WO2025068267A1

WO2025068267A1 - A mechanical polypropylene recycling process

Info

Publication number: WO2025068267A1
Application number: PCT/EP2024/076906
Authority: WO
Inventors: Alexandra Romina ALBUNIA; Peter Denifl; Bernadette DUSCHER; Anthony BERTHELIER; Baris KAYNAK; Manuel NUNEZ; Paul Baumann; Dietmar SALABERGER
Original assignee: Borealis GmbH
Current assignee: Borealis GmbH
Priority date: 2023-09-27
Filing date: 2024-09-25
Publication date: 2025-04-03
Anticipated expiration: 2026-03-27

Abstract

A mechanical polypropylene recycling process for achieving high purity recyclate grades, a mixed-plastic polypropylene blend corresponding to said high purity recyclate grades, articles containing said high purity recyclate grades and use of said high purity recyclate grades for the production of polypropylene labels.

Description

A mechanical polypropylene recycling process

Field of the Invention

The present invention relates to a mechanical polypropylene recycling process for achieving high purity recyclate grades, a mixed-plastic polypropylene blend corresponding to said high purity recyclate grades, articles containing said high purity recyclate grades and use of said high purity recyclate grades for the production of polypropylene labels.

Background to the Invention

During the last decade, concern about plastics and the environmental sustainability of their use in current quantities has grown. This has led to new legislation on disposal, collection and recycling of polyolefins. There have additionally been efforts in a number of countries to increase the percentage of plastic materials being recycled instead of being sent to landfill.

In Europe, plastic waste accounts for approximately 27 million tons of waste a year; of this amount in 2016, 7.4 million tons were disposed of in landfill, 11.27 million tons were burnt (in order to produce energy) and around 8.5 million tons were recycled. Polypropylene based materials are a particular problem as these materials are extensively used in packaging. Taking into account the huge amount of waste collected compared to the amount of waste recycled back into the stream (amounting to only about 30 %), there is still a great potential for intelligent reuse of plastic waste streams and for mechanical recycling of plastic wastes.

Taking the automobile industry as an example. In Europe the end of life (ELV) directive from the EU states, that 85%/95% of materials from vehicles should be recyclable or recoverable. The present rate of recycling of automobile components is significantly below this target. On average vehicles consist of 9 wt.-% plastics, out of this 9 wt.-% only 3 wt.-% is currently recycled. Therefore, there is still a need to be met if targets for recycling plastics in the automobile industry are to be achieved. This invention particularly focuses on mechanically recycled waste streams as opposed to “energetic recycling” where polyolefins are burnt and used for energy. However, due to cost reasons, poor mechanical properties and inferior processing properties waste streams containing cross-linked polyolefins are often used for energy recovery (e.g. incineration in a district heating plant or for heat generation in the cement industry) and are less often recycled into new products. One major trend in the field of polyolefins is the use of recycled materials that are derived from a wide variety of sources. Durable goods streams such as those derived from waste electrical equipment (WEE) or end-of-life vehicles (ELV) contain a wide variety of plastics. These materials can be processed to recover acrylonitrile-butadiene-styrene (ABS), high impact polystyrene (HIPS), polypropylene (PP) and polyethylene (PE) plastics. Separation can be carried out using density separation in water and then further separation based on fluorescence, near infrared absorption or Raman fluorescence. However, it is commonly quite difficult to obtain either pure recycled polypropylene or pure recycled polyethylene. Generally, recycled quantities of polypropylene on the market are mixtures of both polypropylene (PP) and polyethylene (PE); this is especially true for post-consumer waste streams. Commercial recyclates from post-consumer waste sources have been found generally to contain mixtures of PP and PE, the minor component reaching up to < 50 wt.-%.

The better the quality, i.e. the higher the purity, of the recycled polyolefin the more expensive the material is. Moreover, recycled polyolefin materials are often cross-contaminated with non-polyolefin materials, such as polyethylene terephthalate, polyamide, and polystyrene or non-polymeric substances like wood, paper, glass or aluminium.

In addition, recycled polypropylene rich materials normally have properties that are much worse than those of the virgin materials are, unless the amount of recycled polyolefin added to the final compound is extremely low. For example, such materials often have poor performance in odor and taste, limited stiffness, limited impact strength and poor mechanical properties (such as e.g. brittleness) thus, they do not fulfil customer requirements.

For certain applications, the polymer grade will need to be of high purity and meeting strict requirements, which is often difficult to achieve when employing recyclates for the reasons described above. Polypropylene labels are one such application. In addition to the requirements for balanced mechanical properties and high purity, polypropylene labels are often required to be white or transparent. As such, the development of recycling processes that yield high purity recyclates having a desirable balance of properties (including color) is important for allowing recyclates to be used in a broader range of applications. Summary of the Invention

The present invention is based on the observation that high levels of purity can be achieved via a mechanical recycling process that involves providing a precursor polypropylene recycling stream specifically being made up of polypropylene labels and undertaking a particular combination of washing steps, with the combination of the correctly provided starting material and the washing contributing to the unexpectedly impressive properties of the final polypropylene recy elate.

Thus, in a first aspect, the present invention is directed to a mechanical polypropylene recycling process comprising, in the given order, the steps of: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); b) optionally sorting the precursor polypropylene recycling stream (A) by polymer type, thereby removing any pieces that contain polymers other than polypropylene, thereby generating a purified polypropylene recycling stream (B); c) washing the purified polypropylene recycling stream (B) or, in the case that step b) is absent, the precursor polypropylene recycling stream (A), in one or more washing steps, thereby obtaining a washed polypropylene stream (C); d) optionally separating the washed polypropylene stream (C) into a heavy fraction and a light fraction polypropylene recycling stream (D); e) melt extruding, preferably pelletizing, the light fraction polypropylene recycling stream (D) or, in the case that step d) is absent, the washed polypropylene stream (C), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, recycled polypropylene composition (E); and f) optionally aerating the recycled polypropylene composition (E) to remove volatile organic compounds, thereby generating an aerated extruded recycled polypropylene product (Fl); wherein the order of steps f) and e) can be interchanged, such that the light fraction polypropylene recycling stream (D) or, in the case that step d) is absent, the washed polypropylene stream (C) is first aerated to form aerated recycled polypropylene flakes (F2) that are subsequently extruded, preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, aerated recycled polypropylene product (F3).

In a second aspect, the present invention is directed to a mixed-plastic polypropylene blend (PP) having a melt flow rate (MFR₂), determined according to ISO 1133 at 230 °C and 2.16 kg, in the range from 3.5 to 8.0 g/10 min, wherein the polymeric part of said mixed-plastic polypropylene blend (PP) has: i) an ethylene content (C2(total)), determined according to CRYSTEX QC analysis, in the range from 0.0 to 5.0 wt.-%; ii) a crystalline fraction (CF) content, determined according to CRYSTEX QC analysis, in the range from 93.0 to 100.0 wt.-%; iii) a soluble fraction (SF) content, determined according to CRYSTEX QC analysis, in the range from 0.0 to 7.0 wt.-%; and iv) an ethylene content of the crystalline fraction (C2(CF)), determined according to CRYSTEX QC analysis, in the range from 0.0 to 5.0 wt.-%.

It is particularly preferred that the process of the first aspect produces a mixed-plastic polypropylene blend (PP) of the second aspect.

It is also preferred that the mixed-plastic polypropylene blend (PP) of the second aspect is produced by the process of the first aspect.

In a third aspect the present invention is directed to articles comprising the mixed-plastic polypropylene blend (PP) of the second aspect, wherein the articles are selected from the group consisting of labels and films.

In a final aspect, the present invention is directed to the use of the mixed-plastic polypropylene blend (PP) of the second aspect for the production of polypropylene labels containing recycled material. Definitions

Post-consumer waste refers to objects having completed at least a first use cycle (or life cycle), i.e. having already served their first purpose; while industrial waste refers to manufacturing scrap, which does not normally reach a consumer.

Recycling streams may contain both articles for recycling and fragments of articles for recycling, for example flakes. In the context of the present invention, the content of the recycling streams will be referred to as pieces, irrespective of whether these pieces are whole articles, fragments thereof, or flakes thereof. In certain embodiments, the pieces may be flakes, whereas in other embodiments pieces may be larger objects that may be converted into flakes at a later stage.

In the context of the present invention, a mixed plastic recycling stream may be any stream suitable for recycling, wherein polyolefin is present and the stream does not only contain a single polyolefin product, as would be the case, for example, for certain post-industrial waste recycling streams wherein the production waste of a single polyolefin grade, or a single polyolefin-containing article may be the only piece present in the stream. Generally speaking, polyolefin-containing post-consumer waste recycling streams will be mixed plastic recycling streams, as will many polyolefin-containing post-industrial waste recycling streams. A “polyolefin recycling stream” according to the present invention may be a mixed- plastic recycling stream or it may have already undergone a pre-sorting process whereby it has been enriched in a particular type of polyolefin. Alternatively or additionally, the polyolefin recycling stream may have a high purity of one type of polyolefin due to optimized waste collection management, wherein only certain types of waste are collected into a given recycling stream.

The term “article form”, as used herein, refers to the shape and form of articles present in a polyolefin recycling stream. Such articles may be present, inter alia, in the form of films, bags, and pouches, which may be considered as flexible articles, and, inter aha, in the form of molded articles such as food containers, skin-care product containers, and plastic bottles, which may be considered as rigid articles. Commercial optical sorters, such as Tomra Autosort, RTT Steinert Unisort, and Redwave Pellenc, are able to separate so-called rigid articles from so-called flexible articles via their aerodynamic properties (i.e. a stream of gas is typically applied to the stream and those articles being rigid articles will fall with a different arc than flexible articles), converting streams containing such articles into so-called rigid streams and flex streams.

Furthermore, the skilled person would be aware that state of the art sorting processes, such as those involving automated sorters of the type discussed below, do not result in perfect sorting, meaning that any wording such as “wherein the stream contains only a single color” or “wherein the stream contains only a single polyolefin type” are to be interpreted broadly, wherein the streams thus described contain substantially only the stated color or polyolefin type, but are not 100% pure due to technical limitations of the sorting steps.

The person skilled in the art would be aware that pH values of greater than 14.0 and lower than 0.0 are theoretically possible; however, they would also be aware that the determination of such pH values is incredibly difficult using conventional pH probes. As such, in the context of this invention, aqueous solutions having an effective pH of greater than 14.0 are considered to have a pH of 14.0 and aqueous solutions having an effective pH of lower than 0.0 are considered to have a pH of 0.0.

