Microwave Synthesis and Melt Blending of Glycerol Based

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Microwave synthesis and melt blending of glycerol based toughening agent with poly(lactic acid) Gildas Coativy, Manjusri Misra, and Amar K. Mohanty ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.5b01596 • Publication Date (Web): 07 Mar 2016 Downloaded from http://pubs.acs.org on March 17, 2016

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ACS Sustainable Chemistry & Engineering

Microwave synthesis and melt blending of glycerol based toughening agent with poly(lactic acid) Gildas Coativy1, Manjusri Misra1, 2 and Amar Mohanty1, 2,* 1

Bioproducts Discovery and Development Centre, Department of Plant Agriculture, Crop Science Building, University of Guelph, Guelph, N1G 2W1, Ontario, Canada. 2 School of Engineering, Thornbrough Building, University of Guelph, Guelph, N1G 2W1, Ontario, Canada, *E mail: [email protected]

Abstract Glycerol is a by-product of the biodiesel industry. The target of the following work was to produce a biopolyester based on glycerol, and to blend it with poly (lactic acid) (PLA) to increase its ductility. Microwave synthesis was used to conduct the reactions of glycerol with a diacid (sebacic acid) and a monoacid (stearic acid) at 180°C in bulk. Progress of the synthesis was stopped when a gel was obtained (after 3.45h). The produced resin was found to be soluble in tetrahydrofuran (THF). The study of the product by infrared spectrometry showed an effective esterification of acids with glycerol. Calorimetric study evidenced a glass transition at -27°C and a melting peak at 29°C. PLA was then blended with various amounts of this biopolyester ranging from 0 to 20% via twin screw extrusion followed by injection molding. Morphologic characteristics of blends were studied by scanning electron microscopy. Biopolyester phases ranging from 100 nm to 10 µm were observed for all concentrations. In the particular case of 20% of biopolyester, micrometric phases greater than 10 µm in size were detected, leading to a decrease in mechanical performance. Tensile testing showed a ductile behaviour for all concentrations higher than 5% of biopolyester, with an optimum performance achieved with 10% of biopolyester in which strain at break reached 93%. Keywords: Poly condensation, toughening, PLA, fatty acid, glycerol, sebacic acid, ester

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Introduction Poly(lactic acid) (PLA) is one of the most promising bio-based polyesters to replace certain petroleum based polymers. However, in spite of its competitive price (1-1.5 lb/$), high stiffness (3 GPa) and good optical properties, PLA is brittle at room temperature (3-5% of strain at break).1–3 Consequently, the improvement of its toughness is the topic of several scientific studies. Two main strategies are used to succeed : thermomechanical treatments of PLA and melt blending of PLA with soft polymer, oligomer or small molecules having a glass transition temperature lower than room temperature.1 Among these soft components, the use of an immiscible oligomer/polymer blend with PLA seems to be the best way to obtain a stable blend (no migration of the soft component or structural change with time), with limited loss of stiffness and without lowering heat deflection temperature, which is already low for PLA.

1–3

In

accordance with the chemical nature of PLA and physical requirements, polyhydroxylalkanoates, rubbers and more recently new bio-based polyester have been used to toughen PLA.1,4,5 The target of the following study is to create a new toughening agent made of cheap bioreagents. Glycerol is a triol which can be obtained from petroleum resources since the 1940’s and more recently as a by-product of the biodiesel industry.6 Glycerol, coming from biodiesel industry, is named crude glycerol and contains variable amounts of methanol, salts, and free fatty acids.6,7 Refining process allows to different grades of glycerol, with the purest reaching 99.7%.8 Due to the increase of biodiesel production, the price of glycerol is dropping and a surplus is expected.9 In addition to its common uses (food , personal care, tobacco), new applications should be found to reduce this surplus amount.9 Gycerol can also be used as a solvent or as potential reagent.6,9,10 For example, its polycondensation with diacid produces polyesters with


