Manufacturing process for a recyclable fibrous architecture

Abstract

A process for manufacturing recyclable fibrous architectures, comprising the following steps: a) supplying an aqueous solution in which at least one water-soluble polymer is dissolved, b) functionalizing the water-soluble polymer by reacting a first diene-type reagent and / or a second dienophile-type reagent, the first and second reagents forming a cycloaddition pair capable of carrying out a reversible cycloaddition reaction, in particular a reversible Diels-Alder cycloaddition reaction, c) respective addition of the second and / or first reagents of the reagent pair to obtain a precursor formulation of the adhesive formulation, d) coating polymer fibers with the precursor formulation.e) application of a heat treatment to crosslink the precursor formulation to obtain an adhesive formulation capable of reversibly assembling the polymer fibers into a recyclable fibrous architecture. Figure 4,

Description

Title of the invention: Method for manufacturing a recyclable fibrous architecture

[0001] The invention relates to the field of padding used in the manufacture of seats and seating components for means of transport, particularly road, rail, and aircraft transport. The invention relates in particular to the manufacture of a recyclable fibrous structure usable for such padding and to its recycling process.

[0002] The padding used today in the automotive industry is made of polyurethane (PU) foams, formed from a mixture of isocyanates and polyols. The cross-linking reaction between the reactants is rapid. The PU foaming occurs simultaneously with polymerization, for example, by adding water, which releases CO2 in reaction with the isocyanates. The resulting PU foams can have varying densities, on the order of 50 to 100 g / m³, for example, and varying hardnesses, simply by modifying the isocyanate / polyol ratio or by changing the nature of the monomers.

[0003] Despite all these advantages, the use of polyurethane has several significant drawbacks. First, the isocyanates used in their manufacturing process are highly toxic compounds, posing numerous safety problems, and are likely to be regulated in the future (notably by REACH). Furthermore, these isocyanates are themselves derived from phosgene, which is very harmful from an environmental and toxicological standpoint.

[0004] Furthermore, thermosetting polyurethanes are currently very difficult to recycle. Several recycling or waste treatment methods exist: mechanical, chemical, and thermal recycling, as well as, without considering it a recycling method, landfilling.

[0005] Mechanical recycling consists of grinding or micronizing PU foams and reincorporating them as a filler in the initial monomer formulation. This method is primarily used to repurpose production waste and remains limited in terms of the quantity of PU that can be reinjected into the formulation without loss of properties.

[0006] Thermal recycling involves burning PU and the emitted gases to recover energy. Not to mention the obvious environmental problems associated with the method (COx and NOx emissions), the precursors used in PU manufacturing are lost.

[0007] Chemical recycling consists of depolymerizing PUs to obtain basic monomers, which allows the monomers obtained to be reintroduced into the PU cycle or in other chemical industries. This method, while promising on paper, consumes a great deal of energy, since it requires first breaking all the polymer bonds, then expending more energy to separate the resulting mixture of compounds. Furthermore, the recovery rate of the PU material is generally not 100%, as unwanted reactions can occur during the process.

[0008] In this context, the transportation industry, and particularly the automotive sector, is seeking alternative methods to address these problems. One approach involves replacing PU foams with other materials. Among the alternatives is the use of fibers as padding material for seat cushions, particularly polymer fibers, which are readily available and inexpensive, notably PET fibers (polyethylene terephthalate, generally referred to as polyester fibers in the textile industry). The properties and problems associated with these cushions are already documented in the literature: loss of thickness due to fiber compression and deformation leads to the degradation of their seating properties over time, unlike PU foam.Indeed, while fibers can slip against each other under stress and not return to their initial state, when PU is subjected to compression, being formed of a single block, it transmits the stress throughout the material, allowing it to remain within a macroscopic range of elasticity.

[0009] Work then focused on linking discrete fibers with a polymer binder to overcome this problem of fiber slippage. For example, a packaging material replacing expanded polystyrene chips was developed by forming a composite from bagasse fibers (natural fibers) bonded with a water-soluble polymer, polyvinyl alcohol (PVA), and foaming the assembly with a chemical foaming agent, sodium tetraborate. However, this system containing PVA and bagasse exhibited significant sensitivity to water, and its presence was likely to destroy the crosslinking via the sodium tetraborate. Furthermore, the thermal performance of these systems was not reported, given that in automotive applications, it is important to maintain a stable base up to temperatures of 80°C, typically reached in a vehicle on a sunny summer day.Another solution involves using a mixture of PES / PET type polymer fibers and a binder, applied as an aqueous emulsion, such as polyurethane or chloroprene, but the use of thermosetting binders prevents any recycling.

