Method for recovering additives and / or polymer material from plastic material

Abstract

The invention relates to a method for recovering at least one polymer material and / or at least one additive from a plastic material, the method comprises the contacting of the plastic material with a solvent to obtain a suspension comprising a solution and solid particles, the solution comprising the dissolved at least one polymer material and the solid particles comprise the at least one additive. 5 The method further comprises the addition of an organic compound to the suspension to obtain a supernatant and a sediment. The organic compound is insoluble in the solvent and comprises a polymeric chain having at least 5 carbon atoms. The organic compound has a number of hydrogen bond donors (HBD) and a number of hydrogen bond acceptors (HBA), with the ratio HBD / HBA ranging from 0 to 1. 10 The sediment comprises aggregate particles having a size larger than the size of the solid particles.

Description

Method for recovering additives and / or polymer material from plastic materialField of the invention

[0001] The present invention relates to the field of plastic recycling, in particular to methods for the recovering of polymer material and / or additives such as pigments from plastic material, for example from plastic waste material.Background art

[0002] The global demand for plastic materials, such as those used in packaging, continues to grow due to their superior functional properties, including but not limited to oxygen, moisture and light barrier properties, printability and food compliance.

[0003] This increasing demand for plastic materials results in significant volumes of post-industrial and post-consumer plastic waste that needs to be managed effectively.

[0004] For many years, plastic material has been produced in a linear production system, but today a shift towards a circular system is indispensable. Due to the wide range of applications that requires a significant number of properties for the final products, plastic recycling presents many challenges.

[0005] A major challenge is the removal of additives intentionally incorporated in the plastic material for example to improve the physicochemical properties of the plastic material, such as thermal and impact resistance, strength, stiffness and also to overcome processing problems related to high temperature / viscosity, ageing properties and environmental instability.

[0006] The presence of some additives has a direct impact on the recyclability of the plastic material or even leads to degradation of the plastic material. In particular, the presence of pigments significantly complicates the recycling process. The recycling of pigmented plastic material tends to result in dark coloured material which has a much lower market value.

[0007] Solvent-based recycling is of increasing interest today as it allows to recover polymer material, without the energy need of cracking the polymer. Solvent-based methods are for example described in patents DE102005026451 and EP945481.

[0008] DE102005026451 describes a method for recycling plastic materials containing at least two polymers, copolymers or blends thereof based on polystyrene. First, the plastic material is mixed with a solvent. A second solvent which acts as an anti-solvent for the polymer is then added to induce its precipitation while keeping unwanted additives in solution.

[0009] EP945481 describes a method for recycling a polyvinyl chloride (PVC)-based polymer by first shredding the article in fragments, contacting the fragments with an anhydrous solvent capable of dissolving the PVC-based polymer and capable of forming an azeotrope with water and precipitating the polymer dissolved in the solvent by injecting steam in the solution to recover the polymer.

[0010] None of these solvent-based methods allows to recover additives such as pigments from the plastic material.

[0011] With respect to the recovery of pigments, particular attention has been paid to TiO2 as it is the most widely used pigment, for example for polyolefin polymer matrices (such as polyethylene and polypropylene) and for polyinyl chloride. The main approach to recover the white pigment is by pyrolysis. However, the main disadvantage of recovering plastic material comprising TiO2 as pigment is that the polymer matrix is destroyed by the high temperature of the process and is not suitable for further recycling. In addition, the recovered TiO2 has a dark colour and of poor quality.

[0012] US 11 ,407,877 proposes a solvent-based recycling method involving the flocculation of insoluble particles under acidic conditions at elevated temperatures. This method aims to address the recycling of polystyrene, polypropylene, polyethylene, and polyvinylchloride wastes. However, it does not specifically address the challenges associated with pigment removal and the recycling of polymer matrices.

[0013] US 2.914,492 describes a method to dissolve polystyrene containing titanium dioxide in toluene. The method comprises the addition of glacial acetic acid and water. Subsequently, the solution is filtered using diatomaceous earth as filtering aid.

[0014] CA802332 describes the dissolution of polyethylene and carbon black in xylene. Hydrochloric acid (HCI) is added as a coagulant to allow the carbon black to coagulate.

[0015] Therefore, there is a need for methods to recover polymer material and / or additives such as pigments from plastic material.Summary of the invention

[0016] It is an object of the present invention to provide a method for recovering additives for example pigments from plastic material, for example from plastic waste material.

[0017] It is another object of the present invention to provide a method for recovering polymer material from plastic material, for example from plastic waste material.

[0018] It is a further object of the present invention to provide a method for recovering both polymer material and additives, for example pigments, from plastic material, for example from polymer waste material.

[0019] It is a further object of the present invention to provide a method for recovering polymer material from plastic material allowing to provide uncoloured polymer material while avoiding downgrading of the polymer material so that the recovered polymer material can be reused for high value applications.

[0020] It is still a further object of the present invention to provide a method for recovering additives such as pigments from plastic material allowing to reuse the additives.

