Enzymatic synthesis and curing of biodegradable epoxide-containing polyesters from renewable resources

Chemo-Enzymatic Derivatization of Glycerol-Based Oligomers: Structural Elucidation and Potential Applications

Switching from oil-based to bio-based feedstocks to ensure the green transition to a sustainable and circular future is one of the most pressing challenges faced by many industries worldwide. For the cosmetics and personal and house care industries there is a strong drive to accelerate this transition from the customers that starts favoring the purchase of naturally derived and bio-degradable products over the traditionally available products. In this work we developed a series of fully biobased macromolecules constituted of a glycerol-based oligoester backbone. Based on the subsequent derivatization with fatty acids or peptides, the resulting products may find application as emulsifiers, wetting agents, and potential vectors for the delivery of bioactive peptides. All steps of the resulting macromolecules were conducted following the green chemistry principles with no toxic or environmentally damaging compounds that were used in the overall production process.

Enzymes in "Green" Synthetic Chemistry: Laccase and Lipase

Enzymes play an important role in numerous natural processes and are increasingly being utilized as environmentally friendly substitutes and alternatives to many common catalysts. Their essential advantages are high catalytic efficiency, substrate specificity, minimal formation of byproducts, and low energy demand. All of these benefits make enzymes highly desirable targets of academic research and industrial development. This review has the modest aim of briefly overviewing the classification, mechanism of action, basic kinetics and reaction condition effects that are common across all six enzyme classes. Special attention is devoted to immobilization strategies as the main tools to improve the resistance to environmental stress factors (temperature, pH and solvents) and prolong the catalytic lifecycle of these biocatalysts. The advantages and drawbacks of methods such as macromolecular crosslinking, solid scaffold carriers, entrapment, and surface modification (covalent and physical) are discussed and illustrated using numerous examples. Among the hundreds and possibly thousands of known and recently discovered enzymes, hydrolases and oxidoreductases are distinguished by their relative availability, stability, and wide use in synthetic applications, which include pharmaceutics, food and beverage treatments, environmental clean-up, and polymerizations. Two representatives of those groups-laccase (an oxidoreductase) and lipase (a hydrolase)-are discussed at length, including their structure, catalytic mechanism, and diverse usage. Objective representation of the current status and emerging trends are provided in the main conclusions.

Synthesis of Biorenewable Terpene Monomers Using Enzymatic Epoxidation under Heterogeneous Batch and Continuous Flow Conditions

A commercially available Lipase B from Candida antarctica immobilized onto a macroporous support (Novozym 435) has been employed in the presence of H2O2 as a benign oxidant for the epoxidation of various biorenewable terpenes. This epoxidation protocol was explored under both heterogeneous batch and continuous flow conditions. The catalyst recyclability was also investigated demonstrating good activity throughout 10 cycles under batch conditions, while the same catalyst system could also be productively used under continuous flow operation for more than 30 h. This practical and relatively safe sustainable flow epoxidation of di- and trisubstituted alkenes by H2O2 allows for the production of gram quantities of a range of terpene epoxides. As a proof of principle, the same protocol can also be applied to the epoxidation of biobased polymers as a means to post-functionalize these macromolecules and equip them with cross-linkable epoxy groups.

Enzymatic Synthesis of Polyesters and Their Bioapplications: Recent Advances and Perspectives

This article reviews the most important advances in the enzymatic synthesis of polyesters. In first place, the different processes of polyester enzymatic synthesis, i.e., polycondensation, ring opening, and chemoenzymatic polymerizations, and the key parameters affecting these reactions, such as enzyme, concentration, solvent, or temperature, are analyzed. Then, the latest articles on the preparation of polyesters either by direct synthesis or via modification are commented. Finally, the main bioapplications of enzymatically obtained polyesters, i.e., antimicrobial, drug delivery, or tissue engineering, are described. It is intended to point out the great advantages that enzymatic polymerization present to obtain polymers and the disadvantages found to develop applied materials.

