Process for recycling thermoplastic matrix composite materials and industrial installation for its implementation

Abstract

The invention relates to a method for recycling synthetic waterproofing membranes based on polymers composed of two or more layers laminated to each other and between which is inserted a weft of glass or polyester fiber in which the following steps are carried out on the membranes: Mechanical crushing and densimetric separation; Treatment by pulsed power; drying and densimetric separation. The invention also proposes an industrial installation. Figure for the abstract: Fig. 1

Description

Title of the invention: Process for recycling thermoplastic matrix composite materials and industrial installation for its implementation General technical field and prior art

[0001] The present invention relates to a new technology for recycling composite materials based on thermoplastic polymers composed of at least two layers including at least one reinforcement based on mineral or synthetic fibers.

[0002] A typical use of thermoplastic matrix composites consists of flexible membranes for waterproofing roofs, terraces, or even swimming pools or basins, truck tarpaulins, garden hoses, etc. They can comprise a single layer or several layers of reinforcements.

[0003] The reinforcements are generally in the form of woven or non-woven fabrics based on glass fiber, synthetic fibers such as polyester fiber, polyolefins, etc. or natural fibers such as linen fiber, cotton, etc. Thermoplastic polymers are synthetic polymers such as ethylene-propylene-diene (EPDM), poly(vinyl chloride) (PVC) and thermoplastic polyolefins (TPO)...

[0004] The interest in recycling these thermoplastic composite materials is to be part of a circular and sustainable economy aimed at reusing the raw material and reducing the use of virgin raw material.

[0005] Another interest is to reduce the carbon footprint of the manufacturing processes of thermoplastic composite materials by reincorporating recycled material instead of virgin material and thus greatly reducing (up to 400%) the carbon impact of said composite materials.

[0006] And taking into account the weight that the purchase of raw materials represents in the cost price, the use of recycled material instead of virgin material and without altering the mechanical properties of the product makes it possible to reduce the manufacturing cost.

[0007] There are conventional techniques for recycling thermoplastic matrix composite materials based on very fine mechanical grinding (of the order of a millimeter) which, after successive mechanical grinding steps, separate the granular particles of different weights and densities by air flow. After this grinding and separation phase, the ground plastic material is transmitted to an extruder which allows it to be remelted and transformed into granules. Depending on the applications, these recycled granules can replace all or part of the virgin polymers in new manufacturing. The reinforcing fibers can be thermally recycled.

[0008] However, the recycling techniques known to date are not entirely satisfactory. Fine mechanical grinding requires a high level of energy. It also often requires the use of cryogenics to achieve the desired particle sizes, making it expensive.

[0009] On the other hand, in the case of thermoplastic matrix composite materials, the grinding and separation steps do not allow 100% of the fibers to be extracted. In fact, it is estimated that, with a mechanical recycling process, up to 20% of the quantity of residual fibers remains:

[0010] - either encapsulated between the polymer layers

[0011] - either fixed to the surface of the polymers by electrostatic charge.

[0012] The presence of 20% of residual fibers in these so-called "semi-finished" products quickly clogs / blocks the filters of the granulating extruder and makes the mechanical recycling operation difficult to industrialize.

[0013] These fibers further contribute to the poor quality of the recycled polymer raw material.

[0014] Finally, thermal recycling is not feasible for all types of fibers. For example, polyester fibers have a melting point > 230°C, which means that up to this temperature, the fibers remain in the form of fibers and can generate complexity in the processes (clogging, complex filtration, deterioration of the mechanical properties of the membranes produced from these products, etc.).

[0015] There is therefore a significant need for a specific technology for recycling thermoplastic matrix composite materials which, for example, can come from production offcuts, construction site waste and building renovation.

[0016] Techniques for recovering materials and / or products using pulsed power are already known, in particular from patent WO2010 / 092136. General presentation of the invention

[0017] An aim of the invention is to propose an industrially viable process for recycling thermoplastic matrix composite materials.

[0018] Another aim of the invention is to propose a process allowing excellent polymer / reinforcement separation without degradation of the polymer, in order to have a high-performance recycled thermoplastic raw material for new applications.

[0019] Another aim of the invention is to propose a recycling process for recovering the fibers from the extracted reinforcements.