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thermo-mechanical properties which depend on the purity of glycerol and on the nature of the diacid. 11–13 The polycondensation of glycerol with sebacic acid can produce tough polyesters, which can be used in biomedical applications.11,12 However, due to the presence of three functional groups in glycerol, the obtained polymers are cross-linked14–16 and are consequently not melt processable with PLA. To overcome this issue, Gu et al. stopped the reaction of glycerol with sebacic acid at low viscosity (3 Pa·s)17 and then blended it with PLA. Another way to address this issue is to add a monoacid to the reaction; Waig Fang et al.16 used fatty acid to convert a multifunctional alcohol into diol and polymerized the diol with alipthalic diacid to produce noncrosslinked biobased polyester. In the present work, we aim to obtain a non-crosslinked biopolyester and to use it as toughening agent for PLA. Sebacic acid (10 carbons) as diacid, and stearic acid as monoacid are reacted with glycerol in one step in bulk. The choice of reagents is mainly due to their potential natural origins 6,7,15, 18–20 and their high boiling points (over 200°C), which makes it possible to carry out their reaction at 180°C. Microwave was chosen as the source of heating to perform the synthesis, since the reagents and the water produced by the reaction are polar and liquid at the reaction temperature, and thus are highly sensitive to microwave radiation.21,22 In their work on poly (butyl succinate) microwave synthesis, Velmathi and co-workers23 highlight that microwave radiation is a good way to perform step growth polymerization. They attribute this efficiency to a better evaporation of the water produced by condensation during the microwaving process than with conventional heating. It leads to the orientation of this reversible reaction through the polymer synthesis direction.23,24 This strategy was chosen also to follow principles of green



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chemistry23,25, limiting the energy used for processing, working without solvent and with nonhazardous reagents.


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Materials and methods Materials Sebacic acid and pure glycerol (99 wt%) were purchased from Fischer Scientific. At room temperature, sebacic acid is a white powder (Tm= 133°C) and glycerol is a transparent liquid (Tm=18°C). Stearic acid was purchased from Sigma Aldrich as reagent grade (95%) and is also a white powder (Tm= 70°C). Their chemical structures are presented in Figure 2. PLA 3251 D is a product of Natureworks. This polymer was dried at least 6 hours at 80°C before processing. Glycerol was dried before synthesis at 80°C under vacuum for 1 hour. Processing Preparation of reagents before microwave synthesis 21.1g of Glycerol was manually blended with 46.3g of sebacic acid and 32.5 g of stearic acid to have a molar ratio of (1:1:0.5) in a 250 ml beaker . This ratio was expecting to give the possibility for glycerol and sebacic acid to polymerize, and the addition of a ratio of 0.5 stearic acid was utilized to limit crosslinking. Microwave synthesis Step growth polymerization was achieved with a Microwave Synthesis Labstation MicroSYNTH (Milestone, Connecticut, USA). A stirrer bar was added inside the beaker containing the reagents, and a kitchen-like silicon cover with a hole was added on the top of the beaker (with 100 mL of free space) to limit the reagent loss and to give the possibility to water to go out the solution during the synthesis.



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The following procedure was utilized to perform the reaction. The beaker was put inside the microwave oven. The program of heating was as follows: a heating from room temperature to 180°C in 5 minutes, followed by maintaining the temperature at 180°C until the viscosity increased suddenly resulting in the end of magnetic stirring. The maximum power of the microwave was limited to 400 W to avoid an overshoot of temperature. During microwaving, the temperature was measured on the surface of the beaker via an infrared thermometer. A feedback loop was used to adjust the power to follow the pre-set temperature. During the synthesis, a control panel made it possible to observe and record the power delivered by the microwave oven as a function of time, and also to average it over a range of time. Because the power fluctuated during our study, the average power was determined at an interval of 15 minutes and plotted as a function of time. Blend of polyester with PLA A micro 15 cm3 co-rotating twin screw compounder was used to blend PLA with the biopolyester at 180°C, and a micro 12 cm3 injection molding machine (manufactured by DSM Research, Netherlands) was used to produce tensile dogbones (type IV) and impact test samples. Small pieces of the biopolyester were compounded with PLA in order to have weight fractions of 0%, 5%, 10%, 15% and 20% of biopolyester. A residence time of 4 minutes was chosen with a screw round speed of 100 rpm. Injection was carried out at 180°C with a feeding pressure of 1.5 bar, packing pressure of 2.5 bar and mold temperature of 30°C. The samples were kept in sealed bags for at least 2 days prior to testing.

