Note: Descriptions are shown in the official language in which they were submitted.
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2
3
4 BACKGROUND OF THE INVENTION
Field of the Invention
6 The present invention is generally directed to a method of recycling colored
7 polyamides. In particular, the method of the present invention is useful in
recycling post-
8 consumer materials, such as carpets, that contain colored polyamide fibers.
9 Background
io As the amount of available landfill space decreases, and the number of
articles
i i manufactured from synthetic polymers increases, the need for
environmentally
12 responsible methods for disposal of these polymer-containing articles
increases. A
13 welcome alternative to landfill disposal is recycling and reuse of the
synthetic polymer
14 material in products which may be the same as or entirely different from
the original
article.
16 One significant limitation to the utility of recycled synthetic polymer
material is
17 the imparted color. Colorants, additives, or dyes are commonly added to
virgin polymers
18 for both practical and aesthetic reasons. However, the colorant, additive,
or dye may
19 significantly impair the processability of or degrade the polymer during
conventional
recycling processes. Further, the presence of colorant, additive, or dye may
limit the
21 potential downstream uses of the recycled polymeric material, as any color
change
22 desired in the downstream use could be limited if not impossible given the
original
23 article's color. In some cases, an article otherwise suitable for recycling
is rejected
24 completely and deposited in a landfill simply because its color is
undesirable or
inappropriate for a particular downstream use.
26 Processes for stripping dyes from or decolorizing various materials are
known in
27 the art. For example, U.S. Patent No. 4,227,881 discloses a process for
stripping dyes
28 from textile fabric which includes heating an aqueous solution of an
ammonium salt, a
29 sulfite salt and an organic sulfonate to at least 140 F (60 C) and adding
the dyed fabric to
the heated solution while maintaining the temperature of the solution. In
addition to the
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i costly heating and temperature maintenance step, this process has the
drawback of
2 producing fabrics which after processing exhibit a remaining color depth.
U.S. Patent
3 No. 4,783,193 discloses a process for stripping color from synthetic polymer
products by
4 contacting the colored polymer with a chemical system. The described process
uses
unstable dispersions of alkyl halides and aqueous solutions of
bleaching/oxidizing agents
6 to which specified quantities of acids and surfactant/wetting agents are
added. Among
7 the drawbacks are the use of potentially hazardous halogens and the special
provisions
a required to prevent escape of vapors which could cause environmental harm.
Further, the
9 use of the chemical system may restrict or eliminate the polymeric
material's
recycleability. In general, processes which utilize harsh stripping agents
destroy the
iI usefulness of the colorant, thus generating a chemical waste stream that
must be treated
12 or disposed of in an environmentally conscious manner. These methods can
also generate
13 unremovable colorant fragments which limit the downstream recycleability
and utility of
14 the color-stripped material.
Thus an unmet need exists for a cost-effective and environmentally friendly
16 process for separating polymers from colorants, additives, or dyes, without
degrading or
17 otherwise decreasing the polymeric material's potential use.
18 SUMMARY OF THE INVENTION
19 The present invention concerns a process for recycling colored polyamide
material, which comprises the steps of: (a) contacting solid colored polyamide
material
21 with an organic solvent composition at a temperature effective to dissolve
the polyamide,
22 thereby forming a solution containing colorant and dissolved polyamide; and
(b)
23 separating colorant from the polyamide. Although not all of the colorant
present will
24 necessarily be removed after a single separation step, a substantial amount
of the colorant
(e.g., at least about 50% of the colorant present) is preferably removed. The
process can
26 be repeated as many times as necessary to achieve a desired level of
colorant removal.
27 The process can optionally further comprise the step of recovering the
separated
28 colorant. Alternatively, the process can further comprise the step of
recovering the
29 polyamide. Therefore, the process of the present invention can be used to
recover either
one or both of the polymer and colorant. Because the molecular weight of the
polyamide
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i is substantially unchanged (e.g., no more than about a 5% change in average
polymer
2 molecular weight) during this processing, the polymer is very suitable for
reuse.
3 The solid colored polyamide material can be in a variety of forms, such as
fibers,
4 fabrics, shaped solid articles, etc. In a preferred embodiment of the
process, the colored
polyamide of step (a) is from carpet.
6 The temperature at which the polyamide is contacted with the organic solvent
7 composition in step (a) preferably is approximately equal to or higher than
the solution
8 glass transition temperature of the polyamide. In a preferred embodiment of
this process,
9 the temperature of step (a) is between about 140 -220 C, more preferably
about 160-
io 180 C.
i i After dissolution of the polyamide in the solvent, the solution is
preferably then
12 cooled to a temperature effective to cause precipitation of the polyamide.
The
13 precipitated polyamide will contain substantially less (e.g., about 50%
less) colorant than
14 the feed polyamide material. Separation of colorant from polyamide in step
(b)
is optionally can be enhanced by contacting the solution with an active
decoloring agent.
16 The active decoloring agent can be selected from the group consisting of
activated
17 carbon, anion exchange resin, cation exchange resin, ion-pair resin, and
combinations
18 thereof. In other words, use of an active decoloring agent in the solution
prior to cooling
19 can increase the overall removal of colorant.
20 The organic solvent composition preferably is selected from the group
consisting
21 of aliphatic and aromatic ketones, aliphatic and aromatic alcohols, diols,
combinations
22 thereof, and combinations of one or more of these compounds with water.
Solvent
23 compositions comprising at least one alcohol selected from the group
consisting of
24 butanediol, butanol, ethanol, and benzyl alcohol are suitable. Some
preferred organic
25 solvent compositions comprise an aqueous solution or dispersion of 1-
butanol or ethanol.
