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On the crystallization and polymorphism of poly(ethylene furanoate) Vasilios Tsanaktsis, Dimitrios G. Papageorgiou, Stylianos Exarhopoulos, Dimitrios N. Bikiaris, and George Z Papageorgiou Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b01136 • Publication Date (Web): 09 Oct 2015 Downloaded from http://pubs.acs.org on October 18, 2015

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Crystal Growth & Design

1

On the crystallization and polymorphism of poly(ethylene furanoate)

2 3

Vasilios Tsanaktsis1, Dimitrios G. Papageorgiou2, Stylianos Exarhopoulos3,4, Dimitrios

4

N. Bikiaris1, George Z. Papageorgiou3*

5 6 7 8 9 10 11 12 13 14

1

15

Abstract

16

In this work we report the observation of two different crystalline patterns of

17

poly(ethylene furanoate) (PEF), corresponding to bulk and solvent induced

18

crystallization. The crystal form generated by bulk crystallization is the α-form, while

19

that observed on solvent crystallization is the β-form. Crystal transition upon heating

20

was not evidenced. However, in the case of bulk crystallization, the defective (α΄)

21

crystal structure generated under large supercoolings (at temperatures well below

22

180oC), was reorganized to a more perfect structure of the same form (α) when heated

23

above 190oC. Three new peaks at 13.8o, 18.1o and 26.7o were recorded after annealing

24

at such elevated temperatures. Moreover, the melting temperature of PEF steadily

25

increased, with increasing the temperature of isothermal crystallization. TMDSC

26

studies showed enhanced re-crystallization upon heating for the samples crystallized

27

under large supercoolings. However, for samples crystallized at 170oC or above, two

28

non-reversing melting peaks were observed and these were attributed to the melting of

29

crystals of different stabilities. Re-crystallization was evidenced after these melting

30

peaks. For samples crystallized at 200oC, only a weak re-crystallization peak was

31

recorded, after the double non-reversing melting. No indication for re-

32

crystallization/reorganization was observed for the solvent crystallized samples.

33

Finally, it was realized that fresh PEF samples always crystallized faster than those

Laboratory of Polymer Chemistry and Technology, Department of Chemistry, Aristotle University of Thessaloniki, GR-541 24, Thessaloniki, Macedonia, Greece 2 School of Materials and National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom 3 Chemistry Department, University of Ioannina, P.O. Box 1186, 45110 Ioannina, Greece 4 Department of Food Technology, Technological Educational Institute of Thessaloniki, PO Box 141, GR-57400 Thessaloniki, Greece

1 ACS Paragon Plus Environment


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1

who suffered repeating melting. This was also observed for other furanoates, but is in

2

contrast to what is observed for their terephthalate or napthalate counterparts.

3

furanoates,

poly(ethylene

furanoate),

crystallization,

4

Keywords:

5

furandicarboxylic acid

6

Corresponding authors: George Z. Papageorgiou [email protected]

2,5-

7 8

1. Introduction

9

Furanoate polyesters are an exceptional class of biobased polymers 1. They offer the

10

advantages of reduced carbon footprint, reduced non-renewable energy for their

11

production and excellent properties, especially referring to their gas barrier properties

12

2

13

high cost, when compared with their fossil based homologues, was always a major

14

drawback. The biorefinery concept seems to be answer to the problem 5. Chemicals

15

from vegetable feedstocks like sugars, vegetable oils, organic acids, glycerol and

16

others have been proposed as monomers for polymer production 6. Carbohydrates and

17

lignin are the major sources of aromatic monomers, with 2,5-furandicarboxylic acid

18

(FDCA) and vanillic acid being the most important examples 7. In particular, FDCA

19

has been screened to be one of the most important building blocks or top value-added

20

chemicals derived from biomass by the U.S. Department of Energy 8. Polyesters

21

bearing furan

moieties

22

poly(butylene

2,5-furan

23

furandicarboxylate) (PPF) are considered as the biobased alternatives to their

24

terephthalate homologues 9, 10.

25

PEF and other similar furanic polymers have gained an increasing interest, due to

26

their renewable nature and promising properties 2, 11, 12. An impressive 19-fold and 10-

27

fold reduction was found in CO2 and oxygen permeability, respectively, for PEF

28

compared to PET 13, 14. It was reported that PEF also exhibits mechanical and thermal

29

properties comparable to those of PET. The combination of these favorable properties

30

could enable light-weighting of beverage packaging 15.

31

Although synthesis of furanoates has been reported in a number of papers, only a

32

limited number of publications appeared in open literature. The thermal properties and

. The idea for polymers from renewable resources is not new

like

poly(ethylene 2,5-furan

dicarboxylate)

(PBF)

and

3, 4

but their relatively

dicarboxylate) (PEF), poly(propylene

2,5-


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1

isothermal and non-isothermal crystallization of PEF have been investigated just

2

recently 2, 10-13, 16-19.

3

For PET, the commonly cited crystal structure was determined by Daubeny et al.

4

using X-ray diffraction measurements on drawn PET fibers. This crystal structure is

5

triclinic with dimensions of a=0.456 nm, b=0.594 nm, c=1.075 nm, α=98.5ο, β=118ο

6

and γ=112ο, which comprises one repeating unit and yields a crystal density of 1.455

7

g/cm3 20. For PEN, the α-crystalline structure is triclinic with dimensions a =0.651nm,

8

b = 0.575nm c = 1.320nm, α = 81.33o, β = 144.00o γ = 100.00o and the crystal density

9

is 1.407 g/cm3 21.

