WO2005039844A1

WO2005039844A1 - Method for the production of lightweight construction components with wood fibres and lightweight construction profiles produced by said method

Info

Publication number: WO2005039844A1
Application number: PCT/DE2004/002320
Authority: WO
Inventors: Michael Busch; Klaus Gehrmann; Steffen Meinicke; Rainer Starke; Günter Wilczek; Frank Nagel
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2003-10-21
Filing date: 2004-10-19
Publication date: 2005-05-06
Also published as: DE10348804A1

Abstract

The invention relates to a method for the production of lightweight construction components from a fibre composite material and lightweight construction profiles produced by said method. According to the method, wood fibres are mixed with a thermoplastic material and extruded to form the lightweight construction component. The method is characterised in that wood fibres, produced by means of a thermomechanical refiner method with a mean fibre length of 2-20 mm with an aspect ratio of ? 5 are used and firstly processed to give a dosable fibre agglomerate which is then extruded to form the lightweight construction components. Said method permits the production of lightweight construction components with high mechanical strength.

Description

Process for producing lightweight components with wood fibers and lightweight profiles that can be produced using the process

TECHNICAL FIELD OF APPLICATION The present invention relates to a method for producing lightweight components from a fiber composite material, in which wood fibers mixed with a thermoplastic are extruded to form the lightweight component. The invention further relates to

Lightweight profiles that can be produced using the process.

Fiber composites, so-called composites, are increasingly being used to replace pure wood in the manufacture of flat components. There is already a large market for so-called decking materials that are used in the field of building construction. The fiber composite materials essentially consist of a thermoplastic, into which fiber-like materials are introduced for reinforcement. As expected, the consistency of the reinforcing materials has a major influence on the mechanical properties of the component made from the fiber composite material. Examples of mechanical

Characteristic values are tensile and bending properties as well as impact strength. PRIOR ART Glass fibers are still the most common reinforcing material for heavy-duty components made of a fiber composite material based on a thermoplastic. Instead of glass fibers, however, organic fiber materials, for example made of wood or annual plants, are also increasingly being used to reinforce the thermoplastics. These fillers lead to improved recyclability or disposability of the composite materials, due to the lower weight of the organic fibers compared to glass fibers, a weight saving for the components and due to the lower abrasiveness to significantly longer service life of the processing machines for the manufacture of the components.

For example, EP 1172404 A1 specifies a process for producing a component from a fiber composite material, in which fibrous particles are made from a wood material, in particular from

Soft or hardwood can be mixed with a thermoplastic in order to obtain a base material for the manufacture of the lightweight component. In this publication it is stated that preferably wood particles with an aspect ratio of 4 to 80 with a length of 2 to

6 mm should be used. However, there is no indication of the preservation and handling of wood particles with the high aspect ratios. Rather, in the specific exemplary embodiment, wood particles with a maximum length of 3 mm and one

Aspect ratio of 4 used, ie wood particles as they usually occur in the form of wood chips. These wood particles are mixed with the thermoplastic and processed directly in the extruder. From WO 97/30838 AI it is known to mix a natural cellulose fiber material with the thermoplastic and to extrude this mixture directly to the component. WO 02/083824 AI also describes a process for the production of components made of a thermoplastic, to which cellulose fibers made of wood or other vegetable products are added.

However, the positive effects of using organic fiber materials as fillers are offset by poorer mechanical properties of these composite materials compared to glass fiber composites. Higher filling levels of the

Composite materials compared to glass fiber composites improve the mechanical characteristics, but reduce the advantage of saving weight. Another risk when using natural fibers, such as flax or hemp, lies in the fluctuating quality of the products available. The reinforcement potential of the fibers is influenced by origin, climatic conditions and the various fiber production technologies. Basically, the use of fibers with a larger aspect-

The ratio with regard to the mechanical parameters is advantageous, however, fibers of this length have not hitherto been extruded with a thermoplastic, or only with considerable effort, so that generally only shorter fibers or fiber particles than

Fillers are used. Due to the mentioned disadvantages of composite materials with organic reinforcing fibers, these are now only in Components with low mechanical demands, such as door panels or hat racks in the automotive industry, are used. DE 101 34 995 AI describes a filler based on wood fibers for the production of plastic moldings. The filler consists of natural cellulose-based fibers and is supplied in granular form. The primary fibers used are wood fibers, which pass through

Fibrillation of wood can be obtained and thus have a more chip-like geometry. The chips are processed with a maximum of 20% plastic content with a melt index> 50 into pellets and then broken into pellets by breaking the pellets.

