IMPREGNATED WOOD PRODUCT FIELD OF THE INVENTION

The present invention relates to impregnated wood products, in particular, cured furan polymer impregnated wood products, methods for producing such products, and

formulations for impregnating wood products.

BACKGROUND TO THE INVENTION

Modified wood are pieces of treated timber with improved properties such as durability. Furfuryl alcohol (FA) treatment and polymerization within wood, termed "furfurylation", is a well-known wood modification technology to enhance the dimensional stability and hardness of wood (Lande, S., O. Hoibo, and E. Larnoy, Variation in treatability of Scots pine (Pinus sylvestris) by the chemical modification agent furfuryl alcohol dissolved in water. Wood Science and Technology, 2010. 44(1) : p. 105-118.). Typically, furfurylation of wood results in a darker coloured wood. With some species, such as Radiata pine, this colour change can be significant. This darker, brown colouring arises from the polymerization of FA into a highly conjugated furan polymer including Diels-Alder coupling and cross-linking between furan polymer chains (Gandini, A., Furans as offspring of sugars and polysaccharides and progenitors of a family of remarkable polymers: a review of recent progress, 2010. p. 245- 251; Gandini, A. and M.N. Belgacem, Furans in polymer chemistry. Progress in Polymer Science, 1997. 22(6) : p. 1203-1379.).

Living wood is protected physically by bark and chemically by terpenes and other chemicals that have anti-microbial and anti-fungal properties. In sawn and dried timber, the bark no longer offers physical protection, meaning surfaces (and in the absence of treatments the interior or the wood) are exposed to microbes and fungi that use the wood as a food source and to UV light that can contribute to the degradation of the cell wall, particularly polymers such as cellulose, lignin, hemicellulose etc. Additionally, terpenes, etc are no longer generated by living cells and may be degraded in the drying process thus resulting in a decrease in resistance to fungi and microbes. Depending on the timber species, wood extractives leaching, degrading and being washed away may remove or change components that contribute to wood colour.

Silvering of wood products on weathering is typically a combination of UV aging (particularly photo-oxidation of lignin), extractive changes and colonisation of the wood surface by microbes and fungi. When wood is treated with strong biocides the effect is predominantly light based, until the biocides leach away and the whole wood starts to decay. When untreated with biocides, fungi play a significant role. Wood treatments such as polymerised FA reduce vulnerability to degradation both by filling lumen and other spaces in the wood structure to limit physical access or microbes and fungi and possibly to an extent UV light. Furfurals also provide some chemical protection but surfaces exposed to light, moisture, etc remain somewhat vulnerable so still change at least in appearance. Dark materials generally have greater perceived colour change on weathering, as they lighten and grey. Light coloured materials on weathering can darken or yellow (yellowing is mostly an oxidation of lignin effect) but the perceived change tends to be lesser/slower.

There is an ongoing need for wood products with modified properties, including for example hardness, brittleness, dimensional stability, colour, and weathering characteristics. It is an object of the present invention to go some way to meeting this need; and/or to at least provide the public with a useful choice.

Other objects of the invention may become apparent from the following description which is given by way of example only.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date.

SUMMARY OF THE INVENTION

In a first aspect, the present invention broadly consists in a cured furan polymer

impregnated wood product, wherein the cured furan polymer comprises a cured reaction product of:

a furan monomer and

an initiator that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction; and/or

a monomer, oligomer, or polymer that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction.

In another aspect, the present invention broadly consists in a method of producing a cured furan polymer impregnated wood product, the method comprising :

impregnating a wood product with

a furan monomer and

an initiator that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction; and/or a monomer, oligomer, or polymer that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction; and

reacting the furan monomer and the initiator and/or the monomer, oligomer, or polymer under conditions effective for polymerisation to produce a cured furan polymer comprising a cured reaction product of the furan monomer and the initiator and/or the monomer, oligomer, or polymer.

In another aspect, the present invention broadly consists in a cured furan polymer impregnated wood product produced by a method of the present invention.

In another aspect, the present invention broadly consists in a formulation for impregnating a wood product, the formulation comprising :

a furan monomer; and

an initiator that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction; and/or

a monomer, oligomer, or polymer that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction.

The following embodiments and preferences may relate alone or in any combination of any two or more to any of the above aspects.

In various embodiments, the wood product is lumber, timber, a wood composite, or wood fibres, particles, flakes, strands, chips, or sheets.

In various embodiments, the wood product is lumber.

In various embodiments, the furan monomer is selected from the group consisting of furfuryl alcohol (FA), bishydroxymethyl furan (BHMF), tri hydroxymethyl furan (THMF), furfural, oligomers thereof, condensation products thereof, and combinations thereof.

In various embodiments, the furan monomer is furfuryl alcohol (FA).

In various embodiments, the monomer, oligomer, or polymer that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction is a prepolymer comprising a reaction product of a furan monomer and an initiator that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction.

In various embodiments, the monomer modifies the helicity of the furan polymer and/or the spacing between furan units of different chains in the furan polymer. In various embodiments, the initiator is capable of Diels Alder reaction with the furan monomer and/or polymerised chains thereof.

In various embodiments, the initiator is an imide, preferably a cyclic imide, preferably maleimide, N-methyl maleimide, or succinimide, preferably maleimide.

In various embodiments, the initiator is a cyclic imide. In various embodiments, the initiator is selected from the group consisting of maleimide, N-methyl maleimide, or succinimide.

In various embodiments, the initiator is maleimide.

In various embodiments, the initiator is an oxazolidine, preferably an oxazolidine that is a methylene donor, preferably an oxazolidine formed from the condensation of formaldehyde and tris(hydroxymethyl)methylamine (Tris), an oxazolidine formed from the condensation of formaldehyde and 2-amino-2-methyl-l, 3-propanediol, or 2,3-dihydro-l,3-benzoxazole, preferably an oxazolidine formed from the condensation of formaldehyde and

tris(hydroxymethyl)methylamine (Tris), preferably l-aza-5-methylol-3,7- dioxabicyclo[3.3.0]octane.

In various embodiments, the initiator is selected from the group consisting of an oxazolidine formed from the condensation of formaldehyde and tris(hydroxymethyl)methylamine (Tris), an oxazolidine formed from the condensation of formaldehyde and 2-amino-2-methyl-l,3- propanediol, or 2,3-dihydro-l,3-benzoxazole. In various embodiments, the initiator is an oxazolidine formed from the condensation of formaldehyde and

tris(hydroxymethyl)methylamine (Tris). In various embodiments, the initiator is l-aza-5- methylol-3,7-dioxabicyclo[3.3.0]octane.

In various embodiments, the initiator is a methylene donor.

In various embodiments, the initiator is a dialdehyde.

In various embodiments, the initiator is an olefinically unsaturated aldehyde.

In various embodiments, the initiator is a cyclic or acyclic diene.

In various embodiments, the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1 :30, 1 :25, 1 : 20, 1 : 15, 1 : 12, 1 : 10, 1 :7, or 1 : 5, preferably at least 1 : 15, and useful ranges may be selected between any two of these values, for example from about 1 :30 to 1 : 5, 1 :25 to 1 : 5, 1 :20 to 1 : 5, 1 : 15 to 1 : 5, 1 :30 to 1 :7, 1 :25 to 1 :7, 1 :20 to 1 :7, 1 : 15 to 1 :7, 1 :30 to 1 : 10, 1 :25 to 1 : 10, 1 :20 to 1 : 10, or 1 : 15 to 1 : 10. In various embodiments, the stoichiometric ratio of initiator to furan rings provided by the furan monomer is from about 1:30 to 1:5, 1:25 to 1:5, 1:20 to 1:5, 1:15 to 1:5, 1:30 to 1:7, 1:25 to 1:7, 1:20 to 1:7, 1:15 to 1:7, 1:30 to 1:10, 1:25 to 1:10, 1:20 to 1:10, or 1:15 to 1:10.

In various embodiments, the initiator is an imide and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1:15, for example at least 1:12, 1:10, 1:7, or 1:5, and useful ranges may be selected between any two of these values, for example from about 1:15 to 1:5, 1:15 to 1:7, or 1:15 to 1:10.

In various embodiments, the initiator is an imide and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1 : 12. In various embodiments, the initiator is an imide and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1:10. In various embodiments, the initiator is an imide and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1:7. In various embodiments, the initiator is an imide and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1:5. In various embodiments, the initiator is an imide and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is from about 1:15 to 1:5, 1:15 to 1:7, or 1:15 to 1:10.

In various embodiments, the initiator is an oxazolidine and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1:27, for example at least about 1:25, 1:20, 1:15, 1:12, 1:10, 1:7, or 1:5, and useful ranges may be selected between any two of these values, for example from about 1:27 to 1:5, 1:25 to 1:5, 1:20 to 1:5, 1:15 to 1:5, 1:27 to 1:7, 1:25 to 1:7, 1:20 to 1:7, 1:15 to 1:7, 1:27 to 1:10, 1:25 to 1:10, 1:20 to 1:10, or 1:15 to 1:10.

In various embodiments, initiator is an oxazolidine and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1:20. In various embodiments, initiator is an oxazolidine and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1:15. In various embodiments, initiator is an oxazolidine and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1:12. In various embodiments, initiator is an oxazolidine and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1:10. In various embodiments, initiator is an oxazolidine and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1:7. In various embodiments, initiator is an oxazolidine and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1:5. In various embodiments, initiator is an oxazolidine and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is from about 1:27 to 1:5, 1:25 to 1:5, 1:20 to 1:5, 1:15 to 1:5, 1:27 to 1:7, 1:25 to 1:7, 1:20 to 1:7, 1:15 to 1:7, 1:27 to 1:10, 1:25 to 1:10, 1:20 to 1:10, or 1:15 to 1:10.

In various embodiments, the initiator is an oxazolidine that is a methylene donor and the stoichiometric ratio of initiator, on a methylene donor basis, to furan rings provided by the furan monomer is at least about 1:14, for example at least 1:12, 1:10, 1:7, or 1:5, and useful ranges may be selected between any two of these values, for example from about 1 : 14 to 1 : 5, 1 : 14 to 1 : 7, or 1 : 14 to 1 : 10.

In various embodiments, the initiator is an oxazolidine that is a methylene donor and the stoichiometric ratio of initiator, on a methylene donor basis, to furan rings provided by the furan monomer is at least 1:12. In various embodiments, the initiator is an oxazolidine that is a methylene donor and the stoichiometric ratio of initiator, on a methylene donor basis, to furan rings provided by the furan monomer is at least 1 : 10. In various embodiments, the initiator is an oxazolidine that is a methylene donor and the stoichiometric ratio of initiator, on a methylene donor basis, to furan rings provided by the furan monomer is at least 1:7.