20

10

Three crystal modifications of PEN have been reported, known as a, b and γ. The a-

11

modification has a triclinic unit cell with a=0.6541 nm, b=0.757 nm, c=1.32 nm,

12

α=81.33 ο, β=144ο, γ=100ο and a density of 1.407 g /cm3. The b modification was

13

suggested to be triclinic with a=0.926 nm, b=1.559 nm, c=1.273 nm, α=121.6 ο, β

14

=95.57 ο, γ =122.52 ο and a density of 1.439 g /cm3. Moreover, a monoclinic unit cell

15

was also proposed for the b modification, with a=1.304 nm, b=0.926 nm, c=1.3 nm, α

16

=131.478, β=γ=90ο and a density of 1.368 g /cm3. The γ modification was found in a

17

PEN single crystal and the unit cell has not been determined yet 21-24.

18

For PEF, the crystal structure was estimated in an early study by Kazaryan and

19

Medvedeva 25. PEF also yielded a triclinic unit cell, but with dimensions a=0.575 nm,

20

b=0.535 nm, c=2.010 nm, α=133.3ο, β=90ο and γ=112ο, comprising two repeating

21

units and resulting in a crystal density of 1.565 g /cm3. The density of the amorphous

22

phase is 1.4299 g /cm3 compared to 1.3346 g /cm3 for PET

23

publication has appeared on the crystal structure of PEF. Just recently a systematic

24

work was published on the effect of temperature on melt and cold-crystallization of

25

PEF

26

structure and crystallization process.

16

26

. However, no recent

. In contrast, several studies have been reported on PET and PEN crystal

27

In our previous work we studied the thermal transitions and crystallization

28

kinetics of PEF 16. Moreover, in a series of papers we also presented the synthesis and

29

thermal behaviors of poly(butylene furanoate) (PBF), poly(propylene furanoate)

30

(PPF), and other furan based polyesters

31

explore the effect of different conditions on the crystallization, including

32

polymorphism, crystal stability, reorganization and kinetics of transformation. In

33

particular, melt and cold-crystallization but also solvent induced crystallization were

34

investigated in detail.

27-31

. In this work we made an effort to



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1

2. Experimental

2

2.1. Materials

3

Dimethyl-2,6-naphthalate (DMN) was obtained from Amoco Chemicals and Fine

4

Acids Co (purum 99%). Dimethyl terephthalate (DMT) was obtained from Du Pont

5

De Nemours Co and 2,5-furan dicarboxylic acid (purum 97 %) was purchased from

6

Aldrich Co. Ethylene glycol and tetrabutyl titanate (TBT) catalyst of analytical grade

7

were purchased also from Aldrich Co. All other materials and solvents used were of

8

analytical grade.

9 10

2.2. Polyester synthesis

11

The polyesters were prepared by the two-stage melt polycondensation method

12

(esterification and polycondensation) in a glass batch reactor 16, 32. Details of synthesis

13

were described in our previous work

14

completed, the polyesters were easily removed, milled and washed with methanol.

15

Especially for PEF, 10 g of milled polyester were transferred into a beaker where 200

16

mL of dichloromethane were added. The mixture was stirred till a part of the amount

17

of PEF was dissolved. After filtered, a white-colored material was isolated on the

18

Gooch-filter. Pure PEF stayed overnight under vacuum to remove the residue of the

19

used solvent.

16

. After the polycondensation reaction was

20 21

2.3. Polyester characterization

22

2.3.1. Intrinsic viscosity measurement.

23

Intrinsic viscosity [η] measurements were performed using an Ubbelohde viscometer

24

at 30 oC in a mixture of phenol/1,1,2,2-tetrachloroethane (60/40, w/w).

25

Number-average molecular weight (Mn) was measured by Gel permeation

26

chromatography (GPC) using a Waters 150οC apparatus equipped with differential

27

refractometer as detector and three ultrastyragel (103, 104, 105Å) columns in series.

28

Hexafluoroisopropanol was used as mobile phase at a flow rate 0.5 mL/min at 40oC.

29

Calibration was performed using polystyrene standards with a narrow molecular

30

weight distribution.

31 32

2.3.2. Wide angle X-Ray diffraction patterns (WAXD).


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1

X-ray diffraction measurements of the samples were performed using a MiniFlex II

2

XRD system from Rigaku Co, with CuKα radiation (λ=0.154 nm) in the angle 2θ

3

range from 5 to 65 degrees.

4 5

2.3.3. Differential Scanning Calorimetry (DSC).

6

A Perkin–Elmer, Pyris Diamond DSC differential scanning calorimeter, calibrated

7

with pure Indium and Zinc standards, was used. The system also included an

8

Intracooler 2P cooling accessory, in order the DSC apparatus to achieve function at

9

sub-ambient temperatures and high cooling rates. Samples of 5±0.1 mg sealed in

10

aluminium pans were used, to test the thermal behavior of the quenched polymers.

11

The samples were cooled to 25oC and then heated at a rate 20°C/min to above the

12

melting temperature. In order to obtain amorphous materials, the samples were heated

13

to 40 oC above the melting temperature and held there for 5 min, in order to erase any

14

thermal history, before cooling in the DSC with the highest achievable rate

15

(80oC/min).

