Method for producing textile fibers

Abstract

Method for producing polyurethane-based textile fibers from articles or materials to be recycled. The method provides at least to dissolve a polyurethane fraction of such articles or materials in a polar solvent, thus obtaining a diluted polyurethane solution.

Description

[0001] “METHOD FOR PRODUCING TEXTILE FIBERS”

[0002] FIELD OF THE INVENTION

[0003] The present invention concerns a method for producing polyurethane-based textile fibers starting from articles to be recycled at least partly consisting of polyurethanes, for example clothing articles and accessories or textile materials.

[0004] BACKGROUND OF THE INVENTION

[0005] Articles and materials at least partly consisting of polyurethanes in the form of fibers, laminates, membranes, films or other suitable forms are known. For example, in the clothing sector, there are textile materials at least partly consisting of polyurethane-based fibers (Elastane, also known by the trade name Lycra®). For example, stockings such as tights or suchlike generally consist of mixed woven fibers based on polyamide (Nylon 6 and Nylon 6,6) and on polyurethane. In these stockings, the polyamide fraction typically represents about 85% of the total weight, or in any case a different, generally majority percentage of the textile material.

[0006] For example, shoe soles can contain laminates containing at least one polyurethane fraction.

[0007] For example, materials for clothing articles and accessories such as faux leather can comprise one or more thin polyurethane-based layers, for example a thin cover, or a polyurethane film placed (in jargon, “spread”) on fabrics or bases of different material.

[0008] The polyurethane fiber is primarily prepared by dry spinning, using solvents such as dimethyl acetamide (DMA) or dimethyl formamide (DMF). Other spinning methods (for example, melt spinning) are possible, but generally the materials obtained are of inferior quality in terms of elasticity and general characteristics of the yam. The polyurethanes used are generally copolymers obtained from diisocyanates, both aliphatic and aromatic, with both polyester- and polyether-based polyols. In general, contents by weight of the polyurethane fraction between about 10% and 60% are used for spinning, which guarantee a viscosity that is optimal for spinning. The spinning of more diluted solutions does not allow to obtain good quality fibers.

[0009] Polyurethanes and polyamides cannot be recycled together because the two polymers do not form stable polymer blends usable for injection and compression molding or spinning. For this reason, their direct mechanical recycling is not possible. Various methods for recycling mixed fibers using chemical dissolution or recycling methods are known. WO 2013 / 032408 Al provides to thermally degrade the polyurethane fraction and then recycle it chemically by depolymerization.

[0010] EP 2596932 A2, WO 2021 / 021031 Al and US 5,278,282 provide to dissolve the polyurethane part in a suitable solvent, such as DMF or DMA, in order to recover the clean and therefore recyclable polyamide fraction. The solvents used have to be capable of dissolving polyurethane-based polymers, but not polyamide- based polymers.

[0011] Known solvents with these characteristics are for example DMA, DMF, cyrene or levoglucosenone, mixtures of dimethyl sulfoxide (DMSO) with tetrahydrofuran (THF) and several others, see for example Phan K. et al., “ Analysing the potential of the selective dissolution of elastane from mixed textile fiber waste”, Resources, Conservation and Recycling 191 (2023): 106903 or Vonbriil L. et al. “Solvent Blends for Selective Elastane Dissolution and Recovery from Mixed Polyamide Fabrics” (2023), preprint, available in SSRN 4537767.

[0012] The solubility of polyurethane fibers in the aforementioned solvents is very low: for example, up to 50 liters of DMA are required to effectively recover 1 kilogram of polyurethane fraction from polyamide- and polyurethane-based stockings. This means that the concentration of the solution at exit from the dissolution process can be very low, that is, comprised between 0.1% and 5% by weight of polyurethane fraction depending on the conditions and temperature used in the dissolution process.

[0013] In order for the process to be both economically and environmentally sustainable, the solvent has to be completely recovered and reused in subsequent cycles. The dissolved polyurethane fraction is recovered by evaporation of the solvent or by precipitation in a non-solvent, for example water or ethanol. These processes have several drawbacks.

[0014] The main problem of solvent recovery by evaporation is linked to the high boiling temperatures of the solvent used. For example, the boiling temperature of DMA is 165°C, which requires a lot of energy. In addition, the fluid to be evaporated is very viscous and the evaporation requires complex and expensive equipment, for example agitated film evaporation columns. The evaporation process is especially energy-intensive in the final part of the evaporation, because of the increase in viscosity due to the higher concentration of the polymer solution. Precipitation, on the other hand, requires the subsequent separation of the solvent and the non-solvent by distillation, which can be difficult due to the formation of azeotropes, for example between water and dimethyl acetamide.

