The invention relates to a process for preparing a bio-based cured epoxy resin from an epoxy resin and one or more bio-based epoxy resin curatives (also known as a hardener). In particular, the process of the present inventions produces a cured epoxy resin comprising an elevated level of bio-based carbon content of at least 40%. The process involves the stoichiometric reaction of an epoxy resin and an epoxy resin curative. In the present invention, the epoxy resin curative, and preferably also the epoxy resin, are partially or fully derived from bio-based feedstocks. The bio-based epoxy resin curative is specifically selected to have a particular balance of properties such that it is able to contribute an uncharacteristically high bio-carbon content to the cured resin, whilst maintaining reaction stoichiometry with the epoxy resin.

BACKGROUND OF THE INVENTION

There is an array of cross-linking agents available for epoxy functional materials, but amines and products derived from amines offer the greatest versatility for curing epoxy resins. Collectively these materials offer the means for formulating systems that can provide the potential for curing in thin films and/or bulk over a broad spectrum of temperatures. Cured epoxy resins are often formed using a cross linking reaction between epoxide groups present in an epoxy resin and amine or hydroxyl groups present in an epoxy resin curative.

Many commercially available epoxy resin curatives are based on amines such as aliphatic, cyclo-aliphatic, araliphatic and to a lesser extent aromatic amines or combinations thereof. These amines are generally modified in order to enhance the processing and/or performance aspects, as well as to reduce the toxicity of the amine.

The proportion in which the epoxy resin and the epoxy resin curative are combined is such that there is approximately a 1 :1 ratio between the epoxide groups of the epoxy resin and the active amine hydrogens, or hydroxyl groups of the epoxy resin curative. This is achieved by determining the amount of epoxide groups of the epoxy resin and providing stoichiometric balance with the amount of active amine hydrogens, or hydroxyl groups, of the epoxy resin curative that is provided, as outlined below. Active Hydrogen equivalent weights (AHEW) for commonly used basic amines employed as epoxy resin curatives for epoxy resins or as feedstock for manufacturing epoxy resin curatives are typically in a range of between 15 to 75. Modification of the basic amine may be achieved through adduction, association salts, formation of amido-amines and poly-amido amines, ketimines or Mannich bases, along with inclusion of inert modifiers. These materials generally have AHEW values of between 45 and 190.

Where the epoxy resin curative is an amine, the AHEW of the epoxy resin curative can be calculated from the molecular weight of the amine divided by the number of amine hydrogens:

Alternatively, AHEW can also be calculated using the amine value:

56,100 AHEW = (Amine value) — x 7 (A7 -varage numb 7 -er of 77 h7y7d -rogens per amine)

The amine value is defined as the number of milligrams of KOH equivalent to one gram of epoxy resin curative and can be calculated by the number of nitrogens x 56.1 (Mwt of KOH) x 1000 (convert to milligrams) divided by molecular mass of the amine compound. The amine value can also be measured experimentally by a number of standard ASTM methods, such as ASTM D2896.

The AHEW of a mixture of epoxy resin curatives (A + B) can also be calculated as follows:

100

The epoxy equivalent weight (EEW), also referred to as the weight per epoxide, is defined as the number of grams of epoxy resin required to give 1 mole of epoxide groups. Commonly used epoxy resins are often bisphenol A diglycidyl ether-based resins produced from bisphenol A and epichlorohydrin. Bisphenol A diglycidyl ether-based resins will usually comprise some degree of self-polymerisation between epoxide groups to form, for example, dimeric, or polymeric ethers. The structure of bisphenol A diglycidyl ether and a self-polymerised bisphenol A diglycidyl ether are shown below.

Self-polymerised bisphenol A diglycidyl ether

A sample of pure bisphenol A diglycidyl ether has an EEW of 170.2, which is the molecular weight of bisphenol A diglycidyl ether divided by the number of epoxide groups (340.4 I 2 = 170.2). However, in practice, commercial bisphenol A diglycidyl ether-based liquid epoxy resins have EEW values of approximately 185 to 190 g/equivalent due to a slightly increased average molecular weight due to a degree of self-polymerisation. The other extremely common epoxy resin is a solid “1 type” epoxy resin, again derived from bisphenol A, which has a higher EEW of approximately 450 to 500 g/equivalent. As solid resins, they are very often diluted in solvent. The greater the degree of self-polymerisation present in the epoxy, the larger the EEW and the melting point will be.

When being formulated into systems it is customary to formulate for a stoichiometric balance between the AHEW and EEW values to combine each active hydrogen with each available epoxide group. The amount of epoxy resin curative in parts per hundred (PHR) of the epoxy resin for a stoichiometric mixture can be calculated as follows:

AHEW

PHR = — — X 100

EEW

An example of a traditional stoichiometric epoxy resin system using D.E.R. 331 (RTM) (a bisphenol A diglycidyl ether-based liquid epoxy resin having an EEW of 190) and diethylenetriamine (AHEW = 20.6). The PHR of diethylenetriamine required for a stoichiometric mixture thus equals 10.8.

20.6 PHR = - X 100 = 10.8

190

Therefore, a stoichiometric mixture would require 10.8 grams of epoxy resin curative for every 100 grams of epoxy resin. Some variations from stoichiometric levels may occasionally be used in order to modify mechanical properties but generally the level remains within a +/- 10% deviation from the standard. As would be appreciated, epoxide groups and primary and secondary amine groups have a high reactivity and may confer toxic, corrosive, irritant, or otherwise hazardous properties to a resin comprising them. A 1 :1 stoichiometric mix provides an optimised matrix with the best chemical resistance, thermal and mechanical properties. An abundance of unreacted epoxy groups or residual nucleophilic amine groups can also give rise to different network structures and/or different retained chemical functionalities as discussed, for instance, in F.N. Alhabill et al. “Effect of resin/hardener stoichiometry on electrical behavior of epoxy networks”, IEEE Transactions on Dielectrics and Electrical Insulation, 24 (6), 3739-3749 (doi:10.1109/TDEI.2017.006828). Deviations from the 1 :1 stoichiometric ratio can have deleterious effects on performance properties of the cured epoxy resin. For instance, residual epoxy groups can lead to moisture sorption and increased UV-light sensitivity in the cured resin as well as an impact on network structure, which can affect the glass transition temperature, T _g , in undesirable ways. On the other hand, residual reactive amine groups can have detrimental effects on electrical properties.

It is therefore generally considered of importance in the art that the preparation of a cured epoxy resin avoids or minimises the presence of residual unreacted epoxide groups or residual unreacted primary or secondary amines, by having less than a 10% (+/-) deviation from stoichiometry. It is for this reason that stoichiometric reaction is preferred in order to ‘quench’ both the epoxide and nucleophilic amine groups in order to avoid detrimental impact on the prevailing properties of the cured epoxy resin.

It is also known in the art to use phenolic polymers as epoxy resin curatives. In this case, the hydroxy groups act as the nucleophile which reacts with the epoxide group of the epoxy resin. Where hydroxy groups are used as the nucleophile in the epoxy resin curative, in the absence of primary or secondary amines, the ratio of hydroxy groups to epoxide groups should similarly approach 1 :1. The hydroxyl equivalent weight of the epoxy resin curative can be similarly calculated from the molecular weight of the alcohol divided by the number of hydroxy groups:

Mw of alcohol

Hydroxyl Equivalent Weight = - ; - — — - - -

Number of hydroxyl groups

Alternatively, hydroxyl equivalent weight can also be calculated using the hydroxyl value:

56,100

Hydroxyl Equivalent Weight = - - - _{; ;} —

Hydroxyl Value

The hydroxyl value is defined as the number of milligrams of KOH required to neutralize the acetic acid taken up on acetylation of one gram of the epoxy resin curative having free hydroxyl groups and can be calculated as is the number of hydroxyl groups x 56.1 (Mwt of KOH) x 1000 (convert to milligrams) divided by molecular mass of the hydroxyl functional compound. The hydroxyl value can also be measured experimentally by a number of standard ASTM methods, such as: ASTM E222-10.