In various embodiments, the initiator is an oxazolidine that is a methylene donor and the stoichiometric ratio of initiator, on a methylene donor basis, to furan rings provided by the furan monomer is at least 1:5. In various embodiments, the initiator is an oxazolidine that is a methylene donor and the stoichiometric ratio of initiator, on a methylene donor basis, to furan rings provided by the furan monomer is from about 1:14 to 1:5, 1:14 to 1:7, or 1:14 to 1:10.

In various embodiments, the impregnated wood product comprises at least about 15% (w/w) of the cured furan polymer for example at least 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, or 80% (w/w), and useful ranges may be selected between any two of these values, for example 15 to 80, 20 to 80, 30 to 80, 40 to 80, 15 to 70, 20 to 70, 30 to 70, or 40 to 70%.

In various embodiments, the weight uptake of the cured furan polymer in the impregnated wood product is at least about 20% (w/w) of the wood product prior to impregnation, for example at least about 22, 25, 27, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or 85% (w/w), and useful ranges may be selected between any two of these values for example 20 to 85, 30 to 85, 40 to 85, 20 to 80, 30 to 80, 40 to 80, 20 to 70, 30 to 70, or 40 to 70%.

In various embodiments, the impregnated wood product has CIE value for L* of from about 35 to 75, for example from about 35 to 70, 35 to 65, 35 to 60, 35 to 55, 40 to 75, 40 to 70, 40 to 65, 40 to 60, 40 to 55, 45 to 75, 45 to 70, 45 to 65, 45 to 60, or 45 to 55, preferably from about 45 to 55.

In various embodiments, the impregnated wood product has CIE value for L* of from about 45 to 55.

In various embodiments, the impregnated wood product has a CIE value for L* of at least 60% of the wood product prior to impregnation, for example at least 65, 70, 75, or 80%.

In various embodiments, the impregnated wood product has a Janka hardness, as measured in accordance with ASTM D143, from about 50% to about 150% of the wood product prior to impregnation, for example from about 60 to 150, 70 to 150, 80 to 150, or 90 to 150%.

In various embodiments, the impregnated wood product has an anti-shrink efficiency (ASE) of at least 40%, preferably 50%, preferably 60%. In various embodiments, the

impregnated wood product has an anti-shrink efficiency (ASE) of at least 50%. In various embodiments, the impregnated wood product has an anti-shrink efficiency (ASE) of at least 60%.

In various embodiments, the impregnated wood product further comprises one or more impregnatable colourants, pigments, or dyes. In various embodiments, the one or more impregnatable colourants, pigments, or dyes prevent or reduce the appearance of a change in colour on weathering of the impregnated wood product, for example for a period at least 3, 4, 5, or at least 6 months, preferably for a period of about 3-6 months. In various embodiments, the one or more impregnatable colourants, pigments, or dyes prevent or reduce the appearance of a change in colour on weathering of the impregnated wood product for a period of about 3-6 months.

In various embodiments, the impregnated wood product further comprises and/or the cured reaction product is produced in the presence of a source of acid, for example a lactone, preferably lactide; and/or a source of base.

In various embodiments, the impregnated wood product further comprises a source of acid, for example a lactone, preferably lactide; and/or a source of base. In various embodiments, the impregnated wood product further comprises a lactone. In various embodiments, the impregnated wood product further comprises a lactide.

In various embodiments, the cured reaction product is produced in the presence of a source of acid, for example a lactone, preferably lactide; and/or a source of base. In various embodiments, the cured reaction product is produced in the presence of a lactone. In various embodiments, the cured reaction product is produced in the presence of a lactide.

In various embodiments, the impregnated wood product further comprises and/or the cured reaction product is produced in the presence of one or more additives capable of reacting with the furan monomer, for example an amine, such as an amino acid and/or amino alcohol, for example lysine and/or Tris.

In various embodiments, the impregnated wood product further comprises one or more additives capable of reacting with the furan monomer, for example an amine, such as an amino acid and/or amino alcohol, for example lysine and/or Tris. In various embodiments, the impregnated wood product further comprises an amine. In various embodiments, the impregnated wood product further comprises an amino acid and/or amino alcohol. In various embodiments, the impregnated wood product further comprises lysine and/or Tris.

In various embodiments, the cured reaction product is produced in the presence of one or more additives capable of reacting with the furan monomer, for example an amine, such as an amino acid and/or amino alcohol, for example lysine and/or Tris. In various

embodiments, the cured reaction product is produced in the presence of an amine. In various embodiments, the cured reaction product is produced in the presence of an amino acid and/or amino alcohol. In various embodiments, the cured reaction product is produced in the presence of lysine and/or Tris.

In various embodiments, the method comprises impregnating the wood product with the furan monomer and the initiator.

In various embodiments, the method comprises impregnating the wood product with the furan monomer and the monomer, oligomer, or polymer.

In various embodiments, the monomer, oligomer, or polymer that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction is a prepolymer comprising a reaction product of a furan monomer and an initiator that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction; and the method further comprises the step of producing the prepolymer, prior to impregnation.

In various embodiments, producing the prepolymer comprises reacting the furan monomer and the initiator under conditions effective for Diels Alder reaction.

In various embodiments, producing the prepolymer comprises reacting the furan monomer and the initiator at an elevated temperature, for example at a temperature from about 40 to 80, 45 to 75, or 50 to 70°C, preferably 60°C, for a period of time, for example at least 1, 3, 6, or 12h, preferably about 12h; and optionally allowing the mixture to stand for a period of time, for example at least 24h, 48h, 72h, a week, two weeks, a month, or two or more months.

In various embodiments, producing the prepolymer comprises reacting the furan monomer and the initiator at from about 40 to 80, 45 to 75, or 50 to 70°C, for at least 1, 3, 6, or 12h, preferably about 12h. In various embodiments, producing the prepolymer comprises reacting the furan monomer and the initiator at about 60°C, for about 12h. In various embodiments producing the prepolymer comprises allowing the mixture to stand for two or more months.

In various embodiments, the method further comprises: providing a liquid formulation comprising the furan monomer and the initiator and/or the monomer, oligomer, or polymer; and

impregnating the wood product with the liquid formulation.

In various embodiments, the impregnating comprises: subjecting the wood product to a vacuum in a vessel;

immersing the wood product in the liquid formulation; and

pressurising the vessel.

In various embodiments, the reacting to produce the cured furan polymer comprises heating the wood product at a temperature from about 70 to about 140°C, preferably from preferably 90 to 120°C. In various embodiments, the reacting to produce the cured furan polymer comprises heating the wood product at a temperature from about 90 to 120°C.

In various embodiments, the reacting to produce the cured furan polymer comprises heating the wood product at a first temperature from about 60 to about 90°C, preferably 90°C, for a first period of time, and heating the wood product at a second temperature from about 100 to 120°C, preferably 120°C, for a second period of time.

In various embodiments, the reacting to produce the cured furan polymer comprises heating the wood product at about 90°C, for a first period of time, and heating the wood product at a second temperature about 120°C, for a second period of time.

In various embodiments, the method further comprises impregnating the wood product, preferably prior to reacting to produce the cured furan polymer, with one or more impregnatable colourants, pigments, or dyes. In various embodiments, the method further comprises impregnating the wood product, prior to reacting to produce the cured furan polymer, with a source of acid, for example a lactone, preferably lactide; and/or a source of base. In various embodiments, the method further comprises impregnating the wood product, prior to reacting to produce the cured furan polymer, with a lactone. In various embodiments, the method further comprises impregnating the wood product, prior to reacting to produce the cured furan polymer, with a lactide.

In various embodiments, the method further comprises impregnating the wood product, prior to reacting to produce the cured furan polymer, with one or more additives capable of reacting with the furan monomer, for example an amine, such as an amino acid and/or amino alcohol, for example lysine and/or Tris. In various embodiments, the method further comprises impregnating the wood product, prior to reacting to produce the cured furan polymer, with an amine. In various embodiments, the method further comprises

impregnating the wood product, prior to reacting to produce the cured furan polymer, with an amino acid and/or amino alcohol. In various embodiments, the method further comprises impregnating the wood product, prior to reacting to produce the cured furan polymer, with lysine and/or Tris.

In various embodiments, the method further comprises recovering unimpregnated liquid formulation comprising the furan monomer and the initiator and/or the monomer, oligomer, or polymer for reuse.

In various embodiments, the method comprises impregnating the wood product with a liquid formulation comprising the furan monomer and the initiator and/or the monomer, oligomer, or polymer, wherein the liquid formulation is an unimpregnated liquid formulation recovered for reuse.

In various embodiments, the formulation further comprises one or more impregnatable colourants, pigments, or dyes.

In various embodiments, the formulation further comprises a source of acid, for example a lactone, preferably lactide; and/or a source of base.

In various embodiments, the formulation further comprises one or more additives capable of reacting with the furan monomer, for example an amine, such as an amino acid and/or amino alcohol, for example lysine and/or Tris.

In various embodiments, the formulation further comprises an amine. In various

embodiments, the formulation further comprises an amino acid and/or amino alcohol. In various embodiments, the formulation further comprises lysine and/or Tris. In various embodiments, the formulation is a liquid, optionally comprising one or more diluents and/or solvents suitable for impregnation.

In various embodiments, the formulation is a liquid comprising one or more diluents and/or solvents suitable for impregnation. In various embodiments, the formulation is a liquid comprising one or more diluents suitable for impregnation. In various embodiments, the formulation is a liquid comprising one or more solvents suitable for impregnation.

In various embodiments, the formulation is anhydrous.

In various embodiments, the formulation is aqueous.

In various embodiments, the impregnated wood product has a CIE value for L* that is at least 10% greater, for example at least 15%, 20%, 25%, 30%, 40%, or at least 50% greater, than the CIE value for L* of a corresponding impregnated wood product formed in the absence of the initiator and/or the monomer, oligomer, or polymer.

The invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9, and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5, and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art. To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

Although the present invention is broadly as defined above, those persons skilled in the art will appreciate that the invention is not limited thereto and that the invention also includes embodiments of which the following description gives examples.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will be described with reference to the accompanying figures, in which :

Figure 1 is a photograph showing a control sample and FA treated samples after cure and conditioning, as described in Example 1. Left to right are: Control (left); 3% maleimide; 5% maleimide; 10% maleimide; and 5% maleimide with dye.

