High performances multimodal ultra high molecular weight polyethylene

Abstract

The present invention relates to a reactor system for a multimodal polyethylene polymerization process, comprising; (a) a first reactor; (b) a hydrogen removal unit arranged between the first reactor and a second reactor comprising at least one vessel connected with a depressurization equipment, preferably selected from vacuum pump, compressor, blower, ejector or a combination thereof, the depressurization equipment allowing to adjust an operating pressure to a pressure in a range of 100-200 kPa (abs); (c) the second reactor; and (d) a third reactor and use thereof as a sheet.

Claims

1. A process for producing a multimodal polyethylene composition in a reactor system comprising: (a) a first reactor, (b) a hydrogen removal unit arranged between the first reactor and a second reactor comprising at least one vessel connected with depressurization equipment; (c) the second reactor; and (d) a third reactor, the process comprising: (a) polymerizing ethylene in an inert hydrocarbon medium in the first reactor in the presence of a catalyst system, selected from Ziegler-Natta catalyst or metallocene, and hydrogen in an amount of 0.1-95% by mol with respect to the total gas present in the vapor phase in the first reactor to obtain a low molecular weight polyethylene having a weight average molecular weight (Mw) of 20,000 to 90,000 g/mol or medium molecular weight polyethylene having a weight average molecular weight (Mw) of more than 90,000 to 150,000 g/mol wherein the low molecular weight polyethylene, respectively the medium molecular weight polyethylene, has a density at least 0.965 g/cm3, and the low molecular weight polyethylene has MI2 in the range from 10 to 1,000 g/10 min and the medium molecular weight polyethylene has MI2 in the range from 0.1 to 10 g/10 min; (b) removing in the hydrogen removal unit 98.0 to 99.8% by weight of the hydrogen in a slurry mixture obtained from the first reactor at an operation pressure in the range of 103-145 kPa (abs) and transferring the obtained residual mixture to the second reactor; (c) polymerizing ethylene and optionally α-olefin comonomer in the second reactor in the presence of a catalyst system, selected from Ziegler-Natta catalyst or metallocene, and in the presence of hydrogen in an amount obtained in step (b) to obtain a first high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 150,000 to 1,000,000 g/mol or a first ultra high molecular weight polyethylene in the form of a homopolymer or a copolymer having a weight average molecular weight (Mw) of more than 1,000,000 to 5,000,000 g/mol and transferring a resultant mixture to the third reactor; and (d) polymerizing ethylene, and optionally α-olefin comonomer in the third reactor in the presence of a catalyst system, selected from Ziegler-Natta catalyst or metallocene, and hydrogen, wherein the amount of hydrogen in the third reactor is in a range of 0.1-70% by mol, with respect to the total gas present in the vapor phase in the third reactor or optionally substantial absence of hydrogen to obtain a second high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 150,000 to 1,000,000 g/mol or a second ultra high molecular weight polyethylene copolymer having a weight average molecular weight (Mw) of more than 1,000,000 to 5,000,000 g/mol.

2. The process according to claim 1, wherein, in the step of removing 98.0-99.5% by weight of the hydrogen in the slurry mixture obtained from the first reactor is removed.

3. The process according to claim 1, wherein the operation pressure in the hydrogen removal unit is in the range of 104-130 kPa (abs).

4. The process of claim 1, wherein the depressurization equipment is selected from the group consisting of a vacuum pump, a compressor, a blower, an ejector, and a combination thereof.

5. The process of claim 1, wherein the hydrogen removal unit further comprises a stripping column for the separation of hydrogen and a liquid diluent.

6. A multimodal polyethylene composition obtained by a process according to claim 1, said composition comprising; (A)30 to 65 parts by weight of the low molecular weight polyethylene having a weight average molecular weight (Mw) of 20,000 to 90,000 g/mol or medium molecular weight polyethylene having a weight average molecular weight (Mw) of more than 90,000 to 150,000 g/mol; (B) 5 to 40 parts by weight of the first high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 150,000 to 1,000,000 g/mol or the first ultra high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 1,000,000 to 5,000,000 g/mol; and (C) 10 to 60 parts by weight of the second high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 150,000 to 1,000,000 g/mol or the second ultra high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 1,000,000 to 5,000,000 g/mol wherein a MI.sub.21 of the multimodal polyethylene composition is less than 3.0 g/10 min, and a Charpy impact strength at 23° C. of a compressed specimen of the multimodal polyethylene composition is at least 70 kJ/m.sup.2, measured by ISO179.