[0015] It follows that all known recovery methods are complex and not economically and energy efficient, therefore it is generally not convenient to recover more than about 80% of the solvent, in which case the solution formed by the polyurethane fraction dissolved in the remaining 20% of solvent constitutes an unrecovered waste.

[0016] Furthermore, the material obtainable by eliminating all the solvent cannot be melt spun or injection molded, due to its inherent chemical-physical properties, since it is extremely flexible (low elastic modulus) and has, in melting, low viscosity. It follows that, in order to spin the recovered polyurethane fraction, it has to be redissolved in an appropriate solvent.

[0017] Therefore, while the possible polyamide fraction is recoverable in a known manner, the polyurethane fraction poses process problems for its exploitation at an industrial level that is economically sustainable, also for environmental aspects.

[0018] There is therefore the need to perfect a method for producing polyurethane- based textile fibers starting from articles or materials to be recycled that can overcome at least one of the disadvantages of the state of the art. To do this, it is necessary to solve the technical problem of recovering both the polyurethane material as well as the solvent, so that both can be reused.

[0019] In particular, one purpose of the present invention is to provide a method for producing polyurethane-based textile fibers starting from articles or materials to be recycled that allows to reuse substantially all the polyurethane fraction of the articles or materials to be recycled in an economically sustainable manner. Another purpose of the present invention is to provide a method for producing polyurethane-based textile fibers starting from articles or materials to be recycled that allows to recover substantially all of the solvent used.

[0020] The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

[0021] SUMMARY OF THE INVENTION

[0022] The present invention is set forth and characterized in the independent claim. The dependent claims describe other characteristics of the present invention or variants to the main inventive idea.

[0023] In accordance with the above purposes and to resolve the technical problem described above in a new and original way, also achieving considerable advantages compared to the state of the prior art, a method according to the present invention for producing polyurethane-based textile fibers comprises supplying articles or materials comprising at least one non-polyurethane fraction and one polyurethane fraction.

[0024] In accordance with one aspect of the present invention, the method also comprises: - subjecting the articles or materials to dissolution in the presence of a polar solvent suitable to selectively dissolve the polyurethane fraction. In this way, the polyurethane fraction is dissolved, and a diluted polyurethane solution is obtained;

[0025] - concentrating the diluted polyurethane solution by removing a first part of the solvent by means of evaporation, thus obtaining a concentrated polyurethane solution. The concentrated polyurethane solution has a concentration suitable to be subjected to spinning;

[0026] - spinning the concentrated polyurethane solution. During the spinning, a second part of solvent is separated from the polyurethane fraction. This second part of solvent is suctioned and recovered, together with the first part, in order to reuse the solvent in the dissolution.

[0027] Doing so achieves the advantage of recovering the solvent, which is therefore not dispersed in the environment but can be reused in a new recycling method or in other processes, and at the same time new polyurethane-based textile fibers are produced. In accordance with another aspect of the present invention, the materials are textile materials based on mixed polymer fibers comprising a polyamide fraction between 75% and 95% by weight, in particular between 80% and 90% by weight of the total weight of the textile materials. In accordance with another aspect of the present invention, the polar solvent is chosen from dimethyl acetamide (DMA), dimethyl formamide (DMF), cyrene (levoglucosenone), mixtures of dimethyl sulfoxide (DMSO) with tetrahydrofuran (THF) or other suitable polar solvent that dissolves the polyurethane fraction without degrading it.

[0028] The polar solvent used to dissolve the polyurethane fraction can be used in the quantity of approximately 40 - 60 liters per kilogram of polyurethane fraction present in the articles or materials.

[0029] The concentrated polyurethane solution can comprise polyurethane polymer between 10% and 60% by weight.

[0030] The spinning can be dry spinning, or electrospinning, or wet spinning.

[0031] The solvent recovered by evaporation and suction can be substantially all of the solvent initially used to dissolve the polyurethane fraction.

[0032] The spinning can produce polyurethane-based single-component fibers, or multi-component mixed fibers based on polyurethane and another type of polymer.

[0033] The spinning can produce non-woven fabrics (NWF), or the polyurethane-based fibers obtained from the spinning can be used to create warp and weft textile materials.

[0034] DESCRIPTION OF SOME EMBODIMENTS We will now refer in detail to the possible embodiments of the invention. We must clarify that the function of the phraseology and terminology used in the present description is to provide a non-limiting example of the invention itself, since the scope of protection is defined by the claims. It is understood that elements and characteristics of one embodiment can be conveniently combined or incorporated into other embodiments without further clarifications.

[0035] The present invention concerns a method for producing polyurethane-based textile fibers starting from articles or materials to be recycled comprising at least one polyurethane fraction, such as clothing articles and accessories or textile materials at least partly consisting of polyurethanes in the form of fibers, laminates, membranes, films or other suitable forms.

