A PROCESS FOR RECYCLING A LAMINATE AND A SOLUTION THEREFOR

Abstract

The present invention relates to a recycling process for a laminate and a solution used in such a process. The present invention finds particular application in the removal of an adhered overlay from an underlying substrate material such as plastic. The process includes subjecting the laminate to an impact frictional striking force, thereby substantially separating the substrate layer from the one or more surface layers of the overlay and then washing the substrate layer with a washing solution to remove the remaining surface layers of the overlay and glue from the substrate layer. The washing solution may be an aqueous solution including a surfactant, a solvent and a base.

Claims

1. A process for recycling a laminate that includes a substrate layer and an overlay adhered to the substrate layer with a glue, the overlay including one or more surface layers, the process including: subjecting the laminate to an impact frictional striking force, thereby substantially separating the substrate layer from the one or more surface layers of the overlay; and then washing the substrate layer with a washing solution to remove the remaining surface layers of the overlay and glue from the substrate layer.

2. The process of claim 1, wherein the subjecting step is conducted in substantially dry conditions.

3. The process of claim 1, wherein the subjecting step is conducted in wet conditions.

4. The process of claim 3, wherein the subjecting step is conducted in the presence of water.

5. The process of claim 3 or claim 4, wherein the subjecting step is followed by drying a mixture of the substrate and the one or more surface layers of the overlay.

6. The process of any one of the preceding claims, wherein the impact frictional striking force is imparted on the laminate by one or more impactors, wherein the one or more impactors have a relatively blunt leading edge.

7. The process of claim 6, wherein the impact frictional striking force is controlled by adjusting one or more of the following operational parameters: rotational speed of the impactors, peripheral speed of the impactors, force, strain, temperature and pressure.

8. The process of any one of the preceding claims, further including, after the subjecting step but before the washing step, segregating a mixture of the separated substrate layer and one or more surface layers of the overlay.

9. The process of claim 8, wherein the segregating step includes removing the one or more layers of the overlay by applying suction or blowing to the mixture.

10. The process of any one of the preceding claims, further including drying the washed substrate layer.

11. The process of any one of the preceding claims, wherein the substrate layer includes a high-density polyethylene (HDPE) material.

12. The process of any one of the preceding claims, wherein the one or more surfaces of the overlay together form a label.

13. The process of any one of the preceding claims, wherein the washing solution is an aqueous solution comprising a surfactant and/or polymeric dispersing agent, and a solvent.

14. The process of claim 13, wherein the washing solution comprises a base.

15. The process of any one of the preceding claims, wherein the subjecting step also fragments the laminate.

16. A process for recycling a laminate that includes a substrate layer and an overlay adhered to the substrate layer with a glue, the overlay including one or more surface layers, the process including: washing the substrate layer with a solution to remove the one or more surface layers of the overlay from the substrate layer and the glue, the solution including a surfactant and/or a polymeric dispersing agent, and a solvent.

17. The process of claim 15, further including subjecting the laminate to an impact frictional striking force, thereby substantially separating the substrate layer from the one or more surface layers of the overlay.

18. A process for recycling a laminate that includes a substrate layer and an overlay adhered to the substrate layer with a glue, the overlay including one or more surface layers, the process including: subjecting the laminate to an impact frictional striking force, thereby substantially separating the substrate layer from the one or more surfaces of the overlay, wherein the subjecting step also fragments the laminate.

19. The process of claim 18, further including washing the substrate layer with a solution to remove the one or more surface layers of the overlay from the substrate layer and the glue, the solution including a surfactant and/or a polymeric dispersing agent, and a solvent.

20. Use of a solution comprising a surfactant and/or a polymeric dispersing agent, and a base for removing a glue from a laminate comprising a substrate and an overlay adhered to the substrate with the glue, the overlay comprising one or more surface layers.

21. A recycling process including: washing a laminate, which includes a substrate layer adhered to an overlay including one or more surface layers, with a washing solution to remove one or more surface layers of the overlay from the substrate layer, the washing solution comprising a surfactant and/or polymeric dispersing agent, a solvent and optionally a base, wherein the surfactant and/or polymeric dispersing agent has/have a cloud point that is below a boiling point of the washing solution; and heating the washing solution to above the cloud point of the surfactant and/or polymeric dispersing agent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 provides a scanning electron microscopy (SEM) image of a label overlay adhered to a HDPE bottle substrate by a layer of glue;

[0050] FIG. 2 is an illustrative diagram of an impact delamination step in accordance with an embodiment of the present invention;

[0051] FIG. 3 provides an infrared (IR) spectrum on the glue used to adhere the label overlay to the HDPE bottle substrate;

[0052] FIG. 4 provides an IR spectrum on a clean HDPE sample;

[0053] FIG. 5 provides an IR spectrum on a HDPE sample following a conventional recycling process;

[0054] FIG. 6 provides an SEM image of the surface of a substrate following a conventional recycling process;

[0055] FIG. 7 provides an IR spectrum on a HDPE sample obtained after an impact delamination step in accordance with an embodiment of the invention;

[0056] FIG. 8 provides an SEM image of a clean HDPE surface substantially free of any of the label or adhesive obtained after an impact delamination step and a washing step in accordance with an embodiment of the invention;

[0057] FIG. 9 provides an IR spectrum a clean HDPE surface substantially free of any of the label or adhesive obtained after an impact delamination step and a washing step in accordance with an embodiment of the invention; and

[0058] FIG. 10 provides an image of a phase separated washing solution which has been heated after being used in a washing step in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0059] Embodiments of the present invention will be described below. The invention relates to a recycling process for recycling a laminate that includes a substrate layer and an overlay adhered thereto. The overlay includes one or more surface layers.

