Reduced Water Permeability Research Articles

Reduced Water Permeability of Biodegradable PCL Nanocomposite Coated Paperboard Packaging

Reduced Water Permeability of Biodegradable PCL Nanocomposite Coated Paperboard Packaging

Evolution of the Microstructure of Sustained-release Matrix Tablets during Dissolution and Storage

Glyceryl behenate based-matrix tablets allowed obtaining a sustained release of theophylline for up to 12 hours. The diluent selected as pore-forming agent (lactose or dibasic calcium phosphate anhydrous) affected the drug release and its stability after 3-months storage at 40°. Lactose-containing matrix tablets exhibited a quicker drug release than those containing dibasic calcium phosphate anhydrous because of its higher water-solubility. After 3-month storage at 40°, tablets containing lactose showed the same drug release whereas a significantly slower release was observed for dibasic calcium phosphate anhydrous-containing tablets. Synchrotron radiation-based X-ray micro computed tomography was used for the evaluation of eventual changes in the microstructure of the matrix tablets during dissolution and after long-term storage. X-ray images provided new insights into the interplay of pharmaceutical ingredients and the importance of excipient surface structure on drug release overtime. The solid-lipid excipient could be adsorbed on the textured surface of mesoporous dibasic calcium phosphate anhydrous resulting in reduced water permeability of the matrix and therefore slower drug release. These findings provide formulators with fundamental formulation considerations for the development of sustained release matrix tablets using glyceryl dibehenate as release retarding agent.

Dynamic microstructure of graphene oxide membranes and the permeation flux

Graphene oxide (GO) membranes have been reported to be a promising separation barrier that can retain small molecules and multi-valent salts because of the well-defined interlayer space between GO flakes. However, while some studies suggested fast liquid transport through the extremely tortuous transport path, contradictory observations (e.g. low permeation flux) have also been obtained. This paper revealed the dynamic microstructure of GO membranes, which affected the membrane performance significantly. We showed that all GO membranes prepared by varied methods and on different substrates presented a severe reduction in water permeability during filtration, due to the compaction of their original loose microstructure. The water flux could drop continuously from tens of LMH bar−1 to <0.1 LMH bar−1 after more than ten hours. This result demonstrated that the structure of GO membranes prepared by current approaches was far from the ideal laminar structure. The high permeability of GO membranes observed could be contributed by the disordered membrane microstructure. Therefore, the transport mechanisms assuming perfect laminar structure in GO membranes, and the fast transport hypothesis may not fully describe the water transport in GO membranes. Interestingly, the loosely packed microstructure of GO membranes was also found reversible depending on the storage conditions.

Preparation of photocatalytic TiO 2 -based self-cleaning coatings for painted surface without interlayer

Abstract Photocatalytic TiO 2 provides a promising route to produce self-cleaning coating surfaces, but it often causes decomposition of organic substrates and other coating components. An interlayer is often employed to insulate photocatalytic activity from sensitive substrate layers, complicating the application of these self-cleaning coatings. Herein, photocatalytic TiO 2 -based coatings were prepared based on an aqueous TiO 2 dispersion in a hybrid binder synthesized from tetraethyl orthosilicate and methyl trimethoxy silane via a sol-gel process. Coatings with various levels of nano TiO 2 were prepared and found to be transparent to visible light; i.e., the clear coating could be directly cast on architectural latex coatings without changing its original appearance. The photocatalytic coating system was composed of a TiO 2 -based clear top coat and an opaque latex film underneath. The coatings were evaluated through outdoor exposure studies and accelerated weathering tests. Results of these tests showed that the photocatalytic coatings with a TiO 2 content range of 33–45% exhibited excellent self-cleaning performance, while displaying none of the expected degradation. In fact, this nano TiO 2 -based clear coating actually protected the latex film from UV-induced damage. The increased stability of the organic film may have resulted from reduced UV transmission through the photo-catalyst containing clear coat as well as reduced water permeability. It was demonstrated that the combination of appropriate TiO 2 content and a suitable binder are crucial for the fabrication of robust photocatalytic self-cleaning coatings for painted surfaces without the need for an interlayer.

