Pipe and polypropylene composition for its manufacture

Abstract

A polypropylene composition comprising: A) 91 wt.% to 97.0 wt.% of a propylene copolymer containing 0.8 wt.% to 4.8 wt.% of 1-hexene derived units; B) 3 wt.% to 9 wt.% of a terpolymer of propylene ethylene and 1-hexene having an ethylene derived unit content ranging from 20.0 wt.% to 30.0 wt.%; and a 1-hexene derived unit content ranging from 20.0 wt.% to 30.0 wt.%.

Description

Technical Field

[0001] The present disclosure relates to polypropylene-based compositions containing 1-hexene-derived units and the use of said compositions for producing pipes, in particular chlorine-resistant pipes. Background Art

[0002] Polymeric materials are often used to make pipelines for various purposes, such as fluid delivery, during which fluid can be non-pressurized or pressurized. Polyolefin compositions are easy to degrade during processing and final use. When material is exposed to certain environmental conditions such as high energy radiation (such as UV exposure), mechanical shearing and high temperature, especially degraded. In addition, when transporting in polypropylene pipelines, chlorinated water also has a negative impact on polymer. Due to these reasons, polymer has the life span and aging performance of reduction.

[0003] Degradation is carried out with a free radical mechanism and will eventually destroy the polymer properties. Polyolefins undergo an aging process. Typically, the initial step in the degradation process is the loss of hydrogen atoms from the polymer chain. The polymer free radical (R*) can react with an oxygen (O2) molecule to form a peroxy radical (ROO*), which in turn will capture another hydrogen atom from another polymer chain to form a hydroperoxide (ROOH). The hydroperoxide can split into two new free radicals (RO*) and (*OH), which continue to expand the reaction to other polyolefin molecules.

[0004] In polyolefins, free radical attack can lead to chain scission. One way to interrupt this process is to add antioxidants to the composition.

[0005] The applicant has found that specific polypropylene compositions are able to reduce degradation due to chlorine without the addition of antioxidants.

[0006] WO-A1-2020 / 069828 relates to a pipe comprising a resin formed from: a polypropylene composition comprising:

[0007] A) 88.0 wt.% to 98.0 wt.% of a propylene copolymer containing 0.8 wt.% to 4.8 wt.% of 1-hexene-derived units; the propylene random copolymer having:

[0008] Melt flow rate: measured according to ISO 1133 (230°C, 5Kg), ranging from 0.5 to 4.4 g / 10min;

[0009] B) 2.0 wt.% to 12.0 wt.% of a terpolymer of propylene ethylene and 1-hexene having an ethylene derived unit content ranging from 35 wt.% to 60 wt.%; and a 1-hexene derived unit content ranging from 1 wt.% to 6 wt.%.

[0010] This document does not deal with the chlorine resistance of the compositions.

[0011] Applicants have discovered that chlorine resistance in pipes can be improved by using a polypropylene composition comprising a propylene 1-hexene copolymer and a propylene ethylene, 1-hexene terpolymer having specific characteristics. Summary of the invention

[0012] Therefore, the object of the present disclosure is a polypropylene composition comprising:

[0013] A) 91 wt.% to 97 wt.% of a propylene copolymer containing 0.8 wt.% to 4.8 wt.% of 1-hexene-derived units; the random copolymer of propylene and 1-hexene having a melt flow rate in the range of 0.5 to 4.4 g / 10 min as measured according to ISO 1133 (230° C., 5 Kg);

[0014] B) 3 wt.% to 9 wt.% of a terpolymer of propylene, ethylene and 1-hexene having an ethylene derived unit content ranging from 20.0 wt.% to 30.0 wt.%; and a 1-hexene derived unit content ranging from 20.0 wt.% to 30.0 wt.%;

[0015] wherein the polypropylene composition is endowed with:

[0016] i) Melt flow rate: measured according to ISO 1133 (230° C., 5 kg), ranging from 0.5 to 5.0 g / 10 min;

[0017] ii) a xylene soluble fraction at 25°C ranging from 4.0 wt.% to 13.0 wt.%;

