POLYETHYLENE COMPOSITION

Abstract

The invention is related to a polyethylene composition comprising an ethylene polymer having a density in the range from ≥950 kg/m3 to ≤958 kg/m3, determined according to ISO 1183-1:2004, a melt flow rate MFR 5 (190° C., 5 kg) in the range from ≥0.16 g/10 min to ≥0.26 g/10 min, determined according to ISO 1133:1997, a melt flow ratio FRR (190° C., 21.6/5 kg) in the range from ≥22 to ≤40, a complex viscosity at 100 rad/s and 190° C. (eta100) of at least 2500 Pa.Math.s and a complex viscosity at 0.01 rad/s and 190° C. (eta0.01) of at least 250000 Pa.Math.s.

Claims

1. A polyethylene composition comprising an ethylene polymer having a density in the range from ≥950 kg/m.sup.3 to ≤958 kg/m.sup.3, determined according to ISO 1183-1:2004, a melt flow rate MFR 5 (190° C., 5 kg) in the range from ≥0.16 g/10 min to ≤0.26 g/10 min, determined according to ISO 1133:1997, a melt flow ratio FRR (190° C., 21.6/5 kg) in the range from ≥22 to ≤40, a complex viscosity at 100 rad/s and 190° C. (eta100) of at least 2500 Pa.Math.s and a complex viscosity at 0.01 rad/s and 190° C. (eta0.01) of at least 250000 Pa.Math.s.

2. A polyethylene composition according to claim 1 wherein the ethylene polymer has a density in the range from ≥952 kg/m.sup.3 to ≤955 kg/m.sup.3, determined according to ISO 1183-1:2004 and/or a melt flow rate MFR 5 (190° C., 5 kg) in the range from ≥0.17 g/10 min to ≤0.25 g/10 min, determined according to ISO 1133:1997 and/or a melt flow ratio FRR (190° C., 21.65 kg) in the range from ≥23 to ≤38 and/or a complex viscosity at 100 rad/s and 190° C. (eta.sub.100) of at least 2700 Pa.Math.s, and/or a complex viscosity at 0.01 rad/s and 190° C. (eta.sub.0.01) of at least 280000 Pa.Math.s.

3. A polyethylene composition according to claim 1, wherein the ethylene polymer has a Mw in the range from ≥270 kg/mol to ≤350 kg/mol, and/or a Mw/Mn in the range from ≥20 to ≤35.

4. A polyethylene composition according to claim 1, wherein the ethylene polymer comprises at least two fractions wherein at least one fraction is an ethylene homopolymer fraction and at least one fraction is an ethylene copolymer fraction and wherein the at least one ethylene copolymer fraction is a copolymer of at least one alpha olefin selected from alpha olefins having 3-12 carbon atoms.

5. A polyethylene composition according to claim 1, wherein the ethylene polymer comprises at least two fractions wherein at least one fraction is an ethylene homopolymer fraction and at least one fraction is an ethylene copolymer fraction and wherein the at least one copolymer fraction is a copolymer of at least one alpha olefin selected from alpha olefins having 4-6 carbon atoms.

6. A polyethylene composition according to claim 4, wherein the at least one ethylene homopolymer fraction and the at least one ethylene copolymer fraction have a different molecular weight Mw.

7. A polyethylene composition according to claim 4, wherein the weight (wt) % of the homopolymer fraction is in range of 50-60 wt %, based on the total amount of the ethylene polymer and/or wherein the MFI1.2 (190° C., 1.2 kg), determined according to ISO 1133:1997 of the homopolymer fraction is in the range from ≥2.0 to 30≤g/10 min.

8. A polyethylene composition according to claim 1, wherein the ethylene polymer has a comonomer content in the range from ≥0.1 to ≤0.3 mol %, preferably in the range from ≥0.15 to ≤0.25 mol %.