[0036] In the following disclosure, we will refer in particular to textile articles or materials to be recycled consisting of woven fibers containing at least polyurethane-based fibers, such as textile materials based on mixed polymer fibers comprising at least a first type of polymer fibers and a different second type of polyurethane-based fibers, where the second type of fibers constitutes a polyurethane fraction of the textile materials to be recycled. However, the method described here can also be applied to different materials or accessories to be recycled having at least one polyurethane fraction in the form of fibers, laminates, membranes, films or other suitable forms.

[0037] Preferably, but with no limitation whatsoever, the first type of fibers comprises polyamide-based fibers. The textile materials to be recycled can comprise woven polyamide- and polyurethane-based mixed fibers. These materials preferably comprise a polyamide fraction between 75% and 95% by weight, in particular between 80% and 90% of the total weight of the textile materials, for example about 85%.

[0038] The method comprises at least one dissolution step, in which the polyurethane fraction of the textile material to be recycled is subjected to dissolution in a polar solvent suitable to selectively dissolve the polyurethane fraction without degrading it, for example dimethyl acetamide (DMA), dimethyl formamide (DMF), cyrene or levoglucosenone, mixtures of dimethyl sulfoxide (DMSO) with tetrahydrofuran (THF) or others.

[0039] This material can be immersed, in a known manner, in the solvent for a sufficient period of time, under agitation at a temperature comprised between ambient temperature and the boiling temperature of the solvent. The solvent has to be chosen in such a way that any other components of the textile material, such as polyamide fibers, are not soluble in it.

[0040] In some embodiments, a mixture obtained at the end of the dissolution step can be treated in a known manner, for example filtered, in order to separate polyurethane components of the textile material to be recycled from any other components. A diluted polyurethane solution is thus obtained, formed by the solvent and the polyurethane fraction dissolved therein.

[0041] The method then comprises a step of spinning this polyurethane fraction, which can occur in a known manner, with any spinning method whatsoever that starts from polyurethane polymers dissolved in a solvent, for example in dry mode, that is, dry spinning (for example, but not limited to, electrospinning), or wet mode, that is, wet spinning. Advantageously, spinning allows both to obtain new polyurethane-based fibers starting from the material to be recycled, and also to recover the solvent, which is therefore not dispersed in the environment but can be reused in a new recycling method or in other processes, for example spinning processes. Due to the low solubility of the polyurethane, the amount of solvent needed in the dissolution step is generally high, for example of the order of 40 L (liters) - 60 L of solvent per kilogram of polyurethane fraction. At these concentrations, the diluted polyurethane solution is not spinnable to obtain filaments with good properties. The method can therefore comprise a concentration step prior to the spinning step.

[0042] In the concentration step, a part of the solvent can be easily removed from the diluted polyurethane solution, for example by evaporation, thanks to the reduced viscosity of the diluted polyurethane solution, since this viscosity increases as the amount of solvent decreases. The solvent evaporated in this step can be recovered, for example by condensation, to be reused in a new recycling method or in other processes. We must highlight that up to about 80% of the solvent can be recovered by evaporation in an economically sustainable manner.

[0043] The concentration step provides to concentrate the diluted polyurethane solution by removing a first part of the solvent therefrom until a concentrated polyurethane solution is obtained, having a concentration suitable to undergo spinning. The concentration value to be achieved depends on the type of spinning to be carried out, for example dry spinning or electrospinning, and the type of fiber to be obtained. The weight of the polyurethane fraction in the concentrated polyurethane solution can be between about 10% and 60% of the total weight, that is, a range of concentrations corresponding to viscosities suitable for spinning.

[0044] In the spinning step, the concentrated polyurethane solution is spun, and an additional part of solvent is separated from the spun material. This additional part of solvent can be recovered in a known manner, for example by suction, as is normally the case in known processes for spinning polyurethane-based fibers.

[0045] Given the high ratio between surface area and volume of the fibers, the evaporation of the solvent during spinning is highly efficient, in particular much more efficient than the evaporation only from the surface of the concentrated polyurethane solution, which instead becomes increasingly energy- intensive as the solvent evaporates and the viscosity of the polyurethane solution increases.

[0046] Unlike known methods, the method described heretofore allows to recover substantially all the solvent used in the dissolution step and at the same time to obtain a final product ready to be reused for a new dissolution step or other applications. This decreases the number of steps and processes between the product to be recycled and the new product, achieving clear advantages from an energy, economic and sustainability point of view.

[0047] The method described above can be carried out to recycle not only dry-spun polyurethane fibers using solvents such as DMA and DMF, but also polyurethane fibers obtained by any other method, for example melt spinning, wet spinning, or other industrial techniques. In fact, these fibers are also soluble in DMA or similar solvents, and therefore spinnable again.

