Biodegradable aliphatic copolyesters containing PEG-like sequences for sustainable food packaging applications

Polymer Degradation and Stability 105 (2014) 96e106

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Biodegradable aliphatic copolyesters containing PEG-like sequences for sustainable food packaging applications Matteo Gigli a, Nadia Lotti a, *, Massimo Gazzano b, Valentina Siracusa c, Lara Finelli a, Andrea Munari a, Marco Dalla Rosa d a

Dipartimento di Ingegneria Civile, Chimica, Ambientale e dei Materiali, Università di Bologna, Via Terracini 28, 40131 Bologna, Italy Istituto per la Sintesi Organica e la Fotoreattività, CNR, Via Selmi 2, 40126 Bologna, Italy Dipartimento di Ingegneria Industriale, Università di Catania, Viale A. Doria 6, 95125 Catania, Italy d Dipartimento di Scienze e Tecnologie Agro-Alimentari, Università di Bologna, Piazza Goidanich, 60 47521 Cesena, Italy b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 12 December 2013 Received in revised form 19 March 2014 Accepted 11 April 2014 Available online 21 April 2014

A series of novel random copolymers of poly(butylene 1,4-cyclohexanedicarboxylate) (PBCE) containing triethylene glycol sub-unit (P(BCEmTECEn)) were synthesized and characterized in terms of molecular and solid-state properties, among these barrier properties to different gases (oxygen and carbon dioxide). In addition, biodegradability studies both in soil and in compost and ecotoxicological analysis, by means of the Lepidium sativum test, have been conducted. The copolymers displayed a high and similar thermal stability with respect to PBCE. At room temperature, all the copolymers appeared as semicrystalline materials: the main effect of copolymerization was a lowering of crystallinity degree (cc) and a decrease of the melting temperature compared to the parent homopolymer. The Baur’s equation well described the Tm-composition data. Final properties and biodegradation rate of the materials under study were strictly dependent on copolymer composition and cc. As a matter of fact, hydrophilicity regularly increased with the increasing of TECE mol%, due to the PEG-like portion. The elastic modulus and the elongation to break decreased and increased, respectively, as TECE unit content was increased. As to the barrier properties, the selectivity ratios for the examined samples increased with the increasing of TECE mol%, confirming the correlation between the permeability and the chemical composition. The copolymers with lower TECE unit content (up to 30 mol%) showed improved barrier properties with respect to polylactide films tested under the same conditions. Lastly, the biodegradation rate of P(BCEmTECEn) copolymers increased with the increasing of TECE mol%, while PBCE remained almost undegraded in the explored conditions. Ó 2014 Elsevier Ltd. All rights reserved.

Keywords: Poly(butylene 1,4cyclohexanedicarboxylate) Triethylene glycol Random copolymers Solid-state properties Polymer gas permeability

1. Introduction Packaging represents over 60% of the total plastic waste produced in Europe: only in 2012 almost 9.6 Mt of polymeric packages ended up in the waste stream [1]. Many different polymers are currently employed in this field, both in contact or not with the food: [2] 1) polyolefins, which include polyethylenes (low-, linear low-, and high-density polyethylene) (LDPE, LLDPE and HDPE) and polypropylene (PP);

* Corresponding author. Tel.: þ39 051 2090354; fax: þ39 051 2090322. E-mail address: [email protected] (N. Lotti). http://dx.doi.org/10.1016/j.polymdegradstab.2014.04.006 0141-3910/Ó 2014 Elsevier Ltd. All rights reserved.

2) copolymers of ethylene, such as ethylene-vinyl acetate (EVA) or ethylene-vinyl alcohol (EAA); 3) substituted olefins like polystyrene (PS), poly(vinyl alcohol) (PVA) and poly(vinyl chloride) (PVC); 4) polyesters, among all poly(ethylene terephthalate) (PET); 5) polycarbonates (PC); 6) polyamide (PA). The polymers listed above are the most common plastics used in the packaging industry because of their good performances and relatively low cost; however, as it is well known [3e5], they possess very slow degradability in marine and terrestrial environments. Moreover, due to the contamination with organic matter, recycling of these materials is impracticable and economically not convenient [6]. As a consequence, thousands of tons of plastic packaging are disposed in landfills every year, causing a continuous pollution

M. Gigli et al. / Polymer Degradation and Stability 105 (2014) 96e106

increment, besides various municipal waste management problems. Therefore, the need of an alternative to these traditional materials is becoming more and more urgent. In this view, in recent years both academic and industrial researchers focused their attention on the use of biodegradable materials. In particular, poly(lactic acid) (PLA), starch and cellulose based packages are already available on the market [7]. PLA is the most extensively used biodegradable polymer for packaging, but it suffers of some drawbacks. Actually, the most important limitations for food packaging applications of this polymer are the medium barrier to gases and its brittleness [6]. In this framework, new biodegradable materials have to be developed in order to overcome the lacks of PLA and satisfy the requirements for any specific application. Other aliphatic polyesters can represent a valid solution in this respect, because they combine promising physico-mechanical properties, with biodegradability: moreover, they can be produced at a reasonable cost [8]. Within this polymeric class, poly(butylene 1,4cyclohexanedicarboxilate) (PBCE) offers different advantages: the presence of an aliphatic ring in the monomeric unit enables the polymer to have good thermal stability (even higher than poly(butylene terephthalate) (PBT)) [9] and high resistance to heat, light and humidity [10]. Moreover, the stereochemistry of the ring deeply influences the final properties of the polymer: the trans stereoisomer is in fact more symmetrical than the cis, thus improving chain packing, capacity to crystallize and crystal perfection. [9,10] Unfortunately, due to its high crystallinity degree, PBCE is a brittle material and it shows a slow biodegradation rate [11]. As it is well known, copolymerization represents one of the most interesting tools to tailor the properties of a material: through this strategy, it is in fact possible to obtain new polymers with a wide range of properties depending on the kind, relative amount and distribution of the comonomeric units along the polymer chain. Recently, our group directed its research efforts to the introduction of ether and thioether-linkages along the polymer chains of some noteworthy aliphatic polyesters (i.e. poly(butylene succinate) and PBCE) by reactive blending [12e15] or copolycondensation [16,17] with the aim of improving their properties. This approach had a deep impact on the crystallinity degree and hydrophilicity of the new copolymeric systems, due to the reduced chain symmetry and to the presence of electronegative oxygen and sulphur atoms, respectively. As a consequence, the final properties of the parent homopolymers resulted notably modified: mechanical and barrier properties [17], and biodegradation rate [18e20] can be tuned by simply varying the molecular architecture or the copolymer composition. In the present research activity we propose a novel class of PBCE-based aliphatic polyesters containing ether-linkages (P(BCEmTECEn)). In this case, through copolycondensation with triethylene glycol, we introduced PEG-like sequences along the PBCE backbone: the presence of two ether oxygens per repeating unit in the very mobile TE subunit is expected to confer to the polymer higher wettability with respect to P(BCEmBDGn) copolymers [17] and therefore an enhanced biodegradation rate; on the other hand, the aliphatic rings contained in both the co-units should improve the rigidity of the obtained polymers. The structural, thermal and mechanical properties, together with surface wettability have been investigated. In addition, the permeability to oxygen and carbon dioxide has been evaluated. Lastly, biodegradation studies both in compost and in soil and ecotoxycological analyses have been performed. The results obtained have been correlated to copolymer composition.

