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Abstract(s)
Esta tese de doutoramento, realizada em ambiente industrial, tem por objectivo optimizar concomitantemente o desempenho de tecidos mistos de lã e poliéster no que se refere às propriedades mecânicas e de superfície, de forma que a correspondente definição, em projeto, das características estruturais dos tecidos possibilite que a primeira amostra de tecido produzido cumpra integralmente todos os requisitos exigidos nas especificações técnicas do caderno de encargos.
Este trabalho de investigação aprofunda um trabalho anterior realizado por Monteiro (2011) no sentido da optimização simultânea das propriedades mecânicas e de superfície de desempenho dos tecidos, em função das características estruturais adequadas, bem como da consideração do efeito global nas propriedades de desempenho das operações de acabamento dos tecidos destinadas a incrementar determinadas propriedades, o que lhe confere um carácter inovador.
Para este propósito, foram estudadas as propriedades mecânicas e de superfície de tecidos mistos de lã e poliéster, com dois diâmetros diferentes para cada uma das fibras e em duas composições distintas; construídos com três tipos de ligamento (sarja de 4 pesada, sarja de 3 pesada e tafetá); produzidos com fios Nm 2/46 com dois níveis de torção, quer a um cabo, quer a dois cabos, de acordo com a tipologia de tecidos de mercado. As propriedades de desempenho dos tecidos estudadas foram a resistência e o alongamento à rotura por tracção, quer à teia, quer à trama, a resistência ao rasgo, quer à teia, quer à trama, a propensão à formação de borboto e a resistência à abrasão, por se tratarem das especificações técnicas mais relevantes dos cadernos de encargos.
Para o desenvolvimento da investigação consideram-se 48 amostras de tecido com acabamento normal (Monteiro, 2011), as quais foram submetidas a três tratamentos especiais de acabamento dando origem a 4 grupos de 48 amostras cada, perfazendo um total de 192 amostras. Os acabamentos especiais considerados foram: tratamento de foulardagem para incrementar a resistência ao rasgo; tratamento de foulardagem para Incrementar a resistência à abrasão e tratamento de limpeza a seco. As propriedades de desempenho e as características estruturais das 192 amostras de tecido foram determinadas laboratorialmente de acordo com as normas de ensaio em vigor.
A modelização das propriedades mediante o cálculo das superfícies de resposta, o cálculo das funções de conveniência, assim como os cálculos da análise de variância e a estimativa dos intervalos de confiança das médias das propriedades em função das características estruturais, efetuou-se utilizando um software estatístico convencional (Statgraphics, 2002).
O tratamento estatístico dos dados foi realizado por aplicação da técnica de análise de regressão para desenvolver modelos de previsão dos valores de cada uma das propriedades para cada ligamento e cada tratamento de acabamento dos tecidos, de forma a ter disponíveis os modelos matemáticos que permitam prever o valor de cada propriedade para cada ligamento e cada tipo de acabamento, em função das características das fibras e do fio. Aplicando a técnica da análise de variância determinaram-se os efeitos e interacções mais significativas que influenciam cada propriedade em cada ligamento em estudo. Efectuou-se a optimização de resposta múltipla mediante a aplicação da função de conveniência e determinaram-se as condições experimentais que conduziram a um tecido com propriedades o mais próximas possível dos valores optimos para cada uma delas.
Quanto aos coeficientes de determinação R², encontrados para cada propriedade em estudo, que expressam a percentagem da soma dos quadrados, explicada pelos efeitos e interacções significativas, de um modo geral são bastante altos. Em todos os casos, com exceção da propensão à formação de borboto, as variáveis relacionadas com a fibra, com o fio, com o ligamento e com o tipo de acabamento explicam de maneira bastante satisfatória a evolução dos parâmetros de resistência e alongamento à rotura por tracção, de resistência ao rasgo e de resistência à abrasão.
Na maioria das propriedades de desempenho dos tecidos, os elevados coeficientes de determinação das equações de regressão mostram um nível muito aceitável em termos de explicação, com excepção da propensão à formação de borboto em tecidos com ligamento sarja de 4 e com acabamento para incrementar a resistência à abrasão, bem como em tecidos com ligamento tafetá e com os quatro acabamentos diferentes.
A melhor combinação de valores das variáveis que originou a conveniência óptima, com valores da função de conveniência superiores a 0,9, para os tecidos considerando todos os ligamentos e todos os tipos de acabamento, é:
- Torção do fio a um cabo: 720 v/m
- Diâmetro da fibra de lã: 21,4 μm
- Diâmetro da fibra de poliéster: 4,4 dtex
- Percentagem de lã: 45%
Por último, este trabalho permitiu encontrar três fenómenos que permitem contribuir para o conhecimento aplicado em projectos de engenharia de tecidos na prática industrial, carecendo, contudo, das justificações científicas e tecnológicas que devem ser estudadas em investigações futuras.