16

For Temperature Modulated DSC studies a TA Instruments TMDSC (TA

17

Q2000) combined with a cooling accessory was also used. The instrument was

18

calibrated with indium for heat flow and temperature, while the heat capacity was

19

evaluated using a sapphire standard. Nitrogen gas flow of 50 ml/min was purged into

20

the DSC cell. The sample mass was kept around 5 mg. The Al sample and reference

21

pans were of identical mass with an error of ± 0.01 mg. The TMDSC scans were

22

performed at a heating rate of 5oC/min, with temperature modulation amplitude of

23

1oC and a period of 60 s. The samples were initially cooled to 0°C and then heated at

24

a rate of 20°C/min at temperatures 40oC higher than the melting temperature. In order

25

to obtain amorphous materials, the samples were held there for 5 min, in order to

26

erase any thermal history, before cooling in the DSC with the highest achievable rate

27

(80oC/min).

28

Isothermal crystallization experiments of the polymers at various temperatures below

29

the melting point were performed after self-nucleation of the polyester sample. Self-

30

nucleation measurements were performed in analogy to the procedure described by

31

Fillon et al. 33. The protocol used is a modification of that described by Müller et al. 34

32

and can be summarized as follows: a) melting of the sample at 40 oC above the

33

observed melting point for 5 min to erase any previous thermal history; b) cooling at



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1

20 oCmin-1 to room temperature; c) initiate cold-crystallization to create a ‘‘standard’’

2

thermal history and partial melting by heating at 5 oCmin-1 up to a ‘‘self-nucleation

3

temperature’’, Ts which was 224oC for PEF ; d) thermal conditioning at Ts for 1 min.

4

Depending on Ts, the crystalline polyester will be completely molten, only self-

5

nucleated or self-nucleated and annealed. If Ts is sufficiently high, no self-nuclei or

6

crystal fragments can remain (Ts Domain I - complete melting domain). At

7

intermediate Ts values, the sample is almost completely molten, but some small

8

crystal fragments or crystal memory effects remain, which can act as self-nuclei

9

during a subsequent cooling from Ts, (Ts Domain II-self - nucleation domain). Finally,

10

if Ts is too low, the crystals will only be partially molten, and the remaining crystals

11

will undergo annealing during the 1 min at Ts, while the molten crystals will be self-

12

nucleated during the later cooling, (Ts Domain III - self-nucleation and annealing

13

domain); e) cooling scan from Ts to the crystallization temperature (Tc), where the

14

effects of the previous thermal treatment will be reflected on isothermal

15

crystallization. In the case of high crystallization temperatures close to the self-

16

nucleation temperature, at which crystallization and nucleation are slow, i.e. above

17

195oC, the cooling rate was 20oC/min. This was chosen prior to achieve equilibration

18

of the instrument and before recording the isothermal crystallization. However, in the

19

case of lower Tcs, where crystallization and especially nucleation proceed much

20

faster, the sample was first cooled form Ts to (Tc + 10)oC at 80oC/min and finally

21

cooled to Tc at 20oC/min to achieve equilibration. The crystallization temperature

22

range for the fastest crystallization was close to 165oC. Therefore, the rate of

23

80oC/min was chosen beforehand, to prevent crystallization or nucleation on cooling

24

at this particular range. f) Heating scan at 20 oCmin-1 for standard DSC scans, or

25

heating at an underlying rate 5oC/min in case of TMDSC studies, to 40oC above the

26

melting point, where the effects of the thermal history will be apparent on the melting

27

signals. Experiments were performed to check that the sample did not crystallize

28

during the cooling to Tc and that a full crystallization exothermic peak was recorded

29

at Tc. In case that some other method was applied, this will be discussed in the

30

corresponding part.

31 32 33


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1

3. Results and discussion

2

As was also described in the experimental part, PEF, PET and PEN polyester samples

3

were synthesized by applying the two step polycondensation method 16. The intrinsic

4

viscosity values were 0.45 dL/g for PEF, 0.43 dL/g for PEN samples and 0.47 dL/g

5

for PET. GPC showed that the number average molecular weight (Mn) values were

6

13700, 12100 and 11200 g/mol for the PET, PEN and PEF sample, respectively.

7

Figure 1a shows the WAXD patterns of PEF samples crystallized under

8

different conditions. As it can be seen, there are substantial differences between the

9

patterns of the samples after solvent induced crystallization and after cold

10

crystallization at 150oC, or cold-crystallization at 150oC and annealing for 2h at

11

210oC. These observations lead to the conclusion that the α-crystalline form can be

12

obtained by bulk-crystallization (cold-or melt-crystallization), while a second

13

different crystal form β, can be generated by solvent induced crystallization. Similarly

14

to PET, the α-crystalline form is more stable thermodynamically than the other forms,

15

unless the material is remelted. In general, the WAXD patterns of the cold-

16

crystallized samples (α-crystal form) showed peaks at angles 2θ; 9.1o, 13.7o, 15.4o,

17

17.3o, 18.1o, 20.1o, 22.6o, 23.3o, 25.9o, 27.6o. The solvent crystallized PEF (β-crystal

18

form) showed peaks at angles 2θ; 10.0o, 14.8o, 16.3o, 18.9o, 20.8o, 23.5o, 24.7o, 27.7o,

19

29.7o, 32.3o. Furthermore, it can be realized that the quenching of the sample for the

20

cold-crystallization procedure, affected significantly the crystalline type, suggesting a

21

possible metastable nature of the crystals (α΄) of PEF. The diffractogram of the

22

sample which was solvent-crystallized after annealing at 210oC for 2h, remained

23

essentially the same, although the intensity of the peaks increased. Finally, the solvent

24

treated sample, after complete melting and cold-crystallization at 165oC for 1h, gave a

25

pattern very similar to the one that was observed after melt or cold-crystallization. In

26

this case it seems that the polymer sample after washing, was free of oligomers and

27

crystallization resulted in finer structure and sharp peaks in the WAXD pattern.

