Method for recycling a silicone material

Abstract

The invention relates to a method for recycling a silicone material obtained via polyaddition reaction, the method comprising the following steps: providing a silicone material obtained via polyaddition reaction, grinding the material to obtain a silicone powder, mixing the powder with at least one organopolysiloxane having, per molecule, at least two alkenyl groups bonded to silicon and at least one organohydrogenpolysiloxane to obtain a silicone composition, and crosslinking the silicone composition, thereby obtaining a novel silicone material comprising the recycled silicone powder.

Description

[0001] DESCRIPTION

[0002] TITLE: Method for recycling a silicone material

[0003] Technical field

[0004] The present invention relates to the field of recycling a silicone material, and more precisely a silicone powder which can be recycled as a catalytic filler in a silicone composition crosslinking by polyaddition.

[0005] State of the prior art

[0006] The recycling of industrial and manufactured plastics, particularly used silicone products, is a very important contemporary issue. Recycling silicone polymers could reduce gas emissions (CO, CO2) related to the silicone industry by reducing the volume of silicone waste and providing new recycled materials for new uses.

[0007] The so-called mechanical recycling, as opposed to chemical recycling, of silicones is not new. Already in 1994, Japanese patent application JP H06-100779A from Shinetsu Chemical described a method for obtaining a molded silicone elastomer from a silicone elastomer powder and a binder. Said silicone elastomer powder is obtained by pulverizing an old crosslinked silicone elastomer, for example, burrs, sprues, and other waste from the silicone elastomer molding steps, but also from the molded objects themselves after use. After mixing with a binder, which may be a silicone elastomer composition, it is possible to reuse the composition in typical silicone elastomer applications. Similarly, US patent US 5,350,804 proposed recovering the whiskers of crosslinked silicone elastomers, grinding them finely and dispersing them in a matrix of an organic elastomer.The scientific publication by Ghosh et al. in 2003 (“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) proposes a study of the impact of incorporating mechanically ground crosslinked silicone elastomer powder into a virgin silicone elastomer. The difficulty of reincorporating ground silicone powder into a virgin matrix is ​​addressed, for example, in patent applications CN 108 276 776 A and CN 107 029 557 A, which propose carrying out a preliminary surface treatment of the powder. Neither of these two documents addresses the specific nature of the used silicone material, nor its initial production process.

[0008] In contrast to mechanical recycling, chemical recycling consists of depolymerizing the used silicone material by a chemical, and possibly thermal, process, typically in the presence of a catalyst. 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, a previously ground silicone elastomer used as an insulator is depolymerized using an alcoholysis agent, chosen from unsaturated alcohols, and a catalyst, chosen from a list of zinc catalysts. In

[0009] CN 117 209 843 A, the previously ground used silicone elastomer is first mixed with a solvent to swell it, then depolymerized using an alcoholysis agent.

[0010] 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 way of recycling silicone elastomers, consisting of using these used materials as a precursor for ceramics. For this, used silicone elastomers are pyrolyzed at 600°C or 850°C, then the resulting residues are used as mechanical reinforcement filler in new silicone elastomers.

[0011] It has emerged that, quite surprisingly, powders obtained by mechanical grinding of crosslinked silicone elastomer have only been considered as reinforcing filler in new silicone matrices. The objective of past studies was limited to incorporating as much powder as possible while maintaining correct mechanical properties compared to virgin silicone material.

[0012] Against all expectations, the inventors of the present invention discovered that the powders obtained by mechanical grinding of certain crosslinked silicone elastomers exhibited catalytic properties for the crosslinking of new silicone elastomers. Thanks to this discovery, the powders can now be used as catalytic fillers in certain systems.

[0013] Summary of the invention

[0014] The present invention relates to a method for mechanically recycling a silicone material. It will therefore be clear to those skilled in the art that this method does not include a chemical depolymerization step. Typically, this method preferably does not use an agent for chemically degrading the silicone material, in particular no alcoholysis agent, nor strong base or strong acid, nor possibly chain blockers. Preferably, the recycling method according to the present invention does not use a solvent. Those skilled in the art may refer to the public literature describing the chemical depolymerization routes for silicones, for example the review by Wolf, A.T. and Stammer, A., “Chemical Recycling of Silicones — Current State of Play (Building and Construction Focus)”, Polymers 2024, 16, 2220.

[0015] The present invention therefore relates to the use of a powder obtained by a method comprising the following steps: providing a silicone material obtained by polyaddition reaction, and grinding said material; as a catalytic filler for a silicone composition crosslinking by polyaddition, or to totally or partially replace the polyaddition catalyst in a silicone composition crosslinking by polyaddition.

[0016] The subject of the present invention is a method for recycling a silicone material obtained by polyaddition reaction, said method comprising the following steps: - having a silicone material obtained by polyaddition reaction,

[0017] - grind said material to obtain a silicone powder,

[0018] - mixing said powder with at least one organopolysiloxane having, per molecule, at least two C2-C12 alkenyl groups linked to silicon and at least one organohydrogenpolysiloxane to obtain a silicone composition, and

[0019] - crosslinking said silicone composition, to obtain a new silicone material comprising the recycled silicone powder.

[0020] Another subject of the present invention consists of the silicone composition comprising at least one organopolysiloxane having, per molecule, at least two C2-C12 alkenyl groups bonded to silicon, at least one organohydrogenpolysiloxane and a silicone powder obtained by grinding a silicone material obtained by polyaddition reaction. The new silicone material comprising said recycled silicone powder, capable of being obtained by crosslinking by polyaddition of said silicone composition, is also an object of the present invention.

[0021] Furthermore, the present invention relates to a method for preparing a silicone powder, said method comprising the following steps:

[0022] - have a silicone material obtained by polyaddition reaction, and

[0023] - crush said material.