9. A polyethylene composition according to claim 1, wherein the ethylene polymer has a Charpy impact strength in the range from ≥15 kJ/m.sup.2 to ≤30 kJ/m.sup.2, measured according to ISO 179-1eA at −30° C. and/or a Charpy impact strength at 23° C. in the range from ≥25 kJ/m.sup.2 to ≤40 kJ/m.sup.2, measured according to ISO 179-1eA and/or a strain hardening modulus of at least 42 MPa, measured according to ISO/DIS 18488, and/or a strain hardening modulus in the range from ≥42 MPa to ≤65 MPa, measured according to ISO/DIS 18488 and/or a yield stress in the range from ≥20 MPa to ≤30 MPa, and/or a creep at 5.4 MPa and 80° C. after 60 min of ≤6%.

10. A polyethylene composition according to claim 1, wherein the polyethylene composition comprises at least 95 wt % of the ethylene polymer based on the total amount of the composition.

11. A process for the production of a polyethylene composition according to claim 1, wherein the ethylene polymer is produced in a multi-stage process.

12. The process according to claim 11, wherein the ethylene polymer is polymerised in the presence of a Ziegler Natta catalyst comprising a solid catalyst component which is contacted with an aluminium based cocatalyst.

13. An article, comprising the polyethylene composition according to

14. (canceled)

15. (canceled)

16. An article, comprising a polyethylene composition obtained by the process according to claim 11.

17. The polyethylene composition according to claim 2, wherein the ethylene polymer has a complex viscosity at 100 rad/s and 190° C. (eta.sub.100) of at least 2800 Pa.Math.s, and/or a complex viscosity at 0.01 rad/s and 190° C. (eta.sub.0.01) of at least 300000 Pa.Math.s.

18. The polyethylene composition according to claim 17, wherein the ethylene polymer has a complex viscosity at 0.01 rad/s and 190° C. (eta.sub.0.01) of at least 320000 Pa.Math.s.

19. The polyethylene composition according to claim 3, wherein the ethylene polymer has a Mw in the range from ≥280 kg/mol to ≤340 kg/mol, and/or a Mw/Mn in the range from ≥23 to ≤35.

20. The polyethylene composition according to claim 3, wherein the ethylene polymer has a Mw in the range from ≥290 kg/mol to ≤330 kg/mol and/or a Mw/Mn in the range from ≥23 to ≤33.

Description

EXAMPLES

1. Measurement Methods

Density

[0113] The density of the polymers is measured according to IS01183.

Viscosity Number (J)

[0114] The viscosity number is determined according to ISO 1628-3.

Melt Flow Rate (MFR)

[0115] The melt flow rates (MFR's) are determined according to ISO 1133:1997 under a load of 5 kg (MFR 5), 10 kg (MFR 10) and 21.6 kg (MFR 21.6) at 190° C.

[0116] The Flow Rate Ratio (FRR) is being calculated as MFR 21.6 divided by MFR 5.

Tensile Test

[0117] The tensile tests are performed according to ISO 527-2, test bar type 1B.

Charpy Impact Strength

[0118] The impact strength is measured according to Notched Charpy measurement at 23° C. and at −30° C. according to ISO 179, test bar type 1eA.

Strain Hardening

[0119] The resistance to slow crack growth is measured using the strain hardening method according to ISO/DIS 18488

Dynamic Rheological Spectroscopy (DMS)

[0120] The rheological parameters Eta.sub.100 and Eta.sub.0.01 are determined by DMS. Rheological measurements are carried out on an oscillatory rheometer ARES 4/A14 with 25 mm diameter parallel plates. Measurements are carried out on compression moulded plates of 2 mm thickness using nitrogen atmosphere and setting a strain within the linear viscoelastic regime. The frequency sweep experiment is performed at 190° C. at dynamic frequencies in range of 10.sup.−2 to 100 rad/s. The complex dynamic shear viscosities, eta.sub.100 in Pa.Math.s, at dynamic frequency of 100 rad/s and Eta.sub.0.01, at a dynamic frequency of 0.01 rad/s are determined directly from the viscosity data of the frequency sweep experiment measured at 190° C.

Creep Strain Test

[0121] Creep strain tests have been used to rank materials for pressure resistance.