A parameter used in the art to quantify deviation from the stoichiometric mixture is hardener percentage (HP) (“hardener” being used in the art interchangeably with the term “epoxy resin curative” herein).

Mass of the epoxy resin curative used

HP (%) = - - — - ; - X 100

Epoxy resin curative stoichiometric mass The epoxy resin stoichiometric mass refers to the mass of epoxy resin curative required to afford a 1 :1 ratio between epoxide groups of the epoxy resin and amine hydrogens, or hydroxyl groups of the epoxy resin curative. Therefore, a cured epoxy resin having a 1:1 stoichiometric ratio will have a HP of 100% and no epoxide or amine hydrogens left unreacted. A HP of 50% means that half of the epoxide groups remain unreacted, whereas a HP of 200% means that half of the amine hydrogens or hydroxyl groups remain unreacted. Thus, HP can be another way of quantifying the extent of residual unreacted epoxide groups or residual unreacted amine hydrogens or hydroxyl groups. For the reasons outlined above, deviation from an HP of 100% is ideally limited to at most 10% (+/-).

The drive to replace the use of non-petrochemical based materials with bio-based materials has never been greater. The introduction of green alternatives for common materials is thus of high importance and value. Historically, there have been epoxy resin curatives generated with some sustainable feedstocks which are used in conventional stoichiometric ratios with the epoxy resin, as detailed above. These curing agents are only capable of providing a minor degree of bio-based carbon to cured epoxy resin systems. Furthermore, the introduction of bio-based liquid epoxy resins (e.g. where an epichlorohydrin component useful in forming the resin is derived from glycerine obtain biodiesel production) having FEW values of, for instance, around 190 g/equivalent as described above, introduces a bio-based carbon content of around 28% to the cured epoxy resin.

Thus, the use of these products allows the generation of systems with some bio-carbon content, but as the resin and hardener ratio invariably involves a higher mass of epoxy resin than the curative/hardener in the system formula, the resulting cured epoxy resins have bio-based carbon contents falling below 40%. With an increasing drive towards a circular economy and introduction of sustainable feedstocks, the present invention offers a means for significantly increasing the bio-carbon content of cured epoxy resins whilst achieving comparable resin performance properties as with conventional resins derived from petrochemical sources.

SUMMARY OF THE INVENTION In one aspect, the present invention provides a process for preparing a cured epoxy resin, said process comprising contacting an epoxy resin with at least one epoxy resin curative to form a cured epoxy resin, wherein the at least one epoxy resin curative comprises one or more bio-based epoxy resin curatives, said one or more bio-based epoxy resin curatives comprising: i) primary and/or secondary amine groups; or ii) hydroxyl groups in the absence of primary or secondary amine groups, capable of reaction with the epoxide groups of the epoxy resin, wherein the one or more bio-based epoxy resin curatives forms a greater proportion by mass of the total combined mass of epoxy resin and one or more bio-based epoxy resin curatives, and wherein the cured epoxy resin formed has a bio-based carbon content of at least 40%.

In another aspect, the prevent invention provides a cured epoxy resin having a biobased carbon content of at least 40% prepared, or preparable, by the processes described herein.

In another aspect, the present invention provides a bio-based epoxy resin curative, or mixture of bio-based epoxy resin curatives, which comprises or consists of a furalkamine Mannich base and/or phenalkamine Mannich base, wherein the AHEW of the bio-based epoxy resin curative, or mixture of bio-based epoxy resin curatives, is at least 250 g/equivalent, preferably 300 g/equivalent, more preferably at least 350 g/equivalent, even more preferably at least 400 g/equivalent.

In yet another aspect, the present invention provides the use of one or more bio-based epoxy resin curatives, for increasing the bio-based carbon content of a cured epoxy resin by reacting the one or more bio-based epoxy resin curatives in greater mass proportion relative to the epoxy resin.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 demonstrates the Gel-time temperature profile of a comparative process of forming a cured epoxy resin using a known mixture of an epoxy resin and an epoxy resin curative; and

Figure 2 demonstrates the Gel-time temperature profile of a process of forming a cured epoxy resin according to the present invention. DETAILED DESCRIPTION

Definition of terms

For the purposes of the present invention, the following terms as used herein shall, unless otherwise indicated, be understood to have the following meanings. Other terms that are not as defined below are to be understood as their normal meaning in the art.

The term "alkyl" as used herein refers to a monovalent straight- or branched-chain alkyl group. Unless specifically indicated otherwise, the term “alkyl” does not include optional substituents.

The term “hydrocarbyl” as used herein refers to a monovalent straight- or branched- chain, or cyclic group consisting of hydrogen and carbon atoms. A hydrocarbyl group may or may not comprise a degree of unsaturation, for example, a hydrocarbyl group may comprise one or more double bonds or triple bonds. Unless specifically indicated otherwise, the term “hydrocarbyl” does not include optional substituents.

The term “monoamine” as used herein refers to an organic compound having one amine group having active hydrogens, i.e. one primary amine or secondary amine.

The term "polyamine" as used herein refers to an organic compound having a plurality of amine groups having active hydrogens, i.e. one or more primary amines and/or secondary amines. For the avoidance of doubt, in the context of the present invention a “diamine” having two such amino groups is considered to fall within the scope of a “polyamine”, and a “monoamine” having one such amino group is not considered to fall within the scope of a “polyamine”.

The term "phenalkamine" as used herein refers to an organic compound having an optionally substituted phenol group attached to a primary or secondary amine by a linker comprising at least one carbon linker-atom (e.g. a methylene group). For example, phenalkamines may be Mannich bases formed by reaction of the optionally substituted phenolic compound with an amine and an aldehyde. Additionally, the term "phenalkamine" also encompasses polyphenol based phenalkamines, for example, Mannich bases formed by reaction of an optionally substituted polyphenol polymer with an amine and an aldehyde.

The term "furalkamine" as used herein refers to an organic compound having an optionally substituted furan or polyfurfuryl group attached to a primary or secondary amine by a linker comprising at least one carbon linker-atom (e g. a methylene group). For example, furalkamines may be Mannich bases formed by reaction of a furan or polyfurfuryl alcohol with an amine and an aldehyde, or by reaction of an amine with a methylol group of a furfuryl alcohol or polyfurfuryl alcohol.

The term “epoxy resin” as used herein refers to an organic compound having one or more epoxide groups. In the context of the present invention the term “epoxy resin” may be used to refer to a monomeric, or polymeric organic compound, having one or more epoxide groups.

The term “epoxy resin curative” as used herein refers to a monomeric, or polymeric organic compound, having one or more primary amine, secondary amine, and/or hydroxyl groups capable of performing a nucleophilic addition to the epoxide group of an epoxy resin.

The term “cured epoxy resin” as used herein refers to an organic compound produced by reaction of an “epoxy resin” with an “epoxy resin curative”, for example by the processes described herein.

The term “bio-based”, as used herein refers to a material that is derived in whole or in part from biomass resources. Biomass resources are organic materials that are available on a renewable or recurring basis such as crop residues, wood residues, grasses, and aquatic plants. Cardanol, derived from cashew nutshell liquid, for instance, is a well- known example of a bio-based material derived from biomass resources, so too is furfural which is derived from lignocellulosic material. Cardanol and furfural are precursors for phenalkamine and fufuralkamine compounds useful in the present invention.

