Permeable Polymer Research Articles

Investigate the Physical Properties and Transmitted sunlight of PVC/PMMA/ ZnO Nanocomposite Films

Pure blend (PVC0.3g +PMMA 0.2g) and blend/ZnO nanocomposite films with different amounts were created using the solution casting technique. Different amounts of zinc oxide from (0.001, 0.002, 0.003, 0.004, and 0.005)g were investigated and added to blend polymer with a fixed amount (0.5) g of PVC/PMMA in 15ml tetrahydrofuran (THF). The XRD results demonstrated the amorphous structure of the admixture film and the hexagonal crystal structure of ZnONPs. The ZnONPs in the film were also atomically dispersed resulting in the incorporation of the ZnONPs peaks within the polymer matrix. FESEM image of the mixture and ZnO revealing small white spots scattered on the surface of the mixture with some agglomerates. FTIR spectroscopy data showed no chemical interaction between the polymer blend and ZnONPs. The increasing amounts of ZnONPs improved the absorbance, absorption coefficient, and extinction coefficient of the blend polymer. The blended polymer's permeability and energy gap decreased from 4.48eV to 3.91eV with the increase in the number of ZnONPs in the nanocomposites. The transmitted sunlight intensity was measured through the blended pure polymer films and the blended nanocomposites/ZnO nanocomposites. At the beginning of September 2021, the intensity of transmitted sunlight was measured in Baghdad for a period of 7 days. As can be observed, almost all films have the same ratio of the intensity of transmitted radiation to the intensity of sunlight for all hours and days.

3D‐Shape Recoverable Hydrogel with Highly Efficient Water Transport for Solar Water Desalination

AbstractPorous hydrogels have been developed to be highly efficient interfacial solar vapor generation materials for obtaining affordable freshwater supplies. However, realizing hydrogel materials with portability, adequate water supply, and durable mechanical properties remains challenging. Herein, a scalable and portable hydrogel with 3D‐shaped recovery, highly efficient water transport, and robust mechanical stability is reported, which is prepared by foaming polyvinyl alcohol (PVA) and modification of phosphotungstic acid (PTA). Due to the interconnected porous structure and highly permeable polymer network, the PVA/PTA‐PH hydrogel has good repetitive compressibility and rapid shape recovery when in contact with water. Combined with light‐absorbing nanoparticles, the PVA/PTA‐PH hydrogel presents an impressive solar evaporation rate of 3.876 kg m−2 h−1 and a photothermal conversion efficiency of ≈94% under 1‐sun irradiation. With 3D‐shape recovery and highly efficient water transport, the compressed hydrogel can be quickly unfolded without human intervention and restored to five times the original size for the working state. The good portability, excellent seawater desalination performance, and simple preparation process are anticipated to make the PVA‐/PTA‐PH hydrogel a promising material to continuously and conveniently produce pure water from seawater.

Study on Bonding Characteristics of Polymer Grouted Concrete-Soil Interface.

The issue of interfacial shear damage has been a significant challenge in the field of geotechnical engineering, particularly in the context of diaphragm walls and surrounding soils. Polymer grouting is a more commonly used repair and reinforcement method but its application to interface repair and reinforcement in the field of geotechnical engineering is still relatively rare. Consequently, this paper presents a new polymer grouting material for use in grouting reinforcement at the interface between concrete and soils. The bonding characteristics and shear damage mode of the interface after grouting were investigated by the direct shear test, and the whole process of interface shear damage was investigated by digital image correlation (DIC) technology. Finally, the reinforcement mechanism was analyzed by microscopic analysis. The results demonstrate that the permeable polymer is capable of effectively filling the pores of soil particles and penetrating into the concrete-soil interface. Through a chemical reaction with water in the soil, the polymer cements the soil particles together, forming chemical adhesion at the interface and thereby achieving the desired reinforcement and repair effect. In the shear process, as the normal stress increased, the horizontal displacement and horizontal compressive strain at the distal end of the loading end decreased, while the maximum vertical displacement and maximum vertical strain of the cured soil also decreased. The results of scanning electron microscopy (SEM) demonstrated that the four groups of test polymers exhibited a reduction in soil porosity of 53.47%, 58.79%, 52.71%, and 54.12%, respectively. Additionally, the form of concrete-soil interfacial bonding was observed in the concrete-cohesive layer-cured soil mode. The findings of this study provide a foundation for further research on diaphragm wall repair and reinforcement.

