Recycled paper and manufacturing method therefor

Abstract

The present invention relates to recycled paper and a manufacturing method therefor, wherein the recycled paper includes regenerated cellulose derived from a recycling operation of waste fibers. The recycled paper ensures durability, strength, color characteristics, etc., and thus can be used in various fields.

Description

Recycled paper and its manufacturing method

[0001] The present invention relates to a recycled paper manufactured using regenerated cellulose obtained from waste fibers and a method for manufacturing the same.

[0002] As the problem of waste plastics has become increasingly serious, active development of technologies to recycle them is underway. Among waste plastics, polyester is a relatively easy material to chemically recycle. Polyester polymers can be broken down into monomers through chemical reactions, which can then be used to produce high-quality recycled polyester.

[0003] However, chemical recycling of polyester has technical limitations. When polyester is mixed with other materials, complex purification and separation processes are required. Therefore, currently, only bottles made solely of polyester, which are easy to collect and sort, are considered recyclable materials.

[0004] Considering that a significant portion of total polyester production is consumed in fiber manufacturing, recycling limited to polyester bottles is insufficient to meet social and environmental needs. Therefore, chemical recycling of polyester fibers is essential for the ultimate recycling of waste plastic.

[0005] As mentioned above, chemical recycling of polyester is difficult when mixed with other components, and polyester fibers are a prime example. In fact, blended fibers containing various components in addition to polyester are commonly used in the production of clothing and textiles. The most common blend of polyester fibers is that of polyester and cotton. Blended fibers, typically in a 65 / 35 or 80 / 20 ratio, are used to manufacture clothing and textiles, imparting the durability and wrinkle resistance of polyester with the softness and breathability of cotton.

[0006] Chemical recycling of polyester involves depolymerization, which utilizes reactions with highly polar solvents. Depending on the solvent used, depolymerization processes include glycolysis, hydrolysis, alcoholysis, and aminolysis.

[0007] Among these reactions, depolymerization of polyester / cotton blend fibers by methods such as alcoholysis or aminolysis can yield regenerated monomers and regenerated cellulose.

[0008] One industry that can utilize regenerated cellulose is the paper industry. Wood pulp is primarily used for papermaking, while cotton pulp is used for high-quality paper. Using cotton pulp as a paper material yields high-quality paper with longer fibers and higher purity than wood pulp. It is relatively soft and durable, and its low lignin content prevents yellowing or brittleness. Cotton pulp can be obtained from cotton fibers directly harvested from the plant, linters (short fibers around cottonseeds, suitable for pulping) left over from the garment manufacturing process, or from waste fibers (textiles). However, when regenerated cellulose extracted from waste fibers (textiles) is used to make paper, the dyes contained in the waste fibers limit its ability to meet the color characteristics required for writing and printing.

[0009] Meanwhile, for high-quality paper, titanium dioxide (TiO2) is added to cotton pulp to improve paper properties. TiO2 is non-toxic, has strong hiding power, and a high refractive index (2.5-2.7). Paper containing TiO2 strongly reflects light, making it appear brighter. It also scatters light, preventing the other side of the paper from being visible. However, as a high-quality additive, TiO2 increases the unit price of the paper.

[0010] During the textile production process, titanium dioxide (TiO2) is added as a matting agent to control the gloss and increase the opacity of the fiber. For example, polyester fibers contain up to 2.4-2.5% titanium dioxide (TiO2), and outdoor blended fibers contain approximately 0.9% titanium dioxide (TiO2) to control gloss. Despite the high-quality additive titanium dioxide (TiO2) contained in textiles, they are difficult to recycle once they are used, and are therefore incinerated or landfilled, causing environmental problems. Recently, some attempts have been made to produce recycled paper through the chemical recycling of waste textiles, but the color characteristics of the recycled paper are significantly reduced. Furthermore, no attempts have been confirmed to reuse the titanium dioxide (TiO2) contained in waste textiles.

[0011] Accordingly, the object of the present invention is to provide recycled paper having improved durability, strength, color characteristics, etc. by controlling the chemical recycling process of waste fibers to reuse titanium dioxide (TiO2) and improve the quality of regenerated cellulose.

[0012] In addition, another object of the present invention is to provide a method for manufacturing recycled paper that can economically manufacture recycled paper.

[0013] In addition, another object of the present invention is to provide regenerated cellulose that enables obtaining high-quality recycled paper.

[0014] To solve the above problem, the present invention provides recycled paper including regenerated cellulose (r-cellulose) containing titanium dioxide (TiO2).

[0015] In addition, the present invention provides a method for manufacturing recycled paper, comprising the steps of pretreating waste fibers; depolymerizing the pretreated waste fibers to obtain regenerated cellulose (r-cellulose) and a depolymerized product; and forming a fiber layer from a raw material including the regenerated cellulose, wherein the regenerated cellulose includes titanium dioxide (TiO2).

[0016] In addition, the present invention provides regenerated cellulose derived from a recycling process of waste fibers and containing titanium dioxide (TiO2).

[0017] The present invention provides a method for producing recycled paper by controlling a chemical recycling process of waste fibers to obtain regenerated cellulose containing titanium dioxide (TiO2), and using the same to manufacture recycled paper, thereby economically providing recycled paper with improved durability, strength, color characteristics, etc. In particular, since the recycled paper according to the present invention includes regenerated cellulose containing titanium dioxide (TiO2), it can have a desired level of brightness and opacity without separately adding titanium dioxide (TiO2) to the recycled paper, thereby further improving economic efficiency and environmental friendliness.

[0018] Hereinafter, the present invention will be described in detail. Herein, the present invention is not limited to the contents described below, and may be modified in various forms as long as the gist of the invention is not changed.

[0019] The word "comprising" or "including" in this specification is intended to specify particular features, regions, steps, processes, elements and / or components, and does not exclude the presence or addition of other features, regions, steps, processes, elements and / or components, unless specifically stated to the contrary.

