CS243996B1 - A method for the intensive degradation of polypropylene and / or propylene copolymers - Google Patents

Abstract

A method for the intensive degradation of polypropylene and/or propylene copolymers with other monomers, which may optionally be combined with additional reactions, e.g. oxidation. The essence of this degradation method, which is based on the action of heat and possibly also other degradation factors, such as the addition of a degradation initiator (degradant) or the action of radiation, consists in the fact that the degraded polymer is heated in the molten state to the degradation temperature in an extremely thin layer, preferably 0.3 to 3 mm thick, the surface of which is preferably constantly renewed by stirring during the degradation process. The method is particularly suitable for those applications where a controlled reduction of the average molecular weight is required - e.g. in the preparation of polymer materials suitable for electrostatic coating with subsequent heat fixation.

Description

The invention relates to a process for the intensive degradation of polypropylene and / or copolymers of propylene with other monomers, which may optionally be associated with additional reactions, e.g. oxidation processes. The degradation process according to the invention is particularly suitable for those applications where controlled molecular weight reduction is required.

A number of different methods of degradation of polypropylene or copolymers of propylene with other monomers are currently known, and these individual degradation processes have been and are being elaborated based on the requirements of the resulting degradation product. they use mainly heat, radiation (ultraviolet and ionization), mechanical stress, addition of a degradation initiator (degradant), etc., or possibly a combination of some of these factors ·

For example, a method for degrading polypropylene by heating to a temperature of at least 160 ° C in a nitrogen atmosphere with the addition of 5 wt.% Boron trifluoride is known. This process yields a blend of lower average molecular weight polymer products containing no fluorine or boron. melt flow rate than original polymer · Melting point practically unchanged by this degradation process ·

In the presence of metal chelates IV · b of a subgroup of the periodic system and aluminum, the amorphous polypropylene is heated to 300 ° C in a nitrogen atmosphere by quantitatively olefins with 90 to 15 carbon atoms in the chain, normally liquid.

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Another method of degrading polypropylene is based on the action of ionizing and ultraviolet radiation. This degradation produces simultaneously an insoluble gel and low molecular weight polypropylene, while the degradation process can be further influenced to a large extent by the choice of the atmosphere surrounding the degraded polymer. When irradiation is carried out in an oxygen-containing atmosphere, normal oxidative destruction occurs; degradation takes place in an inert atmosphere, resulting in a simple increase in the melt flow index.

As indicated in the previous procedure, in addition to simple degradation, polypropylene also has degradation methods associated with additional reactions, in particular oxidation reactions. For example, a process for oxidizing polypropylene with molecular oxygen at pressures greater than 0.1 MPa in a solution of organic solvents at relatively low temperatures is described. However, since the use of organic solvents has a number of technical disadvantages (increased operating costs, deterioration of the working environment, fire hazard, etc.), oxidation processes at higher temperatures or higher temperatures are used to a greater extent. longer time - eg at 310GfcSř 480 ° C and reaction time 30 minutes, or at 240 ° C and reaction time 5 hours.

To accelerate oxidative degradation, active ingredients (degradants) can be added - eg based on peroxides.

A significant disadvantage of all the above degradation methods is their very limited applicability. This limitation, due to the low efficiency of the known degradation processes, is characterized on the one hand by the maximum achievable degree of degradation, which is unsatisfactory for some applications (eg preparation of polymers for spinning) and on the other hand extreme reaction conditions - long reaction times, high temperatures. pressures o It is obvious that these factors are then directly reflected further - eg in disproportionate energy demands, complex measures to ensure safety at work, etc.

- 3 243 996 degradation in terms of controlling the degree of degradation achieved is very difficult, sometimes even impossible ·

Some improvement in this respect is achieved by the process of degradation of polypropylene in a screw extruder used on an industrial scale in the preparation of a melt for spinning. This is essentially a thermo-mechanical degradation with limited oxidative interaction of air oxygen. This degradation process, controlled to some extent by the extruder mode, can reduce the average molecular weight of the polypropylene so that the melt flow index increases from the initial value of about 3 g / 10 min. However, even at this relatively large increase in the melt index, the melting point remains virtually unchanged. From this fact it is clear that even this, currently the most effective method of degradation of polypropylene ₍ in the prime chip retains the main disadvantage of all previously described methods.

The possible addition of peroxide-based degradation initiators does not contribute to the improvement of this situation. This intervention only accelerates the degradation process, but the resulting product does not change much - again, it is a polymer having a higher melt index than the starting material, but virtually the same melting point.

It follows from the above analysis that more substantial changes in the melting point of the polypropylene, respectively. copolymers of propylene are entirely categorically conditioned by deeper changes in its average molecular weight and thus necessarily by the formulation of a new degradation method.

The process of intensely degrading the polypropylene and / or propylene copolymers of the present invention contributes greatly to solving this problem. The essence of this degradation method, which is based on the action of heat and possibly other degradation factors, such as the addition of a degradation initiator or the action of radiation, is that the degraded

243996 in the melt state, the lymer is heated to a degradation temperature in an extremely thin layer, preferably with a thickness of 0.3ft-3mm, the surface of which is preferably constantly renewed by agitation during the degradation process.

