Method for producing wood fibre pellets

Abstract

A process for producing pellets or granules comprising fibres of a lignocellulousic material, for use as a feedstock in plastics manufacture, conveying in a dry or wet air stream and applying to the fibres a liquid formulation comprising one or more polymers, monomers, or oligomers, forming the fibres into a solid product, and breaking down the solid product to produce said pellets or granules. Typically the conduit conveys the fibres in a plant for manufacture of fibre board.

Claims

1. A process for producing pellets or granules comprising wood fibres, for use as a feedstock in plastics manufacture, which comprises applying to wood, wood fibres or fibre bundles prior to a blowline, the wood fibres or fibre bundles being produced by mechanically or thermomechanically or chemo-thermomechanically or chemo-mechanically breaking down the wood in a refiner, a liquid formulation comprising one or more thermoplastic polymers, monomers, or oligomers to coat or partially coat the fibres, pressing the fibres into a solid product, and breaking down the solid product into wood fibre-containing pellets or granules, the pellets or granules comprising 0.3 to 25 parts per 100 parts of fibre by dried weight of one or more thermoplastic polymers or thermoplastic oligomers.

2. The process of claim 1, comprising applying the liquid formulation to the fibres in the refiner.

3. The process of claim 1, further comprising applying to the fibres while conveying the fibres in an air stream a formaldehyde or isocyanate resin, or a further liquid formulation comprising one or more thermoplastic polymers, monomers, or oligomers.

4. The process of claim 2, further comprising applying to the fibres while conveying the fibres in an air stream a formaldehyde or isocyanate resin, or a further liquid formulation comprising one or more thermoplastic polymers, monomers, or oligomers.

5. The process according to claim 3 including conveying the fibres along a conduit in a dry or wet stream and introducing the formaldehyde or isocyanate resin or liquid formulation into the interior of the conduit to apply the formaldehyde or isocyanate resin or liquid formulation to the fibres while the fibres are moving through the conduit, or introducing the formaldehyde or isocyanate resin or liquid formulation into the conduit by spraying the formaldehyde or isocyanate resin or liquid formulation into the interior of the conduit as the fibres move through the conduit, to coat or partially coat the fibres.

6. The process according to claim 4 including conveying the fibres along a conduit in a dry or wet stream and introducing the formaldehyde or isocyanate resin or liquid formulation into the interior of the conduit to apply the formaldehyde or isocyanate resin or liquid formulation to the fibres while the fibres are moving through the conduit, or introducing the formaldehyde or isocyanate resin or liquid formulation into the conduit by spraying the formaldehyde or isocyanate resin or liquid formulation into the interior of the conduit as the fibres move through the conduit, to coat or partially coat the fibres.

7. The process according to claim 1 including conveying the fibres along a conduit in a dry or wet stream wherein the conduit conveys the fibres from the refiner in a plant for manufacture of fibre board.

8. The process according to claim 2 including conveying the fibres along a conduit in a dry or wet stream wherein the conduit conveys the fibres from the refiner in a plant for manufacture of fibre board.

9. The process according to claim 5 wherein the conduit conveys the fibres from the refiner in a plant for manufacture of fibre board.

10. The process according to claim 6 wherein the conduit conveys the fibres from the refiner in a plant for manufacture of fibre board.

11. The process according to claim 1 including conveying the fibres along a conduit in a dry or wet stream wherein the conduit conveys the fibres to or from a drying stage or drier.

12. The process according to claim 2 including conveying the fibres along a conduit in a dry or wet stream wherein the conduit conveys the fibres to or from a drying stage or drier.

13. The process according to claim 5 wherein the conduit conveys the fibres to or from a drying stage or drier.

14. The process according to claim 6 wherein the conduit conveys the fibres to or from a drying stage or drier.

15. The process according to claim 1 including pressing the fibres into a solid product by pressing the fibres to a solid product in planar form.

16. The process according to claim 15 including pressing the fibres between heated plattens.

17. The process according to claim 1 wherein the wood fibres or fibre bundles are MDF fibre.

18. The process according to claim 15 including pressing the fibres into a sheet of up to about 2 cm in thickness.

19. 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.

20. The process according to claim 1, wherein a major fraction of the fibres have an aspect ratio of at least 10:1.

21. 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.

22. A process for manufacture of plastics products or intermediates which includes introducing pellets or granules produced by the process of claim 1 as a feedstock into a plastics extrusion or moulding machine.

23. A process for producing pellets or granules comprising wood fibres, for use as a feedstock in plastics manufacture, which comprises applying to wood, wood fibres or fibre bundles prior to a blowline, the wood fibres or fibre bundles being produced by mechanically or thermomechanically or chemo-thermomechanically or chemo-mechanically breaking down the wood in a refiner, a liquid formulation comprising one or more thermoplastic polymers, monomers, or oligomers to coat or partially coat the fibres, conveying the fibres along a conduit in a dry or wet stream and introducing a formaldehyde or isocyanate resin or a further liquid formulation comprising one or more thermoplastic polymers, monomers, or oligomers into the interior of the conduit to apply the formaldehyde or isocyanate resin or liquid formulation to the fibres while the fibres are moving through the conduit, the conduit conveying the fibres from the refiner or to or from a drying stage or drier in a plant for manufacture of fibre board, pressing the fibres into a solid product, and breaking down the solid product into wood fibre-containing pellets or granules, the pellets or granules comprising 0.3 to 25 parts per 100 parts of fibre by dried weight of one or more thermoplastic polymers or thermoplastic oligomers.

