WO2004058843A1

WO2004058843A1 - A tannin, aldehyde, amino compound- based resin composition and its use as a binding agent for composite wood products

Info

Publication number: WO2004058843A1
Application number: PCT/AU2003/001712
Authority: WO
Inventors: Leslie Gordon Wingham
Original assignee: Borden Chemical Australia Pty Ltd
Priority date: 2002-12-24
Filing date: 2003-12-22
Publication date: 2004-07-15
Also published as: AR043321A1; AU2002953568A0

Abstract

The invention provides a resin composition comprising a copolymer of : (a) a tannin ; (b) an amino compound (such as urea, monomethylol urea or dimethylol urea); (c) an aldehyde (such as formaldehyde, paraformaldehyde or acetaldehyde); (d) a stabilizer (such as an amino-based heterocyclic compound, examples of which include melamine, monomeric melamine-formaldehyde adducts, benezoguanamine, melam, melon, ammeline and other melamine derivatives) to impart stability to the tannin-amino compound-aldehyde copolymer. The stability being manifest as a shelf life of at least 21 days at 12°C or at least 8 days 25°C.

Description

A TANNIN, ALDEHYDE, AMINO COMPOUND-BASED RESIN COMPOSITION AND ITS USE AS A BINDING AGENT FOR COMPOSITE WOOD PRODUCTS

Field of the invention

This invention relates to resin compositions, methods of making them, and products made by using them. It has particular, although not exclusive application to resin compositions for use as binding agents to bind solid particles together so as to form useful products therefrom. The invention has particular application to the manufacture of wood composite products, such as particle boards and medium density fibreboard (MDF), for use in the construction industry. The background to the invention will therefore be described with specific reference to this application to which it is particularly suited.

Background to the Invention

The use of non-natural materials in building and construction is nowadays commonplace. In many instances, artificial or synthetic materials have advantages over their natural counterparts, when used in construction. For example, wood- based composite materials can have aesthetic and structural advantages over natural timbers. It is therefore desirable to have efficient processes for manufacturing such items, as industry and consumer demand mandate that they be available for use in building projects.

One particular kind of wood-based composite product is generically known as 'particle board'. 'Particle board' is made up from wood particulates (typically derived from saw milling and similar techniques for processing natural timbers), combined with a binding agent. Useful binding agents for this purpose are natural and synthetic resins. Synthetic resins have particular advantages in this area, because they can be made to impart desirable properties to the resultant wood composite product (eg: improved water resistance over those possessed by natural timbers). Resins that are made containing condensed tannins are particularly attractive for use in the manufacture of particle board, because tannins are known in particular, for their ability to impart a degree of water resistance to resins formed from them.

The use of condensed tannins as binding agents in the manufacture of wood composite materials requires the addition of a cross-linking agent just before their application to the substrate to be bound. Usually, this cross-linking agent is paraformaldehyde powder, or a Urea formaldehyde concentrate. Once added to the aqueous tannin solution, a chemical reaction between the two elements commences, which results in the stability (and thus the shelf life) of the resultant resin being compromised. In this context, stability is usually measured as the time taken for the resin system to become unstable, either physically and/or chemically.

Tannins (and especially condensed tannins) are poly flavonoids of the general formula X depicted below:

Formula X

They are poly flavonoids based on a heterocyclic ring system derived from phenylalanine [B] and polyketide [A] biosynthesis. Condensed tannins are classified according to the hydroxylation patterns of the A and B rings.

The most common reactions of the A ring are examples of the electrophilic aromatic substitution, including where an electrophile displaces the hydrogen atom at C6 and/or C8. For resorcinolic derivatives, the favoured site is C6. Basic conditions increase the reactivity of the system. The phenolic hydroxyl is a powerful electron donor, especially under basic conditions, increasing the electron density in the A Ring, thus making it a better nucleophile, as well as stabilising carbocation intermediates that result from nucleophilic attack. Condensed tannins contain repeating units of the formula X depicted above, linked to one another by an inter- flavonoid bond. The A Ring of the constituent flavonoid units retains only one highly reactive nucleophilic centre, the remainder of each unit accommodating the inter- flavonoid bond. In one particular condensed tannin, mimosa tannin, the flavonoid unit is repeated between 2 and 11 times, with an average degree of polymerisation of 4 to 5. An exemplary tannin polymer of the kind described is represented in the formula Y depicted below.

