Method for recycling of silicone materials

Abstract

The present invention relates to a process for recycling a silicone material obtained by polyaddition reaction, said process comprising the steps of providing a silicone material obtained by polyaddition reaction, grinding said material to obtain a silicone powder, mixing said powder with at least one organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule and at least one organohydrogenopolysiloxane to obtain a silicone composition, and crosslinking said silicone composition to obtain a new silicone material comprising recycled silicone powder.

Description

Technical Field

[0001] This invention relates to the field of recycling organosilicon materials, and more particularly to organosilicon powders that can be recycled as catalytic feedstocks in polyaddition crosslinking organosilicon compositions. Background Technology

[0002] Recycling of industrial and manufacturing plastics (especially used silicone products) is a very important issue today. Recycling silicone polymers can reduce emissions of gases (CO, CO2) associated with the silicone industry by reducing the volume of silicone waste and providing new recycled materials for new uses.

[0003] The so-called "mechanical" recycling of silicone (as opposed to chemical recycling) is not a new concept. As early as 1994, Japanese patent application JP H06-100779A (from Shin-Etsu Chemical) described a method for obtaining silicone elastomers molded from silicone elastomer powder and a binder. The silicone elastomer powder was obtained by spraying old crosslinked silicone elastomer, such as burrs, scrap, and other waste from the silicone elastomer molding process, but also from the used molded articles themselves. This composition could be reused in typical silicone elastomer applications after being mixed with a binder (which could be a silicone elastomer composition). Similarly, US patent US 5,350,804 proposed recycling the burrs of crosslinked silicone elastomers by finely grinding and dispersing them within a matrix of silicone elastomer. In their 2003 scientific publication, Ghosh et al., "Recycling of Silicone Rubber Waste: Effect of Ground Silicone Rubber Vulcanizate Powder on the Properties of Silicone Rubber",... Polymer Engineering and Science (February 2003, Vol. 43, No. 2) A study on the effects of incorporating mechanically ground cross-linked silicone elastomer powder into new silicone elastomers was presented. The difficulties of re-incorporating ground silicone powder into new matrices are discussed, for example, in patent applications CN 108 276 776 A and CN 107 029 557A, which propose pre-surface treatment of the powder. Neither of these documents focuses on the specific properties of the used silicone material, nor on its initial production process.

[0004] In contrast to mechanical recycling, chemical recycling involves depolymerizing used silicone materials, typically in the presence of a catalyst, through chemical and possibly thermal processes. Examples of chemical recycling are described in patent applications CN 117 264 274 A and CN 117 209 843 A. In CN 117 264 274 A, pre-ground silicone elastomers used as insulating materials are depolymerized using an alcoholysis agent (selected from unsaturated alcohols) and a catalyst (selected from the list of zinc catalysts). In CN 117 209 843 A, pre-ground waste silicone elastomers are first mixed with a solvent to swell, and then depolymerized using an alcoholysis agent.

[0005] The scientific publication by Raymond HAJJ et al. (“Silicone-recycled pyrolyzed fillers for enhanced thermal- and flame-resistant silicone elastomers”) Polymer Degradation and Stability (Volume 200, June 2022, 109947) describes another approach for recycling silicone elastomers, which involves using these waste materials as ceramic precursors. For this purpose, the silicone elastomers used are pyrolyzed at 600°C or 850°C, and the resulting residue is then used as a mechanical reinforcing filler in new silicone elastomers.

[0006] It has been shown, quite surprisingly, that powders obtained by mechanically grinding crosslinked silicone elastomers are considered merely reinforcing fillers within the new silicone matrix. Past research has focused on incorporating as much powder as possible while maintaining acceptable mechanical properties compared to the new silicone material.

[0007] Contrary to all expectations, the inventors of this invention have discovered that powders obtained by mechanically grinding certain cross-linked silicone elastomers possess catalytic properties for the cross-linking of novel silicone elastomers. As a result of this discovery, the powders can now be upgraded to catalytic feedstocks in certain systems. Summary of the Invention

[0008] Overview of the Invention

[0009] This invention relates to a method for the mechanical recycling of organosilicon materials. Those skilled in the art will therefore clearly recognize that this method does not include a chemical depolymerization step. Typically, this method preferably does not use any chemical degrading agents for organosilicon materials, especially not alcoholysis agents, strong bases or strong acids, and optionally not chain-end agents. Preferably, the recycling method according to the invention does not use solvents. Those skilled in the art can refer to published literature describing the chemical depolymerization route of organosilicon, such as the review by Wolf, AT and Stammer, A.: “Chemical Recycling of Silicones—Current State of Play (Building and Construction Focus)”. Polymers 2024, 16, 2220.

[0010] One subject of the present invention is therefore the use of a powder obtained by a method comprising the following steps as a catalytic feedstock for polyaddition crosslinking organosilicon compositions or for completely or partially replacing a polyaddition catalyst in a polyaddition crosslinking organosilicon composition: providing an organosilicon material obtained by a polyaddition reaction, and broyering the material.

[0011] This invention relates to a method for recycling organosilicon materials obtained through a polyaddition reaction, the method comprising the following steps:

[0012] - Provides organosilicon materials obtained through polyaddition reactions.

[0013] - Grind the material to obtain organosilicon powder.

[0014] - The powder is mixed with at least one C2-C bonded to silicon per molecule. 12 An organopolysiloxane with an alkenyl group and at least one organohydrogen polysiloxane are mixed to obtain an organosilicon composition, and

[0015] - Crosslink the silicone composition to obtain a new silicone material containing recycled silicone powder.

[0016] Another subject of the present invention is an organosilicon composition comprising at least one C2-C per molecule having at least two silicon-bonded C2-C bonds. 12 Organosilicon powder obtained by grinding an organosilicon material obtained through a polyaddition reaction with an alkenyl group, at least one organohydrogenated organosilicon, and an organosilicon powder. New organosilicon materials containing the recycled organosilicon powder, obtainable through the polyaddition crosslinking of the said organosilicon composition, are also the subject of this invention.

[0017] Furthermore, the subject of this invention is a method for preparing organosilicon powder, the method comprising the following steps:

[0018] - Provides organosilicon materials obtained through polyaddition reactions, and

[0019] - Grind the material.