[0021] According to a first aspect of the invention a method for recovering polymer material and / or additive(s) such as pigments or fillers from a plastic material is provided. The method comprises the steps of- providing a plastic material comprising at least one polymer material and at least one additive,- providing a suitable solvent, whereby the at least one polymer material is soluble in the solvent whereas the at least one additive is not soluble in the solvent;- contacting the plastic material with the solvent to obtain a suspension comprising a solution and solid particles, the solution comprising the dissolved at least one polymer material and the solid particles comprising the at least one additive;- adding an organic compound to the suspension to obtain a supernatant and a sediment, the supernatant comprising the dissolved at least one polymer and the sediment comprising the at least one additive, the organic compound being insoluble in the solvent, the organic compound comprising a carbon-carbon chain having at least 5 carbon atoms, the organic compound having a number of hydrogen bond donors (HBD) and a number of hydrogen bond acceptors (HBA), with ratio HBD / HBA ranging from 0 to 1 , the sediment comprising heterocoagulated particles formed by physicochemical interactions of the solid particles and the organic compound, the heterocoagulated particles having a size larger than the size of the solid particles.

[0022] The method according to the present invention allows to recover polymer material from the plastic material and / or the method according to the present invention allows to recover one or more additive, for example one or more pigments, form the plastic material.

[0023] In particular embodiments, the method according to the present invention allows to recover both polymer material(s) and additive(s) such as pigments from a plastic material. Furthermore, the method allows to obtain uncoloured polymer material and additives such as pigments of high quality suitable for high value applications. In addition, the method according to the present invention allows to recover the organic compound.

[0024] For the method according to the present invention, the selection of the solvent is critical. The at least one polymer should dissolve in the solvent whereas the at least one additive present in the plastic material should not dissolve in the solvent. By choosing an appropriate solvent, the chains of the at least one polymer material will disentangle while dissolving in the solvent, allowing the release of insoluble additives. In this way a suspension comprising a solution and solid particles is obtained. The solution comprises the dissolved at least one polymer material and the solid particles comprise the at least one additive.

[0025] The degree of solubility of a substance (a polymer) in another substance (a solvent) can be determined using the Hansen Solubility Parameters (HSP).The HSP (6) include three parameters (with a unit of MPa1 / 2) : an energy (6D) from dispersion force between molecules, an energy (bp ) from polar force between molecules, and an energy (6H) from hydrogen bonding between molecules. These three parameters are regarded as coordinates in a three-dimensional space called a "Hansen space," and have a relationship of "b2= (bo)2+ (bp)2+ (bn)2The Hansen solubility parameters of two substances are placed in the Hansen space. The substances at a smaller distance in the Hansen solubility parameters are determined to be highly soluble.

[0026] The HSP and interaction radius Ro of some commonly used substances can be found in databases. For example, the Hansen solubility parameters (bo, bp, bn) as well as the interaction radius Ro of polystyrene (PS), polyvinylchloride (PVC) and low-density polyethylene (LDPE) are given below:PS : bD= 21 .3, bp = 5.8, bH= 4.3, Ro= 12.7PVC : bD= 17.4, bp = 7.8, bH= 3.8, Ro= 7.7PS : bD= 15, bp = 5.3, bH= 2.5, Ro= 10.1

[0027] Assume that the Hansen solubility parameters of the polymer material (bo.p , bp,P, H,P) and the Hansen solubility parameters of the solvent (bD,s,bp,s,bH.s) are given. Then, the distance Ra, the distance between the Hansen solubility parameters of the polymer material and the solvent in the Hansen space can be calculated using formula (1)

[0028] Further, assume that the polymer material has the value of an interaction radius Ro,Pand a sphere with a radius Ro,Pabout the Hansen solubility parameter coordinates of the polymer material is within the Hansen space. The relative energy difference (RED) is then represented by Ra / Ro.p. The polymer material is insoluble in the solvent in the case of RED > 1 , and is soluble in the case of RED < 1 .

[0029] In the method according to the present invention the solvent and polymer material are selected such that a relative energy difference (RED) between the polymer material and the solvent, represented by Ra / Ro,P, is less than 1 .

[0030] In particular embodiments a combination of polymer material and solvent is selected such that the relative energy difference (RED) between the polymer material and the solvent is less than 0.90, less than 0.70 or less than 0.60.

[0031] For the purpose of this invention, the at least one additive is considered to be insoluble in a substance (solvent) when the solubility of the at least one additive in the substance (solvent) is lower than 0.1 w / w %.

[0032] The solid particles typically have a particle size ranging between 2 nm and 5 pm, for example ranging between 5 nm and 3 pm, preferably ranging between 0.1 pm and 1 pm, forexample between 0.2 pm and 0.6 pm. The particle size can for example be determined using dynamic light scattering or light scattering image analysis.The method according to the present invention comprises the step of adding an organic compound to the suspension to obtain a supernatant comprising the dissolved at least one polymer material and a sediment comprising the at least one additive. The sediment comprises a solid residue. The sediment comprises heterocoagulated particles formed by physicochemical interactions of the solid particles and the organic compound.Heterocoagulation (or heteroaggregation) refers to a process in which particles of different composition, shape or surface charge coagulate / aggregate. Physicochemical interactions include for example electrostatic attraction or repulsion, Van der Waals forces and hydrogen bonding.

[0033] The organic compound is insoluble in the solvent.

[0034] Preferably, the organic compound is soluble in water.

[0035] The organic compound preferably comprises a polymeric chain having at least 5 carbon atoms. In preferred embodiments, the organic compound has a polymeric chain of at least 10 or at least 12 carbon atoms.

[0036] In particular embodiments, the organic compound comprises a polymeric chain comprising a primary unit of at least 5 carbon atoms, at least 6 carbon atoms, at least 10 carbon atoms or at least 12 carbon atoms.