[0048] Furthermore, this method can also be carried out for other systems with mixed fibers and pre- and post-consumption waste containing Elastane (polyurethane- based fibers) and / or polyurethane fibers or fractions in general. For example, the method can be carried out starting from clothing articles and accessories or textile materials at least partly consisting of polyurethanes in the form of fibers, laminates, membranes, films or other suitable forms.

[0049] The method can provide to carry out the dissolution, concentration and spinning steps in a same industrial facility or plant, therefore providing to start from articles or materials to be recycled containing at least a polyurethane fraction, to obtain new textile materials containing at least polyurethane-based fibers.

[0050] In some embodiments, the new textile material can be made entirely of polyurethane-based fibers (Elastane). For example, the spinning step can produce polyurethane-based single-component fibers. The spinning step can provide electrospinning to produce non-woven fabrics (NWF) and / or semi-permeable membranes usable as selective membranes for separations or for breathable clothing.

[0051] The new textile material can also comprise both polyurethane-based fibers and also other materials. For example, the spinning step can provide to produce, in a known manner, multi-component mixed fibers based on polyurethane and based on at least one other type of polymer, for example polyamide (Nylon). In some embodiments, the polyurethane-based fibers obtained from the spinning are used to create warp and weft textile materials.

[0052] In some embodiments, the spinning step and / or the concentration step can be preceded in a known manner by additions of additives and / or dyes to the concentrated polyurethane solution.

[0053] In some embodiments, the spinning step can be preceded in a known manner by operations of filtering and / or decoloring the concentrated polyurethane solution.

[0054] In general, the concentrated polyurethane solution obtained as described above can undergo spinning exactly like a concentrated polyurethane solution prepared from virgin polyurethane polymers, that is, not recovered from pre-existing materials.

[0055] According to possible embodiments, the method can provide to carry out the spinning step in a facility or plant different from the one in which the dissolution and concentration steps are carried out, thus considering the concentrated polyurethane solution as a product of a method for recovering articles or materials that include polyurethane, comprising the dissolution and concentration steps, and as a raw material for a spinning method carried out elsewhere.

[0056] It is clear that modifications and / or additions of parts may be made to the method as described heretofore, without thereby departing from the field and scope of the present invention, as defined by the claims.

[0057] It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art will be able to achieve other equivalent forms of method for producing textile fibers, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

[0058] In the following claims, the sole purpose of the references in brackets is to facilitate their reading and they must not be considered as restrictive factors with regard to the field of protection defined by the claims.

Claims

CLAIMS1. Method for producing polyurethane-based textile fibers, comprising:- supplying articles or materials comprising at least one non-polyurethane fraction and one polyurethane fraction,- subjecting said articles or materials to dissolution in the presence of a polar solvent suitable to selectively dissolve said polyurethane fraction, thus obtaining a diluted polyurethane solution,- concentrating said diluted polyurethane solution so that it can be subjected to spinning by removing a first part of said solvent by means of evaporation,- spinning said concentrated polyurethane solution, wherein during said spinning a second part of said solvent is separated from said polyurethane fraction and said second part of said solvent is suctioned and recovered, together with said first part, in order to reuse said solvent in said dissolution.

2. Method as in claim 1, characterized in that said materials are textile materials based on mixed polymer fibers comprising a polyamide fraction between 75% and 95% by weight, in particular between 80% and 90% by weight of the total weight of said textile materials.

3. Method as in any claim hereinbefore, characterized in that said polar solvent is chosen from dimethyl acetamide (DMA), dimethyl formamide (DMF), cyrene (levoglucosenone), mixtures of dimethyl sulfoxide (DMSO) with tetrahydrofuran (THF) or other suitable polar solvent that dissolves said polyurethane fraction without degrading it.

4. Method as in any claim hereinbefore, characterized in that said polar solvent is used in the quantity of approximately 40 - 60 liters per kilogram of polyurethane fraction present in said articles or materials.

5. Method as in any claim hereinbefore, characterized in that said concentrated polyurethane solution comprises polyurethane polymer between 10% and 60% by weight.

6. Method as in any claim hereinbefore, characterized in that said spinning is dry spinning, or electrospinning, or wet spinning.

7. Method as in any claim hereinbefore, characterized in that said solvent recovered by evaporation and suction is substantially all of the solvent initially used to dissolve said polyurethane fraction.

8. Method as in any claim hereinbefore, characterized in that said spinning produces polyurethane-based single-component fibers or multi-component mixed fibers based on polyurethane and another type of polymer.

9. Method as in any claim hereinbefore, characterized in that said spinning produces non-woven fabrics (NWF) or said polyurethane-based fibers obtained from said spinning are used to create warp and weft textile materials.

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