Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
FIBER CEMENT PRODUCTS COMPRISING HYDROPHOBIZED NATURAL FIBERS
Document Type and Number:
WIPO Patent Application WO/2019/197496
Kind Code:
A1
Abstract:
The present invention relates to fiber cement products comprising natural fibers and methods for production thereof. The present invention further relates to uses of these fiber cement products in the building industry. In particular, the present invention provides fiber cement products at least comprising cement and fibers, characterized in that said fibers at least comprise hydrophobized natural fibers. Furthermore, the present invention provides processes for the production of fiber cement products comprising hydrophobized fibers, at least comprising the steps of: a. Preparing a fiber cement slurry at least comprising water, cement and hydrophobized natural fibers; b. Producing a green fiber cement product by means of fiber cement manufacturing process chosen from the group consisting of a Hatschek process, a Magnani process, a flow-on process, an extrusion process and the like; and c. Curing the green fiber cement product.

Inventors:
IGNATYEV, Igor A. (Sint Bernadettestraat 93, 9000 Gent, 9000, BE)
DE LHONEUX, Benoit (Avenue de la Vecquée 17, 5000 Namur, 5000, BE)
Application Number:
EP2019/059154
Publication Date:
October 17, 2019
Filing Date:
April 10, 2019
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
ETEX SERVICES NV (Kuiermansstraat 1, 1880 Kapelle-op-den-Bos, 1880, BE)
International Classes:
C04B28/04; C04B20/10; C04B111/00
Domestic Patent References:
WO2004113248A22004-12-29
WO2005012203A22005-02-10
Foreign References:
EP2796434A12014-10-29
EP0331666A11989-09-06
Attorney, Agent or Firm:
VAECK, Elke (Kuiermansstraat 1, 1880 Kapelle-op-den-Bos, 1880, BE)
Download PDF:
Claims:
CLAIMS

1. A fiber cement product at least comprising:

cement and fibers,

characterized in that said fibers at least comprise hydrophobized natural fibers.

2. The fiber cement product according to claim 1, wherein said hydrophobized natural fibers are present in an amount of between about 3 weight% and about 6weight% compared to the total weight of the dry components of said fiber cement product.

3. The fiber cement product according to claims 1 or 2, wherein said hydrophobized natural fibers are hydrophobized cellulose fibers.

4. The fiber cement product according to any of claims 1 to 3, wherein said hydrophobized natural fibers are with siliconate hydrophobized natural fibers.

5. The fiber cement product according to claim 4, wherein said siliconate is potassium methyl siliconate.

6. The fiber cement product according to any of claims 1 to 5, wherein said hydrophobized natural fibers have an average length between 2 mm and 3 mm.

7. The fiber cement product according to any of claims 1 to 6, further comprising synthetic fibers.

8. A process for the production of a fiber cement product as defined in claim 1, at least comprising the steps of:

a. Preparing a fiber cement slurry at least comprising water, cement and hydrophobized natural fibers;

b. Producing a green fiber cement product by means of fiber cement manufacturing process chosen from the group consisting of a Hatschek process, a Magnani process, a flow-on process, an extrusion process and the like; and

c. Curing the green fiber cement product.

9. The process according to claim 8, wherein said step a) of preparing a fiber cement slurry is performed such that said hydrophobized natural fibers are present in an amount of between about 3 weight% and about 6weight% compared to the total weight of the dry components of said fiber cement slurry.

10. The process according to claims 8 or 9, wherein said hydrophobized natural fibers are hydrophobized cellulose fibers.

11. The process according to claims 8 to 10, wherein said hydrophobized natural fibers are with siliconate hydrophobized natural fibers.

12. The process according to any of claims 8 to 11, wherein said hydrophobized natural fibers are with potassium methyl siliconate hydrophobized natural fibers.

13. The process according to any of claims 8 to 12, wherein said curing step is performed by means of autoclave-curing or by means of air-curing.

14. Use of the fiber cement product according to any of claims 1 to 7 as a building product.

15. Use of the fiber cement product according to claim 14 as a slate.

Description:
FIBER CEMENT PRODUCTS COMPRISING HYDROPHOBIZED NATURAL FIBERS

Field of the invention

The present invention relates to fiber cement products comprising natural fibers and methods for production thereof. The present invention further relates to uses of these fiber cement products in the building industry.

Background of the invention

The use of natural fibers, such as for instance cellulose fibers, for strengthening various composite materials is well known.

Attempts have been made to improve the performance of cellulose fibers in fiber cement products, in particular with regard to increasing their chemical stability in alkaline environment and optimizing their dimensional stability.

