AU2022241579A1

AU2022241579A1 - Improved particleboard

Info

Publication number: AU2022241579A1
Application number: AU2022241579A
Authority: AU
Inventors: Steven CHIUTA; Marcus Cameron Wong
Original assignee: Laminex Group Pty Ltd
Current assignee: Laminex Group Pty Ltd
Priority date: 2021-12-07
Filing date: 2022-09-30
Publication date: 2023-06-22

Abstract

An improved particleboard and a process for manufacturing the same when the process includes steps of chipping virgin bamboo culm to a size of less than 120mm; 5 drying, flaking and milling the bamboo chips to produce particles and optionally mixing with wood particles and forming into a particle board product. 1/9 Figures Figure 1 5Ore Surface

Description

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Title of Invention

Improved Particleboard

Technical Field

[0001] The present invention relates to a manufacturing process in order to produce particleboards. The manufacturing process includes the use of virgin bamboo culm that has been processed by control of the cutting and mixing such that it is able to produce a medium density particleboard with good mechanical properties, and ease of processing in that only a short press time is required. The process includes the steps of first cutting the culm to a manageable size, before then flaking and milling the culm to particles of a size of preferably less than 10mm. The bamboo is preferably mixed with wood in specific ratios for processing. A thermoset resin, hardener and water are also included in the mix.

[0002] The present invention also relates to an improved particleboard. In particular, the invention relates to a flat engineered lignocellulosic composite panel that is produced from a mix of wood and bamboo particles, or fully from bamboo particles that have been produced by the process of the invention. In one embodiment, the wood and bamboo particles are bound together with a thermoset resin together with additives such as a wax, hardeners and water. In a preferred embodiment, the particleboard will be constructed as three layers having a central core layer and two surface layers. The particle size mix in each layer is controlled.

[0003] In further preferred embodiments, the improved particleboard and the process for manufacturing will be a moisture resistant particleboard and may include other additives to further enhance its termite resistance, flame retardant, acoustic or insulation properties.

[0004] The particleboard may be used in a diverse area of applications, including but not limited to flooring, furniture, wall and ceiling panelling. It may also provide a suitable flat substrate onto which decorative panels, foils or laminates may be applied.

Background of Invention

[0005] The manufacture of particleboards is largely based on wood, particularly softwoods such as pine. In recent times, the forest and forest products industry in Australia has been facing the challenge of the rising cost of wood chip, due to a number of reasons including availability and an increased volume of export to overseas jurisdictions, while there is minimal investment in new plantation land. The supply chain for softwood products cannot be guaranteed.

[0006] The use of pine for the manufacture of particleboards also suffers from an environmental perspective as it has become evident that the carbon sequestration capabilities of pine is relatively low. Further, the yield period of pine trees in a plantation tends to be around 12 to 15 years or longer for trees to mature, which can lead to a reduced yield based on tonnes per hectare per year compared to that of faster growing plantation species.

[0007] Bamboo is a material that does have far higher carbon sequestration capabilities due to its fast growth rate. Whereas it has been used in the manufacture of particleboards, it has presented manufacturing difficulties as species that have generally been used for solid timber (engineered bamboo) products such as Bambusa balcooa or Dendrocalamus asper have high levels of silica of between 2-3%. This creates manufacturing problems due to increased tool wear when cutting and sanding.

[0008] Further, bamboo may be particularly stringy and often forms into strands when cut. The use of such material can lead to entanglement, bridging and blocking during manufacturing processes as the particles are unable to flow freely.

[0009] Particleboards that have been manufactured with a bamboo content generally have a density in the order of greater than 750 kg/m3 and require quite substantial pressing cycles of greater than 6 minutes and up to 10 minutes. The focus in the manufacturing process for such prior art particleboards has been on the final chip size and the higher silica bamboo species which tends to lead to a higher density final product. Planar waste, offcuts, shavings and treatment residues generated from engineered bamboo processing is used in the manufacture of such prior art particleboards. The resins used in prior bamboo-based boards include urea formaldehyde, pMDI or biobased resins which can lead to the need for longer press cycles.

[0010] It is a desired feature of the present invention to overcome or at least alleviate one or more of the difficulties associated with processes that rely on the use of softwoods such as pine for the manufacture of particleboard. This includes the difficulties with processes and products that rely solely on the use of bamboo or a mix of wood and bamboo particles in the manufacture of particleboards.

[0011] It is a further desired feature of the present invention to provide a standard, moisture-resistant, termite resistant or flame-retardant particleboard that is less reliant upon the use of softwoods such as pine in the manufacture.

[0012] It is a further desired feature of the present invention to provide a particleboard that incorporates virgin bamboo culm with or without softwood particles. The use of bamboo from a bamboo plantation improves the carbon sequestration capabilities of the plantation source for the manufacturing of the particleboards of the invention.

[0013] It is a further desired feature of the present application to rely upon a lignocellulosic material that is able to be harvested in a relatively short period of time compared to pine.

[0014] It is a further desired feature of the present application to rely upon a lignocellulosic material that is high clumping so as to improve yields per hectare of land.

