Recycling Polyester/Cotton Blend Fabrics by Dissolving Polyester

Europaisches Patentamt J European Patent Office © Publication number: 0 636 646 A1 Office europeen des brevets

EUROPEAN PATENT APPLICATION

© A process is described for recycling polyester and cotton blend fabrics by separating the polyester from the cotton fabric. The novel process to recycle the polyester/cotton blend fabrics includes the steps of (a) providing a polyester and cotton blend fabric; (b) charging said blend into a sulfone solvent; (c) dissolving the polyester in the sulfone solvent; (d) separating the dissolved polyester and sulfone solvent solution from the cotton fabric; (e) filtering the cotton to obtain isolated, cotton fabric.

CO CO CO 00 CO

Rank Xerox (UK) Business Services (3. 10/3.09/3.3.4) 1 EP 0 636 646 A1 2

Field of the Invention diester by crystallization and the alcohol from the resulting reaction mixture by distillation. The present invention relates to a process for A process has been disclosed in U. S. Patent recycling polyester and cotton blend fabrics in No. 3,801,273 providing a method of recovering such a way as to separate the polyester from the 5 waste cellulose fibers from mixtures of waste cel- cotton fabric. lulosic fibers, waste polyester and/or acrylic fibers Large volumes of textile wastes are produced and synthetic, cross-linked resinous material. The annually in the manufacture of clothing and other methods therein disclose heating a mixture of the textile products. A large percentage of the textile waste cellulosic fibers, waste polyester and/or waste is accounted for by polyester/cellulosic fab- io acrylic fibers and synthetic, cross-linked resin ma- rics such as polyester/cotton and polyester/rayon terials within the range of from 212 to 275 degrees blends. The reuse of the blended materials is com- Fahrenheit for a period of from 3/4 to 5 hours in an plicated by the fact that there are inherent differ- aqueous treating solution containing an alkali metal ences in the physical properties and composition of hydroxide and one or more added, normally liquid the two components. Additionally, the fabrics are 75 chemical agents such as ketones, alcohols, lac- treated with resinous materials and other finishes tones, and sulfides which initiate the decomposition such as flame retardants which limit reusability. or solubilization of the waste polyester and/or acryl- This makes it nearly impossible to find potential ic fibers and synthetic, cross-linked resin materials; commercial end uses for this material other than adding a neutral or alkaline oxidising agent to the rags or cloth scraps which are of little monetary 20 mixture of waste fibers and synthetic, cross-linked value. resin materials; heating the mixture of waste fibers Disposal of such large volumes of solid waste in synthetic, cross-linked resin materials in the is an increasing problem for the apparel industry. presence of the neutral or alkaline oxidizing agent The rising cost, reduction in available space, and to complete the decomposition or solubilization of concern for the environment are making burning 25 the waste polyester; and the recovery of the waste and landfilling the textile waste dwindling options. cellulosic fibers. Therefore, potential methods of recycling polyes- Various methods have been described in the ter/cotton fabric blends have been pursued. prior art for the recovery of polyester from cellulose Waste polyester scrap can be recycled for fibers. U. S. Patent No. 3,937,671 discloses a pro- reuse by various processes. It is known that poly- 30 cess in which textile waste composed of blended esters can be dissolved in solvents and solvent polyester and cellulose fibers are subjected to the systems such as 1,1,1,3,3,3 - hexafluoropropanol, action of glacial acetic acid and acetic anhydride in phenol/tetrachloroethane, or trichloroacetic the presence of a catalyst under conditions which acid/chloroform. Technical, economic, and environ- serve to convert the cellulose component of the mental considerations of this process limit its ap- 35 waste to cellulose acetate which is separated from plicability. These are among the reasons that sol- the unreacted polyester component in the form of a vent systems such as these are only of interest for solution adapted to be used in the manufacture of analytical investigations. cellulose derivatives where the polyester is re- Another method for recovery of polyester scrap moved in a form which may be garnetted to obtain is by means of dissolution of the polyester in 40 a staple fiber for reuse. various solvents, thereafter precipitating and re- A process is disclosed in U. S. Patent No. covering the polyester. A process has been dis- 3,937,675. In the disclosed process, textile waste closed in U. S. Patent No. 4,003,880 providing a formed of blended cellulose and polyester fibers method whereby dye-stripping, separation, and are treated with a mineral acid agent such as polyester recovery are combined in such a way as 45 sulfuric acid, under conditions which serve to that the dye-stripping phase actually constitutes the hydrolyze the cellulose and convert it to a form first step of the dissolution and separation phase. which is readily removed from the polyester fibers After the dye-stripping is completed, the fibers while leaving the polyester fibers substantially un- remain saturated with a dye-stripping solvent, affected. The cellulosic material is recovered in the which can also be used for dissolution of the poly- 50 form of fibrets adapted for use as such or for ester. The dissolution of the polyester and its sub- treatment in producing other cellulosic compounds sequent precipitation and separation from the sol- whereas the polyester fiber recovered may be gar- vent serves to complete the dye removal in addi- netted for reuse in either spun yarn manufacture or tion to the separation and recovery of the polyes- in nonwoven processes. ter. 55 Both U. S. Patent No. 3,937,671 and U. S. Alternatively, there are processes which involve Patent No. 3,937,675 are very expensive operations degrading the polyester with a lower alkyl alcohol and have not been commercially successful. U. S. and subsequently recovering the dicarboxylic Patent No. 3,937,671 requires large quantities of

