Method for converting soft plastics to hard plastics

Abstract

The present invention relates to a method for converting co-mingled thermoplastics into a feedstock master batch for use in end-product applications. The method includes mechanically breaking co-mingled thermoplastic waste material into particles; heating the particles to a predetermined temperature to form a molten blend; extruding the molten polymer blend; and granulating the extruded polymer material to form a master batch comprising granules of the extruded polymer blend.

Description

METHOD FOR CONVERTING SOFT PLASTICS TO HARD PLASTICSTECHNICAL FIELD

[0001] The present invention relates to a method of recycling plastics and more particularly to a method for converting co-mingled thermoplastic waste to a feedstock master batch for use in end-product applications.BACKGROUND OF THE INVENTION

[0002] Currently, there are approximately 400 million tonnes of plastics that are discarded globally per annum, with polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) being the major contributors.

[0003] PE, PP, and PET belong to a type of plastics called thermoplastics or soft plastics which are polymers that become pliable or mouldable when heated and harden when cooled. Given the challenges in effective recycling and the continuing reliance and demand for more thermoplastics, these plastics represent a significant biological and environmental hazard.

[0004] To date, the plastics moulding industry has relied on the continuous use of homogenous polymers (or blends) for moulding new products. Because the end product properties are known at the point of moulding (i.e. manufacture), it is straightforward to salvage and reuse any residual or excess materials resulting from the moulding process. Thermoplastics salvaged from the moulding process can then be reground and this regrind can be included in the master batch for reuse. About 3- 7% of the master batch can be comprised of this regrind.

[0005] As a closed loop and contained solution for waste thermoplastic recycling within a moulding facility, this process is relatively robust. However, outside of such closed loop or contained settings, plastics recycling is not as simple and, evidently, not well practised.

[0006] Recycling of thermoplastics requires accurate, timely and costly identification, separation, and authentication of a specific thermoplastic from typically many hundreds of grades of contemporary commercial thermoplastics. However, many industrial thermoplastic mouldings and products are a bi-polymer / dual polymer,(i.e. laminates or blends of different materials and polymers and / or special blends of polymer) that cannot be segregated and may also consist of other inclusions such as metal, paint, adhesive, etc.

[0007] Plastic recycling with conventional techniques is problematic and as a result, currently very little plastic is recycled.

[0008] Present approaches include depolymerisation which includes a chemicalbased recovery of the monomers which are then used to make new polymers or converted to fuel oil. This process is costly and potentially hazardous.

[0009] Also used are processes involving regrinding, where the thermoplastic is sorted, reground and added to a new plastic batch for further processing. Since only between 3-7% of thermoplastic regrind can be added to the new batch of thermoplastic, the polymer industry and associated end users rely on the exponential growth of usage of plastics to absorb previous volumes of used or spent thermoplastic. That is, the current recycling methods do not address the current usage of thermoplastics let alone the stockpiles of used and spent thermoplastics globally.

[0010] Another approach is the burning of thermoplastic waste for fuel, but this has economic and environmental limitations. In simple terms, conventional plastics recycling methods are costly and typically only applied to clean feedstocks and typically only accurately segregate single polymer types. The result is an ever- increasing diversion to landfill and pollution of waterways.

[0011] Currently, all re-cycling (i.e. so-called “circular) methods for thermoplastics are based on a limited re-use capacity. However, over time, the structure of thermoplastics deteriorates rendering them potentially incapable of functioning for the intended application. Therefore, recycling can be considered down-cycling, where there is a degradation curve or “half-life” of the thermoplastic in industrial applications (i.e. a dilution of performance over time).