[0010] One of the aims of the present invention is to overcome the aforementioned drawbacks. To this end, the present invention proposes a method for manufacturing recyclable fibrous structures, particularly for use as padding, the manufacturing method comprising the following steps: - a) supply of an aqueous solution in which at least one water-soluble polymer is dissolved, in particular a polymer selected from a poly- alcohol vinyl PVA, polyethylene glycol PEG, and a polysaccharide, the aqueous solution comprising distilled water; - b) functionalization of the water-soluble polymer by reaction of a first diene-type reagent and / or a second dienophile-type reagent, the first and second reagents forming a cyclo-addition couple capable of carrying out together a reversible cyclo-addition reaction, in particular a reversible Diels-Aider type cyclo-addition reaction, for example the first reagent includes furan and / or anthracene groups and the second reagent includes maleimide groups. - c) respective addition of the second reactant and / or the first reactant of the cycloaddition pair, so as to obtain a precursor formulation of the adhesive formulation, - d) coating of polymer fibres, in particular polyethylene terephthalate (PET) or polyamide (PA) fibres, by the formulation of precursors, in particular by casting onto the fibres or by immersing the fibres in the precursor formulation, - e) application of a heat treatment for crosslinking the precursor formulation, so as to obtain an adhesive formulation capable of reversibly assembling the polymer fibers into a recyclable fibrous architecture.

[0011] Thus, the invention proposes a method for manufacturing a recyclable fibrous architecture in which the fibers do not slip, and which is suitable for producing mattresses based on polymer fibers, bonded by a polymeric adhesive that is reversibly cross-linked, allowing for the recycling and separation of the constituent elements for reuse. It is understood that in this document, the polymer fibers are distinct from the water-soluble polymer as defined in the invention.

[0012] Since the adhesive formulation is prepared in water, the adhesive is applied in aqueous solution to the fibers and then simultaneously dried and crosslinked. Crosslinking is achieved via a reversible covalent chemistry using cycloaddition of the Diels Aider type. The reversible covalent crosslinking chemistry is chosen to maintain the adhesive properties stable over time and within a temperature range up to approximately 100 °C. The reversibility of the chemistry (or retro-Diels Aider) can be triggered under specific conditions: by immersion in an aqueous medium at a temperature above 100 °C (therefore under water pressure), so that it cannot be triggered under normal operating conditions of the padding. As will be seen later, this reversible chemistry also ensures the recyclability of the fibrous architecture by allowing the separation of the used fibers from the The adhesive formulation remains intact, allowing for its reuse in the same application. Indeed, at the end of the separation process, the adhesive returns to an aqueous solution, and the fibers can be filtered to separate them from the adhesive solution. The adhesive formulation can then be reused as is, or after possible concentration.

[0013] This process makes it possible to obtain recyclable fibrous structures with a load-bearing capacity identical to that of polyurethane foam but a lower density than PU (between 36 and 43 kg / m³ for the fibrous structure versus approximately 60 kg / m³ for PU foam). The fillings obtained from these structures are thus lighter, which is highly desirable in the transportation sector, particularly in the automotive, aviation, etc. industries.

[0014] According to one possibility, the recyclable fibrous architectures obtained by said process exhibit a bearing capacity of between 5 and 50kPa at 50% strain, for example 7kPa at 50% strain.

[0015] According to one arrangement, the hydrophilic polymer comprises hydroxyl end groups. These hydroxyl end groups constitute preferred reaction sites with the first and / or second reactant of the cycloaddition couple. The hydrophobic nature of these reactants helps to reduce the hydrophilic character of the functionalized polymer, so the initial content of hydroxyl end groups in the polymer is high to maintain the soluble character of the functionalized polymer.