Characterization Fourier transformed infrared (FTIR) spectroscopy


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Chemical analysis was performed using an attenuated total reflectance (ATR) accessory (Smart Orbit) coupled to a Nicolet 6700 FT-IR spectrometer (Thermo Scientific). A wavenumber range from 500 to 4000 cm-1 was utilized. Depending on the nature of the sample, thin layers of sample were cut or small amount of powder was put and compressed on the ATR surface of the accessory to ensure good contact. Calorimetry A TA DSC Q200 was used to study the calorimetric behaviour of the samples. Samples having a typical weight of 10 mg were studied in a hermetic aluminum pan. The samples were heated from -50°C to 180°C with a heating ramp of 10°C/min. From the obtained thermograms, the temperature of fusion or crystallization (taken at the top of the peaks) and the glass transitions temperature (taken as the midpoint of the heat capacity jump) were determined. Dynamic mechanical analysis A DMA TA Q800 was used to study the viscoelastic behaviour of the sample under a heating ramp of 3°C/min starting from -100°C to 100°C. The material was kept for 10 minutes at -100°C before starting the experiment to ensure a thermal equilibrium, then a periodic deformation of 0.02% in dual cantilever mode was applied to the sample with a frequency of 1 Hz. The storage modulus E’ and the tan (δ) (ratio of loss modulus with storage modulus) were then plotted as a function of temperature. Thermogravimetric analysis Thermal degradation of the sample was studied using thermogravimetric analysis with a TA Q500 machine. For this test, samples with a typical weight of 10 mg were heated from 20 to 500°C with a ramp of 10°C/min under nitrogen atmosphere. 7 ACS Paragon Plus Environment


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Scanning electron microscopy The morphologies of the blends were studied with a Phenom ProX Scanning Electron Microscope (Phenom-World BV, Eindhoven) using a 5 kV tension acceleration. The cross sections of

non-used impact test bars were observed after preparation; samples were initially immersed in liquid nitrogen, and then cryo-fractured. Finally, a thin layer of gold was deposited on samples.

Tensile testing

The tensile dogbone samples were studied using a tensile testing machine two days after processing. An INSTRON tensile test machine, model 3382, was used to deform samples with a speed of elongation of 5 mm/min at room temperature. Five samples per composition were tested in this manner, and the standard deviation of each test datum was determined. Notched Izod impact test Notched Izod impact strength of PLA and the blends were studied with a TMI 43-02 (Testing Machine Inc.) impact tester. Samples were notched 2 days prior to testing using a TMI notching cutter. The impact strength was then measured using a 5 ft-lb pendulum.


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Results and discussion

Synthesis of the biopolyester Microwaving

Figure.1 displays the power delivered by the microwave oven to achieve the pre-set temperature. During the first five minutes, the power increased from 0 to 400 W to go from room temperature to 180°C. When the temperature of 180°C was achieved, the power dropped to 128 W and increased with time until reaching 193 W. This increase could be attributed to a lower amount of small polar molecules, coming from poly condensation and water loss. Indeed, the specificity of the microwave heating is that the efficiency of this source of power is strongly dependent on the chemical nature of the reactants and their states; it is highly efficient with polar liquids.26 The reaction was stopped when a gel was obtained (Figure 1.A), indicated by the end of magnet bar rotation (after 3.45 h ± 15 min). The reason for stopping the reaction was that the gelation suggests that one of our goals of obtaining macromolecules was achieved, and also that without stirring the microwave heating was assumed to be inhomogeneous. Due to the low depth of penetration of microwave 22 (a few centimeters), we can expect that without stirring, the heating of reagents would be inhomogeneous due to the absence of convection. After synthesis, and at room temperature, the product becomes a yellowish translucent soft solid (Figure 1) with a density of 1.05 g/cm3. The product was found to be soluble in THF. Its solubility suggests the absence of a continuous covalent tridimensional network, which is necessary for its blend with PLA. Consequently, the obtained gel is a pseudo gel or physical gel.27 The mass loss occurring during the reaction was equal to 10 %±0.1%, which is close to the