[0020] Organosilicon powder that can be obtained by this method and recycled into new organosilicon materials is also the subject of this invention.

[0021] Finally, the subject of this invention is the use of the powder as a catalytic feedstock for polyaddition crosslinking organosilicon compositions.

[0022] Detailed Description of the Invention

[0023] Unless otherwise stated, all viscosities of silicone oils considered in this disclosure correspond to so-called “Newtonian” dynamic viscosity values ​​at 25°C, i.e., dynamic viscosity measured using a Brinell viscometer in a manner known per se at a shear rate gradient that is sufficiently low for the viscosity being measured and thus independent of the rate gradient.

[0024] The subject of this invention is therefore a method for recycling organosilicon materials obtained by polyaddition reactions. A polyaddition reaction (also known as a hydrosilylation reaction) can be defined as the reaction of a compound containing at least one double bond with a compound containing at least one hydrosilyl functional group (i.e., a hydrogen atom bonded to a silicon atom). Polyaddition reactions are particularly used for crosslinking organosilicon compositions containing organopolysiloxanes with alkenyl units and organopolysiloxanes containing hydrosilyl functional groups.

[0025] In this paper, the term "organosilicon material obtained by polyaddition reaction" refers to any organosilicon material that has been crosslinked by polyaddition reaction in the presence of a metal polyaddition catalyst.

[0026] The metal polyaddition catalyst may be particularly selected from platinum and rhodium compounds, and may also be selected from silicon compounds, such as those described in patent applications WO 2015 / 004396 and WO 2015 / 004397; germanium compounds, such as those described in patent application WO 2016 / 075414; or nickel, cobalt, or iron complexes, such as those described in patent applications WO 2016 / 071651, WO 2016 / 071652, and WO 2016 / 071654.

[0027] The metal polyaddition catalyst is preferably a compound derived from at least one metal belonging to the platinum group. More preferably, the metal polyaddition catalyst is a compound derived from platinum. These polyaddition catalysts are well known. Speier hexachloroplatinic acid is typically mentioned. Platinum complexes with organic products can also be used, such as those described in patents US 3 159 601 (platinum-olefin complexes), US 3 220 972 (complexes obtained by reaction of chloroplatinic acid with alcohols, ethers or aldehydes), EP 0 057 459 (platinum-styrene complexes), EP 0 188 978 (platinum-triene complexes) and EP 0 190 530 (platinum-alkenylcyclohexene complexes), as well as platinum complexes with vinyl organosiloxanes, such as those described in patents US 3 419 593 (platinum-organosiloxane complexes with terminal unsaturation), US 3 715 334 (platinum-vinylsiloxane complexes in the absence of halogens) and US 3 814 730 (platinum-silane or unsaturated siloxane complexes). Preferably, the polyaddition catalyst is Karstedt platinum, i.e., Pt(0) of the general formula Pt2(divinyltetramethyldisiloxane)3 (or abbreviated as Pt2(DVTMS)3).

[0028] Alternatively, metal polyaddition photocatalysts can be used. These catalysts can be activated by irradiation, preferably by UV irradiation. Platinum-based photocatalysts can be selected, for example, from: bis(acetylacetone)platinum, trimethyl(acetylacetone)platinum, trimethyl(2,4-pentanedione)platinum, trimethyl(3,5-heptanedione)platinum, trimethyl(methylacetoacetate)platinum, bis(2,4-pentanedione)platinum, bis(2,4-hexanedione)platinum, bis(2,4-heptanedione)platinum, bis(3,5-heptanedione)platinum, and bis(1-phenyl-1,3-butanedione)platinum.

[0029] The organosilicon material obtained by polyaddition reaction preferably contains at least 5 ppm by mass, more preferably 5 ppm to 200 ppm, more preferably 6 ppm to 100 ppm, and even more preferably 10 ppm to 50 ppm of platinum metal, based on the total weight of the organosilicon composition.

[0030] According to one embodiment, the silicone material obtained by the polyaddition reaction can be selected from silicone elastomers (or "rubber"), silicone gels, and silicone foams. More particularly, the silicone material obtained by the polyaddition reaction can be selected from the group consisting of:

[0031] - RTV-type polyaddition crosslinked silicone elastomer;

[0032] - LSR type polyaddition crosslinked silicone elastomer;

[0033] - HCR type polyaddition crosslinked silicone elastomer;

[0034] - Polyaddition crosslinked silicone gel; and

[0035] - Polyaddition crosslinked silicone foam.

[0036] Preferably, the silicone material obtained by polyaddition reaction can be selected from silicone elastomers and silicone foams, more preferably silicone elastomers and silicone foams having a Shore A hardness of at least 20.

[0037] The polyorganosiloxane-based compositions contemplated according to the present invention can be crosslinked by polyaddition reaction at room temperature or by exposure to heat. The terms RTV, LSR, and HCR are well known to those skilled in the art: RTV stands for "Room Temperature Vulcanizing"; LSR stands for "Liquid Silicone Rubber"; and HCR stands for "Heat-Cured Rubber".

[0038] RTVs can be single-component (RTV-1) or two-component (RTV-2). Prior to crosslinking, one or more components are in liquid or paste form. In the case of RTV-2, each component of the system contains a crosslinking agent or catalyst, and when the components are mixed, both components react together according to a polyaddition reaction. Polyaddition RTV-1 is less common: the crosslinking agent and catalyst are provided as a single component, but the polyaddition reaction is delayed by various means.

[0039] LSR is typically a two-part liquid composition that is quite viscous. The two parts are mixed to initiate crosslinking.

[0040] Unlike RTV and LSR, HCR exists as a highly viscous gel before crosslinking. It is typically obtained from silicone rubber (i.e., linear chains of very high molecular weight polysiloxanes). HCR is crosslinked using heat.

