Melt processing of ethylene 2,5-furandicarboxylate polyester

Abstract

Process comprising subjecting poly(ethylene-2,5-furandicarboxylate) to (i) crystallizing, (ii) storing, (iii) drying, and (iv) melt processing, wherein the poly(ethylene-2,5-furandicarboxylate) comprises at most 2.1 %wt of units derived from diethylene glycol and is contacted with oxygen during one or more of the steps (i), (ii) and (iii).

Description

[0001] FUR352 PD

[0002] MELT PROCESSING OF ETHYLENE 2,5-FURANDICARBOXYLATE POLYESTER

[0003] Technical Field

[0004] The present invention relates to a process for melt processing of poly(ethylene-2,5-furandicarboxylate).

[0005]

[0006] 2,5-Furandicarboxylic acid (FDCA) is known in the art to be a highly promising building block for replacing petroleum-based monomers in the production of high performance polymers such as the polyester poly(ethylene-2,5-furanoate) (PEF). In recent years FDCA and PEF have attracted a lot of attention. PEF can be bio-based and recyclable with superior performance properties compared to today's widely used plastics. These materials could significantly reduce the dependence on petroleum-based polymers and plastics while at the same time allowing for a more sustainable management of global resources.

[0007] Comprehensive research was conducted to arrive at a technology for preparing FDCA and PEF in a commercially viable way.

[0008] FDCA is typically obtained by oxidation of molecules having furan moieties, e.g. 5-hydroxymethylfurfural (5-HMF) and the corresponding 5-HMF esters or 5-HMF ethers that are typically obtained from plant-based sugars, e.g. by sugar dehydration. A broad variety of oxidation processes is known from the prior art using enzymes or metal containing catalysts such as described in WO2010 / 132740 and WO2011 / 043660.

[0009] While a lot of research was directed at the efficient production of FDCA monomer in the early days of the technology, researchers soon realized that arriving at efficient processes for preparing high-performance polyesters from FDCA was at least as challenging. FDCA is oftentimes considered a structural and functional analogue to terephthalic acid (TA) which is used in the production of the widely used polyester polyethylene terephthalate (PET). However, techniques known from the PET industry frequently were found not to be suitable to produce high-performance PEF.

[0010] With the further development of the manufacture of PEF and its applications, It was found that in many cases it is advantageous to improve the optical properties of PEF. In the processes of WO 2022 / 043500 and WO 2022 / 043501, optical properties can be improved by carrying out both solid state polymerization and crystallization under an inert gas atmosphere. A disadvantage of an inert atmosphere is that it tends to be cumbersome to exclude oxygen.

[0011] Even if the colour of the poly(ethylene-2,5-furandicarboxylate) seemed good after manufacture, including storage and subsequent drying, the colour after melt processing frequently was found to have substantially deteriorated. Without wishing to be bound to anyFUR352 PD

[0012] theory, it is thought that the exposure to air during previous steps affects the resin resulting in a more highly colored product after melt processing.

[0013] An objective of the present invention was to be able to prepare poly(ethylene-2,5-furandicarboxylate), allow it to cool to allow for storage and optionally transport, and subsequently dry and melt process such poly(ethylene-2,5-furandicarboxylate) without requiring to exclude the presence of oxygen especially during crystallization, storage and drying.

[0014] Disclosure of the invention

[0015] We now have surprisingly found that the above-mentioned objective can be attained by reducing the amount of diethylene glycol derived units.

[0016] The present invention relates to a process comprising melt processing of poly(ethylene-2,5-furandicarboxylate) which process comprises (i) crystallizing poly(ethylene-2,5-furandicarboxylate) to obtain crystallized or semi-crystallized poly(ethylene-2,5-furandicarboxylate), (ii) storing the crystallized or semi-crystallized poly(ethylene-2,5-furandicarboxylate), (iii) drying the stored poly(ethylene-2,5-furandicarboxylate) of step (ii) to obtain dried poly(ethylene-2,5-furandicarboxylate), and (iv) subjecting the dried poly(ethylene-2,5-furandicarboxylate) to melt processing, wherein the poly(ethylene-2,5-furandicarboxylate) comprises at most 2.1 % by weight (%wt) of units derived from diethylene glycol based on amount of poly(ethylene-2,5-furandicarboxylate) and measured by1H-NMR and the poly(ethylene-2,5-furandicarboxylate) is in contact with oxygen during one or more steps from the group consisting of the crystallization step (i), the storing step (ii) and the drying step (iii).

