WO2010075609A1

WO2010075609A1 - Method and apparatus for degrading plastics

Info

Publication number: WO2010075609A1
Application number: PCT/AU2010/000003
Authority: WO
Inventors: David Alexander Thompson
Original assignee: Goody Environment Pty Ltd
Priority date: 2009-01-05
Filing date: 2010-01-05
Publication date: 2010-07-08

Abstract

An apparatus for degrading photodegradable plastic materials, the apparatus including a conveying system adapted to support the photodegradable plastic material to be degraded and convey it from a loading zone to a UV radiation zone, the UV radiation zone including a UV radiation source capable of irradiating the photodegradable plastic material in the radiation zone, wherein the output of the UV radiation source and/or the residence time of the plastic in the radiation zone can be selected so as to expose the photodegradable plastic to a dose of UV radiation sufficient to cause substantial photodegradation of the plastic material.

Description

METHOD AND APPARATUS FOR DEGRADING PLASTICS

This international patent application claims priority from Australian provisional patent application 2008900018 filed on 5 January 2009, the contents of which are to be taken as incorporated herein by this reference.

Field of the Invention

The present invention relates to degradable plastics, and in particular to the processing of photodegradable plastics.

Background of the Invention

The annual consumption of plastic materials on a worldwide basis has increased from around 5 million tonnes in the 1950s to about 100 million tonnes today. The growth in plastic use is due to the beneficial properties of plastics, such as: relatively inexpensive to produce; versatility and ability to be tailored to meet specific technical requirements; lighter weight than competing materials; durability; resistance to chemicals, water and impact; good safety and hygiene properties for food packaging; excellent thermal and electrical insulation properties.

The disposal of plastics products contributes significantly to their environmental impact. Most plastics are non-degradable and therefore they take a long time to break down, possibly up to hundreds of years. Plastic waste, such as plastic bags, often becomes litter. With more and more plastics products, particularly plastics packaging, being disposed of soon after purchase, the landfill space required by plastics waste is a growing concern.

Also of concern is the failure of the recycling industry to address the volumes of plastic waste unable to be collected or recycled due to contamination due to food contact or other contamination issues, which results in only about 10% of plastics being recycled with 90% ending up as litter or landfill. Having said that, concerns are also currently observed from the recycling industry around the world that it has not been commercially viable to collect and recycle plastics due to the low commercial values of scrap waste plastics.

In response to concerns regarding the disposal of plastics products, degradable plastics have been developed. Degradable plastics degrade under certain conditions or after a predetermined length of time. There are two types of degradable plastic: bio-degradable plastics, which contain a small percentage of non oil-based material, such as corn starch; and photo- and/or oxo-degradable plastics, which will break down when exposed to sunlight and/or aerobic conditions. Degradable plastics are already being used commercially in such things as bio-degradable foils (shopping and garbage bags etc), cutlery and single use plastic packaging including PET bottles used for beverages, and a variety of other commercial and industrial applications.

Many photodegradable plastics are polyolefins and copolymers thereof. These polymers undergo degradation and become fragile when exposed for prolonged periods to sunlight. For many applications, radiation absorbing agents are added to the polymers in order to retard such ageing, but for many other applications it is desirable to accelerate ageing. The latter applies, for example, to mulching films used in agriculture and horticulture and to disposable packaging of all types, such as films, bags, bottles, hollow articles of other forms, and cellulose sheet materials, such as paper, cardboard or regenerated cellulose, which are coated or lined with polyolefins.

There are a number of concerns over the use of photodegradable plastics. For example, a photodegradable plastic product will not degrade if it is buried in a landfill site where there is no light. Furthermore, mixtures of degradable and non-degradable plastics may complicate plastics sorting systems.

There is a need for improved processes for handling photodegradable plastics so that they can more readily be incorporated into typical waste management cycles. Summary of the Invention

The present invention provides an apparatus for degrading photodegradable plastic materials, the apparatus including a conveying system adapted to support the photodegradable plastic material to be degraded and convey it from a loading zone to a UV radiation zone, the UV radiation zone including a UV radiation source capable of irradiating the photodegradable plastic material in the radiation zone, wherein the output of the UV radiation source and/or the residence time of the plastic in the radiation zone can be selected so as to expose the photodegradable plastic to a dose of UV radiation sufficient to cause substantial photodegradation of the plastic material.

