Polypropylene composition for pipes

Abstract

The present invention relates to a polypropylene composition for pipes, characterized in that the polypropylene composition comprises a random copolymer of propylene and an α-olefin having a low melt flow rate and comonomer content, and a high polydispersity index (PI) and shear thinning index SHI(2.7 / 210), a pipe comprising the polypropylene composition in an amount of more than 90.0 wt%, and the use of the polypropylene composition as a pipe.

Description

[0001] Polypropylene Composition for Pipes The present invention relates to a polypropylene composition for pipes, characterized in that the polypropylene composition comprises a random copolymer of propylene and an α-olefin having a low melt flow rate and comonomer content, and a high polydispersity index (PI) and shear thinning index SHI(2.7 / 210), a pipe comprising the polypropylene composition in an amount of more than 90.0 wt%, and the use of the polypropylene composition as a pipe. Technical Background Polypropylene (PP) materials are frequently used due to their good cost-to- performance ratio for various pipe applications, such as fluid transport during which the fluid is pressurized and / or heated. In particular, polypropylene materials are used in applications for plumbing and heating, such as in-house hot and cold water pressure pipes and fittings, floor and wall heating systems and radiator connections. However, in order to further improve the cost-to-performance ratio of PP pipes, thereis still a need to improve the pipe material properties so that inter alia the wallthickness of the pipes can be reduced, thereby saving costs in material and reducing the related carbon footprint. Accordingly, polypropylene material suitable for pipes with a reduced wall thickness needs to show an improved resistance against pressure in order to compensate for the thinner walls. It was now surprisingly found that a pipe produced from a polypropylene composition comprising a random copolymer of propylene and an α-olefin having a low melt flow rate, low comonomer content, a polydispersity index (PI) of more than4.00 and a shear thinning index SHI(2.7 / 210) of more than 160 has a substantiallyincreased pressure resistance compared to a polypropylene composition comprising a random copolymer of propylene and an α-olefin with a polydispersity index (PI) of less than 4.00 and shear thinning index SHI(2.7 / 210)of less than 160. Definitions Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although, any methods and materials similar or equivalent to those described herein can be used in practice for testing of the present invention, the preferred materials and methods are described herein. In describing and aspecting the present invention, the following terminology will be used in accordance with the definitions set out below. For the purposes of the present invention, the term "consisting of" is considered to be a preferred embodiment of the term "comprising of". If hereinafter a group is defined to comprise at least a certain number of elements, this is also to be understood to disclose a group, which preferably consists only of these elements. Where an indefinite or definite article is used when referring to a singular noun, e.g. "a", "an" or "the", this includes a plural of that noun unless something else is specifically stated. A random copolymer of propylene and an α-olefin (RACO) is a copolymer of propylene monomer units and α-olefin comonomer units, in which the α-olefin comonomer units are distributed randomly over the polymeric chain. A polypropylene composition in the present disclosure is a composition in which the polymeric components have a combined amount of units derived from propylene of at least 50 wt%, based on the total weight of the polymeric components. Usually, a propylene polymer comprising at least two propylene polymer fractions (components), which have been produced under different polymerization conditions resulting in different (weight average) molecular weights and / or different comonomer contents for the fractions, preferably produced by polymerizing in multiple polymerization stages with different polymerization conditions, is referred to as “multimodal”. The prefix “multi” relates to the number of different polymer fractions the propylene polymer is consisting of. As an example of multimodal propylene polymer, a propylene polymer consisting of two fractions only is called “bimodal”, whereas a propylene polymer consisting of three fractions only is called “trimodal”. A unimodal propylene polymer only consists of one fraction. Thereby, the term “different” means that the propylene polymer fractions differ from each other in at least one property, preferably in the weight average molecular weight – which can also be measured in different melt flow rates of the fractions – or comonomer content or both. The regio-defects of propylene polymers can be of three different types, namely 2,1- erythro (2,1e), 2,1-threo (2,1t) and 3,1 defects. A detailed description of the structure and mechanism of formation of regio-defects in polypropylene can be found in Chemical Reviews 2000, 100(4), pages 1316 to 1327. These defects are measuredusing 13C NMR as described in more detail below.The term "2,1 regio-defects" as used in the present invention defines the sum of 2,1 erythro regio-defects and 2,1 threo regio-defects. Summary of the invention The present invention relates to a polypropylene composition for pipes, characterized in that the composition comprises -a random copolymer of propylene and an α-olefin (RACO), wherein theα-olefin is selected from a C4 to C8 α-olefin; wherein the random copolymer (RACO) -comprises units derived from the α-olefin in a total amount in the range offrom 0.5 to 5.0 mol%, preferably of from 0.5 to 2.0 mol%, determined by quantitative 13C NMR spectroscopy;- has a polydispersity index (PI), determined by dynamic shearmeasurements at 200 °C, of more than 4.00, preferably in the range of from 4.10 to 8.00, more preferably from 4.20 to 6.00; -has a melt flow rate (MFR2), determined according to ISO 1133 at 230 °Cat a load of 2.16 kg, in the range of from 0.1 to 1.0 g / 10 min; and -has a shear thinning index, SHI(2.7 / 210), determined according to ISO 6721-1 at 200 °C, of more than 160, preferably in the range of from 200 to 400, more preferably of from 230 to 290. Further, the present invention relates to a pipe comprising the polypropylene composition as described above or below in an amount of more than 90.0 wt%. Still further, the present invention relates to a use of the polypropylene composition as described above or below as a pipe. Detailed Description Polypropylene composition for pipes The inventive polypropylene composition for pipes comprises -a random copolymer of propylene and an α-olefin (RACO), wherein theα-olefin is selected from a C4 to C8 α-olefin; wherein the random copolymer (RACO) -comprises units derived from the α-olefin in a total amount in the range offrom 0.5 to 5.0 mol%, preferably of from 0.5 to 2.0 