Method for material-specific fibre separation in textile recycling

Abstract

A method (10) for material-specific fibre separation in textile recycling comprises the following steps: i) providing a fibre mixture, comprising fibres of different fibre materials, in the form of a suspension (S18), ii) adding an additive into the suspension, and iii) separating fibres of one fibre material from the rest of the fibre mixture by flotation. According to the invention, step iii) includes a step iii-a) (S30) of separating first fibres of a first fibre material from the rest of the fibre mixture by flotation and a step iii-b) (S36) of separating second fibres of a second fibre material from the rest of the fibre mixture by flotation, wherein step ii) includes, before step iii-a), a step ii-a) (S28) of adding a first additive into the suspension for changing the flotation behaviour of the first fibre material and, before step iii-b), a step ii-b) (S34) of adding a second additive into the suspension for changing the flotation behaviour of the second fibre material, the first additive and the second additive differing at least in their respective physical operating principles, which are based on an interaction of the respective additive with the respective fibre material that changes the floatation behaviour of the respective fibre material.

Description

[0001] 68536P WO Lena Strobl

[0002] - 1 -

[0003] Methods for material-specific fiber separation in textile recycling

[0004] Description

[0005] The present invention relates to a method for material-specific fiber separation in textile recycling, comprising the following steps: i) providing a fiber mixture with fibers of different fiber materials as a suspension, ii) adding an additive to the suspension, iii) separating fibers of one fiber material from the rest of the fiber mixture by flotation.

[0006] Such a process is known from WO 2020 / 127453 A1 for separating cellulose-based and non-cellulose-based fibers from textile waste. The aim of this known process is to purify the cellulose-based fibers and to remove non-cellulose-based fibers, i.e., essentially plastic fibers, from the initial fiber mixture. For this purpose, WO 2020 / 127453 A1 teaches first to mechanically comminute the fiber mixture in order to break up fiber conglomerates. Furthermore, WO 2020 / 127453 A1 teaches to shorten the chain length of the cellulose-based fibers below a target length and to adjust a fiber concentration in the weight percent range of 0.1 to 4 wt.% in a preferably aqueous fiber suspension.

[0007] Subsequent flotation allows the cellulose-based fibers, shortened in their chain length, to be separated from the non-cellulose-based fibers, which are not affected by the chain length shortening, on a density-based basis, especially since the cellulose-based fibers swell in aqueous solution and their density thus increases.

[0008] Prior to separation by flotation, a surfactant can be added. Possible technical objectives for such an additive, disclosed in WO 2020 / 127453 A1, include hydrophobizing a solid surface, influencing bubble formation, influencing the kinetics of particle adhesion to bubbles, and increasing the stability of particle-bubble aggregates. (68536P WO Lena Strobl)

[0009] - 2 - the prevention of foam formation or the stabilization of foams already formed, and the modification of the hardness of the water used in the flotation cell.

[0010] The flotation step can be multi-stage, for example, to separate fibers of different sizes using different bubble sizes. In this process, the less dense, non-cellulose-based fibers always rise to the surface, while the cellulose-based fibers sink.

[0011] From WO 2021 / 181007 A1, a process for separating cellulose-based and non-cellulose-based fibers from a corresponding mixed-fiber textile material is known. This process comprises mechanically comminuting the textile material to open the textile structures within the material. In a subsequent first chemical process step, the mechanically opened structures are wetted with an acid, and in a subsequent second chemical process step, they are wetted with an alkali.

[0012] The comminution of the textile material in the known process is intended to provide fibers of no more than 40 mm in length, with a fiber length in the range of 1 to 5 mm being preferred. The textile material contains cellulose-based fibers, such as cotton fibers, and non-cellulose-based fibers, such as polyester fibers, and fibers made of elastane, polyurethane, polyamide, isoprene-containing material, polyethylene, and polypropylene are also possible.

[0013] The acid treatment is intended to mimic the conditions prior to hydrolysis in the production of chemical pulp, for example, using pre-hydrolysis Kraft pulp technology. The acid treatment reduces the degree of polymerization of the cellulose in the cellulose-based fibers and produces a fiber sludge of suspended fiber mixture. Furthermore, the acid dissolves any metals that may be present in the shredded textile material. The subsequent wetting with alkali is intended to wash the non-cellulose-based components out of the fiber sludge, leaving behind a fiber sludge consisting primarily of purified cellulose-based fibers. The alkali also causes the 68536P WO Lena Strobl

[0014] - 3 - existing cellulose, which improves its accessibility to other substances, such as bleaching agents, in subsequent process steps. Furthermore, the alkali removes a large proportion of the existing color pigments. Polyester is removed by alkaline hydrolysis. Inorganic material is also removed.

[0015] The second chemical process step of the process known from WO 2021 / 181007 A1 comprises wetting the acid-treated fibers with an unspecified surfactant, such as a cationic, non-ionic, or anionic surfactant. Remaining non-cellulose-based material can be separated from the cellulose-based material obtained by the two chemical process steps using density-based separation by one or more centrifuges and / or by one or more flotation cells.

[0016] WO 2019 / 138101 A1 teaches that, to separate a target fiber component from a quantity of shredded textile waste, the water-swellable target fiber component, commonly known as cellulose fiber, is to be swelled by wetting it with aqueous alkali. The alkaline environment in the solution causes the cellulose fiber to swell, resulting in the incorporation of alkali ions, which are heavier than water, into the fibrous structure. This leads to an increase in the density of the target fiber component, which can then be separated from the remaining textile waste based on its density.

