BG61833B1 - Method for the transformation of initial material containing at least two different thermoplastic materials into a new homogenous thermoplastic material - Google Patents

Abstract

The method is used in recycling or secondary use of wasteplastic materials produced from food or domestic productpackaging. It prevents or at least reduces the storage of suchmaterial in nature and delays the exhaustion of the source ofirreplaceable raw materials. The method consists in mixing andagitation of at least two different thermoplastic polymers orcopolymers being in a separated state at initial determination ofthe energy consumption. Treatment stops after the maximum increaseof the energy consumption occurs and when in principle a constantquantity of the energy consumption has been reached after itsmaximum growth.7 claims, 5 figures

Description

Technical field

The invention is useful in the recycling or reuse of plastic waste materials derived from food packaging or household items to prevent or at least reduce their accumulation in nature and to delay the depletion of non-recoverable raw materials, in particular oil as a raw material in the production of plastics.

BACKGROUND OF THE INVENTION

Currently, recyclable thermoplastic polymers require the separate recovery and reuse of plastics of different chemical nature, since they are usually not susceptible to mixing. By reusing mixtures of solid particles of different thermoplastic polymers with the same machines and under the same operating conditions as those used in the case of a single thermoplastic polymer, products are obtained which are made of a heterogeneous material whose mechanical, physical and chemical characteristics such as tensile strength, flexural strength, compressive strength, chemical attack resistance of various liquid and gaseous substances, etc., are not well defined.

In practice, the need for the separate, i.e. separate recovery and reuse of the various thermoplastic materials poses an economic limitation which significantly reduces the recycling potential of plastic waste materials, in particular those contained in household waste (household waste).

A method of recovering heterogeneous plastic waste material is known, which comprises the following steps: mixing under cold conditions the powdered material, heating this material in a first temperature range to obtain a material with an initial plasticization state, after which this mass is subjected of heating at a second temperature range to obtain a homogeneous melt (1). During the two heating steps which take place in the absence of air, the mixture is continuously stirred. The second stage of heating is carried out in the absence of rapid temperature and pressure transitions.

A disadvantage of the known method is the insufficient homogeneity of the product obtained, which has unsatisfactory physical and mechanical parameters.

It is an object of the invention to provide a method for recycling waste polymer thermoplastic materials to obtain a homogeneous thermoplastic material which can be used in the same technique and technology as those used in the case of original plastic polymers in the need to eliminate the need for prior art. separation or selection of these wastes depending on the chemical nature of the polymers from which they are made.

SUMMARY OF THE INVENTION

The object of the invention is a method of processing plastic materials that enables the transformation of a raw starting material containing at least two different thermoplastic polymers or copolymers into a homogeneous thermoplastic material.

Furthermore, it is an object of the invention to provide a new thermoplastic material that can be used in the same way and in the same field of industrial application as known thermoplastic materials from at least two thermoplastic materials of different chemical nature.

The method of treating non-uniform plastic materials involves providing at least two different thermoplastic polymers or copolymers in a separate state, mixing and stirring the polymers with a stirrer and stirring agents in the initial determination of energy consumption. According to the invention, the treatment stops after the maximum increase in energy consumption occurs.

In addition, blending and stirring treatment according to the invention ceases when, in essence, a constant amount of energy consumption is reached after its maximum increase.

According to the invention, the mixing and stirring treatment is carried out in a chamber with mechanical agitators, which may include a multi-blade impeller.

In addition, according to the invention, at least two different thermoplastic polymers or copolymers in a separate state and at least one monolithic material that is not susceptible to mixing with thermoplastic polymers and copolymers are treated with a starting material, at least one filtration operation is performed to produce of non-uniform thermoplastic material so that particles other than the article are separated and dispersed therefrom.

According to the invention, the article is subjected to granulation.

The plastic material obtained according to the invention is characterized in that it is produced by injection of a non-uniform thermoplastic material.

The process according to the invention can be carried out as continuous or interrupted, i.e. by treating the starting initial mixture of thermoplastic polymers or copolymers in successive portions.