[0024] The silicone powder obtainable by this method, and which can be recycled into a new silicone material, is also an object of the present invention.

[0025] Finally, the subject of the present invention is the use of said powder as a catalytic filler for a silicone composition crosslinking by polyaddition.

[0026] Detailed description of the invention

[0027] Unless otherwise indicated, all viscosities of the silicone oils discussed in this disclosure correspond to a dynamic viscosity quantity at 25°C known as “Newtonian”, i.e. the dynamic viscosity which is measured, in a manner known per se, with a Brookfield viscometer at a shear rate gradient sufficiently low so that the measured viscosity is independent of the rate gradient.

[0028] The present invention therefore relates to a method for recycling a silicone material obtained by polyaddition reaction. Also called hydrosilylation, the polyaddition reaction can be defined as the reaction of a compound comprising at least one double bond with a compound comprising at least one hydrogenosilyl function, i.e. a hydrogen atom linked to a silicon atom. The polyaddition reaction is notably used to crosslink silicone compositions comprising organopolysiloxanes bearing alkenyl units and organopolysiloxanes comprising hydrogenosilyl functions. By "silicone material obtained by polyaddition reaction" is meant in the present text any silicone material which has crosslinked following a polyaddition reaction in the presence of a metal polyaddition catalyst.

[0029] The polyaddition metal catalyst may in particular be chosen from platinum and rhodium compounds but also 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 applications 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.

[0030] 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 can typically be cited.It is also possible to use complexes of platinum and an organic product, such as those described in US patents 3,159,601 (platinum-olefin complexes), US 3,220,972 (complexes obtained by reaction of chloroplatinic acid with an alcohol, an ether or an aldehyde), EP 0 057 459 (platinum-styrene complexes), EP 0 188 978 (platinum-triene complexes) and EP 0 190 530 (platinum-alkenylcyclohexene complexes), and complexes of platinum and vinyl organosiloxanes, such as those described in US patents 3,419,593 (platinum-organosiloxane complexes with terminal unsaturation), US 3,715,334 (platinum-vinylsiloxane complexes in the absence of halogen) and US 3,814,730 (platinum-silane or unsaturated siloxane complexes). Preferably, the polyaddition catalyst is a Karstedt platinum, i.e. a Pt(O) of general formula Pt2(divinyltetramethyldisiloxane)3 (or abbreviated Pt2(DVTMS)3).

[0031] Alternatively, a polyaddition metal photocatalyst may be used. Such a catalyst may be activated by irradiation, preferably by UV irradiation. A platinum-based photocatalyst may be selected, for example, from: platinum bis(acetylacetonate), platinum trimethyl(acetylacetonate), platinum trimethyl(2,4-pentanedione), platinum trimethyl(3,5-heptanedione), platinum trimethyl(methyl acetoacetate), platinum bis(2,4-pentanedione), platinum bis(2,4-hexanedione), platinum bis(2,4-heptanedione), platinum bis(3,5-heptanedione) and platinum bis(1-phenyl-1,3-butanedione).

[0032] The silicone material obtained by polyaddition reaction preferably contains at least 5 ppm by mass of platinum metal, based on the total weight of the silicone composition, more preferably from 5 ppm to 200 ppm, more preferably from 6 ppm to 100 ppm, and even more preferably from 10 ppm to 50 ppm.

[0033] According to one embodiment, the silicone material obtained by polyaddition reaction can be chosen from silicone elastomers (or “rubber”), silicone gels and silicone foams. More specifically, the silicone material obtained by polyaddition reaction can be chosen from the group consisting of:

[0034] - a silicone elastomer crosslinked by polyaddition of the RTV type;

[0035] - a silicone elastomer crosslinked by polyaddition of the LSR type;

[0036] - a silicone elastomer crosslinked by polyaddition of the HCR type;

[0037] - a silicone gel crosslinked by polyaddition; and

[0038] - a silicone foam crosslinked by polyaddition.

[0039] Preferably, the silicone material obtained by polyaddition reaction can be chosen from silicone elastomers and silicone foams, more preferably silicone elastomers having a Shore A hardness of at least 20 and silicone foams.

[0040] The polyorganosiloxane-based compositions considered according to the invention can crosslink by polyaddition reactions either at room temperature or by exposure to heat. The expressions RTV, LSR and HCR are well known to those skilled in the art: RTV is the abbreviation for “Room Temperature Vulcanizing”; LSR is the abbreviation for “Liquid Silicone Rubber”; HCR is the abbreviation for “Heat Cured Rubber”.

[0041] An RTV can be one-part (RTV-1) or two-part (RTV-2). Before curing, the part(s) are in liquid or paste form. In the case of RTV-2, each part of the system includes either a crosslinker or a catalyst, and these two elements react together in a polyaddition reaction when the parts are mixed. Polyaddition RTV-1s are less common: the crosslinker and catalyst are supplied as a single part, but the polyaddition reaction is delayed by various retarding means.

[0042] An LSR comes in the form of a two-part liquid composition that is generally quite viscous. The two parts are mixed to initiate crosslinking.

[0043] Unlike RTVs and LSRs, an HCR is a high-consistency gum before crosslinking. It is typically obtained from silicone gums, i.e., linear chains of very high molecular weight polyorganosiloxanes. An HCR crosslinks with heat.