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theoretical water mass produced during the reaction: 10.3 % in the case of a full reaction of sebacic acid and stearic acid.

Figure.1 Power delivered by the microwave oven and resulting temperature as a function of time of reaction and photos of the product at: A) 180°C and B) at room temperature

Chemical characterization

Chemical analysis was performed using infrared spectroscopy. Figure 2 presents the spectra of glycerol, sebacic acid, stearic acid and of the synthesized biopolyester. On the patterns of stearic acid and sebacic acid, the peaks at 2850 and 2910 cm-1 are coming from the stretching of -CH3 and -CH2- groups of aliphatic chains, while the peak at 1700 cm-1 and the


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shoulder between 2500 cm-1 and 3000 cm-1 are assigned respectively to the carbonyl and hydroxyl groups of carboxylic acid.

28

In glycerol, the sharp peak in the region of 3200 – 3700

cm-1 is coming from the presence of hydroxyl groups of alcohol. The peaks at 1030 cm-1 and at 1100 cm-1 (highlighted by two arrows), are respectively attributed to the C-O stretching of primary and secondary alcohol functions.28 The two peaks observed at 2900 cm-1 correspond to the asym/sym stretching of -CH2- and -CH- groups of glycerol.28 The comparison of the references with the product shows three main chemical changes induced by microwave synthesis, which are highlighted on the curves by dash lines. The pattern of the product presents a peak at 1170 cm-1 associated to the creation of -C-O-C- linkage and a second peak at 1740 cm-1 coming from the presence of C=O carbonyl groups of the ester, while on the references no peak is observed at 1170 cm-1, and the C=O group is located at 1700 cm-1. 28,29

A small shoulder is present in the range of 3000-3700 cm-1, coming from unreacted hydroxyl

groups in glycerol. The absence of the peak at 1030 cm-1, and the presence of the peak at 1100 cm-1, suggests that all the primary alcohol functions of glycerol have been reacted, while some of its secondary alcohol functions are still present after reaction. The resulting proposed chemical structure of the biopolyester is sketched in figure 2.c). This study highlighted the presence of ester functionality in the product. Due to the physical aspect of the product (pseudo gel or physical gel) and its chemistry (ester groups), we assume that the product is made of oligoester and polyester. Thus, the product will be referred as biopolyester.



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Figure.2 a) FTIR spectra of: glycerol, sebacic acid, stearic acid and biopolyester (dash lines highlight the main chemical changes induced by the reaction) b) Chemical structure of the reagents c) proposed chemical structure of biopolyester (half of OH groups denoted * are substituted by stearic acid and sebacic acid, the other half remains unreacted)


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Thermal stability

Thermogravimetric analysis was performed on both the pure reagents and the biopolyester. The percentage of remaining weight and its derivate as a function of temperature are respectively displayed in Figure 3.a) and Figure3.b). No mass loss for pure sebacic acid and stearic acid is observed until 180°C (temperature of melt blending of PLA with biopolyester). For glycerol, two mass losses are observed: a small 1% loss between room temperature and 150°C, and a sharp loss between 150 and 220°C. This last result highlights that glycerol which is liquid, can be evaporated during the reaction, and especially in the presence of water.30 In our study, the measurement of the mass lost during the synthesis and the presence of remaining OH groups revealed by infrared spectroscopy suggest that this phenomenon was not critical because the reaction was performed in bulk with a silicon cover on the top of the beaker. Finally, the biopolyester exhibits three mass losses. The first appears between 200°C and 250°C, and can be attributed to remaining unreacted sebacic acid and stearic acid since it was also observed for the pure reagents. The second and the third occur between 250 and 310°C and between 310°C and 450°C respectively, revealing the inhomogeneity of the biopolyester. It could be attributed to a polydispersity of the biopolyester (oligomer/polymer)31 or to the presence of blocks32 containing more or less stearic acid. Finally, these results demonstrate that the produced biopolyester is relatively stable up to 180°C, which was the temperature chosen to melt blend the biopolyester with PLA.



