CS259619B1 - A method of stabilizing linear polymers of ethylene and its copolymer with propylene - Google Patents

Abstract

Linear polyethylene and ethylene-propylene copolymers containing 0.01 to 4.1 mol % propylene component produced on supported catalysts with a flow index of 0.2 to 20 g/10 min. can be effectively stabilized with 0.01 to 0.1 wt % 2,6-ditertbutyl-4-methylphenol and 0.01 to 0.1 wt % tris-2,4-(1'-phenylethylphenyl)phosphite, if stabilization with a phenolic stabilizer is carried out at a temperature of 35 to 70 °C.

Description

The present invention relates to a process for stabilizing linear polyethylene and its copolymers with propylene.

Polyolefinic types of polymers are among the least stable polymers in terms of thermo-oxidative and photo-oxidative stability. The oxidative failure of the polymer chains can occur already in the primary stage immediately after polymerization, during processing into granules, during production of the final product and during its application. The stabilization of polyolefins against thermo-oxidative degradation must therefore always be carried out if at least the essential performance properties of the polymer material are to be maintained. The difficulty of the processing conditions or the demanding application determines the level of stabilization.

Linear polyethylene and its copolymers with propylene are protected similarly to other polyolefinic types of polymers. The phenolic, phosphite and sulfur compounds used stabilize the polymer to such an extent that it can be granulated without damage and processed to the final product in the next stage.

The present process for the production of linear polyethylene and its copolymers with propylene consists of polymerization of ethylene or mixtures of ethylene with propylene on supported catalysts in a fluidized bed, transporting the powdered polymer produced from the polymerization reactor space to the storage silo. for granules.

Due to the complexity of the power management of each production unit, it is customary to extrude the stabilized powdered polymer or copolymer by usually mixing the phenolic antioxidant with an appropriate amount of the powdered polymer or copolymer and granulating it. The concentrations of the stabilizer additive typically range from 0.5% by weight to future applications. As a general principle, the higher the molecular weight polymer or copolymer is processed, the more thoroughly it is necessary to stabilize.

The lowest concentrations of stabilizers can be used to stabilize the low molecular weight types. Usually, high molecular weight stabilizers are used which, although low in volatility from the polymer, require a very perfect polymer dispersion. Furthermore, the use of high molecular weight stabilizers at very low concentrations is highly disadvantageous because the curves characterizing the concentration-dependency of the stabilizing activity (eg, induction periods of thermooxidation) exhibit disproportionately low steepness in the low concentration range and only after reaching a critical concentration. Therefore, the use of high molecular weight stabilizers at low concentrations is very inefficient and therefore economically inefficient.

We have now found a process for stabilizing linear polyethylene and its propylene copolymers using low molecular weight phenolic and phosphite stabilizers, wherein linear polyethylene or ethylene-propylene copolymers containing 0.01 to 4.1% molar propylene components produced on supported catalysts having an index of flow 0.2 to 20 g / 10 min. stabilize by means of the premix at 35 to 70 ^° C, first 0.01 to 0.1% by weight of 2,6-di-tert-butyl-4-methylphenol and then, at the entrance to the mixer, 0.01 to 0.1% by weight of tris [2,4- (1'-phenylethyl) phenyl] phosphite.

By raising the stabilization temperature, a sufficiently high partial pressure of a volatile phenolic stabilizer such as 2,6-di-tert-butyl-4-methylphenol is achieved so that when mixing the stabilization premix with the powdered polymer or copolymer, the stabilizer pairs can deactivate the catalyst residues prior to entry into the extruder.

When mixing powdered polymer or copolymers heated to 35-70 ° C with a volatile phenolic antioxidant, two competing reactions occur in the presence of atmospheric oxygen: Passivation of polymerization catalysts while trace trace oxidation of the polymer or copolymers. If this stabilization is carried out within said temperature range, the deactivation process predominates before oxidation.

The desired temperature of the polymer or copolymer is achieved either by passing the polyethylene powder through a suitable exchanger or by a force management organization that allows the extrusion of the polymer powder at a suitable time after the polymerization. Optimum results are achieved in such cases where the air-to-air transport medium is completely or at least partially replaced by inert (nitrogen).

The following examples illustrate the invention. % in the examples are by weight.

Additives used

Additive 1: 2,6-di-tert-butyl-4-methylphenol (Antioxidant 4K)

Additive 2: tris [2,4- (l‘-phenylethyl) phenyl] phosphite (Antioxidant 6)

Additive 3: tetrakis (methylene-3- (3 ', ^{5'-di-tertbutyl-4!} Hydroxyphenyl-propionate)] methane (Irganox 1010)

Used polymers

Polymer A: powdered linear polyethylene prepared on supported catalysts with a flow index of 0.21 g / 10 min.

