CA1209736A - Radiation-stable polyolefin compositions - Google Patents

Abstract

Abstract of the Disclosure An olefinic polymer composition is provided which comprises an olefinic polymer selected from homopolymers and copolymers made from aliphatic, ethylenically unsaturated monomers containing from 2 to about 10 carbon atoms and from about 100 to about 10,000 ppm of a stabilizer selected from benzhydrol or benzhydrol derivative compound of the formula:

Description

;-~c 1 02 ~ z ~ 9 ~DIATIO~-STAB1.L7 1'01.YOL~F1N C(1~05IT1(1NS

The present invention re:Lates to compositions 01 oleEi.nic polymers suitable for high energy radiation treatment. ~lore particularly, the present .
invention relates to olefinic polymer comp()sitions wh:ich are stab].e tosterlliz-ing dosages oE high energy radiation such as gan11na radiation.
Olefini.c polymers, suc1l as polyethyler1e and polypropylene, have a wide variety o:E known end use applications. Recently, as disclosed for instance in U. S. Patent No. 3,940,325 to ~1i.rao (Chisso), ole:Einic polymers have been clisclosed to be useEuL in the manuf;1cture of shapecl articles for l.O medical uses and for food packaging uses where the articles must undergo sterilization or be disinfected. It has also been reported that sterilization of such shaped art:icles may advantageous:1.y be accon11)lished by :irradiatlng the 1 article with high energy radiclt:ion sucl1 as gam1na radiation.
il Notwithstanding the significant known advantages of sterilization ¦ by means of high energy radiation, several disadvantages are known to be associated with such sterilization techniques. Fi.rst, when treated with radiation energy :in an amount suff-icient to achieve the desired sterilization,such polyole:Ein compositions may become d:iscolored. As reported in U. S.
l Patent No. 3,537,967 to Ke]ly et a:L. (Dart Tr1dustries), Lhis co.1.oration may ¦ occur :Eor a variety of reasons such as the use o certain adclitives in the polymer, as well as the presenc:e oE high arnounts oE cata:1.ytic: residues suchas titaniwn and chlorine. Simp.Le remova:L of the ad(1:itives from the olefinic polymer composition has not been Eound to be a satisEactory solution to the l problem because, as reportec1 by ~1irao, wh-il.e polymers which do not containl the standard additives ;nay not be subject to such co:Loration, the ptlysical properties of the shaped articles made :from such pol.ymers after irradiation with, for instance, x-rays may be disadva[ltageously degraded.

I

~ ~Z~9736 Some of the most common additives found in polyolefin polymer compositions tobe made into shaped articles, especially where increased melt temperatures or higher melt index polymers are required, are the so-called primary antioxidants employed to retard radical chain oxidation. The most common primary antioxidants are phenolic in nature. Examples include Goodrite*
3114 and 3125 which are phenolic antioxidants available from B. F. Goodrich Chemical Company. When used at effective concentrations to provide both processing and radiation stability these compounds have been found to cause the shaped article, which has been irradiated with a sterilizing dose, to be unacceptably discolored.
Accordingly, it would be highly desirable to provide olefinic polymer compositions which may be made into silaped articles that may be irradiated with sterilizing amounts of radiation while minimizing or eliminat-ing undesirable discoloration or degrad;ltioll in physical properties. The ¦ olefinic polymer compositions and shaped articles made therefrom according to ¦ the present invention may be employed to accompish such desirable results.
¦ ~ccording to the present invention an olefinic polymer composition ¦ is provided which comprises an olefinic polymer selected from homopolymers and ¦ copolymers made from aliphatic, ethylenically unsaturated monomers containing ¦ from 2 to about 10 carbon atoms and from about 100 to about 10,000 ppm of a ¦ stabilizer selected from benzhydrol or a benzhydrol derivative compound of ~ the formula: 1~3 l l l R2 ~ I - H
Rl wherein Rl and R2 are each independelltly selected from an aromatic group l-a~-ing from 6 to about 26 carbon atoms, and R3 is selected Erom hydrogen, an al~yl¦
group having from 1 to about 20 carbon ntollls, or an acyl group having from about 2 to about 20 carbon atoms.