Cardanol is a C15 alkyl or alkenyl substituted phenolic lipid obtained from anacardic acid, the main component of cashew nutshell liquid. Anacardic acid may be decarboxylated to yield cardanol by simple decarboxylation processes known to the skilled person. Cardanol includes more than one compound because the composition of the C15 hydrocarbyl side-chain varies in its degree of unsaturation, comprising from 0 to 3 double bonds. Tri-unsaturated cardanol is the major component (41%). The remaining cardanol is 34% mono-unsaturated, 22% bi-unsaturated, and 2% saturated.

The term “biocarbon” as used herein describes an atom of carbon that is “bio-based”, i.e. that the atom of carbon in question is derived from a biomass resource.

The skilled person is able to determine if a material is from a biomass resource, provided that the source of the material is known. Therefore, a skilled person is also able to determine if a material is derived from a from biomass resource, providing they have knowledge of the precursor material from which the material in question is derived. Nevertheless, objective tests may also be used to identify “biocarbon”. ASTM D6866 and ISO 16620-2 both provide methods of identifying “biocarbon” based on isotopic analysis. “Biocarbon” has a higher abundance of ¹⁴ C than, for example, carbon derived from fossil fuels. Thus, the skilled person is also able to objectively test the biocarbon content of a given material.

“Bio-based carbon content” may be represented either as: a) the percentage of biomass-derived carbon in a product as compared to its total organic carbon content (bio-based carbon to TOC), as per ASTM D6866; or b) the percentage of biomass-derived carbon in a product as compared to its total carbon content (bio-based carbon to TC), as per ISO 16620-2.

Nevertheless, as the scope of the present invention encompasses only organic compounds, each of these methods are identical and interchangeable in the context of the present application.

The present invention relates to the introduction of higher sustainable feedstock content into a cured epoxy resin, at least in part by virtue of an unconventional mass ratio between epoxy resin and epoxy resin curative components, whilst retaining stoichiometry between reactive groups of the epoxy resin and epoxy resin curative. In the present invention the at least one epoxy resin curative comprises or consists of one or more bio-based epoxy resin curatives used in a greater mass proportion than the epoxy resin, this increases the percentage of bio-based carbon in the cured epoxy resin provided by the process of the present invention.

Thus, in one aspect, the present invention provides a process for preparing a cured epoxy resin, said process comprising contacting an epoxy resin with at least one epoxy resin curative to form a cured epoxy resin, wherein the at least one epoxy resin curative comprises one or more bio-based epoxy resin curatives, said one or more bio-based epoxy resin curatives comprising: i) primary and/or secondary amine groups; or ii) hydroxyl groups in the absence of primary or secondary amine groups, capable of reaction with the epoxide groups of the epoxy resin, wherein the one or more bio-based epoxy resin curatives forms a greater proportion by mass of the total combined mass of epoxy resin and one or more bio-based epoxy resin curatives, and wherein the cured epoxy resin formed has a bio-based carbon content of at least 40%.

The at least one epoxy resin curative may consist of the one or more bio-based epoxy resin curatives, in which case the one or more bio-based epoxy resin curatives makes up the whole of the at least one epoxy resin curative. Alternatively, the at least one epoxy resin curative may comprise one or more additional epoxy resin curatives which are not bio-based, in addition to the one or more bio-based epoxy resin curatives. However, n this case it is still necessary that the bio-based epoxy resin curatives make up a sufficiently large mass proportion of the at least one epoxy resin curative that the features that: the bio-based epoxy resin curatives forms a greater proportion by mass of the total combined mass of epoxy resin and the one or more bio-based epoxy resin curatives, and that the cured epoxy resin formed has a bio-based carbon content of at least 40%, are still achieved. Therefore, only a relatively minor proportion of non biobased epoxy resin curative may be tolerated as part of the at least one epoxy resin curative.

The one or more bio-based epoxy resin curative may be a single compound or a mixture of compounds, for example a mixture of polymeric compounds varying in their chain length and/or monomer arrangement (for example in the case of a cardanol based polymer, each repeating unit comprises a C15 hydrocarbyl side chain which may vary in terms its degree of unsaturation). In the context of the present invention, the AHEW of the one or more bio-based epoxy resin curatives is the AHEW of the mixture of bio-based epoxy resin curatives, in the case that the one or more bio-based epoxy resin curatives is a mixture of compounds.

As would be appreciated, tertiary amines may not react with an epoxide group, whereas primary amines may react with two epoxide groups, whereas secondary amines and hydroxyl groups may react with one epoxide group. The term “stoichiometric” as used herein reflects these ratios. For example, a stoichiometric ratio of epoxide to primary amine is 2:1 , whereas a stoichiometric ratio of epoxide to secondary amine or hydroxyl is 1 :1. In both cases, the stoichiometric ratio of epoxide to amine hydrogens is 1 :1.

The mass of the one or more bio-based epoxy resin curatives useful in the present invention is greater than that of the epoxy resin useful in the present invention. The cured epoxy resin formed has a bio-based carbon content of at least 40%. As the one or more bio-based epoxy resin curatives of the present invention is bio-based, using one or more bio-based epoxy resin curatives having a greater mass than the epoxy resin will ensure that a higher proportion of the resulting cured epoxy resin is bio-based. The one or more bio-based epoxy resin curatives forms a greater proportion of the total combined mass of epoxy resin and one or more bio-based epoxy resin curatives, but without deviating from the stoichiometric mixture between the two. This provides for the preparation of high bio-based carbon content cured epoxy resins, and without the detriment to the cured epoxy resin properties that is incurred by deviation from the stoichiometric ratio and a substantially 100% HP.

In some embodiments, the ratio of epoxide groups in the epoxy resin to the number of amine hydrogens, or the number of hydroxyl groups, in the one or more bio-based epoxy resin curatives capable of reaction with the epoxide groups of the resin is from 1.1 :1 to 1 :1.1 , preferably 1.09: 1 to 1 :1.09, more preferably 1.08:1 to 1 :1.08, more preferably 1.07: 1 to 1 :1.07, more preferably 1.06:1 to 1 :1.06, more preferably 1.05:1 to 1 : 1.05, more preferably 1.04:1 to 1 :1.04, more preferably 1.03:1 to 1 :1.03, more preferably 1.02: 1 to 1 :1.02, most preferably 1.01 : 1 to 1 :1.01.

In some embodiments, the cured epoxy resin formed has a hardener percentage of 90% to 110%, preferably 92% to 108%, more preferably 94% to 106%, even more preferably 96% to 104%, even more preferably 98% to 102%, most preferably 99% to 101 %, for example 100%.

The process of the present invention may optionally include the use of additives, such as diluents, solvents, flow control additives, antifoam agents, or anti-sag agents, as well as other additives such as pigments, reinforcing agents, fillers, elastomers, stabilisers, extenders, plasticisers, or flame retardants depending on the application. Preferably any additives have bio-based carbon content. For the avoidance of doubt, any additives are not considered when calculating the bio-based carbon content of the cured epoxy resin.

In a preferred embodiment, the one or more bio-based epoxy resin curatives has a 55 % or greater mass proportion relative to the combination of the epoxy resin and the one or more bio-based epoxy resin curatives, preferably the one or more bio-based epoxy resin curatives has a 60 % or greater mass proportion relative to the combination of the epoxy resin and the one or more bio-based epoxy resin curatives, more preferably the one or more bio-based epoxy resin curatives has a 65 % or greater mass proportion relative to the combination of the epoxy resin and the one or more bio-based epoxy resin curatives, more preferably the one or more bio-based epoxy resin curatives has a 70 % or greater mass proportion relative to the combination of the epoxy resin and the one or more biobased epoxy resin curatives, most preferably the one or more bio-based epoxy resin curatives has a 75 % or greater mass proportion relative to the combination of the epoxy resin and the one or more bio-based epoxy resin curatives.

