WO2024089105A1

WO2024089105A1 - Polyester of improved colour stability

Info

Publication number: WO2024089105A1
Application number: PCT/EP2023/079784
Authority: WO
Inventors: Hendawy ELFEKI; Matheus Adrianus Dam
Original assignee: Furanix Technologies BV
Current assignee: Furanix Technologies BV
Priority date: 2022-10-26
Filing date: 2023-10-25
Publication date: 2024-05-02
Anticipated expiration: 2025-04-26
Also published as: EP4608892A1

Abstract

Process for the preparation of a composition comprising poly(ethylene 2,5- furandicarboxylate) polymer which process comprises polycondensation of poly(ethylene 2,5- furandicarboxylate) prepolymer in the presence of both antioxidant and phosphoric acid; composition comprising poly(ethylene 2,5- furandicarboxylate) polymer, of from 5 to 5000 ppmw of antioxidant, based of weight of antioxidant on weight of total composition, and of from 2 to 2000 ppmw phosphoric acid, based on weight of phosphor on weight of total composition.

Description

POLYESTER OF IMPROVED COLOUR STABILITY

The present invention relates to a process for the preparation of poly(ethylene 2,5- furandicarboxylate) polymer from polyethylene 2,5- furandicarboxylate) prepolymer.

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. In recent years FDCA and the plant-based polyester poly (ethylene-2, 5- furandicarboxylate) (PEF) have attracted a lot of attention. PEF is a recyclable plastic 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. Comprehensive research was conducted to arrive at a technology for producing FDCA and PEF in a commercially viable way.

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 comprising e.g. enzymatic and metal catalysed processes such as described in W02010/132740 and WO2011/043660.

While a lot of research effort 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 producing high-performance polyesters from FDCA was at least as challenging. While FDCA is oftentimes considered a structural and functional analogue to terephthalic acid (TA) as used in the production of the widely used polyester polyethylene terephthalate (PET), it became apparent that established techniques known from the PET industry could not be easily adapted to produce high-performance polyesters from FDCA that meet the requirements of the relevant industries. Comprehensive prior art is available on processes for producing polyesters from FDCA focussing on different aspects of the technology, e.g. EP 3116932, EP 3116934, WO 2013/1209989 and US 2010/0174044.

Similarly to PET, PEF tends to degrade during its thermal processing and as a result discoloration can occur. This is mainly attributed to thermal and thermo-oxidative degradation reactions as described in the article “Effect of additives on the thermal and thermos-oxidative stability of poly (ethylene furanoate) biobased polyester” by Zoi Terzopoulou et al., Thermochimica Acta 686 (2020) 178549. It is described that the thermo- oxidative degradation was affected by the catalyst type used. It is common practice to add thermal stabilizers during the synthesis or the processing of thermoplastic polyesters. The article of Thermochimica Acta describes the addition of a commercial phenolic antioxidant (Irganox 1098) and addition of phosphorus-containing thermal stabilizers during PEF synthesis with the use of antimony catalyst.

The primary objective of the present invention was to provide a composition comprising poly(ethylene 2,5- furandicarboxylate) polymer having improved colour stability especially having good colour after melt processing.

Colour itself is subjective and is influenced by the wavelength and intensity of light that is reflected. The colour of polymer particles is additionally influenced by crystal size and the presence of optical brighteners. Precipitated polymer particles tend to be fine and thereby appear to have good colour. To objectively assess the colour, it is to be assessed by the absorption of yellow light, specifically 400 nm, of a solution of the polymer per se.

Colour stability is especially relevant when exposing PEF to elevated temperatures in particular in the presence of oxygen such as can occur during melt processing including recycling.

The aim of CN 108586717 was the use of bio-based polyesters to reduce static electricity and electrostatic discharge. A bio-based and permanent static dissipative polymer was obtained by esterifying a mix of furan dicarboxylic acid, terephthalic acid and isophthalic acid with ethylene glycol followed by condensation polymerisation in the presence of inorganic salt, catalyst and stabiliser.

CN 108727575 teaches the use of a titanium-silicon-cobalt composite catalyst in combination with ester formed by reacting FDCA and an aliphatic diol referred to as guide, in the preparation of FDCA based copolyesters to reduce side-reactions. The copolyesters are based on a variety of diols and additional diacids besides FDCA. In the examples in which phosphoric acid is used, the copolyester is based on terephthalic acid, FDCA, ethylene glycol and propylene glycol (Example 1), FDCA, azelaic acid, sebacic acid, butanediol and heptanediol (Example 6) or FDCA, pimelic acid, heptanediol and pentanediol (Example 12) or FDCA, succinic acid, hexanediol and decanediol (Example 15) or FDCA, isophthalic acid, propylene glycol and hexanediol (Example 16) or FDCA, terephthalic acid, propylene glycol and butanediol (Example 17).

