Method for treating and recycling a polyamide composition

Abstract

The invention relates to a method for treating a polyamide composition comprising at least one compound capable of generating phosphorus hydride, wherein the method comprises the steps of: (i) mixing the polyamide composition with at least one oxidising compound; (ii) reacting the polyamide composition with the at least one oxidising compound; (iii) optionally, drying the mixture obtained in step (i) at a temperature of 140°C or lower.

Description

[0001] METHOD FOR TREATING AND RECYCLING A COMPOSITION OF

[0002] POLYAMIDE

[0003] Field of invention

[0004] The present invention relates to a method for treating a polyamide composition, in particular a used polyamide composition, with a view to recycling it. The invention relates in particular to a method for reducing phosphine emissions during the recycling of a polyamide composition comprising compounds capable of generating phosphine emissions.

[0005] Technical background

[0006] Polyamides, particularly polyamide powders used for 3D printing or lithography printing, are generally stabilized by adding antioxidant compounds, particularly organic phosphites or phosphines. When recycling these polyamides, particularly by compounding, the organic phosphite or phosphine compounds decompose into phosphine (or phosphorus hydride PH3). This decomposition of phosphites or organic phosphine into phosphorus hydride occurs when recycling the polyamide at a temperature above 130°C (phosphorus hydride being generated above 130°C).

[0007] Phosphorus hydride, easily detected by its characteristic odor, is toxic by inhalation.

[0008] There is no method for preventing phosphorus hydride emissions. The current solution is to extract phosphorus hydride emissions, particularly by suction or by trapping them within a composition, for example through a Michael reaction.

[0009] Document CN 111499 922 concerns the use of an aldehyde to trap, by Michael reaction, the phosphine generated by the red phosphorus included in a polyamide matrix. This method therefore makes it possible to trap the emitted phosphine but does not prevent the formation of this phosphine. In addition, the addition of reactive molecules such as aldehydes within the polyamide matrix leads to a degradation of the properties of the resin and in particular its color.

[0010] There is therefore a real need to provide a process for treating polyamide compositions, in particular used polyamides, to avoid or at least reduce phosphorus hydride emissions during recycling or processing processes for these polyamides, in particular by compounding. There is a need to provide a process that does not trap the phosphine that forms but prevents its formation. It is also necessary to provide such a process that does not degrade the polyamide, so as not to have a reduction in the mechanical and rheological properties of the polyamide. In addition, there is a need to provide a process that makes it possible to obtain a recycled resin with a high use value, i.e. little degraded and little polluted.

[0011] Still other objectives will appear upon reading the description of the invention which follows.

[0012] Summary of the invention

[0013] The present application relates to a method for treating a polyamide composition comprising at least one compound capable of generating phosphorus hydride, comprising the steps of:

[0014] (i) Mixing the polyamide composition with at least one oxidizing compound;

[0015] (ii) Reaction between the polyamide composition and the at least one oxidizing compound, preferably at controlled temperature;

[0016] (iii) Optionally drying the mixture obtained in step (ii) at a temperature less than or equal to 140°C.

[0017] The oxidizing compound is preferably selected from inorganic oxidants, preferably inorganic peroxides or perchlorates, preferably in the form of an aqueous solution, preferably aqueous solutions of inorganic oxidants such as aqueous solutions of inorganic peroxides, in particular aqueous solutions of percarbonate, for example sodium percarbonate, of persulfates, for example sodium persulfate, or of hydrogen peroxide, and aqueous solutions of perchlorates, for example sodium perchlorate, or from organic peroxides such as methyl ethyl ketone peroxide, dibenzoyl peroxide, or di(n-propyl) peroxydicarbonate or peroxyesters. Preferably the oxidizing compound is an aqueous solution of hydrogen peroxide.

[0018] The compound capable of generating phosphorus hydride is preferably chosen from the group consisting of:

[0019] - hypophosphorous acid (H3PO2) or one of its salts;

[0020] - an organic phosphite, for example a phosphite of formula: P(OR)3 with R, identical or different, represents an organic residue notably chosen from phenyl; alkyl comprising from 1 to 20 carbon atoms, linear or branched; phenyl substituted by at least one, preferably 1, 2 or 3, alkyl group, identical or different, comprising from 1 to 20 carbon atoms, linear or branched; two Rs can be linked to form a cycle comprising the phosphorus atom and the two oxygen atoms carrying the two R groups linked together; with R, identical or different, represents an alkyl group comprising from 1 to 20 carbon atoms, linear or branched;

[0021] P(OR)2-O-Ph-CH(CH3)2-Ph-OP(OR)2 with R, identical or different, representing an alkyl group comprising from 1 to 20 carbon atoms, linear or branched and Ph representing a phenyl group.

