POLYETHYLENE COMPOSITION AND PIPE COMPRISING SUCH COMPOSITION

Abstract

A pipe including polyethylene produced in the presence of a solid catalyst and a co-catalyst, wherein the solid catalyst is prepared by the steps of: (a) contacting a dehydrated support having hydroxyl groups with a compound of formula MgR.sup.1R.sup.2; (b) contacting the product of step (a) with modifying compounds (A), (B) and (C), wherein: (A) is carboxylic acid, carboxylic acid ester, ketone, acyl halide, aldehyde or alcohol; (B) is of formula R.sup.11.sub.f(R.sup.12O).sub.gSiX.sub.h wherein f, g and h 0 to 4 and the sum of f, g and h=4 provided that when h=4 then compound (A) is not an alcohol; (C) is a compound of formula (R.sup.13O).sub.4M, wherein M is a titanium atom, a zirconium atom or a vanadium atom; and (c) contacting the product of step (b) with a titanium halide TiX.sub.4, whereby the polyethylene has a molecular weight of 720,000 to less than 2,500,000 g/mol.

Claims

1. A pipe comprising polyethylene or a polyethylene composition comprising polyethylene and carbon black, wherein the polyethylene is produced in the presence of a solid catalyst component and a co-catalyst, wherein the solid catalyst component is prepared by a process comprising the steps of: (a) contacting a dehydrated support having hydroxyl groups with a magnesium compound having the general formula MgR.sup.1R.sup.2, wherein R.sup.1 and R.sup.2 are the same or different and are independently selected from the group comprising an alkyl group, alkenyl group, alkadienyl group, aryl group, alkaryl group, alkenylaryl group and alkadienylaryl group; (b) contacting the product obtained in step (a) with modifying compounds (A), (B) and (C), wherein: (A) is at least one compound selected from the group consisting of carboxylic acid, carboxylic acid ester, ketone, acyl halide, aldehyde and alcohol; (B) is a compound having the general formula R.sup.11.sub.f(R.sup.12O).sub.gSiX.sub.h, wherein f, g and h are each integers from 0 to 4 and the sum of f, g and h is equal to 4 with a proviso that when h is equal to 4 then modifying compound (A) is not an alcohol, Si is a silicon atom, O is an oxygen atom, X is a halide atom and R.sup.11 and R.sup.12 are the same or different and are independently selected from the group comprising an alkyl group, alkenyl group, alkadienyl group, aryl group, alkaryl group, alkenylaryl group and alkadienylaryl group; (C) is a compound having the general formula (R.sup.13O).sub.4M, wherein M is a titanium atom, a zirconium atom or a vanadium atom, O is an oxygen atom and R.sup.13 is selected from the group comprising an alkyl group, alkenyl group, alkadienyl group, aryl group, alkaryl group, alkenylaryl group and alkadienylaryl group; and (c) contacting the product obtained in step (b) with a titanium halide compound having the general formula TiX.sub.4, wherein Ti is a titanium atom and X is a halide atom, whereby the polyethylene has a molecular weight Mz+1 of at least 720,000 g/mol and less than 2,500,000 g/mol.

2. The pipe according to claim 1 wherein the polyethylene has a density of about 910 kg/m.sup.3to about 925 kg/m.sup.3.

3. The pipe according to claim 1 wherein the polyethylene has a molecular weight distribution of 3.6 to 5.5 and/or an Mz/Mw of between 2.8 and 4.5 and/or an Mz+1/Mw of between 6 and 10.

4. The pipe according to claim 1 wherein the polyethylene has a molecular weight Mz+1 of at least 800,000 g/mol or a molecular weight Mz between 350,000 g/mol and 1,200,000.

5. The pipe according to claim 1 wherein the polyethylene has a melt stretching force of at least 5 cN as determined by a capillary rheometer at 190° C.

6. The pipe according to claim 1 wherein the polyethylene has a melt stretching stress of at least 1.2 N/mm2 as determined by a capillary rheometer at 190° C.

7. The pipe according to claim 1, wherein the composition comprises 80-99 wt % of the polyethylene and 1-10 wt % of the carbon black and 0-19 wt % of optional additives, with respect to the total composition, which represents 100 wt %.

8. The pipe according to claim 1, wherein the polyethylene or the composition comprises additives selected from one or more of stabilizers, acid scavengers and/or antistatic agents and utilization agents, whereby the total amount of these additives is between 0 wt % and 19 wt % based on the total amount of the polyethylene or polyethylene composition, which represents 100 wt %.

9. A pipe consisting of the polyethylene or the composition according to claim 1.

10. The pipe according to claim 9, wherein the pipe is a drip irrigation pipe.

11. A process for making the pipe according to claim 1, comprising the steps of: providing the composition, melting the composition and extruding the melted composition from a die to form the pipe.