In a preferred embodiment, the mass ratio of the one or more bio-based epoxy resin curatives to epoxy resin is from 3:1 to 1.5:1 , preferably from 2.5:1 to 1.5:1 , more preferably 2:1 to 1.5:1.

In a preferred embodiment, the one or more biobased epoxy resin curatives has a biobased carbon content of at least 45%, preferably at least 55%, more preferably at least 60%, even more preferably at least 70%.

In a preferred embodiment, the one or more bio-based epoxy resin curatives has a biobased carbon content of from 45 to 70%, preferably from 50 to 65%. In a preferred embodiment, the epoxy resin used in the process of the invention has a bio-based carbon content. One source of bio-based carbon content in epoxy resins is epichlorohydrin that is derived from glycerol. The preparation of epichlorohydrin from glycerol is within the common general knowledge of the skilled person. As would be appreciated, bio-based glycerol can be easily derived from fatty acids. Epichlorohydrin is used in the preparation of glycidyl ethers or glycidyl esters, such as those used in epoxy resins. Therefore, epoxy resin having a bio-based carbon content may be derived from bio-based glycerol. In a preferred embodiment, the epoxy resin is derived from the reaction of a glycerol precursor which is obtained from a renewable resource (e.g. from a biodiesel production process).

The epoxy resin may, for example, be selected from polyglycidyl ethers of polyhydric phenols, epoxidised novolacs or similar glycidated polyphenolic resins, polyglycidyl ethers of alcohols, glycols or polyglycols, and polyglycidyl esters of polycarboxylic acids. In a preferred embodiment the epoxy resin is selected from polyglycidyl ethers of a polyhydric phenol, more preferably polyglycidyl ethers of a bisphenol, even more preferably polyglycidyl ethers of bisphenol A. In some embodiments there may be a degree of polymerisation within the epoxy resin, for example, bisphenol A diglycidyl ether epoxy resin may include a degree of self-polymerised bisphenol A diglycidyl ether.

In a preferred embodiment, the epoxy resin is a bisphenol A diglycidyl ether-based resin, preferably wherein the epoxide groups of the bisphenol A diglycidyl ether are derived from bio-based glycerol.

Further bio-based carbon content can be included in epoxy resins by using a bio-based alcohol or bio-based carboxylic acid, preferably using a bio-based alcohol and epichlorohydrin derived from bio-based glycerol. Examples of bio-based alcohols useful in the preparation of bio-based epoxy resins include sugars, such as glucose, xylose, isosorbide or materials derived from sugars. Bio-based alcohols or carboxylic acids, such as 2,5-bis(hydroxymethyl)furan and 2,5-furan dicarboxylic acid may also be derived from bio-based furfural or 5-(hydroxymethyl)furfural.

In a preferred embodiment, the epoxy resin has a bio-based carbon content of at least 10%, preferably at least 15%, more preferably at least 20%. In a preferred embodiment, the bio-based carbon content of the cured epoxy resin is at least 50%, preferably at least 55%, more preferably at least 60%, most preferably at least 70%.

It has been found to be particularly advantageous to increase AHEW in the one or more bio-based epoxy resin curatives compared to conventional curatives in achieving the high bio-based carbon contents exhibited by the cured epoxy resins obtainable by the present invention. An increased AHEW means that the one or more bio-based epoxy resin curatives makes up an increased proportion of the mass of the combination of the at least one epoxy resin curatives and the epoxy resin, when combined in a stoichiometric ratio and with a substantially 100% HP. This means that one or more biobased epoxy resin curative having an increased AHEW contributes an increased percentage of bio-based carbon to the cured epoxy resin.

In a preferred embodiment, the one or more bio-based epoxy resin curatives comprises amine groups sufficient for stoichiometric reaction with the epoxy groups of the epoxy resin, preferably the AHEW of the one or more bio-based epoxy resin curatives is at least 200 g/equivalent, preferably at least 250 g/equivalent, more preferably at least 300 g/equivalent, more preferably at least 350 g/equivalent, most preferably at least 400 g/equivalent.

As primary and secondary amine groups tend to be more nucleophilic than hydroxyl groups, in the case of an epoxy resin curative comprising amine groups sufficient for stoichiometric reaction with the epoxy groups of the epoxy resin, any hydroxyl groups present in the epoxy resin curative may be disregarded when considering the stoichiometric ratio, since the amine groups will react preferentially. This is the case with, for example, a phenalkamine Mannich base, which comprises one or more amine groups in addition to a phenolic hydroxyl group. In this scenario, only the AHEW need be considered with regard to the stoichiometric ratio.

In a preferred embodiment, the one or more bio-based epoxy resin curatives comprises or consists of a Mannich base compound. In a more preferred embodiment, the one or more bio-based epoxy resin curatives comprises or consists of a furfuryl amine Mannich base compound and/or a phenalkamine Mannich base compound. In a preferred embodiment, the one or more bio-based epoxy resin curatives comprises or consists of a mixture of furfuryl amine Mannich base compound and a phenalkamine Mannich base compound.

For example, the furfuryl amine Mannich base compound may be derived from the reaction of i) furfuryl alcohol, polyfurfuryl alcohol, and/or a co-polymer of furfuryl alcohol, and ii) a primary or secondary monoamine and/or a polyamine comprising primary and/or secondary amino groups.

For example, a bio-based phenalkamine Mannich base compound may be derived from the reaction of i) a phenolic compounds, such as cardanol, ii) an aldehyde, and iii) a primary or secondary monoamine and/or a polyamine comprising primary and/or secondary amino groups. Depicted below is an example of a phenalkamine Mannich base derived from Mannich reaction of A/,A/-Dimethyldipropylenetriamine (DMAPAPA), formaldehyde and cardanol (in the case of cardanol R = a C15 chain comprising 0 to 3 double bonds). In this example the AHEW ranges from 234.7 to 237.7 g/equivalent.

Phenalkamine Mannich Base

For example, further bio-based carbon and increased AHEW may be introduced into such a bio-based phenalkamine Mannich base compound by use of a bulky bio-based aldehyde such as furfural. Furfural is a product of the dehydration of sugars, as occurs in a variety of agricultural by products, including corncobs, oat, wheat bran, and sawdust. For example, a furanyl phenalkamine Mannich base may be prepared by using furfural as the aldehyde in the Mannich reaction. Depicted below is an example of a furanyl phenalkamine Mannich base derived from Mannich reaction of DMAPAPA, furfural and cardanol (in the case of cardanol R = a C15 chain comprising 0 to 3 double bonds). In this example the AHEW ranges from 267.9 to 270.9 g/equivalent.

Furanyl Phenalkamine Mannich Base

For example, further bio-based carbon, and increased AHEW may be introduced into a bio-based phenalkamine Mannich base compound by the use of a polymeric bio-based phenolic compound such as a polymeric cardanol. Depicted below is an example of a polymeric phenalkamine Mannich base derived from Mannich reaction of DMAPAPA, formaldehyde and a cardanol based polymer (in the case of cardanol R = a C15 chain comprising 0 to 3 double bonds). The AHEW of the epoxy resin curative can be adapted depending on the value of x.

Polymeric Phenalkamine Mannich Base

For example, a bio-based furalkamine Mannich base compound may be derived from the reaction of i) polyfurfuryl alcohol, ii) an aldehyde, and iii) a primary or secondary monoamine and/or a polyamine comprising primary and/or secondary amino groups. The AHEW of the epoxy resin curative can be adapted depending on the value of y and z.