[0041] Silicone gels are semi-solid and semi-liquid, traditionally used to protect vibration-, shock-, and temperature-sensitive electronic devices and as basic medical materials, particularly for the development of prostheses, implants, or dressings. In this document, the term "silicone gel" refers to a cross-linked silicone product characterized, in particular, by a permeability (or "penetration") of 50 to 500 mm. This permeability was measured using a Petrotest permeameter, model PNR 12, typically according to the permeability determination method of standard NF ISO 2137, where the total weight of the rod and cone was fixed at 62.5 g. The cone permeability of the silicone gel was determined at 25°C by measuring the depth of the cone penetrating into the sample, obtained by releasing the cone assembly of the permeameter and allowing the cone to act for 5 seconds.

[0042] The term "silicone foam" refers to an organopolysiloxane composition in foam form. Typically, silicone foam can be obtained from an organosilicon composition that simultaneously undergoes polyaddition crosslinking and releases gases that allow for foaming.

[0043] All silicone materials can be derived from various pre- or post-consumer sources. Examples that may be mentioned include cables and pipes, profiles, consumer or industrial molds, seals, foams, prototypes, and 3D printed parts.

[0044] Preferably, the organosilicon material obtained by polyaddition reaction contains no or substantially no amine compounds.

[0045] The recycling method according to the invention includes the steps of providing an organosilicon material obtained by a polyaddition reaction and grinding it to obtain organosilicon powder.

[0046] The grinding method can be selected from mechanical grinding methods of elastomers. Among these, grinding at temperatures greater than or equal to ambient temperature and cryo-broyage will be mentioned in particular. The statement "grinding at temperatures greater than or equal to ambient temperature" refers to a grinding process carried out at a temperature greater than or equal to 15°C, for example, 15°C–150°C. A temperature control system, especially a cooling system, can be provided to prevent overheating of the material during the grinding step. In contrast, cryo-broyage refers to a grinding step carried out at very low temperatures in the presence of a liquefied gas (usually liquid nitrogen). However, from an ecological point of view, cryo-broyage is not a preferred grinding method because it is very energy-intensive.

[0047] A mill is a device for converting initial material into powder. The mill can be selected from mechanical mills, which include one or more movable elements that contact the silicone material to reduce it to powder. The mill can be selected from: twin-roll mills, disc mills, impact mills, hammer mills, ball mills, rod mills, and knife mills. Alternatively, mills using fluid energy, such as jet mills (e.g., air-jet mills), can be used. According to another embodiment, grinding can be performed by extrusion, for example using a twin-screw extruder or a single-screw extruder.

[0048] The use of mills with rotating parts (e.g., co-rotating twin-screw extruders) is described in patents ES 2276607 B1, US9527978 B2, US 9598550 B2, WO 2022 / 044031 A1, US 2023 / 0028139 A1, etc., specifically for grinding rubber.

[0049] Regardless of the grinding method used, the method may include one step or more consecutive steps.

[0050] According to a preferred embodiment, the method according to the invention preferably includes a preliminary step prior to grinding, which involves substantially reducing the size of the silicone material, for example by cutting, shearing, or tearing, followed by at least one grinding step as described above, to obtain silicone powder. At the end of this preliminary step, the silicone material may be in the form of small particles or fragments, typically about 5-15 mm. The size of the particles or fragments is adjusted to be compatible with the means of feeding the material to the equipment used in the grinding step.

[0051] Furthermore, the method according to the invention may include subsequent steps of particle size classification, typically performed by sieving.

[0052] At the end of the grinding step, the organosilicon powder has an average particle size of 10 μm to 200 μm, preferably 10 μm to 100 μm, and even more preferably 15 μm to 50 μm.

[0053] Anti-caking additives, such as talc or calcium carbonate, can be added to silicone powders. Other process additives known in the powder industry, such as antistatic agents or agents that limit the water absorption of the powder, can also be added.

[0054] At the end of the grinding step, the organosilicon powder contains, on average, as much catalytic metal as the organosilicon material obtained by the polyaddition reaction and already ground. Therefore, the organosilicon powder preferably contains at least 5 ppm by mass, more preferably 5 ppm to 200 ppm, more preferably 6 ppm to 100 ppm, and even more preferably 10 ppm to 50 ppm of platinum metal, based on the total weight of the organosilicon composition.

[0055] Contrary to all expectations, the inventors of this invention have discovered that powders obtained by mechanically grinding certain crosslinked silicone elastomers possess catalytic properties for crosslinking new silicone elastomers. However, not wishing to be bound by this theory, the inventors believe that the catalytic metals contained in the initial silicone material, and most notably platinum, exist in the ground powder in a catalytically active form. The silicone powder can therefore be recycled as a catalytic feedstock into silicone compositions.

[0056] The method according to the invention includes mixing the organosilicon powder with at least one C2-C bonded to silicon per molecule. 12 The step of mixing an alkenyl group of organopolysiloxane and at least one organohydrogen polysiloxane to obtain a new organosilicon composition.

[0057] The content of organosilicon powder in the novel organosilicon composition according to the present invention is preferably 1%-70%, more preferably 5%-50%, and even more preferably 10%-40%.

[0058] According to one embodiment, the silicone powder is mixed with other components using methods typically used for mixing powdered fillers. Any apparatus known to those skilled in the art can be used, such as a Z-arm mixer or a butterfly mixer.

[0059] Optionally, the silicone powder may undergo surface treatment, which may be heat treatment, chemical treatment, or a combination of heat treatment and chemical treatment. The silicone composition may optionally contain an agent for treating the silicone powder. The silicone powder may be heat-treated before being mixed into the silicone composition. Alternatively, the silicone composition may be heat-treated after mixing the alkenyl organopolysiloxane, the silicone powder, and optionally the agent for treating the silicone powder.

[0060] Each molecule has at least two C2-C bonds with silicon. 12 The organopolysiloxane with an alkenyl group is preferably an organopolysiloxane formed from the following units:

[0061] - At least two silyloxy units of the following formula: Y a R 1 b SiO (4-a-b) / 2

[0062] Where Y represents C2-C 12 Alkenyl groups, preferably vinyl groups; R 1 This indicates a monovalent hydrocarbon group containing 1-12 carbon atoms, preferably selected from alkyl groups containing 1-8 carbon atoms such as methyl, ethyl, or propyl, cycloalkyl groups containing 3-8 carbon atoms, and aryl groups containing 6-12 carbon atoms; a = 1 or 2, b = 0, 1, or 2, and the sum of a + b = 1, 2, or 3.