CN 109054007 aims to provide bio-furan dicarboxylic acid polyester having excellent gas barrier properties by reacting furan dicarboxylic acid with a glycol selected from the group consisting of 2-methyl-1 ,3-propanediol, 2,2-dimethyl-1 ,3-propanediol, 2-methyl-2- ethyl-1,3-propanediol, 2-methyl-2-propyl-1 ,3-propanediol, 2-ethyl-2-butyl-1 ,3-propanediol, 2- ethyl-2-pentyl-1 ,3-propanediol and 2-ethyl-2-hexyl-1 ,3-propanediol.

US2021/0130311 describes a wide range of color stabilizing additives. In the examples, the development of color was investigated for a solution of the dimethyl ester of FDCA dissolved in isopropanol in combination with the additives butylated hydroxyanisole (BHA), 2-tert-butylhydroquinone (TBHQ), 2,6-dimethoxyphenol (DMP), 2-6-di-tert-butyl-4- methoxylphenol (DTMP), 4,4’-bis(a,a-dimethylbenzyl)diphenylamine (XDPA), pentaerythritol tetrakis[3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionate (PETC), Irganox 245 (ethylenebis(oxyethylene) bis-(3-(5-ter-butyl-4-hydroxy-m-tolyl)-propionate)), Irganox B900 (20 %wt octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate and 80 %wt tris(2 ,4-di- tert-butylphenyl)phosphite)) and Irganox B225 (50 %wt PETC and 50 %wt tris (2,4-di-tert- butylphenyl)phosphite). Additionally, the development of color was investigated for a solution of FDCA dissolved in triethylene glycol monomethyl ether or propylene glycol in combination with the additives butylated hydroxyanisole (BHA), Irganox 245, Irganox B900, Irganox B22, Dovernox 10 (PETC) and Dovernox 76 (octadecyl-3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate). No information is provided on the effect of these additives on PEF polymer.

WO 2022/043500 and WO 2022/043501 describe processes in which germanium catalyst was found to allow preparation of polyester comprising 2,5-furandicarboxylate units having a high molecular weight and good optical properties such as a low absorbance of 400 nm light. The starting compositions of these processes can comprise typical stabilizers that are known from the prior art such as phosphorous containing compounds and hindered phenolic compounds.

It now surprisingly has been found that colour degradation due to melt processing of PEF can be reduced by the use of a combination of antioxidant and phosphoric acid. Moreover, it was found that especially good polyester is obtained if antioxidant is present during esterification while phosphoric acid is added after esterification. Furthermore, it was found that especially good results were obtained using germanium containing polycondensation catalyst especially by using a solution of germanium.

The present invention relates to a process for the preparation of a composition comprising poly(ethylene 2,5-furandicarboxylate) polymer wherein the process comprises (a) preparing or providing polyethylene 2,5-furandicarboxylate) prepolymer, and (b) subjecting the prepolymer to polycondensation at reduced pressure in the presence of a polycondensation catalyst to obtain the polymer, which polycondensation is carried out in the presence of both antioxidant and phosphoric acid.

The present invention further relates to a composition comprising poly(ethylene 2,5- furandicarboxylate) polymer and of from 5 to 5000 parts per million by weight (ppmw) of antioxidant, based of weight of antioxidant on weight of total composition, and of from 2 to 2000 ppmw phosphoric acid, based on weight of phosphor on weight of total composition.

Additionally, the present invention relates to a process comprising melt processing a composition comprising polyethylene 2,5-furandicarboxylate) polymer obtainable by a process according to the present invention and/or a poly(ethylene 2,5-furandicarboxylate) composition according to the present invention more specifically in the presence of oxygen. A reduced increase in A_400 absorption after melt processing was observed for such PEF polymer.

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 features of embodiments to obtain an especially preferred embodiment. The preferred amounts and kinds of antioxidants and the amounts of phosphoric acid apply to both the prepolymer and the polymer.

The antioxidant preferably comprises a primary antioxidant selected from the group consisting of compounds comprising hindered phenols and compounds comprising phenols substituted with propionic acid and/or propionate. Hindered phenols are phenols with one or more bulky functional groups preferably tertiary butyl.

