Polyamide composition prepared from recycled polyamide powder

Abstract

Polyamide composition prepared from recycled polyamide powder. The application relates to a process for preparing a polyamide composition comprising the steps of: a) supplying a mixture comprising virgin polyamide (vPA) and recycled polyamide (rPA) in the form of an unprocessed powder obtained from additive manufacturing by sintering or a powder coating or electrostatic spraying process, or from powder obtained by grinding a polyamide-based part of an article to be recycled; b) molten mixing of said mixture, thereby obtaining a polyamide composition; c) recovery of said polyamide composition, the resulting polyamide composition, and its uses for the preparation of articles by extrusion, injection, or overmolding. Figure for the abstract: 1

Description

Title of the invention: Polyamide composition prepared from recycled polyamide powder

[0001] The present invention relates to a process for preparing a polyamide composition from unprocessed powder obtained from additive manufacturing by sintering or from a powder coating process or from electrostatic spraying or from powder obtained by grinding a polyamide-based part of an object to be recycled, a polyamide composition, and its use for the preparation of articles.

[0002] Additive manufacturing (AM) has experienced rapid growth in recent years, particularly due to the possibility of designing objects of very diverse shapes, the short time between design and production, and the associated environmental and economic advantages.

[0003] Powder sintering by melting (hereinafter "sintering") is induced by radiation, such as, for example, a laser beam ("laser sintering" or "selective laser sintering" SLS), infrared radiation, UV radiation, or any electromagnetic radiation source that melts the powder layer by layer to create three-dimensional objects. The SLS technique produces a part by applying powder layer by layer, each layer being in the form of a thin powder bed, generally on the order of 100 pm. A laser is used to melt a portion of this powder at the desired location, and then a new layer of powder is deposited. The process is repeated until a thermoplastic polymer object is formed layer by layer.

[0004] One can also mention selective sintering processes using an absorber, in particular the technologies known as "High Speed ​​Sintering" (HSS) and "Multi-Jet Fusion" (MJF). In these technologies, the fabrication of 3D objects is also done layer by layer, using a polyamide-based powder that is melted in a controlled manner for each layer constituting the 3D object: an absorber is deposited on the layer (for example by means of a liquid ink in the "inkjet process") before the layer is exposed to electromagnetic radiation (for example infrared) which causes the areas containing said absorber to melt.

[0005] Sintering generates a large quantity of unprocessed powder. For each layer, the powder that was not targeted by the radiation is not incorporated into the final object. Therefore, a large amount of unprocessed powder remains.

[0006] This is difficult to valorize because it is generally degraded. Indeed, the powder bed is preheated and maintained at a temperature close to the powder's melting point, typically 5 to 15°C below its melting point. This allows a Good melting of the powder targeted by the laser and good definition of each layer of the laser-formed object are essential. At this temperature, the unprocessed powder undergoes aging-related degradation, such as solid-state polycondensation and oxidation reactions. This leads to an increase in polymer chain length, resulting in a decrease in the melt flow rate (MFR). Consequently, these degraded powders generally cannot be directly reused in subsequent additive manufacturing by sintering, especially when the viscosity of the degraded powder is significantly different from that of the original powder.Any attempt to reuse these powders results in parts with a poor surface finish, for example an orange peel appearance, and reduced mechanical properties, in particular lower elongation at break, because the defects act as break initiators during tensile tests.

[0007] Recycling this unprocessed powder for other types of processing (extrusion, injection molding) is not easy. Indeed, the heating during the sintering process affects the intrinsic viscosity of the powder. Generally, extruding or molding this degraded powder results in spongy articles and / or articles whose mechanical properties, particularly strength, and aesthetic properties, particularly with regard to color (which tends towards brown), are inferior to those of articles formed from virgin polymer.

[0008] A large quantity of waste is thus generated by additive manufacturing processes using sintering in the form of unprocessed, degraded powder. This powder is very rarely recycled.

[0009] Taking polyamide 12 (PA 12) as an example, which is the main type of plastic used in the SLS process, PA 12 powder waste can represent up to 50%, or even up to 90%, of the total powder used in the process. This represents a significant loss of PA 12 powder, since this powder waste must be disposed of.

[0010] The literature reports several attempts to recycle this polyamide powder waste. US application 2022 / 0064405 describes a recycled polyamide composition comprising polyamide waste, preferably from additive manufacturing, a lubricating agent, and a crystallizing agent. The invention described in this application is based on increasing the crystallization temperature and improving the fluidity conferred by these agents. The composition described in this application is free of virgin polyamide.

[0011] There is therefore a need to recycle polyamide powder waste from additive manufacturing.

[0012] Furthermore, it is known to use polymer powders to manufacture coatings for substrates, particularly metallic ones, typically by powdering or by Electrostatic spraying. A powdered polymer composition is applied to the substrate as a loose powder, for example, by electrostatic spraying or by immersing the substrate to be coated in a fluidized bed of powder. The polymers used for powder production are usually thermosetting resins, but thermoplastic polymers can also be used. Polyamides, due to their high chemical and thermal resistance, are polymers of choice for demanding applications, such as coating dishwasher baskets.

[0013] However, these powders are not easily recyclable. Indeed, the fraction of powder that does not reach the substrate during spraying, called "overspray", which is worth recovering for recycling, generally does not have the same composition and / or the same properties as the powder initially used, and the coatings obtained from it therefore do not correspond to it in terms of appearance and properties.

[0014] There is therefore a need to recycle waste polyamide powders from a powder coating or electrostatic spraying process.

[0015] The weaker mechanical properties of polyamide powder waste from additive manufacturing or from a powder coating or electrostatic spraying process, in particular the reduced elongation at break, make them less attractive than virgin polyamides, especially for the preparation of articles.

