WO2018065242A1

WO2018065242A1 - Propylene-based composition for pipes

Info

Publication number: WO2018065242A1
Application number: PCT/EP2017/074120
Authority: WO
Inventors: Monica Galvan; Claudio Cavalieri; Francesca Tisi; Giampaolo Pellegatti; Thomas Böhm
Original assignee: Basell Poliolefine Italia S.R.L.
Priority date: 2016-10-06
Filing date: 2017-09-22
Publication date: 2018-04-12
Also published as: EP3523370A1; CN109790344B; BR112019004611B1; RU2713738C1; BR112019004611A2; US10501616B2; EP3523370B1; CN109790344A; US20190338113A1

Abstract

A polyolefin composition comprising: A) from 85.0 wt% to 99.5 wt%; of a propylene 1-hexene copolymer B) from 0.5 wt% to 15.0 wt%; of a propylene, ethylene copolymer composition comprising: b1) from 12 wt% to 52 wt%; of a propylene homopolymer or a propylene/ethylene copolymer b2) from 48 wt% to 88 wt% of a propylene ethylene copolymer having a content of ethylene derived units ranging from 15.0 wt% to wt% to 42.0 wt%; wherein the resulting polyolefin composition has an melt flow rate (230°C/5 kg.. ISO 1133) ranging from 0.2 g/lOmin to 4.0 g/10min; the sum A+B being 100 and the sum b1+b2 being 100.

Description

TITLE

PROPYLENE-BASED COMPOSITION FOR PIPES

FIELD OF THE INVENTION

[0001] The present disclosure relates to a composition comprising a propylene/ 1-hexene copolymer and an heterophasic propylene ethylene copolymer particularly fit for the production of pipes especially for high pressure pipes.

BACKGROUND OF THE INVENTION

[0002] Pipes comprising propylene and 1-hexene terpolymers are already known in the art. WO 2013/083617 relates to a polyolefin composition comprising from 85 wt to 99.5 wt % of a propylene ethylene 1-hexene terpolymers and an heterophasic copolymer. This composition is particularly fit for the production of small diameter pipes having improved impact properties especially at low temperature.

SUMMARY OF THE INVENTION

[0003] The applicant found it is possible to obtain pipes having improved stress resistance specially at high pressure with a composition comprising a propylene 1-hexene copolymer having certain features and an heterophasic propylene ethylene copolymer. Thus an object of the present disclosure is a polyolefin composition comprising:

[0004] A) from 85.0 wt to 99.5 wt of a propylene 1-hexene copolymer wherein:

[0005] i) the content of 1-hexene derived units ranges from 0.6 wt to 6.0 wt ;

[0006] ii) the melt flow rate (MFR) (ISO 1133 230°C, 5 kg) ranges from 0.6 to 5.0 g/10 min;

[0007] iii) the xylene soluble content measured at 25 °C lower than 10 wt ; preferably lower than 8 wt ; more preferably lower than 5 wt ;

[0008] B) from 0.5 wt to 15.0 wt of a propylene, ethylene copolymer composition comprising:

[0009] bl) from 12 wt to 52 wt of a propylene homopolymer or a propylene/ethylene copolymer having a content of ethylene derived units ranging from 0.1 wt to 4.5 wt ; and having a xylene soluble content measured at 25 °C lower than 10 wt ; [0010] b2) from 48 wt to 88 wt of a propylene ethylene copolymer having a content of ethylene derived units ranging from 15 wt to 42 wt ;

[0011] wherein the resulting polyolefin composition has an melt flow rate (230°C/5 kg.. ISO 1133) ranging from 0.2 g/lOmin to 4.0 g/lOmin;

[0012] the sum of the amount of components A+B being 100 and the sum of the amount of components bl+b2 being 100.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The applicant found it is possible to obtain pipes having improved stress resistance specially at high pressure with a composition comprising a propylene 1-hexene copolymer having certain features and an heterophasic propylene ethylene copolymer. Thus an object of the present disclosure is a polyolefin composition comprising:

[0014] A) from 85.0 wt% to 99.5 wt%; preferably 90.0 wt% to 99.5 wt% more preferably from 99.5 wt% to 93.0 wt% ; even more preferably from 96.5 wt% to 94.0 wt% of a propylene 1- hexene copolymer wherein:

[0015] i) the content of 1-hexene derived units ranges from 0.6 wt% to 6.0 wt ;

[0016] ii) the melt flow rate (MFR) (ISO 1133 230°C, 5 kg) ranges from 0.6 to 5.0 g/10 min; preferably from 0.9 to 2.5 g/10 min;

[0017] iii) the xylene soluble content measured at 25 °C lower than 10 wt ; preferably lower than 8 wt% ; more preferably lower than 5 wt ;

[0018] B) from 0.5 wt% to 15.0 wt%; preferably from 0.5 wt% to 10.0 wt%; more preferably from 0.5 wt% to 7.0 wt% even more preferably from 3.5 wt% to 6.0 wt% of a propylene, ethylene copolymer composition comprising:

[0019] bl) from 12 wt% to 52 wt ; preferably from 15 wt% to 43 wt ; more preferably from 20 wt% to 33 wt% of a propylene homopolymer or a propylene/ethylene copolymer having a content of ethylene derived units ranging from 0.1 wt to 4.5 wt ; and having a xylene soluble content measured at 25 °C lower than 10 wt ; preferably lower than 8 wt% ; more preferably lower than 7 wt ;

[0020] b2) from 48 wt% to 88 wt preferably from 57 wt% to 85 wt ; more preferably from 67 wt to 80 wt% of a propylene ethylene copolymer having a content of ethylene derived units ranging from 15 wt% to wt% to 42 wt ; [0021] wherein the resulting polyolefin composition has an melt flow rate (230°C/5 kg.. ISO 1133) ranging from 0.2 g/lOmin to 4.0 g/lOmin; preferably from 0.4 g/lOmin to 3.0 g/lOmin; more preferably from 0.5 g/10 min to 2 g/lOmin; the sum A+B being 100 and the sum bl+b2 being 100.

[0022] Preferably the component A) is endowed with one or more of these features:

[0023] (i) the content of 1-hexene derived units ranges from 1.0 wt to 4.5 wt ; preferably from 1.1 wt to 4.1 wt ; more preferably from 2.5 wt to 3.9 wt ; even more preferably from 2.8 wt% to 3.7wt%;

[0024] (ii) the melting temperature (DSC) ranging from 155° C to 130° C; preferably from 150°C to 136°C.

[0025] (iii) a polydispersity index (PI) ranging from 2.0 to 7.0, preferably from 3.0 to 6.5, more preferably from 3.5 to 6.0.

[0026] In the component B) component bl) is preferably a propylene homopolymer or a propylene ethylene copolymer having an content of ethylene derived units ranging from 1.1 wt wt to 4.2 wt ; more preferably from 2.3 wt to 3.9 wt ; more preferably is a propylene homopolymer.

[0027] In the component B) component b2) is preferably a propylene ethylene copolymer having an content of ethylene derived units ranging from 18 wt to 38 wt ; preferably from 21 wt to 34 wt , more preferably from 23 wt to 31 wt ; said copolymer having an intrinsic viscosity of the xylene soluble fraction at 25°C ranging from 2.0 dl/g to 5.0 dl/g; preferably from 2.5 dl/g to 4.5 dl/g.

[0028] The term copolymer used herein means that the polymer contains only two type of monomers such as propylene/ethylene or propylene/l-hexene.

[0029] With the composition of the present disclosure it is possible to obtain pipes, in particular pipes fit to be used even under pressure and high temperature.

[0030] Thus a further object of the present disclosure is a pipe comprising the composition of the present disclosure.

[0031] The term "pipe" as used herein also includes pipe fittings, valves and all parts which are commonly necessary for e.g. a hot water piping system. Also included within the definition are single and multilayer pipes, where for example one or more of the layers is a metal layer and which may include an adhesive layer. [0032] Such articles can be manufactured through a variety of industrial processes well known in the art, such as for instance moulding, extrusion, and the like.

