Production of cellulose from cotton or cotton blends

Abstract

A method for producing a cellulose polymer having a cellulose content of 92% or more from textile waste, It is a mixture of cotton and PET, and the raw material (educt) is less than 1mm in length. The mixture is treated in a reactor with subcritical water at a temperature of 130 to 200° C., particularly preferably 160 to 200° C., and a pressure of 1 to 25 bar, preferably 1 to 10 bar, for about 1 to 120 minutes. A method for producing a cellulose polymer having an average degree of polymerization of 450 to 650.

Description

[Technical field]

[0001] This disclosure relates to the production of cellulose from cotton and cotton blends. [Background technology]

[0002] Circular economy is one of the hot topics that influences collective efforts to achieve a sustainable and environmentally responsible approach to raw materials and energy consumption. The issue of reuse (is it wearable?) alone requires considering and solving many issues, ranging from the orderly separation and recovery of currently available “raw materials” to recycling and reuse. Political initiatives, such as new rules in EU directives dealing with used textile products and their recovery, partially support this process. One of the barriers to the reprocessing and reuse of old textile products is the fact that recycling textiles is usually more expensive than producing new ones. One of the reasons for this is that textile materials are often made up of multiple fibers and are therefore complex materials. Also, the large variations in the molecular properties of cellulose, as seen in DP, are also cited. This of course has advantages in terms of the functionality of the material, but when returning it to the product cycle, the mixture of fibers must be treated, which requires complex separation steps.

[0003] The processing of pure raw materials such as cotton into cellulose is known in the prior art, but does not allow obtaining products with the desired quality due to the need for harsh additives and energy-consuming processing steps, which affect the quality of the final product. The addition of acids and bases as catalysts and other reaction aids leads to unstable polymer fibers and undesirable by-products such as terephthalic acid, which is difficult to remove from the reaction mixture. In addition to purity, the average degree of polymerization is the most important quality parameter for cellulose. Summary of the Invention

[0004] Therefore, it is an object of the present disclosure to provide a method for obtaining high quality polymeric fibers having a cellulose content of 90% or more, in which the DP value is optionally within a predetermined range. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0005] The object of the present disclosure is achieved by a method for producing a cellulose polymer having a cellulose content of 90% or more, preferably 92% or more, from textile waste. In this method, an educt obtained from cotton or a mixture of cotton and PET and having a fiber length of 1 mm or less is treated with subcritical water in a reactor at a temperature of 130 to 180°C and a pressure of 1 to 10 bar for about 1 to 120 minutes. This produces a cellulose polymer having an average degree of polymerization (DP) of 300 to 1000 DP, preferably 450 to 650. The raw material (educt) may be made of pure cotton. The reason why it is important to set the DP value to a predetermined range in advance is that the quality of the final material to be produced is designed to have a purity within a specific DP value range. For example, lyocell is obtained from pulp with a DP value of 550 to 600, and viscose is obtained from pulp with a DP value of 300 to 700. Here, the quality of the final product is guaranteed by keeping the DP in the pulp constant. Thus, in the method of the present disclosure, the DP range of the pulp can be predetermined.

[0006] Cellulose polymers with a purity of 90%-92% or more are high-quality raw materials that can be used to manufacture several other high-quality products. As mentioned above, viscose and lyocell are the products of interest. Viscose is usually produced from chemical cellulose obtained from various types of wood and cotton. Here, the quality of cellulose is different from that for papermaking, and cellulose of a specified chain length and purity must be used. Lyocell fibers are known for their high dry and wet strength, softness, and excellent moisture absorption. Textiles made from this material have a "smooth" and "cool" feel and a flowing drape. They are virtually wrinkle-free and can be washed and dry-cleaned. To retain these characteristics, only extremely pure raw materials can be used in production. Furthermore, the DP value must be adjusted to allow seamless processing by the textile manufacturer. The DP value must meet the fiber-specific requirements and be within the DP value range preset by the textile manufacturer. For viscose fibers, the DP value ranges from 300 to 700. The DP value of the cellulose used in the lyocell fiber is 500-700, and preferably 550-600.

[0007] Thus, the polymer fibers produced by the method of the present disclosure are "upcycling" products. The fiber length of the raw material is 1 mm or less, which means that the raw material is pre-ground. This makes the subsequent reactions easier. The fiber length also contributes to standardizing the process parameters during production, which will be described later. The method of the present disclosure has been found to be particularly advantageous for producing high-purity cellulose from textile waste with a predefined DP in the range of 300 to 1000. In very specific embodiments, educts with fiber lengths in the range of 0.2 mm to 8 mm are used. The shorter the fiber length, the better it mixes with water.