In the context of the present invention, the term “rinse” is used to indicate the addition of a solvent, typically water, which is used to remove foreign material or remaining liquid from the surface of the polyolefin. This can be achieved in very short times, i.e. less than 5 minutes, often less than 1 minute, in contrast to “washing” steps that typically require a longer time, and agitation, to remove adherent foreign material from the surface of the polyolefin and potentially extract volatile organic compounds from the polyolefin.

Where the term "comprising" is used in the present description and claims, it does not exclude other non-specified elements of major or minor functional importance. For the purposes of the present invention, the term "consisting of is considered to be a preferred embodiment of the term "comprising of. If hereinafter a group is defined to comprise at least a certain number of elements, this is also to be understood to disclose a group, which preferably consists only of these elements.

Where an indefinite or definite article is used when referring to a singular noun, e.g. "a", "an" or "the", this includes a plural of that noun unless something else is specifically stated.

Detailed Description

The mechanical polypropylene recycling process

In a first aspect, the present invention is directed to a mechanical polypropylene recycling process comprising, in the given order, the steps of: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); b) optionally sorting the precursor polypropylene recycling stream (A) by polymer type, thereby removing any pieces that contain polymers other than polypropylene, thereby generating a purified polypropylene recycling stream (B); c) washing the purified polypropylene recycling stream (B) or, in the case that step b) is absent, the precursor polypropylene recycling stream (A), in one or more washing steps, thereby obtaining a washed polypropylene stream (C); d) optionally separating the washed polypropylene stream (C) into a heavy fraction and a light fraction polypropylene recycling stream (D); e) melt extruding, preferably pelletizing, the light fraction polypropylene recycling stream (D) or, in the case that step d) is absent, the washed polypropylene stream (C), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, recycled polypropylene composition (E); and f) optionally aerating the recycled polypropylene composition (E) to remove volatile organic compounds, thereby generating an aerated extruded recycled polypropylene product (Fl); wherein the order of steps f) and e) can be interchanged, such that the light fraction polypropylene recycling stream (D) or, in the case that step d) is absent, the washed polypropylene stream (C) is first aerated to form aerated recycled polypropylene flakes (F2) that are subsequently extruded, preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, aerated recycled polypropylene product (F3).

In one embodiment, the process comprises the following steps in the given order: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); c) washing the precursor polypropylene recycling stream (A) in one or more washing steps, thereby obtaining a washed polypropylene stream (C); and e) melt extruding, preferably pelletizing, the washed polypropylene stream (C), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, recycled polypropylene composition (E).

In another embodiment, the process comprises the following steps in the given order: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); b) sorting the precursor polypropylene recycling stream (A) by polymer type, thereby removing any pieces that contain polymers other than polypropylene, thereby generating a purified polypropylene recycling stream (B); c) washing the purified polypropylene recycling stream (B) in one or more washing steps, thereby obtaining a washed polypropylene stream (C); and e) melt extruding, preferably pelletizing, the washed polypropylene stream (C), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, recycled polypropylene composition (E).

In yet another embodiment, the process comprises the following steps in the given order: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); c) washing the precursor polypropylene recycling stream (A) in one or more washing steps, thereby obtaining a washed polypropylene stream (C); d) separating the washed polypropylene stream (C) into a heavy fraction and a light fraction polypropylene recycling stream (D); and e) melt extruding, preferably pelletizing, the light fraction polypropylene recycling stream (D), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, recycled polypropylene composition (E).

In a further embodiment, the process comprises the following steps in the given order: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); c) washing the precursor polypropylene recycling stream (A) in one or more washing steps, thereby obtaining a washed polypropylene stream (C); e) melt extruding, preferably pelletizing, the washed polypropylene stream (C), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, recycled polypropylene composition (E); and f) aerating the recycled polypropylene composition (E) to remove volatile organic compounds, thereby generating an aerated extruded recycled polypropylene product (Fl).

In yet a further embodiment, the process comprises the following steps in the given order: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); c) washing the precursor polypropylene recycling stream (A) in one or more washing steps, thereby obtaining a washed polypropylene stream (C); f) aerating the washed polypropylene stream (C) to remove volatile organic compounds, thereby generating aerated recycled polypropylene flakes (F2); and e) melt extruding, preferably pelletizing, the aerated recycled polypropylene flakes (F2), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, aerated recycled polypropylene product (F3). In another embodiment, the process comprises the following steps in the given order: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); b) sorting the precursor polypropylene recycling stream (A) by polymer type, thereby removing any pieces that contain polymers other than polypropylene, thereby generating a purified polypropylene recycling stream (B); c) washing the purified polypropylene recycling stream (B) in one or more washing steps, thereby obtaining a washed polypropylene stream (C); d) separating the washed polypropylene stream (C) into a heavy fraction and a light fraction polypropylene recycling stream (D); and e) melt extruding, preferably pelletizing, the light fraction polypropylene recycling stream (D), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, recycled polypropylene composition (E).

In yet another embodiment, the process comprises the following steps in the given order: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); b) sorting the precursor polypropylene recycling stream (A) by polymer type, thereby removing any pieces that contain polymers other than polypropylene, thereby generating a purified polypropylene recycling stream (B); c) washing the purified polypropylene recycling stream (B) in one or more washing steps, thereby obtaining a washed polypropylene stream (C); e) melt extruding, preferably pelletizing, the washed polypropylene stream (C), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, recycled polypropylene composition (E); and f) aerating the recycled polypropylene composition (E) to remove volatile organic compounds, thereby generating an aerated extruded recycled polypropylene product (Fl). In a further embodiment, the process comprises the following steps in the given order: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); b) sorting the precursor polypropylene recycling stream (A) by polymer type, thereby removing any pieces that contain polymers other than polypropylene, thereby generating a purified polypropylene recycling stream (B); c) washing the purified polypropylene recycling stream (B) in one or more washing steps, thereby obtaining a washed polypropylene stream (C); f) aerating the washed polypropylene stream (C) to remove volatile organic compounds, thereby generating aerated recycled polypropylene flakes (F2); and e) melt extruding, preferably pelletizing, the aerated recycled polypropylene flakes (F2), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, aerated recycled polypropylene product (F3).

In yet a further embodiment, the process comprises the following steps in the given order: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); c) washing the precursor polypropylene recycling stream (A), in one or more washing steps, thereby obtaining a washed polypropylene stream (C); d) separating the washed polypropylene stream (C) into a heavy fraction and a light fraction polypropylene recycling stream (D); e) melt extruding, preferably pelletizing, the light fraction polypropylene recycling stream (D), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, recycled polypropylene composition (E); and f) aerating the recycled polypropylene composition (E) to remove volatile organic compounds, thereby generating an aerated extruded recycled polypropylene product (Fl). In another further embodiment, the process comprises the following steps in the given order: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); c) washing the precursor polypropylene recycling stream (A), in one or more washing steps, thereby obtaining a washed polypropylene stream (C); d) separating the washed polypropylene stream (C) into a heavy fraction and a light fraction polypropylene recycling stream (D); f) aerating the light fraction polypropylene recycling stream (D) to remove volatile organic compounds, thereby generating aerated recycled polypropylene flakes (F2); and e) melt extruding, preferably pelletizing, the aerated recycled polypropylene flakes (F2), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, aerated recycled polypropylene product (F3).

In yet another further embodiment, the process comprises the following steps in the given order: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); b) sorting the precursor polypropylene recycling stream (A) by polymer type, thereby removing any pieces that contain polymers other than polypropylene, thereby generating a purified polypropylene recycling stream (B); c) washing the purified polypropylene recycling stream (B) in one or more washing steps, thereby obtaining a washed polypropylene stream (C); d) separating the washed polypropylene stream (C) into a heavy fraction and a light fraction polypropylene recycling stream (D); e) melt extruding, preferably pelletizing, the light fraction polypropylene recycling stream (D), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, recycled polypropylene composition (E); and f) aerating the recycled polypropylene composition (E) to remove volatile organic compounds, thereby generating an aerated extruded recycled polypropylene product (Fl). In a final embodiment, the process comprises the following steps in the given order: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene -containing labels, based on the total weight of the precursor polypropylene recycling stream (A); b) sorting the precursor polypropylene recycling stream (A) by polymer type, thereby removing any pieces that contain polymers other than polypropylene, thereby generating a purified polypropylene recycling stream (B); c) washing the purified polypropylene recycling stream (B) in one or more washing steps, thereby obtaining a washed polypropylene stream (C); d) separating the washed polypropylene stream (C) into a heavy fraction and a light fraction polypropylene recycling stream (D); f) aerating the light fraction polypropylene recycling stream (D) to remove volatile organic compounds, thereby generating aerated recycled polypropylene flakes (F2); and e) melt extruding, preferably pelletizing, the aerated recycled polypropylene flakes (F2), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, aerated recycled polypropylene product (F3).

Without wishing to be bound by theory, it is believed that conducting step f) before step e) can be advantageous since the improved surface area to volume ratio of the polypropylene flakes means that more volatile organic compounds can be removed, whilst conducting step e) before step f) can be advantageous since extrusion can generate new volatile organic compounds through decomposition of the polypropylene or contaminants (e.g. PVC or PET), or can allow volatile organic compounds that were not near the surface of the flakes to migrate to the surface of the extruded product, thereby increasing the odor. Which embodiment is preferable will differ from process to process and should be optimized accordingly.

Step a) involves the provision of a precursor polypropylene recycling stream (A).

This precursor polypropylene recycling stream (A) contains at least 85 wt.-% of polypropylene -containing labels, more preferably at least 90 wt.-% of polypropylene- containing labels, yet more preferably at least 95 wt.-% of polypropylene-containing labels, based on the total weight of the precursor polypropylene recycling stream (A), most preferably the precursor polypropylene recycling stream (A) consists essentially of polypropylene-containing labels.

The use of a label-containing precursor polypropylene recycling stream (A) is one of the key steps that underlies the present invention. Polypropylene-containing labels typically encountered on the market are manufactured from polypropylene grades, such as propylene homopolymers, with these grades being the primary component in multilayer labels (typically approx. 80-90 wt.-% of common multilayer labels). As such, when recycled in an appropriate recycling process, the resultant recyclate is very homogeneous in terms of polymer properties such as molecular weight (typically a low MFR2 of 1 to 5 g/10 min) and comonomer content (minimal, due to predominance of propylene homopolymer).