Graphene-based masterbatch obtained via modified polyvinyl alcohol liquid-shear exfoliation and its application in enhanced polymer composites

A simple and inexpensive method for the production of graphene-based masterbatch via polymer-assisted shear exfoliation of graphite in water was comprehensively investigated. In detail, a modified polyvinyl alcohol (mPVOH) characterized by surface energy comparable with that of graphene was used as surfactant for the production of graphene-like particles. The proposed approach allowed a yield in graphene-like particles higher than that obtained by using common surfactants, along with a narrower size distribution. A mPVOH-masterbatch containing 4.38wt% of graphene-like particles was produced by removing the aqueous solvent from a dispersion and directly used for production of polymer nanocomposites by melt processing. Films prepared by blending the masterbatch with polyvinyl alcohol in order to have a graphene-like particles content equal to 0.3wt% showed a 78% reduction in water permeability and a 48% increase in storage modulus as compared with pristine polymers. Improved barrier properties were also observed for polylactic acid (PLA) and low-density polyethylene (LDPE)-based composite films, whereas an increment of about 520% in the storage modulus was observed for the composite obtained with PLA. The obtained results are very relevant and the proposed process will open up a new pathway for using graphene-based masterbatch in the packaging industry.

Mortar crack repair using microbial induced calcite precipitation method

An experimental investigation has been carried out to repair pre-existing cracks in mortar using the microbiologically induced calcium carbonate precipitation (MICP) technology. In the study, 20 cylinder mortar samples (50 mm in diameter and 40 mm in height) were split to have cracks with various sizes. Sixteen of the cracked samples, an average width ranging from 0.15 to 1.64 mm, were repaired using the MICP method, while four cracked samples, with an average width ranging from 0.17 to 1.72 mm, were soaked under distilled water. The water permeability and splitting tensile strength (TS) of these repaired mortars were tested. The amounts of calcium carbonate (CaCO3) precipitated on the cracked mortar surfaces were evaluated. The morphology of the CaCO3 was observed under a scanning electron microscope (SEM). The results indicated that the MICP repair technique clearly reduced water permeability of the cracked samples. While water-treated samples were too weak to test, the MICP-repaired samples had TS ranging from 32 to 386 kPa after 21 cycles of MICP solution treatment. A relationship between the TS and amount of CaCO3 precipitated was observed for samples with an average crack width between 0.52 and 1.1 mm, which indicated that TS increased with the amount of CaCO3 precipitated on the crack surfaces. The SEM revealed that the precipitated CaCO3 had possibly two forms: vaterite and calcite.

Application of carbonate precipitating bacteria for improving properties and repairing cracks of shotcrete

Shotcreting is a construction technique commonly used in many civil and mining engineering applications. Cracking is an unavoidable and inherent weakness of most cement-based construction materials including shotcrete. In this study, the effect of Bacillus Subtilis on healing and mechanical properties of shotcrete was evaluated. For this purpose, bacteria were introduced into mix design and curing solution in order to examine the effect of each approach on the compressive strength, tensile strength, permeability, porosity and healing of shotcrete specimens. The results of uniaxial compressive test showed up to 30% increase in the compressive strength of bacteria-exposed shotcrete specimens compared to control specimens. This strength improvement was 10% more in shotcrete specimens than in the conventional cast concrete specimens with the same mix design. The presence of bacteria, both in the mix design and curing solution, was found to enhance the tensile strength and decrease the water absorption and porosity of shotcrete. The maximum reduction in water permeability at 28days was observed in the specimens cured in the bacteria-containing solution. The ability of bacteria to heal the cracks created in the specimens was also evaluated in the present work. Bacterial precipitation of calcium carbonate in the pores of specimens was confirmed by SEM/XRD analysis. The results give clear evidence supporting the utility of calcium carbonate precipitating bacteria for healing the cracks and improving the durability of shotcrete.

