EP0446325A1

EP0446325A1 - Composite material

Info

Publication number: EP0446325A1
Application number: EP90914117A
Authority: EP
Inventors: Marc Vanden Broeck; Olivier De Marchi
Original assignee: MARCHI OLIVIER DE
Current assignee: MARCHI OLIVIER DE
Priority date: 1989-10-03
Filing date: 1990-09-26
Publication date: 1991-09-18
Also published as: CA2042410A1; WO1991004852A1

Abstract

Ce matériau comporte une matrice de résine thermodurcissable renfermant des nappes de filaments de carbone. Etant donné le module d'élasticité élevé de ces filaments, ceux-ci ne peuvent pas s'allonger lors du thermoformage du matériau composite. Par ailleurs, ces filaments sont relativement mal mouillables par la résine, de sorte que le thermoformage entraîne notamment un délaminage du matériau composite. C'est la raison pour laquelle une couche médiane à pores ouverts à faible module d'élasticité, compressible, est intercalée entre deux nappes du matériau de renfort filamentaire. Cette couche médiane réalise un excellent accrochage avec la résine et permet d'absorber les contraintes de traction et de compression en raison de sa capacité de compression.This material comprises a matrix of thermosetting resin containing layers of carbon filaments. Given the high elastic modulus of these filaments, they cannot lengthen during thermoforming of the composite material. Furthermore, these filaments are relatively poorly wettable by the resin, so that thermoforming notably causes delamination of the composite material. This is the reason why a middle layer with open pores with a low modulus of elasticity, which is compressible, is interposed between two layers of the filamentary reinforcing material. This middle layer achieves an excellent bond with the resin and makes it possible to absorb the stresses of traction and compression due to its compression capacity.

Description

COMPOSITE MATERIAL

The present invention relates to a composite material based on thermosetting resin reinforced with carbon filaments, rethermoformable at will after polymerization of the resin.

It has already been proposed, in particular in EP-A2-174 216, a thermoformable composite orthosis material, intended to form an orthosis element, composed of a polymerized resin reinforced with fibers. A similar material is described in FR-A1-2 284 634. The fibers or filaments used are intended to reinforce the composite and are chosen for this purpose from the category of materials whose elastic modulus is> 50 GPa. Among these filaments, there are carbon, glass, aramid filaments. Generally these filaments (or multi-filaments) are woven to be incorporated into the re¬ sine.

Reinforcement with glass filaments gives the material good resistance, it allows rethermoforming after polymerization of the resin, but the density of the glass leads to a relatively heavy material, which in the field of orthopedics in particular constitutes a serious drawback.

Reinforcement with generally woven carbon filaments whose elastic modulus is much higher than that of glass and whose density is much lower, gives a light material with high mechanical resistance which lends itself particularly well to orthopedic applications in particular. However, such materials present a very poor aptitude for thermoforming after polymerization of the resin, which constitutes a serious drawback, especially in orthopedics. Under certain conditions, it is possible to thermoform once the material has been formed from thermosetting resin reinforced with carbon filaments, but no such resins are thus known, thus reinforced at will. However, this property is desirable, especially in the orthopedic field, to allow adaptation the orthosis. Indeed, after a fracture for example, it happens that it is accompanied by swelling, requiring a readjustment of the orthosis after disappearance of the swelling. After a few weeks of immobilization, the musculature atrophies requiring a new adaptation. These examples show the need to be able to carry out multiple rethermoformings of the resin reinforced with carbon filament in order to adapt the orthosis to the above-mentioned developments.

In view of their high modulus of elasticity, the carbon filaments cannot elongate during the thermoforming of the composite material. In addition, the wettability of these carbon filaments by the resin is not very good. As a result, during thermoforming, one face of the reinforcing ply is subjected to a tensile force while the opposite face is subjected to a compressive force during the bending of the composite. As a result, the resin cracks on the convex face and forms beads on the concave face. In view of the shear forces between the sheet of carbon filaments and the resin and the problems of wettability, the composite material delaminates. In all cases, such a material can only be thermoformed using a special tool and can then no longer be rethermo-forroated, which prevents the successive adaptations that an orthosis may require, as explained. previously.

It therefore appears that currently the carbon filaments can only be used to reinforce the resin for manufacturing elements, in the field of orthopedics or in other fields, which do not need to be retheroformed at will. after polymerization of the resin constituting the matrix and only the resins reinforced with glass filaments lend themselves to rethermoforming as desired, but leading to a much heavier material and to a lower modulus of elasticity than that reinforced by carbon filaments.