[0060] To provide context, the results of a conventional recycling process will be briefly discussed and ultimately contrasted to a recycling process of the present invention. The following examples relate to a recycling process, whereby the aim is to sufficiently remove or separate the overlay (and any adhesive material) from the substrate, so the substrate material can be recycled. For example, in an embodiment, the process may be used to remove a low density polyethylene (LDPE) label from a high-density polyethylene (HDPE) bottle.

[0061] For example, FIG. 1 is an image taken from a microscope showing a conventional HDPE bottle substrate layer having a multilayer label that is adhered to the substrate layer by a hot melt pressure sensitive adhesive. The multilayer label may include a protective clear polyolefin film, printing ink, a laminating adhesive, and protective clear polyolefin.

[0062] Under conventionally employed recycling processes, there remains excessive contamination of the HDPE bottle due to the remains of the label and/or adhesive (e.g. glue) on the bottle after processing.

[0063] One major difficulty in recycling packaging material is the removal of glue. Glue is used to bind each layer of the laminate together. Optimised processes involve removal of the glue while retaining the maximum amount of the material to be recycled. A scanning electron microscopy (SEM) image of the surface of a substrate following a conventional recycling process is shown in FIG. 6. This image shows that small amounts of glue are retained on the substrate surface following conventional recycling processes. Carrying the adhesive into later stages of recycling can have a significant impact on downstream processes by requiring additional chemical additives, resulting in lower yields of recycled material and/or resulting in increased machinery downtime for cleaning.

[0064] In addition to SEM, the presence of adhesive on the surface of the substrate can be determined by infrared spectroscopy. FIG. 3 is an infrared (IR) spectrum of the glue used to adhere the label to the HDPE bottle, with the circled areas of FIG. 3 denoting the thiol and carbonyl stretches characteristic of the glue. FIG. 4 is an IR spectrum of a clean HDPE sample. FIG. 5 illustrates an IR spectroscopy conducted on a HDPE flake following a conventional process, showing in the circled area of FIG. 5 a carbonyl stretch indicating that some glue remains on the flake surface.

[0065] An embodiment of the present invention will now be described. The HDPE laminate, for example a HDPE bottle, is introduced into a processing region of a processing apparatus having one or more impactors for imparting sufficient force to the laminate in order to produce the desired delamination effect between the HDPE substrate and the overlay. In one embodiment, this step may be preceded by a separate step in which the portion(s) of the bottle having the overlay are separated from the remainder of the laminate after the laminate undergoes a fragmenting step. In such a case, the overlay portion may be separately processed from the remainder of the laminate, or processed together with the remainder of the laminate. The fragmenting step may also be used to produce reduced size flake of the HDPE laminate. However, it will be appreciated that steps of separating the portion(s) of the bottle having the overlay from the remainder of the laminate or undertaking the fragmenting step are not necessary. The entire laminate can simply be subjected to the one or more impactors, with the force imparted by the impactors producing both a fragmenting/cutting effect and the desired impact delamination effect.

[0066] It will be understood that the meaning of the term “flake” used herein includes use of the term as a collective noun as understood by a person skilled in the art. Thus, the term “flake” may refer to a single flake or to a plurality of flakes.

[0067] The following steps will be described from the point of view of the portion(s) of the laminate that have the overlay adhered thereto.

[0068] Upon introduction of the laminate into the processing region, the laminate is subjected to impact frictional forces by one or more rotating impactors, e.g. blades, each blade suitably shaped to impart these forces on the laminate. For illustrative purposes, reference is made to FIG. 2 to describe the impact delamination process. The forces on the laminate, depicted as plastic layers 1 (an overlay layer and a substrate layer), are intended to break the laminate into flake (or further flake), and impart the desired delamination effect. In other words, the intention of the blades 2 is to strike or bash the laminate, invariably penetrating and causing fracture and breakage of the laminate. To this end, the blades 2 are suitably shaped to achieve the desired effect. For example, the blades can have a relatively blunt leading edge (as shown in FIG. 2) so that upon contact with the portion(s) of the laminate, the desired impact frictional striking force is imparted. For example, the impact striking force 3, generally shown acting in a direction substantially normal to the laminate, produces shear forces 4 and bending forces 5, resulting in cracks 6 due to the impact, delamination 7, pulling forces 8, cracks 9 due to bending, and ultimately pulling of the adhesive and separation 10 of the overlay and substrate layers.

