WO1996038499A1

WO1996038499A1 - Amine containing antioxidants for polymers

Info

Publication number: WO1996038499A1
Application number: PCT/US1996/008162
Authority: WO
Inventors: William E. Wright
Original assignee: Paxon Polymer Co LP
Current assignee: Paxon Polymer Co LP
Priority date: 1995-06-01
Filing date: 1996-05-31
Publication date: 1996-12-05
Anticipated expiration: 1997-12-01
Also published as: AR002149A1

Abstract

A composition for stabilizing chromium catalyzed high density polyethylene polymers against oxidative degeneration which includes a phosphite and at least one ethoxylated C12 to C18 alkyl amine. The phosphite is capable of hindering the oxidative degradation of the polymer and the amine is capable of hindering the hydrolysis of the phosphite.

Description

AMINE CONTAINING ANTIOXIDANTS FOR POLYMERS

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to antioxidants for polymers and more particularly to mixtures of antioxidants and amines for chromium catalyzed high density polyethylene (HDPE) polymers.

DESCRIPTION OF THE PRIOR ART It is well known in the art to produce high density polyethylene polymers. Such may be produced using chromium or Ziegler-Natta type catalysts by methods well known in the art as exemplified by U.S. patent 4,857,257. The use of chromium catalysts is preferred for certain classes of high density polyethylenes. In general, HDPE produced with chromium catalysts have terminal double bonds whereas HDPE produced with Ziegler catalysts do not have terminal double bonds. One consequence of these double bonds is that HDPE produced with chromium catalysts is highly susceptible to crosslinking and increase of molecular weight on degradation. Nevertheless, HDPE produced with chromium catalysts has a molecular weight distribution which is more preferred for blow molding applications and hence it has use in particular applications.

It is known that HDPE polymers are subject to oxidative degradation in the presence of atmospheric oxygen and moisture. In order to resist such degradation, organic phosphites are used by those skilled in the art in order to stabilize organic polymers against the oxidative degradation caused by light and/or heat in the presence of atmospheric oxygen and moisture. One particularly important property of phosphites is that they suppress color formation during HDPE processing. Their mode of action includes reaction with hydroperoxides that form through oxidation of the polymer. For example, in the oxidation of polyolefins, alkyl hydroperoxides form through a sequence of reactions involving the intermediate formulation of free radicals. The alkyl hydroperoxides then attack more polymer chains to produce still more free radicals thus leading to further degradation of the polymer. Phosphites are particularly effective in decomposing hydroperoxides thus terminating the chain reactions. Such organic phosphites are disclosed in U.S. patents 3,516,963 and 4,305,866. Unfortunately, these organic phosphites are known to undergo degradation during storage conditions. Phosphites are very reactive with water and oxygen and can decompose to yield products that are ineffective in suppressing degradation. In this process they are converted into inactive compounds and are then no longer effective as antioxidants. The stability of phosphites appears to be even poorer in the presence of chromium and therefore residual chromium in HDPE produced with chromium catalysts can cause the phosphite to degrade faster. Even after phosphites have been compounded into pelletized HDPE resin, their reactivity with moisture and oxygen can lead to their decomposition into nonuseful products. To preserve the usefulness of phosphites as polymer stabilizers it is clear that they should be protected from premature reaction with atmospheric moisture and oxygen during storage. One solution to this problem is proposed by U.S. patent 5,326,803 which suggests coating the phosphite with a dialkoxy or diphenoxy substituted silicone. U.S. patent 4,290,941 suggests a combination of a phosphite and a hindered phenolic antioxidant. U.S. patent 3,922,249 discloses a stabilized antistatic composition for polyolefins which requires adding a preformed admixture of a hindered phenol thermal stabilizer, a tertiary amine antistatic agent and a phosphite which prevents discoloration of the antistatic agent prior to blending with the polyolefin. All of the foregoing patents are incorporated herein by reference.