97

2. Experimental 2.1. Materials 1,4-dimethylcyclohexanedicarboxylate (DMCE), containing 99% of trans isomer, 1,4-butanediol (BD), triethylene glycol (TEG), dichloromethane (DCM), 2-chloroethanol (CE), ethanol (EtOH) and titanium tetrabutoxide (Ti(OBu)4) (Aldrich) were reagent grade products; all reagents were used as supplied, with the exception of Ti(OBu)4 which was distilled before use. 2.2. Synthesis of poly(butylene/triethylene cyclohexanedicarboxylate) copolymers Poly(butylene/triethylene cyclohexanedicarboxylate) random copolymers (P(BCEmTECEn)) were synthesized in bulk starting from DMCE and different ratios BD/TEG, using 20% mol in excess of glycol with respect to dimethylester. Ti(OBu)4 was employed as catalyst (about 150 ppm of Ti/g of polymer). All the syntheses were carried out in a 250-mL stirred glass reactor, with a thermostatted silicon oil bath; temperature and torque were continuously recorded during the polymerization. The polymers were prepared according to the usual two-stage polymerization procedure. In the first stage, under pure nitrogen flow, the temperature was raised to 180e190  C and kept constant until more than 90% of the theoretical amount of methanol was distilled off (about 90 min). In the second stage, the pressure was reduced to about 0.1 mbar to facilitate the removal of the glycol in excess, and the temperature was risen to 220e250  C; the polymerization was carried out until a constant torque value was measured. The copolymers under investigation in this work will be indicated as P(BCEmTECEn) where m and n are the mol% of butylene cyclohexanedicarboxylate (BCE) and triethylene cyclohexanedicarboxylate (TECE) co-units, respectively. The chemical structure of the copolyesters is the following: O O O

O

O

O

O

O

O

O

P(BCEmTECEn)

2.3. Film preparation and thickness determination Films of P(TCEmTECEn) were obtained by hot pressing the polymers between Teflon sheets in a Carver press for 2 min at a temperature T equal to Tm þ 40  C. The films were cooled in press to room temperature by running water. Before analyses the films were stored at room temperature for at least two weeks in order to attain equilibrium crystallinity. The film thickness was determined using the Sample Thickness Tester DM-G, consisting of a digital indicator (Digital Dial Indicator), connected to a computer. Once planted the tool on the film, the reading is made twice per second (the tool automatically performs three readings, minimum value that cannot be changed), measuring a minimum, maximum and average value of a series of measures. The reported results are an average of three experimental tests run at 10 different points on the polymer film surface, at room temperature. Measurements were performed at least in triplicate and the mean value thickness is presented.

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2.4. Molecular characterization

2.6. Water contact angle measurements

The polymers structure and the actual copolymer composition were determined by means of 1H NMR spectroscopy. The samples were dissolved (15 mg/mL) in chloroform-d solvent with 0.03% (v/ v) tetramethylsilane added as an internal standard. 1H NMR spectra were recorded at room temperature for solutions with a polymer concentration of 0.5 wt % (a relaxation delay of 0 s, an acquisition time of 1 s and up to 100 repetitions). The BCE and TECE sequence length was determined by 13C NMR spectroscopy. 13C NMR spectra were obtained using 5 wt% solutions and a full decoupling mode with a NOE effect (a relaxation delay of 2 s, an acquisition time of 1 s and up to 700 repetitions). The measurements were carried out at room temperature, employing a Varian INOVA 400 MHz instrument. A confirmation of the statistical arrangement of the comonomeric units in the chain was obtained through the calculation the degree of randomness b. Molecular weight data were obtained by gel-permeation chromatography at 30  C using a 1100 Hewlett Packard system (Palo Alto, US) equipped with PL gel 5m MiniMIX-C column (250/4.6 length/i.d., in mm) and a refractive index detector. Chloroform was used as eluent at a 0.3 ml/min flow and sample concentrations were adjusted to about 2 mg/mL. A molecular weight calibration curve was obtained by means of several polystyrene standards in the molecular weight range of 2000e100,000.

Static contact angle measurements were performed on polymer films by using a KSV CAM101 instrument (Helsinki, Finland) at ambient conditions by recording the side profiles of deionized water drops for image analysis. Ten drops were observed on different areas for each film and contact angles were reported as the average value  standard deviation.

2.5. Thermal characterization Thermogravimetric analysis was performed under nitrogen atmosphere using a Perkin Elmer TGA7 apparatus (gas flow: 30 mL/ min) at 10  C/min heating rate up to 850  C. Calorimetric measurements were carried out by means of a Perkin Elmer DSC7 instrument equipped with a liquid sub ambient accessory and calibrated with high purity standards (indium and cyclohexane). With the aim of measuring the glass transition and the melting temperatures of the polymers under investigation, the external block temperature control was set at 120  C and weighed samples of c.a. 10 mg were encapsulated in aluminium pans and heated to about 40  C above fusion temperature at a rate of 20  C/min (first scan), held there for 3 min, and then rapidly quenched (about 100  C/min) to 80  C. Finally, they were reheated from 80  C to a temperature well above the melting point of the sample at a heating rate of 20  C/ min (second scan). The glass-transition temperature Tg was taken as the midpoint of the heat capacity increment Dcp associated with the glass-to-rubber transition. The melting temperature (Tm) and the crystallization temperature (Tc) were determined as the peak value of the endothermal and the exothermal phenomena in the DSC curve, respectively. When multiple endotherms were observed, the highest peak temperature was taken as Tm. The specific heat increment Dcp, associated with the glass transition of the amorphous phase, was calculated from the vertical distance between the two extrapolated baselines at the glass transition temperature. The heat of fusion (DHm) and the heat of crystallization (DHc) of the crystal phase were calculated from the total areas of the DSC endotherm and exotherm, respectively. In order to determine the crystallization rate under non-isothermal conditions, the samples were heated at 20  C/ min to about 40  C above fusion temperature, kept there for 3 min and then cooled at 5  C/min. The temperature corresponding to the maximum of the exothermic peak in the DSC cooling-curve (Tcc) can be correlated to the crystallization rate. At least five replicates were run for each sample. Repeated measurements showed excellent reproducibility.