Plant oil-based polymers

Polymer materials derived from natural resources have gained increasing attention in recent years because of the uncertainties concerning petroleum supply and prices in the future as well as their environmental pollution problems. As one of the most abundant renewable resources, plant oils are suitable starting materials for polymers because of their low cost, the rich chemistry that their triglyceride structure provides, and their potential biodegradability. This chapter covers the structure, modification of triglycerides and their derivatives as well as synthesis of polymers therefrom. The remarkable advances during the last two decades in organic synthesis using plant oils and the basic oleochemicals derived from them are selectively reported and updated. Various methods, such as condensation, radical/cationic polymerization, metathesis procedure, and living polymerization, have also been applied in constructing oil-based polymers. Based on the advance of these changes, traditional polymers such as polyamides, polyesters, and epoxy resins have been renewed. Partial oil-based polymers have already been applied in some industrial areas and recent developments in this field offer promising new opportunities.

Cationic UV-Curing of Epoxidized Biobased Resins

Epoxy resins are among the most important building blocks for fabrication of thermosets for many different applications thanks to their superior thermo-mechanical properties and chemical resistance. The recent concerns on the environmental problems and the progressive depletion of petroleum feedstocks have drawn the research interest in finding biobased alternatives. Many curing techniques can be used to obtain the final crosslinked thermoset networks. The UV-curing technology can be considered the most environmentally friendly because of the absence of volatile organic compound (VOC) emissions and mild curing conditions. This review provides an overview of the state of the art of bio-based cationic UV-curable epoxy resins. Particular focus has been given to the sources of the bio-based epoxy monomers and the applications of the obtained products.

A Study of Some Mechanical Properties of Composite Materials with a Dammar-Based Hybrid Matrix and Reinforced by Waste Paper

When obtaining environment-friendly hybrid resins made of a blend of Dammar natural resin, in a prevailing volume ratio, with epoxy resin, it is challenging to find alternatives for synthetic resins. Composite materials reinforced with waste paper and matrix made of epoxy resin or hybrid resin with a volume ratio of 60%, 70% and 80% Dammar were studied. All samples obtained have been submitted to tensile tests and Scanning Electron Microscopy (SEM) analysis. The tensile response, tensile strength, modulus of elasticity, elongation at break and the analysis of the fracture surface were determined. The damping properties of vibrations of bars in hybrid resins and in the composite materials under study were also examined. The mechanical properties of the four types of resins and of the composite materials were compared. The chemical composition for a hybrid resin specimen were obtained using the Fourier Transformed Infrared Spectroscopy (FTIR) and Energy, Dispersive X-ray Spectrometry (EDS) analyzes.

A Study of the Mechanical Properties of Composite Materials with a Dammar-Based Hybrid Matrix and Two Types of Flax Fabric Reinforcement

The need to protect the environment has generated, in the past decade, a competition at the producers’ level to use, as much as possible, natural materials, which are biodegradable and compostable. This trend and the composite materials have undergone a spectacular development of the natural components. Starting from these tendencies we have made and studied from the point of view of mechanical and chemical properties composite materials with three types of hybrid matrix based on the Dammar natural hybrid resin and two types of reinforcers made of flax fabric. We have researched the mechanical properties of these composite materials based on their tensile strength and vibration behavior, respectively. We have determined the characteristic curves, elasticity modulus, tensile strength, elongation at break, specific frequency and damping factor. Using SEM (Scanning Electron Microscopy) analysis we have obtained images of the breaking area for each sample that underwent a tensile test and, by applying FTIR (Fourier Transform Infrared Spectroscopy) and EDS (Energy Dispersive Spectroscopy) analyzes, we have determined the spectrum bands and the chemical composition diagram of the samples taken from the hybrid resins used as a matrix for the composite materials under study. Based on the results, we have suggested that these composite materials could be used in different fields of activity.

