WO2018193398A1 - Pressed board products - Google Patents

Pressed board products Download PDF

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Publication number
WO2018193398A1
WO2018193398A1 PCT/IB2018/052715 IB2018052715W WO2018193398A1 WO 2018193398 A1 WO2018193398 A1 WO 2018193398A1 IB 2018052715 W IB2018052715 W IB 2018052715W WO 2018193398 A1 WO2018193398 A1 WO 2018193398A1
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WO
WIPO (PCT)
Prior art keywords
silicate
precursor mixture
geopolymerisation
weight
pressing
Prior art date
Application number
PCT/IB2018/052715
Other languages
French (fr)
Inventor
Michael Windsor Symons
Tebogo Ankie KHOZA
Goddeti Siva Mohan REDDY
Steven CHIUTA
Original Assignee
Zetland Technologies Limited
Van Der Walt, Louis, Stephanus
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to US201762487816P priority Critical
Priority to US62/487,816 priority
Application filed by Zetland Technologies Limited, Van Der Walt, Louis, Stephanus filed Critical Zetland Technologies Limited
Publication of WO2018193398A1 publication Critical patent/WO2018193398A1/en

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Classifications

    • CCHEMISTRY; METALLURGY
    • C04CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04BLIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/24Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing alkyl, ammonium or metal silicates; containing silica sols
    • C04B28/26Silicates of the alkali metals
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B27WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27NMANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
    • B27N3/00Manufacture of substantially flat articles, e.g. boards, from particles or fibres
    • B27N3/002Manufacture of substantially flat articles, e.g. boards, from particles or fibres characterised by the type of binder
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B27WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27NMANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
    • B27N3/00Manufacture of substantially flat articles, e.g. boards, from particles or fibres
    • B27N3/04Manufacture of substantially flat articles, e.g. boards, from particles or fibres from fibres
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B27WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27NMANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
    • B27N3/00Manufacture of substantially flat articles, e.g. boards, from particles or fibres
    • B27N3/08Moulding or pressing
    • B27N3/18Auxiliary operations, e.g. preheating, humidifying, cutting-off
    • CCHEMISTRY; METALLURGY
    • C04CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04BLIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/006Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing mineral polymers, e.g. geopolymers of the Davidovits type
    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21JFIBREBOARD; MANUFACTURE OF ARTICLES FROM CELLULOSIC FIBROUS SUSPENSIONS OR FROM PAPIER-MACHE
    • D21J1/00Fibreboard
    • D21J1/04Pressing
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P40/00Technologies relating to the processing of minerals
    • Y02P40/10Production of cement, e.g. improving or optimising the production methods; Cement grinding
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02WCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00Technologies for solid waste management
    • Y02W30/50Reuse, recycling or recovery technologies
    • Y02W30/91Use of waste materials as fillers for mortars or concrete

Abstract

A method of producing a pressed board product of a predetermined thickness specification includes subjecting a predetermined mass per unit area of a precursor mixture to pressing in a press, at a predetermined pressing force with or without the application of heat. The precursor mixture comprises particulate material, an alkali metal silicate, polyvinyl alcohol, and a geopolymerisation promoter for promoting geopolymerisation of the alkali metal silicate. The method includes, prior to and/or during and/or after subjecting the precursor mixture to the pressing, allowing at least partial setting by geopolymerization of the alkali metal silicate.

Description

PRESSED BOARD PRODUCTS
FIELD OF THE INVENTION
THIS INVENTION relates to pressed board products. The invention provides a method of producing a pressed board product. The invention also provides a precursor mixture for producing a pressed board product. The invention extends to using the precursor mixture to produce a pressed board product, and to pressed board products produced in accordance with the method of the invention.
BACKGROUND TO THE INVENTION
PRESSED BOARD PRODUCTS typically include fibreboard, which comprises a plurality of fibres, typically wood fibres, which are bound by a binder, and particleboard, which comprises a plurality of non-fibrous particles, e.g. wood shavings, wood chips, sawdust and the like, also bound by a binder.
Natural fibres and particles, i.e. those of plant origin, typically from waste streams thereof, exhibit excellent potential for use in the production of pressed board products. Examples are bamboo, sisal, kenaf, coir, flax, cotton, pulped cellulose fibre, milled dry paper waste streams, paper mill sludge, exploded or defibrated fibres (such as those obtained from defibrating medium density fibre board, such as that used in the furniture industry), the fibres of many grasses, and woodchips or pieces of peeled veneer (such as those that are used in producing orientated strand board or wafer board). While the abovementioned materials therefore have the potential to find application in the manufacture of pressed board products, they have a marked tendency to absorb water, i.e. are hydrophilic, which can be regarded as their greatest shortcoming. Water absorption by these materials result in changes in their dimensions, e.g. through swelling. In a pressed board product, this tendency could give rise to wet/dry structural instability or an increased coefficient of expansion, as is characteristic of cement fibre boards in which cellulose fibres, particularly those sourced from the soft wood pulps, are typically included. Water absorption can therefore lead to a dramatic in loss in strength and binding properties of these materials.
Most pressed board products are manufactured from wood fibres or particles. Wood typically has a composition of approximately 40 to 45% cellulose, 20 to 30% hemi- cellulose and 20 to 30% lignin. Wood also contains fluctuating amounts of other components in small proportion such as resins, fats, comprising of mono, di and tri glycerides, waxes, tannins and sterols.
