IES84697Y1 - A method of transforming a recycled polyolefin into a performance enhanced polymeric material - Google Patents

Description

A method of transforming a recycled polyolefin into a performance enhanced polymeric material Introduction The present invention relates to a method of transforming a recycled polyolefin into a performance enhanced polymeric material and further relates to a performance enhanced polymeric material prepared by that method.

An ever increasing amount of polyolefin waste is produced worldwide each year.

Recycling is one way of dealing with this waste. A polyolefin is a polymer of the alkene family of hydrocarbons. One of the major problems with recycled polyolefins is that they have reduced physical properties, in particular impact resistance, stress crack resistance and stiffness compared to virgin polyolefins. As recycled polyolefins have inherently lower performance their use in further applications generally is limited to low value applications. Additionally, as the cost of recycling polyolefins is high, the recycling cost can more often that not outweigh the value of the resultant recycled polyolefin.

During the initial use of the polyolefin, UV light and oxygen present can break the carbon bonds within the polymeric chains thus reducing the overall molecular weight of the polyolefins. As the molecular weight of the polyolefins is reduced this causes an overall reduction in physical properties. Additionally, stress of the polyolefins during use will cause “creep” of the polymeric molecules. “Creep" is defined as pulling the amorphous or crystalline regions of the polymeric chains apart. This leads to a reduction in the modulus and impact strength of the polyolefins.

The recycling process itself can be quite complicated and costly and generally involves at least mechanical recycling of the polyolefins. During recycling, reprocessing of the polyolefin waste requires a heat processing step, thereby leading to further degradation of the properties of the polyolefins and making repeat use for After heat processing, the same application difficult. the polyolefins are recompounded to reform the crystalline and amorphous regions of the polymeric .730 chains. However, due to the polymeric chain scission which occurs during the initial use of the polyolefin, the polymeric chains cannot reform completely resulting in a reduction in the molecular weight of the polyolefins compared with virgin polyolefins.

This results in a concomitant reduction in the physical properties of the recycled polyolefins and thus limits the use of these recycled polyolefins to low value applications.

There is therefore a need for a method of transforming recycled polyolefins into a performance enhanced polymeric material which can be used in high value applications.

Statements of Invention According to the invention, there is provided a method of transfonning a recycled polyolefin into a performance enhanced polymeric material; characterised in that: the method comprises mixing a modified nanoclay with the recycled polyolefin to form a clay-polyolefin mix; and extruding the clay-polyolefin mix to form the performance enhanced polymeric material.

The advantage of this method is that it uses a low value recycled polyolefin to provide a high value product. The recycled polyolefin is considered to be low value as it has reduced physical properties and its applications are thus limited. By converting this low value product into a performance enhanced polymeric material, the range of applications for which it is suitable is multiplied. This also has an impact on the recycling of polyolefin waste which will also become more attractive as the range of applications for the recycled polyolefins increase and thus having a positive environmental impact.

A further advantage of this method is that some of the physical properties of the :9 7 resultant performance enhanced polymeric material may exceed what would have been expected in a corresponding virgin polyolefin. Thus although it would not previously have been considered practicable to combine such a low priced, low performance material as recycled polyolefin with a high priced, high performance material such as nanoclay, it has been found that due to the unexpected level of improvement in the physical properties of the recycled material that this combination is both cost and technically effective.

In one embodiment of the invention, prior to extruding the clay-polyolefin mix, the method further comprises: adding a virgin polyolefin to one of the modified nanoclay, the recycled polyolefin or the clay-polyolefin mix, and mixing.

In another embodiment of the invention, the method further comprises: preparing a masterbatch by mixing between 10% and 50% of the modified nanoclay by weight of the masterbatch with between 50% and 90% of a masterbatch polyolefin by weight of the masterbatch; and mixing the masterbatch in the amount of between 5% and 40% by weight with a polyolefin matrix resin and extruding to provide the performance enhanced polymeric material; wherein at least one of the masterbatch polyolefin or the polyolefin matrix resin is recycled polyolefin.

The advantage of preparing a masterbatch is that it results in better dispersability of the nanoclay within the polyolefin.

In one embodiment of this invention, the masterbatch is directly extruded with the polyolefin matrix resin at a temperature of between 150°C and 260°C.