7. The multimodal polyethylene composition according to claim 6, wherein the Charpy impact strength at 23° C. of the compressed specimen of the multimodal polyethylene from 78 to 90 kJ/m.sup.2 measured by ISO179.

8. The multimodal polyethylene composition according to claim 6, wherein the multimodal polyethylene composition has a MI.sub.21 from 0.01 to 1.5 g/10 min.

9. The multimodal polyethylene composition according to claim 6, wherein the specimen of the multimodal polyethylene composition has an abrasion resistance in the range of 0.01 to 1.0, measured by ASTM D 4060.

10. The multimodal polyethylene composition according to claim 6, wherein the multimodal polyethylene composition has a weight average molecular weight from 80,000 to 5,000,000 g/mol, measured by Gel Permeation Chromatography.

11. The multimodal polyethylene composition according to claim 6, wherein the multimodal polyethylene composition has a number average molecular weight from 5,000 to 100,000 g/mol, measured by Gel Permeation Chromatography.

12. The multimodal polyethylene composition according to claim 6, wherein the multimodal polyethylene composition has a Z average molecular weight from 700,000 to 10,000,000 g/mol, measured by Gel Permeation Chromatography.

13. The multimodal polyethylene composition according to claim 6, wherein the multimodal polyethylene composition has a density 0.930 to 0.965 g/cm.sup.3measured by ASTM D 1505 and/or an intrinsic viscosity from 1 to 30 dl/g, measured by ASTM D 2515.

14. The multimodal polyethylene composition of claim 6, comprising 30 to 50 parts by weight of the low molecular weight polyethylene.

15. The multimodal polyethylene composition of claim 6, comprising 10 to 35 parts by weight of the first high molecular weight polyethylene.

16. The multimodal polyethylene composition of claim 6, comprising 15 to 60 parts by weight of the second high molecular weight polyethylene.

17. The multimodal polyethylene composition of claim 6, wherein the M.sub.21 of the multimodal polyethylene composition is less than 2.0 g/10 min.

18. The multimodal polyethylene composition of claim 6, wherein the Charpy impact strength at 23° C. of the compressed specimen is 70 to 120 kJ/m.sup.2.

19. A sheet comprising the multimodal polyethylene composition according to claim 6.

20. The sheet according to claim 19, wherein the sheet is a liner, a machinery part, or industrial part.

Description

EXPERIMENTAL AND EXAMPLES

Composition-Related Examples

(1) The medium or high density polyethylene preparation was carried out in three reactors in series. Ethylene, hydrogen, hexane, catalyst and TEA (triethyl aluminum) co-catalyst were fed into a first reactor in the amounts shown in Table 1. A commercial available Ziegler-Natta catalyst was used. The catalyst preparation is for example described in Hungary patent application 08 00771r. The polymerization in first reactor was carried out to make a low molecular weight polyethylene or medium molecular weight polyethylene. All of polymerized slurry polymer from first reactor was then transferred to a hydrogen removal unit to remove unreacted gas and some of hexane from polymer. The operating pressure in the hydrogen removal unit was be varied in a range of 100 to 115 kPa (abs) where residual hydrogen was removed more than 98% by weight but not more than 99.8% by weight from hexane before transferring to a second polymerization reactor. Some fresh hexane, ethylene and/or comonomer were fed into second reactor to produce first high molecular weight polyethylene (HMW1). All of polymerized polymer from second reactor was fed into the third reactor which produce second high molecular weight polyethylene (HMW2). Ethylene, comonomer, hexane and/or hydrogen were fed into the third reactor.

Comparative Example 1 (CE1)

(2) A homopolymer was produced in first reactor to obtain a low molecular weight portion before transferring such polymer to hydrogen removal unit. Reactant mixture was introduced into the hydrogen removal unit to separate the unreacted mixture from the polymer. Residual hydrogen was removed 97.6% by weight when hydrogen removal unit was operated at pressure of 150 kPa. The low molecular weight polymer was then transferred to the second reactor to produce a first high molecular weight polymer. Final, produced polymer from second reactor was transferred to the third reactor to create a second high molecular weight polymer. In third, a copolymerization was carried out by feeding 1-butene as a comonomer.

