MULTIMODAL POLYETHYLENE COMPOSITION WITH HIGH PRESSURE RESISTANCE

Abstract

The present invention relates to a multimodal polyethylene composition which can be manufactured into pipes showing improved pressure resistance comprising a high density multimodal ethylene polymer component (A) having a density of at least 930 kg/m.sup.3, and a MFR.sub.21 of not more than 15 g/10 min, wherein said composition exhibits a LAOS-NLF defined as

[00001]$L.Math..Math.A.Math..Math.O.Math..Math.S-N.Math..Math.L.Math..Math.F=.Math.\frac{G_1^{}}{G_3^{}}.Math.$ where G.sub.1first order Fourier Coefficient G.sub.3third order Fourier Coefficient
of at least 1.7. Such a polyethylene composition is useful for the manufacture of pressure pipes that exhibit improved pressure resistance and creep resistance and do not undergo sagging. Further disclosed is a process for the production of a pipe using such a multimodal polyethylene composition and a pipe comprising such a multimodal polyethylene composition.

Claims

1-14. (canceled)

15. A multimodal polyethylene composition comprising a high density multimodal ethylene polymer component (A) having a density of at least 930 kg/m.sup.3, and a MFR.sub.21 of not more than 15 g/10 min, wherein said composition exhibits a LAOS-NLF defined as $L.Math..Math.A.Math..Math.O.Math..Math.S-N.Math..Math.L.Math..Math.F=.Math.\frac{G_1^{}}{G_3^{}}.Math.$ where G.sub.1first order Fourier Coefficient G.sub.3third order Fourier Coefficient of at least 1.7.

16. The multimodal polyethylene composition according to claim 15 further comprising an ultrahigh molecular weight ethylene polymer component (B)

17. The multimodal polyethylene composition according to claim 16, wherein the ultrahigh molecular weight ethylene polymer component (B) has a nominal viscosity molecular weight (Mv) according to ASTM D 4020-05 in the range of from 1,000,000 to 6,000,000 g/mol.

18. The multimodal ethylene polymer composition according to claim 15, which has a viscosity at a shear stress of 747 Pa (eta747) of 1,000 kPa.Math.s or higher.

19. The multimodal polyethylene composition according to claim 15 whereby the polypropylene base resin has a F30 melt strength of 10 cN or higher at 200 C. measured according to ISO 16790:2005.

20. The multimodal polyethylene composition according to claim 15 having a ratio (eta.sub.0.05)/(eta.sub.300) of the complex viscosity, in Pa.Math.s, at a frequency of 0.05 rad/s (eta.sub.0.05), to the complex viscosity, in Pa.Math.s, at a frequency of 300 rad/s (eta.sub.300) of at least 190.

21. The multimodal polyethylene composition according to claim 15 obtainable by melt-mixing a high density multimodal ethylene polymer component (A) having a density of at least 930 kg/m.sup.3, and a MFR.sub.21 of not more than 15 g/10 min, and extruding said high density multimodal ethylene polymer component (A) in the presence of up to 10 wt. % of additives, based on the weight of the mixture so as to form said multimodal polyethylene composition.

22. Process for the production of a pipe comprising the steps of (a) melt-mixing a high density multimodal ethylene polymer component (A) having a density of at least 930 kg/m.sup.3, and a MFR.sub.21 of not more than 15 g/10 min, (b) extruding the high density multimodal ethylene polymer component (A) so as to form a multimodal polyethylene composition in the presence of up to 10 wt. % of additives, based on the extruded mixture, the multimodal polyethylene composition having an MFR.sub.21 of not more than 15 g/10 min, a density of at least 925 kg/m.sup.3 and a LAOS-NLF defined as $L.Math..Math.A.Math..Math.O.Math..Math.S-N.Math..Math.L.Math..Math.F=.Math.\frac{G_1^{}}{G_3^{}}.Math.$ where G.sub.1first order Fourier Coefficient G.sub.3third order Fourier Coefficient of at least 1.7, and (c) forming said multimodal ethylene polymer composition into a pipe.

23. The process according to claim 22, wherein an ultrahigh molecular weight polymer component (B) is added to the melt-mixing step (a).

24. The process according to claim 22, wherein at least a part of the additives is added in step (b) at a position situated with 50% of the length from the downstream end of the extruder.

25. The process according to claim 22, wherein at least an antioxidant and/or an acid scavenger is added at a position situated within 50% of the length from the downstream end of the extruder.

26. A pipe comprising the multimodal polyethylene composition according to claim 15.

27. The pipe according to claim 26 having a hydrostatic pressure resistance according to ISO 1167-1:2006 with a failure time at 13.9 MPa stress and at 20 C. of at least 30 h.

28. A method for the production of a pipe wherein a multimodal polyethylene composition as defined in claim 15 is extruded and cooled.

Description

EXAMPLES

[0106] 1. Methods

[0107] a) Melt Flow Rate

[0108] The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR is determined at a temperature of 190 C. and a load of 2.16 kg for MFR.sub.2, at a load of 5.0 kg for MFR.sub.5 and at a load of 21.6 kg for MFR.sub.21.

[0109] b) Melting and Crystallisation Temperature

[0110] The melting and crystallisation temperature T.sub.m and T.sub.c are determined according to ISO 11357-3 with a TA-Instruments 2920 Dual-Cell with RSC refrigeration apparatus and data station. A heating and cooling rate of 10 C./min is applied in a heat/cool/heat cycle between +23 and +210 C., the crystallisation temperature T.sub.c being determined in the cooling step and the T.sub.m melting temperature being determined in the second heating step.