The present invention also provides an apparatus for expediting the degradation of photodegradable plastic materials wherein the photodegradable plastic materials are conveyed substantially continuously through a UV radiation zone to degrade the materials so that they are in a form suitable for biodegradation, the apparatus including: (a) a conveyor system for conveying the photodegradable plastic materials into and through the UV irradiation zone; and (b) a UV radiation source for irradiating the photodegradable plastic materials with UV radiation, wherein the output of the UV radiation source and/or the residence time of the plastic in the radiation zone can be selected so as to expose the photodegradable plastic to a dose of UV radiation sufficient to cause substantial photodegradation of the plastic material.

In an embodiment, the apparatus includes a housing which covers the conveying system at least at the radiation zone. The housing may include sidewalls which extend upwardly from the sides of the conveying system and a roof extending between the side walls such that the side walls and roof collectively form the housing covering the conveying system.

To enable plastic material to be loaded or unloaded from the conveying system a loading end and/or an unloading end of the conveying system may extend out of the housing. - A -

In an embodiment, the conveying system is in the form of an endless conveyer belt. The conveyor belt may be drivable via an electric motor that is speed- regulated by a regulating or control unit.

In an embodiment, the radiation source is one or more UV light generators with controlled UV/visible light spectrum and intensity. The UV light generators may emit UV radiation of a wavelength within the range of from 220nm to 290nm, although preferably with a wavelength of about 222 nm.

In an embodiment, the operation and speed of the conveying system and/or the operation of the UV light generators is controlled by a central controller.

The present invention also provides a system for degrading photodegradable plastic materials, the system including an apparatus as described herein and a shredder for comminuting the photodegradable plastic material prior to it being exposed to UV radiation. The shredder may include means for depositing the shredded material onto the conveying system.

The present invention also provides a process for producing a plastics material that is suitable for biodegradation and also for subsequent composting and/or energy capture (such as by using anaerobic digestion processes), the process including exposing a photodegradable plastics material to a UV radiation source for a time sufficient to cause photodegradation of the material so that it is in a form suitable for biodegradation, wherein the time that is sufficient to cause photodegradation is less than the time to cause photodegradation of the material upon exposure to sunlight.

The present invention also provides a process for degrading photodegradable plastic materials, the process including: - conveying the photodegradable plastic material to be degraded from a loading zone to a UV radiation zone, the UV radiation zone including a

UV radiation source; - irradiating the photodegradable plastic material in the radiation zone; and selecting the output of the UV radiation source and/or the residence time of the plastic in the radiation zone so as to expose the photodegradable plastic to a dose of UV radiation sufficient to cause substantial photodegradation of the plastic material.

The present invention also provides a process for accelerating the rate of decomposition of a photodegradable plastic, the process including exposing the photodegradable plastics material to a UV radiation source for a time sufficient to cause photodegradation of the material, wherein the time that is sufficient to cause photodegradation is less than the time to cause photodegradation of the material upon exposure to sunlight.

The process(es) of the present invention may include comminuting the plastics material prior to exposing it to the UV radiation source.

The present invention also provides use of an apparatus as described herein in the degradation of a photodegradable plastic material.

Brief Description of the Drawings

The invention will now be described in relation to various embodiments illustrated in the accompanying drawings. However, it must be appreciated that the following description is not to limit the generality of the above description.

In the drawings:

Figure 1 is a block diagram of a system according to an embodiment of the present invention;

Figure 2 shows a schematic partial side view of a decomposition apparatus according to an embodiment of the present invention; Figure 3 shows a schematic diagram of a decomposition apparatus according to an embodiment of the present invention; and

Figure 4 shows a perspective view of a decomposition apparatus according to an embodiment of the present invention.

Detailed Description of the Invention

Turning now to Figure 1 there is shown a block diagram for a system 10 for accelerating the rate of decomposition of a photodegradable plastic material 12.