[0069] The blades are to be rotated at a suitable speed in order to impart the requisite force and produce the intended impact delamination. Ultimately, the result of this step is to produce a mixture of HDPE flake that are substantially free of the overlay and the now delaminated pulp label material.

[0070] In order to achieve the desired impact delamination, parameters such as rotational speed and/or peripheral speed of the blade, force, strain, temperature, pressure, etc., can be controlled by any means known in the art. Further, one or more sensors may be arranged within or adjacent the processing region, the sensors monitoring one or more of the parameters mentioned above. An operator of the processing apparatus may receive data from the sensors relating to the above mentioned parameters and use this data to make manual adjustments to these parameters in order to improve the impact delamination process. Alternatively, a feedback system may be implemented, whereby the sensor data is sent to a nearby or remote controller, which can utilise this data and adjust parameters to achieve more effective impact delamination.

[0071] Another means to control the impact delamination step is through the design of the impactor, i.e. the physical form of the impactor. In this example, the form of the impactors influences the effectiveness of the impact delamination step. For example, the dimensions, mass, and/or shape of the impactors, or inclination/declination of the leading and/or trailing edges of the impactors may be suitably designed in order to produce the desired impact loads. The impactors may be defined by their sharpness, for example using the BESS, which assumes a substantially circular apex as the BESS is based on the edge apex radius. For example, a score of 500 on the BESS means an edge apex radius of 500 nm (or an edge apex width of 1 micron). Thus, the dimensions of an apex of the impactor may be determined based on its BESS, including any of the BESS scores described herein. Preferred impactors, upon impact with the laminate, may provide both the desired impact delamination and fragmentation of the laminate. These parameters mentioned above, in combination with the speed controls mentioned above, can be provided as an input in the feedback system described above and taken into account by the controller when determining whether adjustment in the process is required.

[0072] In an embodiment, this step of imparting frictional impact forces to the laminate is conducted in dry conditions, i.e. in the absence of any appreciable solution or other liquid. Conducting this step in dry conditions may result in the glue adhering to the removed overlay material, as well as on the stationary components of any equipment used in the system.

[0073] In many cases, the material desired to be retrieved for further processing is the substrate (for example the HDPE flake produced by the impact delamination step above), with the delaminated pulp overlay material being a waste product in this process. In other embodiments, there may be a desire to retrieve and retain the overlay material for later processing.

[0074] In another embodiment, the step of imparting frictional impact forces to the laminate is conducted in wet conditions, i.e. in the presence of a liquid. The glue is preferably insoluble in this liquid. This liquid is preferably water. It has been found that when the subjecting step is conducted in the presence of water, the glue remains on the removed overlay, thereby leaving the substrate and any equipment used during the recycling process relatively clean. In this embodiment, the mixture of HDPE flake and overlay material should be first dried before the process moves forward.

[0075] In any of the cases described above, the mixture of HDPE flakes and overlay material requires segregation/separation. This can be achieved in any suitable manner known in the art. For example, in order to take advantage of the relative difference in compactness between the HDPE flake and the label material, suitable blowing or suction may be applied, thereby physically separating the less compact label material from the more compact HDPE flake. This step of the process may be conducted in combination with a suitable filtering step. The filtering may be achieved by arranging a suitable screen, configured to permit passage of only certain sized material, between the processing region and an exit path. For example, the screen may permit passage of the pulp label material towards the exit path, but restrict passage of the HDPE flake. Preferably, at the conclusion of this step, there remains substantially only the HDPE flakes in the processing region. Alternatively, the screen may permit passage of the HDPE flake towards the exit path, but restrict passage of the pulp label material, thereby substantially only the pulp label material remains in the processing region. It is noted that the desired result at this stage is that HDPE flake are substantially free of the label material and adhesive. However, it may still be the case that there is some remaining adhesive and/or label material remaining on a small portion of the HDPE flake.

[0076] FIG. 7 is an IR spectrum conducted on a HDPE flake obtained by an impact delamination step as described above and in the Examples below. This IR spectrum indicates substantial separation of the substrate and overlay, with low amounts of glue remaining (indicated by the thiol stretch at about 2300 cm.sup.−1). Remaining glue may be substantially removed by a washing step.

[0077] A washing step may now be performed on the remaining HDPE flake. To this end, a suitable solution, which will be described in greater detail below, is introduced into the processing region and onto the HDPE flake. It will be appreciated that the washing step need not take place in the processing region, but may take place away from the processing region. For example, the HDPE flakes may be transferred to another designated washing region of the apparatus (or to another apparatus entirely). Further, the HDPE flake may be transferred to a pre-prepared solution bath.

