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Poly(glycerol-co-diacids) polyesters: from glycerol biorefinery to sustainable engineering applications, a review. Oscar Valerio, Manjusri Misra, and Amar K. Mohanty ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04837 • Publication Date (Web): 28 Mar 2018 Downloaded from http://pubs.acs.org on March 29, 2018

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ACS Sustainable Chemistry & Engineering

Poly(glycerol-co-diacids) polyesters: from glycerol biorefinery to sustainable engineering applications, a review. Oscar Valerioa, b, Manjusri Misraa, b, Amar K. Mohantya, b,* a

School of Engineering, Thornbrough Building, University of Guelph, 50 Stone Road East,

Guelph, N1G 2W1, Ontario, Canada b

Bioproducts Discovery and Development Centre, Department of Plant Agriculture, Crop

Science Building, University of Guelph, 50 Stone Road East, Guelph, N1G 2W1, Ontario, Canada *Corresponding author. E-mail: [email protected]. Tel.: +1-519-824-4120 ext 56664. Fax: +1-519-763-8933.

1 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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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Abstract Upgrading of biobased glycerol to commercial products is a necessary step on sustainable development of oleaginous biomass biorefining. The synthesis of poly(glycerol-co-diacid) polyester materials is an attractive option for glycerol usage that can produce a wide range of products of commercial interest. These polymeric materials could be used on industrial applications as biomedical devices, surfactants and in thermoplastic material development. In this review, the process engineering aspects leading to tailorable polymeric products are comprehensively analyzed with emphasis on control of molecular architecture and functionality. Molecular weight, degree of branching, mechanical properties and surface chemistry of the materials can be controlled by fine tuning synthesis procedures to match custom specifications in end

products.

Potential

usage

of

poly(glycerol-co-diacid)

materials

with

tailored

physicochemical properties on industrially relevant applications is presented. Advantages and challenges in the synthesis of these novel polymeric materials for value added application are addressed and discussed. Keywords: Glycerol, biorefinery, polyglycerol, polyesters, biobased


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Introduction Glycerol, a pivotal resource from biorefineries Glycerol is the common name given to 1,2,3-propanetriol (IUPAC name), the simplest polyol, bearing three hydroxyl groups. Glycerol is naturally synthesized biologically by animals, plants, and microorganisms by diverse pathways 1. Industrially, glycerol can be produced through different processes

2

. Biobased glycerol can be obtained as a coproduct from

saponification or hydrolysis of fats and oils for soap preparation, from fermentation of sugars to glycerol by microorganisms and as a coproduct of transesterification of fats and oils in biodiesel preparation. Petrobased glycerol can be obtained from chlorination of propene under high temperature and from catalytic conversion of allyl alcohol to glycerol. As a consequence of the biodiesel boom in the past decade, from 1999 to 2009 the biobased glycerol production capacity increased ten times reaching more than 2 million tonnes which represented more than 50% of the world glycerol production. Ever since, biobased glycerol has dominated the market of this chemical, and synthetic glycerol (obtained from petroleum resources) represents less than 0.25% of the total 3. The surplus of crude glycerol created last decade caused dramatic effects on the glycerol market. For example, in United states in the period 2004 – 2006 the price of crude glycerol decreased from 25 USD cents per lb to less than 5 USD cents per lb as a consequence of a tenfold increase in biodiesel production forcing many glycerol refineries to stop operations 4. In response to the change of market scenario in glycerol production, new industrial processes to produce value added chemicals were developed. The production of epichlorohydrin, propylene glycol and methanol from glycerol helped to accommodate the glycerol surplus and to increase



Page 4 of 50

its commercial value. By middle of 2014 the commercial value of crude glycerol was 240 USD per tonne (10.9 USD cent per lb) due to the new pathways for utilization of industrial glycerol 3. Further diversification of the glycerol market into new applications is considered a necessary step to consolidate and improve the sustainable development of biorefineries on fuel and chemical sector 5–8. A highly desirable scenario for development of biorefinery of glycerol would involve its utilization for creating various raw chemicals and manufactured products of high volume utilization at relatively low cost 9. This scenario has already started to become true with glycerol being used nowadays as a precursor of several new highly demanded chemicals which were traditionally obtained from petroleum based resources such as propylene glycol 3. Other synthetic products from biobased glycerol such as polyglycerols have reached mature technological state and could become industrially relevant in partial replacement of petroleum based resources in the near future

10

. The synthesis of poly(glycerol-co-diacid) polyester

materials for developing new value added applications in various fields could contribute into further diversification of biobased glycerol market. Process engineering aspects on synthesis of poly(glycerol-co-diacids) polyesters Industrial production of poly(glycerol-co-diacids) in biorefineries The synthesis of glycerol based polyesters is essentially a polycondensation reaction where hydroxyl groups from glycerol react with carboxylic end groups of organic acids or their derivatives. As a result, ester bonds are formed and a condensation product, usually water, is released (Figure 1).


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Figure 1. Schematic of polycondensation reaction between glycerol and a dicarboxylic acid. In a biorefinery context, the synthesis of glycerol based polyesters has been envisioned as an extension in the value chain for oleaginous biomass, where glycerol is a coproduct

11,12

. The

process for the synthesis of poly(glycerol-co-diacids) from biodiesel derived glycerol has been simulated using computational models

13,14

. Under this scheme, the cost of production of the

polyesters has been estimated at 0.9 USD/lb making them attractive candidates for the development of applications 13,14. In practice, glycerol obtained from biorefineries is not always a pure stream

15–17

and thus, purity of the glycerol feedstock must be addressed for a controlled

polyester synthesis. An example of glycerol composition from different biodiesel producing facilities is shown in Table 1. Table 1. Composition of pure glycerol and two different crude glycerol samples. Reprinted with permission from Valerio, O.; Horvath, T.; Pond, C.; Misra, M.; Mohanty, A. Improved utilization of crude glycerol from biodiesel industries: Synthesis and characterization of sustainable biobased polyesters. Ind. Crops Prod. 2015, 78, 141–147. 17

Free glycerol (wt%)

Pure glycerol (PG) 100.3 ± 2.6

Crude glycerol 1 (CG1) 30.2 ± 1.2

Crude glycerol 2 (CG2) 15.4 ± 1.5

Soap (as sodium oleate) (wt%)

BDLa

29.1 ± 1.4

22.4 ± 1.6

FFA (as oleic acid) (wt%)

BDL

0.5 ± 0.1

2.1 ± 0.1

Component/Sample



a.

