SENIOR, David, John (3 Bledlow Close, Ellesmere ParkEccles, Manchester M30 9LP, GB)
35 Claims
1. A method of disposing of PCPW comprising the step of mixing PCPW in the form of particles with a substrate, wherein the PCPW particles have a size distribution of at least 50% of the particles having a size less than or equal to 4000 μm.
2. A method according to claim 1, wherein the PCPW particles have a size distribution of at least 75% of the particles having a size less than or equal to 3000 μm
3. A method according to claim 1, wherein the PCPW particles have a size distribution of at least 85% of the particles having a size less than or equal to 2000 μm.
4. A method according to claim 1, wherein all the PCPW particles have a size less than or equal to 2000 μm.
5. A method according to any preceding claim, wherein the substrate is selected from any of soils, soil improvers, soil conditioners, paints, pastes, concrete, or any medium or substrate which can incorporate PCPW particles.
6. A method according to claim 5, wherein the soil improvers and soil conditioners are selected from ammonium nitrate, basic slag, bio solids, bone meal, compost, digestate, fabaceae, fish emulsion, green manure, humanure, humus, expanded clay pellets (LECA), leaf mould, milorganite, mulch, rockdust, soil inoculant, spent mushroom compost, urea 36 ammonium nitrate solution (UAN), urea, bark or barkdust, clay, gypsum, lime, manure, peat, seaweed fertiliser, or vermiculite.
7. A method according to any preceding claim, wherein the substrate comprises seeds.
8. A method according to any preceding claim, wherein the PCPW particles are present in the range from 0.1 wt.% to 99.9 wt.%.
9. A method according to any preceding claim, wherein the PCPW is formed from polyethylene terephthalate (PET), low density and high density polyethylene (LDPE &
HDPE), co and homo polypropylene (CoPP & HoPP), high impact and general purpose polystyrene (HIPS & GPPS), acrylonitrile butadiene styrene (ABS), polybutylene terephthalate (PBT), polyester (PES), polyamides (PA) (Nylons), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyurethanes (PU), acrylics (PMMA), polycarbonate (PC), polyvinylidene chloride (PVDC), bayblend (PC/ABS), and ethyl vinyl acetate (EVA).
10. A method of forming PCPW particles, the method comprising the steps of: granulating PCPW to provide granulated PCPW; extruding the granulated PCPW through a vented extruder comprising a filtering or screening system; pelletising the extruded PCPW to form pellets; and micronising the PCPW pellets to provide PCPW particles; 37 wherein the resulting PCPW particles have a size distribution of at least 50% of the particles having a size less than or equal to 4000 μm.
11. A method according to claim 10, wherein the method comprises an additional step of sorting the PCPW prior to granulating.
12. A method according to either claim 10 or claim 11, wherein the method comprises shredding the PCPW prior to granulating.
13. A method according to any of claims 10 to 12, wherein the granulated PCPW has a size suitable for feeding in to the vented extruder.
14. A method according to any of claims 10 to 13, wherein the granulated PCPW is passed over a separator prior to extrusion.
15. A method according to claim 14, wherein the separator is a metal separator.
16. A method according to any of claims 10 to 15, wherein the method comprises a mixing or blending step after granulation and prior to extrusion.
17. A method according to any of claims 10 to 16, wherein the vented extruder comprises at least one venting system. 38
18. A method according to any of claims 10 to 17, wherein the filtering or screening system is a screenchanger.
19. A method according to claim 18, wherein the screenchanger is a continuous screenchanger.
20. A method according to any of claims 10 to 19, wherein the pelletising step to form PCPW pellets is performed by passing the extruded PCPW through at least one cutting means.
21. A method according to claims 20, wherein extruded PCPW is passed through a water bath to draw the extruded PCPW in to strands, and passing strands through cutting means to form PCPW pellets, wherein the cutting means are strand cutters.
22. A method according to 20, wherein the cutting means are face cutters.
23. A method according to any of claims 10 to 22, wherein the PCPW pellets are passed though a vibratory classifier.
24. A method according to claim 23, wherein the vibratory classifier removes PCPW pellets having a size greater than 6mm.
25. PCPW particles formed by the method of any of claims 10 to 24. 39
26. A mixture of PCPW particles and a substrate, wherein the PCPW particles have a size distribution of at least 50% of the particles having a size less than or equal to 4000 μm.
