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Synthesis and characterization of poly(isosorbide-co-butylene 2,5-furandicarboxylate) copolyesters
European Polymer Journal 115 (2019) 70–75
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European Polymer Journal journal homepage: www.elsevier.com/locate/europolj
Synthesis and characterization of poly(isosorbide-co-butylene 2,5furandicarboxylate) copolyesters
T
Xiansong Wanga,b, Qingyin Wanga, Shaoying Liua, Gongying Wanga,
⁎
a b
Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu, Sichuan 610041, China National Engineering Laboraory for VOCs Pollution Control Material & Technology, University of Chinese Academy of Sciences, Beijing 101408, China
ARTICLE INFO
ABSTRACT
Keywords: 2,5-furandicarboxylic acid Isosorbide 1,4-butanediol Mechanical properties Biopolymers Copolyesters
Fully biobased copolyesters poly(isosorbide-co-butylene 2,5-furandicarboxylate) (PISBF) were synthesized from 2,5-dimethylfuran dicarboxylate (DMFD), isosorbide (IS) and 1,4-butanediol (BDO) via transesterification and polycondensation reactions. The resulting copolymers were characterized by 1H NMR, 13C NMR, GPC, intrinsic viscosity, DSC, TGA and tensile testing, respectively. The NMR characterizations had confirmed that BDO was successfully introduced into the poly(isosorbide 2,5-furandicarboxylate) (PIF) polyester chains. Over the IS experimental composition range 20–80 % in copolymer chains, PISBF copolymers had TD, 5% values higher than 370 °C and TDM higher than 405 °C, and Tg values within the range of 55 °C and 150 °C. Introduction of BDO units into PIF chains imparted the PISBF copolyester with better mechanical performance than PIF, thus PISBF copolyesters with IS content of 20–50% were strong and toughened copolymers with Young’s modulus about 1400 MPa, tensile strength at break higher than 53 MPa, and elongation at break higher than 46%.
1. Introduction In recent years, considerable researches were focused on production of biobased polymers to replace polymers synthesized from petroleum resources [1–4]. Polymers synthesized from 2,5-Furandicarboxylic acid are the most promising biopolymers, since FDCA has aromatic structure and can be prepared from sugars and polysaccharides [1,5,6]. A series of FDCA based polyesters had been synthesized from FDCA and diols [7–13]. For instance, the first obtained FDCA polymer poly(ethylene 2,5-furandicarboxylate) (PEF) had a glass transition temperature (Tg) about 85 °C [7,14] and a Young’s modulus comparable to that of poly (ethylene terephthalate) (PET) [15]. However, the elongation at break of PEF was lower than 7% [16–18], which significantly hinders its industry application. Although 1,4-Cyclohexanedicarboxylic acid [18] and ε-caprolactone [19] can enhance the toughness of PEF and maintain a higher Young’s modulus at the same time, the corresponding copolyesters’ glass transition temperatures (Tg) were below 35 °C. Xie [20] recently modified PEF with 1,5-pentanediol, the resulting copolyester PE82Pe18F had an elongation at break 115%, a tensile modulus 3200 MPa, and a Tg 75 °C. Xie [21] also modified PEF with PTMG, the copolymer PET1KF-20 possessed an elongation at break 252%, a Young’s modulus 2900 MPa and a Tg 68 °C. The copolymer PET2KF-20 possessed an elongation at break 71%, a Young’s modulus 3100 MPa and a Tg 82 °C. Up to now, no other FDCA polyester which possessed ⁎
improved tensile ductility, and retained high Young’s modulus and high Tg at the same time was reported. Besides FDCA, isosorbide (IS) is also a renewable monomer obtained from biomass resources. When IS was used as building block in polymer chains, the resulting polyesters achieved high Tg values with enhanced thermal stability [22–24]. Poly(isosorbide 2,5-furandicarboxylate) (PIF), for example, which exhibited a Tg within the range of 137–194 °C and the decomposition temperature at maximum weight loss rate (TDM) was between 390 °C and 450 °C [22,25,26]. The isomer of IS, thus isomannide [27] had also been used to modify poly(butylene 2,5-furandicarboxylate) (PBF), the copolyester containing isomannide 40–50 mol % displayed a Tg in the range of 80–97 °C [27]. And isoidide [25,28] is also an effective monomer to enhance the Tg of polymers. Though FDCA polyesters based on IS or its isomers showed excellent thermal properties, the structure of IS is more rigid and complicated than ethylene glycol, we can deduce that PIF is more brittle than PEF. Unfortunately, there were no data about the mechanical properties of PIF to date. Hitherto, FDCA polymers based on IS with high elongation at break were rarely been reported. Inspired by the outstanding Tg values of polymers contained isosorbide or its isomers, and taking the flexibility of polyesters synthesized from FDCA and aliphatic diols into consideration [9,12,15,18–20,29–32], PBF is neither too rigid nor too flexible [9,31–34]. Therefore, we wish to obtain a strong and toughened copolyester with high Tg value and high thermal stability by
Corresponding author. E-mail address: [email protected] (G. Wang).
https://doi.org/10.1016/j.eurpolymj.2019.03.025 Received 20 October 2018; Received in revised form 7 March 2019; Accepted 8 March 2019 Available online 09 March 2019 0014-3057/ © 2019 Elsevier Ltd. All rights reserved.
