Browsing by Author "Rodrigues, Sofia Nogueira"
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- Evaluation of surfactants of thyme oil microcapsules by coacervationPublication . Martins, Isabel M.; Rodrigues, Sofia Nogueira; Barreiro, M.F.; Rodrigues, AlírioThe formation of microcapsules (size, shape and stability) is greatly affected by the conditions used in the o/w emulsion preparation, being particularly relevant the used surfactant. The objective of this work is to study the effect of using different surfactants with hydrophilic-lipophilic balance (HLB) values from 11 to 16.5 in the encapsulation process of thyme oil by coacervation using polylactide (PLA) with polymer wall. Different emulsions of thyme oil were prepared and the surfactants investigated were Tween® 20, Tween® 80, Tergitol™ 15-S-9 and a combination of Tergitol™ 15-S-9 with Span® 85. Microcapsules size, morphology and encapsulation efficiency were studied as a function of the used surfactant.
- Microencapsulatin of thyme oil by coacervationPublication . Martins, Isabel M.; Rodrigues, Sofia Nogueira; Barreiro, M.F.; Rodrigues, AlírioThe objective of this work is to develop a novel coacervation process to produce microcapsules of polylactide (PLA) to encapsulate thyme oil that will be used in cosmetics. The novelty of this approach consists of dissolving PLA in dimethylformamide (DMF) which is a good solvent for PLA but in addition has high solubility in water. Upon contact with water, the homogeneous solution of PLA in DMF promotes the precipitation of PLA around the thyme oil core. The produced microcapsules have bimodal particle size distributions in volume with a mean particle size of 40 mm. Microcapsules analysis by microscopy have confirmed the spherical shape, the rough surface and allowed the estimation of the wall thickness around 5 mm. Quantification of the encapsulated thyme oil was performed by gas chromatography and allowed to evaluate the quality of the encapsulated oil and pointed out for a preferential encapsulation of thyme oil apolar compounds.
- Microencapsulation by coacervation of biodegradable polymer with thyme oilPublication . Martins, Isabel M.; Rodrigues, Sofia Nogueira; Barreiro, M.F.; Rodrigues, AlírioThe objective of this work is to develop a novel coacervation process to produce microcapsules of PLA to encapsulate thyme oil that will be used in cosmetics. PLA is soluble in organic solvents but insoluble in water. Generally, PLA is used to encapsulate water soluble active principles such as drugs, pesticides and dye-stuffs by coacervation, mainly by means of microspheres production or by using double emulsion techniques (o/w/o). However, the objective of this work is to encapsulate thyme oil, a water insoluble active principle that needs, in a first step, the preparation of an oil-in-water emulsion. The novelty of our process consists on dissolving PLA in dimethylformamide (DMF) which is a good solvent for PLA but in addition has high solubility in water. Upon contact with water, the homogeneous solution of PLA in DMF, promotes the precipitation of PLA around the thyme oil core. With this work we demonstrate a new, easy and executable method of coacervation by introducing modifications on microencapsulation process that allow the encapsulation of an oily active principle by simply preparing an o/w emulsion. Control of size and wall thickness of microcapsules, encapsulation efficiency, the influence of surfactants and release of thyme oil were studied. The produced microcapsules have bimodal particle size distributions in volume with a mean particle size of 40 μm. Microcapsules analysis by microscopy have confirmed the spherical shape, the rough surface, and allowed the estimation of the wall thickness around 5 μm. Quantification of the encapsulated thyme oil was performed by gas chromatography and allowed to evaluate the quality of the encapsulated oil and pointed out for a preferential encapsulation of thyme oil apolar compounds.
- Microencapsulation by coacervation of biodegradable polymer with thyme oilPublication . Martins, Isabel M.; Rodrigues, Sofia Nogueira; Barreiro, M.F.; Rodrigues, AlírioThe objective of this work is to develop a novel coacervation process to produce microcapsules of PLA to encapsulate thyme oil that will be used in cosmetics. PLA is soluble in organic solvents but insoluble in water. Generally, PLA is used to encapsulate water soluble active principles such as drugs, pesticides and dye-stuffs by coacervation, mainly by means of microspheres production or by using double emulsion techniques (o/w/o). However, the objective of this work is to encapsulate thyme oil, a water insoluble active principle that needs, in a first step, the preparation of an oil-in-water emulsion. The novelty of our process consists on dissolving PLA in dimethylformamide (DMF) which is a good solvent for PLA but in addition has high solubility in water. Upon contact with water, the homogeneous solution of PLA in DMF, promotes the precipitation of PLA around the thyme oil core. With this work we demonstrate a new, easy and executable method of coacervation by introducing modifications on microencapsulation process that allow the encapsulation of an oily active principle by simply preparing an o/w emulsion. Control of size and wall thickness of microcapsules, encapsulation efficiency, the influence of surfactants and release of thyme oil were studied. The produced microcapsules have bimodal particle size distributions in volume with a mean particle size of 40 μm. Microcapsules analysis by microscopy have confirmed the spherical shape, the rough surface, and allowed the estimation of the wall thickness around 5 μm. Quantification of the encapsulated thyme oil was performed by gas chromatography and allowed to evaluate the quality of the encapsulated oil and pointed out for a preferential encapsulation of thyme oil apolar compounds.
- Microencapsulation of limonen oil for textile applicationPublication . Rodrigues, Sofia Nogueira; Fernandes, Isabel P.; Mata, Vera G.; Barreiro, M.F.; Rodrigues, AlírioThe production of polyurethane-urea microcapsules using the interfacial polymerization technology was performed. Microcapsules were produced in a basic IKA® Miniplant laboratory reactor, in order to produce microcapsules with controlled parameters. In this formulation, limonene, a fragrant chemical characteristic of the lemon oil - was microencapsulated, because lemon oil is the most used oil in perfumery. It resulted in microcapsules with bimodal distribution and average size equal to 10µm. The characterisation of the microcapsules includes particle size distribution, optical microscopy and scanning electron microscopy. Using scanning electron microscopy it is visible the presence of well defined microcapsules on the woven.
