Water Vapor Sorption Capacity Research Articles

A Polyzwitterionic@MOF Hydrogel with Exceptionally High Water Vapor Uptake for Efficient Atmospheric Water Harvesting.

Atmospheric water harvesting (AWH) is considered a promising strategy for sustainable freshwater production in landlocked and arid regions. Hygroscopic salt-based composite sorbents have attracted widespread attention for their water harvesting performance, but suffer from aggregation and leakage issues due to the salting-out effect. In this study, we synthesized a PML hydrogel composite by incorporating zwitterionic hydrogel (PDMAPS) and MIL-101(Cr) as a host for LiCl. The PML hydrogel was characterized using various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and thermogravimetric analysis (TGA). The swelling properties and water vapor adsorption-desorption properties of the PML hydrogel were also assessed. The results demonstrate that the MIL-101(Cr) was uniformly embedded into PDMAP hydrogel, and the PML hydrogel exhibits a swelling ratio of 2.29 due to the salting-in behavior. The PML hydrogel exhibited exceptional water vapor sorption capacity of 0.614 g/g at 298 K, RH = 40% and 1.827 g/g at 298 K, RH = 90%. It reached 80% of its saturated adsorption capacity within 117 and 149 min at 298 K, RH = 30% and 90%, respectively. Additionally, the PML hydrogel showed excellent reversibility in terms of water vapor adsorption after ten consecutive cycles of adsorption-desorption. The remarkable adsorption capacity, favorable adsorption-desorption rate, and regeneration stability make the PML hydrogel a potential candidate for AWH. This polymer-MOF synergistic strategy for immobilization of LiCl in this work offers new insights into designing advanced materials for AWH.

Synthesis and Properties of Modified Biodegradable Polymers Based on Caprolactone.

In this paper, the synthesis and characterization of two polycaprolactone-polydimethylsiloxane (PDMS-CL) copolymers with biodegradable properties are reported. A comparative study was carried out using an aminopropyl-terminated polydimethylsiloxane macro-initiator (APDMS) with two different molecular weights. The copolymers (PDMS-CL-1 and PDMS-CL-2) were obtained by ring-opening polymerization of ɛ-caprolactone using APDMS as initiators and stannous 2-ethylhexanoate as a catalyst. The copolymer's structures were confirmed by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (1H-NMR) spectra, and energy dispersion spectroscopy (EDX). Surface morphology was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The hydrophobic properties of the copolymers were demonstrated by the water contact angle and water vapor sorption capacity. Additionally, biological tests were conducted on San Marzano type tomato plants (Lypercosium esculentum) to assess the synthesized copolymers' susceptibility to the environment in terms of biological stability and metabolic activity. The biodegradation of PDMS-CL-1 and PDMS-CL-2 copolymers does not have a dangerous effect on the metabolic activity of plants, which makes it a convenient product in interaction with the environment.

Mathematical modeling approach for the green synthesis of high-performance nanoporous zeolites Na-X optimized for water vapor sorption

A mathematical approach and green synthesis were employed to develop high-performance nanoporous zeolites with a high water vapor sorption capacity and to optimize the synthesis parameters using natural raw kaolin as the starting alumina-silicate material. The Box-Behnken design model with four factors was employed to elucidate the experimental matrix. The physicochemical and structural properties of the synthesized zeolite were characterized using XRD, FTIR, TG/DSC, 27Al and 29Si solid-state MSA NMR spectroscopy, Raman spectroscopy, FE-SEM, and N2 sorption isotherms. The obtained zeolite sample exhibited a BET surface area of 772.19 m2/g and a microspore volume of 0.16 cm3/g. The maximum water vapor uptake capacity at 25 °C and the highest relative pressure was determined to be 12.1137 mmol/g. The isosteric heat of adsorption and average entropy change were calculated to be − 41.340 KJ·K−1 and 115.308 J·mol−1·K−1, respectively. The resulting zeolite demonstrated excellent stability after five consecutive cycles of water vapor adsorption. The experimental data were fitted using five different isotherm and three kinetic models, and the accuracy of each model was assessed using error functions. GAB model and pseudo-first-order kinetic model exhibited the highest correlation coefficient. The nanoporous zeolite sample obtained through the surface response methodology is well-suited for industrial applications.

