PT117321B - HIGH PERFORMANCE UNSATURATED POLYESTER RESINS BASED ON RENEWABLE RESOURCES - Google Patents

Abstract

THIS INVENTION RELATES TO NEW UNSATURATED POLYESTER RESINS BASED ON BUILDING BLOCKS PARTIALLY OR ALMOST ENTIRELY DERIVED FROM RENEWABLE OR SUSTAINABLE RESOURCES. THE RESINS PRESENTED IN THE INVENTION ARE SUITABLE FOR THE MANUFACTURE OF FIBER REINFORCED POLYMER (FRP) COMPOSITE MATERIALS BY MEANS OF DIFFERENT PROCESSING TECHNIQUES, INCLUDING COLD AND HOT CURING PROCESSES. THE CURED RESINS DEVELOPED WITH THE PRESENT INVENTION HAVE MECHANICAL AND THERMOPHYSICAL PROPERTIES THAT EQUAL OR EXCEED THE PERFORMANCE OF CONVENTIONAL PETROCHEMICAL UNSATURATED POLYESTER RESINS.

Description

DESCRIPTION

HIGH PERFORMANCE UNSATURATED POLYESTER RESINS BASED ON RENEWABLE RESOURCES

Technical Field

[0001] The present disclosure relates to unsaturated polyester resins based on raw materials that are partially or almost entirely derived from renewable resources. The invention allows the production of unsaturated polyester resins which, after curing, exhibit mechanical and thermophysical properties similar to or superior to the properties of comparable conventional petrochemical unsaturated polyester resins.

State of the Art

[0002] Unsaturated polyester resins are thermosetting polymers that can be used to impregnate synthetic fibers in the manufacture of Fiber Reinforced Polymer (FRP) composite materials used in various structural applications. Due to their suitable balance between low cost, processing versatility and good mechanical and thermophysical properties, these resins have been among the most widely used thermosetting polymers in the FRP composites industry for several years. However, their production still depends significantly on petroleum-derived raw materials. The use of petrochemical monomers in the manufacture of polymers used in consumer products is expected to decline in the coming years due to the possible depletion of known reserves, the continued increase in crude oil extraction costs, more restrictive government regulations worldwide in favor of sustainability and the general demand by society for more environmentally friendly products. This context has promoted research into the production of polymers from monomers derived from renewable resources as an alternative to petroleum derivatives.

[0003] The production of sustainable thermosetting unsaturated polyester resins suitable for the manufacture of FRP composite materials, replacing petrochemical resins, is a significant challenge. Indeed, these resins must achieve mechanical, thermophysical and processing properties similar to conventional resins, while incorporating a significant and environmentally friendly renewable content. The growth of bio-based building block production from biorefineries provides supply capacity and progressive cost reduction of these raw materials, making sustainable unsaturated polyester resins strategically and environmentally relevant, in contrast to conventional ones.

[0004] The raw materials used for the synthesis of unsaturated polyester resins are dicarboxylic acids, dihydroxyl alcohols and a reactive diluent with at least one vinyl group. In order to maintain or improve the mechanical properties of such resins (when compared to conventional ones), it is known that a balance between aliphatic and aromatic or cyclic compounds within the polyester backbone must be maintained. The viscosity and mechanical properties of the resins of the present invention are largely due to the molar fractions between the diols 1,3-propanediol and isosorbide (aliphatic and cyclic, respectively).

[0005] As an example, 2,5-furan dicarboxylic acid is a potential replacement monomer for petroleum-derived diacids or anhydrides, such as phthalic anhydride and iso- and ortho-phthalic acids. This furan building block occupies a prominent position among the monomers for condensation polymers, as it generally provides higher mechanical strength and glass transition temperature (Tg) when compared to the above-mentioned aromatic diacids or even terephthalic acid. It is also known that polyesters based on 2,5-furan dicarboxylic acid exhibit a semicrystalline structure, but crystallize at a slower rate than polyesters containing an aromatic ring. This results in greatly improved barrier properties against oxygen, carbon dioxide and water vapor, which can be beneficial for various structural applications, particularly in more aggressive environments. Complete replacement of phthalic anhydride by 2,5-furan dicarboxylic acid on an industrial scale is still economically unfeasible due to the relatively high market prices of the latter monomer; however, prices have been decreasing substantially in recent years due to increased production of this renewable furan building block with increasing use for the production of plastics [1]

[0006] Isosorbide is another building block derived from renewable sources; when used as a monomer, it can provide polyester with a balance between high performance and sustainability. Isosorbide is a cyclic glycol structure that confers rigidity to the unsaturated polyester backbone structure, resulting in polyesters with a higher glass transition temperature than conventional aliphatic diols. However, the viscosity is significantly increased when high fractions of isosorbide are incorporated into the polyester structure, making it difficult to dilute it with the reactive diluent, most likely due to the presence of polysaccharides formed during reactor heating; this may limit its use in the processing of FRP composite materials that require low viscosities for fiber impregnation. US20040092703A1 [2] reported a way to overcome this limitation by dissolving isosorbide in water before being fed to the reactor where polyester polymerization occurs. Thus, isosorbide can be easily pumped into the esterification portion of the polyester process. US patent 8487041B2 [3] registered an unsaturated polyester containing isosorbide and itaconic acid, in the presence of 1,2-propylene glycol and/or 1,3-propanediol, maintaining a low viscosity of the polyester prepolymer using a combination of hydroquinone and toluhydroquinone as inhibitors. Example 9 of that patent shows a polyester prepolymer that is entirely bio-derived; however, after dilution in styrene, the final content of this resin was 65%. In contrast, no information was provided on the glass transition temperature. The lack of such information limits its range of applicability, especially with regard to its use as a matrix for the manufacture of FRP composite materials for structural applications, where the glass transition temperature has a significant influence on the maximum service temperature that can be considered in the design of the structural object. Furthermore, the resin curing process was carried out with initiators and accelerators suitable for cold molding processes, which prevents its use in rapid molding processes that require high curing temperatures.

[0007] Patents US20190375890A1 [4], US20170129994A1 [5] and US9580542B2 [6] reported a series of thermoplastic polyesters based on 2,5-furan dicarboxylic acid and isosorbide. However, the authors were able to verify that, for some applications or under some conditions of use, these polyesters do not present all the required properties. For example, (i) either they do not have adequate processability to impregnate the fibers during the production of FRP composites; (ii) either no information was provided on the elastic modulus and deformation at break, (iii) or the glass transition temperature was obtained by differential scanning calorimetry (DSC), not properly reflecting the changes in mechanical properties caused by the glass transition process. In fact, changes in material stiffness (or damping), which are very relevant for structural applications, are more accurately estimated by dynamic mechanical analysis (DMA). Thus, polyesters resulting from the synthesis between 2,5-furan dicarboxylic acid and isosorbide must be balanced by the addition of aliphatic structures (diols) to obtain a lower viscosity of the pure polymer. In contrast, the aromatic diacid or furan increases the solubility of the unsaturated polyester in vinyl monomers, especially in styrene, which allows the storage, handling and processing of the resin. The appropriate balance between (i) 2,5-furan dicarboxylic acid and phthalic anhydride; (ii) 2,5-furan dicarboxylic acid and isosorbide, and (iii) 2,5-furan dicarboxylic acid and vinyl monomers, were surprisingly found to ensure that most of the content (by weight) is derived from renewable resources, without impairing the mechanical and thermophysical properties, for different manufacturing methods such as hand rolling, vacuum infusion and pultrusion.

