NZ264187A

NZ264187A - A method of producing a wood derived material by mixing a cellulosic product with a bonding agent

Info

Publication number: NZ264187A
Application number: NZ264187A
Authority: NZ
Inventors: Antonio Pizzi; Willi Roll; Berthold Dombo
Original assignee: Ruetgerswerke Ag
Priority date: 1993-08-21
Filing date: 1994-08-05
Publication date: 1995-05-26
Also published as: DE4402159A1; EP0639608A1; GR950300015T1; CZ9402006A3; NO943068D0; ATE170892T1; FI943836A; CA2129936A1; MX9405910A; SI9400325A; ES2068171T1; HU9402410D0; HUT71636A; FI943836A0; DE59406873D1; ES2068171T3; CA2129936C; NO943068L; AU7036694A; SK99094A3

Abstract

Thermocurable binders for cellulose-containing products contain tannin and a substance which liberates formaldehyde at elevated temperature. Materials produced using these binders exhibit good strength properties and low swelling values after immersion in water.

Description

<div class="application article clearfix" id="description"> New Zealand Paient Spedficaiion for Paient Number £64187 Patents Form 5 2fi»-l-^g- iwGnijjieie I" cJ: VT .Co^.WS /oo. co'i J Vjoo,; cp; . .Cp«S»9(|^ J Wflr^kft-v, : putic 1 - c • 2 6 MAY 1995 ^ : - f- ....133^ MO n <0 & 1" ?• ^? .«s Nv l/n^Vi?iiVuS N.Z. No. NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION A METHOD OF PRODUCING A WOOD-DERIVED MATERIAL We. RUTGERSWERKE AKTIENGESELLSCHAFT. a company incorporated under the laws of the Federal Republic of Germany, of Mainzer Landstrasse 217, D-60326 Frankfurt/Main. Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- - 1 - (Followed by 1A) 1A 7 A method of producing a wood-derived material This invention relates to a method for the production of a wood-derived material, particularly particle boards, in which tannins are used as the bonding agent. t In the context of the search for natural — and especially-renewable — raw materials for the production of bonding agents for wood-derived materials, the use of tannins is known in the art (J. Macromol. SCI.-Chem. A 16 (7), 1243-1250 (1981)). In spite of their good availability, however, the use of tannins has not become generally established, because the tensile strength of tannin-bonded wood-derived materials, particularly after they have been stored in water, is not satisfactory. It is therefore the aim of the invention to provide a tannins-based bonding agent which can be used tc produce wood-derived materials with considerably improved mechanical properties - This aim is achieved by: a method of producing a wood-derived material according to claims 1 to 6; It was found that tannins of the pecan nut and pine bark 2 264 Q exhibit outstanding adhesiveness (compared with other tannins) when used, in conjunction with hexamethylenetetramine (Hexa) as a bonding agent for wood chips. The tensile strength of such products is increased, reaching values such as those of e.g. corresponding materials bonded with phenolic resin. The drop in transverse tensile strength after storage in water is considerably reduced, and the swelling values in boiling water are also reduced. A further advantage here is that these tannins can be used without a breakdown treatment such as is commonly used with other tannins. Suitable tannins are those from the pine bark or pecan nut group. Mixtures of these tannins with e.g. mimosa or quebracho tannin in a ratio of from 2:5 to 5:2 have a longer hardening time, but can nevertheless be used. These tannins are commercially available products and have long been in use, mainly as tanning agents. The commercial grade of these products is adequate for use according to the invention. 3 264187 The tannis of the present invention are mixed with hexamethylenetetramine, the hexamethylenetetramine content of the bonding agent being 3.0 to 9% by weight relative to the tannin content. It is also within the scope of the invention if the bonding agent contains not only the special types of tannin and addition, up to 50% by weight of a novolak or up to 2 0% by weight of an at-least difunctional isocyanate compound, e.g. diisocyanatonaphthaline, 4,4',4''-triisocyanato-triphenylmethane, or isophorone-, toluene-, or hexamethylene-diisocyanate or diisocyanato-diphenylmethane (MDI); in which case, in practical use, the di- or poly-isocyanate is applied to the cellulose-containing products at the same time as the application of the dried mixture of tannin according to the invention and hexamethylenetetramine before said cellulose-containing products are pressed to form the resultant materials. Suitable cellulose-containing products are e.g. wood chips, or cellulose-based fibres such as cotton, flax, or straw hexamethy lenetratramine but also, in from which particle boards, non-woven fabrics, or sound and heat insulation boards are to be produced. The production of materials is performed as follows: the bonding agents used according to the invention are mixed with cellulose-containing products, the mixture is placed in a mould, ana is hardened under pressure at a temperature above the decomposition temperature of the formaldehyde-releasing material and below the decomposition temperature of the tannin, 'i.e preferably 150 to 210°C. The pressure used is in the range from 0.1 to 4 MPa/mm2, depending on the material used and the desired density. Thus the production of e.g. three-layer particle boards is also possible, using a pressure of 2 to 3.5 MPa/mm2. Depending on the desired material and the desired strength, the amount of bonding agent used ranges from 4 to 20% by weight relative to the amount of cellulose-containing product. The bonding agent can be in the form of a mixture of solids, or a solution of the components in water, alcohol or a water-alcohol mixture. Such solutions can be stored at room temperature for a number of weeks without a large increase in viscosity. In the case of aqueous solutions, however, the simple addition of a fungicide is recommended to prevent any fungal attack. The following examples show the use of the method according to the invention for the production of particle boards. Examples Wood chips are sprayed with a water-alcohol solution containing the bonding agent. The amount of bonding agent in the solution by weight is 11% of the weight of the wood. The wood chips are dried and then moulded, pressed, and hardened in a manner known in the art {2.5 N/irun2; 195°C) to form boards of 400 x 350 x 12 mm. S'C 5 The following are determined: the density and transverse tensile strength of the boards in (a) the dry state and (b) the wet state after being kept in water (2 hours in boiling water, followed by drying for 16 hours at 105°C) and also the thickness swell after 2 hours in boiling water, for different variations of the mixing ratios of the bonding-agent components, the amount of bonding agent, and the duration of pressing. Examples 1 to 5 In Example 1, the proportion of hexamethylenetetramine ranges from 7.5 % to 5.5% of the bonding agent. Correspondingly, the proportion of pecan nut tannin ranges from 92.5% to 94.5%. In Example 2, the proportion of hexamethylenetetramine relative to tannin is 6.4%, i.e. the proportion of pecan nut tannin is 93.6%. The duration of pressing is varied. Example 3 shows the values for a three-layer particle board with 6.4% hexamethylenetetramine in the bonding agent, and a bonding-agent content of 10% in the inner layer and 12% in the outer layers. Examples 4 and 5 show the data for the use of mimosa (wattle) tannin, as a comparison for Examples 1 and 2. The following tables show the values obtained: r TABLES Example 1 - Hexamethylenetetramine Example 4 (Comparison) 7.5% 6.4% 5.5% 7.5% 6.5% Pressing time (sec/mm) 17.5 17.5 17.5 17.5 17.5 Density (kg/m3) 729 730 736 731 711 Transverse tensile strength, dry (MPa) 0.82 0.81 0.79 0.45 0.43 Transverse tensile strength, after period in water (MPa) 0.25 0.27 0.26 0.09 0.07 Swelling (%) 25.0 23.9 22.1 32.1 31.5 HCHO Emission (mg/lOOg; WKI) 1.71 1,45 0.84 2.01 1.87 7 Example 5 Example 2 - (Comparison) (6.4% Hexa) (6.5% Hexa) Pressing time (sec/mm) 17.5 12.5 8.5 30.0 17.5 12.5 Density (kg/m3) 730 738 733 714 711 722 Transverse tensile strength, dry (MPa) 0.81 0.75 0.67 0.5 0.45 0.41 Transverse tensile strength, after period in water 0.27 0.19 0.17 0.13 0.09 0.03 (MPa) Swelling (%) 23.9 22.4 20.9 29.7 32.1 36.7 HCHO Emission (mg/lOOg; WKI) 1.45 1.32 1.1 1.64 2.01 1.28 • l: f? 8 g V Example 3 Pressing time (sec/mm) 12.5 Binding agent (%) Middle/Outer Layer 10/12 Moisture of chips after bonding (%) Middle/Outer Layer 28/26 Density (kg/m3) 723 Transverse tensile strength, dry (MPa) 0.83 Transverse tensile strength after period in water (MPa) 0.27 Swelling (%) 22.1 HCHO emission (mg/lOOg, WKI) 1.4 Example 5 Single-layer particle boards were produced and tested according to the general conditions for the examples (pressing time lb s/'mm at 190 C, 2.5 N/mm-j. Bonding agent: Tannin from pine bark (37% aqueous solution) 337 parts by weight Hexamethylenetetramine (40% aqueous solution) 19.3 parts by weight Zinc acetate (25% aqueous solution) 19.3 parts by weight Water 10 parts by weight Results: Density (kg/m3) 708 Transverse tensile strength, dry (MPa) 0.80 Transverse tensile strength, after period in water (MPa) 0.23 HCHO emission (mg/100 g) 0.1 Example 7 Triple-layer particle boards were produced and tested according to the general conditions for the examples (pressing time 15 s/mm at 190°C, 2.5 N/mm2). </div>