[0018] iii) an intrinsic viscosity of the xylene-soluble fraction at 25° C. ranging from 1.5 dl / g to 3.5 dl / g;

[0019] The sum of the quantities of A) and B) is 100. DETAILED DESCRIPTION

[0020] Therefore, the object of the present disclosure is a polypropylene composition comprising:

[0021] A) from 91 wt.% to 97 wt.%; preferably 92 wt.% to 96 wt.%; more preferably 93 wt.% to 95 wt.% of a propylene copolymer containing 0.8 wt.% to 4.8 wt.%, preferably 1.4 wt.% to 4.1 wt.%, more preferably 1.8 wt.% to 3.6 wt.%, even more preferably 1.9 wt.% to 2.9 wt.% of 1-hexene-derived units; the random copolymer of propylene and 1-hexene having a melt flow rate as measured according to ISO 1133 (230°C, 5 Kg) in the range of 0.5 to 4.4 g / 10 min; preferably 0.6 to 3.7 g / 10 min; more preferably 0.7 to 2.3 g / 10 min;

[0022] B) 3 wt.% to 9 wt.%; preferably 4 wt.% to 8 wt.%; more preferably 5 wt.% to 7 wt.% of a terpolymer of propylene ethylene and 1-hexene, having an ethylene-derived unit content ranging from 20.0 wt.% to 30.0 wt.%; preferably 22.0 wt.% to 28.0 wt.%; even more preferably 23.0 wt.% to 27.0 wt.%; and a 1-hexene-derived unit content ranging from 20.0 wt.% to 30.0 wt.%; preferably 22.0 wt.% to 28.0 wt.%; even more preferably 23.0 wt.% to 27.0 wt.%;

[0023] wherein the polypropylene composition is endowed with:

[0024] i) a xylene soluble fraction at 25°C ranging from 4.0 wt.% to 13.0 wt.%; preferably from 5.0 wt.% to 12.0 wt.%; more preferably from 6.0 wt.% to 11.0 wt.%;

[0025] ii) melt flow rate, MFR, measured according to ISO 1133 at 230°C with a load of 5.0 Kg, ranging from 0.2 g / 10 min to 2.0 g / 10 min; preferably comprised between 0.4 g / 10 min and 1.6 g / 10 min; more preferably comprised between 0.7 g / 10 min and 1.3 g / 10 min;

[0026] iii) the intrinsic viscosity of the xylene-soluble fraction at 25° C. is in the range of 1.5 dl / g to 3.5 dl / g; preferably in the range of 1.8 dl / g to 3.0 dl / g; more preferably in the range of 2.2 dl / g to 2.9 dl / g;

[0027] The sum of the quantities of A) and B) is 100.

[0028] The term "copolymer" as used in this patent application refers to a polymer prepared by the polymerization of two different types of monomers, such as propylene and 1-hexene. The term "terpolymer" as used in this patent application refers to a polymer prepared by the polymerization of three different types of monomers, such as propylene, ethylene and 1-hexene.

[0029] The polypropylene compositions of the present disclosure can be advantageously used in the preparation of pipes, especially pipes having enhanced chlorine resistance.

[0030] Therefore, another object of the present disclosure is a pipe comprising the polypropylene composition of the present disclosure.

[0031] The term "pipe" as used herein also includes pipe fittings, valves and all components typically required for, for example, hot water pipe systems. Also included in this definition are single-layer and multi-layer pipes, where, for example, one or more layers are metal layers and may include adhesive layers.

[0032] In another embodiment of the present disclosure, the polypropylene composition further comprises an inorganic filler in an amount of 0.5 to 60 parts by weight relative to 100 parts by weight of the polypropylene composition. Typical examples of such fillers are calcium carbonate, barium sulfate, titanium dioxide and talc. Talc and calcium carbonate are preferred. Many fillers may also have a nucleating effect, such as talc which is also a nucleating agent. The amount of the nucleating agent is typically 0.5 to 5 wt.% relative to the amount of the polymer.