[0037] Preferably, the organic compound has a molecular weight higher than 100 g / mol, for example higher than 200 g / mol, higher than 500 g / mol, higher than 1000 g / mol, higher than 2000 g / mol, higher than 3000 g / mol, higher than 5000 g / mol or higher than 10 000 g / mol.

[0038] The organic compound has a number of hydrogen bond donors (HBD) and a number of hydrogen bond acceptors (HBA), with the ratio HBD / HBA ranging from 0 to 1 , with 0 and 1 included. The ratio HBD / HBA is for example ranging from 0.1 to 1 , from 0.3 to 0.8 or from 0.3 to 0.7. The ratio HBD / HBA is for example 0, 0.1 , 0.3, 0.5 or 0.7.

[0039] A HBA is an atom or a group of atoms within a molecule that can accept a hydrogen bond from a hydrogen donor. HBAs are typically electronegative atoms, such as oxygen (O), nitrogen(N), or fluorine (F), which have a partial negative charge. These electronegative atoms attract the hydrogen atom of another molecule, forming a hydrogen bond. The acceptor atom must have a lone pair of electrons available for bonding. This lone pair interacts with the hydrogen atom, resulting in a relatively strong and directional interaction.

[0040] A HBD, on the other hand, refers to a molecule or atom that can donate a hydrogen bond. HBDs are typically atoms with a hydrogen atom bonded to an electronegative atom, such as oxygen(O) or nitrogen (N). The hydrogen atom in the donor molecule carries a partial positive charge due to the electronegativity difference between the hydrogen and the electronegative atom.

[0041] In case the absolute value of the zeta potential of the at least one additive is higher than 10 mV, for example higher than 20 mV, such as 30 mV or 40 mV, the organic compound (heterocoagulant) preferably has a zeta potential charge opposite in sign to the one of the at least one additive.

[0042] For a polymer material comprising TiO2 pigments, in particular R-105 TiO2 pigments, as additive good results were obtained using cyclohexanone as solvent and using cationic polyacrylamide (PAM+) as organic compound (fheterocoagulant). Experiments showed a maximum turbidity reduction of 95%. The zeta potential of R-105 TiO2 pigments in cyclohexanone is -37 mV, the zeta potential of PAM+ in cyclohexanone is + 15 mV.

[0043] Although applicant does not want to be bound by any theory, it is assumed that the organic compound facilitates the destabilization of the suspension of particles, creating a supernatant (comprising the dissolved at least one polymer material) and a (solid) sediment (comprising the at least one additive). The sediment comprises heterocoagulated particles having a size larger than the size of the solid particles present in the suspension. Preferably, the size of the heterocoagulated particles is at least 2 times the size of the solid particles, for example at least 5 times the size of the solid particles or at least 10 times the size of the solid particles.

[0044] The particles size of the aggregate particles typically increase from less than 1 pm (for example TiO2 0.25 - 0.35 pm) to larger than 1 pm. In a particular example the size of TiO2 particles is increased from 0.25-0.35 pm to 10 pm.

[0045] In particular embodiments, the method according to the present invention further comprises the step of separating the sediment from the supernatant. The sediment can be separated from the supernatant by any technique known in the art, for example by filtration, centrifugation or (gravity) sedimentation.

[0046] The method according to the present invention may further comprise the step of recovering the at least one polymer material from the supernatant and / or the step of recovering the at least one additive from the sediment.

[0047] The polymer material can be recovered from the supernatant by any technique known in the art, for example by precipitation or evaporation. A preferred method comprises precipitation by adding an anti-solvent. The anti-solvent is for example added to the (purified) supernatant. The ratio anti-solvent / solvent is typically 3:1 . This way the polymer material, having low affinity with the antisolvent will precipitate in a solid state. Subsequently, the precipitated polymer material can be recovered from the solvent / anti-solvent solution for example by filtration.

[0048] The additive(s) such as the pigments can be recovered from the sediment by any technique known in the art, for example by drying the sediment. In a preferred method to recover theadditive(s) first the organic compound, solvent and polymer residues are removed from the sediment. The organic compound can for example be removed by washing the sediment with water. The solvent can be removed by drying. Polymer residues can be washed away with a solvent, for example the same solvent used to dissolve the polymer material. Alternatively, the polymer residues can be removed by a thermal treatment whereby the polymer material is degraded by the high temperature (for example 500 °C).

[0049] Furthermore the method may comprise the step of recovering the organic compound. The organic compound may be recovered by washing the sediment with water, as the organic compound is typically soluble in water. The washing water will dissolve the organic compound and the organic compound can then be recovered from the water solution by drying.

[0050] These and further aspects and preferred embodiments of the invention are described in the following sections and in the appended claims. The subject-matter of the appended claims is hereby specifically incorporated in this specification.

[0051] As shown in the experimental section, the method according to the present invention allows to recover polymer material and / or additives that are insoluble in the polymer material. In particular the method according to the present invention allows to recover both polymer material and additives that are insoluble in the polymer material.

[0052] Experimental results further confirmed that the method according to the present invention results in recovering different types of polymer material and different types of additives such as pigment.