The precursor polypropylene recycling stream (A) and the polypropylene-containing labels of the precursor polypropylene recycling stream (A) preferably originate from postconsumer waste.

The provision of the precursor polypropylene recycling stream (A) may be achieved in a number of ways.

In its broadest sense, the manner in which the precursor polypropylene recycling stream (A) is provided is not critical, so long as the precursor polypropylene recycling stream (A) contains at least 85 wt.-% of polypropylene-containing labels. As such, whilst some embodiments of the process according to the first aspect involve a step or steps by which the polypropylene-containing labels are obtained via sorting from other polymer-based articles, other embodiments of the present invention may involve simply buying a precursor polypropylene recycling stream (A), for example from a PET-recycling organization. Such embodiments where the sorting step has taken place previously, often at a different location and by a different person/by different people, still fall within the scope of the present invention, since key requirement of step a) is that a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene-containing labels is provided, irrespective of the manner in which the precursor polypropylene recycling stream (A) is obtained.

In certain embodiments, the provision of the precursor polypropylene recycling stream (A) involves the sorting of polypropylene-containing labels from other polymer-based articles.

Polypropylene -containing labels are typically found as labels on bottles, such as PET bottles, as well as being found in the form of so-called “pressure labels” on other containers. Polypropylene-containing labels on bottles are often only lightly adhered to the bottle and often only at a single point or certain points of the label. On the other hand, so-called pressure labels are typically attached to rigid polyolefm-containing articles via adhesive, thus the labels will need to be detached more forcibly than for polypropylene-containing labels on bottles.

In one embodiment, the step of providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene-containing labels is achieved by separating polypropylene-containing labels from bottles, preferably PET-containing bottles, then collecting the polypropylene-containing labels, thereby obtaining the precursor polypropylene recycling stream (A).

In this embodiment, the obtaining of polypropylene-containing labels is achieved as a byproduct of a PET-recycling process. Precursor polypropylene recycling streams (A) obtained in this manner are often highly pure, since it is relatively straightforward to separate polypropylene bottle labels from the PET-containing bottles (given how dissimilar polypropylene and PET are), as well as from the polyethylene (typically HDPE) bottle lids. The polypropylene-containing labels are generally the only polypropylene-containing components, thus can be easily collected without any significant contamination.

Furthermore, by utilizing a byproduct of a PET recycling process, this process helps to reduce wastage and improves the overall impact of the PET recycling process on the circular economy. Alternatively, the step of providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene-containing labels is achieved by separating polypropylene-containing labels that are attached to rigid polyolefm-containing articles via adhesive, then sorting the polypropylene-containing labels from the rigid polyolefm- containing articles and collecting the polypropylene-containing labels, thereby obtaining the precursor polypropylene recycling stream (A).

Whilst the polypropylene-containing labels cannot be separated from the rigid polyolefm- containing articles as easily as from PET-bottles, given how much more similar the polyolefin of the polyolefm-containing article is to the polypropylene (compared to PET, at least), it is relatively straightforward to sort the polypropylene labels from rigid polyolefm- containing articles by a simple dry-state density separation technique, which enables flexible pieces (e.g. films and labels) to be separated from rigid pieces, based on their aerodynamic properties. Such separation techniques are well known in the art. Suitable techniques include pneumatic classifying, wind sifters and zig zag cascade or air separators.

The precursor polypropylene recycling stream (A) contains at least 85 wt.-% of polypropylene-containing labels, based on the total weight of the precursor polypropylene recycling stream (A); however, these polypropylene-containing labels do not need to be in their complete article form (i.e. a complete label). Other pieces, such as shredded labels may also contribute to the total label-content in the precursor polypropylene recycling stream.

In some embodiments, it is preferred to reduce the size of the pieces prior to the washing step, either directly on the precursor polypropylene recycling stream (A) or on the purified polypropylene recycling stream (B).

The size reduction of this further step may be carried out by any method known to the person skilled in the art. One suitable method involves milling the precursor polypropylene recycling stream (A) or the purified polypropylene recycling stream (B). An alternative method involves shredding the precursor polypropylene recycling stream (A) or the purified polypropylene recycling stream (B). It is particularly preferred that the size-reduction of this further step is a shredding step. The shredding of this further step may be a wet-shredding process or a dry-shredding process. If this step is carried out on the precursor polypropylene recycling stream (A) prior to step b), then it is preferred that the shredding of the further step is a dry-shredding process. Alternatively, if the step is carried out on the precursor polypropylene recycling stream (A) or the purified polypropylene recycling stream (B) directly prior to step c), then it is preferred that the shredding of the further step is a wet-shredding process, wherein the precursor polypropylene recycling stream (A) or the purified polypropylene recycling stream (B) is first contacted with an aqueous solution and the obtained suspension is subjected to shredding.

The choice of aqueous solution is not particularly limited; however, it is preferred that the aqueous solution has a pH in the range from 8.0 to 14.0, more preferably in the range from 10.0 to 14.0, most preferably in the range from 12.0 to 14.0.

It is particularly preferred that the aqueous solution is a recycled aqueous washing solution that has previously been used in step c).

Step b), if present, involves sorting the precursor polypropylene recycling stream (A) by polymer type, thereby removing any pieces that contain polymers other than polypropylene, thereby generating a purified polypropylene recycling stream (B).

The method used to sort the precursor polypropylene recycling stream (A) by polymer type is not particularly limited.

In one embodiment, the sorting of step b) may be carried out using one or more optical sorters. In the context of the present invention, the term “optical sorter” refers to a sorting unit that uses any form of electromagnetic (EM)-radiation (visible or non-visible) to differentiate the pieces of the precursor polypropylene recycling stream (A).

Suitable methods for sorting the recycling stream according to polyolefin type include near- IR spectroscopic analysis, mid-IR spectroscopic analysis, high-speed laser spectroscopic analysis, Raman spectroscopic analysis, Fourier-transform infrared (FT-IR) spectroscopic analysis. Particularly preferred is near-IR spectroscopic analysis.

The sorting of step b) can be achieved through simple sorting algorithms, wherein the optical sensor(s) are programmed to assess which pieces should be selected or rejected based on simple binary considerations. Alternatively, more complex Al-based systems can be used to achieve a more precise sorting, wherein the optical sorter can recognize certain articles, possibly having certain branding, and from this recognition would know what polymers are contained in said article without having to manually determine the polymer content (e.g. by IR-spectroscopic analysis).

Alternatively, the sorting of step b) can be achieved using dry-state density separation techniques such as those discussed above, thereby removing non-polypropylene -containing rigid pieces (articles or flakes).

Whilst the precursor polypropylene recycling stream (A) is already, by its nature, highly pure, an extra sorting step at this stage helps to ensure as high a purity as possible, yielding a purified polypropylene recycling stream (B) that is even more enriched in polypropylene- containing labels. Furthermore, any polypropylene-containing labels that contain significant amounts of polyolefins other that polypropylene can also be removed at this stage.

Step c) involves washing the purified polypropylene recycling stream (B) or, in the case that step b) is absent, the precursor polypropylene recycling stream (A), in one or more washing steps, thereby obtaining a washed polypropylene stream (C).

Whilst in the broadest sense, the nature of the washing step(s) is not limited, it is preferred that the one or more washing steps of step c) are continued until at least 85% of all ink has been removed from the purified polypropylene recycling stream (B) or, in the case that step b) is absent, the precursor polypropylene recycling stream (A).

The primary contaminant on polypropylene labels is, generally speaking, inks. Coloration of labels is rarely achieved via the addition of one or more pigments within the polypropylene- based compositions used to make the labels, as would usually be the case for rigid (i.e. thicker) articles, but rather is achieved via the application of ink layers onto the surface of the label. With few exceptions, the polypropylene compositions used to produce polypropylene-containing labels are generally either natural (i.e. no pigment present) or white. In the case of white polypropylene compositions, the white appearance is typically the result of cavitation, often related to the presence of calcium carbonate. Cavitation is often combined with white pigments, typically with titanium dioxide.

Whilst the presence of inks and/or ink-derived contaminants in the final recyclate grade does not unduly affect the polymer properties, such as rheological or mechanical properties, it does have a significant influence on the appearance of the recyclate, typically contributing to a dark grey or black color. For some applications, a dark grey or black is an appropriate color, but that is often not the case. By removing at least 85% of all ink from the purified polypropylene recycling stream (B) or, in the case that step b) is absent, the precursor polypropylene recycling stream (A), the appearance of the final recyclate grade can be improved, as well as reducing the content of ink-derived contaminants, such as various metal ions and other organic compounds that may contribute to unpleasant odors (the inks (or binders) themselves are highly unlikely to be odorous in nature, but degradation of the inks (or binders) during compounding may generate volatile odorous compounds) or otherwise contribute to deleterious effects in the final recyclate grade (e.g. metal ions catalyzing degradation pathways).

It is further preferred that the one or more washing steps of step c) are continued until at least 90%, more preferably at least 95%, most preferably essentially 100% of all ink has been removed from the purified polypropylene recycling stream (B) or, in the case that step b) is absent, the precursor polypropylene recycling stream (A).

As would be clear to the person skilled in the art, the extent of ink removal may be monitored throughout the one or more washing steps to ensure that enough ink has been removed. Additionally or alternatively, it is within the skills of the person skilled in the art to suitably optimize the washing conditions in order to achieve this degree of ink removal, with key parameters such as washing temperature, washing duration, choice of washing solution, presence/absence of agitation, affecting the ink removal of washing steps known in the art.

For example, suitable conditions for the removal of inks during polyolefin recycling have been disclosed in WO 2021/018605 Al and WO 2021/104797 Al. In these documents, either acid washes (preferably cone. H2SO4) or acid/oil emulsions (preferably cone. FbSOVcyclohcxanc) are used to good effect. The conditions in these documents are also suitable for the removal of other foreign materials, such as metal layers, adhesives, paper labels etc.

It is, however, preferred that at least one of the one or more washing steps of step c) uses an alkaline aqueous washing solution and is conducted at a temperature in the range from 40 to 85 °C. More preferably, all of the one or more washing steps of step c) use an alkaline aqueous washing solution and are conducted at a temperature in the range from 40 to 85 °C.

The choice of alkaline aqueous washing solution is not particularly limited; however, it is preferred that the alkaline aqueous washing solution has a pH in the range from 8.0 to 14.0, more preferably in the range from 10.0 to 14.0, most preferably in the range from 12.0 to 14.0.