EP0331666-A1 discloses the treatment of cellulose fibers suitable for use in fiber cement products with amorphous silica particles in the presence of a polyelectrolyte.

These treatments have generally drawbacks such as a low or non-durable efficiency due to an insufficient bonding of the treating agent to the fiber and/or, a reduction of fiber strength due to the treatment conditions.

Accordingly, there is a remaining need for improved natural fiber-based cement products.

Summary of the invention

It is an object of the present invention to provide improved fiber cement products, which are based on natural fibers.

In this respect, it has been found by the current inventors that natural fibers that have been treated or impregnated with a hydrophobizing agent perform particularly well in fiber cement products. More specifically, it has been demonstrated by the present inventors that hydrophobized natural fibers are chemically and dimensionally stable in an alkaline cementitious environment. Moreover, it has been shown that the fiber cement products comprising hydrophobized natural fibers according to the present invention have an improved quality and mechanical strength compared to the known natural fiber-based cement products.

According to a first aspect, the present invention provides fiber cement products at least comprising cement, and fibers, characterized in that the fibers at least comprise hydrophobized natural fibers. In particular embodiments, the hydrophobized natural fibers are present in an amount of between about 3 weight% and about 6weight% compared to the total weight of the dry components of the fiber cement product.

In further particular embodiments, the hydrophobized natural fibers are hydrophobized natural fibers are hydrophobized cellulose fibers.

In yet further particular embodiments, the hydrophobized natural fibers are natural fibers, which are hydrophobized with a siliconate.

In yet further particular embodiments, the hydrophobized natural fibers are natural fibers, which are hydrophobized with potassium methyl siliconate.

In still further particular embodiments, the hydrophobized natural fibers have an average length between 2 mm and 3 mm.

In further particular embodiments, the fiber cement products further comprise synthetic fibers.

According to a second aspect, the present invention provides processes for the production of a fiber cement product according to the present invention, said processes at least comprising the steps of:

a. Preparing a fiber cement slurry at least comprising water, cement and hydrophobized natural fibers;

b. Producing a green fiber cement product by means of fiber cement manufacturing process chosen from the group consisting of a Hatschek process, a Magnani process, a flow-on process, an extrusion process and the like; and

c. Curing the green fiber cement product.

In particular embodiments of the processes according to the present invention, step a) of preparing a fiber cement slurry is performed such that the hydrophobized natural fibers are present in an amount of between about 3 weight% and about 6weight% compared to the total weight of the dry components of the fiber cement slurry.

In further particular embodiments of the processes according to the present invention, the hydrophobized natural fibers are hydrophobized cellulose fibers. In yet further particular embodiments of the processes according to the present invention, the hydrophobized natural fibers are natural fibers, which are hydrophobized with a siliconate.

In yet further particular embodiments of the processes according to the present invention, the hydrophobized natural fibers are natural fibers, which are hydrophobized with potassium methyl siliconate.

In yet further particular embodiments of the processes according to the present invention, the curing step is performed by means of autoclave-curing or by means of air-curing.

According to a third aspect, the present invention provides uses of the fiber cement products according to the present invention as a building product.

In particular embodiments, the present invention provides uses of the fiber cement product according to the present invention as a fagade element or a roofing element, such as but not limited to a slate.

The independent and dependent claims set out particular and preferred features of the invention. Features from the dependent claims may be combined with features of the independent or other dependent claims, and/or with features set out in the description above and/or hereinafter as appropriate.

The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

Detailed description

The present invention will be described with respect to particular embodiments.

It is to be noted that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, steps or components as referred to, but does not preclude the presence or addition of one or more other features, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Throughout this specification, reference to "one embodiment" or "an embodiment" are made. Such references indicate that a particular feature, described in relation to the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, though they could. Furthermore, the particular features or characteristics may be combined in any suitable manner in one or more embodiments, as would be apparent to one of ordinary skill in the art.

The following terms are provided solely to aid in the understanding of the invention.

As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise.

The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps.

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints.

The term "about" as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of +/-10% or less, preferably +/-5% or less, more preferably +/-1% or less, and still more preferably +/-0.1% or less of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention. It is to be understood that the value to which the modifier "about" refers is itself also specifically, and preferably, disclosed.

