WO1994026491A1

WO1994026491A1 - Moulding composition

Info

Publication number: WO1994026491A1
Application number: PCT/GB1994/001028
Authority: WO
Inventors: John S. Wood
Original assignee: STEMFORM PRODUCTS Ltd
Current assignee: STEMFORM PRODUCTS Ltd
Priority date: 1993-05-14
Filing date: 1994-05-12
Publication date: 1994-11-24
Anticipated expiration: 1995-11-14
Also published as: GB9309917D0; GB9409769D0; GB2278365B; AU6654594A; GB2278365A

Abstract

A moulding composition and method of making such composition is provided in which the composition is particularly useful for machine moulding purposes. The composition incorporates fibre in the form of fibrous organic material, such as straw, and plastics material which is compatible with the composition of the organic material, such as a polymer plastics material. The organic material is dried to a low moisture content and the organic material is reduced in size to less than about 8mm in its maximum dimension before mixing with the plastics.

Description

Moulding Composition

This invention relates to moulding compositions and in particular to compositions incorporating plastics material and fibre which is of use in machine moulding applications such as injection moulding, compression moulding and extrusion moulding processes.

It has been proposed to form moulding compositions by mixing fibres with thermo-plastics material. Such compositions have been used in ther oset plastics, such as are used in hand lay up moulding. Hitherto the fibres have been glass fibres, which are relatively expensive, and textile fibres formed into a mat, the fibres being effective in reinforcing the plastics material.

An object of the invention is to provide an improved moulding composition and a method of producing such composition for use in a machine moulding operation.

According to -the invention a method of producing a moulding composition in which fibrous organic material, is dried to reduce the moisture content, the organic material is comminuted to a small size, the organic material is maintained in its dry condition and combined with a plastics material at an elevated temperature at which the plastics material becomes fluid, and the combined organic and plastics material is cooled to provide the moulding composition.

Preferably the organic material is dried until the moisture content is less than 4% and is preferably in the range 1 - 3%, or more particularly 1.5 - 2%. At dryness levels of less than about 1%, depending on the nature of the organic material, the material has a tendency to lose its fibrous qualities. At dryness levels above about 2 - 4%, depending on the organic material, the moisture released during heating of the mixture of plastics material and organic material turns into steam and must be released or a hazardous situation comes about. Although the moisture may be vented from the mixture excessive moisture release can give rise to problems.

Hence it has been found important to maintain a close control of the moisture content of the organic material. Since dried organic material is often hygroscopic the dried material must be prevented from taking up significant moisture after drying and prior to mixing with the plastics material.

The maximum dimension of the fibre is preferably less than 8mm and more conveniently less than 6mm. The maximum dimension has to have regard to the size of the particles or pieces of the eventual moulding composition and should preferably be no greater than the maximum dimension of such pieces. The pieces are usually in the form of cylindrical pellets of, say, 6mm diameter and less than 6mm in length, preferably 2 - 4mm in length, and the pellets are conveniently formed by cutting continuous lengths of the composition as extruded through circular nozzles.

Before use of the moulding composition the composition should be dried to remove any moisture which has become associated therewith.

The plastics material with which the fibres are mixed should be of a kind capable of forming a homogeneous mix with the organic fibres which preferably contain cellulosic material. Certain components of the organic material migrate into the plastics material to form the homogeneous composition and this generally occurs using a cellulosic or polymer plastics. Acrylics and epoxy based plastics are not normally suitable. Suitable plastics include polyvinylchloride, polypropylene, polyethylene, polystyrene, polyurethane, vinylchloride, vinylchloride ethylene, polybutene, polyester, ABS, nylon and polycarbonate. Such base plastics may be cross linked to produce the desired characteristics. The invention also provides a moulding composition which comprises organic fibrous material such as straw, haulm, hay and other plant stems and leaf material in admixture with thermo-plastics material to form a homogeneous fibre reinforced plastics material.

The proportion of organic fibrous material to plastics depends on the desired characteristics of the moulding composition but can be in the range 5 - 70%, preferably 20 - 60%, fibrous material to plastics material by volume. Greater proportions may, however, be used for some moulding compositions, such as for making moulded board or sheet.

In drying the organic material to the low levels required it has been found that de-humidified air is conveniently drawn through the organic material until it reaches the desired moisture levels. It has been found that the addition of the plastics material to the organic material in proportion of, say, 10% plastic can improve the drying rate of the organic material. After drying the organic material should be kept dry by preventing its exposure to atmospheric air.

