Method and system for obtaining a food grade plastic material from a mixed waste material stream

Abstract

The present disclosure relates to a method (100) for obtaining a food grade plastic material (10) from a mixed waste material stream (PS). The method (100) comprises discriminating (110a) a first type of plastic material from other types of material in the material stream (PS) using a near infrared spectroscopy system (222) and / or a visible spectroscopy system, diverting (110b) the first type of plastic material from other types of material into a first plastic material fraction, discriminating (111a) a first type of food grade plastic material from other types of material in the first plastic material fraction using a camera-based object recognition system (226), diverting (111b) the first type of food grade plastic material from other types of material in the first plastic material fraction, thereby sorting out other types of material from the first plastic material fraction, thereby obtaining the food grade plastic material (10). The present disclosure further relates to a system (1) for obtaining a food grade plastic material (10).

Description

[0001] METHOD AND SYSTEM FOR OBTAINING A FOOD GRADE PLASTIC MATERIAL FROM A MIXED WASTE MATERIAL STREAM

[0002] Field of invention

[0003] The present invention generally relates to a method for obtaining a food grade plastic material from a mixed waste material stream. The present invention also generally relates to a system for obtaining a food grade plastic material from a mixed waste material stream.

[0004] Technical background

[0005] Food packages, bottles and containers are just some examples of products that may be made out of plastic. Plastic materials are advantageous as material due to its many advantageous properties e.g. it is a light material, it resists water and has a long lifetime. The combination of these properties result in that plastic material is extensively used and needed in many industries, but when the plastic material ends up in the nature it causes problems for the plant and wildlife. Thus, it is important that the used plastic is gathered and sent to a dump.

[0006] Usually, the plastic that reaches the dump is sent to incineration, landfilling, or is recycled, through chemical or mechanical processes. Those are currently the main techniques used to manage plastic waste. However, there are many problems associated with managing plastic waste. One problem is that high value materials are lost and cannot be used further if plastic waste is incinerated. Another problem related to incineration of plastics resides in that the incineration process produces many products that are harmful to humans and the environment such as carbon monoxide, carbon dioxide, chlorine, and other hydrocarbons. These gases also contribute to the problem with global warming. A problem with discarding plastics waste in landfills is that it takes up landfill space and that it is labour intensive. Further, plastics discarded in landfills are prone to releasing harmful substances over time. Moreover, waste-to-energy conversion is not efficient when discarding plastics waste.

[0007] Therefore, recycling is a good way to take care of plastic waste. When recycling plastic, the purity levels for various types of plastic is important or else the final product will suffer from an inferior quality. For instance, it is not possible to achieve a high-quality recycled plastic if the recycled material is formed of a mix of different materials, such as different types of plastic. Thus, it is of high importance that the plastic waste is sorted properly based on for instance type, application or market use and origin. Various processes may be used for sorting the plastic into different fractions. However, the existing processes are generally too labour-intensive, and the plants used are not flexible enough to be adapted to different conditions. Further, the existing processes are not able to achieve high enough purity levels for each plastic type or fraction. This results in that plastic materials sorted by existing methods cannot generally be used for forming virgin plastics when being recycled. In other words, recycled plastics are typically degraded in quality and or purity and cannot be used for the same purpose as before being recycled. There is a need of a more accurate method for sorting out these types of plastic products with a high efficiency at high throughput and with a high purity level in the resulting fraction in both an efficient and effective way.

[0008] Summary of invention

[0009] In view of the above, it is an object of the present disclosure to provide an improved method for obtaining a food grade plastic material from a mixed waste material stream.

[0010] It is also an object of the present disclosure to provide an improved system for obtaining a food grade plastic material from a mixed waste material stream.

[0011] It is also an object to provide a solution that addressees at least some of the criteria described above, namely, to provide a solution that can recover or sort a mixed waste material stream into different fractions with a higher precision, creating higher purity level of desired plastic material.

[0012] A further object is to provide a method that is able to sort out a number of different food grade plastic materials from each other into separate fractions with a higher efficiency.

[0013] To achieve at least one of the above objects, and also other objects that will be evident from the following description, a method having the steps defined in claim 1 is provided according to the present disclosure. Preferred variants of the method will be evident from the dependent claims.

[0014] More specifically, there is provided according to a first aspect a method for obtaining a food grade plastic material from a mixed waste material stream, the method comprising, discriminating a first type of plastic material from other types of material in the material stream using a near infrared spectroscopy system and / or a visible spectroscopy system, diverting the first type of plastic material from other types of material in the material stream into a first plastic material fraction, thereby sorting out material of the first type of plastic material from the material stream, discriminating a first type of food grade plastic material from other types of material in the first plastic material fraction using a camera-based object recognition system, diverting the first type of food grade plastic material from other types of material in the first plastic material fraction into a first food grade plastic material fraction, thereby sorting out other types of material from the first plastic material fraction, thereby obtaining the food grade plastic material.

[0015] The method may be advantageous as the camera-based object recognition system is provided to discriminate if objects in the first plastic material fraction is food grade plastic material. Food grade plastic material is valuable to be sorted out as the food grade plastic material are safe to be in food contact applications. Hence, the food grade plastic material can be recycled and reused for food grade products. If the recycled material is of mixed type, it is not allowed to be used in food grade products, such as food wrappers. Thereby, recycled material may be used for food grade products which result in that less of the packages for food grade products need to be manufactured by new materials. This may reduce the energy consumption for the packages as they may be made of recycled material. Furthermore, as the method is able to sort out a food grade plastic material from the mixed waste material stream, the amount of material which ends up for incineration may be reduced.

[0016] To achieve high enough purity levels of the food grade plastic material, the material is subjected to a discriminating and diverting step by the near infrared spectroscopy system and / or a visible spectroscopy system to limit or reduce the amount of material that enters the camera-based object recognition system. The first step of discriminating and diverting may be advantageous as it sorts out the possible relevant plastic material from the mixed waste material stream. Thereby, a first separation of the objects is performed.

[0017] When discriminating the first type of plastic material from other types of material, with the near infrared spectroscopy system and / or a visible spectroscopy system, the discrimination may be done dependent on the composition of the first type of plastic material. The material type may also be combined with the colour, such that the first type of plastic material may be of a specific composition with a specific colour. When the first type of plastic material is discriminated it is diverted into the first type of plastic material fraction based on the information from the step of discrimination. In other words, the step of diverting, diverts the already discriminated first type of plastic material. By diverting is meant that the first type of plastic material is separated from the other types of material such that the first type of plastic material and the other materials end up into different streams or fractions. The first type of plastic material may be removed from the mixed waste material stream. Other types of material may be removed from the mixed waste material stream.

[0018] The first sorting made in the first discriminating and diverting steps result in that a reduced amount of material reaches the second discriminating and diverting steps which may improve the discrimination accuracy or quality done by the camera-based object recognition system as fewer of the objects will be stacked. This may result in a higher purity of the sorted material. The higher purity of the food grade plastic material may result in an end product with a higher quality.

[0019] The method allows for sorting with a high accuracy while having a high throughput as the plastic materials can be identified by its material makeup and through the use of intelligent sorting. This increases the purity of the recycled material. This method may as an example be performed before the sorted plastic material enters further mechanical or chemical recycling processes.