mol%, determined by quantitative 13C NMR spectroscopy;- has a polydispersity index (PI), determined by dynamic shearmeasurements at 200 °C, of more than 4.00, preferably in the range of from 4.10 to 8.00, more preferably from 4.20 to 6.00; -has a melt flow rate (MFR2), determined according to ISO 1133 at 230 °Cat a load of 2.16 kg, in the range of from 0.1 to 1.0 g / 10 min; and- has a shear thinning index, SHI(2.7 / 210), determined according to ISO 6721-1 at 200 °C, of more than 160, preferably in the range of from 200 to 400, more preferably of from 230 to 290. It is preferred that the main component of the polypropylene composition is the random copolymer of propylene and an α-olefin (RACO). Accordingly, it is preferred that the composition comprises the random copolymer of propylene and an α-olefin (RACO) in an amount of more than 90 wt%, more preferably in the range of from 95.0 wt% to 99.9 wt%, yet more preferably of from 98.0 wt% to 99.9 wt%, based on the total weight of the composition. The polypropylene composition preferably has a melt flow rate (MFR2), determined according to ISO 1133 at 230 °C at a load of 2.16 kg, in the range of from 0.1 to 1.0 g / 10 min, more preferably 0.2 to 0.5 g / 10 min. The melt flow rate (MFR5), determined according to ISO 1133 at 230 °C at a load of 5 kg, of the polypropylene composition is preferably in the range of from 1.1 to 2.0 g / 10 min, more preferably 1.3 to 1.9 g / 10 min. The polypropylene composition preferably has a xylene cold soluble content (XCS), as determined according to ISO 16152, in the range of from 1.5 to 6.0 wt%, more preferably in the range of from 2.0 to 5.0 wt%. Although the polypropylene composition can have a considerably high xylene cold soluble content (XCS), it is preferred that the polypropylene composition is monophasic. Accordingly, it is preferred that the polypropylene composition does not comprise a matrix phase and a dispersed phase. Further, it is preferred that the polypropylene composition has a Flexural modulus, determined according to ISO 178 method A (3-point bending test) on 80 × 10 × 4 mm³ specimens, in the range of 800 to 2000 MPa, more preferably 1000 to 1300 MPa. The notched Charpy impact strength (NIS) at 23 °C, determined according to ISO 179-1 / 1eA on notched 80 × 10 × 4 mm³ specimens (specimens were prepared according to EN ISO 1873-2 ), of the polypropylene composition is preferably more than 4 kJ / m2, more preferably in the range of from 5 to 10 kJ / m2. It is preferred that the inventive polypropylene composition does not comprise further polymeric components besides the random copolymer of propylene and an α- olefin (RACO). Thus, the polypropylene composition preferably consists of the random copolymer of propylene and an α-olefin (RACO) in an amount in the range of from 98.0 wt% to 99.9 wt% and additives in an amount in the range of from 0.1 to 2.0 wt%, wherein the amounts are based on the total weight of the composition. Suitable additives are known in the state of the art. Typically, such additives are commercially available and for example described in “Plastic Additives Handbook”, 6th edition 2009 of Hans Zweifel (pages 1141 to 1190). In the following, the random copolymer of propylene and an α-olefin (RACO) is described in more detail. Random copolymer of propylene and an α-olefin (RACO) The random copolymer of propylene and an α-olefin (RACO) of the inventive polypropylene composition comprises units derived from the α-olefin in a total amount in the range of from 0.5 to 5.0 mol%, preferably of from 0.5 to 2.0 mol%,determined by quantitative 13C NMR spectroscopy. The α-olefin of the random copolymer of propylene and an α-olefin (RACO) is selected from a C4 to C8 α-olefin. Preferably, the α-olefin is selected from 1-butene or 1-hexene. More preferably, the α-olefin is 1-hexene. Further, the random copolymer of propylene and an α-olefin (RACO) has a polydispersity index (PI), determined by dynamic shear measurements at 200 °C, of more than 4.00, preferably in the range of from 4.10 to 8.00, more preferably from 4.20 to 6.00. The melt flow rate (MFR2), determined according to ISO 1133 at 230 °C at a load of 2.16 kg, of the random copolymer of propylene and an α-olefin (RACO) is in the range of from 0.1 to 1.0 g / 10 min.The random copolymer of propylene and an α-olefin (RACO) has a shear thinningindex, SHI(2.7 / 210), determined according to ISO 6721-1 at 200 °C, of more than 160, preferably in the range of from 200 to 400, more preferably of from 230 to 290. The random copolymer of propylene and an α-olefin (RACO) is preferably monophasic. It is preferred that the random copolymer of propylene and an α-olefin (RACO) is polymerized in the presence of a Ziegler-Natta-catalyst system. Accordingly, the random copolymer of propylene and an α-olefin (RACO)preferably has a content of 2,1-regio-defects, as determined by quantitative 13C-NMRspectroscopy, of less than 0.40 mol%, preferably less than 0.05 mol%, more preferably of 0.0 mol%. In a preferred embodiment, the random copolymer of propylene and an α-olefin (RACO) is polymerized in the presence of a bicomponent Ziegler-Natta-catalyst system including a first Ziegler Natta catalyst component (ZN1) and a second Ziegler Natta catalyst component (ZN2), wherein at least the internal donors of the first and second Ziegler Natta catalyst components differ structurally. It is further preferred that each of the first and second Ziegler Natta catalyst components comprises compounds of a transition metal of Group 4 to 6 of IUPAC, like titanium, a Group 2 metal compound, like a magnesium, and an internal donor being a non-phthalic compound. Preferably the first Ziegler Natta catalyst component (ZN1) comprises an internal donor selected from the group of maleates, citraconates, cyclohexene-1,2- dicarboxylates and any derivatives and / or mixtures thereof. More preferably, the first Ziegler Natta catalyst component (ZN1) comprises a citraconate as an internal donor. Suitable Ziegler Natta catalyst for the first Ziegler Natta catalyst component (ZN1) are described for example in WO 2016 / 066446 A1. Preferably the second Ziegler Natta catalyst component (ZN2) is a >4thgeneration, high yield Ziegler Natta catalyst. It is preferred that the second Ziegler Natta catalyst component (ZN2) is a solid catalyst with an external support material, like silica or MgCl2, preferably MgCl2. The bicomponent Ziegler-Natta-catalyst can thereby be obtained by mixing the first Ziegler Natta catalyst component (ZN1) and the second Ziegler Natta catalyst component (ZN2) before introducing it into the polymerization reactor. It is preferred that the random copolymer of propylene and an α-olefin (RACO) is a multimodal random copolymer of propylene and an α-olefin (RACO) in view of the α-olefin content and comprises at least two random copolymer of propylene and an α-olefin fractions (RACO-F1) and (RACO-F2), wherein the combined amount of the two random copolymer of propylene and an α-olefin fractions (RACO-F1) and (RACO-F2) is at least 90 wt%, preferably in