It is possible that the antioxidant consists of both a primary and a secondary antioxidant. In such case, the secondary antioxidant preferably is selected from the group consisting of phosphor(lll) containing compounds and compounds containing a benzyl group.

Compounds can contain functional groups which make that these can be considered to be both a primary and a secondary antioxidant. In such case, the compound is considered a primary antioxidant.

The antioxidant preferably comprises a compound comprising hindered phenol. More preferably, the antioxidant consists of compounds comprising hindered phenol. An especially preferred antioxidant was found to be a compound comprising hindered phenol and cinnamic acid and/or cinnamate, especially tetrakis methylene (3,5-di-t-butyl-4-hydroxy- hydrocinnamate)methane. The latter compound is commercially available from Dover Chemical Corporation as Dovernox 10.

The amount of antioxidant preferably is of from 1 to 10,000, more specifically of from 5 to 5000 parts per million by weight (ppmw), based of weight of antioxidant on weight of total composition.

The amount of phosphoric acid preferably is from 1 to 5000, more specifically of from 2 to 5000, more specifically of from 2 to 2000, more specifically of from 2 to 1000 ppmw of phosphoric acid, more specifically 5 to 500 ppmw, based on weight of phosphor on weight of total composition. Phosphoric acid can be added as such or as a compound which is converted into phosphoric acid during preparation of the polyester composition.

Poly(ethylene 2,5-furandicarboxylate) contains ethylene moieties and 2,5- furandicarboxylate moieties. It may also contain a limited amount of other diacids and diol residues such as oligomers of ethylene glycol namely diethylene glycol and triethylene glycol. The amount of other diol or diacid residues is suitably at most 10 mol%, based on the molar amount of 2,5-furandicarboxylate moieties. Poly(ethylene 2,5- furandicarboxylate) polymer also is referred to as polyester.

The poly(ethylene-2,5-furandicarboxylate) polymer prepared by the present process suitably has a relatively high melting point. The melting point of the poly(ethylene-2,5- furandicarboxylate) is typically influenced by the presence of comonomers other than ethylene glycol and 2,5-furandicarboxylic acid, if any, or by its crystallinity. Suitable melting points of the poly(ethylene-2,5-furandicarboxylate) tend to be at least 215°C. The melting point of the poly(ethylene-2,5-furandicarboxylate) may be as high as 245 °C. The melting point of a polymer is easily determined by Differential Scanning Calorimetry (DSC) and measured at the top of the endothermic peak. The ISO 11357-3 standard describes such a melting determination. The polyester composition according to the present invention suitably has a melting point of at least 215 °C, more specifically of from 215 to 245 °C measured by DSC according to ISO 1357-3 standard.

Poly(ethylene 2,5-furandicarboxylate) prepolymer can be prepared from a starting composition comprising 2,5-furandicarboxylic acid, or its ester, and ethylene glycol. The esterification of a diol compound with an acid compound is a reaction that is well known to the skilled person. A method for its preparation for example has been described in WO 2015/137804. The 2,5-furandicarboxylic acid or its ester and the ethylene glycol preferably constitute 90 % or more, preferably 95 % or more, most preferably 98 % or more of the starting composition by weight. Preferably, the poly(ethylene 2,5-furandicarboxylate) prepolymer is prepared from a starting compostion containing ethylene glycol and furandicarboxylic acid and/or its ester as sole monomors, more preferably ethylene glycol and furandicarboxylic acid as sole monomers. In other words, the prepolymer preferably is prepared from the sole monomers ethylene glycol and furandicarboxylic acid and/or its ester, more preferably from the sole monomers ethylene glycol and furandicarboxylic acid. Preferably, further compounds which can become part of the PEF polymer, such as chain extenders, are absent from the starting composition.

Besides the kind of acid or ester and diol present, the chemical constitution of the prepolymer and polyester also depend on the molar ratio of the starting materials used in the starting composition. Preferably, the poly(ethylene 2,5-furandicarboxylate) prepolymer is prepared from 2,5-furandicarboxylic acid and ethylene glycol wherein the molar ratio of 2,5- furandicarboxylic acid to ethylene glycol in the starting mixture is of from 1 : 1.01 to 1 : 1.15.

