Method for reclaiming elastomeric silicone waste for the production of recycled silicone materials

Abstract

The present invention relates to a method for treating a material comprising one or more silicone elastomers, the method comprising a step of decrosslinking the material in the presence of a metal catalyst and of a solvent selected from the group consisting of alcohols, carboxylic acids, esters, ethers, and mixtures thereof, resulting in the formation of a mixture comprising fragmented chains of silicone elastomer.

Description

Process for the recovery of silicone elastomer waste for the production of recycled silicone materials TECHNICAL FIELD OF THE INVENTION The present invention relates to a process for treating a material comprising one or more silicone elastomers. STATE OF THE ART Silicones, compounds based on silicone elastomer(s), are ubiquitous in several current industrial sectors, including construction, cosmetics, coatings, transportation, electronics and health. Thanks to their insulating, flexible and heat-resistant properties, they have become indispensable materials in our daily lives. However, despite their prevalence, options for their recovery and recycling remain limited.In the domestic context, silicone waste is generally treated as non-hazardous waste, while the majority of industrial waste is disposed of as non-hazardous industrial waste (NIW), particularly through landfilling. This approach not only has environmental consequences, but also eliminates the possibility of reusing these expensive and high-value-added materials. Other methods, namely the mechanical recovery of crosslinked silicone elastomers by grinding and micronization, have been explored, but they only allow low levels of incorporation into virgin formulations, generally less than 10% or even 5%. These products are therefore poorly represented in industry. The prior art also proposes methods for the total depolymerization of silicones to return to cyclic monomers. [1], or cyclosiloxanes, as illustrated in Scheme 1 below, in which a strong acid and then an inorganic base are used successively; other organic and metallic catalysts can also be employed. Two recent reviews summarize the state of the art on the use of electrophiles or nucleophiles to catalyze depolymerization [2] . Using various catalysts and solvents, the degradation of silicones can reach moderate yields, usually around 50-60%. These cyclic monomers can then be reused in the manufacture of new silicones by ring opening polymerization (ROP). Scheme 1: Example of a reaction for the production of cyclosiloxanes from silicone. EP0523323 A1 [1a], from Tremco LLC, therefore proposes to immerse pieces of silicone in an organic solvent and then carry out a double step of acid and then basic catalysis at approximately 150°C to recover, after distillation, cyclosiloxanes. WO2014130948 [1b] by Dow Corning describes a two-step depolymerization of a silicone rubber in the presence of montmorillonite and optionally a thermoplastic polymer. A first step in a screw conveyor initiates the depolymerization, which is completed in a conventional reactor. Cyclosiloxane yields can reach 100%. EP 10086 A2 from Yazaki Corp. depolymerizes a silicone material in the presence of dimethyl carbonate, a proton donor (methanol), and sulfuric acid, resulting in a mixture of oligosiloxanes with a yield of more than 90%. [3]. After distillation of the dimethoxysilane, it is transformed into poly(methylhydrogensiloxane) in the presence of a dichlorosilane and a catalyst. EP1057855 from Yazaki Corp. proposes to hydrolyze a polysiloxane using a protonic solvent, for example methanol, in the supercritical state (240°C, 8 MPa) possibly in the presence of water. [4] This digestion process is rapid (15 minutes), but the final mixture obtained is not described and this solution appears to be expensive. EP3744774 by the Wacker company proposes to 'digest' polysiloxanes via a mixture of weak (acetic acid) and strong (triflic acid) acids. [5] . The resulting product is an oligomer with terminal acetate functions. Ultrasonic devulcanization of silicones Ultrasonic devulcanization is a decrosslinking method proposed by Shim et al. to recycle vulcanized silicones [6]. Devulcanization of precipitated silica-filled silicone rubber was carried out using a continuous ultrasonic reactor. Significant differences were observed between the filled and unfilled systems. A decrease in the gel fraction and crosslink density was observed, allowing reprocessing and revulcanization of the devulcanized silicone rubber. However, a Degradation of the mechanical properties of revulcanizates was observed for filled rubbers. In order to improve the properties, the devulcanized filled rubbers were blended with virgin filled rubber, which led to a significant improvement in the performance characteristics of the blend revulcanizates. Usable mechanical properties could be obtained with only 25% virgin material. In another study by Shim et al. [7], the recycling of fumed silica-filled PDMS was studied using an extruder equipped with a high-power ultrasonic sonotrode. The results showed that fumed silica strongly impacts the devulcanization process. Higher power is required to devulcanize fumed silica-filled PDMS compared to precipitated silica-filled PDMS, due to the strong interaction between fumed silica particles and PDMS chains. In addition, the influence of filler concentration on devulcanization was studied, showing that scission of the main chains (Si-O) and crosslinked bridges (Si-C and CC) occurs simultaneously during the process. The nature of silica and its concentration have major impacts on the properties of devulcanized materials as well as recycled materials and are therefore parameters to consider for silicone recycling.Silicone Pyrolysis: Silicone pyrolysis is a thermal recycling method that uses the chemical decomposition of polymers at high temperatures in the absence of oxygen. A study by ZM. Qin et al. explored the use of titanium dioxide (anatase) as a catalyst for silicone pyrolysis. [8]. The results showed that the catalyst promotes the breaking of siloxane bonds and improves pyrolysis efficiency, even at relatively low temperatures (50-100 C). The volatile substances thus obtained are mainly cyclosiloxanes with 4 and 5 silicon atoms. Chemical depolymerization of silicones: In recent years, several new approaches in catalysis have been presented by different research teams to optimize the depolymerization of silicones. In a study conducted by D. Krug and R. Laine, a method for recycling highly crosslinked thermosetting silicone resins was developed [9] The researchers demonstrated that small amounts of fluoride ions could effectively depolymerize silicone resins, producing oligomers that were easily recoverable and reusable. V. Monteil's team presents an efficient method for solvent-free depolymerization of linear polydimethylsiloxanes (PDMS) using a [polydentate-silanolate ligand] complex, which promotes the chemical recycling of silicones into cyclic monomers from many industrial substrates.

[0010] This method requires only a small amount of catalyst (0.1%wt) for high yields of cyclosiloxanes (up to 98-99%) and at moderate temperatures (60-170 °C). Solvent-catalyzed chemical degradation has also been studied on rubber-like silicones (HCR for heat cured rubber). In this study, R. Petrus et al. demonstrated the effectiveness of simple solvolysis using fatty acids on high molar mass silicones.