26 In another embodiment of the process, the colorant comprises an acid dye,
and the
27 process further comprises adding a base to the solution of step (a),
thereby causing the
28 acid dye and the added base to form an insoluble salt. This insoluble salt
can be
29 removed, for example, by filtration. Quaternary ammonium compounds are
useful as the
30 base in this embodiment of the invention.
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1 One particular embodiment of the invention is a process for recycling post-
2 consumer carpet containing colored polyamide fibers. This process comprises
the steps
3 of: (a) contacting solid colored polyamide fibers with an organic solvent
composition at a
4 temperature at least as high as the solution glass transition temperature of
the polyamide,
s thereby forming a solution containing dissolved polyamide; and (b)
separating colorant
6 from the polyamide. Optionally, the process can further comprise the step of
physically
7 separating the backing of the carpet from the colored polyamide fibers prior
to step (a).
8 This physical separation can be accomplished, for example, by a method
selected from
9 the group consisting of shearing, cutting with a hot wire, cutting with a
laser, and
io combinations thereof. Whether or not the backing is removed, it is
presently preferred to
i i reduce the colored polyamide fibers into smaller particles (e.g., by
shredding or grinding)
12 prior to being dissolved. After dissolution at elevated temperature,
insoluble materials
13 can be separated from dissolved polyamide, for example, by a method
selected from the
14 group consisting of filtration, centrifugation, and combinations thereof.
15 Another particular embodiment of the invention is a process for recycling
post
16 consumer carpet containing colored nylon fibers, comprising:
(a) separating dirt and other loosely-attached foreign materials from carpet
having
18 nylon face fibers;
19 (b) grinding, cutting, or shearing the colored nylon fibers into particles
having
20 reduced size;
21 (c) dissolving the nylon in a solvent composition comprising alcohol at a
22 temperature at least as high as the solution glass transition temperature
of the polyamide;
23 (d) separating insoluble materials from dissolved nylon by a method
selected from
24 the group consisting of filtration, centrifugation, and combinations
thereof;
25 (e) separating colorant from nylon by contacting the solution with an
active
26 decoloring agent; and
27 (f) cooling the dissolved nylon to a temperature of 140 C or less, thereby
causing
28 nylon to precipitate. The alcohol solution in which the nylon is dissolved
preferably
29 comprises at least about 50% by weight alcohol, and the remainder water.
After
30 dissolution the nylon preferably makes up from about 10-20 weight % of the
solution.
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i The process can optionally further comprise washing the precipitated nylon
with a
2 liquid selected from the group consisting of alcohol, water, and mixtures
thereof. The
3 alcohol used in washing preferably is selected from the group consisting of
ethanol,
4 butanol, isopropanol, benzyl alcohol, 1,4-butanediol, 1,5-pentanediol, and
mixtures
thereof.
6 Another embodiment of the invention is a process for removing colorant from
7 colored polyamide, comprising:
s (a) dissolving a colored polyamide in a solubilizing solvent so as to give a
first
9 polymer-containing solution, the polymer-containing solution including
polyamide and
io soluble colorants;
i i (b) decreasing the concentration of the soluble colorants in the first
polymer-
12 containing solution so as to give a second polymer-containing solution, the
second
13 polymer-containing solution having a decreased amount of soluble colorants
and the
14 solubilizing solvent, and
is (c) recovering the polyamide from the second polymer-containing solution.
In
16 this embodiment of the invention, the second polymer-containing solution is
what is left
17 behind after dye and adhesive are removed from the first polymer-containing
solution.
-s Yet another embodiment of the invention is a process for recovering
polyamide
19 from post-consumer carpets containing polyamide and soluble colorant
components, the
20 process comprising:
21 (a) dissolving at least a portion of the polyamide component and at least a
portion
22 of the soluble colorant component in a solubiliziiig solvent so as to give
a first
23 polyamide-containing solution and undissolved carpet materials, the first
polyamide-
24 containing solution including at least a portion of the polyamide and at
least a portion of
25 the soluble colorant components;
26 (b) separating the undissolved carpet materials from the first polyamide-
27 containing solution;
28 (c) contacting the first polyamide-containing solution with an active
decoloring
29 agent in an amount and for a period of time sufficient to decrease the
concentration of the
30 soluble colorant component from the first polyaniide-containing solution;
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1 (d) separating the active decoloring agent from the first polyamide-
containing
2 solution so as to give a second polyamide-containing solution; and
3 (e) recovering the polyamide from the second polyamide-containing solution.
4 Prior art decolorization methods have often involved removing colorants from
a
solid polymeric material, such as fibers, fabrics, carpets, or molded resins.
The present
6 invention instead removes colorant from a polymer-containing solution, and
offers an
7 economical and simple means of recycling colored polymer materials. The
present
8 invention does not substantially degrade the polymer and therefore the
recovered polymer
9 can be used in new polymeric materials or articles without the need for
repolymerization.
The present invention can remove a wide variety of color-imparting agents from
the
i i polymeric material, and can remove substantial amounts of colorants from
polymer, even
12 if the colorants are deeply penetrated into the polymeric material or are
in the form of
13 large aggregates inside voids in the polymeric material. The present
invention can also
14 remove impurities other than colorants from the polymeric material. One
particularly
is advantageous use of the present invention is in recycling post-consumer
carpet.
16 Because the process of the present invention does not substantially degrade
the
17 dye or other colorant in the process of separating it from the polymer, the
colorant itself
-s can be recovered and reused. Therefore, in different embodiments of the
invention, the
19 process might involve recovering only the polymer, recovering only the
colorants, or
recovering both the polymer and the colorants for separate reuse.
