Gas separation properties of poly(ethylene glycol)/poly(tetramethylene glycol) based polyurethane membranes

Development of activated carbons derived from wastes: coffee grounds and olive stones as potential porous materials for air depollution

Agro-industrial byproducts and food waste necessitate an environmentally friendly way of reducing issues related to their disposal; it is also necessary to recover as much new raw material from these resources as possible, especially when we consider their potential usage as a precursor for preparing depolluting materials, such as activated carbon. In this work, coffee grounds and olive stones were chosen as precursors and the adsorption capacity of the obtained porous carbons for volatile organic compounds (VOCs) was studied. Microporous activated carbons (ACs) were prepared using chemical (K2CO3) and physical (CO2) activation. The influence of the activation process, type, and time of activation was also investigated. Measurements of VOCs adsorption were performed, and methyl-ethyl-ketone (MEK) and toluene were chosen as the model pollutants. The surface areas and total pore volumes of 1487 m2/g and 0.53 cm3/g and 870 m2/g and 0.22 cm3/g for coffee ground carbons and olive stone carbons, respectively, were obtained via chemical activation, whereas physical activation yielded values of 716 m2/g and 0.184 cm3/g and 778 cm2 g-1 and 0.205 cm3/g, respectively. As expected, carbons without activation (biochars) showed the smallest surface area, equal to 331 m2/g and 251 m2/g, and, hence, the lowest adsorption capacity. The highest adsorption capacity of MEK (3210 mg/g) and toluene (2618 mg/g) was recorded for chemically activated coffee grounds. Additionally, from the CO2 isotherms recorded at a low pressure (0.03 bar) and 0 °C, the maximum CO2 adsorption capacity was equal to 253 mg/g.

Rational Design, Synthesis, and Structure-Property Relationship Studies of a Library of Thermoplastic Polyurethane Films as an Effective and Scalable Encapsulation Material for Perovskite Solar Cells

Hybrid organic-inorganic metal halide perovskite solar cell (PSC) technology is experiencing rapid growth due to its simple solution chemistry, high power conversion efficiency (PCE), and potential for low-cost mass production. Nevertheless, the primary obstacle preventing the upscaling and widespread outdoor deployment of PSC technology is the poor long-term device stability, which stems from the inherent instability of perovskite materials in the presence of oxygen and moisture. To address this issue, in this work, we have synthesized a series of thermoplastic polyurethanes (TPUs) through a rational design by utilizing polyols having different molecular weights and diverse isocyanates (aromatic and aliphatic). Thorough characterization of these TPUs (ASTM and ISO standards) along with structure-property relationship studies were carried out for the first time and were then used as the encapsulation material for PSCs. The prepared TPUs were robust and adhered well with the glass substrate, and the use of low temperature during the encapsulation process avoided the degradation of the perovskite absorber and other organic layers in the device stack. The encapsulated devices retained more than 93% of their initial power conversion efficiency (PCE) for over 1000 h after exposure to harsh environmental conditions such as high relative humidity (80 ± 5% RH). Furthermore, the encapsulated perovskite absorbers showed remarkable stability when they were soaked in water. This article demonstrates the potential of TPU as a suitable and easily scalable encapsulant for PSCs and pave the way for extending the lifetime and commercialization of PSCs.

High-Loading Poly(ethylene glycol)-Blended Poly(acrylic acid) Membranes for CO2 Separation

