DE2720699A1 - PROCESS FOR PRODUCING A FIBER REINFORCED COMPOSITE MATERIAL - Google Patents

Description

I nachgerbio htI

Applicant: Stuttgart, May 5, 1977

Hughes Aircraft Company P3364 S / kg Centinela Avenue and Teale Street

Culver City, Calif ", V.St.A.

Representative;

Kohler - Schwindling - Späth patent attorneys
Hohentwielstrasse 41 7000 Stuttgart 1

Process for the production of a fiber-reinforced composite material

The invention relates to a method for producing a fiber-reinforced composite material, the fibers of which are regularly aligned with one another.

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Well-known fiber-reinforced composites are made by using natural or synthetic fibers be added to a liquid resin. The resin is then solidified by cooling or curing, with it it forms a matrix surrounding the fibers. The fibers can be in many forms, such as Form of loose sections, woven webs and endless threads «This is where the fibers have when they are attached to the matrix resin be admitted to their final shape. As a result of their inclusion in the composite material, they are neither in their shape changed yet improved in their properties.

In the patent literature there is a description of processes in which two immiscible polymers with one another blended and then the mass formed is extruded in a completely molten state. These Processes seem to some extent to orientate and fiberize the one polymer in the To lead others «Such extruded mixtures were made by solvent extraction or by mechanical Filtration of the matrix fiber materials obtained · However, the extruded material does not form a usable material Composite material and the fibers obtained from the extruded mass are relatively thick and of relatively low tensile strength.

There is a need for fiber reinforced fibers in many fields Composites that have a high strength to weight ratio and low cost

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cause. The invention provides a method which leads to a new composite material, that meets these requirements.

The method according to the invention consists in first producing a fiber-reinforced composite material is made up of fibers that are randomly oriented in all dimensions and connected to one another and a hardened, thermoplastic plastic matrix, with which the fibers are impregnated, and that this composite material is then brought to elevated temperatures, in which the plastic matrix assumes a plastic state, whereupon the plastic plastic matrix pressure or Is subjected to tensile forces which cause the matrix to flow in a straight line, so that the fibers are in the Align the matrix by itself parallel to the flow direction of the matrix, and that finally the plastic matrix below Maintaining a constant pressure is cooled until it hardens.

The composite material according to the invention can be produced like "in the form of extruded or drawn profiles, in a certain direction reinforced plates and _E from plates may continue to multiple layer materials are produced in which the direction of the fibers in the various layers changed

The composite made according to the invention has unique properties related to alignment of three-dimensionally interconnected fibers

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be returned within the matrix of the composite material. It is also advantageous that the Fibers of the composite material according to the invention very much have much smaller cross-sections than the fibers used in conventional composites »

Further details and refinements of the invention emerge from the following description of the FIG Drawing illustrated Ausführungsbeiapiele, The The description and the features to be taken from the drawing can be used individually in other embodiments of the invention can be used individually or in groups in any combination. Show it

Fig. 1 shows a device through which a cured composite material with randomly oriented Fibers can be made to flow in a straight line,

2 shows a schematic representation of a composite material before and after the application of heat and pressure,

3 shows a photographic of one according to the invention

manufactured composite material part with radially oriented fibers,

4 is a photomicrograph of the broken end of an elongated composite and

Fig. 5 is a photograph of fibers formed from a composite made in accordance with the invention have been dissolved out and then dried.

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In the method according to the invention, first Composites made containing fibers extending in all directions, which are interconnected to form networks. The fiber masses are made from fiber-forming polymers in one Solvent produced that is either a polymerizable is liquid resin, which is subsequently cured to a solid polymer, or it is an inert one Solvent, which is separated after the formation of the fibers, whereupon the fiber mass with a curable Resin is impregnated to form a solid composite material.

The cured composite is then exposed to elevated temperatures that are still below the melting point of the reinforcing fibers, in which, however, the polymer matrix becomes plastic. Then the Composite material exerted pressure in such a way that the plastic matrix becomes a rectilinear flow is initiated. For this purpose, the composite material can be brought into a shape as shown in FIG. 1 is shown schematically. Here, heat is supplied to the plastic body 11 by means of the plates 12 of the mold. When pressure is then exerted with the plates, the plates tend to compress the plastic body, so that the plastic body softened by the heat flows in a directed manner.

When flowing, a differential shear effect arises between the plastic matrix and the fibers, the one

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Alignment, orientation and stretching of the fiber mass causes. The fibers are essentially in the highly viscous flowing matrix by the drag forces aligned parallel to the flow direction of the matrix. This appearance is due to the very fine structure of the fibers that support the "in situ" treatment of the fibers is achieved.

