WO2021148352A1

WO2021148352A1 - Pipe for transport of water containing chlorinated disinfectant

Info

Publication number: WO2021148352A1
Application number: PCT/EP2021/050952
Authority: WO
Inventors: Patrick Elisabeth Luc Voets; Mark Johannes Boerakker; Sarah Van Mierloo
Original assignee: Sabic Global Technologies B.V.
Priority date: 2020-01-21
Filing date: 2021-01-18
Publication date: 2021-07-29

Abstract

The invention relates to a pipe comprising a polymer composition comprising a polyolefin and a hindered amine light stabilizer, wherein the amount of the hindered amine light stabilizer is 0.02 to 3.0 wt% with respect to the total polymer composition, wherein the hindered amine light stabilizer comprises a compound represented by formula (I), wherein R², R⁴ and R⁶ are independently a straight or branched C1 -C4 alkyl group and R¹, R³, R⁵ and R⁷ are independently represented by a group of formula (II), wherein R⁸, R⁹, R¹⁰ and R¹¹ are independently selected from the group consisting of hydrogen, straight or branched C1 -C4 alkyl groups and a group of formula (III) wherein R¹² is hydrogen or a straight or branched C1-C4 alkyl group or is an OR¹³ group wherein R¹³ is hydrogen or a straight or branched C1-C4 alkyl group.

Description

PIPE FOR TRANSPORT OF WATER CONTAINING CHLORINATED DISINFECTANT

The present invention relates to a pipe comprising a polymer composition. The present invention further relates to a process for the preparation of such pipe and the use of the pipe for the transport of chlorinated water.

The term “pipe” is herein understood as a hollow elongated article. The cross section may be of various shapes e.g. circular, elliptical, square, rectangular or triangular.

Pipes for the transport of gas, for sanitation and for water supply may be produced with polyolefin compositions, for example polyethylene or polypropylene compositions.

Pipes based on a polyolefin have a very good resistance to water. However their lifetime is shortened when the pipes come into contact with chlorinated disinfectants which are often added to water for hygienic reasons. Chlorine is present in most disinfected drinking-water at concentrations of 0.2 to 1 mg/litre (White GC. Current chlorination and dechlorination practices in the treatment of potable water, wastewater and cooling water. In: Jolley RL, ed. Water chlorination: environmental impact and health effects. Vo I. 1. Ann Arbor, Ml, Ann Arbor Science, 1978:1-18). Chlorine dioxide used as disinfectant in water degrades most materials including polyolefin (Colin, Aging of polyethylene pipes transporting drinking water disinfected by chlorine dioxide, part I, Chemical aspects; Polymer engineering and Science 49(7); 1429-1437; July 2009). Other chlorinated disinfectants are for example chloramine and chlorine. It is known in the art to use additives, for example antioxidants and stabilizers to prevent said degradation.

US2005/0148700 discloses a composition comprising a polyolefin which is in permanent contact with chlorinated water and a stabilizer such as an epoxidized fatty acid and an organotin compound.

WO2015/162155 discloses a specific photoinitiator for use in a cross-linked polyolefin pipe. WO2015/162155 mentions that the pipe may satisfy long term stability chlorine resistance requirement according to ASTM F2023. The pipe may comprise a hindered amine light stabilizer (HALS).

Although some known pipes may be suitable for use in transportation of chlorinated water, there is still a need in the art for a pipe having a high resistance to chlorinated disinfectants, in particular resistance represented by the value of retention of elongation at break after aging.

It is an object of the present invention to provide a pipe having a high resistance to chlorinated disinfectants.

