WO2001032405A1

WO2001032405A1 - Fibre reinforced thermoplastic composite

Info

Publication number: WO2001032405A1
Application number: PCT/AU1999/000255
Authority: WO
Inventors: Ross Ernest Griffith; Saul Thomas Griffith
Original assignee: Griffith Research And Development Enterprises Pty. Limited
Priority date: 1998-04-03
Filing date: 1999-04-06
Publication date: 2001-05-10
Also published as: AUPP281998A0

Abstract

The present invention relates to a method for forming fibre reinforced thermoplastic composite sheets and other articles, and to the sheets and other articles so formed. More particularly the invention relates to such methods and articles that may include waste or recycled materials. The method includes a first step of sourcing waste fibrous material, such as a textile, and a second step of sourcing or producing a comminuted waste thermoplastic material, such as chipped polyethylene. A flock is then produced from the fibrous material and commingled with the thermoplastic material, preferably in a weight ratio of between 1:9 to 7:3. The commingled material is then heated under pressure so as to at least partly melt the thermoplastic material and to cause it to partly fuse in the composite article.The composite is held under pressure until the temperature of the article falls below the melting temperature of the thermoplastic material.

Description

"Fibre reinforced thermoplastic composite" Technical Field

The present invention relates to a method for forming fibre reinforced thermoplastic sheets and other articles, and to the sheets and other articles so formed. More particularly the invention relates to such methods and articles that may include waste or recycled materials. Background Art

It is known to reinforce thermosetting resins with woven or knitted fabric or with linear arrays of fibre to produce composite articles. Such composites have the advantage of physical properties that are not present in either of the component materials themselves. While such composites are available they are relatively expensive. It is also known to reinforce thermoplastic resins with mineral, organic and glass fibres.

The recycling of waste materials has attracted a lot of attention in recent times. A major problem has become apparent in that many processes for recycling are not tolerant to contamination of the recycled feedstock, i.e. they require a substantially pure stream of the required recycled material. The present invention is directed to the production of articles that comprise a fibre reinforced plastics material that is a new combination of materials and which may include recycled materials in such a way that the process and the resultant articles are relatively tolerant of impure or mixed feedstock. Disclosure of Invention

In a first aspect the present invention resides in a method for the formation of a fibre reinforced thermoplastic composite article, including the steps of:-

(1) producing a fibrous flock from textile fibres;

(2) comminuting a thermoplastic material:

(3) commingling the flock and the thermoplastic material in a weight ratio of from 1:9 to 7:3: and

(4) heating the commingled material under pressure so as to at least partly melt the thermoplastic material and to cause the comminuted thermoplastic materials to at least partly fuse.

In a preferred embodiment of this aspect, the method also includes the step of:

(5) cooling the article under pressure. In the first aspect, it will be realised that steps (1) and (2) need not occur sequentially. Further, in one embodiment, the step of producing a fibrous flock and commingling the flock with the thermoplastic material can occur substantially simultaneously. In a second aspect the invention resides in a composite article produced by the method according to the first aspect.

In a third aspect, the present invention resides in a fibre reinforced thermoplastic sheet containing from 10 to 70%, more preferably 30 to 70%. by weight of at least one fibrous flock that has been at least partly formed from reprocessed fibre and from 90 to 30%, more preferably 70 to 30%. of a thermoplastic material at least part of which has been recycled, the thermoplastic material being dispersed within the fibrous flock.

The thermoplastic material is preferably reasonably uniformly dispersed throughout the fibrous flock. In an alternative embodiment, the thermoplastic material can be dispersed between webs of the fibrous flock.

The present invention combines the physical properties of a mass of essentially non-constrained fibres and those of a thermoplastic material. It has been found by the present inventors that a wide range of flocks and a wide range of thermoplastic materials, even if all derived from waste sources. may be combined to produce suitable composite articles without the requirement for the expensive and time consuming task of carefully separating the various types of waste materials. After formation, the composite articles may be reshaped by heating and applying pressure to the article. The present inventors have found that the presence of the fibre reinforcement as a fibrous mass assists in allowing the composite to be reshaped. The individual fibres are able to reorientate and re-position in the article during the application of heat and pressure to the article.

In the first aspect, the step of heating the commingled material under pressure can occur by placing the material between the heated platens of a press or by placing the material in a compression mould such that under the application of heat and pressure and subsequent cooling, a finished composite article of desired shape is produced.

