Method

Abstract

The present invention relates to processing of cured composites, and in particular provides a method for processing of a cured composite made from an unsaturated polyester resin, said method comprising: (i) Providing a cured composite made from an unsaturated polyester resin, wherein said unsaturated polyester resin comprises an unsaturated polyester component obtainable by reaction of a polyhydric alcohol with methacrylic acid or with an alkyl methacrylate, or obtainable by reaction of methacrylic acid with an epoxy resin, and (ii) Digesting the cured composite using one or more alcohols.

Description

METHODCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 593,097, filed October 25, 2023 and European Patent Application No. 23211217.7, filed November 21, 2023, the contents of each of which are incorporated herein by reference.TECHNICAL FIELD

[0002] The present invention relates to processing of cured composites produced from unsaturated polyester resins.BACKGROUND

[0003] Cured composites are a class of material obtained by curing an unsaturated resin. A particularly common class of cured composites are those obtained by curing of unsaturated polyester resins, or “UPR’s”. In particular, unsaturated polyester resins can be used in the production of composites such as fibre reinforced plastics and filled plastic products, including sanitary -ware, tanks, pipes, gratings, and high performance components for the marine and transportation industry such, as closure and body panels, fenders, boat hulls / decks and other large plastic articles. Unsaturated polyester resins also find uses in coatings and adhesives.

[0004] An unsaturated polyester resin generally comprises an unsaturated polyester component of relatively high molecular weight and viscosity mixed with a reactive diluent component of relatively low molecular weight and viscosity. The curing of the mixture causes cross-linking of the polyester chains with the reactive diluent. Curing usually comprises adding an initiator. Curing can involve heating but many resins can be cured at room temperature. The unsaturated polyester resin may be, and commonly is, mixed with fillers or reinforcing materials before curing in a suitable mold.

[0005] The exact properties of the produced composite are determined by the unsaturated polyester and reactive diluent components of the UPR, as well as the other components which may be added, such as fillers and reinforcing materials.

[0006] The unsaturated polyester component of the UPR may generally be considered as an oligomer component. Historically they have been produced by the condensation of a polyhydric alcohol with a blend of saturated and unsaturated acids or anhydrides. Many commercial unsaturated polyester components are derived from phthalic and maleic anhydride as saturated and unsaturated components and 1,2-propylene glycol as a diol, but other glycols and acids or anhydrides can be used.

[0007] Historically the most commonly used reactive diluent has been styrene. Due to health concerns styrene has occasionally been replaced in resin systems by other less toxic reactive diluents such as vinyl toluene, vinyl acetate, methyl methacrylate and allyl ethers as well as by difunctional monomers such as diacrylates and dimethacrylates.

[0008] Conventional cured composites based on unsaturated polyester resins are not easy to chemically recycle. Recycling to date had therefore generally involved physically chopping the cured composite. It would be desirable however to be able to chemically recycle a cured composite, preferably to recover components which can be reused, and most preferably reused for production of “new” unsaturated polyester resins and / or new cured composites.

[0009] JP 2005255780 A discloses the use of a glycol to “decompose” a composite. In particular, this document notes the difficulties of recycling materials based on fumarates and styrene, and then discloses the use of a glycol to decompose fumarate based or glycol / phthalic acid based material. A key feature of the process disclosed in this document is the use of a radical generator to assist the decomposition.

[0010] JPH 10147621 A describes what it refers to as the “decomposition” of compositions based on unsaturated polyesters. This is performed using a decomposition solution containing a base and at least one solvent selected from the group consisting of water, methanol, ethanol, and ethylene glycol. In this document it is a requirement of the claimed compositions that a specific separate aliphatic polyester / binding component is present, such as polycaprolactone. In the decomposition step it is the ester bonds formed with this component which are decomposed, allowing separation of resin components of the composition from other materials, such as metal or glass fibres. Without the separate polyester / binding component in the composition limited if any decomposition occurs.

[0011] Neither of the above documents disclose composites where the main unsaturated polyester component comprises methacrylate.SUMMARY

[0012] We have now found that a particular class of cured composites, namely based on an unsaturated polyester component which comprises unsaturation derived from methacrylate groups, can be chemically recycled using relatively simple methods.

[0013] Thus, in a first embodiment the present invention provides a method for processing of a cured composite made from an unsaturated polyester resin, said method comprising:(i) Providing a cured composite made from an unsaturated polyester resin, wherein said unsaturated polyester resin comprises an unsaturated polyester component obtainable by reaction of a polyhydric alcohol with methacrylic acid or with an alkyl methacrylate, or obtainable by reaction of methacrylic acid with an epoxy resin, and(ii) Digesting the cured composite using one or more alcohols.

