DE1053780B - Process to improve the resistance to oxidation of polyethylene - Google Patents

Description

Process for improving the oxidation resistance of polyethylene The effect of oxygen or gases containing oxygen, such as air, on polyethylene at elevated temperature, in addition to deterioration of the mechanical, is extremely evident and other properties in a breakdown of the molecule, which is what is known by visosimetric Can easily determine measurements. This breakdown occurs both with solid as well as dissolved polyethylene.

It has now been found that by adding small amounts of phenthiazine (Thiodiphenylamine) or some of its derivatives have the oxidation resistance of Polyethylene can improve significantly.

Phenthiazine is known to be used as an antioxidant for oils, but it was not foreseeable that a similar effect would also occur in the case of high molecular weight Polyethylene enters. It has been shown that a large number of lubricating oils or gasoline, the suggested oxygen inhibitors for polythene are none or only has a weak inhibitory effect. This is e.g. B. the case with benzenesulfonyl butidinium chloride, which improves the oxidation resistance of turbine oil, but that of polyethylene has no inhibitory effect.

The amount of the present invention as an antioxidant for polyethylene Phenthiazines used or of 1, 2-arylene thiazines can be used within a wide range Range between 0.001 and 100 "/ o, based on polyethylene; in general a sufficient effect is achieved with additions of 0.01 to 0.50 / o. The additives according to the invention can be used in various ways, in solid or dissolved form Form to which polyethylene is added. You can e.g. B. with the help of calenders can be incorporated or by means of a screw press during granulation or other processing. The antioxidants can also can be added during the polymerization, provided that they are selected in each case Do not hinder the type of polymerization. So z. B. phenthiazine or polymerization according to Ziegler can be added without disturbing the course of the reaction.

The possibility of doing the last mentioned way without Impairing the polymerization is surprising in that phenthiazine in connection with p-tert-butylpyrocatechol already as an effective polymerization inhibitor, z. B. in the polymerization of chloroprene has been proposed.

Compared with previously known antioxidants for polyethylene show the agents that can be used according to the invention, the phenthiazine or the 1,2-arylene thiazines, a superior effect with both high-pressure and low-pressure polyethylene, such as can be proven numerically based on the following examples.

The ability of the additives mentioned, also in solutions of polyethylene To exert their effect is, among other things, for the viscometry of polyethylene solutions significant. It is advisable to use higher concentrations of the additives to choose.

For example, powdered polyethylene, which had been produced by Ziegler by the low-pressure process, was mixed with 0.1% antioxidant. From this mass, foils with a wall thickness of 0.4 mm were produced within 5 hours by pressing under a pressure of 0.05 kg per cm 2. The reduced viscosity of the starting polyethylene was 9.3. After the films had been produced, the reduced viscosity was determined again. The drop in viscosity caused by oxidation, expressed as a percentage of the original value, is a measure of the effectiveness of the antioxidant used. Stabilizers | in ° / o in I'henthiazine 0, 0 1, 2-benzophenthiazine 7, 7 Epoxy resin, Molecular weight 3801) 23, 1 Molecular weight 9001) .......... 12.7 Molecular weight 1400 t) 19, 2 2-mercaptobenzimidazole ........... 34, 6 N, N'-diphenylguanidine 65, 4 1) produced by condensation of epichlorohydrin with diphenylolpropane.

The reduced viscosity given in the present example is calculated from the dynamic viscosity ale. a polythene solution with a concentration of c = 0.2 (g per 100 ccm of decahydronaphthalene at 135 ° C) and the dynamic viscosity #D of the decahydronaphthalene at 135 ° C as follows: #L - #D #rod = # #D # c For example 2.0374 g of the low-pressure polyethylene used in Example 1 are dissolved in 100ccm of decahydronaphthalene at 350.degree. C. with the addition of 0.1 g of antioxidant. After shaking the solution with air at 135 ° C. for 6 hours, the decrease in the reduced viscosity was determined. Stabilizing agent, viscous waste in ° / o Phenthiazine 20, 0 1. 2-Benzophenthiazine .............. 32, 5 2-mercaptobenzimidazole1) .......... 34, 0 47, 0 Epoxy resin, Molecular weight 900 ............... 67, 5 Molecular weight 1400 ............... 68.0 Diphenylguanidine 68, 5 Epoxy resin, molecular weight 380 71, 5 1) Only partial solution.