Preferably, the alkaline aqueous washing solution is an aqueous solution of a base selected from the group consisting of calcium hydroxide, potassium hydroxide, magnesium hydroxide, lithium hydroxide, sodium bicarbonate, sodium hydroxide and mixtures thereof. Most preferably, the alkaline aqueous washing solution is an aqueous solution of sodium hydroxide.

It is preferred that the amount of the base in the alkaline aqueous washing solution is in the range from 0.05 to 10 wt.-%, more preferably in the range from 0.10 to 7 wt.-%, most preferably in the range from 0.50 to 5 wt.-%, relative to the total weight of the alkaline aqueous washing solution. In one particularly preferred embodiment, the alkaline aqueous washing solution is a sodium hydroxide solution having a sodium hydroxide concentration in the range from 0.50 to 5.0 wt.-%, relative to the total weight of the alkaline aqueous washing solution.

Alkaline washing solutions suitable for use in the one or more washing steps of step c) may comprise a detergent in an amount in the range from 0.1 wt.-% to 1.0 wt.-%, relative to the total weight of the alkaline aqueous washing solution.

The detergent(s) may be commercially available detergent mixtures or may be composed in any way known to the person skilled in the art. Suitable detergents include TUBIWASH SKP, TUBIWASH GFN, TUBIWASH EYE and TUBIWASH TOP, commercially available from CHT, KRONES colclean AD 1004, KRONES colclean AD 1002 and KRONES colclean AD 1008 from KIC KRONES, and P3-stabilon WT, P3 stabilon AL from ECOLAB Ltd.

It is further preferred that the washing of step c) involves the application of agitation during one or more of the washing steps, wherein the agitation is selected from the group consisting of mechanical mixing, ultrasonic treatment, mechanical grinding or pump around loop. This agitation helps to expose the flakes in the recycling stream to fresh washing solution, thus ensuring that the process is not hindered through the buildup of contaminants (e.g. ink) in the immediate vicinity of the piece.

The person skilled in the art would be aware that multiple individual methods as provided above could be combined to improve the agitation, for example a combination of mechanical mixing and ultrasonic treatment. Furthermore, anti-foaming agents may be added to help prevent foaming and thus improve agitation of the flakes, resulting in a higher washing efficiency.

The washing of step c) may be carried out for a duration in the range from 5 minutes to 2 hours, more preferably in the range from 10 minutes to 1 hour, most preferably in the range from 10 minutes to 30 minutes. It is particularly preferred that each of the individual washing steps of step c) comprises, in the given order, the following steps: ci) contacting relevant polypropylene recycling stream with the washing solution at a controlled temperature for a controlled duration, thereby generating a suspended polypropylene recycling stream (Cl); and cii) removing at least part of the washing solution and any material not floating on the surface of the washing solution, thereby generating a washed polypropylene recycling stream (C2), wherein the final individual washing step of step c) preferably further comprises the following step: ciii) drying the washed polypropylene recycling stream (C2), thereby obtaining a dried polypropylene recycling stream (C3), wherein the dried polypropylene recycling stream (C3) or, in the case that step ciii) is absent, the washed polypropylene recycling stream (C2) generated in the final individual washing step, is then used as the washed polypropylene stream (C) in subsequent steps.

By removing each washing solution in turn, the inks and other contaminants (such as adhesives and/or paper labels) removed during the washing are removed from the recycling stream.

Following one or more of the steps cii), the washed polypropylene recycling stream may be optionally rinsed with water to remove traces of the washing solution remaining on the surface of the pieces of the washed polypropylene recycling stream (C2). Preferably at least the final individual washing step of step c) has a step of rinsing with water to remove traces of the washing solution remaining on the surface of the pieces of the washed polypropylene recycling stream (C2) before step ciii).

If present, any rinsing step(s) would have a duration of less than 5 minutes.

The use of rinsing not only removes all trace of the washing solution but also any residual contamination (e.g. ink) contained in said residual washing solution. Step d), if present, involves separating the washed polypropylene stream (C) into a heavy fraction and a light fraction polypropylene recycling stream (D).

The light fraction polypropylene recycling stream (D) typically contains labels and label- derived pieces, whilst the heavy fraction contains rigid pieces.

The separation of step d) can be carried out by any known dry-state density separation technique known in the art. Suitable techniques include pneumatic classifying, wind sifters and zig zag cascade or air separators.

As would be understood by the person skilled in the art, the separation into a light fraction and heavy fraction by such methods would not solely be influenced by the density of the flakes, but more critically by the aerodynamic properties of the flakes (typically influenced by surface area to weight ratio). As such, flat labels are separated from the bulkier polyolefin flakes. The terms “light fraction” and “heavy fraction” are commonly used in the art and do not strictly refer to classification by density alone. The meaning of these terms in the present invention matches these generally understood terms in the art.

In addition to the separation of step d), pieces that are not derived from labels and/or films may be removed via other sorting operations, other than dry-state density separation techniques. Suitable methods include the use of optical sorters that sort by article form, such as camera systems (operating in the visible range of the EM-spectrum). The sorting of this step can be achieved through simple sorting algorithms, wherein the optical sensor(s) are programmed to assess which pieces should be selected or rejected based on simple binary considerations. Alternatively, more complex Al-based systems can be used to achieve a more precise sorting, in particular when sorting according to article form.

Additionally or alternatively, non-polypropylene materials may be removed via a float/ sink separation step that sorts according to density. Between step d) and step e) an additional step may be present, wherein any pieces having a longest dimension of less than 2 mm (so-called fines) are removed. Any method known to the person skilled in the art may be employed, for example using screens or sieves.

Step e) involves melt extruding, preferably pelletizing, the light fraction polypropylene recycling stream (D) or, in the case that step d) is absent, the washed polypropylene stream (C), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, recycled polypropylene composition (E).

The extrusion of the recycled polypropylene composition (E) in step e) is preferably undertaken using an extruder, more preferably a twin-screw extruder.

In particular, it is preferred to use a conventional compounding or blending apparatus, e.g. a Banbury mixer, a 2-roll rubber mill, Buss-co-kneader or a twin-screw extruder. More preferably, mixing is accomplished in a co-rotating twin-screw extruder. The extruded recycled polypropylene composition (E) recovered from the extruder is preferably in the form of pellets, i.e. it is a pelletized recycled polypropylene composition (E).

It is preferred that the melt extrusion of step e) preferably includes a melt filtration step, wherein gels and other fine particles are removed from the melt by filtration. This notably improves the purity of the resultant recyclate, which is particularly relevant when the recyclate is used in the production of new labels, which have high purity/visual appearances requirements.

Any additives (Ad) added during step e) are selected from additives known in the art, preferably selected from the group consisting of antioxidants, stabilizers, fillers, colorants, nucleating agents, antistatic agents, and mixtures thereof.

Such additives are generally commercially available and are described, for example, in "Plastic Additives Handbook", pages 871 to 873, 5th edition, 2001 of Hans Zweifel. Step f), if present, involves aerating the recycled polypropylene composition (E) to remove volatile organic compounds, thereby generating an aerated extruded recycled polypropylene (Fl).

The aeration of step f) may be achieved, inter aha, through the use of air, inert gases or steam.

Preferably, the aeration of step f) is achieved by contacting the recycled polypropylene composition (E) or, in the case that step e) and step f) are interchanged, the washed polypropylene stream (C), with a gas being at least 60% by volume N2 gas.

The temperature at which the aeration according to step f) takes place is preferably in the range from 50 to 155 °C, more preferably in the range from 100 to 150 °C.

It may also be beneficial to conduct the aeration according to step f) at reduced pressure, for example less than 500 mbar, more preferably less than 200 mbar, most preferably less than 100 mbar.

The aeration according to step f) ensures that the content of volatile organic compounds is minimized in the aerated extruded recycled polypropylene (Fl) or the aerated recycled polypropylene flakes (F2), avoiding any unpleasant odors that are typically associated with similar recycled polyolefin blends. These volatile organic compounds typically result from contamination of the polyolefin during the first consumer use, for example through contact with foods, skin care products or other toiletries, or simply through decomposition of the polyolefin into volatile oligomeric chains during processing steps.

In addition to the steps discussed above, it is preferred that the process of the first aspect further comprises a step of sorting the polypropylene pieces of either the washed polypropylene stream (C), the light fraction polypropylene recycling stream (D), or the aerated recycled polypropylene flakes (F2) by color, removing any polypropylene pieces that are not either white or transparent. Since labels are generally produced from either white or transparent polypropylene grades, with any coloring being the result of surface ink(s), rather than from any pigments contained within the polypropylene itself, the removal of any polypropylene pieces that are not either white or transparent helps to further improve the purity of the final recyclate, since polypropylene pieces that are not derived from labels can be straightforwardly removed via the color sort.

It is further preferred that the white and transparent pieces are separated from one another and exposed to the following steps in the process of the first aspect as separate streams. This additional separation can either occur simultaneously with the removal of polypropylene pieces that are not either white or transparent (i.e. a 3-way sort between white, transparent, and other) or alternatively may be carried out as a binary sort after the initial removal of polypropylene pieces that are not either white or transparent.

It is preferred that the color sort of this further step is carried out using an optical sorter. In the broadest sense, any optical sorter can be used to achieve the sorting of the further step. In the context of the present invention, the term “optical sorter” refers to a sorting unit that uses any form of EM-radiation (visible or non-visible) to differentiate the pieces of respective recycling stream.

It is preferred that the optical sorters of step c) sort via a method selected from the group consisting of camera systems (operating in the visible range of the EM-spectrum) and visible reflectance spectroscopy.

Whilst sorting for color in this further step, further sorting criteria may be applied, such as additionally sorting by polyolefin type (removing any non-polypropylene pieces that may have missed in previous sorting steps).

In some embodiments, a single sensor type (e.g. near-IR sensor or camera system operating in the visible range of the EM spectrum) can be used to distinguish more than one property (e.g. color and polyolefin type). Furthermore, many near-IR sensor units comprises visible reflectance units or may be configured to measure both the near-IR and visible areas of the EM spectrum, meaning that a single sensor unit may use multiple detection methods.

Multiple detection methods and/or multiple sensors can be employed to achieve the sorting of the further step.

The sorting of the further step can be achieved through simple sorting algorithms, wherein the optical sensor(s) are programmed to assess which pieces should be selected or rejected based on simple binary considerations. Alternatively, more complex Al-based systems can be used to achieve a more precise sorting.

