Note: Descriptions are shown in the official language in which they were submitted.
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CHEMICAL COMPOUNDS AND METHODS FOR REMOVING
DYE
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to chemical compounds and methods for
removing dye from polyester fibers, and more particularly to removing dye
from panel fabric made from recycled polyethylene terephthalate) fibers.
2. Description of Related Art
Panel fabric, also known as vertical fabric, is used in furniture
upholstery, wall systems and tackboards. Panel fabric is increasingly
produced from synthetic materials such as polyester, most commonly PET
(poly(ethylene terephthalate)). Panel fabric is replaced periodically and as
a result, is often discarded in landfills. Many of the materials used in panel
fabric are not biodegradable; thus disposal of it contributes to the
environmental problems that arise from the over-use of landfills.
Manufacturers of panel fabrics and other materials incorporating
PET are concerned about the effect of depletion of petroleum (used to
make the polymers in the fabric) and the over-use of landfills on the
environment. In an effort to reduce the amount of non-biodegradable waste
that finds its way into landfills, some manufacturers use fiber made from
recycled PET (often from recycled PET bottles, such as 2-liter soft drink
bottles) in panel fabric. However, when the furniture incorporating
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recycled or virgin panel fabric is discarded or refurbished, the fabric may
nevertheless end up in a landfill. Reducing the vast amount of used panel
fabric that is discarded annually as landfill waste by finding other uses for
such materials is therefore advantageous.
However, merely fording other, lower valued uses for the PET in the
panel fabric does not alone provide environmental sustainability. As the
material is continually downgraded (i.e., used in increasingly less valuable
ways), demand for PET for the higher valued uses remains to be satisfied
with either virgin PET, or PET that has been recycled from other uses.
Accordingly, it is desirable to find a way to avoid downcycling the PET in
panel fabric, i.e., to reuse the PET in a way that is economically and
environmentally of the same value as the panel fabric itself. Ideally, the
PET in the panel fabric would be recycled into fiber that can be reused,
e.g., suitable for weaving into new panel fabric. In this way, the material is
not only rendered recyclable, but recyclable in a sustainable fashion,
decreasing the need for virgin PET or PET recycled from bottles, which
can then be put to other uses.
Currently, when furniture incorporating panel fabric made from
recycled PET is discarded or refurbished, any PET that may be recovered
when garnetted into loose fibers is unsuitable for significant reuse in panel
fabric and carpet manufacturing. The staple fiber is generally too short to
be reused in the yarn spinning process at more than about 3%. If the fibers
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could be melted, pelletized and extruded into full-length fiber, they could
be recycled at about 100%. Unfortunately, the presence of dyes in the
fibers makes them difficult to melt and extrude. The dye molecules char
and burn at extrusion temperatures, forming a residue that blocks the
extrusion spinnerets. As a result, a process capable of removing dye before
extrusion is needed.
Existing processes may strip or decrease dye levels in polyester, but
they do so by breaking the chromophore of the dye. Methods commonly
used for color removal employ harsh chemicals like sodium bisulfate,
which hydrolyze or oxidize the dye, leaving the decolorized dye in the
fiber. This eliminates the color, but leaves the remainder of the dye
molecule in the fiber. Thus, when the fiber is melted and extruded, the
remaining molecule chars and burns, blocking the extrusion spinnerets.
J.R. Aspland, Textile Dyeing and Coloration (American Assn of
Textile Chemists & Colorists 1997) describes the removal of dye from a
polyester fiber at room temperature using methylene chloride. However,
this solvent damages the polymer by swelling the PET fiber and solvating
the dye. The damage caused is partial hydrolysis of the PET, which causes
loss of strength and brittleness in the fibers. For at least this reason, this
method is inappropriate for use in manufacturing new carpet or panel
fabric. There is therefore a need in the art for a dye removal process that
does not damage PET, but effectively removes dye from it.
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SUMMARY OF THE INVENTION
The invention solves some or all of the above mentioned problems
by providing methods and compositions for removing dye molecules from
polyester, PET in particular. The invention allows the PET to be reused by
pelletizing and extruding it into fiber suitable for panel fabric or other
applications calling for virgin PET, without disrupting the extrusion
process by dye molecule charring.
The invention addresses the problem of downcycling the PET in
panel fabric by providing a way to use recycled PET that is economically
and environmentally of the same value as the panel fabric itself. By using
the method of the invention, the PET can be melted, extruded and reused as
panel fabric. The invention is an improvement over existing processes
because it completely removes the dye molecules from the PET, instead of
breaking only the chromophore of the dye. Thus, when the method of the
present invention is used, the PET may be melted and extruded, without
remaining dye molecules burning or blocking the extrusion spimlerets.
Furthermore, the method of the present invention does not damage the PET
by swelling.
