DESC:FIELD OF THE INVENTION:

The present invention relates to a process for recycling non degradable post-consumer polyethylene wherein the properties of the recycled polyethylene is enhanced in desirable manner for usage in multiple applications.

BACKGROUND OF THE INVENTION:

Polyethylene is used for packaging of various consumable products. The advantages of the polyethylene are vast, ranging from easy operations to safe storage. But the disadvantage is plastic pollution.

Polyethylene can be used as multi-layer packaging plastic bags mainly made form LLDPE/LDPE combination providing it various properties that enhances the shelf life of product as well as provides ease of transportation and storage.

After usage, polyethylene account for major plastic pollution mainly due to its non-biodegradability resulting in accumulating in nature. Recycling of any kind of plastic requires number of steps where collection and cleaning accounts for the major steps. Plastic can be burnt but it leads to emission of greenhouse gases. Only a small proportion of entire plastic waste is currently being recycled as secondary polymers which have poor quality and give low financial returns.

Recycling of polyethylene is a major challenge as the recycled polymer product is of poor polymer quality. Hence the application of the recycled polymer becomes restricted.

WO2012139967A1 describes the system of recycling of high-density polyethylene from domestic polymer waste to obtain polyethylene blend having excellent mechanical properties. It is further directed to such polyethylene blend as well as to articles comprising such polyethylene blend.

WO2005121231A1 relates to a method for recycling the waste of printed polyolefinic films by compounding extrusion, the composition to be extruded being formed from the waste of printed films and a mineral load. The inventive method leads to the production of a masterbatch which is easily used in the formation of an excellent-quality thin film having a thickness of less than 30 µm.

US20170232416 describes a system for treating recycled polymeric material in a continuous manner where a hopper is configured to feed the recycled polymeric material into the extruder. An extruder can turn the recycled polymeric material in a molten material and the molten material is de-polymerized using alumina or zeolite based catalyst. Here the waste polymeric material feed includes any type of polyethylene.

US20190023867 describes another application of any type of polyethylene waste to be converted into wax and hence to be used as viscosity modifier and processing aid for polymers.

EP2610290A1 describes the polymer compositions, for example, recycled polymer compositions, the processes for the production thereof, to functional fillers for use in said compositions and to articles formed from the polymer compositions.

Most of the aforesaid prior art process discloses the recycled product with poor properties. Due to heat treatment mainly in melt flow process, recycled polyethylene becomes more prone to degradation hence has poor properties, leading to limitation in applications. Also, during heating, the polyethylene pouches may undergo burning which are hazardous and threat to the environment.

Hence there is still a need of a new process for recycling pro-consumer polyethylene waste materials which could provide the recycled product with better properties.

OBJECTIVES OF THE PRESENT INVENTION:

It is the primary objective of the invention to provide a process for recycling non degradable post-consumer polyethylene waste more particularly polyethylene pouches or bags comprising low density polyethylene and linear low density polyethylene, wherein the properties of the recycled polyethylene is enhanced in desirable manner for usage in multiple applications.

Another objective of the invention that the recycled product recovered from the post-consumer polyethylene waste with enhanced properties can be used in multiple applications i.e., for making drip-tape, bottles.

SUMMARY OF THE INVENTION

The present invention relates to a process for recycling post-consumer polyethylene comprising:
a. providing the polyethylene feed comprising linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE);
b. shredding the polyethylene feed into small pieces to obtain shredded feed ;
c. cleaning the shredded feed;
d. agglomerating and modifying the cleaned feed with a modifier to obtain recycled polymer.

