Method for recycling used polyamide compositions

Abstract

The present invention provides a post-consumer polyamide composition with a unimodal melting endotherm and a single melting temperature (T f1 max ), a method for recycling polyamide into a recycled polyamide powder having i. contacting a post-consumer polyamide composition with a solvent to obtain a mixture; ii. heating the mixture to dissolve the polyamide in the solvent; iii. Bring the mixture in the solvent to a precipitation temperature (T p ), which results in a non-unimodal melting endotherm and (T f1 max ) is the highest melting temperature; iv. The precipitated polyamide powder has a unimodal melting endotherm and melting temperature (T f1 max ) until the temperature of the mixture reaches at most T p temperature, especially T p -0.1℃~T p maintaining a temperature in the range of -15°C; and v. A step of recovering the resulting recycled polyamide powder. The present invention relates to a method, comprising:

Description

[Technical Field]

[0001] The present invention relates to a post-consumer polyamide composition, which is obtained by treating a polyamide powder with a polyamide powder having a melting point and a crystallization point that are different from the melting point and the crystallization point (T f1 -T c The present invention relates to a method for recycling polyamide powder into polyamide powder having increased carbon black content.

[0002] Polyamide-based powder T f1 and T c This large difference between is useful in many applications, especially in the technique of powder agglomeration by melting or sintering induced by radiation, such as a laser beam (laser sintering), infrared or ultraviolet radiation, or any electromagnetic radiation source that allows the powder to melt to produce an object.

[0003] The present invention also relates to the polyamide powder obtainable according to this method.

[0004] Finally, the invention relates to the use of this powder and to articles made from it. [Background technology]

[0005] The agglomeration of polyamide powder under a laser beam is used in a variety of fields to produce three-dimensional objects such as prototypes and models.

[0006] The thin layer of polyamide powder is heated to the crystallization temperature T c and melting temperature T f1 The powder is deposited on a horizontal plate held in a chamber heated to a temperature between 0 and 1000 K. The laser causes the powder particles to aggregate at different points in the powder layer according to the geometry corresponding to the object, for example by using a computer that stores the shape of the object in a memory and reproduces this shape in the form of slices. The powder areas exposed to the laser reach a temperature above the crystallization temperature T c, it solidifies as soon as it drops below 0. The horizontal plate is then lowered a distance corresponding to the thickness of the powder layer, a new layer of powder is then deposited, and the laser agglomerates the powder particles according to the geometry corresponding to this new slice of the object, and so on. This procedure is repeated until the entire object is produced. In the chamber, an object is obtained surrounded by unagglomerated powder. The assembly is then slowly cooled.

[0007] Once fully cooled, the object is separated from the powder, which can be reused in another process.

[0008] Immediately after the action of the laser beam, the temperature of the exposed area rises above the crystallization temperature (T c ). However, if the temperature is reduced below this temperature too quickly, for example by applying a new, cooler layer of powder, it can cause deformation of the part being printed (known as "curl"). Similarly, if the temperature of the powder in the machine drops below the powder's melting temperature (T f1 ) can cause solidification around the part (known as "caking"), manifested by the formation of clumps of powder that affect print quality.

[0009] Therefore, to avoid these phenomena, the powder temperature T c Powder T f1 It is important to keep the temperature as far away as possible from the powder temperature difference T f1 -T c determines the working temperature range of the equipment used to agglomerate powder particles by radiation-induced melting. This working range is defined by its upper and lower temperature limits. The upper limit of the working range corresponds to the temperature at which agglomeration or "caking" occurs. The lower limit of the working range corresponds to the temperature at which distortion, deformation, or curling occurs. This working range should be greater than the temperature fluctuations within a 3D printing machine, which are typically around ±3°C.

[0010] Furthermore, it has a high heat of fusion (ΔH f) is advantageous for optimizing the geometric definition of the manufactured parts. In particular, if it is too low, there is a risk that the energy delivered by the laser will sinter, by heat conduction, the powder particles around the workpiece part being built, which limits the geometric accuracy of the parts obtained.

[0011] It is clear that everything described so far regarding the agglomeration of polyamide powder under a laser beam is valid regardless of the electromagnetic radiation that causes the melting and whether the melting process is selective or non-selective.

[0012] U.S. Patent No. 5,932,687 discloses a method for preparing precipitated polyamide powders with narrow particle distribution and low porosity. The method comprises a first step of cooling a polyamide predissolved in an alcohol solvent to a temperature T1 (higher than the precipitation temperature of the polyamide in the solvent) to obtain germination of the polyamide, followed by a second cooling step to obtain supersaturation of the medium and thus precipitation of the polyamide at a temperature T2. The resulting suspension is then cooled and dried to recover the polyamide powder.

[0013] U.S. Patent Application Publication No. 2008 / 0166496 discloses polyamide 11 powders that can be used in powder agglomeration processes, particularly for producing three-dimensional objects. These powders are prepared according to a method that involves cooling a polyamide predissolved in ethanol to a temperature at which the polyamide precipitates. Due to the heat generated by the precipitation, the medium is maintained at this temperature for 25 minutes, after which the temperature is slightly reduced and an isothermal state is achieved for 35 minutes. At the end of this stationary phase, the mixture is cooled and the precipitated polyamide powder is separated.

[0014] However, the inventors have been able to observe that the prior art methods result in polyamide powders whose analysis by differential scanning calorimetry shows, upon the first heating, the presence of two temperature peaks associated with two relatively close but different melting temperatures, revealing the presence of at least two different crystalline phases. For the reasons mentioned above, this heterogeneity in the thermal properties of the powder narrows the working range and can therefore have a negative effect on the quality of the objects produced according to the method of powder agglomeration by electromagnetic radiation-mediated melting, in particular their definition.

[0015] These methods involve the preparation of virgin polyamide powder.

[0016] As mentioned above, the described technique does not aggregate, but rather allows the T f1 This process produces large amounts of damaged powder due to exposure to temperatures close to 1000 K. Recycling these powders is advantageous to reduce energy and resource consumption. A method for recycling polyamides, especially those contained in post-consumer compositions obtained from 3D printing waste, is described.

[0017] CN110483986 thus describes a method for recycling residual polyamide 12 powder after selective laser sintering. The method involves dissolving the recycled powder in an acidic solution, then neutralizing and atomizing the solution to obtain recycled polyamide powder. This method is specific to the treatment of 3D printing waste and involves processing in an acidic medium that is highly aggressive to polyamide. Furthermore, it is not possible to separate the polyamide from other products present in the composition, nor is it possible to control the physicochemical characteristics of the recycled polyamide powder, particularly its viscosity, particle size, or thermal properties. Furthermore, special equipment is required, and the flow of the acidic solution must be managed, making implementation particularly cumbersome.

[0018] CN109810284 describes a method for dissolving polyamide 12 waste from 3D printing using a complex solvent system containing a mixture of hydrochloric acid, formic acid, and acetic acid. A solid / liquid separation step is performed at high temperature before precipitating the polyamide by adding water as a non-solvent. However, this dissolution / precipitation method in an acidic medium is very aggressive to polyamide and does not allow for control of the physicochemical characteristics of the recycled powder. Furthermore, managing the flow of the acidic solution makes this method cumbersome to implement.

[0019] There is therefore a real need for a method for recycling used polyamide compositions into recycled polyamide powder, which is particularly useful in the technique of powder agglomeration by electromagnetic radiation mediated melting, and which makes it possible to overcome these drawbacks. Summary of the Invention

[0020] The inventors have now made it possible to recycle used polyamide compositions and obtain a unimodal melting endotherm, thereby eliminating the difference T f1 -T c We developed a dissolution / precipitation method that effectively increases the

[0021] More specifically, by introducing a temperature-steady state phase of sufficient duration at the end of the polyamide precipitation stage, a non-unimodal melting endotherm and (T f1 max ) is the highest melting temperature, f1 The precipitated polyamide powder is characterized by a unimodal melting endotherm and a (T f1 max ) is equal to the single melting temperature (T f1 ) and converted into polyamide powder, which is characterized by the temperature difference (T f1 -T c It has been found that it is possible to increase the temperature gradient. The inventors have been able to demonstrate in particular that this temperature gradient phase leads to densification of the crystals and thus makes it possible to obtain a single crystalline phase.

[0022] The polyamide powders obtained are therefore particularly advantageous for use in methods of powder agglomeration by electromagnetic radiation mediated melting, in particular in that the working range can be increased and therefore the quality and / or definition of the objects produced from these powders can be improved.

