Bimodal high-density polyethylene resins and compositions with improved properties and methods of making and using the same

Abstract

Bimodal high-density polyethylene polymer compositions with increased high melt strength and good processability. The compositions comprise a base resin having a density of about 945 kg/m.sup.3 to about 955 kg/m.sup.3, and 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). The composition has a complex viscosity at a shear rate of 0.01 rad/s ranging from about 200 to 450 kPa.Math.s and a complex viscosity at a shear rate of 100 rad/s ranging from about 1900 to 2500 Pa.Math.s. Articles made from these compositions, such as pipes and fittings achieve long-term oxidative resistance and have a low wall thickness variability while maintaining high production output.

Claims

1. An oxidative resistant article comprising a polyethylene polymer 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 (no) greater than about 800 kPa.Math.s, a complex viscosity at a shear rate of about 0.01 rad/s ranging from about 200 to about 450 kPa.Math.s, a complex viscosity at a shear rate of about 100 rad/s ranging from about 1900 to about 2600 Pa.Math.s, a melt index MI.sub.5 ranging from about 0.1 to about 0.5 g/10 min, and a high load melt index (HLMI) ranging from about 7 to about 11 g/10 min, wherein the article achieves oxidative resistance of at least category 1 when measured at a pressure of 2.48 MPa and a temperature of 90° C. according to ASTM D3350-14.

2. The article according to claim 1, wherein the article is selected from the group consisting of a pipe and a pipe fitting.

3. The article according to claim 1, wherein the article achieves oxidative resistance ranging from category 1 to category 3 when measured at a pressure of 2.48 MPa and a temperature of 90° C. according to ASTM D3350-14.

4. The article according to claim 1, wherein the article achieves oxidative resistance of at least category 1 when measured at a pressure of 2.76 MPa and a temperature of 90° C. according to ASTM D3350-14.

5. The article according to claim 1, wherein the article achieves oxidative resistance ranging from category 1 to category 3 when measured at a pressure of 2.76 MPa and a temperature of 90° C. according to ASTM D3350-14.

6. The article according to claim 1, wherein the article achieves oxidative resistance of at least category 1 when measured at a pressure of 3.1 MPa and a temperature of 90° C. according to ASTM D3350-14.

7. The article according to claim 1, wherein the article achieves oxidative resistance ranging from category 1 to category 3 when measured at a pressure of 3.1 MPa and a temperature of 90° C. according to ASTM D3350-14.

8. The article according to claim 1, wherein the article exhibits a minimum required strength (MRS) according to ISO 9080 at 20° C. of at least about 10 MPa (1450 psi).

9. The article according to claim 1, wherein the article exhibits a hydrostatic design basis (HDB) according to ASTM D2837 at 23° C. of at least about 11 MPa (1600 psi).

10. The article according to claim 2, which is a pipe having a diameter greater than 24 inches.

11. The article according to claim 2, wherein the pipe has a wall thickness greater than 2.25 inches.

12. The article of claim 1, wherein the ethylene polymer (A) has a density of at least about 971 kg/m.sup.3 and the ethylene polymer (B) has a density lower than the density of ethylene polymer (A), wherein the ratio of ethylene polymer (A) to ethylene polymer (B) ranges from 45:55 to 55:45.

13. The article according to claim 12, wherein ethylene polymer (A) has a melt index (MI.sub.2) of about 200 to about 600.

14. The article according to claim 12, wherein the resin has a melt elastic modulus (G′) at a reference melt viscous modulus (G″) value of G″=3000 Pa ranging from about 1600 to about 2500 Pa.

15. The article according to claim 12, wherein the resin has a minimum required strength (MRS) according to ISO 9080 at 20° C. of at least about 10 MPa (1450 psi).

16. The article according to claim 1, wherein the article possesses a wall thickness variability of between about 3% and about 12% when measured at 23° C. and 50% relative humidity, and a production output of at least 2300 lbs/hr.

17. 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/m3 to about 955 kg/m3, a zero-shear viscosity (η.sub.0) greater than about 800 kPa.Math.s, a complex viscosity at a shear rate of about 0.01 rad/s ranging from about 200 to about 450 kPa.Math.s, a complex viscosity at a shear rate of about 100 rad/s ranging from about 1900 to about 2600 Pas, a melt index MI.sub.5 ranging from about 0.1 to about 0.5 g/10 min, and a high load melt index (HLMI) ranging from about 7 to about 11 g/10 min, wherein the article possesses a wall thickness variability of between about 3% and about 12% when measured at 23° C. and 50% relative humidity, and a production output of at least about 2300 lbs/hr.

18. The article according to claim 17, wherein the article is selected from the group consisting of a pipe and a pipe fitting.

19. The article according to claim 18, wherein the article possesses a wall thickness variability of between about 5% and about 9% when measured at 23° C. and 50% relative humidity.

20. The article according to claim 17, wherein the article exhibits a minimum required strength (MRS) according to ISO 9080 at 20° C. of at least about 10 MPa (1450 psi).

