POLYETHYLENE COMPOSITION

Abstract

The invention relates a polymer composition comprising polyethylene and a stabiliser package comprising: a) a phenolic stabiliser or mixtures thereof, b) an organic phosphite and/or phosphonite or mixtures thereof, c) zinc sulphide, and d) an acid scavenger. The polymer composition can be applied in the production of articles which are used in applications where a high temperature resistance is needed.

Claims

1. A polyethylene composition comprising polyethylene and a stabiliser package comprising: a) a phenolic stabiliser or mixtures thereof, b) an organic phosphite and/or phosphonite or mixtures therof, c) zinc sulphide, and d) an acid scavenger.

2. The polyethylene composition according to claim 1 comprising bimodal polyethylene and a stabiliser package comprising: a) 0.1 wt % and 0.6 wt % of a phenolic stabiliser or mixtures thereof relative to the total amount of polyethylene and stabiliser package comprising components a)-d), and/or b) 0.1 wt % and 0.3 wt % of an organic phosphite and/or a phosphonite or mixtures thereof relative to the total amount of polyethylene and stabiliser package comprising components a)-d), and/or c) 0.01 wt % and 0.09 wt % zinc sulphide relative to the total amount of polyethylene and stabiliser package comprising components a)-d), and/or d) 0.1 wt % and 0.3 wt % of an acid scavenger relative to the total amount of polyethylene and stabiliser package comprising components a)-d).

3. The polyethylene composition according to claim 1 comprising bimodal polyethylene and a stabiliser package comprising: a) 0.4 wt % and 0.6 wt % of a phenolic stabiliser or a mixture thereof relative to the total amount of polyethylene and stabiliser package comprising components a)-d), and/or b) 0.1 wt % and 0.2 wt % of an organic phosphite and/or a phosphonite relative to the total amount of polyethylene and stabiliser package comprising components a)-d), and/or c) 0.01 wt % and 0.05 wt % zinc sulphide relative to the total amount of polyethylene and stabiliser package comprising components a)-d), and/or d) 0.1 wt % and 0.3 wt % an acid scavenger relative to the total amount of polyethylene and stabiliser package comprising components a)-d).

4. The polyethylene composition according to claim 1, wherein the polyethylene is a multimodal high density polyethylene (HDPE) having a polymer density 940 and 965 kg/m.sup.3 and/or a melt flow rate 190/5 in the range 0.1 and 4.0 g/10 min, wherein the density is measured according to ISO 1183 A and the melt flow rate MFR 190/5 is measured according to ISO 1133-1(190 C.; 5.0 kg).

5. The polyethylene composition according to claim 1, wherein the polyethylene is a compound comprising a carbon black content in the range 1.5 wt % and 3.0 wt % relative to the total amount of the composition.

6. The polyethylene composition according to claim 1, wherein the phenolic stabiliser is selected from tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] methane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane; 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, bis(3,3-bis(4-hydroxy-3-t-butylphenyl)butanoic acid]-glycol ester; tris(3,5-di-t-butyl-4-hydroxy benzyl)isocyanurate; 1,3,5-tris(4-t-butyl-2,6-dimethyl-3-hydroxy-benzyl)isocyanurate, 3,5-di-t-butyl-4-hydroxy-hydrocinnamic acid triester of 1,3,5-tris(2-hydroxyethyl)-s-triazine-2,4,6(1H, 3H, 5H)-trione; p-cresol/dicyclopentadiene butylated reaction product and/or 2,6-bis(2-bis-hydroxy-3-t-butyl-5-methyl-phenyl-4-methyl-phenol.