[0020] In this specification, the terms first, second, primary, secondary, etc. are used for the purpose of distinguishing one component from another, and the components are not limited by the terms.

[0021] In this specification, singular expressions may be interpreted to include the singular or plural as interpreted in the context, unless otherwise specified.

[0022] In this specification, when numerical values ​​with limited upper and lower limits are described to illustrate the size, physical properties, etc. of a component, it can be understood that a numerical range in which these upper and lower limits are combined is also included in the exemplary range of the present invention.

[0023]

[0024] recycled paper

[0025] The recycled paper according to the present invention comprises regenerated cellulose (r-cellulose) containing titanium dioxide (TiO2).

[0026] The regenerated cellulose (r-cellulose) described above may refer to natural cellulose chemically processed or recycled waste cellulose. Specifically, the regenerated cellulose may be derived from a recycling process for waste fibers. More specifically, the regenerated cellulose may be derived from a recycling process for waste blended fibers. The recycling process may include a depolymerization process for the waste fibers.

[0027] For example, according to the present invention, the regenerated cellulose is derived from a recycling process of waste fibers, and the waste fibers may include cotton; and polyester, polyurethane, polyethylene, polypropylene, polycarbonate, nylon, polyacrylonitrile, or a combination thereof. Specifically, the waste fibers may be waste blended fibers comprising cotton and polyester, and the regenerated cellulose may be derived from a recycling process of the waste blended fibers.

[0028] The above waste fibers may be surface-treated or water-repellent treated. The surface treatment may include physical surface treatments such as sanding, calendaring, and heat setting; chemical surface treatments such as chlorine treatment, alkali treatment, acid treatment, and hydrophobic / hydrophilic treatment; physical / chemical surface treatments such as plasma treatment and corona treatment; biological surface treatments such as enzyme treatment, or a combination thereof. The water-repellent finishing may include fluorine compound treatment, silicone compound treatment, wax treatment, paraffin treatment, oil treatment, or a combination thereof.

[0029] According to the present invention, the titanium dioxide (TiO2) contained in the regenerated cellulose may be derived from a recycling process of waste fibers. Specifically, the titanium dioxide may be derived from a recycling process of waste fibers including cotton, and polyester, polyurethane, polyethylene, polypropylene, polycarbonate, nylon, polyacrylonitrile, or a combination thereof. More specifically, the titanium dioxide may be derived from an additive (e.g., a gloss control agent, a catalyst, a UV blocker, etc.) contained in the polyester. For example, the titanium dioxide may be derived from an additive generated by the decomposition of polyester during the depolymerization process of waste fibers including polyester (specifically, waste blended fibers of cotton and polyester). That is, the titanium dioxide may be an inorganic substance derived from an additive contained in polyester and remaining in the regenerated cellulose. Here, the polyester may be polyethylene terephthalate (PET).

[0030] According to the present invention, the content of titanium dioxide contained in the regenerated cellulose may be 10 to 30,000 ppm, 50 to 28,000 ppm, 80 to 25,000 ppm, 100 to 23,000 ppm, 500 to 22,000 ppm, 700 to 21,000 ppm, 1,000 to 20,000 ppm, 800 to 1,500 ppm, 1,000 to 1,300 ppm, 15,000 to 20,000 ppm, or 18,000 to 20,000 ppm. As the content of titanium dioxide is within the above range, the surface quality of the recycled paper can be improved while ensuring the opacity, strength, durability, and economic feasibility.

[0031] Additionally, the regenerated cellulose may have a brightness of 40 or more, 42 or more, 44 or more, 46 or more, 48 or more, 50 or more, 53 or more, 55 or more, 57 or more, 60 or more, 62 or more, or 65 or more (e.g., 40 to 70, 45 to 68, 50 to 67, or 55 to 65). As the brightness of the regenerated cellulose is within the above range, the color characteristics of the recycled paper can be improved.

[0032] In addition, the regenerated cellulose may have a degree of polymerization (DP) of 200 or more and a fiber length of 50 ㎛ or more. Specifically, the degree of polymerization (DP) may be 203 or more, 205 or more, 210 or more, 215 or more, 217 or more, 220 or more, 224 or more, 228 or more, or 300 or more (e.g., 200 to 350, 203 to 300, 205 to 270, or 210 to 250), and the fiber length may be 100 μm or more, 150 μm or more, 200 μm or more, 300 μm or more, 400 μm or more, 500 μm or more, 600 μm or more, or 700 μm or more (e.g., 50 to 750 μm, 300 to 730 μm, 400 to 710 μm, or 450 to 700 μm). As the polymerization degree and fiber length of the above-mentioned regenerated cellulose are each within the above range, the durability, strength, printability, and process stability of the recycled paper can be improved.

[0033] According to the present invention, the content of the regenerated cellulose may be 0.1 to 100 wt% based on the total weight of the recycled paper. Specifically, the content of the regenerated cellulose may be 0.5 to 99 wt%, 1 to 98 wt%, 5 to 97 wt%, 10 to 96 wt%, 20 to 95 wt%, 25 to 95 wt%, 30 to 90 wt%, 35 to 85 wt%, 40 to 80 wt%, 50 to 80 wt%, or 30 to 50 wt%. When the content of the regenerated cellulose is within the above range, the color characteristics of the recycled paper can be secured while improving economic efficiency and environmental friendliness.

[0034] Recycled paper containing such regenerated cellulose may be composed solely of the regenerated cellulose, or may contain virgin cellulose (virgin pulp) together with the regenerated cellulose. The mixing ratio of the regenerated cellulose and the virgin cellulose (virgin pulp) contained in the recycled paper is not particularly limited, but may be a weight ratio of 5:95 to 95:5, a weight ratio of 10:90 to 90:10, a weight ratio of 20:80 to 80:20, a weight ratio of 30:70 to 70:30, a weight ratio of 40:60 to 60:40, or a weight ratio of 45:55 to 50:50.

