WO2011047803A1

WO2011047803A1 - Ethylene polymer having improved resistance against degradation in the presence of liquid fuels comprising peroxides and plastic fuel tanks made of it

Info

Publication number: WO2011047803A1
Application number: PCT/EP2010/006301
Authority: WO
Inventors: Thomas Lindner; Harald Schmitz
Original assignee: Basell Polyolefine Gmbh
Priority date: 2009-10-22
Filing date: 2010-10-15
Publication date: 2011-04-28
Also published as: CN106117598A; CN102597087A

Abstract

An ethylene homo- or copolymer composition is stabilized conferring improved resistance against thermo-oxidative degradation which occurs in the presence of liquid fuels comprising peroxides (dirty fuel). The stabilizers comprise a combination of at least two sterically hindered amine compounds or N-hydroxy- or N-oxylderivatives thereof in an amount of from 100 to 10 000 ppm. Such ethylene homo- or copolymer composition is highly suitable for articles of plastic and components for the transport and storage of liquid fuels contaminated by peroxides, preferably for plastic fuel tanks for automotive vehicles driven by combustion engines.

Description

Ethylene polymer having improved resistance against degradation in the presence of liquid fuels comprising peroxides and plastic fuel tanks made of it. The present invention relates to an ethylene homo- or copolymer composition stabilized by suitable stabilizers conferring improved resistance against degradation occurring in the presence of liquid fuels (gasoline) comprising peroxides, sometimes also addressed as "Dirty fuel". The invention also relates to articles made of plastics and components for the transport and storage of liquid fuels comprising peroxides such as plastic fuel tanks for automotive vehicles, which are produced using such ethylene homo- or copolymer compositions stabilized by adding suitable stabilizers according to the-present invention.

In automotive fuel systems an increasing use of plastic fuel tanks (PFTs) of polyethylene is observed. In certain territorial areas in the world gasoline contains an elevated share of peroxides of which Laurylperoxid and DTBP are the major representatives.

However, such peroxides prove to be aggressive to many of the plastic materials used in the fuel system of a motor vehicle. Even high molecular mass, high density polyethylene, as is used for the manufacture of PFTs and other hollow articles, may be attacked if exposed for a longer time period to peroxides. Its effect thereby is to accelerate the embrittlement of the polymer material, thereby impairing its long-term service properties.

It is the object of the present invention to provide ethylene homo- or copolymer compositions, for producing articles of plastic and components for the storage and transport of liquid fuels comprising peroxides, which are further stabilized and exhibit improved resistance against degradation in the presence of "Dirty fuels". We have found surprisingly that this object is achieved according to the instant invention by ethylene homo- and copolymers stabilized by a combination of at least two sterically hindered amine compounds or N- hydroxy- or N-oxylderivatives thereof in an amount ranging from 100 to 10 000 ppm, calculated on total weight of the stabilized polymer.

The total amount of stabilizer present in the polymer is defined as the sum of each single amount of each single stabilizer, whereby the ratio of the single amounts of the single stabilizers to each other ranges from 1 : 0,2 to 1 : 2, preferably from 1 : 0,5 to 1 : 1 ,5, based on weight-%.

Another solution of the problem is the preparation of articles of plastic and components for the storage and for the transport of liquid fuels comprising peroxides, especially plastic fuel containers, from such ethylene homo- or copolymer compositions.

Especially, the ethylene homo- or copolymer composition of the instant invention comprises a combination of Chimassorb^® 944 and Tinuvin^® 770 as sterically hindered amine compounds.

The stabilizer Chimassorb 944 is thereby understood to have the following chemical formula:

addressed as: poly[[6-(1 , 1 ,3,3-tetramethylbutyl)amino]1 ,3,5-triazin-2,4- diyl][2,2,6,6-tetramethyl-4-piperidinyl)imino]-1 ,6-hexandiyl[(2,2,6,6- tetramethyl-4-piperidinyl)imino]], whereby n is an integer ranging from 2 to 20.

The stabilizer Tinuvin 770 has the following chemical composition:

addressed as: Bis-(2,2,6,6-tetramethyl-4-piperidinyl)-sebacate.

We have also found articles of plastic and components for the transport and storage of liquid fuels comprising peroxides, produced using such stabilized polymers, and ethylene homo- or copolymer compositions stabilized by adding the combination of the two sterically hindered amines Chimassorb 944 and Tinuvin 770 in a preferred amount of from 400 to 5000 ppm, more preferred from 500 to 3000 ppm, calculated as the sum of both sterically hindered amines on total weight of the stabilized polymer.