[0011] . However, the repolymerization of these recyclates has proven to be difficult. Indeed, this reaction leads to the formation of small functionalized -OR molecules of the MD type xM, with 1 <x<4. La réaction utilise des aryloxydes métalliques à base de Mg-Na / K. Les rendements présentés vont de 17 à 79%. L'activité de divers additifs favorisant les réactions d'équilibre des siloxanes est examinée et quantifiée sur des composés modèles dans les travaux de D. Z. Khedaioui et coll

[0012] . In particular, they found that the "superbase" phosphazene derivative P4- tBu can promote very rapid exchanges (a few seconds at 90°C) with the Si-O-Si bond even at low concentrations (<0.1% by mass). This work shows that permanent silicone networks can be transformed into dynamic networks that can be reprocessed and recycled. However, this approach requires thermal evaporation of the introduced additives in order to restore the permanent nature of the silicone network. Indeed, "high-temperature annealing degrades the additives and deactivates the dynamic properties of the silicone networks, making them return to permanent networks. A simple rheological experiment and the corresponding model allow extracting the critical kinetic parameters to predict and control such deactivations." The properties of the silicones obtained remain limited and the process seems difficult to transpose industrially. In their recent work, JL Torgunrud and SA Miller

[0013] investigated the depolymerization of silicones by diols. Initially, a numerical approach allowed them to determine that hexylene diol (HG) appears to have a very favorable conformation for the chelation of a hydroxy-terminated PDMS. They were thus able to assume a reaction guided by thermodynamics, the product formed being much more stable (a hybrid cyclic monomer, M2HG or 2,2,4,4,6-pentamethyl-1,3-dioxa-2-silacyclohexane). These tests were confirmed in the laboratory, with distillation yields of up to nearly 80%. The authors subsequently focused on the recycling of PDMS from these degradation products by cationic ROP (cROP). The yields of this last step are between 21 and 67% but the technique has the advantage of being able to polymerize Mn chains of the order of 50,000 g / mol. Limitation of the processes mentioned above To date, most chemical approaches to silicone recycling propose recycling by total depolymerization towards small monomers / oligomers for repolymerization towards new polymer chains by repolymerization of these products. These methods are therefore mainly aimed at the treatment of end-of-life waste. Another disadvantage is that the yield of these recycling methods is partial, since the fillers introduced into the silicone must be separated from the cyclic monomers; it is not explained in the literature and the patents mentioned here whether these fillers are reusable and / or reused.A third disadvantage is that this method of completely depolymerizing silicones requires as much energy, and is as expensive, as producing silicone from virgin material.

[0014] . In this context, it becomes evident that the silicone sector is in urgent need of new recycling solutions. More specifically, there is a clear need for the development of methods that can not only facilitate the processing of silicone elastomer waste, but also make their recycling energetically and economically viable.SUMMARY OF THE INVENTION The present invention therefore relates to a method for treating a material comprising one or more silicone elastomer(s), the method comprising a step of decrosslinking the material in the presence of a metal catalyst and one or more solvents, at least one solvent being chosen from the group consisting of alcohols and mixtures thereof, leading to the formation of a mixture comprising fragmented chains of silicone elastomers, the metal catalyst comprising a metal chosen from the group consisting of: Bi, Na, K, B, Mg, Al, Ca, Bi, Ti, Mn, Fe, Co, Cu, Ni, Cu, Sn, Zn, Zr, Hf and mixtures thereof. Other aspects of the invention are as described below. DETAILED DESCRIPTION OF THE INVENTION Surprisingly, a method has been discovered for treating a material comprising one or more silicone elastomer(s) allowing their decrosslinking into fragmented chains of silicone elastomers. The fragmented chains of elastomers are of different weight-average molar masses and advantageously contain alkoxysilyl functions (R a OSi) resulting from the reaction between a siloxane function (SiOSi) and an alcohol (R a OH), R a which may be an alkyl chain comprising from 1 to 12 carbon atoms. R ais preferably a C1-C6 alkyl. The present invention relates, more particularly, to a treatment process carried out under mild conditions in the presence of non-toxic, bio-sourced and recyclable reagents, as well as preferably non-toxic metal catalysts. The present invention makes it possible to reform silicone materials from one or more silicone elastomer(s) by reducing the energy consumption necessary for this synthesis and by limiting the number of post-treatment steps required. This invention also makes it possible to recycle all of the original material, including the fillers originally present in the material, into a new material. The proposed process allows for simple, rapid and economical treatment. It is also potentially less impactful for the environment and less energy-intensive than current state-of-the-art processes.For example, but without being bound by any limitation, the present invention is a new recovery route for materials comprising one or more silicone elastomer(s) derived from waste, scrap or production offcuts. The term "Cx-Cy alkyl" denotes a saturated, linear or branched monovalent hydrocarbon chain comprising x to y carbon atoms; x and y being whole numbers. For example, for C1-C6 alkyl, the following groups may be cited: methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isoamyl, neopentyl, or hexyl, preferably methyl, ethyl, propyl, or isopropyl. Material comprising one or more silicone elastomer(s) The expression “silicone elastomer(s)” designates one or more polymer materials whose main matrix is ​​a polysiloxane, i.e. a chain of siloxane bonds (-SiR. b 2-O-), R bwhich may be a saturated or unsaturated hydrocarbon chain, linear or branched, comprising from 1 to 12 carbon atoms, an aryl, or a hydrogen atom. R b is preferably a C1-C6 alkyl. The material comprising one or more silicone elastomer(s) is typically composed of one or more crosslinked polymers. Typically, the silicone elastomers of the material have Mc values ​​ranging from 1 to 100 kg / mol or from 2 to 50 kg / mol. Mc denotes the average molar mass of the polymer chains between crosslinking nodes. It is determined by swelling in a solvent, typically methylcyclohexane.