[0008] The disclosed method uses a reactor that uses subcritical water, which is liquid water between its atmospheric boiling point (i.e., 100°C) and its critical temperature (i.e., 374°C). Under these conditions, water has special or unusual properties. These properties affect the density, dielectric constant, ion concentration, diffusivity, and solubility in the subcritical state. In this state, the ionization constant increases with temperature and is about three orders of magnitude higher than that of water in normal conditions. Also, the dielectric constant decreases from 80 to 20. This dramatic change in physical properties causes the crosslinks in the cotton and PET textile waste material to rapidly dissolve.

[0009] The increase in the ionization constant also plays a part in the different pH values ​​of the water. This effect is enough to open the cellulose chains in the cotton fibers, so that the DP can be adjusted to the target DP range. This indicates that the resulting cellulose has good solubility properties and high purity in addition to the DP.

[0010] The treatment of fibers in a high-temperature and high-pressure aqueous system is called hydrothermal. The reactor can therefore be a hydrothermal reactor. The temperature of the reactor is between 130°C and 200°C, particularly preferably between 160°C and 200°C. The pressure is adjusted in the range of 1 to 25 bar. The reaction time is between 1 and 120 minutes. Depending on the given parameters, the reactor can affect the raw material, i.e. the textile waste, at the fiber level, weakening the bond strength between the fibers or even disentangling the interwoven fiber strands from each other. At the same time, any polyester residues that may be present are also decomposed. The degree of polymerization of the product can also be influenced by the main operating parameters during the operation of the reactor. It is noted here that subcritical water as a solvent is non-toxic, highly environmentally compatible and cost-effective. Subcritical water, by its nature, has a neutral pH and therefore does not have aggressive properties as a solvent.

[0011] Currently, the product cellulose polymer has a purity of at least 90%-92% and an average degree of polymerization (DP) of 300-1000, or even 450-650. If the reaction is suitably adjusted, the product can have an average degree of polymerization (DP) of 550-600. Such a degree of polymerization indicates that the educt is degraded to a degree that allows it to be suitably processed into lyocell, and that the reaction is homogeneous. The degree of polymerization indicates the number of basic building blocks per polymer molecule. It is the same as the average molar mass of the polymer divided by the molar mass of its repeating units (monomer units). The exact value is usually the average value of the sample under consideration. This average value is called the average degree of polymerization (DP). For fiber-forming polymers, it is an important parameter for processing and use properties.

[0012] The degree of polymerization of a sample is usually determined by its molar mass. Such methods include, for example, GPC, methods for determining colligative properties (freezing point depression, vapor pressure osmometry, etc.), viscometry, light scattering, and many others. Other methods are technically important but require accurate calibration of the sample. The melt flow index method is mentioned here. For example, the viscosity of a plastic melt increases with increasing degree of polymerization. The average value can be determined indirectly (i.e. relative to a chemically comparable standard) using the MFI method.

[0013] The degree of polymerization and the spatial geometric distribution of monomers in the molecule (i.e., the stereochemical arrangement of the molecular branches) have a significant effect on the physical properties of the polymer, especially the mechanical properties. However, according to Staudinger, fiber strength does not change proportionally to the degree of polymerization. The DP is, for example, 3000 for cotton, 250-700 for viscose fibers, 100-180 for polyamides, and 130-220 for polyesters. Determining the average degree of polymerization is particularly important for cellulose fibers, as it allows the chemical damage to these fibers to be numerically characterized. In a preferred embodiment, the cotton / PET mixture consists of a composition with a PET component of 5% or less. However, even if the contaminating fiber portion is composed of other fibers rather than PET, this does not pose an obstacle to the method of the present disclosure. These contaminating fibers are also processed without affecting the final product. In experiments with a contaminating fiber content of 5% or less, no obstacles are observed in the process sequence and the final product. If the contaminating fiber is polyurethane (elastane) or PES / PET, it does not remain in the final product. The presence or absence of coloring components in the fiber mixture has no effect. Azo dyes, sulfur dyes, diphenylmethane dyes, thiazole dyes, triphenylmethane dyes, nitro dyes, anthraquinone dyes, nitroso dyes, indigo dyes, quinoline dyes, indigozole acridine dyes, quinoneimine dyes, cyanine dyes (azine, oxazine, thiazine), and phthalocyanine dyes can be used without any problems. These are currently the most commonly used fiber dyes. In some methods, the dyes are removed from the educt in an upstream process. However, in the method disclosed herein, such a process is unnecessary. Furthermore, the metal content of the educt may exceed 10 ppm. Both small metal residues and large metal inclusions are reliably dissolved and removed from the educt. However, alkaline earth metals, alkali metals, and many heavy metals can cause lumps to form in the reaction mixture. These lumps cause filter clogging and inhibit the reaction. It has also been pointed out that heavy metals have catalytic properties and can cause undesirable side reactions. However, if the amount of heavy metals is within the range of 10 ppm or less, it will not affect the reaction. The addition of antioxidants can also be used to deal with high levels of heavy metals.Similarly, in the method of the present disclosure, the educt may be present in the form of a suspension. When the educt is present with a degree of polymerization of 700 or more, the product has a DP value of 450 to 650. Thus, the method of the present disclosure makes it possible to reduce the size of cellulose fibers in the textile waste, to peel the cellulose fibers from the textile waste, or both.