[0022] Preferably, the compound capable of generating phosphorus hydride is hypophosphorous acid or one of its salts.

[0023] The aqueous solution of inorganic peroxide, preferably hydrogen peroxide, preferably comprises from 0.2 to 50% by weight, preferably from 0.5 to 40% by weight, preferably from 0.5 to 10% by weight, more preferably from 0.5 to 3% by weight, of inorganic peroxide, relative to the total weight of the solution.

[0024] The polyamide composition is preferably in powder form, in particular having a volume median diameter (Dv50), measured according to the ISO 9276 standard, of less than 3 mm, preferably less than 500 pm, preferably less than 200 pm, more preferably less than 100 pm, preferably the Dv50 is between 5 and 250 pm, preferably between 5 and 200 pm, more preferably between 5 and 150 pm, even more preferably between 10 and 100 pm.

[0025] The process preferably comprises, before step (i), a step (i0) of grinding the polyamide composition, preferably until a powder is obtained whose particles have a Dv50, measured according to ISO 9276, of less than 3 mm, preferably less than 500 pm, preferably less than 200 pm, more preferably less than 100 pm. The mixing in step (i) is preferably carried out at a temperature of between -10 and 60°C, preferably between 10 and 40°C.

[0026] The reaction of step (ii) is preferably carried out at a temperature, preferably controlled, of between 45 and 140°C, preferably between 60 and 130°C, for example between 70 and 100°C.

[0027] Step (iii) can be carried out under vacuum, in particular at a pressure of less than 800 mbar, preferably less than 300 mbar, even more preferably less than 100 mbar.

[0028] In step (iii), preferably, the temperature is less than or equal to 140°C, preferably less than or equal to 130°C, preferably less than or equal to 120°C, preferably less than or equal to 110°C, more preferably less than or equal to 100°C, for example between 50 and 140°C, more preferably between 60 and 90°C, even more preferably between 70 and 80°C.

[0029] Preferably:

[0030] - the molar ratio of oxidizing compound / compound capable of generating phosphorus hydride is between 1 and 2000, preferably between 1 and 1000, preferably between 3 and 1000, preferably between 10 and 1000, preferably between 3 and 300, more preferably between 10 and 100; and / or

[0031] - the polyamide / aqueous solution mass ratio comprising the inorganic peroxide is between 0.05 and 50, preferably between 0.05 and 30, preferably between 0.1 and 20, preferably between 1 and 50, preferably between 5 and 50, preferably between 7 and 20.

[0032] The present invention also relates to a polyamide composition obtained from the process according to the invention, in which the amount of H3PO2 is less than 100 ppm.

[0033] The present invention also relates to a polyamide composition obtained from the process of the invention comprising from 98 to 99.98% by weight of polyamide and from 20 to 8000 ppm, preferably from 20 to 1500 ppm, of compound capable of generating phosphorus hydride, preferably H3PO3, and 0 to 100 ppm of FhPCh. The present invention also relates to a process for recycling a used polyamide composition comprising at least one compound capable of generating phosphorus hydride, comprising:

[0034] - the treatment of the used polyamide composition according to the process of the invention; and

[0035] - the mixture of the polyamide obtained with a native polyamide by compounding.

[0036] Detailed description

[0037] The invention is now described in more detail and in a non-limiting manner in the following description.

[0038] Unless otherwise stated, all percentages are by mass.

[0039] In this text, the quantities indicated for a given species may apply to this species according to all its definitions (as mentioned in this text), including the more restricted definitions.

[0040] Polyamide treatment process

[0041] The invention relates firstly to a method for treating a polyamide composition comprising at least one compound capable of generating phosphorus hydride, said method comprising the steps of:

[0042] (i) Mixing the polyamide composition with at least one oxidizing compound;

[0043] (ii) Reaction between the polyamide composition and the at least one oxidizing compound, preferably at controlled temperature,

[0044] (iii) Optionally drying the mixture obtained in step (ii) at a temperature less than or equal to 140°C.

[0045] The compound capable of generating phosphorus hydride is a compound which decomposes, in particular under the action of heat, for example at a temperature above 130°C, into phosphorus hydride. This decomposition occurs in particular during recycling by compounding of the polyamide composition.

[0046] The compound capable of generating phosphorus hydride is preferably chosen from the group consisting of:

[0047] - hypophosphorous acid (H3PO2) or one of its salts; - an organic phosphite, for example a phosphite of formula:

[0048] • P(OR)3 with R, identical or different, represents an organic residue notably chosen from phenyl; alkyl comprising from 1 to 20 carbon atoms, linear or branched; phenyl substituted by at least one, preferably 1, 2 or 3, alkyl group, identical or different, comprising from 1 to 20 carbon atoms, linear or branched; two Rs can be linked to form a cycle comprising the phosphorus atom and the two oxygen atoms carrying the two R groups linked together;

[0049] - R, identical or different, represents an alkyl group comprising from 1 to 20 carbon atoms, linear or branched;

[0050] • P(OR)2-O-Ph-CH(CH3)2-Ph-OP(OR)2 with R, identical or different, representing an alkyl group comprising from 1 to 20 carbon atoms, linear or branched and Ph representing a phenyl group.