Thermal Upgrade of Enzymatically Synthesized Aliphatic and Aromatic Oligoesters

The enzymatic synthesis of polyesters in solventless systems is an environmentally friendly and sustainable method for synthetizing bio-derived materials. Despite the greenness of the technique, in most cases only short oligoesters are obtained, with limited practical applications or requiring further chemical processing for their elongation. In this work, we present a catalyst-free thermal upgrade of enzymatically synthesized oligoesters. Different aliphatic and aromatic oligoesters were synthesized using immobilized Candida antarctica lipase B (iCaLB) as the catalyst (70 °C, 24 h) yielding poly(1,4-butylene adipate) (PBA, M_w = 2200), poly(1,4-butylene isophthalate) (PBI, M_w = 1000), poly(1,4-butylene 2,5-furandicarboxylate) (PBF, M_w = 600), and poly(1,4-butylene 2,4-pyridinedicarboxylate) (PBP, M_w = 1000). These polyesters were successfully thermally treated to obtain an increase in M_w of 8.5, 2.6, 3.3, and 2.7 folds, respectively. This investigation focused on the most successful upgrade, poly(1,4-butylene adipate), then discussed the possible effect of di-ester monomers as compared to di-acids in the thermally driven polycondensation. The herein-described two-step synthesis method represents a practical and cost-effective way to synthesize higher-molecular-weight polymers without the use of toxic metal catalysts such as titanium(IV) tert-butoxide, tin(II) 2-ethylhexanoate, and in particular, antimony(IV) oxide. At the same time, the method allows for the extension of the number of reuses of the biocatalyst by preventing its exposure to extreme denaturating conditions.

Multiple grafting to enzymatically synthesized polyesters

Enzymatic polymerization is an environmentally benign process for the synthesis of biodegradable and biocompatible polymers. The regioselectivity of lipase B from Candida Antarctica (CAL-B) produces linear functional polyesters without protection-deprotection steps. In this work, two different methods for the enzymatic synthesis of functional polyesters based on renewable resources, as, e.g., glycerol, using CAL-B are outlined. Poly(glycerol adipate) was synthesized by enzymatic transesterification between glycerol and divinyl adipate or dimethyl adipate. Methods are also reported to graft poly(glycerol adipate) with different amounts of hydrophobic side chains (lauric, stearic, behenic, and oleic acids) and hydrophilic poly(ethylene glycol) side chains, respectively. The hydrophilicity or lipophilicity of grafted polyesters is well controlled by changing the degree of grafting of hydrophilic and hydrophobic side chains. The multiple grafted polyesters are characterized by NMR spectroscopy, differential scanning calorimetry, gel permeation chromatography, and X-ray diffraction. Furthermore, the self-assembly of the graft copolymers in water and their use as steric stabilizers for cubosomes are discussed. For this purpose mainly dynamic light scattering and small angle X-ray scattering have been employed.

Aliphatic Diacidic Long-Chain C16 Polyesters from 10,16-Dihydroxyhexadecanoic Acid Obtained from Tomato Residual Wastes

10,16-dihydroxyhexadecanoic acid obtained from agroresidual tomato waste, was oxidized to produce 7-oxohexadecanedioic acid in good yield (>70%) and purified without oxidation side products in one step. Polycondensation with 1,8-octanediol, yielded the polyester (poly(ω-carboxyl PA-co-OD)) with M_w = 2155.15 and M_n = 1637.27. The best enzymatic reaction conditions to get the polyester were using lipase CAL-B (%-by-wt relative to monomer) in toluene as a solvent for 1 h at 60 °C. The poly(ω-carboxyl PA-co-OD) was characterized by ¹H- and ¹³C-NMR, mass spectrometry (MALDI-TOF) and the polyester film formed with a Langmuir-Blodgett Trough was analyzed by means of spectroscopic ellipsometry and atomic force microscopy.

The Influence of Non-Uniformities on the Mechanical Behavior of Hemp-Reinforced Composite Materials with a Dammar Matrix

As a result of manufacture, composite materials can appear to have variations to their properties due to the existence of structural changes. In this paper, we studied the influence of material irregularity on the mechanical behavior of two categories of bars for which we have used hemp fabric as a reinforcing material. The common matrix is a hybrid resin based on Dammar and epoxy resin. We molded two types of bars within each of the previously mentioned categories. The first type, also called "ideal bar", was made of layers in which the volume proportion and the orientation of the reinforcing material was the same in each section. The ideal bar does not show variations of mechanical properties along it. The second type of bar was molded to have one or two layers where, between certain sections, the reinforcing material was interrupted in several segments. We have determined some mechanical properties, the characteristic curves (strain-stress), the tensile strength, and elongation at break for all the sample sets on trial. Moreover, we have studied the influence of the non-uniformities on the mechanical behavior of the composites by entering certain quality factors that have been calculated after experimental determinations.