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Figure.3 a) Weight and b) Derivative Weight of the reagents and of the biopolyester under nitrogen flow with a heating ramp of 10°C/min


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Melt blending of PLA with the biopolyester Morphology After melt processing with twin-screw extrusion, PLA was transparent, while the PLA/biopolyester blends were translucent. SEM study was performed on the cross sections of cryo-fractured samples to study the microscopic morphology of the blends. The obtained images are presented in Figure 4. A magnification of 3000x was used to study PLA blends containing a concentration of 5%, 10% and 20% biopolyester. Figures 4 a), b) and c) show two phases: one light and one dark. The light phase corresponds to the PLA rich phases, while the dark is associated with voids coming from the rubbery biopolyester phase pulling out during cryo-fracturing, induced by both the shrinkage of rubbery phase and the cutting of the sample. It also suggests a low adhesion between the continuous phase of PLA and biopolyester droplets.33,34 The observed morphology is close to what was previously reported on PLA/ rubber systems32–36 in which the size of the rubber droplets varies with its concentration. For concentrations ranging from 5% to 10%, a continuous phase of PLA is observed with two populations of inclusions which are also present in the blend of 20% biopolyester. The first one is highlighted by a red circle in Figure 4 d); this population is micrometric in scale. The second population is made of inclusions on the scale of hundreds of nanometers, and is highlighted by a red arrow. For the 20% biopolyester blend, in addition to nanometric and micrometric inclusions, phases with a size of about ten micrometers are observed. They are highlighted with a yellow circle on Figure 4 c). The increase of the size of the biopolyester droplets with concentration is a



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result of the coalescence phenomenon34 induced by the immiscibility of the biopolyester with PLA.

Figure.4 SEM micrographs of freeze fractured surface of samples with various concentration of biopolyester: a) 5% biopolyester (*3000), b) 10% biopolyester (*3000), c) 20% biopolyester (* 3000), d) 20% biopolyester (* 12 000) Calorimetry


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A calorimetric study on biopolyester, PLA and their blends was performed at 10°C/min. The resulting curves of the first heating scan are presented in Figure 5. For biopolyester, a glass transition is observed at -27°C. A wide endothermic peak at 29°C is detected and corresponds to the melting of the biopolyester. In the case of poly (glycerol sebacate), the same synthesis without fatty acid, the temperature of glass transition is observed between -40°C and -30°C, and the peak of melting is observed between -5 and 20°C.29 The synthesis of glycerol with sebacic acid and stearic acid was not found in literature. However, the closest synthesis involving aliphatic glycerol based polyesters in which fatty acids were added exhibits a melting peak in the same temperature range (between 20 and 40°C), with the melting temperature increasing with the length of the aliphatic chain of the monoacid.16,37 To sum up, at room temperature the biopolyester is made of a rubbery phase having a glass transition at -27°C, and a crystalline one having a melting temperature at 29°C. PLA has a glass transition at 59°C, a crystallization peak at 97°C and a melting peak at 168°C. The PLA/biopolyester blends also present these thermal events, but both glass transition and crystallization temperatures are depressed. The glass transition of PLA is slightly decreased by 2°C for 5% of biopolyester and by 4°C for the other concentrations. Concerning the crystallization peak, for 5% biopolyester, its maximum is at 95°C, while for 15% and 20% the maximum is at 90°C. The blend containing 10% biopolyester exhibits two overlapped peaks: one at 95°C and another at 87°C. The presence of these two peaks of crystallization for the 10% biopolyester blend suggests the presence of two populations: one having a bulk behavior of PLA, and another coming from PLA interacting with biopolyester in its interface. The bulk behaviour disappears for concentrations higher than 10%. Finally, the melting peak of PLA is not affected by the presence of biopolyester. The melting peak is preceded by an exothermic transition of α’