12. The pipe according claim 1, wherein the pipe is a drip irrigation pipe.

13. The pipe according to claim 1 wherein the polyethylene has a density of about 910 kg/m.sup.3 to about 925 kg/m.sup.3; the polyethylene has a molecular weight distribution of 3.6 to 5.5 and/or an Mz/Mw of between 2.8 and 4.5, and/or an Mz+1/Mw of between 6 and 10. the polyethylene has a molecular weight Mz+1 of at least 800,000 g/mol, or a molecular weight Mz between 350,000 g/mol and 1,200,000 g/mol; the polyethylene has a melt stretching force of at least 5 cN as determined by a capillary rheometer at 190° C.; the polyethylene has a melt stretching stress of at least 1.2 N/mm.sup.2 as determined by a capillary rheometer at 190° C.

14. The pipe according to claim 13, wherein the polyethylene or the composition comprises an additive that is antioxidant agent and a processing aid agent, whereby the total amount of these additives is between 0 wt % and 19 wt % based on the total amount of the polyethylene or polyethylene composition, which represents 100 wt %.

15. A pipe consisting of the polyethylene or the composition according to claim 13.

16. The pipe according to claim 14, wherein the pipe is a drip irrigation pipe.

17. The pipe according to claim 13 wherein the polyethylene has an Mz/Mw of between 2.8 and 4.5 and/or an Mz+1/Mw of between 7 and 9; the polyethylene has a molecular weight Mz+1 of 900,000 g/mol and 1,700,000 g/mol, or a molecular weight Mz between 400,000 g/mol and 1,000,000 g/mol;

18. The pipe according to claim 17, wherein the polyethylene has an Mz/Mw of between 3.4 and 3.7 and/or an Mz+1/Mw of between 8 and 9; and the polyethylene has a molecular weight Mz+1 of between 1,000,000 g/mol and 1,600,000 g/mol or a molecular weight Mz between 550,000 g/mol and 750,000 g/mol.

19. A pipe consisting of the polyethylene or the composition according to claim 18.

20. The pipe according to claim 18, wherein the pipe is a drip irrigation pipe.

Description

EXAMPLES

Example I

[0071] A solid catalyst component was prepared according to Example 48 of WO2012/069157:

[0072] 340 g of Sylopol 955 silica which had been dehydrated at 600° C. for 4 hours under a nitrogen flow was placed in a 10 liter flask. 2040 cm.sup.3 of isopentane was added to slurry the silica, then 340.0 mmol of di-n-butylmagnesium was added to the flask and the resultant mixture was stirred for 60 minutes at a temperature of 35° C. Then, 476.0 mmol of methyl n-propyl ketone was added to the flask and the resultant mixture was stirred for 60 minutes at a temperature of 35° C. Then, 34.0 mmol of tetraethoxysilane was added to the flask and the resultant mixture was stirred for 30 minutes at a temperature of 35° C. Next, 34.0 mmol of titanium tetraethoxide was added to the flask and the resultant mixture was stirred for 30 minutes at a temperature of 35° C. Subsequently, 238.0 mmol of titanium tetrachl oride was added to the flask and the resultant mixture was stirred for 30 minutes at a temperature of 35° C. Finally, the slurry was dried using a nitrogen purge at 70° C. for 3.5 hours to yield a free-flowing solid product.

[0073] In accordance with Example 50 of WO2012/069157, the solid catalyst component thus obtained (SS-2) was used for the synthesis of 1-butene linear low density polyethylene (LLDPE) with a melt index of 1.0 g/10 min and a polymer density of 918 kg/m3 was produced in a fluidized bed gas phase polymerization reactor. The fluidized bed gas phase polymerization reactor had a 45 cm internal diameter and was operated with a 140 cm reaction zone height. The solid catalyst component was fed to the reactor using a dry solid catalyst feeder to maintain a production rate at 10 kg per hour. Ethylene, 1-butene, hydrogen and nitrogen were introduced to the reactor to yield polymer with the required specifications. 5 wt. % triethylaluminum (co-catalyst) solution in isopentane was continuously introduced to the reactor at a feed rate 0.08 kg per hour. The reactor temperature was maintained at 86° C., ethylene partial pressure at 7.0 bar, total reactor pressure at 20.7 bar and superficial gas velocity at 0.42 m/s. The solid catalyst component was ran for three consecutive days in the fluidized bed gas phase polymerization reactor and corresponding polymerization data is as follows:

TABLE-US-00001 Hydrogen 1-Butene to to Fines Productivity Bulk Ethylene Ethylene % <125 g PE/g Density Molar ratio Molar ratio microns catalyst kg/m.sup.3 0.11 0.41 0.03 6316 346

[0074] 200 ppm of Irganox 1076, 500 ppm of zinc stearate and 800 ppm of Weston 399 were added as additives in a Henschel mixer and mixed for 5 minutes together with 25 kg of the 1-butene linear low density polyethylene resin produced. The compounded material was pelletized using a ZSK-30 twin-screw extruder under the following conditions: a temperature profile of 130° C. to 210° C., screw speed of 200 rpm, screw diameter of 30 mm, screw length to diameter ratio of 26 and an output rate of 20 kg per hour. Evaluation of the pellet is reported in Table 1.

