WO1996014970A1

WO1996014970A1 - Wood-based form parts and a method for the preparation thereof

Info

Publication number: WO1996014970A1
Application number: PCT/FI1995/000623
Authority: WO
Inventors: Kirsti Riipola; Hellevi Botska; Saila JÄMSÄ; Pertti Viitaniemi
Original assignee: VTT Technical Research Centre of Finland Ltd
Current assignee: VTT Technical Research Centre of Finland Ltd
Priority date: 1994-11-11
Filing date: 1995-11-13
Publication date: 1996-05-23
Anticipated expiration: 1997-05-11
Also published as: FI98502B; AU3873295A; FI945337L; FI945337A0; FI98502C

Abstract

The invention relates to wood-based form parts, which are composed of a finely-divided wood material which is mixed with a binder and hardened into the desired shape, a method for the preparation thereof and the use of the form parts. According to the invention, the binder of the form parts comprises at least partially gluten or a similar cereal-based protein product, the weight ratio between the gluten and the wood raw material being about 0.05 to 3. Preferably, the finely-divided wood material comprises wood chips, wood fibres or wood flour. According to a preferred embodiment, the form parts contain also cement and/or gypsum and possibly a foaming agent, glycerol, glycol and/or a boron-containing substance. The form parts according to the invention can be employed for preparing heat insulation boards which are easily shaped. The thermal resistance of the heat insulation boards is of the order of 0.05 to 0.08 W/m °C.

Description

Wood-based form parts and a method for the preparation thereof

The present invention relates to wood-based form parts according to the preamble of claim 1.

Such form parts generally contain a finely-divided wood material, which has been mixed with a binder and hardened to desired shape.

The invention also concerns a method according to the preamble of claim 8 for preparing wood-based form parts.

Furthermore, the invention relates to the use of the present form parts as heat insulation.

Mineral wool belongs to the most common heat insulation materials of buildings. In horizontal constructions cellulose wool is also used. Wood fibre boards have been used as insulation elements particularly in remodelled buildings. Before the development of the heat insulation materials industry, wood chips and saw dust were used for heat insulation purposes.

Considerable problems are, however, associated with the prior art. Thus, the dust released from mineral wool during handling is a considerable problem; it is suspected that the dust might cause cancer. For this reason it is possible that the use of mineral wool will be banned in the future in some industrial countries, e.g., Germany.

Furthermore, mineral wool constructions behave differently under humid conditions than solid constructions, for which reason typical wool constructions generally have to be provided with a polymer foil working as a steam barrier. Cellulose wool is usually suitable only for horizontal constructions. The use of it for vertical constructions has been tested by spraying wet cellulose wool onto the walls. However, by this way the construction is subjected to a large humidity stress. Cellulose wool cannot be used in any other way for insulation of vertical constructions. The heat insulation of fibre boards is not as good as of mineral wool and the thickness of the products is limited. The thermal resistance of chips has found to be rather poor. As an additional problem it should be mentioned that wood chips without binders settle and the heat insulation of the upper part of the construction will deteriorate with time.

It is an object of the present invention to eliminate the problems related to the prior art and to provide entirely novel wood-based form parts which can be used, for instance, as board-shaped heat insulation materials, and a process for the preparation thereof.

The invention is based on the concept of using gluten or a similar cereal-based protein as a binder of finely-divided wood material. Mixed with the wood raw material gluten will improve its mixability, it will work as a foaming agent and as a binder, and as a result, by using the gluten it will become possible to prepare porous parts, which have good thermal resistance and sufficiently good mechanical properties.

In particular, the form parts according to the invention are mainly characterized by what is stated in the characterizing part of claim 1.

The method according to the invention is, again, characterized by what is stated in the characterizing part of claim 8.

