BIMODAL HIGH-DENSITY POLYETHYLENE RESINS AND COMPOSITIONS WITH IMPROVED PROPERTIES AND METHODS OF MAKING AND USING THE SAME

Abstract

The present disclosure is related to bimodal high-density polyethylene polymer compositions with increased high melt strength and good processability comprising a base resin which has a density of about 945 kg/m.sup.3 to about 955 kg/m.sup.3, and comprises an ethylene polymer (A) having a density of at least about 968 kg/m.sup.3, in an amount ranging from 45% to 55% by weight and an ethylene polymer (B) having a density lower than the density of polymer (A) wherein said composition has a complex viscosity at a shear rate of 0.01 rad/s ranging from about 200 to about 450 kPa.Math.s and a complex viscosity at a shear rate of 100 rad/s ranging from about 1900 to about 2500 Pa.Math.s. The present disclosure also relates to methods of making, and using the present compositions, and to articles made from there composition, and preferably to pipes and fittings.

Claims

1-61. (canceled)

62. A polyethylene polymer article made with a resin comprising: an ethylene polymer (A) having a density of at least about 968 kg/m.sup.3 in an amount ranging from about 45% to about 55% by weight; and an ethylene polymer (B) having a density lower than the density of ethylene polymer (A), wherein the resin has a density of about 945 kg/m.sup.3 to about 955 kg/m.sup.3, a zero shear viscosity (*0) greater than about 800 kPas, a complex viscosity at a shear rate of 0.01 rad/s ranging from about 200 to about 450 kPa.Math.s, a complex viscosity at a shear rate of 100 rad/s ranging from about 1900 to about 2600 Pa.Math.s, a melt index MI5 ranging from about 0.1 to about 0.5 g/10 min, an HLMI ranging from 7 to 11 g/10 min and a PENT failure time greater than 7900 hours.

63. The article according to claim 62, wherein the article is selected from the group consisting of a pipe or a pipe fitting.

64. The article according to claim 63, wherein the article exhibits PENT failure time greater than 10,000 hours.

65. The article according to claim 63, wherein the article exhibits a Minimum Requires Strength (MRS) according to ISO9080 at 23 C. of at least 10 MPa (1450 psi).

66. The article according to claim 63, wherein the article exhibits a Hydrostatic Design Basis (HDB) according to ASTM D2837 at 23 C. of at least 11 MPa (1600 psi).

67. The article according to claim 63, wherein the pipe has a diameter greater than 24 inches.

68. The article according to claim 63, wherein the pipe has a wall thickness greater than 2.25 inches.

69. The article according to claim 62, further comprising mixing conventional additives selected from the group consisting of antioxidizing agents, anti-UV pigments, antistatic agents, pigments, processing aids, stabilizers anti-UV agents, and mixtures thereof, in an amount of up to 10% by weight of the base resin into the extruder.

70. A polyethylene resin, comprising: an ethylene polymer (A) having a density of at least about 971 kg/m.sup.3 and an ethylene polymer (B) having a density having a density lower than the density of ethylene polymer (A), wherein the ratio of polymer (A) to polymer (B) ranges from 45:55 to 55:45, and the resin has a zero shear viscosity (*0) greater than about 800 kPas, a complex viscosity at a shear rate of 0.01 rad/s greater than 200 kPa.Math.s, a melt index MI5 ranging from about 0.1 to about 0.5 g/10 min, and an HLMI ranging from 7 to 11 g/10 min.

71. The high-density polyethylene resin according to claim 70, wherein the resin has a complex viscosity at a shear rate of 0.01 rad/s of 450 kPa.Math.s or less.

72. The polyethylene resin according to claim 70, wherein the resin has a complex viscosity at a shear rate of 100 rad/s ranging from about 1900 to about 2600 Pa.Math.s

73. The polyethylene resin according to claim 70, wherein the resin has a density of about 945 kg/m.sup.3 to about 955 kg/m.sup.3.

74. The polyethylene resin according to claim 70, wherein ethylene polymer (A) has a Melt Index (MI2) of about 200 to 600.

75. The polyethylene resin according to claim 70, wherein the resin has a melt elastic modulus (G) at a reference melt viscous modulus (G) value of G=3000 Pa ranging from 1600 to 2500 Pa.

