A method for separating synthetic fibers from fabrics with mixed composition

Abstract

A method for separating synthetic fibers from cellulosic fibers contained in a fabric with a mixed composition comprising the following steps: (a) soaking the fabric in an aqueous solution of at least one soluble metaperiodate; (b) adding to the solution at least one cellulose solubilizing compound, achieving the solubilization of the cellulosic fibers; (c) filtering the solution by separating the solubilized cellulosic fibers from the synthetic fibers.

Description

[0001] "A method for separating synthetic fibers from fabrics with mixed composition"

[0002] ★ ★ ★

[0003] TECHNICAL FIELD

[0004] This invention concerns a method for separating and recovering synthetic fibers from fabrics with mixed composition, i.e. containing cellulosic derivatives.

[0005] TECHNOLOGICAL BACKGROUND

[0006] Mixed fabrics, consisting of a combination of natural fibers (such as cotton and other cellulosic fibers) and synthetic fibers (such as polyester and nylon) , represent a significant challenge for the textile recycling industry. These materials are widely used in clothing and other textile products for their combined properties of comfort, resistance and versatility. However, the presence of different fibers makes their separation and efficient recycling difficult .

[0007] The main causes of this difficulty are attributable to :

[0008] 1. Material Incompatibility: the different chemical and physical properties of natural and synthetic fibers make their treatment with conventional methods complicated .

[0009] 2. Quality Degradation: current recycling methods often result in a significant loss of material quality, making it difficult to reuse the fibers in new high- quality textile products.

[0010] 3. High Costs: Existing mechanical and chemical separation techniques are expensive and not always efficient, limiting their use on a large scale.

[0011] OBJECT AND SUMMARY The object of this invention is to provide a method for recovering synthetic fibers from fabrics with a mixed composition that is applicable industrially, i.e. that does not involve degradation of the synthetic fibers and is economically sustainable.

[0012] According to one or more embodiments, these objects are achieved thanks to what is specifically referred to in the attached claims, which constitute an integral part of this description.

[0013] In one embodiment, this invention concerns a method for separating synthetic fibers from cellulosic fibers contained in a fabric with a mixed composition comprising the following steps:

[0014] (a) soaking the fabric in an aqueous solution of at least one soluble metaperiodate;

[0015] (b) adding to the solution:

[0016] (b-1) at least one primary or secondary amine, or at least one hydrazine or hydrazide, or

[0017] (b-2) at least one oxidizing compound, achieving the solubilization of the cellulosic fibers ;

[0018] (c) filtering the solution by separating the solubilized cellulosic fibers from the synthetic fibers.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention will now be described, by way of example only, with reference to the attached drawings, where :

[0021] - Figure 1: SEC curve recorded with DAD detector extracting the wavelength at 254 nm on a reference polyester sample.

[0022] - Figure 2: SEC curve recorded with DAD detector extracting the wavelength at 254 nm on a polyester sample treated with the method according to this invention. - Figure 3 : DSC trace of a reference polyester s amp 1 e .

[0023] - Figure 4 : DSC trace of a polyester sample treated with the method according to this invention .

[0024] DETAILED DESCRIPTION OF SOME EXEMPLARY EMBODIMENTS

[0025] In the following description, numerous speci fic details are presented to provide a complete understanding of the embodiments . The embodiments may be practiced without one or more of the specific details , or with other methods , components , materials , etc . In other cases , well-known structures , material s , or operations are not shown or described in detail to avoid obscuring certain aspects of the embodiments .

[0026] Throughout this speci fication, reference to "one embodiment" or "an embodiment" means that a particular configuration, structure , or feature described in connection with the embodiment is included in at least one embodiment . Thus , the appearance of the phrases " in one embodiment" or " in a certain embodiment" at various places throughout this speci fication does not necessarily refer to the same embodiment . Furthermore , the particular configurations , structures , or features may be combined in any suitable manner in one or more embodiments .

[0027] The headings and references used herein are merely for convenience and do not construe the scope or meaning of the embodiments .

[0028] Ef fectively separating mixed textile materials not only allows the recovery of natural and synthetic f ibers for the production of new fabrics , but also the reuse of recovered raw materials in industries other than textiles , expanding application opportunities in areas such as the production of composites , construction industry, production of plastics , and other innovative applications .

[0029] Furthermore , recycling and reusing existing fibers not only reduces pressure on natural resources but also contributes to a more sustainable management of raw materials in the textile sector .