[0078] Irrespective of the approach taken above, the conclusion of the impact delamination step has been found to leave adhesive material on components in, or adjacent regions of, the processing region where the impact delamination step is performed. Thus, the process may include a separate cleaning step, whereby the processing region is cleaned by introducing the solution into this region. If the HDPE flake are still in the processing region for this, the cleaning step can form part of the overall washing step. Alternatively, the cleaning step may take place separately to the washing of the HDPE flake at any point after the impact delamination step.

[0079] In this example, the HDPE flake is transferred to a separate washing region for the washing step of the process. The HDPE flake is introduced into a pre-prepared solution bath in the washing region. Once the HDPE flake is placed into the solution bath, the washing region is sealed and heated to a suitable temperature for a predetermined period of time with stirring. This washing step is vigorous and results in substantially any remaining label portions and adhesive detaching from the HDPE flake.

[0080] The HDPE flake can then be removed from the solution bath, and sufficiently rinsed and dried. Rinsing of the HDPE flake can include further filtering or washing of the HDPE flake with water. Drying of the HDPE flake can be conducted under a controlled temperature for a predetermined amount of time. It will be appreciated that these steps may be performed in any other suitable manner known in the art.

[0081] The end result of the process described above are HDPE flake that are now substantially free of any label portions or adhesives. This is best shown in FIGS. 8 and 9, which illustrate a clean HDPE surface substantially free of any of the label or adhesive. Thus, effectively pure HDPE flake can be used in a suitable HDPE recycling process to produce recycled HDPE that is free of contaminants and suitable for high grade applications, such as for food-grade applications.

[0082] In some embodiments, the washing solution is an aqueous solution comprising a surfactant and/or a polymeric dispersing agent, and a solvent. Further, if the laminate comprises a crosslinked glue, the solution may further comprise a base.

[0083] The solution may comprise any surfactant and/or polymeric dispersing agent that is able to solubilise the glue used to adhere the overlay to the substrate layer. In some embodiments, the solution comprises a surfactant. In other embodiments, the solution comprises a polymeric dispersing agent. In some embodiments, the solution comprises both a surfactant and a polymeric dispersing agent.

[0084] The surfactant may be an anionic, cationic or non-ionic surfactant, or a combination thereof. Blends of surfactants may include multiple surfactants of the same type, or combination of different classes of surfactant. Preferably, the surfactant is a low-foam surfactant, such as Teric BL9. A low foam surfactant reduces the foaming of the solution and therefore provides handling advantages in the processes of the invention.

[0085] Suitable non-ionic surfactants include ethoxylated alkanols, in particular ethoxylated fatty alcohols and ethoxylated oxoalcohols, such as ethoxylated lauryl alcohol, ethoxylated isotridecanol, ethoxylated cetyl alcohol, ethoxylated stearyl alcohol, and esters thereof, such as acetates; ethoxylated alkylphenols, such as ethoxylated nonylphenyl, ethoxylated dodecylphenyl, ethoxylated isotridecylphenol and the esters thereof, e.g. the acetates alkylglucosides and alkyl polyglucosides, ethoxylated alkylglucosides; ethoxylated fatty amines, ethoxylated fatty acids, partial esters, such as mono-, di- and triesters of fatty acids with glycerine or sorbitan, such as glycerine monostearate, glycerine monooleate, sorbitanmonolaurate, sorbitanmonopalmitate, sorbitanmonostearate, sorbitan monooleate, sorbitantristearate, sorbitan trioleate; ethoxylated esters of fatty acids with glycerine or sorbitan, such as polyoxyethylene glycerine monostearate, polyoxyethylene sorbitanmonolaurate, sorbitanmonopalmitate, polyoxyethylene sorbitanmonostearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitantristearate, polyoxyethylene sorbitan trioleate; ethoxylates of vegetable oils or animal fats, such as corn oil ethoxylate, castor oil ethoxylate, tallow oil ethoxylate; ethoxylates of fatty amines, fatty amides or of fatty acid diethanolamides.

[0086] Suitable anionic surfactants include salts, in particular, sodium, potassium calcium or ammonium salts of alkylsulfonates, such as lauryl sulfonate, isotridecylsulfonate, alkylsulfates, in particular fatty is alcohol sulfates, such as lauryl sulfate, isotridecylsulfate, cetylsulfate, stearylsulfate—aryl and alkylarylsulfonates, such as napthylsulfonate, dibutylnaphtylsulfonate, alkyldiphenylether sulfonates such as dodecyldiphenylether sulfonate, alkylbenzene sulfonates such as cumylsulfonate, nonylbenzenesulfonate and dodecylbenzene sulfonate; sulfonates of fatty acids and fatty acid esters;—sulfates of fatty acids and fatty acid esters; sulfates of ethoxylated alkanols, such as sulfates of ethoxylated lauryl alcohol; sulfates of alkoxylated alkylphenols; alkylphosphates and dialkylphosphates; dialkylesters of sulfosuccinic acid, such as dioctylsulfosuccinate, acylsarcosinates, fatty acids, such as stearates, acylglutamates, ligninsulfonates, low molecular weight condensates of naphthalinesulfonic acid or phenolsulfonic acid with formaldehyde and optionally urea.

