyester melted by the heat treatment may be cooled to recover the polyester as a solid from the treatment liquid. The polyester may be recovered, for example, by filtering the treatment liquid after the recovery of the polymer material A, or by a known solid-liquid separation treatment such as centrifugation.

[0103] The aforementioned cooling can be performed to a temperature at which the polyester solidifies, for example, preferably cooled to below 90°C, more preferably below 60°C, further preferably below 40°C, and can also be above 0°C. That is, as a cooling temperature, it is preferably 0 to 90°C, more preferably 0 to 60°C, and further preferably 0 to 40°C. In addition, as a cooling method, there is no particular limitation, and natural cooling can be performed, or a known cooling device can be used. In addition, in the case of recovering the solidified polyester by filtration, the pore size of the filter material can be set to a size that the solidified polyester cannot pass through, for example, preferably below 0.1mm, more preferably below 50μm, and further preferably above 0.1μm. That is, the pore size of the filter material is preferably 0.1μm to 0.1mm, and more preferably 0.1 to 50μm.

[0104] The weight average molecular weight of the recovered polyester is preferably 1000 or more, more preferably 1100 or more, and even more preferably 1200 or more, and is preferably 10000 or less, more preferably 9500 or less, and even more preferably 9000 or less. That is, the weight average molecular weight of the recovered polyester is preferably 1000 to 10000, more preferably 1100 to 9500, and even more preferably 1200 to 9000.

[0105] Since the polyester is separated from the solid mixture by melting, the recovered polyester is not completely decomposed, and the weight average molecular weight can be within the above range. The weight average molecular weight of the polyester can be determined by gel permeation chromatography (GPC).

[0106] The use of the recovered polyester is not particularly limited, and for example, the recovered polyester can be depolymerized and used as a monomer for chemical recycling.

[0107] In chemical recycling, by performing repolymerization or copolymerization, or both, a recycled polyester product containing recovered polyester in at least a portion of the raw materials can be formed.

[0108] <Recycled polymer fibers>

[0109] In the method of the present invention, when polymer A fibers are recovered from a fiber product as a solid mixture (hereinafter, polymer A fibers obtained by the method of the present invention are also referred to as recycled polymer fibers), it is preferred to maintain the form of the recycled polymer fibers when used as a fiber product. For example, when the fiber product is a knitted fabric, the recycled polymer fibers preferably maintain the form of a loop.

[0110] The recycled polymer fiber is preferably a fiber having a melting point exceeding 255° C. or a fiber that is solid at a temperature of 255° C. and has no melting point, and is particularly preferably a cotton fiber.

[0111] The recycled polymer fiber may contain polyester derived from the solid mixture, and the content of the polyester is preferably 5% by mass or less. In addition, the weight average molecular weight of the contained polyester is preferably 1,000 or more and 10,000 or less.

[0112] Recycled polymer fibers can be reused as single fibers, or blended with other fibers to make blended yarns, or used as cushioning fillers, etc.

[0113] The fiber products made of recycled polymer fibers are fibers in which degradation of the recycled polymer fibers is suppressed, and thus can be satisfactory as products in terms of durability and appearance.

[0114] For example, when the recycled polymer fiber is cotton fiber, it is possible to produce a recycled cotton product such as a knitted fabric, a woven fabric, or a nonwoven fabric containing the cotton fiber in at least a part of the raw material.

[0115] This application claims the benefit of priority based on Japanese Patent Application No. 2022-121193 filed on July 29, 2022. The entire contents of the specification of Japanese Patent Application No. 2022-121193 filed on July 29, 2022 are incorporated herein by reference.

[0116] Example

[0117] The present invention is described in more detail below with reference to the following embodiments, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the aforementioned and subsequent purposes, all of which are included in the technical scope of the present invention.

[0118] <Equivalent circle diameter of fiber cross section>

[0119] The equivalent circle diameter was measured by taking a magnified photograph (1000 times) of a cross section of the fiber using a scanning electron microscope (S-4800, manufactured by Hitachi High-Technologies Corporation).

[0120] <Polyester content>

[0121] The polyester content in the sample was evaluated using a 600 MHz nuclear magnetic resonance spectrometer (AVANCE NEO 600, manufactured by BRUKER). The measurement conditions were an acquisition time of 4 seconds, a waiting time of 5 seconds, and a solvent of deuterated chloroform / hexafluoroisopropanol-d=90 / 10 in volume ratio.

[0122] The quantitative method is as follows. First, a weighed sample and 2 mg of dimethyl isophthalate (DMI) as a quantitative standard sample are added to a solvent and the measurement is performed. The peaks of the components of the polyester and the integral values ​​of the peaks of water and DMI contained in the sample are obtained from the spectrum, and the relative amount of substance and the relative mass (Wa) are calculated from the proton amount of the peak. For example, in the case of polyethylene terephthalate, when the peak of deuterated chloroform is set to 7.28 ppm, the peaks of each substance are 8.08 ppm for terephthalic acid and 4 for proton amount, 4.70 ppm for ethylene glycol and 4 for proton amount, and 3.92 ppm for diethylene glycol and 4 for proton amount, and the relative mass (Wa) is calculated from the respective integral values.

[0123] Peak integral value / proton quantity of the peak of the substance = relative mass

[0124] Relative mass × molecular weight = relative mass (Wa)

[0125] Regarding polyester, the total relative mass of each component is defined as Wa[polyester]. The mass of polyester (Wb[polyester]) and the mass of water (Wb[water]) contained in the sample are calculated from the ratio of Wa[DMI] of DMI to the actually added mass Wb[DMI].