It was found that esterification of the starting composition comprising ethylene glycol and FDCA or its ester preferably is conducted at a temperature in the range of 180 to 260 °C, preferably 185 to 240 °C, more preferably 190 to 230 °C. Preferably, the esterification is conducted at a pressure in the range of 40 to 400 kPa, preferably 50 to 150 kPa, more preferably 60 to 110 kPa. While the actual reaction time depends on the employed starting materials and their amounts, the esterification is typically conducted for a time in the range of 30 to 480 min, preferably 60 to 360 min, more preferably 120 to 300 min, most preferably 180 to 240 min.

It is possible that the polycondensation catalyst is already present during preparation of the prepolymer. The prepolymer of step (a) preferably is prepared in the presence of antioxidant. It is possible that phosphoric acid also is present during preparation of the prepolymer depending on the further compounds which are present such as the polycondensation catalyst and if so, what polycondensation catalyst.

The preparation of prepolymer preferably is carried out in the presence of suppressant for suppressing ether formation between the aliphatic diol molecules. The suppressant preferably is selected from the group consisting of amines and lithium hydroxide. A variety of amines can be used such as primary amines, secondary amines or tertiary amines. The suppressant preferably is selected from the group consisting of primary amines, secondary amines, tertiary amines and lithium hydroxide, preferably selected from the group consisting of primary amines, tertiary amines and lithium hydroxide, more preferably selected from the group consisting of 2-(diethylamino)ethanol (Et2NEtOH), N,N-dimethyldodecylamine (Me2NDodec), 3-aminocrotonic acid ester with butanediol (ACAEBD) and lithium hydroxide, most preferably selected from the group consisting of 2-(diethylamino)ethanol and N,N- dimethyldodecylamine. It can be preferred that the suppressant is lithium hydroxide.

Preferably, the concentration of the suppressant in the starting composition is in the range of 5 to 1300 ppm, preferably 20 to 700 ppm, more preferably 30 to 450 ppm, by weight with respect of the weight of the starting composition.

Starting composition to be subjected to esterification conditions to produce prepolymer in step (a) preferably comprises ethylene glycol and FDCA and/or its ester, antioxidant and suppressant and optionally phosphoric acid and/or polycondensation catalyst.

The prepolymer is contacted with a polycondensation catalyst during the polycondensation of step (b). Many polycondensation catalysts already can be added to the starting composition as their presence does not deteriorate the preparation of prepolymer.

If germanium containing polycondensation catalyst is present at preparation of the prepolymer, it is preferred that the phosphoric acid is added after preparation of the prepolymer. Especially good polyester is obtained by the present process if phosphoric acid is added to germanium polycondensation catalyst containing prepolymer.

Polycondensation is used for producing polyethylene 2,5-furandicarboxylate) polymer by forming additional ester moieties between the compounds of the prepolymer by means of esterification and transesterification, wherein e.g. water and/or aliphatic diol are released in the condensation process, and are typically removed from the reaction due to the elevated temperatures and reduced pressures used during polycondensation.

The polycondensation may be conducted in one or more steps and could suitably be operated as either batch, semi-continuous or continuous processes.

Other intermediate steps can be conducted in between step a) and step b), e.g. a prepolycondensation step. A pre-polycondensation step is typically conducted at a pressure lower than applied in esterification and can be used to remove the most volatile components, such as free diol and other low molecular weight compounds, before reducing the pressure even further to begin polycondensation. Preferably, the prepolymer of step (a) is subjected to step (b) without addition of further compounds other than polycondensation catalyst, antioxidant and/or phosphoric acid more specifically as described herein.

The polycondensation preferably is conducted at a temperature in the range of 240 to 300 °C, preferably 260 to 290 °C, more preferably 265 to 285 °C. Preferably, the polycondensation is conducted at reduced pressure in the range of 0.05 to 100 kPa, preferably 0.05 to 10 kPa, more preferably 0.1 to 1 kPa while the polycondensation is typically conducted for a time in the range of 10 to 260 min, preferably 30 to 190 min, more preferably 60 to 120 min.

The polycondensation catalyst can contain metals such as aluminium, antimony, tin and germanium. Suitable polycondensation catalysts have been described for example in WO2022/136332, WO 2022/043500 and WO 2022/043501. Preferably, the polycondensation catalyst contains germanium. Germanium polycondensation catalyst can be present in the catalyst system as the metal or as the cation. Preferred is a process wherein the germanium containing catalyst is selected from the group consisting of germanium oxide and germanium salts, preferably selected from the group of organic germanium salts and germanium oxide. In the present context, an organic germanium salt comprises a salt of a germanium cation and at least one kind of hydrocarbon anion. Most preferably, the germanium containing catalyst consists of germanium oxide.