Claims

<div class="application article clearfix printTableText" id="claims"> 10 Bonding agent: Core Outer layer layers Tannin from pine bark (37% aqueous solution) 327 327 parts by weight Hexamethylenetetramine (40% aqueous solution) 19.5 19.5 parts by weight Zinc acetate (25% aqueous solution) 24.0 19.5 parts by weight Water 12 — parts by weight Results: Density (kg/m3) 723 Transverse tensile strength, dry (MPa) 0.80 Transverse tensile strength, after period in water (MPa) 0.29 HCHO emission (mg/100 g) 0.16 - • Q 11 264187 WHAT WE CLAIM IS:

1. A method of producing a wood-derived material, by mixing a bonding agent with products containing cellulose, putting the mixture into a mould, and processing it at a temperature in the range of 150 to 210 'C and at a pressure in the range of 0.1 to 4 MPa/mm2, characterised in that the bonding agent contains tannin of the pecan nut and/or pine bark, together with hexamethy lenetetramine.

2. A method in accordance with claim 1, characterised in that the hexamethylenetetramine component is 3.0 to 9% by weight relative to the tannin content.

3. A method in accordance with claim 1 or claim 2, characterised in that the bonding agent contains a novolak, the amount thereof being up to 50% by weight.

4. A method in accordance with claim 1 or claim 2, characterised in that the bonding agent contains up to 20% by weight of an isocyanate compound that is at least difunctional.

5. A method in accordance with claim 1, characterised in that the bonding agent is mixed with the cellulose-containing products in the form of a powder.

6. A method in accordance with claim 1, characterised in that the bonding agent is sprayed onto the cellulose-containing products in the form of a solution.

7. A method according to claim 1 substantially as herein described or exemplified. RUTGERSWERKE AKTIENGESELLSCHAFT By Their Attorneys HENRY HUGHES vtx-r^f'0/y *\ - r V \° </div>