[0008] 1,3-Propanediol is a renewable aliphatic diol derived from the fermentation of corn sugar, having low viscosity (liquid at room temperature) and is capable of adjusting the viscosity of polyester with rigid or aromatic cyclic morphology, maintaining the mechanical and thermophysical properties of the product after curing. The state of the art of polyester resins and the respective patents, such as US20120157618A1 [7] and US20090312485A1 [8], report that the use of 1,3-propanediol instead of non-renewable aliphatic diols does not significantly affect the thermophysical properties of unsaturated polyester resins, especially their glass transition temperature. The present invention proposes the use of 1, 3-propanediol to decrease the viscosity of isosorbide-based polyester, and this approach unexpectedly improves the mechanical and thermophysical properties when compared to conventional polyester resins based on 1,2-propylene glycol and diethylene glycol.

[0009] The sustainability of unsaturated polyester can be further increased by replacing maleic anhydride (derived from petroleum) with fumaric acid. Fumaric acid is non-toxic and is formed naturally or can be obtained from by-products of the agri-food industry [9-11]. The present invention proposes the use of only fumaric acid (derived from renewable resources, such as the fermentation of sugarcane bagasse) as the unsaturated monomer in the main structure of the polyester, since it increases the renewable content of the polyester and, in addition, the double bond of fumarate is more reactive than that of maleate, resulting in a more complete radical polymerization and with less need for post-curing treatment. The balance between thermophysical properties and toughness is determined, among other parameters, mainly by the crosslinking density in the structure of the main chain of the unsaturated polyester. The higher the crosslinking density, the higher the heat deflection temperature and glass transition temperature; however, as the crosslinking density increases, the toughness decreases, requiring a balance between strength and ductility for each type of application. The invention presented in this document surprisingly managed to promote a good balance between the glass transition temperature and toughness, by adjusting the proportion between saturated and unsaturated acids in the polyester main chain structure.

[0010] The shrinkage of polyester, one of its historical disadvantages compared to other thermosetting resins, has been overcome in the present invention by incorporating dimerized acid segments into the polyester backbone structure. Dimeric acids are the main product of the oligomerization (dimerization) of unsaturated vegetable fatty acids such as tallow fatty acid as well as oleic or linoleic acid, and have been used as a raw material in polyester since the 1920s, especially for the production of alkyd resins for the coatings industry. Triglyceride-based acids are rich in long aliphatic chains and have a high molecular weight, which contributes to the high incorporation of bio-content in polyester. Recently, patent US7985826B2 [12] reported the preparation of unsaturated polyester based on soybean oil, 1,3-propanediol, maleic anhydride, ethylene glycol and dicyclopentadiene, to improve the surface quality of the resulting materials. However, after incorporation with styrene, the resin presented a biocontent of around 30%. The increase in the amount of dimerized fatty acids in the polyester structure leads to a relatively lower glass transition temperature, due to its amorphous structure and high conformational flexibility of the polymer main chains, which results in a flexible segment of the ester copolymers and a sacrifice of thermophysical properties. In addition, polyesters comprised of dimerized fatty acids present a segmented formation, biphasic or multiphasic structure and high deformation capacity. In the present invention, it was surprisingly found that dimerized fatty acids reduce polyester shrinkage, showing behavior similar to low-shrinkage additives, especially in moldings that require high temperatures during processing, maintaining the thermophysical properties of the cured resin.

[0011] Resins used as matrix in FRP composites must have a low enough viscosity and a long enough gel time to ensure adequate time for proper impregnation of the reinforcing fibers. Therefore, different variants of resin composition must be available to allow adjustment for processes such as pultrusion and vacuum infusion, and for simple lamination processes such as open mold applications, which are more prone to lower viscosity resins. Excessive resin viscosity can be overcome in different ways; for example, by increasing the amount of styrene to lower the target viscosity of the polyester resin. However, large amounts of reactive diluent tend to decrease the thermophysical properties of the cured resin - it is not recommended to use more than 40% (by weight) of styrene in the resin composition, and the molar excess with respect to the double bonds of the main chain should be less than 15%. Unreacted styrene or excess of other reactive monomers will result in a plasticizing effect, decreasing the modulus as well as the long-term performance. This can be a problem in structural elements exposed to high temperatures, such as building elements (e.g. roofs and facades), bridge decks and tank elements. The balance between low viscosity and high thermophysical properties can be achieved by altering the morphology and chemical composition of the diol present in the polyester backbone. In the present invention, it has been found that a combination of a low absolute viscosity aliphatic diol and a cyclic diol contributes to achieving this balance. A lower absolute viscosity should be governed by the higher aliphatic diol ratio, while an increase in the cyclic diol ratio provides better thermophysical properties to the resin. Furthermore, the crosslinking density of the prepolymer, defined by the ratio of saturated to unsaturated dicarboxylic acids, should be adjusted in a range of at least 1:2 and at most 1:4.

[0012] Furthermore, typical reactive diluents used in unsaturated polyester resins, such as styrene, are generally considered to be Hazardous Air Pollutants (HAPs) and/or Volatile Organic Compounds (VOCs), especially in the plausible occurrence of trace amounts of Ozone, since styrene epoxide is carcinogenic. Recently, extensive research efforts have been devoted to finding ways to eliminate or reduce the use of these highly hazardous reactive diluents. For example, methacrylate was reported by patent US20190031801A1 [13] as an alternative to replace styrene, since methacrylate contains polymerizable radicals through double bonds, which provide similar reactivity to styrene, but is less harmful to the environment.

[0013] In order to reduce styrene emission and also to replace it, several alternatives have been tested. The addition of paraffin with unsaturated polymer has proven effective, as it forms thin films on the resin surface. However, this approach reduces interlaminar adhesion in composites. It was reported in US20040220340A1 [14] that the complete replacement of styrene by acrylate-type monomers in unsaturated polyester resins is inadequate, as atmospheric oxygen slows down the polymeric reaction, leaving the surface sticky and uncured; this problem has been solved in the present invention.

[0014] One acrylate that has been investigated is 2-hydroxyethyl methacrylate (HEMA). At room temperature, HEMA is a colorless, viscous liquid. It is used as a monomer to produce several types of polymers. HEMA has hydrophilicity because it has a hydrophilic pendant group in the structure.

[0015] In general, acrylate-type polymers are well known for their physical properties, such as hardness, elasticity, crack resistance, and excellent oil and heat resistance. At room temperature, they behave like a rubber, since their glass transition temperature is below room temperature [15]. Several studies have shown HEMA as a suitable alternative to styrene [16-17]. US5747597A [18] demonstrated the feasibility of replacing styrene with acrylate in unsaturated polyester resin, and WO 99/23122 [19] also reported an unsaturated polyester resin free of styrene but with HEMA. However, it was noted that the main chain of the developed biobased unsaturated polyester is incompatible with the diluent monomer HEMA alone. Therefore, HEMA was used together with styrene as the diluent monomer in the developed unsaturated polyester resin, since the reactivity between HEMA and styrene has been previously reported [20]. This resulted in a smooth surface with satisfactory level of hardness and a non-sticky surface after curing. Furthermore, the resin was found to exhibit improved mechanical and thermophysical properties when compared to the conventional unsaturated polyester resin crosslinked with styrene alone. Emphasis was placed on reducing the percentage of styrene in the unsaturated polyester resin as much as possible while maintaining the properties required for performance under service conditions. Reducing the styrene concentration is an additional advantage of this innovative bio-based unsaturated polyester resin.