[0012] There are also a number of problems associated with the processing of thermoplastics for re-cycling. Thermoplastics / soft plastics have a tendency to possess high elongation to break characteristics. As such, reducing larger sections of soft plastics to granular size or chips necessary for further applications, such as bulk fillers, is achallenge, where typically traditional processing equipment can become regularly clogged and in need of cleaning. When mixed with a binder, “chipped” soft plastics have a tendency to clump together resulting in resin-rich or resin-poor areas, that are not consistent with optimal end-material performance. Because of the typical shallow depth of the “chipped” soft plastic granules (i.e. x, y length and width dimensions with minimal z axis depth), there is a tendency for the chipped soft plastic, when used as a bulk filler, to display stratification characteristics and therefore the end material display inter-laminate / stratification bonding issues. Soft plastics, by their nature are ‘second hand’ and will / do have issues with possible contamination and / or of themselves represent elements that are considered as contaminates. Therefore, the post use of “raw” soft plastics can represent a possible contamination or leaching threat to the environment. Furthermore, although some soft plastics may be considered “Engineering Polymers” they cannot typically be associated with endurance and have a tendency to wear, degrade, convert to microplastics etc. over time.

[0013] Accordingly, a need exists for a method of recycling co-mingled soft plastics that alleviates some of the challenges for processing soft plastics. There also exists a need for a plastic recycling method that does not require identification, sorting, and separation of different types of thermoplastic polymers and removal of nonthermoplastic contaminants. A need exists for a recycling method that allows the soft plastic waste to be used directly and / or in higher volumes for end-product applications.

[0014] Furthermore, a typical standard industry plastic master batch has a singularity of granular geometry and dimension (i.e. spherical, cylindrical or tube like). This master batch will therefore contain large voids between granules that require more binder to fill those voids. This results in an end product with properties more reliant on the “glue” strength (i.e. binder).

[0015] Accordingly, there exists a need for a method of preparing a plastic master batch that relies less on the binder.

[0016] Throughout the description and claims of this specification, the word “comprise” and variations of that word, such as “comprising” and “comprises” are not intended to exclude other additives, steps or integers.

[0017] Any discussion of background art throughout the specification should in no way be considered as an admission that any of the documents or other material referred to was published, known or forms part of the common general knowledge.SUMMARY OF THE INVENTION

[0018] The present invention relates to a method for converting co-mingled thermoplastics into a feedstock master batch for use in end-product applications including: mechanically breaking co-mingled thermoplastic waste material into particles; heating the particles to a predetermined temperature to form a molten blend; extruding the molten polymer blend; and granulating the extruded polymer material to form a master batch comprising granules of the extruded polymer blend.

[0019] Preferably, the co-mingled thermoplastic waste material includes one or more thermoplastic polymers and / or non-thermoplastic materials.

[0020] In embodiments, mechanically breaking co-mingled thermoplastic waste material into particles includes masticating, shredding or grinding the co-mingled thermoplastic waste

[0021] Preferably, the predetermined temperature is between an optimum melt temperature and an optimum mould temperature of the one or more thermoplastics in the co-mingled thermoplastic waste material.

[0022] Preferably, the optimum melt temperature is in a range from 160°C to 450°C.

[0023] Preferably, the optimum mould temperature is in a range from 40°C to 250°C.

[0024] In embodiments, extrusion of the molten blend includes forcing the molten blend through a die.

[0025] In embodiments, the die comprises a plurality of apertures to form extrusions with profiles of various shapes and sizes.

[0026] Preferably, each one of the apertures has a dimension in a first axis that is substantially similar to a dimension in a second axis that is perpendicular to the first axis.

[0027] Preferably, each one of the apertures has similar breadth and length dimensions.

[0028] Preferably, at least some of the apertures have a shape selected from a group of shapes including square, triangle, star, circle, star or cross shapes.

[0029] Preferably, at least some of the apertures have a shape adapted to form a multi-linear shaped extrusion.

[0030] Preferably, each one of the apertures has a dimension in a first axis that is substantially larger than a dimension in a second axis that is perpendicular to the first axis.

[0031] Preferably, each one of the apertures has different breadth and length dimensions.

[0032] Preferably, at least some of the apertures have a shape selected from a group of shapes including elongated rectangular, slender, zig-zag or castellated shapes.

[0033] Preferably, at least some of the apertures have a shape adapted to form a platelet shaped extrusion.

[0034] In embodiments, granulation of the extruded material includes cutting the extruded material that exits the die at intervals.

[0035] Preferably, granulation of the extruded material includes grinding the extruded material.