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copolymerizing 2,5-dimethylfuran dicarboxylate (DMFD), isosorbide and 1,4-butanediol. In this work, 1,4-butanediol was employed to modify poly(isosorbide 2,5-furandicarboxylate) (PIF), and a series of poly(isosorbideco-butylene 2,5-furandicarboxylate) (PISBF) copolyesters were synthesized from DMFD, IS and BDO by transesterification and polycondensation reactions. Their chemical structures and compositions were determined by 1H NMR and 13C NMR. The molecular weights, thermal properties, thermal stabilities and mechanical properties were investigated by GPC, DSC, TGA, and tensile testing, respectively.
260 °C at rate of 10 °C/min and held at this temperature for 3 min to erase thermal history, then it was cooled down to 0 °C with the cooling speed of 10 °C/min, subsequently, the second heating scan was performed with the heating rate of 10 °C/min to 260 °C. For PIF, the highest DSC scanning temperature was 290 °C. Thermal stability measurements were investigated by a TGA instrument (NETZSCH STA 449 F3), it was performed under nitrogen atmosphere (50 mL/min) with a heating rate of 20 °C/min from 40 °C to 800 °C. Tensile testing was performed using a universal testing machine (NKK 3010D) according to ISO 527-2: 1993 with a stretching rate of 10 mm/min at 25 °C. Dumbbell shaped specimens were prepared by press-molding at 200 °C. For each sample, at least five specimens were tested and the average values were reported.
2. Experimental 2.1. Materials
3. Results and discussion
2,5-Dimethylfuran dicarboxylate (DMFD, 98%, Shanghai Macklin Biochemical Co.,Ltd., China), isosorbide (IS, 98%, Shanghai Yuanye Bio-Technology Co.,Ltd., China), 1,4-butanediol (BDO, 99%, ChengDu KeLong Chemical Co.,Ltd., China), tetrachloroethane (99%, ChengDu KeLong Chemical Co.,Ltd., China), dibutyltin oxide (DBTO, 98%, Acros Organics, USA), phenol (99%, GuangDong GuangHua Technology Co.,Ltd., China), deuterated trifluoroacetic acid (TFA-D, 99.5% + 0.03% V/V TMS, Cambridge Isotope Laboratories, Inc., USA). All chemicals were used as received.
3.1. Compositions and molecular weights In this work, PISBF copolyesters were synthesized via the combination of transesterification reaction and polycondensation reaction (Scheme 1). These copolyesters were named as PIS80B20F, PIS70B30F, PIS60B40F, PIS50B50F, PIS40B60F, PIS30B70F and PIS20B80F according to the molar ratio of IS to BDO in diols feed. The final composition of PISBF copolyester ([IS]/[BDO]) was determined by the integration of protons H7, 10 and H5 arising from IS and BDO units (Fig. 1). As seen in Table 1, the IS molar ratio in the copolyesters was about 2–5% lower than feed, this is due to the fact that a part of IS vaporized during the polycondensation procedure and other uncontrollable causes. All in all, the composition of PISBF copolyesters can be easily controlled by the molar ratio of IS to BDO in diols feed. The molecular weight (Mw) of PISBF with IS molar ratio from 20% to 60% was between 18,400 and 37,400 g/mol. However, the intrinsic viscosity of PIF was very low, this may be due to the different reactivity of the two hydroxy groups of IS [28]. As increasing the BDO content in PIF chains, the copolyester achieved higher molecular weight and intrinsic viscosity compared to PIF. It means that BDO is an effective comonomer to improve the molecular weight of PIF.
2.2. Synthesis of PIF, PISBF and PBF PISBF copolyesters were synthesized by the combination of transesterification and polycondensation reactions (Scheme 1). Firstly, DMFD, BDO, IS (DMFD/Diols, 1/1.6) and DBTO (0.15 mol % of DMFD) were transferred into a 50 mL three-necked round bottom flask equipped with a condenser, a mechanical stirrer and a N2 inlet. The air in the flask was purged with N2 gas 5 min, subsequently, the reaction system was heated to 200 °C (salt bath temperature) under N2 for 2 h with agitating at 150 rpm, then 210 °C for 1 h. Secondly, the salt bath temperature was increased to 250 °C and the pressure of the reaction system was reduced to 100 Pa in 0.5 h, the polycondensation reaction was conducted for 6 h with agitating at 200 rpm (for PBF, 230 °C, 3 h). Finally, the reaction system was returned to atmospheric pressure by introducing nitrogen and cooled to room temperature. PISBF copolyesters with different IS contents were obtained by controlling the molar ratio of IS to BDO in feed. PIF and PBF were synthesized by the same procedures. All polyesters were used without purification.