28

Besides PEF, two poly(ethylene furanoate-co-succinate) (PEFS) copolymers

29

with compositions EF/SF mol/mol 95/5 and 80/20, respectively, were also

30

synthesized. In Figure 1b, the patterns of two copolymers with compositions EF/SF

31

mol/mol 95/5 and 80/20, respectively, are also presented. It is worth to note that the

32

PEFS samples exhibited an identical pattern with the solvent-crystallized PEF. This

33

fact, along with the fact that the two sets of samples were prepared in the same way, is



1

another confirmation that the specific procedure induces the presence of the β-

2

crystalline form, which is in principle different than the α-form.

(a)

Intensity (counts)

Solvent Crystallized

Solvent Crystallized o annealed at 210 C o

Cold Crystallized at 150 C o annealed at 210 C, 2hr

Solvent treated, melted and cold crystallized o at 165 C, 1hr 5

10

15

20

25

30

35

2theta (degrees)

3 4

(b) PEFS 80/20 solvent crystallized Intensity (counts)

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Page 8 of 24

PEFS 95/5 solvent crystallized PEF solvent crystallized PEF Soxhlet PEF melt crystallized PEF Amorphous 0

10

20

30

40

50

60

70

2theta (degrees)

5


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1

Figure 1. a) Comparison between WAXD patterns of solvent crystallized and cold-

2

crystallized PEF samples and b) WAXD patterns of solvent crystallized PEF and

3

poly(ethylene furanoate-ran-ethylene succinate) copolymers, melt crystallized and

4

amorphous PEF.

5 6

The WAXD patterns of PEF were also compared with those of PET and PEN. The

7

patterns of the solvent crystallized PEF were rather similar to that of the α-crystalline

8

form of PEN, obtained after cold crystallization at 210oC. In contrast, the pattern of

9

the PEF sample that was cold-cystallized and annealed at 210oC, showed similarities

10

with that of the α-crystalline form of PET obtained after cold crystallization at 200oC

11

(Figure 2a).

(a) PEF solvent (100)

Intensity (counts)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(010)

(-112) (-111)

(-110)

(001)

PEN α-form PEΤ α-form PEF cold-cryst

5

10

15

20

25

30

35

2theta (degrees)

12 13



(b) 4 mW Heat Flow (mW) Endo Up

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Page 10 of 24

o

PEF Melt crystallized at 195 C

PEF Solvent crystallized

PEF Amorphous

-50

0

50

100

150

200

250

300

o

Temperature ( C)

1 2

Figure 2. a) WAXD patterns of solvent and cold-crystallized PEF compared to cold-

3

crystallized PET and PEN. b) DSC traces of PEF samples after bulk or solvent

4

induced crystallization.

5 6

As standard DSC heating traces at 20oC/min showed (Figure 2b), the melting

7

peak temperature of the solvent treated PEF appeared at 219oC, and it was essentially

8

the same with that of the sample that was melt-crystallized at 195oC.

9

The WAXD patterns of samples cold crystallized at 150oC and then annealed

10

at increasing temperatures, can be seen in Figure 3. As it can be seen, crystal

11

transition did not occur upon heating PEF at increasing temperatures. However, three

12

new peaks at 13.8o, 18.1o and 26.7o became evident after annealing at temperatures

13

above 185oC. Stoclet et al.

14

structure called α΄ is formed, while the more perfect one α is formed upon

15

crystallization at higher temperatures. The specific phenomenon of the crystalline

16

perfection for a specific crystalline type has been also observed in the past in more

17

common polymers, such as polypropylene 35-37.

19

proposed that below 170oC a less perfect crystalline

18

In the DSC traces of PEF samples melt-crystallized above 185oC (Figure 4a),

19

a continuous increase can be observed in the melting temperatures, obviously due to

20

increased perfection and crystal thickening. The peak temperature for the sample

21

crystallized at 210oC was 232oC and the temperature at the end of the melting peak


Page 11 of 24

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1

was about 237oC. As a matter of fact, successful crystallization at elevated

2

temperatures and examination of the thermal behavior of samples crystallized well

3

above 190oC can only be achieved by applying self-nucleation before melt

4

crystallization.

