AQUEOUS DISPERSION OF PARTICLES OF AT LEAST ONE THERMOPLASTIC POLYMER, METHOD FOR PREPARING AND APPLICATIONS THEREOF, ESPECIALLY FOR SIZING REINFORCING FIBRES

Abstract

The invention relates to the use of giant micelles as shear-thinning agent in an aqueous dispersion of particles of at least one thermoplastic polymer. It also relates to an aqueous dispersion of particles of at least one thermoplastic polymer, comprising giant micelles located around the particles of the thermoplastic polymer(s), and also to a method that makes it possible to prepare this aqueous dispersion. Applications: all fields in which it is desirable to coat a substrate with a thermoplastic film and, in particular, the sizing of reinforcing fibres intended to be incorporated into the composition of parts made of thermoplastic matrix composite materials and, in particular, of structural parts for the aeronautical and space industries.

Claims

1-18. (canceled)

19. An aqueous dispersion of particles of at least one thermoplastic polymer, comprising giant micelles located around the particles of the thermoplastic polymer.

20. The aqueous dispersion of claim 19, wherein the giant micelles comprise molecules of a cationic or zwitterionic surfactant.

21. The aqueous dispersion of claim 19, wherein the giant micelles comprise molecules of a cationic surfactant with a quaternary ammonium group.

22. The aqueous dispersion of claim 21, wherein the cationic surfactant is an alkyltrimethylammonium salt of formula (C.sub.nH.sub.2n+1)N.sup.+(CH.sub.3).sub.3,X.sup., wherein n is greater than or equal to 10 and X.sup. is an inorganic or organic counterion.

23. The aqueous dispersion of claim 22, wherein the alkyltrimethylammonium salt is a hexadecyltrimethylammonium salt.

24. The aqueous dispersion of claim 20, wherein the giant micelles further comprise an inorganic salt, an organic salt or an organic acid.

25. The aqueous dispersion of claim 20, wherein the giant micelles further comprise salicylic acid.

26. The aqueous dispersion of claim 19, wherein the thermoplastic polymer is a polyaryletherketone, a polyethyleneimine, a polyolefin, a polyamide, a polyimide, a thermoplastic polyurethane, a polyphenylene sulphide, a polyethylene or polybutylene terephthalate, a polysulphone, a polycarbonate, or a polyvinyl chloride.

27. The aqueous dispersion of claim 26, wherein the thermoplastic polymer is a polyaryletherketone, a polyetherimide, or a polysulphone.

28. The aqueous dispersion of claim 27, wherein the giant micelles are formed of a mixture of molecules of hexadecyltrimethylammonium chloride and salicylic acid.

29. The aqueous dispersion of claim 28, comprising from 5 mmol/L to 100 mmol/L of the mixture.

30. The aqueous dispersion of claim 19, comprising from 0.1% to 1% by weight of thermoplastic polymer particles with respect to a total weight of the aqueous dispersion.

31. A method for preparing an aqueous dispersion of particles of at least one thermoplastic polymer, the aqueous dispersion comprising giant micelles which are located around the particles of the thermoplastic polymer, comprising: a) bringing into contact, under stirring, an organic phase comprising the thermoplastic polymer dissolved or dispersed in an organic solvent, non-miscible with water, with an aqueous phase comprising giant micelles; and b) evaporating the organic solvent; whereby the thermoplastic polymer is transferred in the form of particles from the organic phase to the aqueous phase.

32. The method of claim 31, wherein a) and b) are carried out simultaneously.

33. A method for sizing reinforcing fibres for thermoplastic matrix composite materials, comprising: immersing the reinforcing fibres in an aqueous dispersion of at least one thermoplastic polymer, the aqueous dispersion comprising giant micelles which are located around the particles of the thermoplastic polymer; then removing the reinforcing fibres from the aqueous dispersion and drying the reinforcing fibres.

34. The method of claim 33, wherein the reinforcing fibres are glass fibres, carbon fibres, graphite fibres, silica fibres, metal fibres, ceramic fibres, synthetic organic fibres, natural organic fibres or mixtures thereof.