Suitable stabilizers for the ethylene homo- and copolymers are preferably the two sterically hindered amines themselves. However, their N-hydroxy- or N-oxylderivatives may also be useful and other stabilizers may be added in addition thereto, such as sterically hindered amines including other secondary amines whose substitution on the carbons adjacent to the amine nitrogen is such that no single hydrogen remains at these positions. Preference is given to derivatives of 2,2,6,6-tetramethylpiperidine, substituted either at the 4-position or on the amine nitrogen, and to derivatives of quinoline and of diphenylamine.

Some preferred amine compounds in the aforementioned sense are:

2,2,6,6-tetramethylpiperidine, 2,2_>6,6-tetramethylpiperidine-4-ol,

2,2_>6_>6-tetramethylpiperidine-4-one,

2,2,6, 6-tetramethylpiperidine-4-yl acetate,

2,2,6,6-tetramethylpiperidine-4-yl 2-ethylhexanoate,

2,2,6,6-tetramethylpiperidine-4-yl stearate,

2,2,6,6-tetramethylpiperidine-4-yl benzoate,

2,2,6,6-tetramethylpiperidine-4-yl 4-tert-butylbenzoate,

Bis(2,2,6,6-tetramethylpiperidine-4-yl) succinate,

Bis(2,2,6,6-tetramethylpiperidine-4-yl) adipate,

Bis(2,2,6,6-tetramethylpiperidine-4-yl) n-butylmalonate,

Bis(2,2,6,6-tetramethylpiperidine-4-yl) phthalate,

Bis(2,2,6,6-tetramethylpiperidine-4-yl) isophthalate,

Bis(2,2,6,6-tetramethylpiperidine-4-yl) terephthalate,

Bis(2,2,6,6-tetramethylpiperidine-4-yl) hexahydroterephthalate,

N,N'-bis(2,2,6,6-tetramethylpiperidine-4-yl)adipinamide,

N-(2,2,6,6-tetramethylpiperidine-4-yl)caprolactam,

N-(2,2,6,6-tetramethylpiperidine-4-yl)dodecylsuccinimide,

2,4,6-tris-[N-butyl-N-(2,2,6,6-tetramethylpiperidine-4-yl)]-s-triazine,

4,4'-ethylenebis(2,2,6,6-tetramethylpiperazine-3-one) and

tris(2,2,6,6-tetramethyl-1-oxylpiperidine-4-yl) phosphite

and the N-hydroxy and N-oxyl derivatives thereof, as well.

The ethylene homo- or copolymer compositions used in accordance with the invention comprise the combination of sterically hindered amines or it comprises their N-hydroxy or N-oxyl derivatives.

The term ethylene homo- or copolymer composition is understood to address a polymer comprising ethylene as a main component which has been prepared by polymerization under low pressure conditions in the presence of a suitable polymerization catalyst. Common catalysts for the polymerization of olefins are titanium based Ziegler catalysts or chromium based Philips catalysts. These catalysts are used world wide for the manufacture of polymers in world scale production plants. Other suitable catalysts are zirconium based metallocene catalysts which have been developed within the last twenty years and which are now described in many publications world wide. As co-monomers for the ethylene, other homologue olefins are suitable comprising from 3 to 10 carbon atoms, such as 1 -propene, 1-butene, 1 - pentene, 1-hexene, 1-heptene, 1 -octene and 1 -decene. The co-monomers may be present during the polymerization of the ethylene in an amount of from 1 to 8 % by weight, preferably from 2 to 7 % by weight, calculated on total weight of the monomers present in the reaction mix.

The polymerization takes place in a polymerization reactor, whereby different techniques are possible such as slurry polymerization in stirred vessels or in loop reactors or gas phase polymerization in stirred bed or fluidized bed reactors.

For use in the further processing technique of extrusion and blow moulding, the polyethylene preferably has a melt flow rate MFR (190/21.6) of from 1 to 25 g/10 min, in particular from 2 to 20 g/10 min, and for use in the field of injection moulding, an MFR (190/2.16) of from 0.1 to 100 g/10 min is preferred, in particular from 0.2 to 10 g/10 min.

Particularly suitable for use in accordance with the invention are ethylene homo- and copolymers having a density of from 0.930 to 0.970, in particular from 0.940 to 0.960 g/cm³, and, with particular advantage, the polymer employed is HDPE as normally used, for example, to produce plastic fuel tanks (PFTs).