[0014] It is important to carry out the reaction steps without catalysts. In conventional methods, fibers are usually decomposed with the help of acids or bases to adjust the DP value and then further processed. Adding materials to adjust the pH has the disadvantage that the final product is damaged by aggressive chemicals. These chemicals can be removed from the reaction mixture by additional steps, but the damage already caused cannot be restored. Additional washing steps are of course laborious, costly and time-consuming. Disposal of the solvents also becomes more difficult due to contamination. The non-catalytic reaction in the disclosed method is therefore an important step towards a sustainable, environmentally friendly and, if carried out at current reaction temperatures, energy-saving fiber recycling. No PH neutralization of the pulp needs to be carried out. The pH value of the entire process in the disclosed method is about 5.0-9.0. The reaction is carried out in subcritical water at 130-180°C. The reaction time is 1-120 minutes and the pressure is 1-25 bar. The reaction solution has a neutral pH (here measured values ​​of 5-7) and a solid / liquid ratio of 1:10-1:20. No acids, bases or other catalysts are added. The disclosed method is carried out in the absence of oxygen. However, oxygen added in a controlled or predetermined manner can cause oxidative changes, especially changes in the DP value. Moreover, it has been shown that even small applied pressure ratios of 1 bar or even 10 bar or less are sufficient to advantageously carry out the disclosed method.

[0015] That is, the only steps required to obtain the product are filtering, washing, squeezing, and drying by evaporator (e.g. to about 90% dryness). There is no step of pH neutralization of the pulp. Such a step is not necessary. The product is then cut to size for further use.

[0016] In the following, it will be explained that the fiber length of the raw material (educt) affects the stirrability of the mixture. The fiber length also affects the reaction. For example, if the fiber length of the reactant is 1 mm and the mass ratio is 2.5 mass%, the mixture is stirrable, but if the mass ratio is 5 mass%, stirring is difficult, and if the mass ratio is 7.5 mass%, stirring is impossible.

[0017] When the length of the reactive fibers is 0.2 mm, the mixture is easy to stir at a mass percentage of 2.5 mass%, is easy to stir at a mass percentage of 5 mass%, and is stirrable at a mass percentage of 7.5 mass%.

[0018] The mill used, namely the Fritsch universal mill PULVERISETTE 19 (5000 W, 400 V, 3-50 / 60 Hz, 13 Nm, rotation speed: 300-3000 rpm, sieve inlet size: 0.2-1 mm), has proven to be particularly suitable, although other mills can also be used. EXAMPLES

[0019] Non-limiting exemplary embodiments of the present disclosure are described below.

[0020] Old textile fabrics made of cotton with a 5% PET content are selected and cut to a fiber length of 1 mm. Such short fiber length reactants were initially adopted with the aim of comparing many experiments and series of experiments with each other. The length of the raw material contributes to the reaction behavior of the disclosed method due to the different surfaces. The cutting device can be a normal tea shredder. However, the length of the torn and cut textile waste should be as equal as possible. As mentioned above, the degree of coloring of the waste is irrelevant. By carrying out the disclosed method, almost all the textile dyes are dissolved. It is also not a hindrance to the method according to the invention if the raw material is present as a suspension, i.e. finely dispersed in a liquid.

[0021] The raw material can be successfully processed even if it has an average degree of polymerization of 700 or more. The higher the degree of polymerization of the raw material, the more complex the depolymerization that occurs in the reaction process. Finally, an average degree of polymerization of 300-1000, usually 450-650 or even 550-600, is achieved. The more homogeneous and precisely the DP of the final product is adjusted, the better the processability of the final product. Therefore, in this process according to the invention, no preparatory reaction step is necessary.