the range of 95 to 100 wt%, based on the total weight of the random copolymer of propylene and an α-olefin (RACO). Accordingly, it is preferred, that the multimodal RACO is a bimodal RACO, i.e. consists of the two random copolymer of propylene and an α-olefin fractions (RACO-F1) and (RACO-F2). In the case that the random copolymer of propylene and an α-olefin (RACO) is a multimodal random copolymer of propylene and an α-olefin (RACO), the α-olefin content of the first random copolymer of propylene and an α-olefin fraction (RACO- F1) is in the range of 0.1 to 1.0 mol%, more preferably in the range of 0.4 to 0.8 mol%, and the α-olefin content of the second random copolymer of propylene and an α-olefin fraction (RACO-F2) is in the range of 0.8 to 2.0 mol%, more preferably in the range of 1.2 to 1.8 mol%. Preferably, the α-olefin content of the first random copolymer of propylene and an α-olefin fraction (RACO-F1) is lower than the α- olefin content of the second random copolymer of propylene and an α-olefin fraction (RACO-F2), and more preferably the α-olefin content of the first random copolymer of propylene and an α-olefin fraction (RACO-F1) is at least 0.2 mol%, even more preferably 0.3 to 1.0 mol%, lower than the α-olefin content of the second random copolymer of propylene and an α-olefin fraction (RACO-F2). The weight ratio between the first random copolymer of propylene and an α-olefin fraction (RACO-F1) and the second random copolymer of propylene and an α-olefin fraction (RACO-F2) is preferably in the range of 40:60 to 60:40. Besides the multimodality in view of the α-olefin content, the random copolymer of propylene and an α-olefin (RACO) can also be multimodal in view of the melt flow rate MFR2of the fractions. Accordingly, it is preferred that the MFR2of the first random copolymer of propylene and an α-olefin fraction (RACO-F1) is in the range of 0.3 to 1.0 g / 10 min, more preferably in the range of 0.4 to 0.8 g / 10 min, and the MFR2 of the second random copolymer of propylene and an α-olefin fraction (RACO-F2) is in the range of 0.1 to 0.5 g / 10 min, more preferably in the range of 0.1 to 0.3 g / 10 min. Preferably, the MFR2 of the first random copolymer of propylene and an α-olefin fraction (RACO-F1) is higher than the MFR2of the second random copolymer of propylene and an α-olefin fraction (RACO-F2), and more preferably the MFR2content of the first random copolymer of propylene and an α-olefin fraction (RACO- F1) is at least 0.1 g / 10 min, even more preferably 0.2 to 0.5 g / 10 min, higher than the MFR2of the second random copolymer of propylene and an α-olefin fraction (RACO-F2). A preferred way of achieving multimodality is by polymerizing the respective polymer in a multistage polymerization process. Thus, the random copolymer of propylene and an α-olefin (RACO) is preferably polymerized in a multistage process, which is a sequential polymerization process with at least two polymerization reactors connected in series. In a particularly preferred embodiment, a first polymer fraction of the random copolymer of propylene and an α-olefin (RACO-F1) is produced in a slurry phase reactor and subsequently a second polymer fraction of the random copolymer of propylene and an α-olefin (RACO-F2) is produced in a gas phase reactor. A preferred multistage process is a “loop-gas phase”-process, as developed by Borealis (known as BORSTAR®technology) and is described e.g. in patent literature, such as in EP 0887379, WO 92 / 12182 WO 2004 / 000899, WO 2004 / 111095, WO 99 / 24478, WO 99 / 24479 or in WO 00 / 68315. A further suitable slurry-gas phase process is the Spheripol®process of LyondellBasell Industries. In a preferred embodiment, the random copolymer of propylene and an α-olefin (RACO) is obtainable, preferably obtained by the process comprising the steps ofa) randomly polymerizing propylene and an α-olefin in the presence of abicomponent Ziegler-Natta catalyst system in a first polymerization reactor for producing a first random copolymer of propylene and an α-olefin fraction (RACO-F1);b) transferring a polymerization mixture comprising the bicomponent Ziegler-Nattacatalyst system and the first random copolymer of propylene and an α-olefin fraction (RACO-F1) from the first polymerization reactor to a second polymerization reactor;c) polymerizing propylene and the same α-olefin as in the first polymerizationreactor in the presence of the bicomponent Ziegler-Natta catalyst system in the second polymerization reactor for producing a second random copolymer of propylene and an α-olefin fraction (RACO-F2);d) obtaining a random copolymer of propylene and an α-olefin (RACO) comprisingthe first and second random copolymer of propylene and an α-olefin fractions (RACO-F1 and RACO-F2). The first polymerization reactor preferably is a slurry phase reactor, such as a loop reactor. The second polymerization reactor preferably is a gas phase reactor, such as a fluidized bed gas phase reactor. The preparation of the first and second polymer fractions can comprise in addition to the (main) polymerization stages in the at least two polymerization reactors prior thereto a pre-polymerization in a pre-polymerization reactor upstream to the first polymerization reactor. In the pre-polymerization reactor, a polypropylene is produced. The pre- polymerization is preferably conducted in the presence of the bicomponent Ziegler- Natta catalyst system. According to this embodiment, the bicomponent Ziegler-Natta catalyst system is introduced to the pre-polymerization step. However, this shall not exclude the option that at a later stage for instance further co-catalyst is added in the polymerization process, for instance in the first reactor. In one embodiment, all components of the bicomponent Ziegler-Natta catalyst system are only added in the pre-polymerization reactor, if a pre-polymerization is applied. The pre-polymerization reaction is typically conducted at a temperature of 0 to 60 °C, preferably from 10 to 40 °C, and more preferably from 12 to 30 °C. In a preferred embodiment, the pre-polymerization is conducted as bulk slurry polymerization in liquid propylene, i.e. the liquid phase mainly comprises propylene, optionally with inert components dissolved therein. It is possible to add other components also to the pre-polymerization stage. Thus, hydrogen may be added into the pre-polymerization stage to control the molecular weight of the polypropylene as is known in the art. Further, antistatic additives may be used to prevent the particles from adhering to each other or to the walls of the reactor. The precise control of the pre-polymerization conditions and reaction parameters is within the skill of the art. Due to the above defined process conditions in the pre-polymerization, preferably a mixture of the bicomponent Ziegler-Natta catalyst system and the polypropylene produced in the pre-polymerization reactor is obtained. Preferably, the bicomponent Ziegler-Natta catalyst system is (finely) dispersed in the polypropylene. In other words, the bicomponent Ziegler-Natta catalyst