[0016] Finally, there is a need to recycle many polyamide-based parts belonging to defective and / or recyclable items in order to promote the circular economy and the reuse of materials. Due to the previous use these parts have undergone, the polyamide they contain generally does not have properties as good as those of virgin polyamide.

[0017] One of the objectives of this application is to enable the recycling of unprocessed powders from additive manufacturing or from a powder coating or electrostatic spraying process, or powders obtained by grinding a polyamide-based part of an object to be recycled.

[0018] One of the objectives is to reduce the environmental impact and lower the cost price:

[0019] - additive manufacturing or powder coating processes or by electrostatic projection by recycling their unprocessed powders,

[0020] - methods for preparing new polyamide articles using as raw material, said unprocessed powders or a powder obtained by grinding a polyamide-based part of an object to be recycled.

[0021] One of the objectives of the application is to provide a PA11 or PA12 polyamide composition having certain improved mechanical and / or physicochemical properties than those of a polyamide composition prepared from exclusively virgin polyamides.

[0022] One of the objectives of the application is to provide a polyamide composition whose processability (suitability for implementation, for transformation) by extrusion, by injection or by overmolding is improved.

[0023] To this end, according to a first object, the invention relates to a process for preparing a polyamide composition comprising the steps of:

[0024] a) supply of a mixture comprising:

[0025] of 5 to 90% by weight of virgin polyamide vPA,

[0026] of 10 to 95% by weight of recycled polyamide rPA,

[0027] the polyamide to be recycled rPA being in the form of an unprocessed powder from additive manufacturing by sintering or a coating process by powder coating or electrostatic spraying, or powder obtained by grinding a polyamide-based part of an object to be recycled,

[0028] b) mixing said mixture in its molten state, thereby obtaining a composition of polyamides,

[0029] c) recovery of said polyamide composition.

[0030] The process includes a step a) of supplying a mixture comprising a virgin polyamide vPA, a recycled polyamide rPA, the recycled polyamide rPA being in powder form.

[0031] For the purposes of this application, "vPA" means virgin polyamide. This has not undergone any prior processing, and in particular it has not been used in a prior additive manufacturing process by sintering or by powder coating or electrostatic spraying, and it does not originate from a part of a pre-existing article.

[0032] By "prior" means a process taking place before step a) of the process according to the invention.

[0033] For the purposes of this application, "rPA" refers to a recyclable polyamide, also called recycled polyamide. The latter is:

[0034] - either in the form of unprocessed powder resulting from additive manufacturing by sintering or a powder coating or electrostatic spraying process, preferably in the form of unprocessed powder from additive manufacturing by sintering, also known as 3D sintering printing,

[0035] - either in powder form obtained by grinding a polyamide-based part of an object to be recycled.

[0036] By "unprocessed powder from additive manufacturing by sintering" is meant powder that was not exposed to radiation during a prior additive manufacturing process by sintering and that was not used to form the object formed during the prior additive manufacturing process. Typically, this powder has passed at least 1 minute at a temperature above 100 °C in an additive manufacturing device.

[0037] By "unprocessed powder from a powder coating or electrostatic spraying process" is meant powder that was not used to form the coating on the substrate in the prior powder coating or electrostatic spraying process. Typically, this powder was used in a process of coating a substrate by powder coating or electrostatic spraying (electrospray).

[0038] In both cases, the unprocessed powder used as recycled polyamide in the process according to the invention corresponds to polyamide powder waste from a prior process. The recycled polyamide (rPA) has therefore undergone degradation, generally thermal.

[0039] The term "polyamide-based part of an object to be recycled" means a part obtained through a prior transformation, for example, injection molding, extrusion, or overmolding. The object to be recycled (or the part) may be used, broken, of poor quality, and / or unfit for its intended function. The polyamide in this part is therefore also waste.

[0040] The unprocessed powder, or the powder obtained by grinding a polyamide-based component of an object to be recycled, generally comprises more than 10%, typically more than 50%, or even more than 75% polyamide (or a mixture of polyamides) by weight relative to the weight of the powder. The proportion of polyamides is generally less than 99.9% by weight.

[0041] The powder is generally such that the median volume diameter (Dv50) of the particles it contains is in the range of 5 to 250 µm, in particular 5 to 200 µm, preferably in the range of 10 to 150 µm. According to this application, the "average volume diameter" or "Dv" is the average volume diameter of a powdered material as measured according to ISO 9276 - parts 1 to 6: "Representation of data obtained by particle size analysis", in its version valid in 2022. Different diameters are distinguished. More specifically, Dv50 designates the median volume diameter, that is to say, the diameter corresponding to the 50th percentile by volume, and Dv10 and Dv90 designate, respectively, the average volume diameters below which 10% or 90% by volume of the particles lie. The average diameter in volume can be measured in particular by means of a laser granulometer, for example a laser granulometer (Malvern Insitec System).Associated software (RT sizer) then allows the volumetric distribution of a powder to be obtained and the DvlO, Dv50 and Dv90 to be deduced.

[0042] Polyamide rPA and vPA can independently be a homopolyamide, a copolyamide, a polyamide-polyether block copolymer (PEBA) or their mixture. Polyamide rPA and vPA can independently also be a mixture of polyamide and at least one other polymer, with the polyamide forming the matrix and the other polymer(s) forming the dispersed phase.

[0043] Preferably, polyamide rPA and vPA are independently a condensation product:

[0044] - of one or more amino acids;

[0045] - of one or more lactams; or

[0046] - of one or more salts or mixtures of diamines with diacids.

[0047] As an example of an amino acid, it is possible to cite alpha-omega amino acids, such as aminocaproic acid, amino-7-heptanoic acid, amino-11-undecanoic acid, n-heptyl-11-aminoundecanoic acid and amino-12-dodecanoic acid.