[0015] M's determination cby swelling in methylcyclohexane is carried out as follows. Extraction and swelling measurements of the materials are carried out to determine Mc via the Flory-Rehner equation. Samples of initial dry weight Wi are immersed in 100 mL of methylcyclohexane in a sealed bottle. After 5 days, the samples are extracted, gently wiped on each side to remove excess solvent from the surface of the samples and immediately weighed to measure the equilibrium swollen weight W s . The samples are then dried overnight at 110 °C and weighed again (Wf). The extractable matter fraction and the volume fraction of swollen polymer, respectively E and V, are calculated as follows: where c represents the total mass fraction of additive(s) not swelling with the solvent, in particular fillers (e.g. silica and other mineral fillers), ρs and ρp the densities of the solvent and the polymer respectively. From this volume fraction, M c is calculated via the Flory–Rehner equation: with M s the molar mass of the solvent, and χ (Greek letter "chi") the interaction parameter of Flory-Huggins of the polymer-solvent couple used, for example in the case of the PDMS-methylcyclohexane couple, χ = 0.45. The material comprising one or more silicone elastomer(s) may be derived from crosslinking by polycondensation, crosslinking by polyaddition or even radical crosslinking. The material comprising one or more silicone elastomer(s) may be in the form of, for example, a tube, a pipe, a seal or a foam. Commonly, the material is a solid. The material comprises at least 30% by mass of silicone elastomer(s), or at least 50% by mass or even 30% to 80% by mass or even 60% to 80% by mass of silicone elastomer(s) relative to the total mass of the material. The material may be made of silicone elastomer(s). The silicone elastomers of the material may further comprise fillers, for example inorganic fillers.The term "filler" refers to all the solid constituents, typically inorganic, added to the elastomer to provide specific properties and / or reduce the total cost of the elastomer. Generally, the "fillers" can be: reinforcing fillers (e.g. fumed silica, precipitated silica, etc.), semi-reinforcing fillers (e.g. calcium carbonate, carbon black, etc.) or non-reinforcing / diluting fillers (e.g. quartz, mica, etc.), as well as other additives (fire retardant, antioxidant, etc.). Typically, the silicone elastomers of the material have a quantity of fillers, typically inorganic, varying from 0 to 70% by mass, typically from 1 to 70% by mass, more frequently from 10 to 60% by mass or even from 20 to 40% by mass relative to the total mass of the material.The material comprising one or more silicone elastomers may be derived from the production of silicones and may be, for example, waste, scrap, post-expiration product, production offcuts or a mixture of these different classes. The material may also come from any end-of-life silicone object. These silicone objects may come from, but are not limited to, the transportation, construction, electronics, energy, health, cosmetics and / or special systems sectors. Generally, the material is in the form of pieces having a size less than or equal to 10 cm, or even less than 1 cm and typically ranging from 0.1 to 10 cm, or even ranging from 0.1 to 1 cm. The term "size" designates the largest dimension of the fragment or piece. These fragment or piece sizes are typically obtained by mechanical treatment. Thus, the method according to the invention may comprise, before the step of decrosslinking the material, a mechanical treatment step aimed at homogenizing the physical characteristics of the material. Typically, the mechanical treatment step is carried out for a solid material comprising one or more silicone elastomer(s) in the form of pieces having a size greater than 10 cm with the aim of reducing and homogenizing the sizes of fragments or pieces. Advantageously, the mechanical treatment step makes it possible to facilitate the implementation and optimize the performance of the decrosslinking step.The mechanical treatment step can be carried out by cutting or grinding or any other methods known to those skilled in the art. The pieces can also be washed. The material obtained at the end of the mechanical treatment can be in the form of submillimeter particles. Typically, the particles have a size less than or equal to 1000 µm, or varying from 50 to 1000 µm. Decrosslinking step The method according to the invention comprises a step of decrosslinking the material comprising one or more silicone elastomer(s) in the presence of a metal catalyst, one or more solvents, optionally a swelling solvent, leading to the formation of a mixture containing fragmented chains of silicone elastomers and optionally the fillers initially present in the material.Commonly, the decrosslinking step is carried out at a temperature less than or equal to 250°C, typically less than or equal to 200°C, or even less than or equal to 150°C, generally ranging from 40 to 150°C, or even from 50 to 120°C, or even ranging from 50 to 90°C. The decrosslinking step is commonly carried out at atmospheric pressure. It can also be carried out at a pressure greater than or equal to 0.1 MPa, or even higher. or equal to 1 MPa, generally ranging from 0.1 to 10 MPa, or even from 0.15 to 4 MPa or even from 0.2 to 2 MPa. Advantageously, the decrosslinking step makes it possible to carry out at low temperature, that is to say a temperature less than or equal to 250°C or even less than or equal to 200°C, a controlled decrosslinking of the material into a mixture of fragmented chains of silicone elastomers and possibly fillers, generally in the form of a paste. The decrosslinking step carried out according to the present invention (in the presence of a metal catalyst) does not require the action of a base, whether it is a mineral or organic base. As examples of bases, alkali metal or alkaline earth hydroxides such as NaOH, KOH or LiOH may be cited or alkali metal alcoholates such as MeONa, MeOK, EtONa or EtOK. The decrosslinking step carried out in the presence of a metal catalyst allows good control of the fragmentation of the elastomers.When this step is carried out under the action of a base, the depolymerization is violent and uncontrolled, leading to products with low molar masses (less than 500 g / mol). Solvent(s) The solvent is chosen from the group consisting of alcohols, carboxylic acids, esters, ethers and their mixtures. The solvent is commonly a protic organic solvent such as an alcohol and / or an acid. Preferably, the solvent is chosen from the group consisting of alcohols and their mixtures. The decrosslinking step can therefore be carried out in the presence of one or more solvents, at least one solvent being chosen from the group consisting of alcohols and their mixtures. Advantageously, one or more solvents is an alcohol. The term "alcohol" designates a linear or branched molecule comprising from 1 to 20 carbon atoms and at least one (-OH) group. Alcohols can therefore comprise several (-OH) groups, for example two (-OH) groups.The alcohols may comprise from 1 to 12 carbon atoms, or from 1 to 8 carbon atoms, or even from 1 to 6 carbon atoms, for example from 1 to 4 carbon atoms or even 1, 2, 3 or 4 carbon atoms, preferably these carbon atoms form a saturated, linear or branched hydrocarbon chain. The alcohols are preferably chosen from primary alcohols. The alcohols are typically selected from the group consisting of methanol, ethanol, propanol, iso-propanol, butanol, iso-butanol, sec-butanol, tert-butanol, ethanediol, propane-1,3-diol, propane-1,2-diol, butane-1,4-diol, pentane-1,5-diol and mixtures thereof, preferably from the group consisting of methanol, ethanol, propanol, iso-propanol, butanol, iso-butanol or sec-butanol and mixtures thereof. The term "carboxylic acid" designates a linear or branched molecule comprising from 2 to 20 carbon atoms and at least one (-COOH) group. Carboxylic acids may contain from 2 to 12 carbon atoms, or from 2 to 8 carbon