In an embodiment the modifier used in the process for recycling post-consumer polyethylene is selected from organic peroxides, multifunctional acrylate monomer, hydroperoxides, peracids, metal alkyls, metal aryls and combinations thereof.
In a preferable embodiment, the modifier is a combination of the organic peroxides and the multifunctional acrylate monomer. The organic peroxides and the multifunctional acrylate monomer are in the weight ratio from 50:1 to 1:1.
In another embodiment, the organic peroxide is selected from 3,6,9-Triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexoxonane, and 2,5-dimethyl-2,5-(di tert-butylperoxy) hexane, or a combination thereof.
In yet another embodiment, the multifunctional acrylate monomer is selected from the group consisting of trimethylolpropane triacrylate (TMPTA), trimethylolpropane ethoxylate triacrylate, glycerol propoxylate (1PO/OH) triacrylate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, tris[2-(acryloyloxy)ethyl]isocyanurate, pentaerythritol tetraacrylate, di(trimethylol propane) tetraacrylate, dipentaerythritol hexaacrylate (DPEHA), Zinc methacryalte, Pentaerythritol tri acrylate (PETA)
In a preferable embodiment, the multifunctional acrylate monomers can be selected from pentaerythritol triacrylate (PETA), zinc methacrylate, pentaerythritol tetraacrylate or a combination thereof.
In yet preferable embodiment, the multifunctional acrylate monomer is pentaerythritol triacrylate (PETA).
In an embodiment, the post-consumer polyethylene can be selected from milk pouches, food packaging films, consumer product packaging, plastic liners, shopping bags, agricultural films, and shrink/stretch films.
In another embodiment, the process of cleaning of the shredded feed comprises
a. washing the shredded feed with detergent or surfactant followed by water;
b. treating the feed with oxidising agent selected from the group consisting of hydrogen peroxide, potassium permanganate, potassium dichromate, baking soda, ethyl alcohol, hypochlorous acid or combination thereof;
c. treating the oxidised feed with reducing agent selected from the group consisting of oxalic acid, Formic acid, Ascorbic acid, Iodides, potassium oxalate, ferrous oxalate or combination thereof;
d. removing moisture from the feed obtained in step c. at 60°C for 2 hours to obtain cleaned shredded feed.
In another embodiment, recycled polymer is used for making drip-tape, bottles for chemical storage and bitumen packaging.
Advantages of the present invention:

The following are the advantages of the present invention over the prior art process:
• New process for handling non-degradable polyethylene waste particularly polyethylene pouches
• Provides recycled polyethylene with better properties for wider applications

BRIEF DESCRIPTION OF DRAWING:

Figure 1 depicts a graphical representation of melt strength of post-consumer PE extruded granules modified of Example 1 as compared to post consumed PE extruded granules

Figure 2 depicts a graphical representation of melt strength of post-consumer PE extruded granules modified prepared by varying the ratios of Peroxide Y to MFC-C modifiers.

Figure 3a and 3b depicts a graphical representation of melt strength of post-consumer PE extruded granules modified prepared by varying the combination of modifiers.

DESCRIPTION OF THE INVENTION:

The present disclosure provides a process of recycling post-consumer polyethylene.

The term "polyethylene" is used to denote a homopolymer of ethylene or any copolymer comprising ethylene in at least 50 wt%, relative to the total weight of said copolymer.

The term “low density polyethylene”, which may be abbreviated as "LDPE", is generally used to denote polyethylenes having a density range of 0.910–0.940 g/cm3.

The term, "linear low density polyethylene" which may be abbreviated to “LLDPE” is meant to include copolymers of ethylene and at least one alpha-olefin comonomer. The term includes copolymers, terpolymers, etc. Linear low density polyethylenes are generally copolymers of ethylene and alpha-olefins such as propene, butene, 4-methyl-pentene, hexene, octene and decene.

The term “post-consumer polythene” includes milk pouches, food packaging films and consumer product packaging, plastic liners, shopping bags, agricultural films, shrink/stretch films etc.
The term “Recycling” refers to processing materials for use in its original end use purpose or for other purpose.

The term “post-consumed PE extruded modified granules” or “modified granules” or “recycled polymer” can be used interchangeably.

The present disclosure relates to a process for recycling non degradable post-consumer polyethylene wherein the properties of the recycled polyethylene is enhanced in desirable manner for usage in multiple applications.