2 3 EP 0 636 646 A1 4 reactants per weight of waste material. Added ex- Description of the Preferred Embodiments pense is incurred due to the fact that the recovered materials must be dried. In the case of U. S. Patent In accordance with the present invention, sour- No. 3,937,675, high reaction temperatures and ces for polyester/cotton blends may be obtained large quantities of acid are necessary. It also re- 5 from various sources including, but not limited to, quires that the recovered materials must be dried. cut and sew waste from manufacturers, spinning An additional method described in the prior art waste from manufacturers and post consumer gar- for the recovery of polyester from cellulose fibers ments. It is noted that foreign materials should be is disclosed in Democratic Republic of Germany removed from such sources, including other poly- Patent No. 1,548,043. It describes a process for io mers such as nylon, and metallic objects such as obtaining polyethylene terephthalate in the form of zippers and buttons. It is also preferred that the a powder from pure starting materials or from fabric not be dyed although dissolution is still pos- wastes by dissolving the polyethylene terephthalate sible for such materials. in a solvent at a temperature above the boiling Once the scrap material has been accumu- point of the solvent and at a vapor pressure of the 15 lated, it is preferred that the scrap material be cut solvent corresponding to this temperature. This and chopped into small pieces for ease of handling step is followed by cooling to precipitate the poly- and transfer in the appropriate vessel. One exam- ethylene terephthalate in the form of a powder. The ple would be one inch squares of fabric. It is solvent used is a halogenated hydrocarbon, the important that the samples are dried beforehand in boiling point which is below 100 degrees Celsius at 20 order to prevent degradation of the polyester dur- atmospheric pressure and the molecular weight of ing the process. which is below 200, or a solvent mixture which Preferably, the solvent system of choice is a contains such a halogenated hydrocarbon. sulfone solvent. In general sulfones are normally A disadvantage associated with implementation stable, crystalline substances of high boiling point. of Democratic Republic of Germany Patent No. 25 Certain sulfones exist as liquids while others are 1,548,043 is that measures must be taken to cap- solids. Preferably, the sulfones used for the dis- ture the solvent vapor that is released during the solution of the polyester are alkyl sulfones which process. This problem arises due to the fact that consist of carbon chains ranging from Ci to Cio- the solvent must be heated to temperatures above Additionally, they usually exhibit much lower toxic- its boiling point. 30 ity than the solvents currently being used for poly- It is an object of this invention to recover ester dissolution. polyester fibers and cellulosic materials in useful Preferably, the concentration of the solvent so- forms from such textile waste. It is another object lution is based upon a 5 weight percent polyester of this invention to provide a process for recycling content. For example, 380 grams of tetramethylene polyester/cotton blends which avoids the expense 35 sulfone plus an additional 15 grams solvent for associated with returning the polyester to its con- distillate collection and 40 grams of a 50/50 polyes- stituent chemicals. These and other objects of the ter/cotton blend fabric can be used. invention will be apparent to one skilled in the art After the addition of the solvent to the vessel, it as the description thereof proceeds. is preferable to raise the temperature of the solvent 40 to collect distillate in order to remove any impuri- Summary of the Invention ties that might be present. The distillate includes any water that may be present in the system. At The present invention provides a process this point, it is preferable to apply a blanket of which is an effective and economical means of nitrogen for the remainder of the process to pre- recycling polyester/cotton blend fabrics by separat- 45 vent degradation of the polyester and oxidation of ing the polyester from the cotton fabric. In particu- the cotton. lar, the present invention discloses a process for At approximately 150 degrees Celsius the poly- dissolving polyester with a sulfone solvent while ester/cotton fabric samples are charged into the maintaining the integrity of the cotton. The process vessel. Preferably, the samples are submerged in to recycle the polyester/cotton blend fabrics in- 50 the solvent bath with constant agitation for about 90 cludes the steps of (a) providing a polyester and minutes at 150 degrees Celsius. The purpose of cotton blend fabric; (b) charging said blend into a this step is to thoroughly wet out the polyes- sulfone solvent; (c) dissolving the polyester in the ter/cotton fabric samples with the solvent and allow sulfone solvent; (d) separating the dissolved poly- the solvent to fully penetrate all the fibers of the ester and sulfone solvent solution from the cotton 55 blend. fabric; (e) filtering the cotton to obtain isolated, The temperature of the solution is raised until it cotton fabric. reaches a temperature of about 190 degrees Cel- sius. The polyester/cotton fabric samples in the