[0033] In a further embodiment of the disclosure, the composition of the present disclosure further comprises an inorganic filler agent in an amount ranging from 0.5 to 60 parts by weight with respect to 100 parts by weight of the said composition. Typical examples of such filler agents are calcium carbonate, barium sulphate, titanium bioxide and talc. Talc and calcium carbonate are preferred. A number of filler agents can also have a nucleating effect, such as talc that is also a nucleating agent. The amount of a nucleating agent is typically from 0.2 to 5 wt% with respect to the polymer amount.

[0034] The composition of the disclosure is also suitable for providing pipes with walls of any configuration other than those with smooth inner and outer surface. Examples are pipes with a sandwich-like pipe wall, pipes with a hollow wall construction with longitudinally extending cavities, pipes with a hollow wall construction with spiral cavities, pipes with a smooth inner surface and a compact or hollow, spirally shaped, or an annularly ribbed outer surface, independently of the configuration of the respective pipe ends.

[0035] Articles, pressure pipes and related fittings according to the present disclosure are produced in a manner known per se, e.g. by (co-)extrusion or moulding, for instance.

[0036] Extrusion of articles can be made with different type of extruders for polyolefin, e.g. single or twin screw extruders.

[0037] The composition of the present disclosure can be prepared by blending the various components A), bl) and b2) or by preparing component A) and blend this component with component B) prepared in a single polymerization process by sequential polymerization steps.

[0038] The polymerization of A) and B) can be carried out in the presence of Ziegler-Natta catalysts. An essential component of said catalysts is a solid catalyst component comprising a titanium compound having at least one titanium-halogen bond, and an electron-donor compound, both supported on a magnesium halide in active form. Another essential component (co-catalyst) is an organoaluminium compound, such as an aluminium alkyl compound.

[0039] An external donor is optionally added.

[0040] The catalysts generally used in the process of the disclosure are capable of producing polypropylene with a value of xylene insolubility at ambient temperature greater than 90%, preferably greater than 95%. [0041] Catalysts having the above mentioned characteristics are well known in the patent literature; particularly advantageous are the catalysts described in US patent 4,399,054 and European patent 45977. Other examples can be found in US patent 4,472,524.

[0042] The solid catalyst components used in said catalysts comprise, as electron-donors (internal donors), compounds selected from the group consisting of ethers, ketones, lactones, compounds containing N, P and/or S atoms, and esters of mono- and dicarboxylic acids.

[0043] Particularly suitable electron-donor compounds are esters of phtalic acid and 1,3- diethers of formula:

[0044] wherein R¹ and R¹¹ are the same or different and are C C^ alkyl, C3-Ci8 cycloalkyl or C₇-C₁₈ aryl radicals; R^EI and R^w are the same or different and are CrC₄ alkyl radicals; or are the 1,3-diethers in which the carbon atom in position 2 belongs to a cyclic or polycyclic structure made up of 5, 6, or 7 carbon atoms, or of 5-n or 6-n' carbon atoms, and respectively n nitrogen atoms and n' heteroatoms selected from the group consisting of N, O, S and Si, where n is 1 or 2 and n' is 1, 2, or 3, said structure containing two or three unsaturations (cyclopolyenic structure), and optionally being condensed with other cyclic structures, or substituted with one or more substituents selected from the group consisting of linear or branched alkyl radicals; cycloalkyl, aryl, aralkyl, alkaryl radicals and halogens, or being condensed with other cyclic structures and substituted with one or more of the above mentioned substituents that can also be bonded to the condensed cyclic structures; one or more of the above mentioned alkyl, cycloalkyl, aryl, aralkyl, or alkaryl radicals and the condensed cyclic structures optionally containing one or more heteroatom(s) as substitutes for carbon or hydrogen atoms, or both.

[0045] Ethers of this type are described in published European patent applications 361493 and 728769.

[0046] Representative examples of said diethers are 2-methyl-2-isopropyl-l,3- dimethoxypropane, 2,2-diisobutyl- 1 ,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl- 1 ,3- dimethoxypropane, 2-isopropyl-2-isoamyl-l,3-dimethoxypropane, 9,9-bis (methoxymethyl) fluorene.

