Attempts to modify the surface of oxidized cellulose microfibrils were made using amine terminated molecules. First, native cellulose was oxidized with catalytic amounts of ...2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO), sodium hypochlorite and sodium bromide in water. The primary alcohol moieties were selectively oxidized into carboxyl groups. Then, the oxidized cellulose was coupled with amines derivatives by a peptidic reaction by using carbodiimide and hydroxysuccimide as catalyst and amidation agent. The obtained coupled cellulose showed low polarity, with stability in non-polar solvents. The products were characterized by FTIR, ¹³C NMR, rheology and conductometric titration as well as transmission electron microscopy. Their hydrophobic character was evaluated by observing their behavior in polar and non-polar solvents.
The rheology of cellulose microfibril suspensions from TEMPO-oxidized pulp was investigated. The suspension showed a pseudo-plastic and thixotropic behavior, slowly evolving with time under a given ...shear rate. The viscosity was proportional to the concentration up to the critical concentration of 0.23%. Above it, the viscosity followed a power law with exponents from 2 to 6 depending on the shear rate, and the system showed shear thinning behavior and behaved gel-like. Below this concentration, the system was more Newtonian. Birefringence measurement of 0.44% and 0.78% suspension showed that microfibrils alignment saturated at a small shear rate with a Herman's orientation parameter below 0.65 probably due to the interconnection of microfibrils.
Aging in polymers of intrinsic microporosity has slowed exploitation due to a decay in performance over time since densification makes them unsuitable for industrial applications. This work aimed to ...study the impact of the operation and storage temperature on the gas separation properties and aging rates of PIM-1 self-standing films. The permeability, diffusivity, and solubility of the tested membranes were monitored through permeation tests for pure carbon dioxide and nitrogen at a maximum upstream pressure of 1.3 bar for temperatures ranging from −20 °C to 25 °C. This study found significant benefits in the operation of glassy polymeric membranes at low temperatures, resulting in a favourable trade-off in separation performance and a reduction in the aging rate by three orders of magnitude. This brings new opportunities for the industrial application of PIMs in innovative carbon capture processes.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Numerous studies have been reported on CO2 facilitated transport membrane synthesis, but few works have dealt with the interaction between material synthesis and transport modelling aspects for ...optimization purposes. In this work, a hybrid fixed-site carrier membrane was prepared using polyallylamine with 10 wt% polyvinyl alcohol and 0.2 wt% graphene oxide. The membrane was tested using the feed gases with different relative humidity and at different CO2 partial pressures. Selected facilitated transport models reported in the literature were used to fit the experimental data with good agreement. The key dimensionless facilitated transport parameters were obtained from the modelling and data fitting. Based on the values of these parameters, it was shown that the diffusion of the amine-CO2 reaction product was the rate-controlling step of the overall CO2 transport through the membrane. It was shown theoretically that by decreasing the membrane selective layer thickness below the actual value of 1 µm to a value of 0.1 µm, a CO2 permeance as high as 2500 GPU can be attained while maintaining the selectivity at a value of about 19. Furthermore, improving the carrier concentration by a factor of two might shift the performances above the Robeson upper bound. These potential paths for membrane performance improvement have to be confirmed by targeted experimental work.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Gas transport properties of PIM-EA(H₂)-TB, a microporous Tröger's base polymer, were systematically studied over a range of pressure and temperature. Permeability coefficients of pure CO₂, N₂, CH₄ ...and H₂ were determined for upstream pressures up to 20 bar and temperatures up to 200 °C. PIM-EA(H₂)-TB exhibited high permeability coefficients in absence of plasticization phenomena. The permeability coefficient of N₂, CH₄ and H₂ increased with increasing temperature while CO
permeability decreased with increasing temperature as expected for a glassy polymer. The diffusion and solubility coefficients were also analysed individually and compared with other polymers of intrinsic microporosity. From these results, the activation energies of permeation, diffusion and sorption enthalpies were calculated using an Arrhenius equation.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Among the available membranes, dense polymer composite hollow-fiber membranes are promising for gas permeation applications coupled with the use of gas/liquid contactors, but they are also used in ...other membrane processes such as pervaporation. This study focuses on a coating process, starting from a polymer solution, to control the thickness and regularity of the coated polymer. The thickness of the liquid film coated onto a fiber is related to the coating velocity, the physical and chemical properties of the liquid, and the coating geometry. Depending on the dominating forces, several regimes are defined: two unstable regimes, in which a thin and regular polymer layer cannot be produced, and two stable regimes, which are of interest for reaching our objectives at the laboratory or industrial scale. The theoretical laws were compared to experimental coatings with solutions of poly(trimethylsilyl)propyne (PTMSP) dissolved in cyclohexane coated onto poly(ether sulfone) (PES) hollow fibers. The viscosities, surface tensions, and densities of the solutions used were measured. The experimental thicknesses of coated polymer layers were compared to values calculated from Landau’s law, which describes the thickness behavior in the viscocapillary regime. The results showed good behavior agreement, but the experimental thickness was underestimated by the calculations. Four different kinds of composite membranes were prepared using two different porous supports (MicroPES and Oxyphan) and two different permeable polymers (PTMSP and Teflon AF2400) for coating. The obtained composites hollow fibers were characterized. All four presented low-energy surfaces with no wetting phenomena. They also exhibited high CO2 and N2 permeabilities with CO2/N2 selectivities between 3.4 and 2.5. The mechanical properties of the composites remained stable except for composites based on PES affected by the drying step during the coating process.