Enantio-, Regio-, and Chemoselective Lipase-Catalyzed Polymer Synthesis

In contrast to chemical routes, enzymatic polymerization possesses favorable characteristics of mild reaction conditions, few by-products, and high activity toward cyclic lactones which make it a promising technique for constructing polymeric materials. Meanwhile, it can avoid the trace residue of metallic catalysts and potential toxicity, and thus exhibits great potential in the biomedical fields. More importantly, lipase-catalyzed polymer synthesis usually shows favorable enantio-, regio-, and chemoselectivity. Here, the history and recent developments in lipase-catalyzed selective polymerization for constructing polymers with unique structures and properties are highlighted. In particular, the synthesis of polymeric materials which are difficult to prepare in a chemical route and the construction of polymers through the combination of selective enzymatic and chemical methods are focused. In addition, the future direction is proposed especially based on the rapid developments in computational chemistry and protein engineering techniques.

Synthesis and Properties of a Novel Environmental Epoxidized Glycidyl Ester of Ricinoleic Acetic Ester Plasticizer for Poly(vinyl chloride)

A novel renewable plasticizer based on castor oil, epoxidized glycidyl ester of ricinoleic acetic ester (EGERAE), was synthesized and applied into Poly(vinyl chloride) (PVC) for the first time. Its molecular structure was characterized by FT-IR and ¹H NMR. The effects of replacement of petroleum-based commercial plasticizer dioctyl phthalate (DOP) with EGERAE in poly(vinyl chloride) (PVC) films were researched. Thermal stability, dynamic mechanical property and mechanical properties of PVC films were investigated with thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and tensile tests. The results indicated that this castor oil-based plasticizer was able to improve the thermal stability of PVC blends when partially of completely substituting for DOP. Furthermore, EGERAE endowed PVC resin with enhanced flexibility. In addition, the exudation, volatility and extraction resistance characteristics of plasticizers were researched. The degradation mechanism and possible interaction between EGERAE and PVC molecules in the plasticized system were also investigated.

His-Tag Immobilization of Cutinase 1 From Thermobifida cellulosilytica for Solvent-Free Synthesis of Polyesters

For many years, lipase B from Candida antarctica (CaLB) was the primary biocatalyst used for enzymatic esterification and polycondensation reactions. More recently, the need for novel biocatalysts with different selectivity has arisen in the biotechnology and biocatalysis fields. The present work describes how the catalytic potential of Thermobifida cellulosilytica cutinase 1 (Thc_Cut1) was exploited for polyester synthesis. In a first step, Thc_Cut1 was immobilized on three different carriers, namely Opal, Coral, and Amber, using a novel non-toxic His-tag method based on chelated Fe(III) ions (>99% protein bounded). In a second step, the biocatalyzed synthesis of an array of aliphatic polyesters was conducted. A selectivity chain study in a solvent-free reaction environment showed how, in contrast to CaLB, Thc_Cut1 presents a certain preference for C₆ -C₄ ester-diol combinations reaching monomer conversions up to 78% and M_w of 878 g mol^-1 when the Amber immobilized Thc_Cut1 was used. The synthetic potential of this cutinase was also tested in organic solvents, showing a marked activity decrease in polar media like that observed for CaLB. Finally, recyclability studies were performed, which showed an excellent stability of the immobilized Thc_Cut1 (retained activity >94%) over 24 h reaction cycles when a solvent-free workup was used. Concerning a practical application of the biocatalyst's preparation, the production of oligomers with M_n values below 10 kDa is usually desired for the production of nanoparticles and for the synthesis of functional pre-polymers for coating applications that can be crosslinked in a second reaction step.

Enzymatic Synthesis of Biobased Polyesters and Polyamides

Nowadays, "green" is a hot topic almost everywhere, from retailers to universities to industries; and achieving a green status has become a universal aim. However, polymers are commonly considered not to be "green", being associated with massive energy consumption and severe pollution problems (for example, the "Plastic Soup") as a public stereotype. To achieve green polymers, three elements should be entailed: (1) green raw materials, catalysts and solvents; (2) eco-friendly synthesis processes; and (3) sustainable polymers with a low carbon footprint, for example, (bio)degradable polymers or polymers which can be recycled or disposed with a gentle environmental impact. By utilizing biobased monomers in enzymatic polymerizations, many advantageous green aspects can be fulfilled. For example, biobased monomers and enzyme catalysts are renewable materials that are derived from biomass feedstocks; enzymatic polymerizations are clean and energy saving processes; and no toxic residuals contaminate the final products. Therefore, synthesis of renewable polymers via enzymatic polymerizations of biobased monomers provides an opportunity for achieving green polymers and a future sustainable polymer industry, which will eventually play an essential role for realizing and maintaining a biobased and sustainable society.