76. A process for producing the polyethylene resin according to claim 70, comprising: preparing a base resin comprising an ethylene polymer (A) having a density of at least about 971 kg/m.sup.3 and an ethylene polymer (B) having a density lower than the density of ethylene polymer (A), wherein the ratio of polymer (A) to polymer (B) ranges from 45:55 to 55:45; introducing the base resin into an extrusion device; mixing a decomposable thermal initiator in an amount ranging from about 50 ppm to about 150 ppm over the weight of the base resin into the extrusion device, wherein the high-density polyethylene resin has a zero shear viscosity (*0) greater than about 800 kPa.Math.s, a complex viscosity at a shear rate of 0.01 rad/s greater than 200 kPa.Math.s, a melt index MI5 ranging from about 0.1 to about 0.5 g/10 min, and an HLMI ranging from 7 to 11 g/10 min.

77. The process according to claim 76, wherein the decomposable thermal initiator is selected from the group consisting of 2,5 Dimethyl 2,5 Di(tert-butylperoxyl)hexane, dicumyl peroxide, tert-butylcumyl peroxide, 1,3-1,4 Bis(tertbutylperoxyisopropyl)benzene, di-tert-butyl peroxide and 2,5 Dimethyl 2,5 Di(tertbutylperoxyl)hexyne.

78. The process according to claim 76, wherein the decomposable thermal initiator is 2,5 Dimethyl 2,5 Di(tert-butylperoxyl)hexane.

79. The process according to claim 76, wherein the decomposable thermal initiator is added to the extruder at full concentration.

80. The process according to claim 76, wherein the decomposable thermal initiator is dispersed in a carrier before being added to the extruder.

81. The process according to claim 80, wherein the carrier of the decomposable thermal initiator is selected from a liquid carrier or a solid carrier.

82. The process according to claim 80, wherein the solid carrier is selected from polyethylene or polypropylene.

83. The process according to claim 76, further comprising mixing conventional additives selected from the group consisting of antioxidizing agents, anti-UV pigments, antistatic agents, pigments, processing aids, stabilizers, anti-UV agents, and mixtures thereof, in an amount of up to 10% by weight of the base resin into the extruder.

Description

EXAMPLES

[0058] Testing Methods

[0059] Melt Index

[0060] Melt indexes were determined according to ISO1133 or ASTM D1238 and the results are indicated in g/10 min, but both tests will give substantially the same results. For polyethylenes a temperature of 190 C. is applied. MI.sub.2 is determined under a load of 2.16 kg, MI.sub.5 is determined under a load of 5 kg and HLMI is determined under a load of 21.6 kg.

[0061] Density

[0062] Density of the polyethylene was measured according to ISO 1183-1 (Method A) and the sample plaque was prepared according to ASTM D4703 (Condition C) where it was cooled under pressure at a cooling rate of 15 C./min from 190 C. to 40 C.

[0063] Comonomer Content

[0064] The C.sub.4-C.sub.8 alpha-olefin content is measured by .sup.13C NMR according to the method described in J. C. Randall, JMS-Rev. Macromol. Chem. Phys., C29(2&3), p. 201-317 (1989). The content of units derived from C.sub.4-C.sub.8 alpha-olefin is calculated from the measurements of the integrals of the lines characteristic of that particular C.sub.4-C.sub.8 alpha-olefin in comparison with the integral of the line characteristic of the units derived from ethylene (30 ppm). A polymer composed essentially of monomer units derived from ethylene and a single C.sub.4-C.sub.8 alpha-olefin is particularly preferred.

[0065] Environmental Stress Crack Resistance (ESCR)

[0066] Environmental stress crack resistance (ESCR) is determined by Notched Pipe Test (NPT). The notched pipe test was performed according to ISO 13479: 1997 on a pipe of diameter 110 mm and thickness 10 mm (SDR 11). The test was run at 80 C. at a pressure of 9.2 bar.

[0067] Stress Crack Resistance (PENT)

[0068] Another method to measure environmental stress crack resistance is the Pennsylvania Notched Tensile Test (PENT), ASTM D1473. PENT is the North American accepted standard by which pipe resins are tested to classify their ESCR performance. A molded plaque is given a specified depth notch with a razor and tested at 80 C. under 2.4 MPa stress to accelerate the stress cracking failure mode of a material. The time in which the specimen fails, breaks completely or elongates over a certain length, is used for its ESCR classification. A PE4710 by definition must not fail before 500 hours. Materials described in this patent would test over 10,000 hours without failure and be considered high performance materials.

[0069] Resistance to Rapid Crack Propagation (RCP)

[0070] Resistance to rapid propagation of cracks (RCP) is measured according to method S4 described in ISO standard 13477. The critical temperature was determined on a pipe of diameter 110 mm and thickness 10 mm (SDR 11) at a constant pressure of 5 bar. The critical temperature is defined as the lowest crack-arrest temperature above the highest crack propagation temperature; the lower the critical temperature, the better the resistance to rapid crack propagating.