Formula Y

Formaldehyde reacts with tannins to produce polymerisation through methylene bridge linkages at reactive sites on the flavonoid molecules, primarily on the A rings. The reactivity for mimosa tannin is comparable to resorcinol. The addition of formaldehyde to a tannin solution results in rapid polymerisation. Due to their size and shape, tannin molecules become immobile at low levels of concentration with formaldehyde, so that reactive sites are too far apart for further methylene bridge formation. The resulting cured resin is thus extremely water- and boil-resistant.

The intermolecular distances can be overcome by using bridging agents. One way of achieving this would be to form a polymer with a Urea moiety. A similar approach is currently used for the synthesis of melamine-urea-formaldehyde (MUF) resins. MUF resins are extensively used to impart water resistance to particle board and fibreboard. However, melamine (a petrochemical based material) is subject to large cost fluctuations and is usually more expensive (and often much more expensive) than tannin. Tannin is a natural product, more cost stable, cheaper than Melamine and can potentially be sourced locally.

Based on economic considerations, tannins are therefore a suitable candidate for this purpose. However, due to the relatively large size of many tannin molecules, only a relatively small degree of polymeric condensation is required, before the resin viscosity is such that the resin is commercially unusable as a binding agent for forming a composite wood product. In addition, tannin and formaldehyde react readily with one another. This high reactivity makes it very difficult to maintain stability in the final resin solution. Free formaldehyde in the resin solution continues to react with the tannin, thereby increasing its viscosity and at the same time, shortening its shelf life. Conversely, reducing the level of available formaldehyde in the resin does alleviate this problem, but this reduces the reactivity of the components, and thus, the ability of the resin to cure during the formation of wood composite or like products, during manufacture.

The present invention aims to address one or more of the prior art problems mentioned above.

General disclosure of the Invention

The invention generally provides a resin composition, the composition comprising a co-polymer of:

(a) a tannin;

(b) an amino compound;

(c) an aldehyde; and

(d) a stabiliser.

Preferably, the molar ratios of the elements of the composition (Tannin (molecular weight=1300): Amino compound : Aldehyde).are: 1 :13 to 44:15 to 61.

Tannins suitable for use in the invention may be obtained from wood and bark materials found throughout the world. Preferred tannins for use in the invention are those known as condensed tannins. These tannins are obtained from the bark of the black wattle (mimosa) and other Acacia species, various species of pine, and from the wood of the quebracho tree.

A particularly preferred amino compound for use in the invention is urea. Urea can be used in the form of a powder, prill, in granular form or as an aqueous solution. Amino compounds suitable for this purpose also include the use of urea- formaldehyde monomeric products, such as monomethylol urea and dimethylol urea. In order to be suitable for use in the invention, the stabiliser compound chosen must be such as to impart stability to the tannin-amino compound-aldehyde co-polymer. In this context, stability means that the co-polymer has a shelf life of:

(a) at least 21 days, when the composition is stored at 12°C; or

(b) at least 8 days, at 25°C.

The stabiliser compound may also be an amino-based heterocyclic compound. Suitable compounds in this category include melamine (2₍4,6-triamino-1 ,3,5 triazine), melamine-formaldehyde monomeric products and melamine formaldehyde concentrate solutions. Other suitable triazine materials include benzoguanamine, melam, melon, ammeline and other melamine derivatives.

Many aldehydes may be used in the invention. Aldehydes suitable for use in the invention include formaldehyde, acetaldehyde and propionaldehyde. In this specification, the term "Aldehydes" also includes aldehyde generating agents, such as hexamine. Preferably, the aldehyde used in the invention is formaldehyde. This can be used in the invention in many forms, including:

•formaldehyde solutions stabilised with methanol;

• non-stabilised formaldehyde solutions;

• urea formaldehyde solutions (and particularly, concentrated urea formaldehyde solutions); and

• paraformaldehyde.

