Renewable Semi-Interpenetrating Polymer Networks Based on

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Renewable semi-Interpenetrating Polymer Networks based on Vegetable oils used as plasticized systems of poly(3-hydroxyalkanoate)s Carine Mangeon, Tina Modjinou, Agustin Rios de Anda, France Thevenieau, Estelle Renard, and Valérie Langlois ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04692 • Publication Date (Web): 28 Feb 2018 Downloaded from http://pubs.acs.org on March 2, 2018

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ACS Sustainable Chemistry & Engineering

Renewable semi-Interpenetrating Polymer Networks based on Vegetable oils used as plasticized systems of poly(3-hydroxyalkanoate)s

Carine Mangeon†,‡, Tina Modjinou†, Agustin Rios de Anda†, France Thevenieau†, Estelle Renard†, Valérie Langlois*†. †

Institut de Chimie et des Matériaux de Paris-Est, UMR 7182, CNRS-UPEC, 2-8 rue Henri

Dunant, 94320 Thiais, France ‡

Avril, 11 rue Monceau, 75008 Paris, France

Corresponding Author * Phone: 33 (0)1 49 78 12 17. E-mail: [email protected]

ABSTRACT: Biobased

semi-Interpenetrating

Polymer

Networks

(semi-IPNs)

in

which

poly(3-

hydroxybutyrate-co-3-hydroxyvalerate)s, PHBHV, are embedded in a tridimensional network were developed to improve the mechanical properties of polyesters. Semi-IPNs are obtained by crosslinking sunflower oil (SO) and trimethylolpropane tris(3-mercaptopropionate) (TriSH) using a photoactivated thiol-ene reaction in presence of 2,2’-dimethoxy-2-phenyl acetophenone. The SO-TriSH contents in the network varied from 20 to 45% wt. Homogeneous semi-IPNs containing from 20 to 40% of SO-TriSH content exhibited lower glass temperature from 4 to -15°C, higher strain at break values from 7 to 150% and better thermal stability than those of pristine PHBHV. This reveals an improvement of the deformability of PHBHV due to the plasticization domains by the SO-TriSH domains. The fact that a fraction of the interpenetrating networks follows Fox equation, which is usually verified by well-mixed plasticizer/polymer systems, could be a positive signature of an interpenetrating effect between reticulated SO-TriSH and PHBHV chains. Those properties were achieved without degrading the intrinsic crystalline structure of PHBHV as demonstrated by WAXS measurements.

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Keywords : Biopolyesters, PHBHV, bio-based networks, photo-activated thiol-ene, vegetal oils

INTRODUCTION The most promising alternative to petroleum-derived plastics is their substitution by polymers obtained from renewable resources. Among these bio-based polymers, poly(3hydroxyalkanoate)s (PHAs) provide an environmental-friendly alternative to their synthetic polyester counterparts. PHAs are synthesised by a large number of microorganisms when they are subjected to stress conditions, as intracellular carbon and energy storage materials1–6. Their biosynthesis is determined by the enzyme (PHA synthase) specificities of the bacterial strain and the carbon source. PHAs are semi-crystalline, isotactic, and hydrophobic polymers. An interesting property of these macromolecules is their biodegradability due to the existence of depolymerase systems which are able to entirely degrade these polymers into CO2 and H2O in aerobic conditions7–11. Although the most well-studied PHAs is the poly(3hydroxybutyrate) (PHB), over 140 constitutive monomer units have been investigated12. PHAs can be classified according to their side chain length. Short chain length PHAs (sclPHAs) are composed of 3 to 5 carbon atoms, while medium chain length (mcl-PHAs) and long chain length (lcl-PHAs) consist of 6 to 14 and over 14 carbon atoms, respectively. PHAs can thus be considered as polymers with high potential for environmental, medical or pharmaceutical applications such as drug delivery systems and tissue engineering thanks to their biodegradable and biocompatible properties13–22. Nevertheless, short chain length PHAs as poly(3-hydroxybutyrate) PHB and poly(3-hydroxybutyrate-co-hydroxyvalerate) PHBHV are brittle due to their relative high degree of crystallinity. To overcome this problem, various methods were developed to enhance the thermal stability and deformability of PHAs to enlarge their fields of application 23,24. Bacterial synthesis of copolymers, chemical synthesis of copolymers or blending with other polymers25–32 have been so far studied. Amongst them, the use of vegetable oils may offer a good alternative to improve the processability of PHAs by lowering their processing temperature and to reduce their brittleness due to the presence of long fatty acid chains that can act as plasticizers33,34. The literature reports the use of soybean oil (SO), epoxidized soybean oil (ESBO), epoxidized linseed oil (ELO) and epoxidized broccoli oil30 as plasticizers for PHAs. Such vegetable oils are generally epoxidized before their use as plastic additives due to the higher interfacial interaction between the epoxy groups 2 ACS Paragon Plus Environment