[0051] The compound capable of generating phosphorus hydride is preferably selected from the group consisting of: hypophosphorous acid or one of its salts, triphenyl phosphite, triisodecyl phosphite, isodecyl diphenyl phosphite, 2-ethylhexyl diphenyl phosphite, tris(nonylphenyl) phosphite, tris(2,4-di-tert-butylphenyl) phosphite, 3,9-Bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, tetra-C12-15-alkyl(propane-2,2-diylbis(4,1-phenylene))bis(phosphite), 2,2'-methylenebis(4,6-di-tert-butylphenyl)2-ethylhexyl phosphite, bis(2,4-di-tert-butyl-6-methylphenyl)ethylphosphite.

[0052] Preferably, the content of compound capable of generating phosphorus hydride in the polyamide composition is between 100 ppm and 20,000 ppm, preferably between 200 ppm and 20,000 ppm, preferably between 300 ppm and 20,000 ppm, preferably between 400 and 20,000 ppm, preferably between 1,000 and 20,000 ppm, preferably between 1,500 ppm and 20,000 ppm. These contents are in particular measured by NMR.

[0053] Preferably, the polyamide composition according to the invention does not contain red phosphorus.

[0054] Preferably, the compound capable of generating phosphorus hydride is hypophosphorous acid or one of its salts.

[0055] The polyamide composition according to the invention may be in any form and in particular in the form of particles having a volume median diameter (Dv50) of less than 3 mm, preferably less than 500 pm, preferably less than 200 pm, more preferably less than 100 pm, preferably the Dv50 is between 5 and 250 pm, preferably between 5 and 200 pm, more preferably between 5 and 150 pm, even more preferably between 10 and 100 pm.

[0056] The apparent specific surface area of ​​the particles, measured according to ISO9277:2022, is preferably between 0.01 and 40 m 2 / g, advantageously between 0.05 and 25 m 2 / g, especially 0.1 and 10 m 2 / g.

[0057] By particles according to the invention, we mean forms of the granular, powder or ground type.

[0058] Preferably, the polyamide composition according to the invention is in the form of a powder having a volume median diameter (Dv50) of less than 3 mm, preferably less than 500 pm, preferably less than 200 pm, more preferably less than 100 pm, preferably the Dv50 is between 5 and 250 pm, preferably between 5 and 200 pm, more preferably between 5 and 150 pm, even more preferably between 10 and 100 pm.

[0059] According to the present application, the "volume mean diameter" or "Dv" the volume mean diameter of a powdery material is as measured according to ISO 9276 - parts 1 to 6: "Representation of data obtained by particle size analysis", in its version in force in 2022. Different diameters are distinguished. More specifically, Dv50 designates the volume median diameter, i.e. that corresponding to the 50th percentile by volume, and Dvl0 and Dv90 respectively designate the volume mean diameters below which 10 or 90% by volume of the particles are located. The volume mean diameter can be measured in particular by means of a laser granulometer, for example a laser granulometer (Malvern Insitec System). Associated software (RT sizer) then makes it possible to obtain the volumetric distribution of a powder and to deduce the Dvl0, Dv50 and Dv90 therefrom.

[0060] If necessary, the polyamide composition may be ground before step (i).

[0061] The polyamide according to the invention may be any type of polyamide, in particular amorphous or semi-crystalline. Preferably, the polyamide is an aliphatic, cycloaliphatic or semi-aromatic polyamide. Preferably:

[0062] - the aliphatic polyamide is chosen from polyamide 6 (PA-6), polyamide

[0063] 11 (PA-11), polyamide 12 (PA-12), polyamide 66 (PA-66), polyamide 46 (PA-46), polyamide 610 (PA-610), polyamide 612 (PA-612), polyamide 613 -(PA 613), polyamide 1010 (PA-1010), polyamide 1012 (PA-1012), polyamide 11 / 1010 and polyamide 12 / 1010, or a mixture thereof or a copolyamide thereof, and polyetheramide or polyetheresteramide copolymers (PEBA) (or polyamide block and polyether block copolymer), or