- Microencapsulation of limonene for textile applicationPublication . Rodrigues, Sofia Nogueira; Fernandes, Isabel P.; Martins, Isabel M.; Mata, Vera G.; Barreiro, M.F.; Rodrigues, AlírioPolyurethane−urea microcapsules with limonene oil as the active agent were produced by interfacial polymerization, and their suitability for textile applications was studied. Experimental conditions for the textile substrates impregnation were based on industrial requirements and set up at laboratory scale using a mini-foulard. The success of the polymerization reaction leading to the formation of the polyurethane−urea shell was checked by Fourier transform infrared spectroscopy. Particle size distributions and morphology of the microcapsules were studied using a particle size analyzer (Coulter LS230), optical microscopy, and scanning electron microscopy. The effectiveness of the textiles impregnation and the durability of the impregnation effect were evaluated by scanning electron microscopy and by headspace/GC/FID. Under the present research, a product was developed and its performance, in regard to industrial requirements, was successfully tested.
- Polylactide-based thyme oil microcapsules production: evaluation of surfactantsPublication . Martins, Isabel M.; Rodrigues, Sofia Nogueira; Barreiro, M.F.; Rodrigues, AlírioThe objective of this work is to prepare microcapsules of polylactide-containing thyme oil by coacervation using a variety of nonionic surfactants with different hydrophilic-lipophilic balance (HLB) values and evaluate the encapsulation efficiency of polar and apolar compounds of oil. Thus, Tween 20, Tween 80, Tergitol 15-S-9, and a combination of Tergitol 15-S-9 with Span 85 have been used. The HLB value was comprised between 11 and 16.5. For all the studied cases, microcapsules are spherical in shape and have bimodal particle size distribution with mean size between 30 and 40 μm. The amount of encapsulated thyme oil reaches a maximum of 65% for Tergitol 15-S-9, a polyglycol ether surfactant with a HLB value of 13.3. The results confirm the dependence of the encapsulation efficiency as result of the hydrophobic properties of the surfactants. Moreover, it was confirmed a preferential encapsulation of apolar compounds of thyme oil in detriment of polar ones.
- Release of thyme oil from polylactide microcapsulesPublication . Martins, Isabel M.; Rodrigues, Sofia Nogueira; Barreiro, M.F.; Rodrigues, AlírioMicroencapsulation reveals numerous advantages over conventional applications of flavors or fragrances. Thus, the goal of this work was to study the release rate of thyme oil through the polylactide (PLA) microcapsules prepared by coacervation. Microcapsules have spherical shape and a mean particle size of 36 μm. The results show that the release of thymol is faster in the first hour and remains almost constant in the next days. Moreover, it was observed that the release of the polar compounds of thyme oil is faster than the apolar ones. The diffusion coefficient in the first hour of release was 1.39 × 10–15 m2/s for thymol and 5.21 × 10–17 m2/s for p-cymene. For a period of 5 days, diffusion coefficients of 3.81 × 10–17 m2/s for thymol and 1.43 × 10–18 m2/s for cymene were determined. The diffusion of thyme oil from the PLA cross-linked membrane was dependent on the microcapsules morphological characteristics.
- Release studies of essential oil of Thymus vulgaris L. from PLA microcapsulesPublication . Martins, Isabel M.; Rodrigues, Sofia Nogueira; Barreiro, M.F.; Rodrigues, AlírioThe incorporation of essential oils, perfumes, deodorants and other active agents in microcapsules with the purpose of controlled release over a certain period of time is being a topic of considerable research in recent years. The controlled release systems are used to deliver compounds such us drugs, pesticides, fragrances or flavors at prescribed rates, together with improved efficacy, safety and convenience. Nowadays, core-shell microcapsules have been investigated extensively for utilization in controlled release systems, especially in drug delivery, where the polymeric wall is a permeable element with porosity that can determine the release behavior of core materials. The aim of this work is to study the release of essential oil of Thymus vulgaris L. (thyme oil) during the first days of release and develop a general diffusion model for predicting mass transport phenomena in biodegradable polymer microcapsules prepared by a coacervation technique. The release of this essential oil was investigated for microcapsules in solution by comparing calculated and experimental diffusion profiles of oil across de polymer membrane. Control of size and wall thickness of microcapsules and encapsulation efficiency were also studied.
- Release studies of essential oil of Thymus vulgaris L. from PLA microcapsulesPublication . Martins, Isabel M.; Rodrigues, Sofia Nogueira; Barreiro, M.F.; Rodrigues, AlírioThe incorporation of essential oils, perfumes, deodorants and other active agents in microcapsules with the purpose of controlled release over a certain period of time is being a topic of considerable research in recent years. The controlled release systems are used to deliver compounds such us drugs, pesticides, fragrances or flavors at prescribed rates, together with improved efficacy, safety and convenience. Nowadays, core-shell microcapsules have been investigated extensively for utilization in controlled release systems, especially in drug delivery, where the polymeric wall is a permeable element with porosity that can determine the release behavior of core materials. The aim of this work is to study the release of essential oil of Thymus vulgaris L. (thyme oil) during the first days of release and develop a general diffusion model for predicting mass transport phenomena in biodegradable polymer microcapsules prepared by a coacervation technique. The release of this essential oil was investigated for microcapsules in solution by comparing calculated and experimental diffusion profiles of oil across de polymer membrane. Control of size and wall thickness of microcapsules and encapsulation efficiency were also studied.