[0044] Silicone gels, half-solid, half-liquid, are traditionally used for the protection of electronic equipment sensitive to vibrations, shocks, temperature and as a basic medical material, in particular for the development of prostheses, implants or dressings. In this text, the expression "silicone gel" designates a crosslinked silicone product characterized in particular by a penetration rate (or "penetrability") of between 50 and 500 tenths of a mm. Penetrability is measured by penetrometry typically according to standard NF ISO 2137, using a penetrometer model PNR 12 Petrotest with a total weight of the rod and cone set at 62.5 g. The cone penetrability of a silicone gel is determined at 25°C by measuring the depth of penetration of the cone into the sample, this being obtained by releasing the cone assembly from the penetrometer and leaving the cone to act for 5 seconds.The term "silicone foam" or "silicone foam" refers to an organopolysiloxane composition in the form of a foam. Generally speaking, a silicone foam can be obtained from a silicone composition which simultaneously crosslinks by polyaddition and releases a gas enabling the foaming phenomenon.

[0045] All silicone materials can come from various pre-consumer or post-consumer sources. Examples include cables and pipes, profiles, consumer or industrial molds, seals, foams, prototypes and 3D printing parts, etc.

[0046] Preferably, the silicone material obtained by polyaddition reaction does not contain, or substantially does not contain, amino compounds.

[0047] The recycling method according to the present invention comprises the step of providing a silicone material obtained by polyaddition reaction and grinding it to obtain a silicone powder.

[0048] The grinding method may be chosen from among the mechanical grinding methods for elastomers. Among these, mention may be made in particular of grinding at a temperature greater than or equal to room temperature and cryogrinding. By "grinding at a temperature greater than or equal to asbestos temperature" is meant a grinding process which is carried out at a temperature equal to or greater than 15°C, for example between 15°C and 150°C. A temperature control system, in particular a cooling system, may be provided to prevent excessive heating of the materials during the grinding step. In contrast, cryogrinding refers to a grinding step at very low temperature, carried out in the presence of a liquefied gas, generally liquid nitrogen. However, cryogrinding is not a preferred grinding method from an ecological point of view, cryogrinding being very energy-intensive.

[0049] A mill refers to the device for transforming the initial material into powder. The mill may be chosen from mechanical mills, which comprise one or more moving elements that come into contact with the silicone material to reduce it to powder. The mill may be chosen from: a twin-roll mill, a disc mill, an impact mill, a hammer mill, a ball mill, a rod mill, a knife mill. Alternatively, a mill using fluid energy, such as a jet mill, for example an air jet mill, may be used. According to another embodiment, the grinding may be carried out by extrusion, for example using a twin-screw extruder or a single-screw extruder.

[0050] The use of grinding machines with rotating parts, for example co-rotating twin-screw extruders, is described in particular for grinding rubber in patents ES 2276607 B1, US 9527978 B2, US 9598550 B2, WO 2022 / 044031 A1, US 2023 / 0028139 A1, etc.

[0051] Regardless of the grinding method implemented, this method may comprise one or more consecutive steps. According to a preferred embodiment, the method according to the invention preferably comprises a preliminary step to the grinding consisting of roughly reducing the size of the silicone material, for example by cutting, shearing or shredding, then at least one grinding step as described above, to obtain a silicone powder. At the end of this preliminary step, the silicone material may be in the form of chips or granules of small dimensions, typically of the order of 5 to 15 mm. The size of the chips or granules is adapted to be compatible with the feed device of the equipment of the grinding step.

[0052] Furthermore, the method according to the invention may comprise a subsequent step of granulometric classification, typically by sieving.

[0053] At the end of the grinding step, the silicone powder has an average particle size of between 10 pm and 200 pm, preferably between 10 pm and 100 pm, and even more preferably between 15 pm and 50 pm.

[0054] An anti-caking additive can be added to the silicone powder, for example talc or calcium carbonate. Other technological additives known in the field of powders can also be added, such as antistatic agents or to limit the water uptake of the powder.

[0055] At the end of the grinding step, the silicone powder contains on average as much catalytic metal as the silicone material obtained by polyaddition reaction which has been ground. Thus, the silicone powder preferably contains at least 5 ppm by mass of platinum metal, based on the total weight of the silicone composition, more preferably from 5 ppm to 200 ppm, more preferably from 6 ppm to 100 ppm, and even more preferably from 10 ppm to 50 ppm.

[0056] Against all expectations, the inventors of the present invention have discovered that the powders obtained by mechanical grinding of certain crosslinked silicone elastomers have catalytic properties for the crosslinking of new silicone elastomers. Without wishing to be bound by this theory, the inventors believe that the catalytic metal, and in particular platinum, contained in the initial silicone material is found in the ground powder in a catalytically active form. The silicone powder can therefore be recycled into a silicone composition as a catalytic filler.

[0057] The method according to the present invention comprises a step of mixing said silicone powder with at least one organopolysiloxane having, per molecule, at least two C2-C12 alkenyl groups bonded to silicon and at least one organohydrogenpolysiloxane to obtain a new silicone composition. The content of silicone powder in the new silicone composition according to the invention may preferably be between 1% and 70%, more preferably between 5% and 50%, and even more preferably between 10% and 40% by weight.

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

[0059] Optionally, the silicone powder may undergo a surface treatment, which may be a heat treatment, a chemical treatment, or a combination of a heat treatment and a chemical treatment. The silicone composition may optionally comprise a silicone powder treatment agent. A heat treatment may be performed on the silicone powder before it is mixed into the silicone composition. Alternatively, the silicone composition may be subjected to a heat treatment after mixing the alkenylated organopolysiloxane, the silicone powder, and optionally the silicone powder treatment agent.

[0060] The organopolysiloxane having, per molecule, at least two C2-C12 alkenyl groups linked to silicon, may preferably be an organopolysiloxane formed:

[0061] - at least two siloxyl units of the following formula: Y a R 1 bSiO<4 ab) / 2 in which Y represents a C2-C12 alkenyl group, preferably a vinyl group; R 1 represents a monovalent hydrocarbon group having from 1 to 12 carbon atoms, preferably selected from alkyl groups having from 1 to 8 carbon atoms such as methyl, ethyl, propyl groups, cycloalkyl groups having from 3 to 8 carbon atoms and aryl groups having from 6 to 12 carbon atoms; a = 1 or 2, b = 0, 1 or 2 and the sum a+b = 1, 2 or 3, and

[0062] - possibly patterns of the following formula: R 1 c SiO<4 C ) / 2 in which R 1 has the same meaning as above and c = 0, 1, 2 or 3.