35. A method for sizing reinforcing fibres for thermoplastic matrix composite materials, comprising: spraying an aqueous dispersion of at least one thermoplastic polymer on the reinforcing fibres, the aqueous dispersion comprising giant micelles which are located around the particles of the thermoplastic polymer; then drying the reinforcing fibres.

36. The method of claim 35, wherein the reinforcing fibres are glass fibres, carbon fibres, graphite fibres, silica fibres, metal fibres, ceramic fibres, synthetic organic fibres, natural organic fibres or mixtures thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0068] FIG. 1 illustrates the evolution of the stability of a first aqueous dispersion in accordance with the invention, as determined by multiple light scattering over a period of 50 hours, this first aqueous dispersion being a dispersion of particles of a polyetherimide.

[0069] FIG. 2 illustrates the rheograms of said first aqueous dispersion as established twice, on the one hand, on the day of its preparation (symbols .box-tangle-solidup. and ) and, on the other hand, after 7 days of rest and re-dispersion by simple manual stirring (symbols .circle-solid. and ).

[0070] FIG. 3 is a transmission electron microscope (TEM) image of said first aqueous dispersion.

[0071] FIG. 4 is a scanning electron microscope (SEM) image of a film obtained by deposition of said first aqueous dispersion on a graphite plate and drying of said plate.

[0072] FIG. 5 is a diagram illustrating the sizing device having been used to size carbon fibres with said first aqueous dispersion.

[0073] FIGS. 6A and 6B are SEM images of filaments of a carbon fibre having been sized with said first aqueous dispersion by means of the device shown in FIG. 5 and using a running speed of 10 m/minute.

[0074] FIGS. 7A and 7B are SEM images of filaments of a carbon fibre having been sized with said first aqueous dispersion by means of the device shown in FIG. 5 and using a running speed of 15 m/minute.

[0075] FIGS. 8A and 8B are SEM images of filaments of a carbon fibre not having been sized, these images being given for comparison purposes.

[0076] FIG. 9 is an SEM image of a film formed by deposition of a second aqueous dispersion in accordance with the invention on a graphite plate and drying of said plate, said second aqueous dispersion being a dispersion of particles of a polyethersulphone.

[0077] FIG. 10 is an SEM image of a film formed by deposition of a third aqueous dispersion in accordance with the invention on a graphite plate and drying of said plate, said third aqueous dispersion being a dispersion of particles of a polysulphone.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

Example I

Aqueous Dispersion of Particles of a Polyetherimide

[0078] I.1 Preparation of the dispersion:

[0079] An aqueous dispersion of particles of a polyetherimide (Ultem 1000 PEI resinGE Plastics), hereafter designated dispersion 1, is prepared by emulsion/evaporation. This PEI has a glass transition temperature of 217 C.

[0080] To do so, 0.71 g of the PEI resin is dissolved in 13.6 mL of dichloromethane under magnetic stirring.

[0081] In parallel, also under magnetic stirring, 1.868 g of cetyltrimethylammonium chloride (CTAC) are dissolved in 136.4 mL of distilled water (i.e. a concentration of CTAC of 4.11.10.sup.2 mol/L) then, to the solution thereby obtained, is added 0.805 g salicylic acid (i.e. a concentration of salicylic acid also of 4.11.10.sup.2 mol/L).

[0082] The organic resin solution is added drop by drop to the aqueous solution of CTAC/salicylic acid under stirring with the Ultra-TurraxIKA. The addition lasts around 5 minutes. The stirring is set at 12,000 rpm and is maintained up to complete evaporation of the dichloromethane, i.e. around 30 minutes.

[0083] An aqueous dispersion with 0.51% by weight of particles of PEI is thereby obtained.

[0084] I.2Properties of the dispersion: [0085] Particle size:

[0086] The mean diameter and the polydispersity index of the particles of dispersion 1 are determined by means of a Zetasizer Nano S dynamic light scattering apparatusMALVERN Instruments, using a high power laser (50 mW) emitting at the wavelength of 532 nm and collecting the light signal scattered by the sample to analyse in backscattering (angle of) 173. The measurement is carried out at 25 C.