The resultant recycled polyethylene can be used be for making drip-tape, bottles for chemical storage, bitumen packaging etc.

An embodiment of the present disclosure provides a process for recycling post-consumer polyethylene comprising:
a. providing the polyethylene feed comprising linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE);
b. shredding the polyethylene feed into small pieces to obtain shredded feed;
c. cleaning the shredded feed;
d. agglomerating and modifying the cleaned feed with a modifier to obtain recycled polymer.
The process for recycling post-consumer polyethylene waste material comprising shredding, cleaning and modification in continuous manner.

The non-degradable post-consumer polyethylene used in the present invention is made of multilayer LLDPE/LDPE in desired composition. The non degradable post-consumer polyethylene can be sourced from anywhere.
The first step of the process of recycling post-consumer polyethylene is shredding.

Before the first step is performed, the non degradable post-consumer polyethylene are sourced and collected at the collection point. It is desirable that the non-degradable post-consumer polyethylene is treated manually to remove dirt and dust using any of the methods described in state of the art. This is termed as feed. In an embodiment, the feed can contain trace quantities of undesirable additives, such as ash, grit, or other unknown particles.

The collected feed is then shredded into a shredder. The shredder used in the process of recycling non-degradable polyethylene pouches shreds the feed into small pieces from powder to 50mm.
The shredder can be any plastic shredding machine capable of handling polyethylene for examples, but not limiting to, grinders, chippers, shear shredders, granulators, hammer mills, and all-purpose shredders. In another embodiment, the shredding conditions like speed, time and power of the motor are kept in such a combination that the shredded feed is not sheared or degraded. The second step of the process of non degradable post-consumer polyethylene is cleaning. In an embodiment, the cleaning step may comprise washing of shredded feed with cleaning additives, such as surfactants, detergents and the like preferably in water having the temperature range from 25-60°C. This is followed by water washing step to remove traces of detergent accordingly. The shredded feed may be mechanically agitated to facilitate the removal of solid and volatile impurities like oil or fat sticking to the shredded feed. Through the removal of volatile and solid impurities, unpleasant odors associated with such impurities are also reduced or eradicated.
In another embodiment, the cleaning comprises treating the shredded feed with suitable oxidizing agents to remove unpleasant odor from the shredded feed. The suitable oxidizing agents may include hydrogen peroxide, potassium permanganate, potassium dichromate, baking soda, ethyl alcohol, hypochlorous acid and the likes. The combination of oxidizing agents can also be used. The oxidizing agent can be used as neat or in dilution, preferably in dilution. The diluents used can be water, alcohol, amine, ester, ether and the likes. The diluent used is water. After the removal of oxidizing agent, the shredded feed is treated with reducing agent, preferably oxalic acid. After the removal of reducing agent, the shredded feed is dried to remove moisture, preferably at 60°C for 2 hours. This is cleaned shredded feed.
In an aspect, the cleaning of shredded feed may involve both water washing as well as treatment with oxidizing and reducing agents as described above.
The third step of the process of non degradable post-consumer polyethylene is modification.
During the modification step, the cleaned shredded feed is agglomerated and treated with modifiers that enhance the polymer product properties. The treatment with modifier can be during agglomeration or during extrusion.

In an embodiment, the cleaned shredded feed density is increased by using an agglomerator. The agglomerator is operated at high speed ranging from 20 to 5000 RPM maintained at temperature range from 40°C to 250°C for 1 to 75 minutes.

Modifier
In another embodiment, the modifier can be added during agglomeration. The modifier added enhances the recycled polyethylene properties. The modifier may for example be organic peroxides, multifunctional acrylate monomers, hydroperoxides, peracids, metal alkyls, metal aryls and combinations thereof.

The preferred modifier used in the present process is a combination of organic peroxide and multifunctional acrylate monomers. The invention should not be construed as being limited to such embodiments.