2.7. Structural characterization X-ray diffraction (XRD) patterns of polymeric films were carried out in the wide angle region by using a PANalytical X’PertPro diffractometer equipped with a fast solid state X’Celerator detector and a copper target (l ¼ 0.15418 nm). Data were acquired in the 5e 60 2q intervals, by collecting 100 s at each 0.10 step. The indices of crystallinity (Xc) were evaluated from the XRD profiles by the ratio between the crystalline diffraction area (Ac) and the total area of the diffraction profile (At), cc ¼ Ac/At. The crystalline diffraction area has been obtained from the total area of the diffraction profile by subtracting the amorphous halo. The amorphous was modelled as bell shaped peak baseline. The non-coherent scattering was taken into consideration. 2.8. Stressestrain measurements Stressestrain measurements were performed using an Instron 4465 tensile testing machine equipped with a 100N load cell, on rectangular films (5 mm wide and 0.2 mm thick). The gauge length was 20 mm and the cross-head speed was 5.0 mm/min. Loaddisplacement curves were obtained and converted to stresse strain curves. Tensile elastic modulus was determined from the initial linear slope of the stressestrain curve. At least six replicate specimens were run for each sample and the results were provided as the average value  standard deviation. 2.9. Permeability measurements The permeability determination was performed by a manometric method using a Permeance Testing Device, type GDP-C (Brugger Feinmechanik GmbH), according to ASTM 1434-82 (Standard test Method for Determining Gas Permeability Characteristics of Plastic Film and Sheeting), DIN 53 536 in compliance with ISO/DIS 15 105-1 and according to Gas Permeability Testing Manual, Registergericht München HRB 77020, Brugger Feinmechanik GmbH. The polymeric film to test is placed between two chambers. The chamber on the film is filled with the gas used in the experiments (CO2 or O2), at a pressure of 1 atm. A pressure transducer, set in the chamber below the film, records the increasing of gas pressure as a function of the time. From pressure/time plot the software automatically calculates permeation, which can be converted in permeability, knowing the film thickness. The gas transmission rate (GTR), i.e. the value of the film permeability to gas, was determined considering the increase in pressure in relation to the time and the volume of the device. Time Lag (tL), Diffusion coefficient (D) and Solubility (S) of the tested gases were measured according to the mathematical relations reported in literature [21]. Fluctuation of the ambient temperature during the test was controlled by special software with an automatic temperature compensation, which minimizes gas transmission rate (GTR) deviations. All the measurements have been carried out at 23  C, with a relative humidity (RH) of 26%. The operative conditions were: gas

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99

stream of 100 cm3 min1; 0% of gas RH; sample area of 11.34 cm2. The sample temperature was set by an external thermostat HAAKECirculator DC10-K15 type. Permeability measurements were performed at least in triplicate and the mean value is presented.

the GI, or the relative Inhibitory Effect, against the toxic concentration.

2.10. Soil burial test

3.1. Synthesis, molecular and thermal characterization  C).

Tests were carried out at room temperature (21  1 Each polyester film was placed in darkened vessels containing a multilayer substrate. The films (diameter of 16 mm) were sandwiched between two layers of soil (20 g each). Soil used in the test was a mixture 1:1:1 by weight of forest soil, agricultural soil and silt from river bed. Before use, each soil was sieved at 1 mm and dried for 72 h under vacuum at room temperature to remove the residual water. The bottom and top layers were filled with 8 g of perlite moistened with 10 ml of distilled water. Perlite was added to increase aeration of the soil and the amount of water retained. 10 ml of distilled water were supplied from the top of each vessel every 6 weeks. Prior to analyses, partially degraded samples were recovered, gently washed with deionized water, and dried over P2O5 under vacuum for 2 days to constant weight. Experiments were run in triplicate. 2.11. Composting experiments The biodegradation of some of the copolyesters under study was investigated in real composting facilities treating the organic fraction of municipal solid waste of Bologna. Films of 35  35 mm, about 0.2 mm thick, were placed inside the organic matter at 50 cm depth. Dry weight of each sample was measured prior to incubation. After 14 and 42 days of incubation, specimen were recovered, gently washed with deionized water, and dried over P2O5 under vacuum for 2 days to constant weight prior to further characterization. 2.12. Ecotoxicological analysis In order to assess the ecological risks associated with soil contamination due to the release of monomers during the biodegradation process of copolyesters under study, the Lepidium sativum ecotoxicity test was performed on dilutions of three stock solutions containing different ratios of the comonomeric units for a total amount of 2000 ppm, according to the procedures described in literature (Kreysa and Wiesner,1995) and in UNI 11357:2010 guidance, with minor modifications. A total amount of 10 L. sativum seeds were placed on filter paper into glass Petri dishes and exposed to serial dilutions (dilution factor 2) of the three stock solutions, over a fixed germination period of five days, in the dark at room temperature. The root length of the germinated seeds, and their number, was recorded and compared with the root growth of the seeds in an appropriate control containing deionized water. These data were analysed by calculating the Germination Index, according to the following equation:

GI ¼ ððGs*LsÞ=ðGc*LcÞÞ*100

(1)

where Gs and Gc are the average number of germinated seeds in the sample dishes and in the blank ones. Ls and Lc are the average root length measured for the sample solution and the blank, respectively. The EC50 index, defined as the toxicant concentration where the 50% of the organisms are died, was deduced by the graph plotting