Pressed board products made from wood fibres or particles find extensive application in the furniture industry, in which the products are laminated or otherwise decorated, and manufactured in a form ready to use as furniture components in automated or semi-automated processes. In the applicant's experience, approximately 70% of all particle board, based on wood chips, that is manufactured is used in furniture. Of these, approximately 85% use urea formaldehyde as binder. Urea formaldehyde is a water-based thermosetting resin, typically used at 10%o based on the weight of the solid resin and the weight of the wood chips. Products are typically three-layered. The chips are dried to a relative humidity of approximately 1 to 5% prior to blending with the binder, and the chips of the inner layer would then typically have a lower relative humidity, e.g. of approximately 2%. The binder concentration is typically 10 to 12% in the outer layers and 7 to 9% in the inner layer. After blending the urea formaldehyde with the chips, they have a relative humidity of approximately 8 to 18%. In making the particle board, the blend is pressed between the platens of a press, typically in a continuous process using double belt stainless steel belts, which are heated to a temperature between 200° & 220°C. Dwell time between the belts is typically from 6 to 25 seconds per millimetre thickness, depending upon the binder formulation and the density. Press pressures are approximately 1 to 2 newton per square millimetre, but may be as high as 3.5 newton per square millimetre, depending upon the desired board density. During the pressing operation, surface moisture turns to steam and is driven into the core of the board, raising the core temperature to 100°C or greater. This is referred to as "steam-shock", and is critical to the curing of the board and to minimize the dwell time of the board in the press. However, even at a dwell time of 8 seconds per millimetre thickness, a 16mm thick particle board will require over 2 minutes in the press which, if it is running at a speed of 20 metres per minute, will require a press 40 meters or longer in length. Presses suited to this specification are very expensive. The energy required as well as the capital is very high and requires mass production to be competitive. Properties of particle board are typically a specific gravity of 650kg per cubic meter, and internal bond when dry of 0.5 newton per square millimetre, and a thickness swell of 17% or greater when wetted. It is only those boards that comply with the EU Standard V100 that are suitable for extended exposure to moisture, and this is not possible with urea formaldehyde without the addition of a phenolic resin or an isocyanate. Masonite, a specific type of fibreboard, can be de-fibrated, i.e. the fibres thereof separated from each other, by steaming it for 40-seconds at 210°C, and at a pressure of 2 to 4 newton per square millimetre, or alternatively for 5-seconds at 285°C, followed by explosion like steam pressure reduction. The fibres in water are now deposited on a de-watering screen for moulding in a multi daylight press. The pressing time is approximately 2 to 3.5 minutes per millimetre thickness at a temperature 180-200°C. Typical densities of hardboard are from 0.9 to 1.2 grams per cubic centimetre, or for special densified hardboard 1.2 to 1.45 grams per cubic centimetre. Those that are passed through an emulsified oil bath are referred to as "tempered" and are used in wet or high relative humidity circumstances.
Medium density fibre board, on the other hand, can be de-fibrated in an "Asplund" de- fibrator involving 2 to 5 minutes of steam in a pre-heater at 160 to 185°C, and at a pressure of 0.6 to 1.2 newton per square millimetre pressure. After de-fibration, the fibres are dried or semi-dried before resins are applied. The quality is inferior to wet processed products, which are made with Fourdrinier belt principles, similar to the paper making process. Medium density fibre boards are difficult to resinate and pressures and temperatures for dry and semi dry processes are higher than those for the wet process, typically in the region of 7 newton per square millimetre and 200 to 250°C. Typical densities of medium density fibre board are from 0.6 to 0.8 grams per cubic centimetre. They are characterised by a very uniform fibre distribution throughout their thickness and lend themselves to moulded and laminated cabinet doors and other furniture components requiring reliable lamination, and especially edging, and which can be machined to a very high standard. As in the case of particle board, the principle binder used is urea formaldehyde. In the case of wet process products such as Masonite, no binder is added, but cellulose and lignin polymerization takes place at the elevated temperatures and pressures involved, and with the extended time in the press.
In the manufacture of particle board in the application of the binder, a given drop of binder is not captured by an individual wood chip, but rolls from chip to chip leaving a thin glue track. The glue is distributed in a way that only discreet chip areas are covered and glued together, and thus the binder to feedstock ratio is economic. Resination of the bulky dry or semi dry de-fibrated fibres used in medium density fibre board is much more difficult, and the process involves much higher energy than is required for particle board.
It is quite clear from the description above, that the manufacture of pressed board products can be very energy and capital intensive. The relatively high temperatures for the polymerization or setting of the binders, the dwell time in the equipment, the expense of the equipment and, in the case of fibre board products, the requirement for de-fibration, at very high temperatures, all contribute to the high use of energy and capital, and which requires the most rapid production possible. Further challenges are the emission of free formaldehydes, in spite of modern scavengers, if resin cure is not sufficiently complete, the susceptibility of the product to swell in thickness and degrade when subjected to water wetting, and also poor behaviour in fire.