It is particularly preferred that the aerated extruded recycled polypropylene product (Fl) or the extruded aerated recycled polypropylene product (F3) is a mixed-plastic polypropylene blend (PP) according to the second aspect.

All preferred features and fallback positions of the mixed-plastic polypropylene blend (PP) according to the second aspect apply mutatis mutandis to the first aspect.

The mixed-plastic polypropylene blend (PP)

In a second aspect, the present invention is directed to a mixed-plastic polypropylene blend (PP).

In the context of the present invention, the term mixed-plastic polypropylene blend means that more than one polymer grade is present, thereby forming a blend. This blend need not contain polymers other than polypropylene, with blends comprising only polypropylene fractions constituting a mixed-plastic polypropylene blend according to the present invention, which derives at least in part from recycled material. Such mixed-plastic polypropylene blends are typically formed from many different virgin grades that are collected together during a recycling process, thus it would be straightforward for the person skilled in the art to differentiate such mixed-plastic polypropylene blends from virgin grades, which have a well-defined modality, such as unimodal, bimodal etc..

The mixed-plastic polypropylene blend (PP) has a melt flow rate (MFR2), determined according to ISO 1133 at 230 °C and 2.16 kg, in the range from 3.5 to 8.0 g/ 10 min, more preferably in the range from 4.0 to 7.0 g/10 min, most preferably in the range from 4.5 to 6.5 g/10 min.

The mixed-plastic polypropylene blend (PP) may be characterized according to the CRYSTEX QC method using trichlorobenzene (TCB) as a solvent. This method is described below in the determination methods section. In some cases, this method results in more useful data (than for example xylene cold soluble-based methods), since the crystalline fraction (CF) and the soluble fraction (SF) more accurately correspond to the matrix and elastomeric phases of heterophasic propylene ethylene copolymers respectively. Due to the differences in the separation methods of xylene extraction and CRYSTEX QC method the properties of XCS/XCI fractions on the one hand and crystalline/soluble (CF/SF) fractions on the other hand are not exactly the same, meaning that the amounts of matrix phase (i.e. CF or XCI) and elastomeric phase (i.e. SF or XCS) can differ as well as the properties thereof.

CRYSTEX QC analysis quantifies the properties of the soluble fraction (SF) and crystalline fraction (CF) of the polymeric part of the mixed-plastic polypropylene blend (PP), thus any non-polymeric components, such as talc and titanium dioxide, are not considered.

The polymeric part of the mixed-plastic polypropylene blend (PP) has an ethylene content (C2(total)), determined according to CRYSTEX QC analysis, in the range from 0.0 to 5.0 wt.-%, more preferably in the range from 0.0 to 4.0 wt.-%, most preferably in the range from 0.0 to 3.5 wt.-%. The polymeric part of the mixed-plastic polypropylene blend (PP) also has a crystalline fraction (CF) content, determined according to CRYSTEX QC analysis, in the range from 93.0 to 100.0 wt.-%, more preferably in the range from 93.0 to 99.0 wt.-%, most preferably in the range from 94.0 to 99.0 wt.-%.

The polymeric part of the mixed-plastic polypropylene blend (PP) also has a soluble fraction (SF) content, determined according to CRYSTEX QC analysis, in the range from 0.0 to 7.0 wt.-%, more preferably in the range from 1.0 to 7.0 wt.-%, most preferably in the range from 1.0 to 6.0 wt.-%.

The polymeric part of the mixed-plastic polypropylene blend (PP) also has an ethylene content of the crystalline fraction (C2(CF)), determined according to CRYSTEX QC analysis, in the range from 0.0 to 5.0 wt.-%, more preferably in the range from 0.0 to 4.0 wt.- %, most preferably in the range from 0.0 to 3.5 wt.-%.

The polymeric part of the mixed-plastic polypropylene blend (PP) preferably has an intrinsic viscosity of the crystalline fraction (iV(CF)), determined according to CRYSTEX QC analysis, in the range from 1.90 to 2.20 dL/g more preferably in the range from 1.95 to 2.15 dL/g, most preferably in the range from 2.00 to 2.10 dL/g.

As mentioned above, the mixed-plastic polypropylene blend (PP) derives at least in part from recycled material. Preferably, at least 90 wt.-%, more preferably at least 95 wt.-%, yet more preferably at least 98 wt.-% of the mixed-plastic polypropylene blend (PP) derives from recycled material.

If virgin polymers are present, it is preferred that these polymers are masterbatch carrier polymers used to introduce additives during compounding.

It is a finding of the present invention that the mixed-plastic polypropylene blend (PP) of the second aspect has unexpectedly advantageous properties for a recyclate, including improved Flexural Modulus (relative to other recyclates) and is particularly suitably for replacing virgin propylene homopolymers in polypropylene compositions without sacrificing the mechanical performance (as is normally the case when recyclates are added).

The mixed-plastic polypropylene blend (PP) according to embodiments of the present invention furthermore has a distinctive light grey coloring, primarily resulting from the combination of traces of ink that may have not been 100% removed during the recycling process. The more efficient the washing process, the less pronounced this grey coloring will be (i.e. the whiter the mixed-plastic polypropylene blend (PP) will be). Other nonpolypropylene components can also contribute to greying effect, either directly or by forming degradation products that contribute to the greying effect.

The mixed-plastic polypropylene blend (PP) thus preferably has a CIELAB color space (L*a*b), determined according to ISO 11664-4, of: i) L* of from 60.0 to 90.0, more preferably from 70.0 to 85.0; ii) a* of from -5.0 to 0.0; and iii) b* of from 0.0 to 20.0.

Such a CIELAB color space is typical for especially pure recyclates (i.e. being whiter than normal recyclates, but less white than white virgin polymer grades).

Whilst it is possible to obtain virgin grades having a color within this CIELAB color space, this would generally be obtained by the addition of small amounts of black pigment, such as carbon black, to a white polymer grade, meaning that the virgin grade would contain only white and black pigments.

In the mixed-plastic polypropylene blend (PP) of the present invention, the grey coloring does not result from the addition of black pigments, but rather traces of various colors of ink. Whilst the typical black pigments contain carbon (i.e. carbon black) and the white pigments contain, for example, titanium (in titanium dioxide), the mixed inks will contain a wide array of different elements that can be detected by X-ray fluorescence spectroscopy (XRF). The same wide array of different elements is not detected in otherwise equivalent grey virgin materials. As such, the observation of the following elements via XRF analysis is indicative of the recycling origin of the mixed-plastic polypropylene blend (PP). For the following XRF elemental contents, the use of the term “preferably” does not infer that higher amounts of the elements in question are desirable, but rather than the “more preferable” and “most preferable” embodiments more precisely define the recycling origin of the mixed-plastic polypropylene blend (PP).

As such, it is preferred that the mixed-plastic polypropylene blend (PP) has an aluminium (Al) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 60 ppm, more preferably of at least 90 ppm, most preferably of at least 120 ppm.

It is further preferred that the mixed-plastic polypropylene blend (PP) has an iron (Fe) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 30 ppm, more preferably of at least 50 ppm, most preferably of at least 80 ppm.

It is further preferred that the mixed-plastic polypropylene blend (PP) has a sodium (Na) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 20 ppm, more preferably of at least 50 ppm, most preferably of at least 80 ppm.

It is further preferred that the mixed-plastic polypropylene blend (PP) has a sulphur (S) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 5 ppm, more preferably of at least 15 ppm, most preferably of at least 30 ppm.

It is further preferred that the mixed-plastic polypropylene blend (PP) has a zinc (Zn) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 15 ppm, more preferably of at least 25 ppm, most preferably of at least 30 ppm.

It is particularly preferred that the mixed-plastic polypropylene blend (PP) has at least three of, more preferably all of, the following properties: a) an iron (Fe) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 30 ppm; b) a sodium (Na) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 20 ppm; and c) a sulphur (S) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 5 ppm d) a zinc (Zn) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 15 ppm.

Such combinations of Fe, Na, S and/or Zn are not observed in virgin grades. As such, the presence of these elements is indicative of the recyclate nature of the mixed-plastic polypropylene blend (PP), especially in combination with the CIELAB color space described above.

It is especially preferred that the sum of the iron (Fe) content, the sodium (Na) content, the sulphur (S) content, and the zinc (Zn) content, each determined by X-ray fluorescence spectroscopy (XRF), is at least 80 ppm, more preferably at least 150 ppm, most preferably at least 300 ppm.

Likewise, the presence of Al in such high amounts is a clear indication of the recyclate nature of the mixed-plastic polypropylene blend (PP), particularly of recyclates deriving from labels.

It is further preferred that the mixed-plastic polypropylene blend (PP) has a bromine (Br) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 0.5 ppm, more preferably of at least 1.0 ppm, most preferably of at least 2.0 ppm.

It is further preferred that the mixed-plastic polypropylene blend (PP) has a potassium (K) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 1 ppm, more preferably of at least 5 ppm, most preferably of at least 15 ppm.

It is further preferred that the mixed-plastic polypropylene blend (PP) has a strontium (Sr) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 1 ppm, more preferably of at least 5 ppm, most preferably of at least 10 ppm. It is further preferred that the mixed-plastic polypropylene blend (PP) has a calcium (Ca) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 100 ppm, more preferably of at least 500 ppm, most preferably of at least 800 ppm.

It is further preferred that the mixed-plastic polypropylene blend (PP) has a chlorine (Cl) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 25 ppm, more preferably of at least 35 ppm, most preferably of at least 40 ppm.

It is further preferred that the mixed-plastic polypropylene blend (PP) has a titanium (Ti) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 200 ppm, more preferably of at least 600 ppm, most preferably of at least 1000 ppm.

It is further preferred that the mixed-plastic polypropylene blend (PP) has a magnesium (Mg) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 50 ppm, more preferably of at least 80 ppm, most preferably of at least 90 ppm.

It is further preferred that the mixed-plastic polypropylene blend (PP) has a silicon (Si) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 50 ppm, more preferably of at least 100 ppm, most preferably of at least 120 ppm.

Another indicator of the recyclate nature of the mixed-plastic polypropylene blend (PP) may be obtained from measuring the phosphorus (P) content.