[0036] In embodiments, the intervals between cuts are non-regular to form granules of varying lengths.

[0037] Preferably, the lengths of the granules are determined to optimise one or more objective functions of the master batch of the extruded polymer granules.

[0038] Preferably, the one or more objective functions are selected from maximum interlocking of granules, maximum coefficient of friction between granules, and minimum gaps between the extruded polymer granules in the master batch.

[0039] In a second aspect, the invention also provides a master batch comprising granules of an extruded polymer blend for use as a feedstock in end-product applications, formed by the method of any one of the preceding claims.

[0040] In further aspect, the invention also provides a method of moulding thermoplastics using as a feedstock a master batch comprising granules of an extruded polymer blend formed by any one of the embodiments of the above method.

[0041] In yet another aspect, the invention provides a method of forming products including using as a feedstock a master batch comprising granules of an extruded polymer blend formed by any one of the embodiments of the above method; and mixing the feedstock with a binder.

[0042] In embodiments, the binder includes epoxy, polyurethane, polyurea, or a material that exhibits interlocking or cross-linking.BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 illustrates a flow chart of a method according to an embodiment of the invention for converting co-mingled thermoplastics to a master batch for use in end-product applications including providing co-mingle waste, mechanically breaking co-mingled thermoplastic waste material into particles by mastication, heating the particles to become molten and extruding the molten material and granulating the extruded material to form a master batch comprising granules of the extruded polymer blend.

[0044] Figure 2 illustrates a flow chart of a method according to an embodiment of the invention for forming products. The method includes using as a feedstock a master batch comprising granules of an extruded polymer blend formed by the method of Figure 1 , mixing the feedstock with a binder, providing the mixture in a mould and curing the mixture to form a final product.

[0045] Figure 3 illustrates a flow chart of an embodiment of the method of Figure 1 , further including providing a die with openings to form extrusions of the molten material with non-regular profiles, using an algorithm to determine one or more lengths of granulation of the extruded material according to an objective function, granulating the extruded material according to the determined lengths and mixing the granulated material to form a master batch in which the objective function is optimised.

[0046] Figure 4 illustrates a die according to an embodiment of the invention in which the die includes openings with non-regular shapes to form extrusions with multilinear shaped profiles.

[0047] Figure 5 illustrates a die according to another embodiment of the invention in which the die includes openings with non-regular shapes to form extrusions with platelet shaped profiles.

[0048] Figure 6 illustrates another embodiment of the invention wherein extrusions with non-regular shaped profiles are ground.DETAILED DESCRIPTION

[0049] The present invention relates to a method for converting co-mingled thermoplastics to a master batch for use in end-product applications. The method described herein is suitable for converting co-mingled thermoplastic waste without the need for sorting and separating different types of thermoplastics and / or removing nonthermoplastic material inclusions or contaminants. The plastic master batch produced by the method is suitable for applications such as re-moulding and as bulk filler in composite materials.

[0050] Referring to Figure 1 , the method 10, which is for converting co-mingled thermoplastics into a feedstock master batch for use in end-product applications, includes, providing co-mingled thermoplastics 12 and mechanically breaking the comingled thermoplastic waste material into particles 14. The particles are heated to a predetermined temperature to form a molten thermoplastic blend 16. The molten blend is extruded 18 and granulated 20 to form a master batch comprising granules of the extruded polymer blend.

[0051] The method takes co-mingled thermoplastics and converts it to a master batch for use in end-product applications. Co-mingled thermoplastics can include a mixture of different types of thermoplastic polymers and / or a mixture of thermoplastic and non-thermoplastic materials.

[0052] Thermoplastics are polymers that become pliable or mouldable when heated and harden when cooled. Examples of thermoplastics that can be utilised by the present invention includes, but are not limited to, polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene, polybenzimidazole, acrylic, nylon, ethylene vinyl acetate (EVA), and polytetrafluoroethylene (PTFE), or a blend of thermoplastic polymers.

[0053] Examples of non-thermoplastic materials that can be co-mingled with the thermoplastics can include paper, cardboard, metal, glass, paints, adhesive, and fabric.