The polyethylene normally includes additional substances for thermal and in-process stabilization. These substances, which may also be used in combination with the resistance stabilizers used in accordance with the invention, include sterically hindered phenols, which may also contain nitrogen and/or sulfur as heteroelements, lactones, which may also contain nitrogen and/or sulfur as heteroelements, organic esters of phosphorous acid (e.g. trialkyl phosphites), which may also contain nitrogen and/or sulfur as heteroelements, and alkali metal and alkaline earth metal stearates. Examples of stabilizers from the class of sterically hindered phenols are benzenepropanoic acid 3,5-bis (1 , 1-dimethylethyl)-4-hydroxy-2,2-bis[[3- [3,5— brs(1 , 1-dimethylethyl)-4-hydroxyphenyl]-1-oxopropoxy]methyl]-1 ,3- propanediyl ester (lrganox®1010 from Ciba Additives GmbH), benzenepropanoic acid 3,5— bis(1 , 1-dimethylethyl)-4-hydroxyoctadecyl ester (lrganox®1076 from Ciba Additives GmbH), 4-[[4,6-bis(octylthio)- 1 ,3,5-triazin-2-yl]amino]-2,6-bis(1 ,1-dimethylethyl)phenol (lrganox®565 from Ciba Additives GmbH), and N,N'-hexamethylenebis(3,5-di-tert.butyl- 4-hydroxyhydrocinnamamide) (lrganox®1098 from Ciba Additives GmbH). Examples of stabilizers from the class of the lactones are benzofuran-2- ones, such as 5,7-di-t-butyl-3-(3,4-dimethylphenyl)-3H-benzofuran-2- one. Examples of stabilizers from the class of the organic phosphites are 2,4-bis(1 ,1-dimethylethyl)phenol phosphite (lrganox®168 from Ciba Additives GmbH) and phosphorous acid [1 , 1 '-biphenyl]-4,4'-diylbis- - tetrakis[2,4-bis(1 ,1-dimethylethyl)phenyl] ester. The incorporation of the stabilizers into the polymers can take place, for example, during the production of a granular base material or not until during the melting operation in preparation for shaping, which can take place, for example, by extrusion, injection moulding or blow moulding. The ethylene homo- or copolymer compositions used in accordance with the instant invention are outstandingly suited to the production of articles of plastic and components for the transport and storage of liquid fuels comprising peroxides. Such peroxides are usually a mix of many different organic peroxides comprising as main components lauryl peroxide and di- terf.-butyl peroxide (DTBP). The amount of peroxides comprised in the fuel is usually up to a maximum amount of about 50 ppm, preferably up to 30 ppm in maximum. By articles of plastic and components in this context are meant all the plastics parts which are exposed to the liquid fuels for a prolonged period, especially plastic fuel tanks, but also parts such as pipes and feedlines, bottles, canisters, drums, etc. Articles of plastic and components as described before may also comprise multilayered materials prepared par example according to the co-extrusion technique, wherein at least one layer is present comprising the stabilized ethylene homo- or copolymer of the instant invention, whereby that at least one layer comprising the stabilized ethylene homo- or copolymer is preferably the inner layer. The following working examples have been conducted to illustrate the subject and the function of the instant invention in more detail.

The MFR (190/21.6) of the polymer has been measured in accordance to ISO 1 133 at a temperature of 190 °C and under a load of 21 .6 kg.

The intrinsic viscosity in terms of IV was determined according to DIN 51562-3 in decaline as solvent and at a temperature of 120 °C.

Examples 1 to 5 (according to the invention)

An ethylene copolymer was prepared by gas phase polymerization in the presence of a chromium containing silica supported Phillipps catalyst and had a 1 -butene content of 5 weight-%, calculated on total weight of the copolymer. The ethylene copolymer had an MFR (190/21.6) of 7 g/10 min and was stabilized by a mix of two sterically hindered amines Chimassorb 944 and Tinuvin 770, whereby each of the sterically hindered amines was present in an amount of 900 ppm (= 1800 ppm in sum).

The thus stabilized ethylene copolymer was extruded to result in test bars having the dimension of 2 cm width, 10 cm length and 1 cm thickness. Some of the test bars were tested with regard to their intrinsic viscosity (IV), whereby the results appear in the table below. The remaining test bars were put into blown PE bottles having a total volume of 300 ml and a wall thickness of 0.8 mm comprising 200 ml fuel which was contaminated by different amounts of peroxides appearing in the table below. The peroxides were a mix of lauryl peroxide and DTBP in a 1 to 1 molar ratio. The test bars have been stored in the bottles comprising the fuel at constant temperature of 40 °C over a time period of 2000 hours. Thereafter the test bars were removed and were also tested with regard to their mechanical strength, whereby the test results after storage in fuel do appear in the table 1 below, as well.