The invention is also applicable to the processing of a starting material containing at least two different thermoplastic polymers or copolymers in a split state, and at least one solid material which is not miscible with thermoplastic polymers and copolymers. Thereafter, at least one filtration step of the resulting product is carried out to separate particles dispersed therein from different thermoplastic material.

The chemical or physicochemical process or processes carried out in carrying out the method of transforming the initial mixture of different thermoplastic polymers into a homogeneous material are not yet fully understood and the invention is in no way limited by the nature of these processes, by the order in which they flow and their duration.

It has been found that, in the mixing and mixing operations of a mixture of thermoplastic polymers or copolymers, the solids undergo simultaneous rapid individual heating due to their mutual friction and / or friction with the elements of the agitator and the walls of the processing chamber, so they are all heated at virtually the same time to a temperature that is within their respective softening ranges. It also appears that there is a decrease in the average particle size at a certain degree of treatment in which at least one part of the particles is still solid or partially liquefied or pasty.

Regardless of the reasons, a relatively sudden transition from one state is observed in which the various individual thermoplastic polymer or copolymer particles from the original mixture are separated from each other and can be observed individually, and at a later stage in which it is not possible to the individual separation surfaces are more different, ie the boundaries between these particles, and in which the whole mass adopts a homogeneous appearance, except for the possible occurring particles of a material which cannot be mixed with thermoplastic polymers.

These phenomena are unexpected, given that polymer particles with a relatively low melting point, such as polyolefins, and polymer particles with a relatively high melting point, such as polyamides, may be included.

The temperature reached in the mixture of thermoplastic polymers or copolymers subjected to treatment by the process is typically from 150 to 300 ° C.

The homogeneous mass resulting from stirring and combing is usually obtained in the form of a paste having rheological characteristics corresponding to a so-called "pseudoplastic condition".

It is preferable that this homogeneous paste is immediately subjected to a granulation treatment to form granules of the usual type, suitable for use in molded or injected parts of production machines according to known industrial methods and technologies.

In addition, a known method of filtering the paste during the granulation operation may be used, for example, by means of a wire sieve with openings, in such a way as to separate the particles of solid materials, possibly contained in the paste. Such particulate matter may be of thermosetting polymers, metals, inorganic materials, such as fragments of stone, glass, etc., in general of any material which is not miscible with thermoplastic polymers.

The advantages of the process according to the invention are that the recycling of thermoplastic polymers or copolymers is ensured without their prior separation or selection depending on their chemical nature. The resulting product is a homogeneous thermoplastic material.

In addition, the product obtained according to the method of the invention is used to obtain articles made of plastic material by being moistened in the form of articles by injection molding.

The method is carried out in a closed chamber provided with mechanical agitators, preferably they can be coupled to a means of measuring the energy absorbed by the material being treated. The agitator means include at least one agitator element, which may for example be a rotor with multiple blades.

The process realization equipment is also characterized in that it also contains means for introducing the starting material to be processed into the chamber and means for unloading that chamber from the product obtained during the processing of the starting material.

Preferably, the agitators include at least one propeller or rotor with blades and rotating at high speed, for example between 1000 and 2800 rpm.

However, suitable stirring and / or mixing and / or mixing mechanical or non-mechanical means of any other kind may be used.

According to one particularly preferred embodiment of the apparatus, the chamber is cylindrical and has a horizontal axis, and the stirring and mixing means comprise a rotor provided with a plurality of blades. The rotor is coaxially mounted on the axis of the chamber and extends through it, the rotational motion being provided by a connected actuator located outside the chamber.

Any granular machine of the known type, for example, using pressurized extrusion, may be used for the granulation treatment.

Description of the attached figures

The invention is better explained by a detailed description of non-limiting embodiments of the method according to the invention and of one exemplary embodiment, also non-limiting, of an apparatus for realizing this method with reference to the accompanying figures, of which:

Figure 1 is a schematic front view of the facility;

FIG. 2 is a schematic front view of a portion of the apparatus shown in FIG. 1;

Figure 3 is a schematic view of the same part of the equipment shown in Figure 2, but with some elements and sections shown in section;

4 is a schematic cross-sectional view of the equipment;

Figure 5 is a partial schematic view of a rotor forming part of an apparatus.