The terms "fiber cementitious slurry" or "fiber cement slurry" as referred to herein generally refer to slurries at least comprising water, fibers and cement. The fiber cement slurry as used in the context of the present invention may also further comprise other components, such as but not limited to, limestone, chalk, quick lime, slaked or hydrated lime, ground sand, silica sand flour, quartz flour, amorphous silica, condensed silica fume, microsilica, metakaolin, wollastonite, mica, perlite, vermiculite, aluminum hydroxide, pigments, anti-foaming agents, flocculants, and other additives. In the context of the processes of the present invention, the fiber cement slurry can thus be provided by one or more sources of at least cement, water and fibers. Optionally, these one or more sources of at least cement, water and fibers may operatively be connected to a continuous mixing device constructed so as to form a cementitious fiber cement slurry. In particular embodiments, when using cellulose fibers or the equivalent of waste paper fibers, a minimum of about 3%, such as about 4%, of the total slurry mass of these cellulose fibers may be used. In further particular embodiments, when exclusively cellulose fibers are used, between about 4% to about 12%, such as more particularly, between about 7% and about 10%, of the total slurry mass of these cellulose fibers is used. If cellulose fibers are replaced by short mineral fibers such as rock wool, it is most advantageous to replace them in a proportion of 1.5 to 3 times the weight, in order to maintain approximately the same content per volume. In long and cut fibers, such as glass fiber rovings or synthetic high-module fibers, such as polypropylene, polyvinyl acetate, polycarbonate or acrylonitrile fibers the proportion can be lower than the proportion of the replaced cellulose fibers.

The terms "cementitious slurry" or "cement slurry" as referred to herein generally refer to slurries at least comprising water and cement. The cement slurry as used in the context of the present invention may also further comprise other components, such as but not limited to, limestone, chalk, quick lime, slaked or hydrated lime, ground sand, silica sand flour, quartz flour, amorphous silica, condensed silica fume, microsilica, metakaolin, wollastonite, mica, perlite, vermiculite, aluminum hydroxide, pigments, anti-foaming agents, flocculants, and other additives.

"Fiber(s)" present in the fiber cement slurry as described herein may be for example process fibers and/or reinforcing fibers which both may be natural fibers (typically cellulose fibers) or synthetic fibers (polyvinylalcohol, polyacrilonitrile, polypropylene, polyamide, polyester, polycarbonate, etc.).

"Cement" present in the fiber cement slurry as described herein may be for example but is not limited to Portland cement, cement with high alumina content, Portland cement of iron, trass- cement, slag cement, plaster, calcium silicates formed by autoclave treatment and combinations of particular binders. In more particular embodiments, cement in the products of the invention is Portland cement. The term "water-permeable" as used herein when referring to a water-permeable (region of a) transport belt generally means that the material of which the water-permeable (region of the) belt is made allows water to flow through its structure to a certain extent.

The "water-permeability" as used herein when referring to the water-permeability of a (region of a) transport belt generally refers to the extent or degree to which the material of which the water- permeable (region of the) belt is made, allows water to flow through its structure. Suitable materials for water-permeable transport belts are known to the person skilled in the art, such as but not limited to felts.

The terms "predetermined" and "predefined" as used herein when referring to one or more parameters or properties generally mean that the desired value(s) of these parameters or properties have been determined or defined beforehand, i.e. prior to the start of the process for producing the products that are characterized by one or more of these parameters or properties.

The term "fiber cement layer" as used herein generally refers to any flat, optionally substantially rectangular, layer or cake essentially consisting of a fiber cement composition and having a thickness of at least about 1 mm, in particular between about 1 mm and 200 mm, more particularly between about 2 mm and about 150 mm, most particularly between about 4 mm and about 100 mm.

A "Hatschek fiber cement layer" or a "Hatschek layer" as interchangeably used herein refers to a fiber cement layer (as defined herein), which is produced according to a Hatschek process, which at least comprises the steps of:

(i) building a fiber cement film on a sieve, which rotates in contact with a fiber cement slurry in a vat;

(ii) transferring the fiber cement film from the sieve to a felt transport belt, and

(iii) accumulating the fiber cement film on an accumulator roll via the felt transport belt;

A "(fiber cement) sheet" as used herein, also referred to as a panel or a plate, is to be understood as a flat, usually rectangular element, a fiber cement panel or fiber cement sheet being provided out of fiber cement material. The panel or sheet has two main faces or surfaces, being the surfaces with the largest surface area. The sheet can be used to provide an outer surface to walls, both internal as well as external a building or construction, e.g. as fagade plate, siding, etc. The terminology "composition(s) or materials comprising cellulose fibers" as used herein may refer to any suitable material, and is not necessarily limited to paper, recycled paper, and lignocellulosic fiber sources including, but not confined to, retted and green raw hemp, flax, cereal straws, wheat, barley, rye, oats, rice, pomace, spent grain, wood and/or used cotton. As will be understood by the skilled person, the presence of fibers and associated fibrils are part of any suitable material.