[0017] From WO 2013 / 182801 A1, it is known to separate cotton and polyester fibers using a density-based method of flotation. In this process, a fiber mixture obtained by shredding textile waste is saturated with water. Since cotton absorbs considerably more water per unit of time than polyester, which is hydrophobic compared to the hydrophilic cotton, the cotton fibers, whose specific gravity has increased due to water absorption, can be removed as sediment in a flotation process, while the lighter polyester fibers rise to the surface with the gas bubbles generated during flotation.

[0018] A disadvantage of the aforementioned methods is that they essentially always only concern the separation of a specific fiber type from the rest of the textile material. 68536P WO Lena Strobl

[0019] - 4 - and do not treat the remaining textile material beyond general, non-specific instructions.

[0020] It is therefore an object of the present invention to further develop the aforementioned method in such a way that a plurality of fibers of different fiber materials in a fiber mixture resulting from textile waste can be made available for subsequent reprocessing processes.

[0021] The present invention solves this problem by further developing the aforementioned method in such a way that step iii) comprises step iii-a) of separating first fibers from a first fiber material from the remaining fiber mixture by flotation and step iii-b) of separating second fibers from a second fiber material different from the first fiber material from the remaining fiber mixture by flotation, wherein step ii) before step iii-a) comprises step ii-a) of adding a first additive to the suspension to modify the flotation behavior of the first fiber material and before step iii-b) comprises step ii-b) of adding a second additive different from the first additive to the suspension to modify the flotation behavior of the second fiber material.wherein the first and second additives differ at least in their respective physical principles of action, which underlie an interaction of the respective additive with the respective fiber material that alters the flotation behavior of the respective fiber material.

[0022] The process according to the invention is presented in list form as follows: i) providing a fiber mixture with fibers of different fiber materials as a suspension or fiber suspension, ii) adding an additive to the suspension, comprising ii-a) adding a first additive, thereby changing the flotation behavior of a first fiber material based on a first 68536P WO Lena Strobl

[0023] - 5 -

[0024] Interaction of the first additive with the first fiber material, wherein the interaction is based on a first physical principle of action, and ii-b) adding a second additive different from the first additive, thereby changing the flotation behavior of a second fiber material different from the first fiber material on the basis of a second interaction of the second additive with the second fiber material, wherein the second interaction is based on a second physical principle of action different from the first physical principle of action, iii) separating fibers of a fiber material from the rest of the fiber mixture by flotation, comprising iii-a) separating first fibers from the first fiber material from the rest of the fiber mixture by flotation, and iii-b) separating second fibers from the second fiber material from the rest of the fiber mixture by flotation.

[0025] Separation steps iii-a) and iii-b) are preferably carried out in separate flotation processes. To ensure a defined separation of fibers from the first and second fiber materials from each other and from the remaining fiber material, step ii-b) is preferably performed only after step iii-a). The preceding list-like description of the process therefore merely names the steps included in the process, without necessarily prescribing a sequence for all of them. For logical reasons, however, the preparation of the fiber suspension must occur before the addition of additives. Likewise, the flotation behavior of a fiber material must first be modified by the additive before the fibers of this fiber material are separated from and removed from the fiber suspension.

[0026] In contrast to the prior art cited above, the method presented above does not preferably focus on a change in the density of a fiber material as a change in its flotation properties, but rather on a change- 68536P WO Lena Strobl

[0027] - 6 - The wettability of the fiber material by the respective suspension liquid used. Therefore, the separation of fibers from different fiber materials using the method described above is preferably not density-based, but wettability-based. The inventor has recognized that fibers which, due to their shape, have a very large surface area relative to their mass, are captured and entrained by an interface of the suspension liquid surrounding a gas bubble all the more effectively the lower the wettability of the fiber surface by the suspension liquid.

[0028] The described method makes it possible to specifically modify the flotation behavior of individual fiber materials using different additives. By altering the flotation behavior with an additive, the fiber materials whose flotation behavior has been modified or conditioned by different additives can be selectively separated or removed from the fiber suspension in separate flotation processes.

[0029] The fact that the first and second additives alter the flotation behavior of a fiber material due to different physical principles of action forms the basis for the possibility of selectively influencing the flotation behavior of different fiber materials contained in a fiber suspension in different ways and thus at different times. Therefore, it is possible to separate fibers of different fiber materials from the suspension successively using one and the same separation process: flotation.

[0030] Different fiber materials have different inherent properties, so that an influence on the flotation behavior based on a specific physical principle can only affect one fiber material out of a plurality of fiber materials, while the remaining fiber materials are unaffected or less strongly affected by the additive acting according to the specific physical principle.

[0031] In principle, it is therefore possible that an additive consisting of the first and the second additive can influence the flotation behavior of both the first and the second. 68536P WO Lena Strobl

[0032] - 7 -

[0033] The flotation behavior of the first fiber material is altered. To nevertheless allow for the separate removal of both the first and second fiber materials from the provided suspension, it is advantageous to select the first additive such that it alters the flotation behavior of the first fiber material more significantly than the flotation behavior of the second fiber material. Additionally or alternatively, for the same reasons, it is advantageous to select the second additive such that it alters the flotation behavior of the second fiber material more significantly than the flotation behavior of the first fiber material. Preferably, however, during the alteration of the flotation behavior of the second fibers, the first fibers from the first fiber material are already largely, or preferably completely, separated from the suspension and can no longer be influenced by the second additive.