In a preferred embodiment, the composition according to the invention is a tannin-urea-formaldehyde co-polymer.

The invention also provides a method of preparing a resin composition in which the resin composition comprises a tannin-amino compound-aldehyde copolymer, the method comprising the following steps:

(a) reacting the aldehyde with the amino compound so as to derive an amino-aldehyde; and

(b) reacting the amino-aldehyde with a tannin.

Preferably, in the method aspect of the invention, step (a) is performed before step (b).

It is further preferred that in step (a), the aldehyde is reacted with the stabiliser compound under alkaline conditions. A preferred pH range for this reaction is between 7.5 and 9.5.

It is further preferred that the molar ratio of aldehyde to stabiliser compound is from 5:1 to 140:1. A particularly preferred molar ratio is about 40:1. It is further preferred that the temperature of the reactants is from 50°C to 90°C.

Preferably, the resulting solution derived from the aldehyde-stabiliser compound reaction is then reacted further with an amino compound under falling pH conditions. Preferably, this further reaction step is performed at pH values from 9.5 to 6.5. Preferably, the reaction is also carried out at temperatures between 80°C and atmospheric reflux.

Preferably, in step (b) of the method, an aqueous tannin solution containing between 30% and 60% tannin solids (by weight) is then added to the pre-existing reagents according to the preceding steps of the method. Preferably, at this point, the pH in the system is between 5.0 and 7.5. It is further preferred that the temperature of the reaction system is between 40°C and 75°C.

It is further preferred that in step (b) after the tannin solution is added to the reaction system, a further quantity of the amino compound is added to give a molar ratio of aldehyde to amino compound of from 1.45 to 1.9.

It is further preferred that the reaction system is then allowed to react until the desired condensation viscosity is achieved. Preferably, the condensation viscosity is between 60 and 200 cps. Preferably further, the reaction is terminated by:

(a) rapid cooling to below 40°C within 15 -20 minutes;

(b) addition of a sulphite; and

(c) a final quantity of the amino compound.

Preferably, the sulphite comprises sodium sulphite. This can be used either in powder form, or as an aqueous solution.

It is also further preferred that the molar ratio of aldehyde to amino compound in the reaction system is adjusted with a quantity of amino-aldehyde concentrate. It is further preferred that the pH is finally adjusted to between 6.5 and 8.0.

The invention further comprises a resin composition produced in accordance with the method aspect of the invention.

The invention yet further provides a method of using a resin composition containing a tannin-amino-aldehyde co-polymer as a binding agent in the production of a material which comprises solids mixed with the resin. Preferably, the resin composition is a tannin-urea-formaldehyde of the kind previously described. It is further preferred that the products produced by the use of the resin composition are products which contain particulates made from wood (such as wood shavings, wood fibre or other wood particulates) in combination with the resin composition. Particularly preferred wood composite products formed in accordance with the method aspect of the invention include:

(a) particle boards; and

(b) medium-density fibre boards.

Detailed description of a preferred embodiment of the invention

A preferred embodiment of the invention will now be described by way of example only, in the following commentary.

Example

To a reactor, 32.49 grams of 54% formaldehyde solution is charged. The pH of this solution is adjusted to between 8.5 and 9.5 with sodium hydroxide solution. Then,

2.66 grams of melamine powder are added to the reactor and stirred, and the mixture then heated to 80°C.

To this mixture, a quantity of urea (10.42g) is added to yield a formaldehyde to urea molar ratio of 3.36:1 while mixing. The temperature is allowed to rise to 95°C and held there for 10 minutes.

After this hold time the pH of the reaction mixture is adjusted to 9.0 to 9.5 with sodium hydroxide solution.