[0020] When discriminating the first type of plastic material from other types of material, with the camera-based object recognition system, the discrimination may be performed through for example reading of invisible bar codes, visible bar codes, recognizing markings with visible signs, recognizing markings with invisible signs or by recognizing logotypes or portions thereof, or any other suitable method. There may be EAN bar codes at the plastic objects that the camera-based object recognition system is able to recognize and thereby discriminate that the plastic object is food grade or not. The camera-based object recognition system may also be able to recognize different visible signs or logotypes that the camera-based object recognition system has been trained that are food grade objects. For example, there may be specific objects, such as a bottle, that the camera-based object recognition system may recognize.

[0021] As understood by the skilled person, the method may be further adapted to incorporate capturing, reading, and processing information on tracers or markings embedded in the plastic material. A well- known techniques is tracer-based sorting (TBS), which uses a traceable plastic additive or marker that enables or enhances polymer type identification (e.g., fluorescence) and / or decodable markers (e.g., digital watermarks). Such TBS markers may be used in combination with polymer type identification based on the tracer’s unique fingerprint.

[0022] The input material, that is the mixed waste material stream, may originate from bales of mixed waste material or bales of plastic material. The origin of the material may be from municipal solid waste. The municipal solid waste may have already been sorted in a municipal solid waste plant such that the input may be bales of a desired plastic. Thus, the discrimination performed by the near infrared spectroscopy system and / or a visible spectroscopy system may be a purification step if the input is bales of the desired plastic and the discrimination performed by the camera-based object recognition system separates food grade from non-food grade.

[0023] The obtained food grade plastic material may be of a purity level of at least 80%-85%, preferably of a purity level of at least at least 85%-90%, more preferably of a purity level of at least 90%-95% and most preferably of a purity level of at least 95%-99,7%.

[0024] The method may further comprise discriminating a second type of plastic material from other types of material in the material stream, from which the first type of plastic material has been diverted, using a near infrared spectroscopy system and / or a visible spectroscopy system, diverting the second type of plastic material from other types of material in the material stream into a second plastic material fraction, thereby sorting out material of the second type of plastic material from the material stream, discriminating a second type of food grade plastic material from other types of material in the second plastic material fraction using a camera-based object recognition system, diverting the second type of food grade plastic material from other types of material in the second plastic material fraction into a second food grade plastic material fraction, thereby sorting out other types of material from the second plastic material fraction, thereby obtaining a second type of food grade plastic material.

[0025] It may be advantageous to add a second set of discriminating and diverting steps for sorting out a second type of food grade plastic material since it allows the method to handle more kinds of materials at the same time which further enhances the efficiency of the method. The recycling levels may also be increased through sorting out a second type of food grade plastic material. The further steps may also decrease the labour intensity of the method because of the decrease of necessity to move the material that was not of the first type of food grade plastic material to go through the method a second time with a different setting for what type of material that is sorted. Another advantage resides in those settings, for which type of material that is sorted and settings for potential washing may not need to be changed as often as well.

[0026] The step of discriminating a second type of plastic material from other types of mixed waste material in the material stream is performed when the first type of plastic material has already been diverted form the mixed waste material stream. Thereafter, the second type of plastic material fraction is subjected to discrimination by the camera-based object recognition system to discriminate which objects that are food grade. Thereby, sorting out the second type of food grade plastic material.

[0027] As is understood by the skilled person, the method may be adapted to obtain any needed or desired number of food grade plastic materials. By sorting out more types of plastic material the method is easily adapted to the kind of sorting system that is required in a specific area or country.

[0028] The method may further comprise discriminating a further type of plastic material from other types of material in the material stream, from which the second type of plastic material has been diverted, using a near infrared spectroscopy system and / or a visible spectroscopy system, diverting the further type of plastic material from other types of material in the material stream into a further plastic material fraction, thereby sorting out material of the further type of plastic material from the material stream, discriminating the further type of plastic material from other types of material in the further plastic material fraction, using a near infrared spectroscopy system and / or a visible spectroscopy system, diverting the further type of plastic material from other types of material in the material stream into a purified further plastic material fraction, thereby sorting out other types of material from the further plastic material fraction.

[0029] When all the plastic material with potential food grade plastic material or all the desired material with potential food grade plastic material have been separated from the mixed waste material stream there may still be remaining objects of value in the mixed waste material stream. Therefore, to further enhance the efficiency of the method, there may be a further discrimination and diverting step to discriminate and divert further plastic material of value. Thereby, providing a further plastic material fraction. To enhance the purity of the further plastic material fraction, it may be subjected to a second discriminating and diverting step such that a purified further plastic material fraction is provided.

[0030] The method may further comprise reducing a size of material items in the first type of food grade plastic material fraction, subjecting the first type of food grade plastic material fraction to an alkaline washing process and / or a washing process at an elevated temperature, discriminating said first type of food grade plastic material in the washed first type of food grade plastic material fraction from other types of material using a near infrared spectroscopy system and / or a visible spectroscopy system, and diverting said first type of food grade plastic material in the washed first type of food grade plastic material fraction from other types of material, thereby sorting out other types of material from the washed first type of food grade plastic material fraction, thereby obtaining a purified food grade plastic material, and if the second type of food grade plastic material is present; reducing a size of material items in the second type of food grade plastic material fraction, subjecting the second type of food grade plastic material fraction to an alkaline washing process and / or a washing process at an elevated temperature, discriminating said second type of food grade plastic material in the washed second type of food grade plastic material fraction from other types of material using a near infrared spectroscopy system and / or a visible spectroscopy system, and diverting said second type of food grade plastic material in the washed second type of food grade plastic material fraction from other types of material, thereby sorting out other types of material from the washed second type of food grade plastic material fraction, thereby obtaining a purified second type of food grade plastic material.

[0031] It may be advantageous that the types of food grade plastic material are subjected to the step of reducing the size of the material in each type of food grade plastic material fraction and the step of subjecting each type of food grade plastic material fraction to a washing process, as it may increase the level of purity in the obtained type of food grade plastic material. The material items in the sorted type of food grade plastic material fraction may prior to reducing its size be of mixed type. In other words, material items or objects in the sorted type of food grade plastic material fraction may include more than one type of material where the one or more type of material are bound together prior to reducing a size of the items. By reducing the size of the material items material of different types may be split from each other which result in that the discriminating and diverting step may be allowed to sort more accurately with a higher purity as a result. Further, the washing step may remove stickers, signs or similar on the material in the type of food grade plastic material fraction, thereby allowing the subsequent discriminating and the diverting steps to remove these as well. Hence, a higher purity may be achieved.

[0032] The method may further comprise subsequent to subjecting the first type of food grade plastic material fraction, and if present, the second type of food grade plastic material fraction, to the washing process, drying of material in the first type of food grade plastic material fraction, and if present, in the second type of food grade plastic material fraction.

[0033] It may be advantageous to dry the material before it enters the last discriminating and diverting steps due to that material items may get stuck to each other in their wet condition. Wet items may have a tendency to stick to each other or to other entities which may result in that it is harder to divert the correct material item. By drying the material items the level of purity of the obtained plastic material may be further increased.