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FAMEs (wt%)

BDL

22.4 ± 2.6

30.9 ± 4.5

Methanol (wt%)

BDL

14.4 ± 1.3

15.5 ± 0.8

Water (wt%)

BDL

0.9 ± 0.1

5.1 ± 0.1

Ash (wt%)

BDL

3.5 ± 0.1

4.2 ± 0.2

Below detection limit

Crude glycerol obtained from biodiesel production has been envisioned as a feedstock for the production of value added products through fermentation technologies

18

. Impurities present in

crude glycerol streams such as methanol, soaps and salts can limit the usage of glycerol from biorefineries on biotechnological fermentation processes

19

. Similarly, for the synthesis of

polyester materials, impurities contained in crude glycerol such as fatty acids and soaps can participate in the polycondensation reaction, affecting the thermomechanical properties of the products (Figure 2)

17

. The heterogeneous nature of biobased glycerol often requires crude

glycerol purification to at least some extent before industrial utilization

20

. Purification of

glycerol to technical grade (~95 wt% glycerol) was shown as an effective strategy for producing polyester materials with similar properties to pure glycerol based ones

17

. Purification costs of

glycerol could add extra costs of about 0.15 USD/kg to the production costs of polyesters 10.


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Figure 2. Comparison of hypothetical chemical structures of poly(glycerol succinate) synthesized using A) crude glycerol or B) pure glycerol. Reprinted with permission from Valerio, O.; Horvath, T.; Pond, C.; Misra, M.; Mohanty, A. Improved utilization of crude glycerol from biodiesel industries: Synthesis and characterization of sustainable biobased polyesters. Ind. Crops Prod. 2015, 78, 141–147. 17 Numerous diacids have been employed in laboratory scale as monomers in the synthesis of poly(glycerol-co-diacids) including aliphatic diacids of varying chain length (C4 – C14) 22,23

aromatic diacids such as phtalic, terephtalic such as aliphatic unsaturated diacids ketopimelic acid

28

25,26

and iminodiacetic acid

and 2,5 furandicarboxylic acid

24

,

, and others

and functional diacids such as citric acid

29

21

27

, 4-

. From these polymers, the most widely studied is

poly(glycerol sebacate) synthesized from glycerol and sebacic acid

30,31

. This is due to its

reported biocompatibility in vivo, which makes it an attractive material for the development of biomedical applications

32

. Emerging applications of glycerol based polyesters demand for a

precise control of the polycondensation reaction to yield materials of the correct chemistry and molecular features for each requirement. Gelation and its control: neat vs dilute reaction systems The polycondensation reaction of glycerol and diacids corresponds to an A2 + B3 system, where diacids are the linear chain portion (A2) and glycerol can be either linear or branching unit on the polymer backbone (B3). In bulk reactions, the polymerization can lead to gel formation at high conversion of reactants due to the trifunctionality of glycerol. This occurs due to the esterification of the secondary hydroxyl groups on glycerol units, which leads to hyperbranching and eventually to gelation. Gelation marks the onset of the thermoset behavior of the material,



Page 8 of 50

and therefore its control is crucial in polymer design and engineering. Strategies for avoiding gelation involve control of the monomer stoichiometry, quenching of the reaction before gelation, controlled esterification reactions on the secondary hydroxyl group of glycerol and/or the use of dilute polymerization systems. Polymerization simulation has given clear insights about the possibility of avoiding gelation by controlling the molar ratio of reactants 33,34. The glycerol/diacid system achieves gelation on the molar range of 0.33 – 1.33 of glycerol to diacid

34,35

. Thus, polymers synthesized using

stoichiometries outside this range do not form gels. The control of the monomer stoichiometry is a strategy that has been used in the preparation of non-crosslinked glycerol/succinic acid systems 35

. This simple strategy is effective on avoiding gel occurrence. Its major short come is the

decrease of molecular weight in the final product for non – stoichiometric ratios of glycerol/diacids

35

. Hence, if high molecular weight of the final product is desired, this strategy

should not be preferred. In neat glycerol/diacid systems, as the molecules react, an increase in viscosity of the system is observed

36

. Consequently, viscosity monitoring has been employed as a tool for avoiding gel

formation in glycerol and adipic, succinic and maleic anhydride systems

37,38

. In the

glycerol/adipic acid case, the reaction was stopped at viscosities around 5000 mPa s (measured at 100 °C) 37. For the glycerol/succinic acid/maleic anhydride system, the reaction has been stopped at viscosities around 25000 – 35000 mPa s, measured at 100 °C

38

. Quenching of the

polycondensation reaction in order to avoid gelation is typically performed when an exponential increase of viscosity of the media is detected.


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Decreasing or avoiding of esterification reactions on secondary hydroxyl groups of glycerol has also been used as a strategy for avoiding gelation. Usually this is accomplished by using catalysts that present selectivity towards primary alcohol esterification. The most widely used catalyst for this purpose is commercially available Lipase B from Candida Antarctica immobilized on a poly(methyl methacrylate co butyl methacrylate) resin 26,39–45. Recently, diarylborinic acids have been introduced as selective catalyst alternative to the usage of lipases

46

. These could offer

advantages in overcoming thermal and shear stability issues reported for lipase catalysts 47. Another strategy employed in the polycondensation of glycerol and diacids to avoid gelation is the usage of solvents as reaction media. This is commonly known as dilute reaction systems. In dilute reaction systems, the space between molecules is larger, which makes the probability of crosslinking decrease

48

. Several solvents have been used in the synthesis of glycerol/diacid

systems such as toluene, dimethylformamide (DMF) and dimethylsulfoxide (DMSO)

49–51

. The

best results were obtained when synthesis was performed using toluene as solvent media achieving a gel free product of high molecular weight (252 kDa) which is considerable higher than the non-gel product from a bulk polycondensation of the same material 50. Reaction kinetics In the bulk polycondensation of glycerol and diacids in a conventional batch reactor, two phases of reaction can be observed 52. First, a kinetic control of the reaction proceeds, with a first order kinetics with respect to the monomer in default. After certain conversion has been achieved, the reaction changes to diffusion controlled, due to the increase in viscosity of the reaction media, which difficult mass transfer in the system to continue the reaction. Kinetic constants for the initial phase of glycerol/sebacic acid system have been reported for different temperatures and



molar ratio of reactants (Table 2)

52

Page 10 of 50

. The activation energy of the reaction decreased with

increasing molar ratio of glycerol to sebacic acid in the range studied (0.6:1 to 1:1 glycerol : sebacic acid) which indicates that the reaction is favored at equimolar ratio of reactants. The kinetics of reaction is increased with increasing temperature, following a classical Arrhenius behavior. Table 2. Kinetic parameters in poly(glycerol sebacate) synthesis. Reprinted with permission from Maliger, R.; Halley, P. J.; Cooper-White, J. J. Poly(glycerol-sebacate) bioelastomerskinetics of step-growth reactions using Fourier Transform (FT)-Raman spectroscopy. J. Appl. Polym. Sci. 2013, 127 (5), 3980–3986. 52 Molar ratio