[0126] Wa[X]×Wb[DMI] / Wa[DMI]=Wb[X](mg)

[0127] (In the above formula, X is polyester or water.)

[0128] The content (mass %) of the polyester in the sample was evaluated based on the value obtained by subtracting the mass of water from the mass of the sample to be evaluated and the mass of the polyester.

[0129] Polyester content (mass %) = Wb[polyester] / (Wb[sample]-Wb[water])×100

[0130] <Residual Polyester in Sample>

[0131] Calculate it through the following formula.

[0132] Residual rate (mass %) = (polyester content in the polymer material after treatment / polyester content in the solid mixture before treatment) × 100

[0133] <Morphology maintenance of polymer materials>

[0134] The sample in the treatment tank after the heat treatment can be classified into any two or more states of a cloth-like solid with meshes that can be confirmed by a microscope, a powdery solid, and a liquid. According to the state of the cloth-like solid sample, the extent of damage to the sample caused by the treatment is determined as follows.

[0135] (Evaluation of fabric status)

[0136] ○: Can be removed with tweezers, the tear or hole is less than 10% of the cloth area

[0137] △: The cloth can be removed with tweezers but is torn, or the cloth has more than 10% of its area torn or has holes.

[0138] ×: Cannot be removed with tweezers, or no cloth-like solids are present

[0139] (Example 1)

[0140] A knitted fabric is obtained by interweaving 66% by mass of yarn composed of polyethylene terephthalate fibers and 34% by mass of spun yarn composed of cotton fibers. The polyethylene terephthalate fibers have a cross-sectional equivalent circle diameter of 20 μm and a melting point in air of 255° C. The cotton fibers have a cross-sectional equivalent circle diameter of 20 μm, have no melting point, and are solid at 255° C.

[0141] The knitted fabric and 300 mL of water were placed in a reaction vessel with an internal volume of 500 mL and heated to 200° C. The pressure at this time was 1.6 MPa. After pressurization, the knitted fabric was heated in the presence of water for 10 minutes. Then, the pressure was reduced to atmospheric pressure, and the sample (polymer material) was recovered and various evaluations were performed. The evaluation results are shown in Table 1.

[0142] (Examples 2 to 6, Comparative Examples 1 to 2)

[0143] The knitted fabric obtained in Example 1 was used, and the heat treatment was performed in the same manner as in Example 1 except that the treatment conditions (temperature, pressure, time) were changed to those shown in Table 1, and various evaluations were performed using the recovered samples. The evaluation results are shown in Table 1. In addition, microscopic photographs of the knitted fabric in Example 3 before and after the treatment are shown in Table 1. Figure 1 .

[0144] [Table 1]

[0145]

[0146] As shown in Table 1, the polyester content of the polymer materials recovered in Examples 1 to 6 was reduced compared to the knitted fabric before treatment, and the polymer materials were not decomposed and the shape of the knitted fabric was maintained to a certain extent. In contrast, since the temperature during the heating treatment in Comparative Example 1 was low, the shape of the knitted fabric was maintained, but no reduction in polyester was observed. Since the temperature during the heating treatment in Comparative Example 2 was high, the polymer material was decomposed and could not be recovered as a cloth-like solid.

Claims

1. A recycling method for polymer materials, comprising heating a solid mixture of polyester and a polymer material in the presence of water, separating the polyester together with water from the solid mixture by melting, and recovering the polymer material in the form of a solid. When the melting point of the polyester in air is defined as Tm, The polymer material has a melting point higher than Tm, or has no melting point and is solid at Tm, The heating is performed at a temperature of (Tm-70)°C or higher and (Tm-10)°C or lower.

2. The recycling method according to claim 1, wherein: The pressure during heating is the saturated water vapor pressure at the heating temperature.

3. The recycling method according to claim 1 or 2, wherein: The polyester is polyester fiber, the polymer material is at least one polymer fiber selected from synthetic fiber, regenerated fiber, semi-synthetic fiber, inorganic fiber and natural fiber, and the solid mixture is a fiber product composed of polyester fiber and polymer fiber.

4. The recycling method according to claim 3, wherein: The polymer material is at least one natural fiber selected from cotton fiber, wool fiber and silk fiber.

5. The recycling method according to claim 3, wherein: The equivalent circle diameter of the cross section of the polyester fiber is 1 to 100 μm, and the equivalent circle diameter of the cross section of the polymer fiber is 1 to 100 μm.

6. The recycling method according to claim 3, which is a recycling method for recovering the polymer fiber from the fiber product, The fiber product is a knitted fabric, a woven fabric or a non-woven fabric, The polymer fiber maintains the shape when used as a fiber product.

7. A recycled product, comprising, in at least a part of its raw materials, a polymer material obtained by the recycling method according to claim 4, The polymer material is cotton fiber, The recycled product is a recycled cotton product.

8. A method for recycling polyester, comprising recovering the polyester separated from the solid mixture in the recycling method according to claim 1 or 2.

9. A recycled polyester product comprising the polyester obtained by the recycling method according to claim 8 in at least a part of the raw materials.

10. A fiber product comprising a polymer fiber having a melting point exceeding 255°C or being solid at 255°C and having no melting point, wherein the polymer fiber contains a polyester having a weight average molecular weight of 1,000 to 10,000 in an amount of 5% by mass or less.

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