Caratterizzazione delle proprietà morfologiche e di trasporto delle membrane polimeriche a base di PHA

Tale lavoro di tesi ha permesso di individuare nuovi solventi per la produzione di membrane polimeriche a base di PHA. La caratterizzazione morfologica, chimica e fisica ha reso evidente come i polimeri possano essere influenzati sia dall’azione del solvente che dalle condizioni di produzione delle membrane tramite il processo di solvent-casting. Tale influenza è visibile anche nelle proprietà di trasporto di membrane realizzate a partire da solventi diversi. Tale lavoro di tesi non è sufficiente per dimostrare l’efficienza di membrane polimeriche a base di PHA in un’applicazione propria dell’industria di processo, quale la separazione dei gas. Tuttavia questo lavoro potrebbe costituire un spinta ulteriore verso la sensibilizzazione del mondo industriale all’utilizzo dei biopolimeri, considerando come tali sia i polimeri biodegradabili sia i polimeri provenienti da fonti rinnovabili

Development and modelling of sustainable polymer–based membranes for gas separation and packaging

Membrane–based separation of gaseous mixtures is a technology that facilitates environmentally friendly and efficient control of gaseous compositions in industrial applications, from natural gas processing to the product’s shelf–life extension. Polymer–based membranes offer several advantages, such as low energy consumption, manufacturing scalability, and reduced carbon footprint. To fully enhance the overall sustainability of chemical processes, materials currently used in membrane separation should to be replaced with sustainable alternatives, such as biobased and biodegradable materials. This is a non–negotiable option to tackle the end–of–life issues and reduce carbon emissions of membrane–based separations. With a broader outlook, the membrane manufacturing sector requires a substantial shift towards a sustainable–by–design approach applied to the whole production chain, including the solvents used in the fabrication process and additives used to enhance the membrane performance. Despite the attractiveness of biomaterials, several issues might delay their commercialisation and integration into relevant industrial applications, like the difficulty to find an optimal biopolymer formulation for a specific application. Experimental assessment of transport properties is an essential step when the industrial application of a new class of biopolymers is considered for the first time. On the other hand, a systematic experimental study is generally expensive and time–consuming, as there are many possible candidates. Computational approaches offer a cost–effective means to complement the initial experimental investigation, capable to inform future design choices and reduce the time–to–market of biopolymers. Once the relationship between the polymeric structure and its properties is established within a specific class, its performance can be further tailored for a specific application by combining polymeric matrix with materials that can modify the desired properties. Overall, the present Dissertation aims to accelerate the integration of sustainable materials into different industrial membrane–based applications

An Analysis of the Effect of ZIF-8 Addition on the Separation Properties of Polysulfone at Various Temperatures

The transport of H2, He, CO2, O2, CH4, and N2 at three temperatures up to 65 ◦C was measured in dense, thick composite films formed by amorphous Polysulfone (PSf) and particles of the size-selective zeolitic imidazolate framework 8 (ZIF-8) at loadings up to 16 wt%. The morphological and structural properties of the membranes were analyzed via SEM and density measurement. The addition of ZIF-8 to PSf enhances the H2 and He permeabilities up to 480% with respect to the pure polymer, while the ideal H2/CO2 and He/CO2 selectivities of MMMs reach values up to 30–40% higher than those of pure PSf. The relative permeability and diffusivity enhancements are higher than those obtained in other polymers, such as PPO, with the same amount of filler. The Maxwell–Wagner–Sillars model is able to represent the MMM H2/CO2 separation performance for filler volume fractions below 10%

Evaluating sustainable materials for membrane separations through molecular simulations: the case of Polyxydroxyalkanoates (PHA)

Membrane technology is a valid alternative to traditional gas separation processes and a promising solution for Carbon Capture. Even though membrane materials are usually polymer-based, end-of-life treatment planning seldom enters process design considerations. Using degradable biopolymers could increase the sustainability of membrane technology, which is conquering market shares owing to its positive environmental impact. Gas transport properties of different polymers of PHA family were obtained from molecular simulation, with results validated on experimental data. The ultimate purpose of this project is to promote a circular economy mindset through the analysis of potential applicability of bio-based polymers in typical industrial applications