3 5 EP 0 636 646 A1 6 solvent should remain at this temperature for about been present. The distillate included any water 35 minutes. These are the preferred conditions at present in the system. It needed to be removed or which polyester dissolves most effectively in the the polyester would have a lowered IV. Once the solvent. distillate was collected the vacuum was removed. The means of collecting the cotton from the 5 A blanket of nitrogen was then applied for the dissolved polyester includes filtering, centrifuging, remainder of the experiment. At approximately 150 or belt presses. Preferably, in the present embodi- degrees Celsius the polyester/cotton samples were ment, filtering is used. The filtering may be either charged into the vessel. The samples were sub- gravity, a vacuum type filter, or a pressure filter. merged in the solvent bath with constant agitation Subsequent to the filtering the cotton can be io for about 90 minutes at 150 degrees Celsius. The washed with water to remove any residual solvent purpose of this step was to thoroughly wet out the or contaminants from the cotton. polyester/cotton samples with the solvent to fully The dissolved polyester and solvent solution penetrate all the fibers of the blend. The tempera- can be separated by various means. In the present ture was raised until it reached 190 degrees Cel- embodiment, two possible methods can be em- 15 sius. The polyester/cotton in solvent remained at ployed. One option is the dissolved polyester can this temperature for 35 minutes. This is the lowest be allowed to phase out on its own with time at temperature at which polyester dissolves most ef- approximately room temperature. This is made fectively in the solvent. Dissolution occurred rather possible due to the fact that the preferred solvent rapidly, and analytical evaluation verified that all the tetramethylene sulfone is a solid at room tempera- 20 polyester was dissolved from the blend at this time ture. Alternatively, the dissolved polyester can be and temperature. released into a coagulation solution of a second After the 35 minutes was reached, the cap was sulfone solvent and water at which time the polyes- removed from the outlet at the bottom of the auto- ter precipitates out of solution. Preferably, a 10 clave. The tubing connector that was capped had weight percent solvent coagulation bath heated just 25 an approximate diameter of 0.094 in. The thin below the boiling point of the water is used. The stream of solution flowed into a Waring commercial solution is filtered while hot and the filtrate is fil- blender of about 1 gallon capacity. The blender tered repeatedly. was on medium speed and contained a tetramethylene sulfone/water coagulation solution. EXAMPLE 30 The tetramethylene sulfone/water solution was 1000 g in total and was composed of 100 g The experiments were conducted in a standard tetramethylene sulfone and 900 g water heated just 1.5 Liter autoclave vessel. It was equipped with a below the boiling point of the water. When the condenser to collect distillate, a means of dis- dissolved polyester solution reached the coagula- charge at the bottom of the vessel, and access 35 tion bath, the polyester precipitated out of solution. inlets for when the system is under vacuum or The solution was filtered while hot, and the filtrate under a nitrogen atmosphere. The concentration of was filtered repeatedly. The cotton samples were the solution was based upon a 5 weight percent contained within the autoclave. The collected cot- polyester content. Therefore, 380 g of ton was soaked and rinsed in near boiling water to tetramethylene sulfone plus an additional 15 g and 40 remove any dissolved polyester or solvent. This 40 g of polyester/cotton were used. The fabric washing step was repeated at least six times. The sample was an off-white knit, and the assumption collected washings were then vacuum filtered in was precisely 50/50 polyester/cotton by weight. order to collect all the dissolved polyester. The fabric samples were dried overnight in a vacu- The filter cake and the cotton samples were um oven at 100 degrees Celsius at a pressure 45 dried in the vacuum oven. When the experiment below 1 mm Hg. It was important that the samples was conducted under nitrogen the precipitated re- were dried beforehand in order to prevent degrada- covered polyester was white in color. However, tion of the polyester during the process. without the nitrogen the recovered polyester was After the addition of the tetramethylene sulfone light brown in color. The cotton was less discolored to the autoclave, a nitrogen purge was started and 50 when under nitrogen also. continued for about 15 minutes at room tempera- Thus, it is apparent that there has been pro- ture prior to heating. During the purge a stirrer vided in accordance with the invention a method of provided agitation at a moderate speed to the recycling polyester/cotton blend fabrics whereby tetramethylene sulfone bath. Once this was com- the polyester component would be dissolved such pleted, the temperature was raised to 130 degrees 55 that both components of the blend could be recov- Celsius while the system was under full vacuum. ered and recycled. While the invention has been The intention was to collect about 15 g of distillate described in conjunction with the specific embodi- in order to remove any impurities that might have ments thereof, it is evident that many alternatives,