[0063] - Optionally, the unit of the following formula: R 1 c SiO (4-c) / 2

[0064] Where R 1 It has the same meaning as above and c = 0, 1, 2 or 3.

[0065] It should be understood that in the above formula, if there are multiple R... 1 Groups can be the same as or different from each other.

[0066] In the following description of this organopolysiloxane, the following nomenclature is used to represent the silanoxy unit:

[0067] M: Silyoxyl unit R 1 3SiO 1 / 2 ,

[0068] M Vi Selected from YR 1 2SiO 1 / 2 and Y2R 1 SiO 1 / 2 The silyloxy unit,

[0069] D: Silyoxyl unit R 1 2SiO 2 / 2 ,

[0070] D Vi Selected from Y2SiO 2 / 2 and YR 1 SiO 2 / 2 The silyloxy unit,

[0071] T: Silyoxyl unit R 1 SiO 3 / 2 ,

[0072] Q: SiO₂ unit 4 / 2 ,

[0073] Where Y and R 1 As defined above.

[0074] As the terminal M and M Vi Examples of the unit may refer to trimethylsilyloxy, dimethylphenylsilyloxy, dimethylvinylsiloxy, or dimethylhexenylsiloxy.

[0075] As D and D ViExamples of the unit may refer to dimethylsiloxy, methylphenylsiloxy, methylvinylsiloxy, methylbutenylsiloxy, methylhexenylsiloxy, methyldecenylsiloxy, or methyldecadienylsiloxy.

[0076] As an example of a T-unit, methylsiloxy can be mentioned.

[0077] Each molecule has at least two C2-C bonds with silicon. 12 Alkenyl groups in organopolysiloxanes can have linear, branched, or cyclic structures.

[0078] According to one embodiment, each molecule has at least two C2-C bonds to silicon. 12 The organopolysiloxane with an alkenyl group is preferably composed essentially of silanoxy units D and / or D Vi and terminal silyloxy units M and / or M Vi The composition is a linear organopolysiloxane. Examples of linear organopolysiloxanes that can be organopolysiloxanes according to the present invention are:

[0079] - Poly(dimethylsiloxane) with a dimethylvinylsilyl end;

[0080] - Poly(dimethylsiloxane-co-methylphenylsiloxane) with dimethylvinylsilyl end groups;

[0081] - Poly(dimethylsiloxane-co-methylvinylsiloxane) having a dimethylvinylsilyl terminus; and

[0082] - Poly(dimethylsiloxane-co-methylvinylsiloxane) with a trimethylsilyl terminus.

[0083] Preferably, the organopolysiloxane comprises a terminal dimethylvinylsilyl unit, and even more preferably, the organopolysiloxane is a poly(dimethylsiloxane) having a dimethylvinylsilyl terminal.

[0084] According to one embodiment, the organopolysiloxane is an oil with a dynamic viscosity of 100 mPa·s-100,000 mPa·s, preferably 100 mPa·s-80,000 mPa·s, and more preferably 1,000 mPa·s-50,000 mPa·s.

[0085] According to another embodiment, the organopolysiloxane is a diorganopolysiloxane adhesive. This diorganopolysiloxane adhesive is a high molecular weight linear polymer with a viscosity greater than 600,000 mPa·s at 25°C, which typically corresponds to a molecular weight greater than 260,000 g / mol. The adhesive can have a consistency of 500 mm / 10 to 1000 mm / 10 at 25°C.

[0086] The consistency of the adhesive was determined at 25°C using a PNR12 or equivalent transilluminometer (allowing for the application of a cylindrical head to the sample under standardized conditions). The consistency is expressed as the depth to which a calibrated cylinder, expressed as one-tenth of a millimeter, penetrates the sample in one minute. For this purpose, the adhesive sample was introduced into an aluminum hopper with a diameter of 40 mm and a height of 60 mm. The bronze or brass cylindrical head, with a diameter of 6.35 mm and a height of 4.76 mm, was supported by a 51 mm long, 3 mm diameter metal rod suitable for the transilluminator. This rod was ballasted with an additional 100 g load. The total weight of the assembly was 151.8 g. The hopper containing the adhesive sample was placed in a constant temperature bath at 25°C ± 0.5°C for at least 30 minutes. This measurement was performed according to the manufacturer's instructions.

[0087] Although the adhesive is a linear polymer, the presence of small amounts of D or D-type polymers along the diorganopolysiloxane chain cannot be ruled out. Vi The presence of other units (e.g., T or Q units) in proportion to D and D Vi The number of units is at most 2%. Advantageously, the diorganopolysiloxane adhesive has a vinyl unit content of greater than 0.3%, preferably greater than 0.5%, more preferably 0.5%-6%, even more preferably 0.5%-4%, even more preferably 1%-3.5%.

[0088] According to another embodiment, each molecule has at least two C2-C bonds to silicon. 12 The alkenyl group of the organopolysiloxane is preferably a branched organopolysiloxane, characterized in that it contains at least T and / or Q units. It is preferably selected from organosilicon resins having the following formula:

[0089] - MD Vi Q, where vinyl is included in unit D.

[0090] - MD Vi T, where vinyl is included in the D unit.

[0091] - MD Vi TQ, in which vinyl is included in the D unit.

[0092] - MM Vi Q, where vinyl is included as a part of the M unit.

[0093] - MM Vi T, where vinyl is included as a part of the M unit.

[0094] - MM Vi TQ, in which vinyl is included as a part of the M unit.

[0095] - MM Vi DD Vi Q, in which vinyl is included in the M and D units.

[0096] - MM Vi DD Vi T, in which vinyl is included in the M and D units.

[0097] - and its mixtures.

[0098] Each molecule according to the invention has at least two C2-C bonds bonded to silicon. 12 The alkenyl group of organopolysiloxane can be a mixture of several organopolysiloxanes with different structures, such as a mixture of one or more linear organopolysiloxanes and one or more resins.

[0099] The organohydrogen polysiloxane is an organopolysiloxane containing at least two SiH units per molecule. Preferably, the organohydrogen polysiloxane compound contains at least three SiH units.