Accordingly, the present invention provides a pipe comprising a polymer composition comprising a polyolefin and a hindered amine light stabilizer, wherein the amount of the hindered amine light stabilizer is 0.02 to 3.0 wt% with respect to the total polymer composition, wherein the hindered amine light stabilizer comprises a compound represented by formula (I)

wherein R², R⁴ and R⁶ are independently a straight or branched C1 -C4 alkyl group and R¹, R³, R⁵ and R⁷ are independently represented by a group of formula (II)

wherein R⁸, R⁹, R¹⁰ and R¹¹ are independently selected from the group consisting of hydrogen, straight or branched C1 -C4 alkyl groups and a group of formula (III)

wherein R¹² is hydrogen or a straight or branched C1-C4 alkyl group or is represented by -OR¹³ wherein R¹³ is hydrogen or a straight or branched C1-C4 alkyl group.

Surprisingly, the pipe according to the invention was found to have a high resistance to chlorinated disinfectants, which leads to a long lifetime when used for transport of water containing chlorinated disinfectants. The resistance to chlorinated disinfectants may be determined by a retention value of the polymer composition forming the pipe, wherein the retention value is calculated as the ratio between the elongations at break as measured according to ISO IS0527-1 :2012 at room temperature (23 °C) at a strain rate of 50 mm/min of an aged specimen and of a non-aged specimen, wherein the aging is conducted in a continuous water flow having a temperature of 70 ^SC, a chlorine dioxide concentration of 4.4 ppm and a pH of 6.8, at a flow rate of 22.71 L/h for a period of 1000 hours. Preferably, the retention value is at least 80 %.

It is noted that US2005/0148700 discloses as example 1b a composition comprising a block oligomeric hindered amine light stabilizer Chimassorb 2020. Chimassorb 2020 does not have the structure of the HALS required in the composition of the invention. In US2005/0148700, it can be seen by the comparison of example 1b and example 1a that the addition of Chimassorb 2020 leads to a much shorter life time prediction.

The chlorinated disinfectants in the water to be transported by the pipe according to the invention may be chlorine, chlorine dioxide and/or chloramines. The total amount of chlorine, chlorine dioxide and chloramines may be 0.01 to 5.0 ppm by weight with respect to the water comprising the chlorinated disinfectants. In some embodiments, the amount of chlorine dioxide is 0.01 to 5.0 ppm by weight with respect to the water comprising the chlorinated disinfectants. Polymer composition

Preferably, the polymer composition comprising a polyolefin essentially comprises no further polymers other than the polyolefin. The amount of the polyolefin with respect to the total amount of polymers in the polymer composition may be at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt%.

Preferably, the polyolefin has a melt flow index (MFI) measured according to IS01133- 1 :2011 (2.16 kg/230°C) in the range of 0.01 to 3.0 dg/min, more preferably in the range of 0.05 to 2.5 dg/min, even more preferably in the range of 0.1 to 1 .8 dg/min.

Propylene random copolymer

In the present invention, the polyolefin is a propylene random copolymer. The propylene random copolymer is preferably prepared from propylene and at least one comonomer chosen from the group consisting of ethylene and a-olefins having 4 to 10 carbon atoms, preferably wherein the polyolefin is a propylene-ethylene copolymer or a propylene-ethylene-1 -hexene copolymer. Preferably, the propylene random copolymer comprises ethylene comonomer. Preferably, the amount of ethylenecomonomer units in the propylene random copolymer is from 0.50 to 5.0 wt%, more preferably from 1 .4 to 4.5 wt%, more preferably from 3.0 to 4.2 wt% based on the total propylene random copolymer.

In some preferred embodiments, the comonomer of the propylene random copolymer is ethylene, i.e. the propylene random copolymer is a propylene-ethylene copolymer.

In some preferred embodiments, the comonomer of the propylene random copolymer is ethylene and 1 -hexene, i.e. the propylene random copolymer is a propylene- ethylene-1 -hexene copolymer.

The catalyst used to produce the propylene random copolymer used according to the present invention is known to the people skilled in art, for example Ziegler-Natta catalyst or metallocene catalyst. Preferably, the polypropylene according to the present invention is produced with a catalyst which is free of phthalate. In the present invention, it is essential that propylene random copolymer is used as comparing to other type of polypropylene e.g. heterophasic propylene impact copolymer or propylene homopolymer, propylene random copolymer has better long term pressure resistance which is important for pipe application.