[0111] c) Comonomer Content

[0112] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers.

[0113] Quantitative .sup.13C{.sup.1H} NMR spectra were recorded in the molten-state using a Bruker Advance III 500 NMR spectrometer operating at 500.13 and 125.76 MHz for .sup.1H and .sup.13C, respectively. All spectra were recorded using a .sup.13C optimized 7 mm magic-angle spinning (MAS) probe head at 150 C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was packed into a 7 mm outer diameter zirconia MAS rotor and spun at 4 kHz. This setup was chosen primarily for the high sensitivity needed for rapid identification and accurate quantification {[1], [2], [6]}. Standard single-pulse excitation was employed utilizing the transient NOE at short recycle delays of 3 s {[1], [3]) and the RSHEPT decoupling scheme {[4], [5]}. A total of 1024 (1k) transients were acquired per spectrum. This setup was chosen due to its high sensitivity towards low comonomer contents.

[0114] Quantitative .sup.13C{.sup.1H) NMR spectra were processed, integrated and quantitative properties determined using custom spectral analysis automation programs. All chemical shifts are internally referenced to the bulk methylene signal (+) at 30.00 ppm {[9]}.

[0115] Characteristic signals corresponding to the incorporation of 1-hexene were observed {[9]} and all contents calculated with respect to all other monomers present in the polymer.

H=I*.sub.B4

[0116] With no other signals indicative of other comonomer sequences, i.e. consecutive comonomer incorporation, the total 1-hexene comonomer content was calculated based solely on the amount of isolated 1-hexene sequences:

H.sub.total=H

[0117] Characteristic signals resulting from saturated end-groups were observed. The content of such saturated end-groups was quantified using the average of the integral of the signals at 22.84 and 32.23 ppm assigned to the 2s and 3s sites respectively:

S=(1/2)*(I.sub.2S+I.sub.3S)

[0118] The relative content of ethylene was quantified using the integral of the bulk methylene (+) signals at 30.00 ppm:

E=(1/2)*I.sub.+

[0119] The total ethylene comonomer content was calculated based on the bulk methylene signals and accounting for ethylene units present in other observed comonomer sequences or end-groups:

E.sub.total=E+(5/2)*B+(3/2)*S

[0120] The total mole fraction of 1-hexene in the polymer was then calculated as:

fH=(H.sub.total/(E.sub.total+H.sub.total)

[0121] The total comonomer incorporation of 1-hexene in mole percent was calculated from the mole fraction in the usual manner:

H[mol-%]=100*fH

[0122] The total comonomer incorporation of 1-hexene in weight percent was calculated from the mole fraction in the standard manner:

H[wt.-%]=100*(fH*84.16)/((fH*84.16)+((1fH)*28.05))

REFERENCES

[0123] [1] Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382. [0124] [2] Parkinson, M., Klimke, K., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2007; 208:2128. [0125] [3] Pollard, M., Klimke, K., Graf, R., Spiess, H. W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004; 37:813. [0126] [4] Filip, X., Tripon, C., Filip, C., J. Mag. Reson. 2005, 176, 239. [0127] [5] Griffin, J. M., Tripon, C., Samoson, A., Filip, C., and Brown, S. P., Mag. Res. in Chem. 2007, 45, S1, S198. [0128] [6] Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373. [0129] [7] Zhou, Z., Muemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 2007, 187, 225. [0130] [8] Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128. [0131] [9] J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201.

[0132] d) Density

[0133] Unless otherwise described, density of the polymer was measured according to ISO 1183-1:2004 Method A on compression moulded specimen prepared according to EN ISO 1872-2 (February 2007) and is given in kg/m.sup.3.

[0134] e) Molecular Weight

[0135] Mw, Mn and MWD are measured by Gel Permeation Chromatography (GPC) according to the following method:

[0136] The weight average molecular weight Mw and the molecular weight distribution (MWD=Mw/Mn wherein Mn is the number average molecular weight and Mw is the weight average molecular weight) is measured according to ISO 16014-4:2003 and ASTM D 6474-99. A Waters GPCV2000 instrument, equipped with refractive index 10 detector and online viscosimeter was used with 2GMHXL-HT and 1G7000HXL-HT TSK-gel columns from Tosoh Bioscience and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg/l 2,6-Di tert-butyl-4-methyl-phenol) as solvent at 140 C. and at a constant flow rate of 1 mL/min. 209.5 L of sample solution were injected per analysis. The column set was calibrated using universal calibration (according to ISO 16014-2:2003) with at least 15 narrow MWD polystyrene (PS) standards in the range of 1 kg/mol to 12 000 kg/mol. Mark Houwink constants were used as given in ASTM D 6474-99. All samples were prepared by dissolving 0.5-4.0 mg of polymer in 4 mL (at 140 C.) of stabilized TCB (same as mobile phase) and keeping for max. 3 hours at a maximum temperature of 160 C. with continuous gentle shaking prior sampling in into the GPC instrument.

[0137] As it is known in the art, the weight average molecular weight of a blend can be calculated if the molecular weights of its components are known according to:

Mw.sub.b=.sub.i.Math.W.sub.iMw.sub.i

[0138] where Mw.sub.b is the weight average molecular weight of the blend,

[0139] w.sub.i is the weight fraction of component i in the blend and

[0140] Mw.sub.i is the weight average molecular weight of the component i.