The Closure of the Cycle: Enzymatic Synthesis and Functionalization of Bio-Based Polyesters

The polymer industry is under pressure to mitigate the environmental cost of petrol-based plastics. Biotechnologies contribute to the gradual replacement of petrol-based chemistry and the development of new renewable products, leading to the closure of carbon circle. An array of bio-based building blocks is already available on an industrial scale and is boosting the development of new generations of sustainable and functionally competitive polymers, such as polylactic acid (PLA). Biocatalysts add higher value to bio-based polymers by catalyzing not only their selective modification, but also their synthesis under mild and controlled conditions. The ultimate aim is the introduction of chemical functionalities on the surface of the polymer while retaining its bulk properties, thus enlarging the spectrum of advanced applications.

Enzymes as Green Catalysts for Precision Macromolecular Synthesis

The present article comprehensively reviews the macromolecular synthesis using enzymes as catalysts. Among the six main classes of enzymes, the three classes, oxidoreductases, transferases, and hydrolases, have been employed as catalysts for the in vitro macromolecular synthesis and modification reactions. Appropriate design of reaction including monomer and enzyme catalyst produces macromolecules with precisely controlled structure, similarly as in vivo enzymatic reactions. The reaction controls the product structure with respect to substrate selectivity, chemo-selectivity, regio-selectivity, stereoselectivity, and choro-selectivity. Oxidoreductases catalyze various oxidation polymerizations of aromatic compounds as well as vinyl polymerizations. Transferases are effective catalysts for producing polysaccharide having a variety of structure and polyesters. Hydrolases catalyzing the bond-cleaving of macromolecules in vivo, catalyze the reverse reaction for bond forming in vitro to give various polysaccharides and functionalized polyesters. The enzymatic polymerizations allowed the first in vitro synthesis of natural polysaccharides having complicated structures like cellulose, amylose, xylan, chitin, hyaluronan, and chondroitin. These polymerizations are "green" with several respects; nontoxicity of enzyme, high catalyst efficiency, selective reactions under mild conditions using green solvents and renewable starting materials, and producing minimal byproducts. Thus, the enzymatic polymerization is desirable for the environment and contributes to "green polymer chemistry" for maintaining sustainable society.

Enlarging the tools for efficient enzymatic polycondensation: structural and catalytic features of cutinase 1 from Thermobifida cellulosilytica

Catalytic and structural properties make cutinase 1 from Thermobifida cellulosilytica a more efficient biocatalyst for polycondensations, also of short-chain monomers.

Controlled RAFT synthesis of side-chain oleic acid containing polymers and their post-polymerization functionalization

We report the synthesis and characterization of well-defined polymers from oleic acid as the bio-renewable resource. Double bonds in oleate side-chains in the polymer are further modified by thiol-ene reaction, epoxidation, and cross-linking.

Enzyme-Catalyzed Synthesis of Unsaturated Aliphatic Polyesters Based on Green Monomers from Renewable Resources

Bio-based commercially available succinate, itaconate and 1,4-butanediol are enzymatically co-polymerized in solution via a two-stage method, using Candida antarctica Lipase B (CALB, in immobilized form as Novozyme® 435) as the biocatalyst. The chemical structures of the obtained products, poly(butylene succinate) (PBS) and poly(butylene succinate-co-itaconate) (PBSI), are confirmed by ¹H- and ¹³C-NMR. The effects of the reaction conditions on the CALB-catalyzed synthesis of PBSI are fully investigated, and the optimal polymerization conditions are obtained. With the established method, PBSI with tunable compositions and satisfying reaction yields is produced. The ¹H-NMR results confirm that carbon-carbon double bonds are well preserved in PBSI. The differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) results indicate that the amount of itaconate in the co-polyesters has no obvious effects on the glass-transition temperature and the thermal stability of PBS and PBSI, but has significant effects on the melting temperature.