[0035] According to the present invention, the recycled paper may have a brightness of 40 or more. Specifically, the brightness of the recycled paper may be 45 or more, 50 or more, 55 or more, 60 or more, 65 or more, 70 or more, 75 or more, 80 or more, or 85 or more (e.g., 40 to 100, 50 to 90, 60 to 85, 65 to 80, or 70 to 80).

[0036] As such, the recycled paper according to the present invention comprises regenerated cellulose containing titanium dioxide as a raw material, and thus exhibits desired color characteristics while ensuring durability, strength, etc. even without or with the addition of separate titanium dioxide (TiO2) in small amounts, and thus can be utilized in various fields. In particular, the recycled paper can improve economic efficiency (cost reduction) and eco-friendliness (resolution of environmental problems) by including regenerated cellulose containing titanium dioxide derived from the recycling process of waste fibers.

[0037]

[0038] Method for manufacturing recycled paper

[0039] A method for manufacturing recycled paper according to the present invention comprises the steps of pretreating waste fibers; depolymerizing the pretreated waste fibers to obtain regenerated cellulose (r-cellulose) and a depolymerized product; and forming a fiber layer from a raw material including the regenerated cellulose, wherein the regenerated cellulose includes titanium dioxide (TiO2). This manufacturing method may optionally further include a step of posttreating the obtained regenerated cellulose before forming the fiber layer.

[0040] The present invention has a technical feature in that it obtains regenerated cellulose containing titanium dioxide and having relatively high brightness by specifically controlling the recycling process of waste fibers, and then fiberizes the same to manufacture recycled paper. Specifically, the present invention is differentiated from the prior art in that it controls the recycling process such as pretreatment, depolymerization, and post-treatment of waste fibers so that titanium dioxide remains in the regenerated cellulose obtained in the recycling process, thereby reusing titanium dioxide. In other words, through the above manufacturing method, the present invention can implement recycled paper containing titanium dioxide because the regenerated cellulose contains titanium dioxide even without separately adding titanium dioxide in the paper manufacturing process unlike the prior art.

[0041] The manufacturing method of this recycled paper is described in detail as follows.

[0042]

[0043] 1) Pretreatment of waste fibers

[0044] This step is a pretreatment step for waste fibers to remove foreign substances such as impurities (oil, dust, etc.), pigments, and dyes contained in the waste fibers. Specifically, the pretreatment step may be a step for decolorizing the waste fibers.

[0045] The above waste textiles may refer to discarded waste clothing, factory-manufactured but unsold inventory, or unused inventory and defective fabrics discarded as fabrics without being converted into garments. Furthermore, the above waste textiles include fibers used not only for clothing purposes but also for industrial purposes (e.g., industrial materials, non-woven fabrics, fabrics, etc.).

[0046] Specifically, the waste fiber may comprise cotton. Additionally, the waste fiber may comprise polyester, polyurethane, polyethylene, polypropylene, polycarbonate, nylon, polyacrylonitrile, or a combination thereof. For example, the waste fiber may be a waste blended fiber comprising cotton and polyester.

[0047] The above pretreatment of the waste fibers can be performed using a polar organic solvent, an oxidizing agent, a reducing agent, or a combination thereof. Through the above treatment, foreign substances (e.g., dyes, pigments, etc.) contained in the waste fibers can be efficiently removed.

[0048] According to the present invention, the polar organic solvent used for the pretreatment may include cyclohexanone, dimethylacetamide (DMAC), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), a monoalcohol having 1 or more carbon atoms, a dialcohol having 2 or more carbon atoms, or a combination thereof. The monoalcohol may be a monoalcohol having 1 to 10 carbon atoms or 4 to 7 carbon atoms, and specifically, may be n-butanol (n-BD) or benzyl alcohol. The dialcohol may be a dialcohol having 2 to 5 carbon atoms or 2 to 3 carbon atoms, and specifically, may be ethylene glycol (EG). Specifically, this polar organic solvent may be cyclohexanone.

[0049] Additionally, the oxidizing agent may include hydrogen peroxide (H2O2), sodium hypochlorite (NaOCl), or a combination thereof. Specifically, the oxidizing agent may be sodium hypochlorite.

[0050] Additionally, the reducing agent may include sodium hyposulfite (Na2S2O4), sodium thiosulfate (Na2S2O3), or a combination thereof. Specifically, the reducing agent may be sodium hyposulfite.

[0051] The amount of the treatment agent (polar organic solvent, oxidizing agent, reducing agent) used for the above pretreatment is not particularly limited, but may be 50 to 2,000 parts by weight, 100 to 1,800 parts by weight, 500 to 1,700 parts by weight, 700 to 1,500 parts by weight, 800 to 1,300 parts by weight, or 900 to 1,000 parts by weight, based on 100 parts by weight of the waste fiber.

[0052] According to the present invention, the pretreatment of the waste fiber can be performed at a temperature of 40 to 180°C. Specifically, the pretreatment can be performed at a temperature of 50 to 170°C, 60 to 160°C, 70 to 150°C, 75 to 140°C, or 80 to 135°C. By performing the pretreatment at the above temperature, foreign substances contained in the waste fiber (specifically, cellulose) can be efficiently removed while preventing damage to the waste fiber.

[0053] The above pretreatment of the waste fiber may be performed more than once. Specifically, the pretreatment may be performed once or twice.

[0054]

[0055] 2) Depolymerization of waste fibers

[0056] This step is a step of depolymerizing the above-mentioned pretreated waste fiber to obtain regenerated cellulose (r-cellulose) and a depolymerized product.