Poly(ethylene glycol) (PEG) is an amorphous material of interest owing to its high CO₂ affinity and potential usage in CO₂ separation applications. However, amorphous PEG often has a low molecular weight, making it challenging to form into the membrane. The crystalline high average molar mass poly(ethylene oxide) (PEO) cannot exhibit CO₂ separation characteristics. Thus, it is crucial to employ low molecular weight PEG in high molecular weight polymers to increase the CO₂ affinity for CO₂ separation membranes. In this work, poly(acrylic acid) (PAA)/PEG blend membranes with a PEG-rich phase were simply fabricated by physical mixing with an ethanol solvent. The carbonyl group of the PAA and the hydroxyl group of the PEG formed a hydrogen bond. Furthermore, the thermal stability, glass transition temperature, and surface hydrophilicity of PAA/PEG blend membranes with various PEG concentrations were further characterized. The PAA/PEG(1:9) blend membrane exhibited an improved CO₂ permeability of 51 Barrer with high selectivities relative to the other gas species (H₂, N₂, and CH₄; CO₂/H₂ = 6, CO₂/N₂ = 63, CO₂/CH₄ = 21) at 35 °C and 150 psi owing to the enhanced CO₂ affinity with the amorphous PEG-rich phase. These PAA/PEG blend membrane permeation characteristics indicate a promising prospect for CO₂ capture applications.

Organosilica-Modified Multiblock Copolymers for Membrane Gas Separation

Organosubstituted silica derivatives were synthesized and investigated as modifiers of block copolymers based on macroinitiator and 2,4-toluene diisocyanate. A peculiarity of the modified block copolymers is the existence in their structure of coplanar rigid polyisocyanate blocks of acetal nature (O-polyisocyanates). Organosubstituted silica derivatives have a non-additive effect on high-temperature relaxation and α-transitions of modified polymers and exhibit the ability to influence the supramolecular structure of block copolymers. The use of the developed modifiers leads to a change in the gas transport properties of block copolymers. The increase of the permeability coefficients is due to the increase of the diffusion coefficients. At the same time, the gas solubility coefficients do not change. An increase in the ideal selectivity for a number of gas pairs is observed. An increase in the selectivity for the CO2/N2 gas pair (from 25 to 39) by 1.5 times demonstrates the promising use of this material for flue gases separation.

The structure of CO2 and CH4 at the interface of a poly(urethane urea) oligomer model from the microscopic point of view

The world desperately needs new technologies and solutions for gas capture and separation. To make this possible, molecular modeling is applied here to investigate the structural, thermodynamic, and dynamical properties of a model for the poly(urethane urea) (PUU) oligomer model to selectively capture CO₂ in the presence of CH₄. In this work, we applied a well-known approach to derive atomic partial charges for atoms in a polymer chain based on self-consistent sampling using quantum chemistry and stochastic dynamics. The interactions of the gases with the PUU model were studied in a pure gas based system as well as in a gas mixture. A detailed structure characterization revealed high interaction of CO₂ molecules with the hard segments of the PUU. Therefore, the structural and energy properties explain the reasons for the greater CO₂ sorption than CH₄. We find that the CO₂ sorption is higher than the CH₄ with a selectivity of 7.5 at 298 K for the gas mixture. We characterized the Gibbs dividing surface for each system, and the CO₂ is confined for a long time at the gas-oligomer model interface. The simulated oligomer model showed performance above the 2008 Robeson's upper bound and may be a potential material for CO₂/CH₄ separation. Further computational and experimental studies are needed to evaluate the material.

Amphiphilic Poly(dimethylsiloxane-ethylene-propylene oxide)-polyisocyanurate Cross-Linked Block Copolymers in a Membrane Gas Separation

Amphiphilic poly(dimethylsiloxane-ethylene-propylene oxide)-polyisocyanurate cross-linked block copolymers based on triblock copolymers of propylene and ethylene oxides with terminal potassium-alcoholate groups (PPEG), octamethylcyclotetrasiloxane (D4) and 2,4-toluene diisocyanate (TDI) were synthesized and investigated. In the first stage of the polymerization process, a multiblock copolymer (MBC) was previously synthesized by polyaddition of D4 to PPEG. The usage of the amphiphilic branched silica derivatives associated with oligomeric medium (ASiP) leads to the structuring of block copolymers via the transetherification reaction of the terminal silanol groups of MBC with ASiP. The molar ratio of PPEG, D4, and TDI, where the polymer chains are packed in the "core-shell" supramolecular structure with microphase separation of the polyoxyethylene, polyoxypropylene and polydimethylsiloxane segments as the shell, was established. Polyisocyanurates build the "core" of the described macromolecular structure. The obtained polymers were studied as membrane materials for the separation of gas mixtures CO2/CH4 and CO2/N2. It was found that obtained polymers are promising as highly selective and productive membrane materials for the separation of gas mixtures containing CO2, CH4 and N2.