Having regard for the compositions and processes described, there is clearly a need for a new process and composition for the production of pressed board products that minimizes the use of energy, and which may be produced at an economical speed, thereby dramatically reducing both the cost of the equipment and the dwell time of the product in the equipment during the production process, which would allow for the building of micro plants, close to the source of biomass, which can for example employ local, and possibly rural, communities as a vertically integrated enterprise. Considerable amounts of waste material in the form of paper mill sludge, milled disposed pallets, plywood, chipboard, agricultural stovers, sawmill waste and woodworking waste from the furniture industry are available for this purpose.
What is therefore required is a product composed mainly of wood or lignocellulosic particles that can be processed at room temperature, with a short dwell time in a press, that is water resistant, and that may use biomass waste streams that have been appropriately milled to optimum aspect ratio and to which, if necessary, a synthetic fibre may also be added, such as milled carpet or textiles, and which after drying is highly resistant to combustion. It is in this respect that the present invention seeks to find application. SUMMARY OF THE INVENTION
IN ACCORDANCE WITH ONE ASPECT OF THE INVENTION IS PROVIDED a method of producing a pressed board product of a predetermined thickness specification, the method including
subjecting a predetermined mass per unit area of a precursor mixture, comprising
particulate material,
an alkali metal silicate,
polyvinyl alcohol, and
a geopolymerisation promoter for promoting geopolymerisation of the alkali metal silicate, to pressing in a press, at a predetermined pressing force with or without the application of heat; and
prior to and/or during and/or after subjecting the precursor mixture to the pressing, allowing at least partial setting by geopolymerization of the alkali metal silicate.
That pressing takes place with or without the application of heat therefore includes respectively that pressing takes place at ambient temperature without the intentional application of heat to the precursor mixture during pressing, and that pressing takes place at a temperature elevated relative to ambient temperature, through the intentional application of heat to the precursor mixture during pressing.
The pressed board product may be obtained directly after having subjected the precursor mixture to the pressing.
The method may include, after having subjected the precursor mixture to the pressing, allowing setting of the alkali metal silicate by geopolymerisation to go to completion, if it had not yet gone to completion during pressing. The pressed board product may then be obtained directly after setting of the alkali metal silicate by geopolymerisation has gone to completion.
The method may also or alternatively include, after having subjected the precursor mixture to the pressing and, if applicable, after having allowed setting of the alkali metal silicate by geopolymerisation to go to completion after pressing, allowing or causing drying of the precursor mixture by desiccation. The pressed board product may then be obtained directly after drying of the precursor mixture. It is noted that the term "particulate material" includes fibres, flakes, flat ply peelings or shavings (such as that used in oriented strand board, or "OSB"), and chips, in addition to the forms of material that is conventionally understood when referring to "particles".
The particulate material may be selected from organic material, or biomass, inorganic material, and mixtures thereof. Preferably the particulate material is organic material, and more preferably organic material that is cellulosic or lignocellulosic.
In the case of organic material in fibrous form, the preferred particle size is a fibre length of up to about 10mm. In the case of organic materials in particulate form, e.g. flakes and/or peelings, the preferred particle size is from about 150 microns to about 3mm, typically referring to its maximum dimension. It is preferred that the fibres and particles have as high an aspect ratio as possible.
In the case of inorganic particles, a particle size in the range of from about 1 to about 500 microns, or up to about 2mm in diameter is typical, but more preferred is in the range of about 1 to about 75 microns, with an average of 40 microns or less.
Organic material, or biomass, may for example include or be obtained from
waste wood, e.g. from waste pallets, waste plywood, waste chipboard, sawmill waste, woodworking waste, and wooden furniture waste;
organic material contained in waste streams of the paper industry, such as primary paper mill sludge, optionally using milled dry waste paper as a sorbent, or dried paper mill waste; agricultural stovers, e.g. grass species such as wheat, rice, barley and oats; fibrous plant material, e.g. kenaf, sisal, coconut coir, cotton, bagasse, acacia, jute, flax, hemp, pulp (preferably coniferous), or wood chips or fibres,
and mixtures of any two or more thereof.
Inorganic material may typically include or be obtained from waste milled carpets or textiles, and the like.
The alkali metal silicate may be selected from sodium silicate, potassium silicate and mixtures thereof. The sodium silicate and potassium silicate may, independently, be provided as aqueous solutions thereof. Thus, reference to "sodium silicate" and "potassium silicate" should be understood as including reference to aqueous solutions thereof. The sodium silicate may be a sodium silicate with a S1O2 to Na20 ratio of from 3.3: 1 to 2: 1. In the case of an aqueous solution of sodium silicate, the sodium silicate may for example be provided in a concentration of from about 1 % to about 40% solids by weight. For example, the sodium silicate may be selected from sodium silicates 3379 to 2040 by PQ Corporation.
The sodium silicate may typically be present in the precursor mixture in a concentration of from about 7% to about 30% by weight based on the weight of the particulate material on a dry basis. The potassium silicate may be a potassium silicate with a S1O2 to K2O ratio of from 2.55: 1 to 1.45:1 . In the case of an aqueous solution of potassium silicate, the potassium silicate may for example be provided in a concentration of from about 1 % to about 30% solids by weight. For example, the potassium silicate may be selected from potassium silicates K2550 and K1420 by PQ Corporation. The potassium silicate may typically be present in the precursor mixture in a concentration of from about 7% to about 15% by weight, based on the weight of the particulate material on a dry basis.