24. The process according to claim 1, wherein the pellets or granules comprise 0.3 to 8 parts per 100 parts of fibre by dried weight of the one or more thermoplastic polymers or thermoplastic oligomers.

25. The process according to claim 23, wherein the pellets or granules comprise 0.3 to 8 parts per 100 parts of fibre by dried weight of the one or more thermoplastic polymers or thermoplastic oligomers.

Description

EXAMPLE 1

PVA Bonded MDF Fibre Pellets and Reference (Wood Flour) Pellets

(1) Polypropylene (PP) was extruded with radiata pine MDF fibres and then injection moulded to form test specimens. Wood flour and sander dust are used as references, as examples of wood derived fillers conventionally used in industry and reasonably easy to feed in as particulate products compared to a fibre product. Their performance levels, in the composite, are representative of industry or existing norms for compounded or moulded wood reinforced plastics and is included here to demonstrate that performance is not compromised by the utilisation of the fibre materials and processes of the invention. Fibre products are expected to be at least equal to the flour products and superior to them in some properties, as reinforcement, though, direct utilisation of loose low density or entangled fibres is difficult in the feeding into extruders and other machinery in a controlled or measured way. Tensile, flexural and resistance to impact properties of the MDF fibre-reinforced composite materials were determined as a function of fibre content and processing parameters and compared with flour products to ensure properties are not compromised by using the methods of the invention to introduce fibres rather than flour.

(2) Materials

(3) The MDF fibre used was produced at the New Zealand Forest Research PAPRO pilot plant refiner from Pinus Radiata toplog using processing conditions to mimic commercial MDF fibre. The fibre was air dried to approximately 10-15% moisture content before storage in plastic bags. Sander dust (SD) was supplied from local saw-mills. The PVA (polyvinyl acetate) resin used was National Starch & Chemical (NZ) Limited Korlok 442.3060.05. The polypropylene pellets used were Hyundai Seetec grade M1600 with a melt index of 25.

(4) Sample Production

(5) PVA bonded MDF 2 mm panels were produced by spraying 80-100 grams of PVA resin onto 550 grams of fibre using the 500F MDF laboratory blender (Maxiblender), which uses air pressure to reproduce air turbulence, as in a blowline and blows fibres around or along a certain path, with resin application occurring via a nozzle or spray gun, forcing resin into the flowing fibre stream. 100 grams resinated fibre was then formed into a 255 mm280 mm2 mm (700 kg/m.sup.3) panel or sheet, akin to MDF manufacturing. The PVA bonded panels were cut into pieces approximately 5 mm square, and such concentrates or pellets were desiccant dried under vacuum. The wood flour was dried at 80 C. for 24 hours. The polypropylene pellets were used as received without further drying. The PVA bonded wood fibre and polypropylene pellets were mixed in an OMC 19/30 twin screw co-rotating extruder (19 mm screw, L:D 30).

(6) The PVA/MDF fibre pellets were fed using a hopper and the polypropylene was fed using a screw feed with extruder zone temperatures set as indicated in Table 1, though the pellets could be fed via a conventional feeder also.

(7) TABLE-US-00001 TABLE 1 Extrusion conditions screw Zone 4 Zone 3 Zone 2 Zone 1 speed Sample ( C.) ( C.) ( C.) ( C.) (rpm) all 180 180 170 160 200

(8) The fibre pellets may be combined with plastics and other additives in numerous ways, according to common extrusion compounding practices and using metered feeders etc.

(9) Examples of variations demonstrated in this set of examples which illustrate some options, but without limiting use of other approaches, were:

(10) PM=fibre-pellets/PP pellets pre-mixed or introduced at the same port on the extruder

(11) D=dual feed, fibre pellets in first port/PP pellets in second port

(12) F=dual feed, PP fibres in first port/fibre pellets in second port

(13) SD=wood flour (sander dust)/PP pellets pre-mixed or introduced at the same port on the extruder (reference).

(14) The wood flour was compounded by pre-mixing with polypropylene before introduction into the first extruder feed throat using a U-shaped hopper.

(15) The mixtures were extruded through a die, which formed a 3 mm-diameter strand which was then pelletised. When problems occurred cutting the PP/wood flour strand during pelletising, the wood fibre/flour polypropylene mixtures were Wiley milled through a 4 mm mesh. The same approach was also used for the wood-fibre pellets for comparisons. The following wood fibre (PM, D, F) and wood flour (sander dustSD)/polypropylene mixtures were compounded as examples:

(16) PM with 20% and 40% wood fibre (by weight)

(17) D with 20%, 40%6 and 60% wood fibre

(18) F with 25%, 30%, 40% and 60% wood fibre

(19) SD with 20%, 40% and 60% sander dust/wood flour (reference)

(20) The compounded pellets were re-dried at 60 C. for 2-3 days before injection moulding. The dry pellets were injection moulded using a Boy 15S injection moulder (28 mm screw, 20:1 L:D), using processing conditions with a screw speed of 150 rpm, barrel temperatures in the range 190-230 C, and tool temperature set at ambient.