O primeiro fenómeno está associado ao efeito do tratamento de limpeza a seco, que produz reduções muito significativas da resistência ao rasgo dos tecidos, sem modificar duma forma relevante o desempenho das outras propriedades. O segundo fenómeno está relacionado com o tratamento para incrementar a resistência à abrasão, afectando também negativamente a resistência ao rasgo, com reduções de resistência muito significativas. O terceiro fenómeno está relacionado com a cor final dos tecidos, após os tratamentos especiais. Este trabalho revelou que o tratamento por foulardagem para incrementar a resistência à abrasão altera significativamente a intensidade da cor, mantendo-se a sua tonalidade praticamente inalterada.
This doctoral thesis, carried out in an industrial environment, aims to simultaneously optimize the performance of blended fabrics of wool and polyester with regard to mechanical and surface properties, so that the corresponding definition, in design, of the structural characteristics of the fabrics make it possible for the first sample of fabric produced to fully comply with all the requirements set out in the technical specifications. This research work builds on a previous work carried out by Monteiro (2011) in the sense of simultaneously optimizing the mechanical and surface performance properties of fabrics, depending on the appropriate structural characteristics, as well as considering the global effect on the performance properties of the operations of finishing fabrics designed to enhance certain properties, which gives it an innovative character. For this purpose, the mechanical and surface properties of blended wool and polyester fabrics were studied, with two different diameters for each of the fibers and in two different compositions; constructed with three types of weave (heavy 4-twill, heavy 3-twill, and plain); produced with Nm 2/46 yarns with two levels of twist, either one rope or two ropes, according to the type of fabric on the market. The performance properties of the studied fabrics were strength and elongation to breakage by traction, either to the warp or to the weft, the tear strength to the warp or to the weft, the propensity to the formation of pilling and the resistance to abrasion, as they are the most relevant of the technical specifications. For the development of the investigation, 48 samples of fabric with normal finishing were considered (Monteiro, 2011), which were subjected to three special finishing treatments, giving rise to 4 groups of 48 samples each, making a total of 192 samples. The special finishes considered were: padding treatment to increase tear resistance; padding treatment to increase abrasion resistance and dry cleaning treatment. The performance properties and structural characteristics of the 192 fabrics samples were laboratory determined in accordance with current testing standards. The modeling of the properties through the calculation of the response surfaces, the calculation of the convenience functions, as well as the calculations of the analysis of variance and the estimation of the confidence intervals of the averages of the properties as a function of the structural characteristics, were carried out using a software conventional statistical (Statgraphics, 2002). The statistical treatment of the data was carried out by applying the regression analysis technique to develop models to predict the values of each of the properties for each weave and each fabric finishing treatment, in order to have available the mathematical models that allow predicting the value of each property for each weave and each type of finish, depending on the characteristics of the fibers and yarn. Applying the analysis of variance technique, the most significant effects and interactions that influence each property in each weave under study were determined. The optimization of the multiple response was carried out by applying the convenience function and the experimental conditions that led to a fabric with properties as close as possible to the optimal values for each of them were determined. As for the coefficients of determination R² found for each property under study, which express the percentage of the sum of squares, explained by the significant effects and interactions, in general they are quite high. In all cases, with the exception of the propensity for pilling, the variables related to the fiber, the yarn, the weave and the type of finish explain in a very satisfactory way the evolution of the parameters of strength and elongation at break by traction, tear resistance and abrasion resistance. In most of the performance properties of fabrics, the high coefficients of determination of the regression equations show a very acceptable level in terms of explanation, with the exception of the propensity for pilling in fabrics with a 4 twill weave and finished to increase strength to abrasion, as well as on fabrics with plain weave and with the four different finishes. The best combination of values of the variables that gave rise to optimal convenience, with convenience function values greater than 0.9, for fabrics considering all weaves and all types of finish, is: - Yarn twist to a cable: 720 v/m - Diameter of wool fiber: 21.4 μm - Diameter of polyester fiber: 4.4 dtex - Wool percentage: 45% Finally, this work allowed finding three phenomena which allow to contribute to the knowledge applied in fabric engineering projects in industrial practice, lacking, however, the scientific and technological justifications that should be studied in future research. The first phenomenon is associated with the effect of the dry cleaning treatment, which produces very significant reductions in the tear resistance of fabrics, without significantly modifying the performance of other properties. The second phenomenon is related to the treatment to increase the abrasion resistance, also negatively affecting the tear resistance, with very significant resistance reductions. The third phenomenon is related to the final color of fabrics, after special treatments. This work revealed that the padding treatment to increase the abrasion resistance significantly alters the intensity of the color, keeping its tonality practically unchanged.
