Pipes for transporting chlorinated water

Abstract

The present invention relates to the use of a pipe for conveying chlorinated water, wherein the pipe is a biaxially oriented pipe made by a process comprising the steps of: a) forming a polymer composition comprising a polyolefin into a pipe and b) stretching the pipe of step a) in axial and circumferential directions to obtain the biaxially oriented pipe.

Description

[0001] The present invention relates to the use of a pipe produced with a polymer composition comprising a polyolefin for conveying chlorinated water. The pipe has an improved resistance to chlorine-containing disinfectants.

[0002] Pipes for conveying gas, for sanitary installations and for water supply can be produced from, for example, bimodal polyethylene and polypropylene compositions. Pipes have very good water resistance, but their service life is shortened when they come into contact with disinfectants, which are often added to water for hygienic reasons. Chlorine dioxide, used as a disinfectant in water, degrades most materials including polyethylene (Colin, Ageing of polyethylene pipes for conveying drinking water disinfected with chlorine dioxide, Part I, Chemical aspects; Polymer engineering and Science 49(7); 1429-1437; July 2009). Other chlorinated solvents are, for example, chloramines and chlorine.

[0003] It is known in the art to apply additives such as antioxidants and stabilizers to prevent said degradation. Several types of additives have been proposed to protect the polymer during processing and to achieve the desired end-use properties. WO2005 / 056657 discloses a pipe comprising polyethylene for use with chlorinated water, the pipe containing a hindered phenol such as Irganox 1330, Irganox 1010 and / or Irganox 1076 and a phosphite such as Irgafos 168 and a metal deactivator such as Irganox MD 1024 and / or Naugard™ XL1. According to this solution, a suitable combination of stabilizers must be carefully selected, depending on the desired end properties that the polymer article should have.

[0004] WO2017133918 discloses a drinking water pipe produced using a polymer composition comprising polyethylene and zinc sulfide.

[0005] WO2018 / 028921 discloses a pipe for transporting water produced from a polymer composition comprising polyethylene and a polyolefin elastomer, wherein the amount of polyolefin elastomer in the composition is less than 10.0 wt% relative to the total weight of the composition.

[0006] There remains a need in the art for a method of delivering chlorinated water through pipes having a high resistance to chlorine-containing disinfectants.

[0007] Thus, the present invention provides the use of a pipe for conveying chlorinated water, wherein the pipe is a biaxially oriented pipe manufactured by a method comprising the steps of:

[0008] a) forming a polymer composition comprising a polyolefin into a pipe, and

[0009] b) stretching the tube of step a) in axial and circumferential directions to obtain a biaxially oriented tube.

[0010] It has surprisingly been found that biaxially oriented polyolefin tubes have a high resistance to chlorine-containing disinfectants.

[0011] According to another aspect, the present invention provides the use of a biaxially oriented pipe for improving the resistance of the pipe to chlorinated water, wherein the biaxially oriented pipe is manufactured by a method comprising the steps of:

[0012] a) forming a polymer composition comprising a polyolefin into a pipe, and

[0013] b) stretching the tube of step a) in axial and circumferential directions to obtain a biaxially oriented tube.

[0014] The term "chlorinated water" is understood herein to mean water dosed with chlorine, chlorine dioxide and / or chloramines. The total amount of chlorine, chlorine dioxide and chloramines may be 0.01-4.0 ppm relative to the weight of the chlorinated water. In some embodiments, the amount of chlorine dioxide is 0.01-4.0 ppm relative to the weight of the chlorinated water.

[0015] The terms "pipe", "tube" and "tube" are understood herein as hollow elongated articles which may have a cross section of various shapes. The cross section may be, for example, circular, oval, square, rectangular or triangular. The term "diameter" is understood herein as the largest dimension of the cross section.

[0016] Biaxially oriented tubes and methods for their production are well known per se and are described, for example, in WO1993019924 and US6325959, incorporated herein by reference.

[0017] Polymer composition

[0018] Preferably, the polymer composition comprising polyolefin comprises substantially no further polymers than the polyolefin.The amount of polyolefin may be at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% relative to the total amount of polymers in the polymer composition.