3. Results and discussion

At room temperature all the synthesized polyesters appeared as semicrystalline light yellow solids. The polymers are listed in Table 1, which also collects the data of molecular characterization: as it can be seen, the polymers were characterized by relatively high and comparable molecular weights, indicating that appropriate synthesis conditions and a good polymerization control were achieved. In order to have an understanding into their chemical structure, the 1H NMR investigation was performed. The analysis confirmed the awaited structures (see as an example the 1H NMR spectrum of P(BCE70TECE30) shown in Fig. 1). The copolymer composition, calculated from the relative areas of the 1H NMR resonance peak of the 3 aliphatic protons butandiol subunit located at 4.10 ppm and of the 5 protons of the triethylene diol subunit at 4.23 ppm, was found to be close to the feed one (Table 1). Previous studies [10,22] reported that the 1,4-cyclohexylene ring present in DMCE can isomerize during polymer synthesis, due to the high temperatures employed (higher than 260  C) for long times (longer than 1 h), moving toward the thermodynamically stable cis/trans ratio of 34e66%. Therefore, 1H NMR analysis has been also used to calculate the trans percentage in the polymers under study: in particular, the ratio of the areas of the signals centred at 2.28 ppm (trans isomer) and 2.44 ppm (cis isomer) has been considered (Fig. 1). From the data obtained it can be evicted that no significant isomerization from the trans form to the cis one occurred during polymerization, the cis content being in all cases less than 3%. Information on the arrangement of the comonomeric units in the chain can be deduced by the degree of randomness b, which in this case has been determined by 13C NMR spectroscopy, according to the procedure described elsewhere. [12] In particular, the region between d ¼ 27.8 and d ¼ 28.2 ppm (where the signals due to the carbon atoms of the cyclohexanedicarboxylic acid subunit are located) has been considered to evaluate the degree of randomness (Fig. 2). Table 1 lists the value of b obtained for all samples investigated: as it can be seen, the degree of randomness was found closed to 1, indicating the random nature of the copolyesters synthesized. Subsequently, the polymers were subjected to thermogravimetric analysis and the temperature corresponding to 5% weight loss (T5% w.loss) has been determined and collected in Table 2. As Table 1 Molecular characterization data of PBCE and P(BCEmTECEn) copolymers. Polymer

Mna

Db

TECE (mol%) 1 H NMR

LBCEc

LBDGd

be

PBCEf P(BCE90TECE10) P(BCE80TECE20) P(BCE70TECE30) P(BCE60TECE40) P(BCE50TECE50)

38500 38250 41000 39300 36000 38900

2.0 2.1 2.0 2.0 2.0 2.2

0 10.2 20.8 33.3 40.7 49.2

/ 10.1 5.0 3.5 2.8 2.0

/ 1.1 1.2 1.4 1.7 2.1

/ 1.00 1.01 0.99 0.95 0.94

a b c d e f

Number average molecular weight calculated by GPC analysis. Polydispersity index calculated by GPC analysis. Butylene cyclohexanedicarboxylate block length calculated by 13C NMR. Butylene diglycolate block length calculated by 13C NMR. Degree of randomness calculated by 13C NMR. From Ref. [17].

100

M. Gigli et al. / Polymer Degradation and Stability 105 (2014) 96e106 O

1 2' 2 2

2' 1

O

O

4

3

O

O

3

4

All the copolyesters, with the exception of P(BCE50TECE50) that displayed a slightly lower T5% w.loss (Table 2), showed a high thermal stability, comparable with that of PBCE. This is due to the presence of bulky and thermally stable cyclohexylene groups, [23] which render the polymer even more thermally stable than the corresponding aromatic polyester, i.e. PBT. [9] The result demonstrated that the introduction of TECE co-units along the PBCE macromolecular chain did not have any detrimental effect up to 40 mol%; over this value, the presence of ether-oxygen atoms reduces the thermal stability of the parent homopolymer. As a matter of fact, as previously reported, [17] the introduction of ether-linkages along the PBCE polymeric chain can reduce its thermal stability because it favours thermo-oxidative processes. In order to provide the same heat treatments to all the investigated samples, prior to thermal analysis each film was kept at room temperature for two weeks. DSC traces of so-treated samples are reported in Fig. 4a and the data obtained in Table 2. As evidenced in Fig. 4a, all P(BCEmTECEn) copolymers presented a glass transition and a melting endotherm. The glass transition phenomenon is less evident in copolymers with mol% of BCE counits higher than 70%, due to the high amount of crystalline phase present in these samples. As to the melting process, the samples showed multiple melting peaks, which can be ascribed to melterecrystallization processes occurring during the DSC scan in polyesters, similarly to the parent homopolymer. [17] Moreover, the calorimetric results indicate that an increase in the amount of the comonomer TECE leads to a reduction in the samples both of the melting temperature and the heat of fusion, as usually found in random copolymers with the comonomeric units present in minor amount completely rejected from the crystalline phase or partially incorporated in it see (Table 2) [24,25]. Furthermore, in the copolymers, the endotherm region is broader, suggesting the presence of a larger distribution of crystallites with different degree of perfection. Still, all the copolymers demonstrated the ability to crystallize, even for very short average block length (i.e. w2 in the case of P(BCE50TECE50). This is due to the very high crystallization ability of the BCE sequences, as already reported in the literature: [26] very short BCE sequences in trans configuration are able to crystallize, even if in small and imperfect crystallites. This, as expected, leads anyway to lower melting temperatures, as observed in the present case, too. To better understand the nature of the crystalline phase present in the polymers under investigation, the structural characterization of P(BCEmBTECEn) copolymers was carried out by X-ray diffraction

1 2' 2 2

2' 1

7

7

6

O

O

5

O

5

O

O

6

7

TMS

CDCl3 4

3

7

6

trans

6

5

cis

5

4

2

2' 1

3

2

1

0

δ, ppm Fig. 1. 1H NMR spectra of P(BCE70TECE30) with resonance assignments. O

2 3 3' 1 1 3' 2 3

4

O

O

4

5

O

5

O

2 3 3' 1 1 3' 3 2

6

O

8

7

O

8

3,3'

6

O

O

7

O

BD-TEG BD-BD

CDCl3 TEG-TEG 5

28,2

28,0

4

27,8

δ, ppm

2

6 7

1

8

180

160

140

120

100

80

60

40

20

0

δ, ppm Fig. 2. 13C NMR spectrum of P(BCE70TECE30) and resonance assignments with expansion of region between 27.8 and 28.2 ppm.

evidenced in Fig. 3, where the thermogravimetric curves of the parent homopolymer and of the synthesized copolyesters are reported, the weight loss takes place in all cases practically in onestep.

