WO1996015077A1

WO1996015077A1 - Process for preparing compositions containing cellulose-based fibres

Info

Publication number: WO1996015077A1
Application number: PCT/FI1995/000624
Authority: WO
Inventors: Pertti Viitaniemi; Saila JÄMSÄ; Pentti Ek; Kirsti Riipola
Original assignee: Valtion Teknillinen Tutkimuskeskus
Priority date: 1994-11-11
Filing date: 1995-11-13
Publication date: 1996-05-23
Also published as: FI945338A0; FI104569B; AU3873395A; FI945338A

Abstract

The invention concerns a process for preparing compositions containing cellulose-based materials, according to which process a finely-divided cellulose-based material is mixed with an aggregate. According to the invention, the cellulose-based substance, such as wood or cellulose fibres, is first heated at a temperature of 150 to 300 °C before it is mixed with the aggregate. As a result of the heat treatment, the material becomes less hygroscopic, which makes it easier to mix with other substances. Furthermore, the mono- and polysaccharides and extractives contained in wood are partly decomposed and removed during the heat treatment. The wood or cellulose product thus obtained is particularly useful as a filler of concrete, asphalt and plastics, and, e.g., incorporated into a concrete mix, it does not impair the hardening of the mix.

Description

based^df bre ^{eParin9 COm}P°^sitions containing cellulose-

The present invention concerns a process in accordance with the preamble of claim 1 for preparing compositions containing cellulose-based fibres. According to the process, finely-divided cellulose-based material is mixed with an aggregate.

It is difficult to combine cellulose-based fibres and equivalent finely-divided wood and cellulose raw materials with other materials. This is due to the chemical composition of the materials and their hygroscopic character. Thus, for instance, the sugars contained in wood retard the hardening of concrete mixes containing wood fibres. For this^~reason, wood fibres have to be pretreated in different ways if hardening of concrete is to be obtained. However, the processes known in the art, which are based on extraction of the wood fibres, are complicated and time-consuming.

The properties of asphalt have been improved by mixing recycled cellulose-based fibres with the asphaltic mixture. The quality of the recycle fibre varies very much which gives rise to great problems in combining the fibres with the asphalt. Primarily, the problems relate to the mixing of the fibres; untreated cellulose fibres have been found not to mix evenly enough with asphalt compositions.

When wood and polymers are to be combined the hydroscopic character of wood and its different swelling properties causes considerable problems. Because of this, wood and polymers have been very seldom been combined even if cellulose-based fibres offer an interesting and environmentally acceptable possibility of changing the properties of polymer-based materials.

It is an object of the present invention to eliminate the problems related to the prior art and to provide an entirely novel solution for preparing compositions containing cellulo- se-based materials. In particular, it is an object of the invention to provide a process to get cellulose-based materials more evenly mixed with other material and to enhance the compatibility of various materials.

CORRECTED The present invention is based on the finding that when cellulose-based materials, such as wood or cellulose fibres, are heated to a temperature over 150 °C, the properties of the material change radically. The fibres become less hydroscopic which makes it easie to mix them with other materials. Furthermore, during the heat treatment the mono- an polysaccharides and extractives present in wood are decomposed and partially removed from the wood fibre. As a result of the process the wood or cellulose fibre obtained does not retard the hardening of, e.g., concrete mixes. Further, the swelling of wood fibres become smaller, the decay resistance is improved and thermal conductivity is decreased, which help to improve the compatibility of wood fibres with other substances, such as polymers. Thus, a heat-treated cellulose-based material of the present kind can well be mixed with aggregates to form different kinds of compositions

More specifically, the process according to the invention is mainly characterized by what is stated in the characterizing part of claim 1.

In the process according to the invention the cellulose-based material used comprises, for instance, wood fibres, cellulose fibres, wood flour and/or wood chips. The wood raw material is finely-divided, which means that the particle sizes of the wood flour is about 0.01 to 10 mm, preferably about 0.05 to 5 mm. The cross sections and thick¬ nesses, respectively, of the wood fibres and wood chips are also about 0.01 to 10 mm, preferably about 0.05 to 5 mm.