As previously mentioned, phosphites that may be present in HDPE produced using chromium catalysts are particularly susceptible to degradation. Such degradation is apparently not a problem with HDPE produced with Ziegler type catalysts since they show better phosphite retention under severe storage conditions of high heat and relative humidity. With chromium catalyzed HDPE, as the phosphite level decreases, the net hydrolysis products are found at ever increasing levels. Since chromium catalyzed HDPE is more advantageous than Ziegler catalyzed HDPE with respect to molecular weight distribution and toughness for certain applications such as blow molding, it would be desirable to solve the degradation problem in chromium catalyzed HDPE. In high density polyethylenes produced with chromium containing catalysts, it is often beneficial to use cycloalkyldiphosphites, to achieve good natural color and to provide the polymer with superior processing properties. However, under severe storage conditions of warm, moist air, major losses of the phosphite occur over several weeks. This causes a significant loss of performance when the resin is used to produce finished goods such as rigid containers or films. It has now been found that chromium catalyzed HDPE may be stabilized against such oxidative degeneration by forming a melt of the HDPE and then adding thereto an ethoxylated C\2 to Cjg alkyl amine and a dicycloalkyldiphosphite. The amine additive significantly increases phosphite retention. This is achieved effectively by adding a small amount of an ethoxylated amine to the phosphite containing polymer during pelletization of the HDPE. Ethoxylated amines have long been used as antistatic agents in polymers, but for this application they must be used at relatively high concentrations. Thus their use at lower levels for the purpose of suppressing phosphite degradation is unexpected in the art of polymer additives.

SUMMARY OF THE INVENTION

The invention provides a composition which comprises (a) a chromium catalyzed high density polyethylene polymer which undergoes oxidative degradation in the presence of atmospheric oxygen and water; and (b) at least one phosphite capable of hindering, and in an amount sufficient to hinder, the oxidative degradation of the polymer; and (c) at least one ethoxylated C_j2 to C_jg alkyl amine capable of hindering, and in an amount sufficient to hinder, the hydrolysis of the phosphite.

It would be desirable to improve the stability of organic phosphites which are used to hinder the oxidative degradation of chromium catalyzed high density polyethylene polymers and such is accomplished by the composition of this invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the practice of the present invention, a composition is prepared which provides a means for suppressing the loss of phosphite antioxidants when they are blended as stabilizers in pelletized, chromium catalyzed HDPE polymers. High density polyethylenes are well known in the art and generally refers to those having densities in the range of from 0.94 to 0.965 grams per cubic centimeter. As used herein, the term polyethylene includes homopolymers of ethylene and copolymers of at least 85 weight percent ethylene with up to 15 weight percent of one or more C3 to CJQ alpha- olefins, such as 1-butene, 1-hexene, etc. Preferably the copolymers include from 0.1 to 3 weight percent of the alpha-olefin comonomer. The polyethylene preferably has a melt flow index, as measured by the procedures of ASTM D-1238, condition E, of from 0.1 to 100 decigrams per minute, more preferably from 0.1 to 30 decigrams per minute.

Suitable chromium catalyzed high density polyethylenes non-exclusively include those having a number average molecular weight in the range of from 10,000 to 500,000, preferably from 20,000 to 100,000. Preferred chromium catalyzed high density polyethylenes are commercially available from Paxon Polymer Company of Baton Rouge, Louisiana.

Suitable phosphites are those which are in solids at room temperature, and which can be made into paniculate form including granules, pastilles, powders and other particulates, preferably in a powder forms. Suitable phosphites may be defined by the general formula

R²O

\ P-OR¹

I

R³O wherein R¹, R² and R- represent either the same or different hydrocarbyl radicals, which can be either substituted or non-substituted alkyl, cycloalkyl, aryl, alkaryl or aralkyl radicals.

In particular, trialkyl phosphites, dialkyl monophenyl phosphites, diphenyl monoalkyl phosphites and triphenyl phosphates, optionally bearing hydrocarbyl substituents on the benzene ring, are useful phosphite stabilizers. Dicycloalkyldiphosphites are preferred.