Table 2 Thermal and diffractometric characterization data and water contact angles for PBCE and P(BCEmTECEn) copolymers. 1st Scan Polymer PBCE

T5% w.loss ( C)

Tm ( C)

380

166

2nd Scan

DHm (J/g)

(J/ C g)

Tc ( C)

DHc

Tm ( C)

DHm

(J/g)

12

0.065

/

/

166

0

0.110

/

/

7

0.187

/

12

0.197

16 17

Tg ( C)

DCp

Tcc ( C)

Xca (%)

Xcb (%)

WCA ( )

31

144

41  2

45  2

110  2

153

25

129

31  1

41  2

107  4

/

131

22

113

27  1

40  2

98  3

/

/

112

19

86

23  1

37  3

89  3

0.242

/

/

103

17

82

21  1

34  3

88  4

0.384

40

11

78

14

47

18  1

27  3

80  1

(J/g)

33 P(BCE90TECE10)

380

153 25

P(BCE80TECE20)

380

131 22

P(BCE70TECE30)

379

112 19

P(BCE60TECE40)

378

104 17

P(BCE50TECE50)

368

78 15

a b

By DSC. By WAXD.

M. Gigli et al. / Polymer Degradation and Stability 105 (2014) 96e106

101

100

WEIGHT (%)

80 60 40 20

PBCE P(BCE90TECE10) P(BCE80TECE20) P(BCE70TECE30) P(BCE60TECE40) P(BCE50TECE50)

0 100

200

300

400

500

600

T (°C) Fig. 3. Thermogravimetric curves of PBCE and P(BCEmTECEn) copolymers under nitrogen atmosphere (heating rate: 10  C/min).

Fig. 5. X-ray diffraction patterns of PBCE and P(BCEmTECEn) copolymers.

Besides, XRD also DSC can be used to determine the fractional crystallinity content of polymers. Accordingly, the degree of crystallinity (Xc) has been therefore calculated by using equation (1):

Xc ¼

DHm $100 0 DHm

a)

b)

PBCE

PBCE

P(BCE90TECE10)

P(BCE80TECE20)

(1)

where DHm is the melting enthalpy associated to the first heating 0 is the theoretical melting enthalpy of the 100% scan and DHm crystalline PBCE homopolymer (see below). The results obtained are reported in Table 2. As it can be seen, data obtained by DSC differ from those obtained by XRD. This behaviour has already been reported and extensively debated in the literature. [27,28] and it is generally ascribed to the approximations made when the above reported

endo →

endo →

(XRD). The patterns are reported in Fig. 5, together with that of PBCE added for sake of comparison. The XRD profiles of copolymers appeared to be characterized by relatively intense diffraction peaks over the whole composition range. The samples were characterized by the PBCE pattern with the four most intense peaks positioned at the angles 15.0 , 18.1, 20.7, 22.6 (2q); only a modest decrease of the relative intensity of the peak at 22.6 (2q) was observed with the increasing of the TECE co-unit content. Interestingly, copolymers having up to 20% mol of TECE, showed similar crystallinity degree of PBCE, indicating that the crystallizing ability is not highly influenced by the presence of TECE co-unit (Table 2). On the contrary, the presence of a higher amount of TECE units increased the overall disorder in the structure since a decrease in the crystallinity degree was observed (Table 2). Lastly, the position of the reflections is not affected by copolymer composition, indicating that a complete rejection of the TECE co-units from the crystal lattice occurred, with the only exception of P(BCE50TECE50), which displayed a moderate increase of the width of the peak at 15.1 (results not shown).

P(BCE90TECE10) P(BCE80TECE20)

P(BCE70TECE30)

P(BCE70TECE30)

P(BCE60TECE40)

P(BCE60TECE40) P(BCE50TECE50)

P(BCE50TECE50)

-50

-10

30

70

T (°C)

110

150

190

-50

-10

30

70

110

150

190

T (°C)

Fig. 4. Calorimetric curves of PBCE and P(BCEmTECEn) copolymers: (a) 1st scan, (b) 2nd scan after melt quenching.

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M. Gigli et al. / Polymer Degradation and Stability 105 (2014) 96e106

(a)

(b) 0.0028

1/Tm,co (K-1)

Tm,co (°C)

160

130

100

0.0026

0.0024

70 0.5

0.6 0.7 0.8 0.9 BCE molar fraction

1.0

0.3

0.6

0.9

1.2

-[lnx C - 2x C(1-x C)]

Fig. 6. (a) Tm,co e BCE molar fraction plot and (b) 1/Tm,co e composition plot according to Baur’s equation: A P(BCEmBDGn) copolymers [17], C P(BCEmTECEn) copolymers, P(BCE50TECE50).

formula is applied. In particular, the degree of crystallinity is defined at the melting point rather than at RT (where for examples XRD is used), the integration baseline is drawn arbitrarily, specific heats variations with T are not considered and DHm0 is calculated 0 ) [27]. at the equilibrium melting temperature (Tm Other methods, such as the First Law Method, have shown high reliability as the Xc obtained are comparable to the values displayed by other techniques [27,28]. However, the application of the First Law Method requires the knowledge of the specific heat temperature dependence, which can be deducted either from amorphous samples or from the literature. Unfortunately, in the present case this is not possible, as the samples cannot be obtained in the amorphous state (even by quenching in liquid nitrogen, see below) and no data are available in the literature, as this is the first time they have been synthesized. In order to confirm X-ray results about the complete rejection of the TECE co-units from the crystal lattice, the applicability of the

Tcc (°C)

160 120 80 40 0

20

40

60

xTECE (mol %)

endo →

PBCE

P(BCE90TECE10) P(BCE80TECE20) P(BCE70TECE30)

Table 3 Mechanical characterization data of PBCE and P(BCEmTECEn) copolymers.

P(BCE60TECE40) P(BCE50TECE50)

0

30

60

equations proposed in the literature to describe the dependence of Tm on composition was verified. The melting temperatures of copolymers containing from 50 to 90 mol% of TECE units are plotted as a function of BCE molar fraction in Fig. 6a, together with the melting points-composition data of P(BCEmBDGn) copolymers previously investigated in our laboratories [17]. As it can be seen, Tm decreased with the increasing of the co-unit content. Moreover, the Tm data of both the copolymeric systems examined appeared to lie on the same curve. As Tm depends exclusively on the molar fraction of BCE and not on the specific chemical characteristics of the co-units, the total exclusion of these last from the crystalline lattice of PBCE is confirmed, as well as the random nature of the copolymers investigated, with the only exception of P(BCE50TECE50) (square symbols), as already found by means of XRD analysis. On the basis of Baur’s equation, [29] which is applicable in the case of comonomer exclusion, the Tm,co were reciprocally plotted against (lnxC2xC(1xC)) in Fig. 6b and the equilibrium melting temperature and the heat of fusion for the completely crystalline PBCE were extrapolated. As can be noted, the plot shows a good linearity and this result can be considered a further proof of the random nature of the copolymers investigated as well as of the exclusion of the co-units from the crystalline lattice of PBCE. The 0 and DH 0 were found to be 182  C and 82 J/g estimated Tm m respectively, in excellent agreement with the values reported in the literature [26]. It is well known that a partially crystalline material usually exhibits a different glass transition behaviour than the completely amorphous analogous. In fact, although some conflicting results are reported in the literature, [30] crystallinity usually acts like crosslinking and raises Tg through its restrictive effect on the segmental motion of amorphous polymer chains. Therefore, in order to study

90

120

150

180

T (°C) Fig. 7. DSC crystallization exotherms of PBCE and P(BCEmTECEn) random copolymers cooled from the melt at 5  C/min. In the inset: Tcc as a function of TECE unit content.