[0015] It is a further desired feature to provide a particleboard that is of a medium density of less than 700 kg/m3 while still retaining desired characteristics of bending, thickness, bonding and dimensional stability requirements.

[0016] The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

[0017] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

Summary of the Invention

[0018] In one embodiment, the present invention resides in a process for manufacturing a water-resistant particleboard, said process including the steps of chipping virgin bamboo culm to a size less than 120mm; drying the bamboo chips to a moisture content of approximately 40-150%, preferably 80-120% of oven dried mass, flaking and milling the bamboo chips to produce particles and preferably mixing with wood particles where predominantly all particles are of a size of from 0.1 to 10mm; drying the mixed wood and bamboo particles to dry the particles to a moisture content of from 1-10%, preferably 2-3%.

[0019] The mix is then sprayed and mixed with a resin, preferably a thermoset resin. Optionally, a wax, hardener and water may be mixed and sprayed together or at different times to the resin, for example, the wax may be applied first followed by the resin and hardener mixed and then water to required levels. The resinated particle mix is then formed into a mattress and the formed mattress is pressed between platens of a "daylight" hot press preferably for 1-5 minutes, more preferably 3-4 minutes at 150-200°C and preferably a max pressure of 300 bar to form a particleboard sheet. Alternatively, the resonated particle mix is formed into a mattress of a continuous hot press running at a line speed of 50-2000mm/s. The particleboard sheet has superior flexural strength enabled by the efficient interparticle contact owing to the highly slender bamboo particles in the core matrix of the article.

[0020] It is preferred that the virgin bamboo culm is first chipped to a size that is between 40-60mm long; 20-40mm wide and 10-15mm thick. The moisture content when first dried before flaking and milling is preferably around 80 to 120% of oven dry mass, preferably around 100% of oven dry mass.

[0021] In a preferred embodiment, the particleboard is constructed in 3 layers having a core layer and 2 surface layers, the particles having been screened after the bamboo particles have been flaked and milled and separated according to size such that the size distribution of the bamboo and wood particles in the surface layer is from approximately 0.25-8.00mm, and the particle size of the bamboo and wood particles in the core layer is from 0.25-10.0mm; the particles are then sprayed with the resin and optionally mixed with wax, hardener and water. The resinated particles are then formed into a mattress of layers surface/core/surface and hot pressed to form the particleboard sheet.

[0022] In a further preferred embodiment, more than 70% of particles in the surface layers have a particle size of from 0.25 to 1.25mm and more than 40% of the particles in the core layer have a particle size of in the 1.25-2.88mm range.

[0023] It is preferred that the cut bamboo particles after having been flaked and milled have a slenderness ratio higher than that of the wood particles. The slenderness ratio is a measure of the length of the particle divided by its thickness. The slenderness ratio for bamboo may be from 30-40, preferably from 34-36, and this compares to standard wood particles which have a slenderness ratio of from 24-32, preferably 27-29. This indicates that the bamboo particles are on average longer and thinner than the wood particles.

[0024] In a further preferred embodiment, the wood particles are sourced from a softwood, preferably pine, more preferably hoop pine (Araucaria cunninghamii) or slash pine (Pinus elliottii); the bamboo particles are from the culm of a fast growing, clumping (sympodial) species having low silica/grit of less than 1.5%. Preferably the bamboo species is Bambusa Oldhamii. Other low silica species include Phyllostachys pubescens or Phyllostachys edulis, however other varieties that may still be used include Bambusa balcooa, Bambusa textilis var, longinternode, Dendrocalamus asper, Dendrocalamus giganteus, Dendrocalamus latiforus, Dendrocalamus peculiaris although some have higher silica content making them less desirable. In a further preferred embodiment, the resin is a moisture resistant resin, preferably a melamine urea formaldehyde (MUF) resin. Alternatively, the resin may be a formaldehyde free resin including those that are based on natural materials or biobased adhesive systems such as soy, soy-based proteins, animal protein-based adhesives, lignin, latex, acrylic, thermoplastic polymers or copolymers and bio-resins or other thermosetting/thermoforming plastics like polymeric diphenylmethane di- isocyanate (PMDI), phenolics, MUF, phenol formaldehyde (PF) or urea formaldehyde (UF).

[0025] The resin systems may include waterborne-acrylics, polyvinyl chloride, thermoplastic polymers and copolymers, polyvinyl alcohol (PVOH), bio-resins such as polylactic acid (PLA), polyhydroxyl butyrate (PHB) and others, or epoxy resins.

[0026] The resin is preferably sprayed upon the bamboo/wood particles at a loading of 8-20%, preferably 10-15% in the surface layer, and 5-15%, preferably 6 10% in the core layer based on the solid resin relative to dry weight of the bamboo/wood. If the resin system is a UF, PF, MUF or a combination of these materials, the resin preferably has a solid content of 55-65%. The resin is preferably applied with or after the wax but will generally be mixed with the hardener before applying to ensure maximum efficacy of the hardener.