[0017] Modes for carrying out the invention

[0018] Hereinafter, the subject-matter of the invention is discussed in more detail wherein preferred embodiments of the invention are disclosed. It is particularly preferred to combine two or more preferred embodiments to obtain an especially preferred embodiment.

[0019] It is possible to contact poly(ethylene 2,5-furandicaboxylate) according to the invention with oxygen with limited effect on the optical properties after melt processing. The limited effect will result in less highly colored product which is measured by absorption in the LIV / VIS spectrum as described in the examples.

[0020] Generally, the contact with oxygen will consist of contact with air by not excluding contact with air.

[0021] The use of poly(ethylene-2,5-furandicarboxylate) having a strongly reduced content of units derived from diethylene glycol, was found to be especially advantageous if the poly(ethylene-2,5-furandicarboxylate) was in contact with oxygen during the drying of step (iii). In this embodiment, the poly(ethylene-2,5-furandicarboxylate) can also be in contactFUR352 PD

[0022] with oxygen during step (i) and / or (ii). Furthermore, it was found that the difference with conventional poly(ethylene-2,5-furandicarboxylate) was especially pronounced if the poly(ethylene-2,5-furandicarboxylate) was in contact with oxygen in at least two of the steps from the group consisting of the crystallization of step (i), the storing of step (ii) and the drying of step (iii).

[0023] The poly(ethylene 2,5-furandicaboxylate) preferably is prepared from the reactants 2,5-furandicarboxylic acid and ethylene glycol. These reactants will react by esterification and polycondensation. It is known in the art that ethylene glycol can undergo ether formation with other ethylene glycol molecules during esterification thereby preparing higher molecular weight diols with an ether functionality especially diethylene glycol. These ether compounds can become incorporated into the final polyester and are known to influence the properties of the resulting polyester. Certain compounds can suppress such ether formation and are oftentimes labelled DEG suppressants indicating that they are directed at reducing the formation of DEG. Various DEG suppressants can be used. Well known DEG suppressants are ammonium compounds, in particular tetraethyl ammonium hydroxide, alkali phosphates, in particular sodium dihydrogen phosphate and disodium hydrogen phosphate. Further information is disclosed for example in WO2015 / 137805, W02022 / 043500 and WG2022 / 2043501.

[0024] Preferably, the poly(ethylene-2,5-furandicarboxylate) is obtained by a) providing or preparing a starting composition comprising 2,5-furandicarboxylic acid and ethylene glycol, b) subjecting the starting composition in the presence of a compound suppressing the formation of diethylene glycol to elevated temperature to produce an intermediate ester composition, and c) contacting the intermediate ester composition with a polycondensation catalyst at polycondensation conditions to produce the poly(ethylene-2,5-furandicarboxylate) comprising at most 2.1 % %wt of units derived from diethylene glycol. It will be understood that the units derived from diethylene glycol include any residue which would be obtained if diethylene glycol were used in the polymerization.

[0025] In the current process, the poly(ethylene-2,5-furandicarboxylate) comprises at most 2.1 % by weight (%wt) of units derived from diethylene glycol based on amount of poly(ethylene-2,5-furandicarboxylate), preferably at most 2.0 %wt, more preferably at most 1.9 %wt, more preferably at most 1.8 %wt, more preferably at most 1.7 %wt. The presence of such units can be measured by1H-NMR as described in more detail in the experiments. The amount of diethylene glycol derived units generally will be at least 0.5 %wt, more specifically at least 1.0 %wt, more specifically at least 1.2 %wt, more specifically at least 1.4 %wt. The mentioned amount of DEG is before subjecting the poly(ethylene-2,5-furandicarboxylate) to the current process.FUR352 PD

[0026] An especially preferred polycondensation catalyst comprises germanium for example such as described in W02022 / 043500 and W02022 / 2043501. Additionally, further compounds also can be present such as stabilizers during either or both esterification and polycondensation.

[0027] The molar ratio of the amount of diols to the 2,5-furandicarboxylic acid can influence the molecular weight obtainable, and also the velocity of the increase of molecular weight during a subsequent solid state polymerisation. A preferred molar ratio of the aliphatic diol to 2,5-furandicarboxylic acid or its ester of the starting composition is in the range of 1.01 to 1.80, most preferably 1.10 to 1.30.

