RECYCLING OF PRE-IMPREGNATED FIBER MATERIALS

Abstract

A method for recycling prepreg materials including the steps of: a) providing at least one prepreg material including a first thermosetting polymer resin, partially crosslinked, and a weave including fibers, b) applying a vitrimerization reaction mixture to the at least one prepreg material, c) placing the at least one prepreg material coated with the vitrimerization reaction mixture on a mold of a predefined shape, d) applying a thermocompression to the at least one prepreg material at a temperature (T1) greater than or equal to the glass transition temperature (Tg) of the first resin, so as to activate the reaction between the vitrimerization reaction mixture and the thermosetting polymer leading to the formation of a vitrimer polymer and the transformation of the at least one prepreg material into a vitrimer composite material of the predefined shape.

Claims

1-10. (canceled)

11. A method for recycling prepreg materials comprising the steps of: a) providing at least one prepreg material comprising a first thermosetting polymer resin, partially crosslinked, and a weave comprising fibers, b) applying a vitrimerization reaction mixture to the at least one prepreg material, c) placing the at least one prepreg material coated with the vitrimerization reaction mixture on a mold of a predefined shape, d) applying a thermocompression to the at least one prepreg material at a temperature (T1) greater than or equal to the glass transition temperature (Tg) of the first resin, so as to activate the reaction between the vitrimerization reaction mixture and the thermosetting polymer leading to the formation of a vitrimer polymer and the transformation of the at least one prepreg material into a vitrimer composite material of the predefined shape.

12. The recycling method according to claim 11 comprising the steps of: e) arranging the vitrimer composite material shaped according to step d) on a second mold of a determined conformation, f) applying a thermocompression to the vitrimer composite material at the temperature (T1) so as to reshape the vitrimer composite material.

13. The recycling method according to claim 11, wherein the vitrimerization reaction mixture comprises precursor reagents so as to form a second resin comprising accessible hydroxyl groups so as to allow function exchange reactions with the first thermosetting polymer resin.

14. The recycling method according to claim 11, wherein the vitrimerization reaction mixture comprises precursor reagents of a second resin, and a catalyst (III) for transformation into vitrimer resin, chosen from an organometallic or organic compound.

15. The recycling method according to claim 14, wherein the proportion of catalyst (III) is comprised between 2 to 15% by weight of the vitrimerization reaction mixture.

16. The recycling method according to claim 11, wherein the application of the vitrimerization reaction mixture is carried out by spraying onto the at least one prepreg material.

17. The recycling method according to claim 11, wherein the application of the vitrimerization reaction mixture is carried out by: i) soaking the at least one prepreg material in a bath of vitrimerization reaction mixture for coating the at least one prepreg material, ii) filtering the vitrimerization reaction mixture, and recovering the at least one coated prepreg material.

18. The recycling method according to claim 11, wherein the first resin of the at least one prepreg material is made of epoxy-amine polymer and the vitrimerization reaction mixture consists of DGEBA (II), phthalic anhydride (I), zinc acetate (III), and an acetone solvent.

19. The recycling method according to claim 11, which comprises the total recycling steps of: g) arranging the vitrimer composite material in a composition comprising at least one monofunctional alcohol, h) applying a thermal treatment at a temperature (T2) greater than or equal to (Tg) so as to allow the dissolution of the vitrimer resin and the recovery of the fibers of the weave so as to recycle the compounds of the vitrimer composite material.

20. An intermediate material comprising a coated prepreg material including a first partially crosslinked thermosetting polymer resin, a weave comprising fibers, the first resin being coated with a vitrimerization reaction mixture suitable for the vitrimerization of the thermosetting polymer during the application of a thermal treatment at a temperature (T1) greater than or equal to the glass transition temperature (Tg) of the thermosetting polymer.

Description

[0055] Other characteristics and advantages will appear on reading the detailed description below, of two non-limiting examples of implementation, made with reference to the appended figures in which:

[0056] FIG. 1 represents an example of an exchange reaction of ester function by transesterification in a dynamic covalent network according to one embodiment of the invention.

[0057] FIG. 2 represents an example of an exchange reaction of disulfide functions in a dynamic covalent network according to another embodiment of the invention.

[0058] FIG. 3 represents an example of an exchange reaction of silyl ether functions in a dynamic covalent network according to yet another embodiment of the invention.

[0059] FIG. 4 represents the composition of a vitrimerization reaction mixture according to one embodiment of the invention.

[0060] FIG. 5 represents a first step of the anhydride-epoxy reaction from an alcohol.

[0061] FIG. 6 illustrates a second step of the anhydride-epoxy reaction of the vitrimerization reaction mixture.

[0062] FIG. 7 illustrates a function exchange reaction between a partially crosslinked epoxy-anhydride system and a free amine present in the vitrimerization epoxy-anhydride system according to one embodiment of the invention.