DE 102 47 711 relates to a method for producing a thermoplastic natural fiber product. In this process, the natural fiber components are crushed in advance by tearing, breaking, shearing or cutting, for example to form wood pellets. By mixing the wood pellets with a thermoplastic plastic, corresponding pellets are stored as a starting or raw material for further production or one

Device for producing molded parts, for example an extruder.

The object of the present invention is to provide a method for producing lightweight components which are lighter in weight than components made of glass fiber composite materials and have comparable or better mechanical characteristics.

The object is achieved with the method according to

Claim 1 solved. Claim 16 specifies a lightweight profile that has the desired properties and can be produced with the method. In the present process for producing

Lightweight components made of a fiber composite material are extruded to mix wood fibers with a thermoplastic to form the lightweight component. The present method is characterized in that wood fibers obtained with a thermomechanical refiner method, so-called refiner fibers, are used with an average fiber length of 2-20 mm with an aspect ratio of ≥ 5 and are first processed into meterable fiber agglomerates, which are then extruded to form the lightweight component.

Refiner fibers are known from MDF board production. Wood is treated with water vapor in a thermomechanical process (TMP process) and then defibrated in disc mills (refiner) under excess pressure. In contrast to extruded wood, this thermomechanical refiner process produces individual fibers (tracheids) with a high aspect ratio (length / width = 5 -> 100). In the production of MDF boards, these refiner fibers are dried in a hot air stream, glued and processed into scrims using the scattering process, which are pressed into the MDF boards. However, direct processing of such a strongly felting fiber material in an extruder is not possible due to the lack of meterability.

Due to the existing use of such refiner fibers, due to the high aspect ratio of the fibers, highly resilient molded parts can be produced from the fiber composite material, which withstand their mechanical characteristics compared to glass fiber composites and thereby offer additional advantages such as recyclability, weight reduction and less abrasiveness on the equipment show the manufacture. The above-mentioned problem of the lack of meterability of the refiner fibers is solved in the present method by an agglomeration step, by means of which the strongly matting refiner fibers, which are present as loose fibers, can surprisingly be converted into a meterable form without the to impair the fiber geometry necessary for the reinforcing effect or to reduce the mechanical parameters due to thermal damage. It was found that the refiner fibers with a thermoplastic can advantageously be processed into free-flowing agglomerates in a two-stage process without the fiber structure changing. The fiber agglomerates can then be easily heated to a homogeneous fiber-melt mixture in an extruder and shaped into the desired lightweight components using special tools. The fibers and the thermoplastic are preferably mixed in a hot mixer with a special tool in a ratio of 1: 1 to 10: 1, preferably 1: 1 to 3: 1 with slow heating, ie 10 -16 degrees / min. The decisive factor is that of increasing

Friction produced a final, rapid rise in temperature to 150 to 180 ° C, through which the thermoplastic melts and envelops the fibers. Too long dwell times of the fibers at temperatures> 150 ° C should be avoided in order to avoid thermal damage to the fibers.

In a second, subsequent step, in an advantageous embodiment of the method, the resulting composite is immediately cooled in a cooling mixer to a temperature of 80 to 20 ° C., preferably to 50 to 30 ° C., the thermoplastic solidifying and the free-flowing agglomerate being formed , The design and mode of operation of the mixers used ensure that the lowest possible shear forces act on the fibers and thus the fibers with their high reinforcement potential are not destroyed during agglomeration. The resulting meterable refiner fiber agglomerates are then extruded in an extruder to form the lightweight component. The extruder is also designed in such a way that the materials introduced are dispersed well with the lowest possible shear forces so that they do not pass through the fibers

Crush shear. The tool geometry is preferably designed such that the reinforcing fibers introduced into the thermoplastic are preferred align in the extrusion direction. A high reinforcement effect in the longitudinal direction is achieved, which enables the required wall thickness of the component to be reduced to a minimum.