[0034] For example, an additive consisting of the first and second additives can change the flotation behavior of the fiber material associated by physical interaction based on the absorption behavior of the associated fiber material with respect to the suspension liquid of the provided suspension.

[0035] In an advantageously environmentally friendly manner, water can be used as the suspension liquid or at least as the predominant component of the suspension liquid. Preferably, the suspension liquid consists of more than 90% by weight of water. To eliminate or avoid undesirable potential disturbances, the water is preferably demineralized. To increase the efficiency of the flotation processes, a foam-forming and / or foam-stabilizing additive, for example 4-methyl-2-pentanol, can be added to the water.

[0036] Of the fiber materials contained in a fiber mixture of textile origin, individual fiber materials can absorb suspension fluid, especially water, to varying degrees. This means that, within a predetermined time period that is uniform for all fiber materials in the suspension, they absorb or store different amounts of suspension fluid within their own fiber structure. 68536P WO Lena Strobl

[0037] - 8 -

[0038] If the aforementioned additive consisting of the first and second additives, which increases the wettability of a fiber material by the suspension liquid, is mixed into the suspension liquid, the wettability of that fiber material with the highest capacity to absorb the suspension liquid increases the most, since it absorbs the largest quantity of the additive mixed into the suspension liquid in the same amount of time as all the fiber materials present.In a flotation process, after an absorption phase of suitable duration, the less absorbent fiber materials are carried away by the rising bubbles generated in the suspension liquid due to their lower wettability and transported to the surface of the suspension, while the most absorbent fiber material, due to its increased wettability caused by absorption, is not carried away by the bubbles introduced into the suspension liquid and remains as residue or heavy material at the bottom of the flotation cell and can be removed.

[0039] In the case of water as the aforementioned preferred suspension liquid, polyamide, for example, can be separated from the suspension as a fiber material. Polyamide, which, particularly as polyamide-6 and / or polyamide-66, is a fiber material frequently used in textiles, has a greater tendency to absorb or reabsorb water compared to other plastics processed in textiles.If, for example, a polyether, particularly a polyglycol, especially preferably polyethylene glycol, is added to the suspension liquid, in particular water, as an additive acting on the basis of its absorption behavior, polyamide absorbs a particularly large quantity of this additive along with the suspension liquid, in particular water or predominantly water, compared to other fiber materials, and is thereby made more hydrophilic, or more generally, more wettable by the suspension liquid than the other fiber materials. 68536P WO Lena Strobl.

[0040] - 9 -

[0041] Other fiber materials, suspended in a suspension liquid other than water, can have their ability to be wetted by the suspension liquid selectively influenced by a different additive based on their absorption behavior relative to the other suspension liquid.

[0042] The other additive from the first and second additive can, preferably independently of the absorption behavior or at least only in a manner not relevant to the absorption behavior, alter the flotation behavior of the fiber material assigned to this other additive by physical interaction on the basis of an electrical property of the assigned fiber material.

[0043] Different fiber materials can exhibit nominally and / or quantifiably different electrical polarities. For example, a plastic called "polyacrylic," the most common representative of which in textile applications is polyacrylonitrile (PAN), often exhibits anionic groups, such as sulfonates and / or sulfates, at the ends of its molecular chains, both due to the polymerization process and the use of copolymerization with a polar comonomer or additive. These anionic groups, which give polyacrylic and especially PAN a significant electronegativity, are used, for example, in the prior art for dyeing the fibers with cationic dyes.

[0044] Polyester, especially polyethylene terephthalate (PET), which is commonly found in textiles, and elastane, whose main component is the plastic polyurethane, contain hardly any accessible polar groups and therefore exhibit a relatively low electropolarity or are even nonpolar. For example, plastics commonly found in textiles, such as polyester, are slightly electronegative, while polyurethane is slightly electropositive. Therefore, the electronegativity of polyacrylonitrile or polyacrylic can be used as a distinguishing feature from other fiber materials. This allows for the wettability of polyacrylonitrile by the suspension liquid, preferably or predominantly water, compared to other fiber materials of different polarity, to be improved by an additive that interacts specifically with the electronegativity of the polyacrylonitrile. (68536P WO Lena Strobl)

[0045] - 10 -

[0046] To increase nonpolarity. After increasing the wettability of the fiber material, here for example polyacrylonitrile or polyacrylic, by the additive which interacts with a specific fiber material based on an electrical property such as the at least partial polarity or electronegativity of a material, this fiber material, which is more readily wetted by the suspension liquid after interaction with the additive, is less likely to be carried along by the bubbles introduced into the suspension liquid during a flotation process than other fiber materials that are less readily wetted by the suspension liquid.In turn, the less wettable fiber materials are transported to the surface by the bubbles introduced into the suspension fluid in the flotation cell, while the fiber material that is more wettable by the suspension fluid due to the other additive sinks and can be removed as heavy material from the bottom of the flotation cell.

[0047] The additive that interacts with the fiber material based on its electrical properties can be an anionic additive in the case of a fiber material that is more electropositive than other fiber materials, such as polyurethane-based and polyurethane-containing elastane. A sulfide, such as sodium sulfide, is one example of a suitable anionic additive. An additional or alternative anionic additive is a sulfonate, such as lignosulfonate. A sulfate and / or a carboxylate can also be used as an anionic additive, either additionally or as an alternative to the aforementioned anionic additives.