Furalkamine Mannich Base For example, the one or more bio-based epoxy resin curative may comprise a mixture of bio-based epoxy resin curatives, preferably a mixture of bio-based Mannich base compounds. For example, the one or more bio-based epoxy resin curatives may comprise or consist of a mixture of compounds of formula (1 ) and formula (2), shown below.

Formula (1) wherein each n is independently from 0 to 15, preferably from 1 to 12, more preferably from 2 to 10, even more preferably 3 to 8; and wherein each m is 1 or 2, preferably 1 . wherein each R is independently a C15 hydrocarbyl chain comprising 0 to 3 double bonds; wherein each p is independently from 0 to 4, preferably from 0 to 3, more preferably from 0 to 1 ; and wherein each q is 1 or 2, preferably 1.

Preferably the compounds of formula (1 ) and formula (2) are mixed in a ratio of from 95:5 to 5:95 by weight, more preferably from 90:10 to 10:90 by weight, even more preferably 80:20 to 20:80 by weight, even more preferably from 70:30 to 30:70 by weight, even more preferably from 60:40 to 40:60 by weight, for example 50:50 by weight.

It has been discovered that improved properties may be imparted to the cured epoxy resin obtained or obtainable by the processes described herein by virtue of the choice of one or more bio-based epoxy resin curatives. Furalkamine bio-based epoxy resin curatives impart improved acid resistance onto the resulting cured epoxy resin formed therefrom. Phenalkamine bio-based epoxy resin curatives impart improved hydrophobicity onto the resulting cured epoxy resin formed therefrom. Bio-based epoxy resin curatives comprising or consisting of mixtures of furalkamines and phenalkamines may therefore be used to provide a compromise between both acid resistance and hydrophobicity. Various wt/wt ratios can be used depending on the desired compromise between these two properties.

In another embodiment, the polyamine further comprises amido or polyamide functional groups derived from adduction of the polyamine with one or more epoxides and/or modification with one or more fatty acids. For example, a bio-based phenalkamine Mannich base compound may be further reacted with one or more bio-based fatty acids. Depicted below is an example of a fatty acid modified phenalkamine Mannich base compound (in the case of cardanol R = a C15 chain comprising 0 to 3 double bonds). The R ¹ group is dependent on the exact nature of the fatty acid used. For example, one or more saturated, or unsaturated C ₈ to C ₂ 6 fatty acids may be used, preferably saturated, or unsaturated C10 to C20 fatty acids, more preferably saturated, or unsaturated C12 to Cis fatty acids. Alternatively or additionally, one or more dimer acids, such as C30 to C40 dimer acids, preferably C32 to C38 dimer acids, more preferably C34 to C36 dimer acids may also be used. Fatty acids and dimer acids are derivable from bio-based sources, and the AHEW of the epoxy resin curative can be adapted depending on the chain length of the fatty acid.

Fatty Acid Modified Phenalkamine Mannich Base Where a Mannich reaction comprising a monoamine and/or polyamine is used to provide a Mannich base compound useful in the present invention, such as a furfuryl amine Mannich base compound or a phenalkamine Mannich base compound, the monoamine may for example, be selected from alkyl monoamines, alkanolamines and poly(alkylene oxide) amines; and/or the polyamine may be selected from: 1) an aliphatic primary di- or tri-amine; preferably an ether-group-containing aliphatic primary di- or tri-amine; 2) an aliphatic secondary amino-containing poly-amine having two primary aliphatic amino groups; 3) an aliphatic secondary and/or tertiary amino-containing di- or tri-amine having one primary aliphatic amino group; 4) a polyamine having one or two secondary amino groups, preferably products of the reductive alkylation of primary aliphatic polyamines with aldehydes or ketones; or 5) an aromatic polyamine.

The polyamine may also be selected, for example, from an aliphatic primary diamine selected from: 2,2-dimethyl-1 ,3-propanediamine, 1 ,3-pentanediamine (DAMP), 1 ,5- pentanediamine, 1,5-diamino-2-methylpentane (MPMD), 2-butyl-2-ethyl-1, 5- pentanediamine (C11-nododiamine), 1 ,6-hexanediamine, 2,5-dimethyl-1 ,6- hexanediamine, 2,2 (4), 4-trimethylhexamethylenediamine (TMD), 1 ,7-heptanediamine, 1 , 8-octanediamine, 1,9-nonanediamine, 1 ,10-decanediamine, 1 ,11-undecandiamine, 1 ,12-dodecanediamine, 1,2-, 1,3- or 1 ,4-diaminocyclohexane, bis(4-aminocyclohexyl) methane (H 12-MDA), bis(4-amino-3-methylcyclohexyl) methane, bis(4-amino-3- ethylcyclohexyl) methane, bis(4-amino-3,5-dimethylcyclohexyl) methane, bis(4-amino-3- ethyl-5-methylcyclohexyl) methane, 1 -amino-3-aminomethyl-3,5,5-trimethylcyclohexane (isophoronediamine or IPDA), 2- or 4-methyl-1 ,3-diaminocyclohexane or mixtures thereof, 1 ,3-bis(aminomethyl) cyclohexane, 1 ,4-bis(aminomethyl) cyclohexane, 2,5 (2,6)- bis(aminomethyl) bicyclo [2.2.1] heptane (NBDA), 3(4), 8(9)-Bis(aminomethyl) tricyclo [5.2. 1.02 '6] decane, 1 ,4-diamino-2,2,6-trimethylcyclohexane (TMCDA), 1 ,8-Me N- thandiamin, 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro [5.5] undecane, 1 ,3- bis(aminomethyl) benzene (MXDA), 1 , 4-bis(aminomethyl) benzene, and combinations thereof; or wherein the polyamine is an aliphatic primary triamine selected from 4- aminomethyl-1 , 8-octanediamine, 1 ,3,5-tris(aminomethyl) benzene, 1,3,5- tris(aminomethyl) cyclohexane, tris(2-aminoethyl) amine, tris(2-amino-propyl) amine, tris(3-aminopropyl) amine and combinations thereof. The polyamine may also be selected, for example, from an ether-group-containing aliphatic primary diamine selected from: bis (2-aminoethyl) ether, 3,6-dioxaoctane-1 ,8- diamine, 4,7-dioxadecane-1 , 10 diamine, 4,7-dioxadecane-2,9-diamine, 4,9- dioxadodecane-1 , 12-diamine, 5,8-dioxadodecane-3, 10-diamine, 4,7, 10-tri oxatri decan- 1 ,13-diamine, or oligomers of any of the foregoing; polytetrahydrofurandiamines, such as bis(3-aminopropyl) polytetrahydrofurans, cycloaliphatic diamines containing ether groups preferably derived from propoxylation and subsequent amination of 1 ,4- dimethylol cyclohexane, and polyoxyalkylenediamines, such as polyoxypropylenediamines, preferably derived from amination of polyoxyalkylenediols, and combinations thereof; or wherein the polyamine is an ether-group-containing aliphatic primary tri-amine selected from polyoxyalkylenetriamines, preferably derived from amination of polyoxyalkylenetriols.

