GB2093463A

GB2093463A - Radiation-resistant Olefin Polymer

Info

Publication number: GB2093463A
Application number: GB8203207A
Authority: GB
Original assignee: Borg Warner Chemicals Inc
Current assignee: GE Chemicals Inc
Priority date: 1981-02-23
Filing date: 1982-02-04
Publication date: 1982-09-02
Also published as: FR2500461A1; CA1164127A; FR2500461B1; GB2093463B

Abstract

Sterilization of olefin polymer articles with irradiation. The irradiated articles are heat-stable, owing to the presence of small proportions of pentaerythritol phosphites.

Description

SPECIFICATION Radiation-resistant Olefin Polymer The invention of this application relates, as indicated, to radiation-resistant olefin polymer compositions. More particularly, it relates to the sterilization of such olefin polymer compositions by means of radiation without substantial degradation of the polymer. Still more particularly, it relates to the radiation of olefin polymer articles.

Medical articles, such as syringes, hypodermic needles and the like, must be antiseptically clean during use. It is necessary in any such sterilization that the microorganisms, attaching to such articles, which may cause diseases in men be killed, and this can be accomplished in a number of ways. They can be killed by moist heat, i.e., by heating with steam under pressure in an antoclave, pressure cooker, or retort Most commonly, the process is carried out in an autoclave at 121 OC with 1 5 Ibs. pressure for 20 minutes or more. Another method involves heating in dry air, but at higher temperatures and for a longer period of time, e.g., at 1 60-1 650C for at least two hours.

Where the article to be sterilized is susceptible to deterioration at elevated temperatures, ionic radiation may be employed. Any effective source of ionizing radiation is suitable. Thus, one can employ a high energy electron accelerator of the Van de Graaff type, or any of several other types. Other suitable sources of ionizing radiation include X-rays and gamma radiation. This method is quite desirable because it is relatively quick and because it is carried out at ordinary temperatures.

Still another method of sterilization involves treating the article to be sterilized with ethylene oxide. While this is an effective method, the article thus treated, especially if it is a medical instrument, for example, is not always completely safe for its intended use.

U.S. 3,897,388 (Lyons) shows the radiation of a high density polyethylene composition containing large amounts of distearyl pentaerythritol diphosphite. The radiation dosage was 20 Mrads.

The heat stability of such irradiated composition was shown, in certain instances, to be inferior to that of similar polyethylene compositions which also contained large amounts of certain sulfur-containing phenolic antioxidants. The same kind of data is shown for low density polyethylene.

U.S. 4,036,719 (Lyons) shows the radiation of low density and high density polyethylene (also chlorinated polyethylene and an ethylene-vinyl acetate copolymer) compositions containing various organic phosphite esters, including distearyl pentaerythritol diphosphite. Again, the radiation dosage is high, viz., 15 Mrads and the net result is the cross-linking of the polymer.

The invention of this application is a method of sterilizing an article consisting essentially of polypropylene containing a minor effective proportion of a pentaerythritol phosphite ester comprising subjecting said article to ionizing radiation of 2-5 Mrads. The method is effective to sterilize the article without, however, causing any substantial degradation of the olefin polymer.

The polypropylene article may be of any thickness, and, while thickness is not a critical feature of the invention, those articles having a thickness of from about 5 to about 150 mils are especially susceptible to the advantages of the invention.

The pentaerythritol phosphite ester conforms to the structural formula:

where R is the same or different alkyl, alkaryl or aralkyl group. Illustrative examples of R include decyl, tetradecyl, octadecyl (stearyl), eicosyl, isododecyl, 4-tertiarybutylphenyl, 2-nonylphenyl, 2,4 ditertiarybutyiphenyl, 2,4-dinonylphenyl, 2-isooctyiphenyl, 4-n-heptylphenyl, 4-phenyl-n-butyl, 2 methyl-4-phenyl-n-butyl and the like. R should have at least 10 carbon atoms and generally less than 30 carbon atoms. Preferably, R is alkaryl and, especially 2,4-dialkylphenyl. A particularly preferred species of R is 2,4-ditertiarybutylphenyl. It is especially effective as a stabilizer of irradiated polypropylene.

The dosage of radiation is critical. At least enough is required to impart the desired sterilization, of course, but very little more than this is tolerable because it is important that degradation of the olefin polymer be avoided. A dosage of 2-5 Mrads is adequate to meet these requirements.