The invention will now be further explained in detail with reference to various embodiments. It will be understood that each embodiment is provided by way of example and is in no way limiting to the scope of the invention. In this respect, it will be clear to those skilled in the art that various modifications and variations can be made to the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used in another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as encompassed within the scope of the appended claims and equivalents thereof.

It is an object of the present invention to provide improved fiber cement products, which comprise natural reinforcing fibers.

In this respect, it has been found by the inventors that natural fibers that have been pre-treated or pre-impregnated with a hydrophobizing agent are particularly suitable as reinforcing fibers in various types of fiber cement products.

In fact, with natural fiber-based fiber cement products, it is a common problem that the physical properties, and in particular the strength, of the natural fibers is significantly affected by the alkaline environment of the cementitious matrix, in which these fibers reside. This is because the structure of these natural fibers is chemically destroyed by the alkaline pH of cement.

The present inventors now have found a solution to this problem by using natural fibers, which have been treated with a hydrophobizing agent. In this regard, the inventors have found that a hydrophobizing agent has a sufficiently strong bond with the fiber surface and consequently forms a permanent film, protecting the fiber structure from chemical disruption, such as from disintegration by alkaline pH. Moreover, it was found that the pre-treatment with a hydrophobizing agent does not affect the original strength of the natural fibers.

Accordingly, it has been demonstrated by the present inventors that hydrophobized natural fibers are chemically and dimensionally stable in an alkaline cementitious environment. Moreover and most importantly, it has been shown that the resulting fiber cement products as provided by the present invention, which comprise hydrophobized natural fibers, have an improved quality and mechanical strength compared to the known fiber cement products comprising non-treated natural fibers.

According to a first aspect, the present invention provides fiber cement products at least comprising cement and fibers, characterized in that the fibers at least comprise hydrophobized natural fibers.

In the context of the present invention, fiber cement products are to be understood as cementitious products comprising cement and at least natural fibers, such as but not limited to cellulose fibers. The fiber cement products are made out of fiber cement slurry, which is formed in a so-called "green" fiber cement product, and then cured.

Dependent to some extent on the curing process used, the fiber cement slurry typically comprises water, cement, process and/or reinforcing fibers which are natural fibers and, optionally, synthetic organic fibers.

According to certain particular embodiments, the fiber cement products of the present invention comprise 20 to 95 weight % cement as hydraulic binder. Cement in the products of the invention is selected from the group consisting of Portland cement, cement with high alumina content, Portland cement of iron, trass-cement, slag cement, plaster, calcium silicates formed by autoclave treatment and combinations of particular binders. In more particular embodiments, cement in the products of the invention is Portland cement.

According to particular embodiments, the fiber cement products according to the invention optionally comprise further components. These further components in the fiber cement products of the present invention may be selected from the group consisting of water, sand, silica sand flour, condensed silica fume, microsilica, fly-ashes, amorphous silica, ground quartz, the ground rock, clays, pigments, kaolin, metakaolin, blast furnace slag, carbonates, puzzolanas, aluminium hydroxide, wollastonite, mica, perlite, calcium carbonate, and other additives (e.g. colouring additives) etc. It will be understood that each of these components is present in suitable amounts, which depend on the type of the specific fiber cement product and can be determined by the person skilled in the art. Further additives that may be present in the fiber cement products of the present invention may be selected from the group consisting of dispersants, plasticizers, antifoam agents and flocculants. The total quantity of additives is preferably between about 0.1 and about 1 weight % compared to the total initial dry weight of the composition. In particular embodiments, the fiber cement products of the invention have a thickness of between about 4 mm and about 200 mm, in particular between about 6 mm and about 200 mm, more in particular between about 8 mm and about 200 mm, most in particular between about 10 mm and about 200 mm.

The fiber cement products as referred to herein include roof or wall covering products made out of fiber cement, such as fiber cement sidings, fiber cement boards, flat fiber cement sheets, corrugated fiber cement sheets, fiber cement slates and the like. According to particular embodiments, the fiber cement products according to the invention can be roofing or fagade elements, flat sheets or corrugated sheets. According to further particular embodiments, the fiber cement products of the present invention are fiber cement slates.

The fiber cement products according to the present invention, apart from cement, further at least comprise hydrophobized natural fibers.

Natural fibers may be obtained from plant, animal, and mineral sources. Those from plant sources include, without limitation, cotton, flax, hemp, sisal, jute, kenaf, and coconut.

