WO2018028921A1

WO2018028921A1 - Pipe produced with a polymer composition

Info

Publication number: WO2018028921A1
Application number: PCT/EP2017/067675
Authority: WO
Inventors: Mark Johannes Boerakker; Maria Soliman
Original assignee: Sabic Global Technologies B.V.
Priority date: 2016-08-11
Filing date: 2017-07-13
Publication date: 2018-02-15

Abstract

The invention relates a pipe for the transport of water with improved resistance to chlorinated disinfectants. The pipe is produced with a polymer composition comprising polyethylene and polyolefin elastomer.

Description

Pipe produced with a polymer composition

comprising a polyethylene

The present invention relates to a pipe for the transport of water produced with a polymer composition comprising a polyethylene. The pipe has an improved resistance to chlorinated disinfectants.

Pipes for the transport of gas, for sanitation and for water supply may be produced with for example bimodal polyethylene compositions. Pipes have a very good resistance to water however their lifetime is shortened when the pipes come into contact with disinfectants which are often added to water for hygienic reasons. The chlorine dioxide used as disinfectant in water degrades most materials including polyethylene (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 solvents are for example chloramine and chlorine. It is known in the art to apply additives for example antioxidants and stabilizers to prevent said degradation. Several types of additives are proposed to protect polymers during processing and to achieve the desired end-use properties.

WO 2005/056657 A2 discloses for example a pipe comprising polyethylene for use with chlorinated water that contains hindered phenols such as Irganox 1330, Irganox 1010 and /or Irganox 1076 and phosphites such as Irgafos 168 and metal deactivators such as Irganox MD 1024 and/ or NaugardTM XL1.

However, appropriate combinations of stabilizers have to be carefully selected, depending on the desired final properties the polymeric article should have.

It is the object of the present invention to provide pipe applications with improved service lifetime for the transportation of water containing chlorinated disinfectants, for example chlorine dioxide, chloramine and chlorine.

The pipe for the transport of water according to the invention is produced with a polymer composition comprising polyethylene and polyolefin elastomer wherein the amount of polyolefin elastomer in the composition is lower than 10.0 wt% relative to the total weight amount of the composition.

The drinking water pipe, preferably a pressure pipe, based on this polyethylene grade has an improved protection against for example chlorine dioxide containing cold or hot water and consequently a longer life time. It is also possible to transport waste water or water for cooling.

The polyethylene may be multimodal polyethylene for example a bimodal or trimodal polyethylene.

Preferably, the polyethylene is bimodal polyethylene. Suitable examples of polyolefin elastomers include for example ethylene-alpha olefin copolymers and/or vulcanised thermoplastic elastomers.

Suitable examples of elastomeric ethylene-alpha olefin copolymers include for example ethylene -1-octene copolymers and ethylene-1-butene copolymers as described for example by L.T.Kale et al in "Structure property relationship of ethylene - 1-octene copolymer and ethylene-1-butene copolymer made using insite technology" (1995 Polymers, Lamination and coatings Conference, pages 423-433). Suitable ethylene-alpha olefin copolymers are also disclosed in US8729200B2, US6559230B2, EP2076551 B, EP2326654B, EP2077269B, EP2365990B, EP2010576 and

EP218561 1 B.

Suitable examples of vulcanised thermoplastic elastomers comprise thermoplastic polyolefin and vulcanisable rubber as disclosed for example in

EP1234003 and EP1436135. Examples of suitable thermoplastic polyolefins used in the dynamically vulcanized thermoplastic elastomer according to the present invention are thermoplastic polyolefin homo- and copolymers or blends thereof. For example homopolymers of ethylene or propylene, copolymers of ethylene and propylene, copolymers of ethylene and an alpha-olefin with 4-12 carbon atoms or copolymers of propylene and an alpha-olefin with 4-12 carbon atoms may be used. Preferably, a homopolymer of propylene is used. Examples of vulcanizable rubbers that may be used in the dynamically vulcanized thermoplastic elastomer are ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, styrene butadiene rubber, nitrile butadiene rubber, isobutene-isoprene rubber, styrene-ethylene/styrene-butadiene block copolymers, butyl rubber, isobutylene-p-methylstyrene copolymers or brominated isobutylene-p-methylstyrene copolymers and /or natural rubber.