[0023] According to further advantages, the recycling method according to the invention is easy to carry out and does not require the use of acidic conditions. It also makes it possible to control the particle size of the powder, in particular the span factor, and to at least partially separate the polyamide from other compounds present in the used composition, such as additives or fillers. The recycling method therefore makes it possible to obtain a recycled polyamide powder of high purity, which has improved thermal properties compared to used polyamide.

[0024] Therefore, according to a first aspect, the object of the present invention is to convert used polyamide compositions into polyamides having a unimodal melting endotherm and a single melting temperature (T f1 max ), a method for recycling polyamide into a recycled polyamide powder having i. contacting a post-consumer polyamide composition with a solvent to obtain a mixture; ii. heating the mixture to dissolve the polyamide in the solvent; iii. Bring the mixture in the solvent to a precipitation temperature (T p ), which results in a non-unimodal melting endotherm and (T f1 max ) is the highest melting temperature; iv. The precipitated polyamide powder has a unimodal melting endotherm and melting temperature (T f1 max ) until the temperature of the mixture reaches at most T p temperature, especially T p -0.1℃~T p maintaining a temperature in the range of -15°C; and v. A step of recovering the resulting recycled polyamide powder. The object of the present invention is to provide a method comprising:

[0025] Advantageously, the method also has one or more of the following characteristics: Thus, in a particular embodiment, the method according to the invention comprises: the solvent contacted with the polyamide is an alcohol, in particular a C1-C4 aliphatic alcohol, preferably ethanol; - heating of the mixture is carried out at a temperature of 100°C to 200°C, preferably 120°C to 160°C; and / or heating of the mixture has a duration of 1 to 6 hours, preferably 1 to 3 hours; - the cooling of the mixture in step iii) is carried out at a rate of from 1°C to 100°C per hour, preferably from 10°C to 60°C per hour; - the polyamide is polyamide 11, polyamide 6, or polyamide 10.10, or polyamide 10.12, or polyamide 6.10; - Polyamide precipitation temperature T p is between 80°C and 130°C, in particular between 100°C and 120°C; - in step iv), the mixture is maintained at a temperature close to the precipitation temperature, effective from the start of precipitation of the polyamide, for a period of at least 2 hours, in particular between 3 and 12 hours; - step vi) of drying the precipitated polyamide powder recovered in step v) or obtained at the end of step iv), in particular at a temperature between 10°C and 150°C, more particularly between 50°C and 100°C; - drying of the precipitated polyamide powder is carried out at pressures ranging from 10 mbar to atmospheric pressure; - The composition also contains volatile organic compounds (VOCs); the composition contains inorganic fillers, in particular fibres, in particular glass fibres and / or carbon fibres; and / or - in particular after step iv), v) or vi), also comprising a step vii) of separating and recovering inorganic fillers that may be present in the precipitated polyamide powder It is a method.

[0026] According to a second aspect, the object of the present invention is also to provide a method for producing a unimodal melting endotherm and a single melting temperature (T f1 max The object of the present invention is to provide a polyamide powder having the following properties:

[0027] Advantageously, this powder has one or more of the following characteristics: Thus, in a particular embodiment, the powder according to the invention has: - characterized by a volume-average diameter between 10 μm and 200 μm, in particular between 20 μm and 100 μm, preferentially between 40 μm and 80 μm; - characterized in that it has a diameter Dv10 of more than 5 μm, in particular between 10 μm and 70 μm, preferentially between 20 μm and 60 μm; - characterized in that it has a diameter Dv90 of less than 350 μm, in particular between 30 μm and 200 μm, preferentially between 50 μm and 150 μm; - characterized in that it has a median diameter Dv50 between 10 μm and 200 μm, in particular between 20 μm and 100 μm and preferentially between 30 μm and 90 μm; - characterized in that it has a span coefficient between 0.1 and 1.5, preferably between 0.1 and 1.0 and more preferentially between 0.5 and 1.0; - the polyamide is polyamide 11; - Melting temperature (T) between 195℃ and 205℃ f1 max and / or - Melting temperature (T f1 max ) and crystallization temperature (T c ) is between 35℃ and 45℃ It is a polyamide powder.

[0028] According to a third aspect, the present invention provides a polymeric composition having a unimodal melting endotherm and a single melting temperature (T) between 195°C and 205°C. f1 max ) and also has the following features: - volume average diameter between 10 μm and 200 μm, in particular between 20 μm and 100 μm, preferentially between 40 μm and 80 μm; - diameter Dv10 greater than 5 μm, in particular between 10 μm and 70 μm, preferentially between 20 μm and 60 μm; - volume median diameter Dv50 between 10 μm and 200 μm, in particular between 20 μm and 100 μm, preferentially between 30 μm and 90 μm; - diameter Dv90 less than 350 μm, in particular between 30 μm and 200 μm, preferentially between 50 μm and 150 μm; - a span coefficient between 0.1 and 1.5, preferably between 0.1 and 1, more preferentially between 0.5 and 1.0; - an enthalpy of fusion greater than 100 J / g, preferentially between 110 J / g and 160 J / g; and / or - Intrinsic viscosity between 0.8 and 1.8, preferentially between 1.0 and 1.5 The present invention relates to a polyamide 11 powder having at least one of the following:

[0029] According to a fourth aspect, the subject of the present invention is a composition in powder form, in particular for 3D printing by laser sintering, comprising: - polyamide powder according to the invention; and - at least one filler or additive A composition comprising:

[0030] According to a fifth aspect, the present invention relates to a method for producing a polyamide object by powder agglomeration by electromagnetic radiation mediated melting, said powder being as defined above.

[0031] According to a sixth aspect, the present invention relates to an article of manufacture obtained by electromagnetic radiation mediated melting of a powder or composition according to the invention.

[0032] According to a seventh aspect, the subject of the present invention is a method for producing a polyamide having a melting temperature (T f1 ) and crystallization temperature (T c ) and the difference (T f1 -T c ) is the use of the method according to the invention to increase

[0033] According to an eighth aspect, the present invention relates to a recycled inorganic filler obtainable according to the recycling method according to the invention.

[0034] According to one embodiment, the recycled inorganic filler is pre-coated with a polyamide powder having a unimodal melting endotherm and a single melting temperature, obtainable by the recycling method according to the invention. [Brief explanation of the drawings]

[0035] [Figure 1] 1 represents an image obtained by scanning electron microscopy (SEM) (magnification ×120) of a glass fiber pre-coated with PA11 obtained at the end of the method according to Example 1 of the invention. [Figure 2] 1 represents an image obtained by scanning electron microscopy (SEM) (magnification ×240) of carbon fibers pre-coated with PA11 obtained at the end of the method according to example 2 of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] Detailed Description The invention is explained in more detail and in a non-limiting manner in the following description.

[0037] definition It is pointed out that the expressions "from to" and "between and" used in this description should be understood as including each of the limitations mentioned.

[0038] The term "post-consumer polyamide powder composition" means a composition in powder form containing polyamide, optionally in combination with other components, in particular additives or fillers, obtained from the industrial conversion of a polyamide-based composition, for example by extrusion, typically by injection molding, or by 3D printing. It may in particular be a composition obtained from post-consumer finished products or from manufacturing scrap or waste generated during the process of converting a polyamide-based composition.

[0039] These post-consumer compositions are generally characterized by partial degradation of the polyamide polymer chains, which may be in a partially oxidized form and therefore contain imide and / or alcohol and / or primary amide functional groups not present in the virgin polyamide (prior to conversion and any use). The polyamide is also combined with other components, such as stabilizers, which may themselves be subject to degradation. The recycling method according to the present invention advantageously allows for the separation of the polyamide from other components in the post-consumer composition and the production of a substantially pure polyamide powder.

[0040] The term "powder" is understood to mean a solid substance in finely divided form, provided in the form of particles of very small size, generally less than a few hundred micrometers.

[0041] The powders are generally characterized by a thermogram obtained by differential scanning calorimetry (DSC) according to the following: - a first heating, which makes it possible to characterize the melting of the polyamide powder; - cooling, which makes it possible to characterize the crystallization of the polyamide material; - a second heating, which makes it possible to characterize the melting of the polyamide material itself.