[0020] Thus the invention proposes a method for recycling composite materials based on thermoplastic polymers composed of at least two layers including at least one reinforcement based on mineral or synthetic fibers, in which the following steps are implemented: - Mechanical grinding to obtain a polymer ground material of intermediate granulation level, - Separation of polymers and fibers released during this mechanical grinding, - Treatment by pulsed electric power to obtain a finer polymer grind and extract the remaining fibers, - Drying and separation of the polymers from the fibers thus released, - Possibly extrusion and granulation of polymers.

[0021] Thus, the proposed method combines mechanical grinding and complementary treatment by pulsed electrical power.

[0022] This combination makes it possible to relax the requirements on the fineness of the particle size to be obtained at the end of the mechanical grinding step. Typically, as a purely illustrative example, the particle size at the end of the grinding step can be 6 mm instead of 1 mm. With a higher particle size, cryogenics is then not necessary. The cost in grinding power is lower.

[0023] The treatment by pulsed electric power completes the mechanical grinding and allows the residual fibers to be extracted sufficiently to ensure the expected separation quality.

[0024] It also avoids the phenomena of sticking of the reinforcing fibers to the surface of the polymer material, the fibers and the material being on the contrary repelled relative to each other by electrostatic effect during treatment by pulsed electric power.

[0025] Such a process thus makes it possible to extract almost all of the reinforcements (typically, greater than 99% of the initial mass of the fibers) facilitating the potential subsequent granulation steps within an extruder.

[0026] The polymer entering the extruder and the recycled raw material in the form of granules leaving it are thus of excellent quality.

[0027] The method is for example supplemented by the following different characteristics taken alone or in combination: - mechanical grinding is carried out with a power between 0.2 kWh / kg and 55 kWh / kg; - the pulsed power treatment is implemented with a power inversely proportional to that of the mechanical grinding between 0.05 kWh / kg and 3.00 kWh / kg; - pulsed power treatment uses a number of shots per kg of material of between 500 shots and 6000 shots at a discharge frequency of between 1 and 40 Hz, stored energy of between 100 joules and 10,000 joules and a circuit frequency of between 100 and 900 kHz; - the particle size of the material from the mechanical grinding stage is between 2 mm and 6 mm.

[0028] The invention further relates to an industrial installation suitable for implementing a recycling method as proposed, comprising a grinding unit, a reactor for treatment by pulsed power and a drying station by centrifugation or by fluidized bed.

[0029] The installation may further comprise an extrusion and granulation line.

[0030] The separation and drying station may include a density separator.

[0031] Such an industrial installation is for example used for the recycling of composite materials based on thermoplastic polymers composed of at least two layers including at least one reinforcement based on mineral or synthetic fibers, in particular for the recycling of PVC / PET membranes, TPO / PET membranes, reinforced PVC watering pipes, reinforced plasticized PVC truck tarpaulins, etc. Brief description of the drawings

[0032] Other characteristics and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and must be read in conjunction with the appended figures in which: - [Fig.l] schematically illustrates different stages of a method in accordance with a possible mode of implementation for the invention; - [Fig.2] is a schematic representation of an industrial installation for implementing the process of [Fig.l].

[0033] Description of one or more modes of implementation and embodiment

[0034] Generally speaking, the proposed method allows the recycling of composite materials based on thermoplastic polymers composed of at least two layers including at least one reinforcement based on mineral or synthetic fibers.

[0035] By way of illustration, the following will be taken in the case of a synthetic membrane, other applications being of course possible.

[0036] A synthetic membrane to be recycled is presented, for example, in the form of a roll of two layers of PVC laminated to each other and between which is inserted a woven matrix based on PET.

[0037] The proposed recycling process implements several successive steps.

[0038] In a preparatory treatment, the material is shredded so as to be presented in the form of waste strips (step A in [Fig.l]).

[0039] In a first step, the solid waste obtained is subjected to mechanical grinding (step B) to reduce the size of the polymer and the fibers.

[0040] After sieving, this mechanical grinding is repeated until the desired level of particle size is obtained. Typically, for shredded membranes of thickness between 1.2 and 2.0 mm, the average particle size expected at the end of the mechanical grinding step B is between 6 mm and 4 mm, preferably between 3 mm and 2 mm).

[0041] The resulting ground material is then passed through a separator (by air flow or any other densimetric separation technique) (step C).

[0042] Such a separator makes it possible to separate several bulk materials according to their density, shape and size. The lightest material (the fiber) is extracted from the top, the one with the highest density (Polymer) from the bottom.

[0043] This makes it possible to extract a large majority of the fibers (approximately 80% of the initial mass).