[0034] The method may further comprise, subsequent to subjecting the first type of food grade plastic material fraction, and if present, the second type of food grade plastic material fraction, to the washing process, subjecting the first type of food grade plastic material fraction, and if present, the second type of food grade plastic material fraction, to a floating separation process, thereby separating material with a density higher than that of water from material with a density lower than that of water.

[0035] It may be advantageous with a floating separation process since it may separate lighter material from more dense material, which further may improve the purity level of the food grade plastic material. By subjecting the material items for a floating separation process it also provides an alternative method for sorting out different types of material. Material of a type will either float or sink, thereby sorting it out based on its density.

[0036] The first type of plastic material may be a first type of high impact polystyrene material, such that the food grade plastic material is a food grade high impact polystyrene material, and if the second type of plastic material is present, wherein the second type of plastic material may be a second type of high impact polystyrene material, such that the second type of food grade material is a second food grade high impact polystyrene material, and if the further type of plastic material is present, wherein the further type of plastic material may be a mixed high impact polystyrene material.

[0037] Food grade high impact polystyrene material is an economically valuable material especially when it may be sorted out after type into fraction with a high purity. Therefore, a method suitable for sorting out food grade high impact polystyrene material may provide possibilities to reuse the material as discussed above for the food grade plastic material.

[0038] The camera-based object recognition system may discriminate by acquiring, by a camera, an image of an object in the first plastic material fraction, and if present, in the second plastic material fraction, and comparing, by a processor, the acquired image with a database of food grade objects to determine if the object is of food grade.

[0039] The camera-based object recognition system may be provided with a database of food grade objects and by comparing the images acquired by the camera it may recognize if the object is food grade or not. For example, by providing the database with images of known food grade objects in different angles that the camera-based object recognition system is supposed to discriminate as food grade, the camera-based object recognition system may be able to determine if different types of objects are food grade or not. The images are not necessarily full-size images of the objects, it may also be small parts that result in that the object may be classified as food grade. It may for example be a logo, or a specific product text.

[0040] The camera-based object recognition system may discriminate by acquiring, by a camera, an image of an object in the first plastic material fraction, and if present, in the second plastic material fraction, and inputting the acquired image into a machine learning model trained to identify food grade objects in input images, thereby determining if the object in the acquired image is of food grade.

[0041] The machine learning model may thus perform actions based on the patterns and relationships it finds in the acquired image as is known in the art. The actual processes taking place in the machine learning model may typically not be known as is known in the art. However, it is in this regard important that the machine learning model is trained to recognize patterns and make predictions or decisions based on its training to identify food grade objects. The model may thus typically be trained using a set of input data related to or depicting food grade objects and corresponding output data if the object is food grade or not. Based on such data the machine learning model may be trained to make decisions based on patterns, features or similar it finds in the acquired images. In other words, the machine learning model may make a decision whether an object is of food grade or not.

[0042] The camera-based object recognition system may further comprise a tracer-based sorting, TBS, unit which discriminates by; acquiring, by a camera, an image of an object having a TBS marker in the first plastic material fraction, and if present, in the second plastic material fraction, detecting, by a processor, the TBS marker in the acquired image, and comparing, by the processor, the detected TBS marker with a database of TBS markers to determine if the object is of food grade.

[0043] It may be advantageous that the camera-based object recognition system comprises the TBS unit which provides the possibility to detect TBS markers that exists on the objects in first and second plastic material fraction. The TBS markers may be visible, invisible, and fluorescent markings that provides information of the object to the TBS unit. Thereby, a complementary method for determine if the objects are of food grade or not is provided.

[0044] As understood by the skilled person, the method may include decoding the information embedded in such a TBS marker.

[0045] The method may further comprise discriminating the first type of plastic material, and if present, the second type of plastic material, from other types of material in the material stream from which the first type of plastic material has been diverted, or if the second type of plastic material is present, from which the second type of plastic material has been diverted, using a near infrared spectroscopy system and / or a visible spectroscopy system, and diverting the first type of plastic material, and if present the second type of plastic material from other types of material in the material stream into a recovery plastic material fraction that is re-joined with the mixed waste stream.

[0046] It may be advantageous to have a discriminating and diverting step of the material in the mixed waste material stream subsequent to when all the types of plastic material has been diverted. Thereby, material items of each type of plastic material may be sorted out and reintroduced into the start of the mixed waste material stream. The material items of each type of plastic material may because of various reasons not be discriminated or diverted when they should have been. This may be due to stacking of material items which may not allow all of them to be discriminated or due to a miss in a diverting step. Thus, providing the material items that were missed under the first steps of discrimination and diverting with a further chance to be discriminated and diverted into the right type of plastic material further enhances the recycling levels of the method. This loop may continue until the material item is correctly sorted. Therefore, both increasing the effectiveness and the yield of the method.

[0047] Re-joining the recovery material fraction into the initial mixed waste material stream allows all types of plastic material to be transported on a single transport means, such as a single conveyor belt, or any other type of transport means used. This provides a less complex system compared to a system where all types of plastic materials are sorted directly into their respective type of plastic material fraction. Even if only the first type of plastic material that is sorted, re-joining of the recovery material fraction is still advantageous, as this configuration allows for easy scaling of the system at later stages. Additionally, in the case with only the first type of plastic material it is also possible to direct the recovery material fraction into the first plastic material fraction. The method may further comprise, prior to discriminating the first type of plastic material, separating ferrous material from the mixed waste stream using a magnet arrangement, and / or separating non-ferrous material from the mixed waste stream using an eddy current separator.

[0048] It may be advantageous to separate the ferrous material and / or nonferrous material from the mixed waste material stream due to the value of many of the ferrous materials and / or the non-ferrous materials. By separating the ferrous material and the non-ferrous materials it may be recycled and the profit of the method may be further increased. Sorting out ferrous material and / or non-ferrous material may also result in a decrease of material downstream in the mixed waste material stream which may further facilitate the discrimination steps. With non-ferrous material is herein meant nonferrous metal.

[0049] The method may further comprise, prior to discriminating the first type of plastic material, separating objects of the mixed waste stream having a maximum cross-sectional extension larger than 320 mm into a shredder stream using a wind sifter and / or a screen.

[0050] Material items with a larger cross-sectional extension may be separated, which may further enhance the discriminating process and avoid that the larger material items cover other material item and thereby not allowing them to be discriminated. Furthermore, the separating of objects may also separate objects with a cross-sectional extension smaller than a predetermined extension as many of the smaller material such as gravel and sand may be separated from the mixed waste material stream through such sorting.

[0051] The may further comprising, shredding the objects in the shredder stream such that the maximum cross-sectional extension is smaller than 320 mm and re-joining the objects to the mixed waste material stream.

[0052] It may be advantageous to reduce the cross-section extension of the objects to an extension smaller than 320 mm, as then these objects may be allowed to enter the mixed waste material stream with covering other objects.

[0053] According to a second aspect a system for obtaining a food grade plastic material from a mixed waste material stream is provided. The system comprising a first classification and sorting station configured to receive the mixed waste stream, the first classification and sorting station comprising a near infrared, NIR, spectroscopy system and / or a visible spectroscopy system configured to discriminate a first type of plastic material from other types of material in the material stream, and an ejection unit configured to divert the first type of plastic material from other types of material in the material stream into a first plastic material fraction, thereby sorting out material of the first type of plastic material from the material stream, a first food grade classification and sorting station configured to receive the first plastic material fraction, the first food grade classification and sorting station comprising a first camerabased object recognition system configured to discriminate a first type of food grade plastic material from other types of plastic material in the first plastic material fraction, and an ejection unit configured to divert the first type of food grade plastic material from other types plastic material in the first plastic material fraction into a first food grade plastic material fraction, thereby sorting out other types of material from the first plastic material fraction, thereby obtaining the food grade plastic material from the material stream.