21 BRIEF DESCRIPTION OF THE DRAWINGS
22 Figure I is a graph of the relative viscosity (RV) of the polymer recovered
when
23 post-consumer carpet was processed in accordance with the present
invention, using
24 different solvent compositions.
Figure 2 is a graph of the NH2 end groups for the recovered polymers in the
same
26 tests.
27 Figure 3 is a graph of the COOH end groups for the recovered polymers in
the
28 same tests.
29 Figure 4 is a graph of the relative viscosity of the recovered polymer
versus the
sum of the end groups (NH, and COOH) for the recovered polymer in the same
tests.
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- Figure 5 is a graph of the molecular weight distribution of polymer from one
type
2 of carpet in the same tests versus dW f/ d log[M] (i.e., change in weight
fraction, Wf, with
3 change in log of molecular weight)."URI MAX-START" refers to the polymer
before
4 dissolution, "URI-BZOH" refers to the polymer recovered using benzyl
alcohol, "URI-
BUOH" refers to the polymer recovered using 1-butanol/water, and "URI-
ETOH/H20"
6 refers to polymer recovered using ethanol/water as the solvent composition.
7 DESCRIPTION OF SPECIFIC EMBODIMENTS
8 The following terms and phrases are used herein and are intended to have the
9 following meaning:
"Additive" is defined as any intentionally or accidentally added material that
i i affects the properties of the polymeric material.
12 "Color" is defined to include intentionally imparted visual appearance such
as
13 color imparted by dyes and accidentally imparted visual appearance such as
stains and the
14 like.
"Colorant" is defined as any dye, pigment, or colored composition or
16 combinations thereof that may intentionally or accidentally color or stain
polymeric
17 materials.
18 "Dye" is defined as an organic material which imparts color to a polymer
and
19 which chemically bonds to the polymer primarily by ionic or associative
mechanisms.
"Polyamide" is defined as any known polymer, copolymer, terpolymer and the
21 like as well as the blends or alloys thereof having an amide bond as a
principle linking
22 group between monomers. Examples include nylon 6; nylon 6,6; and nylon
6,10.
23 "Solvating agent" is defined as a material capable, under specified
conditions, of
24 interrupting the molecular forces within the polymer matrix, resulting in
the dissolution
of the polymer material. The term "solvate," as utilized herein, is defined as
the
26 substantial dissolution of the macroscopic structure or form or shape of
the polymeric
27 material.
28 All percentages herein are by weight unless otherwise specified.
29 One embodiment of the invention is a process for recovering polyamide from
post
consumer carpet, and includes the steps of (1) preparing the feedstock, (2)
dissolution, (3)
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i removal of insoluble materials, (4) separating polymer from colorant, and
(5) washing the
2 recovered nylon.
3 The first step in this embodiment of the process, preparing the feedstock,
involves
4 separating carpets having polyamide fibers from carpets having only non-
polyamide
fibers (e.g., polypropylene, polyester). Spectral analysis (e.g., near
infrared), solubility
6 analysis, stain analysis, or other fiber identification methods known in the
art could be
7 used for the separation. A particularly preferred polyamide fiber material
for use in this
8 process is nylon 6,6, and a large volume of post-consumer carpet having such
fibers is
9 available.
io The carpet will typically be colored, and thus will contain one or more
dyes or
i i other colorants. The carpet may also contain one or more additives other
than colorants.
12 Dyes for which the process of the present invention is particularly useful
include acid
13 dyes, which are known to impart color to nylons, especially nylon 6,6.
Other dyes can
14 also be removed using the process of the present invention. Other colorants
for which the
process of the present invention would be useful include the natural and
synthetic
16 pigments, such as carbon black or colored transition metal oxides, and
colored
17 compositions that may stain the colored polymeric material, for example
common food
18 items such as coffee, fruit and vegetable material, juices and extracts,
red wine, and
19 natural and synthetic inks.
After separation of non-polyamide carpets, the polyamide carpets can be
21 prepurified before dissolution. The prepurification can include mechanical
separation of
22 dirt and other loosely attached foreign materials, and washing the carpet
with detergent
23 and water.
24 Although it is presently preferred to use whole carpet (i.e., including
backing and
adhesive) in the remainder of the process, it is also possible to first
separate the carpet's
26 face fibers from the carpet backing materials before the dissolution
process. This can be
27 done mechanically, for example by shearing, hot-wire cutting or laser
cutting the fibers
28 from the backing, or by other means known to those skilled in this art.
29 The prepurified feed material (whether containing backing or not)
preferably is
cut, ground, or shredded into particles of reduced size, before being fed to
the dissolution
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i step. This will increase the surface area of the colored polymer that will
contact the
2 solvent composition.
3 The feed is then contacted with an organic solvent composition in order to
cause
4 dissolution of the polymer. The organic solvent composition contains one or
more
solvating agents. The solvating agent should be capable of interrupting the
molecular
6 forces within the polymeric material matrix, resulting in the dissolution of
the polymeric
7 macro-structure. The choice of solvating agent will depend on the nature of
the colored
8 polymeric material and the conditions of the solvating step. For example, if
nylon 6,6 is
9 the polymeric material, the solvating agent may be any material known to be
capable of
io dissolving nylon 6,6. In certain embodiments of the present invention, the
solvating
i i agent may be part of a solvent composition in which the solvating agent is
at least
12 partially miscible with the other components (e.g., water) in the solvent
composition
13 during the solvating step.
