POLYPROPYLENE COMPOSITION FOR THE PRODUCTION OF HIGH PRESSURE PIPES

Abstract

The present invention is directed to a polypropylene composition (C) applicable for the production of pressure pipes, said composition comprising a propylene random copolymer (rPP) and an impact modifier being a polyethylene (PE), as well as an article comprising said composition.

Claims

1. A polypropylene composition (C), comprising i) 80.0 to 99.9 wt. % of a propylene random copolymer (rPP) comprising propylene and at least one comonomer being ethylene and/or a C.sub.4-C.sub.8 α-olefin, said propylene random copolymer (rPP) having a melt flow rate MFR.sub.2 determined according to ISO 1133 at 230° C. and a load of 2.16 kg in the range of 0.05 to 1.0 g/10 min, and ii) 0.3 to 20.0 wt. % of a polyethylene (PE) having a density equal or below 940 kg/m.sup.3, based on the overall weight of the polypropylene composition (C).

2. The polypropylene composition (C) according to claim 1, having a melt flow rate MFR.sub.2 determined according to ISO 1133 at 230° C. and a load of 2.16 kg in the range of 0.05 to 1.0 g/10 min.

3. The polypropylene composition (C) according to claim 1, having a Charpy Notched Impact Strength at 23° C. of at least 15.0 kJ/m.sup.2, determined according to ISO 179/1eA:2000.

4. The polypropylene composition (C) according to claim 1, having a xylene cold soluble content (XCS) in the range of 1.0 to 15.0 wt. %, determined according to ISO 16152.

5. The polypropylene composition (C) according to claim 1, wherein the ratio MFR(C)/MFR(rPP) is in the range of 0.8 to 1.3, wherein MFR(C) is the melt flow rate MFR.sub.2 determined according to ISO 1133 at 230° C. and a load of 2.16 kg of the polypropylene composition (C) and MFR(rPP) is the melt flow rate MFR.sub.2 determined according to ISO 1133 at 230° C. and a load of 2.16 kg of the propylene random copolymer (rPP).

6. The polypropylene composition (C) according to claim 1, wherein the propylene random copolymer (rPP) has i) a comonomer content in the range of 1.0 to 15.0 mol % and/or ii) a xylene cold soluble content (XCS) in the range of 1.0 to 15.0 wt. %, determined according to ISO 16152.

7. The polypropylene composition (C) according to claim 1, wherein the propylene random copolymer i) has a melting temperature below 155° C. and/or ii) is monophasic.

8. The polypropylene composition (C) according to claim 1, wherein the propylene random copolymer (rPP) is at least bimodal.

9. The polypropylene composition (C) according to claim 8, wherein the propylene random copolymer (rPP) is a bimodal propylene random copolymer (rPP-2) comprising: i) 35.0 to 55.0 wt. % of a first propylene random copolymer (rPP-2a), and ii) 45.0 to 65.0 wt. % of a second propylene random copolymer (rPP-2b) which is different from the first propylene random copolymer (rPP-2a), wherein the bimodal random copolymer (rPP 2) has an overall melt flow rate MFR.sub.2 determined according to ISO 1133 at 230° C. and a load of 2.16 kg in the range of 0.01 to 5.0 g/10 min.

10. The polypropylene composition (C) according to claim 9, wherein: i) the first propylene random copolymer (rPP-2a) has a comonomer content in the range of 1.0 to 5.0 mol %, and ii) the bimodal random copolymer (rPP-2) has an overall comonomer content in the range of 3.0 to 10.0 mol %, and wherein the first propylene random copolymer (rPP-2a) and the second propylene random copolymer (rPP-2b) are copolymers of propylene and ethylene and/or a C.sub.4 to C.sub.8 α-olefin.

11. The polypropylene composition (C) according to claim 8, wherein the propylene random copolymer (rPP) is a trimodal propylene random copolymer (rPP-3) comprising: i) 30.0 to 50.0 wt. % of a first propylene random copolymer (rPP-3a), ii) 42.0 to 60.0 wt. % of a second propylene random copolymer (rPP-3b) which is different from the first propylene random copolymer (rPP-3a), and iii) 1.0 to 15.0 wt. % of a third propylene random copolymer (rPP-3c) which is different from the first propylene random copolymer (rPP-3a) and the second propylene random copolymer (rPP-3b), wherein the overall melt flow rate MFR.sub.2 determined according to ISO 1133 at 230° C. of the trimodal propylene random copolymer (rPP-3) is in the range of 0.1 to 3.0 g/10 min.