[0014] As used herein:

[0015] “Unsaturated polyester resin” or “UPR” refers to a mixture comprising an unsaturated polyester component (and in particular comprising the specific unsaturated polyester component as noted) and which can be cured to form a cured composite. The term unsaturated polyester resin / UPR as used herein is used exclusively to refer to such mixtures prior to curing. Typically the UPR is a liquid. Details of preferred UPR mixtures are provided below.

[0016] “ Cured composite” and “composite” are used synonymously, and refer to the product obtained by curing an unsaturated polyester resin. As used herein the term includes composites which include fillers and / or reinforcing materials but also those where no fillers or reinforcing materials are present (sometimes referred to in the art as “castings”).

[0017] In the present invention it has been found that alcohols are able to digest the cured composite. The digestion has been found suitable to break down the cured composite to produce a mixture comprising a solution of polyhydric alcohol and polyalkyl methacrylate in the alcohol. The mixture may also comprise fillers and / or reinforcing materials if these are present in the cured composite. Any such fillers and reinforcing materials may be separated, for example by filtration or decanting, for re-use. The mixture formed may also comprise one or more dialkyl esters of any acids which were added to the unsaturated polyester resin used to form the cured composite. For example, adipic acid (hexanedioic acid) is commonly added to unsaturated polyester resins, in which case there would be produced in the mixture after digestion a dialkyl adipate.

[0018] (For avoidance of doubt the “alkyl” in the polyalkyl methacrylate formed from the digestion step, and also in any dialkyl esters, if present, corresponds to the alkyl group of the alcohol or alcohols used for the digestion. For example, if methanol is used, the alkyl group is methyl, and if butanol is used the alkyl group is butyl.)

[0019] The polyhydric alcohol and polyalkyl methacrylate obtained, and also any dialkyl esters if present, can be separated from the mixture and reused.

[0020] In preferred embodiments the polyhydric alcohol and / or the polyalkyl methacrylate obtained are used to produce a recycled unsaturated polyester resin.

[0021] For example, the polyhydric alcohol can be used to produce a “new” unsaturated polyester component of an unsaturated polyester resin.

[0022] In preferred embodiments the polyalkyl methacrylate is depolymerised to provide alkyl methacrylate. (Rather than being used “directly” as a polyalkyl methacrylate, for example.) Taking the example where methanol is used as the alcohol for the digestion, for example, then there will be formed polymethyl methacrylate, which can be depolymerised to methyl methacrylate. If the polyalkyl methacrylate is depolymerised to provide an alkyl methacrylate this may be used for any conventional application of the specific alkyl methacrylate. Preferably the alkyl methacrylate is reused for production of a “new” unsaturated polyester component of an unsaturated polyester resin.

[0023] In some embodiments, the polyalkyl methacrylate originally formed in the digestion can be transesterified with a different alcohol than that used for the digestion to form a different polyalkyl methacrylate. For example, if butanol is used as the alcohol for the digestion then there will be formed polybutyl methacrylate. This could be transesterified with methanol to form polymethyl methacrylate and butanol. The butanol can be recycled for use in a further digestion. The polymethyl methacrylate may be preferably depolymerised to form methyl methacrylate as already discussed.

[0024] As noted above, in some embodiments one or more dialkyl esters may be formed in the mixture after digestion, and in particular where acids were present in the unsaturated polyester resin used to form the cured composite. Any dialkyl esters can be separated from the mixture. They can then be used “as is”, or, alternatively, they can be hydrolysed to form the original acid and the alcohol originally used for the digestion. The former can be added, if desired, in another unsaturated polyester resin. The latter can be recycled for further digestion.

[0025] In a further option, the polymethyl methacrylate may be separated from the mixture obtained by the digestion to leave a mixture of dialkyl esters and polyhydric alcohol. In embodiments these can be reacted to form oligomers which can be transesterified to form another unsaturated polyester resin.

[0026] In the method of the present invention there is provided (and digested) a cured composite made from an unsaturated polyester resin, wherein the unsaturated polyester resin comprises an unsaturated polyester component obtainable by reaction of a polyhydric alcohol with methacrylic acid or with an alkyl methacrylate, or obtainable by reaction of methacrylic acid with an epoxy resin.

[0027] We will hereafter describe the preferred features of the unsaturated polyester resin from which the provided cured composite has been formed. It should be noted that the unsaturated polyester resin (component) of the present invention may in the art sometimes also be referred to as a vinyl ester resin (component), or VER. Vinyl ester resins are a “subset” of the more general compositions known as unsaturated polyester resins, and in particular based on monobasic acids. They are, for example, generally characterised by reactive unsaturation located predominately in terminal positions. However, the terminology used for VER’s in the art is not always consistent, and since the resin of the present invention comprises both multiple ester functionalities and unsaturation we will for the purposes of the present invention refer use the more general terminology “unsaturated polyester resin” or “unsaturated polyester component”.

