SK50822005A3 - Method for processing thermoplastic polymeric material comprising unstable thermal component - Google Patents

Abstract

It is described a method for processing a thermoplastic polymeric material containing unstable thermal component characterized in that the into a molten polymer or mixture of polymers with a lower melting temperature than the unstable polymer or than a decomposition temperature of low molecular component, is added the second polymer as a solid phase in the powder form. The processing is realized at a temperature higher than the melting temperature of the first component but lower than the melting temperature of the second component.

Description

Technical field

The invention relates to the processing of plastics compositions containing thermally unstable components

BACKGROUND OF THE INVENTION

In the processing of thermoplastics, it is necessary to prepare a composition comprising at least one polymer into which low-molecular components (e.g., processing aids, antioxidants) are admixed, but often another polymer component is part of the composition. In this way, a polymer blend is formed comprising a plurality of polymers and / or reactive components (crosslinking system, chemical modifiers, etc.) that will react during the blending process (reactive processing procedures) or in a separate step after blending the entire blend. In the latter case, the initiation of the desired chemical reaction may occur either by further increasing the temperature or otherwise, for example, by irradiation with UV light, under the influence of atmospheric humidity and the like.

Complications arise if any of the components of the entire mixture begin to react at the melting point of the polymer, which forms a continuous matrix for the mixture. This means that the entire mixture must be heated to this temperature in order to be moldable. This situation can occur, for example, if we want to add a modification reactive system, which, however, must not react significantly during the material shaping. Most often it is about crosslinking when adding additives eg. peroxide in polyethylene crosslinking, or sulfur with vulcanization accelerators in rubber vulcanization. Another case is if we want to process a polymer that is thermally unstable already in the region of its melting point and undergoes significant thermal degradation. Examples of such behavior may be polyphenylene oxide or polyhydroxybutyrate.

So far, these cases have been dealt with in essentially two ways. The principle of the first procedure is the addition of reactants which inhibit the unwanted processes by reacting with the initiator of the undesired process. The simplest example is the addition of an antioxidant to polymers that undergo thermal and / or thermal oxidation. thermooxidative degradation [Daszkiewicz; Zdzislaw,

-2Sudol; Marek Borecki; Joseph, Kyziol; Janusz B., Wyzsza Szkola Pedagogiczna Opole

PL patent 159427B, December 31, 1992]. The antioxidant acts as a free radical scavenger, which initiates the formation of a macroradical on the polymer chain, thereby initiating the chain reaction. The reaction of free radicals with an antioxiant produces little reactive products that are unable to initiate the formation of a macroradical by detaching the proton from the hydrocarbon chain.

Other thermostabilizing agents act in a similar manner, i. hydroperoxide decomposers [Okazaki; Masao, Katsuki; Hirosshi, Terazawa; Takayuki, Sumitomo Chemical Co, GB patent 1239651, July 21, 1971]. These react with a source of primary free radicals and initiate processes whose products are not reactive free radicals suitable for initiating the formation of macro-radicals.

Also described are other ways by which other undesired processes can be slowed down or eliminated completely. For example, to achieve crosslinking of polyolefins or vulcanization of rubbers, additives are added to the material to initiate the process upon heating to a certain temperature. At the same time, for economic reasons, the aim is to achieve the highest processing temperature (saving energy and reducing the mixing time of the extrusion as a result of reducing the viscosity of the polymeric material) and on the other hand to use a crosslinking / vulcanizing system capable of reacting at low temperature yet fast enough Reducing the response time (to increase labor productivity and reduce the energy required to heat the product during the thermally initiated crosslinking process). Since processing takes place at an elevated temperature, there is a real danger that the crosslinking will start at a small fluctuation e.g. temperature or retention in the processing plant prematurely before the product is formed into the final shape. In this case, the viscosity may be unbearable and even partially crosslinked to the extent that the material cannot be removed from the processing device without stopping production and disassembling part of the production line. For this reason, crosslinking or vulcanization inhibitors are added to the mixture, with the amount of vulcanizing agent being slightly overdosed [Guo; Xianquan, Huachang Industry Trade Co. Ltd, CN patent 1500830, June 2, 2004], [Shah Suresh Deepchand, Jar Michael Michael, Abu-Isa Ismat Ali, US Patent 2003052431, March 20, 2003]. The entire system is then set up so that the crosslinking inhibitor runs out during

-3 processing times, consuming only a minor part of the added networking system. After processing, the vulcanization / crosslinking then proceeds rapidly in the absence of inhibitor inhibition.

A different method is the use of various technological processes allowing processing at low temperature below the melting point of the polymer. These processes are included under the common name solid phase extrusion, but require special equipment and are not applicable to any product or material [Khait Klementina, Univ Northwestern, US Patent 6818173, November 16, 2004].