[0042] The following terms relating to thermal properties are to be understood as defined in ISO standard 11357-1:2016: "Peak" refers to a portion of a thermogram obtained by differential scanning calorimetry (DSC) that deviates from the baseline, reaches a maximum or minimum, and then returns to the baseline. Such a peak may represent a first-order transition (crystallization exotherm or melting endotherm); a melting peak, for the purposes of this description, may specifically include multiple peaks or a shoulder before the signal returns to the baseline. - "Baseline" refers to the part of the recorded thermogram that is free of any transitions, and in this case, specifically the part that is free of any first-order transitions of melting or crystallization type. In the transition region, a virtual baseline can be defined. This is an imaginary line plotted through the transition region, assuming that the heat due to the transition is zero. The virtual baseline can be plotted by interpolating the baseline of the sample with a straight line. - "Peak area" refers to the area separated by the peak and the interpolated virtual baseline. This is considered as the transition enthalpy, expressed in J / g. The term "melting enthalpy" is understood to mean the heat required to melt the composition, corresponding to the area under the melting peak of the thermogram, measured according to ISO standard 11357-3:2018.

[0043] The term "melting temperature" is understood to refer to the temperature representative of the melting phenomenon at which an at least partially crystalline polyamide powder or polyamide material transitions into a viscous liquid state, measured according to ISO standard 11357-3:2018. Unless otherwise specified, this is more specifically the temperature corresponding to the maximum intensity of the melting peak measured by DSC. For the purposes of this description, a melting peak comprising multiple peaks or shoulders will therefore be associated with multiple melting temperatures, i.e., one melting temperature for each peak or shoulder.

[0044] The "melting temperatures in the first and second heats" are measured by DSC according to ISO standard 11357-3:2018, corresponding to the maximum signal intensity of the melting peak in the first heat and the second heat, respectively, both performed with a temperature ramp of 20°C / min, and are T for the first heat. f1 , and T for the second heating f2 Therefore, for the purposes of this description, multiple melting temperatures (T f1 ) is detected, the difference (T f1 -T c ) is used to calculate the T corresponding to the lowest melting temperature. f1 Temperature, i.e., T f1 min T f1 max is the maximum melting temperature (T f1 ) and the only melting temperature (T f1 ) corresponds to

[0045] In the following, T c The term "crystallization temperature," denoted as T, refers to the temperature at which an at least partially crystalline compound transitions from a viscous liquid state to a semi-crystalline state, measured with a temperature gradient of -20 °C / min, in accordance with ISO standard 11357-3:2018. The crystallization temperature more specifically corresponds to the temperature measured during cooling after a first melting (first heat) of the compound and before a second melting (second heat), which allows the compound's thermal history to be erased. Unless otherwise specified, this is the temperature of the crystallization peak corresponding to the maximum intensity of the DSC signal. Therefore, for the purposes of this description, if multiple crystallization temperatures are detected during cooling, T c corresponds to the highest crystallization temperature, and the difference (T f1 -T c It is this value that must be used to calculate

[0046] A "unimodal melting endotherm" of a polyamide powder is the portion of a thermogram obtained by differential scanning calorimetry (DSC) that corresponds to the first melting of the polyamide powder and has a single melting temperature T f1 In other words, the melting peak corresponding to the first heat contains only one peak. In contrast, a multimodal melting endotherm is characterized by a melting peak in the first heat having multiple peaks, i.e., multiple melting peak temperatures. Similarly, a melting endotherm in the first heat in which the melting peak has a shoulder would not be considered a unimodal endotherm for purposes of this description.

[0047] In the following, T p The term "precipitation temperature", denoted as , means the temperature at which the mixture formed by the polyamide and the solvent used in the process changes from a homogeneous state to a heterogeneous state. The precipitation temperature is detected using a temperature sensor (PT100 type) combined with a dynamic temperature regulation system (for example the "Petite Fleur" system sold by the company Huber). During precipitation, there is a strong spontaneous contribution of thermal energy (exotherm) that the temperature regulation system may not be able to compensate instantaneously. By IT means, the precipitation temperature can be accurately detected by plotting the derivative of the temperature of the reaction medium as a function of time. The value of this derivative is equal to the cooling rate programmed by the temperature regulation system before and after the precipitation event. The exotherm causes a perturbation in the derivative, which makes it possible to detect it. The temperature corresponding to the onset of the perturbation in the derivative is called the precipitation temperature (T p ) is considered to be

[0048] The term "Dv50" refers to the volume median diameter of powder particles for which the cumulative volume-weighted particle size distribution function is equal to 50%. Similarly, "Dv10" and "Dv90" are the corresponding diameters for which the cumulative volume-weighted particle size function is equal to 10% and 90%, respectively. These values ​​are measured, for example, using a Coulter Counter Multisizer 3 particle size analyzer in accordance with ISO standard 13319-1:2021. Rules for expressing particle size distribution results are specified by parts 1 to 6 of ISO standard 9276.

[0049] The term "span" factor means a factor characterizing the width of the particle size distribution, defined as Span = (Dv90 - Dv10) / Dv50, where the diameters "Dv10", "Dv50", and "Dv90" are as defined above.

[0050] The term "mean diameter" refers to the volume-average diameter value of the particles, which corresponds to the volume-weighted arithmetic mean of the particle sizes, as measured, for example, using a Coulter Counter Multisizer 3 particle size analyzer in accordance with ISO standard 13319-1:2021.

[0051] The term "viscosity" refers to intrinsic viscosity measured with an Ubbelohde viscometer according to ISO standard 307:2019, except using m-cresol as the solvent and at a temperature of 20°C. Intrinsic viscosity has the dimension of the reciprocal of concentration and is equal to the natural logarithm of the relative viscosity divided by the concentration of polymer dissolved in the solvent.

[0052] The term "3D printing" refers to a technology directed to producing parts through additive manufacturing by selectively melting powder with electromagnetic radiation such as laser or infrared radiation.

[0053] The term "VOC" means volatile organic compounds, i.e., organic compounds that have a vapor pressure of 0.01 kPa or more at a temperature of 293.15 K or have a corresponding volatility under specified conditions of use. The most commonly known are butane, toluene, ethanol (90° alcohol), acetone, and benzene.

[0054] Method for recycling used polyamide compositions Therefore, according to a first aspect, the object of the present invention is to convert used polyamide compositions into polyamides having a unimodal melting endotherm and a single melting temperature (T f1 max ), a method for recycling polyamide into a recycled polyamide powder having i. contacting a post-consumer polyamide composition with a solvent to obtain a mixture; ii. heating the mixture to dissolve the polyamide in the solvent; iii. Bring the mixture in the solvent to a precipitation temperature (T p ), which results in a non-unimodal melting endotherm and (T f1 max ) is the highest melting temperature; iv. The precipitated polyamide powder has a unimodal melting endotherm and melting temperature (T f1 max ) until the temperature of the mixture reaches at most T p temperature, especially T p -0.1℃~T p maintaining a temperature in the range of -15°C; and v. A step of recovering the resulting recycled polyamide powder. The object of the present invention is to provide a method comprising:

[0055] In the following description, the term "monomer" should be understood to mean "repeating unit." The case where the repeating unit is a combination of a diamine and a diacid is a special case. The corresponding monomer is considered to be the combination of a diamine and a diacid, i.e., a diamine-diacid pair. This is explained by the fact that neither the diamine nor the diacid can individually provide an amide-type functional group.

[0056] For the purposes of the present invention, the term "polyamide" refers to the condensation product of a lactam, an amino acid, or a diamine-diacid pair. It may be a homopolymer, i.e., a polymer obtained by condensation of the same repeating unit, i.e., the same monomer, or it may be a copolymer obtained by condensation of at least two repeating units, i.e., two different monomers called "comonomers", i.e., at least one monomer and at least one comonomer (a monomer different from the first monomer), to form a copolymer, such as a copolyamide (abbreviated CoPA), as defined below.

[0057] The term "copolyamide" (abbreviated as CoPA) means the polymerization product of at least two different monomers selected from: - amino acid or aminocarboxylic acid type monomers, preferably α,ω-aminocarboxylic acids; - lactam type monomers; - "diamine-diacid" type monomer pairs resulting from the reaction of diamines with dicarboxylic acids; and - In the case of mixtures of amino acid type monomers and lactam type monomers, their mixtures with monomers having different carbon numbers.

[0058] These monomers may be linear, branched, or substituted as desired.

[0059] According to a particular embodiment, the polyamide is a homopolymer.