[0063] It is understood in the above formulas that, if several R groups 1 are present, they can be the same or different from each other.

[0064] In the following section regarding the description of this organopolysiloxane, the following nomenclature has been used to represent the siloxyl units:

[0065] M: siloxyl unit R'sSiO ,

[0066] M V1 : siloxyl unit chosen from YR^SiO and Y2R 1 SiOi / 2, D: siloxyl unit R USiCL^.

[0067] D V1 : siloxyl unit chosen from Y2SiC>2 / 2 and YR'SiCL^,

[0068] T: siloxyl unit R'SiOs^, Q: siloxyl unit SiC>4 / 2, with Y and R 1 as defined above. As examples of terminal motifs M and M V1 , we can cite the trimethylsiloxy, dimethylphenylsiloxy, dimethylvinylsiloxy or dimethylhexenylsiloxy groups.

[0069] As examples of patterns D and D V1 , we can cite the dimethylsiloxy, methylphenylsiloxy, methylvinylsiloxy, methylbutenylsiloxy, methylhexenylsiloxy, methyldecenylsiloxy or methyldecadienylsiloxy groups.

[0070] Examples of T units include the methylsiloxy group.

[0071] The organopolysiloxane having, per molecule, at least two C2-C12 alkenyl groups linked to silicon, can have a linear, branched, or cyclic structure.

[0072] According to one embodiment, the organopolysiloxane having, per molecule, at least two C2-C12 alkenyl groups linked to silicon, may preferably be a linear organopolysiloxane essentially consisting of siloxyl units D and / or D V1 , and terminal siloxyl units M and / or M V1 . Examples of linear organopolysiloxanes which may be an organopolysiloxane according to the invention are:

[0073] - a poly(dimethylsiloxane) with dimethylvinylsilyl ends;

[0074] - a poly(dimethylsiloxane-co-methylphenylsiloxane) with dimethylvinylsilyl ends;

[0075] - a poly(dimethylsiloxane-co-methylvinylsiloxane) with dimethylvinylsilyl ends; and

[0076] - a poly(dimethylsiloxane-co-methylvinylsiloxane) with trimethylsilyl ends.

[0077] Preferably, the organopolysiloxane contains terminal dimethylvinylsilyl units and even more preferably the organopolysiloxane is a poly(dimethylsiloxane) with dimethylvinylsilyl ends.

[0078] According to one embodiment, the organopolysiloxane is an oil with a dynamic viscosity of between 100 mPa.s and 100,000 mPa.s, preferably between 100 mPa.s and 80,000 mPa.s, and more preferably between 1000 mPa.s and 50,000 mPa.s.

[0079] In another embodiment, the organopolysiloxane is a diorganopolysiloxane gum. Diorganopolysiloxane gums are linear, high molecular weight polymers 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. Said gum may have a consistency at 25°C of between 500 mm / 10 and 1000 mm / 10.

[0080] The consistency of a gum is determined at 25°C using a PNR12 type penetrometer or equivalent model allowing a cylindrical head to be applied to the sample under standardized conditions. The consistency of a gum is the depth, expressed in tenths of a millimeter, to which a calibrated cylinder penetrates the sample for one minute. For this purpose, a gum sample is placed in an aluminum cup with a diameter of 40 mm and a height of 60 mm. The bronze or brass cylindrical head measures 6.35 mm in diameter and 4.76 mm in height and is carried by a metal rod 51 mm long and 3 mm in diameter which fits the penetrometer. This rod is weighted with an additional weight of 100 g. The total weight of the assembly is 151.8 g. The cup containing the gum sample is placed in the thermostatically controlled bath at 25°C ± 0.5 for at least 30 minutes. The measurement is carried out following the manufacturer's instructions.

[0081] Although gums are linear polymers, the presence along the diorganopolysiloxane chain of small amounts of units other than D or D V1 , for example of T or Q motifs, is however not excluded in the proportion of at most 2% in relation to the number of D and D motifs V1 Advantageously, the diorganopolysiloxane gum has a mass content of vinyl units greater than 0.3%, preferably greater than 0.5%, more preferably between 0.5% and 6%, even more preferably between 0.5% and 4%, and even more preferably between 1% and 3.5%.

[0082] According to yet another embodiment, the organopolysiloxane having, per molecule, at least two C2-C12 alkenyl groups linked to silicon, may preferably be a branched organopolysiloxane, characterized in that it comprises at least T and / or Q units. It is preferably chosen from the group consisting of silicone resins of the following formulae:

[0083] - MD V1 Q where vinyl groups are included in the D motifs,

[0084] - MD V1 T where vinyl groups are included in the D units,

[0085] - MD V1 TQ where vinyl groups are included in the D motifs,

[0086] - MM V1 Q where vinyl groups are included in part of the M units,

[0087] - MM V1 T where vinyl groups are included in part of the M units,

[0088] - MM V1 TQ where vinyl groups are included in part of the M motifs,

[0089] - MM V1 DD V1 Q where vinyl groups are included in the M and D units,

[0090] - MM V1 DD V1 T where vinyl groups are included in the M and D units,

[0091] - and their mixtures,

[0092] The organopolysiloxane having, per molecule, at least two C2-C12 alkenyl groups linked to silicon, according to the invention may be a mixture of several organopoly siloxanes of different structure, for example one or more linear organopolysiloxanes and one or more resins.

