Method for treating a lignocellulosic material

ES 2 177 019 T3

DESCRIPTION

Procedure to manufacture a lignocellulosic board.

Background of the invention

This invention relates to a process for the preparation of lignocellulosic particles, soft boards and precursors of boards in the form of loamines, for the manufacture of a finished product.

The manufacture of composite board products from wood raw materials is well known. Examples of such products are medium density fibreboard (MDF), high density fibreboard, oriented strand board, chipboard and the like. Most of the time, such boards are glued with condensation resins such as urea, melamine or phenol formaldehyde resol. A new trend is the use of agricultural fibers as raw material, since excellent fibers are produced, resources can be regenerated quickly, pressure on wood resources is removed and logistical constraints are eased. In this case, the desired binders are isocyanates because of the nature of the surface and the composition of the agricultural fibers, the particle shape and the specific surface area make more chromic binders required.

In all lignocellulosic composite board products, plywood, paper products and solid woods, particularly softwoods and marginal hardwoods, water is by far the largest contributor to degradation.

Therefore, a treatment of lignocellulosic products is required to make them highly resistant to water.

This requirement can be achieved by means of the pre-treatment of lignocellulosic materials in particulate form as raw material for the production of boards, or in the form of veneers for the production of plywood, or by means of the subsequent treatment of the composite boards themselves, such as chipboard or MDF, pulp and paper products and solid wood. Document DE 4 223 604A describes the impregnation of cellulosic materials with a solution of one or more polymers, copolymers, oligoomers, prepolymers or water-insoluble monoomers (among others, thermoset isocyanate resins) dissolved in organic solvents (among others, petroleum) .

Secondary improvements such as better mechanical properties, better fire performance, absence of formaldehyde, and resistance to microbial or insect attack can also be provided.

There is always a need for improved processes for making products from lignocellulosic materials.

Summary of the invention

According to a first aspect of the invention, a process is provided for manufacturing a finished product from a lignocellulosic material selected from the group consisting of lignocellulosic particles or fibers, soft boards and board precursors in sheet form, including the process the stages of:

(a) impregnating the lignocellulosic material with an impregnating composition comprising:

(i) a mineral oil; and (ii) a liquid thermoset resin and, if necessary, a catalyst therefor; in the form of a dispersion of the liquid resin in the mineral oil; and (b) compressing the impregnated lignocellulosic material with heating to facilitate infusion of the mineral oil into the lignocellulosic material and polymerization of the thermosetting resin to form the finished product.

When the lignocellulosic material consists of lignocellulosic particles or fibers, the process of the invention preferably includes an additional step, step (c):

(c) before step (a), or preferably before step (b), applying to the lignocellulosic material a thermosetting resin in the form of a finely divided dry powder and, if necessary, a catalyst therefor, so that the thermosetting resin in finely divided dry powder form adheres to the surfaces of the lignocellulosic material.

The lignocellulosic material can be:

A Lignocellulosic particles or fibers, for example, particles, shavings, flakes, strips or fibers of wood or agricultural fibers, for example, those that come from annual or biannual agricultural crop residues, and pulp and the like;

B Soft boards, by what is meant a board that has not necessarily been impregnated or glued with a binder, such as a thermosetting resin or the like. Examples are low-density boards, that is, boards that have a density between 180 and 400 kg / m³ inclusive, formed topically by a process in huomide;

C Lamina-shaped board precursors, by which we mean a coherent web of a lignocellulosic material that has not been resinated with a binder such as a thermosetting resin. An example is a weft of medium density fibers for the production of a medium density fibreboard, preferably after the initial pre-pressing of the medium-density fibers, but before the final high-pressure pressing of the medium fibers to form the board. of medium density fibers.

It should be noted that the impregnating composition does not contain a solvent, which provides

ES 2 177 019 T3 to the process certain advantages, including the fact that there is no need to remove the solvent before carrying out step (b).

The thermosetting resin used in step (a) must be a liquid thermosetting resin, so that it can be infused into the lignocellulosic material and form a dispersion of the resin in the mineral oil.

