FIELD OF THE INVENTION

The present invention relates to a method of polyamide fiber recycling from elastomeric fabrics, i.e. a method of controlled thermal degradation and wash separation of spandex from fabric or garments containing polyamide fiber, in order to prepare the polyamide fiber and/or spandex for recycling or disposal.

More particularly, the present invention pertains to a controlled thermal degradation of spandex and polyamide fabric or garment with minimal reduction in molecular weight, degradation, and oxidation to polyamide fabric and a wash treatment to separate the degraded spandex from high purity polyamide into separate raw material streams for recycling or disposal.

BACKGROUND ART

Fabrics containing polyamide fibers and spandex (i.e. elastomeric fabrics) are used in many apparel, industrial and medical applications. The fabrics can vary in the content of spandex relative to polyamide fiber contents. Typical content levels are 5% - 25% (w/w) spandex and 95% - 75% (w/w) polyamide in the fabrics. Since spandex and polyamide polymers have very different chemical properties and production techniques, the post-industrial and post-consumer fabrics and garments that are retrieved are very difficult to recycle in an economical and environmentally acceptable way.

Spandex global worldwide production in 1997 exceeded 95,000 metric tons, and was growing since then, and in 2010 reached almost 400,000 tons, with prediction to exceed 500,000 tons by 2015. Consequently, increasing quantities of such fabrics will need to be recycled.

Spandex has a known temperature instability, namely it is known that in a heat setting process of fabrics, such as apparel, the temperature treatment must be performed within certain temperature and time limits, because spandex will thermally degrade and oxidize if exposed to excessive temperature for longer periods of time, thereby causing fabric or garment issues, such as mechanical damages or dyeing problems. There are known solvent techniques for dissolving spandex or polyamide fibers from fabrics and garments. To dissolve spandex out of an elastomeric fabric, strong polar solvents such as dimethylacetamide (DMAc) or dimethylformamide (DMF) among others have been used. They will dissolve spandex and leave polyamide in the solvent for recycling. Additionally, formic acid and sulfuric acid can dissolve polyamide and leave spandex for recycling. Both of these solvent-based processes have disadvantages in the amount of solvent needed, environmental issues, dangerous processing, cost of industrial scale-up, operational costs and other issues.

Recycling processes for recycling of polymeric material from carpets and other multi-component structures by means of supercritical fluid extraction were also extensively researched and are disclosed in US patent No. 5,233,021 (Georgia Tech R. C).

The aim and scope of this invention is a method of using thermal degradation and washing for separation of fiber components in elastomeric fabrics so that spandex fibers are dissolved and the remaining polyamide fibers are usable for recycling. The dissolved spandex in the solvent as well as the solvent itself can also be recycled.

Description of the terms used:

As used herein, the term "spandex" refers to elastomeric polyurethane comprising at least 85% (w/w) segmented polyurethanes based on polyethers, polyesters and/or polycarbonates for example. Segmented polyurethanes can be made by reacting a polymeric diol (most often a polyetherglycol or a polyester glycol) with an organic diisocianate to form an isocianate-terminated polymer which is chain-extended by a reaction with a diamine or a diol. Typically "spandex" fibers resemble rubber in both stretch and recovery properties, but are far superior to rubber in their resistance to sunlight, heat, abrasion, oxidation, oils, and chemicals. Spandex has the widest use of any of the elastomeric fibers, and is sold as an elastomeric fiber under that designation or under trade names such as Lycra (made by Invista, previously a part of DuPont), ELASPAN (Invista), RadElast (Radici), Creora (Hyosung), ROICA and Dorlastan (Asahi Kasei), Linel (Fillatice), ESPA (Toyobo), Cleerspan, Glospan, Numa, etc. A typical example of spandex fibers is described in US Patent No. 4,973,647 (E.I. du Pont). Spandex fibers described in the mentioned patent are typically used in combination with nylon-6 yarns for tricot fabrics with edge-curl resistance. As used herein, the term "elastomeric fabric" refers to any fabric from post industrial or post consumer process, containing various portions of spandex fibers and various portions of other synthetic fibers; and the term "elastomeric clothing articles" refers to any apparel article, from post industrial or post consumer process, containing various portions of spandex fibers and various portions of other synthetic fibers.