Olefin polymers, especially polypropylene, are subject to oxidative degradation. This is manifested by surface crazing, cracking, and ultimately complete embrittlement. The undesired oxidation proceeds via a free radical reaction mechanism and, of course, irradiation of an oiefin polymer generates free radicals. It is apparent that care must be exercised in accomplishing the desired sterilization without degrading the sterilized olefin polymer.

The concentration of pentaerythritol phosphite ester should be within the range of from about 0.01 to about 0.8 percent, by weight, of the olefin polymer. A preferred range is from about 0.05 to about 0.5 percent.

The olefin polymer compositions may also contain dialkylthiodipropionates where the alkyl group contains 10-20 carbon atoms, in concentrations of from about 0.1 to about 1.0 percent; polyvalent metal salts of fatty acids such as calcium stearate, magnesium stearate, aluminum stearate, cadmium stearate and barium palmitate, in concentrations ranging from about 0.05 to about 0.2 percent; and phenolic oxidation inhibitors which have a molecular weight greater than 500, and have at least one low molecular weight tertiary alkyl group ortho to each phenolic hydroxyl group, in concentrations of from about 0.01 to about 0.25 percent.

Illustrative phenolic oxidation inhibitors include octadecyl-3-(3',5'-ditertiarybutyl-4' hydroxyphenyl)propionate, 3,5-ditertiarybutyl-4-hydrocinnauric acid triester of 1,3,5-tris-(2hydroxyethyl)-s-triazine-2,4,6-( 1 H,3H ,5 H)-trione, 1 ,3 ,5-tris-(4-tertiarybutyl-3-hydroxy-2 ,6- dimethylbenzyl)- ,3,5-triazine-2,4,6-( 1 H,3H,5H)-trione, 2,4-ditertiarybutylphenyl-3,5-ditertiarybutyl- 4-hydroxybenzoate, terephthalate ester of 2,2-methylene-bis-(2-tertiarybutyl-4-methylphenol), 1 1 ,3- tris-(4-hydroxy-3-tertiarybutyl-6-methylphenyl)butane, tetrabismethyiene-3-(3',5'-ditertiarybutyl-4'hydroxyphenyl)propionate methane and bis-(4-hydroxy-3,5-ditertiarybutylbenzoate) of the monoacetal of 3-(4'-hydroxy-3',5'-ditertiarybutylphenyl)propionaldehyde and pentaerythritol.

The stability of the polypropylene compositions herein is shown by the data set out in Table I, where color ratings (L-b) are assigned to polypropylene compositions containing 0.25 part of distearyl thiodipropionate and varying proportions of pentaerythritol phosphite esters and other indicated ingredients. The test samples are prepared by blending the polypropylene and other ingredients in a twin shell blender for 15 minutes, extruding the resulting mixture at 5100F, pelletizing the extrudate and, finally, injection molding the pellets at 5100 F to form 100-mil plaques (121 inches by 2 inches). The test samples are given a color rating, then irradiated with 60Co to a dosage of 4 Mrads; again rated for color, then heated at 1 000C for 48 hours and rated a third time for color.