[0141] The number average molecular weight can be calculated using the well-known mixing rule:

[00005]$\frac{1}{\mathrm{Mnb}}=\underset{i}{.Math.}.Math..Math.\frac{\mathrm{wi}}{\mathrm{Mni}}$

[0142] where Mn.sub.b is the weight average molecular weight of the blend,

[0143] w.sub.i is the weight fraction of component i in the blend and

[0144] Mn.sub.i is the weight average molecular weight of the component i.

[0145] Nominal viscosity molecular weight (Mv) is calculated from the intrinsic viscosity [] according to ASTM D 4020-05

Mv=5.3710.sup.4[].sup.1.37.

[0146] f) Rheology

[0147] The characterization of polymer melts by dynamic shear measurements complies with ISO standards 6721-1 and 6721-10. The measurements were performed on an Anton Paar MCR501 stress controlled rotational rheometer, equipped with a 25 mm parallel plate geometry. Measurements were undertaken on compression molded plates, using nitrogen atmosphere and setting a strain within the linear viscoelastic regime. The oscillatory shear tests were done at a temperature of 190 C. applying a frequency range between 0.01 and 628 rad/s and setting a gap of 1.3 mm.

[0148] In a dynamic shear experiment the probe is subjected to a homogeneous deformation at a sinusoidal varying shear strain or shear stress (strain and stress controlled mode, respectively). On a controlled strain experiment, the probe is subjected to a sinusoidal strain that can be expressed by

(t)=.sub.0 sin(t)(1)

[0149] If the applied strain is within the linear viscoelastic regime, the resulting sinusoidal stress response can be given by

(t)=.sub.0 sin(t+)(2)

[0150] where

[0151] .sub.0 and .sub.0 are the stress and strain amplitudes, respectively,

[0152] is the angular frequency,

[0153] is the phase shift (loss angle between applied strain and stress response),

[0154] t is the time.

[0155] Dynamic test results are typically expressed by means of several different rheological functions, namely the shear storage modulus G, the shear loss modulus, G, the complex shear modulus, G*, the complex shear viscosity, *, the dynamic shear viscosity, , the out-of-phase component of the complex shear viscosity and the loss tangent, tan which can be expressed as follows:

[00006]$\begin{array}{cc}{G}^{}=\frac{{}_0}{{}_0}.Math.\cos .Math..Math..Math.\left[\mathrm{Pa}\right]& \left(3\right)\\ G^{}=\frac{{}_0}{{}_0}.Math..Math.\sin .Math..Math..Math.\left[\mathrm{Pa}\right]& \left(4\right)\\ G^{*}=G^{}+.Math..Math.G^{}.Math.\left[\mathrm{Pa}\right]& \left(5\right)\\ {}^{*}={}^{}-.Math..Math.{}^{}.Math.\left[\mathrm{Pa}.Math.s\right]& \left(6\right)\\ {}^{}=\frac{G^{}}{}.Math.\left[\mathrm{Pa}.Math.s\right]& \left(7\right)\\ {}^{}=\frac{G^{}}{}.Math.\left[\mathrm{Pa}.Math.s\right]& \left(8\right)\end{array}$

[0156] The values of storage modulus (G), loss modulus (G), complex modulus (G*) and complex viscosity (*) were obtained as a function of frequency (w). Thereby, e.g. *.sub.0.05 rad/s (eta*.sub.0.05 rad/s) is used as abbreviation for the complex viscosity at the frequency of 0.05 rad/s or *.sub.300 rad/s (eta*.sub.300 rad/s) is used as abbreviation for the complex viscosity at the frequency of 300 rad/s.

[0157] Besides the above mentioned rheological functions one can also determine other rheological parameters such as the so-called elasticity index EI(x). The elasticity index EI(x) is the value of the storage modulus, G determined for a value of the loss modulus, G of x kPa and can be described by equation (10).

EI(x)=G for(G=x kPa)[Pa](9)

[0158] For example, the EI (5 kPa) is the defined by the value of the storage modulus G, determined for a value of G equal to 5 kPa.

[0159] The determination ratio between different Eta* values is done, as described in equation (10).

[00007]$\begin{array}{cc}\frac{{\mathrm{Eta}}^{*}.Math..Math.\mathrm{for}.Math..Math.\left(G^{*}=x.Math..Math.\mathrm{kPa}\right)}{{\mathrm{Eta}}^{*}.Math..Math.\mathrm{for}.Math..Math.\left(G^{*}=y.Math..Math.\mathrm{kPa}\right)}.Math.\left[\mathrm{Pa}\right]& \left(10\right)\end{array}$

[0160] According to the present invention, the ratio of the complex viscosity, in Pa.Math.s, at a frequency of 0.05 rad/s (eta.sub.0.05), to the complex viscosity, in Pa.Math.s, at a frequency of 300 rad/s (eta.sub.300) is determined.

[0161] The values are determined by means of a single point interpolation procedure, as defined by Rheoplus software. In situations for which a given G* value is not experimentally reached, the value is determined by means of an extrapolation, using the same procedure as before. In both cases (interpolation or extrapolation), the option from Rheoplus -Interpolate y-values to x-values from parameter and the logarithmic interpolation type were applied.

[0162] The polydispersity index, PI, is defined by equation (11).

[00008]$\begin{array}{cc}P.Math..Math.I=\frac{{10}^5}{G^{}\left({}_{\mathrm{COP}}\right)},{}_{\mathrm{COP}}=.Math..Math.\mathrm{for}.Math..Math.\left(G^{}=G^{}\right)& \left(11\right)\end{array}$

[0163] where, .sub.COP is the cross-over angular frequency, determined as the angular frequency for which the storage modulus, G equals the loss modulus, G.