According to one preferred embodiment suitable wood or cellulose fibres are prepared by grinding a lignocellulosic raw material. The keader milling can be obtained for example with refiners provided with grooved blades, such as disc or core refiners. The following examples can be mentioned as exemplifying embodiments of suitable materials: the wood material used for preparing fibre boards, such as wood fibres for MDF boards, cellulose fibres obtained from mechanical pulping, fibres of recycled pulps and saw dust. Wood and cellulose fibres are particularly preferred.

The cellulose-containing material can be derived from wood, such as spruce, pine, birch and aspen, or from one or annual or perennial plants. Therefore, straw is also useful as a raw material.

According to the invention the cellulose-based material is heated to a temperature of at least 150 °C until the weight of the material has decreased by at least 3 % (calculated on basis of the dry matter). The heating can be continued to a weight loss of about 22 to 25 % without undue weakening of the strength properties of the material.

It is known per se to treat finely-divided wood material at an increased temperature. EP Published Patent Application No. 0 373 726 describes plasticizing of a fibrous cellulose product by heating at a temperature of 150 to 220 °C in the presence of an aqueous plasticizing agent at increased pressure, which is followed by drying and hardening of the product at an increased temperature to provide a cross-linked structure. FI Patent Application No. 920774 relates to a process for treatment of ground wood with steam to improve its paper technical properties. GB Published Patent

Application No. 2 185 748 discloses a process for preparation of a fibre board, the process comprising the step of first heating the wood fibres or chips in an autoclave at a temperature of 100 to 200 °C for at least one hour before they are joined together with a binder in order to form a board. By means of the process it is possible to improve the moisture resistance of the board. A similar method is presented also in EP Published Patent Application No. 0 186 503, wherein wood chips are first treated with water vapour at an increased pressure and then they are formed into a layer which is admixed with a phenol-formaldehyde resin powder, which works as a binder when the chips are pressed together to form a composite board.

The present invention differs from the above described prior art in the sense that, according to the invention, the cellulose-based material is used for forming compositions which do not contain the cellulose-based material as its main component. Within the scope of the present invention, the main components of the compositions are also called "the aggregate" or "the matrix of the compositions". Typically the cellulose- based material forms about 0.1 to 49 %, preferably about 1 to 40 % of the dry weight of the compositions. It is an object of the invention is to improve the properties of the cellulose-based material by heat treatment so that is more suitable for use in compositions in which it is mixed with the aggregate of the composition. This aggregate can be mixed or dissolved in water or an aqueous solvent or some other liquid.

The heat treatment according to the invention affects the chemical properties of the wood; the wood sugars, i.e. the mono- and polysaccharides, and the extractives of wood are removed. At the same time the wood becomes less hygroscopic and its resistance to decay is improved. As a result of the wood being less hygroscopic, the cellulose-based material mixes well with liquids, in particular water and aqueous mixtures. This feature will also appear from Example 1 below.

The heat treatment of the cellulose-based material, e.g. the wood fibres, can be carried out for dry or wet fibres. If the wet fibres are processed, lump-forming has to be prevented during the drying step. Ignition of the material during heat processing can b prevented by carrying out the treatment at oxygen-free conditions. The heat treatment according to the invention is therefore preferably carried out in a moist atmosphere which is saturated with, e.g., water vapour. In contrast to the prior art methods, the heat treatment according to the present invention is preferably carried out at pressure- less conditions.

According to a first embodiment of the invention cellulose-based material obtained fro unseasoned wood or vegetable material is subjected as such to heat treatment at a temperature of at least 150 °C.

According to a second embodiment the heat treatment of moist cellulose-based material is carried out in two stages by first drying the product to the desired moisture content usually less than 15 % . Then the temperature is rapidly increased to over 150 °C (typically to about 180 to 300 °C), and the treatment is continued at that temperature until the weight loss of the product which is being treated is at least 3 % .

