WO2014009163A1

WO2014009163A1 - Polymeric fibre composites modified with single-walled carbon nanotubes

Info

Publication number: WO2014009163A1
Application number: PCT/EP2013/063464
Authority: WO
Inventors: Heinrich Zeininger; Heinrich Kapitza; Christian Seidel
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-07-13
Filing date: 2013-06-27
Publication date: 2014-01-16
Also published as: EP2841491A1; DE102012212290A1

Abstract

The present invention relates to fibre composites made of fibres and a polymer matrix, into which polymer matrix single-walled carbon nanotubes are also inserted. In the fibre composite materials according to the invention the single-walled carbon nanotubes are present homogeneously distributed in the intermediate spaces between the fibres. An improvement of the mechanical properties of the fibre composite materials is thereby achieved.

Description

Description Polymer fiber composites modified with single-walled carbon nanotubes

The present invention relates to fiber composites in which carbon nanotubes (CNT) are homogeneously distributed in the interstices between the fibers.

State of the art

Fiber composites are multiphase or blend materials that generally include at least reinforcing fibers as well as a matrix in which the fibers are embedded. Interaction between the two components improves the properties of the fiber composites in comparison to the individual components. The use of fiber composites is versatile. For example, fiber composites can be used in layered materials.

In general, it is unusual in the case of fiber composite materials to add particles for reinforcement, as is the case with polymers, since fiber composites require particularly good wetting of the fiber in the boundary layer to the matrix for high adhesion between fiber and matrix. Thus, a homogeneous distribution of additives in the fiber composite is important.

JP 2003-238816 discloses carbon fiber reinforced resin compositions for molded articles with which no particular property improvements can be achieved. In addition, WO 2007/044889 describes a textile-reinforced composite friction material based on non-woven fiber mats, in which a carbon material is dispersed in the matrix and which serves to improve the friction. However, the experimental conditions are not specified.

US 2007/0066171 relates to a carbon fiber reinforced carbon in which carbon nanotubes are present in the matrix. However, the high CNT content leads to a high viscosity and the diameter of the CNT is too large, so that the CNTs can not penetrate into the fiber interstices.

Furthermore, US 2010/0098931 discloses fiber-reinforced polymer composites containing carbon nanotubes in which the CNTs are sprayed onto the fibers and do not necessarily interact with the CNT-free matrix after their addition. In addition, functionalized carbon nanotubes were used here. However, in the fiber composites of the prior art, there is still a need to further improve the mechanical properties.

Summary of the invention

The inventors have found that a special reinforcement of a fiber composite material can be achieved when single-walled carbon nanotubes are homogeneously distributed in the interstices between the fibers of the fiber composite material. In particular, the inventors have found that the single-walled carbon nanotubes, by virtue of their homogeneous distribution, strengthen both the fibers and the matrix. Thus, according to the invention, a fiber composite material is disclosed, comprising:

i) a polymer matrix;

ii) fibers; and

iii) carbon nanotubes,

wherein the carbon nanotubes are single-walled carbon nanotubes and are homogeneously distributed in the interstices between the fibers of the fiber composite. Further, the present invention discloses a process for producing a fiber composite comprising i) a polymer matrix;

ii) fibers; and

iii) carbon nanotubes,

wherein the carbon nanotubes are single-walled carbon nanotubes and are mixed with the polymer matrix, and then this mixture is introduced onto and into the fibers so that the carbon nanotubes are homogeneously distributed in the interstices between the fibers of the fiber composite material.

Furthermore, the invention relates to the use of a fiber composite material according to the invention for the production of coating materials and / or fiber composites, a layer material and / or fiber composite, comprising the fiber composite material according to the invention, and the use of the layer material according to the invention and / or fiber composite in X-ray devices, patient beds, electrical machines, Engines, fuselages of aircraft, rotors of helicopters, wind turbine rotor blades, rotor blades in the marine sector, for example of ships, body parts, etc.

Further embodiments of the present invention are set forth in the dependent claims. Brief Description of the Drawings Preferred embodiments of the present invention are illustrated in conjunction with figures.

FIG. 1 shows transmitted light images of a thin section of a glass fiber laminate with 0.3% by weight of multi-walled carbon nanotubes.