(21) Mechanical Property Testing

(22) Samples were conditioned at 23 C. and 50% RH for 2 weeks before measurement and testing.

(23) Tensile properties were evaluated according to ASTM D638-96 (Type I).sup.(7). The specimens were a dog bone shape, with the narrow test section having a nominal width of 13 mm and nominal thickness of 3.2 mm. An Instron model 5567 test machine was used for testing, equipped with a 10 kN load cell and 25 mm extensometer. The initial separation between grips was 100 mm, with a testing speed of 5 mm/min.

(24) Flexural properties were evaluated according to ASTM D790-96a.sup.(8), except that the loading nose and supports had radii of 7.5 mm. The specimens were a rectangular shape, with a nominal width of 13 mm and nominal thickness of 3.2 mm. An Instron model 5567 test machine was used for testing, equipped with a 10 kN load cell. A span of 50 mm and speed of 1.3 mm/min was used for flexural tests.

(25) Impact properties were evaluated according to ASTM D256-93a (Test Method B-Charpy). The specimens were a rectangular shape, with a nominal width of 13 mm and nominal thickness of 3.2 mm. A CEAST 6545/000 test instrument with supports 95.3 mm apart was used for testing, using a 0.5 J hammer.

(26) Tensile Properties

(27) The tensile test results are presented below in Table 2.

(28) TABLE-US-00002 TABLE 2 Tensile test results Strain Tensile Ultimate Strain at Stress at at Fibre/ Modulus Stress Break Yield Yield Sample Filler (GPa) (MPa) (%) (MPa) (%) PP None 1.39 25.2 40.9 13.6 1.09 M-PVA- MDF 2.18 20.8 8.07 12.7 0.68 20PM bonded M-PVA- MDF 2.50 21.1 4.57 13.4 0.63 40PM bonded M-PVA- MDF 2.97 20.9 4.76 12.3 0.49 20D bonded M-PVA- MDF 4.21 20.8 3.16 13.3 0.36 40D bonded M-PVA- MDF 8.71 17.8 0.36 7.9 0.14 60D bonded M-PVA-25F MDF 2.46 21.5 4.25 13.7 0.66 bonded M-PVA-30F MDF 3.45 22.2 3.52 12.5 0.46 bonded M-PVA-40F MDF 4.60 24.2 3.12 10.2 0.26 bonded 20SD Sander 1.97 21.6 5.79 12.6 0.73 dust 40SD Sander 3.41 20.5 2.97 17.5 0.43 dust PM = premixed PP with 20% and 40% wood fibre (both at start hopper, first port) D = PP fed separately with 20%, 40% and 60% wood fibre (in first port, PP in second) F = PP fed separately with 25%, 30%, 40% and 60% wood fibre (second port, PP in first port) SD with 20%, 40% and 60% sander dust (reference - fed premixed at start hopper/first port)

(29) All filled polypropylenes had a significantly higher modulus with fibre usually higher than the wood powder (SD) reference. Tensile strengths for all composites were all lower than neat PP (polypropylene) which is indicative of poor fibre-polymer compatibility. However, the main advantage here was to provide a convenient method to introduce low bulk density fibres into an extruder or moulding machine using conventional feeders or approaches rather than special fibre stuffers or feeders. It is much easier to feed in pellets cut from pressed sheets rather than the loose fibres or highly fluffy fibre bundles. Indeed, the use of pellet feedstocks are preferred to using powders and fine particles. The examples above showed that pressed bound fibres even with thermoset PVA adhesive can be used as a feedstock pellet for thermoplastic processes such as extrusion or injection moulding and achieve performance equal or superior to the powder reference.

(30) Flexural Properties

(31) The flexural test results are presented below. The polypropylene control, 20% pre-mix and 20% sander dust samples did not break before they reached 5% strain, which is the limit of the ASTM test method. The stress values given are at 5% strain. Beyond this point these specimens still showed an increasing load.

(32) TABLE-US-00003 TABLE 3 Flexural test results Flexural Stress at Stain at Stress at Strain at Modulus Break Break Yield Yield Sample (GPa) (MPa) (%) (MPa) (%) PP 1.05 33.8* 5.00** 20.9 2.20 20PM 1.98 39.0* 5.00** 21.7 1.23 40PM 2.37 39.1 3.86 19.4 1.05 20D 2.57 38.9 3.54 24.0 1.13 40D 4.04 39.8 1.57 31.0 0.90 60D 5.28 38.1 0.92 32.4 0.67 25F 2.14 38.8 3.87 23.6 1.21 30F 2.81 40.3 2.54 26.5 1.04 40F 3.75 44.3 1.92 29.7 0.87 60F 4.61 34.0 1.06 28.8 0.81 20SD 1.95 41.2* 5.00** 23.3 1.41 40SD 3.14 40.8 2.39 28.4 1.06 60SD 4.19 33.1 1.29 25.3 0.68 PP = neat polymer SD = sander dust. All others = PVA-MDF fibre pellets. *samples did not break before 5% strain, values given are for stress at 5% strain **samples did not break before 5% strain

(33) Most of the filled polypropylenes had higher flexural strengths than the polypropylene control with the materials made from pellets cut from pressed PVA-fibre sheets showing better performance than wood flour or sander dust (SD) references.