Temperature

Kinetic

Activation

Pre exponential

(glycerol:sebacic

(°C)

constant k

energy (kJ/mol)

factor ln A0

(min-1) x 10-4

acid)

0.6

0.8

1.0

120

5.382

130

8.805

140

24.831

120

7.194

130

14.826

140

23.445

120

7.268

130

10.823

140

20.916

(min-1)

102.8

22.794

79.8

17.225

71.1

14.483


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The kinetics of reaction has also been studied in glycerol/sebacic acid using a extruder as a batch reactor

53

. The kinetic constants obtained were 9.88x10-4 and 5.15 x10-4 min-1 for the reaction

carried on the extruder and in a conventional dilute system, respectively. This showed that the reaction kinetics can be dramatically increased by the usage of high shear systems such as extruders, due to decrease in mass transfer limitations observed in conventional batch systems due to viscosity increments. Additionally, the degree of polymerization of the product was significantly higher in the extruder system as compared to the conventional dilute system at all stages of the reaction. Physico chemical aspects of poly (glycerol co diacids) polyesters Molecular weight evolution and control In the polycondensation of glycerol and diacids, the monomers react to yield branched oligomers first. These oligomers continue reacting with remaining monomers and other oligomers to yield higher molecular weight species. An illustrative example has been provided in the bulk polycondensation of glycerol and succinic acid (Figure 3) where the molecular weight of the products has been followed over the course of the reaction via gel permeation chromatography 36

. After three hours of reaction in bulk at 150 °C and a molar ratio of reactants of 1:1 glycerol to

succinic acid, the monomers are almost completely reacted. The lower molecular weight oligomers continue reacting among themselves over the course of reaction to give rise to higher molecular weight species, represented by peaks at lower retention volumes. Just before gelation, the PGS products were composed of different populations of oligomers, with a higher presence of species in the molecular weight range of 4000 – 7000 g/mol, but also some species of lower



Page 12 of 50

molecular weight and the presence of small amounts of unreacted monomers. Thus, a high polydispersity of the final product was obtained (PDI = 3.6).

Figure 3. Gel permeation chromatography traces at different reaction times in poly(glycerol succinate) synthesis in bulk. Adapted with permission from Pin, J. M.; Valerio, O.; Misra, M.; Mohanty, A. Impact of Butyl Glycidyl Ether Comonomer on Poly(glycerol-succinate) Architecture

and

Dynamics

for

Multifunctional

Hyperbranched

Polymer

Design.

Macromolecules 2017, 50 (3), 732–745. Copyright 2017 American Chemical Society. 36 Polycondensations of glycerol and sebacic acid carried in bulk for long reaction times (> 24 h) at lower temperatures (120 – 130 °C) using vacuum have produced products of molecular weight Mn up to 6.3 – 21.3 kDa with polydispersities around 2 to 4 54–58. Reaction at lower temperatures coupled with efficient vacuum assisted water removal result in esterification mainly at primary hydroxyl groups in glycerol, delaying branching and gel onset which allow for a higher polymerization degree 59. Deviations from stoichiometric ratio of reactants (1:1 molar of glycerol to diacid) result in lower molecular weights 35,60,61. This is the result of the imbalance of reactive hydroxy or carboxyl groups for allowing further reactions between oligomers.


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In dilute systems, it has been reported that the attainable molecular weight before gelation can be drastically enlarged due to the spacing of growing oligomers preventing early gelation

50,51

. In

toluene diluted systems, the polycondensation products displayed remarkably higher molecular weights that those reported for bulk systems, achieving molecular weights as high as 252 kDa for a 1:1 molar ratio of glycerol : succinic acid synthesized at 155 °C for 24 h 50. Degree of branching As the reaction in bulk between glycerol and diacids proceeds, different topological units arise, as shown in Figure 4. The evolution of the different species has been described for both the glycerol/succinic acid system and the glycerol/adipic acid system 36,60. Initially, the glycerol units are esterified by diacids preferentially on primary hydroxyl positions, due to the higher reactivity of these groups in comparison with secondary hydroxyl positions. As the reaction proceeds further, the monosubstituted glycerol units evolve to disubstitued units and finally to trisubstituted glycerol units, giving raise to hyperbranched polyesters.

Figure 4. Molecular evolution of chemical species on poly(glycerol succinate synthesis). Adapted with permission from Pin, J. M.; Valerio, O.; Misra, M.; Mohanty, A. Impact of Butyl Glycidyl Ether Comonomer on Poly(glycerol-succinate) Architecture and Dynamics for 13 ACS Paragon Plus Environment


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Multifunctional Hyperbranched Polymer Design. Macromolecules 2017, 50 (3), 732–745. Copyright 2017 American Chemical Society. 36 The degree of branching on glycerol and diacid polycondensation products has been defined by Frey 62 as:

‫= ܤܦ‬

ଶ஽ ଶ஽ା௅భ,మ ା௅భ,య

(1)

∗ 100

where D represents the amount of trisubstituted glycerol units and L1,2 and L1,3 represent disubstituted glycerol units with substitution on a primary and a secondary hydroxyl or in both primary hydroxyl groups respectively. This quantity ranging from 0 to 100% expresses the deviation from linear architecture of the synthesized products. In hyperbranched polymers, the degree of branching usually ranges from 40 to 60%

63

. In glycerol and succinic acid

polycondensation products synthesized in bulk at stoichiometric ratios (1:1 mol of glycerol to succinic acid), the degree of branching obtained was near 35% 36. Similarly to molecular weight, the degree of branching is also influenced by the molar ratio of reactants and temperature of reaction. An excess of glycerol tends to lower the degree of branching whereas an excess of diacid tends to increase the degree of branching

37,49,60

. Lower temperatures of reaction (~120

°C) decrease esterification of secondary hydroxyls in glycerol, thus decreasing branching degree 59

.