[0019] Preferably, the polyolefin in the polymer composition is selected from polypropylene and polyethylene and a combination of polypropylene and polyethylene. More preferably, the polyolefin in the polymer composition comprises polyethylene.

[0020] In some embodiments, the polymer composition comprises substantially no additional polymers other than polyethylene. The amount of polyethylene may be at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% relative to the total amount of polymers in the polymer composition.

[0021] Preferably, the polyolefin in the polymer composition is selected from high density polyolefin (HDPE), linear low density polyethylene (LLDPE), low density polyethylene (LDPE) and ultra high molecular weight polyethylene (UHMwPE). More preferably, the polyolefin in the polymer composition comprises HDPE.

[0022] In some embodiments, the polyolefin comprises HDPE and another polyethylene other than HDPE. The other polyethylene may, for example, be a linear low density polyethylene (LLDPE), a low density polyethylene (LDPE), or a combination of LLDPE and LDPE. Preferably, the other polyethylene is LLDPE or a combination of LLDPE and LDPE. More preferably, the other polyethylene is LLDPE. In the case where the other polyethylene is a combination of LLDPE and LDPE, the weight ratio of LLDPE to LDPE may, for example, be at least 0.1, such as at least 0.2 or at least 0.3 and at most 10, such as at most 5 or at most 3. Preferably, the weight ratio of LLDPE to LDPE is at least 1, such as 2-10. Preferably, the weight ratio of HDPE to the other polyethylene in the polymer composition is greater than 1, preferably 1.2-5, such as 1.5-4 or 2-3.

[0023] In some embodiments, the polymer composition comprises substantially no additional polymers other than HDPE.The amount of HDPE may be at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt%, relative to the total amount of polymers in the polymer composition.

[0024] The polymer composition may comprise components other than the polyolefin, such as additives and fillers.

[0025] Examples of additives include nucleating agents; stabilizers, such as heat stabilizers, antioxidants, UV stabilizers; colorants such as pigments and dyes; clarifying agents; surface tension modifiers; lubricants; flame retardants; mold release agents; flow improvers; plasticizers; antistatic agents; external elastic impact modifiers; foaming agents; and / or components that enhance the interfacial bonding between polymer and filler, such as maleated polyethylene. The amount of additives is typically 0-5 wt%, such as 1-3 wt%, relative to the total composition.

[0026] Examples of fillers include glass fibers, talc, mica, nanoclay. The amount of filler is typically 0-40 wt%, such as 5-30 wt% or 10-25 wt%, relative to the total composition.

[0027] Thus, in some embodiments, the polymer composition further comprises 0-5 wt% additives and 0-40 wt% fillers.

[0028] The polymer composition can be obtained by melt mixing the polyolefin and any other optional components.

[0029] Preferably, the total amount of polyolefin and optional additives and optional fillers is 100 wt %, relative to the total composition.

[0030] In some embodiments, the total amount of HDPE and optional additional polyethylene is at least 95 wt%, at least 98 wt%, at least 99 wt%, or 100 wt%, relative to the total amount of polymers present in the polymer composition.

[0031] In some embodiments, the total amount of HDPE and optional additional polyethylene is at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt%, or 100 wt% relative to the total composition.

[0032] Preferably, the polymer composition has a melt flow rate measured according to ISO 1133-1:2011 (190°C / 5kg) of 0.1 to 4 g / 10 min, more preferably 0.1 to 1 g / 10 min.

[0033] The production methods of HDPE, LLDPE and LDPE are summarized in The Polyethylene Handbook by Andrew Peacock (2000; Dekker; ISBN 0824795466), pages 43-66.

[0034] HDPE

[0035] Preferably, the HDPE is bimodal or multimodal. Such HDPE has properties suitable for the production of pipes. In addition, such HDPE can be stretched at low draw ratios without causing a local reduction in cross-sectional area known as polymer necking.

[0036] It is understood that a bimodal HDPE has a molecular weight distribution with two peaks, corresponding to a first median and a second median at various stages in the polymerization. Similarly, it is understood that a multimodal HDPE has a molecular weight distribution with multiple peaks, corresponding to a first median, a second median and one or more additional medians at various stages in the polymerization.