[0063] As will be seen in the detailed examples below, the invention consists in allowing the reuse of prepreg materials out of use for reasons of aging (storage outside ideal conditions, storage too long), such as only scraps of cuttings. To do this, the method consists in applying a reaction mixture of activator compounds to the prepreg material which will integrate with the first prepreg resin and allow the final composite material to have the characteristics of a dynamic covalent network, capable of exchange reactions so as to allow its reshaping when hot, despite a significant state of crosslinking, taking advantage of the use of the dynamic covalent chemistry. The dynamic covalent networks, or vitrimer networks, are crosslinked polymer networks with the particularity of having characteristics of thermosetting at low temperatures and of thermoplastics at high temperatures. These characteristics arise from the presence of dynamic covalent chemical bonds, that is, exchange reactions may occur between chains and rearrange the topologyo of the network, while maintaining a constant crosslinking rate (refer to one example of exchange reaction FIG. 1). These exchanges are controlled kinetically and may only take place once the glass transition temperature of the polymer has been exceeded (conditions the mobility necessary for the reactions) and once the minimum temperature for the reaction to take place, linked to the activation energy of the exchange reaction.

[0064] The invention therefore consists in using the residual reactivity of the first incompletely crosslinked resin to integrate chemical patterns making it possible to obtain a dynamic covalent network. The added patterns are preferably similar to those of the first resin used in the prepreg, such as epoxy-amine or epoxy-anhydride systems etc., or may be based on different exchange chemistries disulfide, silyl ethers-FIGS. 1 to 3))

[0065] Typically, the epoxy amines create amines, epoxy anhydrides create esters. In both cases, disulfide or silyl-ether bonds are integrated into the existing epoxy-amine network. This may be done in particular by adding precursors carrying groups reactive with epoxy or amines existing in the first partially crosslinked resin (e.g. alcohols or amines which can react with epoxy, anhydrides, epoxy which can react with amines)

[0066] Typically, if disulfide bonds are desired, a compound carrying a disulfide bridge and at least two amines or alcohols may be reacted so that it is integrated into the existing resin and acts as a dynamic crosslinker.

[0067] Example of embodiment 1: application of a vitrimerization reaction mixture by impregnation via a solvent bath.

[0068] A vitrimerization reaction mixture (FIGS. 4 to 6) is formed from: [0069] 500 ml of acetone, [0070] 25 g of epoxy DGEBA II (0.073 mol), [0071] 16 g of phthalic anhydride I (0.108 mol), and [0072] 10 g of zinc acetate III (0.045 mol)

[0073] Then 50 g of prepreg materials reinforced with carbon fibers, based on a first epoxy-amine resin, stored at ambient temperature for more than 30 days, with dimensions 1 cm by 2 cm, are immersed in the bath of the reaction mixture described above at ambient pressure and temperature.

[0074] After 24 hours of immersion with light stirring at ambient temperature, the prepreg materials are filtered from the reaction mixture, then dried at ambient temperature for 4 hours.

[0075] Two prepreg materials are then placed one against the other, then between 2 steel plates covered with fiber-reinforced Teflon. Everything is placed in a hot press, heated to 240? C., under 10 MPa pressure, for a period of 5 minutes. The pressure is then removed and the two prepreg materials are recovered. We then observe an adhesion between the two prepreg materials, without apparent destruction of the fibrous structures. The first thermosetting resin having now crosslinked and being vitrimerized, a vitrimer composite material is obtained. According to another possibility, at least two pieces of prepreg materials are juxtaposed two by two in the mold so as to enlarge the surface of the final vitrimer composite material. According to yet another possibility, at least two pieces of prepreg materials are disposed on top of each other so as to give the desired shape and properties to the final vitrimer composite.

[0076] The vitrimer composite material thus formed is then reshaped under stress and temperature. The assembly of 2 prepregs is placed on a mold including an angle at 90? C., and heated to 240? C. A stress is gradually applied to the composite until reaching 10 MPa. The vitrimer composite is capable of deforming without breaking until it matches the angle of the mold. It retains this shape after cooling.

[0077] For comparison, when 2 pieces of prepreg materials not previously immersed in the vitrimerization reaction mixture are compressed under the same conditions, numerous cracks are visible on the surface due to the loosening of the crosslinked resin from the fibers.

[0078] Example of embodiment 2: application of the vitrimerization reaction mixture by spraying

[0079] A vitrimerization reaction mixture (FIGS. 4 to 6) is formed from: [0080] 50 ml of acetone, [0081] 25 g of DGEBA II (0.073 mol) [0082] 16 g of phthalic anhydride I (0.108 mol) and [0083] 10 g of zinc acetate III (0.045 mol)

[0084] This solution is then deposited by spraying onto the surfaces of two prepreg materials reinforced with carbon fiber, based on a first epoxy-amine resin, stored at ambient temperature for more than 30 days, with dimensions 1 cm by 2 cm.

[0085] The two prepreg materials are then hot compressed as described in Example 1. A vitrimer composite material is obtained, without the presence of defects, cracks, or fiber breakage. It may be remodeled in a second mold of a predefined conformation for its future application.

[0086] According to other possibilities not described in the detailed examples, the vitrimerization reaction mixture may be consist of other systems allowing the function exchanges and a dynamic covalent chemistry, such as epoxy/phenol, epoxy/amine (FIG. 7), epoxy/disulfide systems.

[0087] Thus, the present invention has the advantage of allowing the reuse of unused prepreg materials or cutting scraps and in particular the obtention of a vitrimer composite material which may be reshaped several times during its lifespan. The invention therefore allows, through a method that is simple to implement and inexpensive, the reuse of poorly valued prepreg waste as well as the obtention, with this waste, of a completely recyclable composite material, unlike existing methods.