The organic peroxide used in the present invention may be 3,6,9-Triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexoxonane and the multifunctional acrylate monomer can be selected from the group consisting of trimethylolpropane triacrylate (TMPTA), trimethylolpropane ethoxylate triacrylate, glycerol propoxylate (1PO/OH) triacrylate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, tris[2-(acryloyloxy)ethyl]isocyanurate, pentaerythritol triacrylate (PETA), di(trimethylol propane) tetraacrylate, dipentaerythritol hexaacrylate (DPEHA), Zinc methacryalte, Pentaerythritol tetracrylate and the like. PETA is a preferred multi-functional acrylate.
In another embodiment, weight ratio of peroxide to multi-functional acrylate is from 50:1 to 1:1.
The desired final product application depends on the ratios and the combination of modifiers.
It has been noted that the post-consumer polyethylene granules on modification with a ratio higher to 50:1 of peroxide: acrylate will result in cross linking in polymer and will results in drastic reduction of melt flow of the polymer and results in cross linking. The MFI of such formulation at 190°C, 2.16Kg is less than 0.1 and hence the feasibility of measurement of melt strength is not possible.
In a preferable aspect, a weight ratio of 3,6,9-Triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexoxonane to multifunctional acrylate is from 50:1 to 1:1. The combination of 3,6,9-Triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexoxonane and multifunctional acrylate monomer reduces gel formation during processing of the recycled polymer.
Further, in an embodiment, the modified recycled polymer product is passed through extruder to get the post-consumer PE extruded modified granules (can be referred as “modified granules”) of desired polymer product.
The modified recycled polymer is having enhanced polymer properties such as melt strength.
In another embodiment, the recycled polymer with enhanced properties can be used for making drip-tape, bottles for chemical storage, bitumen packaging etc.
Experimental details:
A. Measuring Methods
The following measurement methods are used in the examples below.
Measuring Melt strength
Melt strength of the modified granules were measured using extensional viscosity rheometer called Rheotens. (Gottfret make). The Rheotens is aligned and kept below a capillary rheometer. The molten material is extruded through die of 2.0mm diameter having L/D 16:1) at a constant speed of 19.2mm/min fitted at capillary rheometer at a temperature of 220°C. Alignment of rheotens and capillary rheometer is made in such a way that the molten filament is fed directly between the centre of the rotating wheels of Rheotens and the distance between the exit of die and the top of the wheel is maintained as 100 mm. The distance is selected such a way that the filament touching the wheels of rheotens is in molten form. The speed of the wheels at the start of the experiment is maintained at 18 cm/s and goes up to 250cm/s or till the filament breaks at an acceleration of 10mm/s2. During the acceleration, the Force in (cN) is recorded against the pull speed (mm/s) till the filament breaks. A graph is generated as F (cN) in Y axis and Draw ratio in X axis. Highest Force recorded at the time of filament break is reported as melt strength in cN.

Making the film by blow film process:
Following procedure was adopted to convert the modified granules to a film of thickness 100 microns.
The modified granules are melted in a Polymer extruder where the temperature range is maintained at 140 to 200°C between various sections of heating. The molten polymeric material is then passed through a die with circular orifice to form a tubular film which is termed as bubble. The interior of the bubble is inflated to as desired diameter / blow up ratio using air. The Diameter of the die used is 6 inch, Bubble diameter is maintained in range of 12-13 inch. Then bubble is passed through Nip rolls to collapse the bubble and rolled.

Measuring of tensile properties of film:
The tensile properties of film thus produced were determined as per ASTM D882 in universal testing machine of TIRA Germany make after being conditioned as per ASTM D618 standard.
Measuring of MFI:
Melt flow index of the modified granules was determined according to ASTM D1238 at 190°C, 2.16Kg load and 5 Kg load in Automatic multiload MFI machine of Gottfret make.
B. Examples
It is well known that Polyethylenes are prone to crosslinking in the presence of peroxides and multifunctional acrylates. The cross linking can be observed as sudden decrease in MFI. Very low MFI are not preferred in the industry. In the below examples, the peroxides and MFC are so chosen that the desired properties are increased and the cross linking is avoided to a much extent. This is evident from similar melt flow index of the recycled polymers/ modified granules. Examples have shown that melt strength is increased which is beneficial for the further converting recycled polymers/ modified granules to films and other products without much decrease in the MFI.

