Search

Due to the high use and misuse of antibiotics over the years, microbes have developed resistance to a significant number of drugs (so-called antimicrobial resistance - AMR) [1]. Therefore, the necessity for the development of natural antimicrobial agents to overcome growing bacterial resistance against synthetic antibiotics has been recognized. Thymol is a natural monoterpenoid, with proven anti-inflammatory, antioxidant, and antimicrobial properties and it has been recognized as safe by the FDA (it has GRAS status). With the aim to fabricate material with antibacterial activity, supercritical solvent impregnation (SSI) was applied for loading of commercial PLA-based absorbable surgical sutures with thymol in a green medium, supercritical CO2. Operating temperature and pressure were set to 35 °C and 10 MPa, while contact time was varied between 1 and 6 h. The SSI process was performed under mild processing parameters to obtain an effective amount of loaded thymol against tested bacteria keeping in mind the recommended safe content of thymol for human blood cells (in terms of cytotoxicity and mutagen effect) [2]. Selected process conditions enabled thymol loadings of 3.9–5.6% (Fig. 1) [3]. SEM analyses was used to monitor sutures' morphological change from swelling to agglutination induced by the increased amount of thymol in the material. ...

Aerogels are materials with high specific surface area and high porosity, which can be produced from polysaccharides such as starch [1,2]. Starch is an abundant and low-cost polymer with versatility in processing. Aerogel properties are influenced by the process parameters including starch-to-water ratio, gelatinization temperature (T), selection of non-solvent for water replacement in hydrogels, selection of drying method, drying pressure (P) and T, etc. [1,2]. Supercritical drying, which employs supercritical carbon dioxide (scCO2), is an environmentally friendly process that allows relatively fast production of aerogels. Despite the superior properties of starch aerogels, they do not express biological activity. This can be overcome by the incorporation of bioactive compounds (BCs) into aerogels using the supercritical impregnation (SCI) process [3,4]. SCI implies the dissolution of BCs in scCO2, diffusion of BC-scCO2 solution into a polymer matrix, possible chemical or physical interaction of BC with polymer, and complete removal of scCO2 from the BC-polymer after a decrease of P and T to atmospheric. This process allows one-step production of solvent-free added value materials at relatively low T and the incorporation of high amounts of BC with various biological activities. Aerogels can be impregnated with pharmaceutical drugs but also with natural BCs (single or mixture) such as plant extracts [3,4]. To produce aerogels, 10 g of cornstarch (amylose content 20−30%, HeMoss, Serbia) was mixed with 100 mL of distilled water, gelatinization T was changed from 70 to 100 °C, water contained in hydrogels was replaced with acetone or ethanol during 1 or 5 days, drying P was varied from 8 to 20 MPa while drying T was 35 or 40 °C. Drying of gels was performed in a 25 mL high-pressure view cell while impregnation of aerogels with BCs was performed in a 280 mL high-pressure unit (Eurotechnica GmbH, Germany). Developed aerogels were tested as possible carriers of hemp and

The integrated supercritical fluid extraction–impregnation process (SFE-SSI) was performed to fabricate material with antiviral properties against the herpes simplex virus (HSV). Cotton gauze and starch/chitosan polymer films (SCF) were impregnated with components extracted from Melissa officinalis at 10 MPa and 40 °C using a green medium, supercritical carbon dioxide (scCO2). The influences of the processing mode regarding the flow of the supercritical fluid through the system, and the mass ratio of the plant material and the solid carrier, on the impregnation yield of M. officinalis extract were studied. The results revealed that the introduction of a fresh amount of CO2 into the system enabled the highest impregnation yield of 2.24% for cotton gauze and 8.71% for SCF. The presence of M. officinalis extract on the surface of both impregnated cotton gaze and SCF was confirmed by FTIR and GC analyses after the re-extraction of the impregnated samples. The M. officinalis impregnated materials showed a strong inhibitory effect against Bovine herpesvirus type 1 (BHV-1).