Specific examples of such organic phosphites are diphenyl-2-ethylhexyl phosphite, triphenyl phosphite, tris(2,5 di-tert-butyl-phenyl)phosphite, tris(2-tert-butyl- phenyl)phosphite, tris(2-phenylphenyl)phosphite, tris[2-(l, l-dimethylpropyl]phosphate, tris(2-cyclohexylphenyl)phosphite, tris(2-tert-butyl-4-phenylphenyl)phosphite, tris(2- tert-butyl-4-methylphenyl)phosρhite, tris(2,4-tert-amylphenyl)phosphite, tris(2,4-di- tert-butylphenyl)phosphite, and 2,2-methylene-bis(4, 6-di-t-butylphenyl)octyl phosphite.

Other organic phosphites which can be stabilized according to the present invention is definable by the general formula

O-CH₂ CH₂-O

/ \ / \

R⁴-O-P C P-O-R⁴

\ / \ /

O-CH₂ CH₂-O wherein each R⁴ radical is the same or different and represent hydrocarbyl radicals, which can be either substituted or non-substituted alkyl, cycloalkyl, aryl, alkaryl or aralkyl radicals.

Specific examples of such organic phosphites are bis(2,4-di-tert- butylphenyl)pentaerythritol diphosphite, bis(2,6-di-tert-butyl- methylphenyl)pentaerythritol diphosphite, bis (2,4,6-tri-tert-butylphenyl)pentaerythritol diphosphite, distearyl pentaerythritol diphosphite. 3,9-di(octadocyloxy)-2,4,8,10- tetraoxa-3,9-diphosphaspiro[5,5]undecane, 3,9-di(phenoxy)-2,4,8,10-tetraoxa-3,9- diphosphaspiro[5,5]undecane, 3,9-di(methoxy)-2,4,8, 10-tetraoxa-3,9- diphosphaspiro[5,5]undecane, 3,9-di(cyclohexyloxy)-2,4,8, 10-tetraoxa-3,9- diphosphaspiro[5, 5]undecane, 3-phenoxy-9-isodecyloxy-2,4,8,10-tetraoxa-3,9- diphosphaspiro[5 , 5]undecane, 3,9-di(o-chlorophenoxy)-2,4,8, 10-tetraoxa-3,9- diphosphaspiro[5,5]undecane, 3-methoxyethyl-9-isodecyloxy-2,4,8, 10-tetraoxa-3,9- diphosphaspiro[5,5]undecane, and the like. The most preferred phosphite is bis (2,4- di-tert-butylphenyl) pentaerythritol diphosphite available commercially as Ultranox 626 from General Electric.

The phosphite component is preferably present in an amount of at least 0.005% to 5% by weight of the HDPE polymer. A more preferred range is from 0.01% to .5% based on weight of the polymer, and most preferably from 0.05% to 0.2% based on weight of the polymer.

The composition contains an ethoxylated Cι to Ci g alkyl amine. Suitable ethoxylated amines include bis (2-hydroxyethyl)tallow amine, bis(2-ethoxyethyl) cocoamine; bis (2-hydroxyethyl)oleyl amine and bis(2-ethoxyethyl) stearyl amine and bis(2-ethoxyethyl) dodecanamine which are respectively available as Armostat 310, 410, 710, 1800 and 2000 from Akzo Nobel. Bis (2-hydroxyethyl) oleyl amine is also available commercially as Chemstat 172 from Chemax.

The ethoxylated amine is preferably present in an amount of at least 0.005% by weight of the HDPE polymer. A more preferred range is from 0.01% to 0.15% and most preferably from 0.01 % to less than 0.02 %.

The composition may optionally contain other conventional additives which are typically used in the compounding of HDPE, such as thermal stablilizers, for example hindered phenolics, pigments such as titanium dioxide and carbon black, fillers such as mica, talc and mixtures thereof, antioxidants, rubbers, antistatic agents, extrusion aids, UV stabilizers, lubricants, fillers, and the like, in amounts which are easily determined by those skilled in the art.

The compositions of this invention can be prepared by any conventional technique. They can be dry or melt blended in one or more steps. Preferably they are melt blended in standard commercial extruders or blenders.

The following examples which are illustrative and not exclusive, show the effectiveness of the additives used in this invention to protect phosphite antioxidants from premature decomposition.