The application of the pressure that causes the plastic to flow also changes the external shape of the composite material changed. The plastic body is pressed or flattened. The pressure is kept until the composite has cooled below the solidification temperature of the plastic matrix. After the When cooling down, the fibers in the composite material remain in the orientation achieved; Ea is this orientation three-dimensional fibers within the hardened matrix, which lead to an increase in heat resistance and Tensile strength of the pressed composite material known fiber-reinforced composites leads.

The formation and orientation of organic fibers in a plastic matrix that result in a composite material Leads with improved thermal and mechanical properties is in the art of fiber-reinforced Composite materials unique. The resulting composite is light in weight and significant increased strength in the direction of the grain. Until now

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Fiber-reinforced composites were made by adding strips of glass, carbon or other Fibers were impregnated in large sheets, from which parts were then cut out and given the desired shape The material was then placed on top of each other under the action of heat and pressure in a press, cured in an autoclave, vacuum mold or otherwise in order to obtain the desired part

According to the method of the invention, the desired Parts are manufactured by hot pressing in molds or by injection molding, with the result that the component reinforced with "in situ" produced organic fibers has improved mechanical and thermal properties Has properties.

The invention is further illustrated below with the aid of a few examples.

Example I.

to 30 ml of xylene was such an amount of polyethylene and isotactic polypropylene was added so that a concentration of 4.5% by weight was achieved. The ratio of Polyethylene to iaotactic polypropylene was about 3: 1. The polymers were dissolved at about 125 ° C, whereupon the solution was placed on a vibrating table in a wide test vessel. The vibration frequency of the vibrating table was varied between 700 and 70 Hz, whereby

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periodic vibrations took place at a fixed frequency During the hut, the temperature of the solution was reduced so that a three-dimensional Fiber mass was created. The pulp was removed from the test vessel and placed in a Soxhlet extractor Washed for 24 hours. The pulp was then dried in vacuo and impregnated with catalyzed styrene. The mixture was then kept at 50 ° C. for 7 days cured and then post-cured for 20 hours at 100 ° C.

The composite disc obtained in this way was uniaxially pressed to form a film 1.25 mm thick, by exerting pressure on the mold shown in FIG. 1 at 150.degree. The - ^ robe contained about 25 now Pure polystyrene that did not contain any fibers and pressed together with the composite material to form a film “This measure was useful in order to make a comparison between pure polystyrene and the composite material to be able to produce

The tensile strength of composites produced in this way is given in Table I. Also, the strength of unreinforced material, unreinforced material after pressing and stretching as well as reinforced material without pressing given for comparison purposes to the very strong increase in Detect tensile strength that is achieved in the fiber-reinforced, stretched material.

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Example 2

The invention also allows the production of fiber-reinforced plastic matrices in the axial and radial directions by simply pressing round discs of the composite material at selected temperatures and with selected pressures. Fig. 2 illustrates the change in configuration experienced by an uncompressed composite made according to Example Λ. A photographic of a disk pressed in this way using polarized light is shown in FIG. The radial alignment of the fibers is clearly visible.

Example 3

A composite was made by adding a Mixture of equal parts of styrene and methyl methacrylate, in which a fiber mass of isotactic polypropylene was generated, was polymerized. The concentration of polypropylene in this resin was before Fiber formation about 7% by weight «,

This composite material became a rod about 12.5 mm in diameter at a temperature of ° drawn. This temperature is about 30 ° C above the Glass transformation point of the resin matrix. The rod was stretched to about four times * its original length.

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Then samples were cut from the stretched material for tensile tests and compared with material, that had not been subjected to any under-stretching. The following results were achieved:

Table 2 tensile strenght ■ χ strain N / cm ² 5.1 χ 10 * % 3.3 x 10 ⁵ 1: 1 styrene / methyl methacrylate 4.3 Gopolymer without fibers 9.5 χ 1O ^P 1.7 Undeformed composite Composite with directional 16.1 Fibers

A photomicrograph of the end of a portion of the stretched material broken in the tensile test is shown in Fig. M- . The fibrous structure is clearly visible.

Example H-

According to the method of Example 1, uniaxially pressed films were produced. Then the fibers were extracted, by dissolving the matrix in toluene at 50 ° C. for 4 hours and then extracting with acetone. the extracted and dried fibers are shown in the photographic of FIG.

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Requests have been made to determine the tensile strength of these extracted fiber mats, but Ea was impossible to determine the absolute cross-section of the loaded material because of its fine-fiber nature. Approximate values of the cross-section were obtained using the sample weight and the known density of the die Fibers forming material calculated according to the following formula:

with from · * cross-sectional area W «sample weight D «density of the fiber-forming material c = sample length.

Tensile strengths of about 9000 N / cm were determined by first adding the one to be expended for breaking for each sample Force was measured and then the approximate cross-section was taken as a basis. However, the measured one must also Breaking strength can be considered approximated because the fibers are cross-linked and not uniform in the direction of the Direction of force action or c-axis run parallel.