The flock may be formed by the random collection of unprocessed fibre of a suitable length, which will typically be from 1 to 75 mm. more preferably 5 to 50 mm. These fibres will typically have a diameter of less than 50 microns and usually between 5 and 30 microns. It is preferable that the flock is produced by the processing of textile waste of a woven or knitted form as there is a lot of such material available. The woven or knitted fabric can be passed through a rag tearing machine or some other suitable device in order to substantially destroy the woven or knitted form of the fabric and to produce a flock of non-constrained fibres substantially free of inter-woven or knitted fibres. Such flocks will preferably contain fibres falling within the length range outlined above. The fibre mass to be included in the composite is preferably formed from a plurality of fibrous webs. Such webs may conveniently be produced by carding the flock or by air laying fibres into a fibrous web. In one embodiment, each web can be formed such that it has a density of from 10 to 80 grams per square meter. These webs can be stacked on top of one another to form a fibre mass. The fibre orientation in the individual webs lies preferably in the plane of the respective webs. In one embodiment, this may be achieved by carding the flock before forming it into a web as described above.

In one embodiment, the fibre mass may be needle punched or otherwise loosely inter-connected in a non-woven manner provided that the individual fibres are not unduly constrained by such inter-connection. Light needle punching of superposed webs makes the resulting fibre mass easier to handle for subsequent processing. It will however have the disadvantage of applying some unwanted constraint on reorientation of fibres within the composite if it is required to mould the composite into a new shape after it has been formed. Persons skilled in the art will be able, by simple experimentation, to determine the amount of needle punching that is acceptable for any given usage of the resultant composite.

The fibres present in the composites according to the present invention are preferably organic in nature but may include glass fibres and other mineral fibres. Such organic fibres include cellulosic fibres such as rayon, cotton and flax, and fibres of synthetic plastics materials. Typically, the fibres in the flock will comprise one or more of nylon, polyester, polyacrylonitrile, rayon and cotton.

Optimum interfacial bonding between polymer and fibre in the article will be achieved when the textile waste is washed and dried prior to combination with cleaned, washed and dried thermoplastic material. This will reduce the presence of moisture and dirt in the resultant composite article. The thermoplastic material may be any suitable thermoplastic material. Suitable thermoplastic materials that are available as waste material include one or more of polypropylene, polyester, polyethylene (either high or low density), polyvinyl chloride, polyamide, polyurethane and mixtures or blends thereof. The polymer may be in the form of powder, granules, chips, flakes, fibres or other comminuted form. If the flock includes a substantial proportion of thermoplastic fibres it is desirable to select a thermoplastic material from a resin that has a melting point sufficiently low that there will not be significant deterioration of the thermoplastic fibres in the flock during formation of the composite. The step of heating the commingled material will depend on the thermoplastic material selected to be used in the composite. It will be appreciated that in the step of heating the commingled material under pressure, the desired temperature of the commingled material is preferably such so as to meet the requirement of causing the selected comminuted thermoplastic material to at least partially fuse.

The flock and the thermoplastic material may be commingled in a number of different ways. In one preferred embodiment of the invention a flock is formed into a fibre mat by carding the flock into a web and forming the fibre mat from a plurality of the webs. A powdered thermoplastic polymer may then be introduced into, or onto, the fibre mat. The process may be repeated by stacking a number of such polymer impregnated fibre mats one on top of another. The impregnated fibre mat or mats are then subject to heat and pressure to form a composite sheet or other article. In an alternative preferred approach two or more fibre mats may be inter-layered with layers of chipped or flaked plastics material such as is produced by the recycling of post-consumer plastics products. The chips or flakes could alternatively be replaced by granules or pellets of the thermoplastic material. In yet another form of the invention, the thermoplastic may be formed into staple fibres that can be blended with the flock such that an intimate mixture of the two is achieved prior to. or during, the formation of the web. In another embodiment, the thermoplastic material may be sourced in a fibrous form, such as recycled polypropylene carpets or waste polypropylene fibres extracted from carpet. In a still further embodiment, the thermoplastic material may be recycled fibres, especially of polyolefins from post-consumer waste streams of apparel or other fabric forms. In a still further aspect of the present invention the thermoplastic material may be melted and then the web introduced into the molten thermoplastic material.