Figure 2 is a photograph showing colours of pairs of a control sample and treated wood samples post-cure using pre-reacted FA treatment formulations, as described in Example 2 and Table 3. Untreated (left), standard FA/B130 6: 1, FA/B130-heat (pre-reacted),

FA/B130-re-used and FA/maleimide-heat (pre-reacted) (right). FA/B130 samples were treated at pH 4, with all samples cured using the 90°C and 120°C stepped heating ramp described herein.

Figure 3 is a photograph showing colours of pairs of a control sample and treated wood samples post-cure using differing FA/Oxazolidine ratios or methylene content as described in Example 2 and Table 3. Untreated (left), FA/B130 9: 1, 14: 1 and 18: 1 cured with 120°C heat ramp and FA/B130 14: 1 and FA/M130 28: 1 cured with stepped (90°C, 120°C) heating ramp (right). All samples treated as pH 4 FA/Oxazolidine solutions.

Figure 4 is a photograph showing colours of pairs of a control sample and treated wood samples post-cure using different differing formulations including additional catalysts, alternate methylene donors post-cure as described in Example 2 and Table 3. Untreated control (left). FA/B130 14: 1, FA/Tris, FA/Hexamine, FA/B130/lysine, FAB130/5%lactide and FA/Tris/5%lactide (right). All samples treated at pH 4 and cured with the 90°C and 120°C stepped heating ramp. Figure 5 are photographs taken from different angles showing colouring contributed by different FA treatments, as described in Example 4. Left to right: unmodified wood; FA/Mal; FA/NMM; FA/Succ; FA/Mal/AHPO; FA/APD; and FA/BPh.

Figure 6 is a graph showing CIE L* (horizontal lined bars - leftmost in each set of 3), a* (sideways hashed bars - middle in each set of 3), and b* (grey bars - rightmost in each set of 3) colour values for different FA treatments, as described in Example 4. Colour-meter measurements undertaken on freshly sanded surfaces. In the graph the sample labelled FA/Mal/Ox equates to FA/Mal/AHPO.

Figure 7 is a graph showing heating ramps and hold temperatures employed in FA/B130 curing regimes, as described in Example 3. The timelines for curing will vary depending on the size of the wood substrate and the treatment formulation.

DETAILED DESCRIPTION OF THE INVENTION

The term "comprising" as used in this specification and claims means "consisting at least in part of". When interpreting each statement in this specification and claims that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

As used herein the term "and/or" means "and" or "or", or both.

As used herein "(s)" following a noun means the plural and/or singular forms of the noun.

The general chemical terms used, for example, in the formulae herein have their usual meanings.

The term "alkyl" as used herein refers to a radical of a straight-chain or branched saturated hydrocarbon group. In some embodiments, alkyl groups have from 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groups include but are not limited to methyl, ethyl, n- propyl, isopropyl, n-butyl, tert-butyl, sec-butyl, iso-butyl, n-pentyl, 3-pentanyl, amyl, neopentyl, 3-methyl-2-butanyl, tertiary amyl, n-hexyl, and the like.

The term "carbocyclic" as used herein refers to a ring system in which all of the ring atoms are carbon atoms. Carbocyclic ring systems include monocyclic and bicyclic ring systems. The ring(s) of the carbocyclic ring system may be saturated, unsaturated (including partially unsaturated), or aromatic. Carbocyclic ring systems include phenyl, cycloalkyl (e.g., cyclopentyl, cyclohexyl and the like), and cycloalkenyl (e.g., cyclopentenyl, cyclohexenyl, and the like) ring systems. In various embodiments, carbocyclic ring systems comprise from 3 to 12 ring carbon atoms, for example from 3 to 10, 3 to 8, 3 to 6, 4 to 12, 5 to 12, 5 to 10, 5 to 8, or 5 or 6 ring carbon atoms. Examples of carbocyclic ring systems include but are not limited to phenyl, cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl,

cyclohexadienyl, cycloheptyl, cycloheptadienyl, and the like.

The term "heterocyclic" as used herein refers to a carbocyclic ring system in which one or more of the ring carbon atoms are replaced with a heteroatom. Heterocyclic ring systems include monocyclic and bicyclic ring systems. The ring(s) of the heterocyclic ring system may be saturated, unsaturated (including partially unsaturated), or aromatic. In various embodiments, the heterocyclic ring system may comprise 1, 2, 3, or 4 ring heteroatoms. In various embodiments, each heteroatom is independently selected from O, N, S. In various embodiments, heterocyclic ring systems comprise from 3 to 12 ring atoms, for example from 3 to 10, 3 to 8, 3 to 6, 4 to 12, 5 to 12, 5 to 10, 5 to 8, or 5 or 6 ring atoms. Examples of heterocyclic ring systems include, but are not limited to, pyrrolidines, pyrroles, imidazoles, triazoles, thiophenes, oxazoles, pyridines, piperidines, pyrans, azepines, and indoles.

The present invention relates to a cured furan polymer impregnated wood product. The cured furan polymer comprises a cured reaction product of a furan monomer and an initiator that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction; and/or a monomer, oligomer, or polymer that prevents or reduces crosslinking between chains of polymerised furan monomer by furan- furan Diels Alder reaction.

The term "wood product" as used herein unless otherwise indicated refers to a product comprising wood. Examples of wood products include, but not limited to, lumber, timber, and wood composites. Examples of wood composites include, but are not limited to, particleboard, oriented strand board, waferboard, fibreboard, parallel strand lumber, laminated strand lumber, plywood, laminated veneer lumber, finger jointed lumber, and the like. Wood products also include wood fibres, particles, flakes, strands, chips, or sheets, for example from which wood composites may be produced.

The wood may be a softwood or hardwood. Specific woods useful in the invention described herein include pine, for example Pinus radiata, Scots pine, or southern yellow pine, beech, ash, maple, birch, alder, oak, aspen, poplar, and the like.

The wood product may be any suitable dimension. In some embodiments, the wood product is a large dimension product, for example a large piece of lumber or timber. The moisture content of the wood product that is impregnated can vary and, for example, may be of up to about 30%, for example from about 5 to 30, 10 to 30, 15 to 30, 5 to 25, 10 to 25, 5 to 20, or 10 to 20% by weight of the wood product prior to impregnation.

The cured furan polymer comprises a cured reaction product produced by reacting the furan monomer and the initiator and/or the monomer, oligomer, or polymer to polymerise the furan monomer and cure the resultant polymer. The reaction product may, thus, be referred to herein as a polymerisation reaction product.

The furan monomer is a monomer comprising one or more furan rings capable of polymerising to provide a furan polymer. Examples of suitable furan monomers include but are not limited to furfuryl alcohol (FA), bishydroxymethyl furan (BHMF), tri hydroxymethyl furan (THMF), furfural, oligomers thereof, condensation products thereof, and combinations thereof. A preferred furan monomer is furfuryl alcohol (FA).

It is known that furfuryl alcohol polymerises to form black crosslinked products (Gandini, A., Furans as offspring of sugars and polysaccharides and progenitors of a family of remarkable polymers: a review of recent progress, Polymer chemistry, 2010. p. 245-251.). This dark colour is primarily due to Diels-Alder reaction between furan rings of different polymer chains, which results in a crosslinked or conjugated structure.

The initiator and/or the monomer, oligomer, or polymer prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction, compared to reaction products formed in the absence of the initiator and/or the monomer, oligomer, or polymer. This prevention or reduction in crosslinking via furan-furan Diels Alder reaction between chains of polymerised furan monomer results in the impregnated wood product having a lighter colour.

Compared to traditional acid-catalysed furfurylation treatments embodiments of the present invention can provide cured furan polymer impregnated wood products that are lighter in colour and may be less brittle, but are still dimensionally stable.

The initiator is a compound capable of initiating polymerisation of the furan monomer, in addition to preventing or reducing crosslinking by furan-furan Diels Alder reaction. In some embodiments, the initiator may be capable of reacting in a Diels Alder reaction with furan rings of the furan monomer and/or polymerised chains thereof.

In some embodiments, the initiator is an imide. As used herein unless otherwise indicated, an "imide" is a compound comprising two acyl groups bound to a nitrogen atom. An imide may be a cyclic or acyclic. In some embodiments, the imide may comprise from 4 to 20 carbon atoms, for example 4 to 16, 4 to 12, 4 to 10, 4 to 8, or 4 to 6 carbon atoms. A cyclic imide may comprise a 5-8 membered ring, preferably 5 or 6 membered ring, preferably a 5 membered ring, comprising the imide nitrogen. The ring may be a saturated ring or an unsaturated, non-aromatic ring. Preferably, the cyclic imide is an imide of a dicarboxylic acid. The nitrogen atom of the imide may unsubstituted or substituted, for example with an alkyl group of 1 to 6 carbon atoms, such as a methyl group. Examples of suitable imides include but are not limited to maleimide, N-methyl maleimide, and succinimide. A preferred imide is maleimide.

In some embodiments, the initiator is an oxazolidine. As used herein unless otherwise indicated, an "oxazolidine" is a compound comprising a 5-membered ring with an oxygen atom at the 1 position, a nitrogen atom at the 3 position, and carbons atoms at the remaining positions of the ring. Oxazolidines include monocyclic and bicyclic oxazolidines. In some embodiments, the oxazolidine may comprise from 5 to 12 ring atoms, preferably 5 or 8 ring atoms, and/or from 3 to 20 carbon atoms, for example 3 to 16, 3 to 12, 3 to 10, 3 to 8, 5 to 20, 5 to 16, or 5 to 12 carbon atoms. Bicyclic oxazolidines include but are not limited to compounds wherein the 5 membered oxazolidine ring is fused to another ring via the carbon atoms at positions 4 and 5 of the oxazolidine ring or via the nitrogen atom and the carbon atom at position 4 of the oxazolidine ring. The ring fused to the oxazolidine ring may be a 5-8 membered, preferably 5 or 6 membered carbocyclic or heterocyclic ring, which may be saturated, unsaturated, or aromatic. In some embodiments, the oxazolidine is a methylene donor. In such embodiments, the carbon atom at position 2 of the oxazolidine ring is bound to two hydrogen atoms. Such oxazolidines may be formed by condensation of an appropriate amino alcohol with formaldehyde by methods well known in the art.