[0164] g) Shear Viscosity Eta747

[0165] The measurement principle is to apply a certain torque to the plate axis via a precision motor. This torque is then translated into a shear stress in the sample. This shear stress is kept constant. The rotational speed produced by the shear stress is recorded and used for the calculation of the viscosity of the sample. The conditions applied are generally described in ISO 6721-10:1999.

[0166] The creep test was performed on an Anton Paar MCR 501 stress controlled rotational rheometer, using a parallel plate geometry of 25 mm and setting a gap of 25 1.8 mm. Sample preparation was done by compression moulding at 200 C. The melting and pressure loading process used on the compression moulding, were done for a total time of 5 minutes. The creep test was done at 190 C., by the application of a constant shear stress, of 747 Pa. The measurement starting was set for a normal force of less than 3.5 N. The resulting response was monitored in terms of both deformation, and shear viscosity, , over a total creep time of 1860 s. The so-called eta747 is the shear viscosity determined for a creep time of 1740 s.

[0167] The appropriate applied creep stress was previously determined by means of an oscillatory shear measurement, in order to ensure a creep response within the linear viscoelastic region.

REFERENCES

[0168] [1] Rheological characterization of polyethylene fractions Heino, E. L., Lehtinen, A., Tanner J., Seppl, J., Neste Oy, Porvoo, Finland, Theor. Appl. Rheol., Proc. Int. 10 Congr. Rheol, 11th (1992), 1, 360-362 [0169] [2] Definition of terms relating to the non-ultimate mechanical properties of 15 polymers, Pure & Appl. Chem., Vol. 70, No. 3, pp. 701-754, 1998.

[0170] h) LAOS Non-Linear Viscoelastic Ratio

[0171] The investigation of the non-linear viscoelastic behavior under shear flow was done resorting to Large Amplitude Oscillatory Shear. The method requires the application of a sinusoidal strain amplitude, .sub.0, imposed at a given angular frequency, , for a given time, t. Provided that the applied sinusoidal strain is high enough, a non-linear response is generated. The stress, is in this case a function of the applied strain amplitude, time and the angular frequency. Under these conditions, the non-linear stress response is still a periodic function; however, it can no longer be expressed by a single harmonic sinusoid. The stress resulting from a non-linear viscoelastic response [1-3] can be expressed by a Fourier series, which includes the higher harmonics contributions:

[00009]$\left(t,,{}_0\right)={}_0.Math.\underset{n}{.Math.}.Math.\left[G_n^{}\left(,{}_0\right).Math.\sin \left(n.Math..Math..Math..Math.t\right)+G_n^{}\left(,{}_0\right).Math.\cos \left(n.Math..Math..Math..Math.t\right)\right]$

with, stress response [0172] ttime [0173] frequency [0174] .sub.0strain amplitude [0175] nharmonic number [0176] G.sub.nn order elastic Fourier coefficient [0177] G.sub.nn order viscous Fourier coefficient

[0178] The non-linear viscoelastic response was analysed applying Large Amplitude Oscillatory Shear (LAOS). Time and Strain sweep measurements were undertaken on an RPA 2000 rheometer from Alpha Technologies coupled with a standard biconical die. Approx. 3.2 grams' sample is conditioned for 4 mins at a temperature of 190 C., a frequency of 10.5 rad/s and a strain amplitude of 0.5% (time sweep). Thereafter the LAOS measurement starts. During the course of the measurement the test chamber is sealed and a pressure of about 6 MPa is applied. The LAOS test is done applying a temperature of 190 C., an angular frequency of 0.628 rad/s and at strain amplitudes of 50%, 100%, 300%, 500% and 1000% (strain sweep). In order to ensure that steady state conditions are reached, the non-linear response is only determined after at least 20 cycles per measurement are completed. The results generated at the strain of 1000% were used to calculate Large Amplitude Oscillatory Shear Non-Linear Factor (LAOS-NLF).

[0179] The Large Amplitude Oscillatory Shear Non-Linear Factor (LAOS-NLF) is defined by:

[00010]$L.Math..Math.A.Math..Math.O.Math..Math.S-N.Math..Math.L.Math..Math.F=.Math.\frac{G_1^{}}{G_3^{}}.Math.$

[0180] where G.sub.1first order Fourier Coefficient [0181] G.sub.3third order Fourier Coefficient

[0182] More details concerning the measurement are given in [0183] 1. J. M. Dealy, K. F. Wissbrun, Melt Rheology and Its Role in Plastics Processing: Theory and Applications; edited by Van Nostrand Reinhold, New York (1990) [0184] 2. S. Filipe, Non-Linear Rheology of Polymer Melts, AIP Conference Proceedings 1152, pp. 168-174 (2009) [0185] 3. M. Wilhelm, Macromol. Mat. Eng. 287, 83-105 (2002) [0186] 4. S. Filipe, K. Hofstadler, K. Klimke, A. T. Tran, Non-Linear Rheological Parameters for Characterisation of Molecular Structural Properties in Polyolefins, Proceedings of Annual European Rheology Conference, 135 (2010),

[0187] the documents (1) to (4) being incorporated by reference herewith.

[0188] i) Melt Strength and Drawability Test

[0189] The test described herein follows ISO 16790:2005.

[0190] The strain hardening behaviour is determined by the method as described in the article Rheotens-Mastercurves and Drawability of Polymer Melts, M. H. Wagner, Polymer Engineering and Science, Vol. 36, pages 925 to 935. The content of the document is included by reference. The strain hardening behaviour of polymers is analysed by Rheotens apparatus (product of Gttfert, Siemensstr.2, 74711 Buchen, Germany) in which a melt strand is elongated by drawing down with a defined acceleration.