[0048] Lactam monomers preferably comprise between 3 and 12 carbon atoms on the main ring and may be substituted. Examples of lactams include [3,[3-dimethylpropriolactam, α,α-dimethylpropriolactam, amylolactam, caprolactam, capryllactam, oenantholactam, 2-pyrrolidone, and lauryllactam.

[0049] Preferably the diamine entering into the composition of the polyamide rPA and / or vPA is an aliphatic diamine, an aryl diamine and / or a saturated cyclic diamine having 6 to 12 carbon atoms. Examples of diamines include hexamethylenediamine, decanediamine, piperazine, tetramethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, 1,5-diaminohexane, 2,2,4-trimethyl-1,6-diaminohexane, diamine polyols, isophorone diamine (IPD), methylpentamethylenediamine (MPDM), bis(aminocyclohexyl)methane (BACM), bis(3-methyl-4-aminocyclohexyl)methane (BMACM), methaxylyenediamine, bis-p-aminocyclohexylmethane, and trimethylhexamethylenediamine.

[0050] Preferably, the dicarboxylic acid in the composition of the polyamide rPA and / or vPA has between 4 and 18 carbon atoms. Examples of dicarboxylic acids include adipic acid, sebacic acid, azelaic acid, suberic acid, isophthalic acid, butanedioic acid, 1,4-cyclohexyldicarboxylic acid, terephthalic acid, the sodium or lithium salt of sulfoisophthalic acid, dimerized fatty acids (these dimerized fatty acids have a dimer content of at least 98% and are preferably hydrogenated) and dodecanedioic acid HOOC-(CH2)10-COOH.

[0051] Preferably, the rPA and / or vPA copolyamide results from the condensation of at least two different monomers, for example, at least two different alpha-omega aminocarboxylic acids or two different lactams or a lactam and an alpha-omega aminocarboxylic acid with different numbers of carbon atoms. It is also It is possible to cite copolyamides resulting from the condensation of at least one alpha-omega aminocarboxylic acid (or a lactam), at least one diamine, and at least one dicarboxylic acid. It is also possible to cite copolyamides resulting from the condensation of an aliphatic diamine with an aliphatic dicarboxylic acid and at least one other monomer chosen from aliphatic diamines other than the previous one and from aliphatic diacids other than the previous one.

[0052] Preferably, the rPA and / or vPA polyamide powder comprises at least one polyamide or copolyamide comprising at least one monomer selected from the group consisting of 4.6, 4T, 5.4, 5.9, 5.10, 5.12, 5.13, 5.14, 5.16, 5.18, 5.36, 6, 6.4, 6.9, 6.10, 6.12, 6.13, 6.14, 6.16, 6.18, 6.36, 6T, 9, 10.4, 10.9, 10.10, 10.11, 10.12, 10.13, 10.14, 10.16, 10.18, 10.36, 10T, 11, 12, 12.4, 12.9, 12.10, 12.12, 12.13, 12.14, 12.16, 12.18, 12.36, 12T, MXD6, MXD10, MXD12, MXD14, and their mixtures.

[0053] Preferably, the polyamide rPA and / or vPA is selected from the group consisting of PA 6, PA 6.6, PA 10.10, PA 11, PA 12, PA 10.11, PA 6.10, PA6.12, PA 6.13 and mixtures thereof.

[0054] By way of example of a copolyamide, one can cite copolymers of ca-prolactam and lauryllactam (PA 6.12), copolymers of caprolactam, adipic acid and hexamethylene diamine (PA 6.66), copolymers of caprolactam, lauryllactam, adipic acid and hexamethylene diamine (PA 6.12.66), copolymers of caprolactam, lauryllactam, amino-II-undecanoic acid, azelaic acid and hexamethylene diamine (PA 6.69.11.12), copolymers of caprolactam, lauryllactam, amino-II-undecanoic acid, adipic acid and hexamethylene diamine (PA 6.66.11.12), copolymers of lauryllactam, azelaic acid and hexamethylene diamine (PA 69.12), copolymers of amino-II-undecanoic acid, terephthalic acid and decamethylene diamine (PA 11.10T).

[0055] Preferably, the average number of carbon (C) atoms relative to the nitrogen (N) atom of the polyamide rPA and / or vPA is greater than or equal to 8, in particular greater than or equal to 10, preferably greater than or equal to 11. Particularly preferred, the average number of carbon (C) atoms relative to the nitrogen (N) atom of the polyamide rPA and / or vPA is 11 or 12.

[0056] Preferably, the polyamide rPA and the vPA are independently selected from PA 11, PA 10.10, PA 10.12, PA 12, PA 12.12, PA 10.14 or PA 12.14 and their mixtures, preferably PA11 or PA12 or a mixture thereof.

[0057] The nomenclature used to define polyamides is described in ISO 1874-1:2010 "Plastics — Polyamide (PA) materials for molding and extrusion — Part 1: Designation", in particular on page 3 (tables 1 and 2) and is well known to those skilled in the art.

[0058] Preferably, the polyamide of the rPA polyamide and the vPA polyamide are of a nature identical. For example, virgin polyamide is vPA1, recycled polyamide rPA is rPA1. According to another example, virgin polyamide is vPA12, recycled polyamide rPA is rPA12.

[0059] Virgin polyamide vPA generally has an inherent viscosity less than or equal to 1.50, in particular less than or equal to 1.40, preferably less than or equal to 1.30. For the purposes of the application, the inherent viscosity is such as measured using a Ubbelohde tube at 20°C on a 0.5% by weight solution in m-cresol according to ISO 307:2019.