[0048] Accordingly, prior to an interaction between a fiber material and an additive, the electrical potential of the fiber material can be increased by at least one suitable measure, such as plasma treatment, alkaline treatment, acid treatment, or ozone wetting, so that the fiber material subsequently responds more strongly to the additive and enters into the desired interaction with it. 68536P WO Lena Strobl

[0049] - 11 -

[0050] If the fiber material intended for separation from the fiber suspension is more electronegative than the other fiber materials present due to its electrical properties, a cationic additive can be used. A possible cationic additive is a nitrogen-containing chemical compound, in particular an ammonium compound, most preferably a quaternary ammonium compound. Examples of such a nitrogen-containing chemical compound are carbonic acid diamide or an ammonium salt, such as ammonium sulfate.

[0051] Thus, in principle, two different fibers can be selectively separated from the provided fiber suspension, advantageously using the same separation method, namely flotation.

[0052] Each flotation process or flotation step for separating fibers of a fiber material from the suspension can be designed in multiple stages to increase the fiber yield of the flotation process. Different bubble sizes can be used in different stages of the same flotation process.

[0053] In principle, at least one of the following parameters of the suspension fluid can be changed between at least two stages of the same flotation process or flotation step, or between two different flotation processes or flotation steps:

[0054] - Temperature of the suspension fluid,

[0055] - pH value of the suspension liquid,

[0056] - electrical conductivity of the suspension fluid, and

[0057] - Size of the gas bubbles introduced into the suspension fluid.

[0058] A single flotation process within the meaning of the present application is a flotation process or flotation step aimed at the precipitation of a target fiber material. This can take place in several stages. Different flotation processes or flotation steps aim at the precipitation of different target fiber materials. 68536P WO Lena Strobl

[0059] - 12 -

[0060] The fibers used in modern textiles can be selected from a wide variety of fiber materials, not just the first and second fiber materials discussed so far. However, the process presented above can form the core of a general process for recycling fiber materials, in which fibers of different fiber materials can be successively separated from an initial fiber suspension containing a multitude of fibers of different fiber materials through sequential process steps.

[0061] In an advantageous embodiment of the process described above, a third step may be added for separating fibers from a third fiber material in the suspension from the remaining fiber mixture by flotation. This third fiber material is different from the first and second fiber materials in the sense explained above.

[0062] An advantage of this approach is that a flotation process with one or more flotation stages can be used again to separate fibers from the third fiber material from the suspension. Therefore, existing plant infrastructure can, in principle, also be used to separate the third fiber material from the suspension.

[0063] Preferably, the third fibers are separated in the third flotation process without modifying their flotation behavior by an additive. This means that preferably no additive needs to be added to the suspension liquid in preparation for separating the third fibers from the fiber suspension.

[0064] Such separation of third fibers can be carried out for third fibers that, due to their inherent material properties, exhibit higher wettability with respect to the chosen suspension liquid than the other fibers from the other fiber materials. Cellulose is one such material relevant to the textile industry, and cotton is therefore a preferred third fiber material. Cotton is often the only natural fiber in a textile consisting of a fiber blend. 68536P WO Lena Strobl

[0065] - 13 -

[0066] Cotton is inherently more hydrophilic than synthetic fibers used in textiles, which are more hydrophobic compared to cellulose or cotton. This means that cotton can be more readily wetted by a predominantly water-based suspension fluid than synthetic fibers present in the fiber suspension. Therefore, the effect described above can be utilized here as well: when bubbles are introduced into the fiber suspension, the less wettable fibers are transported to the surface more readily by the bubbles introduced for flotation, while the more wettable fibers are less readily carried along by the bubbles and sink in the flotation cell. Thus, these third fibers, considered heavier, can be removed from the bottom of the flotation cell after a flotation process and extracted from the suspension.

[0067] According to a further embodiment of the present invention, the presented method can include a first step of density-based separation of fourth fibers made from a fourth fiber material from the remaining fiber mixture of the suspension. The ordinal number "first" does not necessarily mean that there must also be a second step of density-based separation, but merely identifies the density-based separation step described below as the first one mentioned in the present application.

[0068] The fourth fiber material is different from each fiber material from the first to the third fiber material.

[0069] In order to perform density-based separation, a first embodiment of this further development of the process requires that the suspension liquid have a higher density than the fourth fiber material, but a lower density than a plurality of other fiber materials, particularly preferably than all other fiber materials in the fiber suspension. Therefore, the first step of a density-based separation preferably involves providing the fiber mixture in a fiber suspension with a suspension liquid whose density is greater than the density of the fourth fiber material, but less than the density of at least one fiber material in the remaining fiber mixture. In this case, the fibers of the fourth fiber material can be removed as lightweight material. 68536P WO Lena Strobl

[0070] - 14 -

[0071] Alternatively, according to a second embodiment of this further development of the process, the suspension liquid can have a lower density than the fourth fiber material, but a higher density than a plurality of other fiber materials, particularly preferably than all other fiber materials in the fiber suspension. In this case, the first step of a density-based separation is preferably preceded by providing the fiber mixture in a fiber suspension with a suspension liquid whose density is lower than the density of the fourth fiber material, but higher than the density of at least one fiber material in the remaining fiber mixture. In this case, the fibers of the fourth fiber material can be removed as the heavier material.