-2-* trade mark, lZ~97~i Examples of such aromatic groups include phenyl and substituted phenyl groups.
Such substituents may be provided in the ortho, meta and/or para positions of the phenyl group and may include alkyl groups of the formula Cn~2n~1 e.g. methyl, ethyl, isopropyl, tert-butyl, nonyl, dodecyl, or eicosyl groups where n is from 1 to about 20. Examples of alkyl groups which may be employed include methyl, ethyl, isopropyl, tert butyl, nonyl, dodecyl and eicosyl groups. Examples of acyl groups include those of the formula acetyl, propinyl, lauryl and stearyl groups.
The stabilizers which may be employed according to the present invention may be very broadly described as having the structural formula set forth above. In general such stabilizers may be employed in an amount of from about 100 to about 10,000 parts per million (ppm) based on the weight of the total composition. Preferably, the amount employed may be from about 500 to about 5,000 ppm. Examples of preferred stabilizers that may be employed include benzhydrol and benzhydrol derivatives such as those set forth in Table I below:

T~B~E 1 Compound Molecular WeightMelting Point C
benzhydrol 184 67 phenyl2CHOCHphenyl2 350 108-110 C(CH20CHPh2)4 800 135-137 4,4'-dimethylbenzhydrol 212 67- 68 4,4'-di-t-butylbenzhydrol 296 91- 94 /~ 290 142-145 OH OH
~1~.~

-3-~,J l ; ~ 3~

The olefinic polymer compositions of the present invention may include the benzhydrol compound as the sole stabilizer, ~r the benæhydrol compound may be provided as a stabilizer together with one or more so-called secondary antioxidants or syner~ists. These secondary antioxidants are known for use in association with phenolic~type primary stabilizers and include a wide variety of compounds which in general may function by converting harmful peroxide compounds present in the polymeric composition to non-harmful, non-radical product. Examples of such secondary antioxidants include dilauryl thiodipropionate, distearyl thiodipopionate, trisnonylphenyl phosphite, dilauryl phosphite, and Weston 618 and Weston 619, which are phosphorus-containing antioxidants available from ~org Warner. In general, such secondary stabilizers may be used in an amount of from about 100 to about 10,000, preferably about 500 to about 3,000 ppm.
It has also been found that the olefinic compositions may contain ; 15 one or more known, phenolic based, primary stabilizers, such as hindered phenolic-type compounds in addition to the benzhydrol or benzhydrol derivative compound. This is particularly significant since it may not be possible in the practical world to process polypropyLene without a phenolic primary anti-oxidant,the presence of which may lead to yellowing on irradiation. The present invention may provide a remedy for this phenomenon. In such instance, even stabilizers which have been observed to cause discoloration in the polymer composition when subjected to radiation sterilization may not cause such dis-coloration when the benzhydrol or benzhydrol derivative compound is also present in the composition. I~hen present, such primary stabilizers may be provided in the composition in an amount of from about 100 to about 3,000 ppm, preferably from about 500 to about 2,000 ppm.
Olefinic polymers that may be employed according to the present invention include a w:ide range of olefinic homopolymers and copolymers of ethylene, propylene, butylene and higher homologues containing up to about

-4-* t~ade mark.

~ ..

~ 736 10 carbon atoms. Typically such polymers may have a molecular weight of from about :L0,000 to about 500,000, preferably about 30,000 to about 300,000. The preferred polymers applicable for use according to this invention are homo-polymers oE propylene and random or block copolymers of propylene with other mono- ~ -olefins such as ethylene, butene-l and higher homologues containing up to 10 carbon atoms. ~lencls of such propylene polymers with other polymers such as polyethylene are also included within the scope of this invention.
Generally the proportion of polymerized propylene in the total resin phase of the composition should be at least about 60 percent by weight.
In general, the radiation treatment can be applied to polymers of propylene useful particularly for medical purposes although this particular end use should not be understood to be a limitation upon the scope of the present invention. Thus, for instance, the olefinic polymer compositions of the present invention may be employed ~or otller end uses wilere such radiation treatment is necessary or desirable, e.g., meat packagin~" preserving food in retail packages and other uses.
The high energy radiation treatment of the olefinic polymer com-positions of the present invention may include any of a wide variety of known treatment techniques. One convenient racl:Lation source is a cobalt 60 source.
Other radiation treatments that may be employed include high energy x-rays, or high energy electrons (~- radiation). In general, radiation dosages that can be applied may range up to about 5 megarads. For sterilization purposes, a shaped article may be generally sterilized by applying 2.5 megarads under gamma radiation.
The following examples are provided to illustrate the invention but are not to be construed as uncluly limiting the subject matter thereof which is defined in the appended claims.