[0057] The above depolymerization is not particularly limited as long as it is a commonly known chemical depolymerization (e.g., glycolysis, methanolysis, hydrolysis under water or acid / base conditions, alkaline hydrolysis under basic conditions (NaOH, KOH), etc.). Specifically, the depolymerization can be performed through alcoholysis using a solvent containing methanol, n-butanol, ethylene glycol, or a combination thereof. Through the alcoholysis, the desired regenerated cellulose and depolymer can be obtained in high yield. For example, the waste fiber can be a waste blended fiber containing cotton and polyester, and through the alcoholysis, the cotton can be decomposed into regenerated cellulose and the polyester can be decomposed into a depolymer, thereby obtaining regenerated cellulose and a depolymer. Here, the regenerated cellulose includes titanium dioxide derived (or caused) from an additive generated during the decomposition process of the polyester.

[0058] The reaction conditions for performing the above alcohol decomposition are not particularly limited, but the reaction temperature may be 180 to 250°C, 185 to 240°C, 190 to 235°C, or 195 to 230°C, and the reaction time may be 1 to 10 hours, 2 to 8 hours, 3 to 6 hours, or 3 to 4 hours.

[0059] The above alcoholysis can be carried out in the presence of a commonly known catalyst. For example, the catalyst can include at least one selected from the group consisting of Zn(OAc)2, Co(OAc)2, Mn(OAc)2, Mg(OAc)2, Ca(OAc)2, Ba(OAc)2, LiOAc, NaOAc, KOAc, Zn(OAc)2·2H2O, Co(OAc)2·4H2O, Pb(OAc)2, Mn(OAc)2·4H2O, Mg(OAc)2·4H2O, Pd(OAc)2, Ti(OBu)4, Ti(OiPr)4, GeO2, Al(OiPr)3, Na2CO3, K2CO3, dibutyltin(IV)oxide, tin octoate, titanium phosphate, and terephthalic acid.

[0060] By depolymerizing the above-described pretreated waste fiber through the alcoholysis, the present invention can obtain regenerated cellulose containing titanium dioxide and a depolymerized product having excellent color characteristics and high purity at a high yield. In particular, by filtering the product obtained through the depolymerization of the waste fiber through a specific filter having controlled size, the regenerated cellulose containing (residual) titanium dioxide and the depolymerized product can be efficiently separated and obtained. The size (pore size) of the filter can be specifically 80 to 120 μm (e.g., 100 μm).

[0061] According to the present invention, the depolymerization product may include recycled bis(2-hydroxyethyl)terephthalate (r-BHET), recycled dimethyl terephthalate (r-DMT), recycled dibutyl terephthalate (r-DBTP), or a combination thereof.

[0062] The depolymer may have a yellowness index (YID) of less than 30. Specifically, the yellowness index of the depolymer may be 25 or less, 20 or less, 15 or less, 10 or less, 9 or less, 8 or less, 7 or less, or 6 or less (e.g., greater than 0 to 25, 1 to 20, 2 to 10, or 2.5 to 6).

[0063] These depolymers can be converted into regenerated monomers such as terephthalic acid (TPA) through conventional hydrolysis processes.

[0064]

[0065] Meanwhile, the regenerated cellulose obtained through the above depolymerization may undergo a further post-treatment step before undergoing the fiber layer formation step described below. Specifically, the post-treatment may be a step of decolorizing the regenerated cellulose.

[0066] The post-treatment of the above regenerated cellulose can be performed using a polar organic solvent, an oxidizing agent, a reducing agent, or a combination thereof. The above treatment can increase the decolorization efficiency while preventing the loss of titanium dioxide contained in the regenerated cellulose.

[0067] The polar organic solvent used for the above post-treatment may include cyclohexanone, dimethylacetamide (DMAC), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), a monoalcohol having 1 or more carbon atoms, a dialcohol having 2 or more carbon atoms, or a combination thereof. The monoalcohol may be a monoalcohol having 1 to 10 carbon atoms, or 4 to 7 carbon atoms, and specifically, may be n-butanol (n-BD) or benzyl alcohol. The dialcohol may be a dialcohol having 2 to 5 carbon atoms, or 2 to 3 carbon atoms, and specifically, may be ethylene glycol (EG).

[0068] Additionally, the oxidizing agent may include hydrogen peroxide (H2O2), sodium hypochlorite (NaOCl), or a combination thereof.

[0069] Additionally, the reducing agent may include sodium hyposulfite (Na2S2O4), sodium thiosulfate (Na2S2O3), or a combination thereof.

[0070] The amount of the treatment agent (polar organic solvent, oxidizing agent, reducing agent) used for the above post-treatment is not particularly limited, but may be 50 to 2,000 parts by weight, 100 to 1,800 parts by weight, 300 to 1,500 parts by weight, 500 to 1,300 parts by weight, 1,000 to 1,200 parts by weight, or 1,800 to 2,000 parts by weight, based on 100 parts by weight of regenerated cellulose.

[0071] The post-treatment of the above regenerated cellulose can be performed at 30 to 80°C, 35 to 75°C, 40 to 70°C, 45 to 65°C, or 50 to 60°C. By performing the post-treatment at the above temperatures, the decolorization efficiency can be increased while preventing damage to the regenerated cellulose and loss of titanium dioxide.

[0072] Meanwhile, the treatment agent used for pretreatment of the above-mentioned waste fiber and the treatment agent used for post-treatment of the above-mentioned regenerated cellulose may be the same or different.

[0073]

[0074] 3) Formation of fiber layer

[0075] This step is a step for forming a fiber layer from a raw material containing the obtained regenerated cellulose (or post-treated regenerated cellulose). The step for forming the fiber layer can be performed through a conventionally known papermaking process. For example, the regenerated cellulose can be dispersed in water to produce a paper stock, which is the raw material, and then filtered to form a fiber layer.

[0076] Thereafter, by pressing and drying the fiber layer, the recycled paper according to the present invention can be obtained.

