BRANCHED POLYPROPYLENE FOR FOAM APPLICATIONS

Abstract

The present invention relates to a polypropylene composition comprising a branched polypropylene (b-PP) having high melt strength (HMS). Furthermore, the present invention also relates to a method for providing the corresponding polypropylene having composition comprising the branched polypropylene (b-PP) and to a foam with the polypropylene composition comprising the branched polypropylene (b-PP). The branched polypropylene (b-PP) is based on a random copolymer with a small amount of ethylene.

Claims

1. Polypropylene composition comprising a branched polypropylene (b-PP) wherein the polypropylene composition and/or the branched polypropylene (b-PP) have an ethylene content of 0.1 to 1.0 wt % have a melt flow rate MFR.sub.2 (230° C./2.16 kg) measured according to ISO 1133 of 1.0 to 5.0 g/10 min have a F30 melt strength of 30 cN to 60 cN and a v30 melt extensibility of 220 to 300 mm/s, have a F200 melt strength of 10 cN to 40 cN and a v200 melt extensibility of 220 to 300 mm/s wherein the F30 and F200 melt strength and the v30 and v200 melt extensibility are measured according to ISO 16790:2005.

2. Polypropylene composition according to claim 1 or 2, wherein the branched polypropylene (b-PP) comprises at least 95 wt % of the polypropylene composition.

3. Polypropylene composition according to any one of the preceding claims, wherein the branched polypropylene (b-PP) and/or the polypropylene composition has 2,1 erythro regio-defects of ≦0.4 mol.-% determined by .sup.13C-NMR spectroscopy.

4. The polypropylene composition according to any one of the preceding claims, wherein the polypropylene composition and/or the branched polypropylene (b-PP) has a LAOS-NLF (500%), defined as $\mathrm{LAOS}-\mathrm{NLF}\left(500.Math.\%\right)=.Math.\frac{G_1^{\prime }}{G_3^{\prime }}.Math.$ where G.sub.1′—first order Fourier Coefficient G.sub.3′—third order Fourier Coefficient with both coefficients being calculated from a measurement performed at 500% strain, of at least 6.0±s, wherein the standard deviation s is ≦0.5.

5. The polypropylene composition according to any one of the preceding claims, wherein the polypropylene composition and/or the branched polypropylene (b-PP) has a LAOS-NLF (1000%), defined as $\mathrm{LAOS}-\mathrm{NLF}\left(1000.Math.\%\right)=.Math.\frac{G_1^{\prime }}{G_3^{\prime }}.Math.$ where G.sub.1′—first order Fourier Coefficient G.sub.3′—third order Fourier Coefficient with both coefficients being calculated from a measurement performed at 1000% strain, of at least 6.0±s, wherein the standard deviation s, is ≦0.5.

6. Polypropylene composition according to any one of the preceding claims, wherein the branched polypropylene (b-PP) is provided by reacting a linear polypropylene (1-PP) having an ethylene content of 0.1 to 1.0 wt % and a melt flow rate MFR.sub.2 (230° C./2.16 kg) of 0.5 to 4.0 g/10 min with a thermally decomposing free radical-forming agent, preferably with a peroxide, and optionally with a bifunctionally unsaturated monomer, preferably selected from divinyl compounds, allyl compounds or dienes, and/or optionally with a multifunctionally unsaturated low molecular weight polymer, preferably having a number average molecular weight (Mn)≦10000 g/mol, synthesized from one and/or more unsaturated monomers, obtaining thereby the branched polypropylene (b-PP).

7. Polypropylene composition according to claim 6, wherein the linear polypropylene (l-PP) has a particle size distribution d.sub.95 of below 1500 μm and/or a particle size distribution d.sub.50 of below 1000 μm and/or a d.sub.95/d.sub.50 ratio of below 2.50.

8. Polypropylene composition according to claim 6 or 7, wherein the linear polypropylene (l-PP) has a porosity of ≦10% and/or a specific pore volume of ≦0.20 cm.sup.3/g.