atoms, or even from 2 to 6 carbon atoms, for example from 2 to 4 carbon atoms or even 2, 3 or 4 carbon atoms. They may also contain from 4 to 12 carbon atoms, in particular from 4 to 8 carbon atoms, in particular from 4 to 6 carbon atoms.Carboxylic acids are typically selected from the group consisting of acetic acid, propanoic acid, butanoic acid, hexanoic acid, or lauric acid. The term "ether" refers to an alcohol in which the proton of the (-OH) group is replaced by a linear or branched carbon chain comprising from 1 to 20 carbon atoms and conventionally from 1 to 12 carbon atoms, or from 1 to 8 carbon atoms, or even from 1 to 6 carbon atoms, for example from 1 to 4 carbon atoms or even 1, 2, 3 or 4 carbon atoms. The ethers are typically selected from the group consisting of, but not limited to, diethyl ether, dimethyl ether, diisopropyl ether, dibutyl ether, diethyl ether, tert-butyl ether, diphenyl ether.The term "ester" refers to an acid in which the proton of the group (-COOH) is replaced by a linear or branched carbon chain comprising from 1 to 20 carbon atoms and typically from 1 to 12 carbon atoms, or from 1 to 8 carbon atoms, or even from 1 to 6 carbon atoms, for example from 1 to 4 carbon atoms or even 1, 2, 3 or 4 carbon atoms. Esters are typically chosen from the group consisting of methyl, ethyl, propyl, butyl, isoamyl acetates, tert-butyl ethyl acetate, and phthalates. A mixture of solvents may also be used to carry out the decrosslinking step in particular. Conventionally, the mixture is a mixture of at least two alcohols, one alcohol and one carboxylic acid, or two carboxylic acids. The solvent is commonly used in excess of the silicone elastomer(s). Typically, the solvent is introduced at a rate of 20 to 300% by mass of solvent, or 50 to 200% by mass of solvent, or even 80 to 150% by mass of solvent relative to the mass of the material. Optionally, the decrosslinking step may also be carried out in the presence of a swelling solvent. The swelling solvent is commonly an aprotic solvent. The aprotic solvent causes the network comprising one or more crosslinked silicone elastomers to swell. The swelling solvent can advantageously facilitate the decrosslinking of the material by facilitating the contact between the alcohol and the polymer chains.The swelling solvent may be selected from the group consisting of alkanes, cycloalkanes, alkenes, cycloalkenes, aromatics and mixtures thereof. The term "alkane" designates a saturated, linear or branched hydrocarbon molecule of general formula CnH2n+2 with n between 1 and 20 carbon atoms. Alkanes in the liquid state at room temperature may comprise from 5 to 12 carbon atoms, or from 5 to 8 carbon atoms, or even 5 or 6 carbon atoms. The term "cycloalkanes" designates an alkane as defined above comprising at least one cycle, of general formula C. n H 2n. The term “alkene” designates an unsaturated hydrocarbon molecule corresponding to an alkane as defined above which also has at least one carbon-carbon double bond. Typically, an alkene comprising a carbon-carbon double bond has the formula CnH2n. The term “cycloalkene” designates a cycloalkane as defined above which also has at least one carbon-carbon double bond. The term “aromatic” designates a molecule comprising from 5 to 20 carbon atoms or from 6 to 12 carbon atoms and at least one aromatic nucleus, such as, for example, toluene. More particularly, the swelling solvent is selected from the group consisting of, but not limited to, pentane, hexane, heptane, octane, cyclohexane, methylcyclohexane, toluene and mixtures thereof. The swelling solvent may be present at a mass percentage ranging from 25% to 75% by mass of swelling solvent relative to the total mass of the material. Metal catalyst The metal catalyst generally comprises a metal selected from the group consisting of alkalis, metalloids, transition metals, post-transition metals, lanthanides, actinides and mixtures thereof. The metal may be selected from the group consisting of: Bi, Na, K, B, Mg, Al, Ca, Bi, Ti, Mn, Fe, Co, Cu, Ni, Cu, Sn, Zn, Zr, Hf and mixtures thereof or from the group consisting of Sn, Zn, Al, Cu, Co, Ni, Zr, Ti, Hf, Bi and mixtures thereof. The metal can be Zn, Zr, Fe or Sn. Typically, the metal is Zn or Sn.Generally, the oxidation state of the metal of the metal catalyst varies from (II) to (IV) depending on the nature of the metal. The metal catalyst may be any catalyst that can catalyze the siloxane bond breaking reaction (Si-O-Si). It is understood that the catalysts according to the invention may be in anhydrous form or in one of their hydrated forms where appropriate. The metal catalyst is generally a catalyst used in polycondensation syntheses. The metal catalyst may be of formula M(L). nwith: - M representing a metal atom as defined above, in particular chosen from the group consisting of Bi, Na, K, B, Mg, Al, Ca, Bi, Ti, Mn, Fe, Co, Cu, Ni, Cu, Sn, Zn, Zr and Hf; - each L independently representing an anionic or neutral monodentate or bidentate ligand; - n representing an integer ranging from 1 to 4, preferably 2 or 4. In a preferred embodiment, each L independently represents a halogen atom, =O, -O-R1, -O-Si(R1)3, -OC(O)R1, a (C1–C 20 ), an acetate or an acetylacetonate; in particular a group =O, -OC(O)R1, a (C4–C12) alkyl group, an acetate or an acetylacetonate, with R1 representing a (C1–C 20 ). According to a particular embodiment, the ligands L are identical. Examples of (C1-C20) alkyl groups that may be cited are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl or 2-ethylhexyl groups. Examples of (C4-C12) alkyl groups that may be cited are butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl or 2-ethylhexyl groups.The metal catalyst may be selected from the group consisting of dioctyl tin oxide (SnO(Oct)2), tin octoate (also called tin 2-ethylhexanoate), dioctyltin dineodecanoate (Sn(neo)2Oct2), dibutyltin dilaurate (DBTL), dibutyltin diacetate (DBTA), zinc bis(2,4-pentanedionato) (Zn(acac)2), anhydrous or hydrated zinc diacetate, bismuth tris(neodecanoate), iron(II) acetate, iron(III) acetate, zirconium acetate, and a mixture thereof, typically selected from the group consisting of tin octoate, dioctyltin dineodecanoate (Sn(neo)2Oct2), dibutyltin dilaurate (DBTL), dibutyltin diacetate dibutyltin (DBTA), zinc bis(2,4-pentanedionato) (Zn(acac)2), bismuth tris(neodecanoate) and a mixture thereof.The decrosslinking step is typically carried out in the presence of 0.1 to 20% by mass of metal catalyst, preferably 0.5 to 10% by mass or even 1 to 5% by mass of metal catalyst relative to the initial mass of material comprising one or more silicone elastomer(s). Without being bound to any theory, the decrosslinking step consists of cutting the silicone chains in places, and this is not limited to the crosslinking nodes. For example, when the solvent is an alcohol, in the silicone elastomer a disiloxane bond (Si-O-Si) is replaced by two alkoxysilyl bonds (2Si-OR), as illustrated in diagram 2 below. This makes it possible to move from a solid 3-dimensional chemical network of the elastomer to individual fragmented chains constituting a liquid, in which the presence of the fillers generally induces a significant viscosity. Fragmented chains of silicone elastomers The decrosslinking step results in obtaining a mixture of fragmented chains of silicone elastomers and possibly fillers initially present. Typically, the fragmented chains of silicone elastomers of the mixture obtained at the end of the decrosslinking have weight-average molar masses, Mw, less than or equal to 1000 kg / mol, preferably less than or equal to 500 kg / mol or even less than or equal to 300 kg / mol, or even less than or equal to 100 kg / mol. Typically, a portion of the fragmented chains of silicone elastomers, designated part A or fragmented chains A, has a weight-average molar mass less than 5 kg / mol, or even less than or equal to 2 kg / mol, or even less than or equal to 1 kg / mol, as determined by SEC. Typically, part A of the fragmented chains has