[0072] Preferably, the aforementioned suspension liquid, which predominantly comprises or consists of water, is also used for the first step of the density separation. The fourth fiber material can then be a polyolefin whose density is approximately 8 to 10% lower than that of water. This fourth fiber material can be, for example, polyethylene or polypropylene, with polypropylene being by far the most common polyolefin fiber material found in textiles. The previously mentioned possible fiber materials—cotton, elastane, or generally polyurethane or polyurethane-based fiber materials, polyamide, polyacrylonitrile, or generally polyacrylic, as well as polyethylene terephthalate or generally polyester, which is also frequently found in textiles—all have a higher density than water.

[0073] The first step of a density-based separation can be carried out, for example, in a hydrocyclone or a float-sink separator in a manner known per se.

[0074] To achieve the greatest possible degree of fiber material separation, the process can, in a further development, include a second step involving density-based separation of fifth fibers from a fifth fiber material from the remaining fiber mixture in the suspension. The fifth fiber material is different from each fiber material in the first through fourth fiber materials. 68536P WO Lena Strobl

[0075] - 15 -

[0076] The same applies to the ordinal numbers used for fiber materials as were stated above regarding density-based fiber material separation: the ordinal numbers merely reflect the order in which the fiber materials are listed in the present application and do not indicate the existence of fiber materials with a lower ordinal number than the fiber material currently under consideration. For example, the present method can be configured to successively separate a first, a second, and a fourth fiber material from a fiber suspension without the fiber suspension containing a third fiber material that would require separation.

[0077] For the second step of the density-based separation to function correctly, the ratio of the density of the fifth fiber material to the density of the suspension liquid is again crucial. Therefore, according to a first embodiment of this further development of the process, the second step of a density-based separation is preceded by the preparation of the fiber mixture in a fiber suspension containing a suspension liquid whose density is lower than the density of the fifth fiber material but higher than the density of at least one fiber material, preferably all other fiber materials of the remaining fiber mixture. The above statements regarding the density-based separation of the fibers of the fourth fiber material apply mutatis mutandis to the density-based separation of the fibers of the fifth fiber material from the suspension. In this first embodiment, the fibers of the fifth fiber material can be extracted as heavy material.

[0078] Alternatively, according to a second embodiment of this further development of the process, the second step of a density-based separation can be preceded by providing the fiber mixture in a fiber suspension with a suspension liquid whose density is greater than the density of the fifth fiber material but less than the density of at least one fiber material, preferably all other fiber materials of the remaining fiber mixture. In this second embodiment, the fibers of the fifth fiber material can be extracted as lightweight material.

[0079] Often, due to prior separation steps, a fiber suspension will only contain fibers from fiber materials with a higher density. 68536P WO Lena Strobl

[0080] - 16 - exhibit characteristics other than the suspension liquid preferred above, which is predominantly or entirely composed of water. A required increase in the density of the suspension liquid can be achieved by adding at least one additive to the suspension liquid in order to adjust the density of the suspension liquid to a required value. This addition of at least one density-increasing additive is also a possible further development step of the process presented here.

[0081] Thus, the suspension liquid of the second step of a density-based separation can be a free-flowing mixture of a base liquid and at least one additive, where the density of the suspension liquid is the average density of the free-flowing mixture. The base liquid is preferably the suspension liquid of a preceding separation step.

[0082] The fifth fiber material comprises or is preferably a polyester, and the polyester is a polyethylene terephthalate that is preferred and frequently used in the textile industry.

[0083] A particularly preferred embodiment of the method presented here comprises all the separation steps described above, and most preferably all the process steps described above. Although the method functions independently of the chosen sequence of the individual separation steps, the following sequence of separation steps for separating the first to fifth fibers is particularly advantageous: a) the first step of a density-based separation of fourth fibers, b) the separation of the third fibers by flotation, c) the separation of the first fibers by flotation, d) the separation of the second fibers by flotation, e) the second step of a density-based separation of fifth fibers.

[0084] The process starts with the most common fiber materials found in textile products and attempts to separate them by type for subsequent reprocessing or reuse. 68536P WO Lena Strobl

[0085] - 17 -

[0086] Of the most common fiber materials found in textiles, only polyolefins, and among these predominantly polypropylene, are the only fiber material with a lower density than water, or indeed the fiber material with the lowest density. Therefore, polyolefin or polypropylene can be separated from the suspension relatively quickly and easily using the density-based separation method described above.

[0087] The subsequent, preferred separation of the third fibers by flotation without the addition of any additive, solely utilizing the inherent material properties, is the flotation-based separation step requiring the least preparation and is therefore the preferred second separation step after the removal of polyolefin fibers. This allows cotton fibers, or cellulose-based fibers in general, to be removed from the suspension simply and reliably.

[0088] Subsequently, additives are generally required to remove further fibrous materials from the suspension, either to selectively modify the flotation properties of the remaining fibers or to alter the density of the suspension liquid. The mildest of these modifications to the suspension liquid is the addition of additives to influence the flotation properties of the remaining fibers. For this reason, the flotation-based separations of the first and second fiber materials, as described above, are preferably carried out as the next separation steps, each after the addition of a suitable additive.