Permeability of porous membrane polymers modified by supercritical carbon dioxide

An approach to predict the gas permeability of membrane polymers after supercritical CO2 treatment is proposed. The approach is based on the connection of the temperatures of secondary relaxation transitions with the effective sizes of mobile free volume elements in the polymers. The correlation between permeability of nitrogen and effective sizes of mobile holes for a set of polymers is established. The effect of supercritical CO2 on the nitrogen permeability of polycarbonate, polysulfone, polyvinylbutyral is analyzed by FTIR spectroscopy of low-molecular weight conformationally-inhomogeneous compounds introduced in the polymers. Membranes were exposed at 40 MPa and 333 K for 4 h through static treatment and dynamic treatment separately. For polyvinylbutyral, the nitrogen permeability did not change after supercritical CO2 modification while for polysulphone, the effective volume of mobile holes increased, but the nitrogen permeability decreased. For polycarbonate after supercritical CO2, the effective volume of mobile holes and the nitrogen permeability increased.

An electrochemical flow cell for operando XPS and NEXAFS investigation of solid–liquid interfaces

Suitable reaction cells are critical for operando near ambient pressure (NAP) soft x-ray photoelectron spectroscopy (XPS) and near-edge x-ray absorption fine structure (NEXAFS) studies. They enable tracking the chemical state and structural properties of catalytically active materials under realistic reaction conditions, and thus allow a better understanding of charge transfer at the liquid–solid interface, activation of reactant molecules, and surface intermediate species. In order to facilitate such studies, we have developed a top-side illuminated operando spectro-electrochemical flow cell for synchrotron-based NAP-XPS/-NEXAFS studies. Our modular design uses a non-metal (PEEK) body, and replaceable membranes which can be either of x-ray transparent silicon nitride (SiN x ) or of water permeable polymer membrane materials (e.g. NafionTM). The design allows rapid sample exchange and simultaneous measurements of total electron yield, Auger electron yield and fluorescence-yield. The developed system is highly modular and can be used in the laboratory or directly at the beamline for operando XPS/ x-ray absorption spectroscopy investigations of surfaces and interfaces. We present examples to demonstrate the capabilities of the flow cell. These include an operando NEXAFS study of the Cu-redox chemistry using a SiN x /Ti-Au/Cu working electrode assembly (WEA) and a NAP-XPS/-NEXAFS study of water adsorption on a NafionTM polymer membrane based WEA (NafionTM/C/IrO x catalyst). More importantly, the spectro-electrochemical flow cell is available for user community of B07 beamlines at Diamond Light Source.

Microporous Electrode Binders for Anion Exchange Membrane Water Electrolyzers.

In anion exchange membrane (AEM) water electrolyzers, AEMs separate hydrogen and oxygen, but should efficiently transport hydroxide ions. In the electrodes, catalyst nanoparticles are mechanically bonded to the porous transport layer or membrane by a polymeric binder. Since these binders form a thin layer on the catalyst particles, they should not only transport hydroxide ions and water to the catalyst particles, but should also transport the nascating gases away. In the worst case, if formation of gases is >> than gas transport, a gas pocket between catalyst surface and the binder may form and hinder access to reactants (hydroxide ions, water). In this work, the ion conductive binder SEBS-DABCO is blended with PIM-1, a highly permeable polymer of intrinsic microporosity. With increasing amount of PIM-1 in the blends, the permeability for water (selected to represent small molecules) increases. Simultaneously, swelling and conductivity decrease, due to the increased hydrophobicity. Ex situ data and electrochemical data indicate that blends with 50% PIM-1 have better properties than blends with 25% or 75% PIM-1, and tests in the electrolyzer confirm an improved performance when the SEBS-DABCO binder contains 50% PIM-1.

Robust Electrostatic-Templated Polymerization for Controllable Synthesis of Stable and Permeable Polyelectrolyte Vesicles.

