NZ609226B - Method for the recycling of plastics products - Google Patents
Method for the recycling of plastics productsInfo
- Publication number
- NZ609226B NZ609226B NZ609226A NZ60922613A NZ609226B NZ 609226 B NZ609226 B NZ 609226B NZ 609226 A NZ609226 A NZ 609226A NZ 60922613 A NZ60922613 A NZ 60922613A NZ 609226 B NZ609226 B NZ 609226B
- Authority
- NZ
- New Zealand
- Prior art keywords
- layer
- density
- pet
- plastics
- sorting
- Prior art date
Links
- 229920003023 plastic Polymers 0.000 title claims abstract description 44
- 239000004033 plastic Substances 0.000 title claims abstract description 44
- 238000004064 recycling Methods 0.000 title description 6
- 239000000463 material Substances 0.000 claims abstract description 135
- 239000004698 Polyethylene (PE) Substances 0.000 claims abstract description 51
- 229920000573 polyethylene Polymers 0.000 claims abstract description 51
- 238000001035 drying Methods 0.000 claims abstract description 16
- 239000005038 ethylene vinyl acetate Substances 0.000 claims abstract description 12
- 229920001200 poly(ethylene-vinyl acetate) Polymers 0.000 claims abstract description 12
- 238000010008 shearing Methods 0.000 claims abstract description 10
- 229920000139 polyethylene terephthalate Polymers 0.000 claims abstract description 9
- 239000005020 polyethylene terephthalate Substances 0.000 claims abstract description 9
- 238000010438 heat treatment Methods 0.000 claims abstract description 6
- 239000007788 liquid Substances 0.000 claims abstract description 6
- -1 polyethylene terephthalate Polymers 0.000 claims abstract description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 5
- 238000005520 cutting process Methods 0.000 claims abstract description 4
- 238000000926 separation method Methods 0.000 claims description 28
- 230000003068 static Effects 0.000 claims description 5
- 238000003756 stirring Methods 0.000 claims description 4
- 239000000853 adhesive Substances 0.000 claims description 3
- 230000001070 adhesive Effects 0.000 claims description 3
- 239000010410 layer Substances 0.000 description 38
- 239000000047 product Substances 0.000 description 21
- 238000000034 method Methods 0.000 description 17
- 239000002699 waste material Substances 0.000 description 12
- 235000013305 food Nutrition 0.000 description 10
- 238000004519 manufacturing process Methods 0.000 description 9
- 238000003475 lamination Methods 0.000 description 8
- 239000000203 mixture Substances 0.000 description 7
- VOLSCWDWGMWXGO-UHFFFAOYSA-N cyclobuten-1-yl acetate Chemical compound CC(=O)OC1=CCC1 VOLSCWDWGMWXGO-UHFFFAOYSA-N 0.000 description 6
- 238000004140 cleaning Methods 0.000 description 5
- 238000001125 extrusion Methods 0.000 description 5
- 238000007789 sealing Methods 0.000 description 5
- 239000007787 solid Substances 0.000 description 4
- 238000007765 extrusion coating Methods 0.000 description 3
- 238000003856 thermoforming Methods 0.000 description 3
- 102000014961 Protein Precursors Human genes 0.000 description 2
- 108010078762 Protein Precursors Proteins 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000006227 byproduct Substances 0.000 description 2
- 239000000356 contaminant Substances 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 238000005755 formation reaction Methods 0.000 description 2
- 238000001746 injection moulding Methods 0.000 description 2
- 239000011229 interlayer Substances 0.000 description 2
- 239000004626 polylactic acid Substances 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- OZAIFHULBGXAKX-UHFFFAOYSA-N precursor Substances N#CC(C)(C)N=NC(C)(C)C#N OZAIFHULBGXAKX-UHFFFAOYSA-N 0.000 description 2
- 238000003855 Adhesive Lamination Methods 0.000 description 1
- 241000219430 Betula pendula Species 0.000 description 1
- 229920002456 HOTAIR Polymers 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminum Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229920001871 amorphous plastic Polymers 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000009470 controlled atmosphere packaging Methods 0.000 description 1
- 230000004059 degradation Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000008187 granular material Substances 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 238000010102 injection blow moulding Methods 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 238000009448 modified atmosphere packaging Methods 0.000 description 1