[0033] The polypropylene compositions of the present disclosure are also suitable for providing polypropylene pipes having walls of any configuration other than those having smooth inner and outer surfaces. Examples are pipes having sandwich-like pipe walls, pipes having a hollow wall structure with longitudinally extending cavities, pipes having a hollow wall structure with spiral cavities, pipes having a smooth inner surface and a compact or hollow, spiral or annular ribbed outer surface, regardless of the configuration of the corresponding pipe ends.

[0034] The polypropylene composition can be prepared according to known polymerization methods.

[0035] The method for preparing the aforementioned polypropylene composition can be carried out by a sequential polymerization comprising at least two sequential steps, wherein components A) and B) are prepared in separate subsequent steps, in each step except the first step, operating in the presence of the formed polymer and the catalyst used in the previous step. Preferably, the catalyst is added only in the first step, because its activity generally makes it still active for all subsequent steps. The order of the polymerization stages is not a critical process feature, however component A) is preferably prepared before component B).

[0036] The polymerization can be carried out in liquid phase, gas phase or liquid-gas phase.

[0037] For example, a propylene polymerization stage using liquid propylene as diluent and a subsequent copolymerization stage can be carried out in gas phase with no intermediate stages except partial degassing of the propylene.

[0038] Examples of suitable reactors are continuously operated stirred reactors, loop reactors, fluidized bed reactors or horizontally or vertically stirred powder bed reactors. Of course, the reaction can also be carried out in a plurality of reactors connected in series.

[0039] The polymerisation can be carried out in a cascade of stirred gas phase reactors connected in series, in which the powdery reaction bed is kept in motion by means of vertical stirrers. The reaction bed generally comprises the polymer polymerised in the individual reactors.

[0040] With respect to the reaction time of the polymerization step, pressure and temperature are not critical, however it is optimal if the temperature is from 20 to 150° C., especially from 50 to 100° C. The pressure may be atmospheric pressure or higher.

[0041] The molecular weight is regulated by using known regulators, in particular hydrogen.

[0042] According to a particularly preferred embodiment the polypropylene composition is produced by a sequential polymerization process comprising the production of component A) in a first gas phase polymerization apparatus comprising two interconnected polymerization zones and a second step of producing a propylene, ethylene copolymer by polymerizing the monomers in a separate fluidized bed reactor.

[0043] A gas phase polymerization plant for carrying out the first step of the process is described in patent application EP-A1-782587.

[0044] In detail, the method comprises feeding one or more monomers to the polymerization zone under reaction conditions in the presence of a catalyst and collecting a polymer product from the polymerization zone. In the process, growing polymer particles flow upward through one (first) of the polymerization zones (risers) under fast fluidization conditions, leave the riser and enter another (second) polymerization zone (downcomer), they flow downward through the other (second) polymerization zone in a densified form under the action of gravity, leave the downcomer and are reintroduced into the riser, thereby establishing a circulation of the polymer between the riser and the downcomer.

[0045] In the downcomer, high solid density values ​​are reached, which are close to the bulk density of the polymer. A positive pressure gain can therefore be obtained in the flow direction, making it possible to reintroduce the polymer into the riser without the aid of special mechanical devices. In this way, a "loop" circulation is established, which is defined by the pressure balance between the two polymerization zones and the head loss introduced into the system.

[0046] Typically, fast fluidization conditions in the riser are established by feeding a gas mixture including the relevant monomers into the riser. Preferably, the feeding of the gas mixture is carried out below the point where the polymer is reintroduced into the riser by using a gas distributor device where appropriate. The velocity of the conveying gas entering the riser is higher than the conveying velocity under operating conditions, preferably from 0.8 to 15 m / s.

[0047] Typically, the polymer and gas mixture leaving the riser is conveyed to a solid / gas separation zone. Solid / gas separation can be achieved using conventional separation means. From the separation zone, the polymer enters a downcomer. The gaseous mixture leaving the separation zone is compressed, cooled and transferred to the riser, and if appropriate, additional monomers and / or molecular weight regulators are added. The transfer can be achieved by a circulation line for the gas mixture.

[0048] Control of the polymer circulating between the two polymerisation zones can be achieved by metering the amount of polymer leaving the downcomer using suitable means for controlling the flow of solids, such as a mechanical valve.