12. The polypropylene composition (C) according to claim 11, wherein: i) the first propylene random copolymer (rPP-3a) has a comonomer content in the range of 1.0 to 4.9 mol %, and ii) the trimodal propylene random copolymer (rPP-3) has an overall comonomer content in the range of 4.0 to 12.0 mol %, wherein the propylene random copolymer (rPP-3a), the propylene random copolymer (rPP-3b) and the propylene random copolymer (rPP-3c) are copolymers of propylene and ethylene and/or a C.sub.4 to C.sub.8 α-olefin.

13. The polypropylene composition (C) according to claim 1, wherein the propylene random copolymer (rPP) consists of a copolymer of propylene and ethylene.

14. The polypropylene composition (C) according to claim 1, wherein the polyethylene (PE) has a melt flow rate MFR.sub.2 determined according to ISO 1133 at 190° C. and a load of 2.16 kg in the range of 0.1 to 6.0 g/10 min.

15. The polypropylene composition (C) according to claim 1, wherein the polyethylene (PE) is a low density polyethylene (LDPE).

16. The polypropylene composition (C) according to claim 1, wherein the sum of the propylene random copolymer (rPP) and the polyethylene (PE) is at least 80 wt. %, based on the total amount of the polypropylene composition (C).

17. An article comprising the polypropylene composition (C) according to claim 1.

18. The article according to claim 17, wherein the article is a pipe.

Description

EXAMPLES

1. Measuring Methods

[0200] The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

[0201] MFR.sub.2 (230° C.) is measured according to ISO 1133 (230° C., 2.16 kg load).

[0202] MFR.sub.21 (230° C.) is measured according to ISO 1133 (230° C., 21.6 kg load).

[0203] MFR.sub.2 (190° C.) is measured according to ISO 1133 (190° C., 2.16 kg load).

[0204] The xylene solubles (XCS, wt.-%): Content of xylene cold solubles (XCS) is determined at 25° C. according ISO 16152; first edition; 2005-07-01. The part which remains insoluble is the xylene cold insoluble (XCI) fraction.

Quantification of Microstructure by NMR Spectroscopy

[0205] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content and comonomer sequence distribution of the polymers. Quantitative .sup.13C {.sup.1H} NMR spectra were recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for .sup.1H and .sup.13C respectively. All spectra were recorded using a .sup.13C optimised 10 mm extended temperature probehead at 125° C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in 3 ml of 1,2-tetrachloroethane-d.sub.2 (TCE-d.sub.2) along with chromium-(III)-acetylacetonate (Cr(acac).sub.3) resulting in a 65 mM solution of relaxation agent in solvent (Singh, G., Kothari, A., Gupta, V., Polymer Testing 28 5 (2009), 475). To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatary oven for at least 1 hour. Upon insertion into the magnet the tube was spun at 10 Hz. This setup was chosen primarily for the high resolution and quantitatively needed for accurate ethylene content quantification. Standard single-pulse excitation was employed without NOE, using an optimised tip angle, 1 s recycle delay and a bi-level WALTZ16 decoupling scheme (Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225; Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128). A total of 6144 (6k) transients were acquired per spectra. Quantitative .sup.13C {.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm using the chemical shift of the solvent. This approach allowed comparable referencing even when this structural unit was not present. Characteristic signals corresponding to the incorporation of ethylene were observed Cheng, H. N., Macromolecules 17 (1984), 1950).

[0206] For polypropylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

[0207] Characteristic signals corresponding to regio defects (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253; Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157; Cheng, H. N., Macromolecules 17 (1984), 1950) or comonomer were observed.

[0208] The tacticity distribution was quantified through integration of the methyl region between 23.6-19.7 ppm correcting for any sites not related to the stereo sequences of interest (Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443; Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromoleucles 30 (1997) 6251).

[0209] Specifically the influence of regio defects and comonomer on the quantification of the tacticity distribution was corrected for by subtraction of representative regio defect and comonomer integrals from the specific integral regions of the stereo sequences.

