Browsing by Author "Cuma, Diana Francisco"
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- Materiais de base poliuretano com resistência incrementada à fadiga térmica para calçado de segurançaPublication . Cuma, Diana Francisco; Rafael, Helder Martins; Fernandes, Isabel P.; Gomes, Helder; Pinto, Vera; Ferreira, Maria José; Barreiro, M.F.A perda de propriedades ao longo do tempo de vida útil do calçado esta relacionada com a variação térmica e esforço mecânico ocorrido em condições de utilização, o calçado pode ser utilizado de forma intercalada a temperaturas elevc:1das e a temperaturas baixas (p.exe. o calçado usado por militares que operam no deserto). Os materiais de base poliuretano (PUs), nomeadamente os microcelulares, são convencionalmente aplicados na construção de calçado sendo associados a boas propriedades de conforto. Devido as exigências dos consumidores quanto a produtos de elevado desempenho, o desenvolvimento de novos PUs microcelulares com resistência incrementada a fadiga térmica e um tópico de elevado interesse industrial. Assim, o presente trabalho esta focado no desenvolvimento de PUs microcelulares resistentes a fadiga térmica, partindo de uma formulação e de um sistema químico de base poliester tipico para a produção de entressolas para calçado, e onde o incremento desta propriedade e realizado pela aditivação do PU com nanocargas inorgânicas. Produziram-se PUs moldados correspondentes à formulação base e a formulações modificadas com o aditivo inorgânico nano-A (tamanho medio de partícula<1 0 μm) através da incorporação de 1, 3, 5, 7 e 10% (m/m) (Fig.1 (1 a)). Os PUs produzidos foram caracterizados quanto a estrutura celular por microscopia ótica (MO) (Fig.1 (2a)) e Scanning Electron Microscopy (SEM), servindo tambem esta ultima técnica para verificar a distribuição das cargas nas células (Fig. 1 (3a)). As propriedades térmicas foram avaliadas por Differential Scanning Calorimetry (DSC). Para avaliar o efeito da fadiga termica nas propriedades dos PUs, desenvolveu-se um teste laboratorial que consistiu em colocar as amostras numa estufa a 60°C durante 12 horas, seguido de um período a 4 °C (frigorifico) durante 12 horas. Este procedimento foi repetido durante 5 ciclos, seguindo-se a analise por DSC de forma a avaliar o efeito nas propriedades térmicas. Os resultados obtidos por MO permitiram observar que a introdução do aditivo originou distribuições de tamanho de células mais homogéneas, e que esta característica melhorou com o aumento do teor de 1 para 10%. A analise por DSC das amostras após produção evidenciou que a incorporação do aditivo incrementou o valor de Tm de 292.1 (PUbase) para 311.7 oc (PU10nano-A), enquanto após o teste de fadiga térmica os valores de Tm variaram entre 292.7 (PUbase) e 314.7 oc (PU10nano-A). Este resultado aponta para um efeito positivo da utilização deste tipo de cargas no aumento da resistência do PU a temperaturas elevadas.
- Microencapsulation by spray coagulation method: Study of the alginate crosslinking by different calcium saltsPublication . Cuma, Diana Francisco; Fernandes, Isabel P.; Barreiro, M.F.The use of biopolymers such as alginate has been growing in the last decades due to properties such as non-toxicity and biodegradability. In this work, the microencapsulation of curcumin and safranin, used as model compounds for hydrophobic and hydrophilic active principles, respectively, was studied with alginate matrices by the spray coagulation technique. The alginate ionic crosslinking with three calcium sources (calcium chloride (CaCl2), calcium gluconate and calcium lactate) was considered. The obtained microcapsules were characterized in terms of load, encapsulation efficiency (EE), rehydration capacity, and particle size. The release profiles of both active principles were also studied. Through FTIR analysis the contribution of the calcium source, and the presence of the active principles inside the microcapsules, was identified, while the TGA evidenced an increasing of the thermal stability due to the alginate crosslinking effect, particularly when CaCl2 was used. The overall results showed that CaCl2 is the most effective calcium source for alginate crosslinking, while calcium lactate lead to a more gradual release of the active principles.
- Microencapsulation using alginate systems: spray-coagulation versus superhydrophobic surfaces approachPublication . Cuma, Diana Francisco; Barreiro, M.F.; Fernandes, Isabel P.The use of biopolymers such as alginate has been growing in the last decades due to properties such as biocompatibility, non-toxicity and biodegradability. In this work the microencapsulation of a hydrophobic (curcumin) and a hydrophilic (safranin), used as model compounds with alginate matrices, was studied by comparing two encapsulation methods (spray coagulation and superhydrophobic surfaces) and by testing three calcium sources (calcium chloride, calcium gluconate and calcium lactate) to promote the alginate ionic crosslinking. The microspheres obtained through the spray/coagulation technique were characterized in terms of load, encapsulation efficiency and rehydration capacity. The release profiles of both active principles were evaluated. The results revealed that when calcium chloride is used a higher encapsulation efficiency was obtained (99.25% and 98.50%, respectively for curcumin and safranin), followed by calcium gluconate (98.45% and 97.55 for curcumin and safranin) and finally calcium lactate (97.91% for curcumin and 97.42 for safranin). Regarding the release profile, a lower release was achieved, for both compounds, when calcium chloride was used (5.70% of curcumin in ethanol medium, and 4.15% of safranin in distilled water), followed by the calcium gluconate crosslinked microspheres (8.3% for curcumin and 4.42% for safranin). Calcium lactate crosslinked microspheres give rise to the systems with higher release (12.1% for curcumin and 4.76% for safranin). The microspheres had a spherical conformation and the larger particle size (volume distribution) was obtained with the calcium gluconate-based systems (131.46, 78.85 and 91.46 μm for curcumin, safranin and empty microspheres, respectively). The calcium chloride-base systems give rise to the smallest ones (91.65, 60.10 and 80.31 μm, respectively for curcumin, safranin and empty microspheres). Through Fourier Transform Infrared Spectroscopy the contribution of the calcium source and the active principle on the microspheres spectra was identified, and thermogravimetric analysis evidenced an increasing of the thermal stability due to the alginate crosslinking effect, particularly when calcium chloride was used. Regarding the comparison of the two microencapsulated systems, the superhydrophobic surfaces showed a good performance having in view the encapsulation with alginate systems, since no loss of the active principle to the surface during the process was observed (qualitative analysis). This constitute an advantage particularly for the case of the hydrophilic active principles.