[0054] In co-mingled thermoplastics comprising thermoplastic and nonthermoplastic materials, the thermoplastic materials comprise at least 8% of the total weight of the co-mingled thermoplastics.

[0055] The co-mingled thermoplastics can be used directly without the need to presort and grade the thermoplastics and / or remove any non-thermoplastic materials. However, the co-mingled thermoplastics may also be sorted to separate nonthermoplastic materials of value such as metals and / or glass.

[0056] In embodiments, inclusions may be added to the co-mingled thermoplastics to achieve a desired characteristic of the master batch. For example, a heavier material such as a mineral can be incorporated into the co-mingled thermoplastics before or during the process to obtain master batch granules that have a higher density. This is advantageous in end-product applications, where the master batch is combined with a binder as it prevents the master batch from floating or separating from the binder.

[0057] In embodiments, mastication and heating of the co-mingled thermoplastics results in the melting of the thermoplastic polymers resulting in a molten blend.

[0058] The co-mingled thermoplastics are heated to a predetermined temperature, preferably between an optimum melt temperature and an optimum mould temperature of the thermoplastics. Thermoplastic melt temperature can typically range from approximately 160°C to 450°C, whereas the mould temperature can range from approximately 40°C to 250°C.

[0059] Through a process of compaction, heating, and mastication, the polymer contained in the co-mingled thermoplastics reaches its optimum mould temperature(s) and becomes folded, squeezed and melted into porous non-thermoplastic inclusions. The molten thermoplastics may also encapsulate the porous and non-porous nonthermoplastic material inclusions and / or other material (such as paper, cardboard, metal, wood, glass and minerals etc.) inclusions.

[0060] The heating and mastication process can neutralise or kill bacterial matter, that might be present in the co-mingled thermoplastics, thereby neutralising potential biohazards.

[0061] The use of a temperature between optimum melt temperature and optimum mould temperature preserves the properties of the materials present in the co-mingled thermoplastics, whilst using less energy, reducing carbon output, and / or waste due to polymers and other inclusions burning.

[0062] Typically, many encapsulation techniques rely on exploiting the melt temperature of the thermoplastics to ensure a necessary state change for encapsulation. However, in the present invention, using melt temperature on the comingled thermoplastic waste can have a detrimental effect on the non-thermoplastic material inclusion and / or potential multiple thermoplastics with differing melt temperature ranges co-existing within the co-mingled thermoplastics. High temperatures necessary to melt certain thermoplastics could degrade other comingled materials which could result in underperformance of the master batch, production of potentially hazardous gases, creation of excess carbon from these materials as they char and burn, and / or usage of potentially more energy than derived in the conversion process.

[0063] The molten blend is usually in a viscous state and is further compacted and masticated then driven into a die to form an extruded material. The die includes oneor more apertures configured such that the molten blend is extruded into the desired shape.

[0064] Preferably, the die has one or more apertures with a plurality of shapes and / or sizes. The plane of the die aperture may be expressed as the X and Y plane of a Cartesian coordinate system and the direction in which the molten material is extruded from the die is the Z axis.

[0065] Figure 4 illustrates a die 30 according to an embodiment of the invention. The die 30 includes openings or apertures 32 with non-regular shapes to for extrusions 34 with multi-linear shaped profiles. Each one of the apertures 32 has a dimension in a first axis (X axis) that is substantially similar to a dimension in a second axis (Y axis) that is perpendicular to the first axis. Preferably, each one of the apertures 32 has a breadth dimension similar to a length dimension. At least some of the apertures 32 have a shape selected from a group of shapes including square, triangle, star, circle, star or cross shapes. Therefore, at least some of the apertures have a shape adapted to form an extrusion with a multi-linear shaped profile. The resulting topographical shape or profile of the resulting granules, with their multi-linear directions are characterised by providing maximum interlocking X and Y capability and, in some embodiments to minimise gaps between granules.