The term "polyamide fibers" refers to polyamide fibers including polyamide 6 (caprolactam), polyamide 6.6 (hexamethylene adipamide), their copolymers, any combination thereof or any combination thereof with other polyamides.

DESCRIPTION OF THE INVENTION

The present invention relates to a method of separation of spandex from fabric or garment containing polyamide fiber involving the following steps: a. ) controlled thermal degradation of spandex in an atmosphere containing any combination of gasses that do not cause excessive degradation of polyamide fibers, preferably in an inert gas atmosphere; b. ) removal of degraded spandex by washing in a solvent, preferably polar solvent, such as Ethanol, DMAc, DMF or water; and c. ) removal of excess solvent possibly containing degraded spandex from remaining polyamide fibers.

Thermal degradation step is based on inability of spandex to withstand high temperatures under moderate pressure without thermally degrading. The thermal degradation process in this invention will change the structure of spandex into short soft fibers and particulate sections which can readily be removed by washing with an appropriate solvent. The temperatures and pressures used for thermal degradation of spandex as outlined in this invention have a limited negative impact on physical properties of polyamide fibers which still renders them usable for recycling. After the process of thermal degradation, the fabric is then washed with a solvent, preferably polar solvent such as ethanol, to effectively remove degraded spandex. Excess solvent is then removed from polyamide fibers. The resulting polyamide fibers exhibit high purity and physical properties that are suitable for recycling into high quality products, such as low side reactions, low levels of degradation and oxidation. The degraded spandex fiber is optionally filtered and distilled to recover the solvent for re-use. Spandex fractions can optionally be extracted, preferably using filtration and/or distillation and have many potential end-use applications.

A schematic of the process is as follows: a) . Thermal treatment of elastomeric fabric and elastomeric clothing articles

Thermal treatment is carried out in an autoclave or other suitable vessel at controlled conditions (atmosphere, time, temperature, pressure, humidity). It is carried out in an inert gas atmosphere or air atmosphere. It can also be carried out in any other suitable atmosphere that does not cause excessive degradation of polyamide fibers. Temperature range used during thermal treatment if polyamide fibers include polyamide 6 fiber is 150'C - 220°C, preferably from 190°C -216"C. In case polyamide fibers consist predominantly of polyamide 6.6, the temperature range is 150°C - 260°C, preferably from 190°C -216°C. Temperatures can either be maintained in this range during the whole duration of thermal treatment or optionally achieved before the end of the thermal treatment. Elastomeric fabrics are treated for between 0.1 hours and 24 hours, preferably 0.5 - 4 hours. The pressure in thermal treatment is 0.1 - 10 bar. Humidity is controlled within the range of 0.001% - 10%. No additive is added. b) . Washing treatment of elastomeric fabric and elastomeric clothing articles

Washing treatment is carried out at controlled processing conditions (solvent selection, time, temperature, agitation level, pressure).

Polar solvents are used, preferably ethanol. The temperature range used is 5°C - 78°C. The time of treatment used is 0.01 - 10 hours. Solution containing fabrics is agitated during washing treatment. One or more washing cycles are applied, more washing cycles result in higher degree of spandex removal and higher degree of purity of remaining polyamide fibers. c) . Removal of excess solvent, separation and collection of individual fiber components

Typically, components after washing treatment are: solvent, spandex and polyamide fibers. Excess solvent is removed from polyamide fibers and polyamide fibers are collected for further recycling. Solvent is filtered and purified (distilled), recollected and returned for re-use in washing process. Spandex and its degraded components are collected from filters and distillation impurities for disposal as waste or collected for further recycling.

The invention is further described using figures and the following examples:

Figure 1: Conditions of heating up in autoclave

a) Thermal treatment

Inert atmosphere conditions

Following conditions are applied during thermal treatment in an autoclave with an inert atmosphere (argon), shown in Table 1.