7. The polyethylene composition according to claim 1, wherein organic phosphite and/or phosphonite is selected from triphenyl phosphite, diphenyl alkyl phosphites, phenyl dialkyl phosphites, tris(nonylphenyl) phosphite, trilauryl phosphite, trioctadecyl phosphite, distearyl pentaerythritol diphosphite, tris(2,4-di-tert-butylphenyl) phosphite, diisodecyl pentaerythritol diphosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphate, bis(2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphate, bisisodecyloxy-pentaerythritol diphosphite, bis(2,4-di-tert-butyl-6-methylphenyl) pentaerythritol diphosphite, bis(2,4,6-tri-tert-butylphenyl) pentaerythritol diphosphite, tristearyl sorbitol triphosphite, tetrakis(2,4-di-tert-butylphenyl) 4,4-biphenylenediphosphonite, 6-isooctyloxy-2,4,8,10-tetra-tert-butyl-12H-dibenzo[d,g]-1,3,2-dioxaphosphocin, 6-fluoro-2,4,8,10-tetra-tert-butyl-12-methyldibenzo[d,g]-1,3,2-dioxaphosphocin and/or bis(2,4-di-tert-butyl-6-methylphenyl) methyl phosphite, bis(2,4-di-tert-butyl-6-methylphenyl) ethyl phosphite.

8. The polyethylene composition according to claim 1, wherein the acid scavenger is selected from calcium stearate or magnesium stearate, calcium lactate, hydrotalcite and/or zinc oxide.

9. The polyethylene composition according to claim 1, wherein the polyethylene composition comprises polyethylene and a stabiliser package comprising: a) the phenolic stabilisers tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] methane and/or 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, and/or b) the organic phosphite tris(2,4-di-tert-butylphenyl) phoshite, and c) zinc sulphide, and/or d) the acid scavenger calcium stearate.

10. The polyethylene composition according to claim 1, wherein the total amount of the stabiliser package in the composition is 0.7 wt % and 3.0 wt % relative to the total amount of polyethylene and stabiliser package comprising components a)-d).

11. The polyethylene composition according to claim 1, wherein the total amount of the stabiliser package in the composition is 0.7 wt % and 1.5 wt % relative to the total amount of polyethylene and stabiliser package comprising components a)-d).

12. The polyethylene composition according to claim 1, wherein the polyethylene is HDPE with pigments, for example carbon black, and has the following characteristics, Tensile modulus between 900 and 1400 MPa (according to ISO 527-2), Yield stress between 22 and 32 MPa (according to ISO 527-2), Full Notch Creep Test (FNCT) between 1000-20000 h (according to ISO 16770 @ 80 C./4 MPa) and Charpy between 17 and 35 kJ/m.sup.2 @ 23 C. (according to ISO 179-1eU).

13. The polyethylene composition according to claim 1, wherein the polyethylene composition comprises polyethylene a stabiliser package comprising: a) 0.1 wt % and 0.5 wt % of tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] methane relative to the total amount of polyethylene and stabiliser package comprising components a)-d) and 0.1 wt % and 0.5 wt % of 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene relative to the total amount of polyethylene and stabiliser package comprising components a)-d), b) 0.1 wt % and 0.3 wt % tris(2,4-di-tert-butylphenyl) phosphite and relative to the total amount of polyethylene and stabiliser package comprising components a)-d), c) 0.005 wt % and 0.3 wt % zinc sulphide relative to the total amount of polyethylene and stabiliser package comprising components a)-d), d) 0.12 wt % and 0.5 wt % calcium stearate relative to the total amount of polyethylene and stabiliser package comprising components a)-d).

14. The polyethylene composition according to claim 1, wherein the polyethylene composition comprises polyethylene a stabiliser package comprising: a) 0.1 wt % and 0.2 wt % of tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] methane relative to the total amount of polyethylene and stabiliser package comprising components a)-d) and 0.3 wt % and 0.5 wt % of 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene relative to the total amount of polyethylene and stabiliser package comprising components a)-d), b) 0.1 wt % and 0.2 wt % tris(2,4-di-tert-butylphenyl) phosphite and relative to the total amount of polyethylene and stabiliser package comprising components a)-d), c) 0.01 wt % and 0.05 wt % zinc sulphide relative to the total amount of polyethylene and stabiliser package comprising components a)-d), d) 0.12 wt % and 0.3 wt % calcium stearate relative to the total amount of polyethylene and stabiliser package comprising components a)-d).

