CS204552B1 - Polyolefins treatment method - Google Patents

Description

SUMMARY OF THE INVENTION The present invention provides a method of treating polyolefins and mixtures thereof to improve weather resistance with simultaneous antistatic treatment.

Polyolefins do not have sufficient stability properties during use, as they are subject to heat aging under elevated temperatures and weather aging under long-term effects of climatic factors.

They are therefore protected against the effects of weather by the addition of various stabilizing agents. Among the most effective methods of stabilization are an additive combination of light stabilizers and antioxidants capable of suppressing the cause of aging, oxidative degradation induced by the initiating effect of the ultraviolet component of sunlight.

The patent literature encompasses a wide variety of methods of protecting polyolefins against the effects of weathering by suitable stabilization methods. In many cases, this involves the use of stabilization systems consisting of benzophenone uv absorbers and antioxidants. Organic phosphites are also effective antioxidants for these polymers.

A number of patents also protect the use of organic phosphorus compounds to stabilize polyolefins. These include combinations of different phosphites as applications of derivatives themselves. Furthermore, stabilization procedures based on the use of pentaerythritol phosphites and derivatives thereof, alone or in combination thereof, are protected.

It has now been found that an extremely high weather protection in stabilizing olefin polymers, copolymers and mixtures of these polymers with copolymers can be achieved by combining benzophenone uv absorbers with phosphites of pentaerythritol derivatives, further enhancing their effect in polyolefin polymers by providing rapid and complete dispersion in these polymers by adding the necessary amount of a suitable surfactant-surfactant. This results in a very homogeneous dispersion of the stabilizing additives, even during short processing processes such as injection molding or extrusion. The result of this dispersion is an increase in the stability and thus the durability of the stabilized products, even in the case of products of low thickness, such as films or fibers.

A further benefit of the new stabilization method is the fact that by suitable selection of a dispersant, an antistatic treatment of the polymeric material is also obtained along with the dispersion, which prevents, for example, the soiling of the product surface for a long time.

A few examples of a new method of stabilizing polyolefins against the effects of weathering are given, which, of course, cannot exhaust all the possibilities resulting therefrom, but prove the excellent effect of the system on product lifetime prolongation as well as the suppression of surface electrostatic charges.

Moreover, long-term exposures of products stabilized in the proposed manner have never seen local defects of a degrading nature, such as color change and cracking, which, especially on larger surface products such as foils and boards, usually exhibit eye-visible external aging and indirectly show insufficiently homogeneous dispersing the stabilizing ingredients in the polymeric material.

The main degradative process of polyolefins is oxidation, also causing changes in the mechanical properties of products. Therefore, an evaluation of the development of the content of the main oxidation product —CO groups, usually determined by IR analysis, from the evolution of the absorbance band of these groups at 1715 cm ¹ is usually used for objective assessment of the stability of the polymer sample. develops during gradual hardening and brittleness of products.

Therefore, the so-called carbonyl index proto A / d was chosen to evaluate the effects of the stabilization system, where Δ = change in absorbance band of CO groups, d = thickness of the measured sample in mm and decrease in ductility, expressed as% of its original amount. The stabilized sample is always compared with an unstabilised, exposed under the same conditions, the duration of exposure of the natural weathering test being expressed in the amount of global radiant energy of sunlight received by the sample surface unit in k J.cm ^-2 .

An objective view of the level of antistatic treatment gives a measure of the formation and dissolution of electrostatic charges. By electrification device (eg EP 70) it is possible to measure the maximum electric field intensity at a distance of 1 cm above the surface of the measured foil (E in kV.icm ^-1 ) and the half-life of charge (Xi and S). halving the E.

To illustrate the effectiveness of the proposed method, several examples are given:

Example 1

The standard type of domestic branched polyethylene Bralen RA 2-19 was stabilized by the addition of 0.1 wt. % distearyl-pentaerythritol diphosphite and 0.4 wt. % 2-hydroxy-4n-octoxybenzophenone with the addition of surface active substances which _T, 0.1 wt. % of a mixture of mono-di and tri-ethanolamides of oleic acid and 0.2 wt. % substituted amine.