[0037] HDPE may be an ethylene homopolymer or may contain comonomers such as butene or hexene.

[0038] Preferably, HDPE has a density of 940-960 kg / m 3 , more preferably 940-955kg / m 3 density.

[0039] Preferably, the HDPE has a melt flow rate measured according to ISO 1133-1:2011 (190°C / 5kg) of 0.1-4 g / 10 min, more preferably 0.1-1 g / 10 min.

[0040] In some embodiments, the polymer composition comprises a compound comprising HDPE and a colorant, wherein the compound has a carbon content of 947-965 kg / m 3 The colorant may be, for example, carbon black or a pigment having a color such as black, blue or orange. The amount of colorant is typically 1-5 wt%, more typically 2-2.5 wt%, relative to the compound comprising HDPE and colorant, the remainder typically being HDPE.

[0041] HDPE can be produced by using a low pressure polymerization process. For example, pipe materials of performance grades PE 80 and PE 100 are known, which are usually produced in cascade equipment by so-called bimodal or multimodal processes. The production process of bimodal HDPE is summarized in "PE 100 Pipe System" (edited by Bromstrup; Second edition, ISBN 3-8027-2728-2) pages 16-20. Suitable low pressure methods are slurry cascades of stirred reactors, slurry cascades of loop reactors and combinations of different methods, such as slurry loop gas phase reactors. Multimodal polyethylene, preferably trimodal polyethylene (as described in, for example, WO2007003530) can also be used as high density polyethylene pipe material.

[0042] Performance grades PE 80 and PE 100 are discussed in "PE 100 Pipe Systems" (edited by Bromstrup; 2nd edition, ISBN 3-8027-2728-2), pages 35-42. Quality test methods are described on pages 51-62 of "PE 100 Pipe Systems".

[0043] Alt et al. describe the production of bimodal high density polyethylene (HDPE) by a low pressure slurry process in "Bimodal Polyethylene - Interaction of Catalysts and Processes" (Macromol. Symp. 2001, 163, 135-143). In a two-stage cascade process, the reactor can be continuously fed with a mixture of monomers, hydrogen, catalyst / cocatalyst and hexane (recycled from the process). In the reactor, the polymerization of ethylene occurs as an exothermic reaction at a pressure between, for example, 0.5 MPa (5 bar) and 1 MPa (10 bar) and at a temperature between, for example, 75° C. and 85° C. The heat of the polymerization reaction is removed by cooling water. The properties of the polyethylene depend, inter alia, on the catalyst system and on the applied concentrations of the catalyst, comonomer and hydrogen.

[0044] Alt et al., "Bimodal Polyethylene - Interaction of Catalysts and Processes" (Macromol. Symp. 2001, 163), pp. 137-138, explain the concept of a two-stage cascade process. The reactors are arranged in a cascade, with different conditions in each reactor, including a low hydrogen content in the second reactor. This allows the production of HDPE with a bimodal molecular weight distribution and a defined comonomer content in the polyethylene chain of each reactor.

[0045] The trimodal HDPE suitable for use in the present invention can be produced by a three-stage cascade process. The three-stage cascade process corresponds to a process in which an additional reactor is added to the two-stage cascade process described above. A mixture of monomers, hydrogen, catalyst / cocatalyst and hexane (recycled from the process) is fed to the additional reactor, similar to the reactor used in the two-stage cascade process.

[0046] Examples of HDPE include bimodal PE 80, bimodal PE 100, and multimodal HDPE. PE 80 is a PE material having an MRS (minimum required strength after 50 years in water at 20°C) of 8 MPa, and PE 100 is a PE material having an MRS of 10 MPa. Pipe classification is explained on page 35 of "PE 100 Pipe Systems" (edited by Bromstrup; second edition, ISBN 3-8027-2728-2).