[0071] Creep Resistance

[0072] Creep resistance is measured according to ISO 1167 on a pipe of diameter 50 mm and thickness 3 mm (SDR17) pipes to determine the lifetime prior to failure at a temperature of 20 C. and 80 C. and a stress of between 5 and 13 MPa.

[0073] Melt Rheology at Constant Shear Rate

[0074] Dynamic rheological measurements to determine the complex viscosities *as a function of shear rate are carried out, according to ASTM D 4440, on a dynamic rheometer (e.g., ARES), such as a Rheometrics, Ares model 5 rotational rheoineter, with 25 mm diameter parallel plates in a dynamic mode under an inert atmosphere. For all experiments, the rheometer has been thermally stabilised at 190 C. for at least 30 minutes before inserting the appropriately stabilized (with anti-oxidant additives), compression-molded sample onto the parallel plates. The plates are then closed with a positive normal force registered on the meter to ensure good contact. After about 5 minutes at 190 C., the plates are lightly compressed and the surplus polymer at the circumference of the plates is trimmed. A further 10 minutes is allowed for thermal stability and for the normal force to decrease back to zero. That is, all measurements are carried out after the samples have been equilibrated at 190 C. for about 15 minutes and are run under full nitrogen blanketing.

[0075] Two strain sweep (SS) experiments are initially carried out at 190 C. to determine the linear viscoelastic strain that would generate a torque signal which is greater than 10% of the lower scale of the transducer, over the full frequency (e.g. 0.01 to 100 rad/s) range. The first SS experiment is carried out with a low applied frequency of 0.1 rad/s. This test is used to determine the sensitivity of the torque at low frequency. The second SS experiment is carried out with a high applied frequency of 100 rad/s. This is to ensure that the selected applied strain is well within the linear viscoelastic region of the polymer so that the oscillatory rheological measurements do not induce structural changes to the polymer during testing. In addition, a time sweep (TS) experiment is carried out with a low applied frequency of 0.1 rad/s at the selected strain (as determined by the SS experiments) to check the stability of the sample during testing.

[0076] The frequency sweep (FS) experiment was then carried out at 190 C. using the above appropriately selected strain level between dynamic frequencies range of 10.sup.2 to 100 rad/s, under nitrogen. The dynamic rheological data thus measured were then analysed using the rheometer software (viz., Rheometrics RHIOS V4.4 or Orchestrator Software) to determine the melt elastic modulus G(G=3000) at a reference melt viscous modulus (G) value of G=3000 Pa. If necessary, the values were obtained by interpolation between the available data points using the Rheometrics software.

[0077] The term Storage modulus, G(), also known as elastic modulus, which is a function of the applied oscillating frequency, , is defined as the stress in phase with the strain in a sinusoidal deformation divided by the strain; while the term Viscous modulus, G(), also known as loss modulus, which is also a function of the applied oscillating frequency, , is defined as the stress 90 degrees out of phase with the strain divided by the strain. Both these moduli, and the others linear viscoelastic, dynamic rheological parameters, are well known within the skill in the art, for example, as discussed by G. Marin in Oscillatory Rheometry, Chapter 10 of the book on Rheological Measurement, edited by A. A. Collyer and D. W. Clegg, Elsevier, 1988.

[0078] Melt Rheology at Constant Shear Stress

[0079] The rheological properties of a material at a low shear rates were measured to better understand the material as it sags under gravitation forces. A constant stress test was used to determine the complex viscosity * at low shear stress. The experiments were conducted using an ARES G2 manufactured by TA Instruments. In this transient experiment, the sample was placed under a low shear stress where the viscosity was no longer shear stress dependent. In this region at very low shear stresses, the shear rate is also expected to be very low, much lower than the complex viscosity measured at 0.01 rad/s, and the viscosity in the region is expected to be shear rate independent. The compliance is a function of shear stress and time and defined as the ratio of time dependent strain over a constant stress. The experiments were conducted at low shear stress values where the creep compliance becomes independent of shear stress and linear with time allowing the determination of zero shear viscosity. The inverse slope of the compliance plot can be defined as the material's zero shear viscosity and can be seen in Table 1. The experiments were carried out at 190 C. under nitrogen using a 25 mm diameter parallel plate. The distance between the parallel plates during the experiment was 1.7 mm1%. Stress control loop parameters were run and calculated prior to the test using a strain amplitude determined in the linear visco-elastic region. A total time of 6 minutes was used to condition the sample and transducer. A low shear stress of 747 Pa is then applied to the sample and maintained for 1800 seconds. After this time the viscosity of the sample is measured. The zero shear viscosity is determined from the time dependent creep compliance.