The polyamine may also be selected, for example, from an aliphatic secondary aminocontaining polyamine having two primary aliphatic amino groups selected from: 3-(2- aminoethyl) aminopropylamine, bis(hexamethylene) triamine (BHMT), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA) or higher homologs of linear polyethyleneamines, such as polyethylenepolyamine with 5 to 7 ethylenepolyamine units (HEPA), products of the multiple cyanoethylation or cyanobutylation and subsequent hydrogenation of primary polyamines having at least two primary amino groups, such as Dipropylenetriamine (DPTA), N-(2-aminoethyl)-1 ,3-propanediamine (N3-amine), N,N'-bis(3-aminopropyl) ethylenediamine (N4-amine), N,N'-bis (3-aminopropyl)-1 ,4-diaminobutane, N5-(3- aminopropyl)-2-methyl-1 ,5-pentanediamine, N3-(3-aminopentyl)-1 ,3-pentanediamine, N5-(3-Amino-1-ethyl-propyl)-2-methyl-1 ,5-pentanediamine, N,N'-bis (3-amino-1-ethyl- propyl)-2-methyl-1 ,5-pentanediamine, and combinations thereof.

The polyamine may also be selected, for example, from a polyamine having one or two secondary amino groups selected from: N1-benzyl-1 ,2-propanediamine, N1-(4- methoxybenzyl)-1,2-propanediamine, N-benzyl-1 ,3-bis (aminomethyl) benzene, N,N'- Dibenzyl-1 ,3-bis (aminomethyl) benzene, N-2-ethylhexyl-1 ,3-bis (aminonyl) benzene, N,N'-bis(2-ethylhexyl)-1,3-bis(aminomethyl) benzene, and partially styrenated polyamines, such as partially styrenated 1 ,3-bis(aminomethyl) benzene (MXDA), and combinations thereof. The polyamine may also be selected, for example, from an aliphatic secondary and/or tertiary amino-containing di- or tri-amine having one primary aliphatic amino group, selected from: N,N-Dimethylpropane-1,3-diamine (DMAPA) and N,N- Dimethyldipropylene triamine (DMAPAPA).

The polyamine may also be selected, for example, from m- and p-phenylenediamine, 4,4'-, 2,4'- and/or 2,2'-diaminodiphenylmethane, 3,3'-dichloro-4,4 - diaminodiphenylmethane (MOCA) diisocyanate, 2,4- and I or 2,6-toluene diamine, mixtures of 3,5-dimethylthio-2,4- and -2,6-toluene diamine, mixtures of 3,5-diethyl -2,4- and -2,6-toluylenediamine (DETDA), 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane (M-DEA), 3,3',5,5'-tetraethyl-2,2'-dichloro-4,4'-diaminodiphenylmetha ne (M-CDEA), 3,3'- diisopropyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane (M-MIPA), 3, 3', 5,5'- tetraisopropyl-4,4'-diaminodiphenylmethane (M-DIPA), 4, 4' -diamino diphenylsulfone (DDS), 4-amino-N-(4-aminophenyl) benzenesulfonamide, 5,5'-methylenedianthranilic acid, dimethyl (5,5'-methylenedithethranilate), 1 ,3-propylenebis(4-aminobenzoate), 1 ,4- butylenebis(4-aminobenzoate), polytetramethyleneoxide-bis(4-aminobenzoate), 1 ,2- bis(2-aminophenylthio)ethane, 2-methylpropyl (4-chloro-3,5-diaminobenzoate), t-Butyl (4-chloro-3,5-diaminobenzoate), and combinations thereof.

Additionally or alternatively, the Mannich base obtained may be: a) modified by adduction; b) modified with an accelerator, preferably selected from acidic accelerators (such as salicylic acid), tertiary amines and imidazoles; and/or c) modified with a diluent or extender.

As with increasing AHEW, increasing the hydroxyl equivalent weight, in the case of an epoxy resin curative comprising hydroxyl groups capable of stoichiometric reaction with the epoxy groups of the epoxy resin, in the absence of primary or secondary amine groups, provides a similar advantage in terms of mass proportion. One or more biobased epoxy resin curatives having an increased hydroxyl equivalent weight also makes up an increased proportion of the mass of the combination of the one or more bio-based epoxy resin curatives and the epoxy resin. This means that a bio-based epoxy resin curative having an increased hydroxyl equivalent weight contributes an increased percentage of bio-based carbon to the cured epoxy resin. In another embodiment, the one or more bio-based epoxy resin curatives comprises hydroxyl groups sufficient for stoichiometric reaction with the epoxy groups of the epoxy resin, in the absence of primary or secondary amine groups.

For example, the one or more bio-based epoxy resin curatives may comprise or consist of a polyphenol polymer, such as a novolac. Preferably, the polyphenol polymer is a cardanol-based polymer (e.g. derived from the reaction of cardanol with formaldehyde acetaldehyde, furfuraldehyde, acrolein and/or hexamine, preferably formaldehyde and/or hexamine).

Depicted below is an example of a cardanol-based polymer derived from the reaction of cardanol with hexamine. R = a C15 hydrocarbyl chain comprising 0 to 3 double bonds. The chain length of the polymer is represented by w. However, as each repeating unit has the same number of hydroxyl groups (one), and approximately the same molecular weight (312 to 318 depending on the degree of unsaturation in the cardanol), the overall hydroxyl equivalent weight remains approximately the same regardless of the number of repeating units. In this example, the hydroxyl equivalent weight thus ranges from 312 to 318 g/equivalent.

Cardanol-Based Polymer

In a preferred embodiment, the hydroxyl equivalent weight of the one or more bio-based epoxy resin curatives is at least 200 g/equivalent, preferably at least 250 g/equivalent, more preferably at least 300 g/equivalent, more preferably at least 350 g/equivalent, most preferably at least 400 g/equivalent.

In another aspect, the prevent invention provides a cured epoxy resin having a biobased carbon content of at least 40% prepared, or preparable, by the processes described herein. In another aspect, the present invention relates to a bio-based epoxy resin curative or mixture of bio-based epoxy resin curatives, which comprises or consists of a furalkamine Mannich base or phenalkamine Mannich base, for example, a furalkamine Mannich base or phenalkamine Mannich base as described herein, wherein the AHEW of the biobased epoxy resin curative, or mixture of bio-based epoxy resin curatives, is at least 250 g/equivalent, preferably 300 g/equivalent, more preferably at least 350 g/equivalent, even more preferably at least 400 g/equivalent.

In a preferred embodiment, the bio-based epoxy resin curative comprises or consists of compounds of formula (1 ):

Formula (1) wherein each n is independently from 0 to 15, preferably from 1 to 12, more preferably from 2 to 10, more preferably 3 to 8; and wherein each m is 1 or 2, preferably 1 .

In a preferred embodiment, the bio-based epoxy resin curative comprises or consists of compounds of formula (2): wherein each R is independently a C15 hydrocarbyl chain comprising 0 to 3 double bonds; wherein each p is independently from 0 to 4, preferably from 0 to 3, more preferably from 1 to 2; and wherein each q is 1 or 2, preferably 1.

In a preferred embodiment, the mixture of bio-based epoxy resin curatives comprises or consists of a mixture of a furalkamine Mannich base and a phenalkamine Mannich base, preferably a polymeric phenalkamine Mannich base, more preferably a cardanol based polymeric phenalkamine Mannich base. In a preferred embodiment, the mixture of biobased epoxy resin curatives comprises or consists of a mixture of the compound of formula (1) and the compound of formula (2). Preferably the mixture of a furalkamine Mannich base and a phenalkamine Mannich base, for example, the mixture of the compound of formula (1) and formula (2), are in a ratio of from 95:5 to 5:95 by weight, more preferably from 90:10 to 10:90 by weight, even more preferably 80:20 to 20:80 by weight, even more preferably from 70:30 to 30:70 by weight, even more preferably from 60:40 to 40:60 by weight, for example 50:50 by weight.

In one embodiment, the bio-based epoxy resin curative, or mixture of bio-based epoxy resin curatives, which comprises or consists of a furalkamine Mannich base and/or a phenalkamine Mannich base, has 50 % or more of bio-based carbon, preferably 60 % or more of bio-based carbon, more preferably at least 70 % or more of bio-based carbon, more preferably 80 % or more of bio-based carbon, more preferably 90 % or more of bio-based carbon, most preferably 100 % of bio-based carbon.