[0028] It is possible that a limited amount of further reactants is added to the starting composition. The poly(ethylene-2,5-furandicarboxylate) preferably contains at most 5 %wt, more specifically at most 3 %wt, more specifically at most 1 %wt, of units derived from other compounds added tot he starting composition, based on weight amount of poly(ethylene-2,5-furandicarboxylate). Preferably the poly(ethylene 2,5-furandicaboxylate) is prepared solely from the reactants 2,5-furandicarboxylic acid and ethylene glycol.

[0029] The desired amount units derived from DEG can be obtained by using the appropriate amount of DEG suppressant. An appropriate concentration of DEG suppressant can be at least 500 parts per million by weight with respect to the theoretical maximum weight of the polyester obtainable from the respective starting composition (ppmw), preferably at least 800 ppmw, more preferably at least 1000 ppmw. Preferably, the amount of DEG suppressant is at most 2500 ppmw, preferably at most 2000 ppmw, more preferably at most 1500 ppmw. A preferred DEG suppressant is tetraethyl ammonium hydroxide.

[0030] The poly(ethylene-2,5-furandicarboxylate) preferably comprises at most 250 ppm of germanium, calculated as metal on weight amount of poly(ethylene-2,5-furandicarboxylate), more preferably at most 200 ppm of germanium, more preferably at most 150 ppm of germanium, more preferably at most 120 ppm of germanium, more preferably at most 100 ppm of germanium, more preferably at most 90 ppm of germanium. The amount of germanium is calculated as weight amount of metal independent of the actual form of the germanium. The amount of germanium can be measured by digesting poly(ethylene-2,5-furandicarboxylate) in nitric acid and subsequently measuring the amount of germanium by inductively coupled plasma optical emission spectroscopy (ICP-OES). This amount of germanium tends to be lower than the amount of germanium given with respect to the theoretical maximum weight of polyester as described in the below experiments.

[0031] The poly(ethylene-2,5-furandicarboxylate) can further comprise stabilizer. Stabilizers include phosphorous containing compounds, in particular phosphite containing compounds, phosphate containing compounds and phosphonate containing compounds, preferablyFUR352 PD

[0032] phosphoric acid, and hindered phenolic compounds.

[0033] The crystallinity of the poly(ethylene-2,5-furandicarboxylate) is expressed in the unit J / g, and is taken as the net enthalpy of the melting peak (endotherm) after correcting for any crystallization (exotherm) which occurs on the upheat. After the crystallization of step (i), the crystallized or semi-crystallized particles obtained preferably have a net enthalpy of more than 20 J / g, preferably more than 25 J / g, more preferably more than 30 J / g as measured via Differential Scanning Calorimetry (DSC) using a heating rate of 10 °C / min.

[0034] In order to increase molecular weight, the crystallized or semi-crystallized poly(ethylene-2,5-furandicarboxylate) particles obtained in step (i) can be subjected to solid state polymerization before being subjected to step (ii). A preferred solid state polymerization is carried out at a pressure of from 10 to 110 kPa and a temperature in the range of from 160 to 240 °C, preferably 170 to 220 °C. After solid state polymerization, the poly(ethylene-2,5-furandicarboxylate) preferably has a number average molecular weight of at least 25 kg / mol, preferably more than 30.0 kg / mol determined as described in the below examples. The product obtained by solid state polymerization can be treated further in accordance with the process of the invention in steps (ii) to (iv).

[0035] The skilled person is well aware of a number of suitable methods for analyzing polyesters, including titration, infrared and proton-nuclear magnetic resonance (1H-NMR) methods. A.T Jackson and D.F. Robertson have published an1H-NMR method for end group determination in PET in “Molecular Characterization and Analysis of Polymers” (J.M. Chalmers en R.J. Meier (eds.), Vol. 53 of “Comprehensive Analytical Chemistry”, by B. Barcelo (ed.), (2008) Elsevier, on pages 183-193. A similar method can be carried out for polyesters that comprise 2,5-furandicarboxylate units. In the framework of the present invention, the method as described in the Experiments is used to determine the content of DEG.