Figure 2 illustrates macro-filtration effects that occur with the use of multi-walled carbon nanotubes. FIG. 3 shows transmitted light images of fiber composite materials in which the fibers are modified with single-walled carbon nanotubes (right image), compared to unmodified samples (left image). FIG. 4 shows the measurement results of the modulus of elasticity parallel to the fiber direction of the reference example, Examples 1 and 2 and Comparative Examples 1 and 2.

FIG. 5 shows the measurement results of the bending strength parallel to the fiber direction of the reference example, Examples 1 and 2 and Comparative Examples 1 and 2.

FIG. 6 shows the measurement results of the modulus of elasticity perpendicular to the fiber direction of the reference example, Examples 1 and 2 and Comparative Examples 1 and 2.

FIG. 7 shows the measurement results of the bending strength perpendicular to the fiber direction of Reference Example, Examples 1 and 2, and Comparative Examples 1 and 2. Detailed description of the invention

The present invention is characterized in that the single-walled carbon nanotubes homogeneously distributed in the

Gaps are introduced between the fibers of the fiber composite material. In the context of the invention, the single-walled carbon nanotubes are homogeneously distributed in the matrix before the matrix with the single-walled carbon nanotubes is then applied to the fibers and penetrates into the intermediate spaces between the fibers. This achieves both a better connection or connection between the fiber and the matrix on the one hand and a better connection or connection between the fibers (fiber matrix and fiber-fiber connection or connection). In addition, the rigidity or strength of the matrix itself is also improved by the presence of the single-walled carbon nanotubes. The single-walled carbon nanotubes can in this case come into contact with one or more fibers.

The polymer matrix of the fiber composite is not particularly limited, and any known polymer materials commonly used in the production of fiber composites can be used. Polymers in the polymer matrix can be duromers, elastomers as well as thermoplastics. Examples of polymers are epoxy resins, vinyl esters, polyesters, polyurethanes, or bioplastics, as well as mixtures thereof. Epoxy resins are preferably used.

The polymer matrix may further include a hardener, which is not limited. For example, the polymer matrix, a curing system, so both a polymer as also include a curing agent suitable for curing the polymer, and optionally an accelerator or initiator. Thus, when reactive resins are used as the polymer, the polymer matrix can be prepared by using a resin as a polymer and a curing agent and optionally an accelerator or initiator. In such a case, the ratio of hardener and optionally accelerator or initiator to resin is not limited and can be suitably adjusted by the skilled person. For example, the ratio of resin to hardener can range from 80:20 to 20:80 in terms of weight ratio. In certain embodiments, a resin to hardener ratio of about 50:50 in terms of weight ratio may also be present.

Suitable epoxy-based curing systems are, for example, mixtures of Araldit LY556 / Aradur 917 / DY 070, for example in a mixing ratio of 100/90/1, and mixtures of RIM135 / RIMH 1366, for example in a mixing ratio of 100/30. The amount of polymer matrix in the fiber composite material can be between 30 and 80% by weight, based on the fiber composite material.

The fibrous material in the present invention may be arbitrarily selected as long as the carbon nanotubes can be bonded to the fibers. For example, aramid fibers, carbon fibers, glass fibers, alumina ceramic fibers, mullite, SiBCN, SiCN, Sic, etc., boron fibers, steel fibers, nylon fibers or natural fibers may be used.

It is possible in certain embodiments that the fibers are surface modified to allow bonding to the carbon nanotubes and / or the matrix material. A modification can in this case in a known manner by functional groups that can interact with functional groups of the carbon nanotubes. For example, functionalization by amine or carboxyl groups may be advantageous when the carbon nanotubes have hydroxyl groups. A modification can also be carried out, for example, by optional addition of sizes. When using an epoxy resin, such a size can have, for example, C = C or C = O bonds, which can then interact with the epoxy resin.

The fiber composites are preferably in the form of carbon fiber-reinforced plastics (CFRP) or glass-fiber reinforced plastics (GFRPs), i. the use of carbon fibers or glass fibers is preferred.

Moreover, in the present invention, the fibers are preferably unidirectional. More preferably, the fibers are present as fiber bundles or rovings. The distances between the

Fibers in such bundles or rovings are in this case preferably between 1 and 30 nm, more preferably between 2 and 20 nm and particularly preferably between 3 and 10 nm. The amount of fibers in the fiber composite material can be between 20 and 70% by weight, based on the Fiber composite material amount.