[0064] - the semi-aromatic polyamide is a semi-aromatic polyamide optionally modified by urea units, in particular a PA MXD6 and a PA MXD10 or a semi-aromatic polyamide of formula A / XT in which A is chosen from a unit obtained from at least one amino acid, a unit obtained from at least one lactam and at least one unit corresponding to the formula (Ca diamine). (Cb diacid), with a representing the number of carbon atoms of the diamine and b representing the number of carbon atoms of the diacid, a and b each being between 4 and 36, advantageously between 9 and 18, the unit (Ca diamine) being chosen from aliphatic, linear or branched diamines, cycloaliphatic diamines and alkylaromatic diamines and the unit (Cb diacid) being chosen from aliphatic, linear or branched diacids, cycloaliphatic diacids and aromatic diacids; X.T denotes a unit obtained from the polycondensation of a Cx diamine and terephthalic acid, with x representing the number of carbon atoms of the Cx diamine, x being between 6 and 36, advantageously between 9 and 18, in particular a polyamide of formula A / 6T, A / 9T, A / 10T or A / 11T, A being as defined above, in particular a polyamide PA 6 / 6T, a PA 66 / 6T, a PA 6I / 6T, a PA MPMDT / 6T, a PA PA11 / 10T, a PA 11 / 6T / 10T, a PA MXDT / 10T, a PA MPMDT / 10T, a PA BACT / 10T, a PA BACT / 6T, a PA 11 / BACT, PA BACT / 10T / 6T, a PA 11 / BACT / 10T, T corresponds to terephthalic acid, MXD stands for m-xylylenediamine, MPMD stands for methylpentamethylenediamine and BAC stands for l,3-bis(aminomethyl)cyclohexane.

[0065] Preferably, said at least one polyamide is chosen from:

[0066] - an aliphatic polyamide chosen from polyamide 11 (PA-11), polyamide

[0067] 12 (PA-12), polyamide 66 (PA-66), polyamide 46 (PA-46), polyamide 610 (PA-610), polyamide 612 (PA-612), polyamide 1010 (PA-1010), polyamide 1012 (PA-1012), polyamide 11 / 1010 and polyamide 12 / 1010, or a mixture thereof or a copolyamide thereof, and polyetheramide or polyetheresteramide (PEBA) copolymers (or polyamide block and polyether block copolymer), or

[0068] - a semi-aromatic polyamide, optionally modified by urea units, in particular a PA MXD6 and a PA MXD10 or a semi-aromatic polyamide of formula A / XT in which A is chosen from a unit obtained from at least one amino acid, a unit obtained from at least one lactam and at least one unit corresponding to the formula (Ca diamine). (Cb diacid), with a representing the number of carbon atoms of the diamine and b representing the number of carbon atoms of the diacid, a and b each being between 4 and 36, advantageously between 9 and 18, the unit (Ca diamine) being chosen from linear or branched aliphatic diamines, cycloaliphatic diamines and alkylaromatic diamines and the unit (Cb diacid) being chosen from linear or branched aliphatic diacids, cycloaliphatic diacids and aromatic diacids; X.T denotes a unit obtained from the polycondensation of a Cx diamine and terephthalic acid, with x representing the number of carbon atoms of the Cx diamine, x being between 6 and 36, advantageously between 9 and 18, in particular a polyamide of formula A / 6T, A / 9T, A / 10T or A / 11T, A being as defined above, in particular a polyamide PA 6 / 6T, a PA 66 / 6T, a PA 6I / 6T, a PA MPMDT / 6T, a PA PA11 / 10T, a PA 11 / 6T / 10T, a PA MXDT / 10T, a PA MPMDT / 10T, a PA BACT / 10T, a PA BACT / 6T, a PA 11 / BACT, PA BACT / 10T / 6T, a PA 11 / BACT / 10T, T corresponds to terephthalic acid, MXD stands for m-xylylenediamine, MPMD stands for methylpentamethylenediamine and BAC stands for l,3-bis(aminomethyl)cyclohexane.

[0069] Preferably, the polyamide is a semi-aromatic polyamide chosen from a PA MPMDT / 6T, a PA PA11 / 10T, a PA 11 / BACT, a PA 11 / 6T / 10T, a PA MXDT / 10T, a PA MPMDT / 10T, a PA BACT / 10T, a PA BACT / 6T, PA BACT / 10T / 6T, a PA 11 / BACT / 6T, PA 11 / MPMDT / 10T, PA 11 / BACT / 10T, one PA 11 / MXDT / 10T.

[0070] Preferably, the polyamide has a C / N ratio greater than or equal to 6.5, preferably greater than 6.5, preferably greater than or equal to 7.5, preferably greater than 7.5, for example between 7.5 and 12, more preferably between 9 and 11. Preferably, the polyamide is PAU or PA12, preferably PA11.

[0071] Preferably, the polyamide composition according to the invention has an inherent viscosity of between 0.9 and 3, preferably between 1.1 and 2.5.

[0072] For the purposes of the application, the inherent viscosity is as measured using an Ubbelohde tube at 20°C on a 0.5% by weight solution in m-cresol according to ISO 307 of 2019.