[0047] Other suitable electron-donor compounds are phthalic acid esters, such as diisobutyl, dioctyl, diphenyl and benzylbutyl phthalate.

[0048] The preparation of the above mentioned catalyst component is carried out according to various methods.

[0049] For example, a MgCi₂-nROH adduct (in particular in the form of spheroidal particles) wherein n is generally from 1 to 3 and ROH is ethanol, butanol or isobutanol, is reacted with an excess of TiCl₄ containing the electron-donor compound. The reaction temperature is generally from 80 to 120° C. The solid is then isolated and reacted once more with TiCl₄, in the presence or absence of the electron-donor compound, after which it is separated and washed with aliquots of a hydrocarbon until all chlorine ions have disappeared.

[0050] In the solid catalyst component the titanium compound, expressed as Ti, is generally present in an amount from 0.5 to 10% by weight. The quantity of electron-donor compound which remains fixed on the solid catalyst component generally is 5 to 20% by moles with respect to the magnesium dihalide.

[0051] The titanium compounds, which can be used for the preparation of the solid catalyst component, are the halides and the halogen alcoholates of titanium. Titanium tetrachloride is the preferred compound.

[0052] The reactions described above result in the formation of a magnesium halide in active form. Other reactions are known in the literature, which cause the formation of magnesium halide in active form starting from magnesium compounds other than halides, such as magnesium carboxylates.

[0053] The Al-alkyl compounds used as co-catalysts comprise the Al-trialkyls, such as Al- triethyl, Al-triisobutyl, Al-tri-n-butyl, and linear or cyclic Al-alkyl compounds containing two or more Al atoms bonded to each other by way of O or N atoms, or S0₄ or S0₃ groups.

[0054] The Al-alkyl compound is generally used in such a quantity that the Al/Ti ratio be from 1 to 1000.

[0055] The electron-donor compounds that can be used as external donors include aromatic acid esters such as alkyl benzoates, and in particular silicon compounds containing at least one Si-OR bond, where R is a hydrocarbon radical. [0056] Examples of silicon compounds are (tert-butyl)₂Si(OCH₃)2, (cyclohexyl)(methyl)Si (OCH₃)₂, (cyclopentyl)₂Si(OCH₃)₂ and (phenyl)₂Si(OCH₃)₂ and (1,1,2- trimethylpropyl)Si(OCH₃)₃.

[0057] 1,3-diethers having the formulae described above can also be used advantageously. If the internal donor is one of these diethers, the external donors can be omitted.

[0058] In particular, even if many other combinations of the previously said catalyst components may allow to obtain compositions according to the present disclosure, the components A) and B) are preferably prepared by using catalysts containing a phthalate as internal donor and (cyclopentyl)₂Si(OCH₃)₂ as outside donor, or the said 1,3-diethers as internal donors.

[0059] Component A) is produced with a polymerization process illustrated in EP application 1 012 195.

[0060] In detail, the said process comprises feeding the monomers to said polymerisation zones in the presence of catalyst under reaction conditions and collecting the polymer product from the said polymerisation zones. In the said process the growing polymer particles flow upward through one (first) of the said polymerisation zones (riser) under fast fluidisation conditions, leave the said riser and enter another (second) polymerisation zone (downcomer) through which they flow downward in a densified form under the action of gravity, leave the said downcomer and are reintroduced into the riser, thus establishing a circulation of polymer between the riser and the downcomer.

[0061] In the downcomer high values of density of the solid are reached, which approach the bulk density of the polymer. A positive gain in pressure can thus be obtained along the direction of flow, so that it become possible to reintroduce the polymer into the riser without the help of special mechanical means. In this way, a "loop" circulation is set up, which is defined by the balance of pressures between the two polymerisation zones and by the head loss introduced into the system.