Table 1

Starting material Conditions in the autoclave

Example Type of Composition of Temperature Time of Environment sample sample reached at the end treatment

(polyamide 6 of treatment ( ^e C) (hours)

/spandex (w/w))

Example 1 Warp 80°/o/20% 180 Dry, argon knitted

fabric

Example 2 Warp 80%/20% 193 1.5 Dry, argon knitted

fabric

Example 3 Warp 80°/o/20% 204 Dry, argon knitted

fabric

Example 4 Warp 80 /20% 210 2.5 Dry, argon knitted

fabric

Example 5 Warp 80%/20% 213 Dry, argon knitted

fabric

Example 6 Warp 80%/20% 216 3.5 Dry, argon knitted

fabric Temperature in the autoclave is gradually increased with time of treatment necessary to obtain the desired higher temperature. The time curve of heating up of the samples in autoclave is shown in Figure 1.

Example 1

10 g of elastomeric fabric were introduced into a 200-ml autoclave. The autoclave was filled with argon gas and then closed. The autoclave contents were heated to 180 ^e C. Autoclave reached this temperature gradually in 1 hour. After this temperature was reached the autoclave was left to cool down for 45 minutes, and then samples were taken from the autoclave and cooled to room temperature.

Example 2

10 g of elastomeric fabric were introduced into a 200-ml autoclave. The autoclave was filled with argon gas and then closed. The autoclave contents were heated to 193 ^e C. Autoclave reached this temperature gradually in 1.5 hour. After this temperature was reached the autoclave was left to cool down for 45 minutes, and then samples were taken from the autoclave and cooled to room temperature.

Example 3

10 g of elastomeric fabric were introduced into a 200-ml autoclave. The autoclave was filled with argon gas and then closed. The autoclave contents were heated to 204"C. Autoclave reached this temperature gradually in 2 hours. After this temperature was reached the autoclave was left to cool down for 45 minutes, and then samples were taken from the autoclave and cooled to room temperature.

Example 4

10 g of elastomeric fabric were introduced into a 200-ml autoclave. The autoclave was filled with argon gas and then closed. The autoclave contents were heated to 210"C. Autoclave reached this temperature gradually in 2.5 hours. After this temperature was reached the autoclave was left to cool down for 45 minutes, and then samples were taken from the autoclave and cooled to room temperature.

Example 5

10 g of elastomeric fabric were introduced into a 200-ml autoclave. The autoclave was filled with argon gas and then closed. The autoclave contents were heated to 213°C. Autoclave reached this temperature gradually in 3 hours. After this temperature was reached the autoclave was left to cool down for 45 minutes, and then samples were taken from the autoclave and cooled to room temperature.

Example 6

10 g of elastomeric fabric were introduced into a 200-ml autoclave. The autoclave was filled with argon gas and then closed. The autoclave contents were heated to 216°C. Autoclave reached this temperature gradually in 3.5 hours. After this temperature was reached the autoclave was left to cool down for 45 minutes, and then samples were taken from the autoclave and cooled to room temperature.

For comparison of the degradation and oxidation of polyamide fibers, polyamide 6 multi-filament yarn fibers were exposed to the same conditions as described in examples 1 - 6 and compared to an untreated polyamide 6 multi-filament yarn sample. The results are shown in Table 2. Relative viscosity of the polymer is a measure of molecular weight. Lower relative viscosity indicates higher degradation. Lower whiteness index and higher yellowness index indicate higher oxidation levels.

Table 2

Change of polyamide 6 yarn

Conditions in the autoclave

properties

Temperature Total time of Relative Whiteness Yellowness reached at the end treatment (hours) viscosity (-) index index

of treatment (°C)

- 0 2.42 83.3 -0.3

180 1 2.39 80.0 -0.8

193 1.5 2.38 78.6 2.3

204 2 2.40 50.1 12.6

210 2.5 2.31 33.5 18.7

213 3 2.29 19.4 24.2

216 3.5 2.17 2.4 32.2 Air atmosphere conditions

Following conditions are applied during thermal treatment using a thermofixing machine with air atmosphere, shown in Table 3.