The thermosetting resin used in step (a) is preferably an isocyanate thermosetting resin or a precursor thereof, more preferably a resin derived from diphenylmethane 4,4'-diisocyanate (MDI).

The thermosetting resin in finely divided dry powder form used in step (c) is preferably a novolak resin, based on phenol and formaldehyde.

The liquid thermosetting resin used in step (a) is preferably used in an amount of 1% to 20% by mass, inclusive, relative to the mass of the dry lignocellulosic material, preferably 2% to 10% by mass, inclusive, with respect to the mass of dry lignocellulosic material.

Mineral oil is preferably used in an amount of 5% to 30% by mass, inclusive, relative to the mass of the dry lignocellulosic material, more preferably in an amount of 10% to 20% by mass relative to the mass of the material. dry lignocellulosic.

The thermosetting resin in the form of a finely divided dry powder used in step (C) can be used in an amount from 0% to 20% by mass, inclusive, relative to the mass of the dry lignocellulosic material, preferably in an amount of 3% 10% by mass, inclusive, relative to the mass of the dry lignocellulosic material.

Preferably, before step (a), the lignocellulosic material is dried to a desired moisture content, preferably a moisture content of between 5% and 20% by mass inclusive.

In step (a), the lignocellulosic material can be impregnated with the impregnating composition in any suitable way, for example, by spraying or applying the impregnating composition on the lignocellulosic material, mixing the impregnating composition with the lignocellulosic material in particulate form. or fibers in conventional mixing equipment, or when the lignocellulosic material is a soft board or a sheet-shaped board precursor, applying the impregnation composition on the board or board precursor, on one or both sides, by means of any coating, spraying or immersion technique.

In step (b), the impregnated lignocellulosic material can be compressed and heated in a suitable press or molded at temperatures between 120 ° C and 250 ° C inclusive, preferably up to 220 ° C ', and at pressures of 2 to 70 kg / cm² inclusive, preferably 10 to 60 kg / cm² inclusive, for a period of time from 5 seconds to 20 seconds inclusive per mm of thickness, to facilitate the infusion of the mineral oil in the lignocellulosic material and to polymerize the thermosetting resin or resins present.

The impregnation composition can also include various optional components such as:

(iv) a preservative, such as a bactericide, fungicide or insecticide, or the like, preferably in an amount of 0.25% to 10% by mass, inclusive, with respect to the impregnating composition of the preservative;

(v) a wax soluble in the impregnation composition at an elevated temperature or a wax in the form of dry particles;

(vi) other additives selected from flame retardants, ultraviolet light absorbers, anti-oxidants and the like.

According to a second aspect of the invention, a process is provided for preparing a lignocellulosic material impregnated from a lignocellulosic material selected from the group consisting of lignocellulosic particles or fibers, soft boards and precursors of boards in the form of loamine, for the manufacture of a finished product, including the procedure the stage of:

(a) impregnating the lignocellulosic material with an impregnating composition comprising:

(i) a mineral oil; and (ii) a liquid thermoset resin and, if necessary, a catalyst therefor;

in the form of a dispersion of the liquid resin in the mineral oil.

When the lignocellulosic material consists of lignocellulosic particles or fibers, the process may include an additional step, step (c), before or after step (a):

(b) before or after step (a), applying to the lignocellulosic material a thermosetting resin in the form of a finely divided dry powder and, if necessary, a catalyst therefor, so that the thermosetting resin in the form of a dry powder finely divided adhere to the surfaces of the lignocellulosic material.

Description of achievements

The essence of the invention is a process for manufacturing a finished product from a lignocellulosic material selected from the group consisting of lignocellulosic particles or fibers, soft boards and precursors of loamine-shaped boards.

Lignocellulosic material refers to any plant material derived from a photosynthetic phenomenon.

The lignocellulosic material can be, firstly, lignocellulosic particles or fibers ta3

ES 2 177 019 T3 them as, for example, the raw material for the manufacture of a composite board product such as a chip board, a particle board, a medium density fibreboard, an oriented strand board and the like . The raw material may be in the form of particles, individual fibers or small bundles of fibers, chains, flakes or wood chips or, alternatively, in the form of short length fibers extracted from agricultural fiber feed materials, such as Annual or biannual agricultural plants, particularly crop debris such as hemp, pita, cotton stalks, wheat or other cereals, straw, bamboo, jute, saltwater reeds, palm leaves, flax, peanut shells, cereal shells and the like.