5

This research was also focused on samples crystallized under large

6

supercoolings; that is in the low crystallization temperature range. Figure 4b shows

7

the effect of the heating rate on the melting peaks of samples isothermally melt-

8

crystallized at 165oC. This was the temperature where the faster crystallization rates

9

were determined in this work and it is in a perfect agreement with the value that was

10

calculated using kinetic parameters by Codou et al.18. Here, one should emphasize on

11

two points: the triple melting behavior for the heating rate of 5oC/min and the increase

12

of the ultimate melting peak temperature with decreasing heating rate. These findings

13

show that the effect of recrystallization is important for samples crystallized under

14

large supercoolings. By virtue such samples are dominated by metastable crystalline

15

phases, susceptible to reorganization upon heating. In the case of the slow heating

16

scan, the ultimate temperature melting peak is expected to be associated with the

17

melting of the recrystallized material. This behavior however is completely different

18

with that for samples crystallized above 190oC, where fine crystal phases were formed

19

and increased lamella thickening occurred, resulting in a dramatic increase of the

20

melting temperature.

21



o

150 C o 155 C o 160 C o 165 C o 170 C o 175 C o 180 C o 185 C o 190 C o 195 C o 200 C o 205 C o 210 C

o

Intensity (counts)

210 C

o

150 C 12,5

15,0

17,5

20,0

22,5

25,0

27,5

30,0

32,5

Angle 2theta (deg)

1 2

Figure 3. WAXD patterns of PEF samples melt-crystallized at different temperatures.

(a) Heat Flow (mW) Endo Up

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Page 12 of 24

o

210 C o 205 C o 200 C o 195 C o 190 C o 185 C o 180 C o 175 C o 170 C 2 mW

170

180

190

200

210

220

230

240

250

o

Temperature ( C)

3


Page 13 of 24

Heat Flow (mW) Endo Up

(b)


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III

o

2 mW

5 C/min II I 150

175

200

225

250

o

Temperature ( C) o

5 C/min o 20 C/min o 40 C/min

0

50

100

150

200

250

o

Temperature ( C)

1 2

Figure 4. (a) DSC heating traces 20oC/min at of PEF samples melt-crystallized at

3

different temperatures and b) DSC traces recorded at different heating rates for PEF

4

samples crystallized at 165oC.

5 6

TMDSC was also elaborated and a series of samples crystallized under

7

different conditions, were examined. Figure 5a shows the TMDSC curves for a melt-

8

quenched PEF sample. The cold-crystallization exothermic peak appeared at about

9

167oC in this run, at an underlying heating rate 5oC/min. Extensive re-crystallization

10

occurred just after the cold-crystallization, as it can be seen in the non reversing signal

11

and the two peaks are not well resolved. It can be realized once again that the rate

12

applied for the quenching (80oC/min) is enough to avoid nucleation during cooling,

13

since the strong peaks of cold-crystallization and the well-defined glass transition

14

allow this conclusion. Samples effectively melt-crystallized on cooling with slow

15

cooling rates i.e. 2.5oC/min and 1.5oC/min, were also tested (Figure 5b, 5c). In this

16

case self nucleation was applied first, by heating to 180oC at 5oC/min and holding for

17

1 min at this temperature, before the cooling scan. However, crystallization upon

18

cooling at the slower rate of 1.25oC/min occurred at higher temperatures, as it started

19

at 168oC compared to 164oC for the cooling scan at 2.5oC/min. This lead to formation

20

of more stable crystals and also higher final degree of crystallinity. Re-crystallization

21

can be observed in the non-reversing signal curve in two stages. For the sample 13 ACS Paragon Plus Environment


1

cooled at 1.25oC/min, the re-crystallization started at about 160oC while for the

2

sample cooled at 2.5oC/min at 140oC (see blue arrows in the non-reversing curves).

3

This fact indicates the lower stability of the crystals formed upon faster cooling.

4


PEF Quenched

2 mW Total

Reversing Non Reversing

0

50

100

150

200

250

o

Temperature ( C)

5 6

(b)

o

PEF cooled at 2.5 C/min from the melt

1 mW


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 24

o

164 C

Total Reversing o

140 C

Non Reversing

0

50

100

150

200

250

o

Temperature ( C)

7


Page 15 of 24

(c) o

PEF cooled at 1.25 C/min from the melt


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 mW o

168 C

Total

Reversing o

160 C

Non Reversing 0

50

100

150

200

250

o

Temperature ( C)

1 2

Figure 5. TMDSC signals for PEF samples: a) quenched, b) cooled after self-

3

nucleation at 180oC at 2.5oC/min and c) cooled after self-nucleation at 180oC at

4

1.25oC/min.

5 6 7

The behavior of isothermally melt-crystallized samples was tested as it can be seen in

8

Figure 6. An example is given in Figure 6a where the steps followed prior to perform

9

self-nucleated isothermal crystallization at 195oC and the subsequent TMDSC heating

10

scan are listed. As can be seen first, the sample was heated to 260oC at 20oC/min to

11

achieve complete melting, cooled at the same rate down to 20oC. Subsequently it was

12

heated at the slow rate of 5oC/min, prior to give the sample enough time to cold-

13

crystallize, up on heating to 224oC and held for 1min. Then, it was cooled to a

14

temperature equal to (Tc + 10)oC at the fast rate of 80oC/min to prevent crystallization

15

or nucleation on cooling, then reached Tc by cooling at a slower rate of 20oC/min for

16

better equilibration of the instrument. It was held at Tc till complete crystallization

17

before cooling to 20oC at 50oC/min. In the case of high crystallization temperatures

18

close to Ts, where crystallization and nucleation are both slow, a rate of 20oC/min was

19

chosen for cooling from Ts to Tc, prior to achieve better equilibration of the

20

instrument. Finally, a TMDSC scan was performed at an underlying heating rate of

21

5oC/min up to 260oC. Crystallization after self-nucleation was accelerated so 15 ACS Paragon Plus Environment


1

experiments could be completed within a reasonable timescale, even at high

2

temperatures. For example, as one can see in the inset of the lower graph in Figure 6a,

3

crystallization at 195oC was complete within 30min, after successful self-nucleation.