[0030] Improving the ef ficiency of textile recycling is a crucial factor in reducing production costs . A more ef ficient recycling method allows companies to reduce the costs associated with purchasing new raw materials and waste management . This , in turn, increases the competitiveness of companies in the market , allowing them to of fer products at more competitive prices and to better respond to growing consumer demands for sustainability .

[0031] In addition, separating and recycling mixed fabrics signi ficantly contributes to reducing the amount of textile waste that ends up in landfills . Currently, a considerable part of non-recycled fabrics is disposed of as waste , creating environmental problems and taking up valuable space in landfills . An ef ficient recycling system allows materials that would otherwise be wasted to be reintroduced into the production cycle , reducing the overall environmental impact .

[0032] Ef ficient recycling of textile materials also saves precious natural resources such as water and energy that would otherwise be needed to produce new fibers . The production of new fibers , especially synthetic ones , requires signi ficant energy and water consumption, as well as the use of chemicals . Recycling existing fibers reduces the demand for these resources , contributing to a more sustainable management of the environment .

[0033] Recycling synthetic and natural fibers helps reduce CO2 emissions associated with the production of new materials . The production of virgin fibers involves a high consumption of energy and resources , which results in signi ficant greenhouse gas emissions . Recycling, on the other hand, requires less energy and produces fewer emissions , helping to mitigate climate change . Promoting textile recycling helps to create a more sustainable production cycle and reduce the carbon footprint of the textile industry .

[0034] The method according to this invention allows to signi ficantly reduce the dependence on virgin raw materials such as cotton and polyester, which require signi ficant resources for their production .

[0035] The use of the method according to this invention for separating mixed textile materials not only improves recycling ef ficiency but also stimulates innovation within the textile industry . These new methodologies can lead to advanced technological developments , creating new opportunities for the industry and fostering the growth of new technologies . This technological dynamism is essential to keep the texti le industry abreast of global trends and to develop increasingly advanced and sustainable products .

[0036] In one embodiment , this invention relates to a method for separating synthetic fibers from cellulosic fibers contained in a fabric with a mixed composition comprising the following steps :

[0037] ( a ) soaking the fabric in an aqueous solution of at least one soluble metaperiodate ;

[0038] (b ) adding to the solution at least one cellulose solubili zing compound selected from :

[0039] (b- 1 ) a primary or secondary amine , a hydrazine or a hydrazide , or

[0040] (b-2 ) an oxidi zing compound, achieving the solubili zation of the cellulosic fibers ;

[0041] ( c ) filtering the solution by separating the solubilized cellulosic fibers from the synthetic fibers.

[0042] In one embodiment, the synthetic fibers are selected from fibers based on polyester, nylon (polyamide) , polypropylene, polyethylene, elastane (spandex, lycra) .

[0043] In one embodiment, the synthetic fibers obtained in step (c) are washed, dried and optionally melted to produce synthetic chips.

[0044] In one embodiment, the at least one soluble metaperiodate is selected from sodium metaperiodate, potassium metaperiodate, ammonium metaperiodate, or metaperiodic acid.

[0045] In one embodiment, the at least one soluble metaperiodate is added to the solution in an amount of 5 to 60% by weight based on the weight of the fabric.

[0046] In one embodiment, step (a) is carried out at room temperature .

[0047] In one embodiment, step (a) is carried out at a temperature of 10 to 80°C.

[0048] In one embodiment, step (a) lasts for 10 to 90 minutes .

[0049] In one embodiment, at the end of step (a) the fabric is rinsed with water.

[0050] In one embodiment, the at least one primary amine has the formula (I)

[0051] R1-NH2 (I) where Ri is a linear or branched Ci-s alkyl group, preferably C1-6, unsubstituted or substituted with one or more substituents, or an aryl or heteroaryl group containing 5 or 6 carbon atoms, unsubstituted or substituted with one or more substituents, wherein the one or more substituents are independently selected from hydroxyl , carbonyl, carboxyl or amine.

[0052] In a preferred embodiment, the at least one primary amine of formula (I) is selected from ethanolamine, methylamine, ethylamine, diethylenediamine, butylamine, aniline, phenylalanine, tryptophan, lysine, histidine, glycine, propylamine, isopropylamine, pentylamine, cyclohexylamine, benzylamine, serine and threonine.

[0053] In one embodiment, the at least one secondary amine has the formula (II)

[0054] R2-NH-R3 (II) where R2 and R3 are independently selected from a linear or branched Ci-s alkyl group, preferably C1-6, unsubstituted or substituted with one or more substituents, or an aryl or heteroaryl group containing 5 or 6 carbon atoms, unsubstituted or substituted with one or more substituents, wherein the one or more substituents are independently selected from hydroxyl, carbonyl, carboxyl or amine.