[0054] In general, features of this aspect provide similar advantages as discussed above in relation to the previous aspects of the invention. The features of the method may be provided for the system by themselves or as combination. Consequently, said features and advantages will not be repeated in order to avoid undue repetition.

[0055] A further scope of applicability of the present invention will become apparent from the detailed description given below. However, it should be understood that the detailed description and specific examples, while indicating preferred variants of the present inventive concept, are given by way of illustration only, since various changes and modifications within the scope of the inventive concept will become apparent to those skilled in the art from this detailed description.

[0056] Brief description of the drawings

[0057] The aspects of the present inventive concept, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings. The figures are provided to illustrate the general structures of the present inventive concept. Like reference numerals refer to like elements throughout.

[0058] Fig. 1 is a flow chart over a system for obtaining a food grade plastic material from a mixed waste material stream.

[0059] Fig. 2 is a flow chart over a system for obtaining food grade plastic material from a mixed waste material stream with further stations in the system as compared to the system of Fig. 1 .

[0060] Fig. 3 is a perspective schematic view of a classification and sorting station.

[0061] Fig. 4 is a flow chart illustrating the different steps in a method for obtaining a food grade plastic material from a mixed waste material stream.

[0062] Fig. 5 is a flow chart illustrating the different steps in a method for obtaining a food grade plastic material from a mixed waste material stream with further steps in the method as compared to the method of Fig. 4.

[0063] Detailed description of the preferred embodiments

[0064] The present inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred variants of the inventive concept are shown. This inventive concept may, however, be implemented in many different forms and should not be construed as limited to the variants set forth herein; rather, these variants are provided for thoroughness and completeness, and fully convey the scope of the present inventive concept to the skilled person.

[0065] Fig. 1 illustrates a flow chart of a system 1 for obtaining a food grade plastic material 10 from a mixed waste material stream PS. The system 1 comprises a first classification and sorting arrangement 20. At the first classification and sorting arrangement 20 a first sorting is provided. A first classification and sorting station 22, in the first classification and sorting arrangement 20, receives the mixed waste material stream PS. The input material, that is the mixed waste material stream PS, may originate from bales of mixed waste material or bales of plastic material. However, it should be noted that if the plastic material is a high impact polystyrene material, the origin of the material may be from municipal solid waste that has already been sorted in a municipal solid waste plant such that bales of mixed polystyrene material already is sorted out and may be used in the system 1 .

[0066] Now also referring to Fig. 3, the first classification and sorting station 22 comprises a near infrared, NIR, spectroscopy system 222 and / or a visible spectroscopy system configured to discriminate a first type of plastic material from other types of material in the material stream PS, and an ejection unit 224 configured to divert the first type of plastic material from other types of material in the material stream PS into a first plastic material fraction 2. When discriminating the first type of plastic material from other types of material the discrimination may be done dependent on the composition of a first type of plastic material. The material type may also be combined with a colour, such that a first type of plastic material may be of a specific composition with a specific colour. After the first type of plastic material has been discriminated it is diverted into the first type of plastic material fraction 2 based on the information from the discrimination. In other words, the first classification and sorting station 22 diverts the already discriminated first type of plastic material. In yet other words, the first classification and sorting station 22 diverts the already discriminated first type of plastic material from other materials present in the mixed waste material stream PS. By diverting is meant that the first type of plastic material is separated from the other types of material into different streams or fractions. The first type of plastic material may be removed from the mixed waste material stream PS, or other types of material may be removed from the mixed waste material stream PS. The other materials that are diverted from the classification and sorting station is represented in the figures by a dotted arrow. All the classification and sorting stations in the system 1 may be the same type of station having different kind of systems. In other words, the same type of station may be at multiple positions in the system. An example of such a station will be further described in connection to Fig. 3.

[0067] The first classification and sorting arrangement 20 further comprises a first food grade classification and sorting station 25 comprising a camera-based object recognition system 226 and an ejection unit 224. The first food grade classification and sorting station 25 receives the first type of plastic material fraction from the first classification and sorting station 22 and sorts the first plastic material fraction into food grade or non-food grade. Thereby, obtaining a first food grade plastic material 10.

[0068] When discriminating the first type of plastic material from other types of material, with the first food grade classification and sorting station 25 using the camera-based object recognition system 226, the discrimination may be performed through by for example scanning invisible bar codes, recognizing markings with visible signs, or by recognizing logotypes. There may be bar codes at the plastic objects that the camera-based object recognition system 226 is able to recognize and thereby discriminate that the plastic object is food grade or not. The camera-based object recognition system 226 may also be able to recognize different visible signs or logotypes that the camerabased object recognition system 226 has been learned that are food grade objects. For example, there may be specific objects, such as a bottle, that the camera-based object recognition system 226 may recognize. How the camera-based object recognition system 226 functions will be further described in connection to Fig. 3.

[0069] Turning to Fig. 2 an example of the system 1 for obtaining a food grade plastic material 10 from a mixed waste material stream PS with further stations in the system 1 is illustrated. The stations that already has been described in connection to Fig. 1 forms part of the system 1 in Fig. 2 as well and will not be further described in this section. It should be stressed that the stations in system 1 in Fig. 1 are sufficient to reach a synergy effect when sorting the mixed waste material stream PS.

[0070] In Fig. 2 there are examples of which type of stations that may further be part of the system 1. The stations may alone form part of the system 1 in Fig. 1 or together with other stations. The stations are illustrated together to facilitate the understanding of the description. The different stations described below may be used alone or in any combination depending on the requirement of the plant in which the system 1 is operating.

[0071] The system 1 in Fig. 2 further comprises a pre-sorting arrangement 60. The pre-sorting arrangement 60 comprises a bale opener 61 that is configured to open the bales that the mixed waste material stream PS may originate from. The pre-sorting arrangement 60 further comprises a magnet arrangement 62 that is configured to separate ferrous material from the mixed waste material stream PS into a ferrous material fraction 63. Ferrous material often has a high value and by separating ferrous material it may be recycled and the profit of the system may be further increased. The pre-sorting arrangement 60 comprises an eddy current separator 62b that is configured to separate non-ferrous material from the mixed waste material stream PS into a non-ferrous material fraction 63b. Non-ferrous material or non-ferrous metals often has a high value and by separating non-ferrous material it may be recycled and the profit of the system may be further increased.

[0072] The pre-sorting arrangement 60 further comprises a screener 64 that separates material items with a maximum cross-sectional extension smaller than a pre-set screen range to a waste fraction 65 and material items with a larger maximum cross-sectional extension than the pre-set screen range to a pre-shredder 68. As an example, the pre-set screen range may be 20 mm - 320 mm. The pre-shredder 68 of the pre-sorting arrangement 60 shreds the material such that the maximum cross-sectional extension is smaller than the upper value in the pre-set screen range. The shredded material items are reintroduced in the mixed waste material stream PS.

