EP1904559A1

EP1904559A1 - Composite material

Info

Publication number: EP1904559A1
Application number: EP06708804A
Authority: EP
Inventors: Andrea Gaio; Luca Mezzo
Original assignee: Fibre e Tessuti Speciali SpA
Current assignee: Fibre e Tessuti Speciali SpA
Priority date: 2005-07-05
Filing date: 2006-03-21
Publication date: 2008-04-02
Also published as: WO2007003449A1; EP1741742A1

Abstract

The composite material comprises a fibrous support and a thermosetting resin having a glass transition temperature of no less than 30°C which impregnates the support. The support comprises a plurality of assembled thread-like first and second elements. The first thread-like elements are based on or coated by a thermoplastic phenoxy polymer having a glass transition temperature (Tg) of no less than 20°C and the formula (I), (II), or (III), in which R1 and R2 are mutually independently selected from among H, C1-C10 alkyl and optionally substituted phenyl, R3 is selected from among H, C1-C10 alkyl, C1-C10 car- boxyethyl and COR4 where R4 denotes H or a C1-C9 alkyl, and n is an integer of between 30 and 200. The second thread-like elements are fibres selected from the group consisting of carbon, glass, basalt, p-aramid and polyphenylenebenzobisoxazole (PBO) fibres and mixtures thereof.

Description

Composite material

The present invention relates to the sector of composite materials composed of fibrous supports and thermosetting resins .

Typically, such a support, which is formed from thread-like elements assembled for example from interwoven fibres, is impregnated with thermosetting resin and then heated for the period of time necessary to bring about curing of the resin and so obtain the desired composite material.

One important requirement in the production processes for said composite materials is that the dimensional stability of the fibrous support is maintained during the various processing phases (for example cutting, die cutting, positioning in the mould, etc.), so preventing the constituent fibres from becoming too close together or too spaced apart .

In order to achieve this result, it has been proposed to increase the quantity of fibre per unit area, but this has the disadvantage of complicating the subsequent impregnation with the thermosetting resin.

In order to ensure dimensional stability without compromising the subsequent impregnation phase, it has accordingly- been proposed to coat the fibrous support with thermoplastic polymers, such as polyamides, polyesters and the copolymers thereof, which, after having been softened by heating, hold the fibres of the support together. However, these thermoplastic resins have physico-chemical properties which are significantly different from those of the thermosetting resins, for example epoxy resins, which are typically used for impregnation. These differences mean that tensions are generated in the interface which forms between the thermoplastic polymer and thermosetting resin, which are essentially due to the different coefficients of thermal expansion, which result in the formation of cracks which then initiate failure of the composite material by delamination or detachment of the thermosetting resin from the fibrous support.

With the aim of avoiding the above-mentioned disadvantages of the prior art, it is thus an object of the present invention to provide a composite material comprising a fibrous support and a thermosetting resin having a glass transition temperature of no less than 3O⁰C which impregnates the support, said support comprising a plurality of assembled thread-like first and second elements, said first thread-like elements being based on or coated by a thermoplastic phenoxy polymer having a glass transition temperature (Tg) of no less than 2O⁰C and the formula

or

in which

Ri and R₂ are mutually independently selected from among H, Ci-Ci₀ alkyl and optionally substituted phenyl ,

R₃ is selected from among H, Ci-Ci₀ alkyl , Ci-Ci₀ car- boxyethyl and COR₄ where R₄ denotes H or a Ci-C₉ alkyl , and n is an integer of between 30 and 200, and said second thread-like elements being fibres selected from the group consisting of carbon, glass, basalt, p-aramid and polyphenylenebenzobisoxazole (PBO) fibres and mixtures thereof.

The above-stated phenoxy polymer preferably has the formula

in which n is an integer of between 30 and 200 and preferably between 45 and 160.

The phenoxy polymer used in the fibrous support according to the invention is insoluble in the thermosetting resins typically used for the production of composite materials, and is also chemically inert towards them, such that it provides an effective dimensional stabilisation action of the fibrous support both during and after the impregnation thereof with the thermosetting resin. It is furthermore capable of imparting advantageous thermoformability properties to the fibrous support. The first thread-like elements may be produced in substantially any physical form, for example in the form of multifilament yarn, monofilament yarn, split yarn, long and short staple yarn, such as wool and cotton yarn, fibre, and any desired combination thereof. Such first elements may be composed entirely of phenoxy polymer or comprise further minor components other than this, for example plasticisers such as epoxy resins. The phenoxy polymer may also be used as a coating for fibres or yarns of a different chemical nature .