a weight-average molar mass ranging from 0.1 to 2 kg / mol or from 0.1 to 1 kg / mol.Part A of the fragmented chains is commonly soluble and in solution in the solvent(s) used during the decrosslinking step. Typically, a portion of the fragmented silicone elastomer chains, referred to as part B or fragmented silicone elastomer chains B, has a weight-average molar mass varying from 5 to 1000 kg / mol, or even varying from 5 to 500 kg / mol or from 10 to 300 kg / mol or even from 10 to 100 kg / mol. Part B of the fragmented chains is commonly in the form of a viscous phase, also referred to as a viscous paste or pasty phase. Generally, part B of the fragmented chains is insoluble in the solvent, and can be recovered in the form of a viscous phase also containing the filler(s), typically inorganic.Generally, the mixture of fragmented silicone chains typically consists of: A) 0 to 100% by mass, typically 10 to 80% by mass, or even 30 to 70% by mass or even 40 to 60% by mass (relative to the initial mass of the material) of fragmented chains A of silicone elastomer having a weight-average molar mass, Mw, of less than 5 kg / mol; and / or B) 0 to 100% by mass, typically 20 to 90% by mass, or even 30 to 70% by mass or even 40 to 60% by mass (relative to the initial mass of the material) of fragmented chains B of silicone elastomers having a weight-average molar mass, M. w , greater than or equal to 5 kg / mol. The mixture of fragmented silicone chains may consist of: A) from 5 to 60% by mass, typically from 10 to 50% by mass (relative to the initial mass of the material) of fragmented chains A of silicone elastomer having a weight-average molar mass, Mw, of less than 5 kg / mol, or even less than or equal to 2 kg / mol, or even less than or equal to 1 kg / mol; and B) from 40% to 95%, preferably from 50% to 90% by mass (relative to the initial mass of the material) of fragmented chains B of silicone elastomers having a weight-average molar mass, Mw has a weight-average molar mass varying from 5 to 1000 kg / mol, preferably from 5 to 500 kg / mol. Without being linked to any theory, the proportions between fragmented chains A and fragmented chains B can be controlled depending on the conditions of the decrosslinking step and in particular the quantity of metal catalyst used.For example, the greater the quantity of metal catalyst, the greater the proportion of fragmented chains in part A with a weight-average molar mass, Mw, of less than 1 kg / mol. Part B of the fragmented chains obtained at the end of the decrosslinking step may comprise a quantity of filler varying from 0 to 70% by mass, typically from 1 to 70% by mass or from 10 to 60% by mass or even from 20 to 40% by mass relative to the initial mass of material. The fillers are as defined above. Generally, the quantity of fillers in the mixture of fragmented chains of silicone elastomers is identical to the quantity of fillers present in the initial material. Commonly, the weight-average molar masses of the fragmented chains of silicone elastomer can be determined by size exclusion chromatography (SEC), in particular by the method described in the examples.The nature of the fragment obtained and in particular the nature of the functions resulting from the decrosslinking reactions can be determined by nuclear magnetic resonance analysis of silicon (. 29 If NMR), carbon ( 13 C NMR) and proton ( 1 H NMR). Optional separation step The process may comprise, at the end of the decrosslinking step, a separation step leading to the production of fragmented chains of silicone elastomers in liquid form and / or viscous paste. The separation step may be carried out, for example, by drying, filtration, decantation, distillation or any other method known to those skilled in the art. Conventionally, the recovered fragmented silicone elastomer chains are - on the one hand in part A as defined above, typically in liquid form; and - on the other hand in part B as defined above, typically in the form of a viscous paste. The fragmented chain paste B obtained by the above process may contain less than 10% by mass of fragmented chains A defined above relative to the total mass of silicone paste, typically less than 1% by mass, or even less than 0.1% by mass or even less than 0.01% by mass. The separation step may also comprise a step of recovering some or all of the solvent used during the decrosslinking step.Typically, the solvent can be recovered by distillation, or any other method known to those skilled in the art. The solvent thus recovered can be recycled, for example, in the decrosslinking step of the process according to the invention. The fragmented chains of silicone elastomers obtained by the process according to the invention, whether part A or part B, can be used as a basis for the formulation of various silicone products such as, for example, sealants, recycled raw material (RPM) or any other silicone-based product, including paints, coatings, adhesion primers, antifoams, solid foams. The invention also relates to the paste of fragmented chains of silicone elastomers obtained or capable of being obtained by the above treatment process. It also relates to the solutions containing the fragmented chains A of silicone elastomers.Size exclusion chromatography (SEC) and nuclear magnetic resonance analyses of silicon (. 29 If NMR) are used to determine the proportions and weight-average molar masses of the fragmented chains of silicone elastomers obtained according to the invention and in the examples below. The process according to the invention therefore offers the possibility of efficiently degrading by decrosslinking a wide range of silicone elastomers, in particular addition and condensation RTV types, addition and radical HTVs, as well as addition LSRs. The fragmented chains of silicone elastomers obtained by the process according to the invention can be used in admixture or not with virgin material for the manufacture of various products such as sealants, adhesion agents, water repellent precursors and coatings. This versatility opens new perspectives for the recovery of silicone waste and contributes to a more sustainable approach in the production of innovative materials. In the sense of the present invention, the different embodiments presented in the entire description can be used alone or in combination with each other, without limitation of combination.EXAMPLES The following examples illustrate a particular embodiment of the invention without limiting its scope. Materials The expressions used in the examples below have the following meanings: ^ The expression "condensation silicone" designates a two-component cold-curable silicone (RTV2) (RTV for 'room temperature vulcanizing', 2 ​​because two components are mixed) from the Elastosil® range marketed by the company Wacker, a material crosslinked by tin-catalyzed polycondensation. This condensation silicone is representative of the entry-level silicones used for stuffing and encapsulating electronic equipment, for example. It is a hard silicone with limited mechanical properties (typically 40 Shore A hardness, 1.8 MPa breaking stress and 130% strain at break in tensile testing).