[0073] The pre-sorting arrangement 60 further comprises a wind sifter that separates film material from the mixed waste material stream PS into a film fraction 67.

[0074] At the first classification and sorting arrangement 20 a second sorting is provided by a second classification and sorting station 23 that receives the mixed waste material stream PS, from which the first type of plastic material has been diverted, from the first classification and sorting station 22. The depicted second classification and sorting station 23 comprises a near infrared, NIR, spectroscopy system 222 and / or a visible spectroscopy system configured to discriminate a second type of plastic material from other types of mixed waste material in the material stream PS, and an ejection unit 224 configured to divert the second type of plastic material from other types of material in the material stream PS into a second plastic material fraction 3, see also Fig. 3. In other words, the second classification and sorting station 23 discriminates and diverts a plastic material that is different from the first plastic material in either composition and / or colour. When the second type of plastic material has been discriminated it is diverted into the second type of plastic material fraction 3 based on the information from the discrimination. The second classification and sorting station 23 handles the mixed waste material stream PS in a similar way as the first classification and sorting station 22 with the major exception that the first type of plastic material already has been diverted and that it is a second type of plastic material that is discriminated and diverted.

[0075] The first classification and sorting arrangement 20 further comprises a second food grade classification and sorting station 26 comprising a camera-based object recognition system 226 and an ejection unit 224. The second food grade classification and sorting station 26 receives the second type of plastic material fraction from the second classification and sorting station 23 and sorts the second plastic material fraction into food grade or non-food grade. Thereby, obtaining a second food grade plastic material 11 .

[0076] As is understood by the skilled person, if the system 1 needs to sort out a third type of food grade plastic material, a third classification and sorting station and a third food grade classification and sorting station may be added to the system 1 .

[0077] At the first classification and sorting arrangement 20 a further sorting is provided by a further classification and sorting station 27 that receives the mixed waste material stream PS from the second classification and sorting station 23. The further classification and sorting station 27 comprises a near infrared, NIR, spectroscopy system 222 and / or a visible spectroscopy system configured to discriminate a further type of plastic material from other types of mixed waste material in the material stream PS, and an ejection unit 224 configured to divert the further type of plastic material from other types of material in the material stream PS into a further plastic material fraction, see also Fig. 3.

[0078] When all the plastic material with potential food grade plastic material have been separated from the mixed waste material stream there may still be remaining objects of value in the mixed waste material stream. Therefore, to further enhance the efficiency of the method, there may be a further discrimination and diverting step to discriminate and divert further plastic material of value. Thereby, providing a further plastic material fraction.

[0079] The classification and sorting arrangement 20 further comprises a further cleaning classification and sorting station 28. As the further cleaning classification and sorting station 28 are of the same type of station as the first 22 and second 23 and further 27 classification and sorting station, how the stations functions will not be repeated.

[0080] The further cleaning classification and sorting station 28 is configured to sort out the further type of plastic material to further clean the further type of plastic material fraction. The further cleaning classification and sorting station 28 are in other words configured to divert other material from the further type of plastic material fraction. These steps further enhance the level of purity in the further type of plastic material fraction, thereby providing a purified further plastic material fraction 4.

[0081] The classification and sorting arrangement 20 further comprises a recovery classification and sorting station 24, which is of the same type as the other classification and sorting stations. The recovery classification and sorting station 24 is configured to receive the mixed waste material stream PS from the further classification and sorting station 27 and to discriminate and divert the first type of plastic material, the second type of plastic material and the further type of plastic material such that these types of plastic material is reintroduced into the mixed waste material stream PS that enters the first classification and sorting station 22. The material items of each type of plastic material may because of various reasons not be discriminated or diverted when they should have been, i.e. earlier in the process. This may be due to stacking or sticking of material items which may not allow all of them to be discriminated or due to a miss in a diverting step. Thus, providing the material items that were missed under the first steps of discrimination and diverting with a further chance to be discriminated and diverted into the right type of plastic material further enhances the recycling levels of the method. This loop may continue until the material items is correctly sorted.

[0082] Hereafter when the different arrangements and stations that handles the first type of food grade plastic material fraction 2 and second type of plastic material fraction 3 will be described, only the arrangements and stations that handles the first type of plastic material fraction 2 will be described. The second type of plastic material fraction 3 passes through substantially the same type of arrangement and stations. In Fig. 2 only the arrangements as such are illustrated for the second type of plastic material fraction 3. More specifically, a second material item size reduction arrangement 30a, a second washing arrangement 40a and a second purifying classification and sorting arrangement 50a are schematically illustrated in Fig. 2.

[0083] The system 1 further comprises, a material item size reduction arrangement 30, a washing arrangement 40, and a purifying classification and sorting arrangement 50.

[0084] The first type of plastic material fraction 2 is received by the material item size reduction arrangement 30. At the material item size reduction arrangement 30 the size of the material items in the first type of food grade plastic material fraction 2 are reduced. The material items are shredded in the material item size reduction arrangement 30 by a shredder 32 to a smaller size. The material items may be shredded to a size with a maximum cross- sectional extension that may be at most 18 mm.

[0085] A first washing station 42 of the washing arrangement 40 receives the first type of food grade plastic material fraction 2 from the material item size reduction arrangement 30. The fact that the material items have been shredded may result in they are more exposed and hence accessible for a washing process. The washing of the first type of food grade plastic material fraction 2 may be in an alkaline washing process and / or a washing process at an elevated temperature. The temperature and how alkaline the washing process is dependent on what the first type of food grade plastic material fraction 2 has for composition and / or on what kind of material that needs to be removed, by being washed away, from the first type of plastic material. The washing process may be used to remove stickers, labels or similar on the material items in the first type of food grade plastic material fraction 2.

[0086] The washing arrangement 40 further comprises a density separation station 44. The density separation station 44 receives the cleaned first type of food grade plastic material fraction 2 from the first washing station 42 and separates material with a density higher than that of water from material with a density lower than that of water. It may be advantageous with a floating separation process since it may separate lighter material from more dense material, which further may improve the purity level of the food grade plastic material 10. By subjecting the material items to a floating separation process it also provides an alternative method for sorting out different types of material. Material of a type will either float or sink, thereby sorting it out based on its density.

[0087] The wet material items from the washing station may have a tendency to stick to each other or to other entities which may result in that it is harder to divert the correct material item. Therefore, a first drying station 46 is added to the washing arrangement 40 of the system 1 . The first drying station 46 dries the first type of food grade plastic material fraction 2. The drying may be performed using air circulation and / or an elevated temperature or other known methods for drying. The dried material items of the first type of food grade plastic material fraction are then subjected to two steps of sorting. The first step of sorting is performed in a first wind sifter 48 of the washing arrangement 40 where air is used to separate lighter material from denser material by using compressed air that blows the lighter material away. The first wind sifter 48 receives the first type of food grade plastic material fraction 2 from the first drying station 46. The second step of sorting is performed in a first screener 49 of the washing arrangement 40 that sort material items based on its cross-sectional size. The first screener 49 receives the first type of food grade plastic material fraction 2 from the first wind sifter 48.