Heterogeneous ion exchange membranes based on thermoplastic polyurethane (TPU): effect of PSS/DVB resin on morphology and electrodialysis

In this research, novel heterogeneous cation exchange membranes based on thermoplastic polyurethane (TPU) have been prepared by the solution casting technique. The effects of incorporation level of sulfonated polystyrene divinyl-benzene (PSS/DVB) resin on water uptake, ion exchange capacity, membrane potential and salt extraction have been elucidated. Morphological and water uptake studies suggested a two-phase heterogeneous membrane morphology owing to the presence of hard and soft segments in the TPU backbone and swelling of PSS/DVB particles. This morphology was shifted to a semi-gelled morphology throughout the membrane bulk when resin loading exceeded 50 wt%. The physically cross-linked hard segments in the TPU backbone ensured a compact membrane morphology and prevented the formation of water channels. The membrane potential showed that increasing the resin content increased the membrane transport number (max. 0.95) up to 50 wt% resin loading and beyond this, the transport number started decreasing showing a pronounced effect of voids and water flow channels developing on excessive swelling. The permselectivity reached a maximum (up to 0.92) and salt extraction values also increased (by varying voltage) up to 50 wt% loading and started decreasing beyond this optimum content. This study shows successful development of low-cost heterogeneous cation exchange membranes based on TPU with acceptable electrochemical properties.

Ionic liquid tethered PEG-based polyurethane-siloxane membranes for efficient CO2/CH4 separation

This study introduces a new polyethylene glycol (PEG) based polyurethane-siloxane membrane containing a quaternary ammonium ionic liquid for CO₂/CH₄ separation. The designed ionic liquid was prepared in two steps: (i) (3-chloropropyl)triethoxysilane (CPS) and N,N-dimethylpropyl amine (NDPA) were reacted with each other to form the methoxysilane-functionalized quaternary ammonium component, then (ii) chloride ion (Cl^-) of the product was exchanged with tetrafluoroborate ion (BF₄^-). The resulting compound, a reactive methoxysilane-functionalized ionic liquid (Si-IL) was chemically anchored to the polymer backbone through the sol-gel hydrolysis and condensation reaction. Based on the permeation tests, the IL containing PEG-based polyurethane-siloxane membranes at different concentration of Si-IL (XSi-PPUIL) were found to be potential candidates for CO₂ removal from CH₄. For instance, the CO₂/CH₄ selectivity of XSi-PPUIL membranes with the Si-IL content of 10 wt% was 3.3-fold greater than the Si-IL free membranes; while, the CO₂ permeability for IL tethered membranes was 9.7% higher than the corresponding IL-free membrane.

Nanostructured poly(l-lactic acid)-poly(ethylene glycol)-poly(l-lactic acid) triblock copolymers and their CO2/O2 permselectivity

Biodegradable poly(l-lactic acid)-poly(ethylene glycol)-poly(l-lactic acid) (PLLA-PEG-PLLA) copolymers were synthesized by ring-opening polymerization of l-lactide using dihydroxy PEG as the initiator. The effects of different PEG segments in the copolymers on the mechanical and permeative properties were investigated. It was determined that certain additions of PEG result in composition-dependent microphase separation structures with both PLLA and PEG blocks in the amorphous state. Amorphous PEGs with high CO₂ affinity form gas passages that provide excellent CO₂/O₂ permselectivity in such a nanostructure morphology. The gas permeability and permselectivity depend on the molecular weight and content of the PEG and are influenced by the temperature. Copolymers that have a higher molecular weight and content of PEG present better CO₂ permeability at higher temperatures but provide better CO₂/O₂ permselectivity at lower temperatures. In addition, the hydrophilic PEG segments improve the water vapor permeability of PLLA. Such biodegradable copolymers have great potential for use as fresh product packaging.