EXAMPLE 1

One kilogram of high density polyethylene powder (MI22 = 3.7g/10 min; density = 0.953 g/cc) was thoroughly mixed with 0.50g of Irganox 1010-tetrakis methylene (3,5- di-tert-butyl-4-hydroxy hydrocinnamate)] methane from Ciba-Geigy; 1.00 g of bis (2,4-di-tert-butyl-phenyl) pentaerythritol diphosphite and .40 g of zinc stearate in a large nitrogen filled polyethylene bag. The mixture was then subjected to three consecutive extrusions at 230 °C using a 2.54 cm (1^H) diameter Rheomex 259 single screw extruder 25:1 length to diameter ratio operating at 60 rpm. 200 g of the pelletized extrudate were placed in a one liter beaker equipped with a loosely fitting lid and containing a large number of holes to allow easy ingress of hot moist air. The beaker was then placed in an oven which was kept at 60 °C (140 °F) and through which moist air was circulated continuously.

15 gram samples of the pellets were periodically removed from the beaker for analysis. HPLC analyses showed that the phosphite component was severely depleted within a few weeks.

One kg samples of the same virgin polyethylene powder used in the above experiment was compounded with the same stabilizer package (0.50 g Irganox 1010; 1.00 g Ultranox 626; 0.40 g ZnSt) in the way described above. However, in these subsequent formulations varying amounts of bis (2-hydroxyethyl) oleyl amine were also added.

Samples removed from each of these pelletized materials were also analyzed periodically and the concentration of Ultranox 626 recorded. The results are shown in Table 1.

TABLE 1

EFFECT OF ADDING BISf2 HYDROXYETHYL OLEYL AMINE

ON RETENTION OF PHOSPHITE IN HDPI

PPM of Phosphite

AmineCppm) O 100 2OO 400 300

DAYS

AT 60 °C

(140 °F)

O 449 596 538 673 617

7 379 535 580 583 540

21 119 562 615 620 561

63 O 394 623 628 508

93 O 318 576 565 453

The data clearly show that the phosphite additive is protected from degradation by the addition of bis (2-hydroxyethyl)oleyl amine at levels of 100 ppm and higher.

EXAMPLE 2 Four kilograms of an HDPE powder (Mr₂₂ =8.50 g/10 min) are thoroughly mixed with 7.6 grams of a mixture containing 2.8 g of Irganox 1010-tetrakis methylene (3,5- di-tert-butyl-4-hydroxy hydrocinnamate)] methane from Ciba-Geigy, 4.0g Ultranox 626 and 1.6 g of zinc stearate. One kilogram of the resulting powder was passed through a 2.54 cm (1 ) diameter extruder at 230 °C using a screw speed of 60 rpm. The pelletized product was extruded twice more under the same conditions to yield a product A for a storage stability test of the type described in Example 1. The unused three kilograms of powder was divided into three equal portions and small amounts of bis (2-hydroxyethyl)oleyl amine were added to each to give powders containing 100 ppm, 200 ppm and 300 ppm. Each of these powders was extruded three times to give three pelletized products: B (100 ppm), C (200 ppm) and D (300 ppm). 200 grams of each of the pelletized products was subjected to storage at 140 °F in an atmosphere of moist air.

Aliquots were removed for analysis from each test material periodically and analyzed by HPLC to determine how much remained intact. The results are shown in Table 2. TABLE 2

EFFECT OF BIS f2-HYDROXYETHYL OLEYL AMINE ON THE

RETENTION OF PHOSPHITE IN HDPE

PPM of Phosphit e

Aminefppm) O 100 2OO 300

DAYS

AT 60 °C

(140 °F)

0 659 675 734 683

7 712 698 726 667

23 639 653 691 652

52 320 593 640 692

78 122 657 682 641

The data shows the strong protection offered by the compound bis (2- hydroxyethyl)oleyl amine to the phosphite.

EXAMPLE 3

Using the procedure described in Example 2, four separate kilogram portions of HDPE powder (MI₂₂ = 5.6 g/10 min) were pelletized using the same quantities of Ultranox 626, zinc stearate and bis (2-hydroxyethyl)oleyl amine as in Example 2. Storage stability data showed the following Table 3. TABLE 3

EFFECT OF BIS f2-HYDROXYETHYL) OLEYL AMINE ON THE

RETENTION OF PHOSPHITE IN HDPE

PPM of Phosphil :e

AmineCppm O 100 2OO 300

DAYS

AT 60 °C

(140 °F) O 568 547 667 692

20 511 536 677 683

30 444 578 715 755

37 335 571 652 692

63 81 520 685 700 96 0 393 666 699

The results again show the protective effect offered by bis (2-hydroxyethyl)oleyl amine to preserve the phosphite.