[0016] To overcome the disadvantages of the prior art, the present invention discloses acrylic building blocks based on carbonyl methacrylate compounds used to obtain polyester with lower styrene content. The use of 2-hydroxyethyl methacrylate is an alternative to reduce the styrene content, and is reported in this invention.

[0017] These facts are disclosed in order to illustrate the technical problem addressed by this disclosure.

General Description

[0018] The present invention relates to unsaturated polyester resins incorporating a high bio-derived content by weight, presenting similar or improved mechanical and thermophysical properties compared to conventional unsaturated polyester resins derived from petroleum.

[0019] The resin of the present invention is suitable for various processing techniques typically used to manufacture FRP composite materials, such as hand rolling, vacuum infusion, and pultrusion.

[0020] This new sustainable unsaturated polyester resin provides increased sustainability and versatility compared to conventional resins.

[0021] In a preferred mode, the present invention discloses a composition comprising unsaturated polyester resins, the resin comprising a prepolymer and at least one reactive diluent;

wherein the prepolymer is in an amount of 50% to 70%, preferably 60% (by weight);

and wherein the prepolymer and the at least one reactive diluent are derived from renewable natural resources.

[0022] In another embodiment, the present invention discloses a composition wherein the reactive diluent is a mixture of:

styrene and HEMA;

styrene, HEMA and pentaerythritol tetracrylate (PETA);

or styrene and PETA.

[0023] In another embodiment, the present invention discloses a composition in which the maximum amount of styrene in relation to the total amount of unsaturated polyester and reactive diluent is 30% (by weight), preferably 20% (by weight), more preferably 10% (by weight).

[0024] In another embodiment, the present invention discloses a composition comprising 20% (by weight) styrene, 10% (by weight) HEMA and 10% (by weight) PETA.

[0025] In another embodiment, the present invention discloses a composition in which the prepolymer is a reaction product obtained by the polycondensation of:

at least 1,3-propanediol and isosorbide as aliphatic and cyclic polyol, respectively;

at least one unsaturated C4-dicarboxylic acid or anhydride as an unsaturated dicarboxylic acid; or one dimerized fatty acid or one furan dicarboxylic acid, both as a saturated dicarboxylic acid.

[0026] In another embodiment, the present invention discloses a composition comprising an unsaturated polyester structure, the unsaturations being originated by bio-based fumaric acid.

[0027] In another embodiment, the present invention discloses a resin or cured resin comprising the composition of the present invention.

[0028] In another embodiment, the present invention discloses a resin or cured resin wherein 40% to 60% (by weight) comprises ester groups and is derived from renewable sources.

[0029] In another embodiment, the present invention discloses a product comprising the composition, resin or cured resin of the present invention, wherein the tensile strength, modulus of elasticity and strain at break are greater than or equal to 44 MPa, 2.9 GPa and 1.5%, respectively.

[0030] In another embodiment, the present invention discloses a product comprising the composition, resin or cured resin of the present invention, wherein the Tg is at least 51 °C, defined on the basis of DMA (dynamic mechanical analysis), namely from the beginning of the decay of the storage modulus curve.

[0031] In another embodiment, the present invention discloses an object, preferably a structural element comprising the product of the present invention.

[0032] In another embodiment, the present invention discloses a process for obtaining the composition of the present invention comprising the following steps:

React at least two dicarboxylic acids/anhydrides and at least two polyols to obtain a prepolymer;

wherein at least the two dicarboxylic acids/anhydrides comprise 0 to 1.5 mol% of a C36-dicarboxylic acid;

16 mol% of an aromatic C8-dicarboxylic acid; 0 to 12 mol% of a furan dicarboxylic acid; 31 to 38 mol% of an unsaturated C4-dicarboxylic acid;

wherein at least two polyols comprise 0 to 18 mol% of a C2-aliphatic diol; 17 to 38 mol% of a C3-aliphatic diol; 17 to 18 mol% of a C6-cyclic dihydric alcohol;

and where mol% is in terms of the total amount of prepolymer.

[0033] In another embodiment, the present invention discloses a process that further comprises the step of:

mixing the prepolymer with at least two reactive diluents comprising (i) 10 to 30 parts of styrene, (ii) 10 to 20 parts of 2-hydroxyethyl methacrylate and (iii) 10 to 20 parts of pentaerythritol tetraacrylate, to obtain a resin.

[0034] In another embodiment, the present invention discloses a process that further comprises the step of:

mixing the prepolymer with at least three reactive diluents comprising (i) 10 to 30 parts of styrene, (ii) 10 to 20 parts of 2-hydroxyethyl methacrylate and (iii) 10 to 20 parts of pentaerythritol tetraacrylate, to obtain a resin.

[0035] In another embodiment, the present invention discloses a process that further comprises the step of:

curing the resin by means of an open molding process in the presence of an accelerator, preferably a redox agent, to obtain an object or structural part comprising the cured resin.

[0036] In another embodiment, the present invention discloses a process that further comprises the step of:

post-curing the cured resin at 80 °C to 120 °C, preferably at 90 °C to 110 °C, even more preferably at 100 °C for at least 4 hours.

[0037] In another embodiment, the present invention discloses a process in which the accelerator is an amine or an organometallic compound.

[0038] In another embodiment, the present invention discloses a process in which the step of mixing the prepolymer to obtain a resin is carried out in the presence of an initiator, preferably comprising a peroxide, to obtain a cured resin.

[0039] In another embodiment, the present invention discloses a process in which the reaction step of at least two dicarboxylic acids/anhydrides and at least one polyol to obtain a prepolymer is carried out in the presence of hydroquinone and/or toluhydroquinone as a radical inhibitor.

[0040] In another embodiment, the present invention discloses a process in which the reaction step of at least two dicarboxylic acids/anhydrides and at least one polyol to obtain a prepolymer is carried out in the presence of imidazole or tetraisopropyl titanate as esterification catalysts.

[0041] In another embodiment, the present invention discloses a process in which the C36-dicarboxylic acid is a dimerized acid obtained from the dimerization of tallow.

[0042] In another embodiment, the present invention discloses a process wherein the unsaturated C4-dicarboxylic acid is fumaric acid derived from a non-petrochemical source.

[0043] In another embodiment, the present invention discloses a process in which the furan dicarboxylic acid is 2,5-furan dicarboxylic acid obtained from renewable resources.

[0044] In another embodiment, the present invention discloses a process in which the C6-cyclic dihydric alcohol is

1, 4:3, 6-dianhydro-D-glucitol or isosorbide derived from natural sugars.

[0045] In another embodiment, the present invention discloses the use of the composition, resin, cured resin or product of the present disclosure in the manufacture of fiber reinforced polymer composite materials for civil, naval, automotive, aerospace and wind energy structures.

[0046] In another embodiment, the present invention discloses the use of the composition, resin, cured resin or product of the present disclosure in manufacturing by hand lamination, vacuum infusion, filament winding, resin transfer molding and pultrusion.