Polymer vesicles are of profound interest for designing delivery vehicles and nanoreactors toward a variety of biomedical and catalytic applications, yet robust synthesis of stable and permeable vesicles remains challenging. Here, we propose an electrostatic-templated polymerization that enables fabrication of polyelectrolyte vesicles with simultaneously regulated stability and permeability. In our design, cationic monomers were copolymerized with cross-linkers in the presence of a polyanionic-neutral diblock copolymer as a template. By properly choosing the block length ratio of the template, we fabricated a type of polyion complex vesicle consisting of a cross-linked cationic membrane, electrostatically assembled with the template copolymer which can be removed by sequential dissociation and separation under concentrated salt. We finally obtained stable polyelectrolyte vesicles of regulated size, membrane permeability, and response properties by tuning the synthesis factors including ionic strength, cross-linker type, and fraction as well as different monomers and concentrations. As a proof-of-concept, lipase was loaded in the designed cationic vesicles, which exhibited enhanced enzyme stability and activity. Our study has developed a novel and robust strategy for controllable synthesis of a new class of stable and permeable polymer (polyelectrolyte) vesicles that feature great potential applications as functional delivery carriers and nanoreactors.

Physicochemical and structural characteristics of hybrid nanocomposites based on branched polyimide with a low content of inorganic component

The series of organic-inorganic hybrid nanocomposites based on branched polyimide matrix and with different amounts of tetraethoxysilane (TEOS) (5, 20, and 50 wt.% of the initial polyamic acid mass) were synthesized and studied using nitroxyl paramagnetic probe, measuring dielectric permittivity, X-ray structural analysis and optical microscopy. It was shown that in some cases the introduction of inorganic component is accompanied by a decrease in the segmental mobility of polyimide matrix as a result of the partial immobilization of organic macrochains during the formation of inorganic microregions. In the presence of inorganic component, a weak dependence of the polymer permeability on the content of the organic component in the system is observed, also the specific density changes little with an increase in TEOS content. Extreme changes in the segmental mobility and dielectric permittivity of the branched matrix formed in the presence of 5 wt% TEOS were found compared to systems of other compositions. This can be caused to a large extent by structural changes in the system. At a low content of TEOS occurs significant «loosening» of organic matrix, a sharp decrease in the dielectric constant and a significant increase in the segmental mobility of the polyimide matrix. Small angle X-ray scattering diffractograms demonstrate drastic changes in polyimide composite heterogeneity in the presence of 5 wt.% TEOS content. According to the optical microscopy data, the introduction of TEOS into polyimide is accompanied by the formation of microaggregates of inorganic nanoparticles in the system, the number and average size of which depend on the SiO2 content and looks most homogeneous at a low TEOS content.

Highly permeable and selective polymer inclusion membrane for Li+ recovery and underlying enhanced mechanism

Polymer inclusion membrane (PIM) has become a potential alternative in efficient Li + separation from brines typically with Mg2+ and Li+, due to its exceptional stability and selectivity. However, the practical application of PIMs is still greatly restricted by its slow mass transfer and related unclear transport mechanism. Here, we fabricated an efficient PIM with tributyl phosphate (TBP) along with sodium tetraphenylborate (NaBPh4) as carriers and cellulose triacetate (CTA) as a polymer skeleton for highly selective and permeable Li + separation from high Mg2+/Li+ aqueous solutions, offering an initial flux of 3–20 times higher than other PIMs. With increasing TBP content in the PIM, a nonmonotonical trend (sharp increase-leveling off-slow decrease) of its initial flux was observed. The improvement of the solubility (compatibility) of NaBPh4 in CTA matrix by introducing TBP was demonstrated by scanning electron microscope (SEM) coupled with X-ray energy dispersive spectroscopy (EDS) images, which was highly consistent with binding energy simulation. X-ray diffraction (XRD) and positron annihilation lifetime spectroscopy (PALS) results verify that moderate TBP content in the PIM could enlarge the distance of polymer chains and enhance the initial flux of PIMs, while excessive TBP can occupy the free volume sites, leading to an adverse effect on the permeability. Our study provides valuable information on the compatibility effect on the mass transfer through the polymer matrix including PIMs, which exhibits prospect in a wide range of applications of metal separation.