Where the thermoplastic material is being sourced in fibrous form, it can be mixed with the fibrous flock during formation of the flock, such as when the fibrous material is passed through a rag tearing machine or some other similar device. In an alternative embodiment, the fibres of thermoplastic material can be mixed with the flock in a conventional textile fibre blending apparatus. The mixture of the fibres of thermoplastic material and the flock can be formed into webs by conventional carding followed by crosslapping to produce a mat of the desired mass/unit area. Alternatively, the mat can be produced directly from the mixture by conventional air laying.

In an alternative embodiment, the flock and thermoplastic material can be mixed together during air-laying of a mat. In this embodiment, the thermoplastic material is preferably a material with a low specific mass, such as shredded film, eg. polymeric packaging materials, like plastic shopping bags.

In any one of the above processes, heat and pressure are used to consolidate the composite and to integrate the flock and the thermoplastic together. The heating and pressure may be such that a fully dense product is obtained. In an alternative embodiment, less pressure may be used to produce a porous product that may have increased sound and thermal insulating properties or other controlled mechanical properties such as a desired flexibility or rigidity. The pressure applied to the commingled material preferably lies in the range 0.05MPa-4MPa. and more preferably in the range 0.15-2MPa.

In one embodiment of the invention, the composite is initially subject to heat and pressure over only a part of the area of the composite. This part could be. for instance, a grid pattern over the surface of the composite. This would produce a stable plastics impregnated mat that could be subjected to heat and pressure over its whole area during a second stage of processing, such as during the forming of the composite sheet into a finished article. The heat and pressure to the composite may be applied in a continuous manner or in a batch manner. Continuous processing of the composite may be achieved by double band hot pressing, calendering, hot rolling or the like. Continuous production is preferred for some applications due to potentially lower costs. Batch processing is preferably done by compression moulding.

The composite article is preferably initially formed as a flat sheet preparatory to use or further processing. When the output of the method is flat sheet, it may be used as produced as concrete formwork. a building cladding material, as a packaging material or any one of numerous other uses. The sheet of composite may alternatively be formed, on its own or after lamination with another material, into a formed article. Such formed articles may have application in the automotive, aerospace and furniture industries. In this case, the composite article can be cut to shape and then placed in an enclosed mould such that through the application of heat and subsequent cooling under pressure, a finished article of desired shape is produced.

The fibres have been found to be able to reorient themselves within the composite when the sheet is heated and deformed. This property gives the composite good formability. The thermoplastic nature of the plastics material in the composite allows the composite to be laminated without the use of an adhesive. The composite sheet can be heated to melt a surface portion thereof and then brought into contact with the material with which it is to be laminated. In one preferred embodiment of the invention a sheet of the composite can be laminated and shaped simultaneously. A flexible laminate, such as a textile fabric, can be laid over a sheet of the composite and then subjected to heat and pressure in a suitable mould. The composite sheet will be simultaneously bonded to the fabric and also formed to the desired shape.

Brief Description of Drawings

The following description of a preferred embodiment of the present invention is provided as an example of the invention and is described with reference to the accompanying drawings, in which:- Figure 1 is a schematic flow diagram of a process according to the present invention. Best Mode for Carrying Out the Invention

Waste textile material, comprising clippings from the clothing industry and/or post consumer clothing and textiles, is collected as indicated at 10 and is passed through a conventional rag tearing machine 11 to produce a flock.

The fibres comprising the waste textile material preferably have a length between about 1 and 75mm and a diameter less than about 50 microns. The flock is then carded in carding machine 12. with the carded fibres from the flock forming a thin web. Successive passes of web are then layered together in a layering machine 13 to form a fibre mass. While the depicted process uses recycled textile fibres, it will be appreciated that virgin fibres could also be utilised in the process.

Waste polyethylene bottles are collected as is shown at 15 and passed through a chipping machine 16 to cut the bottles into chips. The chips of polyethylene are then passed through a screening machine 17 to remove all chips that cannot pass through an 8mm screen. Again, while the depicted process is using recycled chipped polyethylene bottles, it will be appreciated that other thermoplastic materials, including mixtures and blends thereof, could be utilised as appropriate. The thermoplastic material could also be utilised in other forms, including in the form of powder, granules, flakes and fibres.

