NOVEL RECYCLING PROCESS OF POLYETHYLENE

Abstract

Recycling of waste products has become increasingly common practice in the last decades. The recycling of plastic materials is important and widely carried out by many industries and households around the world. A multitude of everyday consumer items are made from plastic materials, such as bottles, bags, products, and especially liquid food board-based packaging. It is important to recycle and reuse the polymers.

Claims

1. A process of recycling a polyethylene composition, wherein the recycled polyethylene composition comprises: a) at least 50 weight % of recycled polyethylene, and b) 0.5 to 15 weight % of an ethylene copolymer comprising hydrolysable silicon-containing groups, wherein the process comprises compounding said recycled polyethylene composition, and wherein the recycled polyethylene composition treated by 0.5 to 15 weight % of an ethylene copolymer comprising hydrolysable silicon-containing groups has at least 15% lower MFR.sub.2 compared to the recycled polyethylene.

2. The process according to claim 1, wherein the amount of recycled polyethylene in the recycled polyethylene composition is at least 75 weight %.

3. The process according to claim 1, wherein the amount of a copolymer comprising hydrolysable silicon-containing groups in the recycled polyethylene composition is from 1 to 10 weight %.

4. The process according to claim 1, wherein the ethylene copolymer comprising hydrolysable silicon-containing groups is an LDPE.

5. The process according to claim 4, wherein the copolymer comprising hydrolysable silicon-containing groups is free from peroxide or peroxide residues.

6. The process according to any prior claim 5, wherein the recycling process is free from silane condensation catalyst.

7. The process according to claim 1, a copolymer comprising hydrolysable silicon-containing groups is a polyethylene that is grafted.

8. The process according to claim 1, wherein recycled polyethylene comprises LDPE, LLDPE, and/or HDPE.

9. The process according to claim 8, wherein the polyethylene composition comprises an acidic part.

10. The process according to claim 9, wherein the acidic part comprises EMAA, EAA, MAH grafted polyolefin and/or a low molecular weight organic acid.

11. The process according to claim 8, wherein the recycled polyethylene is obtained from a liquid food board-based packages.

12. A recycled polyethylene composition, wherein the recycled polyethylene composition comprises: a) at least 50 weight % of recycled polyethylene, and b) 0.5 to 15 weight % of an ethylene copolymer comprising hydrolysable silicon-containing groups, wherein said recycled polyethylene composition is compounded, said polyethylene composition after the compounding having a MFR.sub.2 of 0.4 to 4 g/10 min.

13. A recycled film, wherein the film is provided by forming the recycled polyethylene composition according to claim 12 into a film.

14-15. (canceled)

Description

Experimental

DRAWINGS

[0067] FIG. 1 depicts a photograph of a film from comparative example 4, RPM 40; and

[0068] FIG. 2 depicts a photograph of a film from Inventive example 7, RPM 60

MEASUREMENT METHODS

[0069] The melt flow rate (MFR) is determined as MFR.sub.2 according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR.sub.2 of polyethylene is measured at a temperature 190 C. and a load of 2.16 kg. All examples of compositions with at least 50 weight % of polyethylene are measured at 190 C. The melt flow rate is preferably determined according to ISO 1133-2:2011.

[0070] Complex viscosity was measured at 190 C. using a TA Instrument ARES-G2 TA rheometer. The configuration is a 25 mm plate/plate geometry with 1% strain. Frequency sweep was from 100 to 0.1 rad/sec.

[0071] Elongation viscosity was measured at 150 C. using a TA Instrument ARES-G2 rheometer equipped with an extensional viscosity fixture (EVF). The extension rate (Hencky rate) was 0.5 1/s and the final Hencky strain was 3.4.

[0072] Optical microscopy was performed using a Dino-Lite Digital microscope at 20 magnification.

Materials

[0073] EVS is LE-4423, commercially available from Borealis. The EVS is a low-density polyethylene copolymer comprising hydrolysable silicon-containing groups. The copolymer is made in a high-pressure reactor. The density of the polymer is 923 kg/m.sup.3 and it has an MFR.sub.2 of 1.0 g/10 min.

[0074] Recycled polyethylene 1 has a MFR.sub.2 of 8.7 g/10 min. The polymer is obtained by collecting various liquid food board-based packages mainly from packages with layers of board, polymer and aluminium. First the board layer is separated, and then the aluminium layer is separated by an acid-based delamination method prior to regranulation. The liquid food board packages originate from PCR and comprise the following polymers regranulated: LDPE>LLDPE>ethylene-co-acrylic and/or-co-methacrylic acid>HDPE>PET>MAH-grafted polyolefins and pigments. The PCR further comprises contaminations that are decreased by melt filtration during the regranulation process.