[0028] We would also note that although a cured composite is chemically modified by the curing process compared to the initial unsaturated polyester resin, the cured composite nevertheless has and retains properties directly based on the unsaturated polyester resin used. It is therefore common to characterise cured composites based on the unsaturated polyester resin used to form the cured composite.

[0029] In view of this, but also for ease of reference, we herein use the present tense to describe the properties of the unsaturated polyester resin and / or the components thereof. Since it is a cured composite formed from the unsaturated polyester resin which is provided in the present invention, it will be understood that the present and past tenses may be used synonymously when referring to the unsaturated polyester resin and / or its components. (For example, “comprises” is synonymous with “comprised” and “has” or “have” are synonymous with “had” when referring to the UPR or components used to form the cured composite.)BRIEF DESCRIPTION OF THE DRAWING

[0030] These and other aspects and features of the present implementations will become apparent to those ordinarily skilled in the art upon review of the following detailed description in conjunction with the accompanying figure.

[0031] Figure 1 is an illustration of a solid disclosed herein analysed by Fourier-Transform IR spectroscopy (FTIR).DETAILED DESCRIPTION

[0032] In the present invention, the unsaturated polyester resin comprises an unsaturated polyester component obtainable by reaction of a polyhydric alcohol with methacrylic acid or with an alkyl methacrylate, or obtainable by reaction of methacrylic acid with an epoxy resin. The unsaturated polyester component may, and generally will, comprise a mixture of polyesters and some monoester products ( / molecules). Typically, however, at least 10%, and preferably at least 20%, of the molecules in the unsaturated polyester resin component have more than one methacrylate ester group. The unsaturated polyester component preferably has a molecular weight of at least 500 g / mol. The molecular weight is preferably less than 5000 g / mol, such as in the range 500 to 1,500 g / mole.

[0033] The required component / required molecular weight may be obtained by selection of a suitable polyhydric alcohol, a suitable alkyl methacrylate where used, or a suitable epoxy resin.

[0034] For example, where the unsaturated polyester resin comprises an unsaturated polyester component obtainable by reaction of a polyhydric alcohol with methacrylic acid, then the required component can be obtained by selection of a suitable polyhydric alcohol, whilst, where the unsaturated polyester resin comprises an unsaturated polyester component obtainable by reaction of a polyhydric alcohol with an alkyl methacrylate, then the required component can be obtained by selection of the polyhydric alcohol and the alkyl methacrylate.

[0035] In either option, the polyhydric alcohol preferably has 2 to 4, such as 2 or 3 alcohol (hydroxy) groups. The polyhydric alcohol preferably is a saturated alcohol i.e. having no carbon to carbon double or triple bonds More generally, the polyhydric alcohol preferably has a molecular weight of at least 60 g / mol, such as in the range 60 to 500 g / mol. Preferred polyhydric alcohols include C2 to C8 glycols and triols, oligomers (e.g. dimers, trimers) of C2 to C8 glycols, and polymers of C2 to C8 glycols. Most preferred polyhydric alcohols include ethylene glycol, propylene glycol, neopentyl glycol, diethylene glycol, polyethylene glycol, dipropylene glycol and glycerin (glycerol).

[0036] In the option where the unsaturated polyester resin comprises an unsaturated polyester component obtainable by reaction of a polyhydric alcohol with an alkyl methacrylate then the polyhydric alcohol is preferably as already defined above. The alkyl methacrylate used may be any suitable alkyl methacrylate. Preferably the alkyl group is a Cl to C8 alkyl group, such as a Cl to C4 alkyl group. For avoidance of doubt, the term “alkyl” as used herein refers to a saturated hydrocarbon comprising hydrogen and carbon atoms only i.e. with no heteroatoms or other functional groups. Thus, the only functional group in the alkyl methacrylate is the methacrylate group itself.

[0037] In one embodiment the polyhydric alcohol, such as those listed above, may be reacted with difunctional acids or anhydrides prior to reaction with methacrylic acid or alkyl methacrylate. Suitable acids and anhydrides are generally C2 to C8 difunctional acids and anhydrides, such as succinic acid or anhydride, adipic acid, isophthalic or terephthalic acid, and orthophthalic acid or anhydride. In particular, the polyhydric alcohol can react with a difunctional acid or anhydride to provide a polyhydric alcohol of increased molecular weight which can then be reacted (“capped”) with methacrylic acid or an alkyl methacrylate.