In another embodiment of this invention, the masterbatch is compounded with the polyolefin matrix resin to form a nanocomposite; and the nanocomposite is extruded at a temperature of between 150°C and 260°C.

In a further embodiment of the invention, the process further comprises: preparing a masterbatch by mixing between 10% and 50% of the modified nanoclay by weight of the masterbatch with between 50% and 90% of a masterbatch polyolefin by weight of the masterbatch; forming a polyolefin masterbatch by mixing between 10% and 50% of the masterbatch by weight of the polyolefin masterbatch with between 50% and 90% of a first polyolefin matrix resin by weight of the polyolefin masterbatch; mixing the polyolefin masterbatch in the amount of between 5% and 50% with a second polyolefin matrix resin and extruding to provide the performance enhanced polymeric material; wherein at least one of the masterbatch polyolefin, the first polyolefin matrix resin, or the second polyolefin matrix resin is recycled polyolefin.

It has been found that by providing two masterbatch steps, the dispersability of the nanoclay within the polyolefin is further increased.

In one embodiment of this invention, the polyolefin masterbatch is directly extruded with the second polyolefin matrix resin at a temperature of between 150°C and 260°C.

In another embodiment of this invention, the polyolefin masterbatch is compounded with the second polyolefin matrix resin to form a nanocomposite; and the nanocomposite is extruded at a temperature of between 150°C and 260°C.

Preferably, the method further comprises grafting the masterbatch polyolefin with at least one monomer which is capable of reacting with the polyolefin in a molten condition. In one embodiment of the invention, the masterbatch polyolefin is grafted prior to adding the nanoclay to the masterbatch polyolefin. In another embodiment of the invention, the nanoclay is added to the masterbatch polyolefin during grafting of the masterbatch polyolefin.

Preferably, the monomer is in the amount of less than 2% by weight of the polyolefin.

Further preferably, the monomer is selected from the group comprising ethylenically unsaturated carboxylic acids, ethylenically unsaturated carboxylic acids and anhydrides and mixtures thereof. Still further preferably, the monomer is maleic anhydride.

In one embodiment of the invention, the masterbatch polyolefin and polyolefin matrix resin are homopolymers selected from the group consisting of one or more of polyethylene and polypropylene. Preferably, the polyethylene is selected from the group consisting of one or more of High Density Polyethylene (HDPE). Medium Density Polyethylene (MDPE), Low Density Polyethylene (LDPE), Linear Low Density Polyethylene (LLDPE), Low Density Low Molecular Weight Polyethylene (LDLMWPE).

In another embodiment of the invention, the masterbatch polyolefin and polyolefin matrix resins are copolymers selected from the group consisting of one or more of butene-1, hexene-1, 4 methylpentene-1 (4MP—i ).

The invention also relates to a perfomnance enhanced polymeric material prepared using recycled polyolefin and by the method of the invention. The invention, further relates to a performance enhanced polymeric material comprising at least between 45% and 99% of a recycled polyolefin and a modified nanoclay, and more preferably between 90% and 99% of a recycled polyolefin.

Detailed l_)escrip;ion of the lnventi_o_n The invention will be more clearly understood from the following description thereof: All of the equipment used in carrying out each of the processes is well known equipment and accordingly does not require any further description.

The performance enhanced polymeric material may be prepared by mixing modified nanoclay directly with recycled polyolefin and then extruding to provide the performance enhanced polymeric material. it is also possible to mix the modified nanoclay with virgin polyolefin as well as recycled polyolefin and extruding to provide the performance enhanced polymeric material. in the above embodiments the amount of nanoclay added to provide the perfonnance enhanced polymeric material is between 1% and 10% by weight of the material. The preferable amount of clay to be added to the recycled polyolefin or recycled and virgin polyolefin will depend on the amount and/or type of recycled polyolefin. in the first embodiment of mixing nanoclay with recycled polyolefin only, the amount of clay required will depend on the grade and state of the recycled polyolefin. Thus, more specifically, the lower the grade of the recycled polyolefin and the greater the damage to the recycled polyolefin, the higher proportion of clay will be required.

In the second embodiment of mixing nanoclay with recycled and virgin polyolefin, the proportion of nanoclay required will depend on the grade and state of recycled polyolefin as well as the amount of recycled polyolefin compared to virgin polyolefin.