In yet another aspect, the present invention relates to use of one or more bio-based epoxy resin curatives, preferably in the form of a Mannich base as described herein, for increasing the bio-based carbon content of a cured epoxy resin by reacting the one or more bio-based epoxy resin curatives in greater mass proportion relative to the epoxy resin.

In a preferred embodiment, the AHEW or the hydroxyl equivalent weight in the absence or primary or secondary amine groups, of the one or more bio-based epoxy resin curatives and the EEW of the epoxy resin have a ratio of from 1.1 :1 to 1 : 1.1 , preferably from 1.08:1 to 1 :1.08, more preferably from 1.06:1 to 1 :1.06, even more preferably from 1.04: 1 to 1 :1.04, even more preferably from 1.02: 1 to 1 :1.02, most preferably from 1.01 : 1 to 1 :1.01 , for example 1 :1. In a preferred embodiment, the one or more bio-based epoxy resin curatives has a 55 % or greater mass proportion relative to the combination of the epoxy resin and the one or more bio-based epoxy resin curatives, preferably the one or more bio-based epoxy resin curatives has a 60 % or greater mass proportion relative to the combination of the epoxy resin and the one or more bio-based epoxy resin curatives, more preferably the one or more bio-based epoxy resin curatives has a 65 % or greater mass proportion relative to the combination of the epoxy resin and the one or more bio-based epoxy resin curatives, more preferably the one or more bio-based epoxy resin curatives has a 70 % or greater mass proportion relative to the combination of the epoxy resin and the one or more biobased epoxy resin curatives, most preferably the one or more bio-based epoxy resin curatives has a 75 % or greater mass proportion relative to the combination of the epoxy resin and the one or more bio-based epoxy resin curatives.

All of the features of and possible modifications to the processes as described herein may also be similarly applied to the use of the one or more bio-based epoxy resin curatives as described herein.

Epoxy resin systems comprising an epoxy resin and an epoxy resin curative have applications as adhesives. These high-performance adhesives are used in the construction of aircraft, automobiles, bicycles, boats, golf clubs, skis, snowboards, and other applications where high strength bonds are required. Epoxy adhesives can be developed to suit almost any application, such as adhesives for wood, metal, glass, stone, and some plastics.

Epoxy resin adhesives, such as an adhesive prepared or preparable from the epoxy resin systems described herein provide a high degree of strength, such as shear strength to a joint. Joints formed by epoxy adhesives, such as an adhesive prepared or preparable from the epoxy resin systems described herein are resistant to high temperatures, solvents, UV light and impact.

In another aspect, the present invention relates to the use of a cured epoxy resin having a bio-based carbon mass content of at least 40% prepared, or preparable, by the processes described herein as an adhesive, preferably wherein the adhesive has an Aluminium : Aluminium single lap shear strength of the bio-based cured epoxy resin is at least 10.0 MPa, as measured in accordance with ASTM D1002, preferably at least 15.0 MPa, more preferably at least 20.0 MPa, even more preferably at least 25.0 MPa, even more preferably at least 30.0 MPa, even more preferably at least 35.0 MPa, even more preferably at least 40.0 MPa, even more preferably at least 45.0 MPa, most preferably at least 50.0 MPa.

In some embodiments, the cured epoxy resin formed by the processes described herein has an Aluminium : Aluminium single lap shear strength of the bio-based cured epoxy resin is at least 10.0 MPa, as measured in accordance with ASTM D1002, preferably at least 15.0 MPa, more preferably at least 20.0 MPa, even more preferably at least 25.0 MPa, even more preferably at least 30.0 MPa, even more preferably at least 35.0 MPa, even more preferably at least 40.0 MPa, even more preferably at least 45.0 MPa, most preferably at least 50.0 MPa.

The invention will now be described by reference to the following non-limiting Examples and the Figures.

EXAMPLES

EXAMPLE 1 - Cured Epoxy Resin with Enhanced Bio-based Carbon Content

In this example, the bio-based carbon content of a cured epoxy resin formed by a known process (Table 1 ) is compared with the bio-based carbon contents of a cured epoxy resin formed by process of the present invention (Table 2).

Table 1 highlights that even though known epoxy resin curatives, for example, Cardamine H 811 may contain a degree of bio-based carbon content, this is not sufficient to achieve a 40% or greater total bio-based carbon content of the resulting cured epoxy resin, even in the case that a partially bio-based epoxy resin, for example, Envipoxy 525 (RTM) is used to further contribute towards the bio-based carbon content of the resulting cured epoxy resin.

Table 1. Comparative example of a conventional process for preparing a cured epoxy resin having a bio-based carbon content.

1 . SPOLCHEMIE Czech Republic

2. ANACARDA LTD UK.

Enviropoxy 525 (RTM) is a known epoxy resin having some degree of bio-based carbon content. Cardamine H 811 is a known phenalkamine epoxy resin curative, also having some degree of bio-based carbon content. The process exemplified in Table 1 is not within the scope of the present invention but is useful in illustrating the impact that the mass proportion has on the total bio-based carbon content of the resulting cured epoxy resin. Table 2 below outlines a process according to the present invention wherein the mass of the bio-based epoxy resin curative is greater than that of the epoxy resin, and wherein the cured epoxy resin formed has a bio-based carbon content of at least 40%.

Table 2. Example of a process according to the present invention for preparing a cured epoxy resin having an increased bio-based carbon content.

3. CHEMICAL PROCESSING SERVICES LTD

Mixture A is a 50:50 wt/wt mixture of a furalkamine Mannich base according to formula (1) above, and a phenalkamine Mannich base according to formula (2) above. The system exemplified in Table 2 is within the scope of the present invention. As shown in Table 2, the process of the present invention results in a cured epoxy resin having a significantly higher bio-based carbon content than is achieved with known comparative process and without deviating from a stoichiometric mixture of the epoxy resin and epoxy resin curative.

Furthermore, the mixtures outlined in Table 1 and Table 2 have very similar handling properties as is shown in Table 3 below. This demonstrates that the process of the present invention allows for the provision of cured epoxy resins having an increased biobased carbon content, and without sacrificing other desirable properties.

Table 3. Comparison of the handling properties of the mixtures outlined in Tables 1 and 2. The reactivity profile of the two systems demonstrates that the result of altering the stoichiometric value of the components such that the curing agent character and structure liberates less energy. This in turn reduces the peak exotherm temperature when undertaking a semi-adiabatic cure profile with constant mass. This is represented graphically in Figures 1 and 2.

Figure 1 is the Gel-time temperature profile of the mixture outlined in Table land Figure 2 is the Gel-time temperature profile of the mixture outlined in Table 2.

Figure 1 depicts a gel-time of 39.0 minutes at a temperature of 131.1 °C. Figure 1 also depicts a peak exotherm of 131 .8 °C at 40.0 minutes.

Figure 2 depicts a gel-time of 42.2 minutes at a temperature of 102.1 °C. Figure 2 also depicts a peak exotherm of 104.2 °C at 44.0 minutes.

EXAMPLE 2 - Preparation and Properties of Bio-based Novolac

A bio-based novolac epoxy resin curative was prepared from cardanol using the following procedure. Cardanol is a bio-based feedstock that is derived from waste cashew nut-shell liquid.