[0044] Nevertheless, the higher the average particle size of the ground materials from step B and step C (greater than 5 mm), the greater the probability of finding a significant quantity of encapsulated fibers in these ground materials, as initially, between the two layers of polymer.

[0045] This prevents the direct reuse of the polymer shreds obtained, in a possible extrusion-granulation circuit, and consequently requires additional treatment.

[0046] Steps A, B and C are implemented in the same shredding, grinding and separation unit 1 as illustrated in [Fig.2]. For shredding, depending on the type and size of the material, this unit 1 incorporates guillotines or shredders.

[0047] It also comprises, for example, a knife mill which provides grinding and a separator.

[0048] In a subsequent step of the process (step D), the polymer ground materials thus obtained are subjected to a grinding treatment by electric pulsed power (energy discharges). This step D is carried out in a separate reactor compared to unit 1 - reactor 2 of [Fig.2]).

[0049] The polymer mixture containing encapsulated fibers and / or fibers attached to the surface by electrostatic force is for this purpose conveyed to the high voltage zone of said reactor 2, for example by a conveyor.

[0050] The reactor 2 comprises one or more sets of tip electrodes, as well as a power unit with storage capacitor(s) and / or inductance(s) which, with a power switch, make it possible to discharge a succession of very high power electrical pulses onto products and materials previously immersed in a liquid ambient medium.

[0051] The resistivity of the liquid, the switching time as well as during the pulses cause the passage of electric arc channels charged with energy inside the material immersed between the two electrodes and passing through said material. immersed. The passage of the electric arc through said material separates the constituents of the materials.

[0052] The discharge circuits allow ultra-fast switching with a switching time between 50 ns and 150 microseconds. The voltages between electrodes are of the order of ten to several hundred kilovolts. The energy used for each reactor is of the order of 50 joules to 10,000 joules, which can be of the order of 100 joules to 10,000 joules. The discharge frequency is from 1 to 40 Hz at a frequency and the circuit frequency between 100 and 900 kHz.

[0053] Thus, for example, starting from an electrical energy source delivering IkW, it is possible to store an energy of 10 kJ in capacitors or storage inductors for 10 s. The energy is restored by power in 10 ps, ​​which makes it possible to deliver a power of 1GW.

[0054] A pulsed power treatment uses a succession of discharges, typically a number of discharges of between 500 and 6000 shots per kg of polymer material to be treated, preferably less than 3000 shots per kg and even more preferably less than 1500 shots per kg of material for example.

[0055] The duration and energy required to extract almost all of the residual fibers by the pulsed electric power treatment are linked to the quantity of residual fibers present and the form of their adhesion to the polymers after the mechanical grinding operation of step B and the separation step C.

[0056] At the end of step D, a ground material of the same diameter as at the end of the mechanical grinding of step B is obtained, but almost free of its encapsulated fibers by the effect of sonic and subsonic shock waves and electronic avalanche.

[0057] Furthermore, with this pulsed electrical power treatment step, and contrary to what would have been the effect of mechanical grinding alone (micronization), the residual fibers and the surfaces of the polymer grinds are electrically charged and move away from each other.

[0058] The ground assembly thus obtained is transmitted to a third unit (unit 3 in [Fig.2]) where it is treated and dried (step E). If necessary in combination with screening, it is also subjected in this unit 3 to treatment by a densimetric separator (air flow or other technique) (step F) which separates the reinforcing fibers and the polymer ground material.

[0059] The polymer material thus isolated is of optimized quality: the treatment by pulsed electric power makes it possible to separate during this stage the fibers and the polymer shreds, which would otherwise have been stuck together by surface effect and electrostatic charge.

[0060] It should be noted that the micronization of polymers does not constitute a relevant solution for the recycling of synthetic membranes based on polymers. In fact, it becomes difficult or even impossible to separate the fiber from the polymers by air flow or by density, and the increase in the specific surface area also increases the fraction of fibers electrostatically bonded to the surface of the aggregates. Furthermore, the micronization of a thermoplastic matrix composite requires cryogenic grinding and cooling of the materials below their glass transition temperature, which increases the cost of processing.

[0061] At the end of step F, more than 99.9% of the fibers have been removed. This provides a polymer free of any reusable fiber with or without regranulation. The mechanical properties of the recycled polymer thus obtained (breaking load (N / mm2) and elongation at break (%)) are equivalent to the virgin polymer.