Chitosan/gelatin and chitosan/gelatin/zeolite films prepared by solvent casting method were impregnated with a mixture of thymol and carvacrol using a green solvent, supercritical carbon dioxide at 35 °C and 30 MPa, during 18 h. Proposed method enabled preparation of biocompatible and biodegradable blends with strong antioxidant and antibacterial activity, whereby amounts of loaded thymol/carvacrol mixture were in the range from 3.3-6%. After initial burst release, both types of films exhibited gradual release of bioactive compounds, with around 72 and 96% of impregnated thymol/carvacrol mixture released in water and PBS (pH 7.4) during tested period of 10 days, respectively. Results of water vapor transmission rate (> 76 gm-2 day-1) confirmed that prepared composites are suitable for wound dressing application. Thermal analysis showed superior properties of prepared thymol/carvacrol loaded films compared to control samples. In addition, mechanical and structural properties, as well as solubility and swelling behavior of the obtained films were investigated in detail.

Chitosan/gelatin and chitosan/gelatin/zeolite films prepared by solvent casting method were impregnated with a mixture of thymol and carvacrol using a green solvent, supercritical carbon dioxide at 35 °C and 30 MPa, during 18 h. Proposed method enabled preparation of biocompatible and biodegradable blends with strong antioxidant and antibacterial activity, whereby amounts of loaded thymol/carvacrol mixture were in the range from 3.3-6%. After initial burst release, both types of films exhibited gradual release of bioactive compounds, with around 72 and 96% of impregnated thymol/carvacrol mixture released in water and PBS (pH 7.4) during tested period of 10 days, respectively. Results of water vapor transmission rate (> 76 gm-2 day-1) confirmed that prepared composites are suitable for wound dressing application. Thermal analysis showed superior properties of prepared thymol/carvacrol loaded films compared to control samples. In addition, mechanical and structural properties, as well as solubility and swelling behavior of the obtained films were investigated in detail.

Poly(lactic acid) (PLA) stands out as the most promising biodegradable alternative to conventional petrochemical-based polymers for manufacturing of high-performance materials applied in medicine, pharmacy, food, textile, and electronic industry. This review was aimed to present the conventional and up-to-date technologies for PLA processing including melt blending and molding, hot melt extrusion, 3D printing, foaming, impregnation, thermally induced phase separation, nano- and microparticles preparation, wet and dry spinning processes. In addition, the effect of the processing parameters and polymer characteristics on the properties of the final material was elaborated. Diverse possibilities to tailor properties of PLA-based materials by variation in polymer characteristics and concentration, solvent selection, drying method, processing pressure and temperature, incorporation of bioactive components, and so on were highlighted. The examples of the relations between processing methods, parameters, and end-product properties are given for a better understanding of all aspects that need to be perceived for fabrication of PLA-based materials with required performances.

Bilberries (Vaccinium myrtillus) are believed to have one of the highest antioxidant levels of all common fruits and vegetables. As a source of antioxidants, they have been used in traditional medicine to reduce inflammation and protect against diseases associated with oxidative stress, such as cardiovascular disease, diabetes, and age-related cognitive decline, as well as a remedy for eye conditions. The biological activity of bilberries is associated with the high content of anthocyanins, a large group of water-soluble flavonoids. Besides the complex anthocyanin profile, bilberries also contain other phenolic compounds including flavonols, tannins, and phenolic acids. Supercritical fluid extraction (SFE) isa a green and environmentally friendly process based on the use of supercritical fluids, most commonly CO2, as an alternative to organic solvents, to obtain solvent-free and highly valuable plant extracts. Utilization of supercritical CO2 (scCO2) extraction also enables the preservation of thermally labile compounds working at low temperatures, and good selectivity accomplished by the appropriate choice of operating pressure and temperature. In this study, scCO2 extraction was investigated as a method for isolating the extract from bilberry dried fruit. Extractions were performed at temperature of 70 °C and pressures of 15 and 30 MPa, with and without the ethanol as co-solvent, with the aim to optimize the yield of the obtained extract based on the composition. The obtained extraction yields ranged from 1.2 to 7% and the highest yield was obtained, as expected, at a higher pressure of 30 MPa. The effect of ethanol as co-solvent in the scCO2 extraction was studied with the goal to modify scCO2 selectivity and enhance the solubility of polar substances. The results showed a positive effect on the extraction yield, while total phenolic content (TPC) analysis revealed that extracts obtained using co-solvent have higher TPC values. Chemical analysis of the obtained e