[0060] Generally, the inherent viscosity of virgin polyamide vPA is lower than that of the powder of the mixture, typically the inherent viscosity of virgin polyamide vPA is lower by at least 10%, in particular by at least 20%, preferably by at least 30% than that of the powder of the mixture.

[0061] The powder of the mixture generally has an inherent viscosity greater than or equal to 1.50, preferably greater than or equal to 1.60, and most often in the range of 1.70 to 5.00.

[0062] Generally, the weight polydispersity index Ip of virgin polyamide vPA is lower than that of recycled polyamide rPA. Typically, the weight polydispersity index Ip of virgin polyamide vPA is at least 20% lower, in particular at least 35%, and preferably at least 50% lower than the weight polydispersity index Ip of recycled polyamide rPA. The weight polydispersity index Ip is the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn.

[0063] Generally, the z-polydispersity index Iz of virgin polyamide vPA is lower than that of recycled polyamide rPA. Typically, the z-polydispersity index Iz of virgin polyamide vPA is at least 30% lower, in particular at least 50%, and preferably at least 70% lower than the z-polydispersity index Iz of recycled polyamide rPA. The z-polydispersity index Iz is the ratio of the average molecular weight in z-millimeters Mz to the number molecular weight Mn.

[0064] The number average molecular masses Mn, weight average Mw and z average Mz are measured by size exclusion chromatography (or gel permeation chromatography) according to ISO 16014-1 of 2012. Typically, the polyamide is solubilized in hexafluoroisoproponol stabilized with 0.05 M potassium trifluoroacetate for 24 h at room temperature (20°C) at a concentration of 1 g / L. The resulting solution is then filtered through a PTFE membrane with a porosity of 0.2 µm and injected at a flow rate of 1 mL / min into a liquid chromatography system equipped with a set of PFG columns from Polymer Standards Service, consisting of a 50 x 8 mm pre-column, a 1000 Å column measuring 300 x 8 mm with a particle size of 7 µm, and a 100 Å column measuring 300 x 8 mm with a particle size of 7 µm. Molar masses are measured by the refractive index and are expressed in PMMA equivalents, used as a calibration standard, then converted to g / mol.

[0065] The mixture in step a) comprises:

[0066] from 5 to 90% by weight, generally from 5 to 70% by weight, in particular from 20 to 65% by weight, preferably from 40 to 60% by weight, of virgin polyamide vPA,

[0067] of 10 to 95% by weight, generally of 30 to 95% by weight, in particular of 35 to 80% by weight, preferably of 40 to 60% by weight, of recycled polyamide rPA,

[0068] in relation to the total weight of the mixture.

[0069] The mixture in step a) may include components other than virgin polyamide vPA or recycled polyamide rPA.

[0070] The mixture in step a) may include a chain-limiting agent comprising at least one, preferably at least two, functional groups, each independently selected from carboxylic acids and amines. This embodiment is particularly preferred when the proportion of recycled polyamide (rPA) in the mixture is greater than 50% by weight.

[0071] This chain-limiting agent can be a dicarboxylic acid, a diamine, or an amino acid. It allows reaction with the amide, amine, or carboxylic acid functions of the rPA and / or vPA during molten mixing and reduces the inherent viscosity of the polyamide composition obtained by the process.

[0072] The amino acid can be chosen from aminocaproic acid, 7-aminoheptanoic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, and / or a mixture thereof.

[0073] The proportion by weight of chain limiting agent in the mixture is generally between 0 and 4% by weight, in particular between 0.01 and 4% by weight, preferably from 0.1 to 1%, advantageously from 0.2 to 0.8%.

[0074] In order to ensure good properties (flexibility, burst strength, tear strength, rheology, alloy morphology, compatibilization, homogeneity, consistency, adhesion) and, in particular, good shock resistance properties and shock resistance after aging (especially oxidative aging at high temperature), it is possible to add to the mixture a shock modifier, in particular of an elastomeric nature and preferably polar.

[0075] Thus, the mixture may comprise up to 20% by weight, relative to the total weight of the mixture, of a shock modifier consisting of a non-rigid polymer having a flexural modulus of less than 100 MPa measured according to ISO 178 of 2010.

[0076] This non-rigid polymer is preferably as flexible as possible and has the lowest possible glass transition temperature (Tg), i.e., below 0°C. This shock modifier is, if necessary, chemically functionalized so as to be able to react with the polyamide and form an alloy compatible with them.

[0077] The shock modifier is preferably made up of one or more polyolefins, part or all of which carry a function chosen from among the carboxylic acid, carboxylic acid anhydride, epoxide and any other function capable of reacting chemically with the polyamides, typically with its amine chain ends (case of carboxylic acid, maleic anhydride) or its acid chain ends (case of epoxide, in particular glycidyl methacrylate).For example, the polyolefin is chosen from: an elastomeric ethylene-propylene copolymer (EPR), an ethylene-butene copolymer, an ethylene-octene copolymer, an elastomeric ethylene-propylene-diene copolymer (EPDM) and an ethylene / alkyl (meth)acrylate copolymer, for example anhydride-grafted EPR such as Exxon's Exxelor VA 1803, or polyethylene, ethyl acrylate and maleic anhydride (coPE / EA / MAH) copolymer such as SK's Lotader 4700.

[0078] The mixture may also include polyamide additives, such as: pigments, colorants, light (UV) and / or heat stabilizers, plasticizers, surfactants, optical brighteners, antioxidants, natural waxes, release agents, fillers, reinforcing fibers or mixtures thereof.

[0079] The fillers envisaged include mineral fillers, such as those chosen from the group, given by way of non-limiting, comprising talc, kaolin, magnesia, slags, silica, carbon black, carbon nanotubes, expanded or unexpanded graphite, titanium oxide.