Generally, the most preferable amount of nanoclay is between 2% and 5% by weight of the perfonnance enhanced material.

Alternatively a masterbatch can be prepared by mixing either recycled or virgin polyolefin or both with modified nanoclay. The masterbatch can be either combined by compounding with a polyolefin matrix resin to yield a nanocomposite material and then extruding or alternatively extruding the masterbatch and polyolefin matrix resin directly. It will be appreciated that if the masterbatch is prepared using modified nanoclay and virgin polyolefin only that at least a portion of the polyolefin matrix resin will be recycled polyolefin.

The method of the invention may also comprise preparing a masterbatch by mixing either recycled or virgin polyolefin or both with modified nanoclay. The masterbatch may then be mixed with a first polyolefin matrix resin to form a polyolefin masterbatch. This polyolefin masterbatch can then be mixed with a second polyolefin matrix to yield a nanocomposite material and then extruded or alternatively the polyolefin masterbatch and polyolefin matrix resin may be extruded directly. It will be appreciated that if the masterbatch is prepared using modified nanoclay and virgin polyolefin only that at least a portion of either the first or second polyolefin matrix resin will be recycled polyolefin. in each of the embodiments, mixing of the nanoclay with polyolefin which is either recycled or virgin is generally carried out in an extruder. The mixing temperature can be between 150°C and 260°C and more preferably between 170°C and 230°C.

Mixing can be carried out at speeds of between 30rpm and 100rpm for between 5 to minutes.

In the specification the term “extrusion" refers to the compacting of material in a die.

Extrusion may be in the form of extrusion blow moulding, rotomoulding, injection moulding or compression moulding. Blow moulding has been found to provide the most performance enhanced polymeric material. The clay-polyolefin mixes, masterbatches or nanocomposites which are extruded by blow moulding result in articles which have the most improved properties. During the blow moulding process the melted polyolefin undergoes stretching in both the machine direction and transverse direction. This has the effect of orientating the polymeric chains of the polyolefin. This orientation also has the effect of orienting the clay platelets so that these platelets are atigned in a more parallel manner to each other. This parallel orientation results in increased physical properties such as improves flex modulus and resistance to permeation. Other process which give a degree of orientation such as fill blowing or pipe drawing can be used.

Either a single screw extruder or a twin screw extruder can be used for extrusion, however it will appreciated that the mixing capabilities of the twin screw extruder are considered to be more effective. It will further be appreciated that both single and twin screw extruders often have multiple heating zones. The extruder temperatures are in the region of between 150°C and 260°C, however the temperature of the individual zones of the extruder would vary within this range and increase gradually along the barrel of the extruder.

The performance enhanced polymeric material can either be extruded into a particular shaped article or can be extruded or pelletised for further processing such as moulding or further extrusion to a finished product.

The performance enhanced polymeric material can be made into a number of products including blow-moulded containers for transportation of dangerous goods such as chemicals, blow-moulded mussel floats, blow-moulded intermediate bulk containers, extruded pipes, blown film and other suitable types of polymeric products.

The addition of the nanoclays to the recycled polyolefins either directly or in the form of a masterbatch transforms the recycled polyolefin from a low value polyolefin to a performance enhanced polymeric material. The particular physical properties which have been shown to be enhanced include the modulus of stiffness, tensile strength, tensile modulus, and stress crack resistance.

The combination of nanoclay and recycled polyolefin results in a performance enhanced polymeric material with properties which far exceed the original properties of the recycled polyolefin and even the properties of a corresponding virgin polyolefin.

Due to the condition of recycled polyolefin following use and recycling, it would not previously have been considered possible to return the recycled polyolefin even to its original condition. Specifically due to the level of polymeric chain scission it would not have been considered possible to add any type of component to the recycled polyolefin which would result in reformation of the polymeric chains.

It has been found that even though the nanoclays do not cause the polymeric chains to reform, that they result in a technical effect which exceeds what would have been expected if the polymeric chains did reform.