^ The term "addition silicone" refers to the two-component RTV 3428 silicone from the Bluesil® range marketed by Elkem, a material crosslinked by platinum-catalyzed polyaddition. This addition silicone is a flexible silicone (30 Shore A) with good tear strength (20 kN / m) and high mechanical properties (6 MPa / 600% at break by tensile test). ^ The term "transparent silicone" refers to the Bluesil® RTV 141 silicone marketed by Elkem and crosslinked by platinum-catalyzed polyaddition. This silicone is hard (50 Shore A), unfilled (no silica, composed mainly of silicone resins) and has acceptable mechanical properties (6 MPa, 120% at break in tension). ^ The term "radical silicone" refers to the Elastosil® R400 silicone marketed by Wacker, which crosslinks by radical reaction in the presence of peroxide. This silicone is representative of rubber-type silicones used for demanding applications. It has very high mechanical properties: hardness of 60 Shore A, 11 MPa / 500% at break in tension and good tear strength of 26 kN / m. ^ The term "vulcanizable silicone 1" refers to the Elastosil® R865 silicone marketed by Wacker.This silicone crosslinks by radical reaction in the presence of peroxide and cures up to 40 Shore A. The mechanical properties in tension are high: 8.0 MPa / 430% at break. ^ The term "vulcanizable silicone 2" refers to the Elastosil® R701 silicone marketed by Wacker. This silicone crosslinks by radical reaction in the presence of peroxide. This silicone is hard (80 Shore A). It has acceptable mechanical properties in tension (7.6 MPa / 200% at break according to the supplier). The catalysts used in these examples are as follows: ^ Cat 1 designates Sn(neo)2Oct2:dioctyltin bis neodecanoate (68299-15-0) marketed either in the form of a ready-to-use hardener (T40, Wacker) where it is mixed with a crosslinking agent (tetraethylorthosilicate, TEOS) in respective proportions of 30 / 70% by mass, or pure (TIB KAT 318, TIB Chemicals) for example.^ Cat 2 denotes Sn(EHO)2: Tin(II) 2-ethylhexanoate (301-10-0), TK 129 (TIB Chemicals) ^ Cat 3 denotes Zn(acac)2: Zinc acetylacetonate hydrate (108503-47-5), Bis(2,4-pentanedionato)zinc (Merck / Sigma Aldrich) ^ Cat 4 denotes Ti(OBu)4: titanium tetrabutoxide (5593-70-4) or orthotitanic acid tetrabutyl ester (TNBT, Tyzor® TBT) or tetrabutyl orthotitanate (Merck / Sigma Aldrich). ^ Cat 5 denotes dioctyl tin oxide (870-08-6), e.g. TIB KAT417 (TIB Chemicals). The post-crosslinking agent used in these examples is as follows: ^ Crosslinker 1 denotes PDMS-OH 4K: dihydroxy-polydimethylsiloxane 4 kg / mol The amounts of catalyst are expressed in % by mass relative to the mass of material introduced in the decrosslinking step. General protocol of examples 1 to 4 The material comprising one or more silicone elastomer(s) is previously conditioned in parallelepipedal pieces of approximately 2 mm on each side. The conditioned material (20 g) is introduced into a stainless steel reactor equipped with a resistance heating jacket controlled by a regulation unit. The solvent (50 mL) and the metal catalyst (1, 5 or 10% by mass) are then added. The reactor is locked by cross-tightening.The mixture is heated to the decrosslinking temperature (90°C, 120°C or 150°C) for a time varying from 1 to 7 days, and at a pressure of 0.2 MPa, 0.8 MPa or 1.1 MPa respectively depending on the decrosslinking temperature. At the end of the decrosslinking step, the reactor is cooled for 30-45 minutes to approximately 70°C. The mixture obtained at the end of decrosslinking is separated into a liquid phase and a pasty phase. These two phases are analyzed by size exclusion chromatography (SEC) and silicon nuclear magnetic resonance (. 29If NMR). General protocol of examples 5 to 9 The material comprising one or more silicone elastomer(s) is previously conditioned in parallelepipedal pieces of approximately 2 mm on each side or in spherical shape of approximately 1 mm in diameter. The conditioned material (16 g) is introduced into a climatic chamber. The solvent (8 mg) and the metal catalyst (4 or 10% by mass) are then added. The mixture is heated to the decrosslinking temperature (80 °C or 115 °C) for a time varying from 1 to 30 days. At the end of the decrosslinking step, the conditioned material is returned to room temperature. The mixture obtained at the end of decrosslinking is analyzed by size exclusion chromatography (SEC) and by silicon nuclear magnetic resonance (NMR). 29 If). SEC Analysis Chromatographic analysis is a technique for separating macromolecular chains based on their molar mass. These analyses are performed on a Malvern GPC Max Viscotek device equipped with 3 detectors (RI refractometer, IV viscosity, LS light scattering). The analytical solvent is toluene. The solvent elution flow rate is set at 1 mL / min and the temperature of the columns and the RI detector is 40 °C. A calibration curve was constructed from a range of polystyrene standards (molar masses ranging from 104 to 300000 g / mol). The weight average mass (Mw) results are from a conventional calibration in PS equivalent (RI detector). Example 1: Tests 1 to 6 were performed with condensation silicone according to the general protocol under the conditions summarized in Table 1 below.Table 1: Tests Solvent Catalyst Temperature Time (% by mass) (°C) (h) 1 ethanol Cat 2 (10) 90 96 2 ethanol Cat 2 (1) 120 36 3 ethanol Cat 2 (10) 150 24 4 isopropanol Cat 1 (5) 90 24 5 isopropanol Cat 3 (5) 90 168 6 butanol Cat 2 (5) 90 24 The quantities of catalyst are expressed in % by mass relative to the mass of material introduced at the decrosslinking stage. Tests 1 to 6 above all made it possible to obtain fragmented chains of silicone elastomers after a decrosslinking time varying from 1 to 7 days. These results show that the process according to the invention makes it possible to decrosslink under mild conditions (temperature, % catalyst, solvent) a material comprising a condensation silicone elastomer. At the end of the decrosslinking step, the mixture obtained was separated into a liquid phase and a pasty phase. As an example for test 2, after separation, the following were obtained: - a pasty phase whose mass corresponds to 60% of the initial mass of the material (condensation silicone). The pasty phase is composed of fragmented chains of silicone elastomers having an Mw varying from 5 to 300 kg / mol. This pasty phase may contain traces (<0.1% by mass) of fragmented chains of silicone elastomers with an Mw lower than 1 kg / mol; and - a liquid phase after evaporation of the solvent whose mass corresponds to 40% of the initial mass of the material (condensation silicone). The liquid phase is composed of fragmented chains of silicone elastomers having an MW lower than 2 kg / mol. Example 2 Tests 7 and 8 were carried out with addition silicone in accordance with the general protocol under the conditions summarized in Table 2 below.Table 2: Tests Solvent Catalyst Temperature Time (% by mass) (°C) (h) 7 methanol Cat 2 (1) 90 96 8 ethanol Cat 2 (10) 150 15 Tests 7 and 8 above made it possible to obtain fragmented chains of silicone elastomers after a decrosslinking time varying from 1 to 4 days. These results show that the process according to the invention also makes it possible to decrosslink a material comprising an addition silicone elastomer under mild conditions in terms of temperature and quantity of catalyst used. At the end of the decrosslinking step, the mixture obtained was separated into a liquid phase and a pasty phase. As an example for test 7, after separation, the following were obtained: - a pasty phase corresponding to 90% of the initial mass of the material (condensation silicone). The pasty phase is composed of fragmented chains of silicone elastomers having an Mw varying from 5 to 300 kg / mol.This pasty phase may contain traces of fragmented chains of silicone elastomers with an Mw less than 1 kg / mol; and. - a liquid phase after evaporation of the solvent corresponding to 10% of the initial mass of the material (condensation silicone). The liquid phase is composed of fragmented chains of silicone elastomers having an Mw of less than 2 kg / mol. Example 3: Tests 9 and 10 were carried out with other silicone materials in accordance with the general protocol under the conditions summarized in Table 3 below. Table 3: Silicone Tests Solvent Catalyst Temperature Time (% by weight) (°C) (h) 9 Addition transparent ethanol Cat 2 (10) 150 45 10 Radical ethanol Cat 2 (10) 150 18 Tests 9 and 10 demonstrate that the process according to the invention also allows the decrosslinking of silicones either crosslinked by radical reaction with peroxide, or uncharged and crosslinked with platinum. Thus, the method according to the invention makes it possible to treat all types of materials comprising one or more silicone elastomer(s).Example 4: Recycling tests (reformation of a network) were carried out using pastes