[0080] The reinforcing fibers are chosen from among the fibers, in particular short ones. The fibers may be of synthetic origin, in particular glass or carbon fibers, or natural, typically of plant origin such as flax, reed, bamboo or hemp fibers.

[0081] Common stabilizers used with polymers include phenols, phosphites, UV absorbers, HALS (Hindered Amine Light Stabiliser) type stabilizers, metal iodides, and thioethers. Examples include Irganox 1010, 245, 1098, Irgafos 168, 126, Tinuvin 312, 770, Iodide P201 from Ciba, Nylostab S-EED from Clariant, and AO 412S from Adeka Palmarole.

[0082] Preferably, the additives of the mixture may be present in a quantity less than or equal to 10%, and more particularly less than 5% by weight relative to the weight of the mixture.

[0083] The sum of virgin polyamide vPa and powder comprising recycled polyamide rPa generally represents at least 40% by weight, in particular at least 60% by weight, or even at least 80% by weight of the mixture, sometimes at least 95% of the mixture, or even 100% of the mixture.

[0084] Preferably, the mixture is free from a crystallizing agent (such as a salt in organic acid (e.g. sodium, potassium or calcium benzoate) and / or lubricating agent (such as zinc, calcium or magnesium stearate).

[0085] Preferably, the mixture is free of H3PO2 and / or H3PO3. For the purposes of this application, H3PO2 and H3PO3 are not considered additives. Unprocessed powders from additive manufacturing by sintering that are recycled have the advantage of containing few or no precursor species for phosphine formation, unlike virgin polyamide powders. This advantage makes it possible to process (by extrusion, injection molding in particular) recycled 3D powders more safely than virgin polyamide powders.

[0086] In one embodiment, the mixture consists of a mixture of:

[0087] from 5 to 70% by weight, in particular from 20 to 65% by weight, preferably from 40 to 60% by weight weight, of virgin polyamide vPA,

[0088] of 30 to 95% by weight, in particular 35 to 80% by weight, preferably 40 to 60% by weight, of recycled polyamide rPA,

[0089] of 0 and 4% by weight, in particular between 0.01 and 4% by weight, preferably from 0.1 to 1%, advantageously from 0.2 to 0.8% of a chain-limiting agent, in particular as defined above,

[0090] from 0 to 20% by weight, in particular 0 to 10% by weight of a shock modifier, in particular as defined above, and

[0091] from 0 to 10% by weight, in particular 0 to 5% by weight of additives, in particular as defined above,

[0092] in relation to the total weight of the mixture.

[0093] The process includes a step b) of mixing said mixture in the molten state, by which a composition of polyamides is obtained.

[0094] The composition according to the invention is particularly simple to prepare since it is sufficient to carry out a mixing in the molten state of a mixture of vPA and rPA.

[0095] Typically, the mixing temperature is at least 5°C higher, preferably at least 10°C higher, than the higher melting point of vPA or rPA. This temperature should generally remain below 330°C to avoid thermal degradation of the polyamides.

[0096] Typically, the temperature during mixing is above 200°C and below 330°C, preferably above 220°C and below 320°C, for example between 220°C and 310°C, or for example between 230°C and 300°C.

[0097] Generally, the residence time of the mixture during kneading is less than 10 minutes, in particular less than 5 minutes, or less than 3 minutes or even less.

[0098] This molten mixing process is preferably carried out using a single screw, co-rotating twin screws or a BUSS type co-mixer.

[0099] The process includes a step c) of recovering the polyamide composition obtained after mixing in the molten state. The recovery step c) can be carried out using methods known to those skilled in the art.

[0100] It generally comprises an extrusion of the polyamide composition obtained after mixing in the molten state.

[0101] Extrusion can be carried out in a mixer under shear such as a single or twin screw extruder.

[0102] Extrusion can be carried out through a granulation die to produce granules. The median volume diameter Dv50 of the granules is advantageously within a range of 1 to 10 mm, and in particular from 2 to 4 mm. Alternatively, extrusion can be carried out through a die to a cooled rolling mill in which the mixture solidifies, or using a calender. The solidified mixture can then be fed to a crusher to produce flakes. These flakes typically have an average size of 5 x 5 x 1 mm.

[0103] Typically, the recovery step consists of an extrusion step, a step of cooling the composition in the molten state using a coolant generally containing water, a step of cutting the composition into granules, and a step of separating the coolant and the cooled composition.

[0104] The cutting step can be carried out during the cooling step, or after the cooling step, and before the separation step or after the separation step.

[0105] The recovery step can be followed by a grinding step to obtain the composition in the form of flakes or powder.

[0106] These shapes are adapted for its subsequent shaping by extrusion, injection or overmolding.

[0107] The process can be discontinuous ('batch' in English).

[0108] The process can be continuous.

[0109] According to a second object, the invention relates to a polyamide composition that can be obtained by the process described above.

[0110] The embodiments described above, in particular for the mixture and its constituents and their proportions, and the form of the composition obtained, are of course applicable, since the polyamide composition is likely to be obtained from the process described above.

[0111] Advantageously, the composition according to the invention exhibits a better elongation at break as measured by ISO 527 IA of 2019 than an identical composition except that the recycled polyamide rPA is replaced by virgin polyamide vPA (therefore compared to a composition free of rPA).

[0112] Advantageously, the composition according to the invention has better resistance to Cold impact resistance is comparable to that of an identical composition except that recycled polyamide (rPA) is replaced by virgin polyamide (vPA) (i.e., compared to a composition free of rPA). Cold impact resistance is advantageously improved by at least 10%, preferably by at least 30%, and in particular by at least 50%. Impact resistance can be determined according to ISO 179-leA:2010.