Example 1:
The collected waste milk pouches (~10Kg) were shredded in polymer shredder at room temperature at high speed to smaller dimension up to 20 mm. The shredded polyethylene was cleaned using detergent followed by water washing.
The shredded pouches were then treated with potassium permanganate followed by washing with water. Further, treatment with oxalic acid was carried out, water washed and dried in hot air oven at 60 ? for 2 hours.
Agglomeration of shredded polyethylene was carried out in high speed mixer/agglomerator where the shredded pouches were mixed at high speed at 80 to 100? for 2-20 mins.
The combination of 3,6,9-Triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexoxonane (referred herein as “peroxide –Y”) and pentaerythritol triacrylate (PETA) (referred herein as “MFC-C”) in the ratio of 10:1 were added to the shredded feed during agglomeration to produce post-consumer PE agglomerated modified polymer
The agglomerated modified polymer was extruded in twin-screw extruder (Labtech) having screw diameter of 26mm and Length/Diameter ratio 40:1 and maximum screw rotating speed 800rpm. Speed of the extruder is maintained at 100-200 rpm and barrel temperature range maintained at 100-250°C, feeding rate 8-20Kg/hr. The extrudate of modified batches are pelletized after cooling in water bath to obtain the post-consumed PE extruded modified granules/ recycled polymer of size 2-3 mm.
Increase in melt strength of the post-consumer PE extruded modified granule over the post-consumer PE extruded granule is illustrated in Figure 1.
Examples 2-5:
The modified post-consumer polyethylene extruded modified granules were prepared varying the ratio of peroxide Y and acrylate MFC-C according to the method described above.

Table 1 list out the various combinations varying the ratio of MFC–C and Peroxide Y used in modifying the post-consumer polyethylene waste and the resulted MFI values of the post consumed PE extruded modified granules.

S.NO Peroxide Y MFC-C Solvent 1
MFI @190°C, 2.16KG MFI @190°C, 5KG
ratio ratio ml/kg
*Comparative EXP1 - - - 0.85 2.7
EXP 1 10 1 30 0.80 2.6
EXP2 1 1 30 0.79 2.5
EXP3 1 2 30 0.78 2.4
EXP4 2 1 30 0.75 2.3
EXP5 2 2 30 0.7 2.2

* Comparative EXP 1 is the recycled polyethylene without using modifiers.
Melt strength of various composition of the post-consumer PE extruded modified granules using Rheotens has been graphically represented in Figure 2.
Table 2: Summarizes the film properties of post-consumer PE extruded modified granules made from EXP 5.
S.No Sample description Tensile strength % Elongation at Max force TS at break % Elongation at break
MPa % MPa %
1 Film made from Post consumed PE extruded Modified granules (100 microns thickness) 11.0 14.5 3 260

Example 6-11:
The post consumed PE extruded modified granules are obtained by varying the modifiers. Three different type of multifunctional acrylate monomer used are Zinc methacryalate (referred herein as “MFC-A”), pentaerythritol tetra acrylate (referred herein as “MFC-B”) and pentaerythritol triacryalte or MFC-C in combination with two type of peroxides. 3,6,9-Triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexoxonane (Peroxide Y) and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (referred herein as “Peroxide X”).