[0027] In a further preferred embodiment, the hardener is an acidic catalyst of pH < 6 and optionally includes a crosslinker, preferably urea.

[0028] In a further embodiment, the invention resides in a particleboard comprising a lignocellulosic material selected from bamboo or a mix of bamboo and wood particles; wherein if the material is a mix of bamboo and wood particles, the bamboo to wood ratio is from 10:90 to 60:40, preferably 20:80 to 40:60, the bamboo being sourced from virgin bamboo culm; the bamboo and optionally the wood particles having been prepared by chipping to a size of less than 120mm, preferably from 40-60mm long, 20-40mm wide and 10-15mm thick; dried, and mixed with the wood particles, then flaked and/or milled such that predominantly all particles are of a size of from 0.1mm to 10mm, the slenderness ratio of the bamboo is preferably higher than that of the wood.

[0029] Preferably, the particle mix further includes a resin, wax, a hardener and water.

[0030] Whereas the particleboard may comprise 100% bamboo, in a preferred embodiment, the ratio of bamboo to wood is in the range of from 10:90 to 60:40 and preferably from 20:80 to 40:60. The bamboo culm is preferably first chipped to a size of from 40-60mm long, 20-45mm wide and 10-15mm thick.

[0031] In a preferred embodiment, the particleboard is constructed in 3 layers having a core layer and 2 surface layers, the particles having been screened after the bamboo particles have been flaked and milled and separated according to size such that the size distribution of the bamboo and wood particles in the surface layer is from approximately 0.25-8.00mm, and the particle size of the bamboo and wood particles in the core layer is from 0.25-10.0mm; the mix of particles includes a thermoset resin, wax, a hardener and water.

Brief Description of Drawings

[0032] Figure 1 is an annotated cross section of a bamboo/wood composite particleboard which illustrates the relative thicknesses of the core layer and the two surface layers.

[0033] Figure 2 is a graph of density vs % bamboo in the mix.

[0034] Figure 3 is a graph of the thickness of a particleboard vs % bamboo.

[0035] Figure 4 is a graph of the Modulus of Elasticity (MOE) vs % bamboo.

[0036] Figure 5 is a graph of the Modulus of Rupture (MOR) vs % bamboo.

[0037] Figure 6 is the Internal Bond (IB) vs % bamboo.

[0038] Figure 7 is the Surface Soundness (SS) vs % bamboo.

[0039] Figure 8 is the Wet Bending (WB) vs % bamboo.

[0040] Figure 9 is the 24-hour Thickness Swelling (24h TS) vs % bamboo.

[0041] Figure 10 is a comparison of the slenderness ratio of bamboo and wood particles

Detailed Description

[0042] The present application relates to a particleboard that comprises lignocellulosic material that is either bamboo or a mix of wood and bamboo particles making up roughly 85 to 90% by solids of the board. The particle board would also include moisture resistant resin, optionally together with a wax, a hardener and water.

The invention further resides in the process of manufacturing a particleboard that comprises either bamboo or a mix of bamboo and wood particles.

[0043] In a preferred embodiment, the particleboard would be constructed as a three-layered particleboard, with two thinner surface layers which would be constructed of finer particles surrounding a thicker core layer which is preferably constructed of coarser flake particles. The surface layers preferably comprise between 10 and 25% of the board by mass, while the core layer would comprise from 50 to 80% by mass. Whereas either the surface layers, and/or the core layer may comprise 100% bamboo, in a preferred embodiment, the ratio of bamboo to wood particles would be from 10:90 to 60:40 but preferably in the region of from 20:80 to 40:60 in both the surface layers and the core layer.

[0044] Preferably, the bamboo particles are from the culm of a fast growing, clumping (sympodial) species having low silica/grit of less than 1.5%, preferably the bamboo species is Bambusa Oldhamii. Other low silica species include Phyllostachys pubescens or Phyllostachys edulis, however other varieties that may still be used include Bambusa balcooa, Bambusa textilis var, longinternode, Dendrocalamus asper, Dendrocalamus giganteus, Dendrocalamus latiforus, Dendrocalamus peculiaris although some have higher silica content making them less desirable.

[0045] The wood particles are preferably sourced from softwood, preferably pine and more preferably hoop pine (Araucaria cunninghamii) or slash pine (Pinus elliottii). Alternatively, the particle board is constructed using only bamboo products together with the thermoset resin, optionally with wax, a hardener and water.

[0046] In the process of the invention, the bamboo culm, that is the above the ground jointed stem, is sourced from fast growing, clumping (sympodial) species of bamboo that preferably contains low silica/grit content. This is preferably below 1.5%. Previous species of bamboo that have been harvested for wood products include Bambusa balcooa or Dendrocalamus asper which includes high levels of silica between 2-3%. This does create problems due to increased cutting and sanding tool wear.