Table 3

Starting material Conditions in the thermofixing machine

Composition of Environment

Time of

sample

Type of Temperature during

Example (polyamide 6 treatment

sample treatment (X)

/spandex

(hours)

(w/w))

Example Warp dry, air

7 knitted 80%/20% 180 0.1 - 2.0

fabric

Example Warp dry, air

8 knitted 80%/20% 190 0.1 - 2.0

fabric

Example Warp dry, air

9 knitted 80%/20% 200 0.1 - 2.0

fabric

Example Warp dry, air

10 knitted 80%/20% 213 0.1 - 2.0

fabric

Example 7

10 g of elastomeric fabric were introduced into a thermofixing machine. Sample was inserted in the thermofixing machine immediately after the set temperature of 180"C was reached, and treated at 180°C from 0.1 - 2.0 hours.

Example 8

10 g of elastomeric fabric were introduced into a thermofixing machine. Sample was inserted in the thermofixing machine immediately after the set temperature of 190 ^e C was reached, and treated at 190"C from 0.1 - 2.0 hours. Example 9

10 g of elastomeric fabric were introduced into a thermofixing machine. Sample was inserted in the thermofixing machine immediately after the set temperature of 200 ^e C was reached, and treated at 200'C from 0.1 - 2.0 hours.

Example 10

10 g of elastomeric fabric were introduced into a thermofixing machine. Sample was inserted in the thermofixing machine immediately after the set temperature of 213 ^e C was reached, and treated at 213°C from 0.1 - 2.0 hours.

For comparison of the degradation and oxidation of polyamide fibers, polyamide 6 multi-filament yarn fibers were exposed to the same conditions as described in examples 7 - 10 and compared to an untreated polyamide 6 multi-filament yarn sample. The results are shown in Table 4. Lower relative viscosity indicates higher degradation. Lower whiteness index and higher yellowness index indicate higher oxidation levels.

Table 4

Conditions in the Change of polyamide 6 yarn properties thermofixing machine

Temperature Total time Relative NH ₂ Whiteness Yellowness during of viscosity index index treatment treatment (.) (meqv/kg)

(°C) (hours)

- 0 2.42 42.6 81.3 -0.90

190 0.75 1.87 24.0 -26.1 51.6

200 0.75 1.78 20.4 -30.6 61.6

Treatment in air atmosphere caused severe degradation of polyamide 6, especially at temperatures above 200°C. Temperature 213°C gave very poor results as material reached dark brown colour within 15 - 30 minutes. Loss of relative viscosity of approximately 25% and loss of -NH ₂ end groups of approximately 50%, was measured for polyamide 6 after 0.75 hours of treatment at 200°C. These results indicate that in order to preserve properties of polyamide 6, presence of air must be avoided during the thermal treatment. As high as possible level of preservation of polyamide fibers is important for the recycling.

On the other hand, 45 minutes at 200°C were very good conditions to reach the desired level of degradation and softening of spandex. But in these conditions also spandex was oxidized to similar degree as polyamide 6 which is unfavorable.

b) Washing treatment

In each example, a state of the sample pieces textile structure was observed before and after washing. The textile structure of the sample pieces after washing was evaluated by way of a microscopic examination and FT-IR analysis. The success of removal of spandex from the sample pieces during washing was evaluated gravimetrically and calculated as the percentage of removed portion of fibers from the fabric.

The percentage value of removed portion of fibers is calculated from a sample weight before a washing treatment and a sample weight after a washing treatment. An increase in percentage value means increase in quantity of removed spandex fibers from the fabrics textile structure. The starting percentage of spandex within the elastomeric fabrics before washing was 20%. Washing treatment was performed in a glass flask. Ethanol p.a. was used as a solvent for all examples. The weight of solvent used in each washing step was from 5 to 67 times the weight of the samples. The intensity of agitation during treatment was variable. The times of treatment were between 2 and 35 minutes.