[0093] Organohydrogenpolysiloxane is an organopolysiloxane having, per molecule, at least two SiH units. Preferably, the organohydrogenpolysiloxane compound comprises at least three SiH units.

[0094] The organohydrogenpolysiloxane may advantageously be an organopolysiloxane comprising at least two, preferably at least three, siloxyl units of the following formula: HdR 2 e SiO(4 d e ) / 2 in which R 2 represents a monovalent radical having from 1 to 12 carbon atoms, d = 1 or 2, e = 0, 1 or 2 and d+e = 1, 2 or 3; and optionally other units of the following formula: R 2 fSiO<4 f) / 2 in which R 2 has the same meaning as above, and f = 0, 1, 2, or 3. It is understood that, if several groups R 2 are present in the above formulas, they can be the same or different from each other.

[0095] Preferably, R 2may represent a monovalent radical selected from the group consisting of alkyl groups having 1 to 8 carbon atoms, optionally substituted by at least one halogen atom such as chlorine or fluorine, cycloalkyl groups having 3 to 8 carbon atoms and aryl groups having 6 to 12 carbon atoms. R 2 may advantageously be selected from the group consisting of methyl, ethyl, propyl, 3,3,3-trifluoropropyl, xylyl, tolyl and phenyl.

[0096] The symbol d is preferably equal to 1.

[0097] In the following section regarding the description of organohydrogenpolysiloxane, the following nomenclature has been used to represent the siloxyl units:

[0098] M: siloxyl unit R 2 3SiOi / 2,

[0099] M': siloxyl motif R 2 2HSiOi / 2,

[0100] D: siloxyl unit R 2 2SiC>2 / 2,

[0101] D': siloxyl motif R 2 HSiC>2 / 2,

[0102] T: siloxyl unit R 2 SiC>3 / 2,

[0103] Q: siloxyl unit SiC>4 / 2, with R 2 as defined above.

[0104] The organohydrogenpolysiloxane may have a linear, branched, or cyclic structure. The degree of polymerization is preferably greater than or equal to 2. Generally, it is less than 5000. Preferably, the viscosity of the organohydrogenpolysiloxane is between 1 mPa.s and 5000 mPa.s, more preferably between 1 mPa.s and 2000 mPa.s, and even more preferably between 5 mPa.s and 1000 mPa.s.

[0105] When linear polymers are concerned, these are essentially constituted of siloxyl units D and / or D', and of terminal siloxyl units M and / or M'. When cyclic polymers are concerned, these are essentially constituted of siloxyl units D and / or D'. Examples of organohydrogenpolysiloxanes which may be organohydrogenpolysiloxanes according to the invention are:

[0106] - a poly(dimethylsiloxane) with hydrogenodimethylsilyl ends;

[0107] - a poly(dimethylsiloxane-co-methylhydrogensiloxane) with trimethylsilyl ends;

[0108] - a poly(dimethylsiloxane-co-methylhydrogensiloxane) with hydrogenodimethylsilyl ends;

[0109] - a poly(methylhydrogensiloxane) with trimethylsilyl ends; and

[0110] - a cyclic poly(methylhydrogensiloxane).

[0111] When the organohydrogenpolysiloxane has a branched structure, it is preferably chosen from the group consisting of silicone resins of the following formulae:

[0112] - M'Q where the hydrogen atoms linked to silicon atoms are carried by the M groups; - MM'Q where the hydrogen atoms linked to silicon atoms are carried by part of the M units;

[0113] - MD'Q where the hydrogen atoms linked to silicon atoms are carried by the D groups;

[0114] - MDD'Q where the hydrogen atoms linked to silicon atoms are carried by part of the D groups;

[0115] - MM'TQ where the hydrogen atoms linked to silicon atoms are carried by part of the M motifs;

[0116] - MM'DD'Q where the hydrogen atoms linked to silicon atoms are carried by part of the M and D motifs;

[0117] - and their mixtures.

[0118] Preferably, the organohydrogenpolysiloxane has a mass content of hydrogenosilyl SiH functions of between 0.2% and 91%, more preferably between 3% and 80% and even more preferably between 15% and 70%.

[0119] The organohydrogenpolysiloxane according to the invention may be a mixture of several organohydrogenpolysiloxanes of different structure, for example one or more linear organohydrogenpolysiloxanes and one or more resins.

[0120] The silicone powder according to the present invention is recycled into the new silicone composition, where it is used as a catalytic filler. The catalytic filler function of the silicone powder according to the present invention is remarkable, and makes it possible to propose new uses for this silicone powder. It can constitute on its own the contribution of catalytic filler to a new silicone composition. Alternatively, it can constitute, in combination with an additional polyaddition catalyst, an additional contribution of catalytic filler, making it possible either to obtain a more reactive composition, the crosslinking kinetics of which will be higher, or to obtain a composition of the same reactivity but with less additional polyaddition catalyst.

[0121] According to a first embodiment, the silicone powder according to the present invention is the only catalytic filler of the new silicone composition. According to a preferred variant, in the process according to the invention, no additional catalyst based on platinum, palladium, ruthenium or rhodium is used. For example, the total weight quantity of platinum-based compounds added to the new silicone composition (excluding silicone powder), calculated as the weight of platinum-metal, is preferably less than 5 ppm by mass, preferably between 0 and 2 ppm by mass, based on the total weight of the new silicone composition.

[0122] According to a second embodiment, the new silicone composition further comprises an additional polyaddition catalyst. In this case, the catalytic charge consists of the silicone powder according to the invention and an additional polyaddition catalyst. Said additional polyaddition catalyst may be chosen from catalysts well known to those skilled in the art, in particular those described above in the present text. The mass ratio between the catalytic metal, preferably platinum, provided via the silicone powder according to the invention and the catalytic metal, preferably platinum, provided via the additional polyaddition catalyst (by weight of metal) 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.