4

A similar program was followed for all the tested temperatures prior to evaluate

5

crystallization kinetics and record the subsequent melting behavior after isothermal

6

crystallization. Figure 6b shows the TMDSC signals for a PEF sample melt-crystallized at

8

170oC. In the non-reversing signal curve a first non-reversing melting appeared at

9

192oC and a second one at 214oC. Then, re-crystallization started. This shows that

10

crystals grown at 170oC are relatively stable, and this is consistent with the

11

observation of the more stable α-form above this temperature. However, re-

12

crystallization occurred above 216oC, till complete melting. For the sample

13

crystallized at 195oC (Figure 7a), two non-reversing melting peaks appeared at 204oC

14

and 216oC, respectively. Finally, limited re-crystallization occurred on further

15

heating. Two non-reversing melting peaks were revealed at 211 and 220oC,

16

respectively, in the non-revering signal curve of PEF crystallized at 200oC (Figure

17

7b). There was a weak indication for re-crystallization after the non-reversing

18

melting. So, stable crystals can only be obtained upon crystallization above 200oC. 300 250

Self-nucleation

20 oC/ min

(a) Temperature (oC)

7

200

o

o

Heati ng at

150 100 50 0 -20

0

g tin a He

20

at

5

in m C/

Isothermal

M

40

60

80

C DS

He

100

26 24 22 20 18 16 14 12 10

a

g tin

at

120

5

C/

in m

140

160

21.8



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Page 16 of 24

21.6

21.4

21.2

21.0

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20.6

65

70

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85

90

Time (min)

-20

0

20

40

60

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140

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Time (min) 19


Page 17 of 24

(b) o


PEF Crystallized at 170 C

1 mW

Total

Reversing

Non Reversing 0

50

100

150

200

250

o

Temperature ( C)

1 2

Figure 6. a) Schematic of the self-nucleation and TMDSC scan for PEF, b) TMDSC

3

signals for PEF melt-crystallized at 170oC.

(a) o

PEF Crystallized at 195 C Heat Flow (mW) Endo Up

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 mW

Total Reversing Non Reversing 0

50

100

150

200

250

o

Temperature ( C)

4



(b) o

PEF Crystallized at 200 C


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Page 18 of 24

1 mW

Total Reversing Non Reversing 0

50

100

150

200

250

o

Temperature ( C)

1 2

Figure 7. TMDSC signals for PEF melt-crystallized at a) 195oC and b) 200oC.

3 4 5

The TMDSC traces of the solvent crystallized PEF can be seen in Figure 8a. In the

6

non-reversing signal, a large non-reversing melting can be observed. A relatively

7

limited reversing melting was also detected in the high temperature side of melting

8

(222oC), in the reversing signal curve. This behavior is consistent with a highly stable

9

crystalline phase.

10

Figure 8b shows the TMDSC curves of solvent crystallized PEF after annealing at

11

200oC for 2h. In this case, the non-reversing melting was enhanced, while a very

12

small reversing melting peak remained at 224oC. In both cases, the glass transition

13

was not clear. As a matter of fact, in the original sample, a non-reversing relaxation

14

was detected around 50oC. At this point, it should be mentioned that the reversing

15

endothermic signal is actually representing the partial melting of lamellae. In contrast,

16

the non-reversing endothermic signal is associated with complete melting of separate

17

lamellae or stacks of lamellae 38. It has been reported that for perfected crystals with

18

melting points not too far from their equilibrium melting point, at lower degrees of

19

supercooling, the recrystallization procedure is not fast enough. Thus, annealing

20

polyesters at high temperatures, results in crystals which have high Tm, relatively to

21

their equilibrium melting point and consequently their non-reversing signal is

22

dominated by a very large melting endotherm 38.

23 18 ACS Paragon Plus Environment

Page 19 of 24


PEF Solvent Crystallized

1 mW

Total

Reversing

Non Reversing -50

0

50

100

150

200

250

300

o

Temperature ( C)

1

(b) PEF Solvent Crystallized o & Annealed at 200 C for 2hr Heat Flow (mW) Endo Up

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2 mW

Total Reversing

Non Reversing -50

0

50

100

150

200

250

300

o

Temperature ( C)

2 3

Figure 8. TMDSC signals for solvent crystallized PEF a) original and b) after

4

annealing at 200oC for 2h.

5 6

The isothermal crystallization of PEF was studied by direct cooling from the melt

7

after self-nucleation as was reported previously. The peaks from isothermal

8

crystallization at various temperatures can be seen in Figure 9a. These peaks directly

9

prove that after self-nucleation, crystallization from the melt was fast despite the

10

sufficient molecular weight of the polyester sample (Mn=11200 g/mol). Self

11

nucleation allowed crystallization even at temperatures above 190oC. Otherwise,

12

isothermal crystallization was very slow. It should be also noted at this point that in

13

contrast to other polyesters like PET, PEN or aliphatic ones which degrade and then 19 ACS Paragon Plus Environment


1

crystallize faster after repeating meltings, PEF showed significantly slower

2

crystallization. This was observed even after self-nucleation of samples, previously

3

melted for a prolonged time. The results presented in Figure 9b confirmed that the

4

crystallization kinetics is faster when the sample is crystallized for the first time after

5

self-nucleation. The crystallization temperatures where the sample presents the faster

6

rates, range between 150 and 180oC. Another plausible explanation for the slower

7

crystallization of PEF might be the gradual removal of the absorbed humidity or

8

solvent traces, which act as plasticizers for the polyester. Finally, Stoclet et al.