[0036] The crystallization step (i) preferably is conducted at an elevated temperature in the range of 100 to 200 °C, preferably 140 to 180 °C, more preferably 140 to 170 °C. The crystallization preferably is conducted for a time in the range of 0.5 to 48 hours, preferably 30 to 720 minutes, more preferably 1 to 8 hours. While crystallization can be carried out at reduced pressure such as at less than 100 kPa or less than 10 kPa, the crystallization preferably is conducted at or near ambient pressure. The conditions described for the crystallization apply to this step (i) only. The process conditions for the optional solid state polymerisation which can be carried out after step (i) and before step (ii), have been described above.

[0037] If solid state polymerization is carried out, it is preferred that the crystallized or semi-FUR352 PD

[0038] crystallized polyester obtained in step (i) is granulated to obtain a degree of granulation in the range of 20 to 180 pellets per g, preferably 40 to 140 pellets per g.

[0039] The crystallized or semi-crystallized particles obtained in step (i) which optionally have been subjected to solid state polymerization, subsequently can be stored and optionally transported in step (ii) before drying in step (iii) and melt processing in step (iv). Step (i) and the optional solid state polymerization can be carried out in batch, semi-continuously or continuously.

[0040] Storage of crystallized or semi-crystallized poly(ethylene-2,5-furandicarboxylate) can be carried out in any way known in the art. After the crystallization of step (i), the poly(ethylene-2,5-furandicarboxylate) tends to be cooled before being stored. Preferably, the temperature during storage and optional transport of step (ii) is substantially lower than the melting temperature of the poly(ethylene-2,5-furandicarboxylate) which generally is 220 °C. Transport can be carried out as part of step (ii) before and / or after storage. The crystallized or semi-crystallized poly(ethylene-2,5-furandicarboxylate) can be stored for a long time. The present poly(ethylene-2,5-furandicarboxylate) is especially suitable if the presence of air is allowed during such extensive time.

[0041] Poly(ethylene-2,5-furandicarboxylate) is dried after storage in order to be suitable for melt processing. The drying preferably is carried out at a temperature of at least 100 °C, preferably at least 120 °C, more preferably at least 140 °C. To prevent sticking, the temperature during drying preferably is at most its melting temperature, preferably at most 200 °C, more preferably at most 180 °C. Drying generally will be carried out for a time in the range of 0.5 to 48 hours, preferably 30 to 720 minutes, more preferably 3 to 10 hours, more preferably from 4 to 9 hours.

[0042] Step (iv) involves melt processing. Melt processing is considered any process in which the poly(ethylene-2,5-furandicarboxylate) is used as a melt. In melt processing, the poly(ethylene-2,5-furandicarboxylate) is heated to a temperature of from its melting temperature (Tm) to Tm + 80 °C, more specifically of from its melting temperature (Tm) to Tm + 60 °C. A typical melt processing temperature range is from 220 to 300 °C, more specifically of from 240 to 290 °C, more specifically of from 240 to 290 °C, more specifically from 240 to 280 °C.

[0043] The melt can be used in many different processes such as extrusion, blow molding, thermoforming and injection moulding. It will be clear to the person skilled in the art what additives can be added for a specifc process. An especially suitable process is injection moulding which comprises heating and mixing polyester to obtain a melt and injecting the poly(ethylene-2,5-furandicarboxylate) containing melt into a mould where it cools andFUR352 PD

[0044] hardens to the configuration of the cavity to obtain the injection moulded article.

[0045] The invention will be further illustrated by means of the following examples.

[0046] Experiments

[0047] Abbreviations and Measurements:

[0048] In the experiments, concentrations of DEG suppressant, catalytic metal and phosphoric acid are given with respect to the theoretical maximum weight of the polyester obtainable from the respective starting composition, that is calculated by multiplying the mols of FDCA in the starting composition with the molecular weight of the corresponding theoretical polymer repeat unit (i.e. weight of FDCA in grams / 158 x 182).

[0049] DEG indicates the amount of diethylene glycol incorporated in the polyester in weight percent with respect to the total weight of the polyester. Herein, the values for the amount of diethylene glycol (DEG) in the polyester were obtained by1H-NMR using deuterated 1, 1,2,2-tetrachloroethane (TCE-d2) to determine the content of DEG incorporated in the polyester. Peak assignments are set using the TCE peak at a chemical shift of 6.04 ppm. The furan peak at a chemical shift of 7.28 ppm is integrated and the integral is set at 2.000 representing the two protons on the furan ring. The content of DEG is determined from the integral of the respective shift of the protons adjacent to the ether functionality, e.g. shifts at 3.82 to 3.92 ppm for DEG, representing four protons.

