PIPE MADE OF PEROXIDE-CROSSLINKED POLYETHYLENE OF HIGH UV STABILITY

Abstract

The present invention relates to a pipe which comprises (i) a peroxide-crosslinked polyethylene, and (ii) a sterically hindered amine which comprises the following repeating unit of formula (I).

##STR00001##

Claims

1-15. (canceled)

16. A pipe comprising a peroxide-crosslinked polyethylene and a sterically hindered amine which comprises the following repeating unit of formula (I): ##STR00008## wherein x is 4-8, R.sub.1 and R.sub.2, independently from each other, are H or methyl; R.sub.3 and R.sub.4, independently from each other, are H, a C.sub.2-12 alkyl group, a C.sub.5-7 cycloalkyl group, or a saturated nitrogen-containing heterocyclic group; or R.sub.3 and R.sub.4, together with the nitrogen atom to which they are attached, form a 5- to 7-membered saturated heterocyclic ring.

17. The pipe according to claim 16, wherein x is 6, R.sub.3 is a C.sub.2-12 alkyl group, and R.sub.4 is H or a saturated nitrogen-containing heterocyclic group.

18. The pipe according to claim 16, wherein the sterically hindered amine is poly((6-((1,1,3,3-tetramethylbutyl)amino)-1,3,5-triazine-2,4-diyl)((2,2,6,6-tetramethyl-4-piperidinyl)imino)-1,6-hexanediyl((2,2,6,6-tetramethyl-4-piperidinyl)imino)); 1,6-hexanediamine, N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)-, polymer with 2,4,6-trichloro-1,3,5-triazine, reaction products with N-butyl-1-butanamine and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine; or a mixture thereof.

19. The pipe according to claim 16, wherein the sterically hindered amine is present in an amount of 0.01 wt % to 1 wt %, based on the weight of the peroxide-crosslinked polyethylene.

20. The pipe according to claim 16, further comprising one or more antioxidants.

21. The pipe according to claim 20, wherein the one or more antioxidants are selected from pentaerythrityl tetrakis-3-(3′,5′-di-tert-butyl-4-hydroxyphenyl) propionate (CAS number 6683-19-8), octadecyl-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate (CAS No. 2082-79-3), and 1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (CAS number 1709-70-2).

22. The pipe according to claim 20, wherein the antioxidants are present in the following amounts, based on the weight of the crosslinked polyethylene: 0.05 to 0.5 wt % of pentaerythrityl tetrakis-3-(3′,5′-di-tert-butyl-4-hydroxyphenyl) propionate; and/or 0.03 to 0.45 wt % of octadecyl-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate; and/or 0.15 to 0.7 wt % of 1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)benzene.

23. The pipe according to claim 16, wherein the peroxide-crosslinked polyethylene is obtained by a crosslinking treatment with a peroxide in the absence of any non-peroxide crosslinking agent.

24. A process for preparing the pipe according to claim 16, which comprises providing a crosslinkable composition comprising a crosslinkable polyethylene, a peroxide, and a sterically hindered amine which comprises the following unit of formula (I): ##STR00009## wherein x is 4-8, R.sub.1 and R.sub.2, independently from each other, are H or methyl; and R.sub.3 and R.sub.4, independently from each other, are H, a C.sub.2-12 alkyl group, a C.sub.5-7 cycloalkyl group, or a saturated nitrogen-containing heterocyclic group; or R.sub.3 and R.sub.4, together with the nitrogen atom to which they are attached, form a 5- to 7-membered saturated heterocyclic ring, forming the crosslinkable composition into a pipe and crosslinking the crosslinkable polyethylene.

25. The process according to claim 24, wherein the crosslinkable polyethylene has a density, measured according to ISO 1183/1872-2B, of from 920 kg/m.sup.3 to 973 kg/m.sup.3; and/or a melt flow rate, measured according to ISO 1133 at 190° C. and a load of 21.6 kg, of from 0.1 g/10 min to 100 g/10 min.

26. The process according to claim 24, wherein the crosslinkable polyethylene has 0.05 terminal vinyl groups/1000 carbon atoms to 2.5 terminal vinyl groups/1000 carbon atoms.

26. The process according to claim 24, wherein the peroxide is the only crosslinking agent which is present in the crosslinkable composition.

27. The process according to claim 24, wherein the crosslinkable composition is provided by preparing pellets which contain the crosslinkable polyethylene and the sterically hindered amine, and the pellets are brought into contact with the peroxide.

28. The process according to claim 24, wherein the pipe is formed by extrusion, in particular screw extrusion or ram extrusion.

29. A method of transporting water comprising transporting water through the pipe according to claim 16.

Description

EXAMPLES

[0110] In Inventive Examples IE1-IE2, and Comparative Example CE1, pellets were prepared by extrusion from the compositions outlined below in Table 1. Each of the pellet compositions was made of a polyethylene, phenolic antioxidants, and a sterically hindered amine (“HALS”). The polyethylene of IE1-IE2 and CE1 had an MFR (190° C., 21.6 kg) of 9 g/10 min, a density of 952 kg/m.sup.3, and 0.47 terminal vinyl groups/1000 carbon atoms. No internal vinylidene groups (RR′C═CH.sub.2), internal cis-vinylene groups (E-RCH═CHR′), internal trans-vinylene groups (Z—RCH═CHR′) and internal trisubstituted vinylene groups (RCH═CR′R″) were detected.