(34) Impact Properties

(35) The Table below shows that the fibre, as introduced by the methods of the invention, demonstrates higher impact performance than the powder samples (SD) at equivalent loadings.

(36) TABLE-US-00004 TABLE 4 Impact test results Impact Strength Sample (J/m) PP 102.50 20PM 42.08 40PM 43.23 20D 45.27 40D 45.69 60D 30.00 25F 40.46 30F 41.16 40F 53.51 60F 31.86 20SD 42.46 40SD 40.34 60SD 26.22

EXAMPLE 2

Use of Coupling Agents and Binders in Pre-Pelletised MDF Feed Stock

(37) Polypropylene composites containing natural fibres/fillers were produced by compounding in a twin screw extruder and subsequently injection moulding samples. Fibre (MDF), and wood flour, along with three different coupling agents (polyvinyl acetate, maleic anhydride modified polypropylene emulsion and solid maleic anhydride modified polypropylene) were used.

(38) Materials

(39) The MDF fibre used was produced at the New Zealand Forest Research Institute PAPRO pilot plant refiner from Pinus Radiata toplog using processing conditions to mimic commercial MDF fibre. The fibre was air dried to approximately 10-15% moisture content before storage in plastic bags. The wood flour used was standard grade Pinus Radiata supplied by Kingsland Seeds.

(40) The polypropylene resin used was Hyundai Setec grade M1600 supplied as pellets. Zinc stearate powder was AR grade obtained from BDH. The maleic anhydride modified polypropylene (MAPP) emulsion used was Michem 43040 supplied by Michelman Inc. The PVA resin used was National Starch & Chemical (NZ) Limited Korlok grade 442.3060.05. Epolene G3015 (Eastman Chemical Co) was also used as a source of solid MAPP, added into the extruder.

(41) Sample Production

(42) PVA and MAPP (Michem emulsion) bonded MDF 2 mm panels were produced by spraying resin emulsions/dispersions onto 550 grams of fibre, in a flowing stream, using the 500F MDF Maxiblender to obtain a resin solids loading of either 4% or 8%. 100 grams of resin coated fibre was formed into a 255 mm280 mm2 mm (700 kg/m.sup.3) MDF panel. The MDF panel was cut into pieces approximately 5 mm square. All of the natural fibres and fillers were dried at 60 C. for 48 hours before compounding except for the PVA bonded MDF, which was desiccant dried using silica gel under vacuum.

(43) An OMC 19/30 twin screw co-rotating extruder (19 mm screw, L:D 30) was used for compounding with a screw speed of 150-200 rpm and a temperature range of 160-210 C. The natural fibres/fillers and polypropylene pellets were fed in two separate streams. The polypropylene was fed first, followed by the natural fibre/filler partway along the extruder barrel. The mixture was extruded through a die, which formed a 3 mm-diameter strand. To minimise moisture uptake, the extruded strand was not cooled in a water bath and pelletised as standard, but was air cooled and ground using a Wiley mill through a 4 mm mesh. The samples produced are given below.

(44) TABLE-US-00005 TABLE 5 Wood fibre polypropylene composites produced Composition (%) Epolene Michem Label Fibre fibre PP 3015.sup.a 43040.sup.b PVA.sup.b M-M MDF 36.8 60 3.2 bonded M- MDF 38.4 58.25 1.75 1.6 ME bonded M- MDF 36.8 60 3.2 PVA bonded WF wood flour 40 60 WF-E wood flour 40 56.5 3.5 PP-E PP control 96.5 3.5 PP PP control 100 .sup.aapplied in extruder .sup.bapplied by spraying into the flowing fibre stream, pressed and bonded as in a MDF sheet-making process then chopped into fibre concentrates for mixing in extruder with PP to make pellets for final injection moulding. WF = references/control also.

(45) The sample sets are labelled with the fibre type first (M=MDF, WF=wood flour) followed by any additives after the hyphen (E=Epolene solid MAPP, M=Michem MAPP emulsion. PVA=poly(vinyl acetate)).

(46) The compounded materials were re-dried at 60 C. for 48-72 hours before injection moulding. The dry pellets were injection moulded using a Boy 15S injection moulder (28 mm screw, 20:1 L:D), using a screw speed of 100-200 rpm, and a temperature range of 200230 C.

(47) In all cases the feeding in of pellets or chopped sheet into the extruders was much more convenient than using loose fibres (or flour), which were difficult to introduce uniformly in any metered way, and also easier than handling of wood flour or sander dust.

(48) Mechanical Property Testing

(49) The samples were evaluated as to their tensile, flexural, and impact properties as described in Example 1.

(50) Tensile Properties

(51) The tensile test results are given below Table 6.