Comparison of hydration water properties of common and durum wheat brans upon grinding with different loading modes

Wheat bran brings healthy properties in food products. However, its incorporation requires a first milling step during which it is subject to various loading modes which have an influence on its properties. This study investigated the influence of the loading modes (high shear or impact) generated by grinders during the milling on the hydration properties of common and durum wheat brans. An original study at molecular scale to target the distribution and intensity of hydration water bonds was carried out by gravimetric and spectroscopic methods. Results were analyzed in regards to the particle size distribution and shape factors as well as biochemical composition to highlight the process-structure-function relationships at macro and microscales. Impact grinder has a stronger effect on water vapor sorption capacity and FTIR multimer water at 3600 cm−1 of durum wheat bran as well as a red shift in the band at 1030 cm−1 related to a high decrease in residual starch crystallinity degree (about 17%). High shear grinder tends to increase the proportion of water strongly bound. Low field NMR analysis revealed differences in the high mobility water peak and a significant lower relaxation time T2 for native and ground durum wheat bran (up to 1.7 fold less).

Edible films based on potato and quince peels with potential for the preservation of cured cheese

Edible and biodegradable films for food packaging were developed based on starch (S) and agro-industrial residues, such as potato peels (P) and/or quince (Q) peels. All films exhibited hydrophilic nature, as revealed by the swelling behavior, water contact angles, water vapor sorption capacity and water vapor permeability results. Films with quince peel were the most flexible, possibly due to the presence of sugars and pectin, that act as plasticizers. The SPQ formulation film was chosen for the proof of concept with cured cheeses, and during ripening, the edible film of the cheeses was evaluated, as well as the sensory characteristics and acceptability of the cheeses by consumers. The developed film increased cheese hardness, when compared to the control and to cheeses coated with natamycin. Moreover, the film did not change the sensory properties of the cheeses, being a promising film for application in this type of food product.

Influence of the cellulose purification process on the properties of aerogels obtained from rice straw

Cellulose aerogels were obtained from purified rice straw cellulose fibres (CF) by applying different extraction methods: the conventional alkaline treatment (ALK) and alternative aqueous extraction based on the ultrasound combined with reflux heating (USHT) and subcritical water extraction (SWE) (160 and 180 °C). The composition and properties of the CFs were significantly affected by the purification process. The USHT treatment was as efficient as the ALK at eliminating the silica content, but the fibres maintained a notable ratio of hemicellulose (∼16 %). The SWE treatments were not so effective at removing silica (15 %) but greatly promoted the selective extraction of hemicellulose, especially at 180 °C (3 %). The CF compositional differences affected their hydrogel formation capacity and the properties of aerogels. A higher hemicellulose content in the CF led to better-structured hydrogels with better water-holding capacity, while the aerogels exhibited a more cohesive structure with thicker walls, higher porosity (99 %) and water vapour sorption capacity, but lower liquid water retention capacity (0.2 g/g). The residual silica content also interfered with the hydrogel and aerogel formation, giving rise to less structured hydrogels and more fibrous aerogels, with lower porosity (97–98 %).

Biomaterials Based on Chitosan and Polyvinyl Alcohol as a Drug Delivery System with Wound-Healing Effects

The excellent biological properties of chitosan (CS) together with the increased oxygen permeability of polyvinyl alcohol (PVA) were the prerequisites for the creation of a wound healing dressing that would also function as a system for L-arginine (L-arg) and caffeine (Caff) delivery. Using the freezing/thawing method, 12 hydrogels were obtained in PVA:CS polymer ratios of 90:10, 75:25, and 60:40, and all were loaded with L-arg, Caff, and the mixture of L-arg and Caff, respectively. Afterwards, an inorganic material (zeolite-Z) was added to the best polymeric ratio (75:25) and loaded with active substances. The interactions between the constituents of the hydrogels were analyzed by FTIR spectroscopy, the uniformity of the network was highlighted by the SEM technique, and the dynamic water vapor sorption capacity was evaluated. In the presence of the inorganic material, the release profile of the active substances is delayed, and in vitro permeation kinetics proves that the equilibrium state is not reached even after four hours. The synergy of the constituents in the polymer network recommends that they be used in medical applications, such as wound healing dressings.