27. Use of PCPW particles as a soil improver, wherein the PCPW particles have a size distribution of at least 50% of the particles having a size less than or equal to 4000 μm, and wherein the PCPW particles are present in a mixture with a substrate. |
Method of Processing and Disposing of Plastic Waste
The present invention relates to processing and disposal of plastic waste material, and in particular post consumer plastic waste (PCPW).
Environmental issues in general have received a large amount of recent attention. One such issue is how we dispose of our waste material to ensure that the impact to the surrounding environment is minimised. It is widely acknowledged that the growing amount of waste produced commercially, industrially, and domestically is a significant problem that needs to be addressed both in the UK and also worldwide.
As used herein, PCPW is understood to refer to plastics waste which is discarded, and commonly termed rubbish or garbage. PCPW typically comprises empty or used packaging formed from plastics, wherein the contents of the packaging have been consumed with the packaging being discarded.
Plastic waste material and specifically PCPW is a significant part of the overall waste problem, and makes up around 25% of all domestic packaging waste in the UK. Although some of this plastic waste is currently recycled, long term forecasts foresee only about 25% of this type of waste being recovered or recycled, leaving the remaining 75% to be disposed of by other methods.
In addition, recycling rates for plastic waste often lag far behind those of other waste materials such as newspaper (around 80% in the UK) and cardboard (around 70% in the UK). The main reason for this disparity is the large number of different plastics used, many of which are incompatible for the purposes of recycling.
Sorting the items by the type of plastic is prohibitively expensive because many of the articles contain two or more incompatible plastics, for example polyethylene terepthalate (PET) bottles that have polypropylene caps (PP) and polyvinyl chloride (PVC) labels attached.
Additionally, there are a lack of recycling facilities for plastic post consumer waste, and indeed many other materials as well, with only a few existing in the whole of the UK. It is also unrealistic to expect the general public to be able to discern the difference between various types of plastic.
It should be borne in mind that no matter what percentage of plastic waste is recycled this merely slows down the rate at which new plastic is required, and in any event recycled plastic waste will become plastic waste again when its useful life ends and has to be disposed.
Due to the aforementioned difficulties, large amount of plastic waste and specifically PCPW are not recycled, and are put in to landfill or incinerated. The disadvantage of disposing of PCPW in landfill is that it is very bulky thereby exerting pressure on the
limited landfill capacity available. Additionally, the landfilled PCPW does not degrade for a long time.
The option of incineration is a possible solution, and due to the high calorific value, PCPW could be considered as a fuel. However, incineration disadvantageously results in the release of carbon dioxide in to the atmosphere along with other chemicals such as CFCs.
Currently much of the PCPW is compressed and baled to effect a reduction in volume and sent to other countries such as China. It is unlikely that the compacted waste is disposed of any differently in these countries when compared to the UK, which raises ethical questions. Additionally, there is the disadvantage of the increased amounts of greenhouse gases released in to the atmosphere due to the extra shipping, loading, unloading, and transportation needed to move the PCPW such large distances.
There is a considerable need to solve the problem of disposal of plastic waste, and specifically PCPW, without recourse to existing landfill or incineration.
The present invention seeks to provide a method of disposing of plastic waste, and specifically PCPW, in an improved economic and environmental method in comparison to prior attempts as described herein.
The present invention also seeks to provide uses for the resulting products of the method of disposing of PCPW as described herein. The present invention also seeks to provide a method of changing the PCPW in to a form which is suitable for subsequent disposing.
According to a first aspect of the present invention there is provided a method of disposing of PCPW comprising the step of mixing PCPW in the form of particles with a substrate, wherein the PCPW particles have a size distribution of at least 50% of the particles having a size less than or equal to 4000 μm.
The method of disposing of PCPW may also comprise the step of forming the PCPW particles as described herein prior to mixing with a substrate. Therefore, the method of the first aspect may comprise the method of the fourth aspect.
According to a second aspect of the present invention there is provided a mixture of PCPW particles and a substrate, wherein the PCPW particles have a size distribution of at least 50% of the particles having a size less than or equal to 4000 μm.
The PCPW particles in the mixture of the second aspect may be formed by the method of the fourth aspect.
It has been found that reducing the size of the plastic waste results in the waste being in a form which can be disposed of more easily. The plastic waste particles of the first aspect have a larger surface area to volume ratio, and therefore the process of degradation of the
plastic waste would be accelerated in comparison to plastic waste not subjected to the method of the present invention.