Alternatively, the lignocelluliosic material may be in the form of a low density soft board, that is, a soft board having a density of 180 to 400 kg / m³, produced by a process called the wet process, or in the form of a hard board produced by a process such as that typified by Temple-Island Fiber Products or Masonite Corporation Operations.

In addition, alternatively, the lignocellulose material may be in the form of a laminated board precursor, preferably a pre-pressed web of MDF fibers that has not yet been subjected to the final high pressure pressing.

The soft board or board precursor must be such that oil can penetrate through the soft board or board precursor during subsequent pressing, and that the liquid thermoset resin can be intimately dispersed therein, to produce a finished product with suitable characteristics.

Natural plant fibers or particles, or the end products formed from them, were composed of hemi-celluloses, celluloses, and lignin. An increase in the moisture content of these materials causes swelling, because the polymers in the cell wall of the material contain hydroxyl groups or other oxygen-containing groups that attract water through hydrogen bonds. Hemi-celluloses are my hygroscopic component. It is the moisture that swells the cell walls and causes the material to expand until the cell walls are saturated with water. Obviously, this can lead to degradation as a result of attack by microorganisms, as well as increased volume and dimensional instability which, in the case of panel composites, can lead to their destruction. This phenomenon applies to all groups of lignocellulose materials described in this invention.

The chemical modification of lignocellulosic materials is known, mainly through the use of anhydrides, and the synergistic resinization of the material with isocyanate resins. Chemical modification of celluloses serves to minimize hydrogen bonding phenomena by reducing the number of available hydroxyl groups. However, the essence of this invention is that the contact of these groups with water is minimized by the interposition of a hydrophobic cohesive film, formed by the combination of mineral oil / thermosetting resin.

Thus, the essence of this invention is that the lignocelluliosic material is impregnated with an impregnation composition which must comprise a mineral oil and a liquid thermosetting resin dispersed therein.

The oil should be a mineral oil, preferably a low viscosity paraffinic or naphthalene mineral oil that is inert.

Examples of suitable mineral oils are:

Waksol-F, provided by the Carbo-Tar Division of Sasol Chemical Industries Limited of South Africa, which is a coal-derived mineral oil with a flash point of 107.5 ° C, a water content of 0.05% and a wax content between 10 and 15% of a wax dissolved in the oil at elevated temperatures, the wax having a pour point of 30 to 40^°C. The density of this oil is 0.9 g / cm³.

Parprol 22 from Engen (Mobil Chemicals) of South Africa, which is a paraffinic process oil derived from petroleum, honey colored, low viscosity, with or without wax inclusion. Parprol 22 has a density of 0.859 g / cm³, a viscosity in cSt at 40^°C of 20.6 (1cSt = 1 x 10^-6 m^{2 / s}), the following analyzes and percentages of carbon types - aromaitic 3, naphthenic 28 and paraffinic 69, a neutralization index mgKOH / g of 0.01 and a flash point of 196^°C.

Shell Base Oil, code MVI (P1300), with a polycyclic aromatic group content of 2.9%, a sulfur percentage of 2% and a total acid number of 0.1 mg KOH / g.

Other examples are Quendilla 19, a process oil, or Transcal N, which is a low viscosity heat transfer oil, both being British Petroleum oils.

In general, paraffinic oils are preferred over naphthenic oils because of cost. Mineral oils in the context of the invention are process oils for waterproofing lignocellulose materials, they are inert and do not form cross-links with thermosetting resins, that is, isocyanate or novolac resins that can be used, as there are no hydroxyl groups. nor other reactive groups available in its chemical structure.

The impregnation composition must also include a liquid thermosetting resin and, if necessary, a catalyst therefor.

The thermosetting resin is preferably an isocyanate thermosetting resin.