[0191] The Rheotens experiment simulates industrial spinning and extrusion processes. In principle a melt is pressed or extruded through a round die and the resulting strand is hauled off. The stress on the extrudate is recorded, as a function of melt properties and measuring parameters (especially the ratio between output and haul-off speed, practically a measure for the extension rate). For the results presented below, the materials were extruded with a lab extruder HAAKE Polylab system and a gear pump with cylindrical die (L/D=6.0/2.0 mm). The gear pump was pre-adjusted to a throughput of 2.1 g/min with pressure before the gear pump of 100 bar, and the melt temperature was set to 200 C. The spinline length between die and Rheotens wheels was 100 mm. At the beginning of the experiment, the take-up speed of the Rheotens wheels was adjusted to the velocity of the extruded polymer strand (tensile force zero): Then the experiment was started by slowly increasing the take-up speed of the Rheotens wheels until the polymer filament breaks. The acceleration of the wheels was small enough so that the tensile force was measured under quasi-steady conditions. The acceleration of the melt strand (2) drawn down is 120 mm/s.sup.2. The Rheotens was operated in combination with the PC program EXTENS. This is a real-time data-acquisition program, which displays and stores the measured data of tensile force and drawdown speed. The end points of the Rheotens curve (force versus pulley rotary speed) is taken as the melt strength and drawability values.

[0192] j) Short Term Pressure Resistance (STPR)

[0193] The pressure test on un-notched 32 mm SDR 11 pipes having a length of 450 mm is carried out in water-inside and water-outside environment according to ISO 1167-1:2006. End caps type A were used. The time to failure is determined in hours. A hoop stress of of 13.9 MPa and a temperature of 20 C. were applied.

[0194] k) Xylene Insoluble Content (XHI)

[0195] About 0.3 g of the polymer (m1) are weighed and put in a mesh of metal. The polymer and the mesh are weighed together (m2). The metal mesh (with polymer) is left in 700 ml boiling xylene for 5 hours in a 1000 ml round bottom flash under reflux. Thereafter the metal mesh (with polymer) is dropped directly into about 700 ml fresh xylene and boiled for another hour. Subsequently the mesh is dried under vacuum over night at 90 C. and weighed again (m3). The XHI (%) is calculated according to the formula below:

XHI (%)=100((m2-m3)100/ml)

[0196] l) Tensile Modulus

[0197] As a measure for stiffness, the tensile modulus (E-modulus) of the compositions was measured at 23 C. on compression molded specimens according to ISO 527-2:1993. The specimens (1B type) were milled from plaques of 4 mm thickness prepared by compression molding according to ISO 293:2004 using the conditions defined in chapter 3.3 of ISO 1872-2:2007. The modulus was measured at a speed of 1 mm/min.

[0198] m) Charpy Impact Strength

[0199] Charpy impact strength was determined according to ISO179/1eA:2000 on V-notched samples of 80*10*4 mm.sup.3 at 0 C. (Charpy impact strength (0 C.)). Samples were milled from plaques of 4 mm thickness prepared by compression molding according to ISO 293:2004 using the conditions defined in chapter 3.3 of ISO 1872-2:2007.

[0200] 2. Compositions:

[0201] UHMWPE M2 homopolymer was purchased from Jingchem Corporation. It has a narrow, quite well defined My of 2,750 kg/mol by ASTM 4020-81 (denoted in material info from the supplier).

[0202] Properties of UHMWPE M2

TABLE-US-00001 Mv Density Tm kg/mol kg/m.sup.3 C. UHMWPE M2 2,750 935 135

[0203] A bimodal high density polyethylene (PE1) was manufactured according to the following conditions.

TABLE-US-00002 Prepolymerisation Temperature C. 40 Pressure bar 61 Split % 2.0 Loop Temperature C. 95 pressure bar 56 MFR.sub.2 g/10 min 450 Density kg/m.sup.3 >970 Split % 48 GPR Temperature C. 85 Pressure bar 20 C6/C2 ratio mol/kmol 29 Split % 50 Base resin kg/m.sup.3 948 MFR.sub.21 g/10 min 9.0

[0204] Additives

[0205] The following additives were used in the reactive compounding step described below:

[0206] Antioxidant: Irganox B225 (mixture of Irganox 1010 and Irgafos 168, available from Ciba-Specialty Chemicals),

[0207] Acid scavenger: calcium stearate (CEASIT-AV/T, available from Baerlocher GmbH),

[0208] The carbon black is added as a masterbatch (CBMB) containing 39.5 wt. % carbon black (Elftex TP, distributed by Cabot), 0.1 wt. % Irganox 1010 (from Ciba, now part of BASF) and 60.4 wt. % ethylene-butylene copolymer having a comonomer content of 1.7 wt. %, an MFR.sub.2 (2.16 kg, 190 C., ISO 1133) of 30 g/10 min and a density of 959 kg/m.sup.3 in an amount of 5.75 wt. %., Peroxide: Trigonox BPIC-75 (0.4 to 0.7 wt.-% tert-butylperoxy isopropyl carbonate (CAS No. 2372-21-6), 75% solution in mineral spirits, commercially available from Akzo Nobel, NL),

Example A

[0209] The above-described bimodal high density ethylene polymers with or without the UHMW ethylene homopolymer M2 were reactively extruded in a parallel co-rotating twin-screw extruder (Theysohn TSK-N060). For extrusion on TSK-N060, a screw speed of 120 rpm and throughput rate of 5060 kg/h were set for all compounding sequences. The extrusion temperature profile was adjusted according to extrudability of each sequence. The temperature of the two barrels next to the main hopper was set to lower than 50 C. Set temperatures of all other barrels varied from 200 to 240 C. In the inventive samples a peroxide masterbatch was added to induce LCB/cross-linking reaction during compounding.