[0049] The operating parameters, such as temperature, are those conventionally used in gas phase olefin polymerization processes, for example 50-120°C.

[0050] The operating pressure may be 0.5 to 10 MPa, preferably 1.5 to 6 MPa.

[0051] Advantageously, at least one inert gas is maintained in the polymerization zone in such an amount that the sum of the partial pressures of the inert gases is preferably between 5 and 80% of the total pressure of the gases. The inert gas may be, for example, nitrogen or propane.

[0052] The polymer leaving the first polymerization device is discharged from the downcomer to a gas-solid separator and then collected and transferred to the second stage, which is preferably carried out in a conventional fluidized bed gas phase reactor operating under conventional temperature and pressure conditions.

[0053] Preferably, the various catalyst components are fed into the riser at any point of said riser. However, they may also be fed at any point of the downcomer. The catalyst may be in any physical state, so solid or liquid catalysts may be used.

[0054] The preferred catalyst used in the polymerization process is a Ziegler-Natta catalyst comprising a solid catalyst component comprising a titanium compound having at least one titanium-halogen bond and an electron donor compound, both supported on magnesium halide in active form as a preferred support, optionally with silica as a co-support.

[0055] Catalysts having the above characteristics are well known in the patent literature; particularly advantageous are the solid catalyst components used in the catalysts described in patent documents US Pat. No. 4,399,054, EP-A2-045,977 and EP-A2-395,083.

[0056] The solid catalyst component used for the catalyst comprises as electron donor compound (internal electron donor compound) a compound selected from ethers, ketones, lactones, compounds containing N, P and / or S atoms and esters of monocarboxylic acids and dicarboxylic acids. Particularly suitable electron donor compounds are phthalic acid esters, such as diisobutyl phthalate, dioctyl phthalate, diphenyl phthalate and benzylbutyl phthalate, and esters of succinic acid.

[0057] Particularly suitable internal electron donor compounds are selected from the succinate esters disclosed in International Patent Application WO-A1-00 / 63261.

[0058] Other particularly suitable electron donors are the 1,3-diethers as described, for example, in European Patent Applications EP-A1-361493 and EP-A1-728769.

[0059] The above catalyst components are prepared according to various methods. For example, MgCl 2 n The ROH adduct (particularly in the form of spherical particles) is reacted with an excess of TiCl4 containing an electron donor compound, wherein n is generally 1 to 3 and ROH is ethanol, butanol or isobutanol. The reaction temperature is generally 80 to 120°C. The solid is then separated and reacted once more with TiCl4 in the presence or absence of the electron donor compound, after which it is separated and washed with an aliquot of a hydrocarbon until all chloride ions disappear. In the solid catalyst component, the titanium compound represented by Ti is generally present in an amount of 0.5 to 10 wt.%. The amount of the electron donor compound retained fixed on the solid catalyst component is generally 5 to 20 mol% relative to the magnesium dihalide. Titanium compounds that can be used to prepare the solid catalyst component are titanium halides and halogen alcoholates. Titanium tetrachloride is a preferred compound.

[0060] The above reactions lead to the formation of magnesium halides in active form. Other reactions are known in the literature which lead to the formation of magnesium halides in active form starting from magnesium compounds other than halides, such as magnesium carboxylates.

[0061] The Ziegler-Natta catalyst also includes a cocatalyst, namely an organoaluminum compound, such as an alkylaluminum compound. An external donor is optionally added to the organoaluminum compound.

[0062] Alkyl aluminum compounds used as cocatalysts include trialkyl aluminums such as triethyl aluminum, triisobutyl aluminum, tributyl aluminum, and linear or cyclic alkyl aluminum compounds containing two or more Al atoms bonded to each other via O or N atoms or SO4 or SO3 groups.

[0063] The alkylaluminum compound is generally used in such an amount that the Al / Ti ratio is 1 to 1,000.