system introduced in the pre- polymerization reactor is split into smaller fragments that are evenly distributed within the growing polypropylene. The sizes of the introduced bicomponent Ziegler- Natta catalyst system as well as of the obtained fragments are not of essential relevance for the instant invention and within the skilled knowledge. As mentioned above, if a pre-polymerization is used, subsequent to said pre- polymerization, the mixture of the bicomponent Ziegler-Natta catalyst system and the polypropylene produced in the pre-polymerization reactor is transferred to the first polymerization reactor. Typically, the total amount of polypropylene produced in the pre-polymerization reactor is rather low and typically not more than 1.0 wt%, more preferably in the range from 0.1 to 1.0 wt%, based on the total combined weight of the polymer fractions. The amount of the polypropylene produced in the pre-polymerization reactor, if present, is generally added to the amount of the first polymer fraction produced in the first polymerization reactor. In case that pre-polymerization is not used, propylene and the other ingredients such as the bicomponent Ziegler-Natta catalyst system can be directly introduced into the first polymerization reactor. The residence times of the polymerization mixtures in the different polymerization stages are adjusted to obtain the amounts of the first and second polymer fractions in the combined first and second polymer fractions. Preferably the first polymer fraction (RACO-F1) is present in an amount of from 45 to 65 wt%, more preferably from 52 to 60 wt%, based on the total weight of the random copolymer of propylene and an α-olefin (RACO). Preferably the second polymer fraction (RACO-F2) is present in an amount of from 35 to 55 wt%, more preferably from 40 to 48 wt%, based on the total weight of the random copolymer of propylene and an α-olefin (RACO). Pipe and Use The invention further relates to a pipe comprising the polypropylene composition as described above or below in an amount of more than 90.0 wt%, preferably consisting of the polypropylene composition as described above or below, wherein the pipe is preferably for use in hot and / or cold water applications, more preferably is a pressure pipe for use in hot and / or cold water applications. The pipe preferably has a time to failure in a pipe pressure test according to ISO 1167-1 and-2 on pipes having a diameter of 32 mm and a wall thickness of 3 mm at a hoop stress of 16 MPa at a temperature of 20 °C of at least 4000 h, more preferably of at least 5000 h, yet more preferably of at least 6000 h. Further, the pipe preferably has a time to failure in a pipe pressure test according to ISO 1167-1 and-2 on pipes having a diameter of 32 mm and a wall thickness of 3 mm at a hoop stress of 4.1 MPa at a temperature of 95 °C of at least 4000 h, more preferably of at least 5000 h, yet more preferably of at least 6000 h. Further, the invention also relates to the use of the polypropylene composition as described above as a pipe, preferably as a pressure pipe for hot and / or cold water applications. All aspects the polypropylene composition described above or below also apply to the pipe and the use of the invention. Examples1. Determination methodsThe 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. Quantification of microstructure by NMR spectroscopy Isotacticity and regio-regularity of the polymers Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the isotacticity and regio-regularity of the polymers.Quantitative 13C{1H} NMR spectra were recorded in the solution-state using aBruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for1H and 13C respectively. All spectra were recorded using a 13C optimised 10 mmextended temperature probehead at 125°C using nitrogen gas for all pneumatics.For polymers approximately 200 mg of material was dissolved in 1,2-tetrachloroethane-d2(TCE-d2). 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.Quantitative 13C{1H} NMR spectra were processed, integrated and relevantquantitative properties determined from the integrals using proprietary computer programs. For propylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm. 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. 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). 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. 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) 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). 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: P21e= (Ie6+ Ie8) / 2 The amount of 1,2 primary inserted propylene 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: P12= ICH3+ P12eThe total amount of propylene was quantified as the sum of primary inserted propylene and all other present regio-defects: Ptotal = P12 + P21e The mole percent of 2,1 erythro regio-defects was quantified with respect to all propylene: [21e] mol% = 100 * (P21e / Ptotal) Comonomer content (propylene-hexene copolymer) Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers.Quantitative 13C{1H} NMR spectra recorded in the molten-state using a BrukerAvance NEO 500 NMR spectrometer operating at 500.13 and 125.76 MHz for 1Hand 13C respectively. All spectra were recorded using a 13C optimised 7 mm magic-angle spinning (MAS) probehead at 180°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.{klimke06,parkinson07, castignolles09} Standard single-pulse excitation was employed utilising the NOE at short recycle delays of 3s {pollard04, klimke06} and the RS- HEPT decoupling scheme{fillip05,griffin07}. A total of 1024 (1k) transients were acquired per spectra.Quantitative 13C{1H} NMR spectra were processed, integrated and relevantquantitative properties determined from the integrals. All chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm. The amount of primary (1,2) inserted propene was quantified based on the propene methylene sites between 48.1 and 45.0 ppm (ICH2) with correction for any included sites not related to primary insertion: P12 = ICH2 + H Ptotal = P12Characteristic signals corresponding to the incorporation of 1-hexene were observed and the comonomer fraction calculated as the fraction of 1-hexene in the polymer with respect to all monomer in the polymer: fHtotal = Htotal / (Ptotal + Htotal) The amount isolated 1-hexene incorporated in PPHPP sequences was quantifiedusing the integral of the ^B4 sites at 44.2 ppm accounting for the number ofreporting sites per comonomer: H = I^B4 / 2 With no sites indicative of consecutive incorporation observed the total 1-hexen comonomer content was calculated solely on this quantity: Htotal = H The mole percent comonomer incorporation is calculated from the mole fraction: H [mol%] = 100 * fHtotal The weight percent comonomer incorporation is calculated from the mole fraction: H [wt%] = 100 * ( fHtotal * 84.16 ) / ( (fHtotal * 84.16) + ((1-fHtotal)) * 42.08) ) References: klimke06: Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys.2006;207:382. parkinson07: Parkinson, M., Klimke, K., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys.2007;208:2128. pollard04: Pollard, M., Klimke, K., Graf, R., Spiess, H.W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004;37:813. filip05: Filip, X., Tripon, C., Filip, C., J. Mag. Resn.2005, 176, 239 griffin07: Griffin, J.M., Tripon, C., Samoson, A., Filip, C., and Brown, S.P., Mag. Res. in Chem.200745, S1, S198 castignolles09: Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373Calculation of α-olefin (C4-8) comonomer content of the second random copolymerof propylene and an α-olefin fraction (RACO-F2):^^4−8( ^^^^^^^^) − ^^(^^^^^^^^ − ^^1) × ^^4−8(^^^^^^^^ − ^^1)^^ =(^^^^^^^^ − ^^2) ^^4−8(^^^^^^^^ − ^^2)wherein w(RACO-F1) is the weight fraction [split wt%] of the first random copolymer of propylene and an α-olefin fraction (RACO-F1), w(RACO-F2) is the weight fraction [split wt%] of second random copolymer of propylene and an α-olefin fraction (RACO-F2),C4-8(RACO-F1) is the comonomer content [in wt%] of the first randomcopolymer of propylene and an α-olefin fraction (RACO-F1), C4-8(RACO) is the comonomer content [in wt%] of the random copolymer of propylene and an α-olefin (RACO),C4-8(RACO-F2) is the calculated comonomer content [in wt%] of the secondrandom copolymer of propylene and an α-olefin fraction (RACO-F2). The α-olefin (C4-8) comonomer content in mol% can be obtained analogously. Melt Flow Rate The melt flow rate (MFR) was 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 MFR2of polypropylene is determined at a temperature of 230 °C and a load of 2.16 kg, and MFR5of polypropylene is determined at a temperature of 230 °C and a load of 5.0 kg.Calculation of the MFR2 of the second random copolymer of propylene and an α-olefin fraction (RACO-F2): log( ^^^^^^2 (^^^^^^^^) )− ^^(^^^^^^^^−^^1) × log( ^^^^^^2(^^^^^^^^−^^1) )10^^(^^^^^^^^−^^2) = ^^^^^^2( RACO− F2)w(RACO-F1) is the weight fraction [split wt%] of the first random copolymer of propylene and an α-olefin fraction (RACO-F1), w(RACO-F2) is the weight fraction [split wt%] of second random propylene- ethylene random copolymer fraction (RACO-F2), MFR2(RACO-F1) is the MFR2 [in g / 10 min] of the first random copolymer of propylene and an α-olefin fraction (RACO-F1), MFR2(RACO) is the MFR2 [in g / 10 min] of the random copolymer of propylene and an α-olefin (RACO), MFR2(RACO-F2) is the calculated MFR2 [in g / 10 min] of the second propylene- ethylene random copolymer fraction (RACO-F2). Xylene Solubles (XCS) The xylene soluble (XCS) content as defined and described in the present invention was determined in line with ISO 16152 as follows: 2.0 g of the polymer were dissolved in 250 ml p-xylene at 135 °C under agitation. After 30 minutes, the solution was allowed to cool for 15 minutes at ambient temperature and then allowed to settle for 30 minutes at 25 + / - 0.5 °C. The solution was filtered with filter paper into two 100 ml flasks. The solution from the first 100 ml vessel was evaporated in nitrogen flow and the residue dried under vacuum at 90 °C until constant weight is reached. The xylene soluble fraction (percent) can then be determined as follows: XS [%] = (100^m^V0) / (m0^V); m0 = initial polymer amount [g]; m = weight of residue [g]; V0= initial volume [ml]; V = volume of analysed sample [ml]. Flexural modulus The flexural modulus was determined according to ISO 178. The test specimens have a dimension of 80 x 10 x 4.0 mm³ (length x width x thickness) and were prepared by injection molding according to EN ISO 1873-2. The length of the span between the supports was 64 mm, the test speed 2 mm / min. Notched impact strength (NIS) The Charpy notched impact strength (NIS) was measured according to ISO 1791eA at +23 °C, using injection moulded bar test specimens of 80 x 10 x 4 mm3prepared in accordance with EN ISO 1873-2. Rheological parameters The characterization of polymer melts by dynamic shear measurements complies with ISO standards 6721-1 and 6721-10. The measurements were performed on a rotational rheometer MCR501 from Anton Paar, equipped with a 25 mm parallel plate geometry. Measurements were undertaken on compression moulded plates using nitrogen atmosphere and setting a strain within the linear viscoelastic regime. The oscillatory shear tests were done at 200 °C applying a frequency range between 0.01 and 628 rad / s and setting a gap of 1.3 mm. 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 byγ(t) = γ0 sin(ωt)If the applied strain is within the linear viscoelastic regime, the resulting sinusoidal stress response can be given by σ(t) = σ0 sin(ωt +δ) (2)where σ0, and γ0 are the stress and strain amplitudes, respectively; ω is the angularfrequency; δ is the phase shift (loss angle between applied strain and stress response); t is the time. 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: G' =^^0^^0 cosδ [Pa] (3)G'' =^^0^^0 sinδ [Pa] (4)G* = G‘ + iG‘‘ [Pa] (5) ′η'' = ^^^^ [Pa·s] (8)The determination of so-called Shear Thinning Index (SHI), which correlates withMWD and is independent of Mw, is done as described in equation 9. The SHI(2.7 / 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. The values of storage modulus (G'), loss modulus (G"), complex modulus (G*) and complex viscosity (η*) were obtained as a function of frequency (ω). Thereby, e.g. η*300rad / s (eta*300rad / s) is used as abbreviation for the complex viscosity at the frequency of 300 rad / s and η*0.05rad / s (eta*0.05rad / s) is used as abbreviation for the complex viscosity at the frequency of 0.05 rad / s. 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. tan0.05is used as abbreviation for the ratio of the loss modulus (G") and the storage modulus (G') at 0.05 rad / s and tan300 is used as abbreviation for the ratio of the loss modulus (G") and the storage modulus (G') at 300 rad / s. The elasticity balance tan0.05 / tan300is defined as the ratio of the loss tangent tan0.05and the loss tangent tan300.The polydispersity index, PI, is defined by equation 11. where ωCOP is the cross-over angular frequency, determined as the angular frequency for which the storage modulus, G', equals the loss modulus, G". 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), theoption from Rheoplus "Interpolate y-values to x-values from parameter" and the"logarithmic interpolation type" were applied. References: [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. [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. [3] “Definition of terms relating to the non-ultimate mechanical properties of polymers”, Pure & Appl. Chem., Vol.70, No.3, pp.701-754, 1998. Pipe pressure test The pressure test performance of pipes produced from the inventive composition and the comparative composition was tested in accordance with ISO 1167-1 and-2. The pipes having a diameter of 32 mm and a wall thickness of 3 mm were produced in accordance with ISO 1167-2 on a conventional pipe extrusion line, then subjected to a circumferential (hoop) stress of 16 MPa or 4.1 MPa at a temperature of 20°C or 95 °C, respectively, in a water-in-water setup in accordance with ISO 1167-1. The time in hours to failure was registered.