[0210] The base resin PE1 together with the UHMWPE and the carbon black masterbatch CBMB was added into the main hopper of TSK-N060 (located at barrel 1, the most upstream barrel of the extruder). Peroxide was added into the melting zone by feeding the additive to the barrel next to the main hooper of TSK-N060. The antioxidant mixture and the calcium stearate were added directly upstream of the most downstream screw into the sider feeder of TSK-N060, within 25% of the length from the downstream end of the extruder

TABLE-US-00003 TABLE 1 Compounding recipe for reactive extrusion and reference CE1 IE1 IE2 IE3 IE4 IE5 PE1 bimod. % 93.88 88.78 88.68 83.78 83.68 93.68 HDPE Irganox antioxidant % 0.22 0.22 0.22 0.22 0.22 0.22 B225 CEASIT- Ca- % 0.15 0.15 0.15 0.15 0.15 0.15 AV/T stearate CBMB % 5.75 5.75 5.75 5.75 5.75 5.75 M2 UHMWPE % 5.00 5.00 10.00 10.00 Trigonox peroxide % 0.1 0.2 0.1 0.2 0.2 BPIC-75 MB

[0211] Pipe Extrusion

[0212] Pipe extrusion was performed on a Krauss Maffei 45 single screw extruder with L/D ratio of 36. It has 5 cylinder zones, 6 tool zones and 2 vacuumed water bath tanks.

[0213] Extrusion conditions were as follows: melt temperature Tm: 215-240 C., screw speed 4060 rpm, output 3050 kg/h. The temperature in the cylinder zone 15 varied from 200 to 225 C. The sprayed water temperature in the water batch tanks was kept at 20 C.

[0214] Pipe Testing

[0215] The pressure test on un-notched 32 mm SDR 11 pipes having a length of 450 mm is carried out in water-inside and water-outside environment according to ISO 1167-1:2006. End caps of type A were used. The time to failure is determined in hours.

[0216] Pipe properties of multimodal polyethylene compositions according to the invention are shown in Table 2 in comparison to the comparative composition CE1.

TABLE-US-00004 TABLE 2 CE1 IE1 IE2 IE3 IE4 IE5 MFR.sub.5 g/10 min 0.3 0.07 0.04 0.05 0.05 0.01 MFR.sub.21 g/10 min 9.0 5.8 0.5 3.7 0.61 1.5 Density kg/m.sup.3 859.5 956.6 956 955.3 955.3 955.8 Eta-0.05 Pa .Math. s 183,700 401,100 933,200 790,800 849,300 863,200 Eta-300 Pa .Math. s 1,139 1,273 1,337 1,684 1,474 1,315 eta-0.05/ 161 315 690 470 576 656 eta-300 XHU % 0 0.33 1.85 0.9 1.6 2.6 Eta747 kPa .Math. s 691 6,522 47,568 17,056 35,182 54,717 Fmax cN 31 41 80 70 80 64 Vmax mm/s 164 172 192 187 190 199 LAOS-NLF 1.33 2.85 5.72 3.38 3.94 6.69 Pipe 13.9 MPa/20 C. H <10 35 90 34 100 73

[0217] All compositions according to the invention prepared by reactive extrusion with/without presence of UHMWPE have improved melt strength (increased F.sub.max and V.sub.max), creep resistance (increased Eta747) and pressure resistance than the reference CE1. This was achieved with only marginal increase in gel content (XHU) and reduction in density. The MFR of all materials are lower than CE1, however, due to pronounced shear thinning, viscosities in the high frequency range of most materials are not much higher than CE1 (Table 2). This means although the samples of the invention had substantially higher molecular weights, the processability was still comparable to the comparative sample CE1. Yet, the inventive samples show a surprising increase in rheological as well as mechanical properties as indicated above.

Example B

[0218] Two compositions were used for the reactive compounding step (Table 3). One is the composition used in the above CE1, the other is PE1 to which 10 wt. % of UHMWPE was mixed corresponding to the composition of IE3, but in Example B no peroxide was used so that non-crosslinked mixtures were obtained in the extrusion step.

[0219] The comparative compositions CE2 and CE3 were compounded in a parallel co-rotating twin-screw extruder ZSK 40. The polymer powder, the UHMWPE, the CBMB and all additives were premixed and fed into the main hopper at the most upstream zone for extrusion. The temperature of barrel 2 was set to 150 C. while that of all other barrels was set to 235 C.; a screw speed of 120 rpm and a throughput rate of 20 kg/h were set for all compounding sequences.

[0220] The inventive compositions IE6 and IE7 were compounded in a parallel co-rotating twin-screw extruder TSK-N060. A screw speed of 120 rpm and throughput rate of 5060 kg/h were set for all compounding sequences. The temperature of the 2 barrels next to the main hopper was set to 180 C. Temperatures of all other barrels varied from 200 to 240 C. The base resin and 5.75% carbon black masterbatch (CBMB) containing 39.5 wt. % carbon black (Elftex TP, distributed by Cabot), 0.1 wt. % Irganox 1010 (from Ciba, now part of BASF) and 60.4 wt. % ethylene-butylene copolymer having a comonomer content of 1.7 wt. %, an MFR.sub.2 (2.16 kg, 190 C., ISO 1133) of 30 g/10 min and a density of 959 kg/m.sup.3 were fed into the main hopper that is located at barrel 1, the most upstream feeder of the extruder. The antioxidant and the calcium stearate were fed directly upstream of the most downstream screw into the side feeder of TSK-N060, within 25% of the length from the downstream end of the extruder.