The object of the present invention is to allow the production of a light composite material, reinforced with carbon filaments which is rethermoformable at will. To this end, the present invention relates to a thermoformable laminate material according to claim 1.

The presence of an open pore middle layer with low elastic modulus, which is compressible, makes it possible to achieve excellent bonding between the resin and the middle layer and to absorb the tensile and compressive stresses thanks to the compression capacity of this middle layer. Therefore there are no more cracks, beads, or delamination after bending the composite material and it can be rethermoformed dozens of times without undergoing any degradation.

Other advantages of the composite material which is the subject of the invention will become apparent during the description which follows.

The structure of the composite material according to the invention is always symmetrical with respect to a middle layer which can be produced in particular from polyurethanes, polyolefins, polyvinyl chloride (PVC), etc. in the form of a layer 0.1 to 10 mm thick, porous with open pores and having a modulus of elasticity <2 GPa and a density less than 1.

On either side of this middle layer, the material comprises at least one layer of reinforcing filaments which can be in the form of a fabric whose elastic modulus is> 50 GPa composed of carbon filaments.

The whole of this structure is embedded in a resin matrix which is a thermosetting resin, preferably a mixture of an unsaturated resin with low functionality, which confers flexibility, and of an unsaturated resin with high functionality, which confers hardness, the proportion between the two, varying according to the desired hardness / flexibility balance. The polymerization initiator is an organic peroxide.

To increase flexibility and decrease density, fine, light, porous, inorganic or organic fillers can be incorporated into the mixture. The fine filler can be obtained by cryogenic grinding of porous polymers, for example porous PVC whose density is less than 1.

The resin can be tinted using a compatible dye and a certain proportion of high mineral charges. thermal conductivity can be incorporated to speed up polymerization.

Preferably, the structure described above is complemented by at least two plies of a fabric whose elastic modulus is between 2 and 5 GPa and the elongation at break is between 40% and 300%. These thermoplastic fabrics are commonly produced from polyesters, aliphatic polyamides, polyacrylics, etc. These two plies with modulus of elasticity are arranged on the side of the external face of each ply of reinforcing filaments. At least two plies with additional modulus of elasticity can be inserted respectively between the middle layer and the two plies of carbon filaments.

In all cases each ply of carbon filaments and each ply with medium modulus of elasticity can be doubled so as to be in adjacent pairs in the composite material rather than in the form of a single ply.

Furthermore, as a variant, the middle layer can also be doubled, a sheet of carbon filaments being inserted between the two middle layers.

One of the characteristics of the composite material according to the invention lies in the fact that, the middle layer being formed by a polymer with open pores, the resin can penetrate to a surface depth by the two faces of this middle layer and form a homogeneous binding interphase. This characteristic is extremely important, insofar as it is well known in interface theory, that the presence of an interphase avoids the concentration of forces and thus makes it possible to reduce the risks of delamination under the effect of shearing. This interphase is also extremely important for transferring the reinforcing effect between the different layers of the laminate material.

To form the middle layer, PVC is of great interest since it can participate in the polymerization process as a radical donor or accelerator of the decomposition of peroxide. A confirmation of this phenomenon is given by the fact that there is a greater thermal development and a shorter polymerization time. in the presence of PVC in the resin. In addition, this middle layer gives the laminated material flexibility, from low to medium temperature, and at the same time makes it compressible. Thanks to this faculty of deformation and compression and to the symmetrical structure of the layers, the stresses can be dissipated and redistributed increasing the durability of the material and its capacity for thermoforming and multiple rethermoforming.

We will describe below, by way of example, different embodiments of the laminated material which is the subject of the present invention.

Example 1

Two methacrylic resins marketed with different functionalities are used, Degaplast, Orthocryl. Although the proportions can be varied due to the desired properties, the preferred mixture for orthopedic applications consists of 20 parts by weight of low functionality resin and 80 parts by weight of high functionality resin. The benzoyl peroxide initiator (Roland Frey 5504 Othmarsingen, Switzerland) used is of the order of 1 to 3% by weight. A further 2% by weight of a Ruconix blue dye (Ruff and Co, Glattbrugg, Switzerland) is added.

As reinforcement with elastic modulus> 50 GPa we use

2 a 0.2 kg / m carbon multifilament fabric reference

028500-120 (Roland Frey 5504 Othmarsingen, Switzerland).