[0055] In a preferred embodiment, the at least one secondary amine of formula (II) is selected from diethylamine, dimethylamine, ethylmethylamine, piperidine, morpholine, N-methylethanolamine, N- ethylethanolamine, N-phenethylamine, N-methylaniline, N, N-dimethylpropylamine and N, N-diethylpropylamine .

[0056] In one embodiment, the at least one hydrazine has formula (III) :

[0057] R4-NH-NH2 (HI) wherein Ri, R2, R3, and R4are independently selected from a linear or branched Ci-s alkyl group, or an aryl group, each unsubstituted or substituted with one or more substituents independently selected from hydroxyl, carbonyl, carboxyl, and amine.

[0058] In one preferred embodiment, the at least one hydrazine of formula (III) is selected from methylhydrazine, ethylhydrazine, isopropylhydrazine, phenylhydrazine, 4-aminophenylhydrazine, and hydrazine hydrate .

[0059] In one embodiment, the at least one hydrazide has formula ( IV) :

[0060] R4-CO-NH-NH2(IV) wherein Ri, R2, R3, and R4are independently selected from a linear or branched Ci-g alkyl group, or an aryl group, each unsubstituted or substituted with one or more substituents independently selected from hydroxyl, carbonyl, carboxyl, and amine.

[0061] In one preferred embodiment, the at least one hydrazide of formula (IV) is selected from carbohydrazide, adipic acid dihydrazide (ADH) , benzoic acid hydrazide, succinic dihydrazide, and isophthalic acid dihydrazide.

[0062] In one embodiment, the at least one primary or secondary amine is added to the solution in an amount of 0.1 to 20% by weight based on the weight of the fabric.

[0063] In one preferred embodiment, the at least one hydrazine or hydrazide is added to the solution in an amount of 0.1 to 20.0% by weight based on the weight of the fabric.

[0064] In one embodiment, step (b-1) is carried out at a temperature of 10 to 80°C.

[0065] In one embodiment, step (b-1) lasts for 1 to 90 minutes .

[0066] In one embodiment, step (b-1) is carried out in the presence of at least one acid, preferably at least one weak acid.

[0067] In one embodiment, the at least one weak acid is selected from organic or inorganic acids having a pKabetween 3.5 and 10.5, preferably between 3.5 and 7, measured in an aqueous solution having an ionic strength of 0 and a temperature of 25°C. The acid maintains the pH of the solution containing the at least one primary and / or secondary amine at a value typically between 3 and 6, preferably between 4.5 and 5.5. In this way, the slightly acidic environment favors the condensation reaction between an aldehyde and a primary or secondary amine. Controlling the pH in this range allows avoiding excessive protonation of the amine, keeping it available for reaction with the aldehyde and at the same time prevents degradation of the aldehyde itself. This environment therefore allows greater efficiency, stabilizing the reaction product without negatively affecting the process rate.

[0068] In a preferred embodiment, the at least one acid is selected from acetic acid, citric acid, lactic acid, phosphoric acid, ascorbic acid and formic acid.

[0069] In one embodiment, at the end of step (a) and before step (b-2) , at least one strong base is added to the solution .

[0070] In one embodiment, the at least one strong base is selected from organic or inorganic bases having a pKb between 0.2 and 4.75, measured in an aqueous solution having an ionic strength of 0 and a temperature of 25°C.

[0071] In a preferred embodiment, the at least one strong base is selected from caustic soda, caustic potash, calcium hydroxide or ammonium hydroxide.

[0072] The strong base used in this step allows the depolymerization of the cellulose by breaking the polymer chains by an alkaline hydrolysis process.

[0073] In one embodiment, the at least one strong base is added to the solution in an amount of 1 to 15% by weight based on the weight of the fabric.

[0074] In one embodiment, the reaction with the at least one strong base is carried out for a period of time of 1 to 90 minutes.

[0075] In one embodiment, the at least one oxidizing compound has a standard redox potential (E°) preferably equal to or greater than +0.5 V with respect to a standard hydrogen electrode (SHE) .

[0076] In one embodiment, the at least one oxidizing compound has a standard redox potential (E°) preferably equal to or greater than +1.0 V with respect to a standard hydrogen electrode (SHE) .

[0077] In one embodiment, the at least one oxidizing compound is selected from oxidizing compounds having a standard redox potential (E°) greater than +1.0 V with respect to a standard hydrogen electrode (SHE) , such as chlorite, permanganate, hydrogen peroxide, periodate, peracetic acid, ozone, hypochlorite, dichromate, nitric acid, bromine.