Polyethylene

In some embodiments, the polymer composition comprises polyethylene.

The polyethylene may be selected from the group consisting of high density polyolefin (HDPE), linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE) and ultrahigh molecular weight polyethylene (UHMwPE). More preferably, the polyolefin in the polymer composition comprises HDPE.

The production processes of HDPE, LLDPE and LDPE are summarised in Handbook of Polyethylene by Andrew Peacock (2000; Dekker; ISBN 0824795466) at pages 43- 66

HDPE

Preferably, the HDPE is bimodal or multimodal. Such HDPEs have properties suitable for producing a pipe.

It is understood that a bimodal HDPE has a molecular weight distribution having two peaks corresponding to the first median and the second median of the respective stages in the polymerization. It is similarly understood that a multimodal HDPE has a molecular weight distribution having multiple peaks corresponding to the first median, the second median and one or more further medians of the respective stages in the polymerization.

HDPE may be an ethylene homopolymer or may comprise a comonomer, for example 1 -butene or 1 -hexene.

For example, the HDPE may have a density of at least 0.935 g/cm³, at least 0.938 g/cm³, at least 0.940 g/cm³, at least 0.942 g/min³ and/or at most 0.960 g/cm³, according to ISO 1183-1 :2004.

The HDPE may e.g. have a melt flow index (MFI) in the range of 0.01 to 3.0 dg/min, more preferably in the range of 0.05 to 2.5 dg/min, even more preferably in the range of 0.1 to 1.8 dg/min measured according to IS01133-1 :2011 (5 kg/190 ^SC). The HDPE can be produced by using low pressure polymerisation processes. For example, pipe materials of the performance class PE 80 and PE 100 are known, which are generally produced in cascade plants by a so called bimodal or multimodal process. The production processes for bimodal HDPE are summarised at pages 16-20 of "PE 100 Pipe systems" (edited by Bromstrup; second edition, ISBN 3-8027-2728-2). Suitable low pressure processes are slurry cascade of stirred reactors, slurry cascade of loop reactors and a combination of different processes such as slurry loop gas phase reactor. It is also possible to use a multimodal polyethylene, preferably trimodal polyethylene, as described for example in W02007003530, as high density polyethylene pipe material.

The performance classes PE 80 and PE 100 are discussed at pages 35- 42 of "PE 100 Pipe systems" (edited by Bromstrup; second edition, ISBN 3-8027-2728- 2). The quality test methods are described at pages 51 -62 of "PE 100 Pipe systems".

The production of bimodal high density polyethylene (HDPE) via a low pressure slurry process is described by Alt et al. in "Bimodal polyethylene-interplay of catalyst and process" (Macromol.Symp. 2001 , 163, 135-143). In a two stage cascade process the reactors may be fed continuously with a mixture of monomers, hydrogen, catalyst/cocatalyst and hexane recycled from the process. In the reactors, polymerisation of ethylene occurs as an exothermic reaction at pressures in the range between for example 0.5 MPa (5 bar) and 1 MPa (10 bar) and at temperatures in the range between for example 75 ^SC and 85 ^SC. The heat from the polymerisation reaction is removed by means of cooling water. The characteristics of the polyethylene are determined amongst others by the catalyst system and by the applied concentrations of catalyst, co monomer and hydrogen.

The concept of the two stage cascade process is elucidated at pages 137-138 by Alt et al. "Bimodal polyethylene-interplay of catalyst and process" (Macromol.Symp. 2001 , 163). The reactors are set up in cascade with different conditions in each reactor including low hydrogen content in the second reactor. This allows for the production of HDPE with a bimodal molecular mass distribution and defined co monomer content in the polyethylene chains in each reactor. A trimodal HDPE suitable for use in the present invention may be produced by a three stage cascade process. The three stage cascade process corresponds to a process wherein one additional reactor is added to the two stage cascade process as described above. The additional reactor is fed with a mixture of monomers, hydrogen, catalyst/co catalyst and hexane recycled from the process, similar to the reactors used in the two stage cascade process.