[0080] Preparation of Black Composition

[0081] The manufacture of a base resin I comprising ethylene polymers was carried out in suspension in isobutane in two loop reactors, connected in series and separated by a device which makes it possible continuously to carry out the reduction in pressure. Isobutane, ethylene, hydrogen, triethylaluminium and the catalyst were continuously introduced into the first loop reactor and the polymerization of ethylene was carried out in this mixture in order to form the homopolymer (A). This mixture, additionally comprising the homopolymer (A), was continuously withdrawn from the said reactor and was subjected to a reduction in pressure, to remove at least a portion of the hydrogen. The resulting mixture, at least partially degassed of hydrogen, was then continuously introduced into a second polymerization reactor, at the same time as ethylene, I-hexene, isobutane and hydrogen, and the polymerization of the ethylene and of the hexene was carried out therein in order to form the ethylene/1-hexene copolymer (B). The suspension comprising the composition comprising ethylene polymers was continuously withdrawn from the second reactor and this suspension was subjected to a final reduction in pressure, so as to flash the isobutane and the reactants present (ethylene, hexene and hydrogen) and to recover the composition in the form of a dry powder, which was subsequently treated in a purge column in order to remove most of the process components trapped in the polymer particles. Catalysts were used as described in EP-B-2021385. The other polymerization conditions and copolymer properties are presented in Table 1.

[0082] Additives were incorporated to the powder particles and subsequently intensively mixed together prior to feeding the compounding equipment, a conventional twin screw extruder. The additives included at least one acid neutralizer like calcium stearate or zinc stearate in an amount between 500 and 2000 ppm or a mixture of both, and at least one process antioxidant like Irgafos 168 in an amount between 500 and 2500 ppm and a at least one thermal antioxidant like Irganox 1010 in an amount between 500 and 2500 ppm. Small quantities of processing aid, such as SOLEF 11010/1001, may also be added. The additives also include Carbon Black in an amount of 2.0-2.4 wt %. A thermal decomposition agent, 2.5-dimethyl-2,5-di(tert-butylperoxy)hexane (DHBP) is optionally incorporated in the feed via a 7.5 wt % master batch in polypropylene.

[0083] This mixture of flake/additives/peroxide enters the mixing section of the extruder where the material is heated, melted, and mixed together. The time the material spends in the mixing and extrusion sections is considered the reaction's residence time. The other pelletization conditions and properties of the pelletized resin are specified in Table 2.

TABLE-US-00001 TABLE 1 Polymerization conditions and properties for base polymer 1 EXAMPLE I Reactor 1 C2 (mol %) 1.75 H2/C2 (mol/mol %) 42.1 T ( C.) 95 Residence time (h) 2.17 wt % (A) 49 MI.sub.2 (g/10 min) * 400 Density (kg/m.sup.3) 973 Reactor 2 C2 (mol %) 2.61 C6/C2 (mol/mol %) 137.3 H2/C2 (mol/mol %) 0.19 T ( C.) 85 Residence time (h) 0.87 Final composition (base resin) MI.sub.5 (g/10 min) 0.31 Density (kg/m.sup.3) 948.5 Comonomer content (mol %) 0.60 * Measured according to ISO1133

TABLE-US-00002 TABLE 2 Pelletisation condition and properties of pelletised resins EXAMPLE C1 2 3 4 Pelletisation conditions DHBP7.5% IC5 0 400 700 1000 Peroxide amount (ppm MB) Peroxide amount (ppm pure) 0 30 53 75 Carbon black content [wt %] 2.2 2.1 2.2 2.2 Total specific energy [kWh/t] 278 278 279 280 Max melt temperature [ C.] 312 313 314 312 Properties polymer composition (after pelletisation - black compound) MI.sub.5 (g/10 min)** 0.29 0.26 0.25 0.24 HLMI (g/10 min)** 8.5 9.2 9.8 9.5 HLMI/MI.sub.5 29 35 38 40 Density (kg/m.sup.3) 959.9 959.2 959.8 959.0 G(G = 3000) (Pa) 1,276 1,664 1,927 2,096 *.sub.0.01 (Pa .Math. s) 185,778 215,823 257,745 299,653 *.sub.100 (Pa .Math. s) 2,504 2,382 2,396 2,401 SHI 2.7/210 () 44 61 76 96 * at G* = 2.7 kPa (Pa .Math. s) 150,519 197,229 255,503 311,613 *.sub.747 (kPa .Math. s) 280 446 647 889 NPT 80 C. - 9.2 bar on >8 800 >8 800 >8 800 >8 800 110SDR11 pipes (h) RCP S4 Critical Temperature on 17.5 27.5 17.5 110SDR11 pipes ( C.) creep at 20 C./12.4 MPa (h) 2,269 688 803 creep at 20 C./12.1 MPa (h) 2,632 3,080 2,139 3,066 creep at 20 C./11.8 MPa (h) >7,200 >7,200 >7,200 >7,200 creep at 80 C./5.7 MPa (h) 207 490 1,236 4,066 creep at 80 C./5.5 MPa (h) >7,800 >7,800 >7,800 >7,800 **measured according to ISO1133