9. Process for producing a polypropylene composition comprising a branched polypropylene (b-PP) wherein the polypropylene composition and/or the branched polypropylene (b-PP) have an ethylene content of 0.1 to 1.0 wt % have a melt flow rate MFR.sub.2 (230° C./2.16 kg) measured according to ISO 1133 of 1.0 to 5.0 g/10 min have a F30 melt strength of 30 cN to 60 cN and a v30 melt extensibility of 220 to 300 mm/s, wherein the F30 melt strength and the v30 melt extensibility are measured according to ISO 16790:2005 and wherein the branched polypropylene (b-PP) is provided by reacting a linear polypropylene (l-PP) having an ethylene content of 0.1 to 1.0 wt % and a melt flow rate MFR.sub.2 (230° C./2.16 kg) of 0.5 to 4.0 g/10 min with a thermally decomposing free radical-forming agent, preferably with a peroxide, and optionally with a bifunctionally unsaturated monomer, preferably selected from divinyl compounds, allyl compounds or dienes, and/or optionally with a multifunctionally unsaturated low molecular weight polymer, preferably having a number average molecular weight (Mn)≦10000 g/mol, synthesized from one and/or more unsaturated monomers, obtaining thereby the branched polypropylene (b-PP).

10. Process according to claim 8, wherein the ratio of the MFR.sub.2 of the polypropylene composition and/or of the branched polypropylene (b-PP) to the MFR.sub.2 of the linear polypropylene (l-PP) is from >1.25 to 6.

11. Process according to any one of claim 9 or 10, wherein the linear polypropylene (l-PP) is polymerised in the presence of a solid Ziegler-Natta catalyst which is prepared by an emulsion-solidification method or by a precipitation method.

12. Process according to claim 11, wherein the catalyst is in particulate form and is obtained by a) providing a solution of a1) at least a Group 2 metal alkoxy compound (Ax) being the reaction product of a Group 2 metal compound and an alcohol (A) comprising in addition to the hydroxyl moiety at least one ether moiety optionally in an organic liquid reaction medium; or a2) at least a Group 2 metal alkoxy compound (Ax′) being the reaction product of a Group 2 metal compound and an alcohol mixture of the alcohol (A) and a monohydric alcohol (B) of formula ROH, optionally in an organic liquid reaction medium; or a3) a mixture of a Group 2 metal alkoxy compound (Ax) and a Group 2 metal alkoxy compound (Bx) being the reaction product of a Group 2 metal compound and the monohydric alcohol (B), optionally in an organic liquid reaction medium; or a4) a Group 2 metal alkoxy compound of formula M(OR1)n(OR2)mX2-n-m or mixture of Group 2 alkoxides M(OR1)n′X2-n′ and M(OR2)m′X2-m′, where M is Group 2 metal, X is halogen, R1 and R2 are different alkyl groups of C2 to C16 carbon atoms, and 0≦n≦2, 0≦m≦2 and n+m+(2-n-m)=2, provided that both n and m≠0, 0<n′≦2 and 0<m′≦2; and b) adding said solution from step a) to at least one compound of a transition metal of Group 4 to 6 and c) obtaining the solid catalyst component particles, and adding an internal electron donor (ID) at any step prior to step c).

13. Extruded foam comprising the polypropylene composition according to any one of claims 1 to 8.

Description

EXAMPLES

[0197] 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.

1. Measuring Methods

Comonomer Content

[0198] 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 rotatory 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 was quantitatively needed for accurate ethylene content quantification. Standard single-pulse excitation was employed without Nuclear Overhauser Effect (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.

[0199] Quantitative .sup.13C {.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using 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 as described in Cheng, H. N., Macromolecules 17 (1984), 1950). With characteristic signals corresponding to 2,1 erythro regio defects observed (as described in L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 2000, 100 (4), 1253, in Cheng, H. N., Macromolecules 1984, 17, 1950, and in W-J. Wang and S. Zhu, Macromolecules 2000, 33, 1157) the correction for the influence of the regio defects on determined properties was required. Characteristic signals corresponding to other types of regio defects were not observed.