[0100] The organohydrogen polysiloxane can advantageously be an organosiloxane containing at least two, preferably at least three, silanoxy units of the following formula: H d R 2 e SiO (4-d-e) / 2

[0101] Where R 2 This indicates a monovalent group containing 1-12 carbon atoms, where d = 1 or 2, e = 0, 1 or 2, and d + e = 1, 2 or 3;

[0102] And optionally, other units having the following formula: R 2 f SiO (4-f) / 2 , where R 2 It has the same meaning as above, and f = 0, 1, 2 or 3.

[0103] It should be understood that if there are multiple R in the above formula... 2 If the groups are the same as or different from each other, then they can be the same as or different from each other.

[0104] Preferably, R 2It can represent a monovalent group selected from the following: an alkyl group having 1-8 carbon atoms, optionally substituted with at least one halogen atom such as chlorine or fluorine; a cycloalkyl group having 3-8 carbon atoms; and an aryl group having 6-12 carbon atoms. R 2 Advantageously selected from methyl, ethyl, propyl, 3,3,3-trifluoropropyl, xylyl, tolyl and phenyl.

[0105] The symbol d is preferably equal to 1.

[0106] In the following section describing organohydrogen polysiloxanes, the following nomenclature is used to represent the silanoxy unit:

[0107] M: Silyoxyl unit R 2 3SiO 1 / 2 ,

[0108] M′: Silyoxyl unit R 2 2HSiO 1 / 2 ,

[0109] D: Silyoxyl unit R 2 2SiO 2 / 2 ,

[0110] D': Silyoxyl unit R 2 HSiO 2 / 2 ,

[0111] T: Silyoxyl unit R 2 SiO 3 / 2 ,

[0112] Q: SiO₂ unit 4 / 2 ,

[0113] Where R 2 As defined above.

[0114] The organohydrogen polysiloxane may have a linear, branched, or cyclic structure. The degree of polymerization is preferably greater than or equal to 2. Typically, it is less than 5000. Preferably, the viscosity of the organohydrogen polysiloxane is 1 mPa·s to 5000 mPa·s, more preferably 1 mPa·s to 2000 mPa·s, and even more preferably 5 mPa·s to 1000 mPa·s.

[0115] When linear polymers are involved, they are essentially composed of silanoxy units: silanoxy units D and / or D' and silanoxy units M and / or M'. When cyclic polymers are involved, they are essentially composed of silanoxy units D and / or D'. Examples of organohydrogen polysiloxanes that can be organohydrogen polysiloxanes according to the present invention are:

[0116] - Poly(dimethylsiloxane) with a hydrogen dimethylsilyl terminus;

[0117] - Poly(dimethylsiloxane-co-methylhydrosiloxane) with trimethylsilyl ends;

[0118] - Poly(dimethylsiloxane-co-methylhydrosiloxane) with a dimethylsilyl end;

[0119] - Poly(methylhydrosiloxane) with a trimethylsilyl terminus; and

[0120] - Cyclic poly(methylhydrosiloxane).

[0121] When the organohydrogen polysiloxane has a branched structure, it is preferably selected from organosilicon resins of the following formula:

[0122] - M'Q, where the hydrogen atom bonded to the silicon atom is carried by the M group.

[0123] - MM'Q, where the hydrogen atoms bonded to silicon atoms are carried by a portion of the M units.

[0124] - MD'Q, where the hydrogen atom bonded to the silicon atom is carried by the D group.

[0125] - MDD'Q, where the hydrogen atoms bonded to silicon atoms are partially carried by D groups.

[0126] - MM'TQ, where the hydrogen atoms bonded to silicon atoms are carried by a portion of the M units.

[0127] - MM'DD'Q, where the hydrogen atoms bonded to silicon atoms are carried by a portion of the M and D units.

[0128] - and its mixtures.

[0129] Preferably, the organohydrogen polysiloxane has a mass content of 0.2%-91% of silyl Si-H functional groups, more preferably 3%-80%, and even more preferably 15%-70%.

[0130] The organohydrogen polysiloxane according to the present invention can be a mixture of several organohydrogen polysiloxanes with different structures, such as a mixture of one or more linear organohydrogen polysiloxanes and one or more resins.

[0131] The organosilicon powder according to the invention is recycled into a new organosilicon composition in which it is used as a catalytic feedstock. The catalytic feedstock function of the organosilicon powder according to the invention is demonstrated, enabling new uses for the organosilicon powder. It can constitute a supply of catalytic feedstock for a new organosilicon composition on its own. Alternatively, it can be combined with another polyaddition catalyst to constitute an additional supply of catalytic feedstock, thereby obtaining either a more reactive composition (with higher crosslinking kinetics) or a composition with the same reactivity but with fewer additional polyaddition catalysts.

[0132] According to a first embodiment, the organosilicon powder according to the invention is the sole catalytic raw material for the novel organosilicon composition. According to a preferred variant, no additional platinum, palladium, ruthenium, or rhodium-based catalysts are used in the method according to the invention. For example, the total weight of platinum-based compounds added to the novel organosilicon composition (excluding the organosilicon powder), calculated in platinum metal weight, is preferably less than 5 ppm, more preferably 0-2 ppm, based on the total weight of the novel organosilicon composition.

[0133] According to a second embodiment, the novel organosilicon composition further comprises an additional polyaddition catalyst. In this case, the catalytic feedstock consists of organosilicon powder according to the invention and the additional polyaddition catalyst. The additional polyaddition catalyst may be selected from catalysts well known to those skilled in the art, particularly those described herein as above. The mass ratio (by weight of metal) between the catalytic metal (preferably platinum) provided via the organosilicon powder according to the invention and the catalytic metal (preferably platinum) provided via the additional polyaddition catalyst may be between 1:100 and 100:1, or between 1:50 and 50:1, or between 1:10 and 10:1, or between 1:5 and 5:1, or between 1:2 and 2:1.

[0134] In the first or second embodiment, the total weight of the catalyst, calculated by the weight of platinum metal, is preferably between 2 ppm and 400 ppm by mass, more preferably between 5 ppm and 200 ppm, more preferably between 6 ppm and 100 ppm, and even more preferably between 10 ppm and 50 ppm, based on the total weight of the new organosilicon composition.