[0210] The isotacticity was determined at the pentad level and reported as the percentage of isotactic pentad (mmmm) sequences with respect to all pentad sequences:

[mmmm] %=100*(mmmm/sum of all pentads)

[0211] The presence of 2,1 erythro regio defects was indicated by the presence of the two methyl sites at 17.7 and 17.2 ppm and confirmed by other characteristic sites.

[0212] Characteristic signals corresponding to other types of regio defects were not observed (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253).

[0213] The amount of 2,1 erythro regio defects was quantified using the average integral of the two characteristic methyl sites at 17.7 and 17.2 ppm:

P.sub.21e=(I.sub.c6+I.sub.c8)/2

[0214] The amount of 1,2 primary inserted propene was quantified based on the methyl region with correction undertaken for sites included in this region not related to primary insertion and for primary insertion sites excluded from this region:

P.sub.12=I.sub.CH3+P.sub.12e

[0215] The total amount of propene was quantified as the sum of primary inserted propene and all other present regio defects:

P.sub.total=P.sub.12+P.sub.21e

[0216] The mole percent of 2,1 erythro regio defects was quantified with respect to all propene:

[21e] mol %=100*(P.sub.21e/P.sub.total)

[0217] For copolymers characteristic signals corresponding to the incorporation of ethylene were observed (Cheng, H. N., Macromolecules 17 (1984), 1950).

[0218] With regio defects also observed (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253; Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157; Cheng, H. N., Macromolecules 17 (1984), 1950) correction for the influence of such defects on the comonomer content was required.

[0219] The comonomer fraction was quantified using the method of Wang et. al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157) through integration of multiple signals across the whole spectral region in the .sup.13C {.sup.1H} spectra. This method was chosen for its robust nature and ability to account for the presence of regio-defects when needed. Integral regions were slightly adjusted to increase applicability across the whole range of encountered comonomer contents.

[0220] For systems where only isolated ethylene in PPEPP sequences was observed the method of Wang et. al. was modified to reduce the influence of non-zero integrals of sites that are known to not be present. This approach reduced the overestimation of ethylene content for such systems and was achieved by reduction of the number of sites used to determine the absolute ethylene content to:

E=0.5(Sββ+Sβγ+Sβδ+0.5(Sαβ+Sαγ))

[0221] Through the use of this set of sites the corresponding integral equation becomes:

E=0.5(I.sub.H+I.sub.G+0.5(I.sub.C+I.sub.D))

[0222] using the same notation used in the article of Wang et. al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157). Equations used for absolute propylene content were not modified.

[0223] The mole percent comonomer incorporation was calculated from the mole fraction:

E[mol %]=100*fE

[0224] The weight percent comonomer incorporation was calculated from the mole fraction:

E[wt %]=100*(fE*28.06)/((fE*28.06)+((1−fE)*42.08))

[0225] The comonomer sequence distribution at the triad level was determined using the analysis method of Kakugo et al. (Kakugo, M., Naito, Y., Mizunuma, K., Miyatake, T.

[0226] Macromolecules 15 (1982) 1150). This method was chosen for its robust nature and integration regions slightly adjusted to increase applicability to a wider range of comonomer contents.

Number Average Molecular Weight (M.sub.n), Weight Average Molecular Weight (M.sub.w) and Molecular Weight Distribution (MWD)

[0227] Molecular weight averages (Mw, Mn), and the molecular weight distribution (MWD), i.e. the Mw/Mn (wherein Mn is the number average molecular weight and Mw is the weight average molecular weight), were determined by Gel Permeation Chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-99. A PolymerChar GPC instrument, equipped with infrared (IR) detector was used with 3×Olexis and 1×Olexis Guard columns from Polymer Laboratories and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg/L 2,6-Di tert butyl-4-methyl-phenol) as solvent at 160° C. and at a constant flow rate of 1 mL/min 200 μL 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 0.5 kg/mol to 11 500 kg/mol. Mark Houwink constants for PS, PE and PP used are as described per ASTM D 6474-99. All samples were prepared by dissolving 5.0-9.0 mg of polymer in 8 mL (at 160° C.) of stabilized TCB (same as mobile phase) for 2.5 hours for PP or 3 hours for PE at max. 160° C. under continuous gentle shaking in the autosampler of the GPC instrument.