[0073] The polyamide composition may be a native polyamide composition or one comprising at least one native polyamide and comprising a compound capable of generating phosphorus hydride or a used polyamide composition, for example from post-production or post-consumer waste and preferably ground.

[0074] In the context of the present invention, native polyamide means polyamide resulting from a polyamide manufacturing process and having neither been formulated nor previously used.

[0075] In the context of the present invention, the compositions of used polyamides, also called polyamides to be recycled, can be:

[0076] - unprocessed polyamide compositions resulting from additive manufacturing by sintering or from a powder coating or electrostatic spraying process, preferably unprocessed polyamide compositions resulting from additive manufacturing by sintering also called 3D printing by sintering;

[0077] - polyamide compositions derived from a polyamide-based part of an object to be recycled, said object preferably being previously ground;

[0078] - polyamide compositions resulting from a 3D printing or lithography process or a rotational molding process.

[0079] “Unprocessed polyamide from additive manufacturing by sintering” means a polyamide that has not been subjected to radiation in a prior additive manufacturing process by sintering and that has not been used to form the object formed in the prior additive manufacturing process. Typically, this polyamide has spent at least 1 minute at a temperature above 100°C in an additive manufacturing device. “Unprocessed polyamide from a powder coating or electrostatic spraying process” means the polyamide that has not been used to form the coating on the substrate in the prior powder coating or electrostatic spraying process. Typically, this polyamide has been involved in a process for coating a substrate by powder coating or electrostatic spraying (electrospray).

[0080] In both cases, the unprocessed polyamide used as the polyamide to be recycled in the process according to the invention corresponds to polyamide waste from a previous process. The polyamide to be recycled has therefore undergone degradation, generally thermal.

[0081] A "polyamide-based part of an object to be recycled" means a part obtained by a previous transformation, for example injection, extrusion or overmolding. The object to be recycled (or the part) may be used, broken, of poor quality, and / or unfit for its function. The polyamide in this part is therefore also waste.

[0082] The composition of polyamides to be recycled, unprocessed or obtained by grinding a polyamide-based part of an object to be recycled, generally comprises more than 10%, typically more than 50%, or even more than 75% of polyamide (or mixture of polyamides) by weight relative to the weight of the powder. The proportion of polyamides is generally less than 99.9% by weight.

[0083] In one embodiment, the oxidizing compound of the invention is an inorganic oxidant, preferably an inorganic peroxide or a perchlorate, preferably the antioxidant compound is in the form of an aqueous solution, for example an aqueous solution of an inorganic oxidant, selected from a perchlorate solution, for example sodium perchlorate or an aqueous solution of an inorganic peroxide, for example an aqueous solution of a persulfate, for example sodium persulfate, an aqueous solution of a percarbonate, for example sodium percarbonate or an aqueous solution of hydrogen peroxide. Preferably, the oxidizing compound of the invention is an aqueous solution of hydrogen peroxide. In one embodiment, the oxidizing compound of the invention is an organic peroxide such as methyl-ethyl-ketone-peroxide, dibenzoyl-peroxide or di(n-propyl) peroxydicarbonate or peroxyesters.

[0084] Preferably, the oxidizing compound is an aqueous solution of hydrogen peroxide.

[0085] In case the oxidizing compound is an aqueous solution of inorganic oxidant, preferably an aqueous solution of inorganic peroxide then the drying step (iii) is necessary.

[0086] The inventors have shown that in a particularly advantageous manner the use of an oxidant according to the invention, preferably an aqueous solution of inorganic peroxide, preferably an aqueous solution of hydrogen peroxide, allows selective oxidation of the compound capable of generating phosphorus hydride without oxidizing, or at least by limiting the degradation, in particular by oxidation, of the polyamide. This oxidant according to the invention therefore makes it possible to avoid the formation of phosphine by modifying the compound capable of generating said phosphine.

[0087] When the oxidant is an aqueous solution of inorganic oxidant, preferably an aqueous solution of inorganic peroxide, the aqueous solution comprises from 0.2 to 50% by weight, preferably from 0.5 to 40% by weight, preferably from 0.5 to 10% by weight, more preferably from 0.5 to 3% by weight, relative to the total weight of the solution, of inorganic oxidant, preferably inorganic peroxide, preferably the aqueous solution of inorganic peroxide is a solution of hydrogen peroxide.

[0088] Advantageously, hydrogen peroxide makes it possible to limit the pollution of the polyamide. Advantageously, the use of a hydrogen peroxide solution in the process of the invention releases water which can be easily removed, for example by drying, and does not release any by-products.