15. An article produced with a composition according to claim 1.

16. A pipe produced with a composition according to claim 1.

17. The polyethylene composition according to claim 1, comprising bimodal polyethylene and a stabiliser package consisting of a) 0.1 wt % and 0.6 wt % of a phenolic stabiliser or mixtures thereof relative to the total amount of polyethylene and stabiliser package comprising components a)-d), and/or b) 0.1 wt % and 0.3 wt % of an organic phosphite and/or a phosphonite or mixtures thereof relative to the total amount of polyethylene and stabiliser package comprising components a)-d), and/or c) 0.01 wt % and 0.09 wt % zinc sulphide relative to the total amount of polyethylene and stabiliser package comprising components a)-d), and/or d) 0.1 wt % and 0.3 wt % of an acid scavenger relative to the total amount of polyethylene and stabiliser package comprising components a)-d).

18. The polyethylene composition according to claim 1 comprising bimodal polyethylene and a stabiliser package consisting of a) 0.4 wt % and 0.6 wt % of a phenolic stabiliser or a mixture thereof relative to the total amount of polyethylene and stabiliser package comprising components a)-d), and/or b) 0.1 wt % and 0.2 wt % of an organic phosphite and/or a phosphonite relative to the total amount of polyethylene and stabiliser package comprising components a)-d), and/or c) 0.01 wt % and 0.05 wt % zinc sulphide relative to the total amount of polyethylene and stabiliser package comprising components a)-d), and/or d) 0.1 wt % and 0.3 wt % an acid scavenger relative to the total amount of polyethylene and stabiliser package comprising components a)-d).

19. The polyethylene composition according to claim 1, wherein the polyethylene is a multimodal high density polyethylene (HDPE) having a polymer density 940 and 965 kg/m3 and/or a melt flow rate 190/5 in the range 0.1 and 4.0 g/10 min, wherein the density is measured according to ISO 1183 A and the melt flow rate MFR 190/5 is measured according to ISO 1133-1(190 C.; 5.0 kg); wherein the polyethylene is a compound comprising a carbon black content in the range 1.5 wt % and 3.0 wt % relative to the total amount of the composition, wherein the phenolic stabiliser is selected from tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] methane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane; 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, bis(3,3-bis(4-hydroxy-3-t-butylphenyl)butanoic acid]-glycol ester; tris(3,5-di-t-butyl-4-hydroxy benzyl)isocyanurate; 1,3,5-tris(4-t-butyl-2,6-dimethyl-3-hydroxy-benzyl)isocyanurate, 3,5-di-t-butyl-4-hydroxy-hydrocinnamic acid triester of 1,3,5-tris(2-hydroxyethyl)-s-triazine-2,4,6(1H, 3H, 5H)-trione; p-cresol/dicyclopentadiene butylated reaction product and/or 2,6-bis(2-bis-hydroxy-3-t-butyl-5-methyl-phenyl-4-methyl-phenol, wherein the organic phosphite and/or phosphonite is selected from triphenyl phosphite, diphenyl alkyl phosphites, phenyl dialkyl phosphites, tris(nonylphenyl) phosphite, trilauryl phosphite, trioctadecyl phosphite, distearyl pentaerythritol diphosphite, tris(2,4-di-tert-butylphenyl) phosphite, diisodecyl pentaerythritol diphosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphate, bis(2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphate, bisisodecyloxy-pentaerythritol diphosphite, bis(2,4-di-tert-butyl-6-methylphenyl) pentaerythritol diphosphite, bis(2,4,6-tri-tert-butylphenyl) pentaerythritol diphosphite, tristearyl sorbitol triphosphite, tetrakis(2,4-di-tert-butylphenyl) 4,4-biphenylenediphosphonite, 6-isooctyloxy-2,4,8,10-tetra-tert-butyl-12H-dibenzo[d,g]-1,3,2-dioxaphosphocin, 6-fluoro-2,4,8,10-tetra-tert-butyl-12-methyldibenzo[d,g]-1,3,2-dioxaphosphocin and/or bis(2,4-di-tert-butyl-6-methylphenyl) methyl phosphite, bis(2,4-di-tert-butyl-6-methylphenyl) ethyl phosphite, wherein the acid scavenger is selected from calcium stearate or magnesium stearate, calcium lactate, hydrotalcite and/or zinc oxide, and wherein the total amount of the stabiliser package in the composition is 0.7 wt % and 3.0 wt % relative to the total amount of polyethylene and stabiliser package comprising components a)-d).