Cellulose is the main component of vegetable fibers, several of which serve in the manufacture of paper and cloth. Examples include cotton, jute, flax, ramie, sisal, and hemp.

Vegetable fibers can be further categorized into the following types:

• Seed fiber: These are fibers collected from seeds or seed cases. Examples include cotton and kapok.

• Leaf fiber: These are fibers collected from leaves. Examples include sisal and agave.

• Bast fiber or skin fiber: These fibers are collected from the skin or bast surrounding the stem of the plant source. They have higher tensile strength than other fibers. Therefore, these fibers are used for durable yarn, fabric, packaging, and paper. Some examples are flax, jute, kenaf, industrial hemp, ramie, rattan, soybean fiber, and even vine fibers and banana fibers.

• Fruit fiber: These fibers are collected from the fruit of the plant, such as coconut (coir) fiber.

• Stalk fiber: These fibers are actually the stalks of the plant. Examples are straws of wheat, rice, barley, and other crops including bamboo and grass. Tree wood is also such a fiber.

• Cellulose fibers are selected from but not limited to vegetable fibers such as jute, flax, cotton, straw, hemp, bagasse, ramie, and abaca, waste wood pulps and wood pulps for paper making processes. In particular embodiments, the present invention provides fiber cement products comprising hydrophobized cellulose fibers. In further particular embodiments, these cellulose fibers are obtained from wood pulp, more preferably from chemical wood pulp. Kraft pulp is particularly preferred. The cellulose fibers can be bleached or unbleached. Preferable pulps are processed from softwood, e.g. Pinus Radiata, or from hardwood. Good results can be obtained with cellulose fibers from unbleached, softwood kraft pulp. Cellulose fibers characterized by a Kappa number in the range of 20 to 40 as determined by TAPPI method T236 cm-85, more particularly in the range of 20 to 30 are especially preferred. The cellulose fibers can be refined or unrefined, and can be characterized by a Schopper-Riegler degree as measured according to ISO 5267/1 which is advantageously in the range of 12 to 80. Preference is given to cellulose fibers with a length determined according to TAPPI method T271 in the range of from 0.8 to 4 mm, and preferably from 2 to 3 mm. Cellulose fibers with an alkali soluble content as measured according to TAPPI method T212 below 3.5 wt% are preferred.

In particular embodiments, the fiber cement products of the present invention comprise hydrophobized natural fibers, which are present in an amount of between about 3 weight% and about 6 weight% compared to the total weight of the dry components of the fiber cement product. In further particular embodiments, the fiber cement products of the present invention comprise hydrophobized cellulose fibers, which are present in an amount of between about 3 weight% and about 6 weight% compared to the total weight of the dry components of the fiber cement product.

According to particular embodiments, the fiber cement products according to the invention may additionally comprise other inorganic or organic reinforcing fibers in a weight % of about 0.1 to about 5. In particular embodiments, organic fibers are organic synthetic fibers selected from the group consisting of polypropylene, polyvinylalcohol polyacrylonitrile fibers, polyethyelene, polyamide fibers, polyester fibers, aramide fibers and carbon fibers. In further particular embodiments, inorganic fibers are selected from the group consisting of glass fibers, rockwool fibers, slag wool fibers, wollastonite fibers, ceramic fibers and the like. In further particular embodiments, the fiber cement products of the present invention may additionally comprise fibrils fibrids, such as for example but not limited to, polyolefinic fibrils fibrids % in a weight % of about 0.1 to 3, such as "synthetic wood pulp".

In particular embodiments, the hydrophobized natural fibers are natural fibers, which are hydrophobized with a siliconate. Siliconates comprise at least one Si - OZ, wherein Z is any of elements belonging to alkali metals, such as for example but not limited to sodium or potassium.

In further particular embodiments, the natural fibers in the fiber cement products of the present invention are hydrophobized by pre-treatment with an alkali metal organosiliconate, such as an alkali metal methyl siliconate. In some embodiments, an alkali metal is potassium or sodium.

In yet further particular embodiments, the natural fibers in the fiber cement products of the present invention are hydrophobized by impregnation with potassium methyl siliconate or with sodium methyl siliconate or with a combination of potassium methyl siliconate and sodium methyl siliconate.

In yet further particular embodiments, the hydrophobized natural fibers are natural fibers, which are hydrophobized with potassium methyl siliconate.

The production of hydrophobized natural fibers can be done by any standard method in the art.