Examples of suitable oxazolidines include but are not limited to oxazolidines formed by the condensation of formaldehyde and tris(hydroxymethyl)methylamine (Tris), 2-amino-2- methyl-1, 3-propanediol, and 2-aminophenol. Condensation of one or two equivalents of formaldehyde with Tris provides the oxazolidines

(4,4-bis(hydroxymethyl)-l,3-oxazolidine)

methylol-3,7-dioxabicyclo[3.3.0]octane), respectively. Condensation of two equivalents formaldehyde and 2-amino-2-methyl-l, 3-propanediol provides the oxazolidine l-aza-5- methyl-3,7-dioxabicyclo[3.3.0]octane. Condensation of formaldehyde and 2-aminophenol provides the oxazolidine 2,3-dihydro-l,3-benzoxazole. A preferred oxazolidine is the oxazolidine formed by the condensation of Tris and two equivalents of formaldehyde, i.e. 1- aza-5-methylol-3,7-dioxabicyclo[3.3.0]octane. Illustrative of suitable oxazolidines there can be mentioned the various 1,3-oxazolidines shown in US 3,281,310 which is incorporated herein in its entirety by reference; and those of US 3,256,137 which is also incorporated herein in its entirety by reference.

The compounds of US 3,281,310 wherein the nitrogen is part of only one ring can be represented the formula :

wherein R ² is hydrogen, alkyl of 1 to 8 carbon atoms, hydroxyalkyl of 1 to 8 carbon atoms, benzyl, or phenylcarbamyl, and each of R ³ , R ⁴ , and R ⁵ is hydrogen or an alkyl of 1 to 8 carbon atoms. Illustrative of such oxazolidines there can be mentioned : 4,4-dimethyl-l,3- oxazolidine; 3-(2-hydroxyethyl)-l,3-oxazolidine; 3-(2-hydroxypropyl)-5-methyl-l,3- oxazolidine; 5-methyl-l,3-oxazolidine; 3-ethyl-l,3-oxazolidine; 3-benzyl-l,3-cyclohexyl-5- methyl-l,3-oxazolidine; 3-phenylcarbamyl-4,4-dimethyl-l,3-oxazolidine; as well as the corresponding bis(l,3-oxazolidino)methanes such as bis(4,4-dimethyl-l,3- oxazolidino)methane.

The oxazolidine compounds of US 3,256,137 wherein the nitrogen is directly attached to a first and a second ring of a bicyclic heterocycle can be represented by the formula :

wherein R is hydrogen, methyl, ethyl, n-propyl, isopropyl, methylol, beta-hydroxyethyl, acetoxymethyl or methoxymethyl. Illustrative of such oxazolidines there can be mentioned : l-aza-3,7-dioxabicyclo[3.3.0]octane; l-aza-5-methyl-3,7-dioxabicyclo[3.3.0]octane; 1-aza- 5-ethyl-3,7-dioxabicyclo[3.3.0]octane; l-aza-5-n-propyl-3,7-dioxabicyclo[3.3.0]octane; 1- aza-5-isopropyl-3,7-dioxabicyclo[3.3.0]octane; l-aza-5-methylol-3,7- dioxabicyclo[3.3.0]octane; l-aza-5-acetoxymethyl-3,7-dioxabicyclo[3.3.0]octane; l-aza-5- methoxymethyl-3,7-dioxabicyclo[3.3.0]octane. A preferred oxazolidine is l-aza-5-methylol- 3,7-dioxabicyclo[3.3.0]octane, such as that sold under the trademark ZOLDINE ZT-55 by Angus Chemical Company. In some embodiments, the initiator is a methylene donor. The methylene donor may be an oxazolidine, as described herein. However, other methylene donors are also useful in the invention. Examples of other suitable methylene donors include but are not limited to oxazinanes, dioxolanes, dioxanes, imidazolidines, piperizines, hexamines, and the like, preferably oxazinanes, dioxolanes, imidazolidines, and hexamines. As with the oxazolidines contemplated herein, the oxazinanes, dioxolanes, dioxanes, imidazolidines, and piperizines contemplated herein include monocyclic or bicyclic compounds. Bicyclic oxazinanes, dioxolanes, dioxanes, imidazolidines, piperizines include fused bicyclic compounds, including an oxazinane, dioxolane, dioxane, imidazolidine, or piperazine ring and a fused 5-8 membered, preferably 5 or 6 membered, carbocyclic or heterocyclic ring, which fused ring may be saturated, unsaturated, or aromatic.

In some embodiments, the initiator is a dialdehyde. In some embodiments, the dialdehyde comprises from 4 to 10 carbon atoms, for example from 4 to 8 carbon atoms, or from 4 to 6 carbon atoms. One example of a suitable dialdehyde is glutaraldehyde. Other suitable aldehydes will be apparent to those skilled in the art.

In some embodiments, the initiator is an olefinically unsaturated aldehyde comprising one or more one olefin (non-aromatic carbon-carbon double bond) and one or more aldehyde.

In some embodiments, the olefinically unsaturated aldehyde comprises from 4 to 10 carbon atoms, from 4 to 8 carbon atoms, or from 4 to 6 carbon atoms. In some embodiments, the olefinically unsaturated aldehyde comprises an a,b-unsaturated aldehyde. In some embodiments, the olefinically unsaturated aldehyde comprises two or more olefins, which optionally may be conjugated. One example of a suitable unsaturated aldehyde is sorbaldehyde. Other suitable olefinically unsaturated aldehydes will be apparent to those skilled in the art.

In some embodiments, the initiator is a cyclic or acyclic diene. In some embodiments, the diene is capable of undergoing a 2+2 addition to a furan ring. In some embodiments, the diene comprises from 4 to 16 carbon atoms, 4 to 10 carbon atoms, from 4 to 8 carbon atoms, or from 4 to 6 carbon atoms. The cyclic diene may be carbocyclic or heterocyclic. Carbocyclic or heterocyclic dienes may comprise from 4 to 12 ring atoms, preferably 5 to 12 ring atoms. Cyclic dienes include monocyclic and bicyclic dienes. The cyclic diene may be a non-aromatic carbocyclic diene or an aromatic or non-aromatic heterocyclic diene, the heterocyclic diene preferably comprising one or more oxygen, nitrogen, or sulfur atoms in the ring(s). In some embodiments, the cyclic or acyclic diene comprises a conjugated diene. Examples of suitable cyclic or acyclic dienes include thiophene and 2-(alkyl) butadienes (for example, 2-methylbutadiene), respectively. Any suitable amount of the initiator may be used. The amount may depend on the initiator used and the desired properties of the impregnated wood product, for example colour, hardness, dimensional stability, and the like. To reduce costs, it is generally desirable to use the minimum amount of initiator necessary to obtain the desired properties in the impregnated wood product. In some embodiments, the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1 :30, 1 :25, 1 :20, 1 : 15, 1 : 12, 1 : 10, 1 :7, or 1 : 5, preferably at least 1 : 15. In some embodiments, the initiator is an imide and the stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1 : 15. In other embodiments, the initiator is an oxazolidine and the

stoichiometric ratio of initiator to furan rings provided by the furan monomer is at least about 1 :27. In other embodiments, the initiator is an oxazolidine that is a methylene donor and the stoichiometric ratio of initiator, on a methylene donor basis, to furan rings provided by the furan monomer is at least about 1 : 14. It has been found that such ratios provide wood products having relatively light colour compared to traditional furfurylation, and in some embodiments useful other properties, such as reduced hardness or brittleness.

Any suitable monomer, oligomer, or polymer in the present invention that prevents or reduces crosslinking by furan-furan Diels Alder reaction between chains of polymerised furan monomer may be used in the invention. Examples of suitable monomers, oligomers, or polymers include but are not limited to furan monomers comprising a sterically bulky group, for example at position 3 or 4 of the furan ring, and oligomers and polymers comprising such monomers.

In various embodiments, the monomer modifies the helicity of the furan polymer and/or the spacing between furan units of different chains in the furan polymer. Without wishing to be bound by theory, it is believed that furan polymers exhibit helicity and that the reaction of a monomer that leads to a modification, for example reduction, in the helicity of the chains of the furan polymer produced (compared to the helicity of a corresponding polymer formed in the absence of the helicity modifying monomer) which prevents or reduces crosslinking, in particular furan-furan Diels Alder reactions, between chains of polymerised furan monomer. Similarly, without wishing to be bound by theory, it is believed that reacting a monomer that modifies the spacing, i.e. distance, between furan units of different chains of the furan polymer also prevents or reduces such crosslinking. In some embodiments, the monomer that modifies the spacing between furan units of the polymer also modifies the helicity of the polymer. Modification of helicity and/or spacing may be due to the incorporation of such a monomer or a group derived therefrom into chains of the polymer (e.g. between two adjacent furan units of a chain) or substitution of chains of the polymer with such a monomer or group. In some embodiments, the monomer that modifies helicity and/or spacing comprises a sterically bulky group (such as the 3- or 4-substituted furan monomers described above) and/or other group that increases the distance between furan units of different chains.

In some embodiments, the monomer, oligomer, or polymer is a prepolymer comprising a reaction product of a furan monomer and an initiator that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction. Such prepolymers may be prepared as described herein.

The amount of cured furan polymer in the wood product can vary. In some embodiments, the impregnated wood product may comprise at least 15% (w/w) of the cured furan polymer. In some embodiments, the weight uptake of the cured furan polymer in the impregnated wood product is at least 20% (w/w) of the wood product prior to impregnation.

A colour may be defined by the International Commission on Illumination (French

Commission Internationale de I'eclairage) colour space coordinates L*, a* and b* (CIELAB). In the CIELAB 3-dimensional colour space, one dimension L* is lightness, one dimension a* is colour extending from green (-a) to red (+a), and one dimension b* is colour extending from blue (-b) to yellow (+b). The rectangular colour coordinates a* and b* may be converted to polar form to be represented by hue (ho) being the angular component and chroma (C*) being the radial component. Colours of materials according to embodiments of the present invention may be defined by L*, and the rectangular coordinates a* and b* and/or the polar coordinates ho and C*.

A range of colours may be defined by a Delta-E metric that provides a measure of the difference between two colours, for example, the International Commission on Illumination CIE DE2000 Delta-E value. Unless otherwise specified, in this specification and claims, Delta-E is the CIE DE2000 value.

The L*, a* and b* measurements referred to herein unless indicated otherwise relate to freshly prepared surfaces, for example freshly sanded surfaces for lumber, as the colour of surfaces can change over time.

The impregnated wood product of the invention may have a CIE value for L* of from about 35 to 75, preferably from about 45 to 55; and/or a CIE value for L* of at least 60% of the wood product prior to impregnation.

The prevention or reduction in crosslinking provided by the initiator and/or the monomer, oligomer, or polymer is characterised by the impregnated wood product having a lighter colour compared to a corresponding impregnated wood product formed in the absence of the initiator and/or the monomer, oligomer, or polymer, for example by traditional furfurylation in the presence of an acid catalyst, such as zinc-chloride. The lighter colour may be determined visually or by other suitable methods. In some embodiments, the lighter colour is determined by an increased CIE value for L*. In some embodiments, the impregnated wood product has a CIE value for L* that is at least 10% greater, for example at least 15%, 20%, 25%, 30%, 40%, or at least 50% greater than the CIE value for L* of a corresponding impregnated wood product formed in the absence of the initiator and/or the monomer, oligomer, or polymer reacted in the present invention.