Experimental Study on Compressibility and Microstructure of Loess Solidified by Permeable Polymer

This study aims to investigate the compressive and microstructural properties of loess before and after treatment with a new permeable polymer. To enhance the compressive properties of loess, specimens were infused with the new polymer, and one-dimensional consolidation tests were performed to assess the compressibility of solidified loess (SL) and unsolidified loess (UL) at different water contents. Additionally, the microstructure and pore morphology of UL and SL were examined using a scanning electron microscope (SEM) and the Particles (Pores) and Cracks Analysis System (PCAS). Statistical methods were employed to analyze the relationships between microstructural parameters and compression modulus. The experimental results demonstrate a significant improvement in the compressibility of loess when treated with the polymer. The complexity of pore structure and variability in pore size are reduced, leading to a more uniform pore distribution. Moreover, all microstructural parameters exhibit a strong correlation with the compression modulus. The results pertaining to the compressive and microstructural properties of loess reinforced with permeable polymer grouting can provide insights into the variations in the curing effect, serving as a theoretical foundation for the application of permeable polymer in loess treatment.

Practical organic electronic noses using semi-permeable polymer membranes

Electronic noses (E-noses) mimic olfactory organs and quantify volatile organic compounds (VOCs), emulating the sense of smell, with applications in real-time monitoring of VOCs in food, healthcare, and law enforcement industries. Organic field-effect transistor (OFET) based sensors can be fabricated in large arrays by economical processes, however, lack the selectivity necessary to differentiate wide varieties of VOCs. Here, we explore the use of permeable polymer membranes with OFET sensors to improve their selectivity. Acylated poly(vinyl alcohol) (PVA) derivatives were synthesized, characterized, and evaluated in OFET vapor sensors as tunable membranes. Sensors with and without acylated PVA membranes were tested with VOC analytes. By monitoring drain current over time, we found that membranes dramatically changed responses to different analytes. We show that VOCs including methanol, ethanol, hexane, toluene, tetrahydrofuran, methyl ethyl ketone, and ethyl acetate can all be detected and differentiated with much greater selectivity than sensors without membranes. In particular, methanol and ethanol, which are difficult to differentiate in vapor sensors, showed significant quantitative differences in the initial slope (0.0403 s−1 vs 0.0192 s−1 respectively; 6 σ) and decay constants (5.5 s vs 15.9 s respectively; 26 σ) of their current vs time responses, allowing methanol and ethanol to be differentiated with 100 % confidence. This approach enables the economical fabrication of large varieties of unique organic vapor sensors by simply changing the membrane layer and results in an outstanding level of selectivity for OFET vapor sensors.

Single and mixed gas permeability studies on mixed matrix membranes composed of MIL-101(Cr) or MIL-177(Ti) and highly permeable polymers of intrinsic microporosity

The gas transport properties of mixed matrix membranes (MMMs), prepared by dispersing nanoparticles of MOFs MIL-101(Cr) or MIL-177(Ti) into highly permeable Polymers of Intrinsic Microporosity PIM-EA-TB or PIM-TMN-Trip, were investigated. The homogeneity of the dispersion was confirmed by means of Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray (EDX) mapping analysis. Single gas time-lag measurements provided the permeability and ideal selectivity of different gas pairs, both after treatment of the MMMs with methanol and after natural aging over an extended period (up to 2000 days). This data demonstrated that the gas size-sieving pores of MIL-101(Cr) and MIL-177(Ti) and their good dispersion into the PIM matrix results in MMMs with enhanced gas separation performance, as compared to films composed solely of the polymer. The comparison of actual permeability with the Maxwell model for PIM-EA-TB with both MOFs confirmed the good dispersion and the absence of anomalies, whereas the inconsistency of permeability with prediction data for PIM-TMN-Trip suggests that the MOFs improved the polymer properties, stiffening or occupying the polymer free volume. In particular, the incorporation of MIL-101(Cr) into PIM-EA-TB significantly enhances the H2 permeability from ∼6000 to 13,000 Barrer, with a concurrent increase of the H2/N2 selectivity from 14 to 21. MIL-177(Ti) also enhances the H2/N2 selectivity to 20 due to a slight reduction of the N2 permeability. The addition of MIL-101(Cr) and MIL-177(Ti) into the ultra-permeable PIM-TMN-Trip showed more modest increases in H2 permeability and H2/N2 selectivity from 4.6 to ∼ 10. Hence the data for some of the MMMs surpass the 2008, and even approach the 2015/2019 Robeson’s upper bounds, particularly for gas pairs including H2.