- 230000003287 optical Effects 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 229920000915 polyvinyl chloride Polymers 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- KKEYFWRCBNTPAC-UHFFFAOYSA-L terephthalate(2-) Chemical compound [O-]C(=O)C1=CC=C(C([O-])=O)C=C1 KKEYFWRCBNTPAC-UHFFFAOYSA-L 0.000 description 1
- 238000009823 thermal lamination Methods 0.000 description 1
- 229920001169 thermoplastic Polymers 0.000 description 1
Abstract
ABSTRACT - 609226 The disclosure relates to a method of treating of a multilayer article comprising at least one layer of a first plastics material, at least one layer of a second plastics material, and at least one layer of a third material between the layer of first material and the layer of plastics material, wherein the first material is amorphous polyethylene terephthalate (PET), the second plastics material is polyethylene (PE) and the third material is ethylene vinyl acetate (EVA); and wherein the first material has a first density and the second material has a second density and the first density is different from the second density; the method comprising the steps of: (a) cutting and/or shredding the article, (b) physically separating the first material from the second material through shearing action and heating at a temperature of from 80 to 100°C; (c) sorting the first material from the second material, wherein the sorting step comprises applying centrifugal force to separate the first material from the second material and is carried out in a liquid medium, such as water; and (d) drying the sorted first material. astics material, wherein the first material is amorphous polyethylene terephthalate (PET), the second plastics material is polyethylene (PE) and the third material is ethylene vinyl acetate (EVA); and wherein the first material has a first density and the second material has a second density and the first density is different from the second density; the method comprising the steps of: (a) cutting and/or shredding the article, (b) physically separating the first material from the second material through shearing action and heating at a temperature of from 80 to 100°C; (c) sorting the first material from the second material, wherein the sorting step comprises applying centrifugal force to separate the first material from the second material and is carried out in a liquid medium, such as water; and (d) drying the sorted first material.
Description
METHOD FOR THE RECYCLING OF PLASTICS PRODUCTS
The present invention relates to the recycling of multilayer products and more
particularly, to a method for the treatment of multilayered plastics sheets and components and
their manufacturing and post-use waste. Multilayered sheets are used in the production of a
variety of plastics products, such as containers.
For example, plastics containers are widely used to package, store, transport and display
fresh food. They can be made by a variety of techniques, but the commonly accepted methods
for high volume production are injection moulding, blow moulding and thermo-forming. In
this latter event, plastics flakes and/or pellets are extruded in the form of sheets, which are
subsequently moulded into the required shape of container.
Clear plastics containers may be made of polethylene terephthalate (PET). The use of
PET provides a high clarity product that enables a user to view readily the contents of the
container. Recycled PET may also be used, to manufacture such containers offering
environmental and, sometimes, economical benefits. These containers may be sealed with a
lidding film to protect the food within the container from the surrounding environment, or to
create a modified atmosphere within the closed package, so-called Modified Atmosphere
Packaging (MAP) or Controlled Atmosphere Packaging (CAP). Although it is perfectly
possible to attach a lidding film to PET containers, it is an inconvenient substrate for sealing
and requires high sealing temperatures, long sealing times, expensive materials and is
particularly sensitive to contamination on the sealing face arising from inadvertent transfer
from the goods being packaged.
A known solution to the problem outlined above is making the containers from PET
coated with a layer of polyethylene (PE). The PE provides a surface that a lidding film readily
attaches to, thereby facilitating the production of sealed containers. The PE layer can be
applied by a variety of techniques including, but not limited to, thermal lamination, adhesive
lamination, co-extrusion and extrusion coating.