The impregnated wood product may have Janka hardness, as measured in accordance with ASTM D143, from about 50% to about 150% of the wood product prior to impregnation.

The Janka hardness will depend in part on the wood product, with some wood products being harder than others.

The impregnated wood product preferably has useful dimensional stability. Dimensional stability may be determined by anti-shrink efficiency (ASE). The impregnated wood product may have an ASE of at least 40%, preferably 50%, preferably 60%.

The impregnated wood product may comprise one or more impregnatable colourants, pigments, or dyes, for example that prevent or reduce the appearance of a change in colour on weathering of the impregnated wood product, for example for a period at least 3, 4, 5, or at least 6 months, preferably for a period from about 3-6 months. Any suitable impregnatable colourant, pigment, or dye for wood products may be used.

The impregnated wood product may comprise and/or the cured reaction product may be produced in the presence of one or more additional agents, for example a source of acid, for example a lactone, preferably lactide; and/or a source of base; and/or one or more additives capable of reacting with the furan monomer, for example an amine, such as an amino acid and/or amino alcohol, for example lysine and/or Tris.

Depending for example on the intended application, the furan polymer impregnated wood product may comprise or be impregnated with various other compounds, agents,

compositions, and formulations, such as resins and wood preservation formulations, for example pesticides, fire retardants, and anti-sapstains.

The present invention also relates to a method of producing a cured furan polymer impregnated wood product. The method comprises:

impregnating a wood product with

a furan monomer and an initiator that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction; and/or

a monomer, oligomer, or polymer that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction; and

reacting the furan monomer and the initiator and/or the monomer, oligomer, or polymer under conditions effective for polymerisation to produce a cured furan polymer comprising a cured reaction product of the furan monomer and the initiator and/or the monomer, oligomer, or polymer.

The wood product; the furan monomer; the initiator; and/or the monomer, oligomer, or polymer; may be as described herein with respect to the cured furan polymer impregnated wood product of the invention.

In some embodiments, the monomer, oligomer, or polymer that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction is a prepolymer comprising a reaction product of a furan monomer and an initiator that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction; and the method further comprises the step of producing the prepolymer prior to impregnation. The conditions for producing the prepolymer depend, in part, on the initiator used. For example, where an initiator capable of reacting with furan monomer via Diels Alder reaction is used, producing the prepolymer may comprise reacting the furan monomer and the initiator under conditions effective for Diels Alder reaction.

Producing the prepolymer typically comprises reacting the furan monomer and the initiator at an elevated temperature for a period of time. In some embodiments, the elevated temperature may be from about 40 to 80, 45 to 75, or 50 to 70°C, preferably 60°C. The period of time for which the reaction mixture is heated can vary. In some embodiments, the period of time is at least 1, 3, 6, or 12h, preferably about 12h. The temperature and period of time may be selected such that the furan monomer does not polymerise to any significant extent, for example any oligomers or polymers formed remain soluble in the solution. After heating, the mixture may be allowed to stand for a period of time, for example at least 24h, or even weeks or months.

The furan monomer and the initiator and/or the monomer, oligomer, or polymer may be impregnated into the wood product separately or together in the form of liquid

formulation(s). The impregnation of a single liquid formulation comprising all of the ingredients to be impregnated is typically preferred. The stoichiometric ratio of initiator to furan rings provided by the furan monomer in the material impregnated into the wood product and/or the impregnated wood product may be as described herein with respect to the impregnated wood product of the invention.

Any suitable method for impregnating the wood product may be used, for example vacuum pressure soaking (VPS). In various embodiments, the impregnating comprises subjecting the wood product to a vacuum in a vessel; immersing the wood product in the liquid formulation; and pressurising the vessel. In other embodiments, impregnation may be carried out without pressure and/or vacuum.

Following impregnation, the furan monomer and the initiator and/or the monomer, oligomer, or polymer are then reacted under conditions effective for polymerisation to produce the cured furan polymer. This polymerisation and curing step typically comprises delivering heat to the wood product. Heat may be delivered by any suitable means, for example hot air, steam, or high frequency heating. The heat activates the initiators and starts polymerisation. Reacting to produce the cured furan polymer may comprise heating the wood product at a temperature from about 70 to about 140°C, preferably from preferably 90 to 120°C. In some embodiments, reacting to produce the cured furan polymer comprises heating at a first temperature from about 60 to about 90°C, preferably 90°C, for a first period of time, and heating at a second temperature from about 100 to 120°C, preferably 120°C, for a second period of time. The period of time for which the wood product is heated for polymerisation and curing will vary, for example depending on the size of the wood product and the type of oven or kiln. Times may range from about 0.5h to about 24h, for example from 1 to 24, 1 to 18, 1 to 12, 6 to 24, 6 to 18, or 6 to 12h.

The method may further comprise impregnating one or more additional agents, prior to reacting to produce the cured furan polymer, for example one or more impregnatable colourants, pigments, or dyes; and/or with a source of acid, for example a lactone, preferably lactide; and/or a source of base; and/or one or more additives capable of reacting with the furan monomer, for example an amine, such as an amino acid and/or amino alcohol, for example lysine and/or Tris. The one or more additional agents may be in the liquid formulation for impregnating the furan monomer and the initiator and/or the monomer, oligomer, or polymer.

Prior to polymerisation and curing, unimpregnated liquid formulation comprising the furan monomer and the initiator and/or the monomer, oligomer, or polymer may be recovered for reuse, and recycled in the method. Such recycling can provide significant cost savings.

The present invention also relates to a cured furan polymer impregnated wood product produced by a method of the present invention. The present invention also relates to a formulation for impregnating a wood product, the formulation comprising :

a furan monomer; and

an initiator that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction; and/or

a monomer, oligomer, or polymer that prevents or reduces crosslinking between chains of polymerised furan monomer by furan-furan Diels Alder reaction.

The wood product; the furan monomer; the initiator; and/or the monomer, oligomer, or polymer; and/or the stoichiometric ratio of initiator to furan rings provided by the furan monomer may be as described herein with respect to the cured furan polymer impregnated wood product of the invention.

The formulation may further comprise various additional agents for impregnation, for example one or more impregnatable colourants, pigments, or dyes, a source of acid, for example a lactone, preferably lactide; and/or a source of base; and/or one or more additives capable of reacting with the furan monomer, for example an amine, such as an amino acid and/or amino alcohol, for example lysine and/or Tris. The source of acid and/or a source of base may be used to control the pH of the formulation, for example prior to and/or on impregnation.

The formulation may be a liquid, solid, semisolid or other suitable form. A liquid formulation may be provided in the form of a concentrate that is diluted prior to impregnation or in the form of a ready to use formulation comprising a suitable diluent and/or solvent. Solid or semisolid formulations are converted to liquid form for impregnation, for example by dissolving or suspending in a suitable diluent and/or solvent. Diluents and/or solvents suitable for impregnation will be apparent to those skilled in the art and include but are not limited to water, alcohols, for example ethanol, and the like. The formulation may be anhydrous or aqueous. In some embodiments, aqueous formulations are preferred.

The following non-limiting examples are provided to illustrate the present invention and in no way limit the scope thereof.

EXAMPLES

Abbreviations

The following abbreviations are used for the oxazolidines used in the Examples that follow:

• "bis 1,3 oxazole" or "B130" is l-aza-5-methylol-3,7-dioxabicyclo[3.3.0]octane, the reaction product of two equivalents of paraformaldehyde and Tris as described in the Examples and Scheme 2, and shown as initiator in Scheme 3. • "mono 1,3 oxazole" or "M130" is the intermediate product in Scheme 2.

• "2-amino-2-methyl-l, 3-propanediol oxazolidine" or "AHPO" is the reaction product of paraformaldehyde and 2-amino-2-methyl-l, 3-propanediol described in Example 4.

Example 1

Methods & materials

Materials

Pinus radiata wood was obtained green and kiln-dried (KD, 90/60°C) to 12% moisture content. Samples (18 x 18 x 100 mm) were then machined and set aside prior to treatment.

Preparation of FA/maleimide treatment solution

An aqueous 75% furfuryl alcohol (FA) solution was prepared by adding furfuryl alcohol, water and ethanol (FA: H20: EtOH 15:4: 1). To this FA solution (100 g) maleimide was added at 3%, 5% and 10% (w/w) and thoroughly mixed. In the case of the 5% maleimide solution, the relative ratios of components are 71.1% FA, 5.1% maleimide, 19% water and 4.7% ethanol.

Wood treatment

Kiln-dried wood samples (18x18x100 mm) were immersed in the FA treatment solution and subjected to a vacuum pressure soak treatment. A vacuum was drawn for 30 mins followed by pressure (1400 kPa) for 1 h. Samples were then heated in a steam box for 12 h followed by conditioning in a kiln (90/60°C) for 2 h. Samples were then equilibrated at 65% relative humidity (RH) and 20°C to achieve constant weight.

Hardness testing

Relative hardness measurements used Janka hardness testing protocols (ASTM D143). A 5 mm ball bearing was pushed into the wood and the maximum force calculated to achieve the penetration depth. Treated and reference samples were first conditioned at 20°C and 65% RH then testing undertaken on both radial and tangential faces.

Anti-shrink efficiency (ASE) / Dimensional Stability Testing

Conditioned samples (18 x 18 x 20 mm) were accurately measured and weighed. Samples were first subjected to vacuum pressure soaking in water (30 minutes vacuum and then 1 h 200 bar). Samples were then re-weighed and measured before being placed in an oven (105°C) for at least 16 h. At least 12 specimens were used per sample. Average ASE values are based on sample volume swell and were calculated by:

ASE = (Suntreated ^— Streated)/S untreated X 100 (eq uation 1)

Where S = (VWS-VOD)/VOD x 100 (equation 2) Untreated = untreated control samples

Treated = treated samples (FA treated samples)

V = volume change; WS = water soaked sample; OD = oven dried sample

Maleimide furfuryl alcohol treatments

Using maleimide as FA polymerisation initiator provided a range of treated wood colours which were lighter than the traditional acid-catalysed FA treatments (Figure 1) (Lande, S., O. Hoi bo, and E. Larnoy, Variation in treatability of Scots pine (Pinus syivestris) by the chemical modification agent furfuryl alcohol dissolved in water. Wood Science and

Technology, 2010. 44(1) : p. 105-118.). A comparison of earlywood sections revealed little visual distinction between the differing maleimide contents with arguably the 10% maleimide sample the lightest colour. This was indicative of maleimide being incorporated into the FA polymer which has the effect of reducing furanyl ring conjugation and a dark colour. Average weight uptakes were calculated to range from 40 to 64% with dependency on maleimide content (Table 1).