[0038] In one option the unsaturated polyester resin comprises an unsaturated polyester component obtainable by reaction of methacrylic acid with an epoxy resin. (Note that the term “epoxy resin” refers to a material which has multiple epoxide groups i.e. is a polyepoxide.) The product of such a reaction (the unsaturated polyester component) is a methacrylate ester. Examples of epoxy resin compounds which could be used in this option are those based on phenols, such as bisphenol A or novolac. Preferred examples include the diglycidyl ether of bisphenol A (Bisphenol A diglycidyl ether or “BADGE”), the polyglycidyl ether of a phenol formaldehyde novolac resin, and the diglycidyl ether of tetra bromo bisphenol A. Such epoxy resin compounds may be extended by reacting with a diphenol, an anhydride or a diacid which is soluble in the epoxy resin to make a higher molecular weight epoxy resin prior to reaction with the methacrylic acid. Examples of suitable diphenols and anhydrides include bisphenol A, tetrabromo bisphenol A, maleic anhydride and phthalic anhydride.

[0039] In the art an unsaturated polyester resin typically comprises both an unsaturated polyester resin component and a reactive diluent component.

[0040] In a first option, and which option is preferred in the present invention, the unsaturated polyester resin may be such a “conventional” material. Thus, in the first option the unsaturated polyester resin comprises: a. An unsaturated polyester component obtainable by reaction of a polyhydric alcohol with methacrylic acid or with an alkyl methacrylate, or obtainable by reaction of methacrylic acid with an epoxy resin, and b. A reactive diluent component.

[0041] In such resins, the unsaturated polyester component of the unsaturated polyester resin generally has a higher molecular weight than the reactive diluent component.

[0042] In this first option, a most preferred unsaturated polyester resin comprises: a. An unsaturated polyester component which has a molecular weight of at least500 g / mol, andb. A reactive diluent component which has a molecular weight of less than 500 g / mol.

[0043] Most preferably the unsaturated polyester resin comprises at least 20% by weight of the unsaturated polyester component. For example, the ratio of unsaturated polyester component (a) to reactive diluent component (b) in the unsaturated polyester resin is typically in the range 20:80 to 80:20 by weight, such as in the range 30:70 to 70:30 by weight.

[0044] The unsaturated polyester component (component (a)) preferably has a molecular weight of less than 5000 g / mol, such as in the range 500 to 1,500 g / mole as already described. As also already noted, the required component / required molecular weight may be obtained by selection of a suitable polyhydric alcohol, a suitable alkyl methacrylate where used, or a suitable epoxy resin.

[0045] Generally the unsaturated polyester component has both a relatively high molecular weight and a relatively high viscosity compared to a reactive diluent component. The unsaturated polyester component in the present invention preferably has a cone and plate viscosity (I.C.I.) of 2-20 poise @75° C, such as of 5 to 15 poise@75°C, and most preferably in the range 8 to 12 poise @75° C. (As used herein, the cone and plate viscosity (I.C.I.) of an unsaturated resin component is the value obtained by measuring the viscosity at 75°C and a shear rate of 5 / sec. Any suitable viscometer may be used, such as a Brookfield CAP2000+ viscometer, produced by AMETEK Brookfield.)

[0046] As already noted, the unsaturated polyester component is obtainable by reaction of a polyhydric alcohol with methacrylic acid, or with an alkyl methacrylate, or obtainable by reaction of methacrylic acid with an epoxy resin. In particular, the methacrylic acid or alkyl methacrylate react on the alcohol groups or with the epoxy resin to produce a polyester which is a polymethacrylate i.e. having multiple methacrylate groups.

[0047] In contrast, the reactive diluent component (component (b)) preferably has a molecular weight of less than 250 g / mol, such as from 80 to 160 g / mol.

[0048] As already noted, the use of reactive diluents in unsaturated polyester resins is well known in the art. In general terms, the reactive diluent generally comprises at least one unsaturation per molecule. (And in the art may also be referred to as “monomer” or “reactive monomer”.) There may be a single or multiple unsaturations per molecule, but usually there are less than 4 unsaturations per molecule of the reactive diluent, and more usually 1 or 2 unsaturations per molecule of the reactive diluent. In a preferred embodiment of this first option the reactive diluent component itself comprises methacrylic acid or an ester thereof. The ester is generally the ester obtainable by reaction of methacrylic acid with an alcohol.Methacrylate esters of methacrylic acid with an alcohol with a single alcohol functionality, for example, have a single unsaturation. Methacrylate esters of methacrylic acid with an alcohol with more than one alcohol functionality, for example diols or triols, have the corresponding number of unsaturations in the ester.