It has also been found that the plastic waste particles are in a form in which they can be added to various substrates for further uses such as combining with soil. As well as allowing for disposal of the plastic waste particles, use in this way may also provide for advantageous properties imparted to the substrate to which they are added, and these properties are discussed herein. Therefore, in certain instances, the mixture of substrate and PCPW can provide advantageous and efficacious properties.
The method of disposing of the PCPW as described herein provides a cheap, efficient way to dispose of PCPW. Additionally, the mixture provided by combining the PCPW particles and substrate can be used in a number of applications such as for covering landfill sites, as a top cover for playing fields and parkland when compost or soil is the substrate, and as a soil improver in agriculture.
The term "size" and "particle size" used herein is understood to refer to the longest dimension of a three dimensional body or particle. The term is applicable to any shape or size of three dimensional bodies or particle.
Additionally, the term "size" and "particle size" as used herein refers to mean size as it is envisaged that the sizes of individual three dimensional bodies or particles will vary across a size distribution.
The term "particles" used herein with reference to the product of the granulation and micronisation steps is understood to mean discrete bodies. The term particles is used interchangebly with the term powder.
The term "mixing" as used with reference to the first aspect of the invention is understood to include mixing by mechanical dispersion, as well as placing or scattering on, and placing in a substrate. The mixing may take place with a substrate prior to use of the PCPW particles, or may take place in-situ. Mechanical dispersion of the PCPW particles in the substrate is preferred.
The substrate may be selected from any of soils, soil improvers, and soil conditioners. Additionally, the substrate may be paints, pastes, concrete, or any medium or substrate which can incorporate PCPW particles.
In particular, it may be preferable to mix the PCPW particles with a particulate substrate. Preferably, said particulate substrate is soil.
The particulate substrate may have a particle size may be in the range of 100 mm to 0.001 mm. Preferably, the particulate substrate size may be in the range of 75 mm to 0.002 mm.
Soil improvers and soil conditioners are known as materials which are added to soil to improve plant growth and health, and aid root growth.
Suitable soil improvers include, by way of example, ammonium nitrate, basic slag, bio solids, bone meal, compost, digestate, fabaceae, fish emulsion, green manure, humanure, humus, expanded clay pellets (LECA), leaf mould, milorganite, mulch, rockdust, soil inoculant, spent mushroom compost, urea ammonium nitrate solution (UAN), or urea.
Suitable soil conditioners include, by way of example, bark or barkdust, clay, gypsum, lime, manure, peat, seaweed fertiliser, or vermiculite.
The PCPW particles may be mixed with the soil improvers or soil conditioners using any suitable method. The resulting mixture may then be applied to a surface of the ground by any suitable method. An example of a suitable method is spreading, and in particular using a farm or industrial type spreader.
It is envisaged that the PCPW particles may be mixed with the soil improvers or soil conditioners prior to retailing to a consumer, thereby being in a 'ready mixed' form. Alternatively, the PCPW particles may be mixed with the soil improvers or soil conditioners in-situ immediately prior to use.
The PCPW particles may be mixed with one soil improver or soil conditioner. Alternatively, the PCPW particles may be mixed with a plurality of soil improvers and/or soil conditioners in any suitable combination.
In an alternative embodiment, the PCPW particles may be mixed with soil. The mixing with soil may be performed in-situ, and the soil may preferably be topsoil.
It is anticipated that the introduction of PCPW particles would be to the non-detriment of the soil.
The substrate may include additional ingredients, such as seeds.
In a further alternative embodiment, the PCPW particles may be mixed with a substrate of paint or paste. The addition of PCPW particles to paint or paste may provide a textured aggregate.
The PCPW particles may be mixed with concrete as a way of disposing of the particles.
The PCPW particles as referred to herein may have a size distribution of at least 75% of the particles having a size less than or equal to 3000 μm. Preferably, at least 85% of the particles having a size less than or equal to 2000 μm. More preferably, at least 95% of the particles having a size less than or equal to 1600 μm.
It is desirable that the PCPW particles may have a size distribution of at least 98% of the particles having a size less than or equal to 1200 μm.
The PCPW particles may all have a size less than or equal to 2000 μm.
The PCPW particles may be present in any amount suitable for the purpose. PCPW particles may be present in the range from 0.1 to 99.9 wt.%. Preferably, in the range from 5 wt.% to 50 wt.%.
The PCPW particles may be taken to landfill sites and mixed at various ratios with soil, such as topsoil, and grass seed. The resulting mixture may be used to provide landscaped areas, or to cover existing landfill sites when full or no longer required. Alternatively, the mixture could be used as a basis for growing other plants such as root vegetables, fruit trees, cereal, and fodders.