Several layers of the fibre mass are passed continuously to an assembly machine 18 where chipped and screened polyethylene is evenly spread between each layer of the fibre mass. The fibre mass and the chipped polyethylene are combined in a weight ratio of 1:1. The assembled composite is then fed into a double band hot press 19 designed to simultaneously compress and heat the composite sheet therebetween. The press heats the composite under pressure to a temperature sufficient to at least partially fuse the polyethylene in the composite. The press also acts as a cooling zone in which the composite is allowed to cool to a temperature below the melting point of the thermoplastic material in the composite whilst keeping the composite under pressure. The press is adapted to apply a pressure to the composite at a value somewhere between 0.15MPa and 2MPa while the composite is being heated and cooled. During this process step, the pressure applied by the press 19 to the article can change. On leaving the press 19. the composite is able to further cool towards room temperature. The solidified composite sheet is cut to length in a cutting machine 21 and the sheets stacked in a stacking machine 22.

In a modification of this process when the fibre mass is of sufficient thickness it may be fed from the web layering machine 13 to a needle punching machine to be lightly needle punched so that the fibre web will be more easily handled. In a further modification the flock produced in the rag tearing machine 11 may be fed directly to an air laying machine to produce a web without the intermediate step of carding the flock.

In one embodiment of the invention, the thermoplastic material can be sourced in a fibrous form. For example, separately recycled polypropylene fibres from polypropylene carpets can be used as a source of fibres. In this case, the polypropylene fibres can be commingled with the flock in a fibre blending machine. In this case, the commingled fibres are fed directly to the card. In this case, steps 15-17 of Fig. 1 are not required.

In an alternative process, when the thermoplastic material is sourced in fibrous form, such as polypropylene fibres, the flock and thermoplastic material can be commingled in an air-laying device during air-laying of the flock and fibrous thermoplastic material.

In a different process to that depicted in Fig. 1. the thermoplastic material, such as the chipped polyethylene, can be firstly melted in a bath. The fibrous flock can then be dipped into and commingled with the molten thermoplastic material. The commingled material can then be pressed, while the thermoplastic material is still molten, and then allowed to cool under pressure.

While a continuous process is depicted in Fig. 1, it will be appreciated that batch processing can be used to form the composite articles. In one example of a batch process, Fig. 1 could be modified to the extent that the double band hot press 19 would be replaced with a press adapted to press a compression mould filled with the fibre mass output by the assembly machine 18. Once the pressed and cooled sheet is produced by the process depicted in Fig. 1 or the other processes described herein, the sheet can be used in its produced form. For example, the sheet can be used as a formwork for concrete or a building cladding material. The produced sheet can. however, be heated and pressed subsequent to its production and so be moulded into other desired shapes. The sheet can also be heated to melt at least a surface portion thereof and then brought into contact with a laminate material, such as a textile.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A method for the formation of a fibre reinforced thermoplastic composite article, including the steps of:-

(1) producing a fibrous flock from fibres: (2) comminuting a thermoplastic material;

(3) commingling the flock and the thermoplastic material in a weight ratio of from 1:9 to 7:3; and

2. The method of claim 1 further including the step of:

(5) cooling the article under pressure.

3. The method of claim 2 wherein the application of pressure to the article is removed once the temperature of the article is less than the melting temperature of the thermoplastic material.

4. The method of any one of the preceding claims wherein the applied pressure is in the range 0.05 to 4 MPa.

5. The method of any one of the preceding claims wherein the flock is produced from a collection of unprocessed fibres.

6. The method of claim 5 wherein the unprocessed fibre has a length between about 1 and 75 mm.

7. The method of claim 6 wherein the unprocessed fibre has a length between about 5 and 50 mm.

8. The method of any one of claims 4 to 7 wherein the fibres have a diameter of less than 50 microns.

9. The method of claim 8 wherein the fibres have a diameter between 5 and 30 microns.

10. The method of any one of the preceding claims wherein the step of producing the fibrous flock includes the step of shredding waste textile material.

11. The method of any one of the preceding claims wherein the fibrous flock is formed from organic fibres.

12. The method of claim 11 wherein the organic fibres are selected from the group comprising cellulosic fibres such as rayon, cotton, and flax, and fibres of synthetic plastics materials such as nylon, polyester and polyacrylonitrile.

13. The method of any one of the preceding claims wherein the thermoplastic material is selected from the group comprising polypropylene. polyester, polyethylene (either high or low density), polyvinyl chloride, polyamide, polyurethane and mixtures or blends thereof.