According to a preferred embodiment of the invention the ethylene-alpha olefin copolymer is ethylene-octene copolymer.

According to a further preferred embodiment of the invention the pipe is produced with a composition comprising

(a) polyethylene

(b) polyolefin elastomer

(c) polyphenolic compound and/or

(d) organic phosphite and/or phosphonite.

Preferably the weight ratio (b): (c+d) ranges between 20:1 and 1 : 1.

Suitable polyphenolic compounds include for example tetrakis[methylene-3- (3',5'-di-t-butyl-4-hydroxyphenyl)propionate] methane; 1 , 1 ,3-tris(2-methyl-4-hydroxy-5-t- butylphenyl)butane; 1 ,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, bis(3,3-bis(4'-hydroxy-3'-t-butylphenyl)butanoic acid]-glycol ester; tris(3,5-di-t-butyl-4- hydroxy benzyl)isocyanurate; 1 ,3,5-tris(4-t-butyl-2,6-dimethyl-3-hydroxy- benzyl)isocyanurate; 5-di-t-butyl-4-hydroxy-hydrocinnamic acid triester with 1 ,3,5-tris(2- hydroxyethyl)-s-triazine-2, 4, 6(11-1, 3H, 5H)-trione; p-cresol/ dicyclopentadiene butylated reaction product; 2,6-bis(2'-bis-hydroxy-3'-t-butyl-5'-methyl-phenyl-4-methyl-phenol).

A preferred polyphenolic compound is 1 ,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4- hydroxybenzyl)benzene (Irganox 1330 supplied by BASF).

Suitable organic phosphites and phosphonites include for example triphenyl phosphite, diphenyl alkyl phosphites, phenyl dialkyl phosphites, tris(nonylphenyl) phosphite, trilauryl phosphite, trioctadecyl phosphite, distearyl pentaerythritol diphosphite, tris(2,4-di-tert-butylphenyl) phosphite, diisodecyl pentaerythritol diphosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphate, bis(2,6-di-tert- butyl-4-methylphenyl) pentaerythritol diphosphate, bisisodecyloxy-pentaerythritol diphosphite, bis(2,4-di-tert-butyl- 6-methylphenyl) pentaerythritol diphosphite, bis(2,4,6- tri-tert-butylphenyl) pentaerythritol diphosphite, tristearyl sorbitol triphosphite, tetrakis(2,4-di-tert-butylphenyl) 4,4'- biphenylenediphosphonite, 6-isooctyloxy-2,4,8,10- tetra-tert-butyl-12H-dibenzo[d,g]-1 ,3,2-dioxaphosphocin, 6-fluoro-2,4,8,10-tetra-tert- butyl-12-methyldibenzo[d,g]-1 ,3,2-dioxaphosphocin, bis(2,4-di-tert-butyl-6- methylphenyl) methyl phosphite, bis(2,4-di-tert-butyl- 6-methylphenyl) ethyl phosphite.

A preferred phosphite is tris(2,4-di-tert-butylphenyl) phosphite (Irgafos 168 supplied by BASF).

According to another preferred embodiment of the invention the pipe is produced with a polyethylene composition comprising

(a) multimodal polyethylene

(b) polyolefin elastomer

(c) polyphenolic compound and

(d) organic phosphite and/or phosphonate wherein the weight ratio (b): (c+d) ranges between 20:1 and 1 :1.

Preferably (b, (c) and (d) are added during the granulation step of the multimodal, for example bimodal, high density polyethylene powder.

(a) multimodal polyethylene

(b) ethylene-octene copolymer

(c) polyphenolic compound and (d) organic phosphite and/or phosphonate wherein the weight ratio (b): (c+d) ranges between 20:1 and 1 :1.

Preferably the polyethylene is multimodal polyethylene for example bimodal or trimodal polyethylene.

More preferably, the polyethylene is bimodal polyethylene.

The multimodal ethylene polymer may be an ethylene homo- or copolymer. The comonomer may be for example butene or hexene.