[0077]

[0078] regenerated cellulose

[0079] The regenerated cellulose according to the present invention is derived from a recycling process of waste fibers and contains titanium dioxide (TiO2).

[0080] Since the description of the above waste fiber is the same as that described above, a detailed description thereof will be omitted. Specifically, the waste fiber may be a waste blended fiber including cotton; and polyester, polyurethane, polyethylene, polypropylene, polycarbonate, nylon, polyacrylonitrile, or a combination thereof. For example, the waste fiber may be a waste blended fiber including cotton and polyester.

[0081] The above-mentioned waste fiber recycling process may include a waste fiber pretreatment process, a waste fiber depolymerization process, and a regenerated cellulose posttreatment process. Since the above-mentioned processes are described in detail above, their detailed descriptions are omitted.

[0082] The titanium dioxide (TiO2) contained in the above-mentioned regenerated cellulose may be derived from the depolymerization process of waste fibers. Specifically, the titanium dioxide may be derived from additives (e.g., gloss control agents, catalysts, UV blockers, etc.) generated by the decomposition of polyester during the depolymerization process of waste fibers containing polyester.

[0083] According to the present invention, the content of titanium dioxide included in the regenerated cellulose may be 10 to 30,000 ppm, 50 to 28,000 ppm, 80 to 25,000 ppm, 100 to 23,000 ppm, 500 to 22,000 ppm, 700 to 21,000 ppm, 1,000 to 20,000 ppm, 800 to 1,500 ppm, 1,000 to 1,300 ppm, 15,000 to 20,000 ppm, or 18,000 to 20,000 ppm.

[0084] Additionally, the regenerated cellulose may have a brightness of 40 or more, 42 or more, 44 or more, 46 or more, 48 or more, 50 or more, 53 or more, 55 or more, 57 or more, 60 or more, 62 or more, or 65 or more (e.g., 40 to 70, 45 to 68, 50 to 67, or 55 to 65).

[0085] Additionally, the regenerated cellulose may have a degree of polymerization (DP) of 200 or more, 203 or more, 205 or more, 210 or more, 215 or more, 217 or more, 220 or more, 224 or more, 228 or more, or 300 or more (e.g., 200 to 350, 203 to 300, 205 to 270, or 210 to 250).

[0086] Additionally, the regenerated cellulose may have a fiber length of 50 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, 300 μm or more, 400 μm or more, 500 μm or more, 600 μm or more, or 700 μm or more (e.g., 50 to 750 μm, 300 to 730 μm, 400 to 710 μm, or 450 to 700 μm).

[0087] This regenerated cellulose possesses optimized brightness, degree of polymerization, and fiber length, making it suitable for various applications. Specifically, the regenerated cellulose can be used in the production of nanocellulose, cellulose derivatives (e.g., CMC), cotton, rayon, paper, nonwoven fabrics, and the like. In particular, the regenerated cellulose possesses a degree of polymerization favorable for pulping, a fiber length that ensures mechanical strength, and a relatively high brightness, making it effective in the production of paper (regenerated paper).

[0088] The present invention is described in more detail through the following examples. However, the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention.

[0089]

[0090] [Example 1] Pretreatment of waste fiber (primary decolorization)

[0091] [Example 1-1]

[0092] 1,000 g of cyclohexanone was added to 100 g of a navy colored waste blended fiber having a composition of 70 wt% PET and 30 wt% cotton, and stirred at 120°C for 1 hour. Next, the waste blended fiber was cooled to room temperature and recovered through solid-liquid separation. Next, the treatment of the waste blended fiber using cyclohexanone was repeated once more to recover the waste blended fiber, and then the residual cyclohexanone was removed through dehydration and high-temperature vacuum drying to obtain a pretreated waste blended fiber.

[0093]

[0094] [Example 1-2]

[0095] 100 g of a navy colored waste blended fiber composed of 70 wt% PET and 30 wt% cotton was added with 2,000 g of a 1% NaOCl solution, and stirred at 80°C for 2 hours. Next, the waste blended fiber was cooled to room temperature and recovered through solid-liquid separation. Next, the recovered waste blended fiber was washed with 500 g of water and then subjected to a high-temperature vacuum drying process to remove residual water, thereby obtaining a pretreated waste blended fiber.

[0096]

[0097] [Example 1-3]

[0098] 100 g of a navy colored waste blended fiber having a composition of 70 wt% PET and 30 wt% cotton was added with 4 g of Na2S2O4, 5 g of NaOH, and 2,000 g of water, and stirred at 130°C for 2 hours. Next, the waste blended fiber was cooled to room temperature and recovered through solid-liquid separation. Next, the recovered waste blended fiber was washed with 500 g of water, and then subjected to a high-temperature vacuum drying process to remove residual water, thereby obtaining a pretreated waste blended fiber.

[0099]

[0100] [Example 1-4]

[0101] A pretreated waste blended fiber was obtained through the same process as Example 1-1, except that a black colored waste blended fiber having a composition of 80 wt% PET and 20 wt% Cotton was used instead of a navy colored waste blended fiber.

[0102]

[0103] [Example 1-5]

[0104] A pretreated waste blended fiber was obtained through the same process as Example 1-2, except that a black colored waste blended fiber having a composition of 80 wt% PET and 20 wt% Cotton was used instead of a navy colored waste blended fiber.

[0105]

[0106] [Example 1-6]

[0107] A pretreated waste blended fiber was obtained through the same process as Example 1-3, except that a black colored waste blended fiber having a composition of 80 wt% PET and 20 wt% Cotton was used instead of a navy colored waste blended fiber.

[0108]

[0109] [Example 1]

[0110] The pretreated waste mixed fibers were measured using a spectrophotometer (KONICA MINOLTA CM-3600A) to confirm the Color L*, a*, and b*, and the results are shown in Table 1 below.