The PCPW particles and soil may be mixed using mechanical mixing or mechanical blending. Preferably, the mechanical mixing or blending may provide a homogenous or substantially homogeneous mixture. By way of example, a mixture of PCPW particles and soil may be prepared by placing and mixing the materials in a mixer, for example a ribbon blender.
The PCPW particles may themselves act as a soil conditioner or soil improver. Without wishing to be bound by any particular theory, it is thought that the plastic materials
normally present in the PCPW are slightly hygroscopic. The PCPW particles have a large surface area in relation to particle size, and in combination with the hygroscopic properties it is theorised that the compost/soil particle mix is more efficient at holding water in the mixture in comparison to compost/soil alone.
The PCPW particles may be used as soil improver in agriculture inasmuch that the addition of PCPW particles reduces the bulk density of the mixture in comparison with soil on its own. This reduction of bulk density aids drainage and provides a mixture which is more resistant to compaction. The mixture may therefore be of interest to commercial farmers and have a commercial value in its own right when sold to farmers.
It is understood that PCPW particles are typically alkaline in nature. This may be because of the presence of unused bleaches and detergents in the plastic articles in the PCPW. As the PCPW plastics gradually degrade, this alkalinity will be released into the soil.
It is envisaged that a mixture of soil and grass seed, or compost and grass seed, with the PCPW particles may be formed in various percentages to provide an optimum mix. The percentages of each of the components present in such a mix may depend on the density of the soil/compost used, or the pH of the resultant mixture.
The particles may be used in the development of parkland, golf courses or disposed of in any environment where grass is grown. This could be done simply by scattering the
PCPW particles over a given area in the manner of liming familiar to farmers and then ploughing into the existing soil thereby finding an economic and environmentally sound way to dispose of the original PCPW.
The PCPW used to form the PCPW particles may also comprise additional components, such as pigments and additives, which are encapsulated in the plastic articles during their original manufacture. These substances may comprise compounds which may be conducive to the improvement of soil/compost for use in growing plants, crops etc. As the plastic degrades, these elements may be released into the soil over time.
For example, a high percentage of articles in PCPW are coloured and many of the pigments, colourants and additives used are or comprise metal salts which may be a source of plant nutrients.
An example of components which may be present in the plastic material, and which may be beneficial to the soil, include organic and inorganic colouring pigments which are typically present at levels of 0.2 to 4 %.
Thus, according to a third aspect of the present invention, there is provided the use of PCPW particles as a soil improver, wherein the PCPW particles have a size distribution of at least 50% of the particles having a size less than or equal to 4000 μm, and wherein the PCPW particles are present in a mixture with a substrate.
Additionally, due to the large increase in surface area of the PCPW in relation to the particle size, the degradation of the plastic will be significantly accelerated when it is mixed with a substrate and subsequently placed in the ground.
It is envisaged that the PCPW used in the present invention is that collected from residential properties. In an alternative embodiment, PCPW from commercial or industrial properties may be used. Mixtures of residential, commercial, and industrial PCPW in any combination may be used in the method of the present invention.
The PCPW may be collected by kerbside post consumer waste collectors. The collected kerbside PCPW may be compacted and baled prior to size reduction. Alternatively, the PCPW used in the present invention may be in a non-compacted form.
The PCPW may comprise waste formed from any suitable plastics. Preferably, the PCPW is substantially formed from thermoplastic or thermosetting plastic. PCPW typically comprises empty or used packaging formed from plastics, wherein the contents of the packaging have been consumed. The PCPW may be in sheet or solid body form, and may be items such as plastic bottles, containers, cartons, and other plastic items or packaging.
Suitable PCPW for the present invention may typically but not exclusively include, by way of example, waste formed from polyethylene terephthalate (PET), low density and high density polyethylene (LDPE & HDPE), co and homo polypropylene (CoPP &
HoPP), high impact and general purpose polystyrene (HIPS & GPPS), acrylonitrile butadiene styrene (ABS), polybutylene terephthalate (PBT), polyester (PES), polyamides (PA) (Nylons), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyurethanes (PU), acrylics (PMMA), polycarbonate (PC), polyvinylidene chloride (PVDC), bayblend (PC/ABS), and ethyl vinyl acetate (EVA).