9

reported a value of 3500 ±1000 g/mol for the entanglement molecular weight of PEF,

10

compared to Me=1450 g/mol for PET 19. The comparison of the number of monomers

11

between entanglements (Me/M0) shows that there are more monomers between two

12

entanglements for PEF than for PET: ≈27 vs. ≈7. This may be attributed to the stiffer

13

character of the PEF polymer chain that restricts chain mobility and consequently

14

chain folding 19, 26.

(a)

0.05 0.00 -0.05


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Page 20 of 24

-0.10 -0.15 -0.20 -0.25

o

o

165 C o 175 C o 185 C o 195 C o 205 C

-0.30 -0.35 -0.40

170 C o 180 C o 190 C o 200 C

-0.45 0

5

10

15

20

25

30

Time (min)

15 16 17


Page 21 of 24

(b) Crystallization Half-Time (min)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


50

Fresh Sample after SN Old Sample after SN Fresh Sample

40

30

20

10

0

120

130

140

150

160

170

180

190

200

210

o

Temperature ( C)

1 2

Figure 9. (a) DSC traces of isothermal crystallization of PEF at various temperatures,

3

(b) crystallization half time of samples prior and after self-nucleation

4 5 6

4. Conclusions

7

The crystallization and polymorphic nature of the eco-friendly polyester,

8

poly(ethylene furanoate) (PEF) have been discussed in detail. Crystallization under

9

different conditions, such as solvent or bulk crystallization attributed different

10

crystalline structure to the material. Bulk crystallization at high temperatures resulted

11

in α-crystals, while at low temperatures a less ordered structure α΄ (metastable) was

12

formed, which was reorganized to α upon heating. A thorough temperature-modulated

13

DSC study revealed that for the samples crystallized under large supercoolings,

14

enhanced re-crystallization occurred upon heating. Moreover, for temperatures above

15

170oC two non-reversing melting peaks were observed, which were attributed to the

16

melting of crystals of different stabilities. For samples crystallized at 200oC, only a

17

weak re-crystallization peak was recorded, after the double non-reversing melting.

18

The solvent-crystallized samples on the other hand, did not exhibit any of the melting-

19

recrystallization phenomena such as in the melt-crystallized ones. Finally, the solid

20

samples crystallized faster than the melt-crystallized ones, as a result of their higher

21

nucleation density. 21 ACS Paragon Plus Environment


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References (1) Sousa, A. F.; Vilela, C.; Fonseca, A. C.; Matos, M.; Freire, C. S.; Gruter, G.-J. M.; Coelho, J. F.; Silvestre, A. J. Polym. Chem. 2015, 6, 5961-5983. (2) Burgess, S. K.; Mikkilineni, D. S.; Daniel, B. Y.; Kim, D. J.; Mubarak, C. R.; Kriegel, R. M.; Koros, W. J. Polymer 2014, 55, (26), 6870-6882. (3) Vilela, C.; Sousa, A. F.; Fonseca, A. C.; Serra, A. C.; Coelho, J. F.; Freire, C. S.; Silvestre, A. J. Polym. Chem. 2014, 5, 3119-3141. (4) Moore, J.; Kelly, J. E. J. Pol. Sci. Polym. Chem. Ed. 1978, 16, 2407-2409. (5) Esposito, D.; Antonietti, M. Chem. Soc. Rev. 2015, 44, 5821-5835. (6) Partenheimer, W.; Grushin, V. V. Adv. Synth. Catal. 2001, 343, 102-111. (7) Gandini, A.; Lacerda, T. M. Prog. Polym. Sci. 2015, 48, 1-39 (8) Werpy, T.; Petersen, G. Top Value Added Chemicals from Biomass: Results of screening for potential candidates from sugars and synthesis gas. ed.; [U.S. Department of Energy [Office of] Energy Efficiency and Renewable Energy: 2004. (9) Thiyagarajan, S.; Vogelzang, W.; Knoop, R. J.; Frissen, A. E.; van Haveren, J.; van Es, D. S. Green Chem. 2014, 16, 1957-1966. (10) Knoop, R. J.; Vogelzang, W.; Haveren, J.; Es, D. S. J. Pol. Sci. Part A: Polym. Chem. 2013, 51, 4191-4199. (11) Burgess, S. K.; Mubarak, C. R.; Kriegel, R. M.; Koros, W. J. J. Pol. Sci. Part B: Polym. Phys. 2015, 53, 389-399. (12) Burgess, S. K.; Mikkilineni, D. S.; Daniel, B. Y.; Kim, D. J.; Mubarak, C. R.; Kriegel, R. M.; Koros, W. J. Polymer 2014, 55, 6861-6869. (13) Burgess, S. K.; Kriegel, R. M.; Koros, W. J. Macromolecules 2015, 48, 21842193. (14) Burgess, S. K.; Karvan, O.; Johnson, J.; Kriegel, R. M.; Koros, W. J. Polymer 2014, 55, 4748-4756. (15) Gopalakrishnan, P.; Narayan-Sarathy, S.; Ghosh, T.; Mahajan, K.; Belgacem, M. N. J. Polym. Res. 2014, 21, 1-9. (16) Papageorgiou, G. Z.; Tsanaktsis, V.; Bikiaris, D. N. Phys. Chem. Chem.Phys. 2014, 16, 7946-7958. (17) van Berkel, J. G.; Guigo, N.; Kolstad, J. J.; Sipos, L.; Wang, B.; Dam, M. A.; Sbirrazzuoli, N. Macromol. Mater. Eng. 2015, 300, 466-474. (18) Codou, A.; Guigo, N.; van Berkel, J.; De Jong, E.; Sbirrazzuoli, N. Macromol. Chem. Phys. 2014, 215, 2065-2074. (19) Stoclet, G.; du Sart, G. G.; Yeniad, B.; de Vos, S.; Lefebvre, J. Polymer 2015, 72, 165-176. (20) Daubeny, R. d. P.; Bunn, C. In The crystal structure of polyethylene terephthalate, Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences, 1954; The Royal Society: 1954; pp 531-542. (21) Mencik, Z. Chemick'y Prumysl 1967, 17, 78-83. (22) Liu, J.; Sidoti, G.; Hommema, J.; Geil, P.; Kim, J.; Cakmak, M. J. Macromol. Sci., Part B: Phys. 1998, 37, 567-586. (23) Buchner, S.; Wiswe, D.; Zachmann, H. Polymer 1989, 30, (3), 480-488. (24) Zachmann, H. G. Die Makromol. Chem. 1985, 12, 175-188. (25) L.G. Kazaryan; Medvedeva, F. M. Vysokomolekulyarnye Soedineniya, Seriya B: Kratkie Soobshcheniya 1968, 305-306. (26) Burgess, S. K.; Leisen, J. E.; Kraftschik, B. E.; Mubarak, C. R.; Kriegel, R. M.; Koros, W. J. Macromolecules 2014, 47, 1383-1391.