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of epoxidized vegetable oils and hydroxyl groups at the PHAs end chains35. Choi et al. showed that the plasticization efficiency of epoxidized vegetable oils was higher than that of natural vegetable oil31. They also reported that blending PHBHV with ESBO yields an increase in both the impact resistance and the elongation at break of the polymer. Seydibeyoğlu et al.32 reported the plastification effect of ELO on PHBHV properties leading to a slight increase in elongation at break and a reduction of the tensile strength and Young’s modulus. In both cases, a slight decrease in the melting point was observed. The addition of both ELO and ESBO also leads to a significant increase in thermal stability of PHB. However, phase separation and/or poor interfacial adhesion between PHAs and the blends may limit the homogeneity of the matrix, thus influencing the overall polymer properties. In this context, semi-interpenetrating polymer networks (semi-IPNs) are a promising strategy to increase the compatibility of these two components. The use of natural oils without any chemical modifications has several advantages such as renewability, availability, versatility and presence of reactive unsaturated groups. An interesting approach to obtain thermoset networks consists on the reaction between the unsaturated groups on the triglycerides structure with multifunctional thiol units. The advantage of crosslinked materials prepared by thiol-ene reaction is that they exhibit improved flexibility. We have previously reported the great potential of these UV-photoinitiated systems for elaborating flexible antibacterial materials36,37. Furthermore, the choice of the photocurable thiol-ene process is particularly suitable since the reaction occurs at room temperature. In this study, semi-IPNs based on PHBHV and crosslinked vegetable oils using a trithiol coagent were prepared (Figure 1). Crosslinking was achieved directly through unsaturated groups of native oil and thiol groups of trimethylolpropane tris(3-mercaptopropionate). The thermal and mechanical properties of the obtained semi-interpenetrating networks were investigated afterwards.

EXPERIMENTAL SECTION

Materials Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

(PHBHV)

containing

12

mol%

hydroxyvalerate (HV) with average Mw ~210 000 g.mol-1 was purchased from Goodfellow. Trimethylolpropane tris (3-mercaptopropionate) (TriSH) and all solvents were purchased from Sigma-Aldrich and used without purification. 2,2’-dimethoxy-2-phenylacetophenone



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DMPA (Irgacure 651) used as photoinitiator was obtained from BASF and sunflower oil (SO) was kindly supplied by Lesieur. Instrumentation Raman spectroscopy measurements were performed using a LabRAM HR spectrometer from Horiba Jobin Yvon (Longjumeau, France) equipped with a laser emitting at 633 nm. Thermal characterization was performed using a Perking Elmer Diamond DSC apparatus. Measurements under a nitrogen flow of 50ml/min were conducted with the following procedure: -80 to 200 °C with a heating rate of 10 °C/min, 200 to -80 °C with a cooling ramp of 200 °C/min, isotherm for 5 min at -80 °C/min, and finally a heating cycle from -80 to 200 °C at 10 °C/min. The degree of crystallinity χC is calculated according to equation 1:

∆H m × 100% equation 1 w PHBHV ∆H m* where ∆Hm is the heat fusion measured for a given PHBHV/SO-TriSH network, wPHBHV the

χC =

1

×

weight fraction of PHBHV in this network and ∆H*m the heat fusion of crystalline PHBHV, taken as 146 J/g38. Structural characterization was carried out by X-ray diffraction (XRD) using a D8 advance Bruker diffractometer (Cu Kα radiation). Data were recorded over a 2θ range from 5 to 60° by step of 0.017° at an incident wavelength λ of 1.542 Ǻ. From the patterns, the cell parameters a, b and c of the orthorhombic unit cell were calculated from the maxima of the (040), (110), and (121) peaks according to equation 2 :