[0060] According to a first type, the polyamides result from the condensation of aliphatic, cycloaliphatic or aromatic dicarboxylic acids, in particular containing from 4 to 36 carbon atoms, preferably from 6 to 18 carbon atoms, with aliphatic, cycloaliphatic or aromatic diamines, in particular containing from 2 to 20 carbon atoms, preferably from 6 to 14 carbon atoms.

[0061] Examples of dicarboxylic acids include 1,4-cyclohexanedicarboxylic acid, butanedioic acid, adipic acid, azelaic acid, suberic acid, sebacic acid, dodecanedicarboxylic acid, octadecanedicarboxylic acid, terephthalic acid, and isophthalic acid, but also dimerized fatty acids.

[0062] Examples of diamines include tetramethylenediamine, hexamethylenediamine, 1,10-decamethylenediamine, dodecamethylenediamine, trimethylhexamethylenediamine, bis(4-aminocyclohexyl)methane (BACM), bis(3-methyl-4-aminocyclohexyl)methane (BMACM), and isomers of 2,2-bis(3-methyl-4-aminocyclohexyl)propane (BMACP), para-aminodicyclohexylmethane (PACM), isophoronediamine (IPDA), 2,6-bis(aminomethyl)norbornane (BAMN), and piperazine (Pip).

[0063] Advantageously, the polyamide is selected from PA 4.6, PA 4.10, PA 4.12, PA 4.14, PA 4.18, PA 6.10, PA 6.12, PA 6.14, PA 6.18, PA 9.12, PA 10.10, PA 10.12, PA 10.14, and PA 10.18. In the notation PA XY, as is conventional, X represents the number of carbon atoms derived from the diamine residue and Y represents the number of carbon atoms derived from the diacid residue.

[0064] In certain embodiments, the polyamide is selected from polyamide 11, polyamide 6, polyamide 10.10, polyamide 10.12, or polyamide 6.10. Preferably, the polyamide is PA 11.

[0065] Steps i) and ii) The indefinite article "a" or the definite article "the" before the term "polyamide" used in the process according to the invention means, in the context of the present specification, "at least one polyamide" and "said at least one polyamide", respectively.

[0066] Thus, in a first step i), a used polyamide composition, ie a used composition comprising "at least one" polyamide, is contacted with a solvent to obtain a mixture.

[0067] Preferably, in this method only one polyamide is used.

[0068] However, it is also possible to use a mixture of several, in particular two, polyamides, preferably with a predominant polyamide representing more than 80% by weight of the total weight of the polyamides used in step i), in order to obtain a co-precipitation of the polyamide mixture.

[0069] In certain embodiments, the solvent contacted with the polyamide may be selected from ethanol, propanol, butanol, isopropanol, heptanol, formic acid, acetic acid, N-methylpyrrolidone, N-butylpyrrolidone, butyrolactam, and caprolactam.

[0070] Preferably, the solvent brought into contact with the polyamide is a C1-C4 aliphatic alcohol, more preferentially ethanol, and even more preferentially 96% pure technical grade ethanol (containing water and modified with 2-butanone and propan-2-ol).

[0071] The polyamide may have a weight fraction in the solvent of 0.01 to 0.30, preferably 0.1 to 0.3, in particular 0.01 to 0.05; 0.05 to 0.1; or 0.1 to 0.15 or 0.15 to 0.2; or 0.2 to 0.25; or 0.25 to 0.3.

[0072] The resulting mixture is then heated in step ii) until the polyamide is dissolved, ie a homogeneous mixture is obtained.

[0073] Heating of the mixture can be carried out especially at temperatures between 100°C and 180°C, preferably between 120°C and 160°C.

[0074] In certain embodiments, the mixture can be heated to a temperature of, for example, 100°C to 105°C; or 105°C to 110°C; or 110°C to 115°C; or 115°C to 120°C; or 120°C to 125°C; or 125°C to 130°C; or 130°C to 135°C; or 135°C to 140°C; or 140°C to 145°C; or 145°C to 150°C; or 150°C to 155°C; or 155°C to 160°C; or 160°C to 165°C; or 165°C to 170°C; or 170°C to 175°C; or 175°C to 180°C; or 180°C to 185°C; or 185°C to 190°C; or 190°C to 195°C; or 195°C to 200°C.

[0075] In certain embodiments, heating the mixture, particularly maintaining the mixture at the dissolution temperature, can have a duration of 1 to 6 hours, preferably 1 to 3 hours. Thus, heating the mixture can last for 1 hour to 1 hour 30 minutes, or 1 hour 30 minutes to 2 hours, or 2 hours to 2 hours 30 minutes, or 2 hours 30 minutes to 3 hours, or 3 hours to 3 hours 30 minutes, or 3 hours 30 minutes to 4 hours, or 4 hours to 4 hours 30 minutes, or 4 hours 30 minutes to 5 hours, or 5 hours to 5 hours 30 minutes, or 5 hours 30 minutes to 6 hours.

[0076] In a particular embodiment, the heating comprises at least one step of increasing the temperature to reach a maximum temperature between 100°C and 200°C, in particular between 120°C and 160°C.

[0077] In a particular embodiment, the heating comprises at least one step in which the temperature is kept essentially constant at a value between 100°C and 200°C, in particular between 120°C and 160°C.

[0078] Process iii) Then, in step iii), the mixture is cooled to precipitate the polyamide in powder form.

[0079] Precipitation temperature (T p ) may vary for the same polyamide depending on the solvent. Similarly, it may vary for the same solvent depending on the polyamide. Specifically, precipitation of polyamide is accompanied by the release of heat, resulting in a slight increase in internal temperature. At the end of precipitation, no further heat is released and the internal temperature returns to its nominal temperature.

[0080] The precipitation temperature may be between 80°C and 130°C, especially between 100°C and 120°C, especially when the solvent is a C1-C4 aliphatic alcohol.

[0081] This cooling can be carried out to reduce the temperature to 50° C. or higher. Thus, for example, cooling can be carried out to reduce the temperature to 50° C. Thus, for example, cooling can be carried out to a temperature in the range of 50° C. to 60° C., or 60° C. to 70° C., or 70° C. to 80° C., or 80° C. to 90° C., or 90° C. to 100° C., or 100° C. to 110° C., or 110° C. to 120° C., or 120° C. to 130° C.

[0082] Furthermore, this cooling can be carried out at a rate of 1 to 100° C. per hour, preferably 10 to 60° C. per hour, and more preferably 20 to 50° C. per hour. For example, cooling may be carried out at a rate of 1 to 5°C per hour; 5 to 10°C per hour; 10 to 15°C per hour; or 15 to 20°C per hour; or 20 to 25°C per hour; or 25 to 30°C per hour; or 30 to 35°C per hour; or 35 to 40°C per hour; or 40 to 45°C per hour; or 45 to 50°C per hour; or 50 to 55°C per hour; or 55 to 60°C per hour; or 60 to 65°C per hour; or 65 to 70°C per hour; or 70 to 75°C per hour; or 75 to 80°C per hour; or 80 to 85°C per hour; or 85 to 90°C per hour; or 90 to 95°C per hour; or 95 to 100°C per hour.

[0083] In certain embodiments, in order to promote precipitation, a certain amount of polyamide can be introduced in step i) of charging the starting materials. Preferably, the amount of this polyamide is 20% by weight or less, preferably 10% by weight or less, based on the total weight of polyamide used in step i). The polyamide may be the same or different from the one dissolved in the solvent, preferably the same. The polyamide may be selected from polyamide 11, polyamide 6, polyamide 10.10, polyamide 10.12, and polyamide 6.10, in particular.

[0084] The amount of polyamide added may therefore represent 0.1% to 1% by weight; or 1% to 2% by weight; or 2% to 3% by weight; or 3% to 4% by weight; or 4% to 5% by weight; or 5% to 8% by weight; or 8% to 12% by weight; or 12% to 16% by weight; or 16% to 20% by weight of polyamide, relative to the total weight of polyamide used in step i).

[0085] Step iii) is advantageously carried out with stirring. In a given stirring system, the volume-average diameter of the particles can be controlled by the stirring speed. Generally, as the stirring speed increases, the average diameter of the polyamide particles decreases. Conversely, as the stirring speed decreases, the average diameter of the polyamide particles increases.

[0086] Process iv) During the cooling step, when the precipitation temperature of the polyamide in the solvent is reached, the precipitation stage begins, which corresponds to the start of step iv) of the process according to the invention.