3.2. Chemical structures The chemical structures of PIF, PISBF and PIF were identified with H NMR (Fig. 1). For PIF, the chemical shifts between 7.46 ppm and 7.56 ppm (H3′) are attributed to the vinyl protons of furan ring, the chemical shifts from 5.76 ppm to 5.80 ppm (H7,10) and chemical shift at 5.48 ppm (H9), 5.08 ppm (H8), and chemical shifts from 4.37 ppm to 4.52 ppm (H6,11) are arising from the protons in IS units [25,28]. As for PBF, the chemical shift at 7.43 ppm (H3) is belong to the protons in furan ring, the chemical shifts at 4.61 ppm (H4) and 2.08 ppm (H5) are arising from butylene protons [9,35]. As can be seen in Fig. 1, the chemical shifts of protons in furan ring (H3, 3′), the signals of protons in BDO units (H4, H5) and the signals of protons in IS units (H7, 10, H9, H8 and H6,11) are appeared in the 1H NMR spectra of PISBF copolyesters. The 13C NMR spectra of PIF, PB50IS50F and PBF are depicted in Fig. 2. For PIS50B50F, the chemical shifts at 70.67 ppm (C11), 73.17 ppm (C6), 75.38 ppm (C9), 78.93 ppm (C8), 81.42 ppm (C10) and 85.77 ppm (C7) are assigned to IS units, the peaks at 119.87 ppm (C3), 120.83 ppm (C3′), peaks from 145.66 ppm to 147.36 ppm (C2, 2′), and peaks from 159.42 ppm to 161.12 ppm (C1, 1′) are assigned to FDCA units, the signals at 66.84 ppm (C4) and 24.55 ppm (C5) are belong to BDO units 1
2.3. Characterization The intrinsic viscosity was measured in an Ubbelohde viscometer at 25 °C, the mixture of phenol and tetrachloroethane (1/1, W/W) was used as solvent. The molecular weight was determined by Waters Model 1515 pump and a Model 2414 refractive index detector with two columns (PLgel 5 μm Mixed-C 300 × 7.5 mm) at 35 °C. Chloroform was used as eluent at a flow rate of 1 mL/min and polystyrene standards were used for calibration. PIF and PBF were not measured by GPC since they did not dissolve in chloroform. PIS80B20F and PIS70B30F were partly soluble in chloroform, so they were also not measured by GPC. The chemical structures were confirmed by 1H NMR (400 MHz) and 13C NMR (100 MHz) in CF3COOD using a Burke AVANCE III 400 M NMR spectrometer at 25 °C. DSC measurements were carried out with a DSCQ20 instrument under nitrogen atmosphere. The sample was heated to
Scheme 1. Synthesis route of PISBF copolyester from DMFD, IS and BDO. 71
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[25,28,35]. The nonprotonated carbons (C2 or C2′) of FDCA units are sensitive to the linking groups [27]. The signals of these nonprotonated carbons in PIS50B50F split into four peaks (Ca, Cc, Cd and Cb), which are corresponding to the BDO-F-IS, BDO-F-BDO, IS-F-IS and IS-F-BDO triads (Fig. 2). The degree of randomness (B) of PIS50B50F was calculated from these four peaks areas and the value was 0.97 [36], thus PIS50B50F exhibited random copolymer character. The presence of chemical shifts 147.36 ppm (Ca) and 145.66 ppm (Cb) in PIS50B50F indicated that the BDO unit had been successfully introduced into the PIF backbones. 3.3. Thermal properties The thermal properties of PIF, PISBF and PBF were examined by DSC (Fig. 3), the results are listed in Table 2. PIF was amorphous since no melt crystallization peak upon cooling scan or melting peak at second heating scan was found. And PIF had a Tg 162.7 °C. PBF was semicrystalline polyester with a Tg 42.3 °C and a Tm 168.3 °C (second heating scan), and a Tc 125.8 °C (cooling scan). The PISBF copolymers with IS molar ratio from 30% to 80% exhibited neither melt crystallization peaks upon cooling scan nor melting peaks at the second heating scan, suggesting that they were amorphous. The glass transition temperature of the PISBF copolyester was within the range of 55 °C and 150 °C, which decreased gradually as increasing the BDO content in the copolymer backbones. Moreover, the Tg values of PISBF copolyesters agree well with the results calculated from the Fox equation (Fig. 5), which further indicates the random structure of PISBF copolyesters. The thermal stabilities of PIF, PISBF and PBF were analysed by TGA (Fig. 4). All the copolymer (PISBF) and homopolymers (PIF, PBF) decomposed in one step under nitrogen atmosphere. The TD,5% value of PISBF copolyester with IS molar ratio from 20% to 80% was higher than 370 °C, and the TD, 5% value of PISBFs was higher than 405 °C higher. From these results, it can be concluded that the thermal stability of PISBF copolyester is between that of PBF and PIF.
Fig. 1. 1H NMR spectra of PIF, PISBFs and PBF. Table 1 Composition and molecular weight of PIF, PISBFs and PBF. Polyester
PIF PIS80B20F PIS70B30F PIS60B40F PIS50B50F PIS40B60F PIS30B70F PIS20B80F PBF a
[η] dL g−1
Composition
GPC
[IS]/[BDO]/mol %
Mn
Mw
Feed
Copolyestera
g mol−1
g mol−1
PDI
– 80/20 70/30 60/40 50/50 40/60 30/70 20/80 –
– 76.3/23.7 65.2/34.8 55.3/46.7 47.6/52.4 37.5/62.5 24.7/75.3 15.9/84.1 –
– – – 9300 13,100 15,900 17,700 19,100 –
– – – 18,400 25,500 32,400 35,700 37,400 –
– – – 1.98 1.94 2.04 2.01 1.96 –
0.27 0.45 0.51 0.58 0.69 0.74 0.77 0.83 1.23
3.4. Mechanical properties The Young’s modulus and elongation at break of FDCA-based polyesters are still subject to improvement in order to meet the thermal
Values obtained from 1H NMR.
Fig. 2. (a)
13
C NMR spectrum of PIF, PIS50B50F and PBF; (b) Assignments of the α-carbons of FDCA units in PIS50B50F for different triads.
