Method for producing wood fibre pellets
A process for producing pellets or granules comprising fibers of a lignocellulousic material, for use as a feedstock in plastics manufacture, conveying in a dry or wet air stream and applying to the fibers a liquid formulation comprising one or more polymers, monomers, or oligomers, forming the fibers into a solid product, and breaking down the solid product to produce said pellets or granules. Typically the conduit conveys the fibers in a plant for manufacture of fiber board.
1. A process for producing pellets or granules comprising fibres of a lignocellulosic material or natural fibres, for use as feedstock in plastics manufacture, which comprises:
conveying loose or divided fibres or fibre bundles, produced by mechanically or thermomechanically or chemo-thermomechanically or chemo-mechanically breaking down a lignocellulosic material, or natural fibres, in a dry or wet air stream and applying to the fibres while so conveying the fibres a liquid formulation comprising one or more thermoplastic polymer, monomer, or oligomer,
forming the fibres into a solid product, and
breaking down the solid product to produce pellets or granules,
wherein the pellets or granules comprise between 0.3 to 25 parts of one or more thermoplastic polymers, per 100 parts of fibre by dried weights.
2. The process according to claim 1 including conveying the fibres along a conduit in a dry or wet stream and introducing the formulation of the polymer, monomer or oligomer into the interior of the conduit to apply the formulation to the fibres while the fibres are moving through the conduit.
3. The process according to claim 2 including introducing the formulation into the conduit by spraying the formulation into the interior of the conduit as the fibres move through the conduit, to coat or partially coat the fibres.
4. The process according to claim 3 wherein the conduit conveys the fibres from a refiner stage in a plant for manufacture of fibre board.
5. The process according to claim 4 wherein the conduit conveys the fibres to or from a drying stage or drier.
6. The process according to claim 1 including forming the fibres into a solid product by pressing the fibres to a solid product in planar form.
7. The process according to claim 6 including pressing the fibres between heated platens.
8. The process according to claim. 6 including pressing the fibres into a sheet of up to about 2 cm in thickness.
9. The process according to claim 6 including pressing the fibres into a sheet of up to about 1 cm in thickness.
10. The process according to claim 1 including breaking down said solid product to said pellets or granules by cutting or sawing the solid product.
11. The process according to claim 1 wherein the fibres have an average fibre length or fibre-bundle length of at least about 0.8 mm.
12. The process according to claim 1 wherein the fibres have an average fibre length of loose fibres or of fibre bundles of at least about 1 mm.
13. The process according to claim 11 wherein a major fraction of the fibres have an aspect ratio of at least 10:1.
14. The process according to claim 11 wherein a major fraction of the fibres have an aspect ratio of at least 20:1.
15. The process according to claim 11 wherein a major fraction of the fibres have an aspect ratio of at least 25:1.
16. The process according to claim 1 including breaking down the solid product to produce pellets which are longer than the average fibre length of the fibres within the pellets.
17. The process according to claim 1 wherein the fibres are wood fibres.
18. The process according to claim 1 including breaking down the solid product down to produce pellets or granules by chopping and including applying to the fibres sufficient of the polymer, monomer or oligomer formulation to bind the fibres together to withstand pelletisation or granulisation by chopping.
19. The process according to claim 1 wherein the liquid formulation is an aqueous solution, dispersion or emulsion.
20. The process according to claim 1 wherein the thermoplastic polymer has a melting point below 230° C.
21. process according to claim 1 wherein the thermoplastic polymer has a melting point below 200° C.
22. The process according to claim 21 wherein the polymer is a polyvinyl alcohol, polyvinyl acetate, polyester, starch based, or a polymer or copolymer with one or more of an acid, anhydride, epoxy, amine, isocyanate, silane, or silanol group.
23. The process according to claim 22 including subsequently applying one or more second polymers, monomers, or oligomers or paraffin or wax to the fibres.
24. The process according to claim 6 wherein said pressing step comprises first and second pressing operations, said second pressing operation being carried out at a higher temperature than said first pressing operation.
25. The process for manufacture of plastics products or intermediates which includes introducing pellets or granules by the process of claim 1 as a feedstock into a plastics extrusion or moulding machine.
26. The process according to claim 1 , wherein the pellets or granules comprise between 0.3 to 20 parts of the one or more thermoplastic polymers per 100 parts of fibre by dried weights.
27. The process according to claim 1 , wherein the pellets or granules comprise between 0.3 to 15 parts of the one or more thermoplastic polymers per 100 parts of fibre by dried weights.
28. The process according to claim 1 , wherein the pellets or granules comprise between 0.3 to 10 parts of the one or more thermoplastic polymers per 100 parts of fibre by dried weights.