14 It will be apparent to one of ordinary skill in the art that the exact
nature and
is amount of solvating agent utilized in the solvating composition will vary
depending upon
16 the conditions, such as temperature, pressure, pH, residence time, etc.,
utilized during the
17 solvating step. In embodiments where the dye is to be re-used, it should
also be kept in
-a mind that the solvating composition should preferably be substantially non-
reactive with
19 the dye.
20 Examples of suitable solvating agents include aliphatic and aromatic
alcohols,
Zi aliphatic and aromatic ketones, water, and mixtures, solutions, emulsions
or dispersions
22 thereof. One group of preferred solvating agents is C, to Cio alcohols.
Diols are another
23 suitable example. Particularly preferred examples include benzyl alcohol,
methanol,
24 ethanol, 1- and 2-propanol, 1-butanol, cyclohexanol, 1,4-butanediol, and
1,5-pentanediol,
25 as well as mixtures thereof with each other and with water. Ethanol is
particularly
26 preferred because it is an inexpensive, easy to handle, environmentally
friendly
27 compound. Where the solvent composition comprises an alcohol and water, the
alcohol
28 preferably makes up at least about 5% by weight of the composition.
29 The colored polymeric material preferably is contacted with the solvent
30 composition under elevated temperature. The pressure at which the solvating
step is
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i carried out will depend upon the solvent since the pressure is a result of
the solvent vapor
2 pressure. It is preferred that the solvating step be carried out at a
temperature above the
3 solution glass transition temperature (Tg) of the colored polymeric material
in the process
4 envirorunent (i.e., in the presence of the solvent). It should be recognized
that the glass
transition temperature changes when solvent is added to the polymer. Preferred
6 temperatures for nylon 6,6 are between about 10-250 C, more preferably
between about
7 80-250 C. In certain embodiments of the process, the temperature is
preferably between
s about 120-250 C, more preferably between about 140-220 C, most preferably
between
9 about 160-180 C. Suitable pressures can be between about atmospheric
pressure and
io about 300 psig, preferably between about atmospheric pressure and 250 psig.
Elevated
iI pressure may be that provided by an inert gas, such as nitrogen or argon,
or it may be the
12 pressure generated by the vaporization of the liquids in the solvating
composition in a
) 3 pressure vessel.
14 The residence time for solvating the colored polymeric material can be
controlled
is to ensure the most economic recovery of material. Suitable residence times
for the
16 solvating step will depend on the polymer and the conditions of the
solvating step, but
17 will usually range from about 0.5 - 60 minutes, preferably form about 0.5-
30 minutes. In
18 embodiments where the total solvation of the polymeric material is not
desired, the
19 preferred residence time can be between about 0.5 - 20 minutes, more
preferably between
20 about 1- 10 minutes. For example, in one experiment, total solvation was
achieved in
21 five minutes at 170 C. In another embodiment of the process, the time of
contact can
22 suitably be between about 10-30 minutes. The solution containing the
polymer and the
23 solvent preferably has an alcohol concentration of from about 50-100 weight
percent, and
24 a nylon concentration between about 0.1 - 35 weight percent, most
preferably between
25 about 10-20 weight percent.
26 The amount of solvating agent in the solvent composition will depend on the
27 desired conditions of the solvating step and on each other. Further
variables such as the
28 nature and amount of the polymeric material, the nature and amounts of the
dye(s) or
29 other colorant(s) present in the polymer, the depth of color shade, and the
like, are
30 preferably considered.
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i The solvating step may include a plurality of solvating stages wherein the
colored
2 polymeric material is contacted repeatedly with a solvating agent.
3 The solvating step may be performed using a variety of techniques known to
4 person having ordinary skill in the art. Such techniques include inunersing
the colored
polymeric material in the solvating agent, applying an effective amount of the
solvating
6 agent onto the polymeric material, and the like. The solvating step can be
carried out as
7 either a batch or continuous process.
8 Agents to modify pH are generally not needed. High pH would enhance the
9 solubility of a dye and retard removal by, e.g., activated carbon.
io After the polymer is dissolved, any insoluble materials that are present
can be
i i removed. Examples of materials that can be removed in this step are carpet
backing
12 materials, such as polystyrene butadiene, calcium carbonate, and
polypropylene, and
13 insoluble colorants and other additives such as carbon black, pigment, and
titanium
14 dioxide. It should be appreciated that while some of the colorants in the
carpet may be
is insoluble and thus subject to removal in this step, other colorants may be
soluble in the
16 same solution that dissolves the polymer. The process of the present
invention can be
17 used with carpet that contains either type of colorant, or both.
18 The insoluble materials can be removed by a variety of methods, including
19 filtration, centrifugation, and the like.
20 After removal of insolubles, at least some of the remaining soluble
colorants (and
21 other soluble non-polyamide materials) can be separated from the nylon or
other
22 polyamide. One way of doing this is to cool the solution to less than about
140 C (e.g.,
23 by air cooling), so that the polyamide present in the solution will
precipitate. In this
24 embodiment of the invention, the precipitated polyamide can then be
removed, by, for
25 example, filtration or centrifugation. Further removal of soluble colorants
can be
26 achieved by dissolving in more solvent and precipitating the polyamide
optionally
27 without use of the decoloring agent. This can be repeated as many times as
necessary to
28 achieve the decolored polyamide. It should be recognized that after
separation of dye
29 from the polymer solution, there will usually be some impurities in both
the dye and the
30 solvent.
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i Separation techniques include ultrafiltration (although ultrafiltration will
typically
2 not remove the dye but will remove other impurities in the solution), ion
exchange,
3 extraction (e.g., supercritical fluid extraction), contacting with an active
decoloring agent,
4 and combinations of these methods. Choice of the appropriate recovery method
will
depend on the characteristics of the dye and the formulation of the solvating
composition,
6 and the solubility characteristics of both the dye and the polymer.