Earthen construction materials as enabler for circular construction

The construction sector in Germany is one of the largest contributor to climate change. The majority of waste generation, resource consumption as well as CO2 emissions relate to the construction and operation of buildings [1][2][3]. In order to tackle such negative impacts, the construction industry has to undergo a major transformation. Circular construction is the most promising answer to close effectively material cycles and to reduce CO2 emissions related to the manufacturing of construction materials. Stakeholders involved in construction have to review the entire life cycle of building products and buildings and develop new approaches that address such shortcomings to turn the linear way of construction into a circular one. Nowadays the strong focus on economic considerations, lacking knowledge as well as unresolved warranty issues amongst others impede this transformation process. To demonstrate the benefits of earthen materials with regards to circular construction, this study analyses the potential of two different internal partition wall systems, based on earthen as well as conventional building materials in a holistic way. Several aspects have been taken into consideration, evaluated through the physical dismantling of both wall systems as well as a LCA assessment. Construction cost as well as other material benefits, such as the hygroscopic performance of construction materials have been investigated as well. The results demonstrate that earthen materials reduce both, construction and demolition waste as well as CO2 emissions and demonstrate a much higher water vapour sorption capacity, a material parameter relevant for the reduction of mechanical ventilations systems. Although the economical assessment shows expectable lower construction cost for the wall system based on conventional materials such figures have to be placed in relation with the other results. In fact, the analysis demonstrates clearly that a holistic approach is needed in order to achieve the necessary shift.

Salting-in Effect of Zwitterionic Polymer Hydrogel Facilitates Atmospheric Water Harvesting

Hygroscopic salt-hydrogel composite sorbents have attracted increasing attention for atmospheric water harvesting (AWH) applications but suffer from the salting-out effect. To this end, this work, for the first time, discovers that the salting-in effect possessed by a zwitterionic hydrogel is able to facilitate water vapor sorption by the hygroscopic salt under otherwise the same conditions. For demonstration, zwitterionic hydrogel of poly-[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (PDMAPS) was synthesized, and the hygroscopic salt of LiCl was embedded into PDMAPS to produce the salt-hydrogel composite. LiCl salt not only endows the sorbent with high water vapor sorption capacity but also facilitates the dissociation of self-association between cationic and anionic groups of PDMAPS. This salting-in effect was evaluated and confirmed experimentally and via density functional theory (DFT) calculation. The salting-in effect renders the zwitterionic hydrogel matrix with enhanced swelling capacity, leading to the sorbent’s high AWH performance. With a photothermal component of CNT integrated into the sorbent, a fully solar energy-driven AWH process was demonstrated outdoors. This study provides important guidance to the design of hydrogel-based AWH sorbents.

Analysis of Spontaneous Ignition of Grass: Chemical Oxidation and Water Vapor Sorption

Self-heating of biomass by chemical oxidation, which can cause spontaneous ignition, is a safety and management concern. This process can be accelerated by aerobic fermentation and water vapor sorption. The chemical oxidation and water vapor sorption of grass were studied in a laboratory oven, measuring the variations in weight and the internal temperature of a sphere with grass within a flexible polymeric network. Both processes were simulated to prove that the proposed mathematical model could fit the experimental data. It was observed that the water vapor sorption capacity of the grass was high, so the experimental increase in the internal temperature of a spherical body was around 47 K, from 73°C to 120°C. This fact can be very important because the chemical oxidation of grass accelerates at high temperatures. For scaling, simulation programs were used to study the sorption and oxidation processes with an increase in internal temperature in spherical bodies and infinite plane slabs. These results can be used to obtain those of other geometric symmetries by interpolation. It was deduced that at 70°C and with vapor sorption, the ignition time can be around 3 days to 5 days, while without vapor sorption, the ignition times can be around 110 days to 140 days. For 35°C the ignition times with vapor sorption can be around 12 days to 18 days, while without vapor sorption the ignition times can be around 3700 days to 4500 days. These results can be of interest for warehouses of similar biomass and for forestry research and management groups of wildfires.Graphical

Study on highly thermostable low‐k polymer films based on fluorene‐containing polyetherimides