[0087] Suitable cationic surfactants include quaternary ammonium compounds, in particular alkyltrimethylammonium salts and dialkyldimethylammonium salts, e.g. the halides, sulfates and alkylsulfates.

[0088] When present, the concentration of surfactant in the washing solution may vary depending on the material to be recycled, surfactant properties selected and depending on the other ingredients included. In some embodiments, the minimum concentration of the surfactant may be at least about 0.1 wt %, 0.5 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt % or 4.5 wt %. The maximum concentration of the surfactant may be up to about 30 wt %, 25 wt %, 20 wt %, 15 wt %, 10 wt %, 9 wt %, 8 wt %, 7 wt %, 6 wt % or 5 wt %. The washing solution may comprise the surfactant in a concentration from any of these minimum values to any of these maximum values, for example, from about 0.1 wt % to about 30 wt % or about 1 wt % to about 10 wt %.

[0089] The polymeric dispersing agent may be any agent capable of interacting with the glue and any contaminants to assist their removal from overlay and/or substrate layer. While most embodiments of suitable polymeric dispersing agents may also be considered surfactants, some embodiments of polymeric dispersing agent would not classically be within the surfactant class. Thus, in some embodiments, the polymeric dispersing agent may be a surfactant.

[0090] The polymeric dispersing agent may be non-ionic, anionic, cationic and/or zwitterionic. In some embodiments, the polymeric dispersing agent may comprise a hydrophobic group (such as Orotan series copolymers, e.g. a sodium salt of a maleic anhydride copolymer). Hydrophobic groups may improve interactions of the polymeric dispersing agent with any hydrophobic contaminants present in the overlay, glue and/or substrate layer. In some embodiments, the polymeric dispersing agent may include polymers/copolymers comprising a hydrophilic group capable of micellizing at elevated temperatures. Suitable examples include poly(NIPAM), or polymers/copolymers which can phase separate the glue into a removeable oil layer including copolymers of poly(ethylene oxide)/poly(propylene oxide) (Pluronic copolymers). In some embodiments, the polymeric dispersing agent comprises both a hydrophilic group and a hydrophobic group, and in these embodiments the polymeric dispersing agent may be any of the surfactants described herein capable of polymer dispersal in solution.

[0091] Anionic polymeric dispersing agents include charged polymers/copolymers of polyacids and polyacid copolymers such as poly(acrylic acid) salts, poly(methacrylic acid) salts, poly(styrene sulfonic acid) salts, poly(styrene-co-maleate) salts, poly(hydroxy ethyl (meth)acrylate phosphate) salts (Visiomer HEMA-P 70M), and poly(vinylphosphonate) salts. Any suitable salt form of these agents may be used, including any commercially available salt form. Cationic polymeric dispersing agents include polymers/copolymers of quaternized ammonium salts such as poly(diallyldimethylammonium chloride) (poly(DADMAC)) and its copolymers, poly(dimethylaminoethyl(meth)acrylate) and its copolymers, and poly(vinylpyrridine). Non-ionic polymeric dispersing agents include poly(vinyl alcohol), polyacrylamide, poly(N-isopropylacrylamide) (polyNIPAM), polyethylene glycol (polyethylene oxide), poly(propylene oxide), hydroxy functionalized poly(meth)acrylates (poly hydroxy ethyl acrylate, polyhydroxy ethyl methacrylate) and polyvinyl pyrrolidone. Zwitterionic polymeric dispersing agents include poly(sulfobetaine (meth)acrylate), poly(carboxybetaine (meth)acrylate), poly(phosphobetaine) such as poly(2-methacryloyloxyethyl phosphorylcholine), poly(2-acryloyloxyethyl phosphorylcholine) and copolymers of cationic and anionic monomers.

[0092] When present, the concentration of polymeric dispersing agent in the washing solution may vary depending on the material to be recycled, dispersing agent properties selected and depending on the other ingredients included. In some embodiments, the minimum concentration of the polymeric dispersing agent may be at least about 0.1 wt %, 0.5 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt % or 4.5 wt %. The maximum concentration of the polymeric dispersing agent may be up to about 30 wt %, 25 wt %, 20 wt %, 15 wt %, 10 wt %, 9 wt %, 8 wt %, 7 wt %, 6 wt % or 5 wt %. The washing solution may comprise the polymeric dispersing agent in a concentration from any of these minimum values to any of these maximum values, for example, from about 0.1 wt % to about 30 wt % or about 1 wt % to about 10 wt %.

[0093] In one embodiment, the surfactant and/or polymeric dispersing agent has/have a cloud point below the boiling point of the washing solution. The use of surfactants/polymer dispersing agent with cloud point below the boiling point of the washing solution may be advantageous to induce phase separation in the wash solution when heated to above a washing temperature (e.g. about 95° C.). The used washing solution may be heated while in contact with the laminate, or in a separate step after completion of the washing step in the methods described herein. After heating, washed glue may separate into a separate phase, typically a less dense phase floating at the surface of the used washing solution. Partitioning the glue into a separate phase forms a liquid layer that can be removed. Where a hydrophobic solvent is used, separating the hydrophobic layer may take place in a settling tower which may be connected to the reactor. Separating dissolved glue from the used washing solution, may allow the washing solution to be refurbished and reused (see, for example, Example 2A). The reusability of the washing solution is advantageous for cost and environmental reasons.