The carbon nanotubes in the present invention are preferably such that they can penetrate into the interstices between the fibers.

The carbon nanotubes are preferably single-walled carbon nanotubes which are incorporated into the Interspaces between the fibers (such as rovings) can penetrate. The inventors have found that when multiwall-modified carbon nanotubes are incorporated into the fiber composites, macro and micro filtration effects occur because they tend to form agglomerates such that the multiwall carbon nanotubes do not penetrate into the fiber interstices. This leads to reduced fiber-matrix interactions and thus to a decrease of the mechanical properties instead of an improvement.

Such microfiltration effects are evident, for example, from FIG. 1, which show glass fiber rovings into which multi-walled carbon nanotubes (black coloring) can not penetrate and thus agglomerate outside the rovings.

Macrofiltration effects can be seen in Fig. 2, in which it can be seen that the multi-walled carbon nanotubes are filtered out during introduction onto and into the fibers, and thus only pure resin arrives in the rear part

(White) .

On the other hand, single-walled carbon nanotubes which agglomerate only to a small extent can effectively penetrate into the fiber interstices, and the mechanical properties of the modified fiber composites with the introduced carbon nanotubes are improved.

The penetration of the single-walled carbon nanotubes, for example, from the transmitted light shots Fig. 1 can be seen. The right image in Fig. 1 shows fiber composites modified with single-walled carbon nanotubes and the left panel shows unmodified fiber composites. The fibers are perpendicular in their diameter to the fiber direction recognizable as white dots. In addition, the fibers are unidirectional in these images. It can be seen clearly that no visible microfiltration or agglomeration occurs in the modified fiber composite, so that the matrix with the carbon nanotubes has effectively penetrated into the interstices between the fibers. More precisely, this can also be observed on samples by means of scanning electron microscopy or transmission electron microscopy, for example on samples prepared by means of thin-section grinding. Furthermore, in the left-hand image of FIG. 1, an area with a black stripe is also visible, in which there are no fibers and only the matrix.

The single-walled carbon nanotubes can be introduced unmodified or modified in the present invention, for example with polar groups. They can also be used without pretreatment.

End-modified single-walled carbon nanotubes are better able to dock with modified fibers and thus provide stronger bonding to the fiber which provides additional reinforcement of the fiber composite in addition to reinforcement due to van der Waals forces between the fibers and the carbon nanotubes.

However, a better enhancement of the mechanical properties is observed with unmodified, ie non-functionalized, single-walled carbon nanotubes. In the fiber composites according to the invention, it is possible in particular to achieve a reinforcement of the mechanical properties of more than 50% for certain parameters. In particular, the modulus of elasticity and the flexural strength are improved parallel to the fibers, since the single-walled carbon nanotubes Tubes can attach to the fibers or wrap around them, so that the interactions between different adjacent fibers is increased. This effect occurs due to the presence of the fibers in the interstices between the fibers, in particular not only for the fibers at the edge regions of fiber bundles, but also to fibers within such bundles, so that such an effect occurs more intensively in fiber bundles or rovings. In addition, however, a reinforcement of the modulus of elasticity or the bending strength is observed perpendicular to the fiber direction, since the single-walled carbon nanotubes attach to the fibers or can wrap around them, so that a breakage of the fibers, especially at flaws, better prevented.

The single-walled carbon nanotubes are preferably used in an amount of less than 3% by weight, more preferably less than 2% by weight, more preferably less than 1.5% by weight, even more preferably less than 1% by weight, and ins % of less than 0.6% by weight, more preferably less than 0.4% by weight, based on the polymer matrix. At higher levels, introduction of the single-walled carbon nanotubes in the interstices between the fibers is increasingly difficult, and there is also an increase in the viscosity of the matrix, which makes it increasingly difficult to introduce the matrix into the fibers themselves. The single-walled carbon nanotubes are furthermore preferably present in an amount of more than 0.05% by weight, more preferably more than 0.10% by weight, more preferably more than 0.20% by weight and particularly preferably 0.25% by weight. or more, based on the polymer matrix. With too small amounts of single-walled carbon nanotubes, a reinforcing effect hardly occurs due to the low concentration of carbon nanotubes. The diameter of the single-walled carbon nanotubes is preferably between 0.4 and 5 nm and more preferably between 0.6 and 4 nm. Furthermore, the single-walled carbon nanotubes preferably have a length of 50 to 1500 nm. If the fibers are too short, no improvement in the mechanical properties of the fiber composite, and if the fibers are too long, they can not effectively penetrate into the interstices between the fibers and distribute themselves homogeneously there. A preferred length is between 70 and 1000 nm.