There are however environmental consequences of using a PET/PE product.
During the manufacture of PET/PE containers by thermo-forming, multiple containers are
formed from large and often continuous sheets of PET/PE material and individual containers
are cut from these large sheets. Waste material is formed from those parts of the large sheets
that are not used in the individual containers. This waste material, known as “skeletal waste”,
contains a mixture of PET and PE, which when re-melted and homogenised as part of a re-
processing step forms a cloudy product that cannot be used to form clear plastics containers.
The presence of the PE disrupts the optical properties of the PET and so the PET/PE product
is of a lower clarity than a pure, single polymer PET product. Since clear plastics containers
are more desirable than opaque plastics containers, the waste is less economical to recycle.
An alternative route for the manufacture of food trays as described above is by means of
injection moulding. Then there is no skeletal waste as described above for thermo-forming,
but there is also no easy and cost-effective way to apply the layer of PE to the tray that will
facilitate easy sealing to a top-film.
Additionally, strict purity standards are applicable to the use of recycled PET in the
food industry. For example, Commission Regulation (EC) 282/2008 of 27 March 2008
regulates the quality of recycled plastics materials and articles intended to come into contact
with foods and the removal of unwanted substances from the PET requires a so-called “super-
clean” recycling process. The currently available super-cleaning processes all necessitate
processing the PET flakes at temperatures well above the melting point of PE, and so are not
suitable for processing of PET/PE flakes as this leads to widespread clumping and
agglomeration as a result of the PE sticking to itself. Whilst Regulation (EC) 282/2008 is
framed around processing of post-consumer PET materials and specifically excludes in-house
factory waste (skeletal, off-cuts etc) it contains useful protocols for operation of super-
cleaning systems that lead to enhanced security of food safety in the use of recycled polymers,
whether of post consumer or factory origin. It is note-worthy that there exists a growing trend
to collection of post-use PET/PE trays via household recycling collections.
Furthermore, the presence of PE on PE affected PET flakes renders difficult the
conventional technique for processing PET, whereby the flake is pre-crystallised and dried at
elevated temperatures, prior to extrusion into sheet or into other formed articles. This is
because the presence of PE leads to soft and sticky material at the temperatures normally
utilised for crystallising and drying of PET with a resultant tendency to clump and
agglomerate. Removing the PE would usefully facilitate these processes.
The growing use of recycled plastics as food contact material creates a need for an
economical and efficient method for treating contaminated plastics material and it is an object
of this invention to mitigate problems such as those described above. It is an alternative
object of the invention to provide a method of treating of a multilayer article. It is a further
alternative object of the invention to at least provide the public with a useful choice.
According to a first aspect of the invention, there is provided a method of treating of a
multilayer article comprising at least one layer of a second plastics material, wherein the first
material is different from the second material; the method comprising the steps of (a)
physically separating the first material from the second material through shearing action and
application of heat; and (b) sorting the first material from the second material.
The PET/PE articles (and their pre-cursors, wastes and by-products) are advantageously
first rendered into a size band where their critical dimensions are in the range 2-20mm. This
can be effected with a cutting or shredding step.
The process was first developed using articles (and their pre-cursors, wastes and by-
products) comprising a PET sheet laminated with a PE layer. The PE contaminant was
successfully removed and high purity PET (>99%) was obtained. However, the present
method is advantageous in that it can be applied to a wide range of multilayered structures.
In a preferred embodiment, the multilayer article comprises at least one layer of a third
material between the layer of first material and the layer of plastics material.
According to a second aspect of the invention, there is provided a method of treating of
a multilayer article comprising at least one layer of a first plastics material, at least one layer
of a second plastics material and at least one layer of a third material between the layer of first
material and the layer of plastics material, wherein the first material is amorphous
polyethylene terephthalate (PET), the second plastics material is polyethylene (PE) and the
third material is ethylene vinyl acetate (EVA); the method comprising the steps of:
(a) physically separating the first material from the second material through shearing
action and application of heat; and
(b) sorting the first material from the second material.
