DE1229725B - Process for stabilizing highly crystalline polypropylene - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

C08f

German class: 39 b -22/06

Number: 1 229 725

File number: St 20124IV c / 39 b

Filing date: December 22, 1962

Opening day:! December 1966

The invention relates to a method for stabilizing highly crystalline polypropylene, in particular to inhibit degradation at elevated temperatures by phenolic disulfides, which characterized in that 4,4'-dithio-bis (2-cyclohexylphenol) is used as the phenolic disulfide.

Crystalline polypropylene has recently gained great importance. Because of its superiority physical properties, intensive work has been carried out on the development of this crystalline polymer, and it is now commercially available in a variety of forms - casts, films, and fiber.

The highly crystalline polypropylenes have ^{melt indices between 0.01 and 50 at a temperature of 190 °} C. and are therefore particularly suitable for the production of synthetic fibers and films. Other desirable and beneficial physical properties of crystalline propylene are exceptional transparency, strong mechanical strength, and resistance to chemicals and solvents.

Despite the excellent physical and chemical properties of crystalline polypropylene, a major disadvantage of this material is that its properties deteriorate at elevated temperatures, apparently as a result of oxidative degradation. How quickly crystalline polypropylene is subject to air oxidation is best demonstrated when polypropylene fibers spun in the melt are heated ^{at 125 ° C. in an air circulation oven.} After 50 hours the fibers have lost about 50% of their strength and, if exposed to this treatment for 100 hours, they become a powdery substance.

Although all polypropylenes are more or less subject to the above-described air oxidation, however the crystalline stereoregular form is particularly exposed to such degradation.

For the reasons mentioned, it is necessary to oppose polypropylene in its highly crystalline form to stabilize oxidative degradation, and there are already many different antioxidants used Solution to this problem has been proposed. So it is z. B. known that bis (dialkylphenol) sulfides, -monosulphides and -disulphides have a stabilizing effect against oxidative degradation if they Polyethylene are added. However, if these bisphenol sulfides are incorporated into polypropylenes, especially in those with predominantly crystallinity, the result is a significantly lower strength Process for stabilizing highly crystalline polypropylene

Applicant:

Stauffer Chemical Company,

New York, N.Y. (V. St. A.)

Representative:

Dr. W. Beil, A. Hoeppener and Dr. H. J. Wolff,

Lawyers, Frankfurt / M., Adelonstr. 58

Named as inventor:

Silvio Louis Giolito, Whitestone, N.Y .;

Gerald Levine, Brooklyn, N.Y. (V. St. A.)

Claimed priority:
V. St. v. America December 29, 1961
(163 069)

compared to oxidative degradation than, for example, in the case of polyethylene stabilized in this way.

It has now been found that an excellent stabilization of crystalline polypropylene is possible is when a specific bisphenol is used, namely 4,4 '- dithio - bis - (2 - cyclohexylphenol) der formula

HO

An excellent stabilization against oxidative degradation at high temperatures is about 0.05 to 5% of the antioxidant of the type described herein. In most cases already about 0.5% antioxidant lead to excellent protection for the crystalline Polypropylene, but without changing the physical properties of the polymer, that is for example the color and the strength.

609 729/446

For example, 4,4'-dithio-bis- (2-cyclohexylphenol) in a concentration of 0.5% in crystalline Incorporated polypropylene, the result is an embrittlement time of about 700 hours while under the same test conditions with the corresponding monosulfide an embrittlement time of only 220 hours is achieved. Similar results are obtained in comparative tests with other phenol sulfides and disulfides.

The following example illustrates the process for stabilizing highly crystalline polypropylene.

example

10 g of powdered polypropylene with an antioxidant content of 0.5% were poured into the center of a stainless steel plate (size 15.2 × 15.2 cm). A steel plate of the same type was then placed over the powder and gently pushed down. The whole thing was then placed in the center of the platen of a hydraulic press that had previously been heated to 177 ° C. The lower press surface was raised until both surfaces contacted the lower and upper stainless steel plates. The powder sample was allowed to warm for about 4 minutes or until the resin melted. When the resin began to melt, the lower pressing surface was raised slightly to ensure that both surfaces were in contact with the steel plates surrounding the sample. After an additional 4 minutes, or when the resin melted, the lower surface was raised until there was a load of about one ton and this pressure was maintained for 2 minutes. Then the vent valve was opened to let off the steam, and then cold water was fed in to cool the ^{press surfaces and plates to a temperature of 10 ° C.} The molded resin flake was round and about 0.62 to 0.76 mm thick.

Discs of 25.4 mm in size were cut from the plate, placed in petri dishes and then exposed in a forced draft oven at 15O ⁰ C. The samples were examined a few hours later and checked for signs of discoloration, crystallization, clouding, charring of the edges, complete embrittlement and cracking. After the samples were removed from the oven, they were compared to control samples that did not contain an antioxidant. The results obtained when using the stabilizer according to the invention and conventional bisphenol sulfides and disulfides can be seen from the table below:

Results of the oven at 150 ⁰ C Alterungsversuehe

link time to Ver for ver search brittleness No. - (unstabilized polypropylene) .. in 4,4'-thio-bis (2-benzylphenol) .... hours 1 2,2'-thio-bis- (4-benzylphenpl) 1 2 4,4'-dithio-bis- (2-sec.butylphenol) 88 3 2,2'-dithio-bis- (4-sec-butylphenol) 126 4th 4,4'-dithio-bis (2-cyclohexylphenol) 261 5 138 6th 707

This table clearly shows the superiority of the stabilizer used according to the invention.

The mixture of powdered polypropylene and antioxidant used in the experiment was prepared by intimately mixing polypropylene and antioxidant in a Waring mixer until a homogeneous mixture of the ingredients was obtained. As an unstabilized polypropylene, useful for general use polypropylene of isotactic or crystalline type was used with high molecular weight at 230 ⁰ C had a melt index of 4 and a specific gravity of 0.905.

Claims (1)

Claim: Process for stabilizing highly crystalline polypropylene by means of phenolic disulfides, characterized in that a compound of the phenolic disulfide formula HO H ₂
used. H ₂ ' ^S H ₂ Documents considered: German Auslegeschrift No. 1 111 382; interpreted documents of Belgian patents Nos. 576 972, 598 732; British Patent Nos. 879 691, 857 448, 780 289. 609 729/446 11.66 Bundesdruckerei Berlin