(52) TABLE-US-00006 TABLE 6 Tensile test results Strength/ Strain at Label MPa break/% M-M 32.98 1.56 M-ME 46.58 1.83 M-PVA 20.81 3.16 WF 21.11 2.97 WF-E 29.56 1.77 PP 25.16 40.94 PP-E 23.23 6.71

(53) Composite samples prepared with the MDF fibre were examples of the invention. The PVA bonded example illustrates that other resins can be used to aid fibre introduction via the fibre pellet process and good moduli data are obtained. In this PVA case the fibre-PP (matrix) interaction is unoptimised. The use of alternative, more polar, matrix and/or added coupling in the matrix would be able to be used to improve the overall performance in using PVA, or other adhesively bonded MDF. The use of PVA and Michem adhesives to bind MDF into sheets prior to pellet-making from the sheets, were applied via an example of the process of the invention to the MDF fibre composites led to increases in the tensile modulus. SEM micrographs of the composites show the different types of fibre are separated rather than being in fibre bundles, such as may be originally present in the fibre concentrates or pressed sheets.

(54) The addition of natural fibre reduced the maximum tensile stress of the uncoupled polypropylene composites in all cases. There were no significant differences in the tensile strength of the different fibre composites when no additives were used.

(55) The addition of Michem (via precoating, sheet-making and chopping into fibre concentrate prior to extrusion ad injection moulding) increased the maximum tensile stress above that of unfilled polypropylene. The examples M-M and M-ME represent examples of the invention in a preferred mode, wherein the binder is applied can also act as compatibiliser. Superior properties are observed.

(56) Thus, the invention has provided a convenient route to introducing fibres and compatibiliser into plastics via the use of precoated pellets, prepared by essentially an MDF-type process, followed by cutting of the MDF-like sheet.

(57) Flexural Properties

(58) The flexural test results are given in Table 7. The stress (strength) values given are at 5% strain. Beyond this point these specimens still showed an increasing load.

(59) TABLE-US-00007 TABLE 7 Flexural test results Modulus/GPa Strength/MPa M-M 3.59 57.95 M- 4.04 39.78 PVA WF 3.14 40.78 WF-E 3.06 53.55 PP 1.05 33.81 PP-E 1.06 38.29 *samples did not break before 5% strain, values given are for stress at 5% strain

(60) The addition of the natural fibres increased the flexural modulus of all samples compared to unfilled polypropylene. The addition of Michem or PVA improved the flexural modulus of the MDF composites. The addition of the natural fibres increased the maximum flexural stress of all the composites compared to unfilled polypropylene. The addition of Michem also improved the flexural strength.

(61) Impact Properties

(62) The impact strength test results for natural fibre filled polypropylene composites are listed below in Table 8.

(63) TABLE-US-00008 TABLE 8 Impact test results Impact Energy J/m2 M-M 46.5 M-ME 45.5 M-PVA 45.7 WF 40.3 WF-E 43.7 PP 102.6 PP-E 105.3

(64) The MDF (M) fibre samples gave higher impact strengths than the wood flour (WF) samples.

(65) Thus, in summary the use of longer aspect ratio fibres (eg MDF fibres) manufactured as pellets with compatibilser, manufactured and introduced via the methods of the invention lead to superior performance in strength, stiffness and impact properties compared to wood flour or similar products. Even uncompatiblised (for PP matrix. PVA bondedicoated fibres) pellets have equivalent or superior performance to uncompatibilised wood flour usage, and are more easily handled and processed in metered additions.

EXAMPLE 2A

(66) In a further set of composites produced as described in Example 2, at different fibre loadings (20-60 wt %) the following data were obtained, illustrating that the unoptimised fibre-pellets perform better than wood flour, in addition to being more readily introduced to plastics processing machinery.

(67) TABLE-US-00009 TABLE 9 Impact strength of Further Composites Impact Strength Average Sample (J/m) 20% M-PVA 45.27 40% M-PVA 45.69 60% M-PVA 30.00 20% WF 42.46 40% WF 40.34 60% WF 26.22

(68) Commonly used resins for MDF such as urea-formaldehyde (UF) resins, melamines, isocyanates etc as well as PVAsand other common resins, may also be used with good effect to aid fibre pellet manufacture for subsequent introduction in to extruders or injection moulders

EXAMPLE 3

Wood Fibre Biopolymer Composites

(69) Materials and Sample Production

(70) Three resins, a starch, a poly-vinyl alcohol (PVAI), and a melamine-urea-formaldehyde (MUF) resin were each, added, in separate experiments, to MDF fibre (thermomechanical pulp from the MDF refiner blowline at NZ Forest Research Institute, Run 128), by spraying or injecting the polymer additives, as a dispersion or solution in water, using a Laboratory Maxiblender. The Maxiblender blows a fibre stream with air or steam or gas with high turbulence, and has an injection port for spraying resin or additives onto the flowing fibre stream. The impregnated MDF fibres were then collected and pressed into two millimetre thick 300300 mm panel using heat and pressure and subsequently processed into 5 mm square pellets. The MDF pellet squares were made from sheet and extrusion compounded with biopolymer PLA (polylactic acid) and polyhydroxybutyrate (Biopol) at 180-200 C. Various compositions of fibre reinforced biopolymers with 40% (w/w) fibre content were thus made and pelletised and then injection moulded into test specimens, as listed in Table 10 below.