Modelling across Multiple Scales to Design Biopolymer Membranes for Sustainable Gas Separations: 1—Atomistic Approach

In this work, we assessed the CO2 and CH4 sorption and transport in copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate (PHBV), which showed good CO2 capture potential in our previous papers, thanks to their good solubility–selectivity, and are potential biodegradable alternatives to standard membrane-separation materials. Experimental tests were carried out on a commercial material containing 8% of 3-hydroxyvalerate (HV), while molecular modelling was used to screen the performance of the copolymers across the entire composition range by simulating structures with 0%, 8%, 60%, and 100% HV, with the aim to provide a guide for the selection of the membrane material. The polymers were simulated using molecular dynamics (MD) models and validated against experimental density, solubility parameters, and X-ray diffraction. The CO2/CH4 solubility–selectivity predicted by the Widom insertion method is in good agreement with experimental data, while the diffusivity–selectivity obtained via mean square displacement is somewhat overestimated. Overall, simulations indicate promising behaviour for the homopolymer containing 100% of HV. In part 2 of this series of papers, we will investigate the same biomaterials using a macroscopic model for polymers and compare the accuracy and performance of the two approaches

Evaluating sustainable materials for membrane separations through molecular simulations: the case of Polyxydroxyalkanoates (PHA)

Polyxydroxyalkanoates (PHA) are a family of linear optically active semi-crystalline polyesters produced by bacterial fermentation, known for their overall sustainability, including biodegradability and biocompatibility. PHA are also characterized by thermoplasticity and good mechanical properties, comparable to those of commercially relevant standard polymers. The gas transport properties of these materials are still scarcely characterized experimentally, and their determination is complicated by a number of uncertainty sources, such as a time-dependent degree of crystallinity. In this study we aim at evaluating the physicochemical and transport properties of such materials with molecular simulations, to gain information about their applicability in the membrane gas separation field. In order to draw correlation between the molecular structure and the performance of these materials, three homopolymers and two copolymers of the PHA family were considered: \u2022 poly(3-hydroxybutyrate) (P3HB); \u2022 poly(3-hydroxyvalerate) (P3HV); \u2022 poly(4-hydroxybutyrate) (P4HB); \u2022 poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV); \u2022 poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (PHBB). Molecular models of each material were simulated using Molecular Dynamics (MD), obtaining amorphous density and solubility parameter values, that were successfully validated with experimental data found in literature2,3. The simulated values of radius of gyration, accessible free volume, density, cohesive energy and elastic modulus in the different copolymers were correlated to their chemical composition. Sorption and diffusion in the polymers were then analysed for three gases, O2, CH4 and CO2, by means of Grand Canonical Monte Carlo (GCMC) and MD simulations. The results were compared with experimental values, obtained through permeation tests at different temperatures, performed on PHBV with 8% of 3-hydroxyvalerate monomers purchased from Merck-Sigma

Characterization of a copolymer belonging to the PHA family: the case of poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxyvalerate)

Polyxydroxyalkanoates (PHA) are a family of linear optically active polyesters produced by bacterial fermentation and known for their overall sustainability, including biodegradability and biocompatibility. Because of their thermoplasticity and good mechanical properties, somehow similar to those of commercially relevant standard polymers, a study aimed at correlating their molecular structure to their behavior in terms of transport properties was initiated. The case study is a random copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxyvalerate) (PHBVV), gently supplied by Bio-on S.p.A. (Italy). This PHA copolymer contains 24%mol of 3-hydroxyvalerate (3-HV) units and <1%mol of 4-hydroxyvalerate (4-HV) units. Compared to pure homopolymer poly(3-hydroxybutyrate) (PHB), the simplest and most diffused polymer of the PHA family, PHBVV is more flexible, transparent and less crystalline. The thermal properties of PHBVV were investigated by differential scanning calorimetry (DSC), it’s structure and physical properties were investigated by Fourier Transform Infrared Spectroscopy (FT-IR) and by Gel Permeation Chromatografy (GPC). Ultimately it’s transport properties were analysed through permeability and absorption tests. At last, the capability of PHBVV to form very thin films through spin coating was examined. The main conclusion, which can be made analysing experimental data, regards the fact that the presence of HV monomeric units affects drastically both structural and thermal properties of the material. In particular, it destabilises the crystalline structure which is typical of PHB, causing the on-set of melting at low temperatures and the presence of multiple peaks in the DSC curve. From the point of view of transport properties, PHBVV presents a mixed behaviour. It is characterized by the solubility-driven selectivity and reduced size-sieving ability although a direct dependence of permeability from the kinetic diameter of penetrants is observable. The ultimate purpose of this project is to promote industrial sustainability through the analysis of potential applicability of bio-based polymers in typical industrial applications