Polymer B: a powdered linear copolymer of ethylene with propylene, containing 4.1 mol% propylene component, prepared on supported catalysts, with a flow index of 0.22 g / 10 min.

Polymer C: Powdered linear polyethylene, prepared on supported catalysts with a flow index of 6.9 g / 10 min.

Polymer D: a propylene ethylene-propylene linear copolymer containing 0.01% of a molar propylene component prepared on supported catalysts, with a flow index of 7.2 g / 10 min.

Polymer E: Powdered linear polyethylene, prepared on supported catalysts with a Flow Index of 19.2 g / 10 min.

Polymer F: a powdered linear copolymer of ethylene with propylene containing 3.1% propylene component, prepared on supported catalysts, with a flow index of 18.9 g / 10 min.

Polymer G: powdered linear polyethylene prepared on supported catalysts with a flow index of 0.1 g / 10 min.

Examples:

Example 1

Polymer powder ý heated to temperature

35.2 ° C was first homogenized with 0.1% adittva 1 and in the next stage in a 0.1% admixture mixer 2 and granulated. The resulting granulate was subjected to a 4-fold test extrusion. The melt flow index of 0.20 g / 10 min was measured for the granulated final sample.

Example 2

Powder polymer B heated to temperature

35.2 ° C was first homogenized with 0.1% additive 1 and next in a mixer with 0.1% additive 2 and granulated. The resulting granulate was subjected to a 4-fold test extrusion. The melt flow rate of 0.20 g / 10 minutes was measured for the granulated final sample.

Example 3

Polymer C powder heated to temperature

47.8 ° C was first homogenized with 0.015 why. additive 1 and the next stage in a mixer with 0.015% additive 2 and granulated. The resulting granulate was subjected to a 4-fold test extrusion. The melt flow rate of 6.75 g / 10 min was measured for the granulated final sample.

Example 4

Powder polymer D heated to temperature

48.0 ° C was homogenized with 0.015% additive 1 and next in a mixer with 0.015% additive 2 and granulated. The resulting granulate was subjected to extrusion four times. The melt index of the granulated final sample was 7.11 g / 10 min. Example 5

The powdered linear polymer E heated to a temperature of 69.8 ° C was first homogenized with 0.01% additive 1 and in the next stage in a mixer with 0.01% additive 2 and granulated. The resulting granulate was subjected to a 4-fold test extrusion. The melt index of the granulated final sample was 19.08 g / 10 min.

Example 6

The powdered linear polymer F, heated to a temperature of 69.8 ^° C, was first homogenized with 0.01% additive 1 and in the next stage in a mixer with 0.01% additive 2 and granulated. The resulting granulate was subjected to a 4-fold test extrusion. The melt flow index of the granular final sample was 18.80 g / 10 min.

Example 7

The powdered linear polymer G heated to a temperature of 44.1 ° C was first homogenized with 0.05% additive 1 and then in a mixer with 0.05% additive 2 and granulated. The resulting granulate was subjected to extrusion twice. Further extrusion could not be performed to crosslink the polymer.

Example 8

The powdered linear polymer A having a temperature of 18 ° C was homogenized with 0.1% additive 1 and next in a mixer with 0.1% additive 2 and granulated. The resulting granulate was subjected to extrusion three times. Further extrusion could not be performed to crosslink the polymer.

Example 9

The powdered polymer A heated to 91 ° C was homogenized with 0.1% additive 1 and next in a mixer with 0.1% additive 2 and granulated. The resulting granulate was subjected to repeated extrusion. The polymer was completely crosslinked on the third pass through the extruder.

Example 10

The powdered polymer A heated to 52 ° C was homogenized with 0.05% additive 3 and granulated. The resulting granulate was subjected to repeated extrusion. The polymer was completely crosslinked on the third pass through the extruder.

Claims (1)

SUBJECT OF THE INVENTION Process for stabilizing linear polymers of ethylene and its propylene copolymers by means of low molecular weight phenolic and phosphite stabilizers, characterized in that the powdered linear polyethylene and its propylene copolymers containing 0.01 to 4.1 mol% of propylene component produced on supported catalysts with a flow index of 0.2 to 20 g / 10 min. are stabilized by means of a powder premix at 35 to 70 ° C, first 0.01 to 0.1% by weight of 2,6-di-tert-butyl-4-methylphenol and then 0.01 to 0.1% by weight of tris [2,4- (1 1-phenylethylphenyl] phosphite.