[0087] The mean intensity diameter of the particles is 209 nm.

[0088] Their polydispersity index is 0.265. [0089] Stability of the dispersion:

[0090] The stability of dispersion 1 is assessed by means of a Turbiscan LAB-FORMULACTION device which makes it possible to characterise precisely and rapidly the stability of a liquid dispersion by multiple light scattering (MLS).

[0091] Multiple light scattering is a well-known method which consists in sending photons (.sub.emission=880 nm) into the sample to analyse. These photons, after having been scattered multiple times by the particles of the dispersion, come out of the sample and are detected by two detectors, one working in transmission, the other in backscattering (angle of) 135. The analysis is carried out at 25 C.

[0092] The backscattering intensity is directly linked to the transport length of the photons. Also, this intensity depends on the size and the concentration of the particles.

[0093] Monitoring of the difference between the intensity of the backscattered light at time t0 and at time t (R.sub.t0R.sub.t) is carried out for several days with an interval of 3 hours between each measurement.

[0094] FIG. 1 illustrates, in the form of a curve, the evolution of the variation in the backscattering intensity with respect to the backscattering intensity at time t0 (i.e. (R.sub.t0R.sub.t)/R.sub.t0), noted AR and expressed in percentages, such as obtained for dispersion 1 over a period of 50 hours.

[0095] As shown in this figure, the curve shows a modification of slope, characteristic of a start of sedimentation of the particles as of 22 hours. Dispersion 1 thus begins to be destabilised only after 22 hours. [0096] Rheological analysis of the dispersion:

[0097] The rheology of dispersion 1 is assessed by tests which consist in measuring the viscosity of said dispersion by applying to it a shear rate ranging from 0.6 s.sup.1 to 500 s.sup.1, and doing so, on the one hand, on the day of its preparation and, on the other hand, after 7 days at rest and re-dispersion by simple manual stirring. Each test is performed twice.

[0098] FIG. 2 illustrates the rheograms thereby obtained, the viscosity being expressed in mPa.Math.s and the shear rate in s.sup.1. In this figure, the symbols .box-tangle-solidup. and correspond to the rheograms obtained on the day dispersion 1 is prepared whereas the symbols .circle-solid. and correspond to the rheograms obtained after 7 days of rest of said dispersion.

[0099] As shown in FIG. 2, dispersion 1 has, on the day of its preparation, a viscosity of the order of 800 mPa.Math.s without shear and its viscosity drops to 500 mPa.Math.s from the moment that a shear rate of 1 s.sup.1 is applied.

[0100] It also shows that simple manual stirring suffices for dispersion 1 to recover, after 7 days at rest, a viscosity close to that which it had on the day of its preparation. [0101] Microscopic analysis:

[0102] As shown in FIG. 3, which corresponds to a TEM image of dispersion 1, said dispersion comprises spherical particles (shown on the image in the form of white circles) which have a maximum diameter of 200 nm, encased in the middle of cylindrical micelles.

[0103] The size distribution of these particles is polydisperse (the size of the particles ranging from 20 nm to 200 nm) in agreement with the results obtained by dynamic light scattering. [0104] Film-forming properties:

[0105] The aptitude of dispersion 1 to form a film on a substrate is firstly tested by depositing a drop of said dispersion on a graphite plate using a Pasteur pipette, by spreading this drop then by placing the plate in a drying oven at 100 C. to dry said deposit.

[0106] As is visible in FIG. 4, which corresponds to an SEM image of the graphite plate after drying of the deposit, the film obtained is homogenous and shows a good coalescence of PEI particles.

[0107] Moreover, the aptitude of dispersion 1 to form a film on a substrate is also tested by sizing multifilament carbon fibres (IM7 fibres with 12,000 filamentsHEXCEL) with this dispersion.