21. The article according to claim 17, wherein the article exhibits a hydrostatic design basis (HDB) according to ASTM D2837 at 23° C. of at least about 11 MPa (1600 psi).

22. The article according to claim 17, which is a pipe having a diameter greater than 24 inches or a wall thickness greater than 2.25 inches or both.

23. The article according to claim 17, wherein ethylene polymer (A) has a melt index (MI.sub.2) ranging from about 200 to about 600.

24. The article according to claim 17, wherein the resin has a melt elastic modulus (G′) at a reference melt viscous modulus (G″) value of G″=3000 Pa ranging from about 1600 to about 2500 Pa.

25. The article according to claim 24, wherein the resin has a minimum required strength (MRS) according to ISO 9080 at 20° C. of at least about 10 MPa (1450 psi).

Description

EXAMPLES

(1) Testing Methods

(2) Melt Index

(3) 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.

(4) Density

(5) 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.

(6) Comonomer Content

(7) The C.sub.4-C.sub.8 alpha-olefin content was 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 was 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.

(8) Environmental Stress Crack Resistance (ESCR)

(9) Environmental stress crack resistance (ESCR) was 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.

(10) Stress Crack Resistance (PENT)

(11) 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 was 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, was used for its ESCR classification. A PE4710 by definition must not fail before 500 hours. Materials described in this patent tested over 10,000 hours without failure and are considered high performance materials.

(12) Resistance to Rapid Crack Propagation (RCP)

(13) Resistance to rapid propagation of cracks (RCP) was 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.

(14) Creep Resistance

(15) Creep resistance was 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.

(16) Melt Rheology at Constant Shear Rate

(17) Dynamic rheological measurements to determine the complex viscosities Was a function of shear rate were carried out, according to ASTM D 4440, on a dynamic rheometer (e.g., ARES), such as a Rheometrics, Ares model 5 rotational rheometer, with 25 mm diameter parallel plates in a dynamic mode under an inert atmosphere. For all experiments, the rheometer was thermally stabilized 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 were then closed with a positive normal force registered on the meter to ensure good contact. After about 5 minutes at 190° C., the plates were lightly compressed and the surplus polymer at the circumference of the plates was trimmed. A further 10 minutes was allowed for thermal stability and for the normal force to decrease back to zero. That is, all measurements were carried out after the samples had been equilibrated at 190° C. for about 15 minutes and were run under full nitrogen blanketing.

(18) Two strain sweep (SS) experiments were initially carried out at 190° C. to determine the linear viscoelastic strain that would generate a torque signal which was 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 was carried out with a low applied frequency of 0.1 rad/s. This test was used to determine the sensitivity of the torque at low frequency. The second SS experiment was carried out with a high applied frequency of 100 rad/s. This was to ensure that the selected applied strain was 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 was 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.

(19) 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 analyzed 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.

(20) The term “Storage modulus”, G′(w), also known as “elastic modulus”, which is a function of the applied oscillating frequency, co, is defined as the stress in phase with the strain in a sinusoidal deformation divided by the strain; while the term “Viscous modulus”, G″(co), also known as “loss modulus”, which is also a function of the applied oscillating frequency, co, 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.

(21) Melt Rheology at Constant Shear Stress

(22) 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 η* 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 mm±1%. 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.

(23) Oxidative Resistance

(24) Chlorine resistance testing was performed in accordance with ASTM F2263-14, Standard Test Method for Evaluating the Oxidative Resistance of Polyethylene (PE) Pipe to Chlorinated Water. The testing methodology follows the Jana Mode 3 Shift Functions approach to assess polyethylene compound performance in potable water applications. Experiments were conducted in general accordance with ASTM F2263-14 with the following modifications: (1) at least 6 samples were tested at 90° C.; (2) testing was conducted on 4 foot, DR 11 IPS pipe according to the dimensional requirements of ASTM D3035-15; (3) the flow rate established an average oxidation reduction potential (ORP) of the test fluid above 825 mV; (4) the external test environment was not air or non-chlorinated water; (5) the calculation of the log average time to failure included all failures; (7) if one sample failed due to defective test apparatus, sample preparation, or other anomaly with test procedure, the log average testing time of the remaining 5 samples may have been used to determine categorization; and (8) the sample was categorized according to Table 2 of ASTM D3350-14.

(25) Wall Thickness Variability

(26) Wall thickness variability was measured in accordance with ASTM D2122-16, Standard Test Method for Determining Dimensions of Thermoplastic Pipe and Fittings. Testing was conducted at 23° C. and 10% relative humidity. A cylindrical or ball anvil tubing micrometer was used to make a series of measurements at closely spaced intervals. At least the necessary minimum of eight measurements were taken. The measurements are used to calculate the wall thickness variation (or range), E.

(27) Preparation of Black Composition

(28) 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, 1-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.

(29) 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.

(30) 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.