From the polymer mixture thus obtained, 0.12 mm thick films were prepared by blow molding under conventional conditions. These films, together with the films of unstabilized branched polyethylene, have been tested for natural weathering in our climate. After the summer period corresponding to 225 kJ.cm ^{-2 of} global radiant energy, the values of stabilized and non-stabilized films were as follows:

Feature: stabilized, non-stabilized

foil foil: carbonyl index 0.40 1.62 ductility (% of initial value) 100 ALIGN! 49.2 tensile strength (% v.h.) 96 65.8 E (kV.cm ^-1 ) max 0.8 4.0 t, (S) 5 600

These results clearly confirm a very good stabilizing effect and a substantial increase in weathering resistance as well as the antistatic effect of the surfactant combination used.

Example 2

100 g of powdered branched polyethylene resp. Polypropylene powder was stabilized by the addition of 0.2 g distearyl-pentaerythritol diphosphite and 0.4 g 2-hydroxy-4n-octoxybenzophenone while adding 0.1 mixture of mono-di and triethanolamides of oleic acid and homogenized for 2 min. in a mixer at 300 rpm. Films were prepared from the obtained polymer blends by compression molding about 0.1 mm thick and subjected to both natural and artificial weathering tests in the Xenotest 150. For comparison, films containing only stabilizing ingredients and also without any ingredients were prepared from the same starting polymers. The following endpoints were obtained during exposure:

foil polyethylene exposure time to Δ A / d = 3.0 v h without additives 930 + stabilizers 3030 + stabilizers + surfactant 3125 foil polypropylene without additives 350

-I- stabilizers 1710 + stabilizers -l- surfactant 1920

Natural weather aging foil polyethylene amount of globes. heat. energ. to reach

Δ A / d = 3.0. Θ ² ° ^{/ o} P ^uv;

tažn.

without additives + stabilizers + stabilizers + surfactants, fabric

235 kJ.cm ² 730 kJ.cm ^-2

760 kJ.cm ²

220 kJ.cm ²

720 kJ.cm ^-2

770 kJ.cm ^-2

These results show a high stabilizing effect for both polymers, which is further enhanced by the presence of surfactants.

Example 3

A 1: 1 mixture of branched polyethylene and ethylene vinyl acetate copolymer having a content of 12% VAc was stabilized by the addition of 0.2 wt. % distearyl-pentaerythritol diphosphite or diisooctyl-pentaerythritol diphosphite and 0.4% 2-hydroxy-4n-octoxybenzophenone. The molded films of about 0.1 mm thickness were subjected to a natural OBJECTIVE aging test during which the following endpoint values were obtained:

The time to reach the carbonyl index Δ A / d = 3.0 for branched polyethylene alone was 320 kJ.cm ² and to a ductility drop to 20% of the original value then 350 kJ.cm ² .

In contrast, the tensile properties of the stabilized blend of both polymers decreased after exposure for 1.5 years at 600 kJ.cm ² as follows:

- tensile strength to 72% of initial value - elongation to 25.2% of initial value.

Claims (1)

Process for the treatment of polyolefins such as branched polyethylene, linear polyethylene or polypropylene, copolymers thereof or mixtures thereof, containing a copolymer of ethylene vinyl acetate with 0.1-10% vinyl acetate component, to improve weathering resistance with simultaneous antistatic treatment, characterized by admixing them a stabilizing system consisting of a benzophenone uv absorber in an amount of 0.11 wt. % as light stabilizer and pentaerythritol phosphite or a derivative thereof in an amount of 0.01-0.3 wt. % or a combination of dialkylthiodipropionate with a spherically shielded phenol in an amount of 0.01-0.3 wt. % as antioxidants and fatty acid alkylolamide, alkyl-bis-alkoxyamine, ethylene oxide fatty acid amide, alkyl polyglycol ether, or combinations thereof in an amount of 0.01-0.5 wt. % on the polymer component as surfactant.