The second thread-like elements provide to the composite material the mechanical properties which are requested for structural applications, for example in the building, automotive and aerospace sectors . Such second thread-like elements are inert in respect of the impregnating thermosetting resins, so as they do not noxiously interact with them.

Typical physical parameters of the second thread-like elements are the following.

Carbon fibers :

- tensile strength: 1100-5500 MPa

- tensile modulus: 50-850 GPa

- elongation at break: 0.3-2%

- density: 1,65-1,85 g/cm³

Glass fibers:

- tensile strength: 1800-3700 MPa

- tensile modulus: 70-90 GPa

- elongation at break: 3,4-4,2% - density: 2,52-2,59 g/cm³

P-aramide fibers :

- tensile strength: 2810-3170 MPa

- tensile modulus: 65-120 GPa

- elongation at break: 2,50-3,70 %

- density: 1,45 g/cm³

Basalt fibers :

- tensile strength: 2800-4900 MPa

- tensile modulus: 75-95 GPa

- elongation at break: 3-3,5%

- density: 2,8g/cm³

Overall, the fibrous support of the composite material according to the invention may, for example, be produced in the form of nonwoven fabric, orthogonal fabric, unidirectional fabric, multiaxial fabric, three-dimensional fabric, and any desired combination thereof. In particular, said support may comprise a plurality of layers of identical or different types joined to one another, for example by means of stitching, coupling, resin bonding and the like.

The impregnating thermosetting resin is, for example, selected from the group consisting of epoxy, vinyl ester, polyester, phenolic and phenoxy resins and mixtures thereof.

Epoxy resin is preferred thanks to the similarity between its molecular structure and that of phenoxy resin, from which it differs only by the presence of epoxy groups, instead of hydroxyl groups, as molecular chain ends. This structural similarity results in a similarity of the respective coefficients of thermal expansion (55*10^~6 mm/ ⁰C for the phenoxy polymer and 55-70*10^~6 mm/ ⁰C for the epoxy matrix) . The combination of phenoxy polymer elements with an epoxy resin is thus particularly suitable for the production of composite materials subjected to fatigue stress.

In the fibrous support of the composite material of the invention, the percentage by weight of the first thread-like elements is for example between 5 and 60% of the total weight of the support and more preferably between 5 and 40%, whereas the percentage by weight of the second thread-like elements is for example between 95 and 40 % of the total weight of the support and more preferably between 95 and 60%.

One specific example of a composite material of the invention is composed of a unidirectional fabric with a phenoxy polymer yarn weft and a carbon fibre warp, the fabric being impregnated with a thermosetting epoxy system.

Further advantages and features of the present invention will become clear from the following examples of embodiment which are provided by way of non-limiting example.

EXAMPLE 1

Using a INCHEM PKHH phenoxy polymer having a number average molecular weight of 13000 dalton, a weight average molecular weight of 52000 dalton, a viscosity at 25⁰C of 525-715 cP, a Tg of 92⁰C, a density of 1.18 g/cm³ and a melt index at 200⁰C of 4, a yarn with the following properties was obtained: Linear density: 520 dtex Tenacity: approx. 8 cN/tex Modulus: 206 cN/tex Elongation at break: approx. 29%.

Said yarn was subjected to compatibility testing with an epoxy system and the individual components thereof, which are typically used for the production of thermosetting matrices for composite materials.

Said yarn was subjected at atmospheric pressure to a thermal cycle comprising firstly heating at 2°C/min up to 12O⁰C followed by a plateau at 12O⁰C for 50 minutes, under the following conditions : a) in air; b) immersed in pure epoxy resin; c) immersed in pure dicyandiamide curing agent; d) immersed in epoxy resin and curing agent mixed together so as to form a thermosetting system; giving rise to the following results: a) no dimensional variation, even if the Tg is exceeded; b) no diffusion of phenoxy resin into the epoxy resin, nor any colour changes due to any possible reactions; c) no diffusion of phenoxy resin into the dicyandiamide; d) no diffusion of phenoxy resin into the thermosetting epoxy system; the yarn did, however, have the appearance of a more compact agglomerate than in case a) , where the individual filaments are, in contrast, still visible .

By way of confirmation of the results of the above-stated tests, FT-IR spectra were obtained for the epoxy resin (Figure 1), the phenoxy resin (Figure 2) and the interfa- cial zone between the two polymers (Figure 3) . The spectrum of the interfacial zone does not differ from those for the pure polymers, so confirming their non-miscibility under the test conditions .