As for the fabric whose elastic modulus is between 2 and 5 GPa, it is a Perlon® polyamide fabric reference 028400-120 (Roland Frey 5504 Othmarsingen, Switzerland).

Finally, the porous middle layer is 3 mm thick PVC Aire or Simosel.

The structure of the laminate material is as follows:

1. Two sheets of Perlon fabric

2. Two layers of carbon multifilament fabric

3. PVC Airex 3mm middle layer sanded and drilled at regular intervals 4. Two layers of carbon multifilament fabric

5. Two tablecloths of Perlon fabric

To make the laminated material, a set of five components in the order listed above is placed in a 30 x 60 cm mold coated with a humidified PVA film and used for demolding. The mold is closed and a vacuum of 78.5 kPa is produced in order to inject 700 g of the above-mentioned methacrylic resin with the 3% benzoyl peroxid therein. The whole is left to polymerize for 30 min.

Example 2

The laminated material of this example differs from that of Example 1 only by the fact that two sheets of Perlon fabric are interposed between components 2 and 3 as well as between components 3 and 4 of Example 1.

Example 3

The laminated material of this example differs from that of Example 1 only in the structure of the middle layer 3 which comprises two layers of PVC Aire of 3mm between which two layers of the fabric of carbon multi-filaments are arranged, so that the middle layer is itself formed of a laminate.

Example 4

The laminate material of this example differs from that of Example 1 only by the fact of the elimination of the components 1 and 5 each consisting of two layers of Perlon fabric.

The samples of the laminated material according to Examples 1 to 4 were subjected to thermoforming tests using a hot air fan delivering air at 250 ° C. The heated samples are quickly bent at right angles to form a round. After cooling, the samples were reheated to quickly straighten them to bring them back to their initial state.

These tests have been successfully passed 40 times by four samples corresponding to the respective examples above, that is to say that no delamination or cracks were found on the outside of the curvature and beads on the inside, defects which we have found in the above-mentioned commercial products without a porous middle layer.

Rupture tests of these samples carried out by folding at room temperature revealed the role of components 1 and 5 of Example 1 formed of two layers of

AT

Perlon or equivalent components of the samples according to Examples 2 and 3 compared to Example 4 which is devoid of these components. Indeed, with the samples according to Examples 1 to 3, there is a break without separation, while in the case of the sample according to Example 4, there is a break with separation into two pieces. The sheets of fabric with high elongation at break therefore constitute safety elements in the event of breakage or impact.

A study of the thermomechanical and dynamic properties was carried out using the samples produced according to Examples 3 and 4 which 1 'were compared with four other samples 5, 6, 7 and 8 each composed of the resin matrix in which only some of the components of the laminate material according to Example 1 were incorporated, namely s

sample 5 resin 20/80 + PVC Airex ^β 3mm

A sample 6 resin 20/80 + Perlon + multifilaments

A carbon + Perlon sample 7 resin 20/80 + Perlon sample 8 resin 20/80 + carbon multifilaments

Instead of using conventional measurement on an Instron instrument, we have adapted the viεcoelastic technology using a "Dynamic Mechanical Analyzer DMA 983" measuring device controlled by a "9900 Thermal Analyzer" manufactured by Du Pont Instruments in the USA . This technology is used for the in-depth study of the viscoelastic properties of composite materials. The study conditions are as follows:

DMA Fixed Frequency 1 Hz

Temperatures -20 ° to 200 ° C

Increase 3 ° C / minute

Poisson's ratio: 0.420 for composite

0.450 for PVC

The meanings of the viscoelastic symbols are as follows:

E 'Elastic modulus in bending

E 'Viscous module in bending

Tandelta: E "/ E '

Tg Glass transition temperature alpha for high Tg beta for medium Tg gamma for low Tg

Tfr brittleness temperature: temperature of the transition from the elastic phase to the transition phase

Tfl Flexibility temperature: temperature of transition from the alpha transition phase to the viscous phase = temperature of the maximum of the Tandelta curve in the alpha transition zone.

Theoretically, the material is thermoformable when heated to a temperature between Tg alpha and Tfl. We can admit that Tfl is equal to the thermoformability temperature Tth, because at this temperature, the mobility of the chains polymers reaches the maximum.

First, a PMMa resin composite reinforced with carbon filaments was compared, with a laminate in accordance with Example 4. The results obtained were as follows:

The presence of the middle layer based on porous PVC

AT

Area according to Example 4 completely changes the thermomechanical and dynamic properties compared to the PMMa / carbon composite.