[0049] The required degree of unsaturation, as well as the required molecular weight may be obtained by selection of a suitable alcohol. Reactive diluents with a single unsaturation or two unsaturations (for example a methacrylate ester of a diol) are most preferred. In particular, it is preferred that the reactive diluent component is an alkyl methacrylate or an alkanediol dimethacrylate. (Mixtures of methacrylic acid with an ester thereof, or of two or more esters thereof may be used. In this case it is preferred that there is an average of between 1 and 2 unsaturations per molecule.)

[0050] Particularly preferred reactive diluents for the present invention are alkyl methacrylates where the alkyl is a C1-C8 alkyl, with methyl methacrylate and butyl methacrylate most preferred.

[0051] It will be recognised that the compositions of the unsaturated polyester component and of the reactive diluent component in this first option can both be based on methacrylate esters formed by reactions of alcohols and methacrylic acid or related compounds. As already noted, however, the reactive diluent component generally has a lower molecular weight and also a lower viscosity than the unsaturated polyester component. Usually the viscosity is significantly lower as well. For example, methacrylic acid has a viscosity at 20°C of 0.014 poise and methyl methacrylate has a viscosity at 20°C of 0.0056 poise. The reactive diluent component more generally preferably has a viscosity of less than 1.5 poise @20° C, such as of less than 0.5 poise @20° C, for example in the range 0.002 to 0.1 poise@ 20°C. (The viscosity of the reactive diluent component may be known. If necessary any suitable viscometer may be used to measure the value at 20°C, such as a Brookfield CAP2000+ viscometer, produced by AMETEK Brookfield.)

[0052] Nevertheless, due to the similarities between components which may be used to form a “conventional UPR” (i.e. based on an unsaturated polyester component and a separate diluent component where the unsaturated polyester component has a relatively high molecular weight and a relatively high viscosity compared to a reactive diluent component), it is also possible in the present invention for the cured composite to have been made from an unsaturated polyester resin which does not comprise specific separate unsaturated polyester and diluent components. In particular, an unsaturated polyester resin may be formed in a “onepot” synthesis which produces a mixture of esters and polyesters which can be used as the unsaturated polyester resin without separate addition of a diluent component.

[0053] Thus, in a second option, the unsaturated polyester resin may be formed by reacting a polyhydric alcohol with methacrylic acid or with an alkyl methacrylate to form a mixture of unsaturated polyester and monoester components which can be used as an unsaturated polyester resin without a separate reactive diluent component.

[0054] As a specific example, methyl methacrylate could be reacted with a mixture formed by reacting a diol such as neopentyl glycol in the presence of a less than stoichiometric amount (compared to the glycol) of a diacid, such as adipic acid or phthalic acid, to form a mixture which will comprise the mono and dimethylmethacrylate esters of neopentyl glycol, and the mono and dimethylmethacrylate esters of a neopentyl glycol-diacid oligomers. By ensuring sufficient of the lower molecular weight and relatively low viscosity esters are present no additional diluent need be added prior to curing. Independently of how the unsaturated polyester resin is formed, it may also comprise filler and / or reinforcing fibres, these then also being present in the cured composite.

[0055] The unsaturated polyester component obtainable by reaction of a polyhydric alcohol with methacrylic acid or with an alkyl methacrylate or obtainable by reaction of methacrylic acid with an epoxy resin and, where present, any reactive diluent component which is present, preferably together constitute at least 80% of the weight of the unsaturated polyester resin excluding any such fillers and reinforcing fibres present which is then cured, and more preferably at least 90% of the weight of the unsaturated polyester resin excluding any fillers and reinforcing fibres present. Put another way, the unsaturated polyester component and any reactive diluent component are at least 80% by weight, more preferably at least 90% by weight, of all reactive components present prior to curing in the unsaturated polyester resin. (Filler and fibres would generally be considered as inert.)

[0056] Subject to the requirements of the present invention as already defined (in particular the requirements for the unsaturated polyester resin and the reactive diluent component), the unsaturated polyester resin may have been formed and cured by any suitable method. One example of a suitable method can be found, for example, in US 6489406, with suitable selection of the components for the “linear unsaturated polyester” (corresponding to the unsaturated polyester component herein) and the “one or more reactive monomers” (corresponding to the reactive diluent component herein).

[0057] In the present invention the cured composite is digested using one or more alcohols.Although more than one alcohol may be used, preferably a single alcohol is used, since use ofa mixture of alcohols tends to lead to mixed alkyl groups in the products of the digestion. (Nevertheless, it is possible to use a mixture of alcohols which produces initial digestion products which comprise different alkyl groups, and then transesterify with a single alcohol.) The one or more alcohols may comprise a diol, but preferably alcohols having a single alcohol functionality are used, and more preferably a single alcohol having a single alcohol functionality is used. The alcohols are most preferably selected from Cl to C6 alcohols. The most preferred alcohol is methanol.