[0123] In the first embodiment or in the second embodiment, the total weight quantity of catalyst, calculated as the weight of platinum metal, is preferably between 2 ppm and 400 ppm by mass, preferably between 5 ppm and 200 ppm, more preferably from 6 ppm to 100 ppm, and even more preferably from 10 ppm to 50 ppm based on the total weight of the new silicone composition.

[0124] The new silicone composition may also include functional additives that are common in silicone compositions. Examples of common functional additive families include:

[0125] - fillers, typically reinforcing, semi-reinforcing, or bulking fillers, and functional fillers, such as thermally conductive fillers and electroconductive fillers

[0126] - adhesion promoters,

[0127] - inhibitors or retarders of the hydrosilylation reaction,

[0128] - adhesion modulators,

[0129] - silicone resins,

[0130] - additives to increase consistency,

[0131] - pigments (organic or mineral),

[0132] - thermal resistance, oil resistance or fire resistance additives, for example metal oxides, and

[0133] - pore-forming agents for the manufacture of foams.

[0134] The filler that may be provided is preferably mineral. The filler may be a very finely divided product with an average particle diameter of less than 0.1 μm. The filler may be siliceous in particular. In the case of siliceous materials, they may act as reinforcing or semi-reinforcing fillers. The reinforcing siliceous fillers are chosen from colloidal silicas, combustion and precipitation silica powders or mixtures thereof. These powders have an average particle size generally less than 0.1 μm (micrometers) and a BET specific surface area greater than 30 m 2 / g, preferably between 30 and 350 m 2 / g. Semi-reinforcing siliceous fillers such as diatomaceous earth or ground quartz may also be used. These silicas may be incorporated as such or after being treated with organosilicon compounds commonly used for this purpose. These compounds include methylpolysiloxanes such as hexamethyldisiloxane, octamethylcyclotetrasiloxane, methylpolysilazanes such as hexamethyldisilazane, hexamethylcyclotrisilazane, tetramethyldivinyldisilazane, chlorosilanes such as dimethyldichlorosilane, trimethylchlorosilane, methylvinyldichlorosilane, dimethylvinylchlorosilane, alkoxysilanes such as dimethyldimethoxysilane, dimethylvinylethoxysilane, trimethylmethoxysilane, and mixtures thereof. As for non-siliceous mineral materials, they can be used as semi-reinforcing or bulking mineral fillers.Examples of these non-siliceous fillers that can be used alone or in mixtures are calcium carbonate, possibly surface-treated with an organic acid or an ester of an organic acid, calcined clay, rutile-type titanium oxide, iron, zinc, chromium, zirconium, magnesium oxides, different forms of alumina (hydrated or not), boron nitride, lithopone, barium metaborate, barium sulfate and glass microbeads. These fillers are coarser with generally an average particle diameter greater than 0.1 µm and a specific surface generally less than 30 µm. 2 / g. These fillers may have been surface-modified by treatment with the various organosilicon compounds usually used for this purpose. Preferably, the filler is silica, and even more preferably combustion silica. Advantageously, the silica has a BET specific surface area of ​​between 75 m 2 / g and 410 m 2 / g.

[0135] The new silicone composition further comprising silicone powder, it is possible to reduce the typical quantity of mineral fillers, in particular silica fillers. For example, compared to the same silicone composition without silicone powder, the new silicone composition according to the invention may contain 10% by weight, more preferably 20% by weight, more preferably 30% by weight, more preferably 40% by weight, and even more preferably 50% by weight, less mineral fillers.

[0136] The formulation of the silicone composition, the respective quantities of the different components, and the nature and quantity of fillers will be defined by those skilled in the art depending on the desired new silicone material.

[0137] The novel silicone composition according to the invention can be prepared from a single-component, two-component or multi-component system. In the typical case of two- or multi-component silicone compositions, the silicone composition is characterized in that one of the parts comprises the silicone powder, and optionally the additional polyaddition catalyst, and does not comprise organohydrogenpolysiloxane, while at least one other part comprises the organohydrogenpolysiloxane and does not comprise the silicone powder, and optionally the additional polyaddition catalyst.

[0138] The step of crosslinking the silicone composition may have a variable duration depending in particular on the temperature and the silicone composition, typically the concentration of catalyst and inhibitor in the silicone composition. The silicone composition may crosslink without external intervention if the reactivity between the parts brought into contact beforehand is sufficient. It is possible to thermally activate the crosslinking reaction. The means of thermal activation of the crosslinking are conventionally ovens or infrared sources. This thermal activation may be supplemented by actinic activation and / or by electron bombardment. The crosslinking may be carried out at room temperature. However, preferably, the crosslinking temperature may be greater than 60°C, preferably between 80°C and 200°C.

[0139] Depending on the formulation of the silicone composition, the silicone material obtained after crosslinking can typically be a silicone elastomer (or “rubber”), a silicone gel or a silicone foam. More specifically, the new silicone material comprising the recycled silicone powder can be selected from the group consisting of:

[0140] - a silicone elastomer crosslinked by polyaddition of the RTV type;

[0141] - a silicone elastomer crosslinked by polyaddition of the LSR type;

[0142] - a silicone elastomer crosslinked by polyaddition of the HCR type;

[0143] - a silicone gel crosslinked by polyaddition;

[0144] - a silicone foam crosslinked by polyaddition.

[0145] This new silicone material, comprising recycled silicone powder, has many advantageous aspects from a technical and environmental point of view.

[0146] From a technical point of view, these crosslinked silicone materials, obtained according to the present invention using the silicone powder, do not present any major differences compared to the same crosslinked silicone materials which would have been obtained without the silicone powder. In particular, the mechanical performances evaluated are substantially identical.