Table 1. Summary properties of wood samples treated with FA

Evaluation of treated wood hardness and dimension stability indicate the FA/maleimide treatments resulted in property enhancements that were typical of FA-based treatments (Table 1). Across the three maleimide contents Janka hardness values ranged between 3800 and 4100 N compared to the untreated control (2100 N). There were no significant differences between the maleimide content used or calculated FA uptakes. Anti-shrink efficacy (ASE) testing revealed higher FA uptakes were associated with greater dimensional stability of treated wood.

Using maleimide to initiate the cure of FA treatments has revealed FA weight uptake was greater with higher maleimide content, but the three initiator loadings used led to visually similar treated wood colour. A higher maleimide content was distinguished in wood hardness. The 5% maleimide/FA treatment provided a useful balance of uptake and property enhancement while providing reduced colour compared to typical FA treatment.

Example 2

Methods & materials

Wood Sampling

The wood used was kiln-dried radiata pine with approximated 12% MC. Parent boards (6 in total) in green state were sourced from a local saw mill (Red Stag Ltd) and then kiln-dried in-house using a standard 90/60 drying regime. Boards were then cut into 18x18x100 mm specimens and stored at EMC (20°C/65% RH) until required.

Treatment Formulations

The oxazolidine B130 solution was prepared by mixing paraformaldehyde (18.24 g) and water (46.4 g) and thoroughly dispersing before adding tris(hydroxymethyl)methylamine ("Tris") (35.6 g). After further mixing the solution was left to stand overnight giving a colourless B130 solution.

An aqueous 75% furfuryl alcohol solution was prepared by adding furfuryl alcohol and water (FA:water 3: 1). This aqueous FA solution (100 g) and B130 solution (7.5 g) were then mixed and allowed to stand for at least 7 days before use. Each formulation was prepared in sufficient volume (>600 mL) to undertake treatment of 8 (18x18x100 mm) KD specimens by vacuum pressure soaking.

All FA/B130 treatment solutions were adjusted to their specified pH by adding either lactic acid or 40% sodium hydroxide solution.

Treatment, Impregnation and Curing Conditions

Kiln-dried wood samples (18x18x100 mm) were immersed in the FA treatment solution and subjected to a vacuum pressure soak treatment. A vacuum was drawn for 30 mins followed by an over pressure (1400 kPa) for 1 h. Samples were then heated in a metal box for >14 h using the stated curing regime. Samples were then equilibrated at 65% RH and 20°C to achieve constant weight. Specimens were accurately weighed and measured before and after treatment and when equilibrated.

Anti-shrink efficiency (ASE) and Hardness Testing were performed according to Example 1.

Wood specimens (treated or retained as untreated, reference samples) were cut from 6 individual radiata pine parent boards. While attempts were made to obtain identical, matched boards for comparative purposes, subsequent conditioning and testing of samples revealed variations in wood density and properties which manifest in (un)treated sample data sets.

Pre-treated FA formulations for reduced treated wood colouring

To further investigate routes to inhibiting Diels-Alder-induced darkening of FA polymers (Gandini A; Gandini and Belgacem) within wood, both FA/B130 and FA/maleimide (FA/Mal) formulations were pre-reacted at elevated temperature prior to treatment. To induce maleimide Diels-Alder coupling with FA, a pre-reaction temperature of 60°C was employed for 12 h. Both pre-reacted formulations were then allowed to stand for several days prior to wood treatment. On treating wood, these modified formulations provided high FA uptakes (Table 2). Modification with FA/Mal led to 81% uptake while the FA/B130 uptake was 57%. Recycling and re-use of the recovered FA/B130 treatment solution (as treatment

"kickback") led to an uptake of 47%. The FA/Mal treated sample colour was lighter than the pre-reacted FA/B130 treatment and considered visually similar to the standard 6: 1

FA/B130 treatment (Figure 2). The ASE values for the pre-reacted FA/B130 treatment were ca. 40% for both the pre-reacted and recycled treatments which were comparable to that achieved with the standard FA/B130 formulation. Hardness testing revealed maximum load values (ca. 2.6 kN) that were also similar to the standard FA/B130 treatment. Given the high uptake of the pre-reacted FA/Mal treatment, ASE values were also relatively high (63%). However, this FA/Mal treated sample had a hardness value (ca. 2.4 kN) similar to FA/B130 treatments.

Overall, the thermal pre-treatment of the FA/Mal formulation combined with the curing regime employed led to a high FA uptake (81%) which was greater than those observed for FA/Mal in Example 1. Without wishing to be bound by theory, it is believed this high uptake together with a relatively light brown colouring and high ASE value suggests the 60°C/12 hour pre-reaction of maleimide with the FA initially induced Diels-Alder coupling but also allowed further FA polymerization within wood. Table 2. Summary of FA treatment uptake and dimensional stability (as anti-shrink efficiency) performance using differing initiators and pre-reaction of treatment formulations

Colour evaluations A CIE colour comparison of the FA/B130 and FA/Mal formulations having undergone heat- conditioning prior to treatment revealed the pre-reaction of FA/B130 to deliver a relatively darker colouring than the standard FA/B130 6: 1 and pre-reacted FA/Mal treatments. An L* value of 47 was obtained for the pre-reacted FA/B130 compared to >56 for wood treated with the standard FA/B130 6: 1 formulation. While this lower L* value was consistent with the visual darkening of the pre-reacted treatment solution at 60°C, this should not be viewed as an indicator of the FA-induced colour which manifests in the treated wood. Other FA treatment combinations were also considered very dark in liquid form, but delivered relatively light brown colourings to the treated wood. For the FA/Mal treatment, an L* value >50 was surprising given the relatively high uptake of this treatment (81%). Moreover, the colour imparted by this FA/Mal formulation was comparable to that of the standard FA/B130 6: 1 formulation where each gave similar DE values (< 25) (see Table 3 below). Visual comparisons were also performed (see Figure 2).

Further variations

For the purpose of evaluating the efficacy of variations to the treatment, further

experiments were conducted in addition to the pre-reaction treatments described above. These variations included: pH; molar ratio of B130 initiator; structure of oxazolidine used (M130, B130, Tris); alternative or additional initiators; in addition to the pre-reactions (see Table 3 below).

Visual comparisons were also performed (See Figures 2, 3 and 4). Table 3. CIE L* a* and b* colour measurements of FA treated samples.

Where: DE = V(AL)2 + (Aa)2 + (Ab)2

Colour-meter measurements made on freshly sanded surfaces.

Anti-shrink efficiency testing For the samples produced with pre-reacted formulations, the FA/Mal formulation produced an ASE value of 63% which was consistent with the high uptake of this sample (Table 2 above). In comparison, the pre-reacted FA/B130 formulation and recycling this formulation produced an ASE of ca. 40%, which was comparable to the standard FA/B130 formulation.

Hardness testing Modification with various FA/B130 formulations generally led to similar or reduced wood hardness, which appeared independent of treatment uptake (Table 4). Furthermore, there was high variability in maximum load values. This is primarily due to the differing matched boards used to produce test specimens, but may also reflect the variability in individual specimen FA uptakes. Lastly, despite the high uptake, the FA/Mal-heat modification did not contribute increased sample hardness, which differs to the FA/Mal treated samples in Example 1 in which higher uptake was associated with relatively darker colouring. Table 4. Summary of hardness testing and maximum load values for various FA treated samples

Average of at least 10 specimens per sample.

Discussion

Overall, this Example shows the oxazolidine moiety plays a significant role in the cure and modified wood properties. The colouring of FA/B130 treated samples was relatively consistent, despite the apparent variability in individual specimen uptakes.

In evaluating differing initiator combinations with FA/B130 it was evident darker brown samples were associated with increased sample hardness (Table 4). This suggests that disruption to Diels-Alder induced furan ring crosslinking of FA polymers may affect formation of a rigid (crosslinked) FA polymer matrix. Instead, FA curing in the presence of oxazolidine may lead to more "linear" condensation polymers which have lower degrees of crosslinking. Potentially these FA polymers may also form differing interpenetrating networks with wood components compared to more crosslinked FA polymers. Nonetheless, the FA/B130 treatment and extent of FA polymerization did impact cell wall properties, given the increased dimensional stability observed with ASE values (>40%) with uptakes of FA 45-50%.

In the case of the FA/Mal formulation, pre-curing at 60°C led to high FA uptake (>80%) and excellent ASE values >60%. While this might be expected of a laboratory-scale FA treatment, the retention of a light colouring with high FA uptake was surprising. In contrast, similar pre-curing of the FA/B130 formulation did not retain a lighter colouring associated with samples treated with the standard FA/B130 treatment. Without wishing to be bound by theory, it is believed that this suggests either oxidation or Diels-Alder conjugation of furan rings occurred on heating at 60°C, with this occurring at a lower temperature than the B130 coupling reaction (ca. 90°C). While both FA/B130 and pre-heated FA/Mal formulations contributed no increase in wood hardness, this could be beneficial to the bulk properties of FA treated wood. With

commercial furfurylation, FA-treated products are typically associated with increased wood brittleness. As testing outcomes suggest FA/B130 does not appear to deliver a rigid crosslinked FA polymer, it may be anticipated there is no significant change in wood brittleness. This appears to also be the case for the pre-reacted FA/Mal treatment which was revealed to have lower hardness than found with FA/Mal work in earlier Examples. Furthermore, in providing a lighter colour with increased dimensional stability, it is possible the greater densification achieved with FA deposition in the wood may also manifest in other wood properties beyond brittleness.

Summary

While improved FA uptakes have led to enhanced ASE efficacy, the FA/B130 modifications do not provide increased wood hardness. Additionally, in evaluating the pre-reaction of the FA/B130 formulation alongside the FA/Mal formulation, the resulting colour and

performance of the FA/Mal treated wood also suggests this modification can be enhanced through controlling FA polymerization and use of the curing scheme employed. Lastly, a comparison of outcomes suggests the pre-reacted FA/Mal formulation offers greater potential given the higher FA uptake, ASE efficacy and retention of a relatively colour- neutral modified wood than achieved with FA/B130/pH 4.