The nanoclay which is added may be a natural or synthetic silicate clay. Suitable types of nanoclays are the smectite clays which include montmorillonite, saponite, beidellite, nontronite and hectorite or any analogue thereof. The nanoclay should also be modified by a cation exchange with an alkyl ammonium ion as this allows a better interaction with the polyolefins. The nanoclay has a large surface area for interaction with the polyolefin and comprises swellable nanoclay platelets which disperse within the polymeric chains of the recycled polyolefin. It has been found that the nanoclay platelets both assist in increasing the formation of crystalline sites on the polymeric chains and in plating out the amorphous regions of the chains. It has also been found that the nanoclay platelets fill the gaps in the polymeric chains which have been caused by chain scission. This results in a polymeric material with increased strength and enhanced physical properties.

All types of recycled polyolefin are suitable for this invention‘ Recycling can involve either or both of mechanical or chemical recycling, but more commonly only mechanical recycling is carried out. Mechanical recycling of polyolefins involves sorting of the plastic items into their specific polyolefin types. This is generally carried out by x-ray fluorescence or flotation methods. The plastic items are then washed and any labels are removed. Each item is then sliced into flakes, rewashed, melted together, and extruded through small holes to fomw small plastic pellets.

The molecular weight of the virgin polyolefin will depend on the type of polyolefin used, however generally will be in the region of between 200,000 and 700,000 daltons. The virgin polyolefins will generally have a melt index of 2-3g/10 min at 21.6 kg load and °C, and a viscosity of between 1500 Pas and 1700 Pas at a shear rate of 100 1/5.

Other optional components which are typically used in polymeric material processing such as pigments can be added.

The following examples are given by way of illustration only and should not be construed as limited the subject matter of the invention.

Examples In each of the examples the following materials were used: _]_O_ Recycled polyolefin: Recycled polyethylene: The recycled polyethylene was a high molecular weight polyethylene in the form of a 20OL drum. The drum was originally made using HM542O supplied by BP Chemicals Ltd in 1999. The original use of the drum is unknown, however prior to this experiment it is known that the drum had been used as a marine float. The drum was first washed with water to remove all contamination and chipped into pellets circa 1-5 mm.

Recycled polypropylene: The recycled polypropylene was obtained from chipping up transport pallets. The age and grade of the polypropylene was unknown.

Nanoclay: The nanoclay used was Nanomer l3OP sourced from Nanocor |nc., which had been organically modified by cation exchange with an alkyl ammonium ion.

Virgin polyolefin: The virgin polyolefin used was a virgin polyethylene from one of the following sources: A) Commercially available maleated High Density Polyethylene (HDPE), Fusbond MB10OD which was sourced from DuPont.

B) Commercially available High Density Polyethylene (HDPE), Fina Sl508 C) Commercially available High Density Polyethylene (HDPE), Lupolen D) Commercially available Low Density Polyethylene (LDPE), Exxon 61_1]__ Example 1: Mechanical properties of recycled polypropylene plus nanoclay prepared on a Brabender Plastograph EC.

Test Material A g of recycled polypropylene and 2g of modified nanoclay were added to a Brabender Plastograph EC at 210°C. The polypropylene and nanoclay were then mixed for 10 minutes at 60rpm to form a clay-polyolefin mix. The resulting mix which contained 5% nanoclay was then compression moulded and tested according to ISO 178 to determine the flex modulus.

The flex modulus of a sample of recycled polypropylene with no clay was also tested for comparison purposes. The flex modulus results are shown in Table 1.1.

Table 1.1 Material Flexural modulus (GPa) Standard Deviation Recycled polypropylene flake 1.033 0.055 Test Material A (Recycled 1.321 0.035 polypropylene flake + 5% nanoclay) Example 2: Mechanical properties of recycled polyethylene and virgin polyethylene compared to performance enhanced polymeric material prepared from recycled polyethylene.

Test Material B The preparation of a performance enhanced polymeric material using a recycled high molecular weight polyethylene was carried out using the following method and according to the quantities outlined in Table 2.1. .12.

Table 2.1 Component Amount (°/o) Nanoclay 4.8 Masterbatch polyolefin (maleated virgin HDPE) 7.2 Polyolefin Matrix resin (recycled polyethylene) 88.0 The nanoclay and masterbatch polyolefln were first compounded in a Dr Collin ZK25 twin screw extruder to yield a masterbatch. The extruder parameters are outlined in Table 2.2.