[0094] The washing solution comprises a solvent, which may be any non-aqueous solvent (or combination thereof) that is capable of solubilising the adhesive and assisting in the separation of the substrate layer and overlay.

[0095] The solvent is also preferably food safe. Food safe solvents are preferred to minimise the risk of contamination in recycled materials for preparing food packaging. However, even in such processes, a solvent may be used in the process that is not food safe provided it is substantially removed (eg at least to below food safe levels) prior to the recycled material contacting food. Further, depending on the desired use of the recycled material, the process need not produce food safe recycled materials.

[0096] Suitable solvents for this process can include dimethyl sulfoxide, N-methylpyrrolidone, dimethyl acetamide, N,N-dimethylformamide, propylene carbonate, acetonitrile, 2-methoxyethanol, pyridine, ethylene glycol, ethanol, methanol, acetone, 1,4-dioxane, methyl ethyl ketone, ethyl acetate, chloroform, tetrahydrofuran, dimethoxyethane, n-propyl alcohol, n-butyl acetate, isopropyl alcohol, 1,2-dichloroethane, dichloromethane, diethyl ether, o-dichlorobenzene, o-xylene, toluene, cyclohexane, hexane, heptane, cyclopentane, pentane, benzyl alcohol, 1,3-butylene glycol, an edible oil (eg castor oil), mono- and di-glycerides and/or esters thereof, glycerol, glyceryl alkylate (eg glyceryl mono- di- or triacetate, mono-, di-, or tri-butyrate), hexane, isopropyl alcohol, 1,2-propylene glycol, propylene glycol mono-esters and diesters of fat-forming fatty acids, triethyl citrate or mixtures thereof. Suitable solvents are also described in Industrial Solvents Handbook, 5th Ed. by Ernest W. Flick, 9780815514138, Westwood, N.J.: Noyes Data Corp., 1998, which is hereby entirely incorporated by reference.

[0097] Suitable food safe solvents include dimethyl sulfoxide, propylene carbonate, acetone, benzyl alcohol, 1,3-butylene glycol, an edible oil (eg castor oil), mono- and di-glycerides and/or esters thereof, ethyl acetate, ethanol, glycerol, glyceryl alkylate (eg glyceryl mono- di- or triacetate, mono-, di-, or tri-butyrate), hexane, isopropyl alcohol, methanol, methyl ethyl ketone, dichloromethane, 1,2-propylene glycol, propylene glycol mono-esters and diesters of fat-forming fatty acids, triethyl citrate and combinations thereof.

[0098] In some embodiments, the solvent is propylene carbonate optionally in combination with one or more further solvents, for example selected from the above list.

[0099] The concentration of solvent in the washing solution may vary depending on the material to be recycled, solvent properties and depending on the other ingredients included. There is no particular limit on the amount of solvent that can be used in the washing solution, except that allowance needs to be made for the amount of surfactant that is included. In general, the amount of solvent used will be governed by cost and safety. As a broad generality, the more solvent present the quicker the washing operation and the lower the temperature required. Thus, there is a balance between ease of washing and low heating time and cost, against cost of solvent and cost of solvent disposal. In some embodiments, the minimum concentration of the solvent may be at least about 0.1 wt %, 0.5 wt %, 1 wt %, 1.5 wt %. 2 wt %, 2.5 wt %, 3 wt %, 3.5 wt % or 4 wt %. The maximum concentration of the solvent may be up to about 30 wt %, 25 wt %, 20 wt %, 15 wt %, 10 wt %, 9 wt %, 8 wt %, 7 wt %, 6 wt %, 5 wt % or 4.5 wt %. The washing solution may comprise the solvent in a concentration from any of these minimum values to any of these maximum values, for example, from about 0.1 wt % to about 30 wt % or about 1 wt % to about 15 wt %.

[0100] In some embodiments, the solution comprises a base. The base is typically suitable to hydrolyse ester/acid functional groups on contaminants or within the glue adhering the one or more layers of the overlay to the substrate layer. The base may also assist in breaking any cross-linking formed within the glue. Hydrolysed contaminants and degraded glue tend to be more hydrophilic so more readily removed in the washing step. Typically, the base is a strong base; however, in some embodiments the base may comprise a mixture of a strong base and one or more weak bases. In some embodiments, the base is selected from a hydroxide (eg sodium hydroxide, potassium hydroxide, ammonium hydroxide, and so on including combinations thereof), an alkoxide (eg a sodium or potassium salt of methoxide, ethoxide, iso-propoxide and so on including combinations thereof) or a combination thereof. In some embodiments, the base is sodium hydroxide.