[0047] Preferably, the HDPE or a compound comprising HDPE and a colorant has one or more of the following characteristics, preferably all of them:

[0048] - a tensile modulus of 500-1400 MPa, preferably 700-1200 MPa (according to ISO 527-2);

[0049] - a yield stress of 15-32 MPa, preferably 18-28 MPa (according to ISO 527-2);

[0050] - Full notch creep test (FNCT): 100-20000 hours (according to ISO 16770, at 80°C / 4MPa);

[0051] - At 23°C, 10-40 kJ / m 2 , preferably 14-35 kJ / m 2 Notched Charpy impact value (according to ISO1eA).

[0052] LLDPE

[0053] The polymer composition may comprise LLDPE.

[0054] Suitable technologies for LLDPE production include gas phase fluidized bed polymerization, solution polymerization, polymerization in the polymer melt at very high ethylene pressures, and slurry polymerization.

[0055] LLDPE comprises ethylene and a C3-C10 α-olefin comonomer (ethylene-α-olefin copolymer). Suitable α-olefin comonomers include 1-butene, 1-hexene, 4-methylpentene and 1-octene. The preferred comonomer is 1-hexene. Preferably, the α-olefin comonomer is present in an amount of about 5 to about 20 wt % of the ethylene-α-olefin copolymer, more preferably in an amount of about 7 to about 15 wt % of the ethylene-α-olefin copolymer.

[0056] Preferably, LLDPE has a hardness of 900-948 kg / m 3 , more preferably 915-935kg / m 3 , more preferably 920-935kg / m 3 density.

[0057] Preferably, the LLDPE has a melt flow rate measured according to ISO 1133-1:2011 (190°C / 2.16kg) of 0.1-3.0 g / 10 min, more preferably 0.3-3.0 g / 10 min.

[0058] LDPE

[0059] The polymer composition may comprise LDPE.

[0060] LDPE can be produced using autoclave high pressure technology and by tubular reactor technology.

[0061] LDPE may be an ethylene homopolymer or may contain comonomers such as butene or hexene.

[0062] Preferably, the LDPE has a density of 916-940 kg / m 3 , more preferably 920-935kg / m 3 density.

[0063] Preferably, the LDPE has a melt flow rate of 0.1-3.0 g / 10 min, more preferably 0.3-3.0 g / 10 min, measured according to ISO 1133-1:2011 (190° C. / 2.16 kg).

[0064] UhWp

[0065] The polymer composition may comprise UHMwPE. UHMwPE is a substantially linear polyethylene having a relative viscosity of 1.44 or more at 135°C in decalin at a concentration of 0.02%. UHMwPE is further described in ASTM D4020 2011.z.

[0066] Cross-linking

[0067] The crosslinking of polyolefins is known, for example, from WO97 / 19807 and WO2015 / 162155. WO97 / 19807 mentions radiation crosslinking, peroxide crosslinking, crosslinking with crosslinkable groups, ionomer crosslinking from page 10, line 25 to page 11, line 11. WO2015 / 162155 mentions the PEX-a process ("Engel process") using peroxides under the influence of heat and high pressure in

[0004] , the PEX-b process using moisture and heat in

[0005] , the PEX-c process using high-energy electron beam radiation in

[0006] of WO2015 / 162155, and UV curing in

[0007] .

[0068] The degree of crosslinking can be quantified according to the following references to ASTM F876:

[0069] "6.8. Degree of cross-linking

[0070] - When tested in accordance with 7.9, the degree of crosslinking of the PEX pipe material shall be in the range of 65-89% (inclusive).

[0071] Depending on the method used, the following minimum crosslinking percentage values ​​should be achieved: 70% by peroxide (PEX-a), 65% by azo compounds, 65% by electron beam (PEX-c) or 65% by silane compounds (PEX-b)"

[0072] Preferably, the polyolefin in the polymer composition is a substantially non-crosslinked polyolefin. The term "substantially non-crosslinked polyolefin" may refer to a polyolefin having a crosslinking degree of less than 50%, less than 40%, less than 30%, less than 20%, less than 10% or less than 5% as measured according to ASTM F876.

[0073] The term "substantially uncrosslinked polyolefin" may refer to a polyolefin that has not been subjected to the crosslinking method described in WO97 / 19807, page 10, line 25 to page 11, line 11 and

[0004] to

[0007] of WO2015 / 162155.