Example 3

Maleimide for FA polymerization

Treatment solutions were generally prepared using an aqueous 75% furfuryl alcohol solution (furfuryl alcohol:water:ethanol, 15:4: 1 or 5 parts water only). This FA solution had 5%

(w/w) maleimide added weight for weight to complete the treatment solution. Typically, the treatment solution was applied "as is" (71% FA calc content). Variations in which the treatment solution was further diluted to ca. 66% and 50% FA content for wood treatment have also been tried.

To evaluate the maleimide content, the 75% FA solution had maleimide added at 3%, 5% and 10% (w/w). On treating wood, cured FA weight uptake was greater with higher maleimide content, but the three initiator loadings gave visually similar treated wood colour. Higher maleimide gave greater wood hardness and anti-shrink efficiency (dimensional stability). Treatment with 5% maleimide/FA provided a useful a balance of uptake and property enhancement while providing reduced colour compared to typical FA treatment. Calculation of the mole ratio of FA to maleimide for the 3%, 5% and 10% (w/w) treatment solutions are 25: 1, 15: 1 and 7.5: 1 (FA: Mal), respectively. At 5% maleimide incorporation, just 1 maleimide unit is added per 15 furan units. The results suggest this ratio and coupling chemistries disrupt conjugation between FA polymers. Pre-reaction of FA solution and maleimide was undertaken at 60°C for 12 h which was based on inducing Diels-Alder coupling of FA (Ghandini, 1997 & 2010). Treatment with the pre-reacted formulation coupled with 90 & 120°C cure ramps provided one of the highest observed FA uptakes (81%, 18x18x100mm). This resulted in high ASE (63%), modest hardness (2.4 kN) and light colouring, comparable to FA/B130 (see Table 3). Without wishing to be bound by theory, it is believed that reaction of maleimide with FA can potentially result in a range of modifications to the FA polymer. These may include the Diels Alder 4+2 reaction cycloaddition product produced at 60°C, 2+2 di-ene addition and the imido/amido function reacting with the methylol group during condensation polymerization. In each case steric hindrance, increasing length between furan rings or modification to FA polymer helicity could be introduced which will reduce/inhibit furan ring cycloaddition and conjugation (dark colour).

Scheme 1. Possible chemistries resulting from coupling maleimide with furan rings either as FA alone or within a FA polymer. Top: reversible 4+2 cycloaddition and Bottom: FA coupling products incorporating 2+2 di-ene addition or amido group functionality. FA/B130 for FA polymerization

B130 use in FA treatment solutions from neutral to acidic pH have been tested. The inclusion and elimination of alcohol (ethanol or glycol) has also been tested. Generally, the treatment solutions had the same FA/B130 ratio. Typically, the 75% FA solution has been formulated with 7.5% B130 solution which calculates to a FA mole ratio of FA to B130 of 27: 1 or, on a "methylene" donor basis, 14: 1 (FA: B130).

FA/B130 treatment solutions at pH 4, 7 and 9 were adjusted with lactic acid (or acetic acid) or sodium hydroxide at least 24 hours (typically >72 h) prior to treatment. Curing at 110- 120°C (ramp/hold) delivered a relatively colour-neutral modification with pH 7 and pH 9 whereas the pH 4 treatment gave a light brown colour and moderately greater hardness and ASE.

Comparison of the FA/B130 ratio revealed only subtle differences between 9: 1, 14: 1 and 18: 1 ratios. A visible perception between the 9: 1 and 18: 1 (darker) treatment impact sample colour (Figure 3). ASE values of the 9: 1 and 14: 1 treatments were better than the 18: 1 with no distinction in hardness (ca. 2.6 kN) of samples.

Manipulation of the B130 chemistry to deliver only 1 equivalent of "methylene" (CH ₂ ) per Tris unit, rather than 2 equivalents, was investigated. A procedure analogous to that described above for preparation of the B130 solution was followed but only one mole equivalent of formaldehyde was reacted with the Tris (Scheme 2). Use of this "methylene" donor reduced performance of FA treated samples. Direct comparison of the oxazolidines that delivered 1 or 2 equivalents of "methylene" as formulations with FA to oxazolidine mole ratios of 27: 1 and 14: 1, respectively, showed lower FA uptake (19%) for the former compared with the latter (14: 1) treatment (41%) when using a 90/120 heating ramp. The latter 14: 1 treatment had visually lighter colouring and better ASE (43%) compared to the former 27: 1 sample (22%). Similar hardness (ca. 2.6 kN) was achieved for both

treatments.

Across the differing FA/B130 ratios, FA uptakes, colour and dimensional stability concluded the 14: 1 ratio was likely the minimum ratio to effect a change in FA polymerization cure and treated wood properties.

Scheme 2. Reaction schemes for the preparation of B130 using Tris and either 1 or 2 equivalents of formaldehyde

The results show contrasting treated sample colour attributable to differing cure regimes. The curing regimes are shown in Figure 7.

• Heating to 110°C with a >12 hour hold provided FA uptakes of only ca. 30% with FA/B130 (Figure 7, solid line "110 heat & hold").

• Extending heating to 120°C with FA/B130 at pH 4 led to FA uptakes of 56% and darker colour (Figure 7, dashed line "120 heat & hold").

· Heating to 90°C with a 5 hour hold before heating to 120°C gave 41% FA uptake with reduced colouring (Figure 7, dotted line "90-120 ramp & holds").

The basis for this 90°C hold is B130 reportedly reacting with FA below 100°C. Without wishing to be bound by theory, it is believed introducing the 90°C hold before heating above 100°C is may induce FA/B130 coupling as well as potentially avoid volatilisation (loss) of FA from the wood above this temperature.

The heating regime used was dependent on sample dimensions and kiln size/packing.

Without wishing to be bound by theory, as with maleimide, inclusion of B130 to wood furfurylation formulations can impact FA uptake and the treated wood colour and properties. B130 can react with the methylol (-CH2OH) giving amino functionality, or grafting to C2 and C3 via alkylation. The steric hindrance or modified FA polymer helicity is sufficient to reduce/inhibit furan ring cycloaddition and conjugation (dark colour). Interestingly, the minimum, effective mole ratio of FA to B130 was 14: 1, which is relatively similar to that for FA/Mal (15: 1).

Scheme 3. Possible coupling chemistries of B130 coupling with FA alone or introduced along a FA polymer.

Lactide-catalysed curing of FA within wood Lactide, a cyclic lactone (the di-ester of lactic acid), has been used to substitute the organic acid or anhydride in furfurylation treatments. The FA/lactide formulation has been scaled, with treatments undertaken on 50x100x1200mm samples.

FA/B130 treatments were combined with lactide, lysine and Tris to compare amine and carboxylic functionalities in FA/B130 treatments solutions. FA/B130 with lactide led to 48% FA uptake, similar to FA/B130/Lysine (50%). Samples have a range of brown colours darker than FA/B130 (Figure 4) as well as differing hardness (2.2 to >4 kN). ASE values were all ca. 45%, similar to FA/lactide. Overall, the lactide-modified FA/B130 formulations give uptakes and dimensional stability typical of wood furfurylation, but provide other colour options, including neutral to light brown colour options, and variants to formulate FA treatments.

Example 4

Materials

Kiln-dried radiata pine

Succinimide, 2-amino-2-methyl-l, 3-propanediol, and 2-amino-2-hydroxymethyl-l,3- propanediol (as Trizma® base, aka tris(hydroxymethyl)methylamine, Tris) were sourced from Sigma (USA). 2-Aminophenol and N-methylmaleimide were sourced from Aldrich (USA). Lactic acid (>85%), maleimide and paraformaldehyde were sourced from Sigma Aldrich (USA). Furfuryl alcohol (technical grade) was sourced from Chunzhu Aroma Co. (China).

Treatment Solutions

Preparation of FA/Mal treatment solution (as reference) was the same as Example 1.

Preparation of FA/APD treatment solution

Firstly, amino-methylpropanediol (APD) oxazolidine solution was prepared.

Paraformaldehyde (36.4 g) and water (82.0 g) were thoroughly dispersed. 2-Amino-2- methyl-1, 3-propanediol (63 g) was then added and allowed to dissolve by occasional mixing and standing overnight. This yielded the colourless amino-methylpropanediol oxazolidine solution.

To form the FA/APD treatment solution, a 75% aqueous FA solution (1000 g) was prepared by combining furfuryl alcohol (750 g) and water (250 g). The APD oxazolidine solution (68 g) was then added, mixed and allowed to stand for at least 7 days before use. 24 Hours prior to wood treatment this FA/APD solution was adjusted to pH 4.7 with lactic acid and then left overnight.

Preparation of FA/BPh treatment solution

Benzoxazolidine (BPh) was first formed by mixing 2-aminophenol (51.9 g) and water (190 g) and thoroughly dispersing. Next paraformaldehyde (14.5 g) was carefully added with stirring of this solution. The solution was then allowed to stand overnight to yield a BPh benzoxazolidine suspension.

To form the FA/BPh treatment solution, furfuryl alcohol (750 g) and water (120 g) were combined first. The BPh benzoxazolidine suspension was then added to the aqueous FA solution, mixed and then allowed to stand for at least 7 days prior to use. This dark solution was then adjusted to pH 4.7 with lactic acid 24 hours prior to FA/APD treatment.

Preparation of FA/Succ treatment solution

The FA/Succ treatment solution was formed by adding succinimide (Succ) (52 g) to a 75% aqueous FA solution (1000 g). After mixing and then standing for at least 24 h the solution was heated at 60°C for 12 hours. This FA/Succ solution was then allowed to stand before wood treatment. Preparation of FA/NMM treatment solution

The FA/NMM treatment solution was formed by adding N-methyl maleimide (NMM) (58 g) to a 75% aqueous FA solution (1000 g) then mixed and allowed to stand for at least 24 h. This solution was then heated at 60°C for 12 hours prior to FA/NMM treatment.

Preparation of FA/Mal/AHPO treatment solution

A 2-amino-2-methyl-l,3-propanediol oxazolidine (AHPO) solution was prepared first.

Paraformaldehyde (18.24 g) and water (46.4 g) were combined and thoroughly dispersed. 2-Amino-2-methyl-l, 3-propanediol (35.6 g) was then added and the solution mixed allowed to stand overnight to yield the colourless AHPO solution.

The FA/Mal/AHPO treatment solution was prepared by combining a 75% aqueous FA solution (1000 g) with maleimide (50 g) and mixing. Next, AHPO solution (75 g) was added and the solution thoroughly mixed. After standing for 24 h, this treatment solution was pre- reacted at 60°C for 12 h. Prior to treatment, the solution was adjusted to pH 4.7 with lactic acid 24 h prior to wood treatment.