[0113] Advantageously, in the molten state, the composition according to the invention has better rheological properties at representative implementation frequencies (for example at an angular frequency between 5 and 500 rad / s) by extrusion, injection or overmolding than an identical composition except that the recycled polyamide rPA is replaced by virgin polyamide vPA (i.e. compared to a composition free of rPA), which is an advantage for shaping the composition by extrusion or injection.

[0114] Without being bound by any particular theories, the recycled polyamide (rPA) in the powder generally has a higher molecular weight and a higher polydispersity index (Iz(Mz / Mn)) and / or Ip(Mw / Mn) than virgin polyamide (vPA) of the same nature. For example, rPA1 generally has a higher molecular weight and a higher polydispersity index (Iz(Mz / Mn)) and / or Ip(Mw / Mn) than vPA1. This allows, when this powder is added to a virgin polyamide grade, for an increase in cold impact resistance and elongation at break of the articles (compared to an article free of rPA).

[0115] This also improves the processability / implementation of the composition according to the invention. Indeed, the higher polydispersity index Iz (Mz / Mn) of the polyamide composition according to the invention compared to that of virgin polyamide vPA improves the melt strength (composition in the molten state) during extrusion, molding, or overmolding to form an article or part.

[0116] Furthermore, rPA has more oxidized functions than vPA, and therefore more polar groups. The addition of rPA to a grade of vPA confers better adhesion properties and thus facilitates the implementation of the composition according to the invention by overmolding. The improvement in adhesion properties can, for example, be demonstrated with a peel test at the interface of two parts joined by overmolding.

[0117] Indeed, during the additive manufacturing process, new species resulting from oxidation mechanisms, in particular amide functions and / or methylene in alpha of said amide functions, such as primary amide functions, nitriles, methyl groups at the end of the chain (CH3(CH2)n, alkenes (CH2=CH-), formamides, imides, carboxylic acids and alcohols, appear in the structure of polyamides.

[0118] Infrared allows the detection of the presence or absence of said new species resulting from oxidation mechanisms.

[0119] Thus the absorption band from 1700 to 1740cm1 corresponds to an imide, that from 1680 to 1720 cm1 to the carbonyl of the carboxylic acid and that from 3580 to 3670 cm-1 corresponds to the alcohol function of the carboxylic acid.

[0120] The absorption band from 3580 to 3670 cm1 corresponds to the free alcohol function.

[0121] The amide function is characterized on the one hand by a pair of absorption bands from 3100 to 3500 cm1 and from 1560 to 1640 cm1 which corresponds to the NH group of the amide and on the other hand by the absorption band from 1650 to 1700 cm1 which corresponds to the carbonyl group of the amide.

[0122] The quantification of said new species resulting from the oxidation mechanisms is carried out by proton NMR in dichloromethane-d2, by adding HFIP (hexafluoroisopropanol) to solubilize the polyamide.

[0123] For example, 20 mg of polymer can be dissolved in 0.7 mL of solvent with an HFIP / CD2C12 ratio of 1 / 3.

[0124] Some of the functional groups mentioned below can, for example, be observed by 13C NMR. Thus, the 36 ppm line corresponds to the α-CH2 of the primary amide, and the 34 ppm line corresponds to the α-CH2 of the carboxylic acid. These species can be quantified by integrating the area under the lines and comparing it to the area under the 37.1 ppm line corresponding to the secondary amide.

[0125] Similarly, the lines corresponding to the carbonyl groups of the primary amide, carboxylic acid and secondary amide functions are observed at 181.2 ppm, 179.6 ppm and 177.4 ppm respectively.

[0126] The line at 16.7 ppm corresponds to the CH2 in the α of the nitrile group.

[0127] The formamide group gives a chemical shift at 163.0 ppm and 166.3 ppm.

[0128] Other functional groups mentioned above can be observed by proton (¹H) NMR in the solvent HFIP / CD2C12 as described above. The CHO group line of the formamides is observed at 7.92 and 8.01 ppm. The line corresponding to the α-CH2 groups of the primary amides can be observed at 2.30 ppm. The 0.9 ppm line corresponds to the CH3 group of the type CH3-(CH2)n. The line at 2.40 ppm corresponds to the α-CH2 group of the nitrile functional group. Similar to what is described for carbon NMR, the ratios of new functional groups to secondary amides can be determined by integrating the area under the lines and comparing them to the area under the line corresponding to the α-CH2 group of the secondary amide (2.20 ppm).

[0129] Preferably, the inherent viscosity of the polyamide composition according to the invention is lower by at least 10%, in particular by at least 20%, preferably by at least 30%, compared to that of the powder of the mixture used in step a).

[0130] Preferably, when the average number of carbon (C) atoms relative to the nitrogen (N) atom of the rPA and vPA polyamide is greater than or equal to 8, in particular greater than or equal to 10, preferably greater than or equal to 11, in particular when the virgin polyamide and the polyamide to be recycled used as starting materials in the mixture are independently of PA11 or PA12, the inherent viscosity of the polyamide composition according to the invention is less than or equal to 1.50, preferably less than or equal to 1.40, 1.30, 1.25, 1.20, 1.15, or even less than or equal to 1.10. For example, the inherent viscosity of the polyamide composition can be between 0.80 and 1.50, preferably between 0.90 and 1.40, between 0.90 and 1.30, between 0.90 and 1.20 (inclusive limits).

[0131] Preferably, when the average number of carbon atoms (C) relative to the nitrogen atom (N) of the polyamide rPA and vPA is greater than or equal to 8, in particular greater than or equal to 10, preferably greater than or equal to 11, in particular when the virgin polyamide and the polyamide to be recycled used as starting materials in the mixture are independently of PA11 or PA12, the melt flow index (MFI or MFR) of the composition according to the invention, as measured at 235 °C, under 2.16 kg, is between 0.1 and 60 cmVIO min, advantageously between 0.2 and 45 cmVIO min.