[0074] Advantageously, when the polyolefin in the polymer composition is a substantially non-crosslinked polyolefin, the pipe can be manufactured by a simple process.

[0075] Method steps

[0076] The process for making the pipe can be performed as a continuous process or as a batch process.A continuous process is herein understood as a process wherein the polymer composition is fed continuously for the pipe making step a), while the stretching step b) is performed continuously.

[0077] The polymer composition may be formed into a tube by any known method such as extrusion or injection molding (step a). Biaxial stretching (step b) may be performed by any known method.

[0078] A method of forming a polymer composition into a tube and the biaxial stretching of the tube are described in US6325959:

[0079] Conventional equipment for extruding plastic pipes comprises an extruder, a nozzle, a calibration device, a cooling device, a pulling device and a device for cutting or coiling the pipe. By passing the polymer melt from the extruder through the nozzle until calibration, cooling and the finished pipe is subjected to shearing and elongation in the axial direction of the pipe, a substantially uniaxial orientation of the pipe in its axial direction will be obtained. Another reason for facilitating the orientation of the polymer material in the direction of material flow is that the pipe can withstand the tension associated with manufacturing.

[0080] To achieve biaxial orientation, the equipment can be supplemented downstream of the traction device with a device for controlling the temperature of the tube to a temperature suitable for biaxial orientation of the tube, an orientation device, a calibration device, a cooling device, and a traction device for supplying the biaxially oriented tube to a cutting device or a coiler.

[0081] The biaxial orientation can also be carried out directly in connection with the first calibration after extrusion, in which case the above-mentioned additional device is located downstream of the first calibration device.

[0082] Biaxial orientation of the tube can be performed in various ways, such as mechanically by an internal mandrel, or by an internal pressurized fluid such as air or water, etc. Another method is to orient the tube by rollers, such as by placing the tube on a mandrel and rotating the mandrel and tube relative to one or more pressure rollers engaged with the tube, or by internally disposed pressure rollers that rotate relative to the tube against an externally disposed die or calibration device.

[0083] Conditions of step b)

[0084] A person skilled in the art can select suitable conditions (such as temperature) for step b) to obtain a biaxially oriented tube.Step b) is performed at a stretching temperature that results in orientation of the polyolefin in the polymer composition.

[0085] The stretching temperature is selected to be lower than the melting point of the polyolefin in the polymer composition. When the polyolefin composition comprises one type of polyolefin, step b) is preferably performed at a stretching temperature 1-30°C lower than the melting point of the polyolefin in the polymer composition, such as 2-20°C or 3-10°C lower than the melting point of the polyolefin in the polymer composition.

[0086] When the polymer composition includes different polyolefins with different melting points, the stretching temperature can be determined to achieve orientation of most of the polyolefins. The technician can appropriately determine the appropriate stretching temperature according to the type and amount of the polyolefin present in the polymer composition. Usually, the stretching temperature can be selected in a temperature range of 1-30°C lower than the melting point of each polyolefin present in the polymer composition, and the stretching temperature does not exceed the lowest melting point of the polyolefin present in the polymer composition. In the case where the melting point difference of the polyolefin present in the polymer composition is very large, the stretching temperature can be selected based on the polyolefin present in the main amount. For example, the stretching temperature can be selected to be 1-30°C lower than the melting point of the polyolefin present in the highest amount in the polymer composition. When determining the stretching temperature, the polymer present in a small amount (e.g., less than 5wt% of the polymer composition) can also be ignored.

[0087] In some embodiments, the polyolefin in the polymer composition is HDPE, and step b) can be performed at a stretching temperature 1-30°C below the melting point of HDPE, such as 2-20°C or 3-10°C below the melting point of HDPE.

[0088] In some embodiments, step b) is performed at a stretching temperature of 115-125° C., preferably 115-123° C. This is particularly suitable when the polyolefin in the polymer composition is HDPE.

[0089] In some embodiments, the polyolefin in the polymer composition is polypropylene, and step b) may be performed at a stretching temperature 1-30°C below the melting point of the polypropylene, such as 2-20°C or 3-10°C below the melting point of the polypropylene.