Detailed Description

[0047] According to the invention, the prepolymer is a reaction product obtained by the polycondensation of (i) at least 1,3-propanediol and isosorbide as aliphatic and cyclic polyol, respectively, (ii) optionally a dimerized fatty acid as saturated dicarboxylic acid, and (iii) at least one unsaturated C4-dicarboxylic acid or anhydride as unsaturated dicarboxylic acid.

[0048] In another embodiment, the total amount of saturated acids should be balanced between the dimerized acid and/or building blocks comprising at least one aromatic dicarboxylic acid, e.g., phthalic acid (or its anhydride form) and, optionally, 2,5-furan dicarboxylic acid, respectively.

[0049] In one embodiment of the present invention, in the prepolymer, the molar amount of ethylene glycol or other dihydric alcohol derived from petroleum is at most 33%, relative to the total amount of glycol to be used in the reaction mixture.

[0050] In one embodiment of the present invention, in the prepolymer, the molar amount of 1,3-propanediol is (i) preferably at least 33% and at most 67%, (ii) more preferably at least 50% and at most 67% and (iii) even more preferably at least 60% and at most 67%, relative to the total amount of glycol to be used in the reaction mixture.

[0051] In one embodiment of the present invention, in the prepolymer, the molar amount of isosorbide is (i) preferably at least 25% and at most one third in percentage, (ii) more preferably at least 28% and at most one third in percentage and (iii) even more preferably at least 30% and at most one third in percentage, relative to the total amount of glycol to be used in the reaction mixture.

[0052] In one embodiment of the present invention, isosorbide must be diluted before being loaded into the reactor, in a solution comprising at least 15% and at most 30% (by weight) of water, relative to the total weight of isosorbide to be used in the reaction mixture.

[0053] In one embodiment of the present invention, the molar amount of 2,5-furan dicarboxylic acid relative to the total amount of saturated diacids is (i) preferably at least 50% up to full substitution, (ii) more preferably at least 75% up to full substitution and (iii) even more preferably full substitution.

[0054] In one embodiment of the present invention, the molar amount of relative dimerized fatty acid is (i) preferably at most 1.4%, (ii) more preferably at most 1.2% and (iii) even more preferably at most 1.0%, relative to the total molar amount of the monomers (diacids and diols) to be used in the reaction mixture.

[0055] In one embodiment of the present invention, the acid number of the prepolymer is (i) preferably in the range of 35 to 60 mgKOH/g resin, (ii) more preferably in the range of 35 to 55 mgKOH/g resin and (iii) even more preferably in the range of 35 to 50 mgKOH/g resin. The acid number of the prepolymer is determined by titration according to the International Organization for Standardization (ISO) according to ISO 2114:2000 [21].

[0056] In one embodiment, the weight average molecular weight (Mw) of the unsaturated polyester is (i) preferably at least 2500 g/mol and at most 7000 g/mol, and (ii) more preferably at least 3500 g/mol and at most 5000 g/mol, and (iii) even more preferably at least 3500 g/mol and at most 4000 g/mol.

[0057] In one embodiment, the number average molecular weight (Mn) of the unsaturated polyester is (i) preferably at least 1200 g/mol and at most 2000 g/mol, and (ii) more preferably at least 1400 g/mol and at most 2000 g/mol, and (iii) even more preferably at least 1500 g/mol and at most 2000 g/mol.

[0058] In one embodiment, because PRF composites comprising polymerized unsaturated polyester resins used in structural applications may be subjected to elevated temperatures according to the invention, the glass transition temperature (Tg) of the unsaturated polyester resins, measured from a dynamic mechanical analysis (DMA) based on the onset of decay of the storage modulus curve, is (i) preferably at least 60 °C, (ii) more preferably at least 65 °C, and (iii) even more preferably at least 70 °C.

[0059] In one embodiment, the prepolymer is advantageously prepared in the presence of at least one radical inhibitor selected from hydroquinone, benzoquinone or toluhydroquinone, (i) more preferably in the presence of toluhydroquinone, and (ii) even more preferably in the presence of hydroquinone and toluhydroquinone.

[0060] In one embodiment, the prepolymer is advantageously prepared in the presence of at least one esterification catalyst, preferably imidazole or tetraisopropyl titanate, more preferably in the presence of imidazole.

[0061] In one embodiment, the unsaturated polyester resin composition comprises more than one reactive diluent, preferably being styrene and acrylate type monomers.

[0062] In one embodiment of the present invention, a mixture of styrene and HEMA is used as a reactive diluent.

[0063] In another embodiment of the present invention, a mixture of styrene and PETA is used as a reactive diluent. PETA is obtained by the synthesis of 1 mole of pentaerythritol and 4 moles of methyl acrylate, the latter being a bio-based monomer.

[0064] In another embodiment of the present invention, a mixture of styrene, HEMA and PETA is used as a reactive diluent.

[0065] Under the definition of reactive diluent shall be any substance that reduces the viscosity of an unsaturated polyester resin for processing and becomes part of the resin during its subsequent curing by copolymerization.

[0066] In one embodiment of the present invention, the unsaturated polyester resin composition comprises at least 60% (by weight) prepolymer.

[0067] In an embodiment according to the invention, the maximum amount of styrene in the resin composition is (i) preferably at most 30% (by weight), (ii) more preferably at most 20% (by weight), and (iii) most preferably at most 10% (by weight), relative to the total amount of unsaturated polyester and reactive diluent present in the resin composition.

[0068] In one embodiment of the present invention, the amount of HEMA in the resin composition is (i) preferably at least 10% and at most 20% (by weight), (ii) more preferably at least 15% and at most 20% (by weight) and (iii) most preferably 20% (by weight), relative to the total amount of unsaturated polyester and reactive diluent present in the resin composition.

[0069] In the present invention, the amount of PETA in the resin composition is (i) preferably at least 10% and at most 20% (by weight), (ii) more preferably at least 15% and at most 20% (by weight), and (iii) most preferably 20% (by weight), relative to the total amount of unsaturated polyester and reactive diluent present in the resin composition.

[007 0] According to the invention, the resin can be cured by two distinct processes, depending on the application. In both processes, the resin is cured in the presence of a free radical initiator. The first curing process, for cold curing applications, is used in temperature ranges suitable for manual lamination and/or vacuum infusion, when the initiator is a redox, wherein the curing is carried out at a temperature (i) in the range of 10 to 80 °C, (ii) preferably in the range of 0 to 70 °C, and (iii) more preferably in the range of 10 to 60 °C. For cold curing processes, the present invention describes the use of an organic peroxide as a redox agent (initiator), more preferably methyl ethyl ketone peroxide (MEKP), in combination with at least one accelerator, more preferably cobalt octoate. The second curing process is for high temperature curing in processes such as pultrusion, where an accelerator is optionally required, since the curing process can be achieved for temperatures in the range of at least 170 °C and at most 180 °C. The present invention suggests the use of di-tert-butyl peroxide, di-tert-butyl diperphthalate, di-tert-butyl peroxide, methyl isobutyl ketone peroxide or tert-butyl peroxybenzoate.