[0122] Measurements are performed as follows: The PE granules are compression moulded according to ISO 1872-2. ISO 527-2 type 1BA specimens are milled from the compression moulded sheet. Zwick 1455 tensile testing machine having a Zwick 1 kN load cell are used for performing the creep measurements at 80° C. The specimens are equilibrated at a temperature of 80° C. for 30 min prior measurement. A load is applied to the sample (5.4 MPa) for 60 minutes and the elongation measured. The elongation of the sample after set time (60 minutes) is used as a measure to rank the materials for their pressure resistance.

Size Exclusion Chromatography (SEC)

[0123] The molecular weight and molecular weight distribution is measured by using size exclusion chromatography (SEC) using universal calibration. SEC is performed on the granule samples and weight average molecular weight (Mw), number average weight (Mn) and z-average molecular weight (Mz) are all measured in accordance with ASTM D6474-12 (Standard Test Method for Determining Molecular Weight Distribution and Molecular Weight Averages of Polyolefins by High Temperature Gel Permeation Chromatography).

[0124] In addition to the method specified by ASTM D6474-12, the method is performed using a Polymer Laboratories PL-GPC220 instrument equipped with 3 columns (Polymer Laboratories 13 μm PLgel Olexis, 300×7.5 mm) at an oven temperature of 160° C. A refractive index (RI) detector, a viscosity detector (Polymer Laboratories PL BV-400 viscometer) and an IR detector (Polymer Char IR5) are used. 1,2,4-trichlorobenzene stabilized with 1 g/L butylhydroxytoluene (also known as 2,6-di-tert-butyl-4-methylphenol or BHT) is used as eluent. The molar mass is determined based on a calibration using linear PE standards (narrow and broad (Mw/Mn=4 to 15)) in the range of 0.5-2800 kg/mol.

[0125] Samples of polymer granules are mixed with Tris (2,4-di-tert-butylphenyl)phosphite (Irgafos 168) and 1,1,3-Tris (2-methyl-4-hydroxy-5-tert-butylphenyl)butane (Topanol CA) in a weight ratio sample:Irgafos:Topanol of 1:1:1, after which the mixture thus obtained is dissolved in 1,2,4-trichlorobenzene stabilized with 1 g/L BHT until the concentration of the mixture in 1,2,3-trichlorobenzene stabilized with 1 g/L BHT is 0.03 wt %. Samples are dissolved for 4 hours at 150° C. in a nitrogen environment before the solution is filtrated offline (1.2 μm filter) or online using the Polymerchar system.

Nuclear Magnetic Resonance (NMR)

[0126] For 13C-NMR measurements, 150 mg of each sample is dissolved at 135° C. in 3 ml of a deuterated 1,1,2,2-tetrachloroethane-d2 (TCE-d2)/butylated hydroxytoluene (BHT) stock solution using a 10 mm NMR tube. The stock solution is made by dissolving 5 mg on BHT in 25 ml of TCE-d2. Oxygen concentration in the tube was reduced by flushing the tube for at least 1 min with nitrogen before dissolution.

[0127] All NMR experiments are carried out on a Bruker 500 Advance III HD spectrometer equipped with a 10 mm DUAL (proton and carbon) cryogenically cooled probe head operating at 125° C. The 13C-NMR measurements are performed using a spectral width of 220 ppm, an acquisition time of about 1.4 seconds and a relaxation delay of 20 seconds between each of the 512 transients. Zero-filling and Fourier Transformation with resolution enhancement are done to process the data. The spectra are calibrated by setting the central signal of TCE's triplet at 74.2 ppm.

[0128] The 13C resonances are assigned according to literature [1-8].

[0129] The co-monomer content is calculated as follows:

[00001]$\mathrm{mol}.Math..Math.\%=\frac{I_{\mathrm{comperC}}}{\left(I_{\mathrm{total}}-n*I_{\mathrm{comperC}}\right)/2+I_{\mathrm{comperC}}}*100.Math.\%$$\mathrm{wt}.Math..Math.\%=\frac{I_{\mathrm{comperC}}*M_{\mathrm{com}}}{\left(I_{\mathrm{total}}-n*I_{\mathrm{comeperC}}\right)*14+I_{\mathrm{comperC}}*M_{\mathrm{com}}}*100.Math.\%$