[0090] In some embodiments, step b) is performed at a stretching temperature of 145-155° C. This is particularly suitable when the polyolefin in the polymer composition is polypropylene.

[0091] In some embodiments, the polyolefin in the polymer composition comprises HDPE in an amount of at least 50 wt%, at least 75 wt%, or at least 90 wt%, relative to the polymer composition, and step b) is performed at a stretching temperature that is 1-30°C lower than the melting point of HDPE, such as 2-20°C or 3-10°C lower than the melting point of HDPE.

[0092] In some embodiments, the polyolefin in the polymer composition comprises polypropylene in an amount of at least 50 wt%, at least 75 wt%, or at least 90 wt% relative to the polymer composition, and step b) is performed at a stretching temperature that is 1-30°C lower than the melting point of the polypropylene, such as 2-20°C or 3-10°C lower than the melting point of the polypropylene.

[0093] Stretch ratio

[0094] Typically, step b) is performed with an axial stretch ratio of 1.1 to 5.0 and an average hoop stretch ratio of 1.1 to 3.0.

[0095] Preferably, the average hoop stretch ratio is 1.1-2.0.

[0096] Preferably, the axial stretch ratio is 1.1-4.0, such as 1.1-3.6 or 1.1-3.2. To obtain a biaxially oriented tube with a larger outer diameter, the axial stretch ratio is usually larger.

[0097] In some embodiments, the polyolefin in the polymer composition is a bimodal or multimodal HDPE, and

[0098] Step b) is performed with an axial stretch ratio of 1.1 to 3.2 and an average hoop stretch ratio of 1.1 to 2.0, and the obtained biaxially oriented tube has an outer diameter of at least 60 mm and a wall thickness of at least 5.5 mm, or

[0099] Step b) is performed with an axial stretching ratio of 1.1-1.9 and an average hoop stretching ratio of 1.1-2.0, and the obtained biaxially oriented tube has an outer diameter of less than 60 mm.

[0100] The use of bimodal or multimodal HDPE in combination with these specific stretch ratios selected according to the outer diameter size allows for the stable, neck-free production of pipes with good crack resistance. In these embodiments, to obtain a biaxially oriented pipe with an outer diameter of at least 60 mm, an axial stretch ratio of 1.1-3.2 is selected, and an average hoop stretch ratio of 1.1-2.0 is selected. The wall thickness is at least 5.5 mm. Preferably, the axial stretch ratio is at least 1.2, at least 1.3, at least 1.5 or at least 1.8 and / or at most 3.0, at most 2.8 or at most 2.5. Preferably, the average hoop stretch ratio is at least 1.2 or at least 1.3 and / or at most 1.8 or at most 1.6. Preferably, the outer diameter is 60-2000 mm, for example 60-150 mm or 150-2000 mm. Preferably, the wall thickness is 5.5-100 mm, for example 5.5-15 mm or 15-100 mm. In some embodiments, the biaxially oriented tube according to the present invention has an outer diameter of 60-150 mm and a wall thickness of 5.5-15 mm.

[0101] In these embodiments, to obtain a biaxially oriented tube with an outer diameter of less than 60 mm, an axial stretch ratio of 1.1-1.9 is selected, and an average hoop stretch ratio of 1.1-2.0 is selected. Preferably, the axial stretch ratio is at least 1.2, at least 1.3 or at least 1.5 and / or at most 1.8 or at most 1.7. Preferably, the average hoop stretch ratio is at least 1.2 or at least 1.3 and / or at most 1.8 or at most 1.6. Preferably, the outer diameter is 10 mm to less than 60 mm, for example 10-40 mm or 40 mm to less than 60 mm. Preferably, the wall thickness is 1-10 mm, for example 1.5-5 mm. In some embodiments, the biaxially oriented tube according to the present invention has an outer diameter of 10-40 mm and a wall thickness of 1.5-5 mm.

[0102] The axial stretch ratio of the stretched tube is defined as the ratio of the cross-sectional area of ​​the starting isotropic tube to the cross-sectional area of ​​the biaxially oriented tube (i.e., the product), i.e.,

[0103]

[0104] OD stands for outside diameter and ID stands for inside diameter.