The system 10 includes an apparatus 14 for accelerating the rate of decomposition of the photodegradable plastic material 12. The apparatus 14 includes a UV radiation source 16 configured to form a UV radiation zone 18. A conveying system 20 is adapted to support the photodegradable plastic 12 and move it from a loading zone 22 to the radiation zone 16.

In the radiation zone 18, UV radiation from the radiation source 16 is incident upon the photodegradable plastic material 12 so that it is irradiated with UV radiation. The output of the UV radiation source 16 and/or the residence time of the plastic 12 in the radiation zone 18 can be selected so as to expose the photodegradable plastic 12 to a dose of UV radiation sufficient to cause substantial photodegradation of the plastic. In this way, degradation of photodegradable plastics can be accelerated. Indeed, the time that is sufficient to cause photodegradation is considerably less than the time to cause photodegradation of the material upon exposure to sunlight. Typically, the point of embrittlement (i.e. the level of degradation where the plastic has virtually no strength and breaks down into small pieces) is reached in a period of several minutes to several hours, depending on the thickness of the photodegradable plastic 12 and the sufficiency of any pre-shredding of the photodegradable plastics that may be conducted (see below). The system 10 shown in the block diagram in Figure 1 also includes a shredder 32. The shredder 32 comminutes the photodegradable plastic material 12 and the shredded material is introduced onto the conveying system 20 as described in more detail later.

In use, products made from photodegradable plastics, such as agricultural mulch film, trash bags, retail shopping bags, tubs, cups, bottles, etc, that have been collected as waste are introduced into the shredder 32. The shredded plastic material 12 that exits the shredder is then fed onto the conveying system 20 at the loading zone 22 after which it moves into the UV radiation zonei δ. The material that exits the UV radiation zone is substantially degraded as a result of the exposure to UV radiation and air (oxygen). This material is suitable for introduction to land fill or compost heaps where it is able to undergo biodegradation by natural microorganisms. The apparatus, systems and processes of the present invention speed up the photodegradation process such that it occurs in a significantly shorter time frame than if the plastic products had only been exposed to sunlight.

In embodiments of the invention that are shown in Figures 2 and 4, the apparatus 10 includes a housing 34 which covers the conveying system 20 at least at the radiation zone 18. Sidewalls 36a and 36b of the housing extend upwardly from the sides of the conveying system 20. A roof 38 extends between the side walls 36a and 36b such that the side walls 36a/36b and roof

38 collectively form the housing 34 covering the conveying system. The housing 34 does not cover the entire length of the conveying system 20.

Rather, a loading end 28 and an unloading end 30 of the conveying system 20 extend out of the housing 34, thereby making it relatively easy to load and unload plastic material 12 onto and from the conveying system 20. In the embodiments of the invention that are shown in Figures 2 and 4, the housing 34 has an arched profile in cross section. However, the skilled person will appreciate that any suitable cross section could be used. The housing 34 is formed from a suitable sheet metal and is fastened to a support frame 40 of the conveying system 34. The housing 34 may be fastened to the support frame 40 by welding, bolting, etc.

The support frame 40 can be any structure that supports the weight of the conveying system 20 and the contents that are loaded on the belt. Support frames for conveying systems are known in the art. In embodiments of the invention, the support frame 40 has a set of wheels 42 attached thereto. The wheels 42 make it easy to move the apparatus 14 from one location to another, such as from one composting heap to another in a waste depot, or from one waste depot to another.

The conveying system 18 is in the form of an endless conveyer belt 48. The conveyor belt 48 passes over two or more rollers 50. The conveyor belt 48 is drivable via an electric motor 24 that is electronically speed-regulated by a regulating or control unit 26. The UV radiation zone 18 is positioned between the loading end 28 and the unloading end 30 of the conveying system 20. The loading end 28 is in the loading zone 22 and at that end a uniform layer of pieces of previously shredded photodegradable plastic product 12 is deposited on the belt 20. The shredded plastic product 12 can be deposited on the belt 48 manually or it may be automatically fed onto the belt 48. For example, the outlet of a shredder 32 (discussed later) may be positioned adjacent the loading end 28 of the belt 48 so that shredded material that exits from the shredder is directly deposited onto the belt. In use, the belt is continually moving at a constant speed and as such, the shredded material is able to be fed continuously onto the loading end 28 of the belt 48 and hence the conveying system 20.