[0053] Further, the present method allows to recover polymer material not suffering from degradation.Brief description of the drawings

[0054] The present invention will be discussed in more detail below, with reference to the attached drawings, in which:Figure 1 shows zeta potential measurements of hydrophobic coated TiO2 in cyclohexanone;Figure 2 and Figure 3 show zeta potential measurements and particle size distribution of polyethylene glycol (PEG) in cyclohexanone;Figure 4, Figure 5, Figure 6, Figure 7 and Figure 8 show relative turbidity reduction measurements in simplified systems comprising a solvent, a pigment and an organic compound (heterocoagulant) according to the present invention;Figure 9, Figure 10, Figure 11 , Figure 12, Figure 13 show relative turbidity reduction measurements of a system comprising a polymer, a pigment, a solvent and an organic compound (heterocoagulant) according to the present invention;Figure 14 shows relative reduction measurements in a system comprising cyclohexanone and model PVC (1 w / w%) using PEG as organic compound (heterocoagulant);Figure 15 shows relative turbidity reduction measurements of a system comprising PS in xylene (1 w / w%) using PEG as organic compound (heterocoagulant);Figure 16 shows the particle size distribution of a sediment sample for a simplified system comprising xylene as solvent and TiO2 R-105 as pigment, when PEG was used as organic compound (heterocoagulant).Description of embodiments

[0055] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings are only schematic and are non-limiting. The size of some of the elements in the drawing may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0056] When describing the invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.

[0057] As used in the specification and the appended claims, the singular forms "a", "an," and "the" include plural referents unless the context clearly dictates otherwise. By way of example, "a step" means one step or more than one step.

[0058] The term ‘and / or’ when listing two or more items, means that any one of the listed items can by employed by itself or that any combination of two or more of the listed items can be employed.

[0059] The terms ‘first’, ‘second’ and the like used in the description as well as in the claims, are used to distinguish between similar elements and not necessarily describe a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0060] When referring to the endpoints of a range, the endpoints values of the range are included. The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1 , 2, 3, 4 when referring to, for example, a number of elements, and can also include 1 .5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of endpoints also includes the end point valuesthemselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.Plastic material

[0061] The plastic material to be used in the method of the present invention comprises at least one polymer material and at least one additive such as a pigment or filler. The plastic material comprises for example a polymer material comprising one or more polymers selected from the group consisting of polyolefins (such as polyethylene (PE), including low-density polyethylene (LDPE) and high-density polyethylene (HDPE), and polypropylene (PP)), polyethylene terephthalate (PET), polyurethane (PU), polyamide (PA), polystyrene (PS), polycarbonate (PC), ethyl vinyl alcohol (EVOH), ethylene vinyl acetate (EVA), polyvinyl chloride (PVC), and copolymers thereof.

[0062] The plastic material can be any plastic material including rigid plastic material such as bottles, trays or household items or non-rigid plastic material such as packaging, plastic bags, plastic labels, etc. The term plastic material also encompasses plastic waste, either rigid or non- rigid plastic waste. Plastic waste may comprise post-industrial plastic waste and post-consumer plastic waste. Post-industrial plastic waste includes plastic material that is used or produced in a manufacturing process and comprises for example plastic films such as stretch films. Post-industrial plastic waste usually comprises homogeneous material, composed of a single polymer type or of a limited number of polymer types and is usually clean. Post-consumer plastic waste includes plastic material that has already been used by the end user and comprises for example bottles, trays, plastic packaging and household items. Post-consumer plastic waste usually comprises a mixture of different polymer materials and may be highly contaminated and dirty. The polymer material possibly suffered from degradation during service life. Plastic material encompasses for example waste flows comprising polyvinyl chloride (PVC) based polymer material, polystyrene (PS) based polymer material or polyolefin based polymer material such as PE or PP, either rigid or non-rigid.

[0063] In particular embodiments, a plastic material comprises a plastic film. As used herein, a “plastic film” refers to a continuous polymer material, which is typically non-rigid or flexible, and usually thin.

[0064] The plastic material, for example plastic film, may be composed of one type of polymer material or comprise a blend of two or more types of polymers. In embodiments, the plastic material, or plastic film, comprises one or more polymers selected from the group comprising or consisting of a polyolefin (such as polyethylene (PE), including low-density polyethylene (LDPE) and high- density polyethylene (HDPE), and polypropylene (PP)), polyethylene terephthalate (PET), polyurethane (PU), polyamide (PA), polystyrene (PS), polycarbonate (PC), ethyl vinyl alcohol (EVOH), ethylene vinyl acetate (EVA), polyvinyl chloride (PVC), and copolymers thereof, preferably a polyolefin and / or PET.

[0065] In addition to said polymer material, the plastic material, or plastic film, may typically comprise contaminants and / or dirt. “Contaminants” as used herein, refer to components of the plastic material that are not part of the polymeric structure. Contaminants include, for example, but without limitation, additives, coatings such as barrier coatings, metal coatings or biocoatings, adhesives (e.g. glue), inks and labels such as plastic labels or paper labels. A particular group of additives comprises dyes and pigments. Pigments are defined as substances comprising small particles that are practically insoluble in their application system, i.e. polymer matrix. Pigments differ from dyes in that the latter are almost completely soluble in their application medium, i.e. polymer matrix.

[0066] As used herein, “dirt” refers to impurities that adhere to the plastic material, or plastic film, during their life cycle such as dust, soil, grease, organic waste, etc. In certain embodiments, the plastic material, or plastic film, comprises a metal material such as, for example, aluminium. In certain embodiments, the plastic material, or plastic film, comprises or is provided with ink. The ink, coating and / or adhesive layer that may be present in the plastic materials described herein can be composed of various types of polymers such as, without limitation, polyurethane, nitrocellulose, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate, methyl methacrylate / butyl methacrylate copolymer, polyvinyl butyral, poly(methyl methacrylate), poly(n- butyl methacrylate), hydroxyl containing copolymer of vinyl chloride and acid esters, polyvinyl acetate, acrylic polymers, etc.