Preferably, the precursor mixture comprises sodium silicate and potassium silicate as the aqueous solutions thereof. For example, the precursor mixture may comprise, of sodium silicate and potassium silicate, 3 parts of sodium silicate to 1 part of potassium silicate, referring to the aqueous solutions thereof.
The geopolymerisation promoter may be an oxide, typically being selected from metal oxides, silicon oxide, and a combination thereof.
The geopolymerisation promoter may be provided by a geopolymerisation agent. The geopolymerisation agent may consist of the geopolymerisation promoter. More typically, however, the geopolymerisation agent may comprise the geopolymerisation agent as one component of a plurality of components / ingredients thereof. In particular, the geopolymerisation agent may be selected from fly ash, metakaolin, and a combination thereof.
The geopolymerisation agent, particularly when it is flyash, may typically be one that has a 65% by weight or higher, e.g. up to 75%, content of the oxides of silicon (typically as silica), iron and aluminium. The precursor mixture may comprise from about 5% to about 30% by weight, more preferably from about 8% to about 20% by weight, or more preferably up to about 15% by weight of the geopolymensation agent, based on the weight of the particulate material on a dry basis.
Reaction between the geopolymerisation promoter and the alkali metal silicate typically causes rapid setting of the precursor composition due to geopolymerisation of the alkali metal silicate, typically within 20 to 90 seconds from mixing thereof with the alkali metal silicate. This setting provides a cohesive mass comprising the particulate material of the precursor mixture therein.
The geopolymerisation agent may optionally be modified by, i.e. may include, caustic soda and/or sodium hydroxide.
The polyvinyl alcohol may be partially hydrolysed with a degree of hydrolysis less than 90. Preferably, the polyvinyl alcohol would be in aqueous solution. Typically, in aqueous solution, the polyvinyl alcohol would have a solids concentration between 5 wt.% and 30 wt.%, but more preferably between 10 wt.% and 20 wt.%.
The precursor mixture may also include aluminium hydroxide, gypsum di-hydrate, ettringite, or a mixture or two or more thereof. Preferably, the aluminium hydroxide is in the form of aluminium hydroxide trihydrate. For example, the ON series by Alcoa may be suitable. The aluminium hydroxide, gypsum di-hydrate, ettringite, or mixture thereof may be in finely divided particulate form. The precursor mixture may include the aluminium hydroxide, gypsum di-hydrate, ettringite, or mixture thereof in a proportion of from about 5% to about 20% by weight, more preferably from about 7% to about 12% by weight, based on the weight of the particulate material on a dry basis. The aluminium hydroxide, gypsum di-hydrate, ettringite, or mixture or two or more thereof acts as a coolant in fire by releasing water vapour and removes its latent heat of vaporisation from the pressed board product in fire. It also acts as a refractory, minimizing particulate emissions in fire.
The precursor mixture may also include pigments, preferably in dry micronized form. For example, iron oxide, such as Bayferrox by Bayer, preferably red oxide, may be added. Such pigments may further mitigate against combustion of the pressed board product and aid binding of the precursor mixture by the alkali metal silicate, but primarily impart a uniform, more pleasing appearance on the pressed board product and signifies, by colour distinction, a non-combustible pressed board product. The precursor mixture may also include gauging water, if necessary, to ensure intimate surface wetting of particulate material. Typically, however, most of the wetting would be provided by the aqueous alkali metal silicate solution/s.
The precursor mixture may also include a liquid isocyanate. The isocyanate may be present in a concentration of from about 0.5% to about 4% by weight, more preferably from about 1 % to about 3% by weight, based on the weight of the precursor mixture on a dry basis, including the isocyanate. Typically, the isocyanate may be added to the alkali metal silicate solution, or to a mixture of the alkali metal silicate solution and the particulate material. The isocyanate may, for example, be Duthane 5005 by Industrial Urethanes of the AECI group, which is better described as a diphenylmethane diisocyanaate (MDI), isomers and homologues, or diisocyanato diphenylmehanediisocyanate (MDI) based composition.
Typically, in providing the precursor mixture, the particulate material, geopolymerisation promoter typically provided by the geopolymerisation agent, and the aluminium hydroxide, gypsum di-hydrate, ettringite, or mixture or two or more thereof are blended. Thereafter, the alkali metal silicate and hydrophobic agent are added and intimately blended with the mixture of the particulate material, the geopolymerisation promoter typically provided by the geopolymerisation agent, and the aluminium hydroxide, gypsum di-hydrate, ettringite, or mixture or two or more thereof.
The method may include pre-treating the particulate material with a hydrophobic agent, for example a methyl potassium siliconate. The hydrophobic agent may be used in a concentration of from about 0.5% to about 3% in water. It is preferred, for the benefit of the hydrophobic agent, that the particulate material is then first dried with heated CO2, before proceeding to prepare the precursor mixture.
In subjecting the precursor mixture to pressing, the method may include spreading the precursor mixture onto a platen or moving belt, at a predetermined specific mass per unit area, from which it proceeds into the press. The press may, for example, be a daylight or single opening press, accommodating a single or up to fifty or more batches of precursor mixture on platens. The platens may have good release properties, e.g. may be of polyethylene- or Teflon-coated metal. The press may alternatively be a double belt continuous press. Subjecting the precursor mixture to pressing may be for a period that is from about 15 seconds and about 8 minutes, more preferably from about 20 seconds to about 5 minutes, e.g. from about 20 seconds to about 120 seconds. Pressing results in the precursor mixture being compressed into a cohesive sheet, with the silicate having set at least partially through geopolymerisation, without spring- back or volumetric change after pressing. Thus, flammable constituents are encapsulated by the alkali metal silicate and water resistance is imparted to it, thereby producing a flame-resistant water-resistant pressed board product from inherently flammable and hydrophilic particulate material.
