Aqueous impregnation bath for reinforcement fibres and uses thereof

Abstract

The invention relates to an aqueous impregnation bath for reinforcement fibers for manufacturing prepregs having a thermoplastic matrix, resulting in highly satisfactory consolidation, in terms of residual porosity, of the composite material parts manufactured using the prepregs. The impregnation bath includes a least one thermoplastic polymer, a surfactant and water, and is characterized in that the surfactant is an ethoxylated stearyl alcohol of formula: HO(CH.sub.2CH.sub.2O).sub.nCH.sub.2(CH.sub.2).sub.16CH.sub.3 wherein n is 100. The invention also relates to a method for impregnating reinforcement fibers using the impregnation bath, to a method for manufacturing a prepreg having a thermoplastic matrix using the impregnation method, and to a method for manufacturing a part made of a composite material having a thermoplastic matrix using the method for manufacturing a prepreg. The invention is useful in any field for manufacturing parts made of composite materials and, specifically, in the aeronautical, space, rail, shipping and automotive industries.

Claims

1. An impregnation bath for reinforcement fibres for a manufacture of a prepreg having a thermoplastic matrix, comprising at least one thermoplastic polymer, a surfactant and water, wherein the surfactant is an ethoxylated stearyl alcohol of formula: HO(CH.sub.2CH.sub.2O).sub.nCH.sub.2(CH.sub.2).sub.16CH.sub.3 wherein n is 100.

2. The impregnation bath of claim 1, which comprises from 0.25% to 5% by weight of the surfactant with respect to the thermoplastic polymer.

3. The impregnation bath of claim 1, which comprises from 10% to 50% by weight of the thermoplastic polymer with respect to water.

4. The impregnation bath of claim 1, wherein the thermoplastic polymer is a polyaryletherketone, a polyethyleneimine, a polyolefin, a polyamide, a polyimide, a thermoplastic polyurethane, a polyphenylene sulphide, a polyethylene terephthalate, a polybutylene terephthalate, a polysulphone, a polycarbonate, a polyvinyl chloride or a polyvinyl alcohol.

5. The impregnation bath of claim 4, wherein the thermoplastic polymer is a polyetheretherketone.

6. The impregnation bath of claim 1, wherein the thermoplastic polymer is in a micronized form.

7. A method for impregnating reinforcement fibres for a manufacture of a prepreg having a thermoplastic matrix, comprising an immersion of the reinforcement fibres in an impregnation bath comprising at least one thermoplastic polymer, a surfactant and water, wherein the surfactant is an ethoxylated stearyl alcohol of formula: HO(CH.sub.2CH.sub.2O).sub.nCH.sub.2(CH.sub.2).sub.16CH.sub.3 wherein n is 100.

8. The method of claim 7, wherein the reinforcement fibres are glass fibres, carbon fibres, graphite fibres, silica fibres, metal fibres, ceramic fibres, synthetic organic fibres or natural organic fibres.

9. The method of claim 7, wherein the reinforcement fibres are carbon fibres and the impregnation bath comprises from 35% to 75% by weight of immersed reinforcement fibres with respect to the total weight of the reinforcement fibres and the thermoplastic polymer.

10. The method of claim 7, wherein the reinforcement fibres are glass or silica fibres and the impregnation bath comprises from 45% to 82% by weight of immersed reinforcement fibres with respect to the total weight of the reinforcement fibres and the thermoplastic polymer.

11. A method for manufacturing a prepreg having a thermoplastic matrix, comprising a step of impregnating reinforcement fibres, the impregnating step comprising an immersion of the reinforcement fibres in an impregnation bath comprising at least one thermoplastic polymer, a surfactant and water, wherein the surfactant is an ethoxylated stearyl alcohol of formula: HO(CH.sub.2CH.sub.2O).sub.nCH.sub.2(CH.sub.2).sub.16CH.sub.3 wherein n is 100.

12. A method for manufacturing a part made of a composite material having a thermoplastic matrix, comprising a step of impregnating reinforcement fibres, the impregnating step comprising an immersion of the reinforcement fibres in an impregnation bath comprising at least one thermoplastic polymer, a surfactant and water, wherein the surfactant is an ethoxylated stearyl alcohol of formula: HO(CH.sub.2CH.sub.2O).sub.nCH.sub.2(CH.sub.2).sub.16CH.sub.3 wherein n is 100.