(71) TABLE-US-00010 TABLE 10 List of MDF filled-biopolymer composites made. Polymer Label Description of Fibre and Additives BP = Biopol; PLA = polylactic acid BP - 4% Starch.sup.a 40% MDF squares from Run128 with 4% Gelose starch 173/ 60% Biopol G400 BP - 4% PVAl.sup.a 40% MDF squares from Run 128 with 4% poly-vinyl-alcohol/ 60% Biopol G400 BP - 2% MUF.sup.a 40% MDF squares from Run 128 with 2% melamine-urea- formaldehyde/60% Biopol G400 Pure BP Polymer 100% Biopol G400 PLA - 4% Starch.sup.a 40% MDF squares from Run 128 with 4% Gelose starch 173/ 60% PLA 3001D PLA - 4% PVAl.sup.a 40% MDF squares from Run 128 with 4% poly-vinyl-alcohol/ 60% PLA 3001D Pure PLA Polymer 100% PLA 3010D .sup.aapplied by spraying into the fibre stream

(72) The additives used were a melamine-urea-formaldehyde (MUF) added at two percent, an Aldrich 90% hydrolysed poly-vinyl alcohol (PVAI), and a Penford's plasticised Gelose starch 173.

(73) The poly-vinyl alcohol (PVAI) was dissolved into solution at 10% solids using a temperature-controlled stirrer-hotplate to keep the temperature at 90 C. The solution was then cooled and the solution sprayed onto the fibre. Due to the low solids the fibre had to dried for two hours before being resprayed with a second quantity (2% based on solids to MDF fibre solids) to bring the level of additive up to the required, for this comparison, 4% solids. Lower or different levels may be applied. The invention provides a convenient route to introducing difficult materials such as polyvinylalcohol (commonly available as solutions or films) in to reinforced plastics by first pre-coating the fibres and then pelletising via the MDF-type processes and pressing methods.

(74) Penford's Gelose Starch 173 was dissolved in a mixture of water and glycerol (20:80) to prepare the plasticised starch for spraying onto MDF fibre (27.31% starch content in dispersion)/solution).

(75) Reference samples with wood flour added at 40 wt % in biopolymer were also produced (PLA-WF and BP-WF). The wood flour.sup.1 (WF) used was standard grade Pinus Radiata supplied by Kingsland Seeds. A sieve analysis of the flour indicated a particle distribution with >77%<250 microns.

(76) TABLE-US-00011 Size Weight (mm) (g) % <0.063 0.04 0.2 0.063-0.125 0.36 27.3 0.25-0.5 0.75 49.8 0.5-1 2.5 15 >1 1.37 7.2 0.01 0.8

(77) The bioplastics were dried according to manufacturer's recommendations, typically from 60-80 C. for 2-4 hours.

(78) An OMC 19/30 twin screw co-rotating extruder (19 mm screw, L:D 30) was used for compounding with a screw speed of 120 rpm and a temperature range of 140-170 C. for Biopol extrusion and 170-190 C. for PLA. The pre-compressed MDF squares and biopolymer pellets were fed in two separate streams. The biopolymer was fed first, followed by the MDF squares partway along the extruder barrel, nearer the exit die. The 40% MDF/60% biopolymer and additives were extruded through a die, which formed a 3 mm-diameter strand. The strand was pelltised with a Laboratory Pelletiser.

(79) The Biopol-MDF compounded materials were re-dried at 60 C. for 24 hours before injection moulding into test specimens. The test specimens were moulded using a Boy 15S injection moulder (28 mm screw, 20:1 L:D), using a screw speed of 100-200 rpm, and a screw temperature range of 150-190 C.

(80) PLA-MDF compounded materials were re-dried at a temperature of 80 C. for 24 hours before injection moulding into test specimens. The test specimens were moulded using a Boy 15S injection moulder (28 mm screw, 20:1 L:D), using a screw speed of 100-200 rpm, and a screw temperature range of 165-210 C.

(81) The compounded WF pellets were re-dried at 40 C. until the moisture content was below 0.5%, typically for 5-8 days, then dried at 80 C. for two hours immediately before injection moulding. The dry pellets were injection moulded using a Boy 15S injection moulder (28 mm screw, 20:1 L:D) using similar conditions as above.

(82) Mechanical Property Testing

(83) Samples were conditioned at 23 C. and 50% RH for 1 week before measurement and testing.

(84) Flexural properties were evaluated according to ASTM method D790-96a.sup.(8), except that the loading nose and supports had radii of 7.5 mm. An Instron model 5567 test machine was used for testing the three point bending specimens and was equipped with a 10 kN load cell. A span of 50 mm and speed of 1.3 mm/min was used for flexural tests.

(85) The densities and flexural properties of the MDF filled biopolymer composites are given below in Tables 11 and 12.