[0047] The bamboo is preferably chopped down above the stem using a mechanical harvester, where it is then brought to a central location for chipping. The chipping is done by feeding the bamboo culm into a knife chipper to reduce the size to less than 120mm. The desired outcome of the chipping is to produce a bamboo chip of regular size by ensuring complete cut-through across the waxy epidermis skin of the virgin bamboo culm. This assists in realizing efficient manufacture of the particleboard article. This also reduces the slithers (long and thin strands) which often results from inefficient chipping. These slithers cannot be used in manufacturing of the particleboard as they may cause undesirable process challenges such as equipment malfunction and inefficiencies due to blockages.

[0048] In order to achieve a regular size for the bamboo culm chips, it is preferred that the bamboo culm is reduced to a size of from 35-65mm long, 15-45mm wide and 5-20mm thick, although preferably this is between 40-60mm long, 20-40mm wide and 10-15mm thick.

[0049] The chipped bamboo is then dried. This is usually done by ambient air drying to achieve a moisture content of the chopped bamboo of around 40-150%, but preferably around 80-120% of oven dried mass. The drying allows for the chip to settle at an equilibrium moisture content depending on surrounding atmospheric conditions, allowing for ratios of chip types to be accurately weighed out in production.

[0050] The air-dried bamboo chips are then flaked and milled. The wood and bamboo chips are fed into the process at the same time to allow for mixing of the wood and bamboo particles. The ratio of bamboo to wood is controlled by the rate in which both particles are fed into the system. The preferred ratio of bamboo to wood particles would be from 10:90 to 60:40 but preferably in the region of from 20:80 to 40:60.

[0051] The flaking and milling assist to produce adequately sized bamboo and wood particles that allow for them to be screened for sorting to preferred particle size for both the surface and core layers. The bamboo and wood chips are then reduced in size, preferably with a knife ring flaker, then hammermilled to further reduce the particle size. The knife ring flaker and hammermill form longer and thinner particle geometry (higher slenderness ratio) for the bamboo compared to the wood particles. The slenderness ratio for the bamboo particles will be 30-40, preferably 34 to 36 with examples produced having a slenderness ratio averaging 35.4, compared to a slenderness ratio for wood particles of between 24-32, preferably 27-29 with examples averaging but typically around 28.4. Both the bamboo and wood particles should now preferably be of a size of from 0.1 to 10mm.

[0052] The flaked and milled particles are then dried preferably by convective drying by passing the mixed bamboo and wood particles through a co-current rotary drier to dry the flaked particles to a moisture content of preferably 1-5%, more preferably 2-3%. The drying reduces the moisture content in particles to allow for unhindered interaction between particles and resin. If there was not adequate drying, there is potential for excessive steam to form during hot pressing creating steam pressure which could result in blown boards when the press is released.

[0053] The particles are then screened and sorted using mechanical vibrating screens and air classification to achieve the particle size distribution suitable for use in the surface and core layers. Preferably, the size distribution of the bamboo and wood particles in the surface layer is from approximately 0.25-8.00mm, and the particle size of the bamboo and wood particles in the core layer is from 0.25-10.0mm. It is preferred that more than 70% of particles in the surface layers have a particle size of from 0.25 to 1.25mm and more than 40% of the particles in the core layer have a particle size of in the 1.25-2.88mm range. A typical size distribution for one example that may be achieved is shown in Table 1.

Table 1

Particle size (mm) Surface(%) Core(%)

x > 8.0 0.0 8.8

8.0 > x > 2.8 0.0 27.9

2.8 > x > 1.25 8.4 50.4

1.25 > x > 0.25 81.2 9.5

x < 0.25 10.4 3.5

[0054] The appropriate size fractions may be stored in silos or at separate locations for use in manufacturing the core and surface layers, while oversized particles are recycled back to milling and undersized particles are sent to waste or incinerated.

[0055] The screened and sorted particles may then be sprayed with the moisture resistant resin in liquid form, optionally along with wax, hardener, and water. The resin and additives are sprayed onto the core and surface particles and preferably mixed in separate blenders and then sent to be spread into a mattress for hot pressing.

[0056] The thermoset resin is preferably a moisture resistant resin and is most preferably a melamine urea formaldehyde (MUF) resin. It is preferably sprayed onto the bamboo/wood flakes in a rotating mixing device at a loading of 8-20%, preferably 10-15% in the surface layer, and 5-15%, preferably 6-10% for the core layer particles. The resin loading is based on the solid resin relative to the dry weight of the bamboo/wood. If the resin is UF, PF or MUF, it preferably has a solid content of 55 65%. Alternatively, a no-added formaldehyde resin may be used to produce a sustainable panel that does not produce formaldehyde emissions during and post manufacturing. Alternatively, a standard resin system may be used for "standard" or non-moisture resistant particleboard.

[0057] The hardener is preferably an acidic catalyst having a pH of less than 6. The hardener is used to speed up the polymerisation of the resin. Allowing the polymerisation to occur in a shorter period of time when hot pressing enables higher throughput and ultimately lower normalized production costs. Optionally, the hardener may also include a cross-linker, such as urea, which further aids the polymerisation reaction.