Examples of the HDPE include a bimodal PE 80, a bimodal PE 100 and a multimodal HDPE. PE 80 is a PE material with an MRS (minimum required strength after 50 years for water at 20 degrees Celsius) of 8 MPa and PE 100 is a PE material with an MRS of 10 MPa. The pipe classification is elucidated at page 35 of "PE 100 Pipe systems" (edited by Bromstrup; second edition, ISBN 3-8027-2728-2).

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

- Tensile modulus of 500-1400 MPa, preferably 700-1200 MPa (according to ISO 527-

2)

- Yield stress of 15-32 MPa, preferably 18-28 MPa (according to ISO 527-2)

- Full Notch Creep Test (FNCT): 100 - 20000 h (according to ISO 16770 @ 80 degrees centigrade / 4 MPa)

- notched Charpy impact value of 10-40 kJ/m² @ 23 ^SC, preferably 14-35 kJ/m² (according to ISO 1 eA).

LLDPE

The polymer composition may comprise LLDPE.

The technologies suitable for the LLDPE manufacture include gas-phase fluidized-bed polymerization, polymerization in solution, polymerization in a polymer melt under very high ethylene pressure, and slurry polymerization.

The LLDPE comprises ethylene units and units of a C3-C10 a-olefin comonomer. Suitable a-olefin comonomers include 1 -butene, 1 -hexene, 4-methyl pentene and 1- octene. The preferred comonomer is 1 -hexene. Preferably, the a-olefin comonomer units are present in an amount of about 5 to about 20 wt% of the ethylene- a-olefin copolymer, more preferably an amount of from about 7 to about 15 wt% of the ethylene-a-olefin copolymer. Preferably, the LLDPE has a density of 0.900-0.948 g/cm³, more preferably 0.915- 0.935 g/cm³, more preferably 0.920-0.935 g/cm³, determined according to IS01872-2. Preferably, the LLDPE has a Melt Flow Rate of 0.1 -3.0 g/1 Omin, more preferably 0.3- 3.0 g/1 Omin, determined according to IS01133-1 :2011 (190°C/2.16kg).

LDPE

The polymer composition may comprise LDPE.

The LDPE may be produced by use of autoclave high pressure technology and by tubular reactor technology.

LDPE may be an ethylene homopolymer or may comprise a comonomer, for example butene or hexene.

Preferably, the LDPE has a density of 0.916-0.940 g/cm³, more preferably 0.920-0.935 g/cm³, determined according to IS01872-2. Preferably, the LDPE has a Melt Flow Rate of 0.1 -3.0 g/1 Omin, more preferably 0.3-3.0 g/1 Omin, determined according to IS01133-1 :2011 (190°C/2.16kg).

UHMwPE

The polymer composition may comprise UHMwPE. UHMwPE is a substantially linear polyethylene which has a relative viscosity of 1 .44 or greater, at a concentration of 0.02 %, at 135°C, in decahydronaphthalene. UHMwPE is described further in ASTM D4020 2011.

Crosslinking Crosslinking of a polyolefin is known e.g. from W097/19807 and WO2015/162155. WO97/19807, p.10, l.25-p.11 , 1.11 mentions radiation cross-linking, peroxide crosslinking, cross-linking with cross-linkable groups, ionomer cross-linking.