[0087] In step iv), the mixture is then heated to a temperature above the precipitation temperature (T p ), at most equal to this precipitation temperature, and in particular within −0.1° C. to −15° C. of this precipitation temperature, for a time sufficient to allow the production of a precipitated polyamide powder having a unimodal melting endotherm and an elevated melting temperature.

[0088] In other words, the method comprises in step iv) a temperature stationary phase in which the temperature is held constant for a period of time t. More specifically, the temperature is held constant for the entire duration of the polyamide precipitation phase, i.e. for a period of time t1, and then for an additional period of time t2 so as to allow the crystal lattice of the precipitated polyamide to densify, thereby obtaining a polyamide powder with a unimodal melting endotherm and an elevated melting temperature.

[0089] Typically, duration t1 is much shorter than duration t2, so that the total duration t of the temperature steady state phase is generally very close to t2.

[0090] The additional time required to produce a unimodal melting endotherm can be determined by analyzing samples collected at different intervals using differential scanning calorimetry (DSC) according to ISO standard 11357-3.

[0091] By way of example, at the end of the precipitation stage of polyamide 11, i.e., at the end of period t1, the inventors were able to observe by DSC the formation of a bimodal melting endotherm characterized by two distinct melting temperatures during the first heating. By holding the temperature constant for a sufficient additional time t2 at a temperature close to the precipitation temperature of the polyamide in the solvent, the inventors were able to observe a change from the bimodal melting endotherm of the polyamide particles to a unimodal melting endotherm, as indicated by the disappearance of the peak associated with the lowest melting temperature in the DSC thermogram in favor of the peak associated with the highest melting temperature. Advantageously, this temperature-steady state phase of total duration t1 + t2 allows the temperature T f1 -T c This allows both increasing the difference between the melting points and obtaining a unimodal melting endotherm.

[0092] According to a particular embodiment, in step iv), the mixture is kept at a constant temperature for a time t2 of at least 2 hours, in particular 3 to 12 hours, preferably at least 4 hours, in particular 4 to 12 hours, effective from the end of the precipitation of the polyamide. This additional time after the end of the precipitation of the polyamide can be 2 to 3 hours; or 3 to 4 hours; or 4 to 5 hours; or 5 to 6 hours; or 6 to 7 hours; or 7 to 8 hours; or 8 to 9 hours; or 9 to 10 hours; or 10 to 11 hours; or 11 to 12 hours.

[0093] In a particular embodiment, in step iv), the mixture is maintained at a constant temperature for a time t of at least 2 hours, in particular 3 to 12 hours, preferably at least 4 hours, in particular 4 to 12 hours, effective from the onset of polyamide precipitation. This time from the onset of polyamide precipitation can be 2 to 3 hours; or 3 to 4 hours; or 4 to 5 hours; or 5 to 6 hours; or 6 to 7 hours; or 7 to 8 hours; or 8 to 9 hours; or 9 to 10 hours; or 10 to 11 hours; or 11 to 12 hours.

[0094] Steps v) and vi) After the end of the temperature-steady state phase carried out in step iv), the precipitated polyamide particles are recovered in powder form from the mixture in step v) by conventional solid-liquid separation means.

[0095] This step generally involves cooling the resulting mixture, draining the liquid from the reactor, and separating the resulting precipitated polyamide particles from the solvent, particularly by filtration.

[0096] The process for producing a polyamide powder may also comprise a step vi) of drying the polyamide powder obtained in step iv) or recovered in step v). The drying step may be carried out, for example, in an agitator dryer or a rotary dryer.

[0097] In a particular embodiment, drying may be carried out at a temperature of 10° C. to 150° C., in particular 50° C. to 100° C., preferably 25° C. to 85° C., more preferentially 70° C. to 80° C. Drying may be carried out at a temperature of, for example, 10° C. to 20° C., or 20° C. to 30° C., or 30° C. to 40° C., or 40° C. to 50° C., or 50° C. to 60° C., or 60° C. to 70° C., or 70° C. to 80° C., or 80° C. to 90° C., or 90° C. to 100° C., or 100° C. to 110° C., or 110° C. to 120° C., or 120° C. to 130° C., or 130° C. to 140° C., or 140° C. to 150° C., or 150° C. to 160° C.

[0098] In certain embodiments, drying can be carried out under a vacuum of less than 100 mbar, preferably less than 50 mbar. Thus, drying can be carried out at a pressure of 1 to 10 mbar; or 10 to 20 mbar; 20 to 30 mbar; 30 to 40 mbar; 40 to 50 mbar; 50 to 60 mbar; 60 to 70 mbar; 70 to 80 mbar; 80 to 90 mbar; 90 to 100 mbar; 100 to 150 mbar; 150 to 200 mbar; 200 to 250 mbar; or 250 to 300 mbar; or 300 to 500 mbar; or 500 to 700 mbar; or 700 mbar to less than 1 bar (absolute pressure).

[0099] Alternatively, drying may be carried out at atmospheric pressure.

[0100] Advantageously, drying of the organic solvent facilitates the removal of VOCs that may be present in the composition as originally used.

[0101] Process vii) The particles recovered in step v) and optionally dried in step vi) may optionally be subjected to a step vii) aimed at separating them from any inorganic material, in particular inorganic material in the form of fillers, that may be present in the used polyamide composition involved in step i).

[0102] Examples of inorganic fillers that may be present in the post-consumer polyamide composition include hollow beads, fibers such as glass or carbon fibers, talc, carbon black, carbon nanotubes or other nanotubes.

[0103] The inorganic filler can be separated from the polyamide by taking advantage of the difference in density. By way of example, this separation can be carried out by decantation, using a cyclone, etc.

[0104] The precipitated polyamide particles may be separated from the inorganic filler by conventional means, for example by decanting the mixture from a suitable liquid such as a mixture of water and glycerol, and recovered at the end of step vii), and may optionally be dried under conditions similar to those of step v).

[0105] The polyamide powder and inorganic filler can be recovered separately and reused.

[0106] Advantageously, the inorganic fillers such as fibers recovered at the end of step vii) are coated with crystallized polyamide, which makes them particularly compatible with the polymer matrix for use as fillers in subsequent applications.

[0107] Thus, according to a particular embodiment, the present invention relates to an inorganic filler that can be obtained according to the recycling method described above, in particular according to steps i) to vii).

[0108] According to another embodiment, inorganic fillers that may be present in the used polyamide composition can be separated and recovered before precipitation of the polyamide, in particular before step iii). Specifically, during step i), the polyamide is generally dissolved in a solvent, while the inorganic fillers remain in suspension. They can then be separated and recovered by conventional solid-liquid separation techniques, such as filtration.

[0109] Polyamide powder obtainable according to the recycling method of the present invention. According to a second aspect, the present invention provides a method for recycling a polyethylene terephthalate (PEP) polymer having a unimodal melting endotherm and a single melting temperature (T f1 max ) polyamide powder.

[0110] In certain embodiments, the polyamide powder has an intrinsic viscosity of 0.8 to 1.7, preferably 1.0 to 1.5. Thus, for example, the powder may have an intrinsic viscosity of 0.8 to 0.9; or 0.9 to 1.0; or 1.0 to 1.1; or 1.1 to 1.2; or 1.2 to 1.3; or 1.3 to 1.4; or 1.4 to 1.5; or 1.5 to 1.6; or 1.6 to 1.7. In the above, intrinsic viscosity is (g / 100g) -1 It is expressed as:

[0111] Intrinsic viscosity is measured using a micro-Ubbelohde tube. Measurements are carried out at 20°C on 75 mg of powder sample at a concentration of 0.5% (m / m) in m-cresol. Intrinsic viscosity is (g / 100g) -1 and is calculated according to the following formula:

[0112] Intrinsic viscosity=ln(t s / t0)x1 / C, where C=m / px100, t s is the flow time of the solution, t0 is the flow time of the solvent, m is the mass of the sample whose viscosity is to be measured, and p is the mass of the solvent.

[0113] In a particular embodiment, the precipitated polyamide powder has a crystallization temperature (T c The polyamide powder may in particular have a crystallization temperature of 100°C to 110°C; or 110°C to 120°C; or 120°C to 130°C; or 130°C to 140°C; or 140°C to 150°C; or 150°C to 160°C; or 160°C to 170°C; or 170°C to 180°C; or 180°C to 190°C; or 190°C to 200°C.