[0066] Figure 5 illustrates a die 40 according to another embodiment of the invention in which the die 40 includes openings or apertures 42 with non-regular shapes to form extrusions 44 with platelet shaped profiles. Each one of the apertures has a dimension in a first axis (X axis) that is substantially larger than a dimension in a second axis (Y axis) that is perpendicular to the first axis. Preferably, each one of the apertures 42 has a breadth dimension different to a length dimension. Preferably, at least some of the apertures 42 have a shape selected from a group of shapes including elongated rectangular, slender, zig-zag or castellated shapes. The resulting topographical shape or profile of the resulting granules, with their platelet shaped profile are characterised by providing maximum sheer interlocking and / or torsional interlocking capability and, in some embodiments to improve sheer resistance in a product resulting from their use.

[0067] In embodiments, the co-mingled thermoplastics comprise thermoplastic polymers of various melt temperatures. In this circumstance, it is possible that only some of the thermoplastic polymers are melted and the unmelted thermoplastics remain suspended in the molten blend. The larger unmelted thermoplastics may pose a problem, for example, by clogging or blocking an extrusion die.

[0068] In embodiments, the co-mingled thermoplastics are ground into particles of a predetermined size. Preferably, the co-mingled thermoplastics are ground to particles with a size less than an aperture of an extrusion die.

[0069] In other embodiments, the co-mingled thermoplastics are filtered to separate larger materials. The larger materials can then be ground into particles of a predetermined size.

[0070] The extruded material with the desired x and y-axis geometry as shaped by the die aperture is extruded in a generally continuous form. The extruded material is then granulated by cutting to pre-determined length (Z axis length) to form a master batch comprising granules.

[0071] In embodiments, the extruded material is cut into various lengths to obtain granule of different sizes. This can be done by cutting at non-regular intervals as the extruded material passes the die.

[0072] In embodiments, the master batch is comprised of granules of at least three granular sizes.

[0073] If necessary, further Z axis topography can be created on the extruded material, pre or post z axis reduction using formers that emboss the curve or otherwise define the surface of the material to blend in the Z axis direction.

[0074] Post forming, the blend has transformed into the master batch with the predesignated ratio of granular (particulate) topography and distribution, designed as best for a given application.

[0075] In embodiments, granulation of the extruded material is performed by grinding the extruded material. This results in a lower grade or randomly granulated master batch.

[0076] Figure 6 illustrates another embodiment of the invention wherein extrusions 54 exiting openings 52 of a die 50, which have non-regular shaped profiles, are ground by grinding wheels 56.

[0077] The master batch produced by the method preferably has characteristics such as maximum interlocking of granules, maximum coefficient of friction between granules, minimum gaps between the granules and an inherent “stiffness” within the “dry” master batch. This is achieved by controlling the X, Y, and Z-axis geometry and dimension of the granules of the master batch and / or having irregular or non-uniform shape and size granules.

[0078] In embodiments wherein the die has one or more apertures with a plurality of shapes and / or sizes, the one or more apertures of the die have dimensions in the x-axis substantially similar to the y-axis. For example, the one or more apertures can have circular, star, and / or cross-shaped cross-sections in the X and y plane. This results in master batch granules that have irregular X and Y profiles, which is advantageous as it maximises the interlocking capability of the master batch granules.

[0079] In other embodiments, the one or more apertures of the die have dimensions in the X-axis substantially longer than in the y-axis, or vice versa. For example, the one or more apertures can have rectangular or linear cross section in the X and Y plane. This type of X and Y cross-section of the extruded material is advantageous for end-product applications that rely on shear or twisting force to bond the master batch together. Shear or twisting force on the generally linear or plateshaped master batch increases the friction bond between the plates and improves the overall shear resistance properties of the master batch.

[0080] In embodiments, the lengths of the granules are determined to optimise one or more objective functions of the master batch selected from maximum interlocking of granules, maximum coefficient of friction between granules, and minimum gaps between the granules.

[0081] The resulting master batch can be used as a bulk filler for composite materials, which includes combining the master batch with a binder. Preferably, the binder includes epoxy, polyurethane, polyurea, or a material that exhibits interlocking or cross-linking.