[0147] From an environmental point of view, thanks to the use of silicone powder, the new silicone material contains a portion of recycled materials. The present invention thus contributes to reducing waste generation through recycling.

[0148] The content of recycled products in the novel silicone composition according to the invention, and consequently in the crosslinked silicone material obtained from this composition, may preferably be greater than 1%, or greater than 5%, or greater than 10%, or greater than 20%, or greater than 30%, and preferably be less than 70%, or less than 50% or less than 40%. By "recycled product content" is meant the proportion by mass of recycled material in a product, as defined in the European standard EN 15343: 2007 on recycled plastics.

[0149] However, the environmental benefit of this material is not limited to the simple incorporation of a recycled material. Indeed, the silicone powder according to the invention can advantageously partially or totally replace the polyaddition catalyst essential for the production of the crosslinked material. Currently, the polyaddition metal catalyst very preferably used in the field of polyaddition silicone elastomers is a compound derived from at least one metal belonging to the platinum group. However, the environmental impact of platinum and other platinum group metals is very high, in particular due to their rarity, their extraction and treatment process. The life cycle analysis of platinum highlights in particular the impact on environmental indicators: climate change, fine particles, acidification, ecotoxicity in fresh water, depletion of mineral resources and metals.Platinum is listed on the European Union's list of critical and strategic raw materials, highlighting the supply and environmental issues surrounding this resource. The present invention thus offers a solution to the depletion of mineral and metal resources. This efficient use of resources is part of a circular economy approach. A life cycle analysis of polyaddition silicone products has highlighted that one of the main environmental issues is the use of a platinum-based catalyst. Also, the at least partial replacement of the new polyaddition catalyst by the silicone powder according to the invention is a major advantage. In this way, the present invention advantageously contributes to sustainable management and efficient use of natural resources.

[0150] For example, if the crosslinked 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 to the same crosslinked silicone material without silicone powder.

[0151] The carbon footprint calculation follows the “GHG Protocol” and ISO 14040 and 14044 standards for carrying out life cycle analyses (LCA).

[0152] Other details or advantages of the invention will appear more clearly from the examples given below for information purposes only.

[0153] Examples

[0154] Unless otherwise stated, % and ppm are % by weight and ppm by weight.

[0155] Several ground silicone powders were evaluated. Grinding was carried out in a rotating grinding machine at room temperature. The particle size distribution of the powders was evaluated by SEM photographs.

[0156] [Table 1]

[0157] Examples 1, 2 and 3:

[0158] A silicone composition was prepared by mixing the following compounds:

[0159] - 63% of a polydimethylsiloxane oil with dimethylvinylsilyl ends, having a viscosity of approximately 10,000 mPa.s;

[0160] - 30% of a polydimethylsiloxane oil with dimethylvinylsilyl ends, having a viscosity of approximately 60,000 mPa.s;

[0161] - 6% of a poly(methylhydrogeno)(dimethyl)siloxane oil with SiH groups in the middle and end of the chain (a / co), having a SiH content of approximately 2% by weight, having a viscosity of approximately

[0162] 400 mPa.s;

[0163] - 1% of a polydimethylsiloxane oil with SiH groups at the end of the chain (a / co), having a SiH content of 5.7% by weight, having a viscosity of approximately 8.5 mPa.s;

[0164] - 0.012% 1-ethynyl-l-cyclohexanol.

[0165] The ground silicone powder was incorporated into the silicone composition at different rates as shown in Table 2:

[0166] [Table 2]

[0167] The product was poured into a 6 cm diameter and 6 mm thick mold, then placed in an oven at 120°C. After a defined time, the product was touched and its crosslinking was assessed.

[0168] - OK: the product is crosslinked. After crosslinking, the material obtained is a silicone gel.

[0169] - NOK: the product is not crosslinked.

[0170] [Table 3] Examples 4 and 5 and Comparatives 1 and 2:

[0171] The same silicone composition as in Examples 1 to 3 was used. The ground silicone powder was incorporated into the silicone composition at different rates as shown in Table 4:

[0172] [Table 4]

[0173] The product was poured into a 6 cm diameter and 6 mm thick mold, then placed in an oven at 120°C. After a defined time, the product was touched and its crosslinking was assessed.

[0174] - OK: the product is crosslinked. After crosslinking, the material obtained is a silicone gel.

[0175] - NOK: the product is not crosslinked. Norm gel: The product is placed in a test tube, itself placed in an enclosure at 80°C. A rod is immersed in the tube, rises and falls in it thanks to the mechanism of the device, in a timed manner. When the product begins to gel, the rod is blocked in the product, thus carrying the test tube, and stopping the stopwatch. The time recorded characterizes the gel time.

[0176] [Table 5]

[0177] Examples 6, 7 and 8 and Comparative 3:

[0178] The compounds shown in Table 6 below were mixed:

[0179] [Table 6]

[0180] Vinyl oil * = polydimethylsiloxane oil with dimethylvinylsilyl terminations, having a viscosity of approximately 3500 mPa.s

[0181] Crosslinking oil ** = dihydrogen poly siloxane oil with trimethylsilyl terminations, with a SiH content of 44.5% by weight, with a viscosity of approximately 20 mPa.s. The product was poured into a mold 6 cm in diameter and 6 mm thick, then placed in an oven at 120°C. After a defined time, the product was touched and its crosslinking was assessed.

[0182] - OK: the product is crosslinked. After crosslinking, the material obtained is a silicone gel.

[0183] - NOK: the product is not crosslinked.

[0184] [Table 7]

[0185] Examples 9-12 and Comparatives 4-6:

[0186] The ground silicone powder was incorporated into a HCR type silicone composition crosslinking by polyaddition.

[0187] [Table 8] *** HCR grade crosslinking by polyaddition, non-catalyzed, marketed by the company Elkem

[0188] Silicones

[0189] Rheometry measurements were performed using a Monsanto MDR rheometer at 170°C.