[0200] 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. 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 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(S.sub.ββ+S.sub.βγ+S.sub.βδ+0.5(S.sub.αβ+S.sub.αγ))

[0201] 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))

using the same notation as 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. The mole percent comonomer incorporation was calculated from the mole fraction:

E [mol %]=100*fE

[0202] The weight percent comonomer incorporation was calculated from the mole fraction:

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

[0203] Quantification of Microstructure by NMR Spectroscopy

[0204] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the isotacticity and regio-regularity of the propylene homopolymers.

[0205] 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.

[0206] For propylene homopolymers approximately 200 mg of material was dissolved in 1,2-tetrachloroethane-d.sub.2 (TCE-d.sub.2). 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 needed for tacticity distribution quantification (Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443; Busico, V.; Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromolecules 30 (1997) 6251). Standard single-pulse excitation was employed utilising the NOE and 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, 11289). A total of 8192 (8k) transients were acquired per spectra.

[0207] Quantitative .sup.13C {.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs.

[0208] For propylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

[0209] 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.

[0210] 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., Macromolecules 30 (1997) 6251).

[0211] 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.

[0212] 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)

[0213] 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. 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).

[0214] 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.e6+I.sub.e8)/2

[0215] 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

[0216] 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

[0217] 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)

[0218] MFR.sub.2 (230° C./2.16 kg) is measured according to ISO 1133 (230° C., 2.16 kg load)

[0219] F30 and F200 Melt Strength and v30 and v200 Melt Extensibility

[0220] The test described herein follows ISO 16790:2005. An apparatus according to FIG. 1 of ISO 16790:2005 is used.

[0221] 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 Sience, 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 Göttfert, Siemensstr. 2, 74711 Buchen, Germany) in which a melt strand is elongated by drawing down with a defined acceleration.

[0222] 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). For measuring F30 melt strength and v30 melt extensibility, the pressure at the extruder exit (=gear pump entry) is set to 30 bars by by-passing a part of the extruded polymer. For measuring F200 melt strength and v200 melt extensibility, the pressure at the extruder exit (=gear pump entry) is set to 200 bars by by-passing a part of the extruded polymer.

[0223] The gear pump was pre-adjusted to a strand extrusion rate of 5 mm/s, and the melt temperature was set to 200° C. The spinline length between die and Rheotens wheels was 80 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 drawn down is 120 mm/sec2. 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), where the polymer strand ruptures, are taken as the F30 melt strength and v30 melt extensibilty values, or the F200 melt strength and v200 melt extensibilty values, respectively.

[0224] The Xylene Soluble Fraction at Room Temperature (XS, Wt.-%):

[0225] The amount of the polymer soluble in xylene is determined at 25° C. according to ISO 16152; first edition; 2005 Jul. 1.

[0226] 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):

[0227] 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 and heat of crystallization (H.sub.c) are determined from the cooling step, while melting temperature and heat of fusion (H.sub.f) are determined from the second heating step p.

[0228] Particle Size/Particle Size Distribution

[0229] A sieve analysis according to ISO 3310 was performed on the polymer samples. The sieve analysis involved a nested column of sieves with wire mesh screen with the following sizes: >20 μm, >32 μm, >63 μm, >100 μm, >125 μm, >160 μm, >200 μm, >250 μm, >315 μm, >400 μm, >500 μm, >710 μm, >1 mm, >1.4 mm, >2 mm, >2.8 mm. The samples were poured into the top sieve which has the largest screen openings. Each lower sieve in the column has smaller openings than the one above (see sizes indicated above). At the base is the receiver. The column was placed in a mechanical shaker. The shaker shook the column. After the shaking was completed the material on each sieve was weighed. The weight of the sample of each sieve was then divided by the total weight to give a percentage retained on each sieve. The particle size distribution and the characteristic median particle size d50 as well as the top-cut particle size d95 were determined from the results of the sieve analysis according to ISO 9276-2.

[0230] Porosity and Specific Pore Volume

[0231] The porosity and the specific pore volume of the polymer are measured by mercury porosimetry according to DIN 66133 in combination with helium density measurement according to DIN 66137-2. The samples were first dried for 3 hours at 70° C. in a heating cabinet, then stored in an desiccator until the measurement. The pure density of the samples was determined on milled powder with helium at 25° C. in a Quantachrome Ultrapyknometer 1000-T (DIN 66137-2). Mercury porosimetry was performed on non-milled powder in a Quantachrome Poremaster 60-GT in line with DIN 66133.