1 h k l = 2+ 2+ 2 2 d a b c

equation 2

where h, k, and l are the Miller crystallographic indexes and d is the interplanar distance defined by Bragg’s law d =

λ ଶୱ୧୬θ

with θ the scattering angle and λ the wavelength of the

incident wave (=1.542 Ǻ). From these values, the lattice volume V was calculated according to the volume of an orthorhombic unit cell: V = a x b x c. Dynamic mechanical analyses (DMA) were undertaken thanks to a TA Instruments Q800 analyzer in tension film mode and equipped with a liquid nitrogen cooling system. The temperature ramp was performed on films having dimensions of 20 mm length, 5-6 mm width and a thickness of 0.25 mm, from -40 °C to 160 °C at a ramp rate of 5 °C/min. The frequency was set at 1 Hz and the strain was of 0.04 %. All tests were done in a closed furnace.


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Mechanical properties of semi-IPNs were studied with an Instrom 5965 universal testing machine, at crosshead displacement rate of 2mm/min at room temperature. The tensile strength and the fracture behaviour were investigated. The thermal and decomposition characteristics of the materials were determined by thermal gravimetric analyses (TGA) on a Setaram Setsys Evolution 16 apparatus, with a temperature range of 20-800 °C and a heating rate of 10 °C/min under an air flow of 80 mL/min. Sample preparation PHBHV (0.3 g), sunflower oil and TriSH at stoichiometric ratios of C=C and SH groups were dissolved in 2 mL of dichloromethane (CH2Cl2). Different weight ratios of SO-TriSH were added. SO-TriSH weight was set to be 15, 20, 30 or 45 wt% as regards to the weight of PHBHV. The mixtures were supplemented with a small catalytic amount of DMPA (~3.0 wt% of total amount) to accelerate the coupling reaction, and the solutions were stirred using a magnetic stirrer for 20 min. Homogeneous PHBHV/SO-TriSH mixtures were transferred into petri glass dishes with a diameter of 5.5 cm. After a solvent casting step, the filled petri dishes were placed under UV irradiation during 5 min at room temperature, using a Lightningcure LC8 (L8251) spot light source from Hamamatsu, equipped with a Mercury xenon lamp (200W) coupled with a flexible light guide. The maximum intensity at the sample position (at ∼11 cm from the lamp head) of 180 mWcm-2 with a wavelength ranging between 250 and 450 nm was measured by radiometry (International Light Technologies ILT 393). The resulting films, hereafter noted PHBHV/SO-TriSH (X/100-X), were kept overnight at room temperature before further testing.

RESULTS AND DISCUSSION

Preparation of the semi-interpenetrating network PHBHV/SO-TriSH (X/100-X)

In the objective to prepare novel materials based on PHBHV and sunflower oil, the compatibility of these two components were evaluated by the Hansen solubility parameters that considers various supramolecular interactions such as the non-polar (dispersion) (d), the polar (permanent) (p) and the hydrogen bonding forces (h) contributions31,39,40. The calculated solubility parameters of PHBHV and sunflower oil are listed in Table 1. The solubility parameters of PHBHV, and in particular its polar and hydrogen bonding components were not 5 ACS Paragon Plus Environment