7 If an active decoloring agent is used, it can be, for example, activated
carbon,
a cation exchange resin, anion exchange resin, ion-pair resin, or a
combination of one or
9 more of these materials. One suitable activated carbon material that is
commercially
io available is Type CPG Granular Carbon (e.g., mesh size 12 x 40), available
from Calgon
I i Carbon Corporation. (Activated carbon having mesh size between 12 mesh and
40 mesh
12 is preferred.) The active decoloring agent is preferably added to the
solution in a weight
13 ratio of about 200:1 decoloring agent:dye or a weight ratio of about 1:1
decoloring agent:
14 polymer. The contact time between the solution and the active decoloring
agent is
is sufficient to remove the desired degree of color. Then, the active
decoloring agent can be
16 separated from the solution by, e.g., filtration.
17 After the polyamide and the colorants are thus separated, the polyamide can
18 optionally be washed, to remove any residual dye, colorant, or solvating
agent.
19 Alternatively, the washing step can itself perform the function of
separating polyamide
20 and colorants. Suitable washing agents should at least partially solubilize
the residual
21 dye, colorant, or solvating agent without harm to the decolorized colored
polymeric
22 material. Washing agents preferably are polar liquids such as alcohols,
water, and
23 mixtures thereof. Preferred examples include C)-C4 aliphatic alcohols, C3-
C6 ketones,
24 and mixtures thereof. Specific preferred alcohols for this step include
ethanol,
25 isopropanol, n-butanol, benzyl alcohol, 1,4-butanediol, and 1,5-
pentanediol. Acetone,
26 water, and mixtures thereof are another preferred group of liquids for the
washing step.
27 The washing is preferably conducted at a temperature between about 10-140
C.
28 The polymer left after this processing can then be formed into new articles
for
29 sale, such as fibers, shaped articles, and the like. The polymer can have
new colorants
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1 added to it, and they need not impart the same color to the polymer as it
previously had
2 before recycling.
3 One object of the process of the present invention is to perform the
solvating step
4 so as to avoid any substantial degradation of the polymer. Although the
general shape
and integrity of the form of the colored polymeric material, for example
fiber, molded
6 part, or the like, is not maintained during the solvating step, the
molecular weight of the
7 polymer is not dramatically reduced. Therefore, the polymer can be reused
without the
8 expense of repolymerization.
9 The colorants can also be reused after they are separated from the polymer.
In
io some instances, the colorants might be sufficiently more valuable than the
polymer that
i i the operator of the process would recover and reuse the colorant, while
merely disposing
12 of the polymer rather than reusing it. Therefore, commercial embodiments of
the present
13 invention could include recovering only the polymer for reuse, recovering
only one or
14 more colorants for reuse, and recovering both polymer and colorant(s) for
reuse.
is The process of the present invention permits the decolorization of colored
16 polymeric materials without the need for harsh stripping agents. Stripping
agents are
17 defined herein as materials which oxidize, reduce or otherwise destroy the
dye
18 chromophore. Because of the highly reactive chemical nature of such
stripping agents,
19 their use can limit or prevent the reuse of the recovered materials. The
solvating step in
20 the process of the present invention is preferably conducted in the absence
of such
21 stripping agents. Thus the resulting polymeric material can fully replace
or be blended
22 with virgin polymer for use in articles that conventionally decolorized
polymeric material
23 cannot presently be used.
24 The following examples are included to demonstrate certain specific
embodiments
25 of the invention.
26 Example 1
27 A sample of acid-dyed nylon 6,6 was dissolved in butanediol at a
temperature
28 from about 140 to 220 C (e.g., 160 C) and at a nylon concentration of 0.1
to 35 weight
29 percent, giving a colored solution including nylon 6,6 and soluble acid
dye. Activated
30 carbon in an amount of 0.001 to 100% of the total estimated weight of the
nylon 6,6 in
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i solution, was added into the colored solution. The mixture was agitated so
as to
2 thoroughly contact the polymer-containing solution with the activated
carbon. After a
3 contact time of about 0.1 to about 120 minutes, the activated carbon will be
separated
4 from the polymer-containing solution by filtering through a series of
filters having a pore
size of 1 to 100 microns to remove the activated carbon. Upon cooling below
140 C and
6 the removal of any pressure, substantially decolored nylon 6,6 will
precipitate from the
7 nylon 6,6-containing solution. Not all of the colorant was removed from the
nylon, but
8 the removal was sufficient to permit the polymer to be redyed a different
color.
9 Example 2
The procedure of Example 1 was used with a combination of ethanol and water as
iI the solvent instead of butanediol. The solvent was 30-90% ethanol.
12 Example 3
-3 The procedure of Example 1 was used with a combination of n-butanol and
water
14 as the solvent instead of butanediol. The solvent was 30-90% n-butanol.
Example 4
16 The procedure of Example 1 was used with benzyl alcohol as the solvent
instead
17 of butanediol.
18 Example 5
19 The procedures of Examples 1 to 4 can be repeated substituting for the
activated
carbon either commercially available cation exchange resin, anion exchange
resin, or ion-
21 pair resin. The alternative decoloring agent can suitably have a particle
size of greater
22 than 10 microns and a pore size suitable to allow the dye molecules to
absorb, but a size
23 too small for the polymers to absorb.