Furthermore, the carbon nanotubes preferably have a low defect density, which can be determined for example by Raman microscopy in the ratio of graphitic peak and defect peak.

In addition to the single-walled carbon nanotubes, it is optionally possible to add further auxiliaries, such as flow aids or sizing in amounts of from 0 to 20% by weight, to the polymer matrix.

The amount of polymer matrix, fibers and carbon nanotubes as well as optionally further excipients in the fiber composite material replenishes to 100 wt.%. The composition of the fiber composite material can be determined here for example by scanning electron microscopy (SEM) or transmission electron microscopy (TEM). Defects on fibers can also be detected by Raman microscopy, for example.

The fiber composite material according to the invention is preferably an endless fiber-reinforced thermoset semifinished product. The addition of the single-walled carbon nanotubes and the other excipients to the polymer matrix is not particularly limited. For example, if a resin system resin and hardener resin system is used as the polymer matrix, the carbon nanotubes and optional further adjuvants may be added to the hardener or resin and then the mixture or resin or hardener added. It is also possible that the single-walled carbon nanotubes and optional further auxiliaries are added to the mixture of hardener and resin. It is also possible that carbon nanotubes and optionally certain optional further auxiliaries, respectively, may be added to the resin or hardener and other optional auxiliaries, respectively, to the hardener or resin. In addition, in certain embodiments, the single-walled carbon nanotubes of the polymer matrix may be added in dry form, for example as a powder, in pasty form in admixture with a liquid, for example water, as a suspension or as a masterbatch. Thus, additional additional substances can be introduced into the polymer matrix even when adding the single-walled carbon nanotubes, if the single-walled carbon nanotubes are added, for example, in the form of a paste, suspension or masterbatch. Fiber composites according to the invention comprising a polymer matrix, fibers and single-walled carbon nanotubes can be produced, for example, by mixing the single-walled carbon nanotubes in dry form with the polymer matrix and optionally adding further auxiliaries, and then introducing this mixture onto and into the fibers such that the single-walled ones Carbon nanotubes homogeneously distributed in the spaces between the fibers of the fiber composite material present. The mixing of the single-walled carbon nanotubes and the polymer matrix as well Optional further auxiliaries can be carried out, for example, by a three-high mill or a bead mill. When using a three-mill this is preferably passed through several times.

The fiber composite materials according to the invention are suitable for the production of composite materials and fiber composites which can be used in various applications in medical technology, in electrical machines or components of the aerospace / automotive / sports industry or in the marine sector. According to the invention, coating materials and fiber composites comprising the fiber composite materials according to the invention are therefore also included. In particular, the use of unidirectional composite materials or fiber composites in medical technology is preferred in those applications where the rigidity of the material is important, such as patient or x-ray equipment, mammography, etc. Herein, the special structure can be achieved by the homogeneous introduction the carbon nanotubes in the interstices between the fibers, an enhancement of interlaminar fiber-matrix adhesion within the layers, preferably prepregs, and between the layers and thus an isotropic properties profile can be achieved.

Furthermore, the coating materials and fiber composites according to the invention can also be used in other devices and components due to their improved properties, in which layer materials and fiber composites are usually used. For example, they can be used in the manufacture of electrical machines, components of the aviation / automotive / sports industry and in the marine sector, such as engines, fuselages, for example of aircraft, aircraft engines. Doors of helicopters, wind turbine rotor blades, rotor blades in the marine sector, such as ships, body parts, etc.