[0111]

[0112] Example Before pretreatment Waste blended fiber color L* / a* / b* Pretreatment After pretreatment Waste blended fiber color L* / a* / b* 1-13 3.2 / 0.31 / -5.00 (Navy color) cyclohexanone 40.5 / 0.65 / -5.1 1-2 NaOCl 64.3 / 7.70 / 13.9 11-3 Na2S2O 450.3 / -0.43 / 3.3 51-4 3.0 / 2.20 / -0.15 (Black color) cyclohexanone 57.78 / 1.87 / 0.7 11-5 NaOCl 48.19 / 12.00 / 10.5 41-6 Na2S2O 444.2 / 1.29 / 4.02

[0113] Referring to Table 1 above, it can be confirmed that the pretreated waste mixed fiber according to the present invention has an increased Color L* value and changes in Color a* and b* values, indicating that decolorization was successfully achieved through pretreatment.

[0114]

[0115] [Example 2] Depolymerization (alcoholization) of waste fibers

[0116] [Example 2-1]

[0117] 100 g of waste mixed fibers pretreated in Example 1-1, 1,000 g of ethylene glycol and Zn(OAc) in a high-pressure reactor 2· After adding 0.42 g of 2H2O, the mixture was reacted at 195°C for 4 hours. After completion of the reaction, the reaction solution was cooled to 70°C and filtered through a 100 μm filter to obtain the liquid product and insoluble cellulose, respectively.

[0118] The above insoluble cellulose was washed with ethylene glycol at 70°C and then dried to recover r-cellulose.

[0119] The above liquid product was concentrated to remove ethylene glycol, and then subjected to thin-film distillation to obtain a primary purified product (containing BHET). Subsequently, 125 g of water was added to 50 g of the purified product and stirred at 90°C to dissolve the purified product. Next, 2 g of activated carbon was added and stirred at 90°C for 30 minutes. The activated carbon was then filtered off using a hot filter, and the resulting mixture was cooled to room temperature to obtain the precipitated (crystallized) r-BHET.

[0120]

[0121] [Example 2-2]

[0122] r-cellulose and r-BHET were obtained through the same process as Example 2-1, except that the waste mixed fibers pretreated in Example 1-2 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0123]

[0124] [Example 2-3]

[0125] r-cellulose and r-BHET were obtained through the same process as Example 2-1, except that the waste mixed fibers pretreated in Example 1-3 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0126]

[0127] [Example 2-4]

[0128] 100 g of waste mixed fibers pretreated in Example 1-1, 400 mL of n-butanol and Zn(OAc) in a high-pressure reactor 2· After adding 0.1 g of 2H2O, the mixture was reacted at 220°C for 4 hours. After completion of the reaction, the reaction solution was cooled to room temperature and filtered through a 100 μm filter to obtain the liquid product and insoluble cellulose, respectively.

[0129] The above insoluble cellulose was washed with n-butanol at 25°C and then dried to recover r-cellulose.

[0130] The above liquid product was concentrated to remove n-butanol and ethylene glycol, and then purified by distillation to obtain r-DBTP.

[0131]

[0132] [Example 2-5]

[0133] R-cellulose and r-DBTP were obtained through the same process as Example 2-4, except that the waste mixed fibers pretreated in Example 1-2 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0134]

[0135] [Example 2-6]

[0136] R-cellulose and r-DBTP were obtained through the same process as Example 2-4, except that the waste mixed fibers pretreated in Example 1-3 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0137]

[0138] [Example 2-7]

[0139] 100 g of waste mixed fibers pretreated in Example 1-1, 400 mL of methanol and Zn(OAc) in a high-pressure reactor 2· After adding 0.1 g of 2H2O, the mixture was reacted at 220°C for 4 hours. After completion of the reaction, the reaction solution was cooled to 60°C and filtered through a 100 μm filter to obtain the liquid product and insoluble cellulose, respectively.

[0140] The above insoluble cellulose was washed with methanol at 60°C and then dried to recover r-cellulose.

[0141] The above liquid product was distilled under reduced pressure to remove methanol, thereby obtaining r-DMT.

[0142]

[0143] [Example 2-8]

[0144] R-cellulose and r-DMT were obtained through the same process as Example 2-7, except that the waste mixed fibers pretreated in Example 1-2 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0145]

[0146] [Example 2-9]

[0147] R-cellulose and r-DMT were obtained through the same process as Example 2-7, except that the waste mixed fibers pretreated in Example 1-3 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0148]

[0149] [Example 2-10]

[0150] r-cellulose and r-BHET were obtained through the same process as Example 2-1, except that the waste mixed fibers pretreated in Example 1-4 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0151]

[0152] [Example 2-11]

[0153] r-cellulose and r-BHET were obtained through the same process as Example 2-1, except that the waste mixed fibers pretreated in Example 1-5 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0154]

[0155] [Example 2-12]

[0156] r-cellulose and r-BHET were obtained through the same process as Example 2-1, except that the waste mixed fibers pretreated in Example 1-6 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0157]

[0158] [Example 2-13]

[0159] R-cellulose and r-DBTP were obtained through the same process as Example 2-4, except that the waste mixed fibers pretreated in Example 1-4 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0160]

[0161] [Example 2-14]

[0162] R-cellulose and r-DBTP were obtained through the same process as Example 2-4, except that the waste mixed fibers pretreated in Example 1-5 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0163]

[0164] [Example 2-15]

[0165] R-cellulose and r-DBTP were obtained through the same process as Example 2-4, except that the waste mixed fibers pretreated in Example 1-6 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0166]

[0167] [Example 2-16]

[0168] R-cellulose and r-DMT were obtained through the same process as Example 2-7, except that the waste mixed fibers pretreated in Example 1-4 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0169]

[0170] [Example 2-17]

[0171] R-cellulose and r-DMT were obtained through the same process as Example 2-7, except that the waste mixed fibers pretreated in Example 1-5 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0172]

[0173] [Example 2-18]

[0174] R-cellulose and r-DMT were obtained through the same process as Example 2-7, except that the waste mixed fibers pretreated in Example 1-6 were used instead of the waste mixed fibers pretreated in Example 1-1.