The choice of fillers high in oxides of silicon (typically as silica), iron and alumina, of very low bulk density to add volume and therefore influence final density, but which also promote geopolymerisation of the alkali metal silicate, includes hollow glass or siliceous micro cells or balloons.
Some of these are synthetic or expanded Perlite, other are by-products such as high silica fractions of micronized coal burnt in power stations which are recovered, including fly ash. Examples are Cenolite by Ash Resources of South Africa or Filite of Runcorn in Kent, UK.
However a preferred filler is a refined mineral by Silbrico Corporation called Sil-Cell which is a glass micro cellular filler comprising of hollow glass particles whose shapes vary to combine different geometries, both spherical and irregular. These shapes present the advantage of not only low final product density, but reinforcement and impact resistance. Due to the irregular shape of the particles, greater tensile strength is derived and a mechanical key in packing occurs during the processing operation. Each particle consists of multiple minute cells of micro bubbles and the effective specific gravity is in the range 0.18 or 180kg/m3 (bulk density is in line range 20 to 300 grams per litre). The chemical properties of the material are reflected in Table 1 , the physical properties in Table 2, and the typical size distribution in table 3:
Table 1 : Chemical properties of Sil-Cell
Figure imgf000016_0001
Table 2: Physical properties of Sil-Cell
Grades Sil-32 Sil-42 Sil-35 Sil-43
Oil Absorption ASTM-D-1483 gms. Oil per 100cc 30 36 38 40
Hygroscopic Moisture 0 0 0 0
Surface pH 7.0 7.0 7.0 7.0
Thermal Conductivity 0.36 0.40 0.41 0.43
Colour White White White White
Dry Bulk Density, Ib/cu.ft. 7.0 8.5 9.0 10.5
Average Particle Size, Microns 75 45 40 35
Effective Particle Density, Ib./cu. Ft. (g/cm3) 11 .2 15.6 15.6 18.7
(0.18) (0.25) (0.25) (0.30)
Particle Size Range, Microns 1 -300 1 -210 1-150 1-150
Fusion Point (F) 2300 2300 2300 2300 Table 3: Typical particle size distribution of Sil-Cell
Figure imgf000017_0001
Other hollow glass micro spheres are those by Glaverbel of Belgium. These are boro- silicate glass micro bubbles with wall thicknesses of from 1 to 3 microns, filled with an odourless non-toxic gas. These have the registered name Microcel, and grade M28 consists of 73% silicon dioxide, having been surface treated with a silane coupling agent and have a bulk density of 0.17, a particle size as low as 5 microns, a softening temperature of 800°C, a compressive strength of 140 bar and a thermal conductivity of 0.055.
A further candidate, which was mentioned above, is Cenolite, which is a lightweight vitreous hollow sealed sphere produced as a by-product from pulverised coal burnt in power stations. These have a silicon dioxide content of 51 % and an aluminium oxide content of 40% by mass. The bulk density at 450g/£ is high for the purpose of the invention, but they have a melting point of 1250°C which is at the high end of the melt spectrum due to the high aluminium oxide percentage.
Filite of Runcorn, Cheshire of the U.K. is a similar product. Particle sizes of these spheres tend on average to be larger than glass micro balloons, but range from as low as 3μ up to 300, with a mean in the range 50 to 200. A particularly suitable geopolymensation agent is fly ash of the analysis set out in Table 4:
Table 4: Fly ash analysis
TEST CERTIFICATE for Class S Fly Ash (SFA)
The values shown below are from results obtained on WEEK 42, 2015, taken from our onqoina qualitv manaaement systems as reauired bv the South African National Standard iSANS}
SANS 50450-1 :2011 Fly Ash for Concrete (Siliceous Fly Ash)
Chemical Requirements Tested Specification
percentages SANS 50450-1 :2011
Loss if ignition 1 ,1 Max. 5,0% by mass
Chloride contents (CI ) 0,0 Max. 0,10% by mass
Sulfuric anhydride (SO3) 1 ,0 Max 3,0% by mass
Free calcium oxide ** 1 ,2 Max. 2,5% ** or 1 ,0% by mass
Calcium oxide 6,4% Max. 10,0% by mass
Reactive calcium oxide Not required Calcium oxide < 10%
Reactive silicon dioxide Not required No co-combustion
Si. dioxide, Al. oxide and Ir. oxide Not required No co-combustion
Na2<D (equivalent) Not required No co-combustion
Magnesium oxide ( gO) Not required No co-combustion
Soluble phosphate (P2O5) Not required No co-combustion
Chemical Requirements Tested results Specification
SANS 50450-1 :2011
Fineness retained on the 45 micron sieve 8,0% Max. 12,0% by mass
Activity index 82% Min. 75% @ 28 days
Activity index Due 23/03/16 Min. 85% @ 90 days
Soundness, expansion ** 0mm Max. of 10mm
Particle density 2300kg/m3 Max. ±200kg/m3 of declaration
Initial setting times Not required No co-combustion Water requirement 95 % Max. 95% by mass of control
Chemical Composition Typical percentages
Si02 51 ,6
AI203 30,4
Fe203 2,9
CaO 6,4
MgO 1 ,8
K20 1 ,3
Na Eq = Na2O+(0,658*K2O) 0,9
Ti02 1 ,8
Note that the principal oxides, reactive with alkali silicates are of the order of 85%.
