CS256575B1 - A method of increasing the stability of ethylene polymers - Google Patents

Abstract

The stability of polyethylene and its copolymers stabilized by a derivative of 2,2,6,6-tetramethylpiperidine is increased by increasing the time of processing such a polymer mixture under heat in the kneader chamber to 10 to 100 min., preferably 40 to 60 min., or by 2 to 30 times, preferably 5 to 15 times, processing on a kneading-granulating device. In this way, a significant increase in the stability of ethylene polymers is achieved, which may be greater than when the stabilizer concentration is doubled. The solution can be used in the production of ethylene polymers intended for objects used in the wild, e.g. agricultural films.

Description

The present invention relates to a process for increasing the stability of ethylene polymers containing 2,2,6,6-tetramethylpiperidine derivative as a stabilizer against the effects of weathering by a suitable processing method.

It is known that most polyethylene products and copolymers thereof must be effectively protected against the adverse effects of weathering in use. To this end, a new, very effective class of stabilizers based on shielded piperidine derivatives has been developed in recent years. Such compounds and their uses are abundantly described in the patent literature as, e.g. Brit. U.S. Patent 1,196,224, Belg. U. S. Patent No. 554,444, U.S. Patent 4,136,083, Eur. U.S. Patent 4,182,703, USSR Patent 660,140. These stabilizers are typically used in stabilization systems in combination with effective types of stabilizers and antioxidants. This method proved to be unsuitable and according to MS. AO 236 375 is preferably used in the ethylene polymers of the 2,2,6,6-tetramethylpiperidine derivative itself. All of these stabilization methods have in common that an increase in stability can only be achieved by increasing the stabilizer dosage. However, this method is economically disadvantageous due to the relatively high cost of the stabilizer, and the level of stability that can be achieved is also limited.

These drawbacks are overcome by a method of increasing the stability of polyethylene and its copolymers containing 0.01 to 1.0 pens as stabilizer. wt. %, preferably 0.1 to 0.3 wt. of a 2,2,6,6-tetramethylpiperidine derivative, by a suitable treatment process for weathering effects. This consists in prolonging the heat treatment time of the polymer blend either in the kneader chamber for 10 to 100 minutes, preferably 40 to 60 minutes, or 2 to 30 times repetition of the treatment on a kneader-granulation device, preferably 5 to 15 times.

The advantage is that during prolonged treatment in the presence of atmospheric oxygen, oxidation products are formed in the polymer which subsequently react with the stabilizer to form new compounds that are more effective stabilizers than the parent product.

Example 1

Low-density polyethylene film prepared by kneading polyethylene with the addition of 2,2,6,6-tetramethylpiperidinol stearate in a Brabender plastograph chamber at 180 degrees Celsius for 5 minutes followed by compression at 180 ° C to a depth of 0.16 millimeters. It is exposed to an Xenotest of 1,200. During exposure, the carbonyl number representing the absorbance of the foil at 1,720 cm ^-1 calculated to a depth of 0.1 mm is evaluated by IR spectrography. The time to increase the carbonyl number by 0.3 is for the different stabilizer content given in Table 1.

Table 1 constr. Exposure time (% by weight) (h)

0.1

0.2

0.3

0.4

Example 2

1680 1950 2,100 2,200

Low-density polyethylene film with a content of 0.2 wt. The 2,2,6,6-tetramethyl 4-piperidinol stearate prepared as in Example 1 but with a kneading time in Brabender of 5, 10, 30 and 60 minutes is exposed to Xenotest 1200. Exposure time values at which the carbonyl number increases by 0 , 3 are given in Table 2 for different kneading times.

Table 2

Kneading time (min)

Exposure time (h)

1950 2,420 2,630 2,850

Example 3

Low-density polyethylene film with a content of 0.2 wt. The 2,2,6,6-tetramethyl-4- [5- (oxazolidin-2-cycloundecan-4-one)] piperidine prepared as in Example 2 is exposed to Xenotest 1200. Exposure time values at which the carbonyl number increases by 0 , 3 for the different kneading times are given in Table 3.

Table 3

Kneading time (min)

Example 4

Exposure time (h)

1830 1870 1950 2,020

Low-density polyethylene film with a content of 0.2 wt. 2,2,6,6-tetramethyl-4-piperidinol stearate prepared by mixing polyethylene with a stabilizer in a fluidic mixer by multiple processing on a kneading granulator at a melt temperature of 180 ^and C and blowing at 180 ° C to a thickness of 0.10 mm. in Xenotes5 te 1 200. Table 4 shows the values of time required to achieve a carbonyl number change of 0.3 depending on the number of processing cycles in the kneading-granulation apparatus.

Table 4

Number of processing cycles

Exposure time (h) í 5 10 20

900

320 2,500 2,450

Table 5 shows the times of tensile strength decrease to 50% of the original value in Xenotest 3 200 over 1 and 20-fold polyethylene blends.

T a. b u 1 'k and 5

Number of processors. Half-life of tensile strength cycles (h)

2 500

3 200

The subject of the invention can be used in the production of ethylene polymers for articles used in the wild, e.g. agricultural foil.

SUBJECT

Claims (1)

SUBJECT A process for increasing the stability of ethylene polymers containing from 0.01 to 1.0 wt. %, preferably 0.1 to 0.3 wt. of the 2,2,6,6-tetramethylpiperidine derivative against the effects of weathering, characterized in that the processing time is prolonged BACKGROUND the polymer blend in a kneader chamber for 10 to 100 min. preferably 40 to 60 min. or 2 to 30 times, preferably 5 to 15 times, the repeating process on a kneading granulator.