[0135] The new organosilicon composition may also include functional additives commonly found in organosilicon compositions. Categories of commonly used functional additives may be mentioned:

[0136] - Fillers, typically reinforced, semi-reinforced, or augmented fillers, as well as functional fillers such as thermally conductive and electrically conductive fillers.

[0137] - Adhesion accelerator,

[0138] - Inhibitors or retarder of the hydrosilylation reaction

[0139] - Adhesive modifier,

[0140] - Organosilicon resin,

[0141] - An additive used to improve viscosity.

[0142] - Pigments (organic or inorganic pigments)

[0143] - Additives for heat resistance, oil resistance, or flame retardancy, such as metal oxides, and

[0144] - A pore-forming agent used to manufacture foam.

[0145] The filler provided is preferably mineral. This filler can be a very finely divided product with an average particle size of less than 0.1 µm. In particular, the filler can be siliceous. In the case of siliceous materials, they can function as reinforcing or semi-reinforcing fillers. Reinforcing siliceous fillers are selected from powders of colloidal silica, fumed silica, and precipitated silica, or mixtures thereof. These powders typically have an average particle size of less than 0.1 µm and a BET specific surface area greater than 30 m². 2 / g, preferably 30-350m 2 / g. Semi-reinforced silica fillers, such as diatomaceous earth or ground quartz, can also be used. These silicas can be added as is or after treatment with organosilicon compounds commonly used for this purpose. Among these compounds, methyl polysiloxanes such as hexamethyldisiloxane, octamethylcyclotetrasiloxane, methyl polysilazanes such as hexamethyldisilazane, hexamethylcyclotrisilazane, tetramethyldivinyldisilazane, chlorosilanes such as dimethyldichlorosilane, trimethylchlorosilane, methylvinyldichlorosilane, dimethylvinylchlorosilane, alkoxysilanes such as dimethyldimethoxysilane, dimethylvinylethoxysilane, trimethylmethoxysilane, and mixtures thereof can be mentioned. Regarding non-silica mineral materials, they can be used as semi-reinforced or filled mineral fillers. Examples of non-silica fillers that can be used alone or in mixtures include calcium carbonate optionally surface-treated with organic acids or esters of organic acids, calcined clay, rutile titanium dioxide, oxides of iron, zinc, chromium, zirconium, or magnesium, various forms of alumina (hydrated or non-hydrated), boron nitride, zinc barium white, barium metaborate, barium sulfate, and glass microspheres. These fillers are relatively coarse, typically with an average particle size greater than 0.1 µm and a specific surface area typically less than 30 m². 2 / g. These fillers may have been surface-modified with various organosilicon compounds commonly used for this purpose. Preferably, the filler is silica, and even more preferably fumed silica. Advantageously, the silica has a 75m² content. 2 / g-410m 2 / g BET specific surface area.

[0146] Because the new organosilicon composition also contains organosilicon powder, the typical amount of mineral filler (especially silica filler) can be reduced. For example, compared to the same organosilicon composition without organosilicon powder, the new organosilicon composition according to the invention may contain 10% less by weight, more preferably 20% less by weight, more preferably 30% less by weight, more preferably 40% less by weight, and even more preferably 50% less by weight of mineral filler.

[0147] The formulation of the organosilicon composition, the corresponding amounts of each component, and the properties and amounts of the fillers will be determined by those skilled in the art based on the desired new organosilicon material.

[0148] The novel organosilicon compositions according to the invention can be prepared from single-component, two-component, or multi-component systems. In a typical two-component or multi-component organosilicon composition, the composition is characterized in that one portion comprises organosilicon powder and optionally an additional polyaddition catalyst, and does not contain an organohydrogen polysiloxane, while at least one other portion comprises an organohydrogen polysiloxane and does not contain organosilicon powder and optionally an additional polyaddition catalyst.

[0149] The crosslinking step of this organosilicon composition has a variable duration, which depends particularly on the temperature and the organosilicon composition, and typically on the concentrations of catalysts and inhibitors in the organosilicon composition. If the reactivity between the pre-contacted parts is sufficient, the organosilicon composition can crosslink without external intervention. The crosslinking reaction can be thermally activated. Thermal activation of crosslinking is conventionally achieved by an oven or infrared source. This thermal activation can be supplemented by photochemical activation and / or electron bombardment. Crosslinking can be carried out at ambient temperature. However, preferably, the crosslinking temperature can be greater than 60°C, more preferably 80°C–200°C.

[0150] Depending on the formulation of the silicone composition, the resulting crosslinked silicone material can typically be a silicone elastomer (or "rubber"), silicone gel, or silicone foam. More specifically, new silicone materials containing recycled silicone powder can be selected from:

[0151] - RTV-type polyaddition crosslinked silicone elastomer;

[0152] - LSR type polyaddition crosslinked silicone elastomer;

[0153] - HCR type polyaddition crosslinked silicone elastomer;

[0154] - Polyaddition crosslinked silicone gel;

[0155] - Polyaddition crosslinked silicone foam.

[0156] From both a technical and environmental perspective, this new silicone material, which incorporates recycled silicone powder, offers numerous advantages.

[0157] From a technical perspective, these cross-linked silicone materials obtained using silicone powder according to the present invention do not differ significantly from the same cross-linked silicone materials obtained without silicone powder. In particular, the evaluated mechanical properties are substantially the same.

[0158] From an environmental perspective, because of the use of organosilicon powder, the new organosilicon material contains some recycled materials. Therefore, this invention helps to reduce waste generation through recycling.

[0159] The content of recycled product in the novel organosilicon composition according to the invention, and therefore in the crosslinked organosilicon material obtained from the composition, is preferably greater than 1%, or greater than 5%, or greater than 10%, or greater than 20%, or greater than 30%, and preferably less than 70%, or less than 50%, or less than 40%. The term "content of recycled product" refers to the mass percentage of recycled material in the product, as defined in European Standard EN 15343:2007 concerning recycled plastics.