[0071] The prepolymer synthesis was prepared by catalyzed bulk polycondensation, carried out in a 2-liter reactor (with bottom drain valve) with a 4-outlet top cover, equipped with a mechanical anchor blade stirrer, a thermocouple to control a heating blanket, a nitrogen inlet (one bubble per second), and a condenser connected to a Dean-Stark adapter to collect water (formed in the reaction and solubilization of the raw material).

[0072] According to the invention, the following steps must be carried out to prepare the prepolymer present in the resin composition:

load the reactor with isosorbide and water;

charging the reactor with: (i) unsaturated dicarboxylic acid and/or anhydride and, optionally, other diacids; (ii) aliphatic diols and, optionally, other diols; and (iii) adding the catalyst and a portion of at least one inhibitor;

increase the heating of the reactor to a temperature of 200 °C to 206 °C;

cool the reaction mixture when the unsaturated polyester prepolymer reaches an apparent viscosity of a maximum of 3000 cP or the acid number is less than 60. The reaction mixture should be cooled to a temperature preferably between 140 °C and 150 °C, and;

dilute the unsaturated polyester (prepolymer) with reactive diluent at a mixing temperature not exceeding 85 °C to obtain an unsaturated polyester resin.

[0073] Gel permeation chromatography (GPC) tests were performed to determine the number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the main chain of the polyester samples, using tetrahydrofuran as eluent, according to ISO 13885-1:2008 [22], at an approximate concentration of 1 mg/ml. The samples were filtered and injected into the system with columns packed with a monodisperse standard, i.e. polystyrene crosslinked with divinylbenzene (gel).

[0074] The viscosity test was carried out on a Cone & Plate viscometer instrument from REL (Research Equipment London Ltd.) according to ISO 2884-2:2003 [23], which consists of placing only two drops of resin on a surface which is subsequently pressed by a rotating cone (at constant speed). The viscosity was taken as the average value of 3 measurements.

[0075] Gel time was used as a parameter to monitor reactivity/gelation time. 12 g samples were placed in 160 mm long and 16 mm diameter glass tubes and tests were performed on a Gelnorm® gel timer instrument.

[0076] Barcol hardness tests were performed using the Barber Colman Barcol durometer, following the American Society for Testing of Materials standard.

American Society for Testing and Materials, ASTM) ASTM D2583-13 [24]. The test was conducted starting 3 mm from the edge of the specimen. In order to produce a uniform force distribution, the plate specimens were continuously supported on a rigid, hard, supported surface to minimize false data due to flexure of the material. Twenty-five tests were performed on each plate specimen. After testing, the average of the results was calculated and considered as Barcol hardness.

[0077] Dumbbell-shaped tensile specimens (type IA) were prepared in accordance with part 2 of ISO 527 [25]. The specimens have a prismatic shape with widening of the cross-section at the ends to avoid fracture in the gripper area. The cross-section transition is made with a constant radius of 24 ± 1 mm. The tests were carried out in displacement control, at a speed of 2 mm/min. From the test results, the average values of the tensile properties were obtained, namely the tensile strength, the modulus of elasticity and the deformation at rupture.

[0078] To measure the Tg of unsaturated polyester resins based on the onset of decay of the storage modulus curve, DMA tests were performed using a TA Instruments model DMA Q800 dynamic mechanical analyzer. Specimens with dimensions of 60 mm x 10 mm x 4 ± 0.5 mm were fabricated according to ASTM E1640-09 [26], and were tested in a bi-encased configuration in a 35 mm span, where the specimen is clamped at both ends and flexed at mid-span. The specimens were subjected to a deformation amplitude of 15 μιη at a constant oscillation frequency of 1 Hz and subjected to a temperature sweep at a constant heating rate of 2 °C/min, starting at -30 °C and ending at 150 °C. The Tg based on the peak tan δ was also determined.

Examples

The invention is now demonstrated by means of a series of examples and comparative experiments. All examples and experiments support the scope of the claims. The invention, however, is not restricted to the specific embodiments as shown in the following examples.

[0079] Examples 1, 2, 3 and 4 cover the main building blocks currently available, namely, 2,5-furan dicarboxylic acid (FDCA), isosorbide, 1,3propanediol, dimer acids, showing a considerable improvement compared to the state of the art by introducing a higher bio-content while maintaining the most suitable properties for the purpose of the resin, which are, inter alia, the basis of a matrix for the impregnation of fibers for the manufacture of FRP composites.

IA to 1C Examples

[0080] Examples 1A to 1C were prepared according to the standard synthesis procedure using the reagents listed in Table 1. These examples focus on the use of different ratios between phthalic anhydride and fumaric acid without changing the proportions of diols. Isosorbide, 1,3-propanediol, and fumaric acid were used as raw materials derived from renewable sources, while ethylene glycol and phthalic anhydride were derived from petroleum. Water was used to dissolve isosorbide prior to the reaction at a corresponding weight of 30% isosorbide. To carry out the curing process, methyl ethyl ketone peroxide and cobalt octoate were used as initiator and accelerator, respectively. The samples of Examples 1A to 1C were post-cured at 100 °C for 4 h to perform mechanical and thermophysical tests.

[0081] Examples IA to 10 show that the polyester prepolymer discovered by this invention is capable of containing a high content derived from renewable raw materials, always above 68%, reaching more than 76%.

[0082] Examples IA to 1C have acid numbers equal to or less than 50, which are very similar to those of conventional unsaturated polyesters produced in the petroleum industry.

[0083] The resins obtained from examples IA to 1C exhibit mechanical and thermophysical properties equal to or superior to those of conventional unsaturated polyester resins derived from petroleum, as can be seen in Table 1.

[0084] The resins of examples 1A and 1B have a glass transition temperature equal to or higher than those derived from petroleum, with the advantage of having a renewable content greater than 44% by weight.

[0085] The different ratios between petroleum-derived phthalic anhydride and bio-derived fumaric acid presented in examples 1Ά to 1C show that the invention is capable of presenting different viscosity ranges, which allows it to be used as a matrix for different manufacturing techniques for the FRP composites industry, namely, manual lamination, vacuum infusion and pultrusion.

[0086]

Table 1: IA to 1C examples

Monomer Unit Examples AI 1B 1C Phthalic anhydride mol % 9, 47 11, 84 15.79 Fumaric acid mol % 37.89 35.53 31.58 1,3-propanediol mol % 17.54 17.54 17.54 Isosorbide mol % 17.54 17.54 17.54 Ethylene glycol mol % 17.54 17.54 17.54 Hydroquinone ppm 200 200 200 Toluhydroquinone ppm 200 200 200 Imidazole g 3.0 3, 0 3.0 Prepolymer Reaction time h 5 7 7 acidity index mgKOH/g 38 45 50 Mn g/mol 1564 1458 1421 M _w g/mol 2766 2756 3995 Dispersivity (D) adm. 1.77 1.89 2, 81 Viscosity at 125 °C cP 1150 1900 1700 Bio-content weight % 76.8 73.7 68.7 Incorporation Styrene Q. The 20 20 20 HEMA Q. The 20 20 20 Resin Viscosity at 25 °C cP 750 1050 780 Bio-content weight % 46.1 44.2 41.2 Healing MEKP weight % 2 2 2 Cobalt octoate weight % 1 1 1 Gel time at 25 °C min 106 94 90 Properties Tensile strength MPa 59 60 55 Modulus of elasticity GPa 3.3 3, 9 3.2 Deformation at break Q. The 2.5 2, 0 2.4 Hardness Barcol 31 33 30 T _g E' (tan δ) °C 70 (106) 62 (95) 56 (86)

Examples 2A and 2B

[0087] Examples 2A and 2B were prepared according to the standard synthesis procedure using the reagents listed in Table 2, where partial or total replacement of phthalic anhydride by 2,5-furan dicarboxylic acid derived from renewable sources was tested. Water was used to dissolve isosorbide prior to the reaction at a corresponding weight of 30% isosorbide. To carry out the curing process, MEKP and cobalt octoate were used as initiator and accelerator, respectively. The samples of examples 2A and 2B were post-cured at 100 °C for 4 h to perform mechanical and thermophysical tests.