[0062] It will be noted that for a given average granulometry expected at the end of step F, the energy consumed during step D of treatment by pulsed electrical power is a function of the energy consumed during mechanical step B.

[0063] The lower this energy, the larger the diameter of the intermediate ground material obtained at the end of step B, which will require significant energy at the level of the grinding step using pulsed electrical power.

[0064] Conversely, the higher the mechanical grinding energy of step B, the finer the intermediate ground material and the more the pulsed electrical power treatment step can be limited.

[0065] Typically, in the case of membrane recycling given here by way of illustration, for an objective of average particle size of the order of 1 mm at the outlet of step F, the mechanical grinding can be implemented with a power of between 0.2 kWh / kg and 1.22 kWh / kg, while the treatment by pulsed power is implemented with a power depending on that of the mechanical grinding of between 0.083 kWh / kg and 0.67 kWh / kg, preferably between 0.17 kWh / kg and 0.33 kWh / kg.

[0066] The ground polymer material thus obtained and separated can then be regranulated in an extruder included in unit 3 (step G).

[0067] For an extruder with a flow rate of 28 kg / h, an outlet filter with openings of 200 μm and a pressure of less than 165 bars at said filter, it is considered necessary to change the filter when the injection pressure reaches between 80 and 100 bars. For membranes 1.5 mm thick in plasticized PVC, with a particle size of between 2 and 3 mm and a number of shots equal to 1000 shots or less, this allows an operating time without clogging of the filter of 20 minutes.

[0068] By increasing the number of shots (1500 shots or more), times greater than 40 minutes of continuous operation could be observed.

[0069] The recycled plasticized PVC thus obtained is of good quality. It does not show any deterioration. The proposed process allows processing rates of 700 kg per hour up to 1000 kg per hour. The recycling rate and efficiency are uniform regardless of the input for use in industrial conditions.

[0070] The separated fibers can be reused by being directly baled, re-extruded or even chemically recycled by glycolysis, for example.

[0071] It should also be noted that the proposed process is thus environmentally friendly since it requires no chemical additives and no heat treatment.

[0072] The proposed method applies generally to the recycling of composite materials based on thermoplastic polymers composed of at least two layers including at least one reinforcement based on mineral or synthetic fibers.

[0073] It finds, for example, advantageous application for the recycling of waterproofing membranes made of plasticized PVC reinforced with polyester grids, waterproofing membranes made of plasticized TPO reinforced with polyester grids, watering pipes made of reinforced PVC, truck tarpaulins made of reinforced plasticized PVC, other applications being of course possible.

Claims

Claims

1. Process for recycling composite materials based on thermoplastic polymers composed of at least two layers including at least one reinforcement based on mineral or synthetic fibers, in which the following steps are carried out: - Mechanical grinding to obtain a ground polymer of intermediate granulation level, - Separation of the polymers and fibers released during this mechanical grinding, - Treatment by pulsed electric power to obtain a finer ground polymer and extract the remaining fibers, - Drying and separation of the polymers from the fibers thus released, - Optionally Extrusion and granulation of the polymers.

2. A method according to claim 1, wherein the mechanical grinding is carried out with a power of between 0.2 kWh / kg and 55 kWh / kg.

3. A method according to claims 1 to 2, wherein the pulsed power treatment is carried out with a power inversely proportional to that of the mechanical grinding of between 0.05 kWh / kg and 3.00 kWh / kg.

4. A method according to claims 1 to 3, wherein a pulsed power treatment implements a number of shots per kg of material of between 500 shots and 6000 shots at a discharge frequency of between 1 and 40 Hz, a stored energy of between 100 joules and 10,000 joules and a circuit frequency of between 100 and 900 kHz.

5. Method according to one of the preceding claims, in which the particle size of the material resulting from the mechanical grinding step is between 2 mm and 6 mm.

6. Industrial installation adapted to implement a recycling method according to one of the preceding claims, comprising a grinding unit, a reactor for treatment by pulsed power and a drying station by centrifugation or by fluidized bed.

7. Industrial installation according to claim 6, further comprising an extrusion and granulation line.

8. Industrial installation according to claim 6, in which the drying station comprises a density separator.

9. Use of an industrial installation according to one of claims 6 to 8 for the recycling of composite materials based on thermoplastic polymers composed of at least two layers including at least one reinforcement based on mineral or synthetic fibers.

10. Use according to claim 9 of PVC / PET, TPO / PET membranes.

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