Starch is an abundant and low-cost polysaccharide obtained from renewable resources. Biocompatibility, biodegradability, and versatility of starch enable its application in several industries including food and pharmaceutical. In this work, supercritical CO2 drying process was tested for preparation of stable and porous starch-based material. First, a hydrogel was formed from an aqueous solution (cornstarch to water mass ratio 1:10) at 95 °C. Subsequently, water was replaced with acetone during several days to form an acetogel. Finally, acetogels were subjected to supercritical CO2 drying at pressures of 8, 10, 20 MPa and temperatures of 35 and 45 °C up to 3 h to form aerogels. Obtained aerogels were compared with starch xerogels prepared by air drying of acetogels. The SEM, FTIR, and porosity analysis confirmed significant effect of supercritical CO2 drying process conditions on starch aerogels properties and their suitability to form nanostructured matrices. SEM analysis showed that aerogels were filamentous with filament diameter less than 100 nm. Due to their low density (0.273-0.773 g/cm3) and high porosity (48-82%) obtained starch aerogels present promising candidates as matrices and carriers for bioactive substances.

In the present study, supercritical solvent impregnation (SSI) has been applied to incorporate thymol into bio-composite polymers as a potential active packaging material. Thymol, a natural component with a proven antimicrobial activity, was successfully impregnated into starch-chitosan (SC) and starch-chitosan-zeolite (SCZ) films using supercritical carbon dioxide (scCO2) as a solvent. Experiments were performed at 35 °C, pressures of 15.5 and 30 MPa, and an impregnation time in the range of 4–24 h. The highest impregnation yields of SC films with starch to chitosan mass ratios of 1:1 and 1:2 were 10.80% and 6.48%, respectively. The addition of natural zeolite (15–60%) significantly increased the loading capacity of films enabling thymol incorporation in a quantity of 16.7–27.3%. FTIR and SEM analyses were applied for the characterization of the films. Mechanical properties and water vapor permeability of films before and after the impregnation were tested as well. Thymol release kinetics in deionized water was followed and modeled by the Korsmeyer-Peppas and Weibull model. SCZ films with thymol loading of approximately 24% exhibited strong antibacterial activity against E. coli and methicillin-resistant Staphylococcus (S.) aureus (MRSA).