[0089] The separation steps carried out so far in the preferred method have already removed fibers from a maximum of four different fiber materials from the initial fiber suspension.

[0090] The second step of a density-based separation then takes place, which generally requires a change in the density of the suspension liquid used so far. This removes fibers of a fifth fiber material from the suspension. If the suspension contains only one other fiber material, 68536P WO Lena Strobl

[0091] - 18 - this too can be obtained as sediment or as heavy material from density separation, as the only remaining fibrous material.

[0092] The advantage of this process with separation steps a) to e) lies in the fact that it can be carried out regardless of the composition and without knowledge of the specific composition of the textile waste initially fed into the recycling process and the resulting fiber suspension. This process extracts a maximum of five different fiber materials from a fiber suspension, with any remaining suspended fibers being considered a sixth fraction, provided this residue is homogeneous. Should the provided fiber suspension contain only two or three different fiber materials, all separation steps can still be carried out, especially in the preferred order. Consequently, only some of the separation steps would be ineffective.However, the process allows for its establishment and operation on an industrial scale, as it is able to separate at least five of the most commonly used fibers in textiles into essentially pure types.

[0093] If the process is carried out on a fiber suspension with an unknown fiber material composition, it can be directed towards the separation of one target fiber material from the fiber suspension per separation process step. At least one other target fiber material then replaces at least one of the aforementioned remaining fiber materials in the suspension. Each of the first to fifth fiber materials mentioned above is also a first, second, third, fourth, or fifth target fiber material, respectively. Those target fiber materials of the process that are not the target fiber material of a specific process step are, with respect to that specific process step, considered other target fiber materials.

[0094] The term "fiber" here refers to the smallest linear element of a textile material. In fiber tangles, such as nonwovens, fibers can be directly processed into a textile material through physical interlocking. 68536P WO Lena Strobl

[0095] - 19 -

[0096] In the class of textile fabrics with the greatest relative frequency on the market, woven and knitted fabrics, yarns are used to form them. A yarn is made up of several fibers, which are usually twisted together to create the yarn.

[0097] Textile waste, which forms the basis for textile recycling and thus for the material-specific separation process presented here, generally does not initially contain free fibers, but rather textile fibers as the object of the separation process in mechanically bound form as tangles or yarn. The yarn itself is mechanically bound by weaving or knitting. To obtain free, isolated fibers that can be provided in a suspension, the step of providing a fiber mixture with isolated fibers of different fiber materials as a suspension preferably includes shredding the textile material in a shredding machine and / or using shredding technology. Various devices are suitable as shredding machines, such as a textile mill and / or a tearing drum.Different shredding machines can also work together sequentially to shred textile waste. Possible designs for textile mills include cutting mills, pin mills, disc mills, colloid mills, and the like. The principle is that the more tightly the individual textile fibers to be recovered are mechanically bound in the original textile material by physical entanglement, the more intensive the shredding must be.

[0098] Similarly, the step of providing a fiber mixture with fibers of different fiber materials as a suspension preferably includes sorting out non-textile components, such as zippers, buttons, hooks and eyes, and the like.

[0099] The present application also relates to a sorting and separation system for material-specific fiber separation in textile recycling, which is designed to carry out the process described above. The devices of the sorting and separation system, which are suitable for carrying out the respective process step, are described in 68536P WO Lena Strobl.

[0100] - 20 - and therefore may be part of the sorting or separation system, are mentioned in connection with the process step concerned.

[0101] The present invention will be explained in more detail below with reference to the accompanying drawing. It illustrates:

[0102] Fig. 1 shows a rough schematic flow diagram of the process for material-specific fiber separation of the present application.

[0103] In Fig. 1, the sequence of an embodiment of the method described above is generally designated by 10.

[0104] The method of this embodiment begins with step S10, in which textile waste, such as discarded clothing, is provided, either by delivery, collection, or the like. In step S10, the textile waste is provided uncontaminated, i.e., without significant soiling, but generally used.

[0105] In a subsequent sorting step S12, the textile waste from step S10 is cleaned of non-textile components, such as fasteners and non-textile decorations, so that after step S12 the textile waste consists essentially exclusively of textile material. Special textiles, such as functional clothing with specific impregnations or membranes, can also be sorted out in sorting step S12.

[0106] In a subsequent step S14, the product of step S12 is further reduced in size by textile mills and shredding drums until the fiber material contained in the textile waste is essentially unbound. The composition of the fiber material is unknown and is irrelevant for the execution of the following process steps. However, it is reasonable to assume that the fiber material consists predominantly of one or more fiber materials from the materials used for textile fibers: cotton (including viscose, rayon, and similar cotton derivatives), polypropylene, polyamide, elastane, or, more generally, polyurethane. 68536P WO Lena Strobl

[0107] - 21 - polyurethane-based fiber materials, polyester and polyacrylic. These fiber materials constitute the target fiber materials, the individual separation of which from the provided fiber mixture is the aim of the present process.

[0108] In the subsequent step S16, the isolated fibers obtained in step S14, which preferably have a length in the single-digit millimeter range, are suspended in a suspension liquid that consists predominantly, i.e., at least 90 wt.%, preferably at least 95 wt.%, and particularly preferably at least 98 wt.% of water. The suspension is preferably stirred to achieve the most homogeneous distribution possible of the fiber components in the suspension liquid.

[0109] In this case, steps S10, S12, S14 and S16 form a first step complex S18, which provides a fiber suspension from a mixture of individual textile fibers.