The above examples demonstrate that when a very small amount of an ethoxylated amine is added to a chromium catalyzed HDPE containing a phosphite antioxidant it prevents the latter from degrading during storage. Consequently, the desirable properties of the phosphite, namely, suppressing color formation and stabilizing melt flow during subsequent processing) are retained.

Claims

CLAIMS I Claim:

1. A composition which comprises (a) a chromium catalyzed high density polyethylene polymer which undergoes oxidative degradation in the presence of atmospheric oxygen and water; and

(b) at least one phosphite capable of hindering, and in an amount sufficient to hinder, the oxidative degradation of the polymer preferably wherein the phosphite is a dicycloalkyldiphosphite, more preferably wherein the phosphite is bis (2,4-di-tert- butyl-phenyl) pentaerythritol diphosphite; and

(c) at least one ethoxylated C_j2 to C_jg alkyl amine capable of hindering, and in an amount sufficient to hinder, the hydrolysis of the phosphite, and preferably wherein the amine is selected from the group consisting of bis (2-hydroxyethyl)tallow amine, bis(2- ethoxyethyl) cocoamine; bis (2-hydroxyethyl)oleyl amine and bis(2-ethoxyethyl) stearyl amine and bis(2-ethoxyethyl) dodecanamine, more preferably 1 wherein the amine is bis (2-hydroxyethyl)oleyl amine.

2. The composition of claim 1 wherein the amine is bis(2-ethoxyethyl) tallow amine, and wherein the phosphite is bis (2,4-di-tert-butyl-phenyl) pentaerythritol diphosphite.

3. The composition of claim 1 wherein the high density polyethylene polymer has a number average molecular weight in the range of from 10,000 to 500,000.

4. The composition of claim 1 wherein the phosphite is present in an amount of from 0.005% to 5%, wherein the amine is present in an amount of at least 0.005%, preferably wherein the amine is present in an amount of from 0.01% to 0.15%, more preferably wherein the amine is present in an amount of from 0.01% to less than 0.02% both based on weight of the polymer.

5. A method of hindering the oxidative degradation of a chromium catalyzed high density polyethylene polymer which undergoes oxidative degradation in the presence of atmospheric oxygen and water, which comprises forming a melt of the polymer and adding thereto at least one phosphite capable of hindering, and in an amount sufficient to hinder, the oxidative degradation of the polymer preferably wherein the phosphite is a dicycloalkyldiphosphite, more preferably wherein the phosphite is bis (2,4-di-tert- butyl-phenyl) pentaerythritol diphosphite; and at least one ethoxylated C_j2 to C_jg alkyl amine capable of hindering, and in an amount sufficient to hinder, the hydrolysis of the phosphite.

6. The method of claim 5 wherein the amine is selected from the group consisting of bis (2-hydroxyethyl)tallow amine, bis(2-ethoxyethyl) cocoamine; bis (2- hydroxyethyl)oleyl amine and bis(2-ethoxyethyl) stearyl amine and bis(2-ethoxyethyl) dodecanamine.

7. The method of claim 5 wherein the high density polyethylene polymer has a number average molecular weight in the range of from 10,000 to 500,000.

8. The method of claim 5 wherein the phosphite is present in an amount of from 0.005% to 5% by weight of the polymer and the amine is present in an amount of at least 0.005% based on weight of the polymer.

9. The method of claim 5 wherein the high density polyethylene polymer has a molecular weight in the range of from 10,000 to 500,000; wherein the phosphite is bis (2,4-di-tert-butyl-phenyl) pentaerythritol diphosphite and is present in an amount of from 0.005% to 5% by weight of the polymer; and the amine is bis (2- hydroxyethyl)oleyl amine or bis(2-ethoxyethyl) tallow amine and is present in an amount of at least 0.005% by weight of the polymer.