72
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Fig. 3. DSC curves of PIF, PISBFs and PBF. (a): Cooling scan, (b): Second heating scan.
dumbbell shaped specimens during press-molding, thus no data about the mechanical properties of PIF were reported in this work. In this work, PBF performed as a strong and toughened thermoplastic polyester with a Young’s modulus 1502 ± 101 MPa, a tensile strength at break 53 ± 2 MPa, and an elongation at break 685 ± 32%. PIS80B20F and PIS70B30F were brittle thermoplastic without yielding point. PIS60B40F just fractured after achieving the yielding point. PIS50B50F got a distinct yielding point with Young’s modulus 1471 ± 61 MPa and tensile strength at break 63 ± 4 MPa, but the elongation at break had decreased to 46 ± 7%. PIS40B60F, PIS30B70F and PIS20B80F were also toughened plastic with Young’s modulus about 1400 MPa and elongation at break higher than 170%. In brief, over the IS experimental composition range 20–80 % in copolymer chains, the Young’s modulus of PISBF copolyester decreased from 1900 MPa to 1400 MPa. The tensile strength at yield and break decreased gradually as decreasing the IS content, and the elongation at yield also decreased. However, the elongation at break increased rapidly from 46 ± 7% to 435 ± 31% while decreasing the IS content from 50% to 20%. According to the tensile testing results, the fully biobased PISBF polyesters with IS content range 20–50 % had maintained higher
Table 2 DSC and TGA results of PIF, PISBFs and PBF. Polymer
PIF PIS80B20F PIS70B30F PIS60B40F PIS50B50F PIS40B60F PIS30B70F PIS20B80F PBF
DSC (cooling and the second heating scan)
TGA
Tg °C
Tc °C
ΔHc J/g
Tm °C
ΔHm J/g
TD,
162.7 150.6 130.0 110.4 103.1 87.2 68.9 55.3 42.3
– – – – – – – – 125.8
– – – – – – – – 37.9
– – – – – – – – 168.3
– – – – – – – – 30.6
377.2 376.1 375.5 373.4 373.0 372.6 370.8 370.4 373.4
5%
°C
TDM °C 419.7 416.9 413.4 411.3 410.6 412.3 405.0 405.0 408.0
TD, 5%: The decomposition temperature at 5% weight lost. TDM : The decomposition temperature at maximum weight loss rate.
and mechanical properties demands in industry. The tensile stressstrain curves of PISBF copolyesters and PBF are depicted in Fig. 6. Their Young’s modulus, tensile strength at yield and break, elongation at yield and break were listed in Table 3. PIF was too brittle to make
Fig. 4. TGA (a) and DTG (b) curves of PIF, PISBFs and PBF. 73
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Table 4 The mechanical properties of PIS50B50F, PE53Pe47F and PE48H52F. Polyester
E (MPa)
σy (MPa)
σb (MPa)
εy (%)
εb (%)
PIS50B50F PE53Pe47F [20] PE48H52F [29]
1471 ± 61 2760 ± 370 1830 ± 170
104 ± 6 72 ± 2 48 ± 2
63 ± 4 29 ± 2 40 ± 4
31 ± 1 3.9 ± 0.1 2.7 ± 0.2
46 ± 7 265 ± 12 275 ± 26
E: Young’s modulus, σy: tensile strength at yield, σb: tensile strength at break, εy: elongation at yield, εb: elongation at break.
mechanical properties of PEPeF copolyester (PE53Pe47F) and PEHF copolyester (PE48H52F) were compared with PIS50B50F under almost the same comonomer content (50%) in Table 4. The Young’s modulus and elongation at break of PIS50B50F was lower than that value of PE53Pe47F and PE48H52F. However, PIS50B50F possessed higher tensile strength at yield and break than these two copolyesters, the elongation at yield of PIS50B50F was also much higher than PE53Pe47F and PE48H52F. From the different mechanical performances of PIS50B50F, PE53Pe47F and PE48H52F, it follows that aliphatic diol with longer chains will be beneficial to the elongation at break of FDCA polyesters, and IS which possess stronger stiffness than ethylene glycol is in favor of the tensile strength at yield and break of FDCA polyesters.
Fig. 5. Composition dependence of the Tg values of PISBF copolyesters. The dashed line shows the results calculated from the Fox equation: 1/Tg = wIF/ TgPIF + wBF/TgPBF.
4. Conclusions Fully biobased copolyesters poly(isosorbide-co-butylene 2,5-furandicarboxylate) (PISBF) were successfully prepared from 2,5-dimethylfuran dicarboxylate, isosorbide and 1,4-butanediol via transesterification and polycondensation reactions. The DSC and TGA analyses revealed that the Tg values of PISBF copolyesters were within the range of 55 °C and 150 °C, the TD, 5% values were higher than 370 °C and the TDM values were higher than 405 °C. Introduction of 1,4-butanediol units into poly(isosorbide 2,5-furandicarboxylate) polyester chains imparted the ensuing PISBF copolyesters with better mechanical performance than PIF. Thus, PISBF copolyesters with IS molar ratio from 20% to 50% were strong and toughened polymers, which possessed Young’s modulus about 1400 MPa, tensile strength at break higher than 53 MPa and elongation at break higher than 46%. Acknowledgments This work was supported by the National Key R&D Program of China (Project No: 2016YFB0301900), the Science and Technology Support Program of Sichuan Province (Project No: 2015GZ0065).