[0064] Electron donor compounds useful as external donors include aromatic acid esters such as alkyl benzoates, and in particular silicon compounds containing at least one Si-OR bond, wherein R is a hydrocarbon group. Useful examples of silicon compounds are (tert-butyl)2Si(OCH3)2, (cyclopentyl)2Si(OCH3)2, (cyclohexyl)(methyl)Si(OCH3)2 and (phenyl)2Si(OCH3)2.

[0065] 1,3-Diethers of the abovementioned general formula can also be used advantageously.

[0066] If the internal donor is one of these diethers, the external donor can be omitted.

[0067] Before the polymerization process, the catalyst can be pre-contacted with a small amount of olefin (prepolymerization) to improve the performance of the catalyst and the morphology of the polymer. Prepolymerization is carried out by keeping the catalyst in a suspension in a hydrocarbon solvent (e.g., hexane or heptane) and polymerizing at a temperature of ambient temperature to 60° C. for a time sufficient to produce a polymer in an amount of 0.5 to 3 times the weight of the solid catalyst component. It can also be carried out in liquid propylene under the above temperature conditions, and the amount of polymer produced can reach up to 1000 g / g of catalyst component.

[0068] The articles, pressure pipes and related fittings according to the present disclosure are produced in a manner known per se, for example by (co)extrusion or molding.

[0069] The extrusion of the article can be carried out using different types of polypropylene extruders, such as single-screw or twin-screw extruders.

[0070] The following examples are given to illustrate but not to limit the present disclosure.

[0071] Example

[0072] The polymer composition pipes obtained therefrom were characterized using the following analytical methods.

[0073] Melt flow rate: measured according to ISO 1133 (230°C, 5 Kg).

[0074] Intrinsic viscosity: measured in tetralin at 135°C.

[0075] Xylene soluble fraction at 25°C (XS)

[0076] Xylene solubles at 25°C were determined according to ISO 16152:2005; the solution volume was 250 ml, precipitation was carried out at 25°C for 20 minutes, of which 10 minutes were stirred with the solution (magnetic stirrer), and drying was carried out at 70°C. According to the formula XS tot =Xs A W A +Xs B W B Calculate the xylene soluble fraction of component b);

[0077] where Xstot is the xylene soluble portion of the total composition, Xs A is the xylene soluble part of component A, W A is the amount of component A; Xs B is the xylene soluble part of component B, W B is the amount of component B; where W A +W B =1.

[0078] Determination of 1-hexene content by NMR

[0079] Acquired on an AV-600 spectrometer operating at 150.91 MHz in Fourier transform mode at 120 °C 13 C NMR spectrum. The peak of propylene CH at 28.83 was used as an internal reference. The following parameters were used to obtain 13 C NMR spectroscopy:

[0080] Spectral Width (SW) 60ppm Spectral Center (O1) 30ppm Decoupling Sequences WALTZ 65_64pl Pulse Program ZG Pulse length (P1) For 90° Total Points(TD) 32K Relaxation delay 15s Number of transients 1500

[0081] The total amount of 1-hexene as a mole percent was calculated from the identified dyads present in the measured NMR using the following relationship:

[0082] [P] = PP + 0.5PH

[0083] [H]=HH+0.5PH

[0084] Propylene / 1-hexene copolymer 13 The assignments of C NMR spectra were calculated according to the following table:

[0085] area Chemical shift distribute sequence 1 46.93–46.00 <![CDATA[S αα ]]> PP 2 44.50–43.82 <![CDATA[S αα ]]> PH 3 41.34-4.23 <![CDATA[S αα ]]> HH 4 38.00-37.40 <![CDATA[S αγ +S αδ ]]> PE 5 35.70-35.0 <![CDATA[4B4]]> H 6 35.00-34.53 <![CDATA[S αγ +S αδ ]]> HE 7 33.75 33.20 CH H 8 33.24 <![CDATA[T δδ ]]> EPE 9 30.92 <![CDATA[T βδ ]]> PPE 10 30.76 <![CDATA[S γγ ]]> XEEX 11 30.35 <![CDATA[S γδ ]]> XEEEE 12 29.95 <![CDATA[S δδ ]]> EEE 13 29.35 <![CDATA[3B4]]> H 14 28.94–28.38 CH P 15 27.43–27.27 <![CDATA[S βδ ]]> XEE 16 24.67-24.53 <![CDATA[S ββ ]]> XEX 17 23.44-23.35 <![CDATA[2B4]]> H 18 21.80–19.90 <![CDATA[CH3]]> P 19 14.22 <![CDATA[CH3]]> H