Isocyanates are compounds that contain the group -N = C = O and are characterized by the general formula:

R (NCO) x where x is variable and denotes the number of NCO groups, and R denotes a suitable group.

Examples of organic isocyanates include aromaitic isocyanates such as m-yp-phenylene diisocyanate, 2-4- and 2,6-phenylene diisocyanate.

ES 2 177 019 T3 toluene, 4,4'-diphenylmethane diisocyanate, 2,4 diphenylmethane diisocyanate, 2,4-chlorophenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4'-diisocyanate-3,3 '-dimethyldiphenyl, 4,4'-3-methyldiphenylmethane diisocyanate and diphenyl ether diisocyanate, 2,4,6-triisocyanatotoluene and 2,4,4'-triisocyanatodiphenyl ether. Mixtures of isocyanates may also be present, for example a mixture of toluene diisocyanate iséomers such as the commercially available mixtures of 2,4 and 2,6 iséomers, and also the mixtures of diisocyanates and higher polyisocyanates produced by phosgenation of aniline / formaldehyde condensates. Such mixtures are well known in the art and include the crude phosgenation products containing mixtures of polyphenyl polyisocyanates with methylene linkages, including diisocyanates, triisocyanates and higher polyisocyanates together with any phosgenation by-products.

Preferred compositions are those in which the isocyanate is an aromatic diisocyanate or polyisocyanate of higher functionality, in particular crude mixtures of methylene-linked polyphenyl polyisocyanates containing diisocyanates, triisocyanates and polyisocyanates of higher functionalities. Methylene-linked polyphenylpolyisocyanates are well known in the art, sometimes being called polymeric methylene-linked polyphenyl diisocyanates (MDI), which have an isocyanate functionality ranging from 2.5 to 3, and on other occasions crude MDIs, which have superior functionality. They are prepared by phosgenating corresponding mixtures of polyamines obtained by condensation of aniline and formaldehyde.

Specific examples of suitable isocyanates are those having a percentage (NCO) content preferably greater than 20% and most preferably greater than 25%. These isocyanates promote latency or reduce reactivity due to the high number of NCO groups, and provide the maximum ability to bind hydroxyl groups. Examples are Desmadur VKS or Desmadur VK from Bayer, which are solventless mixtures of aromatic polyisocyanates such as diphenyl methane 4,4-diisocyanate and polymeric materials. These and other similar compounds are among the so-called MDIs in the industry. Another description used is a diisocyanate-diphenylmethane, additional examples being Suprasec DNR-5005, which is a polymeric MDI, or Suprasec 2020, which is a monomeric MDI, with available NCO percentages of 30.7% and 29% and which are a polymeric MDI with conventional functionality and a monomeric MDI respectively. Suprasec resins are supplied by ICI. Another example of a crude MDI is Voronate M 229, from the Dow Chemical Company.

Other suitable diisocyanates are toluene diisocyanates with the alternative names tolylene diisocyanate or tolylene diisocyanate, abbreviated TDI, such as Bayer Desmadur L75.

It should be noted that the term "isocyanate thermoset resin" is intended to include resins per se, as well as components that can be considered precursors to resins, such as

MDI and TDI.

Another example of the principle of esterification of wood is the use of ethyl isocyanate, which reacts with hydroxyl groups to form ethyl carbamate (urethane) according to the formula:

C₂H₅NCO + H₂Or NH₂COOC₂h₅

The isocyanate resins react with the hydroxyl groups present in the cellulose and hemicellulose molecules of the lignocellulose material forming a wood eester. In this way, they form a chemical bond adhesion rather than a cohesive bond. Isocyanates help bind mineral oil within the lignocellulose matrix.

Other examples of suitable thermosetting resins are listed below:

Epoxy resins, such as Epikote series from Shell Chemical or Araldite PY 340.2 from CibaGeigy, with latent catalysts activated by heat in the 80 ° C range, such as boron trifluorides from Anchor Chemicals or aromatic polyamines such as Ancamine SRX.

Methyl methacrylates, acrylics or methacrylic acid esters, with appropriate catalysts.

The liquid thermosetting resin is preferably used in an amount of 1% to 20% inclusive, more preferably 2% to 10% by mass, inclusive, relative to the mass of the dry lignocellulosic material.