The conveying system 20 may be any suitable conveyor belt system, numerous of which are available commercially.

In a typical arrangement, the system 10 will also include a shredder 32. The shredder 32 may be any suitable shredder, many of which are commercially available. Photodegradable plastic material 12 which has been sorted from other waste at a waste sorting facility or the like is fed into the shredder 32. The plastic material 12 may be manually fed into the shredder 32 or it may be fed in automatically or semi-automatically from a hopper (not shown) or a conveyor belt system (not shown).

The plastic material 12 will generally be in the form of plastic articles, such as bottles, films, containers etc that have been collected from household and commercial waste and sorted to separate it from non-photodegradable plastic waste. The shredder 32 comminutes the plastic material 12 into smaller particles. By comminuting the plastic material 12 into smaller particles, it is possible to speed up the photodegradation process because the surface area of plastic material 12 exposed to both UV radiation and air (oxygen) in the radiation zone 18 is greater. While the most ideal surface area may vary depending on time and rates of degradation required, as a guide the shredded pieces of photodegradable will ideally be of a size of about 0.5cm x 2cm and will be no larger than about 2cm x 10cm.

The radiation source 16 is in the form of one or more UV light generators 44 with controlled UV/visible light spectrum and intensity. The UV light generators 44 emit UV radiation of a wavelength range of 220 -290 nm, or any single value within this range, for example, of 222 nm. In this embodiment, the UV light generators 44 are fitted inside the housing 34 and are positioned along the length of the conveying system 20 in the radiation zone 18.

By way of example, there may be six UV light generators 44 positioned in pairs along the length of the radiation zone 18. The UV light generators 44 are positioned so as to direct as much UV light as possible onto or adjacent the surface of the conveying system in the radiation zone. The amount of UV radiation generated by the UV light generators 44 and incident upon the shredded plastic material 12 on the conveying system is sufficient to initiate and propagate photodegradation of the plastic material 12. The housing 34 effectively contains the UV radiation inside the housing. As a result, there is less chance of workers being inadvertently exposed to UV radiation whilst the apparatus 10 is in use. The housing 34 and UV radiation source 16 effectively form a UV tunnel through which the photodegradable plastic 12 passes on a more or less continuous basis. In this respect, it should also be appreciated that the housing 34 may also be arranged in such a way that the shredded plastic material 12 may be tumbled or agitated with the housing 34 as it is exposed to the UV radiation, or the UV radiation source 16 may itself be configured to move to further increase or alter the UV exposure of the shredded plastic material 12.

The UV degradation of photodegradable plastics provides a photodegraded material in which the oxidation and decomposition are accelerated when the material is placed in, for example, a composting heap, either under aerobic composting conditions (windrows) or anaerobic (landfill) conditions. Advantageously, the accelerated degradation process also ensures sterilisation of the contents preventing unwanted microbes, moulds and fungi being introduced to such a composting heap. This ensures optimum biodegradation under optimum, controlled composting conditions according to the regulations and standards adopted by local councils, states and national/federal authorities/governments. Indeed, similar benefits are also obtainable when the photodegraded material produced by the present invention is used in subsequent energy capture processes

The apparatus 14 of the present invention may be used to accelerate the photodegradation of any of a wide range of polymers. Photodegradability is an inherent property of some polymers which undergo gradual reaction with atmospheric oxygen, particularly in the presence of light. In certain cases, the photodegradability of a polymer can be enhanced by the use of photosensitising additives which absorb ultraviolet light (e.g., from sunlight). The additive, in the photo-excited state, then undergoes a chemical reaction that leads to the generation of free radicals, which leads to an auto-oxidation and eventual degradation of the plastic. Photodegradation has generally involved two technological approaches: (a) introduction of photosensitive functional group into the polymer; or (b) adding of photosensitive reagents to the polymer.