The presence of phosphorus in polymer grades is almost 100% attributable to phosphorus- based stabilizers, such as antioxidants. The content of such additives in a virgin grade is very consistent across almost all commercially available grades, corresponding to the amount required to sufficiently stabilize the polymer grade for the anticipated number of compounding steps (given that it is typically during these high temperature compounding steps that oxidation is most likely to occur) without incurring unnecessary costs by using too much stabilizer. By the time that a consumer article is recycled, the stabilizers will be largely used up (i.e. they will have been oxidized, preventing further use as an antioxidant) and further phosphorus-based stabilizers will need to be added to stabilize the recyclate grade, meaning that in recyclates the phosphorus present will either a) be at atypical level for a virgin grade, but be predominantly oxidized, or b) will be at a significantly higher level than would be typical for a virgin grade.

The total phosphorus content can be analyzed by X-ray fluorescence spectroscopy (XRF), whilst the ratio of non-oxidized stabilizer (tris (2,4-di-tert-butylphenyl)phosphite) and oxidized stabilizer (tris (2,4-di-tert-butylphenyl)phosphate) can be evaluated by HPLC analysis.

As such it is preferred that the content of tris (2,4-di-tert-butylphenyl)phosphate expressed relative to the total content of tris (2,4-di-tert-butylphenyl)phosphite and tris (2,4-di-tert- butylphenyl)phosphate, as determined by HPLC analysis, is in the range from 60% to 100% and the total phosphorus content, as determined by X-ray fluorescence spectroscopy (XRF), is in the range from 15 to 60 ppm.

This would be consistent with a recyclate grade that has not been further additivated.

Alternatively, it is preferred that the total phosphorus content, as determined by X-ray fluorescence spectroscopy (XRF), is greater than 60 ppm. This would be consistent with a recyclate grade that has been further additivated with an additional source of phosphorus.

It is also preferred that the mixed-plastic polypropylene blend (PP) has a content of inorganic residues, determined by thermogravimetric analysis (TGA) according to DIN 1172 of 0. 10 to 7.5 wt.-%, relative to the total weight of the mixed-plastic polypropylene blend (PP), more preferably in the range from 0.20 to 5.0 wt.-%, most preferably in the range from 0.5 to 4.0 wt.-%.

The mixed-plastic polypropylene blend (PP) preferably has a total amount of volatile organic compounds (TVOC), determined according to the measurement given in the determination methods, in the range from 0 to 25 pg/g, more preferably in the range from 0 to 18 pg/g, most preferably in the range from 0 to 15 pg/g. It is especially preferred that the mixed-plastic polypropylene blend (PP) is obtainable by, more preferably produced by, the process according to the first aspect.

All preferred features and fallback positions of the first aspect apply mutatis mutandis to the mixed-plastic polypropylene blend (PP) obtainable by, more preferably produced by, the process according to the first aspect.

Articles

The articles of the third aspect preferably comprise at least 90 wt.-%, more preferably at least 95 wt.-%, most preferably at least 98 wt.-%, relative to the total weight of the article, of the mixed-plastic polypropylene blend (PP) of the second aspect.

If other polymers other than the mixed-plastic polypropylene blend (PP) of the second aspect are present, then these may be modifiers or virgin polymer grades used to modify the properties of the mixed-plastic polypropylene blend (PP).

All preferred features and fallback positions of the mixed-plastic polypropylene blend (PP) according to the second aspect apply mutatis mutandis to the articles of the third aspect comprising said mixed-plastic polypropylene blend (PP).

Use

In a final aspect, the present invention is directed to the use of the mixed-plastic polypropylene blend (PP) of the second aspect for the production of polypropylene - containing labels containing recycled material. All preferred features and fallback positions of the mixed-plastic polypropylene blend (PP) according to the second aspect apply mutatis mutandis to the articles of the use of said mixed-plastic polypropylene blend (PP) of the fourth aspect.

E X A M P L E S

1. Determination methods

The following definitions of terms and determination methods apply for the above general description of the invention including the claims as well as to the below examples unless otherwise defined.

CRYSTEX QC analysis

Crystalline and soluble fractions method

The crystalline (CF) and soluble fractions (SF) of the polypropylene (PP) compositions as well as the comonomer content and intrinsic viscosities of the respective fractions were analyzed by use of the CRYSTEX instrument, Polymer Char (Valencia, Spain). Details of the technique and the method can be found in literature (Ljiljana Jeremie, Andreas Albrecht, Martina Sandholzer & Markus Gahleitner (2020) Rapid characterization of high-impact ethylenepropylene copolymer composition by crystallization extraction separation: comparability to standard separation methods, International Journal of Polymer Analysis and Characterization, 25:8, 581-596)

The crystalline and amorphous fractions were separated through temperature cycles of dissolution at 160 °C, crystallization at 40 °C and re-dissolution in 1 ,2,4-trichlorobenzene at 160 °C. Quantification of SF and CF and determination of ethylene content (C2) were achieved by means of an integrated infrared detector (IR4) and for the determination of the intrinsic viscosity (IV) an online 2-capillary viscometer was used.

The IR4 detector was a multiple wavelength detector measuring IR absorbance at two different bands (CH; stretching vibration (centred at app. 2960 cm ¹) and the CH stretching vibration (2700-3000 cm ¹) that serve for the determination of the concentration and the Ethylene content in Ethylene-Propylene copolymers. The IR4 detector was calibrated with series of 8 EP copolymers with known Ethylene content in the range of 2 wt.-% to 69 wt.-% (determined by ¹³C-NMR) and each at various concentrations, in the range of 2 and 13mg/ml. To encounter for both features, concentration and ethylene content at the same time for various polymer concentrations expected during Crystex analyses the following calibration equations were applied: Cone = a + b*Abs(CH) + c*(Abs(CH))² + d*Abs(CH₃) + e*(Abs(CH₃)² + f*Abs(CH)*Abs(CH₃) (Equation 1)

CH₃/1000C = a + b*Abs(CH) + c* Abs(CH₃) + d * (Abs(CH₃)/Abs(CH)) + e * (Abs(CH₃)/Abs(CH))² (Equation 2)

The constants a to e for equation 1 and a to f for equation 2 were determined by using least square regression analysis.

The CH₃/1000C was converted to the ethylene content in wt.-% using following relationship:

Wt.-% (Ethylene in EP Copolymers) = 100 - CH₃/1000TC * 0.3 (Equation 3)

Amounts of Soluble Fraction (SF) and Crystalline Fraction (CF) were correlated through the XS calibration to the “Xylene Cold Soluble” (XCS) quantity and respectively Xylene Cold Insoluble (XCI) fractions, determined according to standard gravimetric method as per ISO16152. XS calibration was achieved by testing various EP copolymers with XS content in the range 2-31 wt.-%. The determined XS calibration was linear:

Wt.-% XS = 1 ,01 * Wt.-% SF (Equation 4)

Intrinsic viscosity (IV) of the parent EP copolymer and its soluble and crystalline fractions were determined with a use of an online 2-capillary viscometer and were correlated to corresponding IV’ s determined by standard method in decalin according to ISO 1628-3. Calibration was achieved with various EP PP copolymers with IV = 2-4 dL/g. The determined calibration curve was linear:

IV (dL/g) = a* Vsp/c (equation 5)

The samples to be analyzed were weighed out in concentrations of lOmg/ml to 20mg/ml. To avoid injecting possible gels and/or polymers which do not dissolve in TCB at 160 °C, like PET and PA, the weighed out sample was packed into a stainless steel mesh MW 0, 077/D 0,05mmm. After automated filling of the vial with 1,2,4-TCB containing 250 mg/1 2,6-tert-butyl-4- methylphenol (BHT) as antioxidant, the sample was dissolved at 160 °C until complete dissolution was achieved, usually for 60 min, with constant stirring of 400 rpm. To avoid sample degradation, the polymer solution was blanketed with the N2 atmosphere during dissolution.

A defined volume of the sample solution was injected into the column filled with inert support where the crystallization of the sample and separation of the soluble fraction from the crystalline part was taking place. This process was repeated two times. During the first injection the whole sample as measured at high temperature, determining the IV[dL/g] and the C2[wt.-%] of the PP composition. During the second injection the soluble fraction (at low temperature) and the crystalline fraction (at high temperature) with the crystallization cycle were measured (wt.-% SF, wt.-% C2, IV).

Melt Flow Rate

The melt flow rate (MFR) was determined according to ISO 1133 and was indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR2 of polypropylene was determined at a temperature of 230 °C and a load of 2.16 kg.

X-ray fluorescence (XRF)

The instrument used for the XRF measurements was a wavelength dispersive Zetium (2,4kW) from Malvern Panalytical. The instrument was calibrated with Adpol, RoHs, Toxel standards from Malvern Panalytical and from a custom set of calibration standards (referred to in the following as “Custom”) also from Malvern Panalytical according to the following table

The analysis was conducted under vacuum on a plaque with a diameter of 40mm and a thickness of 2mm. The method is used to determine the quantitative content of Na, Mg, Al, Si, P, S, Ca, Ti, Zn, Cu, Br, Cl, K, Sr, Fe in a given polyolefin matrix within defined ranges of these standards.

The content of each precise element was evaluated with the following standards (LOD = limit of detection):

Elements which are not covered by standards, or the content is outside of the calibrated standard range, are then analyzed with a semi-quantitative mode (software Omnian from Malvern Panalytical). For elements not covered by the calibration standards, no value is reported if the corresponding peak is not visible and therefore cannot be analysed with the software Omnian. The CH content needed to run the semiquantitative evaluation with Omnian was estimated by the software itself.

In the context of the present invention, the presence of a wide range of elements not generally encountered in virgin polymer grades (at least certainly not in combination) is an indicator that a particular polypropylene grade is at least partially derived from recycled material.

The following table presents typical data for a number of virgin grades and a number of recycled grades (i.e. r-PP), which demonstrate that the presence of certain elements is indicative of recycling origin:

* - measured prior to additivation (i.e. prior to the addition of additional, fresh, stabilizers, whereas all other r-PP values are measured after additivation)

** - only observed in some samples, not all.

HPLC analysis

The content of antioxidants (compounds like Irganox® 1010 and Irgafos® 168, i.e., Pentaerythrityl-tetrakis(3-(3’,5’-di-tert. butyl-4-hydroxyphenyl)-propionate) and Tris (2,4-di- t-butylphenyl) phosphite, as well as oxidised variants thereof) was determined via high performance liquid chromatography (HPLC) after extraction with ethyl acetate. First, about 10 g of the sample were cryo-milled with the aid of liquid nitrogen. After that, a 0.5 g of the milled sample was extracted using ethyl acetate as a solvent. Extraction was performed at 95 °C for 90 min under constant stirring. After letting the mixture cool down to room temperature again it was filtered and put to the HPLC test for the quantification of antioxidants. The HPLC system was equipped with a C18 column for the separation and a diode array detector (DAD) for detection.