[0058] If the resin used is MUF, its mechanism of polymerisation takes place via condensation, whereby free protons H+ allows for an intermediate between melamine and formaldehyde or urea and formaldehyde to be formed, following which ejection of water occurs. Therefore, a mildly acidic catalyst, such as ammonium chloride or ammonium sulphate is preferred to provide a source of free protons. Moreover, this catalyst also contains a small amount of crosslinkers, such as urea, which can polymerize with the resin and further reinforce and strengthen the particleboard. Urea and ammonium sulphate or urea and ammonium chloride solution may be sprayed onto the bamboo/wood particles to assist in the polymerisation reaction. The hardener preferably has a solids content of 25-40% and loadings are preferably 1-2% for the surface layer and 3-5% for the core layer.

[0059] Preferably, the wax is a hydrophobic material that is used to coat the surface of the cellulosic material and resin matrix. Since bamboo and wood are both hydrophilic, they readily absorb water, which could lead to dimensional swelling of the final particleboard product. It could also lead to reversal and weakening of the polymeric resin matrix. Therefore, the addition of a small amount of wax or other hydrophobising additive assists to provide the board with moisture resistant properties by reducing the penetration of water to the surfaces. The melamine modification of the MUF resin also aids in providing greater moisture resistance than conventional urea formaldehyde resins given melamine's heterocyclic structure leads to the formation of 3-dimensional crosslinking that is more stable than the more linear structures formed by urea.

[0060] Paraffin wax is a preferred wax. It acts as a water repellent agent to provide a coating to prevent excess absorption of water by the hydrophilic bamboo and wood particles. The wax preferably has a solids content of from 40-75%, more preferably 50-65% and is sprayed into the bamboo/wood flakes at a loading of from 0.5-4%, preferably 0.5-2%. Other water repellent agents include but are not limited to silicones, silanes, fluorinated chemicals, fatty acid surfactants, and inorganic hydrophobising agents.

[0061] Other additives may be incorporated to achieve desirable properties. For example, additives such as boric acid, insecticides and/or pyrethroids may be used to afford termite resistance. Flame retarding agents including but not limited to ammonium polyphosphate, boric acid, cement, magnesium dihydroxide and/or aluminium trihydate or combinations of these additives can be used to improve the fire resistance of the particleboards. Dyes and pigments may be added to the mixture to colour the particleboard for marketing and/or aesthetic reasons. Fillers such as talc or CaC03 may be used to decrease the cost of the boards. Fillers such as pearlite or foamed polymers may be used to decrease the panel density.

[0062] Water may be applied to ensure the resinated surface particles reach a moisture level of 10-20%, preferably 12-17% and core particles reach a moisture content of from 5-15%, preferably 8-12%. This non-uniform moisture distribution initiates a steam shock effect where upon hot pressing the resinated bamboo/wood furnish at high temperatures in excess of 1500C, steam is almost immediately generated in the surface layer and transfers down the equilibrium gradient to the core layer leading to increased core temperature greater than 1000C, which allows for faster curing of the resins in the thicker core layer. The residence time or press factor of the board between the press platens is about 8-15 seconds per millimetre thickness for a daylight press, or at a line speed of 50-2,000 mm/second for a continuous press.

[0063] The resinated core and surface particles are then metered to a forming station where the particles are then spread evenly into the preferred three-layered surface/core/surface mattress structure so as to produce a final product as illustrated in Figure 1. In a preferred construction, the core layer is such that it is 50-80% of the thickness while each of the surface layers are from 10-25% of the overall thickness of the final particleboard structure.

[0064] The formed mattress is then pressed between platens in a hot press. A discontinuous or "daylight" press may only be for 1-5 minutes, preferably 3-4 minutes, preferably at 150-200C and a maximum pressure of 300 bar. The preferred press factor is about 8 to 12 sec/mm for a daylight press. This allows the core to be heated to a temperature of preferably around 100-110°C which condenses the resin into a polymeric matrix. The particleboard may then be taken to be cooled to room temperature and stacked on top of each other for several days as conditioning, to ensure the resin has fully set before further transportation. For a continuous press, the line speed is approximately 50 - 2,000mm/s.

[0065] The final particleboard produced preferably has a density of preferably less than 700kg/m3 and can achieve good properties even with densities down to 635kg/m 3. It is common that boards produced with known techniques have a higher density above 750kg/m 3 . Particleboards having the medium density of the present application ensure that the boards are lightweight enough to be used in furniture and other uses and improves ease of transportation and production costs. Lower density products may be produced for specific applications including door cores and other light weight panels. The panels may be routed on one surface to achieve a curved surface for decorative architectural applications such as curved wall linings.

[0066] The final particleboard may be decorated with melamine resin impregnated printed or coloured decorative papers, which are fused to the board using a low pressure heated platen press. Alternatively, the inventive particleboard may be decorated with metallic foils, PVC or polypropylene films adhered using conventional adhesive systems. The decorative surface itself may be further modified with biocidal agents (e.g. silver) to afford antimicrobial, antifungal and antiviral surface properties.

[0067] The raw or decorated panels may be routed, machined and fabricated into articles including furniture, cabinetry, wall or ceiling linings. The raw panels may be routed and used for tongue and groove flooring applications. The raw panels may be painted, sealed or coated with waterproofing membranes for use in flooring. The acoustic properties of the panels can be modified with additives or the surface may be modified to achieve acoustic properties.