~ 7:~6 ~X~?~LE_I
To the Grignard reagent prepared Lrom 47.2g of p-bromotoluene and 7.2g of magnesium in 200 ml of ether was added dropwise 30g of p-tolualdehyde in 50 ml oE ether with cooling. When the addition was complete the reaction was refluxed for 15 minutes, cooled in ice, and 40 ml of saturated NH~(l solu-tion was added dropwise. The reaction was filtered and the ether was re-moved under reduced pressure to give a yellow oil which crystallized on standing. Recrystallization from petroleum ether gave 26.1g of nearly color-less 4,4l-dimethylbenzhydrol, m.p. 70-71.

EXA~PLE II
4,4'-di-t-butylbenzhydrol was prepared using the procedure oE
Example I. From 16.7g of p-bromo-t-butylbenzene, 3.2g of magnesium, and 17.5g of p-t~butylbenzaldehyde, there was obtained, after recrystallization from aqueous ethanol, 10.8g of the colorless benzhydrol derivative, m.p. 91-94.

EXA~LE III
To a stlrred slurry of 56g of aluminum chloride in 150 ml of benzene under reflux was added dropwise ~Og of terephthaloyl chloride dissolved in 250 ml of benzene. When the addition was complete the reaction was re-Eluxed Eor 15 minutes, cooled, and 250 ml of water was added slow:Ly. The benzene layer was separated and the aqueous layer was extracted with methylene chloride t2 x 300 ml). The combined organic layers were washed with 1~ NaO~I
solution (2 x 400 ml) and water (400 ml), dried (~IgS04), filtered, and the solvents were removed under reduced pressure to a nearly colorless solid.
Recrystallization from 95/o ethanol gave 46.8g of colorless 1,4-dibenzoyl-benzene, m.p. 160-162. Reduction of 20g of this material w:ith 1.8g of sodium borohydride in 250 ml oE ethanol gave 14.2g of color:Less 1,4-dibenzylolbenzene ~.p. 14~-145 .

~ 736 EXAMPLE IV
1,4-di(4'-t-butylbenzoyl) benzene was prepared as in Example III.
From 28g of aluminum chloride, 275 m:L of t-butylbenzene, and 20g of terephthalyl chloride then was obtained 11.8g oE the colorless material, m.p. 159 -161 . Reduction of 20g of this material with 1.8g of sodium borohydride in 250 ml of ethanol gave 16.1g of colorless 1,4-di(4'-t-butylbenzylol) benzene, m.p. 156-:L58.

EX~IPLE V
A mixture of 37g of chlorodiphenylmethane and 100 ml of water were refluxed under nitrogen for 16 hours. ~fter cooling the water was decanted and 40 ml of ethanol was added to induce crystallization. The yellow solid was re-crystallized 3 times from ethanol to give 21.9g oF dibenzhydryl ether, m.p.
108-110.

E~AMPLE VI
~ mixture of ~l1.8g of benzhydroL, 5.5g of pentaerythritol, 30 ml of dimethylsulfoxide, 300 ml of toluene, and 0.6g of p-toluenesulfonic acid were brought to reflux with water removal through a Dean-Stark trap. ~fter 2~l hours the toluene was removed under reduced pressure, the residual oil was taken up -ln methylene chloride (200 ml)~ washed with water (2 times 200 ml), dried (MgS0~), filtered, and the solvent was removed under reduced pressure.
The residual solid was purifiecl by multiple extraction-recrystallization with methanol to give 13.8g of pure tetraben~hydryl pentaerythrityl ether, m.p.
135-137.