I.sub.com per C=integral per C-atom of the comonomer
I.sub.total=Integral for the area 0-50 ppm
n=number of C-atoms per comonomer

REFERENCES

[0130] 1. M. de Pooter et al., Journal of Applied Polymer Sci. 42, 399 (1991), [0131] 2. J. C. Randall, J. Macromol. Sci. Rev. Macromol. Chem. Phys. C229, 225 (1989) [0132] 3. G. Xu and E. Ruckenstein, Macromolecules 1998, 4724 [0133] 4. Randall, I. M. S. Rev. Macromol. Chem. Phys. C29 (2/3), 201-317 (1989) [0134] 5. Sahoo et al. Macromolecules, 36, 4017-4028 (2003) [0135] 6. R. Seeger, G. Maciel, Anal. Chem. 76, 5734-5747 (2004) [0136] 7. W. Liu, P. Rinaldi, Macromelecules, 34, 4757-4767 (2001) [0137] 8. Rinaldi, Macromolecules 2003, 36.4017-4028

2. Preparation of Samples

1. Preparation of a Hydrocarbon Solution Comprising the Organic Oxygen Containing Magnesium Compound and the Organic Oxygen Containing Titanium Compound (MGT)

[0138] 100 grams of granular Mg(OC.sub.2H.sub.5).sub.2 and 150 millilitres of Ti(OC.sub.4H.sub.9).sub.4 were brought in a 2 litre round bottomed flask equipped with a reflux condenser and stirrer. While gently stirring, the mixture was heated to 180° C. and subsequently stirred for 1.5 hours. During this, a clear liquid was obtained. The mixture was cooled down to 120° C. and subsequently diluted with 1480 ml of hexane. Upon addition of the hexane, the mixture cooled further down to 67° C. The mixture was kept at this temperature for 2 hours and subsequently cooled down to room temperature. The resulting clear solution was stored under nitrogen atmosphere and was used as obtained. Analyses on the solution showed a titanium concentration of 0.25 mol/l.

2. Preparation of the Catalyst

[0139] In a 0.8 liters glass reactor, equipped with baffles, reflux condenser and stirrer, 424 ml hexane and 160 ml of the complex MGT were dosed. The stirrer was set at 1200 rpm. In a separate flask, 100 ml of 50% ethyl aluminum dichloride (EADC) solution was added to 55 mL of hexane. The resulting EADC solution was dosed into the reactor in 15 minutes using a peristaltic pump. Subsequently, the mixture was refluxed for 2 hours. After cooling down to ambient temperature, the obtained red/brown suspension was transferred to a glass P4 filter and the solids were separated. The solids were washed 3 times using 500 ml of hexane. The solids were taken up in 0.5 L of hexane and the resulting slurry was stored under nitrogen. The solid content was 64 g ml.sup.−1.

3. Polymerisation of Inventive Sample 1 (Inv. 1)

[0140] The polymerization was carried out in a 20 litres autoclave using 10 litres purified hexane as a diluent. 8 mmols of tri-isobutylaluminum were added to the 10 litres purified hexane. In the first stage of the polymerization reaction the mixture was heated to 85° C. and pressurized with 1.2 bars ethylene and a hydrogen to ethylene ratio in the headspace of 1.7 v/v (volume/volume). Subsequently a slurry containing 30 mg of the catalyst obtained as described under 2. was dosed. The temperature was maintained at 85° C. and the pressure was kept constant by feeding ethylene. The amount of ethylene, needed to maintain constant pressure was monitored and is considered to be a direct measure for the amount of polymer produced. The hydrogen to ethylene ratio in the headspace was measured via online-GC and hydrogen was fed to maintain this ratio constant at 1.7 v/v. The first phase of the reaction was stopped after 180 minutes. Stopping was performed by de-pressurizing and cooling down the reactor contents. The second stage of the reactor is started raising the temperature to 80° C. At 80° C. the pressure is released, followed by the addition of 1-hexene (165 ml) and pressurizing the reactor with ethylene and hydrogen. The set partial pressure of ethylene in the second phase is 1.7 bar and the ratio for hydrogen to ethylene is 0,030 v/v. The reaction was stopped when a split of 57 had been reached. This split can be calculated directly by comparing the amount of ethylene uptake during the different stages of polymerisation. The polymerisation was stopped by de-pressurizing and cooling down the reactor. The reactor contents were passed through a filter; the polymer powder was collected and subsequently dried.