The concentration of the germanium containing catalyst in step (b), calculated as the metal per se, preferably is in the range of 10 to 1000 ppm, preferably 30 to 500 ppm, more preferably 50 to 300 ppm, most preferably 70 to 150 ppm, by weight with respect of the weight of the prepolymer. Therefore, the compositions of the present invention preferably comprise an amount of germanium, calculated as the metal per se, in the range of from 5 to 5000 ppmw, more specifically 10 to 1000 ppm, preferably 30 to 500 ppm, more preferably 50 to 300 ppm, most preferably 70 to 150 ppm, by weight with respect of total weight of composition.

Preferred is a process according to the invention, wherein the PEF polymer after polycondensation has a number average molecular weight of 20 kg/mol or more, preferably 25 kg/mol or more, preferably 30 kg/mol or more. The number average molecular weight is determined through the use of gel permeation chromatography (GPC) with hexafluorisopropanol with 0.05 M potassium trifluoroacetate as eluent and calibrated using polymethylmethacrylate standard.

The melting temperature of PEF polymer is typically in the range of 190 to 230°C. Preferably, the process of the present invention further comprises melt processing of the product of step (b) optionally after the product of step (b) has been subjected to solid state polymerization as described below. Melt processing of such polymer generally involves a temperature of at least 200 °C, more specifically at least 210 °C, more specifically at least 220 °C, more specifically at least 230 °C. Preferably, the melt processing involves a temperature ranging from 240 to 310°C, in particular from 240 to 300 °C, to ensure that the composition is in a molten state and has the desired viscosity. For some melt processing applications, the temperature can be at most 290 °C, more specifically at most 280 °C. Melt processing tends to be applied in recycling of polymer and in the manufacture of fibers and packaging including films and containers. The compositions of the present invention are suitable for use in such melt processing or may have been subjected to such melt processing.

While the PEF polymer obtained after polycondensation can be used directly for specific applications, it is in some cases beneficial to carry out further processing steps. These steps can comprise a step of crystallizing the polymer for obtaining a crystallized polymer and subjecting the crystallized polymer to a solid-state polymerization for increasing the molecular weight. Therefore, it can be preferred that the process further comprises the steps: c) crystallizing the PEF polymer obtained in step b) to obtain a crystallized or semicrystallized polymer, and d) subjecting the crystallized polymer produced in step c) to a solid state polymerization for increasing the molecular weight. Such solid state polymerization can be conducted at an elevated temperature in the range of Tm - 80 °C to Tm - 20 °C, preferably Tm - 60 °C to Tm - 25 °C, more preferably Tm - 60 °C to Tm - 30 °C, wherein Tm is the melting point of the PEF polymer in °C, wherein the solid state polymerization is preferably conducted at an elevated temperature in the range of 160 to 240 °C, more preferably 170 to 220 °C, most preferably 180 to 210 °C. The melting point of a polymer is easily determined by DSC and measured at the top of the endothermic peak. The ISO11357-3 standard describes such a melting determination. The crystallization preferably is conducted at an elevated temperature in the range of 100 to 200 °C, preferably 120 to 180 °C, more preferably 140 to 160 °C. The crystallization preferably is conducted for a time in the range of 0.5 to 48 h, preferably 1 to 6 h, wherein step d) is conducted directly after step c) without cooling the polyester comprising 2,5-furandicarboxylate units below 50 °C. The crystallization preferably is conducted at or near ambient pressure or, less preferred, at reduced pressure of less than 100 kPa or less than 10 kPa. The solid state polymerization preferably is conducted under inert gas atmosphere, preferably nitrogen, helium, neon or argon atmosphere. It is preferred that the crystallized or semi-crystallized PEF polymer obtained in step c) 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.

Solid state polymerization can produce PEF polymer having a number average molecular weight of 30 kg/mol or more, preferably 45 kg/mol or more, more preferably 60 kg/mol or more.

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

Examples

Abbreviations and Measurements:

The FDCA used in the experiments comprised less than 500 ppm FCA.

A starting composition comprising ethylene glycol and 2,5-furandicarboxylic acid in a molar ratio of 1.21 to 1 in combination with 210 ppm tetraethylammonium hydroxide DEG suppressant (TEAOH) was subjected to esterification at 220 °C and at atmospheric pressure. Additionally, 200 ppm of GeC>2 (calculated as amount of Ge metal) polycondensation catalyst was added as a solution of 200 ppm of GeO2 in 75 ml water.