WO2015/162155 mentions PEX-a process using peroxide under the influence of heat and high pressure (“Engel Method”) in [0004], PEX-b process using moisture and heat in [0005], PEX-c process using high energy electron beam irradiation as in [0006] of WO2015/162155 and UV curing in [0007] The degree of crosslinking can be quantified in accordance with the following citation from ASTM F876: "6.8. Degree of Crosslinking

-When tested in accordance with 7.9, the degree of crosslinking for PEX tubing material shall be within the range from 65 to 89% inclusive. Depending on the process used, the following minimum percentages crosslinking values shall be achieved: 70% by peroxides (PEX-a), 65% by Azo compounds, 65% by electron beam (PEX-c), or 65% by silane compounds (PEX-b).”

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

The term “substantially non-crosslinked polyolefin” may mean a polyolefin which has not been subjected to the crosslinking methods described in W097/19807, p.10, 1.25- p.11 , 1.11 and WO2015/162155 [0004]-[0007]

It is advantageous that the pipe can be made by a simple process when the polyolefin in the polymer composition is a substantially non-crosslinked polyolefin.

Hindered amine light stabilizer

The polymer composition comprises a hindered amine light stabilizer (HALS), which is a compound in which an amine group is sterically hindered by adjacent functional groups. Various types of HALS are per se known, for example described in WO 2010/138816, at paragraph [0050] on pages 15 to 17, which paragraph is incorporated herein by reference.

The HALS in the polymer composition comprises the compound (I). Preferably, the amount of the compound (I) in the composition with respect to the amount of the HALS in the composition is at least 50 wt%, at least 75 wt%, at least 90 wt%, at least 95 wt%. Most preferably, the HALS in the composition consists of the compound (I). The amount of the HALS with respect to the total composition is 0.02 to 3.0 wt%, preferably 0.03 to 2.0 wt%, more preferably 0.05 to 1.0 wt%, more preferably 0.10 to 0.50 wt%.

Preferably, the amount of the compound (I) with respect to the total composition is 0.02 to 3.0 wt%, preferably 0.03 to 2.0 wt%, more preferably 0.05 to 1 .0 wt%, more preferably 0.10 to 0.50 wt%. In formula (I), preferably, R², R⁴ and R⁶ are independently a straight C2-C4 alkyl group. More preferably, R² and R⁶ are independently a straight C3 alkyl group and R4 is a C2 alkyl group.

In formula (II), preferably, R⁸ is n-butyl and R⁹ is represented by formula (III) wherein R¹² is preferably methyl, and

R¹⁰ is n-butyl and R¹¹ is represented by formula (III) wherein R¹² is preferably methyl.

Most preferably, the compound (I) is Chimassorb® 119 represented by the following formula:

Preferably, the polymer composition does not contain Chimassorb® 2020.

Preferably, the polymer composition does not contain Chimassorb® 944 LD. Further components

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

Examples of the additives include nucleating agents; stabilisers, e.g. heat stabilisers, anti-oxidants, UV stabilizers; colorants, like pigments and dyes; clarifiers; surface tension modifiers; lubricants; flame-retardants; mould-release agents; flow improving agents; plasticizers; anti-static agents; external elastomeric impact modifiers; blowing agents; and/or components that enhance interfacial bonding between polymer and filler, such as a maleated polyethylene. The amount of the additives is typically 0 to 4 wt%, for example 1 to 3 wt%, with respect to the total composition. It will be appreciated that the amount of the additives as used herein do not include the amount of the HALS.

Preferably, the polymer composition comprises less than 0.02 wt%, less than 0.01 wt%, less than 0.005 wt%, less than 0.001 wt% or 0 wt% with respect to the polymer composition of a photoinitiator represented by formula IV:

wherein in formula IV:

R¹ is selected from -C4-C24 alkyl, -(CH₂)_m(C2-C24-m alkenyl), -(CH₂)m(C2-C24-m alkynyl), - C4-C24 haloalkyl, -(CH₂)_m(C2-C24-m haloalkenyl), -(CH₂)m(C2-C24-m haloalkynyl), - (CH2)n[0(CH2)p]_q(CH₂)rR⁴;