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closed to those of sunflower oil, suggesting that these molecules are not miscible together. So the synthesis of semi-IPN networks was achieved in order to promote compabilization between them. Biobased semi-IPNs PHBHV/SO-TriSH were synthesized by using natural PHBHV and crosslinked sunflower oil, SO, using TriSH as crosslinking agent (Figure 1). The crosslinking was achieved by thiol-ene reaction between the unsaturated groups of SO and thiol groups of TriSH in presence of DMPA as photoinitiator leading to the formation of the corresponding SO-TriSH network within PHBHV. Some side reactions can occur during thiol-ene reaction using UV-irradiation, at high temperature (90°C and 150°C), such as disulfide bond formation41. In our case, the thiol-ene reaction using UV-irradiation was achieved at ambient temperature (25°C), so the synthesis of semi-IPNs only yielded to a thioether formation. The presence of double bonds of the SO chains offers the possibility to obtain the network directly without any previous functionalization. The synthetic route to obtain the aforementioned networks is shown in Figure 1. The thiol-ene procedure is a straightforward synthetic methodology for the preparation of networks with variable properties36,37,42. Figure 2 shows the thermograms of SO and SO-TriSH (50/50 in w/w%). In the case of SO, the thermogram exhibits an endothermic peak at -25°C (Tm-2) and two shoulderings at -12°C and -35°C (Tm-1 and Tm-3) respectively. These peaks are characteristic of sunflower oil melting temperatures and correspond to the more or less saturated fatty acid chains43–45. Concerning the SO-TriSH sample, its thermogram differs completely from that of SO. Indeed, no oil melting peaks are observed, however the appearance of a step-like transition herein considered to be a glass-transition Tg at -40°C is noted. Consequently, semi-IPN PHBHV/SOTriSH were prepared according to the same experimental protocol in presence of PHBHV. For all compositions, the stoichiometry ratio C=C/SH was set at 1/1. Further evidence of this reaction was monitored by Raman spectroscopy. Figure 3 shows the Raman spectra of (a) PHBHV/SO-TriSH (60/40) unreacted blend and (b) semi-IPN PHBHV/SO-TriSH (60/40). The intensities of the absorption peaks are comparable quantitatively between the samples since the data analysis in this study were normalized to the peak at 1725 cm-1, assigned to the COO group in PHBHV. The Raman spectrum of the PHBHV/SO-TriSH unreacted blend (Fig 3a) shows the presence of peaks at 1656 cm-1 and 1725 cm-1, attributed to the stretching vibration of -HC=CH- characteristic of sunflower oil46– 48

and ester groups of PHBHV respectively. The peak positioned at 2577 cm-1 represents the

absorption of -SH groups of TriSH49. Both of these absorption peaks at 1656 cm-1 and 2577 6 ACS Paragon Plus Environment

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cm-1 disappear completely after UV exposure (Fig. 3b), suggesting that the thiol-ene reaction is quantitative. Structural and thermomechanical characterization of the semi-IPNs PHBHV/SO-TriSH DSC measurements revealed a noticeable reduction of the glass transition temperature (Tg) values from 4 to -15°C for the semi-IPNs with a SO-TriSH content from 0 to 40 wt% attesting of an effective increase on the mobility PHBHV chains (Table 2). The presence of only one Tg, intermediate between that of PHBHV and that of the SO-TriSH network, shows the good miscibility between the PHBHV and the SO-TriSH networks. The experimental Tg data were similar to the theoretical values (Figure 4) calculated from the equation (3)

w w 1 = PHBHV + SO Tg Tg ( PHBHV ) Tg (SO)

50–52

defined by

equation 3

where wPHBHV and wSO are the weight fractions of PHBHV and SO-TriSH networks respectively. However when the SO-TriSH content is about 45 wt% two transition temperatures are observed. This would be due to the appearance of two phases, a phase rich in PHBHV with a Tg of -1°C and a second phase containing the semi-IPNs PHBHV/SO-TriSH with a Tg of -24°C. The PHBHV remains partially miscible with the SO-TriSH network. The first Tg corresponds to the transition of the amorphous part of PHBHV. The second Tg corresponds to the phase transition of the PHBHV containing nearly 45 wt% of the SO-TriSH, because this Tg is close to the value predicted by the Fox equation. All IPNs remain semicrystalline with a melting temperature close to that of PHBHV. However the presence of the networks certainly formed in the amorphous phase seems to hinder the crystallization because the crystallinity decreases from 34 to 25%. This suggests that the crosslinks hinder the formation and proliferation of crystallites, hence yielding a lower degree of crystallinity. The crystalline structures of the semi-IPNs PHBHV/SO-TriSH were studied by X-Ray diffraction at wide angles (WAXS). The obtained diffraction patterns for such samples are shown in Figure 5 as a function of 2θ. The crystalline PHBHV molecules are packed in an orthorhombic unit cell in a helical form with space group P212121. The polymer has a compact and a right-handed helix with a twofold screw axis. The crystal lattice parameters are a=5.76 Å, b=13.20 Å, and C=5.96 Å53–56 . The crystallographic parameters of the semi-IPNs PHBHV/SO-TriSH are given in Table 3. The diffraction profile obtained for the different networks are typical of semi-crystalline polymers. The a, b and c parameters as well as the lattice volume V are found to be very similar. From these measurements it can be concluded that the presence of SO-TriSH has no influence on the crystalline structure of PHBHV. This 7 ACS Paragon Plus Environment