[0016] According to a particular embodiment of the process, it includes a step (i) of applying a pre-crosslinking thermal pretreatment before the coating step (d) of the process, so as to partially crosslink the precursor formulation. The temperature and / or duration of the applied pre-crosslinking thermal pretreatment is just sufficient to obtain partial crosslinking of the precursor formulation, so that the precursor formulation is not fully crosslinked at the end of step (i). This step (i) increases the viscosity of the formulation, facilitating coating onto the fibers according to step (d), if applicable. Indeed, when the aqueous precursor formulation is very liquid, coating is more difficult. If it is carried out by pouring, the liquid tends to flow without having time to impregnate the polymer fibers.In cases where the coating is applied by immersion, again, depending on the viscosity of the formulation, the fibers do not retain the formulation sufficiently, particularly because the capillary forces are insufficient.

[0017] Preferably, step i) is stopped before the viscosity of the precursor formulation reaches a value of 10¹⁰ Pa·s, or even 10 HPa·s, and preferably 10¹² Pa·s. This latter value constitutes the threshold beyond which application to the fibers will be too difficult. Viscosity is measured, for example, by viscometer or rheometer.

[0018] According to one possibility, the application of a heat treatment for crosslinking according to step e) carried out after coating according to step d) finalizes the crosslinking of the functionalized polymer and lasts less time than in the absence of step i).

[0019] According to one provision, the process includes, before and / or during the application step of a crosslinking heat treatment (e), a compression step (ii) of the coated polymer fibers, so as to wring out the polymer fibers and remove excess precursor formulation. This step also allows the fibers to be shaped and to achieve the load-bearing capacity suitable for the intended purpose.

[0020] According to one possibility, the process includes arranging the polymer fibers in a mold having the desired final shape, before step ii) of applying compression.

[0021] According to one arrangement, the compression step ii) includes the application of a differential pressure achieved by locally applying different pressure values ​​so as to obtain more or less dense regions in the recyclable fibrous architecture at the end of step e). This arrangement makes it possible to achieve a fibrous architecture exhibiting localized stiffnesses, particularly suitable for applications in upholstery, especially of mattresses, seats and other seating elements.

[0022] Advantageously, the step of applying differential pressure ii) is carried out by using a mold comprising a counter-form suitable for applying differential pressure according to different regions of the coated fibers.

[0023] According to one provision, the application of the heat treatment for crosslinking is carried out by a flow of hot air. This ensures crosslinking and drying.

[0024] According to one possibility, the water-soluble polymer is a vinyl polyacetate derivative comprising a hydrolysis rate of 95%.

[0025] According to one arrangement, the water-soluble polymer is a vinyl polyacetate derivative, and the degree of functionalization with furan groups is in the range of 1% to 6.5% by mol. Indeed, furan is a hydrophobic reagent which, once grafted onto a hydrophilic polymer, decreases the solubility of the latter, so it is necessary to limit the functionalization.

[0026] According to one provision, the relative proportions of water-soluble polymer, first diene-type reagent, second dienophile-type reagent, and polymer fibers are chosen such that the mass ratio of dry adhesive to polymer fibers is between 10 and 30% in the recyclable fibrous architecture obtained in step e). It is understood that the mass of dry adhesive corresponds to the mass of polymer that has been cross-linked and dried from the aqueous solvent. This can be calculated from the mass of the recovered fibrous architecture, once it has been oven-dried (100 °C) and is stable (absence of residual water), less the mass of the polymer fibers added in step d).