Mechanical properties Mechanical properties for crosslinked polycondensation products have been reported in terms of tensile and compressive testing. Crosslinked specimens were obtained by curing of prepolymers at high temperature (110 – 180 °C) for several hours or days. The mechanical properties of these


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glycerol and diacids polycondensation products are highly dependent on the diacid monomers employed, the synthesis parameters, as well as of the curing conditions employed. Thus, the range of mechanical properties reported in literature is wide. In terms of tensile properties, various glycerol based polyesters have been studied using diacids of increasing chain length. Films of poly(glycerol glutarate) (C5 on diacid) have been produced at different ratio of reactants and curing conditions. Tensile strength, Young’s modulus and elongation at yield ranged from 0.41 to 1.05 MPa, 1.94 to 8.28 MPa and 16.3 to 26.9% respectively

64,65

. In the glycerol/azelaic acid system (C9 on diacid), the values of tensile

strength, Young’s modulus and elongation at break obtained were in the ranges 0.26 – 0.85 MPa, 0.98 -11.1 MPa and 17 - 36% respectively

66

. In the glycerol/sebacic acid system (C10 on

diacid), both porous and non porous specimens have been produced. Porous materials displayed an elongation at break higher than 200% (267 ± 59%) and a low Young’s modulus (0.282 MPa) and tensile strength (0.5 MPa)

32

. In non-porous poly(glycerol sebacate) specimens, values for

tensile strength and Young’s modulus in the range of 0.23 - 0.47 MPa and 0.056 - 1.2 MPa were obtained, respectively 67. In the synthesis of poly(glycerol dodecanoate) (C12 in diacid), tensile tests revealed a clear influence of temperature on the mechanical properties of poly(glycerol dodecanoate). At 21 °C, the Young’s modulus, tensile strength and strain at break of the samples was 136.6 MPa, 7 MPa and 225% respectively, whereas at 37 °C these properties decreased to 1.08 MPa, 0.5 MPa and 123.2%. This can be explained in terms of the glass transition temperature (Tg) of the material, reported as 32.1 °C. Thus at temperatures lower than Tg, the material exhibits an elastic plastic behavior, whereas at temperatures higher than Tg the material exhibits elastomeric behavior. These illustrative results highlight both the effect of the curing conditions as well as the diacid monomer employed in the tensile properties of glycerol based 15 ACS Paragon Plus Environment


Page 16 of 50

polyesters. In general, it can be concluded that higher temperatures or curing times can produce polymer products with higher tensile strength and modulus. The same is realized in most cases for samples synthesized at excess of acid. This can be explained by the higher occurrence of condensation reactions at terminal hydroxyl groups of polymer branches, increasing crosslinking density. In terms of diacid chain length the higher mechanical effects are given by the differences in glass transition and crystallinity of the samples, which tend to increase with increasing chain length of the diacid employed. In fact, polyesters synthesized using carbon chain lengths lower than C10 on the diacid such as succinic acid and azelaic acid have been reported as fully amorphous materials 17,68, whereas polyesters synthesized using chain length higher than C9 such as sebacic acid or dodecanoic acid have been reported as semi-crystalline 69,70. In the case of compressive properties, a detailed study on the influence of synthesis and curing conditions on the mechanical properties of poly(glycerol sebacate) has been reported recently 71. The results for compressive strength and modulus followed the same trend that tensile properties, that is, higher curing times and temperatures led to higher compressive strength and modulus on the polyester products. The compressive modulus attained on the optimum curing conditions (1:1 molar ratio of sebacic acid to glycerol, 130 °C, 48 h) was 4.63 MPa. Other studies have reported lower compressive modulus of poly (glycerol sebacate) which may be attributed to the presence of uncrosslinked oligomeric species acting as plasticizers

52

. The compressive modulus of

poly(glycerol dodecanoate) samples was significantly higher than that of poly (glycerol sebacate) for similar curing conditions (75 MPa)

70

. The significantly higher modulus achieved in the

poly(glycerol dodecanoate) samples can be attributed to its semi crystallinity at room temperature. Polymer architecture and functionality and its control 16 ACS Paragon Plus Environment

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Linear polyesters bearing hydroxyl pendant groups In the synthesis of linear functionalized glycerol based polyesters, enzymatic catalysis is usually employed as the first step for the synthesis of a linear glycerol co diacid polyester backbone with pendant hydroxyl groups. This is possible due to the selectivity of the enzymatic catalyst, particularly of lipases, which can selectively attack primary hydroxyl groups on glycerol under specific conditions 72. Under similar reaction conditions and molar ratio of reactants, enzymatic catalysts were able to produce poly(glycerol sebacate) polymers with a percentage of dendritic (trisubstituted) glycerol units considerably lower than the chemical catalyst (12.7 vs 16.6%)

26

.

The ability of the enzymatic catalysts to produce linear glycerol based polyesters depends of the temperature of the reaction media. An increase in degree of branching from 5 to 30% was observed with a temperature increase from 50 to 70 °C for enzyme catalyzed synthesis of poly(glycerol adipate)

42

. Several authors have synthesized linear polymers using lipases as

catalysts on the glycerol/diacid systems

26,39,41,42,44,73

. This effective strategy usually yields

polymers of higher Mn than bulk polycondensations. However, research challenges are still present in the enzyme recovery and reutilization in these systems, as well as in the increase of branching degree of these polymers at higher temperatures which limits the possibility of decrease reaction times by increasing the synthesis temperature. Recently the utilization of diarylboronic acids has been shown as an alternative catalyst for the synthesis of linear glycerol based polyesters. In this case the synthesis was carried at a temperature of 70 °C yielding linear poly(glycerol sebacate) of high molecular weight (Mn = 19.2 kDa) with a percentage of tribustituted glycerol units lower than 1% after 5 h reaction

46

.

Further research should address the possibility of conducting the reaction in bulk systems and at



Page 18 of 50

higher temperatures and the utilization of non-modified diacids for obtaining similar type of synthesis products using these novel catalysts. Hyperbranched polyesters with customized terminal end groups In the synthesis of hyperbranched polyesters which are performed in bulk systems, it is of especial interest the possibility of manipulating the reaction stoichiometry for producing hydroxyl or carboxyl terminated polyesters. This has been clearly shown for the glycerol/adipic acid system; larger glycerol to diacid molar ratios result on hydroxyl terminated polymers and viceversa

74

. The bulk reaction system theoretically allows for the synthesis of hyperbranched

polyesters with tailored end groups using glycerol in combination with any dicarboxylic acid 34. In practice, limitations in the polyesterification of some diacids in bulk can arise from poor solubility of the diacid on glycerol or by excessively high melting temperature of the diacid. High melting point diacids requiring a higher reaction temperature may enhance irreproducibility and reduction of reaction extent due to glycerol volatilization 59,75. The bulk reaction in excess of glycerol or diacid to tailor end functional groups produces oligoesters containing a considerable amount of unreacted monomers and low molecular weight species

34

. This may create the

necessity of purification of the products before their application, which in some cases may involve the usage of solvent purification, creating additional costs and environmental concerns on the sustainability of their production. Functionalized polyesters with tailored side groups Functionalized polyesters can be obtained either by the addition of comonomers with reactivity towards hydroxyl or carboxyl end groups during the polyesterification (in situ functionalization) or by functionalization of the polyester after completion of the synthesis. The former strategy 18 ACS Paragon Plus Environment