For example, a method to hydrophobized natural fibers may be to prepare an aqueous dispersion of a siliconate in water, wherein the concentration of siliconate ranges from 0.1% to 20% by weight in water. In particular embodiments, a suitable dispersion can comprise from 0.1% to 10% of an alkali metal organosiliconate by weight of the aqueous dispersion. In further particular embodiments, a suitable dispersion can comprise from 1% to 7.5% of an alkali metal organosiliconate by weight of the dispersion. In further particular embodiments, a suitable dispersion can comprise from 1% to 5% of an alkali metal organosiliconate by weight of the aqueous dispersion.

The aqueous dispersion is then stirred, optionally in the presence of inorganic fillers. Inorganic fillers can optionally act as a catalyst. A suitable inorganic filler is for example but without limitation sodium silicate. In particular embodiments, the aqueous siliconate dispersion further comprises between 0.5% and 5% of sodium silicate, such as between 1% and 4% of sodium silicate, such as preferably between 1% and 3% of sodium silicate.

When the siliconate is for example potassium siliconate, one obtains the following reaction: 2 CH 3 -Si-

In this way, siliconates react according to a hydrolysis in the presence of carbon dioxide to provide silanols and a metal salt as reaction products.

Once the aqueous dispersion of a siliconate is produced, the natural fibers in the form of for example cellulosic material, paper or textile, are impregnated or coated by means of impregnation or conventional coating devices for coating, such as for example a type of size press.

The step of impregnation is preferably performed by immersion of the cellulosic material in a bath containing the solution comprising the aqueous siliconate dispersion. When the natural (cellulosic) fibers are offered as (paper) sheets or rolls, this impregnation can be done using e.g. a dip bath in which the sheets or rolls are soaked with the solution.

Alternatively, the natural (cellulosic) fibers can be pulped in the solution, and the fibers can as such be soaked in the solution. The excess of solution can be drained of, e.g. by dripping out, filtering and/or sucking out the excess of solution. The step of impregnation can also be carried by spraying the solution comprising a siliconate, or by using a blade coater or a roll coater.

The step of coating or impregnation is carried out in the presence of a catalyst based on a metal ester.

Cellulose fibers with a moisture content in the range between 5 and 20 weight % of water are preferred. Cellulose fibers shaped as a paper sheet are preferably used in the methods according to the invention.

The methods according to the present invention optionally comprise an intermediate step of squeezing the siliconate solution from in between the cellulose fiber walls. This step of squeezing can be performed by a method selected from but not limited to methods using a belt press or a screw press, vacuum filtration, compression filtration, ultracentrifugation, heat or vacuum treatment. According to preferred embodiments of the present invention, the step of squeezing in the methods for the treatment of cellulose fibers can be performed by passing the impregnated cellulose fibers through a roller press.

Pressing the impregnated fibers through the roller press, also called a padding mangle, or by any other means, may force the solution comprising the siliconate to penetrate into the cellulose fiber lumen and even into the cellulose fiber walls such as to obtain precipitated silica in the latter, and squeezes the excess of solution from in between the impregnated cellulose fibers.

The step of squeezing in the methods according to the present invention is optionally performed directly after the step of impregnation of the cellulose fibers.

A subsequent step of drying may be performed in a ventilated oven (such as a thermic oven, preferably an infrared oven) or under vacuum, and at temperatures possibly ranging from 20°C to 120°C, preferably from 25°C to 80°C. The step of drying of the treated natural fibers may reduce the presence of volatile organic compounds in products which are manufactured with the treated fibers. The dry cellulose fibers still may comprise an amount of solvent, which tends not to evaporate completely. A remaining content of 15%w of solvent in the dried cellulose fibers may be present. The removed solvent and the hydrolysis products are preferably recovered which is economical and ecologic.

The cellulose fibers can be subjected to additional fiber treatments such as biocide treatment. After deposition of the dispersion on the natural fibers in the form of cellulosic material, paper and/or textile, the impregnated material is heated to remove water. After the treatment, an invisible chemical siliconate coating is obtained on and into the impregnated material, which coating still allows pulping of the material into coated or hydrophobized fibers.

According to a second aspect, the present invention provides processes for the production of a fiber cement product according to the present invention, the processes at least comprising the steps of:

a. Preparing a fiber cement slurry at least comprising water, cement and hydrophobized natural fibers;

b. Producing a green fiber cement product by means of fiber cement manufacturing process chosen from the group consisting of a Hatschek process, a Magnani process, a flow-on process, an extrusion process and the like; and

c. Curing the green fiber cement product.

Fiber cement products are manufactured starting from an aqueous fiber cement slurry comprising hydraulic binders, fibers, and possibly fillers and additives. This aqueous suspension is mixed in order to obtain a uniform distribution of the components. The suspension is then dewatered. The so obtained green fresh product can be shaped into a flat sheet, a corrugated sheet or a tube. The green shaped product is then hardened under atmospheric conditions (air-curing) or under specific pressure and temperature conditions (autoclaving).