[0067] The plastic material, or plastic film, may have a monolayer structure or a multilayer structure. As used herein, a “multilayer” plastic material or plastic film refers to a material or film comprising at least two plastic layers configured in an alternating arrangement to form a laminate structure. In particular embodiments, the plastic material, or plastic film, is a multilayer plastic material, or a multilayer plastic film, comprising at least two polymer layers, each polymer layer independently comprising one or more polymers selected from the group comprising or consisting of a polyolefin (such as polyethylene (PE), including low-density polyethylene (LDPE) and high- density polyethylene (HDPE), and polypropylene (PP)), polyethylene terephthalate (PET), polyurethane (PU), polyamide (PA), polystyrene (PS), polycarbonate (PC), ethyl vinyl alcohol (EVOH), ethylene vinyl acetate (EVA), polyvinyl chloride (PVC), and copolymers thereof, preferably a polyolefin and / or PET.

[0068] The multiple plastic layers may be adhered to one another by means of an adhesive layer, e.g. a glue. The two or more plastic layers may be the same or distinct from each other. For example, a multilayer plastic material or plastic film may comprise two PE layers, or a PET layer and a PE layer. In certain embodiments, a multilayer plastic material is used comprising at least two different plastic layers. A multilayer plastic material or plastic film may further comprise a nonplastic layer such as a metal or metallised layer (e.g. an aluminium layer), or a coating layer (e.g. a varnish). For example, a multilayer plastic material or plastic film may comprise a PET layer and a PE layer, and an Al layer between these polymer layers.

[0069] In certain embodiments, the plastic material, or plastic film, comprises or is provided with ink. Ink may be provided on an outer surface of a plastic material or plastic film, or may be covered by one or more layers. For examples, ink may be provided between two plastic layers of a multilayer plastic material, or between a plastic layer and a coating. Ink can also be embedded in a layer, such as a polymer based layer, a varnish, or barrier layer. The ink can be applied on the plastic material by any technique known in the art, for example a printing technique. The main ingredients of inks are pigments, dyes, solvents, binders and additives, for example surfactants and / or solubilizers. Pigments (organic or inorganic) or dyes give color and opacity to the ink and may influence the fluidity of the ink. Binders, usually low-molecular-weight polymeric resins, disperse the pigments and retain them on the plastic surface after printing. The solvent is a liquid, providing fluidity and allowing the transfer of the ink from the printing system to the substrate. Additives in the ink may for example comprise waxes, surfactants, drying agents and antioxidizing agents.

[0070] As mentioned above the plastic material comprises at least one additive. The at least one additive comprises preferably solid particles, either inorganic or organic solid particles. It is clear that the plastic material may comprise more than one additive.

[0071] The additives have preferably have a particle size ranging between 2 nm and 5 pm, for example ranging between 5 nm and 3 pm, preferably ranging between 0.1 pm and 1 pm, for example between 0.2 pm and 0.6 pm. The particle size can for example be determined using dynamic light scattering or light scattering image analysis.

[0072] In particular methods according to the present invention it is an object to recover the at least one additive from the plastic material. As mentioned above the at least one additive is not soluble in the solvent used in the contacting step wherein the plastic material is brought in contact with the solvent.

[0073] The at least one additive comprises for example one or more pigment(s), one or more filler(s) and / or one or more impact modifier(s). In particular embodiments the plastic material comprises a combination of one or more pigment(s), one or more filler(s) and possibly also one or more impact modifier(s).

[0074] Pigments are defined as small particles that are practically insoluble in their application system, i.e. in the polymer material.

[0075] The main reason for incorporating pigments into plastic material is to introduce colour, either for aesthetic reasons and market appeal or because of functional reasons. However, the optical role of a pigment can be broader than simply providing colour, as it plays a critical role in determining whether the material is opaque or transparent. Pigments, for example TiO2 or carbon black, can also perform useful functions beyond their optical role, such as mechanical reinforcement or inhibition of polymer degradation. Some pigments such as TiO2 are used for UV protection.

[0076] Pigments can be incorporated into plastics by a variety of methods. Direct dry colouring, in which the pigment is incorporated into the molten polymer often along with other additives using high-shear dispersing equipment, can be used. An other method comprises the use of predispersed concentrates of masterbatches of pigments. A masterbatch is a concentrated mixture of pigments and additives dispersed into a carrier resin, typically in pellet form. The masterbatch pellets are mixed with the raw plastic material during processing (such as extrusion, injection molding, or blow molding) to introduce color.

[0077] Pigments are conveniently classified as either inorganic or organic. Examples of inorganic pigments comprise metal oxides such as titanium dioxide (TiO2, rutile or anatase), iron oxide, chromium oxide; mixed metal oxides; ferrites as for example cobalt ferrite; spinels as for example COAI2O4 or CrAhO4; zirconium based pigments as for example ZrSiO4; cadmium based pigments such as CdS; vanadates such as bismuth vanadate, chromates such as lead chromate and carbon black. Examples of organic pigments comprise azo compound (mono- or di-azo compounds), polycyclic compounds and metal complexes. Particular examples of azo-compounds comprise for example dinitroaniline orange and ortho-nitroaniline orange. Other examples of organic pigments comprise triaryl carbonium pigments (e.g. Pigment Blue 1 , Pigment Violet 3), anthraquinone pigments (e.g. Pigment Red 177), dioxazine pigments (Pigment Violet), quinophthalone (e.g. Pigment Yellow 138) and copper phthalocyanine blue pigments (Pigment blue 15:3).