[0232] The porosity is calculated by equation (II) like

[00006]$\begin{array}{cc}\mathrm{Porosity}\left[\%\right]=\hspace{1em}[.Math.\mathrm{specific}.Math..Math.\mathrm{pore}.Math..Math.\mathrm{volume}/\left(\mathrm{specific}.Math..Math.\mathrm{pore}.Math..Math.\mathrm{volume}+\frac{1}{\mathrm{density}}\right)]*100& \left(\mathrm{II}\right)\end{array}$

2. Examples

[0233] Polymerization of Linear Polypropylenes (l-PP)

[0234] All inventive and comparative examples (except l-PP 3) were produced in a Borstar® pilot plant with a prepolymerization reactor, one slurry loop reactor and one gas phase reactor. For the polymerization process of linear polypropylenes l-PP 1a and l-PP 1b the catalyst of the example section of WO 2010009827 A1 (see pages 30 and 31) comprising bis(2-ethylhexyl)phthalate as internal donor along with triethyl-aluminium (TEAL) as co-catalyst and dicyclo pentyl dimethoxy silane (D-donor) as external donor was used. The aluminium to donor ratio, the aluminium to titanium ratio and the polymerization conditions are indicated in Table 1

TABLE-US-00001 TABLE 1 Polymerization and polymer properties l-PP 1a l-PP1b l-PP 2a l-PP 2b l-PP 3 Polymerization Co/ED ratio mol/mol 6.5 6.5 7.5 7.5 Co/TC ratio mol/mol 110.0 110.0 120.3 120.3 Loop (Reactor 1) Time h 0.40 0.40 0.30 0.30 Temperature ° C. 75 75 75 75 MFR.sub.2 g/10 min 0.30 1.0 0.48 1.0 XCS wt.-% 3.9 3.9 2.3 2.3 C2 content wt.-% 0.2 0.2 0 0 H.sub.2/C3 ratio mol/kmol 0.20 0.50 0.31 0.60 C2/C3 ratio mol/kmol 0.5 0.5 0 0 amount wt.-% 43 43 45 45 GPR (Reactor 2) Time h 1.45 1.45 1.25 1.25 Temperature ° C. 80 80 85 85 Pressure kPa 2200 2200 2300 2300 MFR.sub.2 g/10 min 0.30 1.0 0.51 1.3 C2 content wt.-% 0.3 0.3 0 0 H.sub.2/C3 ratio mol/kmol 0.60 1.25 0.42 0.95 C2/C3 ratio mol/kmol 3.2 3.2 0 0 amount wt.-% 57 57 55 55 Catalyst kg(PP)/g(cat) 7 11 29 50 productivity Powder properties porosity % 7.5 7.5 15 15 7.7 specific pore volume cm.sup.3/g 0.09 0.09 0.24 0.24 0.10 median particle size d.sub.50 μm 650 650 1120 1120 420 top-cut particle size d.sub.95 μm 1220 1220 1730 1730 1130 Ratio d.sub.95/d.sub.50 1.88 1.88 1.54 1.54 2.69 Average Particle Size mm 0.88 1.03 2.02 2.44 0.25 Polymer properties Ethylene content wt % 0.3 0.3 0 0 0 I(E) content % n.d. n.d. n.d. n.d. n.d. XCS wt % 4.5 4.5 2.4 2.4 2.2 MFR.sub.2 g/10 min 0.3 1.0 0.3 1.3 0.6 T.sub.m (DSC) ° C. 158 158 165 165 163

[0235] For the polymerisation of linear polypropylenes l-PP 2a and l-PP 2b a trans-esterified high yield MgCl.sub.2-supported Ziegler-Natta polypropylene catalyst component comprising diethyl phthalate as internal donor was used. Triethyl-aluminium (TEAL) was used as co-catalyst and dicyclo pentyl dimethoxy silane (D-donor) was used as external donor. The catalyst component and its preparation concept are described in general for example in patent publications EP491566, EP591224 and EP586390.