[0075] The obtained pellets were converted to 25 micron blown film using a Battenfeld machine under the following conditions: a temperature profile of 190° C. to 200° C., a screw speed of 60 rpm, a screw diameter of 60 mm, screw length to diameter ratio of 27, a die gap of 2.3 mm, a frost line height of 40 cm, a blow-up ratio (BUR) of 2.5:1 and an output rate of 58 kg per hour.

Comparative Experiment

[0076] As comparative experiment, pellets and a film product was made from a commercial Ziegler Natta LLDPE by the same extruder under the same extrusion conditions as above. Amounts and types of the additives were also the same as above. Evaluation of the pellets and the film product obtained is reported in Table 1.

[0077] The LLDPE according to the invention shows better results for various properties compared to the LLDPE made using a conventional ZN catalyst (comparative LLDPE).

[0078] The density of the LLDPE according to the invention and the comparative LLDPE were similar without any significant differences.

[0079] The melt index (MI 2.16 kg/190° C.) of the LLDPE according to the invention and the comparative LLDPE were similar without any significant differences.

[0080] The High Load Melt Index (HLMI 21.6 kg/190° C.) of the LLDPE according to the invention was higher than that of the comparative LLDPE, which is an indication of the ease of the processability and the broader MWD of the LLDPE according to the invention.

[0081] The MFR (Melt Flow Ratio 21.6 kg/2.16 kg) of the LLDPE according to the invention was higher than that of the comparative LLDPE, which is an indication of the ease of the processability and broader MWD of the LLDPE according to the invention.

[0082] Mn and Mw determined by GPC were higher for the LLDPE according to the present invention than for the comparative LLDPE. The higher Mw indicates higher tensile properties. The MWD was broader for the LLDPE according to the present invention, which shows an easier processability. The broader MWD means higher melt strength, higher die swell and higher strain hardening. The broader MWD also means a higher ESCR (Environmental Stress Crack Resistance), which is desirable for applications such as the drip irrigation pipe.

[0083] Mz and Mz+1 were significantly higher for the LLDPE according to the present invention. The higher Mz+1 means more co-monomer incorporation in the high molecular weight zone of the distribution, thus, more tie bonds. This translates to excellent ESCR. Also, the higher Mz+1 means higher die swell.

[0084] Atomic Force Microscopy (AFM) of the film showed that the spherulites are smaller and tightly packed in in the LLDPE according to the invention. The finer spherulites indicate that the pipe of the present invention can be coiled into bundles more easily. This is especially suitable for use in a drip irrigation pipe which has to be coiled into bundles during the off season in agriculture.

[0085] The melt stretching force and melt stretching stress were determined by a capillary rheometer by attaching an end of a melt strand of the polyethylene placed in the capillary rheometer to a pulley and accelerating the pulley at 0.12 cm/s.sup.2 at 190° C. until the melt strand breaks. The capillary rheometer has a die diameter of 1 mm and a die length of 10 mm. The melt stretching force and stress were higher for the LLDPE according to the invention compared with the comparative LLDPE. The higher melt strength is an indication of a better ESCR which is advantageous for a drip irrigation pipe and less sagging of the pipe.

[0086] The DSC crystalline melting and crystallinity temperatures were similar between the LLDPE according to the invention and the comparative LLDPE.

[0087] The results as obtained showed that the crystallinity temperature of LLDPE according to the invention was higher than comparative LLDPE by 2.56° C.; this means that LLDPE according to the invention cools faster than the comparative LLDPE due to the finer spherulites of the LLDPE according to the invention.

[0088] It can be concluded that the LLDPE according to the invention is highly suitable for making a pipe, especially a drip irrigation pipe, due to the higher melt strength indicating a higher ESCR and less sagging of the pipe.

TABLE-US-00002 TABLE 1 Comparative TEST METHOD Example 1 experiment Density kg/m.sup.3 ASTM D-792-08 920 920 MI(2.16/190° C.) g/10 min ASTM D-1238-04 0.92 0.942 HLMI(21.6/190° C.) g/10 min ASTM D-1238-04 28.11 24.64533 MFR(21.6/2.16) ASTM D-1238-04 28.82 25.5775 Co-monomer type ASTM D-5017-96 Butene Butene Co-monomer content % ASTM D-5017-96 4.448 4.7 mole Branching per 1000 C. ASTM D-5017-96 21.507 22.52333 Mn g/mole ASTM D-6474-99 43369.00 34689.33 Mw g/mole ASTM D-6474-99 180733 121061.3 MWD (Mw/Mn) ASTM D-6474-99 3.97 3.5091 Mz g/mole ASTM D-6474-99 647074.25 344405.7 Mz + 1 g/mole ASTM D-6474-99 1450908.55 711863.7 Mz/Mw ASTM D-6474-99 3.580 2.845 Mz + 1/Mw ASTM D-6474-99 8.028 5.880 Crystallinity % ASTM D-3418-08 42.45 43.015 Crystalline melting ASTM D-3418-08 122.69 121.01 temperature ° C. Crystallinity temp. TC ° C. ASTM D-3418-08 108.46 105.9 Melt stretch force (cN) described above 6.89 4.66 Melt stretch stress (N/mm.sup.2) described above 3.8 1.07