The tensile strength of the fibers was also determined by their contribution to the tensile strength of the composite material was determined in the following way:

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where (TS) _f «tensile strength of the fibers (TS) _r = tensile strength of the resin (TS) ^ _n = tensile strength of the composite materials

COlD p

V = volume fraction of the resin r

V_ = volume fraction of the fibers.

This method leads to a tensile strength of the fibers

on the order of 56,000 N / cm. This value

6 2 approaches the theoretical value of 2.6 χ 10 N / cm (3 »7 x 10 psi), which with an ideal orientation of the Molecules of the fiber polymer would have to be achieved (see H. Mark in "Polymer Science and Materials", Wiley-Interscience, N.Y. 1971, chapter 11).

Example 5

According to the method of Example 1, composite materials reinforced by directed fibers were produced then three sheets of this material with different orientations of the fibers are placed on top of one another. The ruling one The grain direction in the layers was as follows:

1 ο shift 0

2 «shift + 60 ° in relation to layer 1 3 · shift -60 ° in relation to layer 1

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The resulting layered material with crossed fiber layers was tested for its tensile strength. It was found to be essentially isotropic Has properties.

The above examples demonstrate the application of the invention to a limited number of fiber-forming agents Fabrics. However, the invention is applicable to a variety of composite materials made up of different Polyalkane fibers have been made, for example from ifcotaktiachem polypropylene, polyethylene, isotactic poly (4-methylpentene-1), isotactic Poly (butene-I) and polystyrene as well as made of polyethylene oxide and nylon

The solvents that can be used in the process of the present invention can be polymerizable or non-polymerizable be. Suitable polymerizable solvents are, for example, styrene, acrylic acid, divinylbenzene, Methyl methacrylate and allyl glycidyl ether · Typical non-polymerizable solvents are Toluene and xylene. It goes without saying that the choice of Solvent depends on various factors, for example on the type of fiber-forming to be dissolved Polymer and the type of end product desired.

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TABLE I.
Tensile strength of polystyrene reinforced with oriented fibers

description No. of material Fiber- Medium train fracture comment Ki rehearse stretching through focus strength job O Flow tration -3 2
χ 10 N / cm 2
N / cm cm / cm CD σ
(O Group 1 6th 4700% 7% 4.90 150 C press, single foil CO
CO G roup 2 6th 4700 % -O- 1.90 ___ 150 C press, single foil cn Q Group 3 6th 1000 % 7 «7c 2.25 150 C press, single foil <n Group 4 5 1000% -O- 1, 90 150 C press, single foil cn ο Group 5 4th 4700% -O- 2.35 150 C press, combination 3 4700% 7% 4.60 made of fiber-free and fiber reinforced foil Group 6 3 4700% -O- 3.20 150 C press, combination 4th 4700% 7% 5.30 made of fiber-free and fiber reinforced foil Group 7 7th 4700% 7% 5.95 107 150 C press, single foil Group 8 7th 4700% -O- 3.15 26.0 150 ° C press, single film control 6th -O- -O- 2.10 uncompressed 9 -0- 7% 2.30

Note: The tensile tests were carried out in the direction of the fiber orientation.

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Claims (2)

Claims 1. A method for producing a fiber-reinforced composite material, the fibers of which are regularly aligned with one another, characterized in that that first of all a fiber-reinforced composite material is produced, which is made up of interconnected fibers that are randomly oriented in all dimensions and a cured, thermoplastic plastic matrix with which the fibers are impregnated, that this composite material is then brought to elevated temperatures at which the plastic matrix assumes a plastic state, whereupon the plastic plastic matrix is subjected to compressive or tensile forces, which cause the matrix to flow in a straight line, so that the fibers in the matrix are parallel by themselves align with the direction of flow of the matrix, and that finally the plastic matrix while maintaining a constant pressure is cooled until it hardens. 2. The method according to claim 1, characterized in that to produce the fiber-reinforced composite material with arbitrarily oriented fibers first the fibers "in situ" in a solution of a fiber-forming polymer in an inert solvent produced and then after separating the solvent with; a curable thermoplastic synthetic resin impregnated, which is then hardened 809845/0558 Method according to claim 1, characterized in that that »ur production of the fiber-reinforced composite material with randomly oriented fibers the fibers "in situ" in a solution of a fiber-forming polymer in a curable thermoplastic Synthetic resin produced as a solvent and then the thermoplastic synthetic resin cured will. Method according to one of the preceding claims, characterized in that the fiber-forming Polymer isotactic polypropylene, polyethylene, isotactic poly (4-methylpentene-i), isotactic Poly (butene-i), polystyrene, nylon or polyethylene oxide is used· 809845/0558