Polymer

E (MPa)

PBCEa P(BCE90TECE10) P(BCE80TECE20) P(BCE70TECE30) P(BCE60TECE40) P(BCE50TECE50)

459 383 264 155 136 56

a

From Ref. [17].

     

11 17 9 5 6 2

sb (MPa) 33 26 12 13 12 7

     

1 1 1 1 2 1

εb (%) 31 28 236 363 412 573

     

11 2 12 34 25 41

M. Gigli et al. / Polymer Degradation and Stability 105 (2014) 96e106

103

Table 4 tL, GTR, D and S for O2 gas of P(BCEmTECEn) copolymers. Polymer

tL (s)

PBCEa P(BCE90TECE10) P(BCE80TECE20) (PBCE70TECE30) P(BCE60TECE40) P(BCE50TECE50) PLAb

1129 1722 305 372 n.a. 187 34

a b

GTR (cm3 m2 d1 bar1)    

2 3 2 1

1 4

56 107 126 169 259 357 488

      

1 1 1 1 1 1 3

S (cm3 cm2 bar1)

D (cm2 sec1)

2.84$102 8.27$102 1.58$102 2.59$102 n.a. 2.61$102 5.00$102

3.42$108 2.33$108 1.56$107 1.28$107 n.a. 2.81$107 3.52$108

   

4$104 5$104 2$104 5$105

 1$104  4$103

   

2$1010 2$1010 1$109 1$109

 8$1010  4$1009

From Ref. [17]. From Ref. [35].

the influence of chemical structure on the glass transition of random copolymers, the phenomenon should be examined in the total absence of crystallinity. In this view, all the samples under investigation were subjected to rapid cooling (quenching) from the melt. The DSC curves after melt quenching are shown in Fig. 4b: the calorimetric traces of PBCE and P(BCEmTECEn) copolymers containing up to 40 mol % of TECE units showed a melting endotherm phenomenon, indicating the partially crystalline nature of these samples. P(BCE50TECE50) displayed a glass transition followed by an exothermal “cold crystallization” peak and a melting endotherm at higher temperature. The enthalpy associated with the crystallization phenomenon is lower than that of the fusion endotherm, indicating that this sample cannot be frozen into a completely amorphous state by quenching. The DSC curve of such sample is therefore typical of partially crystalline polymer too. Therefore, in the range of composition investigated, the phase behaviour of P(BCEmTECEn) copolymers is not affected composition: as a matter of fact, after melt quenching, all semicrystalline samples are obtained. As to the glass transition temperature, the high value observed for PBCE (Tg ¼ 12  C) can be explained as due to the presence of the aliphatic ring, which creates numerous impediments to chain mobility in the amorphous phase. [9] For the copolymers, as reported in Table 2, the glass transition temperature is influenced by the amount of TECE units in the chain. As a matter of fact, it can be observed that Tg values decreased as TECE unit content was increased: this result can be explained on the basis of the enhanced flexibility given by the triethylene glycol subunit, which is characterized by the presence of two additional ether-oxygen atoms and methylene groups with respect to the butandiol one. To evaluate the tendency of PBCE to crystallize in the copolymers under study, non-isothermal experiments were carried out, subjecting the samples to a controlled cooling rate from the melt. The exothermic crystallization peaks of the samples under investigation are shown in Fig. 7. As it can be observed, the temperature of the maximum of the exothermal crystallization peak regularly decreased as the TECE unit content was increased, as also shown in the inset of Fig. 7. This fact indicates a decrement of the overall crystallization rate of PBCE, due to the presence of the co-units which act as obstacles in the regular packing of polymer chains. In order to investigate the relative hydrophilicity of PBCE and P(BCEmTECEn) films, water contact angle (WCA) measurements were performed. It has to be pointed out that surface wettability reflects surface hydrophilicity but, in the present case, it cannot be directly correlated with bulk material hydrophilicity. Table 2 reports the contact angle values for each polymer. Once more, the data obtained showed that the surface wettability is remarkably affected by the copolymer composition too: as a matter of fact, hydrophilicity regularly increased with the increasing of the TECE mol%, due to the PEG-like portion. In particular, P(BCE50TECE50) showed a hydrophilic behaviour, with a WCA of 80 .

3.2. Mechanical characterization In an application perspective, the analysis of the mechanical properties of the polymers under study is of primary importance. Therefore, P(BCEmTECEn) copolymers were subjected to stresse strain measurements. In Table 3 their elastic modulus (E), stress at break (sb), and deformation at break (εb) are shown, together with the data of PBCE added for sake of comparison. As it can be seen, the elastic modulus regularly decreased as TECE unit content was increased; on the contrary, the elongation to break, increased with the increasing of the molar amount of TECE co-unit. Since all the investigated polymers display a soft amorphous phase (Tg values are in all cases well below room temperature), the observed trend can be ascribed to two parameters: copolymer composition and crystallinity degree (Table 2). It is in fact well known [31e32] that crystallinity degree has a considerable effect on the mechanical properties of a polymer: in particular high Xc results in harder, stiffer and less ductile behaviour. As therefore expected, the higher the BCE content, the higher the elastic modulus and the stress at break and the lower the elongation ability of the investigated polymers. Interestingly, P(BCE90TECE10) and P(BCE80TECE20) showed a substantial difference in the mechanical behaviour, even if displaying a similar Xc. This effect can be attributed to the enhanced elasticity provided by the increased amount of PEG-like sequences in P(BCE80TECE20). Moreover, it is worth emphasizing that the copolymers containing more than 30 mol% of TECE are characterized by an elastomeric behaviour. In conclusion, a new class of aliphatic polyesters with tunable mechanical properties has been here presented. Indeed, by just varying the molar composition of the copolymers, it is possible to synthesize a new material which can be used for rigid plastic containers or soft wrapping films. 3.3. Barrier properties Carbon dioxide and oxygen are the main permeating agents studied in packaging applications because they may transfer from or to the environment through the polymer package wall, continuously influencing the product quality and durability. Permeability measurements were carried out on the polymeric films of a measured thickness. GTR values, together with tL, S and D of the tested gases are reported in Table 4 and Table 5 for O2 and CO2 pure gas, respectively. As well described in literature [21,33e34], GTR gives an indication of the material gas permeability, the S parameter expresses the volume solubility of the gas dissolved in one volume of polymer material, the D parameter gives information on how the gas molecules diffuse through the material and the tL parameter represents the time required by the diffusion process to reach the steady-state. Another interesting parameter is the permeability ratio (also called selectivity ratio) between O2 and CO2 gases which