[0175]

[0176] [Example 3] Post-treatment of r-cellulose (secondary decolorization)

[0177] [Example 3-1]

[0178] To 30 g of r-cellulose recovered in Example 2-1, a 1% NaOCl solution 20 times the amount of r-cellulose was added, and the mixture was stirred at 50°C for 2 hours. Subsequently, r-cellulose was obtained through filtration, and a certain amount of water was added to the obtained r-cellulose to further remove the remaining NaOCl solution, followed by drying to obtain post-treated r-cellulose.

[0179]

[0180] [Examples 3-2 to 3-18]

[0181] Post-treated r-cellulose was obtained through the same process as Example 3-1, except that instead of the r-cellulose recovered in Example 2-1, the r-cellulose recovered in each of Examples 2-2 to 2-18 was used.

[0182]

[0183] [Example 2]

[0184] 1) Recovery rate of r-cellulose

[0185] The recovery rate (%) of r-cellulose was calculated by converting the content of r-cellulose obtained (recovered) through depolymerization into a percentage compared to the content of cotton in the waste blended fiber before depolymerization, and the results are shown in Table 2 below.

[0186] 2) Yield of depolymerized product

[0187] The yield (%) of the depolymer was calculated by converting the mole number of the depolymerized product (r-BHET / r-DBTP / r-DMT) obtained by depolymerization into a percentage based on the total mole number of PET unit molecules in the waste blended fiber before depolymerization, and the results are shown in Table 2 below.

[0188] 3) Purity of the depolymerized product

[0189] After diluting the depolymer (r-BHET / r-DBTP / r-DMT) to 1 wt / v% in methanol (MeOH), high-performance liquid chromatography (HPLC) analysis was performed to calculate the purity (%) of the depolymer, and the results are shown in Table 2 below.

[0190] 4) Color YID of the depolymerized product

[0191] After diluting the depolymer (r-BHET / r-DBTP / r-DMT) to 10 wt / v% in dimethylformamide, the color YID value of the depolymer was calculated by measuring it with a colorimeter (HunterLab ColorFlex EZ Spectrophotometer), and the results are shown in Table 2 below.

[0192]

[0193] Example Waste mixed fiber pretreatment depolymerization process r-cellulose recovery rate (%) Post-treatment depolymerization product (r-BHET / r-DBTP / r-DMT) yield (%) Purity (%) Color YID3-1 Navy Color cyclohexanone EG (r-BHET) 94 NaOCl 8999.75.83-2 NaOCl 929099.74.33-3 Na2S2O 4959099.84.03-4 cyclohexanone BuOH (r-DBTP) 909599.83.83-5 NaOCl 909499.63.53-6 Na2S2O 4929499.72.73-7 cyclohexanone MeOH (r-DMT) 919498.94.53-8 NaOCl 909699.1 4.83-9Na2S2O4929697.34.63-10Black colorcyclohexanoneEG(r-BHET)948999.85.53-11NaOCl928999.74.23-12Na2S2O4959099.73.93-13cyclohexanoneBuOH(r-DB TP)909499.33.53-14NaOCl909599.53.23-15Na2S2O4929599.72.83-16cyclohex anoneMeOH(r-DMT)919597.24.63-17NaOCl909698.35.83-18Na2S2O4929299.04.3

[0194] Referring to Table 2 above, it can be confirmed that the recovery rate of r-cellulose is high and the yield, purity, and color characteristics of the depolymerized product are excellent as the depolymerization and post-treatment of the pretreated waste mixed fiber are performed as in the present invention.

[0195]

[0196] [Example 3]

[0197] 1) Fiber field

[0198] The fiber length of the recovered r-cellulose was measured using a fiber image analyzer (Lorentzen & Wettre L&W Fiber Tester Plus) according to ISO 16065-2, and the results are shown in Table 3 below.

[0199] 2) Degree of polymerization of r-cellulose

[0200] The degree of polymerization of the recovered r-cellulose was calculated using the IV (relative viscosity) analysis method, and the results are shown in Table 3 below.

[0201] 3) Brightness of r-cellulose

[0202] The brightness of the recovered r-cellulose was measured according to the ISO-2470-1 standard, and the results are shown in Table 3 below.

[0203]

[0204] Example Pretreatment Posttreatment Fiber length (㎛) Brightness (%) Degree of polymerization 3-1 cyclohexanone NaOCl 6 6 2 4 0.42 2 9 3-2 NaOCl 5 6 9 6 3.72 2 5 3-3 Na2S2O 4 6 9 4 6 2.52 4 1 3-4 cyclohexanone 5 7 3 4 2.52 0 6 3-5 NaOCl 4 9 8 6 4.22 0 4 3-6 Na2S2O 4 6 2 5 6 1.52 1 0

[0205] Referring to Table 3 above, it can be confirmed that by performing depolymerization and post-treatment of the pretreated waste mixed fiber as in the present invention, depolymerization and decolorization are efficiently achieved, and r-cellulose having improved color characteristics while having the size and degree of polymerization of fine fibers is obtained.

[0206]

[0207] [Manufacturing Example] Manufacturing of Recycled Paper

[0208] [Manufacturing Example 1]

[0209] The post-treated r-cellulose of Example 3-1 was dispersed solely in water to produce a paper material, which was then filtered in a thin layer to form a fiber layer. The fiber layer was then pressed to remove moisture, and then heat-dried to produce recycled paper.

[0210]

[0211] [Manufacturing Example 2]

[0212] Recycled paper was manufactured through the same process as Manufacturing Example 1, except that a paper stock containing post-treated r-cellulose and virgin pulp (virgin cellulose) of Example 3-1 dispersed in water at a weight ratio of 70:30 was applied.