24 Example 6
The procedures of Examples 1 to 5 can be carried out utilizing a nylon in
which
26 more than one colorants are present. For example a combination of acid dyed
and
27 pigmented nylon 6,6 sample can be used. In such a combination, the colored
nylon
28 would be dissolved in a suitable solvent such as ethanol/water (90/10)
under pressure
29 generated by the heating of a closed system to above 160 C. Upon
dissolution the
solution should be filtered through a series of increasingly finer filters so
as to remove the
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H2J1047(4Y9Z01' DOC)
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1 solid particles present in solution including the pigment particles. To the
filtered
2 solution, a suitable decoloring agent having a particle size greater than 10
microns will be
3 added. The decoloring agent can be selected from activated carbon, cation
exchange
4 resin, anionic exchange resin, ion pair resin, size exclusion resin, or
combinations of
these. The total amount of decoloring agent utilized to remove the acid dye
colorant will
6 depend upon both the amount of dye present in the nylon and the desired
contact time.
7 One of skill in the art should be able to vary these parameters within the
ranges disclosed
8 herein to achieve the desired level of decolorization. After the desired
contact time is
9 reached, the mixture of decolorizing agent and nylon solution would be
filtered through a
micron filter to remove the decolorizing agent particles, preferably a filter
for particles
I I greater than 10 microns. Once the decolorizing agent is removed, cooling
of the solution
12 to below the boiling point of the ethanol solvent will reduce the pressure
and a
13 substantially decolorized polymer will be recovered.
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i Example 7
2 The procedures of Examples 1 to 6 may be run in a continuous manner by
passing
3 the polymer containing solution through a column packed with active
decolorizing agent.
4 In such an embodiment, the colored nylon would be dissolved in a suitable
solvent such
as ethanoVwater (60/40) under pressure generated by the heating of a closed
system to
6 above 160 C. Upon dissolution the solution would first be filtered through a
series of
7 increasingly finer filters so as to remove the solid particles present in
solution including
8 any pigment particles. The filtered solution would then be passed through a
packed
9 column containing a suitable decoloring agent. The decoloring agent should
be selected
io from activated carbon, cation exchange resin, anionic exchange resin, ion
pair resin, size
i i exclusion resin, or combinations of these. The total amount of decoloring
agent utilized
12 to form the column will depend upon the diameter and length of the column.
The size
13 and diameter of the column should be sufficient enough so as to contain
enough active
14 decoloring agent to reduce the concentration of colorant in the polymer
solution. By
is adjusting the length of the column and the flow of the polymer solution
through the
16 column, the desired level of decolorization will be achieved. One of skill
in the art should
17 be able to vary these parameters within the ranges disclosed herein to
achieve the desired
18 level of decolorization. After passage through the column, the polymer-
containing
19 solution should be filtered through a micron filter to remove any residual
particles,
20 preferably a filter for particles greater than 10 microns. Cooling of the
solution and
21 reduction of pressure to ambient conditions and a substantially decolorized
polymer will
22 be recovered.
23 Example 8
24 The studies of examples 8-11 were performed in an autoclave with pressure
25 furnished by a nitrogen cylinder.
26 Twelve samples of carpet (3 g each) were each placed in a solution
consisting of
27 40 ml of an alcohol/water mixture. All of the samples were placed in the
autoclave at the
28 same time. The samples were heated in the autoclave for one hour at 159-171
C under a
29 pressure of 250 psig. Nylon was separated from the other components in the
carpet and
30 recovered by precipitation from the solution.
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CA 02261304 1999-02-05
- Table 1
2
Sample number Alcohol Weight ratio alcohol/water
1 methanol 40/60
2 methanol 50/50
3 methanol 60/40
4 ethanol 40/60
ethanol 50/50
6 ethanol 60/40
7 n-butyl alcohol 40/60
8 n-butyl alcohol 50/50
9 n-butyl alcohol 60/40
benzyl alcohol 40/60
11 benzyl alcohol 50/50
12 benzyl alcohol 60/40
3
4 In this study, n-butyl alcohol was the most stable, with the various
components
5 remaining separated and held in suspension over a period of several weeks.
6 Example 9
7 Nylon was recovered from whole carpets which during construction had been
8 dyed a deep shade of blue. The solvents used were methanol, ethanol, and n-
butyl
9 alcohol mixed 60/40 (weight %) with water. Three grams of each carpet sample
were
io added to 40 ml of solvent solution. Samples 13-18 were processed at pH of
10 or 12
11 following the addition of several drops of dilute solutions of NaOH.
Samples 19-24
12 contained, in addition to the alcohol solutions described above, either 10
or 20%
13 hexamethylenediamine.
14 Table 2
Sample number Solvent composition pH
13 60/40 methanol/water 10
14 60/40 methanol/water 12
15 60/40 ethanol/water 12
16 60/40 ethanol/water 10
17 60/40 n-butanoVwater 10
18 60/40 n-butanol/water 12
16
17
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CA 02261304 1999-02-05
i Table 3
2
Sample number Hexamethylenediamine Solvent composition
content (%)
19 20 20/20/60 HMD/water/methanol
20 10 10/10/20/60 HMD/water/added
water/methanol
21 20 20/20/60
HMD/water/ethanol
22 10 10/ 10/20/60 HMD/water/added
water/ethanol
23 20 20/20/60
HMD/water/n-butanol
24 10 10/10/20/60 HMD/water/added
water/n-butanol
3
4
The samples were heated in the autoclave for one hour at 159-167 C under a
6 pressure of 250 psig. Upon cooling to room temperature, all of the samples
had separated
7 into layers, some with the nylon powder held in suspension and the backing
at the bottom
8 of the test tube, others in several different layers. All of the solutions
were blue in color,
9 some a very dark blue.