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would mean that any effect of such networks on the properties of PHBHV will be derived from an influence on the crystalline fraction of the matrix and/or the molecular mobility of its amorphous phase. Furthermore, the diffraction patters also show the presence of an amorphous halo, characteristic of the polymers amorphous phase, which increase with a higher content of SO-TriSH networks. Dynamic Mechanical Analysis (DMA) measurements were performed on these materials to study the influence of sunflower oil networks on PHBHV thermomechanical properties. Figure 6 shows the mechanical elastic modulus E’ as a function of temperature obtained for the studied PHBHV/SO-TriSH interpenetrating networks. It was observed that the presence of SO-TriSH networks induces a decrease of the elastic modulus E’, which can be regarded as an effective plasticizing effect (Table 2). A weak α* transition is observed on the rubbery plateau region at around 60°C as it was previously reported by Chen et al (2007) in the PHBHV57. This thermal transition is associated with the slippage between crystallites and extends the using range of PHBHV above the Tg. Figure 6 reveals that, with increasing amount of SO-triSH, the α* transition becomes less important, which is probably due to the fact that the formation of the network reduces the PHBHV crystallinity and the motion of the slippage of the crystallites pass each other. Moreover, the main relaxation process (at 1 Hz comparable to the calorimetric Tg) seen as the step-like drop of elastic modulus with increasing temperature, seems to become wider and larger when the content of SO-TriSH networks increases. This may mean that the main relaxation process becomes more heterogeneous. To clarify such assumption we studied the mechanical loss moduli E’’ and the dissipation factor tan δ for all PHBHV/SO-TriSH interpenetrating networks. These results are plotted in Figure 7. The interpenetrating networks containing 20%wt of sunflower oil induce a widening of the peaks corresponding to the main relaxation observed in both the loss modulus E’’ and tan δ signals. This widening on the tan δ signal, varying from 50°C for pristine PHBHV to 70°C for the PHBHV/SO-TriSH (80/20) network was quantified. This would denote that the presence of SO-TriSH has indeed an influence on the mesoscopic-scale structure and the molecular mobility of PHBHV. Furthermore, for the interpenetrating networks containing 30 wt% of SO-TriSH or more the appearing of shoulders was observed. The concerned peaks were deconvoluted with individual Gaussian peaks using the Multipeak Fitting package of IgorPro. Two peaks were ascertained to optimally fit the experimental data for both the loss modulus E’’ and tan δ signals. The maxima of the loss modulus E’’ was considered to be the main relaxation 8 ACS Paragon Plus Environment

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transition temperature Tα since identifying two steps in the elastic modulus E’ revealed to be difficult and imprecise. DMA results show that for SO-TriSH contents of 30 wt% or higher, two separate Tα relaxation processes are observed for the PHBHV/SO-TriSH interpenetrating networks. The presence of two different processes can be interpreted as the presence of heterogeneous fractions at the molecular level in the interpenetrating networks. Indeed in the case of the DMA and DSC results we observe that for samples expressing two transition temperatures, the higher one is closer to that of pristine PHBHV. This would mean that a fraction of PHBHV would be little affected by the presence of SO-TriSH for the samples containing a high content of such networks. However there seems to be a fraction of PHBHV within the whole material that is effectively influenced by the presence of SO-TriSH networks. Moreover, the drop on the elastic modulus E’ observed by DMA would also confirm this hypothesis. Undoubtedly, if the obtained PHBHV/SO-TriSH interpenetrating networks were completely segregated, a higher drop on the elastic modulus E’ provoked by this segregation would be observed. In our case, the drop seems to follow a constant and continuous pattern with the amount of SO-TriSH content. These results lead to presume that a high fraction of SO-TriSH and PHBHV chains form an effective interpenetrating network. Thermal stability and mechanical properties TGA measurements of neat PHBHV and PHBHV/SO-TriSH semi-IPNs are shown in Fig. 8. Only one degradation step was observed for neat PHBHV with a maximum thermal degradation temperature Tmax of 272°C. The semi-IPNs are found to be thermally stable below 200°C, exhibiting four weight loss steps. A slight weight loss of about 5%, attributed to the evaporation of the soluble and small compounds, was observed. The second stage that occurs between 245 and 350°C, with a Tmax of 282°C, is assigned to the decomposition of PHBHV main chains. The shift of this degradation temperature towards higher values is attributed to the polymer being entrapped inside the crosslinked structure. The degradation between 350 and 450°C corresponds to the decomposition of the crosslinked bulk, while the stage from 450 to 570°C is associated with the oxidation of organic carbon in air58. These results imply that the thermal stability of the semi-IPN samples being higher than that of neat PHBHV is due to the crosslinking network within their structures. Concerning the mechanical properties of PHBHV/SO-TriSH networks, the presence of SOTriSH derives in the drop of PHBHV Young’s modulus and stress at break (Figure 9). Even though if the stress at break decreases from 31 MPa to 15 MPa in the presence of SO-TriSH, 9 ACS Paragon Plus Environment