An exemplary embodiment of the invention

The apparatus of FIGS. 15 comprises a cylindrical chamber 2 with a horizontal axis provided with one feed hopper 4 arranged in one top position and one discharge tank 5. One rotor 6 coaxially mounted inside the chamber 2 is driven by an electric motor 7. The walls of the chamber 2 are made up of one group 10 formed by joining two semi-cylindrical shells 11 and 12, assembled together with hinged hinges located along one longitudinal end 13, and a securing closing device 14. is available married along the end 15 opposite end 14.

The upper shell 12 is connected to a pneumatic device 16 of a known type, which makes it possible to open it by rotating around the hinges 13. The rotational motion of the motor 7 is transmitted to the rotor 6 with a pneumatically controlled clutch 18. The rotary motion of the rotor 6 can be interrupted as desired by a brake device 21, also pneumatically controlled.

The rotor 6 is supported at each of its two ends by bearings 22 mounted on supports 23. A threaded labyrinth connection 24 makes it possible to pass each of the ends of the rotor shaft 6 tightly through the walls of the chamber 2.

A guard 26 (Figure 1) encloses the portion of the apparatus enclosing the chamber 2 and the rotor bearings 22.

As can best be seen from Figure 5, the rotor 6 comprises a cylindrical shaft 30 provided with a plurality of radial blades 31, 32 whose shapes are of two different types. In particular, the orientation of the blades 32, which are attached to each end of the shaft 30, is such that it acts to impart to one load (fill) of the material processed in the chamber 2 a movement which tends to push this material away from the chamber walls adjacent to the ends of the shaft 30 to return it back to the interior of the chamber through an area subjected to the agitating and mixing action of the blades 31.

Preferably, the diameter of the chamber 2 and the length of the blades 31 and 32 are such that when the rotor 6 is at or near room temperature, the clearance (light opening) between the tips of the blades 31 and 32 and the inner wall 40 the chamber 2 should be in the range of about 0.5 to 1 mm.

Preferably, the rotor 6 and its drive motor 7 are sized relative to the internal volume of the chamber 2 so that the maximum mechanical energy flowing into the material to be processed in the chamber 2 of the rotor 6 is in the order of 1 to 2 sq. for each liter of this material. For example, for a total (total) internal volume of the chamber 2 of 85 1 (the case of an experimental prototype), it is found that the maximum power supplied by the motor is preferably in the order of 128 square meters.

Example 1. The starting material used is a mixture of thermoplastic polymers in the form of irregularly shaped pieces, but all of which are smaller than 5 mm in size, resulting from the recovery (recovery) of waste plastic materials in household waste (garbage) and which after separation they are simply washed with water from the other ingredients of the mixture and then dried.

The average composition of this mixture is as follows in% by weight:

ABS resin - 50 Polyvinyl chloride - 20 Polypropylene - 15 Polyethylene - 5 Polyamide - 5 Polymethyl methacrylate (PMMA) - 5 To process this mixture take use-

In an apparatus of the type described above, in which the agitator and agitator chamber has an internal volume of 85 l, the motor used to provide rotary motion of the rotor is a three-phase electric motor with a pole switch, with a maximum power of 140 sq. m. with a current of 380 V / 50 Hz, and with a cosine value fi (φ) of 0.85. After a period of rotation of the rotor in the order of 3 min, a steep increase is observed, followed immediately by the stabilization of the power consumption by the mass under stirring and mixing, which shows a peak in the intensity of the electric current supplied to the motor reaching maximum value in the order of 270 to 280 A at the top of the elevated part. The duration of the increase of the electric current between the initial value and the peak of the increased part, as well as the subsequent decrease of the intensity (up to a stabilized value which is above the initial value), covers about 5 s simultaneously. The rotation time of the rotor spans a period of about 10 to 20 s after stabilizing the intensity of the electrical current that feeds the electric motor driving the rotor, after which the rotor stops and the homogeneous gel-like paste mass resulting from the processing of the polymer mixture. , is immediately retrieved for recovery.