AbstractHighly thermostable low‐k polymer films with potential applications as dielectric materials in microelectronic industry were synthesized starting from 9,9‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]fluorene dianhydride and various diamines. A polyetherimide/silica nanocomposite film was obtained using methyltriethoxysilane as precursor of inorganic phase. The chemical structure was confirmed by FTIR and 1H NMR spectroscopy. Water vapor's sorption capacity, thermal stability, glass transition temperature, thermal diffusivity, specific heat, thermal conductivity, and dielectric characteristics of the films were determined. All the films exhibited excellent thermal stability, with an initial decomposition temperature in the range of 500–530°C. They showed low dielectric constant of 1.98–2.86 and low dielectric loss of 0.0037–0.011, at a frequency of 1 Hz and room temperature. The subglass γ‐ and β‐relaxations, primary α‐relaxation, and conductivity relaxation processes were discussed according to the chemical structure of the samples. Quantitative structure–property relationship (QSPR) study was conducted, and linear regression models were formulated to describe the causal relationships between different parameters and polyetherimide properties.

Design of Chitosan and Alginate Emulsion-Based Formulations for the Production of Monolayer Crosslinked Edible Films and Coatings.

This study aimed to develop edible monolayer emulsion-based barriers with polysaccharides as film-forming components (chitosan and sodium alginate), soy lecithin as a surfactant and olive oil as a hydrophobic barrier. Monolayer barriers in the form of films were prepared by casting filmogenic emulsions composed of 2% w/v chitosan (dissolved in lactic acid 1% v/v) or 1% w/v sodium alginate, with different lipid contents (25, 50 and 100% w/w biopolymer basis) and different surfactant concentrations (5, 10 and 25% w/w, lipid basis). Glycerol was used as a plasticizer (25 % w/w, biopolymer basis). After the emulsion drying process, the obtained stand-alone films were sprayed with a crosslinking solution, achieving an optimized crosslinker content of 3.2 mgCa2+/cm2 alginate film and 4 mg tripolyphosphate/cm2 chitosan film. The effect of oil and lecithin contents, as well the presence of crosslinking agents, on the film’s water vapour permeability (WVP), water vapour sorption capacity, mechanical properties and colour parameters, was evaluated. The results have shown that the lowest WVP values were obtained with formulations containing 25% lipid and 25% surfactant for chitosan films, and 100% lipid and 25% surfactant for alginate films. The application of the crosslinking agents decreased even further the WVP, especially for chitosan films (by 30%). Crosslinking also increased films’ resistance to deformation under tensile tests. Overall, the films developed present a good potential as polysaccharide-based barriers with increased resistance to water, which envisages the use of the designed formulations to produce either edible/biodegradable films or edible coatings.

POLY(VINYLPYRROLIDONE)-CHITOSAN HYDROGELS AS MATRICES FOR CONTROLLED DRUG RELEASE

In this study, hydrogels based on poly(vinylpyrrolidone) and chitosan, derived from different mixing ratios of poly(vinylpyrrolidone)/chitosan, were synthesized by the freeze-drying technique with the aim of obtaining new systems that could be used to release tetracycline hydrochloride (TH). Freeze-drying methods were also used to prepare the hydrogels containing TH. The hydrogels were characterized using Fourier transform infrared spectroscopy and scanning electron microscopy, as well as in terms of dynamic water vapour sorption capacity. The poly(vinylpyrrolidone)/chitosan hydrogels were evaluated with regard to the release of TH. The release profiles of TH from the poly(vinylpyrrolidone)/chitosan hydrogels depended on the chitosan content. It could be seen that if the concentration of chitosan was too high, the release was delayed and not fully achieved, because the release of the drug was prevented by the crystalline areas of the chitosan. According to the release study, the drug release mechanism of the poly(vinylpyrrolidone)/chitosan hydrogels loaded with TH perfectly fitted the Higuchi and the Korsmeyer-Peppas models. The highest value of water vapor sorption capacity was obtained for the hydrogel with the poly(vinylpyrrolidone)/chitosan ratio of 50/50. PVP-CS loaded with 3 wt% TH may potentially be used for the controlled delivery of tetracycline to treat oral infections.