[0089] Mixture of the polyamide composition and at least one oxidizing compound

[0090] The mixture of the polyamide composition and at least one oxidizing compound, preferably the aqueous solution of inorganic oxidizing agent, preferably the aqueous solution of inorganic peroxide, must be sufficient to allow good diffusion of the oxidizing compound, in the polyamide composition allowing the oxidation of the majority, and preferably all, of the compound capable of generating phosphorus hydride.

[0091] In case the oxidizing compound is an aqueous solution of inorganic oxidant, preferably an aqueous solution of inorganic peroxide, it is not recommended to use too large a quantity since this will require a more extensive drying step.

[0092] Preferably, the polyamide / aqueous solution of inorganic oxidant mass ratio is between 0.05 and 50, preferably between 0.05 and 30, preferably between 0.1 and 20, preferably between 1 and 50, preferably between 5 and 50, preferably between 7 and 20.

[0093] Preferably, the oxidizing compound is in the form of an aqueous solution of hydrogen peroxide and the polyamide / aqueous solution of hydrogen peroxide mass ratio is preferably between 0.05 and 50, preferably between 0.1 and 20, preferably between 5 and 50, preferably between 7 and 20.

[0094] Preferably, the molar ratio of oxidizing compound / compound capable of generating phosphorus hydride is between 1 and 2000, preferably between 1 and 1000, preferably between 3 and 1000, preferably between 10 and 1000, preferably between 3 and 300, more preferably between 10 and 100. It should be understood, in cases where the oxidizing compound is in the form of an aqueous solution, that the molar ratio is determined by taking the molar quantity of oxidizing compound in the aqueous solution.

[0095] The duration of the mixing step depends on the temperature and the size of the polyamide particles and is preferably between 1 and 20 hours, preferably between 2 and 8 hours.

[0096] Preferably, the mixing of the polyamide composition with the at least one oxidizing compound is carried out at a temperature between -10 and 60°C in order in particular not to decompose the oxidizing compound.

[0097] The reaction of step (ii) is then preferably carried out at a controlled temperature, preferably at a temperature between 45 and 140°C.

[0098] Preferably, the oxidizing compound is an aqueous solution of hydrogen peroxide and the mixing of step (i) of the polyamide composition with the aqueous solution of hydrogen peroxide is preferably carried out at a temperature of between -10 and 60°C, preferably between 10 and 40°C. The reaction of step (ii) is preferably carried out at a controlled temperature, preferably at a temperature of between 45 and 140°C, preferably between 60 and 130°C, for example between 70 and 100°C. of polyamide and the solution EU

[0099] Step (iii) is necessary in the case where the oxidizing compound is in the form of an aqueous solution, in particular an aqueous solution of inorganic oxidant, preferably an aqueous solution of inorganic peroxide.

[0100] The drying step (iii) is then carried out at a temperature less than or equal to 140°C, preferably less than or equal to 130°C, preferably less than or equal to 120°C, preferably less than or equal to 110°C, more preferably less than or equal to 100°C, for example between 50 and 140°C, more preferably between 60 and 90°C, even more preferably between 70 and 80°C.

[0101] The lower temperatures are advantageously preferred to have good oxidation selectivity.

[0102] Preferably, the drying step is carried out in dry air or under vacuum, preferably at a pressure of less than 800 mbar, preferably less than 300 mbar, more preferably less than 100 mbar.

[0103] Steps (ii) and (iii) can be implemented in any type of device known to those skilled in the art, they can be implemented in different devices or in a single device.

[0104] For example, step (ii) can be carried out in a solid / liquid mixer. Step (iii) can, for example, be carried out in a rotary or fluidized bed dryer or a countercurrent dryer.

[0105] A rotary dryer with bicone geometry which can in particular be heated using a heat transfer fluid in a double wall, equipped with a vacuum device can advantageously be used to carry out steps (ii) and (iii).

[0106] Preferably, the amount of residual H3PO2 after carrying out the process is less than 50 ppm by weight, preferably less than 20 ppm by weight. Polyamide obtained after the treatment process

[0107] The present invention also relates to a polyamide composition resulting from the treatment method defined above.

[0108] This composition preferably comprises at least 50%, preferably at least 70%, preferably at least 80%, preferably at least 90%, more preferably at least 95%, preferably from 98 to 99.98%, by weight of polyamide and from 20 to 1500 ppm of compound capable of generating phosphorus hydride, preferably H3PO3, and 0 to 100 ppm of HsPCh. These contents are measured by NMR.

[0109] Preferably, the polyamide obtained after implementing the process according to the invention has an inherent viscosity of between 0.9 and 2.2, preferably of between 1.2 and 2.2.

[0110] Polyamide recycling process

[0111] The present invention also relates to a process for recycling a polyamide composition comprising the treatment process defined above, in particular a process for recycling by compounding.

[0112] Preferably, the polyamide composition to be recycled comes from a 3D printing or lithography process or a rotational molding process.