Within the scope of the present invention, "gluten" denotes the protein substance of the seed protein of wheat consisting of proteins soluble in alcohol (i.e. gliadine) and of proteins insoluble in alcohol and water (i.e. glutelin). The last-mentioned protein- fraction is soluble in acids and bases. Gluten, which in Finnish also is called "sitko", is in its pure form a light yellow, neutral or weakly alkaline powder and its proteins contain on an average about 17.5 % nitrogen. It is of great importance for the baking properties of wheat. Gluten is, however, used also as a vegetable protein in the food industry, for instance for preparation of glutamates, and as a glue. Gluten, its preparation and properties have been discussed, i.a., in the following articles: Pence et al., Cereal Chem. 22 (1950) 335 and Meredith, Cereal Sci. Today 2 (1964) 33, 54.

According to the present invention gluten is particularly preferred but other vegetable proteins having corresponding properties can also be used as well. It is important that the protein be at least partially water insoluble and that it forms a colloidal mixture with water. Suitable proteins are, for instance, the alcohol-insoluble protein fraction on maize which is a product known as a prolamine protein. It is called by the name zein and its properties are rather similar to those of gluten. Gluteiin which forms a part of gluten can also be obtained from oats, in which case it is called avenine, and from rice (oryzenin).

In addition to pure products it is possible in the present process to use only extraction fractions containing vegetable-based proteins. Thus, from the extraction of gluten, which is effected by "washing" out by a water most of the wheat starch, the water- soluble proteins and the pentosanes, a viscoelastic mass is obtained which contains about 65 to 70 % water and which has a dry matter containing about 85 % proteins, about 8 % lipids, about 6 % starch and about 1 % mineral substances. This product which thus contains abundantly water can suitably be used instead of pure gluten as a binder. By combining the preparation of form parts with the extraction of gluten, the process steps relating drying and purification can be eliminated from the latter manufacturing process. From the preparation of the form parts it is possible to leave out the dissolution of the gluten in water. In this case the finely-divided wood material is directly mixed with the viscoelastic mass.

In addition to gluten, calcium-containing binders, such as gypsum (CaSO₄) and cement can be used as binders of the wood-based form parts. The cements can be traditional cements, such as Portland-cements, but also rapid cements are suitable for use. The cements used can be comprised of slag-based cements, in which case alkali can be separately added to the mix as an activator of the cement.

The wood raw material used for the preparation of the form parts according to the invention comprise, for example, wood 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 thicknesses, respectively, of the wood fibres and wood chips are also about 0.01 to 10 mm, preferably about 0.05 to 5 mm.

The strength and porosity of the mixtures can be improved by using suitable foaming agents. As examples of these agents various carbonate-based substances, such as sodium bicarbonate and baking powder, which under the influence of heat and acid release carbon dioxide, can be mentioned. The frothing is important for the provision of a sufficiently light structure which has the desired heat insulation properties.

Glycerol and/or glycol can further be used during manufacture. The purpose of these substances is to improve moisture resistance.

The biological resistance of the product (against mould and insects) can be improved by adding a wood protection agent, e.g. a boron-containing agent which simultaneously works as a flame retardant.

The weight ratio between the gluten and the wood raw material is preferably 0.05 to 3. The general composition of a suitable mixture is as follows:

finely-divided wood raw material 50 - 1,000 parts by weight gluten 0.25 - 3000 parts by weight glycerol 0 - 500 parts by weight glycol 0 - 500 parts by weight cement 0 - 20.000 parts by weight gypsum 0 - 10.000 pans by weight foaming agent 0 - 500 parts by weight borax 0 - 1 ,000 parts by weight

Particularly preferred are the following compositions:

finely-divided wood raw material 100 - 500 parts by weight gluten 100 - 500 parts by weight glycerol 0 - 200 parts by weight glycol 0 - 200 parts by weight cement 0 - 3,000 parts by weight gypsum 0 - 1,000 parts by weight feinting agent 0 - 50 parts by weight borax 0 - 200 parts by weight

The amount of water is preferably about 0.1 to 10 times the weight of dry matter.