4 7 EP 0 636 646 A1 8 modifications and variations will be apparent to fone solvent; those skilled in the art in light of the foregoing separating the dissolved polyester and first description. Accordingly, it is intended to embrace sulfone solvent solution from the cotton fabric; all such alternatives, modifications that fall within releasing the dissolved polyester into a this sphere and scope of the invention. 5 coagulation solution of second sulfone solvent and water at which time the polyester Claims precipitates out of solution; separating the dissolved polyester from 1. A process for recycling polyester and cotton the solution of a second sulfone solvent and blend fabrics comprising the steps of: io10 water; providing a polyester and cotton blend fab- filtering the cotton fabric as to obtain iso- ric; lated, cotton fabric. charging said blend in a sulfone solvent; dissolving the polyester in said sulfone sol- 10. The process according to claim 9 wherein said vent; is sulfone solvent is an alkyl sulfone. separating the dissolved polyester and sulfone solvent solution from the cotton fabric; 11. The process according to claim 10 wherein allowing the dissolved polyester solution to said alkyl sulfone was tetramethylene sulfone. phase out on its own with time; filtering the cotton fabric as to obtain the 20 12. The process according to claim 11 wherein isolated, cotton fabric. said solvent was 99% pure.

2. The process according to claim 1 wherein said 13. The process according to claim 9 wherein said sulfone solvent is an alkyl sulfone. alkyl sulfone includes methylethyl sulfone, 25 methyl propyl sulfone, dimethyl sulfone, and 3. The process according to claim 2 wherein said diethyl sulfone. alkyl sulfone was tetramethylene sulfone. 14. The process according to claim 9 where the 4. The process according to claim 3 wherein said second sulfone solvent may be either solvent was 99% pure. 30 methylethyl sulfone, methyl propyl sulfone, dimethyl sulfone, diethyl sulfone, or 5. The process according to claim 1 wherein said tetramethylene sulfone. alkyl sulfone includes methylethyl sulfone, methyl propyl sulfone, dimethyl sulfone, and 15. The process according to claim 14 wherein diethyl sulfone. 35 said second sulfone solvent was tetramethylene sulfone. 6. The process according to claim 1 where the fabric samples were dried at an appropriate 16. The process according to claim 9 wherein the temperature, pressure, and time interval as to coagulation bath of said second sulfone sol- prevent degradation of the polyester during the 40 vent and water is heated to about the boiling process. temperature of water.

7. The process according to claim 1 where con- 17. The process according to claim 9 wherein constant agitation is provided during both the satu- stant agitation is provided in the coagulation ration and dissolution steps. 45 bath.

8. The process according to claim 1 wherein the 18. The process according to claim 9 where the dissolving step is carried out at a temperature fabric samples were dried at an appropriate of about 190 degrees Celsius for a period of temperature, pressure, and time interval as to less than about 35 minutes. 50 prevent degradation of the polyester during the process. 9. A process for recycling polyester and cotton blend fabrics comprising the steps of: 19. The process according to claim 9 wherein con- providing a polyester and cotton blend fab- stant agitation is provided during both the satu- ric; 55 ration and dissolution steps. charging said blend in a first sulfone solvent; 20. The process according to claim 9 wherein the dissolving the polyester in said first sul- dissolving step is carried out at a temperature

5 9 EP 0 636 646 A1 of about 190 degrees Celsius for a period of less than about 35 minutes.

55 Application Number EP 94 11 1597

DOCUMENTS CONSIDERED TO BE RELEVANT Citation of document with indication, where appropriate, Relevant CLASSIFICATION OF THE Category of relevant passages to daim APPLICATION (Int.C1.6) DE-A-26 26 358 (HORIZONS RESEARCH INC.) 1-3,7 C08J 11/08 * claims 1,7,9 * //C08L67:02, * page 2, line 25 - page 3, line 6 * C08L1:02 * page 9; table I; last line * * page 14, line 10 - line 20 * * page 16, line 18 - line 25 * * example 8; table II *

US-A-4 345 039 (COWAN J.C. ET AL) * claims 1,3 *

TECHNICAL KlfcLUS SEARCHED (Int.C1.6) C08J C08G C08L

The present search report has been drawn up for all claims Place of search Date of CMnpletkM of the search THE HAGUE 10 October 1994 Niaounakis, M CATEGORY OF CITED DOCUMENTS T : theory or principle underlying the invention E : earlier patent document, but published on, or X : particularly relevant if taken alone after the filing date Y : particularly relevant if combined with another D : document cited in the application document of the same category L : document cited for other reasons A : technological background O : non-written disclosure & : member of the same patent family, corresponding P : intermediate document document