Transient slow motion of a porous sphere

The start-up creeping motion of a porous spherical particle, which models a permeable polymer coil or floc of nanoparticles, in an incompressible Newtonian fluid generated by the sudden application of a body force is investigated for the first time. The transient Stokes and Brinkman equations governing the fluid velocities outside and inside the porous sphere, respectively, are solved by using the Laplace transform. An analytical formula for the transient velocity of the particle as a function of relevant parameters is obtained. As expected, the particle velocity increases over time, and a particle with greater mass density lags behind a corresponding less dense particle in the growth of the particle velocity. In general, the transient velocity is an increasing function of the porosity of the particle. On the other hand, a porous particle with a higher fluid permeability will have a greater transient velocity than the same particle with a lower permeability, but may trail behind the less permeable particle in the percentage growth of the velocity. The acceleration of the porous particle is a monotonic decreasing function of the elapsed time and a monotonic increasing function of its fluid permeability. In particular, the transient behavior of creeping motions of porous particles may be much more important than that of impermeable particles.

Natural gas dehydration membranes prepared by incorporating environmentally friendly metal‐organic framework MIP‐202 into polyetherimide

AbstractUsing porous materials to selectively adsorb H2O from natural gas is a promising method to dehydrate methane (CH4). The structure of a Zirconium metal‐organic framework (Zr‐MOF), namely, MIP‐202, features a high density of amino groups, which can produce strong hydrogen bonding with H2O molecules. MIP‐202 is cost‐effective, green and scalable, and it exhibits good chemical stability under various conditions. This work incorporated MIP‐202 nanoparticles into the high permeability polymer polyetherimide (PEI), and the obtained Mixed Matrix Membranes (MMMs) was used for the gas separation of H2O/CH4. It is found that MMMs loaded with 20 wt% of MIP‐202 demonstrated a high H2O/CH4 selectivity of 832.2, which was about 760 times of that of the pure PEI. This approach offers a new route to fabricate functional membranes for energy‐efficient gas separations.

Rapid preparation of extremely highly permeable covalent organic polymers nanofiltration membranes for alcohol recovery via interfacial polymerization

Covalent organic polymers (COPs) membranes have been widely investigated in recent years for the application and preparation of composite nanofiltration (NF) membranes due to the abundant pore structure. However, there are still difficulties in the easy and reliable preparation of scalable and highly permeable COPs membranes. In this work, the polyaminophenylene (PAP) layer was constructed on polysulfone (PSF) ultrafiltration membranes by diazonium-induced anchoring process (DIAP), and then used as a substrate to prepare ultra-thin and highly permeable COPs NF membranes by interfacial polymerization (IP) in only 20 ​s. The presence of PAP layer increases the aqueous phase monomer storage to promote the forward progression and limits the reaction zone of IP, thus resulting in ultrathin and highly crosslinked COPs membranes. In addition, the PAP layer covalently grafted onto the PSF molecular chain also participates in the IP reaction, thus the separation layer is connected to the substrate as a whole for better stability and can operate for long periods of time in an alcohol-based organic solvent environment. The methanol permeance of optimal NF-PAP membrane prepared based on the above strategy can reach 362-398 ​L−1m−2h−1bar−1, which almost achieves an order of magnitude enhancement relative to other reported COPs organic solvent nanofiltration (OSN) membranes. The retention rate of the COPs composite membrane for naphthol green B (Mw ​= ​878) dye was about 98.5 ​%, demonstrating good alcohol recovery ability. In conclusion, this study offers a potential strategy for the development and application of COPs OSN membranes.