A new beta transition zone appears between -20 ° C and + 6B ° C (Tg beta: 47 ° C). Its presence explains the high value of Tandelta and the improvement in impact resistance at room temperature (25 ° C). At this temperature, the PVC-free material is still in the elastic phase.

The ease of thermoformability of the new material is proven by the following viscoelastic properties:

- Lower brittleness temperature Tfr

- The presence of the beta transition

- The low value of the elastic modulus E 'at the thermoformability temperature Tfl Table 2 gives the viscoelastic properties of the various constituents of the laminated material which is the subject of the invention.

TABLE 2

No 8 No 6 No 5

PMMa PMMa PMMa Carbon Perlone Aire β Carbon

25.98 4.085 0.456 704.5 221.4 57.04

0.027 0.054 0.067 106.1 106.3 82.6 40 57.5 -17 117 120 89

It follows from these DMA measurements with regard to the elastic as well as viscous modulus that:

Carbon filaments give the highest modulus

AT

Perlon fabric provides the medium modulus AIREX® PCV provides the lowest modulus

The combination of the different components gives an intermediate module material (see Example 4 in Table 1). Contrary to the forecast, the reduction in the elastic modulus of the laminate made with carbon filaments (No 8) is greater when combined with the polyamide fabric (No 6) than with the PVC AIREX® sample 4 in the table 1. This can be explained by the presence of an interphase between the resin and the PVC which allows a better transfer of the reinforcing effect of the carbon filaments to the middle layer of PVC. It is also well known that the wetting of the polyamide fabric by the resin is not good.

Regarding the thermomechanical effect: Carbon filaments are the constituents which increase the rigidity of the laminate by raising the glass transition temperature alpha.

AT

Perlon gives better flexibility at medium temperature because of its own beta transition between 10 ° C and 60 ° C (Tg beta = 40 ° C). The high value of Tandelta indicates its good ability to dissipate bending stresses.

PVC increases the impact resistance and the thermoformability of the laminate. In fact, PVC introduces two transition zones, namely:

Gamma transition at -17 ° C: plasticizers Beta transition at 5B ° C: PVC resin

This is the reason why the laminate according to the invention which has very wide transition zones, presents good rigidity, good impact resistance, delamination and good thermoformability.

Table 3 gives the viscoelastic properties of the laminated material according to Examples 3 and 4

TABLE 3

Sample According to Ex. 4 According to Ex. 3

E '25 ° C GPa 9,767 3,700

E "25 ° C MPa 397.7 90.91

Tg alpha ° C 113 95.9

Tg beta ° C 47.5 60.6

Tfl ° C 124 104

E 'Tfl GPa 0.2348 0.1467

Density 0.98 0.94

AT

As has already been observed, Perlon and PVC of relatively large thickness reduce the rigidity and favorite the thermoformability by lowering Tg alpha and Tfl. The insertion of carbon filaments in the middle layer increases its rigidity. Tg beta is moved to a higher temperature.

The density of the laminate <1 is significantly lower than that of the resin / carbon filament products which is between 1.2 and 1.4.

Claims

1. Composite material based on thermosetting resin reinforced with carbon filaments rethermoformable at will after polymerization of the resin, characterized in that these carbon filaments are arranged in at least two layers, on either side of a middle layer of a polymer produced in porous form with open pores whose modulus of elasticity is <2 GPa, whose thickness is between 0.1 and 10 mm and whose density is <1.

2. Composite material according to claim 1, caracté¬ ized in that at least two plies of a fabric of a thermoplastic polymer whose elastic modulus is between 2 and 5 GPa and whose elongation at the rupture is between 40% and 300% are respectively arranged on the external side of the two layers of carbon filaments.

3. Composite material according to claim 1, caracté¬ ized in that the sheet of carbon filaments, available on each side of the middle layer is itself disposed between at least two layers of a fabric of a polymer thermoplastic whose elastic modulus is between 2 and 5 GPa and whose elongation at break is between 40 -s and 300%.

4. Composite material according to claim 1, caracté¬ ized in that the middle layer comprises two layers of said polymer arranged on either side of at least one layer of carbon filaments.

5. Composite material according to one of claims 1 to 4, characterized in that said resin matrix is made of PMMa.

6. Composite material according to one of claims 2 to 4, characterized in that said plies in a thermoplastic polymer fabric are made of aliphatic polyamide.

7. Composite material according to one of claims 1 to 4, characterized in that said middle layer is made of PVC.