The reinforcing fibers used in the manufacture of the fiber cement products of the present invention are from natural origin. Optionally, synthetic fibers, such as poly(vinylalcohol), polypropylene and polyacrylonitrile fibers, may additionally be present in the fiber cement slurry.

The Hatschek process is most widely known for the manufacturing of fiber-cement products. Other manufacturing processes known by the man skilled in the art which can be cited are Magnani, Mazza, flow-on, extrusion and injection. The Hatschek process is based on the use of a dewatering cylindrical sieve. In this way, a layer originating from a diluted suspension of fibers, cement, fillers and additives contained in a vat is transferred to a felt, through a cylindrical sieve; this layer is then enrolled on a forming drum until the required thickness of the sheet is obtained.

The fiber cement sheet shaped on the forming drum is cut and removed from the drum, once the desired thickness is obtained.

The processes according to the present invention may further comprise the step of cutting the fiber cement products to a predetermined length to form a fiber cement product. Cutting the fiber cement products to a predetermined length can be done by any technique known in the art, such as but not limited to water jet cutting, air jet cutting or the like. The fiber cement products can be cut to any desirable length, such as but not limited to a length of between about 1 m and about 15 m, such as between about 1 m and about 10 m, more particularly between about 1 m and about 5 m, most particularly between about 1 m and about 3 m.

It will be understood by the skilled person that the processes of the present invention may further comprise additional steps of processing the produced fiber cement products.

For instance, in certain particular embodiments, during the processes of the present invention, the fiber cement slurry and/or the fiber cement products may undergo various intermediate treatments, such as but not limited to treatment with one or more hydrophobic agents, treatment with one or more flocculants, additional or intermediate pressing steps, etc.

As soon as the fiber cement products are formed, these are trimmed at the lateral edges. The border strips can optionally be recycled through immediate mixing with the recycled water and directing the mixture to the mixing system again.

In yet a further step of the methods for the production of fiber cement products of the invention, the obtained fiber cement products are cured. Indeed, after production, fiber cement products can be allowed to cure over a time in the environment in which they are formed, or alternatively can be subjected to a thermal cure (e.g. by autoclaving or the like).

In particular embodiments, the "green" fiber cement product is cured, typically by curing to the air (air cured fiber cement products) or under pressure in presence of steam and increased temperature (autoclave cured). For autoclave cured products, typically sand is added to the original fiber cement slurry. The autoclave curing in principle results in the presence of 11.3 A (angstrom) Tobermorite in the fiber cement product.

In further particular embodiments, the "green" fiber cement product may be first pre-cured to the air, after which the pre-cured product is further air-cured until it has its final strength, or autoclave- cured using pressure and steam, to give the product its final properties.

In particular embodiments of the present invention, the methods for the production of fiber cement products of the invention may further comprise the step of thermally drying the obtained fiber cement products. After curing, the fiber cement product being a panel, sheet or plate, may still comprise a significant weight of water, present as humidity. This may be up to 10 even 15 %w, expressed per weight of the dry product. The weight of dry product is defined as the weight of the product when the product is subjected to drying at 105°C in a ventilated furnace, until a constant weight is obtained.

In certain embodiments, the fiber cement product is dried. Such drying is done preferably by air drying and is terminated when the weight percentage of humidity of the fiber cement product is less than or equal to 8 weight %, even less than or equal to 6 weight %, expressed per weight of dry product, and most preferably between 4 weight % and 6 weight %, inclusive.

The fiber cement products comprising the cellulose fibers which have been treated according to the method of the present invention may have an improved durability over fiber cement products not comprising the treated cellulose fibers according to the present invention.

The amount of treated cellulose fibers in the fiber cement products is preferably in the range of 0.5 to 8 weight % with respect to the dry weight of the hydraulic composition, preferably between 3 and 6 weight % with respect to the dry weight of the hydraulic composition.

The dry weight of the hydraulic composition is to be understood here as the weight of the hydraulic composition before dilution with water necessary to prepare the fiber cement slurry which is used in the manufacture of the fiber cement product.

In further particular embodiments of the processes according to the present invention, the hydrophobized natural fibers are hydrophobized cellulose fibers.

In yet further particular embodiments of the processes according to the present invention, the hydrophobized natural fibers are natural fibers, which are hydrophobized with a siliconate.

In yet further particular embodiments of the processes according to the present invention, the hydrophobized natural fibers are natural fibers, which are hydrophobized with potassium methyl siliconate.