Small Diameter Vascular Grafts Coated with Gelatin

In the field of tissue engineering, there is an increased demand for small diameter vascular grafts to treat peripheral vascular pathologies and ischemic heart diseases. The limited availability of suitable autogenous veins and the drawbacks related to the use of synthetic materials, such as polyethylene terephthalate (Dacron®) and expanded polytetrafluoroethylene (ePTFE), especially when they are used as substitutes for small diameter vessels, have attracted several investigators turning their attention toward the fabrication of alternative biocompatible grafts. In this study, small diameter tubular grafts (2 mm), made of poly (e- caprolactone) (PCL) and poly (glycerol sebacate) (PGS) at a ratio of 1:1 (v/v) were obtained by electrospinning. With the aim to reduce water permeability, their surface was modified by dynamic coating of gelatin at 37 °C for 1 h, followed by UV-irradiation. Thickness, fiber diameters, porosity, mass loss, fluid uptake, water permeability, gelatin release, mechanical properties, cytotoxicity, and hemocompatibility of gelatin-coated electrospun scaffolds (GCS) were studied and compared with uncoated scaffolds (UCS). Scanning electron microscopy (SEM) images showed that the gelatin surface modification did not affect the 3D structure and pore interconnectivity of the scaffolds. A significant decrease in the water permeability was noticed when gelatin was used as coating agent. The results of this study highlighted the importance of a very low cost surface treatment with gelatin to improve the properties of PCL:PGS electrospun grafts. In conclusion, these gelatin-coated prostheses could be considered as a good candidate for vascular replacement in tissue engineering.

Evaluation of Water Permeability in Fibre Reinforced Hydraulic Lime Mortar Intended for Conservation

Much of the existing water infrastructure across the world was constructed using masonry in the last 200 years and many of these structures were built with pre-Portland cement binders. Although these mortars exhibit good workability and high water retention in the plastic state, the water tightness deteriorates over the years resulting in a pressing need for suitable repair materials. The addition of polypropylene micorfibre in cement-based systems was found to be effective in reducing water permeability. But the effect of polymeric fibres on the permeability coefficient of hydraulic lime mortar (HLM) is unknown. Therefore, this paper focuses on measuring water permeability in fibre reinforced HLM. Besides, this study examined the application of nanolime onto the aforementioned mortars and its effect on their water permeability. Accordingly, a permeability cell was setup to monitor the onset of the steady state condition in fluid flow. Companion data was generated for the mechanical performance of these mortars. The results show that in hydraulic lime mortar, there is likely an optimal fibre dosage in order to reduce the permeability coefficient. Unlike with Portland cement mortar, this dosage is significantly lower. As well, applying nanolime was most beneficial in limiting water permeability in the natural hydraulic lime mortars.

Effect of hydrate nucleation mechanisms and capillarity on permeability reduction in granular media

AbstractA model for water permeability reduction in hydrate‐bearing sediments is presented by considering capillary effect in hydrate nucleation. Both grain‐coating and pore‐filling cases are considered. The model is developed from a series of lattice Boltzmann flow simulations. Results show that the permeability decreases quasi‐linearly with increasing hydrate saturation during grain‐coating nucleation and that the permeability tends to be higher than predicted by previous analytical models, in which capillarity is not taken into account. The permeability follows unique reduction curve and is not so sensitive to initial sediment bulk density and grain size distribution. Simulations further show that there is a transition zone at Shyd = 0.3~0.4, where permeability reduction trend switches from grain‐coating model to pore‐filling model. Analyses of tortuosity and surface area confirm that the permeability reduction mechanisms result from pore‐channel blocking in grain‐coating case and pore size reduction in pore‐filling case.