Example 1 (E1)

(3) Example 1 was carried out in the same manner as Comparative Example 1 except that the hydrogen removal unit was operated at pressure of 115 kPa. The residual of hydrogen from first reactor was removed 98.0% by weight. Characteristic properties of these multimodal polymers are shown in Table 2. As it can be seen, an improvement of stiffness-impact balance was observed when the percentage of removed hydrogen residual increased compared with the properties of Comparative Example 1.

Example 2 (E2)

(4) Example 2 was carried out in the same manner as Comparative Example 1 except that the hydrogen removal unit was operated at pressure of 105 kPa. The residual hydrogen from the first reactor was removed to an extend of 99.1% by weight. The operational of hydrogen removal unit under this pressure leads to an expansion of a polymer properties range. As seen in Table 2, a final melt flow rate of E2 was lower than a final melt flow rate of CE1 resulted in an improvement of Charpy impact while still maintained the flexural modulus.

Comparative Example 2 (CE2)

(5) Comparative Example 2 was carried out in the same manner as Comparative Example 1 except that the hydrogen removal unit was operated at pressure of 102 kPa. The residual of hydrogen from first reactor was removed to an extend of 99.9% by weight. The operational of hydrogen removal unit under this pressure leads to an expansion of a polymer properties range. As seen in Table 2, the final melt flow rate and a density of CE2 were quite similar to a final melt flow rate and a density of E2. A decay of Charpy impact was showed in CE2 compared to E2.

Comparative Example 3 (CE3)

(6) A homopolymer was produced in a first reactor to obtain a low molecular weight portion before transferring the polymer to a hydrogen removal unit. Reactant mixture was introduced into the hydrogen removal unit to separate the unreacted mixture from the polymer. Hydrogen residual was removed to an extend of 97.9% by weight when hydrogen removal unit was operated at pressure of 150 kPa. The low molecular weight polymer was then transferred to a second reactor to produce a first high molecular weight polymer. In the second reactor, a copolymerization was carried out by feeding 1-butene as a comonomer. Finally, in-situ bimodal copolymer from second reactor was transferred to a third reactor to create a second high molecular weight copolymer portion. Characteristic properties of this multimodal polymers is shown in Table 2. A significant improvement in Charpy impact at room temperature could be obtained by decreasing a density of final polymer when co-polymer was produced in both the second and the third reactor.

Example 3 (E3)

(7) Example 3 was carried out in the same manner as Comparative Example 3 except that the hydrogen removal unit was operated at pressure of 105 kPa. The residual of hydrogen from first reactor was removed to an extend of 98.8% by weight. The polymer obtained by this process operation had a melt flow rate of 0.195 g/l0 min (5 kg loading) lower than such value obtained from CE3. As seen in Table 2, it revealed an improvement of stiffness-impact balance when the percentage of removed hydrogen residual increases compared with the properties of Comparative Example 3.

Example 4 (E4)

(8) A homopolymer was produced in the first reactor to obtain a medium molecular weight portion before transferring such polymer to hydrogen removal unit. The hydrogen removal unit was operated at pressure of 105 kPa (abs) to separate the unreacted mixture from the polymer. The residual of hydrogen from first reactor was removed to an extend of 98.9% by weight. The medium molecular weight polymer was then transferred to the second reactor to produce a first ultra high molecular weight polymer. Finally, produced polymer from second reactor was transferred to the third reactor to create a second ultra high molecular weight polymer. The second and third reactors are operated under hydrogen depleted polyethylene polymerization.

Comparative Example 4 (CE4)

(9) A homopolymer was produced in first reactor to obtain a low molecular weight portion before transferring such polymer to hydrogen removal unit. Reactant mixture was introduced into the hydrogen removal unit to separate the unreacted mixture from the polymer. Residual hydrogen was removed 97.6% by weight when hydrogen removal unit was operated at pressure of 150 kPa (abs). The low molecular weight polymer was then transferred to the second reactor to produce a first high molecular weight polymer. Final, produced polymer from second reactor was transferred to the third reactor to create a second high molecular weight polymer. In third, a copolymerization was carried out by feeding 1-butene as a comonomer. As seen in Table 2 and 3, the final melt flow rate of CE4 were quite similar to a final melt flow rate of E5. A decay of charpy impact and flexural modulus were showed in CE4 compared to E5, even it showed lower density of E5.