This doctoral thesis, carried out in an industrial environment, aims to simultaneously optimize the performance of blended fabrics of wool and polyester with regard to mechanical and surface properties, so that the corresponding definition, in design, of the structural characteristics of the fabrics make it possible for the first sample of fabric produced to fully comply with all the requirements set out in the technical specifications. This research work builds on a previous work carried out by Monteiro (2011) in the sense of simultaneously optimizing the mechanical and surface performance properties of fabrics, depending on the appropriate structural characteristics, as well as considering the global effect on the performance properties of the operations of finishing fabrics designed to enhance certain properties, which gives it an innovative character. For this purpose, the mechanical and surface properties of blended wool and polyester fabrics were studied, with two different diameters for each of the fibers and in two different compositions; constructed with three types of weave (heavy 4-twill, heavy 3-twill, and plain); produced with Nm 2/46 yarns with two levels of twist, either one rope or two ropes, according to the type of fabric on the market. The performance properties of the studied fabrics were strength and elongation to breakage by traction, either to the warp or to the weft, the tear strength to the warp or to the weft, the propensity to the formation of pilling and the resistance to abrasion, as they are the most relevant of the technical specifications. For the development of the investigation, 48 samples of fabric with normal finishing were considered (Monteiro, 2011), which were subjected to three special finishing treatments, giving rise to 4 groups of 48 samples each, making a total of 192 samples. The special finishes considered were: padding treatment to increase tear resistance; padding treatment to increase abrasion resistance and dry cleaning treatment. The performance properties and structural characteristics of the 192 fabrics samples were laboratory determined in accordance with current testing standards. The modeling of the properties through the calculation of the response surfaces, the calculation of the convenience functions, as well as the calculations of the analysis of variance and the estimation of the confidence intervals of the averages of the properties as a function of the structural characteristics, were carried out using a software conventional statistical (Statgraphics, 2002). The statistical treatment of the data was carried out by applying the regression analysis technique to develop models to predict the values of each of the properties for each weave and each fabric finishing treatment, in order to have available the mathematical models that allow predicting the value of each property for each weave and each type of finish, depending on the characteristics of the fibers and yarn. Applying the analysis of variance technique, the most significant effects and interactions that influence each property in each weave under study were determined. The optimization of the multiple response was carried out by applying the convenience function and the experimental conditions that led to a fabric with properties as close as possible to the optimal values for each of them were determined. As for the coefficients of determination R² found for each property under study, which express the percentage of the sum of squares, explained by the significant effects and interactions, in general they are quite high. In all cases, with the exception of the propensity for pilling, the variables related to the fiber, the yarn, the weave and the type of finish explain in a very satisfactory way the evolution of the parameters of strength and elongation at break by traction, tear resistance and abrasion resistance. In most of the performance properties of fabrics, the high coefficients of determination of the regression equations show a very acceptable level in terms of explanation, with the exception of the propensity for pilling in fabrics with a 4 twill weave and finished to increase strength to abrasion, as well as on fabrics with plain weave and with the four different finishes. The best combination of values of the variables that gave rise to optimal convenience, with convenience function values greater than 0.9, for fabrics considering all weaves and all types of finish, is: - Yarn twist to a cable: 720 v/m - Diameter of wool fiber: 21.4 μm - Diameter of polyester fiber: 4.4 dtex - Wool percentage: 45% Finally, this work allowed finding three phenomena which allow to contribute to the knowledge applied in fabric engineering projects in industrial practice, lacking, however, the scientific and technological justifications that should be studied in future research. The first phenomenon is associated with the effect of the dry cleaning treatment, which produces very significant reductions in the tear resistance of fabrics, without significantly modifying the performance of other properties. The second phenomenon is related to the treatment to increase the abrasion resistance, also negatively affecting the tear resistance, with very significant resistance reductions. The third phenomenon is related to the final color of fabrics, after special treatments. This work revealed that the padding treatment to increase the abrasion resistance significantly alters the intensity of the color, keeping its tonality practically unchanged.
Description
Keywords
Engenharia de Tecidos Tecidos Lã/Poliéster Propriedades Mecânicas e de Superfície Características Estruturais Optimização do Desempenho Função de Conveniência