Fig. 6. Stress-strain curves of PISBFs and PBF. Table 3 Mechanical properties of PISBFs and PBF. Polyester
E (MPa)
PIS80B20F PIS70B30F PIS60B40F PIS50B50F PIS40B60F PIS30B70F PIS20B80F PBF
1900 1735 1590 1471 1408 1488 1464 1502
± ± ± ± ± ± ± ±
60 68 42 61 54 91 100 101
Appendix A. Supplementary material
σy (MPa)
σb (MPa)
εy (%)
εb (%)
– – 136 ± 5 104 ± 6 83 ± 5 71 ± 3 54 ± 2 39 ± 2
77 ± 3 140 ± 11 134 ± 3 63 ± 4 59 ± 2 57 ± 4 53 ± 3 53 ± 2
– – 30 31 26 22 18 19
15 ± 3 28 ± 2 32 ± 2 46 ± 7 173 ± 12 306 ± 28 435 ± 31 685 ± 32
± ± ± ± ± ±
1 1 2 1 1 1
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Synthesis and characterization of poly(isosorbide-co-butylene 2,5furandicarboxylate) copolyesters
T
Xiansong Wanga,b, Qingyin Wanga, Shaoying Liua, Gongying Wanga,
⁎
a b
Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu, Sichuan 610041, China National Engineering Laboraory for VOCs Pollution Control Material & Technology, University of Chinese Academy of Sciences, Beijing 101408, China
ARTICLE INFO
ABSTRACT
Keywords: 2,5-furandicarboxylic acid Isosorbide 1,4-butanediol Mechanical properties Biopolymers Copolyesters
Fully biobased copolyesters poly(isosorbide-co-butylene 2,5-furandicarboxylate) (PISBF) were synthesized from 2,5-dimethylfuran dicarboxylate (DMFD), isosorbide (IS) and 1,4-butanediol (BDO) via transesterification and polycondensation reactions. The resulting copolymers were characterized by 1H NMR, 13C NMR, GPC, intrinsic viscosity, DSC, TGA and tensile testing, respectively. The NMR characterizations had confirmed that BDO was successfully introduced into the poly(isosorbide 2,5-furandicarboxylate) (PIF) polyester chains. Over the IS experimental composition range 20–80 % in copolymer chains, PISBF copolymers had TD, 5% values higher than 370 °C and TDM higher than 405 °C, and Tg values within the range of 55 °C and 150 °C. Introduction of BDO units into PIF chains imparted the PISBF copolyester with better mechanical performance than PIF, thus PISBF copolyesters with IS content of 20–50% were strong and toughened copolymers with Young’s modulus about 1400 MPa, tensile strength at break higher than 53 MPa, and elongation at break higher than 46%.
1. Introduction In recent years, considerable researches were focused on production of biobased polymers to replace polymers synthesized from petroleum resources [1–4]. Polymers synthesized from 2,5-Furandicarboxylic acid are the most promising biopolymers, since FDCA has aromatic structure and can be prepared from sugars and polysaccharides [1,5,6]. A series of FDCA based polyesters had been synthesized from FDCA and diols [7–13]. For instance, the first obtained FDCA polymer poly(ethylene 2,5-furandicarboxylate) (PEF) had a glass transition temperature (Tg) about 85 °C [7,14] and a Young’s modulus comparable to that of poly (ethylene terephthalate) (PET) [15]. However, the elongation at break of PEF was lower than 7% [16–18], which significantly hinders its industry application. Although 1,4-Cyclohexanedicarboxylic acid [18] and ε-caprolactone [19] can enhance the toughness of PEF and maintain a higher Young’s modulus at the same time, the corresponding copolyesters’ glass transition temperatures (Tg) were below 35 °C. Xie [20] recently modified PEF with 1,5-pentanediol, the resulting copolyester PE82Pe18F had an elongation at break 115%, a tensile modulus 3200 MPa, and a Tg 75 °C. Xie [21] also modified PEF with PTMG, the copolymer PET1KF-20 possessed an elongation at break 252%, a Young’s modulus 2900 MPa and a Tg 68 °C. The copolymer PET2KF-20 possessed an elongation at break 71%, a Young’s modulus 3100 MPa and a Tg 82 °C. Up to now, no other FDCA polyester which possessed ⁎
improved tensile ductility, and retained high Young’s modulus and high Tg at the same time was reported. Besides FDCA, isosorbide (IS) is also a renewable monomer obtained from biomass resources. When IS was used as building block in polymer chains, the resulting polyesters achieved high Tg values with enhanced thermal stability [22–24]. Poly(isosorbide 2,5-furandicarboxylate) (PIF), for example, which exhibited a Tg within the range of 137–194 °C and the decomposition temperature at maximum weight loss rate (TDM) was between 390 °C and 450 °C [22,25,26]. The isomer of IS, thus isomannide [27] had also been used to modify poly(butylene 2,5-furandicarboxylate) (PBF), the copolyester containing isomannide 40–50 mol % displayed a Tg in the range of 80–97 °C [27]. And isoidide [25,28] is also an effective monomer to enhance the Tg of polymers. Though FDCA polyesters based on IS or its isomers showed excellent thermal properties, the structure of IS is more rigid and complicated than ethylene glycol, we can deduce that PIF is more brittle than PEF. Unfortunately, there were no data about the mechanical properties of PIF to date. Hitherto, FDCA polymers based on IS with high elongation at break were rarely been reported. Inspired by the outstanding Tg values of polymers contained isosorbide or its isomers, and taking the flexibility of polyesters synthesized from FDCA and aliphatic diols into consideration [9,12,15,18–20,29–32], PBF is neither too rigid nor too flexible [9,31–34]. Therefore, we wish to obtain a strong and toughened copolyester with high Tg value and high thermal stability by
Corresponding author. E-mail address: [email protected] (G. Wang).
https://doi.org/10.1016/j.eurpolymj.2019.03.025 Received 20 October 2018; Received in revised form 7 March 2019; Accepted 8 March 2019 Available online 09 March 2019 0014-3057/ © 2019 Elsevier Ltd. All rights reserved.
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copolymerizing 2,5-dimethylfuran dicarboxylate (DMFD), isosorbide and 1,4-butanediol. In this work, 1,4-butanediol was employed to modify poly(isosorbide 2,5-furandicarboxylate) (PIF), and a series of poly(isosorbideco-butylene 2,5-furandicarboxylate) (PISBF) copolyesters were synthesized from DMFD, IS and BDO by transesterification and polycondensation reactions. Their chemical structures and compositions were determined by 1H NMR and 13C NMR. The molecular weights, thermal properties, thermal stabilities and mechanical properties were investigated by GPC, DSC, TGA, and tensile testing, respectively.