The mixture is allowed to cool to 90°C at which time a solution of 50% tannin is charged. The temperature is allowed to drop to 70°C. Immediately a quantity of urea is added to result in a formaldehyde: urea molar ratio of 1.79:1.

The final temperature is maintained at 60°C and pH between 5.9 and 6.4. The reacting mixture is then condensed to 140cps measured at 25°C or Gardner tube value F.

Upon reaching this viscosity, the reacting mixture is cooled to below 30°C while charging 1g of (20%) sodium sulphite solution and 11.25 g of urea.

Finally, a quantity of urea formaldehyde concentrate is added to effect a final formaldehyde to urea molar ratio of 1.26:1.

The pH of the product is then adjusted to between 7 and 7.5 with sodium hydroxide solution to achieve a final viscosity of between 70 and 90 cps and a solid content of 59.8%.

It is to be understood that wherever used in this specification (including both the description and the claims), forms of the word 'comprise' are equivalent in meaning to the corresponding forms of the word 'include', and are thus not to be taken as excluding or implying the exclusion of a feature or integer. It will be also understood that the invention disclosed in this specification extends to all combinations of two or more of the individual features mentioned or evident from or implicit in the text of this specification (including the example given in it). All such different combinations constitute various alternative aspects of the invention.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A resin composition comprising a co-polymer of:

(a) a tannin;

(e) an amino compound;

(f) an aldehyde; and

(g) a stabiliser.

2. A resin composition as claimed in claim 1, in which the molar ratios of the elements (a) to (c) in the composition are:

(a) tannin: 1

(b) amino compound 13 to 44

(c) aldehyde:15 to 61.

3. A resin composition as claimed in claim 1 or claim 2 in which the tannin is derived from a natural source.

4. A resin composition as claimed in claim 3, in which the tannin is derived from wood or bark.

5. A resin composition as claimed in claim 4, in which the resin is a condensed resin.

6. A resin composition as claimed in claim 5, in which the condensed tannin is derived from one or more of the following sources:

(a) black wattle (mimosa);

(b) another acacia species;

(c) a species of pine tree (pinus); and

(d) the wood of the quebracho tree.

7. A resin composition as claimed in any of the preceding claims, in which the tannin comprises poly flavonoids of the general formula:

8. A resin composition as claimed in any of the preceding claims, in which the amino compound comprises either or both:

(a) urea; and

(b) a urea-formaldehyde monomeric product.

9. A resin composition as claimed in claim 8, in which the amino compound is urea. \

10. A resin composition as claimed in claim 9, in which the urea is in one or more of the following forms:

(a) a powder;

(b) as prill

(c) in granular form; and

(d) an aqueous solution.

10 A resin composition as claimed in claim 8, in which the amino compound comprises either or both of:

(a) monomethylol urea; and

(b) dimethylol urea.

11. A resin composition as claimed in any of the preceding claims, in which the stabiliser imparts stability to the tannin-amino compound-aldehyde co-polymer.

12. A resin composition as claimed in claim 11 , in which the composition has a shelf life of:

(a) at least 21 days, when the composition is stored at 12°C; or

(b) at least 8 days, when the composition is stored at 25°C.

13. A resin composition as claimed in either of claims 11 or 12, in which the stabiliser is an amino-based heterocyclic compound.

14. A resin composition as claimed in claim 13, in which the stabiliser is selected from the group comprising:

(a) melamine;

(b) melamine-formaldehyde monomeric compounds;

(c) melamine-formaldehyde concentrate solutions;

(d) benzoguanamine;

(e) melam;

(f) melon;

(g) ammeline; and

(h) melamine derivative compounds.

15. A resin composition as claimed in any of the preceding claims, in which the aldehyde is selected from the group comprising:

(a) formaldehyde;

(b) acetaldehyde;

(c) propionaldehyde; and

(d) aldehyde generating agents.

16. A resin composition as claimed in claim 15, in which the aldehyde is hexamine.

17. A resin composition as claimed in any of the preceding claims, in which the composition is a tannin-urea-formaldehyde co-polymer.