[0058] The digestion step of the method of the present invention does not require the presence of a radical generator. Thus, in preferred embodiments the method of the present invention does not add a radical generator.

[0059] The digestion step of the method of the present invention may take presence in the presence of a catalyst. Suitable catalysts include acids and bases, although bases are generally preferred. Weak bases having a pKb of 6 or above, such as 8 or above, are particularly suitable. Most preferred catalysts are metal salts of organic acids, such as metal salts of C2 to C6 carboxylic acids or acetylacetone. Suitable metals include zirconium, tin and zinc. One suitable catalyst is zinc acetate, for example.

[0060] The digestion step of the method of the present invention does not require the presence of an aliphatic polyester component in the unsaturated polyester resin or the cured composite. Nevertheless, the presence of such a component is not necessarily excluded.

[0061] In embodiments, the unsaturated polyester resin does not comprise polypropiolactone, polyglycolic acid, polylactic acid, polyethylene adipate, polytetramethylene adipate, polyethylene succinate, polybutylene succinate, polycaprolactone diol, polycaprolactone triol or poly (3- hydroxy alkanoate).

[0062] In embodiments, the unsaturated polyester resin preferably comprises less than 10wt%, based on the total weight of the unsaturated polyester resin, of aliphatic polyester components, such as less than 5wt% or less than lwt% of aliphatic polyester components, most preferably it does not comprise any aliphatic polyester components.

[0063] Prior to digestion the cured composite is usually cut or ground into pieces of a suitable size. There is no particular limit on the particle size. Smaller particles may digest faster due to the larger surface area to volume ratio, but production of smaller particles tends to require more time or energy in the first place. In some embodiments the ground particles may be in the form of chips or flakes with a maximum dimension of 0.1 to 50 cm, preferably 1 to 10 cm.

[0064] Typically the digestion takes place at elevated temperature and pressure. For example the digestion typically takes place at temperatures above 150°C, such as in the range 200 to 300°C. The pressure is selected to be sufficient to maintain the alcohol in a liquid state at the desired temperature.

[0065] The digestion of the cured composite using alcohol produces a mixture which comprises a polyhydric alcohol and polyalkyl methacrylate in solution in the alcohol used for the digestion e.g. methanol. If the cured composite comprises filler and / or reinforcing materials then typically these remain as solids.

[0066] In embodiments, any filler and / or reinforcing materials are separated from the mixture obtained after digestion. These can be separated by any suitable method for separating solids from a liquid. Decantation and / or filtration may be used for example.

[0067] In preferred embodiments the fillers and / or reinforcing materials may be recycled for use as fillers and / or reinforcing materials in production of new cured composites.

[0068] In embodiments, the method comprises a step of separating the polyalkyl methacrylate from the mixture. It is generally preferred to separate the polyalkyl methacrylate to leave a mixture comprising the polyhydric alcohol in solution in the alcohol (and, when present, dialkyl ester). For example, the polyalkyl methacrylate can be separated from the mixture by cooling the solution to precipitate the polyalkyl methacrylate as a solid, which can then be separated. Again this separation can be by any suitable method for separating solids from a liquid, such as decantation and / or filtration, or by distillation to remove methanol and polyhydric alcohol.

[0069] In some embodiments, separation of the polyalkyl methacrylate from the mixture may be performed by distilling off the alcohol and the polyhydric alcohol from the mixture, preferably as separate products e.g. distilling off of the alcohol first, followed by the polyhydric alcohol.

[0070] In other embodiments, solely the alcohol is separated from the mixture to leave a mixture of polyhydric alcohol and polyalkyl methacrylate (and, when present, dialkyl ester).

[0071] It will be apparent that generally any fillers and / or reinforcing materials are most easily removed first, and in particular whilst the other products are in solution. Thus, separation of any filler and / or reinforcing materials is preferably performed at elevated temperature and pressure. Suitably this step is performed at the same or a similar temperature and pressure as the digestion.

[0072] It is known that polyalkyl methacrylates can be depolymerised to yield the corresponding alkyl methacrylate Thus, in preferred embodiments the polyalkyl methacrylateobtained after the digestion of the present invention is separated and then treated to depolymerise the polyalkyl methacrylate and yield alkyl methacrylate. This step can be performed “on site” or the separated polyalkyl methacrylate may be provided or sold to a processor for this purpose.

[0073] The alkyl methacrylate obtained from such a depolymerisation process may be used for any suitable conventional use of the alkyl methacrylate. It will be apparent that this could include reuse in the production of unsaturated polyester resins and, subsequently, in a cured composite. (These therefore can be considered a recycled UPR and recycle cured composite.)