~ 7~6 EX~'LE ~II
The additives were blended into polypropylene powder (Hercules Profax*6301) at 0.3% by weight concentrations, extruded into pellets, and then injection molded into 55mil thick plaques and standard tensile bars. The molded samples were irradiated to a 10 Mrad dose with a cobalt-60 ~-ray source.
The yellowness indices were determined on a Hunter*Colorimeter (ASTM D 1925).
Percentage elongation at break was used as a measure of embrittlement and was recorded on an Instron*testing machine using a strain rate of 5 in./min.
(ASTM D 638). This data for various additives is shown in Table II.
TABLE II
% Elongation Additive (0.3%) Yellowness Index _ at Break none 6.30 8.5 benzhydrol 3.16 21.9 dibenzhydryl ether 3.69 18.8 tetrabenzhydryl pentaerythrityl ether 4.36 24.0 4,4'-dimethylbenzhydrol 5.68 33.6 4,4'-di-t-butylbenzhydrol 3.81 22.5 1,4-dibenzylol benzene 3.48 23.8 1,4-di(4'-t-butylbenzylol)benzene 6.35 28.3 Goodrite 3114 24.00 26.4 Goodrite 3125 13.79 32.0 EX~LE VIII
Three samples containing benzhydrol with and without commercial synergistic antioxidants were prepared irradia~ed,and tested as in Example VII. The test results are shown in Table III.

* trade mark, v$

~ 73~

TABLE III
Yellowness % Elongation Sample # Additives (% Concentration) Index at Break 1 benzhydrol (0.3~) 3.16 21.9 2 benzhydrol (0.3%) 4.97 32.2 .
dilauryl thiodipropionate (0.1%) 3 benzhydrol (0.3%) 3.90 3105 Weston*619 (0.1%) EX~IE IX
Two samplescontaining Goodrite 3114 (a commercial phenolic anti-oxidant) were prepared, irradiated, and tested as in Example VII. The test results are shown in Table IV.

TABLE IV
Yellowness % Elongation ¦Sample # Additives (% Concentration) _ Index at Break l Goodrite*3114 (0.1%) 1].55 19.6 2 Goodrite*3114 (0.1%) 8.66 26.2 benzhydrol (0.3%) * trade mark.

'~3 1

Claims (5)

WHAT IS CLAIMED IS:

1. An olefinic polymer composition which comprises an olefinic polymer selected from homopolymers and copolymers made from aliphatic, ethylenically unsaturated monomers containing from two to about ten carbon atoms and from about 100 to about 10,000 ppm of stabilizer selected from benzhydrol or a benzhydrol derivative compound of the formula:

wherein R1 and R2 are each independently selected from an aromatic group having from 6 to about 26 carbon atoms, and 23 is selected from hydrogen, an alkyl group having from 1 to about 20 carbon atoms, or an acyl group having from about 2 to about 20 carbon atoms.

2. The olefinic polymer composition of claim 1 wherein said benzhydrol or benzhydrol derivative compounds are selected from the following compounds:

benzhydrol; 4,4'-dimethylbenzhydrol;
phenyl2CHOCHphenyl2 4,4'-di-t-butylbenzyhydrol;

C(CH2OCHPh2)4;

3. The olefinic polymer composition of claim 1 wherein said benzhydrol or benzhydrol derivative compound is provided as a primary stabil-izer together with a secondary stabilizer in an amount of from about 100 to about 10,000 ppm.

4. The olefinic polymer composition of claim 1 wherein said benzhydrol or benzhydrol derivative compound is provided as a primary stabil-izer and wherein the composition also includes at least one other phenolic-type primary stabilizer in an amount of from about 100 to about 3,000 ppm.

5. The olefinic polymer composition of claim 1 wherein said olefinic polymer is selected from homopolymers of polypropylene and random or block copolymers of polypropylene with other mono-.alpha.-olefins containing up to 10 carbon atoms.