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to α crystal

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, and the melting temperature is also 168°C. The melting enthalpy divided by the

fraction of PLA is equal to 42 J/g for pure PLA and 45 J/g for each of the blends. In addition to the PLA melting peak, the blends also present an endothermic peak coming from the biopolyester melting at 29°C. However, the glass transition of the biopolyester does not appear clearly on the blends.

Figure.5 Differential scanning calorimetry, first scan of pure PLA, pure biopolyester and their blends under a ramp of heating of 10°C/min

Dynamic mechanical thermal analysis

Dynamic mechanical thermal analysis was performed on pure PLA and PLA blends. Figure 6 a) and Figure 6 b) display their storage modulus and their loss factor. The curves of storage modulus of PLA and of the 5% blend have the same profiles; the modulus is in the range of 3 GPa between -100°C and 60°C, drops to 4 MPa by crossing the glass transition, and finally 18 ACS Paragon Plus Environment

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increases due to crystallization. The curve profiles of the other blends are different. The modulus drop of PLA is still present as well as the modulus increase coming from its crystallization, but the glass transition coming from the biopolyester phase is responsible for a second modulus drop at -27°C (Tg of biopolyester determined by DSC). At -100°C, the value of the storage modulus of the blends is lower than for pure PLA; it is equal to 2.5 GPa for the 20% biopolyester sample. Intermediate values are observed for the in-between concentrations. At 90°C (above the glass transition), the modulus is equal to 2.5 MPa for the 20% biopolyester blend. Figure 6 b) displays the loss factor as a function of the temperature. For PLA, a shoulder was observed at -35°C and a strong peak was present at 69°C. They are respectively related to the β relaxation (sub segmental motion) and the α relaxations (segmental motion) of PLA.39 The curves of the blends are more complex; in addition to the two peaks of PLA, they present a peak at -17°C corresponding to the α relaxation of the biopolyester, and another for the 20% blend at 29°C corresponding to its melting. The relaxation occurring at -17°C was already observed in previous work involving pure poly (glycerol sebacate) 29 without addition of monoacid at -20°C. It suggests that the presence of stearic acid in the biopolyester does not strongly affect the α relaxation of the poly (glycerol sebacate) backbone. Finally, the presence of relaxations of both the PLA and biopolyester in blends shows, as it was previously demonstrated by SEM, that the two components of the blend are not miscible.



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Figure.6 Dynamic mechanical analysis of the pure PLA and the biopolyester/PLA Blends (3°C/min, f=1Hz) a) storage modulus b) loss factor


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Mechanical properties

Mechanical properties were studied at room temperature using tensile testing. Representative tensile curves for each sample are plotted in Figure 7. For low deformation, the stress increases and reaches a yield at 2%. After the yield, the pure PLA and the 5 % of biopolyester are broken, demonstrating a relative brittle behavior, while the other samples exhibit a ductile one; a plateau is reached before breaking in which necking is observed.

Figure.7 Typical tensile curves of pure PLA and PLA/biopolyester blends obtained at room temperature

Figure 8 summarizes the mechanical properties. The maximum of stress and the modulus decrease continuously when the mass fraction of biopolyester increases. The Stress decreases from 64 MPa to 30 MPa with the addition of 20% of biopolyester and the modulus from 3.6 GPa



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to 2.7 GPa. Such a result was expected since the added biopolyester contains a soft phase at room temperature.