Table 2.2 Parameter Range I Value Processing temperature °C - 190°C Screw speed 200rpm Melt temperature 209°C Motor amps 8.2 amps Throughput 4kg/hr The masterbatch was then extruded with polyolefin matrix resin in a Killlon 38mm single screw extruder to provide extruded sheets of performance enhanced polymeric material. The extruder parameters are outlined in Table 2.3.

Table 2.3 Parameter Range I Value Processing temperature 240°C - 255°C Screw speed 75rpm Melt temperature 285°C Motor amps 12 amps Line speed 0.21 m/min Melt pressure 390 bar Die gap 2.2mm Nip roll gap 2.1mm Sheet die 600mm Test Material C The preparation of a performance enhanced polymeric material using recycled high molecular weight polyethylene was carried out by directly extruding the nanoclay, virgin polyethylene and recycled polyethylene in a Dr Collin ZK25 twin screw extruder according to the quantities outlined in Table 2.4.

Table 2.4 Component Amount (%) Nanoclay 5.0 Virgin polyethylene (maleated virgin HDPE) 7.0 Recycled polyethylene 88.0 The extruder parameters are outlined in Table 2.5.

Table 2.5 Parameter Range I Value Processing temperature 200°C - 225°C Screw speed 200rpm Melt temperature 231°C Motor amps 7.7 amps Throughput 4.8kg/hr Further extrusion was then carried out in a Killion 38mm single screw extruder to provide extruded sheets of performance enhanced polymeric material. The processing parameters of the single screw extruder were the same as for Test Material B (Table 2.3), with the exception that the lower line speed of the extruder was 0.195 m/min.

Test Material D The recycled polyethylene was fed directly into the Killion 38mm single screw extruder to provide an extruded sheet as a reference sample. The processing parameters of the single screw extruder are the same as for Test material B (Table 2.3), with the _ A exception of the following parameters outlined in Table 2.6.

Table 2.6 Parameter Range I Value Melt temperature 292°C Motor amps 9.5 amps Line speed 0.1 m/min Melt pressure 430 bar Physical testing Flexural modulus was evaluated on the resultant 2 mm sheets using 60mm long, mm wide strips, a test span of 40mm and a test speed of 2mm/min. In all other respects the testing complied to lSO178.

The properties of the test pieces are shown in Table 2.7.

Table 2.7: Mechanical Properties of test pieces and standard.

Material Detail Clayl PE Flex Modulus Delta ratio (%) (MPa) over ref Test Material Masterbatch 4.8% 1 188 +28% B (nanoclay + maleated HDPE) + recycled polyethylene Test Material Nanoclay, maleated 5% 1233 +33% C HDPE + recycled polyethylene All blended together Test Material Recycled none 926 - D polyethylene only Standard Virgin Polyethylene none ~110O — only Table 2.7 shows increased Flex Modulus for clay containing recycle compared to the reference recycle material only. Typical flex modulus results for the original virgin polyethylene from which the drum was made is circa 1100 MPa showing that clay has raised the stiffness of the recycle to in excess of the original material.

Example 3: Mechanical Properties of recycled polyethylene plus nanoclay prepared on Brabender Plastograph EC.

A masterbatch of modified nanoclay and virgin polyethylene was prepared by grinding both materials to powder, dry blending and then feeding them into a Dr Collin ZK25 twin screw extruder and extruding as pellets.

The extruder parameters are outlined in Table 3.1.

Table 3.1 Parameter Range I Value Processing temperature 150°C - 190°C Screw speed 200rpm Melt temperature 209°C Motor amps 8.2 amps Throughput 4.0kg/hr The masterbatch was then added to recycled polyethylene in a Brabender Plastograph EC according to the quantities outlined in Table 3.2.

Table 3.2 Material Masterbatch (g) Recycled Polyethylene (9) Clay (%) Test Material E O 50.0 0 Test Material F 1.25 48.75 1 Test Material G 6.25 43.75 5 Test Material H 12.5 37.25 _]_6_ The masterbatch and recycled polyethylene were mixed over a 2 minute period followed by a further 8 minutes mixing at 185°C at 60rpm. The resulting mixture was then transferred and extruded by compression moulding to give 3mm plaques. The test material plaques were tested for flexural modulus according to ISO 178.

The flex modulus results are shown in Table 3.3.