[0105] The average hoop stretch ratio can be defined as:

[0106]

[0107] in

[0108]

[0109] It was unexpectedly discovered that relatively low stretch ratios improve time to failure properties.

[0110] Biaxial directional tube

[0111] Examples of suitable biaxially oriented tubing for use in accordance with the present invention have the following outer and inner diameters and wall thicknesses:

[0112] Outer diameter(mm) Inner diameter (mm) Wall thickness(mm) 110 90 10.0 90 73.6 8.2 75 61.4 6.8 63 51.4 5.8 32 26 3.0

[0113] The present invention also provides a method for transporting chlorinated water through a biaxially oriented tube, the tube being made by a method comprising the steps of:

[0114] a) forming a polymer composition comprising a polyolefin into a pipe, and

[0115] b) stretching the tube of step a) in axial and circumferential directions to obtain a biaxially oriented tube.

[0116] It should be noted that the present invention relates to all possible combinations of features described herein, particularly preferred are those combinations of features present in the claims. Therefore, it should be understood that all combinations of features relating to the composition according to the invention, all combinations of features relating to the method according to the invention, and all combinations of features relating to the composition according to the invention and to the method according to the invention are described herein.

[0117] It should also be noted that the terms "comprising", "including" or "containing" do not exclude the presence of other elements. However, it should also be understood that a description of a product / composition comprising certain components also discloses a product / composition consisting of these components. A product / composition consisting of these components may be advantageous because it provides a simpler and more economical method for preparing the product / composition. Similarly, it should also be understood that a description of a method comprising certain steps also discloses a method consisting of these steps. A method consisting of these steps may be advantageous because it provides a simpler and more economical method.

[0118] When a value for a lower limit and an upper limit of a parameter is mentioned, it is also understood that a range formed by the combination of the value of the lower limit and the value of the upper limit is disclosed.

[0119] The present invention will now be illustrated by the following examples, but is not limited thereto.

[0120] HDPE: SABIC Vestolen A 6060R grade, with 959kg / m 3 Density (black compound density) and MFR (5kg / 190°C) of 0.3g / 10min. Bimodal PE.

[0121] Production of biaxial oriented tubes:

[0122] HDPE was pelletized using a twin screw extruder. The processing temperature and screw profile were standard for polyethylene compounding.

[0123] These compounded pellets were used to produce thick tubular profiles of approximate dimensions of about 60 mm outer diameter and about 24 mm inner diameter. These thick tubes were stretched through an expansion tapered mandrel of 61-65 mm outlet diameter and 15 degree half angle at a temperature of 120°C at a stretching speed of 100 mm / min. The axial stretch ratio was varied as shown in Table 1, and the average hoop stretch ratio was 1.4.

[0124] ClO2 resistance test

[0125] The circulation loop is used for water containing ClO2. The ClO2 concentration in the water is 1.0±0.1ppm. The pH value of the water is 6.8±0.2. The water temperature is 40±1°C. The flow rate is 54l / h, and the fluid pressure is 6bar. The typical free tube length is 500mm, the tube outer diameter is 63mm, and the wall thickness is based on the stretch ratio of the tube and is shown in Table 1. The circulation loop for ClO2 testing is made of inert materials to avoid contamination of the test liquid. The internal environment is the above-mentioned ClO2 aqueous solution, and the external environment is air. The test setup is the same as ASTMF2023.

[0126] Table 1

[0127]

[0128] The inner surface of the biaxially oriented tube was not affected after 26331 hours, while the inner surface of the isotropic tube showed many cracks and finally failed after 13871 hours or 13407 hours.