[0113] Advantageously, the oxidizing components, preferably the aqueous solution of hydrogen peroxide (H2O2), will also make it possible, if the polyamide composition to be recycled has a coloration due to its subsequent use or to the presence of chromophore, to bleach the polyamide to be recycled. Advantageously, this makes it possible to lower the yellowness index (Yi).

[0114] The process may further comprise a step of mixing the polyamide obtained from the treatment process with native polyamide, preferably by compounding. It is thus possible to obtain a composition comprising, by weight relative to the total weight of the composition, 30 to 99% of recycled polyamide according to the process of the invention with 1 to 70% of native polyamide and optionally 0.1 to 6% of additives.

[0115] The polyamide composition resulting from the recycling process can then be used in the same way as native polyamide, in particular for the manufacture of injected, extruded, molded parts, parts obtained by 3D printing or lithography, etc.

[0116] The invention also relates to a method for reducing phosphorus hydride emissions during the recycling of used polyamide compositions comprising at least one compound capable of generating phosphorus hydride, comprising a step of pre-treatment of the polyamide composition, before the step of recycling by compounding, comprising mixing the polyamide with at least one oxidizing compound according to the invention, preferably an aqueous hydrogen peroxide composition, a step of reaction between the polyamide composition and the oxidizing compound and optionally a step of drying the mixture thus obtained.

[0117] The polyamide, the compound capable of generating phosphorus hydride, the oxidizing compound, the mixing step, the reaction and the drying step being as described above.

[0118] The invention will be explained in more detail in the following examples.

[0119] Examples

[0120] Unless otherwise stated, percentages are expressed by weight relative to the total weight of the composition.

[0121] In a rotary dryer (bicone type, 120 I with strainer and possibility of vacuum or sweeping) we load the PA 11 powder recovered after use for 3D printing (20.00 kg in total with an average diameter of 60 mm) followed by the loading of the hydrogen peroxide solution comprising 93 g of 100% hydrogen peroxide and 3.00 kg of deionized water. The rotary dryer is rotated for one hour to homogenize the mixture. It is heated to reach 60°C followed by a 4-hour hold at 60°C to carry out the reaction.

[0122] Once this treatment is completed, a progressive vacuum of up to 100 mbar for 8 hours is applied to dry the powder.

[0123] Finally, the reactor and its container are cooled to room temperature and the reactor is emptied.

[0124] Example 2

[0125] Same treatment for PA12 powder recovered after use in 3D printing. In a 100 ml stirred reactor, 10 g of PAU powder formulated for 3D printing are added. Then, 10 g of 40% H2O2 solution are added and the mixture is stirred for 8 hours at 50°C to carry out the reaction. After treatment, the mixture is filtered and the powder is dried for 24 hours at 50°C under a vacuum of 30 mbar.

[0126] Example 4

[0127] In a 100 ml stirred reactor, 10 g of PAU powder formulated for 3D printing is added. Then, 30 g of 10% H2O2 solution is added and the mixture is stirred for 8 hours at 50 ° C to carry out the reaction. After treatment, the mixture is filtered and the powder is dried for 24 hours at 90 ° C under a flow of dry nitrogen.

[0128] Determination of the elimination rate of hypophosphorous acid

[0129] The phosphorus content and its nature are determined by P31 NMR analysis on an AVANCE 400 NEO spectrometer. The samples were solubilized at room temperature in a HFIP / CD2CI2 mixture (3 / 1 v / v). The test sample is of the order of 500 mg. The analysis is carried out using the method without internal standard. That is to say, from the proton NMR spectrum, the mass content of H3PO2 is determined in relation to the polyamide and the additive (= PA + additives + phosphorus species = 100%). From the P31 NMR spectrum, the molar ratio H3PO2 / H3PO3 / H3PO4 is determined, which allows the H3PO3 and H3PO4 content to be deduced.

[0130] Detection of phosphorus hydrogen during extrusion at 250°C

[0131] The various polyamides exemplified were extruded using a ZSK 26 twin-screw at a flow rate of 20 kg / h and a temperature of 250°C. A pump and tubes supplied by the company Dràger were placed 2 cm from the extruder die in order to detect possible releases of phosphorus hydrogens. The tubes used are the reference tubes: 81 01 611. The thermal degradation of hypophosphorous acid and its derivatives are the main cause of the generation of phosphine during the melting of the powder.

[0132] Table 1

[0133] Table 2

Claims

Claims 1. Method for treating a polyamide composition comprising at least one compound capable of generating phosphorus hydride, comprising the steps of: (i) Mixing the polyamide composition with at least one oxidizing compound; (ii) Reaction between the polyamide composition and the at least one oxidizing compound; (iii) Optionally drying the mixture obtained in step (i) at a temperature less than or equal to 140°C.