The PCPW may comprise small proportions (typically less than 5 wt.%) of non-plastic waste materials. Examples of other non-plastic materials include, for example, paper labels affixed to the PCPW. It is envisaged that small proportions of non-plastic waste in the PCPW would not adversely affect the method of the present invention.
PCPW arising as a by-product from industrial processes may be used in the method of the present invention. For example, plastic waste which collects in the exhaust systems of manufacturing processes, such as in the manufacture of plastics or plastic articles, could be used as a feedstock of PCPW.
According to a fourth aspect of the present invention there is provided a method of forming PCPW particles, the method comprising the steps of: granulating PCPW to provide granulated PCPW; extruding the granulated PCPW through a vented extruder comprising a filtering or screening system; pelletising the extruded PCPW to form pellets; and micronising the PCPW pellets to provide PCPW particles;
wherein the resulting PCPW particles have a size distribution of at least 50% of the particles having a size less than or equal to 4000 μm.
According to a fifth aspect of the present invention there is provided PCPW particles formed by the method as described herein.
Granulating the PCPW provides for reduction in the size of the PCPW, and produces granulated PCPW.
The granulating step may be carried out with any suitable machine capable of reducing the PCPW to the desired size. Preferably, the size of the granulated PCPW is suitable for feeding in to the vented extruder. The granulating step is therefore carried out by means of mechanical granulation, and is not intended to include non-mechanical granulation processes such as natural decay or degradation of the sheet or body forms of the PCPW.
Preferably, the granulated PCPW has a size of less than 20 mm. More preferably, the granulated PCPW has a size of less than 15 mm prior to extrusion.
Preferably, a granulator may be used for the granulating. The granulator may comprise a grinding chamber.
Suitable granulators are available commercially, by way of example, from Neue Herbold GmbH of Sinsheim, Germany (www.neue-herbold.com/e_lp_grinder_granulator- types.htm), or Blackfriars Limited of Whaley Bridge, UK.
The method may comprise shredding the PCPW prior to granulating. The shredding may be performed using any suitable mechanical shredder. The shredding step may be used in order to reduce the size of the PCPW to approximately no more than 10 cm. Shredding of the PCPW prior to granulating would allow for faster subsequent granulating.
The size of the granulated PCPW may be determined by using a screen comprising round holes or openings with diameters corresponding to the desired size. The screen may be part of, or arranged in proximity to, the granulator to allow for removal of the granulated PCPW once it has been reduced to the desired size.
The granulating step may comprise one continuous granulating step to produce granulated PCPW of the desired size.
In an alternative embodiment, the granulating step may comprise multiple granulating steps, such that each step progressively reduces the size of the PCPW until the desired size is obtained.
The granulating step may comprise, for example, a first granulating step for reducing the size of the PCPW to an intermediate size, and feeding the intermediate size PCPW in to a second granulating step for further reducing the granulate to a suitable size for extrusion.
The method of forming the PCPW particles may also comprise a mixing or blending step after granulation and prior to extrusion.
The mixing or blending of the granulated PCPW may be performed by any suitable blending apparatus, and may provide blended or cross-blended granulated PCPW prior to extrusion.
Mixing or blending the granulated PCPW may allow for formation of more homogenised PCPW particles. The granulated PCPW may comprise granulate which varies in size and thickness and mixing or blending will reduce any localised variations resulting in more consistent granulated PCPW for feeding in to the extruder.
Any suitable type of blender may be used for cross blending, with fountain blenders being preferred. Typically fountain blenders would provide the cheapest option for performing the blending step.
Suitable mixers or blenders are available commercially, by way of example, from Colormax Limited of Telford, UK (www.colormaxltd.com/products/bulk_blenders.cfm).
18 they will also separate out non magnetic metals. However, this is a much more expensive option.
The metal separation step may comprise separating the metal prior to extrusion. Therefore, the method of forming PCPW particles would include a combination of metal separator, and a screenchanger arranged on the extruder.
The extrusion of the granulated PCPW may be performed by any suitable extruder.
The vented extruder comprises at least one venting system. The extruder melts the granulated PCPW which causes gases to be produced. These may be passively removed using a venting system, or alternatively may be actively removed by sucking the gases out of the extruder.
The granulated PCPW is heated and melted before it reaches the vent as it passes through the extruder. The molten granulated PCPW may then be extruded through die holes which are present in the extruder.
The extruder comprises a filtering or screening system. The terms filtering system and screening system are used interchangeably. The filtering or screening system may comprise a screenchanger.