Table 5 shows the conditions applied in several examples of the washing treatment Table 5

Sample:Solvent Time of No. of

Temperature

Example Weight ratio treatment Intensity of treatment washing

(°C)

(w:w) (min) steps

Example 11 1:67 78 2, 5, 10, Constant stirring 1

15

Example 12 1:50 40 2, 5, 10, Constant stirring 1

15

Example 13 1:50 22 2, 5, 10, Strong agitation with 1

15 shaking

Example 14 1:50 22 30 Static; no stirring or 1 agitation

Example 15 1:67 78 10 Constant stirring 1

Example 16 1:10 22 30 Strong agitation with 2 shaking

Example 17 1:5 22 15 Strong agitation with 1 shaking

Example 18 1:5 22 15 Strong agitation with 2 shaking

Example 19 1:10 78 35 Static, with strong 1 agitation every 5

minutes for 1-2 minutes

Example 20 1:10 78 35 Static, with strong 2 agitation every 5

minutes for 1-2 minutes

Example 21 1:10 78 35 Static, with strong 3 agitation every 5

minutes for 1-2 minutes

Example 11

1.5 g of elastomeric fabric that was previously thermally treated according to Example 4 was introduced into a 50-ml glass flask. Solvent was added at a sample:solvent weight ratio 1:67. Solvent temperature was 78°C. Constant stirring was applied to the samples. A washing period was variable, 2 minutes, 5 minutes, 10 minutes, 15 minutes. Samples were washed by this procedure in one washing cycle. Example 12

1.5 g of elastomeric fabric that was previously thermally treated according to Example 4 was introduced into a 50-ml glass flask. Solvent was added at a sample:solvent weight ratio 1:50. Solvent temperature was 40 ^e C. Constant stirring was applied to the samples. A washing period was variable, 2 minutes, 5 minutes, 10 minutes, 15 minutes. Samples were washed by this procedure in one washing cycle.

Example 13

1.5 g of elastomeric fabric that was previously thermally treated according to Example 4 was introduced into a 50-ml glass flask. Solvent was added at a sample:solvent weight ratio 1:50. Solvent temperature was 22 ^e C. Strong agitation with shaking in vertical and horizontal direction was applied to the samples. A washing period was variable, 2 minutes, 5 minutes, 10 minutes, 15 minutes. Samples were washed by this procedure in one washing cycle.

Example 14

1.5 g of elastomeric fabric that was previously thermally treated according to Example 4 was introduced into a 50-ml glass flask. Solvent was added at a sample:solvent weight ratio 1:50. Solvent temperature was 22 ^e C. No stirring was applied to the samples. A washing period was 30 minutes. Samples were washed by this procedure in one washing cycle.

Results of Examples 11-14 are shown in Table 6.

Table 6.

conditions Example 11 Example 12 Example 13 Example 14 during Fabric vs. Ethanol Fabric vs. Ethanol Fabric vs. Ethanol Fabric vs. Ethanol thermal ratio 1:67 (w/w) ratiol:50 (w:w) ratiol:50 (w:w) ratiol:50 (w:w) treatment

Removed Removed Removed Removed Time portion of Time portion of Time portion of Time portion of Example (min) fibers (%) (min) fibers (%) (min) fibers (%) (min) fibers (%)

Example 4 2 17.21 2 16.98 2 18.34 Example 4 5 17.57 5 17.42 5 18.42 - Example 4 10 16.66 10 17.75 10 18.69 - -

Example 4 15 16.92 15 18.05 15 19.04 - -

Example 4 - - - - - - 30 15.02

Example 15

1.5 g of elastomeric fabric that was previously thermally treated according to one of Examples 1 - 6 was introduced into a 50-ml glass flask. Solvent was added at a sample:solvent weight ratio 1:67. Solvent temperature was 78°C. Constant stirring was applied to the samples. A washing period was 10 minutes. Samples were washed by this procedure in one washing cycle.

Example 16

1.5 g of elastomeric fabric that was previously thermally treated according to one of Examples 1 - 6 was introduced into a 50-ml glass flask. Solvent was added at a sample:solvent weight ratio 1:10. Solvent temperature was 22 ^e C. Strong agitation with shaking in vertical and horizontal direction was applied to the samples. A washing period was 30 minutes. Samples were washed by this procedure in two washing cycles.

Example 17

1.5 g of elastomeric fabric that was previously thermally treated according to one of Examples 2 - 6 was introduced into a 50-ml glass flask. Solvent was added at a sample:solvent weight ratio 1:5. Solvent temperature was 22 ^l C. Strong agitation with shaking in vertical and horizontal direction was applied to the samples. A washing period was 15 minutes. Samples were washed by this procedure in one washing cycle.

Example 18

Example 17 was repeated but samples were washed by this procedure in two washing cycles.