Examples

Example 1

[0068] A series of particleboards were manufactured in accordance with the process as outlined above for use as flooring panels. The flooring particleboard aims to have a thickness of 19mm and a higher density than moisture resistant particleboard in order to achieve greater mechanical and durability properties required for high load bearing and weathering resistance purposes. The bamboo was Bambusa oldhamii. while the wood was pine. The particleboard produced met with all Australian and New Zealand standards as well as global standards such as those of JIS, ANSI, EN and ISO.

[0069] A list of the properties achieved for the 19mm flooring particleboard is shown in Table 2.

Table 2

P ropetiesAS/NZS 1860.1

Thickness (mm) 19.0

Moisture (%) > 7.0 8.3

Density (kg/m) 709

MOE (MPa) > 2850 3580

MOR(MPa) >20.0 23.5

Internal Bond (MPa) > 0.65 0.88

Surface Water Absorption (MPa) < 135 103

24 h Thickness Swelling(%) < 7.0 5.0

Wet Bending C (MPa) > 5.0 7.0

Glue Bond Quality (MPa) < 11.0 17.9

Thickness Stability(%) < 14.0 9.1

Grit(%) 0.489

Example 2

[0070] A series of three-layered moisture-resistant particleboards was produced with an aim to have a thickness of 16mm and at a lower density. Such particleboards would be useful for wall panelling or furniture. The bamboo was Bambusa oldhamii, while the wood was pine. The medium density particleboard produced met with all Australian and New Zealand standards as well as global standards such as those of JIS, ANSI, EN and ISO.

[0071] The properties achieved for the 16mm moisture-resistant particleboard is shown in Table 3

Table 3

Results Properties 1859.1

Thickness (mm) 16.4

Density (kg/m) 662

MOE (MPa) > 1800 3265 MOR (MPa) > 12.0 19.0 Internal Bond (MPa) > 0.30 0.58 Surface Soundness (MPa) > 0.9 1.15 24 h Thickness Swelling(%) < 15.0 9.5 Wet Bending A (%) > 4.5 7.4

The AS/NZ standards do vary for the particleboards that are manufactured for flooring applications compared to those moisture-resistant or standard particleboards that are manufactured for wall panelling or furniture. For example, the required standard for Modulus of Elasticity (MOE) is higher for particleboards used for flooring (>2850 MPa) than for moisture-resistant purposes (>1800 MPa); the standard for Modulus of Rupture (MOR) is higher for flooring (>20.0 MPa) than for moisture-resistant purposes (>12.0 MPa); and the standard for the Internal Bond (IB) must be higher for flooring (> 0.65 MPa) than for moisture-resistant purposes (>0.30 MPa).

The Examples demonstrate that the standards may be met and the properties manipulated depending on the end use of the product.

Description of the Figures

[0072] Figure 1 relates to a cross section of a typical three-layered structure having a core central layer, surrounded by two surface layers. The particle size mix within the surface layers is smaller than that in the core layer.

[0073] Figures 2-9 show graphs representing various properties of particleboards manufactured in accordance with the process of the invention for a 16mm moisture resistant particleboard that will have an end use for wall panelling or furniture. Each graph shows a particular physical property of the particleboard where the particleboard includes 0% added bamboo to 100% bamboo.

[0074] The results represent three-layered particleboards produced with a surface/core/surface structure; the three-layered structure is from the particleboard pressed as a whole. The particleboards of the Examples satisfy the AS/NZS standards for moisture resistant and flooring particleboards.

[0075] Figure 10 is a graph showing typically slenderness ratios by chip type for both wood and bamboo particles

[0076] The statistical tests were conducted per ANOVA, relative to a 0% bamboo, 100% wood control, as marked in red on each graph. The use of * indicates p<.05.** indicates p<.01 and ***indicates p<.001 levels of statistical significance. Results shown as a mean, 95% confidence interval.

[0077] In Figure 2, the density in Kg/m3 is shown against the % of bamboo. A target of 635 Kg/m3 would be aimed for. The graph indicates results ranging from 610 Kg/m3 (10% bamboo) to 670 Kg/m3 (90% bamboo) were obtained which compared to the control 615 Kg/m3 with 100% wood particles in lab samples.

[0078] In Figure 3, the thickness of the particleboard is shown compared to the

% of bamboo. A target for the thickness would ideally be 16mm for a three-layered structure. The results produced a particle board ranging from 14.6mm (90% bamboo) to 16.4mm (30% bamboo)

[0079] In Figure 4, the Modulus of Elasticity (MOE) is shown against the % of bamboo. The results range from 2700 MPa to 3900 MPa with the control of 100% wood being 3100 MPa.