The form parts can easily be shaped into the form required by the specific application by casting the foamed mixture into a mould and by letting it harden therein. Thus, utility articles, such as parts of furniture, can be prepared from the hardened mixtures.

According to a preferred embodiment the mixture is formed into a board, which can be used as insulation of buildings. Typically the density of a board of this kind is about 50 to 750 kg/m³, for example about 70 to 450 kg/m³, preferably about 70 to 200 kg/m³. In particular, heat insulation materials are produced having a thermal conductivity of less than 0.07 W/m°C.

The products according to the present invention are prepared by a process according to which finely-divided wood material is mixed with gluten (or an equivalent protein product) to form a mixture which can be hardened, the mixture is shaped into desired form and - it is hardened to produce a form part.

According to a particularly preferred embodiment a dry mixture is first formed from the wood raw material and gluten, water is added to the dry mixture to achieve an aqueous mixture, - the mixture is foamed and the foamed mixture is hardened.

This alternative is suitable for use when the gluten is present in the form of a dried powder.

According to this preferred embodiment, liquid adjuvants, such as glycerol and glycol, are added to the aqueous mixture preferably before frothing. The amounts of gluten and foaming agents, if any, are selected so that by frothing the mixture a mix is obtained whose density after hardening is about 50 to 750 kg/m³, preferably, as mentioned above, about 70 to 200 kg/m³.

Of the dry matter of the hardened mixture, gluten makes up 10 to 750 parts by weight and the cement 0 to 750 parts by weight.

According to one particularly preferred embodiment the finely-divided wood material is heat treated before it is mixed with gluten. The heat treatment not only increases the dimensional stability of the wood material but it also lowers the sugar content of the wood material. The last-mentioned fact is of importance for form parts which are prepared using also cement as a binder, because sugars are known to retard the hardening of cement. A heat treatment of the indicated kind can be carried out at 150 to 300 °C in dry or preferably moist air.

The mixture can be hardened either at room temperature or at an increased temperature. In the latter alternative the temperature is kept at about 50 to 300 °C. The hardening time at room temperature depends on the size of the part, but it generally lasts for a couple of days. At an increased temperature the mixture can be hardened within a few hours.

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

The invention will provide considerable advantages. Thus, as already mentioned above, heat insulation products can be prepared from the form parts according to the invention. A typical feature of these products is the use of renewable raw materials (wood, gluten of wheat) or waste materials (gypsum). Cement increases the strength of the material at the same time as the energy consumption of the preparation decreases. The product can be prepared to the desired thickness. The product contains so much wood raw material that it can be used for preparing walls without moisture barriers. This will make it possible to build without plastics. The gluten works as a foaming agent and the products prepared are being characterized by lightness and good lambda-values. The thermal resistance of the products is rather good, usually on the order of 0.05 to 0.08 W/m°C, for cement-free products even below 0.05, which are fully comparable with the values for mineral wool: 0.04 to 0.05 W/m°C.

In the following, the preparation of the new form parts is described with the aid of working examples:

Example 1

Form parts containing wood fibres, cutter chips and gluten

A mixture was prepared containing

200 g wood fibres

200 g cutter chips

200 g gluten

100 g glycol

1,750 ml water

The dry substances were dry mixed in a mixer. Then the water and the liquid adjuvants were added under vigorous mixing. During the addition of water the mixture started foaming.

A board of the size of about 0.3 x 0.5 x 0.05 m was prepared. It was kept at 200 °C for 1 hour and then it was dried at 150 °C for 3 hours and furtheron overnight in a heating chamber at 80 °C. During the heat treatment swelling of the board took place, but a part of the swelling was reversed after cooling of the board.