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produces random functionalized products whereas in the latter it is possible to tune the polymer architecture and degree of functionality, therefore achieving a higher control of the polymer physicochemical properties. Randomly functionalized lauroyl poly (glycerol succinate) 76, palmitoyl poly (glycerol succinate) 77

and stearyl poly (glycerol sebacate)

69

polyesters have been produced by the simultaneous

reaction of glycerol and the corresponding diacids and monoacids in bulk. Although theoretically fatty acids of any chain length could be used for the random acyl functionalization of glycerol polyesters, in practice solubility issues arise limiting the reactivity of the system for chain lengths higher than C11 for uncatalyzed bulk reactions 78. This limitation can be overcome either by the utilization of enzymatic catalysts or by the usage of polymerizable comonomers acting as solvents in the reaction media

45,78,79

. Recently, a novel strategy for the in situ functionalization

of poly (glycerol succinate) has been introduced, consisting in the addition of epoxy bearing fatty acid tails onto the polyesterification 36. This strategy could be potentially applicable to fatty acid tails of different chain length and other functional side groups, although solubility issues may still be a limiting factor when using long chain fatty acid derivatives. Post synthesis functionalization of glycerol based polyesters has been achieved by catalyzed grafting of fatty acid chlorides onto hydroxyl groups of linear polyester backbones. Fatty acids of different chain length and at different grafting percentage have been grafted onto poly (glycerol adipate) backbones such as butyric (C4) 43, caprylic (C8) 39, lauric (C12) 73, stearic (C18) 39, oleic (C18:1)

41

and behenic (C21)

73

acid. These acyl functionalization and their fine control in

percentage of grafting allows for the design of materials with tailored physicochemical properties, such as surface tension, and self-assembly character into nanoparticles with controlled morphology and particle size

39,41,43,73

. An interesting example of post 19

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Page 20 of 50

functionalization of glycerol based polyesters is the production of acrylated poly(glycerol sebacate) (Acryl-PGS) (Figure 5) 80. This modification is of interest since it allows for the photo crosslinking of Acryl-PGS, making the curing process much faster and less energy intensive in comparison with conventional thermal curing of glycerol based polyesters. Very recently, photocurable PGS was obtained by a direct acylation method consisting in treating PGS with 2Isocyanatoethyl methacrylate (PGS-IM) 54. This new method allows for a direct acylation of the linear PGS backbone under milder conditions compared to functionalization using acyl chlorides.

Figure 5. Example of synthesis route to acrylated functionalized poly(glycerol sebacate) polyesters (Acryl - PGS). Adapted with permission from Nijst, C. L. E.; Bruggeman, J. P.; Karp, J. M.; Ferreira, L.; Zumbuehl, A.; Bettinger, C. J.; Langer, R. Synthesis and characterization of photocurable elastomers from poly(glycerol-co-sebacate). Biomacromolecules 2007, 8 (10), 3067–3073. Copyright 2007 American Chemical Society. 80 Copolyesters based on glycerol and diacids The copolymerization of glycerol, diacids and diols or multifunctional polyacid/polyol monomers has been introduced mainly as a tool to modulate the mechanical behavior and


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physicochemical properties of the synthesized materials. For example, the synthesis of poly(glycerol sebacate)-co-lactide (PGS-co-PLA) with tunable hydrophilicity was realized by controlling the molecular weight of the copolymerized PLA segments

81

. Modification of PGS

by copolymerization with PLA allows and adjustment of the mechanical behavior and biodegradation rate of the resulting elastomers

82

in biomedical applications as surgical sealants

. PGS-co-PLA elastomers have been proposed 83

. The introduction of poly(ethylene glycol)

(PEG) into poly(glycerol sebacate) has also been reported 84. By incorporating hydrophilic PEG on the PGS structure, the water uptake capacity and degradation rate was remarkably increased, and the Young’s modulus of the material could be controlled in a wide range (0.01– 2.2 MPa). PGS-co-PEG copolymers have been proposed as enhancers materials for tricalcium phosphate based bone tissue engineering 85. Poly(glycerol adipate) has been also copolymerized with PEG, yielding elastomers with tunable Young’s modulus in the range 0.07 – 8.33 MPa 86. Additionally, both PEG and PLA have been simultaneously copolymerized with poly(glycerol sebacate) to yield PGS-co-PEG-co-PLA elastomers with a wide range of mechanical properties

87

. Another

example of biocompatible copolyesters is poly(glycerol sebacate)-co-caprolactone synthesized from the polycondensation of glycerol, sebacic acid and ε-caprolactone

88

synthesis

prepared

of

poly(glycerol-co-sebacate)-co-poly(hydroxybutyrate),

. Recently, the from

polycondensation of glycerol, sebacic acid and poly(hydroxybutyrate) diols of different molecular weight, has been reported as a biocompatible material with tunable mechanical properties 89. Prospective applications of polyesters Biomedical applications



Page 22 of 50

Tissue engineering Due to its elastomeric mechanical behavior, the polyesters synthesized from glycerol and diacids have been mainly proposed as synthetic scaffolds for the development of soft tissue engineering. These applications need for high purity glycerol, due to biocompatibility requirements. Poly(glycerol-co-diacids) have been synthesized in diverse ways and processed by different means for specific tissue engineering applications. Typically, a prepolymer is first obtained by polycondensation and then thermally cured 90. Nevertheless, strategies for curing the prepolymer at room temperature have also emerged as an alternative to thermal curing for achieving a better control of properties of cured specimens 56,91. For skin tissue engineering, researchers have formulated biocompatible porous poly (glycerol sebacate) (PGS) scaffolds 92. These biodegradable scaffolds have been used for in vitro studies of biocompatibility, demonstrating non-toxic nature and cell proliferation of mouse dermal fibroblasts on their surface. PGS based scaffolds modified by the addition of silk fibroins and chitosan showed enhanced crosslinking density, better cell adhesion and proliferation as well as slower degradation rate as compared to unmodified PGS porous scaffolds

93

. In vivo tests are

necessary to fully reveal the potential of these materials on skin replacement applications. Nerve tissue engineering has seen advances both on in vitro and in vivo models. Poly (glycerol sebacate) (PGS) modified by grafting of poly (methyl methacrylate) has been proposed as candidates for nerve tissue engineering 94 Electrospun nanofibers of PMMA-PGS in blends with gelatin supported differentiation of PC12 cells onto neuron like phenotypes. Unmodified PGS has also been shown a promising material on nerve regeneration in vivo