R² is selected from -H and -O-R³; R³ is selected from -C4-C24 alkyl, -(CH₂)_m(C2-C24-m alkenyl), -(CH₂)m(C2-C24-m alkynyl), - C4-C24 haloalkyl, -(CH₂)_m(C2-C24-m haloalkenyl), -(CH₂)m(C2-C24-m haloalkynyl), - (CH2)n[0(CH2)p]_q(CH₂)rR⁵;

R⁴ and R⁵ are independently selected from -H and -O-R⁶;

R⁶ is selected from -H, -C1 -C18 alkyl, -(CH₂)_s(C2-Ci8-s alkenyl), or -(CH₂)_s(C2-Ci8-s alkynyl); m is 2 - 22; n is 1 - 12; p is 2, 3, 4, 5 or 6; q is 2 - 10; and r is 0, 1 or 2; s is 2 - 16; wherein when R² is -H, R¹ comprises at least 7 carbon atoms

Preferably, the polymer composition comprises less than 0.02 wt%, less than 0.01 wt%, less than 0.005 wt%, less than 0.001 wt% or 0 wt% with respect to the polymer composition of a photoinitiator.

Preferably, the polymer composition does not contain an epoxidized fatty acid having 3 to 22 carbon atoms or an alkyl ester thereof having 1 to 18 carbon atoms; or an organotin compound.

Examples of fillers include glass fibers, talc, mica, nanoclay. The amount of fillers is typically 0 to 40 wt%, for example 5 to 30 wt% or 10 to 25 wt%, with respect to the total composition.

Accordingly, in some embodiments, the polymer composition further comprises 0 to 5 wt% of additives and 0 to 40 wt% of fillers.

Preferably, the polymer composition consists of the polyolefin, the HALS, the optional additives and the optional fillers, i.e. the total amount of the polyolefin, the HALS, the optional additives and the optional fillers is 100 wt% with respect to the total polymer composition.

Preferably, the total amount of the polyolefin and the optional fillers with respect to the total polymer composition is at least 95.0 wt%, more preferably at least 97.0 wt%, more preferably at least 98.5 wt%.

The amount of the polyolefin in the polymer composition with respect to the total polymer composition may be at least 55.0 wt%, at least 65.0 wt%, at least 75.0 wt%, at least 85.0 wt%, at least 90.0 wt%, at least 95.0 wt%, at least 97.0 wt% or at least 98.5 wt%. In some embodiments, the composition comprises fillers. In this case, the amount of the polyolefin with respect to the total composition may typically be 55.0 to 98.5 wt%, for example 60 to 90 wt%.

In some embodiments, the composition comprises little or no amount of fillers. In this case, preferably, the amount of the polyolefin with respect to the total composition is at least 95.0 wt%, more preferably at least 97.0 wt%, more preferably at least 98.5 wt%. Process and use

The composition in the pipe according to the invention may be prepared by a process comprising the step of melt-mixing the polyolefin, the HALS and optionally other components e.g. in an extruder. There are two advantageous points of such process: The polymer composition is obtainable in the form of pellet or granular which is easy to be processed into a shaped article; The obtained polymer composition is homogeneous and has well-defined concentrations of the additives.

Suitable conditions for melt-mixing, such as temperature, pressure, amount of shear, screw speed and screw design when an extruder is used are known to the skilled person.

The present invention further relates to a process for the preparation of the pipe according to the invention comprising the step of extruding the polymer composition of the invention to obtain the pipe.

Preferably, the amount of the polymer composition is at least 95 wt%, preferably at least 97 wt%, more preferably at least 98 wt% or 100 wt% based on the total pipe.

The present invention further relates to the use of the aforementioned polymer composition for the preparation of a pipe for the transport of water containing chlorinated disinfectant.

The present invention further relates to the use of the aforementioned pipe for the transport of water containing chlorinated disinfectant. The present invention further relates to the use of the compound (I) for improving the resistance of a pipe against water containing chlorinated disinfectants, wherein the pipe is made from a polymer composition comprising the compound (I).