13. The method of claim 11, further comprising: a step of drying the impregnated reinforcement fibres, a step of heating the dried reinforcement fibres to a temperature above the melting temperature of the thermoplastic polymer, and a step of calendering the heated reinforcement fibres.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a diagram illustrating the device for continuously forming prepregs having been used to produce prepregs within the framework of experimental tests aiming to validate the invention.

(2) FIGS. 2A to 2E illustrate the mappings obtained by ultrasonic non-destructive testing of composites, all prepared in the same experimental conditions but using prepregs having been, for their part, prepared by impregnation in different impregnation baths; thus, FIG. 2A corresponds to a composite obtained using a prepreg prepared in accordance with the prior art; FIGS. 2B and 2C correspond to two composites obtained using prepregs prepared in accordance with the invention whereas FIGS. 2D and 2E correspond to two composites obtained using prepregs serving as comparative examples.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(3) The invention has been validated by carrying out experimental tests consisting in: preparing a series of batches of prepregs by impregnation of rovings of carbon fibres (HexTow IM7 fibresHEXCEL) in aqueous impregnation baths comprising a polyetheretherketone (PEEK 150PVICTREX) dispersed in micronized form and a surfactant, but by changing, from one batch of prepregs to the next, the surfactant, the proportion by weight of said surfactant with respect to PEEK or the weight content of fibres; subjecting the preforms prepared by manual draping of said prepregs to an operation of consolidation in drying oven; and assessing the material integrity (that is to say the consolidation quality) of the materials thereby obtained by an ultrasonic non-destructive test (NDT).

(4) Preparation of the Batches of Prepregs:

(5) 5 batches of prepregs are prepared, designated L1 to L5, using the device 10 illustrated schematically in FIG. 1, which makes it possible to continuously form prepregs, in the form of calibrated tapes, using rovings of reinforcement fibres.

(6) As may be seen in this figure, said device (which is known per se) comprises: a tank 11 filled with an impregnation bath 12; a spool 13 which is situated upstream (in the direction of circulation of the rovings of reinforcement fibres in the device 10) of the tank 11 and on which are wound the rovings of reinforcement fibres 14 before their introduction in the impregnation bath; an infrared oven 15 which is situated downstream of the tank 11 and which makes it possible to dry the rovings of reinforcement fibres when they come out of the impregnation bath; a series of hot air ovens 16 situated downstream of the oven 15 and which make it possible to melt the polymer impregnating the rovings of reinforcement fibres and to consolidate said rovings; a calendering device 17 which is situated downstream of the series of ovens 16 and which makes it possible to give to the rovings of reinforcement fibres the desired shape and dimensions; a spool 18 which is situated downstream of the calendering device 17 and on which are wound the rovings of reinforcement fibres when they come out of said calendering device; and a synchronous drive system (not represented in FIG. 1) ensuring the circulation of the rovings of reinforcement fibres from the spool 13 to the spool 17.

(7) The composition of the impregnation baths and the contents by weight of fibres having been used for batches L1 to L5 are specified hereafter.

(8) L1: According to the Teaching of Reference [1]

(9) PEEK 150P: 1 kg

(10) Water: 2 kg per kg of polymer

(11) Surfactant: cetearyl alcohol 25 times ethoxylated (Cremophor A 25BASF)1.5% (w/w) of the polymer

(12) Weight content of fibres: 59%

(13) L2:

(14) PEEK 150P: 1 kg

(15) Water: 2 kg per kg of polymer

(16) Surfactant: stearyl alcohol 100 times ethoxylated (Brij S100CRODA)1.0% (w/w) of the polymer

(17) Weight content of fibres: 62%

(18) L3:

(19) Impregnation bath of composition identical to that used for batch L2

(20) Weight content of fibres: 59%

(21) L4:

(22) PEEK 150P: 1 kg

(23) Water: 2 kg per kg of polymer

(24) Surfactant: stearyl alcohol 20 times ethoxylated (Brij S20CRODA)1.5% (w/w) of the polymer

(25) Weight content of fibres: 59%

(26) L5:

(27) PEEK 150P: 1 kg

(28) Water: 2 kg per kg of polymer

(29) Surfactant: polyoxoethylene sorbitan monolaurate (Polysorbate 20SIGMA-ALDRICH)2.0% (w/w) of the polymer

(30) Weight content of fibres: 62%

(31) The impregnation baths are maintained under agitation throughout the duration of the impregnation (2 hours).