[0075] Recycled polyethylene 2 has a MFR.sub.2 of 4.2 g/10 min. The polymer is obtained by collecting various liquid food board-based packages mainly from packages with layers of board, polymer and aluminium. First the board layer is separated, and then the aluminium layer is separated by an acid-based delamination method prior to regranulation. The liquid food board packages originate from PCR and comprise the following polymers regranulated: LDPE>LLDPE>ethylene-co-acrylic or-co-methacrylic acid>HDPE>PET>

[0076] MAH-grafted polyolefins and pigments. The PCR further comprises contaminations decreased or removed by melt filtration during the regranulation process.

[0077] Recycled polyethylene 3 has a MFR.sub.2 of 4.4 g/10 min. The polymer is obtained by collecting various liquid food board-based packages mainly from packages with layers of board, polymer and aluminium. First the board layer is separated, and then the aluminium layer is separated by an acid-based delamination method prior to regranulation. The liquid food board packages originate from PCR and comprise the following polymers regranulated: LDPE>LLDPE>ethylene-co-acrylic or-co-methacrylic acid>HDPE>PET>MAH-grafted polyolefins and pigments. The PCR further comprises contaminations decreased or removed by melt filtration during the regranulation process.

[0078] Recycled polyethylene 4 has a MFR.sub.2 of 3.6 g/10 min. The polymer is obtained by collecting various liquid food board-based packages mainly from packages with layers of board, polymer and aluminium. First, the board layer is separated, and then the aluminium layer is separated by an acid-based delamination method prior to regranulation. The liquid food board packages originate from PCR and comprise the following polymers regranulated: LDPE>LLDPE>ethylene-co-acrylic or-co-methacrylic acid>HDPE>PET>MAH-grafted polyolefins and pigments. The PCR further comprises contaminations decreased or removed by melt filtration during the regranulation process.

[0079] LDPE-22 is 1922NO and is commercially available from Sabic. The polymer is made in a tubular reactor and is virgin and additive free. The density of the polymer is 919 kg/m.sup.3 and it has an MFR.sub.2 of 22 g/10 min.

[0080] LDPE-7 is 19N430 and is commercially available from Ineos. The density of the polymer is 920 kg/m.sup.3 and it has an MFR.sub.2 of 7.5 g/10 min.

[0081] LDPE-1 is LDPE 320E and is commercially available from Dow. The density of the polymer is 925 kg/m.sup.3 and it has an MFR.sub.2 of 1 g/10 min.

Examples

[0082] The compositions shown in Table 1 were compounded in a single screw extruder SSE (Axon BX-25) at 220 rpm equipped with a water bath at room temperature before strand pellettization. The temperature settings of the extruder were 170, 220, 220, 220, 220, 220 C.

TABLE-US-00001 TABLE 1 Comp. Comp. Inventive Inventive Inventive example 1 example 2 example 1 example 2 example 3 Recycled 100 97.5 95 90 polyethylene 1 [weight %] EVS 100 2.5 5 10 [weight %] MFR.sub.2 8.7 0.9 2.9 1.1 0.4 [g/10 min] Relative 0% na 67% 87% 95% difference [+/ %]

[0083] In comparative example 1 the MFR.sub.2 change has been measured in polymer composition with only recycled polyethylene 1. In Table 1 all examples have been preheated 5 minutes before the MFR.sub.2 were measured.

[0084] In comparative example 2 only EVS is used. The MFR.sub.2 remains similar. In inventive example 1-3 recycled polyethylene 1 is mixed with different amounts of EVS. The MFR.sub.2 decreases with added amount of EVS.

[0085] The relative difference is calculated as the ratio of MFR.sub.2 of the recycled polyethylene composition (P) divided by MFR.sub.2 of the recycled polyethylene (A) minus 100%.

[0086] The examples in Table 2 were compounded in a single screw extruder SSE (Axon BX-25) at 220 rpm equipped with a water bath at room temperature before strand pellettization. The temperature settings of the extruder were 170, 220, 220, 220, 220, 220 C.

TABLE-US-00002 TABLE 2 Comp. Inv. Inv. Comp. Inv. Inv. Comp. Comp. Ex. 3 Ex. 4 ex. 5 Ex. 4 Ex. 6 Ex. 7 Ex. 5 Ex. 6 Recycled 100 97.5 95 polyethylene 2 [weight %] Recycled 100 97.5 95 97.5 95 polyethylene 3 [weight %] LDPE-1 2.5 5 EVS 2.5 5 2.5 5 [weight %] MFR.sub.2 4.2 3.0 1.3 4.4 2.1 1.0 4.2 3.9 [g/10 min] Relative 0% 28% 69% 0% 52% 77% 4% 11% difference [+/ %]

[0087] In Table 2 all examples have been preheated 5 minutes before the MFR.sub.2 were measured. The results are consistent with the results from Table 1.

[0088] 5 The extruder and process conditions in Table 3 are the same as in Table 2.

TABLE-US-00003 TABLE 3 Comp. Inventive Inventive example 7 example 8 example 9 Recycled 100 97.5 95 polyethylene 4 [weight %] EVS 2.5 5 [weight %] MFR.sub.2 3.6 1.3 0.48 [g/10 min] Relative 0% 64% 87% difference [+/ %]

[0089] Table 3 discloses further examples of the invention.