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[0033] According to one possibility, the process includes, prior to step e), a step iii) of structuring the precursor formulation, in particular by foaming, or by adding agents having the same function, before or during application to the polymer fibers. According to one provision, since the water-soluble polymer PVA tends to foam naturally, step iii) of structuring is carried out at the time of coating by injecting a gas into the precursor formulation. The functionalization of hydrophilic polymer by a hydrophobic reagent chosen from the first diene-type reagent and / or the second dienophile-type reagent is less than 15 mol% of hydrophilic functions, and preferably less than 10% so as to avoid the polymer functionalized at the end of step b) precipitating in the aqueous solution. According to another aspect, the invention also proposes a method for recycling the recyclable fibrous architecture obtained according to the manufacturing process described above. The recycling process comprises the following steps: - x) placing the fibrous architecture in an autoclave in the presence of water, - y) applying a heat treatment at a temperature between 100 and 130 °C for a few hours, - z) filtration of polymer fibers allowing separation of polymer fibers on the one hand and a filtrate comprising the water-soluble polymer and the reagents of the cyclo-addition couple on the other hand. This process utilizes the reversibility of the chemical reactions involved in the manufacturing process. The heat treatment application step (see step y) is carried out in a closed autoclave and enables a retro-Diels Aid reaction. These conditions allow the pressure to rise to approximately 4 bar. In all cases, the pressure remains below 5 bar in the autoclave. The aqueous solution can be reused in the manufacturing process of the fibrous architecture. According to other features, the manufacturing process of the invention comprises one or more of the following optional features considered alone or in combination: - The functionalization reaction according to step b) includes the formation of covalent bonds between the water-soluble polymer and the first and / or second reactant of the cyclo-addition couple. - Hydrophilic polymer hydroxyl terminations are functionalized partly by the first diene-type reagent and partly by the second dienophile-type reagent. - Hydrophilic polymer hydroxyl end groups are functionalized

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[0038] in part by a first diene-type reagent comprising either furan groups and / or anthracene groups. - The first diene-type reagent is chosen from furfural, 2-furoyl chloride and a mixture of these reagents. - The second dienophile-type reagent is chosen from among the bis-maleimides and for example 1,2-phenylene bis-maleimide (PDM). - The polymer fibers are chosen from PET fibers and / or polyamide fibers. - Polymer fibers include polymers of different natures. - Polymer fibers comprise or are made of a single type polymer. - Polymer fibers come in various diameters, notably between 10 micrometers and 2 mm. - Polymer fibers come in various lengths, notably between 1 and 50 cm. - The polymer fibers are pre-organized so as to be entangled prior to step d), in particular by needle-punching processes. - Step ii) of compression is maintained during step e) of application of the crosslinking heat treatment. - The mold includes drainage holes configured to ensure the evacuation of excess precursor formulation. - The concentration of hydrophilic polymer in the aqueous solution is between 5 and 9% by mass at step a). Other aspects, objects, and advantages of the present invention will become clearer upon reading the following description of an embodiment thereof, given by way of non-limiting example and with reference to the accompanying drawings. In the remainder of this description, for the sake of simplicity, identical, similar, or equivalent elements of the different embodiments are referred to by the same numerals in the figures in which: Figure [1] illustrates three examples of water-soluble polymer according to an embodiment of the process according to the invention. Figure [Fig. 2] illustrates an example of a functionalization reaction of the water-soluble polymer by a first diene-type reagent according to an embodiment of the process according to the invention. Figure 3 illustrates a Diels Aider type reaction starting from a first diene-type reagent and a second dienophile-type reagent forming a cycloaddition couple according to an embodiment of the process according to the invention. Figure 4 illustrates an example of crosslinking between a hydrophilic polymer Activated by a furan group and a bis-maleimide reagent by forming a reversible Diels Aider type cycloaddition according to an embodiment of the process according to the invention.

[0039] Fig. 5 illustrates another example of crosslinking between a hydrophilic polymer functionalized by a furan group and a hydrophilic polymer functionalized by a bis-maleimide group by forming a reversible Diels Aider type cycloaddition according to another embodiment of the process according to the invention.

[0040] Figure 6 illustrates an NMR spectrum of a polymer functionalized with furfural and residual free furfural.

[0041] The process for manufacturing a recyclable fibrous architecture includes steps consisting of linking the polymer fibers together by a polymeric adhesive precursor, then applying a heat treatment so as to crosslink the precursors and fix the polymer fibers according to a recyclable fibrous architecture.

[0042] First, the process of the invention comprises steps for preparing a precursor formulation of the polymeric adhesive using a reversible and clean chemistry, mainly carried out in aqueous solution. To this end, the process considers a hydrophilic polymer (for example, PVA among the examples in [Fig. 1]) which will form the backbone of the polymeric adhesive, to dissolve it and form an aqueous solution.