(86) TABLE-US-00012 TABLE 11 Densities of MDF filled Biopolymer samples Density Label of Average Sample (kg/m.sup.3) BP - Starch 1304 BP - PVAl 1296 BP - MUF 1293 Pure BP polymer (neat) 1234 PLA - Starch 1310 PLA - PVAl 1303 Pure PLA polymer (neat) 1254

(87) TABLE-US-00013 TABLE 12 Flexural Properties of MDF - Biopolymers Stress at Modulus Max Load Sample (GPa) (MPa) PLA - Starch 6.92 100.9 PLA - PVAl 7.93 110.6 PLA - neat 3.82 116.6 PLA - WF ref 6.43 78.4 BP - Starch 4.58 54.8 BP - PVAl 6.43 61.0 BP - MUF 5.23 51.9 BP - neat 7.52 50.5 BP - WF ref 5.45 45.5 Neat = plastic without fibre present. WF = wood flour added at 40%. Others = 40% loading fibre, as in Table 10 above - with pre-impregnated MDF fibre, according to the invention.

(88) Significant improvements in properties such as strength are achieved in the bioplastics by use of the pre-coated fibre pellets as manufactured by the process of the invention, compared to a wood flour reference. Particular benefits are seen from the use of polyvinylalcohol as the fibre coating. Modified polyvinyl alcohols and/or copolymers may be expected to perform well as fibre coatings also. Even the use of MUF, a thermoset resin binder, provides performance advantages over reference materials (wood flour), in addition to aiding introduction of wood fibre into the extruder or moulding machine.

EXAMPLE 4

Direct Injection Moulding of Pellets Made by the Invention

(89) Wood fibre pellets with polyvinylacetate (National Starch; 4% dry weight loading on fibres) were manufactured according to the invention as previously described and cut into 5 mm squares and dried. The pellets were then injection moulded with added PLA, as above with simple pre-mixing of the fibre pellets with added plastic (PLA)_pellets to produce injection moulded samples.

(90) The directly injection moulded fibre pellets with added polymer exhibited a flexural strength of 67.9 MPa and a flexural modulus of 6.27 GPa at a fibre loading in the final plastic composite of about 20 wt %. Thus this high modulus was achieved with fibres present at a loading of 20 wt %about half that of the wood flour loading used in Example 3 to achieve a similar modulus. Through simple optimisation of the additives, as described earlier, further enhanced performance would be achieved. This demonstrates that direct injection moulding (no intermediate extrusion compounding) of the fibre pellets with added polymer can be achieved.

EXAMPLE 5

MDF Manufacturing Pilot Plant Trials

(91) Trials at an MDF pilot plant at NZ Forest Research Institute were undertaken using refiner-blowline polymer addition, as in the MDF or particleboard industries, for the production of fibre-polymer pellet feedstocks for use in plastic processes.

(92) Fibre from wood chips was produced in the Forest Research Mechanical Pulping Pilot Plant under typical conditions for high temperature/mechanical pulps, as used in MDF industry.

(93) Michem 43040 emulsion was added to hot fibre in the MDF refiner-blowline and dried at 140 C. in a tube drier to a targeted moisture content of 12 to 16%. The MDF fibre was pressed into two millimetre thick 300300 mm panels at three densities (500, 700 and 900 kg/m.sup.3) and subsequently processed (chopped) into 5 mm squares. The MDF squares were made from sheet with coupling agent additives and then extrusion compounded with polypropylene on an extruder at 180-200 C. Various compositions of fibre reinforced polypropylene with 40% (w/w) fibre content were then made and pelletised before being injection moulded into test specimens.

(94) The results indicate that the addition of an emulsified coupling agent or binder to the blowline of a commercial MDF plant and manufacturing of the pellets in a process representative of commercial MDF or particleboard manufacturing, will give a similar performance to the laboratory examples earlier and with a performance and processability superior to wood flour equivalents.

(95) The binder or coupling agent may be added at various points in the refiner-blowline process and could be added at the refiner, or at various points along the blowline. Two or more points of addition may be used to apply the same or different polymers or additives sequentially.

(96) Materials

(97) Example trial fibres of thermo-mechanical pulpMDF fibre were produced on the PAPRO pilot plant refiner at Forest Research, Rotorua. Fibre 129 had 4% Michem emulsion injected onto the fibre which was flowing in the blowline.

(98) The polypropylene resin used was Hyundai Setec grade M1600 supplied as pellets. The maleic anhydride modified polypropylene emulsion used was Michem 43040 (a non-ionic emulsion) supplied by Michelman Inc.

(99) Approximately 20 kg of coated fibres for each run was dried using the MDF drying tube to blow hot (140-160 C.) air onto fibre that was collected with a cyclone dropping the fibre into a plastic bag.

(100) The fibre was measured for moisture content and adjustments made to correct for variation in moisture content. Michem 43040 was added to hot fibre at the MDF refiner blowline and coated fibre was dried at 140 C. to a targeted moisture content of 12 to 16%. The MDF fibres were pressed into two millimetre thick 300300 mm panels at three densities (500, 700 and 900 kg/m.sup.3) at 180 C and subsequently processed or chopped into 5 mm squares. The pellets were compounded with polypropylene on an extruder at 180-200 C. and pelletised before being injection moulded into test specimens. Other dimensions for the sheets or the pellets are of course entirely feasible. All of the pre-compressed MDF squares, with coupling agent, were dried at 60 C. for 48 hours before compounding.