[0078] In one embodiment, the at least one oxidizing compound is selected from oxidizing compounds having a standard redox potential (E°) between +0.5 V and +1.0 V with respect to a standard hydrogen electrode (SHE) , such as chlorine, hypochlorous acid, ferrate ion.

[0079] The oxidizing compound is capable of oxidizing the dialdehyde formed into dicarboxylic acids with consequent solubilization of the cellulosic fibers.

[0080] In one embodiment, the at least one oxidizing compound is added in an amount between 1 and 20% by weight based on the weight of the fabric.

[0081] In one embodiment, step (b-2) is carried out for a period of time between 1 and 90 minutes.

[0082] In one embodiment, step (b-2) is carried out at a temperature between 10 and 80°C.

[0083] In one embodiment, at the end of step (b-2) , in order to salify and therefore solubilize the previously carboxylated cellulose fibers, the at least one strong base is added to the solution.

[0084] In one embodiment, the at least one strong base is added in an amount between 0.1% and 1% by weight based on the weight of the fabric.

[0085] It is important to note that, at the end of the dicarboxylation reaction (step b-2) , the addition of a strong base in small amounts promotes the salification and solubilization of the cellulosic fibers (providing the cation necessary for the salification of the carboxylic groups) , effectively completing the process.

[0086] In one embodiment, the fabric is subjected to a shredding operation before step (a) .

[0087] In one embodiment, step (b) is carried out under stirring of the solution containing the at least one cellulose solubilizing compound (primary or secondary amine, hydrazine, hydrazide, or oxidizing compound) .

[0088] In one embodiment, step (b) is carried out under mechanical stirring at a speed ranging from 200 to 600 rpm.

[0089] The stirring speed can be easily selected from the skilled man in view of the viscosity of the medium and the f abric-to-liquor ratio. Stirring ensures homogeneous dispersion of the cellulose solubilizing compound and maximizes fiber-liquid contact.

[0090] In one embodiment, the mechanical stirring was carried out by means of a magnetic stirrer or overhead mechanical stirrer, depending on the batch size.

[0091] Agitation is maintained throughout the entire duration of the step (b) , and it is critical for preventing fiber sedimentation and promoting efficient reagent penetration into the fiber structure.

[0092] In one embodiment, step (b) comprises an ultrasonic irradiation of the solution containing the at least one cellulose solubilizing compound (primary or secondary amine, hydrazine, hydrazide, or oxidizing compound) .

[0093] In one embodiment, the ultrasonic irradiation is applied at a potency comprised between 100 and 400 W.

[0094] In one embodiment, the ultrasonic irradiation is applied at a frequency comprised between 20 and 40 kHz, preferably 24 kHz.

[0095] In one embodiment, the ultrasonic irradiation is applied at an amplitude comprised between 20 and 100 %, preferably between 40 and 60% for delicate substrates .

[0096] In one embodiment , the ultrasonic irradiation is carried out for a period of time comprised between 1 and 30 minutes , preferably 5 minutes , depending on the fabric density and bath ratio .

[0097] These parameters were optimi zed using a probe-type sonicator (Hielscher UP400St ) equipped with a titanium sonotrode ( 40 mm diameter ) to ensure ef fective cavitation and promote rapid separation of the cellulosic matrix without damaging the synthetic fibers .

[0098] The method according to this invention represents an innovation in the field o f chemistry applied to the recycling of fabrics . This method introduces a procedure based on chemical reactions to ef fectively separate cellulosic fibers from synthetic fibers in mixed fabrics without damaging the synthetic material . In particular, the use of a soluble metaperiodate to create dialdehyde groups on the cel lulosic fibers represents an innovative and promising approach in the field . This method occurs through the selective oxidation of vicinal dihydroxyl groups present in the anhydroglucose units of cellulose , resulting in the opening of the ring between the C2 and C3 positions , and the formation of two aldehyde groups . Subsequently, the dialdehyde groups can react with a primary or secondary amine to form a soluble polymeric compound or with an oxidi zing compound to carboxylate the aldehyde groups and solubili ze the cellulose . An additional advantage of this technique is that the entire process never exceeds a temperature of 60 ° C, making it safer and more energy ef ficient , as well as avoiding damage to the synthetic fibers for their reuse .

[0099] The method according to this disclosure has numerous advantages :

[0100] High Separation Ef ficiency : the chemical technique allows for precise and complete separation of the fibers, significantly improving the quality of the recycled material;

[0101] - Reduction of Recycling Costs: thanks to the use of specific and reusable chemical reagents, operating costs can be reduced compared to traditional methods. Furthermore, the fact that the method operates at relatively low temperatures contributes to further energy savings.