[0221] From the above it is apparent that the composition for CE2 and IE6 were the same, as were the compositions of CE3 and IE7, respectively. The different characteristics and effects of the respective final products are based on the different processing in the compounding step of the compositions in the extruder, as described above.

[0222] The pipe extrusion was done in the same manner as in Example A. The conditions for the pipe testing were the same as in Example A as well. The ingredients of the compositions used for reactive extrusion are shown in Table 3 below and selected pipe properties of the obtained samples are shown in Table 4 below.

TABLE-US-00005 TABLE 3 Compounding recipes for reactive extrusion CE2 CE3 IE6 IE7 PE1 bimod. % 93.88 83.88 93.88 83.88 HDPE Irganox antioxidant % 0.22 0.22 0.22 0.22 B225 CEASIT- Ca- % 0.15 0.15 0.15 0.15 AV/T stearate CBMB % 5.75 5.75 5.75 5.75 M2 UHMWPE % 10.00 10.00

TABLE-US-00006 TABLE 4 CE2 IE6 CE3 IE7 MFR.sub.5 g/10 min 0.30 0.22 0.07 0.08 MFR.sub.21 g/10 min 8.97 11.80 3.15 4.84 Eta747 kPa .Math. s 691 2,169 1,957 4,874 Eta-0.05 Pa .Math. s 183,700 205,200 345,700 341,200 Eta-300 Pa .Math. s 1,139 1,005 1,472 1,277 Eta-0.05/ 161 204 235 267 Eta-300 LAOS NLF 1.33 3.73 1.40 2.02 XHU % 0 0 0.82 0 Tensile MPa 1,076.9 1,109.0 1,075.3 1,082.7 modulus Pipe 13.9 MPa/ h <10 48 n.d. 29 20 C.

[0223] The inventive examples show significantly improved eta747 shear viscosity (suggesting better sagging resistance) and similar MFR values to the comparative examples. This was achieved without increasing the gel content of the material or loss in stiffness that is normally linked to pressure resistance of PE100. The improvement in the sagging resistance is so effective that equivalent values are obtained for standard PE100 resin (IE6) and PE100 resin added with 10 wt. % UHMW PE (CE3) at much higher MFR values (much lower molecular weight facilitating processing of the resin). In comparison to the comparative materials produced with ZSK 40, the two inventive samples have higher viscosity in the low frequency region while lower viscosity in the high frequency region. Hence they have higher eta747 (signifying better creep resistance) and therefore enhanced resistance to sagging, but comparable or even better processability than the comparative materials. Moreover, the LAOS NLF values in Table 4 were much higher for the inventive materials IE6 and IE7 than for the comparative materials CE2 and CE3, suggesting that the inventive compositions have increased long chain branching and show pronounced non-linear behaviour.

Example C

[0224] High density polyethylene compositions were produced with two different pre-polymerisation conditions. PE2 is a bimodal high density polyethylene which was produced with a prepolymerisation temperature of 70 C. and a prepolymeriser split of 1-2%. The target MFR.sub.5 for the prepolymer was 10 g/10 min. The loop reactor was operated under supercritical conditions at 95 C. The target MFR.sub.2 was 400 g/10 min. The loop reactor split was 50%. Both prepolymer and polymer produced in the loop reactor are homopolymers. The gas phase reactor was operated at 85 C. with 48% split. 1-hexene was used as comonomer so that the final powder density was targeted to 952.5 kg/m.sup.3. Final MFR.sub.5 was target to be 0.20 g/10 min. The compounding of the samples CE4 and CE5 was done in a JSW CIM 460 extruder.

[0225] PE3 is a trimodal high density polyethylene which was produced with a prepolymerisation temperature of 50 C. and no H.sub.2 was fed into the prepolymeriser. The final MFR of the prepolymer was not measurable. Based on the analysis of spot samples collected from the prepolymeriser, the prepolymer was an UHMW ethylene homopolymer having a Mv3*10.sup.6 g/mol, with a split of about 1%. The loop reactor was operated at constant conditions (H.sub.2 feed, temperature, C.sub.2 partial pressure). The MFR.sub.2 of the loop product under the above prepolymerisation conditions was ca. 150 g/10 min. There was slightly increased H.sub.2 feed in the gas phase reactor to compensate for the lower loop MFR, otherwise the gas phase reactor conditions were the same as in the preparation of PE2.

[0226] The polymerisation catalyst used for preparing both polymers PE2 and PE 3 was prepared as follows. 87 kg of toluene were added into the reactor. Then 45.5 kg Bomag A (butyloctyl magnesium) in heptane were also added in the reactor. 161 kg 99.8% 2-ethyl-1-hexanol were then introduced into the reactor at a flow rate of 24 to 40 kg/h. The molar ratio between BOMAG-A and 2-ethyl-1-hexanol was 1:1.83.