[0090] In Table 4 the complex viscosity changes are measured. The compositions were compounded on a single screw extruder SSE (Axon BX-25) at 220 rpm with the temperature settings of 170, 220, 220, 220, 220, 220 C. before strand pellettization. The samples were then compression moulded in in a hydraulic press machine.

[0091] Press temperature 155 C.

[0092] Time: 2 min pre-heating, 2 min full press, 5 min cooling to prepare a cylindrical sample (25 mm diameter and 1 mm thickness).

[0093] The complex viscosity was measured at 190 C. The configuration was a 25 mm plate/plate geometry with 1% strain. Frequency sweep was from 100 to 0.1 rad/sec.

TABLE-US-00004 TABLE 4 Comp. Inventive Inventive Comp. Inventive Inventive example example example example example example 1 1 2 3 4 5 Recycled 100 97.5 95 polyethylene polymer 1 [weight %] Recycled 100 97.5 95 polyethylene 2 [weight %] EVS 2.5 5 2.5 5 [weight %] Complex 2705 3954 4423 2727 3076 4281 viscosity [Pa .Math. s] 0.1 rad/s Complex 783 1408 1442 1567 1754 2173 viscosity [Pa .Math. s] 1 rad/s Complex 153 212 199 269 300 331 viscosity [Pa .Math. s] 100 rad/sec

[0094] The addition of EVS to the recycled polyethylene increases the complex viscosity of the composition. This is a proof of molecular enlargement and shear thinning of the recycled polyethylene composition (P).

[0095] In Table 5 the effect of EVS on the elongation viscosity is reported for Recycled polyethylene 2. The effect of strain hardening (higher melt elasticity and viscosity) for the inventive example can be observed.

TABLE-US-00005 TABLE 5 Comp. Inventive Inventive example 3 example 4 example 5 Recycled 100 97.5 95 polyethylene 2 [weight %] EVS 2.5 5 [weight %] Elongation viscosity 2724 3015 3135 [Pa .Math. s] after 0.01 s Elongation viscosity 119492 134515 211241 [Pa .Math. s] after 2.0 s Maximum elongation 125522 177091 437487 viscosity [Pa .Math. s] Step time at maximum 2.6 3.1 3.8 elongation viscosity (s)

[0096] The examples show the improved melt elasticity properties of the invention.

[0097] Additional examples of mixing virgin LDPE with different MFR.sub.2 with EVS are shown in Table 6. The compositions were made according to Table 1.

TABLE-US-00006 TABLE 6 Comp. Comp. Comp. Comp. Comp. example example example example example 8 9 10 11 12 LDPE-22 100 97.5 [weight %] LDPE-7 100 97.5 95 EVS 2.5 2.5 5 [weight %] MFR.sub.2 21.1 19.1 7.2 6.7 6.5 [g/10 min] Relative 0% 9% 0% 7% 10% difference [+/ %]

[0098] When adding EVS to virgin LDPE the MFR.sub.2 is decreased. The decrease is due to the low MFR.sub.2 of the EVS and the decrease of MFR.sub.2 is significantly lower compared to that observed in the inventive examples.

[0099] Additional film examples have been produced on a laboratory scale film blowing machine. The examples in Table 7 show the improved film forming properties of the invention. The recycled polyethylene compositions from comparative example 4 and inventive examples 6 and 7 were compounded on a single screw Brabender & Collins extruder 19/25D, air cooled, equipped with a barrier screw 2.5:1 with a mixing element. The revolutions per minute (RPM) of the extruder were varied.

[0100] Film blowing die head with a cooling ring (diameter 2 cm) Temperature setting (profile): 190-210-210-210 C.

TABLE-US-00007 TABLE 7 Comp. Inventive Inventive example 4 example 6 example 7 Recycled 100 97.5 95 polyethylene 3 [weight %] EVS 2.5 5 [weight %] MFR.sub.2 4.4 2.1 1.0 [g/10 min] Relative 0% 52% 77% difference [+/ %] RPM 40 No film formed Film formed, Film formed, Greatly improved Film quality film quality stable unstable RPM 60 No film formed Film formed, Greatly improved film quality stable

[0101] The inventive examples show that stable film production can be achieved by the invention. The MFR is lowered and the blowability is improved.

[0102] A microscope photo of a film blown from the recycled material without EVS (comparative example 4) shows an inhomogeneous material with separate phases. The dispersed phases are elongated in the machine direction due orientation effects at the exit of the die. During film blowing, the continuous phase will take the stresses and as the phase is only a part of the total volume the stress in this phase becomes too high, easily leading to breakage. With the addition of 5% EVS the microscope photo shows a homogenous material. The EVS works as a compatibilizer that evens out the phase boundaries. Meaning that the phases interact mechanically, which means that the total volume of the material can take up stresses. Thus, improved film blowing properties of inventive example 6 and 7.