[0082] The irregular X and Y shape and non-uniform length (Z axis) of the granules allows for better interlocking and minimises the gaps between the granules when used as a bulk filler. These granular characteristics contribute to the mechanical properties of the end-product. Furthermore, this end-product application is advantageous as it uses a significant percentage of co-mingled thermoplastics as a bulk filler. It is not restricted to low percentage use (3-7%) as an additive for example to a virgin master batch destined for a thermoplastic moulding application, which could alleviate the problems with the compounding effect of more traditional thermoplastics recycling.

[0083] Alternatively, the thermoplastics contained in the master batch can be utilised to form, mould, and / or bond the master batch into a solid end-product by friction welding, microwave, heat, or solvent bonding.

Claims

CLAIMS1. A method for converting co-mingled thermoplastics into a feedstock master batch for use in end-product applications including: mechanically breaking co-mingled thermoplastic waste material into particles; heating the particles to a predetermined temperature to form a molten blend; extruding the molten polymer blend; and granulating the extruded polymer material to form a master batch comprising granules of the extruded polymer blend.

2. The method of claim 1 , wherein the co-mingled thermoplastic waste material includes one or more thermoplastic polymers and / or non-thermoplastic materials.

3. The method of claim 1 , wherein mechanically breaking co-mingled thermoplastic waste material into particles includes masticating, shredding or grinding the co-mingled thermoplastic waste4. The method of claim 2, wherein the predetermined temperature is between an optimum melt temperature and an optimum mould temperature of the one or more thermoplastics in the co-mingled thermoplastic waste material.

5. The method of claim 4, wherein the optimum melt temperature is in a range from 160°C to 450°C.

6. The method of claim 4, wherein the optimum mould temperature is in a range from 40°C to 250°C.

7. The method of claim 1 , wherein extruding the molten blend includes forcing the molten blend through a die.

8. The method of claim 7, wherein the die comprises a plurality of apertures to form extrusions with profiles of various shapes and sizes.

9. The method of claim 8, wherein each one of the apertures has a dimension in a first axis that is substantially similar to a dimension in a second axis that is perpendicular to the first axis.

10. The method of claim 8, wherein each one of the apertures has similar breadth and length dimensions.

11. The method of claim 8, wherein at least some of the apertures have a shape selected from a group of shapes including square, triangle, star, circle, star or cross shapes.

12. The method of claim 8, wherein at least some of the apertures have a shape adapted to form an extrusion with a multi-linear shaped profile.

13. The method of claim 8, wherein each one of the apertures has a dimension in a first axis that is substantially larger than a dimension in a second axis that is perpendicular to the first axis.

14. The method of claim 8, wherein each one of the apertures has different breadth and length dimensions.

15. The method of claim 8, wherein at least some of the apertures have a shape selected from a group of shapes including elongated rectangular, slender, zig-zag or castellated shapes.

16. The method of claim 8, wherein at least some of the apertures have a shape adapted to form a platelet shaped extrusion.

17. The method of claim 8, wherein granulating the extruded material includes cutting the extruded material that exits the die at intervals.

18. The method of claim 8, wherein granulating the extruded material includes grinding the extruded material.

19. The method of claim 17, wherein the intervals between cuts are non-regular to form granules of varying lengths.

20. The method of claim 19, wherein the lengths of the granules are determined to optimise one or more objective functions of the master batch of the extruded polymer granules.

21. The method of claim 20, wherein the one or more objective functions are selected from maximum interlocking of granules, maximum coefficient of friction between granules, and minimum gaps between the extruded polymer granules in the master batch.

22. A master batch comprising granules of an extruded polymer blend for use as a feedstock in end-product applications, formed by the method of any one of the preceding claims.

23. A method of moulding thermoplastics using as a feedstock a master batch comprising granules of an extruded polymer blend formed by the method of any one of claims 1 to 21.

24. A method of forming products including: using as a feedstock a master batch comprising granules of an extruded polymer blend formed by the method of any one of claims 1 to 21; and mixing the feedstock with a binder.

25. The method of claim 24, wherein the binder includes epoxy, polyurethane, polyurea, or a material that exhibits interlocking or cross-linking.

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