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US-20260125532-A1 - POLYAMIDE COMPOSITION PREPARED FROM A POWDER OF POLYAMIDES TO BE RECYCLED

US20260125532A1US 20260125532 A1US20260125532 A1US 20260125532A1US-20260125532-A1

Abstract

The application relates to a method for preparing a polyamide composition, which comprises the steps of: a) providing a mixture comprising a virgin polyamide vPA and a polyamide to be recycled rPA in the form of an untransformed powder resulting from additive manufacturing by sintering or from a coating method by powdering or by electrostatic spraying, or powder obtained by grinding a polyamide-based part of an object to be recycled; b) kneading the mixture in the molten state, as a result of which a polyamide composition is obtained; and c) recovering the polyamide composition. The invention also relates to the polyamide composition obtained and to the uses thereof for preparing articles by extrusion, injection or overmoulding.

Inventors

  • Thomas PRENVEILLE
  • Ornella ZOVI
  • Florent Abgrall

Assignees

  • ARKEMA FRANCE

Dates

Publication Date
20260507
Application Date
20230922
Priority Date
20220923

Claims (19)

  1. 1 - 15 . (canceled)
  2. 16 . A composition preparation method for preparing a polyamide composition which comprises the steps of: a) providing a mixture comprising: from 5 to 90% by weight of a virgin polyamide vPA; from 10 to 95% by weight of a polyamide to be recycled rPA; relative to the total weight of the mixture; the polyamide to be recycled rPA being in the form of an untransformed powder resulting from additive manufacturing by sintering or from a coating method by powdering or by electrostatic spraying, or of a powder obtained by grinding a polyamide-based part of an object to be recycled; the molecular weight-polydispersity index Ip (Mw/Mn) of the virgin polyamide vPA being lower than the polydispersity index Ip of the polyamide to be recycled rPA, where Mw and Mn are measured by steric exclusion chromatography in accordance with the standard ISO 16014-1 of 2012; b) kneading the said mixture in the molten state (melt kneading), as a result of which a polyamide composition is obtained whereof the molecular weight-polydispersity index Ip is greater than or equal to 1.5; c) recovering the said polyamide composition.
  3. 17 . The method according to claim 16 , wherein the polyamide to be recycled rPA and the virgin polyamide vPA are homopolyamides.
  4. 18 . The method according to claim 16 , wherein the average number of carbon atoms (C) relative to the nitrogen atom (N) of the polyamide to be recycled rPA and/or of the virgin polyamide vPA is greater than or equal to 8.
  5. 19 . The method according to claim 16 , wherein the polyamide to be recycled rPA and the virgin polyamide vPA are independently selected from among PA11 or PA12.
  6. 20 . The method according to claim 16 , wherein the polyamide to be recycled rPA and the virgin polyamide vPA are identical in nature.
  7. 21 . The method according to claim 20 , wherein the virgin polyamide is vPA11 and the polyamide to be recycled rPA is an rPA11, or the virgin polyamide is vPA12 and the polyamide to be recycled rPA is an rPA12.
  8. 22 . The method according to claim 16 , wherein the inherent viscosity of the virgin polyamide vPA is lower than or equal to 1.50; and/or the powder of the mixture has an inherent viscosity that is greater than or equal to 1.50.
  9. 23 . The method according to claim 22 , wherein the inherent viscosity of the virgin polyamide vPA is lower than or equal to 1.40; and/or the powder of the mixture has an inherent viscosity that is greater than or equal to 1.60.
  10. 24 . The method according to claim 23 , wherein the inherent viscosity of the virgin polyamide vPA is lower than or equal to 1.30; and/or the powder of the mixture has an inherent viscosity that is from 0.70 to 5.00.
  11. 25 . The method according to claim 16 , wherein the molecular weight-polydispersity index Ip (Mw/Mn) of the virgin polyamide vPA is lower by at least 20% relative to the polydispersity index Ip of the polyamide to be recycled rPA; or the polydispersity index Iz (Mz/Mn) of the virgin polyamide vPA is lower by at least 30% relative to the polydispersity index Iz of the polyamide to be recycled rPA, where Mn and Mz are measured by steric exclusion chromatography in accordance with the standard ISO 16014-1 of 2012.
  12. 26 . The method according to claim 16 , wherein the molecular weight-polydispersity index Ip of the virgin polyamide vPA is from 1.6 to 2.2, and/or the molecular weight-polydispersity index Ip of the polyamide to be recycled rPA is from 2.5 to 15.0.
  13. 27 . The method according to claim 26 , wherein the molecular weight-polydispersity index Ip of the virgin polyamide vPA is from 1.6 to 2.1, and/or the molecular weight-polydispersity index Ip of the polyamide to be recycled rPA is from 2.8 to 10.0.
  14. 28 . The method according to claim 16 , wherein the proportion by weight of chain limiting agent within the mixture is less than or equal to 1.0%.
  15. 29 . A polyamide composition that is obtainable by the method according to claim 16 , wherein the molecular weight-polydispersity index Ip (Mw/Mn) of the polyamides is greater than or equal to 1.5, where Mw and Mn are measured by steric exclusion chromatography in accordance with the standard ISO 16014-1 of 2012.
  16. 30 . The polyamide composition according to claim 29 , wherein the z average-polydispersity index Iz (Mz/Mn) of the polyamides of the composition is higher than that of the virgin polyamide used as starting material in the mixture, and/or the molecular weight-polydispersity index Ip of the polyamides of the composition is higher than that of the virgin polyamide used as starting material in the mixture, where Mn and Mz are measured by steric exclusion chromatography in accordance with the standard ISO 16014-1 of 2012.
  17. 31 . The polyamide composition according to claim 29 , wherein the z average-polydispersity index Iz of the polyamides of the composition (Mz/Mn) is greater than or equal to 3.0; and/or the molecular weight-polydispersity index Ip of the polyamides of the composition (Mw/Mn) is greater than 2.0.
  18. 32 . The polyamide composition according to claim 29 , whereof the inherent viscosity, as measured using an Ubbelohde tube at 20° C. on a 0.5% by weight solution in m-cresol according to the standard ISO 307 of 2019, is between 0.80 and 1.50.
  19. 33 . An article preparation method for preparing an article that comprises a step of extrusion, moulding or overmoulding of the composition according to claim 29 , as a result of which an article is obtained.