[0111] The pellet compositions only differed in the type of sterically hindered amine.

[0112] Inventive Example 1: Chimassorb® 944

[0113] Inventive Example 2: Chimassorb® 2020

[0114] Comparative Example 1: Sabostab® UV62

TABLE-US-00001 TABLE 1 Pellet compositions used for preparing the pipes IE1 IE3 CE1 Sterically 0.2 wt % 0.2 wt % 0.2 wt % hindered Chirnassorb ® Chirnassorb ® Sabostab ® UV amine 944 2020 62 Polymer 99.05 wt % Polyethylene; MFR.sub.21: 9 g/10 min; Density: 952 kg/m.sup.3 0.2 wt % Irganox ® 1010 Phenolic 0.15 wt% Irganox ® 1076 AOs 0.4 wt % Irganox ® 1330

[0115] As already indicated above, the sterically hindered amines of Chimassorb® 944 and Chimassorb® 2020 have the following chemical structures:

##STR00006##

[0116] The sterically hindered amine of Sabostab® UV 62 is butanedioic acid, 1,4-dimethyl ester, polymer with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol; CAS No. 65447-77-0, molecular weigh Mn of about 3100-4000 g/mol, and has the following repeating unit:

##STR00007## [0117] Irganox® 1010: Pentaerythrityl tetrakis-3-(3′,5′-di-tert-butyl-4-hydroxyphenyl) proionate, CAS number 6683-19-8 [0118] Irganox® 1076: Octadecyl-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate, CAS No. 2082-79-3 [0119] Irganox® 1330: 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene; CAS No. 1709-70-2

[0120] The pellets of IE1-IE2 and CE1 were soaked with the same amount and type of organic peroxide (3,3,5,7,7-pentamethyl-1,2,4-trioxepane, Trigonox® 311), extruded under identical conditions to a pipe, and the polyethylene of each pipe was crosslinked under identical conditions, thereby obtaining crosslinked pipes.

[0121] The degree of crosslinking of the crosslinked pipes is shown in Table 2.

TABLE-US-00002 TABLE 2 Degree of crosslinking IE1 IE2 CE1 Degree of 70 71 70 crosslinking [%]

[0122] For the assessment of photo-oxidative stability, both the non-crosslinked pellet compositions and the crosslinked pipe compositions were subjected to a weathering treatment, and the treated materials were subjected to oxidation induction time (OIT) tests after pre-defined periods of treatment.

[0123] The weathering treatment was subjected under the following conditions:

[0124] Artificial weathering—Xenon arc sources

[0125] according to ISO 4892-1:1999(E) and ISO 4892-2:1994(E)

[0126] Exposure according Kalahari standard,

[0127] Specimens that fit 60×120 mm clamping;

[0128] Spectral range in nm: Kalahari 300-400;

[0129] Irradiation: 75 W/m.sup.2

[0130] Black standard temperature: 90° C.

[0131] Humidity: 20%

[0132] The pipe segments were mounted on a specimen holder. The outer side of the pipe was irradiated. The measurements were done on the weathered side of the pipe.

[0133] The OIT test results of both the non-crosslinked and the crosslinked samples are summarized below in Tables 3 and 4.

TABLE-US-00003 TABLE 3 OIT tests carried out on non-crosslinked samples IE1 IE2 CE1 OIT [min], No weathering 83.5 90.6 40.2 Heating to Weathering for 120 hours 36.7 43.7 17.5 220° C. Weathering for 336 hours 11.3 17.1 4.4 Weathering for 650 hours 6.1 4.4 2.2 OIT [min], Weathering for 650 hours 50.5 98.9 26.5 Heating to Weathering for 1000 hours 59 71.6 16.3 200° C.

[0134] The longer the non-crosslinked polyethylene compositions are subjected to the weathering treatment, the lower is oxidation induction time. However, due to the presence of a sterically hindered amine comprising the repeating unit of formula (I), the reduction in OIT is significantly less in IE1-IE2 if compared to CE1.

[0135] Accordingly, the non-crosslinked polyethylene compositions of IE1-IE2 show improved photo-oxidative stability.

TABLE-US-00004 TABLE 4 OIT tests carried out on crosslinked samples IE1 IE2 CE1 OIT [min], No weathering 55.4 70.9 11 Heating to Weathering for 120 hours 22.4 45.4 6.6 220° C. Weathering for 336 hours 16.2 18.3 3.4

[0136] Just like the non-crosslinked polyethylene samples, the crosslinked polyethylene samples of IE1-IE2 show significantly higher OIT values if compared to CE1. Furthermore, if crosslinked, the polyethylene compositions of IE1-IE2 show a smaller decrease in OIT as a function of weathering period. Just as an example, while OIT (220° C.) of the non-crosslinked sample of IE2 decreases by 52% after a weathering treatment of 120 hours, the crosslinked sample of IE2 shows a decrease of OIT (220° C.) of only 36% after a weathering treatment of 120 hours.