According to a preferred embodiment of the invention polyethylene is a multimodal high density polyethylene (HDPE) having a polymer density≥ 940 and≤ 965 kg/m³ and a melt flow rate 190/5 in the range≥ 0,1 and < 4.0 g / 10 min. More preferably, the density is≥ 945 and≤ 955 kg/m³ and the melt flow rate 190/5 in the range≥ 0,1 and≤ 0,6 g / 10 min. The density is measured according to ISO 1 183 A. The melt flow rate MFR 190/5 is measured according to ISO 1 133 -1 (190 °C; 5.0 kg). The HDPE may for example be natural, yellow, orange or blue colored.

According to a preferred embodiment of the invention the polyethylene is a compound comprising multimodal high density polyethylene and carbon black as pigment, wherein the density is in the range≥ 950 and≤ 970 kg/m³ and MFR (190/5) in the range≥ 0,1 and≤ 4.0g/10 min, wherein the density is measured according to ISO 1 183 A and the melt flow rate MFR 190/5 is measured according to

ISO 1133 -1 (190 °C; 5.0 kg).

According to a preferred embodiment of the invention the components are added to the polyethylene resin while the polyethylene is in a molten state during extrusion.

The components may be added together and may be added separately.

Preferably the components are added in one step.

Preferably the amount of polyethylene in the composition is higher than 90.0 wt%, more preferably higher than 95.0 wt%,

Preferably the amount of polyolefin elastomer in the composition is lower than 5.0 wt%.

More preferably the amount of polyolefin elastomer in the composition ranges between 1.5 and 4.0 wt%.

Said amounts polyolefin elastomer in the composition according to the invention protect the pipe against chlorine dioxide during a long period.

The multimodal ethylene polymer may be an ethylene homo- or copolymer. The multimodal ethylene grades to be applied in pipe applications may comprise additives such as for example carbon black, pigments, stearates, a UV stabilizer for example a sterically hindered amine, fillers, minerals, lubricants and/or other stabilisers.

The production processes for bimodal high density polyethylene (HDPE) are summarised at pages 16-20 of "PE 100 Pipe systems" (edited by Bromstrup; second edition, ISBN 3-8027-2728-2).

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). Bimodal high density

polyethylene may be produced via a low pressure slurry process for the production of comprising a polymerisation stage, a powder drying stage, an extrusion and pellet handling stage, a recycling stage and a wax removal unit. In a two stage cascade process the reactors may be fed continuously with a mixture of monomers, hydrogen, catalyst/co-catalyst and diluent 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 °C and 88 °C. 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 concentrations of catalyst, co monomer and hydrogen. The production of bimodal high density polyethylene (HDPE) via a low pressure slurry process may also be performed via a three stage process.

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.

Suitable catalysts for the production of multimodal polyethylene include Ziegler Natta catalysts, chromium based catalysts and single site metallocene catalysts. In all potential possible technologies the process and the catalyst have to form a well- balanced system. The catalyst is crucial for the polymerisation reaction of multimodal polyethylene. By cooperation of process and catalyst a definite polymer structure is produced.

EP1724289 A1 discloses a polymer composition based on polypropylene homopolymer and polypropylene random copolymer comprising an additional elastomeric copolymer in an amount of 5 to 15 wt%, the elastomeric copolymer being of propylene and at least one olefin comonomer. It is the object of EP1724289 A1 to provide a pipe of high stiffness and high durability. EP1724289 is not directed to polyethylene pipe with improved service lifetime for the transportation of water containing chlorinated disinfectants.

EP2535374 A1 discloses a propylene resin composition which contains an ethylene-propylene random copolymer having an ethylene content of 0.5 to 3.0 parts by mass; an elastomer having an average particle diameter of 10 to 800 nm in an amount of 1 to 10 parts by mass based on 100 parts by mass of the ethylene- propylene random copolymer; and a crystalline nucleating agent, and in which after kneading thereof, the kneaded propylene resin composition exhibit a melt flow rate (MFR) of 0.01 to 1.00 g/10 min ( MFR determined at 230°C and under the application of the test load of 2.16kg). It is the object of EP2535374 A1 to provide a polypropylene composition having excellent properties such as transparency, heat resistance, impact resistance and creep resistance. EP2535374 is not directed to polyethylene pipe with improved service lifetime for the transportation of water containing chlorinated disinfectants.