[0102] The following describes the different steps of the method according to this invention.

[0103] (a) Soaking of the Fabric in a Metaperiodate Solution: The mixed fabrics are soaked in the solution of a soluble metaperiodate preferably maintaining the temperature below 60°C. The soluble metaperiodate reacts with the cellulosic component of the fabric, forming dialdehyde groups on the cellulosic fibers.

[0104] (b-1) Reaction with a Primary or Secondary Amine, or hydrazine or hydrazide: The amines react with the dialdehyde groups of the cellulosic fibers creating a functionalized and soluble cellulosic compound. The hydrazine or hydrazide react with the aldehyde moieties at C2 and C3 positions of the oxidized glucose units in the cellulose, creating stable hydrazone bonds (-CH=N- NH-) or dihydrazone networks, which can enhance the structural integrity, reduce crystallinity, and introduce new functional groups for further derivatization .

[0105] OR

[0106] (b-2) Reaction with an Oxidizing Compound: The oxidizing compound transforms the dialdehyde groups into carboxylic groups, which can then be salified (e.g. by adding a base) . The cellulosic fibers are then subsequently solubilized for separation.

[0107] (b) Ultrasonic irradiation: Ultrasonication of the solution containing the at least one cellulose solubilizing compound drastically reduces the reaction time compared to mechanical stirring, enabling rapid and efficient contact between the liquid phase and the fiber. A visible separation of a cellulose-rich pulp from the remaining synthetic fiber fraction occurs. The separated phase exhibits a gel-like consistency and is easily removed from the polyester mesh. The cavitation effect induced by ultrasound enhances the penetration of the cellulose solubilizing compound (b-1) or (b-2) and improves mass transfer at the fiber interface. The ultrasonic activation of the cellulose solubilizing compounds (b-1) or (b-2) acts as a selective condensing agent capable of inducing physical separation between cellulose and synthetic fiber fractions. This enables novel recycling or derivatization strategies for mixed textile substrates. The solubilization yield is strongly influenced by the liquid-fiber exchange, which is significantly enhanced under ultrasound.

[0108] (c) Polymer Compound Separation: The soluble cellulose compound is filtered and collected, effectively separating the solubilized cellulose fibers from the residual synthetic fibers without damaging the synthetic matrices.

[0109] (d) Synthetic Fiber Recycling: The recovered synthetic fibers are washed, dried and then melted to create new synthetic chips.

[0110] Reactivity of Dialdehyde Groups with Primary or Secondary Amines

[0111] When an aldehyde reacts with an amine, a condensation reaction is triggered, leading to the formation of compounds called Schiff bases (or imines) . These reactions are fundamental in organic chemistry, with numerous applications, such as the formation of bonds in biopolymers and synthetic materials. Reaction with Primary Amine : An aldehyde (R-CHO) can react with a primary amine (R1-NH2 ) , resulting in the formation of a Schi f f base (R-CH=N-Ri ) . This reaction occurs through the elimination of a water molecule (H2O) . The resulting Schi f f base has a double bond between carbon and nitrogen ( C=N) .

[0112] - Reaction with Secondary Amine : When the aldehyde (R-CHO) reacts with a secondary amine (R2-NH-R3 ) , a product known as an enamine is formed (R-CH=CH-N (R2 ) (R3 ) ) • The enamine has a carbon-carbon double bond adj acent to the amine nitrogen, and is a reactive intermediate .

[0113] The condensation reactions between aldehydes and amines may require ( i ) the presence of a weak acid to facilitate protonation ( Schi f f base / imine / enamine ) .

[0114] The Schi f f bases formed with primary amines are generally stable , while enamines formed with secondary amines may be less stable and more reactive .

[0115] In the context of the method according to this invention, the reaction between the dialdehyde groups formed on the cellulosic fibers and a primary or secondary amine creates a soluble polymeric compound . The solubility may vary based on the functionalities associated with the reactive amine . This allows the ef ficient separation of synthetic fibers from treated cellulosic fibers .

[0116] Reactivity of Dialdehyde Groups with Hydrazine or Hydrazide

[0117] The dialdehyde groups introduced into the cellulose backbone can react ef ficiently with hydrazine or hydrazide compounds , leading to the formation of hydrazone type bonds . This reaction typically involves the nucleophilic -NH2group attacking the carbonyl carbon of the aldehyde , followed by the elimination of water . The result is the formation of a -CH=N-NH-R linkage , which can be either terminal or part of a crosslinked structure , depending on the nature of the reagent .