Table 1

Examples 6 to 10 (according to the invention) The same test bars as described in examples 1 to 5 stabilized by the mix of the two sterically hindered amines Chimassorb 944 and Tinuvin 770, whereby each of them was present in an amount of 900 ppm (= 1800 ppm in sum) have been tested in the bottles comprising fuel and a mix of lauryl peroxide and DTBP in a 1 to 1 molar ratio in an amount of 30 ppm over different time periods appearing in the table 2 below.

Table 2

Examples 1 1 to 15 (comparative tests)

Examples 1 to 5 were repeated with the sole difference that the ethylene copolymer did not comprise any sterically hindered amine stabilizers. The test bars have been stored in the bottles comprising the fuel with different peroxide content at constant temperature of 40 °C over a time period of 2000 hours. The results of examples 1 1 to 15 appear in the table 3below. Table 3

Apparently the test bars of the comparative tests (Ex. 1 1 to 15) which are not protected by any stabilization are subjected to a progressive chain degradation by the influence of the peroxides within the fuel resulting into lower IV values and in connection therewith into a loss of mechanical strength and barrier properties. In contrast thereto the test bars stabilized according to the instant invention (Ex. 1 to 10) maintained their IV values over a long time period in the presence of high peroxide concentrations.

* * * * *

Claims

Claims:

1. Ethylene homo- or copolymer composition stabilized against thermo- oxidative degradation occurring in the presence of liquid fuels comprising peroxides, whereby the ethylene homo- or copolymer composition comprises a combination of at least two sterically hindered amine compounds or N-hydroxy- or N-oxylderivatives thereof in an amount ranging from 100 to 10 000 ppm, calculated as the sum of all sterically hindered amines on total weight of the stabilized polymer.

2. Ethylene homo- or copolymer composition according to claim 1 , whereby the amount of the at least two sterically hindered amine

compounds or their N-hydroxy- or N-oxylderivatives ranges from 400 to 5000 ppm, calculated as the sum of all sterically hindered amines on total weight of the stabilized polymer.

3. Ethylene homo- or copolymer composition according to claim 1 , whereby the amount of the two sterically hindered amine compounds or their N-hydroxy- or N-oxylderivatives ranges from 500 to 3000 ppm, calculated as the sum of all sterically hindered amines on total weight of the stabilized polymer.

4. Ethylene homo- or copolymer composition according to one or more of claims 1 to 3, whereby at least one of the sterically hindered amine compounds has the chemical formula:

wherein n is an integer ranging from 2 to 20.

5. Ethylene homo- or copolymer composition according to one or more of claims 1 to 3, whereby at least one of the sterically hindered amine compounds has the chemical formula:

6. Ethylene homo- or copolymer composition according to one or more of claims 1 to 5, whereby the polymer comprises in addition other stabilizers such as sterically hindered amines including all secondary amines whose substitution on the carbons adjacent to the amine nitrogen is such that any single hydrogen does not remain at these positions, whereby preference is given to derivatives of 2,2,6,6-tetramethylpiperidine, substituted either at the 4-position or on the amine nitrogen, and to derivatives of quinoline and of diphenylamine.

7. Ethylene homo- or copolymer composition according to one or more of claims 1 to 6, whereby the polymer for use in the technique of extrusion and blow moulding has a melt flow rate MFR (190/21 .6) of from 1 to 25 g/10 min, in particular from 2 to 20 g/10 min, and whereby the polymer for use in the technique of injection moulding has an MFR (190/2.16) of from 0.1 to 100 g/10 min, preferably from 0.2 to 10 g/10 min.

8. Ethylene homo- or copolymer composition according to one or more of claims 1 to 7, whereby the polymer has a density of from 0.930 to 0.970, in particular from 0.940 to 0.960 g/cm³.

9. Use of an ethylene homo- or copolymer composition according to one or more of claims 1 to 8, for the preparation of articles of plastic and components for the transport and storage of "dirty fuels", preferably for plastic fuel tanks for automotive vehicles driven by combustion engines, comprising single layered or multilayered articles.

10. The use of a combination of at least two sterically hindered amine compounds to render resistance against thermo-oxidative degradation occurring in the presence of liquid fuels comprising peroxides in an ethylene homo- or copolymer composition, whereby at least one of the sterically hindered amine compounds has the chemical formula:

wherein n represents an integer in the range of from 2 to 20 and whereby at least one of the sterically hindered amine compounds has the chemical formula:

1 1. Articles of plastic and components for the transport and storage of liquid fuels comprising peroxides, preferably plastic fuel tanks for automotive vehicles driven by combustion engines produced from an ethylene homo- or copolymer composition according to one or more of claims 1 to 8.