In said second embodiment a finely-divided substance can be used as a starting material 5 which is dried in any suitable conditions (even outdoors at ambient temperature) to the desired moisture content of less than 15 %. According to a preferred embodiment of the invention the product is, however, dried at increased temperature, e.g. at a temperature of 90 to 120 °C. A darkening of the colour of the wood product will then take place. When the product has been dried to a moisture content of less than 15 %, the treatment is continued at a higher temperature. In the second stage of the process, the temperature is kept higher than in the first stage. It is preferred to operate the process at about 150 to 300 °C in an atmosphere saturated with steam. The temperature can also be increased in the middle of the second stage. The duration and the temperature of the treatment will depend on each other; at a high temperature the duration of the treatment is shorter than at a lower temperature. Typically the heat treatment of the second stage will last for at least 1 minute, preferably for 0.05 to 20 hours and in particular for about 0.1 to 10 hours. By controlling the weight loss of the product with the help of the heat treatment, its mixing properties can be changed as desired. The resistance of the product against mould and decay is also improved already at a 3 % weight loss, but said resistance can further be improved by continuing the heating until a weight loss of at least about 5 %, preferably at least about 6 or even 8 %, has taken place.

As specific examples of the aggregates of the compositions according to the present invention the one already indicated above can be mentioned: cements with possible fillers, such as stone aggregate; polymers, in particular thermoplastics, preferably polyolefins, polyesters or polyethers, together with any fillers including pigments, and bitumen and asphalt mixes optionally containing stone aggregate or another fillers. In many cases the compositions are hardened at, e.g., room temperature or by heat treatment which achieves crosslinking or crystallization of the aggregate or it stiffens or solidifies in some other way. The proportion of the aggregate of the prepared composition is typically about 1 to 99.9 % , preferably about 10 to 99 % (of dry matter).

According to one particularly preferred embodiment of the invention the heat-treated finely-divided wood material can be used for preparing wood-based form part, which contain a binder comprising at least partially cement or a similar calcium-containing binder. In this working embodiment as well as in the above concrete embodiments, the cements can be traditional Portland cements, but also rapid cements are suitable for use The cements used can further comprise slag-based cements, in which case an alkali can be separately added to the mixture as an activator of the cement. In addition to the cement, some suitable resin adhesive or a protein-based binder, such as gluten, can be used as a binder in the preparation of the form parts.

The composition or mixture used for preparing the form parts can be hardened either a room temperature or at increased temperature. In the latter alternative the temperature is kept at about 50 to 300 °C. The hardening time at room temperature differs depending on the size of the part but it usually last for a couple of days. At increased temperature the mixture can be hardened within a few hours.

The use of the heat-treated wood raw material makes it possible to achieve a hardening of cement-containing mixes at room temperature.

The present form parts contain so much wood raw material that it can be used for making a wall without moisture barriers. Thus, in this way plastic-free building can be attained. The thermal resistance of the products is rather good, usually of the order of 0.05 to 0.08 W/m°C, which is fully comparable with the corresponding values for mineral wool: 0.04 to 0.05 W/m°C.

The invention provides considerable advantages. Thus, normally when a cellulose-based material, such as wood fibres, are mixed with, for example, water, the fibres will form lumps and a deposition on the bottom of the mixing vessel. By heat modification of the wood fibre it is possible to get it evenly distributed throughout the water phase. There i no lump-forming and a deposition is slowly formed on the bottom of the vessel. Heat modification will reduce the thermal conductivity of wood fibres, which makes it possible to use it in combination with other products as, e.g., frost insulation. During heat modification the wood fibre will become lighter. Furthermore heat modification of the wood fibre improves the compatibility with, e.g., cement. The mix will harden at room temperature. As the same time it becomes possible to increase the portion of the wood fibres among concrete. .