[0088] Subsequent to the washing process the material items of the washed first type of food grade plastic material fraction 2 are once again discriminated, where the first type of food grade plastic material is discriminated from other types of material. The other types of material may be material that has been separated from the first type of food grade plastic material during the size reducing process or the washing process. The purifying classification and sorting arrangement 50 comprises a first purifying classification and sorting station 52 configured to receive the washed first type of food grade plastic material fraction 2 from the first washing arrangement 40. The first purifying classification sorting station 52 of Fig. 1 is of the same type as the first classification and sorting station 22. How it works will for the sake of efficiency not be repeated and the classification and sorting stations will be further described in connection to Fig. 3. A major difference between the first classification and sorting station 22 and the purifying classification and sorting station 52 is that the purifying classification and sorting station 52 is sorting out other types of material from the washed first type of plastic material fraction 2 and thereby obtaining the purified food grade plastic material 10'.

[0089] It should be noted that even thou plastic material have been used throughout the description, the plastic material may be a specific plastic material such as high impact polystyrene, or a food-grade plastic material, or a food grade high impact polystyrene. The system described above functions for these types of plastic material as well.

[0090] Turning to Fig. 3 a perspective schematic view of a classification and sorting station 700 is illustrated. The first 22 and second 23 and further 27 classification and sorting stations, the first 25 and second 26 food grade classification and sorting station, the recovery classification and sorting stations 24, the further cleaning classification and sorting stations 28, and the first purifying classification and sorting station 52 may all be of the same type as the classification and sorting station 700 that is described here. Each of said stations may have one or more of the features described below. However, in the following the station 700 is for reasons of simplicity described as a classification and sorting station 700.

[0091] The classification and sorting station 700 is fed with pieces or items of material 710. The pieces of material 700 are conveyed through a detection zone 720. However, the pieces of material 700 may be provided through the detection zone 720 by any suitable mean or manually without any technical means. A light source arrangement 730 and a NIR spectroscopy system 222 are provided. The spectroscopy system 222 is adapted to receive and analyse light 732, from the light source arrangement 730, which is reflected and / or scattered by the pieces of material 710 in the detection zone 720. Hence, the NIR spectroscopy system 222 typically acquires a spectrum of the pieces of material 710 from the stream of material that is conveyed through the detection zone 720. The NIR spectroscopy system 222 of the classification and sorting station 700 is configured to discriminate a first type of plastic material from other materials, such as plastic materials, based on the acquired spectrum. In other words, the NIR system 222 is typically set up such that a specific type of plastic material is discriminated from other types of material owing from its spectrum.

[0092] The classification and sorting stations may further comprise a light spectroscopy system 760 configured to acquire a spectrum of plastic material originating from the stream of material PS that is conveyed through the detection zone 720. The ejection unit 224 of the classification and sorting station 700 may be further configured to divert said type of plastic material originating from the mixed waste material stream PS based on the acquired spectrum thereby sorting the first type of plastic material fraction based on its colour.

[0093] The light spectroscopy system 760 may through the acquired spectrum determine the different colours of the plastic material that is conveyed through the detection zone 720. An advantage of determining the colours of the plastic material is that it may be sorted into different fractions.

[0094] The classification and sorting station 700 may further comprise a laser triangulation system 740 configured to determine height information of material 710 that is conveyed through the detection zone 720. The ejection unit 224 of said at least one classification and sorting station may be further configured to divert said plastic material based on the determined height information.

[0095] The laser triangulation system 740 is typically configured to emit a line of laser light 742 towards the detection zone 720. The depicted laser triangulation system 740 includes a camera-based sensor arrangement 744 configured to receive and analyse light 746 which is reflected and / or scattered by the piece of material 710 in the detection zone 720. By means of the laser triangulation system 740 the classification and sorting station 700 may be able to detect plastic material that the NIR spectroscopy system 222 have difficulties to detect. One example of such plastic material may be black plastic material. By detecting height differences on a conveyor belt used to convey the material being sorted, the classification and sorting station may combine such height information with the acquired information from the NIR spectroscopy system 222 to determine if there is any black plastic material or plastic material that is hard to detect on the conveyor belt. Accordingly, further plastic material may be recycled.

[0096] The classification and sorting station 700 may further comprise a camera-based object recognition system 226 comprising a camera 750 configured to acquire images of plastic material originating from the stream of material that is conveyed through the detection zone 720. The classification and sorting station 700 may further comprise a tracer-based sorting, TBS, unit 226a, configured to acquire images of plastic material origination from the stream of material that is conveyed through the detection zone 720 and where such plastic material include a TBS marker. The depicted camerabased object recognition system 226 and / or the TBS unit 226a further comprises at least one processor (not shown in figure) that may compare the acquired image and / or the image with the TBS marker with a database of food grade objects to determine if the object is of food grade.

[0097] Additionally, or alternatively the TBS unit 226a may discriminate by inputting the acquired image with the TBS into a TBS decoding processor to obtain a decoded TBS, thereby determining if the object or objects in the acquired image is of food grade.

[0098] Additionally, or alternatively the camera-based object recognition system 226 may discriminate by inputting the acquired image and, optionally, the decoded TBS into a machine learning model trained to identify food grade objects in input images, thereby determining if the object or objects in the acquired image is of food grade. The machine learning model performs actions based on the patterns and relationships it finds in the acquired image as is known in the art. The machine learning model may typically be trained to recognize patterns and make predictions or decisions based on its training to identify food grade objects. The model may typically be trained using a set of input data regarding food grade objects and corresponding output data if the object is food grade or not. Based on such data the machine learning model may typically be trained to make decisions based on patterns, features or similar it finds in the acquired images. In other words, the machine learning model may make a decision whether an object is of food grade or not.

[0099] The classification and sorting station 700 may comprise an artificial neural network in combination with the camera 750. Such artificial neural network may be configured to detect different characteristics of plastic material that is conveyed through the detection zone 720 based on images acquired by the camera 750, and, optionally, the decoded TBS. The ejection unit 224 of the classification and sorting station 700 may in this case be further configured to divert plastic material that is conveyed through the detection zone 720 based on the detected characteristics of plastic material. In other words, characteristics of plastic material may thus be determined by the artificial neural network from the, by the camera 750, acquired images.

[0100] The characteristics may be a shape, a colour, features at the surface or anything in the visual appearance of the plastic material that may be determined and classified by the artificial neural network. With the TBS unit 226a it further allows the camera 750 to use information from invisible or fluorescence markings or other TBS markings that are not visual to determine if the object is food grade. The camera 750, may provide the possibility to further sort the material into different fractions. With the help of the artificial neural network it may be possible to sort plastic material of the same material composition into different fractions depending on quality and origin.

[0101] The camera-based object recognition system 226 may comprise one camera acquiring all the images or a plurality of cameras to cover different areas or to detect different information from the objects.

[0102] Now turning to Fig. 4, a method 100 for obtaining a food grade plastic material 10 from a mixed waste material stream PS will now be described. The method 100 starts by discriminating 110a a first type of plastic material from other types of material in the material stream PS using a near infrared spectroscopy system 222 and / or a visible spectroscopy system.

[0103] The method 100 proceeds with diverting 110b the first type of plastic material from other types of material in the material stream PS into a first plastic material fraction 2, thereby sorting out material of the first type of plastic material from the material stream PS.

[0104] The method proceeds with discriminating 111a a first type of food grade plastic material from other types of material in the first plastic material fraction using a camera-based object recognition system 226.