EXAMPLE 2

Tests similar to those of Example 1, conditions a) and d) , were carried out with the only difference that a pressure of 0.32 MPa was used instead of atmospheric pressure.

In case a) , the yarn was highly deformed and its individual constituent filaments could no longer be recognised. In case d) , the yarn could no longer be distinguished from the epoxy matrix, apart from the presence of a more opaque zone corresponding to its original position, due to diffusion of the phenoxy polymer into the epoxy resin, where, however, it did not dissolve.

DSC testing was then performed both in the less opaque or translucent zone (see thermogram shown in Fig. 4) and in the more opaque zone (see thermogram shown in Fig. 5) . As is immediately evident, this latter thermogram has two very distinct inflections due to the glass transitions of the individual components, so demonstrating the absence of chemical reactions and solubility between the two components even under pressure.

The tests described in Examples 1 and 2 thus clearly indicate that the phenoxy polymer exhibits good thermoplastic behaviour, readily melting at temperatures of the order of 12O⁰C, but without dissolving at the interface with the ep- oxy matrix nor reacting therewith.

EXAMPLE 3

A fibrous support composed of a unidirectional fabric with a carbon fibre warp and a PKHH phenoxy polymer weft (made of yarns of the same kind disclosed in examples 1 and 2) was first hot calendered to ensure diffusion of the phenoxy polymer of the weft, allowing the warp fibres to spread out and remain dimensionally stabilised. The fabric was then impregnated with a thermosetting epoxy system in an amount of 43% relative to the total weight of the composite material and was then placed in a flat mould at ambient temperature. The mould was closed and heated up to 12O⁰C at a heating rate of 2°C/min, was then held at 12O⁰C for 1 hour to permit complete crosslinking of the thermosetting system, and was finally cooled. In this manner, a composite material was obtained in the form of a flat sheet usable in various structural applications, for example as reinforcement for beams in the building sector.

Naturally, the principle of the invention remaining the same, the details of performance and forms of embodiment may be varied widely with respect to those described purely by way of example, without thereby departing from the claimed scope.

Claims

1. Composite material comprising a fibrous support and a thermosetting resin having a glass transition temperature of no less than 3O⁰C which impregnates the support, said support comprising a plurality of assembled thread-like first and second elements, said first thread-like elements being based on or coated by a thermoplastic phenoxy polymer having a glass transition temperature (Tg) of no less than 2O⁰C and the formula

OH OR₃

(D IK)-CH-.-CH- CH, ^■°-<D ®-O-CfiU—CH-ClU OH ' n

in which

Ri and R₂ are mutually independently selected from among H, Ci-Ci₀ alkyl and optionally substituted phenyl,

R₃ is selected from among H, Ci-Ci₀ alkyl, Ci-Ci₀ car- boxyethyl and COR₄ where R₄ denotes H or a Ci-C₉ alkyl, and n is an integer of between 30 and 200, and said second thread-like elements being fibres selected from the group consisting of carbon, glass, basalt, p- aramid and polyphenylenebenzobisoxazole (PBO) fibres and mixtures thereof.

2. A composite material according to claim 1, in which said phenoxy polymer has formula

3. A composite material according to claim 1 or claim 2, in which said first thread-like elements are produced in the form of a multifilament yarn, monofilament yarn, split yarn, long and short staple yarn, such as wool and cotton yarn, fibre, and any desired combination thereof.

4. A composite material according to any one of the preceding claims, in which said fibrous support is in the form of nonwoven fabric, orthogonal fabric, unidirectional fabric, multiaxial fabric, three-dimensional fabric, and any desired combination thereof.

5. A composite material according to any one of the preceding claims, in which said fibrous support is in the form of a unidirectional fabric with a carbon, glass, basalt, p- aramid or polyphenylenebenzobisoxazole fibre warp and a phenoxy polymer yarn weft.

6. A composite material according to claim 5, in which said fibre warp is carbon fibre warp.

7. A composite material according to any one of the preceding claims, in which said thermosetting resin is selected from the group consisting of epoxy, vinyl ester, polyester, phenolic and phenoxy resins and mixtures thereof .

8. A composite material according to claim 6, in which said thermosetting resin is an epoxy resin.

9. A composite material according to any one of the preceding claims, in which the percentage by weight of the first thread-like elements is between 5 and 60% of the total weight of the support, and the percentage by weight of the second thread-like elements is between 95 and 40 % of the total weight of the support.

10. A composite material according to claim 9, in which the percentage by weight of the first thread-like elements is between 5 and 40% of the total weight of the support, and the percentage by weight of the second thread-like elements is between 95 and 60 % of the total weight of the support .