[0050] The amount of carboxylic end groups (CEG) in eq / t was measured by titration based on ASTM D7409, i.e. by titration of a solution of 0.4 to 1.3 g of the polymer sample dissolved in 20 mL of o-cresol with 30 ml chloroform using a 0.01 M solution of potassium hydroxide in ethanol to its endpoint using bromocresol green as indicator.

[0051] The LIVA / IS was measured as a solution of 30 g / l of PEF in a mixture of dichloromethane and hexafluoroisopropanol (80:20 ratio) and absorbance across the visible spectrum of 360 to 780 nm light with pathlength of 2.5 cm. If desired, the data measured for the 2.5 cm diameter vial can be converted to a customary 1 cm equivalent path length by dividing the measured data by 2.5.

[0052] The number average molecular weight was determined through the use of gel permeation chromatography (GPC). GPC measurement was performed at 35 °C using two columns with precolumn (PSS PFG linear M 7 pm, 8x300 mm, commercially available from Agilent). Hexafluorisopropanol with 0.05 M potassiumtrifluoroacetate was used as eluent. Flow rate was set to 1.0 mL / min, injection volume was 50 pL and the run time was 50 min. The calibration was performed using polymethylmethacrylate standards.

[0053] The reaction was carried out in a reactor vessel in an oil bath. The reaction temperature mentioned is the temperature of the oil bath.

[0054] Example 1FUR352 PD

[0055] A starting composition comprising ethylene glycol and 2,5-furandicarboxylic acid in a molar ratio of 1.21, germanium catalyst and tetraethyl ammonium hydroxide as DEG suppressant was subjected to a temperature of 227 °C under a nitrogen atmosphere at 1.02 bara. The germanium catalyst consisted of 0.252 g germanium(IV) oxide dissolved in 37.5 g water, corresponding with 100 ppmw germanium. For the preparation of Polyester A, 1100 ppmw of tetraethyl ammonium hydroxide was added as DEG suppressant and esterification was carried out during 172 minutes at 227 °C. For the preparation of Polyester B, 210 ppmw of tetraethyl ammonium hydroxide was added as DEG suppressant and esterification was carried out during 180 minutes at 227 °C. After such esterification, a solution of 0.10 g of 85 %wt H3PO4 in 4.40 g ethylene glycol was added, corresponding with 15 ppmw of phosphorus. Polycondensation was conducted at 260°C for Polyester A for a time period of 106 min and for Polyester B for a time period of 112 min.

[0056] The resins obtained after polycondensation were crystallized at atmospheric pressure under air or nitrogen at a temperature of 160 °C for 6 hours before being subjected to solid state polymerization for 24 h at atmospheric pressure using a nitrogen gas flow of 175 mL / min at a temperature of 200 °C.

[0057] Polyester A was found to contain 1.6 %wt of DEG, 42 mmol / kg of CEG and have a number average molecular weight of 32.1 kg / mol.

[0058] Polyester B was found to contain 2.3 %wt of DEG, 44 mmol / kg of CEG and have a number average molecular weight of 31.3 kg / mol.

[0059] The particles obtained were stored for 5 weeks at 25 °C under air or nitrogen and dried for 6 hours at 160 °C at atmospheric pressure using a gas flow of 175 mL / min of either air or nitrogen. The thus obtained polyester was heated to obtain a melt which was used in compression moulding which exposed the polyester to air at 270 °C during 15 minutes.

[0060] In the below Tables we show the LIV / VIS of the polyesters after having been subjected to compression moulding.

[0061] Table 1

[0062] Polyester A Polyester B (Crystallized under nitrogen, (Crystallized under nitrogen, stored under nitrogen, stored under nitrogen, dried under nitrogen) dried under nitrogen) 0.027 0.026

[0063]

[0064] Table 2FUR352 PD

[0065] Polyester A Polyester B (Crystallized under nitrogen, (Crystallized under nitrogen, stored under nitrogen, stored under nitrogen, dried under air) dried under air) 0.033 0.035

[0066] Table 3

[0067] Polyester A Polyester B (Crystallized under air, (Crystallized under air, stored under nitrogen, stored under nitrogen, dried under nitrogen) dried under nitrogen) 0.064 0.065

[0068]