In the following the invention will be examined in more detail with the help of a couple of working examples:

Example 1

The use of wood fibres for preparing asphalt

The applicability of cellulose-based fibres for admixing with asphalt can be checked with a quick-test, wherein 4 - 5 g of the fibres are added to 200 ml distilled water. The mixture is mixed with a pencil. If the pen remains standing in the mixture, the mixability can be considered good.

Spruce and aspen fibres heat processed (3 h, 205 °C) according to the previous quick test mix well. The same test was made to fibres, which caused the fibres to adhere to the other fibres. And, as a result, the fibres gel together on the bottom of the mix and the pen does not stand.

Example 2 The use of wood fibres for preparing concrete

During manufacture of conventional concrete it has been found that hardening will commence within 7 days of the preparation of the mix. The compression strength test is carried out according to the standards after a 28 day hardening period.

When normal wood fibres are added to concrete mixes the hardening of the mix is essentially retarded of even prevented. When heat-processed wood fibres are added to a cement mix the hardening process will proceed in a conventional manner without any disturbances. 8

Example 3

The use of wood fibres together with cement and gluten for preparing form pieces

Form pieces containing gluten and cement as binders, were prepared according to t following receipt:

200 g wood-treated wood fibres (aspen, 205 °C, 3 h)

200 g wood-treated cutter chips (aspen, 205 °C, 3 h)

100 g gluten 600 g cement

1500 ml water

The dry substances were first dry mixed in a mixer. Then, water was added under vigorous mixing to obtain foaming of the mix. The mix was shaped as desired into form piece, which was allowed to dry at room temperature for one week. The end product obtained comprised a light, sheet-shaped insulation element, which can be u in a similar was as rigid board of mineral wool. It can be processed with ordinary t (knife and saw).

Claims

Claims:

1. A process for preparing a composition containing cellulose-based material, according to which process

- a finely-divided cellulose-based material is mixed with an aggregate, characterized in that

- the cellulose-based material is heat treated first at a temperature over 150 °C until a 3 % loss of product weight has been reached, and then, subsequently, it is mixed with the aggregate.

2. The process according to claim 1, wherein the cellulose-based material is dried to a moisture content of less than 15 % and then it is kept in a moist atmosphere at a temperature of 150 °C to 300 °C until loss of product weight of about 3 to about 25 % is reached.

3. The process according to claim 2, characterized in that the cellulose- based substance is dried to a moisture content of less than 15 % at room temperature.

4. The process according to claim 2, characterized in that the cellulose- based substance is dried to a moisture content of less than 15 % at about 90 to 100 °C.

5. The process according to any of the previous claims, characterized in that the cellulose-based material is treated at 180 to 300 °C for 0.05 to 20 hours, preferably for about 0.1 to 10 hours.

6. The process according to claim 1, characterized in that during the heat treatment the atmosphere is kept saturated with water vapour.

7. The process according to claim 1, characterized in that the heat treatment is carried out at least essentially at pressure-less conditions.

8. The process according to any one of the previous claims, characterized in that the cellulose-based material used comprises wood fibres, cellulose fibres, wood powder and/or wood chips.

9. The process according to claim 8, characterized in that the cellulose- based substance used comprises fibres obtained by grinding.

10. The process according to any one of the previous claims, characterized in that the aggregate used comprises a calcium-containing binder, such as cement, possibly together with a filler.

11. The process according to claim 10, characterized in that the heat processing is continued until at lease a part of the mono- and polysaccharides of the cellulose-based substance have been removed.

12. A process according to claim 10 or 11, characterized by preparing from the cellulose-based material together with cement and possibly another binding agent, such as gluten, a composition which can be hardened to the desired shape.

13. The process according to any one of claim lto9, characterized in that the aggregate used comprises asphalt mass.

14. The process according to any one of claims lto9, characterized in that the aggregate used comprises a polymer.

15. The process according to any one of claim 1 to 9, wherein a liquid composition is prepared, characterized in that the cellulose-based substance is heated in order to make it mix better in the liquid.