19
The molten extruded PCPW may be passed through an in-situ filtering system or screenchanger on the extruder.
The screenchanger comprises filters which allow filtering of the extruded PCPW, and may have a plurality of filter areas which are operable to be moved between an active position and an inactive position. The screenchanger may be selected from a hydraulic, manual, or continuous screenchanger.
Alternatively, the extruder may comprise a continuous screenchanger.
Continuous screenchangers are typically extremely expensive, but provide the advantage that little if any production time is lost compared to the use of a hydraulic or manual screenchangers in which the extruder has to be stopped during the course of the process.
Filtering by the sceenchanger may remove contaminants such as paper or wood, which would otherwise block the die holes of the extruder, and prevent the formation of strands.
Gases such as steam escape through the vent and the PCPW material may then continue along its path passing through the screenchanging section which contains screens (filters), and then exit the extruder through die holes in the die-head.
The extruded PCPW may then be fed in to a pelletiser as described herein to form PCPW pellets.
20
The pelletising step to form PCPW pellets may be performed by passing the extruded PCPW through at least one cutting means.
In one embodiment, the extruded PCPW is passed through a water bath to draw the extruded PCPW in to strands, and the strands are passed through cutting means which are strand cutters to form PCPW pellets.
In an alternative embodiment, the PCPW pellets may be formed by cutting the extruded PCPW using a die faced cutter as the cutting means.
Preferably, the PCPW pellets are formed using die faced cutters.
Suitable extruders and pelletisers are available commercially, by way of example, from Leistritz of Nurnberg, Germany
(www.leistritz.com/extrusion/en/04_products/doppelschneck enextruder/zse50.html).
The PCPW pellets may be passed though a vibratory classifier. The vibratory classifier may be attached to the pelletiser. The vibratory classifier may be set to remove large pellets over a specific size, thereby stopping large pellets going through system. These large pellets would otherwise melt in the pulveriser or microniser due to frictional heat.
21
For example, the vibratory classifier may be set to remove pellets having a size greater than 6mm (typically less than 1% of the pellets) by sieving.
Suitable vibratory classifiers are available commercially, by way of example, from Rotex Europe Limited of Runcorn, UK (www.rotex.com/Olproducts/plasticpellet.aspx).
The removed oversized or large PCPW pellets can be recycled by reintroduction to the blending stage prior to extrusion. The remaining PCPW pellets are used for micronising.
The PCPW pellets are micronised to provide for a reduction in size in order to produce PCPW particles.
The micronising may be performed by any suitable microniser or pulveriser capable of reducing the PCPW pellets to the desired size. The terms microniser and pulveriser are used interchangeably herein.
Suitable micronisers include, by way of example, those available commercially from Neue Herbold of Sinsheim, Germany (www.neue- herbold.corri/e_lp julverizers_finegrinders_zm.htm), and Pallman Pulverisers Inc of New Jersey, USA.
The PCPW pellets may be fed in to the microniser or pulveriser by a vibratory tray feeder. The vibratory tray feeder may part of, or in proximity to, the microniser or
22 pulveriser. The vibratory tray feeder may be metered to allow for measuring and metering specific amounts of PCPW pellets at a desired level, and therefore allowing even flow rates from variations in flow rate which might otherwise be present.
It is envisaged that due to the normal variances in the micronising step, the PCPW particles may not have a uniform size, and may have a size distribution within the desired range.
The micronised PCPW particles are the finished product, and it is possible in practice to set a standard of 98% less than 1200 μm and 100% less than 3000 μm.
The PCPW particles obtained from the micronising provide for a significant reduction in storage volume required to store an equivalent mass of PCPW not subjected to the method of the present invention. The reduction in storage volume required may typically be in the range of 50 - 90 vol.%. The reduction in volume may be in the range of 80 - 90 vol.%.
The PCPW particles are therefore obtained by use of a mechanical size reduction process as described in the fourth aspect of the present invention. It is not intended to include formation of PCPW particles by natural degradation or decay process.
The method of forming the PCPW particles may comprise an additional step of sorting the PCPW prior to granulating. The sorting may be performed to remove any waste,
23 either plastic or non-plastic, which would otherwise be incompatible with the method of the present invention. The sorting step may be performed manually by hand, or may be performed used automation or suitable sorting machines.
A particular advantage of the present invention is the relatively low capital expenditure required for set-up and subsequent running. The exact cost of setting up a suitably sized plant would depend upon the capacity required.