[0101] The concentration of base in the washing solution may vary depending on the material to be recycled, base properties and depending on the other ingredients included. In some embodiments, the minimum concentration of the base may be at least about 0.1 wt %, 0.5 wt %, 1 wt %, 1.5 wt % or 2 wt %. The maximum concentration of the surfactant may be up to about 10 wt %, 9 wt %, 8 wt %, 7 wt %, 6 wt %, 5 wt %, 4 wt %, or 3 wt %. The washing solution may comprise the surfactant in a concentration from any of these minimum values to any of these maximum values, for example, from about 0.1 wt % to about 10 wt % or about 0.5 wt % to about 5 wt %.

[0102] In some embodiments, the molarity of the base may be at least about 0.1M, 0.2M, 0.3M, 0.4M, 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1M, 2M, 3M, 4M, 5M, 6M, 7M, 8M, 9M, 10M or greater. The molarity of the base in the washing solution may be from any of these values to any other value, for example, from about 0.1M to about 10M or about 0.5M to about 0.8M.

[0103] The balance of the washing solution will typically be water. In some embodiments, the washing solution comprises water in a minimum concentration of at least about 40 wt %, 45 wt %, 50 wt %, 55 wt %, 60 wt %, 65 wt %, 70 wt %, 75 wt %, 80 wt %, 85 wt % or 89 wt %. The washing solution may comprise water in a maximum concentration of up to about 99.7 wt %, 99 wt %, 95 wt %, or 90 wt %. The concentration of water may be from any of these minimum amounts to any of these maximum amounts, for example, from about 50 wt % to about 99.7 wt % or about 75 wt % to about 95 wt %.

[0104] Whilst the embodiment described above involves a recycling process that includes both an impact delamination step and a washing step in order to produce satisfactory removal of an overlay and adhesive from an underlying substrate, it will be appreciated that the use of either one of these steps in existing recycling processes can improve the end result of those processes.

[0105] It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

EXAMPLES

[0106] The invention will be further described by way of non-limiting example(s). It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.

Example 1a. Impact Delamination of HDPE Milk Bottle Labels

[0107] Labelled high density polyethylene (HDPE) pieces (8 cm×10 cm) were removed from empty 2 L (Country Valley brand) milk bottles. They were washed and dried then cut into two (4 cm×10 cm) sections using scissors. Six (6) such sections were loaded into the 500 mL cup of a blender (NutriBullet 1000 series) equipped with 6 blunt extractor blades. The blender was run for approximately 30 seconds (25,000 rpm) to produce a mix of mostly clean, label free HDPE flake (approximately between 0.25-4 cm.sup.2) and delaminated fluffy labels. However, a small amount of flake still had the label fragments attached while adhesive from the milk bottle label was observed to build up on the cup interior. After blending, more compact HDPE flake (both clean or label attached) were separated from the light and fluffy delaminated labels by air blowing. FTIR showed that most of the label free HDPE flake was substantially free of adhesive (see FIGS. 3, 4, 5 and 7).

Example 1b. Chemical Washing of Mechanically Delaminated HDPE Flake

[0108] A solution was prepared by dissolving the alcohol alcoholate non-ionic surfactant Teric BL9 (12.5 g) and sodium hydroxide (6.0 g) in water (250.0 g) and dimethylsulfoxide (DMSO, 12.0 g) in a glass jar. To this solution, HDPE flake (30.0 g) from Example 1a was added. The jar was sealed and heated at 95° C. for 30 minutes under magnetic stirring. After heating, the remaining labels were observed to detach from the HDPE flake. Flake were filtered, washed with cold water then dried in an oven overnight at 50° C. After drying, the HDPE flake was separated from the light and fluffy labels by air blowing. FTIR showed that the washed HDPE flake was free of label adhesive.

Example 2a. Chemical Washing of Mechanically Delaminated HDPE Flake Using Propylene Carbonate as Solvent

[0109] A solution was prepared by dissolving Teric BL9 surfactant (12.5 g) and sodium hydroxide (6.0 g) in water (250.0 g) and propylene carbonate (PC, 12.0 g) in a glass jar. To this solution, HDPE flake (30.0 g) from Example 1, a) was added. The jar was sealed and heated at 95° C. for 30 minutes under magnetic stirring. After heating, the remaining labels were observed to detach from the HDPE flake. Flake was filtered, washed with cold water then dried in an oven overnight at 50° C. After drying, the HDPE flake was separated from the light and fluffy labels by air blowing.

[0110] The used washing solution was then heated to 95° C., whereupon it phase separated into a dirty dark green oily top layer (containing glue and other contaminants) and slightly cloudy bottom layer (wash solution) as shown in FIG. 10. The oily layer was carefully removed using a separating funnel and the remaining solution was kept for future use in sample washing.