[0043] Then, according to step b) of the process, a hydrophilic polymer functionalization reaction is carried out with a first diene-type reagent, here furfural ([Fig. 2]). Once this functionalization is achieved, the process includes step c) of adding a second dienophile-type reagent ([Fig. 3]) to the functionalized polymer to obtain an aqueous solution containing a cycloaddition couple, enabling a reversible Diels-Aider reaction as illustrated in [Fig. 3]. These steps lead to the formulation of precursors for the polymeric adhesive. Polymer fibers are then coated with this formulation (step d), and a crosslinking heat treatment is applied. This results in an adhesive formulation (network A+B in Figures 4 and 5), which, once dried, fixes the polymer fibers in a recyclable fibrous architecture. Functionalization of the hydrophilic polymer

[0044] A concrete embodiment is described. In a 500 mL round-bottom flask equipped with a motorized mechanical stirrer, 16 g of grade 56-98 PVA and 200 g of distilled water are placed. The mixture is heated for 1 h with stirring at 90 °C until the PVA is completely dissolved. The aqueous solution is acidified with APTS (p-toluenesulfonic acid) until a pH of approximately 1.7 is reached. The APTS is used as a catalyst to enhance the electrophilic character of the aldehyde in order to synthesize an acetal. Then, after cooling to room temperature, 2.26 mL of furfural (first diene-type reagent) are added to the mixture and stirred for 6 h to perform step b) of PVA functionalization. The solution is then neutralized to neutral pH with KOH solution, and the functionalized polymer is slowly precipitated by adding ethanol. The polymer is thus purified, then filtered and air-dried. The furfural grafting can be observed by NMR ([Fig. 6]). Diels-Aider type cycloaddition

[0045] The polymer thus functionalized with furans is then dissolved in water at a concentration of 6% by mass by heating for one hour at 90 °C. For 5 g of functionalized polymer, 60 mg of N,N'-(1,3-Phenylene) bismaleimide (PDM) is added as a second dienophile-type reagent (or crosslinking agent) under mechanical stirring. Crosslinking begins immediately. A gel is obtained after 2.5 hours of heating at 60 °C, demonstrating the crosslinking of the functionalized polymer and forming the adhesive formulation. Coating on polymer fibers

[0046] Precursor formulations comprising 2%, 4%, and 6% wt. of PVA in water and PDM are prepared as previously described. To optimize the viscosity of the formulation, a heat treatment is applied at 60 °C for 30 min (step i) of the process). Then, approximately 2 g of 60 mm long dTex 33 PET fibers are fully immersed, according to step d) of the process, in each of the solutions (2%, 4%, and 6% wt. of PVA with PDM). The fibers are then placed in a mold having drainage holes for the precursor formulation and compressed to remove some of the formulation via a spacer the size of the mold. The applied pressure can be between 50 and 500 kPa, in particular approximately 200 kPa.Next, the spacer is partially raised to two-thirds of the initial height of the fibers, allowing them to decompress without returning to their original state. The entire assembly is then placed in an oven at 80°C for 24 hours to achieve cross-linking. The spacer height is generally adjusted according to the target density of the padding. A fibrous architecture is thus obtained, comprising the PET fibers bonded together by the adhesive formulation. Using this method, respective quantities of 0.23 g, 0.46 g, and 0.84 g of dry adhesive are deposited onto the fibers with an initial PVA concentration of 2%, 4%, and 6% by mass, respectively, resulting in PVA / PET fiber ratios of 11%, 23%, and 42%, respectively. Application in the upholstery

[0047] The padding formed from the fibrous architectures obtained from the 6% mass aqueous solution of PVA exhibited a very high rigidity, incompatible with the intended application.

[0048] The padding formed in the same way from the fibrous architectures obtained from the aqueous solution at 2% mass of PVA was within the limit of acceptable flexibility for the intended application. Recycling of fibrous architecture

[0049] A padding formed similarly to the previous example, comprising a fibrous architecture made up of 1 g of fibers and 0.5 g of adhesive, is placed in 300 mL of water in a 600 mL autoclave. Heat treatment is applied at 120 °C for 2 h. The atmosphere in the autoclave increases slightly in pressure during the process (less than 5 bar). At the end of the process, the fibers are recovered, rinsed with distilled water, and the aqueous medium is collected separately. It has the same appearance as before crosslinking; it is yellow and foamy. After drying, the fibers are observed under an optical microscope and reveal an adhesive-free surface. The fibers are weighed and have a mass of 0.52 g.