[0062] Generally, the condition of fast fluidization in the riser is established by feeding a gas mixture comprising the relevant monomers to the said riser. It is preferable that the feeding of the gas mixture is effected below the point of reintroduction of the polymer into the said riser by the use, where appropriate, of gas distributor means. The velocity of transport gas into the riser is higher than the transport velocity under the operating conditions, preferably from 2 to 15 m/s. [0063] Generally, the polymer and the gaseous mixture leaving the riser are conveyed to a solid/gas separation zone. The solid/gas separation can be effected by using conventional separation means. From the separation zone, the polymer enters the downcomer. The gaseous mixture leaving the separation zone is compressed, cooled and transferred, if appropriate with the addition of make-up monomers and/or molecular weight regulators, to the riser. The transfer can be effected by means of a recycle line for the gaseous mixture.

[0064] The control of the polymer circulating between the two polymerisation zones can be effected by metering the amount of polymer leaving the downcomer using means suitable for controlling the flow of solids, such as mechanical valves.

[0065] The operating parameters, such as the temperature, are those that are usual in olefin polymerisation process, for example between 50 to 120° C.

[0066] This first stage process can be carried out under operating pressures of between 0.5 and 10 MPa, preferably between 1.5 to 6 MPa.

[0067] Advantageously, one or more inert gases are maintained in the polymerisation zones, in such quantities that the sum of the partial pressure of the inert gases is preferably between 5 and 80% of the total pressure of the gases. The inert gas can be nitrogen or propane, for example.

[0068] The various catalysts are fed up to the riser at any point of the said riser. However, they can also be fed at any point of the downcomer. The catalyst can be in any physical state, therefore catalysts in either solid or liquid state can be used.

[0069] The following examples are given to illustrate the present disclosure without limiting purpose.

EXAMPLES

[0070] Characterization methods

[0071] Melting temperature and crystallization temperature: Determined by differential scanning calorimetry (DSC), weighting 6 ±1 mg, is heated to 220 ±1° C at a rate of 20 °C/min and kept at 220 ±1° C for 2 minutes in nitrogen stream and it is thereafter cooled at a rate of 20° C/min to 40 ±2° C, thereby kept at this temperature for 2 min to crystallise the sample. Then, the sample is again fused at a temperature rise rate of 20° C/min up to 220° C ±1. The melting scan is recorded, a thermogram is obtained, and, from this, melting temperatures and crystallization temperatures are read. [0072] Melt Flow Rate: Determined according to the method ISO 1133 (230° C, 5 kg).

[0073] Solubility in xylene: Determined as follows.

[0074] 2.5 g of polymer and 250 ml of xylene are introduced in a glass flask equipped with a refrigerator and a magnetical stirrer. The temperature is raised in 30 minutes up to the boiling point of the solvent. The so obtained clear solution is then kept under reflux and stirring for further 30 minutes. The closed flask is then kept for 30 minutes in a bath of ice and water and in thermostatic water bath at 25° C for 30 minutes as well. The so formed solid is filtered on quick filtering paper. 100 ml of the filtered liquid is poured in a previously weighed aluminium container, which is heated on a heating plate under nitrogen flow, to remove the solvent by evaporation. The container is then kept on an oven at 80° C under vacuum until constant weight is obtained. The weight percentage of polymer soluble in xylene at room temperature is then calculated.

[0075] Determination of 1-hexene content by NMR

[0076] 13 C NMR spectra are acquired on an AV-600 spectrometer operating at 150.91 MHz in the Fourier transform mode at 120 °C. The peak of the propylene CH was used as internal reference at 28.83. The 13 C NMR spectrum is acquired using the following parameters:

[0077] The total amount of 1-hexene as molar percent is calculated from diad using the following relations:

[0078] [P] = PP + 0.5PH

[0079] [H] = HH + 0.5PH

[0080] Assignments of the 13 C NMR spectrum of propylene/ 1-hexene copolymers have been calculated according to the following table:

Ethylene (C2) content

¹³C NMR of propylene/ethylene copolymers [0081] C NMR spectra were acquired on a Bruker AV-600 spectrometer equipped with cryoprobe, operating at 160.91 MHz in the Fourier transform mode at 120°C.