Performance evaluation of optimized preformed particle gel (PPG) in porous media

Preformed particle gels (PPGs) are used as conformance control agents to improve oil production and control excess water production. This paper talks about optimized PPGs that are designed for high-temperature and high-salinity oil reservoirs and their synthesize process. The influence of cross linker concentration, size of dry PPGs, injection rate, temperature, permeability, and brine salinity on resistance factor (RF) and residual resistance factor (RRF) of PPG in porous media are investigated. The focus of study is to see how PPGs would perform in porous media by creating flow resistance to injected fluid, hence enhancing the sweep efficiency. A set of 51-cm slim tubes packed with carbonate cores from one of the Iranian oil reservoir is used to evaluate the performance of optimized PPG at wide range of different temperatures and permeabilities.PPG injection pressure increases with cross linker concentration, PPGs particle size, and brine concentration and injection flow rates but decreases with the increase of permeability and temperature during PPG injection. It was shown that increased injection rate does not increase PPG injection pressure to the same level and the reduction in water permeability caused by swollen PPG prepared in high salinity brine is higher than that prepared in low salinity brine. Synthesized PPGs can also change the permeability of different slim tubs to the same level. Resistance factor (RF) and residual resistance factor (RRF) increase with the increase in PPGs particle size, brine salinity and cross linker concentration. But, they decrease with the increase of temperature and the flow rate. Initially RRF increased gradually as the permeability of slim tubes decreased from 395 to 137Darcy but a sharp increase in RFF caused by swollen PPG in low permeability slim tube was observed.

Low-Fouling Antibacterial Reverse Osmosis Membranes via Surface Grafting of Graphene Oxide.

Azide-functionalized graphene oxide (AGO) was covalently anchored onto commercial reverse osmosis (RO) membrane surfaces via azide photochemistry. Surface modification was carried out by coating the RO membrane with an aqueous dispersion of AGO followed by UV exposure under ambient conditions. This simple process produces a hydrophilic, smooth, antibacterial membrane with limited reduction in water permeability or salt selectivity. The GO-RO membrane exhibited a 17-fold reduction in biofouling after 24 h of Escherichia coli contact and almost 2 times reduced BSA fouling after a 1 week cross-flow test compared to its unmodified counterpart.

Effect of Cattle Grazing Routine on Erosion Processes, Harvest Yield and Quality of Fodder in Subalpine Belt of North Ossetia

Background/Objectives: The research is aimed at studying the effect of the pastureland use routine on altering the indicators of the soil fertility and on the erosion process development. Methods/Statistical Analysis: The studies were conducted in the mountains at an altitude of 1570 m above sea level on the mountain meadow subalpine soils with acidic reaction of soil solution (рН=5,9). The chemical analyses of the average runoff sample and that of the washout sample were carried out to determine the contents of the accessible forms of such nourishing elements as nitrogen, phosphorus and potassium. Findings: This study shows that in the middle of the last century a significant amount of agricultural products were produced in the North Caucasus Mountains; this output was significantly reduced due to soil erosion caused by poorly plant-protected surface and livestock congestion. Erosion leads to dispersion of soil horizon structure, megastructure reduction and increase in dust, it also results in increased soil specific weight and solid phase unit weight, in decreased air and capillary porosity with reduction of aggregate water stability and water permeability. In the absence of grazing, the total losses of nitrogen, phosphorus and potassium amounted to 7.84 kg/ha and 296.56 kg/ha with intensive pasturing, which was higher by 37.8 times. With the admissible levels of grazing intensity no reliable data for the productivity alteration was obtained, and in the grazing routine modes of 2/15, 3/10, 3/15 a decrease in the productivity was established. Grazing lowers the grass stand quality, while increasing the proportion of fiber, fat and ash. The yield of nutritional chemicals per 1 hectare increased under optimal grazing conditions and decreased under intensive grazing routines. Applications/Improvements: Recommendations for cattle grazing routines have been developed with regard to degraded and normally functioning pasturelands. It is proposed to avoid excessive grazing routines

Polymersome Membrane Permeability and Ionic Transport Properties in the Presence of Sub-2nm Carbon Nanotube Porins