A further hollow glass bubble by 3M is bubble type C15-250 with a nominal average particle density of 0.015mm and an average bulk density in the range 6 to 12 grams/litre and a compressive strength of 17 bar. These are sodium boro-silicate glasses with a softening point in excess of 700°C.
Another example of a glass micro balloon are those by Dicapearl of California, such as the 512 grade, suitable for the method of the invention.
A further lightweight glass balloon is that by Dennert under the trademark Poraver. These beads are of a wide range of diameters and densities. Those suitable for the method of the invention are of a diameter of below 1 mm up to 8mm. They have the further advantage of being alkali resistant, are chemically inert and highly compression stable. For example, granules of Poraver in the size range 2mm to 4mm have a bulk density of 190g/£, have an average pressure value in kN of 14 and pH value in the range 9 to 12. Particle sizes as small as 40μ are available. Poraver is pure glass which is generated from recycling. They have a softening point of 700°C and in the case of those with the lowest bulk densities have thermal insulation properties appropriate to the invention.
Another suitable extender is expanded Perlite. Perlite refers to a siliceous rock. This is a form of volcanic glass which when heated to approximately 800°C or more expansion occurs due to the release of water inside the semi-molten rock. If the expansion is done carefully a closed cell results at a density as low as 90kg/m3, the diameter of which depends on the particle size before expanded. If the rock is milled to a small enough particle size, then it is possible to produce the expanded version in particle sizes appropriate for the method of the invention i.e. 200 micron or smaller. Properties of Perlite are as given in Table 5:
Table 5: Properties of Perlite
Typical Chemical Analysis ' Typical Product Data
Silicon 33.8 Colour White
Aluminium 7.2 G.E. Brightness, % 70-80
Potassium 3.5 Refractive Index 1.47
Sodium 3.4 Specific Gravity 2.2-2.4
Iron 0.6 Apparent or Bulk Density, lb/ft3
gm/cc 5-15
0.08-0.24
PH Neutral
Calcium 0.6 Oil Absorption 120-240* Magnesium 0.2 Softening Point, °F 1800 °C 980
Traces 0.2 Moisture, % <1.0 Water Absorption 195-350*
Oxygen (by difference) 47.5 Ignition Loss, 3hr 1700°F (930C) 1.5% max**
Net total 97.0 Mean Particle Diameter, Microns As
Bound Water 3.0 small as 10***
Total, % 100.0
*lbs (kgs) oil or water/100 lbs (kgs)
** Due to residual combined water
* All analysis are shown in elemental *** Varies with product
form.
A still further inorganic volume extender is exfoliated vermiculite. Vermiculite is sourced from iron bearing phlogopite or biotite. At 900 to 1000°C vermiculite exfoliates when inter lamina water is expelled causing exfoliation and volume extension perpendicular to the lamina plates resulting in 6 to 15-fold expansion and decrease in bulk density from 1000kg/m3 down to 60 to 180kg/m3. The micron grade is of 500 micron to 1 .5mm in size, and may beneficially be blended with bentonite at up to 2% by weight. The pressed precursor mixture that exits the pressing operation are typically trolley stacked to allow the chemistry to go to completion, and are then dried in typically a kiln at ambient temperatures of from 20 to 90°C, after which they are trimmed to exact dimension and sanded to exact thickness. High drying temperatures are avoided in order to minimise board instability during drying.
Optional inclusions in the precursor mixture of the invention include a thermoplastic emulsion, i.e. acrylic dispersible in alkaline media; acid precursors, instead of borates or calcium compounds;
sodium hydroxide (as mentioned);
cement or gypsum as binders and calcium donors;
small particle lightweight extenders, expanded perlite, or exfoliated vermiculite (as mentioned);
metakaolin;
polyvinyl alcohol; and
MDI's or isocyanates auxiliary binders dispersible in an alkaline medium (as mentioned).
Typical ranges of the weight % of components of the precursor mixture are given in table 6:
Table 6: Typical ranges of the weight % of components of the precursor mixture
Isocyanate or MDI resin 0-7
Small particle fly ash and/or metakaolin 7-30
Sodium silicate solution 35 - 70% solids, optionally including caustic soda 10-30
Lignocellulosic furnish or fibrous recycle (carpets or textiles) 25-60
Aluminium trihydrate, gypsum di hydrate or ethingite 5-20
Borax 5% solution 0-6
Polyvinyl alcohol 5-10
Cement or gypsum hemi-hydrate 0-40
Water 0-10
Exfoliated vermiculite micron 0-10
Potassium silicate solution 20% to 30% solids 0-10
Expanded perlite 0-8 Lightweight inorganic volume extenders for density control 0 - 8
Calcium compound or borates 0 - 1
IN ACCORDANCE WITH ANOTHER ASPECT OF THE INVENTION IS PROVIDED a precursor mixture as hereinbefore described for providing a pressed board product. THE INVENTION EXTENDS TO use of the precursor mixture hereinbefore described in producing a pressed board product.