Examples of polymers containing photosensitive chemical groups that are known to be photodegradable include ethylene copolymers containing carbonyl groups such as random copolymers of ethylene with carbon monoxide or copolymers produced by copolymerising ethylene with a vinyl ketone or grafting a vinyl ketone onto polyethylene. It is also known to blend a minor proportion of a photodegradable polymer with another conventional polymer in order to enhance its photodegradability. In general, the photodegradable polymer used in such blends consists mainly of the same repeating units as the major polymer but contains a relatively small quantity of functional carbonyl groups, usually 10% or less by weight, randomly distributed along the polymer backbone. The photodegradable polymer is generally selected to be substantially miscible with the bulk polymer.

Examples of photosensitive reagents that have been added to thermoplastic polymers include: metal salts of fatty acids and free carboxylic acids; an organic photosensitiser and at least one organic derivative of a transition metal; one or more transition metals; a complex of two different metals; a photosensitiser, such as benzophenone, anthroquinone, fluorene, xanthone, phenylalkyl ketones, phenacyl halides, camphorquinone, para-substituted benzenes.

However, even with articles made from many of these polymers decomposition cannot be achieved at a desired time solely by 'natural' photodegradation. The system and appratus of the present invention allows for the photodegradation of these articles to be accelerated. During photodegraration, the plastics are broken down into smaller particles of plastic that are more readily biodegradable by microoganisms in the soil or in a composting heap.

Photodegradable plastics have found use in applications such as agricultural mulch film, trash bags, retail shopping bags, tubs, cups, bottles, etc. The operation and speed of the conveying system 20 and/or the operation of the UV light generators 44 and/or the operation of the shredder 32 are controlled by a central controller 46. The controller 46 may be a microprocessor having suitable software installed thereon.

Finally, it will be appreciated that various modifications and variations of the methods and compositions of the invention described herein will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention that are apparent to those skilled in the art are intended to be within the scope of the present invention.

Claims

1. An apparatus for degrading photodegradable plastic materials, the apparatus including a conveying system adapted to support the photodegradable plastic material to be degraded and convey it from a loading zone to a UV radiation zone, the UV radiation zone including a UV radiation source capable of irradiating the photodegradable plastic material in the radiation zone, wherein the output of the UV radiation source and/or the residence time of the plastic in the radiation zone can be selected so as to expose the photodegradable plastic to a dose of UV radiation sufficient to cause substantial photodegradation of the plastic material.

2. An apparatus for degrading photodegradable plastic materials according to claim 1 , wherein the apparatus includes a housing which covers the conveying system at least at the radiation zone.

3. An apparatus for degrading photodegradable plastic materials according to claim 2, wherein the housing includes sidewalls which extend upwardly from the sides of the conveying system and a roof extending between the side walls such that the side walls and roof collectively form the housing covering the conveying system.

4. An apparatus for degrading photodegradable plastic materials according to either claim 2 or claim 3, wherein a loading end of the conveying system extends out of the housing.

5. An apparatus for degrading photodegradable plastic materials according to any one of claims 2 to 4, wherein an unloading end of the conveying system extends out of the housing.

6. An apparatus for degrading photodegradable plastic materials according to any one of claims 2 to 4, wherein the conveying system is in the form of an endless conveyer belt.

7. An apparatus for degrading photodegradable plastic materials according to claim 6, wherein the conveyor belt is drivable via an electric motor that is speed-regulated by a regulating or control unit.

8. An apparatus for degrading photodegradable plastic materials according to any one of claims 2 to 7, wherein the radiation source is one or more UV light generators with controlled UV/visible light spectrum and intensity.

9. An apparatus for degrading photodegradable plastic materials according to claim 8, wherein the UV light generators emit UV radiation at a wavelength range of between about 220nm and about 290nm or any individual wavelength within this range.

10. An apparatus for degrading photodegradable plastic materials according to either claim 8 or claim 9, wherein the UV light generators are fitted inside the housing and are positioned along the length of the conveying system in the radiation zone.

11. An apparatus for degrading photodegradable plastic materials according to any one of claims 1 to 10, wherein the operation and speed of the conveying system and/or the operation of the UV light generators is controlled by a central controller.