The efficiency of the intensive degradation process of the present invention can be further enhanced by providing the atmosphere surrounding the surface of the degraded polymer layer with an atmosphere that is active in terms of the possibility of initiating and conducting complementary reactions, particularly an oxidizing reaction atmosphere.

The main advantage of the degradation process according to the invention is, in comparison with the hitherto known methods, in particular a substantial increase in the degradation efficiency. In practice, the degradation process of the present invention results in products having a significantly lower melting point than the starting polymer - e.g., polypropylene having an original melting point of 166 ° C can be degraded to a product having a melting point of 9 ° C. ° C; ethylene-propylene copolymer having an original melting point of 165 ° C can be degraded to a product with a melting point of 85 ° C. In this case, the degradation process can be controlled even at this high efficiency - for example by the mixing intensity of the degraded polymer layer. This does not allow any of the previously known degradation methods. Indeed, in the present degradation processes, the process should be at least minimally controllable, as mentioned above, only products whose melting point differs only slightly from the melting point of the starting polymer can be prepared (although this may result in a relatively large increase in the melt flow index) .

The reason for the considerably higher efficiency of the degradation process according to the invention is that, due to the low layer thickness of the degraded polymer material, both the negative effects of the low thermal conductivity of the polymer and the slow diffusion processes, which are the main causes of low degradation efficiency in matter. Obviously, an increase in degradation efficiency, which can be further exacerbated by mixing the degraded polymer layer, also has a direct economic impact, particularly in terms of reducing the energy intensity of the degradation process. Since the heating of the material in the thin layer is very fast, there is no need to consider a temperature gradient - in the exothermic reaction, the thin layer process is practically isothermal. As a result, the degradation is uniform throughout the layer and the molecular weight distribution of the products obtained is therefore considerably narrower than for products resulting from the known degradation processes. In addition, the entire process can be further regulated by adjusting the degradation conditions to produce products of the desired physical properties due to its uniform course throughout the layer. The possibility of sensitively influencing the process by external conditions and the homogeneity of the resulting products is of great importance from a practical point of view especially in those applications where it is necessary to obtain products with a very narrow molecular weight distribution - for example in preparing polymeric materials suitable for spinning.

The following examples serve to illustrate the invention in greater detail:

Example 1

Polypropylene having a melting point of 166 ° C and a melt index of 5 g / 10 min. (type Tatren TE 451) was heated in a melt state in a stationary layer of 0.5 mm thickness. to the temperature

Mp 240 ° C. Thermodegradation was carried out at atmospheric pressure and in the air. After 25 hours of heating, a product with a melting point of about 90 ° C and a very high (non-measurable assay) melt index was obtained.

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The degradation in the constantly stirred layer of the melt was beyond the melt

of the same conditions prepared product of the same characteristics in 20 £ three 30 minutes ·

Note: the thermodegradation in the stationary layer was accomplished by melting and then heating a layer of polypropylene powder on a backing and raised edges, housed in an enclosed air-filled space that was heated to the above temperature ·

The blended layer thermodegradation was carried out as follows: Polypropylene powder was applied to the surface of the cylinder with horizontal axis of rotation and melted. slightly off-axis to the cylinder axis ·

Example 2

The ethylene-propylene copolymer having a melting point of 165 ° C and a melt flow index of 0.8 g / 10 min · (typ. Mosten 52 217) was heated ^{in the} melt state in a stationary layer having a thickness of 0.54? 1 mm at 180 ° C · Thermodegradation was carried out at atmospheric pressure and in the air · After 17 hours of heating a product with a melting point of about 85 ° C and a very high (not measurable) melt index was obtained ·

Addition of 2% by weight of dicumyl peroxide degradation initiator produced the same result under the same conditions in 30 min ·

Similarly, irradiation of the melt layer during degradation by high-pressure, mercury-vapor lamps occurred under the same conditions and with the same degradation result in 2 hours ·

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The summary results of the above examples indicate that the method of intense degradation according to the invention allows to obtain the degradation of polypropylene and / or copolymers of propylene products € point and lower than 100 ° C · by making the degradation of the same material as an existing ways of degradation in the mass remains _t relative to substantially lower efficacy degradation, i.e., the melting of the products at virtually the same value as ieptoin. melting of the starting polymer, i.e. at 165 ° C. For example, in the case of degradation in a screw extruder, the melt flow index will increase from about 3 g / 10 min. about 20 g / 10 min ·, but the melting point of the product remains practically the same as the melting point of the starting polymer (165 ° C) ·

Claims (3)

P 5 E D ISS OF THE INVENTION 243 996 A method of intensifying degradation of polypropylene and / or propylene copolymers by heat and optionally other degradation factors such as addition of a degradation initiator or radiation, characterized in that the degraded polymer is heated to the degradation temperature in an extremely thin layer in the melt state, preferably with a thickness of 0.3 mm to 3 mm, the surface of which is preferably continuously renewed by stirring during the degradation process. Method according to claim 1, characterized in that the external atmosphere surrounding the surface of the degraded polymer layer is an active atmosphere with respect to the possibility of formation and course of supplementary reactions, in particular an atmosphere allowing oxidative reactions 3. A process according to claim 1, characterized in that the desired reactions are further accelerated by the action of radiation of suitable energy.