-o For samples 13-18, nylon was recovered by means of a pipette, repulped
several
i I times in water, and then dried in a forced air oven. The polymer, which
now was a very
12 light blue, was arranged in order from the lightest to the darkest in
shade: 17 > 18 > 14 >
13 16>13>15.
14 Example 10
is Fiber was cut from a carpet which had never been dyed and which contained
only
16 the primary backing. The fiber was washed several times in D.I. water
before use to
17 remove any finish. Three grams of fiber was placed in an amount of solvent
solution that
is varied from sample to sample. Samples 25-30 were dissolved in a mixture of
n-butyl
19 alcohol or ethylene glycol with water. Samples 31-36 were processed in a
manner similar
20 to that for previous samples 13-18 except for addition of a salt to the
solvent mixture.
21 Samples 25-36 were processed in the autoclave at the same time for one hour
at a
22 temperature from 154-163 C and a pressure of 250 psig.
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i Table 4
2
Sample no. Solvent Weight nylon Vol. solvent Approx. %
Gber (g) (ml) Fiber in
Solution
25 60/40 n-butyl 3 40 6.98
alcohol/water
26 60/40 n-butyl 3 30 9.09
alcohol/water
27 60/40 n-butyl 3 24 11.11
alcohol/water
28 60/40 n-butyl 3 20 13.04
alcohol/water
29 60/40 ethylene 3 40 6.98
glycol/water
30 60/40 ethylene 3 24 11.11
glycol/water
3
4
Table 5
6
Sample Solvent Salt Weight Weight salt pH
no. carpet (g) (g)
31 60/40 n-butyl 2% NaCI 3 1 10
alcohoUwater
32 60/40 n-butyl 2% choline 3 1 10
alcohoUwater chloride
33 60/40 n-butyl 2% CaCl, 3 1 10
alcohoUwater
34 70/30 2% NaCl 3 I 10
ethanoUwater
35 70/30 2% choline 3 1 10
ethanol/water chloride
36 70/30 ?% CaCl, 3 I 10
ethanol/water
7
8 The results of this study indicate that at least 13% nylon could be
dissolved using
9 a 60/40 n-butyl alcohol/water mixture. Electrolytes such as NaC1 might
enhance dye
io removal. Magnesium sulfate, used as a coagulant, might also help in the dye
removal.
11 Choline chloride, an example of a quaternary ammonium compound, neutralizes
the
12 negatively charged nylon dyes and also helps in the color removal. In this
study, ethylene
13 glycol was not a good solvent for nylon 6,6 under the conditions employed.
The same
14 was true of glycerol in a subsequent study. It appears that the greater the
number of
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CA 02261304 1999-02-05
i hydroxyl groups on the solvent molecule, the less effective the solvent is
in the present
2 process.
3 Example 11
4 Eighteen runs were performed with twelve samples in each run, for a total of
216
samples in all. The alcohols used included ethanol, isopropanol, and n-
butanol. The
6 nylon used was white, virgin fiber. The runs were performed at temperatures
of 140, 160,
7 or 180 C and at a pressure of 250 psig. The weight ratio of alcohol to water
was 60/40,
8 70/30, 80/20, or 90/10. The concentration of fiber in solution was 8.0,
10.5, or 13.0%,
9 based on weight of fiber. The time the samples were held at temperature was
30 minutes
io for the first set of runs and five minutes for the second set of runs. The
results are
i i summarized in the following tables.
12 Table 6
13 Dissolution of Nylon Fiber in Aqueous Solution
14 of 60-90% Ethano'.
is
Test Temp. ( C) Time (min.) Polymer (%) Ethanol (%) Observation
1 140 30 8-13 60-90 fiber
2 160 30 8-13 60-90 100% dissolved
3 180 30 8-13 60-90 100% dissolved
4 140 5 8-13 60-90 fiber
5 160 5 8-13 60-90 100% dissolved
6 180 5 8-13 60-90 100% dissolved
16
17 Table 7
18 Dissolution of Nylon Fiber in Aqueous Solution
19 of 60-90% Isopropanol
Test Temp. ( C) Time (min.) Polymer (%) Isopropanol Observation
( %)
1 140 30 8-13 60-90 fiber
2a 160 30 8-13 90 fiber
2b 160 30 8-13 60-80 100% dissolved
3 180 30 8-13 60-90 100% dissolved
4 140 5 8-13 60-90 fiber
5a 160 5 8-13 90 fiber
5b 160 5 8-13 60-80 100% dissolved
6a 180 5 8-13 90 fiber
6b 180 5 8-13 60-80 100%dissolved
21
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1 Table 8
2 Dissolution of Nylon Fiber in Aqueous Solution
3 of 60-90% n-Butanol
4
Test Temp. ( C) Time (min.) Polymer (%) Isopropanol Observation
(%)
1 140 30 8-13 60-90 fiber
2 160 30 8-13 60-90 100% dissolved
3 180 30 8-13 60-90 100% dissolved
4 140 5 8-13 60-90 fiber
5a 160 5 8-13 90 both fiber and ppt.
5b 160 5 8-13 60-80 100% dissolved
6a 180 5 8-13 60-90 100% dissolved
6 The 90% isopropanol solvent was unable to dissolve the nylon at either 160
or
7 180 C within a five minute period. The n-butanol solvent was unable to
dissolve the
8 nylon at 160 C in that same time period. Thus, it appears that under certain
conditions
9 some water is necessary when using either isopropanol or n-butanol, but not
when using
lo ethanol.
II Example 12
12 Five types of post-consumer carpet were tested with four solvent
compositions:
13 1,4-butanediol, benzyl alcohol, 1-butanol/water (60/40), and ethanol/water
(60/40) at
14 140-190 C at pressures from atmospheric to 250 psig. The estimated
components of the
carpet are given in Table 9.