The mineral oil is preferably used in an amount of 5% to 30% inclusive, more preferably in an amount of 10% to 20% by mass, inclusive, relative to the mass of the dry lignocellulosic material.

It should be noted that the amounts of liquid thermosetting resin and mineral oil to be used are delivered to the mass of the dry lignocellulose material. In this regard, in the process of the present invention it is desirable that the mineral oil and the liquid thermosetting resin are applied to the lignocellulose material after it has been dried to a desired moisture percentage, generally between 5 and 20% inclusive, in mass. Thus, by dry lignocellulosic material is meant a lignocellulosic material with a moisture content of between 5% and 20% by mass inclusive. Furthermore, as indicated above, the mineral oil is applied in the absence of water or a non-aqueous solvent for the mineral oil. This avoids the need to remove the solvent before further processing.

When the lignocellulosic material consists of lignocellulosic particles or fibers, the process of the invention preferably includes step (c), before step (a) or step (b), of applying a thermosetting resin in powder form to the lignocellulosic material. finely divided dry and, if necessary, a catalyst therefor, so that the thermosetting resin adheres to the surface of the lignocellulose material.

The thermosetting resin is preferably a novolak resin, based on phenol and formaldehyde, such as a resin in which the molar ratio between phenol and formaldehyde exceeds equality, or

ES 2 177 019 T3 is a modified with cashew oil extracts or used in conjunction with long chain alkyl prepolymers of cashew oil and which may contain a catalyst such as hexamethylenetetramine. These products, upon decomposition with heat, provide a source of formaldehyde that induces condensation of the polymer to form a stable three-dimensional network with minimal shrinkage, which is hard, strong, and insoluble in water.

Examples of suitable novolac resins are from BP Chemicals, code CH113; a cashew prepolymer also from BP Chemicals J3100L; or Schennectady SA 891 or PRP 3337 from Polyresin Products of South Africa, which are high flow novolac resins.

The thermosetting resin in the form of a finely divided dry powder is preferably used in an amount of 0% to 20% inclusive, more preferably in an amount of 3% to 10% by mass, inclusive, relative to the mass of the dry lignocellulosic material.

The impregnating composition may also include a preservative, such as a bactericide, fungicide, insecticide or the like, particularly a termiticide, preferably in an amount of 0.25% to 10% by mass of the preservative relative to the impregnating composition. Examples of complex biocides of boron, atrazines, thiazoles, or carbamates are, and examples of termiticides are zinc or copper naphthanates, pyrethroids, oil-compatible high-boiling tar acids, pentachlorophenol, or tri-butyl tin-lindane oxide. .

The impregnating composition can also include other additives as listed below.

Advantageously, flame retardant or flame retardant chemicals can be added to the impregnating composition. There must be considerable compatibility with the other components of the impregnating composition and the flame retardants used are selected for their solubility in the solvents of choice. Examples are Flyrol FR2-LV from Akzo Chemicals, which is a tris (1,3-dichloroisopropyl) phosphate, and Flyrol DMMP, which is a dimethyl metalphosphenate with a phosphorus content of 25% and an acid number of 1.3 mgKOH. / g. These agents also acted as effective viscosity reducers. Flame retardants are added in a proportion of 0.25 to 5% of the total mass of the impregnating composition.

The impregnating composition of the invention can also include a soluble wax in the impregnating composition.

The first stage of the process of the invention is to impregnate the lignocelluliosic material with the impregnation composition. This can be achieved in any suitable way.

For example, when the lignocellulose material is in particulate or fiber form, the impregnating composition can be applied to the particles or fibers by a finely atomized spray in an insufflation line, optionally followed by the application of a thermosetting resin. as a finely divided dry powder at a downstream position in the insufflation line.

Alternatively, and again when the lignocellulosic material is in particulate or fiber form, the impregnating composition can be supplied to a mixer and mixed with the particles or fibers, for example, using conventional mixing equipment such as ribbon mixers. screw or paddle, optionally followed by subsequent application of a thermosetting resin in the form of a finely divided dry powder.