[0213]

[0214] [Manufacturing Example 3]

[0215] Recycled paper was manufactured through the same process as Manufacturing Example 1, except that a paper stock containing post-treated r-cellulose and virgin pulp (virgin cellulose) of Example 3-1 dispersed in water at a weight ratio of 50:50 was applied.

[0216]

[0217] [Manufacturing Example 4]

[0218] The post-treated r-cellulose of Example 3-13 was dispersed solely in water to produce a paper material, which was then filtered in a thin layer to form a fiber layer. The fiber layer was then pressed to remove moisture, and then heat-dried to produce recycled paper.

[0219]

[0220] [Manufacturing Example 5]

[0221] Recycled paper was manufactured through the same process as Manufacturing Example 4, except that a paper stock containing post-treated r-cellulose and virgin pulp (virgin cellulose) of Example 3-13 dispersed in water at a weight ratio of 70:30 was applied.

[0222]

[0223] [Manufacturing Example 6]

[0224] Recycled paper was manufactured through the same process as Manufacturing Example 4, except that a paper stock containing post-treated r-cellulose and virgin pulp (virgin cellulose) of Example 3-13 dispersed in water at a weight ratio of 50:50 was applied.

[0225]

[0226] [Example 4]

[0227] 1) TiO2 content of r-cellulose and recycled paper

[0228] The post-treated r-cellulose and recycled paper were analyzed by energy dispersive X-ray spectroscopy (EDS) to determine the TiO2 content (ppm), and the results are shown in Table 4 below.

[0229] 2) Brightness of recycled paper

[0230] The brightness of recycled paper refers to the color reflected when irradiated with a light source of wavelength (457 nm), and was measured according to the ISO-2470-1 standard, with the brightness of MgO set at 100, and the results are shown in Table 4 below.

[0231]

[0232] Manufacturing example r-celluloser-celluloseTiO2 content (ppm)Recycled paper r-cellulose content (%)Recycled paper TiO2 content (ppm)Brightness (%)1Example 3-11,1661001,16663.727081777.935058373.94Example 3-1320,00010020,00040.457013,95070.96509,86062.2

[0233] Referring to Table 4 above, it can be confirmed that the recycled paper according to the present invention exhibits a relatively high brightness due to the inclusion of TiO2 derived from waste blended fibers (specifically, waste polyester). In particular, it can be seen that the recycled paper exhibits a brightness of 40 or higher even when it contains only r-cellulose.

Claims

Recycled paper comprising regenerated cellulose (r-cellulose) containing titanium dioxide (TiO2). In the first paragraph, Recycled paper, wherein the content of titanium dioxide contained in the regenerated cellulose is 10 to 30,000 ppm. In the first paragraph, Recycled paper, wherein the content of the regenerated cellulose is 0.1 to 100 wt% based on the total weight of the recycled paper. In the first paragraph, The above regenerated cellulose is derived from the recycling process of waste fibers, and is recycled paper. In paragraph 4, The above waste fibers are cotton; and recycled paper comprising polyester, polyurethane, polyethylene, polypropylene, polycarbonate, nylon, polyacrylonitrile, or a combination thereof. In paragraph 5, Recycled paper, wherein the titanium dioxide is derived from an additive contained in the polyester. In paragraph 4, The above waste fiber is surface-treated or water-repellent treated, recycled paper. In the first paragraph, The above recycled paper is recycled paper with a brightness of 40 or higher. In the first paragraph, The above regenerated cellulose is a regenerated paper having a degree of polymerization (DP) of 200 or more and a fiber length of 50 ㎛ or more. Step of pretreating the waste fiber; A step of depolymerizing the above-mentioned pretreated waste fiber to obtain regenerated cellulose (r-cellulose) and a depolymerized product; and Comprising a step of forming a fiber layer from a raw material including the above regenerated cellulose, A method for manufacturing recycled paper, wherein the above-mentioned regenerated cellulose contains titanium dioxide (TiO2). In paragraph 10, A method for manufacturing recycled paper, wherein the pretreatment of the above waste fiber is performed at 40 to 180°C. In paragraph 10, A method for manufacturing recycled paper, wherein the pretreatment of the above waste fiber is performed through treatment using a polar organic solvent, an oxidizing agent, a reducing agent, or a combination thereof. In paragraph 12, A method for producing recycled paper, wherein the polar organic solvent comprises cyclohexanone, dimethylacetamide, dimethyl sulfoxide, dimethylformamide, a monoalcohol having 1 or more carbon atoms, a dialcohol having 2 or more carbon atoms, or a combination thereof. In paragraph 12, A method for manufacturing recycled paper, wherein the oxidizing agent comprises hydrogen peroxide, sodium hypochlorite, or a combination thereof. In paragraph 12, A method for manufacturing recycled paper, wherein the reducing agent comprises sodium hyposulfite, sodium thiosulfate, or a combination thereof. In paragraph 10, A method for manufacturing recycled paper, wherein the pretreatment of the above waste fiber is performed at least once. In paragraph 10, A method for manufacturing recycled paper, further comprising a step of post-treating the obtained regenerated cellulose before forming the fiber layer. In paragraph 10, A method for manufacturing recycled paper, wherein depolymerization of the above-mentioned pretreated waste fibers is performed through alcoholysis using a solvent containing methanol, n-butanol, ethylene glycol, or a combination thereof. In paragraph 10, The above depolymerization agent comprises recycled bis(2-hydroxyethyl)terephthalate, recycled dimethyl terephthalate, recycled dibutyl terephthalate, or a combination thereof, A method for manufacturing recycled paper, wherein the yellowness index (YID) of the above-mentioned depolymerization product is less than 30. Regenerated cellulose derived from the recycling process of waste fibers and containing titanium dioxide (TiO2).