According to one embodiment of the invention, a method is
provided for removing dye from polyester fiber or fabric by contacting the
polyester with a dye removal composition containing an aqueous solution
of at least one leveling agent; heating the mixture of polyester and dye
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removal composition until it reaches an elevated temperature and pressure
level higher than the equilibrium pressure of the dye removal composition
at the elevated temperature; cooling the mixture; and removing the
decolorized polyester from the mixture.
According to another embodiment of the invention, a composition
for removing dye from polyester is provided. The composition includes an
aqueous solution of about 0.5 wt% to about 8.0 wt% of at least one leveling
agent.
In another embodiment, the invention relates to a device for
removing dye from polyester according to the present invention. The
device includes a sealable vessel and a dye removal composition. The dye
removal composition includes an aqueous solution of about 0.5 wt% to
about 8.0 wt% of at least one leveling agent.
The invention is also directed to a method for recycling panel fabric
comprising polyester. The method involves removing from the fabric any
structural elements, removing the dye from the fabric using a dye removal
composition comprising an aqueous solution of at least one leveling agent,
recovering the polyester fibers, melting the fibers, pelletizing the melted
fiber and extruding the pellets into full-length fiber.
In a particular embodiment of the invention, the dye removal
composition comprises at least one leveling agent selected from the group
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consisting of anionic leveling agents, nonionic leveling agents and mixtures
thereof.
In another particular embodiment of the invention, the dye removal
composition further comprises at least one chemical selected from the
group consisting of scouring agents, wetting agents and leveling carriers.
Leveling agents may perform one or more of these functions in addition to
their function as leveling agents.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
The invention provides for a method of removing dye molecules
from polyester fiber, and is particularly useful with PET fiber. The
polyester may be used in the process as woven fabric or, alternatively,
garnetted into loose fibers. The polyester is contacted with a dye removal
composition comprising an aqueous solution of at least one leveling agent.
This may be conveniently done in a standard dyeing vessel commonly used
for disperse dyeing of polyester, which is sealable and temperature
controlled.
Effective leveling agents have good wetting, emulsifying and
dispersing properties and will prevent redeposition. A leveling agent that
promotes maximum coverage and color yield is also desirable. Leveling
agents particularly suited for high temperature polyester dyeing will
generally be suitable for the present invention. Effective leveling agents
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can also inhibit cationic dye from staining and settling on the walls of
stainless steel equipments.
The dye removal composition comprises an aqueous solution of at
least one leveling agent. Suitable leveling agents include anionic leveling
agents, nonionic leveling agents and mixtures thereof. The dye removal
composition may further comprise leveling carriers, scouring agents and
mixtures thereof. In a particular embodiment of the invention, the scouring
agent or wetting agent is nonionic. In another embodiment of the
invention, the leveling carrier comprises a nonionic leveling carrier.
More particularly, examples of suitable leveling agents include
those that comprise alkyl polyglycol ether, isopropyl alcohol, n-butyl
phthalimide or nonyl phenol ethoxylate. Examples of suitable leveling
carriers include those containing alkyl phthalimide. Examples of suitable
scouring agents include scouring agents containing polyoxyethene ether or
propylene glycol ether. In a most preferred embodiment of the invention,
the dye removal composition comprises isopropyl alcohol, n-butyl
phthalimide, nonyl phenol ethoxylate, and propylene glycol ether.
Particular leveling agents that may be used for the present invention
include AVOLAN IW LIQUIDTM nonionic leveling agent and scouring
agent (Bayer, Pittsburgh, PA), DIADAVIN UFNTM nonionic leveling
wetting and scouring agent (Bayer, Pittsburgh, PA), LEVEGAL EAP-4TM
leveling carrier (Bayer, Pittsburgh, PA), R.AYCAPOL TDA-33 scouring
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agent (Clariant, Chicago, IL), RAYCALEV DTM (leveling agent),
CAROLID NOL leveling agent (Bayer, Pittsburgh, PA) and RICHLEV D
leveling agent (Richchem, High Point, NC), BURCO SOUR LFE-810TM
scouring agent (Burlington Chemical Co., Burlington, NC).
When mixed with water or aqueous solution, the leveling agents can
be used in weight ratios ranging from (under certain conditions) about
0.5% to as high as about 8.0% of leveling agent : water. However,
particularly desirable results are achieved when the leveling agents) is
present in an amount ranging from about 2.0 wt% to about 8.0 wt% of the
total solution of leveling agents. An approximately 4.0 wt% aqueous
solution of leveling agents) has been found to be particularly suitable for
most applications. More particularly, an approximately 4.0 wt% solution
comprising propylene glycol ether, isopropyl alcohol, n-butyl phthalimide
and nonyl phenol ethoxylate and water has been found to be suitable for
most applications.
According to this invention, the polyester to be decolorized is
separated from any structural elements and placed in a sealable vessel. The
polyester may be woven fabric or loose fibers. Water and a dye removal
composition comprising at least one leveling agent are added to a vessel at
a temperature of about 20°C to about 25°C. Those with skill in
the art will
understand that any vessel made of a nonreactive material and sealable may
be used in place of a standard dyeing vessel.