260 °C at rate of 10 °C/min and held at this temperature for 3 min to erase thermal history, then it was cooled down to 0 °C with the cooling speed of 10 °C/min, subsequently, the second heating scan was performed with the heating rate of 10 °C/min to 260 °C. For PIF, the highest DSC scanning temperature was 290 °C. Thermal stability measurements were investigated by a TGA instrument (NETZSCH STA 449 F3), it was performed under nitrogen atmosphere (50 mL/min) with a heating rate of 20 °C/min from 40 °C to 800 °C. Tensile testing was performed using a universal testing machine (NKK 3010D) according to ISO 527-2: 1993 with a stretching rate of 10 mm/min at 25 °C. Dumbbell shaped specimens were prepared by press-molding at 200 °C. For each sample, at least five specimens were tested and the average values were reported.
2. Experimental 2.1. Materials
3. Results and discussion
2,5-Dimethylfuran dicarboxylate (DMFD, 98%, Shanghai Macklin Biochemical Co.,Ltd., China), isosorbide (IS, 98%, Shanghai Yuanye Bio-Technology Co.,Ltd., China), 1,4-butanediol (BDO, 99%, ChengDu KeLong Chemical Co.,Ltd., China), tetrachloroethane (99%, ChengDu KeLong Chemical Co.,Ltd., China), dibutyltin oxide (DBTO, 98%, Acros Organics, USA), phenol (99%, GuangDong GuangHua Technology Co.,Ltd., China), deuterated trifluoroacetic acid (TFA-D, 99.5% + 0.03% V/V TMS, Cambridge Isotope Laboratories, Inc., USA). All chemicals were used as received.
3.1. Compositions and molecular weights In this work, PISBF copolyesters were synthesized via the combination of transesterification reaction and polycondensation reaction (Scheme 1). These copolyesters were named as PIS80B20F, PIS70B30F, PIS60B40F, PIS50B50F, PIS40B60F, PIS30B70F and PIS20B80F according to the molar ratio of IS to BDO in diols feed. The final composition of PISBF copolyester ([IS]/[BDO]) was determined by the integration of protons H7, 10 and H5 arising from IS and BDO units (Fig. 1). As seen in Table 1, the IS molar ratio in the copolyesters was about 2–5% lower than feed, this is due to the fact that a part of IS vaporized during the polycondensation procedure and other uncontrollable causes. All in all, the composition of PISBF copolyesters can be easily controlled by the molar ratio of IS to BDO in diols feed. The molecular weight (Mw) of PISBF with IS molar ratio from 20% to 60% was between 18,400 and 37,400 g/mol. However, the intrinsic viscosity of PIF was very low, this may be due to the different reactivity of the two hydroxy groups of IS [28]. As increasing the BDO content in PIF chains, the copolyester achieved higher molecular weight and intrinsic viscosity compared to PIF. It means that BDO is an effective comonomer to improve the molecular weight of PIF.
2.2. Synthesis of PIF, PISBF and PBF PISBF copolyesters were synthesized by the combination of transesterification and polycondensation reactions (Scheme 1). Firstly, DMFD, BDO, IS (DMFD/Diols, 1/1.6) and DBTO (0.15 mol % of DMFD) were transferred into a 50 mL three-necked round bottom flask equipped with a condenser, a mechanical stirrer and a N2 inlet. The air in the flask was purged with N2 gas 5 min, subsequently, the reaction system was heated to 200 °C (salt bath temperature) under N2 for 2 h with agitating at 150 rpm, then 210 °C for 1 h. Secondly, the salt bath temperature was increased to 250 °C and the pressure of the reaction system was reduced to 100 Pa in 0.5 h, the polycondensation reaction was conducted for 6 h with agitating at 200 rpm (for PBF, 230 °C, 3 h). Finally, the reaction system was returned to atmospheric pressure by introducing nitrogen and cooled to room temperature. PISBF copolyesters with different IS contents were obtained by controlling the molar ratio of IS to BDO in feed. PIF and PBF were synthesized by the same procedures. All polyesters were used without purification.