[0228] DSC analysis, melting temperature (T.sub.m) and heat of fusion (H.sub.f), crystallization temperature (T.sub.c) and heat of crystallization (H.sub.c): measured with a TA Instrument Q200 differential scanning calorimetry (DSC) on 5 to 7 mg samples. DSC is run according to ISO 11357/part 3/method C2 in a heat/cool/heat cycle with a scan rate of 10° C./min in the temperature range of −30 to +225° C. Crystallization temperature (T.sub.c) and heat of crystallization (H.sub.e) are determined from the cooling step, while melting temperature (T.sub.m) and heat of fusion (H.sub.f) are determined from the second heating step.

[0229] Density is measured according to ISO 1183-187. Sample preparation is done by compression moulding in accordance with ISO 1872-2:2007.

[0230] The glass transition temperature Tg is determined by dynamic mechanical analysis according to ISO 6721-7. The measurements are done in torsion mode on compression moulded samples (40×10×1 mm.sup.3) between −100° C. and +150° C. with a heating rate of 2° C./min and a frequency of 1 Hz.

[0231] Tensile properties were determined on samples prepared from compression-moulded plaques having a sample thickness of 4 mm. Tensile modulus was determined according to ISO 527-2/1 B at 1 mm/min. and 23° C. To determine stress at yield and strain at yield, a speed of 50 min/min. was used.

[0232] Charpy notched impact test: The charpy notched impact strength (Charpy NIS) was measured according to ISO 179 2C/DIN 53453 at 23° C. and 0° C., using injection molded bar test specimens of 80×10×4 mm prepared in accordance with ISO 294-1:1996

[0233] The flexural modulus was determined in 3-point-bending according to ISO 178 on injection molded specimens of 80×10×4 mm prepared in accordance with ISO 294-1:1996.

Shear Thinning Index SHI.SUB.2.7/210

[0234] 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 190° C. applying a frequency range between 0.01 and 600 rad/s and setting a gap of 1.3 mm.

[0235] 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

γ(t)=γ.sub.0 sin(ωt)  (1)

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

σ(t)=σ.sub.0 sin(ωt+δ)  (2)

where σ.sub.0, and γ.sub.0 are the stress and strain amplitudes, respectively; ω is the angular frequency; δ is the phase shift (loss angle between applied strain and stress response); t is the time.

[0236] 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, η*, the dynamic shear viscosity, η′, the out-of-phase component of the complex shear viscosity, η″ and the loss tangent, tan η, which can be expressed as follows:

[00001]$\begin{array}{cc}{G}^{\prime }=\frac{{\sigma }_0}{{\gamma }_0}.Math.\mathrm{cos\delta }\left[\mathrm{Pa}\right]& \left(3\right)\\ G^{″}=\frac{{\sigma }_0}{{\gamma }_0}.Math.\sin .Math.\delta \left[\mathrm{Pa}\right]& \left(4\right)\\ G^{*}=G.Math.‘+\mathrm{iG}.Math.“\left[\mathrm{Pa}\right]& \left(5\right)\\ {\eta }^{*}={\eta }^{\prime }-{i.Math.\eta }^{″}\left[\mathrm{Pa}.Math.s\right]& \left(6\right)\\ \eta ’=\frac{G^{″}}{\omega }\left[\mathrm{Pa}.Math.s\right]& \left(7\right)\\ \eta ”=\frac{G^{″}}{\omega }\left[\mathrm{Pa}.Math.s\right]& \left(8\right)\end{array}$

[0237] The determination of so-called Shear Thinning Index, which correlates with MWD and is independent of Mw, is done as described in equation 9.

[00002]$\begin{array}{cc}{\mathrm{SHI}}_{\left(x/y\right)}=\frac{E.Math.t.Math.a^{*}.Math..Math.\mathrm{for}.Math..Math.\left(G^{*}=x.Math..Math.\mathrm{kPa}\right)}{E.Math.t.Math.a^{*}.Math..Math.\mathrm{for}.Math..Math.\left(G^{*}=y.Math..Math.\mathrm{kPa}\right)}& \left(9\right)\end{array}$

[0238] For example, the SHI.sub.(27/210) is defined by the value of the complex viscosity, in Pa s, determined for a value of G* equal to 2.7 kPa, divided by the value of the complex viscosity, in Pa s, determined for a value of G* equal to 210 kPa.

[0239] The values of storage modulus (G′), loss modulus (G″), complex modulus (G*) and complex viscosity (η*) were obtained as a function of frequency (ω).