After esterification, 25 ppmw H3PO4 (weight amount of phosphorus on total amount of mixture) was added with antioxidant as indicated in Table 1 below. If present, the total amount of antioxidant was 500 ppmw (weight amount of antioxidant on total amount of mixture).

The primary phenolic antioxidant Dovernox 10 was obtained from Dover Chemical Corporation and is tetrakis methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)methane.

The secondary antioxidant Irgafos 168 was obtained from BASF and is tris(2,4-di-tert.- butylphenyl)phosphite.

The antioxidant ADK STAB A611 was obtained from Adeka and is a mixture of primary hindered phenolic antioxidant and secondary phosphite. The hindered phenolic antioxidant is benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-2,2-bis[[3-[3,5-bis91 ,1- dimethylethyl)-4-hydroxyphenyl]-1-oxopropoxy]methyl]-1,3-propanediyl ester. The phosphite is phenol, 2.4-bis(1 , 1 -dimethylethyl)-, phosphite (3:1).

Subsequently, the mixture was subjected to prepolycondensation at a temperature of 260 °C during 20 minutes and polycondensation for 75 min at 260°C followed by solid state polymerization. The resins obtained after polycondensation were crystallized under a nitrogen flow of 175 ml/min at a temperature of 150 °C before being subjected to solid state polymerization for 24 hours under nitrogen atmosphere at a temperature of 200 °C. The average diameter of the particles subjected to solid state polymerization was 0.6 to 2.0 mm. After solid state polymerization, the fraction having a particle size of 1.4 to 2.0 mm was isolated and used for analytics.

The A_400 absorption after polycondensation and after solid state polymerization was assessed.

A_400 is the absorbance of a 30 mg/mL solution of polyester in a dichloromethane:hexafluoroisopropanol 8:2 (vol/vol) mixture in a 2.5 cm diameter circular vial measured at 400 nm. 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.

Samples of polymer subsequently were heated to a temperature of 260 °C in closed vials for 30 minutes to determine the A_400 absorption increase in the presence of oxygen. The A_400 absorption of all samples was assessed as described above.

The A_400 absorption for the various samples is shown below.

Table 1 - A_400 of PEF samples

It is clear from the above that adding phosphoric acid together with antioxidant, especially a hindered phenolic antioxidant, allows to process poly(ethylene furanedicarboxylate) in the presence of oxygen with limited increase in A_400 absorption i.e. colour increase.

Claims

1. Process for the preparation of a composition comprising poly(ethylene 2,5- furandicarboxylate) polymer, wherein the process comprises

(a) preparing or providing polyethylene 2,5-furandicarboxylate) prepolymer, and

(b) subjecting the prepolymer to polycondensation at reduced pressure in the presence of a polycondensation catalyst to obtain the polymer, which polycondensation is carried out in the presence of both antioxidant and phosphoric acid.

2. Process according to claim 1 in which the antioxidant comprises a primary antioxidant selected from the group consisting of compounds comprising hindered phenols and compounds comprising phenols substituted with propionic acid and/or propionate.

3. Process according to claim 1 in which the antioxidant is a compound comprising hindered phenol.

4. Process according to any one of claims 1 to 3 which process further comprises

(c) melt processing of the composition comprising polyester.

5. Process according to any one of claims 1 to 4 which process further comprises solid state polymerization of polyester obtained in step (b) before use in step (c).

6. Process according to any one of claims 1 to 5 in which process the prepolymer is prepared in the presence of antioxidant in step (a).

7. Composition comprising poly(ethylene 2,5-furandicarboxylate) polymer and of from 5 to 5000 parts per million by weight (ppmw) of antioxidant, based of weight of antioxidant on weight of total composition, and of from 2 to 2000 ppmw phosphoric acid, based on weight of phosphor on weight of total composition.

8. Composition according to claim 7 which composition comprises a primary antioxidant selected from the group consisting of hindered phenols and phenols substituted with propionic acid and/or propionate, preferably consisting of hindered phenols.

9. Composition according to claim 7 or 8, which composition further comprises of from 5 to 5000 ppmw of germanium.

10. Process comprising melt processing a composition comprising poly(ethylene 2,5- furandicarboxylate) polymer obtainable by a process according to any one of claims 1 to 6 or a composition comprising poly(ethylene 2,5-furandicarboxylate) according to any one of claims 7 to 9.