The fibrous organic material is often the byproduct of cereals growing or the production of other crops and the resulting straw, haulm, hay, etc., is reduced to the desired size by any convenient means such as by a hammer mill or by grinding. It is advantageous if the process of reducing the size of the organic material also breaks up the harder components of the organic material such as knuckles or joints in the straw.

Further features of the invention will appear from the following description of an embodiment of the invention given by way of example only and with reference to the drawing which shows a schematic view of apparatus for making a moulding composition.

Referring to the drawing the apparatus is intended for preparing a moulding composition comprising fibrous organic material and plastics material.

The fibrous organic material may be selected from a range of materials having fibres such as straw (which may be wheat, barley or other cereal straw) ; the haulm of rape, maize, peas and beans; hay from various grasses; and other organic material; all of which include cellulose in various proportions. The plastics material may be any plastics material which has moulding properties and which is generally a cellulose polymer plastics material capable of forming a homogeneous mixture with cellulose based organic material.

By way of example the drawing shows the use of cereal straw 1 which is cut by a combine harvester 2 which separates the grain 2A from the straw 3. The straw is fed to a granulator 4 in the form of a grinder or hammer mill which reduces the fibrous material to size suited to the moulding requirements and having regard to the size of the pellets or other pieces of the moulding composition to be formed. Thus, if the pellets are to have a cylindrical shape with a diameter of 4.5mm and a length of 2.5 -3.8mm the fibrous material should have a maximum length of about 3 - 6mm so that there is a reasonable chance of the organic material being encapsulated within the pellets. The granulator 4 may be located remote from the equipment for producing the composition in which case the fibrous material is conveniently bagged in porous sacks (not shown) for storage and transportation.

The comminuted straw passes into a silo 6 through a sieve 5 to prevent straw entering the silo 6 if it is above a predetermined size of, say, 6mm.

A further silo 7 is provided into which is discharged virgin plastic pellets and the plastic pellets and straw are mixed together by a mixer/proportioner 8 and fed into a mixer drum 9. Mixed product from the mixer drum is discharged into a heated container 11 in which the organic material is dried. The container 11 is insulated and supplied with dry air from a de- humidifier 10. The de-humidifier 10 supplies air to the container 11 which has been de-humidified by passing the air through desiccant or by other means. Dry air is discharged towards the base of the container 11 and air is extracted from towards the upper end of the container 11 and passed through the de-humidifier in an air re-circulation arrangement.

By use of the de-humidifier the moisture content of the organic materials and plastics within the container is reduced to the desired level of, say, less than 4% moisture. A vacuum pump 11A is used to discharge the contents of the container towards a proportioner 13 which mixes the contents with a supply of virgin plastics from a hopper 12 in the desired ratio. From the proportioner 13 the organic material and plastics is discharged into a hopper 14 and at this point the organic material is in the ratio of 20 - 60% by volume of the mixture.

The hopper 14 feeds the mixture of organic material and plastics into an extruder barrel 15 which is heated and contains a screw 15B feeding the mixture towards an extrusion die 16. The extruder barrel contains vents 15A for venting to atmosphere gases or moisture contained within the mixture. The contents of the extruder barrel are made fluid by the heat and the mixture is extruded through the die 16 which includes a plate with a plurality of circular holes.

The composition is extruded through the holes and may be cut as it leaves the die to form pellets. In this case the pellets are dropped down through a cascade of water mist into a centrifuge or other container. Alternatively, and as shown, the material extruded through the die forms a plurality of lengths in the form of spaghetti which are cooled in a water bath or underwater sprays (not shown) . The lengths are fed into a pelletiser 18 which cuts the lengths into pellets of the desired length. The cut pellets are filled into sacks at a bag filler 19, the sacks being paper lined to discourage moisture pick up.

Drying of the organic material may be conducted in two stages, the first stage may be, for example, in a cyclone dryer bringing down the moisture content to a predetermined level of say 14% prior to introducing the organic material into the de- humidifier described. The drying process in the de-humidifier is enhanced by adding the plastics to the organic material in relatively low proportions prior to introduction into the de- humidifier. The dried organic material is of a hygroscopic nature and it is important to arrange for the dried material to be introduced into the extruder barrel 15 without it coming into contact with atmospheric air. For this purpose the vacuum pump 11A draws the material down through the proportioner and directly into the hopper 14. The presence of plastic helps to form a seal to prevent the organic material coming into contact with the atmosphere.