It is noted that the invention relates to the subject-matter defined in the independent claims alone or in combination with any possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the composition according to the invention; all combinations of features relating to the process according to the invention and all combinations of features relating to the composition according to the invention and features relating to the process according to the invention are described herein.

It is further noted that the term ‘comprising’ does not exclude the presence of other elements. However, it is also to be understood that a description on a product/composition comprising certain components also discloses a product/composition consisting of these components. The product/composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product/composition. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps. The process consisting of these steps may be advantageous in that it offers a simpler, more economical process.

When values are mentioned for a lower limit and an upper limit for a parameter, ranges made by the combinations of the values of the lower limit and the values of the upper limit are also understood to be disclosed.

The invention is now elucidated by way of the following examples, without however being limited thereto.

Examples

SABIC PP 9421 (Resin) was used as base polymer in all the examples, which is a propylene random copolymer with MFI of 0.28 g/10min measured according to IS01133-1 :2011 (2.16 kg / 230 °C) and total ethylene content of 3.9 wt% determined by ¹³C-NMR. The resin was melt-mixed with the following components as examples for the present invention: • Styrene-isoprene-styrene block copolymer: Kraton D1113PT obtained from Kraton Polymers U.S. LLC;

• HALS: Chimassorb® 119

• ZnS in the form of powder.

Neat SABIC PP 9421 was used as reference. The amounts of the styrene-isoprene- styrene block copolymer, HALS and ZnS are shown in Table 1 , wherein “wt%” in table 1 is based on the total amount of the composition.

The obtained compositions were compression molded using IS01872-2:2007 into plaques, then plaques were cut into tensile bars according to IS0527-1 :2012 (4 mm thick) as testing specimens.

Ageing test: The testing specimens were aged in a continuous water flow at a temperature of 70 ^SC with a chlorine dioxide concentration maintained at 4.4 ppm and a pH maintained at 6.8. Flow rate was regulated at 22.71 L/h. The testing samples were aged for 1000 hrs.

Tensile tests according to Plastics- Determination of tensile properties IS0527-1 :2012 at room temperature (23 °C) at a strain rate of 50 mm/min on aged and non-aged specimens were performed. The elongation at break are reported in Table 1 .

Retention is defined as the ratio between elongation at break after aging and elongation at break before aging. A higher value of retention indicates that the example has better resistance against chlorine.

Table 1 : Elongation at break before, after aging and retention

According to Table 1 , Ex 1 with 0.3 wt% HALS has a higher retention value than the comparative examples 1 and 2 which contain 0.5 wt% styrene-isoprene-styrene block copolymer and ZnS respectively. Accordingly, the composition according to the invention has a better resistance against chlorinated disinfectants than comparative examples.

The composition according to the present invention is suitable to be used in a pipe for the transport of water containing chlorinated disinfectants, for example chlorine dioxide, chloramine and chlorine.

Claims

1 . A pipe comprising a polymer composition comprising a polyolefin and a hindered amine light stabilizer, wherein the amount of the hindered amine light stabilizer is 0.02 to 3.0 wt% with respect to the total polymer composition, wherein the hindered amine light stabilizer comprises a compound represented by formula (I)

wherein R², R⁴ and R⁶ are independently a straight or branched C1-C4 alkyl group and R¹, R³, R⁵ and R⁷ are independently represented by a group of formula (II)

wherein R⁸, R⁹, R¹⁰ and R¹¹ are independently selected from the group consisting of hydrogen, straight or branched C1-C4 alkyl groups and a group of formula (III)

wherein R¹² is hydrogen or a straight or branched C1-C4 alkyl group or is an OR¹³ group wherein R¹³ is hydrogen or a straight or branched C1-C4 alkyl group, wherein the polyolefin is a propylene random copolymer, wherein the propylene random copolymer is prepared from propylene and at least one comonomer chosen from the group consisting of ethylene and a-olefins having 4 to 10 carbon atoms, preferably wherein the polyolefin is a propylene-ethylene copolymer or a propylene- ethylene-1 -hexene copolymer.