[0141] The PE powder was stabilised by adding 2000 ppm of calcium stearate, 2000 ppm of Irganox 1010 and 1000 ppm of Irgafos 168. The stabilised powder was extruded into pellets using a lab scale co-rotating twin screw extruder having a L/D of 25.5, throughput of 50 g/min and rpm of 100. The pellets were used for the mentioned analyses.

4. Polymerisation of Inventive Sample 2 (Inv. 2)

[0142] The polymerization was carried out similarly to the procedure as described in 3. with the exceptions that the hydrogen to ethylene ratio in the first polymerisation stage was maintained at 2.6 and the reaction was stopped after 103 minutes. In the second stage, 1-hexene (165 ml) was used and the ratio of hydrogen to ethylene was maintained at 0,025. Split was 57.

[0143] The split of the bimodal polymer is defined as the weight fraction of the lower molecular weight material in the ethylene polymer. For the semi-batch process as described in the polymerization examples, this translates into the cumulative ethylene consumption from the first polymerization step compared to the cumulative ethylene consumption in the combined first and second step.

[0144] In Table 1 the material properties of the products according to invention, the Inventive Examples (Inv.) 1 and 2 and Comparative Examples (Comp.) 1 to 3 are given. All three Comparative Examples, Comp. 1-3, are commercial PE100 HOPE pipe grades, which are well-established and known in the market. Characterization of product properties is done on stabilized samples.

TABLE-US-00001 TABLE 1 Parameter Unit Inv. 1 Inv. 2 Comp. 1 Comp. 2 Comp. 3 Reactor 1, homopolymer fraction Temperature ° C. 85 85 Ethylene partial pressure bar 1.2 1.2 H.sub.2/C.sub.2 ratio in headspace v/v 1.7 2.6 J1 cm.sup.3/g 130 100 Melt flow rate (MFR) 1.2 g/10 min 5.8 20.0 Split wt % 57 57 Density [kg/m.sup.3] Reactor 2 Temperature ° C. 80 80 Ethylene partial pressure bar 1.7 1.7 H.sub.2/C.sub.2 ratio in headspace v/v 0.030 0.025 Properties measured on granules Melt flow rate (MFR) 5 g/10 min 0.19 0.21 0.26 0.33 0.29 Melt flow rate (MFR) 10 g/10 min 0.78 0.93 Melt flow rate (MFR) 21.6 g/10 min 5.25 6.86 9.51 9.84 8.71 Flow rate ratio (FRR) 27.6 32.7 36.6 29.8 30.0 21.6/5 Density kg/m.sup.3 952.8 953.9 951.5 953.4 950.1 Eta.sub.100 Pa .Math. s 3218 2829 2263 2403 2377 Eta.sub.0.01 Pa .Math. s 323040 330500 232380 180000 195000 Mw kg/mol 300 290 260 — — Mw/Mn kg/mol 24.8 27.9 34.8 — — Endgroups /1000 C. 1.2 1.8 3.0 — — Butyl Branches /1000 C. 0.9 1.2 3.2 — — Hexene content mol % 0.2 0.2 — — Hexene content wt % 0.6 0.7 1.9 — — Charpy impact, 23° C. kJ/m.sup.2 36.5 30.7 37.1 — — Charpy impact, −30° C. kJ/m.sup.2 26.2 19.7 13.4 — — Yield stress MPa 26.6 27.2 24.4 — — E-modulus MPa 1164 1176 937 — — Creep 5.4 MPa 80° C. 60 0/0 4.8 5.0 20.8 — — min SH MPa 44.10 51.00

[0145] The table shows that the samples according to the invention, sample Inv. 1 and Inv. 2 have excellent mechanical properties, such as impact strength, yield stress and E-modulus and stress crack resistance. In particular, the samples show a bow creep strain. Standard PE 100 is known to have a Creep of 9% and higher at 5.4 MPa, 80° C. and 60 min.