Synthetic diblock and triblock copolymer membranes are semi-permeable barriers that are capable of self-assembly into tunable membranes, which have contrasting mechanical properties from biologically derived and synthetic lipid bilayers. These thick and “robust” polymer membranes are typically thicker and have significantly reduced water permeability compared to lipid bilayers. These properties make them valuable alternative membranes for applications requiring exposure to physical stresses such as biosensors, drug delivery, and filtration. Previous attempts to engineer the permeability of these membranes included insertion of protein channels to improve permeably, (eg. Aquaporins), changing the polymer constituent to an inherently leaky polymer (eg. polystyrene-b-polyisocyanoalanine(2-thiophene-3-yl-ethyl)amide (PS-PIAT)), and removal of lipids from a mixed lipid-polymer vesicle following cross-linking and hydrolysis. We report a new strategy for improving permeability of polymer-membranes, based on incorporation of carbon nanotube porins into the polymer matrix. These short CNT pores exhibit the excellent transport properties inherent to carbon nanotubes, but are small enough that they can be easily incorporated into the membrane essentially acting as protein channel mimics. Here, we examine the permeability of diblock co-polymer membranes with and without these CNT pores and report the enhancement of permeability and ion transport characteristics of these novel membrane constructs.

In Situ Test of Grouting Reinforcement for Water-Enriched Sandy Gravel Ground in River Floodplain

The performance of the ground treatment is always critical for a tunnel excavated in unstable stratum. Laodongnanlu Xiangjiang Tunnel (Changsha, China) across the Xiangjiang River will be constructed in a sandy gravel ground which is characterized by loose structure, extensive porosity, elevated sensitivity, poor stability, and a high groundwater table. Permeation grouting will be employed to improve the bearing capacity and mitigate groundwater movement into the excavation. In order to seek suitable injection parameters and grouting method, a field trial of vertical grouting was conducted in the sandy gravel stratum in river floodplain. A series of tests focusing on grout material, grouting sequence of boreholes, injection pressure, and grouting volume were performed to improve the sandy gravel mass strength and reduce water permeability. The examination of the results obtained during water pressure testing and core drilling on completion of the grouting trial successfully demonstrated that the specified injection criteria had led to an expected effect. Grouting control method of this saturated sandy gravel stratum was concluded after the test, which would contribute to the future pregrouting work during the tunnelling.

Study of a Novel Self-Thickening Polymer for Improved Oil Recovery

The utilization of self-thickening polymer (STP) in conformance control was first investigated. Results show that these STP solutions exhibit an increase in viscosity (even like gel) under certain conditions. The optimized application conditions of this novel STP are as follows: mass concentration, 0.25–0.30 wt %; salinity, 4.0–8.0 wt %; and temperature range, 40–70 °C. Environmental scanning images demonstrate that a clear and solid skeleton network structure is formed and the higher the salinity of the brine, the more compact the three-dimensional (3D) network structure. In addition, in-depth flow diversion and water permeability reduction were the main mechanisms of water shut-off treatment for improved oil recovery in oil displacement experiments. Finally, this novel STP with the ability to create a gel-like system is cost-competitive, simpler to apply, and more environmentally friendly than the current polymer–cross-linker system. It provides an alternative candidate for conformance control treatment...

Experimental study of water shutoff gel system field parameters in multi-zone unfractured gas-condensate reservoirs

Excess water production during gas production causes serious operational problems and, may shutoff the wells. Polymer gel is one of the water shutoff (WSO) methods extensively used in mature gas fields in the recent years. In this research, Cr (III)-acetate sulfonated polyacrylamide hydrogels were applied in porous media with radial flow. In order to obtain gel treatment conditions with desirable performance, some sandpack-flooding tests were designed. By statistical design of the experiments using central composite, the sandpack-flooding tests were conducted to investigate the effect of gel penetrated area and reservoir porosity on the WSO efficiency. The results showed that lower gel penetrated depth led to lower gas-condensate permeability reduction and, the utmost reduction of water permeability was in a critical depth of gel penetration. In optimum conditions, a gel penetration of 0.96 cm and a porosity of 31.46% had RRFg (gas-condensate residual resistance factor) of 1.83 and RRFW (water residual resistance factor) of 5510, respectively. Some tests through multi-zone sandpacks were carried out to examine the effect of layers with different porosities and crossflow presence. Multi-zone sandpacks with crossflow between the gas-condensate and water-producing zones showed RRFW in a range of 28.2–244.7. However, the selectivity increased from 90 to 99.9% without crossflow. It was found that the chance of successful WSO treatment increases when the higher permeable layers are over the lower permeable layers.