Claims

1. Use of a pipe for conveying chlorinated water, wherein the pipe is a biaxially oriented pipe made by a process comprising the steps of: a) forming a polymer composition comprising a polyolefin into a pipe, and b) stretching the tube of step a) in axial and circumferential directions to obtain said biaxially oriented tube, in: The polymer composition has a melt flow rate of 0.1-4 g / 10 min measured at 190° C. / 5 kg according to ISO 1133-1:2011, The polyolefin comprises a high-density polyethylene, wherein the high-density polyethylene has a density of 940-960 kg / m 3 density and a melt flow rate of 0.1-4 g / 10 min measured at 190°C / 5 kg according to ISO1133-1:2011, wherein said step b) is performed at a stretching temperature of 115-125°C, and wherein step b) is performed at an axial stretching ratio of 1.1-5.0 and an average hoop stretching ratio of 1.1-3.0, The chlorinated water is water dosed with chlorine, chlorine dioxide and / or chloramines, wherein the total amount of chlorine, chlorine dioxide and chloramines is 0.01-4.0 ppm relative to the weight of the chlorinated water.

2. The use according to claim 1, wherein the amount of chlorine dioxide is 0.01-4.0 ppm relative to the weight of the chlorinated water.

3. The method according to claim 1, wherein the polymer composition further comprises linear low density polyethylene, low density polyethylene, ultra high molecular weight polyethylene and a combination of at least two of the above.

4. The use according to any one of claims 1-2, wherein the polyolefin is the high-density polyethylene.

5. Use according to any one of claims 1-2, wherein the polyolefin is a bimodal or multimodal high density polyethylene.

6. Use according to any one of claims 1 to 2, wherein the amount of the polyolefin is at least 95 wt% relative to the total amount of polymers in the polymer composition.

7. The use according to any one of claims 1 to 2, wherein the polymer composition has a melt flow rate of 0.1 to 1 g / 10 min measured at 190°C / 5 kg according to ISO 1133-1:2011.

8. The use according to any one of claims 1-2, wherein the polymer composition further comprises 0-5 wt% of additives and 0-40 wt% of fillers.

9. The method according to claim 1, wherein step b) is performed at a stretching temperature of 1-30°C below the melting point of the polyolefin present in the highest amount in the polymer composition and / or wherein step b) is performed at a stretching temperature of 115-123°C.

10. The use according to any one of claims 1 to 2, wherein the polyolefin in the polymer composition is an uncrosslinked polyolefin.

11. The use according to any one of claims 1 to 2, wherein the polyolefin in the polymer composition is a polyolefin having a degree of crosslinking measured according to ASTM F876 of less than 50%.

12. Use of a biaxially oriented tube for improving the resistance of the tube to chlorinated water, wherein the biaxially oriented tube is made by a method comprising the steps of: a) forming a polymer composition comprising a polyolefin into a pipe, and b) stretching the tube of step a) in axial and circumferential directions to obtain said biaxially oriented tube, in: The polymer composition has a melt flow rate of 0.1-4 g / 10 min measured at 190° C. / 5 kg according to ISO 1133-1:2011, The polyolefin comprises a high-density polyethylene, wherein the high-density polyethylene has a density of 940-960 kg / m 3 density and a melt flow rate of 0.1-4 g / 10 min measured at 190°C / 5 kg according to ISO1133-1:2011, wherein said step b) is performed at a stretching temperature of 115-125°C, and wherein step b) is performed at an axial stretching ratio of 1.1-5.0 and an average hoop stretching ratio of 1.1-3.0, The chlorinated water is water dosed with chlorine, chlorine dioxide and / or chloramines, wherein the total amount of chlorine, chlorine dioxide and chloramines is 0.01-4.0 ppm relative to the weight of the chlorinated water.

13. The use according to claim 12, wherein the amount of chlorine dioxide is 0.01-4.0 ppm relative to the weight of the chlorinated water.

14. The use according to any one of claims 12-13, wherein the polymer composition further comprises linear low density polyethylene, low density polyethylene, ultra high molecular weight polyethylene and a combination of at least two of the above.

15. The use according to any one of claims 12-13, wherein the polyolefin is the high density polyethylene.

16. Use according to any one of claims 12-13, wherein the polyolefin is a bimodal or multimodal high density polyethylene.

17. The use according to any one of claims 12-13, wherein the polyolefin in the polymer composition is an uncrosslinked polyolefin.

18. The use according to any one of claims 12-13, wherein the polyolefin in the polymer composition is a polyolefin having a cross-linking degree of less than 50% measured according to ASTM F876.

Images