Experimental Investigation on Reinforcement Application of Newly Permeable Polymers in Dam Engineering with Fine Sand Layers

The grinding reinforcement of fine sand layers is a difficult problem in dam engineering construction. As a new type of grouting material, permeable polymer with excellent impermeability and high strength is widely used in dam engineering. In this paper, a series of compressive tests were designed considering different grouting pressures, curing days, moisture content, and porosity of fine sand. The influence of grouting parameters and sand layer conditions on the strength of fine sand layers reinforced by permeable polymers was analyzed. SEM and XDR tests were conducted to analyze the microscopic characteristics of the grouting stone. The functional calculation model of the strength and the influencing factors was established to explore the main factors influencing grouting stones. The compressive strength of grouted stones increases rapidly from the 7th to the 14th day, reaching about 96% of the maximum strength. The degree of influence of different factors is grouting pressure > moisture content > porosity. The compressive strength of the grouted stones increases with the increase of grouting pressure and the number of curing days. The compressive strength decreases with the sand layer’s increasing moisture content and porosity.

Mixed Matrix Membranes Using Porous Organic Polymers (POPs)-Influence of Textural Properties on CO2/CH4 Separation.

Mixed matrix membranes (MMMs) provide the opportunity to test new porous materials in challenging applications. A series of low-cost porous organic polymer (POPs) networks, possessing tunable porosity and high CO2 uptake, has been obtained by aromatic electrophilic substitution reactions of biphenyl, 9,10-dihydro-9,10-dimethyl-9,10-ethanoanthracene (DMDHA), triptycene and 1,3,5-triphenylbenzene (135TPB) with dimethoxymethane (DMM). These materials have been characterized by FTIR, 13C NMR, WAXD, TGA, SEM, and CO2 uptake. Finally, different loadings of these POPs have been introduced into Matrimid, Pebax, and chitosan:polyvinyl alcohol blends as polymeric matrices to prepare MMMs. The CO2/CH4 separation performance of these MMMs has been evaluated by single and mixed gas permeation experiments at 4 bar and room temperature. The effect of the porosity of the porous fillers on the membrane separation behavior and the compatibility between them and the different polymer matrices on membrane design and fabrication has been studied by Maxwell model equations as a function of the gas permeability of the pure polymers, porosity, and loading of the fillers in the MMMs. Although the gas transport properties showed an increasing deviation from ideal Maxwell equation prediction with increasing porosity of the POP fillers and increasing hydrophilicity of the polymer matrices, the behavior of biopolymer-based CS:PVA MMMs approached that of Pebax-based MMMs, giving scope to not only new filler materials but also sustainable polymer choices to find a place in membrane technology.

Three-dimensional reliability stability analysis of earth-rock dam slopes reinforced with permeable polymer

Polymer is a new repair and reinforcement material for earth-rock dams developed in recent years. Models are developed where spatial variability is incorporated into the analytical framework to evaluate the stability and reliability of reinforced three-dimensional dam slopes. The Karhunen-Loeve (K-L) expansion method is employed to generate three-dimensional random fields. The simplified Bishop method and Monte Carlo method are used to calculate the safety factors and failure probabilities of the dam slopes. With the implementation of polymer grouting reinforcement, the safety factors are improved and the failure probabilities are reduced. The reinforcement effect will be affected by the amount of polymer dosing, dam slope characteristics, and polymer grouting parameters. The impact of various longitudinal autocorrelation distances on reliability is influenced by the length of the dam slope itself. An increase of the safety factor by approximately 37% can be achieved through a polymer dosing of around 3%. Nevertheless, with the elevation of dam slope height and slope ratio, the effectiveness of polymer reinforcement is diminished.