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it remains constant when the proportion of the SO-TriSH varies from 20 to 45 wt%, whereas for PHB plasticized with small organic molecules, the stress at break decreases linearly with plasticizer content. In this work, the presence of SO-TriSH interpenetrating networks induces an improvement of the toughness of the PHBHV matrix. Indeed, the elongation at break of PHBHV raises from 7 to 170%. The trend observed between 0 and 40% of SO-TriSH is similar to that already described in the case of PHB59 plasticized by small organic molecules. Herein, the elongation at break increases considerably because of the presence of the SOTriSH network, acting as effective plasticizers, making it possible to reduce the interactions between PHBHV chains in the amorphous zones without modifying the crystalline zones. The elongation at break is the parameter that best reflects the affinity at the interface between the components of a mixture. A good membership implies a good transfer of constraints and finally a less fragile structure. Moreover the semi-IPNs plasticization effect certainly lasts longer since the presence of a tridimensional network hinders the migration observed in the case of the formulation of polymers by conventional plasticizers. When the SO-TriSH content is above 45%, the system becomes considerably brittle, meaning that an increase of SO-TriSH concentration beyond this value is unnecessary and counterproductive.

CONCLUSION Semi-interpenetrating systems based on sunflower oil and trithiol networks in which PHBHV chains are embedded exhibit a toughening improvement of such polyesters. These novel networks with different SO-TriSH contents are obtained by a photochemical process. The crosslinked network is formed inside the amorphous zones of the matrix, making it possible to considerably increase the elongation at break. Although this effect can be compared to the plasticizing phenomenon of small molecules in polymers, the main advantage presented herein lies in the fact that networks do not migrate over time and can act as long-lasting reinforcements of the matrix. Furthermore when the content of crosslinked networks reaches 45%, the material loses some of its thermomechanical properties due to improved phase segregation. It is then advisable to control the content of SO-TriSH within PHBHV in this type of flexible and deformable biosourced materials so as to envisage applications particularly in the packaging industry.


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AUTHOR INFORMATION Corresponding Author *V. Langlois. Phone : 33 (0) 1 49 78 12 17. E-mail: [email protected]. ACKNOWLEDGMENT The authors thank the AVRIL Group for providing Carine Mangeon with a grant. REFERENCES (1)

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Page 16 of 28

Figure 1. Synthesis of PHBHV/SO-TriSH Semi-IPN.


Page 17 of 28

Figure 2: DSC curves of sunflower oil (SO) an SO-TriSH network.

SO - unreacted SO-TriSH network arbitrary Heat Flow (W)

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


Tg

Tm-3 Tm-1

Tm-2

EXO UP -60

-40

-20 Temperature (°C)

0

20



Figure 3. Raman spectra of PHBHV/SO-TriSH (60/40) (a) before and (b) after curing.

intensity (a.u.)

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

Page 18 of 28

(b)

-COO -C=C1600

-SH 2000

2400

(a) 2800

3200

-1

wavelength (cm )


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Figure 4: Experimental Tg and Tα obtained for PHBHV/SO-TriSH semi-IPN compared to values calculated from Fox equation.



Figure 5. WAXS diffraction patterns as a function of 2θ for the semi-IPNs PHBHV/SO-

(222)

(220)

(121) (040)

(021) (111)

(110)

(020)

TriSH.

PHBHV/SO-TriSH(55/45) PHBHV/SO-TriSH(60/40)

Intensity (a.u.)