[0227] 330 kg silica (calcined silica, Sylopol 2100) and pentane (0.12 kg/kg carrier) were charged into a catalyst preparation reactor. Then EADC (Ethylaluminum dichloride) (2.66 mol/kg silica) was added into the reactor at a temperature of below 40 C. during two hours and mixing was continued for one hour. The temperature during mixing was 40-50 C. Then the Mg complex prepared as described above was added (2.56 mol Mg/kg silica) at 50 C. during two hours and mixing was continued at 40-50 C. for one hour. 0.84 kg pentane/kg silica was added into the reactor and the slurry was stirred for 4 hours at a temperature of 40-50 C. Finally, TiCl.sub.4 (1.47 mol/kg silica) was added during at least 1 hour at 55 C. to the reactor. The slurry was stirred at 50-60 C. for five hours. The catalyst was then dried by purging with nitrogen.

[0228] Molar composition of the final catalyst component is:

[0229] Al/Mg/Ti=1.5/1.4/0.8 (mol/kg silica).

[0230] The compounding of the samples IE 8, IE9, IE10, IE11, and IE12 was done in a TSK-N060 extruder as described above. In the compounding step of IE9, IE10, IE11 and IE12 a peroxide additive (Trigonox BPIC-75) was used to facilitate long chain branching/crosslinking.

[0231] The base resin, together with peroxide (when needed), was mixed and added into the melting zone by feeding to the main hopper of TSK-N060. The antioxidant mixture, the carbon black masterbatch (CBMB) containing 39.5 wt. % carbon black (Elftex TP, distributed by Cabot), 0.1 wt. % Irganox 1010 (from Ciba, now part of BASF) and 60.4 wt. % ethylene-butylene copolymer having a comonomer content of 1.7 wt. %, an MFR.sub.2 (2.16 kg, 190 C., ISO 1133) of 30 g/10 min and a density of 959 kg/m.sup.3 in an amount of 5.75 wt. % and the calcium stearate (CEASIT-AV/T, supplied by Baerlocher GmbH) were added into the side feeder of TSK-N060, within 25% of the length from the downstream end of the extruder.

[0232] The ingredients and its amounts of the compositions used in Example C are shown in Table 5 below.

TABLE-US-00007 TABLE 5 CE4 CE5 IE8 IE9 IE10 IE11 IE12 PE2 % 93.88 93.78 93.68 PE3 % 93.88 93.88 93.78 93.68 Irgafos % 0.1 0.1 0.11 0.11 0.11 0.11 0.11 168 Irganox % 0.07 0.07 0.11 0.11 0.11 0.11 0.11 1010 Irganox % 0.1 0.1 1330 CEASIT- % 0.15 0.15 0.15 0.15 0.15 0.15 0.15 AV/T CBMB % 5.75 5.75 5.75 5.75 5.75 5.75 5.75 Trigonox % 0.1 0.2 0.1 0.2 BPIC-75 Extruder JSW JSW TSK- TSK- TSK- TSK- TSK- CIM CIM N060 N060 N060 N060 N060 460 460

[0233] The pipe extrusion was done in the same manner as in Example A. The conditions for the pipe testing were the same as in Example A as well. Pipe properties of the obtained samples are shown in Table 6.

TABLE-US-00008 TABLE 6 CE4 CE5 IE8 IE9 IE10 IE11 IE12 Pipe testing at 20 C. 13.9 MPa Pipe h <10 <10 490 3,000 1,090 510 >1,201 MFR.sub.5 g/10 min 0.15 0.18 0.1 0.01 0 0.04 0.02 MFR.sub.21 g/10 min 6.12 7.02 6.4 1.82 1.08 5.19 4.19 FRR.sub.5/21 40.8 39 64 182 N.A. 129.8 209.5 PI Pa.sup.1 3.2 3.4 5.5 N.A. N.A. N.A. N.A. eta- Pa .Math. s 235,000 206,400 277,000 584,900 831,000 349,300 826,600 0.05 rad/s eta- Pa .Math. s 1,269 1,191 1,230 1,149 1,125 1,254 1,471 300 rad/s eta- 185 173 225 509 739 278.55 561.93 0.05/eta- 300 Eta747 kPa .Math. s 808.5 736.8 3,175.7 29,031 48,185 6.61E+06 5.07E+07 Density kg/m.sup.3 962.7 962.3 962.2 962.9 961.4 963.92 962.36 Tensile MPa 1,332.6 1,304.2 1,258.9 1,241.5 1,185.3 1194 1178.8 modulus Impact kJ/m.sup.2 22.7 22.1 19.7 15.8 16.0 18.34 16.76 strength at 0 C. XHU % 0.01 0.1 0.01 4.2 9.99 0.22 4.64 LAOS- 1.49 1.2 2.19 4.55 6.54 2.65 4.79 NLF 1000% Fmax* cN 34.7 36.8 40 61.7 68.7 48.7 64.7 vmax* mm/s 160 163 174 187 178 177 188

[0234] It can be seen from the above results that the inventive multimodal polyethylene compositions showed increased pressure resistance in the hydrostatic pressure test according to ISO 1167:2003 compared to the comparative compositions. The comparison between CE 5 and IE 8 shows the effect of adding the stabilizer and the acid scavenger only at approx. 22% of the length from the downstream end of the extruder (into the side feeder directly upstream to the most downstream screw), while in CE5 the additives were fed into the extruder jointly upstream at the main hopper. The composition of IE8 showed sharply increased eta747 value indicating an improved sagging resistance and creep resistance while its molecular weight was substantially higher (lower MFR). The increase in LAOS-NLF signifies an increased non-linear behavior. Addition of peroxide in the reactive extrusion step even improved the above results. Especially, the improvement in creep resistance, ratio of eta.sub.0.05/eta.sub.300 and LAOS-NLF are evident (IE11 and IE12).