THE INVENTION EXTENDS TO a pressed board product produced in accordance with the method of the invention.
The pressed board product may include
fire rated door cores;
partitioning;
floor substrates;
sheathing and siding;
door liners of hardboard and door cores;
cabinet worktops that resist water swelling;
pallets;
ceiling boards;
walling systems, interior or exterior;
tile backers;
timber frame buildings;
vehicle flooring;
domestic flooring; exterior boarding or signage;
noise attenuation barriers;
fencing;
decking; and
timber on steal frame building system, for exterior or interior walling.
In some cases, the particulate material may have auxiliary binding by either a Portland cement or gypsum hemi-hydrate to product a pressed board product with a density in the range 600 to 1 500kg/m3, more preferably in the range 700 to 1 350kg/m3, for exterior or interior building boards from 9 to 18mm thickness.
In other cases, the pressed board product may be a high density fibre board aimed at competing with hard board or Masonite type products, and may then have high densities between 900 to 1200kg/m3, or ultra-high densities at up to 1400 kg/m3, and thicknesses typically of 4 to 6mm and at 9 and 12mm, usually used as building boards and other building industry components.
The pressed board product may also be a fibrous board product to compete with work tops used in kitchens or laboratories and laminated with high pressure laminates, in such a case comprising a core of approximately 32mm thick, and at densities of 1250kg/m3 and optionally bound additionally with Portland cement.
For specialist wet areas of buildings, the pressed board product may be produced at thicknesses of from 9 to 45mm for the building industry, at densities of from 600 to 900 to 1200kg/m3. As a board for furniture, shopfitting, signage and similar applications, a major proportion of the particulate material may comprise lignocellulosic material.
As has been pointed out, the pressed board products of the invention may be building products that are resistant to fire, and to the escape or em ission of gas and particulates when exposed to flame.
Finally, inorganic particulate materials may, in particular, impart fire resistance, utilizing expanded perlite or exfoliated vermiculite in particular classified as non- combustible, and which may not have any lignocellulosic inclusion.
The pressed board products of the invention are therefore formed by nearly instant cohesion with cold pressing. Application of heat is within the scope of the invention, as mentioned hereinbefore. Where excess water is involved, this is pressed out by the phenomenon of syneresis where excess water is expelled from the sodium silicates, without removing the gel itself.
EXAMPLE TABLE 7 BELOW, gives an example formulation to manufacture a fire-rated particleboard according to the invention.
The following steps are taken to produce this board: 1 ) 350 grams of oven-dried wood chips are measured, and mixed with 250 grams sodium silicate solution 2) 100 grams fly ash, 35 grams aluminium hydroxide, and 25 grams bayferrox are all measured separately and mixed with the wetted wood chips for a predetermined time of 15 seconds
3) The mixture is poured into a mould of predetermined size: 200 MM X 200MM X 50 MM
4) The mixture is then pressed at ambient temperature with a specifical press pressure of 30 kg-f/cm2 for 75 seconds, after which the board is demoulded.
Table 7: Example formulation for firerated particleboard of size 200 MM X 200MM X16 MM and board density 1000 kg/m3
Resin Resin Cost
Solid Content Mass (g) Loading (%) (US$/m3 wood)
Wood 97,00% 350 0 0
Sodium Silicate 47% 250 34,61 % 40,2
Aluminium hydroxide 100% 35 10,31 % 21 ,9
Fly Ash 100% 100 29,5% 2,8
Bayferrox 6I0 100% 25 7,36% 39, 1
104
In this case, the board produced has a density of 1000 kg/m3. The composition of the resin to bind the wood chips together comprised 34% sodium silicate, 10% aluminium hydroxide, 30% fly ash, and 8% bayferrox.
A total resin cost of US$104 would be required to produce 1 m3 of the fire-rated particleboard using this example formulation. DISCUSSION
THE SODIUM SILICATES are the preferred alkali silicate solutions used in the method of the invention, because of their ready availability, low cost, refractoriness and ability to intumesce in fire.
The invention exploits the synergistic binding contributed by reactive inorganic particles high in the oxides of silicon (typically as silica), iron and aluminium on the one hand and the sodium silicate on the other, both of which can be subjected to setting or gelling process further controlled, if need be, by the use of a complex forming agent such as borates, but in particular the rigidity and dispersion imposed by the alkali silicate and the synergistic gelling of the alkali silicate with di acid sodium hydroxide ester, or other acid precursor or alkali metal compound, particularly calcium components, in the water or disperse continuous phase of the binder components. This allows the precursor composition to be pressed cold, without excluding the possibility to apply heating, in a press in which cohesion and board forming is very rapid. The completion of the chemical binding and the subsequent evaporation of free water are inexpensive and lend themselves to small plants distant from alternative conversion facilities such as particle board plants.
The invention is particularly suitable for maximizing the use of waste streams such as virgin paper mill sludge, optionally blended with virgin long fibres, and recycled paper sludge, suitably shredded to optimise the composite make-up, or synthetic waste such as carpet and textiles. Further waterproofing may be achieved by the additional of additional water proofing agents such as wax emulsions in the water medium. Another option are the siliconates such as Silres® BS16 by Wacker Silicones, which is an aqueous solution of potassium methyl siliconate used in diluted form; the active substance so formed is a polymethylsilicic acid. This type of water proofing suits the preparation of product in an aqueous media, which is the case in the present method of the invention.