Table I Color Ratings After 4.0 Mrads Initial After 4.0 Mrads AndAfter Heating 1. 0.101 72.7 68.3 55.4 0.02 C 2. 0.101 73.8 68.9 60.9 0.02 C 0.10A 3. 0.101 73.5 67.8 65.9 0.02 C 0.10 B 4. 0.101 73.5 68.1 57.7 0.03 D 5. 0.101 74.1 68.1 62.4 0.03 D 0.10A 6. 0.10 1 73.6 66.2 63.8 0.03 D 0.10 B 7. 0.101 73.2 68.7 62.2 0.05 E 8. 0.101 73.8 68.3 64.6 0.05 E 0.10A 9. 0.101 73.4 66.6 64.7 0.05 E 0.108 10. 0.101 71.8 61.8 59.2 0.15F 11. 0.101 73.9 60.8 60.0 0.10F 0.10A 12. 0.101 72.8 61.9 61.3 0.10F 0.108 13. 0.101 72.5 64.9 61.1 0.075 G 14. 0.101 73.5 65.9 64.1 0.075 G 0.10 A Table I (cont.) Color Ratings After 4.0 Mrads Initial After 4.0 Mrads AndAfter Heating 15. 0.101 73.0 66.0 64.2 0.075 G 0.108 16. - 74.0 70.1 55.0 17. 0.10A 74.7 63.9 63.1 18. 0.108 74.3 68.7 61.4 19. 0.10H 72.4 42.6 37.7 A: distearyl pentaerythritol diphosphite B: bis-(2,4-ditertiarybutylphenyl)pentaerythritol diphosphite C: 1 ,3,5-tris-(4-tertiarybutyl-3-hydroxy-2,6-dimethylbenzyl)- 1 ,3,5-triazine-2,4,6- (1 H,3H,5H)trione D: terephthalate ester of 2,2-methylene-bis-(2-tertiarybutyl-4-methylphenol) MW=812 E: 3,5-ditertiarybutyl-4-hydroxylhydrocinnauric acid triester of 1 ,3,5-tris-(2-hydroxyethyl-s- triazine-2,4,6-(1 H,3H,5H)-trione F: 1 ,3-tris-(4-hydroxy-3-tertiarybutyl-6-methyl )butane G: 3 ,5-tris-(4-hydroxy-3,5-ditertiarybutyl)-s-triazine-2,4,6-( 1 H,3H,5H)-trione H: butylated hydroxytoluene I: calcium stearate Further evidence of the resistance of the compositions herein to deterioration at elevated temperatures is shown by the data in Table II. That data is derived from 50-mil plaques prepared as above and containing the ingredients shown in the Table. The plaques are irradiated with a dosage of 4.0 Mrads, then placed in an oven at 1 000C and withdrawn at 24-hour intervals for inspection. When the plaque surface exhibits cracking or crazing, it is adjudged a failure and the time required to reach such condition taken as a measure of the thermal stability of the plaque's composition.

Table II Time to Failure 1. 0.101 48 hours 0.02 C 2. 0.101 48 hours 0.02 C 0.10A 3. 0.101 > 1100 hours 0.02 C 0.108 4. 0.101 48 hours 0.03 D 5. 0.101 48 hours 0.03 D 0.10A 6. 0.101 > 1100 hours 0.03 D 0.108 7. 0.101 48 hours 0.05 E 8. 0.101 > 1100 hours 0.05 E 0.10A 9. 0.101 > 1100 hours 0.05 E 0.108 10. 0.101 > 1100 hours 0.15F 11. 0.101 > 1100 hours 0.15F 0.10 A Table II (cont.) Time to Failure 12. 0.101 > 1100 hours 0.15F 0.10 B 13. 0.10J > 1100hours 0.075 G 14. 0.101 > 1100 hours 0.075 G 0.10A 15. 0.101 > 1100 hours 0.075 G 0.10B 16. - 840 hours 17. 0.10A > 1100 hours 18. 0.10B > 1100 hours 19. 0.10H > 1100 hours All parts and percentages herein, unless otherwise expressly stated, are by weight.

Claims

1. A method of sterilizing an article consisting essentially of an olefin polymer containing a minor effective proportion of a pentaerythritol phosphite ester comprising subjecting said article to ionizing radiation of 2-5 Mrads.

2. The method of Claim 1 wherein the olefin polymer is a polymer of propylene.

3. The method of Claim 1 wherein the olefin polymer is polypropylene.

4. The method of Claim 1 wherein the pentaerythritol phosphite ester is a bis (dialkylphenyl)pentaerythritol diphosphite.

5. The method of Claim 4 wherein the dialkylphenyl groups are 2,4-dialkylphenyl groups.

6. The method of Claim 1 wherein the pentaerythritol phosphite ester is a dialkyl pentaerythritol diphosphite.

7. The method of Claim 1 wherein the olefin polymer article has a thickness of from about 1 to about 1 50 mils.

8. A method of sterilizing an article consisting essentially of an olefin polymer containing a minor effective proportion of a pentaerythritol phosphite ester and a phenolic oxidation inhibitor having a molecular weight greater than 500 and having at least one low molecular weight tertiary alkyl group ortho to each phenolic hydroxy group, comprising subjecting said article to ionizing radiation of 2-5 Mrads.

9. A sterilized olefin polymer article prepared by the method of Claim 1.

10. A sterilized olefin polymer article prepared by the method of Claim 5.

11. A sterilized olefin polymer article prepared by the method of Claim 6.