2. The pipe according to claim 1 , wherein the amount of the hindered amine light stabilizer with respect to the total composition is 0.03 to 2.0 wt%, more preferably 0.05 to 1 .0 wt%, more preferably 0.10 to 0.50 wt%.

3. The pipe according to any one of the preceding claims, wherein the amount of the compound (I) with respect to the total composition is 0.02 to 3.0 wt%, preferably 0.03 to 2.0 wt%, more preferably 0.05 to 1 .0 wt%, more preferably 0.10 to 0.50 wt%.

4. The pipe according to any one of the preceding claims, wherein the amount of the compound (I) in the composition with respect to the amount of the hindered amine light stabilizer in the composition is at least 50 wt%, at least 75 wt%, at least 90 wt% or at least 95 wt%, or the hindered amine light stabilizer in the composition consists of the compound (I).

5. The pipe according to any one of the preceding claims, wherein

R², R⁴ and R⁶ are independently a straight C2-C4 alkyl group, preferably, R² and R⁶ are independently a straight C3 alkyl group and R4 is a C2 alkyl group, and/or R⁸ is n-butyl and R⁹ is represented by formula (III) wherein R¹² is preferably methyl and

6. The pipe according to any one of the preceding claims, wherein the polyolefin has a melt flow index (MFI) in the range of 0.01 to 3.0 dg/min measured according to IS01133-1 :2011 (2.16 kg/230°C).

7. The pipe according to any one of the preceding claims, wherein the polyolefin in the polymer composition is a substantially non-crosslinked polyolefin, which is preferably a polyolefin having a degree of crosslinking as measured according to ASTM F876 of less than 50%, less than 40%, less than 30%, less than 20%, less than 10% or less than 5%.

8. The pipe according to any one of the preceding claims, wherein the polymer composition comprises less than 0.02 wt%, less than 0.01 wt%, less than 0.005 wt%, less than 0.001 wt% or 0 wt% with respect to the polymer composition of a photoinitiator.

9. The pipe according to any one of the preceding claims, wherein the polyolefin is a propylene random copolymer comprising ethylene comonomer, wherein the amount of the ethylene comonomer is from 0.50 to 5.0 wt%, more preferably from 1 .4 to 4.5 wt%, more preferably from 3.0 to 4.2 wt% based on the total propylene random copolymer.

10. The pipe according to any one of the preceding claims, wherein the amount of the polyolefin with respect to the total amount of polymers in the polymer composition is at least 95.0 wt%, preferably at least 98.0 wt%, at least 99.0 wt% or 100 wt%, preferably wherein the amount of the polyolefin in the polymer composition with respect to the total polymer composition is at least 55.0 wt%, at least 65.0 wt%, at least 75.0 wt%, at least 85.0 wt%, at least 90.0 wt%, at least 95.0 wt%, at least 97.0 wt% or at least 98.5 wt%.

11. The pipe according to any one of the preceding claims, wherein the polymer composition further comprises 0 to 5 wt% of additives and 0 to 40 wt% of fillers, wherein the total amount of the polyolefin and the optional fillers with respect to the total polymer composition is at least 95.0 wt%, more preferably at least 97.0 wt%, more preferably at least 98.5 wt%.

12. A process for the preparation of the pipe according to any one of claims 1-12, comprising the step of extruding the polymer composition to obtain the pipe.

13. Use of the pipe according to any one of claims 1 -12 for the transport of water containing chlorinated disinfectant, preferably wherein the the total amount of chlorine, chlorine dioxide and chloramines is 0.01 to 5.0 ppm by weight with respect to the water comprising the chlorinated disinfectants.

14. Use of a compound represented by formula (I)

for improving the resistance of a pipe against water containing chlorinated disinfectants, wherein the pipe is made from a polymer composition comprising a polyolefin.