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

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PHBHV/SO-TriSH(70/30)


PHBHV

10

20

30

40

50

60

2θ θ (°)


Page 21 of 28

Figure 6. Elastic modulus E’ as a function of temperature obtained by DMA measurements for the PHBHV/SO-TriSH interpenetrating networks.

PHBHV PHBHV/SO-TriSH(80/20) PHBHV/SO-TriSH(70/30) PHBHV/SO-TriSH(60/40) PHBHV/SO-TriSH(55/45)

4

Elastic modulus E' (GPa)

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


3

2

1

0 -150

-100

-50 0 50 Temperature (°C)

100

150



Figure 7. (a) Loss factor tan δ and (b) loss modulus E’’ as a function of temperature obtained by DMA measurements for the PHBHV/SO-TriSH interpenetrating networks.

(a)

(b) PHBHV/SO-TriSH(55/45)



Loss modulus E'' (a.u.)


tan δ (a.u.)

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

Page 22 of 28



PHBHV/SO-TriSH(80/20) PHBHV/SO-TriSH(80/20)

PHBHV

-60

-40


40

60

PHBHV

-60

-40


40

60


Page 23 of 28

Figure 8. TGA analysis of PHBHV and PHBHV/SO-TriSH (X/100-X) samples. 0

PHBHV + SO/TriSH (80/20) + SO/TriSH (70/30) + SO/TriSH (55/45)

-20

mass loss (%)

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


-40

-60

-80

-100 100

200

300 400 Temperature (°C)

500

600



Figure 9. (a) Young’s modulus, (b) stress and (c) strain at break of PHBHV/SO-TriSH (X/100-X) as a function of SO-TriSH content 1400

Young's modulus E (MPa)

1200 1000 800 600 400 200

(a) 0

0

10

20 30 %wtSO/TriSH

10

20 30 %wtSO/TriSH

40

50

stress at break σ R (MPa)

40

30

20

10

(b) 0

0

40

50

200

strain at break εR (%)

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

Page 24 of 28

150

100

50

(c) 0

0

10

20 30 %wtSO/TriSH

40

50


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


Table 1: Solubility parameters of PHBHV and SO

Sample

δ p (Mpa) 1/2

δ h (Mpa) 1/2

δ d (Mpa) 1/2

δ (Mpa) 1/2

PHBHV

8.8

8.6

16.5

20.6

SO

1.4

4.7

15.5

16.2



Page 26 of 28

Table 2. DMA and DSC analyses of PHBHV/SO-TriSH (X/100-X) semi-IPNs. E’ a(MPa) Tα a (°C) Tg b (°C) Tm b (°C) ∆Hm b (J/g) PHBHV/SO-TriSH (100/0) PHBHV/SO-TriSH (80/20) PHBHV/SO-TriSH (70/30)

4165 3875 3450

PHBHV/SO-TriSH (60/40)

2055


1455


-

a)

+7 -5 +4 -16 +9 -23 +1 -31 -

+4 -5 -7 -15 -1 -24 -40

χC b (%)

156 152

50 40

34 30

149

36

26

151

39

26

154

35

25

-

-

-

determined by DMA, b) determined by DSC analysis


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


Table 3. Lattice parameters and unit cell volume V of PHBHV and PHBHV/SO-TriSH obtained by WAXS.

PHBHV PHBHV/SO-TriSH (80/20) PHBHV/SO-TriSH (70/30) PHBHV/SO-TriSH (60/20) PHBHV/SO-TriSH (55/45)

a (Å) 5.64 5.67 5.64 5.63 5.61

b (Å) 13.08 13.15 13.08 13.13 13.12

c (Å) 5.96 5.95 6.02 5.93 5.93

V (Å3) 439 443 444 438 436



For Table of contents Use only

O O H

O

O n

O

OH

m

O

HS

O

O

HS

O

CH3

35

Britleness and stiffness

SH 30

O

PHBHV

PHBHV

25

TriSH +

O OO O

DMPA

Stress (MPa)

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

Page 28 of 28

20

Flexibility and elasticity

15 10

PHA/SO-30 semi-IPN 5

O O

0 0

20

Sunflower oil (SO)

40

60

80 100 120 140 160 180

Strain (%)

Synthesis and characterization of novel biobased elastomeric network from Poly(3hydroxyalkanoate)s and sunflower oil using “click” thiol-ene reaction


Renewable Semi-Interpenetrating Polymer Networks Based on

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