[0114] In certain embodiments, the polyamide powder has a heat of fusion of 60 J / g or more, preferably 100 J / g or more, which can be, for example, 60 to 80 J / g; or 80 to 100 J / g; or 100 to 110 J / g; or 110 to 120 J / g; or 120 to 130 J / g; or 130 to 140 J / g; or 140 to 150 J / g; or 150 to 160 J / g.

[0115] In a particular embodiment, the polyamide powder has a melting temperature T between 130°C and 260°C, preferably between 160°C and 210°C. f1 In particular, the polyamide powder may have a melting temperature of 130°C to 140°C, or 140°C to 150°C, or 150°C to 160°C, or 160°C to 170°C, or 170°C to 180°C, or 180°C to 190°C, or 190°C to 200°C, or 200°C to 210°C, or 210°C to 220°C, or 220°C to 230°C, or 230°C to 240°C, or 240°C to 250°C, or 250°C to 260°C.

[0116] The melting temperature (T f1 ) is determined during the first heating, as described above. According to the method of the present invention, at the end of the temperature stationary phase at the end of step iv), a single melting temperature of the polyamide is observed.

[0117] In certain embodiments, the polyamide powder has a molecular weight of 0.1 to 50 m. 2 / g, preferably 1 to 10m 2 / g. Therefore, the precipitated polyamide powder has an apparent specific surface area of ​​0.1 to 1 m 2 / g; or 1 to 5 m 2 / g; or 5 to 10 m 2 / g; or 10-20m 2 / g; or 20-30m 2 / g; or 30-50m 2 / g. The apparent specific surface area (SSA) is measured according to the Brunauer-Emmett-Teller (BET) method, known to those skilled in the art. This is described in particular in The Journal of the American Chemical Society, Vol. 60, p. 309, February 1938, and corresponds to the ISO International Standard 9277:2010. The specific surface area measured according to the BET method corresponds to the surface porosity of the powder, i.e., includes the area formed by the pores on the surface of the particles.

[0118] According to a particular embodiment, the polyamide powder obtained according to the process of the present invention comprises: - volume average diameter between 10 μm and 200 μm, in particular between 20 μm and 100 μm, preferentially between 40 μm and 80 μm; - diameter Dv10 greater than 5 μm, in particular between 10 μm and 70 μm, preferentially between 20 μm and 60 μm; - volume median diameter Dv50 between 10 μm and 200 μm, in particular between 20 μm and 100 μm, preferentially between 30 μm and 90 μm; - diameter Dv90 less than 350 μm, in particular between 30 μm and 200 μm, preferentially between 50 μm and 150 μm; - span coefficient between 0.1 and 1.5, preferentially between 0.5 and 1.0; - enthalpy of fusion greater than 60 J / g, preferentially between 100 J / g and 160 J / g; - Intrinsic viscosity between 0.5 and 2.0, preferentially between 1.0 and 1.5 The present invention is characterized by having the following.

[0119] In a preferred embodiment, the unimodal melting endotherm and single melting temperature (T f1 max ) are characterized in that they have a span factor between 0.1 and 1.5, preferably between 0.1 and 1.0 and more preferentially between 0.5 and 1.0.

[0120] Polyamide 11 powder According to another aspect, the present invention provides a thermoplastic elastomer having a unimodal melting endotherm and a T between 195°C and 205°C, particularly about 200°C. f1 max The single melting temperature T during the first heating is equal to f1 and / or a crystallization temperature T between 150°C and 165°C, in particular about 158°C c The present invention relates to a polyamide 11 powder characterized by having the following properties:

[0121] The polyamide 11 powder is in particular a powder characterized by one or more of the following characteristics, preferably by all of the following characteristics: - volume average diameter between 10 μm and 200 μm, in particular between 20 μm and 100 μm, preferentially between 40 μm and 80 μm; - diameter Dv10 greater than 5 μm, in particular between 10 μm and 70 μm, preferentially between 20 μm and 60 μm; - volume median diameter Dv50 between 10 μm and 200 μm, in particular between 20 μm and 100 μm, preferentially between 30 μm and 90 μm; - diameter Dv90 less than 350 μm, in particular between 30 μm and 200 μm, preferentially between 50 μm and 150 μm; - span coefficient between 0.1 and 1.5, preferentially between 0.5 and 1.0; - enthalpy of fusion greater than 100 J / g, preferentially between 110 J / g and 160 J / g; - Intrinsic viscosity between 0.8 and 1.8, preferentially between 1.0 and 1.5.

[0122] Preferably, the polyamide 11 powder has a unimodal melting endotherm and a T between 195°C and 205°C. f1 max The single melting temperature T during the first heating is equal to f1 and a span factor between 0.1 and 1.5, preferentially between 0.1 and 1 and more preferentially between 0.5 and 1.0.

[0123] A composition in powder form for 3D printing, especially by selective laser sintering. According to yet another aspect, the present invention relates to a composition in powder form, in particular for 3D printing by selective laser sintering, comprising a polyamide powder as defined above in combination with one or more conventional fillers or additives (i.e., suitable for 3D printing techniques).

[0124] This composition is advantageously ready to use.

[0125] The composition may include additives that help improve the deformation characteristics of the powder for use as a function in 3D printing technology.

[0126] The additives generally account for less than 5 wt. % of the total weight of the composition. Preferably, the additives account for less than 1 wt. % of the total weight of the composition. The additives may include flow agents, stabilizers (light stabilizers, especially UV stabilizers, and heat stabilizers), optical brighteners, dyes, pigments, and energy absorbing additives (including UV absorbers).

[0127] The fluidizing agent may be, for example, hydrophilic or hydrophobic silica. Advantageously, the fluidizing agent represents from 0.01% to 0.5% by weight relative to the total weight of the composition. Preferably, the composition comprises from 0.1% to 0.4% by weight of the fluidizing agent.

[0128] The composition may also contain one or more fillers, which can improve in particular the mechanical properties (stress at break and elongation at break) of the part obtained by 3D printing.

[0129] The fillers generally represent less than 50% by weight, preferably less than 40% by weight, of the total weight of the final powder, and include reinforcing fillers, especially inorganic fillers such as carbon black, talc, carbon nanotubes or non-carbon nanotubes, fibers (glass, carbon, etc.), which may or may not be milled.

[0130] The additives or fillers may be mixed with the polyamide before, during (e.g., before dissolving the polyamide in step i) or after precipitation in step iv), or after the polyamide powder production process. Preferably, the additives are introduced after the polyamide powder production process by mixing the additives with the polyamide powder.

[0131] The composition preferably comprises polyamide in an amount of 80% or more, or 81% or more, or 82% or more, or 83% or more, or 84% or more, or 85% or more, or 86% or more, or 87% or more, or 88% or more, or 89% or more, or 90% or more, or 91% or more, or 92% or more, or 93% or more, or 94% or more, or 95% or more, or 96% or more, or 97% or more, or 98% or more, or 99% or more, or 99.1% or more, or It may contain 99.2% or more, or 99.3% or more, or 99.4% or more, or 99.5% or more, or 99.6% or more, or 99.7% or more, or 99.8% or more, or 99.9% or more, or 99.91% or more, or 99.92% or more, or 99.93% or more, or 99.94% or more, or 99.95% or more, or 99.96% or more, or 99.97% or more, or 99.98% or more, or 99.99% or more by weight.

[0132] In a particular embodiment, the polyamide included in the composition is polyamide 11.

[0133] In certain embodiments, the polyamide 11 has a melting temperature (T f1 )

[0134] In certain embodiments, the melting temperature (T f1 ) and crystallization temperature (T c The difference between the two temperatures is between 35℃ and 45℃.

[0135] Use of a polyamide powder obtained according to the recycling method of the present invention, or a composition in powder form containing it, in a method for powder agglomeration by melting. The subject of the present invention is also a method for producing a polyamide object by powder agglomeration by electromagnetic radiation mediated melting, said powder being a polyamide powder or a composition in powder form as defined above.

[0136] The electromagnetic radiation can be infrared, ultraviolet or visible radiation. Preferably, it is laser radiation (hence this manufacturing method is known as "selective laser sintering").