[0088] Examples 2A and 2B show a considerable increase in Tg, reaching up to 70 °C, based on the onset of the decay of the storage modulus curve; surprisingly, the invention allowed to achieve mechanical performance equal to or superior to that of petroleum-derived polyester resins. This demonstrates that 2,5-furan dicarboxylic acid, a bio-derived monomer used almost exclusively by the packaging and paint industry, can be used as a building block for the synthesis of high-performance and environmentally friendly unsaturated polyester resins for structural FRP applications.

[0089] Surprisingly, the high viscosity resulting from the synthesis of polyester based on isosorbide and 2,5-furan dicarboxylic acid, reported in the scientific literature and in other patents, was overcome here by adjusting the reaction inhibitors, especially toluhydroquinone. Viscosities between 1200 cP and 1300 cP shown by examples 2A and 2B are competitive with their petroleum-derived counterparts that are currently available for the manufacture of PRF composites by the pultrusion process.

[0090] Examples 2A and 2B show that the unsaturated polyester resin developed in this invention achieves high mechanical and thermophysical properties with biocontent of up to 55%, reaching almost 60%.

[0091] Table 2: Examples 2A and 2B

Monomer Unit Examples 2A 2B Phthalic anhydride mol % 5, 92 - FDCA mol % 5, 92 11.84 Fumaric acid mol % 35.53 35.53 1,3-propanediol mol % 35, 09 35.09 Isosorbide mol % 17.54 17.54 Hydroquinone ppm 200 200 Toluhydroquinone ppm 200 200 Imidazole g 3, 0 3.0 Prepolymer Reaction time h 7 6 acidity index mgKOH/g 46 42 Mn g/mol 1404 1965 M _w g/mol 5601 3181 Dispersivity (D) adm. 3, 99 1, 62 Viscosity at 125 °C cP 2200 2700 Bio-content weight % 91, 9 99.8 Incorporation Styrene g. o 20 20 HEMA O.o 20 20 Resin Viscosity at 25 °C cP 1290 1250 Bio-content weight % 55.2 59, 8 Healing MEKP weight % 2 2 Cobalt octoate weight % 1 1 Gel time at 25 °C min 86 90 Properties Tensile strength MPa 62 59

Modulus of elasticity GPa 3, 4 4.0 Deformation at break O.o 2.3 1, 6 Hardness Barcol 30 32 T _s E' (tan δ) °C 65 (99) 70 (102)

Examples 3A and 3B

[0092] Examples 3A and 3B were prepared according to the standard synthesis procedure using the reagents listed in Table 3, where partial replacement of phthalic anhydride with dimerized fatty acid derived from renewable sources was tested. Water was used to dissolve isosorbide prior to the reaction at a corresponding weight of 30% of isosorbide. To carry out the curing process, MEKP and cobalt octoate were used as initiator and accelerator, respectively. The samples of examples 3A and 3B were post-cured at 100 °C for 4 h to perform mechanical and thermophysical tests.

[0093] Examples 3A and 3B show that the invention allows replacing petroleum-derived saturated dicarboxylic anhydride (or acid) with dimerized fatty acids derived from tallow, which increases the amount of renewable content in the invention. By partially or fully replacing phthalic anhydride, the invention surprisingly provides Tg above 60 °C based on the onset of the storage modulus decay.

[0094] Examples 3A and 3B present viscosities and gel times suitable for use in the manufacture of composite materials that require more time to impregnate the fibers and need less shrinkage, such as large-sized FRP composites used as faces of sandwich panels.

[0095]

Table 3: Examples 3Ά and 3B

Monomer Unit Examples 3A 3B Phthalic anhydride mol % 12, 18 10, 66 Dimerized fatty acid mol % 1.35 1, 18 Fumaric acid mol % 33, 83 35.53 1,3-propanediol mol % 35, 09 35, 09 Isosorbide mol % 17.54 17.54 Hydroquinone ppm 200 200 Toluhydroquinone ppm 200 200 Imidazole g 3, 0 3, 0 Prepolymer Reaction time h 7 7 acidity index mgKOH/g 44 45 Mn g/mol 1693 1553 M _w g/mol 7153 3490 Dispersivity (D) adm. 4.22 2.25 Viscosity at 125 °C cP 1460 1410 Bio-content weight % 84.5 86, 2 Incorporation Styrene O.o 20 20 HEMA the the 20 20 Resin Viscosity at 25 °C CP 820 860 Bio-content weight % 50.7 51.7 Healing MEKP wt. % 2 2 Cobalt octoate wt. % 1 1 Gel time at 25 °C min 103 129 Properties Tensile strength MPa 46 44 Modulus of elasticity GPa 2, 9 3, 2 Deformation at break the the 2, 0 1.5 Hardness Barcol 28 24 T _s E' (tan δ) °C 60 (91) 61 (92)

Examples 4A and 4B

[0096] Examples 4A and 4B were prepared according to the standard synthesis procedure using the reagents listed in Table 4. These examples do not feature petroleum-derived glycols in their formulation. Water was used to dissolve isosorbide prior to the reaction at a corresponding weight of 30% isosorbide. To perform the curing process, MEKP and cobalt octoate were used as initiator and accelerator, respectively. The samples of examples 4A and 4B were post-cured at 100 °C for 4 h to perform mechanical and thermophysical tests.

[0097] Examples 4A and 4B present bio-content above 50%, with viscosities similar to those of petroleum-derived unsaturated polyester resins to be used as polymeric matrices in the FRP composites industry.

[0098] According to Examples 4A and 4B, the invention surprisingly allows the use of dihydric alcohols entirely derived from renewable resources, which can replace their petroleum-derived equivalents while maintaining or even improving mechanical properties.

[0099]

Table 4: Examples 4A and 4B

Monomer Unit Examples 4A 4B Phthalic anhydride mol % 11.84 9.47 Fumaric acid mol % 35.53 37.89 1,3-propanediol mol % 35.09 35, 09 Isosorbide mol % 17.54 17.54 Hydroquinone ppm 200 200 Toluhydroquinone ppm 200 200 Imidazole g 3 3 Prepolymer Reaction time h 7 8 acidity index mgKOH/g 47 48 Mn g/mol 1452 1239 M _w g/mol 3593 2588 Dispersivity (D) adm. 2, 47 2.09 Viscosity at 125 °C cP 1500 1700 Bio-content weight % 84, 1 87, 1 Incorporation Styrene the the 20 20 HEMA the the 20 20 Resin Viscosity at 25 °C cP 800 820 Bio-content weight % 50, 4 52.3 Curing MEKP weight % 2 2 Cobalt octoate weight % 1 1 Gel time at 25 °C min 87 97 Properties Tensile strength MPa 62 62 Modulus of elasticity GPa 3.3 3, 4 Deformation at break O.o 2.4 2.2 Hardness Barcol 31 32 T _s E' (tan δ) °C 65 (95) 64 (96)

Example 5

[00100] The polyester resin obtained from Example 2B was subjected to a gel time test at 180 °C with 1.0% tert-butyl peroxybenzoate (e.g., Trigonox C™) and 0.5% methyl isobutyl ketone peroxide (e.g., Trigonox HMa ^™ ) as initiator and accelerator, respectively. The gel time was 1 min and 11 seconds, which shows that the invention allows embodiments based on 2,5-furan dicarboxylic acid, which can be used in the pultrusion process.