This mass is subjected either immediately after removal from the treatment chamber or after solidification by cooling a granulation treatment by extrusion into a machine of the known type, filtered using a wire mesh sieve. In this way, granules of thermoplastic material of about 3 mm in size are obtained, with an extremely homogeneous appearance (manifestation), even when magnifying glass experiments are performed. These granules are ideally suited for use in an industrial injection molding machine in the same way as granules made of pure thermoplastic ABS resin, making it possible to obtain molded (molded) parts of excellent quality that present / exhibit perfect isotropy of mechanical and physical properties (properties).

Example 2. The procedure is the same as in Example 1, except that a mixture of thermoplastic materials is used as the raw material with the following average composition in weight%:

High Density / Low Density Polyethylene / Blend Mix Equal Parts -45

Polystyrene -20

Polyvinyl chloride -20

Mixture of two equal parts of polyester and polyamide -12

Polymethyl methacrylate (PMMA) -3

After a rotation of the rotor of about 90 s, an increase in the intensity of the electrical current supplying the motor to a maximum value of the order of 230 A. is observed. The rotation duration is as in Example 1 in the order of about 10 to 20 s after this peak, before extraction of a homogeneous gel-like paste with a pseudoplastic consistency resulting from the treatment.

Extrusion granulation is then carried out with the filtration of the paste as indicated in Example 1.

In this way, granules of thermoplastic material are obtained that are suitable for use in industrial injection molding machines in a manner similar to that of using high density pure polyethylene resin granules.

It should be noted that the method described is well suited to obtain thermoplastic material having predetermined properties, on average between those of the various starting polymers and copolymers, and that it is possible to maintain the constant properties of the finished product, even in case of fluctuations in the average value of the composition of the mixtures used as starting material.

In fact, and as is apparent to one of ordinary skill in the art, it is only necessary to analyze the starting material and the finished product in order to determine the amount of thermoplastic polymers or copolymers of one or more types to be added to the starting mixtures, in order to make the adjustments necessary to obtain the final product with the desired properties and to maintain those qualities in the event of changes in the composition of the raw material.

Obviously, any substance or mixture of substances capable of enhancing the properties of the finished thermoplastic material, for example plasticizers, stabilizing agents, colorants, fillers, etc., may be added to mixtures of thermoplastic polymers or copolymers in a known manner. It is clear that due to the very nature of the operations in the process, which involve one displacement and one stirring, which are extremely efficient, an excellent homogeneous distribution of these substances (substances) in the final product is obtained.

Claims (7)

Claims 1. A method of treating non-uniform plastic materials, comprising providing at least two different thermoplastic polymers or copolymers in a separate state, mixing and stirring the polymers by agitator and stirring agents, in the initial determination of energy consumption, characterized in that the treatment stops after the occurrence of the maximum increase in energy consumption. A method according to claim 1, characterized in that the blending and stirring treatment is stopped when, in essence, a constant amount of energy consumption is reached after its maximum increase. Method according to claim 1, characterized in that the mixing and stirring treatment is carried out in a chamber equipped with mechanical stirring means. A method according to claim 3, characterized in that the agitators include a impeller equipped with a plurality of blades. A method according to claim 1, characterized in that for processing a starting material containing at least two different thermoplastic polymers or copolymers in a separate state and at least one monolithic material which is not susceptible to mixing with said thermoplastic polymers or copolymers, at which method performs at least one filtering operation to obtain an article from a non-uniform thermoplastic material so that particles of material other than said article are separated from it and dispersed therefrom. A method according to claim 1 or 5, 10 characterized in that the article is subjected to granulation. Plastic material according to claim 1, characterized in that it is produced by injection of a non-uniform thermoplastic material.