Before use of the pelletised moulding composition in a moulding process further drying of the pellets may take place to obtain a consistent moisture content throughout the moulding process. By achieving a consistent moisture content consistent characteristics from batch to batch of the mouldings can be achieved. The moulding composition produced by the method described is suitable for injection, compression and extrusion moulding processes. Extruded sheet compositions are suitable for vacuum forming or hot press forming for shaped moulded articles.

In forming the moulding composition the proportion of fibrous organic material to plastics material can be varied by controlling the rate of discharge of the components from the blender-proportioner 13 to the extruder 15. The fibrous material may by this means have a content of 10 - 70%, preferably 20 - 60%, by volume of the moulding composition thereby giving reinforcing properties to the composition and providing a relatively cheap component for the composition compared with other fibrous materials such as fibreglass or textile fibre.

The organic fibrous material is capable of improving the impact strength, tensile strength and/or ductility of moulded products made from the composition and the fibrous material has the effect of providing a homogeneous matrix by a chemical interaction with the plastic material due to the cellulose content of both components.

It has been found that mouldings made from the composition can be coated with fire retardant, when required, and in the event that the mouldings do catch fire a white smoke is produced giving reduced toxicity. The composition can also be used in producing foamed plastics. Materials based upon virgin cellulose polymer plastics of thermoplastic composition are recyclable and environmentally friendly.

Claims

1. A method of producing a moulding composition in which fibrous organic material is dried to reduce the moisture content, the organic material is comminuted to a small size, the organic material is maintained in its dry condition and combined with a plastics material at an elevated temperature at which the plastics material becomes fluid, and the combined organic and plastics material is cooled to provide the moulding composition.

2. A method according to claim 1 wherein the organic material is dried to a moisture content of less then 4% moisture.

3. A method according to claim 1 or 2 wherein the organic material is dried until the moisture content is in the range 1 - 3%.

4. A method according to any one of the preceding claims wherein the organic material is reduced to a size having a maximum dimension of less than 8mm.

5. A method according to any one of the preceding claims wherein the organic material includes cellulosic material.

6. A method according to any one of the preceding claims wherein the plastics material is compatible with the composition of the organic material and is a cellulosic plastics material.

7. A method according to any one of the preceding claims wherein the plastics material is selected from one or more of polyvinylchloride, polypropylene, polyethylene, polystyrene, polyurethane, vinylchloride, vinylchloride ethylene, polybutene, polyester, ABS, nylon and polycarbonate.

8. A method according to any one of the preceding claims wherein the organic material comprises 5 - 70% of the composition, by volume.

9. A method according to claim 8 wherein the organic material comprises 20 - 60% of the composition, by volume.

10. A method according to any one of the preceding claims wherein the organic material is dried by passing de¬ humidified air through the material.

11. A method according to claim 10 wherein the organic material is dried after adding plastics material in particulate form to the organic material.

12. A method according to any one of the preceding claims in which the heated, fluid plastics material combined with the organic material is extruded, cooled and formed into pellets.

13. A method according to any one of the preceding claims wherein the organic material is comminuted to reduce its size in a grinder or hammer mill.

14. A moulding composition formed by the method according to any one of claim 1 to 13 comprising fibrous organic material combined with a plastics material, the plastics material being compatible with the composition of the organic material and the organic material being of small size having a maximum dimension of less than 8mm.

15. A moulding composition according to claim 14 in which the moisture content of the organic material is less than 4%.

16. A moulding composition according to claim 14 or 15 wherein the organic material has a maximum dimension of less than 6mm.

17. A moulding composition according to any one of claims 14 to 16 wherein the plastic material is a cellulosic plastic.

18. A moulding composition according to any one of the claims 14 to 17 wherein the fibrous organic material contains cellulose and is compatible with polymer plastics.

19. A moulding composition according to any one of claims 14 to 18 in the form of pellets of cylindrical shape and having a length of less than 8mm.

20. A moulding composition according to any one of claims 14 to 19 wherein the plastics material is selected from polyvinylchloride, polypropylene, polyethylene, polystyrene, polyurethane, vinylchloride, vinylchloride ethylene, polybutene, polyester, ABS, nylon and polycarbonate, or a combination thereof.

21. A moulding composition according to any one of claims 14 to 20 wherein the fibrous organic material is straw, grass, rape, linseed, vines, hops, maize, peas, beans, rice straw or any combination thereof.

22. A method of producing a moulding composition substantially as described with reference to the description.

23. A moulding composition for machine moulding purposes substantially as described.