[0084] Preparation of Natural Composition

[0085] The manufacture of a base resin TI was carried out as described for base resin I above. Polymerization conditions and copolymer properties are presented in Table 3.

[0086] 2.5-Dimethyl-2,5-di(tert-butylperoxy)hexane (DHBP) was incorporated to the powder particles and subsequently intensively mixed together prior in a Farrel FCM mixer. The balance of the additive formulation (primary antioxidant, etc.) is added via a separate feeder at the same location. This mixture of flake/additives/peroxide enters the mixer where the material is heated, melted, and mixed together. A polymer ribbon then leaves the mixer through the orifice and is fed to the extruder. The material is conveyed to the die where it is then pelletized. The processing time in the mixer and the extruder is defined as the residence time.

[0087] Table 4 presents data for reticulated samples and non-reticulated samples. These predictive rheological tools show no statistically significant difference in processing parameters while a significant shift in low shear viscosity is present. To confirm the predictive measurement for processability and to show that no loss in processability was experienced comparisons of pipe extrusion measurements of processability are shown in the Table 4. Furthermore, the predictive measurement for melt strength was examined and confirmed by the pipe extrusion data offered for reticulated and non-reticulated samples. The wall thickness improvements and similar processability show that a peroxide modified resin will exhibit improved melt strength with no loss of processability as expected from predictive rheological results.

TABLE-US-00003 TABLE 3 Polymerization conditons and properties for base polymer II EXAMPLE II Reactor 1 C2 (mol %) 3.3 H2/C2 (mol/mol %) 47 T ( C.) 96 wt % (A) 49.5 MI.sub.2 (g/10 min)* 400 Density (kg/m.sup.3) 972 Reactor 2 C2 (mol %) 3.0 C6/C2 (mol/mol %) 130 H2/C2 (mol/mol %) 0.17 T ( C.) 85 Final composition (base resin) MI.sub.5 (g/10 min)* 0.30 Density (kg/m.sup.3) 949 *Measured according to ASTM D1238

TABLE-US-00004 TABLE 4 Example C5 6 7 8 Pelletization conditions Peroxide amount 0 75 92 130 (ppm pure) Properties polymer composition (after pelletization natural compound) MI.sub.5 (g/10 min)** 0.26 0.26 0.19 0.22 HLMI (g/10 min)** 7.3 8.4 7.0 7.2 HLMI/MI.sub.5 27.6 32.6 36.6 32.9 Density (kg/m.sup.3) 948.4 949.0 948.9 949.7 G(G = 3000) (Pa) 1,248 1,851 1,985 G(G = 5000) (Pa) 2,370 3,378 3,834 *.sub.0.01 (Pa .Math. s) 187,073 261,190 364,960 428,436 *.sub.100 (Pa .Math. s) 2304 2272 2,403 2,330 Zero Shear Viscosity (.sub.0) 426,112 876,962 1,295,824 3,028,376 (Pa .Math. s) SHI 2.7/210 39 91 115 * at G* = 2.7 kPa 168.3 257.8 399.9 (kPa .Math. s) *.sub.747 (kPa .Math. s) 1,296 PENT Failure Time (h) >10,000 >7,900 >10,000 Pipe Extrusion Data Typical Throughput Rates 1,885 1,500 1,750 2,351 (lb/hr)** Extruder Load (%) 70 83 77 73 Pipe Size 28 DR 24 DR 5 30 DR9 48 DR 11 17 Wall Thickness Limitation 2 4.5 3.33-4 2.82-3.5 (inches) or higher or higher *Measured according to ASTM D1238 **Dependent on extruder capability, extruder size, pipe size and downstream cooling constraints.

[0088] Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the present disclosure. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.