12. An apparatus for expediting the degradation of photodegradable plastic materials wherein the photodegradable plastic materials are conveyed substantially continuously through a UV radiation zone to degrade the materials so that they are in a form suitable for biodegradation, the apparatus including: (a) a conveyor system for conveying the photodegradable plastic materials into and through the UV irradiation zone; and (b) a UV radiation source for irradiating the photodegradable plastic materials with UV radiation, wherein the output of the UV radiation source and/or the residence time of the plastic in the radiation zone can be selected so as to expose the photodegradable plastic to a dose of UV radiation sufficient to cause substantial photodegradation of the plastic material.

13. An apparatus for expediting the degradation of photodegradable plastic materials according to claim 12, wherein the apparatus includes a housing which covers the conveying system at least at the radiation zone.

14. An apparatus for expediting the degradation of photodegradable plastic materials according to claim 13, wherein the housing includes sidewalls which extend upwardly from the sides of the conveying system and a roof extending between the side walls such that the side walls and roof collectively form the housing covering the conveying system.

15. An apparatus for expediting the degradation of photodegradable plastic materials according to either claim 13 or claim 14, wherein a loading end of the conveying system extends out of the housing.

16. An apparatus for expediting the degradation of photodegradable plastic materials according to any one of claims 13 to 15, wherein an unloading end of the conveying system extends out of the housing.

17. An apparatus for expediting the degradation of photodegradable plastic materials according to any one of claims 13 to 16, wherein the conveying system is in the form of an endless conveyer belt.

18. An apparatus for expediting the degradation of photodegradable plastic materials according to claim 17, wherein the conveyor belt is drivable via an electric motor that is speed-regulated by a regulating or control unit.

19. An apparatus for expediting the degradation of photodegradable plastic materials according to any one of claims 13 to 18, wherein the radiation source is one or more UV light generators with controlled UV/visible light spectrum and intensity.

20. An apparatus for expediting the degradation of photodegradable plastic materials according to claim 19, wherein the UV light generators emit UV radiation of a wavelength of 222 nm.

21. An apparatus for expediting the degradation of photodegradable plastic materials according to either claim 19 or claim 20, wherein the UV light generators are fitted inside the housing and are positioned along the length of the conveying system in the radiation zone.

22. An apparatus for expediting the degradation of photodegradable plastic materials according to any one of claims 12 to 21 , wherein the operation and speed of the conveying system and/or the operation of the UV light generators is controlled by a central controller.

23. A system for degrading photodegradable plastic materials, the system including an apparatus of any one of claims 1 to 22, and a shredder for comminuting the photodegradable plastic material.

24. A system for degrading photodegradable plastic materials according to claim 23, wherein the shredder also includes means for depositing the shredded material onto the conveying system.

25. A process for producing a plastics material suitable for biodegradation, the process including exposing a photodegradable plastics material to a UV radiation source for a time sufficient to cause photodegradation of the material so that it is in a form suitable for biodegradation, wherein the time that is sufficient to cause photodegradation is less than the time to cause photodegradation of the material upon exposure to sunlight.

26. A process according to claim 25, wherein the process includes comminuting the plastics material prior to exposing it to the UV radiation source.

27. A process for degrading photodegradable plastic materials, the process including: conveying the photodegradable plastic material to be degraded from a loading zone to a UV radiation zone, the UV radiation zone including a UV radiation source; irradiating the photodegradable plastic material in the radiation zone; and selecting the output of the UV radiation source and/or the residence time of the plastic in the radiation zone so as to expose the photodegradable plastic to a dose of UV radiation sufficient to cause substantial photodegradation of the plastic material.

28. A process according to claim 27, wherein the process includes comminuting the plastics material prior to exposing it to the UV radiation source.

29. A process for accelerating the rate of decomposition of a photodegradable plastic, the process including exposing the photodegradable plastics material to a UV radiation source for a time sufficient to cause photodegradation of the material, wherein the time that is sufficient to cause photodegradation is less than the time to cause photodegradation of the material upon exposure to sunlight.

30. A process according to claim 29, wherein the process includes comminuting the plastics material prior to exposing it to the UV radiation source.

31. Use of an apparatus of any one of claims 1 to 22 in the degradation of a photodegradable plastic material.