Thermoplastics can be used for the process according to the invention, such as those mentioned in the publications WO 97/30838 AI and WO 02/083824 AI mentioned at the beginning. In particular, polyolefins, polyvinyl chloride, polyester or polystyrene, but preferably polyolefins and preferably polypropylene or polyethylene are suitable for the present process. Recycled material from the substances mentioned can also be used. The selection of polyolefins must be made in such a way that it is adequate and quick

Heat generation is achieved through friction and that the melt completely envelops the fibers. Although it can be assumed that the complete coating is achieved with low-viscosity thermoplastics, it has surprisingly been found that the present process can be used particularly advantageously with high-viscosity polypropylene with melt indexes (MFI) of 0.1 to 10.0 g / lOmin, preferably of 0. 5 to 3.0 g / 10 min. Surprisingly, it was also found that the use of

Polypropylene powders have an advantageous effect on agglomeration according to requirements. The necessary processing temperature was reached significantly faster, so that the thermal load on the fibers could be minimized. The use of these thermoplastics leads to lightweight components with very good mechanical characteristics. In order to be able to fully utilize the reinforcement potential of the fibers, adhesion promoters such as those mentioned, for example, in WO 02/083824 AI should also be used. These adhesion promoters are deposited at the interface between the fiber and the coating

Thermoplastic and due to their functionality lead to firm chemical and / or physical bonds, which enables an improved transmission of the forces acting on the component to the refiner fibers. Proven adhesion promoters are carboxylated polyolefins. Polyolefins grafted with acrylic or maleic anhydride are preferably used as adhesion promoters in the present process. In order to achieve partial crosslinking of the thermoplastic matrix, compounds containing epoxy groups, preferably the resin component of commercially available epoxy resin systems and, if appropriate, conventional epoxy resin hardener components are used. This type of adhesion and partial crosslinking of the thermoplastic component significantly improves the mechanical properties of the composite. The fiber contents are preferably 50 to 85% by mass of the composite. These are thermoplastics that are highly filled with refiner fibers.

The lightweight profiles produced with the present process are characterized by a high mechanical strength. Combined with the lower weight, the recyclability and better processability of the composites according to the invention

Thermoplastic and refiner fiber result from this new possibilities, glass fiber reinforced plastics through these materials also in high-quality fields of application to replace. The lightweight construction profiles that can be produced using the present method have a basis weight of 1 to 8 kg / m ² , preferably 2 to 5 kg / m ² and web and belt widths of 1-6 mm, preferably of 2-4 mm. The refiner fibers used here have average fiber lengths of 2-20 mm with an aspect ratio of ≥ 5.

WAYS OF CARRYING OUT THE INVENTION In the present exemplary embodiment, a

Hollow chamber panel made of a fiber composite material according to the present method. For the production, 60% refiner fibers (length 2-16 mm, width 0.1-0.6 mm) with 40% polypropylene (MFI 100) are first mixed in a hot mixer with a sickle tool, up to 185 ° C the polypropylene has melted completely and wetted the fibers. The melt mixture is then transferred to a cooling mixer and cooled to 40 ° C. within 10 minutes. The fiber agglomerates form in the process. These free-flowing fiber agglomerates are then processed in a second process stage in a ratio of 98% fiber agglomerates and 2% of a maleic anhydride-grafted polypropylene

Adhesion promoter dosed into a conical twin-screw extruder, worked up to a homogeneous melt and extruded into the twin-wall sheet. The screw geometry is designed in such a way that the materials entered are dispersed well with the lowest possible shear forces so that the fibers are not shredded by shearing. The extrusion takes place at a melt temperature of 190 ° C, a Melt pressure of 20 MPa and a melt throughput of 120 kg / h. The special extrusion tool for multi-wall sheets has a dry calibration unit from 250 to 500 mm in length and a 4000 mm long wet calibration unit with vacuum tank. The dry calibration is carried out at 60 ° C.

For comparison, a conventional one-stage process of the prior art for producing a hollow chamber panel from a fiber composite material is carried out, in which 60% wood chips (Lignocell P Super, length 1.5-10 mm, width 0.5-3 mm), 38% polypropylene (MFI 100) and 2% adhesion promoter (maleic acid-grafted polypropylene) can be extruded with the extruder into the twin-wall sheet under otherwise identical conditions.

The twin-wall sheet made with both methods is shown in the figure. It has 13 chambers with wall thicknesses of 4 mm. The component thickness is 37 mm, the component width is 425 mm. The mechanical characteristics of the composites produced according to the examples described above can be found in the following table, which shows a comparison between the present process and the known process of the prior art. This table shows in particular the high flexural strength and impact strength of the hollow panel produced. Of course, the present method can also be used to produce other lightweight components, in particular lightweight profiles, with good mechanical characteristics. The breaking load of the hollow panel made of the refiner fiber composite is 1300 N across the profile and 3200 N along the profile.