Description

EXAMPLES

[0133] The resin A used as base polymer in all examples was a bimodal high density polyethylene with melt flow rate MFR190/5 of 0.29 g/10 min and density of 948 kg/m.sup.3. All compositions contained 2.1 wt % carbon black.

Examples I-II and Comparative Examples A-C

[0134] The Example I and Comparative Examples A, B use different additive packages to protect the polyethylene from thermo-oxidative degradation. The compounds as indicated in Table 1 were compounded on a Coperion NT Extruder. The extruder consists of a two-stage compounding system. In the first stage, the plasticizing of the polymer powder is done by means of a smaller, high-speed twin-screw compounder. In the second stage, the melt is homogenized at a slower speed and a high degree of fill on a larger twin screw extruder. Separating the plasticizing from the homogenization into two stages allows the use of screw configurations and process parameters that are optimum for bimodal HDPE.

[0135] The set-up consisted of a ZSK 26 and ZSK 40 in series. The process data are summarized in Table 1.

TABLE-US-00001 TABLE 1 Summary of the process data. Extruder Feed Total feed rate 37.0 kg/h Feeder 1 - base grade powder 34.41 kg/h Feeder 2 - pre-mix of additives, carbon black 2.59 kg/h and base grade powder ZSK 26 Screw speed 430/min Torque 70-72% SEI-VT 0.181-0.186 kWh/kg Throttle valve 40 pm 8-0 58-65 bar ZSK 40 Screw speed 97/min Torque 68-71% SEI-VT 0.121-0.127 kWh/kg pm 8-0 160-170 bar

[0136] The feeders were placed at the forth of the seven barrels of the SKZ26. The barrels were heated to the set points given in Table 2.

TABLE-US-00002 TABLE 2 Set-point of barrel temperatures. ZSK26 ZSK40 T 1 Barrel 1 Barrel 1 T 2 Barrel 2 Barrel 2 T 3 Barrel 3 Barrel 3 230 C. T 4 Barrel 4 40 C. Barrel 4 250 C. T 5 Barrel 5 100 C. Barrel 5 260 C. T 6 Barrel 6 160 C. Barrel 6 260 C. T 7 Barrel 7 190 C. Barrel 7 270 C. T 8 Throttle 230 C. Barrel 8 290 C. T 9 Transition 230 C. 8-0 h 230 C.

[0137] All samples were prepared at the same conditions. The wt % are based on the total amount of stabilisers, carbon black and polyethylene. The compositions are given in Table 3.

TABLE-US-00003 TABLE 3 Compostion of Compounds. Ingredients in wt % Sample A Sample B Sample I Irganox 1010 0.2 0.13 0.15 Irganox 1330 0 0.35 0.35 ZnS 0 0 0.05 Irgafos 168 0.1 0.14 0.14 CaSt 0.2 0.2 0.2

[0138] wherein: [0139] Irganox 1010: Tetrakis [methylen-3-(3,5)-di-t-butyl-4-hydroxyphenyl) propionate] methane commercially available from BASF. [0140] Irganox 1330: 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene; commercially available from BASF. [0141] ZnS: Zinc sulphide, commercially available from Qolor Tech. [0142] Irgafos 168: Tris(2,4-di-tert-butylphenyl) phosphite; commercially available from BASF. [0143] CaSt: Calciumstearate, commercially available from Faci.