[0137] According to this method, a thin layer of powder is deposited on a horizontal plate maintained in a chamber heated to a temperature called the build temperature. The term "build temperature" refers to the temperature to which the powder bed of the constituent layers of the three-dimensional object being built is heated during the process of layer-by-layer sintering of the powder. This temperature is determined by the T of the polyamide powder obtained from the manufacturing process. f1 -T c is selected within the range of f1 -5℃~T c +5°C, and more preferentially T f1 -10℃~T c +10°C. The electromagnetic radiation then provides the energy necessary to sinter the powder particles at different points in the powder layer according to the geometric shape corresponding to the object (for example, using a computer that stores the shape of the object in a memory and reproduces this shape in the form of slices).

[0138] The horizontal plate is then lowered a distance corresponding to the thickness of the layer of powder, and a new layer is deposited. The layer thickness is typically between 0.05 mm and 2 mm, and generally around 0.1 mm. Electromagnetic radiation provides the energy necessary to sinter the powder particles into the geometry corresponding to this new slice of the object, and so on. This procedure is repeated until the object is produced.

[0139] The powders are used in agglomeration processes by melting or sintering. These powders can have a volume average diameter between 10 μm and 200 μm, and advantageously between 20 μm and 100 μm.

[0140] Preferably, the volume average diameter is between 40 μm and 80 μm.

[0141] The invention also relates to an article of manufacture, in particular made by 3D printing, obtained by electromagnetic radiation mediated sintering of a powder as described above.

[0142] The products may be selected from prototypes and models, especially in the fields of automotive, marine, aviation, aerospace, medicine (prosthetics, hearing systems, tissue, etc.), textiles, clothing, fashion, decoration, electronics, telephony, home automation, IT and lighting.

[0143] More generally, the present invention relates to the melting temperature (T f1 ) and crystallization temperature (T c ) and the difference (T f1 -T c The present invention also relates to the use of the above-mentioned manufacturing method for increasing the amount of hydroxybenzoates. [Example]

[0144] The following examples illustrate embodiments of the present invention, but do not limit the invention.

[0145] In all of the following examples: - The particle size of the powders was characterized by measuring the particle size distribution with a Coulter Counter-Multisizer 3 instrument (Beckmann Coulter) according to ISO standard 13319-1:2021. From this, the volume mean diameter and the diameters Dv10, Dv50, and Dv90 were determined. The span values ​​were calculated from these volume mean diameters. - Analysis of the thermal properties is carried out by DSC according to ISO standard 11357-3 "Plastics - Differential Scanning Calorimetry (DSC) Part 3: Determination of Temperatures and Enthalpies of Melting and Crystallization". The temperatures of particular interest here are the first heat melting temperature (T f1 ) and crystallization temperature (T c) In particular, in a method known to those skilled in the art (in the field of manufacturing 3D objects by powder agglomeration by melting), the difference "T f -T c " is T f1 -T c Corresponds to. - The intrinsic viscosity of polyamides is measured with an Ubbelohde viscometer according to ISO standard 307:2019, except using m-cresol as solvent and a temperature of 20°C. - Acidity (which can be considered as the concentration of COOH chain ends of the polyamide) and basicity (which can be considered as the concentration of NH2 chain ends of the polyamide) are measured potentiometrically. Acidity is measured according to the following method: a polyamide sample is dissolved in benzyl alcohol at a concentration of 0.6% by weight, and the sample is then analyzed potentiometrically using a 0.02N tetrabutylammonium hydroxide solution. Basicity is measured according to the following method: a polyamide sample is dissolved in meta-cresol at a concentration of 0.6% by weight, and the sample is then analyzed potentiometrically using a 0.02N perchloric acid solution.

[0146] Example 1 according to the invention: Recycling of post-consumer polyamide compositions containing glass fibers The scrap and cores recovered after injection of Rilsan® BZM30 O TLDA grade were first coarsely ground to facilitate handling, and their composition was as follows: 70 wt. % partially oxidized PA11 and 30 wt. % glass fiber (plus residual antioxidant).

[0147] 85 g of this ground starting material and 425 g of technical-grade ethanol (96% purity) were charged into a reactor (1 L working volume) and mechanically stirred using an impeller-type turbomixer. The stirrer was operated at 500 rpm throughout the test. The medium was then heated to 160°C, followed by an isothermal hold for 1 hour to dissolve only the used polyamide. Controlled cooling was carried out at a rate of -60°C / h to 110°C to precipitate the polyamide, followed by an isothermal hold at this same temperature for 4 hours to allow crystalline densification. The exotherm of crystallization was detected at 115°C, and thermal control was interrupted for a few minutes. The precipitation temperature was 115°C. Controlled cooling was then resumed at the same rate of -60°C / h to 20°C, after which the reactor was drained and the dispersion was dried in an oven at 75°C under atmospheric pressure.

[0148] Using a water / glycerol mixture (45 / 55% by volume), it was possible to separate the used PA11 powder from the glass fibers by decantation. It was then found that 61% by weight of the used PA11 precipitated directly in powder form, while the remaining 39% by weight was able to coat the glass fibers (see Figure 1). The PA11-precoated glass fibers were more easily incorporated than natural glass fibers and had excellent compatibility with the polyamide matrix. In addition to being recyclable, these glass fibers could be more easily used in polyamide-based compositions.

[0149] The resulting PA11 powder has the following characteristics: intrinsic viscosity of 1.30, volume average diameter of 61 μm, and diameters Dv10=29 μm, Dv50=68 μm, and Dv90=91 μm, thus span=0.91. DSC analysis of this PA11 powder shows, on the first heating, a unimodal melting endotherm with a single melting temperature of 201 °C associated with a melting enthalpy of 136 J / g, and a crystallization temperature T c = 158°C. f1 -T c is equal to 43°C.

[0150] Example 2 according to the invention: Recycling of post-consumer polyamide compositions containing carbon fibers The scrap and cores recovered after injection of the Rilsan® BSR30 grade were first coarsely ground to facilitate handling, and their composition was as follows: 70 wt. % partially oxidized PA11 and 30 wt. % carbon fiber (plus residual antioxidants and carbon black).

[0151] 85 g of this ground starting material and 425 g of technical-grade ethanol (96% purity) were charged into a reactor (1 L working volume) and mechanically stirred using an impeller-type turbomixer. The stirrer was operated at 500 rpm throughout the experiment. The medium was then heated to 160°C, followed by an isothermal hold for 1 hour to dissolve only the partially oxidized polyamide. Controlled cooling was carried out at a rate of -60°C / h to 110°C to precipitate the polyamide, followed by an isothermal hold at this same temperature for 4 hours to allow crystalline densification. The exotherm of crystallization was detected at 115°C, and thermal control was interrupted for a few minutes. The precipitation temperature was 115°C. Controlled cooling was then resumed at the same rate of -60°C / h to 20°C, after which the reactor was drained and the dispersion was dried in an oven at 75°C under atmospheric pressure.

[0152] Using a water / glycerol mixture (45 / 55% by volume), it was possible to separate the used PA11 powder from the carbon fibers by decantation. It was then found that 52% by weight of the partially oxidized PA11 precipitated directly in powder form, while the remaining 48% by weight was able to coat the carbon fibers (see Figure 2). The PA11-precoated carbon fibers were more easily incorporated than natural carbon fibers and had excellent compatibility with the polyamide matrix. In addition to being recyclable, these carbon fibers could be more easily used in polyamide-based compositions.

[0153] The resulting PA11 powder has the following characteristics: black color (no carbon black separation), intrinsic viscosity of 1.42, volume average diameter of 55 μm, and diameters of Dv10=29 μm, Dv50=58 μm, and Dv90=77 μm, thus span=0.83. DSC analysis of this PA11 powder shows, on the first heating, a unimodal melting endotherm with a single melting temperature of 200 °C associated with a melting enthalpy of 132 J / g, and a crystallization temperature T c = 159°C. f1 -T c is equal to 42°C.

[0154] Example 3 according to the invention: Recycling of post-consumer polyamide compositions contaminated with VOCs The used pipes were recovered from fuel lines during the dismantling of various vehicles. These pipes were originally obtained by extrusion of Rilsan® BESN Black P20 TL. They were first coarsely crushed to make them easier to handle. These used PA11 pipes contain 4% by weight of VOCs (mainly mineral spirits, toluene, xylene, and trimethylbenzene). The content was determined by thermogravimetric analysis, and the composition was determined by gas chromatography analysis.