[0082] The peak of the S carbon (nomenclature according to "Monomer Sequence

Distribution in Ethylene-Propylene Rubber Measured by 13C NMR. 3. Use of Reaction

Probability Mode " C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 1977, 10,

536) was used as internal reference at 29.9 ppm. The samples were dissolved in 1,1,2,2- tetrachloroethane-d2 at 120°C with a 8 % wt/v concentration. Each spectrum was acquired with a

90° pulse, 15 seconds of delay between pulses and CPD to remove 1H-13C coupling. 512 transients were stored in 32K data points using a spectral window of 9000 Hz.

[0083] The assignments of the spectra, the evaluation of triad distribution and the composition were made according to Kakugo ("Carbon- 13 NMR determination of monomer sequence distribution in ethylene-propylene copolymers prepared with δ-titanium trichloride- diethylaluminum chloride" M. Kakugo, Y. Naito, K. Mizunuma and T. Miyatake,

Macromolecules, 1982, 15, 1150) using the following equations:

[0084]

[0085] PPP = 100 T_Pp/S PPE = 100 T_p8/S EPE = 100 T₈₈/S

[0086] PEP = 100 S_Pp/S PEE= 100 S_p8/S EEE = 100 (0.25 S_y8+0.5 S₈₈)/S

[0087] S = Tpp + Τ_βδ + Τ_δδ + Sp_P + Sp₈ + 0.25 S_≠ + 0.5 S₈₈

[0088]

[0089] The molar percentage of ethylene content was evaluated using the following equation:

[0090] E% mol = 100 * [PEP+PEE+EEE]The weight percentage of ethylene content was evaluated using the following equation:

100 * E% mol * MW_E

E% wt. =

E% mol * MW_{E +} P% mol * MW_P

[0091] where P% mol is the molar percentage of propylene content, while MW_E and MWp are the molecular weights of ethylene and propylene, respectively.

[0092] The product of reactivity ratio r_\r₂ was calculated according to Carman (C.J. Carman, R.A. Harrington and C.E. Wilkes, Macromolecules, 1977; 10, 536) as:

[0093] The tacticity of Propylene sequences was calculated as mm content from the ratio of the PPP mmTpp (28.90-29.65 ppm) and the whole Tpp (29.80-28.37 ppm).

[0094] Ethylene C2 content of component b2 has been measured by measuring the C2 content on component B) and than calculated by using the formula C2tot=XblC2bl+Xb2C2b2 wherein Xbl and Xb2 are the amounts of components bl and b2 in the composition.

[0095]

[0096] Elongation at yield: measured according to ISO 527.

[0097] Elongation at break: measured according To ISO 527

[0098] Stress at break: measured according to ISO 527.

[0099] Impact test: ISO 180-1 A

[0100] Samples for the mechanical analysis

Samples have been obtained according to ISO 1873-2:2007 excepting for the flexural modulus for which ISO 3167 has been used.

[0101] Flexural Modulus

[0102] Determined according to ISO 178.

[0103] Preparation of component Al

[0104] Copolymers are prepared by polymerising propylene and hexene-1 in the presence of a catalyst under continuous conditions in a plant comprising a polymerisation apparatus as described in EP 1 012 195.

[0105] The catalyst is sent to the polymerisation apparatus that comprises two interconnected cylindrical reactors, riser and downcomer. Fast fluidisation conditions are established in the riser by recycling gas from the gas-solid separator. In examples 1-5 barrier feed has been used.

[0106] The catalyst employed comprises a catalyst component prepared by analogy with example 5 of EP-A-728 769 but using micro spheroidal MgCl₂- 1.7C₂HsOH instead of MgCl₂-2.1C₂H₅0H. Such catalyst component is used with dicyclopentyl dimethoxy silane (DCPMS) as external donor and with triethylaluminium (TEA).