The present invention therefore addresses the PCPW problem by allowing for disposal with no harmful side effects. Additionally, as well as being able to act as a soil improver, degradation of the PCPW is accelerated once in particle form due to the increased total surface area for elemental and biological attack.
The present invention therefore provides a method of disposing of PCPW (waste plastic) material which is in a sheet or solid body form by subjecting it to granulation using a mechanical granulation machine, extrusion, pelletising, and micronising to produce PCPW particles, and mixing said particles with a particulate substrate, particularly soil, to provide a homogeneous mixture which can be spread on a surface of the ground.
All of the features described herein may be combined with any of the above aspects, in any combination.
24
In order that the present invention may be more readily understood, reference will now be made, by way of example, to the following description.
Example 1 - Formation of PCPW Particles
A trial was carried out in order to produce PCPW particles. The PCPW used for producing the PCPW particles was obtained by kerbside collector and subsequently baled. The baled PCPW comprised residential plastic waste. The PCPW particles were formed according to the steps described below.
The baled PCPW was granulated using a two stage granulation process. The first stage granulation and second stage granulation took place separately. The baled PCPW was taken to a granulator of waste plastic materials where it was size reduced by granulation to a size suitable for feeding into an extruder.
The PCPW granulate was collected from the contract granulator and taken to an extruder of plastic materials who specialises in the extrusion of coloured and additive compounds and masterbatches used in the article forming sector of the thermoplastics industry.
It was found that the granulated PCPW had a small but significant contamination of metal and therefore, without removal of this metal, the filters in the screenchanger of the extruder would otherwise quickly become blocked thus preventing the material to pass through the die holes and then on to pelletisation. The PCPW granulate was therefore
25 mixed in a mixer, and the mixture was passed through a metal separator to remove any metal contamination which was present in the granulated PCPW.
The granulated PCPW was then fed in to a vented extruder which comprised a filter changer (screenchanger).
The filtered PCPW exited the extruder through the holes in the die head, passed through a water bath, and was drawn into strands. These strands were cut into pellets by a strand pelletiser.
The PCPW pellets exited the pelletiser and entered a classifier where any granules (negligible amount) over 6mm were screened off with the rest collected in bags.
This granulate was then introduced to the microniser and successfully made into PCPW particles. Micronisation was undertaken using a PU300 microniser.
The above process provided 40 kg of PCPW particles.
A sample analysis of particle size distribution was carried out on the PCPW particles made by the above method, and is shown in Table 1.
Table 1 - particle size distribution of analysed PCPW particles.
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The extrusion of the PCPW could also be carried out using an extruder available from Gneuss GmbH of Germany. The Gneuss extruder is a twin screw type, and is available in different sizes to accommodate different production rates. The screenchanger/filtration is continuous. The venting system on the Gneuss extruder is much more advanced than on the Leistritz extruder, but also has the effect of substantially increasing the cost of extrusion.
The PCPW particles formed by the above process take up about 60% of the volume of the compacted baled PCPW, and are easily handled in half tonne sacks or 50 x 20 kg bags to a pallet with a volume of around 2 cubic metres. The PCPW particles are in a form which can be used in the present invention, and therefore mixed with a substrate.
Example 2 - Mixing PCPW Particles with Compost
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The PCPW particles produced in Example 1 were thoroughly mixed with compost to provide a resultant mixture having 25 wt.% particles and 75 wt.% compost. Radish seeds and beans were subsequently sown in the resulting plastic/compost mixture.
The seeded mixture was placed in pots and left outside. Both the radish and the beans flourished without any further attention or action to feed or water them.
It was postulated that the compost comprising the PCPW particles was better at retaining water than conventional composts due to the hydroscopic nature of the plastic.
Example 3 - Mixing PCPW with SoU
PCPW particles of Example 1 were mixed with soil. The PCPW particles were present in a lower amount than Example 2, being present in the amount of 10 wt.%. This was due to the higher density of the soil in comparison to the compost of Example 2. The soil/plastic mixture was arranged in pots in preparation for sowing.
Garlic chive seeds were sown in a pot (pot 1). Pot 1 had holes in the bottom and was placed in a dish to allow watering from the top and the bottom. Pot 1 was placed on a windowsill and watered regularly. The seeds germinated in to healthy plants in Pot 1, and good root development was observed upon inspection. The amount of visible PCPW powder appeared reduced. This points to degradation of the PCPW particles.