Approximately two-thirds of anthropogenic emissions causing global warming are from carbon dioxide. Carbon capture is essential, with membranes proving to be a low cost and energy-efficient solution ...to alternative technologies. In particular, mixed matrix membranes (MMMs) can have higher permeability and selectivity than pure polymer membranes. The fabrication conditions affect the formation of defects within the membranes. In this work, MMMs were created using a PEBAX MH-1657 polymer and a ZIF-8 filler. The effect of casting plate temperature, varying from −5 °C to 50 °C, and the effect of ultrasound treatment time (80–400 min) and method (filler solution only, filler and polymer combined solution only and filler solution followed by combined solution) were investigated, aiming to reduce defect formations hence improving the performance of the MMMs. SEM images and permeation tests using pure CO2 and N2 gas, replicating flue gas for carbon capture, were used to investigate and compare the membranes morphology and performance. The results indicated that the MMMs maintained their permeabilities and selectivities at all tested casting temperatures. However, the neat PEBAX membranes demonstrated increased phase separation of the polyamide and polyether oxide phases at higher temperatures, causing a reduction in permeability due to the higher crystallinity degree, confirmed by DSC experiment. The MMMs fabricated at low ultrasound times displayed a large amount of aggregation with large particle size causing channeling. At high ultrasound times, a well-dispersed filler with small filler diameters was observed, providing a high membrane performance. Overall, defect-free membranes were successfully fabricated, leading to improved performance, with the best membrane resulting from the longest ultrasound time reaching the Robeson bound upper limits.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Mixed-matrix membranes (MMMs) are membranes that are composed of polymers embedded with inorganic particles. By combining the polymers with the inorganic fillers, improvements can be made to the ...permeability compared to the pure polymer membranes due to new pathways for gas transport. However, the fillers, such as hyper cross-linked polymers (HCP), can also help to reduce the physical aging of the MMMs composed of a glassy polymer matrix. Here we report the synthesis of two novel HCP fillers, based on the Friedel-Crafts reaction between a tetraphenyl methane monomer and a bromomethyl benzene monomer. According to the temperature and the solvent used during the reaction (dichloromethane (DCM) or dichloroethane (DCE)), two different particle sizes have been obtained, 498 nm with DCM and 120 nm with DCE. The change in the reaction process also induces a change in the surface area and pore volumes. Several MMMs have been developed with PIM-1 as matrix and HCPs as fillers at 3% and 10wt % loading. Their permeation performances have been studied over the course of two years in order to explore physical aging effects over time. Without filler, PIM-1 exhibits the classical aging behavior of polymers of intrinsic microporosity, namely, a progressive decline in gas permeation, up to 90% for CO
permeability. On the contrary, with HCPs, the physical aging at longer terms in PIM-1 is moderated with a decrease of 60% for CO
permeability.
C spin-lattice relaxation times (T1) indicates that this slowdown is related to the interactions between HCPs and PIM-1.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This study reports for the first time the preparation of an electrospun microfibrous mat of PIM-EA-TB. The electrospinning was carried out using a chloroform/n-Propyl-lactate (n-PL) binary solvent ...system with different chloroform/nPL ratios, in order to control the morphology of the microfibres. With pure chloroform, porous and dumbbell shape fibres were obtained whereas, with the addition on n-PL, circular and thinner fibres have been produced due to the higher boiling point and the higher conductivity of n-PL. The electrospinning process conditions were investigated to evaluate their impact on the fibres’ morphology. These microfibrous mats presented potential to be used as breathable/waterproof materials, with a pore diameter of 11 μm, an air resistance of 25.10−7 m−1 and water breakthrough pressure of 50 mBar.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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