EXAMPLE 3 1.76 g of high-pressure polyethylene with a reduced viscosity of #red = 1.6 were dissolved in decahydronaphthalene with the addition of 0.1 g of stabilizing agent, as described in Example 2. The drop in viscosity was determined after shaking the solution at 135 ° C. with oxygen for 6 hours. Viscosity drop Stabilizers in% Phenthiazine 0, 0 2-mercaptobenzothiazole 6, 1 1, 2-benzophenthiazine 6, 9 2-mercaptobenzimidazole 1) .......... 27, 2 Diplieylguanidine 49, 8 Epoxy resin. Molecular weight 380 55, 9 Molecular weight 900 57, 1 Molecular weight 1400 .................... 57.5 Without 59, 7 3) Only partial solution.

Example 4 Whereas in the previous examples the resistance to oxidation was determined by determining the viscosity drop of polyethylene solutions, In a further experiment, the oxygen uptake was measured directly of polyethylene when stored in an oxygen atmosphere at an elevated temperature.

20 g of polyethylene were placed in a glass vessel with a diameter of 39 mm and 60 ccm content, which is in a larger glass vessel with a diameter of 57 mm and 130 ccm volume. The space between the two vessels was tightened Sodium hydroxide, which is the gaseous oxidation products of polyethylene tape.

The glass jars were placed in a bomb as they were for resistance to oxidation of gasoline according to ASTM regulation D 525-49 is used.

The bomb was filled with 7 kg per cm2 of oxygen and heated to 160 ° C held. The pressure changes that occurred were recorded by means of a recorder.

The table shows the stability period that is used for low pressure and High-pressure polyethylene when using various stabilizers when added of 0.1% was measured. The period in hours is shown under the stability period understood from the beginning of the experiment up to a pressure drop of 0, 2 kg each cm2 elapses. Before starting the tests, the device was completely sealed checked.

The Ziegler low-pressure polyethylene used in the experiments had a reduced viscosity of gred = 2.7; the high-pressure polyethylene was the same product as specified in Example 3. Stability period Stabilizer low pressure high pressure polyethylene polyethylene Phenthiazine .............. 6, 5 30, 0 1, 2-Benzophenthiazine ...... 3, 25 11, 2 2-mercaptobenzothiazole .... 0, 0 2, 0 2-mercaptobenzimidazole ... 0, 0 0, 0 Diphenylguanidine .......... 0, 0 2, 0 Epoxy resin, Molecular weight 380 ....... 0, 0 0, 0 Molecular weight 900 ....... 0, 0 0, 0 Molecular weight 1400 ....... 0, 0 0, 0 Without addition 0, 0 0, 0 When 0.3% of 2-mercaptobenzothiazole was added together with 0.3 of sulfur, the stability period was 1.5 hours for low-pressure polyethylene and 9 hours for high-pressure polyethylene.

PATENT CLAIM: 1. Process for improving resistance to oxidation of polyethylene, characterized in that phenthiazine and / or 1, 2-arylene thiazines in small amounts, preferably in amounts of 0.01 to 0.5 percent by weight, added will.

Claims (1)

2. The method according to claim 1, characterized in that the phenthiazine and or or 1, 2-arylene thiazines before or during the polymerization of ethylene can be added. Documents considered: Belgian Patent Specifications No. 531 883, 548 948; U.S. Patent Nos. 2,576,009, 2,582,510, 2,727,879.