95

. On animal models,

PGS was implanted onto spinal cord defects along a promoter of neuron development (ChABC),


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and the nerve regeneration and functional recovery was evaluated. Animals treated with PGS and ChABC together showed outstanding functional recovery after 12 weeks, and remarkable nerve regeneration with a complete biodegradation of PGS. In the field of corneal tissue engineering, poly (glycerol sebacate) (PGS) has been blended with poly (caprolactone) (PCL) and electrospun into semitransparent mats of nanometric sized fibers 96,97

. It was shown that PGS played a crucial role in modulating the mechanical properties,

adherence and transparency of the electrospun mats. This in turn favored the differentiation of human corneal endothelial cells into a hexagonal morphology, suitable for development of corneal constructs for tissue engineering

98

. Further tests of the candidate materials on in vivo

studies are needed to assess the suitability of these materials for corneal tissue repairing. For heart and arterial tissue engineering, there have been advances reported both in vitro and in vivo studies. Arterial reconstruction using poly(glycerol sebacate) based materials has been demonstrated on in vivo animal models. Vascular grafts of PGS covered by a electrospun layer of poly (caprolactone) (PCL) promoted regeneration of aorta arterial tissue on implants on animal models, with a complete integration of the artificial tissue onto native tissue after 90 days

99

.

Moreover the vascular grafts showed excellent long term performance over a 12 month period on animal models

100

. On cardiac tissue engineering, a remarkable success was reported for PGS

based cardiac adhesives on in vivo studies

57

. Acrylated PGS was prepared which could be

crosslinked upon exposure to ultraviolet light. These UV crosslinkable PGS based adhesive demonstrated capability to seal cardiac and arterial defects on in vivo animal models with a minimal invasive delivering technique.



Page 24 of 50

On bone tissue engineering, there has been advances both on bone/soft tissue interface in vitro engineering as well as in studies on bone regeneration in vivo. Bilayered composites of poly(glycerol sebacate) (PGS) and β-tricalcium phosphate (β-TCP) have been reported as biocompatible materials, with the capability of inducing bone cell adhesion and proliferation on in vitro studies

101

. Composite scaffolds of bioglass coated with neat poly(glycerol sebacate)

(PGS) and poly ethylene glycol modified PGS were shown highly effective on producing healthy bone tissue after tested on in vivo animal models 58. Unmodified poly(glycerol sebacate) showed remarkable results on cell proliferation and bone regeneration on in vivo studies 102. Shape memory materials have been proposed as next generation materials for biomedical usages, given that they could be introduced on host tissue with minimally invasive procedures and change shape once installed on their action site 103,104. Poly(glycerol sebacate) and poly (glycerol dodecanoate) display shape memory properties, being able to recover its original shape after an increase in temperature

105–107

. Moreover, these elastomers present high toughness, mimicking

material behavior of human soft tissue 108. The mechanical properties and stimuli responsiveness of poly(glycerol sebacate) have been engineered through simple chemistry such as grafting of fatty acid tails onto the polymer structure which enabled the material to preserve deformed state at room temperature

109

. Also, poly(glycerol sebacate urethane) modified with cellulose was

capable of recovering shape when exposed to water

110

. A promising way for controlling

mechanical behavior and stimuli responsiveness of these materials has emerged with the isocyanate based curing of poly(glycerol-co-diacids) polymers, which could result on tailorable shape memory materials for tissue engineering applications 56,111. 3D printing


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Three dimensional printing (or 3D printing) is an advanced design technique which allows for the fabrication of complex structures through the layer by layer deposition of a molten polymeric material onto a collector where it cools down and solidifies. The advantages of this technique are numerous, including easier design and fabrication of complex tridimensional scaffolds without the need of soluble supports, fast and reliable prototyping of custom made structures and in the biomedical field, tailoring the design of synthetic polymeric scaffolds to exact dimensions according to each patient specific requirements. Very recently, poly(glycerol sebacate), synthesized from neat polycondensation of glycerol and sebacic acid and further modified with UV curable monomers has been employed for 3D printing of complex shaped porous scaffolds (Figure 6). These types of porous structures would be hard to produce using other conventional processing techniques. PGS modified with acrylated side groups (Acryl-PGS) was firstly employed as a 3D printing material

55

. 3D printed complex porous biodegradable scaffolds

resembling soft tissue human body shapes. demonstrated the capability for supporting cell attachment and proliferation. In another recent study, PGS modified with norbornene pendant groups was used for 3D printing scaffolds with tunable mechanical properties, as well as tunable biodegradation ratio by controlling the polymer/crosslinker ratio 91. Moreover, the scaffolds were shown as biocompatible, supporting cell attachment and proliferation.



Page 26 of 50

Figure 6. Examples of 3D printed scaffolds resembling human hear and nose shapes. Reprinted with permission from Yeh, Y.-C.; Ouyang, L.; Highley, C. B.; Burdick, J. A. Norbornenemodified poly(glycerol sebacate) as a photocurable and biodegradable elastomer. Polym. Chem. 2017, 8 (34), 5091–5099. 91 Drug delivery The usage of poly (glycerol co diacids) on drug delivery applications has been envisioned by means of different strategies. These strategies need the usage of pure glycerol for the synthesis due to biocompatibility requirements. Additionally there is a great need for careful control of polymer physicochemical properties and architecture to achieve controlled sustained release of drugs. The oldest strategy consisted on the encapsulation of drugs onto poly(glycerol-co-diacids) nanoparticles. Both hydrosoluble and liposoluble drugs have been encapsulated onto poly(glycerol adipate) (PGA) nanoparticles. Drug loading and release from the PGA nanoparticles was highly influenced by the type of drug and its molecular interactions with the nanoparticle carriers. For example, the acyl functionalization of PGS backbone with caprylic acid (C8) at 100% grating percentage (all OH groups substituted by the C8 acyl tail) showed beneficial for the encapsulation of one drug model (Dexamethasone phosphate) whereas for 26 ACS Paragon Plus Environment

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another model drug (Cytosine arabinoside) the unmodified PGA nanoparticles performed better 112

. Poly (glycerol adipate) nanoparticles were reported as not cytotoxic on in vitro studies, which

may enable their utilization on in vivo models

113

. A few other model drugs and proteins have

been successfully encapsulated onto nanoparticles of poly (glycerol adipate) and its modifications

114–116

. Poly (glycerol sebacate) has also been used as a material for nanoparticle

encapsulation of drugs

117,118

. Recently, innovative approaches have been demonstrated for the

usage of glycerol based polyesters as drug delivery materials. Core shell electrospun devices of poly (glycerol sebacate)/poly (caprolactone)/gelatin were loaded with dexamethasone and demonstrated capability for sustained release of the drug on in vitro studies