[0074] This polyhydric alcohol obtained can also be reused for any suitable use of such materials. A particularly preferred use is the production of a new polyester component for an unsaturated polyester resin. Hence, this component can also be used for production of recycled UPR’s and, subsequently, a recycled cured composite.

[0075] In a particularly preferred option the polyhydric alcohol can be reacted with an alkyl methacrylate to form an unsaturated polyester component. The alkyl methacrylate for this step may be the alkyl methacrylate obtained by depolymerisation of polyalkyl methacrylate which itself has been obtained from digestion of a cured composite according to the method of the present invention. (This could, of course, be from digestion of the same or a different cured composite than that from which the polyhydric alcohol is obtained.)

[0076] It will be apparent that the present invention can provide recycled UPR’s and recycled cured composites. (“Recycled” in this sense meaning that all or portions of a component of the UPR and / or of the cured composite have been obtained by digesting a previously formed cured composite.)

[0077] Thus, in a second aspect the present invention provides a recycled unsaturated polyester resin, said unsaturated polyester resin comprising an unsaturated polyester component, and wherein the unsaturated polyester component is an ester of a polyhydric alcohol, and wherein one or both of the following apply:(i) the polyhydric alcohol has been obtained by digesting a cured composite using one or more alcohols to produce the polyhydric alcohol, preferably by the method of the first aspect of the present invention, or(ii) the unsaturated polyester component is an ester of a polyhydric alcohol with an alkyl methacrylate, and the alkyl methacrylate has been obtained by digesting a cured composite using one or more alcohols to produce a polyalkyl methacrylate, preferably by the method of the first aspect of thepresent invention, followed by a depolymerisation to produce the alkyl methacrylate.

[0078] Further, in a third aspect the present invention provides a recycled cured composite obtained by curing an unsaturated polyester resin according to the second aspect.

[0079] Example

[0080] The present invention is illustrated by the following Example.

[0081] The cured composite provided was a casting (composite with no filler) made from an unsaturated polyester resin, which unsaturated polyester resin comprised 60wt% bisphenol A diglycidyl ether dimethacrylate (CAS# 1565-94-2) as unsaturated resin component and 40wt% methyl methacrylate as the reactive diluent component.

[0082] (Bisphenol A diglycidyl ether dimethacrylate (CAS# 1565-94-2) has a MW of 512.59 g / mol and a cone and plate viscosity (EC. I.) of 9.2 poise @75° C and measured at a shear rate of 5 / sec. Methyl methacrylate has a MW of 100.12 g / mol and viscosity of 0.0056 poise @20°C.)

[0083] The cured composite had been prepared by curing the unsaturated polyester resin for 16 hours at room temperature in the presence of methyl ethyl ketone peroxide (NOROX®MEKP-925H) and a cobalt catalyst, followed by heating to 150°C.

[0084] For the digestion with methanol the cured composite was provided in a ground (powder) form. 2g of the cured composite was placed in a Fauske and Associates VSP-2 Adiabatic Calorimeter reactor cell with 20g of methanol and 0.18 g of zinc acetate (Zn(OAc)2) and heated to 240°C for 16 hours.

[0085] After treatment the reactor was cooled to room temperature. The cooled mixture comprised a methanol phase and solids, and the methanol phase was separated from the solids by decantation.

[0086] The methanol phase was analysed by NMR. The composition was found to be 97wt% methanol, 2.1wt% of bisphenol A bis(2,3-dihydroxypropyl) ether, 0.6wt% methyl methacrylate and 0.3wt% methacrylic acid.

[0087] The solids, which were in the form of a gel, were washed in acetone, dried and then analysed by Fourier-Transform IR spectroscopy (FTIR). The data is shown in Figure 1 in comparison to a reference spectrum for polymethyl methacrylate. It can be seen that the solids comprise predominantly polymethyl methacrylate.

[0088] Thus, this Example shows that the cured composite can be successfully, and with high conversion, converted to bisphenol A bis(2,3-dihydroxypropyl) ether (a polyhydric alcohol) and polymethyl methacrylate.

Claims

CLAIMS1. A method for processing of a cured composite made from an unsaturated polyester resin, said method comprising:(i) Providing a cured composite made from an unsaturated polyester resin, wherein said unsaturated polyester resin comprises an unsaturated polyester component obtainable by reaction of a polyhydric alcohol with methacrylic acid or with an alkyl methacrylate, or obtainable by reaction of methacrylic acid with an epoxy resin, and(ii) Digesting the cured composite using one or more alcohols.

2. A method according to claim 1 wherein at least 20% of the molecules in the unsaturated polyester resin used to form the cured composite have more than one methacrylate ester group.