Example 5 (E5)

(10) Example 5 was carried out in the same manner as Comparative Example 4 except that the hydrogen removal unit was operated at pressure of 115 kPa (abs). The residual of hydrogen from first reactor was removed to an extend of 98.5% by weight. The polymer obtained by this process operation had a melt flow rate of 48 g/10 min (5 kg loading) lower than such value obtained from CE3. As seen in Table 2, it revealed an improvement of stiffness-impact balance when the percentage of removed hydrogen residual increases compared with the properties of Comparative Example 4.

Example 6 (E6)

(11) Example 6 was carried out in the same manner as Example 4 except that the comonomer feeding in the third ultra high molecular weight polyethylene. The polymer produced by this process leads to an excellent improvement of Charpy impact strength while still maintained the flexural modulus. As shown in table 2, the inventive example 6 with IV of 23 dl/g show the high impact strength (one notched impact without break) and flexural modulus as compared to comparative samples, however, the melt flow index is unmeasurable due to high viscosity and high Mw.

(12) TABLE-US-00001 TABLE 1 CE1 E1 E2 CE2 CE3 E3 E4 CE4 E5 E6 W.sub.A, % 55 55 55 55 45 45 30 50 50 30 W.sub.B, % 20 20 20 20 25 25 30 10 10 30 W.sub.C, % 25 25 25 25 30 30 40 40 40 40 First reactor Polymerization type Homo Homo Homo Homo Homo Homo Homo Homo Homo Homo Temperature, ° C. 80 80 80 80 80 80 80 80 80 80 Total pressure, kPa 800 800 800 800 800 800 800 800 800 800 Ethylene, g 1,100.72 1,100.70 1,100.86 1,100.74 900.30 900.30 540.50 725.21 725.57 485.70 Hydrogen, g 1.62 1.62 1.55 1.55 2.97 2.99 1.34 1.13 1.13 1.23 Hydrogen removal unit Pressure, kPa (abs) 150 115 105 102 150 105 105 150 115 105 Hydrogen remove, % 97.6 98.0 99.1 99.9 97.9 98.8 98.9 97.7 98.5 98.3 Second reactor Polymerization type Homo Homo Homo Homo Copo Copo Homo Copo Copo Homo Temperature, ° C. 70 70 70 70 70 70 70 80 80 70 Total pressure, kPa 250 250 250 250 250 250 400 300 300 400 Ethylene, g 400.52 400.81 400.35 400.06 500.17 500.31 540.36 145.35 145.21 485.78 Hydrogen, g 0 0 0 0 0 0 0 0 0 0 1-butene, g 0 0 0 0 18.84 18.91 0 8 8 0 Third reactor Polymerization type Copo Copo Copo Copo Copo Copo Homo Copo Copo Copo Temperature, ° C. 70 70 70 70 70 70 80 80 80 70 Total pressure, kPa 400 400 400 400 400 400 600 600 600 600 Ethylene, g 500.74 500.11 500.30 500.63 600.02 601.19 720.60 580.53 580.46 647.54 Hydrogen, g 0 0.001 0.001 0.001 0 0.001 0 0.59 1.37 0 1-butene, g 35.05 30.01 30.03 30.04 60.01 60.04 0 27 27 20.60 W.sub.A means percent by weight of Polymer in the first reactor W.sub.B means percent by weight of Polymer in the second reactor W.sub.C means percent by weight of Polymer in the third reactor