[0160] However, the environmental benefits of this material are not limited to simply incorporating recycled materials. In fact, the organosilicon powder according to the invention can advantageously partially or completely replace the polyaddition catalyst necessary for the production of crosslinking materials. Currently, the polyaddition metal catalysts most preferably used in the field of polyaddition organosilicon elastomers are compounds derived from at least one metal belonging to the platinum group. However, platinum and other metals in the platinum group have very strong environmental impacts, especially due to their rarity and their extraction and processing processes. Life cycle analysis of platinum particularly highlights its impact on environmental indicators: climate change, fine particulate matter, freshwater acidification ecotoxicity, and depletion of mineral and metal resources. Platinum is listed in the EU's list of critical and strategic raw materials, highlighting the supply and environmental issues surrounding this resource. Therefore, the present invention proposes a solution to address the depletion of mineral and metal resources. The efficient use of such resources falls within the circular economy approach. Life cycle analysis of polyaddition organosilicon products has revealed that one of the major environmental challenges is the use of platinum-based catalysts. Therefore, replacing fresh polyaddition catalysts at least partially with the organosilicon powder according to the invention is a major advantage. In this way, the present invention advantageously contributes to the sustainable management and efficient use of natural resources.

[0161] For example, if the cross-linked silicone material obtained according to the present invention uses 25% by weight of silicone powder, a 20% reduction in the carbon footprint of the new material is observed compared with the same cross-linked silicone material without silicone powder.

[0162] The calculation of carbon footprint follows the GHG protocol and the standards ISO 14040 and 14044 for performing life cycle analysis (LCA). Detailed Implementation

[0163] Other details or advantages of the invention will become clearer from the embodiments given below by way of example only.

[0164] Example

[0165] Unless otherwise stated, percentages and ppm are weight percentages and weight ppm.

[0166] Several types of ground silicone powders were evaluated. Grinding was performed at ambient temperature in a mill with rotating parts. Particle size was evaluated using SEM images.

[0167] [Table 1]

[0168]

[0169] Examples 1, 2 and 3 :

[0170] Organosilicon compositions are prepared by mixing the following compounds:

[0171] - 63% dimethylvinylsilyl-terminated polydimethylsiloxane oil with a viscosity of approximately 10,000 mPa·s;

[0172] - 30% dimethylvinylsilyl-terminated polydimethylsiloxane oil with a viscosity of approximately 60,000 mPa·s;

[0173] - 6% poly(methylhydro)(dimethyl)siloxane oil with SiH groups in the middle and at the chain ends (α / ω), with a SiH content of about 2% by weight and a viscosity of about 400 mPa·s;

[0174] - 1% of polydimethylsiloxane oil with chain-terminal SiH groups (α / ω), having a SiH content of 5.7% by weight and a viscosity of approximately 8.5 mPa·s;

[0175] - 0.012% 1-ethynyl-1-cyclohexanol.

[0176] The ground organosilicon powder was incorporated into the organosilicon composition in various amounts, as shown in Table 2:

[0177] [Table 2]

[0178]

[0179] The product was poured into a mold with a diameter of 6 cm and a thickness of 6 mm, and then placed in an oven at 120°C. After a specified time, the product was removed from the oven, touched, and its crosslinking was evaluated.

[0180] - OK: The product has been cross-linked. After cross-linking, the obtained material is an organosilicon gel.

[0181] - NOK: The product is not cross-linked.

[0182] [Table 3]

[0183]

[0184] Examples 4 and 5 and Comparative Examples 1 and 2 :

[0185] The same organosilicon compositions as in Examples 1 to 3 were used. The ground organosilicon powder was incorporated into the organosilicon compositions in various amounts, as shown in Table 4:

[0186] [Table 4]

[0187]

[0188] The product was poured into a mold with a diameter of 6 cm and a thickness of 6 mm, and then placed in an oven at 120°C. After a specified time, the product was removed from the oven, touched, and its crosslinking was evaluated.

[0189] - OK: The product has been cross-linked. After cross-linking, the obtained material is an organosilicon gel.

[0190] - NOK: The product is not cross-linked.

[0191] Gel deposition standard: The product is placed in a test tube, which is itself placed in a chamber at 80°C. A rod is immersed in the test tube and raised and lowered within it at timed intervals by a mechanism of the device. When the product begins to gel, the rod is blocked in the product, thereby pulling the test tube out and stopping the timer. The recorded time characterizes the gelation time.

[0192] [Table 5]

[0193]

[0194] Examples 6, 7 and 8 and Comparative Example 3 :

[0195] Mix the compounds shown in Table 6 below:

[0196] [Table 6]

[0197]

[0198] Vinyl oil = Dimethylvinylsilyl-terminated polydimethylsiloxane oil with a viscosity of approximately 3500 mPa·s

[0199] Crosslinked oil = Trimethylsilyl-terminated dihydropolysiloxane oil with a SiH content of 44.5% by weight and a viscosity of approximately 20 mPa·s.

[0200] The product was poured into a mold with a diameter of 6 cm and a thickness of 6 mm, and then placed in an oven at 120°C. After a specified time, the product was removed from the oven, touched, and its crosslinking was evaluated.

[0201] - OK: The product has been cross-linked. After cross-linking, the obtained material is an organosilicon gel.

[0202] - NOK: The product is not cross-linked.

[0203] [Table 7]

[0204]

[0205] Examples 9-12 and Comparative Examples 4-6:

[0206] The ground organosilicon powder is incorporated into the polyaddition crosslinked HCR organosilicon composition.

[0207] [Table 8]

[0208]

[0209] Polyaddition crosslinking HCR grade, uncatalyzed, sold by Elkem Silicones.

[0210] Rheological measurements were performed using a Monsanto MDR rheometer at 170°C.

[0211] [Table 9]

[0212]

[0213] ST2 (“Scorch Time 2”) = Crosslinking Start Time

[0214] T50 = Time required to reach 50% of maximum torque value

[0215] T90 = Time required to reach 90% of maximum torque value

[0216] The ' / ' sign indicates that the value cannot be measured.

[0217] Although the crosslinking kinetics were slower than those of Comparative Composition 4, compositions 9, 10, 11, and 12, containing only silicone powders A or B, were found to crosslink well to produce HCR-type elastomers. In contrast, the comparative compositions containing silicone powder D were either not crosslinked (Comparative Composition 5) or under-crosslinked (Comparative Composition 6).