[0108] This sizing is carried out using the device 10 which is illustrated schematically in FIG. 5 and which comprises:

[0109] a tank 11 which is filled with a sizing bath 12 (here, dispersion 1); [0110] a spool 13 which is located upstream (in the direction of unwinding of the carbon fibres in the device 10) of the tank 11 and on which the carbon fibres 14 are wound before their introduction into the sizing bath; [0111] a drying oven 15 which is located downstream of the tank 11 and which makes it possible to dry the carbon fibres when they come out of the sizing bath; [0112] a spool 16 which is located downstream of the drying oven 15 and on which the carbon fibres are wound when they come out of this drying oven; and [0113] a drive system comprising notably a set of pulleys 17 and ensuring the unwinding of the rovings of reinforcing fibres from the spool 13 to the spool 16.

[0114] The temperature of the drying oven is set at 200 C. such that it is below the glass transition temperature of the PEI.

[0115] Two running speeds of carbon fibres in the device 10 are used: 10 m/min on the one hand, and 15 m/min on the other hand.

[0116] The results are illustrated in FIGS. 6A, 6B, 7A, 7B, 8A and 8B which correspond to SEM images: [0117] filaments of a carbon fibre having been sized at the running speed of 10 m/min (FIGS. 6A and 6B); [0118] filaments of a carbon fibre having been sized at the running speed of 15 m/min (FIGS. 7A and 7B); and by way of comparison [0119] filaments of a carbon fibre not having been sized (FIGS. 8A and 8B).

[0120] These images show that sizing of multi-filament carbon fibres with dispersion 1 leads to the formation of a homogeneous film on the filaments of said fibres, with very good coalescence of the particles of PEI present in said dispersion.

EXAMPLE II

Aqueous Dispersion of Particles of a Polyethersulphone

[0121] II.1Preparation of the dispersion:

[0122] An aqueous dispersion of particles of a polyethersulphone (PES 4100 PSUMIMOTO Chemical), hereafter designated dispersion 2, is prepared by operating as described in point I.1 above, except that PEI is replaced by PES, which forms a stable dispersion in the organic solvent. This PES has a glass transition temperature of 225 C.

[0123] I1.2Properties of the dispersion:

[0124] Dispersion 2 has: [0125] particles of which the mean intensity diameter and the polydispersity index, as determined by dynamic light scattering, are respectively 158 nm and 0.210; [0126] a stability, as assessed by visual observation, of 10 to 12 hours.

[0127] Moreover, as shown in FIG. 9, which corresponds to an SEM image of a graphite plate treated with a drop of dispersion 2 as described in point I.2 above, said dispersion makes it possible to form a homogenous film of PES on the surface of a substrate.

Example III

Aqueous Dispersion of Particles of a Polysulphone

[0128] III.1Preparation of the dispersion:

[0129] An aqueous dispersion of particles of a polysulphone (PSU Ultrason S 2010 NaturelBASF), hereafter designated dispersion 3, is prepared by operating as described in point I.1 above, except that PEI is replaced by PSU. This PSU has a glass transition temperature of 187 C.

[0130] III.2Properties of the dispersion:

[0131] Dispersion 3 has: [0132] particles of which the mean intensity diameter and the polydispersity index, as determined by dynamic light scattering, are respectively 178 nm and 0.297; [0133] a stability, as assessed by visual observation, of 10 to 12 hours.

[0134] Moreover, as shown in FIG. 10, which corresponds to an SEM image of a graphite plate having been treated with a drop of dispersion 3 as described in point I.2 above, said dispersion also makes it possible to form a homogeneous film of PSU on the surface of a substrate.

REFERENCES CITED

[0135] [1] Broyles et al., Polymer 1998, 39(15), 3417-3424

[0136] [2] FR-A-2 960 878;

[0137] [3] Giraud et al., Applied Surface Science 2013, 266, 94-99

[0138] [4] Cates et al., Journal of Physics: Condensed Matter 1990, 2, 6869-6892

[0139] [5] Hassan et al., Current Science 2001, 80(8), 980-989

[0140] [6] Walker, Current Opinion in Colloid & Interface Science 2001, 6, 451-456