16 Table 9
17 Estimated Composition of Carpet
18
Feedstock % Nylon 6,6 % Nylon 6 % SBR % CaCO3 % Polypropylene
HWC STAPLE 99+ 0 trace trace trace
DUPONT 98.5 0 0.4 1.2 trace
URI (min) 61 0 6 18 15
ZIMMER No. 1 45 0 7 28 20
ZIMMER No. 2 70 0 6 18 6
19
The dissolution process was successful with each of these post-consumer carpet
21 samples. Backing was removed from nylon by filtration. Data on the
recovered polymer
22 was collected for the HWC Staple, Dupont, and URI samples.
23 Fig. I shows the relative viscosity (RV) of the polymer recovered using the
24 various solvents. Fig. 2 shows the NHZ end groups and Fig. 3 shows the
carboxylate end
_2')_
11 23i447(4YOzo1' D(C)
CA 02261304 2007-11-22
i groups for the recovered polymers. Fig. 4 shows RV versus the sum of the end
groups
2 (NH2 pius COOH) for the recovered nylon. Fig. 5 shows the molecular weight
3 distribution for polymers recovered from the URI carpet using the various
solvents.
4 The normal value of RV for carpet fiber is from 45-55. From Fig. 1 it is
evident
that all of the solvents except 1,4-butanediol gave RV values between 45-55.
The RV
6 values for 1,4-butanediol were slightly lower, between 39-45. From Fig. 4 it
appears that
7 all of the recovered polymers had low end group values with respect to the
measured RV
8 values. This may be explained by Fig. 5, which indicates that there was a
loss of low
9 molecular weight polymer. It also appears that the sample processed with
benzyl alcohol
to exhibited a small gain in very high molecular weight polymer.
i- Of the solvent compositions used in these tests, 1-butanol/water and
ethanol/water
12 appeared to produce the highest RV values while retaining the best
molecular w=eight
13 distribution and affecting the nylon polymer the least.
14 Example 13
t> In this experiment, three types of dye were used, TectilonTM Blue 4R 200,
TectilonTM
16 : Red 2B 200, and TectilonTM Orange 3G 200, representing the
anthroquinones, monoazo,
17 and diazo type dyes, respectively. These dyes were put into solution with
four different
is solvent compositions: 1,4-butanediol, benzyl alcohol, 1-butanol/water, and
ethanol/water.
19 Different types of Calgon activated carbon were added to the solutions, as
listed in the
2o tables, including two different mesh sizes for the TOG and PCB types. Each
alcohol-dye
21 sample %vas reacted for 15 minutes at the temperature indicated in the
tables usin~~ a 200:1
22 ratio of activated carbon to dye.
23 Table 10
24 1.4-Butanediol/Dve Solutions
2, (test performed at 184 C)
Activated htesh size Tectilon Blue Tectilon Red Tectilon Orange
carbon type removed removed removed
PCB 12x30 moderate none none
CPG-LF 12x40 all all small
TOG 20x30 all small moderate
PCB 30xI40 lar_e none small
TOG 80x32~ all all all
27
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H 7I!w'~~1-~Li' lNx ~
CA 02261304 1999-02-05
i Table 11
2 Benzyl Alcohol/Dye Solutions
3 (test performed at 200 C)
4
Activated Mesh size Tectilon Blue Tectilon Red Tectilon Orange
carbon type removed removed removed
PCB 12x30 none small none
CPG-LF 12x40 none moderate none
TOG 20x30 none moderate none
PCB 30x140 none small none
TOG 80x325 none all none
6 Table 12
7 1-Butanol/Water/Dye Solutions
8 (test performed at 100 C)
9
Activated Mesh size Tectilon Blue Tectilon Red Tectilon Orange
carbon type removed removed removed
PCB 12x30 large none moderate
CPG-LF 12x40 all large all
TOG 20x30 all moderate large
PCB 30x 140 all large large
TOG 80x325 all all all
i i Table 13
12 Ethanol/Water/Dye Solutions
13 (test performed at 80 C)
14
Activated Mesh size Tectilon Blue Tectilon Red Tectilon Orange
carbon type removed removed removed
PCB 12x30 all small moderate
CPG-LF 12x40 all all all
TOG 20x30 all large large
PCB 30x140 all large large
TOG 80x325 all all all
16 Larger mesh size indicates a smaller particle size. Smaller particles of
activated
17 carbon will absorb dye at a faster rate than will larger particle sizes.
Dye absorption
18 capacity is dependent on matching carbon pore size to that of the dye
molecule. Further,
19 having more surface area on the activated carbon increases dye loading
capacity. Larger
dye concentrations produce a faster rate of dye absorption by the activated
carbon.
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H a IP17 Y9Z01 DOC)
CA 02261304 1999-02-05
i Example 14
2 CPG and TOG type activated carbon were introduced into different solutions
of 1-
3 butanol/water in which HWC Atlanta green carpet, a dark green post-consumer
carpet,
4 was dissolved (10 weight % carpet, 90% solvent). The temperature was 170 C,
the
pressure was 225 psig, and a 200:1 ratio of activated carbon to dye was used.
Each
6 solution was agitated for 15 minutes. The nylon polymer recovered after
precipitation
7 was very light green. To the naked eye it appeared as though most of the dye
had been
8 removed.
9
The preceding description of specific embodiments of the present invention is
not
i i intended to be a complete list of every possible embodiment of the
invention. Persons
12 skilled in this field will recognize that modifications can be made to the
specific
13 embodiments described here that would be within the scope of the present
invention.
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