[0078] Fillers are like pigments solid materials that are added to the application medium, i.e. to the polymer material to improve the properties of the system or to reduce the consumption of more expensive binder components. Like pigments, fillers are insoluble in the medium used. Preferred examples comprise calcium carbonate, talk, clay, zinc oxide, (phyllo)silicates such as mica, metal powders, wood powders, asbestos, barium sulphate, glass microspheres and silicious earth.

[0079] Impact modifiers, are compounds that are added to polymer material during the manufacturing process to improve their mechanical and physical properties, for example to improve the material’s toughness and to enhance its resistance to various environmental factors. They are commonly used to boost impact strength, chemical resistance, hydrolysis resistance, and heat resistance in polymers. Preferred examples comprise nuclear-coated acrylic copolymers, maleic anhydride grafted polymers and styrene-butadiene block copolymers.Solvent

[0080] As mentioned above, in order to obtain dissolution of the polymer material in the solvent, the solvent has to meet certain requirements. It is clear that the solvent has to be chosen in function of the polymer material. The solvent is chosen in order to obtain a relative energy difference (RED) between the polymer material and the solvent represented by Ra / Ro,p being less than 1 .

[0081] It will be understood in the context of the present invention, that also mixtures or combinations of organic solvents may be used.

[0082] Examples of solvents comprise toluene, xylene (for example o-xylene), limonene (for example D-limonene), benzene, chlorobenzene, cymene (for example p-cymene), cyrene, pyridine, anisole, cymene (for example p-cymene), valerolactone (for example y-valerolactone), cyclopentyl, methyl ether, butyl benzoate, diethyl carbonate ethyl acetate, butyl acetate, geranyl acetate, tetrahydrofuran (THF), methyltetrahydrofuran, diethyl ketone, cyclohexanone and methylisobutylketone, octane (n-octane) and cyclohexane.

[0083] Some particularly preferred combinations of polymer material and solvents are specified in Table 1 . For each combination the RED is specified.Table 1Organic compound

[0084] Examples of suitable organic compounds comprise polyethylene glycol (PEG), sodium dodecyl sulfate (SDS), cationic polyacrylamide (PAM+), non-ionic polyacrylamide, polysorbate (for example TWEEN 80), polydiallyldimethylammonium chloride (polyDADMAC) and biopolymers (for example cellulose and starch).

[0085] The organic compound can be added to the suspension comprising the solution and solid particles in different ways, for example pure or as a suspension. In case the organic compound is added as a suspension, either the same solvent used in the contacting step, i.e. the step to dissolve the polymer material or a different solvent can be used..Contacting step

[0086] For an efficient recycling process, it is of importance that the plastic material is in mutual contact with the solvent. Therefore, in the method of the present invention, the plastic material is contacted with the solvent to form a mixture. The mixture comprises the plastic material and thesolvent. While the contacting proceeds, the at least partially dissolved polymer material and / or the at least one additive will be present in the mixture. Possibly, also ink, glue and / or other components present in the plastic material will be present in the mixture as well

[0087] The contacting step may be carried out e.g. by immersing the plastic material in the solvent. For example, the plastic material may be introduced in a container and the solvent may be added, or the plastic material may be introduced in a container wherein the solvent was previously introduced.

[0088] Preferably, the concentration of the plastic material in the solvent is lower than 15 w / w%, for example lower than 10 w / w%, for example 5 w / w%.

[0089] It has been found that for the recovering of particular polymer material and / or particular additives higher temperatures during the contacting step may favour the dissolution of the polymer material. The temperature is for example 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C, 120 °C or 150°C. It is clear that the temperature is limited by the boiling point of the solvent.

[0090] In particular embodiments of the present invention, the method further comprises mechanically agitating the mixture while the plastic material is contacted with the solvent. By such mechanically agitation the efficiency of the dissolution process may increase and / or the contact time needed may decrease considerably. In certain embodiments, the mechanical agitation such as the stirring, is continued as long as the plastic material is contacted with the solvent. Mechanical agitation can be applied by any method known in the art. For example, the mixture may be stirred (e.g. magnetic stirring, stirring in a continuous stirred tank reactor (CSTR) using a rotating agitator), mixed, or (high-intensity) sonication may be applied. In particular embodiments, the plastic material is contacted with the solvent under stirring, preferably the plastic material is contacted with the solvent under stirring at 300 rpm or more, more preferably at 500 rpm or more.

[0091] As noted above, temperature, mechanical agitation of the mixture, volume ratio of the solvent, etc. may influence the efficiency of the process and as such determine the contact time needed to achieve dissolution.Pre-treatment step(s)

[0092] Dissolution may also be faster and more efficient by using smaller sizes of plastic material due to higher diffusion rates. Therefore, in certain embodiments, the method may comprise an additional step of reducing the size of the plastic material before the contacting step. Too small sizes on the other hand may become unpractical. In particular embodiments, the plastic material may be reduced in size to obtain plastic material having a sieve diameter between 0.01 cm and 20.00 cm, for example between 0.01 cm and 10.00 cm, between 0.10 cm and 10.0 cm or between 0.10 cm and 4.00 cm, preferably between 0.50 cm and 4.00 cm. The term ‘sieve diameter’ refers to the size of a sieve opening (the width of a square aperture) through which a particle will pass.Techniques for reducing the size of a plastic material are well-known to the skilled person and may include, for example, cutting, shredding, milling and / or grinding.

