High performances multimodal ultra high molecular weight polyethylene

Abstract

The present inventions relates to a multimodal polyethylene composition comprising; (A) 30 to 65 parts by weight, preferably 30 to 50 parts by weight, most preferred 30 to 40 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, preferably 10 to 35 parts by weight, most preferred 15 to 35 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, preferably 15 to 60 parts by weight, most preferred 20 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 2.0 g/10 min, and a Charpy impact strength at 23 C. the of multimodal polyethylene composition is at least 70 kJ/m.sup.2, preferably 70 to 120 kJ/m.sup.2, measured by ISO 179, a sheet comprising the multimodal polyethylene composition as well as the use of the sheet.

Claims

1. A multimodal polyethylene composition comprising; (A) 30 to 65 parts by weight of 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; (B) 5 to 40 parts by weight of 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 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 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 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 3.0 or less, 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; wherein (A), (B), and (C) each have a different weight average molecular weight.

2. The multimodal polyethylene composition according to claim 1, wherein the Charpy impact strength at 23 C. of the compressed specimen of the multimodal polyethylene composition is from 78 to 90 kJ/m.sup.2, measured by ISO179.

3. The multimodal polyethylene composition according to claim 1, wherein the multimodal polyethylene has a MI.sub.21 from 0.01 to 1.5 g/10 min.

4. The multimodal polyethylene composition according to claim 1, 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.

5. The multimodal polyethylene composition according to claim 1, wherein the multimodal polyethylene composition has a weight average molecular weight from 300,000 to 5,000,000 g/mol, measured by Gel Permeation Chromatography.

6. The multimodal polyethylene composition according to claim 1, wherein the multimodal polyethylene composition has a number average molecular weight from 8,000 to 100,000 g/mol, measured by Gel Permeation Chromatography.

7. The multimodal polyethylene composition according to claim 1, wherein the multimodal polyethylene composition has a Z average molecular weight from 2,000,000 to 10,000,000 g/mol, measured by Gel Permeation Chromatography.

8. The multimodal polyethylene composition according to claim 1, wherein the multimodal polyethylene composition has a density 0.930 to 0.965 g/cm.sup.3, measured by ASTM D 1505 and/or an intrinsic viscosity from 4 to 30 dl/g, measured by ASTM D 2515.

9. Sheet comprising the multimodal polyethylene composition according to claim 1.

10. The sheet according to claim 8, wherein the sheet is a liner, a machinery part, or an industrial part.

11. The multimodal polyethylene composition of claim 1, comprising 30 to 50 parts by weight of the low molecular weight polyethylene.

12. The multimodal polyethylene composition of claim 1, comprising 10 to 35 parts by weight of the first high molecular weight polyethylene.

13. The multimodal polyethylene composition of claim 1, comprising 15 to 60 parts by weight of the second high molecular weight polyethylene.

14. The multimodal polyethylene composition of claim 1, wherein the M.sub.21 of the multimodal polyethylene composition is less than 2.0 g/10 min.

15. The multimodal polyethylene composition of claim 1, wherein the Charpy impact strength at 23 C. of the compressed specimen of the multimodal polyethylene composition is from 70 to 120 kJ/m.sup.2, measured by ISO179.

16. The multimodal polyethylene composition of claim 4, wherein the abrasion resistance is in the range of 0.01 to 0.6%, measured by ASTM D 4060.

17. The multimodal polyethylene composition of claim 5, wherein the weight average molecular weight is from 500,000 to 3,000,000 g/mol, measured by Gel Permeation Chromatography.

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

19. The multimodal polyethylene composition according to claim 7, wherein the Z average molecular weight is from 3,000,000 to 8,000,000 g/mol, measured by Gel Permeation Chromatography.

20. The multimodal polyethylene composition according to claim 8, wherein the intrinsic viscosity is from 5 to 25 dl/g, measured by ASTM D 2515.

Description

EXAMPLES

(1) 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.

(2) The inventive and comparative examples were prepared follow the process conditions explained in table 1. 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, MI.sub.21. Then the compositions were prepared into the sheet and their properties were defined in table 1.

Inventive Example 1 (E1)

(3) The inventive example 1 (E1) was produced to make the multimodal polyethylene composition as shown in table 2. 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. The UHMWPE powder with IV of 9.0 dl/g was obtained without comonomer used in the composition.

Inventive Example 2 (E2)

(4) The inventive example 2 (E2) was carried out in the same manner as Example 1 except that the comonomer feeding in the third ultra high molecular weight polyethylene as shown in table 2. The UHMWPE powder with IV of 23 dl/g was obtained with 1-butene comonomer used in the second ultra high molecular weight polyethylene produced in the 3.sup.rd reactor. The inventive example 2 with IV of 23 dl/g show the high impact strength and flexural modulus as compared to comparative samples, however, the melt flow index is unmeasurable due to high viscosity and high Mw.

Inventive Example 3 (E3)

(5) The inventive example 3 (E3) was produced follow the inventive process to make the multimodal polyethylene composition as shown in table 2. 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 1 (CE1)

(6) A unimodal homopolymer was produced in the reactor to obtain an ultra high molecular weight polyethylene as shown in table 2. The UHMWPE powder with IV of 5.2 dl/g was obtained from the polymerization.

Comparative Example 2 (CE2)

(7) The comparative example 2 (CE2) 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.

(8) TABLE-US-00001 TABLE 1 Polymerization conditions for inventive example E1, E2, E3 and comparative example CE1 E1 E2 E3 CE1 W.sub.A, % 30 30 30 100 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

(9) TABLE-US-00002 TABLE 2 Properties of polyethylene compositions E1 E2 E3 CE1 CE2 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 0.15 n/a 0.30 0.14 1.134 Density, g/cm.sub.3 0.9534 0.9409 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

(10) The inventive examples E1 and E3 provide significantly improvement on mechanical properties including the charpy impact strength and abrasion resistance compare to the comparative examples CE1 and CE2. 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 E1 and E3 even with higher MI.sub.21 as compared to that of CE1. The abrasion resistance was even better when the 1-butene comonomer was applied into the compositions. The comparative example CE2 has very low impact strength. This may be affected by the inhomogeneity of the blend.

(11) Samples can be measured with MI apparatus to define MI.sub.21. It was noted that the inventive examples E1 and E3 containing much higher IV. The melt processability was further identified by the complex viscosity, .sub.5 and .sub.100 and shear thinning index, SHI (5/100). The lower melt viscosity was found in the inventive example E1 and E3 compared to CE1. The higher SHI was also observed in inventive examples E1 indicated the easier melt processing.

(12) As compared to inventive sample CE1, it was noted that the inventive sample E2 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 E2, however, the melt viscosity of E2 is comparable to CE1 even it has higher molecular weight. Moreover, the higher SHI can be observed in E2 which indicated the better performance of melt processing.

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

(14) 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.