The invention will be elucidated by means of the following non-limiting examples. Examples

SABIC Vestolen A5924 (Resin A) used as base polymer in all examples was a bimodal high density polyethylene with MFR₅ of 0.24 g/10min and density 958 kg/m³. Examples l-lll and Comparative Examples A-D

The Examples l-lll and Comparative Examples A-D use different additive packages in combination with Resin A to protect the polyethylene from attack by chlorine dioxide (see Table 1 ). The components as indicated in Table 1 were mixed at 245 degrees Celcius using a twin screw extruder. Table 1

wherein:

• Irganox 1010 :Tetrakis [methylen- 3-(3 ',5 ')-di-t-butyl-4 '-hydroxyphenyl)

propionate] methane commercially available from Ciba Speciality Chemicals,

• polyolefin elastomer: Engage 8100 available from The DOW Chemical

Company

• Irganox 1330 : 1 ,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4- hydroxybenzyl)benzene;

· Irgafos 168: Tris(2,4-di-tert-butylphenyl) phosphite ;

• DHT-4A^®, commercially available hydrotalcite from Kisuma Chemicals.

• Resin A: SABIC Vestolen A5924; bimodal high density polyethylene with

MFRs 0.24 g/10min and density 958 kg/m³.

Compounds were compression molded using IS01872-2 resulting in plaques, which were cut to IS0527-1 A tensile bars (4 mm thick).

Ageing test

The tensile bars were aged in a continuous water flow at a temperature of 40 °C with a chlorine dioxide concentration maintained at 1 mg/L and a pH maintained at 7.2. Flow rate was regulated at 200 L/h. Water hardness was regulated to 20 °F. A constant fresh water flow was added during testing allowing full renewal of the testing water each 4 hrs.

The compression molded samples were aged for 1000 hrs.

Tensile tests according to Plastics- Determination of tensile properties IS0527- 1 at room temperature at a strain rate of 50 mm/min on aged tensile bars were performed to determine the residual elongation at break for the aged samples and reported in Table 2. Table 2

From Table 2 it can be concluded that Examples I, II and II demonstrate significantly higher elongation at break after being exposed to water containing chlorine dioxide than Comparative Example A.

Comparing

• Comparative Example B to Example I and

• Comparative Example C to Example II and

• Comparative Example D to Example III

shows that the effect of adding polyolefin elastomer had an additional profound effect on the elongation at break as obtained after exposure to water containing chlorine dioxide.

Claims

1. Pipe for the transport of water produced with a polymer composition comprising polyethylene and polyolefin elastomer wherein the amount of polyolefin elastomer in the composition is lower than 10.0 wt% relative to the total weight amount of the composition.

2. Pipe according to any one of Claims 1 characterised in that the polyolefin

elastomer is ethylene-alpha olefin copolymer and/or vulcanised thermoplastic elastomer.

3. Pipe according to any one of Claims 1-2 characterised in that the polyolefin

elastomer is ethylene-octene copolymer and/or vulcanised thermoplastic elastomer.

4. Pipe according to any one of Claims 1-3 characterised in that the polyolefin

elastomer is ethylene-octene copolymer.

5. Pipe according to any one of Claims 1-4 characterised in that the composition comprises a polyphenolic compound and/or an organic phosphite and/or phosphonite.

6. Pipe according to any one of Claims 1-5 characterised in that the polyethylene is multimodal polyethylene.

7. Pipe according to Claim 6 characterised in that the polyethylene is bimodal

polyethylene.

8. Pipe according to any one of Claims 1-7 characterised in that the amount of polyolefin elastomer in the composition is lower than 5.0 wt%.

9. Pipe according to any one of Claims 5-8 characterised in that the polyphenolic compound is 1 ,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene.

10. Pipe according to any one of Claims 4-10 characterised in that the phosphite is tris(2,4-di-tert-butylphenyl) phosphite.

1 1. Pipe according to any one of Claims 1-10 produced with a composition comprising

(a) polyoethylene

(b) polyolefin elastomer

(c) polyphenolic compound and/or