[0050] After drying the filtrate, a polymer film is obtained and can be isolated. The film must be heated to 120 °C in DMSO to dissolve, which shows that the adhesive re-crosslinked during the drying of the filtrate. NMR analyses of the film dissolved in DMSO show the recovery of furan-modified PVA and the presence of the PDM crosslinker essentially in its reacted form.

[0051] This recycling demonstrates that the polymer fibers are recovered intact and can be reused in the manufacturing process of the invention. The appearance of a polymer film during the drying of the filtrate shows that the initial reactants are indeed recovered and can crosslink again. They can therefore be reused (before the filtrate dries) in the manufacturing process according to the invention.

[0052] Thus, the present invention makes it possible to obtain fibrous architectures at temperatures between 25 and 90 °C, which are recyclable by retro-Diels-Alder at temperatures above 100 °C. These architectures can be used for padding with appropriate load-bearing capacities and lower density, in order to form improved seating, particularly in the transportation sector. The process uses a green solvent, and the chemical reactions involved are reversible, so that the fibrous architecture is recyclable and the components (fiber, hydrophilic polymer, and cycloaddition reagents) can be reused.

[0053] It goes without saying that the invention is not limited to the embodiment variants described above by way of example but includes all technical equivalents and variants of the means described as well as their combinations.

Claims

Claims

1. A method for manufacturing recyclable fibrous architectures, the manufacturing method comprising the following steps: - a) providing an aqueous solution in which at least one water-soluble polymer is dissolved, - b) functionalizing the water-soluble polymer by reacting a first diene-type reagent and / or a second dienophile-type reagent, the first reagent and the second reagent forming a cyclo-addition pair capable of carrying out a reversible cyclo-addition reaction, in particular a reversible Diels Aider-type cyclo-addition reaction, - c) respectively adding the second reagent and / or the first reagent of the pair of reagents so as to obtain a formulation of precursors of the adhesive formulation, - d) coating polymer fibers, by formulating precursors,- e) application of a crosslinking heat treatment of the precursor formulation so as to obtain an adhesive formulation capable of reversibly assembling the polymer fibers into a recyclable fibrous architecture.,

2. The manufacturing method of claim 1, wherein the hydrophilic polymer comprises hydroxyl termini.

3. Manufacturing method according to claim 1, which comprises a step i) of applying a pre-crosslinking heat pre-treatment before step d) of the method, so as to partially crosslink the polymer formulation.

4. Manufacturing method according to claim 1 or 2, which comprises before and / or during the carrying out of the step of applying a crosslinking heat treatment e), a step of compressing ii) the coated polymer fibers so as to wring the polymer fibers and remove the excess of the precursor formulation.

5. Manufacturing method according to claim 4, in which the compression step ii) is carried out by locally applying different pressure values ​​so as to obtain more or less dense regions of variable rigidity in the recyclable fibrous architecture at the end of step e).

6. Manufacturing method according to one of claims 1 to 5, in which the water-soluble polymer is chosen from a polyvinyl alcohol PVA, a polyethylene glycol PEG, and / or a polysaccharide.

7. Manufacturing method according to one of claims 1 to 6, in which the water-soluble polymer is a polyvinyl acetate derivative comprising a hydrolysis rate of 95%.

8. Manufacturing method according to one of claims 1 to 7, in which the water-soluble polymer is a polyvinyl acetate derivative and the level of functionalization by furan groups is within a range from 1% to 6.5% by mole.

9. Manufacturing method according to claim 1 to 7, wherein the mass ratio of dry adhesive per mass of polymer fiber is between 10 and 30% in the recyclable fibrous architecture obtained in step e).

10. Manufacturing method according to one of claims 1 to 9, which comprises a step iii) of structuring the precursor formulation carried out before or during step e).

11. Process for recycling the recyclable fibrous architecture obtained according to the manufacturing process according to claims 1 to 10, comprising the steps of: - x) placing the fibrous architecture in an autoclave in the presence of water, - y) applying a heat treatment at a temperature between 100 and 130°C for a few hours, - z) filtering the polymer fibers to separate the polymer fibers and a filtrate comprising the water-soluble polymer and the first reagent and the second reagent of the cyclo-addition couple.

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