The third option, used especially for thin-walled products of regular shape (especially foil) is the so-called. film casting [Salyer; Ival O., North; Charles J., Monsanto Research Corporation, US Pat Appl 565165, April 4,1975]. The polymer composition is dissolved in a suitable solvent and then poured in a thin layer onto a support. After evaporation of the solvent, a film is formed, whereby the thermal stress of the components is considerably lower compared to the state if the film was prepared by blowing or extruding.

All these methods solve to some extent the problem of thermal instability of the components of the polymeric material. At the same time, however, they have several drawbacks, in particular the fact that they require special, relatively expensive equipment (solid extrusion), do not make it possible to prepare coarser products (casting), or require additional additives, often relatively expensive. The biggest disadvantage of these technologies, which is particularly evident for additive additions, is that they cannot be applied to a wider range of materials and can only be used for certain types of plastics or mixtures thereof.

The proposed process of the invention solves several disadvantages for blends of polymers containing a thermally unstable component.

SUMMARY OF THE INVENTION

The invention consists in a process in which a mixture of two polymers is processed, one of which (component A) has a melting point lower than the critical temperature at which the undesired reaction would proceed at such a rate that significant chemical changes in the system. The second polymer (component B) has a melting point

In an area where the undesired process proceeds fast enough so that during the processing time, there would be adverse changes in polymer properties (thermal degradation of the polymer component, thermally initiated premature decomposition of the low molecular weight initiator, etc.). Component A is melted at a temperature that is lower than the melting temperature of component B, and component B is mixed into a powder mixture similar to the particulate filler. Homogenization of the mixture and shaping takes place largely below the melting point of component B, so that an undesired process does not occur at this stage. The remelting of component B takes place only at the end of the entire homogenization and / or molding process, in which a very short time, typically a few seconds, a maximum of a few tens of seconds, is sufficient for sufficient homogenization. During this time, the unwanted process either does not occur at all or only to a negligible extent. In this way, the polymer mixture is finally obtained with the addition of various additives which is homogeneous but not disturbed by the thermally initiated undesired process. The lower melting point polymer content must be such that the mixture has rheological parameters sufficient for an acceptable degree of processing. Typically, this content is greater than 25 to 30 percent by volume.

DETAILED DESCRIPTION OF THE INVENTION

Example 1:

In a Brabender laboratory mixer, a mixture consisting of 40 percent by volume of low density polyethylene and 60 percent by volume of isotactic polypropylene in powder form is dispensed into a 30 ml chamber. Organic peroxide 2,5-dimethyl-2,5-di-tert-butylperoxy hexin is added in an amount of 3 percent by volume. The chamber temperature during homogenization is 145 ° C. The total homogenization time is 12 minutes. After the homogenization is complete, the mixture is removed and pressed in a press at 190 ° C for 12 minutes. After pressing, the continuous phase is polypropylene, which means that it has been perfectly remelted during the pressing process. The analysis revealed that, after removal of the mixture from the mixer chamber prior to compression, the crosslinked insoluble fraction did not form, whereas after compression, the crosslinked mixture was obtained with an insoluble fraction of at least 87 percent by volume.

-5Example 2:

A blend consisting of 40 percent by volume of low density polyethylene and 60 percent by volume of isotactic polypropylene powder is metered into the extruder. Organic peroxide 2,5-dimethyl-2,5-di-tert-butylperoxy hexin is added in an amount of 3 percent by volume. The temperature in the extruder during homogenization is set at 145 ° C. The retention of the mixture in the extruder is about 4-6 minutes. In the final extrusion phase at the extruder head, the temperature is set to 185 ° C. The residence time of the mixture in this part of the extruder is 3-10 seconds. After extrusion of the mixture from the extruder, the mixture is crushed to granulate and pressed in a press at 190 ° C for 12 minutes. After extrusion from the extruder, the continuous phase is polypropylene, which indicates that a perfect remelting occurred during the temperature increase in the extruder head. The analysis revealed that the extruded mixture was not extruded from the extruder prior to compression, while the crosslinked insoluble fraction had at least 87 percent by volume after compression.

Example 3:

The procedure of Example 2 except that the ratio of polymers is 20 percent by volume LDPE and 80 percent by volume iPP. After pressing, the insoluble crosslinked portion was 84 percent by volume.

Example 4:

The procedure of Example 2 except that the ratio of polymers is 95 percent by volume LDPE and 5 percent by volume iPP. After pressing, the insoluble crosslinked portion was 92 percent by volume. In this case, the continuous phase is polyethylene, but microscopic observation has shown that the polypropylene powder has also melted as the temperature rises.