The third layer can be for example a layer of adhesive which is used to bond a layer of
the first material to a layer of the second material. Preferably, the third material has a
softening temperature which is lower than that of the first and/or the second material.
Preferably, the first material is amorphous polyethylene terephthalate (PET). Other
plastics materials may be used for example, polylactic acid (PLA). Preferably, the second
material is polyethylene (PE). Preferably, the third material is ethylene vinyl acetate (EVA).
When the third material has a softening temperature which is lower than that of the
first and/or the second material, the separation step may comprise the step of heating at a
temperature above the softening temperature of the third material to improve the separation of
the first layer from the second layer. In the case for example of a PET/EVA/PE multilayer
structure, the EVA layer is strongly bonded to the PE layer, but the peel strength between the
EVA and PET layer is weakened with the application of heat.
The separation step may comprise the step of heating at a temperature above the
softening temperature of the third plastics material. The preferred heating temperature ranges
from 80 to 100°C, for example for multilayer materials such as PET/EVA/PE.
The separation step may comprise the step of introducing the product into a separation
vessel and mechanically shearing the article against itself. Alternatively or in addition, one or
more static blades can be mounted within the separation vessel. The article may be pre-cut
and/or pre-shredded into smaller elements. The elements rub against each other so that the
second material layer detaches itself from the first material layer as a result of shearing action
applied at the interlayer boundary between the first and second layers. The output of the
separation step is a mixture of flakes made of the first material and flakes made of the second
material.
As the temperature increases in the separation vessel, the first material and/or the
second material (in particular in the case of plastics materials) will have a tendency to form
lumps and to stick to the walls of the separating vessel. Preferably, the separation vessel
comprises one or more stirring elements to improve the shearing action and to prevent the
formation of lumps and agglomerates.
Preferably, the first material has a first density and the second has a second density and
the first density is different from the second density. This is particularly advantageous where a
density based sorting step is combined to the first separation step. A first example of density
based sorting step is a static sorting method in which the output product of the separation step
is placed in a suitable medium, such as water, so that the first material and the second material
will either “swim” or “sink” according to their respective densities. In a second example of
density based sorting step, centrifugal force is applied to force and accelerate the separation of
the flakes made of the second material from the flakes made of the first material. Fast and
efficient sorting is thereby achieved.
The present method can comprise the further step of (c) drying the sorted first material.
This can be carried out during the sorting step and/or as a subsequent drying step. For
example, if carried out during the sorting step, the mixture can be sorted by application of a
centrifugal force which will separate the first material, not only from the second material but
also from the liquid medium, thereby drying the first material. Heat may be applied within the
sorting container to further dry the first material. Alternatively, the first material may be
further dried in a subsequent step, for example with a drying hopper. High purity can
therefore be achieved.
Thus, the invention seeks to provide a simple and efficient method for processing
contaminated plastics products to obtain high purity plastics material, suitable for re-use in
clear products and which is also suitable for restoring the material to its original food contact
status via an appropriate super-cleaning route.
The invention will be further described with reference to the accompanying drawings
and figures.
Figure 1 is a flow diagram of a process according to the present invention;
figure 2 is a schematic representation of a PE laminated PET sheet; and
figure 3 is a schematic representation of a centrifugal density separation apparatus for
use in a process according to the present invention.
Within the context of the invention, the expression “multilayer product” refers to any
article comprising a structure comprising two or more plastics layers. The second and
subsequent layers can be obtained using any conventional techniques such as coating,
lamination, co-extrusion and extrusion coating. Indeed, the invention can also be deployed on
multi-layer structures of dissimilar materials, such as plastics/aluminium or plastics/paper.
Referring to figure 1, there is illustrated a process according to the present invention,
applied to the treatment of a PET sheet comprising a PE lamination layer as the second
material to be eliminated.