[0093] The plastic material, in particular plastic waste, may also or further be subjected to one or more other pre-treatment steps before the contacting step. For example, paper or cardboard may be removed from the plastic material, and / or the plastic material may be sorted. Polymer sorting techniques include, for example, wind shifting, density separation and / or near infra-red (NIR) separation, and as known to the skilled person. Other pretreatment step may comprise the washing of the plastic material, for example with a water-based medium to remove impurities like organic matter, preferably followed by a drying step.Addition of an organic compound to the suspension

[0094] Preferably, the organic compound is added to the suspension in a concentration ranging between 0.001 w / w % and 2 w / w %, for example in a concentration of 0.003 w / w %, 0.01 w / w %, 0.05 w / w %, 0.1 w / w %, 0.5 w / w %, 1 w / w % or 1 .8 w / w %.

[0095] In embodiments, the method further comprises mechanically agitating the mixture while the organic compound is added or after the addition of the organic compound. Such mechanical agitation may promote the dispersion of the organic compound in the suspension. Mechanical agitation can be applied by any method known in the art. For example, the mixture may be stirred (e.g. magnetic stirring, stirring in a continuous stirred tank reactor (CSTR) using a rotating agitator), mixed, or (high-intensity) sonication may be applied. In particular embodiments, the plastic material is contacted with the solvent under stirring, preferably the plastic material is contacted with the solvent under stirring at 300 rpm or more, more preferably at 500 rpm or more.Examples

[0096] In order to understand the mechanism of the invention a simplified system containing only solvent and TiO2 pigments with different coatings was laboratory tested. Zeta potential measurement were performed. Figure 1 shows zeta potential measurements of hydrophobic coated TiO2 in cyclohexanone.

[0097] Zeta potential measurement and particle size distribution of polyethylene glycol (PEG) in cyclohexanone are shown in Figure 2 and 3.

[0098] Some organic compounds (polyethylene glycol (PEG), sodium dodecyl sulfate (SDS), cationic polyacrylamide (PAM+), non-ionic polyacrylamide, polysorbate (for example TWEEN 80), polydiallyldimethylammonium chloride (polyDADMAC) and biopolymers (for example cellulose and starch) were tested for different pigments (TiO2 pigment, in particular R-105 TiO2; Cr / Sb / Ti oxide based inorganic pigment known under the name Sicotan® Yellow K 2001 and an iron oxide based inorganic pigment known under the name Sicotrans® Red K 2915, carbon black and copper phthalocyanine blue (pigment blue 15:3)) in analogous simplified systems using different solvents(cyclohexanone, xylene, toluene and ethyl acetate). Quantification of pigment separation was performed via turbidity measurement in order to have a quantitative measure of the heterocoagulation efficiency.

[0099] The relative turbidity reduction measurement in a simplified system comprising xylene and TiO2 pigments (R-105 TiO2) using PEG as organic compound (heterocoagulant) at different concentrations is given in Figure 4.

[0100] The relative turbidity reduction measurement in a simplified system comprising cyclohexanone and Sicotrans® Red K 2915 using SDS as organic compound (heterocoagulant) at different concentrations is given in Figure 5.

[0101] The relative turbidity reduction measurement in a simplified system comprising cyclohexanone and Sicotan® Yellow K 2001 using PEG as organic compound (heterocoagulant) at different concentrations is given in Figure 6.

[0102] The relative turbidity reduction measurement in a simplified system comprising cyclohexanone and carbon black using SDS as organic compound (heterocoagulant) at different concentrations is given in Figure 7.

[0103] The relative turbidity reduction measurement in a simplified system comprising cyclohexanone and copper phthalocyanine blue (pigment blue 15:3) using PEG as organic compound (heterocoagulant) at different concentrations is given in Figure 8.

[0104] Further tests have been carried out, gradually increasing the complexity of the system. First dissolved polymer was added to a pigment solution. In subsequent test, a standard formulation of plastic material including other additives was tested. Tests were performed with PS and PVC as polymer material.

[0105] Figure 9 shows relative turbidity reduction measurements of a system comprising xylene and white (TiO2) PS (1 w / w%) using PEG as organic compound (heterocoagulant).

[0106] Figure 10 shows relative turbidity reduction measurements of a system compirsing xylene and whtie (TiO2) HIPS (5 w / w%) using PAM+ as organic compound (heterocoagulant).

[0107] Figure 11 shows relative turbidity reduction measurements of a system comprising xylene and yellow PS (5 w / w%) using PEG as organic compound (heterocoagulant).

[0108] Figure 12 shows relative turbidity reduction measurements of a system comprising xylene and red PS (5 w / w%) using SDS as organic compound (heterocoagulant).

[0109] Figure 13 shows relative turbidity reduction measurements of a system comprising cyclohexanone and white PVC (1 w / w%) using polyacrylamide (PAM+) as organic compound (heterocoagulant).

[0110] Model sample of standard formulation of PVC used for window profile was tested to assess the influence of other additives (e.g. CaCOs,) on the heterocoagulation process. Differentconcentrations and types or organic compounds (heterocoagulants) and polymer concentrations (thus also insoluble particles concentrations) were tested.