Results of Examples 15-18 are shown in Table 7. Table 7.

conditions Example 15 Example 16 Example 17 Example 18 during Fabric vs. Ethanol Fabric vs. Ethanol Fabric vs. Ethanol Fabric vs. Ethanol thermal ratio 1:67 (w:w) ratio 1:10 (w:w) ratio 1:5 (w:w) ratio 1:5 (w:w) treatment

Removed Removed Removed Removed

Time portion of Time portion of Time portion of Time portion of

Example (min) fibers (%) (min) fibers (%) (min) fibers (%) (min) fibers (%)

Comparative

10 1.74 30 2.16 - - - - example

Example 1 10 2.63 30 2.86 - - - -

Example 2 10 11.36 30 6.70 15 4.45 15 6.72

Example 3 10 17.92 30 19.03 15 10.87 15 15.95

Example 4 10 18.69 30 19.17 15 13.07 15 17.05

Example 5 10 18.57 30 19.32 15 12.89 15 16.92

Example 6 10 - 30 19.45 15 11.83 15 16.25

Example 19

1.5 g of elastomeric fabric that was previously thermally treated according to one of Examples 4 and Example 6 was introduced into a 50-ml glass flask. Solvent was added at a sample:solvent weight ratio 1:10. Solvent temperature was 78"C. A strong agitation was applied on the samples every 5 minutes for approx. 1-2 minutes with shaking in vertical and horizontal direction to the samples. A washing period was 35minutes. Samples were washed by this procedure in one washing cycle.

Example 20

Example 19 was repeated. Samples were washed by this procedure in two washing cycles. Example 21

Example 19 was repeated. Samples were washed by this procedure in three washing cycles. Results of Examples 19-21 are shown in Table 8.

Table 8.

In these examples, it was observed that the weight ratio of Sample:Solvent has an important influence on the degree of spandex removal during washing treatment. Best results were obtained for fabric samples fully immersed in a solvent, which was the case for the samples in which quantity of solvent was 10-fold or more compared to the weight of elastomeric fabric (ratio Sample:Solvent 1:10). Good results were obtained also for fabric samples treated with a higher content of solvent (ratio Sample:Solvent 1:50). Samples with ratio Sample:Solvent 1:5 were not fully immersed, and apparently for this reason did not give acceptable results.

Higher agitation during washing treatment contributed to higher % of spandex removal. Best results were obtained at highest level of agitation (as would be applied during washing in home or industrial laundry machine).

Higher number of washing cycles contributed to higher degree of spandex removal. c). Separation and collection of individual fiber component obtained after washing treatment

At the end of washing treatment, solvent and the degraded spandex particles must be completely removed from the fabric. This was achieved with centrifugation and/or another suitable method e.g. ultrasonic treatment etc. followed by drying.

Separated polyamide material can then be collected and can further be recycled.

Ethanol from washing process was collected, filtered and purified (distilled), to be returned back (solvent recycling) to washing process.

Spandex particles removed during washing process were collected for further disposal and possible recycling.

The present inventon therefore describes a method for removal of spandex from polyamide elastomeric fabrics, comprising of polyamide fibers (polyamide 6 and/or polyamide 6.6) including steps of thermal treatment and washing of degraded spandex using solvent. The thermal treatment is performed in the temperature range of 150°C - 220°C, preferably 190°C - 216°C or in the case that polyamide fibers are predominantly polyamide 6.6 fibers of 150°C - 260 ^e C, preferably 190"C - 216°C. The time of thermal treatment is between 0.1 hours and 24 hours, preferably 0.5 - 4 hours. The pressure range between 0.1 bar and 10.0 bar, preferably 1.0 - 3.0 bar. It is preferably performed in an inert gas atmosphere in an autoclave. The washing step is performed in the temperature range from 5°C to 78°C and the time range of washing is between 0.1 hours and 5 hours, preferably 0.1 - 1.0 hours. The amount of solvent is in the range of sample/solvent ratio between 1:1 (w/w) and 1:100 (w/w), preferably between 1:5 (w/w) and 1:20 (w/w). The method also includes a further step of removal of excess solvent possibly containing degraded spandex from remaining polyamide fibers.