[0240] Thereby, e.g. η*.sub.300 rad/s (eta*.sub.300 rad/s) is used as abbreviation for the complex viscosity at the frequency of 300 rad/s and η*.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.

[0241] The loss tangent tan (delta) is defined as the ratio of the loss modulus (G″) and the storage modulus (G′) at a given frequency. Thereby, e.g. tan.sub.0.05 is used as abbreviation for the ratio of the loss modulus (G″) and the storage modulus (G′) at 0.05 rad/s and tan.sub.300 is used as abbreviation for the ratio of the loss modulus (G″) and the storage modulus (G′) at 300 rad/s. The elasticity balance tan.sub.0.05/tan.sub.300 is defined as the ratio of the loss tangent tan.sub.0.05 and the loss tangent tan.sub.300.

[0242] 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]  (10)

[0243] 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.

[0244] The viscosity eta.sub.747 is measured at a very low, constant shear stress of 747 Pa and is inversely proportional to the gravity flow of the polyethylene composition, i.e. the higher eta.sub.747 the lower the sagging of the polyethylene composition.

[0245] The polydispersity index, PI, is defined by equation 11.

[00003]$\begin{array}{cc}\mathrm{PI}=\frac{{10}^5}{G^{\prime }\left({\omega }_{\mathrm{COP}}\right)},{\omega }_{\mathrm{COP}}=\omega .Math..Math.\mathrm{for}.Math..Math.(G\text{'}=G^{\prime }’)& \left(1\right)\end{array}$

where ω.sub.COP is the cross-over angular frequency, determined as the angular frequency for which the storage modulus, G′, equals the loss modulus, G″.

[0246] 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.

REFERENCES

[0247] [1] “Rheological characterization of polyethylene fractions”, Heino, E. L., Lehtinen, A., Tanner J., Seppälä, J., Neste Oy, Porvoo, Finland, Theor. Appl. Rheol., Proc. Int. Congr. Rheol, 11th (1992), 1, 360-362. [0248] [2] “The influence of molecular structure on some rheological properties of polyethylene”, Heino, E. L., Borealis Polymers Oy, Porvoo, Finland, Annual Transactions of the Nordic Rheology Society, 1995. [0249] [3] “Definition of terms relating to the non-ultimate mechanical properties of polymers”, Pure & Appl. Chem., Vol. 70, No. 3, pp. 701-754, 1998.

[0250] Pressure test performance is measured according to ISO 1167. In this test, a specimen is exposed to constant circumferential (hoop) stress of 16 MPa (for PP copolymers) respectively 21 MPa (for PP homopolymers) at elevated temperature of 20° C. in water-in-water or 4.5 MPa (for PP copolymers) respectively 3.5 MPa (for PP homopolymers) at a temperature of 95° C. in water-in-water. The time in hours to failure is recorded. The tests were performed on pipes produced on a conventional pipe extrusion equipment, the pipes having a diameter of 32 mm and a wall thickness of 3 mm.

B. EXAMPLES

[0251] 1. Preparation of Propylene Random Copolymer (rPP) Component: The Bimodal Propylene Random Copolymer (rPP-2) and the Trimodal Propylene Random Copolymer (rPP-3)

Preparation of the Catalyst

[0252] First, 0.1 mol of MgCl.sub.2x 3 EtOH was suspended under inert conditions in 250 ml of decane in a reactor at atmospheric pressure. The solution was cooled to the temperature of −15° C. and 300 ml of cold TiCl.sub.4 was added while maintaining the temperature at said level. Then, the temperature of the slurry was increased slowly to 20° C. At this temperature, 0.02 mol of diethylhexylphthalate (DOP) was added to the slurry. After the addition of the phthalate, the temperature was raised to 135° C. during 90 minutes and the slurry was allowed to stand for 60 minutes. Then, another 300 ml of TiCl.sub.4 was added and the temperature was kept at 135° C. for 120 minutes. After this, the catalyst was filtered from the liquid and washed six times with 300 ml heptane at 80° C. Then, the solid catalyst component was filtered and dried. Catalyst and its preparation concept is described in general e.g. in patent publications EP 491 566, EP 591 224 and EP 586 390.