14. The method of claim 13 wherein the thermoplastic material before the step of commingling is in the form of powder, granules, chips, flakes or fibres.

15. The method of any one of the preceding claims wherein the thermoplastic material is derived at least in part from a waste source.

16. The method of any one of the preceding claims wherein the fibres are washed and dried prior to the step of commingling with the thermoplastic material.

17. The method of claim 16 wherein the thermoplastic material is washed and dried prior to the commingling step.

18. The method of any one of the preceding claims wherein the flock and the thermoplastic material are commingled in a weight ratio of from 3:7 to

7:3.

19. The method of claim 18 wherein the flock and the thermoplastic material are commingled in a weight ratio of 1:1.

20. The method of claim 10 wherein the waste textile material is in a woven or knitted form and the step of processing includes passing the textile material through a rag tearing machine or some other suitable device in order to substantially destroy the woven or knitted form of the fabric and to produce a flock of non-constrained fibres substantially free of inter-woven or knitted fibres.

21. The method of any one of the preceding claims wherein the fibrous flock is further processed, before the commingling step, to produce at least one fibrous web.

22. The method of claim 21 wherein the at least one fibrous web is produced by carding the flock or by air laying the fibrous flock.

23. The method of claim 21 or 22 wherein a plurality of the webs are stacked on top of one another to form a fibre mass.

24. The method of claim 23 wherein the orientation of the fibres in an individual web lie in the plane of that web.

25. The method of claims 23 or 24 wherein the fibre mass is needle punched or otherwise loosely inter-connected in a non-woven manner provided that the individual fibres are not unduly constrained by such interconnection.

26. The method of any one of claims 1 to 18 wherein the step of commingling the flock and thermoplastic material includes the steps of: (i) carding the flock into a fibrous web;

(ii) forming a fibre mat from a plurality of fibre webs; and

(iii) introducing thermoplastic polymer into, or onto, the fibre mat.

27. The method of claim 26 wherein steps (i) to (iii) are repeated to form a stack of polymer impregnated fibre mats one on top of another.

28. The method of any one of claims 1 to 19 wherein when the thermoplastic material is sourced in fibrous form, the thermoplastic fibres are commingled with the fibrous flock during the step of producing the flock.

29. The method of any one of claims 1 to 19 wherein when the thermoplastic material is sourced in fibrous form, the commingled mixture of the fibres of thermoplastic material and the flock is formed into webs by carding followed by crosslapping to produce a mat of the desired mass/unit area.

30. The method of any one of claims 1 to 19 wherein when the thermoplastic material is sourced in fibrous form, the commingled mixture of the fibres of thermoplastic material and the flock is formed into webs by air laying.

31. The method of claims 1 to 19 wherein when the thermoplastic material is sourced in fibrous form, the flock and thermoplastic material are commingled by air-laying of the flock and fibrous thermoplastic material.

32. The method of any one of claims 28 to 31 wherein the fibres are recycled fibres sourced from polypropylene or polyolefin carpets and mats.

33. The method of any one of claims 1 to 20 wherein the thermoplastic material is firstly melted before the fibrous flock is introduced into and commingled with the molten thermoplastic material.

34. The method of any one of the preceding claims wherein the commingled material is initially subject to heat and pressure over only a part of the area of the material.

35. The method of any one of the preceding claims wherein the heat and pressure are applied to the commingled material in a continuous manner.

36. The method of claim 35 wherein the commingled material is fed into a double band hot press.

37. The method of any one of claim 1 to 34 wherein the heat and pressure are applied to the commingled material in a batch manner.

38. The method of claim 37 wherein the commingled material is pressed in a compression mould.

39. The method of any one of claims 36 to 38 wherein the pressure applied to the commingled material is in the range 0.05-4MPa.

40. The method of claim 39 wherein the pressure applied to the commingled material is in the range 0.15-2MPa.

41. A composite article produced by the method according to any one of the preceding claims.

42. A fibre reinforced thermoplastic sheet containing from 10 to 70% by weight of at least one fibrous flock that has been at least partly formed from reprocessed fibre and from 90 to 30% of a thermoplastic material at least part of which has been recycled, the thermoplastic material being dispersed within the fibrous flock.

43. The fibre reinforced thermoplastic sheet of claim 41 containing 30 to 70% by weight of the at least one fibrous flock and from 70 to 30% of the thermoplastic material.