Example 2b. Chemical Washing of Mechanically Delaminated HDPE Flake Using Propylene Carbonate as Solvent

[0111] The chemical solution from example 2a was re-used to wash 30 g dirty HDPE milk bottle flake (Pegras) using the same process. After washing, filtering and drying, the labels were found to be separated from the flake. They were removed from washed HDPE flake by air blowing.

Example 3. Chemical Washing of Mechanically Delaminated HDPE Flake Using Propylene Carbonate as Solvent and Disponil FES993 (Fatty Alcohol Polyglycol Ether Sulphate Sodium Salt, BASF) as a Surfactant

[0112] Same procedure as in Example 2a was used with Disponil FES993 as surfactant. The labels were found to be effectively removed from the HDPE flake.

Example 4. Chemical Washing of Mechanically Delaminated HDPE Flake Using Propylene Carbonate as Solvent and Aerosol MA80-I (Sodium Dihexyl Sulfosuccinate, Solvay) as a Surfactant

[0113] Same procedure as in Example 2a was used with Aerosol MA80-I as surfactant. The labels were found to be effectively removed from HDPE flake.

Example 5. Chemical Washing of Mechanically Delaminated HDPE Flake Using Toluene as a Solvent

[0114] Same procedure as in Example 1 b was used with Toluene as solvent and wash temperature was at 70° C. The labels were found to be effectively removed from HDPE flake.

Example 6. Impact Delamination of HDPE Milk Bottle Labels in Water (Wet Process)

[0115] Same procedure as in Example 1a was used in water (30 g) to produce visually clean delaminated HDPE flake and separated labels with glue attached. FTIR showed that most of the label free HDPE flake was substantially free of adhesive.

Example 7. Impact Delamination of Labelled Polypropylene (PP) Waste

[0116] Same procedure as in Example 1a was used with 20 g of PP pieces with attached labels (Ice cream container, Streets) to produce delaminated PP flake and separated labels with glue attached.

Example 8. Impact Delamination of Labelled Polyethylene Terephthalate (PET) Waste

[0117] Same procedure as in Example 1a was used with 23 g of PET pieces with attached labels (1.25 L Lemonade drink bottle, Schweppes) to produce delaminated PET flake and separated labels with glue attached.

Example 9. Impact Delamination of Labelled Coloured HDPE Waste

[0118] Same procedure as in Example 1a was used with 22 g of coloured HDPE pieces with attached labels (shower gel bottle, Palmolive) to produce delaminated coloured HDPE flake and separated labels with glue attached.

Example 10. Chemical Washing of Mechanically Delaminated PET Flake Using Poly(Ethylene Oxide) (PEO)

[0119] A solution was prepared by dissolving PEO (0.5 g, 100K g/mole) and sodium hydroxide (2.4 g) in water (99.5 g) and dimethylsulfoxide (DMSO, 5.0 g) in a glass jar. To this solution, PET flake (10.0 g) from Example 8 was added. The jar was sealed and heated at 90° C. for 30 minutes under magnetic stirring. After heating, the remaining labels were observed to detach from the PET flake. The flake was filtered, washed with cold water then dried in an oven overnight at 50° C. After drying, the PET flake was separated from the light and fluffy labels by air blowing. The washed flake was visually found to be free of label adhesive.

Example 11. Chemical Washing of Mechanically Delaminated HDPE Flake Using Pluronic F68 Poly Ethylene Oxide/Polypropylene Oxide Copolymer

[0120] Impact delaminated HDPE flake was prepared in the same manner as in Example 1a but with a whole 2 L milk bottle (Country Valley brand) (about 45 g). After removal of detached labels, the HDPE flake was used for further chemical washing. A solution was prepared by dissolving Pluronic F68 (BASF) (0.5 g) and sodium hydroxide (2.4 g) in water (99.5 g) and dimethylsulfoxide (DMSO, 5.0 g) in a glass jar. This solution was used to wash the above flake (10 g) in the same procedure described in Example 10. After washing, the sample of flake was visibly clean.

Example 12. Chemical Washing of Mechanically Delaminated HDPE Flake Using Negatively Charged Orotan 731A Maleic Anhydride Copolymers

[0121] A solution was prepared by dissolving Orotan 731A solution (Dow) (1.0 g) and sodium hydroxide (2.4 g) in water (99.0 g) and dimethylsulfoxide (DMSO, 5.0 g) in a glass jar. This solution was used to wash the above HDPE flake from Example 11a (10 g) in the same procedure described in Example 10. After washing, the sample of flake was visibly clean.

Example 13. Chemical Washing of Mechanically Delaminated HDPE Flake Using Positively Charged Poly(acrylamide-co-diallyldimethyl Ammonium Chloride) (Poly(AAm-co-DADMAC))

[0122] A solution was prepared by mixing poly(AAm-co-DADMAC) solution (Sigma Aldrich) (10 g) and sodium hydroxide (2.4 g) in water (90.0 g) and dimethylsulfoxide (DMSO, 5.0 g) in a glass jar. This solution was used to wash the above HDPE flake from Example 11a (10 g) in the same procedure described in Example 10. After washing, the sample of flake was visibly clean.