[0105] The method proceeds with diverting 111 b the first type of food grade plastic material from other types of material in the first plastic material fraction into a first food grade plastic material fraction 2, thereby sorting out other types of material from the first plastic material fraction, thereby obtaining the food grade plastic material 10.

[0106] It is to be noted that the steps in the steps or acts of the above method 100 may be conducted in any suitable order and hence not just in the order given above. Further, one or more of the steps or acts may be conducted in parallel. It is also to be noted that the steps or acts may be conducted by different equipment, at different times and / or at different sites. In other words, as an example, the method may be performed in a distributed manner at a plurality sites where different steps or acts are conducted at different points in time. However, the method may to advantage be conducted in the sequence described above at a single site.

[0107] Turning to Fig. 5, the method 100 from Fig. 4 is illustrated together with a set of alternative steps. The alternative steps may be added alone or in any combination to the method 100 in Fig. 4 depending on the requirements. The steps already mentioned in connection to Fig. 4 will, for the sake of efficiency, not be described again.

[0108] The method further comprises steps pre-sequent to the step of discriminating 110a, separating 170a ferrous material from the mixed waste stream using a magnet arrangement 62, separating 170b non-ferrous material from the mixed waste stream using an eddy current separator 62b, separating 180 objects of the mixed waste stream having a maximum cross-sectional extension larger than 320 mm into a shredder stream using a wind sifter 66 and / or a screen 64 and shredding 190 the objects in the shredder stream such that the maximum cross-sectional extension is smaller than 320 mm and re-joining the objects to the mixed waste material stream PS.

[0109] Subsequent to the step of diverting 110b, a step of, discriminating 112a a second type of plastic material from other types of material in the material stream PS from which the first type of plastic material has been diverted, using a near infrared spectroscopy system 222 and / or a visible spectroscopy system, is provided.

[0110] The method 100 proceeds with diverting 112b the second type of plastic material from other types of material in the material stream PS into a second plastic material fraction 3.

[0111] The method 100 proceeds with discriminating 113a a second type of food grade plastic material from other types of material in the second plastic material fraction using a camera-based object recognition system 226.

[0112] The method 100 proceeds with diverting 113b the second type of food grade plastic material from other types of material in the second plastic material fraction into a second food grade plastic material fraction 3, thereby sorting out other types of material from the second plastic material fraction, thereby obtaining a second type of food grade plastic material 11 .

[0113] Subsequent to the step of diverting 112b, a step of discriminating 114a a further type of plastic material from other types of material in the material stream PS, from which the second type of plastic material has been diverted, using a near infrared spectroscopy system 222 and / or a visible spectroscopy system is provided.

[0114] The method 100 proceeds with diverting 114b the further type of plastic material from other types of material in the material stream into a further plastic material fraction, thereby sorting out material of the further type of plastic material from the material stream PS.

[0115] The method 100 proceeds with discriminating 115a the further type of plastic material from other types of material in the further plastic material fraction, using a near infrared spectroscopy system 222 and / or a visible spectroscopy system,

[0116] The method 100 proceeds with diverting 115b the further type of plastic material from other types of material in the material stream into a purified further plastic material fraction 4, thereby sorting out other types of material from the further plastic material fraction.

[0117] The method 100 proceeds with discriminating 116a the first type of plastic material, and if present, the second type of plastic material, from other types of material in the material stream PS from which the first type of plastic material has been diverted, or if the second type of plastic material is present, from which the second type of plastic material has been diverted, using a near infrared spectroscopy system 222 and / or a visible spectroscopy system.

[0118] The method 100 proceeds with diverting 116b the first type of plastic material, and if present the second type of plastic material from other types of material in the material stream into a recovery plastic material fraction that is re-joined with the mixed waste stream PS. Re-joining the recovery material fraction into the initial mixed waste material stream allows all types of plastic material to be transported on a single transport means, such as a single conveyor belt.

[0119] Hereafter, the different steps for processing the first 2 and second 3 type of food grade plastic material fraction will be described. For the sake of efficiency the steps will be described together. However, it should be understood that it is two different flows and that the steps are performed parallel to each other and may be performed in different stations.

[0120] The method 100 proceeds with discriminating 111a, 113a the first type of food grade plastic material from other types of material in the first type of food grade plastic material fraction 2 and the second type of food grade plastic material fraction 3 using a near infrared spectroscopy system 222 and / or a visible spectroscopy system.

[0121] The method 100 proceeds with diverting 111 b, 113b other types of material from the first type of food grade plastic material in the first type of food grade plastic material fraction 2 and the second type of food grade plastic material fraction 3, thereby purifying the first type of food grade plastic material fraction 2 and second type of food grade plastic material fraction 3.

[0122] The method 100 proceeds with subjecting 150, 152 the first type of food grade plastic material fraction 2 and the second type of food grade plastic material fraction 3 to a floating separation process, thereby separating material with a density higher than that of water from material with a density lower than that of water.

[0123] The method proceeds with drying 160, 162 of material in the first type of food grade plastic material fraction 2 and the second type of food grade plastic material fraction 3.

[0124] The method 100 proceeds with discriminating 140a, 142a said first type of food grade plastic material 2 and second type of food grade plastic material 3 in the washed first type of food grade plastic material fraction 2 and the second type of food grade plastic material fraction 3 from other types of material using a near infrared spectroscopy system 222 and / or a visible spectroscopy system.

[0125] The method 100 proceeds with diverting 140b, 142b said first type of food grade plastic material 2 and second type of food grade plastic material 3 in the washed first type of food grade plastic material fraction 2 and the second type of food grade plastic material fraction 3 from other types of material, thereby sorting out other types of material from the washed first type of food grade plastic material fraction 2 and the washed second type of food grade material fraction 3, thereby obtaining the purified food grade plastic material 10' and the second purified food grade plastic material 11 ' respectively.

[0126] It is to be noted that the steps in the steps or acts of the above method 100 may be conducted in any suitable order and hence not just in the order given above. Further, one or more of the steps or acts may be conducted in parallel. It is also to be noted that the steps or acts may be conducted by different equipment, at different times and / or at different sites. In other words, as an example, the method may be performed in a distributed manner at a plurality sites where different steps or acts are conducted at different points in time. However, the method may to advantage be conducted in the sequence described above at a single site.

[0127] Additionally, variations to the disclosed variants can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

Claims1 . A method (100) for obtaining a food grade plastic material (10) from a mixed waste material stream (PS), the method (100) comprising, discriminating (110a) a first type of plastic material from other types of material in the material stream (PS) using a near infrared spectroscopy system (222) and / or a visible spectroscopy system, diverting (110b) the first type of plastic material from other types of material in the material stream (PS) into a first plastic material fraction, thereby sorting out material of the first type of plastic material from the material stream (PS), discriminating (111 a) a first type of food grade plastic material from other types of material in the first plastic material fraction using a camera-based object recognition system (226), diverting (111 b) the first type of food grade plastic material from other types of material in the first plastic material fraction into a first food grade plastic material fraction (2), thereby sorting out other types of material from the first plastic material fraction, thereby obtaining the food grade plastic material (10).