[0118] Although this kind of condensation is generally favored under mildly acidic conditions (pH around 5- 6 ) , we have observed that the reaction proceeds ef fectively even under alkaline conditions , particularly when using multi functional hydrazides such as carbohydrazide . In alkaline medium, the increased nucleophilicity of the amine groups may actually promote condensation .

[0119] This flexibility in pH tolerance is signi ficant , as it allows the process to be integrated into workflows where pH control is challenging, or where compatibility with alkaline textile processing steps is important . In our experiments , we noted that under certain al kaline conditions , the use of carbohydrazide even led to macroscopic phase separation between the cellulosic and synthetic fiber components . This opens up interesting possibilities for selective fiber separation, functional finishing, or targeted reactivity .

[0120] Temperature plays a supporting role : the reaction is typically conducted between 20 and 60 ° C, balancing reactivity and structural integrity of the substrate .

[0121] Reactivity of Dialdehyde Groups with an Oxidizing Compound

[0122] The reaction between the dialdehyde groups and an oxidi zing compound leads to the formation of a dicarboxylate compound, trans forming the aldehyde groups into carboxylic acids . This oxidation process is a key reaction in the chemical modi fication of cellulosic fibers that improves their solubility and facilitates further separation and recycling processes .

[0123] The reaction with the oxidi zing compound occurs in aqueous solution at temperatures preferably below 60 ° C, to ensure process stability and conversion efficiency.

[0124] Ultrasound-assisted treatment:

[0125] In some embodiments, the use of ultrasonic irradiation has been adopted as an enhancement technique to improve the efficiency and speed of the separation process. Ultrasound facilitates better penetration of the cellulose solubilizing agents into the fiber structure by inducing cavitation, increasing the liquidsolid exchange and promoting the disintegration of the cellulose matrix. Compared to mechanical stirring, ultrasonic activation significantly reduces reaction time and enables a more uniform and controlled treatment. Additionally, the localized energy input from ultrasonic cavitation contributes to a reduction in the activation energy of the chemical reactions involved, allowing the process to proceed effectively at lower temperatures and with improved reaction kinetics.

[0126] Realization examples

[0127] The objective is to separate the polyester component from the cellulosic component in fabrics with a high content of synthetic fibers by chemical treatment, in order to be able to send the synthetic component to thermo-mechanical recycling.

[0128] Materials Used

[0129] • Fabrics with composition:

[0130] (a) 52% polyester (PES) and 48% cotton (CO)

[0131] (b) 70% polyester (PES) and 30% cotton (CO)

[0132] • Sodium metaperiodate

[0133] • Caustic soda (NaOH) 30% w / w

[0134] • Sodium chlorite

[0135] • Mineral acid (e.g. HC1)

[0136] • Glycine / Ethylenediamine • Carbohydrazide

[0137] • Acetic acid

[0138] Procedure

[0139] 1. Fabric Preparation:

[0140] The fabric is shredded to expose a larger surface area of the cotton fiber to the chemical reagents.

[0141] 2. Cellulose Oxidation:

[0142] The shredded fabric is soaked in an aqueous solution of sodium metaperiodate at various concentrations (See experimental data reported in Table 1) to oxidize the C2 and C3 carbons of the cellulose. The bath ratio is fabric:bath = 1:20.

[0143] 3a. Glycine / Ethylenediamine Treatment:

[0144] Before treating sample (a) with glycine or ethylenediamine, the fabric is rinsed thoroughly with water. Next, reagents are added and the pH is adjusted to about 5 with acetic acid.

[0145] 3b. Sodium Chlorite Treatment:

[0146] Before treating sample (a) with chlorite, the fabric is treated with a caustic soda solution to decrease the molecular weight of the cellulose and facilitate its separation from the synthetic portion of the fabric.

[0147] 3c. Carbohydrazide Treatment:

[0148] Before treating sample (b) with carbohydrazide, the fabric is rinsed thoroughly with water. Next, reagents are added and the pH is adjusted to about 5 with acetic acid .

[0149] After rinsing and air-drying, the oxidized fabric was treated with an aqueous solution of carbohydrazide at a concentration of 5% w / v. The pH of the solution was adjusted to 8.5 by addition of a dilute sodium hydroxide solution. The reaction was carried out at 50 °C for 60 minutes under agitation. The success of the reaction is calculated in terms of the percentage of synthetic fiber missing compared to the initial weight of the sample . The results vary between 15% and 20% , depending on the experimental conditions .