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The mixture of the polyester and dye removal composition are
heated for a period of about 120 minutes. Because the vessel is sealed, as
the temperature increases, there is a corresponding rise in the pressure.
Thus, the pressure is higher than the equilibrium pressure of the dye
removal composition at the elevated temperature. When the pressure has
reached about 28 psi to about 39 psi, more particularly about 33 psi, and
the temperature has reached about 135°C to about 145°C, more
particularly
140°C, the vessel is maintained at that pressure and temperature for
about
30 minutes to about 60 minutes, more particularly about 45 minutes.
The vessel may be agitated during the period when the polyester is
first contacted with the dye removal composition, when it is heated, during
the holding period when the temperature and pressure are maintained, or
any combination of these three. Agitation can be achieved, for example, by
rolling the vessel or by continuously pumping the dye removal composition
through the polyester.
The holding stage is typically followed by a cooling down period of
about 20 minutes to about 40 minutes wherein the temperature is decreased
to about 20°C to about 50°C, more particularly 30°C. The
mixture should
be cooled rapidly to prevent or limit reabsorption of the dye by the
polyester.
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The times and temperatures may vary somewhat depending upon
the dyestuff and the leveling agent chosen, but will generally fall within the
above ranges for most commonly encountered dyes.
The decolorized polyester is then removed from the mixture. Any
residual dye removal composition should be removed from the polyester, in
order to further limit the chance of reabsorption. This can often be
achieved by rinsing thoroughly with water.
This cycle may be repeated as needed to remove additional dye
from the polyester fiber or fabric. Those with skill in the art will recognize
that more intense colors may require additional cycles to sufficiently
decolorize the polyester. The method may be carried out as a batch,
sequential batch semi-continuous or continuous process.
The invention may be used to recycle panel fabric made from
polyester. The invention is also useful for recycling panel fabric made
from polyester that has already been recycled, such as recycled PET. To
recycle panel fabric, it should first be separated from any structural
elements. The fabric can be, but is not required to be garnetted into loose
fibers. In order to fully recycle the panel fabric so that it can be used
again
as panel fabric or some other product of similar economic and
environmental value, any dye should be removed using a dye removal
composition comprising an aqueous solution of at least one leveling agent.
Once the dye has been removed, the polyester fibers can be recovered. The
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fibers can be melted and pelletized before being extruded into full-length
fiber. Panel fabric may be created by weaving the recycled fiber.
The invention can be more clearly understood by reference to the
following examples, which are not intended to limit the scope of the
invention in any way.
EXAMPLE 1
The process was carried out in an Ahiba Polymat dyeing machine in
sealed vessels. Fifty (50) mL of water was added to an empty vessel. Four
(4.0) mL of each of the following chemicals were also added to the vessel:
CAROLID N~LTM leveling agent, BURCO SCOUR LFE-810TM scouring
agent, and RICHLEV DTM leveling agent. Approximately 5.00 g of
polyester was placed into the vessel. Fifty (50) mL of water was added to
the vessel to cover the polyester. The vessel was sealed. The vessel was
rolled to agitate the mixture. The temperature was raised from room
temperature (about 22°C) to 50°C. The temperature was held at
50°C for
3.3 minutes. Next, the temperature was raised, over 40 minutes, to 70°C
at
a gradient of 0.5. The temperature was then raised to 140°C at a
gradient
of 1.5 over a period of 46.7 minutes. Finally, the temperature was reduced,
over 30.0 minutes, to 50°C at a gradient of 0.5. The total running time
was
116.7 minutes.
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The process was carried out in an Ahiba Polymat dyeing machine in
sealed vessels. Fifty (50) mL of water was added to an empty vessel. Four
(4.0) mL of each of the following chemicals were also added to the vessel:
AVOLAN IW LIQUIDTM leveling agent, DIADAVIN UFNTM scouring
agent, LEVEGAL EAP-4TM leveling carrier and RAYCALEV DTM
leveling agent. Approximately 5.00 g of polyester was placed into the
vessel. Fifty (50) mL of water was added to the vessel to cover the
polyester. The vessel was sealed. The vessel was rolled to agitate the
mixture. The temperature was raised from room temperature (about 22°C)
to 50°C. The temperature was held at 50°C for 3.3 minutes. Next,
the
temperature was raised, over 40 minutes, to 70°C at a gradient of 0.5.
The
temperature was then raised to 135°C at a gradient of 1.5 over a period
of
46.7 minutes. Finally, the temperature was reduced, over 30.0 minutes, to
50°C at a gradient of 0.5. The total running time was 116.7 minutes.
The foregoing description is provided for describing various
embodiments and structures relating to the invention. Various
modifications, additions and deletions may be made to these embodiments
and/or structures without departing from the scope and spirit of the
invention.
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