Immobilized Candida antarctica lipase B (CALB)-catalyzed polycondensation of glycerol and sebacic acid at mild reaction conditions resulted in branched poly(glycerol sebacate) (PGS). To understand how PGS chains grow and branch, the kinetics of the CALB-catalyzed polycondensation were studied. The influence of the reaction temperature, solvent, CALB amount, and sebacic acid/glycerol feed ratio on the poly(glycerol sebacate) (PGS) molecular weight, degree of branching, and glyceridic repetitive unit distribution was also investigated. PGS architecture changes from linear to branched with the progression of the reaction, and the branching results from the simultaneous CALB-catalyzed esterification and acyl migration. For reactions performed in acetone at the temperature range from 30 to 50 °C, the apparent rate constant increases from 0.7 to 1.5 h –1 , and the apparent energy of activation of 32 kJ mol –1 was estimated. The higher mass average molecular weight (16 kDa) and degree of branching (41%) were achieved using the equimolar sebacic acid/glycerol feed ratio in acetone at 40 °C with a CALB amount of 13.6 wt % and in the presence of the molecular sieves.

BACKGROUND Carbohydrates are important renewable raw materials and their modification by enzymatic reactions with polymerizable groups is of great importance due the possibility of production of polymers with properties for biomedical applications. In this study, D‐fructose‐ and D‐glucose‐based monomers were prepared by enzymatic reactions and structurally characterized. Moreover, hydrogels based on poly(methacryloyl‐D‐fructose) were also prepared and characterized. RESULTS The conversions of 99% and 34% for D‐fructose and D‐glucose, respectively, were achieved using 2,2,2‐trifluoroethyl methacrylate as the methacrylic donor and commercial lipase Novozyme® 435 (EC 3.1.1.3) as enzymatic catalyst in t‐butanol. The molar ratios of D‐fructose and D‐glucose mono‐ and dimethacrylate were 57/43 and 87/13, respectively. These monomers are an isomeric mixture related to the tautomeric equilibrium of the carbohydrates in solution. Methacryloyl‐D‐fructose was polymerized in the presence of a controlled amount of ethyleneglycol dimethacrylate as crosslinker achieving hydrogels with different crosslinking densities which are mechanically stable when subject to compression–decompression cycles and have a high water swelling capability. CONCLUSION The combination of 2,2,2‐trifluoroethylmethacrylate and Novozym® 435 in a heterogeneous media lead to the continuous carbohydrate solubilization and reaction with the formation of carbohydrates‐based monomers. The control of the monomer functionality enables the synthesis of hydrogels with different crosslinking densities that tune their properties. © 2017 Society of Chemical Industry

In the last few decades, many efforts have been made to make poly­(3-hydroxybutyrate) (PHB) and its copolymers more suitable for industrial production and large-scale use. Plasticization, especially using biodegradable oligomeric plasticizers, has been one of the strategies for this purpose. However, PHB and its copolymers generally present low miscibility with plasticizers. An understanding of the plasticizer distribution between the mobile and rigid amorphous phases and how this influences thermal, mechanical, and morphological properties remains a challenge. Herein, formulations of poly­(hydroxybutyrate-co-valerate) (PHBV) plasticized with an oligomeric polyester based on lactic acid, adipic acid, and 1,2-propanediol (PLAP) were prepared by melt extrusion. The effects of the PLAP content on the processability, miscibility, and microstructure of the semicrystalline PHBV and on the thermal, morphological, and mechanical properties of the formulations were investigated. The compositions of the mobile and rigid amorphous phases of the PHBV/PLAP formulations were easily estimated by combining dynamic mechanical data and the Fox equation, which showed a heterogeneous distribution of PLAP in these two phases. An increase in the PLAP mass fraction in the formulations led to progressive changes in the composition of the amorphous phases, an increase of both crystalline lamellae and interlamellar layer thickness, and a decrease in the melting and glass transition temperatures as well as the PHBV stiffness. The Flory–Huggins interaction parameter varied with the formulation composition in the range of −0.299 to −0.081. The critical PLAP mass fraction of 0.37 obtained from thermodynamic data is close to the value estimated from dynamic mechanical analysis (DMA) data and the Fox equation. The mechanical properties showed a close relationship with the distribution of PLAP in the rigid and mobile amorphous phases as well as with the microstructure of the crystalline phase of PHBV in the formulations.

The mechanism for theCandida antacticalipase B (CALB)-catalyzed polycondensation of glycerol and sebacic acid in polar solvents was proposed based on the profile of formation and consumption of the glyceridic species in the reaction media and on the occurrence of the acyl migration reaction. The acyl migration is mainly responsible for the esterification of the secondary hydroxyl of glycerol and in an opposite way to the regioselective CALB-catalyzed esterification of primary hydroxyls. The enzymatic esterification of glycerol primary hydroxyls occurs preferentially up to carboxylic acid conversions of approximately 0.60–0.75 with rate constants in the range of 0.07–1.44 L mol–1 h–1, depending on the solvent. Above carboxylic acid conversions of 0.60–0.75, acyl migration occurs in parallel to enzymatic esterification with rate constants of approximately 0.04–0.12 h–1 and is the rate-limiting step of the polymerization. The hydrogen bonding accepting ability of the solvents is the main parameter that dictates the enzymatic catalysis rate. However, the magnitude of the polymer–solvent interaction governs the polymer chain growth. Acetonitrile has a lower hydrogen bonding accepting ability and a less favorable polymer–solvent interaction compared with the other polymer–solvent pairs, and polycondensation achieves the highest enzymatic rate constant of approximately 0.84–1.44 L mol–1 h–1; however, low molar mass polymers with M n = 1.4 kDa were formed. On the other hand, acetone has intermediate hydrogen bonding accepting ability and optimal intermediate polymer–solvent interactions and, therefore, an intermediate enzymatic rate constant of approximately 0.41–0.52 L mol–1 h–1, and the highest molar mass polymers with M n = 4.9–9.4 kDa were obtained.