[0022] The raw materials were loaded into a high-pressure reactor, type BR-300, manufactured by Berghof. With a maximum temperature of 300°C and a maximum pressure of 200 bar, this reactor is ideally suited for the disclosed method. In this reactor, the following six experiments were carried out in particular:

[0023] [Table 1]

[0024] The average degree of polymerization shown in the table was measured at a solid:liquid ratio of 1:20, temperatures of 160°C to 200°C, reaction times of 60 to 180 minutes, and severity factors ranging from 3.54 to 5.20. The severity factor is a coefficient that indicates the severity of the subcritical fluid-hydrothermal pretreatment of the product, in this case the product being used fiber. In mathematical terms, the severity factor is the integral of the steam temperature or temperature and the exposure time. It is therefore an indicator of the severity or intensity of the overall reaction conditions (temperature and pressure in this case) in a chemical reaction. The time and temperature can be read from the table. The reaction pressure was 1 to 10 bar. The solid:liquid ratio ranged from 1:10 to 1:20 in the experiments.

[0025] No catalyst is added, hence it is a non-catalytic process. The final mass is filtered, washed, pressed and the liquid residue is evaporated until the dry matter percentage is about 90%. Again, it should be noted that the respective additional steps, including neutralization of the pulp, are not necessary. The product is then cut to size. The product characteristics are as follows: Cellulose content >90%-92% · Average degree of polymerization is 300-1000, preferably 450-650, ideally 550-600. It should be noted that different end products will require different DP values. · Uncolored / whiteness 80 or higher (according to ISO) ·Metal content:<10-20ppm

[0026] Due to the small number of educts, the by-products were also found in small quantities and at low concentrations: some oligomers, glucose, fructose, and xylose. The concentrations in the dough were negligible, close to 0 g / L.

[0027] Through individual experiments and coordination with each processor, it was found that the raw material product met the following requirements: 1.Cellulose content >92%, 2.Silicate content <80ppm 3. Calcium content <80ppm; 4. Iron content < 10ppm; 5.Moisture content 10%

[0028] These values ​​apply to viscose and also to lyocell as a final product.

[0029] The conditions specified at another processing plant are as follows: High purity = Cellulose content (α-cellulose / long-chain cellulose) >90% Low hemicellulose content: <5% Low lignin content: <0.1% Low content of heavy metals: <10ppm

[0030] [Table 2] The X-axis shows the temperature / time reaction combination and the Y-axis shows the degree of polymerization (DP). It is possible to consider exactly which parameters can be used to set the DP value.

[0031] The average degree of polymerization was determined according to the relevant DIN standards.

[0032] Here, Dry the cellulose overnight in an oven at 60°C. Next, 50 mg of cellulose is transferred to a 50 mL rotary joint vessel (c=1 g / L). Then add 2-4 copper spirals and about 20 small ceramic balls. The copper spirals act as antioxidants and the ceramic balls replace the dead volume in the vessel. Add 50mL of Cuoxam solution to the container. Close the container and shake. Place the container on a vibrating plate overnight to completely dissolve the cellulose. For DP measurements, a viscometer (such as Ubbelohde) is set at 25°C (±0.1°C) using a water bath with temperature control. Before measurement, filter the cellulose solution through a glass filter (glass frit Por.1). · Then, 20 mL of the filtrate is filled into the viscometer. The solution is allowed to stand in the viscometer to allow the temperature to equalize. The solution is then aspirated (e.g. using a pipette) to stop the flow time. · Flow velocity is measured four times for each sample and the average value is calculated. Calculate the specific viscosity based on the average value. The specific viscosity is used to calculate the DP.

Claims

1. A method for producing a cellulose polymer, providing a raw material, i.e., a blend of cotton and PET, having a fiber length of 60 mm to 1 mm or less; treating the raw material with subcritical water in a reactor at a temperature of 130 to 200°C, particularly preferably 160 to 200°C, and a pressure of 1 to 25 bar, preferably 1 to 10 bar, for about 1 to 120 minutes, A method for producing cellulose polymers, wherein no catalyst is used, the pH is between 5 and 7 during the entire reaction time, and the method is carried out in the absence of oxygen.

2. The method for producing a cellulose polymer according to claim 1, further comprising subsequent steps of filtration, washing, squeezing and drying.

3. 2. The method for producing a cellulose polymer according to claim 1, wherein the product has a cellulose content of 90% or more, preferably 92% or more, and an average degree of polymerization, which can be preset, of 300 to 1000 DP, preferably 450 to 650.

4. The method for producing a cellulose polymer according to claim 1 , wherein the raw material may further contain 5% or less of impurity fibers and / or PET components.

5. The method for producing a cellulose polymer according to claim 1 , wherein the raw material further contains 35 ppm or less of a metal component.

6. The method for producing a cellulose polymer according to claim 1, wherein the steam pressure explosion is carried out upstream and / or downstream.

7. Cellulose produced by the production method according to any one of claims 1 to 6.

8. 8. Cellulosic fibers, in particular viscose or lyocell, produced from a cellulose material according to claim 7.