(13) TABLE-US-00002 TABLE 2 CE1 E1 E2 CE2 CE3 Powder MI.sub.5, 0.474 0.372 0.240 0.242 0.275 g/10 min MI.sub.21, 13.83 10.80 7.38 7.23 6.40 g/10 min Density, 0.9565 0.9578 0.9555 0.9567 0.9441 g/cm.sup.3 IV, dl/g — — — — — Mw 276,413 244,279 291,295 319,487 252,160 Mn 8,877 8,724 8,843 8,472 8,016 Mz 2,788,607 2,370,678 3,401,041 4,135,007 1,638,224 PDI 31 28 33 38 31 Pellet MI.sub.5, 0.436 0.410 0.232 0.199 0.298 g/10 min MI.sub.21, 14.46 11.68 7.876 6.696 7.485 g/10 min Density, 0.9577 0.9574 0.9568 0.9566 0.9442 g/cm.sup.3 IV, dl/g 2.97 3.03 3.52 3.64 3.12 % Crystallinity, % 64.70 67.24 64.78 66.16 57.49 Charpy, 23.5 29.9 35.3 30.5 47.9 23° C., kJ/m.sup.2 Flexural 1,130 1,210 1,123 1,123 727 modulus, MPa E3 E4 CE4 E5 E6 Powder MI.sub.5, 0.200 — 54.80 48.07 NA g/10 min MI.sub.21, 4.81 0.145 641 653 NA g/10 min Density, 0.9438 0.9534 0.9606 0.9590 0.9409 g/cm.sup.3 IV, dl/g — 9.00 1.07 1.06 23 Mw 306,468 868,813 77,334 91,752 1,269,336 Mn 7,637 24,107 5,400 6,035 23,450 Mz 2,643,953 5,112,060 667,276 1,027,956 5,262,195 PDI 40 36 14 15 54.13 Pellet MI.sub.5, 0.195 — 60.62 55.47 — g/10 min MI.sub.21, 4.604 — 713.1 752.2 — g/10 min Density, 0.9440 — 0.9608 0.9594 — g/cm.sup.3 IV, dl/g 3.37 9.00 1.0 1.1 23 % Crystallinity, % 54.05 68.23 69.52 65.64 58.20 Charpy, 50.9 84.4 1.5 1.8 85.41 23° C., kJ/m.sup.2 Flexural 785 1,109 1,147 1,196 890 modulus, MPa

Sheet-Related Examples

(14) To prepare an inventive sheet from the above compositions, it was found that a sub-range of multimodal polyethylene compositions which might be obtained using the inventive reactor system are particularly preferred. In detail, the compositions suitable to form the inventive sheet are as follows and have the following properties. The following comparative examples refer to the sheet related compositions.

(15) The inventive and comparative examples were prepared follow the process conditions explained in table 3. Most of UHMWPE samples were prepared in the way to provide improved melt processing comparable to general polyethylene. It was initially indicated by the ability to measure the melt flow index, MI21. Then the compositions were prepared into the sheet and their properties were defined in table 4.

Inventive Example 4 (E4)

(16) The inventive example 4 (E4) was produced follow the inventive process to make the multimodal polyethylene composition as shown in table 3. The UHMWPE powder with IV of 9.0 dl/g was obtained without comonomer used in the composition.

Inventive Example 6 (E6)

(17) The inventive example 6 (E6) was produced follow the inventive process to make the multimodal polyethylene composition as shown in table 3. The UHMWPE powder with IV of 23 dl/g was obtained with 1-butane comonomer used in the second ultra high molecular weight polyethylene produced in the 3.sup.rd reactor.

Inventive Example 7 (E7)

(18) The inventive example 7 (E7) was produced follow the inventive process to make the multimodal polyethylene composition as shown in table 3. The UHMWPE powder with IV of 8.4 dl/g was obtained with 1-butene comonomer used in the second ultra high molecular weight polyethylene produced in the 3.sup.rd reactor.

Comparative Example 5 (CE5)

(19) A unimodal homopolymer was produced in the reactor to obtain an ultra high molecular weight polyethylene as shown in table 3. The UHMWPE powder with IV of 5.2 dl/g was obtained from the polymerization.

Comparative Example 6 (CE6)

(20) The comparative example 6 (CE6) is the blend of a homo-polyethylene with commercial UHMWPE SLL-6 series. A homo-polyethylene powder with MI.sub.2 of 26.2 g/10 min and IV of 1.5 dl/g was blended with UHMWPE powder with non-measurable MI.sub.21 and IV of 20.3 by single screw extruder with the composition of 70 parts by weight of homo-polyethylene and 30 parts by weight of UHMWPE. The temperature profiles of single screw extruder were set at 210° C. to 240° C. from the barrel to the die. The blend was extruded and granulated into pellets with obtainable IV of 5.65 dl/g.