2. Method according to claim 1, in which the oxidizing compound is chosen from an aqueous solution of inorganic oxidant, preferably an aqueous solution of inorganic peroxide, for example an aqueous solution of percarbonate or an aqueous solution of hydrogen peroxide or an aqueous solution of persulfate, or an aqueous solution of perchlorate, or from organic peroxides such as methyl-ethyl-ketone-peroxide, dibenzoyl-peroxide, or di(n-propyl) peroxydicarbonate or peroxyesters.

3. A method according to claim 1 or 2, wherein the oxidizing compound is an aqueous solution of hydrogen peroxide.

4. Method according to any one of the preceding claims, in which the compound capable of generating phosphorus hydride is chosen from the group consisting of: - hypophosphorous acid (H3PO2) or one of its salts; - an organic phosphite, for example a phosphite of formula: • P(OR)3 with R, identical or different, represents an organic residue notably chosen from phenyl; alkyl comprising from 1 to 20 carbon atoms, linear or branched; phenyl substituted by at least one, preferably 1, 2 or 3, alkyl group, identical or different, comprising from 1 to 20 carbon atoms, linear or branched; two Rs can be linked to form a cycle comprising the phosphorus atom and the two oxygen atoms carrying the two R groups linked together; - R, identical or different, represents an alkyl group comprising from 1 to 20 carbon atoms, linear or branched; • P(OR)2-O-Ph-CH(CH3)2-Ph-OP(OR)2 with R, identical or different, representing an alkyl group comprising from 1 to 20 carbon atoms, linear or branched and Ph representing a phenyl group.

5. Method according to any one of the preceding claims, in which the compound capable of generating phosphorus hydride is hypophosphorous acid or one of its salts.

6. A method according to any one of the preceding claims, wherein the oxidant is in the form of an aqueous solution and the aqueous solution comprises from 0.2 to 50% by weight, preferably from 0.5 to 40% by weight, preferably from 0.5 to 10% by weight, more preferably from 0.5 to 3% by weight, of oxidizing compound, relative to the total weight of the solution.

7. Method according to any one of the preceding claims in which the polyamide composition is in powder form, in particular having a volume median diameter (Dv50), measured according to the ISO 9276 standard, of less than 3 mm, preferably less than 500 pm, preferably less than 200 pm, more preferably less than 100 pm, preferably the Dv50 is between 5 and 250 pm, preferably between 5 and 200 pm, more preferably between 5 and 150 pm, even more preferably between 10 and 100 pm.

8. Method according to any one of the preceding claims comprising before step (i) a step (i0) of grinding the polyamide composition preferably until a powder is obtained whose particles have a Dv50, measured according to the ISO 9276 standard, of less than 3 mm, preferably less than 500 pm, preferably less than 200 pm, more preferably less than 100 pm.

9. A method according to any one of the preceding claims, wherein the mixing in step (i) is carried out at a temperature between -10 and 60°C, preferably between 10 and 40°C, and step (ii) is carried out at a temperature between 45 and 140°C, preferably between 60 and 130°C, for example between 70 and 100°C.

10. Method according to any one of the preceding claims, in which step (iii) is carried out under vacuum, in particular at a pressure of less than 800 mbar, preferably less than 300 mbar, even more preferably less than 100 mbar.

11. Method according to any one of the preceding claims, wherein in step (iii) the temperature is less than or equal to 140°C, preferably less than or equal to 130°C, preferably less than or equal to 120°C, preferably less than or equal to 110°C, more preferably less than or equal to 100°C, for example between 50 and 140°C, more preferably between 60 and 90°C, even more preferably between 70 and 80°C.

12. A method according to any preceding claim, wherein - the molar ratio of oxidizing compound / compound capable of generating phosphorus hydride is between 1 and 2000, preferably between 1 and 1000, preferably between 3 and 1000, preferably between 10 and 1000, preferably between 3 and 300, more preferably between 10 and 100; and / or - the polyamide / aqueous solution mass ratio comprising the inorganic peroxide is between 0.05 and 50, preferably between 0.05 and 30, preferably between 0.1 and 20, preferably between 1 and 50, preferably between 5 and 50, preferably between 7 and 20.

13. Polyamide composition obtained from the process according to any one of claims 1 to 12, in which the amount of H3PO2 is less than 100 ppm.

14. Composition according to claim 13 comprising from 98 to 99.98% by weight of polyamide and from 20 to 1500 ppm of compound capable of generating phosphorus hydride, preferably H3PO3, and 0 to 100 ppm of HsPCh.

15. Process for recycling a used polyamide composition comprising at least one compound capable of generating phosphorus hydride, comprising: - the treatment of the used polyamide composition according to the method according to any one of claims 1 to 12; and - the mixture of the polyamide obtained with a native polyamide by compounding.

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