[0111] Figure 14 shows relative reduction measurements in a system comprising cyclohexanone and model PVC (1 w / w%) using PEG as heterocoagulant.

[0112] Finally, some tests were performed with real PVC waste from window profiles and waste(HI)PS from packaging. Figure 15 shows relative turbidity reduction measurements of a system comprising PS in xylene (1 w / w%) using PEG as heterocoagulant.

[0113] Particle size analysis of heterocoagulated TiO2 in simplified systems comprising solvent and TiO2 was performed in order to assess the influence of the organic compound (heterocoagulant) on particle size distribution.

[0114] Figure 16 shows the particle size distribution of a sediment sample for a simplified system comprising xylene as solvent and TiO2 R-105 as pigment, when PEG was used as organic compound.

[0115] Figure 17 shows relative turbidity reduction measurements of a system comprising LDPE (Low Density Polyethylene) (1w / w%), TiO2 as pigment, xylene as solvent and SDS as heterocoagulant, according to the present invention.

Claims

P2024 / 043-18-Claims1. A method for recovering at least one polymer material and / or at least one additive from a plastic material, the method comprising:- providing a plastic material comprising at least one polymer material and at least one additive,- providing a suitable solvent, whereby the at least one polymer material is soluble in the solvent whereas the at least one additive is not soluble in the solvent;- contacting the plastic material with the solvent to obtain a suspension comprising a solution and solid particles, the solution comprising the dissolved at least one polymer material and the solid particles comprise the at least one additive;- adding an organic compound to the suspension to obtain a supernatant and a sediment, the organic compound being insoluble in the solvent, the organic compound comprising a carbon-carbon chain having at least 5 carbon atoms, the organic compound having a number of hydrogen bond donors (HBD) and a number of hydrogen bond acceptors (HBA), with the ratio HBD / HBA ranging from 0 to 1 , the sediment comprising heterocoagulated particles formed by physicochemical interactions of the solid particles and the organic compound, the heterocoagulated particles having a size larger than the size of the solid particles.

2. The method according to claim 1 , wherein a relative energy difference (RED) between the polymer material and the solvent, represented by Ra / Ro.p, is less than 1 , with Ro.p being an interaction radius of the at least one polymer material in a Hansen space and with Rabeing a distance between Hansen solubility parameters of the polymer material and the solvent calculated using the formula a=yl^(^D.s ~ D,p) + (^P,s—p p) + 3H S— 8H pwith 8D S, 8P S6H Sbeing the Hansen solubility parameters of the solvent, and with 8D,P , 8p p - 8 i p being the Hansen solubility parameters of the at least one polymer material.

3. The method according to claim 1 or 2, wherein the solubility of the at least one additive in the solvent is lower than 0.1 w / w %.

4. The method according to any one of the preceding claims, wherein the at least one additive comprises inorganic or organic solid particles.P2024 / 043-19-5. The method according to any one of the preceding claims, wherein the at least one additive has a particle size ranging between 2 nm and 5 pm.

6. The method according to any one of the preceding claims, wherein the plastic material comprises a polymer material comprises one or more polymers selected from the group consisting of polyolefins (such as polyethylene (PE), including low-density polyethylene (LDPE) and high-density polyethylene (HDPE), and polypropylene (PP)), polyethylene terephthalate (PET), polyurethane (PU), polyamide (PA), polystyrene (PS), polycarbonate (PC), ethyl vinyl alcohol (EVOH), ethylene vinyl acetate (EVA), polyvinyl chloride (PVC), and copolymers thereof.

7. The method according to any one of the preceding claims, wherein the solvent is selected from the group consisting of toluene, xylene (o-xylene), limonene (D-limonene), benzene, chlorobenzene, cymene (p-cymene), cyrene, pyridine, anisole, cymene (p-cymene), valerolactone (y-valerolactone), cyclopentyl, methyl ether, butyl benzoate, diethyl carbonate ethyl acetate, butyl acetate, geranyl acetate, tetra hydrofuran (THF), methyltetrahydrofuran, diethyl ketone, cyclohexanone and methylisobutylketone, octane (n-octane) and cyclohexane.

8. The method according to any one of the preceding claims wherein the organic compound is selected from the group consisting of polyethylene glycol (PEG), sodium dodecyl sulfate (SDS), cationic polyacrylamide (PAM+), non-ionic polyacrylamide, polysorbate (for example TWEEN 80), polydiallyldimethylammonium chloride (polyDADMAC) and biopolymers (for example cellulose and starch).

9. The method according to any one of the preceding claims, wherein the concentration of the plastic material in the solvent is lower than 15 w / w%.

10. The method according to any one of the preceding claims, wherein the plastic material and the solvent are contacted under mechanical agitation, preferably under stirring, more preferably wherein the plastic material is contacted with solvent at 300 rpm or more, more preferably at 500 rpm or more.

11. The method according to any one of the preceding claims, wherein the plastic material is contacted with the solvent at a temperature ranging between 20 °C and 150°C.

12. The method according to any one of the preceding claims wherein the organic compound is added to the suspension in a concentration ranging between 0.001 w / w % and 2 w / w%.P2024 / 043-20-13. The method according to any one of the preceding claims, further comprising the step of separating the sediment from the supernatant.

14. The method according to any one of the preceding claims, further comprising the step of recovering the at least one polymer material from the supernatant and / or recovering the at least one additive from the sediment.

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