(32) The prepregs of batch L1 (which correspond to prepregs of the prior art and serve as reference) measure around 0.13 mm6.35 mm of traversal section whereas the prepregs of batches L2 to L5 measure around 0.15 mm50 mm of traversal section.

(33) Preparation of the Preforms and Consolidation in Drying Oven:

(34) Preforms of 4 folds, measuring 200 mm by 200 mm, are prepared by manual draping, by forming linking points between the fibres using a soldering iron (soldering tip temperature: 450 C.) using batches L1 to L5 of prepregs. The draping is carried out with a mirror symmetry according to a sequence 90/0/0/90.

(35) Said preforms are consolidated in a drying oven, under bladder (pressure: 850 mbars), by applying the following consolidation cycle: creation of a vacuum in the drying oven; increase in temperature from 20 C. to 300 C. at a rate of 2 C./minute; degassing plateau at 300 C. for 20 minutes; increase in temperature from 300 C. to 395 C. at a rate of 2 C./minute; consolidation plateau at 395 C. for 25 minutes; and decrease in temperature down to 20 C. at a rate of 2 C./minute.

(36) Assessment of the Consolidation of the Composites by NDT:

(37) The consolidation quality of the materials obtained above is assessed by an ultrasonic non-destructive test by immersion according to the double transmission method. This type of testing, which is well known per se, makes it possible to establish a mapping of the defects and, notably, of the residual porosity that a material exhibits after its manufacture without harming the integrity of the structure of said material.

(38) Results:

(39) The results are illustrated in FIGS. 2A to 2E which show the ultrasound mappings obtained for the different composites: FIG. 2A corresponds to a composite prepared using a prepreg of batch L1; FIGS. 2B and 2C correspond to two composites respectively prepared using the prepregs of batches L2 and L3, whereas FIGS. 2D and 2E correspond to two composites respectively prepared using the prepregs of batches L4 and L5.

(40) In these mappings, which are originally in colour but which are presented in the appendix in grey scales, the lightest grey tone, referenced f1, corresponds to an absence of propagation of the ultrasonic wave in the composite, which is the sign of poor consolidation of the composite. The darkest grey tone, referenced f3, corresponds to an attenuation of the ultrasonic wave of the order of 90% and to the presence of porosities in the composite, which is also the sign of poor consolidation of the composite. On the other hand, the intermediate grey tone, referenced f2, corresponds to an attenuation situated between 20% and 30% of the ultrasonic wave in the composite and reflects, for its part, good consolidation of the composite.

(41) It should be noted that the grey tone f2 correspond typically to materials of which the residual porosity is less than 1%, that is to say to materials meeting aeronautical and space requirements.

(42) As FIG. 2A shows, the consolidation of the composite prepared using the prepreg of batch L1 serving as reference is of very poor quality since the mapping obtained for this composite is mainly occupied by a zone with grey tone f1 (absence of propagation of the ultrasonic wave).

(43) The consolidation of the composite prepared using the prepreg of batch L5 (batch of the impregnation bath comprising polyoxoethylene sorbitan monolaurate as surfactant) is also of very poor quality since the mapping obtained is essentially constituted of a juxtaposition of zones with grey tones f1 and f3 (FIG. 2E).

(44) The consolidation of the composite prepared using the prepreg of batch L4 (batch of the impregnation bath comprising stearyl alcohol 20 times ethoxylated as surfactant) is of better quality than that of the preceding composites but irregular zones remain (FIG. 2D).

(45) On the other hand, the consolidation of the composites prepared using the prepregs of batches L2 and L3, in accordance with the invention, is, for its part, very satisfactory (FIGS. 2B and 2C).

(46) These results confirm that the use of a stearyl alcohol 100 times ethoxylated, as surfactant in an aqueous impregnation bath for reinforcement fibres, makes it possible to obtain prepregs having a thermoplastic matrix which results in highly satisfactory consolidation of the composite materials obtained using said prepregs, without external pressurisation (the external pressure being simply atmospheric pressure), which is not the case either with the use of cetearyl alcohol 25 times ethoxylated used in the prior art nor even with that of a stearyl alcohol 20 times ethoxylated instead of 100.

REFERENCE CITED

(47) [1] U.S. Pat. No. 5,888,580