[0150] The di f ferences in the results can be attributed to the di f ferent fabric construction and morphology of the cotton fiber . Experiments 1 , 2 and 3 , where a treatment with sodium metaperiodate was performed, possibly followed by a treatment with caustic soda, represent control experiments .

[0151] Table 1

[0152] Considerations on the Results

[0153] 1. Experiment 1 :

[0154] No significant weight loss and no significant yield .

[0155] 2. Experiment 2 :

[0156] Weight loss of 4.7% and yield of 10.8%.

[0157] Using NaOH after oxidation at room temperature showed a slight effectiveness.

[0158] 3. Experiment 3 :

[0159] Weight loss of 19% and yield of 39.5%.

[0160] Using higher concentration of NalCh and high temperature showed moderate effectiveness.

[0161] 4. Experiment 4 :

[0162] Weight loss of 38.9% and yield of 81%.

[0163] Increasing the temperature during oxidation and using NaClO significantly improved the dissolution of cotton .

[0164] 5. Experiment 5 :

[0165] Weight loss of 44% and yield of 91.66%.

[0166] Using glycine showed one of the best dissolution yields . 6 . Experiment 6 :

[0167] Weight loss of 43% and yield of 89 . 5% .

[0168] The use of ethylenediamine showed a high dissolution yield similar to that of glycine .

[0169] 7 . Experiment 7 :

[0170] Weight loss of 29% and yield of 96 . 6% .

[0171] During the treatment with carbohydrazide , a visible separation of a cellulose-rich pulp from the remaining synthetic fiber fraction was observed . The separated phase exhibited a gel-like consi stency and was easily removed from the polyester mesh .

[0172] Spectroscopic analysis of the treated fabric confirmed the formation of imine bonds via FTIR ( absorption band at ~ 1650 cm- 1) .

[0173] This result demonstrates the applicability of carbohydrazide as a selective condensing agent capable of inducing physical separation between cellulose and synthetic fiber fractions , thereby enabling novel recycling or derivati zation strategies for mixed textile substrates .

[0174] The solubili zation yields strongly depend on the contact between the liquid and the fiber, which can be improved by stirring the system . A greater liquid- fiber exchange between the reagents leads to a higher reaction yield .

[0175] 8 . Experiment 8 (ultrasound assisted using Hielscher sonicator)

[0176] Weight loss of 47 . 9% and yield of 99 . 8 % .

[0177] Treatment was performed with carbohydrazide under ultrasonic irradiation using a Hielscher UP400St probetype sonicator ( 400 W, 24 kHz , amplitude 10% , 4 minutes , 400 mL reaction volume , titanium sonotrode 40 mm diameter ) . Ultrasonication drastically reduced the reaction time compared to mechanical stirring, enabling rapid and ef ficient contact between the liquid phase and the fiber. A visible separation of a cellulose-rich pulp from the remaining synthetic fiber fraction occurred. The separated phase exhibited a gel-like consistency and was easily removed from the polyester mesh. Spectroscopic analysis (FTIR) confirmed the formation of imine bonds (absorption band at ~1650 cm-1) . The cavitation effect induced by ultrasound enhanced the penetration of the reagent and improved mass transfer at the fiber interface. These results demonstrate that carbohydrazide, under ultrasonic activation, acts as a selective condensing agent capable of inducing physical separation between cellulose and synthetic fiber fractions. This enables novel recycling or derivatization strategies for mixed textile substrates. The solubilization yield is strongly influenced by the liquid-fiber exchange, which is significantly enhanced under ultrasound.

[0178] Effect of Dyes

[0179] Tests were performed on fabrics in which only the cellulose component (reactive dyes) or only the polyester component (dispersed dyes) was dyed, to verify how the presence of different types of dyes could influence the method.

[0180] The results showed that the dyes did not interfere with the oxidation reaction and the caustic soda treatment, even if traces of dye from the dyed cotton fabric were found in solution. The same weight loss values were obtained for the undyed fabrics.

[0181] Polyester Analysis Before and After the Separation Process

[0182] The objective of this step is to chemically analyze the polyester before and after the separation method to evaluate the effectiveness of the separation of the polyester polymer without significant chemical modifications .

[0183] Materials Used

[0184] Polyester Samples:

[0185] Reference RES: Untreated dyed polymer yarn.

[0186] Treated PES : Dyed polymer yarn after separation method .

[0187] Analysis Methods

[0188] 1. SEC (Size Exclusion Chromatography) Analysis:

[0189] - Instrument: Shimadzu Nexera LC40.

[0190] - Columns: 4 Phenomenex columns in series.

[0191] - Flow: 1 ml / min.

[0192] - Calibration: Monodisperse polystyrenes, molecular weight range from 1, 600,000 Da to 106 Da.

