New sustainable routes for gas separation membranes: The properties of poly(hydroxybutyrate-co-hydroxyvalerate) cast from green solvents

The gas separation performance of biopolymers is still scarcely characterized, mostly because of their poor thermomechanical properties and high crystallinity which is associated to low permeability. In this work we characterize the gas transport in a poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) random copolymer, that has a relatively low crystallinity and good mechanical properties, combined with a renewable origin, biodegradability and biocompatibility. In the study we also compared several solvents for membrane casting, with different toxicity levels. We found that dimethyl carbonate allows the production of polymer films with transport properties similar to those obtained with the more toxic CHCl3, and it leads also to stable crystallinity of the samples over time. PHBV films show a size-sieving gas separation behaviour, as the permeability decreases significantly with the gas kinetic diameter. However, the strong energetic interactions of CO2 with the polymer matrix, confirmed by the Flory-Huggins model, induce a marked solubility-driven CO2/N2 and CO2/CH4 selectivity, which could make the material potentially interesting for CO2 removal processes

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

One year of surgical mask testing at the University of Bologna labs:Lessons learned from data analysis

The outbreak of SARS-CoV-2 pandemic highlighted the worldwide lack of surgical masks and personal protective equipment, which represent the main defense available against respiratory diseases as COVID-19. At the time, masks shortage was dramatic in Italy, the first European country seriously hit by the pandemic: aiming to address the emergency and to support the Italian industrial reconversion to the production of surgical masks, a multidisciplinary team of the University of Bologna organized a laboratory to test surgical masks according to European regulations. The group, driven by the expertise of chemical engineers, microbiologists, and occupational physicians, set-up the test lines to perform all the functional tests required. The laboratory started its activity on late March 2020, and as of the end of December of the same year 435 surgical mask prototypes were tested, with only 42 masks compliant to the European standard. From the analysis of the materials used, as well as of the production methods, it was found that a compliant surgical mask is most likely composed of three layers, a central meltblown filtration layer and two external spunbond comfort layers. An increase in the material thickness (grammage), or in the number of layers, does not improve the filtration efficiency, but leads to poor breathability, indicating that filtration depends not only on pure size exclusion, but other mechanisms are taking place (driven by electrostatic charge). The study critically reviewed the European standard procedures, identifying the weak aspects; among the others, the control of aerosol droplet size during the bacterial filtration test results to be crucial, since it can change the classification of a mask when its performance lies near to the limiting values of 95 or 98%

ФОТОЭЛЕКТРИЧЕСКИЕ ПРЕОБРАЗОВАТЕЛИ В СИСТЕМЕ СО СПЕКТРАЛЬНЫМ РАСЩЕПЛЕНИЕМСОЛНЕЧНОЙ ЭНЕРГИИ

This paper presents results on the simulation of photo converters in a spectral splitting system where solar radiation is separated into three spectral ranges (∆λ1<500 nm, ∆λ2 = 500−725 nm and ∆λ3>725 nm) by means of dichroic filters and then converted to electrical energy by photoconverters based on InGaN/GaN, GaAs/AlGaAs single−junction heterostructures and monocrystalline silicon c−Si. Special attention is paid to the absorption spectrum spreading due to more efficient conversion of the ultraviolet part of the spectrum. The total efficiency of the system varies from 21% to 37% depending on the design of heterostructures.Представлены результаты моделирования фотоэлектрических преобразователей в системе со спектральным расщеплением солнечной энергии, в которой солнечное излучение разделяется с помощью дихроичных фильтров на три спектральных диапазона (∆λ1 < 500 нм, ∆λ2 = 500÷725 нм, ∆λ3 > 725 нм) и затем преобразуется в электроэнергию фотоэлектрическими преобразователями на основе однопереходных гетероструктур InGaN/GaN, GaAs/AlGaAs и монокристаллического кремния c−Si. Особое внимание уделено исследованию расширения спектрального диапазона поглощения системы за счет более эффективного преобразования ультрафиолетовой части спектра. Суммарный КПД системы на всем спектре варьируется от 21 до 37 % в зависимости от дизайна гетероструктур однопереходных фотоэлектрических пре-образователей и вариантов оптических систем

Структурные, электрические и люминесцентные характеристики ультрафиолетовых светодиодов, выращенных методом хлорид–гидридной эпитаксии

Electrical and luminescent properties of near−UV light emitting diode structures (LEDs) prepared by hydride vapor phase epitaxy (HVPE) were studied. Variations in photoluminescence and electroluminescence efficiency observed for LEDs grown under nominally similar conditions could be attributed to the difference in the structural quality (dislocation density, density of dislocations agglomerates) of the GaN active layers, to the difference in strain relaxation achieved by growth of AlGaN/AlGaN superlattice and to the presence of current leakage channels in current confining AlGaN layers of the double heterostructure.Изучены электрические и люминесцентные характеристики светодиодных структур (СД), излучающих в ближней ультрафиолетовой (УФ) области и выращенных методом хлорид−гидридной эпитаксии. Обнаружены различия в характеристиках УФ СД, выращенных в номинально одинаковых условиях, которые приписывают различиям в структурном совершенстве (плотности дислокаций и дислокационных агломератов) в активных слоях GaN, разнице в степени релаксации напряжений, достигаемой с помощью сверхрешеток AlGaN/AlGaN, а также существованию каналов токовых утечек в слоях AlGaN, ограничивающих заряд в двойной гетероструктуре.

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%

One year of surgical mask testing at the University of Bologna labs: Lessons learned from data analysis

The outbreak of SARS-CoV-2 pandemic highlighted the worldwide lack of surgical masks and personal protective equipment, which represent the main defense available against respiratory diseases as COVID-19. At the time, masks shortage was dramatic in Italy, the first European country seriously hit by the pandemic: aiming to address the emergency and to support the Italian industrial reconversion to the production of surgical masks, a multidisciplinary team of the University of Bologna organized a laboratory to test surgical masks according to European regulations. The group, driven by the expertise of chemical engineers, microbiologists, and occupational physicians, set-up the test lines to perform all the functional tests required. The laboratory started its activity on late March 2020, and as of the end of December of the same year 435 surgical mask prototypes were tested, with only 42 masks compliant to the European standard. From the analysis of the materials used, as well as of the production methods, it was found that a compliant surgical mask is most likely composed of three layers, a central meltblown filtration layer and two external spunbond comfort layers. An increase in the material thickness (grammage), or in the number of layers, does not improve the filtration efficiency, but leads to poor breathability, indicating that filtration depends not only on pure size exclusion, but other mechanisms are taking place (driven by electrostatic charge). The study critically reviewed the European standard procedures, identifying the weak aspects; among the others, the control of aerosol droplet size during the bacterial filtration test results to be crucial, since it can change the classification of a mask when its performance lies near to the limiting values of 95 or 98%