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Another pot (pot 2) without seeds but with the same soil/PCPW powder mix was placed outside on bare earth and left open to the elements. Grass seedlings appeared, and the pot was removed for inspection purposes and good root growth was observed for the seedlings. In addition there appeared to be substantial evidence of the degradation of the PCPW particles as much of it seemed to have disappeared.
Therefore, it can be seen from pot 1 and pot 2 that uninhibited seed germination and plant development takes place when PCPW particles are mixed with soil or compost. Additionally, PCPW degradation appears to take place, and it is suggested that this is due to the increased surface area in contact with the soil therefore encouraging biological and elemental attack.
Example 4 - Soil/PCPW Particle Mixtures
Further tests were also undertaken to identify whether the PCPW particles could be disposed of in soil, and whether grass seed could germinate and propagate in the same way as grass seed sown in otherwise normal soil. Three test beds were prepared which each comprised a soil/PCPW particle mixture. The three soil/PCPW particle mixtures were: A - 100% soil
B - 90% soil and 10% PCPW particles C - 80% soil and 20% PCPW particles
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Tests were undertaken on each test bed at regular intervals to determine bulk density of the soil/PCPW particle mixture and also the pH of the mixture. Test results for both parameters were determined before the mixtures were placed in the respective test beds, and the mixtures were tested repeatedly over time.
Bulk density of the soil/PCPW particle mixture can provide an indication of the degree and rate of possible degradation of the particles in the soil. pH results provide a indication of the effect of the PCPW particles on the acidity/alkalinity of the soil. The initial bulk density of the PCPW particles was 0.5.
The pH of the soil/PCPW particle mixtures was determined by inserting a probe from a pH meter in three different areas in each individual test bed, and recording the average of the three readings.
The bulk densities were determined by filling a measuring cylinder with samples from three different areas in each test bed. Vibration was then applied to the measuring cylinder until the level of the soil ceased to reduce. The volume was then read and the soil weighed. The density was arrived at by dividing the mass (in grams) by the volume (in cm 3 ). The bulk densities are recorded in grams per centimetre cubed (g/cc).
Table 1 - results of bulk density and pH from test beds A, B, and C
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Table 2 - average pH and bulk density values
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It can be seen from the above results that addition of PCPW particles to soil mixtures provides reduced bulk densities in the resulting mixture. These reduced bulk density mixtures can be advantageous as they allow for better drainage of the soil.
Additionally, there is a reduction in the average bulk density over time of the soil/PCPW mixtures indicating some degradation of the PCPW particles.
Example 5 Further test beds were prepared in the same way as described for Example 4 in which various soil/PCPW particle mixtures were placed. The mixtures were made up in the test beds as follows:
D - 100% soil
E - 90% soil and 10% PCPW particles F - 80% soil and 20% PCPW particles
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The test beds were sown with grass seeds to verify whether addition of PCPW particles had any apparent effects on growth of plants. The grass seeds germinated and grew normally in all test beds.
Example 6
Further test beds were prepared in the same way as described for Example 4 in which various soil/PCPW particle mixtures were placed. The mixtures were made up in the test beds as follows: G - 100% soil
H - 90% soil and 10% PCPW particles I - 80% soil and 20% PCPW particles
The test beds were sown with seed potatoes to verify whether addition of PCPW particles had any apparent effects on growth of plants or vegetables. The seed potatoes grew normally in each test bed with no discernable difference between bed G comprising the control soil, and beds H and I having PCPW particles. The resulting potato crop from each bed was harvested and consumed with no ill effects.
Example 7
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Further test beds were prepared in the same way as described for Example 4 in which various soil/PCPW particle mixtures were placed. The mixtures were made up in the test beds as follows:
J - 90% soil and 10% PCPW particles K - 80% soil and 20% PCPW particles
The test beds were sown with seedling tomato plants, with one placed in each bed. Both test beds J and K produced healthy tomato plants which bore tomatoes, and which were consumed with no ill effects.
Example 8
Using original test beds A, B, and C as described with reference to Example 3, geranium seedlings were planted in each test bed. All three test beds produced growing geraniums with no discernable difference between test beds.
Experiments 5, 6, 7, and 8 indicate that use of PCPW particle/soil mixtures does not degrade any ability to grow typical vegetable crops or flowering plants in the mixtures. Additionally, these experiments indicate that the vegetable crops produced in soil/PCPW mixtures are perfectly edible and no different to those produced in normal soil.
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It is to be understood that the invention is not to be limited to the details of the above embodiments, which are described by way of example only. Many variations are possible.