[0110] In step S20, polypropylene fibers contained in the fiber suspension are separated using density-based separation, for example in a hydrocyclone or a float-sink separator. Polypropylene fibers have the lowest density of all fiber materials commonly used in textiles, and, most importantly, they have a lower density than the aqueous suspension liquid. Therefore, they can be easily separated from other fibers by density separation, as these fibers typically have not only a higher density than polypropylene, the target fiber material in step S20, but also a higher density than the suspension liquid.

[0111] In step S22, the discarded polypropylene fibers are fed into a subsequent use.

[0112] Subsequently, a first flotation step S24 is carried out with the heavy material from step S20. The fiber components of different fiber materials that remain in the suspension after the separation of the polypropylene fibers are all suspended in the suspension liquid for the same period of time. (Possibly 68536P WO Lena Strobl)

[0113] - 22 - Pulp-based fibers, especially cotton fibers, contained in the fiber suspension are inherently more hydrophilic than the other plastic fibers contained in the fiber suspension. Therefore, in flotation step S24, which can consist of several successive flotation stages or flotation sub-steps, pulp-based fibers, especially cotton fibers, are not carried along by the bubbles introduced into the fiber suspension, or are carried along less effectively, than the plastic fibers, which are more hydrophobic compared to the pulp-based fibers. Pulp-based material, especially cotton and cotton derivatives, is therefore the target fiber material of step S24.

[0114] The cellulose-based fibers can therefore be removed from the suspension as heavy material after the flotation step S24 has been carried out and fed into a further processing step S26 of cellulose-based fibers.

[0115] The remaining suspension containing the light material from flotation step S24 is mixed with polyethylene glycol as the first additive in step S28. Again, the residence time in the suspension liquid mixed with the first additive is the same for all fiber materials remaining in the suspension.

[0116] Of the remaining fiber materials, polyamide exhibits the strongest absorption properties and absorbs a greater quantity of the suspension liquid mixed with the first additive in the same amount of time than the other fiber materials in the suspension. Due to the correspondingly larger amount of first additive absorbed, polyamide, as the target fiber material of the subsequent step S30, becomes more hydrophilic, or more generally, more readily wettable by the suspension liquid, than the other fiber materials or target fiber materials. Thus, in flotation step S30, textile fibers made of hydrophilized polyamide remain as the heavier material in the flotation cell, while the remaining fibers, made of fiber materials or target fiber materials that are less hydrophilic or more hydrophobic compared to the polyamide fibers, or more generally, less readily wettable by the suspension liquid, rise to the surface in flotation step S30.The polyamide fibers separated from the suspension as heavy material can be fed into step S32 for further processing. 68536P WO Lena Strobl.

[0117] - 23 -

[0118] In a subsequent step S34, a second additive is mixed into the suspension containing the lightweight material resulting from the flotation step S30, which may consist of several stages or sub-steps. While the first additive influenced the flotation behavior of different fiber materials in different ways due to its varying absorption properties, the second additive influences the flotation behavior of the remaining fiber materials differently due to their varying electrical properties.

[0119] Ammonium sulfate, for example, is added as a second additive in a cationic form. This cationic additive reacts with more electronegative fiber materials, while it does not react with more electropositive fiber materials due to their similar polarity. Likewise, the additive does not react with nonpolar fiber materials.

[0120] Of the most commonly used plastic fiber materials mentioned at the beginning, only polyacrylic is electronegative. Due to the cationic additive, which interacts only with polyacrylic because of the prevailing electrical properties, only polyacrylic-containing fiber material, such as polyacrylonitrile, becomes hydrophilic, while the other fiber materials remain more hydrophobic compared to the polyacrylic-containing fiber material. Polyacrylic-containing fiber material, as the target fiber material of step S36, will therefore sink to the bottom of the flotation cell as heavy material in a further flotation step S36, which may comprise several stages or sub-steps, while the fibers from the other fiber materials or target fiber materials will be carried along by the bubbles introduced into the fiber suspension and transported to its surface as light material.

[0121] The polyacrylic-containing fiber material separated by flotation step S36 can be removed from the flotation cell as heavy material and fed into step S38 for further processing of polyacrylic-containing fiber material. 68536P WO Lena Strobl

[0122] - 24 -

[0123] In step S40, the density of the suspension fluid is subsequently increased by adding another additive until it is lower than that of polyester, particularly polyethylene terephthalate, but higher than that of elastane. The density range of polyester, the target fiber material of the subsequent step S42, is typically between 1.36 and 1.41 g / cm³. 3 , that of elastane, which is made up of at least 85 wt% polyurethane, in the range of 1.15 to 1.20 g / cm² 3 The density of the suspension liquid can be increased, for example, to a value in the range of 1.25 to 1.30 g / cm³ by the addition of further additives. 3be hired.

[0124] In a further density-based separation step S42, polyester, especially polyethylene terephthalate, is removed as heavy material from the suspension and fed to a step S44 for further processing of polyester fibers.

[0125] If the remaining suspension contains only polyurethane-based fibers, especially elastane fibers, these are also separated by material-specific means by removing polyester fibers and can be fed into step S46 of further processing of polyurethane-based fibers.

[0126] If, however, the remaining suspension contains other plastic fibers in addition to polyurethane-based fibers, these can be disposed of in a disposal step S48, possibly thermally.