obtained according to the general protocol described above. The decrosslinking tests 11 to 13 presented in Table 4 below were carried out on the RTV condensation silicone described above. The chain populations obtained were characterized by SEC toluene. Table 4: Tests Solvent Catalyst Temperature Time (% by mass) (°C) (h) 11 ethanol Cat 2 (1.5) 150 28 12 ethanol Cat 2 (2.5) 150 24 13 ethanol Cat 2 (2) 150 16. The characteristics of the fragmented chains of silicone elastomers obtained are presented in Table 5 below. Table 5: M tests w BM fragmented chains wFragmented chains A Population ratio B / A (kg / mol) (g / mol) (% by mass) 11 5-500 < 800 75 / 25 12 5-115 < 800 82 / 18 13 5-400 < 1000 90 / 10 The fragmented chains of silicone elastomers from part B were used to prepare new silicone elastomers under the conditions presented in table 6 (tests at a temperature of 80°C, for 48 hours). The mechanical properties of these elastomers presented in table 7 correspond to a material composed of 100% recycled raw material (RPM), i.e. from parts B of tests 11 to 13 presented above. Table 6: Tests Chains Catalyst Crosslinker Time fragmented (% by mass) (% by mass) (h) B from 14 Test 11 Cat 4(5) 0 48 15 Test 11 Cat 2(1) crosslinker 1 (1.5) 48 16 Test 11 Cat 2 (1) Crosslinker 1 (2) 48 17 Test 12 Cat 2 (1) Crosslinker 1 (2) 48 18 Test 13 Cat 2 (1) crosslinker 1 (2) 48 Table 7: Test Strain at Break Stress at Break (%) (MPa) Initial Condensation Silicone 130 1.8 (Control) 14 60 0.97 15 50 1.16 16 75 0.69 17 130 0.6 18 120±20 0.6±0.2 Tensile tests, to evaluate strain and / or stress at break, were carried out on an Instron® machine equipped with a 500 N cell and a video extensometer at a speed of 100 mm / min on type 5A dumbbell specimens (ISO 527-2). Strain at break and stress at break are measured according to ASTM D412 with a crosshead speed of 100 mm / min. The results obtained show that after a recycling cycle by the present invention, the materials have stress and strain values ​​at break representing 30 to 60% of those of the initial material. Example 5: Tests 19 to 22 were carried out with condensation silicone in accordance with the general protocol under the conditions summarized in Table 8 below.Table 8: Test Solvent Catalyst Temperature Time (% by mass) (°C) (h) 19 Ethanol Cat 5 (4) 80 72 20 Butan-1-ol Cat 5 (4) 80 48 21 Butan-1-ol Cat 5 (4) 115 17 22 Ethanol Cat 3 (4) 80 312 Tests 19 to 22 above all resulted in fragmented chains of silicone elastomers after a decrosslinking time ranging from 1 to 13 days. These results show. that the process according to the invention makes it possible to decrosslink under mild conditions (temperature, % catalyst, solvent and in the absence of base) a material comprising a condensation silicone elastomer. The results of test 21 also show that the process according to the invention makes it possible to decrosslink using a tin-free catalyst. At the end of the decrosslinking step, the mixture obtained is analyzed by toluene SEC. As an example for test 20, the sample has a population of fragmented chains of silicone elastomers having a molar mass by weight M wvarying from 0.8 to 160 kg / mol. Example 6: Tests 23 to 26 were carried out with addition silicone in accordance with the general protocol under the conditions summarized in Table 9 below. Table 9: Test Solvent Catalyst Temperature Time (% by mass) (°C) (h) 23 Ethanol Cat 5 (4) 80 120 24 Butan-1-ol Cat 5 (4) 80 72 25 Butan-1-ol Cat 5 (4) 115 17 26 Ethanol Cat 5 (10) 80 288 Tests 23 to 26 above all made it possible to obtain fragmented chains of silicone elastomers after a decrosslinking time varying from 1 to 12 days. These results show that the process according to the invention also makes it possible to decrosslink addition silicones under the same mild conditions (temperature, % catalyst, solvent and absence of base). At the end of the decrosslinking step, the mixture obtained is analyzed by toluene SEC. As an example for test 23, the sample presents: – a population of fragmented chains of silicone elastomers having an M wof 20 kg / mol. The proportion of this population measured by SEC corresponds to 80% of the total sample. and - a population of fragmented chains of silicone elastomers having a Mw lower at 2kg / mol. The proportion of this population measured by SEC represents 20% of the total sample. Example 7: Tests 27 and 28 were carried out with vulcanizable silicone 1 in accordance with the general protocol under the conditions summarized in Table 10 below. Table 10: Test Solvent Catalyst Temperature Time (% by mass) (°C) (h) 27 Ethanol + Cat 5 (4) 80 168 Methylcyclohexane 28 Butan-1-ol Cat 5 (4) 115 96 Tests 27 and 28 above all made it possible to obtain fragmented chains of silicone elastomers after a decrosslinking time varying from 1 to 7 days. These results show that the process according to the invention makes it possible to decrosslink under mild conditions (temperature, % catalyst, solvent and absence of base) a material comprising a silicone elastomer crosslinked by radical reaction with peroxide. At the end of the decrosslinking step, the mixture obtained is analyzed by toluene SEC.As an example for test 27, the sample presents: – a population of fragmented chains of silicone elastomers displaying an M. w of 98 kg / mol. The proportion of this population measured by SEC reaches 55% of the total sample, and - a population of fragmented chains of silicone elastomers having an Mw varying from 3 to 0.8 kg / mol. The proportion of this population measured by SEC is 45%. Example 8: Tests 29 to 30 were carried out with vulcanizable silicone 2 in accordance with the general protocol under the conditions summarized in Table 11 below. Table 11: Test Solvent Catalyst Temperature Time (% by mass) (°C) (h) 29 Ethanol + Cat 5 (4) 80 480 Methylcyclohexane 30 Butan-1-ol Cat 5 (4) 115 384 Tests 29 to 30 above all made it possible to obtain fragmented chains of silicone elastomers after a decrosslinking time varying from 1 to 20 days. These results show that the process according to the invention makes it possible to decrosslink under mild conditions (temperature, % catalyst, solvent and absence of base) a material comprising a silicone elastomer crosslinked by radical reaction with peroxide and having a significant hardness. At the end of the decrosslinking step, the mixture obtained is analyzed by toluene SEC. As an example for test 29, the sample has a population of fragmented chains of silicone elastomers having a M w from 0.6 to 29 kg / mol. REFERENCES [1] (a) T. W. Greenlee, Process for recycling silicone scraps and products relating thereto, EP0523323A1, 1992; (b) D. J. Julian, D. Katsoulis, B. A. Link, T. A. Peitz, B. Zhu, Method of recycling silicone waste with the use of organic polymer and depolymerization catalyst, WO2014130948A1, 2014. [2] (a) Rupasinghe, B. and Furgal, J.C. (2022), Degradation of silicone-based materials as a driving force for recyclability. Polym Int, 71, 521-531 ; (b) B. Rupasinghe, Recycling Silicone- Based Materials: An Overview of Methods, IntechOpen (2023). [3] T. Kawamoto, Process for recycling silicone compounds, EP1008621A2, 1999. [4] T. Kawamoto, Method of recycling crosslinked silicone compound waste, EP1057855A1, 2000. [5] W. Knott, H. Dudzik, D. Schaefer, Method for recycling of silicones, EP3744774B1, 2021. [6] S. E. Shim, A. Isayev, Ultrasonic devulcanization of precipitated silica-filled silicone rubber, Rubber Chem. Technol. 2001, 74, 303-316. [7] S. E. Shim, V. V. Yashin, A. I.Isayev, Environmentally-friendly physico-chemical rapid ultrasonic recycling of fumed silica-filled poly(dimethyl siloxane) vulcanizate, Green Chemistry, 2004, 6, 291-294. [8] Z.-M. Qin, P.-C. Wang, R. Yang, H.-B. Chen, Fast pyrolysis of silicones at low temperatures catalyzed by anatase titanium dioxide, Polym. Degrad. Stab. 2020, 182, 109387. [9] D. J. Krug, M. Z. Asuncion, R. M. Laine, Facile Approach to Recycling Highly Cross-Linked Thermoset Silicone Resins under Ambient Conditions, ACS Omega 2019, 4, 3782-3789.