[0193] - Samples were dissolved with in-house methodology and subsequently analyzed.

[0194] 2. DSC (Differential Scanning Calorimetry) Analysis :

[0195] - Instrument: Mettler Toledo DSC 1.

[0196] - Method: Heating from 25°C to 290°C at 10°C / min.

[0197] - Gas: Nitrogen.

[0198] Results and Discussion

[0199] SEC Analysis

[0200] Figures 1 and 2 show the SEC curves recorded on the two samples with DAD detector extracting the wavelength at 254 nm. Table 2 shows the values of the macromolecular masses and their distributions.

[0201] Table 2 The SEC curves and molecular mass values indicate that the Reference PES and Treated PES samples are very similar to each other.

[0202] No significant differences are found in their macromolecular properties.

[0203] DSC analysis

[0204] Figures 3 and 4 show the DSC traces of the two samples. Table 3 shows the measured thermal properties.

[0205] Table 3

[0206] The DSC traces and thermal properties indicate that the Reference PES and Treated PES samples are very similar to each other.

[0207] No significant differences were found in their thermal properties.

[0208] Conclusions

[0209] The two polyester samples (Reference PES and Treated PES) are very similar to each other both from a thermal point of view and with respect to molecular weights and their distribution. No significant differences were found, indicating that the separation method described herein did not cause significant chemical modifications of the polyester polymer.

[0210] These results confirm the effectiveness of the separation method and the chemical stability of the treated polyester, making it suitable for further applications without compromising its key properties.

Claims

CLAIMS1. A method for separating synthetic fibers from cellulosic fibers contained in a fabric with a mixed composition comprising the following steps:(a) soaking the fabric in an aqueous solution of at least one soluble metaperiodate;(b) adding to the solution at least one cellulose solubilizing compound selected from:(b-1) a primary or secondary amine, a hydrazine or a hydrazide, or(b-2) an oxidizing compound, achieving the solubilization of the cellulosic fibers;(c) filtering the solution by separating the solubilized cellulosic fibers from the synthetic fibers.

2. The method according to claim 1, wherein the synthetic fibers obtained in step (c) are washed, dried and optionally melted to produce synthetic chips.

3. The method according to any one of the preceding claims, wherein the fabric is subjected to a shredding operation prior to step (a) .

4. The method according to any one of the preceding claims, wherein the at least one primary amine has formula (I) and the at least one secondary amine has formula (IT)R1-NH2 (I)R2-NH-R3 (IT) wherein Ri, R2 and R3 are independently selected from a linear or branched Ci-s alkyl group, unsubstituted or substituted with one or more substituents, or an aryl group unsubstituted or substituted with one or moresubstituents, wherein the one or more substituents are independently selected from hydroxyl, carbonyl, carboxyl and amine .

5. The method according to any one of claims 1-3, wherein the at least one hydrazine has formula (III) and the at least one hydrazide has formula (IV)R4-NH-NH2 (HI)R4-CO-NH-NH2 (IV) wherein Ri, R2, R3, and R4are independently selected from a linear or branched Ci-s alkyl group, or an aryl group, each unsubstituted or substituted with one or more substituents independently selected from hydroxyl, carbonyl, carboxyl, and amine.

6. The method according to any one of the preceding claims, wherein the step (b-1) is carried out in the presence of an acid, preferably a weak acid.

7. The method according to any one of the preceding claims, wherein the at least one acid is selected from organic or inorganic acids having a pKabetween 3.5 and 10.5, preferably between 3.5 and 7, measured in an aqueous solution having an ionic strength of 0 and a temperature of 25°C.

8. The method according to any one of claims 1-3 or 5, wherein after the addition of the at least one hydrazine or hydrazide (step b-1) to the solution, or prior to the addition of the at least one oxidizing compound (step b-2) to the solution, at least one strong base is added.

9. The method according to claim 8, wherein the at least one strong base is selected from organic orinorganic bases having a pKb between 0.2 and 4.75, measured in an aqueous solution having an ionic strength of 0 and a temperature of 25°C.

10. The method according to any one of the preceding claims, wherein the at least one oxidizing compound has a standard redox potential (E°) equal to or greater than +0.5 V with respect to a standard hydrogen electrode (SHE) .

11. The method according to any one of the preceding claims, wherein step (b) is carried out under mechanical stirring of the solution containing the at least one cellulose solubilizing compound.

12. The method according to any one of the preceding claims, wherein step (b) comprises an ultrasonic irradiation of the solution containing the at least one cellulose solubilizing compound.

Images