[0086] Determination of ethylene and 1-hexene content by NMR

[0087] Acquired on an AV-600 spectrometer operating at 150.91 MHz in Fourier transform mode at 120 °C 13C NMR spectrum. The peak of propylene CH at 28.83 was used as an internal reference. The following parameters were used to obtain 13 C NMR spectrum:

[0088] Spectral Width (SW) 60ppm Spectral Center (O1) 30ppm Decoupling Sequences WALTZ 16 Pulse Program ZG Pulse length (P1) For 90° Total Points(TD) 32K Relaxation delay 15s Number of transients 1500

[0089] The dyad distribution is calculated according to the following relationship:

[0090] PP=100I1 / Σ

[0091] PH=100I2 / Σ

[0092] HH=100I3 / Σ

[0093] PE=100I4 / Σ

[0094] EE=100(0.5(I12+I15)+0.25I11) / Σ

[0095] Where Σ=I1+I2+I3+I4+0.5(I12+I15)+0.25I11

[0096] The total amount (mole percent) of 1-hexene and ethylene was calculated from the dyads.

[0097] Use the following relationship:

[0098] [P] = PP + 0.5PH + 0.5PE

[0099] [H]=HH+0.5PH

[0100] [E] = EE + 0.5PE

[0101] Propylene / 1-hexene / ethylene copolymer 13 Assignment of C NMR spectra

[0102]

[0103] The amounts of 1-hexene and ethylene in component B were calculated by using the following equations:

[0104] C 6总 =C 6A *A+C 6B *B

[0105] C 2总 =C 2B *B

[0106] Among them C 6总 is the amount of 1-hexene in the composition; C 6A is the amount of 1-hexene in component A); C 6B is the amount of 1-hexene in component B); C2总 is the amount of ethylene in the composition; C 2B is the amount of ethylene in component B); and A and B are the amounts of components A and B.

[0107] Example 1

[0108] Preparation of solid intermediate components

[0109] In a 500 mL four-necked round-bottom flask purged with nitrogen, 250 mL of TiCl4 are introduced at 0°C. Under stirring, 10.0 g of microspherical MgCl2·C2H5OH (prepared according to the method described in Example 1 of EP728769) with an average particle size of 40 μm and containing about 50% of EtOH are added, and a certain amount of diethyl 2,3-diisopropylsuccinate in racemic form is added so that the Mg / succinate molar ratio is 12. The temperature is raised to 100°C and maintained at this value for 60 minutes. Thereafter, stirring is stopped, the liquid is siphoned off and the treatment with TiCl4 is repeated at 110°C for 30 minutes. After siphoning, fresh TiCl4 and a certain amount of 9,9-bis(methoxymethyl)fluorene are added so that the Mg / diether molar ratio is 24. The temperature is then raised to 90°C and maintained for 30 minutes. After settling and siphoning at 85°C, the solid was washed 6 times with anhydrous hexane (6 x 100 ml) at 60°C.

[0110] polymerization

[0111] The catalyst system was formed from the catalyst components prepared as described above, triethylaluminium (TEAL) as cocatalyst and dicyclopentyldimethoxysilane as external donor in the weight ratios shown in the table below.

[0112] The propylene polymer compositions of the examples are prepared in a two-step polymerization process, wherein the random copolymer A) is prepared in a first polymerization step by feeding the monomers and the catalyst system into a gas phase polymerization reactor comprising two interconnected polymerization zones, a riser and a downcomer, as described in European patent EP-A1-782587. The polymerization mixture is discharged from the reactor, conveyed to a gas-solid separator, and the polymerized material is fed to a conventional gas phase fluidized bed reactor, where a polymer of ethylene B) is produced.