[0069] Table 4

[0070] Polyester A Polyester B (Crystallized under nitrogen, (Crystallized under nitrogen, stored under air, stored under air, dried under air) dried under air) 0.028 0.049

[0071] Table 5

[0072] Polyester A Polyester B (Crystallized under air, (Crystallized under air, stored under air, stored under air, dried under nitrogen) dried under nitrogen) 0.065 0.077

[0073] Table 6

[0074] Polyester A Polyester B (Crystallized under air, (Crystallized under air,

[0075]

[0076] FUR352 PD

[0077] stored under nitrogen, stored under nitrogen, dried under air) dried under air)

[0078] 0.068 0.103

[0079]

[0080] Table 7

[0081] Polyester A Polyester B (Crystallized under air, (Crystallized under air, stored under air, stored under air, dried under air) dried under air)

[0082] 0.069 0.109

[0083]

[0084] Table 8 again shows the above results including the LIV / VIS improvement calculated as the LIV / VIS measured for Polymer B minus the LIV / VIS measured for Polymer A divided by the LIV / VIS measured for Polymer B.

[0085] Table 8

[0086] Polyester A Comparative % improvement Polyester B

[0087] Comparative (nitrogen only) 0.027 0.026 - 4 Dried under air 0.033 0.035 6 Crystallized under air 0.064 0.065 2 Stored and dried under air 0.028 0.049 43 Crystallized and stored under air 0.065 0.077 16 Crystallized and dried under air 0.068 0.103 34 Crystallized, stored and dried under air 0.069 0.109 37

[0088]

Claims

FUR352 PDCLAIMS1. Process comprising melt processing of poly(ethylene-2,5-furandicarboxylate) which process comprises(i) crystallizing poly(ethylene-2,5-furandicarboxylate) to obtain crystallized or semicrystallized poly(ethylene-2,5-furandicarboxylate),(ii) storing the crystallized or semi-crystallized poly(ethylene-2,5-furandicarboxylate), (iii) drying the stored poly(ethylene-2,5-furandicarboxylate) of step (ii) to obtain dried poly(ethylene-2,5-furandicarboxylate), and(iv) subjecting the dried poly(ethylene-2,5-furandicarboxylate) to melt processing, wherein the poly(ethylene-2,5-furandicarboxylate) comprises at most 2.1 % by weight (%wt) of units derived from diethylene glycol based on amount of poly(ethylene-2,5-furandicarboxylate) and measured by1H-NMR and the poly(ethylene-2,5-furandicarboxylate) is in contact with oxygen during one or more steps from the group consisting of the crystallization step (i), the storing step (ii) and the drying of step (iii).

2. Process according to claim 1, wherein at least during the drying of step (iii) the poly(ethylene-2,5-furandicarboxylate) is in contact with oxygen.

3. Process according to claim 1 or 2, wherein the poly(ethylene-2,5-furandicarboxylate) is in contact with oxygen during at least two of the steps from the group consisting of the crystallization of step (i), the storing of step (ii) and the drying of step (iii).

4. Process according to any one of claims 1 to 3, wherein the poly(ethylene-2,5-furandicarboxylate) is obtained bya) providing or preparing a starting composition comprising 2,5-furandicarboxylic acid and ethylene glycol,b) subjecting the starting composition in the presence of a compound suppressing the formation of diethylene glycol to elevated temperature to produce an intermediate ester composition, andc) contacting the intermediate ester composition with a polycondensation catalyst at polycondensation conditions to produce the poly(ethylene-2,5-furandicarboxylate) comprising at most 2.1 % %wt of units derived from diethylene glycol.

5. Process according to claim 4, wherein the polycondensation catalyst comprises germanium.FUR352 PD6. Process according to any one of claims 1 to 5 wherein the crystallization is carried out in the presence of air at a temperature of from 140 to 180 °C during of from 30 to 720 minutes.

7. Process according to any one of claims 1 to 6 wherein the drying is carried out in the presence of air at a temperature of from 140 to 180 °C during of from 30 to 720 minutes.

8. Process according to any one of claims 1 to 7, which process further comprises subjecting the crystallized or semi-crystallized poly(ethylene-2,5-furandicarboxylate) particles obtained in step i) to solid state polymerization at a pressure of from 10 to 110 kPa and a temperature in the range of from 160 to 240 °C and subsequently subjecting the poly(ethylene-2,5-furandicarboxylate) obtained to step (ii).

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