[0002] 2. ExperimentalThe polymerization of the random C3C6 copolymers was carried out in pilot scale. A Borstar® loop – gas phase reactor set up was used. A bicomponent Ziegler-Natta catalyst system was used for the polymerization of the inventive C3C6random copolymer (RACO1). The bicomponent Ziegler-Natta catalyst system was a 1:1 (w / w) mixture of two Ziegler-Natta-catalyst systems ZN1 and ZN2 having structurally different internal donors. The used bicomponent Ziegler-Natta catalyst mixture was obtained as described below: 0.5 kg of ZN2 were weighted into a catalyst preparation vessel under the protection of N2. Then 2 kg of white oil (Finavestan A 360 B, CAS-Nr.8042-47-5, supplied by Totalenergies) were add into the vessel. This vessel was tumbled at room temperature about 8 h to form homogeneous mixture. The final mixture had 20 wt% of ZN2 in the white oil. A similar process was applied to ZN1 to form the same mixture with 20 wt% of ZN1. These two mixtures were transferred to the same vessel in a 1:1 weight ratio and tumbled at room temperature for 2 h, thereby obtaining a homogeneous mixture. The obtained 1:1 mixture was used for further polymerization. All the preparations were done under N2protection. As the Ziegler-Natta catalyst system for the comparative C3C6random copolymer (RACO2), the Ziegler-Natta-catalyst system ZN2 was used. ZN1: Non-phthalate based Ziegler-Natta catalyst used in the inventive examples of WO 2016 / 066446 A1 and having citraconate as the internal donor. ZN2: Ziegler-Natta-catalyst ZN180-2M, commercially available from LyondellBasell Industries. As a cocatalyst, triethyl-aluminium (TEAL) was used for both RACO1 and RACO2. The Ziegler-Natta catalyst system was introduced in the pre-polymerization reactor. The polymerization conditions for the RACOs 1 and 2 are shown in table 1 below. Table 1: Polymerization conditions for the RACOs 1 and 2. RACO1 RACO2PrepolymerizationTemp. (°C) 20.0 20.0Catalyst feeding (g / h) 1.4 1.0TEAL feed (g / t C3) 150 150Donor D (g / t C3) 40 40H2 (g / h) 0.8 0.8Loop reactor (RACO-F1)Temp. (°C) 70.0 67.0Press. (kPa) 5435.7 5455.0Feed H2 / C3 ratio (mol / kmol) 0.24 0.26Feed C6 / C3 ratio (mol / kmol) 65.9 67.8Polymer Split (wt%) 56.5 60.3MFR2 (g / 10 min) 0.49 0.55Total C6 (wt%) 1.2 1.2Total C6 (mol%) 0.6 0.6Gas phase reactor (RACO-F2)Temp. (°C) 80.0 80.0Press. (kPa) 2200 2200H2 / C3 ratio (mol / kmol) 0.67 0.84C6 / C3 ratio (mol / kmol) 39.3 40.2calc. MFR2 made in GPR (g / 10 min) 0.22 0.10calc. C6 made in GPR (wt%) 2.79 2.79calc. C6 made in GPR (mol%) 1.41 1.41Polymer Split (wt%) 43.5 39.7Total MFR2 (g / 10 min) 0.33 0.282,1 regio-defects (mol%) 0.0 0.0Total C6 (wt%) 1.89 1.83Total C6 (mol%) 0.96 0.92 The obtained RACOs 1 and 2 were compounded in amounts as shown in table 2 with the following additives: -KINOX-30G (1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl- 4-hydroxybenzyl)benzene, commercially available from HPL Additives Limited; CAS-no.1709-70-2), -Irganox 1010 (pentaerythrityl-tetrakis(3-(3’,5’-di-tert. butyl-4-hydroxyphenyl)-propionate, available from BASF AG, Germany; CAS- no.6683-19-8), -Irgafos 168 (tris (2,4-di-t-butylphenyl) phosphite, available from BASFAG, Germany; CAS-no.31570-04-4), and -Calcium stearate (CAS-no.1592-23-0, commercially available from Faci,Italy).