[0113] The polymer particles leaving the second polymerization step were subjected to steam treatment to remove unreacted monomers and to drying, the operating conditions being shown in Table 1. The characteristics of the polymer obtained are reported in Table 2.

[0114] Table 1

[0115]

[0116] C3 = propylene; C2 = ethylene; C6 = 1-hexene

[0117] Table 2

[0118] Example 1 Component A 1-Hexene Wt.% 2.2 MFR g / 10min 0.96 XS wt.% 1.7 Component B Component B% ％ 6.2 Ethylene Wt.% 25.9 1-Hexene Wt.% 25 Total polymer MFR g / 10min 0.96 Intrinsic viscosity of XS dl / g 2.60 XS wt.% 7.2

[0119] The additives reported in Table 3 were added to the polymers prepared in Example 1 and Comparative Example 2. Comparative Example 2 is Example 1 of WO2020 / 069828

[0120] Table 3

[0121] wt.% DSTDP 0.33 TALC 1.0 Calcium Stearate-M 0.05 IRGAFOS168 0.11 IRGANOX 1010 0.22 IRGANOX 1330 0.11

[0122] Pipes with a diameter of 33 mm and a thickness of 3 mm were prepared using the polymers of Example 1 and Comparative Example 2. The pipes were tested for chlorine resistance according to ASTM F2023-13 using the following conditions:

[0123] Table 4

[0124] pressure 0.34Mpa(50psig) temperature 115℃ Chlorine concentration 4.2ppm pH 6.8 ORP 860mV

[0125] The results were calculated on the average of 6 tests.The pipe of Example 1 showed a resistance of 1798 hours, whereas the pipe obtained using the polymer of Example 2 showed a resistance of 1713 hours.

Claims

1. A polypropylene composition comprising: A) 91 wt.% to 97.0 wt.% of a propylene copolymer containing 0.8 wt.% to 4.8 wt.% of 1-hexene-derived units; the propylene copolymer having a melt flow rate in the range of 0.4 to 4.4 g / 10 min, measured according to ISO 1133, 230°C, 5 Kg; B) 3 wt.% to 9 wt.% of a terpolymer of propylene ethylene and 1-hexene having an ethylene derived unit content ranging from 20.0 wt.% to 30.0 wt.%; and a 1-hexene derived unit content ranging from 20.0 wt.% to 30.0 wt.%; wherein the polypropylene composition is endowed with: i) Melt flow rate: measured according to ISO 1133, 230°C, 5Kg, ranging from 0.5 to 5.0 g / 10min; ii) a xylene soluble fraction at 25°C ranging from 4.0 wt.% to 13.0 wt.%; iii) an intrinsic viscosity of the xylene-soluble fraction at 25° C. ranging from 1.5 dl / g to 3.5 dl / g; The sum of the amounts of A) and B) is 100 wt.%.

2. The polypropylene composition according to claim 1, wherein in component A) the content of 1-hexene derived units is in the range of 1.4 to 4.1 wt.%.

3. The polypropylene composition according to claim 1, wherein in component A), the content of 1-hexene derived units is in the range of 1.8 to 3.6 wt.%.

4. The polypropylene composition according to claim 1, wherein the content of ethylene-derived units in component B ranges from 22.0 wt.% to 28.0 wt.%.

5. The polypropylene composition according to claim 1, wherein the amount of component A) ranges from 93 wt.% to 95 wt.%, and the amount of component B ranges from 3 wt.% to 7 wt.%.

6. The polypropylene composition according to claim 1, having a melt flow rate measured according to ISO 1133, 230°C, 5 Kg, in the range of 0.4 to 1.6 g / 10 min.

7. The polypropylene composition according to claim 1, having a xylene soluble fraction at 25°C in the range of 5.0 wt.% to 12.0 wt.%.

8. The polypropylene composition according to claim 1, wherein the intrinsic viscosity of the xylene soluble portion at 25°C is in the range of 1.8 dl / g to 3.0 dl / g.

9. A pipe comprising the polypropylene composition according to claim 1.

10. A pressure pipe comprising the polypropylene composition according to claim 1.

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