BACKGROUND Readily available feedstock and biocompatibility make carbohydrate‐based hydrogels promising materials for biomedical applications. However, carbohydrate‐based crosslinkers are rather underexplored when compared with crosslinkers derived from fossil resources. In this study, novel fully bio‐based hydrogels derived from enzymatically produced d‐fructose and d‐glucose methacrylate monomers were synthesized with different amounts of d‐fructose dimethacrylate crosslinker. RESULTS The use of a carbohydrate‐based crosslinker endows hydrogels with high swelling coefficients, up to 2400%, and superior mechanical resistance (compressive modulus up to 9.5 kPa with a maximum stress up to 50 kPa) compared with conventional crosslinkers based on fossil resources. Hydrogels shape and crosslinking density influences hydrogel morphology, swelling behavior and mechanical resistance. Moreover, hydrogels presented cell viability, biodegradability and hydrolysis‐resistance over a wide range of pH. CONCLUSION The use of a highly hydrophilic crosslinker based on carbohydrate for hydrogels synthesis enables the use of high crosslinker concentration, which improves mechanical properties, however with minor loss of the water swelling capacity, compared with conventional fossil‐based crosslinkers. This is an important advantage over conventional crosslinkers based on fossil resources. Moreover, slab hydrogels hold higher stress under compression–decompression cycles, and present higher resistance to hydrolysis in basic medium due to the thicker pore walls than cylindrical ones. © 2019 Society of Chemical Industry

Mobile networks are becoming energy hungry, and this trend is expected to continue due to a surge in communication and computation demand. Multi-access Edge Computing (MEC), a key component of 5𝐺 and 6𝐺 networks, will entail energy-consuming services and applications, with non-negligible impact in terms of ecological sustainability. In this paper, we provide a comprehensive review of existing approaches to make edge computing networks greener, including but not limited to the exploitation of renewable energy resources, and context-awareness (e.g., user mobility, or dynamics in the traffic), analyzing their pros and cons. We hence provide an updated account of recent developments on MEC from an energetic sustainability perspective, addressing the initial deployment of computing resources, their dynamic (re)allocation (resource scheduling), as well as distributed and federated learning designs. In doing so, we highlight the energy aspects of these algorithms, advocating the need for energy-sustainable edge computing systems that are aligned with Sustainable Development Goals (SDGs) and the Paris agreement. To the best of our knowledge, this is the first work providing a systematic literature review on the efficient deployment and management of energy harvesting MEC, with special focus on the deployment, provisioning, and scheduling of computing tasks, including federated learning for distributed edge intelligence, toward making edge networks greener and more sustainable. At the end of the paper, open research avenues and challenges are identified for all the surveyed topics. CCS Concepts: • Networks → Network performance evaluation; Wireless access points, base stations and infrastructure; • Computer systems organization → Embedded systems; • Computing methodologies → Planning and scheduling.

In this work, PHBV composites were prepared by melting extrusion using triethyl citrate (TEC) as a biodegradable plasticizer and sugarcane bagasse fibers (SBF) as reinforcement. The plasticizer TEC played a crucial role in the preparation of the formulations by extrusion, reducing the viscosity of the melt and minimizing the thermomechanical degradation of PHBV. Moreover, TEC was an efficient plasticizer for the composites, reducing the glass transition and melting temperatures of PHBV and making the specimens ductile. The increase in the concentration of TEC led to an enlargement of the interlamellar spacing and larger PHBV spherulites without changing the cell parameters. In contrast, the introduction of the SBF elevated the viscosity of the molten during extrusion, leading to thermomechanical degradation of PHBV. The SBF acted as a nucleation agent for the PHBV crystallization and oriented the growth of the PHBV crystals due to the transcrystallization, which contributed to the matrix-filler adhesion, the increase in the lamellae thickness, and changes in the thermal properties of PHBV. The SBF acted as a reinforcing agent, increasing the tensile properties of the matrix. Therefore, TEC and SBF had antagonistic effects on the properties of the formulations, opening opportunities to tune their properties by varying the composition.

The energy sustainability of multi-access edge computing (MEC) platforms is addressed in this paper, by developing Energy-Aware job Scheduling at the Edge (EASE), a computing resource scheduler for edge servers co-powered by renewable energy resources and the power grid. The scenario under study involves the optimal allocation and migration of time-sensitive computing tasks in a resource-constrained internet of vehicles (IoV) context. This is achieved by tackling, as a main objective, the minimization of the carbon footprint of the edge network, whilst delivering adequate quality of service (QoS) to the end users (e.g., meeting task execution deadlines). EASE integrates a i) centralized optimization step, solved through model predictive control (MPC), to manage the renewable energy that is locally collected at the edge servers and their local computing resources, estimating their future availability, and ii) a distributed consensus step, solved via dual ascent in closed form, to reach agreement on service migrations. EASE is compared with existing strategies that always and never migrate the computing tasks. Quantitative results demonstrate the greater energy efficiency achieved by EASE, which often gets close to complete carbon neutrality, while also improving the QoS.