[0080] In Figure 5, the Modulus of Rupture (MOR) is shown against the % of bamboo. The results vary from approximately 16 MPa to 20 MPa which all appear in excess of 100% wood (16 MPa)

[0081] In Figure 6, the Internal Bond strength is shown against the % of bamboo with results ranging from 0.62 MPa to 0.49 MPa which were all less than for the control of 100% wood (0.63 MPa). Each was is in excess of the AS/NZS standard of 0.3 MPa

[0082] In Figure 7, the Surface Soundness is shown with results ranging from 1.0 MPa to 1.3 MPa which again is in excess of the AS/NZS standard of >0.9 MPa

[0083] In Figure 8, the Wet Bending is shown with results ranging from 6.0 MPa to 7.8 MPa which again is in excess of the AS/NZS standard (> 4.5 MPa)

[0084] In Figure 9, the 24-hour thickness swelling is shown with results ranging from 8.0 to 11.5 (%) which is less than the required standard of 15%

[0085] In Figure 10, the slenderness ratio for both the bamboo and wood particles is shown demonstrating the higher slenderness ratio for the bamboo particles. This is believed to assist in contributing to the properties for the particleboards of the invention.

[0086] The bamboo/wood composite particleboard panels demonstrated comparable performance to 100% wood particleboards in almost all mechanical properties apart from MOR. Particleboards in the optimal range of 20-40% bamboo had a significant increase in MOR (18.9-20.4 MPa) relative to 100% wood control (16.1 MPa) per Fisher's LSD test. The high slenderness ratio of bamboo particles leads to an increase in MOR, due to increased interparticle overlap in the composite matrix. However, where the bamboo content was greater than 50%, these positive effects were countered by the increased surface area of particles which led to excess resin absorption so less resin was available for interparticle bonding.

[0087] It was however significant that all moisture resistant boards produced with 10-100% bamboo content passed all AS/NZS standards as outlined in 1859.1:2017. Moreover, particleboards with the preferred bamboo ratio of 20:80 to 40:60 bamboo to wood were shown to have no significant reduction in properties, or noticeable production difficulties, relative to the 100% wood control. These findings point to the capability of bamboo as a direct substitute for softwood, in these preferred ratios, with no modification required to existing production settings

Claims

1. A process for the manufacturing of a particleboard, said process including the steps of chipping virgin bamboo culm to a size less than 120mm, drying the bamboo chips to a moisture content of approximately 40-150% of oven dried mass, preferably 80-120% of oven dried mass, flaking and milling the bamboo chips to produce particles and optionally mixing with wood particles, where predominantly all particles are flaked and milled to a size of from 0.1 to 10mm; and drying the particles to a moisture content of from 1-10%, preferably 2-3%.

2. A process according to claim 1 wherein the dried particles are then sprayed and mixed with a resin and forming the resinated particles into a mattress and hot pressing to form a particleboard sheet.

3. A process according to claim 1 or 2 wherein the formed mattress is pressed between the platens of a discontinuous or daylight hot press for 1-5 minutes, preferably 3-4 minutes at 150-200C and a max pressure of 300 bar to form the particleboard sheet or alternatively the resinated particle mix is formed into a mattress of a continuous hot press at a line speed of 50 - 2,000 mm/s to form the particleboard.

4. A process according to anyone of claism1 to 3 wherein the bamboo particles are mixed with wood such that the ratio between the bamboo to wood is in the ratio of from 10:90 to 60:40, preferably 20:80 to 40:60.

5. A process according to anyone of claims 1 to 4 wherein the virgin bamboo culm is chipped to a size of between 40-60mm long, 20-40mm wide and 10 15mm thick.

6. A process according to anyone of the preceding claims wherein the bamboo chips have a high slenderness ratio compared to the wood chips.

7. A process according to claim 6 wherein the slenderness ratio of the bamboo particles is from 30-40, preferably 34-36 and the slenderness ratio of the wood particles is from 24-32, preferably 27-29.

8. A process according to anyone of the preceding claims wherein the particleboard is constructed in 3 layers having a core layer and 2 surface layers, the particles having been screened and separated according to size such that the size distribution of the bamboo and wood particles in the surface layer is from approximately 0.25-8.00mm, and the particle size of the bamboo and wood particles in the core layer is from 0.25-10.0mm; the particles are then sprayed with the resin, the resinated particles are then formed into a mattress of layers surface/core/surface and hot pressed to form the particleboard sheet.

9. A process according to claim 8 wherein more than 70% of particles in the surface layers have a particle size of from 0.25 to 1.25mm and more than 40% of the particles in the core layer have a particle size of in the 1.25-2.88mm range.

10. A process according to anyone of the preceding claims wherein the wood particles are sourced from a softwood, preferably pine, more preferably hoop pine (Araucaria cunninghamii) or slash pine (Pinus elliottii); the bamboo particles are from the culm of a fast growing, clumping (sympodial) species having low silica/grit of less than 1.5%, preferably Bambusa oldhamii, Phyllostachys pubescens or Phyllostachys edulis.