[0010] N. D. Vu, A. Boulegue-Mondière, N. Durand, J. Raynaud, V. Monteil, Back-to-cyclic- monomers-chemical-recycling-of-silicone-wastes-using-a-polydentate-ligand-potassium- silanolate-complex, Green Chem. 2023, 25, 3869-3877.

[0011] R. Petrus, J. Utko, R. Gniłka, M. G. Fleszar, T. Lis, P. Sobota, Solvothermal Alcoholysis Method for Recycling High-Consistency Silicone Rubber Waste, Macromolecules 2021, 54, 2449-2465.

[0012] D. Z. Khedaioui, C. Tribout, J. Bratasanu, F. D'Agosto, C. Boisson, D. Montarnal, Deciphering Siloxane Bond Exchanges: From a Molecular Study to Vitrimerization and Recycling of Silicone Elastomers, Angew. Chem. Int. Ed. Engl. 2023, 62, e202300225.

[0013] J. L. Torgunrud, A. M. Reverón Pérez, E. B. Spitzberg, S. A. Miller, Entropy-Driven Depolymerization of Poly(dimethylsiloxane), Macromolecules 2023, 56, 10, 3668-3678.

[0014] ecousarecycling.com / silicone-rubber-recycling-process. Reached on 06 / 23 / 2023

[0015] E. Delebecq, N. Hermeline, A. Flers, F. Ganachaud, Looking over Liquid Silicone Rubbers: (2) Mechanic Properties vs Network Topology, ACS Appl. Mater. Interfaces, 2012, 4, 3353-3363.

Claims

CLAIMS 1. A method of treating a material comprising one or more silicone elastomers, the method comprising a step of decrosslinking the material in the presence of a metal catalyst and one or more solvents, at least one solvent being chosen from the group consisting of alcohols and mixtures thereof, leading to the formation of a mixture comprising fragmented chains of silicone elastomers, the metal catalyst comprising a metal chosen from the group consisting of: Bi, Na, K, B, Mg, Al, Ca, Bi, Ti, Mn, Fe, Co, Cu, Ni, Cu, Sn, Zn, Zr, Hf and mixtures thereof.

2. A treatment method according to claim 1, wherein the silicone elastomer(s) has(have) average molar masses of the polymer chains between crosslinking nodes, Mc, ranging from 1 to 100 kg / mol, preferably from 2 to 50 kg / mol. 3.Treatment method according to any one of claims 1 or 2, wherein the silicone elastomers of the material further comprise fillers.

4. Treatment method according to any one of claims 1 to 3, wherein the decrosslinking step is carried out at a temperature less than or equal to 250°C, preferably less than or equal to 200°C, preferably less than or equal to 150°C.

5. Treatment method according to any one of claims 1 to 4, wherein the decrosslinking step is carried out at a pressure greater than or equal to 0.1 MPa, preferably ranging from 0.2 to 2 MPa.

6. Treatment method according to any one of claims 1 to 5, wherein the solvent is selected from the group consisting of methanol, ethanol, propanol, iso-propanol, butanol, iso-butanol, sec-butanol, tert-butanol, ethanediol, propane-1,3-diol, propane-1,2-diol, butane-1,4-diol, pentane-1,5-diol and mixtures thereof.

7. A treatment method according to any one of claims 1 to 6, wherein the decrosslinking step is further carried out in the presence of a swelling solvent selected from the group consisting of alkanes, cycloalkanes, alkenes, cycloalkenes, aromatics and mixtures thereof.

8. A treatment method according to any one of claims 1 to 7, wherein the metal catalyst comprises a metal being Zn, Zr, Fe or Sn.

9. Treatment method according to any one of claims 1 to 8, in which the metal catalyst is of formula M(L) nwith: - M representing a metal atom selected from the group consisting of Bi, Na, K, B, Mg, Al, Ca, Bi, Ti, Mn, Fe, Co, Cu, Ni, Cu, Sn, Zn, Zr and Hf; - each L independently representing an anionic or neutral monodentate or bidentate ligand; - n representing an integer ranging from 1 to 4, preferably 2 or 4.

10. Treatment method according to claim 9, wherein L independently represents a halogen atom, =O, -O-R1, -O-Si(R1)3, -OC(O)R1, a (C1–C20) alkyl group, an acetate or an acetylacetonate; in particular a group =O, -OC(O)R1, a (C4–C12) alkyl group, an acetate or an acetylacetonate, with R1 representing a (C1–C 20).

11. A treatment method according to any one of claims 1 to 10, wherein the metal catalyst is selected from the group consisting of dioctyl tin oxide (SnO(Oct)2), tin octoate (also called 2-ethylhexanoate tin), dioctyltin dineodecanoate (Sn(neo)2Oct2), dibutyltin dilaurate (DBTL), dibutyltin diacetate (DBTA), zinc bis(2,4-pentanedionato) (Zn(acac)2), anhydrous or hydrated zinc diacetate, bismuth tris(neodecanoate), iron(II) acetate, iron(III) acetate, zirconium acetate, and a mixture thereof.

12. A treatment method according to any one of claims 1 to 11, wherein the decrosslinking step is carried out in the absence of a base. 13.Treatment method according to any one of claims 1 to 12, in which the fragmented chains of silicone elastomers obtained at the end of the decrosslinking step have weight-average molar masses, Mw, less than or equal to 1000 kg / mol, preferably less than or equal to 500 kg / mol.

14. Treatment method according to any one of claims 1 to 13, in which the mixture of fragmented chains of silicone elastomers obtained at the end of the decrosslinking step is composed of: A) from 0 to 100% by mass, typically from 10 to 80% relative to the total mass of the material, of fragmented chains of silicone elastomers having a weight-average molar mass, Mw, less than or equal to 5 kg / mol; and / or B) from 0 to 100% by mass, typically from 20 to 90%, or even from 30 to 70% relative to the mass. total mass of the material, of fragmented chains of silicone elastomers having a weight-average molar mass, Mw, greater than 5 kg / mol.

15. Treatment method according to any one of claims 1 to 14, wherein the mixture of fragmented chains of silicone elastomers obtained at the end of the decrosslinking step consists of: A) from 5 to 60% by mass, typically from 10 to 50% by mass (relative to the initial mass of the material) of fragmented chains A of silicone elastomer having a weight-average molar mass, Mw, less than 5 kg / mol, or even less than or equal to 2 kg / mol, or even less than or equal to 1 kg / mol; and B) from 40% to 95%, preferably from 50% to 90% by mass (relative to the initial mass of the material) of fragmented chains B of silicone elastomers having a weight-average molar mass, M w has a weight average molar mass ranging from 5 to 1000 kg / mol, preferably from 5 to 500 kg / mol.

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