Abstract Despite the high potential of the freeze-casting technique for production of porous inorganic substrates, there is a lack of studies on tubular geometries and their mechanical behavior under different pressure scenarios. In this work, the mechanical behavior of tubular freeze-cast alumina substrates was assessed by mathematical models from experimental O-ring tests. The stress distributions revealed a concentration of tensile stresses (within 0.2-25.0 MPa) on the plane of the load, causing brittle fracture. Furthermore, the results confirmed that the honeycomb model for brittle material adequately predicted the mechanical strength of the tubular freeze-cast substrates. Finally, fracture criteria from honeycomb model was used to estimate the maximum homogeneously distributed pressures, such as in fluids, that the substrates can withstand. This configuration represents more precisely practical conditions, though is hard to experimentaly replicate. Therefore, the developed procedure is paramount to simulate the mechanical behaviour of the tubular freeze-cast substrates under real operating conditions.

Development of new ceramic membranes has recently grown due to its superior thermal and mechanical stability. An interesting approach to manufacture asymmetric membranes is the production of aligned pore structure by the freeze-casting method. The lack of studies involving membrane production with tubular freeze-cast substrates warrants more research. In this study, a novel tubular freeze-cast alumina substrate was used for deposition of a silica top layer. The substrate showed radially aligned pores, indicating precise structure control. The obtained pore structure shows high potential for membrane manufacture. The silica layer was produced by the sol-gel method and dip-coated on the substrates with two different withdrawal speeds. The microporous silica showed pores smaller than 2 nm. The highest withdrawal speed resulted in broader substrate coverage. However, a uniform silica layer was only obtained after a second deposition. These results confirm the viability to use tubular freeze-cast substrates for production of nanofiltration membranes.

Resumo Neste trabalho, foram analisadas 251 amostras de alimentos quanto aos teores de gordura total, ácidos graxos TRANS, saturados, monoinsaturados e poli-insaturados de produtos amplamente consumidos pela população, principalmente aqueles com alegação “zero TRANS”. De acordo com a Resolução RDC 360/2003 da ANVISA, é obrigatória a declaração dos níveis de ácidos graxos TRANS na rotulagem dos alimentos embalados quando os teores forem superiores a 0,2 g na porção do alimento. Produtos com valores inferiores a 0,2 g podem ser notificados na rotulagem como “zero TRANS”. O objetivo deste estudo foi avaliar a quantidade de gorduras saturadas e TRANS em diversos grupos de alimentos industrializados, e a adequação, frente à legislação brasileira, da declaração dessas gorduras nos respectivos rótulos. Para as análises, foram utilizados os métodos oficiais de análise de gorduras AOAC 996.01 (modificado) e de ésteres metílicos de ácidos graxos AOAC 996.06. Conforme os resultados obtidos, alguns produtos apresentaram, em 100 g, teores de ácidos graxos TRANS superiores aos recomendados para ingestão total diária em diversos países (2 g/dia). Vários produtos estão conforme a legislação (0,2 g de gordura TRANS por porção), o que não implica necessariamente em zero absoluto, dando a falsa ideia ao consumidor de não estar ingerindo gordura TRANS, independentemente da quantidade consumida. Em apenas 12 amostras, não se detectou gordura TRANS em 100 g de produto analisado. Ressalte-se, ainda, que, muitas vezes, a quantidade consumida é maior do que a porção sugerida, acarretando uma ingestão significativa de ácidos graxos TRANS. Os resultados obtidos nesta avaliação oferecem subsídios para modificações na legislação em vigor, exigindo a declaração de ácidos graxos TRANS na rotulagem.

Summary In this study 251 food samples widely consumed by the population, especially those claiming to be “zero TRANS”, were analys5ed for their total fat contents and for their “TRANS”, saturated, monounsaturated and polyunsaturated fatty acid contents. According to the RDC Resolution 360/2003 of ANVISA, the TRANS fatty acid content of a food must be printed on the label when the level is greater than 0.2 g per food portion. Products containing less than 0.2 g/ per portion can be reported on the label as “zero TRANS.” The aim of this study was to evaluate the amounts of saturated and “TRANS” fats in many groups of processed foods, and the adequacy of the disclosure of these amounts on the product label, considering the Brazilian legislation. The official AOAC methods were used for the analyses specifically nº 996.01 (modified) for the total fat analysis and nº 996.06 for the analysis of the fatty acid methyl esters. According to the results obtained, 100g portions of some of the products contained more than 2g of “TRANS” fatty acids, which is the limit recommended by several countries for the daily intake of “TRANS” fatty acids. Many products were in compliance with the law (up to 0.2 g TRANS fat per serving), which does not necessarily imply absolute zero, giving the consumer the false impression of not ingesting any “TRANS” fat regardless of the amount of product consumed. Only 12 samples really showed 0g of “TRANS” fat per 100g of product analysed. It should also be pointed out that frequently the amount of product consumed is more than the suggested serving, resulting in a significant intake of “TRANS” fatty acids. The results presented here provide subsidies for the reshaping of current Brazilian legislation demanding the printing of the “TRANS” fatty acid content on the food label.