119

. Another recent

approach consisted on the direct grafting of drug molecules onto a linear backbone of poly (glycerol adipate) (PGA) 44. This interesting approach aims for the delivery of drug onto the host as biodegradation of the PGA material itself occurs in vivo avoiding critical processing steps for correct encapsulation and delivery of target drugs. Non-biomedical applications Surfactants Given their branched structure and tunable physicochemical properties, in particular surface hydrophobicity/hydrophilicity by acyl substitution, poly (glycerol co diacid) oligomers have been explored as surfactants. For these applications, the purity of glycerol could be as low as technical glycerol, given that their usage does not necessarily require biocompatibility. Lauroyl poly (glycerol succinate) hyperbranched oligomers synthesized in bulk polycondensations were tested as emulsifiers on aqueous solutions

76

. These products demonstrated good foaming

properties and micellar solubilization properties when compared to commercial standards. In



Page 28 of 50

addition, they were reported as biodegradable. Similar findings have been reported for palmitoyl poly (glycerol succinate) and the modification of these oligomers with sorbitol hydrophilic linkers improved their surfactant properties 77. A detailed study on the effect of the fatty acid tail on the surfactant properties of acyl modified poly (glycerol succinate) showed that their surfactant properties such as foamability, wetting and critical micellar concentration were improved in the range of length C8 – C12 but decreased over that carbon chain length

120

.

Grafting efficiency of longer fatty acid tails was improved by usage of copolymerizable solvents such as lactic acid, yielding surfactant products with improved hydrophobic/hydrophilic balance, and surfactant properties comparable to commercial products 78. Thus, the bulk synthesis of acyl modified poly(glycerol-co-diacids) is a feasible alternative for the development of new biobased and biodegradable surfactants as emulsifiers for application on industrial sector. Thermoplastic materials Due to their elastomeric properties at room temperature, poly (glycerol co diacids) have been used as toughening agents in thermoplastic blends. In analogy to rubber modification of other industrially relevant thermoplastic materials such as polyolefins, this application involves the melt blending of a thermoplastic material with an elastomeric glycerol based polyester to impart toughness to the final blend material. Glycerol of technical grade could be used for these applications as biocompatibility is not an issue. Poly(lactic acid) (PLA), a compostable thermoplastic with good tensile properties but brittle in nature has been toughened by melt blending with poly(glycerol-co-diacids). Poly(glycerol sebacate) (PGS) synthesized in bulk was firstly employed as toughness enhancer for PLA, demonstrating ability for improving elongation at break of PLA by more than 100% with the addition of 15 to 30 wt% of PGS

121

. Similarly,

microwaved synthesized poly(glycerol sebacate) and poly(glycerol sebacate-co-stearate) 28 ACS Paragon Plus Environment

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improved the elongation at break of PLA by 90% upon addition of 10 wt% of the elastomer 69. Poly(glycerol succinate-co-maleate) (PGSMA) was also reported as an effective toughness enhancer for PLA 61. By using a dynamic vulcanization method, involving the reactive extrusion of PLA and PGSMA, the elongation at break and notched Izod impact of PLA were improved by 53% and 175% respectively on a 60/40 wt% PLA/PGSMA blend 38. An example of impact toughness modification by melt blending with glycerol based polyesters was shown for poly(butylene succinate) (PBS) thermoplastic material. By melt blending PBS with gel poly(glycerol succinate) products synthesized in bulk polycondensations, the notched Izod impact properties of the material was improved by 344% whereas elongation at break of the material was maintained

122

. Recently, ternary blends of PLA/PBS/PGSMA were prepared by

reactive extrusion, displaying tensile and impact properties comparable to commercial polypropylene

123

. These results demonstrate the usefulness of glycerol based polyesters in

engineering of biobased thermoplastic blends (Table 3), which could lead to the adoption of these materials in partial replacement of non- biodegradable thermoplastics for applications such as packaging.


ACS Sustainable Chemistry & Engineering 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

Page 30 of 50

Table 3. Examples of mechanical properties of thermoplastic materials containing poly(glycerol-co-diacids)

Blend components Poly(lactic acid) (PLA) Poly(butylene succinate) (PBS) PBS/Poly(glycerol succinate) PLA/Poly(glycerol succinateco-maleate) PLA/Poly(glycerol succinateco-maleate) PLA/PBS/Poly(glycerol succinate-co-maleate) PLA/Poly(glycerol sebacateco-stearate)

100

Tensile strength (MPa) 67.1 ± 0.8

Tensile Modulus (GPa) 3.114 ± 0.02

100

49.5 ± 4

70/30

Composition (w/w%)

Elongation at break (%)

Notched Izod impact (J/m)

4.3 ± 0.3

20.7 ± 0.9

61

0.77 ± 0.02

235..7 ± 42.5

22.5 ± 4.2

122

25.6 ± 0.5

0.331 ± 0.01

220 ± 11

110.9 ± 23.7

122

80/20

43.5 ± 0.8

2.1 ± 0.03

150 ± 15

23.4 ± 8.2

61

60/40

32.2 ± 0.9

1.879 ± 0.09

55.3 ± 11

55.4 ± 7.1

38

35/40/25

33.8 ± 0.7

1.472 ± 0.06

142.6 ± 20.4

158.8 ± 11.9

123

90/10

47.7 ± 1.0

3070 ± 146

92.8 ± 11.7

28.9 ± 6.2

69

Ref


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Concluding remarks and outlook In the emerging bioeconomy paradigm, where society could obtain sustainable fuels and chemicals from biomass, glycerol plays a major role as a precursor for synthesis of commercial products and extension of oleaginous biomass value chain. The usage of poly(glycerol-codiacids) in value added applications is a realistic approach for improving sustainability of biobased chemical sector. Emerging applications for these materials have reached a mature research state in academia that could allow for its technological transfer to industrial chemical producers on biorefineries. Before this transition happens, some key challenges must be overcome for ensuring a succesful transition from laboratories to industrial production. Applications in biomedical engineering as biodegradable scaffolds have been demonstrated for several areas using in vivo animal models. The advancement of this knowledge concerning utilization of these materials on human tissue engineering is the next step on their route. The materials have already shown biodegradable nature, biocompatibility and remarkable results on promoting tissue regeneration on animal model experiments, which is an encouraging scenario towards the testing of these materials on humans. Further experiments on larger animal models could pave the route to a future usage of these polyesters in human tissue engineering. The possibilities of applications are enormous and comprise diverse human tissues such as heart, arterial, nerve, corneal, cartilage and skin tissues. Similarly, potential applications on controlled and localized drug delivery on humans and animals for poly(glycerol-co-diacids) are promising. The existing technologies allow for efficient drug loading on biodegradable and cytocompatible poly(glycerol-co-diacid) carriers. In vivo testing on larger animal models and clinical trials on humans of these newly devised materials could allow for their implementation on human