3. A method according to claim 1 wherein the unsaturated polyester component has a molecular weight of at least 500 g / mol.

4. A method according to claim 1 wherein the polyhydric alcohol has 2 to 4 alcohol groups and is a saturated alcohol.

5. A method according to claim 1 wherein the cured composite is made from an unsaturated polyester resin comprising a. An unsaturated polyester component which has a molecular weight of at least 500 g / mol, and b. A reactive diluent component which has a molecular weight of less than 500 g / mol.

6. A method according to claim 1 wherein the unsaturated polyester resin comprises at least 50% by weight of the unsaturated polyester component.

7. A method according to claim 5 wherein the reactive diluent component is an alkyl methacrylate or an alkanediol dimethacrylate.

8. A method according to claim 1 wherein the digestion of the cured composition uses methanol.

9. A method according to claim 1, wherein digesting the cured composite produces a mixture comprising a polyhydric alcohol and polyalkyl methacrylate, and the method further comprises using the polyhydric alcohol and / or the polyalkyl methacrylate to produce a recycled unsaturated polyester resin.

10. A method according to claim 1, wherein digesting the cured composite produces a mixture comprising a polyhydric alcohol and polyalkyl methacrylate, and the method further comprises depolymerising the polyalkyl methacrylate to yield alkyl methacrylate.

11. A method according to claim 10 which comprises using the alkyl methacrylate to produce a recycled unsaturated polyester resin.

12. A method according to claim 1 wherein the cured composite comprises filler and / or reinforcement components, and the method also comprises a step of separation of these components from the mixture produced by the digestion.

13. A recycled unsaturated polyester resin produced according to the process of claim 9.

14. A recycled cured composite obtained by curing an unsaturated polyester resin according to claim 13.

15. A recycled unsaturated polyester resin produced according to the process of claim 11.

16. A recycled cured composite obtained by curing an unsaturated polyester resin according to claim 15.

17. A recycled unsaturated polyester resin, said unsaturated polyester resin comprising an unsaturated polyester component, and wherein the unsaturated polyester component is an ester of a polyhydric alcohol, and further wherein one or both of the following apply:(i) the polyhydric alcohol has been obtained by digesting a cured composite using one or more alcohols to produce the polyhydric alcohol, or(ii) (ii) the unsaturated polyester component is an ester of a polyhydric alcohol with an alkyl methacrylate, and the alkyl methacrylate has been obtained by digesting a cured composite using one or more alcohols to produce a polyalkyl methacrylate, followed by a depolymerisation to produce the alkyl methacrylate.

18. A recycled cured composite obtained by curing an unsaturated polyester resin according to claim 17.

19. A method according to claim 1 or claim 2 wherein the unsaturated polyester component has a molecular weight of at least 500 g / mol.

20. A method according to any one of claims 1, 2 and 19 wherein the polyhydric alcohol has 2 to 4 alcohol groups and is a saturated alcohol.

21. A method according to any one of claims 1, 2, 19 and 20 wherein the cured composite is made from an unsaturated polyester resin comprising c. An unsaturated polyester component which has a molecular weight of at least 500 g / mol, and d. A reactive diluent component which has a molecular weight of less than 500 g / mol.

22. A method according to any one of claims 1, 2, and 19 to 21 wherein the unsaturated polyester resin comprises at least 50% by weight of the unsaturated polyester component.

23. A method according to claim 21 wherein the reactive diluent component is an alkyl methacrylate or an alkanediol dimethacrylate.

24. A method according to any one of claims 1, 2, and 19 to 23 wherein the digestion of the cured composition uses methanol.

25. A method according to any one of claims 1, 2, and 19 to 24, wherein digesting the cured composite produces a mixture comprising a polyhydric alcohol and polyalkyl methacrylate, and the method further comprises using the polyhydric alcohol and / or the polyalkyl methacrylate to produce a recycled unsaturated polyester resin.

26. A method according to any one of claims 1, 2, and 19 to 25, wherein digesting the cured composite produces a mixture comprising a polyhydric alcohol and polyalkyl methacrylate, and the method further comprises depolymerising the polyalkyl methacrylate to yield alkyl methacrylate.

27. A method according to claim 26 which comprises using the alkyl methacrylate to produce a recycled unsaturated polyester resin.

28. A method according to any one of claims 1, 2, and 19 to 27 wherein the cured composite comprises filler and / or reinforcement components, and the method also comprises a step of separation of these components from the mixture produced by the digestion.

29. A recycled unsaturated polyester resin produced according to the process of claim 25 or claim 27.

30. A recycled cured composite obtained by curing an unsaturated polyester resin according to claim 29.