(31) TABLE-US-00001 TABLE 1 Polymerization conditions and properties for base polymer I 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

(32) 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   η*.sub.0.01 (Pa .Math. s) 185,778    215,823    257,745    299,653    η*.sub.100 (Pa .Math. s) 2,504   2,382   2,396   2,401   SHI 2.7/210 (—)  44  61  76  96 η* at G* = 2.7 kPa (Pa .Math. s) 150,519    197,229    255,503    311,613    η*.sub.747 (kPa .Math. s) 280 446 647 889 NPT 80° C. - 9.2 bar on 110SDR11 >8 800   >8 800   >8 800   >8 800   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

(33) Preparation of Natural Composition

(34) The manufacture of a base resin II was carried out as described for base resin I above. Polymerization conditions and copolymer properties are presented in Table 3.

(35) 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.

(36) 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.

(37) TABLE-US-00003 TABLE 3 Polymerization conditions 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 D123

(38) TABLE-US-00004 TABLE 4 Example C5 6 7 8 Pelletization conditions Peroxide amount (ppm pure) 0 75 92 130 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 η*.sub.0.01 (Pa .Math. s) 187,073 261,190 364,960 428,436 η*.sub.100 (Pa .Math. s) 2304 2272 2,403 2,330 Zero Shear Viscosity (η.sub.0) 426,112 876,962 1,295,824 3,028,376 (Pa .Math. s) SHI 2.7/210 39 91 115 η* at G* = 2.7 kPa (kPa .Math. s) 168.3 257.8 399.9 η*.sub.747 (kPa .Math. s) 1,296 PENT Failure Time (h) >10,000 >7,900 >10,000 Pipe Extrusion Data Typical Output Rates (lb/hr)** 1,885 1,500 1,750 2,351 Extruder Load (%) 70 83 77 73 Pipe Size 28″ DR 11 24″ DR 5 30″ DR9 48″ DR 17 Wall Thickness Limitation 2.25″ 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.

(39) Oxidative Resistance Testing

(40) Chlorine resistance testing was performed in accordance with ASTM F2263-14 and as described above. Six samples prepared according to the parameters above were tested.

(41) Two sets of 3 20-inch long samples were fusion welded together with 4-foot PE SDR 11 end caps on both pipe ends. Both sets were linked together with stainless steel tubing and connected to the chlorine testing station.

(42) The samples were exposed to continuous flowing chlorinated Reverse Osmosis water and tested in a horizontal position. The water was at pH 7±0.2 and the free chlorine present was 3±0.2 mg/L. The nominal ORP was measured to be greater than 825 mV. The fluid temperature was 90° C.±1. The air temperature was 90° C.±1. The fluid and air temperatures were controlled at the same set-point. The water pressure was 95±1% psig. The flow rate was 0.1±10% USGPM. A stress test was conducted with a stress of 450 psi to assess the categorization. The results of the oxidative resistance testing are detailed in Table 5.

(43) TABLE-US-00005 TABLE 5 Sample Stress (psi/MPa) Failure Time (hr) 1 450/3.1 6712 2 450/3.1 7598 3 450/3.1 7598 4 450/3.1 7598 5 450/3.1 7598 6 450/3.1 7598 Log average test time (hr) 7442 Category 3

(44) As seen in Table 5, all pipes formed according to the present disclosure fall within category 3.

(45) Wall Thickness Variability

(46) Wall thickness variability for pipes formed according to this disclosure and prior art was measured and calculated in accordance with ASTM D2122-16, Standard Test Method for Determining Dimensions of Thermoplastic Pipe and Fittings. The results of the wall thickness variability measurements are disclosed in Table 6. Examples 1 and 4 in Table 6 are reference examples.

(47) TABLE-US-00006 TABLE 6 Example Ref. 1 2 3 Ref. 4 5 6 7 8 Zone 1 (° F.) 381 405 405 415 400 405 405 Zone 2 (° F.) 371 380 380 430 425 425 425 Zone 3 (° F.) 363 380 380 380 380 380 380 Zone 4 (° F.) 365 380 380 380 380 380 380 Zone 5 (° F.) 360 370 390 375 375 375 375 Die Zones (° F.) 360 380 380 375 375 375 375 Screw RPM 46 108.8 108.8 53 65 64 65 64 Melt Temp (° F.) 326 397 396 345 360 356 356 356 Line Speed 1885 2425 2340 2200 2400 2380 2360 2410 (lbs/hr) Min Wall (in.) 2.538 2.67 2.727 2.052 2.069 2.058 2.098 Max Wall (in.) 3.105 2.916 2.853 2.181 2.23 2.193 2.25 Hot OD (in.) 28.165 28.28 28.25 42.235 42.03 42.03 42.08 Cold OD (in.) 27.94 28.12 27.875 42.06 41.87 41.85 N/A Wall Thickness 22 9 5 9 6 7 6 6 Range (%)

(48) As seen in Table 6, pipes formed according to the present disclosure unexpectedly and surprisingly exhibited wall thickness variabilities of 9% or lower—which is equal to or better than the reference examples—at higher line speeds than the reference examples.

(49) 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.