U ovoj doktorskoj disertaciji su ispitane mogućnosti natkritične impregnacije (NKI) različitih polimernih nosača (pamučna tkanina, polipropilenski (PP) netkani materijal, poliamidni (PA) tekstilni materijali (tkanina, nanovlakna) i acetat celuloze (AC) u formi granula i filmova) ekstraktom piretrina, kako bi se istražila mogućnost dobijanja funkcionalizovanih materijala sa repelentnim svojstvima. Kao aktivna supstanca u procesima impregnacije je korišćen ekstrakt piretrina iz cveta Chrysanthemum cinerariaefolium zbog svog dokazanog insekticidnog dejstva. Rastvorljivost ekstrakta piretrina u natkritičnom ugljenik(IV)-oksidu (nkCO2) i mogućnost NKI odabranih polimera ekstraktom, ispitane su korišćenjem sledeće opreme: ćelija za rad pod visokim pritiscima (25 cm3) i laboratorijsko postrojenje za rad pod visokim pritiscima (300 cm3), primenom statičke metode. Otpuštanje ekstrakta iz impregniranih supstrata je ispitivano na vazduhu tokom 30 dana u kontrolisanim uslovima temperature (25 °C) u digitalnom inkubatoru. Impregnirani nosači su analizirani sledećim metodama: FT-IR, FE-SEM, DSC, HPLC i metodom živine porozimetrije. Vrednosti rastvorljivosti ekstrakta piretrina u nkCO2 bile su u opsegu od 15,09-48,69 kg/m3. Sadržaji impregniranog ekstrakta na pamučnoj tkanini od 0,5% i 1% obezbedili su repelentnu aktivnost materijala protiv krpelja. Impregnacija PP netkanog materijala je omogućila inkorporaciju velikih količina ekstrakta piretrina u polimer (do 78,01%), dok su prinosi impregnacije polimera na bazi PA bili u opsegu od 4,55-59,59%, a za AC od 0,86-30,43%. Impregnirana PP vlakna su pokazala sposobnost da otpuste velike količine ekstrakta (>70% tokom 30 dana), dok je sadržaj impregniranog ekstrakta u PA polimerima ostao stabilan nakon ispitivanog perioda., This PhD thesis was aimed to investigate the possibility of supercritical solvent impregnation (SSI) of selected polymer materials (cotton fabric, polypropylene (PP) non-woven fabric, polyamide (PA) polymers (fabric, nanofibres) and polymers of cellulose acetate (CA) in the form of granules and films) with pyrethrin extract in order to develop functionalized materials with repellant properties. Pyrethrum extract obtained from Chrysanthemum cinerariaefolium with proven insecticidal properities was selected as an active substance in the impregnation experiments. Determination of the pyrethrum extract solubility in supercritical carbon dioxide (scCO2) and the SSI of selected solids with the same extract were studied in the high pressure view cell (25 cm3) and the high pressure laboratory system (300 cm3) using a static mode. The pyrethrum extract release from the impregnated substrates was evaluated by exposing them to air for 30 days under controlled temperature (25 °C) with an use of digital incubator. Impregnated substrates were analized by FT-IR, FE-SEM, DSC, HPLC and mercury intrusion porosimetry methods. The solubilities of pyrethrum extract in scCO2 were in the range of 15.09-48.69 kg/m3. Impregnated cotton fabrics with pyrethrum contents of 0.5% and 1% exhibited significant repellent activity against ticks. The SSI enabled incorporation of large amounts of the extract into the PP non-woven fabric (up to 78.01%). Impregnation yields of PA and CA polymers were in the range of 4.55-59.59% and 0.86-30.43%, respectively. The impregnated PP non-woven fabrics revieled potential to release large amounts of repellent (>70% for 30 days period), while repellent content in the impregnated PA substrates remined stable after 30 days of exposure to air.