The thermal conductivity was determined at VTT Building Technology according to heat flow meter method (HFM method) of Standard ISO 8301. The λ-value obtained was 0.05 W/m°C. Example 2

Form parts containing wood fibres, wood flour and gluten

200 g wood fibres

200 g wood flour

300 g gluten

50 g glycerol

1,750 ml water

By repeating the procedure described in the previous example a board was prepared having a thermal conductivity of 0.05 W/m°C.

Example 3

Form parts containing wood fibres, wood flour and gluten

140 g wood fibres

200 g wood flour

300 g gluten

50 g glycerol

1,750 ml water

A wood-based board was prepared by using the procedure described in Example 1. The thermal conductivity of the board was 0.05 W/m°C.

Example 4

Compositions containing gluten and cement

200 g wood fibres

200 g cutter chips

200 g gluten

200 g cement

10 g baking powder

2,100 ml water By repeating the procedure of Example 1 a board was prepared which contained cement as a binder in addition to the gluten. The board was hardened as described in Example 1 and its thermal conductivity was determined. It was found to have a λ-value of 0.06 W/m^βC.

Example 5

Form parts containing as binders cement and gluten

Form parts containing gluten and cement as binders, were prepared according to the following recipe:

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 achieve foaming of the mix. The mix was shaped as desired into a form piece, which was allowed to dry at room temperature for one week. The end product obtained comprised a light, board-formed insulation element, which can be used in a similar was as rigid board of mineral wool. It can be processed with conventional tools (knife and saw).

Claims

Claims:

1. A wood-based form pan consisting of a finely divided wood material, which is mixed in a binding agent and hardened to desired shape, c h a r a c t e r i z e d in that the binding agent consist of gluten or a similar cereal-based protein product.

2. The form pan according to claim 1 , wherein the weight ratio of gluten to the wood raw material is 0.05 to 3.

3. The form pan according to claim 1 or 2, wherein the finely-divided wood material comprises wood chips, wood fibres or wood flour.

4. The form pan according any one of claims 1 to 3, wherein it contains cement and/or gypsum and possibly foaming agent, glycerol, glycol and or a boron-containing substance.

5. The form pan according to claim 1, wherein it is shaped into a board, which can be used for insulation of buildings.

6. The form pan according to any one of the previous claims, wherein its density is about 50 to 750 kg/m³, preferably about 70 to 450 kg/m³.

7. The form pan according to any one of claims 1 to 3, wherein its density is about 70 to 200 kg/m³ and its thermal resistance is smaller than 0.05 W/m°C.

8. A process for preparing wood-based form parts, comprising the steps of mixing a finely-divided wood material with a binder to form a mixture which is to be hardened, forming the mixture into the desired shape, and - hardening it to form a form pan, c h a r a c t e r i z e d in that the binder used comprises gluten.

9. The process according to claim 8, wherein cement and/or gypsum is admixed with the mixture which is to be hardened.

10. The process according to claim 8 or 9, wherein the gluten portion of the solid matter is 10 to 750 parts by weight and the cement portion is 0 to 750 parts by weight.

11. The process according to any one of claims 8 to 10, wherein the finely-divided wood substance is heat treated before it is mixed with the gluten.

12. The process according to any one of claim 8 to 11, wherein the foaming agent, glycerol, glycol and/or boron containing substance are admixed with the mixture which is to be hardened.

13. The process according to claim 8, comprising - first forming a dry mixture of the wood raw material and the gluten, then adding water to the dry mixture to form an aqueous mixture, foaming the mixture and hardening the foamed mixture.

14. The process according to claim 13, wherein foaming is continued until a mixture is obtained having a density after hardening of about 50 to 750, preferably about 70 to 200 kg/m³.

15. The process according to claim 13, wherein the liquid adjuvants are added to the aqueous mixture.

16. The process according to any one of claims 8 to 15, wherein the mixture is hardened at a temperature in the range of about 50 to 300 °C.

17. The process according to any one of claims 8 to 15, wherein the mixture is hardened at room temperature.

18. The use of a product according to claim 1 as heat insulation for buildings.