(101) The samples produced are listed below in Table 13.

(102) TABLE-US-00014 TABLE 13 List of MDF fibre-plastics made. Description of Density of 2 mm Panel Label Fibre and Coupling Agents (kg/m.sup.3) 500M4 Run 129 4% Michem addition 500 700M4 Run 129 4% Michem addition 700 900M4 Run 129 4% Michem addition 900 .sup.bapplied by spraying onto fibre 500M4-900M4: MDF fibres as above, pressed in the presence of 4% Michem G3015 coupling agent that was added in the blowline. Fibre hot-pressed at 180 C. for 1 minute to different densities.

(103) An OMC 19/30 twin screw co-rotating extruder (19 mm screw, L:D 30) was used for compounding with a screw speed of 180 rpm and a temperature range of 180-200 C. The pre-compressed MDF squares and polypropylene pellets were fed in two separate streams. The polypropylene was fed first, followed by the MDF squares partway along the extruder barrel. The 40% MDF (with coupling agents precoated/applied)/60% polypropylene agents mixture was extruded through a die, which formed a 3 mm-diameter strand which was pelletised into 5 mm length pellets using a laboratory pelletiser.

(104) The compounded materials were re-dried at 60 C. for 24 hours before injection moulding into test specimens. To ensure the test specimen completely filled the mould cavity. The test specimens were moulded using a Boy 15S injection moulder (28 mm screw, 20:1 L:D), using a screw speed of 100-200 rpm, and a temperature range of 200245 C.

(105) Mechanical Property Testing

(106) Samples were conditioned at 23 C. and 50% RH for 1 week before measurement and testing.

(107) Tensile properties were evaluated according to ASTM method D638-96 (Type I).sup.(3). An Instron model 5567 test machine was used for testing, equipped with a 10 kN load cell and 25 mm extensometer. The initial separation between grips was 100 mm, with a testing speed of 5 mm/min.

(108) Flexural properties were evaluated according to ASTM method D790-96a.sup.(8), loading nose and supports had radii of 7.5 mm. An Instron model 5567 test machine was used for testing, equipped with a 10 kN load cell. A span of 50 mm and speed of 1.3 mm/min was used for flexural tests.

(109) Sample Densities

(110) The densities of the MDF filled polypropylene composites are given below in Table 14.

(111) TABLE-US-00015 TABLE 14 Densities of MDF filled polypropylene samples Density Label Kg/m3 FR Refiner/Blowline 500M4 1047 700M4 1054 900M4 1060 PP 890
Tensile Properties

(112) The tensile test results are given below in Table 15.

(113) TABLE-US-00016 TABLE 15 Tensile test results Strength/ Sample Modulus/GPa MPa Strain/% 500M4 4.66 42.7 1.97 700M4 4.39 41.2 1.78 900M4 4.63 39.4 1.55 PP 1.39 25.2 40.9
Flexural Properties

(114) The flexural test results are given below in Table 16.

(115) TABLE-US-00017 TABLE 16 Flexural test results Stress at Modulus Max Load 500 M4 4.33 72.9 700 M4 4.37 71.8 900 M4 4.54 71.5 PP 1.05 33.8 *samples did not break before 5% strain, values given are for stress at 5% strain

(116) The addition of Michem 43040 binder dramatically improved the tensile and flexural strength of MDF fibre/polypropylene. There was no significant gain in performance when the level of Michem 43040 was increased from 4%, though other levels including lower loadings are entirely feasible. The addition of Michem 43040 to MDF fibre in the pilot plant blowline indicates a similar level of performance achieved in the Laboratory Blender trials. MDF sheet at various densities were able to be used as feedstock for pellets.

REFERENCES

(117) 1 Schut Jan. H., Wood is Good for Compounding, Sheet & Profile. Online article from http:/www.plasticstechnology.com/articles/199903fa1.html (1999). 2 North Wood Plastics Inc., 3220 Crocker Avenue, Sheboygan, W I. 53081 USA, http://www.northwoodplastics.com 3 Brooke, J. G., Goforth, B. D., Goforth, C. L., U.S. Pat. No. 5,082,605, 1992. 4 Deaner, M. J., Puppin, G., Heikkila., U.S. Pat. No. 5,827,607, 1998. 5 Stark. N. M., Rowlands, E. R. (2003). Effects of wood fiber characteristics on mechanical properties of wood/polyproplyene composites. Wood and Fiber Science, 35(2), pp 167-174. 6 Loxton, C., Thumm, A., Grigsby, W. J., Adams, T. and Ede, R. (2000). Resin Distribution in Medium Density Fibreboard: Quantification of UF Resin Distribution on Blowline Blended MDF Fibre and Panels. In Proc. 5th Pacific Rim Biobased Composites Symposium, Canberra. December 10-13, pp 234-242. 7 ASTM D638-96: Standard Test Method for Tensile Properties of Plastics. 8 ASTM D790-96a: Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials. 9 Sears K. D et al (2001). Proc. 6.sup.h International Conference on Woodfibre Plastics Composites, Forest Products Society, 2001, p 27-34 and U.S. Pat. No. 6,270,883.