WO2018104079A1 - Pipe produced with a polymer composition comprising a polyolefin - Google Patents

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 polyolefin and polydialkylsiloxane.

Description

Pipe produced with a polymer composition

comprising a polyolefin

The present invention relates to a pipe for the transport of water produced with a polymer composition comprising a polyolefin. 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. 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 a polyolefin and polydialkylsiloxane wherein the amount of polydialkylsiloxane in the composition is lower than 2.0 wt% relative to the total weight amount of the composition and wherein the polyolefin is based on at least 70 % by weight of olefin monomer.

Suitable polydialkylsiloxanes include for example polydimethylsiloxane, polydiethylsiloxane, polydipropylsiloxane, polydioctylsiloxane, polydibutylsiloxanes, polydipentylsiloxanes, polydihexylsiloxanes, polydiheptylsiloxanes,

polydinonylsiloxanes, polydidecylsiloxanes and mixtures.

According to a preferred embodiment of the invention the polydialkylsiloxane is polydimethylsiloxane.

The drinking water pipe, preferably a pressure pipe, based on this polyolefin 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. Preferably the polyolefin is based on≥ 90 % by weight and≤ 100 % by weight of olefin monomer. Suitable olefin monomers are for example ethylene and propylene.

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 the polyethylene is a multimodal high density polyethylene (HDPE) having a polymer density≥ 940 and < 970 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 or colored. Typical colors are yellow, orange or blue.

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. More preferably, the density is in the range≥ 956 and < 965 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 and the melt flow rate MFR 190/5 is measured according to ISO 1 133 -1 (190 °C; 5.0 kg).

The polyethylene is based on at least 70 % by weight of ethylene monomer more preferably based on≥ 90 % by weight and≤ 100 % by weight of ethylene monomer.

The polypropylene is based on at least 70 % by weight of propylene monomer more preferably based on≥ 90 % by weight and≤ 100 % by weight of propylene monomer.

Preferably, the polyolefin is multimodal polyethylene.

More preferably, the polyolefin is bimodal polyethylene.

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

(a) polyolefin wherein the polyolefin is based on at least 70 % by weight of olefin monomer.

(b) polydialkylsiloxane

(c) polyphenolic compound and/or

(d) organic phosphite and/or phosphonite. Preferably the weight ratio (b): (c+d) ranges between 7:1 and 1 :7.

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) polydialkylsiloxane

(c) polyphenolic compound and

(d) organic phosphite and/or phosphonate wherein the weight ratio (b): (c+d) ranges between 7:1 and 1 :7.

Preferably (b, (c) and (d) are added during the granulation step of the multimodal, for example bimodal, high density polyethylene powder. 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 polyolefin in the composition is higher than 95.0 wt%. Preferably the amount of polydialkylsiloxane in the composition is lower than 1.0 wt%.

More preferably this amount ranges between 0.05 and 0.9 wt%.

These amounts 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.

CN103396626 discloses a wear resistant soft PVC. The PVC composition may comprise a minor amount of HDPE and polydimethylsiloxane. The wear resistant soft PVC composition has improved friction properties and may be applied in the production of many articles for example pipes. CN103396626 does not give any disclosure of pipe applications with improved service lifetime for the transportation of water containing chlorinated disinfectants. The PVC composition according to CN103396626 and the polyolefin composition according to the present invention arew completely different compostions.

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 MFR 190/5 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 BASF,

• polydialkylsiloxane: Polydimethylsiloxane added using MB50-002 available from DOW Corning.

· Irganox 133 : 1 ,3, 5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4- hydroxybenzyl)benzene, commercially available from BASF;

• Irgafos 168: Tris(2,4-di-tert-butylphenyl) phosphite, commercially available from BASF ;

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

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

MFR 190/5 of 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 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

shows that the effect of adding polydimethylsiloxane 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 a polyolefin and polydialkylsiloxane wherein the amount of polydialkylsiloxane in the composition is lower than 2.0 wt% relative to the total weight amount of the composition and wherein the polyolefin is based on at least 70 % by weight of olefin monomer.

2. Pipe according to Claim 1 characterised in that the polyolefin is polyethylene or polypropylene.

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

polydialkylsiloxane is selected from polydimethylsiloxane, polydiethylsiloxane, polydipropylsiloxane, polydioctylsiloxane, polydibutylsiloxanes,

polydipentylsiloxanes, polydihexylsiloxanes, polydiheptylsiloxanes,

polydinonylsiloxanes, polydidecylsiloxanes and mixtures.

4. Pipe according to Claim 3 characterised in that the polydialkylsiloxane is

polydimethylsiloxane.

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 polyolefin is multimodal polyethylene.

7. Pipe according to Claim 6 characterised in that the polyethylene is a multimodal high density polyethylene (HDPE) having a polymer density≥ 940 and≤ 970 kg/m³ and a melt flow rate (MFR190/5) in the range≥ 0,1 and < 4.0 g / 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 1 133 -1 (190 °C; 5.0 kg)

8. Pipe according to any one of Claims 6-7 characterised in that the polyolefin is bimodal polyethylene.

9. Pipe according to any one of Claims 1-8 characterised in that the amount of

polydialkylsiloxane in the composition is lower than 1.0 wt%.

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

1 1. Pipe according to any one of Claims 5-10 characterised in that the phosphite is tris(2,4-di-tert-butylphenyl) phosphite.

12. Pipe according to any one of Claims 1-1 1 produced with a composition comprising (a) polyolefin

(b) polydialkylsiloxane (c) polyphenolic compound and/or

(d) organic phosphite and/or phosphonate wherein the weight ratio (b): (c+d) ranges between 7:1 and 1 :7.