Synthesis and Study of Gas Transport Properties of Polymers Based on Macroinitiators and 2,4-Toluene Diisocyanate

Nowadays, block copolymers hold great promise for the design of novel membranes to be applied for the membrane gas separation. In this regard, microporous block copolymers based on a macroinitiator with an anionic nature, such as potassium-substituted block copolymers of propylene oxide and ethylene oxide (PPEG) and 2,4-toluene diisocyanate (TDI), were obtained and investigated as effective gas separation membranes. The key element of the macromolecular structure that determines the supramolecular organization of the studied polymers is the coplanar blocks of polyisocyanates with an acetal nature (O-polyisocyanate). In the present research, the influence of the content of peripheral polyoxyethylene (POE) blocks in PPEG on the supramolecular structure processes and gas transport characteristics of the obtained polymers based on PPEG and TDI was investigated. According to the study of polymers if the POE block content is 15 wt %, the polyoxypropylene segments are located in the internal cavity of voids formed by O-polyisocyanate blocks. When the POE block content is 30 wt %, the flexible chain component forms its own microphase outside the segregation zone of the rigid O-polyisocyanate blocks. The permeability for polar molecules, such as ammonia or hydrogen sulfide, significantly exceeds the permeability values obtained for non-polar molecules He, N₂ and CH₄. A relatively high permeability is also observed for carbon dioxide. At the same time, the content of POE blocks has a small effect on the permeability for all studied gases. The diffusion coefficient increases with an increase in the POE block content in PPEG for all studied gases.

Recent developments in the field of barrier and permeability properties of segmented polyurethane elastomers

Polyurethane (PU) elastomers represent an important class of segmented copolymers. Thanks to many available chemical compositions, a rather broad range of chemical, physical, and biocompatible properties of PU can be obtained. These polymers are often characterized by high tensile and tear strength, elongation, fatigue life, and wear resistance. However, their relatively high permeability towards gases and water as well as their biocompatibility still limits the PU’s practical application, especially for biomedical use, for example, in implants and medical devices. In this review, the barrier and permeability properties of segmented PUs related to their chemical structure and physical and chemical properties have been discussed, including the latest developments and different approaches to improve the PU barrier properties.

Pentiptycene-Based Polyurethane with Enhanced Mechanical Properties and CO2-Plasticization Resistance for Thin Film Gas Separation Membranes

The development of thin film composite (TFC) membranes offers an opportunity to achieve the permeability/selectivity requirements for optimum CO₂ separation performance. However, the durability and performance of thin film gas separation membranes are mostly challenged by weak mechanical properties and high CO₂ plasticization. Here, we designed new polyurethane (PU) structures with bulky aromatic chain extenders that afford preferred mechanical properties for ultra-thin-film formation. An improvement of about 1500% in Young's modulus and 600% in hardness was observed for pentiptycene-based PUs compared to the typical PU membranes. Single (CO₂, H₂, CH₄, and N₂) and mixed (CO₂/N₂ and CO₂/CH₄) gas permeability tests were performed on the PU membranes. The resulting TFC membranes showed a high CO₂ permeance up to 1400 GPU (10^-6 cm³(STP) cm^-2 s^-1 cmHg^-1) and the CO₂/N₂ and CO₂/H₂ selectivities of about 22 and 2.1, respectively. The enhanced mechanical properties of pentiptycene-based PUs result in high-performance thin membranes with the similar selectivity of the bulk polymer. The thin film membranes prepared from pentiptycene-based PUs also showed a twofold enhanced plasticization resistance compared to non-pentiptycene-containing PU membranes.