Moss-dominated biocrusts enhance water vapor sorption capacity of surface soil and increase non-rainfall water deposition in drylands

Surface soil vapor sorption and non-rainfall water (NRW) deposition are important sources, and can be highly influential in soil water dynamics and biochemical processes in drylands. As an important living skin, biocrusts have great impacts on soil water balance and play a vital role in water transport at near surface soil, while it remains unclear how biocrusts affect soil water vapor sorption and NRW deposition. In this study, we analyzed and modeled the water vapor sorption isotherms (WSIs) of moss-dominated biocrusts and uncrusted surfaces on loess soil and aeolian sand in the Chinese Loess Plateau. Furthermore, the actual NRW deposition amount of the biocrusts and uncrused soil in field was continuously measured across ~4 months in summer. Our results showed that the vapor sorption amount of the biocrusts was increased by up to 130.5% on the loess and 157.1% on the aeolian sand, and soil vapor sorption capacity of the biocrusts was mostly attributed to their higher contents of fine particles (clay and silt) and organic matter, and the moss morphology in comparison to the uncrusted soil. The Guggenheim-Anderson-de Boer (GAB) model performed well (R2 > 0.97, RMSE < 0.0005 g g−1, E < 13.2%) in simulating WSIs of each treatment. Moreover, the biocrusts enlarged the hysteresis effects by > 23.1%-200.0% as compared with the uncrusted soil at 0–10 cm depth. Additionally, the daily NRW amount of the biocrusts was increased by 19.2% on loess soil and 22.0% on aeolian sand, respectively, which means that the biocrusts significantly increased the NRW deposition capacity at 0–10 cm depth (F ≥ 11.12, P < 0.001). Lastly, the surface soil temperature of the biocrust layer was averagely 1.0–2.3 °C higher than that of the uncrusted soil during daytime, indicating that the biocrust layer enlarged the daily soil temperature differences between the crusted and uncrusted soils, and consequently increased the hourly NRW amount. In conclusion, this study demonstrates the important effects of biocrusts in improving vapor sorption capacity and NRW deposition of surface soil, and these properties in return would further generate feedback impacts on surface soil water and heat balances, enhancing microbial activity within the soil profile and nutrient adsorption from NRW in drylands.

The impact of wheat (Triticum aestivum L.) bran on wheat starch gelatinization: A differential scanning calorimetry study

The effect of wheat bran on starch gelatinization temperature was investigated. Dynamic water vapour sorption and water retention capacity experiments showed that bran bound up to 3 times more water than starch. However, examining starch gelatinization in starch-bran-water mixtures with differential scanning calorimetry showed that the effect of substituting starch by bran differed from that of moving into a regime of limiting water. Modelling the effect of the mixture composition on starch gelatinization behavior indicated that the onset (To) and peak (Tp) gelatinization temperatures were positively impacted by the bran concentration in water. The conclusion temperature (Tc) was negatively affected by the water content. Fractionation experiments demonstrated that the increased To and Tp were mainly caused by the extractable wheat bran components, such as potassium and phosphorus, which decrease the plasticization capacity of the solvent. The mechanism behind our observations was explained with the side-chain liquid-crystalline polymeric model for starch.

Polyimide/Ionic Liquid Composite Membranes for Middle and High Temperature Fuel Cell Application: Water Sorption Behavior and Proton Conductivity.

Four water insoluble room-temperature protic ionic liquids (PILs) based on the N-alkylimidazolium cation with the alkyl chain length from 1 to 4 and bis(trifluoromethylsulfonyl)imide anion were synthesized and their chemical structure was confirmed by the 1H NMR and 19F NMR analysis. PILs were revealed to be thermally stable up to 360 and 400 °C. At the same time, the proton conductivity of PILs was found to be dependent mostly on the temperature and, to a less extent, on the type of the cation, i.e., the increase of the conductivity from ~3 × 10−4 S/cm at 25 °C to 2 × 10−2 S/cm at 150 °C was observed. The water vapour sorption capacity of PILs was evaluated as a function of relative humidity and the influence of the alkyl chain length on the phase behaviour in the PIL-water system was discussed. The composite polyimide/PILs membranes were prepared by the PIL immobilization in the porous polymer (Matrimid® 5218) film. The composite membranes showed a high level of proton conductivity (~10−3 S/cm) at elevated temperatures (up to 160 °C). The obtained results reveal that the elaborated composite polyimide/PIL membranes are promising candidates for the application as proton exchange membrane at middle and high temperatures.