Table 3: Summarises the various combinations of multifunctional acrylate and Peroxides used in modifying the post-consumer polyethylene waste and the resulted MFI values of the post consumed PE extruded modified granules.
S.NO Peroxide X Peroxide Y MFC- A MFC- B MFC-C Ratio Peroxide: MFC Solvent 1
MFI @190°C, 2.16KG MFI @190°C, 5KG
Parts Parts Parts Parts Parts ml/kg
EXP6 1 1 1:1 30 0.4 1.5
EXP7 1 1 1:1 30 0.3 1.3
EXP8 1 1 1:1 30 0.3 1.2
EXP9 1 1 1:1 30 0.6 2.2
EXP10 1 1 1:1 30 0.5 1.8
EXP 11 1 1 1:1 30 0.5 1.7

Melt strength of post-consumer polyethylene modified with Peroxide X in combination with MFC- A, B, and C has been shown in Figure 3a and the Melt strength of post-consumer polyethylene modified with Peroxide Y in combination with MFC- A, B, and C has been shown in Figure 3b.
Melt strength of the recycled polyethylene is better to the unmodified polyethylene as shown in figure 1-3.

Example 12:
The post-consumer polyethylene was modified with a ratio higher to 50:1 of 3,6,9-triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexoxonane and penta erithritol triacrylate. The increased ratio resulted in drastic reduction of MFI of the polymer which indicates cross linking. The MFI of such modified granules at 190°C, 2.16Kg is less than 0.1 and hence the feasibility of measurement of melt strength is not possible.
,CLAIMS:1. A process for recycling post-consumer polyethylene comprising:
a. providing the polyethylene feed comprising linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE);
b. shredding the polyethylene feed into small pieces to obtain shredded feed ;
c. cleaning the shredded feed;
d. agglomerating and modifying the cleaned shreaded feed with a modifier to obtain recycled polymer.
2. The process as claimed in claim 1, wherein the modifier is selected from organic peroxides, multifunctional acrylate monomer, hydroperoxides, peracids, metal alkyls, metal aryls and combinations thereof.

3. The process as claimed in claim 2, wherein the modifier is a combination of the organic peroxides and the multifunctional acrylate monomer.

4. The process as claimed in claim 3, wherein the organic peroxides and the multifunctional acrylate monomer are in the weight ratio from 50:1 to 1:1.

5. The process as claimed in claim 2-4, wherein organic peroxide can be selected from 3,6,9-Triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexoxonane, and (2,5-dimethyl-2,5-di (tert-butylperoxy) hexane or a combination thereof.

6. The process as claimed in 2-5, wherein multifunctional acrylate monomer is selected from the group consisting of trimethylolpropane triacrylate (TMPTA), trimethylolpropane ethoxylate triacrylate, glycerol propoxylate (1PO/OH) triacrylate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, tris[2-(acryloyloxy)ethyl]isocyanurate, pentaerythritol triacrylate (PETA), pentaerythritol tetra acrylate, di(trimethylol propane) tetraacrylate, dipentaerythritol hexaacrylate (DPEHA), zinc methacryate or a combination thereof.

7. The process as claimed in 6, wherein multifunctional acrylate monomer is selected from pentaerythritol triacrylate (PETA), zinc methacrylate, pentaerythritol tetraacrylate or a combination thereof.

8. The process as claimed in any of the preceding claims wherein the post-consumer polyethylene is be selected from milk pouches, food packaging films and consumer product packaging, plastic liners, shopping bags, agricultural films, shrink/stretch films

9. The process as claimed in any of the preceding claims, wherein the cleaning of the shredded feed comprises
a. washing the shredded feed with detergent or surfactant followed by water;
b. treating the feed with oxidising agent selected from the group consisting of hydrogen peroxide, potassium permanganate, potassium dichromate, baking soda, ethyl alcohol, hypochlorous acid and their combination thereof;
c. treating the oxidised feed with reducing agent selected from the group consisting of oxalic acid, formic acid, ascorbic acid, iodides, potassium oxalate, ferrous oxalate;
d. removing the moisture from the feed obtained in step k at 60°C for 2 hours to obtain the cleaned shredded feed.

10. A recycled polymer as claimed in claim 1 as and when used for making drip-tape, bottles for chemical storage and bitumen packaging.