Description

The present invention relates to: a polyamide composition preparation method for preparing a polyamide composition from untransformed powder resulting from additive manufacturing by sintering or from a method by powdering or by electrostatic spraying, or a powder obtained by grinding a polyamide-based part of an object to be recycled; a polyamide composition; and the use thereof for preparing articles. Additive manufacturing (AM, as per the accepted terminology) has experienced rapid growth in recent years, in particular thanks to the possibility of designing objects having very diverse forms and shapes, the short duration between design and production, and the associated environmental and economic advantages. The agglomeration of powders by melting or melt agglomeration (hereinafter “sintering”) is caused by radiation, such as for example by means of a laser beam (“laser sintering” or “selective laser sintering” SLS as per the accepted terminology), infrared radiation, UV radiation, or any source of electromagnetic radiation that enables the powder to be melted layer by layer in order to produce three-dimensional objects. The SLS technique produces a part by applying powders layer by layer, each layer being in the form of a thin powder bed, generally of the order of 100 μm. A laser is used in order to melt part of this powder at the desired location, and thereafter a new layer of powder is deposited. The process is repeated until a thermoplastic polymer object is formed layer by layer. Other methods that may also be cited include selective sintering processes using an absorber, in particular technologies known as “High Speed Sintering” (HSS) and “Multi-Jet Fusion” (MJF). In these technologies, the manufacturing of 3D objects is also done layer by layer, using a polyamide-based powder which is melted in a controlled manner for each layer constituting the 3D object: an absorber is deposited over the layer (by means of for example a liquid ink in the “inkjet method”) before exposing the layer to electromagnetic radiation (for example infrared) which causes the melting of the areas containing said absorber. Sintering generates a large quantity of untransformed powder. For each layer, the powder that has not been targeted by the radiation is not incorporated into the final object. Therefore this results in a lot of powder remaining untransformed. This untransformed powder is difficult to recover because it is generally degraded. In fact, the powder bed is preheated and maintained at a temperature close to the melting point of the powder, typically 5 to 15° C. below its melting point. This enables proper fusion of the powder targeted by the laser as well as good definition of each layer of the object formed by the laser. At this temperature, the untransformed powder undergoes ageing degradation such as solid-state polycondensation and oxidation reactions. This leads to an increase in the length of the polymer chain, resulting in a decrease in the melt flow rate (MFR). As a result, these degraded powders cannot usually be directly reused in the subsequent sinter-based additive manufacturing process, particularly when the viscosity of the degraded powder varies far too significantly from that of the original powder. Any attempt to reuse these powders results in parts that have a poor surface finish, for example having an orange peel-like appearance, as well as diminished mechanical properties, in particular lower elongation at break, due to the defects acting as rupture initiators in tensile tests. Recycling of this untransformed powder for other types of transformation processing (extrusion, injection) is not easy. This is because heating during the sintering technique affects the intrinsic viscosity of the powder. Generally speaking, extrusion or moulding of this degraded powder results in articles that are spongy and/or whose mechanical properties, in particular with respect to mechanical strength, and aesthetic properties (particularly with regard to colour, which tends towards brown) are inferior to those of articles formed from virgin polymer. A large quantity of waste is thus generated by sinter-based additive manufacturing methods in the form of degraded untransformed powder. Very little of this powder actually gets recycled. Considering the example of polyamide 12 (PA12), which is the main type of plastic used in the SLS method, PA12 powder waste can represent up to 50%, or even up to 90%, of the total quantity of powder used in the process. This represents a significant loss of PA12 powder, due to the fact that this waste powder must be disposed of. The literature reports a number of attempts to recycle this waste polyamide powder. The patent application US 2022/0064405 describes a recycled polyamide composition that comprises a polyamide waste, preferably derived from additive manufacturing, a lubricating agent, and a crystallising agent. The invention that is the subject matter of this application is b