Polyethylene terephthalate (PET) is a thermoplastic polymer which exists in an
amorphous clear state or a (semi-) crystalline opaque or white state. While virgin PET is often
supplied as a semi-crystallised granulate, ground material, flakes or recycled or skeletal waste
materials would normally consist of amorphous PET.
PET is hygroscopic and must be dried, for example in a drying hopper, to prevent the
degradation of the material due to the presence of absorbed moisture. If PET is not dried,
hydrolysis occurs during the extrusion, which will affect the mechanical properties and
quality of the finished product. Additionally, amorphous plastics materials such as PET will
become sticky and difficult to process during the drying step, as their temperature exceeds
their respective glass transition temperatures (of around 65-70 degrees Celsius in the case of
PET). The material softens, and agglomerates to form lumps which stick to the walls of the
drying hopper. This can be prevented by crystallising the plastics material before drying it.
Once crystalline, the material does not soften until it achieves the melt temperature of about
240 degrees Celsius in the case of PET. Some degree of agitation is often necessary to avoid
clumping.
An example of a process according to the present invention is described below.
Plastics products to be recycled are provided which are made for example of PET sheets
laminated with a layer of PE, or trays arising in the waste stream or as a reject stream in a
production environment, or cut flakes of skeletal production waste. PE laminated PET used in
the food packaging industry typically has a PE layer of less than 10% of the total thickness.
For example, the PET layer can have a thickness of about 400 microns and a PE layer of 20-
50 microns. When the PET sheet has been laminated using for example a roller lamination
process, then the multilayer structure may comprise a layer of an adhesive material such as
EVA.
The products are shredded or granulated into 6mm to 16mm flakes prior to entering the
separation process. The PET/PE flakes are introduced into a separation vessel to carry out the
first step during which the PE is physically liberated from the PET flakes. This requires a
degree of mechanical shear, arising for example by mechanically abrading the product against
itself and/or one or more static blades. Shear is applied at the interlayer boundary between
the PET layer and the PE layer. When amorphous PET is heated, the material softens, and
develops a tendency to agglomerate in the vessel and it is therefore advantageous to use a
stirring element, such as one or more stirring blades, to prevent the formation of lumps.
At the same time, heat is applied for example in the form of hot air. The temperature is
increased, preferably to a temperature of from 80 to 100°C, and for a period of from 60 to 180
minutes. Most preferably, the liberation step is carried out at about 90°C and with a residence
time of about 120 minutes. The combination of temperature and shear occurring as a result of
the self-abrasion and the particular disposition of blades within the separation vessel liberates
the PE lamination from the PET sheet. The resulting output is a mixture of PE film and PET
sheet that forms an intermediate for the sorting stage. The average particle size of the output
material is preferably from about 2 to 16 mm.
In the sorting stage, the difference in densities between the PE lamination film
-3 -3
(approximately 0.94g.cm ) and the PET sheet (approximately 1.3 g.cm ) is exploited, to
separate the two materials from each other.
A forced density separation is preferred in which centrifugal force is applied to separate
the lighter material from the heavier material. The preferred separation medium for the
PE/PET separation step is water for its density, but also because it is environmentally friendly
and readily available.
The PET sheet is recovered as the “solid discharge heavy phase” and the PE lamination
film is recovered as the “solid discharge light phase”. The PET contained in the solid
discharge heavy phase may be dried within the forced density separation system if it is so
designed, and/or, if required may be further dried, for example in a drying-hopper and the
resulting PET is dry high purity PET flakes (>99% purity). The PE contained in the solid
discharge light phase can also be further dried if required to obtain dry PE flakes for
recycling, or if present in insufficient amount, it can simply be disposed of.