Preparation of the Bimodal Propylene Random Copolymer (rPP-2)

[0253] For the preparation of (rPP-2), triethylaluminum (TEAL), dicyclopentyldimethoxysilane (DCPDMS) as donor (Do), and the catalyst as produced above were added into oil, like mineral oil, e.g. Technol 68 (kinematic viscosity at 40° C. 62-74 cSt), in amounts so that Al/Ti was 3-4 mol/mol, and Al/Do was as well 3-4 mol/mol. Catalyst concentration in the final oil-catalyst slurry was 10-20 wt-%.

[0254] For the polymerization of (rPP-2), the catalyst was fed together with propylene to a prepolymerization reactor. Triethylaluminum was used as a cocatalyst and dicyclopentyldimethoxysilane as a donor. The slurry from the prepolymerization stage was directly fed to a loop reactor. Propylene, hydrogen and ethylene were further added to the loop reactor. The slurry from loop reactor was introduced to a gas phase reactor via direct feed line, i.e. without monomer flashing in-between the reactors. Propylene, ethylene and hydrogen were fed to the gas phase reactor. The polymerization conditions and feeds are listed in Table 1.

TABLE-US-00001 TABLE 1 Preparation of rPP-2 Prepolymerization rPP-2 TEAL/Ti [mol/mol] 200 TEAL/donor [mol/mol] 30 Temperature [° C.] 30 Pressure [kPa] 5300 Loop Temperature [° C.] 70 Pressure [kPa] 5300 Split [%] 40 H2/C3 ratio [mol/kmol] 0.65 MFR.sub.2 [g/10 min] 0.75 XCS [wt.-%] 5.0 C2 content [mol-%] 4.4 GPR 1 Temperature [° C.] 80 Pressure [kPa] 1600 Split [%] 60 H2/C3 ratio [mol/kmol] 2.0 Final MFR.sub.2 [g/10 min] 0.3 Final XCS [wt.-%] 6.8 Final C2 content [mol-%] 6.3 C2 ethylene H2/C3 ratio hydrogen/propylene ratio GPR 1 gas phase reactor Loop Loop reactor
Preparation of the Trimodal Propylene Random Copolymer (rPP-3) For the preparation of the trimodal propylene random copolymer (rPP-3), triethylaluminium (TEAL), dicyclopentyldimethoxysilane (DCPDMS) as donor (Do), catalyst as produced above and vinylcyclohexane (VCH) were added into oil, like mineral oil, e.g. Technol 68 (kinematic viscosity at 40° C. 62-74 cSt), in amounts so that Al/Ti was 3-4 mol/mol, Al/Do was as well 3-4 mol/mol, and weight ratio of VCH/solid catalyst was 1:1. The mixture was heated to 60 to 65° C. and allowed to react until the content of the unreacted vinylcyclohexane in the reaction mixture was less than 1000 ppm. Catalyst concentration in the final oil-catalyst slurry was 10 to 20 wt.-%.

[0255] For the polymerisation, the catalyst including polymerised VCH was fed together with propylene to a prepolymerisation reactor. Triethylaluminium was used as a cocatalyst and dicyclopentyldimethoxysilane as a donor. The polymerisation conditions and feeds are listed in Table 2. The slurry from the prepolymerisation stage was directly fed to a loop reactor. Propylene, hydrogen and ethylene were further added to the loop reactor. The polymerisation conditions and feeds are listed in Table 2. The slurry from loop reactor was introduced to a gas phase reactor via direct feed line, i.e. without monomer flashing in-between the reactors. Propylene, ethylene and hydrogen were fed to the first gas phase reactor and further transferred to a second gas phase reactor. The final Poly-VCH content in the obtained final polymer was 200 ppm or less.

TABLE-US-00002 TABLE 2 Preparation of rPP-3 Prepolymerization rPP-3 TEAL feed [g/t (C3)] 740 Donor feed [g/t (PP)] 13 Temperature [° C.] 33 Pressure [kPa] 5300 Loop Temperature [° C.] 72 Pressure [kPa] 5000 Split [%] 39 H2/C3 ratio [mol/kmol] 0.5 MFR.sub.2 [g/10 min] 0.8 XCS [wt.-%] 4.5 C2 content [mol-%] 4.1 GPR 1 Temperature [° C.] 80 Pressure [kPa] 2900 Split [%] 51 H2/C3 ratio [mol/kmol] 1.9 C2 content [mol-%] 6.0 GPR 2 Temperature [° C.] 80 Pressure [kPa] 2400 Split [%] 10 H2/C3 ratio [mol/kmol] 0.50 Final MFR.sub.2 [g/10 min] 0.317 Final XCS [wt.-%] 9.9 Final C2 content [mol-%] 6.7 C2 ethylene H2/C3 ratio hydrogen/propylene ratio GPR 1/2 1st/2nd gas phase reactor Loop Loop reactor