Example 6

[00101] The polyester resin obtained from Example 3B was subjected to a gel time test at 180 °C with 1.0% tert-butyl peroxybenzoate (e.g., Trigonox C ^™ ) and 0.5% methyl isobutyl ketone peroxide (e.g., Trigonox HMa ^™ ) as initiator and accelerator, respectively. The gel time was 57 seconds, indicating fast reactivity and a very short cure time at elevated temperatures in the dimerized fatty acid-based embodiment. This parameter is important for hot processing techniques, which require reduced shrinkage.

Example 7

[00102] The polyester resin obtained in Example 4A was subjected to a gel time test at 180 °C with 1.0% tert-butyl peroxybenzoate (e.g., Trigonox C ^™ ) and 0.5% methyl isobutyl ketone peroxide (e.g., Trigonox HMa ^™ ) as initiator and accelerator, respectively. The gel time was 1 minute and 10 seconds, showing that the invention can be used in hot processing techniques.

Example 8

[00103] The prepolymer obtained in Example 4A was incorporated into a mixture of reactive diluents, in a ratio of 60/20/10/10 parts (by weight) of prepolymer, styrene, HEMA and PETA, respectively, resulting in an unsaturated polyester resin with 54% bio-content. Peroxide and metal salt were used to accelerate the curing of the resin, namely MEKP and cobalt octoate as initiator and accelerator, respectively. After 24 hours at room temperature, the resin was post-cured at 100 °C for 4 hours. The cured product had an average Barcol hardness of 25 and a tensile modulus of elasticity of 3.5 GPa. The glass transition temperatures from the beginning of the decay of the storage modulus curve and the tan δ peak were 55 °C and 95 °C, respectively.

Example 9

[00104] The prepolymer obtained in Example 4A was incorporated into a mixture of reactive diluents, in the proportion of 60/20/20 parts (by weight) of prepolymer, styrene and PETA, respectively, resulting in an unsaturated polyester resin with 58% bio-content. Peroxide and metal salt were used to accelerate the curing of the resin, namely MEKP and cobalt octoate as initiator and accelerator, respectively. After 24 hours at room temperature, the resin was post-cured at 100 °C for 4 hours. The glass transition temperatures from the beginning of the decay of the storage modulus curve and the tan δ peak were 51 °C and 126 °C, respectively.

[00105] The disclosure should not be seen in any way as restricted to the described embodiments and a person of ordinary skill in the art will foresee many possibilities for modifications thereof.

[00106] The modalities described above are combinable.

[00107] The following claims further set out particular modalities of disclosure.

References

[1] Ali Hussain Motagamwala, Wangyun Won, Canan Sener, David Martin Alonso, Christos T. Maravelias, and James A. Dumesic. Toward biomass-derived renewable plastics: Production of 2,5-furandicarboxylic acid from fructose. Science Advances, 4(1), 2018.

[2] Ted Germroth, Sam Turner, and Lanny Treece. Method for making isosorbide containing polyesters, May 2004. US Patent 2004/0092703 AI.

[3] Marian Henryk Szkudlarek, Johan Franz Gradus Antonius Jansen, and Stefanus Jacobus Duyvestijn. Unsaturated polyester, Jul 2013. US Patent 8,487,041 B2.

[4] Nicolas Jacquel Gabriel Degand, René Saint-Loup, Matheus Adrianas Dam, and Bing Wang. 2,5-furandicarboxylic acid-based polyesters, Dec 2019. US Patent 2019/0375890 A1.

[5] Laszlo Sipos, Gerardus Johannes Maria Gruter, Jeffrey John Kolstad, Gabriel Degand, Nicolas Jacquel, René SaintLoup, Matheus Adrianus Dam, and Joseph D. Schroeder. Polyesters comprising 2,5-furandicarboxylate and saturated diol units having a high glass transition temperature, May 2017. US Patent 2017/0129994 AI.

[6] Debkumar Bhattacharjee and Kalyan Sehanobish. FDCAbased polyesters made with isosorbide, Feb 2017. US Patent 9,580,542 B2.

[7] Marian Henryk Szkudlarek and Johan Franz Gradus Antonius Jansen. Unsaturated polyester resin, Jul 2012. US Patent 2012/0157618 A1.

[8] Matthew Arthur Page, Hari Babu Sunkara, and Judith Johanna Van Gorp. Unsaturated polyester resin compositions comprising 1,3-propanediol, Dec 2009. US Patent 2009/0312485 AI.

[9] Feng Guo, Min Wu, Zhongxue Dai, Shangjie Zhang, Wenming Zhang, Weiliang Dong, lie Zhou, Min Jiang, and Fengxue Xin. Current advances on biological production of fumaric acid. Biochemical Engineering Journal, 153: 107397, 2020.

[10] Sang Yup Lee, Hyun Uk Kim, Tong Un Chae, Jae Sung Cho, Je Woong Kim, Jae Ho Shin, Dong In Kim, Yoo-Sung Ko, Woo Dae Jang, and Yu-Sin Jang. A comprehensive metabolic map for production of bio-based chemicals. Nature Catalysts, 2(1):18 33, 2019.

[11] F.S. Carta, C.R. Soccol, L.P. Ramos, and J.D. Fontana. Production of fumaric acid by fermentation of enzymatic hydrolysates derived from cassava bagasse. Bioresource Technology, 68(1):23 28, 1999. Bioprocessing and Characterization of Lignocellulosics.

[12] Hildeberto Nava and Lianzhou Chen. Molding resins using renewable resource components, Jul 2011. US Patent 7,985,826 B2.

[13] Giuseppe R. Palmese, John Joseph La Scala, Joshua Matthew Sadler, and Anh-Phuong Thy Lam. Renewable Bio-Based (Meth)Acrylated Monomers as Vinyl Ester Cross-Linkers, Jan 2019. US Patent 2019/0031801 AI.

[14] John McAlvin, Daniel Oakley, Paul Hutson, David Zwissler, and Thomas Folda. Styrene-free unsaturated polyester resin compositions for coating applications, Nov 2004. US Patent 2004/0220340 AI.

[15] Kingsley Kema Ajekwene. Properties and Applications of Acrylates. In Angel Serrano-Aroca and Sanjukta Deb, editors, Acrylate Polymers for Advanced Applications, chapter 3. IntechOpen, Rijeka, 2020.

[16] Linchon B. Mehta, Kunal K. Wadgaonkar, and Ramanand N. Jagtap. Synthesis and characterization of high biobased content unsaturated polyester resin for wood coating from itaconic acid: Effect of various reactive diluents as an alternative to styrene. Journal of Dispersion Science and Technology, 40(5):756 765, 2019.