[0107] The polymer particles exiting the reactor are subjected to a steam treatment to remove the reactive monomers and volatile substances and then dried. The main operative conditions and characteristics of the produced polymers are indicated in Table 1. [0108] Table 1

C3 propylene; C6 1-hexene

[0109] Properties of the obtained material has been reported in table 2:

[0110] Table 2

[0111] Component A2 comparative

[0112] component A2 is a propylene ethylene 1-hexene terpolymer whose features are reported in Table 3. [0113] Table 3

[0114] Component B)

[0115] Components B) is an heterophasic copolymer obtained by sequential gas phase polymerization, the features of the copolymer are reported on table 4

[0116] Table 4

C2= ethylene derived units [0117] Components A and B have been blended together the resulting blend has been analysed. The results have been reported on table 5

[0118] Table 5

*The remaining amount being component A

[0119] Pipes obtained with composition 1 and comparative blend 2 have been tested with a test based on the European Standard EN IS01167Thermoplastics pipes, fittings and assemblies for the conveyance of fluids - Determination of the resistance to internal

pressure) the results are reported on table 6

Table 6

[0120] From tab e 6 clearly resu Its that pipes obtained with the composition according to the invention 1 have an improved resistance even at high temperature and high pressure with respect to pipes obtained by using the composition of the comparative blend 2.

Claims

CLAIMS What is claimed is:

1. A polyolefin composition comprising:

A) from 85.0 wt to 99.5 wt ; of a propylene 1-hexene copolymer wherein:

(i) the content of 1-hexene derived units ranges from 0.6 1.0 wt to 6.0%;

ii) the melt flow rate (MFR) (ISO 1133 230°C, 5 kg) ranges from 0.6 to 5.0 g/10 min;

iii) the xylene soluble content measured at 25 °C lower than 10 wt%;

B) from 0.5 wt% to 15.0 wt%; of a propylene, ethylene copolymer composition comprising: bl) from 12 wt% to 52 wt%; of a propylene homopolymer or a propylene/ethylene copolymer having a content of ethylene derived units ranging from 0.1 wt% to 4.5 wt%; and having a xylene soluble content measured at 25 °C lower than 10 wt%;

b2) from 48 wt% to 88 wt% of a propylene ethylene copolymer having a content of ethylene derived units ranging from 15.0 wt% to wt% to 42.0 wt%;

wherein the resulting polyolefin composition has an melt flow rate (230°C/5 kg.. ISO 1133) ranging from 0.2 g/lOmin to 4.0 g/lOmin; the sum A+B being 100 and the sum bl+b2 being 100;

wherein the term copolymer means that the polymer contains only two type of monomers.

2. The polyolefin composition according to claim 1 wherein the content of 1-hexene derived units in component A) ranges from 1.0 wt% to 4.5 wt%.

3. The polyolefin composition according to any of claims 1-2 wherein the content of 1-hexene derived units in component A) ranges from 2.5 wt% to 3.9 wt%.

4. The polyolefin composition according to any of claims 1-3 wherein the content of 1-hexene derived units in component A) ranges from 2.8 wt to 3.7wt%.

5. The polyolefin composition according to any of claims 1-4 wherein component b2) is a propylene ethylene copolymer having an content of ethylene derived units ranging from 18 wt to 38 wt said copolymer having an intrinsic viscosity of the xylene soluble fraction at 25°C ranging from 2.0 dl/g to 5.0 dl/g.

6. The polyolefin composition according to any of claims 1-5 wherein the melt flow rate (MFR) (ISO 1133 230°C, 5 kg) of component A) ranges from 0.9 to 2.5 g/10 min.

7. The polyolefin composition according to any of claims 1-6 wherein in component A) the melting temperature (DSC) ranges from 155° C to 130° Cthe melt flow rate (MFR) (ISO 1133 230°C, 5 kg) of component A) ranges from 0.9 to 2.5 g/10 min.

8. The polyolefin composition according to any of claims 1-7 having a melt flow rate (230°C/5 kg.. ISO 1133) ranging from 0.4 g/lOmin to 3.0 g/lOmin;

9. Pipe systems and sheets comprising a polyolefin composition according to claims 1 to 8.

10. Mono- or multilayer pipes and sheets wherein at least one layer comprises the polyolefin composition according to claim 1