Combined effect of Polypropylene fibers and Silica Fume to improve the durability of concrete with natural Pozzolans blended cement

Early age shrinkage and cracking, water permeability and carbonation depth of concretes with natural Pozzolans blended cement (NPC) were investigated in order to assess the combined effect of Polypropylene short fibers (PPF) and Silica Fume (SF) on some durability parameters.The addition of 10% of SF increased compressive strength, shrinkage and cracking, permeability and carbonation depth. But, the combination of 10% SF and 0.07% PPF volumetric fraction mitigated early age cracking and significantly reduced water permeability and carbonation depth.The use of PPF in NPC concrete combined with SF can be recommended to reduce long-term impact of early age cracking, and enhance durability. However, cement should not be reduced when SF is added to mixtures without PPF, because lower CaO reserves may affect final pH, leading to concretes more sensible to carbonation.

Vasopressin receptors V1a and V2 are not osmosensors.

Herein, we investigated whether G protein-coupled signaling via the vasopressin receptors of the V1a and V2 subtypes (V1aR and V2R) could be obtained as a direct response to hyperosmolar challenges and/or whether hyperosmolar challenges could augment classical vasopressin-dependent V1aR signaling. The V1aR-dependent response was monitored indirectly via its effects on aquaporin 4 (AQP4) when heterologously expressed in Xenopus oocytes and V1aR and V2R function was directly monitored following heterologous expression in COS-7 cells. A tendency toward an osmotically induced, V1aR-mediated reduction in AQP4-dependent water permeability was observed, although osmotic challenges failed to mimic vasopressin-dependent V1aR-mediated internalization of AQP4. Direct monitoring of inositol phosphate (IP) production of V1aR-expressing COS-7 cells demonstrated an efficient vasopressin-dependent response that was, however, independent of hyperosmotic challenges. Similarly, the cAMP production by the V2R was unaffected by hyperosmotic challenges although, in contrast to the V1aR, the V2R displayed an ability to support alternative signaling (IP production) at higher concentration of vasopressin. V1aR and V2R respond directly to vasopressin exposure, but they do not have an ability to act as osmo- or volume sensors when exposed to an osmotic gradient in the absence or presence of vasopressin.

Post-fabrication modification of forward osmosis membranes with a poly(ethylene glycol) block copolymer for improved organic fouling resistance

Facile and effective strategies are needed to modify forward osmosis (FO) membranes for improved resistance to organic fouling. Fouling resistant FO membranes will advance the commercial implementation of FO for treating feed waters with high fouling potential, such as wastewater and brines. We report a membrane modification technique for post-fabrication grafting of a poly(ethylene glycol) (PEG) block copolymer to the surface of commercial thin-film composite (TFC) FO membranes via an amide coupling reaction. The PEG concentration for membrane modification is optimized based on increased membrane hydrophilicity and reduced water permeability that result from increasing PEG concentrations during modification. Modified membranes exhibit improved resistance to organic fouling compared to unmodified control membranes when exposed to an aggressive synthetic wastewater mixture. The fouling resistance is achieved despite the non-uniform grafting of PEG, which is attributed to the limited accessibility of carboxylic group binding sites on the membrane surface. The fouling resistance of membranes modified using this post-fabrication technique compares favorably to TFC-FO membranes modified using other procedures. The modification technique we report in this work has the advantages of being relatively inexpensive, easy to implement, and applicable to commercial membranes.