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M. Gigli et al. / Polymer Degradation and Stability 105 (2014) 96e106

Table 5 tL, GTR, D, S for CO2 gas and selectivity ratio CO2/O2 of P(BCEmTECEn) copolymers. Polymer

tL (s)

PBCEa P(BCE90TECE10) P(BCE80TECE20) (PBCE70TECE30) P(BCE60TECE40) P(BCE50TECE50) PLAb

2939 3280 1884 1430 755 726 352

a b

GTR/ (cm3 m2 d1 bar1)       

1 2 2 2 1 1 30

318 761 1009 1601 2661 3740 1201

      

2 1 1 1 1 1 2

S (cm3 cm2 bar1)

D (cm2 sec1)

CO2/O2

4.301 1.13 7.82,101 9.42,101 1.44 1.06 1.10

1.31$108 1.22$108 2.53$108 3.32$108 2.07$108 7.27$108 3.47$109

5.7 7.1 8.0 9.5 10.3 10.5 2.5

      

2$103 1$102 8$104 8$104 8$103 8$103 7$102

      

1$1010 2$1010 1$1010 5$1011 5$1011 7$1011 3$1010

From Ref. [17]. From Ref. [35].

is already known for several polymers [35]. It permits to determine the permeability on respect to a gas knowing the permeability behaviour on respect to the another under the same experimental conditions. Although molecular size of permeating species could affect the transmission speed, in the case of O2 and CO2 there is no relationship between gas molecular size and permeability behavior. In fact, CO2 is more permeable with respect to O2, despite its molecular diameter (3.4  A) is greater than that of oxygen molecules (3.1  A). As it can be seen, higher crystalline samples showed lower permeability to both gases, demonstrating a very high dependence of the permeability behavior on the crystalline/amorphous ratio. In addition, a relation between the selectivity ratio and the Tg can be observed: in copolymers the Tg decreased while the CO2/O2 ratio (reported on Table 5) increased with the increasing of the TECE unit content. This result can be explained on the basis of the enhanced mobility of the polymeric chain, with consequently easier crossing of the CO2 molecules through the polymeric film. CO2 molecules move faster than O2 ones: this is demonstrated by the fact that in all cases the O2 GTR was found lower than the CO2 GTR value. The dependence of the GRT data on sample crystallinity is more evident for the CO2 gas, whose values are in the range of 318e 3740 cm3 m2 d1 bar1. On the contrary, as regards O2, GTR values are between 56 and 357 cm3 m2 d1 bar1, confirming that the CO2 molecules move faster than the O2 ones, despite the morphological structure of the sample. The tL value was found higher in the case of CO2 for all polymers, meaning that the carbon dioxide molecules spent more time to distribute on the polymer film surface than O2 ones due to their faster and very chaotic motion. As a matter of fact, the oxygen molecules are characterized by a slowly and organized motion. As far as the Diffusion coefficient is concerned, different trends have been observed. The PBCE and P(BCE90TECE10) showed a comparable value for O2 and CO2, in both cases the lowest among the polymers under investigation. Not surprisingly, they displayed the highest tL. It means that the diffusion process, i.e. the gas molecules crossing speed through the polymer wall, is low, resulting in a low permeability. With the increase of the TECE mol%, both Diffusion coefficient and GTR values increased and accordingly tL decreased. In addition, as it can be noted from Tables 4 and 5, the CO2 D value increased much faster than the O2 one with the increase of TECE content, reaching in the case of P(BCE50TECE50) a value over 25 times higher for CO2 with respect to O2. As regards the solubility parameter, an opposite trend is displayed: CO2 solubility was higher than that of O2. These results confirmed that, despite the molecule size, CO2 was more soluble into the polymeric matrix, as well explained by the GTR data. For both the analysed gases, the solubility was not influenced by the chemical composition of the polymers, remaining practically constant in all the composition range. Lastly, as far as the selectivity ratio between the two gases is concerned, it increased with the increasing of TECE mol% (Table 5).

This result can be explained on the basis of the enhanced mobility of the polymeric chain (Tg decreased with the increasing of TECE content, Table 2), indicating an easier crossing of the CO2 molecules through the polymer matrix. If we compare the permeability data here obtained with those of P(BCEmBDGn) copolymers previously investigated, [17] it can be noted that the GTR values of P(BCEmTECEn) polyesters are of about 2e4 times higher than those of P(BCEmBDGn) at constant copolymer composition, indicating that the copolymeric system under study possess inferior barrier properties to O2 and CO2. It is worth mentioning that both copolymeric systems display a soft amorphous phase (Tg values are in all cases well below room temperature). Nevertheless, P(BCEmBDGn) samples possess higher crystallinity degree with respect to P(BCEmTECEn) copolymers of comparable molar fraction of BCE. [17] Therefore, both the higher mobility and the higher crystallinity degree of P(BCEmBDGn) copolyesters contribute to the improved barrier properties. Permeability results here presented are anyway of particular relevance if we compare the permeability of the P(BCEmTECEn) copolymers with that of PLA films obtained under the same conditions. [35]\ As reported in Tables 4 and 5, all the copolyesters under investigation showed lower permeability, and therefore improved barrier properties, to O2 gas with respect to polylactide. As regards CO2, only copolymers with TECE mol% lower than 30% displayed better barrier properties compared to those of PLA. In conclusion, also the barrier properties of P(BCEmTECEn) copolymers have been modulated by simply varying their chemical composition. 3.4. Soil burial and composting studies The biodegradability of P(BCEmTECEn) copolymers was monitored by subjecting them to soil burial and composting. Aiming to utilize the polymers under study for packaging applications, both tests can well represent different fates of these plastics at the end of their useful life. Soil burial mimics the degradation of polymers when they are thrown away in the environment is directly after use. On the other hand, composting is a particularly useful technique to biodegrade a polymeric material which has been contaminated by organic matter. Biodegradation rate was investigated by weight loss measurements. As regards soil burial, after 270 days of incubation highest weight loss value was of 4%, measured for P(BCE50TECE50), while PBCE remained practically undegraded. Degradation rate was found dependent on composition: the higher the TECE content, the higher the weight loss. As far as the composting process is concerned, according to the plant procedure, two different steps can be highlighted: the first occurs at higher temperature (about 70  C) and lasts for 14 days, while the second one, of about 28 days, is conducted at lower temperature (it starts from 70  C and goes down to about 40  C at the end of the process). During both steps, a constant air flux is