The sorting can alternatively be carried out using a static separation technique, in which
the PE/PET mixture is introduced into a tank containing a separation liquid. The separation
medium is chosen such that the lighter material, i.e. PE will “swim” near the surface of the
liquid, while the heavier material, i.e. PET, will “sink” to the bottom of the tank. Another
sorting method involves wind or air separating systems that make use of the different ballistic
characteristics of denser, thicker PET flakes when compared to lighter, thinner PE flakes. In
another embodiment of the present invention, sorting can be achieved using electrostatic
systems making use of the different ways that PE and PET accept electrical charges, and/or
the way that those electrical charges decay.
Thus, any combinations of two materials with different densities (or electrostatic
properties if electrostatic systems are used to sort the materials) can be sorted using the
method according to the present invention. Examples of first plastics materials that can be
treated using the present process include for example, PVC and polylactic acid (PLA).
Examples of second plastics contaminants that can be eliminated using the present process
include ethylene vinyl acetate (EVA) and Polypropylene (PP). The process can also be
applied to products comprising more than two plastics materials with different densities, for
example a product comprising a PET/EVA/PE multilayer sheet.
The second material may be present in the product to be recycled as a layer obtained by
lamination, co-extrusion, extrusion coating and other techniques, although it has been
observed that highest purity is achieved using laminated products as a starting material. For
example, a PET purity of more than 99% has been observed, when an article comprising a
PET layer with a PE lamination was separated by abrading and applying heat, the
subsequently sorting using a forced density sorting method (using centrifugal force), and
subsequent drying in a drying hopper.
Thus, from the above description, it can be seen that the present invention provides a
simple and efficient method for processing contaminated plastics materials to obtain high
purity plastics with the potential to be upgraded further by suitable super-cleaning for use in
direct food contact when necessary.
Unless the context clearly requires otherwise, throughout the description and the claims,
the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as
opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not
limited to”.
The reference to any prior art in the specification is not, and should not be taken as, an
acknowledgement or any form of suggestion that the prior art forms part of the common
general knowledge in New Zealand.
Claims (15)
1. A method of treating of a multilayer article comprising at least one layer of a first plastics material, at least one layer of a second plastics material and at least one layer of a 5 third material between the layer of first material and the layer of plastics material, wherein the first material is amorphous polyethylene terephthalate (PET), the second plastics material is polyethylene (PE) and the third material is ethylene vinyl acetate (EVA); the method comprising the steps of: (a) physically separating the first material from the second material through shearing 10 action and application of heat; and (b) sorting the first material from the second material.
2. The method of claim 1, wherein the third material is an adhesive. 15
3. The method of claim 1 or 2, wherein the third material has a softening temperature which is lower than that of the first and/or the second material.
4. The method of any one of the preceding claims, wherein the separation step comprises heating at a temperature of from 80 to 100°C.
5. The method of any one of the preceding claims, wherein the separation step comprises introducing the product into a separation vessel and mechanically shearing the article against itself and/or against one or more static blades. 25
6. The method of claim 5, wherein the separation vessel comprises one or more stirring elements.
7. The method of any one of the preceding claims wherein the shearing action is applied between the first layer and the second layer.
8. The method of any one of the preceding claims, wherein the first material has a first density and the second material has a second density and the first density is different from the second density. 5
9. The method of claim 8, wherein the sorting step comprises applying centrifugal force to separate the first material from the second material.
10. The method of claim 9, wherein the sorting step is carried out in a liquid medium, such as water.
11. The method of any one of the preceding claims, further comprising the step of (c) drying the sorted first material.
12. The method of claim 11, wherein the drying step is carried out during the sorting 15 step and/or as a subsequent drying step.
13. The method of any one of the preceding claims, further comprising the step of cutting and/or shredding the article prior to the separation step (a). 20
14. Plastics material when treated by the method of any one of the preceding claims.
15. A method of claim 1 as described herein with reference to the accompanying drawings and examples.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB1206461.4 | 2012-04-12 |
Publications (1)
Publication Number | Publication Date |
---|---|
NZ609226B true NZ609226B (en) | 2014-05-01 |
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