Standard Treatment Conditions

Kiln-dried wood samples (18x18x100 mm, total of 8) were placed in 2 L Parr vessel and weighted to be below the anticipated treatment solution level. A vacuum was drawn for 30 mins followed by adding the FA treatment solution and flooding the treatment vessel. A pressure (1400 kPa) was then applied for 1 h. The treatment vessel was then de- pressurised. Treated samples were then removed and weighed.

Treated, wet samples were transferred into a hot box and ensuring a >5 mm spacing between specimens. The hot box was then placed in a kiln, fitted with a condensate pipe and heating started. For sample curing, heat treatment was for at least 16 hours and used a standard 90°C and 120°C heat and hold procedure. Generally, this involved heating from ambient temperature to 90°C over 1 h, holding at 90°C for at least 5 h, before then ramping from 90°C to 120°C over 1 h. Samples were then held at 120°C to complete the curing process.

After heat treatment and cure, samples were equilibrated (emc) at 65% RH and 20°C to achieve constant weight. A set of reference (untreated) specimens were also equilibrated at these conditions before testing. Measurements & Testing

For the 8 specimens treated and cured for each sample, 6 were cut up for testing and 2 retained for colour assessment and demonstration purposes.

ASE specimens (18x18x20 mm) were cut from the ends of each treated 18x18x100 mm specimen. The remaining centre section was used for hardness testing. Test specimens are also similarly cut from untreated controls.

Conditioned samples (18 x 18 x 20 mm) are accurately measured and weighed. Samples were first subjected to vacuum pressure soaking in water (30 minutes vacuum and then 1 h 1400 kPa). Samples were then re-weighed and measured before being placed in an oven (105°C) for at least 16 h. At least 12 test specimens were used per sample. At least 12 specimens were used per sample. Average ASE values are based on sample volume swell and were calculated by the equation in Example 1.

ASE and Janka Hardness were tested according to Example 1. Colour CIE measurements were obtained using a Nokia colour-meter. At least 6 measurements across 2 untested demonstration specimens were acquired for each treated sample. These were then converted to L*a*b* values and averaged for each sample.

Results

For the differing FA/Mal-style and FA/Oxazolidine-style treatments, each was prepared, applied and then cured in situ within the treated wood using the same processing protocols described for the FA/Mal and FA/Oxazolidine formulations in the Example 3 above.

Shown in Table 5 are equilibrated FA (%weight) uptakes for the various treatments. The table includes 3 series of data - an "Original" trial with the maleimide style treatment; a "Repeated" trial with the maleimide-style treatments, due to differences in kiln schedules (Table 5). Results show a high degree of variability in specimen weight uptakes, which range from < 15% to greater than 70% weight uptake. While the differences in the maleimide-style treatments can be attributed to the two differing kiln schedules, the range of uptakes in the oxazolidine-style treatments was equally variable and may be attributable to chemical and reactivity differences and FA curing across treatment formulations. Table 5. Summary of furfuryl alcohol treated sample weight uptakes (as FA) on equilibration at 20°C and 65% RH.

provided). Cure schedule variation

The kiln schedule for the curing temperature profiles for three treated sample sets (Table 5) was set up to follow a 90°C and 120°C heat and hold procedure. The set points for this standard schedule were a ramp to 90°C (2 h), 90°C hold (5 h) then ramp to 120°C (1 h) before the final hold at 120°C (>7 h). Initially, for the first treatment series (maleimide- style, "Original"), the wood temperature, reached only 85°C before proceeding to the final 120°C curing step. This resulted in calculated weight gains <40%, attributable to FA loss from these samples (Table 5). The curing schedule was then adapted to first achieve 90°C during the cure before holding. This curing run (oxazolidine-style, "Extended 90") showed the wood temperature profile was near or at 90°C for a period of nearly 12 h. The final 120°C hold was shortened to <4 h. The final set of treated samples (FA/Mal-style,

"Repeated") used further modified schedule and temperature set points resulting in cure profile that may be more desirable in certain embodiments.

These differing curing schedules provide further insights to the impact of the 90°C hold step on the cure profile and FA uptake of treated samples. Failure to achieve the 90°C hold for the "Original" FA/Mal-style samples led to low FA retention and weight gains <40%. At this laboratory-scale, a 90°C hold (>5 h) achieved FA polymerization without FA loss, which can occur as an FA/water azeotrope if heated above temperature (e.g. 100°C). In contrast, an extended time at 90°C for the "Extended 90" FA/oxazolidine-style samples did not impact FA uptakes of the FA/BPh or FA/Mal/AHPO samples.

Weight uptakes

Shown in Table 5 are cured sample weight uptakes at equilibrium moisture content (emc, 65% RH, 20°C). This revealed the maleimide-style treatments have >60% weight uptakes if maleic unsaturation (C=C double bond) was present in the initiator. In contrast, succinimide (no unsaturation) as initiator achieved a lower uptake (ca. 50%). Overall, this suggests maleimide, NMM and succinimide treatments all induce FA polymerization and retention of FA in wood during curing and exposure to 120°C.

Although all FA/Oxazolidine-style treatments were characterised by contrasting weight uptakes, the FA/Mal/AHPO treatment (pH adjusted 4.7) gave a 66% weight uptake which was comparable to FA/Mal (70%). A lower uptake was observed for FA/APD (24%). This lower uptake may suggest a slower or inhibited FA cure, which may contribute to FA losses at elevated temperature (120°C) during cure (despite the pH adjustment and lactic acid present). The FA/BPh treatment produced a dark colouring with a weight uptake >50%.

While a range of uptakes were achieved across samples, it was evident on preparing and testing some of the samples there was still residual FA or that some FA polymer had not fully cured. In these cases, the samples had a "wet look" and/or smelled, which is indicative of residual, uncured FA monomer. This was evident for FA/Mal/AHPO and FA/NMM samples, which exhibited liquid FA material on sample deformation during hardness testing.

Colour

A feature of the modified FA/Mal and FA/Oxazolidine treatments was retention of a lighter treatment colouring. Across the treatment series, treated wood colouring varied

substantially between treatments and, to some extent, the kiln regime used (Figure 5). Although these colour differences were visually evident between samples, CIE (L*a*b*) colour measurements did not appear show these differences to the same extent (Figure 6). Additionally, cutting samples revealed some darkening and bleed of residual, under-cured material evident in end grain of several samples (Figure 5).

Both FA/Mal/AHPO and FA/NMM show relatively lighter colouring (L* = 60-61) together with their high uptakes. For the FA/Mal and FA/Succ treatments, these were marginally darker (L* = 59) than the FA/NMM and FA/Mal/AHPO treated samples (Figure 6). The two FA/Oxazolidine-style treatments produced an overall darker coloured treated wood with this considered darker than found with the standard FA/B130 treatment used in the previous Examples. It should be noted the preparation of FA/BPh led to a very dark, black treatment solution so the sample colouring was not unexpected. Performance

With weight uptakes exceeding 60%, this degree of modification was reflected in sample dimensional stability (Table 6). On vacuum pressure soaking (VPS) soaking and oven drying, anti-shrink efficiency (ASE) testing revealed FA/Mal and FA/Mal/AHPO to have ASE values of ca. 60%. Despite the higher weight uptake of FA/NMM (76%), this sample had an ASE value of 52%. This ASE may be consistent with the amount of FA under-cure visually observed. The FA/Succ and FA/APD treatments led to moderate ASE values of 40%, despite the difference in their respective weight uptakes.

Across all samples, Janka hardness testing revealed treated samples to have relatively similar hardness comparable to the untreated reference sample (1.9 kN, Table 6). This was consistent with preceding Examples where low colour FA treatments produced little or no hardness improvements compared to traditional dark coloured FA/acid treatments. The FA/Mal/AHPO treated sample (2.4 kN) had the greatest hardness, but this did not significantly differ to other samples. Table 6. Summary of treatment uptakes and sample dimensional stability and hardness testing of equilibrated treated samples.

Summary

FA/Maleimide-style Treatments

The FA/Maleimide weight uptake was comparable to that in preceding Examples as was the treated sample colour and performance. This treatment involved the kiln schedule achieving 90°C to induce FA curing and associated performance. The 60°C pre-reaction of

FA/maleimide also provided a lighter coloured treatment solution compared to oxazolidine addition.

For FA/NMM, this treatment was characterised by high uptake with under-cure compared to FA/Mal, which manifested as comparatively poorer ASE properties. N-Methyl maleimide was similar to maleimide in producing low colour, but had a lower degree of cure, which may be due to insufficient cure time (the Kiln regime being too short) and/or the N-methyl impacting on FA cure and cross-linking in the treated sample.

For the FA/Succ treatment, substitution with succinimide led to lower weight uptake

(<50%) with a darker colour and lower performance compared to FA/Mal. Use of the saturated succinimide (2,5-pyrrolidinedione) as FA initiator did not produce a lighter colour treatment comparable to that associated with the unsaturated maleimide (2,5-pyrroledione) treatment. Instead, the residual amino-function likely incorporated into the FA polymer.

This result confirms the Diels-Alder coupling achieved with maleimide and NMM provides lighter colouring.

FA/Oxazolidine-style Treatments

While FA/Ox (oxazolidine) was not included as a control, the combination of both maleimide and oxazolidine in the FA/Mal/AHPO treatment has the benefit of employing different FA cure strategies together. While FA/Mal/AHPO had comparable uptake (66%) and modified wood properties, visually there was some residual liquid polymeric material indicating a degree of under-cure.

Combination of the FA/Maleimide and FA/Oxazolidine strategies gave the high uptake and dimensional stability performance of FA/Maleimide, but visually the extent of cure appeared less when compared to the FA/Maleimide sample suggesting the additional reactivity of an oxazolidine may act to inhibit greater cure of the FA component.

For the FA/APD treatment, this led to the lowest weight uptake (20%) of treated samples. Despite this low uptake, the treated sample colour was darker and the ASE value was 40% which was comparable to the FA/Succ treatment and prior work with Tris-only in FA formulations. This suggests the initial reactivity on oxazolidine formation may be lower for amino-2-methyl-l, 3-propanediol compared to Tris, with this then impacting its reactivity in FA solution as methylene donor.

For the FA/BPh treatment solution, preparing the benzoxazine precursor from aminophenol and formaldehyde was difficult and oxidation contributed to the resulting dark black colour of the treatment solution. While FA/BPh weight uptakes appeared satisfactory (52%), an ASE of 20% was obtained, together with relatively dark colouring of treated wood.

It is not the intention to limit the scope of the invention to the abovementioned examples only. As would be appreciated by a skilled person in the art, many variations are possible without departing from the scope of the invention as set out in the appended claims.