[0127] The present process allows for the material-specific separation of fibers from five, or optionally six, different fiber materials, regardless of the original composition of the initially input textile material. The process can therefore make a valuable contribution to textile recycling.

Claims

68536P WO Lena Strobl - 25 - Claims 1. A method (10) for material-specific fiber separation in textile recycling, comprising the following steps: i) providing a fiber mixture with fibers from different fiber materials as a suspension (S18), ii) adding an additive to the suspension, iii) separating fibers of one fiber material from the rest of the fiber mixture by flotation, characterized in that step iii) comprises step iii-a) (S30) of separating first fibers from a first fiber material from the rest of the fiber mixture by flotation and step iii-b) (S36) of separating second fibers from a second fiber material different from the first fiber material from the rest of the fiber mixture by flotation,wherein step ii) prior to step iii-a) comprises step ii-a) (S28) of adding a first additive to the suspension to modify the flotation behavior of the first fiber material and prior to step iii-b) comprises step ii-b) (S34) of adding a second additive, different from the first additive, to the suspension to modify the flotation behavior of the second fiber material, wherein the first and the second additive differ at least in their respective physical principles of action which underlie an interaction of the respective additive with the respective fiber material that modifies the flotation behavior of the respective fiber material.

2. Method (10) according to claim 1 , characterized in that the first additive changes the flotation behavior of the first fiber material more than the flotation behavior of the second fiber material and that the second additive changes the flotation behavior of the second fiber material more than the flotation behavior of the first fiber material. 68536P WO Lena Strobl - 26 - 3. Method (10) according to claim 1 or 2, characterized in that an additive from the first and second additive changes the flotation behavior of the fiber material associated by physical interaction based on an absorption behavior of the associated fiber material and / or that the other additive from the first and second additive changes the flotation behavior of the fiber material associated by physical interaction based on an electrical property of the associated fiber material.

4. Method (10) according to claim 3, characterized in that the additive interacting with the associated fiber material on the basis of the absorption behavior of the associated fiber material is a polyether, in particular a polyglycol, especially preferably polyethylene glycol.

5. Method (10) according to claim 3 or 4, characterized in that the additive interacting with the fiber material on the basis of the electrical property of the fiber material is an anionic additive, such as a sulfide, in particular sodium sulfide, and / or a sulfonate, in particular lignosulfonate, and / or a sulfate and / or a carboxylate, or a cationic additive, in particular a nitrogen-containing chemical compound, such as an ammonium compound, particularly preferably a quaternary ammonium compound, such as ammonium sulfate.

6. Method (10) according to one of the preceding claims, characterized in that it comprises a step (S24) of separating third fibers from a third fiber material from the remaining fiber mixture by flotation, wherein the third fiber material is different from the first and the second fiber material. 68536P WO Lena Strobl - 27 - 7. Method (10) according to claim 6, characterized in that the third fibers are separated in the third flotation process without modification of their flotation behavior by an additive.

8. Method (10) according to one of the preceding claims, characterized in that it comprises a first step (S20) of a density-based separation of fourth fibers from a fourth fiber material from the remaining fiber mixture, wherein the fourth fiber material is different from each fiber material from the first to the third fiber material, wherein the first step (S20) of a density-based separation is preceded by a provision (S18) of the fiber mixture in a fiber suspension with a suspension liquid whose density is greater or less than the density of the fourth fiber material, but less or greater than the density of at least one fiber material of the remaining fiber mixture.

9. Method (10) according to claim 8, characterized in that the fourth fiber material is a polyolefin, wherein the suspension liquid is water or comprises predominantly water with respect to its mass.

10. Method (10) according to one of the preceding claims, characterized in that it comprises a second step (S42) of a density-based separation of fifth fibers from a fifth fiber material from the remaining fiber mixture, wherein the fifth fiber material is different from each fiber material from the first to the fourth fiber material, wherein the second step of a density-based separation is preceded by a provision of the fiber mixture in a fiber suspension with a suspension liquid whose density is less or greater than the density of the fifth fiber material, but greater or less than the density of at least one fiber material of the remaining fiber mixture. 68536P WO Lena Strobl - 28 - 11. Method (10) according to claim 10, characterized in that the suspension liquid of the second step of a density-based separation is a flowable mixture of a base liquid and at least one additive, wherein the density of the suspension liquid is the mean density of the flowable mixture.

12. Method (!0) according to claim 10 or 11, characterized in that the fifth fiber material comprises or is polyester, in particular polyethylene terephthalate.

13. Method (10) according to one of the preceding claims, including claims 6, 8 and 10, characterized in that the individual steps for separating the first to fifth fibers are carried out in the following order: a) the first step (S20) of a density-based separation of fourth fibers, b) the separation of the third fibers by flotation (S24), c) the separation of the first fibers by flotation (S30), d) the separation of the second fibers by flotation (S36), e) the second step (S42) of a density-based separation of fifth fibers.

14. Method according to one of the preceding claims, characterized in that the step (S18) of providing a fiber mixture with isolated fibers of different fiber materials as a suspension comprises comminution (S14) of textile material in a comminution machine, in particular a cutting mill, tearing tambour, and / or using comminution technology.

15. Method according to one of the preceding claims, characterized in that the step (S18) of providing a fiber mixture with fibers of different fiber materials as a suspension comprises sorting out (S12) non-textile components.

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