[0132] Generally, the z-polydispersity index Iz of the polyamides in the composition according to the invention is greater than that of the virgin polyamide used as a starting product in the mixture, and / or the weight-polydispersity index Ip of the polyamides in the composition is greater than that of the virgin polyamide used as a starting product in the mixture.

[0133] Preferably, the z-polydispersity index Iz (Mz / Mn) of the polyamides of the composition according to the invention is greater than or equal to 3.0, typically greater than or equal to 3.5, in particular greater than or equal to 4.0, preferably greater than or equal to 5.0 and / or the weight-polydispersity index Ip (Mw / Mn) of the polyamides of the composition is greater than or equal to 1.5, typically greater than 2.0, in particular greater than or equal to 2.5, preferably greater than 3.0, or even greater than 4.0. Generally, the z-polydispersity index Iz is less than 30.0, in particular less than 25.0, preferably less than 15.0 and / or the weight-polydispersity index Ip is less than 20.0, in particular less than 15.0, preferably less than 8.0, particularly preferably less than 7.0.

[0134] According to a third object, the invention relates to the process of preparing an article comprising a step of extrusion, molding or overmolding of the composition according to the invention, by which an article is obtained.

[0135] According to a fourth object, the invention relates to a method for preparing an article comprising the steps of:

[0136] a) supply of a mixture comprising:

[0137] of 5 to 90% by weight of virgin polyamide vPA,

[0138] of 10 to 95% by weight of recycled polyamide rPA,

[0139] relative to the total weight of the mixture,

[0140] the recycled polyamide rPA being in the form of an unprocessed powder resulting from additive manufacturing by sintering or from a coating process by powder coating or electrostatic spraying,

[0141] b) mixing in the molten state of said mixture, thereby obtaining a composition of polyamides,

[0142] c) recovery of said polyamide composition,

[0143] d) extrusion, molding or overmolding of the recovered composition, by which an article is obtained.

[0144] According to a fifth object, the invention relates to the article that can be obtained according to the above process.

[0145] The article is preferably a shaped article, such as a fiber, fabric, film, sheet, rod, tube, extruded part, or injected part, comprising the composition as defined above. Thus, the composition according to the present invention is advantageous for the manufacture of articles, in particular articles or components of sporting goods, which must exhibit both good impact resistance and good resistance to mechanical, chemical, UV, and thermal stresses. Examples of such sporting goods include components of sports shoes, sports equipment such as ice skates or other winter sports and mountaineering equipment, ski bindings, snowshoes, sports bats, boards, horseshoes, fins, golf balls, and recreational vehicles, particularly those intended for cold-weather activities.We can also mention, in general, leisure and DIY items, tools and road maintenance equipment subject to climatic and mechanical stresses, protective equipment such as helmet visors, goggles, and goggle frames. Other examples, by way of non-exhaustive list, include car parts such as headlight covers, rearview mirrors, small parts for off-road vehicles, fuel tanks, particularly for mopeds, motorcycles, and scooters, subject to mechanical and chemical stresses, screws, cosmetic products subject to mechanical and chemical stresses, lipstick tubes, pressure gauges, and aesthetic protective elements such as gas cylinders. We can also mention electronic objects or parts requiring adherence to dimensions, for example, parts for mobile phones, computers, and tablets.

[0146] Advantageously, the article according to the invention generally exhibits less exudation than an article prepared from a composition in which recycled polyamide rPA is replaced by virgin polyamide vPA (i.e., compared to a composition free of rPA11 or rPA12). Typically, the exudation is determined on 1 mm plates which are placed for 7 days at 70°C and 62% RH (relative humidity). Exudation is manifested by the appearance of a deposit on the surface and is assessed visually.

[0147] Without wishing to be bound to any particular theory, the increase in the molar masses of the polyamide chains in the powder waste would imply a lower proportion of oligomers in that waste. These oligomers are generally responsible for exudation. The article according to the invention thus has lower exudation than an article obtained from exclusively virgin polyamide.

[0148] The invention is illustrated with the figure and the following examples, which are provided by way of non-limiting reason.

[0149] Fig. 1 represents rheology curves of virgin PA 11 (vPA1), virgin PA 12 (vPA12), unprocessed PA11 powder to be recycled (rPA1) from additive manufacturing by sintering, unprocessed PA 12 powder to be recycled (rPA12) from additive manufacturing by sintering, a composition obtained by hot mixing of 50% by weight of vPA1 and 50% by weight of vPA1 powder, and a composition obtained by hot mixing of 50% by weight of vPA12 and 50% by weight of vPA12 powder.

[0150] Examples

[0151] Example 1: Rheology of compositions according to the invention

[0152] For two types of homopolymer PA (PA11 (with an inherent viscosity of 1.0 and supplied by Arkema) and PA12 (with an inherent viscosity of 1.0 and supplied by AESNO TL)), the rheology of the molten polyamides used as starting materials in the blend (virgin PA and unprocessed recycled PA powder from additive manufacturing by sintering) was determined. These polyamides, blended with a 50% by weight proportion of vPA and 50% by weight of rPA relative to the blend weight, were then mixed in the molten state according to the process of the invention to form two polyamide compositions.

[0153] The rheology curves are illustrated in [Fig.1].

[0154] Capillary rheology analyses show that, at frequencies representative of implementation by extrusion or injection, the two compositions according to the invention exhibit better molten form stability than virgin vPA polyamides, which is an advantage for shaping the composition by extrusion or injection.