18. A method of preparing a resin composition in which the composition comprises a tannin-amino compound-aldehyde co-polymer, the method comprising the following steps:

(b) reacting the amino-aldehyde with a tannin.

19. A method of preparing a resin composition as claimed in claim 18, in which step (a) is performed before step (b).

20. A method of preparing a resin composition as claimed in claims 18 or 19, in which the aldehyde is reacted with the stabiliser under alkaline conditions.

21. A method of preparing a resin composition as claimed in claim 20, in which the aldehyde is reacted with the stabiliser at a pH value between 7.5 and 9.5.

22. A method of preparing a resin composition as claimed in claim 21 , in which the molar ratio of aldehyde to stabiliser is in the range of 5:1 to 40:1.

23. A method of preparing a resin composition as claimed in claim 22, in which the molar ratio of aldehyde to stabiliser is about 40:1.

24. A method of preparing a resin composition as claimed in claims 18 to 23, in which the temperature of the reactants is between 50°C and 90°C.

25. A method of preparing a resin composition as claimed in any of claims 20 to 24, in which a solution derived from reacting the aldehyde with the stabiliser is reacted with an amino compound.

26. A method of preparing a resin composition as claimed in claim 25, in which the reaction between the solution derived from reacting the aldehyde with the stabiliser and the amino compound is performed at a pH value of between 6.5 and 9.5.

27. A method of preparing a resin composition as claimed in claim 26, in which the reaction between the solution derived from reacting the aldehyde with the stabiliser and the amino compound is performed at a temperature between 80°C and atmospheric reflux.

28. A method of preparing a resin composition as claimed in any one of claims 18 and 27, in which in step (b) of the method, an aqueous tannin solution containing between 30% and 60% tannin solids (by weight) is added to the pre-existing reagents.

29. A method of preparing a resin composition as claimed in claim 28, in which the pH of the reagents is between 5.0 and 7.5.

30. A method of preparing a resin composition as claimed in claim 29, in which the reaction is conducted at a temperature of between 40°C and 75°C.

31. A method of preparing a resin composition as claimed in any one of claims 28 to 30, in which, in step (b) of the method, a further quantity of the amino compound is added to the reaction, in order to give a molar ratio of aldehyde to amino compound of between 1.45 and 1.8.

32. A method of preparing a resin composition as claimed in any one of claims 18 to 31 , in which the reaction is allowed to progress until the solution achieves a viscosity between 60 and 200 cps.

33. A method of preparing a resin composition as claimed in claim 32, in which the reaction is terminated by:

(a) cooling to below 40°C within 15 -20 minutes;

(b) addition of a sulphite; and

(c) addition of a final quantity of the amino compound.

34. A method of preparing a resin composition as claimed in claim 32, in which step (b) comprises adding sodium sulphite to the reaction.

35. A method of preparing a resin composition as claimed in claim 33, in which step (b) comprises adding sodium sulphite in either powdered form or as an aqueous solution, to the reaction.

36. A method of preparing a resin composition as claimed in any one of claims 18 to 35, in which the molar ration of aldehyde to amino compound in the reaction is adjusted with a quantity of amino-aldehyde concentrate.

37. A method of preparing a resin composition as claimed in claim 36, in which the pH of the reaction is finally adjusted to a value between 6.5 and 8.0.

38. A method of preparing a resin composition as claimed in any one of claims 18 to 37, in which the resin composition is a tannin-urea-formaldehyde copolymer.

39. A method of using a resin composition comprising a tannin-amino compound- aldehyde co-polymer as claimed in any one of claims 1 to 17 as a binding agent in the production of a material which comprises solids mixed with the resin compound.

40. A method of using a resin composition as claimed in claim 39, in which the resin is a tannin-urea-formaldehyde co-polymer.

41. A method of using a resin composition as claimed in claim 40, in which the solids comprise particulates derived from wood.

42. A method of using a resin composition as claimed in either of claims 39 of 40, in which a material is derived, the material being selected from:

(a) particle boards; and

(b) medium-density fibre boards.