[0144] 1. Sample Preparation

[0145] The aging test was performed on compression molded plaques. The granules were compression molded according to DIN EN ISO 293-2, DIN EN ISO 1872 2 and DIN EN ISO 1873-3. The sample plaques had a size of 1901502 mm, respectively 1701702 mm. A press from Collin, type 200P was used. The compression molding was done at 180 C. with 5 min compression time (1 min at 10 bar, 2 min at 30 bar, 2 min at 40 bar). The plaques were cooled down to 30 C. with a cooling rate of 4 sec/ C. at a pressure of 50 bar.

[0146] 2. Aging Test

[0147] Test a)

[0148] The sample plaques were immersed in a glass container filled with demineralized water. For each compound a separate glass container was used. To ensure complete coverage with water, samples were mounted on a steel wire, separated by a spacer. The glass containers were kept at 80 C. in an air-circulated oven from Binder. The oven temperature was controlled and recorded electronically by Aspen Process Explorer. The water was changed every 500 hours.

[0149] Sample Characterisation

[0150] Oxidation Induction Time (OIT)

[0151] The OIT measurements were done according to ISO11357-6. The samples were heated to 200 C. under nitrogen, after three minutes the atmosphere was switched from nitrogen to oxygen. All measurements were done in duplicate. The average of two independent measurements is reported in Table 4.

[0152] In Table 4 the OIT results are shown as relative values in % comparison to the unaged sample. The value was calculated according to the following formula

Rel. OIT %=(OIT of aged specimen [min]/OIT of unaged specimen [min]).Math.100

TABLE-US-00004 TABLE 4 Relative OIT values in comparison to unaged samples. Sample A Sample B Sample I Aging Time [h] Rel. OIT [%] Rel. OIT [%] Rel. OIT [%] 0 100 100 100 2500 15 45 61 5000 6 21 50 7500 15 41

[0153] Table 4 shows that Example I demonstrates significantly less reduction of the OIT after being exposed to hot water Comparative Example A and B.

[0154] Comparing Comparative Example A and B to Example I shows that the effect of adding zinc sulfide in combination with a phenolic antioxidant had an additional effect on the OIT value as obtained after exposure to hot water.

[0155] Test b)

[0156] Autoclave Test

[0157] The autoclave test was developed to assess the oxidative long-term durability of geotextiles and related products. The method is established as a screening test in European standards (DIN EN ISO 13438, method C).

[0158] The acceleration of the thermo-oxidative aging process was carried out at an elevated temperature of 80 C. and 50 bar oxygen pressure. The autoclave was filled by 80% with demineralized water. The specimens were placed in an appropriate sample holder. Compression molded sample plaques with a size of 100150 mm were tested. During the whole test the samples were completely covered by water. The water was permanently stirred to ensure a good mixing of solvent and solutes. Oxygen pressure and temperature were applied with a precision of 0.5 bar and 0.5 C. Both was monitored at least every 15 minutes. To avoid cross-contamination, each compound was tested in a separate autoclave.

[0159] The plaques were removed after a certain period of time for mechanical evaluation by tensile testing. This was done according to DIN EN ISO 527-2. Tensile bars type 5A are punched out of the plaques. The unaged, control specimens were stored for 24 hours in water at 80 C., The results are shown in Table 5.

TABLE-US-00005 TABLE 5 Results of tensile test before and after ageing. Aging Stress at Elongation time break at break [d] [MPa] % [%] % Sample A 1 37.3 100 497.8 100 39 5.2 14 64 12.9 50 to brittle for measurement Sample B 1 39.6 100 535.7 100 54 28.9 73.1 492.5 91.9 64 12.6 31.7 278.3 52 88 to brittle for measurement Sample I 1 36.9 100 535.7 100 53 36.4 91.9 542.2 101.2 77 13.6 34.3 313.2 58.5