Furthermore, as an alternative, when the lignocellulose material is a soft board, or a board precursor, the impregnation composition can be applied to the board or the board precursor on one or both sides by means of a curtain coater, a coater. roller or in a sprayer. It must be ensured that the full thickness of the board or precursor board is impregnated, which can be ensured by subjecting the board or board precursor to suitable pressure and temperature conditions that propagate through penetration and intimate impregnation by the composition of impregnation, before the polymerization of the resin is completed.

During this process, the board or board precursor can subsequently be pressed into a flat configuration or to a suitable shape.

The second step of the process of the invention is to compress the impregnated lignocelluliosic material with heating in a suitable press or flat or flat mold, to allow the oil present to infuse into the particles, fibers, board or precursor of board and allow all resin present to polymerize to form the finished product.

For example, lignocellulosic material can be compressed and heated in a suitable press or mold at a temperature between 120 ° C and 250 ° C inclusive, preferably 130 ° C to 220 ° C inclusive, and at pressures of 2 to 70 kg / m.³ inclusive.

As indicated above, the third optional step of the process of the invention is to apply to the lignocellulose particles or fibers, before step (a) or preferably before step (b), a thermosetting resin in the form of a finely dry powder. divided and, if necessary, a catalyst for it. Procedures to achieve this have been described above.

The use of an impregnating composition containing a mineral oil has several advantages. First, the mineral oil serves as a vehicle for the liquid thermoset resin, so that the liquid thermoset resin can be dispersed as very small finely divided droplets. As mineral oil has no volatiles, this increases the safety of the resin system, preventing droplets from escaping into the atmosphere.

In addition, very low percentages of liquid thermosetting resin can be applied to the lignocellulosic material, maintaining this material a uniform and reliable distribution, and it is possible not to add any water or other solvents that may interfere with the production of the final product when applied. temperature and pressure.

ES 2 177 019 T3

In addition, mineral oil acts as a hydrophobic agent, preventing the penetration of water and, furthermore, preventing the movement of water by capillarity through the treated lignocellulose material.

Finally, the oil ensures that the finely divided dry powder thermosetting resin, when used, firmly adheres to the surfaces of the lignocellulose material.

As an example to illustrate the efficiency of the use of the impregnation composition, the MDF obtained by the process of the invention has a water swelling after 24 hours of immersion in water of less than 3% and a water absorption of less than 6%. in comparison with an untreated material that exhibits a water swelling of 30% and a water absorption of 70%.

Examples of the process of the invention will be provided below.

Example 1

An impregnating composition is formulated as follows:

Liquid MDI - 60 g

Quendilla 19 - a parapan mineral oil of BP175 g

Liquid MDI is dispersed in mineral oil, in the absence of solvent. 1200 g of wood chips are impregnated with the impregnating composition.

Subsequently, 90 g of a novolac resin, particularly PRP 3337 from Polyresin, are applied to the impregnated wood chips

Products, which is a high flow, medium reactivity novolak resin in the form of a finely divided dry powder (200 mesh or less). The novolac resin particles adhere to the impregnated wood chips.

Subsequently, the impregnated and resin-coated wood chips are pressed to form a board with a density of 975 kg / cm², at a pressure of approximately 25 kg / m³ and at a temperature of 210 ° C, for a period of approximately 8 seconds per mm of thickness.

The board thus formed can be used for moisture exposure applications.

Example 2

A soft board of 225 kg / m³ density and a thickness of 14 mm, it is dried in a dryer to a humidity of 2% by mass.

An impregnating composition comprising a dispersion of 25% by mass of MDI Suprasec 5005 from ICI or Desmodur VKS from Bayer is applied to the softboard, in 75% by mass of Waksol F from Sasol Chemicals (a wax in mineral oil from low viscosity from carbol) by means of a curtain coater, at a rate of 1.5 kg / m³, applying 66% on the upper surface of the board and 34% on the lower surface of the board.

Subsequently, the board is pressed between flattened plates at a pressure of 50 kg / cm² and at a temperature of 180 ° C to form a 4 mm thick, weather-resistant door liner with a density of 170 kg / m³.