Fully Biobased Polyhydroxyalkanoate/Tannin Films as Multifunctional Materials for Smart Food Packaging Applications

Fully biobased and biodegradable materials have attracteda growinginterest in the food packaging sector as they can help to reduce thenegative impact of fossil-based plastics on the environment. Moreover,the addition of functionalities to these materials by introducingactive molecules has become an essential requirement to create modernpackaging able to extend food's shelf-life while informingthe consumer about food quality and freshness. In this study, we presentan innovative bioplastic formulation for food packaging based on poly-(hydroxybutyrate-co-valerate) (PHBV) and tannins as multifunctional additives.As a proof of concept, PHBV/tannin films were prepared by solventcasting, increasing the tannin content from 1 to 10 per hundred ofresin (phr). Formic acid was used to reach a homogeneous distributionof the hydrophilic tannins into hydrophobic PHBV, which is remarkablychallenging by using other solvents. Thanks to their well-known properties,the effect of tannins on the antioxidant, UV protection, and gas barrierproperties of PHBV was evaluated. Samples containing 5 phr bioadditiverevealed the best combination of these properties, also maintaininggood transparency. Differential scanning calorimetry (DSC) investigationsrevealed that films are suitable for application from the fridge topotentially high temperatures for food heating (up to 200 degrees C).Tensile tests have also shown that Young's modulus (900-1030MPa) and tensile strength (20 MPa) are comparable with those of thecommon polymers and biopolymers for packaging. Besides the improvementof the PHBV properties for extending food's shelf-life, itwas also observed that PHBV/tannin could colorimetrically detect ammoniavapors, thus making this material potentially applicable as a smartindicator for food spoilage (e.g., detection of fish degradation).The presented outcomes suggest that tannins can add multifunctionalproperties to a polymeric material, opening up a new strategy to obtainan attractive alternative to petroleum-based plastics for smart foodpackaging applications

Mixed Matrix Membranes Based on Torlon® and ZIF-8 for High-Temperature, Size-Selective Gas Separations

Torlon® is a thermally and plasticization-resistant polyamide imide characterized by low gas permeability at room temperature. In this work, we aimed at improving the polymer performance in the thermally-enhanced He/CO2 and H2/CO2 separations, by compounding Torlon® with a highly permeable filler, ZIF-8, to fabricate Mixed Matrix Membranes (MMMs). The effect of filler loading, gas size, and temperature on the MMMs permeability, diffusivity, and selectivity was investigated. The He permeability increased by a factor of 3, while the He/CO2 selectivity decreased by a factor of 2, when adding 25 wt % of ZIF-8 at 65 °C to Torlon®; similar trends were observed for the case of H2. The MMMs permeability and size-selectivity were both enhanced by temperature. The behavior of MMMs is intermediate between the pure polymer and pure filler ones, and can be described with models for composites, indicating that such materials have a good polymer/filler adhesion and their performance could be tailored by acting on the formulation. The behavior observed is in line with previous investigations on MMMs based on glassy polymers and ZIF-8, in similar conditions, and indicates that ZIF-8 can be used as a polymer additive when the permeability is a controlling aspect, with a proper choice of loading and operative temperature