[0155] Example 2: Inherent viscosity, polydispersity index Ip and Iz of a composition according to the invention

[0156] A virgin vPAl 1 and an unprocessed rPAl 1 powder to be recycled from additive manufacturing by sintering were mixed with a proportion of 50% by weight of vPAl 1 and 50% by weight of rPA relative to the weight of the mixture, and were then mixed in a molten state according to the process according to the invention to form a polyamide composition.

[0157] It proved impossible to implement the rPAl 1 powder by injection molding. The inherent viscosity of rPAl 1 being too high (large Ip and Iz values), the mixture was too viscous for injection molding and did not fill the molds properly, resulting in parts with defects and a poor surface finish. In contrast, the composition obtained by mixing could be injected without difficulty.

[0158] Table 1 below provides the inherent viscosities and polydispersity indices Ip and Iz of the starting products and of the composition according to the invention.

[0159] [Tables 1] Virgin PAU Method Virgin PAU + 50% 3D Powder Recyclable PAU 100% Recyclable 3D Powder PA11 Modulus (MPa) ISO 527 IA (2019) 1437 1432 Nominal break strength (%) ISO 527 IA (2019) 114 252 Difficulties during implementation due to very high inherent viscosity Tensile strength (MPa) ISO 527 IA (2019) 33.4 45.5 Difficulties during implementation due to very high inherent viscosity Impact strength at 23°C (kJ / m²) ISO 179 LEA of 2010 8 8 Difficulties during implementation due to very high inherent viscosity Impact strength at -30°C (kJ / m²) ISO 179 LEA of 2010 9 12 Difficulties during implementation because of very high inherent viscosity. Inherent viscosity according to ISO 307*: 2019: 1.01, 1.07, 2.75. Ip = Mw / Mn calculated from Mw and Mn measured according to ISO 16014-1:2012: 1.8, 3.0, 8.4. Iz = Mz / Mn calculated from Mz and Mn measured according to ISO 16014-1:2012: 2.7, 5.9, 24.4.

[0160] * as measured using a Ubbelohde tube at 20°C on a 0.5% solution in weight in m-cresol except that the measurement temperature is 20°C instead of 25°C

[0161] Inherent viscosities and polydispersity indices Ip and Iz of the starting products and of the composition according to the invention

Claims

Demands

1. A process for preparing a polyamide composition comprising the steps of: a) supplying a mixture comprising: 5 to 90% by weight of virgin polyamide vPA, 10 to 95% by weight of recycled polyamide rPA, relative to the total weight of the mixture, the recycled polyamide rPA being in the form of an unprocessed powder obtained by additive manufacturing by sintering or by a powder coating or electrostatic spraying process, or powder obtained by grinding a polyamide-based part of an article to be recycled, the weight polydispersity index Ip (Mw / Mn) of the virgin polyamide vPA being lower than the weight polydispersity index Ip of the recycled polyamide rPA, b) molten mixing of said mixture, thereby obtaining a polyamide composition having a weight polydispersity index Ip greater than or equal to 1.5, c) recovering said composition from polyamides.

2. A method according to claim 1, wherein the recycled polyamide rPA and the virgin polyamide vPA are homopolyamides.

3. A method according to claim 1 or 2, wherein the average number of carbon atoms (C) relative to the nitrogen atom (N) of the recycled polyamide rPA and / or virgin polyamide vPA is greater than or equal to 8, in particular greater than or equal to 10, preferably greater than or equal to 11.

4. A method according to any one of claims 1 to 3, wherein the recycled polyamide rPA and the virgin polyamide vPA are independently selected from PA11 or PA 12.

5. A method according to any one of claims 1 to 4, wherein the recycled polyamide rPA and the virgin polyamide vPA are of the same nature, preferably: the virgin polyamide is vPA1 and the recycled polyamide rPA is rPA1, or the virgin polyamide is vPA12 and the recycled polyamide rPA is rPA12.

6. A method according to any one of claims 1 to 5, wherein the inherent viscosity of virgin polyamide vPA is lower than that of the powder of the mixture, typically the inherent viscosity of virgin polyamide vPA is at least 10% lower, in particular at least 20%, preferably at least 30% lower than that of the powder of the mixture.

7. A method according to any one of claims 1 to 6, wherein the weight polydispersity index Ip (Mw / Mn) of virgin polyamide vPA is at least 20% lower, in particular at least 35%, preferably at least 50% lower than the polydispersity index Ip of recycled polyamide rPA, or the polydispersity index Iz (Mz / Mn) of virgin polyamide vPA is at least 30% lower, in particular at least 50%, preferably at least 70% lower than the polydispersity index Iz of recycled polyamide rPA.

8. Polyamide composition capable of being obtained according to the process according to any one of claims 1 to 7, wherein the weight polydispersity index Ip (Mw / Mn) of the polyamides is greater than or equal to 1.

5.

9. Composition of polyamides according to claim 8, wherein the z-polydispersity index Iz (Mz / Mn) of the polyamides of the composition is greater than that of the virgin polyamide used as a starting product in the mixture, and / or the weight-polydispersity index Ip of the polyamides of the composition is greater than that of the virgin polyamide used as a starting product in the mixture.

10. Composition of polyamides according to claim 8 or 9, wherein the z-polydispersity index Iz of the polyamides of the composition (Mz / Mn) is greater than or equal to 3.0, typically greater than or equal to 3.5, in particular greater than or equal to 4.0, preferably greater than or equal to 5.0 and / or the weight-polydispersity index Ip of the polyamides of the composition (Mw / Mn) is greater than 2.0, in particular greater than or equal to 2.5, preferably greater than 3.0, or even greater than 4.

0.

11. A method for preparing an article comprising a step of extrusion, molding or overmolding of the composition according to any one of claims 8 to 10, by which an article is obtained.

12. Article that can be obtained according to the process according to claim 11.

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