Mechanistic evaluation of the initial burst release of leuprolide from spray-dried PLGA microspheres

Spray-dried poly(lactic-co-glycolic acid) (PLGA) peptide-loaded microspheres have demonstrated similar long-term in vitro release kinetics compared to those produced by the solvent evaporation method and commercial products. However, the difficult-to-control initial burst release over the first 24 h after administration presents an obstacle to product development and establishing bioequivalence. Currently, detailed information about underlying mechanisms of the initial burst release from microspheres is limited. We investigated the mechanism and extent of initial burst release using 16 previously developed spray-dried microsphere formulations of the hormone drug, leuprolide acetate, with similar composition to the commercial 1-month Lupron Depot® (LD). The burst release kinetics was measured with a previously validated continuous monitoring system as well as traditional sample-and-separate methods. The changes in pore structure and polymer permeability were investigated by SEM imaging and the uptake of a bodipy-dextran probe. In vitro results were compared to pharmacokinetics in rats over the same interval. High-burst, spray-dried microspheres were differentiated in the well-mixed continuous monitoring system but reached an upper limit when measured by the sample-and-separate method. Pore-like occlusions observed by confocal microscopy in some formulations indicated that particle swelling may have contributed to probe diffusion through the polymer phase and showed the extensive internal pore structure of spray-dried particles. Continuous monitoring revealed a rapid primary (1°) phase followed by a constant-rate secondary (2°) release phase, which comprised ∼80% and 20% of the 24-hr release, respectively. The ratio of 1° phase duration (t1°) and the characteristic probe diffusion time (τ) was highly correlated to 1° phase release for spray dried particles. Of the four spray-dried formulations administered in vivo, three spray-dried microspheres with similar polymer density showed nearly ideal linear correlation between in vivo absorption and well-mixed in vitro release kinetics over the first 24 h. By contrast, the more structurally dense LD and a more-dense in-house formulation showed a slight lag phase in vivo relative to in vitro. Furthermore, in vitro dimensionless times (tburst/τ) were highly correlated with pharmacokinetic parameters for spray-dried microspheres but not for LD. While the correlation of increases in effective probe diffusion and 1° phase release strongly suggests diffusion through the polymer matrix as a major release mechanism both in vitro and in vivo, a fixed lower limit for this release fraction implies an alternative release mechanism. Overall, continuous monitoring release and probe diffusion appears to have potential in differentiating between leuprolide formulations and establishing relationships between in vitro release and in vivo absorption during the initial burst period.

The role of solvent temperature and gas pressure on CO2 mass transfer during biogas upgrading within porous and dense-skin hollow fibre membrane contactors

Biogas upgrading uniquely requires pressurisation of hollow fibre membrane contactors (HFMC) to be competitive with classical water absorption, and when complemented with an ambient industrial temperature range, these conditions will determine CO2 mass transport phenomena that are distinct dependent upon whether microporous or nonporous membranes are used. This study therefore examines the independent and concomitant role of temperature and pressure in determining CO2 mass transport, and selectivity, within microporous and nonporous HFMC. At low solvent temperatures, higher CO2 flux was achieved which indicates that solvent solubility is more critical than CO2 diffusivity to enhancing mass transport. Low temperatures also favoured mass transfer within the microporous membrane, explained by the reduction in solvent vapour pressure which limited pore wetting by condensation. In contrast, the nonporous membrane exhibited poorer mass transfer at low temperatures due to a decline in dense polymer permeability. Crucially in this study, neither wetting of the microporous membrane or plasticisation of the nonporous membrane were observed following pressurisation. Consequently, CO2 flux increased in proportion to the applied pressure for both membrane types, emphasising the critical role of pressurisation in augmenting process intensification for biogas upgrading which is typically facilitated at pressures of 7–10 bar. Resistance-in-series analysis illustrated how pressurisation reduced gas-phase resistance, and subsequently enhanced selectivity. Consequently, an outlet gas quality of 98% methane could be achieved within a single microporous module at 4.5 bar, meeting the industrial standard for biomethane whilst reducing solvent requirements, separation energy and methane losses. Comparable behaviour was observed during pressurisation of the nonporous membrane, but with a less significant benefit to CO2 mass transfer and selectivity, ostensibly due to the resistance imparted by the dense polymer. When considered collectively, low solvent temperature and high gas pressure enhance process intensification subsequently reducing process size (e.g., membrane area) and separation energy, while also advancing selectivity to deliver a gas product at the composition required for biomethane with minimum methane losses, which are critical factors in demonstrating microporous HFMC as an industrially competitive solution for biogas upgrading.