Claims

claims

1. A process for the production of lightweight components from a fiber composite material, in which wood fibers mixed with a thermoplastic are extruded to form the lightweight components, characterized in that wood fibers obtained with a thermomechanical refiner process with an average fiber length of 2-20 mm with an aspect ratio of ≥ 5 used and first processed into meterable fiber agglomerates, which are then extruded to form the lightweight components.

2. The method according to claim 1, characterized in that the wood fibers for forming the fiber agglomerates are mixed in a hot mixer with controlled heating with the thermoplastic in a first step, with a resulting, faster friction temperature increase to about 150 - caused by increasing friction 180 ° C is used, in which the thermoplastic melts and envelops the fibers.

3. The method according to claim 2, characterized in that the mixing takes place in the hot mixer with a tool with which the fiber lengths are maintained during the mixing.

4. The method according to claim 2 or 3, characterized in that the melt with the wood fibers is cooled in a second step in a cooling mixer, so that the thermoplastic solidifies to form the fiber agglomerates, the cooling mixer being operated in such a way that form the fiber agglomerates in free-flowing form.

5. The method according to any one of claims 1 to 4, characterized in that a highly viscous material with a melt index MFI <20 is used as the thermoplastic.

6. The method according to any one of claims 1 to 5, characterized in that the wood fibers are processed with the thermoplastic in a ratio of 1: 1 to 10: 1 to the fiber agglomerates.

7. The method according to any one of claims 1 to 5, characterized in that the wood fibers are processed with the thermoplastic in a ratio of 1: 1 to 3: 1 to the fiber agglomerates.

8. The method according to any one of claims 1 to 7, characterized in that polyolefins, polyvinyl chloride, polyester, polystyrene or recycling material of these substances are used as thermoplastics.

9. The method according to any one of claims 1 to 7, characterized in that polypropylene or polyethylene or recycling material of these substances are used as thermoplastics.

10. The method according to any one of claims 1 to 7, characterized in that highly viscous polypropylene is used as a thermoplastic.

11. The method according to any one of claims 1 to 7 or 10, characterized in that polypropylene powder is used as a thermoplastic.

12. The method according to any one of claims 1 to 11, characterized in that in the processing of the wood fibers with the thermoplastic to the fiber agglomerates or in the subsequent extrusion additional adhesion promoters are added.

13. The method according to claim 12, characterized in that for promoting adhesion and partial crosslinking as a thermoplastic component, a reactive system consisting of 2-25%, preferably 5-10% of a compound containing epoxy groups, preferably the resin component of commercially available epoxy resins, 10-98% of a carboxylated polyolefin , preferably grafted with acrylic or maleic anhydride polypropylene, 0-88% of one Thermoplastics according to claim 7, and optionally 1-5% of a conventional epoxy resin hardener component, is used.

14. The method according to claim 12 or 13, characterized in that the epoxy group-containing component is added immediately after the mixing in the hot mixer immediately before the cooling process in order to prevent a premature crosslinking reaction.

15. The method according to any one of claims 1 to 14, characterized in that the fiber agglomerates are converted into a homogeneous melt with a double screw extruder and extruded with a tool for multi-wall sheets, to which a dry calibration unit with a length of 25-50 cm is attached Connect a temperature control in the range of 20-100 ° C, preferably 40-60 ° C, and an approx. 400 cm long wet calibration unit with a vacuum tank.

16. Lightweight construction profile, producible according to a method of claims 1 to 15, from a fiber composite material which contains wood fibers obtained with a thermomechanical refiner method with an average fiber length of 2-20 mm with an aspect ratio of ≥ 5.

17. Lightweight profile according to claim 16 with a basis weight of 1-8 kg / m ² and web and belt widths of 1-6 mm.

18. Lightweight profile according to claim 16 with a weight per unit area of 2-5 kg / m ² and web and belt widths of 2-4 mm.

19. Lightweight profile according to one of claims 16 to 18, wherein the fiber composite material contains 50-85% of the wood fibers, 0-5% adhesion promoter and 15-50% thermoplastics.

20. Lightweight profile according to claim 19, wherein the fiber composite material contains 15-50% polypropylene as a thermoplastic.

21. Lightweight profile according to one of claims 16 to 20, wherein the wood fibers have an average fiber length of 2-20 mm with an aspect ratio of> 5.

22. Use of wood fibers with an average fiber length of 2-20 mm with an aspect ratio of> 5 from a thermomechanical refiner process in fiber composite materials for the production of lightweight components.