The presence of phosphorus in polymer grades is almost 100% attributable to phosphorus- based stabilizers, such as antioxidants. The content of such additives in a virgin grade is very consistent across almost all commercially available grades, corresponding to the amount required to sufficiently stabilize the polymer grade for the anticipated number of compounding steps (given that it is typically during these high temperature compounding steps that oxidation is most likely to occur) without incurring unnecessary costs by using too much stabilizer. By the time that a consumer article is recycled, the stabilizers will be largely used up (i.e. they will have been oxidized, preventing further use as an antioxidant) and further phosphorus-based stabilizers will need to be added to stabilize the recyclate grade, meaning that in recyclates the phosphorus present will either a) be at atypical level for a virgin grade, but be predominantly oxidized, or b) will be at a significantly higher level than would be typical for a virgin grade (see Virgin 1 to 3 in the previous table).

The following table discloses typical values of recyclates corresponding to situation a) (i.e. not yet additivated in the mechanical recycling process) and b) (i.e. already additivated in the mechanical recycling process).

#1 to #4 have typical phosphorus content, as determined by XRF, but a high percentage of the Irgafos is present in oxidized form, whilst 5 to 10 have a phosphorus content, as determined by XRF, that is higher than would be observed in virgin polypropylene grades.

Further tests have been represented graphically in Figure 1, which show precisely the same trends (note: a virgin grade would fall somewhere towards the bottom left of Figure 1, having low total P content of 28-52 ppm and low % of oxidized Irgafos 168)

TVOC - total amount of volatile organic compounds

Determination of the total amount of volatile organic compounds (TVOC) is performed by HS-GC-FID/MS.

The TVOC is measured directly on pelletized samples (i.e. without any milling or other size reduction).

Headspace settings: 100°C for 2 hours, 1 gram of sample.

Quantification of specific components using the signals from the FID chromatograms and external standards of the specific components. TVOC is determined semi quantitatively as toluene equivalent by using all peaks in the FID chromatograms of the sample.

Analysis is performed in duplicate. Amount of iPP, Polystyrene, Polyethylene (and ethylene containing copolymers), poly(ethylene terephthalate), and amount of Polyamide-6

Sample preparation:

All calibration samples and samples to be analyzed were prepared in similar way, on molten pressed plates.

About 2 to 3 g of compounds to be analyzed were melted at 190°C. Subsequently, for 20 seconds, 60 to 80 bar pressure was applied in a hydraulic heating press. Next, the samples were cooled to room temperature in 40 seconds in a cold press under the same pressure, in order to control the morphology of the compound. The thickness of the plates was controlled by metallic calibrated frame plates 2.5 cm by 2.5 cm, 100 to 200 pm thick (depending MFR from the sample); two plates were produced in parallel at the same time and in the same conditions. The thickness of each plate was measured before any FTIR measurements were performed; all plates were between 100 to 200 pm thick.

To control the plate surface and to avoid any interference during the measurement, all plates were pressed between two double-sided silicone release papers.

In case of powder samples or heterogeneous compounds, the pressing process was repeated three times to increase homogeneity by pressed and cutting the sample in the same conditions as described before.

Spectrometer:

Standard transmission FTIR spectroscope such as Bruker Vertex 70 FTIR spectrometer was used with the following set-up: a spectral range of 4000-400 cm ¹, an aperture of 6 mm, a spectral resolution of 2 cm ¹, with 16 background scans, 16 spectrum scans, an interferogram zero fdling factor of 32 Norton Beer strong anodization.

Spectra were recorded and analyzed in Bruker Opus software.

Calibration samples:

As FTIR is a secondary method, several calibration standards were compounded to cover the targeted analysis range, typically from:

0.2 wt% to 2.5 wt% for PA, 0. 1 wt% to 5 wt% for PS

0.2 wt% to 2.5 wt% for PET

0. 1 wt% to 4 wt% for PVC

The following commercial materials were used for the compounds: Borealis HC600TF as iPP, Borealis FB3450 as HDPE and for the targeted polymers such RAMAPET N1 S (Indorama Polymer) for PET, Ultramid® B36LN (BASF) for Polyamide 6. Styrolution PS 486N (Ineos) for High Impact Polystyrene (HIPS), and for PVC Inovyn PVC 263B (under powder form).

All compounds were made at small scale in a Haake kneader at a temperature below 265°C and less than 10 minutes to avoid degradation.

Additional antioxidant such as Irgafos 168 (3000 ppm) was added to minimize the degradation.

Calibration:

The FTIR calibration principle was the same for all the components: the intensity of a specific FTIR band divided by the plate thickness is correlated to the amount of component determined by 1H or 13C solution state NMR on the same plate.

Each specific FTIR absorption band was chosen due to its intensity increase with the amount of the component concentration and due to its isolation from the rest of the peaks, whatever the composition of the calibration standard and real samples.

This methodology is described in the publication from Signoret and al. “Alterations of plastic spectra in MIR and the potential impacts on identification towards recycling”, Resources, conservation and Recycling journal, 2020, volume 161, article 104980.

The wavelength for each calibration band was:

3300 cm-1 for PA,

1601 cm- 1 for PS,

- 1410 cm-1 for PET,

- 615 cm-1 for PVC,

1167 cm-1 for iPP.

For each polymer component i, a linear calibration (based on linearity of Beer-Lambert law) was constructed. A typical linear correlation used for such calibrations is given below:

where

X! is the fraction amount of the polymer component i (in wt%),

Ei is the absorbance intensity of the specific band related to the polymer component i (in a.u. absorbance unit, values see above), d is the thickness of the sample plate, Eh are two coefficients of correlation determined for each calibration curve.

No specific isolated band can be found for C2-rich fraction and as a consequence the C2-rich fraction is estimated indirectly, C2 rich = 100

The Chalk and Talc contents are estimated “semi -quantitatively”. Hence, this renders the C2 rich content “semi-quantitative”.

For each calibration standard, wherever available, the amount of each component was determined by either ’H or ¹³C solution state NMR, as primary method (except for PA). The NMR measurements were performed on the exact same FTIR plates used for the construction of the FTIR calibration curves.

Amount of Talc and Chalk

The talc and chalk contents were measured by Thermogravimetric Analysis (TGA); experiments were performed with a Perkin Elmer TGA 8000. Approximately 15-25 mg of material was placed in a platinum pan. The temperature was equilibrated at 50°C for 10 minutes, and afterwards raised to 950°C under nitrogen at a heating rate of 20 °C/min. The weight loss between ca. 550°C and 700°C (WCO2) was assigned to CO2 evolving from CaCOs, and therefore the chalk content was evaluated as:

Chalk content = 100/44 x WCO2

Afterwards the temperature was lowered to 300°C at a cooling rate of 20 °C/min. Then the gas was switched to oxygen, and the temperature was raised again to 900°C. The weight loss in this step was assigned to carbon black (Web). Knowing the content of carbon black and chalk, the ash content excluding chalk and carbon black was calculated as:

Ash content = (Ash residue) - 56/44 x WCO2 - Web Where Ash residue is the weight% measured at 850°C in the first step conducted under nitrogen. The ash content is estimated to be the same as the talc content for the investigated recyclates.

The Flexural Modulus was determined according to ISO 178 method A (3-point bending test) on 80 mm x 10 mm x 4 mm specimens. Following the standard, a test speed of 2 mm/min and a span length of 16 times the thickness was used. The testing temperature was 23±2 ° C. Injection molding was carried out according to ISO 19069-2 using a melt temperature of 230 °C for all materials irrespective of material melt flow rate.

CIELAB

The method was used for measurement of color on flakes and complies with ISO 11664-4. 60 x 60 x 2 mm injection moulded plaques were prepared from pellets according to ISO standard 19069-2:2020 (PP), which were then subjected to the CIELAB measurement. With a spectrophotometer, the 3 standard color value values X, Y and Z are measured, which are used to calculate the CIE L*, a*, b* and its color distances.

Total content of inorganic residues

The content of inorganic residues was determined by thermogravimetric analysis (TGA) according to DIN 1172.

1. Examples

The following recycling streams were used as precursor recycling streams in the following experiments:

Al a Swedish post-consumer plastic waste stream, enriched in post-consumer flexible PP articles.

A2 a German post-consumer plastic waste stream, fulfilling the specification DSD323-2. A3 a post-consumer polypropylene waste stream available as a byproduct of a bottle recycling process. Unlike Al and A2, A3 contains at least 85 wt.-% of polypropylene -containing labels (in fact A3 essentially consists of polyp ropylene-containing labels).

For the comparative examples (which employ precursor recycling streams that do not contain at least 85 wt.-% of polypropylene -containing labels), General Procedure A was followed:

Step 1 : the precursor recycling stream was sorted by color (the criteria for this sorting step differ from experiment to experiment, see below);

Step 2: the sorted product of step 1 was washed first in a low temperature alkaline washing step, then in a high temperature alkaline washing step;

Step 3: the washed product of step 2 was further sorted to remove any non-polypropylene containing pieces using a near-IR sorter;

Step 4: the sorted product of step 3 was melt extruded to form a recycled polypropylene grade.

CE1 involved exposing precursor Al to General Procedure A, wherein step 1 sorted for transparent pieces (i.e. colored pieces were removed).

CE2 involved exposing precursor A2 to General Procedure A, wherein step 1 sorted for transparent pieces.

CE3 involved exposing precursor A2 to General Procedure A, wherein step 1 was not carried out.

CE4 involved exposing precursor A2 to General Procedure A, wherein step 1 sorted for colored pieces only (i.e. transparent pieces were removed).

For the inventive examples (which employ a precursor recycling stream that does contain at least 85 wt.-% of polypropylene -containing labels), General Procedure B was followed: Step 1 : washing of the precursor A3 in a single high temperature washing step (conditions differ for each experiment, see below), wherein additionally material having a density different to polypropylene is removed via a sink/float separation; Step 2: separating the product of step 1 into a heavy (i.e. rigid pieces) and light (i.e. flexible pieces) fraction using a wind sifter;

Step 3: the light fraction of step 2 was melt extruded to form a recycled polypropylene grade.

(note: as the precursor recycling stream A3 does not contain significant amounts of polypropylene containing pigments (i.e. pigments dispersed in the polypropylene matrix, as opposed to inks on the surface), a color sorting step (i.e. step 1 of General Procedure A) is not necessary).