3.2. Chemical structures The chemical structures of PIF, PISBF and PIF were identified with H NMR (Fig. 1). For PIF, the chemical shifts between 7.46 ppm and 7.56 ppm (H3′) are attributed to the vinyl protons of furan ring, the chemical shifts from 5.76 ppm to 5.80 ppm (H7,10) and chemical shift at 5.48 ppm (H9), 5.08 ppm (H8), and chemical shifts from 4.37 ppm to 4.52 ppm (H6,11) are arising from the protons in IS units [25,28]. As for PBF, the chemical shift at 7.43 ppm (H3) is belong to the protons in furan ring, the chemical shifts at 4.61 ppm (H4) and 2.08 ppm (H5) are arising from butylene protons [9,35]. As can be seen in Fig. 1, the chemical shifts of protons in furan ring (H3, 3′), the signals of protons in BDO units (H4, H5) and the signals of protons in IS units (H7, 10, H9, H8 and H6,11) are appeared in the 1H NMR spectra of PISBF copolyesters. The 13C NMR spectra of PIF, PB50IS50F and PBF are depicted in Fig. 2. For PIS50B50F, the chemical shifts at 70.67 ppm (C11), 73.17 ppm (C6), 75.38 ppm (C9), 78.93 ppm (C8), 81.42 ppm (C10) and 85.77 ppm (C7) are assigned to IS units, the peaks at 119.87 ppm (C3), 120.83 ppm (C3′), peaks from 145.66 ppm to 147.36 ppm (C2, 2′), and peaks from 159.42 ppm to 161.12 ppm (C1, 1′) are assigned to FDCA units, the signals at 66.84 ppm (C4) and 24.55 ppm (C5) are belong to BDO units 1
2.3. Characterization The intrinsic viscosity was measured in an Ubbelohde viscometer at 25 °C, the mixture of phenol and tetrachloroethane (1/1, W/W) was used as solvent. The molecular weight was determined by Waters Model 1515 pump and a Model 2414 refractive index detector with two columns (PLgel 5 μm Mixed-C 300 × 7.5 mm) at 35 °C. Chloroform was used as eluent at a flow rate of 1 mL/min and polystyrene standards were used for calibration. PIF and PBF were not measured by GPC since they did not dissolve in chloroform. PIS80B20F and PIS70B30F were partly soluble in chloroform, so they were also not measured by GPC. The chemical structures were confirmed by 1H NMR (400 MHz) and 13C NMR (100 MHz) in CF3COOD using a Burke AVANCE III 400 M NMR spectrometer at 25 °C. DSC measurements were carried out with a DSCQ20 instrument under nitrogen atmosphere. The sample was heated to
Scheme 1. Synthesis route of PISBF copolyester from DMFD, IS and BDO. 71
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[25,28,35]. The nonprotonated carbons (C2 or C2′) of FDCA units are sensitive to the linking groups [27]. The signals of these nonprotonated carbons in PIS50B50F split into four peaks (Ca, Cc, Cd and Cb), which are corresponding to the BDO-F-IS, BDO-F-BDO, IS-F-IS and IS-F-BDO triads (Fig. 2). The degree of randomness (B) of PIS50B50F was calculated from these four peaks areas and the value was 0.97 [36], thus PIS50B50F exhibited random copolymer character. The presence of chemical shifts 147.36 ppm (Ca) and 145.66 ppm (Cb) in PIS50B50F indicated that the BDO unit had been successfully introduced into the PIF backbones. 3.3. Thermal properties The thermal properties of PIF, PISBF and PBF were examined by DSC (Fig. 3), the results are listed in Table 2. PIF was amorphous since no melt crystallization peak upon cooling scan or melting peak at second heating scan was found. And PIF had a Tg 162.7 °C. PBF was semicrystalline polyester with a Tg 42.3 °C and a Tm 168.3 °C (second heating scan), and a Tc 125.8 °C (cooling scan). The PISBF copolymers with IS molar ratio from 30% to 80% exhibited neither melt crystallization peaks upon cooling scan nor melting peaks at the second heating scan, suggesting that they were amorphous. The glass transition temperature of the PISBF copolyester was within the range of 55 °C and 150 °C, which decreased gradually as increasing the BDO content in the copolymer backbones. Moreover, the Tg values of PISBF copolyesters agree well with the results calculated from the Fox equation (Fig. 5), which further indicates the random structure of PISBF copolyesters. The thermal stabilities of PIF, PISBF and PBF were analysed by TGA (Fig. 4). All the copolymer (PISBF) and homopolymers (PIF, PBF) decomposed in one step under nitrogen atmosphere. The TD,5% value of PISBF copolyester with IS molar ratio from 20% to 80% was higher than 370 °C, and the TD, 5% value of PISBFs was higher than 405 °C higher. From these results, it can be concluded that the thermal stability of PISBF copolyester is between that of PBF and PIF.
Fig. 1. 1H NMR spectra of PIF, PISBFs and PBF. Table 1 Composition and molecular weight of PIF, PISBFs and PBF. Polyester
PIF PIS80B20F PIS70B30F PIS60B40F PIS50B50F PIS40B60F PIS30B70F PIS20B80F PBF a
[η] dL g−1
Composition
GPC
[IS]/[BDO]/mol %
Mn
Mw
Feed
Copolyestera
g mol−1
g mol−1
PDI
– 80/20 70/30 60/40 50/50 40/60 30/70 20/80 –
– 76.3/23.7 65.2/34.8 55.3/46.7 47.6/52.4 37.5/62.5 24.7/75.3 15.9/84.1 –
– – – 9300 13,100 15,900 17,700 19,100 –
– – – 18,400 25,500 32,400 35,700 37,400 –
– – – 1.98 1.94 2.04 2.01 1.96 –
0.27 0.45 0.51 0.58 0.69 0.74 0.77 0.83 1.23
3.4. Mechanical properties The Young’s modulus and elongation at break of FDCA-based polyesters are still subject to improvement in order to meet the thermal
Values obtained from 1H NMR.
Fig. 2. (a)
13
C NMR spectrum of PIF, PIS50B50F and PBF; (b) Assignments of the α-carbons of FDCA units in PIS50B50F for different triads.