Example 5:

The procedure of Example 1 except that the ratio of polymers is 40 percent by volume LDPE and 60 percent by volume iPP and the peroxide content is 0.1 percent by volume. After pressing, the insoluble crosslinked portion was 4.5 percent by volume.

-6Example 6:

The process of Example 1 except that the ratio of polymers is 40 percent by volume LDPE and 60 percent by volume iPP and the peroxide content is 15 percent by volume. After pressing, the insoluble crosslinked portion was 93 percent by volume.

Example 7:

The process of Example 1 except that polycaprolactone (PCL) as the melt and polyhydroxybutyrate (PHB) in the form of particles having a diameter of 1.5-2 µm in a ratio of 40/60 percent by weight are used as polymers. PHB powder is mixed into the PCL melt at 120 ° C for a homogenization time of 8 minutes. After removing the homogenized material from the mixer chamber, the material is pressed at a softening temperature of PHB, 165 ° C, for 7 minutes. After pressing, a material is formed whose continuous phase is PHB. Based on a comparison of the mechanical properties of mixtures prepared in a standard way in the melt (stirring at 190 ° C for 5 minutes and pressing at 170 ° C for 1.5 minutes), and in the patented manner (elongation = 9%, 2 days aging) it can be stated that the above process practically eliminates the effects of thermal degradation of PHB during processing. For example, the ductility of a blend blended in a standard manner is below 2% (2 days of aging), while the blend blended in the patented manner exhibits a ductility of 9% (2 days of aging).

Example 8:

The procedure of Example 7, except that 25 percent by weight of the glycerol triacetate plasticizer (TAC) was blended into the PCL melt in addition to PHB, and after 8 minutes of homogenization, 1 percent by weight of organic tert-butyl perbenzoate peroxide was added. The system is then homogenized for a further 2 minutes. After compression, a crosslinked mixture was formed with an insoluble proportion of 54 percent by weight.

Example 9:

The procedure of Example 7, except that 0.25 percent by weight of the cross-linking coagent of 2,4,6-trialyloxy-1,3,5-triazine and 15 percent by weight of TAC, was blended into the PCL melt in addition to PHB. After 8 minutes of homogenization, 1 percent by weight of organic tert-butyl perbenzoate peroxide was added. The system is then homogenized for a further 2 minutes. The material is briefly melted by pressing above the melting point of PHB at 180 ° C for one minute. The insoluble portion of the mixture was 80 percent by weight.

Example 10:

The process of Example 1, except that a homogeneous mixture of polyphenylene oxide and polystyrene at a ratio of 80/20 percent by volume as Component 1 in the form of powder and polyethylene as component 2 is used as the polymers. by volume of the component 2 is mixed in an extruder at a temperature of 150 ° C, the residence time being about 6-8 minutes. In the last stage of extrusion, i. in the extruder head, the temperature is set at 220 ° C, with a holding time of about 5-10 seconds. After the mixture has been extruded in this manner, Component 1 is a continuous phase, with the mixture having the original pale yellow color, indicating that there is no thermal degradation of the polyphenylene oxide. If the mixture was left in the extruder during extrusion at 220 ° C for 6 minutes, the extruded material had a distinctly dark brown color as a sign of thermal degradation.

Industrial usability

The use is preferably possible in the treatment of a blend of polymers, one of which is thermally unstable at the processing temperature, or when the blend contains a reactive additive whose reaction is initiated at a temperature below the melting point of one of the blend polymers. Examples include a crosslinkable mixture of polyethylene and polypropylene containing organic peroxide, a mixture of polyhydroxybutyrate with another polymer with a melting point below 130 ° C, or a mixture of polyphenylene oxide with a polymer with a melting point below about 170 ° C.

Claims (2)

PATENT CLAIMS A method for treating a thermoplastic polymer material comprising a thermally unstable component, characterized in that a second thermally unstable component is added to the melt of the first component, which is a polymer or a mixture of multiple polymers heated to a temperature below the melting point of the second component. , having a higher melting point, which is a thermally unstable polymer or a mixture of several polymers in an amount of 5 to 85% by volume, then the mixture is homogenized for 2 to 60 minutes at a temperature between the melting points of the first and second components and subsequently for 2 to 600 seconds is heated to a temperature sufficient to melt the second component. 2. A process for treating a thermoplastic polymer material comprising a thermally unstable component, comprising adding to the polymer mixture consisting of two components each of which is a polymer or a blend of polymers, during homogenization, one or more thermally unstable low molecular weight additives which modify the properties of the resulting mixture. , in an amount of 0.05 to 30% by volume, the treatment being carried out at a temperature higher than the melting point of the first component, but lower than the melting point of the second component.