Claims

1. A method of producing a pressed board product of a predetermined thickness specification, the method including
subjecting a predetermined mass per unit area of a precursor mixture, comprising
particulate material,
an alkali metal silicate,
polyvinyl alcohol, and
a geopolymerisation promoter for promoting geopolymerisation of the alkali metal silicate,
to pressing in a press, at a predetermined pressing force with or without the application of heat; and
prior to and/or during and/or after subjecting the precursor mixture to the pressing, allowing at least partial setting by geopolymerization of the alkali metal silicate.
2. The method according to claim 1 , wherein the pressed board product is obtained directly after having subjected the precursor mixture to the pressing, without further treatment.
3. The method according to claim 1 , which includes, after having subjected the precursor mixture to the pressing, allowing setting of the alkali metal silicate by geopolymerisation to go to completion.
4. The method according to claim 3, wherein the pressed board product is obtained directly after setting of the alkali metal silicate by geopolymensation has gone to completion.
5. The method according to claim 1 or claim 3, which includes, after having subjected the precursor mixture to the pressing and, if applicable, after having allowed setting of the alkali metal silicate by geopolymerisation to go to completion after pressing, allowing or causing drying of the pressed precursor mixture by desiccation.
6. The method according to claim 5, wherein the pressed board product is obtained directly after drying of the pressed precursor mixture.
7. The method according to any of claims 1 to 6, wherein the particulate material is selected from organic material, inorganic material, and mixtures thereof.
8. The method according to claim 7, wherein the particulate material is organic material, and is selected from organic material that is cellulosic or lignocellulosic.
9. The method according to any of claims 1 to 8, wherein the alkali metal silicate is selected from
sodium silicate, optionally in aqueous solution;
potassium silicate, optionally in aqueous solution; and
mixtures thereof.
10. The method according to claim 9, wherein the sodium silicate is a sodium silicate with a S1O2 to Na20 ratio of from 3.3:1 to 2:1.
1 1. The method according to claim 9 or claim 10, wherein the sodium silicate is in the form of an aqueous solution of sodium silicate, and the aqueous solution of sodium silicate comprises the sodium silicate in a concentration of from about 1 % to about 40% solids by weight.
12. The method according to any of claims 9 to 11 , wherein the sodium silicate is present in the precursor mixture in a concentration of from about 7% to about
30% by weight based on the weight of the particulate material on a dry basis.
13. The method according to claim 9, wherein the potassium silicate is a potassium silicate with a SiC to K2O ratio of from 2.55:1 to 1.45:1 .
14. The method according to claim 9 or claim 13, wherein the potassium silicate is in the form of an aqueous solution of potassium silicate, and the aqueous solution of potassium silicate comprises the potassium silicate in a concentration of from about 1 % to about 30% solids by weight.
15. The method according to claim 9 or claim 13 or claim 14, wherein the potassium silicate is present in the precursor mixture in a concentration of from about 7% to about 15% by weight, based on the weight of the particulate material on a dry basis.
16. The method according to any of claims 9 to 15, wherein the precursor mixture comprises sodium silicate and potassium silicate as the aqueous solutions thereof, and 3 parts of sodium silicate aqueous solutions to 1 part of potassium silicate aqueous solution.
17. The method according to any of claims 1 to 16, wherein the geopolymerisation promoter is an oxide selected from metal oxides, silicon oxide, and a combination thereof.
18. The method according to any of claims 1 to 18 wherein the geopolymerisation promoter is provided by a geopolymerisation agent selected from fly ash, metakaolin, and a combination thereof.
19. The method according to claim 18, wherein the geopolymerisation agent has a 65% by weight or higher content of the oxides of silicon, iron and aluminium.
20. The method according to claim 18 or claim 19, wherein the precursor mixture comprises from about 5% to about 30% by weight, more preferably from about 8% to about 20% by weight, or more preferably up to about 15% by weight of the geopolymerisation agent, based on the weight of the particulate material on a dry basis.
21. The method according to any of claims 1 to 20, wherein subjecting the precursor mixture to pressing is for a period that is from about 15 seconds and about 8 minutes, more preferably from about 20 seconds to about 5 minutes, more preferably from about 20 seconds to about 120 seconds.
22. The method according to any of claims 1 to 21 , wherein the polyvinyl alcohol is in aqueous solution.
23. A pressed board product produced in accordance with the method of any of claims 1 to 22.
PCT/IB2018/052715 2017-04-20 2018-04-19 Pressed board products WO2018193398A1 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2021023319A1 (en) * 2019-08-06 2021-02-11 First Point a.s. Wood chip material and method of its production

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2875924A1 (en) * 2013-11-26 2015-05-27 Kronotec AG New mineral binder and the use thereof for the manufacturing of wood-based panels
WO2017098483A1 (en) * 2015-12-11 2017-06-15 Zetland Technologies Limited Aggregation of small particles

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2875924A1 (en) * 2013-11-26 2015-05-27 Kronotec AG New mineral binder and the use thereof for the manufacturing of wood-based panels
WO2017098483A1 (en) * 2015-12-11 2017-06-15 Zetland Technologies Limited Aggregation of small particles

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2021023319A1 (en) * 2019-08-06 2021-02-11 First Point a.s. Wood chip material and method of its production

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