[0236] Accordingly, the catalyst component is prepared as follows: First, 0.1 mol of MgCl.sub.2×3 EtOH was suspended under inert conditions in 250 ml of decane in a reactor at atmospheric pressure. The solution was cooled to −15° C. and the 300 ml of cold TiCl.sub.4 was added while maintaining the temperature at said temperature. Then, the temperature of the slurry was increased slowly to 20° C. At this temperature, 0.02 mol of dioctylphthalate (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.

[0237] For the polymerisation of linear polypropylene l-PP 3 the commercially available catalyst Lynx900, available from BASF, was used. Lynx900 is a second generation Ziegler-Natta catalyst and was used in combination with methyl methacrylate as external donor and diethyl aluminium chloride as co-catalyst. For polymerization, a Hercules-type slurry plant with 4 stirred tank reactors in series was applied, operating in n-heptane slurry at 70° C.

[0238] Additive Mixture

[0239] A linear propylene homopolymer having an MFR2 (230° C./2.16 kg) of 2.8 g/10 min. a melting Temperature of 165° C., a F30 melt strength of 4.5 cN and v30 melt extensibility of 75 mm/s was compounded with 10.0 wt % Irganox B225 FF and 2.5 wt % of Hydrotalcit in order to provide an additive masterbatch (AM) for incorporating into a base polymer of branched polypropylene.

Inventive Example IE1 and Comparative Examples CE1 to CE4

[0240] The linear polypropylenes described in Table 1 were subjected to a reactive extrusion in the presence of butadiene and peroxide as described in the following. Both the butadiene and the peroxide (amounts are indicated in table 3) were pre-mixed with the l-PP powder prior to the melt-mixing step in a horizontal mixer with paddle stirrer at a temperature of 65° C., maintaining an average residence time of 15 to 20 minutes. The pre-mixture was transferred under inert atmosphere to a co-rotating twin screw extruder of the type Theyson TSK60 having a barrel diameter of 60 mm and an L/D-ratio of 48 equipped with a high intensity mixing screw having 3 kneading zones and a two-step degassing setup. The melt temperature profile is given in table 2. The screw speed and throughput is indicated in table 3. In the first ¾ of the extruder length the branched polypropylene is produced (b-PP). Subsequently, via a side feeder, i.e. at the last ¼ of the extruder length, an additive mixture (AM) as defined above is fed into the extruder to the produced branched polypropylene (b-PP). The extruded polypropylene composition was discharged and pelletized. The final properties are indicated in table 4.

TABLE-US-00002 TABLE 2 Set temperature profile in the extruder Zone 1 to 6 7 8 and 9 10 and 11 12 13 14 Temperature [° C.] 240 230 220 230 240 230 220

TABLE-US-00003 TABLE 3 Process conditions CE 1 IE 1 CE 2 CE 3 CE 4 PP powder l-PP l-PP l-PP l-PP l-PP 3 1a 1b 2a 2b Peroxide* [wt %] 0.675 0.675 0.675 0.675 0.675 butadiene* [wt %] 1.20 2.10 1.45 1.44 2.30 screw speed [rpm] 350 350 400 350 450 throughput [kg/h] 225 225 225 225 225 additive mixture* [wt %] 2 2 2 2 2 *based on the total amount of the polypropylene composition

TABLE-US-00004 TABLE 4 LAOS- LAOS- Start-MFR End-MFR NLF NLF 230° C./ 230° C./ at at PP 2.16 kg 2.16 kg F30 v30 F200 v200 1000% 500% Example powder g/ 10 min g/10 min cN mm/s cN mm/s — — CE1 l-PP 1a 0.3 2.0 31.4 245 8.2 245 6.1 ± 0.5 6.2 ± 0.4 IE1 l-PP 1b 1.0 2.0 40.9 231 25.7 245 6.5 ± 0.1 7.6 ± 0.1 CE2 l-PP 2a 0.2 1.8 32.6 247 10.0 249 6.4 ± 0.8 6.7 ± 0.8 CE3 l-PP 2b 1.3 2.0 30.8 254 10.0 256 6.9 ± 0.6 6.8 ± 1.0 CE4 l-PP 3 0.6 2.0 39.7 239 12.7 248 6.4 ± 0.3 7.5 ± 0.5