2. The Polyethylene (PE) Component: Low Density Polyethylene (LDPE)

[0256] LDPE is the commercial low density polyethylene FT5230 by Borealis having a density of 923 kg/m.sup.3, a melt flow rate MFR.sub.2 (190° C.) of 0.75 g/10 min and a melting temperature of 112° C.

3. Preparation of the Polypropylene Composition (C)

[0257] The propylene random copolymers (rPP-2) and (rPP-3) were melt blended with the low density polyethylene (LDPE) in amounts as indicated in Tables 3 and 4. The polymer pellets of the inventive and comparative compositions were prepared to test specimens for the mechanical and thermal tests as listed below or were extruded to pipes in order to test the processability of the compositions.

[0258] The properties of the comparative and inventive compositions are summarized in Tables 3 and 4.

TABLE-US-00003 TABLE 3 Composition and properties of comparativ example CE1 and inventive examples IE1 and IE2 CE1 IE1 IE2 rPP-2 [wt.-%] 100 98 95 LDPE [wt.-%] 0 2 5 MFR.sub.2 [g/10 min] 0.30 0.30 0.32 Tm [° C.] 142.0 142.1 142.1 ΔHm [J/g] 75 76 77 Tc [° C.] 103.3 103.1 103.0 ΔHc [J/g] 80 79 83 C2 [mol-%] 6.3 9.6 13.3 XCS [wt.-%] 6.8 7.0 6.6 Mw [kg/mol] 477 477 472 MWD [−] 9.8 10.1 10.2 Eta (0.05 rad/s) [Pa*s] 68800 67900 Eta (300 rad/s) [Pa*s] 667 651 SHI (2.7/210) [−] 131.3 146.0 Tensile Modulus [MPa] 810 780 Tensile stress at yield [MPa] 25.0 24.3 Tensile strain at yield [%] 12.8 13.1 Tensile stress at break [MPa] 28.7 27.9 Nominal strain [%] 460 450 at break Flexural modulus [MPa] 900 880 Charpy notched [kJ/m.sup.2] 38.3 42.6 impact 23° C. Charpy notched [kJ/m.sup.2] 2.48 3.05 impact 0° C. HPT (4.5 MPa/95° C.) [hr] 551 (B).sup.1) 1071 (B).sup.1) .sup.1)brittle failure

TABLE-US-00004 TABLE 4 Composition and properties of comparative example CE2 and inventive examples IE3 and IE4 CE2 1E3 1E4 rPP-3 [wt.-%] 100 98 95 LDPE [wt.-%] 0 2 5 MFR.sub.2 [g/10 min] 0.32 0.33 0.35 Tm [° C.] 147.8 147.9 147.9 ΔHm [J/g] 75 74 75 Tc [° C.] 117.8 117.7 117.7 ΔHc [J/g] 80 79 81 C2 [mol-%] 7.0 10.0 14.0 XCS [wt.-%] 9.9 10.1 11.4 Mw [kg/mol] 469 475 472 MWD [−] 10.1 10.6 10.9 Eta (0.05 rad/s) [Pa*s] 61000 62300 61700 Eta (300 rad/s) [Pa*s] 661 658 641 SHI (2.7/210) [−] 117.6 122.0 134.0 Tensile Modulus [MPa] 820 840 820 Tensile stress at yield [MPa] 25.1 25.4 24.9 Tensile strain at yield [%] 12.7 12.8 13.6 Tensile stress at break [MPa] 26.2 28.9 27.4 Nominal strain at break [%] 440 460 420 Flexural modulus [MPa] 920 900 870 Charpy notched impact 23° C. [kJ/m.sup.2] 60.0 62.9 66.3

[0259] As can be gathered from Tables 3 and 4, the inventive compositions containing small amounts of the polyethylenes LDPE are featured by improved impact properties while the flexural modulus remains on a high level. The HPT performance of the pipes based on the bimodal propylene random copolymer (rPP-2) was good and not significantly affected by the polyethylene impact modifier.