Figure.8 Mechanical properties of PLA and blends, a) Strain at break and notched Izod impact, b) tensile strength and tensile modulus


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Conversely, the impact strength increases continuously from 19.2 to 37.1 J/m for pure PLA and 20% biopolyester respectively. The strain at break follows a more complex trend, it increases from 2.3% to 93% by adding 10% of biopolyester, and then decreases for higher concentrations through 17%. This trend can be correlated with the SEM observations (Figure 4), in the sense that the dispersion of biopolyester was weaker for concentration of 20% than for the others; phases with a size of about ten micrometers were observed. Figure 9 shows the SEM observations of broken tensile test samples after tensile testing. It highlights that in the case of 5% biopolyester, some regions rich in biopolyester contain a lot of holes linked to the presence of biopolyester, while others do not and thus should have a brittle behaviour. On the contrary, the blends containing 10 and 20% biopolyester show well distributed holes associated to the presence of biopolyester. In the case of the 20% biopolyester blend, there is a continuous path of voids responsible for breaking, coming from the phase of biopolyester and having a 20 µm size (Figure 4 c). For the 10% biopolyester blend, there is a remaining continuous PLA rich phase between holes, which responsible for the high performance of the blend. Finally, several studies on PLA toughened with rubber particles have already been made34,35,40, in which the authors obtained blends with an optimal strain at break of 100-200% for blends containing about 5-10% rubber. In this study, the mechanical properties of the blends are similar to those reported previously. We obtained a strain at break of 93% for a blend containing 10% biopolyester. However, the benefit of this study is that a new application for glycerol has been found. Glycerol was used to synthesize a toughening agent for PLA.



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Figure.9 Observation with scanning electron microscope of cross section after tensile breaking of tensile test sample with various biopolyester content: a) 5%, b) 10%, and c) 20%

Conclusions This work demonstrated the possible use of glycerol based biopolyester as a toughening agent for PLA. A one step microwave synthesis was used to polymerize the reagents, leading to a resin that was soluble in THF. Infrared spectrometry showed an efficient esterification of alcohol with acids induced by microwaving. SEM study performed on PLA/biopolyester blends highlighted that the size of the biopolyester droplets is optimal for blends containing 5-10% weight of biopolyester. According to the morphology of the blend, the maximum increase in strain at break was obtained by adding 10% biopolyester, resulting in an increase from 2% to 93%.

This performance is similar to those obtained with natural rubber in which authors

reported strain at break in the range of 100-200% A significant improvement of impact was evidenced, from 19.2 to 37.1 J/m for pure PLA and 20% biopolyester respectively. However, this enhancement remains low in comparison to commercial toughening agent which leads to impact of hundreds of J/m.


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This work opens new perspectives for the reagents; the same procedure could be used to prepare biopolyesters with other monoacids and diacids in order to design macromolecules that match perfectly with the host polymer. The optimization of the synthesis by increasing the time of reaction or by purifying the product, coupled to an in depth study of the structure of the biopolyester, could be the next step of this work. Finally, since microwave synthesis is still marginal in the polymer synthesis industry, the extrapolation of the microwave synthesis results to a normal source of heating would be necessary to obtain a viable product able to match with the market needs. Acknowledgments: The authors are thankful to: the Ontario Ministry of agriculture Food and Rural Affairs (OMAFRA) - University of Guelph Bioeconomy-Industrial uses Research Program Theme (Project # 200001 and 200002); OMAFRA– New Directions & Alternative Renewable Fuels Research program (Project # 049549); the Natural Sciences and Engineering Research Council (NSERC), Canada for the Discovery Grants individual (Project # 400322), and the Ministry of Economic Development and Innovation (MEDI), Ontario Research Fund - Research Excellence Round 4 program (Project # 050231 and 050289), for their financial support to carry out this research work. The authors also thank: Emmanuel Ogunsona, Oscar Valeirio and Rajendran Muthuraj for the discussions and their technical help.



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For Table of Contents Use Only

Microwave synthesis and melt blending of glycerol based toughening agent with poly (lactic acid) Gildas Coativy, Manjusri Misra and Amar Mohanty A biopolyester based on glycerol (a by-product of biodiesel industry) was synthesized and melt blended with PLA to obtain ductile biobased blends.


Microwave Synthesis and Melt Blending of Glycerol Based

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