[0218] Example 13:

[0219] Parts A and B (percentages given by weight) are obtained by mixing the following compounds:

[0220] Part A:

[0221] - 20% dimethylvinylsilyl-terminated polydimethylsiloxane oil with a viscosity of approximately 100 mPa·s.

[0222] - 65% aluminum hydroxide (ATH) powder

[0223] - 15% silicone powder A

[0224] Part B:

[0225] - 10.5% dimethylvinylsilyl-terminated polydimethylsiloxane oil with a viscosity of approximately 100 mPa·s.

[0226] - 85.7% aluminum hydroxide (ATH) powder

[0227] - 1% trimethylsilyl and dimethylhydrosilyl end-capped copolydimethylhydromethyl polysiloxane oil with a viscosity of approximately 300 mPa·s.

[0228] - 2.6% dimethylhydrosilyl-terminated polydimethylsiloxane oil with a viscosity of approximately 8 mPa·s.

[0229] - 0.2% 1-ethynylcyclohexanol

[0230] Part A and part B were mixed in a 1:1 mass ratio. The composition was crosslinked after 1 hour and 40 minutes at 120°C to obtain a thermally conductive RTV-type silicone elastomer.

Claims

1. Use of the powder obtained by a method comprising the following steps as a catalytic feedstock for polyaddition crosslinking organosilicon compositions: - Provides organosilicon materials obtained through polyaddition reactions, and - Grind the material.

2. Use of the powder obtained by the method comprising the following steps for the complete or partial replacement of the polyaddition catalyst in a polyaddition crosslinking silicone composition: - Provides organosilicon materials obtained through polyaddition reactions, and - Grind the material.

3. A method for recycling organosilicon materials obtained through a polyaddition reaction, the method comprising the following steps: - Provides organosilicon materials obtained through polyaddition reactions. - Grind the material to obtain organosilicon powder. - mixing the powder with at least one organopolysiloxane having at least two C2-C6 alkenyl groups bonded to silicon per molecule and at least one organohydrogenpolysiloxane to obtain a silicone composition, and 12 - mixing the powder with at least one organopolysiloxane having at least two C2-C6 alkenyl groups bonded to silicon per molecule and at least one organohydrogenpolysiloxane to obtain a silicone composition, and - Crosslink the silicone composition to obtain a new silicone material containing recycled silicone powder.

4. The method of claim 3, wherein the organosilicon material obtained by the polyaddition reaction comprises at least 5 ppm by mass, more preferably 5 ppm to 200 ppm, more preferably 6 ppm to 100 ppm, and even more preferably 10 ppm to 50 ppm of platinum metal, based on the total weight of the organosilicon composition.

5. The method according to claim 3 or claim 4, wherein the content of organosilicon powder in the organosilicon composition is 1%-70%, more preferably 5%-50%, and even more preferably 10%-40% by weight.

6. The method according to any one of claims 3-5, wherein the organosilicon powder is the sole catalytic raw material of the organosilicon composition.

7. The method according to any one of claims 3-5, wherein the total weight content of the platinum-based compound added to the new organosilicon composition (excluding organosilicon powder) is, calculated by weight of platinum metal, preferably less than 5 ppm by mass, preferably 0 ppm to 2 ppm by mass, based on the total weight of the organosilicon composition.

8. The method according to any one of claims 3-5, wherein the organosilicon composition further comprises an additional polyaddition catalyst.

9. The method according to any one of claims 3-8, wherein the grinding step includes a preliminary step of reducing the size of the silicone material to a small size, preferably about 5 mm to 15 mm.

10. The method according to any one of claims 3-9, wherein the grinding step further comprises a subsequent step of particle size classification, preferably by sieving.

11. The method according to any one of claims 3-10, wherein the organosilicon powder has an average particle size of 10 μm-200 μm, preferably 10 μm-100 μm, and even more preferably 15 μm-50 μm.

12. The method according to any one of claims 3-11, wherein the grinding is carried out at a temperature greater than or equal to the ambient temperature.

13. The method according to any one of claims 3-11, wherein the grinding is cryogenic grinding.

14. The method according to any one of claims 3-13, wherein the grinding is performed using a mechanical mill, preferably selected from: a twin-roll mill, a disc mill, an impact mill, a hammer mill, a ball mill, a rod mill, and a knife mill, or using an extruder, preferably a twin-screw extruder or a single-screw extruder.

15. The method according to any one of claims 3-14, wherein the novel silicone material comprising the recycled silicone powder is a silicone elastomer, silicone gel, or silicone foam.

16. The method of claim 15, wherein the new silicone material comprising the recycled silicone powder is selected from the group consisting of: RTV-type polyaddition crosslinked silicone elastomers; LSR-type polyaddition crosslinked silicone elastomers; HCR-type polyaddition crosslinked silicone elastomers; polyaddition crosslinked silicone gels; and polyaddition crosslinked silicone foams.

17. An organosilicon composition comprising: - at least one organopolysiloxane having at least two C2-C20 alkenyl groups bonded to silicon per molecule, 12 - at least one organopolysiloxane having at least two C2-C20 alkenyl groups bonded to silicon per molecule, - At least one organohydrogen polysiloxane, and - Organosilicon powder obtained by grinding organosilicon materials obtained through polyaddition reaction.

18. An organosilicon material obtainable by crosslinking the organosilicon composition as defined in claim 17, comprising the recycled organosilicon powder.

19. The organosilicon material according to claim 18, wherein the material has a recycled product content of greater than 1% or greater than 5% or greater than 10% or greater than 20% or greater than 30%, and preferably less than 70% or less than 50% or less than 40%.

20. The silicone material according to claim 18 or claim 19, characterized in that Its carbon footprint is reduced by 20% compared to the same cross-linked silicone material without silicone powder.

21. A method for preparing organosilicon powder, the method comprising the following steps: - Provides organosilicon materials obtained through polyaddition reactions, and - Grind the material.

22. Organosilicon powder that can be obtained by the method defined in claim 21.

23. Use of the powder as defined in claim 22 as a catalytic feedstock for polyaddition crosslinking organosilicon compositions.

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