Page 32 of 50

pharmacology in the future, with a tremendous potential for replacement of non-site specific drug carriers. In surfactant applications the technologies developed are already mature and the application of poly(glycerol-co-diacids) on industrial processes could be realized soon. These biodegradable surfactants have shown similar performance to traditional commercial surfactants, thus, their application could happen as a drop in replacement for non-biodegradable surfactants. On thermoplastic material development, although the materials developed so far present some mechanical properties comparable to commercial non biodegradable thermoplastics, further development of the technologies are needed to enable their commercial adoption. In particular, studies concerning the durability and compostability of these materials when in service and after disposal are needed to prove their full potential. Based on findings from biomedical areas it is expected that these thermoplastic materials could be compostable, which would make them very attractive candidates for partial replacement of non-biodegradable thermoplastic materials in some applications, achieving increased sustainability. A key challenge that would further improve the current technologies is the development of efficient and solvent free reaction systems for producing higher molecular weight poly(glycerolco-diacids) products of controlled molecular architecture and functionality. Design of novel catalyst system and engineering of existing chemical and biological ones as well as novel processing schemes and synthesis protocols could help in addressing this issue. Developing strategies for achieving higher control of functionality and architecture for glycerol based polyesters synthesized in bulk could be relevant on decreasing processing and purification costs of the materials. This should allow for the wider adoption of poly(glycerol-co-diacid) materials on fields outside biomedical scope. Strategies for obtaining synthetic products of high purity 32 ACS Paragon Plus Environment

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presenting minimal or no purification needs would be desirable for enabling industrial large scale production of poly(glycerol-co-diacid) materials at competitive costs. In summary, it can be said the polycondensation of glycerol and diacids is a very versatile system with high potential for industrial implementation, provided that some key challenges discussed are addressed. A proper and careful selection of synthesis conditions and process engineering for each particular application could allow for their industrial application on various technological fields. Acknowledgements The authors are thankful to the Chilean National Scholarship Program for Graduate Studies from CONICYT-Chile; the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), Canada/University of Guelph-Bioeconomy for Industrial Uses Research Program Theme (Project #030251); OMAFRA, Canada New Directions Project #050155; Ontario Ministry of Research, Innovation and Science (MRIS), Ontario Research Fund, Research Excellence Program; Round7 (ORF-RE07) (Project # 052850); the Natural Sciences and Engineering Research Council (NSERC), Canada - Discovery Grants (Project # 401111 and 400320) for the financial support to carry out this research work. Biographies



Page 34 of 50

Oscar Valerio is a Chilean researcher with scientific interest on biomass conversion technologies, biorefinery, sustainable chemistry processes and materials science and engineering. He is currently a Ph. D. candidate at the Bioproducts Discovery and Development Center at University of Guelph, ON, Canada. Oscar obtained his Chemical Engineering and Biotechnological Engineering degrees from Universidad de Chile in 2008. After he obtained a M.A.Sc in Biological Engineering from University of Guelph in 2013. He has published 8 peer reviewed journal articles and participated in several international conferences related to biorefinery/sustainable materials. He received the 2nd place award on graduate poster competition on the Society of Plastic Engineers 17th Annual Automotive Composites Conference and Exhibition held in Michigan, USA, September 2017.


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Dr. Amar Mohanty is a Professor and Premier’s Research Chair in Biomaterials and Transportation at the University of Guelph and a former Michigan State University professor. He is an international leader in the field of bioplastics and biobased materials.

He holds the

University Research Leadership Chair Professor and is the Director of the Bioproducts Discovery & Development Centre (BDDC) at the University of Guelph. He has around 750 publications to his credit, including 326 peer-reviewed journal papers, and 55 Patents awarded/applied. Five of his recently invented technologies have been commercialized. The total citation number of his research articles is 23,809, h-index is 71 and i10index is 243 (Google Scholar, February 28, 2018) and his ResearchGate Score of 45.94 is higher than 97.5% of the 11 million ResearchGate members (Research Gate, February 28, 2018). His work was recognized 35 ACS Paragon Plus Environment


Page 36 of 50

by the Lifetime Achievement Award from the BioEnvironmental Polymer Society, USA. Professor Mohanty has also received the Andrew Chase Forest Products Division Award from the Forest Products Division of the American Institute of Chemical Engineers and was the holder of the Alexander von Humboldt Fellowship at the Technical University of Berlin, Germany. Currently, he holds the Director (elect) position of Forest Products Division of the American Institute of Chemical Engineers.


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Dr. Misra is a professor in the School of Engineering and holds a joint appointment in the Dept. of Plant Agriculture at the University of Guelph. Dr. Misra’s current research focuses primarily on novel bio-based composites and nanocomposites from agricultural and forestry resources for the sustainable bio-economy targeting the development of bio-based and eco-friendly alternatives to the existing petroleum-based products. She has authored more than 500 publications, including 289 peer-reviewed journal papers, 23 book chapters, and 15 granted patents. She was an editor of the CRC Press volume, “Natural Fibers, Biopolymers and Biocomposites,” Taylor & Francis Group, Boca Raton, FL (2005); American Scientific Publishers volume “Packaging Nanotechnology”, Valencia, California (2009); “Polymer Nanocomposites”, Springer (2014) and “Fiber Technology for Fiber-Reinforced Composites”, Woodhead Publishing (2017). She was the chief editor of “Biocomposites: Design and Mechanical Performance” Woodhead Publishing (2015). She was the 2009 President of the BioEnvironmental Polymer Society (BEPS). She is one of the Associate Editors of the journal “Advanced Science Letters” and serves in the editorial board of “Journal of Applied Polymer Science”. In 2012, Dr. Misra received the prestigious “Jim Hammar Memorial Award” from BEPS and University of Guelph’s Innovation of the year award in 2016 for the involvement in developing the “compostable single-serve coffee pods”. In 2017, Professor Misra has also received the Andrew Chase Division Award in Chemical Engineering from the Forest Bioproducts Division of the American Institute of Chemical Engineers. Total citations: 22,419; h-index: 67; i10-index: 246 (Google Scholar, February 28, 2018). ResearchGate (RG) Score: 45.53 (higher than 97.5% of ResearchGate members') (ResearchGate, February 28, 2018).



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The tailored synthesis of sustainable glycerol based polyesters as an extension of oleaginous biomass biorefinery is reviewed.

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