[17] Ana C. Fonseca Inês M. Lopes, Jorge F.J. Coelho, and Arménio C. Serra. Synthesis of unsaturated polyesters based on renewable monomers: Structure/properties relationship and crosslinking with 2-hydroxyethyl methacrylate. Reactive and Functional Polymers, 97:1-11, 2015.

[18] Yukiko Fujita, Shinya Ueno, Yoko Kawasaki, Kumiko Fukakusa, Hidefumi Matsuya, Tomomasa Mitania, Akira Komori, and Mika Matsumura. Durable resin composition and coating material composition, May 1998. US Patent 5747597.

[19] Richard M. Anders, Kenneth R. Anders, and Dale K. Becker. Nonstyrenated polyester and vinylester resins, May 1999. WO 99/023122.

[20] Kun Liang, Marco Dossi, Davide Moscatelli, and Robin A. Hutchinson. An Investigation of Free-Radical Copolymerization Propagation Kinetics of Styrene and 2Hydroxyethyl Methacrylate. Macromolecules, 42(20):7736 7744, 2009.

[21] ISO 2114:2000. Plastics (polyester resins) and paints and varnishes (binders) — Determination of partial acid value and total acid value. Technical report, International Organization for Standardization, Geneva, Switzerland, 2000.

[22] ISO 13885:2008. Gel permeation chromatography (GPC) — Part 1: Tetrahydrofuran (THF) as eluent. Technical report, International Organization for Standardization, Geneva, Switzerland, 2008.

[23] ISO 2884:2003. Paints and varnishes — Determination of viscosity using rotary viscometers-Part 2: Disc or bali viscometer operated at a specified speed. technical report,

International Organization for Standardization, Geneva, Switzerland, 2003.

[24] ASTM D2583-13a. Standard Test Method for Indentation Hardness of Rigid Plastics by Means of a Barcol Impressor. Technical report, ASTM International, West Conshohocken, PA, 2013.

[25] ISO 527-2. Plastics — Determination of tensile properties — Part 2: Test conditions for molding and extrusion plastics. Technical report, International Organization for Standardization Geneva, Switzerland, 2012.

[26] ASTM E1640-09. Standard test method for assignment of the glass transition temperature by dynamic mechanical analysis. Technical report, ASTM International, West Conshohocken, Pennsylvania, 2009.

Claims (20)

1) Composition comprising unsaturated polyester resins, characterized by: a) a prepolymer and b) at least one reactive diluent; where the prepolymer is a mixture of: (i) at least 1,3-propanediol and isosorbide as aliphatic and cyclic polyol, respectively; (ii) at least one unsaturated C4-dicarboxylic acid or anhydride as an unsaturated dicarboxylic acid; or (iii) a dimerized fatty acid or furan dicarboxylic acid, both as a saturated dicarboxylic acid; and is in an amount, expressed by weight, of 50% to 70%, preferably 60%; and where the reactive diluent is a mixture of: i) styrene and 2-hydroxyethyl methacrylate (ΗΕΜΆ); íí) styrene, ΗΕΜΆ and pentaerythritol tetraacrylate (PETA); or iii) styrene and PETA; where the maximum amount of styrene in relation to the total amount of unsaturated polyester and reactive diluent, expressed by weight, is 30%, preferably 20%, more preferably 10%. 2) Composition according to claim 1, characterized by comprising 20% styrene, 10% HEMA and 10% PETA, these percentages being expressed by weight. 3) Composition according to any one of the previous claims, characterized by comprising an unsaturated polyester structure, the unsaturations originating from fumaric acid. 4) Resin or cured resin characterized by comprising the composition of any one of claims 1-3. 5) Resin or cured resin according to the previous claim, characterized in that 40% to 60% of its weight contains ester groups. 6) Process for obtaining the composition of any one of claims 1 to 3, characterized by reacting at least two dicarboxylic acids and/or anhydrides and at least two polyols to obtain a prepolymer; wherein at least two dicarboxylic acids and/or anhydrides comprise 0 to 1.5 mol% of a C36-dicarboxylic acid; 0 to 16 mol% of an aromatic C8-dicarboxylic acid; 0 to 12 mol% of a furan dicarboxylic acid; 31 to 38 mol% of an unsaturated C4-dicarboxylic acid; wherein the at least two polyols comprise 0 to 18 mol% of a C2-aliphatic diol; 17 to 38 mol% of a C3-aliphatic diol; 17 to 18 mol% of a C6-cyclic dihydric alcohol; and wherein mol% is in terms of the total amount of prepolymer. 7) Process according to the previous claim, characterized by further comprising the step of: mixing the prepolymer with at least two reactive diluents comprising: (i) 10 to 30 parts styrene, (ii) 10 to 20 parts ΗΕΜΆ and (iii) 10 to 20 parts PETA, to obtain a resin. 8) Process, according to claim 6, characterized by further comprising the step of: mixing the prepolymer with at least three reactive diluents comprising: (i) 10 to 30 parts of styrene, (ii) 10 to 20 parts of ΗΕΜΆ and (iii) 10 to 20 parts of PETA, to obtain a resin. 9) Process, according to claim 7 or 8, characterized by further comprising the step of: curing the resin by an open molding process in the presence of an accelerator, preferably a redox agent, to obtain an object comprising the cured resin. 10) Process, according to the previous claim, characterized by further comprising the step of: post-curing the cured resin at 80 °C to 120 °C, preferably at 90 °C to 110 °C, even more preferably at 100 °C for at least 4 hours. 11) Process according to claim 9, characterized in that the accelerator is an amine or an organometallic compound. 12) Process according to claim 7 or 8, characterized in that the step of mixing the prepolymer to obtain a resin is carried out in the presence of a curing initiator, preferably comprising a peroxide, to obtain a cured resin. 13) Process according to claims 6-12, characterized in that the reaction step of at least two dicarboxylic acids and/or anhydrides and at least one polyol to obtain a prepolymer is carried out in the presence of hydroquinone and/or toluhydroquinone as a radical inhibitor. 14) Process according to claims 6-13, characterized in that the reaction step of at least two dicarboxylic acids and/or anhydrides and at least one polyol to obtain a prepolymer is carried out in the presence of imidazole or tetraisopropyl titanate as esterification catalysts. 15) Process according to any one of claims 6-14, characterized in that the C36-dicarboxylic acid is a dimerized acid obtained from the dimerization of tallow. 16) Process according to any one of claims 6-15, characterized in that the unsaturated C4-dicarboxylic acid is fumaric acid. 17) Process according to any one of claims 6-16, characterized in that the furan dicarboxylic acid is 2,5-furan dicarboxylic acid. 18) Process according to any one of claims 6-17, characterized in that the C6-cyclic dihydric alcohol is 1,4:3,6-dianhydro-D-glucitol or isosorbide. 19) The use of the composition, resin or cured resin according to any one of claims 1 to 5, in the manufacture of fiber-reinforced polymer composite materials for civil, naval, automotive, aerospace and wind energy structures. 20) The use of the composition, resin or cured resin of any one of claims 1 to 5 in manufacturing by hand lamination, vacuum infusion, filament winding, resin transfer molding and pultrusion.