[0190] [Table 9]

[0191] TS2 (“Scorch Time 2”) = start time of crosslinking

[0192] T50 = time required to reach 50% of the maximum torque value

[0193] T90 = time required to reach 90% of the maximum torque value

[0194] “ / ” means the value was not measurable

[0195] Although the crosslinking kinetics are slower than those of comparative composition C.4, it is observed that compositions 9, 10, 11 and 12, containing only silicone powder A or B, crosslink well to produce an HCR type elastomer. In contrast, comparative compositions containing silicone powder D do not crosslink (C.5) or not sufficiently (C.6).

[0196] Example 13:

[0197] Parts A and B were obtained by mixing the compounds below (% are given by weight):

[0198] Part A:

[0199] - 20% polydimethylsiloxane oil with dimethylvinylsilyl ends, having a viscosity of approximately 100 mPa.s

[0200] - 65% aluminum hydroxide powder (ATH)

[0201] - 15% silicone powder A

[0202] Part B:

[0203] - 10.5% polydimethylsiloxane oil with dimethylvinylsilyl ends, having a viscosity of approximately 100 mPa.s

[0204] - 85.7% aluminum hydroxide powder (ATH)

[0205] - 1% of a co-dimethylhydrogenomethylpolysiloxane oil with trimethylsilyl and dimethylhydrogenosilyl endings, having a viscosity of approximately 300 mPa.s.

[0206] - 2.6% of a polydimethylsiloxane oil with dimethylhydrogenosilyl ends, having a viscosity of approximately 8 mPa.s.

[0207] - 0.2% 1-ethynylcyclohexanol

[0208] Part A and Part B were mixed in a mass ratio of 1:1. At 120°C, the composition had cured after 1 hour 40 minutes to a thermally conductive RTV silicone elastomer.

Claims

CLAIMS 1. Use of a powder obtained by a method comprising the following steps: - have a silicone material obtained by polyaddition reaction, and - grinding said material; as a catalytic filler for a silicone composition crosslinking by polyaddition.

2. Use of a powder obtained by a method comprising the following steps: - have a silicone material obtained by polyaddition reaction, and - grinding said material; to totally or partially replace the polyaddition catalyst in a silicone composition crosslinking by polyaddition.

3. Method for recycling a silicone material obtained by polyaddition reaction, said method comprising the following steps: - have a silicone material obtained by polyaddition reaction, - grind said material to obtain a silicone powder, - mixing said powder with at least one organopolysiloxane having, per molecule, at least two C2-C12 alkenyl groups linked to silicon and at least one organohydrogenpolysiloxane to obtain a silicone composition, and - crosslinking said silicone composition, to obtain a new silicone material comprising the recycled silicone powder.

4. Method according to claim 3, in which the silicone material obtained by polyaddition reaction contains at least 5 ppm by mass of platinum metal, based on the total weight of the silicone composition, more preferably from 5 ppm to 200 ppm, more preferably from 6 ppm to 100 ppm, and even more preferably from 10 ppm to 50 ppm.

5. Method according to claim 3 or claim 4, wherein the silicone powder content in the silicone composition is between 1% and 70%, more preferably between 5% and 50%, and even more preferably between 10% and 40% by weight.

6. Method according to any one of claims 3 to 5, in which the silicone powder is the only catalytic filler of the silicone composition.

7. Method according to any one of claims 3 to 5, in which the total weight quantity of platinum-based compounds added to the new silicone composition (excluding silicone powder), calculated by weight of platinum-metal, is preferably less than 5 ppm by mass, preferably between 0 and 2 ppm by mass, based on the total weight of the silicone composition.

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

9. Method according to any one of claims 3 to 8, in which the grinding step comprises a preliminary step of roughly reducing the size of the silicone material to small dimensions, preferably of the order of 5 mm to 15 mm.

10. Method according to any one of claims 3 to 9, in which the grinding step further comprises a subsequent step of particle size classification, preferably by sieving.

11. Method according to any one of claims 3 to 10, in which the silicone powder has an average particle size of between 10 pm and 200 pm, preferably between 10 pm and 100 pm, and even more preferably between 15 pm and 50 pm.

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

13. A method according to any one of claims 3 to 11, wherein the grinding is cryogrinding.

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

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

16. The method of claim 15, wherein the novel silicone material comprising the recycled silicone powder is selected from the group consisting of an RTV type polyaddition crosslinked silicone elastomer; an LSR type polyaddition crosslinked silicone elastomer; an HCR type polyaddition crosslinked silicone elastomer; a polyaddition crosslinked silicone gel; and a polyaddition crosslinked silicone foam.

17. Silicone composition comprising: - at least one organopolysiloxane having, per molecule, at least two C2-C12 alkenyl groups linked to silicon, - at least one organohydrogenopolysiloxane, and - a silicone powder obtained by grinding a silicone material obtained by polyaddition reaction.

18. Silicone material, obtainable by crosslinking the silicone composition as defined in claim 17, comprising said recycled silicone powder.

19. Silicone material according to claim 18, said material having a recycled content greater than 1%, or greater than 5%, or greater than 10%, or greater than 20%, or greater than 30%, and preferably being less than 70%, or less than 50% or less than 40%.

20. Silicone material according to claim 18 or claim 19, characterized in that its carbon footprint is reduced by 20%, compared to the same crosslinked silicone material without silicone powder.

21. Method for preparing a silicone powder, said method comprising the following steps: - have a silicone material obtained by polyaddition reaction, and - grinding said material.

22. Silicone powder obtainable by the method as defined in claim 21.

23. Use of the powder as defined in claim 22 as a catalytic filler for a silicone composition crosslinking by polyaddition.

Images