M. Gigli et al. / Polymer Degradation and Stability 105 (2014) 96e106

105

Fig. 8. Photographs of PBCE and P(BCEmTECEn) after 14 d and 37 d of incubation in compost.

Fig. 9. SEM micrographs of PBCE and P(BCE50TECE50) at different incubation times: a) P(BCE50TECE50) at 0d, b) PBCE in compost after 42d, c) P(BCE50TECE50) in compost after 42d, d) P(BCE50TECE50) in soil after 270d of incubation.

Inhibitory effect (%)

100 80 60 40 20 0 1500

sol a: BD 100% sol b: BD 75% - TEG 25% sol c: BD 50% - TEG 50% 1200

900

600

300

0

Concentration (ppm) Fig. 10. Inhibitory effect of monomers employed in the P(BCEmTECEn) synthesis on the L. sativum growth.

supplied from the bottom of the composting tunnel by forced ventilation. In this view, two samplings have been considered: one after 14 days and the second at the end of the biotransformation (42 days of incubation). Negligible weight losses were measured in the case of PBCE and copolymers with a high molar content of TECE counits, while copolymers containing more 20% of TECE, underwent a decrease in the initial weight. As a matter of fact, weight losses were equal to 3, 6 and 8% for P(BCE70TECE30), P(BCE60TECE40) and P(BCE50TECE50) respectively (Fig. 8). As expected, the higher the crystallinity degree and the surface hydrophobicity of the polymers under study, the lower the biodegradation rate both in soil and in compost; in fact they are well known factors influencing the biodegradation rate of a polymer [18e20]. The morphology of the polymer films was analysed by SEM. As an example, micrographs of PBCE and P(BCE50TECE50) films are reported in Fig. 9. All the copolymers showed a smooth and homogenous surface before incubation (as reported in Fig. 9a for P(BCE50TECE50). After incubation, SEM analyses highlighted results in agreement with

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M. Gigli et al. / Polymer Degradation and Stability 105 (2014) 96e106

weight loss measurements: PBCE film presented only a surface roughening after 42 days of incubation in compost (Fig. 9b), while in the copolymer large damaged areas appeared, even if some differences can be underlined. When incubated in compost (Fig. 9c), the P(BCE50TECE50) copolymer displayed damaged areas, of about 50e60% of the total surface, with numerous cracks and channels. On the other hand, in the case of soil burial experiments (Fig. 9d) smaller damaged areas (30e40% of the total surface) and a different morphology (small holes with elongated shape) were observed. This could be due to the different microorganisms present in the two environments and therefore to the different enzymes operating on the polymeric surfaces. 3.5. Ecotoxicity assessment The L. sativum ecotoxicity test was performed for three stock solutions represented by a mixture of DMCED, BD and TEG monomers for a total concentration of 2000 ppm. The monomers were used to simulate the impact of the possible products released during the biodegradation process of P(BCEmTECEn) copolymers on the L. sativum growth. The three solutions differed from each other in the mutual ratio between BD and TEG (a: 100% BD, b: 75% BD e 25% TEG, c: 50% BD e 50% TEG), while the DMCED amount was kept constant. As reported in Fig. 10, very similar inhibitory effect of the seed’s germination was observed among all three solutions, with an average EC50 of 281 ppm. The concentration of monomers used in the tests was much higher than that expectable in real environment. As reported in literature, [36] taking into account various assumptions, estimations of the concentration of substances in the soil originating from EcoflexÒ composting assume a maximum value of about 130 ppm directly after the application of the compost. As it can be seen from Fig. 9, at the concentration of 130 ppm, an inhibitory effect ranging from 18% in the case of solution c to 22% for solution a is observable. In summary, it can be stated that under practical conditions no toxic effect can be expected from composting P(BCEmTECEn) copolyesters. 4. Conclusion

sequences displayed better barrier properties to both gases with respect to PLA. The biodegradation rate both in compost and in soil resulted in all cases higher than that of PBCE, and once again dependent on the copolymer composition: the higher the TECE mol%, the higher the weight losses of the copolymers under study. Lastly, the ecotoxicological studies evidenced that no toxic effect can be expected by the composting of the P(BCEmTECEn) copolymers. Acknowledgements Composting experiments have been realized thanks to the kind hospitality of Nuova Geovis S.p.A. (Via Romita, 1 - 40019 S. Agata Bolognese (BO)). We are grateful to the staff involved in the project and in particular to Ing. Giampaolo Verzieri and Ing. Francesco Malavolta for their courtesy and technical support. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]

The introduction of PEG-like sequences along the PBCE macromolecular chain has been carried out by the polycondensation reaction of 1,4-dimethylcyclohexanedicarboxylate with 1,4butanediol and triethylene glycol. This easy synthesis strategy allowed the preparation of a new class of aliphatic polyesters with improved properties with respect to the parent homopolymer. Moreover, the final material properties can be effectively tailored simply varying the copolymer composition. As expected, the introduction of ether-linkages in the PBCE resulted in a decrease of the crystallinity degree and melting point, due to a decrement of chain symmetry and regularity, and in a remarkable increase of the surface hydrophilicity, thanks to the presence of highly electronegative oxygen atoms. The higher the mol% of TECE co-units, the greater the effect on these properties. As a consequence, the mechanical and barrier properties and the biodegradation rate turned out to be deeply influenced. As a matter of fact it has been observed a decrease in the elastic modulus and an increase in the elongation to break till to an elastomeric behaviour. As to the barrier properties, a modulation of the permeability behaviour to CO2 and O2, depending on the chemical composition of the copolymers, has been noticed. It is worth mentioning that P(BCEmTECEn) copolymer containing less than 30% of TECE

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