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Fig. 3. DSC curves of PIF, PISBFs and PBF. (a): Cooling scan, (b): Second heating scan.
dumbbell shaped specimens during press-molding, thus no data about the mechanical properties of PIF were reported in this work. In this work, PBF performed as a strong and toughened thermoplastic polyester with a Young’s modulus 1502 ± 101 MPa, a tensile strength at break 53 ± 2 MPa, and an elongation at break 685 ± 32%. PIS80B20F and PIS70B30F were brittle thermoplastic without yielding point. PIS60B40F just fractured after achieving the yielding point. PIS50B50F got a distinct yielding point with Young’s modulus 1471 ± 61 MPa and tensile strength at break 63 ± 4 MPa, but the elongation at break had decreased to 46 ± 7%. PIS40B60F, PIS30B70F and PIS20B80F were also toughened plastic with Young’s modulus about 1400 MPa and elongation at break higher than 170%. In brief, over the IS experimental composition range 20–80 % in copolymer chains, the Young’s modulus of PISBF copolyester decreased from 1900 MPa to 1400 MPa. The tensile strength at yield and break decreased gradually as decreasing the IS content, and the elongation at yield also decreased. However, the elongation at break increased rapidly from 46 ± 7% to 435 ± 31% while decreasing the IS content from 50% to 20%. According to the tensile testing results, the fully biobased PISBF polyesters with IS content range 20–50 % had maintained higher
Table 2 DSC and TGA results of PIF, PISBFs and PBF. Polymer
PIF PIS80B20F PIS70B30F PIS60B40F PIS50B50F PIS40B60F PIS30B70F PIS20B80F PBF
DSC (cooling and the second heating scan)
TGA
Tg °C
Tc °C
ΔHc J/g
Tm °C
ΔHm J/g
TD,
162.7 150.6 130.0 110.4 103.1 87.2 68.9 55.3 42.3
– – – – – – – – 125.8
– – – – – – – – 37.9
– – – – – – – – 168.3
– – – – – – – – 30.6
377.2 376.1 375.5 373.4 373.0 372.6 370.8 370.4 373.4
5%
°C
TDM °C 419.7 416.9 413.4 411.3 410.6 412.3 405.0 405.0 408.0
TD, 5%: The decomposition temperature at 5% weight lost. TDM : The decomposition temperature at maximum weight loss rate.
and mechanical properties demands in industry. The tensile stressstrain curves of PISBF copolyesters and PBF are depicted in Fig. 6. Their Young’s modulus, tensile strength at yield and break, elongation at yield and break were listed in Table 3. PIF was too brittle to make
Fig. 4. TGA (a) and DTG (b) curves of PIF, PISBFs and PBF. 73
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Table 4 The mechanical properties of PIS50B50F, PE53Pe47F and PE48H52F. Polyester
E (MPa)
σy (MPa)
σb (MPa)
εy (%)
εb (%)
PIS50B50F PE53Pe47F [20] PE48H52F [29]
1471 ± 61 2760 ± 370 1830 ± 170
104 ± 6 72 ± 2 48 ± 2
63 ± 4 29 ± 2 40 ± 4
31 ± 1 3.9 ± 0.1 2.7 ± 0.2
46 ± 7 265 ± 12 275 ± 26
E: Young’s modulus, σy: tensile strength at yield, σb: tensile strength at break, εy: elongation at yield, εb: elongation at break.
mechanical properties of PEPeF copolyester (PE53Pe47F) and PEHF copolyester (PE48H52F) were compared with PIS50B50F under almost the same comonomer content (50%) in Table 4. The Young’s modulus and elongation at break of PIS50B50F was lower than that value of PE53Pe47F and PE48H52F. However, PIS50B50F possessed higher tensile strength at yield and break than these two copolyesters, the elongation at yield of PIS50B50F was also much higher than PE53Pe47F and PE48H52F. From the different mechanical performances of PIS50B50F, PE53Pe47F and PE48H52F, it follows that aliphatic diol with longer chains will be beneficial to the elongation at break of FDCA polyesters, and IS which possess stronger stiffness than ethylene glycol is in favor of the tensile strength at yield and break of FDCA polyesters.
Fig. 5. Composition dependence of the Tg values of PISBF copolyesters. The dashed line shows the results calculated from the Fox equation: 1/Tg = wIF/ TgPIF + wBF/TgPBF.
4. Conclusions Fully biobased copolyesters poly(isosorbide-co-butylene 2,5-furandicarboxylate) (PISBF) were successfully prepared from 2,5-dimethylfuran dicarboxylate, isosorbide and 1,4-butanediol via transesterification and polycondensation reactions. The DSC and TGA analyses revealed that the Tg values of PISBF copolyesters were within the range of 55 °C and 150 °C, the TD, 5% values were higher than 370 °C and the TDM values were higher than 405 °C. Introduction of 1,4-butanediol units into poly(isosorbide 2,5-furandicarboxylate) polyester chains imparted the ensuing PISBF copolyesters with better mechanical performance than PIF. Thus, PISBF copolyesters with IS molar ratio from 20% to 50% were strong and toughened polymers, which possessed Young’s modulus about 1400 MPa, tensile strength at break higher than 53 MPa and elongation at break higher than 46%. Acknowledgments This work was supported by the National Key R&D Program of China (Project No: 2016YFB0301900), the Science and Technology Support Program of Sichuan Province (Project No: 2015GZ0065).
Fig. 6. Stress-strain curves of PISBFs and PBF. Table 3 Mechanical properties of PISBFs and PBF. Polyester
E (MPa)
PIS80B20F PIS70B30F PIS60B40F PIS50B50F PIS40B60F PIS30B70F PIS20B80F PBF
1900 1735 1590 1471 1408 1488 1464 1502
± ± ± ± ± ± ± ±
60 68 42 61 54 91 100 101
Appendix A. Supplementary material
σy (MPa)
σb (MPa)
εy (%)
εb (%)
– – 136 ± 5 104 ± 6 83 ± 5 71 ± 3 54 ± 2 39 ± 2
77 ± 3 140 ± 11 134 ± 3 63 ± 4 59 ± 2 57 ± 4 53 ± 3 53 ± 2
– – 30 31 26 22 18 19
15 ± 3 28 ± 2 32 ± 2 46 ± 7 173 ± 12 306 ± 28 435 ± 31 685 ± 32
± ± ± ± ± ±
1 1 2 1 1 1
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