2. The method (100) according to claim 1 further comprising, discriminating (112a) a second type of plastic material from other types of material in the material stream (PS), from which the first type of plastic material has been diverted, using a near infrared spectroscopy system (222) and / or a visible spectroscopy system, diverting (112b) the second type of plastic material from other types of material in the material stream (PS) into a second plastic material fraction, thereby sorting out material of the second type of plastic material from the material stream (PS), discriminating (113a) a second type of food grade plastic material from other types of material in the second plastic material fraction using a camerabased object recognition system,diverting (113b) the second type of food grade plastic material from other types of material in the second plastic material fraction into a second food grade plastic material fraction (3), thereby sorting out other types of material from the second plastic material fraction, thereby obtaining a second type of food grade plastic material (11 ).

3. The method (100) according to claim 2 further comprising, discriminating (114a) a further type of plastic material from other types of material in the material stream (PS), from which the second type of plastic material has been diverted, using a near infrared spectroscopy system (222) and / or a visible spectroscopy system, diverting (114b) the further type of plastic material from other types of material in the material stream into a further plastic material fraction, thereby sorting out material of the further type of plastic material from the material stream, discriminating (115a) the further type of plastic material from other types of material in the further plastic material fraction, using a near infrared spectroscopy system (222) and / or a visible spectroscopy system, diverting (115b) the further type of plastic material from other types of material in the material stream into a purified further plastic material fraction (4), thereby sorting out other types of material from the further plastic material fraction.

4. The method (100) according to any one of the preceding claims further comprising, reducing (120) a size of material items in the first type of food grade plastic material fraction (2), subjecting (130) the first type of food grade plastic material fraction (2) to an alkaline washing process and / or a washing process at an elevated temperature,discriminating (140a) said first type of food grade plastic material in the washed first type of food grade plastic material fraction from other types of material using a near infrared spectroscopy system (222) and / or a visible spectroscopy system, and diverting (140b) said first type of food grade plastic material in the washed first type of food grade plastic material fraction from other types of material, thereby sorting out other types of material from the washed first type of food grade plastic material fraction, thereby obtaining a purified food grade plastic material (10'), and if the second type of food grade plastic material is present; reducing (122) a size of material items in the second type of food grade plastic material fraction (3), subjecting (132) the second type of food grade plastic material fraction (3) to an alkaline washing process and / or a washing process at an elevated temperature, discriminating (142a) said second type of food grade plastic material in the washed second type of food grade plastic material fraction from other types of material using a near infrared spectroscopy system (222) and / or a visible spectroscopy system, and diverting (142b) said second type of food grade plastic material in the washed second type of food grade plastic material fraction from other types of material, thereby sorting out other types of material from the washed second type of food grade plastic material fraction, thereby obtaining a purified second type of food grade plastic material (11 ').

5. The method (100) according to claim 4 further comprising, subsequent to subjecting (130) the first type of food grade plastic material fraction (2), and if present, the second type of food grade plastic material fraction (3), to the washing process,drying (150, 152) of material in the first type of food grade plastic material fraction, and if present, in the second type of food grade plastic material fraction.

6. The method (100) according to claim 4 or 5 further comprising, subsequent to subjecting (130) the first type of food grade plastic material fraction (2), and if present, the second type of food grade plastic material fraction (3), to the washing process, subjecting (160, 162) the first type of food grade plastic material fraction (2), and if present, the second type of food grade plastic material fraction (3), to a floating separation process, thereby separating material with a density higher than that of water from material with a density lower than that of water.

7. The method (100) according to any one of the preceding claims, wherein the first type of plastic material is a first type of high impact polystyrene material, such that the food grade plastic material (10) is a food grade high impact polystyrene material, and if the second type of plastic material is present, wherein the second type of plastic material is a second type of high impact polystyrene material, such that the second type of food grade material (11 ) is a second food grade high impact polystyrene material, and if the further type of plastic material is present, wherein the further type of plastic material is a mixed high impact polystyrene material.

8. The method (100) according to any one of the preceding claims, wherein the camera-based object recognition system (226) discriminates by; acquiring, by a camera (750), an image of an object in the first plastic material fraction (2), and if present, in the second plastic material fraction (3), andcomparing, by a processor, the acquired image with a database of food grade objects to determine if the object is of food grade.

9. The method (100) according to any one of claims 1-7, wherein the camera-based object recognition system (226) discriminates by; acquiring, by a camera (750), an image of an object in the first plastic material fraction (2), and if present, in the second plastic material fraction (3), and inputting the acquired image into a machine learning model trained to identify food grade objects in input images, thereby determining if the object in the acquired image is of food grade.

10. The method (100) according to claim 8 or 9, wherein the camerabased object recognition system (226) further comprises a tracer-based sorting, TBS, unit (226a) which discriminates by; acquiring, by a camera (750), an image of an object having a TBS marker in the first plastic material fraction (2), and if present, in the second plastic material fraction (3), detecting, by a processor, the TBS marker in the acquired image, and comparing, by the processor, the detected TBS marker with a database of TBS markers to determine if the object is of food grade.11 . The method (100) according to any one of the preceding claims further comprising, discriminating (116a) the first type of plastic material, and if present, the second type of plastic material, from other types of material in the material stream (PS) from which the first type of plastic material has been diverted, or if the second type of plastic material is present, from which the second type of plastic material has been diverted, using a near infrared spectroscopy system (222) and / or a visible spectroscopy system, anddiverting (116b) the first type of plastic material, and if present the second type of plastic material from other types of material in the material stream into a recovery plastic material fraction that is re-joined with the mixed waste stream (PS).

12. The method (100) according to any one of the preceding claims further comprising, prior to discriminating (110a) the first type of plastic material, separating (170a) ferrous material from the mixed waste stream using a magnet arrangement, and / or separating (170b) non-ferrous material from the mixed waste stream using an eddy current separator.

13. The method (100) according to any one of the preceding claims further comprising, prior to discriminating (110a) the first type of plastic material, separating (180) objects of the mixed waste stream having a maximum cross-sectional extension larger than 320 mm into a shredder stream using a wind sifter (66) and / or a screen (64).

14. The method (100) according to claim 13 further comprising, shredding (190) the objects in the shredder stream such that the maximum cross-sectional extension is smaller than 320 mm and re-joining the objects to the mixed waste material stream (PS).

15. A system (1) for obtaining a food grade plastic material (10) from a mixed waste material stream (PS), the system comprising; a first classification and sorting station (22) configured to receive the mixed waste stream (PS), the first classification and sorting station (22) comprising a near infrared, NIR, spectroscopy system (222) and / or a visible spectroscopy system configured to discriminate a first type of plastic materialfrom other types of material in the material stream (PS), and an ejection unit configured to divert the first type of plastic material from other types of material in the material stream (PS) into a first plastic material fraction, thereby sorting out material of the first type of plastic material from the material stream (PS), a first food grade classification and sorting station (25) configured to receive the first plastic material fraction, the first food grade classification and sorting station comprising a first camera-based object recognition system (226) configured to discriminate a first type of food grade plastic material from other types of plastic material in the first plastic material fraction, and an ejection unit configured to divert the first type of food grade plastic material from other types plastic material in the first plastic material fraction into a first food grade plastic material fraction (2), thereby sorting out other types of material from the first plastic material fraction, thereby obtaining the food grade plastic material (10) from the material stream (PS).

Images