[0003] Table 2: Ingredients and properties of the compositions. Composition IE CERACO1 wt% 99.35RACO2 99.35KINOX-30G wt% 0.24 0.24I1010 wt% 0.24 0.24I168 wt% 0.1 0.1CaSt wt% 0.07 0.07Properties C6 wt% 1.89 1.83C6 mol% 0.96 0.92MFR2 g / 10min 0.33 0.28MFR5 g / 10min 1.58 1.24PI 4.61 3.98SHI (2.7 / 210) 261.1 140.2FM MPa 1162.0 1180.0NIS kJ / m2 6.4 6.3XCS wt% 3.4 3.6As can be seen in Table 2, the shear thinning index, SHI(2.7 / 210) of the inventivepolypropylene composition (IE) comprising the RACO1 produced with the catalyst mixture of two structurally different Ziegler-Natta catalyst systems is increased by more than 120 compared to the comparative polypropylene composition (CE) comprising the RACO2. Also, the polydispersity index (PI) is increased, while the melt flow rate (MFR2), comonomer content (C6) and mechanical properties, specifically Flexural modulus (FM) and notched Charpy impact strength (NIS), remain similar. From the inventive and the comparative compositions IE and CE, respectively, the inventive pipe IP and the comparative pipe CP were produced on a Battenfeld Pro pipe extrusion line having a diameter of 32 mm and a wall thickness of 3 mm. The typical conditions are following: Melt temperature: 224 °C Output: 30 kg / h Screw speed: 38 rpm Cooling water temperature: 20 °C Vacuum spray tank: 0.23 bar Water flow in calibrator inlet: 4 l / h. The pipes had the following times to failure in a pipe pressure test. Table 3: Pipe properties of the inventive and comparative compositions. Pipe pressure test IP CP20 °C / 16 MPa time to failure [h] >8000 3703type of failure other95 °C / 4.1 MPa time to failure [h] >8000 3835type of failure DuctileAs can be seen, a pipe produced from a C3C6 RACO having a higher SHI and PI has a substantially increased pressure resistance compared to a C3C6RACO having similar melt flow rates and comonomer content, but lower SHI and PI.