330 grams (1 mol) of cardanol was added to a 1 litre, round-bottomed flask equipped with a condenser, mechanical stirrer, addition funnel and thermometer. 23.8 grams (0.17 Mols) of hexamine (approximately 1 mol of formaldehyde liberated) was added to the flask and the agitator started. The mixture was heated to 120 °C and started to liberate water of reaction at 111 °C. The product was distilled at 120 °C monitoring viscosity using a cone and plate viscometer set at 150 °C. The material was held at 120 °C for 26 hours until a stable viscosity of 710 mPa s was obtained. The molten solid material was then discharged to solidify at ambient temperatures. The resulting bio-based novolac had the following properties as outlined in Table 4.

Table 4. Properties of bio-based novolac.

The bio-based novolac may then be subjected to a standard hexamine cure, which is a process known to the skilled person. Table 5 below outlines a hexamine curing process, and the properties of the resulting cured polymer for a comparative known Curaphen 44- 200 novolac vs the above bio-based novolac.

Table 5. Cure regime and resulting properties for a comparative known Curaphen 44- 200 novolac vs the bio-based novolac of the present example.

4 - Widely available

5 - BITREZ LTD UK

6 - CHEMICAL PROCESSING SERVICES LTD

7 - Widely available

Curaphen 44-200 is a known novolac derived from petrochemical based phenolic monomers and thus has zero bio-based carbon content. The bio-based novolac derives its high bio-based carbon content from the cardanol based monomers with the balance of non-bio-based content being derived from the hexamine.

EXAMPLE 3 - Cured Epoxy Resin Derived from Bio-based Novolac

In this example, a process for preparing a cured epoxy resin using the bio-based novolac of Example 2 as an epoxy resin curative is compared to a process for preparing a cured epoxy resin using a petrochemical based novolac (Curaphen 44-200) as an epoxy resin curative.

Table 6. Comparative example of a process for preparing a cured epoxy resin using a petrochemical based novolac as an epoxy resin curative.

1 - SPOLCHEMIE Czech Republic

8 - BITREZ LTD UK

Table 7. Example of a process for preparing a cured epoxy resin using the bio-based novolac of Example 2 as an epoxy resin curative.

9. CHEMICAL PROCESSING SERVICES LTD Table 8. Comparison of curing properties and bio-based carbon content of the processes outlined in Tables 6 and 7.

* A broader transition curve was observed than is observed with a traditional phenolic

10. Widely available

As can be seen, comparable properties can also be achieved for a high bio-based carbon content cured epoxy resin using a bio-based novolac as the epoxy resin curative.

EXAMPLE 4 - Mannich Furalkamines Useful in the Present Invention

An exemplary Mannich furalkamine useful as an epoxy resin curative in the present invention is described below.

Firstly, as a comparative example, triethylenetetramine (TETA) is considered.

The molecular weight of TETA is 146 Da, and the number of active hydrogens is 6. This means that the AHEW can be calculated to be 146/6 = 24.3 g/equivalent. In an embodiment of the invention wherein the AHEW of the bio-based epoxy resin curative is at least 200 g/equivalent, the use of TETA as the bio-based epoxy resin curative is not within the scope of the invention.

Bio-based Mannich furalkamines can be used to provide a more favourable AHEW. For example, a polyfurfuryl alcohol backbone can be reacted with an amine to provide a Mannich furalkamine. In the below example, a polyfurfuryl alcohol having 7 repeating units is reacted with TETA to provide compound A below compound having a molecular weight of 706 Da and 5 active hydrogens. Thus, the AHEW is 706/5 = 141.2 g/equivalent.

Compound A

Another example of a bio-based Mannich furalkamine used to provide a larger AHEW is given below. In the below example, a polyfurfuryl alcohol having 7 repeating units is reacted with 1 ,2-Dimethylethylenediamine to provide compound B below having a molecular weight of 662 Da and 1 active hydrogen. Thus, the AHEW is 662/1 = 662 g/equivalent.

Compound B

An exemplary synthetic procedure for the preparation of a compound of the class of furfuralkamine Mannich base to which compounds A and B belong is outlined below. A polyfurfuryl alcohol Mannich base epoxy resin curative was prepared by the reaction of an ethylene amine, for example, triethylene tetramine, an aqueous solution of formaldehyde and polyfurfuryl alcohol. The product was processed using equimolar quantities of materials and synthesised by first reacting the amine and formaldehyde, before subsequent reaction with the polyfurfuryl alcohol, followed by a final stage of vacuum distillation to afford a substantially anhydrous product.

Specifically, 876 grams (6.0 moles) of triethylene tetramine (having an average molecular weight of approximately 146) and 246 grams (3.0 moles) of formaldehyde (36.5% Formalin solution) were added to a 5-liter, 3-necked round bottom flask equipped with a thermometer, a mechanical agitator, and a Dean-Stark water trap connected to a condenser. The reaction mixture was heated to 80-100°C over 60 minutes using a water bath, which was also used to maintain the desired temperature and avoid excessive heating (i.e. over 100°C). The reaction mixture was then cooled to 60°C and 2100 grams (3.0 moles) of polyfurfuryl alcohol were added incrementally over a 10 minute period whilst maintaining the temperature in the range of 60-80° C.

Following addition, the temperature was raised from 60-80°C to 100°C over a 30 minute period. This temperature was maintained for 1 hour before being increased from 100°C to 120°C over a 1-hour period to remove and recover 210 grams of water in the water trap. The reaction was monitored by way of an amine number titration, as well as by Brookfield viscosity analysis. Following the water removal, a vacuum was applied for 20 minutes to remove the final distillate before cooling to 80-100°C over the course of 20 minutes. 3012 grams of a clear dark amber/red liquid was obtained.

EXAMPLE 5 - Single Lap Shear Strength of the Bio-based Cured Epoxy Resin

Epoxy resins are used in a variety of applications, and their extreme versatility and performance makes them suitable for bonding, sealing, reinforcing, coating and encapsulation in a myriad of markets. They are renowned for their bond strength and adhesion to a variety of substrates with outstanding resistance to creep making them possibly the most widely used structural adhesive.

Many unmodified epoxy resins cure to form brittle solids and use of extenders and modifiers to enhance toughness or selection of specific curing agents can aid wetting, bond strength, and mechanical properties, like flexibility. The basic bisphenol A based epoxy resins employed like EPI LOK 60-600 [Bitrez standard bisphenol A resin] or the bio-based alternative [Envipoxy 525 (RTM)], have the same chemical structure, irrespective of their origin, bio-based or petrochemical. The epoxy resin curative component in many cases will contribute to the level of adhesion conveyed by the system.

There are numerous pre-treatments that can also be undertaken to aid adhesion. In some cases, the low surface energy of the substrate can prove difficult to adhere to as it prevents the adhesive from wetting the surface and making intimate contact. Union is achieved when cure occurs and the cohesive strength develops such that the coupled adhesive and cohesive strength, provide the desirable bond strength.

If the epoxy resin curative in the system can contribute to the substrate wetting and aid adherence, then it stands to reason that the reverse balanced stoichiometric product of this invention may also offer even greater substrate wetting. Evaluation of the single lap shear strength of a product can quantify the resistance of an adhesive to forces in the plane of the bonded surfaces which is reflective of the stress that structural joints are typically subjected to.

The lap shear test is an indicative measure of performance and suitable for quantitative comparison of properties. The failure value can be calculated by dividing the load at fail by the surface area of the bond overlap. The reported stress value is generally lower than the ultimate performance as the distribution of the load is not necessarily even, which can result in peel.

Single-Lap-Joint Adhesively Bonded Specimens is ongoing in accordance with ASTM D1002. Testing is conducted by applying the adhesive to the defined substrate area and clamping the unit. The material is allowed to cure for 2 hours at 60 °C. Test pieces are located in aligned grips and evaluated using standard tension/compression mechanical test equipment.