11. A process according to anyone of the preceding claims wherein the resin comprises one or more of MUF, phenol formaldehyde (PF), UF, PMDI, non formaldehyde resins such as latex, acrylic, epoxy, thermoplastic polymers or copolymers, bioresins, biobased adhesive systems such as soy-based proteins, lignin resins, and/or animal protein-based adhesives, or the resin resin system includes waterborne-acrylics, polyvinyl chloride, thermoplastic polymers and copolymers, polyvinyl alcohol (PVOH), bio-resins such as polylactic acid (PLA), polyhydroxyl butyrate (PHB) and others, or epoxy resins..

12. A process according to anyone of the preceding claims wherein the resin is a moisture resistant resin, preferably a modified melamine urea formaldehyde resin.

13. A process according to claim 12 where in the resin has a solids content of from a loading of 8-20%, preferably 10-15% in the surface layers, and 5-15%, preferably 6-10% in the core layer based on the solid resin relative to dry weight of the bamboo/wood

14. A process according to anyone of the preceding claims wherein a hardener, wax and water are added together or in conjunction with the resin.

15. A process according to claim 13 wherein the hardener is an acidic catalyst of pH < 6 and optionally includes a crosslinker, preferably a urea.

16. A process according to anyone of the preceding claims wherein urea, ammonium sulphate and/or ammonium chloride solution is further sprayed onto the wood/bamboo flakes, the ammonium sulphate and/or ammonium chloride solutions having a solids content of 25-40% with loadings of 1-2% for the surface layers and a 3-5% for the core layer.

17. A process according to anyone of the preceding claims wherein the water is applied such that the resinated particles for the surface layers reach a moisture level of from 12-17% and the resinated particles for the core layer reach a moisture content of 8-12%.

18. A particleboard comprising a lignocellulosic material selected from bamboo or a mix of bamboo and wood particles; wherein if the material is a mix of bamboo and wood particles, the bamboo to wood ratio is from 10:90 to 60:40, preferably 20:80 to 40:60, the bamboo being sourced from virgin bamboo culm; the bamboo and optionally the wood particles having been prepared by chipping to a size of less than 120mm, preferably from 40-60mm long, 20 40mm wide and 10-15mm thick; dried, and mixed with the wood particles, then flaked and/or milled such that predominantly all particles are of a size of from 0.1mm to 10mm, the slenderness ratio of the bamboo is higher than that of the wood; the particle mix further comprising one or more resins.

19. A particleboard according to anyone of claim 18 wherein the resin is composed of one or more of the following: melamine urea formaldehyde (MUF), phenol formaldehyde, urea formaldehyde (UF), PMDI, non-formaldehyde resins such as latex, acrylic, epoxy, thermoplastic polymers and copolymers, bioresins, or biobased systems such as soy-based proteins, lignin resins, and/or animal protein-based adhesives.

20. A particleboard according to claim 18 or 19 wherein the slenderness ratio of the bamboo particles is from 30-40, preferably 34-36 and the slenderness ratio of the wood particles is from 24-32, preferably 27-29.

21. A particleboard according to claim 18, 19 or 20 wherein the wood particles are sourced from a softwood, preferably pine, more preferably hoop pine (Araucaria cunninghamii) or slash pine (Pinus elliottii); the bamboo particles are from the culm of a fast growing, clumping (sympodial) species having low silica/grit of less than 1.5%, preferably Bambusa oldhamii, Phyllostachys pubescens or Phyllostachys edulis.

22. A particleboard according to anyone of claims 18 to 21 wherein the particleboard is constructed in 3 layers having a core layer and 2 surface layers, the size distribution of the bamboo and wood particles in the surface layer is from approximately 0.25mm to 8.00mm with more than 70% of the particles within the range of from 0.25mm to 1.25mm; and the size distribution of the particles in the core layer is from 0.25mm to 10.0mm with more than 40% within the range of from 1.25 to 2.8mm.

23. A particleboard according to anyone of claims 18 to 23 wherein the particle mix further includes a hardener, wax and water.

24. A particleboard according to claim 24 wherein the hardener is an acidic catalyst of pH < 6 and optionally includes a crosslinker, preferably a urea.

25. A particleboard according to anyone of claims 22 to 24 wherein a urea and ammonium sulphate or ammonium chloride solution is sprayed into the wood/bamboo flakes, having a solids content of 25-40% with loadings of 1-2% for the surface layers and a 3-5% for the core layer.

26. A particleboard according to claim 24 wherein the wax is paraffin wax having a solids content of 40-75%, more preferably 50-65% and is sprayed into the bamboo/wood flakes at a loading of from 0.5-4%, preferably 0.5-2%.

27. A particleboard according to anyone of claim 22 to 26 wherein the moisture level for the surface layers in the final product is from 12-17% and the moisture level for the core layer is from 8-12%.

28. A particleboard according to anyone of claims 18 to 28 wherein additives are incorporated during manufacture to provide properties such as flame retardance, moisture resistance, termite resistance, acoustic properties, or improved insulation performance.

29. A particleboard according to anyone of claims 18 to 29 wherein the particleboard is moisture resistant.

30. Articles such as flooring, wall and ceiling linings, furniture and cabinetry made from the particleboard according to anyone of claims 18 to 30.

Figure 1 1/9

Figures

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Figure 9

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