Claims

Claims1. A polypropylene composition for pipes, characterized in that the compositioncomprises -a random copolymer of propylene and an α-olefin (RACO), wherein theα-olefin is selected from a C4 to C8 α-olefin; wherein the random copolymer (RACO) -comprises units derived from the α-olefin in a total amount in the range offrom 0.5 to 5.0 mol%, preferably of from 0.5 to 2.0 mol%, determined by quantitative 13C-NMR spectroscopy;- has a polydispersity index (PI), determined by dynamic shearmeasurements at 200 °C, of more than 4.00, preferably in the range of from 4.10 to 8.00, more preferably from 4.20 to 6.00; -has a melt flow rate (MFR2), determined according to ISO 1133 at 230 °Cat a load of 2.16 kg, in the range of from 0.1 to 1.0 g / 10 min; and -has a shear thinning index, SHI(2.7 / 210), determined according to ISO 6721-1 at 200 °C, of more than 160, preferably in the range of from 200 to 400, more preferably of from 230 to 290.

2. The polypropylene composition of claim 1, characterized in that thecomposition comprises the random copolymer of propylene and an α-olefin (RACO) in an amount of more than 90 wt%, preferably in the range of from 95.0 wt% to 99.9 wt%, more preferably of from 98.0 wt% to 99.9 wt%, based on the total weight of the composition.

3. The polypropylene composition of claim 1 or 2, characterized in that therandom copolymer of propylene and an α-olefin (RACO) has a content of 2,1-regio-defects, as determined by quantitative 13C-NMR spectroscopy, of less than 0.40 mol%, preferably less than 0.05 mol%, more preferably of 0.0 mol%.

4. The polypropylene composition of anyone of claims 1 to 3, characterized inthat the random copolymer of propylene and an α-olefin (RACO) is monophasic.

5. The polypropylene composition of anyone of claims 1 to 4, characterized inthat the α-olefin of the random copolymer (RACO) is 1-butene or 1-hexene, preferably is 1-hexene.

6. The polypropylene composition of anyone of claims 1 to 5, characterized inthat the random copolymer of propylene and an α-olefin (RACO) is a multimodal, preferably bimodal random copolymer of propylene and an α- olefin (RACO) in view of the α-olefin content and comprises at least two, preferably two random copolymer of propylene and an α-olefin fractions (RACO-F1) and (RACO-F2), wherein -the combined amount of the two random copolymer of propylene and anα-olefin fractions (RACO-F1) and (RACO-F2) is at least 90 wt%, preferably in the range of 95 to 100 wt%, based on the total weight of the random copolymer of propylene and an α-olefin (RACO), -the α-olefin content of the first random copolymer of propylene and an α-olefin fraction (RACO-F1) is in the range of 0.1 to 1.0 mol%, preferably in the range of 0.4 to 0.8 mol%, -the α-olefin content of the second random copolymer of propylene and anα-olefin fraction (RACO-F2) is in the range of 0.8 to 2.0 mol%, preferably in the range of 1.2 to 1.8 mol%, and -the α-olefin content of the first random copolymer of propylene and an α-olefin fraction (RACO-F1) is at least 0.2 mol%, preferably 0.3 to 1.0 mol%, lower than the α-olefin content of the second random copolymer of propylene and an α-olefin fraction (RACO-F2).

7. The polypropylene composition of anyone of claims 1 to 6, characterized inthat the composition has a melt flow rate (MFR2), determined according to ISO 1133 at 230 °C at a load of 2.16 kg, in the range of from 0.1 to 1.0 g / 10 min, preferably 0.2 to 0.5 g / 10 min.

8. The polypropylene composition of anyone of claims 1 to 7, characterized inthat the composition has a melt flow rate (MFR5), determined according to ISO 1133 at 230 °C at a load of 5 kg, in the range of from 1.1 to 2.0 g / 10 min, preferably 1.3 to 1.9 g / 10 min.

9. The polypropylene composition of anyone of claims 1 to 8, characterized inthat the composition has a xylene cold soluble content (XCS), as determined according to ISO 16152, in the range of from 1.5 to 6.0 wt%, preferably in the range of from 2.0 to 5.0 wt%.

10. The polypropylene composition of anyone of claims 1 to 9, characterized in that the composition has a Flexural modulus, determined according to ISO 178 method A (3-point bending test) on 80 × 10 × 4 mm³ specimens, in the range of 800 to 2000 MPa, preferably in the range of 1000 to 1300 MPa.

11. The polypropylene composition of anyone of claims 1 to 10, characterized in that the composition has a notched Charpy impact strength (NIS) at 23 °C, determined according to ISO 179-1 / 1eA on notched 80 × 10 × 4 mm³ specimens (specimens were prepared according to EN ISO 1873-2), of more than 4 kJ / m2, preferably in the range of from 5 to 10 kJ / m2.

12. The polypropylene composition of anyone of claims 1 to 11, characterized in that the composition consists of the random copolymer of propylene and an α- olefin (RACO) in an amount in the range of from 98.0 wt% to 99.9 wt% and additives in an amount in the range of from 0.1 to 2.0 wt%, wherein the amounts are based on the total weight of the composition.

13. A pipe comprising the polypropylene composition of anyone of claims 1 to 12 in an amount of more than 90.0 wt%, wherein the pipe is for use in hot and / or cold water applications, more preferably is a pressure pipe for use in hot and / or cold water applications.

14. The pipe of claim 13, characterized in that the pipe has a time to failure in a pipe pressure test according to ISO 1167-1 and-2 on pipes having a diameter of 32 mm and a wall thickness of 3 mm at a hoop stress of 16 MPa at a temperature of 20 °C of at least 4000 h, preferably of at least 5000 h, more preferably of at least 6000 h.

15. Use of the polypropylene composition of anyone of claims 1 to 12 as a pipe, preferably as a pipe for use in hot and / or cold water applications.

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