IE1 involved exposing precursor A3 to General Procedure B, wherein the washing of step 1 was carried out for 10 minutes at 70 °C using an aqueous washing solution of 1.8 wt.-% NaOH and 0.18 wt.-% of a detergent TubiWash EYE. This washing step was insufficient to remove at least 85 wt.-% of the ink present. The process of IE1 was a lab-scale recycling process.

IE2 involved exposing precursor A3 to General Procedure B, wherein the washing of step 1 was carried out for 10 minutes at 80 °C using an aqueous washing solution of 1.8 wt.-% NaOH and 0.18 wt.-% of a detergent TubiWash EYE. This washing step was insufficient to remove at least 85 wt.-% of the ink present. The process of IE2 was a lab-scale recycling process.

IE3 involved exposing precursor A3 to General Procedure B, wherein the washing of step 1 was carried out for 60 minutes at 70 °C using an aqueous washing solution of 3.0 wt.-% NaOH and 0.30 wt.-% of a detergent TubiWash EYE. This washing step was sufficient to remove at least 85 wt.-% of the ink present. The process of IE3 was a lab-scale recycling process.

IE4 involved exposing precursor A3 to General Procedure B, wherein the washing of step 1 was carried out for 60 minutes at 80 °C using an aqueous washing solution of 3.0 wt.-% NaOH and 0.30 wt.-% of a detergent TubiWash EYE. This washing step was sufficient to remove at least 85 wt.-% of the ink present. The process of IE4 was a lab-scale recycling process.

IE5 involved exposing precursor A3 to General Procedure B, wherein the washing of step 1 was carried out for 20 minutes at 80 °C using an aqueous washing solution of 3.0 wt.-% NaOH and 0.30 wt.-% of a detergent TubiWash EYE. This washing step was sufficient to remove at least 85 wt.-% of the ink present. The process of IE5 was an industrial-scale recycling process. Furthermore, instead of a sink/float separation, a hydrocyclone is used to remove material having a density different from polypropylene.

As would be understood by the person skilled in the art, there are differences between a labscale and an industrial scale washing process, with longer washing duration required during lab-scale experiments due to less efficient agitation. The 20 minute industrial scale wash of IE5 is roughly equivalent to the 60 minute lab-scale wash of IE4 in terms of washing efficiency.

Experiments CE1 to CE4 and IE1 to IE5 each yielded mixed-plastic polypropylene blends, the properties of which are given in Table 1.

Table 1 properties of inventive and comparative mixed-plastic polypropylene blends

* - below the limit of detection (LOD) ** - due to the low amount of SF, the iV(SF) and C2(SF) cannot be accurately determined.

*** - no clearly visible peak in the XRF spectrum

As can be seen from the data shown in Table 1, the process of the present invention, wherein the precursor feedstock is derived from polypropylene -containing labels affords a recyclate product having a high purity (see the low content of fillers and PS, with PET amounts also being extremely low, despite the fact that the precursor recycling stream was a byproduct of PET recycling), with MFR in a narrow defined range and low levels of C2 and other contaminants. Furthermore, by selecting appropriate washing conditions, CIELAB L* values of over 70 can be obtained.

Further experiments carried out demonstrated that when General Procedure B was carried out using conditions sufficient to removed 85% of the ink (e.g. those of IE3, IE4 and IE5), then the resultant recyclate grades typically had a polypropylene content of 98 wt.-% (relative to the total polymer content, i.e. ignoring fillers such as talc and chalk).

By including an additional sorting step before step 1 of General Procedure B, wherein an optical (e.g. Near-IR) sorter removed any non-polypropylene pieces, it was possible to improve the polypropylene content to 99 wt.-% (relative to the total polymer content).

Furthermore, by including a further sorting step between steps 2 and 3 of General Procedure B, wherein an optical (e.g. Near-IR) sorter sorted by color, it was possible to obtain approx. 40 wt.-% of a white fraction having significantly higher content of inorganic fillers (approx. 7 wt.-%), approx. 50 wt.-% of a transparent (also termed “natural” above) fraction, having a content of inorganic fillers of less than 0.5 wt.-%, and approx. 10 wt.-% of a colored fraction, which contained pieces that had not been fully deinked, as well as polyethylene pieces (from polyethylene bottle lids that had managed to evade the previous sorting steps). The white and transparent fractions could be employed for different applications, whilst the colored fraction could either be fed into other recycling processes or used for energetic recycling (burning for energy). Pellets produced from these fractions can be seen in Figure 2. The white pellets have CIELAB values of L* 78.7, a* -1.4, and b* 8.6, whilst the transparent pellets have CIELAB values of L* 53.6, a* -0.6, and b* 20.8.

Claims

C L A I M S

1. A mechanical polypropylene recycling process comprising, in the given order, the steps of: a) providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene-containing labels, based on the total weight of the precursor polypropylene recycling stream (A); b) optionally sorting the precursor polypropylene recycling stream (A) by polymer type, thereby removing any pieces that contain polymers other than polypropylene, thereby generating a purified polypropylene recycling stream

(B); c) washing the purified polypropylene recycling stream (B) or, in the case that step b) is absent, the precursor polypropylene recycling stream (A), in one or more washing steps, thereby obtaining a washed polypropylene stream (C); d) optionally separating the washed polypropylene stream (C) into a heavy fraction and a light fraction polypropylene recycling stream (D); e) melt extruding, preferably pelletizing, the light fraction polypropylene recycling stream (D) or, in the case that step d) is absent, the washed polypropylene stream

(C), preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, recycled polypropylene composition (E); and f) optionally aerating the recycled polypropylene composition (E) to remove volatile organic compounds, thereby generating an aerated recycled polypropylene product (Fl); wherein the order of steps f) and e) can be interchanged, such that the light fraction polypropylene recycling stream (D) or, in the case that step d) is absent, the washed polypropylene stream (C) is first aerated to form aerated recycled polypropylene flakes (F2) that are subsequently extruded, preferably wherein additives (Ad) are added in the melt state, to form an extruded, preferably pelletized, aerated recycled polypropylene product (F3).

2. The process according to claim 1, wherein the step of providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene- containing labels, based on the total weight of the precursor polypropylene recycling stream (A), is achieved by separating polypropylene -containing labels from bottles, preferably PET-containing bottles, then collecting the polypropylene -containing labels, thereby obtaining the precursor polypropylene recycling stream (A).

3. The process according to claim 1, wherein the step of providing a precursor polypropylene recycling stream (A) that contains at least 85 wt.-% of polypropylene - containing labels, based on the total weight of the precursor polypropylene recycling stream (A), is achieved by separating polypropylene -containing labels that are attached to rigid polyolefin-containing articles via adhesive, then sorting the polypropylene -containing labels from the rigid polyolefin-containing articles and collecting the polypropylene-containing labels, thereby obtaining the precursor polypropylene recycling stream (A).

4. The process according to any one of the preceding claims, wherein the one or more washing steps of step c) are continued until at least 85% of all ink has been removed from the purified polypropylene recycling stream (B) or, in the case that step b) is absent, the precursor polypropylene recycling stream (A).

5. The process according to any one of the preceding claims, wherein at least one of the one or more washing steps of step c) uses an alkaline aqueous washing solution and is conducted at a temperature in the range from 40 to 85 °C.

6. The process according to any one of the preceding claims, further comprising a step of sorting the polypropylene pieces of either the washed polypropylene stream (C), the light fraction polypropylene recycling stream (D), or the aerated recycled polypropylene flakes (F2) by color, removing any polypropylene pieces that are not either white or transparent.

7. A mixed-plastic polypropylene blend (PP) having a melt flow rate (MFR2), determined according to ISO 1133 at 230 °C and 2.16 kg, in the range from 3.5 to 8.0 g/10 min, wherein the polymeric part of said mixed-plastic polypropylene blend (PP) has: i) an ethylene content (C2(total)), determined according to CRYSTEX QC analysis, in the range from 0.0 to 5.0 wt.-%; ii) a crystalline fraction (CF) content, determined according to CRY STEX QC analysis, in the range from 93.0 to 100.0 wt.-%; iii) a soluble fraction (SF) content, determined according to CRYSTEX QC analysis, in the range from 0.0 to 7.0 wt.-%; and iv) an ethylene content of the crystalline fraction (C2(CF)), determined according to CRYSTEX QC analysis, in the range from 0.0 to 5.0 wt.-%.

8. The mixed-plastic polypropylene blend (PP) according to claim 7, wherein at least 90 wt.-%, more preferably at least 95 wt.-%, yet more preferably at least 98 wt.-% of the mixed-plastic polypropylene blend (PP) derives from recycled material.

9. The mixed-plastic polypropylene blend (PP) according to claim 7 or claim 8, having a CIELAB color space (L*a*b), determined according to ISO 11664-4, of: i) L* of from 60.0 to 90.0, more preferably from 70.0 to 85.0; ii) a* of from -5.0 to 0.0; and iii) b* of from 0.0 to 20.0.

10. The mixed-plastic polypropylene blend (PP) according to any one of claims 7 to 9, having: a) an aluminium (Al) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 60 ppm; and/or at least three of, more preferably all of, the following properties: b) an iron (Fe) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 20 ppm; c) a sodium (Na) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 30 ppm; and d) a sulphur (S) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 5 ppm e) a zinc (Zn) content, determined by X-ray fluorescence spectroscopy (XRF), of at least 15 ppm.

11 . The mixed-plastic polypropylene blend (PP) according to any one of claims 7 to 10, having a total amount of volatile organic compounds (TVOC), determined according to the measurement given in the determination methods, in the range from 0 to 25 pg/g, more preferably in the range from 0 to 18 pg/g, most preferably in the range from 0 to 15 pg/g.

12. The process according to any one of claims 1 to 6, wherein the process produces a mixed-plastic polypropylene blend (PP) according to any one of claims 7 to 11.

13. The mixed-plastic polypropylene blend (PP) according to any one of claims 7 to 11, that is produced by the process according to any one of claims 1 to 6.

14. Articles comprising the mixed-plastic polypropylene blend (PP) according to any one of claims 7 to 11 or 13, preferably in an amount of at least 90 wt.-%, more preferably at least 95 wt.-%, most preferably at least 98 wt.-%, relative to the total weight of the article, wherein the articles are selected from the group consisting of labels and films.

15. Use of the mixed-plastic polypropylene blend (PP) according to any one of claims 7 to 11 or 13 for the production of polypropylene labels containing recycled material.