In a third aspect, the present invention provides fiber cement products obtainable by the methods for the production of fiber cement products according to the present invention.

In a fourth aspect, the present invention provides fiber cement products, and in particular fiber cement building materials, comprising hydrophobized natural fibers.

In a fifth aspect, the present invention provides uses of hydrophobized natural fibers for the preparation of fiber cement compositions and/or for the manufacture of fiber cement products, such as in particular fiber cement building materials. In a sixth aspect, the present invention provides uses of the fiber cement products of the present invention as building materials.

These fiber cement building materials may be porous materials comprising one or more different materials such as a gypsum composite, cement composite, geopolymer composite or other composites having an inorganic binder. The surface of the material may be sanded, machined, extruded, molded or otherwise formed into any desired shape by various processes known in the art. The fiber cement building materials may be fully cured, partially cured or in the uncured "green" state. Fiber cement building materials may further include gypsum board, fiber cement board, fiber cement board reinforced by a mesh or continuous fibers, gypsum board reinforced by short fibers, a mesh or continuous fibers, inorganic bonded wood and fiber composite materials, geopolymer bonded wood and fiber boards, concrete roofing tile material, and fiber-plastic composite material.

In particular embodiments, the fiber cement products of the invention are fiber cement sheets produced by the processes of the present invention and can be used to provide an outer surface to walls, both internal as well as external a building or construction, e.g. as fagade plate, siding, etc.

In particular embodiments, the present invention provides uses of the fiber cement product according to the present invention as a fagade element or a roofing element, such as but not limited to a slate.

Examples

The present invention will be further described with respect to particular embodiments.

It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, steps or components as referred to, but does not preclude the presence or addition of one or more other features, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Throughout this specification, reference to "one embodiment" or "an embodiment" are made. Such references indicate that a particular feature, described in relation to the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, though they could. Furthermore, the particular features or characteristics may be combined in any suitable manner in one or more embodiments, as would be apparent to one of ordinary skill in the art.

Methods and materials a) Fiber treatment

A sample of a paper sheet of unbleached kraft cellulose was impregnated with a solution comprising 10% or 3% of sodium methyl siliconate by immersion in a bath. In some instances, the solution further contained 1% sodium silicate or 3% sodium silicate. The excess solution was removed from the wet paper using a roller press and subsequently the material was dried in an infrared oven. b) Preparation of fiber cement test samples

The fibers treated as explained in the preceding paragraph were dispersed in water using a laboratory desintegrator and mixed afterwards with the other components of the hydraulic composition comprising ordinary Portland cement, amorphous calcium carbonate and amorphous silica. A flocculant based on polyacrylamide was added and the mixture was poured immediately after in a mould of a filter press of dimension 70*200 mm and the excess water was removed by pressure.

The fiber cement test samples were cured under plastic at room temperature for 14 days. c) Ageing cycles

The fiber cement test samples were subjected to 20 consecutive ageing cycles of 15 hours per cycle. One ageing cycle comprised the following steps:

immersion in water for 6 hours;

drying in hot air (60°C) for 1 hour;

drying at room temperature for 1 hour;

exposure in 25% C0 2 environment for 3 hours;

drying in hot air (60°C) for 3 hours;

drying at room temperature for 1 hour. d) Measurement of physico-chemical properties

After 29 days, the formed air-cured fiber cement samples were analyzed for their physico-mechanical characteristics, including modulus of rupture (MOR; expressed in Pa= kg/m.s 2 ). The modulus of rupture (MOR; expressed in Pa= kg/m.s 2 ) was measured by making use of a UTS/INSTRON apparatus (type 3345; cel=5000N).

Example 1

Pre-treated hydrophobized cellulose fibers were redispersed in water and used for the manufacture of fiber cement composite test samples (see Table 1).

Table 1 - Overview of FC formulations prepared in accordance with Example 1 (amounts are % of ingredient based on the total mass of solids). The resulting fiber cement samples were analyzed for their physico-mechanical characteristics (see Table 2)

Table 2 - Overview of mechanical properties (sMOR and MOR/d 2 ) of reference sample and samples 1 to 4 as prepared in accordance with Example 1

It can be observed from Table 2 that the composites containing hydrophobized natural fibers according to the invention better retain their mechanical strength (MOR and work of fracture) than the composites containing untreated fibers.

Conclusion

From the above results, it is clear that fiber cement products according to the present invention, which comprise hydrophobized cellulose fibers showed at least comparable and even improved strength properties when compared to fiber cement products comprising untreated non- hydrophobized fibers.