Table 3.3 Material Flexural modulus (GPa) Standard Deviation Test Material E 1.196 0.073 Test Material F 1.307 0.093 Test Material G 1.849 0090 Test Material H 2.645 0.084 Example 4: Mechanical properties of recycled polyethylene plus nanoclay prepared in a twin screw extruder and then blow moulded to give 10 litre containers Test material I % nanoclay, 30% virgin HDPE, and 30% virgin LDPE were mixed in a Berstoff BD15 40mm twin screw extruder to form a masterbatch comprising 40% nanoclay. 68% of this masterbatch was mixed with 32% Fina SI508 virgin HDPE in the same twin screw extruder to form a polyolefin masterbatch comprising 27.2% nanoclay.

This polyolefin masterbatch was then mixed in a Bekum 10 litre blow moulder. 18% of this polyolefin masterbatch was then mixed with recycled polyethylene to yield a performance enhanced material comprising 4.8% nanoclay.

Test Material J 4.7% nanoclay was added directly to 93% recycled polyethylene and 2% blue pigment and extruded in a Bekum 10 litre blow moulder.

Test Material K 40% nanoclay and 60% virgin polyethylene were mixed to form a masterbatch _1’7_ comprising 40% nanoclay. 25% masterbatch was mixed with virgin Lupolen HDPE in the Berstoff BD15 40mm twin screw extruder to fonn a polyolefin masterbatch comprising 10% nanoclay. 50% of this polyolefln masterbatch was then mixed with 50% recycled polyethylene in a Bekum 10 litre blow moulder to yield a performance enhanced material comprising 5% nanoclay.

Two tests were performed on the test materials. The first of these tests was a stack test and was carried out according to that used in ISO 16104. The loading on the container was 2.586 which in this case (10 litre containers) was 300kg. the temperature was held at 40°C and the containers were filled with wetting agent. The number of days was recorded until the containers failed the stack test. All tests were repeated and an average was taken.

The second test performed was the visual examination of the containers where we examined for evidence of poor dispersion.

The results of both tests are tabulated in Table 4.1 Table 4.1 Test Stack Test (days) Visual Appearance Test Material I 11 Good dispersion Test Material J 9 Some lumps of undispersed clay Test Material K 8 Very good dispersion Recycle only 3.8 — The above results show a more that doubling in stack test performance although the visual appearance suggests that test material K is the optimum.

In this specification the temis “comprise, comprises, comprised and comprising” and the terms “include, includes, included and including" are all deemed totally interchangeable and should be afforded the widest possible interpretation.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail within the scope of the claims.

Claims (5)

Claims

1. A method of transfonning a recycled polyolefin into a performance enhanced polymeric material; characterised in that: the method comprises mixing a modified nanoclay with the recycled polyolefin to form a clay-polyolefin mix; and extruding the clay—po|yolefin mix to form the performance enhanced polymeric material.

2. A method of transforming a recycled polyolefin as claimed in claim 1, further comprising: preparing a masterbatch by mixing between 10% and 50% of the modified nanoclay by weight of the masterbatch with between 50% and 90% of a masterbatch polyolefin by weight of the masterbatch; and mixing the masterbatch in the amount of between 5% and 40% by weight with a polyolefin matrix resin and extruding to provide the performance enhanced polymeric material; wherein at least one of the masterbatch polyolefin or the polyolefin matrix resin is recycled polyolefin.

3. A method of transforming a recycled polyolefin as claimed in claim 1, further comprising: preparing a masterbatch by mixing between 10% and 50% of the modified nanoclay by weight of the masterbatch with between 50% and -20.. 90% of a masterbatch polyolefin by weight of the masterbatch; forming a polyolefin masterbatch by mixing between 10% and 50% of the masterbatch by weight of the polyolefin masterbatch with between 5 50% and 90% of a first polyolefin matrix resin by weight of the polyolefin masterbatch; mixing the polyolefin masterbatch in the amount of between 5% and 50% with a second polyolefin matrix resin and extruding to provide the 1 0 performance enhanced polymeric material; wherein at least one of the masterbatch polyolefin, the first polyolefin matrix resin, or the second polyolefin matrix resin is recycled polyolefin_ 15

4. A method of transforming a recycled polyolefin substantially as described hereinbefore with reference to the accompanying examples.

5. A performance enhanced polymeric material substantially as described hereinbefore with reference to the accompanying examples 20