The invention will now be elucidated by way of exemplary embodiments, which are not intended to limit the invention in any way. Examples

bending test

The bending test was carried out with a 3-point bending measurement. The test piece was 25 mm by 25 mm in size and had a thickness of approximately 1 mm. The distance between the pads was 20 mm.

reference example

It was a fiber composite of carbon fibers (8 layers, 100 g / m ² , about 50 vol.%, Unidirectional) by impregnation with a matrix of the resin LY556 and the hardener Uradur 917 and the accelerator DY 070 in a ratio of 100 / 90/1 produced. The fiber composite was then cured at 80 ° C for 4 hours and at 140 ° C for 8 hours.

Examples 1 and 2, Comparative Examples 1 and 2

Fiber composite materials were produced as in Reference Example, carbon nanotubes (CNT) according to Table 1 below being added to the matrix before being impregnated into the fibers and dispersed in four passes in a rolling mill until they were homogeneously distributed.

Table 1 Matrix type of CNT

composition

Reference example LY556 / A917 -

LY556 / A917 / SWElicarb single-walled

Example 1 (0.5% by weight)

LY556 / A917 / SWElicarb single-walled

Example 2 (0.25% by weight)

LY556 / A917 / B150P Multiwall

Comparative Example 1 (0.5% by weight)

LY556 / A917 / B150P Multiwall

Comparative Example 2 (0.25% by weight)

SWElicarb: One-wall carbon nanotubes by Thomas Swan,

Diameter 0.8-1.2 nm, length 100-1000 nm

B150P: Multiwall carbon nanotubes from Bayer AG The specification% by weight refers to the resin matrix.

The fiber composites of the Reference Example, Examples 1 and 2 and Comparative Examples 1 and 2 were measured according to the bending test given above in terms of their modulus and flexural bending respectively parallel and perpendicular to the fiber direction in the material.

The results of the measurements are shown in FIGS. 4 to 7. In Fig. 4 it can be seen that, in particular with the single-walled carbon nanotubes, a surprisingly large increase in modulus of elasticity parallel to the fiber direction compared to the multi-walled carbon nanotubes can be achieved. FIG. 5 shows that the single-walled carbon nanotubes also increase the bending strength of the fiber composite material. is improved in parallel to the fiber direction. This occurs in particular in Example 1.

Also, by adding single-walled carbon nanotubes, the modulus of elasticity perpendicular to the fiber direction is improved, as shown in FIG. In addition, there is an improvement in the bending strength perpendicular to the fiber direction when using the single-walled carbon nanotubes according to Example 2, as shown in FIG. 7.

It is thus apparent from the examples that the use of single-walled carbon nanotubes leads to an improvement in the mechanical properties of fiber composites. The improvement of the properties occurs both parallel and perpendicular to the fiber direction, so that the effect occurs in particular for materials with unidirectional fibers.

Claims

claims

1. fiber composite material, comprising

i) a polymer matrix;

ii) fibers; and

iii) carbon nanotubes,

wherein the carbon nanotubes are single-walled carbon nanotubes and are homogeneously distributed in the interstices between the fibers of the fiber composite.

2. fiber composite material according to claim 1, wherein the fibers are formed as rovings,

3. fiber composite material according to claim 1 or 2, wherein the distance between the fibers is 1 to 30 nm.

4. fiber composite material according to one of claims 1 to 3, wherein the carbon nanotubes have a diameter of 0.4 to 5 nm.

5. fiber composite material according to one of claims 1 to 4, wherein the carbon nanotubes have a length of 50 to 1000 nm.

6. A method for producing a fiber composite material comprising

i) a polymer matrix;

ii) fibers; and

iii) carbon nanotubes,

wherein the carbon nanotubes are single-wall carbon nanotubes and are mixed with the polymer matrix, and then this mixture is placed on and in the fibers so that the carbon nanotubes are homogeneously distributed exist in the spaces between the fibers of the fiber composite material.

7. The method of claim 6, wherein the mixing of the carbon nanotubes and the polymer matrix is carried out by a three-roll mill or a bead mill.

8. Use of the fiber composite material according to any one of claims 1 to 5 for the production of coating materials and / or fiber composites.

9. Layer material, comprising the fiber composite material ge according to one of claims 1 to 5.

10. fiber composite, comprising the fiber composite material according to one of claims 1 to 5.

11. Use of the coating material according to claim 9

and / or the fiber composite according to claim 10 in X-ray devices, patient beds, electrical machines, motors, fuselages of aircraft, rotor blades, body parts.