[0155] 85 g of this ground starting material and 425 g of technical-grade ethanol (96% purity) were charged into a reactor (1 L working volume) and mechanically stirred using an impeller-type turbomixer. The stirrer was operated at 500 rpm throughout the experiment. The medium was then heated to 160 °C, followed by an isothermal hold for 1 hour to dissolve only the partially oxidized polyamide. Controlled cooling was carried out at a rate of -60 °C / h to 115 °C to precipitate the polyamide, followed by an isothermal hold at this same temperature for 4 hours to allow crystalline densification. The exotherm of crystallization was detected at 120 °C, and thermal control was interrupted for a few minutes. The precipitation temperature was 120 °C. Controlled cooling was then resumed at the same rate of -60 °C / h to 20 °C, and the reactor was then drained, and the dispersion was dried under vacuum (50 mbar) at 90 °C for 6 hours.

[0156] The VOC content of the PA11 powder is 0.35% by mass (mainly consisting of ethanol, with trace contaminants less than 0.1% by mass). Therefore, the process of dissolution in / precipitation from ethanol appears to be able to extract contaminants from PA11, followed by entrainment during vacuum drying to remove the contaminants.

[0157] The resulting PA11 powder has the following characteristics: black color (no carbon black separation), intrinsic viscosity of 1.45, volume average diameter of 51 μm, and diameters of Dv10=25 μm, Dv50=49 μm, and Dv90=62 μm, thus span=0.76. DSC analysis of this PA11 powder shows, on the first heating, a unimodal melting endotherm with a single melting temperature of 199 °C associated with a melting enthalpy of 136 J / g, and a crystallization temperature T c = 159°C. f1 -T c is equal to 40°C.

[0158] Example 3a (Comparative): Removal of VOCs from Used Composition by Drying The same ground starting material as in Example 3 was placed directly in a dryer to extract VOCs from PA11. After drying at 90°C under a vacuum of 50 mbar for 12 hours, only 0.5% by weight of these VOCs could be removed. To remove 3.5% by weight of VOCs, the dryer had to be heated at 150°C under a vacuum of 50 mbar for an additional 12 hours. The ground PA11 powder thus obtained still contained a residual VOC content of 0.5% by weight. Furthermore, its particle size makes it unsuitable for use in 3D printing.

[0159] In addition to recovering powder that can be used directly for 3D printing, the drying of Example 3 in accordance with the present invention advantageously requires less energy to remove VOCs.

[0160] Example 4 (Comparative) According to U.S. Patent Application Publication No. 2008 / 0166496 Diamine-terminated PA11 was prepared by polymerization of 250 g of 11-aminoundecanoic acid in the presence of 1.25 g of 4,4'-diaminocyclohexylmethane (PACM, mixture of isomers). The resulting polyamide 11 had an intrinsic viscosity of 1.42 in combination with a concentration of chain-end COOH groups equal to 19 mmol / kg and chain-end NH groups equal to 67 mmol / kg.

[0161] 85 g of this diamine-terminated PA11 and 425 g of technical-grade ethanol (96% purity) were charged into a reactor (1 L working volume) and mechanically stirred using an impeller-type turbomixer. The stirrer was operated at 500 rpm throughout the entire test. The medium was heated to 152 °C and then isothermally held at this temperature for 1 h. Next, the medium was cooled to 112 °C at a rate of 25 °C / h and then maintained at this temperature for 1 h. During this cooling phase, when the internal temperature reached 125 °C, the jacket temperature had to be reduced by 2–3 °C below the internal temperature. A crystallization exotherm was detected, and controlled cooling was interrupted for a few minutes. After 1 h at this temperature, the medium was cooled to room temperature. The reactor was then drained, and the ethanol was distilled in a stirred oven at 70 °C / 400 mbar, followed by drying the powder at 84 °C / 20 mbar.

[0162] The resulting PA11 powder has the following particle size characteristics: volume average diameter 89 μm, and diameters Dv10=65 μm, Dv50=93 μm, and Dv90=123 μm, thus span=0.62. DSC analysis of this PA11 powder shows, upon the first heating, a bimodal melting endotherm with a shoulder at 193 °C and a peak at 202 °C, associated with a melting enthalpy of 140 J / g, and a crystallization temperature T c = 162°C. The lower of the two melting temperatures is used to calculate the difference T f1 -T c is calculated, and therefore this difference is equal to 29°C.

Claims

1. The used polyamide composition exhibited a unimodal melting endotherm and a single melting temperature (T ｆ１ ｍａｘ ), a method for recycling polyamide into recycled polyamide powder having the following properties: i. contacting a post-consumer polyamide composition with a solvent to obtain a mixture; ii. heating the mixture to dissolve the polyamide in the solvent; iii. The mixture is heated in the solvent to a temperature at which the polyamide is precipitated (T ｐ ), which results in a non-unimodal melting endotherm and a (T ｆ１ ｍａｘ ) is the highest melting temperature; iv. The precipitated polyamide powder has a unimodal melting endotherm and melting temperature (T ｆ１ ｍａｘ The temperature of the mixture is increased to at most T ｐ temperature, in particular T ｐ -0.1℃~T ｐ maintaining a temperature in the range of −15° C.; and v. A step of recovering the resulting recycled polyamide powder. A method comprising:

2. The solvent to be brought into contact with the polyamide is an alcohol, particularly C １ ~C ４ 2. The method of claim 1, wherein the alcohol is an aliphatic alcohol, preferably ethanol.

3. 3. The method according to claim 1, wherein the polyamide is polyamide 11, polyamide 6, or polyamide 10.10, or polyamide 10.12, or polyamide 6.

10.

4. 4. The method according to claim 1, wherein in step iv) the mixture is maintained at a temperature effective from the end of precipitation of the polyamide for a period of at least 2 hours, in particular between 3 and 12 hours.

5. The method of any one of claims 1 to 4, wherein the composition also comprises a volatile organic compound (VOC).

6. The method according to any one of claims 1 to 5, wherein the composition comprises an inorganic filler, in particular fibres, in particular glass fibres and / or carbon fibres.

7. 7. The method according to claim 6, further comprising a step vii) of separating and recovering inorganic fillers that may be present in the precipitated polyamide powder, in particular after step iv), v) or vi).

8. The unimodal melting endotherm and single melting temperature (T ｆ１ ｍａｘ ).

9. Polyamide powder according to claim 8, characterized in that it has a span factor between 0.1 and 1.5, preferably between 0.1 and 1.0, more preferentially between 0.5 and 1.

0.

10. 10. Powder according to claim 8 or 9, wherein the polyamide is polyamide 11.

11. Melting temperature (T ｆ１ ｍａｘ ) and crystallization temperature (T ｃ 11. The powder according to claim 9, wherein the difference between the temperature of the powder and the temperature of the container is between 35°C and 45°C.

12. A unimodal melting endotherm and a single melting temperature (T ｆ１ ｍａｘ ) and further features: a volume-average diameter between 10 μm and 200 μm, in particular between 20 μm and 100 μm, preferentially between 40 μm and 80 μm; a diameter Dv10 of more than 5 μm, in particular between 10 μm and 70 μm, preferentially between 20 μm and 60 μm; a volume median diameter Dv50 between 10 μm and 200 μm, in particular between 20 μm and 100 μm, preferentially between 30 μm and 90 μm; a diameter Dv90 of less than 350 μm, in particular between 30 μm and 200 μm, preferentially between 50 μm and 150 μm; a span factor between 0.1 and 1.5, preferably between 0.1 and 1 and more preferentially between 0.5 and 1.0; an enthalpy of fusion greater than 100 J / g, preferentially between 110 J / g and 160 J / g; and / or an intrinsic viscosity between 0.8 and 1.8, preferentially between 1.0 and 1.5 The polyamide 11 powder according to any one of claims 8 to 11, having at least one of:

13. A composition in powder form for 3D printing, in particular by laser sintering, comprising: - a polyamide powder according to any one of claims 8 to 12; and - at least one filler or additive A composition comprising:

14. A method for producing a polyamide object by powder agglomeration by electromagnetic radiation mediated melting, wherein the powder is as claimed in any one of claims 8 to 13.

15. An article of manufacture obtained by electromagnetic radiation mediated melting of a powder according to any one of claims 8 to 12 or a composition according to claim 13.

16. An inorganic filler obtainable according to the recycling method of claim 6 or 7.

17. 17. The inorganic filler of claim 16, pre-coated with a polyamide powder having a unimodal melting endotherm and a single melting temperature.

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