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(27) Papageorgiou, G. Z.; Tsanaktsis, V.; Papageorgiou, D. G.; Exarhopoulos, S.; Papageorgiou, M.; Bikiaris, D. N. Polymer 2014, 55, 3846-3858. (28) Tsanaktsis, V.; Vouvoudi, E.; Papageorgiou, G. Z.; Papageorgiou, D. G.; Chrissafis, K.; Bikiaris, D. N. J. Anal. Appl. Pyrolysis 2015, 112, 369-378. (29) Papageorgiou, G. Z.; Papageorgiou, D. G.; Tsanaktsis, V.; Bikiaris, D. N. Polymer 2015, 62, 28-38. (30) Papageorgiou, G. Z.; Tsanaktsis, V.; Papageorgiou, D. G.; Chrissafis, K.; Exarhopoulos, S.; Bikiaris, D. N. Eur. Pol. J. 2015, 67, 383-396. (31) Papageorgiou, G. Z.; Guigo, N.; Tsanaktsis, V.; Papageorgiou, D. G.; Exarhopoulos, S.; Sbirrazzuoli, N.; Bikiaris, D. N. Eur. Pol. J. 2015, 68, 115-127. (32) Karayannidis, G. P.; Papageorgiou, G. Z.; Bikiaris, D. N.; Tourasanidis, E. V. Polymer 1998, 39, 4129-4134. (33) Fillon, B.; Wittmann, J.; Lotz, B.; Thierry, A. J. Macromol. Sci., Part B: Phys. 1993, 31, 1383-1393. (34) Cavallo, D.; Gardella, L.; Portale, G.; Müller, A. J.; Alfonso, G. C. Polymer 2014, 55, (1), 137-142. (35) De Rosa, C.; Guerra, G.; Napolitano, R.; Petraccone, V.; Pirozzi, B. European Polymer Journal 1984, 20, 937-941. (36) Naiki, M.; Kikkawa, T.; Endo, Y.; Nozaki, K.; Yamamoto, T.; Hara, T. Polymer 2001, 42, 5471-5477. (37) Papageorgiou, D. G.; Papageorgiou, G. Z.; Bikiaris, D. N.; Chrissafis, K. Eur. Pol. J. 2013, 49, 1577-1590. (38) Sauer, B. B.; Kampert, W. G.; Neal Blanchard, E.; Threefoot, S. A.; Hsiao, B. S. Polymer 2000, 41, 1099-1108.

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1

Page 24 of 24

For Table of Contents Use Only

2 3

On the crystallization and polymorphism of poly(ethylene furanoate)

4 5

Vasilios Tsanaktsis1, Dimitrios G. Papageorgiou2, Stylianos Exarhopoulos3,4, Dimitrios

6

N. Bikiaris1, George Z. Papageorgiou3*

7 8

The crystallization and polymorphic nature of poly(ethylene furanoate) (PEF) have

9

been studied in detail and under a wide variety of testing procedures. Crystallization

10

under different conditions, such as solvent or bulk crystallization enabled the

11

observation of the different crystalline structures of the material.

12


Crystallization and Polymorphism of Poly(ethylene ... - ACS Publications

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