This PhD thesis was aimed to investigate the possibility of supercritical solvent impregnation (SSI) of selected polymer materials (cotton fabric, polypropylene (PP) non-woven fabric, polyamide (PA) polymers (fabric, nanofibres) and polymers of cellulose acetate (CA) in the form of granules and films) with pyrethrin extract in order to develop functionalized materials with repellant properties. Pyrethrum extract obtained from Chrysanthemum cinerariaefolium with proven insecticidal properities was selected as an active substance in the impregnation experiments. Determination of the pyrethrum extract solubility in supercritical carbon dioxide (scCO2) and the SSI of selected solids with the same extract were studied in the high pressure view cell (25 cm3) and the high pressure laboratory system (300 cm3) using a static mode. The pyrethrum extract release from the impregnated substrates was evaluated by exposing them to air for 30 days under controlled temperature (25 °C) with an use of digital incubator. Impregnated substrates were analized by FT-IR, FE-SEM, DSC, HPLC and mercury intrusion porosimetry methods. The solubilities of pyrethrum extract in scCO2 were in the range of 15.09-48.69 kg/m3. Impregnated cotton fabrics with pyrethrum contents of 0.5% and 1% exhibited significant repellent activity against ticks. The SSI enabled incorporation of large amounts of the extract into the PP non-woven fabric (up to 78.01%). Impregnation yields of PA and CA polymers were in the range of 4.55-59.59% and 0.86-30.43%, respectively. The impregnated PP non-woven fabrics revieled potential to release large amounts of repellent ( gt 70% for 30 days period), while repellent content in the impregnated PA substrates remined stable after 30 days of exposure to air., U ovoj doktorskoj disertaciji su ispitane mogućnosti natkritične impregnacije (NKI) različitih polimernih nosača (pamučna tkanina, polipropilenski (PP) netkani materijal, poliamidni (PA) tekstilni materijali (tkanina, nanovlakna) i acetat celuloze (AC) u formi granula i filmova) ekstraktom piretrina, kako bi se istražila mogućnost dobijanja funkcionalizovanih materijala sa repelentnim svojstvima. Kao aktivna supstanca u procesima impregnacije je korišćen ekstrakt piretrina iz cveta Chrysanthemum cinerariaefolium zbog svog dokazanog insekticidnog dejstva. Rastvorljivost ekstrakta piretrina u natkritičnom ugljenik(IV)-oksidu (nkCO2) i mogućnost NKI odabranih polimera ekstraktom, ispitane su korišćenjem sledeće opreme: ćelija za rad pod visokim pritiscima (25 cm3) i laboratorijsko postrojenje za rad pod visokim pritiscima (300 cm3), primenom statičke metode. Otpuštanje ekstrakta iz impregniranih supstrata je ispitivano na vazduhu tokom 30 dana u kontrolisanim uslovima temperature (25 °C) u digitalnom inkubatoru. Impregnirani nosači su analizirani sledećim metodama: FT-IR, FE-SEM, DSC, HPLC i metodom živine porozimetrije. Vrednosti rastvorljivosti ekstrakta piretrina u nkCO2 bile su u opsegu od 15,09-48,69 kg/m3. Sadržaji impregniranog ekstrakta na pamučnoj tkanini od 0,5% i 1% obezbedili su repelentnu aktivnost materijala protiv krpelja. Impregnacija PP netkanog materijala je omogućila inkorporaciju velikih količina ekstrakta piretrina u polimer (do 78,01%), dok su prinosi impregnacije polimera na bazi PA bili u opsegu od 4,55-59,59%, a za AC od 0,86-30,43%. Impregnirana PP vlakna su pokazala sposobnost da otpuste velike količine ekstrakta ( gt 70% tokom 30 dana), dok je sadržaj impregniranog ekstrakta u PA polimerima ostao stabilan nakon ispitivanog perioda.

Like ester type biodiesel fuel, green diesel is a next generation transportation fuel emerging due to the need for a renewable replacement of internal combustion engine fuel, which is also fully compatible with existing automotive powertrain systems. Besides other limitations, the main obstacle for wider application of such renewable fuels is their relatively high production cost, depending mainly on the raw material cost and the application of more efficient processing technology. Green diesel and ester type biodiesel can be produced from waste vegetable oil by catalytic hydrogenation, homogeneous alkali catalysed transesterification and supercritical non-catalytic transesterification. Techno-economic analysis and the sensitivity analysis reveal that economics of these production technologies strongly depend on the process unit capacity and the cost of feedstock. Green diesel production by catalytic hydroprocessing located in a petroleum refinery appears to be the most cost effective option for unit capacity close to and above 200,000 tonnes/year. Conventional ester biodiesel process and non-catalytic ester biodiesel process under supercritical conditions are less profitable at specified capacity. Unit capacities of the investigated processes which are below 100,000 tonnes/year are likely to result in negative net present values after 10 years of project lifetime.