(21) TABLE-US-00003 TABLE 3 Polymerization conditions for inventive example E4, E6, E7 and comparative example CE5 E4 E6 E7 CE5 W.sub.A, % 30 30 30 100 MI.sub.2 (W.sub.A) 4 0.8 2.6 — W.sub.B, % 30 30 30 — W.sub.C, % 40 40 40 — First reactor Polymerization type Homo Homo Homo Homo Temperature, ° C. 80 80 80  80 Total pressure, kPa 800 800 800 800 Pressure, kPa (abs) 105 105 105 — Hydrogen remove, % 98.9 98.3 99 — Second reactor Polymerization type Homo Homo Homo — Temperature, ° C. 70 70 70 — Total pressure, kPa 400 400 400 — Third reactor Polymerization type Homo Copo Copo — Temperature, ° C. 80 70 80 — Total pressure, kPa 600 600 600 —

(22) TABLE-US-00004 TABLE 4 Properties of polyethylene compositions E4 E6 E7 CE5 CE6 IV, dl/g 9.0 23 8.43 5.2 5.65 Butene content, % mol — 0.17 0.44 — — Mv 1,089,648.75 3,940,410.08 996,226.44 513,923.96 575,811.93 Mw 868,813.00 1,269,336.00 614,568.00 651,275.00 592,864.00 Mn 24,107.00 23,450.00 25,544.00 72,637.00 10,990.00 PDI 36.04 54.13 24.06 8.97 53.95 Mz 5,112,060.00 5,262,195.00 3,466,884.00 3,145,020.00 5,579,410.00 MI.sub.21, g/10 min 0.145 n/a 0.30 0.14 1.134 Density, g/cm.sub.3 0.9534 n/a 0.9472 0.9482 0.9631 Tm, ° C. 134 131.02 132 134 132 Tc, ° C. 120 117.76 119 121 120 % X 68.23 58.2 59.39 65.38 82.3 Charpy impact 23 C., 84.4 85.41 83.59 75.42 5.65 kJ/m2 Abrasion resistance 0.1883 0.0100 0.1109 0.4058 0.0347 (% weight loss) Eta (5) Pa .Math. s 96725.76 98108.45 68870.71 98086.31 14758.06 Eta (100) Pa .Math. s 9037.70 7630.77 7239.28 10239.12 2063.89 SHI (5/100) 10.70 12.86 9.51 9.58 7.15

(23) The inventive examples E4 and E7 provide significantly improvement on mechanical properties including the charpy impact strength and abrasion resistance compare to the comparative examples CE5 and CE6. Both properties were enhanced by the ultrahigh molecular weight portion in the multimodal polyethylene compositions as observed as a function of Mw, and Mz on E4 and E7 even with higher MI.sub.21 as compared to that of CE5. The abrasion resistance was even better when the 1-butene comonomer was applied into the compositions. The comparative example CE6 has very low impact strength. This may be affected by the inhomogeneity of the blend.

(24) Samples can be measured with MI apparatus to define MI.sub.21. It was noted that the inventive examples E4 and E7 containing much higher IV. The melt processability was further identified by the complex viscosity, η.sub.5 and η.sub.100 and shear thinning index, SHI ( 5/100). The lower melt viscosity was found in the inventive example E4 and E7 compared to CE5. The higher SHI was also observed in inventive examples E4 indicated the easier melt processing.

(25) As compared to inventive sample CE5, it was noted that the inventive sample E6 contains the higher IV, Mw, and Mz, which reflects on the better abrasion resistance and charpy impact strength. It is important to note that MI.sub.21 is unmeasurable in case of E6, however, the melt viscosity of E6 is comparable to CE5 even it has higher molecular weight. Moreover, the higher SHI can be observed in E6 which indicated the better performance of melt processing.

(26) The specific multimodal polyethylene compositions enhance superior properties of sheet in particular the mechanical properties and processability.

(27) The features disclosed in the foregoing description and in the claims may, both separately and in any combination, be material for realizing the invention in diverse forms thereof.