The effect of triethyl citrate on the dispersibility and water vapor sorption behavior of polylactic acid/zeolite composites

The aim of this study was to investigate the water vapor adsorption behavior and mechanical properties of poly (lactic acid) (PLA)/zeolite (5, 10, or 15 phr) composites prepared with triethyl citrate (TEC; 20 phr) via a melting process. TEC was used to improve the flexibility of the PLA and the dispersibility of the zeolite in TEC-zeolite suspensions that were ultra-sonicated. It was found that zeolite was uniformly dispersed in the PLA matrix, and the interfacial adhesion between the PLA matrix and zeolite was enhanced by TEC. In addition, the tensile strengths and Young's modulus of the composites improved with increasing zeolite content. The PLA/zeolite composites prepared with TEC had increased water vapor permeability and contact angles compared to neat PLA and standard PLA/zeolite due to the presence of TEC. In particular, TEC accelerated the hydrolysis of the PLA surface in a high humidity environment, resulting in an improvement in water vapor sorption capacity. At the same zeolite content of 15 phr, the equilibrium moisture content (EMC) values of PLA/zeolite films prepared with TEC increased by up to 39.25 mg/g whereas those prepared without TEC only increased by up to 24.33 mg/g. The results suggest the possibility of applying PLA/zeolite films prepared with TEC as a flexible active packaging material.

Durability of hemp concretes exposed to accelerated environmental aging

This study examines the evolution of the functional properties of two hemp concretes formulated with two different binders over 2 years in different environmental conditions. Stable environmental conditions (50% RH - 20°C) have been applied to hemp concretes to obtain the reference aging AREF. An accelerated aging process AWD is chosen, consisting of cycles of wetting and drying. In relation to the reference aging, no significant variation of the chemical, microstructural and functional properties is observed, whether in terms of the thermal, acoustic, hydric or mechanical behavior. During accelerated aging, variations of properties are observed: an increase of thermal conductivity, and water vapor sorption capacity for both binders and a decrease of acoustic performance for the lime-based binder. No variation of mechanical properties is observed. These results are linked to alterations of the chemical and microstructural properties: hydration and carbonation of the binder, mineralization, swelling and shrinkage and consumption of vegetal walls by micro-organisms. By comparing these results with measurements carried out under real conditions, this work shows that the performance of hemp concretes should remain stable for several years.

Porosity, thickness distribution and water vapour sorption of thermoformed foamed PP films with dispersed sodium chloride for humidity regulation

Abstract Packaging materials containing certain salts can regulate the humidity of packaged products. This study investigated whether thermoforming of foamed monolayer PP films with dispersed NaCl increases the water vapour sorption capacity and rate. Foamed monolayer PP-films (thickness 630 μm, porosity 0.28) with 6 (g/100 g) dispersed NaCl crystals were thermoformed to cups with depths up to 90 mm. By thermoforming the porosity increased up to 0.63 and the effective water vapour diffusion coefficient elevated by one order of magnitude from 10−11 to 10−10 cm²∙s−1. Therefore, such films absorb and desorb water vapour with a higher rate and they can bind more salt solution which is formed from solid salt crystals by water vapour absorption. Our results are important for packaging producers who thermoform films to cups and trays. This study addresses markets for fresh produce and other products with a high water activity.

Versatile poly(vinyl alcohol)/clay physical hydrogels with tailorable structure as potential candidates for wound healing applications.

Physical poly(vinyl alcohol) (PVA) hydrogels containing up to 3% Laponite RD (LRD) were obtained by freezing/thawing method. The structure and the morphology of PVA/LRD hydrogels were evaluated by ATR-FTIR and SEM measurements, respectively. The morphological analysis of the hydrogels revealed the formation of clay agglomerates and large size aggregates at LRD concentrations above 2.5%. The rheological and mechanical properties of the PVA hydrogels in presence/absence of clay and their structural regeneration capacity after a large deformation were also investigated. The effect of LRD incorporation on the swelling behavior of the PVA hydrogels was discussed. The water vapor sorption capacity of PVA hydrogels decreases by clay addition. The analysis of in-vitro rifampicin release data indicated that the presence of a small amount of LRD into hydrogel affects the drug release mechanism. The antimicrobial activity of PVA hydrogels in presence/absence of LRD loaded with rifampicin against Staphylococcus aureus, Escherichia coli and Candida albicans was studied.